KC8851, a tedisamil analogue with mixed channel blockade, exhibits antiarrhythmic properties against ischemia- and electrically-induced arrhythmias

KC8851, a structural analogue of tedisamil, has previously been found to exhibit mixed blockade of K+ and Na+ currents in isolated rat ventricular myocytes. We have now investigated the antiarrhythmic actions of this compound in the anaesthetized rat and isolated rat heart. In the rat, KC8851, at concentrations as low as 0.2 micromol kg(-1) min(-1), widened the QT intervals of the ECG and prolonged the effective refractory period in a dose-dependent manner. Such actions were consistent with blockade of repolarizing K+ currents. At relatively higher doses (above 0.5 micromol kg(-1) min(-1)), KC8851 increased RSh amplitude suggesting blockade of Na+ currents. The compound was found to be effective against occlusion-induced arrhythmias at doses of 0.5 to 2 micromol kg(-1) min(-1). In isolated hearts, the effects of KC8851 on PR and QRS intervals were potentiated by elevated concentrations of K+ and H+. Overall, KC8851 was found to exhibit antiarrhythmic actions consistent with inhibition of both K+ and Na+ currents.

Arteflene compared with mefloquine for treating Plasmodium falciparum malaria in children

Arteflene is a synthetic peroxide recently developed from an indication of antimalarial activity found in the Chinese plant Artabotrys uncinatus. The new antimalarial was compared against mefloquine in a phase 3, open-labeled, randomized trial in children with uncomplicated Plasmodium falciparum malaria in Gabon. Patients received single oral doses of either 25 mg/kg of arteflene suspension or 15 mg/kg of mefloquine tablets. High-grade (RII and RIII) resistance was observed in eight (40%) of the 20 patients receiving the single dose of arteflene, but in none of the 21 mefloquine-treated patients (P < 0.005). At day 28, only one patient in the arteflene group, compared with all 21 patients in the mefloquine group, was cured (P < 0.001). Arteflene cleared fever slightly but not significantly faster than mefloquine and the 50% and 90% parasite clearance times were comparable in both treatment groups. In vitro results in the arteflene group suggest an increase of arteflene resistance when comparing sensitivity of paired parasite isolates before treatment and at recrudescence. Both treatment regimens were well-tolerated. In conclusion, single dose monotherapy with arteflene was not effective in curing children suffering from uncomplicated P. falciparum malaria in Gabon, while mefloquine proved to be highly effective for this purpose.

GYKI-46 903, a non-competitive antagonist for 5-HT3 receptors

The effects of GYKI-46 903 ((+)endo-4-propionyloxy-6-(4-fluorophenyl)-1-azabicyclo [3.3.1]non-6-ene HCl), on 5-HT3 receptors have been studied and compared with ondansetron in peripheral organs in vitro and in vivo, and in a receptor binding assay in membranes prepared from rat cerebral cortex. GYKI-46 903 was found to be a non-competitive antagonist at 5-HT3 receptors present in non-stimulated longitudinal muscle strip of guinea-pig ileum (pD2' against serotonin = 5.54), and also in 5-methoxytryptamine-pretreated electrically stimulated ileal preparations (pD2' against serotonin = 5.26). On the contrary, ondansetron was found to be a competitive antagonist for 5-HT3 receptors; the pA2 value against serotonin was 7.40 in non-stimulated ileum, and it was 7.08 in electrically stimulated ileal preparation pretreated with 5-methoxytryptamine. In displacement studies, the pIC50 values of GYKI-46 903 and ondansetron against [3H]granisetron binding to rat cerebral cortex membranes were 6.91 and 8.58 respectively. GYKI-46 903, when administered by intravenous infusion, antagonized the decrease in heart rate evoked by serotonin (Bezold-Jarisch reflex) in anaesthetized rats, and the maximal reversal was less than 50%. This was in striking contrast with ondansetron, which, after intravenous injection, completely antagonized the serotonin-induced bradycardia with an ID50 value of 3.28 ug/kg. These data classify GYKI-46 903 as a non-competitive antagonist for 5-HT3 receptors.

