Calcium Oxalate Formation Research Articles

Crystallization kinetics of calcium oxalate hydrates studied by scanning confocal interference microscopy

Scanning confocal interference microscopy (SCIM) is an optical technique that allows the visualization of structures below the limits of classical optical microscopy (⪡250 nm). This study represents the first use of SCIM to analyze the formation of calcium oxalate crystals, the major constituent of kidney stones. Crystals were nucleated and grown on the glass bottom of Petri dishes in the presence and absence of the polyelectrolyte inhibitor poly- l-aspartic acid (poly-asp). In the absence of poly-asp, monoclinic calcium oxalate monohydrate (COM) nucleated from {1 0 0} or {0 1 0} faces. The first observed particles were 70–120 nm in diameter and grew by a step-like progression in the [0 0 1] and [0 1 0] directions. Addition of poly-asp had several effects on calcium oxalate formation. First, the number of particles was increased, but their sizes were decreased. Second, the rate of COM growth in the [0 0 1] direction was decreased to a greater extent than the rate along [0 1 0]. Third, the formation of tetragonal calcium oxalate dihydrate (COD) crystals was favored. Fourth, the rates of COD growth along 〈1 1 0〉 and allied directions were decreased, whereas that parallel to 〈0 0 1〉 is increased. Sequences of highly resolved growth fronts show step displacement for COM and moving crystal edges for COD. Analysis of image sequences suggested that growth is strongly affected by competing and alternating processes, in which diffusion processes are rate-limiting and induce nonlinear growth. This study shows that SCIM is a powerful technique for the quantitative analysis of crystallization processes and for determining the mode of action of inhibitors.

The effect of different processing methods on some anti-nutritional factors content of Ede uhie (<i>Xanthosoma sagittifolium</i>) and Ede ocha (<i>Colocasia esculenta</i>)

Some anti-nutritional content of two Cocoyam species: Ede Uhie (Xanthosoma sagittifoluin) and Ede Ocha (Colocasia esculenta) were investigated. Oxalates (which combines with serum calcium to form calcium oxalate thereby making calcium unavailable to the body), Phytates (which impairs the utilization of protein and minerals) and Tannins (which inhibits digestive enzymes) were investigated. Different processing methods affected the contents of the anti-nutrients. Soaking in (0.01%) EDTA significantly reduced (P

Simultaneous formation of calcium oxalate (mono-, di-, and trihydrate) induced by potassium tartrate in gelatinous system

Calcium oxalate (CaOx) is the major crystalline component of kidney stone. Calcium oxalate mono-(COM), di-(COD), and trihydrate (COT) crystals were simultaneously induced by potassium tartrate (K 2tart) in a gelatinous system by a double diffusion technique. The phase composition and morphology of the crystals were determined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. In the presence of low concentration of K 2tart (0.01 mol/l), the COM crystals with sharp tips are the dominant crystal phase. The percentage of COD is less than 5% and no COT crystals are observed. When the concentration of K 2tart is increased to 0.10 and 0.50 mol/l, the percentage of COT increases to 56% and 82%, respectively. The morphology of COM crystals becomes blunter. The crystallization temperature affects the phase composition and morphology of CaOx crystals. In the presence of 0.01 mol/l K 2tart, COM and COT are the main phases at 37 °C. However, COD is dominant at 7 °C. The result that K 2tart can increase the content of COT and inhibit the aggregation and decrease the surface area of COM crystals indicates K 2tart can inhibit the formation of CaOx stones. This result also supports the clinical use of K 2tart and may be helpful in elucidating the mechanisms by which the formation of CaOx calculi can be inhibited.

Genetic hypercalciuric stone-forming rats

We will describe the pathophysiology of hypercalciuria and the mechanism of the resultant stone formation in a rat model and draw parallels to human hypercalciuria and stone formation. Through inbreeding we have established a strain of rats that excrete 8-10 times more urinary calcium than control rats. These genetic hypercalciuric rats absorb more dietary calcium at lower 1,25-dihydroxyvitamin D3 levels. Elevated urinary calcium excretion on a low-calcium diet indicated a defect in renal calcium reabsorption and/or an increase in bone resorption. Bone from hypercalciuric rats released more calcium when exposed to 1,25-dihydroxyvitamin D3. Bisphosphonate significantly reduced urinary calcium excretion in rats fed a low-calcium diet. Clearance studies showed a primary defect in renal calcium reabsorption. The intestine, bone and kidneys of the hypercalciuric rats had increased numbers of vitamin D receptors. When hydroxyproline is added to their diet they form calcium oxalate stones, the most common stone type in humans. Increased numbers of vitamin D receptors may cause hypercalciuria in these rats and humans. Understanding the mechanism of hypercalciuria and stone formation in this animal model will help clinicians devise effective treatment strategies for preventing recurrent stone formation in humans.

