Physical and chemical modifications of lipid structures to inhibit permeation of free radicals in a supported lipid membrane model

Abstract

Oxidation of encapsulated bioactives in lipid-based nanostructures (e.g., emulsions, liposomes and lipid coatings) is a significant challenge that limits functionality and shelf life of products in many industries including food, cosmetic, and pharmaceutical industries and in biomedical devices. The objective of this study is to investigate how physical and chemical properties of the lipid interface can be engineered to inhibit permeability to environmental free radicals. A glass-supported lipid membrane system is used to model the water–lipid interface. Peroxyl radicals generated in the aqueous phase permeate the supported membrane structure and react with an embedded lipid peroxidation sensor. By using epifluorescence microscopy to monitor the rate of fluorescence decay of the lipid sensor, various physical and chemical modifications of the supported membrane can be compared quantitatively. Physical properties tested include lipid composition (gel phase vs. fluid phase and addition of cholesterol) and a double membrane structure formed via layer-by-layer assembly. Chemical properties include direct addition of antioxidant molecules to either the lipid membrane or the aqueous phase. Results show that increasing molecular order of lipid membranes (with cholesterol or long-chain phospholipids) or assembling an additional protective membrane reduces the rate of permeation of free radicals by a small amount (approximately two-fold with respect to the reference membrane). The results also demonstrate that localization of chemical antioxidants at the lipid interface is an order of magnitude more effective in suppressing membrane permeation of free radicals than either aqueous phase antioxidants or any of the tested physical modifications.