CYTOTOXICITY OF NITRIC-OXIDE IN FU5 RAT HEPATOMA-CELLS - EVIDENCE FORCOOPERATIVE ACTION WITH HYDROGEN-PEROXIDE

The NO-releasing compounds 3-morpholinosydnonimine-N-ethylcarbamide (S IN-1), sodium nitroprusside (SNP) and S-nitroso-N-acetyl-DL-penicillam ine (SNAP) mediated a rapid loss of viability of Fu5 rat hepatoma cell s. SIN-1 in addition to NO also released the superoxide anion radical (O2-.). Its cytotoxicity, however, was not affected by superoxide dism utase. In contrast, the H2O2-converting enzyme catalase significantly, but not completely, diminished cell damage, indicating participation of H2O2 in the tumoricidal activity of SIN-1. Glucose oxidase (5 m-uni ts/ml), producing similar amounts of H2O2 to 5 mM SIN-1, had no effect on cell viability. When 5 m-units/ml glucose oxidase was added to inc ubations with 5 mM SNP, which alone initiated cell injury of about 40% , cell damage was significantly increased up to 95%. Similar results w ere observed with 1 mM SNAP and 20 m-units/ml xanthine oxidase, which mediated cytotoxicity of about 90% when both compounds were added toge ther, compared with 35% and 55% cell injury, respectively, induced by the single compounds. The results indicate that a co-operative action with H2O2 enhances the tumoricidal activity of NO in Fu5 cells. No evi dence for an interplay of NO with O2-. in cytotoxicity, e.g. via the p eroxynitrite anion (ONOO-), was found.