Different taste map for amiloride sensitivity, response frequency, and threshold to NaCl in the rostral nucleus of the solitary tract in rats.

Studies on taste bud cells and brain stem relay nuclei suggest that alternative pathways convey information regarding different taste qualities. Building on the hypothesis that amiloride (epithelial Na channel antagonist)-sensitive neurons respond to palatable salt (low-concentration) and amiloride-insensitive neurons respond to aversive salt (high-concentration), we investigated the histological distribution of taste-sensitive neurons in the rostral nucleus of the solitary tract in rats and their NaCl and amiloride sensitivities. We recorded neuronal activity in extracellular single units using multi-barrel glass micropipettes and reconstructed their locations on the rostrocaudal and mediolateral axes. Seventy-three taste-sensitive neurons were categorized into the best-taste category. The amiloride sensitivities of the 31 neurons were examined for 0.1, 0.2, 0.4, and 0.8 M NaCl. The neuronal distribution of amiloride-sensitive neurons was located in the lateral region, while amiloride-insensitive neurons were located in the medial region. The amiloride-sensitive neurons responded to low salt concentrations, signaling the NaCl levels required by body fluids. Amiloride-insensitive neurons were silent at low salt concentrations but may function as warning signals for high salt concentrations. Low-threshold and/or high-response neurons were located in the rostrolateral region. In contrast, high-threshold and/or low-response neurons were located in the caudal-medial region.

Does a single oral administration of amiloride affect spontaneous arterial baroreflex sensitivity and blood pressure variability in healthy young adults?

Preclinical models indicate that amiloride (AMD) reduces baroreflex sensitivity and perturbs homeostatic blood pressure (BP) regulation. However, it remains unclear whether these findings translate to humans. This study investigated whether oral administration of AMD reduces spontaneous cardiac and sympathetic baroreflex sensitivity and perturbs BP regulation in healthy young humans. Heart rate (HR; electrocardiography), beat-to-beat BP (photoplethysmography), and muscle sympathetic activity (MSNA, microneurography) were continuously measured in 10 young subjects (4 females) during rest across two randomized experimental visits: 1) after 3 h of oral administration of placebo (PLA, 10 mg of methylcellulose within a gelatin capsule) and 2) after 3 h of oral administration of AMD (10 mg). Visits were separated for at least 48 h. We calculated the standard deviation and other indices of BP variability. Spontaneous cardiac baroreflex was assessed via the sequence technique and cardiac autonomic modulation through time- and frequency-domain HR variability. The sensitivity (gain) of the sympathetic baroreflex was determined via weighted linear regression analysis between MSNA and diastolic BP. AMD did not affect HR, BP, and MSNA compared with PLA. Indexes of cardiac autonomic modulation (time- and frequency-domain HR variability) and BP variability were also unchanged after AMD ingestion. Likewise, AMD did not modify the gain of both spontaneous cardiac and sympathetic arterial baroreflex. A single oral dose of AMD does not affect spontaneous arterial baroreflex sensitivity and BP variability in healthy young adults.NEW & NOTEWORTHY Preclinical models indicate that amiloride (AMD), a nonselective antagonist of the acid-sensing ion channels (ASICs), impairs baroreflex sensitivity and perturbs blood pressure regulation. We translated these findings into humans, investigating the impact of acute oral ingestion of AMD on blood pressure variability and spontaneous cardiac and sympathetic baroreflex sensitivity in healthy young humans. In contrast to preclinical evidence, AMD does not impair spontaneous arterial baroreflex sensitivity and blood pressure variability in healthy young adults.

Amiloride versus furosemide for the treatment of edema in patients with nephrotic syndrome: A pilot study (AMILOR).

