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1.
Heart Rhythm ; 18(12): 2177-2186, 2021 12.
Artigo em Inglês | MEDLINE | ID: mdl-34481984

RESUMO

BACKGROUND: Oliceridine is a biased ligand at the µ-opioid receptor recently approved for the treatment of acute pain. In a thorough QT study, corrected QT (QTc) prolongation displayed peaks at 2.5 and 60 minutes after a supratherapeutic dose. The mean plasma concentration peaked at 5 minutes, declining rapidly thereafter. OBJECTIVE: The purpose of this study was to examine the basis for the delayed effect of oliceridine to prolong the QTc interval. METHODS: Repolarization parameters and tissue accumulation of oliceridine were evaluated in rabbit left ventricular wedge preparations over a period of 5 hours. The effects of oliceridine on ion channel currents were evaluated in human embryonic kidney and Chinese hamster ovary cells. Quinidine was used as a control. RESULTS: Oliceridine and quinidine produced a progressive prolongation of the QTc interval and action potential duration over a period of 5 hours, paralleling slow progressive tissue uptake of the drugs. Oliceridine caused modest prolongation of these parameters, whereas quinidine produced a prominent prolongation of action potential duration and QTc interval as well as development of early afterdepolarization (after 2 hours), resulting in a high torsades de pointes score. The 50% inhibitory concentration values for the oliceridine inhibition of the rapidly activating delayed rectifier current (human ether a-go-go current) and late sodium channel current were 2.2 and 3.45 µM when assessed after traditional acute exposure but much lower after 3 hours of drug exposure. CONCLUSION: Our findings suggest that a gradual increase of intracellular access of drugs to the hERG channels as a result of their intracellular uptake and accumulation can significantly delay effects on repolarization, thus confounding the assessment of QT interval prolongation and arrhythmic risk when studied acutely. The multi-ion channel effects of oliceridine, late sodium channel current inhibition in particular, point to a low risk of devloping torsades de pointes.


Assuntos
Arritmias Cardíacas , Canal de Potássio ERG1/antagonistas & inibidores , Compostos de Espiro/farmacocinética , Tiofenos/farmacocinética , Analgésicos Opioides/farmacocinética , Animais , Arritmias Cardíacas/etiologia , Arritmias Cardíacas/metabolismo , Arritmias Cardíacas/fisiopatologia , Arritmias Cardíacas/prevenção & controle , Linhagem Celular , Cricetulus , Humanos , Concentração Inibidora 50 , Síndrome do QT Longo/induzido quimicamente , Síndrome do QT Longo/metabolismo , Síndrome do QT Longo/fisiopatologia , Moduladores de Transporte de Membrana/farmacologia , Quinidina/farmacocinética , Distribuição Tecidual , Bloqueadores do Canal de Sódio Disparado por Voltagem/farmacocinética
2.
Clin Pharmacol Ther ; 105(4): 943-953, 2019 04.
Artigo em Inglês | MEDLINE | ID: mdl-30447156

RESUMO

Balanced multi-ion channel-blocking drugs have low torsade risk because they block inward currents. The Comprehensive In Vitro Proarrhythmia Assay (CiPA) initiative proposes to use an in silico cardiomyocyte model to determine the presence of balanced block, and absence of heart rate corrected J-Tpeak (J-Tpeak c) prolongation would be expected for balanced blockers. This study included three balanced blockers in a 10-subject-per-drug parallel design; lopinavir/ritonavir and verapamil met the primary end point of ΔΔJ-Tpeak c upper bound < 10 ms, whereas ranolazine did not (upper bounds of 8.8, 6.1, and 12.0 ms, respectively). Chloroquine, a predominant blocker of the potassium channel encoded by the ether-à-go-go related gene (hERG), prolonged ΔΔQTc and ΔΔJ-Tpeak c by ≥ 10 ms. In a separate crossover design, diltiazem (calcium block) did not shorten dofetilide-induced ΔQTc prolongation, but shortened ΔJ-Tpeak c and prolonged ΔTpeak -Tend . Absence of J-Tpeak c prolongation seems consistent with balanced block; however, small sample size (10 subjects) may be insufficient to characterize concentration-response in some cases.


