Quantitative analysis of NF-κB-expression in cartilage and synovium of rat knee induced by intra-articular injection of synthetic lipid A

Objective: NF-κB expression in cartilage and synovium of rat knee after intra-articular injection of lipid A was investigated.¶Methods: Inflammation was evaluated in histological sections stained with hematoxylin and eosin, toluidine blue and immunostained with monoclonal anti-NF-κB antibody or monoclonal anti-TNF-α antibody.¶Results: Inflammatory cell infiltration into the synovium, hyperplasia of synovial lining layers, loss of metachromasia of cartilage, TNF-α-positive cells and NF-κB-positive cells in the synovium and cartilage were observed in all 26 rat knees intra-articularly injected with lipid A. The numbers of TNF-α-positive and NF-κB-positive synovial cells and chondrocytes after the injection were significantly greater than those in knees injected with triethylamine (p < 0.05). The amount of inflammatory cell infiltration into the synovium, synovial lining layers, TNF-α-positive synovial cells and NF-κB-positive synovial cells 12 h after the injection was significantly smaller than those after 1 day (p < 0.05).¶Conclusion: Intra-articular injection of lipid A induced NF-κB expression in cartilage and synovium. Cartilage degeneration started earlier than synovitis in this model. Quantitative analysis of NF-κB in cartilage might be useful to evaluate the extreme acute phase of cartilage degeneration.