Passive Mineralization Research Articles

Human versus Rat PRF on Collagen Membranes: A Pilot Study of Mineralization in Rat Calvaria Defect Model.

Platelet-rich fibrin, the coagulated plasma fraction of blood, is commonly used to support natural healing in clinical applications. The rat calvaria defect is a standardized model to study bone regeneration. It remains, however, unclear if the rat calvaria defect is appropriate to investigate the impact of human PRF (Platelet-Rich Fibrin) on bone regeneration. To this end, we soaked Bio-Gide® collagen membranes in human or rat liquid concentrated PRF before placing them onto 5 mm calvarial defects in Sprague Dawley rats. Three weeks later, histology and micro-computed tomography (μCT) were performed. We observed that the collagen membranes soaked with rat PRF show the characteristic features of new bone and areas of mineralized collagen matrix, indicated by a median mineralized volume of 1.5 mm3 (range: 0.9; 5.3 mm3). Histology revealed new bone growing underneath the membrane and hybrid bone where collagen fibers are embedded in the new bone. Moreover, areas of passive mineralization were observed. The collagen membranes soaked with human PRF, however, were devoid of histological features of new bone formation in the center of the defect; only occasionally, new bone formed at the defect margins. Human PRF (h-PRF) caused a median bone volume of 0.9 mm3 (range: 0.3-3.3 mm3), which was significantly lower than what was observed with rat PRF (r-PRF), with a BV median of 1.2 mm3 (range: 0.3-5.9 mm3). Our findings indicate that the rat calvaria defect model is suitable for assessing the effects of rat PRF on bone formation, but caution is warranted when extrapolating conclusions regarding the efficacy of human PRF.

Active and Passive Mineralization of Bio-Gide® Membranes in Rat Calvaria Defects.

Bio-Gide® is a collagen membrane routinely used in guided bone regeneration. Recent studies have shown that this collagen membrane has osteoconductive properties, meaning that it can support the growth of new bone. However, it has also been observed that the collagen membrane has areas of mineralized fibers which can occur spontaneously and independently of osteoblasts. To better understand how this works, we established a model using minced collagen membranes to reduce the active mineralization of intact collagen membranes in favor of passive mineralization. We thus compared the original intact membrane with a minced collagen membrane in a 5 mm calvarial defect model in Sprague Dawley rats. After three weeks of healing, histology and microcomputed tomography (μCT) were performed. Histological analysis confirmed the osteoconductive properties, with new bone growing inside the intact collagen membrane. However, in minced collagen membranes, the osteoconductive properties were restricted to the defect margins. Interestingly, histology revealed large mineralized areas indicating passive mineralization with no signs of bone formation. In the μCT analysis, the intact collagen membranes caused a higher median mineralized volume (1.5 mm3) compared with the minced group (0.4 mm3), but this lacked significance (p = 0.09). The μCT analysis needs to be interpreted carefully, particularly in defects filled with minced membranes, considering that the mineralized tissue may not necessarily be bone but also the result of passive mineralization. Taken together, the findings suggest that Bio-Gide® collagen membranes support bone formation while also exhibiting potential for passive mineralization.

