Effective NSAID treatment indicates that hyperprostaglandinism is affecting the clinical severity of childhood hypophosphatasia.

BACKGROUND: Hypophosphatasia (HP) is an inborn error of bone metabolism characterized by a genetic defect in the gene encoding the tissue-nonspecific alkaline phosphatase (TNSALP). There is a lack of knowledge as to how the variability and clinical severity of the HP phenotype (especially pain and walking impairment) are related to metabolic disturbances or impairments, subsequent to the molecular defect. METHODS: We analyzed the changes in clinical symptoms and the prostaglandin (PG) metabolism in response to treatment with non-steroidal anti-inflammatory drugs (NSAIDs) in six children affected by childhood HP. In addition, by exposing HP fibroblasts to pyridoxal phosphate and/or calcium pyrophosphate in vitro, we analyzed whether the alterations in PG levels are sequelae related to the metabolic defect. RESULTS: Childhood HP patients, who often complain about pain in the lower limbs without evident fractures, have systemic hyperprostaglandinism. Symptomatic anti-inflammatory treatment with NSAIDs significantly improved pain-associated physical impairment. Calcium pyrophosphate, but not pyridoxal phosphate, induced cyclooxygenase-2 (COX-2) gene expression and PG production in HP and normal fibroblasts in vitro. CONCLUSION: Clinical features of childhood HP related to pain in the lower legs may be, at least in part, sequelae related to elevated PG levels, secondary to the primary metabolic defect. Consequently, NSAID treatment does improve the clinical features of childhood HP.

Renal cortical regulation of COX-1 and functionally related products in early renovascular hypertension (rat).

Renal volume regulation is modulated by the action of cyclooxygenases (COX) and the resulting generation of prostanoids. Epithelial expression of COX isoforms in the cortex directs COX-1 to the distal convolutions and cortical collecting duct, and COX-2 to the thick ascending limb. Partly colocalized are prostaglandin E synthase (PGES), the downstream enzyme for renal prostaglandin E(2) (PGE(2)) generation, and the EP receptors type 1 and 3. COX-1 and related components were studied in two kidney-one clip (2K1C) Goldblatt hypertensive rats with combined chronic ANG II or bradykinin B(2) receptor blockade using candesartan (cand) or the B(2) antagonist Hoechst 140 (Hoe). Rats (untreated sham, 2K1C, sham + cand, 2K1C + cand, sham + Hoe, 2K1C + Hoe) were treated to map expression of parameters controlling PGE(2) synthesis. In 2K1C, cortical COX isoforms did not change uniformly. COX-2 changed in parallel with NO synthase 1 (NOS1) expression with a raise in the clipped, but a decrease in the nonclipped side. By contrast, COX-1 and PGES were uniformly downregulated in both kidneys, along with reduced urinary PGE(2) levels, and showed no clear relations with the NO status. ANG II receptor blockade confirmed negative regulation of COX-2 by ANG II but blunted the decrease in COX-1 selectively in nonclipped kidneys. B(2) receptor blockade reduced COX-2 induction in 2K1C but had no clear effect on COX-1. We suggest that in 2K1C, COX-1 and PGES expression may fail to oppose the effects of renovascular hypertension through reduced prostaglandin signaling in late distal tubule and cortical collecting duct.

Pharmacokinetics of a novel oral slow-release form of misoprostol.

BACKGROUND: The pharmacokinetics of a novel slow-release (SR) misoprostol was studied and compared to conventional misoprostol. METHODS: Thirty-one women, pregnant between 8 and 12 weeks, requesting surgical abortion were randomly allocated to receive orally 400 microg conventional misoprostol, 400 microg SR misoprostol or 800 microg SR misoprostol. Venous blood samples were taken at 0, 30, 60, 120, 240 and 360 min after the administration of misoprostol. Misoprostol acid (MPA) was determined in serum samples using liquid chromatography/tandem mass spectrometry. RESULTS: Serum peak concentration (Cmax) was highest for conventional oral misoprostol. The time to peak concentration (Tmax) was similar for all groups. The area under the curve up to 360 min was similar for conventional and for 800 microg SR misoprostol and significantly greater for these groups compared to 400 microg SR misoprostol (P = 0.013). CONCLUSION: The new SR form of misoprostol demonstrated lower peak levels but longer-lasting elevation in plasma levels compared to conventional oral misoprostol. The AUC for 800 microg SR misoprostol was similar to that of 400 microg of conventional oral misoprostol. SR misoprostol may offer an alternative to repeated administration of oral misoprostol or to vaginal administration.

