Department of Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky 40202, USA.
Chem Res Toxicol. 2010 Apr 19;23(4):771-7. doi: 10.1021/tx900412a.
Green tea catechins and hydrolyzable tannins are gaining increasing attention as chemopreventive agents. However, their mechanism of action is poorly understood. We investigated the effects of four green tea catechins and two hydrolyzable tannins on microsome-induced benzo[a]pyrene (BP)-DNA adducts and the possible structure-activity relationship. BP (1 microM) was incubated with rat liver microsomes and DNA in the presence of the test compound (1-200 microM) or vehicle. The purified DNA was analyzed by (32)P-postlabeling. The inhibitory activity of the catechins was in the following descending order: epigallocatechin gallate (IC(50) = 16 microM) > epicatechin gallate (24 microM) > epigallocatechin (146 microM) > epicatechin (462 microM), suggesting a correlation between the number of adjacent aromatic hydroxyl groups in the molecular structure and their potencies. Tannic acid (IC(50) = 4 microM) and pentagalloglucose (IC(50) = 26 microM) elicited as much DNA adduct inhibitory activity as the catechins or higher presumably due to the presence of more functional hydroxyl groups. To determine if the activity of these compounds was due to direct interaction of phenolic groups with electrophilic metabolite(s) of BP, DNA was incubated with anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (anti-BPDE) (0.5 microM) in the presence of test compounds (200 microM) or vehicle. Significant inhibition of DNA adduct formation was found (tannic acid > pentagalloglucose > epigallocatechin gallate > epicatechin gallate). This notion was confirmed by analysis of the reaction products of anti-BPDE with the catechins and pentagalloglucose by electrospray ionization mass spectrometry and liquid chromatography-mass spectrometry. In conclusion, our data demonstrate that green tea catechins and the hydrolyzable tannins are highly effective in inhibiting BP-DNA adduct formation at least, in part, due to direct interaction of adjacent hydroxyl groups in their structures and that the activity is higher with an increasing number of functional hydroxyl groups.
绿茶儿茶素和可水解单宁作为化学预防剂正受到越来越多的关注。然而，其作用机制尚不清楚。我们研究了四种绿茶儿茶素和两种可水解单宁对微粒体诱导的苯并[a]芘（BP）-DNA 加合物的影响及可能的构效关系。BP（1μM）与大鼠肝微粒体和 DNA 孵育，同时加入测试化合物（1-200μM）或载体。用 32P-后标记法分析纯化的 DNA。儿茶素的抑制活性呈以下降序排列：表没食子儿茶素没食子酸酯（IC50=16μM）>表儿茶素没食子酸酯（24μM）>表没食子儿茶素（146μM）>表儿茶素（462μM），这表明分子结构中相邻芳族羟基的数量与它们的效力之间存在相关性。鞣酸（IC50=4μM）和五倍子葡萄糖（IC50=26μM）的 DNA 加合物抑制活性与儿茶素相当或更高，可能是因为它们含有更多的功能羟基。为了确定这些化合物的活性是否是由于酚基团与 BP 的亲电代谢物（s）直接相互作用，在测试化合物（200μM）或载体存在的情况下，将 DNA 与抗苯并[a]芘-7,8-二醇-9,10-环氧化物（抗-BPDE）（0.5μM）孵育。发现 DNA 加合物形成明显受到抑制（鞣酸>五倍子葡萄糖>表没食子儿茶素没食子酸酯>表儿茶素没食子酸酯）。这一观点通过电喷雾电离质谱和液相色谱-质谱分析抗-BPDE 与儿茶素和五倍子葡萄糖的反应产物得到证实。总之，我们的数据表明，绿茶儿茶素和可水解单宁在抑制 BP-DNA 加合物形成方面非常有效，至少部分原因是由于它们结构中相邻羟基的直接相互作用，并且随着功能羟基数量的增加，活性更高。
