MDR1 haplotypes do not affect the steady-state pharmacokinetics of cyclosporine in renal transplant patients

This retrospective study investigated the impact of MDR1 haplotypes derived from the single-nucleotide polymorphisms (SNPs) 2677G>T (exon 21) and 3435C>T (exon 26) on the pharmacokinetics of cyclosporine in 98 renal transplant patients. Based on SNPs 2677 and 3435, four different haplotypes and nine different genotypes were identified in the study sample. Frequencies of SNPs, genotypes, and haplotypes were in agreement with previously reported values. Cyclosporine pharmacokinetics were characterized using a 2-hour AUC (AUC0-12), trough concentrations (C0), and blood concentrations 2 hours after cyclosporine administration (C2). No significant differences in dose-corrected AUC0-12, C0, or C2 values were observed between carriers of different SNP variants and genotypes (Kruskal-Wallis test), as well as between carriers and noncarriers of each haplotype (Mann-Whitney U test). Carriers of haplotype 12 (2677G and 3435T), which has previously been associated with increased digoxin AUC values, had a median AUC0-12 of 18.9 micro g*h*L-1 (range: 9.0-35.2) compared to 17.5 micro g*h*L-1 (range: 7.5-37.1) in the noncarrier group. It was concluded that MDR1 haplotypes derived from the SNPs 2677G>T (exon 21) and 3435C>T (exon 26) are not associated with cyclosporine pharmacokinetics in renal transplant patients.     

CYP3A5和MDR1基因多态性对中国肝移植患者他克莫司药动学的影响

目的探讨细胞色素P450酶3A5（CYP3A5）基因和多药耐药基因（MDR1）C1236T、G2677T／A、C3435T多态性对肝移植患者口服他克莫司（TAC）后体内药动学参数的影响。方法采集28例肝移植患者手术后第1周和第3周血标本,采用LC—MS／MS法检测TAC血药浓度,计算主要药动学参数。采用聚合酶链反应结合基因测序分析28例肝移植患者CYP3A5＊3和MDR1主要基因型。结果携带MDR1 3435T基因型的肝移植患者口服TAC后,药动学参数AUC0→1和ρmax明显高于3435CC型患者,而CYP3A5＊3、MDR1 C1236T和G2677T／A基因多态性对TAC的药动学参数无明显影响。结论携带MDR1 3435T基因型肝移植患者比3435CC型患者需要较高剂量才能达到目标浓度。     

江苏地区汉族儿童多药耐药基因3个单核苷酸多态性位点的单倍型研究

目的分析江苏汉族人群多药耐药基因-1（MDR1）的单核甘酸多态（12外显子1236C→T突变、21外显子2677G→T/A突变、26外显子3435C→T突变）及其构成的单倍型分布。方法通过多重单碱基延伸反应（SNaPshotSNP分型技术）对江苏地区170名健康儿童的MDR1C1236T、G2677T/A、C3435T的SNP位点进行基因分型,统计各基因型频率。UNPHASED软件对MDR1的SNPs（C1236T-G2677T/A-C3435T）进行单倍型分析。结果在170例儿童中,等位基因1236T、2677T、2677A、3435T频率分别为63.5%、37.4%、17.0%和35.0%。基因型频率分布符合Hardy-Weinberg平衡（HWE）,差异无统计学意义（P〉0.05）。MDR1的1236、2677、3435三个位点间（C1236T-G2677T/A-C3435T）存在连锁不平衡性,以TTT（31.8%）、TGC（25.3%）、CGC（17.7%）和CAC（16.2%）四种单倍型为主。结论江苏地区汉族人群MDR1的单核甘酸多态及单倍型分布具有自己的特点。在临床应用相关药物时,进行基因型及单倍型检测,将有助于指导临床个体化用药。     

<Emphasis Type="BoldItalic">MDR1</Emphasis> Haplotypes Conferring an Increased Expression of Intestinal CYP3A4 Rather than MDR1 in Female Living-Donor Liver Transplant Patients

