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PubMed1999

Cell-crystal interactions and kidney stone formation.

BACKGROUND: Renal tubular fluid in the distal nephron is supersaturated with calcium and oxalate ions that nucleate to form crystals of calcium oxalate monohydrate (COM), the most common crystal in renal stones. How these nascent crystals are retained in the nephron to form calculi in certain individuals is not known. METHODS: The results of experiments conducted in this and other laboratories that employ cell culture model systems to explore renal epithelial cell-urinary crystal interactions are described. RESULTS: COM crystals rapidly adhere to anionic sites on the surface of cultured renal epithelial cells, but this process can be inhibited, if specific urinary anions such as glycosaminoglycans, uropontin, nephrocalcin, or citrate are available to coat the crystalline surface. Therefore, competition for the crystal surface between soluble anions in tubular fluid and anions on the apical cell surface could determine whether or not a crystal binds to the cell. A similar paradigm describes adhesion of calcium phosphate (hydroxyapatite) crystals, also a common constituent of human stones. Once bound, COM and hydroxyapatite crystals are quickly internalized by renal cells; reorganization of the cytoskeleton, alterations in gene expression, and initiation of proliferation may then ensue. Each of these cellular events appears to be regulated by a different set of extracellular factors. Over several weeks in culture, renal cells (BSC-1 line) dissolve internalized crystals, although once a cell binds a crystal, additional crystals are more likely to bind, possibly forming a positive feedback loop that results in kidney stone formation. CONCLUSIONS: Increased knowledge about the cell-crystal interaction, including identification of molecules in tubular fluid and on the cell surface that modulate the process, and understanding its mechanism of action appear critical for explaining the pathogenesis of nephrolithiasis.

Crystallization↗
PubMed2003

Optimizing the crystal size and habit of beta-sitosterol in suspension.

The aim of this work was to survey how processing parameters affect the crystal growth of beta-sitosterol in suspension. The process variables studied were the cooling temperature, stirring time and stirring rate during recrystallization. In addition, we investigated the effect a commonly used surfactant, polysorbate 80, has on crystal size distribution and the polymorphic form. This study describes the optimization of the crystallization process, with the object of preparing crystals as small as possible. Particle size distribution and habit were analyzed using optical microscopy, and the crystal structure was analyzed using X-ray diffractometry. The cooling temperature had a remarkable influence on the crystal size. Crystals with a median crystal length of approximately 23 microm were achieved with a low cooling temperature (<10 degrees C); however, a fairly large number of crystals over 50 microm appeared. Higher cooling temperatures (>30 degrees C) caused notable crystal growth both in length and width. Rapid (250 rpm), continuous stirring until the suspensions had cooled to room temperature created small, less than 50 micro m long (median <20 microm), needle-shaped crystals. The addition of surfactant slightly reduced the size of the initially large crystals. Both hemihydrate and monohydrate crystal forms occurred throughout, regardless of the processing parameters. By using an optimized process, it was possible to obtain a microcrystalline suspension, with a smooth texture.

Chemistry, Pharmaceutical↗
PubMed2003

Physicochemical and crystal structure analyses of the antidiabetic agent troglitazone.

The antidiabetic agent troglitazone has two asymmetric carbons located at the chroman ring and the thiazolidine ring and is produced as a mixture of equal amounts of four optical isomers, 2R-5S, 2S-5R, 2R-5R, and 2S-5S. The crystalline powdered drug substance consists of two diastereomer pairs, 2R-5R/2S-5S and 2R-5S/2S-5R. There are many types of crystals obtained from various crystallization conditions. The X-ray structure analysis and the physicochemical analyses of troglitazone were performed. The solvated crystals of the 2R-5R/2S-5S pair were crystallized from several solutions: methanol, ethanol, acetonitrile, and dichloromethane. The ratio of solvent and troglitazone was 1 : 2 (L1/2-form). The monohydrate crystals were obtained from aqueous acetone solution (L1-form). On the other hand, only an anhydrate crystal of the 2R-5S/2S-5R pair was crystallized from various solutions (H0-form). The dihydrous mixed crystal (MA2-form) was obtained from a mixture of the two diastereomer pairs of 2R-5R/2S-5S and 2R-5S/2S-5R in equal amounts by the slow evaporation of aqueous acetone solution. The crystal structure of the MA2-form is similar to the H0-form. When the MA2 crystal was kept under low humidity, it was converted into the dehydrated form (MA0-form) with retention of the single crystal form. The structure of the MA0-form is isomorphous to the H0-form. The MA2-form was converted into the MA0-form and vice versa with retention of the single crystal under low and high humidity, respectively. The crystallization and storage conditions of the drug substances were successfully analyzed.

