Presence Of Osteoblasts Research Articles

The effect of dietary vitamin D metabolites and zinc on normal and ectopic bone formation in weanling rats

The effect of dietary supplementation of rats with vitamin D metabolites and zinc was examined in selected bones and a short-term in vivo implant model. A 2×2×3 factorial design was utilized with two vitamin D metabolites (cholecalciferol-D 3 or 1,25-dihydroxycholecalciferol-1,25(OH) 2D 3); two levels of dietary zinc (marginal-4.5, and adequate-10 ug/g diet); and three time periods (11, 14 and 21 days after implantation). Seventy-two female weanling Long-Evans rats were fed their respective diets for three weeks before subcutaneous implantation with demineralized bone powder. The animals were injected intraperitoneally with 45Ca (0.5uCi/g body weight) 14 h before sacrificing. The ectopic bone implants as well as the femurs, tibias, humeri, scapulas and mandibles were obtained 11, 14 and 21 days following implantation. Implants were fixed, sectioned and stained with toluidine blue. The specific bones and the implants were analyzed for calcium, zinc and 45Ca. There was higher calcium concentration in the femurs of animals fed D 3 compared to 1,25(OH) 2D 3. Activities of enzymes (alkaline phosphatase-marker for formation, and acid phosphatase-marker for resorption) were quantitated in the implants. Enzyme activities, mineral deposition and presence of osteoblasts and osteoclasts all provided definitive evidence that the implant system was mimicking the typical dynamic processes normally occurring in bone tissues. An interaction between the form of vitamin D (D 3 vs 1,25(OH) 2D 3) and level of zinc fed to the rats was demonstrated in the implants; calcium and zinc concentrations were higher in the implants of rats fed D 3 and adequate zinc than rats fed 1,25(OH) 2D 3 and adequate zinc. In summary, adequate dietary zinc concentration modulates the effects of vitamin D metabolites; also D 3 form has a greater anabolic effect on integrity of the bone than 1,25(OH) 2D 3. Furthermore, femur appears to be more sensitive than the other bones tested to changes in calcium concentration due to the two forms of vitamin D.

IL-1 binds to high affinity receptors on human osteosarcoma cells and potentiates prostaglandin E2 stimulation of cAMP production.

IL-1 is a potent bone resorbing agent. Its mechanism of action is unknown, but the presence of osteoblasts was shown to be necessary for IL-1 stimulation of bone resorption by isolated osteoclasts. This study examines the presence of IL-1R and IL-1 effects in osteoblastic cells from a clonal human osteosarcoma cell line, Saos-2/B-10. We found that the binding affinity and the number of binding sites increases substantially during the postconfluent stage. Scatchard and curve-fitting analysis revealed one class of high affinity binding sites, with Kd/Ki's of 40 +/- 17 pM (mean +/- SD) for IL-1 alpha (n = 5) and 9 +/- 7 pM for IL-1 beta (n = 5) and 2916 +/- 2438 (n = 6) receptors/cell. Incubation of the cells with 125I-IL-1 alpha (100 pM) at 4 degrees C, followed by incubation at 37 degrees C up to 4 h, revealed internalization of receptor-bound IL-1 alpha. Chemical cross-linking studies showed that the IL-1R in Saos-2/B-10 cells had a molecular mass of approximately 80 kDa. To assess the biologic effect of IL-1 in Saos-2/B-10 cells, we determined PGE2 content and adenylate cyclase activity. Although IL-1 had no effect on PGE2 synthesis, both IL-1 alpha and IL-1 beta enhanced PGE2 stimulation of adenylate cyclase two- to four-fold in a dose-dependent manner. The half-maximal effect for IL-1 alpha was seen at 8 to 10 pM and for IL-1 beta at 0.6 to 1.8 pM. IL-1 did not enhance basal adenylate cyclase or stimulation by parathyroid hormone, isoproterenol, or forskolin. IL-1 enhancement of PGE2-stimulated adenylate cyclase was detected between 1 to 2 h, was maximal at 4 to 5 h, was not prevented by cycloheximide treatment, and was seen in membranes from IL-1 pretreated cells. These data show effects of IL-1 on a human osteoblast-like cell line that are mediated by high affinity receptors. These IL-1 effects could contribute to the biologic action of IL-1 on bone.

Bone histology in young adult osteoporosis.

