Studies on the relationship between epidermal cell turnover kinetics and permeability of hairless mouse skin.

The primary aim of this study was to develop non-invasive, physical means to quantitatively assess the epidermal turnover kinetics and barrier properties of the skin and relate these to the cutaneous irritation which results from ultraviolet light irradition and mild thermal burns. An improved tape stripping technique, using a special polyester tape, was found particularly suitable for studying epidermal cell turnover kinetics of hairless mice. After systemically injecting radiolabeled glycine, the appearance of radioactivity at the skin's surface indicated the transit time of radiolabeled cells through the skin. By plotting the data as the cumulative specific activity against time and then fitting them with a third order polynomial equation, it is possible to estimate the turnover time of the stratum corneum. The skin turnover was coordinated with non-invasive transepidermal water loss (TEWL) studies determined with an evaporimeter. Depending on the dose of UVB light, the evaporative water loss from UVB irradiated skin sites was increased several times relative to normal skin. Thermally burned skin also showed marked increases in TEWL which depended on the temperature and duration of the burn. Irrespective of the type of injury, the more severe injuries had more protracted elevation of TEWL. Of considerable importance, the changes in the skin brought about by these trauma lead to accelerated tissue turnover, which was the principal cause of the barrier deficient state of the skin. In vitro diffusion studies of the permeability of hydrocortisone through UVB irradiated and thermally burned skin were also performed. The studies indicated that irritated skin offers a relatively low diffusional resistance to hydrocortisone. Depending on the severity of the trauma, the increases in hydrocortisone's permeability coefficient through irritated skin ranged from a low of about 2 times normal to a high of about 210 times normal. Trauma-induced changes in hydrocortisone permeability paralleled changes in TEWL, proving that the barrier deficient state resulting from rapid epidermal turnover is a general phenomenon.PhDPublic healthPharmaceutical sciencesUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/162053/1/8907046.pd