Erin M. Mezzetti

Vascular protection in diabetic stroke: role of matrix metalloprotease-dependent vascular remodeling

Temporary focal ischemia causes greater hemorrhagic transformation (HT) in diabetic Goto-Kakizaki (GK) rats, a model with increased cerebrovascular matrix metalloprotease (MMP) activity and tortuosity. The objective of the current study was to test the hypotheses that (1) diabetes-induced cerebrovascular remodeling is MMP dependent and (2) prevention of vascular remodeling by glucose control or MMP inhibition reduces HT in diabetic stroke. Control and GK rats were treated with vehicle, metformin, or minocycline for 4 weeks, and indices of remodeling including vascular tortuosity index, lumen diameter, number of collaterals, and middle cerebral artery (MCA) MMP activity were measured. Additional animals were subjected to 3 hours MCA occlusion/21 hours reperfusion, and infarct size and HT were evaluated as indices of neurovascular injury. All remodeling markers including MMP-9 activity were increased in diabetes. Infarct size was smaller in minocycline-treated animals. Both metformin and minocycline reduced vascular remodeling and severity of HT in diabetes. These results provide evidence that diabetes-mediated stimulation of MMP-9 activity promotes cerebrovascular remodeling, which contributes to greater HT in diabetes. Metformin and minocycline offer vascular protection, which has important clinical implications for diabetes patients who are at a fourfold to sixfold higher risk for stroke.

Glycemic control prevents microvascular remodeling and increased tone in Type 2 diabetes: link to endothelin-1

Medial thickening and vascular hypertrophy of resistance arteries can lead to cardiovascular complications associated with diabetes. While previous studies have established a role of type 1 diabetes in vascular remodeling, we recently extended these observations to type 2 diabetes and reported increased collagen deposition due to alterations in matrix metalloproteinase expression and activity in mesenteric resistance arteries. These studies also showed that remodeling response was mediated by endothelin-1 (ET-1) via activation of ET(A) receptors, whereas blockade of ET(B) receptors exacerbated the remodeling. However, the effectiveness of glycemic control strategies in preventing these vascular changes, including activation of the ET system still remained unclear. Also, very little is known about whether and to what extent reorganization of the extracellular matrix (ECM) affects vascular compliance and vasomotor tone. Accordingly, this study assessed structural remodeling of mesenteric microvessels, vascular compliance, and myogenic tone, as well as the role of matrix metalloproteinases (MMP) in mediating these processes. Spontaneously diabetic, non-obese Goto-Kakizaki (GK) rats, a model for type 2 diabetes, and normoglycemic Wistar rats were used for the studies. A subset of GK rats were administered metformin to achieve euglycemia. Glycemic control normalized the increased media-to-lumen ratios (M/L) and myogenic tone seen in diabetes, as well as normalizing plasma ET-1 levels and mesenteric ET(A) receptor expression. There was increased collagen synthesis in diabetes paralleled by decreased collagenase MMP-13 activity, while glycemic control attenuated the process. These findings and our previous study taken together suggest that hyperglycemia-mediated activation of ET-1 and ET(A) receptors alter vascular structure and mechanics in type 2 diabetes.

Nox2-Derived Superoxide Contributes to Cerebral Vascular Dysfunction in Diet-Induced Obesity

Background and Purpose— Obesity is an increasing epidemic worldwide; however, little is known about effects of obesity produced by high-fat diet (HFD) on the cerebral circulation. The purpose of this study was to examine the functional and temporal effects of a HFD on carotid and cerebral vascular function and to identify mechanisms that contribute to such functional alterations. Methods— Responses of cerebral arterioles (in vivo) and carotid arteries (in vitro) were examined in C57Bl/6 (wild-type) and Nox2-deficient (Nox2−/−) mice fed a control (10%) or a HFD (45% or 60% kcal of fat) for 8, 12, 30, or 36 weeks. Results— In wild-type mice, a HFD produced obesity and endothelial dysfunction by 12 and 36 weeks in cerebral arterioles and carotid arteries, respectively. Endothelial function could be significantly improved with Tempol (a superoxide scavenger) treatment in wild-type mice fed a HFD. Despite producing a similar degree of obesity in both wild-type and Nox2−/− mice, endothelial dysfunction was observed only in wild-type, but not in Nox2−/−, mice fed a HFD. Conclusions— Endothelial dysfunction produced by a HFD occurs in a temporal manner and appears much earlier in cerebral arterioles than in carotid arteries. Genetic studies revealed that Nox2-derived superoxide plays a major role in endothelial dysfunction produced by a HFD. Such functional changes may serve to predispose blood vessels to reduced vasodilator responses and thus may contribute to alterations in cerebral blood flow associated with obesity.

