Measurement of calcium phosphate crystalluria: influence of pH and osmolality and invariable presence of oxalate

Calcium phosphate and calcium oxalate urinary crystal concentrations in normal and stone-forming subjects were measured. The urinary crystals were examined by light microscopy and urine samples were analysed for oxalate, pH and osmolality. Calcium phosphate crystal concentrations were clearly related to urine pH but unrelated to urine osmolality. An unexpected finding was co-precipitation of oxalate with calcium phosphate. Consequently, precipitated invariable oxalate increased with rising urinary pH. Possible explanations and implications are discussed.

[Reduction of urinary oxalate excretion by administration of calcium and citrate]

Oxalic acid seems to be more important for the formation of calcium oxalate stone than calcium. Three grams of calcium lactate and 3 g of uraly U were administered to 35 urolithiasis patients, whose stones were mainly composed of calcium oxalate. Urinary oxalate level was reduced significantly without raising urinary calcium level by the administration of the two drugs for two weeks. The reduction of oxalic acid was particularly remarkable in patients without hypercalciuria. The mechanism of action of these drugs and the relation to dietary management were discussed.

Wheat bran in the selective therapy of absorptive hypercalciuria: a study performed on 18 lithiasic patients

The binding properties of raw vegetable fiber towards bivalent cations suggested the prescription of brain as a dietary supplement to limit intestinal calcium absorption in hypercalciuric patients. A group of 18 patients with a specific diagnosis of absorptive hypercalciuria received a dietary supplement of 14 gm. wheat bran at the 2 principal meals for 90 days. A complete assessment of mineral metabolism was performed after 45 and 90 days. Mean basal calciuria was 357 mg. per 24 hours and a significant decrease was noted after 45 days (245 mg. per 24 hours) and 90 days (240 mg. per 24 hours), with a p value of less than 0.01. Urinary oxalate did not vary significantly (0.34 to 0.38 to 0.31 mMol. per 24 hours) and neither did phosphate levels (1,020 to 900 to 893 mg. per 24 hours). A slight and pathologically insignificant decrease was noted in serum iron and urinary magnesium; this fact could be considered a side effect owing to the nonselective binding properties of fiber. Therefore, the positive results achieved confirm the effective action of wheat bran in the treatment of correctly diagnosed absorptive hypercalciuria.

[Study of oval crystals in urine]

Urinary crystals were collected by repeated centrifugation from two outpatients with calcium oxalate crystalluria where oval forms predominated and were studied by scanning electron microscopy and X-ray diffraction. Fibrous structure, biconcave surface and prismatic appearance of oval crystals were shown. The side view of oval forms may be prismatic X-ray diffraction patterns of urinary crystals indicated that oval crystals consist of calcium oxalate monohydrate.

Inhibitory effect of pyrophosphate, citrate, magnesium and chondroitin sulphate in calcium oxalate urolithiasis

The inhibitory capacity of pyrophosphate, citrate, magnesium and chondroitin sulphate was investigated, using the urine of 21 calcium oxalate stone-forming patients without metabolic alterations. The inhibitory effect of these substances was assessed by a combination of nephelometry (light scattering) and optical microscopy. The results showed that citrate and magnesium had an inhibitory effect in a significant number of cases. Pyrophosphate and chondroitin sulphate had a less marked effect. The main urinary lithogenic biochemical parameters of the patients were also studied to see if there was a relationship between them and the inhibitory capacity of the compounds.

Urinary enzymes and calcium oxalate urolithiasis

Male Sprague-Dawley rats were challenged with various hyperoxaluric agents including ammonium oxalate, hydroxy-L-proline, and ethylene glycol. All treatments resulted in increased urinary oxalate. Associated with hyperoxaluria was an increase in urinary levels of renal enzymes, gamma-glutamyl transpeptidase, N-acetyl-beta-glucosaminidase, and alkaline phosphatase. Most of the rats did not demonstrate any significant change in urinary levels of beta-galactosidase. There was a highly significant positive correlation between urinary oxalate and N-acetyl-beta-glucosaminidase.

