Elsevier

Advanced Drug Delivery Reviews

Volume 54, Issue 10, 18 November 2002, Pages 1271-1294
Advanced Drug Delivery Reviews

Genetic contribution to variable human CYP3A-mediated metabolism

https://doi.org/10.1016/S0169-409X(02)00066-2Get rights and content

Abstract

The human CYP3A subfamily plays a dominant role in the metabolic elimination of more drugs than any other biotransformation enzyme. CYP3A enzyme is localized in the liver and small intestine and thus contributes to first-pass and systemic metabolism. CYP3A expression varies as much as 40-fold in liver and small intestine donor tissues. CYP3A-dependent in vivo drug clearance appears to be unimodally distributed which suggests multi-genic or complex gene–environment causes of variability. Interindividual differences in enzyme expression may be due to several factors including: variable homeostatic control mechanisms, disease states that alter homeostasis, up- or down-regulation by environmental stimuli (such as smoking, drug intake, or diet), and genetic mutations. This review summarizes the current understanding and implications of genetic variation in the CYP3A enzymes. Unlike other human P450s (CYP2D6, CYP2C19) there is no evidence of a ‘null’ allele for CYP3A4. More than 30 SNPs (single nucleotide polymorphisms) have been identified in the CYP3A4 gene. Generally, variants in the coding regions of CYP3A4 occur at allele frequencies <5% and appear as heterozygous with the wild-type allele. These coding variants may contribute to but are not likely to be the major cause of inter-individual differences in CYP3A-dependent clearance, because of the low allele frequencies and limited alterations in enzyme expression or catalytic function. The most common variant, CYP3A4*1B, is an A-392G transition in the 5′-flanking region with an allele frequency ranging from 0% (Chinese and Japanese) to 45% (African-Americans). Studies have not linked CYP3A4*1B with alterations in CYP3A substrate metabolism. In contrast, there are several reports about its association with various disease states including prostate cancer, secondary leukemias, and early puberty. Linkage disequilibrium between CYP3A4*1B and another CYP3A allele (CYP3A5*1) may be the true cause of the clinical phenotype. CYP3A5 is polymorphically expressed in adults with readily detectable expression in about 10–20% in Caucasians, 33% in Japanese and 55% in African-Americans. The primary causal mutation for its polymorphic expression (CYP3A5*3) confers low CYP3A5 protein expression as a result of improper mRNA splicing and reduced translation of a functional protein. The CYP3A5*3 allele frequency varies from approximately 50% in African-Americans to 90% in Caucasians. Functionally, microsomes from a CYP3A5*3/*3 liver contain very low CYP3A5 protein and display on average reduced catalytic activity towards midazolam. Additional intronic or exonic mutations (CYP3A5*5, *6, and *7) may alter splicing and result in premature stop codons or exon deletion. Several CYP3A5 coding variants have been described, but occur at relatively low allelic frequencies and their functional significance has not been established. As CYP3A5 is the primary extrahepatic CYP3A isoform, its polymorphic expression may be implicated in disease risk and the metabolism of endogenous steroids or xenobiotics in these tissues (e.g., lung, kidney, prostate, breast, leukocytes). CYP3A7 is considered to be the major fetal liver CYP3A enzyme. Although hepatic CYP3A7 expression appears to be significantly down-regulated after birth, protein and mRNA have been detected in adults. Recently, increased CYP3A7 mRNA expression has been associated with the replacement of a 60-bp segment of the CYP3A7 promoter with a homologous segment in the CYP3A4 promoter (CYP3A7*1C allele). This mutational swap confers increased gene transcription due to an enhanced interaction between activated PXR:RXRα complex and its cognate response element (ER-6). The genetic basis for polymorphic expression of CYP3A5 and CYP3A7 has now been established. Moreover, the substrate specificity and product regioselectivity of these isoforms can differ from that of CYP3A4, such that the impact of CYP3A5 and CYP3A7 polymorphic expression on drug disposition will be drug dependent. In addition to genetic variation, other factors that may also affect CYP3A expression include: tissue-specific splicing (as reported for prostate CYP3A5), variable control of gene transcription by endogenous molecules (circulating hormones) and exogenous molecules (diet or environment), and genetic variations in proteins that may regulate constitutive and inducible CYP3A expression (nuclear hormone receptors). Thus, the complex regulatory pathways, environmentally susceptible milieu of the CYP3A enzymes, and as yet undetermined genetic haplotypes, may confound evaluation of the effect of individual CYP3A genetic variations on drug disposition, efficacy and safety.

Section snippets

Multiplicity of CYP3A enzymes

The human CYP3A subfamily, CYP3A4, CYP3A5, CYP3A7 and CYP3A43, is one of the most versatile of the biotransformation systems that facilitate the elimination of drugs, other xenobiotic compounds, and endogenous molecules from the body. Although there has been no systematic analysis of the extent of its contribution, it is generally accepted that CYP3A enzymes play a dominant role in the metabolic elimination of more drugs than any other biotransformation enzyme. CYP3A metabolic versatility may

CYP3A4 genetic variation

Unlike other human P450s (e.g., CYP2D6, CYP2C19), there is no evidence of a ‘null’ allele for CYP3A4. Genetic variation found in the flanking, intronic and exonic regions of the gene may influence the level or function of CYP3A4 protein, but full length mRNA has been detected in all adults studied to date.

