Establishment of urinary exosome-like vesicles isolation protocol for FHHNC patients and evaluation of different exosomal RNA extraction methods.

BACKGROUND: Molecular and cellular pathophysiological events occurring in the majority of rare kidney diseases remain to be elucidated. Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is a rare autosomal recessive disorder caused by mutations in either CLDN16 or CLDN19 genes. This disease is characterized by massive urinary wasting of magnesium and calcium, osmosis deregulation and polyuria. Patients with p.G20D homozygous mutation in CLDN19 gene exhibit different progression to kidney failure suggesting that beyond the pathogenic mutation itself, other molecular events are favoring disease progression. Due to the fact that biopsy is not clinically indicated in these patients, urinary exosome-like vesicles (uEVs) can be envisioned as a valuable non-invasive source of information of events occurring in the kidney. Exosome research has increased notably to identify novel disease biomarkers but there is no consensus standardized protocols for uEVs isolation in patients with polyuria. For this reason, this work was aimed to evaluate and refine different uEVs isolation methods based on differential centrifugation, the gold standard method. RESULTS: Characterization by NTA, cryo-TEM and immunoblotting techniques identified the most appropriate protocol to obtain the highest yield and purest uEVs enriched fraction possible from urine control samples and FHHNC patients. Moreover, we tested five different RNA extraction methods and evaluated the miRNA expression pattern by qRT-PCR. CONCLUSIONS: In summary, we have standardized the conditions to proceed with the identification of differentially expressed miRNAs in uEVs of FHHNC patients, or other renal diseases characterized by polyuria.

Short-Term Effect of High-Dose Pantoprazol on Serum and Urinary Magnesium Levels.

BACKGROUND: Proton pump inhibitor (PPI) induced hypomagnesemia is a completely unexplained issue and cases are still being reported. Long-term use is the main factor, but there are a few articles stating that it may also emerge with short-term use. We aimed to evaluate the changes of serum and urine magnesium levels during shortterm high dose pantoprazol treatment. METHODS: The serum and 24-hour urine magnesium levels of 58 patients were evaluated during the course of 2 days. Of 58 patients, 25 were allowed oral intake on the 3rd day of hospitalization and thus, 24-hour urine for 3 days was collected from 33 patients. RESULTS: There were no significant differences in the mean levels of serum magnesium and the median levels of urine magnesium. When the magnesium levels were evaluated by age over and under 60 years, the baseline serum magnesium level was significantly higher than the 1st level in patients aged ≥ 60 years (p = 0.029). The 3rd day serum magnesium level was significantly higher than the baseline and 1st day levels in those aged < 60 years (p = 0.049). CONCLUSIONS: We showed that plasma levels and urinary excretion of magnesium did not change significantly during high-dose pantoprazol treatment. It can be hypothesized that magnesium levels are not affected by PPIs in short-term usage. Age and other contributing factors may have more impact on PPI induced hypomagnesemia. Patients aged over 60 years might be handled carefully under proton pump inhibitors treatment.

In-depth phenotyping of a Donnai-Barrow patient helps clarify proximal tubule dysfunction.

BACKGROUND: The megalin/cubilin/amnionless complex is essential for albumin and low molecular weight (LMW) protein reabsorption by renal proximal tubules (PT). Mutations of the LRP2 gene encoding megalin cause autosomal recessive Donnai-Barrow/facio-oculo-acoustico-renal syndrome (DB/FOAR), which is characterized by LMW proteinuria. The pathophysiology of DB/FOAR-associated PT dysfunction remains unclear. CLINICAL CASE: A 3-year-old girl presented with growth retardation and proteinuria. Clinical examination was unremarkable, except for a still-opened anterior fontanel and myopia. Psychomotor development was delayed. At 6, she developed sensorineural hearing loss. Hypertelorism was noted when she turned 12. Blood analyses, including renal function parameters, were normal. Urine sediment was bland. Proteinuria was significant and included albumin and LMW proteins. Immunoblotting analyses detected cubilin and type 3 carbonic anhydrase (CA3) in the urine. Renal ultrasound was unremarkable. Optical examination of a renal biopsy did not disclose any tubular or glomerular abnormality. Electron microscopy revealed that PT apical endocytic apparatus was significantly less developed. Immunostaining for megalin showed a faint signal in PT cytosol contrasting with the distribution of cubilin at the apical membrane. The diagnostic procedure led to identifying two mutations of the LRP2 gene. CONCLUSIONS: The functional loss of megalin in DB/FOAR causes PT dysfunction characterized by increased urinary shedding of CA3 and cubilin.