[The role of urine pH in the occurrence of phosphaturia]

The density of calcium phosphate and the pH were determined in 15 postprandial urine specimens with heavy precipitation of amorphous calcium phosphate, that is phosphaturia, collected from 5 patients with calcium urolithiasis (stone-formers) and 3 patients with no known urological disease (controls). Phosphaturia, not related to urinary tract infection or administration of alkalinizing agents, was found repeatedly at our outpatient clinic in these patients. The correlative relationship was not confirmed between the density of calcium phosphate and the pH. The concentration of calcium and phosphorus was also determined in 10 urine specimens with phosphaturia. The concentration of phosphorus was correlated significantly with the pH (r = -0.775, p less than 0.01), although the concentration of calcium was not correlated with the pH. The pH of 11 urine specimens with phosphaturia from the controls was 7.51 +/- 0.31 (mean +/- S.D.) and the pH of 18 urine specimens with phosphaturia from the stone-formers was 6.81 +/- 0.34. The pH was significantly lower in the urine specimens from the stone-formers than in those from the controls (p less than 0.01). We have noted that the occurrence of phosphaturia depends not only on the urinary pH but on the concentration of phosphorus. It is interesting that phosphaturia often occurs in urine specimens with a pH below 7 in stone-formers.

[Analysis of the urinary risk factors of urolithiasis in healthy children]

Since incidence of idiopathic calcium oxalate urolithiasis in children was very low, a study was made to analyze the risk factors of calcium oxalate stone in male volunteers without any episode of urolithiasis. They were divided into four groups, group I: eight years old, group II: 11 years old, group III: 18 to 24 years old, group IV: 41 to 45 years old. Inhibitory activities of urine were significantly higher in groups of children than in groups of adults. However, inhibitory activities of filtered urine, extracted through filters with conserved limit of 25000 of molecular weight, were reduced significantly. Therefore, it was suggested that materials with molecular weight over 25000 participated in the inhibitory activities. Furthermore, the activities of filtered urine of group I were still higher than those of the non-filtered urine in groups of adults. Accordingly it was considered that substances less than 25000 of molecular weight also participated in the inhibitory activities in children. An analysis of uric acid, citrate, magnesium and uronic acid in urine revealed that magnesium excretion volume and magnesium concentration ratio to creatinine were higher in children than in adults. Magnesium seemed to boost the inhibitory activities in children. In the measurement of crystalloid materials, the concentration of calcium was significantly lower in children groups than in groups of adults. It seemed that calcium also takes part in reduction of incidence of urinary stone in children.

[Urinary material affecting calcium oxalate monohydrate stone formation]

We previously reported that the low molecular and uronic acid-rich fractions in the urine from calcium oxalate stone formers promoted aggregation of calcium oxalate monohydrate seed crystals. In this study, we have demonstrated that lyophilized material of the fractions contains hyaluronic acid as a sole glycosaminoglycans, as well as acidic amino acid-rich proteins and urinary pigment which is supposed to combine with protein. It is known that hyaluronic acid is present in stone matrix, that calcium containing stones contain proteins rich in acidic amino acids, and that the external color of calcium oxalate monohydrate calculi is usually brownish. These facts correspond with our present results. Therefore, it is suggested that the urinary material promotes the calcium oxalate crystal aggregation, sticks the crystals together and is incorporated into the stone.

[Effect of urinary material and glycosaminoglycans on calcium oxalate monohydrate crystal aggregation]

We have examined by the coulter counter method whether some substances promote or inhibit calcium oxalate monohydrate crystal aggregation. The substances tested were hyaluronic acid, chondroitin sulfate and urinary lyophilized material of less than 10 k dalton fractions having aggregate activity. As a result, hyaluronic acid promoted aggregation at low concentrations but inhibited it at higher concentrations, and chondroitin sulfate only inhibited it. They seem, therefore, to have quite different effects, depending on their urinary concentrations, on calcium oxalate crystal aggregation process. However, urinary fractions only promoted aggregation in a dose-response manner. This promoting effect might be caused by not only hyaluronic acid that was contained in the fractions but also by some other promoters.