Antimicrobial drug use in hospitalised paediatric patients: a cross-national comparison between Germany and Croatia.

PURPOSE: To compare the utilisation of systemic antimicrobials at the paediatric units of the university hospitals in Marburg (Germany) and Rijeka (Croatia). METHODS: A prospective, observational analysis of hospital records from 300 incident users of antimicrobials in each study centre that were younger than 19 years. Antimicrobial utilisation was analysed in six gender-specific age groups with respect to drug choice, duration of treatment and hospital stay, indication and route of administration. The extent of antimicrobial drug use was assessed by the number of treatment courses. RESULTS: In each hospital, more than 1/3 of the patients were younger than 1 year. The duration of hospital stay was about two-fold longer in Rijeka (18.5 +/- 5.8 days) than in Marburg (8.6 +/- 3.8 days). Pneumonia and other respiratory tract infections were the most common indications in Marburg (38.6%) and Rijeka (58.7%). The cumulative percentage of patients treated with an equal number of different antimicrobials was lower in Rijeka than in Marburg. The most commonly used antimicrobials were ampicillin (40.3%) and cefuroxim (35.9%) in Marburg, but ceftriaxone (43.3%) and cefotaxim (14.0%) in Rijeka. CONCLUSIONS: A shorter treatment duration, less variation in the prescribing pattern and a greater adherence to the use of recommended antimicrobials argue for a more rational antimicrobial drug use in Marburg than in Rijeka. However, a further identification of drug choice determinants is warranted.

Pharmacotyping of hypokalaemic salt-losing tubular disorders.

UNLABELLED: Long standing confusion exists in the terminology of hypokalaemic salt-losing tubulopathies (SLTs). SLTs are autosomal recessively transmitted and characterized by normotensive secondary hyperreninism/hyperaldosteronism with hypokalaemic metabolic alkalosis. Historically, four phenotypical variants have been described: (1) the (classic) Bartter syndrome (cBS), (2) the hypomagnesaemic hypocalciuric Gitelman syndrome (GS), (3) the hypercalciuric hyperprostaglandin-E-syndrome (HPS) or antenatal Bartter syndrome (aBS) and (4) the hyperprostaglandin-E-syndrome with sensorineural deafness (HPS + SND). The latter two syndromes are the most severe variants with antenatal manifestation with polyhydramnios and life-threatening course of salt- and water-loss. Defects in five renal membrane proteins involved in electrolyte reabsorption have been identified: In HPS-patients mutations in (1) either the furosemide-sensitive sodium-potassium-chloride cotransporter NKCC2, or (2) in the potassium channel ROMK have been identified, and (3) HPS + SND is caused by mutations in the beta-subunit of the chloride channels ClC-Kb and -Ka (named barttin), all mimicking the major pharmacological effects of furosemide with minor potassium-wasting in ROMK-patients as seen in patients treated with simultaneous furosemide and amiloride, and minor calcium-wasting in Barttin-patients resembling the combination of furosemide and thiazides. (4) cBS is caused by mutations in the chloride channel ClC-Kb with similar clinical characteristics as seen under combination of thiazides and furosemide, (5) GS is caused by mutations in the thiazide-sensitive sodium-chloride cotransporter NCCT resembling the effect of long-term thiazide administration. CONCLUSION: The combination of pharmacology and genetics suggests a new terminology for the above described SLTs: Furosemide-like-SLT for HPS caused by NKCC2-mutations, furosemide/amiloride-like-SLT for HPS caused by ROMK-mutations, furosemide/thiazide-like-SLT for HPS + SND, thiazide/furosemide-like-SLT for cBS, and thiazide-like-SLT for GS.

