Regulation of Hepatic P450s by Anti-Cholesterol Drugs

描述（由申请人提供）：甲羟戊酸/胆固醇/胆汁酸生物合成途径的内源性代谢物作为肝细胞生理的内分泌调节剂，通过改变孤儿核受体的活性起作用。抑制这一途径关键步骤的抗胆固醇药物将导致这些生物活性分子之一的积累，并激活与介导的核受体相关的多效性反应，其中包括细胞色素P450的诱导。我们的假设是：(1)在诱导肝脏p450的抗胆固醇药物中，只有一部分（例如，某些他汀类药物和角鲨烯单加氧酶抑制剂NB-598）能够直接与外源感应核受体结合，并且这些药物以物种特异性的方式结合；(2)角鲨素1间接诱导大鼠CYP2B（并激活CAR），要么通过引起farnesoid（作为CAR配体的功能）的积累，要么通过引起血红素代谢的紊乱；这种作用的生物活性介质通过孕烯醇酮16（-碳腈（PCN））诱导酶或转运体从肝细胞代谢或消除；(3)抗胆固醇药物治疗和/或补充甲羟戊酸后，在人肝细胞中积累的多种内源性甲羟戊酸/甾醇/胆汁酸途径代谢物，由于PXR的结合和激活，能够诱导CYP3A和CYP2B6的表达。具体目的是：(1)确定抗胆固醇药物与大鼠、小鼠和人类CAR、PXR和ppar - α受体直接相互作用的能力。(2)在原代培养的大鼠肝细胞中，鉴定甲羟戊酸途径中介导角鲨estatin 1诱导的CYP2B表达的特定分支。(3)确定原代培养的大鼠肝细胞中pcn介导的甲戊酸可逆抑制角鲨抑素1诱导的CYP2B表达的机制，并确认在原代培养的大鼠肝细胞中确定的角鲨抑素1介导的CYP2B诱导的机制在体内也是有效的。(4)鉴定甲羟戊酸/甾醇/胆汁酸生物合成通路调节人肝细胞模型中CYP3A和CYP2B6表达的特异性代谢中间体。这些研究将为广泛使用的一类药物的药理学提供重要的新信息，并对诱导P450表达的机制有重要的见解。

DESCRIPTION (provided by applicant): Endogenous metabolites of the mevalonate/chotesterol/bile acid biosynthetic pathway function as intracrine regulators of hepatocyte physiology, which act by modifying the activities of orphan nuclear receptors. An anti-cholesterol drug that inhibits a key step in this pathway will cause the accumulation of one of these bioactive molecules and activate the pleiotropic responses associated with the mediating nuclear receptors, which include induction of cytochromes P450. Our hypothesis is that (1) of the anti-cholesterol drugs that induce hepatic P450s, only a subset (e.g., certain statins and the squalene monooxygenase inhibitor, NB-598) are able to bind directly to a xenobiotic-sensing nuclear receptor, and these do so in a species-specific manner; (2) squalestatin 1 induces rat CYP2B (and activates CAR) indirectly, either by causing the accumulation of a farnesoid, which functions as a CAR ligand, or by provoking a disturbance in heme metabolism; the bioactive mediator of this effect is metabolized or eliminated from the hepatocyte by a pregnenolone 16(-carbonitrile (PCN)-inducible enzyme or transporter; and (3) multiple classes of endogenous metabolites of the mevalonate/sterol/bile acid pathway that accumulate in the human hepatocyte following anti-cholesterol drug treatment and/or mevalonate supplementation are capable of inducing CYP3A and CYP2B6 expression as a consequence of PXR binding and activation. The specific aims are (1) To define the abilities of anti-cholesterol drugs to interact directly with the rat, mouse, and human CAR, PXR, and PPARalpha receptors. (2) To identify the specific branch of the mevalonate pathway that mediates squalestatin 1-inducible CYP2B expression in primary cultured rat hepatocytes. (3) To identify the mechanism that is responsible for PCN-mediated, mevalonate-reversible, suppression of squalestatin 1-inducible CYP2B expression in primary cultured rat hepatocytes, and to confirm that the mechanisms governing squalestatin 1-mediated CYP2B induction that have been defined in primary cultured rat hepatocytes are also operative in vivo. (4) To identify the specific metabolic intermediates of the mevalonate/sterol/bile acid biosynthetic pathway that regulate CYP3A and CYP2B6 expression in human hepatocyte models. These studies will provide essential new information about the pharmacology of a widely-used class of drugs, and important insights into the mechanisms underlying inducible P450 expression.