Effects of NS-2, a new class 1 antiarrhythmic agent, and AFD-19, its active metabolite, on ventricular arrhythmias induced by coronary artery occlusion and reperfusion in anesthetized rats: comparison with disopyramide and mexiletine

Characterisation of mexiletine's translational therapeutic index for suppression of ischaemia-induced ventricular fibrillation in the rat isolated heart

The 'translational therapeutic index' (TTI) is a drug's ratio of nonclinical threshold dose (or concentration) for significant benefit versus threshold for adversity. In early nonclinical research, discovery and safety studies are normally undertaken separately. Our aim was to evaluate a novel integrated approach for generating a TTI for drugs intended for prevention of ischaemia-induced ventricular fibrillation (VF). We templated the current best available class 1b antiarrhythmic, mexiletine, using the rat Langendorff preparation. Mexiletine's beneficial effects on the incidence of VF caused by 120 min regional ischaemia were contrasted with its concurrent adverse effects (on several variables) in the same hearts, to generate a TTI. Mexiletine 0.1 and 0.5 µM had no adverse effects, but did not reduce VF incidence. Mexiletine 1 µM reduced VF incidence to 0% but had adverse effects on atrioventricular conduction and ventricular repolarization. Separate studies undertaken using an intraventricular balloon revealed no detrimental effects of mexiletine (1 and 5 µM) on mechanical function, or any benefit against reperfusion-related dysfunction. Mexiletine's TTI was found to be less than two, which accords with its clinical therapeutic index. Although non-cardiac adversity, identifiable from additional in vivo studies, may reduce the TTI further, it cannot increase it. Our experimental approach represents a useful early-stage integrated risk/benefit method that, when TTI is found to be low, would eliminate unsuitable class 1b drugs prior to next stage in vivo work, with mexiletine's TTI defining the gold standard that would need to be bettered.

Pravastatin Inhibits Arrhythmias Induced by Coronary Artery Ischemia in Anesthetized Rats

We have reported that chronically administered pravastatin prevented coronary artery reperfusion-induced lethal ventricular fibrillation (VF) in anesthetized rats without lowering the serum cholesterol level. The present study was undertaken to evaluate whether pravastatin prevents ischemia-induced lethal VF, simultaneously examining myeloperoxidase (MPO) activity in ischemic myocardial tissues. Anesthetized rats were subjected to 30-min ischemia and 60-min reperfusion after chronic administration of pravastatin (0.02, 0.2, and 2 mg/kg), fluvastatin (2 and 4 mg/kg), or vehicle for 22 days, orally, once daily. ECG and blood pressure were continually recorded, and MPO was measured by a spectrophotometer. Pravastatin and fluvastatin significantly (P<0.05) decreased MPO activities, but only pravastatin decreased the incidence of ischemia-induced lethal VF. Both statins had no significant effects on body weight, blood pressure, heart rate, and QT interval as we reported earlier. Our results prove further that pravastatin has benefits to decrease cardiovascular mortality beyond its cholesterol-lowering effect. Pravastatin is more potent than fluvastatin in prevention of arrhythmias. A decrease in the neutrophil infiltration may be partly involved in the inhibitory effect of pravastatin on the ischemia-induced VF.

Does Cl-/HCO3- exchange play an important role in reperfusion arrhythmias in rats?

The protective effects of Cl(-)/HCO(3)(-) exchange inhibitors, 4,4'-diisothiocyano-stilbene-2,2'-disulfonic acid (DIDS) and 4-acetamido-4'isothiocyanato-stilbene-2,2'-disulfonic acid (SITS), against reperfusion-induced arrhythmias were investigated in anesthetized rats. Rats were subjected to 5-min occlusion of the left coronary artery followed by 10-min reperfusion. All drugs were intravenously administered 5 min before the onset of occlusion. DIDS (75 mg/kg) reduced the incidence of ventricular fibrillation and mortality to 0%, whereas SITS (75 mg/kg) only decreased these parameters to 60%. DIDS simultaneously decreased the mean blood pressure and heart rate, and prolonged PQ and QRS intervals, whereas SITS produced a weaker effect on these parameters and no change in QRS interval. Mexiletine (5 mg/kg), which had been demonstrated to suppress the arrhythmias and reduce the heart rate and mean blood pressure in this model, was shown to prolong PQ and QRS intervals. Verapamil (0.5 mg/kg) or diltiazem (0.4 mg/kg) suppressed the arrhythmias, simultaneously decreasing the heart rate and mean blood pressure and prolonging PQ interval. The results indicate that the protective effect of DIDS on reperfusion arrhythmias in the anesthetized rats is unlikely to be attributed to the inhibitory action on Cl(-)/HCO(3)(-) exchange, but possibly mediated by its blocking effects on cardiac ion channels, such as Na(+) or Ca(2+) channels.