Purpose  This study investigated whether haplotypes in the multidrug resistance 1 (MDR1) gene had effects on mRNA expression levels of MDR1 and cytochrome P450 (CYP) 3A4, and on the pharmacokinetics of tacrolimus in living-donor liver transplant (LDLT) patients, considering the gender difference. Methods  Haplotype analysis of MDR1 with G2677T/A and C3435T was performed in 63 de novo Japanese LDLT patients (17 to 55 years; 44.4% women). The expression levels of MDR1 and CYP3A4 mRNAs in jejunal biopsy specimens were quantified by real-time PCR. Results  Intestinal CYP3A4 mRNA expression levels (amol/μg total RNA) showed significantly higher values in women carrying the 2677TT-3435TT haplotype (median, 10.7; range, 5.92–15.2) than those with 2677GG-3435CC (3.03; range 1.38–4.68) and 2677GT-3435CT (median, 4.31; range, 0.07–9.42) (P = 0.022), but not in men (P = 0.81). However, MDR1 haplotype did not influence mRNA expression levels of MDR1 nor the concentration/dose ratio [(ng/mL)/(mg/day)] of oral tacrolimus for the postoperative 7 days, irrespective of gender. Conclusion   MDR1 haplotype may have a minor association with the tacrolimus pharmacokinetics after LDLT, but could be a good predictor of the inter-individual variation of intestinal expression of CYP3A4 in women.     

Digoxin pharmacokinetics and MDR1 genetic polymorphisms

BACKGROUND: The effect of MDR1 C3435T single nucleotide polymorphism (SNP) in exon 26 on digoxin pharmacokinetics has recently been challenged. OBJECTIVE. To clarify the relationships between MDR1 genetic polymorphisms in exon 26 (C3435T) and 21 (G2677T/A) and digoxin pharmacokinetics. MATERIALS AND METHODS: MDR1 genotypes for C3435T and G2677T/A SNPs were determined in 32 healthy subjects whose single oral dose digoxin pharmacokinetics had been measured over 48 h. RESULTS: A significant relationship was observed between C3435T SNP and digoxin AUCs ( p<0,05). Homozygous TT subjects had 20% higher digoxin plasma concentrations than CT and CC subjects and a trend for higher 48 h digoxin urinary recoveries (TT>CT>CC). Similar results, although not statistically significant, were observed from the MDR1 G2677T/A SNP. CONCLUSIONS: Our results confirm that the MDR1 C3435T single nucleotide polymorphism (SNP) significantly affects digoxin disposition kinetics, with homozygous TT subjects presenting the highest plasma concentrations.     

MDR1基因多态性和单倍体对肾移植术后稳定期患者他克莫司浓度/剂量比值的影响

目的 探讨MDR1 C1236T、G2677T/A和C3435T 基因多态性和单倍体对中国汉族肾移植术后稳定期患者他克莫司浓度/剂量比值的影响,为他克莫司个体化用药提供依据。方法 采用PCR-基因测序法检测104例肾移植术后稳定期患者MDR1 C1236T、G2677T/A和C3435T 的基因多态性,采用均相酶免疫测定方法(EMIT法)测定他克莫司的谷浓度,比较不同基因型患者之间他克莫司血药浓度/(剂量×体质量)(C/D)比值。结果 104例患者中,MDR1 C1236T、G2677T/A和C3435T突变频率分别为56.73%、55.77%和33.17%。MDR1 C3435T、MDR1 TTT单倍体与他克莫司C/D比值具有相关性(P<0.05)。CYP3A5*3*3患者中,MDR1 TTT单倍体与他克莫司C/D比值仍存在显著相关(P<0.05)。MDR1 C1236T、G2677T/A、CGC单倍体与他克莫司C/D比值无显著性差异(P>0.05)。结论 MDR1 C3435T、MDR1 TTT单倍体与中国汉族肾移植术后稳定期患者他克莫司C/D比值具有显著相关性,是影响肾移植患者他克莫司浓度个体化差异的重要因素。     

MDR1 genotypes do not influence the absorption of a single oral dose of 600 mg valacyclovir in healthy Chinese Han ethnic males

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• The absorption of valacyclovir presents a highly negative correlation with the level of P-glycoprotein expression.
• It has been confirmed that a polymorphism of the MDR1 gene in exon 26 is related to the level of P-glycoprotein expression in intestine.
• This study was conducted to find the relationship between polymorphism of MDR1 gene and absorption of valacyclovir.

WHAT THIS STUDY ADDS

• Linkage disequilibrium exists between G2677T/A in exon 21 and C3435T in exon 26, between C1236T in exon 12 and C3435T, but not between C1236T and G2677T/A of MDR1 gene in the Chinese Han ethnic population.
• Three single nucleotide polymorphisms of MDR1 gene do not influence the absorption of valacyclovir in the healthy Chinese Han ethnic population.

