Cardiomyocyte electrophysiology and its modulation: current views and future prospects

Heart rate variability in patients with atrial fibrillation of sinus rhythm or atrial fibrillation: chaos or merit?

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia characterized by consistently irregular atrial and ventricular contractions. Heart rate variability (HRV) refers to the changes in the intervals between consecutive ventricular heartbeats. In sinus rhythm, HRV may be subtle and is quantitatively reflecting the dynamic interplay of the cardiac autonomic nervous system, which plays a crucial role in the onset, development, and maintenance of AF. HRV metrics, consisting of time-domain, frequency-domain, and nonlinear parameters, have been verified to vary significantly before and after AF episodes, and AF treatment-related procedures such as electrical cardioversion, ablation, and surgery of AF. Therefore, HRV may serve as a digital biomarker in predicting AF risk in long-term and acute risk period, identification of patients with AF risk in sinus rhythm and recurrence risk stratification after procedures. HRV in AF rhythm, predominantly influenced by dynamic atrioventricular node conduction under the onslaught of irregular atrial impulses, shows a huge disparity compared to that in sinus rhythm. Despite this, HRV in AF rhythm still provides valuable prognostic information, as reduced HRV may indicate a poor heart function and outcomes in patients with AF. Despite being influenced by lots of variables, HRV can still serve as an independent digital biomarker in the clinical management of AF throughout its entire lifecycle.

Evaluation of phthalates induced cardiotoxicity using human iPSCs-derived cardiomyocyte and dual-cardiotoxicity evaluation methods

Phthalates, known as plasticizers, are endocrine disruptor, and their risks are being highlighted as their use increases worldwide. Di-2-ethylhexyl phthalate (DEHP), the most prevalent of the phthalates, is known to be toxic to humans, and it has recently been reported to be linked to cardiotoxicity. Although many other phthalates are also widely used, data on their cardiotoxic effects are yet to be well established. In this study, we assessed the cardiotoxic potential of various phthalates using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and a microelectrode array-based dual-cardiotoxicity evaluation method previously reported. Cytotoxicity results showed that acute exposure to DEHP, dibutyl phthalate (DBP), benzyl butyl phthalate (BBP), and di-n-octyl phthalate (DnOP) did not affect the viability of hiPSC-CMs. Before examining the functional changes in hiPSC-CMs caused by exposure to these four phthalates, we present changes in field potential (FP) and contractility based on the blocking of major ions for reference. Contrary to concerns, FP results showed a dramatic decrease in spike amplitude, beat period, and FP duration (FPD) at high doses of DBP and BBP rather than DEHP. Interestingly, DnOP resulted in a prolonged FPD, unlike the others. Furthermore, contractility results indicated that, unlike DEHP and DnOP, high doses of DBP and BBP caused beating arrest along with decreased beat amplitude. Overall, this study demonstrated that phthalates other than DEHP can also induce cardiotoxicity, even with acute exposure. It is expected that the application of the established evaluation method will facilitate the development of safe alternatives.

p21-Activated Kinase 1 (Pak1) as an Element in Functional and Dysfunctional Interplay Among the Myocardium, Adipose Tissue, and Pancreatic Beta Cells

This review focuses on p21-activated kinase 1 (Pak1), a multifunctional, highly conserved enzyme that regulates multiple downstream effectors present in many tissues. Upstream signaling via Ras-related small G-proteins, Cdc42/Rac1 promotes the activity of Pak1. Our hypothesis is that this signaling cascade is an important element in communication among the myocardium, adipose tissue, and pancreatic β-cells. Evidence indicates that a shared property of these tissues is that structure/function stability requires homeostatic Pak1 activity. Increases or decreases in Pak1 activity may promote dysfunction or increase susceptibility to stressors. Evidence that increased levels of Pak1 activity may be protective provides support for efforts to develop therapeutic approaches activating Pak1 with potential use in prevalent disorders associated with obesity, diabetes, and myocardial dysfunction. On the other hand, since increased Pak1 activity is associated with cancer progression, there has been a significant effort to develop Pak1 inhibitors. These opposing therapeutic approaches highlight the need for a deep understanding of Pak1 signaling in relation to the development of effective and selective therapies with minimal or absent off-target effects.

