NPT2a gene variation in calcium nephrolithiasis with renal phosphate leak

A decrease in renal phosphate reabsorption with mild hypophosphatemia (phosphate leak) is found in some hypercalciuric stone-formers. The NPT2a gene encodes a sodium-phosphate cotransporter, located in the proximal tubule, responsible for reclaiming most of the filtered phosphate load in a rate-limiting manner. To determine whether genetic variation of the NPT2a gene is associated with phosphate leak and hypercalciuria in a cohort of 98 pedigrees with multiple hypercalciuric stone-formers, we sequenced the entire cDNA coding region of 28 probands, whose tubular reabsorption of phosphate normalized for the glomerular filtration rate (TmP/GFR) was 0.7 mmol/l or lower. We performed genotype/phenotype correlations for each genetic variant in the entire cohort and expressed NPT2a variant RNAs in Xenopus laevis oocytes to test for cotransporter functionality. We identified several variants in the coding region including an in-frame 21 bp deletion truncating the N-terminal cytoplasmic tail of the protein (91del7), as well as other single-nucleotide polymorphisms that were non-synonymous (A133V and H568Y) or synonymous. Levels of TmP/GFR and urine calcium excretion were similar in heterozygote carriers of NPT2a variants compared to the wild-type (wt) homozygotes. The transport activity of the H568Y mutants was identical to the wt, whereas the N-terminal-truncated version and the 91del7 and A133V mutants presented minor kinetic changes and a reduction in the expression level. Although genetic variants of NPT2a are not rare, they do not seem to be associated with clinically significant renal phosphate or calcium handling anomalies in a large cohort of hypercalciuric stone-forming pedigrees.     

Renal phosphate leak in patients with idiopathic hypercalciuria and calcium nephrolithiasis

Although urine phosphate loss has been associated with hypercalciuria, it is debated how frequently renal phosphate leak is present in hypercalciuric patients. We reviewed the records of 100 consecutive adult patients who were diagnosed with idiopathic hypercalciuria and calcium urolithiasis, searching for the presence of renal phosphate leak. The renal phosphate threshold, normalized for the glomerular filtration rate (TmPO4/GFR), of the hypercalciuric patients followed a normal distribution and had a good correlation with serum phosphate (r=0.77; p<0.0001). There were no correlations between TmPO4/GFR and urinary calcium or between serum phosphorus and urinary calcium. We found only nine patients (9%) with renal phosphate leak. These patients had a mean TmPO4/GFR of 2.19 mg% (0.70 mmol/l) and serum phosphorus of 2.65 mg% (0.85 mmol/l). Nevertheless, urinary calcium was not significantly different between patients with or without low TmPO4/GFR. We conclude that renal phosphate leak is an infrequent finding in patients with idiopathic hypercalciuria and is not associated with a higher urinary calcium loss.     

Dipyridamole for renal phosphate leak in successfully renal transplanted hypophosphatemic patients

AIM AND BACKGROUND: Hyphosphatemia can be seen in renal transplant recipients. Hyperparathyroidism, glucocorticoid treatment, renal denervation and impairment of renal tubular phosphate reabsorption are the most common causes of hyphosphatemia in these patients. It is well-known that dipyridamole enhances renal tubular phosphate reabsorption in some clinical conditions. We did not find any information about the effect of dipyridamole in renal transplant recipients (RTRs) with hypophosphatemia. For this reason, we decided to give dipyridamole 11 RTRs with hypophosphatemia. PATIENTS AND METHODS: Eleven RTRs whose serum phosphate and creatinine levels were below 2.5 mg/dl and 2 mg/dl, respectively, were included in this study. None of the patients received drugs altering phosphate metabolism and they did not change their routine diets. Urinary phosphate excretion and tubular phosphate reabsorption (TPR) were calculated before and 3 weeks after dipyridamole treatment. RESULTS: The mean levels of serum-urine (daily) phosphate and TPR before dipyridamole treatment were 1.94 +/- 0.46 mg/dl, 7,187.5 +/- 1,833.49 mg/day and -2.78 +/- 0.62, respectively. After treatment, the mean levels of serum-urine phosphate and TPR were 2.73 +/- 0.46 mg/dl, 4,845.27 +/- 1,138.99 mg/day and -1.48 +/- 0.80, respectively. Serum and urine phosphate levels and TPR were found to be significantly different before and after dipyridamole therapy (p < 0.05). CONCLUSION: Short-term dipyridamole therapy increased TPR and serum phosphate levels and decreased urinary phosphate excretion. We did not observe negative effect on renal functions in these cases. Although the number of the cases included in this study is small, dipyridamole is an effective choice in management of hypophosphatemic RTRs.     