AIM: In rodent models of nephrotic syndrome (NS), edema formation was prevented by blockade of the epithelial sodium channel ENaC with amiloride. However, apart from case reports, there is no evidence favoring ENaC blockade in patients with NS. METHODS: The monocentric randomized controlled AMILOR study investigated the antiedematous effect of amiloride (starting dose 5 mg/day, max. 15 mg/day) in comparison to standard therapy with the loop diuretic furosemide (40 mg/day, max. 120 mg/day) over 16 days. Overhydration (OH) was measured by bioimpedance spectroscopy (BCM, Fresenius). Depending on the OH response, diuretic dose was adjusted on days 2, 5, 8 and 12, and if necessary, hydrochlorothiazide (HCT) was added from d8 (12.5 mg/day, max. 25 mg/day). The primary endpoint was the decrease in OH on d8. The study was terminated prematurely due to insufficient recruitment and a low statistical power due to a low actual effect size. RESULTS: Median baseline OH was +26.4 (interquartile range 15.5-35.1)% extracellular water (ECW) in the amiloride arm and + 27.9 (24.1-29.4)% ECW in the furosemide arm and decreased by 1.95 (0.80-6.40) and 5.15 (0.90-8.30)% ECW after 8 days, respectively, and by 10.10 (1.30-14.40) and 7.40 (2.80-10.10)% ECW after 16 days, respectively. OH decrease on d8 and d16 was not significantly different between both arms. CONCLUSION: The AMILOR study is the first randomized controlled pilot study suggesting a similar antiedematous effect as furosemide. Further studies are required to better define the role of amiloride in NS (EudraCT 2019-002607-18).

Amiloride lowers plasma TNF and interleukin-6 but not interleukin-17A in patients with hypertension and type 2 diabetes.

Interleukin (IL)-17A contributes to hypertension in preclinical models. T helper 17 and dendritic cells are activated by NaCl, which could involve the epithelial Na+ channel (ENaC). We hypothesized that the ENaC blocker amiloride reduces plasma IL-17A and related cytokines in patients with hypertension. Concentrations of IL-17A, IFN-γ, TNF, IL-6, IL-1ß, and IL-10 were determined by immunoassays in plasma from two patient cohorts before and after amiloride treatment: 1) patients with type 2 diabetes mellitus (T2DM) and treatment-resistant hypertension (n = 69, amiloride 5-10 mg/day for 8 wk) and 2) patients with hypertension and type 1 diabetes mellitus (T1DM) (n = 29) on standardized salt intake (amiloride 20-40 mg/day, 2 days). Plasma and tissue from ANG II-hypertensive mice with T1DM treated with amiloride (2 mg/kg/day, 4 days) were analyzed. The effect of amiloride and benzamil on macrophage cytokines was determined in vitro. Plasma cytokines showed higher concentrations (IL-17A ∼40-fold) in patients with T2DM compared with T1DM. In patients with T2DM, amiloride had no effect on IL-17A but lowered TNF and IL-6. In patients with T1DM, amiloride had no effect on IL-17A but increased TNF. In both cohorts, blood pressure decline and plasma K+ increase did not relate to plasma cytokine changes. In mice, amiloride exerted no effect on IL-17A in the plasma, kidney, aorta, or left cardiac ventricle but increased TNF in cardiac and kidney tissues. In lipopolysaccharide-stimulated human THP-1 macrophages, amiloride and benzamil (from 1 nmol/L) decreased TNF, IL-6, IL-10, and IL-1ß. In conclusion, inhibition of ENaC by amiloride reduces proinflammatory cytokines TNF and IL-6 but not IL-17A in patients with T2DM, potentially by a direct action on macrophages.NEW & NOTEWORTHY ENaC activity may contribute to macrophage-derived cytokine release, since amiloride exerts anti-inflammatory effects by suppression of TNF and IL-6 cytokines in patients with resistant hypertension and type 2 diabetes and in THP-1-derived macrophages in vitro.

Safety and efficacy of the epithelial sodium channel blocker idrevloride in people with primary ciliary dyskinesia (CLEAN-PCD): a multinational, phase 2, randomised, double-blind, placebo-controlled crossover trial.

