Acetaminophen nephrotoxicity in the rat. Renal metabolic activation in vitro

Abstract

High doses of acetaminophen (APAP) result in hepatic centrilobular and renal cortical necrosis in man and the F344 rat. Hepatic necrosis is considered to be due to the generation of an arylating intermediate via a microsomal cytochrome P-450 dependent system. Renal microsomes also metabolize APAP to an arylating intermediate via a P-450 dependent mechanism. Thus, at least part of the renal damage from APAP may be due to a biochemical mechanism similar to that in liver. Additionally, APAP is deacetylated to p-aminophenol (PAP) in renal and hepatic cytosol and microsomes. Previous results demonstrated that PAP may be activated in renal microsomes via an NADPH-independent mechanism. Therefore, significant metabolic activation of APAP in the kidney may occur subsequent to deacetylation. Covalent binding of [ ring- 14C]APAP to renal subcellular fractions was used to substantiate this hypothesis. Under appropriate incubation conditions, enzymatic NADPH-independent covalent binding of [ ring- 14C]APAP could be demonstrated in renal microsomes but not in 100,000 g supernatant fractions. Combination of these subcellular fractions resulted in greater covalent binding of [ ring- 14C]APAP than in the individual subcellular fractions alone. Addition of glutathione, bis( p-nitrophenyl)phosphate (a deacetylase inhibitor), or PAP inhibited this covalent binding. In contrast, NADPH-independent covalent binding of [ ring- 14C]APAP could not be demonstrated in any combination of hepatic subcellular fractions. Experiments comparing [ ring- 14C]APAP and [ acetyl- 14C]APAP covalent binding to renal 10,000 g supernatant fractions indicate that the compound which binds to renal macromolecules is derived from PAP. Thus, these results are consistent with the hypothesis that APAP can be metabolically activated in the kidney after deacetylation to PAP.