Parathyroid function in relation to intestinal function and renal calcium reabsorption in patients with nephrolithiasis.

Recently a technique to measure intact parathyroid hormone (PTH), i.e. the biologically active hormone, has been available. The aim of the present study was to apply this method to evaluate the parathyroid function in a material of recurrent renal stone formers (n = 324). Intact PTH was found to be inversely related to both urinary calcium (r = -0.15; p less than 0.01) and serum calcium (p less than 0.02) indicating that in the majority of the patients with hypercalciuria this was accounted for by intestinal hyperabsorption and not by high serum PTH. Hyperabsorption was also the likely explanation for the finding of a positive relationship between the urinary calcium and oxalate excretions (r = 0.22; p less than 0.001) in medication-free patients without intestinal disorders, i.e. without enteric hyperoxaluria. Altogether 25 patients (7%) had elevated serum PTH concentrations. They were followed up with fasting serum and urinary electrolytes and an oral calcium loading test (1 g of calcium) in order to evaluate the importance of renal and intestinal factors responsible for the elevated serum PTH concentrations. The investigation was carried out on a free diet and on low and high calcium intakes, respectively. The incidence of intestinal malfunction, which was sometimes present without clinical symptoms, was found to be approximately the same as that of impaired renal conservation of calcium. The findings in the patients with intestinal malfunction were a reduced intestinal absorption of calcium and an enhanced tubular reabsorption of calcium (TRCa), with greater reabsorption of calcium for higher PTH values. In patients with impaired renal conservation of calcium despite the raised PTH there was no correlation between PTH and TRCa. When PTH was suppressed during the oral calcium load the TRCa was found to be inappropriately low and the renal defect obvious. The intestinal calcium absorption was secondarily increased to compensate for the renal losses.     

Osteopenia/osteoporosis in patients with calcium nephrolithiasis

The objective of this study is to analyze the alterations in bone mineral density and bone and calcium–phosphorus metabolism in patients with calcium nephrolithiasis. We designed a study with 182 patients who were distributed among three groups: group O, 56 patients without nephrolithiasis; group A, 67 patients with calcium nephrolithiasis and mild lithogenic activity; and group B, 59 patients with calcium nephrolithiasis and severe lithogenic activity. Metabolic parameters of blood and urine that were related to calcium–phosphorous and bone metabolism and bone densitometry were assessed in all patients. A comparative study was performed on the variables of bone and calcium–phosphorus metabolism and bone densitometry as well as the presence or absence of osteopenia/osteoporosis. The patients in group B had a greater loss of bone mineral density, measured by the T-score, than the patients in groups O and A. Moreover, the proportion of patients in group B with osteopenia/osteoporosis was statistically significantly higher than the proportion of patients in groups O and A. We observed higher values of calciuria, fasting calcium/creatinine ratio, and 24-h calcium/creatinine among the patients in group B compared to the other two groups. Calciuria, citraturia, and fasting calcium/creatinine were independent factors that showed a relationship with severe lithogenic activity compared to the control group, and β-crosslaps is an independent factor that has a relationship with severe lithogenic activity as compared to mild lithogenic activity. Patients with calcium lithiasis and severe lithogenic activity have a greater loss in bone mineral density and therefore a greater risk of osteopenia/osteoporosis.     

Metabolic evaluation of patients with recurrent idiopathic calcium nephrolithiasis

