Division of Systems Pharmacology and Pharmacy, Leiden Academic Centre for Drug Research, Einsteinweg 55, 2333 CC, Leiden, The Netherlands.
Department of Clinical Pharmacy and Toxicology, Leiden University Medical Center, Leiden, The Netherlands.
Clin Pharmacokinet. 2024 Nov;63(11):1585-1595. doi: 10.1007/s40262-024-01426-8. Epub 2024 Oct 27.
CYP450 (CYP) phenotyping involves quantifying an individual's plasma clearance of CYP-specific probe drugs, as a proxy for in vivo CYP enzyme activity. It is increasingly applied to study alterations in CYP enzyme activity under various (patho)physiological conditions, such as inflammation, obesity, or pregnancy. The phenotyping approach assumes that changes in plasma clearance of probe drugs are driven by changes in CYP enzyme activity. However, plasma clearance is also influenced by protein binding, blood-to-plasma ratio, and hepatic blood flow, all of which may change under (patho)physiological conditions.
Using a physiologically based pharmacokinetic (PBPK) workflow, we aimed to evaluate whether the plasma clearance of commonly used CYP probe drugs is indeed directly proportional to alterations in CYP enzyme activity (sensitivity), and to what extent alterations in protein binding, blood-to-plasma ratio, and hepatic blood flow observed under (patho)physiological conditions impact plasma clearance (specificity).
Plasma clearance of CYP probe drugs is sensitive to alterations in CYP enzyme activity, since alterations in intrinsic clearance between - 90% and + 150% resulted in near-proportional changes in plasma clearance, except for midazolam in the case of > 50% CYP3A4 induction. However, plasma clearance also changed near-proportionally with alterations in the unbound drug fraction, diminishing probe specificity. This was particularly relevant for high protein-bound probe drugs, as alterations in plasma protein binding resulted in larger relative changes in the unbound drug fraction. Alterations in the blood-to-plasma ratio and hepatic blood flow of ± 50% resulted in plasma clearance changes of less than ± 16%, meaning they limitedly impacted plasma clearance of CYP probe drugs, except for midazolam. In order to correct for the impact of non-metabolic determinants on probe drug plasma clearance, an R script was developed to calculate how much the CYP enzyme activity is actually altered under (patho)physiological conditions, when alterations in the unbound drug fraction, blood-to-plasma ratio, and/or hepatic blood flow also impact probe drug plasma clearance.
As plasma protein binding can change under (patho)physiological conditions, alterations in unbound drug fraction should be accounted for when using CYP probe drug plasma clearance as a proxy for CYP enzyme activity in patient populations. The tool developed in this study can support researchers in determining alterations in CYP enzyme activity in patients with (patho)physiological conditions.
CYP450（CYP）表型分析涉及定量测定个体对 CYP 特异性探针药物的血浆清除率，作为体内 CYP 酶活性的替代指标。它越来越多地被应用于研究各种（病理）生理条件下 CYP 酶活性的改变，如炎症、肥胖或妊娠。表型分析方法假设探针药物的血浆清除率的变化是由 CYP 酶活性的变化驱动的。然而，血浆清除率也受到蛋白结合、血液与血浆的比例和肝血流量的影响，所有这些在（病理）生理条件下都可能发生变化。
使用基于生理学的药代动力学（PBPK）工作流程，我们旨在评估常用 CYP 探针药物的血浆清除率是否确实与 CYP 酶活性的改变直接成比例（敏感性），以及（病理）生理条件下观察到的蛋白结合、血液与血浆的比例和肝血流量的改变对血浆清除率的影响程度（特异性）。
CYP 探针药物的血浆清除率对 CYP 酶活性的改变敏感，因为内在清除率在-90%到+150%之间的改变导致血浆清除率几乎成比例的变化，除了 50%以上 CYP3A4 诱导的情况下的咪达唑仑。然而，血浆清除率也随着未结合药物分数的改变而近比例变化，降低了探针的特异性。这在高蛋白结合探针药物中尤为重要，因为血浆蛋白结合的改变导致未结合药物分数的相对变化较大。血液与血浆的比例和肝血流量改变±50%导致血浆清除率的变化小于±16%，这意味着它们对 CYP 探针药物的血浆清除率的影响有限，除了咪达唑仑。为了校正非代谢决定因素对探针药物血浆清除率的影响，开发了一个 R 脚本来计算在（病理）生理条件下，当未结合药物分数、血液与血浆的比例和/或肝血流量的改变也影响探针药物的血浆清除率时，CYP 酶活性实际上发生了多大的改变。
由于（病理）生理条件下的血浆蛋白结合可能发生变化，因此在将 CYP 探针药物的血浆清除率作为患者群体中 CYP 酶活性的替代指标时，应考虑未结合药物分数的变化。本研究中开发的工具可以帮助研究人员确定（病理）生理条件下患者 CYP 酶活性的变化。
