IK1 Channel Agonist Zacopride Alleviates Cardiac Hypertrophy and Failure via Alterations in Calcium Dyshomeostasis and Electrical Remodeling in Rats

Cell size induced bias of current density in hypertrophic cardiomyocytes

Alterations in ion channel expression and function known as "electrical remodeling" contribute to the development of hypertrophy and to the emergence of arrhythmias and sudden cardiac death. However, comparing current density values - an electrophysiological parameter commonly utilized to assess ion channel function - between normal and hypertrophied cells may be flawed when current amplitude does not scale with cell size. Even more, common routines to study equally sized cells or to discard measurements when large currents do not allow proper voltage-clamp control may introduce a selection bias and thereby confound direct comparison. To test a possible dependence of current density on cell size and shape, we employed whole-cell patch-clamp recording of voltage-gated sodium and calcium currents in Langendorff-isolated ventricular cardiomyocytes and Purkinje myocytes, as well as in cardiomyocytes derived from trans-aortic constriction operated mice. Here, we describe a distinct inverse relationship between voltage-gated sodium and calcium current densities and cell capacitance both in normal and hypertrophied cells. This inverse relationship was well fit by an exponential function and may be due to physiological adaptations that do not scale proportionally with cell size or may be explained by a selection bias. Our study emphasizes the need to consider cell size bias when comparing current densities in cardiomyocytes of different sizes, particularly in hypertrophic cells. Conventional comparisons based solely on mean current density may be inadequate for groups with unequal cell size or non-proportional current amplitude and cell size scaling.

Zacopride stimulates 5-HT4 serotonin receptors in the human atrium

Zacopride (4-amino-5-chloro-2-methoxy-N-(quinuclidin-3-yl)-benzamide) is a potent agonist in human 5-HT4 serotonin receptors in vitro and in the gastrointestinal tract. Zacopride was studied as an antiemetic drug and was intended to treat gastric diseases. Zacopride has been speculated to be useful as an antiarrhythmic agent in the human ventricle by inhibiting cardiac potassium channels. It is unknown whether zacopride is an agonist in human cardiac 5-HT4 serotonin receptors. We tested the hypothesis that zacopride stimulates human cardiac atrial 5-HT4 serotonin receptors. Zacopride increased the force of contraction and beating rate in isolated atrial preparations from mice with cardiac-specific overexpression of human 5-HT4 serotonin receptors (5-HT4-TG). However, it was inactive in wild-type mouse hearts (WT). Zacopride was as effective as serotonin in raising the force of contraction and beating rate in atrial preparations of 5-HT4-TG. Zacopride raised the force of contraction in human right atrial preparations (HAP) in the absence and presence of the phosphodiesterase III inhibitor cilostamide (1 µM). The positive inotropic effect of zacopride in HAP was attenuated by either 10 µM tropisetron or 1 µM GR125487, both of which are antagonists at 5-HT4 serotonin receptors. These data suggest that zacopride is also an agonist at 5-HT4 serotonin receptors in the human atrium.

Activation of Kir2.1 improves myocardial fibrosis by inhibiting Ca 2+ overload and the TGF-β1/Smad signaling pathway

The inwardly rectifying potassium channel Kir2.1 is closely associated with many cardiovascular diseases. However, the effect and mechanism of Kir2.1 in diabetic cardiomyopathy remain unclear. In vivo, we use STZ to establish the model, and ventricular structural changes, myocardial inflammatory infiltration, and myocardial fibrosis severity are detected by echocardiography, histological staining, immunohistochemistry, and western blot analysis, respectively. In vitro, a myocardial fibrosis model is established with high glucose. The Kir2.1 current amplitude, intracellular calcium concentration, fibrosis-related proteins, and TGF-β1/Smad pathway proteins are detected by whole-cell patch clamp, calcium probes, western blot analysis, and immunofluorescence, respectively. The in vivo results show that compared to diabetic cardiomyopathy, zacopride (a Kir2.1 selective agonist) significantly reduces the left ventricular systolic diameter and diastolic diameter, increases the left ventricular ejection fraction and left ventricular short-axis shortening, improves the degree of cell necrosis, and reduces the expression of myocardial interstitial fibrosis protein and collagen fibre deposition area. The in vitro results show that the current amplitude and protein expression of Kir2.1 are both decreased in the high glucose-induced myocardial fibrosis model. Additionally, zacopride significantly upregulates the expression of Kir2.1 and inhibits the expressions of the fibrosis-related proteins α-SMA, collagen I, and collagen III. Activation of Kir2.1 reduces the intracellular calcium concentration and inhibits the protein expressions of TGF-β1 and p-Smad 2/3. Activation of Kir2.1 can improve myocardial fibrosis induced by diabetic cardiomyopathy, and the possible mechanism may be related to inhibiting Ca ²⁺ overload and the TGF-β1/Smad signaling pathway.

