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Influence of ABCB1 polymorphisms and haplotypes on tacrolimus nephrotoxicity and dosage requirements in children with liver transplant.

ABSTRACT: AIMS: The aim of this study was to investigate the influence of genetic polymorphisms in ABCB1 on the incidence of nephrotoxicity and tacrolimus dosage-requirements in paediatric patients following liver transplantation. METHODS: Fifty-one paediatric liver transplant recipients receiving tacrolimus were genotyped for ABCB1 C1236>T, G2677>T and C3435>T polymorphisms. Dose-adjusted tacrolimus trough concentrations and estimated glomerular filtration rates (EGFR) indicative of renal toxicity were determined and correlated with the corresponding genotypes. RESULTS: The present study revealed a higher incidence of the ABCB1 variant-alleles examined among patients with renal dysfunction (> or =30% reduction in EGFR) at 6 months post-transplantation (1236T allele: 63.3% vs 37.5% in controls, P= 0.019; 2677T allele: 63.3% vs. 35.9%, p = 0.012; 3435T allele: 60% vs. 39.1%, P= 0.057). Carriers of the G2677->T variant allele also had a significant reduction (%) in EGFR at 12 months post-transplant (mean difference = 22.6%; P= 0.031). Haplotype analysis showed a significant association between T-T-T haplotypes and an increased incidence of nephrotoxicity at 6 months post-transplantation (haplotype-frequency = 52.9% in nephrotoxic patients vs 29.4% in controls; P= 0.029). Furthermore, G2677->T and C3435->T polymorphisms and T-T-T haplotypes were significantly correlated with higher tacrolimus dose-adjusted pre-dose concentrations at various time points examined long after drug initiation. CONCLUSIONS: These findings suggest that ABCB1 polymorphisms in the native intestine significantly influence tacrolimus dosage-requirement in the stable phase after transplantation. In addition, ABCB1 polymorphisms in paediatric liver transplant recipients may predispose them to nephrotoxicity over the first year post-transplantation. Genotyping future transplant recipients for ABCB1 polymorphisms, therefore, could have the potential to individualize better tacrolimus immunosuppressive therapy and enhance drug safety.

SUBMITTER: Hawwa AF

PROVIDER: S-EPMC2766481 | biostudies-literature | 2009 Sep

REPOSITORIES: biostudies-literature

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Influence of ABCB1 polymorphisms and haplotypes on tacrolimus nephrotoxicity and dosage requirements in children with liver transplant.

Hawwa Ahmed F AF McKiernan Patrick J PJ Shields Michael M Millership Jeff S JS Collier Paul S PS McElnay James C JC

British journal of clinical pharmacology 20090901 3

<h4>Aims</h4>The aim of this study was to investigate the influence of genetic polymorphisms in ABCB1 on the incidence of nephrotoxicity and tacrolimus dosage-requirements in paediatric patients following liver transplantation.<h4>Methods</h4>Fifty-one paediatric liver transplant recipients receiving tacrolimus were genotyped for ABCB1 C1236>T, G2677>T and C3435>T polymorphisms. Dose-adjusted tacrolimus trough concentrations and estimated glomerular filtration rates (EGFR) indicative of renal to ...[more]

PMID: 19740399

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Project description:BACKGROUND:Tacrolimus is the first-line immunosuppressant after organ transplantation. It is mainly metabolized by cytochrome P450, family 3, subfamily A (CYP3A) enzymes, but there are large individual differences in metabolism. Interleukin 6 (IL6) has been shown to cause a pan-suppression of mRNA levels of ten major CYP enzymes in human hepatocyte cultures. IL6 has been shown to provide hepatoprotection in various models of liver injury. Rs1800796 is a locus in the IL6 gene promoter region which regulates cytokine production. We speculated that IL6 rs1800796 polymorphisms may lead to individual differences in tacrolimus metabolism by affecting CYP3A enzymes levels and liver function after liver transplantation. METHODOLOGY/PRINCIPAL FINDINGS:Ninety-six liver transplant patients receiving tacrolimus were enrolled in the study. Two single nucleotide polymorphisms (SNP), CYP3A5 rs776746 and IL6 rs1800796, were genotyped in both donors and recipients. The effects of SNPs on tacrolimus concentration/dose (C/D ratio) at four weeks after transplantation were studied, as well as the effects of donor IL6 rs1800796 polymorphisms on liver function. Both donor and recipient CYP3A5 rs776746 allele A showed association with lower C/D ratios, while donor IL6 rs1800796 allele G showed an association with higher C/D ratios. Donor CYP3A5 rs776746 allele A, IL6 rs1800796 allele C, and recipient CYP3A5 rs776746 allele A were associated with fast tacrolimus metabolism. With increasing numbers of these alleles, patients were found to have increasingly lower tacrolimus C/D ratios at time points after transplantation. Donor IL6 rs1800796 allele G carriers showed an association with higher glutamic-pyruvic transaminase (GPT) levels. CONCLUSIONS:Combined analysis of donor CYP3A5 rs776746, IL6 rs1800796, and recipient CYP3A5 rs776746 polymorphisms may distinguish tacrolimus metabolism better than CYP3A5 rs776746 alone. IL6 may lead to individual differences in tacrolimus metabolism mainly by affecting liver function.

