Potassium Channel Blocker Research Articles

1-(4-chloro-3-nitrobenzenesulfonyl)-1H-indol-3-yl]-methanol, an indole-3-carbinol derivative, inhibits glutamate release in rat cerebrocortical nerve terminals by suppressing the P/Q-type Ca2+ channels and Ca2+/calmodulin/protein kinase A pathway

Indole-3-carbinol (I3C), found in cruciferous vegetables, has been proposed to exhibit neuroprotective effects. This study aimed to investigate the effect of the I3C derivative [1(4-chloro-3-nitrobenzenesulfonyl)-1H-indol-3-yl]-methanol (CIM), which has superior pharmacokinetic properties to I3C, on glutamate release in rat cerebrocortical nerve terminals (synaptosomes). We observed that CIM dose-dependently inhibited glutamate release evoked by the potassium channel blocker 4-aminopyridine (4-AP). CIM-mediated inhibition of glutamate release was attributed to reduced exocytosis, as it correlated with the removal of extracellular calcium and blocking of the vesicular glutamate transporter but not the glutamate transporter. In addition, CIM decreased 4-AP-evoked intrasynaptosomal Ca2+ elevation; however, it did not alter the synaptosomal membrane potential. The inhibition of P/Q-typeCa2+ channels abolished the effect of CIM on 4-AP-evoked glutamate release, and the effect was not prevented by intracellular Ca2+ release inhibitors. Moreover, the molecular docking study showed that CIM exhibited the highest binding affinity with the P/Q-type Ca2+channels. Finally, the CIM-mediated inhibition of glutamate release was sensitive to calmodulin, adenylate cyclase (AC), and protein kinase A (PKA) inhibitors. Based on these results, we propose that CIM, through the direct suppression of P/Q-type Ca2+ channels, decreases Ca2+ influx and the activation of Ca2+/calmodulin/AC/PKA signaling, thereby inhibiting glutamate release. This finding is crucial for understanding the role of CIM in the central nervous system and for exploiting its potential in therapeutic interventions.

Development and validation of HPTLC method for estimation of dofetilide in pharmaceutical dosage form and determination of its degradation profile by MS-MS method

Background: Dofetilide is the class III antiarrhythmic drug used as a potassium channel blocker approved by US FDA in 1999 for the maintenance of sinus rhythm in individuals prone to atrial flutter and atrial fabrication. Currently there is no HPTLC-MS method reported for systematic characterization of degradation products dofetilide. Methods: As per the ICH guidelines, the HPTLC method for the determination of dofetilide both in bulk and pharmaceutical formulation has been developed and validated. The degradation products were identified and characterized by using MS/MS. The Rf value was found to be 0.52±0.3. The degradation study was performed as per ICH guidelines (Q2R1). Isolation of the degradation product by HPTLC method and categorized by MS/MS method. Results: The linearity of the method was found suitable over the range 100-600 ng/band with r2 of 0.998. Dofetilide was subjected to stability studies, the drug was found to degrade under various stress conditions. The recovery was found in the range of 98-101%. HPTLC-MS/MS method showed a possible degradation mechanism of 7 degrading products. The degradation of the drug under various stress conditions indicates the storage conditions for the drug and drug product during its shelf life. Conclusion: The HPTLC method developed for its linearity, range, precision studies, LOD and LOQ can be used for the routine quality control of the drug dofetilide in bulk drugs. The degradation pathway of a drug can help in the future to identify the impurities and for the impurity profiling of dofetilide.

