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.