Na+/H+ exchanger and cardiac hypertrophy

Exercise-induced cardiac mitochondrial reorganization and enhancement in spontaneously hypertensive rats

The myocardium is a highly oxidative tissue in which mitochondria are essential to supply the energy required to maintain pump function. When pathological hypertrophy develops, energy consumption augments and jeopardizes mitochondrial capacity. We explored the cardiac consequences of chronic swimming training, focusing on the mitochondrial network, in spontaneously hypertensive rats (SHR). Male adult SHR were randomized to sedentary or trained (T: 8-week swimming protocol). Blood pressure and echocardiograms were recorded, and hearts were removed at the end of the training period to perform molecular, imaging, or isolated mitochondria studies. Swimming improved cardiac midventricular shortening and decreased the pathological hypertrophic marker atrial natriuretic peptide. Oxidative stress was reduced, and even more interesting, mitochondrial spatial distribution, dynamics, function, and ATP were significantly improved in the myocardium of T rats. In the signaling pathway triggered by training, we detected an increase in the phosphorylation level of both AKT and glycogen synthase kinase-3 β, key downstream targets of insulin-like growth factor 1 signaling that are crucially involved in mitochondria biogenesis and integrity. Aerobic exercise training emerges as an effective approach to improve pathological cardiac hypertrophy and bioenergetics in hypertension-induced cardiac hypertrophy.

Small Molecules for the Treatment of Long-COVID-Related Vascular Damage and Abnormal Blood Clotting: A Patent-Based Appraisal

People affected by COVID-19 are exposed to, among others, abnormal clotting and endothelial dysfunction, which may result in deep vein thrombosis, cerebrovascular disorders, and ischemic and non-ischemic heart diseases, to mention a few. Treatments for COVID-19 include antiplatelet (e.g., aspirin, clopidogrel) and anticoagulant agents, but their impact on morbidity and mortality has not been proven. In addition, due to viremia-associated interconnected prothrombotic and proinflammatory events, anti-inflammatory drugs have also been investigated for their ability to mitigate against immune dysregulation due to the cytokine storm. By retrieving patent literature published in the last two years, small molecules patented for long-COVID-related blood clotting and hematological complications are herein examined, along with supporting evidence from preclinical and clinical studies. An overview of the main features and therapeutic potentials of small molecules is provided for the thromboxane receptor antagonist ramatroban, the pan-caspase inhibitor emricasan, and the sodium-hydrogen antiporter 1 (NHE-1) inhibitor rimeporide, as well as natural polyphenolic compounds.

The crossing of two unwound transmembrane regions that is the hallmark of the NhaA structural fold is critical for antiporter activity

Cell pH and Na+ homeostasis requires Na+/H+ antiporters. The crystal structure of NhaA, the main Escherichia coli Na+/H+ antiporter, revealed a unique NhaA structural fold shared by prokaryotic and eukaryotic membrane proteins. Out of the 12 NhaA transmembrane segments (TMs), TMs III-V and X-XII are topologically inverted repeats with unwound TMs IV and XI forming the X shape characterizing the NhaA fold. We show that intramolecular cross-linking under oxidizing conditions of a NhaA mutant with two Cys replacements across the crossing (D133C-T340C) inhibits antiporter activity and impairs NhaA-dependent cell growth in high-salts. The affinity purified D133C-T340C protein binds Li+ (the Na+ surrogate substrate of NhaA) under reducing conditions. The cross-linking traps the antiporter in an outward-facing conformation, blocking the antiport cycle. As many secondary transporters are found to share the NhaA fold, including some involved in human diseases, our data have importance for both basic and clinical research.

Non-coding RNA mediates endoplasmic reticulum stress-induced apoptosis in heart disease

Apoptosis is a complex and highly self-regulating form of cell death, which is an important cause of the continuous decline in ventricular function and is widely involved in the occurrence and development of heart failure, myocardial infarction, and myocarditis. Endoplasmic reticulum stress plays a crucial role in apoptosis-inducing. Accumulation of misfolded or unfolded proteins causes cells to undergo a stress response called unfolded protein response (UPR). UPR initially has a cardioprotective effect. Nevertheless, prolonged and severe ER stress will lead up to apoptosis of stressed cells. Non-coding RNA is a type of RNA that does not code proteins. An ever-increasing number of studies have shown that non-coding RNAs are involved in regulating endoplasmic reticulum stress-induced cardiomyocyte injury and apoptosis. In this study, the effects of miRNA and LncRNA on endoplasmic reticulum stress in various heart diseases were mainly discussed to clarify their protective effects and potential therapeutic strategies for apoptosis.

