Ex vivo detection of calcium phosphate and calcium carbonate in rat blood serum

The total calcium (tCa) in blood serum comprises free Ca²⁺ ions (fCa), protein-bound calcium (prCa), and complexed calcium by small anions (cCa). The cCa fraction, in addition to fCa, has been indicated to have some physiological activity. However, there is little evidence for the structure of its constituents. Here we report an ex vivo detection of the cCa constituents by synchrotron X-ray absorption near-edge structure spectroscopy. We collected the data directly on rat blood serum and, by making use of the reference samples, derived a spectrum that exhibits the features of cCa constituents. Among the features are those of the complexes of calcium phosphate and calcium carbonate. The detected complexes in the cCa fraction are mainly Ca(η²-HPO₄)(H₂O)₄ and Ca(η¹-HCO₃)(H₂O)₅⁺, in which HPO₄^2? and HCO₃^? serve as bidentate and unidentate ligands, respectively. The remained H₂O molecules on the coordination sphere of Ca²⁺ enable these complexes to behave partially like aquated Ca²⁺ ions in protein-binding. Besides, as the dominant part of prCa, albumin-bound calcium (albCa) exhibits a spectrum that closely resembles that of fCa, indicating weak interactions between the protein carboxyl groups and calcium. The weak-bound cCa and albCa, along with fCa and the relevant anions, compose a local chemical system that could play a role in maintaining the calcium level in blood.     

Laboratory studies on the coprecipitation of phosphate with calcium carbonate in the Salton Sea, California

The Salton Sea is a hypereutrophic, saline lake in the desert of southern California. Like many lakes, the primary productivity of the Sea is limited by phosphorus. However, unlike most lakes, the release of P from the sediments is not controlled by the reductive dissolution of Fe(III)-oxide minerals. Most of the iron in the sediments of the Salton Sea is present as Fe(II)-sulfides and silicates. Rather, the sediments are dominated by calcite which is actively precipitating due to alkalinity production via sulfate reduction reactions. We hypothesized that calcite could be an important sink for phosphorus released from the decomposing organic matter. In this work we evaluated the potential for phosphate to coprecipitate with calcite formed in simulated Salton Sea sediment pore water. At calcite precipitation levels and P concentrations typical for the Salton Sea pore water, coprecipitation of P removed 82–100% of the dissolved phosphorus. The amount of P incorporated into the calcite was independent of temperature. The results of this work indicate that the internal loading of P within the Salton Sea is being controlled by calcite precipitation. Management of external P loading should have an immediate impact on reducing algae blooms in the Salton Sea. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife, and People, 1905–2005, held in San Diego, California, USA, March 2005     

In vitro studies of human and rat osteoclast activity on hydroxyapatite,beta-tricalcium phosphate,calcium carbonate

Investigations on the ceramic degradation caused by osteoclasts are designed to assess osteoclast-ceramic interactions and to determine which ceramics are more suitable for use as bone substitute. This study investigated the resorptive activity of osteoclasts on ceramics presenting different solubility rates. Osteoclasts isolated from new-born rat and from human giant cell tumour were cultured on different bioceramics: hydroxyapatite (HA), beta-tricalcium phosphate (TCP) and calcium carbonate (calcite). Cytoskeletal was revealed by actin labelling and ceramic surfaces were observed by scanning electron microscopy (SEM). On all materials, the distribution of actin in typical ring was revealed. SEM examinations showed a clear difference in the shape and the depth of resorption lacunae on different ceramics. On pure HA, a superficial attack, clearly visible but very little extended. Numerous resorption lacunae, deep and well-delimited were observed on pure beta-TCP, but attacks less punctually were detected too. On pure calcite, an attack with form of spikes, very widespread but superficial was revealed. Degradation measurements revealed a significant increase of P release from the phosphocalcic ceramics and of Ca from all ceramics in the presence of osteoclasts. The both cell models found these characteristics, the rat osteoclasts were also an excellent model to study the ceramic resorption.     

The efficacy of exogenous and endogenous interferonization in preventing influenza]

In this work the results of using interferon (IFN), Dibasol and the combination of these preparations for the urgent prophylaxis of influenza and acute respiratory diseases (ARD) among the employees of the Gamaleia Research Institute of Epidemiology and Microbiology (USSR Acad. Med. Sci.) are summarized. Reaferon and Dibasol decrease ARD morbidity 2 times and leukocytic IFN decreases it 1.4 times, while the combined administration of Dibasol and IFN has proved to be ineffective. Reaferon is mainly a prophylactic remedy; it has been found to bring about almost no decrease in the number of patients at the peak of morbidity, while pronouncedly decreasing it in two weeks after the administration of the preparation. Dibasol has a curative effect, sharply interrupting the beginning rise of morbidity. Reaferon normalizes the characteristics of the IFN status, decreasing the amount of circulating IFN and enhancing the capacity of leukocytes for producing alpha-IFN and gamma-IFN. For the prophylaxis of respiratory infections the use of Reaferon is advisable 3-4 weeks prior to the beginning of the epidemic and then, when the first cases of infection are registered, the course of prophylaxis with Dibasol should be carried out.     

