Effect of nonsteroidal anti-inflammatory drugs in children with Bartter syndrome.

BACKGROUND: Bartter syndrome (BS) is a salt-wasting tubulopathy with induced expression of cyclooxygenase-2 in the macula densa, leading to increased prostaglandin production and hyperreninemia. Nonsteroidal anti-inflammatory drugs (NSAIDs) are currently used in BS; however, there is limited information on the impact of NSAIDs at treatment initiation or the potential utility of plasma renin level to guide therapy in patients with BS. METHODS: We included 19 patients with BS treated with NSAIDs between 1994 and 2016. We assessed serum levels of renin, aldosterone, electrolytes, calcium, phosphorus, vitamin D, and intact parathyroid hormone (iPTH) before and after treatment initiation. We also recorded modifications in sodium and potassium supplements and changes in urine calcium. RESULTS: Median age at diagnosis was 0.9 months [IQR 0-6.9]. Seven patients had BS types 1 or 2, 12 had BS type 3 and two had no mutation identified. There was a trend towards a decrease in sodium chloride supplementation after initiation of NSAIDs. When defining response to treatment based on the normalization of plasma renin level, responders had a greater reduction in their electrolytes supplementation. NSAIDs treatment was associated with a reduction in urine calcium. Before treatment, half of the patients had elevated iPTH, but iPTH normalized following initiation of NSAIDs in all but one patient. CONCLUSIONS: This study confirms that NSAIDs reduce urine wasting of sodium and calcium in patients with BS. Monitoring serum renin levels may be useful to identify the lowest effective dose of NSAIDs that optimizes reduction of urine electrolyte losses.

Gitelman syndrome: consensus and guidance from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference.

Gitelman syndrome (GS) is a rare, salt-losing tubulopathy characterized by hypokalemic metabolic alkalosis with hypomagnesemia and hypocalciuria. The disease is recessively inherited, caused by inactivating mutations in the SLC12A3 gene that encodes the thiazide-sensitive sodium-chloride cotransporter (NCC). GS is usually detected during adolescence or adulthood, either fortuitously or in association with mild or nonspecific symptoms or both. The disease is characterized by high phenotypic variability and a significant reduction in the quality of life, and it may be associated with severe manifestations. GS is usually managed by a liberal salt intake together with oral magnesium and potassium supplements. A general problem in rare diseases is the lack of high quality evidence to inform diagnosis, prognosis, and management. We report here on the current state of knowledge related to the diagnostic evaluation, follow-up, management, and treatment of GS; identify knowledge gaps; and propose a research agenda to substantiate a number of issues related to GS. This expert consensus statement aims to establish an initial framework to enable clinical auditing and thus improve quality control of care.

Urinary exosomes in the diagnosis of Gitelman and Bartter syndromes.

BACKGROUND: Gitelman syndrome (GS) and Bartter syndrome (BS) are hereditary salt-losing tubulopathies (SLTs) resulting from defects of renal proteins involved in electrolyte reabsorption, as for sodium-chloride cotransporter (NCC) and furosemide-sensitive sodium-potassium-chloride cotransporter (NKCC2) cotransporters, affected in GS and BS Type 1 patients, respectively. Currently, definitive diagnosis is obtained through expensive and time-consuming genetic testing. Urinary exosomes (UE), nanovesicles released by every epithelial cell facing the urinary space, represent an ideal source of markers for renal dysfunction and injury, because UE molecular composition stands for the cell of origin. On these assumptions, the aim of this work is to evaluate the relevance of UE for the diagnosis of SLTs. METHODS: UE were purified from second morning urines collected from 32 patients with genetically proven SLTs (GS, BS1, BS2 and BS3 patients), 4 with unclassified SLTs and 22 control subjects (age and sex matched). The levels of NCC and NKCC2 were evaluated in UE by SDS-PAGE/western blotting with specific antibodies. RESULTS: Due to their location on the luminal side of tubular cells, NCC and NKCC2 are well represented in UE proteome. The NCC signal is significantly decreased/absent in UE of Gitelman patients compared with control subjects (Mann-Whitney t-test, P < 0.001) and, similarly, the NKCC2 in those of Bartter type 1 (P < 0.001). The difference in the levels of the two proteins allows recognition of Gitelman and Bartter type 1 patients from controls and, combined with clinical data, from other Bartter patients. Moreover, the receiver operating characteristic curve analysis using UE NCC densitometric values showed a good discriminating power of the test comparing GS patients versus controls and BS patients (area under the curve value = 0.92; sensitivity 84.2% and specificity 88.6%). CONCLUSIONS: UE phenotyping may be useful in the diagnosis of GS and BS, thus providing an alternative/complementary, urine-based diagnostic tool for SLT patient recognition and a diagnostic guidance in complex cases.

