Degradation of subcutaneous implants of bone particles from normal and warfarin-treated rats

Osteoclasts are multinucleated cells specific to bone tissue and of hemopoietic origin. They are formed by fusion of mononucleated cells in a manner related to the formation of macrophage polykarions. Subcutaneous implantation of mineralized bone particles induces multinucleated giant cell recruitment. There is controversy, however, about the nature of these cells. Although subcutaneous implantation of bone particles derived from warfarin-treated animals has been applied as an in vivo model to study the role of osteocalcin in bone resorption, the exact nature of multinucleated cells elicited in this model is still unclear. In this paper, subcutaneous implants of bone particles from normal and warfarin-treated rats were implanted in Sprague-Dawley rats. Resorption was assessed in 12 and 16 day implants by chemical analysis (calcium content) and by histomorphometric measurement of the bone particle area and the number of multinucleated and tartrate-resistant acid phosphatase-positive cells. No significant difference in calcium content and bone area were observed, after 12 or after 16 days of implantation, between implants from normal and warfarin-treated rats. The number of tartrate-resistant acid phosphatase-positive cells elicited by bone particles represented less than 25% of the number of multinucleated cells and did not differ between bone particles from normal and warfarin-treated rats. By electron microscopy, a majority of multinucleated cells did not show a ruffled border in contact with bone particles, and their morphological features were suggestive of a foreign body giant cell reaction. In our experience this model appears to elicit only a few osteoclasts among multinucleated macrophagic cells and may not be the most appropriate one for the study of resorption of normal or osteocalcin-depleted bone.