Effects of low animal protein or high-fiber diets on urine composition in calcium nephrolithiasis

BACKGROUND

The purpose of this article is to evaluate the impact of low protein and high fiber intakes on risk factors of stone recurrence in idiopathic calcium stone formers (ICSFs).

METHODS

Ninety-six ICSFs were randomly assigned a low animal protein diet (< 10% of total energy), a high-fiber diet (> 25 g/day), or a usual diet (control group); all patients were recommended to increase their fluid intake. Their daily urine compositions were analyzed at baseline and at four months. Compliance with dietary recommendations was checked by validated food frequency questionnaires. Compliance with total and animal protein intakes was assessed by 24-hour urea and sulfate outputs, respectively. The nutritional intervention (oral instructions, written leaflet, phoning) and food assessment were carried out by a research dietitian.

RESULTS

At baseline, diets and the daily urine composition did not differ between the three groups. At four months, while diets differed significantly, the 24-hour output of calcium and oxalate did not differ significantly within and between groups after adjustment for potential confounders (age, sex, and personal and family history of calcium stones) and baseline values. However, as many as 12 out of 31 ICSFs (95% CI, 22 to 58%) assigned to a low animal protein diet achieved a reduction in the urine urea excretion rate of more than 50 mmol/day and also exhibited a significant decrease in urinary calcium excretion that averaged 1.8 mmol/day. A significant correlation between urea and calcium outputs was observed only among patients with hypercalciuria.

CONCLUSIONS

These results show that only ICSFs who markedly decrease their animal protein intake, especially those with hypercalciuria, can expect to benefit from dietary recommendations.

Oxalate, citrate, and sulfate concentration in human milk compared with formula preparations: influence on urinary anion excretion

BACKGROUND

Nephrocalcinosis is not uncommon in preterm infants, and elevated urinary oxalate excretion is known to be one of the main risk factors. When oxalate excretion was found to be higher in formula-fed than in human milk-fed infants, the formulas' oxalate content was thought to be responsible.

METHODS

The oxalate concentration in human milk (21 samples obtained during lactogenesis; 17 samples obtained during established lactation) and of 16 formula preparations was examined. Citrate and sulfate concentrations were also measured, because both anions influence urinary saturation.

RESULTS

The mean (+/- SE) oxalate content of human milk increased approximately 27% from early lactogenesis (70.4 +/- 6.4 micromol/1) to established lactation (96.4 +/- 9.5 micromol/l; p < 0.05). The latter was not different from the mean oxalate concentration of formula (98.2 +/- 11.4 micromol/l), however a fourfold range of measurements was recorded in both groups. The mean citrate content of human milk increased only slightly after early lactogenesis (2.66 +/- 0.22 mmol/l), but remained significantly lower than in formula (3.34 +/- 0.23 mmol/l; p < 0.05). The mean sulfate concentration did not increase and was 13 times lower in human milk (52.1 +/- 9.5 micromol/l) than in formula (688.7 +/- 95.4 micromol/l; p < 0.0001).

CONCLUSIONS

The higher oxalate excretion in formula-fed infants is not because of the milk's oxalate concentration. Urinary citrate and sulfate excretion may be influenced by their higher concentrations in formula preparations, which may be of clinical importance in the population that is at risk for development of nephrocalcinosis.

[Effect of dexamethasone and spironolactone therapy in calcium and phosphate homeostasis in premature infants with a birth weight under 1,500 g]

BACKGROUND

Dexamethasone and spironolactone are widely used in the management of bronchopulmonary dysplasia in premature infants. There are few data available about adverse effects of this drugs on the urinary excretion of calcium and phosphate in this group of patients.

PATIENTS

24 h-urine samples could be collected in 85 infants between 8 and 40 days. 31 infants received dexamethasone and 32 spironolactone.

METHODS

Multivariate variance analysis was performed to study the influence of dexamethasone and spironolactone on the measured excretion of calcium and phosphate. The influence of gestational and postnatal age, calcium and phosphate intake and theophylline treatment were excluded by use as covariates.

RESULTS

Spironolactone showed no significant influence on the urinary excretion of calcium or phosphate. Dexamethasone treatment increased the daily excretion of phosphate in the urine and decreased the phosphate concentration in serum.

CONCLUSION

None of the examined drugs showed a significant increase of the renal excretion of calcium in preterm infants. Thus a higher risk of nephrocalcinosis development due to these drugs has not been confirmed. Dexamethasone treatment might increase the risk of osteopenia by enhancing phosphate excretion.

