dP/dt(max)--a measure of 'baroinometry'

Amplification of Cardioprotective Response of Remote Ischemic Preconditioning in Rats by Quercetin: Potential Role of Activation of mTOR-dependent Autophagy and Nrf2

OBJECTIVES

Noninvasive remote ischemic preconditioning (RIPC) is a practical, acceptable, and feasible conditioning technique reported to provide cardioprotection in myocardial ischemia-reperfusion injury (MIRI). It has been well-reported that quercetin possesses antioxidant and anti-inflammatory properties. This study investigates the modification of the cardioprotective response of RIPC by quercetin.

METHODS

Adult Wistar rats were randomized into 12 groups of six animals each. MIRI was induced by subjecting the isolated hearts of Wistar rats to global ischemia for 30 min, succeeded by reperfusion of 120 min after mounting on the Langendorff PowerLab apparatus. Hind limb RIPC was applied in four alternate cycles of ischemia and reperfusion of 5 min each by tying the pressure cuff before isolation of hearts.

RESULTS

MIRI was reflected by significantly increased infarct size, LDH-1, and CK-MB, TNF-α, TBARS, and decreased GSH, catalase, and hemodynamic index, and modulated Nrf2. Pretreatment of quercetin (25 and 50 mg/kg; i.p.) significantly attenuated the MIRI-induced cardiac damage and potentiated the cardioprotective response of RIPC at the low dose. Pretreatment of ketamine (10 mg/kg; i.p.), an mTOR-dependent autophagy inhibitor, significantly abolished the cardioprotective effects of quercetin and RIPC.

CONCLUSIONS

The findings highlight the modification of the cardioprotective effect of RIPC by quercetin and that quercetin protects the heart against MIRI through multiple mechanisms, including mTOR-dependent activation of autophagy and Nrf-2 activation.

Peracute Myocardial Infarction: Features of the Influence of α2-Adrenoreceptor Stimulation on the Isolated Heart

We performed a comparative analysis of the effect of α2-adrenoreceptor stimulation on the performance of Langendorff-isolated heart from rats with experimental myocardial infarction in the acute stage and sham-operated animals (control). In animals with peracute myocardial infarction, different agonist concentrations (clonidine, 10-6 and 10-9 M) produced a multidirectional effect on the left-ventricular developed pressure and speed and time parameters of heart contractility. In control rats, both concentrations of the agonist added to the perfused solution reduced contraction force. Clonidine in a concentration of 10-6 M reduced HR in both groups and in a concentration of 10-9 M, it decreased HR in control rats and caused multidirectional changes in rats with myocardial infarction. The coronary flow decreased in all series of experiments.

Hypercontractile Cardiac Phenotype in Mice with Migraine-Associated Mutation in the Na+,K+-ATPase α2-Isoform

Two α-isoforms of the Na⁺,K⁺-ATPase (α₁ and α₂) are expressed in the cardiovascular system, and it is unclear which isoform is the preferential regulator of contractility. Mice heterozygous for the familial hemiplegic migraine type 2 (FHM2) associated mutation in the α₂-isoform (G301R; α₂^+/G301R mice) have decreased expression of cardiac α₂-isoform but elevated expression of the α₁-isoform. We aimed to investigate the contribution of the α₂-isoform function to the cardiac phenotype of α₂^+/G301R hearts. We hypothesized that α₂^+/G301R hearts exhibit greater contractility due to reduced expression of cardiac α₂-isoform. Variables for contractility and relaxation of isolated hearts were assessed in the Langendorff system without and in the presence of ouabain (1 µM). Atrial pacing was performed to investigate rate-dependent changes. The α₂^+/G301R hearts displayed greater contractility than WT hearts during sinus rhythm, which was rate-dependent. The inotropic effect of ouabain was more augmented in α₂^+/G301R hearts than in WT hearts during sinus rhythm and atrial pacing. In conclusion, cardiac contractility was greater in α₂^+/G301R hearts than in WT hearts under resting conditions. The inotropic effect of ouabain was rate-independent and enhanced in α₂^+/G301R hearts, which was associated with increased systolic work.

Augmented Ouabain-Induced Vascular Response Reduces Cardiac Efficiency in Mice with Migraine-Associated Mutation in the Na+, K+-ATPase α2-Isoform

Heterozygous mice (α₂^+/G301R mice) for the migraine-associated mutation (G301R) in the Na⁺,K⁺-ATPase α₂-isoform have decreased expression of cardiovascular α₂-isoform. The α₂^+/G301R mice exhibit a pro-contractile vascular phenotype associated with decreased left ventricular ejection fraction. However, the integrated functional cardiovascular consequences of this phenotype remain to be addressed in vivo. We hypothesized that the vascular response to α₂-isoform-specific inhibition of the Na⁺,K⁺-ATPase by ouabain is augmented in α₂^+/G301R mice leading to reduced cardiac efficiency. Thus, we aimed to assess the functional contribution of the α₂-isoform to in vivo cardiovascular function of wild-type (WT) and α₂^+/G301R mice. Blood pressure, stroke volume, heart rate, total peripheral resistance, arterial dP/dt, and systolic time intervals were assessed in anesthetized WT and α₂^+/G301R mice. To address rate-dependent cardiac changes, cardiovascular variables were compared before and after intraperitoneal injection of ouabain (1.5 mg/kg) or vehicle during atrial pacing. The α₂^+/G301R mice showed an enhanced ouabain-induced increase in total peripheral resistance associated with reduced efficiency of systolic development compared to WT. When the hearts were paced, ouabain reduced stroke volume in α₂^+/G301R mice. In conclusion, the ouabain-induced vascular response was augmented in α₂^+/G301R mice with consequent suppression of cardiac function.

