Enhanced Acetaminophen Hepatotoxicity in Transgenic Mice Overexpressing BCL-2

Abstract

Mitochondria play an important role in the cell death induced by many drugs, including hepatotoxicity from overdose of the popular analgesic, acetaminophen (APAP). To investigate mitochondrial alterations associated with APAP-induced hepatotoxicity, the subcellular distribution of proapoptotic BAX was determined. Based on the antiapoptotic characteristics of BCL-2, we further hypothesized that if a BAX component was evident then BCL-2 overexpression 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 analyses indicated increased mitochondrial BAX-beta content very early after APAP or AMAP treatment. This was paralleled by disappearance of BAX-alpha from the cytosol of APAP treated animals and, to a lesser extent, with AMAP treatment. Early pathological evidence of APAP-induced zone 3 necrosis was seen in bcl-2 (-/+) mice, which progressed to massive panlobular necrosis with hemorrhage by 24 h. In contrast, WT mice dosed with APAP showed a more typical, and less severe, centrilobular necrosis. AMAP-treated bcl-2 (-/+) mice displayed only early microvesicular steatosis without progression to extensive necrosis. Decreased complex III activity, evident as early as 6 h after 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 first time that BAX may be an early determinant of APAP-mediated hepatotoxicity and that BCL-2 overexpression unexpectedly enhances APAP hepatotoxicity.

Overexpression of Aldose Reductase Render Mouse Hepatocytes More Sensitive to Acetaminophen Induced Oxidative Stress and Cell Death

“…On the other hand bcl-x L another antiapoptotic gene more affected by APAP than bcl-2 in this cell, the mRNA of bcl-x L decreased after 6 h and dramatically decreased until 48 h, and over-expression of aldose reductase augmented APAPinduced reduction on bcl-x L . In consistent with that, previous studies demonstrated that transgenic mice overexpressing bcl-2 is more susceptible to APAP induced hepatotoxicity with massive panlobular necrosis by 24 h [20]. Moreover, administration of APAP to BALB/c mice caused extensive centrilobular apoptosis and necrosis, accompanied by up-regulation of anti-apoptotic protein bcl-2 after 24 h [21].…”

Bcl-2 induces pro-oxidant state by engaging mitochondrial respiration in tumor cells

“…9 The role of Bcl-2 as a pro-oxidant protein in live animal models has also been reflected in other model systems. 10 If this scenario were indeed true, it would be of great interest to identify the cellular source(s) of superoxide…”

The mechanism underlying acetaminophen-induced hepatotoxicity in humans and mice involves mitochondrial damage and nuclear DNA fragmentation

“…Hallmarks of apoptotic cell death include several morphological features, such as cell shrinkage, chromatin condensation, and formation of apoptotic bodies as well as extensive caspase activation (60). In general, only very few apoptotic cells are detectable after APAP overdose (23), and there is no relevant caspase activation in mouse livers (23,52,61). Furthermore, pancaspase inhibitor did not protect against APAP hepatotoxicity (23-25, 52, 62, 63).…”