Anti-malarial drugs: Mechanisms underlying their proarrhythmic effects

Malaria remains the leading cause of parasitic death in the world. Artemisinin resistance is an emerging threat indicating an imminent need for novel combination therapy. Given the key role of mass drug administration, it is pivotal that the safety of anti-malarial drugs is investigated thoroughly prior to widespread use. Cardiotoxicity, most prominently arrhythmic risk, has been a concern for anti-malarial drugs. We clarify the likely underlying mechanisms by which anti-malarial drugs predispose to arrhythmias. These relate to disruption of (1) action potential upstroke due to effects on the sodium currents, (2) action potential repolarisation due to effects on the potassium currents, (3) cellular calcium homeostasis, (4) mitochondrial function and reactive oxygen species production and (5) cardiac fibrosis. Together, these alterations promote arrhythmic triggers and substrates. Understanding these mechanisms is essential to assess the safety of these drugs, stratify patients based on arrhythmic risk and guide future anti-malarial drug development.

Effect of injection of different doses of isoproterenol on the hearts of mice

Background

Heart failure (HF) is one of the diseases that seriously threaten human health today and its mechanisms are very complex. Our study aims to confirm the optimal dose ISO-induced chronic heart failure mice model for better study of HF-related mechanisms and treatments in the future.

Methods

C57BL/6 mice were used to establish mice model of chronic heart failure. We injected isoproterenol subcutaneously in a dose gradient of 250 mg/kg, 200 mg/kg, 150 mg/kg, 100 mg/kg and 50 mg/kg. Echocardiography and ELISA were performed to figure out the occurrence of HF. We also supplemented the echocardiographic changes in mice over 30 days.

Results

Except group S and group E, echocardiographic abnormalities were found in other groups, suggesting a decrease in cardiac function. Except group S, myofibrolysis were found in the hearts of mice in other groups. Brain natriuretic peptide was significantly increased in groups B and D, and C-reactive protein was significantly increased in each group.

Conclusion

Our research finally found that the HFrEF mice model created by injection at a dose of 100 mg/kg for 7 days was the most suitable and a relatively stable chronic heart failure model could be obtained by placing it for 21 days.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-022-02852-x.

Tetramisole is a new IK1 channel agonist and exerts IK1 -dependent cardioprotective effects in rats

Cardiac ischemia, hypoxia, arrhythmias, and heart failure share the common electrophysiological changes featured by the elevation of intracellular Ca2+ (Ca2+ overload) and inhibition of the inward rectifier potassium (IK1 ) channel. IK1 channel agonists have been considered a new type of anti-arrhythmia and cardioprotective agents. We predicted using a drug repurposing strategy that tetramisole (Tet), a known anthelminthic agent, was a new IK1 channel agonist. The present study aimed to experimentally identify the above prediction and further demonstrate that Tet has cardioprotective effects. Results of the whole-cell patch clamp technique showed that Tet at 1-100 μmol/L enhanced IK1 current, hyperpolarized resting potential (RP), and shortened action potential duration (APD) in isolated rat cardiomyocytes, while without effects on other ion channels or transporters. In adult Sprague-Dawley (SD) rats in vivo, Tet showed anti-arrhythmia and anticardiac remodeling effects, respectively, in the coronary ligation-induced myocardial infarction model and isoproterenol (Iso, i.p., 3 mg/kg/day, 10 days) infusion-induced cardiac remodeling model. Tet also showed anticardiomyocyte remodeling effect in Iso (1 μmol/L) infused adult rat ventricular myocytes or cultured H9c2 (2-1) cardiomyocytes. Tet at 0.54 mg/kg in vivo or 30 μmol/L in vitro showed promising protections on acute ischemic arrhythmias, myocardial hypertrophy, and fibrosis. Molecular docking was performed and identified the selective binding of Tet with Kir2.1. The cardioprotection of Tet was associated with the facilitation of IK1 channel forward trafficking, deactivation of PKA signaling, and inhibition of intracellular calcium overload. Enhancing IK1 may play dual roles in anti-arrhythmia and antiventricular remodeling mediated by restoration of Ca2+ homeostasis.