AIMS

To investigate the influence of three single nucleotide polymorphisms (SNPs) in exon 12 (C1236T), exon 21 (G2677T/A) and exon 26 (C3435T) of MDR1 gene on the absorption of valacyclovir after a single oral administration in the Chinese Han ethnic population.

METHODS

Two hundred healthy Chinese subjects were genotyped for the SNPs of C1236T, G2677T/A and C3435T in the MDR1 gene using allele-specific polymerase chain reaction. Linkage disequilibrium (LD) was analysed. Twenty-four subjects derived from a large random sample (n = 200) received a single oral dose of 600 mg valacyclovir. Plasma concentrations of acyclovir were determined up to 14 h after administration to obtain a pharmacokinetic profile.

RESULTS

LD existed between G2677T/A in exon 21 and C3435T in exon 26 (P < 0.001), between C1236T in exon 12 and C3435T (P < 0.001), but not between C1236T and G2677T/A (P > 0.05). C_max, AUC_{0–1.5 h} and AUC_0–∞ were used as indices of valacyclovir absorption. AUC_0–∞ for the 2677TA genotype was 17.45 ± 2.40 µg × h/ml, which was much higher compared with the 2677GG, GA and TT genotypes of 10.44 ± 1.00, 11.84 ± 2.83, 11.34 ± 2.32 µg × h/ml, respectively (P < 0.05). Similarly, a statistically significant difference of AUC_0–∞ was also observed for different linked genotypes at position 2677 vs. 3435, and 1236 vs. 3435 (P < 0.05). However, there was no significant difference in valacyclovir absorptive pharmacokinetics between carriers and noncarriers of different haplotypes (P > 0.05).

CONCLUSIONS

Three SNPs of MDR1 gene did not influence the absorption of a single oral dose of 600 mg valacyclovir in healthy Chinese Han ethnic subjects.     

MDR1 haplotype frequencies in Japanese and Caucasian, and in Japanese patients with colorectal cancer and esophageal cancer

The genotype frequencies of MDR1 T-129C, C1236T, G2677A,T and C3435T SNPs were compared in 154 healthy Japanese and 100 healthy Caucasians to provide basic information on the inter-ethnic differences of pharmacotherapeutic outcome. The variants were found at allelic frequencies of 5.5%, 65.6%, 16.6%, 40.6% and 40.6%, for T-129C, C1236T, G2677A, G2677T and C3435T, respectively, in Japanese, and at 5.1%, 45.9%, 3.6%, 46.4% and 56.6%, respectively, in Caucasians, with a statistically significant difference for C1236T, G2677A,T and C3435T (p<0.001). G2677A was about 5-fold more frequent in Japanese than Caucasians. These genotype frequencies were also investigated in 95 Japanese patients with colorectal cancer (CRC) and esophageal squamous cell carcinoma (ESCC), but no significant difference was detected, when compared with healthy Japanese subjects. The haplotype frequency reached a total of about 85% in Japanese with the following 4 major haplotypes; T(-129)-T1236-T2677-T3435 (36.1%), T(-129)-T1236-G2677-C3435 (22.5%), T(-129)-C1236-G2677-C3435 (14.2%) and T(-129)-C1236-A2677-C3435 (13.3%). The second and fourth haplotypes were hardly inferred in Caucasian, whereas T(-129)-C1236-G2677-T3435 (12.8%) was found to be Caucasian-specific. There was a tendency for higher frequencies of the T(-129)/C-(129)-C1236-A2677-C3435 haplotype in Japanese CRC patients and T(-129)-T1236-T2677-T3435 haplotype in Japanese ESCC patients, compared with that in healthy Japanese subjects.     