Crystalluria: a clinically useful investigation in children with primary hyperoxaluria post-transplantation

Primary hyperoxaluria type I (PH I) is a congenital error of metabolism that can be manifested by an increased oxalate production, and ultimately result in kidney failure. After a combined liver/kidney transplantation, children with PH I have persistent excretion of oxalate that causes crystal formation in the urinary tract, and could result in systemic oxalosis and eventual graft failure. We speculated that crystalluria may be predictive of this nephrolithogenic tendency and thus investigated the effect of an intensive therapeutic strategy to prevent crystal formation in 13 children at our hospital. Oxalate crystal volume (OCV) measurements were performed at regular intervals for 36 months, and compared with urine supersaturation measurements. We found that crystalluria with the OCV measurement is non-invasive, easily performed, and gives feedback on the efficacy of PH I therapy within one hour. Further study is needed to determine whether this method is a better predictor of nephrocalcinosis than is supersaturation alone.

Persistent hypercalciuria and elevated 25-hydroxyvitamin D3 in children with infantile hypercalcaemia

The aim of the study was to characterize abnormalities of calcium-phosphate and vitamin D3 metabolism in children with a past history of "mild" Lightwood-type idiopathic infantile hypercalcaemia. Seventeen seemingly healthy children aged 2-12 years, with long-term idiopathic hypercalcaemic syndrome since infancy were studied. Two reference groups were also included (vitamin D3 intoxication/healthy and Williams groups). Despite a long-term milk-restricted diet and a restricted vitamin D3 intake, urinary calcium excretion in the study group was 0.117 +/- 0.07 mumol/kg per 24 h. Compared with the reference groups (0.047 +/- 0.029 and 0.067 +/- 0.06 mumol/kg per 24 h, P < 0.05), there was significant hypercalciuria in the children with idiopathic hypercalcaemia since infancy. Serum concentrations of 25-hydroxyvitamin D3 in the study group were also elevated compared with the reference groups (57.4 +/- 15.5 vs. 34.6 +/- 9.3 and 22.7 +/- 10.5 ng/ml). 1,25-Dihydroxyvitamin D3 levels were at the upper limit of normal (45.9 +/- 13.1 vs. 35.0 +/- 8.1 and 30.0 +/- 13.7 pg/ml). Non-progressive, clinically silent nephrocalcinosis was visible on ultrasound examinations. The disturbances of vitamin D3 and calcium-phosphate metabolism persistent in the normocalcaemic phase of idiopathic infantile hypercalcaemia may be a primary metabolic defect of the condition. The mechanisms leading to elevation of metabolites of 1,25-dihydroxy- and 25-hydroxyvitamin D3 and the relationship between this and persistent hypercalciuria and nephrocalcinosis need pathophysiological explanation.

Urinary inhibitors of crystallization in hypercalciuric children with hematuria and nephrolithiasis

Urinary inhibitors are suggested to play a significant role in reducing crystallization in calcium (Ca) stone former and idiopathic hypercalciuria (IH). Urinary inhibitors such as magnesium (Mg), citrate, and glycosaminoglycans (GAGs) were evaluated, as well as urinary Ca and creatinine (Cr), in IH children with nephrolithiasis (LIT) or with hematuria plus IH (HEM) and were compared with a control group. The mean 24-h urinary excretion of Mg was similar in all groups. However, the urine Ca/Mg ratio was significantly increased (P < 0.005) in LIT and HEM groups. A higher mean value for GAGs and citrate was found in the HEM group, but a very low level of GAGs (less than 60% of the normal value) and citrate (less than 30% of the normal value) was found in the LIT group. These data suggest that, despite a high urinary Ca excretion (3.6 +/- 0.1 mg/kg per day) in the HEM group, elevated urinary GAGs (32.0 +/- 1.0 mg/g Cr) and a normal urinary citrate (428.7 +/- 62.3 mg/24 h) excretion may prevent Ca crystallization and thus renal stones. In contrast, in the LIT group low urinary GAG (10.3 +/- 0.9 mg/g Cr) and citrate (235.2 +/- 52.3 mg/24 h) excretion may precipitate stone formation in the presence of a high urinary Ca excretion. Thus, it is reasonable to suggest that patients with hematuria and IH may not develop overt renal stone due to the presence of normal levels of renal stone inhibitors.

