Monocyte metabolic reprogramming promotes pro-inflammatory activity and Staphylococcus aureus biofilm clearance

Abstract

Biofilm-associated prosthetic joint infections (PJIs) cause significant morbidity due to their recalcitrance to immune-mediated clearance and antibiotics, with Staphylococcus aureus ( S. aureus) among the most prevalent pathogens. We previously demonstrated that S. aureus biofilm-associated monocytes are polarized to an anti-inflammatory phenotype and the adoptive transfer of pro-inflammatory macrophages attenuated biofilm burden, highlighting the critical role of monocyte/macrophage inflammatory status in dictating biofilm persistence. The inflammatory properties of leukocytes are linked to their metabolic state, and here we demonstrate that biofilm-associated monocytes exhibit a metabolic bias favoring oxidative phosphorylation (OxPhos) and less aerobic glycolysis to facilitate their anti-inflammatory activity and biofilm persistence. To shift monocyte metabolism in vivo and reprogram cells to a pro-inflammatory state, a nanoparticle approach was utilized to deliver the OxPhos inhibitor oligomycin to monocytes. Using a mouse model of S. aureus PJI, oligomycin nanoparticles were preferentially internalized by monocytes, which significantly reduced S. aureus biofilm burden by altering metabolism and promoting the pro-inflammatory properties of infiltrating monocytes as revealed by metabolomics and RT-qPCR, respectively. Injection of oligomycin alone had no effect on monocyte metabolism or biofilm burden, establishing that intracellular delivery of oligomycin is required to reprogram monocyte metabolic activity and that oligomycin lacks antibacterial activity against S. aureus biofilms. Remarkably, monocyte metabolic reprogramming with oligomycin nanoparticles was effective at clearing established biofilms in combination with systemic antibiotics. These findings suggest that metabolic reprogramming of biofilm-associated monocytes may represent a novel therapeutic approach for PJI.

Author summary

Prosthetic joint infections (PJIs) are a catastrophic complication following joint replacement surgery and are predominantly caused by staphylococcal species, such as S. aureus. The morbidity associated with PJI results, in large part, from the inability to clear infection, as bacteria are organized into heterogeneous communities known as biofilms, which are recalcitrant to antibiotic therapy and immune-mediated clearance. This study revealed that biofilm-associated monocytes exhibit a metabolic bias towards oxidative phosphorylation (OxPhos), which is linked to their anti-inflammatory properties. We developed a nanoparticle delivery approach using the OxPhos inhibitor oligomycin, which significantly reduced biofilm burden by promoting the pro-inflammatory properties of infiltrating monocytes in a mouse model of S. aureus PJI. Notably, nanoparticle delivery combined with systemic antibiotics reduced biofilm titers in mice to below the limit of detection. These findings suggest that leukocyte metabolic reprogramming could represent a novel therapeutic avenue for circumventing the two-stage revision protocol for patients with PJI by treating an infected implant in situ and alleviating a second surgery, which would represent a significant reduction in patient morbidity.