Alcohol-induced free radicals in mice: Direct toxicants or signaling molecules?

Tumor necrosis factor a (TNF-a) and free radicals are produced in early alc ohol-induced liver injury. Recently, pathology caused by alcohol was blocke d nearly completely in tumor necrosis factor a receptor 1 (TNF-RI) knockout mice. With this model, it is now possible to evaluate whether free radical s are directly toxic or act as redox regulators of TNF-a production. Specif ically, if free radicals were directly toxic, a parallel decrease in free r adicals and pathology in TNF-R1 knockout mice would be predicted. If they o nly affect TNF-a production, radicals would be expected to remain high whil e pathology is diminished. Accordingly, free radical production in TNF-RI k nockout mice was studied here. The enteral alcohol delivery model used mice lacking TNF-R1 (p55) and wild-type control C57B1/6J mice. Animals received a liquid diet continuously with either ethanol or isocaloric maltose-dextr in as control for 4 weeks. Urine ethanol levels fluctuated from 10 to 500 m g/dL in a cyclic pattern in mice receiving ethanol. Ethanol elevated liver: body weight ratios, serum alanine transaminase (ALT) levels, and pathology scores in wild-type mice. These parameters were blunted nearly completely i n TNF-R1 knockout mice. Ethanol treatment increased free radical production in wild-type mice compared with animals fed a high-fat control diet. There were no differences in intensity of free radical signals regardless of the presence or absence of TNF-RI; however, pathology differed markedly betwee n these groups. These findings are consistent with the hypothesis that free radicals act as redox signals for TNF-a production and do not directly dam age cells in early alcohol-induced hepatic injury.