Risk factors for urinary calcium oxalate crystals as revealed by their specific enzymatic assay

Calcium oxalate crystal concentrations were assayed by a new highly specific enzymatic method in 1200 urine samples from normal subjects and stone formers. Examination of the crystals was also carried out by light microscopy and urines were analysed for oxalate, calcium, magnesium, citrate, urate, pH and osmolality. A striking positive correlation was established between urinary oxalate concentration and calcium oxalate crystal concentration as well as incidence of calcium oxalate crystals and aggregates seen by microscopy. A less striking relationship, also supported by light microscopy, was found between calcium oxalate crystal concentration and urinary calcium concentration. A small rise in calcium oxalate crystalluria was seen with increasing osmolality, but no relationship found between concentration or urinary urate, citrate or magnesium and that of calcium oxalate crystals. Higher levels of calcium oxalate crystal concentration appeared in alkaline urines in association with calcium phosphates. The dominance of urinary oxalate as a risk factor for calcium oxalate crystalluria is confirmed.     

A study on the cause of urolithiasis of the upper urinary tract--clinical study of risk factors in the formation of stones in the upper urinary tract

Various risk factors and inhibitors of the stone formation of the upper urinary tract have been pointed out in urine. We examined the amount of daily excretion of several important risk factors (calcium, phosphorus, urate and oxalate) and inhibitors (magnesium and citrate) in the urine of 21 healthy males, 13 male single stone formeks and recurrent and/or multiple stone formers before and after taking the regular diet which contains 500 mg of calcium and 1,000 mg of phosphorus a day. The daily excretion of calcium, phosphorus and magnesium indicated no significant differences among the 3 groups. The excretion of oxalate in urine for 24 hours was significantly decreased in the stone formers after taking the regular diet. The urinary excretion of the urate per body surface area in the stone formers was significantly higher than that in the healthy control. The amount of the excretion of the citrate in urine in the recurrent and/or multiple stone formers was significantly lower than that in the other 2 groups. Many patients of the recurrent and/or multiple urinary stones had more than two abnormal values of above-mentioned risk factors and inhibitors. These results suggest that the causes of the formation of the upper urinary stone were not single but multiple and that the dietary advice to these patients was important against the recurrence of the urolithiasis.     

Crystal agglomeration is a major element in calcium oxalate urinary stone formation

The effects of urines from 36 healthy subjects and 86 calcium oxalate renal stone formers on calcium oxalate monohydrate crystallization kinetics were studied using a seeded crystal growth method in which the solubility, the growth and the agglomeration of the crystals are measured as three separate and system-independent parameters. The urines of healthy subjects were found to increase the solubility and to strongly inhibit the growth and the agglomeration of calcium oxalate monohydrate crystals. The urines of stone formers had a similar effect on the solubility, but a significantly lower ability to inhibit the crystal growth and the crystal agglomeration. Of these two kinetic processes the inhibition of crystal agglomeration was more clearly affected, with 55% of the stone formers having abnormally low values, while the changes in crystal growth inhibition occurred within the normal range. The defect in crystal agglomeration inhibition was related to stone frequency, and urines from patients with very high stone frequency rates had also the most severely impaired ability to inhibit the agglomeration of the calcium oxalate monohydrate crystals. The inhibitory effect of urines on crystal agglomeration was found to be related to its citrate content (r = 0.68, P less than 0.001). All patients with hypocitraturia, except two, had also abnormally low values for crystal agglomeration inhibition. In a group of 15 hypocitraturic stone formers, alkali treatment for a mean period of 18 months resulted in a parallel increase in urinary citrate excretion and in the ability of urines to inhibit crystal agglomeration (r = 0.77, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative study of 24-hour urinary excretion of glycosaminoglycans by renal stone formers and healthy adults

In order to find out the possible aetiological factors for urolithiasis in North-Western India, an endemic region for urinary calculi, we studied the 24-hour urinary excretion of glycosaminoglycans (GAGs), inhibitors of calcium oxalate crystallisation and/or crystal aggregation, in 58 healthy adults and in 100 stone formers. GAGs were colorimetrically estimated in urine in terms of glucuronic acid content after precipitation of GAGs by cetyl pyridinium chloride. The 24-hour urinary excretion of GAGs was significantly less in stone formers as compared to healthy adults (15.32 +/- 6.94 vs. 22.44 +/- 5.54 mumol/day; p less than 0.001). There was no significant difference in the 24-hour urinary excretion of GAGs between male and female stone formers, or between male and female healthy adults. There was no correlation between age and 24-hour urinary excretion of GAGs in any of the groups. In conclusion, 24-hour urinary excretion of GAGs is significantly less both in male and in female stone formers. The 24-hour urinary excretion of GAGs is not related to age or sex in both healthy adults as well as in stone formers.     

