Kelly J D, Eaton D L, Guengerich F P, Coulombe R A
Program in Toxicology and Molecular Biology, Utah State University, Logan 84322-4620, USA.
Toxicol Appl Pharmacol. 1997 May;144(1):88-95. doi: 10.1006/taap.1997.8117.
Inhalation exposure to the carcinogen aflatoxin B1 (AFB1) in certain occupations is considerable. Because circumstantial epidemiological evidence suggests that AFB1 inhalation may cause primary lung cancer, we investigated AFB1 activation by human lung microsomes. Microsomes were incubated with [3H]AFB1 (124 microM), and activation to the AFB1-8,9-epoxide was measured as the AFB1-glutathione (AFB1-GSH) conjugate by HPLC. The formation of AFB1-GSH was in the range of 0.05-0.073 fmol/mg protein/min. The role of cytochrome P450 (CYP) 3A in this activation was investigated by oxidation of nifedipine (a prototype substrate for CYP 3A), by immunoinhibition, and by immunoblot analysis. Nifedipine oxidation varied from 0.2 to 19.2 pmol/mg protein/min in microsomes from different subjects, but did not correlate with AFB1 activation. Anti-human polyclonal CYP 3A4 IgG inhibited AFB1 activation. CYP 3A isoforms were immunoestimated to be in the range of 0.01-1.90 pmol/mg protein. Neither CYP 1A2 nor associated activity was detected in the lung microsomes. These data indicate that human lung microsomes activate AFB1 to form the exo-AFB1-8,9-epoxide and that CYP(s) of the 3A subfamily may be responsible for this activity. The relatively low amount of AFB1 activation in human lung compared to that in human liver can be explained by the scarcity of CYP-containing cells in the lung. In situ AFB1 activation and resultant carcinogenic risk are distinctly possible in occupational settings where inhalation of AFB1-contaminated dusts occurs.
在某些职业中，通过吸入接触致癌物黄曲霉毒素B1（AFB1）的情况相当严重。由于间接的流行病学证据表明吸入AFB1可能会引发原发性肺癌，我们对人肺微粒体激活AFB1的情况进行了研究。将微粒体与[3H]AFB1（124微摩尔）一起孵育，并通过高效液相色谱法将激活生成的AFB1 - 8,9 - 环氧化物测定为AFB1 - 谷胱甘肽（AFB1 - GSH）共轭物。AFB1 - GSH的形成量在0.05 - 0.073飞摩尔/毫克蛋白质/分钟范围内。通过硝苯地平（CYP 3A的原型底物）的氧化、免疫抑制和免疫印迹分析，研究了细胞色素P450（CYP）3A在这种激活过程中的作用。来自不同受试者的微粒体中硝苯地平氧化速率在0.2至19.2皮摩尔/毫克蛋白质/分钟之间变化，但与AFB1激活无关。抗人多克隆CYP 3A4 IgG抑制了AFB1激活。免疫估算CYP 3A同工型的含量在0.01 - 1.90皮摩尔/毫克蛋白质范围内。在肺微粒体中未检测到CYP 1A2及其相关活性。这些数据表明人肺微粒体可激活AFB1形成外消旋AFB1 - 8,9 - 环氧化物，并且3A亚家族的CYP可能负责此活性。与人类肝脏相比，人肺中AFB1激活量相对较低，这可以通过肺中含CYP细胞的稀缺来解释。在发生吸入受AFB1污染粉尘的职业环境中，原位AFB1激活及由此产生的致癌风险是完全可能的。
