Toxicological Significance of Alkylbenzene Metabolism

描述(由申请人提供)：本提案的长期目标是提供信息，帮助确定个体在哪些条件下可能容易受到烷基苯引起的毒性影响。烷基苯在世界各地大量生产。简单的芳香烃(如苯、甲苯和乙苯)是无铅汽油的主要成分，也用于生产各种消费品。P450系统负责芳香烃的脂肪族和芳香族羟基化，与碳氢化合物代谢有关的几种形式，如CYP1A2、CYP2B4和CYP2E1。已知许多碳氢化合物的毒性是由于一小部分母体化合物对活性中间体的生物活化。这一过程需要P450和黄素蛋白NADPH-细胞色素P450还原酶之间的功能相互作用。然而，总的P450水平是还原酶的20：1。此外，P450有多种形式，每种形式都有自己的还原酶结合特性和底物依赖性。这就提出了一个问题：“一个单一的还原酶是如何为所有的P450提供电子的？”第二个问题是：“一个P450能影响第二个P450的功能吗？”拟议的研究旨在解决与P450和还原酶的组织有关的问题，重点是烷基苯类的代谢。在之前的资助期间，我们确定了对底物代谢有实质性影响的CYP2B4、CYP1A2和还原酶之间的重要相互作用。这一结果与具有不寻常的还原酶结合特性的CYP1A2-CYP2B4复合体的形成一致。我们现在建议描述这些相互作用，并确定负责这些蛋白质之间相互作用的区域(S)。我们还打算研究P450-P450在细胞色素P450/细胞色素P450A2/还原酶，和细胞色素P450/细胞色素P450/还原酶系统中的相互作用，并集中在这些相互作用不仅改变碳氢化合物和其他底物的代谢，而且改变活性氧的产生的能力。这些研究将增加我们对P450电子传输链的组织方式的理解，并将为P450系统在芳香烃的生物活化和活性氧的产生中所起的作用提供新的重要信息-这一过程可以对化学毒性产生重大影响。

DESCRIPTION (provided by applicant): The long-term objective of this proposal is to supply information that will aid in identifying conditions under which individuals may be susceptible to alkylbenzene-induced toxicity. Alkylbenzenes are produced in extensive quantities throughout the world. Simple aromatic hydrocarbons (e.g. benzene, toluene, and ethylbenzene) are major components of unleaded gasoline and are also used in the production of a wide variety of consumer products. The P450 system is responsible for both aliphatic and aromatic hydroxylation of the aromatic hydrocarbons, with several forms, CYP1A2, CYP2B4, and CYP2E1, being implicated in hydrocarbon metabolism. The toxicity from many of the hydrocarbons is known to be due to bioactivation of a small percentage of the parent compound to reactive intermediates. This process requires a functional interaction between P450 and the flavoprotein NADPH-cytochrome P450 reductase. However, total P450 levels exceed those of reductase by a ratio of 20:1. In addition, there are multiple forms of P450, each having their own reductase binding characteristics and substrate dependencies. This raises the question: "How does a single reductase supply electrons to all the P450s?" A second question is: "Can one P450 influence the function of a second P450?" The proposed studies are designed to address questions related to the organization of P450 and reductase, focusing on the metabolism of alkylbenzenes. During the prior grant period, we identified important interactions among CYP2B4, CYP1A2 and reductase that have a substantial effect on substrate metabolism. The results are consistent with the formation of a CYP1A2-CYP2B4 complex having unusual reductase binding characteristics. We now propose to characterize these interactions, and to identify the region(s) responsible for the interactions among these proteins. We also intend to examine P450-P450 interactions in the CYP2E1/CYP1A2/reductase, and CYP2E1/CYP2B4/reductase systems, and to focus on the ability of these interactions to alter not only metabolism of hydrocarbons and other substrates, but also generation of reactive oxygen. These studies will increase our understanding of how the P450 electron transport chain is organized, and will provide new important information on the role of the P450 system in the bioactivation of aromatic hydrocarbons and the generation of reactive oxygen - a process that can have a significant influence on chemical toxicity.