Antiarrhythmic Drugs:. Past, Present, and Future

Cardiomyopathy development protection after myocardial infarction in rats: Successful competition for major dihydropyridines' common metabolite against captopril

During the last 25 years angiotensin-converting enzyme inhibitors spectacularly conquered the field of cardiovascular diseases therapy. Nevertheless, lack of new studies concerning side effects associated with their chronic administration seems to be rather confusing. In our previous research, we proved that the main furnidipines' metabolite (M-2) possess multiple cardioprotective actions. Currently, we compared effects of post-infarction long-term oral treatment with M-2 and captopril on hemodynamic parameters and "ischemic cardiomyopathy" development in rats. Myocardial infarction was evoked by permanent left anterior descending coronary artery occlusion for 35 days. Surviving rats were treated with captopril (2 × 25 mg/kg) or M-2 (4 mg/kg) from 6th- 35th day. At 35th day rats' hearts were tested on working heart setup, where following parameters were measured: heart rate, preload pressure, aortic systolic and diastolic pressures, aortic maximum rise and fall, aortic and coronary flow, myocardial oxygen consumption and oximetry in perfusate. Subsequently, heart tissue specimens were assessed during morphological estimation. Captopril caused significant heart rate increase and markedly diminished preload pressure in comparison to M-2. Both drugs evoked essential aortic pressure increase. Aortic flow was significantly decreased after M-2, whereas captopril increased this parameter in comparison to M-2. Both agents caused marked coronary flow increase. Morphologic examination in captopril revealed cardiomyopathic process in 70% of hearts, whereas in M-2 this value reached 30%. Neovascularization of post-infarcted myocardium was visible only after M-2 therapy. Concluding, M-2 presented itself as more attractive agent in long-term post-infarction treatment by preventing cardiomyopathy development, angiogenesis stimulation and preserving cardiac performance.

Dihydropyridines' metabolites-induced early apoptosis after myocardial infarction in rats; new outlook on preclinical study with M-2 and M-3

Our previous studies established cardio-protective effects of furnidipine and its active metabolites called M-2 and M-3. The aim of current research was to compare the effects of single oral pretreatment with 20 mg kg(-1) of M-2 and M-3 on mortality, different forms of arrhythmias, blood pressures parameters and ST-segment changes during occlusion (for 90 min) and reperfusion in the model of myocardial infarction in rats evoked by left anterior descending coronary artery occlusion. Additionally, the development of programmed cell death and biochemical parameters in blood serum were studied at 4th day after infarction. Furnidipines' metabolites effectively reduced mortality index while did not markedly influence on blood pressures parameters, arrhythmias, ST-segment changes as well as biochemical parameters. Intriguingly, programmed cell death study (TUNEL) showed distinct increase in the amount of apoptotic nuclei in post-infarcted myocardium, granulation tissue and what is more in arteriolar walls after M-2 and M-3 application. Moreover, M-2 turned out to be more powerful in stimulation of apoptosis in granulation tissue surrounding infarcted area whereas M-3 presented balanced profile in this matter. Taking into account that programmed cell death plays positive role in post-infarcted heart healing, M-2 presents itself as more attractive agent for oral pretreatment in early stages of ischemia by non-stable individuals due to its more specific action in stimulation repairing processes in granulation tissue as well as in arteriolar walls. While M-2 and M-3 are common metabolites present in degradation pathways of many widely used dihydropyridines in clinic, this key fact put the new outlook on understanding additional mechanism and effects of not only furnidipines' metabolites but also other dihydropyridines.

Back to the future with phenotypic screening

There are no disease-modifying drugs for any old age associated neurodegenerative disease or stroke. This is at least in part due to the failure of drug developers to recognize that the vast majority of neurodegenerative diseases arise from a confluence of multiple toxic insults that accumulate during normal aging and interact with genetic and environmental risk factors. Thus, it is unlikely that the current single target approach based upon rare dominant mutations or even a few preselected targets is going to yield useful drugs for these conditions. Therefore, the identification of drug candidates for neurodegeneration should be based upon their efficacy in phenotypic screening assays that reflect the biology of the aging brain, not a single, preselected target. It is argued here that this approach to drug discovery is the most likely to produce safe and effective drugs for neurodegenerative diseases.

Differential effects of furnidipines' metabolites on reperfusion-induced arrhythmias in rats in vivo

We previously established that furnidipine (FUR) and oxy dihydropyridines prevent rats mortality by strong reduction of the lethal arrhythmias in reperfusion. Therefore we decided to study the influence of three main metabolites (M-2, M-3, M-8) of FUR on ischemia-and reperfusion- induced arrhythmias and hemodynamic parameters in rat model to examine their independent activity. The metabolites (M-2, M-3, M-8) were given orally 20 mg/kg (24 and 1 h before ischemia). Mortality was significantly diminished in M-2 and M-3 treated groups with M-3 preventing animal mortality entirely. All three examined substances significantly reduced the duration and incidence of ventricular fibrillation (VF) with M-3, once again, completely preventing VF. Moreover, only M-3 significantly decreased the duration of ventricular tachycardia but had no influence on their incidence. Through the occlusion and reperfusion periods, M-2 and M-3 were markedly less hypotensive than M-8 and did not influence on heart rate. We conclude that two tested metabolites of FUR, M-3 and M-2 exhibited the most pronounced anti-arrhythmic effect being at the same time the most normotensive and therefore caused the most beneficial effects.