Assuntos
Biomarcadores/metabolismo , Eletrocardiografia/efeitos dos fármacos , Canais Iônicos/antagonistas & inibidores , Moduladores de Transporte de Membrana/uso terapêutico , Preparações Farmacêuticas/administração & dosagem , Adulto , Estudos Cross-Over , Feminino , Frequência Cardíaca/efeitos dos fármacos , Humanos , Síndrome do QT Longo/tratamento farmacológico , Síndrome do QT Longo/metabolismo , Masculino , Miócitos Cardíacos/efeitos dos fármacos , Miócitos Cardíacos/metabolismo , Torsades de Pointes/tratamento farmacológico , Torsades de Pointes/metabolismo
3.
Artigo em Inglês | MEDLINE | ID: mdl-29155283

RESUMO

INTRODUCTION: Cardiotoxicity assessment using human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) forms a key component of the Comprehensive in Vitro Proarrhythmia Assay (CiPA). A potentially impactful factor on iPSC-CM testing is the presence of serum in the experimental media. Generally, serum-free media is used to most accurately reproduce "free" drug concentration. However, caution is needed; drug solubility and cardiomyocyte electrophysiology could be affected by media formulation, potentially impacting interpretation of drug-induced effects. METHODS: Effects of 25 drugs on properties of spontaneous field potentials in iPSC-CMs were assayed using a high-throughput microelectrode array (MEA) in two media formulations: serum-containing and serum-free. Comparative analysis was conducted on rate-corrected field potential duration (FPDc) and prevalence of arrhythmic events. Further MEA experiments were conducted, varying percentages of serum as well as carbon substrate components. Comparative LC-MS/MS analysis was done on two compounds to evaluate drug concentrations. RESULTS: In serum-free media, 9 drugs prolonged FPDc. In serum-containing, 11 drugs prolonged FPDc. Eighteen drugs induced arrhythmias, 8 of these induced arrhythmias at lower concentrations in serum-containing media. At the highest non-arrhythmic concentrations, 13 of 25 drugs exhibited significant differences in FPDc prolongation/shortening between the media. Increasing fractions of serum in media yielded higher FPDc measurements. LC-MS/MS analysis of moxifloxacin and quinidine showed higher concentrations in serum-containing media. DISCUSSION: The present study highlights media formulation as an important consideration for cardiac safety testing with iPSC-CMs. Results described here suggest that media formulation influences both compound availability and baseline electrophysiological properties. Special attention should be paid to media for future iPSC-CM assays.


Assuntos
Arritmias Cardíacas/induzido quimicamente , Cardiotoxicidade/etiologia , Meios de Cultura/efeitos adversos , Meios de Cultura/farmacologia , Células-Tronco Pluripotentes Induzidas/efeitos dos fármacos , Miócitos Cardíacos/efeitos dos fármacos , Soro/metabolismo , Arritmias Cardíacas/metabolismo , Cardiotoxicidade/metabolismo , Células Cultivadas , Fenômenos Eletrofisiológicos/efeitos dos fármacos , Humanos , Síndrome do QT Longo/induzido quimicamente , Síndrome do QT Longo/metabolismo , Miócitos Cardíacos/metabolismo , Medição de Risco
4.
Artigo em Inglês | MEDLINE | ID: mdl-27622857