Characterization of aqueous lead removal by phosphatic clay: Equilibrium and kinetic studies

Immobilization of heavy metals from contaminated environments is an emerging field of interest from both resource conservation and environmental remediation points of view. This study investigated the feasibility of using phosphatic clay, a waste by-product of the phosphate mining industry, as an effective sorbent for Pb from aqueous effluents. The major parameters controlling aqueous Pb removal, viz. initial metal ion concentrations, solution pH, sorbent amounts, ionic strength and presence of both inorganic and organic ligands were evaluated using batch experiments. Results demonstrated that aqueous Pb removal efficiency of phosphatic clay is controlled mainly by dissolution of phosphatic clay associated fluoroapatite [Ca 10(PO 4) 5CaCO 3(F,Cl,OH) 2], followed by subsequent precipitation of geochemically stable pyromorphite [Pb 10(PO 4) 6(F,Cl,OH) 2], which was confirmed by both X-ray diffraction (XRD) and scanning electron microscopic (SEM) analysis. Lead removal efficiency of phosphatic clay increased with increasing pH, sorbent amount and decreasing ionic strength. It also depends on the nature of complexing ligands. Formation of insoluble calcium oxalate and lead oxalate in the presence of oxalic acid explained high uptake of Pb by phosphatic clay from aqueous solution. However, Pb sorption kinetics onto phosphatic clay were biphasic, with initially fast reactions followed by slow and continuous Pb removal reactions. The slow reactions may include surface sorption, co-precipitation and diffusion. The exceptional capability of phosphatic clay to remove aqueous Pb demonstrated its potential as a cost effective way to remediate Pb-contaminated water, soils and sediments.

Synchrotron radiation X-ray diffraction study of the particle formation of pseudo-polymorphic calcium oxalate

The particle formation of two pseudo-polymorphic calcium oxalate hydrates has been examined in situ for reaction times from 15 ms to 30 s. Precipitation of the hydrates has taken place in a tubular reactor which was equipped with a flow cuvette. Using synchrotron X-ray diffraction the mass fraction of the two pseudo-polymorphs in suspension could be determined. The experimental results have been compared to the results of simulation calculations which consider in parallel nucleation as well as growth of the two calcium oxalates by solving population balances for each hydrate. Parameters in the kinetic rate laws were derived from independent experiments. Excellent correspondence of the model simulations with the experimental results was found. The measurements support the idea that the initial ratios of the nucleation and growth rates mainly determine the phase distribution in the solid product. It should be possible to transfer the measuring technique presented here to the precipitation of other crystalline substances.

Effect of Calcium and Magnesium Ions on Calcium Oxalate Formation in Sugar Solutions

During the concentration of sugarcane juice, there is continuous deposition of nonsugar impurities on the surface of evaporator units. Because the scale deposit has a low thermal conductivity, its accumulation impairs heat transfer and eventually renders the process uneconomical owing to reduced throughput. Calcium oxalate is the main intractable scale formed in factories that process sugarcane. It is not removed by conventional chemical cleaning methods. This paper describes studies on the apparent solubility product of calcium oxalate in the presence of sugar and calcium and magnesium ions at different temperatures and pH's. A solubility product model was obtained that states that the apparent solubility product of calcium oxalate decreases with increasing temperature and sugar concentration, but increases with increasing pH. The model was able to predict calcium oxalate solubility changes in raw sugarcane factory processes, indicating that the apparent solubility product of calcium oxalate declines rapidly through the evaporator set. The results also indicated that calcium oxalate solubility is increased in the presence of calcium and, in particular, magnesium ions.

