Metformin suppresses periapical bone resorption in a mouse model of apical periodontitis in vivo and inhibits RANKL-induced osteoclastogenesis in vitro.

OBJECTIVES

Metformin (MET), a widely used antidiabetic drug, has recently gained attention for its anti-bone-resorptive properties. This study evaluated these effects in apical periodontitis (AP) and explored its underlying molecular mechanisms particularly its role in osteoclastogenesis.

METHODS

AP was induced in the mandibular first molars of nine 6-week-old male C57BL/6 JJcl mice by pulp exposure for 21 days. MET (50 mg/kg/day) was administered intraperitoneally beginning 1 d before the procedure. Periapical bone resorption was evaluated using micro-computed tomography and tartrate-resistant acid phosphatase (TRAP) staining. In vitro, RAW264.7 murine macrophages were stimulated into osteoclasts using receptor activator of nuclear factor κB ligand (RANKL; 100 ng/mL) for 7 days, whereas the suppressive effect of MET (0.5 mM) on osteoclastogenesis was evaluated using TRAP staining. The mRNA expression of osteoclastogenesis-related genes was measured by real-time quantitative polymerase chain reaction. The effects of MET on extracellular signal-regulated kinase (ERK) and nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) signaling were determined using western blotting and luciferase assays, respectively.

RESULTS

MET significantly reduced the lesion size and number of TRAP-positive osteoclasts in vivo at day 21. In vitro, MET significantly inhibited RANKL-induced osteoclastogenesis and decreased the number of TRAP-positive osteoclasts (≥3 nuclei). MET significantly suppressed the RANKL-induced mRNA expression of the osteoclastogenesis-related genes osteoclast-associated receptor, acid phosphatase 5, tartrate resistant, and osteoclast stimulatory transmembrane protein. Moreover, it reduced RANKL-induced p-ERK and NFATc1 signaling.

CONCLUSIONS

MET suppresses bone resorption in AP in vivo. In vitro, MET inhibited RANKL-induced osteoclastogenesis by suppressing the ERK-NFATc1 axis, suggesting a potential mechanism for the anti-bone-resorptive effects of MET in AP.