Chemical Phenomena↗
PubMedDate not supplied

Changes in calcium oxalate crystal morphology as a function of supersaturation.

PURPOSE: To study the changes in calcium oxalate crystal morphology induced by different levels of supersaturation (SS) in human urine. MATERIALS AND METHODS: Twenty-four hours urine samples from 5 normal men were collected. Each specimen was centrifuged and filtered. About 200 mL of each sample was dialyzed overnight. Aliquots of 2 mL of urine was then added to a 24-wells tissue culture plate and checked for crystal absence. Calcium oxalate crystals were precipitated from each sample by adding sodium oxalate and calcium chloride in sufficient quantities to induce spontaneous crystallization. Finally, each plate hole was examined with an inverted polarized microscope (X500 magnification). Initial SS of each sample relative to calcium oxalate was calculated using an iterative computer program. RESULTS: Crystal formation was connected to relative calcium oxalate (CaOx) SS. At SS of 10, small crystals of similar shape were formed, mainly CaOx dihydrate morphology. At SS of 30, there was an enormous increase in the number of crystals, that kept the same size. SS greater than 50 produced larger crystals with different shapes and multiple crystalline aggregates. Urine was able to tolerate, i.e., to avoid crystal formation, until SS ratios of approximately 10. CONCLUSIONS: Relative CaOx SS and the concentration ratio of calcium to oxalate are important determinanting factors of crystal morphology. Non-dialyzable urinary proteins can act as inhibitors and influence the structure of formed crystals. Additional studies from patients with kidney stones are needed in order to establish whether crystal size and habit distribution are different from crystals in normal urine.

Calcium Oxalate↗
PubMed1979

[Scanning electron microscopic observations of calcium pyrophosphate crystals of joint tissues and synovial fluid (author's transl)].

The deposition and ultrastructure of calcium pyrophosphate (CPPD) crystals in joint tissues of pseudogout patients and cadavers were studied. Nine calcified menisci, 2 articular cartilages and 6 samples of synovial fluid were examined by scanning electron microscopy (SEM). Some of them were examined by analytical electron microscopy (EMMA). In the samples of menisci and cartilages, the findings were compared with those in the soft X-ray examinations and polarized light microscopy. The results are summarized as follows: 1) SEM observation of the cut surfaces of calcified menisci and cartilages showed a three-dimensional ultrastructure for the CPPD crystals. The crystals in the synovial fluid taken from pseudogout knees were also clearly demonstrated by this method. The EMMA analysis provided the possibility to examine the structure and content of the crystals simultaneously. 2) Crystal deposition in the meniscus varied with the depth of the tissues; it was diffuse in the collagen framework of the superficial layer, but showed accumulation in the deep layer where a clear line of demarcation between the collagen framework and crystals was seen. 3) The crystals in the meniscus were rod, granular or rectangular in shape, and 0.2-6.5 micro by 0.2-3.5 micro in size. Crystals from the articular cartilage were granular or rod-like in shape, and 0.2-3.5 micro by 0.2-1.0 micro in size. Most of the crystals found in the synovial fluid were rod-shaped. 4) X-ray microanalysis of the meniscus crystals by EMMA showed the same pattern of PK alpha, CaK alpha, and CaK beta content as that of CPPD crystals commercially available. The P/Ca ratio was about 0.7. 5) SEM and EMMA examination can be very useful for accurate identification of the form and content of the tiny crystals in joint tissues and synovial fluid. This can also be useful in proving a diagnosis of crystal-induced synovitis.

Calcinosis↗
PubMed1986

Arthropathies associated with calcium-containing crystals.