Alpha1-adrenoceptors activate NLRP3 inflammasome through downregulation of Kir2.1 in cardiac inflammation

NEW FINDINGS

What is the central question of this study? The mechanism of cardiac inflammation induced by α ₁ -AR stimulation by NLRP3 inflammasome activation is unclear. What is the main finding and its importance? In the mechanism of cardiac inflammation induced by α₁ -AR overreaction, Kir2.1 exerts cardioprotective and anti-inflammatory effects by inhibiting the activation of NLRP3 Inflammasome.

ABSTRACT

Overstimulated sympathetic nerves in cardiovascular diseases can lead to impaired cardiomyocyte function and potential heart failure, which activates not only β-AR but also α₁ -AR. A previous report indicated that NLRP3 inflammasome activation is involved in cardiac inflammation induced by the α₁ -AR agonist phenylephrine, but the mechanism is still unknown. Here, we aimed to study whether Kir2.1 is involved in cardiac inflammation caused by phenylephrine. The results from in vitro experiments showed that phenylephrine upregulated the expression levels of NLRP3, Caspase-1, IL-18, and IL-1β and downregulated the expression level of Kir2.1 in H9C2 cells. The Kir2.1 agonist zacopride downregulated the expression of NLRP3, Caspase-1, IL-1β and IL-18, and the Kir2.1 inhibitor ML133 upregulated the expression of these genes. To further explore the mechanism, we found that zacopride downregulated the protein expression level of p-p65 and that ML133 upregulated it. Moreover, the NF-κB signaling pathway inhibitor curcumenol reversed the expression of NLRP3 inflammasomes caused by phenylephrine in H9C2 cells. In vivo experiments, the protein expression level of Kir2.1 in the phenylephrine group was significantly decreased, and the activation of Kir2.1 by zacopride reduced cardiac inflammation. In short, Kir2.1 is related to α₁ -AR overactivation, which induces cardiac inflammation, through the NF-κB signaling pathway, and activating Kir2.1 can downregulate NLRP3 inflammation and exert cardioprotective effects by zacopride. This article is protected by copyright. All rights reserved.

Cardioprotection of an IK1 channel agonist on L-thyroxine induced rat ventricular remodeling

Downregulation of inward rectifier potassium (I_K1) channel is a hallmark in cardiac hypertrophy and failure. The cardioprotection of zacopride (a selective I_K1 agonist) and underlying mechanisms were investigated in L-thyroxine (T4) or Triiodothyronine (T3)-induced cardiac remodeling. In the in vivo study, adult male Sprague-Dawley (SD) rats were randomly divided into control, L-thyroxine, L-thy+zacopride, and L-thy+zacopride+chloroquine (an I_K1 antagonist) groups. Echocardiography, histopathology, TUNEL assay, western blotting and confocal imaging for intracellular Ca²⁺ fluorescence were performed. In the in vitro study, zacopride and nifedipine (a LTCC blocker) were used to compare their effects on Kir2.1, SAP97, autophagy, and [Ca²⁺]_i in H9C2 (2-1) cardiomyocytes. Zacopride treatment attenuated L-thyroxine- or T3 induced cardiac remodeling and dysfunction which manifested as cardiac hypertrophy and collagen deposition, dilated ventricle, decreased ejection fraction (EF), increased cardiomyocytes apoptosis, hyper-activation of CaMKII and PI3K/Akt/mTOR signaling, decreased cardiac autophagy, and increased expression of integrin β3. The cardioprotection of zacopride is strongly associated with the upregulation of I_K1, SAP97, and [Ca²⁺]_i homeostasis in cardiomyocytes. I_K1 antagonist chloroquine or BaCl₂ reversed these effects. Nifedipine could attenuate intracellular Ca²⁺ overload with no significant effects on I_K1, SAP97, and autophagy. This study showed that zacopride could improve cardiac remodeling via facilitating Kir2.1 forward trafficking, and negatively regulating calcium-activated and PI3K/Akt/mTOR signalings, in an I_K1-dependent manner.

