Nanoemulsion as a carrier to improve the topical anti-inflammatory activity of stem bark extract of <em>Rapanea ferruginea</em>

Abstract

The aim of this study was to develop nanoemulsion containing soft extract of stem bark of <i>Rapanea ferruginea</i> to improve the topical delivery and anti-inflammatory activity. The extract of <i>R. ferruginea</i> stem bark was incorporated into the oily phase of the nanoemulsion by the method of phase inversion at low energy. The developed nanoemulsion had an average droplet size of 47.88±8.20 nm and a polydispersibility index of 0.228. Uniformity of size, spherical shape of droplet, and absence of clusters were confirmed by transmission electronic microscopy. The zeta potential was -34.7±1.15 mV. The nanoemulsion showed a moderate degree of skin irritation in the agarose overlay assay in vitro. The content of the extract markers, myrsinoic acids A and B, was 54.10±0.08 and 53.03 μg/g in the formulation, respectively. The formulation demonstrated pseudoplastic and thixotropic rheological behavior. In vitro release of chemical markers was controlled by diffusion mechanism. An extract-loaded nanoemulsion showed a topical anti-inflammatory activity in a croton oil-induced edema ear model, with a decrease in tumor necrosis factor release and myeloperoxidase activity. The nanoemulsion was 160% more efficient than the conventional cream containing 0.13% of the extract. The nanoemulsion showed suitable properties as a carrier for topical use of <i>R. ferruginea</i> extract and the approach for improving the topical anti-inflammatory activity.