Abstract: Objective To observe the protection of human keratinocyte cell line, HaCaT cell, from UVA damage by resveratrol and its possible mechanism. Methods HaCaT cells were incubated with or without 0.01 mmol/L or 0.1 mmol/L resveratrol after exposure to 5 J/cm2 UVA irradiation. Unirradiated HaCaT cells without the treatment with resveratrol served as the control. After another 24-hour culture, MTT assay was used to detect the proliferation of cells，RT-PCR and Western-blot to measure the iNOS mRNA and protein expression respectively, electron microscopic technique to observe the changes in cell ultrastructure. Results After irradiation with UVA of 5 J/cm2, the proliferation of HaCaT cells decreased with the absorbance at 490 nm descending from 0.889 ± 0.083 to 0.542 ± 0.004, while a significant increase was observed in the relative expression level of iNOS mRNA and protein in HaCaT cells （1.532 ± 0.041 vs 0.009 ± 0.003, 1.331 ± 0.046 vs 0.003 ± 0.001, both P < 0.05） with the presence of typical apoptotic cells. The treatment with 0.01 and 0.1 mmol/L resveratrol significantly promoted the proliferation of irradiated cells with the absorbance at 490 nm being 0.753 ± 0.435 and 0.892 ± 0.173 respectively, but inhibited the mRNA （0.853 ± 0.038 vs 1.532 ± 0.041, 0.392 ± 0.033 vs 1.532 ± 0.041, both P < 0.05） and protein expression level （0.809 ± 0.018 vs 1.331 ± 0.046, 0.412 ± 0.026 vs 1.331 ± 0.046, both P < 0.05） of iNOS in irradiated cells, and the resveratrol of 0.1 mmol/L was more effective than that of 0.01 mmol/L in all tested parameters （P < 0.05）. Furthermore, no apoptotic cells or necrotic cells were observed in irradiated cells incubated with resveratrol. Conclusion Resveratrol effectively protects HaCaT cells from UVA damage, which may be related to the inhibition of UVA-induced iNOS expression by resveratrol.

Key words: resveratrol, Ultraviolet