IL-1 beta, IL-1 receptor antagonist and soluble type II IL-1 receptor in synovial fluid of patients with temporomandibular disorders

Salivary Biomarkers and Temporomandibular Disorders: A Systematic Review conducted according to PRISMA guidelines and the Cochrane Handbook for Systematic Reviews of Interventions

BACKGROUND

The present review aimed to investigate the association between salivary biomarkers and temporomandibular disorders (TMD). TMD is a multifactorial condition characterised by pain and dysfunction in the temporomandibular joint (TMJ) and surrounding structures. Salivary biomarkers have emerged as potential diagnostic tools due to their non-invasiveness and easy accessibility. However, the literature on salivary biomarkers in relation to TMD is limited and inconsistent.

METHODS

Electronic databases of Pubmed, Embase, Web of Science, Scopus, Cochrane Library, PsychINFO, CINAHL and Medline were searched using specific search terms and Boolean operators. The search was limited to articles published in English that assessed salivary biomarkers in individuals diagnosed with TMD. Two reviewers independently screened the articles and extracted data. ROB-2 was used to assess the risk of bias.

RESULTS

Eleven clinical papers met the inclusion criteria and were included in the review. The findings provided consistent evidence of a clear association between salivary biomarkers and TMD. Various biomarkers, including cortisol, IL-1, glutamate and several others, were assessed. Some studies reported higher levels of cortisol and IL-1 in TMD patients, indicating potential involvement in stress and inflammation. Glutamate levels were found to be elevated, suggesting a role in pain modulation. Other biomarkers also showed alterations in TMD patients compared to controls: CONCLUSION: The findings from the included studies suggest that salivary biomarkers may play a role in TMD pathophysiology. Though a definitive conclusion can be drawn regarding the specific salivary biomarkers and their association with TMD, the results must be interpreted with caution considering the heterogeneity of the biomarkers assessed. Further research with larger sample sizes, standardised methodology and rigorous study designs is needed to elucidate the role of salivary biomarkers in TMD.

Sensory Neuron-TRPV4 Modulates Temporomandibular Disorder Pain Via CGRP in Mice

Temporomandibular disorder (TMD) pain that involves inflammation and injury in the temporomandibular joint (TMJ) and/or masticatory muscle is the most common form of orofacial pain. We recently found that transient receptor potential vanilloid-4 (TRPV4) in trigeminal ganglion (TG) neurons is upregulated after TMJ inflammation, and TRPV4 coexpresses with calcitonin gene-related peptide (CGRP) in TMJ-innervating TG neurons. Here, we extended these findings to determine the specific contribution of TRPV4 in TG neurons to TMD pain, and examine whether sensory neuron-TRPV4 modulates TMD pain via CGRP. In mouse models of TMJ inflammation or masseter muscle injury, sensory neuron-Trpv4 conditional knockout (cKO) mice displayed reduced pain. Coexpression of TRPV4 and CGRP in TMJ- or masseter muscle-innervating TG neurons was increased after TMJ inflammation and masseter muscle injury, respectively. Activation of TRPV4-expressing TG neurons triggered secretion of CGRP, which was associated with increased levels of CGRP in peri-TMJ tissues, masseter muscle, spinal trigeminal nucleus, and plasma in both models. Local injection of CGRP into the TMJ or masseter muscle evoked acute pain in naïve mice, while blockade of CGRP receptor attenuated pain in mouse models of TMD. These results suggest that TRPV4 in TG neurons contributes to TMD pain by potentiating CGRP secretion. PERSPECTIVE: This study demonstrates that activation of TRPV4 in TG sensory neurons drives pain by potentiating the release of pain mediator CGRP in mouse models of TMJ inflammation and masseter muscle injury. Targeting TRPV4 and CGRP may be of clinical potential in alleviating TMD pain.

Ahmad WMA, Ahmed Asif J, Khoo SP, Husein A, Ab-Ghani Z, Kassim NK. Biomarkers for Temporomandibular Disorders: Current Status and Future Directions

Numerous studies have been conducted in the previous years with an objective to determine the ideal biomarker or set of biomarkers in temporomandibular disorders (TMDs). It was recorded that tumour necrosis factor (TNF), interleukin 8 (IL-8), IL-6, and IL-1 were the most common biomarkers of TMDs. As of recently, although the research on TMDs biomarkers still aims to find more diagnostic agents, no recent study employs the biomarker as a targeting point of pharmacotherapy to suppress the inflammatory responses. This article represents an explicit review on the biomarkers of TMDs that have been discovered so far and provides possible future directions towards further research on these biomarkers. The potential implementation of the interactions of TNF with its receptor 2 (TNFR2) in the inflammatory process has been interpreted, and thus, this review presents a new hypothesis towards suppression of the inflammatory response using TNFR2-agonist. Subsequently, this hypothesis could be explored as a potential pain elimination approach in patients with TMDs.

