Description of the Mechanism of Positive Inotropic Action of the Isoquinoline Alkaloid F-18

This study evaluated the mechanism of inotropic effect of an isoquinoline alkaloid derivative, 1-(2´-bromine-4´,5´-dimethoxyphenyl)-6,7-dimethoxy-1,2,3,4- tetrahydroisoquinoline (F-18) using electrically stimulated rat left ventricular papillary muscle of rat. The F-18 alkaloid have been shown to have positive inotropic effect on papillary muscle contraction activity, IC50 value -14,6 µM. Са2+L-channel blocker - nifedipine was used in experiments. Inotropic effects of F-18 isoquinoline alkaloid on cardiomyocytes were suggested, based on results obtained in experiments carried in cardiomyocytes SR Ca2+- transport systems modulation.

Evaluation of Negative Inotropic Effects of a Isoquinoline Alkaloid N-14

In studies, the alkaloid 1-(2-Chloro-4,5-methylenedioxyphenyl)-2-hydroxyethyl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (N-14) had a negative inotropic effect on the activity of the papillary muscle contraction of the rat heart detected. Ca2+ ions from SR play an important role in the process of contraction of the heart muscle. With this in mind, the negative inotropic effect of the N-14 alkaloid was investigated with the modification of the accumulation processes of Ca2+ ions to SR. To clarify this, we examined the effects of the alkaloid being studied on SERCA2a and RyR2. To do this, the inhibitor of SERCA2a - cyclopiazonic acid (CPA) and RyR activator caffeine, which provide the accumulation of Ca2+ ions in SR, were used.

The Combined Inotropic and Vasorelaxant Effect of DHQ-11, A Conjugate of Flavonoid Dihydroquercetin with Isoquinoline Alkaloid 1-Aryl-6,7-Dimethoxy-1,2.3,4-Tetrahydroisoquinoline.

This study investigated the positive inotropic andvasorelaxant activity ofDHQ-11, aconjugate of flavonoid dihydroquercetin with isoquinoline alkaloid 1-aryl-6,7-dimethoxy-1,2.3,4-tetrahydroisoquinoline.A study was performed using anterior papillary muscle removed from the left ventricle and thoracic aorta dissected from rats. DHQ-11 produceda concentration-dependent positive inotropic effect which was more potent than their parent compounds alone. The positive inotropic effect of conjugate DHQ-11was significantly attenuated by the β-adrenoreceptor inhibitor propranolol and L-type Ca2+ channel blocker nifedipine. Also,conjugate DHQ-11 markedly potentiated first post-rest responses indicating that it can modulate Ca2+ loading/release processes in the sarcoplasmic reticulum.These results suggest that positive inotropic effect produced by conjugate DHQ-11may be mediated through activation oftheβ-AR/AC/cAMP/PKA pathway that leads to increased Ca2+ influx and rises in Ca2+ loading/release in the SR, resulting in increased [Ca2+]i and enhanced contraction force. DHQ-11 significantly relaxed both high KCl- and phenylephrine-induced contractions of rat aortic rings whichwere significantly inhibited by lowering extracellular Ca2+ concentration and in the presence of verapamil.DHQ-11 significantly inhibited phenylephrine-induced contractions in a Ca2+-free medium, in the presence of verapamil. The vasorelaxant effect of the DHQ-11 was significantly reduced by the removal of endothelium and in the presenceof L-NAME and methylene blue as well as glibenclamide and TEA.These results suggest that the vasorelaxation produced by conjugate DHQ-11may be mediatedbyan endothelium-independent mechanism involving activation of KATP and BKCa channels and inhibition of L-type VDCCs and Ca2+ release from the sarcoplasmic reticulum and endothelium-dependent mechanism through activation of the NO/sGC/cGMP/PKG signaling pathway resulting in a decrease of intracellular Ca2+levels. These observations reveal that the conjugate DHQ-11 due to its high positive inotropic and vasorelaxant activity could be a promising compound for the design and development of new drugs for the treatment of heart failure.

