C106-19 Metformin Enhances Macrophage Activity Against Mycobacterium Abscessus

Rationale Metformin is a biguanide prescribed commonly to patients with type 2 diabetes mellitus. Metformin inhibits mitochondrial respiration, which, in turn, increases the ratio of AMP:ATP and ADP:ATP. This metabolic effect of metformin activates AMPK (5’adenosine monophosphate-activated protein kinase) which then inhibits the serine-threonine kinase mTOR (mammalian target of rapamycin), resulting in increased autophagy in phagocytes. Metformin has been shown to augment the ability of mice to control Mycobacterium avium infection; one mechanism is via enhancing ability of macrophages to kill the mycobacteria by activating AMPK. Mycobacterium abscessus infections are notoriously difficult to treat due to intrinsic resistance to several key antimicrobials. Thus, treatments which could enhance natural host immunity are worth pursuing. However, it is not known if metformin enhances control of M. abscessus infection in human differentiated macrophages. Methods Differentiated THP-1 macrophages were infected with M. abscessus subsp abscessus (MOI of 5 mycobacteria:1 macrophage) alone for three hours and then incubated with different concentrations of metformin (0, 0.1, 0.5, and 1 mM). Media ± metformin were replaced daily for cells in the Day 3 timepoint to mitigate metformin degradation. One hour, one day, and three days after incubation, the lysed infected cells were plated onto 7H10 agar and the cell-associated M. abscessus were quantified. To begin to elucidate the potential mechanism by which M. abscessus may affect the burden of cell-associated M. abscessus, we quantified M. abscessus-associated phagosome-lysosome fusion by quantifying co-localization of phagocytosed GFP-labeled M. abscessus with LysoTracker-stained lysosomes in the THP-1 cells. Results At 3 days post infection, incubation with 0.1 mM and 0.5 mM metformin reduced the number of cell-associated M. abscessus but the reductions were not significant. However, macrophages incubated with 1 mM metformin showed ∼3-fold reduction of cell-associated M. abscessus compared to untreated cells at Day 3 post-infection (p < 0.05). Additionally, all metformin concentrations (0.1, 0.5, and 1.0 mM) significantly increased phagosome-lysosome fusion compared to untreated macrophages (p < 0.05, p < 0.01, p < 0.001, respectively). Conclusions Metformin significantly decreased bacterial burden in a differentiated monocytic cell line and increased phagosome-lysosome fusion. These results indicate that metformin could potentially be utilized as an adjunct treatment to enhance host immunity to infection with M. abscessus and perhaps other non-tuberculous mycobacteria. This abstract is funded by: None