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PubMed1985

Cholesterol gallstone pathogenesis: a study of potential nucleating agents for cholesterol crystal formation in bile.

Cholesterol monohydrate crystal formation was measured quantitatively in model bile solutions, which were supersaturated with cholesterol, by a radiochemical method and qualitatively in human gallbladder bile by polarizing microscopy. Various agents, which have been postulated to act as nucleating factors for cholesterol crystal and gallstone formation, were added to bile and their effect on the appearance of cholesterol crystals was determined. These agents included calcium salts found in gallstones (calcite, aragonite, apatite, bilirubinate), Escherichia coli bacteria, pigment residues from cholesterol gallstones, bilirubin and several mucin preparations. Human gallbladder bile, which was collected from patients with and without cholesterol gallstones, was also mixed with model bile to examine whether nucleating or anti-nucleating factors were present. None of the agents tested markedly and consistently promoted cholesterol monohydrate crystal formation in model or human bile, except seed crystals of cholesterol monohydrate which were used as a control. Human gallbladder bile from obese patients without gallstones delayed the appearance of cholesterol crystals in model bile solutions, whereas gallbladder bile from gallstone patients did not. These results do not provide experimental support for the hypothesis that calcium salts and pigment material found in gallstones, or gallbladder mucin at concentrations less than 10 mg/ml, act as nucleating agents for cholesterol crystal and stone formation. The difference between gallbladder biles from patients with and without gallstones in their propensity to form cholesterol crystals may be due to the presence of an anti-nucleating factor in normal bile.

Animals↗
PubMed1997

HbC compound heterozygotes [HbC/Hb Riyadh and HbC/Hb N-Baltimore] with opposing effects upon HbC crystallization.

Compound heterozygotes of variant haemoglobins (Hbs) with HbC, with or without novel phenotypic changes, have provided insight into the molecular basis of the interacting haemoglobins and information concerning the role of specific residues in the crystallization of oxy HbC. A high phosphate buffer system has proved useful for studying the effects of variant haemoglobins (naturally co-existing with HbC in the red cell) on the oxy HbC crystallization process and has led us to conclude that beta87 and beta73 are contact sites of the oxy HbC crystal. We now present investigations from two HbC compound heterozygotes which exhibit opposing effects upon HbC crystallization: HbC/Hb N-Baltimore (beta95 Lys-->Glu) and HbC/Hb Riyadh (beta120 Lys-->Asn). The latter inhibits the in vitro crystallization of HbC, explaining the lack of erythrocyte abnormalities (with the exception of microcytosis) in the doubly heterozygous infant. In contrast, Hb N-Baltimore accelerates the crystallization of HbC, contributing to multiple abnormalities in red cell morphology, albeit in the absence of morbidity. We conclude that (1) beta120 and beta95 are additional contact sites in the crystal, and (2) the HbC/Hb Riyadh haemoglobinopathy demonstrates that crystallization may not be required for the generation of the observed microcytosis and increased red cell density in HbC-containing red cells.

Adult↗
PubMed1999

Inhibition of calcium oxalate crystal growth and aggregation by prothrombin and its fragments in vitro: relationship between protein structure and inhibitory activity.

During blood coagulation, prothrombin (PT) is ultimately degraded to three fragments, thrombin, fragment 1 (F1) and fragment 2 (F2), which, collectively, contain all of the structural features of PT. One of these fragments, F1, is excreted in human urine and is the principal protein occluded into calcium oxalate (CaOx) crystals precipitated from it. This urinary form of F1, which we have named urinary prothrombin fragment 1 is present in calcium stones and is a potent inhibitor of CaOx crystallization in urine in vitro. The aim of this study was to determine whether PT itself and its other activation products, namely, thrombin, F1 and F2 also inhibit CaOx crystallization, by comparing their effects in a seeded, inorganic crystallization system. A secondary objective was to assess the relationship between the structures of the proteins and their inhibitory activities. PT was isolated from a human blood concentrate rich in vitamin K-dependent proteins. Following initial cleavage by thrombin, the resulting fragments, F1 and F2, were purified by a combination of reversed phase HPLC and low pressure column chromatography. The purity of the proteins was confirmed by SDS/PAGE and their individual effects on CaOx crystallization were determined at the same concentration (16.13 nM) in a seeded, metastable solution of CaOx using a Coulter Counter. [14C]Oxalate was used to assess deposition of CaOx and crystals were visualized using scanning electron microscopy. The Coulter Counter data revealed that the proteins reduced the size of precipitated crystals in the order F1 > PT > F2 > thrombin. These findings were confirmed by scanning electron microscopy which showed that the reduction in particle size resulted from a decrease in the degree of crystal aggregation. [14C]Oxalate analysis demonstrated that all proteins inhibited mineral deposition, in the order F1 (44%) > PT (27.4%) > thrombin (10.2%) > F2 (6.5%). It was concluded that the gamma-carboxyglutamic acid domain of PT and F1, which is absent from thrombin and F2, is the region of the molecules which determines their potent inhibitory effects. The superior potency of F1, in comparison with PT, probably results from the molecule's greater charge to mass ratio.

