Abstract:

Objective To investigate the effect of heat treatment combined with narrow band ultraviolet B （NB-UVB） on cultured normal human melanocytes in vitro. Methods Melanocytes were isolated from the foreskin of normal human, cultured in vitro, and irradiated with NB-UVB of different doses （20, 30, 50, 70, 90, 120 and 180 mJ/cm2）. Then, MTT assay was performed to evaluate the proliferation and activity of melanocytes to determine the optimal dose of UVB for the next experiment. Melanocytes were classified into 3 groups to be treated with heat at 42 ℃ for 1 hour （heat group）, irradiated with UVB at 50 mJ/cm2 （UVB group）, or irradiated with UVB at 50 mJ/cm2 followed by heat treatment at 42 ℃ for 1 hour （combination group）, daily for 3 successive days; those receiving no treatment served as the control. After 24-hour culture following the last treatment, tyrosinase activity was evaluated with L-dopa as the substrate, melanin content was detected by NaOH assay, and cell cycle stages were determined by flow cytometry. Results NB-UVB irradiation decreased the viability of melanocytes in a dose-dependent manner, and the optimum dose of UVB was 50 mJ/cm2. The tyrosinase activity of melanocytes was 0.244 ± 0.018 and 0.310 ± 0.015 respectively in the UVB group and combination group, and increased by 3.8% （P < 0.05） and 31.9% （P < 0.05） respectively compared with the control group （0.235 ± 0.018）; the melanin content was 0.201 ± 0.016 and 0.286 ± 0.019, respectively in the UVB group and combination group, and increased by 17.5% （P < 0.05） and 67.3% （P < 0.05） compared with the control group （0.171 ± 0.016）. In comparison with the control group, the percentage of melanocytes in G1 phase was decreased by 23.94% in the UVB group （P < 0.05） and 33.51% in the combination group （P < 0.05）, while that in S phase and G2 phase increased by 15.35% （P < 0.05） and 11.93% （P < 0.05）, respectively in the UVB group, and 17.76% （P > 0.05） and 16.08% （P > 0.05）, respectively in the heat group. Conclusion Heat treatment and NB-UVB can synergistically enhance the tyrosinase activity and accelerate melanogenesis, proliferation and differentiation, of melanocytes.

Key words: Cell Cycle