The Effects of Multiple UVB Exposures on Proliferation and Melanization in Cultured Human Melanocytes

Kim, Jin Hwan; Park, Jai Kyung; Haw, Choong Rim; Lee, Mu Hyoung

Abstract

BACKGROUND: In the skin, the major stimulus for cutaneous pigmentation is ultraviolet radiation. The most important physiologic role of melanin is protection against harmful UV radiation to skin. It is known there are some differences in melanization between a single and multiple exposures of UVB, in vivo. Little if known about the functions of the melanocyte alone in cutaneous pigmentation after ultraviolet exposure, because of the complexity of interactions in the whole epidermis.
OBJECTIVE
To investigate the effects of multiple exposures at various dosages of UVB, and to compare the effect of UVB in multiple divided exposures with a single exposure at the same total dosage of UVB on proliferation and melanization in cultured human melanocyte.
METHODS
Melanocytes were cultured by modified TIC medium. The melanoctes were exposed daily for three consecutive days to UVB at 2, 4, 8 and 16 mJ/cm2and a single exposure at 24 mJ/cm2. The morphologic changes were examined by phase contrast microscopy. The melanocytes were counted by hemocytometer and melanin contents were assayed by spectrophotometer.
RESULTS
1. The effects of multiple UVB exposures: 1) The morphologic changes were as follows: With three time exposures at a dosage of 8 mJ/cm2, themelanocytes enlarged in size, and elongated their dendrites slightly; with three time exposures at a dosage of 16 mJ/cm2, enlargement in sized and elongation of dendrited were more significant. 2) With three time exposures at dosages of 2 nd 4 mJ/cm2, the proliferation of melanocytes was stiumlated significantly(p<0.05). However, with three time exposures at dosages of 8 and 16 mJ/cm2the proliferation was inhibited(p<0.05). 3) With three time exposures at dosages of 2 and 4 mJ/cm2, the melanin contents were decreased. However, with three tiem exposures at a dosage of 16 mJ/cm2, the melanin contents were highly increased(p<0.01). 2. The comparison between multiple divided exposures and a single exposure at the same toal dosage of UVB: 1) There were no morphologic differences of dendrities between with three time exposures at a dosage of 8 mJ/cm2 and with a single exposure at a dosage of 24 mJ/cm2. However enlarged melanocytes were more numerous with a single exposure. 2) The proliferation of melanocytes was more inhibited with a single exposure than with multiple divided exposures(p<0.05). 3) The melanin contents were more increased with a single exposure than with multiple divided exposures(p<0.05).
CONCLUSION
With multiple exposures at lower dosages of UVB, the proliferation of melanocytes was stimulated, and melanization was decreased. However, with multiple exposures at higher dosages of UVB, the proliferation was inhibited, and melanization was increased. At the same total dosage of UVB, the proliferation was more inhibited, and the melanization was more increased with a single exposure than with multiple divided exposures.