IK1 channel agonist zacopride suppresses ventricular arrhythmias in conscious rats with healing myocardial infarction

The beneficial health effects of puerarin in the treatment of cardiovascular diseases: from mechanisms to therapeutics

Cardiovascular diseases (CVDs) are the leading causes of death globally that seriously threaten human health. Although novel western medicines have continued to be discovered over the past few decades to inhibit the progression of CVDs, new drug research and development for treating CVDs with less side effects and adverse reactions are continuously being desired. Puerarin is a natural product found in a variety of medicinal plants belonging to the flavonoid family with potent biological and pharmacological activities. Abundant research findings in the literature have suggested that puerarin possesses a promising prospect in treating CVDs. In recent years, numerous new molecular mechanisms of puerarin have been explored in experimental and clinical studies, providing new evidence for this plant metabolite to protect against CVDs. This article systematically introduces the history of use, bioavailability, and various dosage forms of puerarin and further summarizes recently published data on the major research advances and their underlying therapeutic mechanisms in treating CVDs. It may provide references for researchers in the fields of pharmacology, natural products, and internal medicine.

The Therapeutic Potential of Four Main Compounds of Zanthoxylum nitidum (Roxb.) DC: A Comprehensive Study on Biological Processes, Anti-Inflammatory Effects, and Myocardial Toxicity

Zanthoxylum nitidum (Roxb.) DC. (Z. nitidum) is a traditional Chinese medicinal plant that is indigenous to the southern regions of China. Previous research has provided evidence of the significant anti-inflammatory, antibacterial, and anticancer properties exhibited by Z. nitidum. The potential therapeutic effects and cardiac toxicity of Z. nitidum remain uncertain. The aim of this research was to investigate the potential therapeutic properties of the four main compounds of Z. nitidum in cardiovascular diseases, their impact on the electrical activity of cardiomyocytes, and the underlying mechanism of their anti-inflammatory effects. We selected the four compounds from Z. nitidum with a high concentration and specific biological activity: nitidine chloride (NC), chelerythrine chloride (CHE), magnoflorine chloride (MAG), and hesperidin (HE). A proteomic analysis was conducted on the myocardial tissues of beagle dogs following the administration of NC to investigate the role of NC in vivo and the associated biological processes. A bioinformatic analysis was used to predict the in vivo biological processes that MAG, CHE, and HE were involved in. Molecular docking was used to simulate the binding between compounds and their targets. The effect of the compounds on ion channels in cardiomyocytes was evaluated through a patch clamp experiment. Organ-on-a-chip (OOC) technology was developed to mimic the physiological conditions of the heart in vivo. Proteomic and bioinformatic analyses demonstrated that the four compounds of Z. nitidum are extensively involved in various cardiovascular-related biological pathways. The findings from the patch clamp experiments indicate that NC, CHE, MAG, and HE elicit a distinct activation or inhibition of the IK1 and ICa-L in cardiomyocytes. Finally, the anti-inflammatory effects of the compounds on cardiomyocytes were verified using OOC technology. NC, CHE, MAG, and HE demonstrate anti-inflammatory effects through their specific interactions with prostaglandin-endoperoxide synthase 2 (PTGS2) and significantly influence ion channels in cardiomyocytes. Our study provides a foundation for utilizing NC, CHE, MAG, and HE in the treatment of cardiovascular diseases.

Pacemaker activity and ion channels in the sinoatrial node cells: MicroRNAs and arrhythmia

The primary pacemaking activity of the heart is determined by a spontaneous action potential (AP) within sinoatrial node (SAN) cells. This unique AP generation relies on two mechanisms: membrane clocks and calcium clocks. Nonhomologous arrhythmias are caused by several functional and structural changes in the myocardium. MicroRNAs (miRNAs) are essential regulators of gene expression in cardiomyocytes. These miRNAs play a vital role in regulating the stability of cardiac conduction and in the remodeling process that leads to arrhythmias. Although it remains unclear how miRNAs regulate the expression and function of ion channels in the heart, these regulatory mechanisms may support the development of emerging therapies. This study discusses the spread and generation of AP in the SAN as well as the regulation of miRNAs and individual ion channels. Arrhythmogenicity studies on ion channels will provide a research basis for miRNA modulation as a new therapeutic target.

Regulation of Papillary Muscle Contractility by NAD and Ammonia Interplay: Contribution of Ion Channels and Exchangers

Various models, including stem cells derived and isolated cardiomyocytes with overexpressed channels, are utilized to analyze the functional interplay of diverse ion currents involved in cardiac automaticity and excitation-contraction coupling control. Here, we used β-NAD and ammonia, known hyperpolarizing and depolarizing agents, respectively, and applied inhibitory analysis to reveal the interplay of several ion channels implicated in rat papillary muscle contractility control. We demonstrated that: 4 mM β-NAD, having no strong impact on resting membrane potential (RMP) and action potential duration (APD90) of ventricular cardiomyocytes, evoked significant suppression of isometric force (F) of paced papillary muscle. Reactive blue 2 restored F to control values, suggesting the involvement of P2Y-receptor-dependent signaling in β-NAD effects. Meantime, 5 mM NH₄Cl did not show any effect on F of papillary muscle but resulted in significant RMP depolarization, APD90 shortening, and a rightward shift of I-V relationship for total steady state currents in cardiomyocytes. Paradoxically, NH₄Cl, being added after β-NAD and having no effect on RMP, APD, and I-V curve, recovered F to the control values, indicating β-NAD/ammonia antagonism. Blocking of HCN, Kir2.x, and L-type calcium channels, Ca²⁺-activated K⁺ channels (SK, IK, and BK), or NCX exchanger reverse mode prevented this effect, indicating consistent cooperation of all currents mediated by these channels and NCX. We suggest that the activation of Kir2.x and HCN channels by extracellular K⁺, that creates positive and negative feedback, and known ammonia and K⁺ resemblance, may provide conditions required for the activation of all the chain of channels involved in the interplay. Here, we present a mechanistic model describing an interplay of channels and second messengers, which may explain discovered antagonism of β-NAD and ammonia on rat papillary muscle contractile activity.