RESUMO

Cardiovascular toxicity is a prominent reason for failures in drug development, resulting in the demand for assays that can predict this liability in early drug discovery. We investigated whether iCell® cardiomyocytes have utility as an early QT/TdP screen. Thirty clinical drugs with known QT/TdP outcomes were evaluated blind using label-free microelectrode array (parameters measured were beating period (BP), field potential duration (FPD), fast Na+ amplitude and slope) and live cell, fast kinetic fluorescent Ca2+ transient FLIPR® Tetra (parameters measured were peak count, width, amplitude) systems. Many FPD-altering drugs also altered BP. Correction for BP, using a Log-Log (LL) model, was required to appropriately interpret direct drug effects on FPD. In comparison with human QT effects and when drug activity was to be predicted at top test concentration (TTC), LL-corrected FPD and peak count had poor assay sensitivity and specificity values: 13%/64% and 65%/11%, respectively. If effective free therapeutic plasma concentration (EFTPC) was used instead of TTC, the values were 0%/100% and 6%/100%, respectively. When compared to LL-corrected FPD and peak count, predictive values of uncorrected FPD, BP, width and amplitude were not much different. If pro-arrhythmic risk was to be predicted using Ca2+ transient data, the values were 67%/100% and 78%/53% at EFTPC and TTC, respectively. Thus, iCell® cardiomyocytes have limited value as an integrated QT/TdP assay, highlighting the urgent need for improved experimental alternatives that may offer an accurate integrated cardiomyocyte safety model for supporting the development of new drugs without QT/TdP effects.


Assuntos
Potenciais de Ação/efeitos dos fármacos , Canais de Cálcio/metabolismo , Efeitos Colaterais e Reações Adversas Relacionados a Medicamentos , Células-Tronco Pluripotentes Induzidas/efeitos dos fármacos , Síndrome do QT Longo/induzido quimicamente , Miócitos Cardíacos/efeitos dos fármacos , Cardiotoxicidade , Técnicas de Cultura de Células , Células Cultivadas , Meios de Cultura/química , Avaliação Pré-Clínica de Medicamentos , Humanos , Células-Tronco Pluripotentes Induzidas/metabolismo , Síndrome do QT Longo/metabolismo , Síndrome do QT Longo/fisiopatologia , Microeletrodos , Miócitos Cardíacos/metabolismo , Preparações Farmacêuticas/administração & dosagem
5.
J Pharm Sci ; 105(11): 3415-3424, 2016 11.
Artigo em Inglês | MEDLINE | ID: mdl-27640752

RESUMO

A Quantitative Systems Pharmacology approach was utilized to predict the cardiac consequences of drug-drug interaction (DDI) at the population level. The Simcyp in vitro-in vivo correlation and physiologically based pharmacokinetic platform was used to predict the pharmacokinetic profile of terfenadine following co-administration of the drug. Electrophysiological effects were simulated using the Cardiac Safety Simulator. The modulation of ion channel activity was dependent on the inhibitory potential of drugs on the main cardiac ion channels and a simulated free heart tissue concentration. ten Tusscher's human ventricular cardiomyocyte model was used to simulate the pseudo-ECG traces and further predict the pharmacodynamic consequences of DDI. Consistent with clinical observations, predicted plasma concentration profiles of terfenadine show considerable intra-subject variability with recorded Cmax values below 5 ng/mL for most virtual subjects. The pharmacokinetic and pharmacodynamic effects of inhibitors were predicted with reasonable accuracy. In all cases, a combination of the physiologically based pharmacokinetic and physiology-based pharmacodynamic models was able to differentiate between the terfenadine alone and terfenadine + inhibitor scenario. The range of QT prolongation was comparable in the clinical and virtual studies. The results indicate that mechanistic in vitro-in vivo correlation can be applied to predict the clinical effects of DDI even without comprehensive knowledge on all mechanisms contributing to the interaction.


