Curcumin inhibits the neuroimmune response mediated by mast cells after pulpitis

To analyze the effect of mast cells (MCs) in neurogenic inflammation and the neuroimmune response of trigeminal ganglia (TG) due to pulpitis and detect the regulatory effect of curcumin (Cur) on neuroimmune responses induced by pulpitis.

Immunohistochemistry, toluidine blue staining (TB), and other methods were used to detect the dynamic changes of MCs, as well as tryptase expression changes and protease activated receptor 2 (PAR2) and calcitonin gene-related peptide (CGRP) levels in the neuroimmune response induced by pulpitis. After administering Cur by intraperitoneal injection, the expression levels of Toll-like receptor 4 (TLR4), CGRP, glial fibrillary acidic protein (GFAP), fractalkine (CX3CL1), Tumor necrosis factor (TNF-α), and other factors were examined in the TG of pulpitis-induced rats.

After pulpitis induction, the expression of CGRP-positive neurons and GFAP-positive soluble guanylate cyclase (SGC) in the TG significantly increased. A large number of MCs underwent degranulation. MCs were scattered between the CGRP-positive nerve fibers. MCs showing a typical degranulated state within the TG significantly increased and tryptase-positive MCs surrounded the TG nerve fibers and neurons. After treatment with Cur, the inflammatory response in the periodontal bone induced by pulpitis decreased and promoted early tissue repair. The expression of TNF-α significantly decreased as did degranulation of MCs. In contrast, the expression of CGRP, TLR4-positive neurons, activated SGCs, and PAR2-positive TG neurons significantly decreased. MCs could participate in the neuroimmune response induced by pulpitis by the tryptase signaling pathway.

Importantly, Cur inhibited the degranulation of MCs, downregulated the expression of tryptase and PAR2 in the TG, and attenuated the activation response of osteoclasts in the apical periodontium.