尿苷二磷酸葡醛酸转移酶介导的胆汁酸代谢过程及其内源和外源影响因素研究进展

尿苷二磷酸葡萄糖醛酸转移酶(UDP-glucuronosyltransferases, UGTs)作为人体中一种非常重要的II相代谢酶,不仅参与外源性化合物代谢清除,也在胆汁酸等内源性物质的代谢调控中扮演重要角色。解析尿苷二磷酸葡萄糖醛酸转移酶介导的胆汁酸代谢过程及其内源和外源影响因素有助于增强对相关疾病的治疗和预防。尿苷二磷酸葡萄糖醛酸转移酶对胆汁酸代谢调控作用受到多种内源性和外源性因素影响。本文将重点探讨核受体、遗传因素、外源化合物及肝脏相关疾病等因素对UGT酶作用的影响,讨论体内潜在的胆汁酸动态平衡干预机制。     

尿苷二磷酸葡萄糖醛酸转移酶的调控及其介导的中药-药物相互作用研究进展

尿苷二磷酸葡萄糖醛酸转移酶（UGT）催化的葡萄糖醛酸化反应是的是Ⅱ相代谢中重要的代谢反应之一,对于维持内源性化合物如胆红素、胆汁酸的动态平衡和药物、致癌物等外源性化合物的处置过程起着至关重要的作用。UGTs的表达和酶活性受多维机制的调控。深入研究其调控网络以及UGT介导的相关中药-药物相互作用,对于临床更安全、有效的使用中药提供了指导。因此,本文总结了尿苷二磷酸葡萄糖醛酸转移酶的转录前、转录水平、翻译后修饰等分子调节机制,以及由UGT介导的中药-药物相互作用相关的研究进展。     

尿苷二磷酸葡萄糖醛酸转移酶与内源性物质的相互作用

尿苷二磷酸葡萄糖醛酸转移酶(UGT)是人体重要的II相代谢酶,代谢药物的同时也代谢许多重要的内源性物质,如胆红素、甲状腺激素、雌激素、雄激素、胆汁酸和5-羟色胺等。该酶对许多内源性物质的代谢是灭活和清除这些内源性物质的关键步骤,能够防止内源性物质累积引发的毒性反应,或及时终止内源性激素的信号防止肿瘤的发生。然而,内源性物质对UGT酶也会产生影响,特别是在一些生理病理条件下,某些内源性物质能够抑制UGT酶活性,影响其参与的代谢反应。将就内源性物质和UGT酶的相互作用做一综述,以引起人们对UGT酶和内源性物质相互作用的关注。关键词:药物代谢;尿苷二磷酸葡萄糖醛酸转移酶;内源性物质     

肝损状态下尿苷二磷酸葡萄糖醛酸转移酶研究进展

肝脏是人体内最重要的代谢器官,包含绝大部分的Ⅰ相和Ⅱ相代谢酶,在内源性和外源性物质的代谢解毒方面起着重要的作用.参与葡萄糖醛酸代谢的尿苷二磷酸葡萄糖醛酸转移酶(UGT)是Ⅱ相代谢中最重要的酶,与常见的CYP450酶相比,研究相对滞后,尤其在肝损伤状态下UGT的相关研究仍处于探索阶段.本文参考最新UGT的研究成果,综述了UGT分子生物学目前研究的概况、肝脏分布及其与肝脏疾病的关系;总结了几种不同诱因的肝损伤病理状态UGT表达和葡萄糖醛酸代谢的变化情况并且深入探讨了相关机制,旨在为药物的肝脏代谢尤其是在肝损状态下葡萄糖醛酸结合消除研究提供一定的参考依据,为肝脏疾病患者的临床合理用药提供指导.     

尿苷二磷酸葡萄糖醛酸转移酶基因多态性对药物代谢影响的研究进展

由尿苷二磷酸葡萄糖醛酸转移酶(UDP-glucuronosyltransferase,UGT)催化完成的葡萄糖醛酸结合反应是生物体内重要的Ⅱ相代谢途径,它与毒性或活性物质结合形成葡萄糖醛酸苷,将内源性、外源性化合物通过胆汁或肾脏排出体外。UGT是一个超家族酶,因主要利用UDP-尿苷二磷酸葡糖醛酸为糖基供体而得名。人类UCT广泛分布于体内的各种组织,包括肾、脑、皮肤、肠、脾、胸腺、心脏等,其中以     