МИКРОБНЫЕ СООБЩЕСТВА КАРСТОВЫХ ПЕЩЕР

Special geochemical, hydrological and microclimatic conditions in karst caves lead to the development of unique bacterial communities in them. The microbiota of such communities has complex, often unique mechanisms of interaction, which currently does not allow us to fully identify their species composition. Among the bacteria in caves, the most common are representatives of Alfaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Actinobacteria. Lack of light, lack of nutrients and low temperatures lead to a number of adaptations in bacteria, such as a decrease in cell size, slow metabolism, changes in membrane lipids and enzymes, and a number of others. In aphotic conditions, the basis of trophic chains are chemolithotrophic bacteria. The development of bacteria occurs mostly on the surface of mineral formations, soil, walls and in the upper layer of water. Rocky surfaces of caves represent the largest areas potentially suitable for colonization by microbial communities. There is a widespread assumption among researchers that the bacteria living on the walls are mostly cave microbiota and are the least susceptible to changes under anthropogenic load. Bacteria are actively involved in the geochemical transformations of the environment: corrosion of rocks the subsequent deposition of mineral formations. At present, the hypothesis of biogenic mineralization is generally accepted. On the one hand, crystal formation occurs with the participation of only living microorganisms, on the other hand, a change in the physicochemical conditions of the environment is of no small importance in this process. A significant role, according to researchers, is played by secreted extracellular substances that induce passive mineralization or, conversely, cause the dissolution of calcite. In addition, it is known that microorganisms isolated from caves, while remaining viable, after some time lose their ability to form or destroy mineral formations. Bacteria involved in the transformation of mineral substrates are not confined to taxonomic groups and act as part of multispecies communities.

Bone mineral density and mortality in end-stage renal disease patients.

Osteoporosis characterized by low bone mineral density (BMD) as assessed by dual-energy X-ray absorptiometry (DXA) is common among end-stage renal disease (ESRD) patients and associates with high fracture incidence and high all-cause mortality. This is because chronic kidney disease-mineral bone disorders (CKD-MBDs) promote not only bone disease (osteoporosis and renal dystrophy) but also vascular calcification and cardiovascular disease. The disturbed bone metabolism in ESRD leads to ‘loss of cortical bone’ with increased cortical porosity and thinning of cortical bone rather than to loss of trabecular bone. Low BMD, especially at cortical-rich bone sites, is closely linked to CKD-MBD, vascular calcification and poor cardiovascular outcomes. These effects appear to be largely mediated by shared mechanistic pathways via the ‘bone–vascular axis’ through which impaired bone status associates with changes in the vascular wall. Thus, bone is more than just the scaffolding that holds the body together and protects organs from external forces but is—in addition to its physical supportive function—also an active endocrine organ that interacts with the vasculature by paracrine and endocrine factors through pathways including Wnt signalling, osteoprotegerin (OPG)/receptor activator of nuclear factor-κB (RANK)/RANK ligand system and the Galectin-3/receptor of advanced glycation end products axis. The insight that osteogenesis and vascular calcification share many similarities—and the knowledge that vascular calcification is a cell-mediated active rather than a passive mineralization process—suggest that low BMD and vascular calcification (‘vascular ossification’) to a large extent represent two sides of the same coin. Here, we briefly review changes of BMD in ESRD as observed using different DXA methods (central and whole-body DXA) at different bone sites for BMD measurements, and summarize recent knowledge regarding the relationships between ‘low BMD’ and ‘fracture incidence, vascular calcification and increased mortality’ in ESRD patients, as well as potential ‘molecular mechanisms’ underlying these associations.

Metallogenic Correlations for the Fe‐Nb‐REE Mineralization in the West Mine of the Bayan Obo Deposit, Inner Mongolia, China

AbstractThe West Mine of the Bayan Obo deposit, located in the northern‐central part of Inner Mongolia, China, is enriched in Nb, rare earth elements and iron (Nb‐REE‐Fe) mineral resources. This paper presents a combined method to explore metallogenic correlation of the Nb‐REE‐Fe mineralization at the Bayan Obo West Mine. The method integrates factor analysis and Back Propagation (BP) neural network technology into processing and modeling of geological data. In this study, the Nb and REE contents of samples were transformed into discrete values to analyze the correlations among the metallogenic elements. The results show weak mineralization correlations between Nb and REEs. Nb and U are closely related in the geochemical patterns, while Fe is closely related to both Th and Mn. LREEs are an important factor for the mineralization of the Bayan Obo deposit, while Fe and Nb can be considered as the results of passive mineralization. On the basis of a metallogenic correlation analysis, the factors affecting the Fe‐REE‐Nb mineralization were extracted, and the Nb mineralization model was established by the BP neural network. Based on the BP neural network data computing, the variability of the Nb concentration displays a coupled multi‐factor nonlinear relationship, which can be used to reveal the inherent metallogenic elemental regularities and predict the degree of element mineralization enrichment in the mining area.