Interactions between acidic matrix macromolecules and calcium phosphate ester crystals: relevance to carbonate apatite formation in biomineralization.

Control over crystal growth by acidic matrix macromolecules is an important process in the formation of many mineralized tissues. Earlier studies on the interactions between acidic macromolecules and carboxylate- and carbonate-containing crystals showed that the proteins recognize a specific stereochemical motif on the interacting plane. Here we show that a similar stereochemical motif is recognized by acidic mollusc shell macromolecules interacting with four different organic calcium phosphate-containing crystals. In addition, an acidic protein from vertebrate tooth dentin was also observed to recognize a similar structural motif in one of the crystals. The characteristic motif recognized is composed of rows of calcium ions and phosphates arranged in a plane defined by two free oxygens and a phosphorus atom emerging perpendicular to the affected face. These observations may have a direct bearing on the manner in which control over crystal growth is exerted on carbonate apatite crystals commonly found in vertebrate tissues.     

In vivo efficacy of tobramycin-loaded synthetic calcium phosphate beads in a rabbit model of staphylococcal osteomyelitis

Background

Osteomyelitis is an acute or chronic inflammatory process of the bone following infection with pyogenic organisms like Staphylococcus aureus. Tobramycin (TOB) is a promising aminoglycoside antibiotic used to treat various bacterial infections, including S. aureus. The aim of this study was to investigate the efficacy of tobramycin-loaded calcium phosphate beads (CPB) in a rabbit osteomyelitis model.

Methods

Tobramycin (30 mg/mL) was incorporated into CPB by dipping method and the efficacy of TOB-loaded CPB was studied in a rabbit osteomyelitis model. For juxtaposition, CPB with and without TOB were prepared. Twenty-five New Zealand white rabbits were grouped (n?=?5) as sham (group 1), TOB-loaded CPB without S. aureus (group 2), S. aureus only (group 3), S. aureus?+?CPB (group 4), and S. aureus?+?TOB-loaded CPB (group 5). Groups infected with S. aureus followed by CPB implantation were immediately subjected to surgery at the mid-shaft of the tibia. After 28 days post-surgery, all rabbits were euthanized and the presence or absence of chronic osteomyelitis and the extent of architectural destruction of the bone were assessed by radiology, bacteriology and histological studies.

Results

Tobramycin-loaded CPB group potentially inhibited the growth of S. aureus causing 3.2 to 3.4 log₁₀ reductions in CFU/g of bone tissue compared to the controls. Untreated groups infected with S. aureus showed signs of chronic osteomyelitis with abundant bacterial growth and alterations in bone architecture. The sham group and TOB-loaded CPB group showed no evidence of bacterial growth.

Conclusions

TOB-incorporated into CPB for local bone administration was proven to be more successful in increasing the efficacy of TOB in this rabbit osteomyelitis model and hence could represent a good alternative to other formulations used in the treatment of osteomyelitis.

     

Effect of dietary phosphate on intestinal calcium and phosphate absorption

Intestinal Ca and P absorption was investigated on rachitic chicks raised on diets with a 1% Ca and 0.3% or 1% P contents. 45Ca and 32P absorption was determined by the technique of the isolated gut sac in vivo. In addition, 32P transport was also measured by the everted gut sac procedure in vitro. Treatment with vit. D3 during 7 days increased the 45Ca absorption in animals fed diets containing 0.3% or 1% P. 32P absorption showed an increase after 2 days of treatment and a decrease afterwards. The reduction of 32P absorption was larger in animals fed diet with 1% P. Study of 32P transport with the everted gut sac technique showed an increase after vit. D3 and a loss of intracellular P, regardless the duration of treatment.     

Biomineralization of carbonate and phosphate by moderately halophilic bacteria

We investigated the precipitation of carbonate and phosphate minerals by 19 species of moderately halophilic bacteria using media with variable Mg(2+)/Ca(2+) ratios. The precipitated minerals were calcite, magnesium (Mg) calcite, and struvite (MgNH(4)PO(4) x 6H(2)O) in variable proportions depending on the Mg(2+)/Ca(2+) ratio of the medium. The Mg content of the Mg-calcite decreased with increasing Ca(2+) concentration in the medium. According to the saturation indices, other minerals could also have precipitated. We observed important differences between the morphology of carbonate and phosphate, which may help us to recognize these minerals in natural systems. We studied the growth and pH curves of four bacteria in media specific for carbonate and struvite precipitation. We consider the biomineralization processes that produce carbonate and phosphate minerals, and propose a hypothesis for the lack of struvite in natural environments and ancient rocks.