The Iron Chelator Desferrioxamine Increases the Efficacy of Bedaquiline in Primary Human Macrophages Infected with BCG

Abstract

For over 50 years, patients with drug-sensitive and drug-resistant tuberculosis have undergone long, arduous, and complex treatment processes with several antimicrobials. With the prevalence of drug-resistant strains on the rise and new therapies for tuberculosis urgently required, we assessed whether manipulating iron levels in macrophages infected with mycobacteria offered some insight into improving current antimicrobials that are used to treat drug-resistant tuberculosis. We investigated if the iron chelator, desferrioxamine, can support the function of human macrophages treated with an array of second-line antimicrobials, including moxifloxacin, bedaquiline, amikacin, clofazimine, linezolid and cycloserine. Primary human monocyte-derived macrophages were infected with Bacillus Calmette-Guérin (BCG), which is pyrazinamide-resistant, and concomitantly treated for 5 days with desferrioxamine in combination with each one of the second-line tuberculosis antimicrobials. Our data indicate that desferrioxamine used as an adjunctive treatment to bedaquiline significantly reduced the bacterial load in human macrophages infected with BCG. Our findings also reveal a link between enhanced bactericidal activity and increases in specific cytokines, as the addition of desferrioxamine increased levels of IFN-γ, IL-6, and IL-1β in BCG-infected human monocyte-derived macrophages (hMDMs) treated with bedaquiline. These results provide insight, and an in vitro proof-of-concept, that iron chelators may prove an effective adjunctive therapy in combination with current tuberculosis antimicrobials.

The Effect of Tuberculosis Antimicrobials on the Immunometabolic Profiles of Primary Human Macrophages Stimulated with Mycobacterium tuberculosis

“…Unstimulated, iH37Rv-Mtb-and LPS-Stimulated hMDMs TB antimicrobials optimally elicit direct bactericidal effects on mycobacteria, both in cellular and axenic models of TB infection [5,[22][23][24][25][26][27]. Accordingly, examining how these antimicrobials affect immunometabolic profiles and mitochondrial function in parallel could offer some insight into how these antimicrobials potentially affect immune function [7], particularly in patients with active TB who are subjected to long-term antimicrobial treatment regimens.…”

“…Use of the iH37Rv-Mtb strain was essential to negate any bactericidal effect of the TB antimicrobials on live Mtb. Concentrations of these TB antimicrobials, well documented in killing Mtb, were used as previously described [5,[22][23][24][25][26][27]. At 24 h post stimulation, levels of glycolysis and OXPHOS were determined, measured by assessing extracellular acidification rate (ECAR) and oxygen consumption rate (OCR) respectively, utilising the Seahorse Extracellular Flux Analyser (Figure 1).…”

“…Furthermore, CLO, INH, LIN, and PYZ did not affect secreted levels of Eotaxin (Supplementary Figure S2A,E,H,L), Eotaxin-3 (Supplementary Figure S2B,F,I,M), MIP-1α (Supplementary Figure S2C,J), or TARC (Supplementary Figure S2D,G,K,N). It is now well established that Mtb strains are recognized by a variety of toll-like receptors resulting in differential immune responses (5). Moreover, some evidence suggests that distinct TLR recognition evoked by different Mtb strains may be decisive for shaping innate immune responses in vitro and in vivo, and possibly contribute to the outcome of Mtb infection (5).…”

“…It is now well established that Mtb strains are recognized by a variety of toll-like receptors resulting in differential immune responses (5). Moreover, some evidence suggests that distinct TLR recognition evoked by different Mtb strains may be decisive for shaping innate immune responses in vitro and in vivo, and possibly contribute to the outcome of Mtb infection (5). Therefore, establishing how these antimicrobials also affect hMDMs stimulated with the toll-like receptor-4 agonist LPS, could help to interpret different mechanisms of action in our models.…”

“…Recently, a significant amount of attention has turned to the use of host-directed therapies to modulate immune responses in infected host immune cells [1]. These strategies have been hypothesized to work through augmenting anti-inflammatory [2,3], pro-inflammatory [2,[4][5][6][7], and immunometabolic processes [4,[6][7][8]. Interestingly, in addition to their bactericidal effects, some studies now suggest that TB antimicrobials could also help during TB disease through the modulation of host immune responses by host-directed strategies [9].…”