Assuntos
Ensaios Clínicos como Assunto/métodos , Antagonistas não Sedativos dos Receptores H1 da Histamina/metabolismo , Modelos Biológicos , Terfenadina/metabolismo , Interface Usuário-Computador , Adulto , Interações Medicamentosas/fisiologia , Quimioterapia Combinada/efeitos adversos , Feminino , Antagonistas não Sedativos dos Receptores H1 da Histamina/efeitos adversos , Humanos , Síndrome do QT Longo/induzido quimicamente , Síndrome do QT Longo/metabolismo , Masculino , Pessoa de Meia-Idade , Terfenadina/efeitos adversos , Adulto Jovem
6.
Prog Biophys Mol Biol ; 120(1-3): 89-99, 2016 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-26713558

RESUMO

The Kv11.1 or hERG potassium channel is responsible for one of the major repolarising currents (IKr) in cardiac myocytes. Drug binding to hERG can result in reduction in IKr, action potential prolongation, acquired long QT syndrome and fatal cardiac arrhythmias. The current guidelines for pre-clinical assessment of drugs in development is based on the measurement of the drug concentration that causes 50% current block, i.e., IC50. However, drugs with the same apparent IC50 may have very different kinetics of binding and unbinding, as well as different affinities for the open and inactivated states of Kv11.1. Therefore, IC50 measurements may not reflect the true risk of drug induced arrhythmias. Here we have used an in silico approach to test the hypothesis that drug binding kinetics and differences in state-dependent affinity will influence the extent of cardiac action potential prolongation independent of apparent IC50 values. We found, in general that drugs with faster overall kinetics and drugs with higher affinity for the open state relative to the inactivated state cause more action potential prolongation. These characteristics of drug-hERG interaction are likely to be more arrhythmogenic but cannot be predicted by IC50 measurement alone. Our results suggest that the pre-clinical assessment of Kv11.1-drug interactions should include descriptions of the kinetics and state dependence of drug binding. Further, incorporation of this information into sophisticated in silico models should be able to better predict arrhythmia risk and therefore more accurately assess safety of new drugs in development.


Assuntos
Simulação por Computador , Canal de Potássio ERG1/metabolismo , Síndrome do QT Longo/induzido quimicamente , Bloqueadores dos Canais de Potássio/efeitos adversos , Bloqueadores dos Canais de Potássio/metabolismo , Potenciais de Ação/efeitos dos fármacos , Relação Dose-Resposta a Droga , Humanos , Concentração Inibidora 50 , Cinética , Síndrome do QT Longo/metabolismo , Síndrome do QT Longo/patologia , Modelos Cardiovasculares , Miocárdio/metabolismo , Miocárdio/patologia , Ligação Proteica
7.
Toxicol Appl Pharmacol ; 278(1): 72-7, 2014 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-24742750

RESUMO

Field potential duration (FPD) in human-induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs), which can express QT interval in an electrocardiogram, is reported to be a useful tool to predict K(+) channel and Ca(2+) channel blocker effects on QT interval. However, there is no report showing that this technique can be used to predict multichannel blocker potential for QT prolongation. The aim of this study is to show that FPD from MEA (Multielectrode array) of hiPS-CMs can detect QT prolongation induced by multichannel blockers. hiPS-CMs were seeded onto MEA and FPD was measured for 2min every 10min for 30min after drug exposure for the vehicle and each drug concentration. IKr and IKs blockers concentration-dependently prolonged corrected FPD (FPDc), whereas Ca(2+) channel blockers concentration-dependently shortened FPDc. Also, the multichannel blockers Amiodarone, Paroxetine, Terfenadine and Citalopram prolonged FPDc in a concentration dependent manner. Finally, the IKr blockers, Terfenadine and Citalopram, which are reported to cause Torsade de Pointes (TdP) in clinical practice, produced early afterdepolarization (EAD). hiPS-CMs using MEA system and FPDc can predict the effects of drug candidates on QT interval. This study also shows that this assay can help detect EAD for drugs with TdP potential.


