Yamamoto Tetsuya, Lewis Jill, Wataha John, Dickinson Douglas, Singh Baldev, Bollag Wendy B, Ueta Eisaku, Osaki Tokio, Athar Mohammad, Schuster George, Hsu Stephen
Kochi Medical School, Japan.
J Pharmacol Exp Ther. 2004 Jan;308(1):317-23. doi: 10.1124/jpet.103.058891. Epub 2003 Oct 20.
The green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) possesses promising anticancer potential. Although in vivo studies unveiled the metabolic routes and pharmacokinetics of EGCG and showed no adverse effects, in vitro studies at high concentrations demonstrated oxidative stress. EGCG causes differential oxidative environments in tumor versus normal epithelial cells, but the roles that EGCG, hydrogen peroxide (H2O2), and intracellular catalase play in the epithelial system are largely unknown. The current study employed enzyme activity assays, reactive oxygen species quantification, and immunoblotting to investigate whether EGCG-induced differential effects correlate with levels of key antioxidant enzymes and H2O2. It was found that normal human keratinocytes with high catalase activity are least susceptible to H2O2, whereas H2O2 caused significant cytotoxicity in oral carcinoma cell lines. However, the EGCG-induced differential effects could not be duplicated by H2O2 alone. The addition of exogenous catalase failed to completely prevent the EGCG-induced cytotoxicity and rescue the EGCG-induced growth arrest in the tumor cells. The antioxidant N-acetyl-L-cysteine rescued the tumor cells from H2O2-induced damage only, but not from EGCG-induced mitochondrial damage. Finally, alterations in catalase or superoxide dismutase activities were not observed upon EGCG exposure. In conclusion, although endogenous catalase may play a role in response to H2O2-induced cytotoxicity, the EGCG-induced cytotoxic effects on tumor cells mainly result from sources other than H2O2.
绿茶多酚（-）-表没食子儿茶素-3-没食子酸酯（EGCG）具有良好的抗癌潜力。尽管体内研究揭示了EGCG的代谢途径和药代动力学，且未显示出不良反应，但高浓度的体外研究表明存在氧化应激。EGCG在肿瘤上皮细胞与正常上皮细胞中会导致不同的氧化环境，但EGCG、过氧化氢（H2O2）和细胞内过氧化氢酶在上皮系统中所起的作用在很大程度上尚不清楚。当前的研究采用酶活性测定、活性氧定量和免疫印迹法，以探究EGCG诱导的差异效应是否与关键抗氧化酶和H2O2的水平相关。研究发现，过氧化氢酶活性高的正常人角质形成细胞对H2O2最不敏感，而H2O2在口腔癌细胞系中会引起显著的细胞毒性。然而，仅H2O2无法复制EGCG诱导的差异效应。添加外源性过氧化氢酶未能完全预防EGCG诱导的细胞毒性，也无法挽救EGCG诱导的肿瘤细胞生长停滞。抗氧化剂N-乙酰-L-半胱氨酸仅能使肿瘤细胞从H2O2诱导的损伤中恢复，但无法使其从EGCG诱导的线粒体损伤中恢复。最后，EGCG处理后未观察到过氧化氢酶或超氧化物歧化酶活性的改变。总之，尽管内源性过氧化氢酶可能在应对H2O2诱导的细胞毒性中发挥作用，但EGCG对肿瘤细胞的细胞毒性作用主要源于H2O2以外的其他来源。
