Abstract
Recently the skin damage induced by UV-irradiation has become an interest for the cosmetic industry. Especially in view of photo-induced aging, the importance of UV-A has been emphasized since UV-A penetrates deeply in dermis and is suspected to induce irreversible damage to essential tissue components such as collagen and hyaluronic acid. We examined the skin damage by photodynamic process mainly involving singlet oxygen. Singlet oxygen, which is one of the most reactive of active oxygen species, may induce some damage to biological function of skin. Life-time of singlet oxygen is very short and there has been no method of detecting it evidently. In this work we developed the system of specific detection of singlet oxygen based on emission at 1268nm. Using this system we could directly detect singlet oxygen produced by hematoporphyin-photosensitized reaction. We found that when collagen was exposed to singlet oxygen, α or β chain decreased rapidly and they were converted into γ chain. This reaction was not affected by superoxide dismutase or mannitol. These results indicated that singlet oxygen induced the formation of cross-linked collagen. We suggested that the cross-linking was dependent on histidine residues photo-oxidized by singlet oxygen. Generaly, cross-linking of collagen has been considered to be related to aging but the mechanism of cross-linking has not been investigated intensively. From the result presented here, we speculate that the cross-linked collagen induced by singlet oxygen is related to the photodynamic skin aging.
