Sudden cardiac death while waiting: do we need the wearable cardioverter-defibrillator?

Sudden cardiac death (SCD) is the most frequent cause of cardiovascular death in industrialized nations. Patients with cardiomyopathy are at increased risk for SCD and may benefit from an implantable cardioverter-defibrillator (ICD). The risk of SCD is highest in the first months after myocardial infarction or first diagnosis of severe non-ischemic cardiomyopathy. On the other hand, left ventricular function may improve in a subset of patients to such an extent that an ICD might no longer be needed. To offer protection from a transient risk of SCD, the wearable cardioverter-defibrillator (WCD) is available. Results of the first randomized clinical trial investigating the role of the WCD after myocardial infarction were recently published. This review is intended to provide insight into data from the VEST trial, and to put these into perspective with studies and clinical experience. As a non-invasive, temporary therapy, the WCD may offer advantages over early ICD implantation. However, recent data demonstrate that patient compliance and education play a crucial role in this new concept of preventing SCD.

Diagnostic performance of D-dimer in predicting venous thromboembolism and acute aortic dissection.

BACKGROUND: D-dimer is elevated in a variety of conditions. The purpose of this study was to assess the positive predictive value of D-dimer to rule in patients with confirmed pulmonary embolism, deep vein thrombosis, acute aortic dissection or thrombosis of the upper extremity in comparison to patients with elevated D-dimer for other reasons. METHODS AND RESULTS: We studied 1334 patients presenting to the emergency department with pulmonary embolism (n=193), deep vein thrombosis (n=73), acute aortic dissection (n=22), thrombosis of the upper extremity (n=8) and 1038 controls. The positive predictive value was increased with higher D-dimer concentrations improving the ability to identify diseases with high thrombus burden. Patients with venous thromboembolism, acute aortic dissection and thrombosis of the upper extremity showed a maximum positive predictive value of 85.2% at a D-dimer level of 7.8 mg/L (95% confidence interval (CI) 78.1 to 90.4). The maximum positive predictive value was lower in cancer patients with venous thromboembolism, acute aortic dissection and thrombosis of the upper extremity, reaching 68.9% at a D-dimer level of 7.5 mg/L (95% CI 57.4 to 78.4). The positive likelihood ratio was very consistent with the positive predictive value. Using a cut-off level of 0.5 mg/L, D-dimer showed a high sensitivity of at least 93%, but a very low specificity of nearly 0%. Conversely, an optimised cut-off value of 4.6 mg/L increased specificity to 95% for the detection of life-threatening venous thromboembolism, acute aortic dissection or thrombosis of the upper extremity at the costs of moderate sensitivities (58% for pulmonary embolism, 41% for deep vein thrombosis, 65% for pulmonary embolism with co-existent deep vein thrombosis, 50% for acute aortic dissection and 13% for thrombosis of the upper extremity). Using the same cut-off in cancer patients, higher values were observed for sensitivity at a specificity level of more than 95%. The area under the curve for the discrimination of venous thromboembolism/acute aortic dissection/thrombosis of the upper extremity from controls was significantly higher in cancer versus non-cancer patients (area under the curve 0.905 in cancer patients, 95% CI 0.89 to 0.92, vs. area under the curve 0.857 in non-cancer patients, 95% CI 0.84 to 0.88; P=0.0349). CONCLUSION: D-dimers are useful not only to rule out but also to rule in venous thromboembolism and acute aortic dissection with an at least moderate discriminatory ability, both in patients with and without cancer.

Diagnostic performance of D-dimer in predicting venous thromboembolism and acute aortic dissection.

