Actions of CP-060S on veratridine-induced Ca2+ overload in cardiomyocytes and mechanical activities in vascular strips

In vitro detection of cardiotoxins or neurotoxins affecting ion channels or pumps using beating cardiomyocytes as alternative for animal testing

The present study investigated if and to what extent murine stem cell-derived beating cardiomyocytes within embryoid bodies can be used as a broad screening in vitro assay for neurotoxicity testing, replacing for example in vivo tests for marine neurotoxins. Effect of nine model compounds, acting on either the Na(+), K(+), or Ca(2+) channels or the Na(+)/K(+) ATP-ase pump, on the beating was assessed. Diphenhydramine, veratridine, isradipine, verapamil and ouabain induced specific beating arrests that were reversible and none of the concentrations tested induced cytotoxicity. Three K(+) channel blockers, amiodarone, clofilium and sematilide, and the Na(+)/K(+) ATPase pump inhibitor digoxin had no specific effect on the beating. In addition, two marine neurotoxins i.e. saxitoxin and tetrodotoxin elicited specific beating arrests in cardiomyocytes. Comparison of the results obtained with cardiomyocytes to those obtained with the neuroblastoma neuro-2a assay revealed that the cardiomyocytes were generally somewhat more sensitive for the model compounds affecting Na(+) and Ca(2+) channels, but less sensitive for the compounds affecting K(+) channels. The stem cell-derived cardiomyocytes were not as sensitive as the neuroblastoma neuro-2a assay for saxitoxin and tetrodotoxin. It is concluded that the murine stem cell-derived beating cardiomyocytes provide a sensitive model for detection of specific neurotoxins and that the neuroblastoma neuro-2a assay may be a more promising cell-based assay for the screening of marine biotoxins.

The effect of mebudipine on cardiac function and activity of the myocardial nitric oxide system in ischaemia-reperfusion injury in rats

Objectives

Previous studies have suggested that failure of the synthesis of nitric oxide is involved in the pathophysiology of myocardial ischaemia–reperfusion injury. In this study, we investigated the effect of mebudipine, a new dihydropyridine calcium channel blocker, on cardiac function and activity of the myocardial nitric oxide system in ischaemia–reperfusion injury in isolated rat hearts.

Methods

Forty male Wistar rats (250–300 g) were divided into four groups (n = 10): sham, control, vehicle and drug groups. The animals were anesthetised with sodium pentobarbital (6 mg/kg intraperitoneal). The hearts were quickly removed, mounted on a Longendorff apparatus and perfused with Krebs-Henseleit solution under constant pressure at 37°C. After 20 min stabilisation period, the ischaemic groups received 30 min global ischaemia and 120 min reperfusion. For the drug and vehicle groups, before ischaemia the hearts were perfused with mebudipine (10^-3 µM) or ethanol-enriched solution (0.01%) for 25 min, respectively. Myocardial function, and creatine kinase, lactate dehydogenase and total nitric oxide metabolite (nitrite and nitrate) levels were analysed.

Results

Cardiac functions had recovered significantly in the mebudipine group (p < 0.01). Furthermore, mebudipine remarkably reduced the levels of lactate dehydogenase and creatine kinase in the coronary effluent and increased myocardial nitric oxide metabolite levels compared with the control group.

Conclusion

Our results indicate that mebudipine reduced the intensity of myocardial ischaemia–reperfusion injury, and that activation of the myocardial nitric oxide system played an important role in this regard.

The long-lasting anti-anginal effects of CP-060S in a rat model of arginine vasopressin-induced myocardial ischaemia

