| Areas in the circulation exposed to non-laminar flow patterns are predisposed to atherosclerosis. These disturbances of flow, such as flow separation and reversal, occur at branch points including the common carotid bifurcation, abdominal aortic bifurcation, as well as the aortic arch. Flow reversal causes an oscillatory shear stress (OSS) that is exerted on the innermost arterial layer, the endothelium. For example, oscillations of +13/-9 dynes/cm 2 occur on the endothelial wall of the internal carotid bulb, an area particularly prone to atherosclerotic lesion development. OSS is thought to stimulate atherogenesis by increasing endothelial adhesion molecule expression (including VCAM-1 and ICAM), stimulating monocyte adhesion, and increasing endothelin-l expression. In contrast, unidirectional laminar shear stress (LSS) which increases during exercise, is thought to protect against atherosclerosis by increasing nitric oxide (NO•) levels. NO• , a potent antioxidant, decreases platelet adhesion, decreases smooth muscle cell proliferation, and decreases leukocyte migration.;Because oxidative stress contributes to atherosclerosis, we sought to determine if OSS increases endothelial reactive, oxygen species (ROS) production. Bovine aortic endothelial cells were exposed to static, laminar (15 dynes/cm 2) and OSS (+/- 15 dynes/cm2). OSS increased superoxide (O2•-) production by more than 3-fold over static and laminar conditions as detected using electron spin resonance (ESR). In addition, H2O2 was increased more than 2-fold in endothelial cells exposed to OSS as measured by 2', 7'-dichlorofluorescin diacetate (DCF-DA) and Amplex Red fluorescence. Next, we wished to define the enzyme(s) responsible for this phenomenon. The increase in O2 • and hydrogen peroxide (H2O2) was inhibited by oxypurinol but not by inhibitors of other enzymatic sources, implicating xanthine oxidase (XO) as the primary source of ROS. Xanthine-dependent O 2•- production was increased in homogenates of endothelial cells exposed to OSS. This was associated with a decrease in xanthine dehydrogenase (XDH) protein levels and enzymatic activity, elevating the XO/XDH ratio. In addition, increased uric acid levels were detected by HPLC, indicating increased purine metabolism by the xanthine oxidoreductase (XOR) system.;We also studied endothelial cells lacking the p47phox subunit of the NADPH oxidase. (Abstract shortened by UMI.)... |