Microbially influenced formation of Mg‐calcite and Ca‐dolomite in the presence of exopolymeric substances produced by sulphate‐reducing bacteria

AbstractSome species of sulphate‐reducing bacteria (SRB) are known to mediate the formation of dolomite and Mg‐calcite. However, their exact role in the mineralization process remains elusive. Here, we present the result of a laboratory experiment that was designed to test whether formation of carbonate minerals by SRB can occur in the absence of living cells, through passive mineralization of their exopolymeric substances (EPS). SRB capable of mediating dolomite were cultivated in the laboratory, allowing them to secrete EPS. Microbial activity within the cultures was subsequently inhibited with antibiotics. Only after this step, Ca2+ and Mg2+ were added to the solution and carbonate minerals could form. Mg‐calcite and disordered Ca‐dolomite precipitated in association with EPS. The mol.% of Mg2+ in the crystals increased with longer incubation times. This result demonstrates that organic compounds produced by SRB can mediate the formation of Ca‐Mg carbonates in the absence of an active metabolism.

Frutexites encrustations on rugose corals (Middle Devonian, southern Morocco): complex growth of microbial microstromatolites

Microbially induced Frutexites microstromatolites developed on corallites of the Givetian rugose coral “Amplexus” in the sedimentary cover of a submarine volcanic intrusion in the eastern Anti-Atlas of southern Morocco. The corals lived in proximity to submarine hydrothermal fluid emissions. Frutexites form irregular shrubs encrusting external walls of corallites. The shrubs, consisting of alternations of calcitic and hematitic laminae, grew predominantly on abandoned corallites. Some Frutexites grew within the sediment, whereas others developed entirely above the seafloor, or started their accretion in water and continued to grow during burial. Three types of Frutexites encrustations have been distinguished. They look similar macroscopically, but differ significantly in their microstructure and mineralogical characteristics, resulting primarily from spatial and temporal variations in redox conditions. Both hematitic and calcitic laminae are primary features of Frutexites. The shrubs accreted as a result of mineralization of microbial biofilms under fluctuating environmental conditions, caused by changes in pH, Fe2+-supply and/or oxygenation, presumably related to discharges of reducing hydrothermal fluids. The calcitic laminae are interpreted to have formed due to activity of heterotrophic (mainly sulphate-reducing) microbes, whereas the hematitic laminae developed as a result of enhanced activity of nitrate-reducers or due to periodical passive mineralization of biofilms with iron. Cathodoluminescence data provide evidence that the nitrate and sulphate reduction preceded the Mn(IV) and Fe(III) reduction, presumably due to increased accumulation of organic matter and a high stability of the iron oxides present.

Role of Circulating Osteogenic Progenitor Cells in Calcific Aortic Stenosis

The purpose of this study was to determine the role of circulating endothelial progenitor cells with osteoblastic phenotype (EPC-OCN) in human aortic valve calcification (AVC). Recent evidence suggests that rather than passive mineralization, AVC is an active atherosclerotic process with an osteoblastic component resembling coronary calcification. We have recently identified circulating EPCs with osteogenic properties carrying both endothelial progenitor (CD34, KDR) and osteoblastic (osteocalcin [OCN]) cell surface markers. Blood samples from controls (n = 22) and patients with mild to moderate calcific aortic stenosis (mi-moAS, n = 17), severe calcific AS (sAS, n = 26), and both sAS and severe coronary artery disease (sCAD) (n = 33) were collected during diagnostic coronary angiography. By using flow cytometry, peripheral blood mononuclear cells were analyzed for CD34, KDR, and OCN. Resected normal and calcified aortic valves were analyzed histologically. Patients with mi-moAS and patients with sAS/sCAD had significantly less EPCs (CD34+/KDR+/OCN-) than controls. Patients with sAS showed significantly higher numbers of EPC-OCN (CD34+/KDR+/OCN+) than controls. In addition, the percentage of EPC costaining for OCN was higher in all disease groups compared with controls. A subgroup analysis of younger patients with bicuspid sAS showed a similar pattern of significantly lower EPCs but a high percentage of coexpression of OCN. Immunofluorescence showed colocalization of nuclear factor kappa-B and OCN in diseased and normal valves. CD34+/OCN+ cells were abundant in the endothelial and deeper cell layers of calcific aortic valve tissue but not in normal aortic valve tissue. Circulating EPC-OCN may play a significant role in the pathogenesis and as markers of prognostication of calcific AS.

