Preferential metabolic activation of N-nitrosopiperidine as compared to its structural homologue N-nitrosopyrrolidine by rat nasal mucosal microsomes.
Preferential metabolic activation of N-nitrosopiperidine as compared to its structural homologue N-nitrosopyrrolidine by rat nasal mucosal microsomes.
复制标题
与其结构同系物 N-亚硝基吡咯烷相比，N-亚硝基哌啶被大鼠鼻粘膜微粒体优先代谢激活。
DOI：
10.1021/tx0340495
复制
发表时间：
2003
影响因子：
4.1
通讯作者：
Hecht,StephenS
中科院分区：
文献类型：
--
作者：
Wong,HansenL;Murphy,SharonE;Hecht,StephenS
N-亚硝基哌啶（NPIP）是一种强致癌物，而N-亚硝基吡咯烷（NPYR）是一种弱致癌物。NPIP和NPYR可能是人类癌症的致病因子。P450催化的α-羟基化是亚硝胺类化合物致癌的关键活化途径。我们推测NPIP和NPYR在鼻腔中代谢活化的差异导致了它们不同的致癌活性。在本研究中，研究了Sprague−道利大鼠鼻嗅或呼吸微粒体介导的氚标记NPIP或NPYR α-羟基化的动力学。为了比较两种亚硝胺（氚化2-羟基四氢-2H-吡喃和2-羟基-5-甲基四氢呋喃，主要的NPIP α-羟基化产物）和氚化2-羟基四氢呋喃（主要的NPYR α-羟基化产物）的α-羟基化速率，通过HPLC结合UV吸光度和放射流检测进行定量。这些微粒体比NPYR更有效地催化NPIP的α-羟基化。NPIP的Km值低于NPYR（13.9 - 34.7 vs 484 - 7660 μM）。此外，NPIP的催化效率（Vmax/KM）比NPYR高20 - 37倍。先前的研究表明，存在于大鼠鼻子中的P450 2A 3也表现出这种催化效率的差异。对于两种类型的鼻微粒体，香豆素（100 μM），一种P450 2A抑制剂，抑制NPIP和NPYR α-羟基化的63.8%至98.5%。此外，抗P450 2A 6抗体对这些微粒体中亚硝胺α-羟基化的抑制率为68.8%至78.4%，而抗P450 2 E1抗体对这些反应没有抑制作用。进一步的免疫抑制研究表明P450 2G 1在嗅微粒体代谢NPIP中具有一定的作用。总之，大鼠鼻粘膜的嗅觉和呼吸微粒体优先激活NPIP而不是NPYR，P450 2A 3可能起关键作用。这些结果与亚硝胺的局部代谢活化是其组织特异性致癌性的促成因素一致。
N-Nitrosopiperidine (NPIP) is a potent rat nasal carcinogen whereasN-nitrosopyrrolidine (NPYR), a hepatic carcinogen, is weakly carcinogenic in the nose. NPIP and NPYR may be causative agents in human cancer. P450-catalyzed α-hydroxylation is the key activation pathway by which these nitrosamines elicit their carcinogenic effects. We hypothesize that the differences in NPIP and NPYR metabolic activation in the nasal cavity contribute to their differing carcinogenic activities. In this study, the kinetics of tritium-labeled NPIP or NPYR α-hydroxylation mediated by Sprague−Dawley rat nasal olfactory or respiratory microsomes were investigated. To compare α-hydroxylation rates of the two nitrosamines, tritiated 2-hydroxytetrahydro-2H-pyran and 2-hydroxy-5-methyltetrahydrofuran, the major NPIP α-hydroxylation products, and tritiated 2-hydroxytetrahydrofuran, the major NPYR α-hydroxylation product, were quantitated by HPLC with UV absorbance and radioflow detection. These microsomes catalyzed the α-hydroxylation of NPIP more efficiently than that of NPYR.KMvalues for NPIP were lower as compared to those for NPYR (13.9−34.7 vs 484−7660 μM). Furthermore, catalytic efficiencies (Vmax/KM) of NPIP were 20−37-fold higher than those of NPYR. Previous studies showed that P450 2A3, present in the rat nose, also exhibited this difference in catalytic efficiency. For both types of nasal microsomes, coumarin (100 μM), a P450 2A inhibitor, inhibited NPIP and NPYR α-hydroxylation from 63.8 to 98.5%. Furthermore, antibodies toward P450 2A6 inhibited nitrosamine α-hydroxylation in these microsomes from 68.8 to 78.4% whereas antibodies toward P450 2E1 did not inhibit these reactions. Further immunoinhibition studies suggest some role for P450 2G1 in NPIP metabolism by olfactory microsomes. In conclusion, olfactory and respiratory microsomes from rat nasal mucosa preferentially activate NPIP over NPYR with P450 2A3 likely playing a key role. These results are consistent with local metabolic activation of nitrosamines as a contributing factor in their tissue-specific carcinogenicity.