Prevalence of hyperoxaluria in idiopathic calcium oxalate kidney stone disease

Urinary excretion of oxalate, calcium and urate has been investigated in 88 patients affected by idiopathic calcium oxalate stone disease and in 20 normal subjects. Of these ions, only oxalate was found significantly higher in stone formers. Defining hyperoxaluria as urinary oxalate excretion greater than 2 SD above normal, 50% of stone-forming people were found to be hyperoxaluric. When stone formers were classified in normo- and hyperoxaluric, the prevalence of hypercalciuria, hyperuricuria, family history of stone disease and recurrencies in stone formation was the same in both groups. It is concluded that hyperoxaluria is a frequent finding in finding in idiopathic calcium oxalate renal stone disease.     

The urinary response to an oral oxalate load in recurrent calcium stone formers

PURPOSE: Dietary oxalate may contribute up to 50% to 80% of the oxalate excreted in urine. We studied the urinary response to an oral oxalate load in male and female idiopathic recurrent calcium oxalate stone formers with and without mild hyperoxaluria to evaluate the potential pathophysiological significance of dietary oxalate. MATERIALS AND METHODS: A total of 60 recurrent calcium stone formers underwent an oral oxalate load test. Urine samples were obtained after an overnight fast. Each patient then received an oral oxalate load (5 mM. sodium oxalate dissolved in 250 ml. distilled water) and 3, 2-hour urine samples were obtained 2, 4 and 6 hours after the oxalate load. We compared the response to the oxalate load in patients with and without mild hyperoxaluria, and in male and female patients without hyperoxaluria. RESULTS: The peak urinary response occurred 4 hours after the oral oxalate load in all patients. Those with mild hyperoxaluria had a mean fasting urinary oxalate-to-creatinine ratio +/- SE of 0.027 +/- 0.003 and a mean peak urinary oxalate-to-creatinine ratio of 0.071 +/- 0.006. In comparison, patients with normal oxalate excretion had a fasting and peak urinary oxalate-to-creatinine ratio of 0.018 +/- 0.001 and 0.056 +/- 0.004, respectively (p <0.05). The mean 6-hour increment for urinary oxalate excretion after the oxalate load for patients with hyperoxaluria versus those with normal urinary oxalate excretion was 17.2 +/- 1.9 versus 12.1 +/- 0.98 mg. (p <0.05). In the subset of patients with normal urinary oxalate excretion mean 6-hour cumulative urinary oxalate excretion was 16.8 +/- 1.3 and 13.3 +/- 1.4 mg. in males and females, respectively (p not significant). CONCLUSIONS: Recurrent calcium stone formers with mild hyperoxaluria have higher fasting urinary oxalate and an exaggerated urinary response to an oral oxalate load compared with recurrent calcium stone formers with normal urinary oxalate excretion. Men and women stone formers without hyperoxaluria excrete similar fractions of an oral oxalate load. Increased gastrointestinal absorption and renal excretion of dietary oxalate may be a significant pathophysiological mechanism of stone formation in patients with mild hyperoxaluria.     

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.     

Hyperoxaluria in idiopathic calcium nephrolithiasis--what are the limits?

OBJECTIVE: The object of this study was to investigate the role for measurement of 24-h renal oxalate excretion in the evaluation of idiopathic calcium stone formers. MATERIALS AND METHODS: Renal excretion rates of oxalate and creatinine were measured in 24-h urines in 46 consecutive male recurrent idiopathic calcium stone formers and 61 healthy males. Furthermore, day-to-day variation in renal oxalate excretion in 10 male recurrent stone formers and 10 healthy males were evaluated by measuring 24-h oxalate excretion on 5 different days in each individual. Concentrations of oxalate in urine were measured using an enzymatic method without ascorbate interference. RESULTS: The cumulative frequency distribution curves of 24-h renal oxalate excretion rates of stone formers and controls were congruent, and there were no statistically significant differences in oxalate excretion rates between stone formers and controls. Mean 24-h oxalate excretion (95%-confidence intervals) was 0.22 (0.18-0.25) mmol and 0.21 (0.18-0.24) mmol in stone formers and controls, respectively (p = 0.9). The day-to-day variation study did not reveal any differences in renal oxalate excretion pattern between stone formers and controls, and the presence of intermittent hyperoxaluria could not be confirmed. The oxalate excretion rates were generally low. CONCLUSION: In our region, there appear to be no differences in 24-h renal excretion rates of oxalate between male recurrent idiopathic calcium stone formers and healthy males, and the syndrome of mild hyperoxaluric calcium nephrolithiasis could not be identified in our population of idiopathic stone formers. Hence, a limit of abnormal oxalate excretion that distinguishes an idiopathic stone former from a non-stone former could not be defined in our population. Therefore, the value of routine measurement of urinary oxalate in idiopathic urolithiasis is difficult to accept, and cannot be recommended.     

