The rote of calcium-phospholipid-phosphate complexes in tissue mineralization

Current insights into the mechanisms and management of infection stones

Infection stones are complex aggregates of crystals amalgamated in an organic matrix that are strictly associated with urinary tract infections. The management of patients who form infection stones is challenging owing to the complexity of the calculi and high recurrence rates. The formation of infection stones is a multifactorial process that can be driven by urine chemistry, the urine microenvironment, the presence of modulator substances in urine, associations with bacteria, and the development of biofilms. Despite decades of investigation, the mechanisms of infection stone formation are still poorly understood. A mechanistic understanding of the formation and growth of infection stones - including the role of organics in the stone matrix, microorganisms, and biofilms in stone formation and their effect on stone characteristics - and the medical implications of these insights might be crucial for the development of improved treatments. Tools and approaches used in various disciplines (for example, engineering, chemistry, mineralogy, and microbiology) can be applied to further understand the microorganism-mineral interactions that lead to infection stone formation. Thus, the use of integrated multidisciplinary approaches is imperative to improve the diagnosis, prevention, and treatment of infection stones.

Cellular and molecular gateways to urolithiasis: a new insight

Urolithiasis is a relevant clinical problem in everyday practice with a subsequent burden for the health system. Urolithiasis is classically explained as the derangement in the process of biomineralization involving the equilibrium between promoters and inhibitors of crystallization: a deficit of one or several inhibitors or an excess of one or several promoters plays a pivotal role in the stone formation. The revolutionary introduction of the molecular biology in medicine has given a new insight in urolithiasis too. Genetic factors have also been postulated to play an important role. A review of the current knowledge on urolithiasis based upon a molecular and genetic approach is reported.

Presence of lipids in urine, crystals and stones: implications for the formation of kidney stones

BACKGROUND

Cell membranes and their lipids play critical roles in calcification. Specific membrane phospholipids promote the formation of calcium phosphate and become a part of the organic matrix of growing calcification. We propose that membrane lipids also promote the formation of calcium oxalate (CaOx) and calcium phosphate (CaP) containing kidney stones, and become a part of their stone matrix.

METHODS

Human urine, crystals of CaOx and CaP produced in the urine of healthy individuals, and urinary stones containing struvite, uric acid, CaOx and CaP crystals for the presence of membrane lipids were analyzed. Crystallization of CaOx monohydrate at Langmuir monolayers of dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylserine (DPPS), dioleoylphosphatidylglycerol (DOPG), palmitoyloleoylphosphatidylglycerol (POPG) and dimyristoylphosphatidylglycerol (DMPG) was investigated to directly demonstrate that phospholipid assemblies can catalyze CaOx nucleation.

RESULTS

Urine as well as CaOx and CaP crystals made in the urine and various types of urinary stones investigated contained some lipids. Urine of both CaOx and uric acid stone formers contained significantly more cholesterol, cholesterol ester and triglycerides than urine of healthy subjects. However, urine of CaOx stone formers contained more acidic phospholipids. The organic matrix of calcific stones contained significantly more acidic and complexed phospholipids than uric acid and struvite stones. For each Langmuir monolayer precipitation was heterogeneous and selective with respect to the orientation and morphology of the CaOx crystals. Crystals were predominantly monohydrate, and most often grew singly with the calcium rich (10-1) face toward the monolayer. The number of crystals/mm2 decreased in the order DPPG> DPPC and was inversely proportional to surface pressure and mean molecular area/molecule.

CONCLUSIONS

Stone forming conditions in the kidneys greatly impact their epithelial cells producing significant differences in the urinary lipids between healthy and stone forming individuals. Altered membrane lipids promote face selective nucleation and retention of calcium oxalate crystals, and in the process become a part of the growing crystals and stones.