Distinct haplotype profiles and strong linkage disequilibrium at the MDR1 multidrug transporter gene locus in three ethnic Asian populations

The MDR1 multidrug transporter plays a key role in determining drug bioavailability, and differences in drug response exist amongst different ethnic groups. Numerous studies have identified an association between the MDR1 single nucleotide polymorphism (SNP) exon 26 3435C>T and differences in MDR1 function. We performed a haplotype analysis of the MDR1 gene in three major ethnic groups (Chinese, Malays and Indians) by examining 10 intragenic SNPs. Four were polymorphic in all three ethnic groups: one occurring in the non-coding region and three occurring in coding exons. All three coding SNPs (exon 12 1236C>T, exon 21 2677G>T/A and exon 26 3435C>T) were present in high frequency in each ethnic group, and the derived haplotype profiles exhibited distinct differences between the groups. Fewer haplotypes were observed in the Malays (n = 6) compared to the Chinese (n = 10) and Indians (n = 9). Three major haplotypes (> 10% frequency) were observed in the Malays and Chinese; of these, two were observed in the Indians. Strong linkage disequilibrium (LD) was detected between the three SNPs in all three ethnic groups. The strongest LD was present in the Chinese, followed by Indians and Malays, with the corresponding LD blocks estimated to be approximately 80 kb, 60 kb and 40 kb, respectively. These data strongly support the hypothesis that strong LD between the neutral SNP exon 26 3435C>T and a nearby unobserved causal SNP underlies the observed associations between the neutral SNP and MDR1 functional differences. Furthermore, strong LD between exon 26 3435T and different unobserved causal SNPs in different study populations may provide a plausible explanation for conflicting reports associating the same exon 26 3435T allele with different MDR1 functional changes.     

Analyses of single nucleotide polymorphisms and haplotype linkage of the humanABCB1 (MDR1) gene in Korean

Single nucleotide polymorphisms (SNPs) in theMDR1 gene that are responsible for drug efflux can cause toxicity. Therefore, this study determined the SNPs of the KoreanMDR1 gene, and analyzed the haplotypes and a linkage disequilibrium (LD) of the SNPs determined. The frequency of 9 SNPs from theMDR1 gene was determined by PCR-RFLP analyses of 100 to 500 healthy individuals. The frequcies of the SNPs were C3435T (47.7%), G2677T (37.6%), G2677A (4.4%), T1236C (21.7%), T129C (8%), A2956G (2.5%), T307C (1.5%), A41aG (9.2%), C145G (0%), and G4030C (0%). Analyses of the haplotype structure and an estimation of the LD of the combined polymorphisms demonstrated that the frequency of the 1236T-2677G-3435T haplotype is much higher in Koreans (14.1%) than in Chinese and western black Africans and the C3435T SNP in Koreans appears to have LD with T129C in Koreans for the first time. These results provide insight into the genetic variation ofMDR1 in Koreans, and demonstrated the possibility of a new LD in this gene.     

CYP3A activity measured by the midazolam test is not related to 3435 C >T polymorphism in the multiple drug resistance transporter gene

A recent study with 69 Japanese liver transplants treated with tacrolimus found that the MDR13435 C >T polymorphism, but not the MDR12677 G >T polymorphism, was associated with differences in the intestinal expression level of CYP3A4 mRNA. In the present study, over 6 h, we measured the kinetics of a 75 microg oral dose of midazolam, a CYP3A substrate, in 21 healthy subjects genotyped for the MDR13435 C >T and 2677 G >T polymorphism. No statistically significant differences were found in the calculated pharmacokinetic parameters between the three 3435 C >T genotypes (TT, CT and CC group, respectively: Cmax (mean +/- SD: 0.30 +/- 0.08 ng/ml, 0.31 +/- 0.09 ng/ml and 0.31 +/- 0.11 ng/ml; Apparent clearance: 122 +/- 29 l/h, 156 +/- 92 l/h and 111 +/- 35 l/h; t1/2: 1.9 +/- 1.1 h, 1.6 +/- 0.90 h and 1.7 +/- 0.7 h). In addition, the 30-min 1'OH midazolam to midazolam ratio, a marker of CYP3A activity, determined in 74 HIV-positive patients before the introduction of antiretroviral treatment, was not significantly different between the three 3435 C >T genotypes (mean ratio +/- SD: 3.65 +/- 2.24, 4.22 +/- 3.49 and 4.24 +/- 2.03, in the TT, CT and CC groups, respectively). Similarly, no association was found between the MDR12677 G >T polymorphism and CYP3A activity in the healthy subjects or in the HIV-positive patients. The existence of a strong association between the activity of CYP3A and MDR13435 C >T and 2677 G >T polymorphisms appears unlikely, at least in Caucasian populations and/or in the absence of specific environmental factors.     