The anti-anginal effect of CP-060S, a new cardioprotective agent that prevents myocardial Na+-, Ca2+-overload and has Ca2+-channel blocking activity, was evaluated in a rat model of arginine8-vasopressin (AVP)-induced cardiac ischaemia. Infusion of AVP (0.2 IU kg(-1)) depressed the electrocardiogram (ECG) ST segment, an index of myocardial ischaemia. Vehicle, CP-060S and diltiazem were given orally 1, 2, 4, 8, 12 and 24 h before the administration of AVP. CP-060S, at 3 mg kg(-1) and 10 mg kg(-1), suppressed AVP-induced ST-segment depression for 2 h and 12 h, respectively. In contrast, diltiazem, at 10 and 30 mg kg(-1), suppressed AVP-induced ST-segment depression for only 1 h. The persistent suppression of the AVP-induced ST-segment depression by CP-060S correlated with the time course of changes in its plasma concentration. The minimum effective concentration of CP-060S was estimated to be 30 ng mL(-1) (approximately 50 nM), consistent with its vasorelaxant potency in rat isolated aortic strips (concentration producing 50% relaxation of KCl contraction, IC50 = 32.6+/-8.3 nM). Intravenously administered CP-060S, at 300 microg kg(-1) and diltiazem at 500 microg kg(-1) showed similar haemodynamic changes, whereas CP-060S, at 300 microg kg(-1), significantly suppressed AVP-induced ST-segment depression and diltiazem, at 500 microg kg(-1), had no effect on AVP-induced ST-segment depression. In summary, orally administered CP-060S exerted a long-lasting anti-anginal effect proportionate to the time course of changes in its plasma concentration in a rat model of AVP-induced ischaemia.

Effects of CP-060S, a novel cardioprotective drug, in the methacholine-induced ECG change model in rats

We compared the antianginal effect of CP-060S, a novel cardioprotective drug with Na+ and Ca2+ overload-preventing activity as well as Ca2+ channel antagonistic activity, with that of diltiazem, in an experimental model of vasospastic angina induced by methacholine in anaesthetized rats. Intra-aortic injection of methacholine at the coronary ostium provoked the ST-segment elevation of the electrocardiogram (ECG), indicating myocardial ischemia. CP-060S (3, 5 and 10 mg/kg, i.d.) significantly and dose-dependently suppressed the methacholine-induced ST-elevation, with the duration of action being at least 3 h at the highest dose. In addition, CP-060S at 3 mg/kg could inhibit the ST-elevation without producing significant changes in blood pressure, heart rate or rate-pressure product (RPP). In contrast, diltiazem (10 and 30 mg/kg, i.d.) significantly decreased the RPP, a significant suppression of the ST-elevation could only be achieved at the highest dose and its duration of action was about 2 h. Similar results were obtained with i.v. administration of the drugs, i.e. CP-060S given i.v. could inhibit the ST-elevation with less haemodynamic changes than diltiazem. In conclusion, CP-060S exerted a more potent and sustained protection against myocardial ischemia evoked by methacholine than diltiazem. The characteristics of the effects of CP-060S observed here suggest that this drug may be a desirable drug for the treatment of vasospastic angina.

Mechanisms of vasoinhibitory effect of cardioprotective agent, CP-060S, in rat aorta

Vasoinhibitory effects of (-)-(S)-2-[3,5-bis(1, 1-dimethylethyl)-4-hydroxyphenyl]-3-[3-[N-methyl-N-[2-(3, 4-methylenedioxyphenoxy)ethyl]amino]propyl]-1,3-thiazolidin- 4-one hydrogen fumarate (CP-060S), a synthesized cardioprotective agent, were examined. In the rat aortic rings, the contractile responses to cumulative application of angiotensin II, [Arg(8)]-vasopressin (vasopressin), or prostaglandin F(2alpha) were inhibited by CP-060S in a concentration-dependent manner. The Ca(2+)-induced contractions in the presence of vasopressin or prostaglandin F(2alpha) were also inhibited by CP-060S in a concentration-dependent manner. The inhibitory effect of 10(-5) M CP-060S on phenylephrine-induced contraction was as potent as that of 10(-6) M nifedipine, and the combined addition of 10(-6) M nifedipine and 10(-5) M CP-060S showed the effect similar to that of 10(-5) M CP-060S alone. In rat aorta loaded with a Ca(2+) indicator, fura-PE3, 10(-5) M CP-060S completely inhibited the high K(+)-induced increase in cytosolic Ca(2+) level ([Ca(2+)](i)) and contraction. In contrast, 10(-5) M CP-060S only partially inhibited the increase in [Ca(2+)](i) and contraction due to phenylephrine or prostaglandin F(2alpha). In the presence of 10(-6) M nifedipine, 10(-5) M CP-060S did not inhibit the increase in [Ca(2+)](i) and contraction induced by prostaglandin F(2alpha). In a Ca(2+)-free medium, the phasic increases in contraction and [Ca(2+)](i) induced by phenylephrine were not affected by 10(-5) M CP-060S. These results suggest that the vasoinhibitory effect of CP-060S in rat aortic rings is due mainly to the inhibition of L-type voltage-dependent Ca(2+)-channels.

