[Show abstract][Hide abstract] ABSTRACT: Hemorrhagic transformation (HT) is an important complication of acute ischemic stroke particularly in diabetic patients receiving thrombolytic treatment with tissue plasminogen activator (tPA), the only approved drug for the treatment of acute ischemic stroke (AIS). The objective of the current study was to determine the effects of acute manipulation of potential targets for vascular protection (i.e., NFkB, peroxynitrite, and matrix metalloproteinases) on vascular injury and functional outcome in a diabetic model of cerebral ischemia. Ischemia was induced by middle cerebral artery occlusion in control and type 2 diabetic Goto-Kakizaki rats. Treatment groups received a single dose of peroxynitrite decomposition catalyst FeTPPs,a non-specific NFkB inhibitor curcumin, or a broad-spectrum matrix metalloproteinase (MMP) inhibitor minocycline at reperfusion. Post-stroke infarct volume, edema, hemorrhage, neurological deficits, and MMP-9 activity were evaluated. All acute treatments reduced MMP-9 and HT in diabetic groups. In addition, acute curcumin and minocycline therapy reduced edema in these animals. Improved neurological function was observed in varying degrees with treatment as indicated by beam-walk performance, modified Bederson scores and grip strength; however, infarct size was similar to untreated diabetic animals. In control animals, all treatments reduced MMP-9 activity yet bleeding was not improved. Neuroprotection was only conferred by curcumin and minocycline. Uncovering underlying mechanisms contributing to the success of acute therapy in diabetes will advance tailored stroke therapies.
[Show abstract][Hide abstract] ABSTRACT: Dysregulation of cerebral vascular function and, ultimately, cerebral blood flow (CBF) may contribute to complications such as stroke and cognitive decline in diabetes. We hypothesized that 1) diabetes-mediated neurovascular and myogenic dysfunction impairs CBF and 2) under hypoxic conditions, cerebral vessels from diabetic rats lose myogenic properties because of peroxynitrite (ONOO(-))-mediated nitration of vascular smooth muscle (VSM) actin. Functional hyperemia, the ability of blood vessels to dilate upon neuronal stimulation, and myogenic tone of isolated middle cerebral arteries (MCAs) were assessed as indices of neurovascular and myogenic function, respectively, in 10- to 12-week control and type 2 diabetic Goto-Kakizaki rats. In addition, myogenic behavior of MCAs, nitrotyrosine (NY) levels, and VSM actin content were measured under normoxic and hypoxic [oxygen glucose deprivation (OGD)] conditions with and without the ONOO(-) decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl) prophyrinato iron (III), chloride (FeTPPs). The percentage of myogenic tone was higher in diabetes, and forced dilation occurred at higher pressures. Functional hyperemia was impaired. Consistent with these findings, baseline CBF was lower in diabetes. OGD reduced the percentage of myogenic tone in both groups, and FeTPPs restored it only in diabetes. OGD increased VSM NY in both groups, and although FeTPPs restored basal levels, it did not correct the reduced filamentous/globular (F/G) actin ratio. Acute alterations in VSM ONOO(-) levels may contribute to hypoxic myogenic dysfunction, but this cannot be solely explained by the decreased F/G actin ratio due to actin nitration, and mechanisms may differ between control and diabetic animals. Our findings also demonstrate that diabetes alters the ability of cerebral vessels to regulate CBF under basal and hypoxic conditions.
Journal of Pharmacology and Experimental Therapeutics 05/2012; 342(2):407-15. DOI:10.1124/jpet.111.191296 · 3.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We previously reported enhanced cerebrovascular remodeling and arteriogenesis in experimental type 2 diabetes. This study tested the hypotheses that 1) cerebral but not peripheral angiogenesis is increased in a spatial manner and 2) peroxynitrite orchestrates vascular endothelial growth factor (VEGF)-mediated brain angiogenesis in diabetes. Stereology of brain, eye, and skeletal muscle microvasculature was evaluated in control and diabetic rats using three-dimensional images. Migration and tube formation properties of brain microvascular endothelial cells (BMECs) were analyzed as markers of angiogenesis. Vascular density, volume, and surface area were progressively increased from rostral to caudal sections in both the cerebral cortex and striatum in diabetic rats. Unperfused new vessels were more prominent and the pericyte-to-endothelial cell ratio was decreased in diabetes. Vascularization was greater in the retina but lower in the peripheral circulation. VEGF and nitrotyrosine levels were higher in cerebral microvessels of diabetic animals. Migratory and tube formation properties were enhanced in BMECs from diabetic rats, which also expressed high levels of basal VEGF, nitrotyrosine, and membrane-type (MT1) matrix metalloprotease (MMP). VEGF-neutralizing antibody and inhibitors of peroxynitrite, src kinase, or MMP blocked the migration. Diabetes increases and spatially regulates cerebral neovascularization. Increased VEGF-dependent angiogenic function in BMECs is mediated by peroxynitrite and involves c-src and MT1-MMP activation.