CYP3A5 genetic variation

The CYP3A5 cDNA sequence was first described independently by Aoyama et al. [23] and Schuetz et al. [85]. The allele corresponding to this cDNA and the respective expressed protein was designated wild-type, CYP3A5*1A. Subsequent work described 5′-flanking sequence of two distinctly different genomic clones from a human liver containing CYP3A5 protein [86]. The clones contained identical sequences for exon 1 but differed slightly in the 5′-flanking sequence. The flanking sequence corresponding

Mutations in CYP3A7 5′-flanking, coding and intronic domains

The identification of SNPs in the CYP3A7 gene has lagged somewhat behind research on CYP3A4 and CYP3A5. Compared to the wild-type sequence (CYP3A7*1A [106]), Kuehl et al. [17] identified four unique mutations in the CYP3A7 5′-flanking region. Three of the mutations represent SNPs (CYP3A7*1B, *1D and *1E) and occurred in regions outside of those associated with the regulation of CYP3A transcription. The fourth mutation (CYP3A7*1C) consists of the replacement of 60 bp from the CYP3A4 gene with

CYP3A43 splicing variation

One of the most interesting aspects of the CYP3A43 research to emerge is the apparent propensity for alternative splicing events. Sequence analysis of different cDNA isolated from human liver indicated exon skipping and complete or partial intron exclusion [11]. Subsequent work from the same research group demonstrated the formation of CYP3A43–CYP3A4 mRNA hybrids [110]. Some of these CYP3A43 hybrids (exon 1 of CYP3A43 joined to exons 2–13 of CYP3A4) retained catalytic activity, although the

Summary

Numerous different mutations in the CYP3A genes have been identified. The most significant of these mutations are found in CYP3A5 and CYP3A7. For CYP3A5, a SNP within intron-3 (CYP3A5*3) results in aberrant mRNA splicing and a pronounced reduction in protein synthesis. Depending on ethnicity, the wild-type CYP3A5*1 allele frequency varies between 5 and 45%. Livers and small intestines that have at least one CYP3A5*1 allele exhibit, on average, increased metabolic clearance of midazolam,

Acknowledgements

This work was supported in part by grants from the National Institutes of Health (GM07750, GM63666, ES07033, GM32165, GM60346, GM61393, ES08658, P30 CA21765 and CA51001); and by the American Lebanese Syrian Associated Charities.

References (114)

  • M.W. Voice et al.

    Effects of human cytochrome b5 on CYP3A4 activity and stability in vivo

    Arch. Biochem. Biophys.

    (1999)
  • Y. Li et al.

    Perinatal expression and inducibility of human CYP3A7 in C57BL/6N transgenic mice

    Biochem. Biophys. Res. Commun.

    (1996)
  • M. Kitada et al.

    P-450 HFLa, a form of cytochrome P-450 purified from human fetal livers, is the 16α-hydroxylase of dehydroepiandrosterone 3-sulfate

    J. Biol. Chem.

    (1987)
  • F.P. Guengerich et al.

    Characterization of rat and human liver microsomal cytochrome P450 forms involved in nifedipine oxidation, a prototype for genetic polymorphism in oxidative drug metabolism

    J. Biol. Chem.

    (1986)
  • J.H.M. Schellens et al.

    Lack of bimodality in nifedipine kinetics in a large population of healthy subjects

    Biochem. Pharmacol.

    (1988)
  • R.E. Gammans et al.

    Metabolism and disposition of buspirone

    Am. J. Med.

    (1986)
  • H. Hamzeiy et al.

    Mutation analysis of the human CYP3A4 gene 5′ regulatory region: population screening using non-radioactive SSCP

    Mutat. Res.

    (2002)
  • A. Westlind et al.

    Interindividual differences in hepatic expression of CYP3A4: relationship to genetic polymorphism in the 5′-upstream regulatory region

    Biochem. Biophys. Res. Commun.

    (1999)
  • J. Lai et al.

    CYP gene polymorphisms and early menarche

    Mol. Genet. Metab.

    (2001)
  • J.D. Schuetz et al.

    Characterization of a cDNA encoding a new member of the glucocorticoid-responsive cytochromes P450 in human liver

    Arch. Biochem. Biophys.

    (1989)
  • Y. Jounaidi et al.

    Sequence of the 5′-flanking region of CYP3A5: comparative analysis with CYP3A4 and CYP3A7

    Biochem. Biophys. Res. Commun.

    (1994)
  • C. Finta et al.

    The human cytochrome P450 3A locus. Gene evolution by capture of downstream exons

    Gene

    (2000)
  • E.G. Schuetz et al.