Assuntos
Bloqueadores dos Canais de Cálcio/toxicidade , Síndrome do QT Longo/induzido quimicamente , Miócitos Cardíacos/efeitos dos fármacos , Células-Tronco Pluripotentes/efeitos dos fármacos , Bloqueadores dos Canais de Potássio/toxicidade , Torsades de Pointes/induzido quimicamente , Testes de Toxicidade/métodos , Potenciais de Ação , Células Cultivadas , Relação Dose-Resposta a Droga , Humanos , Síndrome do QT Longo/metabolismo , Síndrome do QT Longo/fisiopatologia , Miócitos Cardíacos/metabolismo , Células-Tronco Pluripotentes/metabolismo , Medição de Risco , Fatores de Tempo , Torsades de Pointes/metabolismo , Torsades de Pointes/fisiopatologia
8.
Am J Physiol Heart Circ Physiol ; 304(1): H104-17, 2013 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-23103500

RESUMO

The use of computational models to predict drug-induced changes in the action potential (AP) is a promising approach to reduce drug safety attrition but requires a better representation of more complex drug-target interactions to improve the quantitative prediction. The blockade of the human ether-a-go-go-related gene (HERG) channel is a major concern for QT prolongation and Torsade de Pointes risk. We aim to develop quantitative in-silico AP predictions based on a new electrophysiological protocol (suitable for high-throughput HERG screening) and mathematical modeling of ionic currents. Electrophysiological recordings using the IonWorks device were made from HERG channels stably expressed in Chinese hamster ovary cells. A new protocol that delineates inhibition over time was applied to assess dofetilide, cisapride, and almokalant effects. Dynamic effects displayed distinct profiles for these drugs compared with concentration-effects curves. Binding kinetics to specific states were identified using a new HERG Markov model. The model was then modified to represent the canine rapid delayed rectifier K(+) current at 37°C and carry out AP predictions. Predictions were compared with a simpler model based on conductance reduction and were found to be much closer to experimental data. Improved sensitivity to concentration and pacing frequency variables was obtained when including binding kinetics. Our new electrophysiological protocol is suitable for high-throughput screening and is able to distinguish drug-binding kinetics. The association of this protocol with our modeling approach indicates that quantitative predictions of AP modulation can be obtained, which is a significant improvement compared with traditional conductance reduction methods.


Assuntos
Simulação por Computador , Canais de Potássio Éter-A-Go-Go/antagonistas & inibidores , Ensaios de Triagem em Larga Escala/métodos , Modelos Cardiovasculares , Bloqueadores dos Canais de Potássio/toxicidade , Testes de Toxicidade , Potenciais de Ação , Animais , Células CHO , Cisaprida/toxicidade , Cricetinae , Cricetulus , Cães , Relação Dose-Resposta a Droga , Canal de Potássio ERG1 , Canais de Potássio Éter-A-Go-Go/genética , Canais de Potássio Éter-A-Go-Go/metabolismo , Humanos , Cinética , Síndrome do QT Longo/induzido quimicamente , Síndrome do QT Longo/metabolismo , Cadeias de Markov , Técnicas de Patch-Clamp , Fenetilaminas/toxicidade , Bloqueadores dos Canais de Potássio/metabolismo , Propanolaminas/toxicidade , Ligação Proteica , Medição de Risco , Sulfonamidas/toxicidade , Torsades de Pointes/induzido quimicamente , Torsades de Pointes/metabolismo , Transfecção
9.
Circ Res ; 106(8): 1374-83, 2010 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-20339117

