Bepridil is potent against SARS-CoV-2 in vitro.

Guided by a computational docking analysis, about 30 Food and Drug Administration/European Medicines Agency (FDA/EMA)-approved small-molecule medicines were characterized on their inhibition of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease (Mpro). Of these small molecules tested, six displayed a concentration that inhibits response by 50% (IC50) value below 100 µM in inhibiting Mpro, and, importantly, three, that is, pimozide, ebastine, and bepridil, are basic molecules that potentiate dual functions by both raising endosomal pH to interfere with SARS-CoV-2 entry into the human cell host and inhibiting Mpro in infected cells. A live virus-based modified microneutralization assay revealed that bepridil possesses significant anti-SARS-CoV-2 activity in both Vero E6 and A459/ACE2 cells in a dose-dependent manner with low micromolar effective concentration, 50% (EC50) values. Therefore, the current study urges serious considerations of using bepridil in COVID-19 clinical tests.

Effects of bepridil on early cardiac development of zebrafish.

Bepridil is a commonly used medication for arrhythmia and heart failure. It primarily exerts hemodynamic effects by inhibiting Na+/K+ movement and regulating the Na+/Ca2+ exchange. In comparison to other Ca2+ inhibitors, bepridil has a long half-life and a complex pharmacology. Additionally, it is widely used in antiviral research and the treatment of various diseases. However, the toxicity of this compound and its other possible effects on embryonic development are unknown. In this study, we investigated the toxicity of bepridil on rat myocardial H9c2 cells. After treatment with bepridil, the cells became overloaded with Ca2+ and entered a state of cytoplasmic vacuolization and nuclear abnormality. Bepridil treatment resulted in several morphological abnormalities in zebrafish embryo models, including pericardium enlargement, yolk sac swelling, and growth stunting. The hemodynamic effects on fetal development resulted in abnormal cardiovascular circulation and myocardial weakness. After inhibiting the Ca2+ transmembrane, the liver of zebrafish larvae also displayed an ectopic and deficient spatial location. Additionally, the results of the RNA-seq analysis revealed the detailed gene expression profiles and metabolic responses to bepridil treatment in zebrafish embryonic development. Taken together, our study provides an important evaluation of antiarrhythmic agents for clinical use in prenatal heart patients.

Effects of Bepridil and Pimozide, Existing Medicines Capable of Blocking T-Type Ca2+ Channels, on Visceral Pain in Mice.

T-Type Ca2+ channels (T-channels), particularly Cav3.2, are now considered as therapeutic targets for treatment of intractable pain including visceral pain. Among existing medicines, bepridil, a multi-channel blocker, used for treatment of arrhythmia and angina, and pimozide, a dopamine D2 receptor antagonist, known as a typical antipsychotic, have potent T-channel blocking activity. We thus tested whether bepridil and pimozide could suppress visceral pain in mice. Colonic and bladder pain were induced by intracolonic administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS) and systemic administration of cyclophosphamide (CPA), respectively. Referred hyperalgesia was assessed by von Frey test, and colonic hypersensitivity to distension by a volume load with intracolonic water injection and spontaneous bladder pain were evaluated by observing nociceptive behaviors in conscious mice. The mice exhibited referred hyperalgesia and colonic hypersensitivity to distension on day 6 after TNBS treatment. Systemic administration of bepridil at 10-20 mg/kg or pimozide at 0.1-0.5 mg/kg strongly reduced the referred hyperalgesia on the TNBS-induced referred hyperalgesia and colonic hypersensitivity to distension. CPA treatment caused bladder pain-like nociceptive behavior and referred hyperalgesia, which were reversed by bepridil at 10-20 mg/kg or pimozide at 0.5-1 mg/kg. Our data thus suggest that bepridil and pimozide, existing medicines capable of blocking T-channels, are useful for treatment of colonic and bladder pain, and serve as seeds for the development of new medicines for visceral pain treatment.

Structural and functional impact of troponin C-mediated Ca2+ sensitization on myofilament lattice spacing and cross-bridge mechanics in mouse cardiac muscle.