Bioactivities and modes of action of VUAA1

The compound 2-((4-ethyl-5-(pyridin-3-yl)-4H-1,2,4-triazol-3-yl)thio)-N-(4-ethylphenyl) acetamide (VUAA1) is reported to be an odorant receptor co-receptor (Orco) agonist in insects with potential use as an insect repellent. For this study, the biological activity of VUAA1 was investigated in several bioassays with Aedes aegypti, including adult contact, spatial repellency, and larval repellency assays, as well as topical, injection, and feeding toxicity assays. Neurophysiological action was further explored by analysis of fruit fly central nervous system firing, cockroach axon recordings, patch clamp analysis of Kv2 potassium channel, and acetylcholinesterase inhibition studies. Finally, the metabolic impact on the toxicity of VUAA1 was explored by applying it in combination with established metabolic synergists. In repellency and bite protection screens, VUAA1 showed little activity against adult mosquitoes, apparently due to its low volatility, since its effectiveness was increased by heating or mixing with transfluthrin acid and citronella oil. It did produce measurable repellency of mosquito larvae that was more potent than N,N-diethyl-m-toluamide (DEET). Overall, VUAA1 showed low acute toxicity to both insects and mice, and it was weakly synergized by triphenyl phosphate. There was no observed cross-resistance in a pyrethroid-resistant strain of Anopheles gambiae. VUAA1 showed a two-phase effect on the central nervous system, with neuroexcitation at 1μmol L-1 and an inhibitory effect at 100 μmol L-1 that may relate to block of Kv2 potassium channels. VUAA1 presented low toxicity, similar to other insect repellents. Its limited solubility, low volatility, and resulting poor adult repellency without additional adjuvants may restrict the utility of VUAA1 in typical public health applications. © 2020 Society of Chemical Industry.

Effect of KATP channel blocker glibenclamide on levcromakalim-induced headache.

Administration of ATP-sensitive potassium channel opener levcromakalim triggers headache in healthy volunteers and migraine attacks in migraine patients. Here, we investigated the effect of ATP-sensitive potassium channel blocker glibenclamide on levcromakalim-induced headache in healthy volunteers. In a randomized, double-blind, placebo-controlled, three-way cross-over study, 15 healthy volunteers aged 18-40 years were randomly allocated to receive glibenclamide and levcromakalim (day 1), glibenclamide and placebo (day 2), and placebo and placebo (day 3) on three different days separated by at least 1 week. The primary endpoints were the difference in incidence of headache and the difference in area under the curve for headache intensity scores (0-12 hours) between the days. Fifteen healthy volunteers completed the 3 days of the study. More participants (12/15, 80%) developed headache on the glibenclamide-levcromakalim day compared to the glibenclamide-placebo day (5/15, 33%) (p = 0.01; mean difference 47%; 95% confidence interval 18-75%) and compared to the placebo-placebo day (1/15, 7%) (p = 0.001; mean difference 73%; 95% confidence interval 48-99%). We found no difference in headache incidence between glibenclamide-placebo day and placebo-placebo day (p = 0.12; mean difference 27%; 95% confidence interval 1.3-52%). The area under the curve for headache intensity was significantly larger on the glibenclamide-levcromakalim day compared to the glibenclamide-placebo day (p = 0.003); and compared to the placebo-placebo day (p = 0.001). We found no difference in the area under the curve between the glibenclamide-placebo day compared to the placebo-placebo day (p = 0.07). The median time to onset for headache after levcromakalim infusion with glibenclamide pretreatment was delayed (180 min) compared to levcromakalim without pretreatment (30 min) from a previously published study. Glibenclamide administration did not cause headache, and glibenclamide pretreatment did not prevent levcromakalim-induced headache. However, glibenclamide delayed the onset of levcromakalim-induced headache. More selective blockers are needed to further elucidate the role of the ATP-sensitive potassium channel in headache initiation.Trial Registration: ClinicalTrials.gov NCT03886922.

Barium blockade of the KcsA channel in open and closed conformation datasets.

