Osteoarthritis synovial fluid activates pro-inflammatory cytokines in primary human chondrocytes

Abstract

Purpose: Two of the most common joint diseases are rheumatoid arthritis (RA) and osteoarthritis (OA). Cartilage degradation and erosions are important pathogenetic mechanisms in both joint diseases and have presently gained increasing interest. The aim of the present study was to investigate the effects of the synovial fluid environment of OA patients in comparison with synovial fluids of RA patients on human chondrocytes in vitro.

Methods: Primary human chondrocytes were incubated in synovial fluids gained from patients with OA or RA. The detection of vital cell numbers was determined by histology and by using the Casy Cell Counter System. Cytokine and chemokine secretion was determined by a multiplex suspension array.

Results: Microscopic analysis showed altered cell morphology and cell shrinkage following incubation with synovial fluid of RA patients. Detection of vital cells showed a highly significant decrease of vital chondrocyte when treated with RA synovial fluids in comparison with OA synovial fluids. An active secretion of cytokines such as vascular endothelial growth factor (VEGF) of chondrocytes treated with OA synovial fluids was observed.

Conclusions: Significantly increased levels of various cytokines in synovial fluids of RA, and surprisingly of OA, patients were shown. Activation of pro-inflammatory cytokines of human chondrocytes by synovial fluids of OA patient supports a pro-inflammatory process in the pathogenesis of OA.

Fig. 1

Chondrocyte morphology after treatment with synovial fluids. Chondrocytes were analyzed by light microscopy after treatment with synovial fluids of RA and OA patients after 24 hours. a Control chondrocytes incubated in medium. b Chondrocytes treated with 2 % Triton X100 in order to induce necrosis. Chondrocytes incubated with OA (c) or RA (d) synovial fluids. One representative result from three independently performed experiments is shown, magnification: lens 10 × 0.25, ocular 10 ×18

Fig. 2

Treatment of chondrocytes with RA but also OA synovial fluids led to reduction of living cells. Chondrocytes were incubated with medium (CTR, n = 3), synovial fluids of patients with RA or OA (four RA/OA patients, treatment of chondrocytes from three donors, total sample number shown n = 12), or the necrosis inductor Triton X100 at 2 % (n = 3) for 24 and 48 hours. The number of vital chondrocytes after incubation is shown, Mann–Whitney U test; the asterisks above the bars refer to the statistical comparison with CTR, * p < 0.05, and *** p < 0.001

Fig. 3

Increase of pro-inflammatory cytokines after treatment of chondrocytes with RA but also OA synovial fluids. Chondrocytes were incubated with synovial fluids of patients with RA or OA (four RA/OA patients, treatment of chondrocytes from three donors, total sample number shown n = 12). The concentrations of IL-6 (A), IL-8 (B), IFNg (C), MCP-1 (D), G-CSF (E) and VEGF (F) were analyzed in synovial fluids ex vivo and after 24/48 hours of incubation, Mann–Whitney U test * p < 0.05, ** p < 0.01, and *** p < 0.001