Amiloride: A review

Acid-sensing ion channel 1 in nucleus tractus solitarii neurons contributes to the enhanced CO2-stimulated cardiorespiratory effect in spontaneously hypertensive rats

AIMS

Activation of central respiratory chemoreceptors provides excitatory drive to both respiratory and sympathetic outputs. The enhanced respiratory-sympathetic coupling contributes to the onset and development of hypertension. However, the specific central targets and molecular mechanisms involved in this process remain elusive. This study aimed to investigate the role of acid-sensing ion channel 1 (ASIC1) in nucleus tractus solitarii (NTS) neurons in CO2-stimulated cardiorespiratory effects in spontaneously hypertensive rats (SHRs).

MAIN METHODS

Respiration and blood pressure of conscious rats were recorded by whole-body plethysmography and telemetry, respectively. Western blot was used to detect the expression difference of ASIC1 protein in NTS region between Wistar-Kyoto (WKY) rats and SHRs. Excitability of NTS neurons were assessed by extracellular recordings.

KEY FINDINGS

Compared to WKY rats, the enhanced CO2-stimulated cardiopulmonary effect and up-regulation of ASIC1 in the NTS were already observed in 4-week-old prehypertensive SHRs. Furthermore, specific blockade of ASIC1 effectively attenuated the CO2-stimulated increase in firing rate of NTS neurons in anesthetized adult SHRs. Intracerebroventricular injections of the ASIC1a blocker PcTx1 or knockdown Asic1 in NTS neurons significantly reduced the heightened CO2-stimulated ventilatory response, and diminished the CO2-stimulated increase in arterial pressure and heart rate in adult SHRs.

SIGNIFICANCE

These findings showed that dysregulated ASIC1 signaling in the NTS contribute to the exaggerated CO2-stimulated cardiorespiratory effects observed in SHRs.

Amiloride reduces fructosamine-3-kinase expression to restore sunitinib sensitivity in renal cell carcinoma

The kidney is a vital organ responsible for water and sodium metabolism, while the primary function of amiloride is to promote the excretion of water and sodium. We investigated amiloride enhanced the sunitinib sensitivity in RCC. We found both sunitinib and amiloride displayed cytotoxicity and exerted the synergy effect in RCC cells in vivo and in vitro arrays. Protein expression profiles were screened via MS/TMT, revealing that FN3K was upregulated in the sunitinib group, and rescued in amiloride and the combination administration. Exogenous FN3K could promote proliferation, invasion and metastasis and decrease the sensitivity of Caki-1 cells to sunitinib, also, exogenous FN3K up-regulated VEGFR2 expression and activated AKT/mTOR signal pathway. More FN3K and VEGFR2 accumulated in R-Caki-1 cells and rescued by amiloride treatment. Co-IP and IF confirmed the interaction between FN3K and VEGFR2. In conclusion, FN3K depletion mediated VEGFR2 disruption promotes amiloride synergized the anti-RCC activity of sunitinib.

Effects of furosemide, acetazolamide and amiloride on renal cortical and medullary tissue oxygenation in non-anaesthetised healthy sheep

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 andP O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ , 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 andP O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ 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 tissueP O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ 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.

Evaluation of the translation of multiple cardiovascular regulatory mechanisms in the anesthetized dog

