Background Although osteoarthritis (OA) is a degenerative joint disorder, it has been demonstrated that inflammation takes part in the development and progression of this condition. Matrix metalloproteinases (MMPs), including MMP-2, are involved in the cartilage breakdown observed in OA. Platelets (PLTs) are involved in different inflammatory conditions, including rheumatoid arthritis, contain and release several MMPs, including MMP-2, and enhance MMPs expression by other cell types. However, their role in OA has not been investigated yet. Hyaluronic acid (HA) is a normal component of extracellular matrix and synovial fluid (SF). Intra-articular (IA) administration of HA in OA is widely employed in clinical practice with good clinical efficacy.
Objectives Aims of our study were to investigate the role of platelets and MMP-2 in the pathogenesis of OA, to test the biologic activity of IA-HA in OA patients and to analyze the effects of HA on the interaction between platelets and synoviocytes in vitro.
Methods Thirty-eight patients with knee OA were screened and twenty-four patients were included in the study. Systemic therapy with non-steroidal anti-inflammatory drugs or corticosteroids and previous IA corticosteroid treatment represented exclusion criteria. Five injections of IA sodium hyaluronate (500-730 KDa) were administrated weekly. SF samples were collected prior to the first (T0) and at the last (T1) injection.
Total cell and PLT count, platelet-leukocyte aggregates (PLT activation marker) and MMP-2 levels were measured in SF.
For clinical assessment at T0, T1 and 3 months after the last injection (T3) the Western Ontario and Mc Masters University (WOMAC) scale and VAS for knee pain were employed.
Fibroblast-like synoviocytes (FLS) were isolated from untreated OA-SF and cultured with PLTs in presence or absence of HA at different concentrations for 24 hours. Platelet P-selectin was measured by flow-cytometry and MMP-2 in culture supernatants was quantified by zymography.
Results Total cell count in SF was significantly reduced after IA-HA (p<0.05). PLT count, platelet-leukocyte aggregates and MMP-2 concentration were significantly decreased at T1 (all p<0.05). WOMAC scale and pain VAS were reduced at T1 (p<0.0001) and this decrease was maintained at T3. MMP-2 production by FLS was significantly higher in the presence of PLTs and this increase was significantly reduced by co-incubation with HA. P-selectin expression, marker of PLT activation, was significantly higher in PLTs cultured with FLS and P-selectin blockade reduced MMP-2 release in culture supernatants.
Conclusions Our results show that PLTs, in addition to other inflammatory cells, participate in the pathogenesis of OA by the induction of MMP-2 release by FLS possibly via P-selectin, thus contributing to cartilage breakdown. Treatment with HA decreases count and activation of PLT and levels of MMP-2 in the SF. PLT and synoviocytes interaction leads to platelet activation and MMP-2 release enhancement. Hence, PLTs may represent a new therapeutic target in OA.
Disclosure of Interest : None declared