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Derivatives of the potassium-sparing diuretic amiloride are preferentially cytotoxic toward tumor cells relative to normal cells, and have the capacity to target tumor cell populations resistant to currently employed therapeutic agents. However, a major barrier to clinical translation of the amilorides is their modest cytotoxic potency, with estimated IC50 values in the high micromolar range. Here we report the synthesis of ten novel amiloride derivatives and the characterization of their cytotoxic potency toward MCF7 (ER/PR-positive), SKBR3 (HER2-positive) and MDA-MB-231 (triple negative) cell line models of breast cancer. Comparisons of derivative structure with cytotoxic potency toward these cell lines underscore the importance of an intact guanidine group, and uncover a strong link between drug-induced cytotoxicity and drug lipophilicity. We demonstrate that our most potent derivative called LLC1 is preferentially cytotoxic toward mouse mammary tumor over normal epithelial organoids, acts in the single digit micromolar range on breast cancer cell line models representing all major subtypes, acts on cell lines that exhibit both transient and sustained resistance to chemotherapeutic agents, but exhibits limited anti-tumor effects in a mouse model of metastatic breast cancer. Nonetheless, our observations offer a roadmap for the future optimization of amiloride-based compounds with preferential cytotoxicity toward breast tumor cells.

Retinoids are known to improve the condition of the skin. Transepithelial transport of sodium and chloride ions is important for proper skin function. So far, the effect of applying vitamin A preparations to the skin on ion transport has not been evaluated. In the study, electrophysiological parameters, including transepithelial electric potential (PD) and transepithelial resistance (R), of rabbit skin specimens after 24 h exposure to retinol ointment (800 mass units/g) were measured in a modified Ussing chamber. The R of the fragments incubated with retinol was significantly different than that of the control skin samples incubated in iso-osmotic Ringer solution. For the controls, the PD values were negative, whereas the retinol-treated specimens revealed positive PD values. Mechanical–chemical stimulation with the use of inhibitors of the transport of sodium (amiloride) or chloride (bumetanide) ions revealed specific changes in the maximal and minimal PD values measured for the retinol-treated samples. Retinol was shown to slightly modify the transport pathways of sodium and chloride ions. In particular, an intensification of the chloride ion secretion from keratinocytes was observed. The proposed action may contribute to deep hydration and increase skin tightness, limiting the action of other substances on its surface. [ABSTRACT FROM AUTHOR]

Epithelial Na+ channels (ENaCs) are activated by proteolysis of the α and γ subunits at specific sites flanking embedded inhibitory tracts. To examine the role of α subunit proteolysis in channel activation in vivo, we generated mice lacking the distal furin cleavage site in the α subunit (αF2M mice). On a normal Na+ control diet, no differences in ENaC protein abundance in kidney or distal colon were noted between wild‐type (WT) and αF2M mice. Patch‐clamp analyses revealed similar levels of ENaC activity in kidney tubules, while no physiologically relevant differences in blood chemistry or aldosterone levels were detected. Male αF2M mice did exhibit diminished ENaC activity in the distal colon, as measured by amiloride‐sensitive short‐circuit current (ISC). Following dietary Na+ restriction, WT and αF2M mice had similar natriuretic and colonic ISC responses to amiloride. However, single‐channel activity was significantly lower in kidney tubules from Na+‐restricted αF2M mice compared with WT littermates. ENaC α and γ subunit expression in kidney and distal colon were also enhanced in Na+‐restricted αF2Mvs. WT mice, in association with higher aldosterone levels. These data provide evidence that disrupting α subunit proteolysis impairs ENaC activity in vivo, requiring compensation in response to Na+ restriction. Key points: The epithelial Na+ channel (ENaC) is activated by proteolytic cleavage in vitro, but key questions regarding the role of ENaC proteolysis in terms of whole‐animal physiology remain to be addressed.We studied the in vivo importance of this mechanism by generating a mouse model with a genetic disruption to a key cleavage site in the ENaC's α subunit (αF2M mice).We found that αF2M mice did not exhibit a physiologically relevant phenotype under normal dietary conditions, but have impaired ENaC activation (channel open probability) in the kidney during salt restriction.ENaC function at the organ level was preserved in salt‐restricted αF2M mice, but this was associated with higher aldosterone levels and increased expression of ENaC subunits, suggesting compensation was required to maintain homeostasis.These results provide the first evidence that ENaC α subunit proteolysis is a key regulator of channel activity in vivo. [ABSTRACT FROM AUTHOR]

Background/Aim: Cigarette smoke has been shown to induce a phenotype in humans known as “acquired cystic fibrosis”. This occurs because the cystic fibrosis transmembrane conductance regulator (CFTR) functions are impaired systemically due to the deleterious effects of smoke components. Elucidation of cigarette smoke effects on the tracheal epithelium is important. The aim of this study was to develop an ex vivo sheep tracheal model to investigate tracheal ion function. In this model, the epithelial sodium channel (ENaC) is inhibited after exposure to cigarette smoke extract (CSE) as a proof of principle. Materials and Methods: Tracheas were isolated from healthy sheep and the tracheal epithelium was surgically excised. Tissues were mounted in Ussing chambers and the short circuit current (Isc) was measured after incubation with 5% CSE in PBS or PBS alone for 30 min. The function of ENaC was investigated by the addition of amiloride (10–5M) apically. Western blot analysis was performed to assess differences in ENaC quantity after CSE exposure. Some specimens were stained with H&E for detection of histological alterations. Results: The amiloride effect on normal epithelium led to a significant decrease in Isc [ΔI=33±5.92 μA/cm²; p<0.001 versus control experiments (ΔI=1.44±0.71 μA/cm²)]. After incubation with CSE, ENaC Isc was significantly reduced (ΔI=14.80±1.96 μA/cm²; p<0.001). No differences in αENaC expression were observed between CSE-exposed and normal tracheal epithelium. Histological images post CSE incubation revealed decreases in the height of the epithelium, with basal cell hyperplasia and loss of ciliated cells. Conclusion: Reduced ENaC inhibition by amiloride after CSE incubation could be due to alterations in the tracheal epithelium. [ABSTRACT FROM AUTHOR]

Abstract Gitelman Syndrome (GS) is a rare autosomal-recessive tubular disorder characterized by hypokalemia, hypomagnesemia, metabolic alkalosis, hyperreninemic hyperaldosteronism, and normotension. Management of GS during pregnancy is particularly challenging due to pregnancy-associated renal physiological changes and due to controversial safety profiles regarding teratogenicity of medications commonly used for GS management in non-pregnant patients. We report a case of a 20-year-old female patient diagnosed of GS who was treated with amiloride during pregnancy and lactation due to persistent hypokalemia resistant to oral supplementation therapy. Use of amiloride facilitated control of hypokalemia and hypomagnesemia in the mother without causing any noticeable side effects in the newborn.

