Activated macrophages increase the susceptibility of rat hepatocytes to ethanol-induced oxidative stress: Conflicting effects of nitric oxide

The aim of this study was to examine how macrophages could act on ethanol-i nduced oxidative stress in rat hepatocytes during inflammatory conditions, well-known to induce nitric oxide (NO) synthase. For this purpose, RAW 264. 7 macrophages were added to primary rat hepatocyte cultures. Co-cultures we re then supplemented with lipopolysaccharide (LPS) and interferon gamma (IF N) for 18 h, in order to induce NO synthase before the addition of 50 mM et hanol. In cultures of hepatocytes alone, the addition of LPS and IFN protec ted from ethanol-induced oxidative stress. It has been shown previously tha t NO generated in hepatocytes was responsible for this effect. When macroph ages were added to primary rat hepatocyte cultures supplemented with LPS an d IFN, protection provided by NO against ethanol-induced oxidative stress i n hepatocytes ceased. Using a pretreatment of macrophages with N-G-monometh yl-L-arginine, a NO synthase inhibitor, it was concluded that NO generated by macrophages was responsible for macrophage toxicity. Taken together, our observations suggest that NO biosynthesis in hepatocytes protects them fro m ethanol-induced oxidative stress, whereas NO production in macrophages de prives hepatocytes of this NO protection.