Inhibition of calcification of glutaraldehyde pretreated porcine aortic valve cusps with sodium dodecyl sulfate: preincubation and controlled release studies

Calcification of bioprosthetic heart valves fabricated from glutaraldehyde pretreated bovine pericardium or porcine aortic valves (PAV) is a frequent cause of the failure of these devices. Of all strategies considered thus far, only detergent preincubations using compounds such as sodium dodecyl sulfate (SDS) inhibited PAV bioprosthetic mineralization in circulatory sheep bioprosthetic valve replacements. The present study sought to characterize the mechanism of action of SDS preinicubation. Results of transport and material characterization studies showed that SDS had a relatively high affinity for PAV, with a maximum uptake of 167.1 +/- 6.8 micrograms SDS/mg tissue over 24 h at 37 degrees C with a partition coefficient of 19.3. The PAV diffusion of SDS was 1.95 +/- 0.35 10(-6) cm2/sec. The principal effect of SDS on PAV was phospholipid extraction. The residual organic phosphate in the SDS pretreated tissue was 2.22 +/- 0.72 nmol/mg tissue compared to the control untreated group with 18.52 +/- 2.1 nmol/mg tissue. Incubations of PAV specimens in a 1% SDS solution for 24 h significantly inhibited calcification after 21 days in subdermal implants in 3-week-old male rats (PAV Ca2+ = 18.0 +/- 11.8 micrograms/mg) compared to control (177.8 +/- 6.0 micrograms/mg). In contrast, coimplants of 30% SDS silicone rubber polymers, for regional sustained SDS administration, did not impede PAV calcification in 21 day implants Ca2+ = 166.0 +/- 14.0 micrograms/mg compared to the nondrug silicone matrix controls, Ca2+ = 173.0 +/- 6.6 micrograms/mg). Thus, we conclude that the mechanisms of SDS inhibition of PAV calcification is due to material effects which occur during preincubation, and is not facilitated by sustained SDS administration.

Dentinogenesis

The formation of dentin, dentinogenesis, comprises a sophisticated interplay between several factors in the tissue, cellular as well as extracellular. Dentin may be regarded as a calcified connective tissue. In this respect, as well as in its mode of formation, it is closely related to bone. Using dentinogenesis as an experimental model to study biomineralization provides several practical advantages, and the results may be extrapolated to understand similar processes in other tissues, primarily bone. After describing dentin structure and composition, this review discusses items such as the morphology of dentinogenesis; the dentinogenically active odontoblast, transport, and concentrations of mineral ions; the constituents of the dentin organic matrix; and the presumed mechanisms involved in mineral formation.

Effects of hydroxyapatite implants on primary mineralization during rat tibial healing: biochemical and morphometric analyses

The effect of 40- to 60-mesh hydroxyapatite (HA) granules (Calcitek, Inc., Carlsbad, CA) on the process of primary mineralization during bone healing was examined following insertion of the HA granules into rat tibial bone after marrow ablation. Response to HA was assessed by monitoring morphometric and biochemical changes in matrix vesicles, which are extracellular organelles associated with initial calcification. Following insertion of HA, matrix vesicle-enriched membranes (MVEMs) were isolated from the tissue adjacent to the implant and from the endosteum of the contralateral limb at 3, 6, 14, and 21 days and from a nonimplanted control group (t = 0). MVEM alkaline phosphatase- and phospholipase A2-specific activities were increased on days 6 (peak) and 14; phosphatidylserine content was also elevated on days 6 and 14 (peak). Comparable changes were seen in the contralateral limb but at lesser magnitudes. Morphological changes were observed as well. The number of matrix vesicles/micron2 matrix increased on days 6 (peak) and 14. The mean diameter of the matrix vesicles was elevated on days 6 (peak), 14, and 21. Mean distance from the calcifying front increased on day 6 but was decreased on days 14 and 21. These results indicated that HA behaves like bone-bonding implants in that there is a stimulation of matrix vesicle enzymes, increased phosphatidylserine content, and increase numbers of matrix vesicles. However, the increases occur only after 6 days postimplantation, indicating a delay in response when compared to normal healing. This delay is confirmed by the morphometric measurements. HA causes a reduction in the response associated with marrow ablation. In addition, the effects of HA are comparable locally and systemically but with different intensity. These observations suggest that osteogenic cells are able to compensate for the inhibitory effects of HA and primary calcification involves normal matrix vesicle production and maturation, if somewhat delayed and reduced in magnitude. The ability to support primary mineral formation may contribute to the successful bonding of HA with surrounding osseous tissue.