The role of cyclooxygenases and prostanoid receptorsin furosemide-like salt losing tubulopathy: the hyperprostaglandin E syndrome.

Hyperprostaglandin E syndrome/antenatal Bartter syndrome is characterized by NaCl wasting and volume depletion, juxtaglomerula hypertrophy, hyperreninism and secondary hyperaldosteronism. Primary causes are mutations in the gene for Na-K-2Cl-cotransporter, NKCC2, or for potassium channel, ROMK, responsible for medullary NaCl malabsorption. Most intriguing aspect of the syndrome is the association with a massively increased renal prostaglandin production which contributes substantially to the clinical picture of the patients. Therefore the term hyperprostaglandin E syndrome has been introduced. It is unclear how prostaglandins aggravate the NaCl transport deficiency. Aspects to prostaglandin synthesis and receptor-mediated function within the kidney in patients suffering from hyperprostaglandin E syndrome/antenatal Bartter syndrome will be discussed.

High efficacy and minor renal effects of indomethacin treatment during individualized fluid intake in premature infants with patent ductus arteriosus.

AIM: To determine the efficacy and the renal side effects of indomethacin treatment for closure of a patent ductus arteriosus (PDA) in premature infants during an individualized fluid regime that avoids hypovolaemia and subsequent prostaglandin-dependent renal perfusion. METHODS: Observational retrospective analysis of the efficacy of indomethacin in premature infants with PDA treated in a single institution from June 1992 to May 2000. The clinical course and renal effects were analysed in the subgroup of infants born from June 1995 to May 2000. The management of infants at risk and the treatment of infants with PDA followed a standardized protocol that included echocardiographic screening for PDA, indomethacin treatment before congestive failure develops (early symptomatic treatment) and an individualized fluid intake. RESULTS: In total, 412 infants with a gestational age < or = 32 wk were identified. Fifty-six infants with a PDA (14%) were treated with indomethacin [mean birthweight 936 (95% confidence interval 866-1006) g; gestational age 27.3 (26.8-27.9) wk]. Indomethacin treatment was successful in 52 infants (93%). The clinical course and renal effects were analysed in 41 infants. Most infants received three indomethacin doses of 0.2 mg kg(-1) every 12 h. Urine output transiently decreased from 5.6 (4.6-6.4) to 4.6 (3.9-5.3) ml kg(-1) (h(-1). Serum creatinine temporarily increased from 0.90 (0.83-0.98) to 1.06 (0.87-1.24)mg dl(-1). Fluid intake was 158 (148-168) ml kg(-1) d(-1) before indomethacin and decreased to 142 (131-154) ml kg(-1) d(-1). CONCLUSION: Indomethacin is very effective for closure of a PDA, even in very premature infants, and is not associated with clinically significant renal side effects.

[Differential diagnosis of a polyhydramnion in hyperprostaglandin E syndrome: a case report]. / Differenzialdiagnose des Polyhydramnions beim Hyperprostaglandin-E-Syndrom: Case-Report.

INTRODUCTION: A polyhydramnion is diagnosed in 0.4 to 3.3 % of all pregnancies. The most common causes of increased amniotic fluid include maternal diabetes mellitus, fetal malformations and chromosomal aberrations, twin-to-twin transfusion syndrome, rhesus incompatibility syndrome, and congenital infections. After exclusion of other etiologies for polyhydramnion, the very rare, autosomal-recessive transferred hyperprostaglandin E syndrome (HPS) has to be considered. PATIENTS AND METHODS: We report on a 31-year-old women who visited our obstetrical outpatient clinics at 22 + 4 weeks of gestation for prenatal ultrasound scanning and amniocentesis. This, the patient's third pregnancy had been without complications so far. She had delivered two children before, one of them bearing the HPS. The women herself suffered from epilepsy. At 26 + 0 weeks of gestation the pregnancy was complicated by a polyhydramnion requiring serial amniocentesis for reducing amniotic fluid load. Among others, her amniotic fluid was analyzed for chloride concentration and for genetic aberrations regarding HPS. Serological investigations and an oral glucose tolerance test (oGTT) were performed. RESULTS: Amniocentesis revealed a normal chromosomal pattern. The oGTT demonstrated values in the normal range. Serological investigations regarding TORCH infections were without pathological findings. The chloride concentration was highly increased in the amniotic fluid, which is suspicious for HPS. Finally, molecular analysis proved an NKCC2-mutation responsible for HPS. A cesarean section was performed at 33 + 3 weeks of gestation. CONCLUSION: If HPS is suspected to be the cause of polyhydramnions, the chloride concentrations in the amniotic fluid and molecular analysis for HPS should be performed. Interdisciplinary care, diagnostics and therapy in an experienced perinatal center are essential for an optimal outcome of the pregnancy and the newborn infant.