Cardioprotective role of A-cycloglycosylated derivative of Rubiadin in diabetic cardiomyopathy in rats

Diabetic cardiomyopathy (DCM) is a kind of idiopathic heart disease, which is one of the main complications of diabetes and seriously threatens the life of diabetic patients. Rubiadin, an anthraquinone compound extracted from the stems and roots of rubiaceae, has been widely discussed for its anti-diabetes, anti-oxidation and other pharmacological effects. However, Rubiadin can cause drug-induced liver injury. Therefore, A-cycloglycosylated derivative of Rubiadin (ACDR) was obtained by modifying its structure. The purpose of this study was to investigate the effect of ACDR on DCM cardiac injury and its mechanism. The DCM animal model was established by streptozotocin, and the success of DCM was verified by blood glucose level, echocardiographic evidence of impaired myocardial functions along with enhanced myocardial fibrosis. We performed liver function tests, morphological staining of the heart and tests for oxidative stress to evaluate cardiac functional and structural changes. Finally, the expression of Na⁺/H⁺ exchanger (NHE1) protein was analyzed by immunohistochemistry and western bolt, and the expression of hairy/enhancer-of-split related with YRPW motif 1 (Hey1) and P-p38 protein was detected by immunofluorescence chemistry and western blotting. The results showed that ACDR can improve cardiac dysfunction, reduce myocardial injury, reduce oxidative stress, and protect the liver in DCM rats. Interestingly, all variations were countered by LiCl. Our study suggests that, along with controlling hyperglycemia, ACDR may improve DCM by reducing NHE1 expression, further inhibiting P-p38 activity and increasing Hey1 expression to reduce oxidative stress.

Phytomolecules as potential candidates to intervene the function of E. coli sodium-proton antiporters; Ec-NhaA

Sodium-Proton antiporter, NhaA is a ubiquitous protein found in cytoplasmic membranes of all the prokaryotic and eukaryotic systems. These antiporters have been widely studied in E. coli and their homologs, observed in humans, are found to be crucial for various pathophysiological conditions, such as hypertension, cardiac diseases, blood pressure fluctuation etc. NhaA is responsible for the virulent properties of many pathogens like Vibrio cholerae, Yersinia pestis etc. In the present work, we have exploited in silico approaches to find lead phytomolecules that have the efficacy to interfere with the activities of sodium-proton antiporters in E. coli. A database of the plant-based natural bioactive compounds was used to screen 350 phytochemicals from various plant sources as potential ligands for the Ec-NhaA protein (PDB ID: 4ATV). Further interactions between Ec-NhaA and ligands were analyzed by AutoDock Vina and proposed 46 ligands with a significant affinity for NhaA where the binding energy range from -7.5 to -9.3 kcal/mol. Physiochemical characterization suggested 26 ligands with non-BBB permeability, good GI absorption and solubility. As a final step, MD simulation for more than 100 ns duration suggested Luteolin, Apigenin and Rhamnocitrin with the best affinity and showing potential stable interaction with the target protein. This study proposed the potential compounds of natural origin as an interfering agent against sodium-proton transport activity that may lead to affect the survival of various pathogenic bacteria.Communicated by Ramaswamy H. Sarma.

Sodium-glucose Cotransporter 2 Inhibitors and Pathological Myocardial Hypertrophy

Sodium-glucose cotransporter 2 (SGLT2) inhibitors are a new type of oral hypoglycemic drugs that exert a hypoglycemic effect by blocking the reabsorption of glucose in the proximal renal tubules, thus promoting the excretion of glucose from urine. Their hypoglycemic effect is not dependent on insulin. Increasing data shows that SGLT2 inhibitors improve cardiovascular outcomes in patients with type 2 diabetes. Previous studies have demonstrated that SGLT2 inhibitors can reduce pathological myocardial hypertrophy with or without diabetes, but the exact mechanism remains to be elucidated. To clarify the relationship between SGLT2 inhibitors and pathological myocardial hypertrophy, with a view to providing a reference for the future treatment thereof, this study reviewed the possible mechanisms of SGLT2 inhibitors in attenuating pathological myocardial hypertrophy. We focused specifically on the mechanisms in terms of inflammation, oxidative stress, myocardial fibrosis, mitochondrial function, epicardial lipids, endothelial function, insulin resistance, cardiac hydrogen and sodium exchange, and autophagy.

