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PubMed1996

Calcium carbonate crystals promote calcium oxalate crystallization by heterogeneous or epitaxial nucleation: possible involvement in the control of urinary lithogenesis.

A large proportion of urinary stones have calcium oxalate (CaOx) as the major mineral phase. In these stones, CaOx is generally associated with minor amounts of other calcium salts. Several reports showing the presence of calcium carbonate (CaCO3) and calcium phosphate in renal stones suggested that crystals of those salts might be present in the early steps of stone formation. Such crystals might therefore promote CaOx crystallization from supersaturated urine by providing an appropriate substrate for heterogeneous nucleation. That possibility was investigated by seeding a metastable solution of 45Ca oxalate with vaterite or calcite crystallites. Accretion of CaOx was monitored by 45Ca incorporation. We showed that (1) seeds of vaterite (the hexagonal polymorph of CaCO3) and calcite (the rhomboedric form) could initiate calcium oxalate crystal growth; (2) in the presence of lithostathine, an inhibitor of CaCO3 crystal growth, such accretion was not observed. In addition, scanning electron microscopy demonstrated that growth occurred by epitaxy onto calcite seeds whereas no special orientation was observed onto vaterite. It was concluded that calcium carbonate crystals promote crystallization of calcium oxalate and that inhibitors controlling calcium carbonate crystal formation in Henle's loop might play an important role in the prevention of calcium oxalate stone formation.

Calcium Carbonate↗

PubMed2003

The effect of ions at the surface of calcium oxalate monohydrate crystals on cell-crystal interactions.

Magnesium is an abundant ion in biologic systems, including renal tubular fluid; however, the precise role of magnesium during the interaction of calcium oxalate crystals with cells has not been previously defined. In addition, the respective roles of calcium and hydrogen ions during the cell-crystal bonding interaction remain poorly defined. Here we report an atomic level three-dimensional study of a single crystal of calcium oxalate monohydrate (COM; whewellite) which was bathed in a solution of magnesium hexahydrate for 1 year. Magnesium was not incorporated into the structure of whewellite to any significant degree. Instead, COM accepted magnesium primarily as an adsorbate in a binding configuration which, as a surface phenomenon, is controlled by localized charge effects. The effect of magnesium and calcium on the efficiency of calcium oxalate crystal binding to renal cells was also investigated. When present in supraphysiologic concentrations (greater than 0.1 M), magnesium progressively inhibited adhesion of pre-formed COM crystals to cultured renal cells. Therefore, even though magnesium does not incorporate into the crystal structure of calcium oxalate, magnesium can exert important surface effects and change the interaction of pre-formed COM with molecules anchored on the cell surface. Similarly, binding was nearly blocked when the exogenous calcium concentration was > or =0.1 M (supraphysiologic range), although in lower concentrations (within the physiologic range) exogenous calcium promoted crystal adhesion. Finally, the ambient hydrogen ion concentration also influenced calcium oxalate crystal interactions with renal cells, with maximal binding occurring at a pH of 4. Therefore, hypercalciuria and/or an acidic urine could each promote renal stone formation via increased crystal adhesion to renal cells, a previously under-appreciated potential mechanism.

Animals↗

PubMed2005

An animal model of calcium oxalate urolithiasis based on a cyclooxygenase 2 selective inhibitor.

Our aim was to develop a stone-forming animal model involving renal tubular injury using a cyclooxygenase 2 selective inhibitor. Male Sprague-Dawley rats fed chow containing 3% sodium oxalate with or without 100 mg/kg celecoxib were compared to animals fed normal chow. Rats were killed after 2 or 4 weeks and the kidneys were harvested for morphological examination. Collections of 24-h urine were made before kidney harvest. After 2 weeks only a few crystals were observed in rats that received oxalate and celecoxib, but after 4 weeks more crystals were observed at the renal papilla than in rats that received only oxalate. Few crystals were found in rats fed normal chow with or without celecoxib. The urinary activities of gamma-glutamyl transpeptidase (GGT) were increased by celecoxib administration whereas creatinine clearance rates were unchanged. In rats fed oxalate, urinary oxalate excretion increased, but calcium excretion decreased. This model using a cyclooxygenase 2 selective inhibitor is a useful stone forming animal model involving mild renal tubular injury together with mild hyperoxaluria.

