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Fig. 1 Pterostilbene improved HaCaT cell viability but repressed UVA-induced intracellular ROS production. (A) Chemical structures of Pterostilbene (Pt) and Resveratrol (Rv). (B–C) Cell viability was calculated by the MTT method. HaCaT cells were pre-incubated with Pt (0–5 μM) or Rv (10 μM) for 24 h followed by irradiation with 3 J/cm2 UVA (B). HaCaT cells were treated with or without Pt (5 μM) for 24 h and then irradiated with different UVA intensities (0, 3, 6, or 12 J/cm2) (C). Cells neither treated with Pt or Rv or UVA-irradiated were considered as the untreated control. (D–E) HaCaT cells were pretreated with Pt (5 μM) or Rv (10 μM) for 24 h, followed by irradiated or not with 3 J/cm2 UVA. The intracellular ROS levels were indicated by DCF and measured by fluorescence microscopy (200× magnification) (D). Fluorescence intensity of the DCF-stained cells for each condition was quantified by Olympus Softimage solution software, and data were denoted as fold difference over untreated control values (E). Cells neither treated with Pt or Rv or UVA-irradiated were considered as the untreated control. Results were denoted as mean ± SD of three or more independent experiments. Statistical significance was considered as *p < 0.05, **p < 0.01 and ***p < 0.001 compared to untreated control. #p < 0.05 and ###p < 0.001 compared to UVA-irradiated cells.