BACKGROUND: Mucociliary clearance is dysfunctional in people with primary ciliary dyskinesia, resulting in the accumulation of dehydrated mucus in the airways that is difficult to clear. We undertook a study to assess the benefit on lung function of treatment with a nebulised epithelial sodium channel (ENaC) blocker, idrevloride, with or without hypertonic saline, in people with primary ciliary dyskinesia. METHODS: The CLEAN-PCD trial was a phase 2, randomised, double-blind, placebo-controlled crossover trial conducted at 32 tertiary adult and paediatric care centres and university hospitals in Canada, Denmark, Germany, Italy, the Netherlands, Poland, the UK, and the USA. People with a confirmed diagnosis of primary ciliary dyskinesia, aged 12 years or older, with a percentage of predicted FEV1 (ppFEV1) in the range of 40% to <90%, were randomly assigned in a 2:2:1:1 ratio (block size=6), stratified by ppFEV1 at screening, to one of four sequences: (1) idrevloride in hypertonic saline in treatment period 1 then hypertonic saline in treatment period 2; (2) hypertonic saline in treatment period 1 then idrevloride in hypertonic saline in treatment period 2; (3) idrevloride in treatment period 1 then placebo in treatment period 2; and (4) placebo in treatment period 1 then idrevloride in treatment period 2. The idrevloride dose was 85 µg and hypertonic saline was 4·2% NaCl. 3 mL of each study treatment was nebulised twice daily for 28 days in treatment periods 1 and 2; the two 28-day treatment periods were separated by a 28-day washout period. The primary endpoint was absolute change from baseline in ppFEV1 after 28 days. Safety assessments and reports of adverse events were made at clinic visits during each treatment period and by a follow-up telephone call 28 days after the last dose of study drug. Additionally, adverse events could be reported at a follow-up telephone call 3 days after the start of dosing and as they arose. Participants who received at least one dose of study drug were included in the safety analyses (safety set), and those who also had spirometry data were included in the efficacy analyses (full analysis set). The completed study is registered (EudraCT 2015-004917-26; ClinicalTrials.govNCT02871778). FINDINGS: Between Sep 14, 2016, and May 31, 2018, 216 patients were screened and 123 were randomly assigned to one of four crossover sequences. Across the two treatment periods, treatment with idrevloride in hypertonic saline was initiated in 80 patients and completed in 78 patients (all 78 had data available and were included in the analysis); hypertonic saline initiated in 81 patients and completed in 76 patients (75 had data available and were included in the analysis); idrevloride initiated in 37 patients and completed in 35 patients (34 had data available and were included in the analysis); and placebo initiated in 36 patients and completed in 34 patients (all 34 had data available and were included in the analysis). Greater absolute increases in ppFEV1 from baseline to 28 days of treatment were seen with idrevloride in hypertonic saline (least-squares mean absolute change from baseline 1·0 percentage points, 95% CI -0·4 to 2·4) than with hypertonic saline alone (least-squares mean absolute change from baseline of -0·5 percentage points, -2·0 to 0·9; difference 1·5 percentage points, 95% CI <0·1 to 3·0; p=0·044). There was no significant difference in ppFEV1 for the parallel comparison of idrevloride in hypertonic saline compared with placebo or the crossover comparison of idrevloride with placebo. Adverse events were similar across treatments (57 to 65% of patients). Cough occurred in a greater proportion of participants during treatments that contained idrevloride or hypertonic saline compared with placebo, and oropharyngeal pain occurred in a greater proportion of participants during idrevloride treatments than during treatment with hypertonic saline alone or placebo, whereas chest discomfort was more common during treatments that included hypertonic saline. INTERPRETATION: In this phase 2 crossover study, idrevloride in hypertonic saline was safe and associated with improved lung function over a 28-day period in people with primary ciliary dyskinesia compared with hypertonic saline alone. Larger, longer clinical studies are warranted to explore the potential benefits of idrevloride in combination with hypertonic saline in people with primary ciliary dyskinesia. FUNDING: Parion Sciences, under agreement with Vertex Pharmaceuticals.

Preclinical evaluation of the epithelial sodium channel inhibitor AZD5634 and implications on human translation.

