GLYCATION, OXIDATIVE STRESS, AND SCAVENGER ACTIVITY GLUCOSE-METABOLISM AND RADICAL SCAVENGER DYSFUNCTION IN ENDOTHELIAL-CELLS

It has been reported that oxidative stress is increased in vivo in the diabetic state, Increased oxidative stress is caused not only by acce lerated production of oxygen-free radicals but also by decreased scave nging of those molecules, Endothelial cells are extremely sensitive to oxidative stress, resulting in impairments of various endothelial cel l function, In this report, we studied the association of intracellula r glucose metabolism and oxygen radical scavenging function via the gl utathione redox (GR) cycle in cells exposed to high-glucose conditions using cultured human umbilical vein endothelial cells, Glutathione-de pendent H2O2 degradation in cells exposed to 33 mmol/l glucose (HG) fo r 5-7 days was reduced by 48% vs, 5.5 mmol/l glucose (NG), This impair ment under tile oxidative stress was D-glucose-specific and concentrat ion-dependent and was also associated with a 42% decrease in intracell ular NADPH content, Exposure of cells to 200 mu mol/l H2O2 stimulated the GR cycle and the pentose phosphate pathway (PPP) at the same time, In the HG condition, activation of PPP was reduced by 50%, which was consistent with a decrease in NADPH content. Inhibition of glycolysis by H2O2 was less marked in HG cells versus NG cells. Activation of pol yol pathway in HG cells is not responsible for the decrease in intrace llular NADPH content, These results indicate that activation of the PP P and NADPH supply to the GR cycle is impaired in HG cells exposed to H2O2, which may result in increased oxidative stress to endothelial ce lls.