人尿苷二磷酸葡萄糖醛酸转移酶基因多态性与相关疾病易感性

尿苷二磷酸葡萄糖醛酸转移酶(UGT)是体内重要的药物代谢Ⅱ相酶,具有明显的基因多态性。评价基因多态性对疾病易感性影响的重要性,建立基因多态性数据库并进行致病基因-疾病易感性的种群研究具有深远意义。本文拟就人UGT基因多态性及相关疾病易感性进行简述。     

药物代谢酶表型鉴定的研究现状

在新药临床前研究中,应对药物的代谢酶表型进行鉴定,获得其主要代谢酶的消除比例,为药物-药物相互作用研究提供重要信息。本文对人体内主要药物代谢酶,包括细胞色素P450酶、尿苷二磷酸葡萄糖醛酸转移酶、含黄素单加氧酶和醛氧化酶的酶表型鉴定研究现状进行综述。     

尿苷二磷酸葡萄糖醛酸转移酶介导的药物相互作用的研究进展

葡萄糖醛酸结合反应是生物体内重要的Ⅱ相代谢途径,由尿苷二磷酸葡萄糖醛酸转移酶(UGT)催化完成,是多种内源性物质和外源性化合物清除与解毒的机制。在新药研发过程中,研究UGT介导的药物代谢以及评估潜在的药物相互作用是非常重要的,吸引了很多研究人员的关注。但目前的研究偏重于由细胞色素P450酶(CYP450)介导的药物相互作用,对UGT的关注相对较少。鉴于UGT在药物代谢中的重要性,有必要对其导致的药物相互作用进行更深入的研究。本文综述了由UGT的抑制引起的药物相互作用的相关研究进展。     

孤儿核受体对尿苷二磷酸葡萄糖醛酸转移酶基因转录调节的研究进展

尿苷二磷酸葡萄糖醛酸转移酶（UDP-glucuro-nosyltransferase,UGT）属于Ⅱ相药物代谢酶。它能催化葡醛酸与其相应底物结合,是化学物质在生物体内进行Ⅱ相生物转化时最重要的一类酶。越来越多的研究发现,孕烷X受体（pregnaneXreceptor,PXR）、组成型雄甾烷受体（constitutiveandrostanere-ceptor,CAR）等孤儿核受体（orphannuclearreceptors）及其他转录因子能调节UGT基因的转录,这些受体及因子分布和活性的差异可导致UGT酶表达和分布的差异。此外,研究表明化合物通过核受体（NR）介导的UGT酶表达量的变化可能是影响化合物体内代谢的一条重要途径。由于UGT酶表达量与激素平衡、药物疗效、药物毒副作用及肿瘤等多种疾病发病预后密切相关,所以研究核受体对Ⅱ相代谢酶的调节作用在预测药物相互作用、指导临床合理用药及人类疾病的预防等方面都具有重要意义。     

影响伊立替康疗效和毒性的遗传因素

伊立替康是一种半合成的喜树碱衍生物,广泛用于多种肿瘤的化疗。伊立替康体内处置过程复杂,药动学和药效学个体差异大,涉及众多多态性药物代谢酶和药物转运蛋白,如羧酸酯酶、尿苷二磷酸葡萄糖醛酸基转移酶、细胞色素P450 3A酶、β-葡萄糖醛酸酶、孕烷X受体、ATP-依赖性转运蛋白等。本文对这些影响因素及其基因多态性的研究进展进行了综述。     

人葡糖醛酸基转移酶介导的黄酮Ⅱ相代谢研究进展

人葡糖醛酸基转移酶(UGT)同工酶在黄酮类化合物Ⅱ相代谢反应中呈重要的作用。本综述总结了近年来国内外学者对黄酮类化合物Ⅱ相代谢中UGT的研究情况,包括各同工酶间的底物差异,结构-代谢活性关系,基因多态性的影响以及黄酮对UGT调控的研究。结果表明,人UGT1A1,1A3,1A8,1A9,1A10和2B15主要参与了广泛黄酮类化合物的葡醛酸结合反应,而UGT1A5,1A7和2B7对黄酮代谢的作用有待于进一步研究证明,UGT的基因多态性、结构-代谢关系、调控机制为生物黄酮的合理利用以及此类化合物的合理药物设计提供了重要的参考依据。     

