Article

Influence of nonsynonymous polymorphisms of UGT1A8 and UGT2B7 metabolizing enzymes on the formation of phenolic and acyl glucuronides of mycophenolic acid. Drug Metab Dispos

Laval University, Quebec City, Quebec, Canada
Drug Metabolism and Disposition (Impact Factor: 3.25). 10/2006; 34(9):1539-45. DOI: 10.1124/dmd.106.010553
Source: PubMed

ABSTRACT

Mycophenolic acid (MPA) is the active metabolite of mycophenolate mofetil (MMF), a standard immunosuppressive drug approved for clinical use in the prevention of acute allograft rejection after organ transplantation. This study examines the role of the genetic variants of UDP-glucuronosyltransferase (UGT) 1A8 and 2B7 enzymes involved in the formation of the primary metabolite of MPA, the inactive phenolic glucuronide (MPAG), and the reactive acyl glucuronide (AcMPAG). The first exon of UGT1A8 was first resequenced in the region encoding for the substrate binding domain in 254 Caucasians and 41 African Americans. Eight nonsynonymous changes were observed and led to the following amino acid substitutions: S43L, H53N, S126G, A144V, A173G, A231T, T240A, and C277Y. Thirteen haplotypes were inferred, comprising only two previously described alleles, namely, UGT1A8*2 (A173G) and UGT1A8*3 (C277Y). Upon stable expression in human embryonic kidney 293 cells, the UGT1A8*3 (C277Y), *5 (G173A240), *7 (A231T), *8 (S43L), and *9 (N53G) proteins were associated with the most profound decreases in the formation of MPAG and AcMPAG, indicating that these amino acids are critical for substrate binding and enzyme function. Altogether, the low-activity UGT1A8 enzymes are carried by 2.8 to 4.8% of the population. The variant of the UGT2B7 protein (UGT2B7*2 Y268), the main enzyme involved in the formation of AcMPAG, demonstrated a catalytic efficiency comparable with that of UGT2B7*1 (H268). In conclusion, although the common UGT2B7*2 variant is predicted to have limited impact, several UGT1A8 variants identified may potentially account for the large interindividual variance in MMF pharmacokinetics and deserve further clinical investigations.

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    • "For UGT1A8, the UGT1A8 * 3 allele is associated with a 4.3-fold lower metabolic capacity of the enzyme toward MPA [14]. By contrast, the results are less clear for the UGT1A8 * 2 allele [14, 20]. As for the other UGTs, UGT2B7 is polymorphically expressed, and two frequent SNPs, the 802C[T (defining the UGT2B7 * 2 allele) and the -842G[A promoter SNPs, have been reported. "
    [Show abstract] [Hide abstract] ABSTRACT: Every month, new releases on the relationship between pharmacogenetic biomarkers and immunosuppressive drug therapy in kidney transplantation are published. However, the systematic clinical application of these discoveries occurs at a very slow pace, and the usefulness of knowing a patient's genotype remains an important matter of debate. This can be partially ascribed to the lack of consistency when looking at the different associations reported across several studies but also the need for a broad-spectrum view and a rigorous analysis of the relevance of the different associations observed to date. For that purpose, we performed a comprehensive analysis of the strength of the different reported genetic associations, and in this article we discuss their potential for clinical implementation in kidney transplantation. For tacrolimus, it is likely that a genotype-based drug dosage can benefit patient outcome, while for ciclosporin A, the data appear less convincing. For the mammalian target of rapamycin inhibitors, sirolimus and everolimus - given the lack of data and the absence of large prospective studies - it is premature to implement pharmacogenetics, but some novel and promising leads have recently been reported. For mycophenolate mofetil, the complex metabolic pathways of its active moiety, mycophenolic acid, complicate analysis of the various published associations. However, at present, some interesting findings can be highlighted and offer potential value to assist clinicians in decision making.
    Full-text · Article · Nov 2012 · Molecular Diagnosis & Therapy
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    • "These observations suggest that these three mutations in the UGT1A9 gene may impact the pharmacokinetics of MPA in Asians. UGT2B7, which metabolizes MPA to its toxic metabolite AcMPAG, has also attracted attention[12]. UGT2B7 G211T (A71S) was first reported in a patient who was a poor responder to morphine. "
    [Show abstract] [Hide abstract] ABSTRACT: Purpose: To explore the impact of UDP-glucuronosyltransferase polymorphisms (UGT1A9-118(dT) 9/10 , UGT1A9 CI399T, UGT1A9 C-440T and UGT2B7 G211T) on the pharmacokinetics of mycophenolic acid (MPA) in healthy Chinese volunteers. Methods: We recruited ten healthy volunteers with no polymorphisms (control group), 11 homozygotes of mutants UGT1A9 CI399T and UGT1A9-118(dT) 9/10 , ten heterozygotes of UGT1A9 C440T and seven carriers of UGT2B7 211T from a total of 518 healthy Chinese volunteers. All the volunteers were orally administered a single dose of 1.5 g mycophenolate mofetil (MMF) after an overnight fast. Plasma was then collected 72 h after MMF administration. MPA, MPA-7-O-glucuronide (MPAG) and its acylglucuronide (AcMPAG) were detected by ultra-pressure liquid chromatography with UV detection. Results: Compared with the control group, the UGT1A9 CI399T and UGT1A9-118(dT) 9/10 mutant homozygotes had higher MPAG plasma concentrations. Subjects with UGT1A9-440TC had enhanced MPA exposure while carriers of UGT2B7 211T had higher concentrations of the toxic metabolite, AcMPAG. Conclusions: The current results indicate that UGT1A9 and UGT2B7 genotypes could significantly alter MPA pharmacokinetics in healthy Chinese volunteers after a single oral dose of MMF.
    Full-text · Article · Oct 2012 · European Journal of Clinical Pharmacology
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    • "It has been demonstrated that in renal transplant recipients, carriers of either or both polymorphisms had lower MPA AUC and C 0 (Johnson et al, 2008; Kuypers et al., 2005; van Schaik et al., 2009). On the other hand, UGT1A8*3 (P277C>Y) polymorphism results in an approximately 30-fold reduction in MPAG formation (Bernard et al., 2006). MPA inhibits inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the pathway for purine synthesis.. "
    Full-text · Chapter · Aug 2011
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