Regulation of Hepatic P450s by Anti-Cholesterol Drugs

描述(申请人提供)：甲氧丙戊酸/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器，通过改变孤儿核受体的活动而起作用。抑制这一途径中关键步骤的抗胆固醇药物将导致这些生物活性分子中的一种积聚，并激活与中介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，只有一小部分药物(如某些他汀类药物和角鲨烯单加氧酶抑制剂NB-598)能够直接与异物敏感的核受体结合，并且以物种特有的方式做到这一点；(2)鳞癌抑素1间接诱导大鼠细胞色素P450(并激活CAR)，要么是通过导致作为CAR配体的法尼醇的积累，要么是通过引起血红素代谢的紊乱；这种作用的生物活性介质是通过孕烯醇酮16(-碳腈(PCN)诱导的酶或转运蛋白从肝细胞代谢或消除；以及(3)在降胆固醇药物治疗和/或甲氧戊酸补充后在人类肝细胞中积聚的甲氧戊酸/固醇/胆汁酸途径的多种内源性代谢物能够由于PXR结合和激活而诱导细胞色素P3A和细胞色素P450 2 B6的表达。具体目的是(1)确定抗胆固醇药物直接与大鼠、小鼠和人类CAR、PXR和PPARpha受体相互作用的能力。(2)在原代培养的大鼠肝细胞中，鉴定甲氧丙戊酸途径中介导鳞癌抑素1诱导的细胞色素P450 2 B表达的特异性分支。(3)明确PCN介导的甲氧戊酸可逆性抑制原代培养大鼠肝细胞角蛋白1诱导的细胞色素P450 2 B表达的机制，并证实已在原代培养大鼠肝细胞中已确定的诱导细胞色素P450 2 B表达的机制也在体内起作用。(4)在人肝细胞模型中鉴定甲氧丙戊酸/甾醇/胆汁酸生物合成途径中调节细胞色素P3A和细胞色素P42B6表达的特定代谢中间产物。这些研究将提供关于一类广泛使用的药物的药理学的基本新信息，以及对诱导P450表达的潜在机制的重要见解。

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.