RESUMO

RATIONALE: Sodium channel blockers are used as gene-specific treatments in long-QT syndrome type 3, which is caused by mutations in the sodium channel gene (SCN5A). Response to treatment is influenced by biophysical properties of mutations. OBJECTIVE: We sought to investigate the unexpected deleterious effect of mexiletine in a mutation combining gain-of- function and trafficking abnormalities. METHODS AND RESULTS: A long-QT syndrome type 3 child experienced paradoxical QT prolongation and worsening of arrhythmias after mexiletine treatment. The SCN5A mutation F1473S expressed in HEK293 cells presented a right-ward shift of steady-state inactivation, enlarged window current, and huge sustained sodium current. Unexpectedly, it also reduced the peak sodium current by 80%. Immunostaining showed that mutant Nav1.5 is retained in the cytoplasm. Incubation with 10 micromol/L mexiletine rescued the trafficking defect of F1473S, causing a significant increase in peak current, whereas sustained current was unchanged. Using a Markovian model of the Na channel and a model of human ventricular action potential, we showed that simulated exposure of F1473S to mexiletine paradoxically increased action potential duration, mimicking QT prolongation seen in the index patient on mexiletine treatment. CONCLUSIONS: Sodium channel blockers are largely used to shorten QT intervals in carriers of SCN5A mutations. We provided evidence that these agents may facilitate trafficking of mutant proteins, thus exacerbating QT prolongation. These data suggest that caution should be used when recommending this class of drugs to carriers of mutations with undefined electrophysiological properties.


Assuntos
Antiarrítmicos/efeitos adversos , Ativação do Canal Iônico/efeitos dos fármacos , Síndrome do QT Longo/tratamento farmacológico , Mexiletina/efeitos adversos , Proteínas Musculares/antagonistas & inibidores , Mutação , Bloqueadores dos Canais de Sódio/efeitos adversos , Potenciais de Ação , Linhagem Celular , Simulação por Computador , Eletrocardiografia , Evolução Fatal , Predisposição Genética para Doença , Humanos , Lactente , Ativação do Canal Iônico/genética , Cinética , Síndrome do QT Longo/genética , Síndrome do QT Longo/metabolismo , Masculino , Cadeias de Markov , Modelos Cardiovasculares , Proteínas Musculares/genética , Proteínas Musculares/metabolismo , Canal de Sódio Disparado por Voltagem NAV1.5 , Fenótipo , Transporte Proteico , Canais de Sódio/genética , Canais de Sódio/metabolismo , Transfecção , Resultado do Tratamento
10.
Channels (Austin) ; 1(4): 273-80, 2007.
Artigo em Inglês | MEDLINE | ID: mdl-18708744

RESUMO

Inherited mutations of SCN5A, the gene that encodes Na(V)1.5, the alpha subunit of the principle voltage-gated Na(+) channel in the heart, cause congenital Long QT Syndrome variant 3 (LQT-3) by perturbation of channel inactivation. LQT-3 mutations induce small, but aberrant, inward current that prolongs the ventricular action potential and subjects mutation carriers to arrhythmia risk dictated in part by the biophysical consequences of the mutations. Most previously investigated LQT-3 mutations are associated with increased arrhythmia risk during rest or sleep. Here we report a novel LQT-3 mutation discovered in a pediatric proband diagnosed with LQTS but who experienced cardiac events during periods of mild exercise as well as rest. The mutation, which changes a single amino acid (S1904L) in the Na(V)1.5 carboxy terminal domain, disrupts the channel inactivation gate complex and promotes late Na(+) channel currents, not by promoting a bursting mode of gating, but by increasing the propensity of the channel to reopen during prolonged depolarization. Incorporating a modified version of the Markov model of the Na(V)1.5 channel into a mathematical model of the human ventricular action potential predicts that the biophysical consequences of the S1904L mutation result in action potential prolongation that is seen for all heart rates but, in contrast to other previously-investigated LQT-3 mutant channels, is most pronounced at fast rates resulting in a drastic reduction in the cells ability to adapt APD to heart rate.