BACKGROUND: Metabolic evaluation in recurrent idiopathic calcium renal stone-formers (RCSF) was analysed with respect to the following questions: (1) do three 24-h urines provide more diagnostic accuracy in the metabolic evaluation of RCSF than 1 or 2 urines?; (2) does time after stone event influence the diagnostic yield?; (3) is urine composition at weekends different from that at mid-week?; (4) what are the prevalences of the most important risk factors (RF) of idiopathic calcium nephrolithiasis, i.e. low volume (LV), hypercalciuria (HC), hyperoxaluria (HO), hyperuricosuria (HU), hypocitraturia (Hypo-Cit), and hypomagnesiuria (Hypo-Mg)?; and (5) do male RCSF differ from females with respect to urinary RFs? METHODS: Seventy-five RCSF (59 men, 16 women) collected three 24-h urines (U1-3) while on free-choice diet. To account for possible variations in lifestyle and diet, U1 and U3 had to be collected midweek and U2 at a weekend. RESULTS: When considering all three urines together (U1 + U2 + U3), the number of RF abnormalities/patient was 2.8 +/- 0.1, higher than numbers of any combination of two urines or of any single urine (P = 0.0001 for all comparisons). The number of RF abnormalities also rose with time after stone event, from 0.8 +/- 0.1 (range 0-4) in U1 to 1.1 +/- 0.1 (range 0- 4) in U3 (P = 0.011 vs U1). Whereas all other RF did not change between collections, urine volume was lower in U2 (1793 +/- 90 ml) than in U1 (2071 +/- 97 ml, P = 0.0001 vs U2) and U3 (1946 +/- 97 ml, P = 0.046 vs U2). At least 1 abnormality was found in 85.3% of all RCSF, and multiple abnormalities occurred in 47%. The most frequent RF was HC (39%), followed by HO and LV (32% each), Hypo-Cit (29%), HU (23%) and Hypo-Mg (19%). Males more often had Hypo-Cit (P < 0.001) and Hypo-Mg (P < 0.01) than females, whereas HO was more frequent in female RCSF (P < 0.025 vs males). CONCLUSIONS: Diagnostic accuracy of metabolic evaluation in RCSF increases both with the number of urines collected and the time passing after a stone event. Urines collected at weekends differ from those of the week only by their lower volumes. Abnormalities of RF for calcium nephrolithiasis can be detected in 85.3% of RCSF, and HC is the most common RF both in male and female RCSF.      

The comprehensive examination of patients with recurrent calcium nephrolithiasis]

Hypercalciuria is one of the main causes of recurrent generation of urinary calcium-containing calculi. 107 patients with recurrent calcium nephrolithiasis were examined and results presented. Concentrations of potassium, sodium, chlorides, calcium, phosphorus, uric acid and creatinine were investigated in serum and urine, as well as indices of acid-base balance in arterial blood. pH-metry, "preliminary" and oral calcium tolerance test were also carried out. The microcomputer data analysis established that the diagnosis of primary hyperparathyroidism may be identified in case of increased serum calcium level before and after calcium load test, the same of parathyroid, and increased urinary cAMP excretion. Renal hypercalciuria is characterized by low blood calcium level in both periods of the oral test, high basal calciuria, increased urinary cAMP excretion and its slight decrease after the oral calcium load test, by a tendency to lower serum magnesium levels in high magnesuria. The patients with absorptive hypercalciuria had an upper normal or increased blood calcium level, a significant calcemic and calciuric "response" to the calcium load, reduction in urinary cAMP elimination and more severe decrease (close to 0) of these indices after oral calcium load and normal magnesium levels in blood and urine. On a base of the "preliminary" test data the patients with relapsing calcium nephrolithiasis and metabolic disorders may be differed from those without calcium and phosphorus metabolic deteriorations. The "preliminary" test defines indications for the oral calcium tolerance test, automatic diagnosis and computer data storage facilitate physician to work and to solve problems of the patients' survey.     

Quantitative analysis on the localization of chondroitin sulfate proteoglycan in renal tissues of patients with calcium nephrolithiasis

Previous studies have shown a significant decrease of heparin sulfate proteoglycan (HSPG) in the basement membrane of the glomerulus and the mucosa of the ureter/renal pelvis in patients with calcium nephrolithiasis. In this study, we looked at the localization of another influential proteoglycan, chondroitin sulfate (CSPG), using similar study groups by indirect immunofluorescence staining. Microscopic images were digitized and image analysis was used to quantitate the staining intensity of CSPG present in the basement membrane of the nephron. Our data showed significant loss of CSPG in the Bowman's capsule and the basement membrane of the mucosa of the ureter/renal pelvis using Mann-Whitney U-Wilcoxon Rank Sum W test with P-values of 0.0043 and 0.0041, respectively. However, absence of staining was noted in the basement membrane of the glomerulus and no significant change in the basement membrane of the tubular epithelium was observed. In conclusion, our results showed changes in the localization of CSPG in the basement membrane of the nephron, accompanied with HSPG, which may contribute to the pathological condition of calcium nephrolithiasis. Received: 9 July 1997 / Accepted: 2 January 1998     