BACKGROUND: D-dimer is elevated in a variety of conditions. The purpose of this study was to assess the positive predictive value of D-dimer to rule in patients with confirmed pulmonary embolism, deep vein thrombosis, acute aortic dissection or thrombosis of the upper extremity in comparison to patients with elevated D-dimer for other reasons. METHODS AND RESULTS: We studied 1334 patients presenting to the emergency department with pulmonary embolism (n=193), deep vein thrombosis (n=73), acute aortic dissection (n=22), thrombosis of the upper extremity (n=8) and 1038 controls. The positive predictive value was increased with higher D-dimer concentrations improving the ability to identify diseases with high thrombus burden. Patients with venous thromboembolism, acute aortic dissection and thrombosis of the upper extremity showed a maximum positive predictive value of 85.2% at a D-dimer level of 7.8 mg/L (95% confidence interval (CI) 78.1 to 90.4). The maximum positive predictive value was lower in cancer patients with venous thromboembolism, acute aortic dissection and thrombosis of the upper extremity, reaching 68.9% at a D-dimer level of 7.5 mg/L (95% CI 57.4 to 78.4). The positive likelihood ratio was very consistent with the positive predictive value. Using a cut-off level of 0.5 mg/L, D-dimer showed a high sensitivity of at least 93%, but a very low specificity of nearly 0%. Conversely, an optimised cut-off value of 4.6 mg/L increased specificity to 95% for the detection of life-threatening venous thromboembolism, acute aortic dissection or thrombosis of the upper extremity at the costs of moderate sensitivities (58% for pulmonary embolism, 41% for deep vein thrombosis, 65% for pulmonary embolism with co-existent deep vein thrombosis, 50% for acute aortic dissection and 13% for thrombosis of the upper extremity). Using the same cut-off in cancer patients, higher values were observed for sensitivity at a specificity level of more than 95%. The area under the curve for the discrimination of venous thromboembolism/acute aortic dissection/thrombosis of the upper extremity from controls was significantly higher in cancer versus non-cancer patients (area under the curve 0.905 in cancer patients, 95% CI 0.89 to 0.92, vs. area under the curve 0.857 in non-cancer patients, 95% CI 0.84 to 0.88; P=0.0349). CONCLUSION: D-dimers are useful not only to rule out but also to rule in venous thromboembolism and acute aortic dissection with an at least moderate discriminatory ability, both in patients with and without cancer.

Cardiac K2P13.1 (THIK-1) two-pore-domain K+ channels: Pharmacological regulation and remodeling in atrial fibrillation.

Cardiac two-pore-domain potassium (K2P) channels have been proposed as novel antiarrhythmic targets. K2P13.1 (THIK-1) channels are expressed in the human heart, and atrial K2P13.1 levels are reduced in patients with atrial fibrillation (AF) or heart failure. The first objective of this study was to investigate acute effects of antiarrhythmic drugs on human K2P13.1 currents. Second, we assessed atrial K2P13.1 remodeling in AF pigs to validate the porcine model for future translational evaluation of K2P13.1-based antiarrhythmic concepts. K2P13.1 protein expression was studied in domestic pigs during AF induced by atrial burst pacing. AF was associated with 66% reduction of K2P13.1 levels in the right atrium at 21-day follow-up. Voltage clamp electrophysiology was employed to elucidate human K2P13.1 channel pharmacology in Xenopus oocytes. Propafenone (-26%; 100 µM), mexiletine (-75%; 1.5 mM), propranolol (-38%; 200 µM), and lidocaine (-59%; 100 µM) significantly inhibited K2P13.1 currents. By contrast, K2P13.1 channels were not markedly affected by quinidine, carvedilol, metoprolol, amiodarone and verapamil. Concentration-dependent K2P13.1 blockade by mexiletine occurred rapidly with membrane depolarization and was frequency-independent. Mexiletine reduced K2P13.1 open rectification properties and shifted current-voltage relationships towards more negative potentials. In conclusion, atrial expression and AF-associated downregulation of K2P13.1 channels in a porcine model resemble human findings and support a general role for K2P13.1 in AF pathophysiology. K2P13.1 current sensitivity to antiarrhythmic drugs provides a starting point for further development of an emerging antiarrhythmic paradigm.

Cloning and characterization of zebrafish K2P13.1 (THIK-1) two-pore-domain K+ channels.