The SARS-CoV-2 envelope (E) protein forms a five-helix bundle in lipid bilayers whose cation-conducting activity is associated with the inflammatory response and respiratory distress symptoms of COVID-19. E channel activity is inhibited by the drug 5-(N,N-hexamethylene) amiloride (HMA). However, the binding site of HMA in E has not been determined. Here we use solid-state NMR to measure distances between HMA and the E transmembrane domain (ETM) in lipid bilayers. 13 C, 15 N-labeled HMA is combined with fluorinated or 13 C-labeled ETM. Conversely, fluorinated HMA is combined with 13 C, 15 N-labeled ETM. These orthogonal isotopic labeling patterns allow us to conduct dipolar recoupling NMR experiments to determine the HMA binding stoichiometry to ETM as well as HMA-protein distances. We find that HMA binds ETM with a stoichiometry of one drug per pentamer. Unexpectedly, the bound HMA is not centrally located within the channel pore, but lies on the lipid-facing surface in the middle of the TM domain. This result suggests that HMA may inhibit the E channel activity by interfering with the gating function of an aromatic network. These distance data are obtained under much lower drug concentrations than in previous chemical shift perturbation data, which showed the largest perturbation for N-terminal residues. This difference suggests that HMA has higher affinity for the protein-lipid interface than the channel pore. These results give insight into the inhibition mechanism of HMA for SARS-CoV-2 E.

Abstract Apparent resistant hypertension (aTRH) is a significant public health issue. Once low adherence to antihypertensive treatment has been ruled out and true resistant hypertension is diagnosed, aldosterone-direct-renin-ratio (ADRR) aids in the screening of an aldosterone-producing adenoma (APA) and primary aldosteronism (PA). Once PA and other secondary causes have been ruled out, the values of aldosterone and renin allow patients to be classified into phenotypes such as low renin hypertension (LRH), Liddle’s-like (LLph), and primary hyperaldosteronism (PAph). These classifications could aid in the treatment decision-making process. However, optimal cut-off points for these classifications remain uncertain. This study aims to assess the prevalence of these phenotypes and the behavior of different cut-offs of the ADRR in an Afro-Colombian population with apparent resistant hypertension, as well to describe their sodium consumption. Afro-descendant individuals 18 years of age or older, diagnosed with resistant hypertension and attending to a primary care center in Colombia were recruited as volunteers. As part of the study, their plasma renin concentration (PRC) and plasma aldosterone concentration (PAC) were measured. The phenotypes were categorized into three groups based on multiple cut-off points from different authors: low renin and low aldosterone phenotype (LLph), low renin and high aldosterone phenotype (PAph), and high renin and high aldosterone phenotype, referred to as the renal phenotype (Rph). The prevalence of ADRR values exceeding the cut-off and phenotypes were calculated. A linear regression model was derived to assess the effect of sodium consumption with PAC, PRC and ADRR. A total of 88 patients with aTRH were included. Adherence to at least 3 antihypertensive medications was 62.5%. The median age was 56 years (IQR 48–60), 44% were female, and 20% had diabetes. The study found that the prevalence of ADRR values exceeding the cut-off ranged from 4.5 to 23%, while low-renin hypertension (LRH) varied from 15 to 74%, Rph was found in approximately 30 to 34% of patients, PAph in 30 to 51%, and the LLph in 15 to 41%, respectively, depending on the specific cut-off value by different authors. Notably, sodium consumption was associated with lower aldosterone (β − 0.15, 95% CI [− 0.27, − 0.03]) and renin concentrations (β − 0.75, 95% CI [− 1.5, − 0.02]), but ADRR showed no significant association with sodium consumption. There were no significant differences in prevalences between the groups taking

Objective(s): Amiloride is a pyrazine compound that inhibits the reabsorption of sodium by blocking sodium channels in the cells of the renal cortex. It has demonstrated promising efficacy in the treatment of cancer in recent times. This study assessed the in vivo biodistribution of amiloride conjugated to dendrimer as a targeted agent utilizing SPECT imaging.Materials and Methods: The dendrimer was synthesised using polyethylene glycol and citric acid as precursors, and dicyclohexyl carbodiimide as a zero-order crosslinker. Amiloride was then conjugated to the dendrimer through the terminal amine group, forming an amide bond with the acidic group of the dendrimer. The synthetic particles were assessed by characterization techniques including FTIR, TEM, LC-Mass, and MAP. The response surface optimization method based on the core chemical was employed to achieve maximum labelling efficiency. The ideal circumstances and biodistribution in the in vivo environment were assessed. Results: TThe characterization findings demonstrated the effective formation and linkage of the nanoconjugate. The Radiochemical purity (RCP) of the dendrimer-amiloride complexes with Technetium-99m, achieved under ideal conditions (28 minutes of incubation, 1.4 units of reduced agent, and 17.5 mg of dendrimer-amiloride), exceeds 90%. This demonstrates the considerable potential of dendrimer-amiloride in forming complexes with Technetium-99m. The results from imaging and biodistribution tests showed that 99mTc-dendrimer–amiloride had a high level of activity (7.8 %ID/g) at the tumor site. This was due to the increased expression of sodium channel. Conclusion: The favorable characteristics and conduct of the produced nanoprobe indicate its potential as an innovative tool for the advancement of radiopharmaceutical-based medication. Furthermore, it has the capacity to envision a broad spectrum of malignancies.

