Cytochrome P450 (CYP) 2C8 is the principal enzyme responsible for the metabolism of the anti-cancer drug paclitaxel (Taxol). It is also the predominant P450 responsible for the metabolism of arachidonic acid to biologically active epoxyeicosatrienoic acids (EETs) in human liver and kidney. In this study, we describe two new CYP2C8 alleles containing coding changes: CYP2C8*2 has an Ile269Phe substitution in exon 5 and CYP2C8*3 includes both Arg139Lys and Lys399Arg amino acid substitutions in exons 3 and 8. CYP2C8*2 was found only in African-Americans, while CYP2C8*3 occurred primarily in Caucasians. Neither occurred in Asians. The frequency of the CYP2C8*2 allele was 0.18 in African-Americans, and that of CYP2C8*3 was 0.13 in Caucasians. CYP2C8*1 (wild-type), CYP2C8*2 and CYP2C8*3 cDNAs were expressed in Escherichia coli, and the ability of these enzymes to metabolize both paclitaxel and arachidonic acid was assessed. Recombinant CYP2C8*3 was defective in the metabolism of both substrates. The turnover number of CYP2C8*3 for paclitaxel was 15% of CYP2C8*1. CYP2C8*2 had a two-fold higher Km and two-fold lower intrinsic clearance for paclitaxel than CYP2C8*1. CYP2C8*3 was also markedly defective in the metabolism of arachidonic acid to 11,12- and 14,15-EET (turnover numbers 35-40% that of CYP2C8*1). Thus, CYP2C8*3 is defective in the metabolism of two important CYP2C8 substrates: the anticancer drug paclitaxel and the physiologically important compound arachidonic acid. This polymorphism has important clinical and physiological implications in individuals homozygous for this allele.

CYP2J2 and CYP2C8 metabolize arachidonic acid (AA) to cis-epoxyeicosatrienoic acids (EETs), which play a central role in regulating renal tubular fluid-electrolyte transport and vascular tone. We hypothesized that functionally relevant polymorphisms in the CYP2J2 or CYP2C8 genes influence hypertension risk. We examined associations between CYP2J2*7 (G-50 T promoter) and CYP2C8*3 (Arg139Lys and Lys399Arg, which are in 100% linkage disequilibrium) polymorphisms and hypertension in a biethnic population from Tennessee. CYP2J2*7 variant allele frequency was significantly higher in African-Americans versus Caucasians (14.1% versus 7.7%, P=0.01), irrespective of hypertension status. When analysed separately by race, the genotype distribution of the CYP2J2*7 variant allele was not significantly different among African-Americans with/without hypertension, but was significantly different among Caucasians with/without hypertension (P=0.03). Indeed, the odds ratio of having hypertension attributable to carrying the CYP2J2*7 variant allele adjusted for age, gender, body mass index and family history was 0.39 (95% confidence interval 0.17-0.89) among Caucasians, suggesting a protective effect. Additional subgroup analyses revealed a significantly lower CYP2J2*7 variant allele frequency in hypertensive versus normotensive Caucasian males (5.6% versus 12.5%, P=0.02) and in hypertensive versus normotensive Caucasians without a family history of hypertension (1.5% versus 11.0%, P=0.03). With respect to the CYP2C8*3 variant, genotype distribution and allele frequencies were similar between normotensive and hypertensive subjects. This study provides evidence for an association between CYP2J2*7 genotype and hypertension in Caucasian males and Caucasians without a family history of hypertension, but suggests no association between CYP2C8*3 genotype and hypertension. Confirmation of these findings in additional populations is warranted.

A full-length cDNA clone encoding a novel form of the cytochrome P450 3A subfamily (Cyp3a-25) has been isolated from a mouse liver cDNA library. The sequence contained 2010 base pairs and encoded a protein with 503 amino acids. The amino acid sequence shared greater identities with rat CYP3A18 (90%) and golden hamster CYP3A10 (81%) sequences than with known mouse sequences (Cyp3a-11, Cyp3a-13, Cyp3a-16, and Cyp3a-41 [68--70%]). CYP3A25 was expressed in the Escherichia coli PCWori(+) expression vector following slight modifications of the N- and C-terminals of the cDNA. The purified CYP3A25 was recognized on an immunoblot by CYP3A1 antibody and has a molecular weight of 50 kD. CYP3A25 was catalytically active in the 6 beta-hydroxylation of testosterone and the N-demethylation of benzphetamine and erythromycin. It was demonstrated by RT-PCR that the CYP3A25 mRNA is present in both fetal and adult tissues, including liver, lung, intestines, kidney, and brain. Northern blotting demonstrated that expression is greatest in the liver and small intestine.