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Role of the Renin-Angiotensin System in the Development of Abdominal Aortic Aneurysms in Animals and Humans
Abstract
The mediators for the initiation, progression, and rupture of abdominal aortic aneurysms (AAAs) have not been defined. Recent evidence has demonstrated that chronic infusion of angiotensin II via subcutaneously placed osmotic pumps can reproducibly form AAAs in mice. The evolution of AngII-induced AAAs in these mice is complex. Rapid medial macrophage accumulation precedes transmedial breaks and large lumen expansion, which are restricted to the suprarenal aorta. After this initial phase, there is a more gradual rate of lumen expansion that is progressive with continued AngII exposure. There is extensive aortic remodeling during this gradual expansion phase. An initial prominent thrombus gradually resolves and is replaced by fibrous tissue containing several types of inflammatory cells. At prolonged intervals of AngII infusion, internal aortic diameters of the suprarenal aorta can increase up to fourfold compared to the same region in saline-infused mice. The extrapolation of these data in mice to the development of human AAAs remains to be determined. However, there are a considerable number of drugs available to potentially test the efficacy of inhibiting the renin-angiotensin system on the progression of the human disease.
... Abdominal aortic aneurysm (AAA) is a severe disease threatening the human health and often causes death by rupture. The main pathological process of AAA includes (1) increasing inflammatory response, especially the macrophage infiltration and monocyte chemoattractant protein-1 (MCP-1) expression, (2) activating matrix metalloproteinases (MMP) and depredating extracellular matrix, and (3) degeneration of vascular media and damaging or breaking of elastic fiber [1,2]. It is documented that statins, angiotensin receptor blockers (ARB), tissue inhibitors of metalloproteinases (TIMP), and some traditional Chinese medicines are beneficial for the treatment of AAA. ...
... Abdominal aortic aneurysm (AAA) is a severe disease threatening the human health and often causes death by rupture. The main pathological process of AAA includes (1) increasing inflammatory response, especially the macrophage infiltration and monocyte chemoattractant protein-1 (MCP-1) expression, (2) activating matrix metalloproteinases (MMP) and depredating extracellular matrix, and (3) degeneration of vascular media and damaging or breaking of elastic fiber [1,2]. It is documented that statins, angiotensin receptor blockers (ARB), tissue inhibitors of metalloproteinases (TIMP), and some traditional Chinese medicines are beneficial for the treatment of AAA. ...
... Furthermore, these 2 Evidence-Based Complementary and Alternative Medicine studies showed that inhibition of RAS activation prevented AAA formation [3,4]. Daugherty's group demonstrated that the AT1 receptor antagonist, losartan, prevented the formation of AAA and AT2 receptor antagonist, PD123319, enhanced the severity of AAA [1][2][3][4]. Another study reported that simvastatin prevented the AngII-induced AAA formation in ApoE −/− mice by inhibiting MMP-2 and MMP-9 activity, MCP-1 protein expression, and ERK activity, indicating that inflammatory response and MAPK activation are involved in the pathogenesis of AAA [5]. ...
Background and Objectives. Curcumin has long been used to treat age-related diseases, such as atherosclerosis and coronary heart disease. In this study, we explored the effects of curcumin on the development of abdominal aortic aneurysm (AAA). Methods. ApoE(-/-) mice were randomly divided into 3 groups: AngII group, AngII + curcumin (AngII + Cur) group (100 mg/kg/d), and the control group. Miniosmotic pumps were implanted subcutaneously in ApoE(-/-) mice to deliver AngII for 28 days. After 4-week treatment, abdominal aortas with AAA were obtained for H&E staining, immunohistochemistry, and Western blotting. Results. The results showed that curcumin treatment significantly decreased the occurrence of AAA. The levels of macrophage infiltration, monocyte chemoattractant protein-1 (MCP-1), and tumor necrosis factors-α (TNF-α) were significantly lower in AngII + Cur group than those in AngII group (all P < 0.01). The level of superoxide dismutase (SOD) was significantly higher in AngII + Cur group than those in AngII group (P < 0.01). The ERK1/2 phosphorylation in AngII + Cur group was significantly lower than that in AngII group (P < 0.01). Conclusions. These results suggested that curcumin can inhibit the AngII-induced AAA in ApoE(-/-) mice, whose mechanisms include the curcumin anti-inflammation, antioxidative stress, and downregulation of ERK signaling pathway.
... Experimental AAAs were induced using a continuous infusion of Ang II as described previously (17). This model shows a strong male gender preference, recapitulating the much higher incidence of human AAA in men than in women (18). Therefore, this study only included male mice in accordance with the guidelines described in the ATVB Council Statement (19). ...
... An imbalance of the renin-angiotensin system has been associated with the pathogenesis of AAA (51), and Ang II-induced AAA formation in ApoE −/− mice shares many characteristic features of the human disease, including chemokine generation, macrophage infiltration, and neovascularization (18). However, weaknesses of our study include that we only used a single model of AAA formation and thus cannot rule out whether the observed MFAP4mediated effects are exclusively dependent on Ang II treatment. ...
Objective: Abdominal aortic aneurysm (AAA) is a common age-related vascular disease characterized by progressive weakening and dilatation of the aortic wall. Microfibrillar-associated protein 4 (MFAP4) is an extracellular matrix (ECM) protein involved in the induction of vascular remodeling. This study aimed to investigate if MFAP4 facilitates the development of AAA and characterize the underlying MFAP4-mediated mechanisms.
Approach and Results: Double apolipoprotein E- and Mfap4 -deficient ( ApoE −/− Mfap4 −/− ) and control apolipoprotein E-deficient ( ApoE −/− ) mice were infused subcutaneously with angiotensin II (Ang II) for 28 days. Mfap4 expression was localized within the adventitial and medial layers and was upregulated after Ang II treatment. While Ang II-induced blood pressure increase was independent of Mfap4 genotype, ApoE −/− Mfap4 −/− mice exhibited significantly lower AAA incidence and reduced maximal aortic diameter compared to ApoE −/− littermates. The ApoE −/− Mfap4 −/− AAAs were further characterized by reduced macrophage infiltration, matrix metalloproteinase (MMP)-2 and MMP-9 activity, proliferative activity, collagen content, and elastic membrane disruption. MFAP4 deficiency also attenuated activation of integrin- and TGF-β-related signaling within the adventitial layer of AAA tissues. Finally, MFAP4 stimulation promoted human monocyte migration and significantly upregulated MMP-9 activity in macrophage-like THP-1 cells.
Conclusion: This study demonstrates that MFAP4 induces macrophage-rich inflammation, MMP activity, and maladaptive remodeling of the ECM within the vessel wall, leading to an acceleration of AAA development and progression. Collectively, our findings suggest that MFAP4 is an essential aggravator of AAA pathology that acts through regulation of monocyte influx and MMP production.
... 19 As found in MS, Ang-II signalling has been implicated in both angiogenesis and pathological vascular growth, 20 and an association has been reported between RAS imbalance and abdominal aortic aneurysm (AAA) pathogenesis. 21 Indeed, Ang-II-induced AAA formation in apoE -/mice shares many characteristic features of the human disease. 22 Furthermore, metabolic changes in patients with AAA have been mainly related to carbohydrate and lipid metabolism. ...
... These initial observations led us to suspect that the CXCL16/CXCR6 axis was probably involved in pathologies associated with vascular inflammation in which Ang-II is a key player. The role of RAS in AAA pathogenesis is widely accepted 21,22 ; however, the role of CXCL16 in this pathology has been scarcely investigated. In the only study performed so far, an increase in CXCL16 mRNA expression was detected in CaCl 2 -induced AAA. ...
Aims:
Angiotensin-II (Ang-II) is the main effector peptide of the renin-angiotensin system (RAS) and promotes leucocyte adhesion to the stimulated endothelium. Because RAS activation and Ang-II signalling are implicated in metabolic syndrome (MS) and abdominal aortic aneurysm (AAA), we investigated the effect of Ang-II on CXCL16 arterial expression, the underlying mechanisms, and the functional role of the CXCL16/CXCR6 axis in these cardiometabolic disorders.
Methods and results:
Results from in vitro chamber assays revealed that CXCL16 neutralization significantly inhibited mononuclear leucocyte adhesion to arterial but not to venous endothelial cells. Flow cytometry and immunofluorescence studies confirmed that Ang-II induced enhanced endothelial CXCL16 expression, which was dependent on Nox5 up-regulation and subsequent RhoA/p38-MAPK/NFκB activation. Flow cytometry analysis further showed that MS patients had higher levels of platelet activation and a higher percentage of circulating CXCR6-expressing platelets, CXCR6-expressing-platelet-bound neutrophils, monocytes, and CD8+ lymphocytes than age-matched controls, leading to enhanced CXCR6/CXCL16-dependent adhesion to the dysfunctional (Ang-II- and TNFα-stimulated) arterial endothelium. Ang-II-challenged apolipoprotein E-deficient (apoE-/-) mice had a higher incidence of AAA, macrophage, CD3+, and CXCR6+ cell infiltration and neovascularization than unchallenged animals, which was accompanied by greater CCL2, CXCL16, and VEGF mRNA expression within the lesion together with elevated levels of circulating soluble CXCL16. Significant reductions in these parameters were found in animals co-treated with the AT1 receptor antagonist losartan or in apoE-/- mice lacking functional CXCR6 receptor (CXCR6GFP/GFP).
Conclusion:
CXCR6 expression on platelet-bound monocytes and CD8+ lymphocytes may constitute a new membrane-associated biomarker for adverse cardiovascular events. Moreover, pharmacological modulation of this axis may positively affect cardiovascular outcome in metabolic disorders linked to Ang-II.
... Angiotensin-II (Ang-II) is the main effector peptide of the renin-angiotensin system and has been implicated in both angiogenesis and pathological vascular growth (Willis et al., 2011). Indeed, an imbalance of the renin-angiotensin system has been associated with the pathogenesis of AAA (Daugherty et al., 2006 ), and Ang-II-induced AAA formation in apolipoprotein E-deficient mice (apoE −/− ) shares many characteristic features of the human disease, including chemokine generation , macrophage infiltration and neovascularization (Zhang et al., 2009). Given the high mortality rate associated with AAA in humans, it is important to find new pharmacological approaches to halt its progression. ...
... This combined therapy inhibited the proliferation, migration and vessel network formation induced by Ang-II in in vitro and in vivo models of angiogenesis. Experimental and clinical evidence endorses the relevance of the renin-angiotensin system in AAA pathogenesis (Daugherty et al., 2006; Zhang et al., 2009), where increased adventitial neocapillary formation is a key feature (Nishibe et al., 2010). In our study, bexarotene and rosuvastatin were co-administered at doses that did not exert any significant effects on vascular inflammation in vivo (Wang et al., 2011; Sanz et al., 2012). ...
Background and purpose:
Abdominal aortic aneurysm (AAA) is a degenerative vascular disease associated with angiogenesis. Bexarotene is a retinoid X receptor (RXR) ligand with anti-angiogenic activity. Statins also exert anti-angiogenic activity and activate PPARs. Because RXR ligands form permissive heterodimers with PPARs and a single anti-angiogenic drug may not be sufficient to combat the wide array of angiogenic factors produced during AAA, we evaluated the effect of combined low doses of bexarotene and rosuvastatin in a mouse model of AAA.
Experimental approach:
The effect of the combined treatment was investigated in a murine model of angiotensin II-induced AAA in apoE(-/-) mice. This combination therapy was also evaluated in in vivo (Matrigel plug assay) and in vitro (endothelial cell differentiation assay) models of angiogenesis as well as the underlying mechanisms involved.
Key results:
Co-treatment with bexarotene plus rosuvastatin reduced aneurysm formation, inflammation and neovascularization compared with each single treatment. In HUVEC, the combination of suboptimal concentrations of bexarotene and rosuvastatin inhibited angiotensin II-induced morphogenesis, proliferation and migration. These effects were accompanied by diminished production of pro-angiogenic chemokines (CXCL1, CCL2 or CCL5) and VEGF, and seemed to be mediated by RXRα/PPARα and RXRα/PPARγ activation. This combined therapy reduced the activation of members of the downstream PI3K pathway (Akt/mTOR and p70S6K1) in vivo and in vitro.
Conclusions and implications:
The combination of RXR agonists with statins at low doses synergistically interferes with the signalling pathways that modulate inflammation and angiogenesis and may constitute a new and safer therapeutic treatment for the control of AAA.
... 25 Chronic infusion of AngII for 28 days into apolipoprotein E (ApoE) knockout mice accelerates not only atherosclerosis but also formation of aortic aneurysms. [25][26][27] In the present study, we report that endothelial Gab1 deletion accelerates AngII-dependent vascular inflammation and atherosclerosis in ApoE knockout mice in association with endothelial downregulation of KLF2 and KLF4. ...
... AngII induces aneurysm formation in ApoE knockout mice. 26, 27 We thus examined the effect of endothelial Gab1 deletion on the abdominal aneurysm formation after AngII treatment. Compared with littermate controls, Gab1ECKO/ApoEKO mice exhibited a dramatic increase in the incidence of aneurysm formation ( Figure S1). ...
Docking protein Grb2-associated binder 1 (Gab1) has critical roles in signal transduction of various growth factors, cytokines, and numerous other molecules. Our previous reports show that Gab1 is essential for postnatal angiogenesis through the analysis of endothelium-specific Gab1 knockout (Gab1ECKO) mice. However, the role of Gab1 in atherosclerosis remains unknown. The aim of the present study was to elucidate the role of endothelial Gab1 in vascular inflammation and atherosclerosis.
We intercrossed Gab1ECKO mice with apolipoprotein E (ApoE) knockout (ApoEKO) mice. Six-month-old male ApoEKO/Gab1ECKO and littermate control (ApoEKO) mice were treated with angiotensin II (AngII) via an osmotic infusion mini-pump. After AngII treatment, ApoEKO/Gab1ECKO mice showed significantly enhanced atherosclerosis and aneurysm formation compared with control mice. The production of proinflammatory cytokines in the aorta was significantly enhanced in ApoEKO/Gab1ECKO mice compared with control mice. Furthermore, the expression levels of Krüppel-like factor (KLF) 2 (KLF2) and KLF4, key transcription factors for endothelial homeostasis, were significantly reduced in the aortic endothelium of ApoEKO/Gab1ECKO mice compared with those of control mice. Consistently, both vascular cell adhesion molecule-1 expression and macrophage infiltration on the aortic walls were enhanced in ApoEKO/Gab1ECKO mice compared with control mice.
Collectively, endothelial Gab1 deletion accelerates AngII-dependent vascular inflammation and atherosclerosis on ApoE-null background presumably in association with downregulation of KLF2 and KLF4.
... The pharmacological model of continuous Ang II infusion offers the benefit of a simple surgical procedure, eliminating the need for invasive aortic manipulations 123 . Ang II infusion results in characteristics such as macrophage infiltration, degradation of the elastic media, the occurrence of aortic dissection, the formation of intramural thrombus, remodeling of the aneurysmal wall and eventual aortic rupture 125 . Periaortic administration of CaCl 2 onto the infrarenal aorta to induce AAA was initially described in rabbits as an animal model of AAA 126,127 . ...
Aortic aneurysm is a chronic disease characterized by localized expansion of the aorta, including the ascending aorta, arch, descending aorta, and abdominal aorta. Although aortic aneurysms are generally asymptomatic, they can threaten human health by sudden death due to aortic rupture. Aortic aneurysms are estimated to lead to 150,000 ~ 200,000 deaths per year worldwide. Currently, there are no effective drugs to prevent the growth or rupture of aortic aneurysms; surgical repair or endovascular repair is the only option for treating this condition. The pathogenic mechanisms and therapeutic targets for aortic aneurysms have been examined over the past decade; however, there are unknown pathogenic mechanisms involved in cellular heterogeneity and plasticity, the complexity of the transforming growth factor-β signaling pathway, inflammation, cell death, intramural neovascularization, and intercellular communication. This review summarizes the latest research findings and current pathogenic mechanisms of aortic aneurysms, which may enhance our understanding of aortic aneurysms.
... This finding is similar to previous studies that report either complete aortic rupture before a dissection occurs or a relatively slow-growing AD that rarely ruptures. 27,28 Nevertheless, the lack of rupture in this model makes it useful for studying chronic changes in thrombus structure. We also found that ultrasound detection paired with ex vivo SEM is an effective research technique for analyzing intramural thrombus formation, opening the potential for studies of thrombus formation and development in both animal models and human samples. ...