Degeneration of osteoblasts involved in intramembranous ossification of fetal rat calvaria

Ossification of calvariae from day-21 rat fetuses was reinvestigated by electron microscopy using different fixation techniques (glutaraldehyde/OsO4, tannic acid, ruthenium red, K-pyroantimonate). An osteoid layer with scattered mineral deposits was found at the mineralization front. Directly beyond this layer, a sheet of one to two layers of necrotic and degenerating osteoblasts was present. Above this sheet, normal and healthy cells were seen, formed by six to eight layers of flattened cells, embedded in a collagenous matrix. The osteoblasts on the less mineralizing opposite side of the calcified calvariae and the osteocytes embedded in the calcified calvariae appeared healthy. Closer inspection of the necrotic zone revealed apatite crystals in vesicles which most probably originated from mitochondria of the degenerated cells. Large K-pyroantimonate deposits were found throughout the osteoid and the necrotic zone, whereas only small granules were scattered in the cytoplasm and at the plasma membrane of the healthy cells directly adjacent to the necrotic zone. A concept of intramembranous mineralization is outlined, according to which osteoblasts store enormous amounts of calcium, which are liberated by physiological cell death in the vicinity of the mineralizing front.

Effect of glass ceramic and titanium implants on primary calcification during rat tibial bone healing

The effect of bone bonding (KG Cera, Mina 13, and titanium) and nonbone bonding (KGy-213, M 8/1) implants on primary calcification in endosteal bone was examined by comparing changes in the morphometry of matrix vesicles to those occurring during normal bone healing following ablation of rat tibial marrow. The concentration of matrix vesicles, their diameter, and their distance from the calcification front were determined using computerized cytomorphometry at the transmission electron microscopic level. The results demonstrated that bone bonding materials supported an increase in matrix vesicle concentration when compared with control bone at 6 and 14 days postimplantation. At 14 days, there were fewer matrix vesicles in the bone adjacent to the nonbonding implants. Though matrix vesicle diameter decreased in the control bone between 6 and 14 days, it increased in all of the experimental samples. Diameters were significantly greater in the bone bonding samples at 14 days and significantly lower in the nonbonding samples at 6 days. Distance from the calcification front decreased between 6 and 14 days in all groups except in bone adjacent to the KGy-213 implants. In bone adjacent to the bone bonding implants, distance from the calcification front was comparable to or further than that of control bone; in the nonbonding samples it was closer to the calcification front. These results demonstrate that production and maturation of matrix vesicles is influenced in a differential manner by the presence of implant materials.

Calcification of soft tissue employed in the construction of heart valve prostheses: study of different chemical treatments

Biological heart prostheses present medium and long-term problems, owing to progressive deterioration and calcification of the tissue. To study the latter problem, we compared the effectiveness of anticalcification treatments in calf pericardium samples implanted into female Wistar rats after the following procedures: group I, control group (glutaraldehyde 0.2%); group II, proteoglycans group, group III, control group (glutaraldehyde 0.625%); groups IV and V, subjected to lipid removal with chloroform/methanol and SDS; group VI, pericardial tissue treated with 0.1 M AI3+ for 24 h; and group VII, chemical treatment with 0.1 M La3+ for 24 h. Positive results were obtained with lipid removal and chemical treatment with AI3+. The selective extraction of proteoglycans resulted in considerable accumulation of calcium salts in the tissue.

A new method for the study of the formation and transformation of calcium phosphate precipitates: effects of several chemical agents and Chinese folk medicines

A simple method of assaying the formation of amorphous calcium phosphate and its transformation to hydroxyapatite using a conventional pH meter and recorder is described. Its validity was confirmed by direct assay of calcium consumption with atomic absorption spectrophotometry. The method was used to study substances which influence the formation of amorphous calcium phosphate and its transformation to hydroxyapatite, such as albumin, casein, chondroitin sulphate, phospholipid, ATP, Mg2+, Sr2+, pyrophosphate and several Chinese folk medicines.