Urinary excretion of beta-2-microglobulin in patients with active metabolic stone disease

The aim of the present work is to evaluate the function of the proximal tubule in patients with active metabolic stone disease (a.m.s.d.), recognizing the urinary excretion of beta-2-microglobulin (B2-M) as a sensitive marker of that function. The investigated group included 30 patients with a.m.s.d. accompanied by chronic pyelonephritis (CP) and 31 patients with a.m.s.d. without CP. The serum and urinary B2-M concentrations were estimated by radioimmunoassay. The clearance of B2-M (CB2-M) and the tubular reabsorption of B2-M (TRB2-M) were estimated. Patients with a.m.s.d. and CP showed an increased excretion of B2-M, significantly higher values of CB2-M and a significantly lower TRB2-M. The results indicate that the proximal tubular dysfunction in the group of patients with a.m.s.d. is a result of a chronic inflammatory process in the urinary tract.

The relation between orthophosphate and pyrophosphate in normal subjects and in patients with urolithiasis

In calcium lithiasis, inhibitors have a significant effect in reducing the crystallization process. This work evaluated orthophosphate in a group of patients with calcium oxalate lithiasis, and in a control group. The study of orthophosphate and pyrophosphate, showed differences between stone formers and the control group. These results could be attributed to a failure in the renal transformation of orthophosphate into pyrophosphate.

Surface interaction between glycosaminoglycans and calcium oxalate

Molecules and macromolecules are known to alter the process of crystallization, either through inhibition or promotion of nucleation, growth, and/or aggregation. One particular group of macromolecules, glycosaminoglycans (GAGs), has been of interest in our laboratory. The GAGs chondroitin A, chondroitin C, heparan sulfate, dermatan sulfate, hyaluronic acid, and keratan sulfate have all been shown to be inhibitors of calcium oxalate crystallization. Heparin, the only GAG which is not naturally present in urine, is the most potent inhibitor of all GAGs. Using the method of Langmuir isotherm adsorption, we studied the adsorption of certain GAGs onto calcium oxalate crystals. Under standardized conditions, heparin, chondroitin C, hyaluronic acid, and pentosan polysulfate (a synthetic polyanionic molecule similar to, but a weaker inhibitor than, heparin) were adsorbed onto calcium oxalate. The total amount of GAG required to maximally cover the crystal surface, as well as the equilibrium concentration at which surface was half-covered with GAG (inversely related to the desorption energy) were measured. Chondroitin C was adsorbed in the greatest amount, followed by heparin, pentosan polysulfate, and finally hyaluronic acid. Using the method of fiducial limits, the only insignificant difference was between heparin and chondroitin C, and between hyaluronic acid and pentosan polysulfate. Pentosan polysulfate required significantly higher equilibrium concentration than heparin and hyaluronic acid to cover half of the surface of the calcium oxalate crystals. The principle of Langmuir isotherm adsorption can be useful in predicting the effects of macromolecules on crystallization. Weaker inhibitors bind with less affinity than do stronger inhibitors. Further work is underway to characterize other inhibitors and promoters.

The effects of citrate on hydroxyapatite induced calcium oxalate crystallization and on the formation of calcium phosphate crystals

The addition of different amounts of hydroxyapatite crystals (HAP) to a solution, metastably supersaturated with respect to calcium oxalate (CaOx) resulted in heterogenous crystallization at seed concentrations exceeding 0.2 mmol/l. The induction period varied between 1 and more than 8 h with the shortest period for a seed concentration of 2 mmol/l. Addition to the system of 1 and 2% of whole urine and citrate in concentrations corresponding to approximately 1% of that found in normal urine inhibited the crystallization for as long as 4 h. In a system supersaturated with respect to calcium phosphate (CaP) the total number of crystals was markedly reduced by citrate concentrations exceeding 0.5 mmol/l. The fractions of medium sized and large crystals were sharply reduced and small crystals predominated at higher citrate concentrations. This might indicate effects of citrate on both crystal growth and crystal aggregation. We conclude that increased citrate concentrations during treatment with alkali leads to a significant inhibition of CaOx growth on HAP as well as to a prevention of the formation of large CaP crystals from solutions supersaturated with respect to CaP.

