DACARBAZINE TOXICITY IN MURINE LIVER-CELLS - A MODEL OF HEPATIC ENDOTHELIAL INJURY AND GLUTATHIONE DEFENSE

The pathophysiology of hepatic veno-occlusive disease is poorly. under stood. These studies were undertaken to determine the initial cellular target and the role of glutathione detoxification of dacarbazine, a t oxin implicated in hepatic veno-occlusive disease. Sinusoidal endothel ial cells (SECs) and hepatocytes were isolated and plated in culture d ishes. Dacarbazine (5-(3,3-dimethyl-triazeno) imidazole-4-carboxamide) , 3 and 6 mM, was toxic to SECs but not to hepatocytes. Onset of toxic ity occurred between 11 and 12 hr as determined by serial MTT assays a nd ethidium homodimer dye exclusion. Glutathione detoxification of dac arbazine in SECs was suggested by: (1) depletion of glutathione before onset of toxicity; (2) exacerbation of toxicity by buthionine sulfoxi mine (BSO) depletion of glutathione; and (3) protection by exogenous g lutathione. Protection by exogenous glutathione may be by uptake of in tact tripeptide rather than by extracellular hydrolysis: neither acivi cin (inhibitor of gamma-glutamyltranspeptidase) nor BSO (inhibitor of gamma-glutamylcysteine synthetase) blocked the protective effect, and glutathione disulfide did not protect. The relative resistance to daca rbazine toxicity seen in hepatocytes is not due to more efficient GSH detoxification, because toxicity was not unmasked in hepatocytes cultu res in medium lacking sulfur amino acid precursors of GSH. In conclusi on, glutathione status may play an important role in the susceptibilit y to toxicity. Furthermore, the findings suggest that the SEC is the i nitial in vivo target of dacarbazine due to a relatively higher level of metabolic activation that more readily overcomes the available deto xification.