Two-pore-domain potassium (K2P) channels conduct background potassium currents in the heart and other tissues. K2P currents are involved in the repolarization of action potentials and stabilize the resting membrane potential. Human K2P13.1 (THIK-1) channels are expressed in the heart and have recently been implicated in atrial fibrillation. The in vivo significance of K2P13.1 currents in cardiac electrophysiology is not known. We hypothesized that Danio rerio (zebrafish) may serve as model to elucidate the functional role of cardiac K2P13.1 channels. This work was designed to characterize zebrafish orthologs of K2P13.1. Two zkcnk13 coding sequences were identified by DNA database searches and amplified from zebrafish cDNA. Human and zebrafish K2P13.1 proteins exhibit 70% (K2P13.1a) and 66% (K2P13.1b) identity. Kcnk13 expression in zebrafish was studied using polymerase chain reaction. Zebrafish kcnk13a and zkcnk13b mRNAs were detected in brain and heart. Human and zebrafish K2P13.1 currents were analyzed in the Xenopus oocyte expression system by voltage clamp electrophysiology. Zebrafish K2P13.1a polypeptides were non-functional, while zK2P13.1b channels exhibited K+ selective, outwardly rectifying currents. Zebrafish and human K2P13.1 currents were similarly activated by arachidonic acid and reduced by barium, mexiletine, lidocaine, and inhibition of phospholipase C. In conclusion, zebrafish K2P13.1b channels and their human orthologs exhibit structural and regulatory similarities. Zebrafish may be used as in vivo model for the assessment of physiology and therapeutic significance of K2P13.1.

Cardiovascular pharmacology of K2P17.1 (TASK-4, TALK-2) two-pore-domain K+ channels.

K2P17.1 (TASK-4, TALK-2) potassium channels are expressed in the heart and represent potential targets for pharmacological management of atrial and ventricular arrhythmias. Reduced K2P17.1 expression was found in atria and ventricles of heart failure (HF) patients. Modulation of K2P17.1 currents by antiarrhythmic compounds has not been comprehensively studied to date. The objective of this study was to investigate acute effects of clinically relevant antiarrhythmic drugs on human K2P17.1 channels to provide a more complete picture of K2P17.1 electropharmacology. Whole-cell patch clamp and two-electrode voltage clamp electrophysiology was employed to study human K2P17.1 channel pharmacology. K2P17.1 channels expressed in Xenopus laevis oocytes were screened for sensitivity to antiarrhythmic drugs, revealing significant activation by propafenone (+ 296%; 100 µM), quinidine (+ 58%; 100 µM), mexiletine (+ 21%; 100 µM), propranolol (+ 139%; 100 µM), and metoprolol (+ 17%; 100 µM) within 60 min. In addition, the currents were inhibited by amiodarone (- 13%; 100 µM), sotalol (- 10%; 100 µM), verapamil (- 21%; 100 µM), and ranolazine (- 8%; 100 µM). K2P17.1 channels were not significantly affected by ajmaline and carvedilol. Concentration-dependent K2P17.1 activation by propafenone was characterized in more detail. The onset of activation was fast, and current-voltage relationships were not modulated by propafenone. K2P17.1 activation was confirmed in mammalian Chinese hamster ovary cells, revealing 7.8-fold current increase by 100 µM propafenone. Human K2P17.1 channels were sensitive to multiple antiarrhythmic drugs. Differential pharmacological regulation of repolarizing K2P17.1 background K+ channels may be employed for personalized antiarrhythmic therapy.

Identification and functional characterization of zebrafish K2P17.1 (TASK-4, TALK-2) two-pore-domain K+ channels.

