Roles of Catalase and Hydrogen Peroxide in Green Tea Polyphenol-Induced Chemopreventive Effects (original) (raw)

Research ArticleCELLULAR AND MOLECULAR

, Jill Lewis, John Wataha, Douglas Dickinson, Baldev Singh, Wendy B. Bollag, Eisaku Ueta, Tokio Osaki, Mohammad Athar, George Schuster and Stephen Hsu

Journal of Pharmacology and Experimental Therapeutics January 2004, 308 (1) 317-323; DOI: https://doi.org/10.1124/jpet.103.058891

Abstract

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 H2O2caused significant cytotoxicity in oral carcinoma cell lines. However, the EGCG-induced differential effects could not be duplicated by H2O2alone. 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.

Footnotes

• This study was supported in part by a grant from the Medical College of Georgia Research Institute and funding through the Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, Medical College of Georgia to S.H.

• DOI: 10.1124/jpet.103.058891.

• ABBREVIATIONS: GTPP, green tea polyphenols; EGCG, (-)-epigallocatechin-3-gallate; ROS, reactive oxygen species; AP-1, activator protein-1; NHEK, normal human primary epidermal keratinocytes; SOD, superoxide dismutase; NAC, _N_-acetyl-l-cysteine; 3-AT, 3-amino-1,2,4-triazole; MTT, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide; DFDA, dihydrofluorescein diacetate; HPS, Hallam's physiological saline; PBS, phosphate-buffered saline.

• • Received August 22, 2003.
  • Accepted October 2, 2003.

• The American Society for Pharmacology and Experimental Therapeutics

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