Metabolic bone disease & related research最新文献

The anatomy of the remodeling sites in bone is only partly reflected by random histologic sections. This study is aimed at reconstructing the three-dimensional morphology of the osteons in human trabecular bone from serial sections of decalcified tissue. The osteons resembled broad bands, which were made up of parallel lamellae, bounded on one side by the marrow surface and on the other side by an irregular cement plane. The mean thickness was much less (<0.2) than the mean extent in the other dimensions. The plate may, therefore, be used as the morphologic model for stereologic studies. The plates were curved and irregular. One three-dimensional osteon can, therefore, give rise to a varying number of profiles in a single random section. The two-dimensional profiles, which are of unequal surface extent, are thus not appropriate sampling units for morphometric studies of, e.g., osteon thickness, osteoid thickness, or calcification rate in trabecular bone. When estimating thickness the number of measuring sites should be sampled proportional to the surface extent of the profiles.

Studies employing the matrix-induced endochondral bone formation system have outlined the processes involved in bone induction. An initial event is increased migration of mesenchymal cells to the implant site prior to endochondral calcification. This suggests that chemotactic factors in the bone matrix may be involved in the osteogenic process.

Extracts of human fetal bone, obtained by sequential demineralization, stimulated the migration of osteoblast-like cells in a dose-dependent fashion, as assayed in the Boyden chamber. In contrast, comparable extracts of normal adult bone (40-year-old male) did not stimulate osteoblast migration. Monocytes, potential osteoclast precursors, did not migrate in response to either of these extracts. These studies suggest that significant differences exist in protein composition and/or distribution between fetal and adult human bones. These differences may well influence the remodeling potential of these bones.

Alkaline phosphatase (AP) has been demonstrated by combined electron microscopy and histochemistry in a transplantable rat osteogenic sarcoma, using a modified Gomori technique (Salomon,1974). During the early stages of growth of subcutaneously implanted tumors, AP was detected in intracellular membrane systems resembling Golgi and on membranes of cells and matrix vesicles. During growth of the tumor, there was extensive development of intercellular collagen, and AP was demonstrated in bodies associated with collagen. In some cases the AP-containing bodies resembled matrix vesicles, but there was considerable size heterogeneity of the AP-containing bodies, suggesting that there may be heterogeneity of matrix vesicles. The amount of detectable AP seemed to increase in all areas of the tumor which were viable, during tumor growth, but no AP could be detected in cell debris of necrotic areas of the tumor (area C) nor associated with collagen in that area. Area D, particularly during later stages of tumor growth, showed the greatest development of calcium deposits, with calcium spicules apparently associated with AP-containing bodies on both cell membranes and collagen. AP-containing bodies also appeared in large numbers in venules during later stages of tumor growth, associated with an amorphous material. This may account for the increase in serum AP activity which occurs during later stages of growth of transplanted tumors. The sites of AP activity in this osteogenic sarcoma were similar to those described in normal tissue, but generally seemed to be more abundant.