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Effects of Angiotensins II and IV on Blood Pressure, Renal Function, and PAI-1 Expression in the Heart and Kidney of the Rat
Abstract
The role of angiotensin II (AII) and angiotensin IV (AIV) as inducers of PAI-1 expression during hypertension was studied in vivo. A 2-week infusion of AII (300 ng/kg/min) via an osmotic pump increased systolic blood pressure (171 +/- 2 vs. 138 +/- 6 mm Hg), urinary protein excretion (32 +/- 6 vs. 14 +/- 2 mg/day), and renal (2.2 +/- 0.5 vs. 1.0 +/- 0.1) and cardiac (1.8 +/- 0.3 vs. 1.0 +/- 0.1) gene expression of plasminogen activator inhibitor 1 (PAI-1). AIV infusion did not affect any of the above with the exception of PAI-1 gene expression which was increased in the left ventricles (1.7 +/- 0.3 vs. 1.0 +/- 0.1). AII-infused rats displayed a decreased creatinine clearance (538 +/- 75 vs. 898 +/- 96 ml/min) and hypertrophic left ventricles (0.275 +/- 0.006 vs. 0.220 +/- 0.011 g/100 g). Our results demonstrate that AII but not AIV infusion is associated with increased renal PAI-1 gene expression.
... However, systemic ANG II alone is not sufficient to induce parenchymal fibrosis. Our results are in accordance with previous studies showing that increased systemic ANG II induces oxidative stress and profound inflammation in the vasculature and the kidneys (1,11,29,35). On the basis of these data, we propose that increased systemic ANG II may participate in the progression of chronic liver diseases. ...
... Our experimental model consisting of infusing ANG II through a subcutaneous pump into rats has been used by many investigators (1,11,15,29,35). In the current study, we used both subpressor and pressor 7. Representative photomicrographs of livers from saline and ANG II-treated rat livers. ...
... Moreover, a marked oxidative stress was found, as assessed by increased lipid peroxidation of protein adducts. Similar in vivo effects have been previously described in the heart, the vasculature, and the kidney (1,29,35,43). In these organs, ANG II induces infiltration by mononuclear cells and progressive fibrosis. ...
Recent evidence indicates that angiotensin II (ANG II) plays an important role in liver fibrogenesis. However, the underlying mechanisms are largely unknown. In advanced chronic liver diseases, circulating levels of ANG II are frequently elevated. We investigated the hepatic effects of prolonged systemic infusion of ANG II in normal rats. Saline or ANG II at subpressor and pressor doses (15 and 50 ng.kg-1.min-1, respectively) were infused to normal rats for 4 wk through a subcutaneous osmotic pump. Infusion of ANG II resulted in liver injury, as assessed by elevated serum liver enzymes. Livers from ANG II-perfused rats showed activation of JNK and ERK as well as increased NF-kappaB and activating protein-1 DNA-binding activity. Moreover, ANG II perfusion induced oxidative stress, increased concentration of proinflammatory cytokines, and upregulated the inflammatory proteins inducible nitric oxide synthase and cyclooxygenase-2. Histological examination of the livers from ANG II-infused rats showed mild portal inflammation as well as thickening and thrombosis of small hepatic vessels. ANG II-treated livers showed accumulation of CD43-positive inflammatory cells and activated hepatic stellate cells (HSCs) at the pericentral areas. A slight increase in collagen synthesis was observed, as assessed by Sirius red staining and hepatic hydroxyproline. All of these effects were observed when ANG II was perfused at subpressor and pressor doses. ANG II also accelerated the activation of primary cultured rat HSCs. In conclusion, increased systemic ANG II can induce liver injury by promoting proinflammatory events and vascular damage. ANG II-induced hepatic effects are not dependent on increase in arterial pressure.
... Our results are consistent with those of previous studies showing that increased systemic Ang II causes oxidative stress and profound inflammation in the vasculature, heart, and kidney. [25][26][27] In a previous study, we demonstrated that prolonged systemic infusion of Ang II into normal rats induces hepatic inflammation and HSC activation. 22 These effects were associated with increased oxidative stress and vascular thrombosis. ...
... This method has been widely used to evaluate the fibrogenic effect of systemic RAS in other organs such as the kidney. 25,27 We showed that increased Ang II circulatory levels markedly exacerbate development of liver fibrosis in bile duct-ligated rats, but not in sham-operated rats. This result suggests that systemic RAS may play a role in the progression of liver fibrosis. ...
Recent evidence indicates that the renin-angiotensin system (RAS) plays a major role in liver fibrosis. Here, we investigate whether the circulatory RAS, which is frequently activated in patients with chronic liver disease, contributes to fibrosis progression. To test this hypothesis, we increased circulatory angiotensin II (Ang II) levels in rats undergoing biliary fibrosis. Saline or Ang II (25 ng/kg/h) were infused into bile duct-ligated rats for 2 weeks through a subcutaneous pump. Ang II infusion increased serum levels of Ang II and augmented bile duct ligation-induced liver injury, as assessed by elevated liver serum enzymes. Moreover, it increased the hepatic concentration of inflammatory proteins (tumor necrosis factor alpha and interleukin 1beta) and the infiltration of CD43-positive inflammatory cells. Ang II infusion also favored the development of vascular thrombosis and increased the procoagulant activity of tissue factor in the liver. Livers from bile duct-ligated rats infused with Ang II showed increased transforming growth factor beta1 content, collagen deposition, accumulation of smooth muscle alpha-actin-positive cells, and lipid peroxidation products. Moreover, Ang II infusion stimulated phosphorylation of c-Jun and p42/44 mitogen-activated protein kinase and increased proliferation of bile duct cells. In cultured rat hepatic stellate cells (HSCs), Ang II (10(-8) mol/L) increased intracellular calcium and stimulated reactive oxygen species formation, cellular proliferation and secretion of proinflammatory cytokines. Moreover, Ang II stimulated the procoagulant activity of HSCs, a newly described biological function for these cells. In conclusion, increased systemic Ang II augments hepatic fibrosis and promotes inflammation, oxidative stress, and thrombogenic events.
... 19 On the other hand, 2-week infusion of either Ang II or Ang IV significantly increased cardiac PAI-1 expression, whereas only Ang II increased renal PAI-1 expression. 20 However, none of these studies delineated the role of specific AT 1 receptor subtypes in Ang II-stimulated PAI-1 expression. ...
... Previous studies using pharmacological receptor antagonists have consistently demonstrated that Ang II induces PAI-1 expression in vitro in cardiomyocytes 22 and VSMCs 22,23 and in vivo 18,20,22 in the heart and aorta via its AT 1 receptor. A recent study in cultured VSMCs from AT 1a À/À suggests that Ang IV also induces PAI-1 expression in VSMCs. ...
Angiotensin (Ang) II stimulates plasminogen activator inhibitor-1 (PAI-1) expression in many cell types by mechanisms that are cell-type specific. We measured effects of Ang II or norepinephrine on PAI-1 expression in wild type (WT) and Ang type-1a receptor knockout mice (AT(1a)-/-) in the presence or absence of the non-specific AT(1) antagonist losartan. Ang II and norepinephrine increased systolic blood pressure equally, whereas losartan decreased the pressor response of the former but not the latter in WT mice. In AT(1a)-/- mice, baseline systolic blood pressure was lower with no effect of Ang II, norepinephrine, or losartan. Ang II stimulated PAI-1 expression in the heart, aorta, and kidney and markedly in the liver of WT mice. In AT(1a)-/- mice, Ang II-stimulated PAI-1 was significantly attenuated compared with the WT in the heart and aorta but significantly enhanced in the kidney. Losartan decreased the induction in the aorta and liver of WT, and in the kidney and liver of AT(1a)-/- mice. Norepinephrine increased PAI-1 expression in WT heart and aorta, and in AT(1a)-/- heart, kidney, and liver with no effect of losartan. Renal PAI-1 expression correlated with AT(1b) receptor mRNA. We conclude that Ang II stimulates PAI-1 expression in part through the AT(1b) receptor in the kidney and liver. Further, norepinephrine induces PAI-1 expression in vivo with AT(1a) receptor deficiency modulating the effect.