Direct cardio-protection of Dapagliflozin against obesity-related cardiomyopathy via NHE1/MAPK signaling

Obesity is an important independent risk factor for cardiovascular diseases, remaining an important health concern worldwide. Evidence shows that saturated fatty acid-induced inflammation in cardiomyocytes contributes to obesity-related cardiomyopathy. Dapagliflozin (Dapa), a selective SGLT2 inhibitor, exerts a favorable preventive activity in heart failure. In this study, we investigated the protective effect of Dapa against cardiomyopathy caused by high fat diet-induced obesity in vitro and in vivo. Cultured rat cardiomyocyte H9c2 cells were pretreated with Dapa (1, 2.5 μM) for 1.5 h, followed by treatment with palmitic acid (PA, 200 μM) for 24 h. We showed that Dapa pretreatment concentration-dependently attenuated PA-induced cell hypertrophy, fibrosis and apoptosis. Transcriptome analysis revealed that inhibition of PA-activated MAPK/AP-1 pathway contributed to the protective effect of Dapa in H9c2 cells, and this was confirmed by anti-p-cJUN fluorescence staining assay. Using surface plasmon resonance analysis we found the direct binding of Dapa with NHE1. Gain and loss of function experiments further demonstrated the role of NHE1 in the protection of Dapa. In vivo experiments were conducted in mice fed a high fat diet for 5 months. The mice were administered Dapa (1 mg·kg-1·d-1, i.g.) in the last 2 months. Dapa administration significantly reduced the body weight and improved the serum lipid profiles. Dapa administration also alleviated HFD-induced cardiac dysfunction and cardiac aberrant remodeling via inhibiting MAPK/AP-1 pathway and ameliorating cardiac inflammation. In conclusion, Dapa exerts a direct protective effect against saturated fatty acid-induced cardiomyocyte injury in addition to the lowering effect on serum lipids. The protective effect results from negative regulating MAPK/AP-1 pathway in a NHE1-dependent way. The current study highlights the potential of clinical use of Dapa in the prevention of obesity-related cardiac dysfunction.

Exploring the interaction of guanidine ligands Amiloride, Rimeporide and Cariporide with DNA for understanding their role as inhibitors of Na+/H+ exchangers (NHEs): A spectroscopic and molecular docking investigation

The inhibition of Na⁺/H⁺ Exchangers (NHEs) has shown efficacy in the pathology of several diseases like tumors, cardiovascular, and neurological disorders. The role of guanidine ligands such as amiloride, cariporide, and rimeporide as NHE inhibitors is very well documented but their interaction studies with genomic DNA are still unexplored. In this study, a combination of various biophysical and molecular docking studies was employed to investigate their binding aspects.UV-Visible, fluorescence, and circular dichroism (CD) studies indicated that guanidine ligands bind to the grooves of Calf Thymus DNA (ctDNA). Fluorescence titration studies depict that amiloride binds to ctDNA with a binding constant in the order of 10² M^-1 and free energy change (ΔG⁰) of -14.05 KJ mol^-1. Competitive fluorescence studies indicated the minor groove binding property of amiloride, whereas major groove binding mode was deduced for rimeporide and cariporide. Molecular docking studies were also found to be in accordance with the experimental results, revealing the information about the binding energy of the guanidine ligand-ctDNA complex. The docked structures depicted binding energy of -6.4 kcal mol^-1 for amiloride and - 6.6 kcal mol^-1 for rimeporide and cariporide. Such physicochemical studies of DNA-ligand interactions may facilitate the understanding of the mechanisms of NHE inhibition.

Na+/H+ Exchanger 1, a Potential Therapeutic Drug Target for Cardiac Hypertrophy and Heart Failure

Cardiac hypertrophy is defined as increased heart mass in response to increased hemodynamic requirements. Long-term cardiac hypertrophy, if not counteracted, will ultimately lead to heart failure. The incidence of heart failure is related to myocardial infarction, which could be salvaged by reperfusion and ultimately invites unfavorable myocardial ischemia-reperfusion injury. The Na⁺/H⁺ exchangers (NHEs) are membrane transporters that exchange one intracellular proton for one extracellular Na⁺. The first discovered NHE isoform, NHE1, is expressed almost ubiquitously in all tissues, especially in the myocardium. During myocardial ischemia-reperfusion, NHE1 catalyzes increased uptake of intracellular Na⁺, which in turn leads to Ca²⁺ overload and subsequently myocardial injury. Numerous preclinical research has shown that NHE1 is involved in cardiac hypertrophy and heart failure, but the exact molecular mechanisms remain elusive. The objective of this review is to demonstrate the potential role of NHE1 in cardiac hypertrophy and heart failure and investigate the underlying mechanisms.

