Continuous UVB irradiation to modify the biophysical properties and protein conformation of rat skin

In order to determine the continuous irradiation effects of UVB on the skin of live Sprague Dawley (SD) rats, the changes in biophysical properties and protein conformation of the skin were studied. The continuous UVB irradiation affecting the water content, skin color and protein structure of the rat skin was investigated by using a skin surface hygrometer, a Chroma meter and an attenuated total reflection (ATR)/Fourier transform infrared (FT-IR) spectroscopy. Test areas on the dorsal skin were continuously irradiated with 600 +/- 10 microW/cm2 UVB for 56 h. Part of the dorsal skin was covered with a bandage as a non-irradiated control. The results indicated that the water content of the irradiated skin decreased with UVB irradiation, but the non-irradiated control skin exhibited a higher level of water content. The decrease in the skin's water-binding capacity from cracks induced by continuous UVB irradiation, and the occlusive dressing of the non-irradiated skin to prevent water loss and form full hydration might be responsible for the results. The decrease of L* value and the increase in a*, b* and delta E values in the skin color parameters with UVB irradiation indicates an incremental darkening of the skin and a marked increase in erythema. However, there was no significant change in skin color for the non-irradiated control skin. A slight modification of the protein secondary structure in the skin after continuous UVB irradiation was also evidenced by transforming the alpha-helix structure into a beta-sheet structure after long-term continuous UVB irradiation. Continuous UVB irradiation of SD rat skin may decrease the skin's water-binding capacity, cause darkening, increase erythema and modify the protein secondary structure of the skin.