Introduction
Osteoarthritis (OA) is a slow progressing degenerative disease characterized by cartilage damage, synovial fibrosis and osteophyte formation which may involve several joints, including the temporomandibular joint (TMJ) (1,2). Once the TMJ is involved, severe handicap and significant pain generally occur. Clinically, temporomandibular joint osteoarthritis (TMJ OA) is characterized by joint pain, crepitus, restricted motion and eventually loss of joint function (1–3).
Recent advances in imaging, particularly magnetic resonance imaging (MRI) and arthroscopy have contributed greatly to the understanding of the intra-articular lesions of the disc and condyle (4,5). Pathological changes, such as disc displacement (DD) may be involved in the development of TMJ OA. In their studies, Macher et al (6) and Ali et al (7) demonstrated that the surgical induction of anterior DD in rabbits might lead to OA. Long et al (8) showed that the degree of anterior DD of TMJ is correlated with OA in rabbits. However, a correlation between the change and detailed pathogenesis remains to be adequately elucidated.
Transforming growth factor-β1 (TGF-β1) is an important inducer of cartilage extracellular matrix (ECM) production and is suggested to be a potential tool to enhance cartilage repair upon damage in OA (9–11). By contrast, matrix metalloproteinases (MMPs) are a large group of matrix degrading enzymes that contribute to joint destruction in OA. High activities of diverse MMPs, especially of MMP-3 are believed to be highly involved in matrix breakdown (12–14). These cytokines can infiltrate the synovium, which may alter the synovial fluid (SF) viscosity and lead to impairment in the lubrication and nutrition of articular cartilage and disc.
The aim of the present study was to investigate the levels of TGF-β1 and MMP-3 in SF to evaluate the initiation and progression of TMJ OA combined with DD and provide a scientific basis for the assessment of treatment effectiveness for these patients.
Patients and methods
Patients
Consecutive patients referred to our department and who had been selected for TMJ surgical treatment were studied. Patients with inflammation or arthritic diseases other than osteoarthritis and patients who had had traumatic events were excluded. The criteria for surgical treatment were unsuccessful non-surgical treatment and a clinical diagnosis of TMJ OA. The surgical technique has been thoroughly described elsewhere (15–17). The inclusion criteria for TMJ OA combined DD staging were a painful impaired TMJ mobility, radiographic signs on the preoperative tomograms and surgical findings at operation (Table I, Fig. 1). The mean age for these patients was 36.75 years (range, 18–58). There were 15 females and 1 male with a mean duration of symptom of 1.6 years (range, 4 months–5 years) (Table II). The present study was approved by the ethics committee of Shanghai Ninth People’s Hospital affiliated to Shanghai JiaoTong University, School of Medicine. Informed consent and written agreement was obtained from each patient.
SF samples from TMJ
The experimental SFs were collected from >16 patients during surgery. The control SFs were collected from 10 healthy check-up examinees with no clinical and radiological evidence of TMJ OA. The TMJ was punctured with a standard disposable needle (diameter of 0.65 mm) inserted into the posterior part of the upper joint compartment. TMJ SF samples were obtained by washing the joint cavity with saline using the push and pull technique. SFs were then centrifuged for 20 min at 2,000 x g using serum monovettes (Sarstedt, Nümbrecht, Germany) and stored at −80°C until use.
Enzyme-linked immunosorbent assay (ELISA)
Commercially available human DuoSet ELISAs (R&D Systems, Inc., Minneapolis, MN, USA) were used to estimate the concentrations of TGF-β1 and MMP-3 in appropriately diluted SFs. Ninety-six-well flat plates were coated overnight with the primary antibody at room temperature (HCl 1 N) for 10 min, following reneutralization (NaOH 2.7 N/HEPES 1 M). Samples and controls of known concentration were added in wells for 2 h and were incubated with the secondary antibody for an additional 2 h. Conjugation with horseradish peroxidase and addition of tetramethylbenzidine and H2O2 produced light emission at 450 nm. Results were corrected by subtraction of light emission at an aborbance value of 540 nm.
Statistical analysis
Data were presented as the mean ± standard error of the mean. The Statistical Package for Social Science (SPSS) software version 11.5 (SPSS, Inc, Chicago, IL, USA) was used for statistical processing. The non-parametric Mann-Whitney U Test was used. P<0.05 was considered to indicate a statistically significant difference.
