Bentley, Michael D.

Objective— Mechanisms of renal injury distal to renal artery stenosis (RAS) remain unclear. We tested the hypothesis that it involves microvascular remodeling consequent to increased oxidative stress. Methods and Results— Three groups of pigs (n=6 each) were studied after 12 weeks of RAS, RAS+antioxidant supplementation (100 IU/kg vitamin E and 1 g vitamin C daily), or controls. The spatial density and tortuousity of renal microvessels (<500 μm) were tomographically determined by 3D microcomputed tomography. The in situ production of superoxide anion and the expression of vascular endothelial growth factor (VEGF), its receptor VEGFR-2, hypoxia-inducible-factor (HIF)-1α, von Hippel-Lindau (VHL) protein, and NAD(P)H oxidase (p47phox and p67phox subunits) were determined in cortical tissue. RAS and RAS+antioxidant groups had similar degrees of stenosis and hypertension. The RAS group showed a decrease in spatial density of cortical microvessels, which was normalized in the RAS+antioxidant group, as was arteriolar tortuousity. RAS kidneys also showed tissue fibrosis (by trichrome and Sirius red staining), increased superoxide anion abundance, NAD(P)H oxidase, VHL protein, and HIF-1α mRNA expression. In contrast, expression of HIF-1α, VEGF, and VEGFR-2 protein was downregulated. These were all significantly improved by antioxidant intervention. Conclusions— Increased oxidative stress in the stenotic kidney alters growth factor activity and plays an important role in renal microvascular remodeling, which can be prevented by chronic antioxidant intervention.

Background— Hypercholesterolemia (HC) and atherosclerosis can elicit oxidative stress, coronary endothelial dysfunction, and myocardial ischemia, which may induce growth-factor expression and lead to myocardial neovascularization. We tested the hypothesis that chronic antioxidant intervention in HC would attenuate neovascularization and preserve the expression of hypoxia-inducible factor (HIF)-1α and vascular endothelial growth factor (VEGF). Methods and Results— Three groups of pigs (n=6 each) were studied after 12 weeks of normal or 2% HC diet or HC+antioxidant supplementation (100 IU/kg vitamin E and 1 g vitamin C daily). Myocardial samples were scanned ex vivo with a novel 3D micro-CT scanner, and the spatial density and tortuosity of myocardial microvessels were determined in situ. VEGF mRNA, protein levels of VEGF and VEGF receptor-1, HIF-1α, nitrotyrosine, and superoxide dismutase (SOD) were determined in myocardial tissue. The HC and HC+antioxidant groups had similar increases in serum cholesterol levels. HC animals showed an increase in subendocardial spatial density of microvessels compared with normal (160.5±11.8 versus 95.3±8.2 vessels/cm 2 , P <0.05), which was normalized in HC+antioxidant (92.5±20.5 vessels/cm 2 , P <0.05 versus HC), as was arteriolar tortuosity. In addition, HC induced upregulation of VEGF, HIF-1α, and nitrotyrosine expression and decreased SOD expression and activity, all of which were preserved by antioxidant intervention. Conclusions— Changes in myocardial microvascular architecture invoked by HC are accompanied by increases in HIF-1α and VEGF expression and attenuated by antioxidant intervention. This underscores a role of increased oxidative stress in modulating myocardial microvascular architecture in early atherogenesis.