Large-scale proteomics and phosphoproteomics of urinary exosomes.

Normal human urine contains large numbers of exosomes, which are 40- to 100-nm vesicles that originate as the internal vesicles in multivesicular bodies from every renal epithelial cell type facing the urinary space. Here, we used LC-MS/MS to profile the proteome of human urinary exosomes. Overall, the analysis identified 1132 proteins unambiguously, including 177 that are represented on the Online Mendelian Inheritance in Man database of disease-related genes, suggesting that exosome analysis is a potential approach to discover urinary biomarkers. We extended the proteomic analysis to phosphoproteomic profiling using neutral loss scanning, and this yielded multiple novel phosphorylation sites, including serine-811 in the thiazide-sensitive Na-Cl co-transporter, NCC. To demonstrate the potential use of exosome analysis to identify a genetic renal disease, we carried out immunoblotting of exosomes from urine samples of patients with a clinical diagnosis of Bartter syndrome type I, showing an absence of the sodium-potassium-chloride co-transporter 2, NKCC2. The proteomic data are publicly accessible at http://dir.nhlbi.nih.gov/papers/lkem/exosome/.

The Urinary Excretion of Uromodulin is Regulated by the Potassium Channel ROMK.

Uromodulin, the most abundant protein in normal urine, is produced by cells lining the thick ascending limb (TAL) of the loop of Henle. Uromodulin regulates the activity of the potassium channel ROMK in TAL cells. Common variants in KCNJ1, the gene encoding ROMK, are associated with urinary levels of uromodulin in population studies. Here, we investigated the functional link between ROMK and uromodulin in Kcnj1 knock-out mouse models, in primary cultures of mouse TAL (mTAL) cells, and in patients with Bartter syndrome due to KCNJ1 mutations. Both global and kidney-specific Kcnj1 knock-out mice showed reduced urinary levels of uromodulin paralleled by increased levels in the kidney, compared to wild-type controls. Pharmacological inhibition and genetic deletion of ROMK in mTAL cells caused a reduction in apical uromodulin excretion, reflected by cellular accumulation. In contrast, NKCC2 inhibition showed no effect on uromodulin processing. Patients with Bartter syndrome type 2 showed reduced urinary uromodulin levels compared to age and gender matched controls. These results demonstrate that ROMK directly regulates processing and release of uromodulin by TAL cells, independently from NKCC2. They support the functional link between transport activity and uromodulin in the TAL, relevant for blood pressure control and urinary concentrating ability.

Unusual case of failure to thrive: Type III Bartter syndrome.

Bartter syndrome Type III is a rare autosomal recessive disorder resulting from an inherited defect in the thick ascending limb of the loop of henle of the nephrons in kidney. The typical clinical manifestations in childhood are failure to thrive and recurrent episodes of vomiting. Typical laboratory findings which help in the diagnosis are hypokalemic metabolic alkalosis, hypomagnesemia and hypercalciuria. We report a case of Type III Bartter syndrome not responding to repeated conventional treatment of failure to thrive.

Novel mutations of the chloride channel Kb gene in two Japanese patients clinically diagnosed as Bartter syndrome with hypocalciuria.

Hypokalemic metabolic tubulopathy, such as in Bartter syndrome and Gitelman syndrome, is caused by the dysfunction of renal electrolyte transporters. Despite advances in molecular genetics with regard to hypokalemic metabolic tubulopathy, recent reports have suggested that the phenotype-genotype correlation is still confusing, especially in classic Bartter and Gitelman syndromes. We report here two Japanese patients who suffered from clinically diagnosed classic Bartter syndrome but who presented hypocalciuria. Hypocalciuria is generally believed to be a pathognomonic finding of NCCT malfunction. To better understand the genotype-phenotype correlation in these two cases, we screened four renal electrolyte transporter genes [Na-K-2Cl cotransporter (NKCC2), renal outer medullary K channel (ROMK), Cl channel Kb (ClC-Kb), and Na-Cl cotransporter (NCCT)] by the PCR direct sequencing method. We identified three ClC-Kb allelic variants, including two new mutations (L27R and W610X in patient 1 and a G to C substitution of a 3' splice site of intron 2 and W610X in patient 2). We did not find any mutations in the other three genes. Our present data suggest that some ClC-Kb mutations may affect calcium handling in renal tubular cells.

Urinary kallikrein excretion in Bartter's syndrome.

Urinary excretion of kallikrein has been studied in a patient with hypokalemic alkalosis, hyperplasia of the renal juxtaglomerular apparatus and hyperreninemia, secondary aldosteronism and resistance to the pressor effect of angiotensin II (Bartter's syndrome). Urinary kallikrein was found exceedingly high in several determination, whereas it was low in patients with essential hypertension and high in patients with primary aldosteronism. Urinary kallikrein decreased after spironolactone therapy. The rise of kallikrein excretion (which is not related to plasma renin) in this case is probably caused by a direct action of the chronic excess of plasma aldosterone; it could not be accounted for as secondary to natriuresis.