Anti-arrhythmic and hemodynamic effects of oxy nifedipine, oxy nimodipine, oxy nitrendipine and oxy nisoldipine

Our previous studies have established cardio-protective effects of furnidipine and its active metabolites. We therefore decided to compare the influence of oral and intravenous administration of furnidipine, nifedipine, nitrendipine and nimodipine to examine their effects on hemodynamics and arrhythmias. Since dihydropyridines are oxidatively metabolized in the body and the oxidized metabolites are among the final products, we studied the influence of four oxidized dihydropyridines (oxy nifedipine, oxy nimodipine, oxy nitrendipine and oxy nisoldipine) on the same parameters. In vivo model of ischemia- and reperfusion-induced arrhythmias of rats was used. Dihydropyridines were administered 5 mg/kg orally (24 and 1 h before ischemia) or 5 μg/kg intravenously (10 min before ischemia). 20 mg/kg of the oxidized dihydropyridines was given orally (24 and 1 h before ischemia). The dihydropyridines exhibited significant anti-arrhythmic actions after both forms of administration but their influence on blood pressure was differential and contrasting and depended on route of administration. The oxidized dihydropyridines imparted strong protection against lethal arrhythmias while exerting differential influences on blood pressure with oxy nifedipine and oxy nisoldipine being hypertensive and oxy nitrendipine being most normotensive. The differential effects observed with the dihydropyridines after the two routes of administration lend strength to the hypothesis that their metabolites may have a significant role in mediating the actions of the parent drug. The strong anti-arrhythmic action of the oxidized dihydropyridines along with their differential effect on blood pressure could indicate their potential use as cardio-protective drugs in certain groups of patients.

Aging is a primary risk factor for cardiac arrhythmias: disruption of intracellular Ca2+ regulation as a key suspect

Aging is an inevitable time-dependent progression associated with a functional decline of the cardiovascular system even in 'healthy' individuals. Age positively correlates with an increasing risk of cardiac problems including arrhythmias. Not only the prevalence but also the severity of arrhythmias escalates with age. The reasons for this are multifactorial but dysregulation of intracellular calcium within the heart is likely to play a key role in initiating and perpetuating these life-threatening events. We now know that several aspects of cardiac calcium regulation significantly change with advancing age - changes that could produce electrical instability. Further development of knowledge of the mechanisms underlying these changes will allow us to reduce what currently is an inevitable increase in the incidence of arrhythmias in the elderly.

Assessment of the Spatial QRS-T Angle by Vectorcardiography: Current Data and Perspectives

The concept of the ventricular gradient (VG) was conceived in the 1930s and its calculation yielded information that was not otherwise obtainable. The VG was not utilized by clinicians at large because it was not easy to understand and its computation time-consuming. Spatial vectorcardiography is based on the concept of the VG. Its current major clinical use is to identify primary [heterogeneity of ventricular action potential (VAP) morphology] in the presence of secondary [heterogeneity in ventricular depolarization instants] T-wave abnormalities in an ECG. Nowadays, the calculation of the spatial VG can be computed on the basis of a regular routine ECG and contributes to localization of arrhythmogenic areas in the heart by assessing overall and local VAP duration heterogeneity. Recent population-based studies suggest that the spatial VG is a dominant ECG predictor of future cardiovascular events and death and it is superior to more conventional ECG parameters. Its assessment warrants consideration for intensified primary and secondary prevention efforts and can be included in everyday clinical practice. This review addresses the nature and diagnostic potential of the spatial VG. The main focus is the role of the spatial VG in ECG assessment of dispersion of repolarization, a key factor in arrhythmogeneity.

A note on a method for determining advantageous properties of an anti-arrhythmic drug based on a mathematical model of cardiac cells

Regional hyperkalemia during acute ischemia may provoke cardiac arrhythmias such as ventricular fibrillation. Despite intense research efforts over the last decades, the problem of finding an efficient anti-arrhythmic drug without dangerous side effects is still open. One approach to analyze the effect of anti-arrhythmic drugs is to do simulations based on mathematical models of collections of cardiomyocytes. Such simulations have recently illuminated the pro-arrhythmic capability of well-established anti-arrhythmic drugs. The purpose of the present note is to introduce a method intended for computing advantageous properties of an anti-arrhythmic drug. For a given model of a normal and an ischemic cell, we introduce a drug as a vector of non-negative real numbers whose components are multiplied by individual terms representing specific ionic currents. The drug vector is computed such that the action potentials of the resulting drugged cells are as close as possible to the action potential of a normal (not drugged) cell. Numerical simulations based on the Luo-Rudy I model and the Hund-Rudy model show that the classical shortened action potential obtained due to hyperkalemia is prolonged by using the drug computed by this method. Furthermore, for both models a 2D collection of spatially coupled ischemic cells give arrhythmogenic solutions before the drug is applied, and stable solutions after the drug is applied. It is emphasized that we do not address the possibility of realizing a drug with the properties computed in this note.

