Influence of uridine diphosphate (UDP)-glucuronosyltransferases and ABCC2 genetic polymorphisms on the pharmacokinetics of mycophenolic acid and its metabolites in Chinese renal transplant recipients

The aim was to investigate the effect of UGT1A9, UGT1A8, UGT2B7 and ABCC2 polymorphism on the pharmacokinetics of mycophenolic acid (MPA) and its metabolites phenolic glucuronide (MPAG) and acyl glucuronide (AcMPAG) in Chinese renal transplant recipients. Single nucleotide polymorphisms (SNP) in UGT1A9-118(dT)₉/₁₀, UGT1A9 T-440C/C-331T, UGT1A8*3, UGT2B7 G211T, UGT2B7 C802T, ABCC2 C-24T, and ABCC2 G1249A were detected. A total of 46 recipients were enrolled in the pharmacokinetics study at day 30 after kidney transplantation. Differences in the MPA pharmacokinetic profiles confirmed large inter-patient variation of MPA exposure. A statistical significant increase in the dose-adjusted AUC_6–12 level of MPA was found in patients bearing the -118(dT)₁₀ allele of the UGT1A9 gene (T₉ = 7.34 ± 4.11 mg h ml^?1 g^?1; T₉/T₁₀ = 11.54 ± 7.62 mg h ml^?1 g^?1; and T₁₀ = 11.89 ±8.76 mg h ml^?1 g^?1, p = 0.041). A similar trend was also observed for the dose-adjusted AUC_0–12 and AUC_6–12 of MPAG. Patients carrying the heterozygous mutant alleles of ABCC2 G1249A exhibited higher AUC_6–12/D of AcMPAG than those with wild-type genotype (p = 0.016). The other SNPs that were genotyped did not cause any significant variation in MPA and MPAG pharmacokinetic parameters. In conclusion, the enterohepatic recirculation of MPA in the patients seems to be more extensive in UGT1A9-118(dT)₁₀ allele carriers, and the exposure of AcMPAG is higher in patients carrying ABCC2 G1249A genotype than those with wild-type genotype.     

Influence of carboxylesterase 2 genetic polymorphisms on mycophenolic acid pharmacokinetics in Japanese renal transplant recipients

1. Mycophenolic acid (MPA), converted from the prodrug mycophenolate mofetil (MMF), is generated by intestinal and hepatic esterases. The role of carboxylesterase (CES) in MMF hydrolysis was examined in vitro using human liver microsomes. V_max and K_m values of MMF hydrolysis in pooled human liver microsomes were 1368?±?44 nmol min^?1 mg^?1 protein and 1030?±?65?μM, respectively.

2. Hydrolytic activity was inhibited by the CES inhibitors phenylmethylsulfonylfluoride, bis-p-nitorophenylphosphate and diisopropylfluorophosphate, with IC₅₀ values of 77.1, 3.59 and 0.0312?μM, respectively.

3. Eighty Japanese renal transplant recipients that received repeated-doses of MMF, tacrolimus and prednisolone, were evaluated for MPA pharmacokinetics 28 days after transplantation to investigate the relationship between MPA pharmacokinetics and CES2 genetic polymorphisms.

4. No significant differences in MPA pharmacokinetics were observed between CES2 A4595G, C8721T or A-1548G genotype groups. CES2 allelic variants also did not appear to affect plasma MPA concentrations between individuals.

5. In conclusion, the study demonstrated that while CES1 and/or CES2 are involved in the hydrolysis of MMF to MPA, CES2 allelic variants appeared to make only a minor contribution to inter-personal differences in MPA pharmacokinetics.

     

Influence of SLCO1B1, 1B3, 2B1 and ABCC2 genetic polymorphisms on mycophenolic acid pharmacokinetics in Japanese renal transplant recipients