Minimally Invasive Approach for Diagnosing TMJ Osteoarthritis

This study's objectives were to test correlations among groups of biomarkers that are associated with condylar morphology and to apply artificial intelligence to test shape analysis features in a neural network (NN) to stage condylar morphology in temporomandibular joint osteoarthritis (TMJOA). Seventeen TMJOA patients (39.9 ± 11.7 y) experiencing signs and symptoms of the disease for less than 10 y and 17 age- and sex-matched control subjects (39.4 ± 15.2 y) completed a questionnaire, had a temporomandibular joint clinical exam, had blood and saliva samples drawn, and had high-resolution cone beam computed tomography scans taken. Serum and salivary levels of 17 inflammatory biomarkers were quantified using protein microarrays. A NN was trained with 259 other condyles to detect and classify the stage of TMJOA and then compared to repeated clinical experts' classifications. Levels of the salivary biomarkers MMP-3, VE-cadherin, 6Ckine, and PAI-1 were correlated to each other in TMJOA patients and were significantly correlated with condylar morphological variability on the posterior surface of the condyle. In serum, VE-cadherin and VEGF were correlated with one another and with significant morphological variability on the anterior surface of the condyle, while MMP-3 and CXCL16 presented statistically significant associations with variability on the anterior surface, lateral pole, and superior-posterior surface of the condyle. The range of mouth opening variables were the clinical markers with the most significant associations with morphological variability at the medial and lateral condylar poles. The repeated clinician consensus classification had 97.8% agreement on degree of degeneration within 1 group difference. Predictive analytics of the NN's staging of TMJOA compared to the repeated clinicians' consensus revealed 73.5% and 91.2% accuracy. This study demonstrated significant correlations among variations in protein expression levels, clinical symptoms, and condylar surface morphology. The results suggest that 3-dimensional variability in TMJOA condylar morphology can be comprehensively phenotyped by the NN.

Expression of Interleukin-1 and temporomandibular disorder: Contemporary review of the literature

OBJECTIVE

Temporomandibular disorders (TMD) are a group of conditions affecting the temporomandibular joint (TMJ), leading to jaw dysfunction, joint and muscle pain, and a decrease in quality of life. A communication network of pro- and anti-inflammatory mediators called cytokines maintains the homeostasis of the TMJ. This review will focus on the Interleukin (IL) family of cytokines, which have been quantified in TMJ synovial fluids in a variety of studies. IL-1α and IL-1β have pro-inflammatory effects, while the endogenous receptor antagonist (IL-1RA) inhibits the pro-inflammatory effects of IL-1.

METHODS

A literature search (2006-2016) to identify eligible studies was completed using the PubMed database. Studies identified used saline irrigation to quantify cytokine profiles in synovial fluid of healthy and/or dysfunctional joints.

RESULTS

The initial search yielded 111 articles, 5 of which met the inclusion criteria after inter-reviewer discussion.

CONCLUSIONS

Articles that compared IL-1 concentrations in TMD vs. control groups found significant differences.

Multisystem dysregulation in painful temporomandibular disorders

Multiple physiological and psychological regulatory domains may contribute to the pathophysiology of pain in temporomandibular disorder (TMD) and other bodily pain conditions. The purpose of this study was to evaluate the relationship between multisystem dysregulation and the presence of TMD pain, as well as the presence of different numbers of comorbid pain conditions in TMD. Secondary data analysis was conducted in 131 non-TMD (without comorbid pain) controls, 14 TMD subjects without comorbid pain, 78 TMD subjects with 1 comorbid pain, and 67 TMD subjects with multiple comorbid pain conditions who participated in a TMD genetic study. Twenty markers from sensory, autonomic, inflammatory, and psychological domains were evaluated. The results revealed that 1) overall dysregulation in multiple system domains (OR [odds ratio] = 1.6, 95% confidence interval [CI] = 1.4-1.8), particularly in the sensory (OR = 1.9, 95% CI = 1.3-2.9) and the psychological (OR = 2.1, 95% CI = 2.1-2.7) domains, were associated with increased likelihood of being a painful TMD case; and 2) dysregulations in individual system domains were selectively associated with the increased odds of being a TMD case with different levels of comorbid persistent pain conditions. These outcomes indicate that heterogeneous multisystem dysregulations may exist in painful TMD subgroups, and multidimensional physiological and psychological assessments can provide important information regarding pathophysiology, diagnosis, and management of pain in TMD patients.

PERSPECTIVE

The concurrent assessment of multiple physiological and psychological systems is critical to our understanding of the pathophysiological processes that contribute to painful TMD and associated comorbid conditions, which will ultimately guide and inform appropriate treatment strategies that address the multisystem dysregulation associated with complex and common persistent pain conditions.

Modulation of temporomandibular joint nociception and inflammation in male rats after administering a physiological concentration of 17β-oestradiol

BACKGROUND

Previous studies have shown 17β-estradiol will reduce temporomandibular joint (TMJ) inflammation and hypersensitivity in female rats. Although male rats contain significant amounts of oestradiol, it was unknown whether a physiological concentration of 17β-estradiol would attenuate male TMJ inflammation and nociception.

