Human osteoclast formation and activity on a xenogenous bone mineral

To date, the majority of studies on bone substitute materials have investigated their regenerative properties; however, little is known about their resorption processes, forasmuch as it is believed that the ideal biomaterial for bone regeneration must be completely resorbable. This study is aimed at defining the in vitro resorption potential of human osteoclasts (OCLs) on a xenogenous bone mineral (XBM). Peripheral blood mononuclear cells from healthy volunteers were used to generate OCLs in vitro in the presence of macrophage colony stimulating factor and receptor activator of NF-κB ligand on bovine bone slices and XBM. By using morphologic and biochemical methods, we observed that OCL formation occurred on XBM and these cells were positive for the major OCL markers. Regarding OCL activity, resorption pits were detected on XBM by reflection and confocal microscopy. However, biochemical analysis revealed that collagen degradation at day 14 and 21 was significantly lower in XBM supernatants when compared to bovine bone, suggesting that XBM underwent a much slower resorption over time. These findings demonstrate that OCLs are generated on, attach to, and resorb XBM though more slowly than native bone, and suggest that cultured human OCLs could be used as a model for comparing resorption rates of bone substitute materials.