Pravastatin Prevents Arrhythmias Induced by Coronary Artery Ischemia/Reperfusion in Anesthetized Normocholesterolemic Rats

HMG-CoA reductase inhibitors (statins) have been shown to decrease cardiovascular mortality. Since ventricular tachyarrhythmias are closely related to cardiovascular mortality, we tested effects of the hydrophilic statin pravastatin and the lipophilic statin fluvastatin in a rat arrhythmia model of ischemia/reperfusion and simultaneously measured serum total cholesterol level. Anesthetized rats were subjected to 5-min ischemia and 10-min reperfusion after chronic administration of oral pravastatin (0.02, 0.2, or 2 mg/kg), fluvastatin (0.2, 2, or 4 mg/kg), or vehicle for 22 days, once daily. The acute effect of pravastatin (0.2 or 2 mg/kg, once orally) was also observed. Chronically administrated pravastatin significantly reduced the incidence of ischemia-induced ventricular tachycardia (VT) from 70% (control) to 9% at 2 mg/kg, and it reduced the incidence of reperfusion-induced lethal ventricular fibrillation (VF) from 90% (control) to 20% at 0.2 mg/kg. Acute pravastatin and chronically administrated fluvastatin had no significant effect on these arrhythmias. There were no significant changes in blood pressure, heart rate, QT interval, and serum cholesterol among pravastatin-, fluvastatin-, and vehicle-treated groups. Hydrophilic pravastatin prevented reperfusion-induced lethal VF in anesthetized rats by chronic administration independent of its cholesterol lowering effect. This may be a new beneficial role of pravastatin in decreasing cardiovascular mortality.

Inhibitory effects of pre-ischemic and post-ischemic treatment with FR 168888, a Na+/H+ exchange inhibitor, on reperfusion-induced ventricular arrhythmias in anesthetized rat

Effects of pre-ischemic and post-ischemic treatment with FR 168888 (5-hydroxymethyl-3-(pyrrol-1-yl) benzoylguanidine methanesulfonate), a Na+/H+ exchange inhibitor, on reperfusion-induced ventricular arrhythmias were examined in an ischemia/reperfusion model of anesthetized rat. FR 168888 (0.3 mg/kg) significantly reduced the incidence of ventricular fibrillation (VF) and mortality induced by reperfusion following 5-min coronary occlusion, when it was intravenously administered 5 min before coronary artery occlusion. Post-ischemic treatment with FR 168888 (0.3-10 mg/kg), i.e. given 3 min after the start of occlusion, reduced the incidence of VF and mortality. In order to examine the optimal time of administration, FR 168888 (3 mg/kg) was administered 1 or 3 min after the start of occlusion or immediately before reperfusion. There was no significant difference in the reduction of VF and mortality among the three post-ischemic treatment groups. FR 168888 (3 and 10 mg/kg) significantly increased the blood pressure during ischemia without affecting the heart rate. These results indicate that FR 168888 has antiarrhythmic effects on reperfusion-induced arrhythmias even administered after coronary occlusion.

The inhibitory effects of carvedilol against arrhythmias induced by coronary reperfusion in anesthetized rats

BACKGROUND

Previous study has shown the antiarrhythmic effects of carvedilol on isolated rat hearts, but little is known about the mechanism of this protective action. This article examines the inhibitory effect of carvedilol against arrhythmias induced by reperfusion in anesthetized rats. In addition, the results are compared with those with propranolol, superoxide dismutase (SOD) plus catalase, and a combination of both in order to elucidate the mechanism of the protective actions.

METHODS AND MATERIALS

Ninety percent of the rats in the control group showed lethal ventricular fibrillation (VF). Carvedilol at the doses of 0.03, 0.1, and 0.3 mg/kg significantly reduced the incidence of lethal VF to 0%, 0%, and 10%, respectively (P <.05). In contrast, propranolol at the doses of 0.3, 1.0, and 3.0 mg/kg and SOD (35,000 units/kg) plus catalase (400,000 units/kg) did not reduce the incidence of lethal VF (80%, 60%, 70%, and 70%, respectively). However, administration of a combination of propranolol (1.0 mg/kg) and SOD plus catalase completely inhibited the occurrence of lethal VF to 0% (P<.05).