Human histamine H2 receptors can initiate cardiac arrhythmias in a transgenic mouse

Histamine is known to lead to arrhythmias in the human heart. A mouse model to mimic these effects has hitherto not been available but might be useful to study the mechanism(s) of H2-histamine receptor-induced arrhythmias and may support the search for new antiarrhythmic drugs. In order to establish such a model in mice, we studied here the incidence of cardiac arrhythmias under basal and under stimulated conditions in atrial and ventricular preparations from mice that overexpressed the human H2-histamine receptors in a cardiac-specific way (H2-TG) in comparison with their wild-type (WT) littermate controls. We had shown before that histamine exerted concentration and time-dependent positive inotropic and positive chronotropic effects only in cardiac preparations from H2-TG and not from WT. We noted under basal conditions (no drug addition) that right atrial preparations from H2-TG exhibited more spontaneous arrhythmias than right atrial preparations from WT. These arrhythmias in H2-TG could be blocked by the H2-histamine receptor antagonist cimetidine. In a similar fashion, histamine and dimaprit (an agonist at H2 and not H1-histamine receptors) more often induced arrhythmias in right atrial preparations from H2-TG than from WT. To understand better the signal transduction mechanism(s) involved in these arrhythmias, we studied partially depolarized left atrial preparations. In these preparations, a positive inotropic effect of histamine was still present in the additional presence of 44 mM potassium ions (used to block sodium channels) in H2-TG but not WT and this positive inotropic effect could be blocked by cimetidine and this is consistent with the involvement of calcium ion channels in the contractile and thus might mediate also the arrhythmogenic effects of histamine in H2-TG. However, compounds reported to release histamine from cells and thereby leading to arrhythmias in humans, namely morphine, ketamine, and fentanyl, failed to induce a more pronounced positive inotropic effect in atrial preparations from H2-TG compared to WT, arguing against an involvement of histamine release in their proarrhythmic side effects in patients. Measuring left ventricular contractility in isolated retrogradely perfused hearts (Langendorff mode), we detected under basal conditions (no drug application) more spontaneous arrhythmias in hearts from H2-TG than from WT. In summary, we noted that overexpression of human H2-histamine receptors in a novel transgenic animal model can lead to arrhythmias. We suggest that this model might be useful to understand the mechanism(s) of histamine-induced cardiac arrhythmias in humans better in a molecular way and may be of value to screen novel antiarrhythmic drugs.

Repeated Aconitine Treatment Induced the Remodeling of Mitochondrial Function via AMPK–OPA1–ATP5A1 Pathway

Aconitine is attracting increasing attention for its unique positive inotropic effect on the cardiovascular system, but underlying molecular mechanisms are still not fully understood. The cardiotonic effect always requires abundant energy supplement, which is mainly related to mitochondrial function. And OPA1 has been documented to play a critical role in mitochondrial morphology and energy metabolism in cardiomyocytes. Hence, this study was designed to investigate the potential role of OPA1-mediated regulation of energy metabolism in the positive inotropic effect caused by repeated aconitine treatment and the possible mechanism involved. Our results showed that repeated treatment with low-doses (0–10 μM) of aconitine for 7 days did not induce detectable cytotoxicity and enhanced myocardial contraction in Neonatal Rat Ventricular Myocytes (NRVMs). Also, we first identified that no more than 5 μM of aconitine triggered an obvious perturbation of mitochondrial homeostasis in cardiomyocytes by accelerating mitochondrial fusion, biogenesis, and Parkin-mediated mitophagy, followed by the increase in mitochondrial function and the cellular ATP content, both of which were identified to be related to the upregulation of ATP synthase α-subunit (ATP5A1). Besides, with compound C (CC), an inhibitor of AMPK, could reverse aconitine-increased the content of phosphor-AMPK, OPA1, and ATP5A1, and the following mitochondrial function. In conclusion, this study first demonstrated that repeated aconitine treatment could cause the remodeling of mitochondrial function via the AMPK–OPA1–ATP5A1 pathway and provide a possible explanation for the energy metabolism associated with cardiotonic effect induced by medicinal plants containing aconitine.

