The Effect of Topical Ascorbic Acid on Epidermal Melanocytes in UV-irradiated Black Mice

Melanin is synthesized by tyrosine by tyrosinase. The synthesis of melanin is influenced by several factors, of which ultraviolet radiation results in increased pigmentation by increase of tyrosinase activity and melanocyte number. To observe the effect of depigmentation of ascorbic acid, we induced activation of melanocytes and melanin pigmentation by UVB irradiation and then topically applied ascorbic acid. Sixty four mice were irradiated UVB 100mJ/cm²/day for 10 days. After then they were divided into 8 groups in random and the topical application of ascorbic acid on each group is as follows, lotion base(control), 3% lotion, 5% lotion, 10% lotion, cream base(control), 3% cream, 5% cream and 10% cream. After irradiation ascorbic acid had been topically applied twice a day on both ears of mice, respectively, for 7 weeks. Two mice in each group were sacrified by the end of the 1st, 3rd, 5th and 7th week of the application. To observe the size and number of melanosomes, electron microscopic examination was done. To estimate the number of the melanocytes, light microscopic preparation of split-DOPA stain was done. The results are summarezed as follows: 1) In all groups except 3% lotion group(3% magnesium ascorbic acid phosphate), the number of DOPA positive melanocytes began to decrease from 1 week but rather increased at 7 weeks. 2) In 5% lotion group(5% magnesium ascorbic acid phosphate) the number of DOPA positive melanoctytes was significantly decreased less than that in 5% cream group (5% ascorbic acid palmitate) 3) In the electron microscopic findings, the number of melanosomes and the ratio of the stage IV melanosomes markedly decreased from 1 week to 7 weeks in 10% lotion group(10% magnesium ascorbic acid phosphate) and 10% cream group(10% ascorbic acid palmitate) compared to lotion base and cream base, respectively.