A simple method to assess osteoclast-mediated bone resorption using unfractionated bone cells.

To determine osteoclastic bone resorption we established a simple assay system in which unfractionated cells obtained from femora of 13-day-old mice were cultured on a dentine slice and the number of osteoclasts and their induced pit area on the slices were measured. When the bone cells (1 x 10(5) cells/dentine slice) were cultured in the presence of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] or human parathyroid hormone (hPTH) for 4 days, at which time newly-formed osteoclasts were not detected, the pit area was dose-dependently increased, being a 4.3- or 4.1-fold respective increase over the control at a 10(-8) M concentration of hormones. Chick calcitonin (cCT) inhibited the osteoclastic bone resorption induced by either of these hormones. cCT alone also suppressed the bone resorption by the cells (3 x 10(5) cells/dentine slice). These findings indicate that 1,25(OH)2D3 or hPTH may mainly activate pre-existing osteoclasts, resulting in increased bone resorption, and that cCT may suppress this osteoclastic activity. When 1,25(OH)2D3 or hPTH was added to the cells pre-cultured in factor-free medium for 6 days, at which time pre-existing osteoclasts had almost degenerated, new osteoclasts were formed, resulting in an increase in pit formation. Thus this system is a useful method which could more sensitively evaluate the effects of hormones or factors on osteoclast formation and activation than other previous systems.