Enhanced acetaminophen hepatotoxicity in transgenic mice overexpressing BCL-2

Mitochondria play an important role in the cell death induced by many drugs , including hepatotoxicity from overdose of the popular analgesic, acetamin ophen (APAP). To investigate mitochondrial alterations associated with APAP -induced hepatotoxicity, the subcellular distribution of proapoptotic BAX w as determined. Based on the antiapoptotic characteristics of BCL-2, we furt her hypothesized that if a BAX component was evident then BCL-2 overexpress ion may be hepatoprotective. Mice, either with a human bcl-2 transgene (-/) or wild-type mice (WT; -/-), were dosed with 500 or 600 mg/kg (i.p.) APAP or a nonhepatotoxic isomer, N-acetyl-m-aminophenol (AMAP). Immunoblot anal yses indicated increased mitochondrial BAX-beta content very early after AP AP or AMAP treatment. This was paralleled by disappearance of BAX-alpha fro m the cytosol of APAP treated animals and, to a lesser extent, with AMAP tr eatment. Early pathological evidence of APAP-induced zone 3 necrosis was se en in bcl-2 (-/+) mice, which progressed to massive panlobular necrosis wit h hemorrhage by 24 h. In contrast, WT mice dosed with APAP showed a more ty pical, and less severe, centrilobular necrosis. AMAP-treated bcl-2 (-/+) mi ce displayed only early microvesicular steatosis without progression to ext ensive necrosis. Decreased complex III activity, evident as early as 6 h af ter treatment, correlated well with plasma enzyme activities at 24 h (AST r (2) = 0.89, ALT r(2) = 0.87) thereby confirming a role for mitochondria in APAP-mediated hepatotoxicity. In conclusion, these data suggest for the fir st time that BAX may be an early determinant of APAP-mediated hepatotoxicit y and that BCL-2 overexpression unexpectedly enhances APAP hepatotoxicity.