Metabolic Immunomodulation of Macrophage Polarization by Pseudomonas aeruginosa Biofilms
Authors: Ammons Mary Cloud Bosworth , Fuchs Amanda L , Tripet Brian P , Copie Valerie 
Published: November 2023

Despite extensive investment in better healthcare practices, hospital acquired infections (HAIs) remain a major public health concern. In 2011, the CDC's HAI Prevalence Survey identified 722,000 patients with infections contracted during treatment at acute care hospitals, resulting in 75,000 deaths. It has been well demonstrated that the establishment of bacterial biofilm in the wound is a major contributor to the failure of acute wound treatment and development of chronic, non‐healing wounds; however how the metabolic phenotype of a colonizing biofilm influences the wound healing process remains unknown. This gap in knowledge inhibits the development of effective treatment protocols and results in chronic wounds being the leading cause of non‐traumatic limb amputations. Herein, we define how metabolic exchange and metabolite competition between P. aeruginosa biofilms and macrophages promotes a pro‐inflammatory polarization of macrophages and inhibits reprogramming of macrophages into a pro‐resolution phenotype.

Using 1D 1H Nuclear Magnetic Resonance (NMR) small molecule metabolomics in conjunction with immunologic profiling, we demonstrate substantial overlap between the metabolic profile of P. aeruginosa biofilm phenotype and the metabolic profile driving macrophage polarization either into the classical inflammatory phenotype (M1) or the non‐classical anti‐inflammatory phenotype (M2). This metabolic overlap included key metabolic pathways that regulate immunomodulation in macrophages such as shifts between the citrate cycle (TCA) and pentose phosphate metabolism (PPP) and selective amino acid metabolism. Furthermore, exposure of non‐polarized macrophages to medium conditioned with soluble, small molecule metabolites (<3 kDa) derived either from P. aeruginosa planktonic cultures (referred to as PCM) or P. aeruginosa biofilm cultures (referred to as BCM) resulted in distinct metabolic profiles directly related to recently characterized metabolic pathways contributing to macrophage immunomodulation such as enhanced glycolysis, uncoupling of the TCA cycle, and selective amino acid uptake and metabolism. Finally, we use novel, naturally‐derived, biofilm‐targeted therapeutics to manipulate the biofilm immunomodulation of macrophage polarization to promote a shift from a pro‐inflammatory phenotype (M1) to a pro‐resolution phenotype (M2) in primary macrophages. Based on these findings, we demonstrate that P. aeruginosa biofilms mediate specific pathological effects against host macrophages through coordinated metabolic interactions, which result in chronic immune polarization and may contribute to deviation from the normal wound healing process and development of a chronic wound. Given the non‐invasive nature of NMR metabolomics profiling, these findings have the potential to lead to novel approaches for prevention and treatment of non‐healing wounds, including development of evidence‐based, personalizable treatment protocols executed at the bedside.

Support or Funding Information

NIH NIGMS 1K01GM103821 to M.C.B.A. Kopriva Research Scholarship ‐ Montana State University to A.L.F.