Detection and characterization of apoptosis in osteoclasts in vitro.

Morphological changes of nuclei and DNA fragmentation undergoing cell death were studied using highly purified rabbit osteoclasts in vitro. Approximately fifty percent of dead osteoclasts exhibited morphological changes of nuclei characterized by apoptosis and approximately 70% of osteoclasts with changes of nuclei exhibited DNA fragmentation in our culture system. These changes of nuclei were confirmed as condensation of chromatin through transmission electronmicroscope. Moreover, biochemical characterizations of these changes were compatible with the characterizations of apoptosis in other cell systems. These results demonstrate that part of osteoclasts die by a mode of apoptosis.