Endogenous Catalase Protects Human Blood Phagocytes Against Oxidative Damage by Extracellularly Generated Hydrogen Peroxide

Abstract

Human blood monocytes and neutrophils were incubated with an H2O2-generating system (glucose plus glucose oxidase) in the presence and absence of 2 mM sodium azide, to assess the importance of catalase in the protection of these cells against heavy external oxidative stress (50 nmole H2O2/ml/min). Before and after these incubations, the cell integrity was determined, as well as the following cell functions: chemotactic response towards casein, and oxygen consumption and release of lysosomal enzymes during zymosan ingestion. The levels of reduced and oxidized glutathione were also measured, as were the activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase. Incubation with the H2O2-generating system in the absence of azide decreased the amount of reduced glutathione in the monocytes by about 25% within 30 min, with a concomitant proportional increase in oxidized glutathione, but had no appreciable effect on the extent of reduction of glutathione in the neutrophils. The cell integrity, cell functions, and enzymic activities were barely affected by this treatment in either type of cell. Incubation with the H2O2-generating system in the presence of azide (to inhibit endogenous catalase) resulted in a strong decrease in the level of reduced glutathione and an increase in oxidized glutathione, especially in the monocytes. The cell integrity and functional responses decreased concomitantly, but the enzymic activities remained normal. Only the glutathione reductase activity in the monocytes decreased significantly. These effects were not seen when the glucose oxidase in the H2O2-generating system was boiled or when azide-treated cells were washed and incubated with the H2O2-generating system plus catalase. Incubation with azide alone had no effect on any of the parameters tested. These results indicate that catalase is needed for adequate protection of monocytes and neutrophils against heavy external oxidative stress. Presumably, the glutathione redox cycle is mainly involved in repair of oxidized cell components, whereas catalase directly decomposes hydrogen peroxide.