... It is strongly implicated in fibrosis of diverse tissues (Kaikita et al., 2001;Eddy, 2002) by preventing degradation of the ECM, regulating the activation of metalloproteinases and accelerating collagen deposition (Yamamoto and Saito, 1998). Ang II is a potent inducer of PAI-1 production in heart (Abrahamsen et al., 2002) and multiple cell types such as cardiac fibroblasts (Kawano et al., 2000) and cardiomyocytes (Takeshita et al., 2004). Moreover, the induction of PAI-1 has also been suggested as a possible mechanism through which Ang II promotes the development of cardiovascular remodelling (Weisberg et al., 2005). ...
... To extend our in vitro studies, we used Ang II-infused rats as the in vivo model. Previous studies have shown the elevation of cardiac PAI-1 and ECM expression in this model (Kim et al., 1995b;Baltatu et al., 2000;Nakamura et al., 2000;Abrahamsen et al., 2002;Zirlik et al., 2004). Consistent with these reports, our findings demonstrated that Ang II infusion promotes cardiac fibrosis, as indicated by a substantial increase of PAI-1, collagen I, collagen III and fibronectin expression in the left ventricle of the rats. ...
Peroxisome proliferator-activated receptor (PPAR)-gamma ligands have been shown to inhibit cardiac fibrosis. However, the underlying mechanisms are poorly understood. We investigated the regulation by PPAR-gamma ligands of angiotensin (Ang) II-induced plasminogen activator inhibitor (PAI)-1, extracellular matrix (ECM) production and cell growth in cardiac fibroblasts.
The effects of PPAR-gamma ligands on Ang II-induced PAI-1, ECM expression and cell growth were assessed in primary-cultured rat cardiac fibroblasts; cardiac PAI-1 and ECM production was examined in Ang II-infused rats.
In growth-arrested cardiac fibroblasts, PPAR-gamma ligands rosiglitazone and 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2) dose-dependently attenuated Ang II-induced cell proliferation and expression of PAI-1, collagen type-I, collagen type-III and fibronectin. An accompanying increase in PPAR-gamma expression and activation was also observed. These suppressive effects were attenuated by the PPAR-gamma antagonists GW9662 and bisphenol A diglycidyl ether (BADGE). Moreover, rosiglitazone and 15d-PGJ2 inhibited in part the expression and phosphorylation of Ang II-induced transforming growth factor (TGF)-beta1, Smad2/3 and c-Jun NH(2)-terminal kinase (JNK). Ang II infusion in rats markedly increased left ventricular production of PAI-1, collagen and fibronectin, with a concurrent increase in the ratios of heart weight/body weight and left ventricle weight/body weight. Co-treatment with rosiglitazone significantly decreased these levels and upregulated PPAR-gamma expression.
Rosiglitazone and 15d-PGJ2 suppress Ang II-induced production of PAI-1 and ECM probably via interactions between PPAR-gamma and TGF-beta1/Smad2/3 and JNK signalling pathways. It is suggested that PPAR-gamma and its ligands may have potential applications in preventing cardiac fibrosis.
... At the kidney, Ang II can promote renal fibroblasts, increase expression of transforming growth factor β1 (TGF-β1), tissue growth factor, and fibronectin and collagen type I, which eventually increases renal fibrosis (Wolf, 1998;Lin et al., 2005). Furthermore, Ang II upregulates plasminogen activator inhibitor-1 and tissue inhibitor of matrix metalloproteinases-1, causing accumulation of extracellular matrix (Abrahamsen et al., 2002). In support of this, it has been shown that the AT 1 receptor antagonist, losartan, can prevent the development of CKD by maintaining renal blood flow, decreasing inflammation and tissue hypoxia following acute renal injury (Rodríguez-Romo et al., 2016). ...
Hypertension is a frequent condition encountered during kidney disease development and a leading cause in its progression. Hallmark factors contributing to hypertension constitute a complexity of events that progress chronic kidney disease (CKD) into end-stage renal disease (ESRD). Multiple crosstalk mechanisms are involved in sustaining the inevitable high blood pressure (BP) state in CKD, and these play an important role in the pathogenesis of increased cardiovascular (CV) events associated with CKD. The present review discusses relevant contributory mechanisms underpinning the promotion of hypertension and their consequent eventuation to renal damage and CV disease. In particular, salt and volume expansion, sympathetic nervous system (SNS) hyperactivity, upregulated renin–angiotensin–aldosterone system (RAAS), oxidative stress, vascular remodeling, endothelial dysfunction, and a range of mediators and signaling molecules which are thought to play a role in this concert of events are emphasized. As the control of high BP via therapeutic interventions can represent the key strategy to not only reduce BP but also the CV burden in kidney disease, evidence for major strategic pathways that can alleviate the progression of hypertensive kidney disease are highlighted. This review provides a particular focus on the impact of RAAS antagonists, renal nerve denervation, baroreflex stimulation, and other modalities affecting BP in the context of CKD, to provide interesting perspectives on the management of hypertensive nephropathy and associated CV comorbidities.
... Angiogenesis inhibitors block production and activation of NO pathway resulting in vasoconstriction, increased peripheral vascular resistance, and in turn, hypertension. NO also suppresses expression of plasminogen activator inhibitor-1 (PAI-1), which is known to be involved in the development of hypertension [39][40][41]. Therefore, inhibition of angiogenesis could initiate and contribute to pathogenesis of hypertension potentially through endothelial dysfunction. ...
Angiogenesis inhibitors, also known as vascular endothelial growth factor (VEGF) or vascular signaling pathway (VSP) inhibitors, have improved care of neoplastic diseases over the past decade. However, cardiovascular toxicities associated with these agents, such as hypertension and less commonly left ventricular systolic dysfunction and heart failure, have often been a limiting factor for continued use. Balancing the benefits of these agents with the associated toxicities is critical to ensure these therapies do not negatively impact oncological outcomes. The care of cancer patients with cardiovascular risks is challenging due to the heterogeneity of cardiovascular complications, paucity of evidence-based guidelines, and lack of channels for collaboration among healthcare providers. Herein, we provide a team-based approach for treatment of angiogenesis inhibitor–induced hypertension along with recommendations on monitoring and appropriate selection of anti-hypertensive agents.
... 41,42 Ang II also promotes the accumulation of extracellular matrix by upregulating plasminogen activator inhibitor-1 and tissue inhibitor of matrix metalloproteinases-1, which inhibit metalloproteinases. 43 Recent animal studies have provided evidence that RAS activation during and after injury play a critical role in AKI-CKD continuum. Losartan, an AT1a receptor antagonist, administration during reperfusion phase can maintain glomerular infiltration and accelerate renal recovery after ischemia-reperfusion injury (IRI). ...
