Synovial calprotectin is a useful marker of inflammation in knee osteoarthritis

Abstract

Purpose: Low-grade synovial inflammation is known to be present in many patients with knee osteoarthritis and appears to have clinical and prognostic inflammation. Calprotectin seems to be more sensitive than CRP to detect minimal inflammatory activity in many inflammatory rheumatic diseases and could be a biomarker in osteoarthritis with inflammatory features. Objective: to determine the levels of synovial calprotectin in patients with knee osteoarthritis showing inflammatory traits and their relationship with clinical and ultrasonographic features and other proinflammatory markers. 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. Pain and disability were assessed by WOMAC-pain and WOMAN-function. Calprotectin, TNF-alfa, IL-6 and high-sensitivity C-reactive protein (hs-CRP) were measured by ELISA in synovial fluid. Summary of clinical data and laboratory parameters and their association with WOMAC scales were performed using non-parametric methods. Medians and Spearman correlation were used for continuous measures, and Mann-Whitney test was applied to categorical variables. Results: Median higher synovial calprotectin levels were associated with worse WIOMAC pain (671.5 vs 431.8 ng/mL, p<0.05).) and function (713.4 vs 400.1 ng/mL, p<0.05).) scores than patients with inferior levels. Patients with moderate to severe synovial effusion (>8mm on midline suprapatellar line) had higher calprotectin levels compared with those with mild effusion (626.1 vs 417.5 ng/mL, p<0.05). Synovial calprotectin levels showed moderate correlations with intraarticular TNF-alfa levels (r= 0.26), hs-CRP (r= 0.27) and a high correlation with synovial IL-6 levels (r= 0.53). Conclusions: Calprotectin showed association with inflammatory features as measured by ultrasound and inflammatory markers such as hs-CRP, TNF-alfa and IL-6, and was related to pain and function in patients with knee osteoarthritis with inflammatory features. Calprotectin appears to be a useful marker of inflammation and could be a useful marker for assessing response to treatments targeting inflammation.