Effect of CYP3A5 polymorphism on tacrolimus metabolic clearance in vitro.

Previous investigations of solid organ transplant patients treated with tacrolimus showed that individuals carrying a CYP3A5*1 allele have lower dose-adjusted trough blood concentrations compared with homozygous CYP3A5*3 individuals. The objective of this investigation was to quantify the contribution of CYP3A5 to the hepatic and renal metabolic clearance of tacrolimus. Four primary tacrolimus metabolites, 13-O-desmethyl tacrolimus (13-DMT) (major), 15-O-desmethyl tacrolimus, 31-O-desmethyl tacrolimus (31-DMT), and 12-hydroxy tacrolimus (12-HT), were generated by human liver microsomes and heterologously expressed CYP3A4 and CYP3A5. The unbound tacrolimus concentration was low (4-15%) under all incubation conditions. For CYP3A4 and CYP3A5, V(max) was 8.0 and 17.0 nmol/min/nmol enzyme and K(m,u) was 0.21 and 0.21 muM, respectively. The intrinsic clearance of CYP3A5 was twice that of CYP3A4. The formation rates of 13-DMT, 31-DMT, and 12-HT were >or=1.7-fold higher, on average, in human liver microsomes with a CYP3A5*1/*3 genotype compared with those with a homozygous CYP3A5*3/*3 genotype. Tacrolimus disappearance clearances were 15.9 +/- 9.8 ml/min/mg protein and 6.1 +/- 3.6 ml/min/mg protein, respectively, for the two genotypes. In vitro to in vivo scaling using both liver microsomes and recombinant enzymes yielded higher predicted in vivo tacrolimus clearances for patients with a CYP3A5*1/*3 genotype compared with those with a CYP3A5*3/*3 genotype. In addition, formation of 13-DMT was 13.5-fold higher in human kidney microsomes with a CYP3A5*1/*3 genotype compared with those with a CYP3A5*3/*3 genotype. These data suggest that CYP3A5 contributes significantly to the metabolic clearance of tacrolimus in the liver and kidney.     

CYP3A5 phenotype-genotype correlations in a British population

AIMS: To develop a polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP)-based assay to genotype for hepatic CYP3A5 expression and to use this assay to study a British population. METHODS: CYP3A5-specific primers were designed with one including a base-pair mismatch to create a RsaI site in samples positive for G6986 (CYP3A5*3 allele) [correction]. Following PCR and RsaI digestion, different band patterns on electrophoresis were predicted for individuals positive for CYP3A5 (CYP3A5*1 allele) compared with those who do not express the gene (CYP3A5*3 homozygotes). The assay was validated by DNA sequencing. DNA samples from a human liver bank consisting of 22 livers whose CYP3A5 expression had been determined by immunoblotting and a group of random individuals (n = 100) from the North-east of England were genotyped by the new assay. RESULTS: In the liver bank, five out of 22 samples expressed CYP3A5 at significant levels (>20 pmol mg-1 protein) and were found to have the genotype CYP3A5*1/CYP3A5*3 by the PCR-RFLP assay. All other liver DNA samples were CYP3A5*3 homozygotes. In the group of 100 random individuals, 13 had the genotype CYP3A5*1/CYP3A5*3 and all others were CYP3A5*3 homozygotes, predicting that 13% (95% confidence interval (CI) 6%, 20%) would show significant hepatic CYP3A5 expression. The frequency for the CYP3A5*1 allele was 0.065 (95% CI 0.032, 0.097). CONCLUSIONS: We have developed a simple assay for the detection of the CYP3A5*1/CYP3A5*3 alleles and shown that in a British population their frequency is similar to that reported previously. We have also shown a good correlation between hepatic CYP3A5 expression and genotype for a British Caucasian liver bank.     

