Cytochrome P450 in Nicotine Metabolism

描述：(申请人提供)尼古丁是公认的 烟草中的成瘾剂及其代谢物在化学上有很好的描述。 令人惊讶的是，负责尼古丁新陈代谢的特定酶是 相当糟糕的特点。在本提案中，个体P450在 尼古丁和可替宁的新陈代谢将被研究。在大多数吸烟者身上 大部分尼古丁被代谢成可替宁。这是第一步 途径是尼古丁5‘-氧化。可替宁被代谢成 反式-3‘-羟基可替宁，吸烟者排出的主要尼古丁代谢物。 据报道，P450 2A6与尼古丁的5‘-氧化有关 可替宁的3‘-羟基化反应。尼古丁并不完全被代谢。 由P450 2A6和P450 2A6催化的尼古丁代谢对 5‘-氧化。我们已经报道了P450 2A6和人肝微粒体 (HLM)催化尼古丁的2‘-氧化。这个反应的产物是 肺癌致癌物NNK的前体。P450 2A13，与之密切相关 TO P450 2A6在肺中表达，是两者的有效催化剂 尼古丁5‘-氧化和NNK代谢激活。尼古丁的含量 这种酶的2‘-氧化作用尚不清楚。P450 2A13可能被证明是一种 NNK诱导吸烟者肺癌发生中的重要酶。P450 2B6是 也是尼古丁5‘-氧化的催化剂，似乎对尼古丁有贡献 HLM的新陈代谢。禁烟剂安非他酮是由P450 2B6代谢的。 安非他酮的作用机制之一可能是其抑制作用。 尼古丁新陈代谢。调查尼古丁重要性的研究 吸烟中的新陈代谢及代谢抑制剂的使用 行为是持续的。为了使这些研究取得成功并优化使用 药物有助于减少吸烟，了解所有这些是至关重要的 参与尼古丁新陈代谢的酶，并对其产物进行表征 每条路径。这项提案的目标是确定 P450 2A6和其他肝脏P450对尼古丁和可替宁的代谢，以 人肺微粒体对尼古丁和可替宁代谢的研究 和P450在肺中的存在，并确定其特异性 肺和肝脏中重要的P450蛋白参与代谢。假设是 测试表明，尼古丁和可替宁都是由P450代谢的，而不是 P450 2A6，这种代谢的特异性在P450之间会有所不同。 其具体目的是：1)确定人肝P450蛋白的其他功能 在尼古丁和可替宁代谢上都比P450 2A6强，2)为了表征 人肺微粒体内尼古丁和可替宁的代谢，3)完全 人肺尼古丁和可替宁代谢产物的特征 微粒体，4)确定安非他酮是否抑制任何途径 HLM中的尼古丁代谢。

DESCRIPTION: (PROVIDED BY APPLICANT) Nicotine is well established to be the addictive agent in tobacco, and its metabolites are chemically well described. Surprisingly, the specific enzymes responsible for nicotine metabolism are rather poorly characterized. In this proposal the role of individual P450s in the metabolism of nicotine and cotinine will be investigated. In most smokers the majority of nicotine is metabolized to cotinine. The first step of this pathway is nicotine 5'- oxidation. Cotinine is metabolized to trans-3'-hydroxycotinine, the major nicotine metabolite excreted by smokers. P450 2A6 is reported to be responsible for both the 5'-oxidation of nicotine and the 3'-hydroxylation of cotinine. Nicotine is not exclusively metabolized by P450 2A6, and P450 2A6-catalyzed nicotine metabolism is not specific for 5'-oxidation. We have reported that both P450 2A6 and human liver microsomes (HLM) catalyze the 2'-oxidation of nicotine. The product of this reaction is the precursor of the lung carcinogen, NNK. P450 2A13, which is closely related to P450 2A6, is expressed in the lung and is an efficient catalyst of both nicotine 5'-oxidation and NNK metabolic activation. The extent of nicotine 2'-oxidation by this enzyme is unknown. P450 2A 13 could prove to be an important enzyme in NNK induced lung carcinogenesis in smokers. P450 2B6 is also a catalyst of nicotine 5'-oxidation and appears to contribute to nicotine metabolism by HLM. The antismoking agent bupropion is metabolized by P450 2B6. It is proposed that one mechanism of bupropion's action may be its inhibition of nicotine metabolism. Studies to investigate the importance of nicotine metabolism in smoking and the use of metabolism inhibitors to modify smoking behavior are ongoing. For these studies to succeed and to optimize the use of pharmacological agents to help reduce smoking, it is critical to understand all the enzymes involved in nicotine metabolism and to characterize the products of each pathway. The goals of this proposal are to determine the contribution of P450 2A6 and other hepatic P450s to nicotine and cotinine metabolism, to investigate the metabolism of nicotine and cotinine by human lung microsomes and P450s present in the lung, and to determine the specificity of that metabolism by the important P450s in the lung and liver. The hypotheses to be tested are that both nicotine and cotinine are metabolized by P450s other than P450 2A6 and that the specificity of that metabolism will vary among, P450s. The specific aims are: 1) .to determine the role of human hepatic P450s other than P450 2A6 in both nicotine and cotinine metabolism, 2) to characterize the metabolism of nicotine and cotinine by human lung microsomes, 3) to completely characterize the products of nicotine and cotinine metabolism by human lung microsomes, 4) to determine whether bupropion inhibits any of the pathways of nicotine metabolism in HLM.