Calcium Oxalate↗
PubMed2002

Osteopontin regulates adhesion of calcium oxalate crystals to renal epithelial cells.

BACKGROUND: The association of calcium crystals with renal tubular cells is an important factor during the formation of urinary stones. We previously reported the strong expression of osteopontin (OPN) on renal tubular cells in the stone-forming kidney, suggesting that OPN plays a role in the crystal-cell interaction. In the present study, we examined the biological consequences of inhibiting OPN expression at the translational level on the formation and adhesion of crystals. METHODS: We synthesized antisense OPN expression vector (pTet-OPNas) using the tetracycline-regulated expression system. The pTet-OPNas was constructed using a mouse OPN cDNA sequence in an inverted (antisense) orientation. Two clones (NRK-52E/ASs) were identified by transfection of pTet-OPNas into NRK-52E cells and they showed a marked reduction of OPN synthesis in the absence of tetracycline. Calcium oxalate (CaOx) crystal suspension was spread homogeneously on top of the NRK-52E cells. After incubation, the association of CaOx crystals and cells was visualized by scanning electron microscopy. RESULTS: Intact NRK-52E cells, NRK-52E cells transfected with empty vector and tetracycline-treated antisense clones (NRK-52E/ASs), under identical conditions, were associated with CaOx crystals. In contrast, the expression of antisense OPN prevented the association of CaOx crystals with NRK-52E cells. CONCLUSIONS: Osteopontin plays a crucial role in the adhesion process of CaOx crystals to renal tubular cells in stone formation.

Animals↗
PubMed1999

Uric acid-binding proteins in calcium oxalate stone formers and their effect on calcium oxalate crystallization.

OBJECTIVES: To study the effect of urinary uric acid-binding proteins of controls and stone formers on calcium oxalate crystal nucleation and aggregation. MATERIALS AND METHODS: Urine samples were collected over 24 h from 20 stone formers and from 20 age-matched normal controls. Uric acid crystallization was induced by adding equal volumes of 2.5 mmol/L uric acid. The bound proteins were separated on a cellulose column, and by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The effect of the separated fractions on calcium oxalate crystal nucleation and aggregation was assessed. RESULTS: The protein bound to unit mass of uric acid crystals was higher in hyperoxaluric urine than in control urine. On cellulose-column separation, the uric acid-crystal binding proteins produced three major protein peaks, i.e. fraction I (buffer), fraction II (0.05 mol/L sodium chloride in Tris-HCl buffer) and fraction III (0.3 mol/L sodium chloride in buffer), with a minor peak obtained on elution with increasing concentrations of sodium chloride in Tris-HCl buffer (pH 7.0). Fraction I derived from either stone formers or controls promoted calcium oxalate crystallization. Fraction II from the control samples was a strong inhibitor, whereas hyperoxaluric fraction II was less inhibitory. CONCLUSION: Uric acid-binding proteins isolated either from the urine of stone formers or controls modulated calcium oxalate crystal growth. Proteins isolated from stone formers were less inhibitory of crystal nucleation and aggregation. These proteins may act as a bridge, leading to the epitaxial deposition of calcium oxalate over a urate core.

