Quantitative Methods for Investigating Dissociation of Fluorescently Labeled Lipids from Drug Delivery Liposomes

A key prerequisite for image-based research on nanocarriers for drug delivery is that the recorded fluorescence can be accurately assigned to originate from the nanocarrier in question. For liposomal nanocarriers, fluorescent labeling is typically achieved by labeling a minority of the lipid species making up the liposome. Early work determined that lipid species can transfer between membrane components within a solution, nevertheless the fluorescently labeled lipids (FLLs) of drug delivery liposomes are intrinsically assumed to stay associated with the liposome, even when placed in a biological environment. To efficiently test this assumption, routine methods capable of investigating the dissociation of FLLs from liposomes should be implemented. Here we present two experimental methodologies able to quantitatively characterize the degree of FLL dissociation from liposomes when subjected to human blood plasma, mimicking the biological environment experienced by the carrier when travelling in the human body. Routine implementation of such methodologies could facilitate the appropriate selection of FLLs displaying low liposome dissociation, hereby facilitating more reliable liposomal uptake and trafficking studies.