Inhalable Microparticles Containing Isoniazid and Rifabutin Target Macrophages and "Stimulate the Phagocyte" to Achieve High Efficacy

Macrophage responses to infection with Mycobacterium tuberculosis (MTB) and treatment with soluble isoniazid (INH) plus rifabutin (RFB) versus microparticles containing equivalent amounts of drugs were compared. It was investigated whether macrophages driven to alternative activation upon infection with MTB could be rescued to display the classical activation phenotype. It was established that microparticles sustain high levels of drugs in the cytosol of macrophages for longer periods as compared to soluble drugs. Microparticles co-localized with intracellular bacteria, and induced a variety of innate bactericidal responses, including induction of free radicals, alteration of mitochondrial membrane potential and apoptosis. The data strongly suggest that additional benefit may be derived from the nature of the drug delivery system, which fulfils Koch’s dictum for curing tuberculosis: “stimulate the phagocyte”.