Monosodium urate crystals are clearly related to acute attacks of gout and to the hard tissue destruction of chronic tophaceous gout. Fortunately, the acute attacks are readily treated with anti-inflammatory drugs, and destructive changes due to tophi may be prevented or reversed, at least in part, by the intelligent control of serum urate levels. Control of gout is one of the premier success stories of modern medicine. In contrast, the number of patients who have arthritis associated with crystals that contain calcium appears to be rising--perhaps a function of better recognition, perhaps related to the aging of the population. CPPD and BCP crystals can be associated with acute or subacute inflammation, but as in acute gout, it is easily controlled with anti-inflammatory drugs or by local injections of corticosteroids. A direct relationship of BCP and CPPD crystals to the associated destructive arthropathies has been hypothesized and is supported by clinical observations, animal studies, and in vivo experiments. Unlike gout, which is usually associated with a systemic metabolic abnormality (i.e., hyperuricemia), calcium crystals deposition seem to be a localized phenomenon, although numerous local sites in several joints are often involved in a given patient. Tissue degeneration in gout clearly follows (tophaceous) crystal deposition. Calcium crystal deposition may follow, rather than precede, destructive joint changes. Alternatively, both destructive changes and crystal deposition may derive independently from a common, still obscure, biochemical abnormality of joint tissues. P. A. Dieppe and colleagues believe that calcium crystal deposition follows either primary or secondary tissue degeneration but that the crystals exert a positive feedback effect (amplification loop) that accelerates degeneration. Each of those formulations of a pathogenetic role for crystals may be true in a given case, analogous to the etiology of primary and secondary forms of hyperuricemia and to sodium urate crystal deposition coexistent with osteoarthritis (tophus formation in Heberden's nodes). Conclusive proof of a significant role for BCP or CPPD crystals in the pathogenesis of human joint tissue damage depends on interrupting the postulated disease mechanism and showing that this prevents joint deterioration and leads to significant repair of existing damage. Our current position is somewhat analogous to that of our colleagues who had to contend with management of gouty arthritis before the advent of effective drugs for control of hyperuricemia.

Aged↗
PubMed1981

Calcium oxalate crystal growth in human urinary stones.

Calcium oxalate stones are very common and increasing. Crystal growth is no less important than the crystal nucleation in the pathogenesis of stone formation. The crystal growth was studied in human calcium oxalate stones by a combined electron microscopy and x-ray diffraction. The main mode of weddellite growth was interpenetration twinning of tetrahedral bipyramids. Bipyramids may form as initial crystal seeds, develop from anhedral crystals (crystals which lack flat symmetric faces) of spherular or mulberry shape, develop on the surface of preformed bipyramids by spiral dislocation mechanisms, or develop on whewellite crystal by heterogeneous nucleation and epitaxy. Heterogeneous nucleations of whewellite on weddellite, and calcium apatite on whewellite were also observed. Whewellite grew mainly by parallel twinning. Interpenetration twinning was exceptional. Transformation of anhedral to euhedral (completely bounded by flat faces that are set ar fixed angles to one another) whewellite occurred by parallel fissurations followed by brick wall like stacking of the crystals, while euhedral transformation of weddellite occurred by protrusion of bipyramids frm anhedral crystal surface. Occasionally, an evidence of crystal dissolution was noted. Although an aggregation of crystals is believed to play a pivotal role in stone nidus formation, growth in size of the formed crystals, and twinning and epitactic crystal intergrowth apparently play a significant role in the obstructive urinary stone formation.

Calcium Oxalate↗
PubMed1994

Formation of cholesterol monohydrate crystals in macrophage-derived foam cells.