The strategic and targeted use of an anesthetized canine cardiovascular model early in drug discovery enables a comprehensive cardiovascular and electrophysiological assessment of potential safety liabilities and guides compound selection prior to initiation of chronic toxicological studies. An ideal model would enable exposure-response relationships to guide safety margin calculations, have a low threshold to initiate, and have quick delivery of decision quality data. We have aimed to profile compounds with diverse mechanism of actions (MoAs) of "non-QT" cardiovascular drug effects and evaluate the ability of nonclinical in vivo cardiovascular models to detect clinically reported effects. The hemodynamic effects of 11 drugs (atropine, itraconazole, atenolol, ivabradine, milrinone, enalaprilat, fasudil, amlodipine, prazosin, amiloride, and hydrochlorothiazide) were profiled in an anesthetized dog cardiovascular model. Derived parameters included: heart rate, an index of left ventricular contractility, mean arterial pressure, systemic vascular resistance, and cardiac output. Species specific plasma protein data was generated (human, dog) and utilized to calculate free drug concentrations. Using the anesthetized dog cardiovascular model, 10 of the 11 drugs displayed the predicted changes in CV parameters based on their primary MoAs and corresponding clinically described effects. Interestingly but not unexpected, 1 of 11 failed to display their predicted CV pattern which is likely due to a delay in pharmacodynamic effect that is beyond the duration of the experimental model (hydrochlorothiazide). The analysis from the current study supports the strategic use of the anesthetized dog model early in the drug discovery process for a comprehensive cardiovascular evaluation with good translation to human.

Role of paraoxonase 3 in regulating ENaC-mediated Na+ transport in the distal nephron

Paraoxonase 3 (PON3) is expressed in the aldosterone-sensitive distal nephron, where filtered Na+ is reabsorbed mainly via the epithelial Na+ channel (ENaC) and Na+ -coupled co-transporters. We previously showed that PON3 negatively regulates ENaC through a chaperone mechanism. The present study aimed to determine the physiological role of PON3 in renal Na+ and K+ homeostasis. Pon3 knockout (KO) mice had higher amiloride-induced natriuresis and lower plasma [K+ ] at baseline. Single channel recordings in split-open tubules showed that the number of active channels per patch was significantly higher in KO mice, resulting in a higher channel activity in the absence of PON3. Although whole kidney abundance of ENaC subunits was not altered in Pon3 KOs, ENaC gamma subunit was more apically distributed within the connecting tubules and cortical collecting ducts of Pon3 KO kidneys. Additionally, small interfering RNA-mediated knockdown of PON3 in cultured mouse cortical collecting duct cells led to an increased surface abundance of ENaC gamma subunit. As a result of lower plasma [K+ ], sodium chloride co-transporter phosphorylation was enhanced in the KO kidneys, a phenotype that was corrected by a high K+ diet. Finally, PON3 expression was upregulated in mouse kidneys under dietary K+ restriction, potentially providing a mechanism to dampen ENaC activity and associated K+ secretion. Taken together, our results show that PON3 has a role in renal Na+ and K+ homeostasis through regulating ENaC functional expression in the distal nephron. KEY POINTS: Paraoxonase 3 (PON3) is expressed in the distal nephron of mouse kidneys and functions as a molecular chaperone to reduce epithelial Na+ channel (ENaC) expression and activity in heterologous expression systems. We examined the physiological role of PON3 in renal Na+ and K+ handling using a Pon3 knockout (KO) mouse model. At baseline, Pon3 KO mice had lower blood [K+ ], more functional ENaC in connecting tubules/cortical collecting ducts, higher amiloride-induced natriuresis, and enhanced sodium chloride co-transporter (NCC) phosphorylation. Upon challenge with a high K+ diet, Pon3 KO mice had normalized blood [K+ ] and -NCC phosphorylation but lower circulating aldosterone levels compared to their littermate controls. Kidney PON3 abundance was altered in mice under dietary K+ loading or K+ restriction, providing a potential mechanism for regulating ENaC functional expression and renal Na+ and K+ homeostasis in the distal nephron.