Nephrocalcinosis in a patient with primary hyperoxaluria type 2

Although nephrocalcinosis is a classical finding in primary hyperoxaluria type 1 (PH 1) associated with a poor renal survival it is exceptional in patients with PH type 2 (PH 2), characterized by a more favorable outcome. We describe an 8-month-old girl who suffered from recurrent urinary tract infections. Imaging studies revealed a profound corticomedullary nephrocalcinosis with no evidence of calculi. Urinary oxalate and D-glycerate excretion were massively elevated, while urinary glycolate or glyoxylate could not be detected, confirming the diagnosis of PH 2. Although the nephrocalcinosis progressed radiologically, renal function remained stable for over 2 years. Only further follow-up will show whether the associated nephrocalcinosis worsens the prognosis of our patient and of PH 2 in general.

Medullary nephrocalcinosis in nephropathic cystinosis

Children with nephropathic cystinosis excrete large amounts of calcium and phosphate due to renal tubular Fanconi syndrome, and also receive substantial supplements of phosphate and alkalinizing agents. Since these constitute risk factors for nephrocalcinosis, we evaluated 41 children age 2 months to 15 years with nephropathic cystinosis and good renal function by performing retroperitoneal ultrasound examinations in a blinded fashion. We also retrospectively analyzed parameters of calcium and phosphate metabolism representing 216 person-years of data on these children. Fifteen children had no evidence of medullary nephrocalcinosis, while 18 had mild nephrocalcinosis, and 8 severe nephrocalcinosis; 5 had renal stones. Mean urine calcium and phosphate concentrations increased from 1.47 mM and 5.30 mM, respectively, in children without nephrocalcinosis to 1.60 mM and 5.69 mM in children with mild nephrocalcinosis to 1.66 mM and 6.19 mM in children with severe nephrocalcinosis. Mean urine pH ranged from 7.5 to 8.1. The mean (+/- SD) age of the 26 patients with nephrocalcinosis was 9.4 +/- 3.8 years compared with 5.1 +/- 3.8 years for those without nephrocalcinosis (P < 0.005). Serum calcium, phosphate, vitamin D, and parathyroid hormone did not correlate with frequency or degree of nephrocalcinosis. We conclude that nephrocalcinosis frequently accompanies nephropathic cystinosis, can be detected by ultrasound examination, and might be managed by reducing oral replacement of phosphate, calcium, vitamin D, and citrate. Consideration should be given to truncating phosphate replacement once bone growth ceases.

Nephrocalcinosis and prematurity: importance of urate and oxalate excretion

Nephrocalcinosis was described in preterm infants by several authors who tried to determine its association with hypercalciuria and furosemide therapy. We evaluated these potential mechanisms along with other lithogenic factors not previously studied in 10 premature babies. Hypercalciuria was an inconsistent finding like in other reports; elevated uric acid excretion and hyperoxaluria were observed in 5 and 6 cases, respectively. The aminocid excretion was normal in all infants. Our data suggest that in addition to hypercalciuria, other lithogenic factors may play a role in the pathophysiology of nephrocalcinosis of premature infants.

Hypercalciuria and nephrocalcinosis in patients with idiopathic low-molecular-weight proteinuria in Japan: is the disease identical to Dent's disease in United Kingdom?

Idiopathic low-molecular-weight (LMW) proteinuria is a newly described renal disease in Japan and Italy. We report on 7 patients who manifested bilateral or unilateral nephrocalcinosis, as demonstrated by abdominal computed tomography scans. Renal histology revealed calcinosis of renal tubules in 2 patients. Computed tomography is a reliable method for the detection of nephrocalcinosis in this disorder. Hypercalciuria was also seen in 6 patients. A calcium-loading test performed in 2 patients suggested that hypercalciuria was of renal origin. Although the true pathogenesis is still not known, hypercalciuria and nephrocalcinosis appear to be a common complication in patients with idiopathic LMW proteinuria. These complications and clinical features suggest that idiopathic LMW proteinuria in Japan is likely to be identical to Dent's disease in the United Kingdom.

Determination of oxalate excretion in spot urines of healthy children by ion chromatography

Evidence for the suitability of spot urines for selective screening in children was obtained by comparing the 24-hour urinary oxalate excretion with the ratio of urinary oxalate to creatinine [mmol/mol] in spontaneously voided urine samples. Spot urines of 169 healthy children aged 1 day to 13 years were analysed in order to establish reference values for the urinary oxalate/creatinine ratio in relation to age and body surface area. Oxalate was measured by automated ion chromatography. Results showed an inverse relationship between the oxalate/creatinine ratio and age. The highest ratios, 131 +/- 57 mmol/mol (mean +/- 2 SD), were found in infants. At age two years, the ratio was 84 +/- 55, at age five years 56 +/- 35, and for children older than ten years 42 +/- 31. This finding can be explained by the gain of muscle mass and hence increased creatinine production with increasing age. Data for the urinary oxalate/creatinine ratio are presented according to body surface area for the assessment of children with abnormal growth. In 19 urine samples from nine patients with primary hyperoxaluria, the oxalate/creatinine ratio greatly exceeded (286-2022 mmol/mol) the above reference ranges. We therefore propose the determination of the oxalate/creatinine ratio in spot urines for the selective screening for hyperoxaluria in children with nephrocalcinosis or urolithiasis.