Pathogenetic role of cyclooxygenase-2 in hyperprostaglandin E syndrome/antenatal Bartter syndrome: therapeutic use of the cyclooxygenase-2 inhibitor nimesulide.

Patients with hyperprostaglandin E syndrome/antenatal Bartter syndrome typically have renal salt wasting, hypercalciuria with nephrocalcinosis, and secondary hyperaldosteronism. Antenatally, these patients have fetal polyuria, leading to polyhydramnios and premature birth. Hyperprostaglandin E syndrome/antenatal Bartter syndrome is accompanied by a pathologically elevated synthesis of prostaglandin E(2), thought to be responsible for aggravation of clinical symptoms such as salt and water loss, vomiting, diarrhea, and failure to thrive. In this study administration of the cyclooxygenase-2 (COX-2) specific inhibitor nimesulide to patients with hyperprostaglandin E syndrome/antenatal Bartter syndrome blocked renal prostaglandin E(2) formation and relieved the key parameters hyperprostaglandinuria, secondary hyperaldosteronism, and hypercalciuria. Partial suppression of serum thromboxane B(2) synthesis resulting from platelet COX-1 activity and complete inhibition of urinary 6-keto-prostaglandin F(1alpha), reflecting endothelial COX-2 activity, indicate preferential inhibition of COX-2 by nimesulide. Amelioration of the clinical symptoms by use of nimesulide indicates that COX-2 may play an important pathogenetic role in hyperprostaglandin E syndrome/antenatal Bartter syndrome. Moreover, on the basis of our data we postulate that COX-2-derived prostaglandin E(2) is an important mediator for stimulation of the renin-angiotensin-aldosterone system in the kidney.

Metabolic mimicry of Bartter's syndrome by covert vomiting: utility of urinary chloride determinations.

Bartter's syndrome characteristically exhibits the constellation of hypokalemic alkalosis with moderate kaliuresis, normotensive hyperreninemia, hyperaldosteronism, urinary hyperexcretion of prostaglandin E (PGE) and vascular hyporesponsivity to pressor agents. We describe precise biochemical mimicry of these metabolic abnormalities in a patient with surreptitious repetitive vomiting, in whom simple urinary chloride excretion data subsequently excluded the diagnosis of Bartter's syndrome.

A new fluorogenic substrate method for the estimation of kallikrein in urine.

Kallikrein in human urine was measured using a fluorogenic peptide substrate, proly-phenyl-alanyl-arginine-4-methylcoumaryl-7-amide (Pro-Phe-Arg-MCA). Using 20 microliters of normal urine, kallikrein activity was quantitatively assayed by incubation with a final concentration of 10(-4) M Pro-Phe-Arg-MCA at 37 degrees C for 90 min. The reaction was terminated by adding 50 units of Trasylolr or 20 microliters of 10% acetic acid. Using this method, kallikrein activity was measured in urine from normal subjects and patients with glomerulonephitis and Bartter's syndrome. These values were comparable with the values obtained by radioimmunoassay using bovine low-molecular-weight kininogen. When normal urine was applied to a column of arginine-Sepharose 4B, two activities, Pro-Phe-Arg-MCA hydrolyzing activity and kinin-releasing activity toward bovine low-molecular-weight kininogen, were eluted in the same fraction. These results indicate that the present method is useful for the estimation of kallikrein in urine, in terms of specificity, sensitivity, and simplicity.

The value of urinary chloride measurement in distinguishing surreptitious vomiting from Bartter's syndrome.

Urinary chloride measurement is a simple and common procedure but its value in clinical practice is not extensive. This case report highlights a practical and important use of this test. A patient presented with most of the clinical and metabolic derangements of Bartter's syndrome but was found to have extremely low or absent urinary chloride excretion. Her ability to excrete chloride was, however, intact during a chloride load test. The finding of low urinary chloride excretion did not support the diagnosis of Bartter's syndrome and suggested an extrarenal loss of chloride. This was confirmed when she eventually admitted to surreptitious vomiting.

Radioimmunoassay for urinary prostaglandins E and F alpha: normal values in different age groups.

A new radioimmunoassay for urinary prostaglandins E and F alpha is described which allows the extraction and chromatographic separation of urinary prostaglandins with an overall recovery of 80.5% and 89.3% for prostaglandins E2 and F2 alpha respectively. The antibodies raised in the rabbit could not distinguish prostaglandins of series 1 and 2 but were found highly specific towards their metabolites and other primary prostaglandins. The sensitivity of the assay developed was at 2.2 pg for prostaglandin E and 2pg for prostaglandin F alpha. This assay was applied to normal adults of both sexes; it was shown that the daily urinary excretion of prostaglandins F alpha and E was greater in men than in women. In children aged from 1 to 114 months, the urinary excretion of prostaglandins increased with age. This increase was more marked during the first two years of life and was significantly related to age.