Aortic dissection occurs when a weakened portion of the intima tears, and a separation of layers propagates along the aortic wall to form a false lumen filled with active blood flow or intramural thrombus. The unpredictable nature of aortic dissection formation and need for immediate intervention leaves limited serial human image data to study the formation and morphological changes that follow dissection. We used volumetric ultrasound examination, histology, and scanning electron microscopy (SEM) to examine intramural thrombi at well-defined timepoints after dissection occurs in apolipoprotein E-deficient mice infused with angiotensin II (n = 71). Stratification of red blood cell (RBC) morphologies (biconcave, intermediate biconcave, intermediate polyhedrocyte, and polyhedrocyte) in the thrombi with scanning electron microscopy (n = 5) was used to determine degree of thrombus deposition/contraction. Very few biconcave RBCs (1.2 ± 0.6%) were in the thrombi, and greater amounts of intermediate biconcave RBCs (25.8 ± 6.7%) were located in the descending thoracic portion of the dissection while more polyhedrocytes (14.6 ± 5.1%) and fibrin (42.3 ± 4.5%; P < .05) were found in the distal suprarenal aorta. Thrombus deposition likely plays some role in patient outcomes, and this multimodality technique can help investigate thrombus deposition and characteristics in experimental animal models and human tissue samples.
... Concerning on the abdominal aorta, the altered metabolism of ECM is shown to be more interlinked with inflammatory response and dyslipidemia condition [33]. Under both states, the excessive stimulation of matrix metalloproteinases (MMPs) is involved in inducing dyslipidemia and inflammatory response in patients with BAV [34][35][36]. ...
Dyslipidemia is correlated with diverse cardiovascular problems, such as obesity, hypertension, and atherosclerosis, which are summarized as metabolic syndrome. Bicuspid aortic valve (BAV), as one of the congenital heart defects, is shown to influence approximately 2.2% of the general population worldwide, inducing the severe pathological development of aortic valve stenosis (AVS) or aortic valve regurgitation (AVR), and also to aortic dilatation. Notably, emerging evidence showed that BAV was correlated with not only the aortic valve and wall diseases but also the dyslipidemic related cardiovascular disorders. Recent results also proposed that multiple potential molecular mechanisms inducing the progression of dyslipidemia played important roles in BAV and the progression of AVS. Several altered serum biomarkers under dyslipidemic condition, including higher low-density lipoprotein cholesterol (LDL-C), higher lipoprotein (a) [Lp(a)], lower high-density lipoprotein cholesterol (HDL-C), and different pro-inflammatory signaling pathways, have proposed to embrace a vital function in the development of BAV correlated cardiovascular diseases. In this review, different molecular mechanisms which embrace an important role in personalized prognosis in the subjects with BAV was summarized. The illustration of those mechanisms might facilitate an accurate follow-up for patients with BAV and give new pharmacological strategies to improve development of dyslipidemia and BAV.
... Since Ang II, the main effector peptide of reninangiotensin system, is involved in both pathological vascular growth and vascular inflammation in AAA. 30 AngII perfusion ApoE(-/-) mouse models could successfully induce experimental AAA which have many characteristics similar to human AAA, including the formation of giant aortic aneurysms, destruction of the aortic media, and infiltration of inflammatory cells (macrophages and T or B lymphocytes). 31 The aneurysm formation of this model is relatively stable, and the operation method is relatively simple. ...
Background:
The inflammatory reaction is an important mechanism of pathogenesis of abdominal aortic aneurysm (AAA). Artesunate (AS) has been found to have anti-inflammatory effects in cardiovascular disease. The purpose of this study was to investigate whether AS could inhibit the development of AAA.
Materials and methods:
AngII infused ApoE (-/-) male mice were selected as AAA model. Mice were spilt into three groups, the experimental control group (AngII), the AS treatment group (AngII + AS) and the negative control group (Vehicle) with 14 in each group. Daily administration of AS (100 mg/kg/d) or vehicle performed 3 day before the perfusion. At the end of the 28-day experiment, animal ultrasound and electronic digital caliper were used to measure the diameter of abdominal aorta. Histologic assays were performed to observe the microstructure of the aorta wall. Immunofluorescence staining was performed to detect inflammatory cells, as well as the levels of matrix metalloproteinases (MMPs). The transcription of cytokines and adhesion molecules were investigated by real-time fluorescence quantitative PCR (qPCR). Western blotting was performed to determine whether the NF-κB pathway is involved in the mechanism.
Results:
While AS failed to reduce the incidence of AAA, AS effectively reduced the diameter of AAA independently of blood pressure effects. Immunofluorescence detection showed that AS effectively reduced the levels of CD45+ cells and MAC3+ macrophages as well as MMP-2 and MMP-9. qPCR revealed that AS reduced mRNA transcription levels of MMP-2, MMP-9, the cytokine IL-1β, TNF-α, adhesion molecules ICAM-1, VCAM-1. AS decreased the levels of NF-κB signaling pathway in aorta.
Conclusions:
AS can attenuate the development of AAA in mice. The possible mechanism is anti-inflammation.
... Regarding abdominal aortic aneurysms, the involvement of Ang II and RAS stimulation has been clearly demonstrated in animals, and strong evidence have been gathered in humans [35,36]. However, when considering cerebral aneurysms, the role of RAS components and AT 1 seems less obvious. ...
The physiological and pathophysiological relevance of the angiotensin II type 1 (AT1) G protein-coupled receptor no longer needs to be proven in the cardiovascular system. The renin–angiotensin system and the AT1 receptor are the targets of several classes of therapeutics (such as angiotensin converting enzyme inhibitors or angiotensin receptor blockers, ARBs) used as first-line treatments in cardiovascular diseases. The importance of AT1 in the regulation of the cerebrovascular system is also acknowledged. However, despite numerous beneficial effects in preclinical experiments, ARBs do not induce satisfactory curative results in clinical stroke studies. A better understanding of AT1 signaling and the development of biased AT1 agonists, able to selectively activate the β-arrestin transduction pathway rather than the Gq pathway, have led to new therapeutic strategies to target detrimental effects of AT1 activation. In this paper, we review the involvement of AT1 in cerebrovascular diseases as well as recent advances in the understanding of its molecular dynamics and biased or non-biased signaling. We also describe why these alternative signaling pathways induced by β-arrestin biased AT1 agonists could be considered as new therapeutic avenues for cerebrovascular diseases.
... It should be emphasized that at least one in vitro study suggests that OPN is down-regulated by peroxisome proliferator-activated receptor (PPAR) ligation [26,27]. The renin-angiotensin system seems to be implicated in the development of abdominal aortic aneurysms in both humans and animals [28]. At prolonged intervals of angiotensin II infusion, internal aortic diameters of the suprarenal aorta can increase up to four-fold compared to the same region in saline-infused mice [29]. ...
... Remodeling and Inflammation in AngII Treated ApoE −/− Mice It has been reported that AngII-infused ApoE knock-out mice mostly present AAAs around the suprarenal area immediately distal to the branch of the renal artery (Daugherty et al., 2006). So, we selected aortic sections from the aneurysm-prone areas for histological characteristics analysis. ...
Abdominal aortic aneurysm (AAA) is a chronic inflammatory disease characterized by aortic dilatation and predominantly affects an elderly population. Accumulating evidence suggests that Interleukin-6 (IL-6) and the signal transducer and activator of transcription 3 (STAT3) play an important role in formation of AAAs. However, it remains unclear whether Bazedoxifene (BAZ) could suppress the activation of IL-6/GP130/STAT3 in vascular cells and the formation of AAA. Here we explored the effect of BAZ on AngII-stimulated AAA formation. ApoE–/– mice infused with AngII for 28 days using osmotic minipumps were treated with placebo or 5mg/kg BAZ. In our results most of the AngII-induced mice developed AAA with exacerbated inflammation, degradation of elastin fibers, STAT3 phosphorylation, and increased expression of matrix metalloproteinases (MMPs). These effects were markedly attenuated by BAZ. Furthermore, BAZ suppressed the stimuli-induced (IL-6 or AngII) expression of P-STAT3, MMP2 and MMP9 in vascular smooth muscle cells (VSMCs). BAZ inhibited wound healing, colony formation and suppressed STAT3 nuclear translocation in vitro. In conclusion, these results indicated that BAZ downregulated IL-6/GP130/STAT3 signaling and interfered with AAA formation induced by AngII in ApoE–/– mice, which indicates a novel potential strategy for the prevention and therapy of AAA.
... Angiotensin II (Ang-II) is the main effector peptide of the reninangiotensin system (RAS). Beyond its role as a potent vasoconstrictor and regulator of blood pressure and fluid homeostasis, Ang-II is involved in the development of vascular lesions in atherosclerosis, hypertension, and AAA through the activation of different immune cells [3,[6][7][8]. Ang-II is also implicated in endothelial dysfunction [9], a proinflammatory and prothrombotic phenotype of the endothelium that precedes vasomotor alterations and stimulates the attachment and subsequent migration of leukocytes [10]. ...
Inflammation and activation of the immune system are key molecular and cellular events in the pathogenesis of cardiovascular diseases, including atherosclerosis, hypertension-induced target-organ damage, and abdominal aortic aneurysm. Angiotensin II (Ang-II) is the main effector peptide hormone of the renin-angiotensin system. Beyond its role as a potent vasoconstrictor and regulator of blood pressure and fluid homeostasis, Ang-II is intimately involved in the development of vascular lesions in cardiovascular diseases through the activation of different immune cells. The migration of leukocytes from circulation to the arterial subendothelial space is a crucial immune response in lesion development that is mediated through a sequential and coordinated cascade of leukocyte-endothelial cell adhesive interactions involving an array of cell adhesion molecules present on target leukocytes and endothelial cells and the generation and release of chemoattractants that activate and guide leukocytes to sites of emigration. In this review, we outline the key events of Ang-II participation in the leukocyte recruitment cascade, the underlying mechanisms implicated, and the corresponding redox-signaling pathways. We also address the use of inhibitor drugs targeting the effects of Ang-II in the context of leukocyte infiltration in these cardiovascular pathologies, and examine the clinical data supporting the relevance of blocking Ang-II-induced vascular inflammation.
... Ang II (angiotensin II)-the major effector peptide of the renin-angiotensin system-is implicated in both vascular inflammation and pathological vascular growth in AAA. 14 Ang II infusion in the apoE (apolipoprotein E) −/− mouse model is known to elicit AAA and recapitulates many features of human AAA, including dramatic aortic dilatation with aneurysm formation, aortic media destruction, and inflammatory cell infiltration. 15 In an effort to find more effective therapeutic strategies to decrease the progression of AAA, we sought to examine the effect of the SGLT-2 inhibitor empagliflozin on Ang II-induced dissecting AAA development in apoE −/− mice. ...
Objective:
Abdominal aortic aneurysm (AAA) is a pathological condition of permanent vessel dilatation that predisposes to the potentially fatal consequence of aortic rupture. SGLT-2 (sodium-glucose cotransporter 2) inhibitors have emerged as powerful pharmacological tools for type 2 diabetes mellitus treatment. Beyond their glucose-lowering effects, recent studies have shown that SGLT-2 inhibitors reduce cardiovascular events and have beneficial effects on several vascular diseases such as atherosclerosis; however, the potential effects of SGLT-2 inhibition on AAA remain unknown. This study evaluates the effect of oral chronic treatment with empagliflozin-an SGLT-2 inhibitor-on dissecting AAA induced by Ang II (angiotensin II) infusion in apoE (apolipoprotein E)-/- mice. Approach and Results: Empagliflozin treatment significantly reduced the Ang II-induced increase in maximal suprarenal aortic diameter in apoE-/- mice independently of blood pressure effects. Immunohistochemistry analysis revealed that empagliflozin diminished Ang II-induced elastin degradation, neovessel formation, and macrophage infiltration at the AAA lesion. Furthermore, Ang II infusion resulted in a marked increase in the expression of chemokines (CCL-2 [chemokine (C-C motif) ligand 2] and CCL-5 [chemokine (C-C motif) ligand 5]), VEGF (vascular endothelial growth factor), and MMP (matrix metalloproteinase)-2 and MMP-9 in suprarenal aortic walls of apoE-/- mice, and all were reduced by empagliflozin cotreatment. Western blot analysis revealed that p38 MAPK (p38 mitogen-activated protein kinase) and NF-κB (nuclear factor-κB) activation was also reduced in the suprarenal aortas of apoE-/- mice cotreated with empagliflozin. Finally, in vitro studies in human aortic endothelial cells and macrophages showed that empagliflozin inhibited leukocyte-endothelial cell interactions and release of proinflammatory chemokines.
Conclusions:
Pharmacological inhibition of SGLT-2 by empagliflozin inhibits AAA formation. SGLT-2 inhibition might represent a novel promising therapeutic strategy to prevent AAA progression ( Visual Overview ).
... Serum concentrations of OPG and OPN are elevated in participants with AAA, and are positively associated with the rate of AAA progression after adjusting for other risk factors [61,66]. An interaction between AngII, TGF-β1, OPG and OPN in promoting cardinal features of AAA, such as inflammation and ECM destruction, is confirmed in multiple in vitro and animal studies [67][68][69][70]. Importantly, AT1 blockade has been demonstrated to inhibit AAA development in three independent animal models of AAA [59,69,71]. ...
Objective:
This mini-review provides the rationale and updated progress for ongoing randomized controlled trials assessing fenofibrate and telmisartan efficacy to limit abdominal aortic aneurysm (AAA) growth.
Methods/results:
There remains an urgent need to identify a drug therapy that will limit AAA growth. Data from preclinical and human studies indicate that fenofibrate and telmisartan have the potential to slow aortic destruction. Fenofibrate has been shown to reduce serum and tissue levels of the proinflammatory protein osteopontin, as well as reducing macrophage recruitment to the aortic wall, both of which are integral processes in the development and progression of AAAs. Telmisartan acts via blockade of the angiotensin II receptor, type 1, and also as a peroxisome proliferator-activated receptor gamma agonist. In turn, this inhibits the production of a range of biomarkers associated with AAA progression, including transforming growth factor-beta one, osteoprotegerin, osteopontin and matrix metalloproteinase- 9. Based on these findings, there are currently three randomized controlled trials assessing both fenofibrate and telmisartan as potential interventions to limit aneurysm growth in AAA patients.
Conclusion:
Fenofibrate and telmisartan have potential as repurposed medications to limit AAA growth, and randomized trials for further assessment in AAA patients are ongoing.
... Ang II has been reported to promote AAA formation in animal models, 13,27 and Ang II has been proposed to induce aortic aneurysms through several mechanisms, including those involving the effects of Ang II on multiple cell types and mediators. 28,29 However, to the best of our knowledge, no study thus far has demonstrated the effect of AT 1a receptor in perivascular VAT on the pathogenesis of AAA. ...
Perivascular adipose tissue exhibits characteristics of active local inflammation, which contributes to the development of atherosclerotic disease as a complication of obesity/metabolic syndrome. However, the precise role of perivascular adipose tissue in the progression of abdominal aortic aneurysm remains unclear. To test the hypothesis that genetic deletion of angiotensin II type 1a (AT1a) receptor in perivascular visceral adipose tissue (VAT) can attenuate aortic aneurysm formation in apolipoprotein E-deficient (ApoE(-/-)) mice, we performed adipose tissue transplantation experiments by using an angiotensin II-induced aneurysm murine model, in which we transplanted VAT from ApoE(-/-) or ApoE(-/-) AT1a(-/-) donor mice onto the abdominal aorta of ApoE(-/-) recipient mice. Compared with ApoE(-/-) VAT transplantation, ApoE(-/-) AT1a(-/-) VAT transplantation markedly attenuated aortic aneurysm formation, macrophage infiltration, and gelatinolytic activity in the abdominal aorta. AT1a receptor activation led to the polarization of macrophages in perivascular VAT toward the proinflammatory phenotype. Moreover, osteopontin expression and gelatinolytic activity were considerably lower in ApoE(-/-) AT1a(-/-) perivascular VAT than in ApoE(-/-) perivascular VAT, and angiotensin II-induced osteopontin secretion from adipocytes was eliminated after deletion of AT1a receptor in adipocytes. Notably, induction of macrophage migration by conditioned medium from angiotensin II-stimulated wild-type adipocytes was suppressed by treatment with an osteopontin-neutralizing antibody, and ApoE(-/-) OPN(-/-) VAT transplantation more potently attenuated aortic aneurysm formation than ApoE(-/-) VAT transplantation. Our findings indicate a previously unrecognized effect of AT1a receptor in perivascular VAT on the pathogenesis of abdominal aortic aneurysm.
... To further develop our understanding of the etiology of the onset, development and progression of aortic aneurysms different animal models have been used in previous studies [29][30][31]. Both pharmacological and surgical techniques have been applied to induce the reproducible development of aortic aneurysms [32]. The most widely used model is based on an ApoE-/-mouse in which angiotensin II is continuously administered [17]. ...
Background
MR-angiography currently represents one of the clinical reference-standards for the assessment of aortic-dimensions. For experimental research in mice, dedicated preclinical high-field MRI scanners are used in most studies. This type of MRI scanner is not available in most institutions. The aim of this study was to evaluate the potential of MR-angiography performed on a clinical MR scanner for the assessment of aortic aneurysms in an experimental mouse model, compared to a preclinical high-resolution ultrasound imaging system and histopathology.