Human K2P17.1 (TASK-4, TALK-2) two-pore-domain potassium (K2P) channels have recently been implicated in heart rhythm disorders including atrial fibrillation and conduction disease. The functional in vivo significance of K2P17.1 currents in cardiac electrophysiology remains incompletely understood. Danio rerio (zebrafish) may be utilized to elucidate the role of cardiac K2P channels in vivo. The aim of this work was to identify and characterize the zebrafish ortholog of K2P17.1 in comparison to its human counterpart. The zkcnk17 coding sequence was amplified from zebrafish cDNA. Zebrafish kcnk17 mRNA expression was assessed by polymerase chain reaction. Human and zebrafish K2P17.1 currents were analyzed using two-electrode voltage clamp electrophysiology and the Xenopus oocyte expression system. Kcnk17 mRNA was detected in zebrafish brain. Human and zebrafish K2P17.1 proteins exhibited 33.4% identity. Zebrafish K2P17.1 channels conducted K+ selective currents with open rectification properties. Both human and zebrafish K2P17.1 were inhibited by barium. In contrast to human K2P17.1, zK2P17.1 currents were not sensitive to extracellular alkalization, likely due to the lack of a lysine residue involved in pH sensing of hK2P17.1. In conclusion, zebrafish and human K2P17.1 channels display similar structural and regulatory properties. Zebrafish may serve as an in vivo model to study neuronal K2P17.1 function but does not appear appropriate for cardiac electrophysiology studies. Differences in pH sensitivity of zK2P17.1 currents need to be considered when zebrafish data are extrapolated to human physiology.

Fully digital data processing during cardiovascular implantable electronic device follow-up in a high-volume tertiary center.

BACKGROUND: Increasing numbers of patients with cardiovascular implantable electronic devices (CIEDs) and limited follow-up capacities highlight unmet challenges in clinical electrophysiology. Integrated software (MediConnect®) enabling fully digital processing of device interrogation data has been commercially developed to facilitate follow-up visits. We sought to assess feasibility of fully digital data processing (FDDP) during ambulatory device follow-up in a high-volume tertiary hospital to provide guidance for future users of FDDP software. METHODS: A total of 391 patients (mean age, 70 years) presenting to the outpatient department for routine device follow-up were analyzed (pacemaker, 44%; implantable cardioverter defibrillator, 39%; cardiac resynchronization therapy device, 16%). RESULTS: Quality of data transfer and follow-up duration were compared between digital (n = 265) and manual processing of device data (n = 126). Digital data import was successful, complete and correct in 82% of cases when early software versions were used. When using the most recent software version the rate of successful digital data import increased to 100%. Software-based import of interrogation data was complete and without failure in 97% of cases. The mean duration of a follow-up visit did not differ between the two groups (digital 18.7 min vs. manual data transfer 18.2 min). CONCLUSIONS: FDDP software was successfully implemented into the ambulatory follow-up of patients with implanted pacemakers and defibrillators. Digital data import into electronic patient management software was feasible and supported the physician's workflow. The total duration of follow-up visits comprising technical device interrogation and clinical actions was not affected in the present tertiary center outpatient cohort.

Ticagrelor promotes atherosclerotic plaque stability in a mouse model of advanced atherosclerosis.

