Bone healing response to a synthetic calcium sulfate/ß-tricalcium phosphate graft material in a sheep vertebral body defect model.

The introduction of a material able to promote osteogenesis and remodelling activity in a clinically relevant time frame in vertebroplasty and kyphoplasty procedures may have patient benefit. We report the in-vivo performance of a biphasic synthetic bone graft material (Genex Paste, Biocomposites, UK) [test material], composed of calcium sulfate and ß-tricalcium phosphate, implanted into a sheep vertebral defect model. Cavities drilled into 4 adjacent vertebrae (L2 to L5) of 24 skeletally mature sheep were; (1) filled with the test material; (2) filled with commercially available polymethylmethacrylate [PMMA] cement; (3) remained empty [sham]. Analysis was performed immediately after implantation and at 8, 16, and 36 weeks post implantation. Sites were evaluated for bone growth with microCT analysis, histological examination, and mechanical testing under compression. The test material exhibited an improved tissue response over the PMMA, indicating a superior biological tolerance. MicroCT and histology indicated marked osteoregenerative capacity of the test material when compared with sham and the PMMA. The percentage of new bone formation was higher for the test material than sham at 16 and 36 weeks post implantation, with bone regeneration almost complete at 36 weeks in this group. Resorption of test material and the integration into new bone tissue were demonstrated.

The effect of static magnetic fields on the rate of calcium/calmodulin-dependent phosphorylation of myosin light chain.

This study reports an attempt to confirm a published and well-defined biological effect of magnetic fields. The biological model investigated was the phosphorylation of myosin light chain in a cell free system. The rate of phosphorylation has been reported to be affected in an approximately linear manner by static magnetic field strengths in the range 0-200 microT. We performed three series of experiments, two to test the general hypothesis and a third that was a direct replication of published work. We found no effect of static magnetic field strength on the rate of phosphorylation. Hence, we were unable to confirm that weak static magnetic fields affect the binding of calcium to calmodulin. In view of the difficulty we and other authors have had making independent verifications of claimed biological effects of magnetic fields, we would urge caution in the interpretation of published data until they have been independently confirmed. There are still few well defined biological effects of low level magnetic fields that have been successfully transferred to an independent laboratory.

Magnetic fields and intracellular calcium: effects on lymphocytes exposed to conditions for 'cyclotron resonance'.

There are a number of claims in the literature that specific combinations of low-level DC and AC magnetic fields can cause biologically significant effects. The combinations of fields required to elicit these responses fulfil the theoretical conditions for classical cyclotron resonance of the selected ion. Because of the biological importance of calcium ions any effects on them are of particular interest, for instance the claimed increase in calcium uptake by electromagnetically exposed lymphocytes. We have measured the intracellular calcium concentration, by means of a sensitive fluorescent probe, during a 60 min exposure of mouse lymphocytes to 'cyclotron resonance' conditions for calcium ions. 'Resonance' conditions at two frequencies (16 Hz and 50 Hz) were tested, with a range of DC field amplitudes used to shift the frequency up to 25% either side of the calculated optimum. Treatment of the lymphocytes with concanavalin A was used as a positive control and caused a significant increase in intracellular calcium concentration. No change in intracellular calcium concentration could be detected when lymphocytes were exposed to 'cyclotron resonance' conditions or to the other magnetic field combinations used.

Fracture healing of chick femurs in tissue culture.

Embryonic chick femurs were isolated, and a transverse osteotomy was performed at the midshaft. The femurs were transplanted individually onto the host chorioallantoic membrane and incubation continued. Cultured femurs were harvested at intervals from 1 to 9 days after the transplant. Histologic examinations showed that repair progressed rapidly: the fracture gap was invaded by blood vessels and fibrous ingrowth. Ossification followed, and the repair process was completed by Day 9.

The effect of low-frequency pulsed magnetic fields on chick embryonic growth.

