Yu M W, Zhang Y J, Blaner W S, Santella R M
Cancer Center, Columbia University, New York, New York.
Cancer. 1994 Feb 1;73(3):596-604. doi: 10.1002/1097-0142(19940201)73:3<596::aid-cncr2820730316>3.0.co;2-n.
There is extensive epidemiologic evidence suggesting a protective role for micronutrients in cancer incidence. This evidence comes from studies of fruit and vegetable intake and serum levels of specific micronutrients. There also is limited in vitro evidence demonstrating that micronutrients can influence the first step in carcinogenesis, binding of chemical carcinogens to DNA. These in vitro studies allow the determination of specific effects of individual micronutrients. The influence of micronutrients on DNA binding of aflatoxin B1 (AFB1), a potent hepatocarcinogen, in mammalian cells is unknown. Woodchuck hepatocytes were used as a model to investigate the effects of vitamin A (all-trans retinol), C (ascorbic acid), ascorbyl palmitate (a synthetic lipophilic derivative of ascorbic acid), vitamin E (alpha-tocopherol), and beta-carotene on AFB1-DNA binding.
Woodchuck hepatocytes were treated with 4 doses (0.080, 0.40, 2.0, and 10 microM) of [3H]AFB1 or with different combinations of AFB1 and the vitamins for 6 hours, and adduct levels determined. Western blot analysis of protein extracts of treated cells was used to determine the effects of vitamin A and beta-carotene on glutathione-S- transferase M1 levels.
Vitamin A inhibited formation of AFB1-DNA adducts in a dose-dependent manner throughout a concentration range of 34-122 microM by 40-80%. Vitamin C (0.080-10 mM) was much less effective than vitamin A as an inhibitor of AFB1-DNA binding. Treatment with 6.0-48.3 microM ascorbyl palmitate reduced adduct levels at lower AFB1 concentrations but had no significant effect at higher AFB1 concentrations. beta-Carotene and vitamin E enhanced covalent binding of AFB1 to DNA. Enhancement with beta-carotene was observed when both tetrahydrofuran or liposomes were used as the administration vehicle. Western blot analysis indicated that neither the vitamin A nor beta-carotene treatment affected glutathione-S-transferase M1 protein levels.
These results demonstrate that micronutrients play a complex role in the process of chemical carcinogenesis. Although protective effects were seen with several antioxidant vitamins, increased DNA adduct formation was observed with beta-carotene and vitamin E. This antioxidant activity may be unrelated to the inhibition of DNA adduct formation. Additional studies are needed to understand the mechanism of enhanced adduct formation.
有大量流行病学证据表明微量营养素在癌症发生中具有保护作用。该证据来自对水果和蔬菜摄入量以及特定微量营养素血清水平的研究。也有有限的体外证据表明微量营养素可影响致癌作用的第一步，即化学致癌物与DNA的结合。这些体外研究有助于确定单个微量营养素的特定作用。微量营养素对黄曲霉毒素B1（AFB1，一种强效肝致癌物）与哺乳动物细胞DNA结合的影响尚不清楚。土拨鼠肝细胞被用作模型来研究维生素A（全反式视黄醇）、C（抗坏血酸）、抗坏血酸棕榈酸酯（抗坏血酸的一种合成亲脂性衍生物）、维生素E（α-生育酚）和β-胡萝卜素对AFB1-DNA结合的影响。
用4种剂量（0.080、0.40、2.0和10微摩尔）的[3H]AFB1或AFB1与维生素的不同组合处理土拨鼠肝细胞6小时，并测定加合物水平。对处理后细胞的蛋白质提取物进行蛋白质印迹分析，以确定维生素A和β-胡萝卜素对谷胱甘肽-S-转移酶M1水平的影响。
在34-122微摩尔的浓度范围内，维生素A以剂量依赖的方式抑制AFB1-DNA加合物的形成，抑制率为40-80%。维生素C（0.080-10毫摩尔）作为AFB1-DNA结合的抑制剂，其效果远不如维生素A。用6.0-48.3微摩尔的抗坏血酸棕榈酸酯处理可降低较低AFB1浓度下的加合物水平，但在较高AFB1浓度下无显著影响。β-胡萝卜素和维生素E增强了AFB1与DNA的共价结合。当使用四氢呋喃或脂质体作为给药载体时，均观察到β-胡萝卜素的增强作用。蛋白质印迹分析表明，维生素A和β-胡萝卜素处理均未影响谷胱甘肽-S-转移酶M1蛋白水平。
这些结果表明微量营养素在化学致癌过程中发挥复杂作用。虽然几种抗氧化维生素具有保护作用，但β-胡萝卜素和维生素E却增加了DNA加合物的形成。这种抗氧化活性可能与抑制DNA加合物形成无关。需要进一步研究以了解加合物形成增加的机制。
