Sheets Patrick, Carlson Gary
School of Health Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
J Toxicol Environ Health A. 2004 Mar 12;67(5):421-30. doi: 10.1080/15287390490273488.
Benzene is an occupational and environmental toxicant. The main human health concern associated with benzene exposure is acute myelogenous leukemia. Benzene produces lung tumors in mice, while its effects on human lung are not clear. The adverse effects of benzene are dependent on its metabolism by the cytochrome P-450 enzyme system. The isozymes CYP2E1 and CYP2F2 play roles in the metabolism of benzene at low, environmentally relevant concentrations. Previous studies indicate that the mouse lung readily metabolizes benzene and that CYP2F2 plays a role in this biotransformation. The significance of CYP2E1 and CYP2F2 in benzene metabolism was determined by measuring their apparent kinetic parameters K(m) and V(max). Use of wild-type and CYP2E1 knockout mice and selective inhibitors allowed the determination of the individual importance of both CYP2E1 and CYP2F2 in mouse liver and lung. A simple Michaelis-Menten relationship involving Lineweaver-Burk plots for the microsomal metabolism of benzene shows the apparent kinetic factors are different between the wild-type (K(m): 30.4 microM, V(max): 25.3 pmol/mg protein/min) and knockout (K(m): 1.9 microM, V(max): 0.5 pmol/mg protein/min) mouse livers. Wild-type lung has a K(m) of 2.3 microM and V(max) of 0.9 pmol/mg protein/min. CYP2E1 knockout lung has similar affinity and metabolic activity with a K(m) of 3.7 microM and V(max) of 1.2 pmol/mg protein/min. These data suggest CYP2E1 is less important in the lung than liver, and that it has a lower affinity for benzene but higher rate of hydroxylated metabolite production than does CYP2F2, which plays the predominant role in metabolizing benzene in mouse lung.
苯是一种职业性和环境性毒物。与苯接触相关的主要人类健康问题是急性髓性白血病。苯可在小鼠体内诱发肺癌，但其对人类肺部的影响尚不清楚。苯的不良反应取决于细胞色素P-450酶系统对其的代谢。同工酶CYP2E1和CYP2F2在环境相关的低浓度苯代谢中发挥作用。先前的研究表明，小鼠肺脏易于代谢苯，且CYP2F2在这种生物转化中发挥作用。通过测量CYP2E1和CYP2F2的表观动力学参数K(m)和V(max)，确定了它们在苯代谢中的重要性。使用野生型和CYP2E1基因敲除小鼠以及选择性抑制剂，确定了CYP2E1和CYP2F2在小鼠肝脏和肺脏中的个体重要性。一个涉及苯微粒体代谢的Lineweaver-Burk图的简单米氏关系表明，野生型（K(m)：30.4 microM，V(max)：25.3 pmol/mg蛋白质/分钟）和基因敲除（K(m)：1.9 microM，V(max)：0.5 pmol/mg蛋白质/分钟）小鼠肝脏的表观动力学因素不同。野生型肺脏的K(m)为2.3 microM，V(max)为0.9 pmol/mg蛋白质/分钟。CYP2E1基因敲除肺脏具有相似的亲和力和代谢活性，K(m)为3.7 microM，V(max)为1.2 pmol/mg蛋白质/分钟。这些数据表明，CYP2E1在肺脏中的重要性低于肝脏，且其对苯的亲和力较低，但与CYP2F2相比，其羟基化代谢产物的生成速率较高，而CYP2F2在小鼠肺脏中苯的代谢中起主要作用。
