Extraction of Oleanolic Acid from Olea Europaea L. leaves using a Lipophilic Deep Eutectic Solvent for direct formulation of self-emulsifying drug delivery systems

Abstract

In this work is presented for the first time a new approach to extract the triterpene oleanolic acid (OA) from Olea Europaea L. leaves by using a lipophilic deep eutectic solvent (LipoDES) constituted of caprylic and lauric acid, as an alternative to conventional solvents, and formulate self-emulsifying drug delivery systems (SEDDSs), exploiting directly OA-containing LipoDES extract, to potentially improve the bioavailability of this BCS class IV bioactive molecule. LipoDES extract was characterized by using a HPLC technique which assessed the presence of OA in the extract and allowed us to quantify it. Subsequently, several preconcentrates were realized mixing the LipoDES extract, used as oily phase, with different surfactants (Cremophor RH-40 and Cremophor EL) and co-surfactants (Labrasol ALF and ethanol) which are well known for their self-emulsifying properties. After self-emulsification, the formulations were characterized by dynamic light scattering in terms of size and polydispersity index (PDI) to select the ones with proper characteristics. Three possible formulations (S_A, S_F and S_I) containing different amounts of extract were selected due to their low size and PDI and further investigated in terms of physical-chemical stability to temperature variations (stability at temperatures higher than 37 °C) and to dispersion and dilution in simulated gastrointestinal fluids. In vitro cytotoxicity and permeation studies were performed on CaCo-2 cells monolayer to prove the safety of SEDDSs and the ability of these systems to increase the permeability of OA. Bodipy alkyne dye (BDP) was selected as tracer in permeability studies, which highlighted an apparent permeability increase up to 10-fold for S_A loaded with BDP (S_A-BDP) compared to BDP alone. Eventually, a one-month chemical stability study was conducted on S_A, which resulted in being stable at least for that period of time if stored at 4 and 25 °C. This research highlights the potential dual use of LipoDES for extraction and formulation of bioactive compounds such as OA, resulting in a novel approach to innovative extraction and oral delivery of plant extracts.