Bioactivation of aflatoxin B1 by human liver microsomes: role of cytochrome P450 IIIA enzymes.
Bioactivation of aflatoxin B1 by human liver microsomes: role of cytochrome P450 IIIA enzymes.
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DOI：
10.1016/0041-008x(91)90090-2
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发表时间：
1991-05
影响因子：
3.8
通讯作者：
H. Ramsdell;A. Parkinson;A. Eddy;D. Eaton
中科院分区：
文献类型：
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作者：
H. Ramsdell;A. Parkinson;A. Eddy;D. Eaton
根据我们以前的观察（H。S. Ramsdell和D. L.伊顿，1990年，癌症研究，50，615-620），即在微粒体孵育过程中，黄曲霉毒素B1（AFB 1）转化为高活性AFB 1 - 8，9-环氧化物的比例随底物浓度的变化而变化。Shimada和F. P. Guengerich（1989，Proc. Acad. Sci. USA，86，462-465），细胞色素P450 IIIA 4主要负责人肝微粒体对AFB 1的活化（环氧化）。在124 μ m和16 μm浓度的黄曲霉毒素B_1（AFB_1）微粒体中，测定了AFB_1 - 8，9-环氧化物和羟化代谢产物的初始生成速率。硝苯地平的微粒体氧化，主要由P450 IIIA酶催化，也通过HPLC测定。黄曲霉毒素B1代谢产物的形成率和硝苯地平的氧化率在黄曲霉毒素B1浓度范围内相关性很差（r2= 0.13-0.41）。在124 μ mAFB_1（r_2 = 0.41）处，AFB_1环氧化与硝苯地平氧化的相关性比在16 μ mAFB_1（r_2 = 0.26）处好。用P450 IIIA酶的特异性抑制剂三乙酰竹桃霉素处理混合微粒体，在高浓度AFB 1时，对AFB 1 - 8，9-环氧化物的形成抑制率为35%，但在16 μm AFB 1时几乎没有影响。抗大鼠细胞色素P450的抗体IIIA 1在高浓度下显著抑制黄曲霉毒素B1的环氧化，而在低浓度下则不显著，而AFQ 1的形成在所有底物水平下均被强烈抑制。这些结果与细胞色素P450 IIIA酶可形成黄曲霉毒素B1 - 8，9-环氧化物的假设一致，但仅在相对高的底物浓度下有效。另一种P450酶似乎主要负责在低AFB 1水平下形成AFB 1 - 8，9-环氧化物，这是典型的饮食暴露。
Based on our previous observations (H. S. Ramsdell and D. L. Eaton, 1990, Cancer Res., 50, 615–620) that the proportion of aflatoxin B1(AFB1) converted to the highly reactive AFB1-8,9-epoxide in microsomal incubations varies with substrate concentration, we have examined the hypothesis of T. Shimada and F. P. Guengerich (1989, Proc. Natl. Acad. Sci. USA, 86, 462–465) that cytochrome P450 IIIA4 is principally responsible for the activation (epoxidation) of AFB1by human liver microsomes. The initial rates of formation of AFB1-8,9-epoxide and hydroxylated AFB1metabolites were determined in microsomes prepared from livers of organ donors (n = 14) at AFB1concentrations of 124 and 16 μm. Microsomal oxidation of nifedipine, catalyzed primarily by P450 IIIA enzymes, was also determined by HPLC. Rates of formation of AFB1metabolites and nifedipine oxidation were poorly correlated at either AFB1concentration (r2= 0.13–0.41). A somewhat better correlation between AFB1epoxidation and nifedipine oxidation was observed at 124 μm AFB1(r2= 0.41) than at 16 μm AFB1(r2= 0.26). Treatment of pooled microsomes with troleandomycin, an apparently specific inhibitor of P450 IIIA enzymes, resulted in 35% inhibition of AFB1-8,9-epoxide formation at the high AFB1level but had little effect at 16 μm AFB1. An antibody against rat cytochrome P450 IIIA1 significantly inhibited AFB1epoxidation at high, but not low, AFB1concentrations, whereas AFQ1formation was strongly inhibited at all substrate levels examined. These results are consistent with the hypothesis that cytochrome P450 IIIA enzyme(s) can form AFB1-8,9-epoxide, but are effective at only relatively high substrate concentrations. Another P450 enzyme(s) appears to be principally responsible for AFB1-8,9-epoxide formation at the low AFB1levels that would be typical for dietary exposures.