Carlile D J, Hakooz N, Houston J B
School of Pharmacy and Pharmaceutical Sciences, University of Manchester, Manchester, United Kingdom.
Drug Metab Dispos. 1999 Apr;27(4):526-32.
To evaluate the theory that within precision-cut liver slices intercellular transport occurs in parallel with cellular metabolism and to illustrate the constraints this places on clearance predictions, the kinetics of ethoxycoumarin O-deethylation have been determined under varying conditions of hepatic cytochrome P-450 activity. Liver slices, isolated hepatocytes, and microsomes were obtained from rats treated with the inducers phenobarbital (PB) and beta-naphthoflavone (betaNF) and the inhibitor aminobenzotriazole (ABT). In hepatocytes and microsomes, a two-site kinetic model with a high-affinity, low-capacity site and an unsaturated low-affinity, high-capacity site described the hydroxycoumarin formation data. There were marked increases in Vmax (2- to 5-fold and 50- to 70-fold for PB and betaNF, respectively) in both systems and in CLint (3- and 9-fold for PB and betaNF, respectively) in hepatocytes and substantial decreases in both parameters (3-8 and 12-23% of control, respectively) in ABT hepatocytes and microsomes. A qualitatively similar response was evident in slices obtained from livers of rats treated with phenobarbital and ABT, but although slices from betaNF livers produced high metabolic rates (comparable to slices obtained from livers of rats treated with phenobarbital), these showed a linear increase with substrate concentration without indication of a high-affinity site. The intrinsic clearance parameters were scaled to full liver capacity using hepatocellularities and microsomal recovery indices to allow direct comparison of these responses. The slice system consistently underestimated the effects of the modifiers. When compared with hepatocytes, estimates of 30, 15, and 1% for ABT, PB, and betaNF, respectively, were observed and the degree of underestimation was dependent on the magnitude of intrinsic clearance and was consistent with the above theory.
为了评估在精密肝切片中细胞间转运与细胞代谢同时发生这一理论，并阐明其对清除率预测的限制，已在不同的肝细胞色素P - 450活性条件下测定了乙氧基香豆素O - 脱乙基化的动力学。从用诱导剂苯巴比妥（PB）和β - 萘黄酮（βNF）以及抑制剂氨基苯并三唑（ABT）处理的大鼠中获取肝切片、分离的肝细胞和微粒体。在肝细胞和微粒体中，一个具有高亲和力、低容量位点和不饱和低亲和力、高容量位点的双位点动力学模型描述了羟基香豆素形成数据。在两个系统中，Vmax均显著增加（PB和βNF分别增加2至5倍和50至70倍），肝细胞中的内在清除率（CLint）分别增加3倍和9倍，而在ABT处理的肝细胞和微粒体中，这两个参数均大幅下降（分别为对照的3 - 8%和12 - 23%）。在用苯巴比妥和ABT处理的大鼠肝脏切片中也观察到了定性相似的反应，但是尽管来自βNF肝脏的切片产生了高代谢率（与来自用苯巴比妥处理的大鼠肝脏的切片相当），但这些切片显示随着底物浓度呈线性增加，没有高亲和力位点的迹象。使用肝细胞密度和微粒体回收率指标将内在清除参数按全肝容量进行缩放，以便直接比较这些反应。切片系统始终低估了调节剂的作用。与肝细胞相比，ABT、PB和βNF的估计值分别为30%、15%和1%，低估程度取决于内在清除率的大小，并且与上述理论一致。