Barium is a potent blocker of the KcsA potassium channel. A strategy using x-ray crystallography and molecular dynamics (MD) simulation has been used to understand this phenomenon as described in Rohaim et al. [1]. Wild type KcsA is purified to homogeneity and crystallized in low and high K+ conditions. Crystals are grown using the hanging drop vapor diffusion method. To examine barium binding in the selectivity filter of KcsA, the crystals are systemically soaked in various concentrations of barium chloride solution. X-ray crystallography datasets are collected at the Advanced Photon Source. A total of 10 datasets are collected for various barium ion concentrations. Diffraction data are processed using the crystallography pipeline software RAPID. The crystal structures are solved by molecular replacement methods. The structure models are visualized using COOT and refined using REFMAC. Anomalous map coefficients are calculated using the phenix.maps tool in the PHENIX software suite. The datasets are deposited in the Protein Data Bank. The data provides a detailed picture of barium ion interaction with potassium channels. Structural analysis of the KcsA channel reveals two distinct configurations, open- and closed- state. Further MD simulation analysis suggests an energetically favorable binding mechanism for barium ion in the selectivity filter. The data could be used to interpret functional experiments related to barium blockade for potassium channels. Also, it is valuable for comparison and cross validation with other relevant potassium channel structures.

The Spasmolytic Effect of Astragalus Sarcocolla on the Intestinal Smooth Muscles of Rabbit In Vitro: Potassium Channel Opening.

IntroductionAstragalus species have been widely used in Chinese herbal medicine to treat gastrointestinal and inflammatory disorders. This study was conducted to evaluate the efficacy of Astragalus sarcocolla (ASE) and to rationalize its medicinal use as an antispasmodic drug for the treatment of spasmodic gastrointestinal and inflammatory disorders associated with increased intestinal motility.MethodsThe ethanolic extract of ASE was studied to examine its antispasmodic effect on the isolated rabbit ileum preparations, and the contractions were recorded on PowerLab (ADInstruments, Sydney, Australia).ResultsASE was able to inhibit spontaneous ileum contractions. It also completely inhibited K+ (25 mM)-induced contractions but was unable to inhibit high K+ (80 mM)-induced sustained contractions. Pretreatment of the tissue with glibenclamide, a potassium channel blocker, caused a rightward shift of the dose-response curve when stimulated with K+ (25 mM) in the presence of an increasing concentration of the extract. Verapamil at very low doses inhibited both the 25 mM and 80 mM K+-induced contractions.ConclusionThe results of our study demonstrated the spasmolytic activity of ASE with the potential mechanism of activation of K+ATP, which provides a strong basis for its medicinal use in motility and inflammatory disorders of the intestine.

Tuning Scorpion Toxin Selectivity: Switching From KV1.1 to KV1.3.

Voltage-gated potassium channels (KVs) perform vital physiological functions and are targets in different disorders ranging from ataxia and arrhythmia to autoimmune diseases. An important issue is the search for and production of selective ligands of these channels. Peptide toxins found in scorpion venom named KTx excel in both potency and selectivity with respect to some potassium channel isoforms, which may present only minute differences in their structure. Despite several decades of research the molecular determinants of KTx selectivity are still poorly understood. Here we analyze MeKTx13-3 (Kalium ID: α-KTx 3.19) from the lesser Asian scorpion Mesobuthus eupeus, a high-affinity KV1.1 blocker (IC50 ~2 nM); it also affects KV1.2 (IC50 ~100 nM), 1.3 (~10 nM) and 1.6 (~60 nM). By constructing computer models of its complex with KV1.1–1.3 channels we identify specific contacts between the toxin and the three isoforms. We then perform mutagenesis to disturb the identified contacts with KV1.1 and 1.2 and produce recombinant MeKTx13-3_AAAR, which differs by four amino acid residues from the parent toxin. As predicted by the modeling, this derivative shows decreased activity on KV1.1 (IC50 ~550 nM) and 1.2 (~200 nM). It also has diminished activity on KV1.6 (~1500 nM) but preserves KV1.3 affinity as measured using the voltage-clamp technique on mammalian channels expressed in Xenopus oocytes. In effect, we convert a selective KV1.1 ligand into a new specific KV1.3 ligand. MeKTx13-3 and its derivatives are attractive tools to study the structure-function relationship in potassium channel blockers.