Impact of plant-derived antioxidants on heart aging: a mechanistic outlook

Heart aging involves a complex interplay of genetic and environmental influences, leading to a gradual deterioration of cardiovascular integrity and function. Age-related physiological changes, including ventricular hypertrophy, diastolic dysfunction, myocardial fibrosis, increased arterial stiffness, and endothelial dysfunction, are influenced by key mechanisms like autophagy, inflammation, and oxidative stress. This review aims to explore the therapeutic potential of plant-derived bioactive antioxidants in mitigating heart aging. These compounds, often rich in polyphenols, flavonoids, and other phytochemicals, exhibit notable antioxidant, anti-inflammatory, and cardioprotective properties. These substances have intricate cardioprotective properties, including the ability to scavenge ROS, enhance endogenous antioxidant defenses, regulate signaling pathways, and impede fibrosis and inflammation-promoting processes. By focusing on key molecular mechanisms linked to cardiac aging, antioxidants produced from plants provide significant promise to reduce age-related cardiovascular decline and improve general heart health. Through a comprehensive analysis of preclinical and clinical studies, this work highlights the mechanisms associated with heart aging and the promising effects of plant-derived antioxidants. The findings may helpful for researchers in identifying specific molecules with therapeutic and preventive potential for aging heart.

Microfluidic platforms for monitoring cardiomyocyte electromechanical activity

Cardiovascular diseases account for ~40% of global deaths annually. This situation has revealed the urgent need for the investigation and development of corresponding drugs for pathogenesis due to the complexity of research methods and detection techniques. An in vitro cardiomyocyte model is commonly used for cardiac drug screening and disease modeling since it can respond to microphysiological environmental variations through mechanoelectric feedback. Microfluidic platforms are capable of accurate fluid control and integration with analysis and detection techniques. Therefore, various microfluidic platforms (i.e., heart-on-a-chip) have been applied for the reconstruction of the physiological environment and detection of signals from cardiomyocytes. They have demonstrated advantages in mimicking the cardiovascular structure and function in vitro and in monitoring electromechanical signals. This review presents a summary of the methods and technologies used to monitor the contractility and electrophysiological signals of cardiomyocytes within microfluidic platforms. Then, applications in common cardiac drug screening and cardiovascular disease modeling are presented, followed by design strategies for enhancing physiology studies. Finally, we discuss prospects in the tissue engineering and sensing techniques of microfluidic platforms.

Recent Development of Chemigenetic Hybrid Voltage Indicators Enabled by Bioconjugation Chemistry

Fluorescent voltage indicators enable the optical recording of electrophysiology across large cell populations with subcellular resolution; however, their application is often constrained by a limited photon budget. To address this limitation, advanced bioconjugation methods have been employed to site-specifically attach bright and photostable organic dyes to cell-specific protein scaffolds in live cells. The resulting chemigenetic hybrid voltage indicators enable sustained monitoring of voltage fluctuations with an exceptional signal-to-noise ratio, both in vitro and in vivo. This Viewpoint discusses recent advancements in the development of these indicators through bioconjugation chemistry.

