Mediterranean essential oils as precious matrix components and active ingredients of lipid nanoparticles

Essential oils are recognized as valuable active pharmaceutical ingredients attributed to a set of biological properties, which include antibacterial, antifungal, antiviral, antioxidant, anticancer, immune-modulatory, analgesic and anti-inflammatory activities. Their use in pharmaceutics is however compromised by their limited water solubility and low physicochemical stability (i.e. volatility, oxidation). In order to overcome these limitations, we aimed to develop nanostructured lipid carriers (NLC) as delivery systems for Mediterranean essential oils, in particular Rosmarinus officinalis L., Lavandula x intermedia "Sumian", Origanum vulgare subsp. hirtum and Thymus capitatus essential oils, selected on the basis of their antioxidant and anti-inflammatory activities. NLC composed of Softisan (as solid lipid) have been produced by phase inversion temperature (PIT) and high-pressure homogenization (HPH), using two different emulsifiers systems. Particles have been further characterized for their mean particle size, polydispersity, zeta potential, morphology and chemical interactions. Best NLC formulations were obtained with Kolliphor/Labrafil as surfactants, and using Rosmarinus, Lavandula and Origanum as essential oils (PDI between 0.126 and 0.141, Zave < 200 nm). Accelerated stability studies have also been carried out to estimate the effect of the production method and surfactant composition on the long-term stability of EOs-loaded NLC. In vitro biological cell viability and anti-inflammatory activities were evaluated in Raw 264.7 cells (macrophage cell line), while in vitro antioxidant activity was checked by DPPH assay. Lavandula and Rosmarinus NLC were shown to be the most biocompatible formulations up to a concentration of 0.1% (v/v), whereas they were able to induce a dose-dependent anti-inflammatory activity in the order Lavandula > Rosmarinus ≥ Origanum.