Biomarkers to Guide Medical Therapy in Primary Aldosteronism

Primary aldosteronism (PA) is an endocrinopathy characterized by dysregulated aldosterone production that occurs despite suppression of renin and angiotensin II, and that is non-suppressible by volume and sodium loading. The effectiveness of surgical adrenalectomy for patients with lateralizing PA is characterized by the attenuation of excess aldosterone production leading to blood pressure reduction, correction of hypokalemia, and increases in renin-biomarkers that collectively indicate a reversal of PA pathophysiology and restoration of normal physiology. Even though the vast majority of patients with PA will ultimately be treated medically rather than surgically, there is a lack of guidance on how to optimize medical therapy and on key metrics of success. Herein, we review the evidence justifying approaches to medical management of PA and biomarkers that reflect endocrine principles of restoring normal physiology. We review the current arsenal of medical therapies, including dietary sodium restriction, steroidal and nonsteroidal mineralocorticoid receptor antagonists, epithelial sodium channel inhibitors, and aldosterone synthase inhibitors. It is crucial that clinicians recognize that multimodal medical treatment for PA can be highly effective at reducing the risk for adverse cardiovascular and kidney outcomes when titrated with intention. The key biomarkers reflective of optimized medical therapy are unsurprisingly similar to the physiologic expectations following surgical adrenalectomy: control of blood pressure with the fewest number of antihypertensive agents, normalization of serum potassium without supplementation, and a rise in renin. Pragmatic approaches to achieve these objectives while mitigating adverse effects are reviewed.

Diagnosis and management of primary hyperaldosteronism in patients with hypertension: a practical approach endorsed by the British and Irish Hypertension Society

Alongside the lack of homogeneity among international guidelines and consensus documents on primary hyperaldosteronism, the National UK guidelines on hypertension do not provide extensive recommendations regarding the diagnosis and management of this condition. Local guidelines vary from area to area, and this is reflected in the current clinical practice in the UK. In an attempt to provide support to the clinicians involved in the screening of subjects with hypertension and clinical management of suspected cases of primary hyperaldosteronism the following document has been prepared on the behalf of the BIHS Guidelines and Information Service Standing Committee. Through remote video conferences, the authors of this document reviewed an initial draft which was then circulated among the BIHS Executive members for feedback. A survey among members of the BIHS was carried out in 2022 to assess screening strategies and clinical management of primary hyperaldosteronism in the different regions of the UK. Feedback and results of the survey were then discussed and incorporated in the final document which was approved by the panel after consensus was achieved considering critical review of existing literature and expert opinions. Grading of recommendations was not performed in light of the limited available data from properly designed randomized controlled trials.

Pharmacological Considerations in the Interpretation of Biochemical Results in Diabetic Patients with Cardiovascular Complications

Diabetes mellitus with cardiovascular diseases is often a multi-systemic disease that requires a multi-therapeutic approach which mostly poses a challenge to laboratory result interpretation. The non-availability of information on many patients due to poor referral, documentation and record keeping has resulted in isolated interpretation of laboratory result of diabetic patients with multisystemic complications. This has led to both analytical and post-analytical errors which has a negative impact on total quality of results. Therefore, this review showed the possible therapeutic treatment of a diabetic patient with cardiovascular disease and how their pharmacological role could affect laboratory result.

Role of Extracellular Vesicles in the Propagation of Lung Fibrosis in Systemic Sclerosis

OBJECTIVES

Systemic sclerosis (SSc) has the highest mortality rate among the rheumatic diseases, with lung fibrosis leading as the cause of death. A characteristic of severe SSc-related lung fibrosis is its progressive nature. Although most research has focused on the pathology of the fibrosis, the mechanism mediating the fibrotic spread remains unclear. We hypothesized that extracellular vesicle (EV) communication drives the propagation of SSc lung fibrosis.

METHODS

EVs were isolated from normal (NL) or SSc-derived human lungs and primary lung fibroblasts (pLFs). EVs were also isolated from human fibrotic lungs and pLFs induced experimentally with transforming growth factor-β (TGFβ). Fibrotic potency of EVs was assessed using functional assays in vitro and in vivo. Transmission electron microscopy, nanoparticle tracking analysis, real-time quantitative polymerase chain reaction (RT-qPCR), immunoblotting, and immunofluorescence were used to analyze EVs, their cargo, extracellular matrix (ECM) fractions, and conditioned media.

RESULTS

SSc lungs and pLFs released significantly more EVs than NL lungs, and their EVs showed increased fibrotic content and activity. TGFβ-stimulated NL lung cores and pLFs increased packaging of fibrotic proteins, including fibronectin, collagens, and TGFβ, into released EVs. The EVs induced a fibrotic phenotype in recipient pLFs and in vivo in mouse lungs. Furthermore, EVs interacted with and contributed to the ECM. Finally, suppressing EV release in vivo reduced severity of murine lung fibrosis.