Prediction of hERG potassium channel blockage using ensemble learning methods and molecular fingerprints

The human ether-a-go-go-related gene (hERG) encodes a tetrameric potassium channel called Kv11.1. This channel can be blocked by certain drugs, which leads to long QT syndrome, causing cardiotoxicity. This is a significant problem during drug development. Using computer models to predict compound cardiotoxicity during the early stages of drug design will help to solve this problem. In this study, we used a dataset of 1865 compounds exhibiting known hERG inhibitory activities as a training set. Thirty cardiotoxicity classification models were established using three machine learning algorithms based on molecular fingerprints and molecular descriptors. Through using these models as the base classifier, a new cardiotoxicity classification model with better predictive performance was developed using ensemble learning method. The accuracy of the best base classifier, which was generated using the XGBoost method with molecular descriptors, was 84.8 %, and the area under the receiver-operating characteristic curve (AUC) was 0.876 in the five fold cross-validation. However, all of the ensemble models that we developed had higher predictive performance than the base classifiers in the five fold cross-validation. The best predictive performance was achieved by the Ensemble-Top7 model, with accuracy of 84.9 % and AUC of 0.887. We also tested the ensemble model using external validation data and achieved accuracy of 85.0 % and AUC of 0.786. Furthermore, we identified several hERG-related substructures, which provide valuable information for designing drug candidates.

Open and Closed Structures of a Barium-Blocked Potassium Channel

Barium (Ba2+) is a classic permeant blocker of potassium (K+) channels. The “external lock-in effect” in barium block experiments, whereby the binding of external K+ impedes the forward translocation of the blocker, provides a powerful avenue to investigate the selectivity of the binding sites along the pore of potassium channels. Barium block experiments show that the external lock-in site is highly selective for K+ over Na+. Wild-type KcsA was crystallized in low K+ conditions, and the crystals were soaked in solutions containing various concentrations of barium. Structural analysis reveals open and closed gate conformations of the KcsA channel. Anomalous diffraction experiments show that Ba2+ primarily binds to the innermost site S4 of the selectivity filter of the open-gate conformation and also the site S2, but no binding is detected with the closed-gate conformation. Alchemical free-energy perturbation calculations indicate that the presence of a Ba2+ ion in the selectivity filter boosts the specificity of K+ binding relative to Na+ in the external sites S0–S2.

Anti-angiogenic activity of chloride and potassium channel modulators: repurposing ion channel modulators

BackgroundExcessive angiogenesis can be the root cause of many pathological conditions. Various types of ion channels are found on the endothelial cells. These ion channels play a vital role in the multi-stepped process of angiogenesis. The study aims to investigate the anti-angiogenic effects of specific ion channel modulators mefloquine (volume-regulated chloride channel blocker), lubiprostone (ClC-2 channel agonist), and 4-aminopyridine (voltage-gated potassium channel blocker).ResultsThe anti-angiogenic activity of ion channel modulators was screened by measuring its effects on the area of neovascularization and histopathological studies by in vivo (corneal neovascularization) method and by in vitro assays, endothelial cell proliferation assay, cell migration assay, and matrigel cord-like morphogenesis assay. The test and standard drug (bevacizumab) groups were compared with the control group using one-way ANOVA, followed by post hoc test, and Dunnett’s test to compare the mean of all the groups with the control mean. The results revealed that mefloquine at the dose of 0.6% w/v and 1.0% w/v, lubiprostone at the dose of 0.5% w/v and 1.0% w/v, and 4-aminopyridine at the dose of 2% w/v and 4% w/v showed significant anti-angiogenic property. In the studies on human umbilical vein endothelial cells, the test drugs (100 nM) showed significant inhibition of proliferation, migration, and decrease in network length of cord-like tubes.ConclusionThe scientific findings indicate that the test drugs have potent anti-angiogenic activity by inhibiting the cell proliferation, inhibiting the cell volume increase, arresting the cell cycle progression and by causing membrane hyperpolarization. The potent anti-angiogenic drugs obtained by repurposing these ion channel modulators, in the further studies, will be able to treat the diseases due to excess angiogenesis from the root cause.Graphical abstract

Aqueous Fraction from Hibiscus sabdariffa Relaxes Mesenteric Arteries of Normotensive and Hypertensive Rats through Calcium Current Reduction and Possibly Potassium Channels Modulation.