High cholesterol feeding may induce tubular dysfunction resulting in hypomagnesemia.

BACKGROUND/AIMS: Hypomagnesemia may induce hypercholesterolemia, but the contrary has not been described yet. Thus, magnesium homeostasis was evaluated in rats fed a cholesterol-enriched diet for 8 days. This study has a relevant clinical application if hypomagnesemia, due to hypercholesterolemia, is confirmed in patients with long-term hypercholesterolemia. METHODS: Both hypercholesterolemic (HC) and normocholesterolemic rats (NC) were divided into sets of experiments to measure hemodynamic parameters, physiological data, maximum capacity to dilute urine (C(H)((2))(O)), variations (Δ) in [Ca(2+)](i) and the expression of transporter proteins. RESULTS: HC developed hypomagnesemia and showed high magnesuria in the absence of hemodynamic abnormalities. However, the urinary sodium excretion and C(H)((2))(O) in HC was similar to NC. On the other hand, the responses to angiotensin II by measuring Δ [Ca(2+)](i) were higher in the thick ascending limb of Henle's loop (TAL) of HC than NC. Moreover, high expression of the cotransporter NKCC2 was found in renal outer medulla fractions of HC. Taken together, the hypothesis of impairment in TAL was excluded. Actually, the expression of the epithelial Mg(2+) channel in renal cortical membrane fractions was reduced in HC. CONCLUSION: Impairment in distal convoluted tubule induced by hypercholesterolemia explains high magnesuria and hypomagnesemia observed in HC.

Hereditary xanthinuria is not so rare disorder of purine metabolism.

Hereditary xanthinuria (type I) is caused by an inherited deficiency of the xanthine oxidorectase (XDH/XO), and is characterized by very low concentration of uric acid in blood and urine and high concentration of urinary xanthine, leading to urolithiasis. Type II results from a combined deficiency of XDH/XO and aldehyde oxidase. Patients present with hematuria, renal colic, urolithiasis or even acute renal failure. Clinical symptoms are the same for both types. In a third type, clinically distinct, sulfite oxidase activity is missing as well as XDH/XO and aldehyde oxidase. The prevalence is not known, but about 150 cases have been described so far. Hypouricemia is sometimes overlooked, that´s why we have set up the diagnostic flowchart. This consists of a) evaluation of uric acid concentrations in serum and urine with exclusion of primary renal hypouricemia, b) estimation of urinary xanthine, c) allopurinol loading test, which enables to distinguish type I and II; and finally assay of xanthine oxidoreductase activity in plasma with molecular genetic analysis. Following this diagnostic procedure we were able to find first patients with hereditary xanthinuria in our Czech population. We have detected nine cases, which is one of the largest group worldwide. Four patients were asymptomatic. All had profound hypouricemia, which was the first sign and led to referral to our department. Urinary concentrations of xanthine were in the range of 170-598 mmol/mol creatinine (normal < 30 mmol/mol creatinine). Hereditary xanthinuria is still unrecognized disorder and subjects with unexplained hypouricemia need detailed purine metabolic investigation.

Localization of the membrane defect in transepithelial transport of taurine by parallel studies in vivo and in vitro in hypertaurinuric mice.