Bone histology was quantitated in 10 osteoporotic patients aged between 17 and 51 years and in six healthy subjects aged between 23 and 43 years. The osteoporosis was of varying aetiology and was clinically stable. All patients were given tetracycline before biopsy and double tetracycline labelling was used in seven patients. Bone forming and resorbing surfaces were defined by the presence of osteoblasts and osteoclasts, respectively, which were identified by histochemical techniques. The associations between bone forming and resorbing surfaces were similar in patients and controls, though the range of values was wider in the patients than in the controls. Mineral apposition rate was normal in the osteoporotic patients, but there was a reduction in mineralising (tetracycline) surface, whether related to osteoid surface or to osteoblast surface. This did not indicate osteomalacia as the directly and indirectly measured mineralisation lag times were normal. The osteoid seams were thinner in osteoporotic patients than in controls. The data suggest that osteoclast and osteoblast numbers were normal in this group of osteoporotic patients but that the metabolic activity of osteoblasts was impaired.

In situ localization of collagen production by chondrocytes and osteoblasts in fracture callus.

An experimental model of fracture-healing was used to study the production of types-I and II collagen by in situ hybridization. The distribution of cartilage matrix in callus was determined by histochemical staining. Messenger RNA (mRNA) for cartilage-specific type-II collagen was detectable as early as the fifth day in a small number of cells that had acquired a chondrocyte phenotype but that also contained type-I collagen mRNA, suggesting an ongoing change in the expression of collagen genes. The location of the first chondrocytes, which were adjacent to cortical bone, suggested that they originated from cells that had derived from the periosteum by differentiation. On the seventh day of callus formation, the presence of both type-I and type-II collagen mRNA in chondrocytes of expanding cartilage suggested that most growth occurred by differentiation of mesenchymal cells and less by proliferation of differentiated chondrocytes. Expansion continued until the tenth to fourteenth day, after which the cartilage was replaced by woven bone. This was characterized by the presence of osteoblasts that were active in the synthesis of type-I collagen.

Ultrastructure of osteoblastoma

The ultrastructure of three cases of osteoblastoma is described. The osteoblasts resemble normal osteoblasts with a few exceptions: irregular, indented nuclei, and occasional mitochondria with curved cristae and electron-lucent areas. The osteocytes and osteoclasts basically resemble their normal counterparts. There are also osteoprogenitor cells in different stages of maturation, some containing glycogen. The ultrastructure of an additional case histologically classified as aggressive osteoblastoma is described. It is essentially similar to the previous three cases of typical osteoblastoma. The only exception is the presence of osteoblasts with electron-lucent nuclei and less prominent organelles than the typical osteoblastoma cells have markedly indented and multilobed nuclei, dilated rough endoplasmic reticulum and lipid droplets. However, these differences from osteoblastoma cells are not pathognomonic. The final diagnosis of osteoblastic tumors rests at the light microscopy level.

Comparison of Regional Bone Blood Flow in Areas with Differing Osteoblastic Activity in the Rabbit Tibia

The relationship between regional bone blood flow (measured using the hydrogen washout method) and regional osteoblastic activity (inferred from presence of osteoblasts on histological sections) was studied in the rabbit tibia. The rate of blood flow in epiphyses with marked osteoblastic activity (0.283 +/- .053 ml/min/ml) was significantly faster than that in epiphyses with minimal activity (0.097 +/- .007 ml/min/ml). Metaphyseal blood flow was significantly faster in areas with marked activity (0.253 +/- 0.040 ml/min/ml) than those with moderate (0.153 +/- .007 ml/min/ml) or minimal (0.126 +/- 0.013 ml/min/ml) osteoblastic activity. Diaphyseal bone blood flow was significantly faster in immature (0.082 +/- 0.005 ml/min/ml) than in mature (0.062 +/- 0.004 ml/min/ml) animals. The results indicate that there is a positive association between regional bone blood flow rate and osteoblastic activity in normal bone.

Visualization of cellular dynamics associated with orthodontic tooth movement

ORTHODONTIC tooth movement appears to be dependent upon the presence Of osteoblasts and osteoclasts within the periodontal ligament and adjacent bone.l-’ A force applied to a tooth creates areas of pressure and tension. In areas of pressure, bone resorption, in association with the appearance of osteoclasts, is stimulated. In areas of tension, osteoblasts arise and form osteoid, which is subsequently calcified. The bone remodeling process allows the tooth to move and thus maintain the physiologic width of the periodontal ligament.lm7 It has been presumed that osteoblasts and osteoclasts a,re derived from the proliferation and differentiation of undifferentiated mesenchymal cells, since increased mitotic activity of mesenchymal cells is observed in the supporting tissues of a tooth subjected to an orthodontic force.*, 3l 7 In fact, however, the histogenesis of these cells is in doubt. On the other hand, cellular proliferation can be documented by the use of radioactive precursors of DNA, because DNA is duplicated during cell division. The appearance of radioactivity within cell nuclei indicates the presence of “new” DNA which had been synthesized in an early phase of the process of cell division.8 Therefore, using a DNA precursor, tritiated thymidine, we investigated the role of cellular proliferation during orthodontic tooth movement, with emphasis on the formation of osteoclasts and osteoblasts.