UGT2B17拷贝数变异的研究进展

尿苷二磷酸葡萄糖醛酸基转移酶（UDP-g1ucuronosyltransferase,UGT）是人体内重要的Ⅱ相代谢酶,UDP-尿苷二磷酸葡萄糖醛酸为其主要的糖基供体。UGT为多基因编码并且含有大量同工酶的超基因家族,包括UGT1和UGT2两个亚家族。UGT2B17是UGT2B家族的一员,越来越多的研究发现UGT2B17基因存在普遍遗传缺失现象,其造成的遗传差异对疾病的影响已引起了众多关注。UGT2B17基因拷贝数变异（Copy Number Variants,CNV）源自4号染色体上一段约120 kb的DNA序列缺失和插入,CNV发生频率高,种族差异明显,与器官移植、骨质疏松、肿瘤发生,乃至兴奋剂检测密切相关。UGT2B17的CNV研究及功能意义具有重大遗传药理学及药物基因组学意义。我们将从UGT2B17的基因拷贝数变异与种族差异、移植排斥反应与肿瘤发生发展等几个方面进行探讨。     

Influence of mutations associated with Gilbert and Crigler-Najjar type II syndromes on the glucuronidation kinetics of bilirubin and other UDP-glucuronosyltransferase 1A substrates

OBJECTIVES: UGT1A1 coding region mutations, including UGT1A1*6 (G71R), UGT1A1*7 (Y486D), UGT1A1*27 (P229Q) and UGT1A1*62 (F83L), have been linked to Gilbert syndrome in Asian populations, whereas homozygosity for UGT1A1*7 is associated with the Crigler-Najjar syndrome type II. This work compared the effects of (a) the individual UGT1A1 mutations on the glucuronidation kinetics bilirubin, beta-estradiol, 4-methylumbelliferone (4MU) and 1-naphthol (1NP), and (b) the Y486 mutation, which occurs in the conserved carboxyl terminal domain of UGT1A enzymes, on 4MU, 1NP and naproxen glucuronidation by UGT1A3, UGT1A6 and UGT1A10. METHODS: Mutant UGT1A cDNAs were generated by site-directed mutagenesis and the encoded proteins were expressed in HEK293 cells. The glucuronidation kinetics of each substrate with each enzyme were characterized using specific high-performance liquid chromatography (HPLC) methods. RESULTS: Compared with wild-type UGT1A1, in-vitro clearances for bilirubin, beta-estradiol, 4MU and 1NP glucuronidation by UGT1A1*6 and UGT1A1*27 were reduced by 34-74%, most commonly as a result of a reduction in Vmax. However, the magnitude of the decrease in the in-vitro clearances varied from substrate to substrate with each mutant. The glucuronidation activities of UGT1A1*7 and UGT1A1*62 were reduced by >95%. Introduction of the Y486D mutation essentially abolished UGT1A6 and UGT1A10 activities, and resulted in 60-90% reductions in UGT1A3 in-vitro clearances. CONCLUSIONS: The glucuronidation of all UGT1A1 substrates is likely to be impaired in subjects carrying the UGT1A1*6 and UGT1A1*62 alleles, although the reduction in metabolic clearance might vary with the substrate. The Y486D mutation appears to greatly reduce most, but not all, UGT1A activities.     

Effects of combined UDP-glucuronosyltransferase (UGT) 1A1*28 and 1A6*2 on paracetamol pharmacokinetics in beta-thalassemia/HbE

In addition to pathophysiological changes, genetic variations can alter drug pharmacokinetics in patients with thalassemia. Numerous drugs are metabolized by UDP-glucuronosyltransferases (UGT) including paracetamol (PCM), a widely used analgesic. Co-occurrence of the UGT1A1 polymorphism (UGT1A1*28) and the UGT1A6 polymorphism (UGT1A6*2) may affect PCM glucuronidation. To elucidate the effect of these combined polymorphisms on the PCM metabolism in thalassemic patients, 15 beta-thalassemia/hemoglobin E subjects with three different UGT1A genotypes received a single oral dose of 1,000 mg PCM. Drug disposition was determined by HPLC. Patients who have UGT1A6*2 without UGT1A1*28 showed a significant, lower area under concentration-time curve (AUC(0)-->infinity) of PCM, PCM-glucuronide and PCM-sulfate than those of the patients with wild-type UGT1A1 and UGT1A6 (p < 0.05). In addition, a high elimination rate constant and clearance of PCM and its metabolites were also found in these patients (p < 0.05). Ourstudy suggests that a subtherapeutic level of PCM may occur in patients who have UGT1A6*2 without UGT1A1*28.     

