Influence of Cu on Osteoclast Formation and Activity In Vitro.

Background: Copper-containing biomaterials are increasingly applied for bone regeneration due to their pro-angiogenetic, pro-osteogenetic and antimicrobial properties. Therefore, the effect of Cu on osteoclasts, which play a major role in bone remodeling was studied in detail.

Methods: Human primary osteoclasts, differentiated from human monocytes were differentiated or cultivated in the presence of Cu. Osteoclast formation and activity were analyzed by measurement of osteoclast-specific enzyme activities, gene expression analysis and resorption assays. Furthermore, the glutathione levels of the cells were checked to evaluate oxidative stress induced by Cu.

Results: Up to 8 µM Cu did not induce cytotoxic effects. Activity of tartrate-resistant acid phosphatase (TRAP) was significantly increased, while other osteoclast specific enzyme activities were not affected. However, gene expression of TRAP was not upregulated. Resorptive activity of osteoclasts towards dentin was not changed in the presence of 8 µM Cu but decreased in the presence of extracellular bone matrix. When Cu was added to mature osteoclasts TRAP activity was not increased and resorption decreased only moderately. The glutathione level of both differentiating and mature osteoclasts was significantly decreased in the presence of Cu.

Conclusions: Differentiating and mature osteoclasts react differently to Cu. High TRAP activities are not necessarily related to high resorption.