Airway dehydration causes mucus stasis and bacterial overgrowth in cystic fibrosis (CF), resulting in recurrent respiratory infections and exacerbations. Strategies to rehydrate airway mucus including inhibition of the epithelial sodium channel (ENaC) have the potential to improve mucosal defense by enhancing mucociliary clearance (MCC) and reducing the risk of progressive decline in lung function. In the current work, we evaluated the effects of AZD5634, an ENaC inhibitor that shows extended lung retention and safety profile as compared with previously evaluated candidate drugs, in healthy and CF preclinical model systems. We found that AZD5634 elicited a potent inhibition of amiloride-sensitive current in non-CF airway cells and airway cells derived from F508del-homozygous individuals with CF that effectively increased airway surface liquid volume and improved mucociliary transport (MCT) rate. AZD5634 also demonstrated efficacious inhibition of ENaC in sheep bronchial epithelial cells, translating to dose-dependent improvement of mucus clearance in healthy sheep in vivo. Conversely, nebulization of AZD5634 did not notably improve airway hydration or MCT in CF rats that exhibit an MCC defect, consistent with findings from a first single-dose evaluation of AZD5634 on MCC in people with CF. Overall, these findings suggest that CF animal models demonstrating impaired mucus clearance translatable to the human situation may help to successfully predict and promote the successful translation of ENaC-directed therapies to the clinic.

Sustained inhibition of ENaC in CF: Potential RNA-based therapies for mutation-agnostic treatment.

Disruption of the equilibrium between ion secretion and absorption processes by the airway epithelium is central to many muco-obstructive lung diseases including cystic fibrosis (CF). Besides correction of defective folding and function of CFTR, inhibition of amiloride-sensitive epithelia sodium channels (ENaC) has emerged as a bona fide therapeutic strategy to improve mucociliary clearance in patients with CF. The short half-life of amiloride-based ENaC blockers and hyperosmotic therapies have led to the development of novel RNA-based interventions for targeted and sustained reduction of ENaC expression and function in preclinical models of CF. This review summarizes the recent advances in RNA therapeutics targeting ENaC for mutation-agnostic treatment of CF.

Salt-Sensitive Hypertension of the Renal Tubular Cell-Specific NFAT5 (Nuclear Factor of Activated T-Cells 5) Knockout Mice.

[Figure: see text].

cAMP triggers Na+ absorption by distal airway surface epithelium in cystic fibrosis swine.

A controversial hypothesis pertaining to cystic fibrosis (CF) lung disease is that the CF transmembrane conductance regulator (CFTR) channel fails to inhibit the epithelial Na+ channel (ENaC), yielding increased Na+ reabsorption and airway dehydration. We use a non-invasive self-referencing Na+-selective microelectrode technique to measure Na+ transport across individual folds of distal airway surface epithelium preparations from CFTR-/- (CF) and wild-type (WT) swine. We show that, under unstimulated control conditions, WT and CF epithelia exhibit similar, low rates of Na+ transport that are unaffected by the ENaC blocker amiloride. However, in the presence of the cyclic AMP (cAMP)-elevating agents forskolin+IBMX (isobutylmethylxanthine), folds of WT tissues secrete large amounts of Na+, while CFTR-/- tissues absorb small, but potentially important, amounts of Na+. In cAMP-stimulated conditions, amiloride inhibits Na+ absorption in CFTR-/- tissues but does not affect secretion in WT tissues. Our results are consistent with the hypothesis that ENaC-mediated Na+ absorption may contribute to dehydration of CF distal airways.

Triamterene induces autophagic degradation of lysosome by exacerbating lysosomal integrity.

The maintenance of lysosomal integrity is essential for lysosome function and cell fate. Damaged lysosomes are degraded by lysosomal autophagy, lysophagy. The mechanism underlying lysophagy remains largely unknown; this study aimed to contribute to the understanding of this topic. A cell-based screening system was used to identify novel lysophagy modulators. Triamterene (6-phenylpteridine-2,4,7-triamine) was identified as one of the most potent lysophagy inducers from the screening process. We found that triamterene causes lysosomal rupture without affecting other cellular organelles and increases autophagy flux in HepG2 cells. Damaged lysosomes in triamterene-treated cells were removed by autophagy-mediated pathway, which was inhibited by depletion of the autophagy regulator, ATG5 or SQSTM1. In addition, treatment of triamterene decreased the integrity of lysosome and cell viability, which were rescued by removing the triamterene treatment in HepG2 cells. Hence, our data suggest that triamterene is a novel lysophagy inducer through the disruption of lysosomal integrity.

