Sensory Denervation Increases Potential Of Bisphosphonates To Induce Osteonecrosis Via Disproportionate Expression Of Calcitonin Gene-related Peptide And Substance P

PURPOSE: Bisphosphonate-related osteonecrosis of the jaw(BRONJ)is a serious side effect of long-term administration of bisphosphonates(BPs)and is often refractory to therapy.The pathogenesis of BRONJ is thought to involve inhibition of osteoclastic bone resorption and remodeling,inhibition of angiogenesis,immune dysfunction,and soft tissue toxicity,which have not yet been clarified.In recent years,the regulation of sensory innervation on bone metabolism and innate immune have become a research hotspot.Studies have shown that sensory nerves release neuropeptides,such as calcitonin gene-related peptide(CGRP)and substance P(SP),to maintain bone and immune homeostasis.The present study explored the effect of sensory innervation on the development of BRONJ and explored the mechanism preliminarily,to provide certain theoretical and experimental basis for clinical prevention and treatment of BRONJ.METHODS: 1.Animal models of different degrees of inferior alveolar nerve injury were established,validation of these models was performed by behavioral test and HE staining.BPs was injected intravenously after that,the effect of sensory innervation on the BPs toxicity was observed by HE,TRAP and Masson staining.2.BRONJ models with different degrees of nerve injury were established,the influence of sensory innervation on the development of BRONJ in socket healing was analyzed by HE and TRAP staining.3.The changes of neuropeptides expression in nerve injury and BPs environment were analyzed by IHC staining and Western blot,in vivo effects of neuropeptides on the development of BRONJ and in vitro effects of neuropeptides on BP-induced preosteoclasts were analyzed to explore the mechanism preliminarily.RESULTS: 1.Behavioral and histological results demonstrated the successful establishment of moderate(inferior alveolar nerve injury,IANI)and severe(inferior alveolar nerve transection,IANT)nerve trauma models.Nerve injury increased the toxicity of BPs to alveolar bone.The number of osteoclasts and the disorder degree of periosteum structure increased with the increase of nerve injury degree,but there was no significant difference in the number of osteoblasts between groups.2.The severity and prevalence of BRONJ,and the number of osteoclasts increased with the increase of nerve injury degree,indicating that unbalanced levels of neuropeptides may be a destructive factor in the pathogenesis of BRONJ.3.CGRP expression decreased and SP expression increased following nerve trauma or ZOL injection.The ratio of CGRP/SP was significantly decreased in the IANT/ZOL group.Administration of CGRP,not SP,decreased BRONJ prevalence.Combined application of CGRP and SP reduced the toxicity of ZOL to preosteoclasts,whereas CGRP or SP applied alone showed no effects.CONCLUSION: Sensory denervation increases potential of BPs to induce osteonecrosis via disproportionate expression of CGRP and SP.There is a complex interaction between CGRP and SP.Increase the CGRP/SP ratio may prevent the development of BRONJ.The optimal ratio of CGRP/SP in promoting bone healing and the mechanism of their interaction still need to be studied.