Green Solid Lipid Nanoparticles by the Fatty Acids Coacervation: an innovative Drug and Gene delivery tool for various applications

Solid Lipid Nanoparticles (SLNs) and Nanostructured Lipid Carriers are nanospheres made up of solid and solid-liquid lipids, respectively. However, they are usually obtained by methods involving either high temperatures and complex equipment or toxic solvents. Therefore, such techniques are associated to several hurdles and high costs. Among alternative formulation techniques, the fatty acid coacervation allows to obtain fatty acid-based SLNs from the corresponding alkaline soaps, owing to simple proton exchange. In this experimental work, natural soaps, obtained from vegetal butters and fats, have been exploited as the starting material to prepare the so called green SLNs. Shea and mango soaps have been selected to this aim. Mango and shea butters are obtained from plant seed kernels, a residual discard during the industrial fruit processing. The quality and abundance of the unsaponifiable fraction depends mainly on the extraction method employed. Green SLNs, produced through fatty acid coacervation from natural soaps, were suitable for sustainable and versatile solutions in cosmetics, ocular gene therapy, peptide oral delivery and therapy for cerebrovascular diseases. In cosmetics, green SLNs were loaded with functional ingredients, including an UV-filter and anti-aging compounds, such as α-Tocopherol and Tocopheryl nicotinate. Physico-chemical characterization confirmed their stability across various storage conditions. A serum and a hydrogel were formulated based on such green SLNs, with mango SLNs-based serum showing superior long-term stability and efficacy. Franz cell studies revealed enhanced permeation of α-Tocopherol through pig-ear skin, while human trials highlighted significant improvements in skin hydration and elasticity. Conversely, insulin oral delivery is a case study. Indeed, Glargine insulin was effectively loaded into the green SLNs lipid matrix, exploiting the hydrophobic ion pairing approach. Ex vivo studies demonstrated the ability of green SLNs to promote the permeation of Glargine insulin into different gut sections, likely due to the presence of monounsaturated fatty acids in the lipid matrix. Furthermore, it is possible to obtain a dispersible powder, by freeze-drying or spray drying of SLNs suspension, suitable for the formulation of solid oral dosage forms, such as granulates and tablets. Green SLNs were also employed as intranasal carriers for treating cerebrovascular and neurological diseases. Loaded with specific therapeutic agents aimed at restoring neurovascular unit function, such SLNs were able to reduce cerebrospinal fluid production in vitro and exert vasoprotective effects in isolated vessel models. Pharmacokinetics and biodistribution studies using fluorescently labelled nanoparticles demonstrated their potential for systemic and targeted brain delivery. Ocular cationic green SLNs, instead, were developed as non-viral vectors for delivering green fluorescent protein encoding plasmid DNA (pDNA), whereas a stable binding, protection and release of pDNA was assessed. While in vitro studies indicated good cellular association, but limited transfection efficiency, ex vivo experiments on rabbit corneas showed promising transfection capabilities for vectors without hyaluronic acid functionalization. This success points out the role of oleic acid in enhancing delivery and transfection performance. In conclusion, green SLNs showcased an eco-friendly preparation method, a multifunctional lipid and unsaponifiable composition, and a broad application potential. Accordingly, their sustainable and adaptable nature paves the way for innovative solutions across various fields, ranging from skin-care cosmetics to therapy for complex diseases, such as corneal pathologies, diabetes and neuropharmacology.