Project description:INTRODUCTION:The human multidrug resistance gene ATP-binding cassette B1 (ABCB1) codes for P-glycoprotein (P-gp), an important membrane-bound efflux transporter known to confer anticancer drug resistance as well as affect the pharmacokinetics of many drugs and xenobiotics. A number of single nucleotide polymorphisms (SNPs) have been identified throughout the ABCB1 gene that may have an effect on P-gp expression levels and function. Haplotype as well as genotype analysis of SNPs is becoming increasingly important in identifying genetic variants underlying susceptibility to human disease. Three SNPs, 1236C-->T, 2677G-->T and 3435C-->T, have been repeatedly shown to predict changes in the function of P-gp. The frequencies with which these polymorphisms exist in a population have also been shown to be ethnically related. METHODS:In this study, 95 individuals representative of the entire ethnic make-up of the USA were compared with 101 individuals from an Ashkenazi-Jewish population. These individuals were analyzed by genomic sequencing and polymerase chain reaction, using restriction fragment length polymorphisms, to calculate their genotype frequencies. RESULTS:A total of 25 SNPs were located in the exons of the ABCB1 gene. All of the polymorphisms identified were in parts of the ABCB1 gene product predicted to be intracellular, and 16 appear to be novel as compared with those listed by the National Center for Biotechnological Information. Frequencies of the 1236C-->T and 2677G-->T/A/C SNPs were similar for the US and Ashkenazi populations (64.2 and 60.4%, respectively for 1236C-->T [chi2: 0.30; p < or = 1]; 55.8 and 64.4%, respectively for 2677G-->T/A/C [chi2: 1.49; p < or = 1]), but were different for 3435C-->T (24.2% for the US population and 69.3% for the Ashkenazi population [chi2: 39.927; p < or = 0.001]). The 1236T/ 2677T/3435T haplotype occurred in 23.6% (standard error: 0.013) of the Ashkenazi population. CONCLUSION:The SNP at location 3435C-->T plays a significant role in the ABCB1 gene. The haplotype and genotype analysis from these data may be used as a basis for studies on the relationship between ABCB1 genotypes and drug efficacy, drug toxicity, disease susceptibility or other phenotypes.

Project description:Interpatient variability in tacrolimus pharmacokinetics is attributed to metabolism by cytochrome P-450 3A5 (CYP3A5) isoenzymes and membrane transport by P-glycoprotein. Interpatient pharmacokinetic variability has been associated with genotypic variants for both CYP3A5 or ABCB1. Tacrolimus pharmacokinetics was investigated in 65 stable Black and Caucasian post-renal transplant patients by assessing the effects of multiple alleles in both CYP3A5 and ABCB1. A metabolic composite based upon the CYP3A5 polymorphisms: ?3(rs776746), ?6(10264272), and ?7(41303343), each independently responsible for loss of protein expression was used to classify patients as extensive, intermediate and poor metabolizers. In addition, the role of ABCB1 on tacrolimus pharmacokinetics was assessed using haplotype analysis encompassing the single nucleotide polymorphisms: 1236C > T (rs1128503), 2677G > T/A(rs2032582), and 3435C > T(rs1045642). Finally, a combined analysis using both CYP3A5 and ABCB1 polymorphisms was developed to assess their inter-related influence on tacrolimus pharmacokinetics. Extensive metabolizers identified as homozygous wild type at all three CYP3A5 loci were found in 7 Blacks and required twice the tacrolimus dose (5.6 ± 1.6 mg) compared to Poor metabolizers [2.5 ± 1.1 mg (P < 0.001)]; who were primarily Whites. These extensive metabolizers had 2-fold faster clearance (P < 0.001) with 50% lower AUC? (P < 0.001) than Poor metabolizers. No differences in C12 h were found due to therapeutic drug monitoring. The majority of blacks (81%) were classified as either Extensive or Intermediate Metabolizers requiring higher tacrolimus doses to accommodate the more rapid clearance. Blacks who were homozygous for one or more loss of function SNPS were associated with lower tacrolimus doses and slower clearance. These values are comparable to Whites, 82% of who were in the Poor metabolic composite group. The ABCB1 haplotype analysis detected significant associations of the wildtype 1236T-2677T-3435T haplotype to tacrolimus dose (P = 0.03), CL (P = 0.023), CL/LBW (P = 0.022), and AUC? (P = 0.078). Finally, analysis combining CYP3A5 and ABCB1 genotypes indicated that the presence of the ABCB1 3435 T allele significantly reduced tacrolimus clearance for all three CPY3A5 metabolic composite groups. Genotypic associations of tacrolimus pharmacokinetics can be improved by using the novel composite CYP3A5?3?4?5 and ABCB1 haplotypes. Consideration of multiple alleles using CYP3A5 metabolic composites and drug transporter ABCB1 haplotypes provides a more comprehensive appraisal of genetic factors contributing to interpatient variability in tacrolimus pharmacokinetics among Whites and Blacks.

Dataset Information

Influence of ABCB1 polymorphisms and haplotypes on tacrolimus nephrotoxicity and dosage requirements in children with liver transplant.

Publications

Influence of ABCB1 polymorphisms and haplotypes on tacrolimus nephrotoxicity and dosage requirements in children with liver transplant.

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