Relationship of polymorphism in CYP2C9 to genetic susceptibility to diclofenac-induced hepatitis

The mechanism by which diclofenac-induced hepatotoxicity occurs is unclear, even though covalent modification of proteins by diclofenac metabolites ap pears to be important in pathogenesis, either by altering protein function or by eliciting an immune response. Adduct formation may be due to metaboli sm of diclofenac via an alternative pathway rather than via its major 4'-hy droxylation pathway mediated by the cytochrome P450 CYP2C9. We hypothesized that possession of variant CYP2C9 alleles might be a risk factor for diclo fenac-induced hepatotoxicity, since the allelic variants CYP2C9*2 and CYP2C 9*3 may be associated with impaired metabolism compared to the wild-type (C YP2C9*1). To investigate in more detail the effects of the polymorphisms on diclofenac metabolism in human liver, the kinetics of diclofenac cl-hydrox ylation by human liver microsomes of known CYP2C9 >genotype were examined, An overall difference in V-max and Vmax/Km between samples homozygous for C YP2C9*1 and heterozygous for CYP2C9*2 or CYP2C9*3 was detected (P = 0.044). However, on subgroup analysis, there was no significant difference between samples homozygous for CYP2C9*1 and heterozygous for CYP2C9*2, although th ere was a borderline difference between the samples homozygous for CYP2C9*1 and those heterozygous for CYP2C9*3 (P = 0.057). The relationship between CYP2C9 genotype and susceptibility to diclofenac-induced hepatotoxicity was further examined by genotyping 24 patients with diclofenac-induced hepatot oxicity together with 100 healthy controls for the CYP2C9*2 and CYP2C9*3 al leles, CYP2C9 genotype frequencies for CYP2C9*2 and CYP2C9*3 were similar i n patients and controls. To assess whether diclofenac-induced hepatotoxicit y was due to rare CYP2C9 mutations, the upstream sequence (-1 to -1000) and all exons and exon-intron boundaries of CYP2C9 from four subjects who had suffered severe hepatotoxicity was determined. However, no ne rv polymorphi sms were detected. We therefore found no evidence that polymorphism in CYP2 C9 is a determinant of diclofenac-induced hepatotoxicity, Pharmacogenetics 10:511-518 (C) 2000 Lippincott Williams & Wilkins.