Examination of the molecular nature of low-molecular-mass chromium(III) ions in isolated osteoarthritic knee-joint synovial fluid

High field 1H NMR spectroscopy demonstrated that equilibration of added Cr(III) ions in osteoarthritic knee-joint synovial fluid (SF) resulted in its complexation by a range of biomolecules, the relative efficacies of these complexants/chelators being threonine ∼ alanine > glycine > glutamine > citrate > histidine ∼ phenylalanine ∼ tyrosine > valine ∼ isoleucine ∼ leucine > glutamate > lactate ∼ acetate ∼ formate ∼ pyruvate, this order reflecting the ability of these ligands to compete for the available Cr(III) in terms of (1) thermodynamic equilibrium constants for the formation of their complexes and (2) their SF concentrations. The significance of these observations with regard to the in vivo corrosion of chromium-containing metal alloy joint prostheses (e.g., CoCr alloys) is discussed.