Visible effects of rapamycin (sirolimus) on human skin explants in vitro

In this manuscript, we report observations of the effects of rapamycin in an organotypic culture of human skin explants. The tissues were cultured for 5 days at the air-liquid interface or in submersed conditions with media with and without rapamycin at 2 nM concentration. Histological analysis of tissue sections indicated that rapamycin-treated samples maintained a better epidermal structure in the upper layers of the tissue than untreated samples, mostly evident when skin was cultured in submersed conditions. A significant decrease in the number of positive proliferative cells using the Ki67 antigen was observed when specimens were treated with rapamycin, in both air-liquid and submersed conditions but apoptosis differences between treated and untreated specimens, as seen by cleaved caspase-3 positive cells, were only observed in submersed specimens. Finally, a decrease and variability in the location in the expression of the differentiation marker involucrin and in E-cadherin were also evident in submersed samples. These results suggest that the development of topical applications containing rapamycin, instead of systemic delivery, may be a useful tool in the treatment of skin diseases that require reduction of proliferation and modulation or control of keratinocyte differentiation.