CYP3A4*18B基因多态性与他克莫司血药浓度的相关性研究

目的:探讨中国汉族肾移植患者CYP3A 4* 18B基因型对术后1个月内他克莫司谷浓度的影响.方法:采用限制性片段长度多态性技术分析了30例汉族患者CYP3A4* 18B基因型,采用酶增强免疫测定技术测定患者他克莫司谷浓度.将血药浓度标准化后对不同基因型患者剂量调整谷浓度差异进行t检验.结果:测得CY P3A 4*18B等位基因频率为0.333,符合Hardy-Weinberg平衡.将患者分成*1/*1型慢代谢组和*1/*18B合并*18B/*18B型快代谢组,两组标准化谷浓度分别为(98.02±18.56) ng·kg·mL-1· mg-1和(62.91±18.15) ng· kg· mL-1· mg-1 (P＜0.01),慢代谢组的FK506剂量调整谷浓度显著高于快代谢组.结论:CYP3A 4* 18B基因多态性与他克莫司剂量调整谷浓度显著相关,该突变可能导致CYP3A4酶活性的提高.     

CYP3A4* 1G基因多态性对肾移植受者他克莫司给药剂量及血药浓度影响的系统评价

目的系统评价CYP3A4*1G基因多态性对肾移植受者他克莫司日剂量、全血谷浓度及浓度剂量比的影响。方法计算机检索Em Base、Pub Med、Cochrane Library、CNKI、万方及Sino Med等数据库,收集CYP3A4*1G基因多态性对他克莫司给药剂量及血药浓度影响的研究,用Revman 5.2软件进行Meta分析。结果共纳入7项研究(中文5篇,英文2篇),包括750名成年肾移植受者。Meta分析结果表明,CYP3A4*1G组他克莫司日剂量显著高于CYP3A4*1/*1组患者(P<0.05)。亚组分析显示,肾移植术后14 d内,2组他克莫司日剂量比较差异无统计学意义(P>0.05);而术后1个月及2~3个月时,CYP3A4*1G组他克莫司日剂量均显著高于CYP3A4*1/*1组(均P<0.05),他克莫司全血谷浓度及浓度剂量比均显著低于CYP3A4*1/*1组(均P<0.05)。结论 CYP3A4*1G基因多态性显著影响肾移植受者他克莫司日剂量及其血药浓度。     

CYP3A5基因多态性分析指导肾移植术后他克莫司的个体化用药

目的:研究肾移植术患者CYP3A5基因多态性与术后个体化给药剂量的关系。方法:采用等位基因特异扩增法对27例肾移植术后患者进行CYP3A5基因分型。采用酶联免疫法测定他克莫司的血药浓度。比较不同基因型之间的他克莫司的血药浓度与给药剂量(C/D)比值的差异。结果:肾移植患者CYP3A5(A6986G)基因多态性,CYP3A5*3的发生频率为50%,CYP3A5*1/*3基因型与*1/*1基因型患者C/D比值相比差异无显著性(P>0.05),但两者C/D比值均显著低于*3/*3基因型患者(P<0.05)。结论:肾移植患者的CYP3A5基因多态性与他克莫司血药浓度具有相关性,CYP3A5*1/*3基因型和*1/*1基因型患者拟取得相似的血药浓度要比*3/*3型患者需服用更高剂量的他克莫司。分析肾移植患者的CYP3A5基因多态性与血药浓度关系,可指导其术后他克莫司的个体化用药方案。     

CYP3A4*18B和CYP3A5*3基因多态性对肾移植患者他克莫司剂量及浓度的影响

研究CYP3A5*3和CYP3A4*18B基因突变对他克莫司血药浓度/剂量×体表面积(C/D′)、不良反应和急性排斥反应的影响。采用聚合酶链反应(PCR)和限制性内切片段长度多态性(RFLP)方法检测227例肾移植患者CYP3A5*3和CYP3A4*18B基因型,比较不同基因型患者之间他克莫司的C/D′值、不良反应和急性排斥反应发生率的差异。测得CYP3A4*18B和CYP3A5*3基因型在肾移植患者中的突变频率分别为30.8%和74.2%。消除CYP3A5*3等位基因影响后,CYP3A4*18B各基因型间他克莫司C/D′值无显著性差异(P>0.05);而消除CYP3A4*18B等位基因影响后,CYP3A5*1/*1和*1/*3基因型患者的他克莫司C/D′值显著低于*3/*3(P<0.01)。CYP3A4*18B和CYP3A5*3基因多态性与不良反应和排斥反应间差异无统计学意义(P>0.05)。     