Acute kidney injury (AKI) can increase the risk of developing incident chronic kidney disease (CKD). The severity, frequency and duration of AKI are crucial predictors of poor renal outcome. A repair process after AKI can be adaptive and kidney recovers completely after a mild injury. However, severe injury will lead to a maladaptive repair, which frequently progresses to nephron loss, vascular rarefaction, chronic inflammation and fibrosis. Although different mechanisms underlying AKI‐CKD transition have been extensively discussed, no definite intervention has been proved effective to block or to retard the transition until recently. In CKD, renin‐angiotensin system (RAS) inhibitor has been proved effective to slow down disease progression. Furthermore, RAS needs to be highlighted again in AKI‐CKD transition because recent animal studies have shown the activation of intra‐renal RAS after AKI, and RAS blockade can reduce the ensuing CKD and mortality. In patients with the complete renal recovery after AKI, administration of RAS inhibitor is associated with reduced risk of subsequent CKD as well. In this article, we will demonstrate the role of RAS in AKI‐CKD transition comprehensively. We will then emphasize the promising effect of RAS inhibitor on CKD prevention in patients recovering from AKI based on evidence from the bench to clinical research. All of these discussions will contribute to the establishment of reliable monitoring and therapeutic strategies for patients with functional recovery from AKI who can be most easily ignored. Renin‐angiotensin system (RAS) is activated after AKI and leads to AKI‐CKD continuum. RAS blockade can reduce the ensuing CKD and mortality. Using RAS blockade could be considered for the monitoring and therapeutic strategies after AKI.
... It is unclear whether ANG IV acts as an exclusive agonist for the putative AT 4 receptor alone or as a partial but active agonist for the AT 1 receptor, mediating its widely reported cardiovascular and renal effects (1, 17, 28 -32, 34). ANG IV has been reported to cause both vasodilatation and vasoconstriction (1,15,18,19,35). For example, infusion of ANG IV directly in cerebral or renal arteries increases cerebral blood flow and renal cortical blood flow (CBF) via a mechanism that appears to be mediated by the AT 4 receptor and nitric oxide (NO; see Refs. ...
... This notion is supported by our in vitro studies on CFs, which are not affected by pressurization or hemodynamic-induced changes, and by the result of the previous study demonstrating that Ets-1 mediated vascular remodeling is not dependent on alteration of blood pressure in response to Ang II [34]. Previous studies have shown that Ang II infusion lead to an increase in cardiac PAI-1 [1] and CTGF [11]. Our experiments further demonstrated that this increase was concurrent with the induction of Ets-1. ...
Ets-1, the prototypical member of the family of Ets transcription factors, has been shown to participate in tissue fibrotic remodeling. However, its role in cardiac fibrosis has not been established. The aim of this study was to investigate the role of Ets-1 in profibrotic actions of angiotensin II (Ang II) in cardiac fibroblasts (CFs) and in the in vivo heart. In growth-arrested CFs, Ang II induced Ets-1 expression in a time-and concentration-dependent manner. Pretreatment with Ang II type 1 receptor blocker losartan, protein kinase C inhibitor bisindolylmaleimide I, extracellular signal-regulated kinase (ERK) inhibitor PD98059, or c-Jun NH(2)-terminal kinase (JNK) inhibitor SP600125 partly inhibited this induction accompanied with impaired cell proliferation and production of plasminogen activator inhibitor-1 (PAI-1) and connective tissue growth factor (CTGF) protein, the two downstream targets of Ets-1. Knockdown of Ets-1 by siRNA significantly inhibited the inductive effects of Ang II on cell proliferation and expression of CTGF and PAI-1. Moreover, the levels of Ets-1, PAI-1 and CTGF protein were simultaneously upregulated in left ventricle of Ang II-infused rats in parallel with an increase in the activation of ERK and JNK. Our data suggest that Ets-1 may mediate Ang II-induced cardiac fibrotic effects.
... Ang II induces the "plasminogen activator inhibitor-1" (PAI-1) and "tissue inhibitor of matrix metalloproteinases-1" (TIMP-1) via AT1R, which inhibits metalloproteinase affecting the matrix turnover, resulting in accumulation of ECM. PAI-1 is also stimulated by Ang IV via AT4R in proximal tubules thereby playing a role in renal fibrosis (110). In DN, Ang IV is formed by the degradation of Ang II when in high concentrations by different enzymes and this induces PAI-I (111). ...
Chronic kidney disease (CKD), diabetes mellitus (DM) and cardiovascular diseases (CVD) are complex disorders of partly unknown genesis and mostly known progression factors. CVD and DM are the risk factors of CKD and are strongly intertwined since DM can lead to both CKD and/or CVD and CVD can lead to kidney disease. In recent years our knowledge of CKD, DM and CVD has been expanded and several important experimental, clinical and epidemiological associations have been reported. The tight cellular and molecular interactions between the renal, diabetic and cardiovascular systems in acute or chronic disease settings is becoming increasingly evident. However, the (patho-) physiological basis of the interactions of CKD, DM and CVD with involvement of multiple endogenous and environmental factors is highly complex and our knowledge still at its infancy. Not only single pathways and mediators of progression of these diseases have to be considered in these processes, but also the mutual interactions of these factors are essential. The recent advances in proteomics and integrative analysis technologies have allowed rapid progress in analyzing complex disorders and clearly show the opportunity for new efficient and specific therapies. More than a dozen pathways have been identified so far, including hyperactivity of the renin-angiotensinaldosterone system, osmotic sodium retention, endothelial dysfunction, dyslipidemia, RAS/RAF/ERK pathway, modification of the purinergic system, phosphatidylinositol 3-kinase (PI 3-kinase)-dependent signaling pathways, andinflammation, all leading to histomorphological alterations of the kidney and vessels of diabetic and non-diabetic patients. Since a better understanding of the common cellular and molecular mechanisms of these diseases may be a key to successful identification of new therapeutic targets, we review in this paper the current literature about cellular and molecular mechanisms of CKD.
... [4][5][6][7] Similarly, also in vivo studies conducted both in animal models and in humans demonstrated that Ang II induces PAI-1 expression. [8][9][10] Blockade of the RAS by angiotensin-converting enzyme inhibitors (ACE-Is) has been generally demonstrated to reduce PAI-1 levels in both experimental and clinical studies. [11][12][13][14][15][16] Contrasting results have been reported about the effects on fibrinolysis of Ang II receptor blockers (ARBs), which inhibit the RAS throughout the block of the effects of Ang II at the AT1 receptor level. ...
To evaluate the relationship between plasma plasminogen activator inhibitor-1 (PAI-1) and angiotensin II (Ang II) changes during treatment with imidapril and candesartan in hypertensive patients with metabolic syndrome. A total of 84 hypertensive patients with metabolic syndrome were randomized to imidapril 10 mg or candesartan 16 mg for 16 weeks. At weeks 4 and 8, there was a dose titration to imidapril 20 mg and candesartan 32 mg in nonresponders (systolic blood pressure (SBP) >140 and/or diastolic blood pressure (DBP) >90 mm Hg). We evaluated, at baseline and after 2, 4, 8, 12 and 16 weeks, clinic blood pressure, Ang II and PAI-1 antigen. Both imidapril and candesartan induced a similar SBP/DBP reduction (-19.4/16.8 and -19.5/16.3 mm Hg, respectively, P<0.001 vs. baseline). Both drugs decreased PAI-1 antigen after 4 weeks of treatment, but only the PAI-1 lowering effect of imidapril was sustained throughout the 16 weeks (-9.3 ng ml(-1), P<0.01 vs. baseline), whereas candesartan increased PAI-1 (+6.5 ng ml(-1), P<0.05 vs. baseline and P<0.01 vs. imidapril). Imidapril significantly decreased Ang II levels (-14.6 pg ml(-1) at week 16, P<0.05 vs. baseline), whereas candesartan increased them (+24.2 pg ml(-1), P<0.01 vs. baseline and vs. imidapril). In both groups there was a positive correlation between Ang II and PAI-1 changes (r=0.61, P<0.001 at week 16 for imidapril, and r=0.37, P<0.005 at week 16 for candesartan). Imidapril reduced plasma PAI-1 and Ang II levels, whereas candesartan increased them. This suggests that the different effect of angiotensin-converting enzyme inhibitors and Ang II blockers on Ang II production has a role in their different influence on fibrinolysis.
