THE EFFECT OF GLYCEROL AND HUMIDITY ON DESMOSOME DEGRADATION IN STRATUM-CORNEUM

Moisturizers are known to have occlusive, emollient and humectant prop erties, all of which help to alleviate the symptoms of skin xerosis. A lthough the biological mode of action of moisturizers is poorly unders tood, the recent observation that skin xerosis is associated with inco mplete desmosome digestion suggests that moisturizers improve the desq uamation process in such conditions, To examine the possibility that c ertain moisturizers act by facilitating desmosomal digestion, we inves tigated the ability of glycerol, a common humectant, to influence this process in stratum corneum in vitro. Examining desmosome morphology i n isolated stratum corneum by electron microscopy, it was observed tha t the desmosomes were in more advanced stages of degradation in glycer ol-treated tissue compared with control tissue. This enhanced desmosom al degradation in glycerol-treated tissue was confirmed by significant decreases in the levels of immunoreactive desmoglein 1, a marker of d esmosome integrity, Desmosomal degradation was also shown to be a humi dity-dependent event, being significantly reduced at low relative humi dity. The effect of glycerol on desmosome digestion was emphasized fur ther in two in vitro model systems. Firstly, glycerol increased the ra te of corneocyte loss from the superficial surface of human skin biops ies in a simple desquamation assay. Secondly, measurement of the mecha nical strength of sheets of stratum corneum, using an extensiometer, i ndicated a dramatic reduction in the intercorneocyte forces following glycerol treatment. These studies demonstrated the ability of glycerol to facilitate desmosome digestion in vitro. Extrapolating from these results, we believe that one of the major actions of moisturizers in v ivo is to aid the digestion of desmosomes which are abnormally retaine d in the superficial layers of xerotic stratum corneum.