孕烷X受体的研究进展及其在药物代谢中的作用

孕烷X受体(pregnane X receptor,PXR)是机体对有毒物质适应性防卫机制的一个重要组成部分,PXR被大量的外源性和内源性化学物质激活,这些物质包括类固醇、抗生素、抗真菌的物质和胆汁酸等.PXR配体结合区域三维结构显示它具有一个特殊球形配体结合腔,这种结构允许PXR与广泛的疏水性化学物质结合.PXR与9-顺式维甲酸受体(9-cis retinoic aid receptor,RXR)以异型二聚体的形式与细胞色素氧化酶P450 3A家族和其他参与药物代谢的Ⅱ相药物代谢酶以及药物转运蛋白的DNA响应元件结合,通过外源物刺激诱导多个基因的表达.分析PXR的结构与功能对药物设计和筛选具有重要的应用价值.     

孕烷X受体及组成性雄甾烷受体的研究新进展

孕烷受体(pregnane X receptor,PXR)和组成性雄甾烷受体(constitutive androstane receptor,CAR)是核受体(nuclear receptor,NR)亚家族的重要成员;为配体活化的转录因子,能调控大量的靶基因。本文主要对其基本结构、机制及参与转录活化的辅助因子作简要介绍,重点讲述了它们在调节药物代谢与转运、糖异生及生酮作用、脂质代谢以及炎症反应等方面的意义。通过对PXR及CAR的研究,可以有效预测和防止药物相互作用;为寻找疾病治疗新靶标提供方向。     

中草药对孕烷X受体和组成型雄烷受体等核受体通路影响的研究进展

孕烷X受体（pregnane X receptor,PXR）是核受体亚家族的成员之一,参与大量的外源性和内源性化学物质的生物转化,能被多种中草药激活,调节下游靶基因的表达,在药物代谢酶和转运体的调节中起重要作用。组成型雄烷受体（constitutive androstane receptor,CAR）和PXR一样能与外源性配体结合调节CYP2B6、CYP3A4、CYP2C19、UGT1A1的表达,共同参与CYP药物代谢酶的调节,成为药物作用的靶标。     

孕甾烷x受体在药物代谢中的作用及研究进展

孕甾烷X受体（Pregnane X receptor,PXR）为核受体超家族中NRII亚家族成员,于肝脏和肠道中广泛表达。该受体作为药物代谢的关键调控因子广泛参与药物的吸收、分布、代谢及排泄过程。本文从药物代谢角度分别对PXR参与调节的Ⅰ、Ⅱ相代谢酶及转运体进行介绍,为临床药物相互作用及针对PXR为靶点的药物研发提供参考。     

孕烷X受体在药物性肝损伤中的研究进展

孕烷X受体(pregnane X receptor, PXR)是核受体家族中的一员,可调控多种药物代谢酶及转运体的表达,从而影响药物在肝脏的处置过程,增加药物性肝损伤发生的风险.深入了解PXR在药物性肝损伤中的作用,可预防或减少药物性肝损伤的发生,并有助于以PXR作为潜在靶点的新型药物的研发.     

斑马鱼在药物代谢中的研究进展

斑马鱼作为模式生物已经被广泛地用于药物研发的各个过程中。斑马鱼中有细胞色素P450酶(cytochrome P450,CYP450)、尿苷二磷酸葡萄糖基转移酶(uridine 5'-diphospho-glucuronosyltransferase,UGT)等多种药物代谢酶和核受体如孕烷X受体(pregnane X receptor,PXR)、芳香烃受体(aryl hydrocarbon receptor,AHR)等的表达。本文综述了斑马鱼中主要的药物代谢酶和核受体的表达情况,以及在药物等外源物代谢研究中的进展。     