... PAI-1 and TIMP-1 inhibit metalloproteinases and thereby matrix turnover, resulting in accumulation of ECM. Through stimulating the expression of PAI-1 in the proximal tubules via the AT 4 receptor, AngIV can play a role in the development of renal fibrosis independent from the activation of AT 1 and AT 2 receptors (42). Because of upregulation of AngIV, which generates enzymes under conditions with high local AngII concentrations and in diabetic nephropathy (10), accelerated degradation of AngII into AngIV could activate AT 4 receptors, inducing PAI-1. ...
Inhibition of the renin-angiotensin-aldosterone system (RAAS) is one of the most powerful maneuvers to slow progression of renal disease. Angiotensin II (AngII) has emerged in the past decade as a multifunctional cytokine that exhibits many nonhemodynamic properties, such as acting as a growth factor and profibrogenic cytokine, and even having proinflammatory properties. Many of these deleterious functions are mediated by other factors, such as TGF-beta and chemoattractants that are induced in the kidney by AngII. Moreover, understanding of the RAAS has become much more complex in recent years with the identification of novel peptides (e.g., AngIV) that could bind to specific receptors, elucidating deleterious effects, and non-angiotensin-converting enzyme (ACE)-mediated generation of AngII. The ability of renal cells to produce AngII in a concentration that is much higher than what is found in the systemic circulation and the observation that aldosterone may be engaged directly in profibrogenic processes independent of hypertension have added to the complexity of the RAAS. Even renin has now been identified to have a "life on its own" and mediates profibrotic effects via binding to specific receptors. Finally, drugs that are used to block the RAAS, such as ACE inhibitors or certain AngII type 1 receptor antagonists, may have properties on cells independent of AngII (ACE inhibitor-mediated outside-inside signaling and peroxisome proliferator-activated receptor-gamma stimulatory effects of certain sartanes). Although blockade of the RAAS with ACE inhibitors, AngII type 1 receptor antagonists, or the combination of both should be part of every strategy to slow progression of renal disease, a better understanding of the novel aspects of the RAAS should contribute to the development of innovative strategies not only to completely halt progression but also to induce regression of human renal disease.
... Ang IV has been shown to regulate cell growth in cardiac fibroblasts, endothelial cells, and vascular smooth muscle cells. In the kidney, Ang IV has been shown to have both vasoconstrictor and vasodilatory effects, and induces PAI-1 expression in an experimental model of hypertension [112]. However, to date, no studies have examined the role of AT 4 /IRAP in the diabetic kidney. ...
Diabetic nephropathy is the single most common cause of end-stage renal disease (ESRD) and accounts for significant morbidity and mortality. While the incidence of ESRD increased dramatically in the 1980s and 1990s, the U.S. Renal Data System (USRDS) 2005 Annual Data Report shows that 338 out of every million Americans had kidney failure in 2003, down slightly from 340 per million in 2002. This report shows that the numbers of people developing ESRD have stabilized despite the persistent increase in the number of people diagnosed with type 2 diabetes mellitus (T2DM). These data attest to both the efficacy of the currently available therapeutic regimens for the treatment of ESRD as well as better overall patient care. Unfortunately, these encouraging statistics do not apply to all patients. According to the USRDS report, the most marked ESRD decrease was seen in young Caucasian men (<40 years of age), while in other patient groups, particularly African Americans, ESRD has not changed much at all. These observations suggest that more in-depth studies, addressing specific issues, such as race, are needed to understand the disease process fully in order to create novel therapeutic strategies to eradicate the disease completely in all patient populations.
The renin-angiotensin-aldosterone system is a physiological system that plays an important role in the regulation of blood pressure and body water-electrolyte balance, in which the kidney, liver and lungs play a role in its activation. This system comes into play in various diseases such as the cardiovascular, renal, pulmonary and nervous system where blood pressure and fluid-electrolyte balance may change. The purpose of this study, which is presented in line with this information, is to explain the working principle of this system, how this system is activated, how it comes into play in the mentioned diseases, and what kind of results occur.
Inhibition of the renin angiotensin aldosterone system (RAAS) is one of the most important therapeutic features to slow progression of chronic renal disease. The understanding of the working mechanisms of angiotensin II (Ang II) has considerably changed in the past decade. Ang II functions as a multi-functional cytokine that exhibits many non-hemodynamic properties, such as acting as a growth factor and profibrogenic cytokine, and even having proinflammatory effects. Understanding of the RAAS has become much more complex with the identification of novel peptides, like angiotensin IV, that could bind to specific receptors. The ability of renal cells to produce Ang II in a concentration that is much higher than what is found in the systemic circulation and the observation that aldosterone may be involved directly in profibrogenic processes independent of hypertension, have added to the complexity of the RAAS. Even renin mediates profibrotic effects after binding to a specific receptor. Drugs used to block the RAAS may have properties on cells independent of Ang II (e.g. ACE inhibitor-induced signal transduction and PPAR-γ stimulatory effects of certain sartanes). Blockade of the RAAS with ACE inhibitors or AT1 receptor antagonists or both should be used in each patient with chronic renal disease.
Diabetic nephropathy, a microvascular complication of diabetes, is clinically characterized by an initial increase in glomerular filtration rate (GFR) and microalbuminuria (Semin Nephrol 23(2), 194–199, 2003). If left untreated, these early pathophysiologic changes will progress to renal fibrosis and tubulointerstitial damage along with a decline in GFR, ultimately leading to kidney failure (Curr Opin Nephrol Hypertens 12(3), 273–282, 2007; J Hypertens 23(11), 1931–1937, 2005). Diabetic nephropathy and its related pathophysiologic alterations in renal microcirculation is thought to develop as a result of the interaction between metabolic and hemodynamic factors that together activate common intracellular pathways that trigger the production of various cytokines and growth factors leading to kidney disease. Persistent elevations in blood glucose alter renal hemodynamics through activation of several vasoactive hormonal pathways, including the renin-angiotensin-aldosterone system, endothelin, and urotensin (Diabet Med 21(Suppl 1), 15–18, 2004; Curr Hypertens Rep 6(2), 98–105, 2004). These hormones then in turn can activate second messenger signaling pathways, including protein kinase C, transcription factors, including NK-κB, and cytokines, including TGF-β, VEGF, and PDGF, all of which can lead to the development of albuminuria, glomerulosclerosis, and tubulointerstitial fibrosis characteristic of diabetic nephropathy (Kidney Int Suppl 106, S49–S53, 2007; Semin Nephrol 27(2), 153–160, 2007). This chapter will provide a detailed review of these hemodynamic and hormonal mechanisms that underlie the development of diabetic nephropathy.