Animals↗

PubMed1999

Direct measurement of calcium oxalate nucleation with a laser probe.

To understand the genesis of urinary stones different crystallization models have been developed to simulate the crystallization processes that occur at the beginning of the stone formation. In this study a laser probe working on the principle of the measurement of back-scattered light was mounted on a batch crystallization model, in which calcium oxalate nucleation was induced by titration of an artificial urine with ammonium oxalate. With the laser probe the particle numbers and particle size distributions in the range from 1-250 microm can be measured in a single experiment. Measurement is performed directly at the place of crystal development and, therefore, falsification of the results (by dilution, mechanical transport or isolation, temperature gap, multiple measurements, mathematical calculations after indirect measurements, etc.) is prevented. In a basic urine, containing 7.5 mmol/l calcium (4.13 mmol/l free calcium), nucleation of calcium oxalate appears at a concentration of 0.58 mmol/l oxalate. At the start of nucleation the particle size rises to 7 microm. After addition of citrate and magnesium in concentrations up to 12 mmol/l the metastable limit is clearly shifted up to 1.50 mmol/l oxalate. Both findings are in good agreement with the literature. The laser crystallization model has proved to be useful for the testing of inhibitors and promoters of urinary stone formation.

Calcium Oxalate↗

PubMed2006

Oxalate contributes to the resistance of Gaillardia grandiflora and Lupinus sericeus to a phytotoxin produced by Centaurea maculosa.

Centaurea maculosa Lam. is a noxious weed in western North America that produces a phytotoxin, (+/-)-catechin, which is thought to contribute to its invasiveness. Areas invaded by C. maculosa often result in monocultures of the weed, however; in some areas, North American natives stand their ground against C. maculosa and show varying degrees of resistance to its phytotoxin. Two of these resistant native species, Lupinus sericeus Pursh and Gaillardia grandiflora Van Houtte, were found to secrete increased amounts of oxalate in response to catechin exposure. Mechanistically, we found that oxalate works exogenously by blocking generation of reactive oxygen species in susceptible plants and reducing oxidative damage generated in response to catechin. Furthermore, field experiments show that L. sericeus indirectly facilitates native grasses in grasslands invaded by C. maculosa, and this facilitation can be correlated with the presence of oxalate in soil. Addition of exogenous oxalate to native grasses and Arabidopsis thaliana (L.) Heynh grown in vitro alleviated the phytotoxic effects of catechin, supporting the field experiments and suggesting that root-secreted oxalate may also act as a chemical facilitator for plant species that do not secrete the compound.

Antioxidants↗

PubMed2007

Serum, urinary and stone zinc, iron, magnesium and copper levels in idiopathic calcium oxalate stone patients.

Many theories have been put forward to explain the mechanism of stone formation and growth. The aim of this study was to investigate the urinary, serum and stone levels of zinc, iron, magnesium, and copper in patients with calcium oxalate stones and to investigate urinary and serum element levels in healthy controls and to find a possible connection between the elements and calcium oxalate stone formation. A total of 104 patients with calcium oxalate stones ranging in age from 3 to 79 years (mean 44.0 +/- 18.1) and 77 healthy controls ranging in age from 18 to 77 (mean 44.2 +/- 17.9) were included in this study. The mean urinary iron and copper levels in stone patients were significantly higher than healthy controls (P = 0.000). The mean urinary zinc and magnesium levels in healthy controls were significantly higher than stone patients (P = 0.000). There was no significant difference in the serum levels of magnesium and copper in stone patients and healthy controls. Serum zinc and iron level were significantly high in healthy controls as compared to stone patients. Each stone had all 4 elements. Zn and Mg have inhibitory effect on calcium oxalate stone formation. Fe and Cu could be promotor of the calcium oxalate stone formation.

Adolescent↗

PubMed1983

Specific and rapid assay of urinary oxalic acid using high-performance liquid chromatography.

