Kinetics of hydrogen peroxide elimination by human umbilical vein endothelial cells in culture.

H2O2 is a key substance in the oxidative stress. To evaluate the antioxidant activity of intact human umbilical vein endothelial cells (HUVEC), we measured the H2O2 removal rate by the cell in monolayer culture at various H2O2 concentrations (1-300 microM). It was shown that the removal reaction can be divided into two kinetically different reactions: reaction 1 apparently following the Michaelis-Menten kinetics and reaction 2 following the first-order kinetics. Reaction 1, which was diminished by treatment with diethyl maleate, could be attributed to GPx. Reaction 2, which was inhibited by aminotriazole, was principally attributable to catalase, though non-enzymatic reactions may contribute to it partially. Furthermore, we have constructed a mathematical model for the H2O2 elimination including the pentose phosphate pathway enzymes, GSSG reductase and GSH peroxidase. On the basis of the known kinetics and observed activities of the enzymes, the model could reproduce well the observed concentration dependence of the H2O2 removal rate. It was suggested from the simulation study that GSSG reductase is more important than G6PD in determining the rate of the NADPH-dependent H2O2 elimination.