CYP3A基因多态性与他克莫司血药浓度的相关性研究

目的:探讨肾移植术后口服免疫抑制剂他克莫司的剂量及其全血谷浓度个体差异的原因。方法:用基质辅助激光解吸电离飞行时间质谱技术对60例肾移植稳定期患者的CYP3AP1、CYP3A5*3的基因型进行检测,并分析各项临床指标对他克莫司血药浓度的影响。结果:60例肾移植患者中,性别、年龄、体质量、身高、激素剂量、血清肌酐对他克莫司浓度/(剂量×体表面积)比值并没有显著影响(P>0.05),术后时间和CYP3AP1、CYP3A5*3是主要影响因素(P<0.05)。CYP3AP1他克莫司浓度/(剂量×体表面积)比值高低依次为GG组相似文献   

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。     

CYP3A5*3基因多态性与他克莫司血药浓度及临床疗效的相关性研究

目的 探讨CYP3A5*3在中国人群中的分布,明确其对他克莫司稳态谷浓度的影响及临床疗效的相关性。 方法 收集55例慢性肾小球肾炎患者的他克莫司稳态谷浓度,酶免疫放大分析法测定其浓度值,根据TL998A荧光检测仪及试剂盒要求进行样品处理及CYP3A5*3基因型测定。分析CYP3A5*3不同基因型对他克莫司血药浓度及临床疗效的影响。 结果 55例患者,共收集他克莫司稳态谷浓度268份, 5~<10 ng.mL_^-1 与10~20 ng.mL_^-1浓度范围他克莫司的临床有效率(82.0%,82.6%)显著高于5 ng.mL_^-1以下浓度范围(45.5%)(p<0.05),同时5~<10 ng.mL_^-1 与10~20μg.mL_^-1浓度范围他克莫司的临床有效率相近(p＞0.05)。CYP3A5*3三种基因型(GA、GG、AA)患者分布频率均符合Hardy－Weinberg平衡(p＞0.05)。三种基因型患者他克莫司血药谷浓度比较,差异无统计学意义(p＞ 0.05);他克莫司剂量和C/D值比较,差异均有统计学意义(p<0.05)。其中突变纯合子GG患者的他克莫司剂量显著低于突变杂合子GA和野生型AA患者,且突变杂合子GA患者显著低于野生型AA患者;突变纯合子GG患者的他克莫司C/D显著高于突变杂合子GA和野生型AA患者,且突变杂合子GA患者显著高于野生型AA患者。C3435T 基因型不同的患者临床有效率相近(p＞ 0.05)。 结论CYP3A5*3基因多态性对我国肾小球肾炎患者他克莫司血药浓度有显著影响,等位基因G携带者他克莫司C/D值更高,且每日所需剂量更低;但CYP3A5*3基因多态性可能与临床疗效无关。     

CYP3A5和ABCB1基因多态性对肾移植患者术后初期他克莫司剂量、浓度及肾功能的影响

目的研究CYP3A5和ABCB1基因多态性对肾移植患者术后初期他克莫司剂量、浓度以及肾功能的影响。方法以200例肾移植患者为研究对象,使用聚合酶链式反应(PCR)-限制性内切片段长度多态性(RFLP)法和测序法检测患者CYP3A5*3和ABCB1(C1236T、G2677T/A、C3435T)基因型,比较肾移植术后28 d内不同基因型患者之间他克莫司血药浓度(C)、剂量(D)、浓度剂量比(C/D)以及肾功能(血清肌酐和胱抑素C水平)的差异。结果 CYP3A5非表达组(CYP3A5*3*3型)的C和C/D在术后7、14、21和28 d均显著高于CYP3A5表达组(CYP3A5*1*1和CYP3A5*1*3型)(P <0.05,P<0.01)。ABCB1 1236基因多态性对CYP3A5表达组患者的他克莫司C、D及C/D均没有显著影响;对于CYP3A5非表达组,ABCB1 1236 CT和TT型患者他克莫司的D及C/D有显著性差异。对于CYP3A5表达组,ABCB1 3435 TT型患者他克莫司的C和D显著低于CC型和CT型患者(P <0.05);而在CYP3A5非表达组中,ABCB1 3435 TT型患者的他克莫司D显著低于CT型。对肾功能的影响:ABCB11236和2677基因型对CYP3A5表达组和非表达组肾功能均没有显著影响。对于CYP3A5非表达组,ABCB1 3435 TT型患者移植后第7或14日肌酐和胱抑素C水平显著高于CC和CT型患者(P <0.05)。结论肾移植术后初期,CYP3A5*3、ABCB1 C1236T和ABCB1 C3435T基因多态性影响他克莫司C和D,ABCB1 C3435T基因多态性对肾功能有影响。     