Comparative study of two tests of renal diluting ability in Bartter's syndrome.

1. Different results concerning distal NaCl reabsorption have been reported for patients with Bartter's syndrome in tests of renal diluting ability. We describe clearance studies performed on 3 patients with Bartter's syndrome using different routes for body fluid content expansion: water was given orally and 0.45% NaCl solution intravenously. The impact of fluid composition was evaluated in one patient who additionally underwent a "reverse test": i.e., intravenous 5% glucose in water and an oral load of 0.45% NaCl solution. 2. Urine flow per ml glomerular filtration rate (GFR) reached higher levels when the iv route was used (20.6 +/- 1.8 vs 11.8 +/- 5.7%, P < 0.05). Fractional excretion of Na+, Cl- and osmoles increased during NaCl infusion but not during the oral load. Also, distal delivery of solute increased and was greater than that observed in the oral test (21.9 +/- 5.5 vs 11.4 +/- 2.1%, P < 0.05). 3. In contrast, fractional distal chloride reabsorption in the iv test reached subnormal values which were lower than in the oral load test (65.0 +/- 11.2 vs 86.8 +/- 11.0%, P < 0.05). A positive correlation was observed between distal delivery and Cl- fractional excretion (r = 0.87; P < 0.005). In one patient, the 5% glucose infusion resulted in greater urine flow and distal delivery when compared to distilled water or 0.45% NaCl taken orally (28.1 vs 13.3 ml/min and 27.3 vs 12.8%, respectively). These values were as high as those observed during iv administration of hypotonic saline. 4. The iv route was always associated with lower rates of fractional distal chloride reabsorption (70.7 vs 89.1%) regardless of the solute composition and should be recommended when testing the renal diluting ability of patients suspected of Bartter's syndrome.

Endothelium-derived vasoactive substances in Bartter's syndrome.

An imbalance between endothelium-derived vasoactive substances such as endothelin and endothelium-derived nitric oxide (NO) might be viewed as a possible determinant of vascular hyporeactivity. To check this possibility the authors evaluated the role of endothelin and NO in the reduced vascular reactivity of Bartter's syndrome. Plasma immunoreactive endothelin (22.07 +/- 7.06 vs 13.80 +/- 1.43 pmol/L, P < 0.011), urinary excretion of NO2- (0.28 +/- 0.10 vs 0.15 +/- 0.02, mumol/mumol of urinary creatinine, P < 0.01) and NO3- (0.17 +/- 0.07 vs 0.09 +/- 0.02 mumol/mumol of urinary creatinine, P < 0.011), and forearm resting blood flow (FRBF) (6.67 +/- 1.69 vs 4.30 +/- 0.38 mL/m'/100 mL, P < 0.005) were increased in patients with Bartter's syndrome in comparison with normal controls (C). No difference in postischemic maximal FBF was found (34.14 +/- 4.67 vs 31.35 +/- 2.86 mL/minute/100 mL), while patients showed a slower recovery after peak flow (PF) (77.57 +/- 61.35 vs 9.42 +/- 3.69 seconds, P < 0.013). Higher plasma endothelin supports the defect in vascular reactivity of Bartter's syndrome already shown for angiotensin II and norepinephrine and is in keeping with the altered intracellular calcium signaling previously demonstrated by the authors in this syndrome. The increased excretion of NO2- and NO3- in this syndrome, together with the higher FRBF and the slower recovery of the FBF and PF, argues in favor of an increased NO synthesis in Bartter's syndrome and of assigning it a role in the vascular hyporeactivity of Bartter's syndrome.

[Hypokalemia and hypoevolutism. Description of a case of Bartter's syndrome]. / Ipokaliemia e ipoevolutismo. Descrizione di un caso di sindrome di Bartter.

In 1962 Bartter et al. described a clinical syndrome characterized by growth and mental retardation, hypokalemic alkalosis, increased aldosterone secretion rate and increased plasma angiotensin II concentration in the presence of normal blood pressure. The inheritance pattern has been reported as autosomal recessive or as sporadic. Since that time 37 cases have been reported in pediatric age, describing a wide spectrum of clinical and biochemical features. For the diagnosis the following criteria must be present: hypokalemia, hypochloremia, alkalosis, hyperreninemia in the presence of a normal blood pressure and elevated urinary K and Cl excretion, in the absence of other conditions that might cause similar features. A case of Bartter's disease is herein reported with our experience in the diagnosis, treatment and follow-up.