Light- and electron-microscopic studies on multinucleated giant cells in sarcoid granuloma: new aspects of asteroid and Schaumann bodies

Ultrastructural studies using transmission, analytical, electron, and light microscopy were performed on epithelioid granulomata in 4 lymph nodes from a case of sarcoidosis, emphasizing the organization of asteroid and Schaumann bodies in multinucleated giant cells and the deposition of chemical elements. Serial sectioning at semithin level showed a single multinucleated giant cell can contain up to 4 asteroid and 1 Schaumann body. Microtubules and centrioles were not found in asteroid bodies, although a centriolar field was present in 1 giant cell close to the plasma membrane, completely unrelated to the asteroid body. In 1 asteroid body, tubulelike structures were observed in a focus showing filament dissociation. A principal ultrastructural finding is intimate envelopment of radiating filamentous arms of the asteroid body by myelinoid membranes, extensive forms of which are also present between the arms. Elemental analysis revealed a definite peak of calcium and a probable phosphorus peak in relation to the asteroid body and associated myelinoid membranes. Calcium and phosphorus with smaller quantities of aluminum and iron were found in Schaumann bodies. Our studies indicate that organization of the asteroid body is more complex than hitherto described, independent of the centriolar and microtubular systems. Evidence for the possible developmental pathway of the Schaumann body is provided by morphological changes within myelinoid figures intimately related to the asteroid body.

Bone cell biology: the regulation of development, structure, and function in the skeleton

Bone cells compose a population of cells of heterogeneous origin but restricted function with respect to matrix formation, mineralization, and resorption. The local, mesenchymal origin of the cells which form the skeleton contrasts with their extraskeletal, hemopoietic relatives under which bone resorption takes place. However, the functions of these two diverse populations are remarkably related and interdependent. Bone cell regulation, presently in its infancy, is a complicated cascade involving a plethora of local and systemic factors, including some components of the skeletal matrices and other organ systems. Thus, any understanding of bone cell regulation is a key ingredient in understanding not only the development, maintenance, and repair of the skeleton but also the prevention and treatment of skeletal disorders.

In vivo hydroxyapatite formation induced by lipids

Proteolipids and complexed acidic phospholipids that cause in vitro hydroxyapatite formation, similarly cause hydroxyapatite deposition in 10-mu pore Millipore chambers when implanted in rabbit muscle pouches. The amount of mineral deposited during a 3-week period, based on the calcium and phosphate contents of the chambers, was directly related to the dry weight of the lipid implanted in the chamber. Chambers containing total lipid extract from rabbit bone from which the complexed acidic phospholipids had been removed, acidic phospholipids from which the the proteolipids had been removed, and empty chambers did not accumulate any detectable mineral during the course of the study. Chambers implanted with synthetic hydroxyapatite served as controls for chemical analyses. The presence of hydroxyapatite in the chambers was established 3 weeks after implantation based on electron microscopic, compositional, and wide-angle X-ray diffraction analyses of the deposits. In the cell-free chambers, lipid-induced hydroxyapatite deposition, but not bone matrix formation occurred. This study demonstrates that proteolipids and complexed acidic phospholipids can cause hydroxyapatite mineral deposition in a physiologic environment. To date, these lipids are the only materials isolated from mineralizing tissues, other than reconstituted collagen, that have been shown capable of causing in vivo mineralization in the absence of cells.

