Quenching effects of (-)-Epigallocatechin gallate for singlet oxygen production and its protection against oxidative damage induced by Ce6-mediated photodynamic therapy in vitro

Background Singlet oxygen ( 1 O 2 ) is highly reactive to biological components such as lipids, proteins and DNA, which induces oxidative damage to cells and tissues. Natural antioxidants may function as 1 O 2 quencher to prevent 1 O 2 involved photosensitized oxidation in biological system. Methods Time-resolved measurement of 1 O 2 luminescence was employed to evaluate the 1 O 2 quenching abilities of natural antioxidants in air-statured phosphate buffered saline (PBS), including (-)-Epigallocatechin gallate (EGCG), Proanthocyanidins, L-carnosine and Vitamin C. The 1 O 2 quenching effects and rate constant of EGCG were investigated by detecting the absorption, fluorescence and 1 H-NMR spectroscopy and 1 O 2 luminescence decay curves, respectively. In addition, the protective activity of EGCG against 1 O 2 oxidative damage caused by Ce6-mediated photodynamic therapy (PDT) was verified in cells. Results EGCG, proanthocyanidins, L-carnosine and Vitamin C efficiently quenched 1 O 2 luminescence at 1270 nm. The triplet-state quenching rate constants of EGCG for Rose Bengal (RB), Chlorin e6, AlPcS and HiPorfin are 2.21 × 10 9 , 4.90 × 10 8 , 3.30 × 10 8 , 1.78 × 10 9 M −1 s −1 , while the 1 O 2 quenching rate constants are 2.80 × 10 8 , 1.50 × 10 8 , 1.30 × 10 8 , 1.70 × 10 8 M −1 s −1 , respectively. Furthermore, EGCG could effectively quench 1 O 2 production to prevent NIH/3T3 cells oxidative damage induced by Ce6-mediated PDT. Conclusions EGCG is an efficient quencher for both triplet-state photosensitizers and 1 O 2 . The quenching ability of EGCG during photosensitization for selected photosensitizers is: RB > HiPorfin > Ce6 > AlPcS. EGCG could be used to protect normal cells and tissue against oxidative damage.