Khan N S, Ahmad A, Hadi S M
Department of Biochemistry, Faculty of Life Sciences, Aligarh Muslim University, Aligarh, India.
Chem Biol Interact. 2000 Mar 15;125(3):177-89. doi: 10.1016/s0009-2797(00)00143-5.
Tannic acid has numerous food and pharmacological applications. It is an additive in medicinal products, and is used as a flavouring agent and as an anti-oxidant in various foods and beverages. We have previously shown that tannic acid in the presence of Cu(II) causes DNA degradation through generation of reactive oxygen species. On the other hand, it exhibits antimutagenic and anticarcinogenic activities, and induces apoptosis in animal cells. It is known that most plant-derived polyphenolic anti-oxidants also act as pro-oxidants under certain conditions. In this paper, we compare the anti-oxidant and pro-oxidant properties of tannic acid and its structural component gallic acid. It is shown that tannic acid is the most efficient generator of the hydroxyl radical in the presence of Cu(II), as compared with gallic acid and its analogues syringic acid and pyrogallol. The anti-oxidant activity of tannic acid was studied by its effect on hydroxyl radical and singlet oxygen mediated cleavage of plasmid DNA. Again, tannic acid provided the maximum protection against cleavage, while gallic acid and its structural analogues were found to be non-inhibitory or partially inhibitory. The results suggest that the structural features of tannic acid that are important for its anti-oxidant action are also those that contribute to the generation of hydroxyl radicals in the presence of Cu(II). Restriction analysis of treated phage DNA and thermal melting profiles of calf thymus DNA indicated that tannic acid strongly binds to DNA. Indirect evidence indicates that modification of DNA bases may also occur.
单宁酸在食品和药理学领域有众多应用。它是药品中的一种添加剂，在各类食品和饮料中用作调味剂和抗氧化剂。我们之前已经表明，单宁酸在铜（II）存在的情况下，通过产生活性氧导致DNA降解。另一方面，它具有抗诱变和抗癌活性，并能诱导动物细胞凋亡。众所周知，大多数植物来源的多酚类抗氧化剂在某些条件下也会充当促氧化剂。在本文中，我们比较了单宁酸及其结构成分没食子酸的抗氧化和促氧化特性。结果表明，与没食子酸及其类似物丁香酸和连苯三酚相比，单宁酸在铜（II）存在时是最有效的羟基自由基生成剂。通过单宁酸对羟基自由基和单线态氧介导的质粒DNA切割的影响来研究其抗氧化活性。同样，单宁酸对切割提供了最大程度的保护，而没食子酸及其结构类似物则被发现无抑制作用或仅有部分抑制作用。结果表明，单宁酸对其抗氧化作用重要的结构特征也是在铜（II）存在时有助于羟基自由基生成的那些特征。对处理后的噬菌体DNA的限制性分析以及小牛胸腺DNA的热解链曲线表明，单宁酸与DNA紧密结合。间接证据表明DNA碱基也可能发生修饰。