Objective We investigated the association between mycophenolic acid (MPA) pharmacokinetics and organic anion-transporting polypeptide (OATP/SLCO)1B1, 1B3, 2B1 and multidrug resistance-association protein 2 (MRP2/ABCC2) genetic polymorphisms and diarrhea. Methods Eighty-seven renal allograft recipients were given repeated doses of mycophenolate mofetil every 12 h at a designated time (09:00 and 21:00). The pharmacokinetics of MPA were analyzed on day 28 posttransplantation. Results The dose-adjusted area under the cuve (AUC)_6–12 of MPA, an estimate of enterohepatic recirculation, was greater in SLCO1B3 T334G GG (or G699A AA) carriers than in TT carriers (or G699A GG) (40 vs. 25 ng·h/mL per milligram, respectively, P = 0.0497). None of the polymorphism of SLCO1B1, SLCO2B1, or ABCC2 C-24T were associated with MPA pharmacokinetics or diarrhea. However, the oral clearance of MPA in recipients having both the SLCO1B3 T334G GG genotype and the ABCC2 C-24T T allele was significantly lower than in patients having both the SLCO1B3 T334G TT and ABCC2 C-24T CC genotypes (0.15 vs. 0.18 L/h per kilogram, respectively, P = 0.0010). Conclusions MPA excretion into bile in patients with SLCO1B3 T334G GG (or G699A AA) was higher than in those with T334G TT (or G699A GG), probably resulting in a higher AUC_6–12 value of MPA. MPA uptake into hepatocytes and excretion into bile at first pass may be greater in SLCO1B3 T334G GG carriers than in TT carriers. In addition, the ABCC2 C-24T polymorphism also seems to be associated with enhanced enterohepatic circulation of MPA. The SLCO1B3 and ABCC2 transporters rather than uridine diphosphate-glucuronosyltransferase (UGT) may partly affect interindividual variety in plasma MPA concentration.     

Influence of UGT1A7 and UGT1A9 intronic I399 genetic polymorphisms on mycophenolic acid pharmacokinetics in Japanese renal transplant recipients

UGT1A7 and UGT1A9 are uridine diphosphate-glucuronosyltransferase isoforms involved in the glucuronidation of mycophenolic acid (MPA). The aim of this study was to elucidate MPA pharmacokinetics in UGT1A7 and UGT1A9 intronic I399 genotypes in Japanese adult renal transplant recipients. Eighty recipients were given repeated doses of combination immunosuppressive therapy consisting of mycophenolate mofetil and tacrolimus every 12 hours at a designated time (9:00 am and 9:00 pm). On day 28 after renal transplantation, plasma MPA concentrations were measured by high-performance liquid chromatography. All patients had UGT1A9 98TT/-275TT/-2152CC and UGT1A10 177GG/605CC genotypes. The UGT1A7*1/*1, *1/*2, *1/*3, *2/*3, and *3/*3 genotypes were detected in 35 (43.8%), five (6.2%), 28 (35.0%), eight (10.0%), and four (5.0%) patients, respectively, and the UGT1A9 I399C/C, C/T, and T/T genotypes were detected in 12 (15.0%), 33 (41.2%), and 35 (43.8%) patients of the 80 Japanese recipients. There were no significant differences in MPA pharmacokinetics among UGT1A7 or UGT1A9 intronic I399 genotype groups. The mean dose-adjusted area under the plasma concentration-time curve from zero to 12 hours (AUC0-12) of MPA in UGT1A7*1/*1, *1/*2, *1/*3, *2/*3, and *3/*3 were 95, 98, 99, 88, and 86 ng.h/mL/mg, respectively (P = 0.9475). The mean dose-adjusted AUC0-12 of MPA in UGT1A9 I399C/C, C/T, and T/T were 87, 99, and 95 ng.h/mL/mg, respectively (P = 0.6937). The dose-adjusted trough levels of MPA in UGT1A9 I399C/C, C/T, and T/T were 5.4, 5.5, and 4.7 ng/mL/mg (P = 0.5845). Although UGT1A7*3 and UGT1A9 I399C/C are known to have low-activity variants when studied in vitro, they do not have reduced in vivo MPA glucuronidation activity. UGT1A7 and UGT1A9 I399 polymorphisms do not contribute to interindividual differences in MPA pharmacokinetics.     

