Polyunsaturated fatty acid analogues differentially affect cardiac NaV, CaV, and KV channels through unique mechanisms

Eicosapentaenoic Acid Rescues Cav1.2-L-Type Ca2+ Channel Decline Caused by Saturated Fatty Acids via Both Free Fatty Acid Receptor 4-Dependent and -Independent Pathways in Cardiomyocytes

Dietary intake of omega-3 polyunsaturated fatty acids (eicosapentaenoic acid, EPA) exerts antiarrhythmic effects, although the mechanisms are poorly understood. Here, we investigated the possible beneficial actions of EPA on saturated fatty acid-induced changes in the L-type Ca2+ channel in cardiomyocytes. Cardiomyocytes were cultured with an oleic acid/palmitic acid mixture (OAPA) in the presence or absence of EPA. Beating rate reduction in cardiomyocytes caused by OAPA were reversed by EPA. EPA also retrieved a reduction in Cav1.2 L-type Ca2+ current, mRNA, and protein caused by OAPA. Immunocytochemical analysis revealed a distinct downregulation of the Cav1.2 channel caused by OAPA with a concomitant decrease in the phosphorylated component of a transcription factor adenosine-3',5'-cyclic monophosphate (cAMP) response element binding protein (CREB) in the nucleus, which were rescued by EPA. A free fatty acid receptor 4 (FFAR4) agonist TUG-891 reversed expression of Cav1.2 and CREB mRNA caused by OAPA, whereas an FFAR4 antagonist AH-7614 abolished the effects of EPA. Excessive reactive oxygen species (ROS) accumulation caused by OAPA decreased Cav1.2 and CREB mRNA expressions, which was reversed by an ROS scavenger. Our data suggest that EPA rescues cellular Cav1.2-Ca2+ channel decline caused by OAPA lipotoxicity and oxidative stresses via both free fatty acid receptor 4-dependent and -independent pathways.

Targeting ion channels with ultra-large library screening for hit discovery

Ion channels play a crucial role in a variety of physiological and pathological processes, making them attractive targets for drug development in diseases such as diabetes, epilepsy, hypertension, cancer, and chronic pain. Despite the importance of ion channels in drug discovery, the vastness of chemical space and the complexity of ion channels pose significant challenges for identifying drug candidates. The use of in silico methods in drug discovery has dramatically reduced the time and cost of drug development and has the potential to revolutionize the field of medicine. Recent advances in computer hardware and software have enabled the screening of ultra-large compound libraries. Integration of different methods at various scales and dimensions is becoming an inevitable trend in drug development. In this review, we provide an overview of current state-of-the-art computational chemistry methodologies for ultra-large compound library screening and their application to ion channel drug discovery research. We discuss the advantages and limitations of various in silico techniques, including virtual screening, molecular mechanics/dynamics simulations, and machine learning-based approaches. We also highlight several successful applications of computational chemistry methodologies in ion channel drug discovery and provide insights into future directions and challenges in this field.

Mechanistic understanding of KCNQ1 activating polyunsaturated fatty acid analogs

The KCNQ1 channel is important for the repolarization phase of the cardiac action potential. Loss of function mutations in KCNQ1 can cause long QT syndrome (LQTS), which can lead to cardiac arrythmia and even sudden cardiac death. We have previously shown that polyunsaturated fatty acids (PUFAs) and PUFA analogs can activate the cardiac KCNQ1 channel, making them potential therapeutics for the treatment of LQTS. PUFAs bind to KCNQ1 at two different binding sites: one at the voltage sensor (Site I) and one at the pore (Site II). PUFA interaction at Site I shifts the voltage dependence of the channel to the left, while interaction at Site II increases maximal conductance. The PUFA analogs, linoleic-glycine and linoleic-tyrosine, are more effective than linoleic acid at Site I, but less effective at Site II. Using both simulations and experiments, we find that the larger head groups of linoleic-glycine and linoleic-tyrosine interact with more residues than the smaller linoleic acid at Site I. We propose that this will stabilize the negatively charged PUFA head group in a position to better interact electrostatically with the positively charges in the voltage sensor. In contrast, the larger head groups of linoleic-glycine and linoleic-tyrosine compared with linoleic acid prevent a close fit of these PUFA analogs in Site II, which is more confined. In addition, we identify several KCNQ1 residues as critical PUFA-analog binding residues, thereby providing molecular models of specific interactions between PUFA analogs and KCNQ1. These interactions will aid in future drug development based on PUFA-KCNQ1 channel interactions.