[Clinical significance of phosphaturia]

From September 1986 to August 1987, heavy precipitation of amorphous calcium phosphate, that is phosphaturia, was found at our outpatient clinic in 153 postprandial urine specimens from 115 patients, in 1.5% of all the specimens examined during this period. One patient was excluded because he had both urolithiasis and urinary tract infection. The remaining 152 specimens with phosphaturia were then divided into 3 groups; Group I from patients with urolithiasis, Group II from patients with urinary tract infection and Group III from patients without either urolithiasis or urinary tract infection (Phosphaturia Group, Table 1). It is evident from this table that phosphaturia is repeated more frequently in patients with urolithiasis than in patients without urolithiasis (p less than 0.01). 200 urine specimens examined during this period were selected randomly. Three bloody or purulent specimens were excluded. The remaining 197 specimens from 189 patients were divided into 3 groups, as in the phosphaturia group (Control Group, Table 2). When the proportion of the number of specimens to the total is compared between the phosphaturia group and the control group, it is clear that phosphaturia is found more frequently in specimens from patients with urolithiasis than in specimens from patients without urolithiasis (p less than 0.01). Since phosphaturia was almost always found in the specimens with urine pH greater than or equal to 7, 486 patients, in whom the pH of the first urine specimen was equal to or above 7, were selected from among 1434 patients undergoing urinalyses during this period and divided into 3 groups as has been described above (Table 3).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of animal and vegetable protein intake on oxalate excretion in idiopathic calcium stone disease

Oxalate excretion was measured in healthy subjects and idiopathic calcium stone-formers on dietary regimens which differed in the type and amount of protein allowed; 24-h urine collections were obtained from 41 practising vegetarians and 40 normal persons on a free, mixed, "mediterranean" diet. Twenty idiopathic calcium stone-formers were also studied while on two low calcium, low oxalate diets which differed in that animal protein was high in one and restricted in the other. Vegetarians had higher urinary oxalate levels than controls and although the calcium levels were markedly lower, urinary saturation with calcium/oxalate was significantly higher. This mild hypercalciuria was interpreted as being secondary to both a higher intake and increased fractional intestinal absorption of oxalate. Changing calcium stone-formers from a high to a low animal protein intake produced a significant decrease in calcium excretion but there was no variation in urinary oxalate. As a result, the decrease in calcium oxalate saturation was only marginal and not significant. It was concluded that dietary animal protein has a minimal effect on oxalate excretion. Mild hyperoxaluria of idiopathic calcium stone disease is likely to be intestinal in origin. Calcium stone-formers should be advised to avoid an excess of animal protein but the risks of a vegetable-rich diet should also be borne in mind.

Does hyperuricosuria play a role in calcium oxalate lithiasis?

This review evaluates the epidemiologic, clinical and experimental evidence for an etiological link between urinary uric acid and the propensity to develop calcium oxalate calculi. While epidemiologic and laboratory studies provide only equivocal support for a synergistic relationship, several clinical trials with allopurinol have demonstrated a reduction in calculus recurrence. These beneficial effects are observed only when allopurinol is given to subjects with calcium oxalate calculi who have isolated hyperuricosuria. The specificity of this effect suggests that there is an important interaction between uric acid and calcium oxalate but the mechanism(s) remain to be elucidated.

[Comparison of calcium oxalate values as indicators of risk for calcium oxalate calcinosis and the degree of urine saturation in patients with calcium urolithiasis and in healthy patients]

Daily excretion of calcium, magnesium, oxalates, and citrates together with daily urine output were determined in 37 patients with calcium urolithiasis and in 25 healthy individuals. Basing on the obtained values, a degree of urine saturation with calcium oxalate with Marshall and Robertson technique and a value of risk factor with Tiselius technique were calculated. It was found that daily diuresis and excretion of calcium with the urine are significantly higher in patients with urolithiasis where as daily excretion of citrates with the urine is significantly lower than in healthy individuals. Risk index proved two-fold higher in the examined patients than in the healthy individuals (p greater than 0.001) while the degree of urine saturation with calcium oxalate did not differ significantly in both groups. The authors, discussing causes of seemingly different changes in both tested parameters, stressed diagnostic value of risk index which includes excretion of crystallization inhibitors (magnesium, citrates) and contrary to the degree of urine saturation is independent of daily urine output.