Acto-myosin cross-bridge kinetics are important for beat-to-beat regulation of cardiac contractility; however, physiological and pathophysiological mechanisms for regulation of contractile kinetics are incompletely understood. Here we explored whether thin filament-mediated Ca2+ sensitization influences cross-bridge kinetics in permeabilized, osmotically compressed cardiac muscle preparations. We used a murine model of hypertrophic cardiomyopathy (HCM) harboring a cardiac troponin C (cTnC) Ca2+-sensitizing mutation, Ala8Val in the regulatory N-domain. We also treated wild-type murine muscle with bepridil, a cTnC-targeting Ca2+ sensitizer. Our findings suggest that both methods of increasing myofilament Ca2+ sensitivity increase cross-bridge cycling rate measured by the rate of tension redevelopment (kTR); force per cross-bridge was also enhanced as measured by sinusoidal stiffness and I1,1/I1,0 ratio from X-ray diffraction. Computational modeling suggests that Ca2+ sensitization through this cTnC mutation or bepridil accelerates kTR primarily by promoting faster cross-bridge detachment. To elucidate if myofilament structural rearrangements are associated with changes in kTR, we used small angle X-ray diffraction to simultaneously measure myofilament lattice spacing and isometric force during steady-state Ca2+ activations. Within in vivo lattice dimensions, lattice spacing and steady-state isometric force increased significantly at submaximal activation. We conclude that the cTnC N-domain controls force by modulating both the number and rate of cycling cross-bridges, and that the both methods of Ca2+ sensitization may act through stabilization of cTnC's D-helix. Furthermore, we propose that the transient expansion of the myofilament lattice during Ca2+ activation may be an additional factor that could increase the rate of cross-bridge cycling in cardiac muscle. These findings may have implications for the pathophysiology of HCM.

Effects of Oral Calcium Dosage and Timing on Ethanol-Induced Sensitization of Locomotion in DBA/2 Mice.

Ethanol (EtOH) dosage, frequency, and paired associative learning affect the risk of alcoholism. Recently, Spanagel et al. reported that acamprosate calcium (Acam Ca) prescribed for alcoholism exerts an anti-relapse effect via Ca. Ca is contained in foods, sometimes consumed with alcohol. Therefore, we investigated the association among oral Ca ingestion, EtOH-induced locomotor sensitization, and plasma Ca levels on how to consume Ca for moderate drinking. We used DBA/2 CrSlc mice, and CaCl2 as water-soluble Ca salts. For pre-administration, elemental Ca (50, 75, 100, or 150 mg/kg, per os (p.o.)) or water for control was administered 1 h before EtOH (2 g/kg, 20 v/v (%) EtOH in saline) administration intraperitoneal (i.p.) for locomotor sensitization or for plasma Ca level changes. For post-administration, elemental Ca (100 mg/kg) was administered 1 h after EtOH. Moreover, we employed bepridil and the dopamine D1 antagonist, SCH-23390 to further examine the mechanism of EtOH-induced sensitization. The locomotor sensitization segmentalized for 300 s had two peaks (0-90 s and 180-300 s). Pre-administration of Ca (50, 75, and 100 mg/kg) significantly reduced the 0-90-s peak, selectively blocked by SCH-23390, but "non-dose dependently" as Ca 150 mg/kg did not have this effect. Bepridil blocked the suppressive effect of pre-administration of Ca (100 mg/kg). The effective pre-doses of Ca (50-100 mg/kg) maintained plasma Ca basal levels against EtOH-induced decrease of Ca. On the contrary, post-administration of Ca inversely led to significant promotion of sensitization of both locomotor peaks. Oral Ca intake had diverse effects on EtOH-induced sensitization depending on Ca dosage and timing.

Short- and long-term inhibition of cardiac inward-rectifier potassium channel current by an antiarrhythmic drug bepridil.