Background/Objectives: Hibiscus sabdariffa L. (H. sabdariffa (HS)) extract has a vascular relaxant effect on isolated rat thoracic aorta, but data on small resistance arteries, which play an important role on the development of hypertension, are still missing. The purposes of this study were (1) to assess the effect on isolated mesenteric arteries (MA) from normotensive (Wistar and Wistar-Kyoto (WKY)) and spontaneous hypertensive rats (SHR); (2) to elucidate the mechanism(s) of action underling the relaxant effect in light of bioactive components. Methods: Vascular effects of HS aqueous fraction (AF) on isolated MA rings, as well as its mechanisms of action, were assessed using the contractility and intracellular microelectrode technique. The patch clamp technique was used to evaluate the effect of HS AF on the L-type calcium current. Extraction and enrichment of AF were carried out using liquid–liquid extraction, and the yield was analyzed using HPLC. Results: The HS AF induced a concentration-dependent relaxant effect on MA rings of SHR (EC50 = 0.83 ± 0.08 mg/mL), WKY (EC50 = 0.46 ± 0.04 mg/mL), and Wistar rats (EC50 = 0.44 ± 0.08 mg/mL) pre-contracted with phenylephrine (10 µM). In Wistar rats, the HS AF maximum relaxant effect was not modified after endothelium removal or when a guanylate cyclase inhibitor (ODQ, 10 µM) and a selective β2-adrenergic receptor antagonist (ICI-118551, 1 µM) were incubated with the preparation. Otherwise, it was reduced by 34.57 ± 10.66% when vascular rings were pre-contracted with an 80 mM [K+] solution (p < 0.001), which suggests an effect on ionic channels. HS AF 2 mg/mL significantly decreased the peak of the L-type calcium current observed in cardiac myocytes by 24.4%. Moreover, though the vasorelaxant effect of HS, AF was reduced by 27% when the nonselective potassium channels blocker (tetraethylammonium (TEA) 20 mM) was added to the bath (p < 0.01). The extract did not induce a membrane hyperpolarization of smooth muscle cells, which might suggest an absence of a direct effect on background potassium current. Conclusion: These results highlight that the antihypertensive effect of HS probably involves a vasorelaxant effect on small resistance arteries, which is endothelium independent. L-type calcium current reduction contributes to this effect. The results could also provide a link between the vasorelaxant effect and the bioactive compounds, especially anthocyanins.

Effects of timing of artificial insemination and treatment of semen with a Slo3 potassium channel blocker on fertility of dairy heifers subjected to the 5-day CIDR-Synch protocol