Methods
All in vivo MR imaging was performed with a clinical 3T MRI system (Philips Achieva) equipped with a clinical gradient system in combination with a single-loop surface-coil (47 mm). All MR sequences were based on clinically used sequences. For ultrasound, a dedicated preclinical high-resolution system (30 MHz linear transducer, Vevo770, VisualSonics) was used. All imaging was performed with an ApoE knockout mouse-model for aortic aneurysms. Histopathology was performed as reference-standard at all stages of aneurysm development.
Results
MR-angiography on a clinical 3T system enabled the clear visualization of the aortic lumen and aneurysmal dilation at different stages of aneurysm development. A close correlation (R² = 0.98; p < 0.001) with histological area measurements was found. Additionally, a good agreement between MR and ultrasound area measurements in systole (R² = 0.91; p < 0.001) and diastole (R² = 0.94; p < 0.001) were measured. Regarding interobserver reproducibility, MRI measurements yielded a smaller 95% confidence interval and a closer interreader correlation compared to ultrasound measurements (-0.37–0.46; R² = 0.97 vs. -0.78–0.88; R² = 0.87).
Conclusion
This study demonstrates that MR-angiography, performed on a clinical 3T MR scanner, enables the reliable detection and quantification of the aortic dilatation at different stages of aneurysm development in an experimental mouse model.
... 27 Ang II-induced AAA, associated with atherosclerosis, most commonly arise as an acute dis- section with associated intramural thrombus. 28 CaCl 2 -induced AAA formation mainly relies on the disruption of the elas- tic network within the media by calcium precipitations and the activation of the inflammatory response. 29 We first examined changes in IMD and its receptor in the Ang II-or CaCl 2 -induced AAA mice model. ...
Objective:
Oxidative stress plays a critical role in the development of abdominal aortic aneurysm (AAA). Intermedin (IMD) is a regulator of oxidative stress. Here, we investigated whether IMD reduces AAA by inhibiting oxidative stress.
Approach and results:
In angiotensin II-induced ApoE(-) (/-) mouse and CaCl2-induced C57BL/6J mouse model of AAA, IMD1- 53 significantly reduced the incidence of AAA and maximal aortic diameter. Ultrasonography, hematoxylin, and eosin staining and Verhoeff-van Gieson staining showed that IMD1- 53 significantly decreased the enlarged aortas and elastic lamina degradation induced by angiotensin II or CaCl2. Mechanistically, IMD1- 53 attenuated oxidative stress, inflammation, vascular smooth muscle cell apoptosis, and matrix metalloproteinase activation. IMD1- 53 inhibited the activation of redox-sensitive signaling pathways, decreased the mRNA and protein expression of nicotinamide adenine dinucleotide phosphate oxidase subunits, and reduced the activity of nicotinamide adenine dinucleotide phosphate oxidase in AAA mice. Expression of Nox4 was upregulated in human AAA segments and in angiotensin II-treated mouse aortas and was markedly decreased by IMD1- 53. In vitro, vascular smooth muscle cells with small-interfering RNA knockdown of IMD showed significantly increased angiotensin II-induced reactive oxygen species, and small-interfering RNA knockdown of Nox4 markedly inhibited the reactive oxygen species. IMD knockdown further increased the apoptosis of vascular smooth muscle cells and inflammation, which was reversed by Nox4 knockdown. Preincubation with IMD17- 47 and protein kinase A inhibitor H89 inhibited the effect of IMD1-53, reducing Nox4 protein levels.
Conclusions:
IMD1- 53 could have a protective effect on AAA by inhibiting oxidative stress.
... Aneurysms rarely occur in the common strains of laboratory rodents, but aortic aneurysms can be seen in rats as a lesion secondary to degenerative changes in the media (Mitsumori 1990). There are also several genetically disposed or experimentally produced animal models (Daugherty et al. 2006). ...
The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Japan (JSTP), Europe (ESTP), Great Britain (BSTP) and North America (STP) to develop an internationally-accepted nomenclature for proliferative and non-proliferative lesions in laboratory animals. The primary purpose of this publication is to provide a standardized nomenclature for characterizing lesions observed in the cardiovascular (CV) system of rats and mice commonly used in drug or chemical safety assessment. The standardized nomenclature presented in this document is also available electronically for society members on the internet (http://goreni.org). Accurate and precise morphologic descriptions of changes in the CV system are important for understanding the mechanisms and pathogenesis of those changes, differentiation of natural and induced injuries and their ultimate functional consequence. Challenges in nomenclature are associated with lesions or pathologic processes that may present as a temporal or pathogenic spectrum or when natural and induced injuries share indistinguishable features. Specific nomenclature recommendations are offered to provide a consistent approach.
... In order to overcome the challenges of studying AAA initiation and progression in humans, an apolipoprotein E knockout (ApoE − / − ) angiotensin II (AngII)-infused mouse model has been developed that produces an aortic aneurysm from a focal breakage point in the medial elastin separating the adventitial and medial layers (Goergen et al., 2011). This animal model has become prominent for the study of AAA as it displays many of the same histological and biological characteristics as native human AAA, including atherosclerotic plaque formation, medial degeneration, thrombus formation, and an increase in matrix-metalloprotease (MMP) activity (Daugherty et al., 2000;Daugherty et al., 2006). This model has allowed recent work to focus on understanding the underlying mechanisms of disease initiation and development, specifically the role of increased MMP production in aneurysmal tissue that appears to be associated with extensive remodeling of the extracellular matrix (ECM) (Freestone et al., 1995;Thompson et al., 1995;Curci et al., 1998a;Davis et al., 1998;Longo et al., 2002). ...
Abdominal aortic aneurysm is a multifactorial disease that is a leading cause of death in developed countries. Matrix-metalloproteases (MMPs) are part of the disease process, however, assessing their role in disease initiation and progression has been difficult and animal models have become essential. Combining Förster resonance energy transfer (FRET) proteolytic beacons activated in the presence of MMPs with 2-photon microscopy allows for a novel method of evaluating MMP activity within the extracellular matrix (ECM). Single and 2-photon spectra for proteolytic beacons were determined
in vitro
.
Ex vivo
experiments using the apolipoprotein E knockout angiotensin II-infused mouse model of aneurysm imaged ECM architecture simultaneously with the MMP-activated FRET beacons. 2-photon spectra of the two-color proteolytic beacons showed peaks for the individual fluorophores that enable imaging of MMP activity through proteolytic cleavage.
Ex vivo
imaging of the beacons within the ECM revealed both microstructure and MMP activity. 2-photon imaging of the beacons in aneurysmal tissue showed an increase in proteolytic cleavage within the ECM (
p
<0.001), thus indicating an increase in MMP activity. Our data suggest that FRET-based proteolytic beacons show promise in assessing MMP activity within the ECM and will therefore allow future studies to identify the heterogeneous distribution of simultaneous ECM remodeling and protease activity in aneurysmal disease.
... In addition to the considerable evidence that components of the RAAS stimulate lesion development, targeting different components of the system has been shown to both reduce lesion formation and to increase markers of plaque stability. For example, in atherosclerosis-prone mice, administration of angiotensin II (Ang II) over long periods promotes lesion formation, whereas angiotensinconverting enzyme (ACE) inhibition, angiotensin 1 receptor antagonism [2] or mineralocorticoid receptor antagonism [3] reduces lesion size. An increasing body of evidence suggests that both Ang II-induced stimulation of lesion formation and the antiatherosclerotic effects of treatment (ACE inhibition/AT1 receptor antagonism) are independent of blood pressure; indicating a direct atherosclerotic effect of Ang II on the cells of the vascular wall. ...
... Aortic aneurysms usually develop in the suprarenal aorta or the aortic arch in Ang II induced mouse models. 10,11 Notably, aortic aneurysms can be attenuated by co-infusion of Ang II with losartan, an angiotensin II type 1 receptor blocker (ARB). 12 This observation implied an analogous situation in human AAA pathogenesis. ...
Objective
Renin Angiotensin System (RAS) has been implicated in the pathogenesis of abdominal aortic aneurysm (AAA). Angiotensin II (Ang II) type 1 receptor blocker (ARB), when given with Ang II prevents AAA formation in mice, but found ineffective in attenuating the progression of pre-existing AAA. This study was designed to evaluate the effect of chronic renin-angiotensin system (RAS) blockers on abdominal aortic diameter in hypertensive patients without known aortic aneurysm.
Methods
Consecutive hypertensive outpatients (n=122) were stratified according to antihypertensive therapy they received for 12 months or more, consisting of either ARB (n=45), angiotensin converting enzyme inhibitor (ACE-I) (n=45), or nonARB/nonACE-I (control therapy; n=32). Abdominal ultrasonography was performed to measure maximal subrenal aortic diameter. 84 patients were re-examined by ultrasonography 8 months later. The correlation between the different antihypertensive therapies and aortic diameter was examined.
Results
Aortic diameters were significantly smaller in ARB than in control patients in the baseline and follow up measurements (P = 0.004, P = 0.0004, respectively). Risk factor adjusted covariance analysis showed significant differences between ARB or ACE-I treated groups and controls (P = 0.006 or P = 0.046, respectively). Ultrasound that was performed 8 months later showed smaller increases in mean aortic diameters of the ARB and ACE-I groups than in controls.
Conclusion
Both ARB and ACE-I therapy attenuated expansion of non-aneurismal abdominal aorta in humans. These results indicate that RAS blockade given prior to advancement of aortic medial remodeling may slow down the development of AAA.
... One thing that our work here has indicated is that there seems to be response in the ApoE −/− AngII infused model by 28 d that is able to reverse some of the functional mechanical response lost at 14 d. This is similar to findings by Daugherty et al., 25 which showed through histology that after 84 d of AngII infusion there was considerable remodeling of aneurysmal tissue with thinning regions not found at 28 d. We know that this late stage response is happening in the ApoE −/− AngII mouse model and this does not happen in the human disease, so beyond a certain time point, the model may not be useful or appropriate for studying the human disease. ...
AAA is a complex disease that leads to a localized dilation of the infrarenal aorta that develops over years. Longitudinal information in humans has been difficult to obtain for this disease, therefore mouse models have become increasingly used to study the development of AAAs. The objective of this study was to determine any changes that occur in the biomechanical response and fiber microstructure in the ApoE (-/-) AngII mouse model of aneurysm during disease progression. Adult ApoE (-/-) AngII infused mice along with wild-type controls were taken at 14 and 28 d. Aortas were excised and tested simultaneously for biaxial mechanical response and ECM organization. Data sets were fit to a Fung-type constitutive model to give peak strains and stiffness values. Images from two photon microscopy were quantified in order to assess the preferred fiber alignment and degree of fiber orientation. Biomechanical results found significant differences that were present at 14 d had returned to normal by 28 d along with significant changes in fiber orientation and dispersion indicating remodeling occurring within the aneurysmal wall. This return of some of the normal biomechanical function, in addition the continuing changes that occur in the microstructure suggest a restorative response that occurs in the ApoE (-/-) AngII infused model after the initial aneurysm formation.
... Risk factors for AAA development and growth include family history, male gender (Aggarwal et al., 2011), smoking (Kent et al., 2010;Stolle et al., 2010) and obesity (Police et al., 2009;Long et al., 2010;Nordon et al., 2011). Previous studies in our laboratory demonstrated that infusion of angiotensin II (AngII) to male hypercholesterolemic mice augments atherosclerosis and causes formation of AAAs ( Daugherty et al., 2000;Daugherty and Cassis, 2002;Daugherty et al., 2006). Longitudinal studies examining AAA pathology in male apolipoprotein E (ApoE) deficient mice demonstrated that early after the onset of AngII infusion macrophages localize to medial smooth muscle of the suprarenal aorta, with macrophages present in the adventitia (Saraff et al., 2003) and perivascular adipose tissue (Police et al., 2009) of formed AAAs. ...
Infusion of angiotensin II (AngII) to hyperlipidemic mice augments atherosclerosis and causes formation of abdominal aortic aneurysms (AAAs). Each of these AngII-induced vascular pathologies exhibit pronounced inflammation. Previous studies demonstrated that coplanar polychlorinated biphenyls (PCBs) promote inflammation in endothelial cells and adipocytes, two cell types implicated in AngII-induced vascular pathologies. The purpose of this study was to test the hypothesis that administration of PCB77 to male apolipoprotein E (ApoE) -/- mice promotes AngII-induced atherosclerosis and AAA formation. Male ApoE-/- mice were administered vehicle or PCB77 (49 mg/kg, i.p.) during week 1 and 4 (2 divided doses/week) of AngII infusion. Body weights and total serum cholesterol concentrations were not influenced by administration of PCB77. Systolic blood pressure was increased in AngII-infused mice administered PCB77 compared to vehicle (156±6 vs 137±5 mmHg, respectively). The percentage of aortic arch covered by atherosclerotic lesions was increased in AngII-infused mice administered PCB77 compared to vehicle (2.0±0.4 vs 0.9±0.1%, respectively). Lumen diameters of abdominal aortas determined by in vivo ultrasound and external diameters of excised suprarenal aortas were increased in AngII-infused mice administered PCB77 compared to vehicle. In addition, AAA incidence increased from 47 to 85% in AngII-infused mice administered PCB77. Adipose tissue in close proximity to AAAs from mice administered PCB77 exhibited increased mRNA abundance of proinflammatory cytokines and elevated expression of components of the renin-angiotensin system (angiotensinogen, angiotensin type 1a receptor (AT1aR)). These results demonstrate that PCB77 augments AngII-induced atherosclerosis and AAA formation.
... The angiotensin II (Ang II)-induced mouse AAA model in the atherosclerotic-susceptible strain (apolipoprotein E deficient; apoE−/−) has become the most widely used model in recent years because of its simplicity and because certain facets of the model resemble human disease acquisition, including male gender preponderance in the setting of mild hypertension with enhanced incidence in the presence of hyperlipidemia (Daugherty et al., 2000, 2001; Saraff et al., 2003; Daugherty and Cassis, 2004). There is a well-defined time course of events in this model with early macrophage infiltration into the smooth muscle-rich medial layer of the aneurysm-prone area, transmedial dissection that causes rapid luminal expansion within the first 7 days of AngII infusion, with subsequent complex inflammatory events that include intramural thrombus formation, elastin degradation and profound remodeling in which the thrombus is often resorbed and replaced by fibrous tissue interspersed with leukocytes (Daugherty et al., 2000, 2006). However, there are still some parameters such as aortic rupture death and hemodynamical changes within the aorta upon aneurysm formation that are poorly defined. ...
An abdominal aortic aneurysm (AAA) is an enlargement of the greatest artery in the body defined as an increase in diameter of 1.5-fold. AAAs are common in the elderly population and thousands die each year from their complications. The most commonly used mouse model to study the pathogenesis of AAA is the angiotensin II (Ang II) infusion method delivered via osmotic mini-pump for 28 days. Here, we studied the site-specificity and onset of aortic rupture, characterized three-dimensional (3D) images and flow patterns in developing AAAs by ultrasound imaging, and examined macrophage infiltration in the Ang II model using 65 apolipoprotein E-deficient mice. Aortic rupture occurred in 16 mice (25%) and was nearly as prevalent at the aortic arch (44%) as it was in the suprarenal region (56%) and was most common within the first 7 days after Ang II infusion (12 of 16; 75%). Longitudinal ultrasound screening was found to correlate nicely with histological analysis and AAA volume renderings showed a significant relationship with AAA severity index. Aortic dissection preceded altered flow patterns and macrophage infiltration was a prominent characteristic of developing AAAs. Targeting the inflammatory component of AAA disease with novel therapeutics will hopefully lead to new strategies to attenuate aneurysm growth and aortic rupture.
... Both genetic and pharmacologic blockade of the 5-LO/LT pathway were evaluated for their impact on aortic aneurysm pathogenesis in apoE −/− mice. The Ang II-induced mouse model of AAA conducted in the present studies, originally described by Daugherty et al. [17] with controlled delivery of Ang II by mini-pumps over the course of 4 weeks, was reported to induce striking remodeling of the suprarenal aorta of male mice that is often characterized by aortic dissection [17,21,22]. The evolution of Ang II-induced AAAs is complex with rapid medial layer macrophage accumulation preceding transmedial breaks and large lumen expansion. ...