Do we need another NSAID instead of indomethacin for treatment of ductus arteriosus in preterm infants?

UNLABELLED: Up until now indomethacin is the most extensively evaluated non-steroidal anti-inflammatory drug (NSAID) in neonatal medicine. If used with due consideration to the physiologic role of prostaglandins, a 90 success rate can be reached and serious adverse drug effects prevented. CONCLUSION: The results reported by Bellander et al. support the idea that we do not need to study other substances of the same therapeutic class, with the same target--cyclooxygenase--in the prostaglandin cascade and with a similar pharmacological profile. Instead, indomethacin treatment regimes should be further improved with respect to their efficacy and safety.

Effects of short-term treatment with diclofenac-colestyramine on renal function and urinary prostanoid excretion in patients with type-2 diabetes.

OBJECTIVE: To determine the effect of short-term administration of diclofenac-colestyramine on glomerular filtration rate (GFR), renal plasma flow (RPF) and urinary excretion of prostanoids in patients with type-2 diabetes without and with impaired renal function. METHODS: In the randomised, single-blind, placebo-controlled, two-period crossover study, 32 patients with type-2 diabetes (group 1: 16 patients without impaired renal function, creatinine clearance > or =80 ml/min and group 2: 16 patients with impaired renal function, creatinine clearance 30-79 ml/min) received 140 mg diclofenac-colestyramine (corresponding to 75 mg diclofenac sodium) or placebo twice a day on days 1 and 2 and once on day 3 with a wash-out period of 6 days between the two periods. GFR was assessed using both measurement of creatinine clearance and calculation of inulin clearance and RPF was assessed using calculation of para-aminohippurate (PAH) clearance after the short-term administration on day 3. Urinary excretion of prostanoids (PGE(2), PGE-M, 6-keto-PGF(1alpha), 2,3-dinor-6-keto-PGF(1alpha), TxB(2), 2,3-dinor-TxB(2) and 11-dehydro-TxB(2)) were measured before and after drug intake. RESULTS: Comparison with placebo showed no effect of diclofenac-colestyramine on creatinine, inulin or PAH clearance ( P>0.05) in patients with type-2 diabetes either without or with impaired renal function. The differences in creatinine, inulin and PAH clearance between the two groups of patients were not influenced by diclofenac-colestyramine. Urinary excretion of PGE(2), PGE-M, 6-keto-PGF(1alpha), 2,3-dinor-6-keto-PGF(1alpha), TxB(2), 2,3-dinor-TxB(2) ( P=1.89) and 11-dehydro-TxB(2) was significantly reduced by diclofenac-colestyramine. CONCLUSION: These results indicate that proven non-specific cyclooxygenase inhibition by short-term administration of diclofenac-colestyramine did not affect renal haemodynamic function (GFR, RPF) in patients with type-2 diabetes either without or with impaired renal function.

Pharmacokinetics of different routes of administration of misoprostol.

