It has been postulated that reactive oxygen species generated by UV irradiation contribute to photo-induced skin damage, such as lipid peroxidation, sunburn reaction, phototoxicity, photoallergy, and photo-aging. [1][2][3][4][5][6][7][8] However, the mechanistic details remain unclear. Among various reactive oxygen species, singlet oxygen, a highly reactive and toxic intermediate with specific reactivity, appears to play an important role because it mediates photosensitized reactions. 9,10) We previously constructed a very sensitive near-infrared emission spectrometer with a germanium (Ge)-detector as a reliable means of singlet oxygen detection. [11][12][13] We used this device to show that coproporphyrin from Propionibacterium acnes (P. acnes) generated singlet oxygen on the surface of healthy skin under UV exposure by detecting the emission at 1268 nm due to singlet oxygen. 13) Patients with erythropoietic protoporphyria, caused by accumulation of protoporphyrin in the skin, are known to suffer severe skin damage during sunlight exposure.14,15) Our data suggested that damage might also occur in healthy skin. In addition, UVA-induced singlet oxygen generation has been shown to induce lipid peroxidation and gene expression. [16][17][18][19] Minami et al. reported that singlet oxygen was involved in UVA-induced oxidation of oleic acid and linoleic acid in mouse skin. However, singlet oxygen generated from coproporphyrin on the human skin surface should immediately attack skin surface lipids, which are mainly derived from sebaceous gland lipids such as triacylglycerol, free fatty acid, wax, squalene and cholesterol. 16,20) Because squalene was hardly oxidized in vitro under UV irradiation alone, a contribution of a factor producing singlet oxygen to squalene peroxidation in the skin was suggested. 21) Thus, there have been several investigations of singlet oxygen and endogenous photosensitizers in the skin under physiological conditions. [22][23][24] Lipid peroxide induces further reactions and is associated with the pathology of acne, atopic dermatitis, psoriasis and pigmentation. 25,26) However, the precise involvement of lipid peroxide in these pathologies has not been well investigated.Here, we first examined the reactivity of squalene with singlet oxygen directly by detection of singlet oxygen emission at 1268 nm and clarified the contribution of coproporphyrin as a photosensitizer to squalene peroxide formation under UV exposure. Then we demonstrated that squalene peroxide participates in UVA-induced skin hyperpigmentation. Cell Culture Human epidermal melanocytes were cultured in the MEDIUM 254 supplemented with the human melanocyte growth supplement (HMGS) at 37°C in 5% CO 2 /95% air condition. Human epidermal keratinocytes were cultured in the HuMedia-KG2 with 0.03 mM CaCl 2 , and hydrocortisone was removed from media 72 h before treatments. Cells and media were from Kurabo Industries Ltd. (Osaka, Japan). MATERIALS AND METHODS MaterialsAnimals Five-week-old female A-1 strain brownish guinea pigs were pur...

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Topical application of plant extracts and xanthine derivatives suppressed wrinkle formation, dermal connective alteration, and collagen accumulation. It is suggested that xanthine derivatives prevented neutrophil infiltration caused by UV-irradiation.

The influence of repeated low-dose ultraviolet B (UVB) radiation, to which we are exposed in daily life, has not been fully clarified, although the damage caused by exposure to high-dose UVB radiation has been well-studied in recent years. To investigate skin damage caused by repeated low-dose exposure, we evaluated the extent of injury to the Langerhans cells which are known to be involved in the cutaneous immune system. The backs of hairless mice were exposed to the following doses of UVB radiation: 100 mJ/cm(2) once, 50 mJ/cm(2) twice, 25 mJ/cm(2) four times or 10 mJ/cm(2) ten times. Skin specimens were taken for histochemical and electron microscopic examination 24 h after the final irradiation. Epidermis exposed to UVB radiation demonstrated a decrease in the number of Langerhans cells which showed less dendricity. The population of these cells in specimens exposed to repeated suberythemal doses was reduced to 40%, whereas exposure to a single high dose of UVB with the same energy resulted in a reduction of only 33%. These results indicate that repeated suberythemal doses injure Langerhans cells more than a single high-dose exposure. Furthermore, Birbeck granules in Langerhans cells of UVB-irradiated epidermis were reduced and tended to show shortening of their rod portion. The present study suggested that repeated challenge with suberythemal UVB radiation, to which we are all exposed in daily life, can cause substantial damage to Langerhans cells.

Reactive nitrogen species, produced during the process of inflammation induced by various factors including UV radiation, modify amino acids in crucial proteins. It is assumed that skin tissue is more likely to be modified, as it is located at the outer layer of a body that is exposed to UV radiation on a daily basis. To investigate the influence of the modified tyrosine on UV-exposed skin, we detected the nitrotyrosine or halogenated tyrosine and dityrosine in photo-aged model mice. The back skin of mice was exposed to a dose of 10 J cm(-2) day(-1) every day for 15 weeks. Samples exhibiting typical symptoms of photo aging were provided to the immunofluorescence study. The quantification of modified proteins was accomplished through a chemical analytical method known as HPLC-tandem mass spectrometry. Analysis of the irradiated skin samples showed that all modified tyrosine except nitrotyrosine demonstrated statistically significant increases. The molecular weights of major modified proteins, confirmed as 25-50 kDa, were measured using Western blot analysis with an anti-nitrotyrosine antibody. Furthermore, the immunofluorescence study verified that the localization of myeloperoxidase conformed to that of nitrotyrosine. This result suggests that the modified tyrosine was produced during the process of inflammation by UV irradiation. In this study, we used a low dose of UV irradiation to which we are exposed in daily life. Our results suggest that UV exposure in daily life may induce the production of modified tyrosines and skin aging.