Calcium Oxalate↗
PubMed2000

A novel basic protein from human kidney which inhibits calcium oxalate crystal growth.

OBJECTIVES: To isolate calcium oxalate-binding proteins from human kidney and characterize the functional properties. MATERIALS AND METHODS: Calcium oxalate crystals were prepared and allowed to interact at two different pH values with Triton-extracted human kidney homogenate. The proteins in the homogenate were isolated and fractionated on a cellulose column, and purified by high-performance liquid chromatography. The protein with the greatest oxalate binding activity at pH 4.5 was analysed for its amino-acid composition and characterized by Scatchard plot analysis, crystal growth, nucleation and aggregation studies. RESULTS: Three major protein fractions were eluted when calcium oxalate monohydrate was adsorbed at both pH values (designated as fractions I-III, according to their order of elution). The yield of fraction I and III was increased when adsorbed at an acidic pH. However, only fraction III had maximum oxalate binding activity at pH 4.5. When purified, this protein had maximum oxalate binding activity of approximately 270 pmol/mg protein and a molecular weight of approximately 23 kDa. Amino acid analysis showed that 18% of the total molar proportion was of basic amino acids, e.g. lysine and arginine, while acidic amino acids accounted for only 11%. Both alanine and glycine constituted approximately 41% of the total molar proportion. Modifications to the lysine group abolished oxalate-binding activity of the protein. The protein inhibited crystal growth by 82% at 0.8 micromol/L, while it inhibited the nucleation and aggregation of the crystals by 6% and 28%, respectively, at 49 nmol/L. The inhibition of both nucleation and aggregation was higher at pH 5.7 than at pH 7.4. Significantly, the protein induced the formation of intertwined calcium oxalate dihydrate crystals in a medium known to induce the formation of individual dihydrate crystals. CONCLUSION: The protein described here is the first reported basic inhibitor of calcium oxalate crystal growth with oxalate-binding activity at pH 4.5 that modulates calcium oxalate crystallization. It is suggested that this protein may play a physiologically significant role in inhibiting stone formation in acidic urine.

Calcium Oxalate↗
PubMed2002

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.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1980

Cholesterol crystals and the formation of cholesterol gallstones.

To examine the relation of cholesterol crystallization to the formation of gallstones, gallbladder bile was obtained by means of duodenal intubation in 54 patients (eight with asymptomatic gallstones) and from 17 patients undergoing cholecystectomy for cholelithiasis. Hepatic bile was obtained from nine patients with common-duct stones. Bile samples were examined for cholesterol monohydrate crystals and analyzed to determine the percentage of cholesterol saturation. Intubation in the eight patients with asymptomatic gallstones revealed a cholesterol saturation of 142 +/- 42 per cent (mean +/- S.D.) and crystals in five patients. Crystals were absent in the other 36 patients with supersaturated bile (cholesterol saturation, 166 +/- 44 per cent) and in the 10 patients with undersaturated bile (cholesterol saturation, 81 +/- 24 per cent). In the 26 patients with symptomatic cholelithiasis or common-duct stones, crystals were not seen in the bile of the seven patients with pigment stones but were present in the bile of all 19 patients with cholesterol stones. (In some cases crystals appeared only after 24 to 48 hours of incubation.) Cholesterol crystallization is probably a prerequisite for the formation of cholesterol gallstones; however, many subjects have no crystallization despite marked supersaturation.

Adult↗
PubMed2004

Adhesion at calcium oxalate crystal surfaces and the effect of urinary constituents.

Kidney stones, aggregates of microcrystals, most commonly contain calcium oxalate monohydrate (COM) as the primary constituent. The aggregation of COM microcrystals and their attachment to epithelial cells are thought to involve adhesion at COM crystal surfaces, mediated by anionic molecules or urinary macromolecules. Identification of the most important functional group-crystal face adhesive combinations is crucial to understanding the stability of COM aggregates and the strength of their attachments to epithelial cell surfaces under flow in the renal tubules of the kidney. Here, we describe direct measurements of adhesion forces, by atomic force microscopy, between various functional groups and select faces of COM crystals immersed in aqueous media. Tip-immobilized carboxylate and amidinium groups displayed the largest adhesion forces, and the adhesive strength of the COM crystal faces decreased in the order (100) > (121) > (010), demonstrating that adhesion is sensitive to the structure and composition of crystal faces. The influence of citrate and certain urinary proteins on adhesion was examined, and it was curious that osteopontin, a suspected regulator of stone formation, increased the adhesion force between a carboxylate tip and the (100) crystal face. This behavior was unique among the various combinations of additives and COM crystal faces examined here. Collectively, the force measurements demonstrate that adhesion of functional groups and binding of soluble additives, including urinary macromolecules, to COM crystal surfaces are highly specific in nature, suggesting a path toward a better understanding of kidney stone disease and the eventual design of therapeutic agents.