Amelioration of circadian disruption and calcium-handling protein defects by choline alleviates cardiac remodeling in abdominal aorta coarctation rats

The key pathophysiological process leading to heart failure is cardiac remodeling, a term referring to cardiac hypertrophy, fibrosis, and apoptosis. We explored circadian rhythm disruption and calcium dyshomeostasis in cardiac remodeling and investigated the cardioprotective effect of choline. The experiments were conducted using a model of cardiac remodeling by abdominal aorta coarctation (AAC) in Sprague-Dawley rats. In vitro cardiomyocyte remodeling was induced by exposing neonatal rat cardiomyocytes to angiotensin II. The circadian rhythms of the transcript levels of the seven major components of the mammalian clock (Bmal1, Clock, Rev-erbα, Per1/2, and Cry1/2) were altered in AAC rat hearts during a normal 24 h light/dark cycle. AAC also upregulated the levels of proteins that mediate store-operated Ca2+ entry/receptor-operated Ca2+ entry (stromal interaction molecule 1 [STIM1], Orai1, and transient receptor potential canonical 6 [TRPC6]) in rat hearts. Moreover, choline ameliorated circadian rhythm disruption, reduced the upregulated protein levels of STIM1, Orai1, and TRPC6, and alleviated cardiac dysfunction and remodeling (evidenced by attenuated cardiac hypertrophy, fibrosis, and apoptosis) in AAC rats. In vitro analyses showed that choline ameliorated calcium overload, downregulated STIM1, Orai1, and TRPC6, and inhibited thapsigargin-induced store-operated Ca2+ entry and 1-oleoyl-2-acetyl-sn-glycerol-induced receptor-operated Ca2+ entry in angiotensin II-treated cardiomyocytes. In conclusion, choline attenuated AAC-induced cardiac remodeling and cardiac dysfunction, which was related to amelioration of circadian rhythm disruption and attenuation of calcium-handling protein defects. Modulation of vagal activity by choline targeting the circadian rhythm and calcium homeostasis may have therapeutic potential for cardiac remodeling and heart failure.

Regulatory mechanism of calcium/calmodulin-dependent protein kinase II in the occurrence and development of ventricular arrhythmia (Review)

Ventricular arrhythmia (VA) is a highly fatal arrhythmia that involves multiple ion channels. Of all sudden cardiac death events, ~85% result from VAs, including ventricular tachycardia and ventricular fibrillation. Calcium/calmodulin-dependent pro-tein kinase II (CaMKII) is an important ion channel regulator that participates in the excitation-contraction coupling of the heart, and as such is important for regulating its electrophysiological function. CaMKII can be activated in a Ca²⁺/calmodulin (CaM)-dependent or Ca²⁺/CaM-independent manner, serving a key role in the occurrence and development of VA. The present review aimed to determine whether activated CaMKII induces early afterdepolarizations and delayed afterdepolarizations that result in VA by regulating sodium, potassium and calcium ions. Assessing VA mechanisms based on the CaMKII pathway is of great significance to the clinical treatment of VA and the de-velopment of effective drugs for use in clinical practice.

The mechanism of BAF60c in myocardial metabolism through the PGC1α/PPARα/mTOR signaling pathway in rats with heart failure

BRM-associated factor (BAF) 60c promotes muscle glycolysis and improves glucose homeostasis. This study explored the mechanism of BAF60c in heart failure (HF). Fetal/adult rat models of HF were established, and the levels of cardiac contractile proteins and energy metabolism-, oxidative metabolism- and glycolysis-related factors were detected. Overexpression/siRNA BAF60c plasmids were injected into adult HF rats to estimate myocardial glucose uptake, high-energy phosphate contents, mitochondrial function, and cell proliferation and apoptosis. The overexpression/siRNA BAF60c plasmids were transfected into cardiac hypertrophic H9C2 cells to explore the in vitro effects. The interaction of BAF60c and PGC1α was detected. The results suggested that adult HF rats presented increased levels of fetal proteins (ssTnI and fTnT), BAF60c and glycolysis-related factors, and reduced levels of cardiac contractile proteins, PGC1α, PPARα, and oxidative metabolism-related factors. BAF60c knockdown improved glucose uptake, maintained the oxidative metabolism/glycolysis balance, promoted H9C2 cell proliferation, and inhibited apoptosis. PGC1α interacted with BAF60c. Knocking down BAF60c also activated the PGC1α/PPARα/mTOR pathway. Overexpression of PGC1α decreased the damage to H9C2 cells caused by BAF60c. Altogether, BAF60c downregulation activated the PGC1α/PPARα/mTOR pathway, maintained the oxidative metabolism/glycolysis balance and improved mitochondrial function in rat models of HF. This study may offer novel insights into HF treatment.

