CELLULAR TARGET OF CYCLOPHOSPHAMIDE TOXICITY IN THE MURINE LIVER - ROLE OF GLUTATHIONE AND SITE OF METABOLIC-ACTIVATION

Hepatic venoocclusive disease (HVOD) is caused by the disruption of th e microcirculation by an as-yet unknown mechanism. Previous in vitro s tudies with azathioprine, monocrotaline, and dacarbazine suggested tha t toxins that cause HVOD initially causing HVOD target sinusoidal endo thelial cells (SEC) perhaps via profound glutathione (GSH) depletion. The current study examines cyclophosphamide toxicity in SEC and hepato cytes, as well as the interplay between the two cell types. Cyclophosp hamide was not directly toxic to SEC, but in coculture of SEC and hepa tocytes, cyclophosphamide was significantly more toxic to SEC. Two cyc lophosphamide metabolites, 4-hydroperoxycyclophosphamide and acrolein, were equally toxic to SEC, and toxicity occurred at 20-fold-lower con centrations than in hepatocytes. 4-Hydroperoxycyclophosphamide deplete d GSH by greater than 95% before inducing cell death in SEC. When hepa tocyte-GSH levels were sustained with supplemental methionine and seri ne in coculture, toxicity in both cell types was diminished. In cocult ure, SEC are significantly more susceptible than hepatocytes to cyclop hosphamide toxicity, and this is likely caused by acrolein generated b y the hepatocyte. As seen with other toxins implicated in HVOD, the pr ofound depletion of SEC GSH precedes the onset of toxicity. The degree of cyclophosphamide toxicity induced in SEC is determined by both met abolic activation and GSH detoxification in the hepatocytes.