Apparent resistant hypertension (aTRH) is a significant public health issue. Once low adherence to antihypertensive treatment has been ruled out and true resistant hypertension is diagnosed, aldosterone-direct-renin-ratio (ADRR) aids in the screening of an aldosterone-producing adenoma (APA) and primary aldosteronism (PA). Once PA and other secondary causes have been ruled out, the values of aldosterone and renin allow patients to be classified into phenotypes such as low renin hypertension (LRH), Liddle's-like (LLph), and primary hyperaldosteronism (PAph). These classifications could aid in the treatment decision-making process. However, optimal cut-off points for these classifications remain uncertain. This study aims to assess the prevalence of these phenotypes and the behavior of different cut-offs of the ADRR in an Afro-Colombian population with apparent resistant hypertension, as well to describe their sodium consumption. Afro-descendant individuals 18 years of age or older, diagnosed with resistant hypertension and attending to a primary care center in Colombia were recruited as volunteers. As part of the study, their plasma renin concentration (PRC) and plasma aldosterone concentration (PAC) were measured. The phenotypes were categorized into three groups based on multiple cut-off points from different authors: low renin and low aldosterone phenotype (LLph), low renin and high aldosterone phenotype (PAph), and high renin and high aldosterone phenotype, referred to as the renal phenotype (Rph). The prevalence of ADRR values exceeding the cut-off and phenotypes were calculated. A linear regression model was derived to assess the effect of sodium consumption with PAC, PRC and ADRR. A total of 88 patients with aTRH were included. Adherence to at least 3 antihypertensive medications was 62.5%. The median age was 56 years (IQR 48–60), 44% were female, and 20% had diabetes. The study found that the prevalence of ADRR values exceeding the cut-off ranged from 4.5 to 23%, while low-renin hypertension (LRH) varied from 15 to 74%, Rph was found in approximately 30 to 34% of patients, PAph in 30 to 51%, and the LLph in 15 to 41%, respectively, depending on the specific cut-off value by different authors. Notably, sodium consumption was associated with lower aldosterone (β − 0.15, 95% CI [− 0.27, − 0.03]) and renin concentrations (β − 0.75, 95% CI [− 1.5, − 0.02]), but ADRR showed no significant association with sodium consumption. There were no significant differences in prevalences between the groups taking < 3 vs ≥ 3 antihypertensive medications. Altered aldosterone-direct-renin-ratio, low renin hypertension, Liddle's-like, and primary hyperaldosteronism are prevalent phenotypes in patients within Afro-Colombian patients with apparent treatment-Resistant hypertension. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

Ubiquitination influences the expression of the epithelial Na+ channel (ENaC). We assessed the mechanisms of selective ubiquitination of the mature, cleaved form of γENaC in both native rodent kidneys and Fisher rat thyroid (FRT) cells expressing the channel heterologously. In both models, singly cleaved and fully cleaved γENaCs were strongly ubiquitinated, implying that the second cleavage releasing an inhibitory peptide was not essential for the process. To see whether location of the protein in or near the apical membrane rather than cleavage per se influences ubiquitination, we studied mutants of γENaC in which cleavage sites are abolished. These subunits were ubiquitinated only when coexpressed with α- and βENaC, facilitating trafficking through the Golgi apparatus. To test whether reaching the apical surface is necessary we performed in situ surface biotinylation and measured ENaC ubiquitination in the apical membrane of rat kidney. Ubiquitination of cleaved γENaC was similar in whole kidney and surface fractions, implying that both apical and subapical channels could be modified. In FRT cells, inhibiting clathrin-mediated endocytosis with Dyngo-4a increased both total and ubiquitinated γENaC at the cell surface. Finally, we tested the idea that increased intracellular Na+ could stimulate ubiquitination. Administration of amiloride to block Na+ entry through the channels did not affect ubiquitination of γENaC in either FRT cells or the rat kidney. However, presumed large increases in cellular Na+ produced by monensin in FRT cells or acute Na+ repletion in rats increased ubiquitination and decreased overall ENaC expression. NEW & NOTEWORTHY: We have explored the mechanisms underlying the ubiquitination of the γ subunit of epithelial Na+ channel (ENaC), a process believed to control channel internalization and degradation. We previously reported that the mature, cleaved form of the subunit is selectively ubiquitinated. Here we show that this specificity arises not from the cleavage state of the protein but from its location in the cell. We also show that under some conditions, increased intracellular Na+ can stimulate ENaC ubiquitination. [ABSTRACT FROM AUTHOR]

While there remains no universally accepted definition for resistant edema, it is generally acknowledged as edema that fails to respond to maximally administered doses of diuretics. Nephrotic edema is characterized by high levels of proteinuria, notably urinary concentrations of serine proteases, which possess the ability to activate the epithelial sodium channel (ENaC), resulting in persistent fluid retention. Loop diuretics are typically preferred as first-line therapy for hypervolemia. However, the sustained activation of ENaC channels may lead to resistance to treatment. Consequently, the blockade of ENaC represents a potential therapeutic approach. We report the case of a 36-year-old man presenting with nephrotic edema managed with a combination of furosemide and human albumin. Despite an initially favorable response, the patient subsequently developed oliguria and progressive weight gain. On the third day, a regimen comprising amiloride (5 mg/day) and hydrochlorothiazide (50 mg/day) was initiated, resulting in complete resolution of edema after 11 days. No hyperkalemia was observed, with only a slight elevation in serum creatinine levels. Although clinical trials are limited, mounting evidence from human and animal studies supports the concept of nephrotic syndrome as an overfill phenomenon and underscores the potential benefits of ENaC blockers in the management of nephrotic edema. [ABSTRACT FROM AUTHOR]

Interleukin (IL)-17A contributes to hypertension in preclinical models. T helper 17 and dendritic cells are activated by NaCl, which could involve the epithelial Naþ 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-c, TNF, IL-6, IL-1b, 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 Kþ 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-1b. 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. [ABSTRACT FROM AUTHOR]