Bone alterations in patients with idiopathic hypercalciuria and calcium nephrolithiasis

Objectives. To verify whether alterations in bone density and turnover in patients with calcium nephrolithiasis and hypercalciuria are observable in various subgroups of patients divided according to the pathogenesis of the hypercalciuria.Methods. Seventy patients with calcium nephrolithiasis and idiopathic hypercalciuria, 19 to 64 years old, were assessed for spine and femur mineral metabolism and bone density using a Dexa evaluation system. After a low calcium diet, the subjects were classified into two groups: fasting hypercalciuria (FH, 39 patients) and absorptive hypercalciuria (AH, 31 patients).Results. Only in the patients with FH was the lumbar spine bone density lower than in the controls (P <0.001). Also, only the patients with FH had higher bone alkaline phosphatase and urinary hydroxyproline levels than the control group (P <0.005 and <0.015, respectively). The blood pH levels were lower, even though within the normal range, in the hypercalciuric patients than in the controls (P <0.01). There was a negative correlation between the urinary hydroxyproline level and lumbar spine and femoral neck density in patients with FH (P <0.001 and <0.005, respectively), and the blood pH correlated positively with the lumbar spine bone density.Conclusions. Altered bone metabolism and overall bone loss were found only in the patients with FH. Overloading of acid valences, perhaps of dietary origin, could be the pathogenic factor responsible.     

Potassium citrate decreases urine calcium excretion in patients with hypocitraturic calcium oxalate nephrolithiasis

Two previous studies (<10 patients each) have demonstrated that alkali therapy may reduce urine calcium excretion in patients with calcium oxalate nephrolithiasis. The hypothesized mechanisms are (1) a decrease in bone turnover due to systemic alkalinization by the medications; (2) binding of calcium by citrate in the gastrointestinal tract; (3) direct effects on TRPV5 activity in the distal tubule. We performed a retrospective review of patients on potassium citrate therapy to evaluate the effects of this medication on urinary calcium excretion. A retrospective review was performed of a metabolic stone database at a tertiary care academic hospital. Patients were identified with a history of calcium oxalate nephrolithiasis and hypocitraturia who were on potassium citrate therapy for a minimum of 3 months. 24-h urine composition was assessed prior to the initiation of potassium citrate therapy and after 3 months of therapy. Patients received 30–60 mEq potassium citrate by mouth daily. Inclusion criterion was a change in urine potassium of 20 mEq/day or greater, which suggests compliance with potassium citrate therapy. Paired t test was used to compare therapeutic effect. Twenty-two patients were evaluated. Mean age was 58.8 years (SD 14.0), mean BMI was 29.6 kg/m² (SD 5.9), and gender prevalence was 36.4 % female:63.6 % male. Mean pre-treatment 24-h urine values were as follows: citrate 280.0 mg/day, potassium 58.7 mEq/day, calcium 216.0 mg/day, pH 5.87. Potassium citrate therapy was associated with statistically significant changes in each of these parameters—citrate increased to 548.4 mg/day (p < 0.0001), potassium increased to 94.1 mEq/day (p < 0.0001), calcium decreased to 156.5 mg/day (p = 0.04), pH increased to 6.47 (p = 0.001). Urine sodium excretion was not different pre- and post-therapy (175 mEq/day pre-therapy versus 201 mEq/day post-therapy, p = NS). Urinary calcium excretion decreased by a mean of 60 mg/day on potassium citrate therapy—a nearly 30 % decrease in urine calcium excretion. These data lend support to the hypothesis that alkali therapy reduces urine calcium excretion.     