BACKGROUND: The pharmacokinetic parameters of four different routes of administration of a single dose of 400 microg of misoprostol were studied. METHODS: A total of 40 women undergoing termination of pregnancy by suction evacuation was randomized by computer model to receive 400 microg of misoprostol by one of four routes: (i) sublingual (ii) oral (iii) vaginal and (iv) vaginal with addition of water. Venous blood samples were taken at 0, 1, 2, 5, 10, 20, 30, 45, 60, 120, 240 and 360 min after the administration of misoprostol. Misoprostol acid (MPA) was determined in serum samples using gas chromatography/tandem mass spectrometry. RESULTS: Sublingual misoprostol achieved the highest serum peak concentration (Cmax) (574.8 +/- 250.7 pg/ml) of MPA and this was significantly higher than those in the other groups [Oral: 287.6 +/- 144.3 pg/ml (P < 0.01), vaginal: 125.2 +/- 53.8 pg/ml (P < 0.001) and vaginal with water: 162.8 +/- 57.1 pg/ml (P < 0.001)]. The time to peak concentration (Tmax) was similar in both the sublingual (26.0 +/- 11.5 min) and oral groups (27.5 +/- 14.8 min) and was significantly shorter than those in both vaginal groups. The area under the MPA concentration versus time curve up to 360 min in the sublingual group (743.7 +/- 291.2 pg.h/ml) was significantly greater than those in oral (402.8 +/- 151.6 pg.h/ml, P < 0.05) and vaginal (433.7 +/- 182.6 pg.h/ml, P < 0.05) groups, but no significant difference was found between sublingual and vaginal administration if water (649.3 +/- 333.8 pg.h/ml) was added. CONCLUSION: The new sublingual route of administration of misoprostol demonstrated a great potential to be developed into a method of medical abortion.

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.

Inhibition of cyclooxygenase-2 attenuates urinary prostanoid excretion without affecting renal renin expression.

This study aimed to assess the impact of cyclooxygenase-2 (COX-2) on the secretion and expression of renin in the kidney cortex. For this purpose renocortical COX-2 expression was moderately stimulated by a low-salt diet or strongly stimulated (increase in mRNA about fivefold) by the combination of a low-salt diet and the angiotensin-I-converting enzyme inhibitor ramipril in male Sprague-Dawley rats. None of these manoeuvres changed medullary COX-2 expression or cortical or medullary COX-1 expression. Treatment with low salt plus ramipril but not with low salt alone led to a three- to fourfold increase of the urinary output of all major prostanoids. The selective COX-2 inhibitor rofecoxib (10 mg/kg per day) markedly lowered basal urinary prostanoid excretion and blunted the stimulation of prostanoid excretion during treatment with low salt plus ramipril. The stimulation of renin secretion by the low-salt diet but not by low salt plus ramipril was attenuated by rofecoxib. The low-salt diet led to a moderate increase of renin gene expression, and additional treatment with ramipril caused a 15-fold increase of renin mRNA. However, no effect of rofecoxib on renin gene expression was observed in any group. These findings suggest that stimulation of COX-2 in the renal cortex leads to the increased formation of all major prostanoids. COX-2-derived prostanoids may play a role in the regulation of renin secretion but not in renin gene expression during the intake of a low-salt diet. However, no major relevance of COX-2-derived prostanoids to renin secretion or renin gene expression during ramipril treatment or a combination of ramipril and a low-salt diet was found.

Evaluation of long-term treatment with indomethacin in hereditary hypokalemic salt-losing tubulopathies.

OBJECTIVE: Evaluation of the benefit/risk ratio of long-term treatment with indomethacin in salt-losing tubulopathies with special attention to renal function. STUDY DESIGN: Twelve patients (median age, 14.9 years) had received indomethacin for a median of 13 years (median cumulative dose, 10.7 g/kg). Creatinine clearance, serum electrolyte levels, endocrine status, and excretion of prostaglandins and electrolytes were examined during indomethacin therapy and after its withdrawal. All patients underwent ultrasound-guided renal biopsy. For statistical evaluation, the Wilcoxon test and Pearson correlation coefficient were used. RESULTS: After indomethacin withdrawal, the biochemical features of the tubulopathy reappeared. The median creatinine clearance rose from 67.4 to 96.5 mL/min/1.73 m(2) (P <.05) but remained subnormal in 4 patients. Ultrasonography elucidated medullary nephrocalcinosis in 8 patients. Renal tissue showed slight/moderate focal tubular atrophy and interstitial fibrosis in 8 patients. Comparison with biopsy specimens, obtained 11 to 14 years before study participation from 5 patients, revealed no progression. A correlation between fractional sodium and magnesium excretion and percentage of altered tubulointerstitial compartment was found (P <.001). The 4 patients with mutations in the gene of the inwardly rectifying adenosine triphosphate-regulated potassium channel (ROMK) had almost normal renal histologic findings and normal renal function. CONCLUSION: Renal function and histology are unaffected by long-term indomethacin treatment.

