RESUMEN
We studied the possibility of supplementing human keratinocytes with exogenous lipids (phospholipids, sphingolipids and cholesterol) and evaluated their influence on cell proliferation, using cells cultured in vitro. Experiments carried out with liposomes composed of cholesterol/GM1 ganglioside and different phospholipids (5:1.5:10, M/M/M), showed that liposomes associated with cells more efficiently when they contained soya lecithin. The treatment with liposomes made of the ternary mixture did not modify the rate of cell proliferation, as assessed by the incorporation of [3H]-thymidine. In contrast, the proliferation rate strongly decreased (65% with respect to the control) using the same liposomes without GM1. Experiments carried out with GM1 alone showed a strong stimulation of the proliferation rate (144% with respect to the control). Fluorescence dequenching experiments, carried out with the probe octadecyl rhodamine B chloride, showed that fusion was the main mechanism of liposome-cell interaction. Metabolic studies established that exogenously administered GM1--either embedded in liposomes or as a pure glycolipid dispersion--led to the production of several products, including ceramide. Altogether, these results show that different, opposing effects can be exerted on cell proliferation by the administration of lipids, separately or in mixtures, to human keratinocytes, and indicate the importance of a correct formulation for supplementing human keratinocytes with exogenous lipids.