No abstract

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) may serve as a new assay for drug testing in a human context, but their validity particularly for the evaluation of inotropic drug effects remains unclear. In this blinded analysis, we compared the effects of 10 indicator compounds with known inotropic effects in electrically stimulated (1.5 Hz) hiPSC-CM-derived 3-dimensional engineered heart tissue (EHT) and human atrial trabeculae (hAT). Human EHTs were prepared from iCell hiPSC-CM, hAT obtained at routine heart surgery. Mean intra-batch variation coefficient in baseline force measurement was 17% for EHT and 49% for hAT. The PDE-inhibitor milrinone did not affect EHT contraction force, but increased force in hAT. Citalopram (selective serotonin reuptake inhibitor), nifedipine (LTCC-blocker) and lidocaine (Na+ channel-blocker) had negative inotropic effects on EHT and hAT. Formoterol (beta-2 agonist) had positive lusitropic but no inotropic effect in EHT, and positive clinotropic, lusitropic, and inotropic effects in hAT. Tacrolimus (calcineurin-inhibitor) had a negative inotropic effect in EHTs, but no effect in hAT. Digoxin (Na+-K+-ATPase-inhibitor) showed a positive inotropic effect only in EHTs, but no effect in hAT probably due to short incubation time. Ryanodine (ryanodine receptor-inhibitor) reduced contraction force in both models. Rolipram and acetylsalicylic acid showed noninterpretable results in hAT. Contraction amplitude and kinetics were more stable over time and less variable in hiPSC-EHTs than hAT. HiPSC-EHT faithfully detected cAMP-dependent and -independent positive and negative inotropic effects, but limited beta-2 adrenergic or PDE3 effects, compatible with an immature CM phenotype.

Cisapride, a gastrointestinal prokinetic agent, has been associated with cases of Torsades de Pointes but its effects on the cardiac action potential have not been described. We investigated its electrophysiological effects on rabbit isolated Purkinje fibres. The results demonstrated that cisapride (0.01-10 tM) lengthened concentration-dependently the action potential duration without modifying other parameters and induced early after depolarizations and subsequent triggered activity. This typical class III antiarrhythmic effect, that showed 'reverse' rate-dependence and was reduced by increasing external K concentration, can account for clinical arrhythmogenesis.

No abstract

Cardiotoxicity is among the leading reasons for drug attrition and is therefore a core subject in non-clinical and clinical safety testing of new drugs. European Centre for the Validation of Alternative Methods held in March 2008 a workshop on "Alternative Methods for Drug-Induced Cardiotoxicity" in order to promote acceptance of alternative methods reducing, refining or replacing the use of laboratory animals in this field. This review reports the outcome of the workshop. The participants identified the major clinical manifestations, which are sensitive to conventional drugs, to be arrhythmias, contractility toxicity, ischaemia toxicity, secondary cardiotoxicity and valve toxicity. They gave an overview of the current use of alternative tests in cardiac safety assessments. Moreover, they elaborated on new cardiotoxicological endpoints for which alternative tests can have an impact and provided recommendations on how to cover them.

No abstract

The anabolic effects of b 2-adrenoceptor (b 2-AR) agonists on skeletal muscle have been demonstrated in various species. However, the clinical use of b 2-AR agonists for skeletal muscle wasting conditions has been limited by their undesired cardiovascular effects. Here, we describe the preclinical pharmacological profile of a novel 5-hydroxybenzothiazolone (5-HOB) derived b 2-AR agonist in comparison with formoterol as a representative b 2-AR agonist that have been well characterized. In vitro, 5-HOB has nanomolar affinity for the human b 2-AR and selectivity over the b 1-AR and b 3-AR. 5-HOB also shows potent agonistic activity at the b 2-AR in primary skeletal muscle myotubes and induces hypertrophy of skeletal muscle myotubes. Compared with formoterol, 5-HOB demonstrates comparable full-agonist activity on cAMP production in skeletal muscle cells and skeletal muscle tissue-derived membranes. In contrast, a greatly reduced intrinsic activity was determined in cardiomyocytes and cell membranes prepared from the rat heart. In addition, 5-HOB shows weak effects on chronotropy, inotropy, and vascular relaxation compared with formoterol. In vivo, 5-HOB significantly increases hind limb muscle weight in rats with attenuated effects on heart weight and ejection fraction, unlike formoterol. Furthermore, changes in cardiovascular parameters after bolus subcutaneous treatment in rats and rhesus monkeys are significantly lower with 5-HOB compared with formoterol. In conclusion, the pharmacological profile of 5-HOB indicates superior tissue selectivity compared with the conventional b 2-AR agonist formoterol in preclinical studies and supports the notion that such tissue-selective agonists should be investigated for the safe treatment of muscle-wasting conditions without cardiovascular limiting effects.

Sparfloxacin, a fluoroquinolone antibacterial, has been reported to prolong cardiac repolarization in some patients. In this study, we have investigated the in vitro cardiac electrophysiological effects of two other fluoroquinolones, levofloxacin and ofloxacin, and compared them with those exerted by sparfloxacin. Cardiac action potentials have been recorded from rabbit Purkinje fibers using conventional glass microelectrodes. The influence of a sudden decrease in stimulation rate on repolarization is examined. It is found that ofloxacin and levofloxacin (1-100 microM) do not alter the action potential parameters even at a concentration as high as 100 microM. The stimulation rate is without effect on repolarization. On the contrary, sparfloxacin (1-100 microM) lengthens concentration-dependently the duration of action potential, this effect being significant from the concentration of 10 microM. A non significant decrease in maximal rate of rise of phase 0 depolarization was observed at the concentration of 100 microM. Under low stimulation rate, the sparfloxacin-induced prolonging effect was magnified and early afterdepolarizations occurred in one of seven fibers from the concentration of 30 microM and in four other fibers at the concentration of 100 microM. These results suggest that levofloxacin and ofloxacin had no effect on cardiac cellular electrophysiology whereas sparfloxacin exerts pure class III electrophysiological effects, which can explain the prolongation of QT interval observed clinically in some patients and might become arrhythmogenic in the presence of other predisposing factors.