Hypokalemic salt-losing tubulopathy with chronic renal failure and sensorineural deafness.

OBJECTIVE: To characterize a rare inherited hypokalemic salt-losing tubulopathy with linkage to chromosome 1p31. METHODS: We conducted a retrospective analysis of the clinical data for 7 patients in whom cosegregation of the disease with chromosome 1p31 had been demonstrated. In addition, in 1 kindred, prenatal diagnosis in the second child was established, allowing a prospective clinical evaluation. RESULTS: Clinical presentation of the patients was homogeneous and included premature birth attributable to polyhydramnios, severe renal salt loss, normotensive hyperreninemia, hypokalemic alkalosis, and excessive hyperprostaglandin E-uria, which suggested the diagnosis of hyperprostaglandin E syndrome/antenatal Bartter syndrome. However, the response to indomethacin was only poor, accounting for a more severe variant of the disease. The patients invariably developed chronic renal failure. The majority had extreme growth retardation, and motor development was markedly delayed. In addition, all patients turned out to be deaf. CONCLUSION: The hypokalemic salt-losing tubulopathy with chronic renal failure and sensorineural deafness represents not only genetically but also clinically a disease entity distinct from hyperprostaglandin E syndrome/antenatal Bartter syndrome. A pleiotropic effect of a single gene defect is most likely causative for syndromic hearing loss.

Effect of preterm formula with and without long-chain polyunsaturated fatty acids on the urinary excretion of F2-isoprostanes and 8-epi-prostaglandin F2alpha.

BACKGROUND: The objective of this study was to evaluate the effect of conventional and long-chain polyunsaturated fatty acids (LCP)-enriched preterm formula on the endogenous formation of F2-isoprostanes and 8-epi-prostaglandin (PG) F2alpha as possible markers of lipid peroxidation in preterm infants during their first weeks of life. METHODS: In a prospective, randomized, double-blind study, infants received either formula enriched with LCP (n = 8), standard preterm formula (n = 7), or (expressed) breast milk (n = 8). Urine was sampled at study entry and after the study period of 3 weeks. The formation of F2-isoprostanes and 8-epi-PGF2alpha was evaluated by measuring the urinary excretion by gas chromatography-mass spectrometry. RESULTS: No differences in the urinary excretion of F2-isoprostanes and 8-epi-PGF2alpha were observed at the end of the study period. CONCLUSIONS: This result suggests that supplementation of a preterm formula with LCP for a period of 3 weeks does not stimulate lipid peroxidation in preterm infants.

Functional heterogeneity of ROMK mutations linked to hyperprostaglandin E syndrome.