Objective(s): Amiloride is a pyrazine compound that inhibits the reabsorption of sodium by blocking sodium channels in the cells of the renal cortex. It has demonstrated promising efficacy in the treatment of cancer in recent times. This study assessed the in vivo biodistribution of amiloride conjugated to dendrimer as a targeted agent utilizing SPECT imaging. Materials and Methods: The dendrimer was synthesised using polyethylene glycol and citric acid as precursors, and dicyclohexyl carbodiimide as a zero-order crosslinker. Amiloride was then conjugated to the dendrimer through the terminal amine group, forming an amide bond with the acidic group of the dendrimer. The synthetic particles were assessed by characterization techniques including FTIR, TEM, LC-Mass, and MAP. The response surface optimization method based on the core chemical was employed to achieve maximum labelling efficiency. The ideal circumstances and biodistribution in the in vivo environment were assessed. Results: TThe characterization findings demonstrated the effective formation and linkage of the nanoconjugate. The Radiochemical purity (RCP) of the dendrimer-amiloride complexes with Technetium- 99m, achieved under ideal conditions (28 minutes of incubation, 1.4 units of reduced agent, and 17.5 mg of dendrimer-amiloride), exceeds 90%. This demonstrates the considerable potential of dendrimer-amiloride in forming complexes with Technetium-99m. The results from imaging and biodistribution tests showed that 99mTc-dendrimer-amiloride had a high level of activity (7.8 %ID/g) at the tumor site. This was due to the increased expression of sodium channel. Conclusion: The favorable characteristics and conduct of the produced nanoprobe indicate its potential as an innovative tool for the advancement of radiopharmaceutical-based medication. Furthermore, it has the capacity to envision a broad spectrum of malignancies. [ABSTRACT FROM AUTHOR]

Obstructive sleep apnea (OSA) and hypertension are common conditions that may be linked through sympathetic activation and water retention. We hypothesized that diuretics, which reduce the body water content, may be more effective than amlodipine, a blood pressure (BP)-lowering agent implicated with edema, in controlling OSA in patients with hypertension. We also aimed to compare the effects of these treatments on ambulatory blood pressure monitoring (ABPM). In a randomized, double-blind clinical trial, we compared the effects of chlorthalidone/amiloride 25/5 mg with amlodipine 10 mg on OSA measured by portable sleep monitor and BP measured by ABPM. The study included participants older than 40 who had moderate OSA (10–40 apneas/hour of sleep) and BP within the systolic range of 140–159 mmHg or diastolic range of 90–99 mmHg. The individuals in the experimental groups were comparable in age, gender, and other relevant characteristics. Neither the combination of diuretics nor amlodipine alone reduced the AHI after 8 weeks of treatment (AHI 26.3 with diuretics and 25.0 with amlodipine. P = 0.713). Both treatments significantly lowered office, 24-h, and nighttime ABP, but the two groups had no significant difference. Chlorthalidone associated with amiloride and amlodipine are ineffective in decreasing the frequency of sleep apnea episodes in patients with moderate OSA and hypertension. Both treatments have comparable effects in lowering both office and ambulatory blood pressure. The notion that treatments could offer benefits for both OSA and hypertension remains to be demonstrated. NCT01896661. • Obstructive sleep apnea (OSA) and hypertension may be linked through sympathetic activation and water retention. • Reduction of body water diuretics is not more effective than amlodipine in controlling OSA in patients with hypertension. • Diuretics and amlodipine have equivalent blood pressure-lowering effects in individuals with OSA and hypertension. [ABSTRACT FROM AUTHOR]

Abstract It has been proposed that diuretics can improve renal tissue oxygenation through inhibition of tubular sodium reabsorption and reduced metabolic demand. However, the impact of clinically used diuretic drugs on the renal cortical and medullary microcirculation is unclear. Therefore, we examined the effects of three commonly used diuretics, at clinically relevant doses, on renal cortical and medullary perfusion and oxygenation in non‐anaesthetised healthy sheep. Merino ewes received acetazolamide (250 mg; n = 9), furosemide (20 mg; n = 10) or amiloride (10 mg; n = 7) intravenously. Systemic and renal haemodynamics, renal cortical and medullary tissue perfusion and PO2, and renal function were then monitored for up to 8 h post‐treatment. The peak diuretic response occurred 2 h (99.4 ± 14.8 mL/h) after acetazolamide, at which stage cortical and medullary tissue perfusion and PO2 were not significantly different from their baseline levels. The peak diuretic response to furosemide occurred at 1 h (196.5 ± 12.3 mL/h) post‐treatment but there were no significant changes in cortical and medullary tissue oxygenation during this period. However, cortical tissue PO2 fell from 40.1 ± 3.8 mmHg at baseline to 17.2 ± 4.4 mmHg at 3 h and to 20.5 ± 5.3 mmHg at 6 h after furosemide administration. Amiloride did not produce a diuretic response and was not associated with significant changes in cortical or medullary tissue oxygenation. In conclusion, clinically relevant doses of diuretic agents did not improve regional renal tissue oxygenation in healthy animals during the 8 h experimentation period. On the contrary, rebound renal cortical hypoxia may develop after dissipation of furosemide‐induced diuresis.

Fungal infections have become an increasing threat as a result of growing numbers of susceptible hosts and diminishing effectiveness of antifungal drugs due to multi-drug resistance. This reality underscores the need to develop novel drugs with unique mechanisms of action. We recently identified 5-(N,N-hexamethylene)amiloride (HMA), an inhibitor of human Na+/H+ exchanger isoform 1, as a promising scaffold for antifungal drug development. In this work, we carried out susceptibility testing of 45 6-substituted HMA and amiloride analogs against a panel of pathogenic fungi. A series of 6-(2-benzofuran)amiloride and HMA analogs that showed up to a 16-fold increase in activity against Cryptococcus neoformans were identified. Hits from these series showed broad-spectrum activity against both basidiomycete and ascomycete fungal pathogens, including multidrug-resistant clinical isolates.