Protective effect of diltiazem against ischemia-induced decreases in regional myocardial flow in rat heart

Diltiazem has cardioprotective properties following myocardial ischemic injury. However, there are controversial results regarding the beneficial effects of diltiazem on regional myocardial flow after ischemia. Therefore, we investigated the effect of diltiazem on changes in regional myocardial flow due to ischemia for different periods. Non-radioactive colored microspheres were used for this measurement in isolated rat heart. After 20 or 40 min of global ischemia and 40 min of reperfusion, regional myocardial flow was decreased, especially in the endocardial layer. The endocardial/epicardial ratio was also decreased. The decreases in endocardial flow and the endocardial/epicardial ratio were more remarkable after 40 min of ischemia than after 20 min of ischemia. Diltiazem (10(-6) M), which was administered 15 min before ischemia, prevented only the decrease in endocardial flow and endocardial/epicardial ratio after 20 min of ischemia, whereas it did not prevent that after 40 min of ischemia. Nifedipine (2x10(-6) M) did not exert a cardioprotective effect. These findings suggested that the effect of ischemia is marked in the endocardium and, also, that the protective effect of diltiazem is seen only during a decrease in endocardial flow following short-term and reversible ischemia.

Effects of CP-060S, a novel Ca(2+) channel blocker, on oxidative stress in cultured cardiac myocytes

The effect of (-)-(S)-2-[3,5-bis(1, 1-dimethylethyl)-4-hydroxyphenyl]-3-[3-[N-methyl-N-[2-(3, 4-methylenedioxyphenoxy)ethyl]amino]propyl]-1,3-thiazolidin- 4-one hydrogen fumarate (CP-060S), a novel Ca(2+) channel blocker, on hydrogen peroxide (H(2)O(2))-induced cytotoxicity was studied in cultured rat cardiac myocytes. The CP-060S effect was compared with that of CP-060R, an optical isomer of CP-060S with a less potent Ca(2+) channel blocking action than CP-060S. H(2)O(2) increased the release of lactate dehydrogenase from cardiac myocytes and decreased the formation of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) (MTT) formazan in cardiac myocytes (i.e., cytotoxic action). Both CP-060S (1 microM) and CP-060R (1 microM) attenuated to a similar extent the foregoing alterations induced by H(2)O(2). On the other hand, 1,3-dimethyl-2-thiourea (10 mM), a scavenger of both H(2)O(2) and hydroxyl radical, also attenuated the H(2)O(2)-induced cytotoxicity whereas diltiazem (10 microM) did not. In an experiment using electron spin resonance (ESR) with 5, 5-dimethyl-1-pyrroline N-oxide (DMPO), a spin-trapping agent, both CP-060S and CP-060R decreased the intensity of DMPO-hydroxyl radical signal concentration dependently. These results suggest that CP-060S protects cardiac myocytes from oxidative stress through its radical scavenging action.

Novel calcium antagonists with both calcium overload inhibition and antioxidant activity. 2. Structure-activity relationships of thiazolidinone derivatives

CP-060 (1), 2-(3, 5-di-tert-butyl-4-hydroxyphenyl)-3-[3-[N-methyl-N-[2-[3, 4-(methylenedioxy)phenoxy]ethyl]amino]propyl]-1,3-thiazolidin-4-on e, is a novel type of Ca(2+) antagonist possessing both Ca(2+) overload inhibition and antioxidant activity. The structure-activity relationships for this series of compounds were studied by synthesizing the analogues and evaluating these three kinds of activity. Ca(2+) antagonistic activity was largely determined by the lipophilicity of the phenyl group at the 2-position and the length of the alkyl chains. As for the antioxidant activity, it was demonstrated that the phenolic hydroxyl group is an essential structural element. Compounds with potent activity were evaluated for their effect on the coronary blood flow in vivo. Among these compounds, compound 1 was shown to be the most potent. Furthermore, the enantiomers of 1 were resolved by high-performance liquid chromatography with a chiral column. Compound (-)-1 showed about 10 times higher Ca(2+) antagonistic activity than (+)-1, though both enantiomers had similar potency in Ca(2+) overload inhibition and antioxidant activity. An X-ray crystal structure determination of (-)-1 hydrogen fumarate identified (-)-1 as having S configuration at the 2-position.