Limited influence of UGT1A1*28 and no effect of UGT2B7*2 polymorphisms on UGT1A1 or UGT2B7 activities and protein expression in human liver microsomes

AIMS: UGT1A1 and UGT2B7 are enzymes that commonly contribute to drug glucuronidation. Since genetic factors have been suggested to contribute to variability in activities and expression levels of these enzymes, a quantitative assessment of the influence of the major genotypes (UGT1A1*28 or UGT2B7*2) on enzyme activities was conducted. METHODS: Using a bank of microsomal samples from 59 human livers, the effect of UGT1A1*28 or UGT2B7*2 polymorphisms were investigated on rates of estradiol 3-glucuronidation (a marker of UGT1A1 enzyme activity) or zidovudine glucuronidation (a marker of UGT2B7 enzyme activity) and levels of immunoreactive protein for each enzyme. Glucuronidation rates for both enzymes were measured at K(m)/S(50) and 10 times K(m)/S(50) concentrations. RESULTS: UGT1A1 and UGT2B7 enzyme activities varied up to 16-fold and sixfold, respectively. Rates at K(m)/S(50) concentration closely correlated with rates at 10 times K(m)/S(50) concentration for both enzymes (but not at 1/10th K(m) for UGT2B7). Enzyme activities correlated with relative levels of immunoreactive protein for UGT1A1 and UGT2B7. Furthermore, rates of zidovudine glucuronidation correlated well with rates of glucuronidation of the UGT2B7 substrate gemcabene, but did not correlate with UGT1A1 enzyme activities. For the UGT1A1*28 polymorphism, consistent with levels of UGT1A1 immunoreactive protein, mean UGT1A1 activity was 2.5- and 3.2-fold lower for TA(6)/TA(7) (P < 0.05) and TA(7)/TA(7) (P < 0.001) genotypes in comparison with the TA(6)/TA(6) genotype. CONCLUSIONS: Relative to the observed 16-fold variability in UGT1A1 activity, these data indicate only a partial (approximately 40%) contribution of the UGT1A1*28 polymorphism to variability of interindividual differences in UGT1A1 enzyme activity. For the UGT2B7*2 polymorphism, genotype had no influence on immunoreactive UGT2B7 protein or the rate of 3'-azido-3'-deoxythymidine glucuronidation.     

UGT1A9C-2152T和UGT2B7G211T突变在中国汉族人群中的分布

目的建立Touch-down PCR/RFLP的方法检测UGT1A9 C-2152T突变,建立PCR/RFLP的方法检测UGT2B7 G211T突变,确定其在中国汉族人群中的突变频率.方法采用Touch-down PCR/RFLP方法,对100名无亲缘关系的汉族男性志愿者进行UGT1A9 C-2152T的基因分型.采用PCR/RFLP方法,对363名无亲缘关系的汉族志愿者(其中男性263名、女性100名)进行UGT2B7 G211T的基因分型.结果在100名中国汉族男性受试者中,末发现UGT1A9 C-2152T的突变,与亚洲人通过测序报道的结果基本一致.在363名汉族受试者中,UGT2B7 G211T突变发生频率为 0.158,与日本人通过测序报道的结果基本一致.中国男性和女性的等位基因频率分别为 0.128 和 0.110,男性的突变频率比女性高(χ2=6.784, P=0.034).结论用PCR/RFLP的方法对UGT2B7 G211T突变分型的方法简便、快速、重复性好,可用于大样本人群的基因检测.UGT2B7 G211T突变在中国汉族人中发生频率较高.     

UGT1A9 C-2152T和UGT2B7 G211T突变在中国汉族人群中的分布

目的：建立Touch-down PCR/RFLP的方法检测UGT1A9C-2152T突变,建立PCR/RFLP的方法检测UGT2B7G211T突变,确定其在中国汉族人群中的突变频率。方法：采用Touch-down PCR/RFLP方法,对100名无亲缘关系的汉族男性志愿者进行UGT1A9C-2152T的基因分型。采用PCR/RFLP方法,对363名无亲缘关系的汉族志愿者（其中男性263名、女性100名）进行UGT2B7 G211T的基因分型。结果：在100名中国汉族男性受试者中,末发现UGT1A9C-2152T的突变,与亚洲人通过测序报道的结果基本一致。在363名汉族受试者中,UGT2B7G211T突变发生频率为0.158,与日本人通过测序报道的结果基本一致。中国男性和女性的等位基因频率分别为0.128和0.110,男性的突变频率比女性高（χ^2=6.784,P=0.034）。结论：用PCR/RFLP的方法对UGT2B7 G211T突变分型的方法简便、快速、重复性好,可用于大样本人群的基因检测。UGT2B7G211T突变在中国汉族人中发生频率较高。     

Glucuronidation of 1'-hydroxyestragole (1'-HE) by human UDP-glucuronosyltransferases UGT2B7 and UGT1A9.

