Histone Deacetylase Inhibitors Promote Mitochondrial Reactive Oxygen Species Production and Bacterial Clearance by Human Macrophages

Juliana K. Ariffin, Kaustav das Gupta, Ronan Kapetanovic, Abishek Iyer, Robert C. Reid, David P. Fairlie, Matthew J. Sweet

Broad-spectrum histone deacetylase inhibitors (HDACi) are used clinically as anti-cancer agents, and more isoform-selective HDACi have been sought to modulate other conditions, including chronic inflammatory diseases. Mouse studies suggest that HDACi down-regulate immune responses and may compromise host defence. However, their effects on human macrophage antimicrobial responses are largely unknown. Here we show that overnight pre-treatment of human macrophages with HDACi prior to challenge with Salmonella enterica serovar Typhimurium (S. Typhimurium) or Escherichia coli (E. coli) results in significantly reduced intramacrophage bacterial loads, which likely reflects the fact that this treatment regime impairs phagocytosis. In contrast, co-treatment of human macrophages with HDACi at the time of bacterial challenge did not impair phagocytosis; instead HDACi co-treatment actually promoted clearance of intracellular S. Typhimurium and E. coli. Mechanistically, treatment of human macrophages with HDACi at the time of bacterial infection enhanced mitochondrial reactive oxygen species generation by these cells. The capacity of HDACi to promote clearance of intracellular bacteria from human macrophages was abrogated when cells were pre-treated with MitoTracker Red CMXRos, which perturbs mitochondrial function. The HDAC6-selective inhibitor, tubastatin A, promoted bacterial clearance from human macrophages, whereas the class I HDAC inhibitor, MS-275, which inhibits HDAC1-3, had no effect on intracellular bacterial loads. These data are consistent with HDAC6, and/or related HDACs, constraining mitochondrial reactive oxygen species production from human macrophages during bacterial challenge. Our findings suggest that, whereas long-term HDACi treatment regimes may potentially compromise host defence, selective HDAC inhibitors could have applications in treating acute bacterial infections.