The anti-ischemic effects of CP-060S during pacing-induced ischemia in anesthetized dogs

CP-060 S, (-)-( S)-2-[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]-3-[3-[N-methyl-N-[2-(3 ,4-methylenedioxyphenoxy)ethyl]-amino]propyl]-1,3-thiazolidin++ +-4-one hydrogen fumarate, is a novel cardioprotective drug which prevents Na+-, Ca2+-overload and has Ca2+ channel blocking activity. We compared the anti-ischemic effects of CP-060S with those of diltiazem, a Ca2+ channel blocker, and R56865, N-[1-[4-(4-fluorophenoxy)butyl]-4-piperidinyl]-N-methyl-2-benzothiazo lamine, a Na+-, Ca2+-overload inhibitor, in a canine pacing-induced ischemia model. CP-060S 100 microg kg(-1) significantly suppressed the pacing-induced ischemic epicardial ST-segment elevation by maximally 75%, while diltiazem 100 microg kg(-1) suppressed it by maximally 35%. R56865 100 microg kg(-1) significantly suppressed the ST-segment elevation by maximally 30%. In addition, diltiazem 100 microg kg(-1) caused synergistic suppression of ST-segment elevation by 70% when administered simultaneously with R56865 100 microg kg(-1). These results suggest that a Na+-, Ca2+-overload preventive action and a Ca2+ channel blocking action independently contribute to the suppression of the ST-segment elevation. Therefore, CP-060S may suppress pacing-induced ST-segment elevation by a dual action by preventing Na+-, Ca2+-overload and the Ca2+ channel blockade.

Effects of CP-060S, a novel cardioprotective drug, on cardiac function and myocardial oxygen consumption

1. We examined the effects of CP-060S on cardiac function and myocardial oxygen consumption (MVO2) in anesthetized dogs. 2. CP-060S (10-300 microg/kg i.v.) decreased heart rate, increased aortic flow and decreased mean blood pressure in a dose-dependent manner. The PR interval was significantly prolonged by administration of CP-060S (300 microg/kg i.v.). 3. CP-060S (10-300 microg/kg i.v.) increased coronary blood flow in a dose-dependent manner. Left ventricular end-diastolic pressure and maximal first derivative of left ventricular pressure were not significantly affected. 4. CP-060S (10-300 microg/kg i.v.) increased coronary sinus blood flow and decreased arteriovenous oxygen difference and MVO2 in a dose-dependent manner. 5. The effects of CP-060S on cardiac function and MVO2 are qualitatively similar to those of diltiazem, a typical Ca2+ antagonist.

Antiischemic effects of CP-060S, an inhibitor of pathologically modified sodium channels, assessed in the canine experimental model of angina pectoris

CP-060S is a novel compound that can inhibit the slow inward calcium current as well as the veratridine-induced, noninactivating sodium current. Antiischemic and cardiovascular effects of CP-060S were assessed by using halothane-anesthetized beagle dogs and compared with the effects of semotiadil, a benzothiazine calcium antagonist. The first or second diagonal branch was narrowed. ECG, unipolar electrograms from both ischemic and nonischemic regions, and systemic and left ventricular pressure were monitored. The left ventricle was electrically driven at 190-240 beats/min for 3 min to induce reversible myocardial ischemia. The severity of ischemia was judged by the magnitude of ST-segment depression. CP-060S (0.1 mg/kg, i.v.) significantly attenuated the pacing-induced ST-segment depression in the ischemic region >2 h, whereas during the sinus rhythm, it showed reversible negative chronotropic, inotropic, and dromotropic effects and induced transient depressor response, which would not necessarily be considered favorable (n = 8). A smaller dose of CP-060S (0.03 mg/kg, i.v.) showed a similar antiischemic and cardiovascular profile, but each effect was less potent than that of the higher dose (n = 7). Semotiadil (0.1 and 0.3 mg/kg, i.v.) also showed cardiovascular suppression similar to that of CP-060S; however, the antiischemic effect was not detected during the whole experimental period (n = 6). Thus the inhibition of the noninactivating sodium current may be the primary reason for the antiischemic effect of CP-060S and could become a new cytoprotective principle in the treatment of patients with ischemic heart disease.

