Mannose-decorated nanostructured lipid carriers improve the intracellular activity of antitubercular drugs against Mycobacterium tuberculosis.

The intracellular persistence of Mycobacterium tuberculosis within macrophages remains one of the major obstacles to successful tuberculosis chemotherapy. Nanostructured lipid carriers (NLCs) functionalized with mannose may improve macrophage-targeted drug delivery and enhance intracellular antibacterial efficacy. Mannose-decorated NLCs encapsulating rifampicin, isoniazid, ethambutol, and amikacin were prepared and characterized for particle size, zeta potential, encapsulation efficiency, morphology, physicochemical stability, drug release behavior, and FTIR profiles. Cytocompatibility was evaluated using J774A.1 macrophages. Antimycobacterial activity was determined against M. tuberculosis H37Rv, four rifampicin-susceptible clinical isolates, and one multidrug-resistant (MDR) isolate using the resazurin microplate assay. Intracellular antibacterial activity was assessed in M. tuberculosis-infected J774A.1 macrophages by colony-forming unit (CFU) enumeration. The developed nanoformulations exhibited nanoscale particle size, narrow size distribution, favorable encapsulation efficiencies, sustained drug release for up to 72 h, and acceptable physicochemical stability during long-term storage. FTIR analysis supported successful drug incorporation without detectable major chemical interactions between the drugs and the lipid matrix. All formulations showed good cytocompatibility toward macrophages, while fluorescence microscopy confirmed efficient cellular internalization. Under extracellular conditions, nanoencapsulation did not significantly alter MIC values compared with the corresponding free antibiotics. In contrast, all antibiotic-loaded NLCs demonstrated enhanced intracellular antimycobacterial activity following macrophage infection, with the greatest reduction in intracellular bacterial burden observed after 72 h of treatment. Rifampicin-loaded NLCs produced the most pronounced intracellular antibacterial effect among the investigated formulations. Mannose-decorated NLCs enhanced the intracellular antibacterial activity of conventional antitubercular drugs while producing minimal changes in their extracellular MIC values, supporting their potential as macrophage-targeted delivery systems for tuberculosis treatment.