Effect of intestinal CYP3A5 on postoperative tacrolimus trough levels in living-donor liver transplant recipients

It has been reported that hepatic and intestinal cytochrome P450 (CYP) 3A4, CYP3A5 and P-glycoprotein affect the pharmacokinetics of tacrolimus, and that these proteins are associated with the large inter-individual variation in the pharmacokinetics of this drug. We previously showed that the concentration/dose ratio of tacrolimus tended to be lower in recipients of living-donor liver transplantation (LDLT) with a CYP3A5*1/*1-carrying graft. However, the effect of intestinal CYP3A5 remains to be elucidated. In the present study, we examined the CYP3A5 genotype in both recipients and donors, and the effect of the recipients' polymorphism on the concentration/dose ratio of tacrolimus in patients after LDLT. The CYP3A5*3 allele frequency was 80% in recipients and 77% in donors. The intestinal CYP3A5 mRNA expression level was significantly associated with genotype. The tacrolimus concentration/dose ratio was lower in recipients with the CYP3A5*1/*1 and *1/*3 genotype (CYP3A5 expressors) compared to the CYP3A5*3/*3 genotype (non-expressors). Amongst the combination of CYP3A5 genotypes between the graft liver and the native intestine, CYP3A5 expressors in both the graft liver and the native intestine had the lowest concentration/dose ratio of tacrolimus during 35 days after LDLT. Patients with the intestinal CYP3A5*1 genotype tended to require a higher dose of tacrolimus compared to the other group with the same hepatic CYP3A5 genotype. These results indicate that intestinal CYP3A5, as well as hepatic CYP3A5, plays an important role in the first-pass effect of orally administered tacrolimus.     

CYP3A5*1-carrying graft liver reduces the concentration/oral dose ratio of tacrolimus in recipients of living-donor liver transplantation

OBJECTIVES: Tacrolimus is widely used for immunosuppressive therapy after organ transplantation, but its pharmacokinetics shows such great interindividual variation that control of its blood concentration is difficult. We have previously reported that an intestinal P-glycoprotein (MDR1) contributes to this variation as an absorptive barrier, but the role of hepatic metabolism is not clear. METHODS: In this study, we have evaluated the genotypes of MDR1 and cytochrome P450 (CYP) 3A in donor and recipient, and the influence of polymorphisms on mRNA expression and the tacrolimus concentration/dose (C/D) ratio in recipients of living-donor liver transplantation (LDLT). RESULTS: The expression level of MDR1 and tacrolimus C/D ratio were not affected by either MDR1 C3435T or G2677T/A. The CYP3A4*1B genotype was not detected, but the CYP3A5*3 genotype had an allelic frequency of 76.3%. The mRNA level of CYP3A5 was significantly reduced by the *3/*3 genotype, and the tacrolimus C/D ratio was decreased in recipients engrafted with partial liver carrying CYP3A5*1/*1 genotype. An analysis of the combination of intestinal MDR1 level and liver CYP3A5 genotype revealed that the tacrolimus C/D ratio was lower in the group with higher MDR1 levels regardless of CYP3A5 genotype during postoperative week 1. CONCLUSIONS: These results indicate that in recipients of LDLT, the pharmacokinetics of tacrolimus is influenced by flux via P-glycoprotein in the intestine during the first week; after that, it is mostly the hepatic metabolism that contributes to the excretion of tacrolimus, and carriers of the CYP3A5*1/*1 genotype require a high dose of tacrolimus to achieve the target concentration.     

肝移植患者他克莫司血药浓度与细胞色素P450 3A5 1*3基因多态性的关系

目的研究细胞色素P450 3A5 1*3基因多态性对肝移植患者他克莫司(免疫抑制剂)血药浓度的影响,探讨他克莫司在不同个体间吸收、代谢差异的基因背景。方法观察150例肝移植术后常规使用他克莫司 吗替麦考酚酯胶囊 醋酸泼尼松三联免疫抑制治疗的成年患者,分别测定术后1、3、6个月和12月的他克莫司全血药浓度,采用等位基因特异PCR测定细胞色素P450 3A5 1*3基因多态性,比较不同基因型之间他克莫司的浓度/剂量比的差异。结果在口服相同剂量的他克莫司时,1个月内CYP3A5 1*1、CYP3A5 1*3和CYP3A5 3*3三种基因型的浓度/剂量比,差异不显著;但3个月后,差异显著;6个月和12个月的浓度/剂量比,差异非常显著。结论CYP3A5 1*3多态性与肝移植患者他克莫司血药浓度具有非常显著的相关性,携带等位基因1*1和1*3患者的血药浓度明显低于3*3纯合子患者。     

