Potent hemodynamic effects of bimakalim, a new potassium channel opener, in humans

Pharmacokinetic/pharmacodynamic evaluation of a novel potassium channel opener, SKP-450, in healthy volunteers

To evaluate the pharmacokinetic/pharmacodynamic characteristics of SKP-450, a novel K+ channel opener, a single blind, randomized, placebo-controlled, dose-rising, parallel-group study was conducted in 28 healthy volunteers. The volunteers were randomly allocated to dosage groups of 50 micrograms, 100 micrograms, 200 micrograms, and 300 micrograms. Single doses of SKP-450 were administered orally, after overnight fasting, and serial blood sampling and pharmacodynamic measurements were performed up to 48 hours after the drug was administered. The 200 micrograms group was further studied for food interactions in a crossover fashion. Drug concentrations in plasma were determined by HPLC. Hemodynamic changes after drug administration were evaluated by serial measurements of blood pressure (BP), pulse rate (PR), cardiac index (CI), and total peripheral resistance (TPR), using computerized impedance cardiography. Changes in plasma renin activity (PRA) and aldosterone concentrations (PAC) were determined 4 and 24 hours after drug administration. Both SKP-450 and SKP-818, an active metabolite, showed linear pharmacokinetic characteristics, and food intake did not significantly affect the pharmacokinetic characteristics of either compound. Dose-related pharmacological effects were obvious for both the 200 micrograms and 300 micrograms groups. Hemodynamic parameters related to vasodilation and reflex tachycardia, such as maximum changes in diastolic BP, PR, CI, and TPR, showed significant dose-dependent changes. The area under the time-effect curve (AUEC) of the parameters also showed a similar dose-dependent pattern. The PRA and PAC exhibited significant changes 4 hours after drug administration in the 300 micrograms group. Adverse effects, such as headaches, were more frequently observed at the higher dose levels. SKP-450 was generally well tolerated by these normotensive subjects. The antihypertensive efficacy of SKP-450 needs to be evaluated in hypertensive patients after multiple dosing.

Adenosine triphosphate-dependent potassium channel modulation and cardioplegia-induced protection of human atrial muscle in an in vitro model of myocardial stunning

OBJECTIVES

Although adenosine triphosphate-dependent potassium channel openers have been shown to enhance cardioplegic protection in animal myocardium, there is a lack of data on human cardiac tissues. We aimed at determining, on human atrial muscle, whether adenosine triphosphate- dependent potassium channels are involved in protection caused by high-potassium cardioplegia and whether adenosine triphosphate-dependent potassium channel activation might improve cardioplegic protection in an in vitro model of myocardial stunning.

METHODS

Human atrial trabeculae were obtained from adult patients undergoing cardiac operations. In an organ bath at 37 degrees C, the preparations were subjected to 60 minutes of hypoxia at a high stimulation rate either in Tyrode solution (control, n = 17) or in St Thomas' Hospital solution without additives (n = 6) or associated with 100 nmol/L bimakalim (n = 7) or 1 micromol/L glibenclamide (n = 7), followed by 60 minutes of reoxygenation and 15 minutes of positive inotropic stimulation with 1 micromol/L dobutamine.

RESULTS

Atrial developed tension was reduced by hypoxia to 27% +/- 5% of baseline and incompletely recovered after reoxygenation to 38% +/- 7%, whereas dobutamine restored contractility to 74% +/- 7% of basal values. St Thomas' Hospital solution with or without bimakalim improved developed tension after reoxygenation and dobutamine (P <.0001 vs control), whereas glibenclamide inhibited these protective effects of cardioplegic arrest (P =.001 vs St Thomas' Hospital solution). After reoxygenation, the protective effect of bimakalim disappeared at a high pacing rate (400- and 300-ms cycle length) but recovered during dobutamine superfusion.

CONCLUSIONS

Adenosine triphosphate-dependent potassium channels are likely involved in the cardioprotective effects of cardioplegia in human atrial trabeculae and adenosine triphosphate-dependent potassium channel activation with bimakalim used as an additive to cardioplegia enhanced protection.

Effects of bimakalim on human cardiac action potentials: comparison with guinea pig and nicorandil and use-dependent study

