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

Changes of electrocardiogram and hemodynamics in response to dipyridamole: In vivo comparative analyses using anesthetized beagle dogs and microminipigs

Microminipigs are expected as a novel animal model for cardiovascular pharmacological experiments. Since inherent vulnerability of coronary circulation of microminipigs has not been characterized, we performed dipyridamole-stress test to both microminipigs and beagle dogs, and compared the results. Dipyridamole in doses of 0.056 and 0.56 mg/kg were intravenously infused over 10 min (n = 4 for each animal). Dipyridamole decreased the systolic/diastolic blood pressures and double product in dogs as well as in microminipigs; but it did not significantly alter the heart rate or the global balance between the myocardial oxygen demand and supply in either animal. While organic coronary arterial stenosis was not detected in either animal, dogs have well-developed epicardial intracoronary networks unlike microminipigs. Like in humans, dipyridamole did not affect the ST segment of microminipigs, whereas it substantially depressed that in dogs. The results indicate the onset of subendocardial ischemia by dipyridamole in dogs may be partly associated with their well-developed native coronary collateral channels. Microminipigs would be more useful to evaluate the drugs which may affect the coronary circulation in the pre-clinical study than dogs.

F 15845 inhibits persistent sodium current in the heart and prevents angina in animal models

BACKGROUND AND PURPOSE

Activation of the persistent sodium current in ischaemic myocardium results in calcium overload which is toxic for the cardiomyocyte. Thus, the activity of 3-(R)-[3-(2-methoxyphenylthio-2-(S)-methylpropyl]amino-3,4-dihydro-2H-1,5 benzoxathiepine bromhydrate (F 15845), a new selective persistent sodium current blocker, in protecting against the effects of cardiac ischaemia was examined, in both in vitro and in vivo models.

EXPERIMENTAL APPROACH

Electrophysiological studies using patch-clamp and conventional microlelectrode techniques, isolated perfused hearts and models of angina in anaesthetized animals were used to assess the protection afforded by F 15845 against ischaemia-induced changes.

KEY RESULTS

F 15845 reduced the persistent sodium current activated by veratridine (IC(50) 1.58 x 10(-6) mol.L(-1)). F 15845 blocked voltage-gated human cardiac sodium channels in a novel, voltage-dependent manner, selectively affecting steady-state inactivation. F 15845 did not affect action potential shape and basal function of guinea pig isolated perfused hearts but did reduce ischaemia-induced diastolic contracture in this model (IC(50) 0.64 x 10(-6) mol.L(-1)). In rabbits, F 15845 given i.v. (ED(50) 0.05 mg.kg(-1)) or orally (ED(50) 0.13 mg.kg(-1)) dose-dependently and powerfully inhibited regional myocardial ischaemia-induced ST segment elevation in the absence of haemodynamic effects, implying direct cardiac activity. In dogs, F 15845 dose-dependently inhibited epicardial ST segment changes (70 +/- 8% at 0.63 mg.kg(-1)) in an experimental angina model of demand ischaemia, again without haemodynamic effects, confirming a direct anti-anginal activity.

CONCLUSIONS AND IMPLICATIONS

F 15845 is a selective, potent blocker of the persistent sodium current, generated by the human Na(v)1.5 channel isoforms, and prevents cardiac angina in animal models.

NIP-141, a multiple ion channel blocker, terminates aconitine-induced atrial fibrillation and prevents the rapid pacing-induced atrial effective refractory period shortening in dogs

AIMS

NIP-141 is a novel multiple ion channel blocker with atrial selective effects. In this study, we examined the effects of NIP-141 on aconitine-induced atrial fibrillation (AF) and rapid atrial pacing-induced atrial effective refractory period (ERP) shortening in dogs.

METHODS AND RESULTS

Aconitine AF was induced by the application of aconitine on the right appendage. NIP-141 (10 mg/kg) converted AF to sinus rhythm in 5 of 6 dogs. The Na(+) channel blockers disopyramide (1 mg/kg) and phenytoin (10 mg/kg) also terminated AF, but the I(Kr) blocker (d-sotalol; 4 mg/kg) and a Ca(2+) channel blocker (verapamil; 0.3 mg/kg) did not terminate AF in this model. To clarify the mechanism of AF termination, we examined the effects on ERP and conduction time, but NIP-141 (10 mg/kg) had no significant effects. In a short-term rapid atrial pacing model, NIP-141 (2.5 mg/kg/10 min, followed by 0.033 mg/kg/min) prevented atrial ERP shortening. We also found NIP-141 bound to Na(+) channel site 2 receptor and L-type Ca(2+) channel, but not to Na(+) channel site 1 receptor using radioligands binding assay.