We investigated the mechanism of taurinuria in three inbred strains of mice: A/J, a normal taurine excretor (taut+); and two hypertaurinuric (taut-) strains, C57BL/6J and PRO/Re. Plasma taurine is comparable in the three strains (approximately 0.5 mM), but taurinuria is 10-fold greater in taut- animals. Fractional reabsorption of taurine is 0.967 +/- 0.013 (mean +/- SD) in A/J); and 0.839 +/- 0.08 and 0.787 +/- 0.05 in C57BL/6J and PRO/Re, respectively. Taurine concentration in renal cortex intracellular fluid (free of urine contamination) is similar in the three strains. Taurine reabsorption is inhibited by beta-alanine, in taut+ and taut- strains. These in vivo findings reveal residual taurine transport activity in the taut- phenotype and no evidence for impaired efflux at basilar membranes as the cause of impaired taurine reabsorption. Cortex slices provide information about uptake of amino acids at the antiluminal membrane. Taurine behaves as an inert metabolite in mouse kidney cortex slices. Taurine uptake by slices is active and, at less than 1 mM, is greater than normal in taut- slices. Concentration-dependent uptake studies reveal more than one taurine carrier in taut+ and taut- strains. The apparent Km values for uptake below 1 mM are different in taut- and taut+ slices (approximately 0.2 mM and approximately 0.7 mM, respectively); the apparent Km values above 1 mM taurine are similar in taut+ and taut- slices. Efflux from slices in all strains in the same (0.0105-0.0113 mumol-min-1-g-1 wet wt), but taut- tissue retains about 10% more radioactivity over the period of efflux. beta-Alanine is actively metabolized in mouse kidney. Its uptake in the presence of blocked transamination, is greater; its intracellular oxidation is attenuated; and its exchange with intracellular taurine is diminished in taut- slices. These findings indicate impaired beta-amino acid permeation on a low-Km uptake system at the luminal membrane in the taut- phenotype. beta-Amino acids are not reclaimed efficiently either from the innermost luminal pool in cortex slices or from the ultrafiltrate in the tubule lumen in vivo. The former leads to high uptake ratios in vitro, the latter to high clearance rates in vivo. In vitro and in vivo data are thus concordant. This is the first time that a hereditary defect in amino acid transport has been assigned to a specific membrane surface in mammalian kidney.

Identification of SLC41A3 as a novel player in magnesium homeostasis.

Regulation of the body Mg(2+) balance takes place in the distal convoluted tubule (DCT), where transcellular reabsorption determines the final urinary Mg(2+) excretion. The basolateral Mg(2+) extrusion mechanism in the DCT is still unknown, but recent findings suggest that SLC41 proteins contribute to Mg(2+) extrusion. The aim of this study was, therefore, to characterize the functional role of SLC41A3 in Mg(2+) homeostasis using the Slc41a3 knockout (Slc41a3(-/-)) mouse. By quantitative PCR analysis it was shown that Slc41a3 is the only SLC41 isoform with enriched expression in the DCT. Interestingly, serum and urine electrolyte determinations demonstrated that Slc41a3(-/-) mice suffer from hypomagnesemia. The intestinal Mg(2+) absorption capacity was measured using the stable (25)Mg(2+) isotope in mice fed a low Mg(2+) diet. (25)Mg(2+) uptake was similar in wildtype (Slc41a3(+/+)) and Slc41a3(-/-) mice, although Slc41a3(-/-) animals exhibited increased intestinal mRNA expression of Mg(2+) transporters Trpm6 and Slc41a1. Remarkably, some of the Slc41a3(-/-) mice developed severe unilateral hydronephrosis. In conclusion, SLC41A3 was established as a new factor for Mg(2+) handling.

Analysis of steroids in urine for differentiation of pseudohypoaldosteronism and aldosterone biosynthetic defect.

The salt-losing syndromes in the neonatal period and early infancy due to adrenal disease can be differentiated by the pattern of excretion of steroids in urine. The presence or absence of metabolites of cortisol, aldosterone, and corticosterone as well as certain precursors can be established in a single analysis of steroids in urine by using gas chromatography with open tubular capillary columns. The profiles of steroid excretion in the urine of 8 infants with renal tubular insensitivity to aldosterone were compared with those in 5 infants with isolated aldosterone biosynthetic defects. The excretion in urine of 18 hydroxytetrahydro-compound A was elevated in all 13 children, but relative to the excretion of tetrahydroaldosterone, a high ratio was found for the biosynthetic defect and clearly distinguished the 2 conditions. Age-related changes in steroid metabolism are described. The diagnosis in each case was supported by clinical investigation together with determinations of PRA and aldosterone concentrations.

