Hepatic effects of repeated oral administration of diclofenac to hepatic cytochrome P450 reductase null (HRN™) and wild-type mice

Hepatic NADPH- cytochrome P450oxidoreductase null (HRN™) mice exhibit normal hepatic and extrahepatic biotransformationenzyme activities when compared to wild-type (WT) mice, but express no functional hepatic cytochrome P450activities. When incubated in vitro with [14C]- diclofenac, liver microsomes from WT mice exhibited extensive biotransformationto oxidative and glucuronidemetabolites and covalent binding to proteins was also observed. In contrast, whereas glucuronideconjugates and a quinone-imine metabolite were formed when [14C]- diclofenacwas incubated with HRN™ mouse liver, only small quantities of P450-derived oxidative metabolites were produced in these samples and covalent binding to proteins was not observed. Livers from vehicle-treated HRN™ mice exhibited enhanced lipid accumulation, bile duct proliferation, hepatocellular degeneration and necrosis and inflammatory cell infiltration, which were not present in livers from WT mice. Elevated liver-derived alanine aminotransferase, glutamate dehydrogenaseand alkaline phosphatase activities were also observed in plasma from HRN™ mice. When treated orally with diclofenacfor 7 days, at 30 mg/kg/day, the severities of the abnormal liver histopathology and plasma liver enzyme findings in HRN™ mice were reduced markedly. Oral diclofenacadministration did not alter the liver histopathology or elevate plasma enzyme activities of WT mice. These findings indicate that HRN™ mice are valuable for exploration of the role played by hepatic P450s in drug biotransformation, but poorly suited to investigations of drug-induced liver toxicity. Nevertheless, studies in HRN™ mice could provide novel insights into the role played by inflammation in liver injury and may aid the evaluation of new strategies for its treatment.