OBJECTIVE: There is increasing evidence supporting the role of platelets in atherosclerotic vascular disease. The G-protein-coupled receptor P2Y12 is a central mediator of platelet activation and aggregation but has also been linked to platelet-independent vascular disease. Ticagrelor is an oral P2Y12 antagonist that is used as a standard treatment in patients after acute myocardial infarction. However, the effects of ticagrelor on advanced atherosclerosis have not been investigated. MATERIALS AND METHODS: Twenty-week-old apolipoprotein-E-deficient mice received standard chow or standard chow supplemented with 0.15% ticagrelor (approximately 270 mg/kg/day) for 25 weeks. The lesion area was evaluated in the aortic sinus by Movat's pentachrome staining and lesion composition, thickness of the fibrous cap, and size of the necrotic core evaluated by morphometry. RAW 264.7 macrophages were serum starved and treated with ticagrelor in vitro for the detection and quantification of apoptosis. In addition, oxLDL uptake in RAW 264.7 macrophages was evaluated. RESULTS: A trend toward the reduction of total lesion size was detected. However, data did not reach the levels of significance (control, n=11, 565,881 µm(2) [interquartile range {IQR} 454,778-603,925 µm(2)] versus ticagrelor, n=13, 462,595 µm(2) [IQR 379,740-546,037 µm(2)]; P=0.1). A significant reduction in the relative area of the necrotic core (control, n=11, 0.46 [IQR 0.4-0.51] versus ticagrelor, n=13, 0.34 [IQR 0.31-0.39]; P=0.008), and a significant increase in fibrous caps thickness (control, n=11, 3.7 µm [IQR 3.4-4.2 µm] versus ticagrelor, n=13, 4.7 [IQR 4.3-5.5 µm], P=0.04) were seen in ticagrelor-treated mice. In vitro studies demonstrated a reduction in apoptotic RAW 264.7 macrophages (control 0.07±0.03 versus ticagrelor 0.03±0.03; P=0.0002) when incubated with ticagrelor. Uptake of oxLDL in RAW 264.7 was significantly reduced when treated with ticagrelor (control 9.2 [IQR 5.3-12.9] versus ticagrelor 6.4 [IQR 2.5-9.5], P=0.02). CONCLUSION: The present study demonstrates for the first time a plaque-stabilizing effect of ticagrelor in a model of advanced vascular disease, potentially induced by a reduction of oxLDL uptake or an inhibition of apoptosis as seen in vitro.

Therapeutic targeting of two-pore-domain potassium (K(2P)) channels in the cardiovascular system.

The improvement of treatment strategies in cardiovascular medicine is an ongoing process that requires constant optimization. The ability of a therapeutic intervention to prevent cardiovascular pathology largely depends on its capacity to suppress the underlying mechanisms. Attenuation or reversal of disease-specific pathways has emerged as a promising paradigm, providing a mechanistic rationale for patient-tailored therapy. Two-pore-domain K(+) (K(2P)) channels conduct outward K(+) currents that stabilize the resting membrane potential and facilitate action potential repolarization. K(2P) expression in the cardiovascular system and polymodal K2P current regulation suggest functional significance and potential therapeutic roles of the channels. Recent work has focused primarily on K(2P)1.1 [tandem of pore domains in a weak inwardly rectifying K(+) channel (TWIK)-1], K(2P)2.1 [TWIK-related K(+) channel (TREK)-1], and K(2P)3.1 [TWIK-related acid-sensitive K(+) channel (TASK)-1] channels and their role in heart and vessels. K(2P) currents have been implicated in atrial and ventricular arrhythmogenesis and in setting the vascular tone. Furthermore, the association of genetic alterations in K(2P)3.1 channels with atrial fibrillation, cardiac conduction disorders and pulmonary arterial hypertension demonstrates the relevance of the channels in cardiovascular disease. The function, regulation and clinical significance of cardiovascular K(2P) channels are summarized in the present review, and therapeutic options are emphasized.

HERG K+ channel-dependent apoptosis and cell cycle arrest in human glioblastoma cells.

Glioblastoma (GB) is associated with poor patient survival owing to uncontrolled tumor proliferation and resistance to apoptosis. Human ether-a-go-go-related gene K(+) channels (hERG; Kv11.1, KCNH2) are expressed in multiple cancer cells including GB and control cell proliferation and death. We hypothesized that pharmacological targeting of hERG protein would inhibit tumor growth by inducing apoptosis of GB cells. The small molecule hERG ligand doxazosin induced concentration-dependent apoptosis of human LNT-229 (EC50 = 35 µM) and U87MG (EC50 = 29 µM) GB cells, accompanied by cell cycle arrest in the G0/G1 phase. Apoptosis was associated with 64% reduction of hERG protein. HERG suppression via siRNA-mediated knock down mimicked pro-apoptotic effects of doxazosin. Antagonism of doxazosin binding by the non-apoptotic hERG ligand terazosin resulted in rescue of protein expression and in increased survival of GB cells. At the molecular level doxazosin-dependent apoptosis was characterized by activation of pro-apoptotic factors (phospho-erythropoietin-producing human hepatocellular carcinoma receptor tyrosine kinase A2, phospho-p38 mitogen-activated protein kinase, growth arrest and DNA damage inducible gene 153, cleaved caspases 9, 7, and 3), and by inactivation of anti-apoptotic poly-ADP-ribose-polymerase, respectively. In summary, this work identifies doxazosin as small molecule compound that promotes apoptosis and exerts anti-proliferative effects in human GB cells. Suppression of hERG protein is a crucial molecular event in GB cell apoptosis. Doxazosin and future derivatives are proposed as novel options for more effective GB treatment.

