Calcified Tissue Research最新文献

Explants from embryonic rat and mouse calvaria were cultivated in the presence of different concentrations of 1, 25-dihydroxycholecalciferol (1, 25-(OH)2D3). The bone resorbing effects of the vitamin D3 metabolite were evaluated by measuring the release of calcium, phosphate, lactate and citrate into the culture medium after 24 h of cultivation. The influence on bone morphology was studied using embryonic mouse radii, in which histological phenomena in the bony, cartilagenous and connective tissue compartments were observed. Both kinds of experiments show that 1, 25-(OH)2D3 has effects on embryonic bone which are typical for high concentrations of parathyroid hormone (PTH). However, the maximal effects on calcium release and on histology are 2.5 times less than those of PTH. In addition, some of the histological features such as the effects on epiphyseal cartilage and on osteoclasts were not observed. 1, 25-(OH)2D3 in concentrations up to 2 X 10(-9) M does not affect basal or PTH-stimulated cAMP levels in embryonic rat calvaria. In a concentration of 1 X 10(-8) M, however, a significant decrease in PTH-stimulated cAMP production was found. It is concluded from these in vitro experiments that (1) 1, 25-(OH)2D3 stimulates bone resorption, and (2) in 1, 25-(OH)2D3-induced bone resorption cAMP is apparently not involved as a second messenger.

Free radicals generated in synthetic apatitic calcium phosphates by X-ray radiation were investigated by electron spin resonance (ESR) spectroscopy. Among the species stable enough at -188 degrees C to be identified were hydrogen atoms, phosphate radicals, and oxygen anion radicals. The ESR spectra were markedly dependent on the specific surface of the mineral. Oxygen radicals dominated the spectra of low specific surface samples while phosphate radicals were the predominant species at higher specific surfaces. Our studies suggest that the oxygen radicals are more stable in the bulk of the crystal while the hydrogen atoms and the phosphate radicals are stabilized at or near the crystal surface. It was concluded that the surface species are potentially capable of serving as probes of biologically relevant mineral-organic interfaces.

The commercial collagenase from Clostridium histolyticum was adsorbed on hydroxyapatite, on bovine femur shaft and on enamel and dentin powders. The substrate specificity of the adsorbed enzyme tested, with chromophore substrate, azocoll and native collagen, differed from that obtained with the soluble enzyme. The adsorption and the substrate specificity was also dependent on the adsorbent used. A pretreatment of hydroxyapatite with chondroitin sulphate, hyaluronate and DNA lowered the adsorption of collagenase. Phosphate ion caused desorption of the enzyme from hydroxyapatite. Sodium fluoride caused partial desorption of the enzyme from hydroxyapatite and enamel and dentin powders. Colangenase adsorbed on root surfaces of teeth liberated hydroxyproline containing material.

The relative importance of genetic factors in the pathogenesis of age related bone loss has been investigated in a study involving 17 monozygotic (MZ) and 8 dizygotic (DZ) pairs of twins aged 64 to 75 years. Radiographic morphometry was performed at the midpoints of the 2nd, 3rd and 4th metacarpals of both hands and the mean total and cortical widths were evaluated. The heritability, h2, was calculated as the difference between the intrapair variances in same sexed DZ and MZ pairs divided by the intrapair variance in DZ pairs. The mean intrapair variance of both total and cortical width was found to be four to five times higher in DZ than in MZ pairs. The differences are highly significant with an h2 value between 0.7 and 0.8, indicating a predominant genetic influence. It is stressed that this result applies only to the population from which the twin sample was drawn.

Low temperature ashing by excited gas (LTA) causes crystallographic and paramagnetic alterations of the human bone and tooth enamel mineral. On the one hand, LTA induces variations of the alpha lattice parameter. These variations depend upon the nature of the gas used, but are little affected by its degree of excitation. Trapping of gas molecules in the crystal structure is demonstrated. On the other hand, LTA produces two preponderant paramagnetic centers in bone and enamel samples at 20 degrees C. Their inorganic origin clearly indicated. One of the two radicals has been identified as O3- (g1 = 2.002, g2 = 2.010, g3 = 2.016) and the other as (CO3-3 (parallel = 1.996, g = perpendicular 2.003). Variations of the alpha lattice parameter and trapping of paramagnetic gas species do not seem to be directly related.

An experiment originally done by McElhaney et al. was repeated to obtain additional information about the effects of electrical fields on osteoporosis of disuse. The right femurs of 35 male rats were immobilized in plaster casts. Sixteen rats were treated with transcutaneous electrical fields of 30 Hz and approximately 100 V/cm for periods of 2 or 8 h a day. While the right femurs of the untreated rats were found to be atrophic with respect to the opposite limb, in the treated rats the immobilized femur was made larger than the opposite bone. Longer daily treatments exaggerated this effect. The tumors found in the previous study were not seen in our experiments. Other similarities and differences in the 2 studies are discussed.