Tacrolimus Elimination in Four Patients With a CYP3A5*3/*3 CYP3A4*22/*22 Genotype Combination

Cytochrome P450 3A5 (CYP3A5) and cytochrome P450 3A4 (CYP3A4) are the predominate enzymes responsible for tacrolimus metabolism. The presence of CYP3A4 and CYP3A5 genetic variants significantly affects tacrolimus clearance and dose requirements. CYP3A5*3 is a loss‐of‐function variant resulting in no CYP3A5 enzyme production. CYP3A4*22 is a variant that reduces production of functional CYP3A4 protein. Caucasians commonly carry these variant alleles but are very rarely homozygous for both CYP3A5*3 and CYP3A4*22. This report describes four kidney transplant recipients who carry a rare genotype combination (CYP3A5*3/*3 and CYP3A4*22/*22). These patients were identified from a larger cohort of Caucasian kidney transplant recipients (n=1366). To understand the significance of this genotype combination on tacrolimus troughs and doses, we compared these patients to recipients without this combination. Patients homozygous for both variants are at risk for profound reductions in metabolism of CYP3A substrates. A 342% and a 90.6% increase in the median dose‐normalized trough was observed, when the CYP3A5*3/*3 and CYP3A4*22/*22 genotype combination was compared to the CYP3A5*1/*1 and CYP3A4*1/*1 genotype combination and the CYP3A5*3/*3 and CYP3A4*1/*1 genotype combination, respectively. These four individuals only required on average 2.5 mg/day of tacrolimus. Knowledge of these genotypes would be useful in selecting appropriate tacrolimus doses to avoid overexposure.     

CYP3A7 protein expression is high in a fraction of adult human livers and partially associated with the CYP3A7*1C allele

Previously, cytochrome P450 3A7 (CYP3A7), which constitutes the major CYP enzyme in fetal livers, has been considered a fetus-specific enzyme. However, CYP3A7 mRNA has recently been shown to be expressed at significant levels in a subset of adult human livers, several of which carry the CYP3A7*1C allele that contains the proximal PXR/CAR element of CYP3A4. The objective of this study was to investigate CYP3A7 expression at the protein level by developing a CYP3A7-specific antibody to allow its quantification. Based on results from 59 adult human liver samples, we found significant CYP3A7 protein expression in approximately one in 10 adult livers amounting for 24-90 pmol/mg microsomal protein, thereby contributing 9-36% to total CYP3A levels in these livers. CYP3A7 protein was detected in five of seven livers carrying the CYP3A7*1C allele (two of which only had trace amounts), whereas an additional three livers expressing CYP3A7 were apparently homozygous for CYP3A7*1. The mean protein expression level of CYP3A7 was 42 pmol/mg within the group of livers expressing CYP3A7 and 4 pmol/mg in all liver samples. CYP3A7 expression was thus higher than that of the polymorphically expressed CYP3A5 in adult human livers, based on a comparison with a previous study using our CYP3A5 peptide-specific antibody. The relatively high level of CYP3A7 protein expression detected in a subset of adult livers may be relevant with respect to the metabolism of exogenous and endogenous substrates, such as retinoic acid and dehydroepiandrosterone.     

CYP3A5基因多态性与肝移植术后早期他克莫司浓度/剂量比的关系

目的:探讨供受体CYP3A5基因多态性对肝移植术后早期他克莫司浓度/剂量比(C/D)的影响.方法:回顾性收集2020年在清华大学附属北京清华长庚医院首次接受肝移植的患者71例,记录其术后2周、3周和4周时服用的他克莫司剂量及相应时间点的血药浓度(C),得到每千克日剂量(D),分别计算C/D.采用荧光原位杂交技术测定供受...     

