본 연구에서는 다양한 생리활성이 보고된 폴리페놀 화합물인 EGCG의 화학안정성, H₂O₂ 생성능 및 세포독성에 대하여 다양한 항산화제와의 조합에 의한 변화를 분석하였다. EGCG는 생리적 조건에서 갈색화합물로 산화되면서 불안정화되는데, catalase를 제외한 각종 항산화제제 SOD, ascorbic acid, NAC 및 GSH는 EGCG 갈색산화물의 생성을 유의적으로 저해하였다. EGCG에 의해 생성되는 H2O2는 catalase에 의해 거의 완벽하게 제거되었으며, SOD와 NAC에 의해서도 유의적으로 감소하였다. 하지만 GSH 및 고농도의 ascorbic acid의 존재 시 오히려 H2O2 수준이 증가 Fig. 4. Changes in cytotoxic effects of EGCG by thiol antioxidants. HeLa cells were incubated with EGCG in the absence or presence of NAC (A) or GSH (B) for 24 h. Viable cells were analyzed using the MTT assay. Effects of different concentrations of GSH on 10 μM EGCGinduced cytotoxicity (C), and changes in IC50 values of EGCG for HeLa cell growth by different concentrations of NAC and GSH (D) were also analyzed. Each value represents the mean±SD (n=7 or 8). Different letters indicate a significant difference (p<0.05) based on one-way ANOVA and the Tukey HSD test.
Epigallocatechin-3-gallate (EGCG) is a polyphenolic compound frequently found in green tea, and its physiological actions have been extensively investigated. In the present study, changes in chemical stability and cytotoxic properties of EGCG in the presence of different types of antioxidants were investigated. The antioxidants used modulated the chemical stability of EGCG. Superoxide dismutase (SOD) significantly increased EGCG stability; EGCG was less stable in the presence of catalase. Ascorbic acid, N-acetylcysteine (NAC), and glutathione (GSH) stabilized EGCG concentration dependently. The H₂O₂ level generated from EGCG was decreased by catalase, SOD, and NAC but not by GSH. The cytotoxic effects of EGCG also decreased in the presence of NAC, catalase, and SOD. GSH, however, showed a complicated modulatory pattern according to the EGCG and GSH concentrations, and ascorbic acid rather enhanced EGCG toxicity. The results suggest that certain antioxidants could modulate the cytotoxic properties of EGCG in a cell culture system not only by removing reactive oxygen species but by modulating chemical stability and other factors, which should be considered carefully when studying reactive oxygen species-dependent mechanisms of EGCG.