A high-performance liquid chromatographic (HPLC) method was developed to determine the levels of oxalic acid in the urine. This acid was extracted from urine with tri-n-butyl phosphate and converted into the fluorescent derivative by esterification with 9-anthryldiazomethane (ADAM). The reaction mixture containing the oxalic acid derivative can be directly chromatographed on HPLC using octadecylsilane reverse-phase column monitoring with a fluorophotometric detector. A linear relationship was observed in the range from 1 to 100 micrograms/ml of standard oxalic acid dissolved in saline. Disease-free Japanese adults excrete 23.8 +/- 9.0 mg (mean +/- SD) of oxalic acid per day. This method should prove valuable for routine measurements of urinary oxalic acid as it is accurate, simple, and specific.

Anthracenes↗

PubMed1984

State of translocated Ca2+ by sarcoplasmic reticulum inferred from kinetic analysis of calcium oxalate precipitation.

Uptake of Ca2+ by sarcoplasmic reticulum in the presence of oxalate displays biphasic kinetics. An initial phase of normal uptake is followed by a second phase coincident with precipitation of calcium oxalate inside the vesicles. The precipitation rate induced by actively transported Ca2+ is depressed by increasing the added Ca2+ concentration. This correlates linearly with the reciprocal of precipitation rate. Therefore, a maximal limit rate could be extrapolated at zero Ca2+ (V0). The rate of precipitation, also a function of added amount protein, gives a linear correlation in a double reciprocal plot. Thus, it was possible to estimate the maximal precipitation rate occurring at infinite protein concentration (V infinity). With the combined extrapolated values a maximal expected precipitation rate could be calculated (V infinity 0). Kinetics of calcium oxalate precipitation was studied in the absence of calcium uptake and empirical equations relating the rate of precipitation with the added Ca2+ were established. Entering V infinity 0 in the equations, an internal free Ca2+ concentration of approx. 2.5 mM was estimated. Additionally, it is shown that the ionophore X-537A does not suppress the Ca2+ uptake, if added during the oxalate-dependent phase, albeit the uptake proceeds at a slower rate after the release of approx. 70 nmol Ca2+/mg protein. This amount presumably equals the internal free Ca2+ not sequestered by oxalate, producing a maximal concentration approx. 14 mM. Taking into account low affinity binding of internal binding sites and the transmembrane Ca2+ gradients built up during the uptake of Ca2+, values of free Ca2+ ranging from 3 to 6 mM, approaching those estimated by the precipitation analysis, could be estimated.

Animals↗

PubMed1978

A new method for determination of oxalate in blood serum by gas chromatography.

A method for the determination of blood oxalate by gas chromatography is described. After clarification of the serum with acetone, the oxalate was extracted, ethylated and analysed on a gas chromatograph. The concentration of oxalate in the sample was determined by comparison with the elution pattern of diethylmalonate used as an internal standard. Using this technique, the recovery of added oxalate was more than 80%. Normal subjects were found to have blood oxalate levels of 27 mumol/l or less.

Chromatography, Gas↗

PubMed1980

Enzymic determination of serum oxalate.

A new colorimetric, enzymic method for determination of serum oxalate is described using oxalate oxidase from barley seedlings. This method, based on a specific reaction of oxalate with oxidase is rapid, simple and precise. The percentage recoveries of oxalate added to serum ranged from 91.5 to 103. The oxalate content in the serum obtained from 50 healthy non-fasting donors varied from 0.06 mg/dl to 0.41 mg/dl. The proposed method showed a good correlation with a chemical method.

Colorimetry↗

PubMed1980

The real and apparent plasma oxalate.

A method for the determination of human plasma oxalate concentration by an enzymatic assay procedure is described using deproteinised plasma. The apparent concentration of oxalate in 20 normal subjects was 1.1--16.0 mumol/l (mean 7.78; S.D. 3.96). It was suspected that these results might be too high, due to the possible conversion of glyoxalate to oxalate, and this reaction was clearly demonstrated to occur in whole blood in vitro. Inhibitors (boric acid, DL-beta-phenyllactic acid, and allopurinol) of this oxidation were therefore added to the freshly taken blood samples, prior to assaying by the same technique. The plasma oxalate concentration from normal subjects was then found to be 0--5.4 mumol/l (mean 2.26; S.D. 1.67). It is concluded that normal blood spontaneously generates oxalate on standing, and the higher values obtained by other in vitro methods must be fallacious.