Liposome-mediated calcium phosphate formation in metastable solutions

The present study examined the effect of anionic liposomes on precipitate formation in supersaturated calcium phosphate solutions. The liposomes were prepared by dispersing 7:2:1 molar mixtures of phosphatidylcholine, dicetyl phosphate, and cholesterol in buffered aqueous solutions containing 0 or 50 mM inorganic phosphate (PI). Unencapsulated PI was removed by gel filtration. The liposomes were then suspended in reaction solutions containing 2.25 mM Ca2+ and either 0, 1.0, or 1.5 mM PI. All experiments were carried out at 22 degrees C, pH 7.4, and 240 mOsm. External solution Ca2+ and PI losses were found to be appreciable only when the membranes of liposomes containing entrapped PI were made permeable to Ca2+ with the addition to the suspension of the ionophore X-537A. The Ca2+ losses, moreover, were up to 3 times as great (1.5 vs 0.5 mM) when accompanied by external PI losses than in PI-free external solutions where Ca2+ alone was involved. Previous studies showed that in this latter situation, decline in external Ca2+ concentration was the result of precipitate formation in the aqueous interiors of the liposomes. The present findings suggest that when the external solution phase was metastable, the apparent coupling of large additional Ca2+ losses with intraliposomal precipitation was due to secondary precipitation brought about by the seeding action of intraliposomal crystals penetrating into the external solution. The results may explain in part the origin of extravesicular mineral deposits in matrix vesicle calcification.

The effect of osteocalcin on in vitro lipid-induced hydroxyapatite formation and seeded hydroxyapatite growth

Osteocalcin, the bone gamma-carboxy glutamic acid containing protein, is one of the major noncollagenous proteins both synthesized and localized in bony tissue. Previously, investigators have suggested, based on the in vitro and in vivo properties of this protein, that it may be involved in controlling initiation of mineralization and/or hydroxyapatite (HA) growth. In this study, the in vitro effects of osteocalcin on lipid-induced HA formation, and HA seeded growth were compared. Although osteocalcin inhibited the growth of HA, as indicated by the osteocalcin concentration-dependent decreases in the first order rate constant, kCa, osteocalcin had no effect on lipid-induced calcification, kCa remaining constant at .033 h-1. Binding studies revealed that osteocalcin did not associate with the lipid macromolecules tested (phosphatidyl serine, phosphatidyl inositol, and the Ca-acidic phospholipid-phosphate (Ca-PL-PO4) complexes prepared from these phospholipids) although the protein bound to HA with high affinity. These data suggest that a) osteocalcin is quite distinct from the gamma carboxy glutamic acid containing clotting proteins which have a high affinity for both the acidic phospholipids and for HA, and b) that osteocalcin has little effect on the initial Ca-PL-PO4-dependent formation of HA.

Lipid changes in the bones of the healing vitamin D-deficient phosphate-deficient rat

The bones of vitamin D-deficient, phosphate-deficient rats have a lipid composition that is significantly different from that of normal bones. Specifically, these bones have elevated cholesterol and reduced lysophosphatide and free fatty acid contents. Treatment of these animals with a single dose of vitamin D and phosphate produces healing within 72 h and causes rapid corrections of alterations in growth plate and cancellous bone lipid composition. Healing of the rachitic/osteomalacic state in these animals was demonstrated radiographically and histologically. Histomorphometric measurements showed that the relative osteoid volume of the cancellous bone rapidly approached the 7% value of normal controls, decreasing from 29% in the rachitic animals to 16% by 12 h and 8.5% by 72 h. Significant changes in ash weight, Ca:P ratio, and crystal-lite size and perfection were detectable at 12 h, with these parameters approaching values found in normal animals within 72 h. Calcium-acidic phospholipid-phosphate complexes, which are known to promote hydroxyapatite formation, peaked in concentration at 12 h in epiphysis, cancellous, and cortical bone, returning rapidly to normal values after that time. In untreated animals the complexed acidic phospholipid content of the nonmineralized epiphysis was comparable to that in normal mineralizing epiphysis, whereas the content of the complexes was reduced in the cancellous bones of the untreated animals.