Pharmacological Screening of Kv7.1 and Kv7.1/KCNE1 Activators as Potential Antiarrhythmic Drugs in the Zebrafish Heart

Long QT syndrome (LQTS) can lead to ventricular arrhythmia and sudden cardiac death. The most common congenital cause of LQTS is mutations in the channel subunits generating the cardiac potassium current IKs. Zebrafish (Danio rerio) have been proposed as a powerful system to model human cardiac diseases due to the similar electrical properties of the zebrafish heart and the human heart. We used high-resolution all-optical electrophysiology on ex vivo zebrafish hearts to assess the effects of IKs analogues on the cardiac action potential. We found that chromanol 293B (an IKs inhibitor) prolonged the action potential duration (APD) in the presence of E4031 (an IKr inhibitor applied to drug-induced LQT2), and to a lesser extent, in the absence of E4031. Moreover, we showed that PUFA analogues slightly shortened the APD of the zebrafish heart. However, PUFA analogues failed to reverse the APD prolongation in drug-induced LQT2. However, a more potent IKs activator, ML-277, partially reversed the APD prolongation in drug-induced LQT2 zebrafish hearts. Our results suggest that IKs plays a limited role in ventricular repolarizations in the zebrafish heart under resting conditions, although it plays a more important role when the IKr is compromised, as if the IKs in zebrafish serves as a repolarization reserve as in human hearts. This study shows that potent IKs activators can restore the action potential duration in drug-induced LQT2 in the zebrafish heart.

Structural determinants of acid-sensing ion channel potentiation by single chain lipids

Acid-sensing ion channels (ASICs) are sensitized to activation by inflammatory mediators such as the polyunsaturated fatty acid (PUFA) arachidonic acid (AA). Previous work has shown that AA can potentiate ASIC currents at subsaturating proton concentrations, but the structural mechanisms of this change in gating are not understood. Here we show that PUFAs cause multiple gating changes in ASIC3, including shifting the pH dependence of activation, slowing the rate of desensitization, and increasing the current even at a saturating pH. The impact on gating depends on the nature of both the head and tail of the lipid, with the head group structure primarily determining the magnitude of the effect on the channel. An N-acyl amino acid (NAAA), arachidonyl glycine (AG), is such a strong regulator that it can act as a ligand at neutral pH. Mutation of an arginine in the outer segment of TM1 (R64) eliminated the effect of docosahexaenoic acid (DHA) even at high concentrations, suggesting a potential interaction site for the lipid on the channel. Our results suggest a model in which PUFAs bind to ASICs via both their tail group and an electrostatic interaction between the negatively charged PUFA head group and the positively charged arginine side chain. These data provide the first look at the structural features of lipids that are important for modulating ASICs and suggest a potential binding site for PUFAs on the channel.

Circulating linoleic acid at the time of myocardial infarction and risk of primary ventricular fibrillation

Primary ventricular fibrillation (PVF) is a major driver of cardiac arrest in the acute phase of ST-segment elevation myocardial infarction (STEMI). Enrichment of cardiomyocyte plasma membranes with dietary polyunsaturated fatty acids (PUFA) reduces vulnerability to PVF experimentally, but clinical data are scarce. PUFA status in serum phospholipids is a valid surrogate biomarker of PUFA status in cardiomyocytes within a wide range of dietary PUFA. In this nested case–control study (n = 58 cases of STEMI-driven PVF, n = 116 control non-PVF STEMI patients matched for age, sex, smoking status, dyslipidemia, diabetes mellitus and hypertension) we determined fatty acids in serum phospholipids by gas-chromatography, and assessed differences between cases and controls, applying the Benjamini–Hochberg procedure on nominal P-values to control the false discovery rate (FDR). Significant differences between cases and controls were restricted to linoleic acid (LA), with PVF patients showing a lower level (nominal P = 0.002; FDR-corrected P = 0.027). In a conditional logistic regression model, each one standard deviation increase in the proportion of LA was related to a 42% lower prevalence of PVF (odds ratio = 0.58; 95% confidence interval, 0.37, 0.90; P = 0.02). The association lasted after the inclusion of confounders. Thus, regular consumption of LA-rich foods (nuts, oils from seeds) may protect against ischemia-driven malignant arrhythmias.