Contribution of Syndecans to the Cellular Entry of SARS-CoV-2.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel emerging pathogen causing an unprecedented pandemic in 21st century medicine. Due to the significant health and economic burden of the current SARS-CoV-2 outbreak, there is a huge unmet medical need for novel interventions effectively blocking SARS-CoV-2 infection. Unknown details of SARS-CoV-2 cellular biology hamper the development of potent and highly specific SARS-CoV-2 therapeutics. Angiotensin-converting enzyme-2 (ACE2) has been reported to be the primary receptor for SARS-CoV-2 cellular entry. However, emerging scientific evidence suggests the involvement of additional membrane proteins, such as heparan sulfate proteoglycans, in SARS-CoV-2 internalization. Here, we report that syndecans, the evolutionarily conserved family of transmembrane proteoglycans, facilitate the cellular entry of SARS-CoV-2. Among syndecans, the lung abundant syndecan-4 was the most efficient in mediating SARS-CoV-2 uptake. The S1 subunit of the SARS-CoV-2 spike protein plays a dominant role in the virus's interactions with syndecans. Besides the polyanionic heparan sulfate chains, other parts of the syndecan ectodomain, such as the cell-binding domain, also contribute to the interaction with SARS-CoV-2. During virus internalization, syndecans colocalize with ACE2, suggesting a jointly shared internalization pathway. Both ACE2 and syndecan inhibitors exhibited significant efficacy in reducing the cellular entry of SARS-CoV-2, thus supporting the complex nature of internalization. Data obtained on syndecan specific in vitro assays present syndecans as novel cellular targets of SARS-CoV-2 and offer molecularly precise yet simple strategies to overcome the complex nature of SARS-CoV-2 infection.

Vascular control of kidney epithelial transporters.

A major pathway in hypertension pathogenesis involves direct activation of ANG II type 1 (AT1) receptors in the kidney, stimulating Na+ reabsorption. AT1 receptors in tubular epithelia control expression and stimulation of Na+ transporters and channels. Recently, we found reduced blood pressure and enhanced natriuresis in mice with cell-specific deletion of AT1 receptors in smooth muscle (SMKO mice). Although impaired vasoconstriction and preserved renal blood flow might contribute to exaggerated urinary Na+ excretion in SMKO mice, we considered whether alterations in Na+ transporter expression might also play a role; therefore, we carried out proteomic analysis of key Na+ transporters and associated proteins. Here, we show that levels of Na+-K+-2Cl- cotransporter isoform 2 (NKCC2) and Na+/H+ exchanger isoform 3 (NHE3) are reduced at baseline in SMKO mice, accompanied by attenuated natriuretic and diuretic responses to furosemide. During ANG II hypertension, we found widespread remodeling of transporter expression in wild-type mice with significant increases in the levels of total NaCl cotransporter, phosphorylated NaCl cotransporter (Ser71), and phosphorylated NKCC2, along with the cleaved, activated forms of the α- and γ-epithelial Na+ channel. However, the increases in α- and γ-epithelial Na+ channel with ANG II were substantially attenuated in SMKO mice. This was accompanied by a reduced natriuretic response to amiloride. Thus, enhanced urinary Na+ excretion observed after cell-specific deletion of AT1 receptors from smooth muscle cells is associated with altered Na+ transporter abundance across epithelia in multiple nephron segments. These findings suggest a system of vascular-epithelial in the kidney, modulating the expression of Na+ transporters and contributing to the regulation of pressure natriuresis.NEW & NOTEWORTHY The use of drugs to block the renin-angiotensin system to reduce blood pressure is common. However, the precise mechanism for how these medications control blood pressure is incompletely understood. Here, we show that mice lacking angiotensin receptors specifically in smooth muscle cells lead to alternation in tubular transporter amount and function. Thus, demonstrating the importance of vascular-tubular cross talk in the control of blood pressure.

Ethyl isopropyl amiloride decreases oxidative phosphorylation and increases mitochondrial fusion in clonal untransformed and cancer cells.