Genetic association studies and pathological analysis of cardiovascular disease specimens implicate a role for the 5-lipoxygenase (5-LO)/leukotriene (LT) pathway in human cardiovascular disease. Previously, we had detected a role for this pathway in the incidence and severity of hyperlipidemic, cholate-containing, diet-induced aortic aneurysm in mice. The goal of the present study was to assess the importance of the 5-LO/LT pathway in angiotensin II (Ang II)-induced murine abdominal aortic aneurysm (AAA) formation. Mice with either genetic (5-LO(-/-)) or pharmacological (MK-0591) inhibition of the 5-LO pathway on an apolipoprotein E-deficient (apoE(-/-)) background were subjected to a normal chow diet with infusion of Ang II (500 ng/kg/min) for 28 days for assessment of AAA incidence and severity. Ang II-induced marked aortic wall remodeling with an incidence of 32, 29 and 40% AAA formation in 5-LO(-/-) apoE(-/-), 5-LO(+/+)apoE(-/-) and 5-LO(+/+)apoE(-/-) mice treated with FLAP inhibitor MK-0591, respectively, with no statistically significant differences in incidence or severity between groups. Abrogation of the 5-LO pathway in mice indicates a lack of role of leukotrienes in Ang II-induced AAA pathogenesis stressing the need for additional non-rodent AAA pre-clinical models to be tested.
Background:
Aortic aneurysm (AA) is a "silent killer" human disease with no effective treatment. Although the therapeutic potential of various pharmacological agents have been evaluated, there are no reports of β-arrestin-biased AT1R agonist (TRV027) used to prevent the progression of AA.
Methods:
We tested the hypothesis that TRV027 infusion in AngII-induced mouse model of AA prevents AA. High-fat-diet-fed ApoE-null mice were infused with AngII to induce AA and co-infused with TRV027 and a clinically used AT1R blocker Olmesartan to prevent AA. Aortas explanted from different ligand infusion groups were compared with assess different grades of AA or lack of AA.
Results:
AngII produced AA in ≈67% male mice with significant mortality associated with AA rupture. We observed ≈13% mortality due to aortic arch dissection without aneurysm in male mice. AngII-induced AA and mortality was prevented by co-infusion of TRV027 or Olmesartan, but through different mechanisms. In TRV027 co-infused mice aortic wall thickness, elastin content, new DNA, and protein synthesis were higher than untreated and Olmesartan co-infused mice. Co-infusion with both TRV027 and Olmesartan prevented endoplasmic reticulum stress, fibrosis, and vasomotor hyper responsiveness.
Conclusions:
TRV027-engaged AT1R prevented AA and associated mortality by distinct molecular mechanisms compared with the AT1R blocker, Olmesartan. Developing novel β-arrestin-biased AT1R ligands may yield promising drugs to combat AA.
Microfibrillar-associated protein 4 (MFAP4) is an extracellular matrix protein belonging to the fibrinogen-related domain family. It has been localized to elastic fiber-rich regions in several tissues including the arteries, lungs, heart and skin. MFAP4 binds collagen, fibrillins and tropoelastin and contributes to the process of microfibrillar assembly and maturation of elastic fibers. MFAP4 can also bind RGD-dependent integrins, predominantly αVβ3 and αVβ5 through its N-terminal RGD sequence, modulating cellular behavior. Circulating MFAP4 was suggested as a robust biomarker for hepatitis C virus- and alcoholic liver disease-related liver fibrosis, cardiovascular disorders and chronic obstructive pulmonary disease. In mice, MFAP4 seems to have a widely redundant role under homeostatic conditions, as global MFAP4 deficiency results in a mild pulmonary phenotype, causing emphysema-like airspace enlargement that progresses with age. However, emerging in vivo and in vitro data suggest that MFAP4 is actively involved in the pathogenesis of remodeling-associated diseases, including fibrosis, cardiovascular disorders, aging, asthma and cancer through activation of integrin-mediated signaling as well as by modulating TGF-β pathway, thus supporting maladaptive matrix remodeling. This review summarizes the current knowledge about MFAP4 structure and localization, its mechanisms of action in disease-induced tissue remodeling as well as its potential role as a clinical biomarker.
AngII (angiotensin II) infusion in mice has been used to provide mechanistic insight into human abdominal aortic aneurysms for over 2 decades. This is a technically facile animal model that recapitulates multiple facets of the human disease. Although numerous publications have reported abdominal aortic aneurysms with AngII infusion in mice, there remain many fundamental unanswered questions such as uniformity of describing the pathological characteristics and which cell type is stimulated by AngII to promote abdominal aortic aneurysms. Extrapolation of the findings to provide insight into the human disease has been hindered by the preponderance of studies designed to determine the effects on initiation of abdominal aortic aneurysms, rather than a more clinically relevant scenario of determining efficacy on the established disease. The purpose of this review is to enhance understanding of AngII-induced abdominal aortic pathologies in mice, thereby providing greater insight into the human disease.
Abdominal aortic aneurysm (AAA) is a vascular disorder with a high case fatality rate in the instance of rupture. AAA is a multifactorial disease and the etiology is still not fully understood. AAA is more likely to occur in men, but women have a greater risk of rupture and worse prognosis. Women are reportedly protected against AAA possibly by premenopausal levels of estrogen and are, on average, diagnosed at older ages than men. Here, we review the current body of research on AAA pathophysiology in humans, animal models, and cultured cells, with an emphasis on sex differences and sex steroid hormone signaling.
Monocyte chemoattractant/chemotactic protein-1 (MCP-1), a member of the CC chemokine family, is one of the key chemokines that regulate migration and tissue infiltration of monocytes/macrophages. Its role in the pathophysiology of several inflammatory diseases has been widely recognized, thus making MCP-1 a possible target for anti-inflammatory treatments. Curcumin (diferuloylmethane) is a natural polyphenol derived from the rhizomes of Curcuma Longa L. (turmeric). Anti-inflammatory action underlies numerous pharmacological effects of curcumin in the control and prevention of several diseases. The purpose of this review is to evaluate the effects of curcumin on the regulation of MCP-1 as a key mediator of chemotaxis and inflammation, and the biological consequences thereof. In vitro studies have shown that curcumin can decrease MCP-1 production in various cell lines. Animal studies have also revealed that curcumin can attenuate MCP-1 expression and improve a range of inflammatory diseases through multiple molecular targets and mechanisms of action. There is limited data from human clinical trials showing the decreasing effect of curcumin on MCP-1 concentrations and improvement of the course of inflammatory diseases. Most of the in vitro and animal studies confirm that curcumin exert its MCP-1-lowering and anti-inflammatory effects by down-regulating the mitogen-activated protein kinase (MAPK) and NF-κB signaling pathway. As yet, there is limited data from human clinical trials showing the effect of curcumin on MCP-1 levels and improvement of the course of inflammatory diseases. More evidence, especially from human studies, is needed to better assess the effects of curcumin on circulating MCP-1 in different human diseases and the role of this modulatory effect in the putative anti-inflammatory properties of curcumin.
Introduction:
The purpose of this study is to examine whether the insertion (I) and deletion (D) polymorphism of the angiotensin-converting enzyme (ACE) confers susceptibility to aortic aneurysms (AAs).
Materials and methods:
A meta-analysis was conducted on the associations between the ACE I/D polymorphism and all AAs and abdominal aortic aneurysms (AAAs).
Results:
Ten studies consisting of 2784 cases and 2682 controls were available for the meta-analysis. Meta-analysis showed a significant association between the D allele and all types of AA (OR 1.378, 95% CI 1.103-1.723, p = 0.005) and AAA (OR 1.274, 95% CI 1.004-1.617, p = 0.046). Meta-analysis of both the DD genotype and the DD vs. II genotype showed an association with AAAs. Stratification by ethnicity indicated an association between the D allele of the ACE I/D polymorphism and AAAs in Europeans (OR = 1.338, 95% CI = 1.026-1.745, p = 0.031), but not in Asians (OR = 0.927, 95% CI = 0.660-1.303, p = 0.663). Furthermore, analysis using the recessive model, dominant model, and homozygote contrast all showed the same pattern for the D allele.
Conclusions:
Our meta-analysis demonstrates that the ACE I/D polymorphism is associated with susceptibility to AAAs in European populations.
A feature of particular interest observed in vivo in murine abdominal aortic aneurysm (AAA) is the presence of a vortex shed from the proximal edge of the abdominal aortic aneurysm. It is unclear whether the occurrence of the shed vortex is due to the periodic nature of the flow-rate waveform, to geometric features, or to the compliant nature of the vessel tissue. Numerical simulations were performed on 3D semi-idealized and 2D axi-symmetric models of the abdominal aortic aneurysm at a mean Reynolds number of 63 and a Womersley number of 2 (for unsteady inflow conditions). The numerical results from the 3D model showed good agreement with the flows visualized by Doppler Ultrasound with respect to the development of the observed shed vortex. The idealized axi-symmetric models under steady flow conditions showed no signs of vortex shedding. Under unsteady inflow conditions, however, shear-layer roll-up occurred near the peak systolic velocity. The presence of a proximal lip was found to lead to vortex separation (from the wall) earlier in the cardiac cycle, and the presence of the proximal narrowing led to the earliest vortex separation. The sensitivity to the inflow waveform shape also showed that the presence of the shedding, in the model with proximal narrowing, disappeared when the peak-to-mean velocity ratio was reduced by approximately half. Therefore, we conclude that the observed intra-aneurysmal vortex shedding is a shear-layer rollup phenomenon; however, the geometry can act to enhance further the observed vortex shedding.
Abdominal aortic aneurysm (AAA) is an important cause of mortality in older adults. Most AAAs are asymptomatic and screening programs have been introduced to identify AAAs at an early stage in some countries. There is currently no accepted therapy for early stage or small AAAs, which are frequently identified by such programs. In this review, we discuss work underway to identify targets for medical treatments to limit progression of small AAAs. Specifically we discuss studies, which have examined the potential of targeting inflammation, proteolysis, the renin angiotensin system, the coagulation system and sex hormones on AAA pathogenesis. As yet, none of the treatment targets have translated into an agent, which can effectively reduce AAA progression in clinical practice
The aorta is a high-pressure conduit that also conserves the energy output of the heart (elastic recoil). The main structural
proteins of the aorta — collagen and elastin — serve these functions. The aortic architecture is not uniform and varies from
the thoracic aorta to the infrarenal aorta. With these basic understandings of the aortic structure and function in mind,
it is clear that inflammation, genetics, and mechanical forces play important roles in the pathogenesis of abdominal aortic
aneurysms. Additional research is needed to further understand the relationship between these factors.
KeywordsAbdominal aortic aneurysm-Pathophysiology-Pathogenesis
The abdominal aortic aneurysm (AAA) is a significant cause of death and disability in the Western world and is the subject of many clinical and pathological studies. One of the most commonly used surrogates of the human AAA is the angiotensin II (Ang II) induced model used in mice. Despite the widespread use of this model, there is a lack of knowledge concerning its hemodynamics; this study was motivated by the desire to understand the fluid dynamic environment of the mouse AAA. Numerical simulations were performed using three subject-specific mouse models in flow conditions typical of the mouse. The numerical results from one model showed a shed vortex that correlated with measurements observed in vivo by Doppler ultrasound. The other models had smaller aneurysmal volumes and did not show vortex shedding, although a recirculation zone was formed in the aneurysm, in which a vortex could be observed, that elongated and remained attached to the wall throughout the systolic portion of the cardiac cycle. To link the hemodynamics with aneurysm progression, the remodeling that occurred between week one and week two of the Ang II infusion was quantified and compared with the hemodynamic wall parameters. The strongest correlation was found between the remodeled distance and the oscillatory shear index, which had a correlation coefficient greater than 0.7 for all three models. These results demonstrate that the hemodynamics of the mouse AAA are driven by a strong shear layer, which causes the formation of a recirculation zone in the aneurysm cavity during the systolic portion of the cardiac waveform. The recirculation zone results in areas of quiescent flow, which are correlated with the locations of the aneurysm remodeling.
Cerebral aneurysms (CAs) have a high prevalence in the general population and cause lethal subarachnoid hemorrhage. We recently demonstrated that chronic inflammation is an underlying pathogenesis of CA. However, we identified the negative involvement of angiotensin receptor signaling in the pathogenesis of CA.
To elucidate the involvement of the renin-angiotensin system (RAS) by assessing the expression and activity of angiotensin-converting enzyme (ACE), a key enzyme of RAS, during CA formation and evaluating the effect of imidapril, an ACE inhibitor and a potent inhibitor of matrix metalloproteinase-9 (MMP-9), on CA formation.
Surgically induced CA models of rats were used. Imidapril was given intraperitoneally to rats, and aneurysm size and medial thickness of CAs were examined 1 month after induction. Then, ACE and MMP-9 expression was assessed by immunostaining and Western blot analysis. The MMP-9 activity was evaluated by gelatin zymography, and ACE expression in human CA walls was assessed by immunostaining.
Imidapril significantly suppressed the size and medial thinning of induced CAs. The expression and activity of ACE were not induced in CA walls. Furthermore, imidapril treatment did not influence ACE expression and activity, suggesting that the inhibitory effect of imidapril was independent of an inhibition of the RAS. Imidapril inhibited MMP-9 activity upregulated in CA walls. In an in vitro study, imidapril suppressed MMP-9 activity in a dose-dependent manner. In human CA walls, as in the rat model, ACE expression was not upregulated.
Angiotensin-converting enzyme is not involved in the pathogenesis of CA formation. Imidapril suppresses CA formation in an ACE-independent and MMP-9-dependent manner.
Because both endothelin-1 (ET-1) and angiotensin II (AngII) are independent mediators of arterial remodeling, we sought to determine the role of ET receptor inhibition in AngII-accelerated atherosclerosis and aortic aneurysm formation. We administered saline or AngII and/or bosentan, an endothelin receptor antagonist (ERA) for 7, 14, or 28 days to 6-week- and 6-month-old apolipoprotein E-knockout mice. AngII treatment increased aortic atherosclerosis, which was reduced by ERA. ET-1 immunostaining was localized to macrophage-rich regions in aneurysmal vessels. ERA did not prevent AngII-induced aneurysm formation but instead may have increased aneurysm incidence. In AngII-treated animals with aneurysms, ERA had a profound effect on the non-aneurysmal thoracic aorta via increasing wall thickness, collagen/elastin ratio, wall stiffness, and viscous responses. These observations were confirmed in acute in vitro collagen sheet production models in which ERA inhibited AngII's dose-dependent effect on collagen type 1 α 1 (COL1A1) gene transcription. However, chronic treatment reduced matrix metalloproteinase 2 mRNA expression but enhanced COL3A1, tissue inhibitor of metalloproteinase 1 (TIMP-1), and TIMP-2 mRNA expressions. These data confirm a role for the ET system in AngII-accelerated atherosclerosis but suggest that ERA therapy is not protective against the formation of AngII-induced aneurysms and can paradoxically stimulate a chronic arterial matrix remodeling response.
Despite being a leading cause of death in the West, the pathophysiology of abdominal aortic aneurysms (AAA) is still incompletely understood. Pharmacotherapy to reduce the growth of small AAAs is limited and techniques for repairing aneurysms continue to evolve. Experimental models play a key role in AAA research, as they allow a detailed evaluation of the pathogenesis of disease progression. This review focuses on in vivo experimental models, which have improved our understanding of the potential mechanisms of AAA development and contributed to the advancement of new treatments.
Current management of aortic aneurysms (AAs) relies primarily on size criteria to determine whether invasive repair is indicated to preempt rupture. We hypothesized that emerging molecular imaging tools could be used to more sensitively gauge local inflammation. Because macrophages are key effector cells that destabilize the extracellular matrix in the arterial wall, it seemed likely that they would represent suitable imaging targets. We here aimed to develop and validate macrophage-targeted nanoparticles labeled with fluorine-18 ((18)F) for positron emission tomography-computed tomography (PET-CT) detection of inflammation in AAs.
Aneurysms were induced in apolipoprotein E-/- mice via systemic administration of angiotensin II. Mice were imaged using PET-CT and a monocyte/macrophage-targeted nanoparticle. AAs were detected by contrast-enhanced micro-CT and had a mean diameter of 1.85 ± 0.08 mm, whereas normal aortas measured 1.07 ± 0.03 (P < 0.05). The in vivo PET signal was significantly higher in aneurysms (standard uptake value, 2.46 ± 0.48) compared with wild-type aorta (0.82 ± 0.05, P < 0.05). Validation with scintillation counting, autoradiography, fluorescence, and immunoreactive histology and flow cytometry demonstrated that nanoparticles localized predominantly to monocytes and macrophages within the aneurysmatic wall.
PET-CT imaging with (18)F-labeled nanoparticles allows quantitation of macrophage content in a mouse model of AA.
The role of adventitial fibroblasts in the vascular inflammation observed in the adventitia of large vessels in numerous cardiovascular diseases remains unclear. Our objective was to explore the contribution of these cells to angiotensin II (Ang II)-induced aortic inflammation and adventitial expansion.
