Single dose radiation is more effective for the UV-induced activation and proliferation of melanocytes than fractionated dose radiation.
OBJECTIVE
To establish whether the effect of fractionating radiation modifies the effects of ultraviolet (UV) radiation on epidermal melanocytes, we compared the clinical and histological effects of single high dose radiation against repeated intermediate to low dose radiation on epidermal melanocytes.


METHODS
Three minimal erythema UV doses (MED) were administered to three sites on the buttocks of healthy volunteers. One site was irradiated with 0.5 MED UV every day for 6 consecutive days, another site was irradiated with 1 MED UV every second day, and a third site received a single dose of radiation with 3 MED UV. The treatment was replicated on the other buttock. For the evaluation of UV-induced erythema and pigmentation, erythema and melanin indices were measured at 2 and 14 days post-irradiation. For purposes of histological evaluation, tissue specimens taken from each irradiated site at 2 and 14 days post-irradiation and were stained with monoclonal antibodies against Mel-5, HMB-45 and tyrosinase. Fontana-Masson silver staining, DOPA staining and split DOPA reactions were also performed.


RESULTS
At 14 days post-irradiation, UV radiation induced melanocyte activation, proliferation and melanogenesis in proportion to the radiation dose administered to each fraction. The most prominent responses were observed after single high doses of radiation.


CONCLUSIONS
When the total administered dose is identical, fractionation of radiation dose diminishes the effects of UV radiation on epidermal melanocytes. Furthermore, long, uninterrupted doses of UV radiation were found to more effective in inducing melanogenesis and melanocyte activation.
An
H T
HT
Department of Dermatology, Seoul National University College of Medicine, and Laboratory for Cutaneous Aging Research, Clinical Research Institute, Seoul National University Hospital, Chongno-Gu, Seoul, Korea.
Yoo
J Y
JY
Lee
M K
MK
Shin
M H
MH
Rhie
G E
GE
Seo
J Y
JY
Chung
J H
JH
Eun
H C
HC
Cho
K H
KH
D000328:Adult; D000951:Antigens, Neoplasm; D000954:Antigens, Surface / Q000032:analysis; D002455:Cell Division / Q000187:drug effects / Q000528:radiation effects; D004295:Dihydroxyphenylalanine / Q000494:pharmacology; D004890:Erythema / Q000209:etiology; D006023:Glycoproteins / Q000032:analysis; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008544:Melanocytes / Q000166:cytology / Q000528:radiation effects*; D058950:Melanoma-Specific Antigens; D014442:Monophenol Monooxygenase / Q000032:analysis; D009363:Neoplasm Proteins / Q000032:analysis; D011829:Radiation Dosage; D012867:Skin / Q000737:chemistry / Q000528:radiation effects; D012880:Skin Pigmentation / Q000528:radiation effects; D014466:Ultraviolet Rays
D000951:Antigens, Neoplasm; D000954:Antigens, Surface; D006023:Glycoproteins; C094218:MEL-5 protein, human; D058950:Melanoma-Specific Antigens; D009363:Neoplasm Proteins; D004295:Dihydroxyphenylalanine; D014442:Monophenol Monooxygenase