DNA AS A CRITICAL TARGET IN TOXIC CELL-DEATH - ENHANCEMENT OF DIMETHYLNITROSAMINE CYTOTOXICITY BY DNA-REPAIR INHIBITORS

Our working hypothesis states that DNA damage is a critical step in to xic cell death. The DNA hypothesis was tested in cultured mouse hepato cytes by examining whether inhibitors of DNA repair would increase dim ethylnitrosamine toxicity and DNA damage in parallel. Inhibitors were chosen for selectivity toward DNA polymerase alpha (aphidicolin, myric etin), DNA ligase (ethidium bromide), or multiple repair enzymes (ara- C, doxorubicin). Dimethylnitrosamine caused concentration-dependent DN A damage at 6 hr and cell death at 24 hr (35% ALT release vs. 8.8% in control cultured hepatocytes). Each repair inhibitor increased dimethy lnitrosamine-induced DNA damage and toxic cell death in parallel. Doxo rubicin maximally elevated DNA fragmentation and toxicity (57% ALT rel ease). Repair inhibitors alone failed to damage DNA or cause cell deat h in this model system. These data support the hypothesis that DNA dam age is an early causal event in toxic cell death caused by alkylating hepatotoxicants.