Abstract
Objective
High molecular weight hyaluronan (HA) is widely used in the treatment of osteoarthritis (OA) and rheumatoid arthritis (RA) by intra-articular injection. However, comparative studies of HA actions on catalytically activated cartilages in different pathologic conditions have rarely been investigated. Fibronectin fragments increased in OA and RA joints are known to cause cartilage damage through their catabolic activities. This study aimed to compare the inhibitory effects of HA on nitric oxide (NO) production by COOH-terminal heparin-binding fibronectin fragment (HBFN-f) between normal and diseased cartilages.
Methods
Articular cartilage explants from normal, OA, or RA joints or isolated chondrocytes in monolayer were incubated with HBFN-f in the presence or absence of HA. Secreted NO levels in conditioned media were determined. Induction of inducible nitric oxide synthase (iNOS) and activation of nuclear factor-?B (NF-?B) were assessed with immunoblotting. Cultures were pre-treated with the specific inhibitor to evaluate the role of NF-?B in HBFN-f action. Immunofluorescence histochemistry was performed using fluoresceinated anti-CD44 antibody.
Results
When articular cartilage explants from normal, OA, or RA joints were incubated with HBFN-f, the RA and OA cartilages produced higher levels of NO compared with normal cartilage. Pre-treatment with 2700 kDa HA resulted in significant suppression of HBFN-f-stimulated NO production in OA and RA cartilages. While CD44 was up-regulated in OA and RA cartilages, anti-CD44 antibody reversed HA inhibition of HBFN-f action in those cartilages. While NF-?B activation contributed to HBFN-f-stimulated NO production, HA inhibited HBFN-f-activated phosphorylation and nuclear translocation of NF-?B.
Conclusion
The present results clearly demonstrated that HA blocked HBFN-f actions in OA and RA cartilages through interaction with CD44. Down-regulation of NF-?B could involve HA inhibition of HBFN-f action. Intra-articular administration of HA, which targets CD44 highly expressed on OA and RA chondrocytes, could suppress catabolic actions by fibronectin fragments like HBFN-f in diseased cartilage.
