Dentin matrix protein 1 immobilized on type I collagen fibrils facilitates apatite deposition in vitro.
(17/221)
During bone and dentin mineralization, the crystal nucleation and growth processes are considered to be matrix regulated. Osteoblasts and odontoblasts synthesize a polymeric collagenous matrix, which forms a template for apatite initiation and elongation. Coordinated and controlled reaction between type I collagen and bone/dentin-specific noncollagenous proteins are necessary for well defined biogenic crystal formation. However, the process by which collagen surfaces become mineralized is not understood. Dentin matrix protein 1 (DMP1) is an acidic noncollagenous protein expressed during the initial stages of mineralized matrix formation in bone and dentin. Here we show that DMP1 bound specifically to type I collagen, with the binding region located at the N-telopeptide region of type I collagen. Peptide mapping identified two acidic clusters in DMP1 responsible for interacting with type I collagen. The collagen binding property of these domains was further confirmed by site-directed mutagenesis. Transmission electron microscopy analyses have localized DMP1 in the gap region of the collagen fibrils. Fibrillogenesis assays further demonstrated that DMP1 accelerated the assembly of the collagen fibrils in vitro and also increased the diameter of the reconstituted collagen fibrils. In vitro mineralization studies in the presence of calcium and phosphate ions demonstrated apatite deposition only at the collagen-bound DMP1 sites. Thus specific binding of DMP1 and possibly other noncollagenous proteins on the collagen fibril might be a key step in collagen matrix organization and mineralization. (+info)
Bone acidic glycoprotein-75 delineates the extracellular sites of future bone sialoprotein accumulation and apatite nucleation in osteoblastic cultures.
(18/221)
Addition of an organophosphate source to UMR osteoblastic cultures activates a mineralization program in which BSP localizes to extracellular matrix sites where hydroxyapatite crystals are subsequently nucleated. This study identifies for the first time novel extracellular spherical structures, termed biomineralization foci (BMF), containing bone acidic glycoprotein-75 (BAG-75), bone sialoprotein (BSP), and alkaline phosphatase that are the exclusive sites of initial nucleation of hydroxyapatite crystals in the UMR model. Importantly, in the absence of added phosphate, UMR cultures after reaching confluency contain two size populations of morphologically identifiable BMF precursors enriched in BAG-75 (15-25 and 150-250 microm in diameter). The shape and size of the smaller population are similar to structures assembled in vitro through self-association of purified BAG-75 protein. After organophosphate addition, BSP accumulates within these BAG-75-containing BMF precursors, with hydroxyapatite crystal nucleation occurring subsequently. In summary, BAG-75 is the earliest detectable biomarker that accurately predicts the extracellular sites of de novo biomineralization in UMR cultures. We hypothesize that BAG-75 may perform a key structural role in the assembly of BMF precursors and the recruitment of other proteins such as alkaline phosphatase and BSP. Furthermore, we propose a hypothetical mechanism in which BAG-75 and BSP function actively in nucleation of apatite within BMF. (+info)
Real-time monitoring of apatite deposition using electrochemical quartz crystal microbalance.
(19/221)
The electrochemical deposition process of apatite was monitored in real-time using an electrochemical quartz crystal microbalance (EQCM). A piezoelectric quartz oscillator with titanium was fixed to a cell and connected to a frequency counter. The electrolyte temperature was maintained at 20, 37, and 60 degrees C and the direct current density was constant at 0.2, 0.5, 1.0, and 2.0 mA/cm2. The deposited amount derived from the frequency change increased as electrolyte temperature and current density increased. The critical times, which are the starting times of quick increases of deposition, decreased with them. The critical times observed in the present study, namely in situ, were much shorter than those obtained from real weight change reported in our previous report. The apparent activation energies of the electrochemical deposition of apatite under 1.0 and 2.0 mA/cm2 were about 36.1 and 31.9 kJ/mol, respectively. These results indicate that electro current loading may reduce the activation energy required for the deposition of calcium phosphates. (+info)
Apatite-mediated actin dynamics in resorbing osteoclasts.
(20/221)
The actin cytoskeleton is essential for osteoclasts main function, bone resorption. Two different organizations of actin have been described in osteoclasts, the podosomes belt corresponding to numerous F-actin columns arranged at the cell periphery, and the sealing zone defined as a unique large band of actin. To compare the role of these two different actin organizations, we imaged osteoclasts on various substrata: glass, dentin, and apatite. Using primary osteoclasts expressing GFP-actin, we found that podosome belts and sealing zones, both very dynamic actin structures, were present in mature osteoclasts; podosome belts were observed only in spread osteoclasts adhering onto glass, whereas sealing zone were seen in apico-basal polarized osteoclasts adherent on mineralized matrix. Dynamic observations of several resorption cycles of osteoclasts seeded on apatite revealed that 1) podosomes do not fuse together to form the sealing zone; 2) osteoclasts alternate successive stationary polarized resorption phases with a sealing zone and migration, nonresorption phases without any specific actin structure; and 3) apatite itself promotes sealing zone formation though c-src and Rho signaling. Finally, our work suggests that apatite-mediated sealing zone formation is dependent on both c-src and Rho whereas apico-basal polarization requires only Rho. (+info)
Osteoblast proliferation behavior and bone formation on and in CO3apatite-collagen sponges with a porous hydroxyapatite frame.
