| BackgroundSince the past half century, modern scientific technology and medical care has been greatly developed. To date, organ transplantation has become the optimal or even unique therapeutic option for end-stage diseases of solid organs such as renal, liver, heart and lung. Besides the benefits from the improvement in organ reservation, operation technique and surgeon material, the exploration and use of immunosuppressive drugs have enabled this strategy to obtain its current place. Of which, tacrolimus (FK506) has become the worldwide used immunosuppressive drug in liver transplantation for its good efficacy and low toxicity. However, it is characterized by a narrow therapeutic index and high interindividual variations in its phannacokinetics, which makes it difficult to establish an empirical dosage regimen of the drug. Physicians have to face the great variations for tacrolimus dosage between individuals when prescribed to patients. As a quantitative correlation between drug dosage and blood concentration is unavailable, tacrolimus dose isfrequently adjusted according to blood concentration.Tacrolimus is mainly metabolized by the cytochrome P450 subfamily CYP3A isoenzymes in liver. CYP3A group is the most abundant CYP subfamily of enzymes, mainly expressed in liver and intestine, and takes the responsibility for the phase I metabolism of over 50% of all clinically used drugs. It has four homologous proteins: CYP3A4, CYP3A5, CYP3A7 and CYP3A43. Tacrolimus is metabolized by the structurally and metabolically similar enzymes CYP3A4 and CYP3A5. recent advances in pharmacogenomics have found several single nucleotide polymorphisms (SNPs) in CYP3A subfamily. The 6986A/G polymorphism in intron 3 of CYP3A5 is correlated with gene expression and enzyme activity for it creates a cryptic splice site and results in a truncated CYP3A5 protein. Only individuals with at least one CYP3A5*1 allele can actually express CYP3A5 protein.It is speculated that the polymorphisms of CYP3A5*1/*3 gene may have relationship with high interindividual variation of tacrolimus dosage. In addition, differed from other organ transplantations, as drug metabolism and biotransformation organ, donor liver carries rather different genetic background from recipient in liver transplantation. Theoretically the metabolism of drug in the body is also affected by drug-metabolizing genes in the donor liver. This study was aimed to analyze the polymorphisms of CYP3A5 gene in the liver transplant recipients and donors, investigate the different effects of donor and recipient CYP3A5*3 gene polymorphisms on the interindividual variation of tacrolimus dosage, and seek for reliable regimen of individualized FK506 dosage for liver transplant patients.Materials and methods53 patients who underwent orthotopic liver transplantation from cadaveric donors between 2004 July and 2005 March in our center and treated with triple-regimen therapy including tacrolimus, MMF and steroid were enrolled in this retrospective study. At three time spots after transplantation, 1 week, 2 weeks and 1 month, the daily dose of tacrolimus was recorded and the blood trough concentrationmeasured.Recipient genomic DNA was extracted from EDTA-anticoagulated blood. CYP3A5*3 gene was amplified by PCR. RFLP array and DNA sequencing were used to determine the SNPs of CYP3A5*3 gene respectively. All the patients were divided into two groups according to their CYP3A5*3 genotypes: expressor group (* 1 /* 1 and * l/*3) and nonexpressor group (*3/*3). The correlation between recipient CYP3A5*3 genotype and tacrolimus dose and blood concentration/dose (C/D) ratio was investigated.Donor genomic DNA was obtained from spleen or EDTA-anticoagulated blood. SNPs of donor CYP3A5*3 gene were determined using same methods. Patients were divided into expressor group (*1/*1 and *l/*3) and nonexpressor group (*3/*3) based on the donor CYP3A5*3 genotypes. The correlation between donor CYP3A5*3 genotype and tacrolimus dose and blood concentration/dose (C/D) ratio was investigated.Then data was reviewed by analyzing for the combination of CYP3A5 genotype in both donor and recipient to further investigate the different effects of donor and recipient CYP3A5 polymorphism on the interindividual variation of tacrolimus dosage.Statistical analyses were performed by the statistical software package SPSS 12.0. Nonparametric tests were used for analyzing. Between-two-group differences of tacrolimus C/D ratio were calculated by use of Mann-Whitney f/test. P<0.05 was considered statistically significant.ResultsThe mean age of the 53 recipients was 45 + 9 years (ranging from 29 to 75). and the mean body weight was 60.4+10.3 kg (ranging from 40 to 85). Of the recipients, 6 (11.3%) were *1/*1 genotype, whereas 27 (50.9%) were heterozygous and 20 (37.8%) homozygous for *3 allele. The distribution in donors presented as 5 (9.4%), 25 (47.2%) and 23 (43.4%) correspondingly.To maintain a target concentration of 7-10ng/ml in the first month, the daily tacrolimus dose for the 53 patients varied from 0.022mg/kg to 0.222mg/kg individually at 1 month post operation, mean 0.097+0.051 mg/kg.According to donor genotype only, significant differences in tacrolimus blood C/D ratio were found between expressor and nonexpressor groups at 2 weeks and 1 month. The C/D ratio in *l/*l(*l/*3) genotype patients was significantly lower than in *3/*3 genotype patients at 2 weeks (mean±SD, 100.99±55.71 vs. 139.83±70.31, p=0.036) and 1 month (100.13±64.27 vs. 141.47±778.92, p=0.021). While the difference was not significant at the first week between *l/*l(*l/*3) genotype and *3/*3 genotype (106.32±46.75 vs. 139.16±70.01, p=0.146) as recipient CYP3A5 genotype was investigated separately, tacrolimus blood C/D ratios were also found lower in *l/*l(*l/*3) genotype than *3/*3 genotype at 1 week (112.85±52.10 vs. 133.31±70.03, p=0.279), 2 weeks (109.12±55.19 vs. 132.25±77.56, p=0.388) and 1 month (112.70±74.43 vs. 126.93±72.28, p=0.240). But the differences were not statistically significant (p>0.05).Further analysis for the combinations of CYP3A5 genotype in both donor and recipient showed: C/D ratios at 2 weeks and 1 month were still significantly lower in group of CYP3A5 expressor in both donor and recipient (19) compared with group of nonexpressor in donor and recipient (9), p<0.05, and the difference was even larger, which suggested that excluded the cross effect of donor and recipient genotype the influence of CYP3A5 gene to tacrolimus metabolism was much more obvious. If the donor was CYP3A5 nonexpressor, the CYP3A5 expressor recipients (14) seemed to have lower C/D ratios than CYP3A5 nonexpressor recipients (9). Comparably, if the donor was CYP3A5 expressor, the C/D ratios were similar between C YP3 A5 expressor and nonexpressor of recipients. And whatever genotype the recipient was, C/D ratios in CYP3A5 expressor donor group were lower than nonexpressor donor group. Those suggest that the influence of recipient CYP3A5 genotype to the interindividual variation of tacrolimus dose requirement may be "diluted" by the effect of donor CYP3A5 genotype.Conclusions1. To obtain a target tacrolimus concentration after liver transplantation, tacrolimus dose requirement varies greatly between individuals.2. The large inter-individual variation of FK506 dose requirement is influenced by the metabolic activity of CYP3A5 which is correlated with gene polymorphisms.3. Polymorphisms of the donor CYP3A5*3 gene seem to contribute more to such variation than that of recipient in liver transplantation. Genotyping the CYP3A5*3 polymorphism of donor rather than recipient would provide useful information to individualize tacrolimus dose. |
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