Cytokine production by primary human aortic adventitial fibroblasts (AoAF) in tissue culture was detected using multiplex ELISA, and increases in cytokine mRNA following Ang II stimulation were quantitated by real-time PCR. The ability of AoAF-derived MCP-1 to attract monocytes was studied in vitro using Boyden assays, and the resulting effect of the monocyte-AoAF interaction on fibroblast proliferation was measured in vitro using proliferation and (3)H-thymidine incorporation assays. Ang II-induced fibroblast proliferation was measured in vivo using aortic digestion of single cells followed by flow cytometric quantification of fibroblast numbers as well as fibroblast and PCNA immunostaining. The ability of monocytes to induce AoAF proliferation was demonstrated in vivo using CCR2(+/+) wild-type monocyte adoptive transfer into Ang II-stimulated CCR2-null mice which can produce MCP-1 but have cells lacking the MCP-1 receptor - CCR2.
AoAF constitutively secreted numerous proinflammatory cytokines, particularly IL-6 and MCP-1, whose gene expressions were further upregulated in response to Ang II stimulation. AoAF-derived MCP-1 was potent in recruiting THP-1 monocytes in vitro, and these monocytes stimulated AoAF proliferation based on a flow cytometric assessment of cell number and (3)H-thymidine incorporation in tissue culture. In vivo, Ang II induced fibroblast proliferation, increased fibroblast and PCNA adventitial staining, and blunted inflammatory responses in the CCR2(-/-) background. Injection of CCR2(+/+) monocytes into Ang II-treated CCR2(-/-) mice restored adventitial thickening which resulted in increased fibrosis secondary to adventitial fibroblast proliferation.
Our results suggest that Ang II-stimulates AoAF to recruit monocytes via fibroblast-derived MCP-1, and the recruited monocytes further activate fibroblast proliferation, adventitial thickening, and additional cytokine production. This fibroblast-monocyte amplification loop may critically mediate hallmarks of adventitial inflammation common to many cardiovascular diseases.
There is strong evidence of a genetic predisposition to abdominal aortic aneurysm (AAA), however the genes involved remain largely elusive. Recently, two large studies have suggested an association between the angiotensin converting enzyme gene and AAA. This study aimed to investigate the possible association between the ACE insertion/deletion polymorphism and abdominal aortic aneurysm (AAA) in order to replicate the findings of other authors.
A case-control study was performed including 1155 patients with aneurysms and 996 screened control subjects. DNA was extracted from whole blood and genotypes determined in 1155 AAAs and 996 controls using a two stage polymerase chain reaction (PCR) technique.
The groups were reasonably matched in terms of risk factors for AAA. No association was found between the ACE gene insertion/deletion polymorphism and AAA in this study.
This study cannot support the findings of previous authors and provides evidence against a link between the ACE gene insertion/deletion polymorphism and AAA.
Thoracic aortic aneurysms result from dysregulated remodeling of the vascular extracellular matrix, which may occur as a result of altered resident cellular function. The present study tested the hypothesis that aortic fibroblasts undergo a stable change in cellular phenotype during thoracic aortic aneurysm formation.
Primary murine aortic fibroblasts were isolated from normal and thoracic aortic aneurysm-induced aortas (4 weeks post induction with 0.5 mol/L CaCl(2) 15 minutes) by the outgrowth method. Normal and thoracic aortic aneurysm cultures were examined using a focused polymerase chain reaction array to determine fibroblast-specific changes in gene expression in the absence and presence of biological stimulation (endothelin-1, phorbol-12-myristate-13-acetate, angiotensin-II). The relative expression of 38 genes, normalized to 4 housekeeping genes, was determined, and genes displaying a minimum 2-fold increase/decrease or genes with significantly different normalized cycle threshold values were considered to have altered expression.
At steady state, thoracic aortic aneurysm fibroblasts revealed elevated expression of several matrix metalloproteinases (Mmp2, Mmp11, Mmp14), collagen genes/elastin (Col1a1, Col1a2, Col3a1, Eln), and other matrix proteins, as well as decreased expression of Mmp3, Timp3, and Ltbp1. Moreover, gene expression profiles in thoracic aortic aneurysm fibroblasts were different than normal fibroblasts after equivalent biological stimuli.
This study demonstrated for the first time that isolated primary aortic fibroblasts from thoracic aortic aneurysm-induced mice possess a unique and stable gene expression profile, and when challenged with biological stimuli, induce a transcriptional response that is different from normal aortic fibroblasts. Together, these data suggest that aortic fibroblasts undergo a stable phenotypic change during thoracic aortic aneurysm development, which may drive the enhancement of extracellular matrix proteolysis in thoracic aortic aneurysm progression.
Cerebral aneurysms (CAs) are the main cause of life-threatening subarachnoid hemorrhage. Given its prevalence and endpoint, CA treatment is a public health issue. Effective medical treatment of CAs is lacking because the detailed mechanisms of CA formation are incompletely understood.
The aim of this contribution is to review recent articles about CA formation, to suggest the underlying mechanisms of CA formation, and to discuss potential therapeutic targets for treatment. Articles were collected by an internet search of PubMed using the keywords 'intracranial' or 'cerebral aneurysm'. WHAT THE READERS WILL GAIN: A review of articles about the pathogenesis of CA formation focusing on inflammation. Recent articles demonstrate that inflammation-related-molecule induction and inflammatory cell infiltration in CA walls and the close relationship between inflammatory responses and CA formation. From studies in experimental models, chronic inflammation triggered primarily by NF-kappaB activation in endothelial cells and subsequent macrophage infiltration have critical roles in CA formation. Inhibition of inflammation-related molecules in CA walls results in the decreased incidence of CA formation.
Agents with anti-inflammatory activity (particularly anti- NF-kappaB effects) have potential as therapeutic drugs for CAs.
Mechanisms of formation and growth of intracranial aneurysms are poorly understood. To investigate the pathophysiology of intracranial aneurysms, an animal model of intracranial aneurysm yielding a high incidence of large aneurysm formation within a short incubation period is needed. We combined two well-known clinical factors associated with human intracranial aneurysms, hypertension and the degeneration of elastic lamina, to induce intracranial aneurysm formation in mice. Roles of matrix metalloproteinases (MMPs) in this model were investigated using doxycycline, a broad-spectrum MMP inhibitor, and MMP knockout mice. Hypertension was induced by continuous infusion of angiotensin II for 2 weeks. The disruption of elastic lamina was achieved by a single stereotaxic injection of elastase into the cerebrospinal fluid at the right basal cistern. A total of 77% of the mice that received 35 milliunits of elastase and 1000 ng/kg per minute of angiotensin II developed intracranial aneurysms in 2 weeks. There were dose-dependent effects of elastase and angiotensin II on the incidence of aneurysms. Histologically, intracranial aneurysms observed in this model closely resembled human intracranial aneurysms. Doxycycline, a broad-spectrum MMP inhibitor, reduced the incidence of aneurysm to 10%. MMP-9 knockout mice, but not MMP-2 knockout mice, had reduced the incidence of intracranial aneurysms. In summary, a stereotaxic injection of elastase into the basal cistern in hypertensive mice resulted in intracranial aneurysms that closely resembled human intracranial aneurysms. The intracranial aneurysm formation in this model appeared to depend on MMP activation.
Hyperlipidimic mice administered angiotensin II have been used for the study of abdominal aortic aneurysms (AAAs). The purpose of this study was to examine the use of MRI for studying AAA development and for examining the effects of pharmacological intervention on AAA development in the apolipoprotein E-deficient mouse.
Suprarenal aortic aneurysms were generated in apolipoprotein E-deficient mice administered angiotensin II (1000 ng/kg per min) for up to 28 days. In vivo MRI was performed serially (once weekly) to assess AAA development and rupture. Comparison of AAA size as measured by in vivo and ex vivo MRI resulted in excellent agreement (r=0.96, P<0.0001). In addition, MRI correlated with histology-derived AAA area assessment (in vivo versus histology: r=0.84, P<0.0001; ex vivo versus histology: r=0.89, P<0.0001). In a separate study, angiotensin II-administered apolipoprotein E-deficient mice were treated with doxycycline (broad-based matrix metalloproteinase inhibitor; 30 mg/kg per day for 28 days). MRI was able to noninvasively assess a reduced rate of AAA development (46% versus 71%, P<0.05), a decreased AAA area (2.56 versus 4.02 mm(2), P<0.01), and decreased incidence of rupture (43% versus 100%) in treated versus control animals. Inhibition of aorta matrix metalloproteinase 2/9 activity was observed in the treated animals.
These results demonstrate the use of MRI to noninvasively and temporally assess AAA development on pharmacological intervention in this preclinical cardiovascular disease model.
To evaluate the use of an ultrasmall superparamagnetic iron oxide (USPIO) contrast agent as a marker for the detection of macrophage in a preclinical abdominal aortic aneurysm animal (AAA) model.
Osmotic pumps were implanted subcutaneously in apoE(-/-) mice for continuous infusion of Angiotensin II (Ang-II). Weekly bright-blood gradient echo scans were performed on the suprarenal abdominal aorta to evaluate aneurysm development. Once an AAA was detected, animals were administered 1000 mumol/kg of the USPIO contrast agent ferumoxtran-10 (Combidex) followed by in vivo scanning 24 h post-USPIO administration. After in vivo imaging, aortas were harvested for ex vivo imaging, histology, iron quantification, and gene expression analysis.
Reduced signal intensity was evident in the post-USPIO transverse images of the abdominal aorta. The areas of reduced signal were primarily along the aneurysm shoulder and outer perianeurysm areas and corresponded to regions of macrophage infiltration and colocalized USPIO determination by means of histological staining. The absolute iron content measured significantly correlated to the area of signal reduction in the ex vivo images (r = 0.9; P < 0.01). In the AAA tissue, the macrophage-driven cytokine gene expression was up-regulated along with a matrix metalloproteinase known to mediate extracellular matrix breakdown in this disease model.
These results demonstrate the feasibility of using an USPIO contrast agent as a surrogate for detecting the acute inflammatory process involved in the development of abdominal aneurysms.
Abdominal aortic aneurysm (AAA) is a very significant health problem in the United States. Current therapeutic options are surgery or endovascular stenting. Medical treatment is not very effective and there is no medical therapy that can effect the regression of AAA. Surgical or endovascular intervention for many older patients will be unnecessary if medications could prevent or reduce the progression rate of small AAA by 50%. Basic research has helped to determine the molecular basis of pathogenesis in AAA. Mediators of aortic damage include angiotensin II, leukotriene-LT4, prostaglandin- PGE2, interleukins, tumor necrosis factor, tissue plasminogen activator, c-Jun N-terminal Kinase, NF-kappaB, Rho kinases, osteoprotegerin and chymases. They work in concert to activate matrix metalloproteinase, serine proteases and cysteine proteases. The result is degradation of aortic wall proteins, extracellular matrix and apoptosis of vascular smooth muscle cells. An enhanced understanding of the pathogenetic pathways has led to significant research and development of new molecules, which can inhibit these pathways and delay the expansion of AAA. We discuss newly patented agents that may have a beneficial role in preventing the progression of AAA.
Murine strains susceptible to atherosclerosis provide valuable models to study factors involved in atherogenesis. In some murine models, limited hypercholesterolemia can be achieved and lesions develop primarily in the aortic origin, in the vicinity of the aortic valve. In other models such as LDL receptor-deficient and apoE-deficient mice, diet-induced or spontaneous hypercholesterolemia and atherogenesis are much greater. To determine whether lesion formation in the aortic origin, where particular pathogenic conditions may exist, correlates with lesion formation throughout the entire aorta, we measured the extent of atherosclerosis in both areas in 8 apoE- and 11 LDL receptor-deficient mice fed cholesterol-rich diets for 3-6 months, as well as in 9 C57BL/6 mice fed an atherogenic diet for a year, using two different morphometric methods. Both apoE-deficient and LDL receptor-deficient mice developed extensive lesions throughout the aorta, and in these models a significant correlation was observed between the extent of lesions in the entire aorta (measured as percent of surface area) and that at the aortic origin (measured as averaged lesion area per cross-section) (r = 0.77, P < 0.0001). In contrast, the plasma cholesterol levels achieved in C57BL/6 mice were much lower, and atherosclerotic lesions were found almost exclusively in the aortic origin. These results demonstrate that in murine models developing extensive aortic lesions, both morphometric methods provide valid and complementary information on the degree and distribution of atherosclerosis, and suggest that under severe atherogenic conditions lesion formation throughout the aorta is determined by the same pathological factors, in each model. Comparison of the extent of atherosclerosis in the entire aorta between genders also showed that male LDL receptor-deficient mice had significantly more lesions than females (29.2 vs. 14.8%, P < 0.005, n = 16). A similar trend was also seen in apoE-deficient mice.
The molecular mechanisms predisposing to atherosclerotic aneurysm formation remain undefined. Nevertheless, rupture of aortic aneurysms is a major cause of death in Western societies, with few available treatments and poor long-term prognosis. Indirect evidence suggests that matrix metalloproteinases (MMPs) and plasminogen activators (PAs) are involved in its pathogenesis. MMPs are secreted as inactive zymogens (pro-MMPs), requiring activation in the extracellular compartment. Plasmin, generated from the zymogen plasminogen by tissue-type plasminogen activator (t-PA) or urokinase-type plasminogen activator (u-PA; refs 14,15), has been proposed as a possible activator in vitro, but evidence for such a role in vivo is lacking. Analysis of atherosclerotic aorta in mice with a deficiency of apoliprotein E (Apoe-/-; ref. 18), singly or combined with a deficiency of t-PA (Apoe-/-:Plat-/-) or of u-PA (Apoe-/-:Plau-/-; ref. 19), indicated that deficiency of u-PA protected against media destruction and aneurysm formation, probably by means of reduced plasmin-dependent activation of pro-MMPs. This genetic evidence suggests that plasmin is a pathophysiologically significant activator of pro-MMPs in vivo and may have implications for the design of therapeutic strategies to prevent aortic-wall destruction by controlling Plau gene function.
Abdominal aortic aneurysms represent a life-threatening condition characterized by chronic inflammation, destructive remodeling of the extracellular matrix, and increased local expression of matrix metalloproteinases (MMPs). Both 92-kD gelatinase (MMP-9) and macrophage elastase (MMP-12) have been implicated in this disease, but it is not known if either is necessary in aneurysmal degeneration. We show here that transient elastase perfusion of the mouse aorta results in delayed aneurysm development that is temporally associated with transmural mononuclear inflammation, increased local production of several elastolytic MMPs, and progressive destruction of the elastic lamellae. Elastase-induced aneurysmal degeneration was suppressed by treatment with a nonselective MMP inhibitor (doxycycline) and by targeted gene disruption of MMP-9, but not by isolated deficiency of MMP-12. Bone marrow transplantation from wild-type mice prevented the aneurysm-resistant phenotype in MMP-9-deficient animals, and wild-type mice acquired aneurysm resistance after transplantation from MMP-9-deficient donors. These results demonstrate that inflammatory cell expression of MMP-9 plays a critical role in an experimental model of aortic aneurysm disease, suggesting that therapeutic strategies targeting MMP-9 may limit the growth of small abdominal aortic aneurysms.
Increased plasma concentrations of angiotension II (Ang II) have been implicated in atherogenesis. To examine this relationship directly, we infused Ang II or vehicle for 1 month via osmotic minipumps into mature apoE(-/-) mice. These doses of Ang II did not alter arterial blood pressure, body weight, serum cholesterol concentrations, or distribution of lipoprotein cholesterol. However, Ang II infusions promoted an increased severity of aortic atherosclerotic lesions. These Ang II-induced lesions were predominantly lipid-laden macrophages and lymphocytes; moreover, Ang II promoted a marked increase in the number of macrophages present in the adventitial tissue underlying lesions. Unexpectedly, pronounced abdominal aortic aneurysms were present in apoE(-/-) mice infused with Ang II. Sequential sectioning of aneurysmal abdominal aorta revealed two major characteristics: an intact artery that is surrounded by a large remodeled adventitia, and a medial break with pronounced dilation and more modestly remodeled adventitial tissue. Although no atherosclerotic lesions were visible at the medial break point, the presence of hyperlipidemia was required because infusions of Ang II into apoE(+/+) mice failed to generate aneurysms. These results demonstrate that increased plasma concentrations of Ang II have profound and rapid effects on vascular pathology when combined with hyperlipidemia, in the absence of hemodynamic influences.
Abdominal aortic aneurysms (AAA) have a high prevalence in aged populations and are responsible for a large number of deaths. Despite the widespread nature of the disease, relatively little is known regarding mechanisms for formation and progression of aortic aneurysms. In part, this lack of knowledge is attributable to a paucity of animal models for this disease. This review summarizes the available animal models of AAA and focuses on a novel model of reproducible AAA generated by infusion of angiotensin II (AngII) into mice rendered hyperlipidemic by the absence of either apolipoprotein E or low-density lipoprotein receptors. AAA generated by AngII infusion have many characteristics of the human disease including marked luminal expansions, perimedial remodeling, inflammation, thrombosis and a link to hyperlipidemia. As in the human disease, male mice are more susceptible to the development of AAA than females. The vascular pathology occurs from the effects of AngII at AT1 receptors present on bone marrow-derived cells. Studies are ongoing to define the mediators responsible for AngII-induced inflammation and degradation of the medial layer of the vascular wall. The AngII-induced model of AAA has the potential to provide novel insights into the underlying mechanisms of this disease and assist with the development of pharmacological therapies.