Essential Fatty Acids as Biomedicines in Cardiac Health

The destructive impact of cardiovascular diseases on health, including heart failure, peripheral artery disease, atherosclerosis, stroke, and other cardiac pathological conditions, positions these health conditions as leading causes of increased global mortality rates, thereby impacting the human quality of life. The considerable changes in modern lifestyles, including the increase in food intake and the change in eating habits, will unavoidably lead to an unbalanced consumption of essential fatty acids, with a direct effect on cardiovascular health problems. In the last decade, essential fatty acids have become the main focus of scientific research in medical fields aiming to establish their impact for preventing cardiovascular diseases and the associated risk factors. Specifically, polyunsaturated fatty acids (PUFA), such as omega 3 fatty acids, and monounsaturated fatty acids from various sources are mentioned in the literature as having a cardio-protective role, due to various biological mechanisms that are still to be clarified. This review aims to describe the major biological mechanisms of how diets rich in essential fatty acids, or simply essential fatty acid administration, could have anti-inflammatory, vasodilatory, anti-arrhythmic, antithrombotic, antioxidant, and anti-atherogenic effects. This review describes findings originating from clinical studies in which dietary sources of FAs were tested for their role in mitigating the impact of heart disorders in human health.

Ventricular voltage-gated ion channels: Detection, characteristics, mechanisms, and drug safety evaluation

Cardiac voltage-gated ion channels (VGICs) play critical roles in mediating cardiac electrophysiological signals, such as action potentials, to maintain normal heart excitability and contraction. Inherited or acquired alterations in the structure, expression, or function of VGICs, as well as VGIC-related side effects of pharmaceutical drug delivery can result in abnormal cellular electrophysiological processes that induce life-threatening cardiac arrhythmias or even sudden cardiac death. Hence, to reduce possible heart-related risks, VGICs must be acknowledged as important targets in drug discovery and safety studies related to cardiac disease. In this review, we first summarize the development and application of electrophysiological techniques that are employed in cardiac VGIC studies alone or in combination with other techniques such as cryoelectron microscopy, optical imaging and optogenetics. Subsequently, we describe the characteristics, structure, mechanisms, and functions of various well-studied VGICs in ventricular myocytes and analyze their roles in and contributions to both physiological cardiac excitability and inherited cardiac diseases. Finally, we address the implications of the structure and function of ventricular VGICs for drug safety evaluation. In summary, multidisciplinary studies on VGICs help researchers discover potential targets of VGICs and novel VGICs in heart, enrich their knowledge of the properties and functions, determine the operation mechanisms of pathological VGICs, and introduce groundbreaking trends in drug therapy strategies, and drug safety evaluation.

Identification of PUFA interaction sites on the cardiac potassium channel KCNQ1

Polyunsaturated fatty acids (PUFAs), but not saturated fatty acids, modulate ion channels such as the cardiac KCNQ1 channel, although the mechanism is not completely understood. Using both simulations and experiments, we find that PUFAs interact directly with the KCNQ1 channel via two different binding sites: one at the voltage sensor and one at the pore. These two amphiphilic binding pockets stabilize the negatively charged PUFA head group by electrostatic interactions with R218, R221, and K316, while the hydrophobic PUFA tail is selectively stabilized by cassettes of hydrophobic residues. The rigid saturated tail of stearic acid prevents close contacts with KCNQ1. By contrast, the mobile tail of PUFA linoleic acid can be accommodated in the crevice of the hydrophobic cassette, a defining feature of PUFA selectivity in KCNQ1. In addition, we identify Y268 as a critical PUFA anchor point underlying fatty acid selectivity. Combined, this study provides molecular models of direct interactions between PUFAs and KCNQ1 and identifies selectivity mechanisms. Long term, this understanding may open new avenues for drug development based on PUFA mechanisms.

Assessing hERG1 Blockade from Bayesian Machine-Learning-Optimized Site Identification by Ligand Competitive Saturation Simulations