CYP3A4/5、ABCB1基因单倍型与中国肾移植患者他克莫司血药谷浓度相关性的研究

目的:探讨CYP3A4*18B、CYP3A5*3、ABCB1基因单倍型对中国肾移植患者术后一月内他克莫司谷浓度(C0/D)的影响。方法:采用限制性片段长度多态性技术分析46名肾移植患者CYP3A4*18B、CYP3A5*3、ABCB1(外显子C1236T、G2677A/T、C3435T)基因型,采用酶增强免疫测定技术测定患者C0值。结果:经分析患者CYP3A4*18B、CYP3A5*3、ABCB1(C1236T,G2677A/T,C3435T)等位基因频率分别为0.304、0.707、0.554、0.478和0.304,均符合HardyWeinberg平衡。CYP3A4-3A5、G2677A/T-C3435T及C1236T-C3435T间均表现为连锁不平衡。术后8~15、16~30天内CYP3A4*18B与患者FK506 C0/D值显著相关,野生型患者C0/D值分别为杂合及突变型患者的1.34和1.67倍。CYP3A5*3基因也与患者FK506 C0/D值显著相关。突变型患者C0/D值在术后1~7、8~15及16~30天时分别为野生及杂合型患者的1.56、1.98及1.99倍。单倍型分析发现CYP3A4/5单倍型GG型携带者C0/D值较非携带者在移植术后8~15、16~30天显著性增加1.43、1.77倍。未观察到ABCB1基因多态性及单倍型对FK506血药浓度的影响。结论:仅CYP3A4/5单倍型与他克莫司C0/D值显著相关,移植前对CYP3A4/5单倍型进行检测将有利于他克莫司给药剂量的调整。     

Sequential analysis of tacrolimus dosing in adult lung transplant patients with ABCB1 haplotypes

The genetic polymorphisms in the ABCB1 gene, which encodes for the membrane pump, P-glycoprotein, have been previously demonstrated to have an association with tacrolimus dosing in organ transplant patients. This study associated the haplotype and genotype for ABCB1 G2677T and C3435T variants with a sequential analysis of tacrolimus blood level (ng/mL) per mg/day dosage ([L/D]) administered to 91 adult lung transplant patients at 1, 3, 6, 9, and 12 months after transplantation. Haplotype 22 carriers had a significantly higher tacrolimus [L/D] value in comparison with nonhaplotype 22 carriers (P = .04) only at 1 month after transplant. Sequential analysis demonstrated that ABCB1 genotypes 00 and 01 had low tacrolimus [L/D] values at 1 and 3 months, but these values increased substantially at 6, 9, and 12 months after transplantation. This was not true of the other genotypes with the exception of genotypes 10 and 21, which had small numbers of patients but had consistently low tacrolimus [L/D]. Haplotype analysis also suggested that the homozygous for ABCB1 2677 variant allele had more of an impact on tacrolimus [L/D] in haplotype analysis than that of ABCB1 3435. In conclusion, sequential analysis of tacrolimus [L/D] with haplotypes can explain previous clinical observations of changes in tacrolimus dosage over time but suggests that this effect is limited to individual patient haplotypes. Sequential analysis of drug dosing and haplotypes relationships can provide important information about the induction or inhibition of drug-drug and disease-drug interactions among specific haplotypes.     

MDR1 C1236T、G2677T/A、C3435T的基因多态性对中国汉族肾移植患者环孢素药动学的影响(英文)

目的探讨中国汉族人中肾移植患者的多药耐药基因(MDR1)外显子exon12 C1236T、exon21 G2677T/A、exon26 C3435T的单核苷酸多态性对免疫抑制剂环孢素(CsA)药动学的影响。方法采用聚合酶联反应和限制性内切片段长度多态性(PCR-RFLP)的方法对89例肾移植术后的患者进行MDR1基因分型。单克隆抗体荧光免疫偏振法测定患者术后CsA的谷浓度(c0)及服药后2 h浓度(c2)。比较不同基因型之间CsA浓度剂量比值的差异。结果在89例肾移植患者中,等位基因1236T、2677T、2677A、3435T突变频率分别为66%、43%、18%和37%。肾移植术后1 mo内,G2677T/A基因多态性与CsA的药动学有相关性,2个等位基因都发生突变的患者,其剂量校正c0,在术后1~7 d、8~15 d和16~30 d比野生型分别提高51%(P=0.005)、32%(P=0.002)和63%(P<0.001)。在术后16~30 d,无论携带有1个或2个突变等位基因的患者,剂量校正c2都要比野生型患者高26%(P=0.007)和19%(P=0.041)。C1236T的剂量校正c0在术后8~15...     