Bepridil is an effective antiarrhythmic drug on supraventricular and ventricular arrhythmias, and inhibitor of calmodulin. Recent investigations have been elucidating that bepridil exerts antiarrhythmic effects through its acute and chronic application for patients. The aim of this study was to identify the efficacy and the potential mechanism of bepridil on the inward-rectifier potassium channel in neonatal rat cardiomyocytes in acute- and long-term conditions. Bepridil inhibited inward-rectifier potassium current (I K1) as a short-term effect with IC50 of 17 µM. Bepridil also reduced I K1 of neonatal cardiomyocytes when applied for 24 h in the culture medium with IC50 of 2.7 µM. Both a calmodulin inhibitor (W-7) and an inhibitor of calmodulin-kinase II (KN93) reduced I K1 when applied for 24 h as a long-term effect in the same fashion, suggesting that the long-term application of bepridil inhibits I K1 more potently than that of the short-term application through the inhibition of calmodulin kinase II pathway in cardiomyocytes.

Effect of polypharmacy on plasma bepridil concentration in patients with heart failure: a multicenter retrospective study.

BACKGROUND: Polypharmacy, defined as the concurrent use of over six drugs, is common in the treatment of heart failure (HF); however, unpredictable drug interactions with bepridil may occur. In this study, we have elucidated the influence of polypharmacy on plasma bepridil concentrations in patients with HF. METHODS: We conducted a multicenter retrospective study involving 359 adult patients with HF who received oral bepridil. Because QT prolongation is an adverse effect following plasma bepridil concentrations ≥800 ng/mL, the risk factors for patients achieving these concentrations at steady state were elucidated via multivariate logistic regression. The correlation between bepridil dose and plasma concentration was examined. The effect of polypharmacy on the value of the concentration-to-dose (C/D) ratio was investigated. RESULTS: A significant relationship was observed between bepridil dose and plasma concentration (p <  0.001), and the intensity of the correlation was moderate (r = 0.503). Based on multivariate logistic regression, the adjusted odds ratios for a daily dose of bepridil ≥1.6 mg/kg, polypharmacy, and concomitant of aprindine, a cytochrome P450 2D6 inhibitor, were 6.82 (95% coefficient interval: 2.104-22.132, p = 0.001), 2.96 (95% coefficient interval: 1.014-8.643, p = 0.047), and 8.63 (95% coefficient interval: 1.684-44.215, p = 0.010), respectively. Despite the moderate correlation in non-polypharmacy, the correlation was not observed in polypharmacy. Therefore, inhibiting metabolism, along with other mechanisms, may contribute to the polypharmacy-induced increase in plasma bepridil concentrations. Moreover, the C/D ratios in the groups receiving 6-9 and 10≤ concomitant drugs were 1.28- and 1.70-fold higher than in those receiving <6 drugs, respectively. CONCLUSIONS: Plasma bepridil concentrations may be influenced by polypharmacy. Moreover, the plasma bepridil concentration increased in correlation with the number of concomitant drugs used. Although the mechanism of this increase could not be determined, plasma bepridil concentrations should be periodically monitored for safe use in patients with HF. TRIAL REGISTRATION: Retrospectively registered.

Suppression of Metastatic Ovarian Cancer Cells by Bepridil, a Calcium Channel Blocker.

Although surgery followed by platinum-based therapy is effective as a standard treatment in the early stages of ovarian cancer, the majority of cases are diagnosed at advanced stages, leading to poor prognosis. Thus, the identification of novel therapeutic drugs is needed. In this study, we assessed the effectiveness of bepridil-a calcium channel blocker-in ovarian cancer cells using two cell lines: SKOV-3, and SKOV-3-13 (a highly metastatic clone of SKOV-3). Treatment of these cell lines with bepridil significantly reduced cell viability, migration, and invasion. Notably, SKOV-3-13 was more sensitive to bepridil than SKOV-3. The TGF-ß1-induced epithelial-mesenchymal transition (EMT)-like phenotype was reversed by treatment with bepridil in both cell lines. Consistently, expression levels of EMT-related markers, including vimentin, ß-catenin, and Snail, were also substantially decreased by the treatment with bepridil. An in vivo mouse xenograft model was used to confirm these findings. Tumor growth was significantly reduced by bepridil treatment in SKOV-3-13-inoculated mice, and immunohistochemistry showed consistently decreased expression of EMT-related markers. Our findings are the first to report anticancer effects of bepridil in ovarian cancer, and they suggest that bepridil holds significant promise as an effective therapeutic agent for targeting metastatic ovarian cancer.