It has been proposed that diuretics can improve renal tissue oxygenation through inhibition of tubular sodium reabsorption and reduced metabolic demand. However, the impact of clinically used diuretic drugs on the renal cortical and medullary microcirculation is unclear. Therefore, we examined the effects of three commonly used diuretics, at clinically relevant doses, on renal cortical and medullary perfusion and oxygenation in non‐anaesthetised healthy sheep. Merino ewes received acetazolamide (250 mg; n = 9), furosemide (20 mg; n = 10) or amiloride (10 mg; n = 7) intravenously. Systemic and renal haemodynamics, renal cortical and medullary tissue perfusion and PO2${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$, and renal function were then monitored for up to 8 h post‐treatment. The peak diuretic response occurred 2 h (99.4 ± 14.8 mL/h) after acetazolamide, at which stage cortical and medullary tissue perfusion and PO2${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ were not significantly different from their baseline levels. The peak diuretic response to furosemide occurred at 1 h (196.5 ± 12.3 mL/h) post‐treatment but there were no significant changes in cortical and medullary tissue oxygenation during this period. However, cortical tissue PO2${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ fell from 40.1 ± 3.8 mmHg at baseline to 17.2 ± 4.4 mmHg at 3 h and to 20.5 ± 5.3 mmHg at 6 h after furosemide administration. Amiloride did not produce a diuretic response and was not associated with significant changes in cortical or medullary tissue oxygenation. In conclusion, clinically relevant doses of diuretic agents did not improve regional renal tissue oxygenation in healthy animals during the 8 h experimentation period. On the contrary, rebound renal cortical hypoxia may develop after dissipation of furosemide‐induced diuresis. What is the central question of this study?What are the effects of commonly used diuretics on renal cortical and medullary perfusion and oxygenation in non‐anaesthetised healthy sheep?What is the main finding and its importance?Diuretic agents do not increase renal tissue oxygen tension in non‐anaesthetised healthy sheep. On the contrary, rebound cortical tissue hypoxia can develop after furosemide‐induced diuresis has dissipated. [ABSTRACT FROM AUTHOR]

Solute carrier family 26 member 4 (SLC26A4) is a member of the SLC26A transporter family and is expressed in various tissues, including the airway epithelium, kidney, thyroid, and tumors. It transports various ions, including bicarbonate, chloride, iodine, and oxalate. As a multiple-ion transporter, SLC26A4 is involved in the maintenance of hearing function, renal function, blood pressure, and hormone and pH regulation. In this review, we have summarized the various functions of SLC26A4 in multiple tissues and organs. Moreover, the relationships between SLC26A4 and other channels, such as cystic fibrosis transmembrane conductance regulator, epithelial sodium channel, and sodium chloride cotransporter, are highlighted. Although the modulation of SLC26A4 is critical for recovery from malfunctions of various organs, development of specific inducers or agonists of SLC26A4 remains challenging. This review contributes to providing a better understanding of the role of SLC26A4 and development of therapeutic approaches for the SLC26A4-associated hearing loss and SLC26A4-related dysfunction of various organs. [ABSTRACT FROM AUTHOR]

Chagas Disease has been considered "the most neglected among the neglected diseases." Only two very toxic drugs developed in the 1960s have been approved to control the disease in its acute phase and are infective in the chronic stage of the illness. It is imperative to find new molecules that can act against the causative parasite, Trypanosoma cruzi. BZ-97 is a synthetic product derived from the benzimidazole scaffold. It was tested against other human parasites, showing the best activity (IC50 = 0.76 μM) towards T. cruzi intracellular stages. The effects of BZ-97 on epimastigotes of the Y strain were analyzed. Signs of changes in the parasite homeostasis were evident by acidocalcisomes alkalinization, calcium mobilization, changes in their morphology and some signs of apoptotic events with a lack of ROS production, which is a crucial advantage over the behavior of the reference drug, benznidazole. Acidocalcisomes alkalinization was evidenced through fluorescence microscopy analysis and the use of 5-[N-ethyl-N-isopropyl] amiloride (EIPA), an inhibitor of the TcNHE pump, confirmed the involvement of this proton pump in the BZ-97-mediated acidocalcisome alkalinization. BZ-97 is presented as a potential lead compound against T. cruzi that is worthy of further studies in the future. [ABSTRACT FROM AUTHOR]

The Dja2 knockout (Dja2−/−) mice had respiratory distress, and >60% died within 2 days after birth. The surviving adult Dja2−/− mice were infertile and the lungs of Dja2−/− mice showed several abnormalities, including the processing defect of prosurfactant protein C in the alveolar epithelial type II cells and the accumulation of glycolipids in enlarged alveolar macrophages. The luminal pH of acidic organelles in Dja2−/− cells was shifted to pH 5.37–5.45. This deviated pH was immediately restored to control levels (pH 4.56–4.65) by the addition of a diuretic, ethyl isopropyl amiloride (EIPA). Although the role of DJA2 in maintaining the pH homeostasis of lysosome‐related organelles is currently obscure, this rapid and remarkable pH resilience is best explained by an EIPA‐sensitive proton efflux machinery that is disorganized and overactivated due to the loss of Dja2. [ABSTRACT FROM AUTHOR]

