The potential of caffeic acid lipid nanoparticulate systems for skin application: in vitro assays to assess delivery and antioxidant effect

The object of this study is a comparison between solid lipid nanoparticles and ethosomes for caffeic acid delivery through the skin. Caffeic acid is a potent antioxidant molecule whose cutaneous administration is hampered by its low solubility and scarce stability. In order to improve its therapeutic potential, caffeic acid has been encapsulated within solid lipid nanoparticles and ethosomes. The effect of lipid matrix has been evaluated on the morphology and size distribution of solid lipid nanoparticles and ethosomes loaded with caffeic acid. Particularly, morphology has been investigated by cryogenic transmission electron microscopy and small angle X-ray scattering, while mean diameters have been evaluated by photon correlation spectroscopy. The antioxidant power has been evaluated by the 2,2-diphenyl-1-picrylhydrazyl methodology. The influence of the type of nanoparticulate system on caffeic acid diffusion has been evaluated by Franz cells associated to the nylon membrane, while to evaluate caffeic acid permeation through the skin, an amperometric study has been conducted, which was based on a porcine skin-covered oxygen electrode. This apparatus allows measuring the O2 concentration changes in the membrane induced by polyphenols and H2O2 reaction in the skin. The antioxidative reactions in the skin induced by caffeic acid administered by solid lipid nanoparticles or ethosomes have been evaluated. Franz cell results indicated that caffeic acid diffusion from ethosomes was 18-fold slower with respect to solid lipid nanoparticles. The amperometric method evidenced the transdermal delivery effect of ethosome, indicating an intense antioxidant activity of caffeic acid and a very low response in the case of SLN. Finally, an irritation patch test conducted on 20 human volunteers demonstrated that both ethosomes and solid lipid nanoparticles can be safely applied on the skin.