Epidermal effects of tretinoin and isotretinoin: influence of isomerism.

The efficacy of tretinoin is well established in the treatment of acne and photoaged skin, however as a typical side effect of tretinoin treatment most patients develop a low-grade irritant dermatitis. Since isotretinoin topical treatment usually shows much lower incidence and intensity of adverse effects than tretinoin topical treatment, histological studies are needed to scientifically evaluate the effects of isotretinoin application on epidermis and also to assess if it can be used in anti-aging products as an alternative to tretinoin. Thus, the aim of this study was to compare the effects of topical use of tretinoin or isotretinoin on hairless mice epidermis, using appropriate histopathological and histometric techniques, in order to evaluate the influence of isomerism on skin effects. For this, gel cream formulations containing or not 0.05% tretinoin or 0.05% isotretinoin were applied in the dorsum of hairless mice, once a day for seven days. Histopathological evaluation, viable epidermal and horny layer thicknesses as well as the number of epidermal cell layers were determined. Our results showed that tretinoin and isotretinoin were effective in the enhancement of viable epidermis thickness and number of epidermal cell layers, suggesting that they could be used for stimulation of cellular renewal. However isomerism influenced skin effects since isotretinoin had more pronounced effects than tretinoin in viable epidermis. In addition only isotretinoin treatment enhanced horny layer thickness when compared to the gel cream treatment.