Can analysis of pro- and anti-inflammatory cytokines in matched synovial fluid and serum determine the inflammatory state in knee osteoarthritis?

Abstract

Background: The concentrations of pro- and anti-inflammatory cytokines in biological specimens may help to determine the inflammatory state of knee osteoarthritis (KOA) in patients. Matrix metalloproteinase-2 and -9 (MMP-2 and MMP-9) are produced in osteoarthritis (OA) and rheumatoid arthritis (RA). Pro-inflammatory cytokines initiate a sequence of events which directly leads to joint destruction, through the subsequent production of matrix metalloproteinases (MMPs) that degrade bone. Objectives: To determine the concentration of IL-6, TNF-α, IFN-γ, IL-17A, IL-13 and IL-10 in the serum and synovial fluid (SF) samples from KOA patients and healthy (asymptomatic) individuals. To compare total MMP-9 concentrations in plasma samples from KOA patients versus the total MMP-9 concentration in the healthy volunteer group. To interpret results to determine the inflammatory state of KOA in patients. Methods: A panel of six cytokines (pro- and anti-inflammatory) were quantified using matched serum and SF from KOA patients undergoing total knee replacement (TKR) surgery, while only serum was used for cytokine analysis in the healthy group due to unavailability of SF in healthy individuals. There were two groups in the study: a group of healthy volunteers recruited from the Institute of Technology Carlow; and a group of KOA patients undergoing TKR surgery at AutEven Hospital, Kilkenny. The enzyme-linked immunosorbent assay (ELISA) was used to quantify cytokines (IL-6, TNF-α, IFN-γ, IL-10, IL-13 and IL-17A) in serum and SF of individual patients and volunteers in the study. For total MMP-9 concentration comparison in KOA and healthy plasma samples, gelatin zymography was carried out followed by band density measurements using ImageJ software analysis. Results: Two cytokines measured, IL-6 and IL-10, showed significant difference in serum between the disease and healthy group in the study. Two cytokines measured, IFN-γ and IL-13, were high in the serum of healthy volunteers in the study. In individual KOA patients, total MMP-9 mean concentrations in plasma were higher than in the healthy samples with a significant difference of 0.03 (P<0.05). Conclusion: Analysis of matched SF and serum confirmed local cytokine secretion within the joint of KOA patients. The concentrations of cytokines in serum were low in many cases which indicated KOA with low inflammation, while other patients had high concentrations of pro-inflammatory cytokines which indicated inflammatory OA. High risk candidates for autoimmune disease were identified in the healthy volunteer group. This may have indicated that the analysis of cytokines might be used as a screening tool for the early detection of autoimmune disease.