Role of Genetic Mutations of the Na+/H+ Exchanger Isoform 1, in Human Disease and Protein Targeting and Activity

The mammalian Na⁺/H⁺ exchanger isoform one (NHE1) is a plasma membrane protein that is ubiquitously present in human cells. It functions to regulate intracellular pH removing an intracellular proton in exchange for one extracellular sodium and is involved in heart disease and in promoting metastasis in cancer. It is made of a 500 amino acid membrane domain plus a 315 amino acid, regulatory cytosolic tail. The membrane domain is thought to have 12 transmembrane segments and a large membrane-associated extracellular loop. Early studies demonstrated that in mice, disruption of the NHE1 gene results in locomotor ataxia and a phenotype of slow-wave epilepsy. Defects included a progressive neuronal degeneration. Growth and reproductive ability were also reduced. Recent studies have identified human autosomal homozygous recessive mutations in the NHE1 gene (SLC9A1) that result in impaired development, ataxia and other severe defects, and explain the cause of the human disease Lichtenstein-Knorr syndrome. Other human mutations have been identified that are stop codon polymorphisms. These cause short non-functional NHE1 proteins, while other genetic polymorphisms in the NHE1 gene cause impaired expression of the NHE1 protein, reduced activity, enhanced protein degradation or altered kinetic activation of the protein. Since NHE1 plays a key role in many human physiological functions and in human disease, genetic polymorphisms of the protein that significantly alter its function and are likely play significant roles in varying human phenotypes and be involved in disease.

Deubiquitinase Ubiquitin-Specific Protease 10 Deficiency Regulates Sirt6 signaling and Exacerbates Cardiac Hypertrophy

Background

Cardiac hypertrophy (CH) is a physiological response that compensates for blood pressure overload. Under pathological conditions, hypertrophy can progress to heart failure as a consequence of the disorganized growth of cardiomyocytes and cardiac tissue. USP10 (ubiquitin‐specific protease 10) is a member of the ubiquitin‐specific protease family of cysteine proteases, which are involved in viral infection, oxidative stress, lipid drop formation, and heat shock. However, the role of USP10 in CH remains largely unclear. Here, we investigated the roles of USP10 in CH.

Methods and Results

Cardiac‐specific USP10 knockout (USP10‐CKO) mice and USP10‐transgenic (USP10‐TG) mice were used to examined the role of USP10 in CH following aortic banding. The specific functions of USP10 were further examined in isolated cardiomyocytes. USP10 expression was increased in murine hypertrophic hearts following aortic banding and in isolated cardiomyocytes in response to hypertrophic agonist. Mice deficient in USP10 in the heart exhibited exaggerated cardiac hypertrophy and fibrosis following pressure overload stress, which resulted in worsening of cardiac contractile function. In contrast, cardiac overexpression of USP10 protected against pressure overload‐induced maladaptive CH. Mechanistically, we demonstrated that USP10 activation and interaction with Sirt6 in response to angiotensin II led to a marked increase in the ubiquitination of Sirt6 and resulted in Akt signaling downregulation and attenuation of cardiomyocyte hypertrophy. Accordingly, inactivation of USP10 reduced Sirt6 abundance and stability and diminished Sirt6‐induced downstream signaling in cardiomyocytes.

Conclusions

USP10 functions as a Sirt6 deubiquitinase that induces cardiac myocyte hypertrophy and triggers maladaptive CH.

An Inhibitor of the Sodium-Hydrogen Exchanger-1 (NHE-1), Amiloride, Reduced Zinc Accumulation and Hippocampal Neuronal Death after Ischemia

Acidosis in the brain plays an important role in neuronal injury and is a common feature of several neurological diseases. It has been reported that the sodium–hydrogen exchanger-1 (NHE-1) is a key mediator of acidosis-induced neuronal injury. It modulates the concentration of intra- and extra-cellular sodium and hydrogen ions. During the ischemic state, excessive sodium ions enter neurons and inappropriately activate the sodium–calcium exchanger (NCX). Zinc can also enter neurons through voltage-gated calcium channels and NCX. Here, we tested the hypothesis that zinc enters the intracellular space through NCX and the subsequent zinc accumulation induces neuronal cell death after global cerebral ischemia (GCI). Thus, we conducted the present study to confirm whether inhibition of NHE-1 by amiloride attenuates zinc accumulation and subsequent hippocampus neuronal death following GCI. Mice were subjected to GCI by bilateral common carotid artery (BCCA) occlusion for 30 min, followed by restoration of blood flow and resuscitation. Amiloride (10 mg/kg, intraperitoneally (i.p.)) was immediately injected, which reduced zinc accumulation and neuronal death after GCI. Therefore, the present study demonstrates that amiloride attenuates GCI-induced neuronal injury, likely via the prevention of intracellular zinc accumulation. Consequently, we suggest that amiloride may have a high therapeutic potential for the prevention of GCI-induced neuronal death.