Effects of Metal Ions Released from Implants on Energy Metabolism in Macrophages

Abstract

Cobalt-chromium-molybdenum (CoCrMo) alloys are used extensively in orthopaedic applications. However, they can undergo wear and corrosion in vivo, leading to the release of Co and Cr ions that can limit implant functionality and survivorship because of their biological effects. Indeed, previous studies have shown that Co2+ and Cr3+ can stimulate the production of bone-resorbing cytokines through the activation of redox-dependent mechanisms and induce an inflammatory response in macrophages. However, the effects of Co2+ and Cr3+ on the energy metabolism of macrophages remain largely unknown. The objectives of this thesis were to determine, in macrophages: 1. the effects of Co2+ and Cr3+ on oxidative stress and mitochondrial function; 2. the effects of Co2+ and Cr3+ on glycolytic flux and the stabilization of HIF-1α. RAW 264.7 murine macrophages were exposed to different Co2+ or Cr3+ concentrations for up to 48h. Biochemical, and immunoblotting assays as well as extracellular flux analyses were performed to analyze reactive oxygen species (ROS) production, oxidative damage, mitochondrial function, glycolytic activity, as well as stabilization of HIF-1α after macrophage exposure to the metal ions. Mitochondrial function and glycolytic activity were assessed by measuring oxygen consumption rates (OCR) and extracellular acidification rates (ECAR). Overall, results showed that Co2+ but not Cr3+ induced oxidative stress as well as a decrease in oxidative phosphorylation (OXPHOS). Both Co2+ and Cr3+ induced an increase in glycolytic flux, albeit to a lower level with Cr3+. Moreover, Co2+ but not Cr3+ induced the stabilization of HIF-1α, likely contributing to the Co2+-induced increase in glycolytic flux. Altogether, results suggest that Co2+ can induce a metabolic shift from OXPHOS towards aerobic glycolysis similar to that observed in macrophages upon polarization towards a pro-inflammatory phenotype. Further elucidation of the molecular mechanisms activated by Co2+ and Cr3+ may facilitate the development of therapeutic approaches to modulate the inflammatory response to metal wear and corrosion products and re-establish immune homeostasis in periprosthetic tissues in order to increase implant longevity.