Description
The rapid rise and global spread of multidrug resistant Gram negative bacteria have renewed interest in polymyxin B (PxB) as a last resort therapeutic option. In pulmonary administration, inhaled antibiotics inevitably interact with pulmonary surfactant (PuS), a lipid–protein complex essential for reducing surface tension and maintaining proper lung mechanics. This study investigates how PxB affects the physicochemical properties of a simplified PuS model. Unilamellar liposomes composed of palmitoyloleoylphosphatidylcholine (POPC) and palmitoyloleoylphosphatidylglycerol (POPG) (9:1, w/w) served as model membranes, with PxB incorporated at 0–20 wt% relative to total lipid content. Drug–membrane interactions were examined using dynamic light scattering (DLS), zeta potential measurements, calcein leakage assays, and static light scattering.
DLS revealed changes in vesicle size and aggregation, while zeta potential measurements tracked alterations in membrane surface charge. Membrane stability and permeability were assessed through calcein release and scattering intensity. The influence of temperature and ionic strength was evaluated in low ionic strength medium (5 mM NaCl) and physiologically relevant PBS.
In both media, membrane destabilization and aggregation began at PxB concentrations of ~7–10 wt%. However, the magnitude and progression of these effects strongly depended on ionic strength. Under low ionic strength conditions, vesicle aggregation was markedly enhanced, accompanied by a rapid increase in hydrodynamic diameter, higher polydispersity, and a pronounced shift in zeta potential from negative to positive values, indicating strong electrostatic interactions between PxB and the lipid bilayer. In contrast, only minor zeta potential changes were observed in PBS, with values remaining negative across all concentrations. Temperature had limited impact on zeta potential but noticeably influenced particle size.
These results underscore the critical role of ionic strength in governing PxB–membrane interactions and demonstrate that environmental conditions significantly affect the stability and aggregation behavior of pulmonary surfactant model membranes.
Acknowledgement: The experiment was supported by VEGA 1/0305/24.