Hyperalgesic change over the craniofacial area following urate crystal injection into the rabbit's temporomandibular joint

Association between oxidative stress and chronic orofacial pain and potential druggable targets: Evidence from a Mendelian randomization study

BACKGROUND

Oxidative stress indicators affect chronic orofacial pain (COFP), but how to reduce these effects is uncertain.

OBJECTIVES

11 oxidative stress biomarkers were collected as exposures, while four forms of COFP were chosen as outcomes for Mendelian randomization (MR) study.

METHODS

The effect estimates between oxidative stress and COFP were calculated using inverse variance-weighted MR (IVW-MR). Then, functional mapping and annotation (FUMA) was utilized in order to carry out SNP-based functional enrichment analyses. In addition, the IVW-MR method was applied to combine effect estimates when using genetic variants associated with oxidative stress biomarkers as an instrument for exploring potential druggable targets.

RESULTS

The results indicated that oxidative stress biomarkers (causal OR of uric acid (UA), 0.998 for myofascial pain, 95% CI 0.996-1.000, p < .05; and OR of glutathione transferase (GST), 1.002 for dentoalveolar pain, 95% CI 1.000-1.003, p < .05) were significantly linked with the probability of COFP. Functional analysis also demonstrated that UA and myofascial pain genes were prominent in nitrogen and uracil metabolism, while GST and dentoalveolar pain genes were enriched in glutathione metabolism. Also, the study provided evidence that solute carrier family 2 member 9 (SLC2A9) and glutathione S-transferase alpha 2 (GSTA2) cause discomfort in the myofascial pain (OR = 1.003, 95% CI 1.000-1.006; p < .05) and dentoalveolar region (OR = 1.001, 95% CI 1.000-1.002; p < .05), respectively.

CONCLUSIONS

In conclusion, this MR study indicates that genetically predicted myofascial pain was significantly associated with decreased UA and dentoalveolar pain was significantly associated with increased GST level. SLC2A9 inhibitor and GSTA2 inhibitor were novel chronic orofacial pain therapies and biomarkers, but clinical trials are called to examine if these oxidative biomarkers have the protective effect against orofacial pain, and further research are needed to explore the underlying mechanisms.

Clinical course of an antigen-induced arthritis model in the rabbit temporomandibular joint

The aim of this study was to investigate clinical features of an antigen-induced arthritis model in the rabbit temporomandibular joint (TMJ) and compare them to those in knee joint (KJ) arthritis. Eighteen adult male New Zealand White rabbits were divided into a TMJ arthritis group and a KJ arthritis group. Monoarthritis was induced unilaterally with ovalbumin and clinical observations, including joint swelling, skin surface temperature (SST) over the joints, and the withdrawal reflex threshold (WRT) to noxious pressure, were performed over a 3 week period. The joints were then evaluated histologically. The WRT was decreased during the 3 weeks after induction of TMJ arthritis, together with mild but significant joint swelling. The arthritic KJ also showed significant swelling and reduced WRT during the 3 week period. A significant increase of SST over the arthritic TMJ was present during the first week, while changes in SST over the KJ were inconsistent. The histological evaluation showed chronic arthritic features in all arthritic joints of both groups and no difference in the severity of arthritis was found between the TMJ and the KJ.