Szeto Yim-Tong, Benzie Iris F F
Department of Nursing and Health Sciences, The Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, People's Republic of China.
Free Radic Res. 2002 Jan;36(1):113-8. doi: 10.1080/10715760210161.
The protective effect of fruits and vegetables against cancer is well established. It is believed that this effect is mediated by antioxidants and decreased oxidative damage to DNA. However, the identity of the antioxidant(s) responsible is not clear. Moreover, a potentially damaging pro-oxidant effect of some antioxidants has been reported. In this study the ex vivo effects of several dietary antioxidants, including quercetin, various catechins, ascorbic acid and alpha-tocopherol, were investigated, at concentrations up to 200 microM, using the single cell gel electrophoresis (comet) assay for DNA damage. Lymphocytes from three healthy subjects were pre-incubated with these antioxidants, and the comet assay was performed on treated, untreated, challenged and unchallenged cells in parallel, oxidant challenge being induced by 5 min exposure to hydrogen peroxide (final concentrations H2O2: 30, 45, or 60 microM). Results using this ex vivo cellular assay showed protection by some antioxidants (quercetin, caffeic acid), no effect by some (catechin, epicatechin, catechin gallate, epicatechin gallate) and an apparently damaging effect by others (epigallocatechin, epigallocatechin gallate). Damage may have been caused by production of H2O2 from these polyphenolics. Neither ascorbic acid nor alpha-tocopherol protected or damaged DNA. Further study of the role of quercetin and caffeic acid in DNA protection is needed.
水果和蔬菜对癌症的保护作用已得到充分证实。人们认为这种作用是由抗氧化剂介导的，并减少了对DNA的氧化损伤。然而，起作用的抗氧化剂的具体成分尚不清楚。此外，有报道称某些抗氧化剂可能具有潜在的促氧化损伤作用。在本研究中，使用单细胞凝胶电泳（彗星）试验检测DNA损伤，研究了几种膳食抗氧化剂（包括槲皮素、各种儿茶素、抗坏血酸和α-生育酚）在浓度高达200微摩尔时的体外作用。从三名健康受试者采集的淋巴细胞预先与这些抗氧化剂孵育，然后对处理过的、未处理的、经氧化剂刺激和未经刺激的细胞同时进行彗星试验，通过暴露于过氧化氢5分钟（过氧化氢最终浓度为30、45或60微摩尔）诱导氧化剂刺激。使用这种体外细胞试验的结果显示，一些抗氧化剂（槲皮素、咖啡酸）具有保护作用，一些抗氧化剂（儿茶素、表儿茶素、儿茶素没食子酸酯、表儿茶素没食子酸酯）无作用，而其他抗氧化剂（表没食子儿茶素、表没食子儿茶素没食子酸酯）则有明显的损伤作用。损伤可能是由这些多酚类物质产生过氧化氢所致。抗坏血酸和α-生育酚对DNA既无保护作用也无损伤作用。需要进一步研究槲皮素和咖啡酸在DNA保护中的作用。