Oxalate induced expression of monocyte chemoattractant protein-1 (MCP-1) in HK-2 cells involves reactive oxygen species

Oxalate is a toxic end product of metabolism largely because of its propensity to crystallize and form calcium oxalate, which is insoluble at physiologic pH and often deposits at very unfortunate sites, notably the kidneys. In the current study, we investigated the oxalate-induced injury and up-regulation of monocyte-chemoattractant protein-1 (MCP-1) in HK-2 cells, a proximal tubular epithelial cell line derived from normal human kidney. The cells were exposed to oxalate ions for different lengths of time. The culture media was tested for LDH release, a cell injury marker. mRNA was isolated from the cells and subjected to reverse transcriptase-polymerase chain reaction. The data showed that oxalate exposure resulted in cell injury in a time and concentration dependent manner. The MCP-1 mRNA increased following exposure to oxalate and was reduced upon treatment with free radical scavengers, catalase and superoxide dismutase. These data support the importance of reactive oxygen species in the induction of expression of MCP-1 in renal epithelial cells. To our knowledge, this is the first report of MCP-1 expression and its upregulation by oxalate exposure in HK-2 cells.

Thiazides Reduce Brushite, but not Calcium Oxalate, Supersaturation, and Stone Formation in Genetic Hypercalciuric Stone–Forming Rats

Over 59 generations, a strain of rats has been inbred to maximize urine calcium excretion. The rats now excrete eight to 10 times as much calcium as controls. These rats uniformly form calcium phosphate (apatite) kidney stones and have been termed genetic hypercalciuric stone-forming (GHS) rats. The addition of a common amino acid and oxalate precursor, hydroxyproline, to the diet of the GHS rats leads to formation of calcium oxalate (CaOx) kidney stones. Hydroxyproline-supplemented GHS rats were used to test the hypothesis that the thiazide diuretic chlorthalidone would decrease urine calcium excretion, supersaturation, and perhaps stone formation. All GHS rats received a fixed amount of a standard 1.2% calcium diet with 5% trans-4-hydroxy-l-proline (hydroxyproline) so that the rats would exclusively form CaOx stones. Half of the rats had chlorthalidone (Thz; 4 to 5 mg/kg per d) added to their diets. Urine was collected weekly, and at the conclusion of the study, the kidneys, ureters, and bladders were radiographed for the presence of stones. Compared with control, the addition of Thz led to a significant reduction of urine calcium and phosphorus excretion, whereas urine oxalate excretion increased. Supersaturation with respect to the calcium hydrogen phosphate fell, whereas supersaturation with respect to CaOx was unchanged. Rats that were fed Thz had fewer stones. As calcium phosphate seems to be the preferred initial solid phase in patients with CaOx kidney stones, the reduction in supersaturation with respect to the calcium phosphate solid phase may be the mechanism by which thiazides reduce CaOx stone formation.

EFFECTS OF URINARY PROTHROMBIN FRAGMENT 1 IN THE FORMATION OF CALCIUM OXALATE CALCULUS

We investigated the effects of urinary prothrombin fragment 1 in the formation of calcium oxalate urolithiasis. Fresh urine and renal parenchyma from patients with calcium oxalate calculus and normal controls were collected. Urinary prothrombin fragment 1 was isolated and purified from urine. It was identified by sodium dodecyl sulfide-polyacrylamide gel electrophoresis and analysis of its first 13 N-amino acids. The inhibitory activity of urinary prothrombin fragment 1 on calcium oxalate crystal growth was tested by the seeded crystallization technique. Meanwhile, the gamma-carboxyglutamic acid composition of urinary prothrombin fragment 1 was analyzed by a previously described method and genetic mutation of the gamma-carboxyglutamic acid domain of urinary prothrombin fragment 1 from renal parenchyma was detected by polymerase chain reaction-single strand conformational polymorphism sequencing. The gamma-carboxyglutamic acid composition of urinary prothrombin fragment 1 was significantly decreased from normal (24.4 to 1.7 mol/1,000 amino acids) in patients with calcium oxalate calculus. The mean growth index +/- SD of urinary prothrombin fragment 1 to calcium oxalate crystals was 42.3 +/- 4.2 compared with the normal index of 19.2 +/- 2.8 (p <0.01). The polymerase chain reaction-single strand conformational polymorphism sequencing technique revealed no genetic mutation of the gamma-carboxyglutamic acid domain of urinary prothrombin fragment 1 in patients with calcium oxalate calculus. The gamma-carboxyglutamic acid composition of urinary prothrombin fragment 1 as well as its ability to inhibit calcium oxalate crystal growth was significantly decreased in patients with calcium oxalate calculus. This was not caused by genetic mutation of the gamma-carboxyglutamic acid domain of urinary prothrombin fragment 1. It is important to elucidate the mechanisms of calcium oxalate stones in view of urinary prothrombin fragment 1.

