Comparative Analysis of Cyp3a Expression in Human Liver Suggests Only a Minor Role for Cyp3a5 in Drug Metabolism

Abstract

This article is available online at http://dmd.aspetjournals.org ABSTRACT:To study mechanisms behind the interindividual variability in CYP3A expression and the relative contribution of the different CYP3A enzymes to the overall CYP3A activity, we have analyzed CYP3A4, CYP3A5, CYP3A43, and PXR mRNA and CYP3A4 and CYP3A5 protein expression, catalytic activity, and polymorphism in the CYP3A5 gene in a panel of 46 Caucasian human livers. Protein quantification was performed by Western blotting using enzymespecific antibodies directed to the C termini of CYP3A4 or CYP3A5, and carrier protein-coupled peptides as standards. The mRNA levels were determined by quantitative real-time PCR. CYP3A activity was measured by analysis of the rate of testosterone 6␤-hydroxylation. A correlation existed between all CYP3A and PXR mRNA transcripts measured. The interindividual variability in CYP3A4 and CYP3A5 mRNA expression was higher than that of CYP3A protein and activity. The CYP3A5 protein was expressed at quantifiable levels in 5 (10.9%) of the livers. Four of those were heterozygous for the CYP3A5*1 allele and had CYP3A5 protein at a mean level of 17% of that of total CYP3A, whereas one liver sample was from a CYP3A5*3 homozygote individual having lower amounts of CYP3A5. In total, CYP3A5 only contributed 2% of the overall CYP3A protein among all samples. In conclusion, our data indicate that CYP3A4, CYP3A5, CYP3A43, and PXR hepatic mRNA expression correlate, indicating common regulatory features, and that the contribution of CYP3A5 to hepatic drug metabolism in Caucasians is insignificant.Interindividual variation in the activity and levels of expression of CYP3A is considerable. This variation is manifested by differences greater than 10-fold in the in vivo metabolism of drugs that are substrates for CYP3As (Kleinbloesem et al

CYP3A5 genotype did not impact on nifedipine disposition in healthy volunteers

“…20 Recently, Westlind-Johnsson et al 21 reported that CYP3A5 did not contribute to total CYP3A activity using CYP3A5 polymorphism and nifedipne pharmacokinetics 22 Although these data seem to support the present findings in vivo, the same was not consistent in the case of midazolam. Based on all these observations, we speculated that the amount of CYP3A5 protein in the liver is much lower than CYP3A4, although we should consider the limitations of our study design.…”

“…25 Interestingly, we have found that mRNA expression of wild-type hPXR is well correlated with mRNA expression of CYP3A4 in liver sample (unpublished data), which is consistent with the recent report. 21 In summary, we revealed that nifedipine disposition in vivo is not affected by the CYP3A5*3 allele. Owing to a discrepancy between the in vitro and in vivo contribution of CYP3A5, the functional relevance of CYP3A5 in humans should be re-evaluated by clinical studies for each drug.…”

Distinction between Human Cytochrome P450 (CYP) Isoforms and Identification of New Phosphorylation Sites by Mass Spectrometry

“…For example, recent data on the relative expression levels of CYP3A4 and CYP3A5 have remained controversial. [11][12][13] Similar problems persist for other larger subfamilies including CYP2C and CYP4F.…”

Warfarin sensitivity related to CYP2C9, CYP3A5, ABCB1 (MDR1) and other factors

“…CYP3A5 is considered to be 17-50% of the total CYP3A content in the livers of people that express it. 25,26 There is considerable intra-and interindividual variation in CYP3A4 enzyme activity, and even though numerous polymorphisms have been found, the molecular basis of this is not yet understood. On the other hand, CYP3A5 exists in distinct fast and slow variants, 25 and is therefore worth studying even if it is less abundant than CYP3A4.…”