[Show abstract][Hide abstract] ABSTRACT: Cerebrovascular complications make diabetic patients 2-6 times more susceptible to a stroke event and this risk is magnified in younger individuals and in patients with hypertension and complications in other vascular beds. In addition, when patients with diabetes and hyperglycemia experience an acute ischemic stroke they are more likely to die or be severely disabled and less likely to benefit from the one FDA-approved therapy, intravenous tissue plasminogen activator. Experimental stroke models have revealed that chronic hyperglycemia leads to deficits in cerebrovascular structure and function that may explain some of the clinical observations. Increased edema, neovascularization and protease expression as well as altered vascular reactivity and tone may be involved and point to potential therapeutic targets. Further study is needed to fully understand this complex disease state and the breadth of its manifestation in the cerebrovasculature.
[Show abstract][Hide abstract] ABSTRACT: Structure and function of the cerebrovasculature is critical for ischemic stroke outcome. We showed that diabetes causes cerebrovascular remodeling by activation of the endothelin A (ET(A)) receptors. The goal of this study was to test the hypotheses that vasculoprotective endothelial ET(B) receptors are decreased and pharmacological inhibition of the ET(B) receptor augments vascular remodeling of middle cerebral arteries (MCAs) in type 2 diabetes. MCA structure, matrix metalloprotease (MMP) activity, and matrix proteins as well as ET(A) and ET(B) receptor profiles were assessed in control Wistar and diabetic Goto-Kakizaki rats treated with vehicle, the ET(B) receptor antagonist (2R,3R,4S)-4-(1,3-benzodioxol-5-yl)-1-[2-[(2,6-diethylphenyl)amino]-2-oxoethyl]-2-(4-propoxyphenyl)pyrrolidine-3-carboxylic acid (A192621) (30 mg/kg/day), or the dual ET receptor antagonist bosentan (100 mg/kg/day) for 4 weeks. Diabetes increased vascular smooth muscle (VSM) ET(A) and ET(B) receptors; the increase was prevented by chronic bosentan treatment. MCA wall thickness was increased in diabetes, and this was associated with increased MMP-2 activity and collagen deposition but reduced MMP-13 activity. Because of up-regulation of VSM ET receptors in diabetes, selective ET(B) receptor antagonism with A192621 blunts this response, and combined ET(A) and ET(B) receptor blockade with bosentan completely prevents this response. On the other hand, A192621 treatment augmented remodeling in control animals, indicating a physiological protective role for this receptor subtype. Attenuation of changes in ET receptor profile with bosentan treatment suggests that ET-1 has a positive feedback on the expression of its receptors in the cerebrovasculature. These results emphasize that ET receptor antagonism may yield different results in healthy and diseased states.
Journal of Pharmacology and Experimental Therapeutics 12/2010; 337(1):9-15. DOI:10.1124/jpet.110.175380 · 3.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have shown hypertrophic cerebrovascular remodelling in the Goto-Kakizaki (GK) rat model of diabetes. This study tested the hypotheses that (1) vascular remodelling develops as the disease progresses and alters myogenic reactivity of resistance vessels important for regulation of cerebral blood flow (CBF), and (2) glycaemic control prevents cerebrovascular remodelling and myogenic dysfunction.
Middle cerebral artery (MCA) lumen diameter, media : lumen (M : L) ratio, cross-sectional area (CSA) and myogenic tone were measured in 10- and 18-week-old control Wistar and diabetic GK rats using pressurized arteriograph (n = 8-14/group). Mean arterial blood pressure (MAP) was measured with telemetry (n = 5/group). Additional GK rats were treated with metformin (300 mg kg(-1) day(-1) ) for glycaemic control starting at 7 weeks after the onset of diabetes until 18 weeks (n = 9).
In the control group, there was no difference in remodelling indices, myogenic tone or MAP between ages. Eighteen week diabetic rats displayed increased M : L ratio and CSA, but decreased lumen diameter and myogenic tone compared to 10-week GK or 18-week control rats. MAP increased starting around 10 weeks of age and remained slightly higher in the GK rats. Glycaemic control normalized M : L ratio, CSA, lumen diameter and myogenic tone with no effect on blood pressure.
