Abstract
Biological membranes are spherical boundaries formed by self-assembled lipid bilayers that enclose an internal aqueous core and are surrounded by an external aqueous environment. Biological membranes have strict biophysical properties that are essential for their function, such as defined thickness, structure, microviscosity, order, lateral pressure, surface charge and permeability. Considering the similarity between biological membranes and liposomes in their ability to mimic biophysical properties of the membrane, it is easy to understand why liposomes are simple but relevant cellular membrane models. In fact, liposomes are widely used to study the drug-induced effects on membrane biophysics, which can often be related to the drug's capacity to cross membranes and distribute to tissues or may be associated with membrane toxicity. In practical terms, the effects of drugs on membrane biophysics can be assessed by changes in the thermotropic behavior of lipid membranes which can be studied by monitoring parameters such as the main phase transition temperature (Tm) and the cooperativity (B) of the phase transition.
Herein we propose a probe-free protocol that uses dynamic light scattering (DLS) as the detection technique to determine Tm and B, taking advantage of the light scattering changes observed when the lipid components of a membrane transit from an ordered gel-phase (Lβ) to a less ordered fluid phase (Lα). This protocol consists of a detailed explanation of a temperature trend standard operating procedure (SOP) based on the Dynamic Light Scattering technique as well as an analysis of the data collected from the thermotropic study of liposomes in the presence and absence of drugs. For its simplicity, standardization and probe-free nature, this protocol has the potential to be used with a variety of drugs and other potential therapeutic agents to screen their effects on membrane biophysics and, more broadly, to relate these effects to drug biodistribution and membrane toxicity.
