Nitric oxide co-operates with hydrogen peroxide in inducing DNA fragmentation and cell lysis in murine lymphoma cells

We examined whether NO and H2O2 could interact in inducing DNA fragmentation and cell death. H2O2 and the NO-releasing compounds sodium nitroprusside (SNP) and S-nitroso-N-acetyl-D,L-penicillamine (SNAP) by themselves elicited lysis of YAC-1 murine lymphoma cells in a concentration-dependent manner. Exposure of the cells to a combination of sublytic concentrations of SNP (0.78 mM) plus H2O2 (7.8 microM) or SNAP (0.18 mM) plus H2O2 (7.8 microM) resulted in cell death which is mediated, in part, through apoptosis. Evidence for this direction is provided by fluorescence microscopic evaluation of the cells, which revealed the presence of changes in nuclear morphology characteristic of apoptosis in 30-40% of lymphoma cells and by the specific pattern of internucleosomal DNA fragmentation detected by gel electrophoresis. The cytotoxic effect of SNP plus H2O2 could be effectively inhibited by either oxyhaemoglobin, which binds NO, or catalase, which eliminates H2O2. Partial protection from SNP-plus-H2O2-induced cell lysis was observed with the poly(ADP-ribose) polymerase inhibitors, nicotinamide and 3-aminobenzamide, parallelling their ability to reverse depletion of cellular NAD+ pools. These results indicate an interaction between NO and H2O2 which leads to a markedly enhanced cytotoxic activity, in part, via induction of apoptosis and suggest that poly(ADP-ribosylation) and subsequent NAD+ depletion mediate, at least in part, this cytotoxic activity.