Denosumab is an anti-bone resorptive drug consisting of complete human monoclonal antibodies that targets receptor activator of nuclear factor κB ligand (RANKL), which is responsible for osteoclast formation. The drug has been adapted for bone diseases, such as osteoporosis and bone metastasis related to cancer, but is not used for alveolar bone destruction related to periodontitis. In the present study, we aimed to clarify whether denosumab prevents bone destruction associated with lipopolysaccharide (LPS)-induced calvaria inflammation and experimental periodontitis in model mice. Denosumab does not bind to mouse RANKL, thus we used anti-mouse monoclonal RANKL antibodies. We also examined the inhibitory effects toward bone destruction of another anti-bone resorptive drug zoledronate, a nitrogen-containing bisphosphonate. Local administration of anti- RANKL antibodies into the calvaria area inhibited LPS-induced osteoclast formation and bone destruction, while zoledronate inhibited bone destruction but not osteoclast formation due to its different action mechanism. In periodontitis model mice, in which the second molars were ligated with a silk suture to induce inflammation, intraperitoneal administration of anti-RANKL antibodies significantly inhibited alveolar bone destruction and tooth root exposure. On the other hand, zoledronate only weakly repressed alveolar bone destruction and failed to inhibit root exposure. These results suggest that denosumab is a promising candidate to prevent alveolar bone destruction associated with periodontitis.

The anti-bone resorptive drugs denosumab, an anti-human-RANKL antibody, and zoledronic acid (ZOL), a nitrogen-containing bisphosphonate, have recently been applied for treatment of pediatric patients with bone diseases, though details regarding their effects in growing children have yet to be fully elucidated. In the present study, we administered these anti-resorptive drugs to mice from the age of 1 week and continued once-weekly injections for a total of 7 times. Mice that received the anti-RANKL antibody displayed normal growth and tooth eruption, though osteopetrotic bone volume gain in long and alveolar bones was noted, while there were nearly no osteoclasts and a normal of number osteoblasts observed. In contrast, ZOL significantly delayed body growth, tooth root formation, and tooth eruption, with increased osteoclast and decreased osteoblast numbers. These findings suggest regulation of tooth eruption via osteoblast differentiation by some types of anti-resorptive drugs.

Backgrounds Anti-bone-resorptive drugs such as denosumab (an anti-RANKL antibody drug) and bisphosphonates are used to treat bone diseases, including osteogenesis imperfecta, steroidal osteoporosis, and giant cell tumors, in both adults and young patients. However, the precise effects of those anti-bone-resorptive drugs on younger patients are unknown. In the present study, we analyzed the effects of anti-mouse RANKL antibody and zoledronate (a bisphosphonate) on body size, bone metabolism and tooth development of young mice. Methods An anti-mouse RANKL antibody (OYC1®, 2.5 mg/kg) or zoledronate (3.0 mg/kg) was subcutaneously administrated into 1-week-old mice by once-weekly injections for 7 weeks or a single-injection. At the age of 8 weeks, body length and weight were measured as a growth index. Femur bone mass and tooth development were analyzed using micro-computed tomography. Osteoclasts and osteoblasts in proximal tibiae or around tooth roots were histologically analyzed. Results The survival rate of saline-(control), anti-RANKL antibody-or zoledronate-treated 8-week-old mice, with once-weekly injections for 7 weeks, were 100%, 100% and 83%, respectively. Body length and weight measurements in the anti-RANKL antibody-treated group were normal, while those in the zoledronate-treated group were significantly reduced even with a single-injection. Apparent increases in femur bone mass were observed in both the anti-RANKL antibodytreated and zoledronate-treated groups compared to control group. The number of tartrate-resistant acid phosphatase (TRAP) positive cells, which were identified as osteoclasts, were markedly decreased in tibiae in the anti-RANKL antibody-treated group but not zoledronate-treated group. Although no osteoclasts existed around the tooth roots, teeth in the anti-RANKL antibody-treated group showed normal development, while those in the group treated with zoledronate exhibited very short tooth roots with increased osteoclasts and decreased osteoblasts around them after onceweekly injections for 7 weeks. Conclusions Our results suggest that denosumab, an anti-RANKL antibody, has fewer undesirable effects in young patients as compared to zoledronate.