Two experiments were conducted to evaluate the effects of the timing of artificial insemination (AI) and incorporation of the Slo3 K+ channel blocker 4-(4-chlorophenyl)butyl-diethyl-heptylammonium to semen extender (CSE) on pregnancy per AI (P/AI) and pregnancy loss in dairy heifers. In experiment 1, Holstein heifers were subjected to the 5-d CIDR-Synch protocol: d -8 GnRH and controlled internal drug-release device (CIDR); d -3 PGF2α and CIDR removal; d -2 PGF2α; d 0 GnRH) and assigned randomly to receive timed AI with control semen on d 0 (72-CON; n = 104), control semen on d -1 (48-CON; n = 100), or CSE-treated semen on d -1 (48-CSE; n = 98). Heifers were fitted with collar-mounted automated estrus detection devices to monitor physical activity and rumination. In experiment 2, Holstein heifers were subjected to the 5-d CIDR-Synch protocol and received a mount detection patch at the first PGF2α injection. Heifers detected in estrus before d 0 were inseminated on the same day, whereas those not detected in estrus received the second GnRH injection and timed AI on d 0. Heifers were assigned randomly to receive AI with control (AI-CON; n = 148) or CSE-treated semen (AI-CSE; n = 110). Four bulls with proven fertility were used in both experiments, and ejaculates from each sire were divided and processed as CON or CSE. Pregnancy was diagnosed by transrectal ultrasonography at 29 and 54 d after AI. Data were analyzed by logistic regression, and statistical models included the fixed effects of treatment and enrollment week. In experiment 1, orthogonal contrasts were built to assess the effects of day of AI (72-CON vs. 48-CON + 48-CSE) and treatment of semen with CSE (48-CON vs. 48-CSE). Pregnancy per AI on d 29 (72-CON = 60.8, 48-CON = 35.2, 48-CSE = 39.8%) and d 54 (72-CON = 58.2, 48-CON = 31.6, 48-CSE = 36.2%) was greater for heifers inseminated on d 0 compared with d -1. However, no effect of semen extender on P/AI was observed in heifers inseminated on d -1. In experiment 2, P/AI tended to be greater for AI-CSE than for AI-CON on d 29 (58.6 vs. 47.3%) and d 54 after AI (55.6 vs. 43.7%). Advancing AI by 24 h decreased the likelihood of pregnancy, and use of CSE was unable to overcome the expected asynchrony between insemination and ovulation. Nevertheless, incorporation of CSE in semen processing tended to improve P/AI when heifers received AI upon detected estrus or timed AI concurrently with the final GnRH of the 5-d CIDR-Synch protocol.

The Study on the hERG Blocker Prediction Using Chemical Fingerprint Analysis.

Human ether-a-go-go-related gene (hERG) potassium channel blockage by small molecules may cause severe cardiac side effects. Thus, it is crucial to screen compounds for activity on the hERG channels early in the drug discovery process. In this study, we collected 5299 hERG inhibitors with diverse chemical structures from a number of sources. Based on this dataset, we evaluated different machine learning (ML) and deep learning (DL) algorithms using various integer and binary type fingerprints. A training set of 3991 compounds was used to develop quantitative structure–activity relationship (QSAR) models. The performance of the developed models was evaluated using a test set of 998 compounds. Models were further validated using external set 1 (263 compounds) and external set 2 (47 compounds). Overall, models with integer type fingerprints showed better performance than models with no fingerprints, converted binary type fingerprints or original binary type fingerprints. Comparison of ML and DL algorithms revealed that integer type fingerprints are suitable for ML, whereas binary type fingerprints are suitable for DL. The outcomes of this study indicate that the rational selection of fingerprints is important for hERG blocker prediction.

Pharmacological characterization of the cardiovascular effect of Nibethione: ex vivo, in vivo and in silico studies.

This work describes the vasorelaxant and antihypertensive effects and the mechanism of action on vascular smooth muscle cells of Nibethione, a synthetic thiazolidinedione derivative. Additionally, evidence of its cytotoxicity is assessed. Nibethione (NB) was synthesized, and its vasorelaxant effect and mechanism of action were assessed through ex vivo experiments. Molecular docking studies were used to predict the mode of interaction with L-type Ca2+ channel, and in vivo antihypertensive activity was assayed on spontaneously hypertensive rats (SHR). The cytotoxicity potential was evaluated in porcine aortic endothelial cells (PAECs) from primary explants. Nibethione vasorelaxant effect was efficient on KCl (80mm) and NE-contraction. This effect was deleteriously modified in the presence of potassium channel block drugs, while the maximal contraction induced with NE was significantly decreased by NB; the CaCl2 -induced contraction was abolished entirely. In vivo experiments showed that NB decreased diastolic blood pressure in 20.3 % after its administration on SHR. The molecular docking showed that NB blocks L-type Ca2+ channel, and in vitro tests showed that NB did not produce cytotoxic activity on PAECs (IC50 >1000µm). Nibethione showed in vivo antihypertensive and ex vivo vasorelaxant effects with implication of voltage-dependent L-type Ca2+ channel blocking, and this may contribute to the research of novel antihypertensive drugs.

