Targeted Uvb Phototherapy Induced Experimental Hyperpigmentation On The Skin Of Brownish Guinea Pigs

OBJECTIVE To study the experimental hyperpigmentation induced by targeted UVB phototherapy on the skin of brownish guinea pigs and provide experimental evidence for treating vitiligo with targeted UVB phototherapy.METHODS Ten brownish guinea pigs were enrolled as the experimental model in this 6-week study. After their back hair removal treatment,four isolated areas were selected on each guinea pigs as control group, low increment dose group, moderate increment dose group and high increment dose group. According to the minimum erythema dose (MED) and the pre-test results of the targeted UVB,we set the initial dose irradiation of each tested group as 90 mJ/cm,180 mJ/cm,270 mJ/cm, while nothing is treated on the control group. Each tested group was treated with different dosages of targeted UVB for twice a week, and the subsequent dose was determined as follows:the dose was increased by 10-20% in every session until the development of erythema was noted. When erythema occurs before the next time of irradiation, the dose of the next session was to maintain the original dose. If symptomatic erythema(burning,pain) or even blistering developed, the treament was suspended until remission, and then the dose of the next session was diminished by 10-20%. Efficatcy was evaluated at the end of the experiment by Masson-Fontana staining, Imokawa's staining and immunohistochemistry to stain NOS.RESULTS All the guinea pigs had completed the study. At the early part of treatment, a small number of guinea pigs had transient erythema and slight desquamating,which can be controled by decreasing the dosage or being suspended the treatment for severy days. Experimental hyperpigmentation was observed and analyzed in each tested group, the differences among the 4 group were statistically significant (P<0.05),except the difference between moderate increment dose group and high increment dose group in pigmentation score. Of course, there was no significant change in all the untreated areas(the contol group). The differences among the 4 groups were proved to be of statistical significances (P<0.05) by Masson-Fontana staining and Imokawa's staining, However, moderate increment dose group were better than high increment dose group. In addition, the expression of iNOS is upregulated by UVB irradiation and the differences between the 4 groups was considered significant (P<0.05).CONCLUSION Targeted UVB phototherapy can induce experimental hyperpigmentation on the skin of brownish guinea pigs in a dose-dependent manner. Selecting a close to or slightly higher than the minimal erythema dose (MED) irradiation can effectively reduce the cumulative dose and the potential risk of cancer with a satisfactory effect.