Pathologic hepatic Tc-99m-MDP uptake in polyostotic fibrous dysplasia

Fibrous dysplasia of bone is a congenital, sporadic developmental disorder characterized by immature fibrous connective tissue and bone deformities. Hepatic Tc-99m-MDP uptake is a rare, serendipitous finding during bone scanning studies. The present patient was a 25-year-old male who had severe polyostotic fibrous dysplasia. On Tc-99m-MDP (methylene diphosphonate) bone scintigraphy, increased activity accumulations were seen on multiple ribs, vertebrae and base of the cranium. In addition, diffuse increased pathologic uptake of Tc-99m-MDP in the liver was shown. Intravenous pamidronate was administered monthly for two months. In the third week of the last administration Tc-99m-MDP bone scintigraphy was performed again, but despite sustained bone involvement, pathologic hepatic uptake was not seen on the scan. We thought that pathologic hepatic Tc-99m-MDP accumulation, may be related to the formation and aggregation of calcium oxalate and phosphate crystals which improved with pamidromat treatment.

Growth of calcium oxalate monohydrate on uric acid crystals at sustained supersaturation

AbstractThe effect of uric acid seeds on calcium oxalate formation was studied at pH 4.50 and 37 °C using a system providing constant supersaturation with respect to calcium oxalate and saturated in uric acid. In all cases the only solid‐phase forming was identified as calcium oxalate monohydrate (COM). Kinetic analysis of the initial rates showed that they were proportional with the relative supersaturation with respect to calcium oxalate monohydrate. The linear dependence of the rate of precipitation of COM on uric acid suggested that growth is mediated through a surface diffusion controlled mechanism. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A study of primary nucleation of calcium oxalate monohydrate: II. Effect of urinary species

AbstractKidney stones consist of various organic and inorganic compounds. Calcium oxalate monohydrate (COM) is the main inorganic constituent of kidney stones. However, the mechanisms for the formation of calcium oxalate kidney stones are not well understood. In this regard, there are several hypotheses including nucleation, crystal growth and/or aggregation of formed COM crystals. The effect of some urinary species such as oxalate, calcium, citrate, and protein on nucleation and crystallization characteristics of COM is determined by measuring the weight of formed crystals and their size distributions under different chemical conditions, which simulate the urinary environment. Statistical experimental designs are used to determine the interaction effects among various factors. The data clearly show that oxalate and calcium promote nucleation and crystallization of COM. This is attributed to formation of a thermodynamically stable calcium oxalate monohydrate resulting from supersaturation. Citrate, however, inhibits nucleation and further crystal growth. These results are explained on the basis of the high affinity of citrate to combine with calcium to form soluble calcium citrate complexes. Thus, citrate competes with oxalate ion for binding to calcium cations. These conditions decrease the amount of free calcium ions available to form calcium oxalate crystals. In case of protein (mucin), however, the results suggest that no significant effect could be measured of mucin on nucleation and crystal growth. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A study of primary nucleation of calcium oxalate monohydrate: II. Effect of urinary species

AbstractKidney stones consist of various organic and inorganic compounds. Calcium oxalate monohydrate (COM) is the main inorganic constituent of kidney stones. However, the mechanisms for the formation of calcium oxalate kidney stones are not well understood. In this regard, there are several hypotheses including nucleation, crystal growth and/or aggregation of formed COM crystals. The effect of some urinary species such as oxalate, calcium, citrate, and protein on nucleation and crystallization characteristics of COM is determined by measuring the weight of formed crystals and their size distributions under different chemical conditions, which simulate the urinary environment. Statistical experimental designs are used to determine the interaction effects among various factors. The data clearly show that oxalate and calcium promote nucleation and crystallization of COM. This is attributed to formation of a thermodynamically stable calcium oxalate monohydrate resulting from supersaturation. Citrate, however, inhibits nucleation and further crystal growth. These results are explained on the basis of the high affinity of citrate to combine with calcium to form soluble calcium citrate complexes. Thus, citrate competes with oxalate ion for binding to calcium cations. These conditions decrease the amount of free calcium ions available to form calcium oxalate crystals. In case of protein (mucin), however, the results suggest that no significant effect could be measured of mucin on nucleation and crystal growth. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Calcium oxalate crystal localization and osteopontin immunostaining in genetic hypercalciuric stone-forming rats