Design, synthesis and evaluation of benzothiazole derivatives as multifunctional agents.

Oxidative stress is the product or aetiology of various multifactorial diseases; on the other hand, the development of multifunctional compounds is a recognized strategy for the control of complex diseases. To this end, a series of benzothiazole derivatives was synthesized and evaluated for their multifunctional effectiveness as antioxidant, sunscreen (filter), antifungal and antiproliferative agents. Compounds were easily synthesized via condensation reaction between 2-aminothiophenols and different benzaldehydes. SAR study, particularly in position 2 and 6 of benzothiazoles, led to the identification of 4g and 4k as very interesting potential compounds for the design of multifunctional drugs. In particular, compound 4g is the best blocker of hERG potassium channels expressed in HEK 293 cells exhibiting 60.32% inhibition with IC50=4.79μM.

Polyamine block of MthK potassium channels.

Polyamines can modulate membrane excitability by blocking ion flux through ion channels. Suma et al. determined the location of the binding site for polyamines inside a model potassium channel pore.

Evaluation of in vitro models of stem cell-derived cardiomyocytes to screen for potential cardiotoxicity of chemicals

Cardiotoxicity is an important toxicological endpoint for chemical and drug safety assessment. The present study aims to evaluate two stemcell-based in vitro models for cardiotoxicity screening of chemicals. Eleven model compounds were used to evaluate responses of mouse embryonic stem cell-derived cardiomyocytes (mESC-CMs) using beating arrest as a readout and the analysis of electrophysiological parameters measured with a multi-electrode array (MEA) platform of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Results revealed that the hiPSC-CM MEA assay responded to all compounds. The mESC-CM beating arrest assay was not responsive to potassium channel blockers and showed a lower sensitivity to sodium channel blockers and Na+/K+ ATPase inhibitors compared to the hiPSC-CM MEA assay. Calcium channel blockers and a β-adrenergic receptor agonist showed comparable potencies in both models. The in vitro response concentrations from hiPSC-CMs were highly concordant with human effective serum concentrations of potassium and sodium channel blockers. It is concluded that both in vitro models enable the cardiotoxicity screening with different applicability domains. The mESC-CM beating arrest assay may be used as a first step in a tiered approach while the hiPSC-CM MEA assay may be the best starting point for quantitative in vitro to in vivo extrapolations.

H2S donor GYY4137 ameliorates paclitaxel-induced neuropathic pain in mice

Paclitaxel-induced neuropathic pain (PINP) is a dose-limiting side effect that largely affects the patient’s quality of life and may limit the use of the drug as a chemotherapeutic agent for treating metastatic breast cancer and other solid tumors. Recently, a putative role for the gaseous mediator hydrogen sulfide (H2S) in nociception modulation has been suggested. The aim of the present study was to investigate the potential efficacy of the slow release H2S donor GYY4137 to alleviate and prevent PINP. Female BALB/c mice that were intraperitoneally (i.p.) injected with paclitaxel (2 mg/kg) for 5 consecutive days developed thermal hyperalgesia, cold and mechanical allodynia and had reduced of H2S, generation in the spinal cord and paw skin. Treatment of mice with established thermal hyperalgesia with GYY4137 or the analgesic positive control drug gabapentin produced antihyperalgesic activities. The antihyperalgesic activity of GYY4137 was antagonized by the ATP sensitive potassium channels (KATP channels) blocker glibenclamide. Co-treatment with GYY4137 and paclitaxel prevented the paclitaxel-induced decrease in H2S, generation as well as the paclitaxel-induced thermal hyperalgesia, cold allodynia and mechanical allodynia. GYY4137 enhanced paclitaxel's anti-proliferative effects against the breast cancer cell line MCF-7. The present results suggest that GYY4137 alleviates paclitaxel-induced thermal hyperalgesia, via KATP channels. GYY4137 prevents PINP possibly by blocking the paclitaxel-induced reduction in the generation of H2S, in the tissues, while enhancing the anti-cancer activity of paclitaxel, and therefore warrants further research as a candidate for prevention of PINP in clinical settings.