Electrophysiologic effects of K(ATP) channel openers (KCOs) are rarely studied for tissue and species specificity, and use-dependent investigations in human tissues are lacking. We therefore investigated in vitro the concentration-dependent effects of the KCO bimakalim [from 10 nM to 10 microM, at 1,000 ms of cycle length (CL) and 37 degrees C] on human (atrium, n = 4, and ventricle, n = 6) and guinea pig (atrium, n = 7, and ventricle, n = 6) transmembrane action potential (AP). The frequency relation (from CL 1,600 to 300 ms, 31 degrees C) of human atrial AP duration 90% (APD90) shortening (10 microM vs. baseline, n = 7) also was determined. A parallel study was performed with the KCO nicorandil (from 10 nM to 1 mM, n = 3) in human atrial APs, at 31 degrees C. Resting membrane potential and maximal upstroke velocity of AP were not modified by bimakalim at maximal concentration, whereas AP amplitude was decreased in both guinea pig preparations (p < 0.05); APD90 was shortened in all tissues (p < 0.01). Median effective concentration (EC50) for APD90 shortening at 37 degrees C was 0.54 and 2.74 microM in atrial and ventricular human tissue, respectively, and 8.55 and 0.89 microM in atrial and ventricular guinea pig tissue, respectively. In human atrial tissue at 31 degrees C, EC50 with bimakalim was 0.39 microM; a much higher value was seen with nicorandil (210 microM). Bimakalim (10 microM)-induced APD90 shortening as a function of stimulation rate was greatest at longest CL. Evidence is provided for (a) species (human vs. guinea pig) and tissue (atrium vs. ventricle) differential AP sensitivity to bimakalim; (b) an approximately 500-fold higher efficacy of bimakalim versus nicorandil to shorten human atrial APD90; and (c) normal use-dependence of human atrial APD90 shortening with bimakalim at 10 microM.

Beneficial effects of intravenous and oral carvedilol treatment in acute myocardial infarction. A placebo-controlled, randomized trial

BACKGROUND

Evidence of efficacy and safety of beta-blockers after thrombolysis for acute myocardial infarction (AMI) is equivocal. Newer beta-blockers such as carvedilol have not been tested in this setting.

METHODS AND RESULTS

This study investigated the effects of acute (intravenous) and long-term (6 months, oral) treatment with carvedilol versus placebo in 151 consecutive patients with AMI. Exercise ECG, ambulatory monitoring, and two-dimensional echocardiography were performed before hospital discharge and at 3 and 6 months. All patients were followed up and cardiovascular events recorded. The Cox proportional hazards model was used to compare time from randomization with the occurrence of a cardiovascular event, and Kaplan-Meier survival curves were calculated. Carvedilol was found to be safe, and it significantly reduced cardiac events compared with placebo (18 on carvedilol and 31 on placebo, P < .02). Fifty-four patients had heart failure at study entry; 34 received carvedilol. There were no adverse effects of carvedilol therapy and no excess events in this subgroup. Carvedilol produced significant reductions in heart rate (P < .0001), blood pressure (P < .005) at rest, and rate-pressure product at peak exercise (P < .003), but exercise capacity was unchanged. Left ventricular ejection fraction was not altered significantly by carvedilol, but stroke volume was higher at pre-hospital discharge examination (63 versus 53 mL; P < .01). Diastolic filling of the left ventricle (E/A ratio) was also improved (1.2 versus 0.9; P < .001). In a subgroup with left ventricular ejection fraction < 45% (n = 49 patients; 24 on carvedilol and 25 on placebo), carvedilol showed attenuation of remodeling.

CONCLUSIONS

Carvedilol was well tolerated and safe to use in patients immediately after AMI, including those with heart failure, and significantly improved outcome.

Pharmacokinetics and safety of a novel, long-acting, prodrug-type potassium channel opener, Y-27152, in healthy volunteers

The pharmacokinetics and safety of a novel, long-acting, prodrug-type K(+)-channel opener, Y-27152, were investigated in healthy male volunteers. In the first phase, single oral doses of 0.1, 0.25, 0.5, 0.75, and 1.0 mg of Y-27152 (n = 3-6 per dose) were given after overnight fasts in a dose-escalating manner. The 0.75-mg dose was given both after an overnight fast or after food to examine the effects of food intake. In the second phase, multiple doses of Y-27152 were taken after meals once daily for 7 consecutive days. In part A of this phase, either placebo (n = 3) or 0.5 mg of Y-27152 (n = 6) was taken for 7 days, and in part B of this phase 0.5-, 0.75-, and 1.0-mg doses were taken in a dose-escalating manner for 1,3, and 3 days, respectively (n = 9). In the single-dose study, peak concentration (Cmax) and area under the plasma concentration-time curve (AUC) of main active metabolite (Y-26763; M1) increased in parallel with dosage. This dose-linearity was less obvious with Y-27152, which had an AUC approximately 6 to 10 times less than that of M1. Administration with food at 0.75 mg resulted in a small but significant decrease (approximately 10%) in the Cmax and AUC of M1. At doses of 0.5 mg or higher, participants experienced headaches and palpitations, which were probably due to the vasodilatory effects and did not require treatment. Mean diastolic blood pressure significantly decreased and pulse rate increased at doses of 0.5 mg or higher compared with predose values. Plasma renin activity was significantly elevated 4 hours after the administration of the 0.75- and 1.0-mg doses, but showed no significant change at 0.5 mg. In the multiple-dose study, the time profile of the plasma concentration of M1 approximately coincided with the simulation curves worked out using the pharmacokinetic parameters obtained in the singledose study. The incidence of headaches tended to increase with dose in part B, but drug administration was not discontinued in any case. Plasma renin activity again increased 4 hours after administration. In phase B of the multiple-dose study, diastolic blood pressure decreased and pulse rate increased compared with predose values. Y-27152 was metabolized to M1 and well tolerated in healthy volunteers, and its pharmacologic effects were likely caused by vasodilation, which could make it an effective antihypertensive agent.