BACKGROUND: Kir4.2 and Kir4.1 play a role in regulating membrane transport in the proximal tubule (PT) and in the distalconvoluted- tubule (DCT), respectively. METHODS: We generated kidney-tubule-specific-AT1aR-knockout (Ks-AT1aR-KO) mice to examine whether renal AT1aR regulates Kir4.2 and Kir4.1. RESULTS: Ks-AT1aR-KO mice had a lower systolic blood pressure than Agtr1aflox/flox (control) mice. Ks-AT1aR-KO mice had a lower expression of NHE3 (Na+/H+-exchanger 3) and Kir4.2, a major Kir-channel in PT, than Agtr1aflox/flox mice. Whole-cell recording also demonstrated that the membrane potential in PT of Ks-AT1aR-KO mice was lesser negative than Agtr1aflox/flox mice. The expression of Kir4.1 and Kir5.1, Kir4.1/Kir5.1-mediated K+ currents of DCT and DCT membrane potential in Ks-AT1aR-KO mice, were similar to Agtr1aflox/flox mice. However, angiotensin II perfusion for 7 days hyperpolarized the membrane potential in PT and DCT of the control mice but not in Ks-AT1aR-KO mice, while angiotensin II perfusion did not change the expression of Kir4.1, Kir4.2, and Kir5.1. Deletion of AT1aR did not significantly affect the expression of αENaC (epithelial Na+ channel) and βENaC but increased cleaved γENaC expression. Patch-clamp experiments demonstrated that deletion of AT1aR increased amiloride-sensitive Na+-currents in the cortical-collecting duct but not in late-DCT. However, tertiapin-Q sensitive renal outer medullary potassium channel currents were similar in both genotypes. CONCLUSIONS: AT1aR determines the baseline membrane potential of PT by controlling Kir4.2 expression/activity but AT1aR is not required for determining the baseline membrane potential of the DCT and Kir4.1/Kir5.1 activity/expression. However, AT1aR is required for angiotensin II--induced hyperpolarization of basolateral membrane of PT and DCT. Deletion of AT1aR had no effect on baseline renal outer medullary potassium channel activity but increased ENaC activity in the CCD. [ABSTRACT FROM AUTHOR]

This study was undertaken to investigate the interaction between the sodium channel blocker amiloride (AML) and human serum albumin (HSA). A combination of multi-spectroscopic techniques and computational methods were employed to identify the AML binding site on HSA and the forces responsible for the formation of the HSA–AML complex. Our findings revealed that AML specifically binds to Sudlow's site II, located in subdomain IIIA of HSA, and that the complex formed is stabilized using van der Waals hydrogen-bonding and hydrophobic interactions. FRET analysis showed that the distance between AML and Trp214 was optimal for efficient quenching. UV-Vis spectroscopy and circular dichroism indicated minor changes in the structure of HSA after AML binding, and molecular dynamics simulations (MDS) conducted over 100 ns provided additional evidence of stable HSA–AML-complex formation. This study enhances understanding of the interaction between AML and HSA and the mechanism responsible. [ABSTRACT FROM AUTHOR]

Background: Malignant ascites commonly occurs in advanced or recurrent stages of epithelial ovarian cancer during peritoneal carcinomatosis and is correlated with poor prognosis. Due to its complex composition of cellular and acellular components malignant ascites creates a unique tumor microenvironment, which mediates immunosuppression and promotes progression of disease. However, the immunosuppressive mechanisms remain poorly understood. Methods: In the present study, we explored the antitumor activity of healthy donor NK and T cells directed against ovarian cancer cells in presence of malignant ascites derived from patients with advanced or recurrent peritoneal carcinomatosis. A wide range of methods was used to study the effect of ascites on NK and T cells (FACS, ELISA, EliSpot, qPCR, Live-cell and confocal microscopy, Western blot and electrolyte flux assays). The ascites components were assessed using quantitative analysis (nephelometry, potentiometry and clinical chemistry) and separation methods (dialysis, ultracentrifugal filtration and lipid depletion). Results: Ascites rapidly inhibited NK cell degranulation, tumor lysis, cytokine secretion and calcium signaling. Similarly, target independent NK and T cell activation was impaired in ascites environment. We identified imbalanced electrolytes in ascites as crucial factors causing extensive immunosuppression of NK and T cells. Specifically, high sodium, low chloride and low potassium content significantly suppressed NK-mediated cytotoxicity. Electrolyte imbalance led to changes in transcription and protein expression of electrolyte channels and impaired NK and T cell activation. Selected inhibitors of sodium electrolyte channels restored intracellular calcium flux, conjugation, degranulation and transcript expression of signaling molecules. The levels of ascites-mediated immunosuppression and sodium/chloride/potassium imbalance correlated with poor patient outcome and selected molecular alterations were confirmed in immune cells from ovarian cancer patients. Conclusion: Our data suggest a novel electrolyte-based mechanism of immunosuppression in malignant ascites of patients with peritoneal carcinomatosis. We show for the first time that the immunosuppression of NK cytotoxicity in coculture assays is correlated to patient poor survival. Therapeutic application of sodium channel inhibitors may provide new means for restoring immune cell activity in ascites or similar electrolyte imbalanced environments. [ABSTRACT FROM AUTHOR]

Background: Data on diuretic treatment in nephrotic syndrome (NS) are scarce. Our goal was to assess the non-inferiority of the combined oral diuretics (furosemide/hydrochlorothiazide/amiloride) compared to intravenous (i.v.) furosemide in patients with NS and resistant edema. Methods: We conducted a prospective randomized trial on 22 patients with resistant nephrotic edema (RNE), defined as hypervolemia and a FENa < 0.2%. Based on a computer-generated 1:1 randomization, we assigned patients to receive either intravenous furosemide (40 mg bolus and then continuous administration of 5 mg/h) or oral furosemide (40 mg/day) and hydrochlorothiazide/amiloride (50/5 mg/day) for a period of 5 days. Clinical and laboratory measurements were performed daily. Hydration status was assessed by bioimpedance on day 1 and at the end of day 5 after treatment initiation. The primary endpoint was weight change from baseline to day 5. Secondary endpoints were hydration status change measured by bioimpedance and safety outcomes (low blood pressure, severe electrolyte disturbances, acute kidney injury and worsening hypervolemia). Results: Primary endpoint analysis showed that after 5 days of treatment, there was a significant difference in weight change from baseline between groups [adjusted mean difference: −3.33 kg (95% CI: −6.34 to −0.31), p = 0.03], with a higher mean weight change in the oral diuretic treatment group [−7.10 kg (95% CI: −18.30 to −4.30) vs. −4.55 kg (95%CI: −6.73 to −2.36)]. Secondary endpoint analysis showed that there was no significant difference between groups regarding hydration status change [adjusted mean difference: −0.05 L (95% CI: −2.6 to 2.6), p = 0.96], with a mean hydration status change in the oral diuretic treatment group of −4.71 L (95% CI: −6.87 to −2.54) and −3.91 L (95% CI: −5.69 to −2.13) in the i.v. diuretic treatment group. We observed a significant decrease in adjusted mean serum sodium of −2.15 mmol/L [(95% CI: −4.25 to −0.05), p = 0.04]), favored by the combined oral diuretic treatment [−2.70 mmol/L (95% CI: −4.89 to −0.50) vs. −0.10 mmol/L (95%CI: −1.30 to 1.10)]. No statistically significant difference was observed between the two groups in terms of adverse events. Conclusions: A combination of oral diuretics based on furosemide, amiloride and hydrochlorothiazide is non-inferior to i.v. furosemide in weight control of patients with RNE and a similar safety profile. [ABSTRACT FROM AUTHOR]