Regulation of vascular calcification in atherosclerosis.

Over a century ago it was recognized that the vessel wall is a predominant site for ectopic calcification which is a hallmark of clinically significant atherosclerotic lesions. Old observational studies, which characterized vascular calcification as osteogenesis, and recent identification of common molecular mechanisms in bone and vascular calcification have led to the new recognition that atherosclerotic calcification is an actively regulated process similar to osteogenesis and distinct from a metastatic passive mineralization. Since the atherosclerotic lesion is composed of a multitude of cells and inflammatory mediators, elucidation of the role of these components in induction and acceleration of calcification is of fundamental importance in better understanding its pathogenesis and identifying possible interventional targets. This article will focus on four important mediators of vascular calcification: 1) calcifying vascular cells, 2) oxidized lipids, 3) cytokines, and 4) leptin.

Coronary calcium: The good, the bad, and the uncertain

Background Coronary calcium deposits have been widely regarded to result from a passive process of encrustation or adsorption of mineral onto advanced, complex atherosclerotic lesions. Increasing interest has focused on noninvasive radiologic detection of these calcium deposits as a diagnostic and prognostic adjunct to clinical evaluation of coronary artery disease, particularly with the use of newer, high-resolution imaging techniques such as electron beam computed tomography. Methods and Results We reviewed the literature on coronary calcium and its relation to pathologic atherosclerosis, angiographic stenoses, and clinical events. Clinical calcium detection studies have demonstrated an association between coronary calcium and both extent of coronary artery disease and risk of adverse events. These studies have in the past tended to reinforce the perception that calcific deposits result from a passive mineralization process, signify advanced coronary artery disease, and foreshadow future coronary events. Conclusions Recent pathologic, genetic, clinical, and biochemical evidence reviewed in this article suggests that coronary calcium deposits are a manifestation of a complex, organized, and regulated process similar in many respects to new bone formation and may not be a reliable indicator of either the extent of coronary disease or the risk of a future event. These studies also suggest that atherosclerosis and calcific deposits may be distinct pathologic entities that frequently occur together and are related to each other in ways that are poorly understood. (Am Heart J 1999;137:806-14.)

An enzyme histochemical study of dental plaque and calculus.

The following investigation was undertaken to study the location in the dental plaque and calculus of certain enzyme activities and to compare the patterns obtained with those of the normal hard tissue formation. Supragingival and subgingival calculus attached to the root surfaces of 30 extracted teeth was studied. The root with its deposits was frozen rapidly in a mixture of hexane and solid CO2 (-75 degrees C). From the frozen block, sections were cut and incubated for histochemical demonstration of lactate dehydrogenase, alkaline phosphatase and acid phosphatase. The plaque seemed to be stratified with regard to enzyme activity. Three different layers could be identified. In the basal layer, approximately 100 microns thick, enzyme activity was low. Lactate dehydrogenase activity could be identified in some sections, but no phosphatase activity. In the middle layer lactate dehydrogenase, alkaline phosphatase and acid phosphatase activities were found in most of the sections. The superficial layer usually showed lactate dehydrogenase but not always acid or alkaline phosphatase activities. The results of the present investigation may suggest that the mineralization of the dental plaque is not only a passive mineralization of dead bacteria, but also an active process promoted by enzymes in the covering bacterial layers.