The inbred genetic hypercalciuric stone-forming (GHS) rats develop calcium phosphate (apatite) stones when fed a normal 1.2% calcium diet. The addition of 1% hydroxyproline to this diet does not alter the type of stone formed, while rats fed this diet with 3% hydroxyproline form mixed apatite and calcium oxalate stones and those with 5% hydroxyproline added form only calcium oxalate stones. The present study was designed to determine the localization of stone formation and if this solid phase resulted in pathologic changes to the kidneys. GHS rats were fed 15 g of the standard diet or the diet supplemented with 1%, 3%, or 5% hydroxyproline for 18 weeks. A separate group of Sprague-Dawley rats (the parental strain of the GHS rats), fed the standard diet for a similar duration, served as an additional control. At 18 weeks, all kidneys were perfusion-fixed for structural analysis, detection of crystal deposits using the Yasue silver substitution method, and osteopontin immunostaining. There were no crystal deposits found in the kidneys of Sprague-Dawley rats. Crystal deposits were found in the kidneys of all GHS rats and this Yasue-stained material was detected only in the urinary space. No crystal deposits were noted within the cortical or medullary segments of the nephron and there was no evidence for tubular damage in any group. The only pathologic changes occurred in 3% and 5% hydroxyproline groups with the 5% group showing the most severe changes. In these rats, which form only calcium oxalate stones, focal sites along the urothelial lining of the papilla and fornix of the urinary space demonstrated a proliferative response characterized by increased density of urothelial cells that surrounded the crystal deposits. At the fornix, some crystals were lodged within the interstitium, deep to the proliferative urothelium. There was increased osteopontin immunostaining in the proliferating urothelium. Thus in the GHS rat, the initial stone formation occurred solely in the urinary space. Tubular damage was not observed with either apatite or calcium oxalate stones. The apatite stones do not appear to cause any pathological change while those rats forming calcium oxalate stones have a proliferative response of the urothelium, with increased osteopontin immunostaining, around the crystal deposits in the fornix.

Calcium oxalate formation in Lemna minor: physiological and ultrastructural aspects of high capacity calcium sequestration.

• The function of calcium oxalate (CaOx) raphide crystal formation, and structural features related to regulation of crystal formation, were studied in Lemna minor fronds using physiological and microscopy techniques. • Specialized crystal-forming cells (crystal idioblasts) increased in number and size; CaOx, but not soluble oxalate, increased in response to increasing calcium in the growth medium. Size and number of idioblasts had a distinct upper limit. • The CaOx crystals are formed in membranous 'chambers' and connected in rows by parallel membrane sheets, both forming de novo in the vacuole. The chambers, but not parallel membranes, had calcium associated with them. A calcium-binding matrix protein was associated with idioblast vacuoles and crystal formation. • Lemna crystal idioblasts function as calcium-inducible, specialized high-capacity but saturable sinks for bulk regulation of calcium, and crystal deposition is a highly controlled process requiring intravacuolar membrane systems and calcium-binding organic matrix materials.

Inhibition of calcium oxalate monohydrate by poly(acrylic acid)s with different end groups

AbstractWater‐soluble low molecular weight polymers are known to affect the crystal habit of scale‐forming minerals and their rates of deposition. Poly(acrylic acid) (PAA) and poly(maleic acid) are commonly used to control scale formation in sugar mill evaporators. Calcium oxalate (both mono‐ and dihydrate) forms the bulk of the hard intractable scale found in Australian sugar mills, causing efficiency losses of significant economic importance. In this work, the formation of calcium oxalate monohydrate in a synthetic juice solution was investigated in the presence of PAAs of varying molecular weights and end‐group functionality and a strong dependency on both of these factors was observed. Terminal functionality was controlled using three chain‐transfer agents (CTA): thioethanol, thioglycolic acid, and dodecanthiol. Effectiveness of inhibition varied with CTA in the order thioethanol ∼ thioglycolic acid &gt; dodecanthiol for all molecular weights. This suggests that polymer end groups play a role in scale inhibition. The polymers that were prepared with dodecanthiol accelerated rather than inhibited calcium oxalate formation, implying a different mode of action on calcium oxalate crystallization. Consistent with previous reports for other scales, the calcium oxalate inhibition tests show optimum effectiveness for PAAs of molecular weight 2000–4000. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2035–2041, 2004