Estragole (4-allyl-1-methoxybenzene) is a naturally occurring food flavoring agent found in basil, fennel, bay leaves, and other spices. Estragole and its metabolite, 1'-hydroxyestragole (1'-HE), are hepatocarcinogens in rodent models. Recent studies from our laboratory have shown that glucuronidation of 1'-HE is a major detoxification pathway for estragole and 1'-HE, accounting for as much as 30% of urinary metabolites of estragole in rodents. Therefore, this study was designed to investigate the glucuronidation of 1'-HE in human liver microsomes in vitro and identify the specific uridine diphosphate glucuronosyltransferase (UGT) isoforms responsible for 1'-HE glucuronidation. The formation of the glucuronide of 1'-HE (1'-HEG) followed atypical kinetics, and the data best fit to a Hill equation, resulting in apparent kinetic parameters of Km = 1.45 mM, Vmax = 164.5 pmoles/min/mg protein, and n = 1.4. There was a significant intersubject variation in 1'-HE glucuronidation in 27 human liver samples, with a CV of 42%. A screen of cDNA expressed UGT isoforms indicated that UGT2B7 (83.94 +/- 0.188 pmols/min/mg), UGT1A9 (51.36 +/- 0.72 pmoles/min/mg), and UGT2B15 (8.18 +/- 0.037 pmoles/min/mg) were responsible for 1'-HEG formation. Glucuronidation of 1'-HE was not detected in cells expressing UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A7, UGT1A8, and UGT1A10. 1'-HE glucuronidation in 27 individual human liver samples significantly (p < 0.05) correlated with the glucuronidation of other UGT2B7 substrates (morphine and ibuprofen). These results imply that concomitant chronic intake of therapeutic drugs and dietary components that are UGT2B7 and/or UGT1A9 substrates may interfere with estragole metabolism. Our results also have toxicogenetic significance, as UGT2B7 is polymorphic and could potentially result in genetic differences in glucuronidation of 1'-HE and, hence, toxicity of estragole.     

焦磷酸测序技术检测UGT1A3和UGT2B7在中国汉族人群中的基因多态性

目的建立焦磷酸测序技术(pyrosequencing)研究二相代谢酶UGT1A3和UGT2B7基因多态性在中国汉族人群中的分布。方法应用带生物素标记扩增引物并经PCR扩增和Beads分离,制备UGT1A3和UGT2B7焦磷酸测序单倍摸板。在PYroMarkID焦磷酸测序上进行焦磷酸测序,检测233血样的DNA标本的17个SNP位点,以确定血样DNA标本的的基因型。结果 233例血样的DNA标本中,UGT1A3等位基因有9种表型,分别为UGT1A3*1*1、UGT1A3*1*2、UGT1A3*1*3、UGT1A3*1*4、UGT1A3*1*5、UGT1A3*2*3、UGT1A3*2*4、UGT1A3*3*3和UGT1A3*3*5。UGT2B7-1和UGT2B7-2各有3种基因型,分别为G/G型、G/T型、T/T和C/C型、C/T型、T/T型。结论我国汉族人群中UGT1A3和UGT2B7基因突变较高。     

Influence of drug transporters and UGT polymorphisms on pharmacokinetics of phenolic glucuronide metabolite of mycophenolic acid in Japanese renal transplant recipients