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.

Anti-Arrhythmic Effects of Sodium-Glucose Co-Transporter 2 Inhibitors

Arrhythmias are clinically prevalent with a high mortality rate. They impose a huge economic burden, thereby substantially affecting the quality of life. Sodium-glucose co-transporter 2 inhibitor (SGLT2i) is a new type of hypoglycemic drug, which can regulate blood glucose level safely and effectively. Additionally, it reduces the occurrence and progression of heart failure and cardiovascular events significantly. Recently, studies have found that SGLT2i can alleviate the occurrence and progression of cardiac arrhythmias; however, the exact mechanism remains unclear. In this review, we aimed to discuss and summarize new literature on different modes in which SGLT2i ameliorates the occurrence and development of cardiac arrhythmias.

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.

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 Agonist of Inward Rectifier Potassium Channel (IK1) Attenuates Rat Reperfusion Arrhythmias Linked to CaMKII Signaling

Inward rectifier potassium channels (IK1, Kir) are known to play critical roles in arrhythmogenesis. Thus, how IK1 agonist affects reperfusion arrhythmias needs to be clarified, and its underlying mechanisms should be determined. Reperfusion arrhythmias were modeled by coronary ligation (ischemia, 15 minutes) and release (reperfusion, 15 minutes). Zacopride (1.5-50 μg/kg in vivo, or 0.1-10 μmol/Lex vivo) was applied in the settings of pretreatment (3 minutes before coronary ligation) and posttreatment (5 minutes after coronary ligation). Hypoxia (45 minutes) /reoxygenation (30 minutes) model was established in cultured H9c2 (2-1) cardiomyocytes. Zacopride or KN93 was applied before hypoxia (pretreatment). In the setting of pre- or posttreatment, zacopride at 15 μg/kg in vivo or 1 μmol/Lin vitro exhibited superlative protections on reperfusion arrhythmias or intracellular calcium overload. Western blot data from ex vivo hearts or H9c2 (2-1) cardiomyocytes showed that I/R (H/R) induced the inhibition of Kir2.1 (the dominant subunit of IK1 channel in ventricle), phosphorylation and oxidation of CaMKII, downregulation of SERCA2, phosphorylation of phospholamban (at Thr17), and activation of caspase-3. Zacopride treatment (1 μmol/L) was noted to strikingly restore the expression of Kir2.1 and SERCA2 and decrease the activity of CaMKII, phospholamban, and caspase-3. These effects were largely eliminated by co-application of IK1 blocker BaCl2. CaMKII inhibitor KN93 attenuated calcium overload and p-PLB (Thr17) in an IK1-independent manner. IK1-depedent inhibition of CaMKII activity is found to be a key cardiac salvage signaling under Ca2+ dyshomeostasis and reactive oxygen species (ROS) stress. IK1 might be a novel target for pharmacological conditioning of reperfusion arrhythmia, especially for the application after unpredictable ischemia.

Atherogenic L5 LDL induces cardiomyocyte apoptosis and inhibits KATP channels through CaMKII activation

Background

Cardiac Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) activation plays a critical role in cardiomyocyte (CM) apoptosis and arrhythmia. Functional ATP-sensitive potassium (K_ATP) channels are essential for cardiac protection during ischemia. In cultured CMs, L5 low-density lipoprotein (LDL) induces apoptosis and QTc prolongation. L5 is a highly electronegative and atherogenic aberrant form of LDL, and its levels are significantly higher in patients with cardiovascular-related diseases. Here, the role of L5 in cardiac injury was studied by evaluating the effects of L5 on CaMKII activity and K_ATP channel physiology in CMs.

Methods

Cultured neonatal rat CMs (NRCMs) were treated with a moderate concentration (ie, 7.5 μg/mL) of L5 or L1 (the least electronegative LDL subfraction). NRCMs were examined for apoptosis and viability, CaMKII activity, and the expression of phosphorylated CaMKIIδ and NOX2/gp91^phox. The function of K_ATP and action potentials (APs) was analyzed by using the patch-clamp technique.

Results

In NRCMs, L5 but not L1 significantly induced cell apoptosis and reduced cell viability. Furthermore, L5 decreased Kir6.2 expression by more than 50%. Patch-clamp analysis showed that L5 reduced the K_ATP current (I_KATP) density induced by pinacidil, a K_ATP opener. The partial recovery of the inward potassium current during pinacidil washout was susceptible to subsequent inhibition by the I_KATP blocker glibenclamide. Suppression of I_KATP by L5 significantly prolonged the AP duration. L5 also significantly increased the activity of CaMKII, the phosphorylation of CaMKIIδ, and the expression of NOX2/gp91^phox. L5-induced apoptosis was prevented by the addition of the CaMKII inhibitor KN93 and the reactive oxygen species scavenger Mn (III)TBAP.

Conclusions

L5 but not L1 induces CM damage through the activation of the CaMKII pathway and increases arrhythmogenicity in CMs by modulating the AP duration. These results help to explain the harmful effects of L5 in cardiovascular-related disease.