In a previous study using the J774 macrophage foam cells, we quantitated the accumulation of unesterified (free) cholesterol derived from cholesteryl ester hydrolysis in lysosomes, after phagocytic uptake of cholesteryl ester droplets. In the present study, we examined whether the accumulation of free cholesterol in lysosomes leads to the formation of cholesterol monohydrate crystals by analyzing the lipid composition of low density lysosome fractions isolated from cholesteryl ester-loaded macrophages after a 24-h incubation. Phase diagrams of the constituent lipids in the lipid-filled lysosomes predicted the formation of cholesterol monohydrate crystals. The formation of cholesterol monohydrate crystals was observed in cholesteryl ester-loaded macrophages after a 48-h incubation by polarizing light microscopy. The crystals had a density of 1.04 g/ml and the morphology of cholesterol monohydrate crystals with an acute edge angle of about 80 degrees. The crystals appeared as needles as well as plates and melted only when heated to greater than 85 degrees C. The physical properties of these crystals are characteristic of cholesterol monohydrate. In our studies, crystal formation was observed even when cells had active acyl-CoA:cholesterol acyltransferase or when cholesterol efflux was stimulated. Electron microscopy and acid phosphatase cytochemistry of lysosomes in cholesteryl ester-loaded cells confirmed that cholesterol crystal formation occurred within lipid-loaded lysosomes. Time-lapse video microscopic studies revealed that most of the cells containing cholesterol monohydrate crystals not only remain viable but also have the capacity to translocate single crystals within cells. The data demonstrate that lysosomal accumulation of free cholesterol in macrophages after phagocytic uptake and hydrolysis of cholesteryl ester droplets leads to the formation of cholesterol monohydrate crystals within lipid-filled lysosomes. Such a process may lead to deposition of free cholesterol and cholesterol monohydrate crystals in macrophage foam cells during the progression of atherosclerosis.

Animals↗
PubMed1995

A rapid, simple high capacity cholesterol crystal growth assay.

Cholesterol crystal "nucleation time", more recently referred to as cholesterol crystal observation time, is defined as the first appearance of cholesterol crystals from isotropic crystal-free biles on light microscopy. This test is used to assess the potency of nucleating agents. Crystal appearance has conventionally been determined by polarizing light microscopy and crystal growth by counting the number of crystals. In this study we adapted a spectrophotometric method to a microtiter plate reader to generate cholesterol crystal growth curves. Model biles were prepared with a cholesterol saturation of 1.2 to 1.3 and total lipid concentration of 10.7 g/dl (taurocholate, 125 mM; cholesterol, 16.8-18.4 mM; phospholipid, 43 mM). Pronucleating IgM samples were used to establish and validate the assay. Cholesterol crystal growth curves were generated by reading absorption at 630 nm daily on a Dynatech microplate reader. Results were correlated to cholesterol crystal counts as determined by polarizing light microscopy. Standard curves generated from absorbencies of known masses of cholesterol crystals were used to quantify the mass of cholesterol crystals formed over the observation period. The assay was applied to known pronucleating biliary immunoglobulins. Results obtained were similar to our previous report that biliary IgM is more potent than biliary IgG. We conclude that using microplates and a microtiter plate reader provides a rapid high capacity method for detecting cholesterol crystal growth to assess potential nucleating agents in nucleation assays.

Bile↗
PubMed1996

Adhesion and endocytosis of calcium oxalate crystals on renal tubular cells.

The present investigation was designed to study interactions between Madin-Darby canine kidney (MDCK) cells and calcium oxalate monohydrate (COM) crystals and to clarify the significance of these crystal-cell interactions in stone pathogenesis. MDCK cells cultured in the presence of COM crystals showed a time-dependent uptake of crystals; this was specific for COM crystals. In the dynamic model system designed to study these phenomena under more physiological conditions, COM crystals adhered to the cell surface and were subsequently internalized. In this endocytotic process, the microvilli of the cell appeared to play an important role. The observation by scanning electron microscopy of complexes consisting of aggregated COM crystals and cell debris led us to speculate that adhesion and endocytosis of crystals might provide the calculus nidus for aggregation and retention of crystals in the renal tubule. Furthermore, glycosaminoglycans and the macromolecular fraction of human urine were shown to have the ability to inhibit the cellular uptake of crystals. Evidence that similar processes may also occur in vivo was obtained using an experimental stone model in rats. Our experiments revealed that most of the COM crystals adhered to the tubular cells and some crystals were endocytosed by the cell. Thus, these crystal-cell interactions might be one of the earliest processes in the formation of kidney stones. Further elucidation of the mechanism and the regulatory factors involved in this process may provide new insight into stone pathogenesis.

Adhesiveness↗
PubMed1995

Control of crystal forms of apoferritin by site-directed mutagenesis.