Blood Proteins↗

PubMed1993

Comparative study of two commercial enzymatic kits for determining oxalate concentrations in urine.

We performed a comparative study of two commercial kits for determining oxalate in urine. These were: (a) an oxalate decarboxylase-based assay (Boehringer Mannheim); (b) an oxalate oxidase-based assay (Sigma). The within-run and between-run imprecision were found to be similar in both methods. The recovery was 94% with the oxalate decarboxylase method. The pH of the specimen had a major effect on the recovery obtained by the oxalate oxidase method (66-86% at pH = 2.5 and 37-68% at pH = 1.5). The decarboxylase method was linear up to at least 2224 mumol/L and the oxidase method was linear up to at least 890 mumol/L. We also studied the interference of ascorbic acid in both techniques and found a positive bias with the oxidase method and a negative bias using the decarboxylase method. The correlation coefficient was 0.592.

Ascorbic Acid↗

PubMed1990

Bond strengths of luting cements to potassium oxalate-treated dentin.

Potassium oxalate is gaining popularity as a dentin treatment to prevent the development of dentin sensitivity. Because treated dentin surfaces are covered with calcium oxalate crystals, the bond strength of cements to oxalate-treated dentin required investigation. This study determined the tensile bond strengths of glass-ionomer, polycarboxylate, and zinc phosphate cements used to cement castings to dentin treated with either water or potassium oxalate. The results indicate that oxalate-treated dentin did not affect the bond strength of glass-ionomer or polycarboxylate cements, but produced a large decrease in the bond strength of zinc phosphate cement.

Dental Bonding↗

PubMed1975

Effect of sodium cellulose phosphate therapy on crystallization of calcium oxalate in urine.

Effects of oral sodium cellulose phosphate therapy (5 g three times a day with meals for 4 days) on renal excretion of oxalate and on the crystallization of calcium oxalate in urine were examined in six patients with absorptive hypercalciuria on a constant metabolic dietary regimen. During treatment, urinary oxalate increased by 9-50 mg/day. However, urinary calcium decreased by 138-225 mg/day (50%-70%). Thus, the state of saturation of urine with respect to calcium oxalate decreased or did not change significantly. There was no consistent or significant change in the formation product ratio (limit of metastability) or in the crystal growth of calcium oxalate in urine.

Administration, Oral↗

PubMed1986

The effect of dietary refined sugars and sugar alcohols on renal calcium oxalate deposition in ethylene glycol-treated rats.

The effect of administering refined carbohydrates in the diet on calcium oxalate deposition in the kidneys of rats given 1% (v/v) ethylene glycol in their drinking-water was investigated. The rats were given 0, 2.5, 10, 30 or 60% sucrose in the feed (w/w) and/or drinking-water (w/v) or 20% (w/w) starch, glucose, sucrose, fructose, galactose, xylitol or sorbitol in the feed for 3 wk. All of the animals remained healthy over the test period as far as could be assessed by the measurement of 19 plasma biochemical parameters. The inclusion of 30 or 60% (w/w) sucrose in the diet resulted in a more than tenfold increase in the deposition of calcium oxalate in the kidneys. However, this deposition could not be predicted from data on urinary pH and urinary excretion of calcium, oxalate and urate, which have been reported to be risk factors for stone formation. There was no evidence of increased rates of oxalate production from ethylene glycol. The administration of fructose, xylitol or sorbitol was associated with the greatest renal deposition of calcium oxalate, and glucose was associated with by far the least.

Animals↗

PubMed1983

Oxalate synthesis from [14C1]glycollate and [14C1]glyoxylate in the hepatectomized rat.

