THU0545 Characterising a mouse model of temporomandibular joint (TMJ) arthritis to study orofacial pain and inflammation
Authors: X. Kodji, J.D.S. Valente, F. Lundy, I. El Karim, S.D. Brain
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> The temporomandibular joints (TMJ) encompass the jawbones (mandibular condyle) and the skull region (temporal bone)<sup>1</sup>. Dysfunctions in these joints and surrounding muscles result in a condition known as TMJ disorder (TMD), which include mastication-related pain. 16%–59% of patients reported painful symptoms while 33%–86% of these patients showed clinical signs<sup>1</sup>. Currently, the etiology of TMD is unknown, although lavage samples from patients showed signs of synovitis, which may lead to the development of degenerative disorders, such as TMJ arthritis<sup>2</sup>. There are only a few murine models available, as the most commonly used animal model is TMJ arthritis in rats. <h3>Objectives</h3> We aimed to characterise a mouse model of TMJ arthritis by mimicking the formation of synovitis using zymosan. We sought to characterise the development of orofacial pain by performing various behavioural measurements and measure joint inflammation. <h3>Methods</h3> All <i>in vivo</i> procedures were carried out according to the UK Home Office Animals (Scientific Procedure) .<sup>Act 1986</sup> Male CD1 mice (6–8 weeks) were anaesthetised transiently using 2% isoflurane. Zymosan (10, 30, or 100 µg; 10 µl), or saline was administered unilaterally into the TMJ as previously described<sup>3</sup>. Spontaneous pain behaviours were observed by counting the number of unilateral cheek wipes. All studies were terminated by cervical dislocation and the tissue was collected for <i>ex vivo</i> analyses. Mean ±SEM was calculated and data were analysed by unpaired Student's T-test or 2-way repeated measures ANOVA with Bonferroni's <i>post hoc</i> test. p&lt;0.05 was accepted as statistically significant. <h3>Results</h3> A dose response study showed that 30 µg, but not 10 µg and 100 µg of zymosan, resulted in a maximal wiping response at 2 hours, which was maintained at 4 hours (table 1; ***p&lt;0.001 zymosan ipsi vs saline ipsi; ## p&lt;0.01 zymosan ipsi vs contra). Hind paw scratching was negligible. Hence, 30 µg was used for subsequent experiments. Increased neutrophils (measured by MPO assay) was observed in zymosan-treated joints (table 1 **p&lt;0.01 saline ipsi vs zymosan ipsi), while a similar trend was also observed in 3-nitrotyrosine protein expression, a marker of protein nitrosylation (p=0.053). Preliminary studies are being undertaken to characterise other inflammatory markers in addition to the development of <i>in vivo</i> orofacial mechanical hyperalgesia using the Von Frey filaments. Table 1 A summary of zymosan-mediated spontaneous orofacial pain behaviours and inflammation. <h3>Conclusions</h3> We have established a mouse model of TMJ arthritis, which showed significant orofacial pain responses <i>in vivo</i>. Our data highlights an inflammatory profile typical of zymosan and shows a potential use for this model to investigate novel TMD treatments. <h3>References</h3> [1] Millam. J Musculoskel Neuron Interact2003;3(4):382–390. [2] Cheng and Israel. J Maxillofac Surg2005;63(6):761–765. [3] Kramer, et al. Physiol Behav2010;99(5):669–678. <h3>Acknowledgements</h3> XK and JV were funded by Arthritis Research UK. <h3>Disclosure of Interest</h3> None declared