Effects of Alendronate and Dexamethasone on Osteoclasts In vitro

Objectives: Glucocorticoids are known to increase the risk of oral osteonecrosis of the jaw associated with bisphosphonate use. The aim of this study was to analyze the influence of bisphosphonate bound to bone (Alendronate [ALN]) and a glucocorticoid (Dexamethasone [DEX]) on osteoclast differentiation and activity and regulatory factors released by osteoclasts.
Methods: Bovine cortical bone slices were trimmed into a surface of 1 cm², treated with solutions containing 10^-5M of ALN or vehicle overnight, then washed, and placed in 2cm² cell culture wells. Cells from mouse marrow were plated in the wells in α-MEM supplemented with 10% fetal bovine serum, plus 1.25-dihydroxyvitamin D3 (10^-8M) and some were supplemented with DEX at 10^-7M. To analyze the influence of these drugs on the cells, viability assays (MTT), staining for tartrate-resistant acid phosphatase (TRAP) activity and immunofluorescence staining for RANKL was performed. Bone slices were assayed for resorption pits by scanning electron microscopy (SEM).
Results: No cytotoxic effect was found with all the treatments and no significant difference was observed in the number of viable cells. More TRAP+ cells were observed in the control group (p<0.05). RANKL labeled cells were detected in all groups, showing alendronate did not suppress expression of RANKL. Resorption analysis showed an increase of pits, when the cells were treated with DEX, while pitting was suppressed on alendronate coated bone.
Conclusions: Although dexamethasone does not induce an increase in the number of clastic cells, it enhances bone resorption. Alendronate suppresses pitting under all conditions. We are examining whether cytokines and RANK-containing extracellular vesicles produced by osteoclasts are altered by ALN and DEX.