Mycophenolic acid (MPA) is mainly glucuronized by uridine diphosphate-glucuronosyltransferases (UGTs) into the phenolic MPA glucuronide (MPAG). MPAG is excreted by transporters such as organic anion-transporting polypeptide (gene SLCO), multidrug resistance protein 2 (gene ABCC2), breast cancer resistance protein (BCRP, gene ABCG2) or P-glycoprotein (gene ABCB1). This study investigated the association of UGTs, SLCOs, ABCB1, ABCC2, and ABCG2 polymorphisms with MPAG pharmacokinetics in 80 Japanese renal transplant recipients. Eighty recipients were given repeated doses of combination immunosuppressive therapy consisting of mycophenolate mofetil and tacrolimus every 12 hours at a designated time (0900 and 2100). On day 28, after renal transplantation, plasma concentrations of MPA and MPAG were measured by high-performance liquid chromatography. There were no significant differences in the area under the plasma concentration-time curve (AUC) ratio of MPAG/MPA between UGT1A1, UGT1A6, UGT1A7, UGT1A8, and UGT1A9 I399C/T genotypes. On the other hand, the median dose-adjusted AUC0-12 of MPAG in SLCO1B1 1a/1a+1a/1b+1b+1b (n = 53) and 1a/*15 + 1b/*15+*15/*15 (n = 27) were 1549 and 1134 mg.h L g, respectively (P = 0.03004 in multivariate analysis). The median dose-adjusted AUC0-12 of MPAG in SLCO1B3 334T/T+T/G (699G/G+G/A, n = 46) and 334G/G (699A/A, n = 34) was 1191 and 1580 mg.h L g, respectively (P = 0.02792 in multivariate analysis). There were no significant differences in the dose-adjusted AUC0-12 of MPAG between the ABCB1 C3435T and ABCC2 C-24T genotypes. However, the dose-adjusted AUC0-12 of MPAG was significantly lower in recipients with ABCG2 421C/A+A/A (n = 44) than in those with C/C (n = 36) (P = 0.0295). In conclusion, our findings showed that MPAG pharmacokinetics were significantly influenced by SLCO1B1 and SLCO1B3 polymorphisms and not by UGT polymorphisms. BCRP rather than multidrug resistance protein 2 seems to be the transporter associated with biliary excretion of MPAG.     

Total and free mycophenolic acid and its 7-O-glucuronide metabolite in Chinese adult renal transplant patients: pharmacokinetics and application of limited sampling strategies

Objective This study aimed to investigate the pharmacokinetic characteristics of total and free mycophnolic acid (MPA) and its 7-O-glucuronide metabolite (MPAG) in Chinese renal transplant recipients. In addition, limited sampling strategies were developed to estimate the individual area under concentration curve (AUC) of total and free MPA. Methods Total and free MPA and MPAG concentrations were determined by high performance liquid chromatography. Whole 12-h pharmacokinetic profiles were obtained on the 10th day after operation in 12 adult Chinese de novo renal transplant recipients administrated with mycophenolate mofetil (MMF, 750 mg bid), cyclosporine and corticosteroids. Limited sampling strategies with jackknife technique, a resampling method, and Bland-Altman analysis were employed to develop equations to estimate total and free MPA AUC. Results The pattern of total and free MPA and MPAG plasma concentration-time curves in the cohort of patients taking lower doses of MMF was consistent with previous reports of Caucasian patients taking MMF 1 g bid, except that dose-normalized exposure of total and free MPAG was much lower in the current study than in those of the Caucasians. The mean C _max and AUC_0–12h of total and free MPA were 9.4 ± 3.4 mg/L, 20.2 ± 6.5 mg·h/L and 0.4 ± 0.4 mg/L, 0.7 ± 0.5 mg·h/L, respectively, whereas mean C _max and AUC_0–12h of total and free MPAG were 97.3 ± 32.6 mg/L, 656.0 ± 148.0 mg·h/L and 29.9 ± 8.5 mg/L, 222.0 ± 58.1 mg·h/L respectively. The mean fractions of free MPA and MPAG were 3.5 ± 2.0 and 34.6 ± 8.0%, respectively. No determinant was identified to influence the pharmacokinetics of total and free MPA and MPAG or the free fraction of MPA and MPAG. The combinations of C _2h−C _4h and C _1h-C _2h-C _3h were the best to estimate free and total MPA AUC_0–12h respectively, whereas the combination of C _2h-C _3h-C _4h and C _1h-C _2h-C _4h was the best to estimate both simultaneously. Conclusion This is the first time that the pharmacokinetics profile of total and free MPA and its main metabolite MPAG has been examined in Chinese adult renal transplant patients. The limited sampling strategies proposed to estimate individual free and total MPA AUC could be useful in optimizing patient care.     

