FIG. 3.

Cytotoxicity versus photo-cytotoxicity of polyphenols. (A) Fluorescence photographs of HaCaT cells stained with acridine orange/ethidium bromide: I, control cells; II–III, cells 3 and 6 hours postirradiation (low-dose noncytotoxic UVA+UVB = 2 + 4 J/cm² for 40 minutes), respectively; IV–VI, cells similarly irradiated in the presence of 50 μM chalcone 3, 6, and 24 hours postirradiation, respectively; VII–IX, cells similarly irradiated in the presence of 50 μM resveratrol 3, 6, and 24 hours postirradiation, respectively. (B) For cytotoxicity determination, HaCaT cells were incubated with 50 μM polyphenols for 40 minutes. Cell viability was determined by a PrestoBlue viability assay 24 hours postincubation in a polyphenol- and serum-free medium in accordance with Materials and Methods section description. For photo-cytotoxicity determination, HaCaT cells were irradiated by low-dose UVA+UVB (2 + 4 J/cm²) in the absence or presence of 50 μM polyphenols for 40 minutes. Cell viability was determined by a PrestoBlue viability assay 24 hours postirradiation and incubation in a polyphenol- and serum-free medium. Results are expressed as mean ± SD of eight measurements in two independent experiments. *p < 0.05; **p < 0.01; ***p < 0.001 versus UV or Control. ND, not done.