Abstract
Green tea polyphenols (GTPPs) are considered beneficial to human health, especially as chemopreventive agents. Recently, cytotoxic reactive oxygen species (ROS) were identified in tumor and certain normal cell cultures incubated with high concentrations of the most abundant GTPP, (–)-epigallocatechin-3-gallate (EGCG). If EGCG also provokes the production of ROS in normal epithelial cells, it may preclude the topical use of EGCG at higher doses. The current study examined the oxidative status of normal epithelial, normal salivary gland, and oral carcinoma cells treated with EGCG, using ROS measurement and catalase and superoxide dismutase activity assays. The results demonstrated that high concentrations of EGCG induced oxidative stress only in tumor cells. In contrast, EGCG reduced ROS in normal cells to background levels. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and 5-bromodeoxyuridine incorporation data were also compared between the two oral carcinoma cell lines treated by EGCG, which suggest that a difference in the levels of endogenous catalase activity may play an important role in reducing oxidative stress provoked by EGCG in tumor cells. It is concluded that pathways activated by GTPPs or EGCG in normal epithelial versus tumor cells create different oxidative environments, favoring either normal cell survival or tumor cell destruction. This finding may lead to applications of naturally occurring polyphenols to enhance the effectiveness of chemo/radiation therapy to promote cancer cell death while protecting normal cells.
Footnotes
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This study was supported in part by funding from the Dental Research Foundation, the Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, and the Medical College of Georgia Research Institute to S.H.
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DOI: 10.1124/jpet.103.054676.
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ABBREVIATIONS: GTPP, green tea polyphenol; EGCG, (–)-epigallocatechin-3-gallate; ROS, reactive oxygen species; SOD, superoxide dismutase; NHEK, normal human primary epidermal keratinocyte; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; DFDA, dihydrofluorescein diacetate; HPS, Hallam's physiological saline; SDH, succinate dehydrogenase; ANOVA, analysis of variance.
- Received May 20, 2003.
- Accepted July 1, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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