Effect of chronic and selective endothelin receptor antagonism on microvascular function in Type 2 diabetes

Vascular dysfunction, which presents either as an increased response to vasoconstrictors or an impaired relaxation to dilator agents, results in worsened cardiovascular outcomes in diabetes. We have established that the mesenteric circulation in Type 2 diabetes is hyperreactive to the potent vasoconstrictor endothelin-1 (ET-1) and displays increased nitric oxide-dependent vasodilation. The current study examined the individual and/or the relative roles of the ET receptors governing vascular function in the Goto-Kakizaki rat, a mildly hyperglycemic, normotensive, and nonobese model of Type 2 diabetes. Diabetic and control rats received an antagonist to either the ET type A (ETA; atrasentan; 5 mg x kg(-1) x day(-1)) or type B (ET(B); A-192621; 15 or 30 mg x kg(-1) x day(-1)) receptors for 4 wk. Third-order mesenteric arteries were isolated, and vascular function was assessed with a wire myograph. Maximum response to ET-1 was increased in diabetes and attenuated by ETA antagonism. ETB blockade with 15 mg/kg A-192621 augmented vasoconstriction in controls, whereas it had no further effect on ET-1 hyperreactivity in diabetes. The higher dose of A-192621 showed an ETA-like effect and decreased vasoconstriction in diabetes. Maximum relaxation to acetylcholine (ACh) was similar across groups and treatments. ETB antagonism at either dose had no effect on vasorelaxation in control rats, whereas in diabetes the dose-response curve to ACh was shifted to the right, indicating a decreased relaxation at 15 mg/kg A-192621. These results suggest that ETA receptor blockade attenuates vascular dysfunction and that ETB receptor antagonism exhibits differential effects depending on the dose of the antagonists and the disease state.

Differential effects of diet-induced dyslipidemia and hyperglycemia on mesenteric resistance artery structure and function in type 2 diabetes.

Type 2 diabetes and dyslipidemia oftentimes present in combination. However, the relative roles of diabetes and diet-induced dyslipidemia in mediating changes in vascular structure, mechanics, and function are poorly understood. Our hypothesis was that addition of a high-fat diet would exacerbate small artery remodeling, compliance, and vascular dysfunction in type 2 diabetes. Vascular remodeling indices [media/lumen (M/L) ratio, collagen abundance and turnover, and matrix metalloproteinase dynamics], mechanical properties (vessel stiffness), and reactivity to pressure and vasoactive factors were measured in third-order mesenteric arteries in control Wistar and type 2 diabetic Goto-Kakizaki (GK) rats fed either a regular or high-fat diet. M/L ratios, total collagen, and myogenic tone were increased in diabetes. Addition of the high-fat diet altered collagen patterns (mature versus new collagen) in favor of matrix accumulation. Addition of a high-fat diet caused increased constriction to endothelin-1 (0.1–100 nM), showed impaired vasorelaxation to both acetylcholine (0.1 nM–1 μM) and sodium nitroprusside (0.1 nM–1 μM), and increased cardiovascular risk factors in diabetes. These results suggest that moderate elevations in blood glucose, as seen in our lean GK model of type 2 diabetes, promote resistance artery remodeling resulting in increased medial thickness, whereas addition of a high-fat diet contributes to diabetic vascular disease predominantly by impairing vascular reactivity in the time frame used for this study. Although differential in their vascular effects, both hyperglycemia and diet-induced dyslipidemia need to be targeted for effective prevention and treatment of diabetic vascular disease.

Endothelin-1-mediated cerebrovascular remodeling is not associated with increased ischemic brain injury in diabetes

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.