Irisin and myostatin serum levels in patients with established rheumatoid arthritis: correlation with radiographic progression and lean body mass

The myokines irisin and myostatin participate in bone and skeletal muscle homeostasis and may characterize the clinical status of these tissues. The study aimed to evaluate the association of myokines serum levels with one-year radiographic progression and lean mass in individuals with rheumatoid arthritis (RA). Forty female individuals with RA, aged ≥ 18 years who met 2010 American College of Rheumatology criteria, and 30 individuals without RA and any chronical disease, matched by sex and body mass index (BMI) were included. Serum levels of irisin and myostatin were determined by immune assay. RA subjects had their radiographs of hands and feet evaluated by Sharp/van der Heijde score (SHS) at two timepoints, baseline and after one year. At baseline, disease activity was calculated by Disease Activity Score 28-C reactive protein (DAS28-CRP), body composition was evaluated using dual X-ray absorptiometry (DXA), muscle strength was assessed by handgrip test and chair rising test (CRT), and physical function was assessed by Health Assessment Questionnaire-Disability Index (HAQ-DI) and timed up and go (TUG) test. Mean age of individuals was 56 ± 7.8 years, mean DAS28-CRP was 3.3 ± 1.3, mean disease duration was 11.2 ± 9.2 years, and mean BMI was 28.1 ± 5.1 kg/m2. Rapid radiographic progression and low lean mass were present in 17.5% and 14.8% of the RA individuals, respectively, and showed no correlation with irisin and myostatin. Myostatin was significantly lower in RA than in controls (3021.7 ± 1217.2 vs. 4049.0 ± 1610.0 pg/ml; p = 0.011), and individuals treated with biologic disease-modifying antirheumatic drugs (bDMARDs) showed higher irisin levels than individuals non-treated with bDMARDs (31.7 ± 7.6 vs. 25.7 ± 6.8 ng/ml; p = 0.033). RA duration was correlated with baseline SHS (r = 0.563; p = 0.001) and appendicular lean mass index (ALMI; r= -0.451; p = 0.004), and irisin levels were positively correlated with TUG (r = 0.338; p = 0.35) in RA. Long-term RA was related with higher SHS and lower ALMI, and the late disease stage of included individuals possibly masked the association of myokines with one-year radiographic progression or low lean mass. Otherwise, bDMARDs treatment influenced myokines circulating levels, specifically irisin.