Successful treatment of bepridil-induced intraoperative torsades de pointes by isoproterenol infusion.

BACKGROUND: Several types of antiarrhythmic drugs are known to induce QT prolongation and torsades de pointes. CASE PRESENTATION: An 84-year-old man was scheduled for open gastrectomy for residual cancer. He had been prescribed bepridil for atrial fibrillation that converted to sinus rhythm with prolonged QT interval in the operating room. After the surgery was initiated under general and epidural anesthesia, the patient's heart rate decreased to 50/min and multifocal premature ventricular contractions appeared, followed by several episodes of torsades de pointes, each lasting for 5 to 15 s. Infusion of isoproterenol was started (0.01 µg/kg/min), and the heart rate was maintained at around 80/min. Premature ventricular contractions disappeared, and torsades de pointes did not recur during the surgery. The operation was completed uneventfully. The serum bepridil concentration was found to be extremely high postoperatively. CONCLUSIONS: Bepridil-induced intraoperative episodes of torsades de pointes were successfully treated by increasing the heart rate with isoproterenol.

Responsiveness to bepridil predicts atrial substrate in patients with persistent atrial fibrillation.

BACKGROUND: The low voltage zone (LVZ) detected with three-dimensional electroanatomical mapping is a surrogate marker of atrial scar in patients with persistent atrial fibrillation (PeAF) and is associated with poor clinical outcomes after catheter ablation. However, fewer studies have reported the relationship between responsiveness to antiarrhythmic drugs and the LVZ. METHODS: We retrospectively analyzed 76 patients who underwent catheter ablation for PeAF at our center. Rhythm control with bepridil was initiated before ablation in all patients, and electrical cardioversion was performed in cases of failure to restore sinus rhythm with bepridil alone. Patients with successful sinus restoration with bepridil alone (≤200 mg/d) were defined as "responders", while those who required electrical cardioversion as well were defined as "non-responders". We compared the LVZ ratio (ratio of the LVZ surface area to the left atrium surface area on three-dimensional electroanatomical mapping) and the recurrence-free rate after ablation between the two groups. RESULTS: Of the 76 patients, 48 (63.2%) were responders to bepridil. The median LVZ ratio was significantly lower in the responder group than in the nonresponder group (7.5% vs 14.0%, P = .009). Multivariate analysis revealed that response to bepridil was an independent predictor of normal voltage (P = .02, odds ratio = 0.20, 95% confidence interval = 0.04-0.76). The recurrence-free rate at 1 year after catheter ablation was significantly higher in the responder group than in the nonresponder group (87.1% vs 62.3%, P = .03). CONCLUSIONS: Response to bepridil is a marker of normal voltage in electroanatomical mapping and is significantly associated with better clinical outcomes after catheter ablation.

Bepridil, a class IV antiarrhythmic agent, can block the TREK-1 potassium channel.