Novel calcium antagonists with both calcium overload inhibition and antioxidant activity. 1. 2-(3, 5-di-tert-butyl-4-hydroxyphenyl)-3-(aminopropyl)thiazolidinones

A series of 2-(3, 5-di-tert-butyl-4-hydroxyphenyl)-3-(aminopropyl)thiazolidinones was synthesized in order to explore novel calcium antagonists with potent antiischemic activity. These compounds were designed to have, in addition to Ca2+ antagonistic activity, both Ca2+ overload prevention and antioxidant activity in one molecule. These three kinds of activity were evaluated by using a K+-depolarized rat aorta, a veratridine-induced Ca2+ overload model of rat cardiomyocytes, and a soybean lipoxygenase-induced lipid peroxidation model of rabbit low-density lipoprotein, respectively. In particular, 2-(3, 5-di-tert-butyl-4-hydroxyphenyl)-3-[3-[N-methyl-N-[2-[3, 4-(methylenedioxy)phenoxy]ethyl]amino]propyl]-1,3-thiazolidin-4-on e (7o) was found to be highly potent and possessed a well-balanced combination of these actions in vitro.

The protective effects of CP-060S on ischaemia- and reperfusion- induced arrhythmias in anaesthetized rats

1. CP-060S is a novel sodium and calcium overload inhibitor, and is also characterized as a calcium channel blocker. As these activities have each been shown independently to ameliorate ischaemia damage in the myocardium, the combination may synergistically exert cardioprotection. In this study, therefore, the protective effect of CP-060S against ischaemia- and reperfusion-induced arrhythmia was evaluated in anesthetized rats. 2. Rats were anaesthetized with pentobarbitone, and the left anterior descending coronary artery was occluded for either 5 min with subsequent reperfusion (a reperfusion-induced arrhythmia model) or 30 min without (an ischaemia-induced arrhythmia model). All drugs were intravenously administered 1 min before the onset of occlusion. 3. In the reperfusion-induced arrhythmia model, the animals in the vehicle-treated group exhibited ventricular tachycardia (VT) in 100%, ventricular fibrillation (VF) in 89%, and death caused by sustained VF in 56%. CP-060S (30-300 microg kg(-1)) dose-dependently suppressed the incidences of arrhythmias. Significant decreases occurred at 100 microg kg(-1) in VF (incidence: 42%) and mortality (8%), and at 300 microg kg(-1) in VT (50%), VF (33%) and mortality (8%). This protective effect of CP-060S was 10 times more potent than that of a pure calcium channel blocker, diltiazem (30-1000 microg kg(-1)) we tested, in terms of effective dose ranges. As both drugs decreased myocardial oxygen consumption estimated by rate-pressure product to a similar extent, the calcium channel blocking activity of CP-060S would not seem to be sufficient to explain its potency. 4. In the same model, co-administration of ineffective doses of diltiazem (300 microg kg(-1)) and a sodium and calcium overload inhibitor, R56865 (100 microg kg(-1)), produced significant suppression of VT (incidence: 62%), VF (46%) and mortality (8%). By contrast, co-administration of R56865 at the same dose with CP-060S (300 microg kg(-1)) did not add to the effect of a single treatment of CP-060S. 5. In the ischaemia-induced arrhythmia model, CP-060S (300 microg kg(-1)) significantly decreased the incidence of VF from 75% to 29%, whereas diltiazem (1 mg kg(-1)) was ineffective. 6. These results suggest that CP-060S inhibits both ischaemia- and reperfusion-induced arrhythmia. The combination of the calcium channel blocking effect and the calcium overload inhibition was hypothesized to contribute to these potently protective effects.