CYP3A4和CYP3A5基因多态性对汉族肾移植患者他克莫司血药浓度的影响

目的:研究CYP3A4* 18B (rs2242480)、CYP3 A5 6989 A/G(rs776746)两个位点的基因多态性对肾移植术后他克莫司血药浓度/校正剂量比值(C/D)的影响,对肾移植患者基因导向的他克莫司个体化给药提供有意义的信息和数据.方法:101名健康志愿者和56例亲体肾移植且随访超过6个月的患者参加本研究,应用基因芯片法检测2个位点的基因型.用均相酶扩大免疫分析法(EMIT)测定术后7d、14 d、1个月、3个月和6个月时血药浓度.比较不同基因型间他克莫司C/D值之间的差异.结果:在101例汉族人群中,CYP3A4、CYP3A5的等位基因频率分别为:23.75％、73.80％.移植术后6个月内,CYP3A5 GG型(*3/*3)的C/D值显著高于AA型(*1/*1)和AG型(*1/*3)(P＜0.05).CYP3A5 AA型与AG型相比较,差异无统计学意义(P＞0.05).CYP3A4 CC型(*1/*1)的C/D值显著高于CT型(*1/*18B)和TT型(*18B/* 18B)(P＜0.05),其中CT型与TT型比较,C/D值差异无统计学意义(P＞0.05) 结论:肾移植患者术后服用他克莫司C/D值与CYP3A4、CYP3A5基因多态性具有显著相关性.     

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。     

Glucuronidation of flavonoids by recombinant UGT1A3 and UGT1A9

Flavonoids are highlighted for their potential roles in the prevention of oxidative stress-associated diseases. Their metabolisms in vivo, such as glucuronidation, are the key points to determine their health beneficial properties. In this paper, we tested the glucuronidation of nineteen flavonoids by both recombinant human UGT1A3 and UGT1A9. Eleven compounds could be catalyzed by both enzymes. In general, both enzymes showed moderate to high catalyzing activity to most flavonoid aglycones, while the catalyzing efficiency changed with structures. Each flavonoid produced more than one monoglucuronide with no diglucuronide detected by liquid chromatography-mass spectrometry (LC-MS). Enzymatic kinetic analysis indicated that the catalyzing efficiency (Vmax/Km) of UGT1A9 was higher than that of UGT1A3, suggesting its important role in flavonoid glucuronidation. Both human UGT1A3 and UGT1A9 preferred flavonoid aglycone to flavonoid glycoside, and their metabolism to arabinoside was stronger than to other glycosides. Of the flavonoids studied, it is the first time to report isorhamnetin, morin, silybin, kaempferol, daidzein, quercetin-3',4'-OCHO-, quercetin xylopyranoside and avicularin as substrates of UGT1A3. Apigenin, morin, daidzein, quercetin-3',4'-OCHO-, quercetin xylopyranoside and avicularin were the newly reported substrates of UGT1A9.     

Interactions between human UGT1A1, UGT1A4, and UGT1A6 affect their enzymatic activities.

