Etudes des relations génotype-phénotype des enzymes du métabolisme et des transporteurs d'efflux des xénobiotiques

Dans l organisme, la détoxification des xénobiotiques (médicaments, carcinogènes, ) fait intervenir des enzymes de métabolisme de phase I et II ainsi que des transporteurs d efflux. Nos travaux ont porté sur plusieurs aspects des relations génotype-phénotype de ces enzymes et transporteurs. Nous avons montré que le polymorphisme fonctionnel du cytochrome P450 (CYP) 3A5 (enzyme de phase I), CYP3A5*3 n avait pas d effet sur le métabolisme d un immunosuppresseur, l évérolimus, in vitro et chez 30 patients transplantés rénaux. L étude de l implication des UDP-glucuronosyltransférases (UGT ; enzymes de phase II) dans le métabolisme de la buprénorphine (traitement substitutif aux opiacés) a montré que les isoformes impliquées étaient les UGT 1A1, 1A3 et 2B7. Nous avons également montré in vitro que chez les porteurs du génotype UGT1A1*1/*1, la présence d au moins un allèle muté du polymorphisme UGT2B7 G- 842A était associée à une activité élevée de glucuroconjugaison de la buprénorphine. Nous avons développé une méthode cocktail pour évaluer l activité de cinq UGTs hépatiques (1A1, 1A4, 1A6, 1A9 et 2B7) in vitro. Cette approche repose sur la mesure simultanée de l activité enzymatique de plusieurs enzymes après incubation d un mélange de substrats sélectifs en présence de microsomes hépatiques humains. Cette méthode a été utilisée pour évaluer l effet inhibiteur de la buprénorphine sur l activité de ces cinq UGT. Enfin, une étude rétrospective de l association entre les polymorphismes génétiques des UGT 1A6, 1A7, 1A8, 1A9 et 2B7 et de transporteurs d efflux (MDR1 et MRP2) et la survenue du cancer colorectal (CCR) a été réalisée en comparant des cas (atteints de cancer colorectal) à deux groupes de témoins (malades atteints de cancer rénal ou volontaires sains). Trois polymorphismes du gène ABCB1/MDR1 (C1236T, G2677T et C3435T) ainsi que son haplotype triplement muté sont significativement liés à une plus faible incidence du CCR. Nous retrouvons également, pour la première fois, une association entre ce cancer et certains haplotypes du gène ABCC2/MRP2. Ces travaux apportent des connaissances, d une part sur l impact de polymorphismes génétiques sur le métabolisme de médicaments et d autre part sur leur implication potentielle dans le développement du CCR.LIMOGES-BU Médecine pharmacie (870852108) / SudocSudocFranceF

CYP3A5 genotype does not influence everolimus in vitro metabolism and clinical pharmacokinetics in renal transplant recipients.

International audienceBACKGROUND: CYP3A5 genotyping might be useful to guide tacrolimus and sirolimus dosing. The aim of this study was to assess the influence of CYP3A5 polymorphism on everolimus metabolism and pharmacokinetics. METHODS: We investigated the effect of CYP3A5 6986A>G polymorphism (CYP3A5*1/*3 alleles) on the pharmacokinetics of everolimus in 28 renal transplant patients and on its in vitro hepatic metabolism using a bank of genotyped human liver microsomes (n=49). We further evaluated in vitro the contribution of CYP3A4, CYP3A5, and CYP2C8 to everolimus hepatic metabolism using recombinant enzymes. RESULTS: We found no association between CYP3A5 polymorphism and everolimus pharmacokinetics in renal transplant patients. On the other hand, no effect of CYP3A5 polymorphism was observed on the intrinsic clearance of everolimus by human liver microsomes, whereas that of tacrolimus (positive control) was 1.5-fold higher in microsomes carrying the CYP3A5*1 allele than in noncarriers. In vitro data showed that CYP3A4 is a better catalyst of everolimus metabolism than CYP3A5, whereas the opposite was observed for tacrolimus. CONCLUSIONS: This study provides direct and indirect evidence that CYP3A5 genotyping cannot help improve everolimus therapy