BACKGROUND: The TWIK-related potassium channel (TREK-1) can be regulated by different stimuli. However, it is not clear whether some antiarrhythmics affect the activity of TREK-1. In the present study, the effect of bepridil on the TREK-1 currents is investigated. METHODS: In a TREK-1 stably-expressed HEK-293 cell line (HEK-TREK-1), U251MG cells, and isolated mouse ventricular myocytes, the TREK-1 current and action potentials were recorded by the patch-clamp technique. The standard voltage protocol was a 200 ms constant potential at 20 mV, followed bya 500 ms ramp from -90 to +20 mV (HEK-TREK-1) or +80 mV (U251MG cells and myocytes) every 10 s. The currents at +20 mV or +80 mV were used for analysis. The docking study of bepridil's binding model in the TREK-1 channel was performed using the Swissdock web service. RESULTS: In HEK-TREK-1 cells, BL1249 induced a significantly large outwardly rectifying current with similar baseline TREK-1 current characteristic, with a reversal potential (-70 mV). The concentration of half-maximal activation (EC50) of BL1249 was 3.45 µM. However, bepridil decreased the baseline TREK-1 currents, with a concentration of half-maximal inhibition (IC50) 0.59 µM and a Hill coefficient of 1.1. Also, bepridil inhibited BL1249-activated TREK-1 currents, with an IC50 4.08 µM and a Hill coefficient of 3.22. The outside-out patch-clamp confirmed bepridil inhibited BL1249-activated TREK-1 currents. In U251MG cells and myocytes, BL1249 activated outwardly rectifying endogenous TREK-1 currents, which could be inhibited by bepridil. BL1249 (10 µM) could decrease the peak value and reduce the duration of the action potential. Bepridil (10 µM) prolonged the duration of action potential of myocytes. The docking study revealed that bepridil might affect the K+ pore domain and the M4 modulator pocket. CONCLUSIONS: Bepridil may be a blocker for the TREK-1K+channel at a clinically therapeutic concentration, providing a new mechanism of TREK-1 regulation and bepridil's antiarrhythmic effect.

Formulation, Stability, Pharmacokinetic, and Modeling Studies for Tests of Synergistic Combinations of Orally Available Approved Drugs against Ebola Virus In Vivo.

Outbreaks of Ebola ebolavirus (EBOV) have been associated with high morbidity and mortality. Milestones have been reached recently in the management of EBOV disease (EVD) with licensure of an EBOV vaccine and two monoclonal antibody therapies. However, neither vaccines nor therapies are available for other disease-causing filoviruses. In preparation for such outbreaks, and for more facile and cost-effective management of EVD, we seek a cocktail containing orally available and room temperature stable drugs with strong activity against multiple filoviruses. We previously showed that (bepridil + sertraline) and (sertraline + toremifene) synergistically suppress EBOV in cell cultures. Here, we describe steps towards testing these combinations in a mouse model of EVD. We identified a vehicle suitable for oral delivery of the component drugs and determined that, thus formulated the drugs are equally active against EBOV as preparations in DMSO, and they maintain activity upon storage in solution for up to seven days. Pharmacokinetic (PK) studies indicated that the drugs in the oral delivery vehicle are well tolerated in mice at the highest doses tested. Collectively the data support advancement of these combinations to tests for synergy in a mouse model of EVD. Moreover, mathematical modeling based on human oral PK projects that the combinations would be more active in humans than their component single drugs.

Efficacy of hybrid therapy using prior administration of bepridil hydrochloride and cryoballoon ablation in patients with persistent atrial fibrillation.

BACKGROUND: Rhythm control before catheter ablation for persistent atrial fibrillation (PeAF) can improve clinical outcomes. We sought to investigate the efficacy of pretreatment with bepridil prior to cryoballoon ablation (CBA) with respect to clinical outcomes in patients with PeAF. METHODS: We retrospectively analyzed 65 consecutive patients with PeAF who underwent CBA following pretreatment with bepridil hydrochloride (bepridil). Electrical cardioversion was additionally performed in cases involving failure of pharmacological sinus restoration before CBA. The primary endpoint was survival free from atrial tachyarrhythmia at the one-year follow-up, and the secondary endpoints were changes in P-wave morphology and left atrium diameter (LAD) before CBA. RESULTS: At the one-year follow-up, 51 patients (78.5%) achieved the primary endpoint (non-recurrence group). Compared to the P-wave duration (Pdur) and dispersion at the time of sinus restoration, they significantly shortened at the time of CBA in the non-recurrence group, while they did not change in the recurrence group. There were no changes in LAD in both groups. Multivariate analysis revealed that refractoriness of bepridil (p = 0.03, odds ratio = 4.72, 95% confidence interval = 1.18-18.92), and longer Pdur at admission for CBA (p = 0.003, odds ratio = 1.08, 95% confidence interval = 1.01-1.14) were independent predictors of recurrence. CONCLUSIONS: Rhythm control with bepridil induced electrical reverse remodeling; bepridil may improve clinical outcomes after CBA.

