MODIFICATION OF LATE EPIDERMAL DIFFERENTIATION IN PHOTOAGED SKIN TREATED WITH TOPICAL RETINOIC ACID CREAM

Background: Retinoic acid (RA) cream treatment alters epidermal prolif eration and differentiation in photoaged skin. Objective: To study the changes in the expression of markers of epidermal differentiation in photoaged skin following RA cream treatment. Methods: Ten subjects wit h photoaged skin were examined before treatment and at regular interva ls during 12 months of once daily application of 0.05% tretinoin cream over the left forearm. Paraffin-embedded biopsy sections from the for earm were stained with loricrin, filaggrin, involucrin and cornifin an tisera in addition to hematoxylin and eosin, The various layers were m easured using a calibrated optical micrometer, Results: The thickness of the epidermis increased rapidly, reaching a substantial increase af ter 1 month of retinoid cream application and retaining it during the following 12 months. The stratum granulosum achieved a transient but s ubstantial increase after 1 and 3 months. Except involucrin, the ratio between the layers expressing the various markers of epidermal differ entiation and the epidermis significantly increased following tretinoi n cream treatment, Conclusion: RA. cream treatment not Only increases the thickness of the epidermis but also the programming of late termin al epidermal differentiation, as expressed by the markers studied. Thu s, RA appears to affect both proliferation and differentiation of kera tinocytes in vivo.