[Evaluation of risk index according to Tiselius in patients with calcium urinary stones]

Daily calcium, oxalates, magnesium, citrates and creatinine excretion with the urine was determined in 36 patients with calcium renal stones and in 25 healthy individuals. Then, risk index according to Tiselius was calculated. It was found that daily calcium excretion is significantly higher and daily citrates excretion is significantly lower in patients with calcium renal stones. Daily excretion of oxalates, magnesium and creatinine with the urine did not differ in both groups. Risk index according to Tiselius was two-fold higher in patients suffering from urolithiasis than in healthy individuals (p greater than 0.001) and better illustrated the tendency to stone formation than the analysis of metabolic disorders.

[Urinary calcium and phosphorus excretion and their relationship in calcium-containing urinary stone formers]

Calcium-containing upper urinary stone formers (group SF-A, n = 116) and normal controls (group Normals, n = 10) were examined for urinary calcium (Ca) and phosphorus (P) excretion (mg/mg creatinine) on usual diet, on Ca-restricted diet and in basal period. As a result, urinary Ca and P excretion decreased significantly both in group SF-A and in normal controls, as the dietary intake was reduced. As compared with normal controls, group SF-A exhibited significant elevation in urinary Ca excretion and showed a slight, though not significant increase, in urinary P excretion. A significant positive correlation between urinary Ca and P excretion was observed in either mode of diet in group SF-A, while no correlation was seen in normal controls. To examine the legitimacy of the result above obtained, another 40 Ca-containing upper urinary stone formers (group SF-B) were studied on usual diet. Thus, better correlation was obtained between urinary Ca and P excretion. In conclusion, urinary Ca and P excretion will be strongly influenced by their dietary intake. Stone formers excrete more Ca and P than normal controls. Finally, a tendency was noted that stone formers excreted the more Ca, the more P.

Oxalate measurement in the picomol range by ion chromatography: values in fasting plasma and urine of controls and patients with idiopathic calcium urolithiasis

Oxalate was measured by ion chromatography in the ultrafiltrate of heparinized plasma from peripheral venous blood, using a membrane with a cut-off molecular weight (Mr). The following criteria were established: sensitivity 0.7 mumol.l-1; intra- and inter-assay coefficients of variation 4% and 12%, respectively; precision of duplicate determinations (expressed as standard deviation) 0.08 mumol.l-1; overall recovery (oxalate added and diluted, respectively) 100.7%. These qualified the method for assessment of plasma oxalate in healthy human controls (males: n = 12) as well as patients with idiopathic renal calcium urolithiasis (males: n = 22; females: n = 16). Renal calcium urolithiasis patients were subclassified into those with normocalciuria and idiopathic hypercalciuria. In male and female controls the mean values (and range) of plasma oxalate were 1.98 (1.4-2.5) and 1.78 (0.7-2.9) mumol.l-1, respectively. In male controls ultrafiltration (membrane cut off Mr 10,000) revealed that 11-16% plasma oxalate was bound to constituents having an apparent Mr above 10,000, and that with use of membranes with smaller pore size, the ultrafilterability of oxalate decreases further. In renal calcium urolithiasis the following values were elicited (mumol.l-1): male normocalciuria 1.78 (0.8-4.0), idiopathic hypercalciuria 1.58 (1.2-2.2); female normocalciuria 1.69 (0.8-3.6), idiopathic hypercalciuria 1.21 (0.8-2.1). The difference from controls is significant in idiopathic hypercalciuria (males and females). In contrast, in fasting urine of renal calcium urolithiasis the oxalate excretion rate (5-45 mumol per 120 min) and oxalate clearance (21-328 ml per min) resemble those in controls, whereas in renal calcium urolithiasis the fractional oxalate clearance (30-357% of creatinine clearance) tended to higher values (p less than 0.01, in male idiopathic hypercalciuria versus controls). It is suggested that 1) ion chromatography allows the reliable assessment of ultrafiltrable plasma oxalate in health and disease states, 2) in renal calcium urolithiasis this technique may help to elucidate oxalate pathophysiology, especially the mode of renal handling of oxalate.