Protective effect of gallic acid derivatives from the freshwater green alga Spirogyra sp against ultraviolet B-induced apoptosis through reactive oxygen species clearance in human keratinocytes and zebrafish

In the present study, we enhanced the phenolic content of 70% ethanol extracts of Spirogyra sp. (SPE, 260.47 +/- 5.21 gallic acid equivalent [GAE] mg g(-1)), 2.97 times to 774.24 +/- 2.61 GAE mg g(-1) in the ethyl acetate fraction of SPE (SPEE). SPEE was evaluated for its antiradical activity in online high-performance liquid chromatography. ABTS analysis, and the peaks with the highest antiradical activities were identified as gallic acid derivatives containing gallic acid, methyl gallate, and ethyl gallate. Isolation of ethyl gallate from Spirogyra sp. was performed for the first time in this study. In ultraviolet B (UVB)-irradiated keratinocytes (HaCaT cells), SPEE improved cell viability by 8.22%, and 23.33% and reduced accumulation of cells in the sub-G(1) phase by 20.53%, and 32.11% at the concentrations of 50 and 100 mu g mL(-1), respectively. Furthermore, SPEE (50 and 100 mu g mL(-1)) reduced reactive oxygen species generation in UVB-irradiated zebrafish by 66.67% and 77.78%. This study suggests a protective activity of gallic acid and its derivatives from Spirogyra sp. against UVB-induced stress responses in both in vitro and in vivo models, suggesting a potential use of SPEE in photoprotection.