UGT2B7 C802T和G211T基因多态性对癫痫患者丙戊酸代谢的影响

目的:检测尿苷二磷酸葡糖醛酰转移酶UGT2B7 C802T和G211T等位基因在癫痫患者中的分布和突变频率,探讨UGT2B7 C802T和G211T基因型对癫痫患者丙戊酸代谢的影响。方法:直接化学发光法测定丙戊酸血药浓度,PCR-RFLP技术检测UGT2B7 C802T和G211T基因多态性,PCR扩增产物直接测序验证基因型检测方法的可靠性。结果:102例癫痫患者中UGT2B7 C802T位点野生型CC14例,杂合突变型和纯合突变型CT、TT分别为46例和42例;UGT2B7 G211T位点的野生型GG78例,突变型GT、TT分别为23例和1例;位点802CC野生基因型患者服用单位剂量(mg·kg^-1)后的血药浓度为(3.02±1.32) μg·kg·ml^-1·mg^-1,CT基因型患者为(2.11±1.26) μg·kg·ml^-1·mg^-1,TT基因型患者为(2.31±1.25) μg·kg·ml^-1·mg^-1,CT、TT患者血药浓度较CC患者明显偏低,差异有统计学意义。位点211GG基因型患者服用单位剂量(mg·kg^-1)引起的血药浓度为(2.28±1.32) μg·kg·ml^-1·mg^-1,GT基因型患者为(2.30±1.38) μg·kg·ml^-1·mg^-1,GG型与GT型患者间无统计学差异。结论:UGT2B7 C802T基因多态性与丙戊酸的血药浓度有显著相关性,UGT2B7 G211T位点基因多态性与丙戊酸的血药浓度无显著相关性。临床上个体血药浓度的差异可能与UGT2B7 C802T基因多态性有关。     

葡萄糖醛酸转移酶UGT2B7-A268G基因多态性对癫痫儿童丙戊酸血药浓度的影响

目的：在丙戊酸（VPA）单药治疗的癫痫儿童中评估葡萄糖醛酸转移酶UGT2B7-A268G位点的遗传基因多态性对VPA血清浓度的影响。方法：本研究纳入200例癫痫患儿的丙戊酸血药浓度,测定VPA稳态血清浓度。对UGT2B7编码区的A268G采用聚合酶链反应（RPLF）扩增进行基因鉴定分型。根据UGT2B7基因多态性分析VPA血清药物浓度与基因多态性的关系。结果：携带变异UGT2B7-268G一个基因型或纯合基因患儿的VPA血清药物浓度显著高于携带AA基因的患儿。由于儿童个体差异较大,根据年龄、体质量调整VPA浓度后与基因多态性仍然显著关联（P<0.05）。UGT2B7-A268G的基因多态性与Hardy-Weinberg平衡一致（P>0.05）,其中UGT2B7-268A>G等位基因频率分布的是30.00%,而G突变的基因分布频率为70.00%。结论：癫痫患儿UGT2B7基因的A268G突变可能改变丙戊酸的药物代谢动力学过程,并且不受年龄、体质量等因素干扰。UGT2B7的基因多态性对儿童丙戊酸血药浓度产生影响,测定其基因型对于获得适当的丙戊酸稳态浓度和设定起始用药剂量有积极意义     

Population pharmacokinetic modelling for enterohepatic circulation of mycophenolic acid in healthy Chinese and the influence of polymorphisms in UGT1A9

AIMS

To establish a population pharmacokinetic model that describes enterohepatic circulation (EHC) of mycophenolic acid (MPA) based on physiological considerations and to investigate the influence of polymorphisms of UGT1A9 on the pharmacokinetics of MPA.

METHODS

Pharmacokinetic data were obtained from two comparative bioavailability studies of oral mycophenolic mofetil formulations. Nonlinear mixed effects modelling was employed to develop an EHC model including both MPA and its main glucuronide metabolite (MPAG) simultaneously. Demographic characteristics and UGT1A9 polymorphisms were screened as covariates.

RESULTS

In total, 590 MPA and 589 MPAG concentration–time points from 42 healthy male volunteers were employed in this study. The chain compartment model included an intestinal compartment, a gallbladder compartment, a central and a peripheral compartment for MPA and a central compartment for MPAG. The typical population clearance (CL/F) estimates with its relative standard error for MPA and MPAG were 10.2 l h⁻¹ (5.7%) and 1.38 l h⁻¹ (6.9%), respectively. The amount of MPA recycled in the body was estimated to be 29.1% of the total amount absorbed. Covariate analysis showed that body weight was positively correlated with CL/F of MPA, intercompartment CL/F of MPA and distribution volume of MPA peripheral compartment. Polymorphisms of UGT1A9 did not show any effect on the pharmacokinetics of MPA and MPAG. The model evaluation tests indicated that the proposed model can describe the pharmacokinetic profiles of MPA and MPAG in healthy Chinese subjects.