Many cancer cells, regardless of their tissue origin or genetic landscape, have increased expression or activity of the plasma membrane Na-H exchanger NHE1 and a higher intracellular pH (pHi) compared with untransformed cells. A current perspective that remains to be validated is that increased NHE1 activity and pHi enable a Warburg-like metabolic reprogramming of increased glycolysis and decreased mitochondrial oxidative phosphorylation. We tested this perspective and find it is not accurate for clonal pancreatic and breast cancer cells. Using the pharmacological reagent ethyl isopropyl amiloride (EIPA) to inhibit NHE1 activity and decrease pHi, we observe no change in glycolysis, as indicated by secreted lactate and intracellular pyruvate, despite confirming increased activity of the glycolytic enzyme phosphofructokinase-1 at higher pH. Also, in contrast to predictions, we find a significant decrease in oxidative phosphorylation with EIPA, as indicated by oxygen consumption rate (OCR). Decreased OCR with EIPA is not associated with changes in pathways that fuel oxidative phosphorylation or with mitochondrial membrane potential but occurs with a change in mitochondrial dynamics that includes a significant increase in elongated mitochondrial networks, suggesting increased fusion. These findings conflict with current paradigms on increased pHi inhibiting oxidative phosphorylation and increased oxidative phosphorylation being associated with mitochondrial fusion. Moreover, these findings raise questions on the suggested use of EIPA-like compounds to limit metabolic reprogramming in cancer cells.

Enhanced epithelial sodium channel activity in neonatal Scnn1b mouse lung attenuates high oxygen-induced lung injury.

Prolonged oxygen therapy leads to oxidative stress, epithelial dysfunction, and acute lung injury in preterm infants and adults. Heterozygous Scnn1b mice, which overexpress lung epithelial sodium channels (ENaC), and their wild-type (WT) C57Bl6 littermates were utilized to study the pathogenesis of high fraction inspired oxygen ([Formula: see text])-induced lung injury. Exposure to high [Formula: see text] from birth to postnatal (PN) day 11 was used to model oxidative stress. Chronic exposure of newborn pups to 85% O2 increased glutathione disulfide (GSSG) and elevated the GSH/GSSG redox potential (Eh) of bronchoalveolar lavage fluid (BALF). Longitudinal X-ray imaging and Evans blue-labeled-albumin assays showed that chronic 85% O2 and acute GSSG (400 µM) exposures decreased alveolar fluid clearance (AFC) in the WT lung. Morphometric analysis of WT pups insufflated with GSSG (400 µM) or amiloride (1 µM) showed a reduction in alveologenesis and increased lung injury compared with age-matched control pups. The Scnn1b mouse lung phenotype was not further aggravated by chronic 85% O2 exposure. These outcomes support the hypothesis that exposure to hyperoxia increases GSSG, resulting in reduced lung fluid reabsorption due to inhibition of amiloride-sensitive ENaC. Flavin adenine dinucleotide (FADH2; 10 µM) was effective in recycling GSSG in vivo and promoted alveologenesis, but did not impact AFC nor attenuate fibrosis following high [Formula: see text] exposure. In conclusion, the data indicate that FADH2 may be pivotal for normal lung development, and show that ENaC is a key factor in promoting alveologenesis, sustaining AFC, and attenuating fibrotic lung injury caused by prolonged oxygen therapy in WT mice.

The Effect of Amiloride on Proteinuria in Patients with Proteinuric Kidney Disease.