In humans, the incidence and severity of abdominal aortic aneurysms (AAA) are greater in males than in females. Chronic infusion of angiotensin II (AngII) into apolipoprotein E-deficient (apoE(-/-)) mice promotes atherosclerosis and causes the formation of AAAs. Just as human males are more susceptible to developing AAAs, male mice are more susceptible to AngII-induced AAAs. We hypothesized that sex steroid hormones mediate gender differences in AngII-induced AAA through regulation of the renin-angiotensin system. To define the role of ovarian hormones, female apoE(-/-) mice were subjected to ovariectomy or sham operation and infused with AngII (1000 ng/kg x min) for 28 d. Ovariectomy had no effect on AngII-induced atherosclerosis, nor did it influence the incidence or severity of AAA. To define the role of testicular hormones, male apoE(-/-) mice were subjected to orchidectomy (orx) or sham operation and infused with AngII (1000 ng/kg x min) for 28 d. Orx resulted in a profound reduction in AAA incidence (85% vs. 18%, sham vs. orx; P = 0.003) to the level observed in females (25%). However, orx had no effect on AngII-induced reductions in plasma renin concentration or spleen AngII receptor density. In contrast, orx resulted in an increase in atherosclerosis (0.46 +/- 0.07 vs. 1.20 +/- 0.21 mm(2), sham vs. orx; P = 0.002). These results suggest that estrogen does not mediate gender differences in AngII-induced AAA. In contrast, androgens mediate a higher incidence of AngII- induced AAA, through mechanisms that do not appear to involve circulating renin or angiotensin receptor density.
Abdominal aortic aneurysms (AAAs) have devastating effects on the morbidity and mortality of a large portion of the elderly population. Current therapeutic options for AAAs are limited to surgical approaches, because there are no proven pharmacologic treatments. Recently, there is evolving evidence that angiotensin II (Ang II) participates in the initiation and propagation of AAAs. Animal studies have consistently demonstrated the ability of Ang II to promote the formation of AAAs, although the mechanisms of this effect have not been defined. Further definition of the role of the renin-angiotensin system in AAA formation and progression will identify potential therapeutic strategies for treatment of this disease.
To examine the role of polymorphisms in angiotensin converting enzyme (ACE, I/D) and angiotensin II receptor (AT1R, A1166C) in the development of abdominal aortic aneurysm (AAA).
We investigated 250 consecutive patients, 217 males and 33 females (median age 72, range 50-83), undergone AAA elective repair and 250 healthy controls, comparable for sex and age. ACE and AT1R polymorphisms were studied by PCR-RFLP analysis. The genotype distribution was in Hardy-Weinberg equilibrium for all polymorphisms.
The genotype distribution and allele frequency of ACE I/D, but not AT1R A1166C polymorphism were significantly different between patients and controls (ACE I/D: p=0.0002 and p<0.0001, respectively, and AT1R A1166C: p=0.6 and p=0.4, respectively). An association between the ACE DD genotype and the predisposition to AAA was found (OR DD vs. ID+II=1.9 95% CI 1.3-2.9, p<0.0001). Multivariate analysis adjusted for age, sex, traditional vascular risk factors and other atherosclerotic localizations, showed ACE DD genotype to be independently related to the disease (OR DD vs. ID+II=2.4, 95% CI 1.3-4.2 p=0.003).
Our findings document that ACE DD genotype represents a susceptibility factor for AAA.
Our objective was to examine the role of an exogenous nitric oxide (NO) donor, DETA-NONOate (DETA), on matrix metalloproteinase (MMP)-9, MMP-2, and tissue inhibitor of matrix metalloproteinases (TIMP)-1 expression and activity in interleukin (IL)-1beta-induced rat aortic smooth muscle cells (RA-SMCs) and rat aortic explants (RAEs). RA-SMCs were incubated with IL-1beta (2 ng/ml), an inflammatory cytokine known to induce MMP-9 expression, and increasing concentrations of DETA (0, 1.0, 10, 100 microM; n = 3/group) for 48 hr. RAEs were incubated with IL-1beta (2 ng/mL) and increasing concentrations of DETA (0, 5.0, 50, 100, and 500 microM; n = 3/group) for 48 hr. Media were collected and assayed for NO(x) by the Griess reaction and MMP-9 activity by zymography. Messenger RNA (mRNA) was extracted from cells and analyzed for MMP-9, MMP-2, and TIMP-1 expression levels by quantitative real-time reverse-transcriptase polymerase chain reaction. All statistical analyses were performed by analysis of variance. In RA-SMCs and RAEs, DETA administration resulted in a dose-dependent increase in media NOx concentration (RA-SCM p < 0.01, RAE p < 0.01) and a concurrent decrease in both MMP-9 expression (RASMC p = 0.01, RAE p = 0.01) and activity (RASMC p = 0.04, RAE p = 0.006). There were no significant differences seen in MMP-2 and TIMP-1 expression or activity in response to DETA exposure. DETA decreased IL-1beta-induced MMP-9 expression and activity in both RA-SMCs and RAEs in a dose-dependent fashion. In addition, DETA administration had no effect on MMP-2 or TIMP-1 expression or activity in vitro. These data suggest that NO donors may be beneficial in decreasing MMP-9 levels and might serve to inhibit MMP-9-dependent vessel wall remodeling seen during abdominal aortic aneurysm formation.
Objective: Cystic medial degeneration (CMD) is a histologic abnormality that is common in aortic diseases such as aortic dilation, aneurysm, or dissection. Although little is known about the mechanism underlying CMD, we have previously demonstrated that angiotensin II signaling via angiotensin II type 2 receptor (AT2R) plays a central role in apoptosis of vascular smooth muscle cells (VSMCs) occurring in CMD associated with Marfan syndrome. The aim of this study is to elucidate the role of angiotensin II signaling in THE pathogenesis of aortic diseases associated with CMD. Method: We investigated the effects of angiotensin-converting enzyme inhibitor (ACEI), temocapril (n = 15), angiotensin II receptor type-1 (AT1R) blocker, CS-866 (n = 15), and vehicle control (n = 17) on 0.25% β-aminopropionitrile monofumarate (BAPN)-induced aortic dissection and histopathologic findings in a rat model. Results: Temocapril significantly prevented aortic dissection (P < .05), CMD (P < .01), and VSMC apoptosis (P < .01) compared with vehicle control in BAPN-fed rats. However, CS-866 did not show any preventive effect. Reversed transcriptase-polymerase chain reaction demonstrated that expression of both AT1R and AT2R was detected in control rat aortas, and that AT2R expression was significantly upregulated in the aortas of BAPN-fed rats (P < .01). Blood pressure was significantly and equally lowered in both temocapril and CS-866 groups compared with control. Conclusions: Differential expression of angiotensin II receptors and AT2R signaling are involved in the pathogenesis of CMD and aortic dissection in BAPN-fed rats. ACEIs might be of clinical value for the prevention and treatment of aortic diseases related to CMD. (J Vasc Surg 2002;36:818-23.)
Inflammatory cells often are seen in the walls of human aortic aneurysms, but their significance is uncertain. To investigate their actions an in vivo model of arterial aneurysms was developed in the rat. Fifteen units of hog pancreatic elastase were infused for 2 hours into the isolated abdominal aorta in 26 rats. The vessels were measured in vivo and were excised for conventional histologic and immunohistologic study at selected intervals. In untreated control rats the diameter of the aorta was 1.04 +/- 0.02 mm. Immediately after infusion with elastase the aorta dilated 26% to 1.31 +/- 0.02 mm (p = NS), with no histologically demonstrable remaining elastic lamellae. Two and one half days after infusion the aorta dilated nearly 300% to 3.09 +/- 0.08 mm (p less than 0.05). These vessels exhibited large numbers of activated macrophages and T cells in the media. Three and 4 days after infusion the vessels dilated 388% to 4.04 +/- 0.09 mm and 367% to 3.82 +/- 0.31 mm, respectively. These vessels also exhibited numerous inflammatory cells in the media. Six days after infusion the vessels enlarged 421% to 4.38 +/- 0.03 mm (p less than 0.05), and the infiltrate persisted staining immunohistologically for macrophages, polymorphic neutrophils, and T lymphocytes. Twelve days after infusion the aneurysms remained enlarged but stable at 4.23 +/- 0.14 mm (p = NS). At this time the number of inflammatory cells regressed to control levels. The temporal correlation between inflammatory infiltrate and aneurysmal enlargement suggests that inflammatory cells may participate in the destruction of the aneurysmal vessel wall thereby promoting progressive enlargement.(ABSTRACT TRUNCATED AT 250 WORDS)
Spontaneous rupture of the internal elastic lamina (IEL) occurs in some arteries of the rat during growth and aging. Inbred, normotensive, Brown Norway (BN) rats are particularly susceptible to rupture of the IEL, especially in the abdominal aorta (AA). Preliminary experiments showed that different angiotensin-converting enzyme (ACE) inhibitors protect against rupture of the IEL in the BN rat to a greater extent than hydralazine, suggesting a role of the renin-angiotensin system (RAS) in this phenomenon. To explore this possibility, we have treated male BN rats from 4.5 to 14 weeks of age with either enalapril or losartan (both at 1, 3, and 10 mg x kg(-1) x d(-1)) or with the calcium antagonists mibefradil (at 3, 10, 30, and 45 mg x kg(-1) x d(-1)) and amlodipine (at 30 mg x kg(-1) x d(-1)). Systolic blood pressure (SBP) was measured weekly, and at the end of treatment we (1) recorded body and heart weights, (2) measured various parameters of the RAS in plasma, (3) quantified interruptions in the IEL on "en face" preparations of AA, and (4) quantified elastin, collagen, and cell proteins in the media of the thoracic aorta. Results showed that enalapril and losartan similarly decrease SBP and rupture of the IEL in the AA, suggesting that enalapril inhibits the latter via a decrease in the production of angiotensin II (Ang II) and not via another effect on ACE. The decrease in IEL rupture and in SBP, as well as the modifications in the parameters of the RAS, were all dose dependent. Mibefradil had little effect on the RAS and, at the highest doses, decreased SBP to an extent similar to that for enalapril at 3 mg x kg(-1) x d(-1) but did not significantly inhibit IEL rupture. Amlodipine decreased SBP, increased plasma renin concentration, and was without effect on IEL rupture. All treatments at the highest doses had a hypotrophic effect on the aortic media but differed in their effects on the heart, with enalapril and losartan decreasing and mibefradil and amlodipine increasing heart weight, suggesting that the inhibition of IEL rupture may be related to a cardiac hypotrophic effect. All these results, taken together, suggest that Ang II plays a role in the rupture of the IEL that is, in part, independent of SBP.
Locally formed angiotensin II (Ang II) and mast cells may participate in the development of atherosclerosis. Chymase, which originates from mast cells, is the major Ang II-forming enzyme in the human heart and aorta in vitro. The aim of the present study was to investigate aortic Ang II-forming activity (AIIFA) and the histochemical localization of each Ang II-forming enzyme in the atheromatous human aorta. Specimens of normal (n=9), atherosclerotic (n=8), and aneurysmal (n=6) human aortas were obtained at autopsy or cardiovascular surgery from 23 subjects (16 men, 7 women). The total, angiotensin-converting enzyme (ACE)-dependent, and chymase-dependent AIIFAs in aortic specimens were determined. The histologic and cellular localization of chymase and ACE were determined by immunocytochemistry. Total AIIFA was significantly higher in atherosclerotic and aneurysmal lesions than in normal aortas. Most of AIIFA in the human aorta in vitro was chymase-dependent in both normal (82%) and atherosclerotic aortas (90%). Immunocytochemical staining of the corresponding aortic sections with antichymase, antitryptase or anti-ACE antibodies showed that chymase-positive mast cells were located in the tunica adventitia of normal and atheromatous aortas, whereas ACE-positive cells were localized in endothelial cells of normal aorta and in macrophages of atheromatous neointima. The density of chymase- and tryptase-positive mast cells in the atherosclerotic lesions was slightly but not significantly higher than that in the normal aortas, and the number of activated mast cells in the aneurysmal lesions (18%) was significantly higher than in atherosclerotic (5%) and normal (1%) aortas. Our results suggest that local Ang II formation is increased in atherosclerotic lesions and that chymase is primarily responsible for this increase. The histologic localization and potential roles of chymase in the development of atherosclerotic lesions appear to be different from those of ACE.
to establish whether deletion of the angiotensin-converting enzyme (ACE) gene is a risk factor predisposing to abdominal aortic aneurysm (AAA) or not.
the study included 125 patients with AAA and 153 controls randomly selected from 328 individuals. The control subjects were confirmed not to have an AAA, but matched with the AAA group for age, sex, hypertension, diabetes mellitus, and hyperlipidaemia. The presence of ACE polymorphism was detected by a polymerase chain reaction using DNA extracted from blood.
the distribution of ACE genotypes and allele frequencies in the control and AAA groups was not significantly different.
the deletion polymorphism in the ACE gene is not a risk factor for AAA.
The purpose of this study was to determine the effect of chronic angiotensin II (AngII) infusion on the severity of the atherogenic process in low density lipoprotein (LDL) receptor -/- mice with established lesions. LDL receptor -/- mice receiving a diet enriched in cholesterol, saturated fat, and cholate, were infused with saline or AngII (500 ng/kg/min) for 28 days. Systolic blood pressure increased in LDL receptor -/- mice following 7 days of AngII infusion, followed by a decline to baseline levels at 28 days, despite continued AngII infusion. Serum cholesterol was not influenced by AngII infusion in LDL receptor -/- mice; however, serum triglyceride concentrations were reduced significantly in LDL receptor -/- mice receiving AngII. The percent of intimal surface area covered by lesion was not increased in LDL receptor -/- mice receiving AngII; however, the content of cholesterol (esterified and unesterified) in lesions of the arch, thoracic, and abdominal aorta was significantly increased in those mice infused with AngII. Of note, in 20% of the LDL receptor -/- mice receiving AngII, large aneurysms were found in the abdominal aorta. Aneurysms appeared as breaks in the media and surrounding tissue of the vessel wall, encompassing amorphous and acellular masses with patches of thrombotic material. These results demonstrate that chronic infusion of AngII promotes the atherogenic processes in LDL receptor -/- mice, manifest as increases in lesion cholesterol content. Effects of AngII to promote atherogenesis were apparent at doses which did not markedly elevate systolic pressure. Importantly, infusion of AngII in LDL receptor -/- mice resulted in the development of aortic aneurysms.
Pathologic remodeling of the extracellular matrix is a critical mechanism in the development and progression of abdominal aortic aneurysms (AAAs). Although angiotensin-converting enzyme (ACE) inhibitors are known to alter vascular wall remodeling in other conditions, their effects on AAAs are unknown. In this study we assessed the effect of ACE inhibitors in a rodent model of aneurysm development.
Male Wistar rats underwent transient aortic perfusion with porcine pancreatic elastase, followed by treatment with one of three ACE inhibitors (captopril [CP], lisinopril [LP], or enalapril [EP]), an angiotensin (AT)1 receptor antagonist (losartan [LOS]), or water alone (9 rats in each group). Blood pressure and aortic diameter (AD) were measured before elastase perfusion and on day 14, with an AAA defined as an increase in AD (DeltaAD) of more than 100%. The structural features of the aortic wall were examined by means of light microscopy.
Aneurysmal dilatation consistently developed within 14 days of elastase perfusion in untreated rats, coinciding with the development of a transmural inflammatory response and destruction of the elastic media (mean DeltaAD, 223% +/- 28%). All three ACE inhibitors prevented AAA development (mean DeltaAD: CP, 67% +/- 4%; LP, 18% +/- 12%; and EP, 14% +/- 3%; each P <.05 vs controls). ACE inhibitors also attenuated the degradation of medial elastin without diminishing the inflammatory response. Surprisingly, the aneurysm-suppressing effects of ACE inhibitors were dissociated from their effects on systemic hemodynamics, and LOS had no significant effect on aneurysm development compared with untreated controls (mean DeltaAD, 186% +/- 19%).
Treatment with ACE inhibitors suppresses the development of elastase-induced AAAs in the rat. Although this is associated with the preservation of medial elastin, the mechanisms underlying these effects appear to be distinct from hemodynamic alterations alone or events mediated solely by AT1 receptors. Further studies are needed to elucidate how ACE inhibitors influence aortic wall matrix remodeling during aneurysmal degeneration.
to assess if deletion of the angiotensin-converting enzyme (ACE) gene is a risk factor for abdominal aortic aneurysms (AAAs) in normotensive patients.