CONCLUSION

NIP-141 terminated AF in aconitine-induced AF and prevented the atrial remodelling by short-term rapid pacing in dogs, possibly via the blocking of Na(+) and Ca(2+) channels.

The anti-diabetic drug miglitol is protective against anginal ischaemia through a mechanism independent of regional myocardial blood flow in the dog

1. In the present study, we attempted to clarify whether the antidiabetic drug miglitol, an alpha-glucosidase inhibitor, has a protective effect against anginal ischaemia. We had reported previously that miglitol reduces myocardial infarct size through inhibition of glycogenolysis during ischaemia in rabbits. However, the effect of miglitol on anginal ischaemia remains unknown. 2. In open-chest beagle dogs with a severely stenosed left anterior descending coronary artery, an epicardial electrode was attached to the surface of the risk area of the left ventricle and a microdialysis probe was implanted into the myocardium to measure ST segment changes and interstitial lactate accumulation. The first episode of anginal ischaemia was induced by atrial pacing and phenylephrine infusion (50-100 microg/min) for 10 min. The second episode of anginal ischaemia was induced 210 min after the first episode. Miglitol (10 mg/kg, i.v.) was administered to the miglitol group (n = 10) 30 min before the second episode of anginal ischaemia, whereas saline was administered to the control group (n = 10). Regional myocardial blood flow was measured using coloured microspheres. 3. There was no significant difference in regional myocardial blood flow in the risk and non-risk areas between the first and second episodes of anginal ischaemia and between the miglitol and control groups. During the first and second episodes of anginal ischaemia, the ST segment was decreased to a similar extent in the control group. Although ST segment depression during the first episode of anginal ischaemia was similar in both groups, ST segment depression during the second episode of anginal ischaemia was significantly attenuated in the miglitol-treated group compared with the control group (1.3 +/- 0.4 vs 2.2 +/- 0.4 mV, respectively). Miglitol significantly attenuated myocardial interstitial lactate accumulation in the risk area. 4. In conclusion, in the present study miglitol improved ST segment depression and attenuated the accumulation of myocardial interstitial lactate during anginal ischaemia without altering regional myocardial blood flow. Miglitol has an anti-anginal ischaemia effect via a mechanism that is independent of regional myocardial blood flow.

Antianginal effects of hydroxyfasudil, a Rho-kinase inhibitor, in a canine model of effort angina

1. The effects of Rho-kinase inhibitor, fasudil, and of a more specific Rho-kinase inhibitor, hydroxyfasudil, on pacing-induced myocardial ischaemia were determined in anaesthetized open-chest dogs. 2. The dogs were subjected to left anterior descending coronary artery (LAD) stenosis producing a sufficient ischaemia as measured by ST-segment depression on electrocardiograms only when the hearts were paced 60 beats min(-1) above the baseline. After a recovery (nonpacing) period, drugs or saline were infused intravenously over 30 min. The animals were again subjected to 5 min of pacing 25 min after the initiation of the treatment. 3. Hydroxyfasudil (0.1 and 0.3 mg kg(-1)) and fasudil (0.3 mg kg(-1)) suppressed the ST-segment depression. Hydroxyfasudil and fasudil also increased the regional blood flow of the LAD perfused endomyocardium region in the canine model of effort angina. 4. To determine the flow profile for hydroxyfasudil in dogs, blood flow in three vascular beds was measured. Hydroxyfasudil (0.3 mg kg(-1) for 30 min) significantly increased coronary blood flow and vertebral blood flow, without significantly changing the femoral blood flow. 5. Hydroxyfasudil had no inotropic or chronotropic effect on the isolated hearts of guinea-pigs. Hydroxyfasudil (2 mg kg(-1) for 20 min) did not affect the PR or QTc interval in anaesthetized dogs. 6. Inhibition of Rho-kinase appears to protect myocardium subjected to pacing-induced ischaemia through the increase in the regional myocardial blood flow. Hydroxyfasudil may be categorized as a novel type of anti-anginal drug, without any inotropic or chronotropic effects.

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.

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.