HiPSC-Derived Cardiomyocyte Model of LQT2 Syndrome Derived from Asymptomatic and Symptomatic Mutation Carriers Reproduces Clinical Differences in Aggregates but Not in Single Cells.

Mutations in the HERG gene encoding the potassium ion channel HERG, represent one of the most frequent causes of long QT syndrome type-2 (LQT2). The same genetic mutation frequently presents different clinical phenotypes in the family. Our study aimed to model LQT2 and study functional differences between the mutation carriers of variable clinical phenotypes. We derived human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) from asymptomatic and symptomatic HERG mutation carriers from the same family. When comparing asymptomatic and symptomatic single LQT2 hiPSC-CMs, results from allelic imbalance, potassium current density, and arrhythmicity on adrenaline exposure were similar, but a difference in Ca2+ transients was observed. The major differences were, however, observed at aggregate level with increased susceptibility to arrhythmias on exposure to adrenaline or potassium channel blockers on CM aggregates derived from the symptomatic individual. The effect of this mutation was modeled in-silico which indicated the reactivation of an inward calcium current as one of the main causes of arrhythmia. Our in-vitro hiPSC-CM model recapitulated major phenotype characteristics observed in LQT2 mutation carriers and strong phenotype differences between LQT2 asymptomatic vs. symptomatic were revealed at CM-aggregate level.

Investigation of the Cellular Pharmacological Mechanism and Clinical Evidence of the Multi-Herbal Antiarrhythmic Chinese Medicine Xin Su Ning.

Xin Su Ning (XSN), a China patented and certified multi-herbal medicine, has been available in China since 2005 for treating cardiac ventricular arrhythmia including arrhythmia induced by ischemic heart diseases and viral myocarditis, without adverse reactions being reported. It is vitally important to discover pharmacologically how XSN as a multicomponent medicine exerts its clinical efficacy, and whether the therapeutic effect of XSN can be verified by standard clinical trial studies. In this paper we report our discoveries in a cellular electrophysiological study and in a three-armed, randomized, double-blind, placebo-controlled, parallel-group, multicenter trial. Conventional electrophysiological techniques were used to study the cellular antiarrhythmic mechanism of XSN. Data was then modeled with computational simulation of human action potential (AP) of the cardiac ventricular myocytes. The clinical trial was conducted with a total of 861 eligible participants randomly assigned in a ratio of 2:2:1 to receive XSN, mexiletine, or the placebo for 4 weeks. The primary and secondary endpoint was the change of premature ventricular contraction (PVC) counts and PVC-related symptoms, respectively. This trial was registered in the Chinese Clinical Trial Register Center (ChiCTR-TRC-14004180). We found that XSN prolonged AP duration of the ventricular myocytes in a dose-dependent, reversible manner and blocked potassium channels. Patients in XSN group exhibited significant total effective responses in the reduction of PVCs compared to those in the placebo group (65.85% vs. 27.27%, P < 0.0001). No severe adverse effects attributable to XSN were observed. In conclusion, XSN is an effective multicomponent antiarrhythmic medicine to treat PVC without adverse effect in patients, which is convincingly supported by its class I & III pharmacological antiarrhythmic mechanism of blocking hERG potassium channels and hNaV1.5 sodium channel reported in our earlier publication and prolongs AP duration both in ventricular myocytes and with computational simulation of human AP presented in this report.