ACE gene polymorphism was examined by polymerase chain reaction in 124 subjects with AAA and in 112 control subjects. AAA normotensive patients (group A, n=56) were compared to normotensive control subjects (group B, n =112) and to AAA hypertensive patients (group C, n =68). All subjects enrolled in this study were Caucasian and from central and southern Italy.
the distribution of ACE genotypes was: normotensive patients with AAAs (group A): 3 II, 14 ID, 39 DD; normotensive control subjects (group B): 36 II, 48 ID, 28 DD; hypertensive patients with AAAs (group C): 14 II, 32 ID, 22 DD. The DD genotype was more common in group A than in control groups (A vs B p<0.001; A vs C p <0.001). The ID genotype was more common in group A as well (A vs B p <0.05; A vs C p <0.005).
our data suggest a role for ACE I/D gene polymorphism in the pathogenesis of AAA in normotensive patients.
To test whether deficiency in endothelial nitric oxide synthase (eNOS) affects atherosclerosis development, we compared lesion formation in apolipoprotein E (apoE)/eNOS-double knockout (DKO) and apoE-knockout (KO) control animals.
After 16 weeks of "Western-type" diet, apoE/eNOS-DKO males and females showed significant increases in lesion area of 93.6% and 59.2% compared with apoE-KO mice. All apoE/eNOS-DKO animals studied developed peripheral coronary arteriosclerosis, associated with perivascular and myocardial fibrosis, whereas none of the apoE-KO mice did. Transthoracic echocardiography showed a significantly increased left ventricular wall thickness and decreased fractional shortening in DKO animals. Mean arterial pressure was increased in DKO mice and was comparable in degree to eNOS-KO animals. Male DKO animals developed atherosclerotic abdominal aneurysms and aortic dissection.
eNOS deficiency increases atherosclerosis in Western-type diet-fed apoE-KO animals and introduces coronary disease and an array of cardiovascular complications, including spontaneous aortic aneurysm and dissection. This phenotype constitutes the first murine model to demonstrate distal coronary arteriosclerosis associated with evidence of myocardial ischemia, infarction, and heart failure. Hypertrophy and reduced left ventricular function cannot be explained by increased blood pressure alone, because eNOS-KO animals do not develop these complications.
Urokinase-type plasminogen activator (uPA) is increased in human abdominal aortic aneurysm (AAA). Chronic infusion of angiotensin II (Ang II) results in AAA in apolipoprotein E-deficient mice. We tested the hypothesis that Ang II infusion results in an elevation of uPA expression contributing to aneurysm formation. Ang II or vehicle was infused by osmotic pumps into apoE-KO mice. All mice treated with Ang II developed a localized expansion of the suprarenal aorta (75% increase in outer diameter), accompanied by an elevation of blood pressure (22 mmHg), compared to the vehicle-treated group. Histological examination of the dilated aortic segment revealed similarities to human AAA including focal elastin fragmentation, macrophage infiltration, and intravascular hemorrhage. Ang II treatment resulted in a 13-fold increase in the expression of uPA mRNA in the AAA segment in contrast to a twofold increase in the atherosclerotic aortic arch. Increased uPA protein was detected in the abdominal aorta as early as 10 days after Ang II infusion before significant aorta expansion. Thus, Ang II infusion results in macrophage infiltration, increased uPA activity, and aneurysm formation in the abdominal aorta of apoE-KO mice. These data are consistent with a causal role for uPA in the pathogenesis of AAA.
We have recently demonstrated that chronic infusion of Angiotensin II into apoE−/− mice promotes the development of abdominal aortic aneurysms. To determine the involvement of specific Angiotensin II receptors in this response, we co-infused Angiotensin II (1000 ng kg−1 min−1 for 28 days) with losartan (30 mg kg−1 day−1) or PD123319 (3 mg kg−1 day−1) to antagonize AT1 and AT2 receptors, respectively.
Infusion of Angiotensin II promoted the development of abdominal aortic aneurysms in 70% of mature female apoE−/− mice. The formation of aortic aneurysms was totally inhibited by co-infusion of Angiotensin II with losartan (30 mg kg−1 day−1; P=0.003). In contrast, the co-infusion of Angiotensin II with PD123319 resulted in a marked increase in the incidence and severity of aortic aneurysms.
To determine whether AT2 antagonism also promoted Angiotensin II-induced atherosclerosis, Angiotensin II was infused into young female apoE−/− mice that had little spontaneous atherosclerosis. In these mice, co-infusion of PD123319 led to a dramatic increase in the extent of atherosclerosis. This increase was associated with no change in plasma lipid concentrations and only transient and modest increases in blood pressure during co-infusion with PD123319.
While antagonism of AT1 receptors totally prevented the formation of aneurysms, antagonism of AT2 receptors promoted a large increase in the severity of Angiotensin II-induced vascular pathology.
British Journal of Pharmacology (2001) 134, 865–870; doi:10.1038/sj.bjp.0704331
the tissue renin-angiotensin system (RAS), which plays an important role in vascular structure and function, is regulated in part by an insertion-deletion polymorphism of the angiotensin converting enzyme (ACE) gene. We hypothesised that ACE genotype might affect rate of AAA expansion via modulating long-term structural changes associated with RAS activation.
fifty-eight patients (50 M, mean age 70 years, mean initial aneurysm size 4.3 cm) with current or previous AAA and serial (>3) annual ultrasound measurements of antero-posterior AAA size provided a sample of leucocyte DNA for ACE genotyping. AAA expansion rate (cm per year) for individual subjects was calculated by linear regression.
median AAA expansion rate was 0.28 cm/year (range 0-1.8 cm/year), and the genotype distribution included DD (n=14), DI (n=29) and II (n=15). Corresponding median AAA expansion rates for each of the three genetic subgroups were 0.22, 0.32 and 0.30 cm/year, respectively (p=0.6, nonparametric).
the wide inter-individual variability in AAA expansion rate is likely to reflect complex genetic and environmental interactions, but the lack of any relationship with ACE genotype suggests that differences in vascular ACE activity in aortic tissue are not major determinants of the variability in rate of AAA dilatation.
We investigated the levels and locations of angiotensin II-forming enzymes, angiotensin converting enzyme (ACE) and chymase, in aneurysmal and normal aortas. Aneurysmal aortic specimens (n = 14) were obtained at the time of operative aneurysm repair from 14 patients ranging in age from 57 to 84 y. Normal aortic specimens (n = 16) were obtained from 16 patients (48 to 72 y) who underwent coronary artery bypass surgery. The ACE and chymase activities were determined using each specimen. Sections of each specimen were immunostained with antibodies for ACE and chymase. The ACE activities in the aneurysmal and normal aortas were 0.82 +/- 0.10 and 0.14 +/- 0.05 mU/mg protein, respectively, and this difference was significant. The chymase activities in the aneurysmal and normal aortas were 17.9 +/- 2.40 and 1.02 +/- 0.18 mU/mg protein, respectively, and this difference was also significant. In the aneurysmal aorta, ACE-positive cells were detected with macrophages in the intima and media and chymase-positive cells were detected with mast cells in the media and adventitia, whereas positive ACE and chymase cells in the normal aorta were located only in the endothelium and adventitia, respectively. Angiotensin II-forming enzymes, chymase and ACE, were significantly increased in the aneurysmal aorta, and increased angiotensin II may be associated with the development of aneurysmal formations.
Cystic medial degeneration (CMD) is a histologic abnormality that is common in aortic diseases such as aortic dilation, aneurysm, or dissection. Although little is known about the mechanism underlying CMD, we have previously demonstrated that angiotensin II signaling via angiotensin II type 2 receptor (AT2R) plays a central role in apoptosis of vascular smooth muscle cells (VSMCs) occurring in CMD associated with Marfan syndrome. The aim of this study is to elucidate the role of angiotensin II signaling in THE pathogenesis of aortic diseases associated with CMD.
We investigated the effects of angiotensin-converting enzyme inhibitor (ACEI), temocapril (n = 15), angiotensin II receptor type-1 (AT1R) blocker, CS-866 (n = 15), and vehicle control (n = 17) on 0.25% beta-aminopropionitrile monofumarate (BAPN)-induced aortic dissection and histopathologic findings in a rat model.
Temocapril significantly prevented aortic dissection (P <.05), CMD (P <.01), and VSMC apoptosis (P <.01) compared with vehicle control in BAPN-fed rats. However, CS-866 did not show any preventive effect. Reversed transcriptase-polymerase chain reaction demonstrated that expression of both AT1R and AT2R was detected in control rat aortas, and that AT2R expression was significantly upregulated in the aortas of BAPN-fed rats (P <.01). Blood pressure was significantly and equally lowered in both temocapril and CS-866 groups compared with control.
Differential expression of angiotensin II receptors and AT2R signaling are involved in the pathogenesis of CMD and aortic dissection in BAPN-fed rats. ACEIs might be of clinical value for the prevention and treatment of aortic diseases related to CMD.
We have previously demonstrated that urokinase-type plasminogen activator (uPA) is highly expressed in the aneurysmal segment of the abdominal aorta (AAA) in apolipoprotein E-deficient (apoE-/-) mice treated with angiotensin II (Ang II). In the present study, we tested the hypothesis that uPA is essential for AAA formation in this model. An osmotic minipump containing Ang II (1.44 mg/kg per day) was implanted subcutaneously into 7- to 11-month-old male mice for 1 month. Ang II induced AAA in 9 (90%) of 10 hyperlipidemic mice deficient in apoE (apoE-/-/uPA+/+ mice) but in only 2 (22%) of 9 mice deficient in both apoE and uPA (apoE-/-/uPA-/- mice) (P<0.05). Although the expansion of the suprarenal aorta was significantly less in apoE-/-/uPA-/- mice than in apoE-/-/uPA+/+ mice, the aortic diameters of the aorta immediately above or below the suprarenal aorta were similar between the 2 groups. Ang II induced AAA in 7 (39%) of 18 strain-matched wild-type C57 black/6J control mice. The incidence was significantly higher in atherosclerotic apoE-deficient (apoE-/-) mice, in which 8 (100%) of 8 mice developed AAA. Only 1 (4%) of 27 uPA-/- mice developed AAA after Ang II treatment. We conclude the following: (1) uPA plays an essential role in Ang II-induced AAA in mice with or without preexisting hyperlipidemia and atherosclerosis; (2) uPA deficiency does not affect the diameter of the nonaneurysmal portion of the aorta; and (3) atherosclerosis and/or hyperlipidemia promotes but is not essential for Ang II-induced AAA formation in this model.
Angiotensin II (AngII) infusion into hyperlipidemic mice leads to the rapid formation of atherosclerotic lesions and abdominal aortic aneurysms (AAAs). To define the role of matrix metalloproteinases (MMPs) in the development of these vascular pathologies, we administered the broad-spectrum MMP inhibitor doxycycline to saline- and AngII-infused LDL receptor-/- mice.
Mice were placed on a high-fat diet for 1 week before infusion with either saline or AngII (1000 ng x kg(-1) x min(-1)) via osmotic pumps for 28 days. Doxycycline (30 mg x kg(-1) x d(-1)) was administered in the drinking water to both saline- and AngII-infused mice. Administration of doxycycline did not significantly influence systolic blood pressure, serum cholesterol concentrations, or lipoprotein-cholesterol distribution. Doxycycline had no effect on the extent of atherosclerosis in saline- or AngII-infused mice. In contrast, doxycycline markedly reduced the incidence of AAA formation (86% vs 35%, AngII vs AngII+doxycycline, respectively; P<0.05), in addition to reducing aneurysm severity.
These data do not imply a role for MMPs in AngII-induced atherosclerosis but provide evidence consistent with a role in AngII-induced AAA formation.
Angiotensin II (Ang II) promotes vascular inflammation, accelerates atherosclerosis, and induces abdominal aortic aneurysm (AAA). These changes were associated with activation of nuclear factor (NF)-kappaB-mediated induction of proinflammatory genes. The incidence of AAA in this model was higher in male than in female mice, and the vascular effects of estrogen may be associated with anti-inflammatory actions. The present study was undertaken to test the hypothesis that estrogen can attenuate Ang II-induced AAA in apolipoprotein E-deficient mice via its anti-inflammatory mechanism.
Infusion of Ang II (1.44 mg/kg per d for 1 month) induced AAA in 90% of the animals (n=20) with an expansion of the suprarenal aorta (diameter 1.9+/-0.14 mm versus <1 mm in normal mice). In mice treated with 17beta-estradiol (E2, 0.25-mg subcutaneous pellets), Ang II induced AAA only in 42% of the animals (n=19) with a significant reduction of average diameters of the suprarenal aorta (1.5+/-0.14 mm). E2 also decreased the expressions of intracellular adhesion molecule-1, vascular cellular adhesion molecule-1, E-selectin, monocyte chemotactic protein-1, and macrophage-colony stimulating factor in the aorta.
These data suggest that attenuation of AAA by E2 is associated with inhibition of proinflammatory gene expression.
We sought to define the temporal characteristics of angiotensin II (AngII)-induced abdominal aortic aneurysms (AAAs) and to provide mechanistic insight into the development of this vascular pathology in apolipoprotein E-deficient (apoE-/-) mice.
Male apoE-/- mice were infused with AngII for 1 to 56 days. Suprarenal arteries were sequentially sectioned, and cellular features were defined by histologic and immunocytochemical techniques. The initial identified event was medial accumulation of macrophages in regions of elastin degradation. Subsequent medial dissection was associated with luminal dilation and thrombus formation. Thrombi were usually constrained by adventitial tissue, although approximately 10% of mice died due to rupture. Thrombi led to profound inflammation that was characterized by infiltration of macrophages and T and B lymphocytes. Remodeling of the tissues was associated with regeneration of elastin fibers and reendothelialization of the dilated luminal surface. Aneurysmal tissue underwent profound neovascularization. Atherosclerotic lesions were only detected after development of the aneurysms.
The initial event in AngII-induced AAA is a focal dissection in the suprarenal region. The progression of AAA precedes the development of overt atherosclerotic lesions.
Many mouse models of abdominal aortic aneurysms have been developed that use a diverse array of methods for producing the disease, including genetic manipulation and chemical induction. These models could provide insight into potential mechanisms in the development of this disease. Although experimental studies on abdominal aortic aneurysms (AAAs) have used a variety of mammalian and avian approaches, there is an increasing reliance on the use of mice. The models recapitulate some facets of the human disease including medial degeneration, inflammation, thrombus formation, and rupture. Most of the mouse models of AAA are evoked either by genetically defined approaches or by chemical means. The genetic approaches are spontaneous and engineered mutations. These include defects in extracellular matrix maturation, increased degradation of elastin and collagen, aberrant cholesterol homeostasis, and enhanced production of angiotensin peptides. The chemical approaches include the intraluminal infusion of elastase, periaortic incubations of calcium chloride, and subcutaneous infusion of AngII. A common feature of these models is the reduction of AAA incidence and severity by the prophylactic administration of matrix metalloproteinase (MMP) inhibitors or genetically engineered deficiencies of specific members of this proteolytic protein family. The validation of mouse models of AAAs will provide insight into the mechanisms of progression of the human disease.
Unlabelled:
Angiotensin II (Ang II) is implicated in atherogenesis by activating inflammatory responses in arterial wall cells. Ang II accelerates the atherosclerotic process in hyperlipidemic apoE-/- mice by recruiting and activating monocytes. Monocyte chemoattractant protein-1 (MCP-1) controls monocyte-mediated inflammation through its receptor, CCR2. The roles of leukocyte-derived CCR2 in the Ang II-induced acceleration of the atherosclerotic process, however, are not known. We hypothesized that deficiency of leukocyte-derived CCR2 suppresses Ang II-induced atherosclerosis.
Methods and results:
A bone marrow transplantation technique (BMT) was used to develop apoE-/- mice with and without deficiency of CCR2 in leukocytes (BMT-apoE-/-CCR2+/+ and BMT-apoE-/-CCR2-/- mice). Compared with BMT-apoE-/-CCR2+/+ mice, Ang II-induced increases in atherosclerosis plaque size and abdominal aortic aneurysm formation were suppressed in BMT-apoE-/-CCR2-/- mice. This suppression was associated with a marked decrease in monocyte-mediated inflammation and inflammatory cytokine expression.
Conclusions:
Leukocyte-derived CCR2 is critical in Ang II-induced atherosclerosis and abdominal aneurysm formation. The present data suggest that vascular inflammation mediated by CCR2 in leukocytes is a reasonable target of therapy for treatment of atherosclerosis.
We have demonstrated previously that infusion of angiotensin II (AngII) into hyperlipidemic mice augments atherosclerosis and results in the formation of abdominal aortic aneurysms (AAA). The purpose of this study was to determine the role of aldosterone in these AngII‐induced vascular pathologies.