The present study proposes two straightforward, responsive and inveterate spectrophotometric techniques for the detection of amiloride hydrochloride. The methodologies are mainly relay on the generation of charge transfer complex, with the reagents 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (Method A) and p-chloranilic acid (Method B), hence an enduring 1:1 stoichiometric complex were accomplished, which are yellow and pink colour correspondingly. The generated chromogens optical densities were measured at 476 and 508 nm respectively. Beer's law been tested in the range of 5-30 µg.ml-1 and 1-6 µg.ml-1. The other analytical parameters like, Limit of Detection (LOD), Limit of Quantification (LOQ), accuracy and precisions were examined. The mentioned approaches were successfully adopted for the determination of the amiloride hydrochloride in tablet formulation with high accuracy, better recoveries and acceptable relative standard deviation. [ABSTRACT FROM AUTHOR]

The article presents a study which showed that the repeated cross-fostering (RCF) paradigm of early maternal separation is associated with enhancements of distinct homeostatic reactions. Topics include RCF-induced altered homeostatic responses across three generations, enhanced Asic transcripts in specific brain areas across three generations, and single-dose nebulized amiloride renormalization of homeostatic responses across three generations.

Albuminuria in kidney transplant recipients (KTRs) is associated with hypertension and aberrant glomerular filtration of serine proteases that may proteolytically activate the epithelial Na+ channel (ENaC). The present nonrandomized, pharmacodynamic intervention study aimed to investigate if inhibition of ENaC increases Na+ excretion and reduces extracellular volume in KTRs dependent on the presence of albuminuria. KTRs with and without albuminuria (albumin-to-creatinine ratio > 300 mg/g, n = 7, and <30 mg/g, n = 7, respectively) were included and ingested a diet with fixed Na+ content (150 mmol/day) for 5 days. On the last day, amiloride at 10 mg was administered twice. Body weight, 24-h urine electrolyte excretion, body water content, and ambulatory blood pressure as well as plasma renin, angiotensin II, and aldosterone concentrations were determined before and after amiloride. Amiloride led to a significant decrease in body weight, increase in 24-h urinary Na+ excretion, and decrease in 24-h urinary K+ excretion in both groups. Urine output increased in the nonalbuminuric group only. There was no change in plasma renin, aldosterone, and angiotensin II concentrations after amiloride, whereas a significant decrease in nocturnal systolic blood pressure and increase in 24-h urine aldosterone excretion was observed in albuminuric KTRs only. There was a significant correlation between 24-h urinary albumin excretion and amiloride-induced 24-h urinary Na+ excretion. In conclusion, ENaC activity contributes to Na+ and water retention in KTRs with and without albuminuria. ENaC is a relevant pharmacological target in KTRs; however, larger and long-term studies are needed to evaluate whether the magnitude of this effect depends on the presence of albuminuria. NEW & NOTEWORTHY Amiloride has a significant natriuretic effect in kidney transplant recipients (KTRs) that relates to urinary albumin excretion. The epithelial Na+ channel may be a relevant direct pharmacological target to counter Na+ retention and hypertension in KTRs. Epithelial Na+ channel blockers should be further investigated as a mean to mitigate Na+ and water retention and to potentially obtain optimal blood pressure control in KTRs. [ABSTRACT FROM AUTHOR]

Background: Zirconium Oxide (ZrO2) is one of the most widely used metal oxide nanoparticles with unique features that permit its usage in various medical applications, including drug delivery, targeting, labelling, and loading. Rutin is a bioflavonoid found in various natural sources and has diverse biological activities and pharmaceutical applications. Some studies have evaluated the impacts of ZrO2 NPs on aquatic creatures, but little is known about their ability to recover after exposure. Since the toxicity of ZrO2 nanoparticles is not known, it would be crucial to investigate their toxicity using zebrafish (Danio rerio) as a model organism. Objectives: In the present work, the toxicity of ZrO2 was investigated in Danio rerio using behavioural alterations, biomarkers of oxidative stress and cellular damage. The morphology of the gill tissues, as well as the optimal amount of rutin for mitigating deleterious effects was evaluated. Materials and Methods: Fish were treated for 14 days, and seven study groups were examined: control, ZrO2 exposure alone at three distinct concentrations (5 mg/L, 10 mg/L, and 20 mg/L), and combined with rutin (100 mg/L). Results: Compared to control groups, Danio rerio treated with ZrO2 alone or in combination with rutin produced worse outcomes. However, rutin-supplemented groups exhibited greater improvement than ZrO2 alone groups. ZrO2 affects cells by causing oxidative stress and decreasing the antioxidants SOD, CAT, GPx, GSH, and Vitamin C. Enhanced oxidative stress induces behavioural and morphological modifications. The structural examination of the gill tissues revealed hyperplasia, lamellar fusion, filament erosion, and a dilated marginal channel or epithelial lifting. Conclusion: According to our data, the sub-lethal concentration of ZrO2 NPs for Danio rerio is 10 mg/L. Although ZrO2 was detrimental to the groups exposed to it, supplementing 100 mg/L of rutin was able to protect against its toxicity. [ABSTRACT FROM AUTHOR]