Adhesiveness↗
PubMed2006

Experiment and theory for heterogeneous nucleation of protein crystals in a porous medium.

The determination of high-resolution structures of proteins requires crystals of suitable quality. Because of the new impetus given to structural biology by structural genomics/proteomics, the problem of crystallizing proteins is becoming increasingly acute. There is therefore an urgent requirement for the development of new efficient methods to aid crystal growth. Nucleation is the crucial step that determines the entire crystallization process. Hence, the holy grail is to design a "universal nucleant," a substrate that induces the nucleation of crystals of any protein. We report a theory for nucleation on disordered porous media and its experimental testing and validation using a mesoporous bioactive gel-glass. This material induced the crystallization of the largest number of proteins ever crystallized using a single nucleant. The combination of the model and the experimental results opens up the scope for the rational design of nucleants, leading to alternative means of controlling crystallization.

Animals↗
PubMed2006

A fast response mechanism for insulin storage in crystals may involve kink generation by association of 2D clusters.

Crystals that are likely rhombohedral of Zn-insulin hexamers form in the islets of Langerhans in the pancreases of many mammals. The suggested functions of crystal formation is to protect the insulin from proteases and increase the degree of conversion of soluble proinsulin. To accomplish these ends, crystal growth should be fast and adaptable to rate fluctuations in the conversion reaction. Zn-insulin crystals grow layer by layer. Each layer spreads by the attachment of molecules to kinks located at the layers' edges, also called steps. The kinks are thought to be generated either by thermal fluctuations, as postulated by Gibbs, or by 1D nucleation of new crystalline rows. The kink density determines the rate at which steps advance, and these two kink-generation mechanisms lead to weak near-linear responses of the growth rate to concentration variations. We demonstrate for the crystallization of Zn-insulin a mechanism of kink generation whereby 2D clusters of several insulin molecules preformed on the terraces between steps associate to the steps. This mechanism results in several-fold-higher kink density, a faster rate of crystallization, and a high sensitivity of the kinetics to small increases of the solute concentration. If the found mechanism operates during insulin crystallization in vivo, it could be a part of the biological regulation of insulin production and function. For other crystallizing materials in biological and nonbiological systems, this mechanism provides an understanding of the often seen nonlinear acceleration of the kinetics.

Animals↗
PubMed2001

Comparing protein-ligand interactions in solution and single crystals by Raman spectroscopy.

By using a Raman microscope, we show that it is possible to probe the conformational states in protein crystals and crystal fragments under growth conditions (in hanging drops). The flavin cofactor in the enzyme para-hydroxybenzoate hydroxylase can assume two conformations: buried in the protein matrix ("in") or essentially solvent-exposed ("out"). By using Raman difference spectroscopy, we previously have identified characteristic flavin marker bands for the in and out conformers in the solution phase. Now we show that the flavin Raman bands can be used to probe these conformational states in crystals, permitting a comparison between solution and crystal environments. The in or out marker bands are similar for the respective conformers in the crystal and in solution; however, significant differences do exist, showing that the environments for the flavin's isoalloxazine ring are not identical in the two phases. Moreover, the Raman-band widths of the flavin modes are narrower for both in and out conformers in the crystals, indicating that the flavin exists in a more limited range of closely related conformational states in the crystal than in solution. In general, the ability to compare detailed Raman data for complexes in crystals and solution provides a means of bridging crystallographic and solution studies.