Human MDR1 polymorphism: G2677T/A and C3435T have no effect on MDR1 transport activities

The two most frequently observed single nucleotide polymorphisms (SNPs) of the human multidrug resistance 1 (MDR1) gene are 2677G/T/A (893Ala/Ser/Thr) and 3435C/T (no amino acid substitution). In this study, six forms of MDR1 cDNAs with the SNPs were expressed in LLC-PK1 cells and their transport activities were determined. Nearly identical amounts of the recombinant MDR1 proteins were expressed in the established cell lines using the Flp recombinase, which integrates a gene of interest at a specific genomic location. Four structurally diverse compounds: verapamil, digoxin, vinblastine and cyclosporin A, were examined for transcellular transport activities and intracellular accumulation. No significant differences were observed between cells expressing five polymorphic types of the MDR1 cDNAs (2677G/3435T, 2677A/3435C, 2677A/3435T, 2677T/3435C, 2677T/3435T) and cells expressing the wild-type (2677G/3435C). These results suggested that the two frequently observed MDR1 SNPs had no effect on the transport activities of MDR1 proteins expressed in LLC-PK1 cells in vitro, and other genetic or environmental factors might control the expression of MDR1 and the in vivo activity of MDR1.     

Expression polymorphism of the blood-brain barrier component P-glycoprotein (MDR1) in relation to Parkinson's disease

Because drug transporters such as P-glycoprotein, the product of the multidrug resistance (MDR1 ) gene, contribute to the function of the blood-brain barrier, we hypothesized that differences in their expression could affect the uptake of neurotoxic xenobiotics, thereby modulating interindividual susceptibility for neurological disorders such as Parkinson's disease. In a pilot case-control study comprising 95 Parkinson's disease patients (25 early-onset patients with onset age < or = 45 years) and 106 controls we analysed the three common polymorphisms, 3435C >T in exon 26, 2677G > T,A in exon 21, and -129T > C in exon 1b. There were no statistically significant associations between any of these polymorphisms and Parkinson's disease. However, a distribution pattern consistent with our hypothesis was observed in that the frequency of the 3435T/T genotype, which had previously been associated with decreased P-glycoprotein expression and function, was highest in the early-onset Parkinson's disease group (36.0%), second-highest in the late-onset Parkinson's disease group (22.9%), and lowest in the control group (18.9%). Furthermore, we confirmed that the MDR1 exon 21 and exon 26 polymorphisms are in significant linkage disequilibrium since the [2677G, 3435C] and [2677T, 3435T] haplotypes were far more frequently observed than expected. In conclusion, MDR1 and other drug transporters represent plausible candidates as Parkinson's disease risk genes. Larger studies are required to confirm this role in the etiology of Parkinson's disease.     

Effect of genetic polymorphisms of CYP3A5 and MDR1 on cyclosporine concentration during the early stage after renal transplantation in Chinese patients co-treated with diltiazem

Objective  The aim of this study was to assess the influence of the cytochrome (CYP450)3A5 and multidrug resistance (MDR1) gene polymorphisms on cyclosporine A (CsA) trough concentration during the early stage after renal transplantation in Chinese patients co-treated with diltiazem. Methods   CYP3A5*3 (A6986G) and MDR1 C1236T, G2677T/A and C3435T polymorphisms were determined by PCR followed by restriction fragment length polymorphism (RFLP) analysis. A total of 112 Chinese renal transplant patients were enrolled in the study. The whole blood trough concentration was measured at 7 days after transplantation, and the dose-adjusted trough levels were compared among the different genotypes. Results  The dose-adjusted trough levels of CsA were significantly higher in MDR1 2677TT carriers than in GG plus GT carriers (59.5 ± 15.9 vs. 34.5 ± 9.4 vs. 43.2 ± 13.6 ng/mL per mg per kg; P < 0.0001). In patients who were co-treated with diltiazem, compared with carriers of haplotype T-T-C, the carriers of haplotype C-G-C and haplotype T-G-T had significantly lower dose-adjusted trough blood concentrations of CsA than the non-carrier group (P = 0.002, P = 0.000 and P = 0.000, respectively). However, no evidence was found that there was a relationship between the CYP3A5*3, MDR1 C1236T and MDR1 C3435T polymorphisms and CsA dose-adjusted trough concentrations. Conclusion  This study demonstrated that the G2677T/A single nucleotide polymorphisms in MDR1 and MDR1 haplotypes C-G-C, T-G-T and T-T-C are associated with the CsA concentration during the very early post-transplant period in Chinese renal transplant patients co-treated with diltiazem. These polymorphisms may be useful for determining the appropriate initial dose of CsA after renal transplantation.     