Zusammenfassung Das komplexe RAAS spielt eine entscheidende Rolle bei der Progression der chronischen Niereninsuffizienz. Renin und Aldosteron können unabhängig von ANG II über die TGF–Synthese zur Nierenfibrose beitragen. Genpolymorphismen der Komponenten des RAAS, agonistische AK gegen den AT1-Rezeptor und AT1-Rezeptor-Dimere können zusätzlich zur Funktionsverschlechterung der Niere beitragen. ACE-Hemmer und AT1-Rezeptor-Antagonisten in Standarddosierungen hemmen die eigenständigen RAAS der Organe nur unvollständig. Zur Kontrolle des Blutdrucks und der Proteinurie sollten ACE-Hemmer oder AT1-Rezeptor-Antagonisten ausdosiert und indikationsgerecht eingesetzt werden. Eine Doppelblockade sollte bei Patienten mit chronischer Niereninsuffizienz und einer Proteinurie über 1 g/Tag erwogen werden. Empfehlungen zur zusätzlichen Gabe eines Aldosteron-Antagonisten sind derzeit aufgrund der mangelnden Datenlage bei Patienten mit Niereninsuffizienz nicht auszusprechen. Eine Zulassung für Renin-Inhibitoren existiert z. Z. nicht.
Background:
Angiotensin II (ANG II) is an important factor for the progression
of renal diseases. ANG II has many pleiotropic effects on the kidney
such as pro–inflammatory and profibrotic actions besides the well–known blood
pressure–increasing effect.
Novel Knowledge:
Organs have local ANG II–generating systems that
work independently from their classic systemic counterpart. Renal proximal
tubular cells could generate and secrete ANG II into the urine in concentrations
that are 10,000 times higher than those found in serum. These local
systems are only incompletely blocked by currently used doses of ACE inhibitors
or AT1 antagonists. There are other enzyme systems besides ACE that
contribute to the formation of ANG II. Alternative pathways generate peptides
such as angiotensin 1–7 that have antagonistic effect compared with ANG II.
Degradation products of ANG II such as angiotensin IV bind at separate receptors
and could mediate fibrosis. The discovery of AT1 receptor dimers and
agonistic antibodies against AT1 receptors contributes to the complexity of
the system.
Clinical Relevance:
The complexity of the renin–angiotensin–aldosterone
system (RAAS) implies that dual blockade with ACE inhibitors and AT1 receptor
antagonists makes sense for pathophysiological reasons. First clinical
studies have shown that such as dual therapy reduces progression of chronic
renal disease more efficiently that the respective monotherapies in certain risk
populations. This shows that novel pathophysiological data could lead to innovative
clinical treatment strategies.
Angiotensin IV (Ang IV) is a hexapeptide fragment corresponding to amino acids 3–8 (VYIHPF) of angiotensin II (Ang II) that
is formed by consecutive actions of aminopeptidase A and aminopeptidase N (1) (Fig. 1). Ang IV acts as a weak agonist at the Ang II AT1 receptor, and was generally believed to have no physiological role because of its ineffectiveness in the regulation of blood
pressure, fluid balance, or adrenal steroid secretion. However, in 1988, specific actions were discovered for Ang IV in the
brain—the peptide was found to facilitate memory retention and retrieval (2). A specific, high-affinity binding site was subsequently described in bovine adrenal membranes, which bound Ang IV saturably,
reversibly, and with nanomolar affinity (3,4). This binding site was termed as the angiotensin AT4 receptor by an IUPHAR nomenclature committee (5). This AT4 receptor site is pharmacologically distinct from both Ang II AT1 and AT2 receptors, and bound Ang II at only micromolar affinity.
Fig. 1.Schematic diagram of the angiotensin system leading to the formation of angiotensin IV.
Besides the importance of the renin-angiotensin system (RAS) in the circulation and other organs, the local RAS in the kidney has attracted a great attention in research in last decades. The renal RAS plays an important role in the body fluid homeostasis and long-term cardiovascular regulation. All major components and key enzymes for the establishment of a local RAS as well as two important angiotensin II (Ang II) receptor subtypes, AT1 and AT2 receptors, have been confirmed in the kidney. In additional to renal contribution to the systemic RAS, the intrarenal RAS plays a critical role in the regulation of renal function as well as in the development of kidney disease. Notably, kidney AT1 receptors locating at different cells and compartments inside the kidney are important for normal renal physiological functions and abnormal pathophysiological processes. This mini-review focuses on: 1) the local renal RAS and its receptors, particularly the AT1 receptor and its mechanisms in physiological and pathophysiological processes; and 2) the chemistry of the selective AT1 receptor blocker, losartan, and the potential mechanisms for its actions in the renal RAS-mediated disease.
Angiotensin IV (ANG IV), an active ANG II fragment, has been shown to induce systemic and renal cortical effects by binding to ANG IV (AT4) receptors and activating unique signaling transductions unrelated to classical type 1 (AT1) or type 2 (AT2) receptors. We tested whether ANG IV exerts systemic and renal cortical effects on blood pressure, renal microvascular smooth muscle cells (VSMCs), and glomerular mesangial cells (MC) and, if so, whether AT1 receptor-activated signaling is involved. In anesthetized rats, systemic infusion of ANG II, ANG III, or ANG IV (0.01, 0.1, and 1.0 nmol·kg-1·min-1 iv) caused dose-dependent increases in mean arterial pressure (MAP) and decreases in renal cortical blood flow (CBF; P < 0.01). ANG II also induced dose-dependent reductions in renal medullary blood flow (P < 0.01), whereas ANG IV did not. ANG IV-induced pressor and renal cortical vasoconstriction were completely abolished by AT1 receptor blockade with losartan (5 mg/kg iv; P < 0.05). When ANG IV (1 nmol·kg-1·min-1) was infused directly in the renal artery, CBF was reduced by >30%, and the response was also blocked by losartan (P < 0.01). In the renal cortex, unlabeled ANG IV displaced 125I-labeled [Sar1,Ile 8]ANG II binding, whereas unlabeled ANG II (10 μM) inhibited 125I-labeled Nle1-ANG IV (AT4) binding in a concentration-dependent manner (P < 0.01). In freshly isolated renal VSMCs, ANG IV (100 nM) increased intracellular Ca2+ concentration, and the effect was blocked by losartan and U-73122, a selective inhibitor of phospholipase C/inositol trisphosphate/Ca2+ signaling (1 μM). In cultured rat MCs, ANG IV (10 nM) induced mitogen-activated protein kinase extracellular/signal-regulated kinase 1/2 phosphorylation via AT1 receptor- and phospholipase C-activated signaling. These results suggest that, at nanomolar concentrations, ANG IV can increase MAP and induce renal cortical effects by interacting with AT1 receptor-activated signaling.
Background and objectives:
Angiotensin-converting enzyme (ACE) probably influences the fibrinolytic system at a central point by converting angiotensin I to angiotensin II, which increases plasminogen activator inhibitor-1 (PAI-1) activity. This effect appears to be mediated in humans via the angiotensin II type 1 (AT(1)) receptor. The objective of this study was to evaluate, in patients with mild to moderate hypertension, the change in tissue plasminogen activator (t-PA) and PAI-1 plasma levels after treatment with an AT(1)-receptor blocker (losartan 50 mg/day) or an ACE inhibitor (delapril 60 mg/day).
