Comparison of bone formed intramuscularly after transplantation of scapular and calvarial osteoblasts

Previous work suggested that osteoblasts determine the size of the bone marrow area within the bone and that calvarial osteoblasts differ from those induced intramuscularly by cartilage formed by transplanted epiphyseal chondrocytes. This study reports morphological observations of bone formed by transplanted scapular and calvarial osteoblasts isolated from bones of young rats. In intact scapulas of 28-day-old rats the percentage area occupied by bone tissue in relation to bone marrow was 6 times larger than in parietal bones of comparable age. Isolated syngeneic scapular osteoblasts usually produced an ossicle with similar general structure and ratio bone tissue/bone marrow area as in intact scapulas. In transplants of calvarial osteoblasts numerous islands of bone tissue with a small amount of bone marrow appeared. Bone formed in allogenic transplants was rejected. These results suggest that osteoblasts from endochondral scapular bone may have different properties than those from intramembranous calvarial bones. Alternatively, the large amount of medullary space in bone produced by transplanted scapular osteoblasts could result from their contamination with bone marrow stromal cells.

Structural differences between bone formed intramuscularly following the transplantation of isolated calvarial bone cells or chondrocytes

Bone formed in intramuscular transplants of isolated syngeneic calvarial bone cells in mice, was compared with endochondral bone induced by cartilage produced by analogous transplants of isolated epiphyseal chondrocytes, as well as with parietal bones forming the bulk of the calvaria. Transplanted calvarial cells produced islands of bone, some of which contained intraosseous cavities. Osteoclasts inside these cavities were observed only in 14-day-old transplants and bone marrow cells in 28-day and older transplants. On the contrary, bone marrow appeared soon after formation of bone trabeculae in endochondral bone. The percentage area occupied by bone marrow in these specimens was about twentyfold larger than in the bone formed by transplanted bone cells. On the other hand, the bone marrow area in the latter type of bone was somewhat smaller but of similar order as in parietal bones. Moreover, both in parietal bones and in bone formed by isolated bone cells, the bone marrow was devoid of fat cells which were numerous in bone arising by endochondral ossification. It appears, therefore, that the ratio of bone marrow to the bone tissue area in parietal bones depends more on the intrinsic properties of osteoblasts than on the local factors in the environment of the developing bone. In the case of bone induced by cartilage, the bone marrow/bone tissue area could be determined both by the extent of cartilage resorption by vascularized tissue and by the properties of osteoblasts.

Natural cell-mediated cytotoxic activity against isolated chondrocytes in the mouse

The ability of lymphoid cells from normal mice to exert a natural cytotoxic activity against isolated syngeneic and allogeneic epiphyseal chondrocytes was studied by means of 51Cr release assay. We found, that both spleen and peritoneal cells, but not thymocytes, exerted an anti-chondrocyte cytotoxic effect. Addition of unlabelled chondrocytes markedly reduced experimental 51Cr release and the inhibitory effect was proportional to the number of 'cold' cells added. This indicate, that chondrocyte lysis was due to specific effector-target interaction. As no cytotoxicity was observed against isolated fibroblasts, our results could not be explained by lysis of fibroblasts contaminating chondrocyte cultures.

Inhibition of tumour-induced angiogenesis by systemically administered protamine sulphate

Systemic administration of protamine sulphate significantly decreased the intensity of angiogenesis induced in X-ray immunosuppressed (BALB/c X DBA/2W) F1 mice by either HEp-2 (human larynx carcinoma) cells or semi-syngeneic splenocytes injected intradermally. In vitro experiments have shown that protamine sulphate markedly decreases the proliferation of human endothelial cells as assessed by 3H-TdR incorporation assay. In contrast, the proliferation of HEp-2 cells was not affected, and only slight inhibition of normal human fibroblasts could be demonstrated. Heparin abolished the inhibitory effect of protamine sulphate, both in vivo and in vitro. These results suggest that the observed inhibitory effect of protamine sulphate on angiogenesis in vivo may be at least partially due to the interaction of this compound with endothelial cells.