Metformin Ameliorates Periapical Lesions Through Suppressing Hypoxia-induced Osteoblast Apoptosis

Objectives: To investigate the effects of metformin on hypoxia-induced apoptosis of osteoblasts and the therapeutic action of intra-canal metformin medicament on induced periapical lesions in rats.
Methods: Human osteoblasts were cultured under normoxia or hypoxia. The influence of metformin on hypoxia-induced mitochondrial superoxide production was examined by MitoSOX fluorescence dye signaling. Release of cytochrome C from mitochondria and cleavage of pro-caspase 9 and poly (adenosine diphosphate ribose) polymerase (PARP) were evaluated by Western blot. Apoptotic cell fraction was assessed by DNA content flow cytometry. In a rat model of induced periapical lesions, the effects of intra-canal metformin on disease progression were appraised by two-dimensional radiography and micro-computed tomography (CT). Oxidative lesions and apoptotic activity of osteoblasts in vivo were estimated respectively by 8-OHdG staining and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL).
Results: Hypoxia enhanced mitochondrial superoxide production in cultured osteoblasts, which was attenuated by metformin. Metformin suppressed hypoxia-induced cytochrome C release from mitochondria and cleavage of pro-caspase 9 and PARP. Apoptotic cell fraction increased under hypoxia, whereas metformin treatment repressed hypoxia-augmented apoptosis. Intra-canal metformin diminished the size of induced periapical lesions in rats. Oxidative damage and apoptotic activity in osteoblasts were also reduced by local metformin medication.
Conclusions: Hypoxia increased oxidative stress in osteoblasts and enhanced cell death through activation of the mitochondrial pathway of apoptosis. Metformin attenuated the oxidative and cytotoxic action of hypoxia. The therapeutic effect of metformin on periapical lesions may be secondary to its anti-oxidative activity.