CONCLUSIONS

Our findings highlight EV communication as a novel mechanism for propagation of SSc lung fibrosis. Identifying therapies that reduce EV release, activity, and/or fibrotic cargo in SSc patient lungs may be a viable therapeutic strategy to improve fibrosis.

Diuretic, Natriuretic, And Ca2+-Sparing Effect Of The Alkaloid Boldine In Rats

BACKGROUND

Previous studies indicate the renal vasodilating effects of boldine, an alkaloid found in Peumus boldus. However, its potential to induce diuresis still needs to be studied.

METHODS

Wistar rats were used and the urine volume was noted for 8 h and further studied.

RESULTS

The acute treatment at 0.1 and 0.3 mg/kg of boldine showed a diuretic, natriuretic, and Ca2+-sparing effect in rats without changing the urinary elimination of K+and Cl-. When boldine was given in combination with hydrochlorothiazide, there was an increase in urinary volume compared to the vehicle group. However, this was not different from the treatments in its isolated form. Urine Ca2+values ​​remained low but were not enhanced by this association. The excretion of Na+and Cl- was significantly increased compared to the group that received only vehicle or boldine. On the other hand, although the association of amiloride plus boldine did not result in a diuretic effect, the increase in Na+and the reduction in K+excretion were significantly potentiated. Furthermore, in the presence of the non-selective muscarinic receptor antagonist atropine, boldine showed reduced capacity to increase urinary volume, maintaining the natriuretic and Ca2+-sparing effect, besides a very evident K+-sparing action. Similar results were obtained in the presence of the non-selective cyclooxygenase inhibitor indomethacin. Furthermore, boldine showed an ex vivo antiurolithiasis activity, reducing calcium oxalate's precipitation and crystallization.

CONCLUSIONS

This study reveals the diuretic, natriuretic, Ca2+-sparing, and antiurolithiatic effects of boldine, an action possibly related to muscarinic receptor activation and prostanoid generation.

Caco-2 Cell Line Standardization with Pharmaceutical Requirements and In Vitro Model Suitability for Permeability Assays

The Caco-2 cell line derived from human colon carcinoma is commonly used to assess the permeability of compounds in in vitro conditions. Due to the significant increase in permeability studies using the Caco-2 cell line in recent years, the need to standardize this biological model seems necessary. The pharmaceutical requirements define only the acceptance criteria for the validation of the Caco-2 cell line and do not specify the protocol for its implementation. Therefore, the aim of this study is to review the conditions for permeability studies across the Caco-2 monolayer reported in the available literature concerning validation guidelines. We summarized the main aspects affecting the validation process of the Caco-2 cell line, including the culture conditions, cytotoxicity, cell differentiation process, and monolayer transport conditions, and the main conclusions may be useful in developing individual methods for preparing the cell line for validation purposes and further permeability research.

Recent Advances in Targeting the Urokinase Plasminogen Activator with Nanotherapeutics

The aberrant proteolytic landscape of the tumor microenvironment is a key contributor of cancer progression. Overexpression of urokinase plasminogen activator (uPA) and/or its associated cell-surface receptor (uPAR) in tumor versus normal tissue is significantly associated with worse clinicopathological features and poorer patient survival across multiple cancer types. This is linked to mechanisms that facilitate tumor cell invasion and migration, via direct and downstream activation of various proteolytic processes that degrade the extracellular matrix─ultimately leading to metastasis. Targeting uPA has thus long been considered an attractive anticancer strategy. However, poor bioavailability of several uPA-selective small-molecule inhibitors has limited early clinical progress. Nanodelivery systems have emerged as an exciting method to enhance the pharmacokinetic (PK) profile of existing chemotherapeutics, allowing increased circulation time, improved bioavailability, and targeted delivery to tumor tissue. Combining uPA inhibitors with nanoparticle-based delivery systems thus offers a remarkable opportunity to overcome existing PK challenges associated with conventional uPA inhibitors, while leveraging potent candidates into novel targeted nanotherapeutics for an improved anticancer response in uPA positive tumors.