Autosomal recessive renal proximal tubulopathy and hypercalciuria: a new syndrome.

BACKGROUND: The best described primary inherited proximal tubulopathies include X-linked hypercalciuric nephrolithiasis (XLHN), caused by a mutation in the chloride channel gene CLCN5, and classic Fanconi's syndrome, the genetic basis of which is unknown. The aim of this study is to examine the clinical, biochemical, and genetic characteristics of a highly consanguineous Druze family with autosomal recessive proximal tubulopathy and hypercalciuria (ARPTH), a syndrome not reported previously. METHODS: Three children (2 girls, 1 boy) of the family referred for evaluation of renal glycosuria and hypercalciuria and 10 of their close relatives were evaluated clinically and biochemically. All study participants underwent genetic analysis to exclude involvement of the CLCN5 gene. RESULTS: Evaluation of the 3 affected children showed glycosuria, generalized aminoaciduria, hypouricemia, uricosuria, low molecular weight (LMW) proteinuria, and hypercalciuria in all 3 children and phosphaturia in 2 children. They had no metabolic acidosis or renal insufficiency. One affected girl had nephrocalcinosis. Two children had a history of growth retardation and radiological findings of metabolic bone disease. Parathyroid hormone and 1,25-dihydroxyvitamin D [1,25(OH)2Vit D] blood levels in affected children were normal. Unaffected family members examined had no renal tubular defects or LMW proteinuria. Genetic linkage analysis excluded cosegregation of the ARPTH phenotype with the CLCN5 locus. CONCLUSION: ARPTH is a new syndrome characterized by nonacidotic proximal tubulopathy, hypercalciuria, metabolic bone disease, and growth retardation. It can be distinguished from XLHN by its autosomal recessive mode of inheritance and normal serum levels of calciotropic hormones, as well as the absence of LMW proteinuria in obligate carriers. The gene mutated in ARPTH remains to be identified.

Fumaric aciduria: a new organic aciduria, associated with mental retardation and speech impairment.

Two siblings are described who present with fumaric aciduria, a hitherto unreported organic aciduria. The results of our analytical investigations using gas chromatography/mass spectrometry, and the clinical presentation of the patients, are consistent with the notion that the fumaric aciduria is caused by an inherited defect which leads to a net secretion of fumaric acid by the renal tubules.

Low urinary excretion of heparan sulfate in three patients with Lowe's syndrome.

Urinary glycosaminoglycans were isolated with the cetylpyridinium chloride (CPC) precipitation method and the excretion of individual species of urinary glycosaminoglycans in three patients with Lowe's syndrome was compared with that of age-matched control children by means of electrophoresis on cellulose acetate membranes and by quantification of hexosamine contents. Total daily excretion of urinary glycosaminoglycans in the patients seemed to be normal, but the relative excretion of urinary heparan sulfate was significantly reduced and ranged from 26 to 46% of the age-matched control mean, when calculated on the basis of relative glucosamine content in urinary glycosaminoglycans. Although electrophoretograms of urines from patients with Lowe's syndrome suggested some excess of low sulfated chondroitin sulfate corresponding in mobility to dermatan sulfate, the enzymatic subunit assay employing chondroitinases did not disclose any significant differences in the excretion pattern or in the degree of sulfation of chondroitin sulfate isomers between lowe's syndrome and control children.

Urinary excretion of a large amount of bound sialic acid and of under sulfated chondroitin sulfate A by patients with the Lowe syndrome.

Urine samples from two patients with the Lowe syndrome were analyzed for sialic acid and mucopolysaccharides. The sialic acid content, relative to the creatinine content, was 4--5 times higher in these patients' urine than in normal urine. Most of the sialic acid was found in unidentified glycoproteins of high molecular weight, but the levels of sialyllactose and free sialic acid were also elevated about 2 fold. A most remarkable finding was the excretion of undersulfated chrondroitin sulfate A without other mucopolysaccharides normally occurring in urine. It is suggested that a disorder in sulfation of mucopolysaccharides is etiologically implicated in the Lowe syndrome.