CP-060S, a novel cardioprotective drug, limits myocardial infarct size in anesthetized dogs

The myocardial infarct size (IS)-limiting effect of CP-060S, a novel cardioprotective drug that prevents Na+-, Ca2+-overload and has Ca2+ channel-blocking activity, was compared with that of diltiazem, a pure Ca2+ antagonist, to determine whether the prevention of Na+-, Ca2+-overload contributes to this IS-limiting effect. Dogs were subjected to 90 min of left circumflex coronary artery (LCx) occlusion followed by 5 h of reperfusion. Either CP-060S (300 microg/kg) or diltiazem (600 microg/kg) was administered intravenously 20 min before the occlusion. CP-060S significantly limited IS compared with that of vehicle (percentage of the area at risk: vehicle, 50.64 +/- 6.08%; CP-060S, 21.13 +/- 3.75%; p < 0.01 vs. vehicle). Although diltiazem exerted a significant decrease in rate-pressure product (RPP; an index of myocardial oxygen consumption) during occlusion equal to that of CP-060S, diltiazem did not significantly reduce IS (33.90 +/- 4.30%). Regional myocardial blood flow (RBF) was not significantly different between any of the groups. Therefore the IS-limiting effect of CP-060S cannot be explained in terms of changes in RPP or RBF. Thus the IS limitation induced by CP-060S is probably the consequence of a direct cardioprotective effect on myocytes. The prevention of Na+-, Ca2+-overload may be the primary reason for this IS-limiting effect.

CP-060S interacts with three principal binding sites on the L-type Ca2+ channel

CP-060S, (-)-(S)-2-[3,5-bis(1,1-dimethylethyl)-4-hydroxypheny1]-3-[3-[N-met hyl-N-[2-(3,4-methylenedioxyphenoxy)ethyl]amino]propyl]-1,3-thi azolidin-4-one hydrogen fumarate is a novel cardioprotective drug, which is able to prevent Na+-, Ca2+-overload and also has Ca2+ channel blocking activity. The latter action of CP-060S was characterized by radioligand binding experiments with rat cardiac membranes in terms of the interaction with the three principal binding sites on the L-type Ca2+ channel, which bind such drugs as the 1,4-dihydropyridines, phenylalkylamines and benzothiazepines. CP-060S exhibited complete and concentration-dependent inhibition of [3H](+)-PN200-110, [3H](-)-desmethoxyverapamil and [3H]cis-(+)-diltiazem binding to their specific binding sites. Saturation studies showed that CP-060S increased the Kd of [3H](+)-PN200-110 and [3H](-)-desmethoxyverapamil without causing a significant change in the maximum binding density. The dissociation kinetics of the three radioligands were accelerated by CP-060S. These results suggest that CP-060S interacts with a novel binding site on the L-type Ca2+ channel and has a negative allosteric interaction with the three principal binding sites for the 1,4-dihydropyridines, phenylalkylamines and benzothiazepines.

Effects of CP-060S on membrane channels in vascular smooth muscle cells from guinea pig

The newly developed cardioprotective drug, CP-060S, (-)-(S)-2-[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]-3-[3-[N-methyl-N- [2-(3,4-methylenedioxyphenoxy) ethyl] amino] propyl]-1,3-thiazolidin-4-one hydrogen fumarate, is reported to possess a vasodilating action. Our objective was to examine the effects of CP-060S on the membrane channels in mesenteric arterial cells from guinea pigs, using whole-cell patch-clamp techniques. CP-060S inhibited the Ca2+ channel current in a concentration-dependent manner (ED50 = 1.7 microM at a holding potential of -80 mV and a stimulation frequency of 0.1 Hz). The inhibition was potentiated by a more depolarized holding potential and a higher stimulation frequency. These effects of CP-060S resembled those of diltiazem and gallopamil more than to those of nifedipine; the inhibition was more frequency dependent and less holding-potential dependent than with nifedipine. Higher concentrations of CP-060S also inhibited the delayed K+ channel currents (ED50 = 18 microM). The present observations suggest that CP-060S exhibits the profile of a Ca2+ channel antagonist, similar to that of diltiazem and gallopamil.