This study was conducted to assess protective effect of an
antioxidant protein,
sericin, on UVB-induced acute damage and
tumor promotion in mouse skin. In experiment 1, HR-1 hairless mice were treated with 180 mJ/cm2 of ultraviolet B light (UVB) once daily for 1 and 7 days. The treatment for 7 days caused red
sunburn lesions of the skin. The intensity of red color and area of these lesions were inhibited by the topical application of
sericin at the dose of 5 mg after UVB treatment. Immunohistochemical analyses showed that the application of
sericin significantly suppressed UVB-induced elevations in
4-hydroxynonenal (4-HNE), expression of
cyclooxygenase-2 (COX-2)
protein, and
proliferating cell nuclear antigen (
PCNA)-labeling index in the UVB-exposed epidermis. In experiment 2, HR-1 hairless mice were treated with 200 nmol of 7,12-dimethylbenz [alpha]
anthracene (DMBA) followed 1 week later by irradiation with 180 mJ/ cm2 of UVB twice weekly for 22 weeks. The protective effect of
sericin was evident in terms of significant reduction in
tumor incidence and
tumor multiplicity at the dose of 5 mg. The results suggest that
sericin possesses photoprotective effect against UVB-induced acute damage and
tumor promotion by reducing oxidative stress, COX-2 and cell proliferation in mouse skin.