Abstract:

Objective To observe the increasing effect of infrared irradiation on tyrosinase activity and melanin content in cultured normal human epidermal melanocytes in vitro and to explore the optimal dose of infrared irradiation. Methods Epidermal melanocytes were isolated from normal human foreskin tissue, and subjected to primary culture. Methyl thiazolyl tetrazolium （MTT） assay was performed to evaluate the effect of different doses（0, 20, 60, 80, 100, 140, 240, 320 J/cm2）of infrared light on the proliferation of melanocytes and to select the optimal irradiation dose. Then, melanocytes were irradiated with infrared light at the optimal dose for 3 consecutive days followed by the determination of tyrosinase activity, melanin content, and cell cycle via dopa oxidation assay, NaOH solubilization method and flow cytometry, respectively. Results The best intervention dose of infrared light was 80 J/cm2. The tyrosinase activity （A492 nm） and melanin content （A492 nm） were 0.3601 ± 0.0301 and 0.2748 ± 0.0243 respectively in melanocytes after irradiation with infrared light of 80 J/cm2 for 3 days, significantly higher than those in unirradiated melanocytes （0.3114 ± 0.0341, 0.2325 ± 0.0254, respectively, both P < 0.05）, with an increase rate of 15.64% and 18.19% respectively. Cell cycle analysis revealed a decline in cell percentage in G1 phase （P < 0.01） but a concomitant increase in cell percentage in G2 and S phase （both P < 0.05） in irradiated melanocytes compared with unirradiated melanocytes. Conclusions The optimal dose of infrared light is 80 J/cm2 for the irradiation of melanocytes, and this dose of infrared light can increase melanin content, tyrosinase activity, differentiation and proliferation of melanocytes.

Key words: vitiligo