Abstract
Lauric acid (LAH) strongly inhibits the growth of acne-causing bacteria. LAH is essentially water-insoluble and the solubility of laurate (LA) salts are medium and temperature dependent. Hence, LAH/LA preparations are difficult to formulate. Here we fully characterized phospholipid vesicles containing up to 50 mol% LAH. Vesicles of dipalmitoylphosphatidylcholine (DPPC) containing LAH, at pHs 7.4 and 5.0, were characterized measuring size, charge, bilayer phase transition temperature (Tm) and permeability of water-soluble probes. Small angle X-ray scattering and cryotransmission electron microscopy showed multilamellar vesicles at low LAH %. Increasing LAH % had a negligible effect on particle size. An internal aqueous compartment in all vesicle's preparations, even at equimolar DPPC: LAH fractions, was demonstrated using water-soluble probes. At pH 5.0, the interaction between DPPC and LAH increased the Tm and phase transition cooperativity showing a single lipid phase formed by hydrogen-bonded DPPC: LAH complexes. At pH 7.4, vesicles containing 50 mol% LAH exhibited distinct phases, ascribed to complex formation between LAH and LA or LAH and DPPC. LAH incorporated in the vesicles minimally permeated a skin preparation at both pHs, indicating that the primary sites of LAH solubilization were the skin layers. These results provide the foundations for developing processes and products containing DPPC: LAH.
Highlights
The inhibition of bacterial growth by free fatty acids (FFA's) is well established [1]
The present study focuses on the physicochemical properties of large unilamellar vesicles (LUVs) prepared with dipalmitoylphosphatidylcholine (DPPC): LAH mixtures
We described a detailed physicochemical characterization of the potential delivery system consisting of DPPC: LAH vesicles
Summary
The inhibition of bacterial growth by free fatty acids (FFA's) is well established [1]. Phospholipid vesicles are efficient drug carriers [9] and both LAH and LA intercalate in their bilayers, changing structure and interfering in the membrane permeability to water-soluble compounds [10,11]. Despite the disruptive effect of fatty acids on phospholipid membranes, some fatty acids, such as oleic acid in the pH range 8–9, form multilamellar vesicles with bilayers stabilized by hydrogen bonding between the protonated and anionic forms [12]. These seemingly diverse actions of fatty acids make the study of these phenomena necessary. Our results may provide the foundations for developing processes and products containing DPPC: LAH
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