Aspirin Blocks Orthodontic Relapse via Inhibition of CD4+ T Lymphocytes.

Immunologic response plays an important role in orthodontic tooth movement (OTM) and relapse. Nonsteroidal anti-inflammatory drugs, such as aspirin, affect immune cells and clinical orthodontic treatment. However, the mechanisms by which nonsteroidal anti-inflammatory drugs regulate immune cells to affect orthodontic relapse are unclear. In this study, male Sprague-Dawley rats were grouped as relapse and relapse + aspirin for 10 d after 14 d of OTM. Silicone impressions of the rats' maxillary dentitions were obtained to record the distance of OTM at the indicated time point. CD4+ T lymphocytes in spleen were examined by flow cytometry. Serum levels of type 1 T-helper (Th1) cell-associated cytokines tumor necrosis factor α (TNF-α), and interferon γ (IFN-γ) were determined through enzyme-linked immunosorbent assay. The effects of aspirin on CD4+ T and Th1 cells were also analyzed in vitro. Aspirin treatment significantly reduced the relapse rate. More interestingly, injection of CD25 neutralizing antibody basiliximab or TNF-α inhibitor etanercept can significantly reduce the relapse rate as well. Correspondingly, aspirin treatment significantly accelerated the decrease of orthodontic force-induced secretion of TNF-α and IFN-γ in serum and the expression of TNF-α and IFN-γ in periodontal ligament during relapse. Furthermore, aspirin treatment in vitro significantly repressed the differentiation of CD4+ T and Th1 cells. Overall, results indicated that aspirin treatment can block orthodontic relapse by regulating Th1 cells.

Deterioration of mechanical properties of discs in chronically inflamed TMJ.

Temporomandibular joint (TMJ) discs frequently undergo degenerative changes in arthritis. However, the biomechanical properties of pathogenic discs remain to be explored. In this study, we evaluated the effects of chronic inflammation on the biomechanical properties of TMJ discs in rats. Chronic inflammation of TMJs was induced by double intra-articular injections of complete Freund's adjuvant for 5 weeks, and biomechanical properties and ultrastructure of the discs were examined by mechanical testing, scanning electron microscopy, and transmission electron microscopy. The instantaneous compressive moduli of the anterior and posterior bands of discs in inflamed TMJs were decreased significantly compared with those in the control group. The instantaneous tensile moduli of the discs of inflamed TMJs also showed significant decreases in both the anterior-posterior and mesial-lateral directions. The relaxation moduli of the discs of inflamed TMJs showed nearly the same tendency as the instantaneous moduli. The surfaces of the discs of inflamed TMJs became rough and porous due to the loss of the superficial gel-like stratum, with many collagen fibers exposed and degradation of the sub-superficial collagen fibrils. Our results suggested that chronic inflammation of TMJ could lead to deterioration of mechanical properties and alteration of disc ultrastructure, which might contribute to TMJ disc displacement.

Estrogen aggravates iodoacetate-induced temporomandibular joint osteoarthritis.

Temporomandibular joint osteoarthritis (TMJOA) is clinically characterized by female preponderance, with a female-to-male ratio of more than 2:1; however, the underlying mechanism remains obscure. We examined the effects of estrogen on TMJOA induced by monosodium iodoacetate. Female rats were randomly and equally divided into 5 groups: control, sham-ovariectomized, and ovariectomized rats treated, respectively, with 17ß-estradiol (E2) at doses of 0 µg, 20 µg, and 80 µg/day until the end of the experiment. After induction of TMJOA, TMJs were evaluated by histopathology and microCT, and the expression of Fas, FasL, caspase 3, and caspase 8 was evaluated by real-time polymerase chain-reaction or immunohistochemistry. Another 5 groups of female rats were used to evaluate the effect of estrogen receptor antagonist ICI 182780 on E2 effects on TMJOA, when injected intraperitoneally into the control, sham-ovariectomized, and 80-µg-E2-treated groups. We found that E2 potentiated cartilage degradation and subchondral bone erosion in iodoacetate-induced TMJOA. E2 also potentiated mRNA expression of Fas, FasL, caspase 3, and caspase 8 in the condylar cartilage. Moreover, the estrogen receptor antagonist partially blocked E2 effects on TMJOA. These findings suggest that E2 could aggravate TMJOA, which may be an important mechanism underlying the sexual dimorphism of TMJOA.

Involvement of trigeminal ganglionic Nav 1.7 in hyperalgesia of inflamed temporomandibular joint is dependent on ERK1/2 phosphorylation of glial cells in rats.

BACKGROUND: Inflammation is a major cause of temporomandibular disorder-related pain. The Nav 1.7 sodium channel has a critical function in pain perceptions. However, whether and how Nav 1.7 in the trigeminal ganglion is involved in temporomandibular joint (TMJ) inflammatory pain remains to be examined. METHODS: TMJ inflammation was induced by complete Freund's adjuvant in female rats. The expression of trigeminal ganglionic Nav 1.7 and other sodium channels was examined using real-time polymerase chain reaction or Western blotting. Immunohistofluorescence with fluorescent retrograde neuronal tracer DiI was used to confirm Nav 1.7 in the trigeminal neurons innervating TMJ. The functions of trigeminal ganglionic Nav 1.7 and extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation were blocked with the microinjection of the Nav 1.7 antibody or U0126 into the trigeminal ganglion. Head withdrawal threshold and food intake was measured to evaluate TMJ nociceptive responses. RESULTS: TMJ inflammation significantly up-regulated Nav 1.7 mRNA and protein; however, the mRNA of Nav 1.3 was not affected and those of Nav 1.8 and Nav 1.9 were only slightly up-regulated. TMJ inflammation specifically induced Nav 1.7 in the neurons innervating TMJ. In addition, blocking the Nav 1.7 function significantly attenuated the hyperalgesia of the inflamed TMJ. Moreover, TMJ inflammation up-regulated ERK1/2 phosphorylation only in the glials; blocking ERK1/2 phosphorylation in the glials blocked Nav 1.7 up-regulation in the neurons and correspondingly attenuated the hyperalgesia of the inflamed TMJ. CONCLUSIONS: Trigeminal ganglionic Nav 1.7 has an important function in the hyperalgesia of the inflamed TMJ, which is dependent on the communication with the satellite glials.

Sustained inflammation induces degeneration of the temporomandibular joint.

The temporomandibular joint (TMJ) undergoes degenerative changes among patients who suffer from arthritis, and yet the pathogenesis of TMJ osteoarthritis and rheumatoid arthritis is poorly understood. We hypothesized that sustained inflammation in the TMJ induces structural abnormalities, and accordingly characterized the disc and synovium in a novel model with double injections of complete Freund's adjuvant (CFA), using behavioral, morphological, cellular, and molecular assessments. Thirty-five days following double CFA injections in seven-week-old female Sprague-Dawley rats, the disc in the CFA-induced inflammation group demonstrated multiple degenerative changes, including marked thickening, opacity, and deformation. The discs in the CFA group further showed significantly greater wet and net weights, and elevated collagen, aggrecan, and total glycosaminoglycan contents. The synovium in the CFA-induced inflammation group showed marked infiltration of mononucleated cells and accumulated sub-synovial adipose tissue. Both the disc and synovium had significantly higher iNOS and IL-1ß mRNA expression than controls (saline injections). These findings are consistent with our hypothesis that sustained TMJ inflammation, even within the presently observed 35 days, may be a predisposing factor for structural abnormalities. Insight into TMJ inflammation and degeneration is anticipated to improve our understanding of the pathogenesis of TMJ arthritis and help design clinically relevant strategies for tissue engineering.