A study of the etiology of idiopathic calcium urolithiasis in children: hypocitruria is the most important risk factor

PURPOSE: To determine the association of metabolic risk factors with pediatric calcium urolithiasis we compared metabolic evaluation data on children with idiopathic calcium stones and those on healthy children. MATERIALS AND METHODS: Metabolic evaluation was done in 78 calcium stone formers 1 to 15 years old (mean age 7.2) who were free of urinary tract infection, anatomical abnormalities, and metabolic, endocrinological and intestinal disorders, and in 24 healthy children. Evaluation included serum biochemistry, and measurement of daily excretion of urinary calcium, oxalate, urate, phosphorus, citrate and magnesium. RESULTS: Demographic characteristics, serum parameters, and daily excretion of calcium, urate, phosphorus and magnesium did not differ statistically in the 2 groups. However, urinary oxalate was significantly higher and urinary citrate was significantly lower in stone formers than in controls (p = 0.002 and 0.028, respectively). Hypocitruria and hyperoxaluria were 4.3 and 3-fold more common in stone formers than in controls, respectively. Multivariate analysis using logistic regression showed that hypocitruria was the only significant risk factor for idiopathic calcium stones (p = 0.008). CONCLUSIONS: Hypocitruria was the most important risk factor in our patients. Hyperoxaluria was also common and accompanied hypocitruria in many stone formers. In contrast to many previous reports, we failed to show that hypercalciuria is an important metabolic defect for idiopathic calcium stones, possibly because our study evaluated a different population.     

Clinical studies of the recurrence of urolithiasis (4). Crystal formation in urine and stone recurrence

Relationship between stone formation and crystal formation in urine was studied. Crystals in the sediments of early morning urine in 238 stone formers and the same numbers of non-stone formers were examined by light microscopy. Almost all crystals found in the early morning urine were composed of calcium oxalate both in stone formers and in non-stone formers. The frequency of calcium oxalate crystal formation was slightly higher in stone formers than in non-stone formers, but, no significant difference was noted. On the other hand, the urine containing calcium oxalate crystals of the stone formers had significantly lower specific gravity than that of the non-stone formers. Calcium oxalate crystals in the urine were formed significantly more frequently in the recurrent or bilateral male stone formers than in male unilateral stone formers without previous stone history. Frequency of calcium oxalate crystal formation was not influenced by urinary excretion of calcium, oxalate, uric acid, phosphate and magnesium. These finding led us to the conclusion that it was clinically useful to measure urinary specific gravity in which calcium oxalate crystals were formed in predicting the risk of stone formation.     

Clinical studies on the recurrence of urolithiasis: (1). Influence of diet on urinary excretion of the stone forming constituents

Twenty-four hour urinary excretion of the stone forming constituents, calcium, oxalate, uric acid, phosphate and magnesium were assayed either under the restricted diet (190 stone formers and 52 non-stone formers) or under the ambulatory free diet (93 stone formers and 14 non-stone formers). Under the ambulatory free diet, urinary excretion of calcium, uric acid and magnesium in the male stone formers, and urinary excretion of calcium and magnesium in the female stone formers was significantly higher than that under the restricted diet. Under the restricted diet, no difference in urinary excretion of calcium, oxalate, uric acid or phosphate was noted between the stone formers and non-stone formers. However, urinary magnesium excretion of the stone formers under the restricted diet was significantly lower than that of the non-stone formers. Under the free diet, no difference in urinary excretion of calcium, oxalate, uric acid, phosphate or magnesium was observed between the stone formers and non-stone formers. Also, there was no significant difference in urinary excretion of calcium, oxalate, uric acid, phosphate or magnesium between the unilateral urolithiasis patients without previous stone history and that of the bilateral or recurrent stone formers. We conclude that urinary excretion of calcium, oxalate, uric acid, phosphate and magnesium have no major role in the stone producing mechanism. However, reduction of urinary excretion of calcium, oxalate, uric acid and phosphate and augmentation of urinary excretion of magnesium are mandatory in preventing stone recurrence until a better understanding of the cause of urolithiasis is obtained.     

