Bovine bone activin enhances bone morphogenetic protein-induced ectopic bone formation.

A 25-kDa homodimeric protein was purified from demineralized bovine bone extract and identified as activin A. The bovine bone activin enhanced formation of ectopic bone in rat subcutis when implanted in combination with partially purified bovine bone morphogenetic protein (BMP-2, BMP-3) in collagen/ceramic carrier. The implants, removed at 14 days, contained markedly elevated levels of alkaline phosphatase activity. Histological examination revealed an extensive formation of woven bone with very little cartilage. In contrast, a combination of transforming growth factor-beta 2 and BMP promoted formation of bone with an abundance of cartilage. The implants with BMP alone exhibited some osteoinductive activity, while the implants with activin alone showed no activity. These results demonstrate that bone is a rich source of activin and that activin plays an important role in modulating bone formation.     

Photoconductivity in bone and tendon.

Ultraviolet light can be used to stimulate electrical current flow in bone and tendon. This stimulated photocurrent is directional. In tendon the photocurrent parallel to the fibrils is greater than the photocurrent perpendicular to the fibrils. In bone, the longitudinal photocurrent is less than the transverse photocurrent.     

Phosphoproteins of chicken bone matrix. Proof of synthesis in bone tissue

Twelve-day-old embryonic chick mandibles were cultured in vitro for 6 days. Measurements of the weights of the explants, their mineral and protein components, and the EDTA-extractable proteins established that bone tissue synthesizes O-phosphoserine- and O-phosphothreonine-containing phosphoproteins which are similar to those present in embryonic and postnatal chicken bone matrix. The synthesis of the phosphoproteins was further confirmed by the demonstration that radioactively labeled O-phosphoserine and O-phosphothreonine were identified in bone and in the EDTA-extractable phosphoproteins after pulse-labeling chick mandibles in vitro with radioactively labeled serine and threonine, respectively.     

Fatty acid oxidation in bone tissue and bone cells in culture. Characterization and hormonal influences.

Fatty acid oxidation and its hormonal modulation were investigated in cultured rat calvaria and in cultivated cell populations. The latter were obtained from calvaria of newborn rats by sequential time-dependent digestion with collagenase, yielding eight cell populations: the early ones containing mainly fibroblasts, the middle ones being osteoblast-like, and late ones osteoblast-osteocyte-like. In calvaria, fatty acid oxidation was increased by adding 0.1 mM- and 1.0 mM-palmitate to the medium, containing 10% (v/v) fetal-calf serum. No effect was found after parathyrin addition in vitro or when injected in vivo. All cell populations obtained by sequential digestion were found to oxidize palmitate, whereby the osteoblast-like cells showed a lower oxidation rate than the other populations. Both parathyrin and calcitonin had no effect on fatty acid oxidation. 1,25-Dihydroxycholecalciferol at 1-100 nM and 24,25-dihydroxycholecalciferol at 100 nM increased oxidation primarily in the population enriched with osteoblast-like cells. Insulin at 1.6 microM diminished it in the cell populations enriched with osteoblast-like cells and in the late bone-cell fraction. However, glucagon had no effect. The energy provided by fatty acid oxidation in this system is approx. 40-80% of glucose metabolism, suggesting that this event may be of importance in the energy metabolism of bone.     

Thermographic stress analysis in cortical bone.

Under adiabatic (or near adiabatic) conditions a volumetric change in an elastic material will produce a corresponding change in temperature. Based upon this principle, thermographic stress analysis (TSA) measures changes in surface heat flux (which are related to changes in surface temperature) and relates them to a coupled form of strains or stresses. To demonstrate the feasibility of using this technique for biomechanical applications, we thermographically measured heat flux from loaded specimens of cortical bone and correlated the results with strain gage data. Regular parallelepipeds were cut from the cortex of bovine femora and loaded sinusoidally at 20 Hz. At this rate of loading, mechanically induced changes in surface temperature could be sampled (via heat flux) prior to a measureable attenuation of the thermoelastic effect. Correlation coefficients demonstrated a significant linear relationship between TSA and measured and computed mechanical parameters (stress, strain, first strain invariant, and strain energy density). TSA therefore appears to be a promising technology for experimental stress analysis in cortical bone.     

A study on bone induction in hydroxyapatite combined with bone morphogenetic protein.

Our present study consisted of an implantation of artificially made hydroxyapatite (HAP) ceramic pellets under the periosteum of the rabbit skull with subsequent inspection of further progress of bone formation and also of an evaluation of the effects of bone morphogenetic protein (BMP). The results revealed that the alkali phosphatase (AL-P) activity of the pellets was elevated only in those of the bone morphogenetic protein group. The results of determination of bone mineral density at the site of the pellets revealed that the increase in bone mineral density was the most remarkable in the bone morphogenetic protein group rather than the control group. The results of the histopathologic examinations revealed that marginal bone formation was found in the pores on the surface between the pellets and the skull in the control group and in the collagen group, whereas in the bone morphogenetic protein group very active bone formation was found not only on the interface in contact with the skull but also surrounding the whole pellet. It also was noted in the animals in the bone morphogenetic protein group that the pellets were corrupted from the peripheries and then absorbed into the newly formed bone. From these results, the efficacy of the hydroxyapatite-collagen-bone morphogenetic protein complex was made clear, and applications in clinical practice are expected in the near future.     

Cortical bone measurements in Turner's syndrome.

Cortical bone width measurements taken at midshaft on the second metacarpal were obtained from 156 hand X-rays of 80 karyotypically documented individuals with Turner's syndrome age 1 to 25 years. Total shaft width, medullary width, cortical width and percent cortical area were grouped by bone age and compared with normal female standards. Total width was significantly and increasingly below normal; medullary width was not consistently different from normal; cortical width was significantly lower from normal from age 14 onward, although it did rise at age 17 (adult bone age); percent cortical area was significantly below normal at ages 14 and 15, but was normal by adulthood. Values for percent cortical area did not indicate severe or widespread osteoporosis. Within the Turners sample cortical bone measurement were not significantly decreased in the presence of the XO sex chromosome constitution compared with other sex chromosome variants. Nor were the measurements decreased in the presence of positive metacarpal sign or a combination of typical Turner stigmata (web neck, low posterior hairline, shield chest). There was evidence that cortical width and percent cortical area increased significantly following estrogen treatment or spontaneous menarche.