METHODS

Intact and castrated rats were given a physiological concentration of oestradiol to examine first, if oestradiol will affect male TMJ nociception/inflammation and, second, if administration of oestradiol would act synergistically with endogenous male hormones to attenuate TMJ nociception. The hormonally treated rats were given TMJ injections of complete Freund's adjuvant (CFA) and then nociception was measured using a validated method in which a lengthening in meal duration is directly correlated to the intensity of deep TMJ nociception. Inflammation was assayed by quantitating pro-inflammatory gene expression.

RESULTS

Meal duration was significantly lengthened after TMJ CFA injection and this lengthening was significantly attenuated in the castrated but not intact males after administering a physiological concentration of oestradiol. A physiological concentration of 17β-estradiol also significantly increased IL-6 expression in the inflamed TMJ of castrated males while 17β-estradiol did not alter IL-1β, CXCL2 and CCL20 expression. Castration increased pro-inflammatory mediators IL-6, IL-1β and CXCL2 suggesting male sex hormones were anti-inflammatory. Calcitonin gene-related peptide in the trigeminal ganglia was unchanged.

CONCLUSIONS

Similar to females, male rats with TMJ inflammation showed a reduced nociceptive response after treatment with a physiological concentration of oestradiol suggesting the effects of oestradiol treatment were not constrained by organizational processes in the males.

Effect of intra-articular administration of interleukin 1 receptor antagonist on cartilage repair in temporomandibular joint

Interleukin 1 (IL-1) plays a central role in cartilage deterioration in osteoarthritis (OA). Interleukin 1 receptor antagonist (IL-1Ra) is a natural receptor antagonist and blocks the effects of IL-1. In this study, partial disk perforation was performed bilaterally to induce an osteoarthritic joint in rabbit temporomandibular joint. Fifty micrograms of recombinant human IL-1Ra was injected into the right joint, and the contralateral joint received vehicle injection 4 weeks postoperatively. Animals were killed at different intervals. Histology and reverse transcription-polymerase chain reaction were performed for comparison. The vehicle-treated joint had typical OA-related cartilage degradation, whereas the lesions in cartilage of the IL-1Ra-treated joint were less severe than the control joint. At 12 weeks, a higher expression of aggrecan and collagen type II and a lower expression of aggrecanase were observed in the treated joint than in the control joint. At 24 weeks after injection, the expression of aggrecan and collagen type II was also higher in the treated joint than in the control joint. However, no difference in either aggrecanase or tumor necrosis factor α was found between 2 groups at 24 weeks. Our results suggest that intra-articular administration of IL-1Ra into the temporomandibular joint may be a good alternative for the treatment of cartilage degeneration in OA. There was also evidence confirming that supplemented IL-1Ra functions by modifying the signal transduction mechanisms specific to IL-1.

Measuring persistent temporomandibular joint nociception in rats and two mice strains

Temporomandibular joint (TMJ) pain has been reported to last for prolonged periods in humans. In rodents a variety of methods have been used to measure TMJ nociception, but for most of these methods the period of measurement has been minutes to a couple of hours. In addition, most measurement protocols required restraint or training of the animal. Previous studies from our laboratory demonstrated that feeding behavior, particularly meal duration, was an indicator of TMJ nociception in unrestrained and untrained male and female Sprague-Dawley rats for up to two days. In this study, we first found that injection of complete Freund's adjuvant (CFA) into the TMJ of rats significantly lengthened meal duration for 19 days and also decreased meal frequency for 42 days. Interestingly, the meal duration varied significantly from day to day within the 19 day period. TMJ interleukin-1 beta (IL-1 beta) and calcitonin gene-related peptide (CGRP) were significantly elevated in the TMJ tissues of CFA-injected animals and the level of these markers was attenuated as the meal duration decreased with time. Control animals injected with saline into the TMJ or CFA into the knee did not show a significant lengthening in meal duration but did show a decrease in meal frequency. In a second study, DBA/1LacJ mice given TMJ CFA injections showed a significantly lengthened meal duration on four of the seven days measured using end-of-the meal definition of 5 or 10 min. No other meal pattern changed significantly. Two days post-CFA injection, the DBA/1LacJ mice showed significantly elevated interleukin-6 (IL-6), but not elevated IL-1 beta. Seven days post-injection, both IL-6 and IL-1 beta were significantly elevated. No change in CGRP was detected. In this study C57Bl/6 mice also received TMJ CFA injections, but they did not show a lengthening in any meal pattern or significant increases in IL-1 beta, IL-6 or CGRP. Our data show, for the first time, that meal duration can be used to measure CFA-induced nociception in the TMJ over the course of several weeks in unrestrained rats and for up to seven days in the DBA/1LacJ mouse strain. In addition, C57Bl/6 mice are resistant to CFA-induced TMJ nociception at the same dose used in the DBA/1LacJ mice.