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.

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.

OBJECTIVEThe 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.RESEARCH DESIGN AND METHODSAngiogenesis (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).RESULTSThe 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.CONCLUSIONSThe 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.

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 Ϫ )-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 Ϫ 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 Ϫ 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.

Aim We have shown hypertrophic cerebrovascular remodeling in the Goto-Kakizaki (GK) rat model of diabetes. This study tested the hypotheses that 1) vascular remodeling develops as the disease progresses and alters myogenic reactivity of resistance vessels important for regulation of cerebral blood flow, and 2) glycemic control prevents cerebrovascular remodeling and myogenic dysfunction. Methods Middle cerebral artery 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/day) for glycemic control starting at 7 weeks after the onset of diabetes until 18 weeks (n=9). Results In the control group, there was no difference in remodeling indices, myogenic tone, or MAP between ages. 18-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. Glycemic control normalized M:L ratio, CSA, lumen diameter and myogenic tone with no effect on blood pressure. Conclusions These findings suggest that diabetic rats develop middle cerebral artery (MCA) remodeling as the disease progresses but this is associated with impaired myogenic reactivity which may ultimately affect cerebral blood flow. Our results also provide evidence that glycemic control is an effective therapeutic strategy to prevent cerebrovascular remodeling and dysfunction.