Different resorption modes on living and devitalized bones by isolated osteoclasts in vitro. The effects of TIMP, E-64, and TGF-alpha.

A new bone resorption model was developed by using living bone substrates and devitalized bones for isolated osteoclasts to act on. The extent of bone resorption was assessed by measuring the area and depth of resorption pits. The area and depth of pits made on living bones were greater than those of pits made on devitalized bone substrates. TIMP (100 micrograms/ml) reduced resorption on living bone in area and depth to the same amount of resorption on devitalized bone. E-64 (60 microM) significantly inhibited the resorption of devitalized bones. TGF-alpha (100 ng/ml) did not have significant effect on the resorption of any substrate. Indomethacin (100 ng/ml) reduced resorption on living bone to the same level of that on devitalized bone. These results suggest that resorption on living bone is aided by osteocyte-synthesis of metalloproteinases, among them collagenase, to degrade bone collagen through prostaglandin synthesis by viable cells in the substrates. The stimulation of bone resorption by TGF-alpha observed in organ culture appears not to be mediated by direct stimulation of osteoclast activity.