Insight into the role of clathrin-mediated endocytosis inhibitors in SARS-CoV-2 infection

Emergence of SARS-CoV-2 variants warrants sustainable efforts to upgrade both the diagnostic and therapeutic protocols. Understanding the details of cellular and molecular basis of the virus-host cell interaction is essential for developing variant-independent therapeutic options. The internalization of SARS-CoV-2, into lung epithelial cells, is mediated by endocytosis, especially clathrin-mediated endocytosis (CME). Although vaccination is the gold standard strategy against viral infection, selective inhibition of endocytic proteins, complexes, and associated adaptor proteins may present a variant-independent therapeutic strategy. Although clathrin and/or dynamins are the most important proteins involved in CME, other endocytic mechanisms are clathrin and/or dynamin independent and rely on other proteins. Moreover, endocytosis implicates some subcellular structures, like plasma membrane, actin and lysosomes. Also, physiological conditions, such as pH and ion concentrations, represent an additional factor that mediates these events. Accordingly, endocytosis related proteins are potential targets for small molecules that inhibit endocytosis-mediated viral entry. This review summarizes the potential of using small molecules, targeting key proteins, participating in clathrin-dependent and -independent endocytosis, as variant-independent antiviral drugs against SARS-CoV-2 infection. The review takes two approaches. The first outlines the potential role of endocytic inhibitors in preventing endocytosis-mediated viral entry and its mechanism of action, whereas in the second computational analysis was implemented to investigate the selectivity of common inhibitors against endocytic proteins in SARS-CoV-2 endocytosis. The analysis revealed that remdesivir, methyl-β-cyclodextrin, rottlerin, and Bis-T can effectively inhibit clathrin, HMG-CoA reductase, actin, and dynamin I GTPase and are more potent in inhibiting SARS-CoV-2 than chloroquine. CME inhibitors for SARS-CoV-2 infection remain understudied.

A 10-mg dose of amiloride increases time to failure during blood-flow-restricted plantar flexion in healthy adults without influencing blood pressure

Amiloride has been shown to inhibit acid-sensing ion channels (ASICs), which contribute to ischemia-related muscle pain during exercise. The purpose of this study was to determine if a single oral dose of amiloride would improve exercise tolerance and attenuate blood pressure during blood-flow-restricted (BFR) exercise in healthy adults. Ten subjects (4 females) performed isometric plantar flexion exercise with BFR (30% maximal voluntary contraction) after ingesting either a 10-mg dose of amiloride or a volume-matched placebo (random order). Time to failure, time-tension index (TTI), and perceived pain (visual analog scale) were compared between the amiloride and placebo trials. Mean blood pressure, heart rate, blood pressure index (BPI), and BPI normalized to TTI (BPInorm) were also compared between trials using both time-matched (TM50 and TM100) and effort-matched (T50 and T100) comparisons. Time to failure (+69.4 ± 63.2 s, P < 0.01) and TTI (+1,441 ± 633 kg·s, P = 0.02) were both significantly increased in the amiloride trial compared with placebo, despite no increase in pain (+0.4 ± 1.7 cm, P = 0.46). In contrast, amiloride had no significant influence on the mean blood pressure or heart rate responses, nor were there any significant differences in BPI or BPInorm between trials when matched for time (all P ≥ 0.13). When matched for effort, BPI was significantly greater in the amiloride trial (+5,300 ± 1,798 mmHg·s, P = 0.01), likely owing to an increase in total exercise duration. In conclusion, a 10-mg oral dose of amiloride appears to significantly improve the tolerance to BFR exercise in healthy adults without influencing blood pressure responses.