Surface charges of protein molecules are not only important to biological functions but also crucial to the molecular assembly responsible for crystallization. Appropriate alteration in the surface charge distribution of a protein molecule induces new molecular alignment in the proper direction in the crystal and, hence, controls the crystal form. Apoferritin molecules are known to crystallize in two- and three-dimensional forms in the presence of cadmium ions, which bridge neighboring protein molecules. Here we report a controlled transformation of the apoferritin 2-D crystal by site-directed mutagenesis. In mutant apoferritin, two amino acid residues binding a cadmium-ion through their negative charge, were replaced by one type of nonionic amino acid residues. The amino acid residues, Asp-84 and Gln-86 in the sequence of recombinant (i.e., wild-type) horse L-apoferritin, were replaced by Ser. The wild-type apoferritin yielded a hexagonal lattice 2-D crystal in the presence of cadmium ions. In contrast, the mutant apoferritin yielded two types of oblique crystals independent of the presence of cadmium ions. Image reconstruction of electron micrographs of the mutant crystals made clear that the mutant apoferritin molecules oriented themselves with the 2-fold symmetry axis perpendicular to the crystal plane in both crystals, while the wild-type apoferritin molecules oriented themselves with the 3-fold symmetry axis perpendicular to the crystal plane. The changes of crystal forms and molecular orientation in the 2-D crystals were well explained by a change of the electrostatic interactions induced by the mutagenesis.

Animals↗
PubMed2001

Ostwald-Meyers Metastable Region in LiBr Crystallization-Comparison of Measurements with Predictions.

Experiments have been performed to measure the Ostwald-Meyers metastable region during crystallization from concentrated LiBr solutions. Solution thermodynamics shows that several hydrated LiBr salts and ice can crystallize depending upon the concentration of LiBr in aqueous solution. The available solubility data were interpreted to give solubility products of several hydrated LiBr salts using the formulation of Helgeson, which accounts for the activity of water. The crystallization temperature was measured by monitoring to +/-0.01 degrees C the temperature of solutions inside test tubes placed in a cooling bath programmed at a cooling rate of 20 degrees C/h. A release of the heat of crystallization identifies the temperature of crystallization. The equilibrium solubility was verified by crystallization with seed crystals present. The crystallization temperature without seeds present was 10 to 20 degrees C less than the equilibrium solubility temperature corresponding to the Ostwald-Meyers metastable region. This crystallization temperature measured at 20 degrees C/h was shown to correspond to nucleation on the surface of the test tube with an interface energy of 40+/-1.2 erg/cm(2). Homogeneous nucleation from solution data shows the crystallization temperature to be from 40 to 50 degrees C below the equilibrium solubility curve and to be accurately predicted by homogeneous nucleation with an interface energy of 26 erg/cm(2), the literature value of the ice/water interface. Since the hydrated LiBr salts have surfaces that expose structured water molecules to the solution, this value is believed to be an appropriate value of the interface energy of the hydrated LiBr crystals. Crystallization temperature measurements were performed at different cooling rates, showing that slower cooling rates gave a narrower Ostwald-Myers metastable zone as is expected. Induction time measurements showed that the time to spontaneous crystallization increases as the supersaturation is decreased. Copyright 2001 Academic Press.

Journal Article↗
PubMed1996

X-ray diffraction, electron microscopy, and Fourier transform infrared spectroscopy of apatite crystals isolated from chicken and bovine calcified cartilage.

Apatite crystals of the calcified zone of the subarticular cartilaginous growth plates of the long bones of young growing chickens and calves were isolated by low temperature reaction with hydrazine and plasma ashing and examined by electron microscopy, electron diffraction and microprobe analysis, and computer-generated deconvolution of the spectra obtained by Fourier transform infrared spectroscopy. The crystal habit was that of wide, very thin, relatively long rectangular plates, which tended to form small clusters of crystals, possibly because reaction with hydrazine alone did not remove all of the organic matrix constituents. Further reaction with low power plasma ashing released more of the isolated crystals although to a lesser extent than was possible with bone. Stereograms of the small clusters showed that many of the crystals in the small isolated aggregates of crystals were bent and/or curved. Together with the resultant overlap of individual adjacent crystals, they also produced images of sharp, very dense lines, reminiscent of the electron-dense needle or rod-like appearances frequently observed by transmission electron microscopy of thin sections of calcified cartilage and thought to represent the habit of the apatite crystals. No true rod or needle-like crystals were observed in the isolated crystals. Although the overall general apatitic structure of the apatite crystals was similar to that of the apatitic crystals of bone, the individual crystals were significantly larger than those of bone from the same specimen, and there were small but significant differences in the concentrations of acid phosphate and carbonate groups and in their short range order.

