Regulation of Hepatic P450s by Anti-Cholesterol Drugs

描述（由申请方提供）：目前认为胆固醇生物合成途径的内源性代谢物不仅作为化学中间体发挥作用，而且作为肝细胞生理学的内分泌调节剂发挥作用，可改变核受体的活性。最近，许多“抗胆固醇药物”已被证明会导致生物活性代谢物在肝脏中积累，导致肝脏基因表达改变。例如，我们发现角鲨烯合酶的抑制剂（例如，角鲨烷抑制素1）通过引起内源性类法尼醇积累来选择性地诱导细胞色素P450 2B（CYP 2B）基因表达，这激活组成型雄烷受体（CAR）。我们认为，法尼醇类化合物的生物活性有助于角鲨烯合酶抑制剂的治疗作用和毒性作用。我们假设，由角鲨烯合酶抑制介导的法尼醇积累引起肝细胞基因表达的独特变化，这些变化从啮齿动物到人类以及从原代培养到体内都是保守的。许多这些变化（例如，CYP2B诱导）可归因于法尼醇积累和CAR活化，并且这些变化通过抑制醇脱氢酶（ADH）催化的法尼醇代谢而增强。其他变化（例如，Slc13A3诱导）由法尼醇衍生的代谢物和CAR非依赖性机制介导。本提案的具体目的是（1）界定和比较（即，在大鼠、小鼠和人中）肝细胞对角鲨烯合酶抑制的整体基因表达反应，并确定CAR是否介导该反应的组分，（2）确定角鲨烯合酶抑制对我们在原代培养的人肝细胞中鉴定的人肝细胞基因表达的影响是否（来自目的1）在体内维持，（3）确定是否一种或多种ADH酶负责在肝细胞中将法尼醇转化为法尼醛，因此，ADH活性是否是一个关键的决定因素，法尼醇水平和影响基因表达后，角鲨烯合成酶抑制，和（4）确定角鲨烯合成酶抑制是否调节个体人CAR同种型的活性。正常人肝细胞中内源性法尼醇代谢和信号传导基本上尚未探索。这些研究将提供关于法尼醇类化合物对肝细胞脂质代谢产生有益作用以及促进肝毒性作用的能力的新信息。这些信息将直接关系到角鲨烯合成酶抑制剂作为抗胆固醇药物的未来作用。

DESCRIPTION (provided by applicant): Endogenous metabolites of the cholesterol biosynthetic pathway are now recognized to function not only as chemical intermediates, but also as intracrine regulators of hepatocyte physiology, which modify the activities of nuclear receptors. Recently, many "anti-cholesterol drugs" have been shown to cause bioactive metabolites to accumulate in the liver, resulting in altered hepatic gene expression. For example, we found that inhibitors of squalene synthase (e.g., squalestatin 1) selectively induce cytochrome P450 2B (CYP2B) gene expression by causing an endogenous farnesoid to accumulate, which activates the constitutive androstane receptor (CAR). We propose that the biological activities of the farnesoids contribute to the therapeutic as well as the toxic effects of squalene synthase inhibitors. We hypothesize that farnesoid accumulation mediated by squalene synthase inhibition causes distinctive changes in hepatocellular gene expression that are conserved from rodent to human and from primary culture to in vivo. Many of these changes (e.g., CYP2B induction) are attributable to farnesol accumulation and CAR activation, and these changes are enhanced by inhibition of alcohol dehydrogenase (ADH)-catalyzed farnesol metabolism. Other changes (e.g., Slc13A3 induction) are mediated by a farnesol-derived metabolite(s) and a CAR-independent mechanism(s). The specific aims of this proposal are (1) to define and compare (i.e., among rat, mouse, and human) the global gene expression response of the hepatocyte to squalene synthase inhibition, and to determine whether CAR mediates the components of this response, (2) to determine whether the effects of squalene synthase inhibition on human hepatocellular gene expression that we identify in primary cultured human hepatocytes (from Aim 1) are maintained in vivo, (3) to determine whether one or more ADH enzymes are responsible for converting farnesol to farnesal in hepatocytes, and hence whether ADH activity is a critical determinant of the farnesoid levels and effects on gene expression that are achieved following squalene synthase inhibition, and (4) to determine whether squalene synthase inhibition modulates the activities of individual human CAR isoforms. Endogenous farnesoid metabolism and signaling in normal human hepatocytes has been essentially unexplored. These studies will provide new information about the abilities of farnesoids to produce beneficial effects on hepatocellular lipid metabolism, as well as effects that promote hepatotoxicity. This information will be directly relevant to the future role of squalene synthase inhibitors as anti-cholesterol drugs.