4-Hydroxybenzoate-3-Monooxygenase↗
PubMed1980

Electron microscope study of the kinetics of the fiber-to-crystal transition of sickle cell hemoglobin.

The intermediates and the rate-limiting step in the crystallization of deoxygenated sickle hemoglobin have been determined by a kinetic study with the use of electron microscopy. In slowly stirred solutions of deoxygenated hemoglobin S [Pumphrey, J. & Steinhardt, J. (1977) J. Mol. Biol. 112, 359--375], the sequential appearance of fibers have a diameter of approximately equal to 210 A, bundles of aligned fibers in well-ordered arrays, "thick" fibers of approximately equal to 470 A diameter, and microcrystals is observed. Only the fibers having a diameter of approximately equal to 210 A and bundles of aligned fibers are assigned as kinetically important intermediates of the fiber-to-crystal transition. Addition of microscopic seed crystals obtained from slowly stirred solutions of deoxyhemoglobin S to a solution composed of only fibers and hemoglobin monomers results in more rapid crystallization than in control solutions. Addition of seed crystals after the formation of bindles of aligned fibers does not alter the overall kinetics of crystallization. The results demonstrate that alignment of fibers is the rate-limiting step in the crystallization process and results in formation of nucleation sites for crystal growth.

Anemia, Sickle Cell↗
PubMed1989

Structural transitions in crystals of native aspartate carbamoyltransferase.

Screened precession x-ray photographs of crystals of native aspartate carbamoyltransferase (EC 2.1.3.2, from Escherichia coli) ligated with L-aspartate and phosphate reveal the presence of a crystal unit-cell dimension that is intermediate between the T (tense) and R (relaxed) states. Characterizing the intermediate (I) crystal is a c-axis unit-cell dimension of 149 A, halfway between the c-axis length of the T (c = 142 A) and R (c = 156 A) states, in the space group P321. Preservation of the P321 space group indicates that the intermediate crystal form retains a threefold axis of symmetry, and therefore the enzyme has at minimum a threefold axis; however, we do not know whether the molecular twofold axis is conserved. The I crystals are formed by soaking T-state crystals with L-aspartate and phosphate. By raising the concentration of L-aspartate we can further transform the I crystals, without fragmentation, to a form that has the same unit-cell dimensions as R-state crystals grown in the presence of N-(phosphonoacetyl)-L-aspartate.

Aspartate Carbamoyltransferase↗
PubMed1995

Overexpression, purification, and crystallization of the DNA binding and dimerization domains of the Epstein-Barr virus nuclear antigen 1.

The Epstein-Barr virus nuclear antigen (EBNA) 1 binds to and activates DNA replication from the latent origin of Epstein-Barr virus. Six different fragments of EBNA1 that retain DNA binding activity were expressed in bacteria, purified, and crystallized. Two fragments, EBNA470-619 and EBNA470-607, formed well ordered crystals that diffracted beyond 2.5-A resolution. Two different EBNA470-619 crystals were grown from sodium formate, pH 6-6.5. One crystal belonged to the trigonal space group P3 with unit cell dimensions a = b = 86.5 A and c = 31.8 A and with two molecules in the asymmetric unit. The other crystal, which appeared only twice and was likely related to the P3 crystal form, belonged to the trigonal space group P312 with cell dimensions a = b = 86.7 A and c = 31.8 A. Crystals of EBNA470-607 were grown by lowering the salt concentration to 0-100 mM NaCl at pH 6.0. These crystals belonged to the orthorhombic space group P2(1)2(1)2(1) and had cell dimensions a = 59 A, b = 66.9 A, and c = 69.8 A with two molecules in the asymmetric unit.

Antigens, Viral↗
PubMed1998

The influence of hydroxyapatite seed on the crystallization induced by volume reduction of solutions with an ion composition corresponding to that in the distal tubule at different pH levels.

