Nanovesicle-based formulations for photoprotection: a safety and efficacy approach

Vesicular nanosystems are versatile and they are able to encapsulate actives with different solubilities, such as lipophilic and hydrophilic compounds. The most well-known vesicular nanosystems are liposomes and niosomes, the last one is formed by non-ionic surfactants. In the present work, we developed photoprotective niosomes containing sunscreens (octyl methoxycinnamate, diethylamino hydroxybenzoyl hexyl benzoate and phenylbenzimidazole sulfonic acid), non-ionic surfactants, cholesterol and stearylamine (positive-charged lipid). Studies based on dynamic light scattering techniques, entrapment efficiency and morphology by transmission electron microscopy were performed to characterize the niosomes. In addition, rheology, pH, in vitro sun protection factor (SPF) efficacy and toxicity and in vivo and in vitro safety were determined for the niosome formulations F-N1 and F-N2. The mean sizes of N1 and N2 were 168 ± 5 nm and 192 ± 8 nm, respectively, and their morphologies were spherical, unilamellar and with an entrapment efficiency of more than 45% for each sunscreen. Both formulations, F-N1 and F-N2 presented characteristics of pseudoplastic non-Newtonian fluids, showing declining viscosity with increasing shear rate applied. SPF values were considered satisfactory, 34 ± 8 for formulation F-N1 and 34 ± 5 for F-N2. The formulations did not present toxicity when tested in macrophages and the pH was compatible with skin, which minimizes allergies. The in vitro safety assay showed lipophilic sunscreens greater affinity for the epidermis, since this layer contains natural lipids. In vivo safety assay suggests that the increased skin retention of N2 is directly correlated with the positive charge of stearylamine. Stable photoprotective niosomes were obtained and were shown to be promising nanostructures to be used against solar radiation. (paper)