(21/221)
To develop a new biodegradable scaffold biomaterial reinforced with a frame, synthesized CO3apatite (CO3Ap) was mixed with a neutralized collagen gel. Then, 0 and 70% (w/w) CO3Ap-collagen mixtures (70% CO3Ap weight/mixture weight) were lyophilized into sponges in a HAp frame ring with 0.5-mm pores. SEM observation of CO3Ap-collagen sponges showed favorable pores for cells invasion. Mouse osteoblast MC3T3-E1 cells were cultured in alphaMEM with 10% FCS for 1, 10 and 20 days. Matrix substances on the pure collagen sponge samples increased with the culture period such that the sponge surface was almost covered. A sectional view of hematoxylin-eosin staining confirmed that osteoblast cells had well invaded the CO3Ap-collagen sponge. When these sponge-frame complexes were implanted beneath the periosteum cranii of rats, newly created bone was observed to grow toward the inner core of the complex from the surface of the periosteum cranii. Based on these results, reinforced CO3Ap-collagen sponges are expected to be used as hard tissue scaffold biomaterials for therapeutic purposes. (+info)
In situ optical histochemistry of human artery using near infrared Fourier transform Raman spectroscopy.
(22/221)
In this paper we demonstrate that near infrared Fourier transform Raman spectroscopy provides unprecedented biochemical information about the extent of atherosclerosis in human aorta. In particular, elastin, collagen, cholesterol, cholesterol esters, lipids, carotenoids, and calcium apatite deposits all can be discerned by using this technique, permitting study of each stage in the disease process. Additionally, these moieties can be detected over 1.5 mm below the irradiated surface of the tissue, possibly allowing extraction of three-dimensional information about the histology of atherosclerotic plaques. We propose that this technique may be utilized for in situ optical histochemical analysis of atherosclerosis in particular and human disease in general. (+info)
Mineralogical composition of the urinary stones from different provinces in Iraq.
(23/221)
For this study, 25 samples of urinary stones were chosen from different provinces in Iraq as representative sampling localities. These samples of urinary stones were collected to represent kidney, urate, and bladder stones. The main objectives of this study are to try to shed some light on the possibilities of tracking down the effective environmental factors that determine the mineralogical and chemical composition of these stones. The stones were examined using several techniques, the most important of which was the use of the X-ray diffraction (XRD) technique to determine the mineralogical composition of these stones. A scanning electron microscopy (SEM) test was conducted to determine the crystallographic forms and structures for the minerals forming these stones. Optical properties of these minerals were studied using a polarizing microscope. All these techniques revealed that the calcium oxalate, represented in Whewellite mineral, is the most dominant type of these stones, in addition to other minerals such as Hydroxy apatite, Struvite, and Uricite. Dittmarite was pointed out for the first time ever in some samples. This mineral has not been determined in any previous study worldwide. Considering the results of mineralogical and chemical examinations of the urinary stones in question, and the statistical information gathered from the Iraqi Health Ministry, statistical analyses were applied. The ratio of male-female cases in this study happened to be 4:1, which was higher than the ratio in the years 1988-1989 and 1993-1994, 2:1; 3:1 respectively. The highest percentage of the cases was in the 15-50 age group, which is considered as the most productive years of human lifetime. This study showed that one of the most significant factors was that the mineralogical variation of urinary stones in some Iraqi provinces was due to geographical differences, which reflect the variation in lithogenic factors and also climatological factors. Other factors may be socioeconomic, genetic, physiological, and pathological, which remain the important factors in forming urinary stones. (+info)
Durability of FTLA treatment as a medicament for dentin hypersensitivity--abrasion resistance and profiles of fluoride release.
(24/221)
The purpose of this study was to evaluate the durability of tubules occluded with FTLA treatment by toothbrush abrasion test on the applied surface and by measuring fluoride release from the FTLA components. Dentin specimens with simulated hypersensitive surfaces were treated with APF containing tannic acid. After which, the specimens received lanthanum-chloride-with-powdered-fluoroapatite-glass-ceramics treatment. The specimens were subjected to toothbrush abrasion test up to 6,000 strokes. SEM observation revealed that dentinal tubules of the FTLA treated specimens were completely occluded with fine deposits even after toothbrush abrasion of 6,000 strokes. EPMA analysis revealed that fluoride, lanthanum, and aluminum were the main FTLA components on the dentin surface after 6,000-stroke abrasion. To measure fluoride release from the FTLA components, a slurry was enclosed in a cellulose tube and suspended in deionized water at 37 degrees C. After fluoride was dialyzed against deionized water, a high concentration of fluoride was found to be released from FTLA the components, indicating FTLA treatment's prominent durability. These results suggested that FTLA treatment has a superior resistance against toothbrush abrasion and a high fluoride-releasing performance. These characteristics lend much weight to showing that the FTLA method is an effective and durable medicament for dentin hypersensitivity. (+info)