Human liver microsomes (HLM) and human hepatocytes (HHEP) are two common in vitro systems used in metabolic stability and inhibition studies. The comparison between the assays using the two systems can provide mechanistic insights on the interplay of metabolism, passive permeability and transporters. This study investigated the critical factors impacting the unbound intrinsic clearance (CL_int,u) and IC₅₀ of CYP3A inhibition between HLM and HHEP. The HLM/HHEP CL_int,u ratio and HHEP/HLM IC₅₀ ratio are inversely correlated to passive permeability, but have no correlation with P-gp efflux ratio. Cofactor-supplemented permeabilized HHEP (MetMax®) collapses the IC₅₀ differences between HHEP and HLM. P-gp inhibitor, encequidar, shows minimal impact on CL_int,u and IC₅₀ in HHEP. This is the first study that is able to separately investigate the effects of passive permeability and efflux transport. These data collectively show that passive permeability plays a critical role in metabolism and enzyme inhibition in HHEP, while P-gp efflux has a minor role. This may be due to low functional P-gp activity in suspension HHEP under the assay conditions. Low passive permeability may limit metabolism and enzyme inhibition in HHEP, leading to lower CL_int,u and higher IC₅₀ in HHEP compared to HLM. When liver microsomes give higher CL_int,u than hepatocytes, microsomes are more predictive of in vivo clearance than hepatocytes.

人肝微粒体（HLM）和人肝细胞（HHEP）是用于代谢稳定性和抑制研究的两种常见的体外系统。使用这两种系统进行的分析之间的比较可以提供有关新陈代谢，被动渗透性和转运蛋白相互作用的机理性见解。本研究调查了影响HLM和HHEP之间的CYP3A抑制的未结合固有清除率（CL _int，u）和IC ₅₀的关键因素。HLM / HHEP CL _int，u比值和HHEP / HLM IC ₅₀比值与被动导磁率成反比，但与P-gp外排率无关。辅因子增透的HHEP（MetMax®）使IC ₅₀崩溃HHEP和HLM之间的差异。P-gp抑制剂encequidar对HHEP中的CL _int，u和IC ₅₀影响最小。这是第一项能够单独研究被动渗透性和外排传输影响的研究。这些数据共同表明，被动通透性在HHEP的代谢和酶抑制中起关键作用，而P-gp外排则起次要作用。这可能是由于在测定条件下，悬浮液HHEP中的功能性P-gp活性较低。低被动通透性可能会限制HHEP中的代谢和酶抑制作用，从而导致HHEP中的CL _int，u较低_， IC ₅₀高于HLM。当肝微粒体给出更高的CL _int时，u 与肝细胞相比，微粒体对体内清除的预测性更高。