Assuntos
Arritmias Cardíacas/genética , Sistema de Condução Cardíaco/metabolismo , Ativação do Canal Iônico/genética , Síndrome do QT Longo/genética , Proteínas Musculares/genética , Mutação , Canais de Sódio/genética , Sódio/metabolismo , Potenciais de Ação , Substituição de Aminoácidos , Arritmias Cardíacas/metabolismo , Arritmias Cardíacas/fisiopatologia , Criança , Eletrocardiografia , Predisposição Genética para Doença , Sistema de Condução Cardíaco/fisiopatologia , Frequência Cardíaca , Humanos , Cinética , Síndrome do QT Longo/complicações , Síndrome do QT Longo/metabolismo , Síndrome do QT Longo/fisiopatologia , Masculino , Cadeias de Markov , Modelos Cardiovasculares , Proteínas Musculares/química , Proteínas Musculares/metabolismo , Canal de Sódio Disparado por Voltagem NAV1.5 , Linhagem , Fenótipo , Conformação Proteica , Canais de Sódio/química , Canais de Sódio/metabolismo
11.
Med Biol Eng Comput ; 44(1-2): 35-44, 2006 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-16929919

RESUMO

Long QT syndrome (LQTS) and Brugada syndrome (BrS) are inherited diseases predisposing to ventricular arrhythmias and sudden death. Genetic studies linked LQTS and BrS to mutations in genes encoding for cardiac ion channels. Recently, two novel missense mutations at the same codon in the gene encoding the cardiac Na+ channel (SCN5A) have been identified: Y1795C (causing the LQTS phenotype) and Y1795H (causing the BrS phenotype). Functional studies in HEK293 cells showed that both mutations alter the inactivation of Na+ current and cause a sustained Na+ current upon depolarisation. In this paper, a nine state Markov model was used to simulate the Na+ current in wild-type Na+ cardiac channel and the current alterations observed in Y1795C and Y1795H mutant channels. The model includes three distinct closed states, a conducting open state and five inactivation states (one fast-, two intermediate- and two closed-inactivation). Transition rates between these states were identified on the basis of previously published voltage-clamp experiments. The model was able to reproduce the experimental Na+ current in mutant channels just by altering the assignment of model parameters with respect to wild-type case. Parameter assignment was validated by performing action potential clamp experiments and comparing experimental and simulated I(Na) current. The Markov model was subsequently introduced in the Luo-Rudy model of ventricular myocyte to investigate "in silico" the consequences on the ventricular cell action potential of the two mutations. Coherently with their phenotypes, the Y1795C mutation prolongs the action potential, while the Y1795H mutation causes only negligible changes in action potential morphology.


Assuntos
Simulação por Computador , Mutação de Sentido Incorreto , Canais de Sódio/genética , Canais de Sódio/metabolismo , Potenciais de Ação , Síndrome de Brugada/genética , Síndrome de Brugada/metabolismo , Linhagem Celular , Humanos , Síndrome do QT Longo/genética , Síndrome do QT Longo/metabolismo , Cadeias de Markov , Modelos Biológicos , Técnicas de Patch-Clamp
12.
Heart Rhythm ; 2(11): 1238-49, 2005 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-16253915

RESUMO

BACKGROUND: Long QT syndrome (LQTS) is a cardiovascular disorder characterized by prolonged QTc time, syncope, or sudden death caused by torsades de pointes and ventricular fibrillation. We investigated the clinical and electrophysiologic phenotype of individual mutations and the compound mutations in a family in which different genotypes could be found. OBJECTIVES: The purpose of this study was to determine the impact of genotype-based diagnostic assessment in LQTS. METHODS: We used cascade screening and functional analyses to investigate the phenotype in a family with LQTS. The contributions of the compound mutations in the KCNQ1 and KCNH2 genes (KCNQ1 R591H, KCNH2 R328C) were analyzed by heterologous expression in Xenopus laevis oocytes using two-electrode voltage clamp and by confocal imaging. RESULTS: KCNH2 R328C did not show any functional phenotype whereas KCNQ1 R591H resulted in severe reduction of current. Neither wild-type nor mutant channels affected each other functionally in coexpression experiments. Therefore, a direct interaction between KCNQ1 and KCNH2 was ruled out under these conditions. CONCLUSION: Assessment of novel mutational findings in LQTS should include accurate genetic and functional analysis. Notably, appropriate studies are needed if two or more mutations in different genes are present in one proband. Our findings prompt reconsideration of the impact of compound mutations in LQTS families and reinforce the need for thorough functional evaluation of novel ion channel mutations before assignment of pathogenic status.