Animals↗
PubMed2005

Chiral symmetry breaking and polymorphism in 1,1'-binaphthyl melt crystallization.

We have studied chiral symmetry breaking in the melt crystallization of 1,1'-binaphthyl. We confirm that chiral symmetry breaking can be induced by stirring the melt as it crystallizes. We find an additional process of vapor crystallization to occur alongside the melt crystallization. This complicates the analysis of the enantiomorphism by introducing a further phenomenon: that of polymorphism. Crystallographic studies by X-ray diffraction reveal two polymorphs of 1,1'-binaphthyl that are made up of two different conformers of each of the two enantiomeric forms of the molecule. Crystals from the melt are generally chiral tetragonal crystals (P42(1)2(1)) composed of (R)- or (S)-1,1'-binaphthyl in a transoid conformer, while those from the vapor are racemic monoclinic crystals (C2/c) made up of the cisoid conformer of both (R)- and (S)-1,1'-binaphthyl enantiomers. The main intermolecular interactions in all these crystals are weak aromatic CH/pi hydrogen bonds, which are responsible for the enantiomeric discrimination in the molecular recognition during crystallization. A tendency for whisker crystal formation is notable in 1,1'-binaphthyl. In stirred crystallization, fluid and mechanical forces can break off these whiskers, which provide secondary nuclei for further crystallization. This autocatalytic mechanism induces chiral symmetry breaking during the crystallization.

Journal Article↗
PubMed2005

Biologic effects of calcium-containing crystals.

PURPOSE OF REVIEW: Calcium-containing crystals can cause the degeneration of articular tissues in two separate pathways. In the direct pathway, crystals directly induce synoviocytes to proliferate and produce metalloproteinases and prostaglandins. The other pathway, the paracrine pathway, involves the interaction between crystals and macrophages/monocytes, which leads to the synthesis and release of cytokines, which can reinforce the action of crystals on synoviocytes and/or induce chondrocytes to secrete enzymes and which eventually causes the degeneration of articular tissues. The purpose of this review is to highlight the recent findings of the biologic effect of these crystals. RECENT FINDINGS: In the past few years, major advances in the understanding of the biologic effect of crystals and the signal transduction pathway of crystal-induced cell activation offer a unique opportunity to examine the role of crystal in osteoarthritis and cartilage degeneration. SUMMARY: Evidence for a causal role of crystals in cartilage degeneration in osteoarthritis is primarily inferential and is based on correlative data. Clinical observations indicate that exaggerated and uniquely distributed cartilage degeneration is associated with these deposits. Measurements of putative markers of cartilage breakdown suggest that these crystals magnify the degenerative process. Studies have shown two potential mechanisms by which crystals cause degeneration. These involve the stimulation of mitogenesis in synovial fibroblasts and the secretion of metalloproteinases by cells that subject these crystals to phagocytosis. New information on how crystals form and how they exert their biologic effects will help in the design of an effective therapeutic approach.

Calcium Phosphates↗
PubMed2001

Biosynthesis of L-ascorbic acid and conversion of carbons 1 and 2 of L-ascorbic acid to oxalic acid occurs within individual calcium oxalate crystal idioblasts.

L-Ascorbic acid (AsA) and its metabolic precursors give rise to oxalic acid (OxA) found in calcium oxalate crystals in specialized crystal idioblast cells in plants; however, it is not known if AsA and OxA are synthesized within the crystal idioblast cell or transported in from surrounding mesophyll cells. Isolated developing crystal idioblasts from Pistia stratiotes were used to study the pathway of OxA biosynthesis and to determine if idioblasts contain the entire path and are essentially independent in OxA synthesis. Idioblasts were supplied with various (14)C-labeled compounds and examined by micro-autoradiography for incorporation of (14)C into calcium oxalate crystals. [(14)C]OxA gave heavy labeling of crystals, indicating the isolated idioblasts are functional in crystal formation. Incubation with [1-(14)C]AsA also gave heavy labeling of crystals, whereas [6-(14)C]AsA gave no labeling. Labeled precursors of AsA (L-[1-(14)C]galactose; D-[1-(14)C]mannose) also resulted in crystal labeling, as did the ascorbic acid analog, D-[1-(14)C]erythorbic acid. Intensity of labeling of isolated idioblasts followed the pattern OxA > AsA (erythorbic acid) > L-galactose > D-mannose. Our results demonstrate that P. stratiotes crystal idioblasts synthesize the OxA used for crystal formation, the OxA is derived from the number 1 and 2 carbons of AsA, and the proposed pathway of ascorbic acid synthesis via D-mannose and L-galactose is operational in individual P. stratiotes crystal idioblasts. These results are discussed with respect to fine control of calcium oxalate precipitation and the concept of crystal idioblasts as independent physiological compartments.