Effects of bisaramil on coronary-occlusion-reperfusion injury and free-radical-induced reactions

The aim of this study was to determine whether bisaramil-an antiarrhythmic compound under clinical investigation-influences the reperfusion-induced arrhythmias and biochemical parameters characterizing occlusion-reperfusion-induced free-radical reactions. The left descending coronary artery (LAD) was occluded for 60 min in anaesthetized dogs followed by one hour of reperfusion. Blood samples were taken at different times of the occlusion and reperfusion for the determination of plasma concentration of malondialdehyde (MDA), reduced (GSH) and oxidized glutathione (GSSG); furthermore of the activity of catalase and superoxide dismutase (SOD). Free-radical generating capacity of polymorph neutrophil granulocytes (PMN) was also measured. At the end of the experiments heart tissue samples were excised from the injured areas and from the intact part of the left ventricular muscle. In tissues samples the concentrations of MDA and GSH and the activity of SOD were determined. Bisaramil was given as an i.v. bolus injection at a dose of 2 mg kg-1 several minutes prior to the end of LAD-occlusion; then the administration was repeated in the 30th minute of reperfusion. In the control group (10 dogs) ventricular fibrillation (VF) occurred in seven cases which resulted in death in three. In the bisaramil-treated group, however. VF was seen in three cases and no death was recorded. Bisaramil inhibited the elevation of the plasma concentration of MDA and GSSG during the reperfusion and abolished the decrease in the plasma concentration of GSH during the occlusion and reperfusion. The activity of SOD and catalase in plasma was much better preserved in the bisaramil-treated group then in the controls. Bisaramil significantly inhibited the increase of the superoxide-radical generating capacity of PMNs during the reperfusion. The data obtained from myocardial tissue samples supported the cardioprotective effect of bisaramil. The biochemical investigation of ischemic-reperfused myocardium showed that bisaramil promoted preservation of SOD-activity and of tissue glutathione. Results of this study clearly showed that bisaramil has a significant effect on ischemiareperfusion injury. Besides its inhibitory effects on ischaemia-reperfusion induced arrhythmias it has a special benefit in influencing free-radical mediated damage leading to better preservation of membranes and to limitations of irreversible cell injuries.

Effects of tedisamil (KC-8857) on cardiac electrophysiology and ventricular fibrillation in the rabbit isolated heart

1. The direct cardiac electrophysiological and antifibrillatory actions of tedisamil (KC-8857) were studied in rabbit isolated hearts. 2. Tedisamil (1, 3, and 10 microM), prolonged the ventricular effective refractory period (VRP) from 120 +/- 18 ms (baseline) to 155 +/- 19, 171 +/- 20, and 205 +/- 14 ms, respectively. Three groups of isolated hearts (n = 6 each) were used to test the antifibrillatory action of tedisamil. Hearts were perfused with 1.25 microM pinacidil, a KATP channel activator. Hearts were subjected to hypoxia for 12 min followed by 40 min of reoxygenation. Ventricular fibrillation (VF) developed during hypoxia and reoxygenation in both the control and 1 microM tedisamil-treated groups (5/6 and 4/6, respectively). Tedisamil (3 microM) reduced the incidence of VF (0/6, P = 0.007 vs. control). 3. In a separate group of hearts, VF was initiated by electrical stimulation. The administration of 0.3 ml of 10 mM tedisamil, via the aortic cannula, terminated VF in all hearts, converting them to normal sinus rhythm. 4. Tedisamil (3 microM) reversed pinacidil-induced negative inotropic effects in rabbit isolated atrial muscle which were equilibrated under normoxia, as well as in atrial muscle subjected to hypoxia and reoxygenation. 5. The results demonstrate a direct antifibrillatory action of tedisamil in vitro. The mechanism responsible for the observed effects may involve modulation by tedisamil of the cardiac ATP-regulated potassium channel, in addition to its antagonism of IK and Ito.

