Objectives: The objectives of this study were to analyze the effect of pH on the growth and activity of osteoclasts treated with different doses of two nitrogen-containing BPs, zoledronate and alendronate.
Materials and methods: Murine osteoclasts cultured on dentine disks were treated with zoledronate (50 or 500 nM) or alendronate (500 or 5 μM) at two different pH values (7.4 or 7.0). Osteoclasts were counted with transmitted light microscopy, apoptosis/necrosis was studied with flow cytometry and confocal microscopy, and resorption pit number and depth were calculated using reflected light and scanning electron microscopy.
Results: The osteoclast count on dentine disks was significantly (p < 0.001) reduced by zoledronate or alendronate treatment at pH 7.0 in comparison to treatment with the same doses at pH 7.4 and untreated disks (controls). The percentage of apoptotic cells was significantly increased by treatment with 500 nM zoledronate or 5 μM alendronate at pH 7.0 in comparison to the same doses at pH 7.4. The number and depth of resorption pits were significantly lower in disks treated at each BP dose studied than in untreated controls at pH 7.0.
Conclusions: Zoledronate and alendronate at therapeutic doses have an adverse effect on the viability and resorptive activity of osteoclasts when the local medium pH is reduced.
Clinical relevance: These findings suggest that periodontal or peri-implant oral cavity infection may be a key trigger of the cascade of events that lead to BRONJ.
Keywords: Activity; Apoptosis; Bisphosphonates; Growth; Jaw; Osteonecrosis.