Plasma Amino Acids Reflect Cartilage Loss, Osteoarthritis Pain, Functional Disability, and Mental Health in a Longitudinal Study with Total Knee Replacement

ObjectiveBiofluid amino acids (AAs) are potential biomarkers and therapeutic targets for knee osteoarthritis (KOA), a disease continuum of both mechanical and inflammatory aspects. Our aim was to identify AAs that would associate with cartilage degradation, subjectively and objectively assessed joint pain and function, and psychological well-being.DesignFasting blood was sampled from 8 healthy controls at baseline, and from 8 end-stage KOA patients before total knee arthroplasty and 1 year post-operatively. Plasma AA profiles were determined with high-performance liquid chromatography, and the obtained results were analyzed with univariate and multivariate statistical tests, and with pathway analysis by MetaboAnalyst.ResultsCystine, <i>β</i>-alanine, and hydroxylysine emerged as potential biomarkers distinguishing KOA patients from controls, and several metabolic pathways were disturbed in baseline KOA. Total knee arthroplasty reduced pain and improved joint function, but the effects on plasma AA metabolism were less obvious. There were significant associations between systemic AA levels and articular cartilage thickness, KOA pain, physical performance, corticospinal excitability, and mental health, independent of age and body adiposity.ConclusionThe results suggest that AA metabolism could play a role in KOA pathophysiology and motivate further studies investigating the potential of AAs as diagnostic biomarkers and therapeutic targets.