Mitochondrial Effects of Common Cardiovascular Medications: The Good, the Bad and the Mixed

Mitochondria are central organelles in the homeostasis of the cardiovascular system via the integration of several physiological processes, such as ATP generation via oxidative phosphorylation, synthesis/exchange of metabolites, calcium sequestration, reactive oxygen species (ROS) production/buffering and control of cellular survival/death. Mitochondrial impairment has been widely recognized as a central pathomechanism of almost all cardiovascular diseases, rendering these organelles important therapeutic targets. Mitochondrial dysfunction has been reported to occur in the setting of drug-induced toxicity in several tissues and organs, including the heart. Members of the drug classes currently used in the therapeutics of cardiovascular pathologies have been reported to both support and undermine mitochondrial function. For the latter case, mitochondrial toxicity is the consequence of drug interference (direct or off-target effects) with mitochondrial respiration/energy conversion, DNA replication, ROS production and detoxification, cell death signaling and mitochondrial dynamics. The present narrative review aims to summarize the beneficial and deleterious mitochondrial effects of common cardiovascular medications as described in various experimental models and identify those for which evidence for both types of effects is available in the literature.

Distribution of acid-sensing ion channel subunits in human sensory neurons contrasts with that in rodents

Acid-sensing ion channels (ASICs) play a critical role in nociception in human sensory neurons. Four genes (ASIC1, ASIC2, ASIC3, and ASIC4) encoding multiple subunits through alternative splicing have been identified in humans. Real time-PCR experiments showed strong expression of three subunits ASIC1, ASIC2, and ASIC3 in human dorsal root ganglia; however, their detailed expression pattern in different neuronal populations has not been investigated yet. In the current study, using an in situ hybridization approach (RNAscope), we examined the presence of ASIC1, ASIC2, and ASIC3 mRNA in three subpopulations of human dorsal root ganglia neurons. Our results revealed that ASIC1 and ASIC3 were present in the vast majority of dorsal root ganglia neurons, while ASIC2 was only expressed in less than half of dorsal root ganglia neurons. The distribution pattern of the three ASIC subunits was the same across the three populations of dorsal root ganglia neurons examined, including neurons expressing the REarranged during Transfection (RET) receptor tyrosine kinase, calcitonin gene-related peptide, and a subpopulation of nociceptors expressing Transient Receptor Potential Cation Channel Subfamily V Member 1. These results strongly contrast the expression pattern of Asics in mice since our previous study demonstrated differential distribution of Asics among the various subpopulation of dorsal root ganglia neurons. Given the distinct acid-sensitivity and activity dynamics among different ASIC channels, the expression differences between human and rodents should be taken under consideration when evaluating the translational potential and efficiency of drugs targeting ASICs in rodent studies.

6-Furopyridine Hexamethylene Amiloride Is a Non-Selective P2X7 Receptor Antagonist

P2X7 is an extracellular adenosine 5′-triphopshate (ATP)-gated cation channel present on leukocytes, where its activation induces pro-inflammatory cytokine release and ectodomain shedding of cell surface molecules. Human P2X7 can be partially inhibited by amiloride and its derivatives at micromolar concentrations. This study aimed to screen a library of compounds derived from amiloride or its derivative 5-(N,N-hexamethylene) amiloride (HMA) to identify a potential P2X7 antagonist. 6-Furopyridine HMA (6-FPHMA) was identified as a novel P2X7 antagonist and was characterized further. 6-FPHMA impaired ATP-induced dye uptake into human RPMI8226 multiple myeloma cells and human P2X7-HEK293 cells, in a concentration-dependent, non-competitive manner. Likewise, 6-FPHMA blocked ATP-induced Ca²⁺ fluxes in human P2X7-HEK293 cells in a concentration-dependent, non-competitive manner. 6-FPHMA inhibited ATP-induced dye uptake into human T cells, and interleukin-1β release within human blood and CD23 shedding from RPMI8226 cells. 6-FPHMA also impaired ATP-induced dye uptake into murine P2X7- and canine P2X7-HEK293 cells. However, 6-FPHMA impaired ATP-induced Ca²⁺ fluxes in human P2X4-HEK293 cells and non-transfected HEK293 cells, which express native P2Y₁, P2Y₂ and P2Y₄. In conclusion, 6-FPHMA inhibits P2X7 from multiple species. Its poor selectivity excludes its use as a specific P2X7 antagonist, but further study of amiloride derivatives as P2 receptor antagonists is warranted.

