Synovial fluid IL-1RA levels are correlated with synovial fluid IL-6 and serum IL-1RA levels in patients with knee osteoarthritis

Abstract

Purpose: Inflammation plays an important role in the pathology of knee osteoarthritis (OA). Articular cartilage decomposition products produced in the joint cause synovitis, inducing release of inflammation-related substances from the synovial tissue. It has also been suggested in recent years that not only intraarticular inflammation but also systemic metabolic inflammation is involved in the development and progression of knee OA. We have shown the relationship between the serum hyaluronic acid levels and the severity of knee OA (BMC Musculoskelet Disord, 2013), as well as between the serum IL-6 levels and severity of pain or depressive state in patients with knee OA (Osteoarthritis Cartilage, 2013; Clin Rheum, 2017). Furthermore, elevated serum IL-1Ra is reportedly a risk factor for joint space narrowing. However, it remains unclear whether inflammatory cytokine levels in a joint are related to inflammatory cytokine levels in the systemic circulation. This study was performed to elucidate the relationship between intraarticular and serum levels of inflammatory cytokines. Methods: The subjects were eighty two outpatients with knee OA who newly visited our hospital due to knee pain, and gave consent to participate in this study between Mar. 2014 and Jun. 2015. Serum and synovial fluid were sampled on the same day in each subject. Pearson correlation coefficients were calculated using SPSS for serum and synovial fluid levels of IL-1Ra and IL-6. Results: A significant positive correlation was observed between synovial fluid IL-1Ra and serum IL-1Ra levels (r=0.41, p<0.01). A significant positive correlation was also observed between synovial fluid IL-1Ra and synovial fluid IL-6 levels (r=0.35, p=0.03). However, no significant correlation was observed between synovial fluid IL-6 and serum IL-6 levels, or between synovial fluid IL-6 and serum IL-1Ra levels. Conclusions: The serum IL-1Ra may reflect the local inflammation within a simple joint. It was also suggested that the profile of inflammatory cytokines related to phenotype of knee OA. And symptoms also might be characterized according to the type of inflammation in knee OA.