Modification of aflatoxin B1 biotransformation in vitro and DNA binding in vivo by dietary broccoli in rats.
Modification of aflatoxin B1 biotransformation in vitro and DNA binding in vivo by dietary broccoli in rats.
复制标题
大鼠膳食西兰花对黄曲霉毒素 B1 体外生物转化和体内 DNA 结合的修饰。
DOI：
10.1080/15287398809531209
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发表时间：
1988
期刊：
影响因子：
--
通讯作者：
Eaton,DL
中科院分区：
文献类型：
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作者：
Ramsdell,HS;Eaton,DL
十字花科蔬菜已被证明具有抗癌作用的动物，但生化机制尚未完全阐明。在这项研究中，研究了食用西兰花对肝癌原黄曲霉毒素B1（AFB）体内DNA结合和体外形成推定致癌中间体AFB-8，9-环氧化物的影响，以及通过与谷胱甘肽（CSH）结合对环氧化物的解毒作用。动物喂食纯化饲料、纯化饲料加25%冻干西兰花或标准啮齿动物饲料3周。测定了黄曲霉毒素B与肝DNA的体内结合。通过HPLC法测定AFB的体外生物转化（微粒体氧化为AFB-8，9-环氧化物以及羟基化代谢物，以及原位生成的AFB-8，9-环氧化物的细胞溶质GSH结合），该方法允许特异性和直接测定AFB代谢物及其形成速率。微粒体混合功能氧化酶和环氧化物水解酶活性以及细胞溶质谷胱甘肽S-转移酶活性也使用常用的替代底物进行测量。黄曲霉毒素B-8，9-环氧化物的胞质结合率在西兰花饮食中增加2.8倍，在普通饲料中增加2.2倍。这些变化没有完全反映在替代底物的活性增加。普通饮食不影响环氧化物水解酶活性，也不影响谷胱甘肽S-转移酶对3，4-二氯硝基苯或苯并[a]芘4，5-氧化物的活性，而西兰花饮食显著增加了这些活性。AFB-8，9-环氧化物的微粒体形成不受饮食处理的影响，而黄曲霉毒素M1的形成增加。普通饮食，而不是西兰花饮食，增加了黄曲霉毒素Q1形成的AFB的量。体内AFB与DNA的结合在西兰花组中显著较低，但在普通饲料喂养的动物中并非如此。这些结果表明，西兰花含有导致AFB代谢物与DNA结合减少的物质，可能是通过诱导谷胱甘肽S-转移酶。西兰花和啮齿动物食物的成分不同，相对于纯化的饮食，它们增加了异生素生物转化酶的水平。结果还表明，依赖于使用替代底物而不是感兴趣的致癌化合物的生物转化途径的测量的局限性。
Cruciferous vegetables have been shown to have anticarcinogenic effects in animals but biochemical mechanisms have not been completely elucidated. The effects of dietary broccoli on in vivo DNA binding of the hepatocarcinogen aflatoxin B1(AFB) and in vitro formation of the putative carcinogenic intermediate, AFB‐8,9‐epoxide, as well as detoxification of the epoxide by conjugation with glutathione (CSH), were examined in this study. Animals were fed a purified diet, a purified diet plus 25% freeze‐dried broccoli, or standard rodent chow for 3 wk. In vivo binding of AFB to hepatic DNA was determined. Biotransformation of AFB in vitro (microsomal oxidation to AFB‐8,9‐epoxide, as well as hydroxylated metabolites, and cytosolic GSH conjugation of AFB‐8,9‐epoxide generated in situ) was measured by an HPLC method that allows specific and direct determination of AFB metabolites and thus, the rates of their formation. Microsomal mixed‐function oxidase and epoxide hydrolase activities and cytosolic glutathione S‐transferase activities were also measured with commonly used surrogate substrates. The rate of cytosolic conjugation of AFB‐8,9‐epoxide was increased 2.8‐fold by the broccoli diet and 2.2‐fold by the chow diet. These changes were not fully reflected by increases in activity with surrogate substrates. The chow diet did not affect epoxide hydrolase activity nor glutathione S‐transferase activity toward 3,4‐dichloronitrobenzene or benzo[alpyrene 4,5‐oxide, whereas these activities were significantly increased by the broccoli diet. Microsomal formation of AFB‐8,9‐epoxide was unaffected by the dietary treatments, whereas formation of aflatoxin M1was increased. The chow diet, but not the broccoli diet, increased the amount of aflatoxin Q1formed from AFB. Binding of AFB to DNA in vivo was significantly lower in the broccoli group but not in the chow‐fed animals. These results indicate that broccoli contains substances that cause a reduction in the binding of AFB metabolites to DNA, possibly through the induction of glutathione S‐transferase(s). Broccoli and rodent chow differ in their constituents that increase levels of xenobiotic biotransformation enzymes relative to a purified diet. The results also indicate the limitations of reliance on measurements of biotransformation pathways using surrogate substrates instead of carcinogenic compounds of interest.