CONCLUSION

These results indicate that carvedilol has the inhibitory effect against reperfusion arrhythmias in rats and suggest that the mechanism of action of this compound is related to the combined effects of beta-blocking and antioxidant.

Effects of HNS-32, a novel antiarrhythmic drug, on ventricular arrhythmias induced by coronary artery occlusion and reperfusion in anesthetized rats

HNS-32 (N1,N1-dimethyl-N2-(2-pyridylmethyl)-5-isopropyl-3, 8-dimethylazulene-1-carboxamidine: CAS 186086-10-2) is a newly synthesized compound, and possesses antiarrhythmic properties with vasodilator action in dog hearts. The aim of this study was to investigate the dose-dependent effects of HNS-32 on ischemia- and/or reperfusion-induced ventricular arrhythmias in anesthetized rats in vivo and compared with those of mexiletine. Saline or drugs were administered intravenously 5 min prior to coronary artery occlusion. On the ischemia-induced ventricular arrhythmias, HNS-32 showed dose-dependent reduction of total number of premature ventricular complexes (PVC) from 2091+/-225 to 656+/-116 and 286+/-69 beats/30 min (p < 0.05), the ventricular tachycardia (VT) duration from 183+/-33 to 28+/-9 and 4+/-2 sec (p < 0.05), the incidence of VT from 100 to 90 (n.s.) and 40% (p < 0.05), and the incidence of ventricular fibrillation (VF) from 50 to 0 and 0% (p < 0.05) with 3 and 5 mg/kg, respectively. Mexiletine also reduced these parameters to 936+/-159 beats/30 min (p < 0.05), 39+/-22 sec (p < 0.05), 90% (n.s.) and 10% (n.s.), respectively. HNS-32 completely suppressed the late reperfusion-induced arrhythmias, however mexiletine did not affect them. On the early reperfusion-induced ventricular arrhythmias, HNS-32 showed dose-dependent reduction of VT duration from 126+/-34 to 37+/-12 and 3+/-2 sec (p < 0.05), incidence of VT from 100 to 90 (n.s.) and 40% (p < 0.05), incidence of VF from 100 to 10 and 0% (p < 0.05), and mortality rate from 90 to 0 and 0% (p < 0.05), with 3 and 5 mg/kg, respectively. Mexiletine also reduced these parameters to 16+/-9 sec (p < 0.05), 80 (n.s.), 50 (p < 0.05), and 10% (p < 0.05), respectively. HNS-32 significantly reduced the heart rate in a dose-dependent manner, from 399+/-14 to 350+/-8 and 299+/-10 beats/min (p < 0.05) with 3 and 5 mg/kg, respectively. The antiarrhythmic effects of HNS-32 were more potent than that of the similar dose of mexiletine against occlusion-induced and reperfusion-induced arrhythmias in in vivo rats.

Effects and interaction, of cariporide and preconditioning on cardiac arrhythmias and infarction in rat in vivo

1. Although Na+-H+ exchange (NHE) inhibitors are reported to protect the myocardium against ischaemic injury, NHE activation has also been proposed as a potential mechanism of ischaemic preconditioning-induced protection. This study was performed to test any modifiable effect of cariporide, an NHE inhibitor, on cardioprotective effects of preconditioning. 2. Anaesthetized rats were subjected to 30 min of coronary artery occlusion and 150 min of reperfusion. The preconditioning (PC) was induced by 3 min of ischaemia and 10 min of reperfusion (1PC) or three episodes of 3 min ischaemia and 5 min reperfusion (3PC). Cariporide (0.3 mg kg(-1)) an NHE inhibitor, was administered 30 min (cari(30)) or 45 min (cari(45)) before coronary ligation (n=8-11 for each group). 3. Ventricular arrhythmias during 30 min ischaemia and infarct size (measured by triphenyltetrazolium (TTC) and expressed as a per cent area at risk (%AAR)) were determined. Cari(30) reduced ventricular fibrillation (VF) incidence and infarct size (from 45 to 0% and 34+/-4 to 9+/-2%; each P<0.05), whereas cari(45) did not. Likewise, 3PC reduced these variables (to 0% and 10+/-2%; P<0.05 in each case) whereas 1PC did not. Moreover, subthreshold preconditioning (1PC) and cariporide (cari(45)), when combined, reduced VF incidence and infarct size (to 0% and 15+3%; each P<0.05 ). 4. In conclusion, changes in NHE activity do not seem to be responsible for the cardioprotective action of ischaemic preconditioning. Protective effects of NHE inhibition and subthreshold preconditioning appear to act additively.

