Relationship between CYP2C8 genotypes and diclofenac 5-hydroxylation in healthy Spanish volunteers

CYP2C8 seems to be involved in diclofenac 5-hydroxylation, while, in vitro, the 4'-hydroxylation and 3'-hydroxylation seem to be mediated mainly by CYP2C9. We have demonstrated the relevance of CYP2C9 genotypes for diclofenac 4'-hydroxylation in healthy volunteers, so that the present study was aimed at analyzing the role of both CYP2C8 and CYP2C9 genotypes on diclofenac metabolism, as well as determining the CYP2C8 allele frequencies and their relationship with CYP2C9 variants.

A group of 142 healthy white Spanish volunteers was studied. Previously, 102 of these subjects had been phenotyped with diclofenac and genotyped for CYP2C9. The CYP2C8 genotypes were determined by allele-specific PCR-RFLP methods. The urinary concentrations of diclofenac and its main metabolites were analysed using an HPLC-UV method after the administration of a single oral dose of diclofenac as described previously for part of the population studied here.

The diclofenac/5-hydroxydiclofenac urinary concentration ratio was higher in individuals carrying a CYP2C8*3 or CYP2C8*4 allele than in those homozygous for wild-type allele CYP2C8*1 (P < 0.05). Moreover, approximately 93% of the subjects with a CYP2C8*3 allele also carried a CYP2C9*2, and 80% of the subjects that had CYP2C9*2 variant also carried a CYP2C8*3. In addition, the four CYP2C9*2/*2 individuals were CYP2C8*3/*3.

This is the first study showing the influence of CYP2C8 genotypes on diclofenac metabolism in vivo. The linkage disequilibrium between CYP2C8*3 and CYP2C9*2 alleles was confirmed in this Spanish population.