Hepatectomy significantly altered the metabolism of [1-14C]glyoxylate and [1-14C]glycollate in the rat. The production of 14CO2 was reduced by 47% and 77-86%, respectively, indicating the involvement of the liver in the oxidation of both substrates. Unidentified intermediates, assumed to be primarily glycine, serine and ethanolamine, were also reduced by over 50%, as would be expected from the removal of the aminotransferase enzymes through the hepatectomy. The biosynthesis of [14C]oxalate from [1-14C]glycollate was reduced by more than 80% in the hepatectomized rat. This suggests that this oxidation is primarily catalyzed by the liver enzymes, glycolic acid oxidase and glycolic acid dehydrogenase, in the intact rat. The limited formation of [14C]oxalate from [14C1]glycollate observed in the hepatectomized rat is probably catalyzed by lactate dehydrogenase or extrahepatic glycolic acid oxidase. Hepatectomy did not significantly alter the rate of formation of [14C]oxalate from [14C1]glyoxylate. However, since saturating concentrations of glyoxylate could not be used because of the toxicity of this substrate, the involvement of glycollic acid oxidase in this oxidation reaction in the intact rat can not be ruled out. In the hepatectomized rat, lactate dehydrogenase appears to be the enzyme making the major contribution, although other as yet not identified enzymes may be contributing. The increased deposition of oxalate in the tissues, oxalosis, may result from the shift in oxalate synthesis from the liver to the extrahepatic tissues.

Animals↗

PubMed2005

Oxalate and root exudates enhance the desorption of p,p'-DDT from soils.

The abiotic desorption of p,p'-DDT from seven Chinese soils spiked with p,p'-DDT and the effects of oxalate at 0.001-0.1M and the root exudates of maize, wheat, and ryegrass were evaluated using batch experiments. Soil organic carbon played a predominant role in the retention of DDT. Oxalate significantly increased the desorption of p,p'-DDT, with the largest increments ranging from 11% to 54% for different soils. Oxalate addition also resulted in the increased release of dissolved organic carbon and inorganic ions from soils. Root exudates had similar effects to those of oxalate. Root exudates significantly increased DDT desorption from the soils, and the general trend was similar among the plant species studied for all the soils (p > 0.05). Low molecular weight dissolved organic carbon amendments caused partial dissolution of the soil structure, such as the organo-mineral linkages, resulting in the release of organic carbon and metal ions and thus the subsequent enhanced desorption of DDT from the soils. The enhancing effects of oxalate and root exudates on DDT desorption were influenced by the contents of soil organic carbon and dissolved organic carbon in soils.

Adsorption↗

PubMed2003

Determination of calcium oxalate (mono- and dihydrate) in mixtures with magnesium ammonium phosphate or uric acid: the use of simultaneous thermal analysis in urinary calculi.

BACKGROUND: The human urinary calculi are mainly formed from calcium oxalate, magnesium ammonium phosphate hexahydrate (MAPH) and uric acid (UA) crystals. It is important for the physician and surgeon to distinguish the two types of hydrates of calcium oxalate, mainly mono- (COM, Whewellite) and dihydrate (COD, Weddelite). This is because COM stones are evacuated two times more frequently than COD, which sometimes needs to be extracted surgically. METHODS: Thermal analysis techniques, such as Differential Thermal Analysis (DTA) and Thermogravimetry (TG), are considered the best techniques for the characterization of the two hydrates of calcium oxalate. A simultaneous thermal analysis method (TG-DTA) was applied to determine the percentage of each hydrate (COM and COD) when present together, in the presence of MAPH or in the presence of UA. RESULTS: The results performed on 156 urinary calculi were as follows (according to the major component): 74.36%, 7.05% and 10.26% for calcium oxalate hydrate, UA and MAPH, respectively. The COD/COM ratios were 0.75 and 1.75, when they are present in mixtures with UA and MAPH, respectively. CONCLUSIONS: Fourier transform infrared (FTIR) and X-ray diffraction (XRD) have been used in urinary calculi analysis. Simultaneous thermal analysis TG-DTA would be an alternative method for quantitative determination of the two types of calcium oxalate in urinary stones.

Calcium Oxalate↗