Anti-inflammatory and anti-nociceptive effects of strontium ranelate on the zymosan-induced temporomandibular joint inflammatory hypernociception in rats depend on TNF-α inhibition.

BACKGROUND: Temporomandibular joint (TMJ) disorders show inflammatory components, heavily impacting on quality of life. Strontium ranelate has previously shown anti-inflammatory and antinociceptive effects on other experimental inflammatory pain models. Thus, we aim to investigate the strontium ranelate efficacy in reducing the zymosan-induced inflammatory hypernociception in the TMJ of rats by evaluating the TNF-α, IL-1β, and hemeoxygenase-1 (HO-1) involvement.
METHODS: Wistar rats were treated with strontium ranelate (0.5, 5 or 50 mg/kg, per os) 1 h before zymosan injection (iart). Mechanical threshold was assessed by Von Frey test and synovial lavage was collected for leukocyte counting and myeloperoxidase measurement, joint tissue and trigeminal ganglion were excised for histopathological analysis (H&E) and TNF-α/IL-1β levels dosage (ELISA). Moreover, rats were pre-treated with ZnPP-IX (3 mg/kg, sc), a specific HO-1 inhibitor, before strontium ranelate administration (0.5 mg/kg, per os), and Evans Blue (5 mg/kg, iv) was administered to assess plasma extravasation. Pre-treatment with indomethacin (5 mg/kg, sc) was used as positive control while the sham group received 0.9% sterile saline (per os and iart).
RESULTS: Strontium ranelate did not reduce leukocyte counting, myeloperoxidase activity, Evans Blue extravasation, IL-1β levels, and TNF-α/IL-1β immunolabeling; but it increased the nociceptive threshold and reduced TNF-α levels. Additionally, HO-1 inhibition did not change the strontium ranelate effects.
CONCLUSION: Strontium ranelate may achieve its antinociceptive effects through the reduction of TNF-α levels in the trigeminal ganglion, but not suppressing IL-1β expression nor inducing the HO-1 pathway.