A critical review on advances and challenges of bioprinted cardiac patches

Myocardial infarction (MI), which causes irreversible myocardium necrosis, affects 0.25 billion people globally and has become one of the most significant epidemics of our time. Over the past few years, bioprinting has moved beyond a concept of simply incorporating cells into biomaterials, to strategically defining the microenvironment (e.g., architecture, biomolecular signalling, mechanical stimuli, etc.) within which the cells are printed. Among the different bioprinting applications, myocardial repair is a field that has seen some of the most significant advances towards the management of the repaired tissue microenvironment. This review critically assesses the most recent biomedical innovations being carried out in cardiac patch bioprinting, with specific considerations given to the biomaterial design parameters, growth factors/cytokines, biomechanical and bioelectrical conditioning, as well as innovative biomaterial-based "4D" bioprinting (3D scaffold structure + temporal morphology changes) of myocardial tissues, immunomodulation and sustained delivery systems used in myocardium bioprinting. Key challenges include the ability to generate large quantities of cardiac cells, achieve high-density capillary networks, establish biomaterial designs that are comparable to native cardiac extracellular matrix, and manage the sophisticated systems needed for combining cardiac tissue microenvironmental cues while simultaneously establishing bioprinting technologies yielding both high-speed and precision. This must be achieved while considering quality assurance towards enabling reproducibility and clinical translation. Moreover, this manuscript thoroughly discussed the current clinical translational hurdles and regulatory issues associated with the post-bioprinting evaluation, storage, delivery and implantation of the bioprinted myocardial patches. Overall, this paper provides insights into how the clinical feasibility and important regulatory concerns may influence the design of the bioink (biomaterials, cell sources), fabrication and post-fabrication processes associated with bioprinting of the cardiac patches. This paper emphasizes that cardiac patch bioprinting requires extensive collaborations from imaging and 3D modelling technical experts, biomaterial scientists, additive manufacturing experts and healthcare professionals. Further, the work can also guide the field of cardiac patch bioprinting moving forward, by shedding light on the potential use of robotics and automation to increase productivity, reduce financial cost, and enable standardization and true commercialization of bioprinted cardiac patches. STATEMENT OF SIGNIFICANCE: The manuscript provides a critical review of important themes currently pursued for heart patch bioprinting, including critical biomaterial design parameters, physiologically-relevant cardiac tissue stimulations, and newly emerging cardiac tissue bioprinting strategies. This review describes the limited number of studies, to date in the literature, that describe systemic approaches to combine multiple design parameters, including capabilities to yield high-density capillary networks, establish biomaterial composite designs similar to native cardiac extracellular matrix, and incorporate cardiac tissue microenvironmental cues, while simultaneously establishing bioprinting technologies that yield high-speed and precision. New tools such as artificial intelligence may provide the analytical power to consider multiple design parameters and identify an optimized work-flow(s) for enabling the clinical translation of bioprinted cardiac patches.

Exosomal Preconditioning of Human iPSC-Derived Cardiomyocytes Beneficially Alters Cardiac Electrophysiology and Micro RNA Expression

Experimental evidence, both in vitro and in vivo, has indicated cardioprotective effects of extracellular vesicles (EVs) derived from various cell types, including induced pluripotent stem cell-derived cardiomyocytes. The biological effects of EV secretion, particularly in the context of ischemia and cardiac electrophysiology, remain to be fully explored. Therefore, the goal of this study was to unveil the effects of exosome (EXO)-mediated cell-cell signaling during hypoxia by employing a simulated preconditioning approach on human-induced pluripotent stem cell-derived cardiomyocytes (hIPSC-CMs). Electrophysiological activity of hIPSC-CMs was measured using a multielectrode array (MEA) system. A total of 16 h of hypoxic stress drastically increased the beat period. Moreover, hIPSC-CMs preconditioned with EXOs displayed significantly longer beat periods compared with non-treated cells after 16 h of hypoxia (+15.7%, p < 0.05). Furthermore, preconditioning with hypoxic EXOs resulted in faster excitation-contraction (EC) coupling compared with non-treated hIPSC-CMs after 16 h of hypoxia (-25.3%, p < 0.05). Additionally, microRNA (miR) sequencing and gene target prediction analysis of the non-treated and pre-conditioned hIPSC-CMs identified 10 differentially regulated miRs and 44 gene targets. These results shed light on the intricate involvement of miRs, emphasizing gene targets associated with cell survival, contraction, apoptosis, reactive oxygen species (ROS) regulation, and ion channel modulation. Overall, this study demonstrates that EXOs secreted by hIPSC-CM during hypoxia beneficially alter electrophysiological properties in recipient cells exposed to hypoxic stress, which could play a crucial role in the development of targeted interventions to improve outcomes in ischemic heart conditions.