β1-Blockers Enhance Inotropy of Endogenous Catecholamines in Chronic Heart Failure

Although β1-blockers impressively reduce mortality in chronic heart failure (CHF), there are concerns about negative inotropic effects and worsening of hemodynamics in acute decompensated heart failure. May receptor theory dispel these concerns and confirm clinical practice to use β1-blockers? In CHF, concentrations of catecholamines at the β1-adrenoceptors usually exceed their dissociation constants (KDs). The homodimeric β1-adrenoceptors have a receptor reserve and display negative cooperativity. We considered the binomial distribution of occupied receptor dimers with respect to the interaction of an exogenous β1-blocker and elevated endogenous agonist concentrations > [KDs], corresponding to an elevated sympathetic tone. Modeling based on binomial distribution suggests that despite the presence of a low concentration of the antagonist, the activation of the dimer receptors is higher than that in its absence. Obviously, the antagonist improves the ratio of the dimer receptors with only single agonist activation compared with the dimer receptors with double activation. This leads to increased positive inotropic effects of endogenous catecholamines due to a β1-blocker. To understand the positive inotropic sequels of β1-blockers in CHF is clinically relevant. This article may help to eliminate the skepticism of clinicians about the use of β1-blockers because of their supposed negative inotropic effect, since, on the contrary, a positive inotropic effect can be expected for receptor-theoretical reasons.

Computational investigation of drug-induced effects on human cardiac electro-mechanics

Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): NC3Rs Infrastructure for Impart Award (NC/P001076/1) Wellcome Trust Senior Research Fellowship in Basic Biomedical Sciences (214290/Z/18/Z) Background Human-based computer modelling and simulations have been widely used in cardiac electrophysiology, to provide a better understanding of the ionic mechanisms underlying risk of arrhythmias, and their modulation by drugs and diseased conditions. More recently, multiscale computer models of human cardiac electro-mechanics have been developed. These models provide the means for a comprehensive investigation of action potential, calcium transient, active force, and their variability in the population, and can predict drug-induced contractility changes in humans. Purpose This study aims to perform a computational investigation of variability in human cardiac contractility biomarkers and their modulation by well-known drugs. Methods We considered the most recent model of human ventricular electro-mechanics (Margara et al. 2020). We constructed a population of 300 cells by randomly varying the main ionic currents in the model, to represent the biological variability observed in human experimental data. We then simulated the effect of 10 reference compounds, 6 of which with known pro-arrhythmic risk. Simulations were performed at 1 Hz for multiple drug concentrations, using the Virtual Assay software. A set of action potential, calcium transient and active force biomarkers were computed, as well as the electro-mechanical window, and the occurrence of early after-depolarisations and after-contractions in the virtual population. Simulation results were compared against clinical risk of drug-induced arrhythmias and experimental recording from human ventricular myocytes from literature. Results Overall, biomarker variability in the virtual population increased following drug application compared to control conditions. All compounds had a negative inotropic effect in simulation, with a marked decrease of the active tension peak, e.g. -80% for nifedipine 8 nM. This is in agreement with human experimental data for all compounds except Dofetilide, for which no inotropic effect was observed in vitro. Compounds with known risk of arrhythmias provoked early after-depolarisations, which in turn caused after-contractions. Their occurrence in the population increased together with the drug concentration, e.g. 3.6% at 0.16 µM and 48% at 0.48 µM for droperidol. In addition, these compounds also displayed prolonged action potential and calcium transient, and a shortening of the electro-mechanical window, all known biomarkers of pro-arrhythmia. Conclusions We evaluated the effect and the cardiac safety of 10 reference compounds in a population of 300 human ventricular electro-mechanical models. Simulation results were in good agreement with experimental data in human ventricular cardiomyocytes, and they allowed to identify the compounds with a known pro-arrhythmic risk based on drug-induced early after-depolarisations and after-contractions. This methodology provides new insights into variability in human cardiac contractility and its modulation by drugs.

