Nicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-butanone metabolism by cytochrome p450 2B6
Nicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-butanone metabolism by cytochrome p450 2B6
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DOI：
10.1124/dmd.105.006718
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发表时间：
2005-12-01
影响因子：
3.9
通讯作者：
Murphy, SE
中科院分区：
文献类型：
--
作者：
Dicke, KE;Skrlin, SM;Murphy, SE
尼古丁是烟草中的主要成瘾剂，主要通过5‘-氧化代谢。4-(甲基亚硝胺)-1-(3-吡啶)-1-丁酮(NNK)是烟草烘烤过程中产生的一种强致癌物质，由P450酶代谢激活。P450 2A6是尼古丁代谢的主要肝脏催化剂，也催化NNKα-羟化，尽管效率较低。此前有报道称，P450 2B6催化尼古丁5‘-氧化。本文研究了P450 2B6作为人肝微粒体内尼古丁5‘氧化和NNKα-羟化的催化剂的相对重要性。用Radioflow高效液相色谱仪和氚底物监测尼古丁和NNK代谢产物。P450 2B6催化尼古丁代谢的主要产物是Delta(1‘(5’))亚胺离子。唯一检测到的其他代谢物是去甲烟碱，它是甲基氧化的产物，其形成速度约为Delta(1‘(5’))亚胺离子的四分之一。我们确定P450 2B6是尼古丁5‘-氧化的有效催化剂，估计KM为820微米。相反，NNKα羟化的KM为33微米。使用P450 2A6和P450 2B6选择性抑制抗体的实验不支持P450 2B6作为HLMS氧化尼古丁5’的重要催化剂，而且这种酶不太可能促进表达P450 2A6的吸烟者的尼古丁代谢。然而，在同时表达P450 2B6和P450 2A6的HLM中，P450 2B6对NNK代谢有显著的促进作用，提示P450 2B6可能在NNK代谢激活中起作用。
Nicotine is the major addictive agent in tobacco; it is primarily metabolized by 5'-oxidation. 4-(Methylnitrosamine)-1-(3-pyridyl)-1butanone (NNK), a potent lung carcinogen generated from nicotine during the curing of tobacco, is metabolically activated by P450 enzymes. P450 2A6 is the primary hepatic catalyst of nicotine metabolism and also catalyzes NNK alpha-hydroxylation, albeit less efficiently. It was previously reported that P450 2B6 catalyzed nicotine 5'-oxidation. The studies presented here investigate the relative importance of P450 2B6 as a catalyst of nicotine 5'-oxidation and NNK alpha-hydroxylation by human liver microsomes (HLMs). Radioflow high-performance liquid chromatography analysis and tritiated substrates were used to monitor the products of nicotine and NNK metabolism. The primary product of P450 2B6-catalyzed nicotine metabolism was the Delta(1'(5')) iminium ion. The only other metabolite detected was nornicotine, the product of methyl oxidation, formed at about one-fourth the rate of the Delta(1'(5')) iminium ion. We determined that P450 2B6 was a much less efficient catalyst of nicotine 5'-oxidation than previously reported, with an estimated Km of 820 mu M. In contrast, the Km of NNK alpha-hydroxylation was 33 mu M. Experiments with P450 2A6-and P450 2B6-selective inhibitory antibodies did not support P450 2B6 as a significant catalyst of nicotine 5'-oxidation by HLMs, and it is unlikely that this enzyme contributes to nicotine metabolism in smokers who express P450 2A6. However, P450 2B6 contributed significantly to NNK metabolism in HLMs expressing both P450 2B6 and P450 2A6, suggesting a possible role for P450 2B6 in NNK metabolic activation.