Endoplasmic reticulum sub-compartments are involved in calcium sequestration within raphide crystal idioblasts of Pistia stratiotes L

To regulate bulk Ca 2+ levels, many plants evolved specialized Ca 2+ oxalate accumulating cells called crystal idioblasts. The crystal idioblast appears to have modified some of its cellular components to accommodate the large fluxes of Ca 2+ that occur during calcium oxalate deposition. In this study we examine the modified endoplasmic reticulum (ER) and its involvement in Ca 2+ sequestration. Using a variety of microscopy techniques, we observe that the crystal idioblast of Pistia stratiotes possesses an elaborate network of ER with unique swollen regions. Light microscopy studies, using chlortetracycline and Calcium Green 2, revealed that idioblast ER contains an abundance of calcium. Transmission electron microscopy studies, using the potassium pyroantimonate technique, showed that the Ca 2+ accumulated primarily in the swollen regions. We hypothesize that these swollen areas function as specialized Ca 2+ storage sub-compartments. Whether these sub-compartments are required for proper ER functions or whether they are part of the Ca 2+ transport system involved in calcium oxalate formation remains to be determined.

The relative effects of supplemental dietary calcium and oxalate on urine composition and calcium oxalate relative supersaturation in healthy adult dogs

The aim of this study was to establish the relative effects of dietary calcium and oxalate (in the form of oxalic acid) on the composition of urine produced by healthy adult Cairn Terriers and Miniature Schnauzers. A nutritionally complete dry dog food was fed to 7 dogs (4 Cairn terriers and 3 Miniature schnauzers) for 24 weeks. The dogs were fed the diet alone, or supplemented with six different combinations of dietary calcium (as carbonate and sulphate) and oxalate (as oxalic acid) commonly found in dry commercially prepared dog foods. Urine pH, volume, specific gravity, and concentrations of 12 analytes were measured for each dog; urinary relative supersaturation (RSS) with calcium oxalate (CaOx) was calculated from these values. The effects of supplemental calcium and oxalate were established using two-way analysis of variance and multiple range tests (least significant difference); P<0.05 was considered significant. The lowest level of dietary calcium and oxalate resulted in the lowest CaOx RSS. The high calcium, low oxalate diet resulted in the highest CaOx RSS, a low calcium diet with increased dietary oxalate also tended to increase CaOx RSS although results were highly variable. Urinary calcium concentration increased significantly with dietary calcium; urinary oxalate increased, although inconsistently, with dietary oxalic acid only when dietary calcium was low. Measures to reduce both calcium and oxalate should be considered when implementing dietary changes to reduce the risk of calcium oxalate formation in dogs. A reduction in dietary calcium without a concomitant decrease in dietary oxalate may increase the risk of CaOx crystallisation in susceptible dogs.

Effects of intraperitoneally administered vitamin E and selenium on calcium oxalate renal stone formation: experimental study in rat

Forty-eight Wistar rats were treated for 3 weeks with water containing 0.7% ethylene-glycol and divided into four groups. The first group, used as control, has received sodium chloride at 1 ml/100 g BW daily. The second group was intraperitoneally injected with selenium at 10 μg/d per 100 g BW as NaSeO 3 for 3 weeks. The third group was intraperitoneally administered with 15 mg Vit E/d per 100 g BW as alpha-tocopherol acetate for 3 weeks. The last group was simultaneously administered vitamin E and Se at the same doses and periods as the precedent groups. One day before the end of the treatment, each animal was placed in a metabolic cage for collection of 24 h urine samples and determination of urinary creatinin, urea, calcium, magnesium, phosphate and oxalate levels. Immediately thereafter, all the rats were anesthetized and aortic blood was collected to determine the same parameters as in urine. The kidneys were also removed to determine calcium oxalate deposits, dry weight and to conduct a histological examination. Our results showed decreased ionic product and increased magnesium fractional reabsorption in the group receiving only selenium and in the group receiving selenium in combination with vitamin E, in comparison with the control animals. In view of the knowledge concerning the same protective action of Vit E and selenium, regardless of tubular membrane alteration, the absence of any inhibitory effect of Vit E on calcium oxalate formation suggests that selenium, like other minerals, could be stuck onto the crystal surface and would inhibit induction of new crystals, growth and aggregation.