Oxidants, Eicosanoids and Endothelium in Diabetes

Boston Medical Center, Boston MA

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Abstract

Our preliminary studies establish new insights into how elevated glucose increases oxidant stress and the mechanisms by which its effects on cell function are mediated. Exposure of cultured human endothelial cells to elevated glucose for 7-10 days increases the production of both NO and superoxide anion (Oa-). NO is inactivated by reacting with 02- to form the reaction product, peroxynitrite (OONO), and increased levels of its reaction product with tyrosine, nitrotyrosine, is found in the cells. Although the fimction of many proteins may be affected, we have found that prostacyclin synthase (PGIS) is inactivated by tyrosine nitration in endothelial cells grown in elevated glucose. This may not only explain why diabetes decreases levels of PGI2, but also why increases have been noted in the PGI2 precursor, PGH2, which activates thromboxane A2 receptors (TPr). Activation of TPr can increase VCAM-1 and ICAM-1 expression as well as apoptosis of human endothelial cells. Expression of adhesion molecules and apoptosis, two events important in atherogenesis, are also enhanced by O2-, and indeed, exposure to elevated glucose enhances adhesion molecule expression and apoptosis by mechanisms which depend on O2- and TPr. Indeed, we have found that blockade of TPr inhibits the dramatic enhancement by diabetes ofatherogenesis in the Apo E deficient mouse. Our overall hypothesis is that the effects of oxidant stress in the endothelium in atherogenesis are importantly mediated via TPr as a result of inactivation of PGIS. Furthermore, in the context of this program, we have found that AICAR, a stimulator of AMP kinase, prevents the oxidant stress in endothelial cells exposed to elevated glucose, and inhibits VCAM-1 expression induced by TNF_. Our aims are: 1) To determine the mechanism by which elevated glucose and fatty acids increases production of NO and 02- and causes tyrosine nitration and inactivation ofPGI synthase. The role of AMP kinase in regulating oxidant stress via PKC will be studied. 2) To determine the role of TPr stimulation by eicosanoid products due to endothelial cell oxidant stress and PGI synthase inactivation in causing the increased leukocyte adhesion and apoptosis caused by high glucose and fatty acids, and 3) to determine if oxidant stress, PGIS inactivation, and TPr contr_ute to the increased atherogenesis caused by diabetes in transgenie mouse models. Activation of AMP kinase as a strategy for reducing oxidant stress will be explored.