BACKGROUND: The renal K(+) channel ROMK (Kir1.1) controls salt reabsorption in the kidney. Loss-of-function mutations in this channel cause hyperprostaglandin E syndrome/antenatal Bartter syndrome (HPS/aBS), which is characterized by severe renal salt and fluid wasting. METHODS: We investigated 10 HPS/aBS patients for mutations in the ROMK gene by single-strand conformation polymorphism analysis (SSCA) and direct sequencing. To assess the functional consequences, Ba(2+)-sensitive K(+) currents were measured in five mutants of the core region as well as one mutant with truncated C-terminus, using the two-electrode voltage-clamp technique after an injection of mutant cRNA into Xenopus oocytes. RESULTS: Three novel ROMK mutations were identified together with six mutations described previously. The mutations were categorized into three groups: (1) amino acid exchanges in the core region (M1-H5-M2), (2) truncation at the cytosolic C-terminus, and (3) deletions of putative promoter elements. While the core mutations W99C, N124K, and I142T led to significantly reduced macroscopic K(+) currents (1 to 8% of wild-type currents), the A103V and P110L variants retained substantial K(+) conductivity (23 and 35% of wild-type currents, respectively). Coexpression of A103V and P110L, resembling the compound heterozygous state of the affected individual, further reduced macroscopic currents to 9% of the wild-type currents. All mutants in the core region exerted a dominant-negative effect on wild-type ROMK1. The C-terminal frameshift (fs) mutation (H354fs) did not change current amplitudes compared with ROMK1 wild type, suggesting that a mechanism other than alteration of the electrophysiological properties may responsible for loss of channel activity. CONCLUSIONS: Analysis of ROMK mutants linked to HPS/aBS revealed a spectrum of mechanisms accounting for loss of channel function. Further characterization of the molecular defects might be helpful for the development of new therapeutic approaches.

Cyclooxygenase-2 expression is associated with the renal macula densa of patients with Bartter-like syndrome.

BACKGROUND: Bartter-like syndrome (BLS) is a heterogeneous set of congenital tubular disorders that is associated with significant renal salt and water loss. The syndrome is also marked by increased urinary prostaglandin E2 (PGE2) excretion. In rodents, salt and volume depletion are associated with increased renal macula densa cyclooxygenase-2 (COX-2) expression. The expression of COX-2 in human macula densa has not been demonstrated. The present studies examined whether COX-2 can be detected in macula densa from children with salt-wasting BLS versus control tissues. METHODS: The intrarenal distribution of COX-2 protein and mRNA was analyzed by immunohistochemistry and in situ hybridization in 12 patients with clinically and/or genetically confirmed BLS. Renal tissue rejected for transplantation, from six adult patients not affected by BLS, was also examined. RESULTS: The expression of COX-2 immunoreactive protein was observed in cells of the macula densa in 8 out 11 patients with BLS. In situ hybridization confirmed the expression of COX-2 mRNA in the macula densa in 6 out of 10 cases. COX-2 protein was also detected in the macula densa in a patient with congestive heart failure. The expression of COX-2 immunoreactive protein was not observed in cells associated with the macula densa in kidneys from patients without disorders associated with hyper-reninemia. CONCLUSION: These studies demonstrate that COX-2 may be detected in the macula densa of humans. Since macula densa COX-2 was detected in cases of BLS, renal COX-2 expression may be linked to volume and renin status in humans, as well as in animals.

Mutations in the chloride channel gene, CLCNKB, leading to a mixed Bartter-Gitelman phenotype.

Gitelman syndrome is an inherited renal disorder characterized by impaired NaCl reabsorption in the distal convoluted tubule and secondary hypokalemic alkalosis. In clinical practice, it is distinguished from other hypokalemic tubulopathies by the presence of both hypomagnesemia and normocalcemic hypocalciuria. To date, only mutations in a single gene encoding the thiazide-sensitive NaCl cotransporter have been found as the molecular basis of GS. We describe three unrelated patients presenting with the typical laboratory findings of GS. Mutational analysis in these patients revealed no abnormality in the SLC12A3 gene. Instead, all patients were found to carry previously described mutations in the CLCNKB gene, which encodes the kidney-specific chloride channel ClC-Kb, raising the possibility of genetic heterogeneity. Review of the medical histories revealed manifestation of the disease within the first year of life in all cases. Clinical presentation included episodes of dehydration, weakness, and failure to thrive, much more suggestive of classic Bartter syndrome than of GS. The coexistence of hypomagnesemia and hypocalciuria was not present from the beginning. In the follow-up, however, a drop of both parameters below normal range was a consistent finding reflecting a transition from cBS to GS phenotype. The phenotypic overlap may indicate a physiologic cooperation of the apical thiazide-sensitive NaCl cotransporter and the basolateral chloride channel for salt reabsorption in the distal convoluted tubule.