Interaction of reactive nitrogen and oxygen intermediates in HL60 and dimethylsulphoxide-differentiated HL60 cells

The interaction of reactive nitrogen intermediates (RNI) with reactive oxygen intermediates (ROI) was inferred from the effect of added L-arginine on luminol-dependent chemiluminescence (LCL) and cytochrome C reduction in HL60 cells, dimethylsulphoxide (DMSO)-differentiated HL60 cells and human neutrophils. Phorbol myristate acetate (PMA)-stimulated HL60 cells had no effect on LCL and a decreased rate of cytochrome C reduction in the presence of increasing concentrations of L-arginine. Inhibition of L-arginine-mediated cytochrome C reduction was relieved by L-N(G)-monomethyl arginine (L-NMMA), an inhibitor of nitric oxide synthesis, in a concentration-dependent manner. In contrast, DMSO-differentiated cells and human neutrophils separated from blood showed decreased rates of LCL and cytochrome C reduction with increasing concentrations Of L-arginine, which were relieved to some extent by L-NMMA in a dose-dependent manner. These results are consistent with a 40% increase in the production of nitrate following stimulation of DMSO-differentiated cells and human neutrophils by PMA compared with only a 6% rise in undifferentiated HL60 cells. Possible inhibition of NADPH oxidase has been suggested to explain the responses of LCL, cytochrome C reduction and nitrate production by nitric oxide in the presence of L-arginine.