Patients and methods:
30 hypertensive patients and 15 controls were enrolled. Essential hypertension was established by a medical history, physical examination and the absence of clinical findings suggestive of a secondary form of hypertension. Preliminary investigations, routine biochemical tests (including clearance of creatinine and oral glucose tolerance test), chest x-ray, standard and 24-hour ECG monitoring, M- and B-mode echocardiography and fundus oculi examinations were performed. No patients had previously received ACE inhibitors or AT(1)-receptor blockers. After a 14-day run-in period with placebo, patients were randomised in a double-blind fashion into two groups: 15 patients were randomised to losartan 50 mg/day (group 1), 15 patients were randomised to delapril 60 mg/day (group 2), and 15 healthy subjects were used as controls (group 3). Plasma PAI-1 and t-PA antigen were determined by enzyme-linked immunosorbent assay and a photometric method at the end of the run-in period and after 6 months of treatment.
Results:
There were no significant differences among the three groups regarding age, sex, body mass index and smoking. After 6 months, both groups of patients showed a reduction in blood pressure values. The losartan group did not demonstrate significant changes in PAI-1 levels (96.52 +/- 23.73 and 99.89 +/- 22.18 mug/L, pre- and post-treatment, respectively) or in t-PA antigen levels (26.17 +/- 6.18 and 27.32 +/- 5.91 mug/L, pre- and post-treatment, respectively). The delapril group showed no significant changes in PAI-1 levels (97.73 +/- 25.75 and 86.12 +/- 13.12 mug/L, pre- and post-treatment, respectively), but did show a statistically significant difference (p < 0.005) in t-PA antigen levels (25.71 +/- 6.40 and 32.24 +/- 5.31 mug/L, pre- and post-treatment, respectively). The losartan group demonstrated significantly higher post-treatment PAI-1 values than the delapril group (p = 0.048).
Conclusion:
The study showed that losartan does not affect fibrinolytic parameters, while delapril resulted in an insignificant reduction in PAI-1 and a significant increase in t-PA levels. Further studies are clearly required in order to establish whether these different effects on the fibrinolytic system between ACE inhibitors and AT(1)-receptor blockers may have clinical relevance.
We have examined whether the extracellular matrix is a biochemical target for transforming growth factor-beta (TGFbeta). We find that TGFbeta increases the expression of the major extracellular matrix proteins, fibronectin and collagen. This effect is a general response to TGFbeta seen in primary cultures and established lines of cells from various types, normal and transformed. The relative incorporation of fibronectin and collagen into the matrix also increases in response to TGFbeta. The effect of TGFbeta on fibronectin levels as characterized in chick embryo fibroblasts is rapid, selective, persistent, and specific, and involves transcriptional events; it is not mimicked by other growth factors tested. The induction of anchorage-independent growth of normal fibroblasts by TGFbeta is mimicked by fibronectin and is specifically blocked by inhibitors of fibronectin binding to its cell surface receptor. The results demonstrate a functional involvement of fibronectin in mediating cellular responses to TGFbeta, and suggest a model for TGFbeta action based on the control of the extracellular matrix in target cells.
Plasminogen activator-inhibitor C-1 (PAI-1) plays a critical role in the regulation of fibrinolysis, serving as the primary inhibitor of tissue-type plasminogen activator. Elevated levels of PAI-1 are a risk factor for recurrent myocardial infarction, and locally increased PAI-1 expression has been described in atherosclerotic human arteries. Recent studies have shown that the administration of angiotensin converting enzyme inhibitors reduces the risk of recurrent myocardial infarction in selected patients. Since angiotensin II (Ang II) has been reported to induce PAI-1 production in cultured astrocytes, we have hypothesized that one mechanism that may contribute to the beneficial effect of angiotensin converting enzyme inhibitors is an effect on fibrinolytic balance. In the present study, we examined the interaction of Ang II with cultured bovine aortic endothelial cells (BAECs) and the effects of this peptide on the production of PAI-1. 125I-Ang II was found to bind to BAECs in a saturable and specific manner, with an apparent Kd of 1.4 nM and Bmax of 74 fmol per mg of protein. Exposure of BAECs to Ang II induced dose-dependent increases in PAI-1 antigen in the media and in PAI-1 mRNA levels. Induction of PAI-1 mRNA expression by Ang II was not inhibited by pretreating BAECs with either Dup 753 or [Sar1, Ile8]-Ang II, agents that are known to compete effectively for binding to the two major angiotensin receptor subtypes. These data indicate that Ang II regulates the expression of PAI-1 in cultured endothelial cells and that this response is mediated via a pharmacologically distinct form of the angiotensin receptor.
Angiotensin II (Ang II) has been implicated in the development of progressive glomerulosclerosis, but the precise mechanism of this effect remains unclear. In an experimental model, we have shown previously that TGF-beta plays a key role in glomerulosclerosis by stimulating extracellular matrix protein synthesis, increasing matrix protein receptors, and altering protease/protease-inhibitor balance, thereby inhibiting matrix degradation. We hypothesized that Ang II contributes to glomerulosclerosis through induction of TGF-beta. Ang II treatment of rat mesangial cells in culture increased TGF-beta and matrix components biglycan, fibronectin, and collagen type I at both the mRNA and protein levels in a time- and dose-dependent manner. Saralasin, a competitive inhibitor of Ang II, prevented the stimulation. Ang II also promoted conversion of latent TGF-beta to the biologically active form. Coincubation of mesangial cells with Ang II and neutralizing antibody to TGF-beta blocked the Ang II-induced increases in matrix protein expression. Continuous in vivo administration of Ang II to normal rats for 7 d resulted in 70% increases in glomerular mRNA for both TGF-beta and collagen type I. These results indicate that Ang II induces mesangial cell synthesis of matrix proteins and show that these effects are mediated by Ang II induction of TGF-beta expression. This mechanism may well contribute to glomerulosclerosis in vivo.
Animal and human proteinuric glomerulopathies evolve to terminal renal failure by a process leading to progressive parenchymal damage, which appears to be relatively independent of the initial insult. Despite the fact that the mechanism(s) leading to renal disease progression has been only partially clarified, several studies have found that the amount of urinary proteins (taken to reflect the degree of protein trafficking through the glomerular capillary) correlated with the tendency of a given disease to progress more than the underlying renal pathology. On the other hand, dietary protein restriction and ACE inhibitors were capable of limiting the progressive decline in GFR to the extent that they could effectively lower the urinary protein excretion rate. A constant feature of proteinuric nephritis is also the concomitant presence of tubulointerstitial inflammation. So far it was not clear if this is a reaction to the ischemic obliteration of peritubular capillaries that follows glomerular obsolescence or whether albumin and other proteins that accumulated in the urinary space are indeed instrumental for the formation of the interstitial inflammatory reaction. In recent years several studies have convincingly documented that excessive and sustained protein trafficking could have an intrinsic renal toxicity. Here we have reviewed the abundant evidence in the literature that the process of reabsorption of filtered proteins activates the proximal tubular epithelium. Biochemical events associated with tubular cell activation in response to protein stress include up-regulation of inflammatory and vasoactive genes such as MCP-1 and endothelins. The corresponding molecules formed in an excessive amount by renal tubuli are secreted toward the basolateral compartment of the cell and give rise to an inflammatory reaction that in most forms of glomerulonephritis consistently precede renal scarring.
