Putt D A, Ding X, Coon M J, Hollenberg P F
Department of Pharmacology, Wayne State University, School of Medicine, Detroit, MI 48201, USA.
Carcinogenesis. 1995 Jun;16(6):1411-7. doi: 10.1093/carcin/16.6.1411.
The nasal mucosa of some mammalian species are susceptible to the toxicity of aflatoxin B1 (AFB1), a potent hepatocarcinogen, but little is known about the nasal enzymes involved in the metabolic activation of AFB1 or the metabolites produced. In the present study, the metabolism of AFB1 was studied with nasal microsomes from rats and rabbits and with several purified isozymes of rabbit P450 in a reconstituted enzyme system. The rates of AFB1-N7-guanine DNA adduct formation with rabbit and rat nasal microsomes are over 3- and 10-fold higher, respectively, than with liver microsomes from the same species. On the other hand, the rates of formation of AFM1 (9a-hydroxy-AFB1) and AFQ1 (3-hydroxy-AFB1) products known to be less toxic, are lower with nasal than with liver microsomes. Of particular interest, nasal microsomes produce high levels of six unidentified polar metabolites that are not formed by microsomes from liver or several other tissues. These same products are also generated by P450 NMa purified from rabbit nasal microsomes in a reconstituted system, but not by five other isozymes of cytochrome P450 (1A2, 2B4, 2E1, 2G1, 3A6) that are known to be present in nasal microsomes. AFB1-DNA adducts are formed by P450 NMa at a rate 3-fold higher than that by nasal microsomes. The DNA adducts are formed at much slower rates by P450s 2G1, 2B4, and 1A2, and adducts are not formed at measurable rates by P450s 2E1 and 3A6. Moreover, AFB1-DNA adduct formation is also catalyzed by cDNA-derived, heterologously expressed P450s 2A10 and 2A11, both of which are known to be present in the purified P450 NMa preparation. The Km and Vmax values of the two isozymes for DNA adduct formation are comparable to those for nasal microsomes. Furthermore, the formation of AFB1-DNA adducts by nasal microsomes is decreased by nicotine, a known inhibitor of P450 NMa. These data indicate that members of the P450 2A gene subfamily play an important role in the metabolic activation of AFB1 in rabbit and rat nasal mucosa and suggest a molecular basis for assessing the health risk associated with inhalation exposure to this procarcinogen in humans.
某些哺乳动物物种的鼻黏膜易受黄曲霉毒素B1（AFB1，一种强效的肝癌致癌物）毒性的影响，但对于参与AFB1代谢活化的鼻酶或所产生的代谢物却知之甚少。在本研究中，利用大鼠和兔子的鼻微粒体以及重组酶系统中几种纯化的兔P450同工酶研究了AFB1的代谢。兔和大鼠鼻微粒体形成AFB1 - N7 - 鸟嘌呤DNA加合物的速率分别比同一物种的肝微粒体高出3倍和10倍以上。另一方面，已知毒性较小的AFM1（9a - 羟基 - AFB1）和AFQ1（3 - 羟基 - AFB1）产物的形成速率，鼻微粒体比肝微粒体低。特别值得关注的是，鼻微粒体产生高水平的六种未鉴定的极性代谢物，这些代谢物不是由肝微粒体或其他几种组织的微粒体形成的。在重组系统中，从兔鼻微粒体纯化的P450 NMa也能产生这些相同的产物，但细胞色素P450的其他五种同工酶（1A2、2B4、2E1、2G1、3A6）则不能，已知这些同工酶存在于鼻微粒体中。P450 NMa形成AFB1 - DNA加合物的速率比鼻微粒体高3倍。P450 2G1、2B4和1A2形成DNA加合物的速率要慢得多，而P450 2E1和3A6则不能以可测量的速率形成加合物。此外，cDNA衍生的、异源表达的P450 2A10和2A11也催化AFB1 - DNA加合物的形成，已知这两种酶存在于纯化的P450 NMa制剂中。这两种同工酶形成DNA加合物的Km和Vmax值与鼻微粒体的相当。此外，已知P450 NMa的抑制剂尼古丁可降低鼻微粒体形成AFB1 - DNA加合物的速率。这些数据表明，P450 2A基因亚家族成员在兔和大鼠鼻黏膜中AFB1的代谢活化中起重要作用，并为评估人类吸入这种前致癌物相关的健康风险提供了分子基础。