Drugs, their targets and the nature and number of drug targets

What is a drug target? And how many such targets are there? Here, we consider the nature of drug targets, and by classifying known drug substances on the basis of the discussed principles we provide an estimation of the total number of current drug targets.

Anti-arrhythmic and cardio-protective effects of furnidipine in a rat model: A dose response study

Protective effects of acute oral or intravenous doses of furnidipine against ischemia and re-perfusion-induced arrhythmias and creatine kinase release were studied in a rat model for cardiac ischemia and re-perfusion. Transient cardiac ischemia was induced by occluding the left coronary descending artery of anaesthetized rats for 7 min, and re-perfusion period studied was 15 min. Pre-treatment period for oral doses (1, 5 or 10 mg/kg) was 1 h, whereas that for the intravenous ones (1.25, 2.5, 5 or 10 microg/kg) was 10 min. After both routes of administration, significant protective effects of furnidipine on creatine kinase release were observed after the two lowest doses only. In contrast, its higher dosages were more effective in preventing re-perfusion-induced mortality, arrhythmias and hypotensive episodes, and for transiently lowering arterial blood pressure before initiation of ischemia. These observations suggest potential uses of furnidipine for preventing re-perfusion triggered lethal arrhythmias. Efforts to evaluate therapeutic potential of low dose furnidipine as a cardio-protective agent seem warrantable.

Elucidation of the spatial ventricular gradient and its link with dispersion of repolarization

The ventricular gradient, a notion conceived by Wilson et al during the 1930s, has contributed considerably to a better understanding of the ECG manifestations of the cardiac repolarization process. The power of the ventricular gradient is its ability to assess the primary factors that contribute to the T wave (i.e., heterogeneity of action potential morphology throughout the ventricles) in the presence of secondary factors contributing to the T wave (i.e., heterogeneity in ventricular depolarization instants). Where T-wave morphology is an ECG expression of heterogeneity of the repolarization, the ventricular gradient discriminates between primary or secondary causes of such heterogeneity. Besides the spatial ventricular gradient (Burger's three-dimensional elaboration of Wilson's two-dimensional concept), body surface mapping of local components of the ventricular gradient has emerged as a technique for assessing local ventricular action potential duration heterogeneity. The latter is believed to contribute to localization of arrhythmogenic areas in the heart. The spatial ventricular gradient, which can be computed on the basis of a regular routine ECG and does not require body surface mapping, aims to assess the overall heterogeneity of ventricular action potential morphology. This review addresses the nature and diagnostic potential of the spatial ventricular gradient. The main focus is the role of the spatial ventricular gradient in ECG assessment of dispersion of repolarization, a key factor in arrhythmogeneity.

Human cardiac potassium channel DNA polymorphism modulates access to drug-binding site and causes drug resistance

Expression of voltage-gated K channel, shaker-related subfamily, member 5 (KCNA5) underlies the human atrial ultra-rapid delayed rectifier K current (I(Kur)). The KCNA5 polymorphism resulting in P532L in the C terminus generates I(Kur) that is indistinguishable from wild type at baseline but strikingly resistant to drug block. In the present study, truncating the C terminus of KCNA5 generated a channel with wild-type drug sensitivity, which indicated that P532 is not a drug-binding site. Secondary structure prediction algorithms identified a probable alpha-helix in P532L that is absent in wild-type channels. We therefore assessed drug sensitivity of I(Kur) generated in vitro in CHO and HEK cells by channels predicted to exhibit or lack this C-terminal alpha-helix. All constructs displayed near-identical I(Kur) in the absence of drug challenge. However, those predicted to lack the C-terminal alpha-helix generated quinidine-sensitive currents (43-51% block by 10 microM quinidine), while the currents generated by those constructs predicted to generate a C-terminal alpha-helix were inhibited less than 12%. Circular dichroism spectroscopy revealed an alpha-helical signature with peptides derived from drug-resistant channels and no organized structure in those associated with wild-type drug sensitivity. In conclusion, we found that this secondary structure in the KCNA5 C terminus, absent in wild-type channels but generated by a naturally occurring DNA polymorphism, does not alter baseline currents but renders the channel drug resistant. Our data support a model in which this structure impairs access of the drug to a pore-binding site.

Drugs that cause Torsades de pointes and increase the risk of sudden cardiac death

Torsades de pointes (TdP) is a potentially life-threatening arrhythmia associated with not only antiarrhythmic drugs, but noncardiac drugs of many different classes. All these drugs prolong the QT interval by their blocking of the potassium channel I(Kr), and many are metabolized by the cytochrome P450 isoenzyme CYP3A4. Polypharmacy with other drugs utilizing the same enzyme, or inhibiting CYP3A4, can lead to TdP. A consistent finding of all the QT-prolonging drugs is predominance of TdP in women. Other risk factors for QT prolongation and TdP include hypokalemia, congestive heart failure, and structural heart disease. Knowledge of potential drug interactions and other risk factors for TdP can help in reducing the number of adverse events associated with the use of QT-prolonging drugs.