Effect of Lipid Composition on the Inhibition Mechanism of Amiloride on Alamethicin Ion Channels in Supported Phospholipid Bilayers

The inhibition effect of amiloride on alamethicin ion channels was studied in a model zwitterionic floating bilayer lipid membrane (fBLM). The EIS studies indicated that amiloride prevents the transport of ions through the alamethicin channels leading to an overall increase in membrane resistance. The PM-IRRAS data demonstrated that amiloride has no influence on the secondary structure of alamethicin but restricts the insertion of the peptides into the bilayer and blocks ion transport through preformed alamethicin channels. The effect of amiloride on ion channel formation in the floating bilayer formed by a zwitterionic lipid was compared to those of previous studies involving negatively charged fBLMs and tethered zwitterionic lipid bilayers. The findings from these studies show that the effects of amiloride on ion channel formation strongly depend on the mobility and charge of the membrane lipids.

Advances of Drugs Electroanalysis Based on Direct Electrochemical Redox on Electrodes: A Review

The strong development of mankind is inseparable from the proper use of drugs, and the electroanalytical research of drugs occupies an important position in the field of analytical chemistry. This review mainly elaborates the research progress of drugs electroanalysis based on direct electrochemical redox on various electrodes for the recent decade from 2011 to 2021. At first, we summarize some frequently used electrochemical data processing and electrochemical mechanism research derivation methods in the literature. Then, according to the drug therapeutic and application/usage purposes, the research progress of drugs electrochemical analysis is classified and discussed, where we focus on drugs electrochemical reaction mechanism. At the same time, the comparisons of electrochemical sensing performance of the drugs on various electrodes from recent studies are listed, so that readers can more intuitively compare and understand the electroanalytical sensing performance of each modified electrode for each of the drug. Finally, this review discusses the shortcomings and prospects of the drugs electroanalysis based on direct electrochemical redox research.

Endogenous ion channels expressed in human embryonic kidney (HEK-293) cells

Mammalian expression systems, particularly the human embryonic kidney (HEK-293) cells, combined with electrophysiological studies, have greatly benefited our understanding of the function, characteristic, and regulation of various ion channels. It was previously assumed that the existence of endogenous ion channels in native HEK-293 cells could be negligible. Still, more and more ion channels are gradually reported in native HEK-293 cells, which should draw our attention. In this regard, we summarize the different ion channels that are endogenously expressed in HEK-293 cells, including voltage-gated Na⁺ channels, Ca²⁺ channels, K⁺ channels, Cl^- channels, nonselective cation channels, TRP channels, acid-sensitive ion channels, and Piezo channels, which may complicate the recording of the heterogeneously expressed ion channels to a certain degree. We noted that the expression patterns and channel profiles varied with different studies, which may be due to the distinct originality of the cells, cell culture conditions, passage numbers, and different recording protocols. Therefore, a better knowledge of endogenous ion channels may help minimize potential problems in characterizing heterologously expressed ion channels. Based on this, it is recommended that HEK-293 cells from unknown sources should be examined before transfection for the characterization of their functional profile, especially when the expression level of exogenous ion channels does not overwhelm the endogenous ion channels largely, or the current amplitude is not significantly higher than the native currents.

Nephrotic Syndrome Complications - New and Old. Part 1

Nephrotic syndrome is a rare condition with an incidence of 2-7 cases/100.000 children per year and three new cases/100.000 adults per year. It occurs as a result of severe alteration of the glomerular filtration barrier of various causes, allowing proteins, mostly albumin, to be lost in the urine. Nephrotic syndrome complications are driven by the magnitude of either proteinuria or hypoalbuminemia, or both. Their frequency and severity vary with proteinuria and serum albumin level. Besides albumin, many other proteins are lost in urine. Therefore, nephrotic patients could have low levels of binding proteins for ions, vitamins, hormones, lipoproteins, coagulation factors. The liver tries to counterbalance these losses and will increase the unselective synthesis of all types of proteins. All of these changes will have different clinical consequences. The present paper aims to discuss the pathophysiological mechanism and new therapeutic recommendations for nephrotic syndrome edema and thromboembolic complications.