Bepridil is potent against SARS-CoV-2 In Vitro.

Guided by a computational docking analysis, about 30 FDA/EMA-approved small molecule medicines were characterized on their inhibition of the SARS-CoV-2 main protease (MPro). Of these tested small molecule medicines, six displayed an IC50 value in inhibiting MPro below 100 µM. Three medicines pimozide, ebastine, and bepridil are basic small molecules. Their uses in COVID-19 patients potentiate dual functions by both raising endosomal pH to slow SARS-CoV-2 entry into the human cell host and inhibiting MPro in infected cells. A live virus-based microneutralization assay showed that bepridil inhibited cytopathogenic effect induced by SARS-CoV-2 in Vero E6 cells completely at and dose-dependently below 5 µM and in A549 cells completely at and dose-dependently below 6.25 µM. Therefore, the current study urges serious considerations of using bepridil in COVID-19 clinical tests.

A simple and sensitive LC-MS/MS method for quantification of Bepridil in rat plasma and its application to pharmacokinetic studies.

Bepridil is potent inhibitor of Na+, K+ and Ca+ channel in cardiomyocytes. It has demonstrated strong antianginal effect with type I antiarrhythmic and with minimum antihypertensive therapeutic effect. Till date, a specific LC-MS/MS method to quantify Bepridil concentrations in biological matrix have not been reported yet. In current study, a highly sensitive, specific and simple LC-MS/MS method for quantification of antianginal drug Bepridil in rat plasma is presented. The LC-MS/MS method was validated in terms of selectivity, specificity, sensitivity, accuracy and precision, matrix effect, extraction recovery and stability as per USFDA's bioanalytical method validation guideline. The validated assay was applied for quantification of Bepridil from pharmacokinetic study in rats following oral and intravenous administration. The lower limit of quantification (LLOQ) of Bepridil was 1 ng/mL. The calibration curve ranges from 1 ng/mL to 1000 ng/mL with desirable linearity and r2 > 0.99. The method exhibited 10-fold dilution integrity. The intra-day and inter-day accuracy were within 101.32-96.80% and 102.87-95.35% with coefficient of variation 10.11-2.89% and 10.45-3.97% respectively. No significant interference observed by endogenous peak at the retention time of Bepridil and IS. The assay was free from any matrix effect, precise recovery across the calibration curve range and samples were stable under all experimental conditions. The validated assay was successfully applied to analyze plasma samples of pharmacokinetic study in rat to determine concentrations of Bepridil. In summary, a novel method for analyzing Bepridil in rat plasma has been successfully validated and is now being utilized for quantification of Bepridil from pre-clinical studies.

Pharmacological Therapy in Brugada Syndrome.

Brugada syndrome (BrS) is a cardiac disease caused by an inherited ion channelopathy associated with a propensity to develop ventricular fibrillation. Implantable cardioverter defibrillator implantation is recommended in BrS, based on the clinical presentation in the presence of diagnostic ECG criteria. Implantable cardioverter defibrillator implantation is not always indicated or sufficient in BrS, and is associated with a high device complication rate. Pharmacological therapy aimed at rebalancing the membrane action potential can prevent arrhythmogenesis in BrS. Quinidine, a class 1A antiarrhythmic drug with significant Ito blocking properties, is the most extensively used drug for the prevention of arrhythmias in BrS. The present review provides contemporary data gathered on all drugs effective in the therapy of BrS, and on ineffective or contraindicated antiarrhythmic drugs.

Withdrawal of prenylamine: perspectives on pharmacological, clinical and regulatory outcomes following the first QT-related casualty.

