Irisin levels are associated with exercise level, pain and function in patients with knee osteoarthritis

Abstract

Purpose: Muscle strengthening and aerobic exercise have been shown to improve joint pain and function in patients with knee osteoarthritis (OA). Irisin is a hormone-like myokine synthetized by skeletal muscle and its secretion is inversely regulated by physical activity. Objective: To determine the levels of irisin synovial fluid and plasma and evaluate their association with exercise level and pain and function in patients with symptomatic knee OA. Methods: Cross-sectional study with systematic inclusion of 108 symptomatic primary knee osteoarthritis patients with ultrasound-confirmed joint effusion. Age, physical exercise, knee osteoarthritis symptoms duration and different anthropometric measurements were collected. Radiographic severity was evaluated according to Kellgren-Lawrence scale. Physical exercise was categorized as never, occasional (less than 150 min per week) or regular (more than 150 min per week. Pain and disability were assessed by the Lequesne algo-functional questionnaire. Irisin was measured by ELISA in synovial fluid and plasma. Summary of clinical data and laboratory parameters and their association with Lequesne scale were performed using non-parametric methods. Medians and Spearman correlation (r) were used for continuous measures, and Mann–Whitney test was applied to categorical variables. Results: Plasma and synovial irisin levels were strongly related (r = 0.7). Plasma and joint irisin levels showed an inversely significant association with the level of exercise in patients with symptomatic knee OA: no exercise 763.3 ng/mL, occasional exercise 631.8 ng/mL and regular exercise 523 ng/mL (P < 0.01). Patients with severe pain and disability (Lequesne algofunctional score >11) had higher plasma (791.5 vs 680.4 ng/mL, P < 0.05) and synovial (711.4 vs 468.7 ng/mL, P < 0.05) irisin levels compared to patients with less algofunctional impairment. No relationship was found between irisin concentration in plasma or synovial fluid and radiographic severity. Conclusions: Irisin levels were associated with pain and function in patients with knee osteoarthritis. Irisin levels were negatively associated with exercise level.