Angiotensin-II (AII) stimulates plasminogen activator inhibitor-1 (PAI-1) gene transcription, translation, and protein secretion from astroglial cells derived from normotensive [Wistar-Kyoto (WKY)] rat brain, an effect mediated by AII type 1 (AT1) receptors. Since abnormal expression of the brain AII system has been demonstrated in spontaneously hypertensive (SH) rats, we investigated the regulation of PAI-1 gene expression by AII in astroglial cells from the brains of these animals. AII caused an increase in PAI-1 gene expression in SH rat astroglia in a manner similar to that observed in WKY-derived cultures. However, both the basal and AII-stimulated levels of PAI-1 mRNA in SH rat astroglia were only 20% of those observed in WKY rat astroglial cultures. Consequently, there was a significant reduction in the de novo synthesis and secretion of PAI-1 from astroglia of SH rat brain. The reduced synthesis and secretion of PAI-1 from SH rat brain astroglia was associated with lower numbers of AT1 receptors in these cells. However, the steady state levels of AT1 receptor mRNA were comparable in both WKY and SH rat astroglia. This reduction in AII-modulated PAI-1 levels in SH rat astroglia is consistent with a proposed role of these interactions in the development of hypertension in these animals.
The effect of local adrenal arterial infusion of the heptapeptide (2-8) and hexapeptide (3-8) fragments of angiotensin 11 on a aldosterone secretion was examined. The heptapeptide (2-8) resembled the octapeptide in activity and stimulated aldosterone whereas the hexapeptide (3-8) had no effect.
We examined the role of the plasminogen activator/plasmin system in extracellular matrix (ECM) degradation by human mesangial cells cultured on thin films of 125I-labeled ECM (Matrigel). ECM degradation (release of 125I into the medium) was dependent on exogenous plasminogen, proportional to the number of mesangial cells and amount of plasminogen added, and coincident with the appearance of plasmin in the medium. ECM degradation was completely blocked (P < 0.001) by two plasmin inhibitors, alpha-2-antiplasmin (40 micrograms/ml) and aprotinin (216 KIU/ml), and partially reduced (-33 +/- 1.8%, P < 0.01) by TIMP-1 (40 micrograms/ml), a specific inhibitor of matrix metalloproteinases. Zymography of medium obtained from cells cultured in the absence of plasminogen revealed the presence of latent matrix metalloproteinase-2 (MMP-2) which was converted to a lower molecular weight, active form in the presence of mesangial cells and plasminogen. Northern analysis of poly A+RNA prepared from cultured human mesangial cells revealed mRNA for tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPA), plasminogen activator inhibitor-1 (PAI-1), and uPA receptor (uPAR). The presence of uPA protein in medium obtained from cultured human mesangial cells was demonstrated by Western blotting and ELISA which revealed a large molar excess of PAI-1 (1.2 +/- 0.1 x 10(-9) M) over uPA (1.2 +/- 0.1 x 10(-12) M) and tPA (0.19 +/- 0.04 x 10(-9) M). ECM degradation was reduced by a monoclonal antibody (MAb) against human tPA (-54 +/- 8.6%) or human uPA (-39 +/- 5.2%) compared to cells treated with identical amounts of non-specific monoclonal IgG (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Recent studies from this laboratory have demonstrated that angiotensin II (Ang II) stimulates the expression of plasminogen activator inhibitor 1 (PAI-1) in cultured endothelial cells. This response does not appear to be mediated via an interaction with either the AT1 or the AT2 receptor subtype. Since a novel angiotensin receptor has been identified in a variety of tissues that specifically binds the hexapeptide Ang IV (Ang II, [3-8]), we therefore examined the effects of Ang IV on the expression of PAI-1 mRNA in bovine aortic endothelial cells. Ang IV stimulated dose- and time-dependent increases in the expression of PAI-1 mRNA. The effect of Ang IV (10 nM) was not inhibited by Dup 753 (1.0 microM), a highly specific antagonist of the AT1 receptor, or by PD123177 (1.0 microM), a highly specific antagonist of the AT2 receptor. In contrast, the AT4 receptor antagonist, WSU1291 (1.0 microM), effectively prevented PAI-1 expression. Although larger forms of angiotensin (i.e., Ang I, Ang II, and Ang III) are capable of inducing PAI-1 expression, this property is lost in the presence of converting enzyme or aminopeptidase inhibitors. These results indicate that the hexapeptide Ang IV is the form of angiotensin that stimulates endothelial expression of PAI-1. This effect appears to be mediated via the stimulation of an endothelial receptor that is specific for Ang IV.
The role of angiotensin as a vasoconstrictor is well established. Lately, several other actions of this hormone on vascular smooth muscle (VSM) cells have been recognized including the induction of hypertrophy and/or DNA synthesis. Platelet-derived growth factor (PDGF), a mitogen recently shown to increase plasminogen activator inhibitor type 1 (PAI-1) synthesis in VSM cells, shares with angiotensin II (Ang II) several steps of its intracellular signaling pathway.
The expression of PAI-1 and tissue-type plasminogen activator (TPA) mRNA in cultured rat VSM cells was studied. Northern blot analysis demonstrated a severalfold increase in the PAI-1 mRNA 3 to 8 hours after stimulation with 300 nmol/L Ang II. A similar response for TPA mRNA was observed. This induction did not require the synthesis of an intermediate protein or peptide because it was not affected by cycloheximide. In the cell-conditioned supernatant, the net result was an increase in PAI-1 activity from 4.18 +/- 1.8 to 13.2 +/- 6.8 IU/mL 6 hours after the addition of 300 nmol/L Ang II (mean +/- SD, P < or = .008, n = 6). The Ang II-induced increase in PAI activity was dose related, with a maximal effect at a concentration of 23 nmol/L (n = 3) and an ED50 of 3.3 +/- 1.5 nmol/L (n = 3). [Sar1-Ile8]angiotensin II, a specific competitive antagonist of Ang II, blocked 90 +/- 9% (n = 3) of the PAI activity induced by 10 nmol/L Ang II. In basal conditions, fibrin overlay zymography demonstrated the presence of free TPA. After stimulation with Ang II, lysis caused by the in situ dissociation of TPA was also present in the region of the TPA/PAI-1 complex. Angiotensin I (Ang I) elicited an increase in PAI activity similar to that obtained with equivalent doses of Ang II. Captopril (5 micrograms/mL), an inhibitor of the angiotensin-converting enzyme (ACE), completely prevented the Ang I effect, demonstrating that VSM cells display an ACE-like activity.
Recent research has demonstrated the existence of a localized vascular renin-angiotensin system. The finding that Ang II can potentially modulate the plasminogen activation in the arterial wall has important biological and therapeutical implications for the evolution of arterial wall thrombi and the migration of cells through the vessel wall in the genesis of atherosclerotic lesions. We speculate that the reduction in thrombotic events observed in patients with a previous myocardial infarction and in high-renin, hypertensive patients treated with ACE inhibitors could be due at least in part to the decreased production of PAI-1 by VSM cells caused by these agents.