有机阴离子转运多肽1B3的研究进展

有机阴离子转运多肽1B3(organic anion transporting polypeptide 1B3,OATP1B3)属于溶质转运体(solute carrier,SLC)超家族,主要负责将内、外源物质转运至肝细胞代谢。OATP1B3是肝脏特异性转运体,通常局限性地分布于肝细胞窦状隙侧肝细胞膜上,近期研究发现在前列腺癌、结肠癌、肺癌等肿瘤组织和细胞中也存在着高表达。溶质转运体1B3(SLCO1B3)具有明显的基因多态性,334T>G和699G>A单体型可明显影响OATP1B3的转运活性,从而介导药物-药物相互作用的发生,导致临床用药的个体差异。此外,OATP1B3可通过作用于孕烷X受体(pregnane X receptor,PXR)和组成性雄甾烷受体(constitutive androstane receptor,CAR)等核受体配体的转运,影响体内PXR和CAR的转录活性,从而调控药物代谢酶如细胞色素P450 3A4(CYP3A4)的表达。本文将对OATP1B3近年来的研究进展进行综述。     

植物药-化疗药物相互作用的研究进展

很多癌症患者在接受化疗药物的同时都会使用一些植物药。化疗药物的治疗窗都比较窄,因此有可能发生有害的药物相互作用。植物药诱导药物代谢酶和ATP结合的盒式膜转运蛋白是它们发生相互作用的主要机制之一。近年来一些研究表明,孕烷X受体(pregnane X receptor,PXR)、组成型雄烷受体(constitutive andro-stane receptor,CAR)、维生素D结合受体(vitamin D-binding receptor,VDR)在代谢酶和药物转运蛋白的诱导中扮演着重要角色。现主要就植物药-化疗药物在药动学方面的相互作用作一简单综述,主要关注药物相互作用发生的机制。     

核受体调控羧酸酯酶表达及活性的研究进展

羧酸酯酶(carboxylesterase,CES)是一类重要的Ⅰ相药物代谢酶,参与许多临床抗癌药物、氨基甲酸酯、拟除虫菊酯类杀虫剂、环境中有毒物质以及前致癌物的体内代谢。有研究表明,许多核受体(nuclear receptor,NR)家族成员在调控人和动物肝脏及肠道CES的表达和活性方面发挥着重要作用。本文查阅有关文献,综述NR对人和动物CES调节作用的研究进展,评价其在药物代谢、药物相互作用等方面的意义。近年来,随着基因敲除小鼠模型和转基因小鼠模型的应用,孕甾烷X受体蛋白(pregnane X receptor,PXR,NR1I2)和雄甾烷X受体蛋白(constitutive androstane receptor,CAR,NR1I3)调控CES的转录机制逐步被阐明,其他NR对CES调控机制的研究也有所突破,但目前有关NR对CES调节方面的研究大多局限于啮齿动物模型,后续可通过运用人源化小鼠模型以及临床试验等来深入探讨NR调控CES的作用机制以指导新药开发及临床合理用药。     

孕烷X受体介导的代谢酶和转运体转录调控及其在化疗药物耐药中的作用

孕烷X受体(PXR,NR1I2)是生物体内药物代谢酶和转运体基因表达的主要调控因子之一.近来研究发现,PXR介导的药物代谢酶和转运体的过表达,与化疗药物多药耐药的产生密切相关.鉴于PXR在药物代谢酶和转运体调控中的重要性和PXR转录调控的多样性,有必要对其导致的多药耐药形成机制进行更深入的研究.本文综述了PXR介导的代谢酶和转运体基因表达调控机制,及其引起化疗药物多药耐药的相关研究进展,为提高化疗药物敏感性、逆转化疗药物的多药耐药提供有效的治疗策略.     