Should recurrent calcium oxalate stone formers become vegetarians?

The hypothesis that the incidence of calcium stone disease is related to the consumption of animal protein has been examined. Within the male population, recurrent idiopathic stone formers consumed more animal protein than did normal subjects. Single stone formers had animal protein intakes intermediate between those of normal men and those of recurrent stone formers. A high animal protein intake caused a significant increase in the urinary excretion of calcium, oxalate and uric acid, 3 of the 6 main urinary risk factors for calcium stone formation. The overall relative probability of forming stones, calculated from the combination of the 6 main urinary risk factors, was markedly increased by a high animal protein diet. Conversely, a low animal protein intake, such as taken by vegetarians, was associated with a low excretion of calcium, oxalate and uric acid and a low relative probability of forming stones.     

草酸钙结石患者尿中蛋白结合型γ-羧基谷氨酸的检测意义

目的　探讨含γ 羧基谷氨酸 (Gla)蛋白质及其Gla残基在尿石形成中的作用。　方法　采用过饱和结晶法从新鲜尿液中提取草酸钙晶体基质 ,高效液相色谱法 (HPLC)测定 2 5例草酸钙结石患者尿液和提取的晶体基质中蛋白结合型Gla含量。　结果　草酸钙结石患者尿蛋白结合型Gla浓度为 (1.32± 0 .2 4)nmol/ml,2 4h尿含量为 (2 .0 4± 0 .6 5 ) μmol,显著低于正常人 ;草酸钙结石患者尿液提取的晶体基质中蛋白结合型Gla含量亦显著低于正常人。　结论　草酸钙结石患者尿液中蛋白结合型Gla含量较少 ,尿液含Gla蛋白质的羧基化程度低下可能是结石形成的重要原因之一。     

Urinary oxalate excretion in female calcium oxalate stone formers with and without a history of recurrent urinary tract infections

Therapy with antibiotics in recurrent urinary tract infections may destroy colonies of Oxalobacter formigenes in the intestinal tract. A lack of oxalate degradation caused by the absence of this bacterium is suggested to contribute to the hyperabsorption of dietary oxalate and to the increase in urinary oxalate excretion. The present study was performed to evaluate the effect of recurrent urinary tract infections and subsequent changes induced in the urinary excretion profile in female calcium oxalate stone formers. Serum biochemical profiles, 24-h urinary parameters, and the personal characteristics of 57 female calcium oxalate stone patients with recurrent urinary tract infections (RUTI) were compared with 78 female calcium oxalate stone patients without a history of urinary tract infection. All subjects were recruited during the same period. In female patients with RUTI, urinary oxalate excretion was significantly higher (0.374 mmol/day) than in females without urinary tract infection (0.308 mmol/day) (P < 0.05). Moreover, the mean 24-h pH value and urinary sodium excretion were significantly higher in women with RUTI than in women without a history of urinary tract infection. The significantly higher urinary oxalate excretion in female calcium oxalate stone formers with recurrent urinary tract infections may be associated with the application of antibiotics and a subsequent temporary or permanent decolonization of Oxalobacter formigenes.     

Effect of cranberry juice consumption on urinary stone risk factors

PURPOSE: We evaluated the effect of cranberry juice on urinary stone risk factors. MATERIALS AND METHODS: A total of 12 normal subjects and 12 calcium oxalate stone formers underwent 2, 7-day phases of study in random order while on a controlled metabolic diet. Subjects ingested 1 l of cranberry juice (CBJ) daily in 1 phase and 1 l of deionized water in the other phase. On the last 2 days of each phase 2, 24-hour urine collections and blood samples were obtained for stone risk factors and serum chemistries. RESULTS: No significant differences were found between normal subjects and stone formers in response to CBJ and, therefore, the groups were combined. CBJ significantly increased urinary calcium (from 154 to 177 mg per day, p =0.0008) and urinary oxalate (from 26.4 to 29.2 mg per day, p =0.04), thereby increasing urinary saturation of calcium oxalate by 18%. Urinary citrate was unchanged and urinary magnesium increased slightly. Urinary pH decreased (from 5.97 to 5.67, p =0.0005), and urinary ammonium, titratable acidity and net acid excretion increased during CBJ ingestion. Urinary uric acid decreased (from 544 to 442 mg per day, p <0.0001) as did serum uric acid. Thus, the urinary saturation of brushite and monosodium urate was reduced by CBJ but the amount of undissociated uric acid increased. CONCLUSIONS: CBJ exerts a mixed effect on urinary stone forming propensity. It reduces urinary pH likely by providing an acid load and decreases urinary uric acid perhaps by retarding urate synthesis. Overall CBJ increases the risk of calcium oxalate and uric acid stone formation but decreases the risk of brushite stones.     