There are many claims made for biological effects of low-frequency pulsed magnetic fields ranging from beneficial to harmful, but few have been independently verified. The ubiquitous nature of both natural and man-made magnetic fields makes the possibility of biological interaction a potentially important subject. We have investigated the claimed stimulatory action of low-frequency pulsed magnetic fields, of a type used clinically, on the growth of embryonic chicks. Four day old embryos were exposed to a magnetic field, peak field strength 2.1 mT pulsed in 5 ms bursts repeated at 15 Hz, for 100 h. Embryo weights and long-bone lengths were compared to sham-exposed controls. Particular care was taken to reduce temperature differences between the test and control groups because this model has a known sensitivity to small temperature changes. We found no increase in embryonic growth due to this low-frequency pulsed magnetic field and hence have been unable to confirm earlier findings by other workers using the same model. We conclude that rigorous design of experimental protocol and a full description of the physical parameters are essential in studies purporting to show effects of electromagnetic fields if the results are to be confirmed by other workers.

An evaluation of serum osteocalcin in Paget's disease of bone and its response to diphosphonate treatment.

We found that serum bone gamma-carboxyglutamic acid-containing protein (BGP) (osteocalcin) had lower sensitivity and specificity for measurement of disease activity in Paget's disease of bone than other biochemical measures of disease activity. The administration of diphosphonates induced suppression of urinary hydroxyproline excretion and a subsequent decrease in alkaline phosphatase values, but no consistent change in BGP values. Serum BGP measurements have limited value as a screening test for Paget's disease or for monitoring treatment of the disorder.

An ultrastructural study of alkaline phosphatase in a transplantable rat osteogenic sarcoma.

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.

The assessment of DNA-synthetic activity.

A method is described by which a numerical value can be assigned to the amount of DNA-synthesis shown graphically by population-histograms obtained by Feulgen cytophotometry. The index appeared to give a reasonable measure of DNA-synthetic activity in populations having very low, moderate and high mitotic indices and closely followed labelling indices obtained by autoradiography. Thus the advantage of a numerical value is that the DNA-synthetic activities in different populations can be compared for statistical analysis.

DNA synthesis in human rheumatoid and nonrheumatoid synovial lining.

The DNA content per nucleus has been measured in the lining cells of 12 specimens of rheumatoid and 12 of nonrheumatoid synovial tissue. Optimal conditions for this reaction on these cells have been defined, and an index of DNA synthesis has been applied to give a quantitative measure of the degree of synthesis. This has given evidence of some DNA synthesis in both types of synoviocytes, compatible with the amount found in a slowly self-replacing tissue. There was no difference in the amount of synthesis in the rheumatoid and nonrheumatoid synoviocytes.

Metabolic properties of hormonally responsive osteogenic sarcoma cells.

There is sufficient impetus from the clinical nature of osteogenic sarcoma to stimulate basic studies of the effects of hormones on tumor growth and differentiation. This can probably best be done first by the use of in vitro studies to determine precisely the effects of certain hormones on tumor cell growth and biochemical function. Such investigations would hopefully indicate the direction of in vivo work. The differentiated transplantable tumor described in this paper is clearly hormone-responsive, and offers a means of investigating the effects of other hormones, including growth hormone, androgens, estrogens and glucocorticoids, on specialized function of the osteogenic sarcoma cells, and on the growth of the tumor.

Radiation induced osteogenic sarcoma in the rat as a model of hormone-responsive differentiated cancer.

An osteogenic sarcoma was induced in an inbred strain of the Sprague Dawley rat using seven serial injections of 32P-orthophosphate. The tumor was maintained by transplantation over a 3-year period in the same inbred strain. During this time it retained its bone-like differentiation. Tumor membranes and freshly isolated tumor cells also retained responsiveness to parathyroid hormone and to prostaglandins of adenylate cyclase and cyclic nucleotide formation respectively. The potencies of these agents and their analogues and metabolites were found to be proportional to their efficacies as bone resorbing agents. Thus, the tumor was shown to be a model for the study of hormone-responsiveness for tumor growth and differentiation, and also of the effects of agonists which act on bone-like cells.

Temporal relationship between glucose 6-phosphate dehydrogenase activity and DNA-synthesis.

Wounds have been inflicted in the skin of guinea-pigs. Measurements were made on the basal cells 39-54 h later, at different times of the day. It has been shown that there can be two peaks of mitosis, one about mid-day and the other about 22 h. Synthesis of DNA, measured by Feulgen microdensitometry, preceded mitotic activity. Marked changes were found in glucose 6-phosphate dehydrogenase activity, measured by quantitative cytochemistry and microdensitometry. The greatest activity preceded DNA-synthesis, indicating that pentose-shunt metabolic activity is involved in biosynthetic processes required for cell proliferation.