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.     

Tacrolimus dosing in adult lung transplant patients is related to cytochrome P4503A5 gene polymorphism

Tacrolimus is a potent immunosuppressive agent used in lung transplantation and is a substrate for both P-glycoprotein (P-gp, encoded by the gene MDR1) and cytochrome (CYP) P4503A. A previous study by the authors identified a correlation between the tacrolimus blood level per dose with CYP3A5 and MDR1 gene polymorphisms in pediatric heart transplant patients. The objective of this study was to confirm the influence of these polymorphisms on tacrolimus dosing in adult lung transplant patients. Adult lung transplant patients who had been followed for at least 1 year after lung transplantation were studied. Tacrolimus blood level (ng/mL) per dose (mg/day) at 1, 3, 6, 9, and 12 months after transplantation was calculated as [L/D]. DNA was extracted from blood. MDR1 3435 CC, CT, and TT; MDR1 2677 GG, GT, and TT; and CYP3A5*1 (expressor) and *3 (nonexpressor) genotypes were determined by PCR amplification, direct sequencing, and sequence evaluation. Eighty-three patients were studied. At 1, 3, 6, 9, and 12 months after the transplant, a significant difference in [L/D] was found between the CYP3A5 expressor versus nonexpressor genotypes (mean +/- SD of 1.49 +/- 0.88 vs. 3.11 +/- 4.27, p = 0.01; 1.23 +/- 0.82 vs. 3.44 +/- 8.97, p = 0.05; 1.32 +/- 0.96 vs. 3.81 +/- 6.66, p = 0.005; 0.95 +/- 1.19 vs. 3.74 +/- 5.98, p = 0.0015; and 0.45 +/- 0.2 vs. 3.76 +/- 6.75, p = 0.0001, respectively). MDR1 G2677T and C3435T genotypes had only minimal effects on [L/D] at 1 and 3 months after transplantation. This study confirms the relationship of CYP3A5 polymorphisms to tacrolimus dosing in organ transplant patients. CYP3A5 expressor genotypes required a larger tacrolimus dose to achieve the same blood levels than the CYP3A5 nonexpressors at all time points during the first posttransplant year. This was not uniformly true for MDR1. The authors therefore conclude that tacrolimus dosing in adult lung transplant patients is associated with CYP3A5 gene polymorphisms.     

Common ATP-binding cassette B1 variants are associated with increased digoxin serum concentration

BACKGROUND AND OBJECTIVE: Digoxin is a known substrate of ATP-binding cassette B1 (ABCB1/MDR1). The results of studies on the association between ABCB1 polymorphisms and digoxin kinetics, however, remain contradictory. Almost all studies were small and involved only single dose kinetics. The goal of this study was to establish ABCB1 genotype effect on digoxin blood concentrations in a large cohort of chronic digoxin users in a general Dutch European population. METHODS: Digoxin users were identified in the Rotterdam Study, a prospective population-based cohort study of individuals aged 55 years and above. Digoxin blood levels were gathered from regional hospitals and laboratories. ABCB1 single nucleotide polymorphisms (SNPs) 1236C-->T, 2677G-->T/A, and 3435C-->T were assessed on peripheral blood DNA using Taqman assays. We studied the association between the ABCB1 genotypes and haplotypes, and digoxin blood levels using linear regression models adjusting for potential confounders. RESULTS: Digoxin serum levels and DNA were available for 195 participants (56.4% women, mean age 79.4 years). All three ABCB1 variants were significantly associated with serum digoxin concentration (0.18-0.21 microg/l per additional T allele). The association was even stronger for the 1236-2677-3435 TTT haplotype allele [0.26 mug/l (95% CI 0.14-0.38)], but absent for other haplotypes (CGC allele considered referent), suggesting an interaction of SNPs in a causal haplotype instead of individual SNP effects. CONCLUSION: We found that the common ABCB1 1236C-->T, 2677G-->T, and 3435C-->T variants and the associated TTT haplotype were associated with higher digoxin serum concentrations in a cohort of elderly European digoxin users in the general population.