BISPHOSPHONATES ACT ON OSTEOBLASTIC CELLS AND INHIBIT OSTEOCLAST FORMATION IN MOUSE MARROW CULTURES

We examined the mode of action of bisphosphonates on osteoclastic cell recruitment using mouse marrow cultures with or without osteoblastic cells. Tartrate-resistant acid phosphatase-positive multinucleated cel ls [TRAP(+) MNC] formed in cultures were determined to be osteoclastic cells. In marrow cultures, TRAP(+) MNC formation in the presence of 1 0(-8) mol/L 1,25(OH)(2)D-3 was not affected by the addition of 10(-6) mol/L dihydrogen (cycloheptylamino)-methylenebisphosphonate monohydrat e (YM175). However, it was inhibited in cocultures of marrow cells wit h osteoblastic cells. The inhibitory effect was evident throughout the entire culture period, YM175 dose dependently inhibited TRAP(+) MNC f ormation, and other bisphosphonates-pamidronate and alendronate-also i nhibited TRAP(+) MNC formation in the coculture. Similar observations were also made in the coculture of spleen cells with osteoblastic cell s. The conditioned media of osteoblastic cells treated with 10(-6) mol /L, YM175 inhibited TRAP(+) MNC formation in marrow cultures. The pres ence of YM175 in methylcellulose cultures affected neither the colony formation of monocyte-macrophage lineage, nor TRAP(+) MNC formation in the succeeding cocultures of recovered cells with osteoblastic cells. These results indicate that YM175 and probably other bisphosphonates as well preferentially inhibit the later stage of osteoclastogenesis t hrough its action on osteoblastic cells. Our findings suggest that par t of the inhibitory action by osteoblastic cells in the presence of bi sphosphonates is mediated through soluble factor(s).