Topical Retinoic Acid Enhances the Repair of Ultraviolet Damaged Dermal Connective Tissue

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Abstract
Ultraviolet (UV) irradiation induces excessive accumulations of elastic fibers in animal and human skin. Collagen is damaged and glycosaminoglycans are vastly increased. Formerly considered an irreversible change, we recently showed, post-irradiation, that a band of normal connective tissue was laid down subepidermally. Because of its ability to stimulate fibroblasts and enhance healing of wounds, we thought it likely that retinoic acid (RA) would promote the formation of this subepidermal zone of reconstruction. Hairless mice were irradiated for 10 weeks with Westinghouse FS20 sunlamps for a total UV dose of 7 J/cm2. Then. 0.05% RA was applied for 5 and 10 weeks. Observations were made by light and electron microscopy. In contrast to controls treated with vehicle, the reconstruction zone was significantly wider in RA-treated mice. The enhanced repair was dose related. Histochemically and ultrastructurally, collagen was normal, fibroblasts were numerous and in a configuration of high metabolic activity.