    Expression of cytochrome P450 3A in amphibian, rat, and human kidney

    Arch. Biochem. Biophys.

    (1992)
  • Y. Yamakoshi et al.

    Human prostate CYP3A5: identification of a unique 5′-untranslated sequence and characterization of purified recombinant protein

    Biochem. Biophys. Res. Commun.

    (1999)
  • F.P. Guengerich

    Cytochrome P-450 3A4: regulation and role in drug metabolism

    Annu. Rev. Pharmacol. Toxicol.

    (1999)
  • K.R. Korzekwa et al.

    Evaluation of atypical cytochrome P450 kinetics with two-substrate-models: evidence that multiple substrates can simultaneously bind to cytochrome P450 active sites

    Biochemistry

    (1998)
  • K.E. Thummel et al.

    In vitro and in vivo drug interactions involving human CYP3A

    Annu. Rev. Pharmacol. Toxicol.

    (1998)
  • S.A. Wrighton et al.

    Studies on the expression and metabolic capabilities of human liver cytochrome P450IIIA5 (HLp3)

    Mol. Pharmacol.

    (1990)
  • M.F. Paine et al.

    Characterization of inter- and intra-intestinal differences in human CYP3A-dependent metabolism

    J. Pharmacol. Exp. Ther.

    (1997)
  • J. Hakkola et al.

    Cytochrome P450 3A expression in the human fetal liver: evidence that CYP3A5 is expressed in only a limited number of fetal livers

    Biol. Neonate

    (2001)
  • S.N. de Wildt et al.

    Cytochrome P450 3A: ontogeny and drug disposition

    Clin. Pharmacokinet.

    (1999)
  • T.L. Domanski et al.

    cDNA cloning and initial characterization of CYP3A43, a novel human cytochrome P450

    Mol. Pharmacol.

    (2001)
  • I. DeWaziers et al.

    Cytochrome P450 isoenzymes, epoxide hydrolase and glutathione transferases in rat and human hepatic and extrahepatic tissues

    J. Pharmacol. Exp. Ther.

    (1990)
  • T. Shimada et al.

    Interindividual variations in human liver cytochrome P450 enzymes involved in the oxidation of drugs, carcinogens and toxic chemicals: Studies with liver microsomes of 30 Japanese and 30 Caucasians

    J. Pharmacol. Exp. Ther.

    (1994)
  • V. Ozdemir et al.

    Evaluation of the genetic component of variability in CYP3A4 activity: a repeated drug administration method

    Pharmacogenetics

    (2000)
  • P. Kuehl et al.

    Sequence diversity in CYP3A promoters and characterization of the genetic basis of polymorphic CYP3A5 expression

    Nat. Genet.

    (2001)
  • E. Hustert et al.

    The genetic determinants of the CYP3A5 polymorphism

    Pharmacogenetics

    (2001)
  • Y. Lin et al.

    Co-regulation of CYP3A5 and CYP3A5 and contribution to hepatic and intestinal midazolam metabolism

    Mol. Pharmacol.

    (2002)
  • J.C. Gorski et al.

    Regioselective biotransformation of midazolam by members of the human cytochrome P450 3A (CYP3A) subfamily

    Biochem. Pharmacol.

    (1994)
  • M.J. Bargetzi et al.

    Lidocaine metabolism in human liver microsomes by cytochrome P450IIIA4

    Clin. Pharmacol. Ther.

    (1989)
  • J. Williams

    Comparative metabolic capabilities of CYP3A4, CYP3A5, and CYP3A7

    Drug Metab. Dispos.

    (2002)
  • H. Yamazaki et al.

    Roles of divalent metal ions in oxidations catalyzed by recombinant cytochrome P450 3A4 and replacement of NADPH-cytochrome P450 reductase with other flavoproteins, ferredoxin, and oxygen surrogates

    Biochemistry

    (1995)
  • N. Hirota et al.

    In vitro/in vivo scaling of alprazolam metabolism by CYP3A4 and CYP3A5 in humans

    Biopharm. Drug Dispos.

    (2001)
  • J.D. Schuetz et al.

    Selective expression of cytochrome P450 CYP3A mRNAs in embryonic and adult human liver

    Pharmacogenetics

    (1994)
  • H.-Y. Yang et al.

    Functional cytochrome P4503A isoforms in human embryonic tissues: expression during organogenesis

    Mol. Pharmacol.

    (1994)
  • K. Kitada et al.

    Four forms of cytochrome P-450 in human fetal livers: purification and their capacity to activate promutagens

    Jpn. J. Cancer Res.

    (1991)
  • L. Speroff

    The endocrinology of pregnancy

  • J. Marill et al.

    Identification of human cytochrome P450s involved in the formation of all-trans-retinoic acid principal metabolites

    Mol. Pharmacol.

    (2000)
  • P.B. Watkins

    Noninvasive tests of CYP3A enzymes

    Pharmacogenetics

    (1994)
  • K.S. Lown et al.

    The erythromycin breath test predicts the clearance of midazolam

    Clin. Pharmacol. Ther.

    (1995)
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