Prenylamine, an antianginal agent marketed since early 1960, became the first casualty of QT interval related proarrhythmias in 1988 when it was withdrawn from the market. The period of its synthesis and marketing is of particular interest since it antedated, first, any serious clinical safety concern regarding drug-induced prolongation of the QT interval which was, in fact, believed to be an efficient antiarrhythmic mechanism; second, the first description of torsade de pointes as a unique proarrhythmia, typically associated with prolonged QT interval; and third, the discovery and recognition of calcium antagonism as an important cardiovascular therapeutic strategy. This review, 30 years almost to the day following its withdrawal, provides interesting perspectives on clinical, pharmacological and regulatory outcomes that followed. Prenylamine underscored torsadogenic potential of other early antianginal drugs on the market at that time and identified QT-related proarrhythmias as a much wider major public health issue of clinical and regulatory concern. This resulted in various guidelines for early identification of this potentially fatal risk. Application of these guidelines would have readily identified its proarrhythmic potential. Prenylamine also emphasized differences in drug responses between men and women which subsequently galvanized extensive research into sex-related differences in pharmacology. More importantly, however, investigations into the mechanisms of its action paved the way to developing modern safe and effective calcium antagonists that are so widely used today in cardiovascular pharmacotherapy.

Anti-atrial Fibrillatory Versus Proarrhythmic Potentials of Amiodarone: A New Protocol for Safety Evaluation In Vivo.

Anti-atrial fibrillatory and proarrhythmic potentials of amiodarone were simultaneously analyzed by using the halothane-anesthetized beagle dogs (n = 4) in order to begin to prepare standard protocol for clarifying both efficacy and adverse effects of anti-atrial fibrillatory drugs. Intravenous administration of 0.3 mg/kg of amiodarone hydrochloride decreased the heart rate and mean blood pressure. Additional administration of 3 mg/kg of amiodarone hydrochloride prolonged the QT interval besides the effects observed by the low dose, whereas it showed 1.6 times larger prolongation in the effective refractory period of the atrium than that of the ventricle, which may explain its clinical efficacy against atrial arrhythmias. However, no significant change was detected by either dose in the early repolarization assessed by corrected J-T peak or the late repolarization done by T peak-T end in the electrocardiogram, although the former tended to be shortened and the reverse was true for the latter. Lack of prolongation in the early repolarization will make it feasible to better understand why amiodarone lacks proarrhythmic potential in spite of the QT-interval prolongation. Thus, these results of amiodarone obtained by current protocol may become a guidance on assessing efficacy and adverse effects of new anti-atrial fibrillatory drugs in vivo.

Characterization of loperamide-mediated block of hERG channels at physiological temperature and its proarrhythmia propensity.

BACKGROUND: Loperamide (Immodium®) is indicated for symptomatic control of diarrhea. It is a µ-opioid receptor agonist, and recently has been associated with misuse and abuse. At therapeutic doses loperamide has not been associated with cardiotoxicity. However, loperamide overdose is associated with proarrhythmia and death - two effects that are likely attributable to its block of cardiac ion channels that are critical for generating action potentials. In this study, we defined loperamide-hERG channel interaction characteristics, and used a ventricular myocyte action potential model to compare loperamide's proarrhythmia propensity to twelve drugs with defined levels of clinical risk. METHODS AND RESULTS: Whole-cell voltage-clamp recordings were performed at 37°C on a HEK293 cell line stably expressing the hERG channel proteins, and loperamide was bath-applied to assess its effects on hERG current. Loperamide suppressed hERG current in a use- and voltage-dependent but frequency-independent manner, with a half-maximal inhibitory concentration <90nM. The onset of current suppression was concentration-dependent and appeared to follow a first-order reaction. Loperamide also altered the voltage-dependence of steady state hERG current properties. Electrophysiological data were integrated into a myocyte model that simulated dynamic drug-hERG channel interaction to estimate Torsade de Pointes risk through comparisons with reference drugs with defined clinical risk. In the context of overdose that would result in loperamide levels far exceeding those produced by therapeutic doses, loperamide is placed in the high risk category, alongside quinidine, bepridil, dofetilide, and sotalol. CONCLUSIONS: The combined in vitro and in silico approach provides mechanistic insight regarding the potential for loperamide to generate cardiotoxicity in overdose situations. This strategy holds promise for improving cardiac safety assessment.