Need for ancillary procedures among patients undergoing tubeless percutaneous renal surgery for nephrolithiasis

PURPOSE: We routinely perform percutaneous nephrolithotomy (PCNL) without the use of nephrostomy tubes. We examined the need for secondary surgery for the treatment of residual stones in patients who underwent both tubeless surgery and PCNL with tube placement. PATIENTS AND METHODS: We retrospectively reviewed the charts of 180 patients who underwent 186 percutaneous nephrolithotomies. Among them, 125 patients had tubeless surgery, and 61 had nephrostomy tubes. We compared the need for ancillary surgical procedures for residual stone disease in the two groups. RESULTS: A total of 99 patients (79%) without tubes and 25 (41%) of those with tubes were stone free after surgery. A total of 45 ancillary procedures were performed for residual stone disease, with 15% of the tubeless and 43% of the patients with tubes requiring a second procedure. Extracorporeal shockwave lithotripsy (SWL) was the most common ancillary procedure. CONCLUSIONS: Patients who are eligible for tubeless PCNL are unlikely to need a secondary procedure, and residual stones can most often be treated with SWL. Patients who required nephrostomy tubes had more complicated disease and a greater need for subsequent surgery.     

Decreased renal phosphate threshold in patients with gout.

Serum and 24-hour urinary phosphate levels in primary gout patients and control subjects were measured. About 45% of gouty patients showed mild hypophosphatemia. However, mean 24-hour urinary excretion of phosphate was significantly elevated as compared with that of controls. Gouty patients showed a significantly decreased tubular reabsorption of phosphate and renal phosphate threshold. It seems that tubular phosphate transport in gouty patients is impaired, and this is the major cause of hypophosphatemia.     

Increased urinary excretion of renal enzymes in idiopathic calcium oxalate nephrolithiasis

Urinary excretion of gamma-glutamyl transpeptidase, angiotensin I converting enzyme, beta-galactosidase and N-acetyl-beta-glucosaminidase was evaluated in 30 patients with idiopathic calcium oxalate urolithiasis. Higher than normal values were observed and the excretory enzyme pattern suggested tubular damage in patients with stones. A parallel study in the rat showed that an oxalate surcharge can promote increased urinary excretion of these enzymes. It is known that urothelium injury may enhance crystal adhesion. If the damage is primary it may be viewed as a promoting factor. If it is secondary it may be considered a factor capable of increasing salt precipitation.     

Determination of heparan sulphate in kidney tissues of patients with calcium nephrolithiasis

While the pathogenic mechanisms responsible for calcium nephrolithiasis remain unknown, the influence of heparan sulphate proteoglycan (HSPG) on disease progression of other diseases, such as polycystic kidneys and diabetic glomerulosclerosis, makes it an important candidate for the study of stone formation. Using the indirect immunofluorescence assay and image analysis, we were able to quantify and visualize the loss of HSPG localized in the basement membrane of the glomerulus and the mucosa of ureter or renal pelvis in patients with recurrent calcium nephrolithiasis as compared to normal subjects. However, no significant change in HSPG was observed in the basement membrane of the tubular epithelium. The decreased HSPG in the glomerulus may reflect the potentially disrupted anion/neutral barrier for glomerular filtration, which would encourage the accumulation of stone solutes. The drop in HSPG staining intensity in the basement membrane of the mucosa of ureter/renal pelvis may suggest the tendency of adhesion of crystal to urothelial surfaces. Based on these immunological data, it appears that HSPG plays a modulatory role in the pathogenesis of this disease.     

Bone mineral density and urine calcium excretion among subjects with and without nephrolithiasis

BACKGROUND: Bone mineral density (BMD) is reduced among patients with idiopathic hypercalciuria (IH) and nephrolithiasis. To disentangle effects of diet, stone formation, and physiology upon BMD, we studied vertebral and femoral neck BMD among relatives of hypercalciuric stone formers, and contrasted those with to those without stones. METHODS: Among 59 subjects from 11 families, vertebral and femoral neck BMD, diet calcium intake, urine excretions of calcium, sodium, ammonium, titratable acid, sulfate, urea nitrogen, and serum levels of calcitriol and markers of bone turnover were studied. RESULTS: Stone formers (SF) consumed less calcium than non-stone formers (NSF). Spine and femoral neck BMD z-scores varied inversely with urine calcium loss and urine ammonium excretion among SF but not NSF. No correlations of BMD z-score were found for bone markers, calcitriol, or any of the other measurements. CONCLUSION: SF consumed less calcium, presumably to prevent more stones, and displayed a bone mineral responsiveness to calcium loss and ammonium excretion not present among NSF, who ate more calcium. Lowered calcium consumption in IH, perhaps in response to stone formation, alters bone responses in a direction that can predispose to mineral loss and eventual fracture.