Xenobiotic-Metabolizing Enzymes

我们已经产生了几种p450的人源化小鼠，这些p450对药物和致癌物代谢至关重要。其中包括表达CYP1A1、CYP1A2、CYP2D6、CYP2E1、CYP3A4和CYP3A7的小鼠。CYP3A4。CYP3A4负责市场上大约50%的药物的代谢，因此参与了大量临床相关的药物-药物相互作用，当两种药物都是CYP3A4底物时，会发生这种相互作用。建立了在肠道中表达人CYP3A4的CYP3A4小鼠模型，命名为hCYP3A4，并证明其表达CYP3A4蛋白，并进行咪达唑仑1'-羟基化和4-羟基化；这些活性几乎完全被抗cyp3a4单克隆抗体抑制（注-这篇论文被授予2003年药物代谢和处置年度论文）。与野生型小鼠相比，口服咪达唑仑改变了药代动力学；静脉给药没有显示药物消除的差异，从而表明肠道中CYP3A4的表达对口服给药药物的药代动力学的重要性。酮康唑，一种已知的CYP3A4抑制剂，增加了口服咪达唑仑的最大血浆浓度。这些结果表明，在临床前药物开发中，hCYP3A4小鼠将是评估人类肠道CYP3A4代谢候选药物以及潜在的食物-药物和药物-药物相互作用的合适动物模型。hCYP3A4小鼠表现出一种显著的表型，为P450的生理功能提供了线索。hCYP3A4雌性小鼠缺乏泌乳，导致幼鼠成活率低。（注：本文中的一个人物被《内分泌学》杂志授予封面图片）。hCYP3A4泌乳小鼠乳腺明显发育不全，泌乳量低。在hCYP3A4小鼠中，泌乳表型受损与血清雌二醇水平显著降低相关。这些结果表明，CYP3A4可能在雌二醇稳态中起重要作用，建议孕妇或哺乳期妇女使用可能增加雌二醇代谢和消除的CYP3A4诱导剂时要谨慎。在含有CYP3A4和CYP3A7的第二组小鼠（命名为hCYP3A4/CYP3A7）中检测了CYP3A4转基因的调控。一项时间过程研究发现，CYP3A4蛋白和RNA在未成熟雄性小鼠的肝脏中表达，并在小鼠6周龄成熟时无法检测到。相比之下，CYP3A4在未成熟和成年雌性中均有表达，研究让人联想到大鼠p450的性别依赖性调节。在hCYP3A4/CYP3A7小鼠的雄性和雌性肝脏中，组成型雄甾体受体（CAR）激活剂苯巴比妥也显著升高CYP3A4，表明药物诱导了该小鼠模型中的CYP3A4转基因。此外，在hCYP3A4/CYP3A7雄性小鼠中持续输注重组生长激素（GH），使肝脏CYP3A4 mRNA和蛋白水平提高到正常水平，从而改变了雄性小鼠低水平的搏动性血浆GH特征。持续GH治疗也使内源性小鼠Cyp2b和Cyp3a44基因的表达女性化。这些数据表明，人类CYP3A4包含所有的顺式元件，以响应内源性激素调控的发育表达和性别二态性，特别是生长激素。还揭示了生长激素在决定人肝脏中CYP3A4的性别依赖性表达中的潜在作用。这些发现与人类肝脏中CYP3A4蛋白和mRNA的性别依赖性表达的研究一致。此外，这些研究表明生长激素治疗可能会改变CYP3A4底物的药代动力学和药效学特性，从而增强人类cyp2e1的代谢和药物处置。

We have generated humanized mice for several P450s that are critical for drug and carcinogen metabolism. These include mice expressing CYP1A1, CYP1A2, CYP2D6, CYP2E1, CYP3A4 and CYP3A7. CYP3A4. CYP3A4 is responsible for the metabolism of approximately 50% of drugs on the market and thus is involved in a large number of clinically relevant drug-drug interactions that occur when two drugs are co-administered that are both CYP3A4 substrates. A CYP3A4 mouse model that expresses human CYP3A4 in the intestine, designated hCYP3A4, was generated and demonstrated to express the CYP3A4 protein and to carry out midazolam 1'-hydroxylation and 4-hydroxylation; these activities were almost completely inhibited by an anti-CYP3A4 monoclonal antibody (Note - This paper was awarded the 2003 Paper of the Year in Drug Metabolism and Disposition). Midazolam pharmacokinetics were altered as compared to wild-type mice when the drug was orally administered; intravenous administration did not reveal a differences in drug elimination thus demonstrating the importance of expression of CYP3A4 in gut on the pharmacokinetics of orally administered drugs. Ketoconazole, a known inhibitor of CYP3A4, increased maximum plasma concentration orally dosed midazolam. These results suggest that the hCYP3A4 mouse would be an appropriate in vivo animal model for the evaluation of human intestine CYP3A4 metabolism of drug candidates and potential food-drug and drug-drug interactions in preclinical drug development.The hCYP3A4 mice displayed a remarkable phenotype that yields clues into the physiological function of this P450. hCYP3A4 female mice were deficient in lactation resulting in low pup survival. (Note - A figure from this paper was awarded the cover picture in Endocrinology). The mammary glands of hCYP3A4 lactating mice were markedly underdeveloped and had low milk content. The impaired lactation phenotype was associated with significantly reduced serum estradiol levels in hCYP3A4 mice. These results suggest that CYP3A4 may play an important role in estradiol homeostasis and suggest caution when treating pregnant or lactating women with CYP3A4 inducers that may increase estradiol metabolism and elimination.Regulation of the CYP3A4 transgene was examined in a second line of mice containing both CYP3A4 and CYP3A7, designated hCYP3A4/CYP3A7. A time course study revealed that CYP3A4 protein and RNA were expressed in the liver of immature male mice and became undetectable when the mice reached maturity at 6 weeks of age. In contrast, CYP3A4 was expressed in both immature and adult females studies were reminiscent of the gender-dependent regulation of P450s in rat. CYP3A4 was also markedly elevated by the constitutive androstane receptor (CAR)-activator phenobarbital in both male and female livers of hCYP3A4/CYP3A7 mice, demonstrating drug induction of the CYP3A4 transgene in this mouse model. Furthermore, continuous infusion of recombinant growth hormone (GH) in hCYP3A4/CYP3A7 male mice, which overrides the low-level pulsatile male plasma GH profile in males, increased hepatic CYP3A4 mRNA and protein to normal female levels. Continuous GH treatment also feminized the expression of endogenous murine Cyp2b and Cyp3a44 genes. These data demonstrated that human CYP3A4 contains all of the cis elements required for it to respond to endogenous hormonal regulators of developmental expression and sexual dimorphism, in particular GH. A potential role for GH in determining the sex-dependent expression of CYP3A4 in human liver was also revealed. These finding are in agreement with studies in humans showing a gender dependent expression of CYP3A4 protein and mRNA in liver. Further, these studies suggest that GH therapy may alter the pharmacokinetic and pharmacodynamic properties of CYP3A4 substrates, leading to enhanced metabolism and disposition of drugs in humans.CYP2E1.