Molecular Mechanism of Palmitic Acid on Myocardial Contractility in Hypertensive Rats and Its Relationship with Neural Nitric Oxide Synthase Protein in Cardiomyocytes

Objective. It is aimed at investigating the mechanism of palmitic acid (PA) on myocardial contractility in hypertensive rats and its relationship with myocardial neural nitric oxide synthase (nNOS) protein. Methods. The rats were randomly divided into sham operation group and hypertensive group, with thirty rats in each group, to prepare angiotensin II-induced hypertensive model rats. The blood pressure of rats was measured by the multianimal multichannel tail cuff noninvasive blood pressure system of Kent Coda, USA. The Ionoptix single-cell contraction detection system was used to detect myocardial cells. ATP level of left ventricular cardiomyocytes was determined by luminescence method, and protein was measured by Western blot. Results. Compared with the sham group, systolic blood pressure and diastolic blood pressure were increased in the hypertensive group over 4 weeks; PA increased the contractility of left ventricular cardiomyocytes in normal rats, but not in hypertensive rats, and PA increased the intracellular ATP level of rats in the sham group but not in the hypertension group. In the hypertension group, the expression of nNOS in the cardiomyocytes was significantly increased, and specific nNOS inhibitor S-methyl-L-thiocitrulline (SMTC) was found to restore the positive inotropic effect of PA in the myocardium of the hypertension group. PA was supplemented after using CPT-1 inhibitor etomoxir (ETO); it was found that ETO inhibited the positive inotropic effect of PA on left ventricular cardiomyocytes in the sham group, and PA was supplemented after using SMTC and ETO, it was found that SMTC + ETO could inhibit the positive inotropic effect of PA on left ventricular cardiomyocytes in myocardium of hypertensive rats. Conclusion. PA could increase the contractility of healthy cardiomyocytes, but had no obvious positive effect on the cardiomyocytes of hypertensive rats, PA enhanced the contractility of cardiomyocytes by increasing ATP level in them, and the inhibitory effect of PA on myocardial contractility in hypertensive rats may be related to the increased nNOS and CPT-1 in cardiomyocytes.

Vitexin Anew Antihypertensive Drug (Isolated from prosopis farcta [Iraq endogenus] plants)

Vitexin was isolated and identified from pods of prosopis farcta (Iraqi endogenous). In vitro and in vivo cardiovascular actions of vitexin were studied. Vitexin produced positive inotropic effect which was not related to B1 adrenergic receptor activation. Vitexin has a vasodilator activities and it could reverse thevasoconstrictor response of isolated pulmonary artery to potassium chloride and phenylphrine. Vitexin has produced a significant increase in ejection fraction in volunteers with mild heart failure. Also vitexin has produced a significant increase in urinary flow and urinary sodium and potassium excretions in healthy and mild hypertensive volunteers, it’s significantly reduced mean arterial blood pressure of the mild hypertensive volunteers. The positive inotropic effect of vitexin is most properly related to the inhibition of phosphodiesterase enzyme by vitexin. The vasodilator activities of vitexin could be mostly associated to the increase in cGMP (attributed to phosphodiesterase inhibitory effect of vitexin) and the activation of K+-channels. The diuretic effects of vitexin could be attributed to the inhibition of Na-Cl symporter system in the renal distal tubule. The most likely mechanisms of action of vitexin as a hypotensive compound are through its vasodilator and diuretic effects. So this agent could be a best new antihypertensive drug compared with present antihypertensive drugs which are in the market now. In addition to that vitexin can be used in heart failure as cardiotonic drug