Impact of MDR1 and CYP3A5 on the oral clearance of tacrolimus and tacrolimus-related renal dysfunction in adult living-donor liver transplant patients

OBJECTIVE: The potential influence of the multidrug resistance 1 (MDR1) gene and the cytochrome P450 (CYP) genes, CYP3A4 and CYP3A5, on the oral clearance (CL/F) of tacrolimus in adult living-donor liver transplant patients was examined. Furthermore, the development of renal dysfunction was analyzed in relation to the CYP3A5 genotype. METHODS: Sixty de novo adult liver transplant patients receiving tacrolimus were enrolled in this study. The effects of various covariates (including intestinal and hepatic mRNA levels of MDR1 and CYP3A4, measured in each tissue taken at the time of transplantation, and the CYP3A5*3 polymorphism) on CL/F during the first 50 days after surgery were investigated with the nonlinear mixed-effects modeling program. RESULTS: CL/F increased linearly until postoperative day 14, and thereafter reached a steady state. The initial CL/F immediately after liver transplantation was significantly affected by the intestinal MDR1 mRNA level (P<0.005). Furthermore, patients carrying the CYP3A5*1 allele in the native intestine, but not in the graft liver, showed a 1.47 times higher (95% confidence interval, 1.17-1.77 times, P<0.005) recovery of CL/F with time than patients having the intestinal CYP3A5*3/*3 genotype. The cumulative incidence of renal dysfunction within 1 year after transplantation, evaluated by the Kaplan-Meier method, was significantly associated with the recipient's but not donor's CYP3A5 genotype (*1/*1 and *1/*3 vs. *3/*3: recipient, 17 vs. 46%, P<0.05; donor, 35 vs. 38%, P=0.81). CONCLUSION: These findings suggest that the CYP3A5*1 genotype as well as the MDR1 mRNA level in enterocytes contributes to interindividual variation in the CL/F of tacrolimus in adult recipients early after living-donor liver transplantation. Furthermore, CYP3A5 in the kidney may play a protective role in the development of tacrolimus-related nephrotoxicity.     

In vitro metabolism of cyclosporine A by human kidney CYP3A5

The objectives of this study were to characterize and compare the metabolic profile of cyclosporine A (CsA) catalyzed by CYP3A4, CYP3A5 and human kidney and liver microsomes, and to evaluate the impact of the CYP3A5 polymorphism on product formation from parent drug and its primary metabolites. Three primary CsA metabolites (AM1, AM9 and AM4N) were produced by heterologously expressed CYP3A4. In contrast, only AM9 was formed by CYP3A5. Substrate inhibition was observed for the formation of AM1 and AM9 by CYP3A4, and for the formation of AM9 by CYP3A5. Microsomes isolated from human kidney produced only AM9 and the rate of product formation (2 and 20 microM CsA) was positively associated with the detection of CYP3A5 protein and presence of the CYP3A5*1 allele in 4 of the 20 kidneys tested. A kinetic experiment with the most active CYP3A5*1-positive renal microsomal preparation yielded an apparent Km (15.5 microM) similar to that of CYP3A5 (11.3 microM). Ketoconazole (200 nM) inhibited renal AM9 formation by 22-55% over a CsA concentration range of 2-45 microM. Using liver microsomes paired with similar CYP3A4 content and different CYP3A5 genotypes, the formation of AM9 was two-fold higher in CYP3A5*1/*3 livers, compared to CYP3A5*3/*3 livers. AM19 and AM1c9, two of the major secondary metabolites of CsA, were produced by CsA, AM1 and AM1c when incubated with CYP3A4, CYP3A5, kidney microsomes from CYP3A5*1/*3 donors and all liver microsomes. Also, the formation of AM19 and AM1c9 was higher from incubations with liver and kidney microsomes with a CYP3A5*1/*3 genotype, compared to those with a CYP3A5*3/*3 genotype. Together, the data demonstrate that CYP3A5 may contribute to the formation of primary and secondary metabolites of CsA, particularly in kidneys carrying the wild-type CYP3A5*1 allele.     