OBJECTIVE: To simulate the crystallization process that might occur in the nephron segment from the distal part of the distal tubule (DTd) to the end of the collecting duct (CD), we evaporated salt solutions with an ion composition assumed to correspond to that in the DTd. MATERIAL AND METHODS: 100-mL samples of DTd solutions with and without dialysed urine (dU) and with hydroxyapatite (HAP) seed crystals were evaporated to a final volume of 10-20 mL at different starting pH levels. After evaporation, the number and volume of crystals were recorded in a Coulter Multisizer and the crystal morphology examined by scanning electron microscopy and x-ray crystallography. RESULTS AND CONCLUSIONS: Volume reduction of solutions with a pH of 6.5 resulted in a crystallization of calcium phosphate (CaP) and calcium oxalate (CaOx). An increased fraction of CaOx in the precipitate was observed when the pH was decreased. In solutions with an initial pH of 5.5, 6.0 and 6.5, the number and volume of crystals were smaller in samples analysed after 60 min than in those analysed immediately after the evaporation. This might reflect dissolution of crystals, as expected, most pronounced in the most acid solutions, but apparently counteracted by dU. The results obtained in these experiments suggest that CaP formed high in the nephron might induce heterogeneous nucleation of CaOx when subjected to the lower pH levels and increased supersaturation with CaOx encountered in the CD. With an alkaline pH in the CD, a pronounced crystallization of CaP can be anticipated.

Calcium Oxalate↗
PubMed1985

Crystallization of the light-harvesting chlorophyll a/b complex within thylakoid membranes.

We have found that treatment of the photosynthetic membranes of green plants, or thylakoids, with the nonionic detergent Triton X-114 at a 10:1 ratio has three effects: (a) photosystem I and coupling factor are solubilized, so that the membranes retain only photosystem II (PS II) and its associated light-harvesting apparatus (LHC-II); (b) LHC-II is crystallized, and so is removed from its normal association with PS II; and (c) LHC-II crystallization causes a characteristic red shift in the 77 degrees K fluorescence from LHC-II. Treatment of thylakoids with the same detergent at a 20:1 ratio results in an equivalent loss of photosystem I and coupling factor, with LHC-II and PS II being retained by the membranes. However, no LHC-II crystals are formed, nor is there a shift in fluorescence. Thus, isolation of a membrane protein is not required for its crystallization, but the conditions of detergent treatment are critical. Membranes with crystallized LHC-II retain tetrameric particles on their surface but have no recognizable stromal fracture face. We have proposed a model to explain these results: LHC-II is normally found within the stromal half of the membrane bilayer and is reoriented during the crystallization process. This reorientation causes the specific fluorescence changes associated with crystallization. Tetrameric particles, which are not changed in any way by the crystallization process, do not consist of LHC-II complexes. PS II appears to be the only other major complex retained by these membranes, which suggests that the tetramers consist of PS II.

Chlorophyll↗
PubMed1999

Enlargement of a lower pole calcium oxalate stone: a theoretical examination of the role of crystal nucleation, growth, and aggregation.

BACKGROUND AND PURPOSE: Nucleation, growth, and aggregation are considered to be the principal crystallization mechanisms in stone development. It is important to understand their relative significance so that appropriate experimental models can be used, and to identify the best therapeutic targets. The aim of this study was to explore a simplistic model of precipitation and aggregation and to determine the impact of these processes on crystal size density (CSD) and stone growth. METHODS: The computer model represents a lower pole calcium oxalate stone and takes into account the limitations imposed by the amount of available oxalate. RESULTS: Stone enlargement is a result of direct precipitation onto the stone or aggregation of suspended crystals. About one third of the available oxalate needs to be precipitated to form a clinically significant stone within a realistic time frame. If all crystallization is directly at the stone surface, then crystal growth rates are limiting for stones less than about 1 mm, and aggregation of suspended particles would be required for significant enlargement. For crystals in suspension, the CSD is taken to result from two mixed-suspension, mixed-product removal crystallizers operating in series. Using realistic values for nucleation and growth rate, the CSD can be consistent with precipitation of a significant proportion of the available oxalate. This CSD is modified by aggregation, which is assumed to be proportional to the number and volume of crystals in each size range, and further modified by considering the aggregation to be shared by stone enlargement and polymerization in suspension. CONCLUSION: The variables in the model are the probability of aggregation, its rate, and the distribution between aggregation in suspension and onto the stone. Under some circumstances, the bimodal CSD of crystalluria seen in stone forming patients can be reproduced.

Calcium Oxalate↗