These findings suggest that diabetic rats develop MCA remodelling as the disease progresses but this is associated with impaired myogenic reactivity which may ultimately affect CBF. Our results also provide evidence that glycaemic control is an effective therapeutic strategy to prevent cerebrovascular remodelling and dysfunction.
[Show abstract][Hide abstract] ABSTRACT: Diabetes increases the risk of as well as poor outcome after stroke. Matrix metalloprotease (MMP) activation disrupts blood-brain barrier integrity after cerebral ischemia. We have previously shown that type 2 diabetes promotes remodeling of middle cerebral arteries (MCA) characterized by increased media/lumen (M/L) ratio and MMP activity in an endothelin (ET)-1-dependent manner in the Goto-Kakizaki (GK) rat model. In the present study, we examined the effects of ET-1-mediated vascular remodeling on neurovascular damage following cerebral ischemic injury in GK rats 5 and 12 weeks after the onset of diabetes. The MCA structure, cerebral perfusion as well as infarct size, and hemorrhage were measured in control and diabetic rats subjected to transient MCA occlusion. M/L ratio was increased after 12 but not 5 weeks of diabetes. The baseline cerebral perfusion was lower and the infarct volume smaller in diabetic rats in both age groups. The incidence of hemorrhagic transformation was higher after 5 weeks of diabetes as compared to that after 12 weeks or in the control groups. These findings provide evidence that ET-1-mediated cerebrovascular remodeling does not worsen the neurovascular damage of ischemic brain injury in diabetes. It is possible that this early remodeling response is compensatory in nature to regulate vascular tone and integrity, especially when ischemia is layered on diabetic vascular disease.
Canadian Journal of Physiology and Pharmacology 08/2010; 88(8):788-95. DOI:10.1139/Y10-040 · 1.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Vascular remodeling, characterized by extracellular matrix deposition and increased media-to-lumen (M/L) ratio, contributes to the development of microvascular complications in diabetes. We have previously shown in type 2 diabetic Goto-Kakizaki (GK) rats that selective ETA receptor blockade prevents medial thickening of mesenteric arteries via regulation of matrix metalloproteases (MMP), whereas selective ETB receptor blockade augments this thickening. The goal of this study was to determine the effect of combined ETA and ETB receptor blockade on resistance vessel remodeling. Vessel structure, MMP activity, and extracellular matrix proteins were assessed in control Wistar and diabetic GK rats treated with vehicle or bosentan (100 mg/kg per day) for 4 weeks (n = 7-9 per group). Bosentan completely prevented the increase in M/L ratio and MMP-2 activity in diabetes but paradoxically increased M/L ratio and MMP activation in control animals. Collagenase (MMP-13) activity and protein levels were significantly decreased in diabetes. Accordingly, collagen deposition was augmented in GK rats. Dual ET receptor antagonism improved enzyme activity and normalized MMP-13 levels in diabetic animals but blunted MMP-13 activity in control animals. In summary, current findings suggest that diabetes-mediated remodeling of resistance arteries is prevented by dual blockade of ETA and ETB receptors and that the relative role of ET receptors in the regulation of vascular structure differs in the control and disease states.
Canadian Journal of Physiology and Pharmacology 06/2010; 88(6):616-21. DOI:10.1139/Y10-034 · 1.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effect of diabetes on neovascularization varies between different organ systems. While excessive angiogenesis complicates diabetic retinopathy, impaired neovascularization contributes to coronary and peripheral complications of diabetes. However, how diabetes influences cerebral neovascularization is not clear. Our aim was to determine diabetes-mediated changes in the cerebrovasculature and its impact on the short-term outcome of cerebral ischemia.
Angiogenesis (capillary density) and arteriogenesis (number of collaterals and intratree anostomoses) were determined as indexes of neovascularization in the brain of control and type 2 diabetic Goto-Kakizaki (GK) rats. The infarct volume, edema, hemorrhagic transformation, and short-term neurological outcome were assessed after permanent middle-cerebral artery occlusion (MCAO).
The number of collaterals between middle and anterior cerebral arteries, the anastomoses within middle-cerebral artery trees, the vessel density, and the level of brain-derived neurotrophic factor were increased in diabetes. Cerebrovascular permeability, matrix metalloproteinase (MMP)-9 protein level, and total MMP activity were augmented while occludin was decreased in isolated cerebrovessels of the GK group. Following permanent MCAO, infarct size was smaller, edema was greater, and there was no macroscopic hemorrhagic transformation in GK rats.
The augmented neovascularization in the GK model includes both angiogenesis and arteriogenesis. While adaptive arteriogenesis of the pial vessels and angiogenesis at the capillary level may contribute to smaller infarction, changes in the tight junction proteins may lead to the greater edema following cerebral ischemia in diabetes.