The Effects of UVB Irradiation and Sunscreen Agents on Photoaging of Hairless Albino Mouse Skin

Choi, Jae Young; Yoon, Kyoung Sik; Cho, Yong Ho; Kim, Nack In

Abstract

BACKGROUND: Photoaging skin is clinically characterized by wrinkled, dry, inelastic and irregularly pigmented skin, skin tumor and histologically by increased epidermal thickness, nurnerous fibroblasts, mast cells and inflammatory cells in the upper dermis, elastosis, degeneration of collagen fibers, increased proportion of type III collagen fibers in the dermis and increased numbers of keratinizing cysts in the lower dormis of hairless albino mouse skin. Chronic exposure to UVB induces photoaging skin and sunscreen agents are used to prevent photodamage to skin and reduce the incidence and extent of the chronic photoaging effects.
OBJECTIVE
To evaluate the photoaging effects of UVB on the skin and to assess the ability of sunscreen agents to protect the skin from photoaging, we examined the clinical, histological and quantitative changes in collagen in the skin of Albino hairless Skh: HR-1 mice.
MATERIALS AND METHODS
The experimental animals were male Albino hairless Skh: HR-1 mice, 12 weeks old. The control group was a chronologically aging group which had not been affected by UVB irradiation. The non-protected group was irradiated with UVB, a half of MED, 3 times weekly(Monday, Wednesday, Fr iday), for 12 weeks. To assess the photoprotective effects of sunscreen agents, the control group, the non-protected group and the sunscreen agent-applicated groups were compared to each other clinically, histologically, and by quantitative collagen analysis. An early increase in type III collagen during UVB irradiation was determined by cyanogen bromide digestion of the whole skin, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and densitometry.
RESULTS
Clinically, the skin of the mice in the non-protected group showed mild changes caused by photoaging. Histoloically, the non-protected group showed increases in the size and number of keratinizing cysts in the lower dermis and increases in the mast cells in the upper dermis compared with the control group. However, no significant findings of increased epidermal thickness, inflammatory cell infiltration, elastic fiber change or degeneration of collagen fibers were shown. By the 12th week, four of the total of nine mice in the non-protected group developed at least one tumor. The sunscreen agent applicated groups showed slightly photoprotected effects clinically and histologically. In the collagen analysis, the proportion of type III collagen was significantly increased in the photoaging skin of mice in the non-protected group compared with the control group. Mice in the sunscreen agent applicated groups showed a significantly decreased proportion of type III collagen compared with the non-protected group.
CONCLUSION
To summarize, UVB exposure of the skin induces photoaging. The number and size of keratinizing cysts increased in the photoaging skin of hairless albino mice. There was also a quantitative change in the collagen fibers. The use of sunscreen agents decreases the photoaging effects of UVB on the skin.