Comparative metabolism of N-nitrosopiperidine and N-nitrosopyrrolidine by rat liver and esophageal microsomes and cytochrome P450 2A3.
Comparative metabolism of N-nitrosopiperidine and N-nitrosopyrrolidine by rat liver and esophageal microsomes and cytochrome P450 2A3.
复制标题
大鼠肝脏和食管微粒体以及细胞色素 P450 2A3 对 N-亚硝基哌啶和 N-亚硝基吡咯烷的比较代谢。
DOI：
10.1093/carcin/24.2.291
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发表时间：
2003
期刊：
影响因子：
4.7
通讯作者：
Hecht,StephenS
中科院分区：
文献类型：
--
作者：
Wong,HansenL;Murphy,SharonE;Wang,Mingyao;Hecht,StephenS
N-亚硝基哌啶 (NPIP) 是一种对大鼠有效的食道致癌物，而结构相似的 N-亚硝基吡咯烷 (NPYR) 会诱发肝脏肿瘤，但不会诱发食道肿瘤。 NPIP 可能是人类食管癌的病原体。我们的目标是从机制上解释食道中这些不同的致癌活动。我们假设这些亚硝胺代谢活化的差异可能是导致其不同致癌性的因素之一。 α-羟基化是导致亚硝胺诱发癌变的关键代谢激活途径。在本研究中，我们检测了雄性 F344 大鼠食管和肝微粒体对 [3,4-3H]NPIP 和 [3,4-3H]NPYR 的 α-羟基化率。 NPIP 和 NPYR 的主要 α-羟基化产物，分别是 2-羟基四氢-2H-吡喃 (2-OH-THP) 和 2-羟基四氢呋喃 (2-OH-THF)，通过高效液相色谱和无线电流检测进行监测。将 NPIP 或 NPYR (4 μM) 与不同浓度的食管微粒体和辅助因子一起孵育。微粒体将 NPIP 转化为 2-OH-THP，其转化速度比 NPYR 转化为 2-OH-THF 的速度高 40 倍。在底物浓度为 4 至 100 μM 的 NPIP 和 NPYR 的研究中观察到了类似的结果。 NPIP α-羟基化动力学为双相；KM 值为 312 ± 50 和 1600 ± 312 μM。表达的细胞色素 P450 2A3 在大鼠食道中含量较低，是 NPIP α-羟基化的良好催化剂 (KM= 61.6 ± 20.5 μM)，但对 NPYR α-羟基化的催化剂较差 (Km= 1198 ± 308 μM)。细胞色素 P450 2A3 可能在大鼠食道中观察到的 NPIP 优先激活中发挥作用。肝微粒体将 NPYR 代谢为 2-OH-THF (Vmax/KM= 3.23 pmol/min/mg/μM)，与 NPIP 代谢为 2-OH-THP (Vmax/KM= 3.80–4.61 pmol/min/mg/μM) 一样有效。我们得出结论，大鼠食管微粒体激活 NPIP 但不激活 NPYR，而大鼠肝微粒体激活 NPIP 和 NPYR。这些结果与之前的发现一致，即亚硝胺的组织特异性激活有助于组织特异性肿瘤的形成。
N-nitrosopiperidine (NPIP) is a potent esophageal carcinogen in rats whereas structurally similarN-nitrosopyrrolidine (NPYR) induces liver, but not esophageal tumors. NPIP is a possible causative agent for human esophageal cancer. Our goal is to explain mechanistically these differing carcinogenic activities in the esophagus. We hypothesize that differences in metabolic activation of these nitrosamines could be one factor accounting for their differing carcinogenicity. α-Hydroxylation is the key metabolic activation pathway leading to nitrosamine-induced carcinogenesis. In this study, we examined the α-hydroxylation rates of [3,4-3H]NPIP and [3,4-3H]NPYR by male F344 rat esophageal and liver microsomes. The major α-hydroxylation products of NPIP and NPYR, 2-hydroxytetrahydro-2H-pyran (2-OH-THP) and 2-hydroxytetrahydrofuran (2-OH-THF), respectively, were monitored by high performance liquid chromatography with radioflow detection. NPIP or NPYR (4 μM) was incubated with varying concentrations of esophageal microsomes and co-factors. Microsomes converted NPIP to 2-OH-THP with a 40-fold higher velocity than NPYR to 2-OH-THF. Similar results were observed in studies with NPIP and NPYR at substrate concentrations between 4 and 100 μM. Kinetics of NPIP α-hydroxylation were biphasic;KMvalues were 312 ± 50 and 1600 ± 312 μM. Expressed cytochrome P450 2A3, found in low levels in rat esophagus, was a good catalyst of NPIP α-hydroxylation (KM= 61.6 ± 20.5 μM), but a poor catalyst of NPYR α-hydroxylation (Km= 1198 ± 308 μM). Cytochrome P450 2A3 may play a role in the preferential activation of NPIP observed in rat esophagus. Liver microsomes metabolized NPYR to 2-OH-THF (Vmax/KM= 3.23 pmol/min/mg/μM) as efficiently as NPIP to 2-OH-THP (Vmax/KM= 3.80–4.61 pmol/min/mg/μM). We conclude that rat esophageal microsomes activate NPIP but not NPYR whereas rat liver microsomes activate NPIP and NPYR. These results are consistent with previous findings that tissue-specific activation of nitrosamines contributes to tissue-specific tumor formation.