Effects of AH-1058, a new antiarrhythmic drug, on experimental arrhythmias and cardiac membrane currents

AH-1058 is a newly synthesized antiarrhythmic agent. We investigated the antiarrhythmic and electrophysiological effects of AH-1058 in experimental arrhythmia models and isolated cardiomyocytes. In the ouabain-induced arrhythmia model of the guinea pig, pretreatment with AH-1058 (0.1-0.3 mg/kg, i.v.) delayed the appearance of premature ventricular complex (PVC) and ventricular fibrillation (VF) induced by intravenous infusion of ouabain. However, disopyramide (10 mg/kg, i.v.) delayed only that of PVC, and verapamil (1 mg/kg, i.v.) failed to affect the ouabain-induced ventricular arrhythmias. In the reperfusion-induced arrhythmia model of the rat, in which 5-min coronary occlusion and 10-min reperfusion were produced, AH-1058 (0.1-0.3 mg/kg, i.v.) inhibited the incidence of both ventricular tachycardia (VT) and VF, whereas disopyramide (5 mg/kg, i.v.) inhibited only reperfusion-induced VF. On the other hand, a higher dose of AH-1058 (1 mg/kg, i.v.) did not affect the aconitine-induced arrhythmias in rats, which were inhibited by disopyramide (5 mg/kg, i.v.). We also confirmed oral activity of AH-1058 in the reperfusion-induced arrhythmia model of the rat. AH-1058, at doses of 2-4 mg/kg, dose-dependently inhibited VT and VF. Electrophysiological experiments with patch-clamp techniques revealed that AH-1058 potently suppressed the L-type Ca2+ currents in isolated cardiomyocytes of the guinea pig. These results suggest that AH-1058 is a potent antiarrhythmic drug having a Ca2+ channel-blocking action. The antiarrhythmic profile of AH-1058 is different from that of disopyramide and verapamil.

Antiarrhythmic effects of cariporide, a novel Na+-H+ exchange inhibitor, on reperfusion ventricular arrhythmias in rat hearts

Cariporide (4-isopropyl-3-methylsulphonylbenzoyl-guanidine methanesulphonate: HOE642) is a novel Na+-H+ exchange subtype 1 inhibitor and has antiarrhythmic effects on ischemia/reperfusion arrhythmias without apparent cardiovascular effects in dogs and rats when given before coronary occlusion. The aim of this study was to determine the minimum effective dose and to examine the dose related effects of cariporide when it was administered before and during coronary occlusion as well as simultaneously with reperfusion. In the pre-treatment group, cariporide dose-dependently reduced the ventricular tachycardia duration from 140 to 36 (P < 0.01), 59 (P < 0.05) and 23 s (P < 0.01) with 0.03, 0.1 and 1 mg/kg, respectively, and reduced the incidence of reperfusion-induced ventricular tachycardia from 100 to 50 and 58% (P < 0.01), ventricular fibrillation from 83 to 8 and 0% (P < 0.01), and mortality from 75 to 8 and 8% (P < 0.01) with 0.1 and 1 mg/kg, respectively. In the post-treatment group, cariporide dose-dependently reduced the ventricular tachycardia duration from 92 to 37, 40, 42 (P < 0.05) and 24 s (P < 0.01) with 0.03, 0.1, 0.3 and 1 mg/kg, respectively, and the incidence of ventricular tachycardia from 100 to 53% (P < 0.01) by 1 mg/kg, and ventricular fibrillation from 87 to 33, 7 and 7% (P < 0.01), and the mortality from 73 to 27 (P < 0.05), 0 and 7% (P < 0.01) with 0.1, 0.3 and 1 mg/kg, respectively. In the group with simultaneous injection, both doses of cariporide (1 and 3 mg/kg) reduced the incidence of ventricular fibrillation from 83 to 42% (P < 0.05). The heart rate, blood pressure and QT interval did not change after drug treatment.