ASIC channels are bilaterian proton-gated sodium channels belonging to the large and functionally-diverse Deg/ENaC family that also includes peptide- and mechanically-gated channels. Here, we report that the non-bilaterian invertebrate Trichoplax adhaerens possesses a proton-activated Deg/ENaC channel, TadNaC2, with a unique combination of biophysical features including tachyphylaxis like ASIC1a, reduced proton sensitivity like ASIC2a, biphasic macroscopic currents like ASIC3, as well as low sensitivity to the Deg/ENaC channel blocker amiloride and Ca2+ ions. Structural modeling and mutation analyses reveal that TadNaC2 proton gating is different from ASIC channels, lacking key molecular determinants, and involving unique residues within the palm and finger regions. Phylogenetic analysis reveals that a monophyletic clade of T. adhaerens Deg/ENaC channels, which includes TadNaC2, is phylogenetically distinct from ASIC channels, instead forming a clade with BASIC channels. Altogether, this work suggests that ASIC-like channels evolved independently in T. adhaerens and its phylum Placozoa. Our phylogenetic analysis also identifies several clades of uncharacterized metazoan Deg/ENaC channels, and provides phylogenetic evidence for the existence of Deg/ENaC channels outside of Metazoa, present in the gene data of select unicellular heterokont and filasterea-related species. The non-bilaterian Trichoplax adhaerens has a proton-activated Deg/ENaC channel with ASIC-like biophysical properties but distinct determinants for proton gating. Phylogenetic evidence for the existence of Deg/ENaC channels outside of animals is also provided. [ABSTRACT FROM AUTHOR]

Although estuarine diatoms have a wide range of salt tolerance, they are often severely stressed by elevated salt concentrations. It remains poorly understood how estuarine diatoms maintain ionic homeostasis under high-salinity conditions. Using a scanning ion-selective electrode technique, this study determined the fluxes of H+, Na+, and K+ involved in the acclimatization of the estuarine diatom Coscinodiscus centralis Ehrenberg after an elevation in salinity from 15 psu to 35 psu. The C. centralis cells exhibited marked H+ effluxes after a transient treatment (TT, 30 min) and short-term treatment (ST, 24 h). However, a drastic shift of H+ efflux toward an influx was induced in the long-term treatment (LT, 10 days). The Na+ flux under TT, ST, and LT salinity conditions was found to accelerate the Na+ efflux. More pronounced effects were observed under the ST and LT salinity conditions compared to the TT salinity condition. The K+ influx showed a significant increase under the LT salinity condition. However, the salinity-induced Na+/H+ exchange in the estuarine diatom was inhibited by amiloride and sodium orthovanadate. These results indicate that the Na+ extrusion in salt-stressed cells is mainly the result of an active Na+/H+ antiport across the plasma membrane. The pattern of ion fluxes under the TT and ST salinity conditions were different from those under the LT salinity conditions, suggesting an incomplete regulation of the acclimation process in the estuarine diatom under short-term salinity stress. [ABSTRACT FROM AUTHOR]

Hypertension is one of the leading causes of death globally and a major risk factor for different cardiovascular outcomes. This led to continuous discovery of new drugs and on-going update of drug combinations. In the present work, sustainable eco-friendly spectrophotometric methods were developed and validated for the estimation of amiloride hydrochloride (AML), hydrochlorothiazide (HCT) and timolol maleate (TIM) in their ternary pharmaceutical formulation. The proposed methods are inspired based on the unique spectral characteristics of this mixture including spectral extension of AML over both HCT and TIM spectra. AML exhibits UV maximum at 362.0 nm that permits its direct estimation by zero order spectrophotometric method without any interference in a linear range of 2.0–20 μg/mL. While for the estimation of HCT and TIM, two methods were applied. The first method is dual wavelength in ratio spectra, while the second one is ratio subtraction in conjunction with the first derivative of ratio spectra method. The two methods were found linear over the concentration range of 2.0–25 µg/mL for HCT and 5–80 µg/mL for TIM. The suggested methods were successfully adopted for the evaluation of the studied drugs in their marketed dosage form and further implemented for content uniformity evaluation. Additionally, method greenness profile was assessed using different assessment metrics. [ABSTRACT FROM AUTHOR]

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.

SARS-CoV-2 is the novel coronavirus that is the causative agent of COVID-19, a sometimes-lethal respiratory infection responsible for a world-wide pandemic. The envelope (E) protein, one of four structural proteins encoded in the viral genome, is a 75-residue integral membrane protein whose transmembrane domain exhibits ion channel activity and whose cytoplasmic domain participates in protein-protein interactions. These activities contribute to several aspects of the viral replication-cycle, including virion assembly, budding, release, and pathogenesis. Here, we describe the structure and dynamics of full-length SARS-CoV-2 E protein in hexadecylphosphocholine micelles by NMR spectroscopy. We also characterized its interactions with four putative ion channel inhibitors. The chemical shift index and dipolar wave plots establish that E protein consists of a long transmembrane helix (residues 8-43) and a short cytoplasmic helix (residues 53-60) connected by a complex linker that exhibits some internal mobility. The conformations of the N-terminal transmembrane domain and the C-terminal cytoplasmic domain are unaffected by truncation from the intact protein. The chemical shift perturbations of E protein spectra induced by the addition of the inhibitors demonstrate that the N-terminal region (residues 6-18) is the principal binding site. The binding affinity of the inhibitors to E protein in micelles correlates with their antiviral potency in Vero E6 cells: HMA ≈ EIPA > DMA >> Amiloride, suggesting that bulky hydrophobic groups in the 5' position of the amiloride pyrazine ring play essential roles in binding to E protein and in antiviral activity. An N15A mutation increased the production of virus-like particles, induced significant chemical shift changes from residues in the inhibitor binding site, and abolished HMA binding, suggesting that Asn15 plays a key role in maintaining the protein conformation near the binding site. These studies provide the foundation for complete structure determination of E protein and for structure-based drug discovery targeting this protein.