Research Summary
A comprehensive comparison of antioxidant defenses in the dermis and epidermis, and their response to exposure to ultraviolet (UV) irradiation, has not previously been attempted. In this study, enzymic and non-enzymic antioxidants in the epidermis and dermis of hairless mice were compared. Enzyme activities are presented both as units per gram of skin and units per milligram of protein, with arguments made for the superiority of skin wet weight as a reference base. Catalase, glutathione peroxidase, and glutathione reductase (units per gram of skin) were higher in the epidermis than in the dermis by 49%, 86%, and 74%, respectively. Superoxide dismutase did not follow this pattern.
Lipid-soluble antioxidants (α-tocopherol, ubiquinol 9, and ubiquinone 9) and water-soluble antioxidants (ascorbic acid, dehydroascorbic acid, and glutathione) were 24-95% higher in the epidermis than in the dermis. In contrast, oxidized glutathione was 60% lower in the epidermis than in the dermis. To examine the response of these cutaneous layers to UV irradiation, mice were irradiated with solar light. After exposure to 25 J/cm² (UVA + UVB from a solar simulator), 10 times the minimum erythemal dose, both epidermal and dermal catalase and superoxide dismutase activities were greatly decreased. α-Tocopherol, ubiquinol 9, ubiquinone 9, ascorbic acid, dehydroascorbic acid, and reduced glutathione decreased in both the epidermis and dermis by 26-93%, while oxidized glutathione showed a slight, non-significant increase.
Because the reduction in total ascorbate and catalase was much more severe in the epidermis than in the dermis, it can be concluded that UV light is more damaging to the antioxidant defenses in the epidermis than in the dermis.
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