Male apolipoprotein E−/− (apoE) mice were infused with either vehicle or aldosterone (50 or 200 ng kg ⁻¹ min ⁻¹ ). Arterial blood pressure was determined throughout the study and serum lipid concentrations and vascular pathology were quantified after 28 days of infusion.
Infusion of aldosterone did not influence body weight or serum cholesterol concentrations. Kidney weight was increased dose‐dependently by aldosterone infusion. Systolic blood pressure was not significantly altered by aldosterone. Plasma aldosterone concentrations were increased dose‐dependently by infusion of aldosterone. However, there was no effect of aldosterone on the extent of atherosclerosis and AAAs were not formed.
Implantation of pellets containing spironolactone (16 mg kg ⁻¹ day ⁻¹ ) in AngII‐infused apoE−/− mice (1000 ng kg ⁻¹ min ⁻¹ ) had no effect on AngII‐induced elevations in blood pressure. Plasma aldosterone concentration was not influenced by coadministration of spironolactone with AngII. Spironolactone administration did not influence the extent of atherosclerosis. Moreover, spironolactone had no significant effect on AngII‐induced AAA (incidence of AAA formation: 80 versus 70% for vehicle versus spironolactone, respectively; not significant).
These studies demonstrate that the AngII‐induced vascular pathologies of atherosclerosis and AAA formation are not mediated through aldosterone.
British Journal of Pharmacology (2005) 144 , 443–448. doi: 10.1038/sj.bjp.0706098
Angiotensin II (Ang II) accelerates atherosclerosis and induces abdominal aortic aneurysm (AAA) in an experimental mouse model. Agonism of a G protein-coupled receptor by Ang II activates Rho-kinase and other signaling pathways and results in activation of proteolysis and apoptosis. Enhanced proteolysis and smooth muscle cell apoptosis are important mechanisms associated with AAA. In this study, we tested the hypothesis that fasudil, a Rho-kinase inhibitor, could attenuate Ang II-induced AAA formation by inhibiting vascular wall apoptosis and extracellular matrix proteolysis.
Six-month-old apolipoprotein E-deficient mice were infused with Ang II (1.44 mg x kg(-1) x d(-1)) for 1 month. Animals were randomly assigned to treatment with fasudil (136 or 213 mg x kg(-1) x d(-1) in drinking water) or tap water. Ang II infusion induced AAA formation in 75% of the mice, which was accompanied by an increase in proteolysis detected by zymographic analysis and quantified by active matrix metalloproteinase-2 activity, as well as apoptosis detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and quantified by both caspase-3 activity and histone-associated DNA fragmentation. The level of DNA fragmentation in the suprarenal aorta correlated with AAA diameter. Ang II also increased atherosclerotic lesion area and blood pressure. Fasudil treatment resulted in a dose-dependent reduction in both the incidence and severity of AAA. At the higher dose, fasudil decreased AAA by 45% while significantly inhibiting both apoptosis and proteolysis, without affecting atherosclerosis or blood pressure.
These data demonstrate that inhibition of Rho-kinase by fasudil attenuated Ang II-induced AAA through inhibition of both apoptosis and proteolysis pathways.
Abdominal aortic aneurysms (AAAs) in humans are associated with locally increased oxidative stress and activity of NADPH oxidase. We investigated the hypothesis that vitamin E, an antioxidant with documented efficacy in mice, can attenuate AAA formation during angiotensin II (Ang II) infusion in apolipoprotein E-deficient mice.
Six-month-old male apolipoprotein E-deficient mice were infused with Ang II at 1000 ng/kg per minute for 4 weeks via osmotic minipumps while consuming either a regular diet or a diet enriched with vitamin E (2 IU/g of diet). After 4 weeks, abdominal aortic weight and maximal diameter were determined, and aortic tissues were sectioned and examined using biochemical and histological techniques. Vitamin E attenuated formation of AAA, decreasing maximal aortic diameter by 24% and abdominal aortic weight by 34% (P<0.05, respectively). Importantly, animals treated with vitamin E showed a 44% reduction in the combined end point of fatal+nonfatal aortic rupture (P<0.05). Vitamin E also decreased aortic 8-isoprostane content (a marker of oxidative stress) and reduced both aortic macrophage infiltration and osteopontin expression (P<0.05, respectively). Vitamin E treatment had no significant effect on the extent of aortic root atherosclerosis, activation of matrix metalloproteinases 2 or 9, serum lipid profile, or systolic blood pressure.
Vitamin E ameliorates AAAs and reduces the combined end point of fatal+nonfatal aortic rupture in this animal model. These findings are consistent with the concept that oxidative stress plays a pivotal role in Ang II-driven AAA formation in hyperlipidemic mice.
Mouse models of abdominal aortic aneurysm (AAA) have been commonly used in many laboratories for studying molecular mechanisms of AAA formation and development, as well as for testing novel therapeutic agents in the treatment of AAA. However, because of the small size of the animal, the quantification and characterization of AAA development and progress is difficult, time-consuming and requires the sacrifice of the experimental animals. We report here a noninvasive method to detect and measure AAA in mice using a high-frequency ultrasound (US) imaging system specifically designed for microimaging of the mice (Vevo 660; VisualSonics, Toronto, ONT, Canada). A total of 21 male apolipoprotein-E-deficient mice were chronically infused with angiotensin II (1.44 mg/kg daily) for 28 days to induce AAA formation. A 2-D echo image of the abdominal aorta was acquired at longitudinal and transverse planes, followed immediately by post mortem dissection of the abdominal aorta for direct measurements. The US images clearly showed a bulge-like expansion localized specifically in the suprarenal region of the abdominal aorta, with a shape strikingly similar to that of the aorta dissected post mortem. In addition, the US images can also provide measurements of the luminal diameter and wall thickness of the abdominal aorta. The average dimensions of the abdominal aorta were not significantly different between the US and post mortem measurements, nor between the transverse and longitudinal US images. The different types of the measurements are also highly correlated with each other, with a linear correlation (r) between 0.7 and 0.9. Thus, we have established and validated a novel application to noninvasively measure AAA development and progress in a mouse model using a high-frequency US imaging system that has the advantages of low cost, rapid imaging speed, reproducibility and high resolution, and makes repeated monitoring of the progress of AAA development over a time-course possible.
Abdominal aortic aneurysm (AAA) is characterized by destruction of the arterial media associated with loss of vascular smooth muscle cells, infiltration of mononuclear cells, and high concentration of metalloproteinases (MMPs) and cytokines. Osteoprotegerin (OPG) has recently been identified in atherosclerosis. The presence and functional importance of OPG in human AAA was investigated.
In 146 men with small AAA followed up by ultrasound for 3 years, serum OPG was weakly correlated with aneurysm growth rate. Western analysis showed 3-, 8-, and 12-fold-greater OPG concentrations in human AAA biopsies compared with biopsies of atherosclerotic narrowed aorta (1.4+/-0.1 versus 0.5+/-0.1 ng/mg tissue; P=0.002), postmortem nondiseased abdominal aorta (1.4+/-0.1 versus 0.2+/-0.1 ng/mg tissue; P<0.001), and nondiseased thoracic aorta (1.4+/-0.1 versus 0.1+/-0.06 ng/mg tissue; P<0.001). Healthy human aortic vascular smooth muscle cells incubated with recombinant human (rh)OPG (0 to 20 ng rhOPG/10(5) cells per 1 mL per 24 hours) developed an aneurysmal phenotype defined by impaired cell proliferation (P<0.001), increased apoptosis (P<0.01), and increased MMP-9 (92 kDa) expression (P<0.001). Incubation of monocytic THP-1 cells with 1 ng rhOPG/10(5) cells per 1 mL per 24 hours induced a 2-fold increase in MMP-9 expression (P<0.001), a 1.5-fold increase in MMP-2 activity (P=0.005), and a 2-fold stimulation of IL-6 production in these cells (P=0.02). Finally, secretion of OPG from human AAA explant was abrogated by treatment with the angiotensin II blocker irbesartan, with the reduction in secreted levels averaging 63.0+/-0.9 ng/mg tissue per 48-hour period.
These findings support a role for OPG in the growth of human AAA and suggest a potential benefit for angiotensin II blockade in slowing aneurysm expansion.
Experimentally sustained increase in angiotensin II (AngII) promotes tissue destruction in various cardiovascular disorders. We examined whether transiently heightened AngII affects subsequent atherosclerosis and aneurysm formation. AngII or saline was administered for 2 weeks to apolipoprotein E (apoE)-deficient mice. Mice were sacrificed at the end of the 2-week infusion or 6- or 14 weeks later. Short-term AngII did not affect atherosclerosis immediately following the infusion or 6 weeks later. By contrast, 14 weeks after infusion there was remarkably more atherosclerosis in previously AngII-exposed mice. Preceding the build up of atherosclerotic lesions, AngII-exposure increased mRNA expression and immunostaining of monocyte chemoattractant protein-1 (MCP-1) and its receptor, CCR2. This was followed by greater macrophage-positivity in AngII-exposed aortae. In contrast to the delayed effects on atherosclerosis, 20% of mice were found to have abdominal aneurysms at the end of AngII-exposure. This effect was not contingent on blood pressure. Moreover, despite amplification in atherosclerosis following AngII, no aneurysms were found 14 weeks later. Our studies reveal that even transient exposure to AngII primes the vessel for subsequent amplification of atherosclerosis which involves activation of MCP-1/CCR2 and influx of macrophages into the nascent atherosclerotic plaque. By contrast, transient AngII-exposure causes prompt aneurysm formation that does not parallel atherosclerosis and disappears even in the face of progressively greater atherosclerotic lesions.
Abdominal aortic aneurysm (AAA) is a common disease among elderly people that, when surgical treatment is inapplicable, results in progressive expansion and rupture of the aorta with high mortality. Although nonsurgical treatment for AAA is much awaited, few options are available because its molecular pathogenesis remains elusive. Here, we identify JNK as a proximal signaling molecule in the pathogenesis of AAA. Human AAA tissue showed a high level of phosphorylated JNK. We show that JNK programs a gene expression pattern in different cell types that cooperatively enhances the degradation of the extracellular matrix while suppressing biosynthetic enzymes of the extracellular matrix. Selective inhibition of JNK in vivo not only prevented the development of AAA but also caused regression of established AAA in two mouse models. Thus, JNK promotes abnormal extracellular matrix metabolism in the tissue of AAA and may represent a therapeutic target.
With the development of aliskiren, blockade of the renin-angiotensin-aldosterone system (RAAS) at the level of the interaction of renin with a substrate has become a clinical reality. This review covers the specific features of the first agent likely to achieve widespread clinical exposure, aliskiren. The potential of renin inhibition must be viewed in the context of the remarkable efficacy of both angiotensin-converting enzyme (ACE) inhibition and angiotensin receptor blockers (ARBs). The implications of blockade of the renin system at its rate-limiting step are reviewed, with the therapeutic implications for both the renin inhibitor employed alone or the renin inhibitor combined with an ACE inhibitor or ARB. The relevant and necessary studies are ongoing.
Inflammation plays an integral role in the development of abdominal aortic aneurysms (AAAs), and the expression of cyclooxygenase (COX)-2 is increased in aneurysmal tissue compared with normal aorta. Nonsteroidal anti-inflammatory drugs, which inhibit the activity of COX-1 and COX-2, decrease AAA expansion in humans and animal models of the disease. In the current study, we investigated the effectiveness of selective inhibition of COX-1 or COX-2 in attenuating AAA formation.
Eight-week-old male apolipoprotein E-deficient mice were treated with selective inhibitors of COX-1 or COX-2, SC-560 (approximately 25 mg.kg(-1).day(-1)), or celecoxib (approximately 125 mg.kg(-1).day(-1)), respectively. COX inhibitors were administered 1 week before angiotensin II (Ang II; 1000 ng.kg(-1).min(-1)) or saline infusion and throughout the time course of the experiment. COX-1 inhibition had no effect on incidence (control: 90% [9:10] versus SC-560: 89% [8:9]) or severity of Ang II-induced AAA formation. In contrast, celecoxib decreased the incidence (control: 74% [22:30] versus celecoxib: 11% [2:19]; P<0.001) and severity (P=0.001) of AAA formation. Celecoxib also decreased the incidence and severity of AAAs in nonhyperlipidemic mice.
COX-2-derived prostanoids play a fundamental role in the development of Ang II-induced AAAs in both hyperlipidemic and nonhyperlipidemic mice.
Infusion of angiotensin II (AngII) via subcutaneous osmotic pumps into mice promotes the development of abdominal aortic aneurysms (AAAs). These AngII-induced AAAs develop via a complex process in which there is a transmedial break, lumen dilation, thrombus formation, inflammation involving cells of both the innate and acquired immune systems, and remodeling. The recent development of a high-frequency ultrasound machine has permitted the noninvasive detection of murine abdominal aortas. We assessed the ability of a Visualsonics Vevo 660 high-resolution imaging system to detect AAAs and sequentially quantify the aortic luminal diameter. This system had 100% accuracy in detecting AngII-induced AAAs in vivo, with intrauser and interuser variation coefficients of less than 10% for quantification of the aortic lumen diameter.
Male apolipoprotein E (apoE)(-/-) mice were infused subcutaneously with either saline or AngII and were monitored with this ultrasonic system to define the temporal changes in aortic lumen diameter. Aortic luminal diameters were measured in the aneurysm-susceptible region of the suprarenal aorta. For internal controls, abdominal aortic diameters were measured at the level of the left renal branch, because this landmark region did not dilate during AngII infusion.
Luminal diameters of the suprarenal aorta did not change significantly in saline-infused mice over 28 days of measurement (P = .71). In contrast, AngII infusion led to rapid dilation of suprarenal aortas during the initial 7 days of infusion (0.071 mm/d; P = .0037 for the change in the initial expansion rate). Further luminal diameter expansions occurred for the remaining 21 days of observation at a more modest rate (0.023 mm/d; P = .0001 for continued expansion after day 7). Within the initial 14 days of AngII infusion, some apoE(-/-) mice died as a result of rupture of the aorta in the suprarenal region. We had previously assumed that aortic dilation and rupture occurred simultaneously. However, in the AngII-infused mice that succumbed to aortic rupture, luminal diameters increased several days before death.
High-frequency ultrasonography demonstrated that suprarenal aortic expansion occurs rapidly after the initiation of AngII infusion into apoE(-/-) mice.
Abdominal aortic aneurysm (AAA) is a common disease that, when surgical treatment is inapplicable, results in rupture of the aorta with high mortality. Although nonsurgical treatment for AAA is eagerly awaited, the destruction of the aortic walls in AAA has been considered an irreversible process. We found that c-Jun N-terminal kinase (JNK) is highly activated in human AAA walls. We also found that JNK activity is essential for the expression of matrix metalloproteinase (MMP)-9 and, concurrently, suppression of the extracellular matrix (ECM) biosynthesis. We therefore investigated the role of JNK in the pathogenesis of AAA in vivo. We created a mouse AAA model by periaortic application of CaCl(2), which was accompanied by activation of JNK and MMPs, and suppression of lysyl oxidase (LOX), which is an essential biosynthetic enzyme for collagen and elastin fibers. Our data indicate that, in addition to MMP activities, suppression of ECM biosynthesis may contribute to the AAA pathogenesis because local LOX gene delivery prevented AAA formation. Treatment of mice with SP600125, a specific JNK inhibitor, completely abrogated the formation of CaCl(2)-induced AAA. Furthermore, SP600125 treatment after the establishment of AAA caused a reduction in the aortic diameters with normalized tissue architecture. SP600125 treatment also caused significant regression of angiotensin II-induced AAA in ApoE-null mice after its establishment, as demonstrated by serial ultrasonographic studies in live animals. These data demonstrate that JNK dictates the abnormal ECM metabolism in AAA pathogenesis by enhancing tissue degradation and suppressing tissue repair. Therefore, inhibition of JNK may provide a novel therapeutic option for AAA.
Deletionpolymorphisminthegene forangiotensin-convertingenzymeisnotariskfactorpredisposingtoabdominal aortic aneurysm
- K Hamano
- M Ohishi
- M Ueda
HAMANO,K.,M.OHISHI,M.UEDA,etal.1999.Deletionpolymorphisminthegene forangiotensin-convertingenzymeisnotariskfactorpredisposingtoabdominal aortic aneurysm. Eur. J. Vasc. Endovasc. Surg. 18: 158–161
TransientlyheightenedangiotensinII hasdistincteffectsonatherosclerosisandaneurysmformationinhyperlipidemic mice
- N Ayabe
- V R Babaev
AYABE,N.,V.R.BABAEV,Y.TANG,etal.2005.TransientlyheightenedangiotensinII hasdistincteffectsonatherosclerosisandaneurysmformationinhyperlipidemic mice. Atherosclerosis 184: 312–321