<Emphasis Type="Italic">In Vitro</Emphasis> metabolism of Jaceosidin and characterization of cytochrome P450 and UDP-glucuronosyltransferase enzymes in human liver microsomes

Jaceosidin is an active component in Artemisia species as well as Eupatorium species and it exhibits antiallergic, anticancer, antioxidant, anti-inflammatory, and antimutagenic activities. Jaceosidin was metabolized to jaceosidin glucuronide, 6-O-desmethyljaceosidin, hydroxyjaceosidin, 6-O-desmethyljaceosidin glucuronide, and hydroxyjaceosidin glucuronide in human liver microsomes. This study characterized the human liver cytochrome P450 (CYP) and UDPglucuronosyltransferase (UGT) enzymes responsible for the metabolism of jaceosidin. CYP1A2 was identified as the major enzyme responsible for the formation of 6-O-desmethyljaceosidin and hydroxyjaceosidin from jaceosidin on the basis of a combination of correlation analysis and experiments including immuno-inhibition, chemical inhibition in human liver microsomes, and metabolism by human cDNA-expressed CYP enzymes. Jaceosidin glucuronidation was catalyzed by UGT1A1, UGT1A3, UGT1A7, UGT1A8, UGT1A9, and UGT1A10. These results suggest that the pharmacokinetics of jaceosidin may be dramatically affected by polymorphic CYP1A2, UGT1A1, and UGT1A7 responsible for the metabolism of jaceosidin or by the coadministration of relevant CYP1A2 or UGT inhibitors or inducers.     

Understanding substrate selectivity of human UDP-glucuronosyltransferases through QSAR modeling and analysis of homologous enzymes

The UDP-glucuronosyltransferase (UGT) enzyme catalyzes the glucuronidation reaction which is a major metabolic and detoxification pathway in humans. Understanding the mechanisms for substrate recognition by UGT assumes great importance in an attempt to predict its contribution to xenobiotic/drug disposition in vivo. Spurred on by this interest, 2D/3D-quantitative structure activity relationships and pharmacophore models have been established in the absence of a complete mammalian UGT crystal structure. This review discusses the recent progress in modeling human UGT substrates including those with multiple sites of glucuronidation. A better understanding of UGT active site contributing to substrate selectivity (and regioselectivity) from the homologous enzymes (i.e. plant and bacterial UGTs, all belong to family 1 of glycosyltransferase (GT1)) is also highlighted, as these enzymes share a common catalytic mechanism and/or overlapping substrate selectivity.     

Human UGT1A6 pharmacogenetics: identification of a novel SNP, characterization of allele frequencies and functional analysis of recombinant allozymes in human liver tissue and in cultured cells

BACKGROUND: UDP-glucuronosyltransferase (UGT) enzymes catalyze the glucuronidation and typically inactivation of endogenous and exogenous molecules including steroid hormones, bilirubin and many drugs. The UGT1A6 protein is expressed predominantly in liver and metabolizes small phenolic drugs including acetaminophen, salicylates and many beta-blockers. Interindividual variation in the capacity of humans to glucuronidate drugs has been observed. RESULTS: We have identified a novel common single nucleotide polymorphism (SNP) in the human UGT1A6 gene resulting in a Ser7Ala change in encoded amino acid. We have further functionally characterized that polymorphism in the context of two previously reported polymorphisms, Thr181Ala and Arg184Ser. These non-synonymous cSNPs define four common haplotypes. Alleles appear with similar frequencies in Caucasian and African-American populations with distributions adhering to Hardy-Weinberg equilibrium. UGT1A6 genotype, rate of substrate glucuronidation and level of immunoreactive UGT1A6 protein was determined. A 25-fold variation in the rate of substrate glucuronidation and an 85-fold variation in level of immunoreactive protein were measured. Liver tissue samples that were homozygous for UGT1A6*2 exhibited a high rate of glucuronidation relative to tissues with other genotypes. Biochemical kinetic studies of recombinant UGT1A6 expressed in HEK293 cells indicated that the UGT1A6*2 allozyme, expressed homozygously, had almost two-fold greater activity toward p-nitrophenol than UGT1A6*1 and when expressed heterozygously (UGT1A6*1/*2) it was associated with low enzyme activity. CONCLUSIONS: These data suggest that common genetic variation in human UGT1A6 confers functionally significant differences in biochemical phenotype as assessed in human tissue and cultured cells expressing recombinant allozymes. This genetic variation might impact clinical efficacy or toxicity of drugs metabolized by UGT1A6.     