Drug-induced cardiotoxicity is a potentially lethal and yet one of the most common side effects with the drugs in clinical use. Most of the drug-induced cardiotoxicity is associated with an off-target pharmacological blockade of K+ currents carried out by the cardiac Human-Ether-a-go-go-Related (hERG1) potassium channel. There is a compulsory preclinical stage safety assessment for the hERG1 blockade for all classes of drugs, which adds substantially to the cost of drug development. The availability of a high-resolution cryogenic electron microscopy (cryo-EM) structure for the channel in its open/depolarized state solved in 2017 enabled the application of molecular modeling for rapid assessment of drug blockade by molecular docking and simulation techniques. More importantly, if successful, in silico methods may allow a path to lead-compound salvaging by mapping out key block determinants. Here, we report the blind application of the site identification by the ligand competitive saturation (SILCS) protocol to map out druggable/regulatory hotspots in the hERG1 channel available for blockers and activators. The SILCS simulations use small solutes representative of common functional groups to sample the chemical space for the entire protein and its environment using all-atom simulations. The resulting chemical maps, FragMaps, explicitly account for receptor flexibility, protein-fragment interactions, and fragment desolvation penalty allowing for rapid ranking of potential ligands as blockers or nonblockers of hERG1. To illustrate the power of the approach, SILCS was applied to a test set of 55 blockers with diverse chemical scaffolds and pIC50 values measured under uniform conditions. The original SILCS model was based on the all-atom modeling of the hERG1 channel in an explicit lipid bilayer and was further augmented with a Bayesian-optimization/machine-learning (BML) stage employing an independent literature-derived training set of 163 molecules. BML approach was used to determine weighting factors for the FragMaps contributions to the scoring function. pIC50 predictions from the combined SILCS/BML approach to the 55 blockers showed a Pearson correlation (PC) coefficient of >0.535 relative to the experimental data. SILCS/BML model was shown to yield substantially improved performance as compared to commonly used rigid and flexible molecular docking methods for a well-established cohort of hERG1 blockers, where no correlation with experimental data was recorded. SILCS/BML results also suggest that a proper weighting of protonation states of common blockers present at physiological pH is essential for accurate predictions of blocker potency. The precalculated and optimized SILCS FragMaps can now be used for the rapid screening of small molecules for their cardiotoxic potential as well as for exploring alternative binding pockets in the hERG1 channel with applications to the rational design of activators.

Insights into Cardiac IKs (KCNQ1/KCNE1) Channels Regulation

The delayed rectifier potassium IKs channel is an important regulator of the duration of the ventricular action potential. Hundreds of mutations in the genes (KCNQ1 and KCNE1) encoding the IKs channel cause long QT syndrome (LQTS). LQTS is a heart disorder that can lead to severe cardiac arrhythmias and sudden cardiac death. A better understanding of the IKs channel (here called the KCNQ1/KCNE1 channel) properties and activities is of great importance to find the causes of LQTS and thus potentially treat LQTS. The KCNQ1/KCNE1 channel belongs to the superfamily of voltage-gated potassium channels. The KCNQ1/KCNE1 channel consists of both the pore-forming subunit KCNQ1 and the modulatory subunit KCNE1. KCNE1 regulates the function of the KCNQ1 channel in several ways. This review aims to describe the current structural and functional knowledge about the cardiac KCNQ1/KCNE1 channel. In addition, we focus on the modulation of the KCNQ1/KCNE1 channel and its potential as a target therapeutic of LQTS.

Polyunsaturated fatty acid-derived IKs channel activators shorten the QT interval ex-vivo and in-vivo

AIM

We aimed to assess the ability of natural and modified polyunsaturated fatty acids (PUFAs) to shorten QT interval in ex-vivo and in-vivo guinea pig hearts.

METHODS

The effect of one natural (docosahexaenoic acid [DHA]) and three modified (linoleoyl glycine [Lin-GLY], docosahexaenoyl glycine [DHA-GLY], N-arachidonoyl taurine [N-AT]) PUFAs on ventricular action potential duration (APD) and QT interval was studied in a E4031 drug-induced long QT2 model of ex-vivo guinea pig hearts. The effect of DHA-GLY on QT interval was also studied in in-vivo guinea pig hearts upon intravenous administration. The effect of modified PUFAs on IKs was studied using Xenopus laevis oocytes expressing human KCNQ1 and KCNE1.

RESULTS

All tested PUFAs shortened ADP and QT interval in ex-vivo guinea pig hearts, however, with different ability in restoring baseline APD/QT interval with specific modified PUFAs being most efficacious. Despite comparable ability in activating the human KCNQ1/KCNE1 channel, Lin-GLY was not as effective in shortening APD/QT interval as DHA-GLY in ex-vivo hearts. By constructing a guinea pig-like KCNE1, we found Lin-GLY to induce less activating effect compared with DHA-GLY on human KCNQ1 co-expressed with guinea pig-like KCNE1. Docosahexaenoyl glycine was studied in more detail and was found to shorten QT interval in in-vivo guinea pig hearts.

CONCLUSION

Our results show that specific PUFAs shorten QT interval in guinea pig hearts. The tendency of modified PUFAs with pronounced IKs channel activating effect to better restore QT interval suggests that modifying PUFAs to target the IKs channel is a means to improve the QT-shortening effect.