Influence of acid-sensing ion channel blocker on behavioral responses in a zebrafish model of acute visceral pain

Acid-sensing ion channels (ASICs) play significant roles in numerous neurological and pathological conditions, including pain. Although acid-induced nociception has been characterized previously in zebrafish, the contribution of ASICs in modulating pain-like behaviors is still unknown. Here, we investigated the role of amiloride, a nonselective ASICs blocker, in the negative modulation of specific behavioral responses in a zebrafish-based model of acute visceral pain. We verified that intraperitoneal injection (i.p.) of 0.25, 0.5, 1.0, and 2.0 mg/mL amiloride alone or vehicle did not change zebrafish behavior compared to saline-treated fish. Administration of 2.5% acetic acid (i.p.) elicited writhing-like response evidenced by the abnormal body curvature and impaired locomotion and motor activity. Attenuation of acetic acid-induced pain was verified at lower amiloride doses (0.25 and 0.5 mg/mL) whereas 1.0 and 2.0 mg/mL abolished pain-like responses. The protective effect of the highest amiloride dose tested was evident in preventing writhing-like responses and impaired locomotion and vertical activity. Collectively, amiloride antagonized abdominal writhing-like phenotype and aberrant behaviors, supporting the involvement of ASICs in a zebrafish-based model of acute visceral pain.

Urokinase plasminogen activator as an anti-metastasis target: inhibitor design principles, recent amiloride derivatives, and issues with human/mouse species selectivity

The urokinase plasminogen activator (uPA) is a widely studied anticancer drug target with multiple classes of inhibitors reported to date. Many of these inhibitors contain amidine or guanidine groups, while others lacking these groups show improved oral bioavailability. Most of the X-ray co-crystal structures of small molecule uPA inhibitors show a key salt bridge with the side chain carboxylate of Asp189 in the S1 pocket of uPA. This review summarises the different classes of uPA inhibitors, their binding interactions and experimentally measured inhibitory potencies and highlights species selectivity issues with attention to recently described 6-substituted amiloride and 5‑N,N-(hexamethylene)amiloride (HMA) derivatives.

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.

Elucidating molecular mechanisms of acquired resistance to BRAF inhibitors in melanoma using a microfluidic device and deep sequencing

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) encodes small envelope protein (E) that plays a major role in viral assembly, release, pathogenesis, and host inflammation. Previous studies demonstrated that pyrazine ring containing amiloride analogs inhibit this protein in different types of coronavirus including SARS-CoV-1 small envelope protein E (SARS-CoV-1 E). SARS-CoV-1 E has 93.42% sequence identity with SARS-CoV-2 E and shared a conserved domain NS3/small envelope protein (NS3_envE). Amiloride analog hexamethylene amiloride (HMA) can inhibit SARS-CoV-1 E. Therefore, we performed molecular docking and dynamics simulations to explore whether amiloride analogs are effective in inhibiting SARS-CoV-2 E. To do so, SARS-CoV-1 E and SARS-CoV-2 E proteins were taken as receptors while HMA and 3-amino-5-(azepan-1-yl)-N-(diaminomethylidene)-6-pyrimidin-5-ylpyrazine-2-carboxamide (3A5NP2C) were selected as ligands. Molecular docking simulation showed higher binding affinity scores of HMA and 3A5NP2C for SARS-CoV-2 E than SARS-CoV-1 E. Moreover, HMA and 3A5NP2C engaged more amino acids in SARS-CoV-2 E. Molecular dynamics simulation for 1 μs (1,000 ns) revealed that these ligands could alter the native structure of the proteins and their flexibility. Our study suggests that suitable amiloride analogs might yield a prospective drug against coronavirus disease 2019.