Cardiac arrhythmogenesis: roles of ion channels and their functional modification

Cardiac arrhythmias cause significant morbidity and mortality and pose a major public health problem. They arise from disruptions in the normally orderly propagation of cardiac electrophysiological activation and recovery through successive cardiomyocytes in the heart. They reflect abnormalities in automaticity, initiation, conduction, or recovery in cardiomyocyte excitation. The latter properties are dependent on surface membrane electrophysiological mechanisms underlying the cardiac action potential. Their disruption results from spatial or temporal instabilities and heterogeneities in the generation and propagation of cellular excitation. These arise from abnormal function in their underlying surface membrane, ion channels, and transporters, as well as the interactions between them. The latter, in turn, form common regulatory targets for the hierarchical network of diverse signaling mechanisms reviewed here. In addition to direct molecular-level pharmacological or physiological actions on these surface membrane biomolecules, accessory, adhesion, signal transduction, and cytoskeletal anchoring proteins modify both their properties and localization. At the cellular level of excitation-contraction coupling processes, Ca2+ homeostatic and phosphorylation processes affect channel activity and membrane excitability directly or through intermediate signaling. Systems-level autonomic cellular signaling exerts both acute channel and longer-term actions on channel expression. Further upstream intermediaries from metabolic changes modulate the channels both themselves and through modifying Ca2+ homeostasis. Finally, longer-term organ-level inflammatory and structural changes, such as fibrotic and hypertrophic remodeling, similarly can influence all these physiological processes with potential pro-arrhythmic consequences. These normal physiological processes may target either individual or groups of ionic channel species and alter with particular pathological conditions. They are also potentially alterable by direct pharmacological action, or effects on longer-term targets modifying protein or cofactor structure, expression, or localization. Their participating specific biomolecules, often clarified in experimental genetically modified models, thus constitute potential therapeutic targets. The insights clarified by the physiological and pharmacological framework outlined here provide a basis for a recent modernized drug classification. Together, they offer a translational framework for current drug understanding. This would facilitate future mechanistically directed therapeutic advances, for which a number of examples are considered here. The latter are potentially useful for treating cardiac, in particular arrhythmic, disease.

Basic science of cardiac contractility modulation therapy: Molecular and electrophysiological mechanisms

In heart failure with reduced ejection fraction and heart failure with preserved ejection fraction, profound cellular and molecular changes have recently been documented in the failing myocardium. These changes include altered calcium handling and metabolic efficiency of the cardiac myocyte, reactivation of the fetal gene program, changes in the electrophysiological properties of the heart, and accumulation of collagen (fibrosis) at the interstitial level. Cardiac contractility modulation therapy is an innovative device-based therapy currently approved for heart failure with reduced ejection fraction in patients with narrow QRS complex and under investigation for the treatment of heart failure with preserved ejection fraction. This therapy is based on the delivery of high-voltage biphasic electrical signals to the septal wall of the right ventricle during the absolute refractory period of the myocardium. At the cellular level, in patients with heart failure with reduced ejection fraction, cardiac contractility modulation therapy has been shown to restore calcium handling and improve the metabolic status of cardiac myocytes, reverse the heart failure-associated fetal gene program, and reduce the extent of interstitial fibrosis. This review summarizes the preclinical literature on the use of cardiac contractility modulation therapy in heart failure with reduced and preserved ejection fraction, correlating the molecular and electrophysiological effects with the clinical benefits demonstrated by this therapy.