Protein-protein interactions between human UDP-glucuronosyltransferase (UGT) 1A1, UGT1A4, and UGT1A6 were investigated using double expression systems in HEK293 cells (UGT1A1/UGT1A4, UGT1A1/UGT1A6, and UGT1A4/UGT1A6). The substrates specific for UGT1A1 (estradiol and bilirubin), UGT1A4 (imipramine and trifluoperazine), and UGT1A6 (serotonin and diclofenac) were used to determine the effects of the coexpression of the other UGT1A isoforms on the enzymatic activity. The coexpression of UGT1A4 and UGT1A6 decreased the S(50) and V(max) values of UGT1A1-catalyzed estradiol 3-O-glucuronide formation and increased the V(max) value of UGT1A1-catalyzed bilirubin O-glucuronide formation. The coexpression of UGT1A1 decreased the V(max) value of UGT1A4-catalyzed imipramine N-glucuronide formation but had no effect on UGT1A4-catalyzed trifluoperazine N-glucuronide formation. The coexpression of UGT1A6 had no effect on UGT1A4-catalyzed imipramine N-glucuronide formation but increased the K(m) and V(max) of UGT1A4-catalyzed trifluoperazine N-glucuronide formation. The coexpression of both UGT1A1 and UGT1A4 increased the V(max) values of UGT1A6-catalyzed serotonin and diclofenac O-glucuronide formation. Thus, the effects of the coexpression of other UGT1A isoforms on the kinetics of specific activities were different depending on the UGT1A isoforms and substrates. Native polyacrylamide gel electrophoresis analysis of the double expression systems showed multiple bands at approximately 110 kDa, indicating the existence of heterodimers as well as homodimers of UGTs. In conclusion, we found that human UGT1A1, UGT1A4, and UGT1A6 interact with each other, possibly by heterodimerization, and that their effects on the enzymatic activities are complex depending on the isoforms and substrates.     

Glucuronidation of piceatannol by human liver microsomes: major role of UGT1A1, UGT1A8 and UGT1A10

Objectives Piceatannol, a dietary polyphenol present in grapes and wine, is known for its promising anticancer and anti‐inflammatory activity. The aim of this study was to analyse the concentration‐dependent glucuronidation of piceatannol in vitro. Methods To determine the glucuronidation of piceatannol, experiments were conducted with human liver microsomes as well as using a panel of 12 recombinant UDP‐glucuronosyltransferase isoforms. Furthermore, the chemical structures of novel glucuronides were identified by liquid chromatography‐tandem mass spectrometry (LC‐MS/MS). Key findings Along with piceatannol it was possible to identify three metabolites whose structures were identified by LC‐MS/MS as piceatannol monoglucuronides (M1–M3). Formation of M1 and M3 exhibited a pattern of substrate inhibition, with apparent K_i and V_max/K_m values of 103 ± 26.6 µm and 3.8 ± 1.3 µl/mg protein per min, respectively, for M1 and 233 ± 61.4 µm and 19.8 ± 9.5 µl/mg protein per min, respectively, for M3. In contrast, formation of metabolite M2 followed classical Michaelis–Menten kinetics, with a K_m of 18.9 ± 8.1 µm and a V_max of 0.21 ± 0.02 nmol/mg protein per min. Incubation in the presence of human recombinant UDP‐glucuronosyltransferases (UGTs) demonstrated that M1 was formed nearly equally by UGT1A1 and UGT1A8. M2 was preferentially catalysed by UGT1A10 and to a lesser extent by UGT1A1 and UGT1A8. The formation of M3, however, was mainly catalysed by UGT1A1 and UGT1A8. Conclusions Our results elucidate the importance of piceatannol glucuronidation in the human liver, which must be taken into account in humans after dietary intake of piceatannol.     

Structure-metabolism relationships for the glucuronidation of flavonoids by UGT1A3 and UGT1A9

Objectives This study tries to find structure–metabolism relationships between flavonoids and human UGT1A3 and UGT1A9. Methods The glucuronidation of flavonoids was studied with recombinant UGT1A3 and UGT1A9, and the glucuronidation activity was determined by HPLC. Key findings Of the flavonoids studied, it was shown for the first time that baicalein, quercetin‐3‐OCH₂OCH₃, quercetin‐4′‐CH₃, quercetin‐3′‐OCH₃ and quercetin‐3′‐Br are substrates of UGT1A3. Wogonin, baicalein, quercetin‐4′‐Cl, quercetin‐3‐OCH₂OCH₃, quercetin‐3‐O‐arabinoside, quercetin‐4′‐CH₃, quercetin‐3′‐OCH₃ and quercetin‐3′‐Br are the newly reported substrates of UGT1A9. The preferred substrates for UGT1A3 and UGT1A9 contain the hydroxyl group at the C7‐position. The glycon and the position of the B ring have conspicuous influences on the glucuronidation activity, and other chemical structures of flavonoids have minor effects. Conclusions From the quantitative study, UGT1A9 in general has higher glucuronidation efficiency than UGT1A3.     