Urinary saturation and nephrocalcinosis in preterm infants: effect of parenteral nutrition

Urinary lithogenic and inhibitory factors were studied in 27 preterm infants; 16 had total parenteral nutrition (TPN) and 11 had breastmilk with an additional glucose-sodium chloride infusion. Urines were collected for 24 hours on day 2 (period A), day 3 (B), and once between days 4 and 10 (C). Urinary calcium oxalate saturation was calculated by the computer program EQUIL 2. Renal ultrasonography was performed every second week until discharge. The calcium/creatinine ratio increased in infants on TPN (A 0.91; C 1.68 mol/mol) and was significantly higher at period C than that in infants on breastmilk/infusion (A 0.52; C 0.36). The oxalate/creatinine ratio was persistently higher with TPN (203 mmol/mol) than with breastmilk/infusion (98; 137). The citrate/creatinine remained constant with TPN (0.44 mol/mol), whereas it increased significantly with breastmilk/infusion (0.26; 0.49). Calcium/citrate rose considerably with TPN, but decreased with breastmilk/infusion to a significantly lower level than with TPN. The urinary calcium oxalate saturation increased with TPN (2.4; 4.5) and decreased with breastmilk/infusion (2.1; 1.5) to a significantly lower value than with TPN. Nephrocalcinosis developed in two infants on TPN. Mean daily calcium intake was similar in both groups, whereas protein, sodium, and phosphorus intake were significantly higher on TPN. It is concluded that the increase in urinary calcium oxalate saturation observed with TPN is due to the combined effect of an increased urinary calcium excretion and higher urinary oxalate/creatinine and calcium/citrate ratios. The changes observed are likely to be caused by TPN itself, which differs in several respects from breastmilk feeding.

Excretion of beta 2-glycoprotein I (apolipoprotein H) in renal tubular disease

beta 2-Glycoprotein I (beta 2GI) was identified as a major urinary protein excreted by patients with several renal tubular diseases, including adult Fanconi syndrome, nephrocalcinosis associated with autoimmune diseases, Lowe's syndrome, and Dent's disease (a familial renal tubular disease). Sixteen patients excreted between 2 and 40 mg of beta 2GI per millimole of creatinine. In contrast, 18 healthy controls had undetectable amounts of beta 2GI in urine. Isoelectric focusing followed by immunoblotting demonstrated multiple forms of beta 2GI with pls between 6.4 and 8.2. These pls are higher than for several other "tubular proteins"; beta 2GI may therefore be less retarded than more-anionic proteins by the glomerular charge-barrier. This could explain why large quantities of beta 2GI are excreted despite its relatively high molecular mass (50 kDa). Excretion of beta 2GI was easily demonstrated by routine electrophoresis of urine proteins. beta 2GI migrates in the beta-gamma region and may be confused with Bence Jones protein. beta 2GI is stable for at least two years in urine frozen at -25 degrees C.

Hypocitraturic and hypercalciuric renal tubular acidosis with nephrocalcinosis in a 4-year-old boy

A 4-year-old boy suffering from hypocitraturic and hypercalciuric renal tubular acidosis with nephrolithiasis and nephrocalcinosis is reported. Renal function tests indicated that the patient had type 1 renal tubular acidosis. Potassium citrate rather than potassium bicarbonate, sodium citrate or bicarbonate is the preferred treatment for stones in RTA-I.

Evidence suggesting hyperoxaluria as a cause of nephrocalcinosis in phosphate-treated hypophosphataemic rickets

Urinary excretion of oxalate and phosphate was measured in twelve vitamin-D-treated, phosphate-supplemented patients with X-linked hypophosphataemia (XLH; four children, eight adolescents and adults) to investigate possible causative factors of nephrocalcinosis other than calcium. Oxalate excretion correlated highly with urinary phosphate excretion and with intake of phosphate supplements corrected for body surface area. Young children received the highest relative doses of phosphate (range 2.27-10.8 g/1.73 m2 daily) and their urinary oxalate excretion was very high (0.94-3.38 mmol/1.73 m2 daily). The urinary oxalate excretion of untreated adults with XLH was within normal limits. Six patients had evidence of nephrocalcinosis on ultrasound. The high urinary oxalate excretion in phosphate-supplemented XLH may be seen as a special type of enteric hyperoxaluria, in which the conditions of calcium-oxalate crystal precipitation could be reached even at normal levels of urinary calcium excretion. Urinary excretion of both calcium and oxalate should therefore be monitored during treatment in young XLH patients.