Antiarrhythmic effects of HOE642, a novel Na(+)-H+ exchange inhibitor, on ventricular arrhythmias in animal hearts

HOE642 (4-isopropyl-3-methylsulphonylbenzoyl-guanidine methanesulphonate), a novel Na(+)-H+ exchange subtype 1 inhibitor, was investigated for its possible antiarrhythmic effects on coronary artery ligation/reperfusion and ouabain-induced arrhythmias in the canine heart which may occur after intracellular Ca2+ overload. Also, the effects of HOE642 on coronary artery ligation/reperfusion of the left coronary artery were tested in rat hearts. HOE642 (1 mg/kg) significantly suppressed the occurrence of fatal ventricular fibrillation during coronary artery ligation and after reperfusion in dogs (2 out of 8 dogs in the treated group compared to 7 out of 8 dogs in the control group, P < 0.05), but did not suppress ventricular premature contractions and ventricular tachycardia during ischemia in the canine hearts. HOE642 at the same dose markedly reduced the total duration and the incidence of reperfusion-induced ventricular tachycardia, and the incidence and mortality of reperfusion-induced ventricular fibrillation in rats (ventricular tachycardia duration, 159 +/- 12 s to 21 +/- 8 s, P < 0.01; ventricular tachycardia, 100% to 69%; ventricular fibrillation, 89% to 0%, P < 0.01; mortality, 89% to 11%, P < 0.01). The heart rate, blood pressure, QT interval and ST segment did not change in the canine and rat hearts. HOE642 slightly decreased the arrhythmic ratio of the ouabain-induced arrhythmia only at two time points (28 and 35 min after injection) in the canine hearts. In conclusion, HOE642 has obvious antifibrillatory effects on ischemia/reperfusion arrhythmias and, in addition, has a weak suppressing effect on the ouabain-induced arrhythmia.

IK independent class III actions of MS-551 compared with sematilide and dofetilide during reperfusion in anaesthetized rats

1. The antiarrhythmic and haemodynamic effects of three class III antiarrhythmic drugs, MS-551, sematilide and dofetilide, were examined in the coronary artery, ligation-reperfusion model of pentobarbitone-anaesthetized rats, a species deficient in functional cardiac IK. MS-551 is a non-selective potassium channel blocker, while both sematilide and dofetilide are selective delayed rectifier potassium (K) channel (IK) blockers. 2. Before coronary ligation, 3 and 10 mg kg-1 MS-551 decreased the heart rate by 6% (P < 0.01) and 12% (P < 0.01), and increased mean arterial pressure (MAP) by 14% (P < 0.05) and 33% (P < 0.01), respectively. Sematilide at 10 and 30 mg kg-1 also decreased the heart rate by 4% (P < 0.01) and 9% (P < 0.01), respectively, and the higher dose of 30 mg kg-1 decreased MAP by 29% (P < 0.01). Dofetilide, 1 mg kg-1, decreased the heart rate (P < 0.01), but had no significant effect on MAP. 3. The QT interval was increased by 10% (P < 0.01) and 31% (P < 0.01), when 3 and 10 mg kg-1 MS-551 were given. Sematilide and dofetilide had no effect on the QT interval. 4. Immediately after reperfusion, lethal ventricular fibrillation (VF) was induced in 80% of the saline group. MS-551 at 3 and 10 mg kg-1, reduced the incidence of lethal VF to 50% and 20% (P < 0.05). Neither dofetilide 1 mg kg-1 nor sematilide (10 and 30 mg kg-1) decreased the incidence of lethal VF (70%, 80% and 50%, respectively). None of the three drugs had any effect on the occurrence of reperfusion-induced VT or the total incidence of VF. However, 10 mg kg-1 MS-551 delayed the onset of reperfusion-induced VF (27 +/- 5 s compared with 12 +/- 2 s of the control group, P < 0.05). 5. In conclusion, in rats which are deficient in cardiac IK MS-551 prolonged the QT interval and reduced the incidence of sustained VF after reperfusion. Blockade of channels other than IK might participate in the defibrillatory effect of MS-551. Sematilide and dofetilide, which are selective IK blockers, did not increase the QT interval nor did they show antiarrhythmic effects Mechanisms other than K channel block may be involved in the different effects of the three drugs on blood pressure.