Assuntos
DNA/genética , Canais de Potássio Éter-A-Go-Go/genética , Canal de Potássio KCNQ1/genética , Síndrome do QT Longo/genética , Mutação de Sentido Incorreto , Alelos , Canal de Potássio ERG1 , Eletrofisiologia , Canais de Potássio Éter-A-Go-Go/metabolismo , Feminino , Predisposição Genética para Doença , Genótipo , Frequência Cardíaca/fisiologia , Humanos , Canal de Potássio KCNQ1/metabolismo , Síndrome do QT Longo/metabolismo , Síndrome do QT Longo/fisiopatologia , Masculino , Pessoa de Meia-Idade , Linhagem , Fenótipo , Reação em Cadeia da Polimerase
14.
J Clin Pharmacol ; 40(5): 468-74, 2000 May.
Artigo em Inglês | MEDLINE | ID: mdl-10806599

RESUMO

Monte Carlo simulation was used to assess the type I error rate and rank order of power for six different metrics using linear mixed-effect models, including two variables recommended by the European Agency for the Evaluation of Medicinal Products (EMEA) in the analysis of QTc interval data. The metrics analyzed were maximal change in QTc interval from baseline, maximal QTc interval, area under the QTc interval-time curve (AUC), average QTc interval, maximal QTc interval with baseline QTc interval as covariate, and AUC with baseline QTc interval as covariate. Two dosing regimens were studied: multiple-dose oral and multiple-dose continuous intravenous infusion. Both regimens were designed to produce similar maximal plasma concentrations, albeit with the infusion regimen maintaining maximal plasma concentrations for a longer period of time. The ability of the metrics to detect a drug effect was examined, assuming drug effect followed either an Emax or linear model. All statistics had a type I error rate near the nominal value. Regardless of pharmacokinetic or pharmacodynamic model, AUC with baseline QTc interval as a covariate had greater power than any other metric examined. The simulations also suggest that mean QTc interval data not be used.


Assuntos
Simulação por Computador , Síndrome do QT Longo/fisiopatologia , Método de Monte Carlo , Administração Oral , Área Sob a Curva , Efeitos Colaterais e Reações Adversas Relacionados a Medicamentos , Eletrocardiografia , Frequência Cardíaca/efeitos dos fármacos , Humanos , Infusões Intravenosas , Síndrome do QT Longo/induzido quimicamente , Síndrome do QT Longo/metabolismo , Farmacocinética , Ensaios Clínicos Controlados Aleatórios como Assunto
15.
Nature ; 400(6744): 566-9, 1999 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-10448858

RESUMO

Advances in genetics and molecular biology have provided an extensive body of information on the structure and function of the elementary building blocks of living systems. Genetic defects in membrane ion channels can disrupt the delicate balance of dynamic interactions between the ion channels and the cellular environment, leading to altered cell function. As ion-channel defects are typically studied in isolated expression systems, away from the cellular environment where they function physiologically, a connection between molecular findings and the physiology and pathophysiology of the cell is rarely established. Here we describe a single-channel-based Markovian modelling approach that bridges this gap. We achieve this by determining the cellular arrhythmogenic consequences of a mutation in the cardiac sodium channel that can lead to a clinical arrhythmogenic disorder (the long-QT syndrome) and sudden cardiac death.


Assuntos
Síndrome do QT Longo/genética , Mutação , Canais de Sódio/genética , Potenciais de Ação , Humanos , Ativação do Canal Iônico , Síndrome do QT Longo/metabolismo , Cadeias de Markov , Modelos Cardiovasculares , Modelos Genéticos , Miocárdio/metabolismo , Fenótipo , Canais de Sódio/metabolismo
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