FURANOCOUMARINS AND DRUGS EFFECT ON CYP3A4

CYP3A4是人体肝脏和小肠中存在的主要P450 上皮细胞(肠上皮细胞)。肠道细胞CYP3A4的作用 消除毒品被认为是实质性的。然而， 区分肠道和肝脏酶的作用， 以及转运蛋白P-糖蛋白的作用，一直以来 这是个问题。我们已经开发出了实验技术，已经 使我们能够在活人体内安全地研究肝脏和肠道细胞CYP3A4。 我们已经证明，存在显著的个体间和个体内 肠细胞色素P3A4活性的变化。我们还表明， 通常情况下，个体之间没有良好的内部相关性 肝脏和肠道中细胞色素P3A4的相对活性。为了进一步 研究这些变化背后的机制，我们选择了 深入观察到一些果汁(西柚) 果汁和塞维利亚橙汁)会导致明显且相对较快的损失 通过一种似乎不涉及丢失的机制来抑制肠细胞色素P3A4 细胞色素P3A4基因的表达。我们已经证明了2种果汁衍生的呋喃香豆素(FC) S)，6‘，7’-二羟基佛手柑(DHB)和相关的二聚体(FC726)，原因 CYP3A4在新的人肠道(Caco-2)细胞中的选择性缺失 单层培养系统，DHB是一种基于机制灭活剂 细胞色素P3A4。然而，DHB和FC726不能完全解释这些影响 它们的作用可能不是对CYP3A4有选择性的。我们会 检验假设多个FC S，这是相当普遍的 水果和蔬菜，导致基于机制的失活和 加速细胞内降解的细胞色素P3A4。为此，我们将 特选Fc S对细胞色素P3A4作用的时程特征 而在人类肠道微粒体中的其他主要肠细胞P450上， 我们的Caco-2细胞系统，以及在健康志愿者身上。我们还将 确定选定的FC S对合成和合成速度的影响 细胞色素P3A4在培养细胞中的降解。最后，我们将测试 假设一些口服药物治疗方案在临床上会导致 肝脏中重要的CYP3A4诱导不会诱导肝脏中的酶 肠道细胞。从拟议研究中获得的数据应提供 对CYP3A4活性变化的基础有实质性的了解 人与人之间，人与人之间，人与人之间 肠子。此外，口服FC的鉴别 S，特异性地阻断肠细胞中的细胞色素P3A4活性(但不是 肝脏)，或选择性地在肝脏中诱导CYP3A4的药物(而不是在 肠道细胞)将提供强大的研究工具来评估 肠细胞和肝脏细胞色素P3A4在细胞周期中的相对贡献 外源物质在活人体内的处置。

CYP3A4 is the major P450 present in human liver and small bowel epithelial cells (enterocytes). The contribution of enterocyte CYP3A4 to drug elimination is believed to be substantial. However, distinguishing the contributions of the intestinal vs. the liver enzyme, as well as the role of the transporter P-glycoprotein, has been problematic. We have developed experimental techniques that have enabled us to safely study liver and enterocyte CYP3A4 in living people. We have shown that there exists marked inter- and intraindividual variation in the activity of enterocyte CYP3A4. We have also shown that there is generally not a good intraindividual correlation between the relative activities of CYP3A4 in liver and intestine. To further investigate the mechanisms underlying these variations, we have chosen to intensively pursue our observation that some fruit juices (grapefruit juice and Seville orange juice) cause a marked and relatively rapid loss of enterocyte CYP3A4 by a mechanism that does not appear to involve loss of CYP3A4 mRNA. We have shown that 2 juice-derived furanocoumarins (FC s), 6',7'-dihydroxybergamottin (DHB) and a related dimer (FC726), cause selective loss of CYP3A4 in a novel human intestinal (Caco-2) cell monolayer culture system, and that DHB is a mechanism-based inactivator of CYP3A4. However, DHB and FC726 can not fully account for the effects of whole juice, and their effects may not be CYP3A4 selective. We will test the hypothesis that multiple FC s, which are quite ubiquitous in fruits and vegetables, cause mechanism-based inactivation and accelerated intracellular degradation of CYP3A4. To this end, we will characterize the time course of the effects of selected FC s on CYP3A4 and on other major enterocyte P450s in human intestinal microsomes, in our Caco-2 cell system, and in healthy volunteers. We will also determine the effects of selected FC s on rates of synthesis and degradation of CYP3A4 in our cultured cells. Finally, we will test the hypothesis that some oral medication regimens that result in clinically important induction of CYP3A4 in liver do not induce the enzyme in enterocytes. The data obtained from the proposed studies should provide substantial insight into the basis for variations in CYP3A4 activity between people, within a person over time, and between liver and intestine. In addition, the identification of orally administered FC s that specifically ablate CYP3A4 activity in enterocytes (but not liver), or drugs that selectively induce CYP3A4 in liver (but not in enterocytes) would provide powerful research tools to assess the relative contributions of enterocyte and hepatic CYP3A4 to the disposition of xenobiotics in living people.