UDP-glucuronosyltransferases

Glucuronidation represents a major pathway which enhances the elimination of many lipophilic xenobiotics and endobiotics to more water-soluble compounds. The UDP-glucuronosyltransferase (UGT) family catalyzes the glucuronidation of the glycosyl group of a nucleotide sugar to an acceptor compound (aglycone) at a nucleophilic functional group of oxygen (eg, hydroxyl or carboxylic acid groups), nitrogen (eg, amines), sulfur (eg, thiols), and carbon, with the formation of a beta-D-glucuronide product. At this time, over 35 different UGT gene products have been described from several different species. UGTs have been divided into two distinct subfamilies based on sequence identities, UGT1 and UGT2. The UGT1 gene subfamily consists of a number of UGTs that result from alternate splicing of multiple first exons and share common exons 2-5. The substrate specificities of the various isoforms have been examined in cultured cell experiments, and include bilirubin, amines, and planar and bulky phenol. The UGT2 gene family is different in that the UGT2 mRNAs are transcribed from individual genes. The UGT2 subfamily consists of numerous enzymes which catalyze the glucuronidation of a diverse chemical base including steroids, bile acids, and opioids. Until recently, the liver has been the major focus for studying the metabolism of xenobiotics and endobiotics. Several groups have identified extrahepatic tissues that express UGT isoforms including the kidney, gastrointestinal tract and brain. This review discusses the two UGT gene families, substrate specificities, and the recent discoveries of UGTs in extrahepatic tissues.     

Frequent co-occurrence of the TATA box mutation associated with Gilbert's syndrome (UGT1A1*28) with other polymorphisms of the UDP-glucuronosyltransferase-1 locus (UGT1A6*2 and UGT1A7*3) in Caucasians and Egyptians

Polymorphisms of drug metabolizing enzymes are frequently associated with diseases and side effects of drugs. Recently, a TATA box mutation of UGT1A1 (UGT1A1*28), a common genotype leading to Gilbert's syndrome, and several missense mutations of other UDP-glucuronosyltransferase 1 (UGT1) family members have been described. Furthermore, co-occurrence of UGT1A1*28 and UGT1A6*2 has been observed. In order to elucidate the basis for co-occurrence of UGT1 mutations, fluorescence resonance energy transfer techniques were developed for rapid determination of polymorphisms of three UGT isoforms (UGT1A1*28, 1A6*2, and 1A7*2/*3). Hundred healthy Caucasians and 50 Egyptians were genotyped. All genotypes followed the Hardy-Weinberg equilibrium. Only three major haplotypes were found, including a haplotype consisting of allelic variants of all three isoforms (29% in Caucasians and 22% in Egyptians), all leading to reduced UGT activity. Frequent haplotypes containing several UGT1 allelic variants should be taken into account in studies on the association between diseases, abnormal drug reactions, and UGT1 family polymorphisms.     

Preparation of a specific monoclonal antibody against human UDP-glucuronosyltransferase (UGT) 1A9 and evaluation of UGT1A9 protein levels in human tissues

Glucuronidation is a major detoxification pathway of drugs and xenobiotics that are catalyzed by the UDP-glucuronosyltransferase (UGT) superfamily. Determination of the protein levels of the individual UGT isoforms in human tissues is required for the successful extrapolation of in vitro metabolic data to in vivo clearance. Most previous studies evaluating UGT isoform expression were limited to the mRNA level because of the high degree of amino acid sequence homology between UGT isoforms that has hampered the availability of isoform-specific antibodies. In this study, we generated a peptide-specific monoclonal antibody against human UGT1A9. We demonstrated that this antibody does not cross-react with the other UGT1A isoforms including UGT1A7, UGT1A8, and UGT1A10 and shows a high degree of amino acid sequence similarity with UGT1A9. Using this antibody, we found that UGT1A9 protein is expressed in the kidney and the liver but not in the jejunum or the ileum, consistent with previous reports of mRNA expression. In a panel of 20 individual human livers, the UGT1A9 protein levels exhibited 9-fold variability. It is noteworthy that the relative UGT1A9 protein levels were not correlated with the UGT1A9 mRNA level (r = -0.13), like other UGT isoforms reported previously, suggesting the importance of evaluating UGT isoform expression at protein levels. In conclusion, we generated a specific monoclonal antibody against UGT1A9 and evaluated the distribution and relative expression levels of the UGT1A9 protein in human tissues. This antibody may serve as a useful tool for further studies of UGT1A9 to evaluate its physiological, pharmacological, and toxicological roles in human tissues.