IMPAIRED ACTIVATION OF GLUCOSE-OXIDATION AND NADPH SUPPLY IN HUMAN ENDOTHELIAL-CELLS EXPOSED TO H2O2 IN HIGH-GLUCOSE MEDIUM

The effects of glucose concentration on D-glucose oxidation and reduce d nicotinamide adenine dinucleotide phosphate (NADPH) supply were stud ied during exposure of cultured human umbilical vein endothelial cells to hydrogen peroxide (H2O2). The activation of glucose oxidation via the pentose phosphate pathway (PPP), induced by exposure of cells to 2 00 mu mol/l H2O2 for 1 h, was reduced by 50% (P < 0.01) in cells cultu red for 5-7 days in 33 mmol/l D-glucose (HG) versus those cultured in 5.5 mmol/l D-glucose without (NG) or with (HR) 27.5 mmol/l D-raffinose . The intracellular NADPH content in HG cells, but not in NG or HR cel ls, was decreased by 42% (P < 0.01) by exposing cells to 200 mu mol/l H2O2. The decrease in NADPH was dependent on D-glucose concentration i n the medium and was prevented in glutathione (GSH)-depleted cells. Th e latter observation suggests that the decrease in NADPH is associated with activation of the GSH redox cycle. In the presence of 200 mu mol /l H2O2, lactate release into the medium, NADH/NAD ratio, and phosphof ructokinase activity in HG cells were 56, 53, and 68% greater, respect ively, than in the NG group, which indicates that inhibition of glycol ysis by H2O2 is less marked in the HG group compared with NG group. Th ese results indicate that activation of the PPP was impaired in endoth elial cells cultured under conditions of high-glucose and oxidative st ress, resulting in a decreased supply of NADPH to various NADPH-depend ent pathways, including the GSH redox cycle.