PKC-dependent activation of human K(2P) 18.1 K(+) channels.

BACKGROUND AND PURPOSE: Two-pore-domain K(+) channels (K(2P) ) mediate K(+) background currents that modulate the membrane potential of excitable cells. K(2P) 18.1 (TWIK-related spinal cord K(+) channel) provides hyperpolarizing background currents in neurons. Recently, a dominant-negative loss-of-function mutation in K(2P) 18.1 has been implicated in migraine, and activation of K(2P) 18.1 channels was proposed as a therapeutic strategy. Here we elucidated the molecular mechanisms underlying PKC-dependent activation of K(2P) 18.1 currents. EXPERIMENTAL APPROACH: Human K(2P) 18.1 channels were heterologously expressed in Xenopus laevis oocytes, and currents were recorded with the two-electrode voltage clamp technique. KEY RESULTS: Stimulation of PKC using phorbol 12-myristate-13-acetate (PMA) activated the hK(2P) 18.1 current by 3.1-fold in a concentration-dependent fashion. The inactive analogue 4α-PMA had no effect on channel activity. The specific PKC inhibitors bisindolylmaleimide I, Ro-32-0432 and chelerythrine reduced PMA-induced channel activation indicating that PKC is involved in this effect of PMA. Selective activation of conventional PKC isoforms with thymeleatoxin (100 nM) did not reproduce K(2P) 18.1 channel activation. Current activation by PMA was not affected by pretreatment with CsA (calcineurin inhibitor) or KT 5720 (PKA inhibitor), ruling out a significant contribution of calcineurin or cross-talk with PKA to the PKC-dependent hK(2P) 18.1 activation. Finally, mutation of putative PKC phosphorylation sites did not prevent PMA-induced K(2P) 18.1 channel activation. CONCLUSIONS AND IMPLICATIONS: We demonstrated that activation of hK(2P) 18.1 (TRESK) by PMA is mediated by PKC stimulation. Hence, PKC-mediated activation of K(2P) 18.1 background currents may serve as a novel molecular target for migraine treatment.

Alternative splicing determines mRNA translation initiation and function of human K(2P)10.1 K+ channels.

Potassium-selective ion channels regulate cardiac and neuronal excitability by stabilizing the resting membrane potential and by modulating shape and frequency of action potentials. The delicate control of membrane voltage requires structural and functional diversity of K+ channel subunits expressed in a given cell. Here we reveal a previously unrecognized biological mechanism. Tissue-specific mRNA splicing regulates alternative translation initiation (ATI) of human K(2P)10.1 K+ background channels via recombination of 5 nucleotide motifs. ATI-dependent expression of full-length protein or truncated subunits initiated from two downstream start codons determines macroscopic current amplitudes and biophysical properties of hK(2P)10.1 channels. The interaction between hK(2P)10.1 mRNA splicing, translation and function increases K+ channel complexity and is expected to contribute to electrophysiological plasticity of excitable cells.

hERG K+ channel-associated cardiac effects of the antidepressant drug desipramine.

