Effect of capsaicin-sensitive neurons on bone resorption in mice with experimental periodontitis

Background Periodontitis is an infectious disease initiated by plaque. However, the role of peripheral nerves in the progression of periodontitis remains unclear.

Objective To study the effect of capsaicin-sensitive neurons on the progression of experimental periodontitis in mice.

Methods Twenty male C57BL/6 mice were randomly divided into ablation group (Cap) and non-ablation group (Veh), 10 mice in each group. The Cap group received injections of high-concentration capsaicin (5 μg/mL) into the ocular/maxillary region of bilateral trigeminal nerves to ablate capsaicin-sensitive neurons, while the Veh group received injections of a vehicle containing 1% DMSO and 10% Tween-80 phosphate-buffered saline. One week later, a ligature was tied around the left maxillary second molar of each mouse, the right maxillary second molar was untreated as a control. The mice were then divided into four groups: non-ablative control (Veh/Con), ablative control (Cap/Con), non-ablative periodontitis (Veh/Lig), and ablative periodontitis (Cap/Lig). One week later, the maxilla was examined by micro-CT to observe the reduction of alveolar bone. After decalcification, the HE staining and the TRAP staining were performed to observe soft and hard tissue destruction and osteoclast formation. Quantitative real-time polymerase chain reaction (RT-qPCR) was employed to detect expression levels of inflammatory factors TNF-α and IL-1β in gum tissue.

Results The results of micro-CT showed that compared with the Veh/Lig group, alveolar bone resorption was decreased in the Cap/Lig group (P < 0.05). HE staining and TRAP staining showed that compared with the Veh/Lig group, damage to soft and hard tissues was reduced in the Cap/Lig group; furthermore, there was also a decrease in the number of osteoclasts around the alveolar bone (P < 0.05). RT-qPCR results indicated that expression levels of inflammatory factors TNF-α and IL-1β were lower in the Cap/Lig group than those in the Veh /Lig group (P < 0.05).

Conclusion Capsaicin-sensitive neurons can promote bone resorption in periodontitis, which may be related to osteoclast differentiation and local tissue inflammation.