Identification and functional characterization of UDP-glucuronosyltransferases UGT1A8*1, UGT1A8*2 and UGT1A8*3

UDP-glucuronosyltransferase (UGT) 1A8 is part of the UGT1 locus and is expressed exclusively in extrahepatic tissues. Analysis of UGT1A8 exon 1 sequence has identified four genotypes from a population of 69 individuals. While there are four alleles, one of the single base pair changes leads to a silent mutation at T255, while the other mutations lead to amino acid substitutions at positions 173 and 277, creating three allelic variants. UGT1A8*1 (A173C277), UGT1A8*1a (T255A>G), UGT1A8*2 (G173C277) and UGT1A8*3 (A173Y277). The allelic frequencies of UGT1A8*1, UGT1A8*1a, UGT1A8*2 and UGT1A8*3 are 0.551, 0.282, 0.145 and 0.022, respectively. To examine the properties of the UGT1A8 proteins, UGT1A8*1 and UGT1A8*2 were cloned from a human colon cDNA library and UGT1A8*3 generated by mutagenesis using UGT1A8*1 as template. The cDNAs were expressed in HK293 cells to examine catalytic function as well as abundance as observed by analysis of UGT1A8-GFP (green fluorescent protein) expression. The single amino acid change that identifies UGT1A8*1 (A173) and UGT1A8*2 (G173) has little impact on function, while the UGT1A8*3 (Y277) is a conserved amino acid alteration represented by a dramatic reduction in catalytic activity. Protein abundance, as determined by Western blot analysis following transient transfection, is not altered. In addition, functional UGT1A8-GFP variants displayed staining in the cytoplasmic region, indicating that each protein is expressed in similar cellular compartments. Together, these data suggest that the null UGT1A8*3 results from structural changes and not a lack of protein expression. Allelic variation leading to singular codon changes could potentially alter drug metabolism in extrahepatic tissues.     

Raloxifene glucuronidation in liver and intestinal microsomes of humans and monkeys: contribution of UGT1A1, UGT1A8 and UGT1A9

1.?Raloxifene is an antiestrogen that has been marketed for the treatment of osteoporosis, and is metabolized into 6- and 4′-glucuronides by UDP-glucuronosyltransferase (UGT) enzymes. In this study, the in vitro glucuronidation of raloxifene in humans and monkeys was examined using liver and intestinal microsomes and recombinant UGT enzymes (UGT1A1, UGT1A8 and UGT1A9).

2.?Although the K_m and CL_int values for the 6-glucuronidation of liver and intestinal microsomes were similar between humans and monkeys, and species differences in V_max values (liver microsomes, humans?>?monkeys; intestinal microsomes, humans?<?monkeys) were observed, no significant differences were noted in the K_m or S₅₀, V_max and CL_int or CL_max values for the 4′-glucuronidation of liver and intestinal microsomes between humans and monkeys.

3.?The activities of 6-glucuronidation in recombinant UGT enzymes were UGT1A1?>?UGT1A8?>UGT1A9 for humans, and UGT1A8?>?UGT1A1?>?UGT1A9 for monkeys. The activities of 4′-glucuronidation were UGT1A8?>?UGT1A1?>?UGT1A9 in humans and monkeys.

4.?These results demonstrated that the profiles for the hepatic and intestinal glucuronidation of raloxifene by microsomes were moderately different between humans and monkeys.     