CONCLUSIONS

The proposed model may provide a valuable approach for planning future pharmacokinetic–pharmacodynamic studies and for designing proper dosage regimens of MPA.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Mycophenolic acid (MPA) undergoes enterohepatic circulation (EHC) in the body and several population models have been proposed to describe this process using sparse data.
• Recent studies in Whites have found that polymorphism in UGT1A9 could partly explain the large interindividual variability associated with the pharmacokinetics of MPA.

WHAT THIS STUDY ADDS

• A new population pharmacokinetic model for EHC combining MPA and its main glucuronide metabolite (MPAG) simultaneously was established based on physiological aspects of biliary excretion using intensive sampling data.
• Pharmacokinetic profiles of MPA and MPAG with the UGT1A9 polymorphism in healthy Chinese were characterized.

     

Contribution of UDP-glucuronosyltransferases 1A9 and 2B7 to the glucuronidation of indomethacin in the human liver

Objective We characterized the kinetics of indomethacin glucuronidation by recombinant UDP-glucuronosyltransferase (UGT) isozymes and human liver microsomes (HLM) and identified the human UGT isozymes involved. Methods Indomethacin glucuronidation was investigated using HLM and recombinant human UGT isozymes. Human UGTs involved in indomethacin glucuronidation were assessed in kinetic studies, chemical inhibition studies, and correlation studies. Results Among the UGT isozymes investigated, UGT1A1, 1A3, 1A9, and 2B7 showed glucuronidation activity for indomethacin, with UGT1A9 possessing the highest activity, followed by UGT2B7. Glucuronidation of indomethacin by recombinant UGT1A9 and 2B7 showed substrate inhibition kinetics with K _m values of 35 and 32 μM, respectively. The glucuronidation of indomethacin was significantly correlated with morphine 3OH-glucuronidation (r = 0.69, p < 0.05) and 3′-azido-3′-deoxythymidine glucuronidation (r = 0.82, p < 0.05), a reaction mainly catalyzed by UGT2B7. Propofol inhibited indomethacin glucuronidation in HLM with an IC₅₀ value of 248 μM, which is between the IC₅₀ value in recombinant UGT1A9 (106 μM) and UGT2B7 (> 400 μM). Conclusions These findings suggest that UGT2B7 plays a predominant role in indomethacin glucuronidation in the human liver and that UGT1A9 is partially involved.     

UGT1A8*2基因多态性与肝移植患者术后吗替麦考酚酯所致不良反应的相关性研究

目的：探究肝移植受者UGT1A8^*2（G173C227）基因多态性是否与霉酚酸酯（mycophenolate mofetil,MMF）所致相关不良反应有关。方法：将105例患者按不良反应类型分为骨髓抑制组、胃肠道反应组、感染组和对照组;记录患者的年龄、性别、身高、质量、BMI值、移植年月等临床资料以及患者移植术后3,6,12,24月时的MMF口服日剂量、浓度、血糖、血常规、血脂及肝功能,并对以上数据进行统计学分析;采用酶增强免疫测定技术（EMIT^©2000）测定肝移植受者霉酚酸（mycophenolic acid,MPA）血药浓度;采用限制性片段长度多态性（PCR-RFLP）法检测105例患者UGT1A8^*2（G173C227）位点的多态性。结果：105例入组患者中,16例骨髓抑制,7例胃肠道反应,11例感染;UGT1A8^*2（G173C227）基因突变频率为58.57%,骨髓毒性组GG基因型的分布明显高于对照组（P<0.05）;术后3月时GG基因型组的谷浓度显著高于CC基因型组（P<0.05）;Logistic回归模型显示,UGT1A8^*2（G173C227）GG基因型是肝移植术后发生MMF所致骨髓抑制毒性的危险因素。结论：UGT1A8^*2（G173C227）位点的多态性与肝移植术后MMF所致相关不良反应有关,GG基因型患者更容易发生骨髓抑制毒性。     

Effect of hepatic drug transporter polymorphisms on the pharmacokinetics of mycophenolic acid in patients with severe renal dysfunction before renal transplantation

1.?The objective of this study was to examine the association of UGT1A9, SLCO, and ABCC polymorphisms with mycophenolic acid (MPA) pharmacokinetics in ABO blood type (ABO) incompatible patients with severe renal dysfunction pre-transplantation.

