• Sten Rasmussen, Kjaer PetersenKristianKDepartment of Health Science and Technology, Aalborg University, Aalborg, Denmark.Department of Health Science and Technology, Faculty of Medicine, Center for Neuroplasticity and Pain, Aalborg University, Aalborg, Denmark., Martin Kaae Kristiansen, Jakob Skallerup, Christopher Aboo, Mikkel Eggert Thomsen, Emilie Skjoldemose, Nia Kristine Jørgensen, Allan Stensballe, and Lars Arendt-Nielsen.
• Department of Clinical Medicine, Aalborg University, Aalborg, Denmark.
• Eur J Pain. 2022 Apr 1; 26 (4): 811-824.

BackgroundThis exploratory study investigates if intra-articular injected gold microparticles in knee osteoarthritis (KOA) reduce immunomodulatory-based pain via proteomic changes in the synovial fluid (SF) and serum.MethodsThirty patients with moderate KOA were included. Intraarticular injections with 20 mg gold microparticles (72.000 particles, 20-40 µm in diameter) using the patient's synovial fluid (SF) as carrier were performed. Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) subscores for pain, stiffness, and function were assessed at inclusion, 8 weeks and 2 years The PainDetect questionnaire, pain pressure threshold (PPT), temporal summation (TS), and conditioned pain modulation (CPM), and pain diary were assessed at inclusion and 8 weeks. Proteome analysis was performed on SF and blood samples before and after 8 weeks of treatment.ResultsA decrease in WOMAC scores (pain (p = 0.0001), stiffness (p = 0.0088), activity (p = 0.0001)), PainDetect (p = 0.0002) and increase in PPT (p = 0.001) and CPM (p = 0.021) and a decrease in TS (p = 0.03) were found after 8 weeks compared to inclusion assessments. At 2 years follow-up compared to baseline there was a decrease in WOMAC scores (pain (p = 0.0001), stiffness (p = 0.007), activity (p = 0.0001)) and PainDetect (p = 0.0001). In SF, 28 different proteins were downregulated and 11 upregulated (p < 0.05) mainly associated immune response. Similarly, 31 proteins were downregulated and 1 upregulated in serum (p < 0.05) reflecting key immune response and anatomical structure development processes. No adverse effects related to the treatment were recorded.ConclusionsGold microparticles injected intra-articular in KOA joints may provide pain relief and an inflammatory modulatory effect based on proteome changes found in SF and serum. A randomized, controlled, double-blind study is needed to infer a conclusion.SignificanceThis study indicates that intra-articular gold may provide advantages in clinical practice for managing knee osteoarthritic pain. The use of intraarticular gold can add new knowledge to the treatment of inflammation and pain.© 2022 The Authors. European Journal of Pain published by John Wiley & Sons Ltd on behalf of European Pain Federation - EFIC ®.

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