Unusual high dose of tacrolimus in liver transplant patient, a case report

CASE: We describe the case of a liver transplant patient who had great difficulty in reaching the desired trough blood levels despite the use of high dose tacrolimus. The patient was homozygous for the CYP3A5*3 allele. However, the respective donor carried the wild-type CYP3A5*1/*1 genotype. Regarding ABCB1 SNPs at exon 21 and 26, the patient showed the 2677GT and 3435CC genotypes. For the corresponding donor we observed the 2677GG and 3435CC wild-type genotypes. One, two and three weeks after transplantation the patient received daily 0.219, 0.287 and 0.273 mg/kg of tacrolimus, respectively. However, the corresponding tacrolimus trough blood levels were of 4.6, 5.6 and 6.1 ng/mL. The tacrolimus target level of 10.4 ng/mL was finally reached after 1 month of therapy. During the entire period of observation the kidney showed no sign of damage. No other signs of toxicity were reported except for the occurrence of an isolated systolic hypertension. CONCLUSIONS: CYP3A5 genotyping may represent a useful tool to better evaluate the appropriate initial dose of tacrolimus for patients carrying a liver with the CYP3A5*1/*1 genotype.     

Clinical implications of CYP3A polymorphisms

Due to their enormous substrate spectrum CYP3A4, -3A5 and -3A7 constitute the most important drug-metabolising enzyme subfamily in humans. CYP3As are expressed predominantly, but not exclusively, in the liver and intestine, where they participate in the metabolism of 45 - 60% of currently used drugs and many other compounds such as steroids and carcinogens. CYP3A expression and activity vary interindividually due to a combination of genetic and nongenetic factors such as hormone and health status, and the impact of environmental stimuli. Over the past several years, genetic determinants have been identified for much of the variable expression of CYP3A5 and -3A7, but not for CYP3A4. Using these markers, an effect of CYP3A5 expression status has been demonstrated beyond doubt for therapies with the immunosuppressive drug tacrolimus. Further associations are likely to emerge for drugs metabolised predominantly by CYP3A5 or -3A7, especially for individuals or tissues with concomitant low expression of CYP3A4. However, as exemplified by the controversial association between CYP3A4*1B and prostate cancer, the detection of clinical effects of CYP3A gene variants will be difficult. The most important underlying problems are the continuing absence of activity markers specific for CYP3A4 and the strong contribution of nongenetic factors to CYP3A variability.     

Co-regulation of CYP3A4 and CYP3A5 and contribution to hepatic and intestinal midazolam metabolism

We recently demonstrated that a variant allele of CYP3A5 (CYP3A5*3) confers low CYP3A5 expression as a result of improper mRNA splicing. In this study, we further evaluated the regulation of CYP3A5 in liver and jejunal mucosa from white donors. For all tissues, high levels of CYP3A5 protein were strongly concordant with the presence of a wild-type allele of the CYP3A5 gene (CYP3A5*1). CYP3A5 represented greater than 50% of total CYP3A content in nearly all of the livers and jejuna that carried the CYP3A5*1 wild-type allele. Overall, CYP3A5 protein content accounted for 31% of the variability in hepatic midazolam hydroxylation activity. Improperly spliced mRNA (SV1-CYP3A5) was found only in tissues containing a CYP3A5*3 allele. Properly spliced CYP3A5 mRNA (wt-CYP3A5) was detected in all tissues, but the median wt-CYP3A5 mRNA was 4-fold higher in CYP3A5*1/*3 livers compared with CYP3A5*3/*3 livers. Differences in wt-CYP3A5 and CYP3A4 mRNA content explained 53 and 51% of the interliver variability in CYP3A5 and CYP3A4 content, respectively. Hepatic CYP3A4 and CYP3A5 contents were not correlated when all livers were compared. However, for CYP3A5*1/*3 livers, levels of the two proteins were strongly correlated (r = 0.93) as were wt-CYP3A5 and CYP3A4 mRNA (r = 0.76). These findings suggest that CYP3A4 and CYP3A5 genes share a common regulatory pathway for constitutive expression, possibly involving conserved elements in the 5'-flanking region.     