Influence of magnesium supplementation on bone turnover in the normal young mouse

The effect of magnesium (Mg) supplementation on bone metabolism has been studied in the normal young mouse. Weanling male mice were given Mg-supplemented drinking water (5 mM or 32 mM Mg) for 4 weeks. Mineral and skeletal changes were assessed by biochemical methods and by histomorphometric analysis of endosteal bone formation and resorption parameters evaluated on tetracycline double-labeled, undecalcified caudal vertebrae. Magnesium supplementation increased serum and urinary Mg concentrations and bone Mg content. Both the calcification rate and the extent of tetracycline double-labeled osteoid surface increased progressively in Mg-treated mice, whereas the mineralization lag time was shortened. The osteoblastic surface was reduced, leading to a fall in osteoid surface. Stimulation of bone mineralization was associated with a rise in extracellular calcium (Ca) and phosphorus (P) concentrations whereas serum 25-OHD and 1,25(OH)2D levels remained normal. The Mg supplementation increased the number of acid phosphatase stained chondroclasts and osteoclasts and the extent of resorbing surface showing histochemically stained osteoclasts. Although urinary OH-proline increased above normal, Ca, P, and cyclic adenylic acid (cAMP) excretion and phosphate concentration (TmP/GFR) remained normal, suggesting that parathyroid hormone (PTH) secretion was not altered. The trabecular bone volume remained normal, showing that the increased bone resorption was balanced by the stimulated bone mineralization. The results show that Mg supplementation influenced both bone formation and resorption in the young mouse, and that the stimulation of bone mineralization was the result of increased extracellular mineral availability.(ABSTRACT TRUNCATED AT 250 WORDS)

hard tissue biochemistry: a comparison of fresh-frozen and formalin-fixed tissue samples

Formalin fixation of hard tissues alters the levels of some, but not all, of the parameters routinely measured by bone researchers. Although mineral parameters (ash weight, particle size (beta 1/2 002) and Ca/PO4 ratio) and lipid parameters (total lipid content and composition, extractability, and Ca-acidic phospholipid phosphate content) are not affected by formalin fixation, the uronate and DNA contents are reduced in formalin-fixed bone while hydroxyproline content is elevated.

Calcium-acidic phospholipid-phosphate complexes in diseased and normal human bone

Ca-acidic phospholipid-PO4 complexes promote in vitro hydroxyapatite nucleation and/or growth and are believed to have similar functions in vivo. The complexed acidic phospholipid content of human bones has been studied in femoral heads obtained at surgery from patients with osteonecrosis and osteoarthritis and compared with age-matched, disease-free control bones. The content of Ca-acidic phospholipid-PO4 complexes was elevated in bones that were judged on the basis of radiographic and histological data to be actively making new bone. These data suggest that the relative concentration of Ca-acidic phospholipid-PO4 in bone may be related to the rate at which bone is being made and mineralized.

Lipid composition of two types of chondrocytes in primary culture

Chondrocytes from articular and growth plate cartilage were grown in primary culture. The lipid content, distribution into different types, as well as the fatty acid patterns of these lipids were compared when the cells had reached stationary phase and were synthesizing maximal amounts of proteoglycans. Numerous significant differences were observed, depending on the origin of the chondrocytes. In particular, growth plate chondrocytes showed increased dry weight, increased lipid content (phosphatides and triglycerides), and decreased cholesterol to phosphatide ratio when compared to articular chondrocytes; they also incorporated more of C18:1 and less C16:0 into their major lipid types. Whether these differences arise from specific metabolic regulation or are a consequence of chondrocyte organization in primary culture remains unclear.

Effect of magnesium on lipid-induced calcification: an in vitro model for bone mineralization

The effect of Mg on hydroxyapatite proliferation induced by phosphatidyl serine, phosphatidyl inositol, and calcium-acidic phospholipid-phosphate complexes has been studied in metastable calcium phosphate solutions of constant ionic strength and variable Mg/Ca ratio. Mg inhibits formation of the Ca-acidic phospholipid phosphate complexes, probably by competing with Ca for sites on the phospholipid molecules. Once the complexed acidic phospholipids were present, Mg has no effect on the proliferation of hydroxyapatite. This is shown by the invariant first-order rate constant for the disappearance of CA during hydroxyapatite proliferation (kCa = 0.0037 h-1) in solutions with Mg/Ca weight ratios ranging 0/1 to 10/1. These studies suggest that the presence of Mg does affect in vivo calcification and that the initiation of calcification by means of a Ca-PL-PO4 complex may be dependent on the Mg/Ca ratio in the calcifying tissue.