Novel noninvasive assessment of cytochrome P450 activity

细胞色素P450可能是人类药物代谢中最具临床意义的酶。 P4503 A4（CYP 3A 4）是数量最丰富的肝和肠上皮细胞。CYP 3A 5代谢许多但不是全部CYP 3A 4底物。CYP 3A酶负责超过50%的所有药物的肝脏代谢，并且越来越多地被认为是口服药物首过代谢（肠和肝脏）的主要决定因素。 CYP 3A活性表现出明显的个体间变异性，这是由于CYP 3A 4表达的广泛水平、CYP 3A 4表达的遗传多态性以及CYP 3A对药物相互作用的敏感性。 一个主要的当务之急是确定药物对CYP 3A 4活性的影响，药物相互作用，并导致临床药物作用的改变。 事实上，FDA关于新药开发的法规要求鉴定代谢酶，评估潜在的临床药代动力学药物相互作用，最好是其药效学结果。不幸的是，鉴定和验证CYP 3A 4/5的理想体内代谢探针的无数努力都没有成功。目前所有CYP 3A探针都有已知的局限性，需要一定的侵入性，并且基于血浆或尿液药代动力学。本研究计划的目标是开发一种灵敏、特异、非侵入性、廉价、稳健、简单和实用的探针，用于评估人体CYP 3A活性和CYP 3A药物相互作用，主要是CYP 3A 4，其次是CYP 3A 5。本研究将检验由CYP 3A 4选择性阿片类药物阿芬太尼（ALF）引起的瞳孔收缩（瞳孔缩小）可用作替代血浆浓度和药代动力学指标的假设，从而作为体内CYP 3A 4活性的无创探针。 也就是说，“效应清除”可以取代血浆清除。 使用咪达唑仑清除率作为CYP 3A 4活性的独立指标和基因型CYP 3A 5分析的一系列临床研究将评价ALF效应清除率与CYP 3A 4活性之间的关系。（“探针”）、ALF血浆清除率和CYP 3A 4活性，以及ALF和咪达唑仑清除率之间的关系，对于1）故意改变肠和肝CYP 3A活性的受试者的静脉和口服ALF，以验证探针，2）评估探针个体间可靠性的广泛人群，3）评估探针个体间重复性的重复研究受试者，以及4）具有特定程度的故意降低CYP 3A活性的受试者，以评估探针的灵敏度。ALF清除效应的成功验证可能为评估人体最重要的药物代谢酶CYP 3A提供一种新的技术。 这种技术可以识别药物处置和反应的个体间差异机制，允许更个性化的给药，并降低药物相互作用研究的成本一个数量级或更多。

Cytochrome P450s of the 3Afamily are perhaps the most clinically significant enzymes in human drug metabolism. P4503A4 (CYP3A4) is the most quantitatively abundant hepatic and intestinal CYP. CYP3A5 metabolized numerous, but not all, CYP3A4 substrates. CYP3A enzymes are responsible for the hepatic metabolism of greater than 50 percent of all drugs, and are increasingly recognized as a major determinant of first-pass metabolism (intestinal and hepatic) of oral drugs. CYP3A activity exhibits marked interindividual variability, owing to broad levels of CYP3A4 expression, genetic polymorphism in CYP3A4 expression, and exquisite CYP3A sensitivity to drug interactions. A major imperative has been the determination of drug influence on CYP3A4 activity, drug interactions, and, resulting alterations in clinical drug effects. Indeed, FDA regulations regarding new drug development require the identification of metabolizing enzyme(s), assessment of potential clinical pharmacokinetic drug interactions, and preferably, their pharmacodynamic consequences. Myriad endeavors to identify and validate an ideal in vivo metabolic probe for CYP3A4/5 have, unfortunately, not succeeded. All current CYP3A probes have known limitations, require some invasiveness, and are based on plasma or urine pharmacokinetics. The goal of this research program is to develop a sensitive, specific, noninvasive, inexpensive, robust, simple, and utilitarian probe for assessing CYP3A activity and CYP3A drug interaction in humans, primarily CYP3A4, and secondarily CYP3A5. This investigation will test the hypothesis that pupil constriction (miosis) caused by the CYP3A4-selective opioid alfentanil (ALF) can be used as a surrogate plasma concentration and pharmacokinetic measure, and thus as a noninvasive probe for in vivo CYP3A4 activity. That is, "effect clearance" can replace plasma clearance. A series of clinical investigations, using midazolam clearance as an independent measure of CYP3A4 activity, and genotypic CYP3A5 analysis, will evaluate the relationship between ALF effect clearance ("the probe"), ALF plasma clearance, and CYP3A4 activity, as well as between ALF and midazolam clearances, for intravenous and oral ALF in 1) subjects with deliberately altered intestinal and hepatic CYP3A activity to validate the probe, 2) a broad population to assess interindividual reliability of the probe, 3) repetitively studied subjects to assess interindividual repeatability of the probe, and 4) subjects with specific degrees of deliberately reduced CYP3A activity, to assess the sensitivity of the probe. Successful validation of ALF effect clearance may provide a novel technology for assessing CYP3A, the most important drug metabolism enzyme in humans. Such technology may identify mechanisms of interindividual variability in drug disposition and response, permit more individualized dosing, and reduce the cost of drug interaction studies by an order of magnitude or more.