School of Biological Sciences, University of Surrey, Guildford, Surrey, GU2 5XH, UK.
Environ Toxicol Pharmacol. 1999 Mar;7(1):41-7. doi: 10.1016/s1382-6689(98)00049-0.
The principal objective of this study was to compare the ability of green, black and decaffeinated black tea to modulate hepatic expression of cytochromes P450 in the rat, and the consequences on the bioactivation of some food-borne carcinogens. Furthermore, these studies allow inferences to be drawn as to the contribution of caffeine and flavanols in the tea-mediated changes in cytochrome P450 expression. Black tea is prepared from fresh tea leaf following oxidation of flavanols by polyphenol oxidases and consequently has a low content of these compounds. All three types of tea enhanced lauric acid hydroxylation but in the case of decaffeinated black tea no statistical significance was attained. Green tea and black tea, but not decaffeinated black tea, stimulated the O-dealkylations of methoxy-, ethoxy- and pentoxy-resorufin indicating upregulation of CYP1A and CYP2B. Immunoblot analysis revealed that green and black tea, but not decaffeinated black tea, elevated the hepatic CYP1A2 apoprotein levels. Hepatic microsomes from green and black tea-treated rats, but not those from the decaffeinated black tea-treated rats, were more effective than controls in converting IQ into mutagenic species in the Ames test. It is concluded that flavanols are not responsible for the effects of tea on the cytochrome P450 system, but caffeine could account for the increase in CYP1A2 and the consequent increase in the bioactivation of IQ.
本研究的主要目的是比较绿茶、红茶和无咖啡因红茶对大鼠肝微粒体细胞色素 P450 表达的调节作用，并研究其对一些食物源致癌剂生物活化的影响。此外，这些研究可以推断出咖啡因和茶黄素在茶介导的细胞色素 P450 表达变化中的作用。红茶是由新鲜茶叶经多酚氧化酶氧化茶黄素制成的，因此其含量较低。三种茶都能增强月桂酸羟化作用，但无咖啡因红茶的效果并不显著。绿茶和红茶，但不是无咖啡因红茶，能刺激甲氧基、乙氧基和戊氧基-Resorufin 的 O-脱烷基化，表明 CYP1A 和 CYP2B 的上调。免疫印迹分析显示，绿茶和红茶能提高肝 CYP1A2 脱辅基蛋白水平，但无咖啡因红茶则不能。与对照组相比，来自绿茶和红茶处理组的肝微粒体比来自无咖啡因红茶处理组的肝微粒体更有效地将 IQ 转化为致突变物质，在艾姆斯试验中。因此，茶黄素并不是茶对细胞色素 P450 系统的影响的原因，但咖啡因可能是 CYP1A2 增加的原因，从而导致 IQ 的生物活化增加。
