In the last decades, a renewed interest in plants and traditional medicine is diffusing all over the world, with particular attention to essential oils (EOs) as promising natural compounds for their different activity (e.g. antibacterial, antifungal, antiviral, antioxidant, anticancer, immune-modulatory, analgesic and anti-inflammatory actions) (Bakkali et al., 2008, Bona et al., 2016). Their complex chemical composition and high concentration of terpenes (monoterpenes, sesquiterpenes, and diterpenes) and other oxygenated compounds (esters, aldehydes, ketones, alcohols, phenols, and oxides) are responsible for their ability in modifying the microorganisms’ membrane and cell wall, with consequent release of cell contents (Altintas et al., 2013). Based on their composition, EOs result particularly interesting for the treatment and prevention of diseases related to inflammation or ROS production (Severino et al., 2015). Furthermore, recent studies highlight the possibility to use these components as active agents for the treatment of candidiasis, for wound healing or even for solid cancers (Bona et al., 2016, Gonzalez-Vallinas et al., 2014, Hammer et al., 1998, Petiwala et al., 2014, Pozzatti et al., 2008, Tampieri et al., 2005, Wang et al., 2012). Currently, EOs and most generally medicinal and aromatic plants, are worldwide considered as one of the most important field for the revalidation of traditional products. Numerous EOs present in plants from the Mediterranean area, such as Origanum spp., Thymus spp. and Rosmarinus spp., commonly used in the food industry and generally recognised as safe (GRAS), have been reported to be effective against several microorganisms, particularly against Candida spp., as recently reviewed by Bona et al. (Bona et al., 2016). However, their hydrophobicity and insolubility in water, the high volatility and instability due to oxidation and hydrolysis, still represent a challenge for the effective use of EOs in food, cosmetic and pharmaceutical industries (Hosseini et al., 2013a, Trinetta et al., 2017). In order to overcome these drawbacks, nanoencapsulation in delivery systems has been suggested as a valid approach for preserving the properties of EOs, increasing their effectiveness (Severino et al., 2015).
With the purpose of exploiting the beneficial effects of EOs as anti-oxidant and anti-inflammatory ingredients, we developed nanostructured lipid carriers (NLC) using EOs extracted from Mediterranean plants as oily components of the lipid matrix.
In particular, Rosmarinus officinalis L., Lavandula x intermedia “Sumian”, Origanum vulgare subsp. hirtum and Thymus capitatus (Coridothymus capitatus) were used both as oily liquid component for the preparation of NLC and active ingredients, prepared by phase inversion temperature (PIT) and high pressure homogenization (HPH) methods. All developed NLC formulations were physicochemically characterised to evaluate the effect of each EO on nanoparticles features, with particular attention to the mean particles size and polydispersity (by dynamic light scattering (DLS), morphological structure (by transmission electron microscopy (TEM), chemical interactions (by Fourier transmission infrared spectroscopy FT-IR) and long-term stability (Turbiscan AGS). In vitro biological cell viability and anti-inflammatory activity of EOs both as pure compounds and as matrix components of NLC, were evaluated in RAW 264.7 cells (macrophage cell line), considered as early stage of inflammation (Kim et al., 2017a, Kim et al., 2017b). Furthermore, in vitro antioxidant activity was studied using the DPPH assay.