Yuan W, Sequeira D J, Cawley G F, Eyer C S, Backes W L
Department of Pharmacology and Experimental Therapeutics, Louisiana State University Medical Center, New Orleans 70112, USA.
Arch Biochem Biophys. 1997 Mar 1;339(1):55-63. doi: 10.1006/abbi.1996.9818.
The goal of the present study was to examine the time course for changes in P450 expression and hydrocarbon metabolism after acute treatment with the simple aromatic hydrocarbon ethylbenzene (EB) and to correlate these alterations with the changes observed in alkylbenzene metabolism. Male Holtzman rats were treated with a single intraperitoneal injection of EB, and the effects on specific P450-dependent activities, immunoreactive P450 isozyme levels, and RNA levels were measured at various times after injection. Toluene was used as the test alkylbenzene for examination of the EB-mediated changes on in vitro hydrocarbon metabolism. In untreated rats, toluene was metabolized almost entirely by aliphatic hydroxylation (to benzyl alcohol); however, in EB-treated rats, significant quantities of benzyl alcohol, o-cresol, and p-cresol were produced. Interestingly, 5-10 h after EB treatment, there was a 40% decrease in benzyl alcohol production. By 24 h, rates of benzyl alcohol formation returned to control levels, whereas there was a 7-fold increase in o-cresol and a greater that 50-fold increase in p-cresol production. The changes in the disposition of toluene were then correlated with changes in particular P450 isozymes. Several P450 isozymes were induced after EB administration. P450 2B1/2-dependent testosterone 16 beta-hydroxylation and P450 2B1/2-immunoreactive protein were elevated 30-fold after EB administration, reaching maxima by 24 h and remaining elevated 48 h after exposure. Changes in P450 2B1 and 2B2 RNA preceded those of the proteins. Similar results were observed with P450 1A1. P450 2E1 RNA levels were elevated after a single EB injection. However, the elevation in P450 2E1-dependent activities and immunoreactive protein levels preceded the changes in RNA, suggesting that multiple steps are affected by EB exposure. In contrast to the increases in some isozymes, P450 2C11 protein was rapidly suppressed (within the first 2-10 h) after hydrocarbon exposure, suggestive of a destabilization of the protein. When comparing the changes in P450 isozymes to alterations in toluene metabolism, the immediate suppression in aliphatic hydroxylation of toluene (in the first 5-10 h) was consistent with the decrease in P450 2C11. Subsequent to this effect, P450 2B1/2 and 2E1 were induced, which elevated production of this metabolite to control levels. The increase in the aromatic hydroxylation of toluene to both o, and p-cresol was consistent with the induction of P450s 2B1/2, 2E1, and 1A1.
本研究的目的是检测用简单芳烃乙苯（EB）急性处理后，细胞色素P450（P450）表达和碳氢化合物代谢变化的时间进程，并将这些改变与在烷基苯代谢中观察到的变化相关联。给雄性霍尔茨曼大鼠腹腔注射一次EB，并在注射后的不同时间测量对特定P450依赖性活性、免疫反应性P450同工酶水平和RNA水平的影响。甲苯用作测试烷基苯，以检测EB介导的对体外碳氢化合物代谢的变化。在未处理的大鼠中，甲苯几乎完全通过脂肪族羟基化代谢为苯甲醇；然而，在EB处理的大鼠中，产生了大量的苯甲醇、邻甲酚和对甲酚。有趣的是，EB处理后5 - 10小时，苯甲醇生成量减少了40%。到24小时时，苯甲醇生成速率恢复到对照水平，而邻甲酚生成量增加了7倍，对甲酚生成量增加了50倍以上。然后将甲苯代谢的变化与特定P450同工酶的变化相关联。EB给药后诱导了几种P450同工酶。EB给药后，P450 2B1/2依赖性睾酮16β - 羟基化和P450 2B1/2免疫反应性蛋白升高了30倍，在24小时达到最大值，并在暴露后48小时仍保持升高。P450 2B1和2B2 RNA的变化先于蛋白质的变化。P450 1A1也观察到类似结果。单次注射EB后，P450 2E1 RNA水平升高。然而，P450 2E1依赖性活性和免疫反应性蛋白水平的升高先于RNA的变化，表明多个步骤受EB暴露影响。与某些同工酶的增加相反，碳氢化合物暴露后P450 2C11蛋白迅速被抑制（在最初2 - 10小时内），提示该蛋白不稳定。当比较P450同工酶的变化与甲苯代谢的改变时，甲苯脂肪族羟基化的立即抑制（在最初5 - 10小时内）与P450 2C11的减少一致。在此作用之后，P450 2B1/2和2E1被诱导，这使该代谢物的生成量升高到对照水平。甲苯向邻甲酚和对甲酚的芳香族羟基化增加与P450s 2B1/2、2E1和1A1的诱导一致。