Effects of CYP3A5 and MDR1 single nucleotide polymorphisms on drug interactions between tacrolimus and fluconazole in renal allograft recipients

OBJECTIVE: Drug interactions between tacrolimus and azole antifungals are characterized by a large clinical variability. The aim of this study was to examine the influence of the CYP3A4, CYP3A5, and MDR1 single nucleotide polymorphisms on changes in tacrolimus exposure and dosing in renal allograft recipients treated with fluconazole. METHODS: Twenty-nine patients who had received documented fluconazole treatment were identified out of a total of 753 renal recipients on maintenance tacrolimus therapy. These 29 patients were genotyped for CYP3A4*1/*1B, CYP3A5*1/*3, MDR1 C3435T, and G2677T/A, and the influence of the latter polymorphisms on tacrolimus exposure and dose before, during, and after fluconazole administration was examined. RESULTS: Dose-corrected trough blood tacrolimus concentration did not change significantly from baseline (1.26+/-1.23-fold) in heterozygous CYP3A5*1 carriers during exposure to fluconazole, in contrast to homozygous CYP3A5*3 carriers (3.28+/-2.34-fold; P=0.04 between CYP3A5*3/*3 and CYP3A5*3/*1 genotypes). Homozygous CYP3A5*3 carriers experienced a significant decrease of weight-corrected tacrolimus dose requirements during fluconazole administration (54.7+/-23.7% from baseline, P<0.05) in contrast to heterozygous carriers of CYP3A5*1 (25.1+/-29.9%; P=0.07 between CYP3A5*3/*3 and CYP3A5*3/*1 genotypes). These findings were not influenced by fluconazole dose or duration of administration. Significantly more CYP3A5*3/*3 carriers were exposed to tacrolimus dose-uncorrected trough blood tacrolimus concentration value greater than or equal to 15 ng/ml during administration of fluconazole compared with CYP3A5*3/*1 carriers (73.9 vs. 16.7%, P=0.01). CONCLUSION: In renal allograft recipients the CYP3A5*3/*1 genotype is associated with a reduced susceptibility for the inhibitory effects of fluconazole on tacrolimus metabolism, thereby identifying a genetic determinant of the clinical variability of CYP3A-mediated drug interactions.     

Influence of the CYP3A5 and MDR1 genetic polymorphisms on the pharmacokinetics of tacrolimus in healthy Korean subjects

AIMS: To determine the frequencies of the genotypes of CYP3A5 and MDR1 and to examine the influence of the polymorphisms of these genes on tacrolimus pharmacokinetics in the Korean population. METHODS: Twenty-nine healthy Koreans who participated in the previous tacrolimus pharmacokinetic study were genotyped for CYP3A4*1B, CYP3A5*3, MDR1 c.1236C-->T, MDR1 c.2677G-->A/T and MDR1 c.3435C-->T. The relationship between the genotypes so obtained and tacrolimus pharmacokinetics observed in the previous study was examined. RESULTS: No subject in this study had the CYP3A4*1B variant. The observed frequencies of CYP3A5*1/*1, *1/*3, and *3/*3 were 0.069 [confidence interval (CI) -0.023, 0.161], 0.483 (CI 0.301, 0.665) and 0.448 (CI 0.267, 0.629), respectively. AUC(0-infinity) for the CYP3A5*1/*1 or *1/*3 genotype was 131.5 +/- 44.8 ng h ml(-1) (CI 109.6, 153.5), which was much lower compared with the CYP3A5*3/*3 genotype of 323.8 +/- 129.3 ng h ml(-1) (CI 253.5, 394.1) (P = 2.063E-07). Similarly, C(max) for the CYP3A5*1/*1 or *1/*3 genotype was 11.8 +/- 3.4 ng ml(-1) (CI 10.1, 13.5), which was also much lower compared with the CYP3A5*3/*3 genotype of 24.4 +/- 12.3 ng ml(-1) (CI 17.8, 31.1) (P = 0.0001). However, there was no significant difference in tacrolimus pharmacokinetics among the MDR1 diplotypes of CGC-CGC, CGC-TTT, CGC-TGC, TTT-TGC or TTT-TTT (P = 0.2486). CONCLUSIONS: This study shows that the CYP3A5*3 genetic polymorphisms may be associated with the individual difference in tacrolimus pharmacokinetics. An individualized dosage regimen design incorporating such genetic information would help increase clinical efficacy of the drug while reducing adverse drug reactions.     