Simultaneous evaluation of six human glucuronidation activities in liver microsomes using liquid chromatography-tandem mass spectrometry.: Simultaneous evaluation of glucuronidation activities

International audienceThis article describes the development of a procedure for the simultaneous evaluation of the activity of six different uridine diphosphate (UDP)-glucuronyltransferases (UGTs) in human liver microsomes (HLMs). The method consists of incubations of probe substrates for UGT1A1 (etoposide), UGT1A3 (chenodeoxycholic acid), UGT1A4 (trifluoperazine), UGT1A6 (serotonin), UGT1A9 (mefenamic acid), and UGT2B7 (azidothymidine) with HLMs. The six substrates were divided into three different incubations (etoposide + mefenamic acid; chenodeoxycholic acid + serotonin + azidothymidine; and trifluoperazine alone), the media of which were pooled before analysis. Glucuronide formation rates were determined in a single run of 20 min using a validated liquid chromatography-tandem mass spectrometry method. No significant difference was observed between glucuronidation activities measured using the current procedure and individual incubations of the probes. The method was used successfully for the determination of UGT activities in 44 individual HLM preparations and for the phenotyping of preparations predicted to have altered UGT1A1 and UGT2B7 activities because of known genetic polymorphisms

Common variants in glucuronidation enzymes and membrane transporters as potential risk factors for colorectal cancer: a case control study

Abstract Background Associations between polymorphisms of UDP-glucuronosyltransferases (UGTs) or efflux transporters (e.g., P-glycoprotein and MRP2) and different types of cancer have been described, whereas the role of influx transporters (e.g. OATP1B1 and OATP2B1) has been seldom explored. The GenColon study investigated potential associations between variant alleles of UGTs, efflux and influx transporters and CRC. Methods Three hundred CRC cases were matched with 300 controls for age, sex and enrolment site. Fifteen SNPs in UGT1A6–9, UGT2B7, ABCB1, ABCC2, SLCO1B1 and SLCO2B1 genes were characterized using Taqman® PCR. Using multivariate conditional logistic regression, we investigated the relationships between CRC and “environmental” risk factors (physical activity, housing and working areas, consumption of red meat, tobacco, alcohol); genetic polymorphisms, in the study population and in the subgroups with “environmental” risk factors. Results No significant association was observed for the analyzed SNPs (or haplotypes). However, an increased CRC risk was found in carriers of the UGT1A8 rs1042597-G variant allele (additive risk OR = 3.39[1.29–8.89], p = 0.02951) in the subgroup of meat-consumers (n = 84), and in carriers of the ABCB1 rs1045642-T (exon26) variant allele (additive risk; OR = 1.89[1.10–3.39], p = 0.0257) in the “never alcohol consumption subgroup” (n = 125). In addition, as previously reported, the following CRC risk factors were identified: absence of physical activity (OR = 6.35[3.70–10.9], p 30 years (3.37[1.63–6.96], p = 0.0010). Conclusions Variant genotypes of influx transporters (OATP1B1 and 2B1) were not associated with CRC. This study confirmed the influence of lifestyle factors, but not the previously reported detrimental effect of SNPs in intestinal UGTs or efflux transporters, except for a UGT1A8 variant in subjects consuming meat and the exon 26 SNP of ABCB1 in the never alcohol consumption subgroup. Trial registration Registered in Direction Générale de la Santé the 1st July 2008 under the number DGS2008–0144

Additional file 1: Table S1. of Common variants in glucuronidation enzymes and membrane transporters as potential risk factors for colorectal cancer: a case control study

SNPs studied and their frequencies in our population. This table contains the description and frequencies of the SNP investigated in the study for ABCB1, UGT, MRP2, SLCO1B1 and SLCO1B2 genes. (DOCX 22 kb