A ferret model of electrical-induction of arterial thrombosis that is sensitive to aspirin

An experimental model of acute thrombosis was developed in pentobarbital- anesthetized ferrets. A 10-min anodal electrical stimulation of 1 mA was delivered to the external surface of the carotid artery while measuring carotid blood flow (CBF). This produced an occlusive thrombus in all vehicle-treated ferrets within 41 +/- 3 min with an average weight of 8 +/- 1 mg (n = 7). These thrombi were enriched in both platelets and fibrin and were adherent at the site of transmural vascular injury as determined by light and electron microscopy. To determine the model's sensitivity to antiplatelet drugs, aspirin or a thromboxane (TxA2) receptor antagonist (ifetroban) were administered 15 min before electrical stimulation. Thrombus weight was reduced 58% by aspirin (10 mg/kg, i.v.) and 74% by ifetroban (1 mg/kg + 1 mg/kg per hr, i.v.). Both drugs also improved CBF and decreased vascular occlusion. Ferrets were more sensitive than rats to aspirin's inhibition of collagen-induced platelet aggregation as determined ex vivo in whole blood. Separate in vitro platelet aggregation studies revealed species differences in reactivity to U-46619 (TxA2 receptor agonist) and collagen in the order of human > ferret > rat, with relatively lesser variations in ADP responses. These studies identify the ferret as a useful species for evaluating antithrombotic drugs in a model in which aspirin is efficacious.

Efficacy of intra-arterial norcantharidin in suppressing tumour 14C-labelled glucose oxidative metabolism in rat Morris hepatoma

Norcantharidin is the demethylated form of Cantharidin, which is the active ingredient of the blister beetle, Mylabris, a long used Chinese traditional medicine. Though not well publicized outside China, Norcantharidin is known to possess significant anti-hepatoma activity, and is relatively free from side effects. In the present study, glucose oxidation in tumour and liver tissue slices harvested from hepatoma-bearing animals was quantified by measuring the radioactivity of 14C-labelled CO2 released from 14C-glucose in oxygen-enriched incubation medium. Results were expressed as a tumour/liver ratio. For comparison, treatments with Norcantharidin, Adriamycin and with hepatic artery ligation were studied. The mean tumour/liver ratio was 4.2 +/- 2.2 in untreated controls, but dropped significantly to 2.3 +/- 0.5 (p < 0.05) with intra-arterial Norcantharidin (0.5 mg/kg) and to 2.3 +/- 0.7 (p < 0.05) with intra-arterial Adriamycin (2.4 mg/kg), and to 2.2 +/- 0.7 (p < 0.05) with hepatic artery ligation. However, with intravenous Adriamycin at 2.4 mg/kg, the mean tumour/liver ratio was reduced to only 3.5 +/- 2.0 and was not significantly different from untreated controls. It is concluded that intra-arterial Norcantharidin is as effective as intraarterial Adriamycin and hepatic artery ligation in suppressing tumour glucose oxidative metabolism. These result simply that Norcantharidin may have a role to play in the chemotherapy of primary liver cancer.

[A randomized crossover comparison of azasetron and granisetron in the prophylaxis of emesis induced by chemotherapy including cisplatin]

The clinical application of 5-HT3 receptor antagonists has enabled continuation of the course of chemotherapy including cisplatin, which induces strong nausea and vomiting, and to prevent the delay of curative treatment for cancer patients receiving neoadjuvant chemotherapy. However, with the development of basic research on the mechanisms of vomiting, each 5-HT3 receptor antagonist has appeared to have different pharmacological actions and, subsequently, the difference in the clinical efficacy of each drug has been reported in Europe and USA. In freshly advanced head and neck carcinoma cases, a randomised crossover study was performed to compare the efficacy and safety profile of a single intravenous dose for 7 days of azasetron (10 mg/day) or granisetron (3 mg/day) in the prophylaxis of nausea and vomiting induced by multi-drug chemotherapy including cisplatin (50 mg/m2 or 60 mg/m2). Anti-emetic effects were evaluated by the protective rates for nausea and vomiting for 7 days following the start of cisplatin administration. Both 5-HT3 receptor antagonists were highly effective in the prophylaxis of acute and delayed emesis induced by chemotherapy, whereas the efficacies of azasetron on day 3 and 4 were superior to those of granisetron. No adverse effect of either drug was observed in this study.