Membrane Interfacial Organization Determines the Functional Performance of Liposomal Linezolid.

Background

Despite extensive development of liposomal antibiotics, the structural determinants governing their stability, release, and biological activity remain poorly understood. This study investigated how the cholesterol content and drug-to-lipid ratio affect membrane organization and thereby determine the physicochemical and biological properties of linezolid-loaded liposomes.

Methods

Nine liposomal formulations, varying in their cholesterol content (10-30 wt%) and drug-to-lipid ratios (1-5%), were prepared by thin-film hydration. Membrane organization was analyzed by ATR-FTIR spectroscopy and principal component analysis. Liposomes were further characterized by particle size, ζ-potential, encapsulation efficiency, storage stability, in vitro release in phosphate buffer with and without bovine serum albumin, antibacterial activity against B. subtilis, and antimycobacterial activity in an ex vivo PBMC-derived Mycobacterium tuberculosis granuloma model.

Results

The cholesterol content and drug-to-lipid ratio markedly altered membrane interfacial organization, particularly the hydration of the carbonyl and phosphate regions. These structural changes correlated with differences in storage stability, protein-responsive release, and antibacterial activity. Functional behavior was non-monotonic, as 30-L showed the highest overall storage stability, while the apparent release depended jointly on the cholesterol content, drug loading, and medium. BSA altered the composition-dependent release pattern instead of producing a uniform effect. In the exploratory granuloma model, the formulations 10-S, 10-L, and 30-M reduced M. tuberculosis CFU by >99%, whereas free linezolid produced approximately 60% inhibition.

Conclusions

Membrane interfacial organization is a key determinant of the functional performance of liposomal linezolid, establishing a structure-property-function relationship that provides a mechanistic basis for the rational design of liposomal antibiotic delivery systems for tuberculosis therapy.