The Protective Effect of Qishen Granule on Heart Failure after Myocardial Infarction through Regulation of Calcium Homeostasis

Qishen granule (QSG) is a frequently prescribed traditional Chinese medicine formula, which improves heart function in patients with heart failure (HF). However, the cardioprotective mechanisms of QSG have not been fully understood. The current study aimed to elucidate whether the effect of QSG is mediated by ameliorating cytoplasmic calcium (Ca²⁺) overload in cardiomyocytes. The HF rat model was induced by left anterior descending (LAD) artery ligation surgery. Rats were randomly divided into sham, model, QSG-low dosage (QSG-L) treatment, QSG-high dosage (QSG-H) treatment, and positive drug (diltiazem) treatment groups. 28 days after surgery, cardiac functions were assessed by echocardiography. Levels of norepinephrine (NE) and angiotensin II (AngII) in the plasma were evaluated. Expressions of critical proteins in the calcium signaling pathway, including cell membrane calcium channel CaV1.2, sarcoendoplasmic reticulum ATPase 2a (SERCA2a), calcium/calmodulin-dependent protein kinase type II (CaMKII), and protein phosphatase calcineurin (CaN), were measured by Western blotting (WB) and immunohistochemistry (IHC). Echocardiography showed that left ventricular ejection fraction (EF) and fractional shortening (FS) value significantly decreased in the model group compared to the sham group, and illustrating heart function was severely impaired. Furthermore, levels of NE and AngII in the plasma were dramatically increased. Expressions of CaV1.2, CaMKII, and CaN in the cardiomyocytes were upregulated, and expressions of SERCA2a were downregulated in the model group. After treatment with QSG, both EF and FS values were increased. QSG significantly reduced levels of NE and AngII in the plasma. In particular, QSG prevented cytoplasmic Ca²⁺ overload by downregulating expression of CaV1.2 and upregulating expression of SERCA2a. Meanwhile, expressions of CaMKII and CaN were inhibited by QSG treatment. In conclusion, QSG could effectively promote heart function in HF rats by restoring cardiac Ca²⁺ homeostasis. These findings revealed novel therapeutic mechanisms of QSG and provided potential targets in the treatment of HF.

Pharmacological and cardiovascular perspectives on the treatment of COVID-19 with chloroquine derivatives

The novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19) and an ongoing severe pandemic. Curative drugs specific for COVID-19 are currently lacking. Chloroquine phosphate and its derivative hydroxychloroquine, which have been used in the treatment and prevention of malaria and autoimmune diseases for decades, were found to inhibit SARS-CoV-2 infection with high potency in vitro and have shown clinical and virologic benefits in COVID-19 patients. Therefore, chloroquine phosphate was first used in the treatment of COVID-19 in China. Later, under a limited emergency-use authorization from the FDA, hydroxychloroquine in combination with azithromycin was used to treat COVID-19 patients in the USA, although the mechanisms of the anti-COVID-19 effects remain unclear. Preliminary outcomes from clinical trials in several countries have generated controversial results. The desperation to control the pandemic overrode the concerns regarding the serious adverse effects of chloroquine derivatives and combination drugs, including lethal arrhythmias and cardiomyopathy. The risks of these treatments have become more complex as a result of findings that COVID-19 is actually a multisystem disease. While respiratory symptoms are the major clinical manifestations, cardiovascular abnormalities, including arrhythmias, myocarditis, heart failure, and ischemic stroke, have been reported in a significant number of COVID-19 patients. Patients with preexisting cardiovascular conditions (hypertension, arrhythmias, etc.) are at increased risk of severe COVID-19 and death. From pharmacological and cardiovascular perspectives, therefore, the treatment of COVID-19 with chloroquine and its derivatives should be systematically evaluated, and patients should be routinely monitored for cardiovascular conditions to prevent lethal adverse events.

Towards the Development of AgoKirs: New Pharmacological Activators to Study Kir2.x Channel and Target Cardiac Disease

Inward rectifier potassium ion channels (I_K1-channels) of the K_ir2.x family are responsible for maintaining a stable negative resting membrane potential in excitable cells, but also play a role in processes of non-excitable tissues, such as bone development. I_K1-channel loss-of-function, either congenital or acquired, has been associated with cardiac disease. Currently, basic research and specific treatment are hindered by the absence of specific and efficient K_ir2.x channel activators. However, twelve different compounds, including approved drugs, show off-target I_K1 activation. Therefore, these compounds contain valuable information towards the development of agonists of K_ir channels, AgoKirs. We reviewed the mechanism of I_K1 channel activation of these compounds, which can be classified as direct or indirect activators. Subsequently, we examined the most viable starting points for rationalized drug development and possible safety concerns with emphasis on cardiac and skeletal muscle adverse effects of AgoKirs. Finally, the potential value of AgoKirs is discussed in view of the current clinical applications of potentiators and activators in cystic fibrosis therapy.