INTRODUCTION: Proteinuric kidney diseases share an aggressive clinical course of developing end-stage renal disease. However, the treatment is limited. Amiloride, an epithelial sodium channel (ENaC) inhibitor, was reported to reduce proteinuria in animal studies and case reports independent of ENaC inhibition. We hypothesized that amiloride not triamterene (an analog of amiloride) would reduce proteinuria in the patients with proteinuric kidney disease. METHODS: Patients with proteinuria >1.0 g/day and estimated glomerular filtration rate (eGFR) >30 mL/min/1.73 m2 on a maximum tolerable dose of angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers were randomized to receive amiloride 5 mg twice daily or triamterene 50 mg twice daily for 8 weeks, followed by 4 weeks of washout, and then crossed over to the other drug for 8 weeks. The primary outcome was 24-h urine protein reduction. Secondary outcomes were changes in body weight, blood pressure (BP), serum potassium, and eGFR. Data were analyzed by analysis of variance. RESULTS: A total of 12 patients completed the study. Amiloride reduced 24-h urine protein by 38.7% (p = 0.002) and decreased systolic BP by 12.3 mm Hg (p = 0.04). Interestingly, triamterene reduced 24 h urine protein as well, by 32.8% (p = 0.02). Triamterene lowered eGFR by 9.0 mL/min/1.73 m2 (p = 0.007), but it was reversible. The average weight change was insignificant in both groups (p = 0.40 and 0.34 respectively). Three patients withdrew the study due to hyperkalemia. CONCLUSIONS: Both amiloride and triamterene significantly reduced proteinuria in patients with proteinuric kidney disease. The anti-proteinuric effect was additive to renin-angiotensin-aldosterone system (RAAS) blockade, given all patients were on RAAS blockade. Hyperkalemia was a safety concern. Larger trials might be needed to examine the antiproteinuric effects of ENaC inhibitors.

New generation ENaC inhibitors detach cystic fibrosis airway mucus bundles via sodium/hydrogen exchanger inhibition.

Cystic fibrosis (CF) is a recessive inherited disease caused by mutations affecting anion transport by the epithelial ion channel cystic fibrosis transmembrane conductance regulator (CFTR). The disease is characterized by mucus accumulation in the airways and intestine, but the major cause of mortality in CF is airway mucus accumulation, leading to bacterial colonization, inflammation and respiratory failure. Several drug targets are under evaluation to alleviate airway mucus obstruction in CF and one of these targets is the epithelial sodium channel ENaC. To explore effects of ENaC inhibitors on mucus properties, we used two model systems to investigate mucus characteristics, mucus attachment in mouse ileum and mucus bundle transport in piglet airways. We quantified mucus attachment in explants from CFTR null (CF) mice and tracheobronchial explants from newborn CFTR null (CF) piglets to evaluate effects of ENaC or sodium/hydrogen exchanger (NHE) inhibitors on mucus attachment. ENaC inhibitors detached mucus in the CF mouse ileum, although the ileum lacks ENaC expression. This effect was mimicked by two NHE inhibitors. Airway mucus bundles were immobile in untreated newborn CF piglets but were detached by the therapeutic drug candidate AZD5634 (patent WO, 2015140527). These results suggest that the ENaC inhibitor AZD5634 causes detachment of CF mucus in the ileum and airway via NHE inhibition and that drug design should focus on NHE instead of ENaC inhibition.

Plasminogen Deficiency and Amiloride Mitigate Angiotensin II-Induced Hypertension in Type 1 Diabetic Mice Suggesting Effects Through the Epithelial Sodium Channel.

Background Diabetic nephropathy is a common diabetes mellitus complication associated with hypertension, proteinuria, and excretion of urinary plasmin that activates the epithelial sodium channel, ENaC, in vitro. Here we hypothesized that the deletion of plasminogen and amiloride treatment protect against hypertension in diabetes mellitus. Methods and Results Male plasminogen knockout (plasminogen-deficient [Plg-/-]) and wild-type mice were rendered diabetic with streptozotocin. Arterial blood pressure was recorded continuously by indwelling catheters before and during 10 days of angiotensin II infusion (ANGII; 30-60 ng/kg per minute). The effect of amiloride infusion (2 mg/kg per day, 4 days) was tested in wild-type, diabetic ANGII-treated mice. Streptozotocin increased plasma and urine glucose concentrations and 24-hour urine albumin and plasminogen excretion. Diabetic Plg-/- mice displayed larger baseline albuminuria and absence of urine plasminogen. Baseline mean arterial blood pressure did not differ between groups. Although ANGII elevated blood pressure in wild-type, diabetic wild-type, and Plg-/- control mice, ANGII did not change blood pressure in diabetic Plg-/- mice. Compared with ANGII infusion alone, wild-type ANGII-infused diabetic mice showed blood pressure reduction upon amiloride treatment. There was no difference in plasma renin, ANGII, aldosterone, tissue prorenin receptor, renal inflammation, and fibrosis between groups. Urine from wild-type mice evoked larger amiloride-sensitive current than urine from Plg-/- mice with or without diabetes mellitus. Full-length γ-ENaC and α-ENaC subunit abundances were not changed in kidney homogenates, but the 70 kDa γ-ENaC cleavage product was increased in diabetic versus nondiabetic mice. Conclusions Plasmin promotes hypertension in diabetes mellitus with albuminuria likely through the epithelial sodium channel.