Araceae↗
PubMed1989

Crystal morphology and decalcification patterns compared in rat and human enamel and synthetic hydroxyapatite.

The purpose of this investigation was to compare morphology and dissolution patterns by ultrastructural examination of rat and human enamel crystals as well as synthetic apatite crystals. Mature enamel crystals were of particular interest, since crystal maturation appears to be inhibited in amelogenesis imperfecta. Specimens were isolated from developing and mature rat incisor enamel. Rat enamel, mature human enamel, and synthetic apatite were thin-sectioned without decalcification and examined by transmission electron microscopy. Some sections were exposed to acid, and selected synthetic apatite sections were further treated for removal of embedding plastic, followed by vacuum-shadow-coating with carbon. Results showed that cross-sections of rat, human, and synthetic crystals had a distortion in the flattened hexagonal outline in regions where the growth of one crystal impinged on another. Crystal dissolution occurred preferentially along the c-axis, producing a central defect or hole in the crystals. Preliminary studies with weak acid on mature human enamel indicate that the relatively soluble crystal core is quickly dissolved, while the outer shell remains intact over a much longer period of time. In the mature rat and human enamel, this crystal hole formation had a consistent dimension of approximately 10-nm thickness. The crystal hole dimension was the same size as crystals that are formed during the early secretory phase in rat amelogenesis. Acid-treated synthetic apatite also showed dissolution of the crystal core along the c-axis, but dimensions of the hole were not consistent.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Ultrastructure, morphology and crystal growth of biogenic and synthetic apatites.

The morphology, structure and crystal growth of apatite crystals isolated from calcified turkey tendon and synthetic carbonated apatites have been examined using high resolution transmission electron microscopy. The biogenic apatite consisted of small (35 x 20 x 5 nm) platelike crystals. Despite their irregular shape and ill-defined edges, individual particles were single domain crystals. Lattice images recorded from isolated turkey tendon crystals indicated that the crystallographic c-axis (0001) of apatite lies in the plane of the plate and parallel to the length of the crystallites. Lattice images suggested that the top face corresponds to the (1100) face of carbonated apatite. Lattice fringes observed in platelike crystallites viewed from the side corresponded to the projection of the apatite structure viewed along the [1120] direction. Thus, it can be argued that crystal growth is constrained along the [1100] direction, extends laterally along the [1120] direction, and is maximal along the [0001] direction. This latter direction is aligned with the collagen fiber axis. A mean length to width ratio (1.7) was determined by systemically measuring the maximum distances parallel and perpendicular to the c-axis identified from lattice images of the crystals. Similar information was obtained from lattice images of crystals located in collagen fibres. This confirmed that the morphological and structural features of isolated turkey tendon apatite crystals correlate directly with the in vivo crystallochemical characteristics of apatite. Crystals of synthetic carbonated apatite prepared at 37 degrees C were also platelike and, although generally much larger, had length to width ratios comparable with the turkey tendon apatite. The synthetic carbonated apatites were noticeably more sensitive to radiolytic damage than the turkey tendon crystals. The crystallographic c-axis of the inorganic particles was aligned parallel with the long, physical axis of the plate and the top face was identified as (1100). Similar data were also obtained from noncarbonated synthetic apatite samples. The results of the present study offer critical information about the crystal growth of individual carbonated apatite crystals in calcified turkey tendon and its relationship to the morphology of the crystallites. As similar growth characteristics are expressed in synthetic analogues, the data bring into question the putative regulatory role of the collagen-based matrix upon the nucleation and growth of biogenic apatite.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