Cardiac side effects of antidepressant drugs are well recognized. Adverse effects precipitated by the tricyclic drug desipramine include prolonged QT intervals, torsade de pointes tachycardia, heart failure, and sudden cardiac death. QT prolongation has been primarily attributed to acute blockade of hERG/I(Kr) currents. This study was designed to provide a more complete picture of cellular effects associated with desipramine. hERG channels were expressed in Xenopus laevis oocytes and human embryonic kidney (HEK 293) cells, and potassium currents were recorded using patch clamp and two-electrode voltage clamp electrophysiology. Ventricular action potentials were recorded from guinea pig cardiomyocytes. Protein trafficking and cell viability were evaluated in HEK 293 cells and in HL-1 mouse cardiomyocytes by immunocytochemistry, Western blot analysis, or colorimetric MTT assay, respectively. We found that desipramine reduced hERG currents by binding to a receptor site inside the channel pore. hERG protein surface expression was reduced after short-term treatment, revealing a previously unrecognized mechanism. When long-term effects were studied, forward trafficking was impaired and hERG currents were decreased. Action potential duration was prolonged upon acute and chronic desipramine exposure. Finally, desipramine triggered apoptosis in cells expressing hERG channels. Desipramine exerts at least four different cellular effects: (1) direct hERG channel block, (2) acute reduction of hERG surface expression, (3) chronic disruption of hERG trafficking, and (4) induction of apoptosis. These data highlight the complexity of hERG-associated drug effects.

Multiple mechanisms of hERG liability: K+ current inhibition, disruption of protein trafficking, and apoptosis induced by amoxapine.

The antidepressant amoxapine has been linked to cases of QT prolongation, acute heart failure, and sudden death. Inhibition of cardiac hERG (Kv11.1) potassium channels causes prolonged repolarization and is implicated in apoptosis. Apoptosis in association with amoxapine has not yet been reported. This study was designed to investigate amoxapine effects on hERG currents, hERG protein trafficking, and hERG-associated apoptosis in order to elucidate molecular mechanisms underlying cardiac side effects of the drug. hERG channels were expressed in Xenopus laevis oocytes and HEK 293 cells, and potassium currents were recorded using patch clamp and two-electrode voltage clamp electrophysiology. Protein trafficking was evaluated in HEK 293 cells by Western blot analysis, and cell viability was assessed in HEK cells by immunocytochemistry and colorimetric MTT assay. Amoxapine caused acute hERG blockade in oocytes (IC(50) = 21.6 microM) and in HEK 293 cells (IC(50) = 5.1 microM). Mutation of residues Y652 and F656 attenuated hERG blockade, suggesting drug binding to a receptor inside the channel pore. Channels were mainly blocked in open and inactivated states, and voltage dependence was observed with reduced inhibition at positive potentials. Amoxapine block was reverse frequency-dependent and caused accelerated and leftward-shifted inactivation. Furthermore, amoxapine application resulted in chronic reduction of hERG trafficking into the cell surface membrane (IC(50) = 15.3 microM). Finally, the antidepressant drug triggered apoptosis in cells expressing hERG channels. We provide evidence for triple mechanisms of hERG liability associated with amoxapine: (1) direct hERG current inhibition, (2) disruption of hERG protein trafficking, and (3) induction of apoptosis. Further experiments are required to validate a specific pro-apoptotic effect mediated through blockade of hERG channels.

hERG: protein trafficking and potential for therapy and drug side effects.

Drug-induced QT interval prolongation is associated with torsade de pointes arrhythmia and sudden cardiac death. Acquired long QT syndrome poses a significant liability in pharmaceutical drug development, and has resulted in drugs being recalled from the market. This off-target property is caused primarily by the inhibition of cardiac hERG K+ currents. As a result, guidelines were established by The International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) requiring the preclinical evaluation of direct hERG channel blockade and QT prolongation. This review discusses established, as well as newly discovered and currently under-recognized, pro-arrhythmic mechanisms that are associated with hERG protein trafficking. Defective hERG trafficking is a research area of intensive scientific activity, and the implementation of screening for this type of hERG liability should be considered in order to improve the risk assessment and detection of drug-associated cardiotoxicity in safety pharmacology.