2.?In all patients, on day 14 after beginning mycophenolate mofetil (MMF) treatment (1 week before transplantation) and on day 28 after renal transplantation, samples were collected just prior to and 1, 2, 3, 4, 6, 9, and 12?h after oral MMF administration.

3.?The median dose-adjusted AUC_0–12 of MPA after renal transplantation was significantly lower than before transplantation (57.9 versus 76.5?μg h/mL, respectively, p?=?0.002).

4.?Although the enterohepatic circulation of MPA pre-transplantation was extremely high (57.6%), this level was significantly reduced after renal transplantation (34.6%).

5.?In the multivariate analysis, pre-transplantation, patients with the SLCO1B3 334T allele (p?=?0.003), higher alanine aminotransferase (p?=?0.002), and lower body weight were independently predictive for a higher dose-adjusted AUC_0–12 of MPA.

6.?In patients with severe renal dysfunction pre-transplantation, MPA is excreted mainly to bile from the liver, and as a consequence, the SLCO1B3 334T?>?G polymorphism was found to be significantly associated with MPA exposure.     

Amino terminal domains of human UDP-glucuronosyltransferases (UGT) 2B7 and 2B15 associated with substrate selectivity and autoactivation

Despite the important role of UDP-glucuronosyltransferases (UGT) in the metabolism of drugs, environmental chemicals and endogenous compounds, the structural features of these enzymes responsible for substrate binding and selectivity remain poorly understood. Since UGT2B7 and UGT2B15 exhibit distinct, but overlapping, substrate selectivities, UGT2B7-UGT2B15 chimeras were constructed here to identify substrate binding domains. A UGT2B7-15-7 chimera that incorporated amino acids 61-194 of UGT2B15 glucuronidated the UGT2B15 substrates testosterone and phenolphthalein, but not the UGT2B7 substrates zidovudine and 11alpha-hydroxyprogesterone. Derived apparent K(m) values for testosterone and phenolphthalein glucuronidation by UGT2B7-15((61-194))-7 were similar in magnitude to those determined for UGT2B15. Moreover, glucuronidation of the non-selective substrate 4-methylumbelliferone (4MU) by UGT2B7-15((61-194))-7 and UGT2B15 followed Michaelis-Menten and weak substrate inhibition kinetics, respectively, whereas 4MU glucuronidation by UGT2B7 exhibited sigmoidal kinetics characteristic of autoactivation. Six UGT2B7-15-7 chimeras that incorporated smaller domains of UGT2B15 were subsequently generated. Of these, UGT2B7-15((61-157))-7, UGT2B7-15((91-157))-7 and UGT2B7-15((61-91))-7 glucuronidated 4MU, but activity towards the other substrates investigated here was not detected. Like UGT2B7, the UGT2B7-15((61-157))-7, UGT2B7-15((91-157))-7 and UGT2B7-15((61-91))-7 chimeras exhibited sigmoidal 4MU glucuronidation kinetics. The sigmoidal 4MU kinetic data were well modelled using both the Hill equation and the expression for a two-site model that assumes the simultaneous binding of two substrate molecules at equivalent sites. It may be concluded that residues 61-194 of UGT2B15 are responsible for substrate binding and for conferring the unique substrate selectivity of UGT2B15, while residues 158-194 of UGT2B7 appear to facilitate the binding of multiple 4MU molecules within the active site.     

DIO2及UGT1A1基因多态性与左甲状腺素剂量关系的研究进展

甲状腺功能减退症是由于各种原因所致的甲状腺激素合成和分泌减少或组织利用不足,为最常见的内分泌系统疾病之一.左甲状腺素(levothyroxine,L-T4)是治疗该病的首选药物,但约10％的甲状腺功能减退症患者应用L-T4替代治疗效果不佳.影响L-T4治疗达标的因素除了年龄、合并用药、患者的依从性等外,遗传因素是另一重要因素,如Ⅱ型脱碘酶基因(type 2 deiodinase gene,DIO2)和尿苷二磷酸葡萄糖醛酸转移酶(uridine diphosphate glucuronosyltransferase,UGT)1 A1基因多态性.了解基因多态性与原发性甲状腺功能减退症患者L-T4治疗剂量间的关系,可以进一步改善患者的预后,为临床用药提供参考依据.