Kajbaf Mahmud, Ricci Raffaella, Zambon Serenella, Fontana Stefano
Bioanalytics, Metabolism and in vitro Technologies, DMPK, Aptuit, Via A. Fleming, 4, 37135, Verona, Italy.
Eur J Drug Metab Pharmacokinet. 2013 Mar;38(1):33-41. doi: 10.1007/s13318-012-0098-5. Epub 2012 Jun 20.
Michaelis-Menten constants K m and V max values were determined by product formation and substrate depletion at several substrate concentrations of 4-methylumbelliferone using rat intestinal microsomes. K m and V max values determined by measuring product formation were in good agreement with substrate depletion approach. We also investigated hepatic and intestinal in vitro intrinsic clearance (CLint) in the liver and intestinal microsomes and compare with reports in the literature using nine test compounds, atorvastatin, 7-ethoxycoumarin, indomethacin, 4-methylumbelliferone, midazolam, nifedipine, testosterone, terfenadine and verapamil, in rats. CLint was determined from the substrate disappearance rate at 0.1 and 0.5 μM in the rat intestinal and liver microsomes, respectively. These results showed that both the liver and the intestine contributed to the metabolism of these compounds. The intestinal intrinsic clearance values of all these drugs, except for terfenadine in the rat intestinal microsomes, were lower than their hepatic intrinsic clearance per milligram protein, showing that there was an organ difference in metabolism between the liver and intestinal. These results make the evaluation using the intestinal more useful and provide a basis for predicting clearance using intestinal.
利用大鼠肠道微粒体，通过在几种4 - 甲基伞形酮底物浓度下产物生成和底物消耗情况来测定米氏常数Km和最大反应速度Vmax值。通过测量产物生成所确定的Km和Vmax值与底物消耗法测定结果高度吻合。我们还研究了大鼠肝脏和肠道微粒体中的肝和肠道体外内在清除率（CLint），并使用九种受试化合物（阿托伐他汀、7 - 乙氧基香豆素、吲哚美辛、4 - 甲基伞形酮、咪达唑仑、硝苯地平、睾酮、特非那定和维拉帕米）与文献报道进行比较。CLint分别根据大鼠肠道和肝脏微粒体中0.1和0.5 μM时底物消失速率来确定。这些结果表明肝脏和肠道均参与了这些化合物的代谢。除大鼠肠道微粒体中的特非那定外，所有这些药物的肠道内在清除率值均低于每毫克蛋白质的肝脏内在清除率，表明肝脏和肠道在代谢方面存在器官差异。这些结果使得利用肠道进行评估更具实用性，并为利用肠道预测清除率提供了依据。