1. The effect of the novel beta-adrenoceptor antagonist and vasodilator, carvedilol (SK&F 105517, approximately 70 mg kg-1 daily in the food), and captopril (approximately 38 mg kg-1 daily in the drinking fluid) on the progression of chronic renal failure in rats was studied. 2. Six weeks following partial renal ablation, the urinary protein excretion of the carvediol- (60 +/- 21 mg day-1) and captopril-treated (35 +/- 9 mg day-1) animals was less than 50% that of control rats (133 +/- 27 mg d-1). 3. Serum creatinine (Scr) and urea nitrogen (SUN) concentrations of the carvedilol-(Scr, 0.63 +/- 0.09 mg dl-1; SUN, 11.3 +/- 1.2 mg dl-1) and captopril-treated (Scr, 0.82 +/- 0.05 mg dl-1; SUN, 14.1 +/- 1.5 mg dl-1) animals were also significantly (P < 0.05) lower than that observed in control animals (Scr, 1.4 +/- 0.3 mg dl-1; SUN, 19.2 +/- 3.9 mg dl-1), indicating that glomerular filtration rate was improved by both drugs. Plasma renin activity was significantly (P < 0.05) higher in captopril-treated rats (24.7 +/- 4.6 ng angiotensin I ml-1 h-1) than in either carvedilol-treated (7.9 +/- 1.4 ng angiotensin I ml-1 h-1) or control animals (7.4 +/- 1.0 ng angiotensin I ml-1 h-1). 4. Histological examination of the kidneys demonstrated a significantly reduced glomerular hypertrophy and glomerulosclerosis in those animals receiving carvedilol or captopril compared to controls. 5. Serum carvedilol concentration measured every 6 h for 24 h was variable and ranged on average from 57 +/- 13 ng ml-1 at 16 h 00 min to 121 +/- 31 ng ml-1 at 03 h 00 min. These data indicate that the rats probably had 24 h systemic exposure to carvedilol.6. The present study indicates that carvedilol is effective in attenuating the progression of chronic renal failure in rats.
Previous studies indicate that angiotensin II (Ang II) stimulates extracellular matrix synthesis through induction of transforming growth factor-beta (TGF-beta) expression. Here we investigate Ang II effects on the plasmin protease system. Plasmin both degrades extracellular matrix itself and activates metalloproteinases which then degrade collagens. Plasmin production is determined by the balance between plasminogen activators (PA) and their inhibitors (PAI-1,2). The data presented here indicate that Ang II treatment of mesangial cells in culture markedly increases PAI-1 gene transcription and PAI-1 mRNA levels but does not change the half life of PAI-1 mRNA. Increased PAI-1 protein was detected 24 hours after Ang II stimulation with a concomitant decrease of PA activity. To determine whether these effects were mediated by TGF-beta, cells were coincubated with Ang II and neutralizing antibody to TGF-beta. Induction of PAI-1 at four hours was not altered but the prolonged effect of Ang II on PAI-1 protein synthesis was markedly diminished. Thus, Ang II acts both through rapid, direct transcriptional up-regulation of the PAI-1 gene and through induction of TGF-beta, providing sustained changes in the PAI-1/PA system, which would favor extracellular matrix accumulation by inhibiting turnover. These data provide further evidence that Ang II can act as a potent fibrogenic molecule independent of its effects on blood pressure.
Angiotensin II, a potent vasoconstrictor, has a key role in renal injury and in the progression of chronic renal disease of diverse causes. In vascular smooth muscle cells, angiotensin II modulates growth, which may lead to hypertrophy and also may inhibit mitogen-stimulated DNA synthesis. The effects of angiotensin II on responsive cells are mediated by two classes of receptors, AT-1 and AT-2. Information obtained in the last decade indicates that angiotensin II increases the production of several autocrine factors, including transforming growth factor beta1 (TGF-beta1), tumor necrosis factor-alpha (TNF-alpha), and platelet-derived growth factor A chain (PDGF). Angiotensin also increases the release of other growth factors such as endothelin, platelet-activating factor (PAF), and interleukin 6. In addition, it increases the "activity" of nuclear factor-kappaB (NF-kappaB) and the synthesis of angiotensinogen. The emerging picture indicates that the actions of angiotensin II may be related to factors that are released or upregulated by angiotensin II, possibly through NF-kappaB activation. It appears likely that many of the effects of angiotensin II on renal disease may be mediated by TGF-beta1, TNF-alpha, and changes in the activity of NF-kappaB. The use of ACE inhibitors or antagonists of AT-1 or AT-2 receptors in experimental animals decreases the levels of angiotensin II or limits its action, thereby interfering with the production and effects of the factors described.
Angiotensin II (Ang II) has been shown to be implicated in the development of renal fibrosis in several forms of chronic glomerulonephritides, but the precise mechanisms of its effects remain unclear. It has recently been reported that Ang II stimulates the expression of plasminogen activator inhibitor-1 (PAI-1) in several cell lines. PAI-1 is a major physiological inhibitor of the plasminogen activator/plasmin system, a key regulator of fibrinolysis and extracellular matrix (ECM) turnover. PAI-1 induction by Ang II in endothelial cells seems to be mediated by Ang IV via a receptor that is different from Ang II type 1 and 2 receptors (AT1 and AT2).
In this study, we sought to evaluate the effects of Ang IV on PAI-1 gene and protein expression in a well-characterized and immortalized human proximal tubular cell line (HK2) by Northern blot and enzyme-linked immunosorbent assay.
Ang IV stimulated PAI-1 mRNA expression, whereas it did not induce a significant increase in tritiated thymidine uptake after 24 hours of incubation. This effect was dose and time dependent. Ang IV (10 nM) induced a 7.8 +/- 3.3-fold increase in PAI-1 mRNA expression. The PAI-1 antigen level was significantly higher in conditioned media and the ECM of cells treated with Ang II and Ang IV than in control cells (both P < 0.02). Although Ang II induced a 4.2 +/- 2. 1-fold increase in PAI-1 mRNA expression, its effect underwent a dose-dependent reduction when amastatin, a potent inhibitor of the endopeptidases that catalyzes the conversion of Ang II to Ang IV, was added. In contrast, amastatin was not able to prevent the expression of PAI-1 mRNA induced by Ang IV. Finally, pretreatment of HK2 cells with losartan and N-Nicotinoyl-Tyr-N3-(Nalpha-CBZ-Arg)-Lys-His-Pro-Ile, the specific antagonists of AT1 and AT2 receptors, failed to modify PAI-1 mRNA expression as induced by Ang II.
Our results demonstrate that Ang II stimulates PAI-1 mRNA expression and the production of its protein in human proximal tubular cells. This is mainly-if not exclusively-due to Ang IV, which acts on a receptor that is different than AT1 or AT2. Therefore, it can be hypothesized that the induction of PAI-1 by Ang IV may be implicated in the pathogenesis of renal interstitial fibrosis in several forms of chronic glomerulonephritides.
The role of ANG II on renal and cardiac gene expression of matrix proteins was studied in rats with progressive renal disease. Induction of renal failure by five-sixths nephrectomy of Sprague-Dawley rats resulted in hypertension (163 +/- 19 vs. control pressures of 108 +/- 6 mmHg), proteinuria (83 +/- 47 vs. 14 +/- 2 mg/day), and increased renal expression of fibronectin, thrombospondin, collagen I and III, transforming growth factor-beta (TGF-beta), and plasminogen activator inhibitor-1 (PAI-1) mRNA. Treatment with the ANG II receptor antagonist, eprosartan (60 mg. kg(-1).day(-1)), lowered blood pressure (95 +/- 5 mmHg) and proteinuria (19 +/- 8 mg/d) and abrogated the increased TGF-beta, fibronectin, thrombospondin, collagens I and III, and PAI-1 mRNA expression. An increase in left ventricular weight was observed in five-sixths nephrectomized rats (0.13 +/- 0.01 vs. 0.08 +/- 0.01 g/100 g body wt), a response that was inhibited by eprosartan treatment (0.10 +/- 0.01 g/100 g). Left ventricular expression of TGF-beta and fibronectin was also increased in rats with renal disease; however, the small decreases in expression observed in eprosartan-treated rats did not reach statistical significance. These data suggest that eprosartan may be beneficial in progressive renal disease and that the mechanism of action includes inhibition of cytokine production in addition to antihypertensive activity.