Dexamethasone induces pregnane X receptor and retinoid X receptor-alpha expression in human hepatocytes: synergistic increase of CYP3A4 induction by pregnane X receptor activators

In this report we show that submicromolar concentrations of dexamethasone enhance pregnane X receptor (PXR) activator-mediated CYP3A4 gene expression in cultured human hepatocytes. Because this result is only observed after 24 h of cotreatment and is inhibited by pretreatment with cycloheximide, we further investigated which factor(s), induced by dexamethasone, might be responsible for this effect. We report that dexamethasone increases both retinoid X receptor-alpha (RXRalpha) and PXR mRNA expression in cultured human hepatocytes, whereas PXR activators such as rifampicin and clotrimazole do not. Accumulation of RXRalpha and PXR mRNA reaches a maximum at a concentration of 100 nM dexamethasone after treatment for 6 to 12 h and is greatly diminished by RU486. A similar pattern of expression is observed with tyrosine aminotransferase mRNA. Moreover, the effect of dexamethasone on PXR mRNA accumulation seems to be through direct action on the glucocorticoid receptor (GR) because the addition of cycloheximide has no effect, and dexamethasone does not affect the degradation of PXR mRNA. Furthermore, dexamethasone induces the accumulation of a RXRalpha-immunoreactive protein and increases the nuclear level of RXRalpha:PXR heterodimer as shown by gel shift assays with a CYP3A4 ER6 PXRE probe. This accumulation of latent PXR and RXRalpha in the nucleus of hepatocytes explains the synergistic effect observed with dexamethasone and PXR activators together on CYP3A4 induction. These results reveal the existence of functional cross talk between the GR and PXR, and may explain some controversial aspects of the role of the GR in CYP3A4 induction.     

Effect of pregnane X receptor ligand on pharmacokinetics of substrates of organic cation transporter Oct1 in rats.

Because rat organic cation transporter 1 (Oct1, SLC22a1) is expressed mainly in the liver and mediates drug transport, its activity may determine the hepatic handling of cationic drugs. Here, we studied the regulation mechanism of the expression of Oct1, focusing on the nuclear receptors. In vitro studies using cultured hepatocytes indicated that expression of Oct1 was up-regulated by treatment with pregnenolone-16 alpha-carbonitrile (PCN) and by overexpression of rat pregnane X receptor (PXR). In addition, isolated rat hepatocytes exhibited an increase of 1-methyl-4-phenylpyridinium (MPP(+)) uptake on treatment with PCN. When rats were subcutaneously administered PCN, an increase of biliary excretion clearance and distribution volume was observed for drugs such as MPP(+), metformin, and tetraethylammonium, although the effects on pharmacokinetic parameters were variable among the tested drugs. In addition, the expression of Oct2 in kidney was increased by treatment with PCN. Thus, PXR ligands appear to regulate the expression of organic cation transporters in rats and thereby to influence the pharmacokinetic properties of cationic drugs. Because PXR ligands include various clinically used drugs, alterations of hepatic drug handling may arise from interactions between cationic drugs that are substrates of Oct1 and ligands of PXR.     

Structural insights into the promiscuity and function of the human pregnane X receptor

The pregnane X receptor (PXR) is a promiscuous nuclear receptor that responds to a wide variety of drugs, xenobiotics and endogenous compounds, and plays a critical role in mediating drug-drug interactions in humans. PXR is the master regulator of the expression of the CYP3A4 gene, which encodes for the most abundant and promiscuous drug-metabolizing enzyme in humans. PXR also regulates the expression of other genes involved in xenobiotic metabolism, including CYP2C8, CYP2C9, CYP2B6, GSTA2 and MDR1, as well as genes critical to bile acid metabolism. While PXR functions as a xenobiotic sensor in numerous vertebrates, its relatively low sequence conservation across species causes the PXRs from different organisms to respond to distinct subsets of xenobiotics. Thus, PXR promiscuity is directed and not random. The recent determination of crystal structures of the ligand binding domain of human PXR has provided the first detailed molecular view of this promiscuous receptor, and has advanced our understanding of its varied biological functions. We review the evidence establishing the binding promiscuity of PXR and its directed specificity in different species, and analyze the structural determinants of these characteristics. In addition, we examine the relationship between the interaction of PXR with ligands and the manner in which CYP3A4 is thought to bind to substrate molecules. The accumulating structural and functional data on PXR may facilitate the development of improved methods for in vitro, in vivo and in silico screening for PXR activation.