Cai Y, Baer-Dubowska W, Ashwood-Smith M, DiGiovanni J
University of Texas MD Anderson Cancer Center, Department of Carcinogenesis, Smithville 78957, USA.
Carcinogenesis. 1997 Jan;18(1):215-22. doi: 10.1093/carcin/18.1.215.
Several naturally occurring coumarins to which humans are routinely exposed have been previously found to be potent inhibitors and inactivators of cytochrome P450 (P450) 1A1-mediated monooxygenase in both murine hepatic microsomes and in a reconstituted system using purified human P450 1A1 [Cai et al. (1993) Chem. Res. Toxicol., 6, 872-879 and Cai et al. (1996) Chem. Res. Toxicol., 9, 729-736]. In the present study, several of these coumarins were investigated for their inhibitory effects on the metabolism and metabolic activation of benzo[a]pyrene (B[a]P) and 7,12-dimethylbenz[a]anthracene (DMBA) in cultured mouse keratinocytes. Initial analysis of B[a]P metabolism in cultured keratinocytes showed that imperatorin, isoimperatorin, coriandrin, and bergamottin, at concentrations of 2 nM equal with B[a]P, reduced the formation of water-soluble metabolites of B[a]P by 33% to 57%. Bergamottin and coriandrin were the most potent inhibitors of the compounds examined. HPLC analysis of organic solvent-soluble metabolites of B[a]P indicated that all the coumarins tested significantly reduced the formation of individual B[a]P metabolites (including phenols, diols and tetraols). However, the greatest effect was on the formation of B[a]P tetraols. Additional experiments determined the ability of selected coumarins to block covalent binding of B[a]P and DMBA to DNA in keratinocytes. Bergamottin preferentially inhibited the binding of B[a]P to DNA by 56%, while coriandrin preferentially inhibited the binding of DMBA to DNA by 48%. Notably, analysis of individual DNA adducts formed from B[a]P and DMBA indicated that both bergamottin and coriandrin specifically inhibited the formation of anti diol-epoxide DNA adducts derived from both hydrocarbons. The preferential inhibitory effect of bergamottin and coriandrin on the formation of anti diol-epoxide adducts derived from DMBA was further confirmed by separation of anti- and syn-diol-epoxide-DNA adducts using immobilized boronate chromatography. The current study demonstrates that certain naturally occurring coumarins inhibited metabolic activation of B[a]P and DMBA in cultured mouse keratinocytes and specifically inhibited the formation of DNA adducts derived from the anti diol-epoxide diastereomers from either hydrocarbon. The current data also suggest that certain naturally occurring coumarins may possess anticarcinogenic activity toward polycyclic aromatic hydrocarbons.
先前已发现，人类日常接触的几种天然香豆素在小鼠肝微粒体以及使用纯化的人细胞色素P450 1A1的重组系统中，都是细胞色素P450（P450）1A1介导的单加氧酶的强效抑制剂和失活剂[Cai等人（1993年）《化学研究毒理学》，6，872 - 879；Cai等人（1996年）《化学研究毒理学》，9，729 - 736]。在本研究中，研究了其中几种香豆素对培养的小鼠角质形成细胞中苯并[a]芘（B[a]P）和7,12 - 二甲基苯并[a]蒽（DMBA）代谢及代谢活化的抑制作用。对培养的角质形成细胞中B[a]P代谢的初步分析表明，浓度与B[a]P相等的2 nM欧前胡素、异欧前胡素、芫荽苷和佛手柑内酯，使B[a]P水溶性代谢物的形成减少了33%至57%。佛手柑内酯和芫荽苷是所检测化合物中最有效的抑制剂。对B[a]P有机溶剂可溶性代谢物的HPLC分析表明，所有测试的香豆素均显著减少了各个B[a]P代谢物（包括酚类、二醇类和四醇类）的形成。然而，对B[a]P四醇类形成的影响最大。进一步的实验确定了所选香豆素阻断B[a]P和DMBA与角质形成细胞中DNA共价结合的能力。佛手柑内酯优先抑制B[a]P与DNA的结合达56%，而芫荽苷优先抑制DMBA与DNA的结合达48%。值得注意的是，对由B[a]P和DMBA形成的单个DNA加合物的分析表明，佛手柑内酯和芫荽苷均特异性抑制了源自这两种碳氢化合物的反式二醇环氧化物DNA加合物的形成。使用固定化硼酸酯色谱法分离反式和顺式二醇环氧化物 - DNA加合物，进一步证实了佛手柑内酯和芫荽苷对源自DMBA的反式二醇环氧化物加合物形成的优先抑制作用。当前研究表明，某些天然香豆素在培养的小鼠角质形成细胞中抑制B[a]P和DMBA的代谢活化，并特异性抑制源自这两种碳氢化合物反式二醇环氧化物非对映体的DNA加合物的形成。当前数据还表明，某些天然香豆素可能对多环芳烃具有抗癌活性。