Effects of genetic polymorphisms on the pharmacokinetics of calcineurin inhibitors.

PURPOSE: The effects of genetic polymorphisms on the pharmacokinetics of calcineurin inhibitors were examined. SUMMARY: The bioavailability and metabolism of cyclosporine and tacrolimus are primarily controlled by efflux pumps and members of the cytochrome P-450 (CYP) isoenzyme system found in the liver and gastrointestinal tract. The number and severity of adverse effects from these drugs are related to the overall exposure, measured by length of therapy and blood drug concentration. One contributing factor to the inconsistent pharmacokinetics of calcineurin inhibitors may be variable expression of functional CYP3A4, CYP3A5, and P-glycoprotein (PGP) efflux pumps, which may be the result of single-nucleotide polymorphisms found on the genes encoding for CYP3A4, CYP3A5, and PGP. CYP3A5*3 and CYP3A5*6 are the most common polymorphisms of CYP3A5. Using genetic markers to adjust initial doses of cyclosporine or tacrolimus may prove difficult, considering the variety of polymorphism known to affect CYP3A4, CYP3A5, and the multidrug resistance-1 (MDR1) gene (the gene that codes for PGP). Studies have found that carriers of CYP3A5*1 consistently have higher clearance rates of tacrolimus than do CYP3A5*3 homozygotes. The influences of CYP3A5 alleles on cyclosporine metabolism and the MDR1 C3435T polymorphism on tacrolimus metabolism remain controversial. CONCLUSION: For renal transplant recipients receiving tacrolimus as an immunosuppressant, practitioners can expect CYP3A5*1 carriers to have a tacrolimus clearance 25-45% greater than that of CYP3A5*3 homozygotes, with proportional dosing needs to maintain adequate immunosuppression. Since inadequate immunosuppression is linked to graft rejection, evaluation of CYP3A5 polymorphisms may be helpful in determining an appropriate starting dosage, rapidly achieving adequate immunosuppression, and ultimately improving the outcome of renal transplantation.     

CYP 3A5*3基因多态性对肾移植术后他克莫司药代动力学的影响

目的探讨CYP3A5*3基因多态性对肾移植术后他克莫司(免疫抑制药)剂量校正给药2h后浓度的影响。方法选取61例肾移植术后患者,用聚合酶链式反应-限制性片段长度多态性的方法,分析CYP 3A5*3基因型;用微粒酶联免疫吸附法,测定患者他克莫司浓度。并分析CYP 3A5*3基因多态性与他克莫司给药剂量、给药2h浓度(C2)及剂量校正给药2h后浓度(C2/D)的相关性。结果肾移植术后1周及1、3个月,CYP 3A5*1/*1 CYP 3A5*1/*3组和CYP3A5*3/*3组他克莫司剂量比较均无显著性差异。术后1周和1个月,2组间他克莫司C2比较无显著性差异;术后3个月,CYP 3A5*1/*1 CYP 3A5*1/*3组的C2显著低于CYP 3A5*3/*3组(P<0.05)。术后1周及1、3个月,CYP 3A5*1/*1 CYP 3A5*1/*3组的C2/D均明显低于CYP 3A5*3/*3组(P<0.05)。结论肾移植术后,他克莫司C2/D的个体化差异与患者CYP3A5*3基因型密切相关。