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Published on: July 12, 2024
Uptake of inhalable microparticles affects defence responses of macrophages infected with Mycobacterium tuberculosis
Rolee Sharma1, Pavan Muttil, Awadh Bihari Yadav
1Pharmaceutics Division, Central Drug Research Institute, Chhattar Manzil Palace, Lucknow 226001, India.
Objectives:
To investigate whether inhalable microparticles containing two anti-tuberculosis agents, isoniazid and rifampicin, evoke host-defence strategies in macrophages in addition to targeting the incorporated drugs.
Methods:
Microparticles were prepared by spray-drying a homogeneous solution of drugs and poly(lactic acid) (PLA; apparent viscosity 1.1 cP). Four parts PLA and three parts rifampicin were dissolved in dichloromethane. One part isoniazid was dissolved in methanol. The two solutions were mixed in the ratio 22 : 3 at which none of the solutes precipitated. These were administered as 'nose-only' inhalations to mice or exposed to cultured J774 mouse macrophages. Targeting to lung macrophages was investigated by transmission electron microscopy. Reactive oxygen species (ROS) were estimated by a cytochrome c assay and flow cytometry. Reactive nitrogen intermediates (RNI) were assayed using Griess reagent. Cytokines in culture supernatants were estimated by ELISA.
Results:
Treatment with inhalable microparticles targeted lung macrophages in vivo and induced intense Golgi activity in the vicinity of microparticle-containing phagosomes. Microparticles induced a respiratory burst involving NADPH oxidase and enhanced NO production by infected macrophages. Microparticle-induced NADPH oxidase activation required optimal calcium ions. Microparticles efficiently induced tumour necrosis factor-alpha (TNF-alpha) secretion by macrophages recovered from infected mice.
Conclusions:
Microparticle phagocytosis induces responses in infected murine macrophages that are indicative of activation of innate bactericidal mechanisms, and are inimical to bacterial survival. It is likely that such responses augment straightforward drug action on the bacterium and contribute to the unexpectedly high efficacy of microparticles in experimental tuberculosis.
Insights
Inhalable microparticles containing anti-tuberculosis drugs activate host immune responses in macrophages, enhancing their ability to fight bacteria. This dual action, combining drug delivery and immune activation, boosts treatment efficacy against tuberculosis.
Area of Science:
- Pharmacology and Immunology
- Nanotechnology in Drug Delivery
- Tuberculosis Research
Background:
- Tuberculosis (TB) remains a major global health challenge, necessitating innovative treatment strategies.
- Conventional TB treatments face challenges including drug resistance and patient compliance.
- Inhalable drug delivery systems offer potential for targeted lung delivery and improved therapeutic outcomes.
Purpose of the Study:
- To evaluate if inhalable microparticles loaded with isoniazid and rifampicin stimulate host immune defenses in macrophages.
- To determine if these microparticles enhance macrophage bactericidal mechanisms beyond direct drug action.
- To investigate the in vivo and in vitro effects of these microparticles on macrophage responses.
Main Methods:
- Microparticles were prepared using spray-drying of poly(lactic acid) (PLA) with isoniazid and rifampicin.
- Inhalable microparticles were administered to mice via 'nose-only' inhalation and tested on cultured J774 mouse macrophages.
- Macrophage responses, including reactive oxygen species (ROS), reactive nitrogen intermediates (RNI), and cytokine secretion (TNF-alpha), were quantified.
Main Results:
- Inhalable microparticles successfully targeted lung macrophages in vivo, inducing significant Golgi activity.
- Microparticles triggered a respiratory burst via NADPH oxidase and increased nitric oxide (NO) production in infected macrophages.
- Macrophages treated with microparticles showed enhanced secretion of tumor necrosis factor-alpha (TNF-alpha).
Conclusions:
- Phagocytosis of these microparticles activates innate bactericidal mechanisms in murine macrophages.
- These immune responses are detrimental to bacterial survival and likely contribute to the high efficacy of microparticles in experimental tuberculosis.
- The study suggests a synergistic effect of drug delivery and host immune modulation for improved tuberculosis treatment.
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