Simvastatin alleviates bone resorption in apical periodontitis possibly by inhibition of mitophagy-related osteoblast apoptosis.

AIM: To assess the connection between mitophagy and hypoxia-induced apoptosis in osteoblasts and whether simvastatin alleviates bone resorption in apical periodontitis through modulation of mitophagy-related apoptosis. METHODOLOGY: Hypoxia-induced generation of reactive oxygen species in mitochondria and changes in mitochondrial membrane potential were evaluated, respectively, by MitoSOX and JC-1 fluorescence dye signalling. Accumulation of mitophagy markers PTEN-induced putative kinase 1 (PINK1) and Parkin in mitochondria was examined by Western blotting and immunofluorescence microscopy. Osteoblast apoptosis was assessed by Western analysis of cleaved-poly (adenosine diphosphate ribose) polymerase (PARP). In a rat model of induced apical periodontitis, the therapeutic effect of simvastatin and its action on osteoblast mitophagy and apoptosis were examined. anova, Fisher's and Student's t-test were used for data analysis. RESULTS: Hypoxia-induced mitochondrial dysfunction and stimulated mitophagy in osteoblasts. Hypoxia also provoked apoptosis in osteoblasts and inhibition of mitophagy decreased hypoxia-augmented apoptotic activity. Simvastatin alleviated hypoxia-induced mitochondrial dysfunction, mitophagy and apoptosis. The protective action of simvastatin against apoptosis was related to its antimitophagy activity. Experiments in the rat model of induced apical periodontitis supported the laboratory findings. Simvastatin treatment mitigated periapical bone loss and reduced the activities of apoptosis and mitophagy in regional osteoblasts. CONCLUSIONS: The results suggest that modulation of osteoblast mitophagy may help diminish bone loss associated with inflammation and has potential as an auxiliary therapy for apical periodontitis.

Sirtuin 6 attenuates periapical lesion propagation by modulating hypoxia-induced chemokine (C-C motif) ligand 2 production in osteoblasts.

AIM: To investigate the attenuating effect of sirtuin 6 (SIRT6) on hypoxia-induced production of chemokine (C-C motif) ligand 2 (CCL2) by osteoblasts and the relevance of this action on the pathogenesis of periapical lesions. METHODOLOGY: Sirtuin 6 was overexpressed in MC3T3-E1 murine osteoblasts by lentivirus-mediated gene transfer. The relationship between the antiglycolytic/antioxidative activities of SIRT6 and its effect on hypoxia-induced CCL2 production were examined. Pathogenetic relevance of the actions of SIRT6 was assessed in a rat model of induced apical periodontitis. The data were analysed statistically using Student's t-test or one-way analysis of variance (anova) and then a Tukey's multiple comparison test. RESULTS: In cultured murine osteoblasts, 24-h hypoxic treatment significantly enhanced the generation of reactive oxygen species (P = 0.003), expression of lactate dehydrogenase A (LDHA) and production of lactate (P = 0.007). A reciprocal effect between hypoxia-induced redox imbalance and hypoxia-enhanced glycolysis was noted which in turn augmented the secretion of CCL2. Through its antiglycolytic and antioxidative effects, SIRT6 blocked the vicious cycle to suppress CCL2 production. In normal periapical tissues of rats, strong expression of SIRT6 and low levels of LDHA and 8-OHdG (a marker of oxidative DNA damage) were found in osteoblasts. In induced apical periodontitis, osteoblastic expression of SIRT6 was significantly suppressed (P = 0.001) which was associated with significantly elevated levels of LDHA (P = 0.003) and 8-OHdG (P = 0.004) and significantly enhanced recruitment of macrophages (P = 0.004). CONCLUSIONS: Sirtuin 6 has a therapeutic effect on periapical lesions through suppression of CCL2 synthesis. The anti-inflammatory action of SIRT6 is closely related to its regulatory activities in cellular metabolism and redox homoeostasis.