Discussion
SF produced by TMJ synovium normally functions as a biological lubricant as well as a biochemical pool through which nutrients and regulatory cytokines traverse (18,19). The cytokines are secreted by chondrocytes in articular cartilage and synoviocytes in synovium and concentrated in the synovial space by the semi-permeable synovial lining (20,21). Synovial membrane permeability can be altered by inflammation, which produces diseased SF because of alterations to biochemical mediators. Therefore, measuring the change of cytokines in TMJ may contribute to understanding the disease process of TMJ OA combined with DD.
The present study has shown that TGF-β1 and MMP-3 in SF are potential markers in assessing microenviroment inflammation or cartilage change in TMJ OA combined with DD. TGF-β1 is mainly released by articular chondrocytes in TMJ and secreted as an inactive complex comprising a TGF-β1 dimer, its propeptide latency-associated peptide (22). Active TGF-β1 stimulates chondrocytes responding with ECM synthesis from cartilage (23,24) and stabilizes the phenotype of the prehypertrophic chondrocytes (25,26). MMP-3 is secreted from synoviocytes and articular chondrocytes in a latent form, and binds with the tissue inhibitor of the metalloproteinase. MMP-3 is reported to crucial in matrix breakdown since it is capable of degrading a number of cartilage components, including proteoglycan, fibronection and collagens (12–14). Thus, in normal TMJ, small quantities of active TGF-β1 and MMP-3 are well-known in the development and homeostasis of cartilage and bone tissues (27–29).
At the initial stage of TMJ OA combined DD, TGF-β1 and MMP-3 levels in SF were increased while the destruction of bone and cartilage was not evident, which manifested as a reparative response at an early stage. Previous studies have shown TGF-β1 to be an important anabolic with proven beneficial effects on cartilage repair in the initiation of OA (30–32). In their study, van der Kraan et al (10) have demonstrated that an upregulated expression of TGF-β1 in early OA is found to be accompanied by increased synthetic activity. Blaney et al (31) have shown that TGF-β stimulates ECM, and counteracts the main catabolic roles at the early stage of murine knee joints OA. Takahashi et al (32) show that TGF-β1 counteracts the interleukin-1 (IL-1) upregulation of MMPs.
In the process of TMJ OA combined with DD, MMP-3 concentrations in SF were higher while TGF-β1 concentrations in SF showed a gradual decrease. MMP gene expression can be enhanced by pro-inflammatory cytokines, such as IL-1 and tumor necrosis factor-α (TNF-α) (33). Previous studies have shown a high prevalence of synovial inflammation in TMJ OA (34,35). Therefore, with the progression of TMJ OA combined DD, MMP-3 may be activated, while an excessive amount of active MMP-3 directly degrades the cartilage matrix. In addition, MMP-3 is able to activate other MMPs, such as MMP-1, MMP-7 and MMP-9. Thus, a significant increase of MMP-3 was not counteracted by insufficient amounts of TGF-β1, which aggravates the destruction of cartilage that results in the release of osteoclasia of cartilage and TMJ disc perforation.
Therefore, TMJ OA combined with DD is not considered to be a simple and unavoidable result of wear and tear, and sustaining or even enhancing the initial process may be an option. In our study, DD on MRI was observed in the 12 patients. This obvious change in TMJ anatomical structure may affect the homeostasis of joint cartilage. Thus, TMJ open disc repositioning procedures were performed on the 10 patients in the early and intermediate stages of TMJ OA, as well as another 2 patients in the late stage of TMJ OA combined DD, who had small disc perforation. Postoperative MRIs after three or six months showed that: i) the displaced disc was placed in its normal anatomical location; ii) preoperative degenerative changes did not exhibit any evident further development. Moreover, physiological remodeling, such as new bone formation was observed. These findings suggest that the displaced disc should be repositioned as early as possible in patients with TMJ OA combined with DD, in order that the aggravation of OA might be terminated and good condylar remodeling be achieved after disc repositioning, since sufficient amounts of TGF-β1 may be able to counteract the destructive effects of MMP-3 at an early stage.
To elucidate the cause of TMJ OA combined with DD, further investigation regarding the regulatory mechanism of TGF-β1 and MMP-3 in pre- and postoperative periods is required in animals and humans.