Influence of genetic variants in UGT1A1 and UGT1A9 on the in vivo glucuronidation of SN-38

The uridine diphosphate glucuronosyltransferase (UGT) 1A1 and 1A9 isoforms are involved in the phase II biotransformation of the irinotecan metabolite, SN-38. Recently, several variants in the UGT1A1 and UGT1A9 genes have been described with altered functionality in vitro. The aim of this study was to evaluate the functional consequence of the UGT1A1(TA)(7)TAA (UGT1A1(*)28), UGT1A9 766G>A (D256N; UGT1A9(*)5), and UGT1A9 98T>C (M33T; UGT1A9(*)3) variants in Caucasian patients treated with irinotecan. Pharmacokinetic studies were performed after the first course of irinotecan in 47 males and 47 females. The mean (SD) area under the curves (AUCs) of irinotecan and SN-38 were 20,348 +/- 6466 ng x h/mL and 629 +/- 370 ng x h/mL, respectively, which is in line with earlier findings. For UGT1A9(*)5,novariant alleles were observed, whereas for UGT1A9(*)3, 1 patient with the variant allele was found (allele frequency, 0.633%). The distribution of the UGT1A1(*)28 variant showed 44 wild-type patients (Wt), 37 heterozygotes (Het), and 5 homozygotes (Var). The median AUC ratio of SN-38G to SN-38 was significantly reduced in carriers of the variant UGT1A1(*)28 allele (7.00 [Wt] vs. 6.26 [Het] vs. 2.51 [Var]; p =.022). It is concluded that UGT1A9 functional variants are rare in Caucasians and likely to be clinically insignificant in irinotecan regimens. Screening for the UGT1A1(*)28 polymorphism may identify patients with altered SN-38 pharmacokinetics.     

Effect of aging on glucuronidation of valproic acid in human liver microsomes and the role of UDP-glucuronosyltransferase UGT1A4, UGT1A8, and UGT1A10

Valproic acid (VPA) is a widely used anticonvulsant that is also approved for mood disorders, bipolar depression, and migraine. In vivo, valproate is metabolized oxidatively by cytochromes P450 and beta-oxidation, as well as conjugatively via glucuronidation. The acyl glucuronide conjugate (valproate-glucuronide or VPAG) is the major urinary metabolite (30-50% of the dose). It has been hypothesized that glucuronidation of antiepileptic drugs is spared over age, despite a known decrease in liver mass. The formation rates of VPAG in a bank of elderly (65 years onward) human liver microsomes (HLMs) were measured by liquid chromatography/tandem mass spectrometry and compared with those in a younger (2-56 years) HLM bank. In vitro kinetic studies with recombinant UDP-glucuronosyltransferases (UGTs) were completed. A 5- to 8-fold variation for the formation of VPAG was observed within the microsomal bank obtained from elderly and younger donors. VPAG formation ranged from 6.0 to 53.4 nmol/min/mg protein at 1 mM substrate concentration (n=36). The average velocities at 0.25, 0.5, and 1 mM VPA were 7.0, 13.4, and 25.4 nmol/min/mg protein, respectively, in the elderly HLM bank. Rates of VPAG formation were not significantly different in the HLM bank obtained from younger subjects. Intrinsic clearances (V(max)/K(m)) for several cloned, expressed UGTs were determined. UGT1A4, UGT1A8, and UGT1A10 also were found to catalyze the formation of VPAG in vitro. This is the first reported activity of these UGTs toward VPA glucuronidation. UGT2B7 had the highest intrinsic clearance, whereas UGT1A1 demonstrated no activity. In conclusion, our investigation revealed no differences in VPAG formation in younger versus elderly HMLs and revealed three other UGTs that form VPAG in vitro.     

Human UGT1A8 and UGT1A10 mRNA are expressed in primary human hepatocytes

It is widely believed that the UGT1A isoforms, UGT1A8 and -1A10, are expressed exclusively in extrahepatic tissues. In this work, human primary hepatocytes from six donors were analyzed for UGT1A8 and -1A10 mRNA expression by semi-quantitative RT-PCR. New primers to amplify UGT1A8 mRNA were designed and found to differ from those previously published. We demonstrated that UGT1A8 and -1A10 mRNA are expressed in hepatocytes. Although basal UGT mRNA levels were detected in untreated hepatocytes, significant up-regulation of the levels of mRNA for these isoforms were seen after treatment with 3-methylcholanthrene (3-MC) and rifampicin (Rif). RT-PCR products for all UGTs were sequenced and unambiguously identified as matching the corresponding cDNA. The discovery of these isoforms in hepatocytes is a novel discovery and will stimulate studies on the potential role for these isoforms in hepatic detoxification.