ACETAMINOPHEN NEPHROTOXICITY IN CD-1 MICE .1. EVIDENCE OF A ROLE FOR IN-SITU ACTIVATION IN SELECTIVE COVALENT BINDING AND TOXICITY

Acetaminophen (APAP) administration (600 mg/kg, ip) to 18-hr-fasted, 3 -month-old male CD-1 mice results in necrosis of the renal convoluted proximal tubules. To selectively inhibit APAP activation in the kidney but not in the liver, 10-week-old male CD-1 mice were castrated under ether anesthesia and allowed to recover for a minimum of 2 weeks befo re use. Microsomal activation of APAP in vitro was monitored by trappi ng the APAP-derived electrophile as an N-acetylcysteine conjugate. Pro duction of the conjugate was significantly decreased in renal microsom es from castrated mice. By contrast, hepatic microsomal production of the APAP conjugate was not changed by castration. Castration also did not alter APAP covalent binding in liver or APAP hepatotoxicity. Also, the overall metabolism of APAP was not altered by castration, as ther e were no significant differences in the 24-hr excretion of APAP urina ry metabolites between castrated and sham-operated mice. However, cast ration did significantly protect mice against APAP nephrotoxicity, as evidenced by decreases in plasma urea nitrogen levels and in the sever ity of histopathologic damage assessed 12 hr after APAP. Castration al so reduced the level of selective covalent binding of APAP metabolites to renal proteins as detected on Western blots with affinity-purified anti-APAP antibodies. These findings suggest that, for the mouse, int rarenal biotransformation of APAP to a reactive electrophile significa ntly contributes to the APAP covalent binding within the kidney and th e subsequent nephrotoxicity. (C) 1994 Academic Press, Inc.