Diffuse nephrocalcinosis and idiopathic renal hypercalciuria

A 12 year old boy presented with primary nocturnal enuresis. Investigation showed extensive bilateral nephrocalcinosis of no obvious or recognised cause. Persistent severe renal hypercalciuria was confirmed by an intravenous calcium infusion. Idiopathic hypercalciuria is not a common cause of nephrocalcinosis and has not previously been described in a child.

Effects of dietary protein and butylated hydroxytoluene on the kidneys of rats

Semipurified diet using Na-caseinate or lactalbumin as the only protein source was given to female rats to study the influence of nephrocalcinosis on butylated hydroxytoluene (BHT) induced kidney damage. The study showed, that BHT induces nephropathy in female rats irrespective of the diet used. Pronounced nephrocalcinosis was only found in rats fed the Na-caseinate diet. Thus, this study does not indicate a connection between the development of the BHT-nephropathy and nephrocalcinosis. The results from this study once more stress the influence of the diet on reaction of the animal to experimental procedures.

Acute effect of indapamide on urine calcium excretion in nephrolithiasis and human essential hypertension

The effects of indapamide (2.5 mg once a day) on urinary composition are reported in 20 patients (10 with recurrent calcium nephrolithiasis and 10 with essential hypertension) compared with 20 controls. Indapamide was well absorbed in every patient (mean plasma level at the steady state was 111 +/- 41 ng/ml) and its antihypertensive action was more pronounced in hypertensive than in normotensive patients. It lowered calcium excretion in 18/20 patients (mean fall on the 7th day of treatment: 53%) and raised the Mg/Ca ratio in 20/20 patients (mean increase on the 7th day: 167%). The effect on Ca2+ and Mg2+ excretion was not associated with a strong diuretic effect. During intravenous calcium loading (0.375 mmol/kg body weight) 6 normal subjects after a single oral dose of indapamide excreted less calcium, suggesting a direct renal hypocalciuric action by the drug. Indapamide could represent an alternative drug to thiazide diuretics in diseases with dangerous renal calcium losses, but long-term studies are needed.

[Clinical variants of idiopathic hypercalciuria in children]

Out of five children with hypercalciuria, four had nephrocalcinosis and one recurrent bladder calculi. Two out of four patients with nephrocalcinosis (patients 1 and 2) had the "hyperprostaglandin E syndrome" and the other two (patients 3 and 4, siblings) had the Royer syndrome (osteopathy, dwarfism, secondary hyperparathyroidism). Treatment with hydrochlorothiazide is effective in patients without increased urinary excretion of prostaglandin, whereas patients with increased prostaglandin excretion respond better to indomethacin therapy.

[Effect of calcium antagonists (nifedipine) on nephrocalcinosis and calcium excretion in the rat]

An animal model was established to test the effect of a calcium antagonist on nephrocalcinosis, which was induced by an atherogenous diet, and its effect on the excretion of calcium and other parameters relevant for stone formation. With the administration of nifedipine (Adalat), the grade of nephrocalcinosis could be significantly reduced. Furthermore, with nifedipine the excretion of calcium and sodium in the urine was raised, while phosphate and potassium levels were lowered. The excretion of magnesium and citrate, reduced by an atherogenous diet, could be raised significantly with the administration of nifedipine. The pathophysiological mechanisms underlying the effect of nifedipine on nephrocalcinosis and on the excretion of the urine parameters are discussed. Apparently hypercalciuria is the result of a reduced reabsorption of calcium in the tubulus. The inhibitory effect on the genesis of nephrocalcinosis is possibly due to the lower calcium influx into the tubular cells.

Impaired renal tubular reabsorption of magnesium (TRMg) in Ca-containing kidney stone formers

Calculations of TRMg% were performed in 69 kidney stone formers. In patients with impaired TRMg significant increment in urinary Ca excretion and urinary Ca/Mg ratio was found. A life-long Mg supplementation is suggested in order to prevent Mg deficiency, stone recurrency and renal insufficiency.