Tooth extraction within 2 weeks before radiotherapy and osteoradionecrosis: A nationwide cohort study

Osteoradionecrosis - an old problem with new consequences

PURPOSE OF REVIEW

Osteoradionecrosis (ORN) is a devasting complication of radiation therapy (RT), especially in head and neck cancers (HNC), and is still poorly understood. The aim of this review is to report its incidence and consider the risk factors associated with ORN to highlight prevention strategies to decrease its incidence.

RECENT FINDINGS

The average incidence of ORN is between 2% and 23%, with incidence decreasing in more recent years with the introduction of modern RT technology and better oral health care. Smoking, diabetes mellitus, oropharyngeal and oral cavity cancers, pre- and post-RT dental extractions and a total radiation dose of over 60 Gy were all identified as risk factors for ORN. In prevention, strategies were mainly structured around minimising risk factors or targeting possible mechanisms of ORN's pathophysiology.

SUMMARY

At present, the controversy surrounding the risk factors and pathogenesis of ORN makes it difficult to establish a set of prevention guidelines for its incidence. In order to achieve this, more research examining its aetiology must be conducted as well as a universal staging system within which ORN may be classified.

ATG7-mediated autophagy protects human gingival myofibroblasts from irradiation-induced apoptosis

BACKGROUND

Apoptosis resistance of myofibroblasts is critical in pathology of irradiation-induced fibrosis and osteoradionecrosis of the jaw (ORNJ). However, molecular mechanism of apoptosis resistance induced by irradiation in oral myofibroblasts remains largely obscure.

METHODS

Matched ORNJ fibroblasts and normal fibroblasts pairs from gingival were primarily cultured, and myofibroblast markers of α-SMA and FAP were evaluated by qRT-PCR and western blot. CCK8 assay and flow cytometric analysis were performed to investigate the cell viability and apoptosis under irradiation treatment. Autophagy-related protein LC3 and ATG7, and punctate distribution of LC3 localization were further detected. After inhibition of autophagy with inhibitor CQ and 3-MA, as well as transfected ATG7-siRNA, cell viability and apoptosis of ORNJ and normal fibroblasts were further assessed.

RESULTS

Compared with normal fibroblasts, ORNJ fibroblasts exhibited significantly higher α-SMA and FAP expression, increased cell, viability and decreased apoptosis under irradiation treatment. LC3-II and ATG7 were up-regulated in ORNJ fibroblasts with irradiation stimulation. After inhibition of irradiation-induced autophagic flux with lysosome inhibitor CQ, LC3-II protein was accumulated and punctate distribution of LC3 localization was increased in ORNJ fibroblasts. Moreover, autophagy inhibitor CQ and 3-MA enhanced the irradiation-induced apoptosis but inhibited viability of ORNJ fibroblasts. Silencing ATG7 with siRNA could obviously weaken irradiation-induced LC3-II expression, and promoted irradiation-induced apoptosis of ORNJ fibroblasts. After knockdown of ATG7, finally, p-AKT(Ser473) and p-mTOR(Ser2448) levels of ORNJ fibroblasts were significantly increased under irradiation.

CONCLUSION

Compared with normal fibroblasts, human gingival myofibroblasts are resistant to irradiation-induced apoptosis via autophagy activation. Silencing ATG7 may evidently inhibit activation of autophagy, and promote apoptosis of gingival myofibroblasts via Akt/mTOR pathway.