Is amiloride a promising cardiovascular medication to persist in the COVID-19 crisis?

In the ongoing coronavirus diseases-2019 (COVID-19) crisis that caused immense suffering and deaths, the choice of therapy for the prevention and life-saving conditions must be based on sound scientific evidence. Uncertainty and apprehension are exacerbated in people using angiotensin-converting enzyme (ACE) inhibitors to control their comorbidities such as hypertension and diabetes. These drugs are reported to result in unfavorable outcome as they tend to increase the levels of ACE2 which mediates the entry of SARS-CoV-2. Amiloride, a prototypic inhibitor of epithelial sodium channels (ENaC) can be an ideal candidate for COVID-19 patients, given its ACE reducing and cytosolic pH increasing effects. Moreover, its potassium-sparing and anti-epileptic activities make it a promising alternative or a combinatorial agent.

Analysis of changes in sodium and chloride ion transport in the skin.

The measurement of electric potential and resistance reflect the transport of sodium and chloride ions which take place in keratinocytes and is associated with skin response to stimuli arising from external and internal environment. The aim of the study was to assess changes in electrical resistance and the transport of chloride and sodium ions, under iso-osmotic conditions and following the use of inhibitors affecting these ions' transport, namely amiloride (A) and bumetanide (B). The experiment was performed on 104 fragments of rabbit skin, divided into three groups: control (n = 35), A-inhibited sodium transport (n = 33) and B-inhibited chloride transport (n = 36). Measurement of electrical resistance (R) and electrical potential (PD) confirmed tissue viability during the experiment, no statistically significant differences in relation to control conditions were noted. The minimal and maximal PD measured during stimulation confirmed the repeatability of the recorded reactions to the mechanical and mechanical-chemical stimulus for all examined groups. Measurement of PD during stimulation showed differences in the transport of sodium and chloride ions in each of the analyzed groups relative to the control. The statistical analysis of the PD measured in stationary conditions and during mechanical and/or mechanical-chemical stimulation proved that changes in sodium and chloride ion transport constitute the physiological response of keratinocytes to changes in environmental conditions for all applied experimental conditions. Assessment of transdermal ion transport changes may be a useful tool for assessing the skin condition with tendency to pain hyperactivity and hypersensitivity to xenobiotics.

Early Stimulation of TREK Channel Transcription and Activity Induced by Oxaliplatin-Dependent Cytosolic Acidification.

Oxaliplatin-induced peripheral neuropathy is characterized by an acute hyperexcitability syndrome triggered/exacerbated by cold. The mechanisms underlying oxaliplatin-induced peripheral neuropathy are unclear, but the alteration of ion channel expression and activity plays a well-recognized central role. Recently, we found that oxaliplatin leads to cytosolic acidification in dorsal root ganglion (DRG) neurons. Here, we investigated the early impact of oxaliplatin on the proton-sensitive TREK potassium channels. Following a 6-h oxaliplatin treatment, both channels underwent a transcription upregulation that returned to control levels after 42 h. The overexpression of TREK channels was also observed after in vivo treatment in DRG cells from mice exposed to acute treatment with oxaliplatin. Moreover, both intracellular pH and TREK channel transcription were similarly regulated after incubation with amiloride, an inhibitor of the Na+/H+ exchanger. In addition, we studied the role of oxaliplatin-induced acidification on channel behavior, and, as expected, we observed a robust positive modulation of TREK channel activity. Finally, we focused on the impact of this complex modulation on capsaicin-evoked neuronal activity finding a transient decrease in the average firing rate following 6 h of oxaliplatin treatment. In conclusion, the early activation of TREK genes may represent a mechanism of protection against the oxaliplatin-related perturbation of neuronal excitability.