TI: H2O2 Release from Human Granulocytes during Phagocytosis. Relationship to Superoxide Anion Formation and Cellular Catabolism of H2O2: Studies with Normal and Cytochalasin B-Treated Cells DT: July 13, 1977 AU: R.K Root, J. Metcalf SO: J. Clin. Invest, Vol. 60, Dec 1977, 1266-1279 AB: Normal and cytochalasin B-treated human granulocytes have been studied to determine some of the interrelationships between phagocytosis-induced respiration and superoxide and hydrogen peroxide formation and release into the extracellular medium by intact cells. By using the scopoletin fluorescent assay to continuously monitor extracellular hydrogen peroxide concentrations during contact of cells with opsonized staphylococci, it was demonstrated that the superoxide scavengers ferricytochrome c and nitroblue tetrazolium significantly reduced the amount of H2O2 released with time from normal cells but did not abolish it. This inhibitory effect was reversed by the simultaneous addition of superoxide dismutase (SOD), whereas the addition of SOD alone increased the amount of detectable H2O2 in the medium. The addition of sodium azide markedly inhibited myeloperoxidase-H2O2-dependent protein iodination and more than doubled H2O2 release, including the residual amount remaining after exposure of the cells to ferricytochrome c, suggesting its origin from an intracellular pool shared by several pathways for H2O2 catabolism. When cells were pretreated with cytochalasin B and opsonized bacteria added, reduced oxygen consumption was observed, but this was in parallel to a reduction in specific binding of organisms to the cells when compared to normal. Under the influence of inhibited phagosome formation by cytochalasin B, the cells released an increased amount of superoxide and peroxide into the extracellular medium relative to oxygen consumption, and all detectable peroxide release could be inhibited by the addition of ferricytochrome c. Decreased H2O2 production in the presence of this compound could not be ascribed to diminished bacterial binding, decreased oxidase activity, or increased H2O2 catabolism and was reversed by the simultaneous addition of SOD. Furthermore, SOD and ferricytochrome c had similar effects on another H2O2-dependent reaction, protein iodination, in both normal and cytochalasin B cells. When oxygen consumption, O2-, and H2O2 release were compared in the presence of azide under identical incubation conditions, the molar relationships for normal cells were 1.00:0.34:0.51 and for cytochalasin B- treated cells 1.00:0.99:0.40, respectively. Nonopsonized, or opsonized but disrupted, bacteria did not stimulate any of these metabolic functions. The results indicate that with normal cells approximately 50% of H2O2 released during phagocytosis is derived directly from O2- by dismutation, the remainder appearing from an (intra)cellular source shared by azide-inhibitable heme enzymes. With cytochalasin B treatment the evidence is consistent with the derivation of all H2O2 from an O2- precursor which is released from the cell surface. Furthermore, when activated by phagocytic particle binding, the neutrophil O2- generating system appears to make more of this compound than can be accounted for by dismutation to H2O2. This establishes conditions for the direct participation of both compounds in the microbicidal and cytocidal activity of these cells.