A CYP2B6-humanized mouse model and its potential applications

CYP2B6 is a human microsomal cytochrome P450 enzyme with broad substrate selectivity. CYP2B6 is the only functional member of the human CYP2B gene subfamily, which differs from the situation in rodents, such as mouse, where multiple functional Cyp2b genes are expressed. Recent studies with Cyp2b knockout or knockdown mouse models have yielded insights into the in vivo roles of mouse CYP2B enzymes in drug disposition and xenobiotic toxicity. A CYP2B6-humanized mouse model (CYP2A13/2B6/2F1-transgenic/Cyp2abfgs-null), which expresses human CYP2B6 in the liver, and human CYP2A13 and CYP2F1 in the respiratory tract, but not any of the mouse Cyp2b genes, has also been established. In the CYP2B6-humanized mouse, the CYP2B6 transgene is expressed primarily in the liver, where it was found to be active toward prototype CYP2B6 substrate drugs. The regulatory elements of the CYP2B6 transgene appear to be compatible with mouse nuclear receptors that mediate CYP2B induction. Therefore, the CYP2B6-humanized mouse is a valuable animal model for studying the impact of CYP2B6 expression or induction on drug metabolism, drug efficacy, drug-drug interaction, and drug/xenobiotic toxicity. In this mini-review, we provide a brief background on CYP2B6 and the Cyp2b-knockout and CYP2B6-humanized mice, and discuss the potential applications and limitations of the current models.     

自拟葛花解酒涤脂汤对酒精性脂肪肝小鼠肝脏脂肪沉积及PXR表达的影响

目的了解自拟葛花解酒涤脂汤对酒精性脂肪肝(AFLD)小鼠肝脏脂肪沉积的影响,并观察其对肝组织孕烷受体(PXR)及其调控靶基因CYP3A11、CYP3A25蛋白及mRNA表达的影响。方法将29只雄性C57BL/6J小鼠随机分为正常组(5只),模型组(8只),高剂量干预组(8只)、低剂量干预组(8只)。采用美国国立卫生研究院酒精滥用和酒精中毒研究所(NIAAA)方法制备AFLD小鼠模型,分别灌胃给予高、低剂量葛花解酒涤脂汤水煎剂干预,连续9 d。采用酶联免疫吸附法检测血清中谷丙转氨酶(ALT)及谷草转氨酶(AST)水平,组织病理学油红O染色检测肝脏脂肪沉积情况;实时荧光定量PCR及免疫组织化学方法分别检测PXR、CYP3A11、CYP3A25 mRNA及PXR蛋白的表达。结果与模型组比较,干预组小鼠肝脏脂肪沉积显著减轻,呈剂量依赖性,具有比模型组和正常组显著增加的PXR、CYP3A25表达水平(P0.01);模型组小鼠血清ALT水平显著增加(P0.01),其余各组相似;各组CYP3A11mRNA转录水平差异无显著性(P≥0.05)。结论自拟葛花解酒涤脂汤对实验小鼠AFLD具有明显的治疗作用,可能与促进PXR及其靶基因CYP3A25表达有关。     

The pregnane X receptor locus is associated with susceptibility to inflammatory bowel disease

BACKGROUND & AIMS: The pregnane X receptor (PXR) regulates an array of genes involved in the response to xenobiotics. Evidence from several studies suggests that xenobiotic metabolism may play a role in inflammatory bowel disease (IBD) and that low levels of PXR may be associated with disease expression. The aim of this study was to investigate the association of functional polymorphisms of the PXR encoding gene (NR1I2) with disease in IBD populations. METHODS: This was a case-control study examining 8 NR1I2 single nucleotide polymorphisms (SNPs) previously associated with altered activity of PXR-regulated genes in an Irish cohort including 422 patients with IBD and 350 ethnically matched controls. RESULTS: We showed significant associations of NR1I2 with IBD, Crohn's disease (CD), and ulcerative colitis (UC) groups compared with a control population for SNPs -23585 (IBD: P = .000008; odds ratio [OR], 1.62; 95% confidence interval [CI], 1.31-2.00) and -24381 (IBD: P = .0002; OR, 1.50; 95% CI, 1.21-1.84). SNPs 7635 (P = .0008) and 8055 (P = .007) were found to be associated with IBD and CD but not UC. Risk of IBD is strongly correlated to genotype at these sites, especially for the -25385CC genotype (P = .00001; OR, 2.92; 95% CI, 1.87-4.66). We also show specific correlations of IBD phenotype with genotypes and haplotypes in the patient group. CONCLUSIONS: These results show that genetic variation in the PXR encoding gene, which has been associated with altered activity of PXR, is strongly associated with susceptibility to IBD, CD, and UC.     

Nuclear receptors: the controlling force in drug metabolism of the liver?

The body is in a constant battle to achieve homeostasis; indeed, the robustness with which it can respond to moves away from homeostasis is a vital part in the survival of the organism as a whole. There thus exists a need for a network of sensors that are able to capture, interpret, and respond to alterations in chemical levels that move the body away from homeostasis and this applies to both endogenous and exogenous chemicals. With respect to external chemicals (xenobiotics), this xenosensing is often carried out through specific interactions with cellular receptors. The phenomenon of ‘xenosensing’ has attracted much interest of late, whereby xenobiotics interact with receptors resulting in the activation of a battery of genes mediating oxidative drug metabolism, conjugation, and transport, thereby enhancing the elimination of the xenobiotic by the organism. However, this beneficial response is counterbalanced by the increasingly recognized role of nuclear receptors in mediating drug–drug interactions via enzyme induction or the production of toxicity through interaction with endogenous pathways. This review will focus on the role of nuclear receptors in mediating these effects, and how such knowledge will contribute to a mechanism-based risk assessment for xenobiotics.     

核受体PXR与耐药相关基因在结肠癌中的表达及意义

目的检测核受体PXR和耐药相关基因在人结肠癌中表达,初步探讨其相互关系在肿瘤免疫和肿瘤耐药中意义。方法分别用RT-PCR和western blot方法检测PXR、MRP2、MRP3、ABCG2、MDR1和CYP3A4在17例结肠癌组织中的表达,并进行半定量统计分析。结果与相应正常组织相比,结肠癌组织中PXR、MRP2和MRP3 mRNA水平和蛋白水平均显著增强(P<0.05)。而结肠癌组织中ABCG2、MDR1和CYP3A4 mRNA水平与相应正常组织相比没有显著差异。在癌组织和正常组织中,MRP3 mRNA水平与PXR mRNA水平呈正相关性(P<0.05)。结论 PXR、MRP2和MRP3可能在结肠癌耐药中具有重要作用,PXR调控MRP3表达可能涉及其耐药机制。