Idiopathic hypercalciuria

Summary 24 h urine compositions of male stone formers with idiopathic hypercalciuria prior to treatment were compared with those of male general practitioners without urolithiasis. Urinary urate was slightly higher in the stone formers than in the normals but this was not statistically significant. Furthermore, when results were corrected for the higher creatinine excretions of the stone formers then the reverse was true and statistically significant. All subjects with urinary urate over 7.0 mmol/24h were separately studied. In these groups the normals had higher urate and creatinine excretions than the stone formers but when results were corrected for creatinine the difference in the urate excretions disappeared. In long term follow up studies urinary calcium was lowered by diet and more so by diet supplemented with either Bendrofluazide or cellulose phosphate. Each drug raised urinary oxalate slightly and this was statistically significant, while both drugs together caused an even bigger rise in oxalate excretion. An unexpected finding was a rise in urinary urate with cellulose phosphate.     

The effect of crystalline monosodium urate on the crystallisation of calcium oxalate in whole human urine

Summary (1) Samples of undiluted urine from normal men were preincubated with crystalline monosodium urate and their metastable limits and responses to a standard oxalate challenge were compared with results obtained from control samples preincubated without urate. (2) Preincubation with urate had no significant effect on the metastable limits of the urines, the morphology, size, or growth rates of calcium oxalate crystals precipitated from the urines, or on the total amount of calcium oxalate deposited in a given time. (3) It was concluded that particulate monosodium urate is unlikely to influence calcium oxalate stone formation by binding to and attenuating the potency of urinary inhibitors.     

Urine composition following jejunoileal bypass

The urinary excretion of oxalate, calcium, citrate, magnesium, urate and creatinine and the inhibition of calcium oxalate crystal growth were determined in 30 patients operated with three different types of jejunoileal bypass. In addition the ion-activity products of calcium oxalate and calcium oxalate saturation were calculated. 15 of the patients had formed urolithiasis postoperatively. The patients were investigated on an out-patient basis with their ordinary diet. All patients had hyperoxaluria. The oxalate excretion did not seem to decrease with time after operation. The patients operated with a biliointestinal shunt had a significantly higher excretion of oxalate than those with the other two types of operation, indicating that variations in the anatomy of the small intestine after jejunoileal bypass might result in different absorption of oxalate or oxalate precursors. Urinary oxalate, calcium oxalate saturation and ion-activity products were higher whereas the excretion of calcium, magnesium and citrate was lower in patients than in controls. The urine volumes, excretion of creatinine and urate and inhibition of calcium oxalate crystal growth were equal in patients and controls. Analogous urine composition was found in patients both with and without urolithiasis with the exception of a higher magnesium excretion observed in stone formers.     

Examination of the urinary potential of hyperuricosuric patients to retard calcium oxalate precipitation

In the present study it has been found that hyperuricosuric calcium oxalate (CaOx) stone formers do not differ from idiopathic CaOx stone formers in their urines' potential to retard in vitro precipitation of CaOx. On the other hand, urines of hyperuricosuric patients with no history of CaOx stone formation have the same potential to inhibit CaOx precipitation as those of normal controls. Reduction of urinary uric acid concentrations by either incubation of specimens with sodium urate or by treatment of hyperuricosuric patients with allopurinol had no effect on the urines' potential to retard CaOx precipitation.     

Oxalate loading test for outpatients with calcium oxalate stones

A spinach loading experiment was performed on 9 normal subjects, 25 outpatients who were single calcium oxalate stone formers and 25 recurrent calcium oxalate stone formers. The experimental diet contained 445 mg of total oxalate, 163 mg of soluble oxalate and 115 mg of calcium. Urinary oxalate excretion was observed 2 hrs before and 6 hrs after the experimental diet was consumed. There was no significant difference in urinary oxalate excretion in preloading urine of normal subjects and stone formers. However, urinary oxalate excretion in postloading urine was significantly elevated in stone formers. This loading test is recommended as a simple and valuable screening method of hyperabsorption of oxalate on outpatients with calcium oxalate stones.