Integrative physiological study of adaptations induced by aerobic physical training in hypertensive hearts

Aerobic physical training reduces arterial pressure in patients with hypertension owing to integrative systemic adaptations. One of the key factors is the decrease in cardiac sympathetic influence. Thus, we hypothesized that among other causes, cardiac sympathetic influence reduction might be associated with intrinsic cardiac adaptations that provide greater efficiency. Therefore, 14 spontaneously hypertensive rats (SHR group) and 14 normotensive Wistar Kyoto rats (WKY group) were used in this study. Half of the rats in each group were trained to swim for 12 weeks. All animals underwent the following experimental protocols: double blockade of cardiac autonomic receptors with atropine and propranolol; echocardiography; and analysis of coronary bed reactivity and left ventricle contractility using the Langendorff technique. The untrained SHR group had a higher sympathetic tone, cardiac hypertrophy, and reduced ejection fraction compared with the untrained WKY group. In addition, reduced coronary bed reactivity due to increased flow, and less ventricular contractile response to dobutamine and salbutamol administration were observed. The trained SHR group showed fewer differences in echocardiographic parameters as the untrained SHR group. However, the trained SHR group showed a reduction in the cardiac sympathetic influence, greater coronary bed reactivity, and increased left intraventricular pressure. In conclusion, aerobic physical training seems to reduce cardiac sympathetic influence and increase contractile strength in SHR rats, besides the minimal effects on cardiac morphology. This reduction suggests intrinsic cardiac adaptations resulting in beneficial adjustments of coronary bed reactivity associated with greater left ventricular contraction.

A novel cardiovascular systems model to quantify drugs effects on the inter‐relationship between contractility and other hemodynamic variables

The use of systems‐based pharmacological modeling approaches to characterize mode‐of‐action and concentration‐effect relationships for drugs on specific hemodynamic variables has been demonstrated. Here, we (i) expand a previously developed hemodynamic system model through integration of cardiac output (CO) with contractility (CTR) using pressure‐volume loop theory, and (ii) evaluate the contribution of CO data for identification of system‐specific parameters, using atenolol as proof‐of‐concept drug. Previously collected experimental data was used to develop the systems model, and included measurements for heart rate (HR), CO, mean arterial pressure (MAP), and CTR after administration of atenolol (0.3–30 mg/kg) from three in vivo telemetry studies in conscious Beagle dogs. The developed cardiovascular (CVS)‐contractility systems model adequately described the effect of atenolol on HR, CO, dP/dtmax, and MAP dynamics and allowed identification of both system‐ and drug‐specific parameters with good precision. Model parameters were structurally identifiable, and the true mode of action can be identified properly. Omission of CO data did not lead to a significant change in parameter estimates compared to a model that included CO data. The newly developed CVS‐contractility systems model characterizes short‐term drug effects on CTR, CO, and other hemodynamic variables in an integrated and quantitative manner. When the baseline value of total peripheral resistance is predefined, CO data was not required to identify drug‐ and system‐specific parameters. Confirmation of the consistency of system‐specific parameters via inclusion of data for additional drugs and species is warranted. Ultimately, the developed model has the potential to be of relevance to support translational CVS safety studies.

Trastuzumab-Induced Negative Chronotropic and Lusitropic Effects in Cynomolgus Monkeys

ABSTRACT

Treatment with trastuzumab, an antihuman epidermal growth factor receptor type 2 humanized monoclonal antibody, has been associated with heart failure in certain patients with cancer; however, the mechanism underlying trastuzumab-induced cardiac dysfunction remains unclear. This study was conducted to clarify the cardiac effects of trastuzumab in cynomolgus monkeys, which are commonly used as cross-reactive species in preclinical safety evaluation. Monkeys were treated with trastuzumab weekly for 1 month (5 doses in total). At first and fifth doses for pressure-volume loop analysis, trastuzumab at 20 mg·kg-1·10 min-1, equivalent to the human therapeutic dose, was administered intravenously to isoflurane-anesthetized animals, followed by 60 mg·kg-1·10 min-1 at a 30-minute interval. The other doses were fixed at 80 mg·kg-1·10 min-1 under unanesthetized conditions. After the first dose, reduced heart rate, decreases in maximal rate of fall of left ventricular pressure, and prolonged time constant for isovolumic relaxation, which are predictors of drug-induced changes in lusitropy, were observed at 20 and 60 mg·kg-1. The changes after the fifth dose were comparable with those after the first dose, indicating trastuzumab did not show exacerbation of cardiac function during the 1-month trial. No significant changes in slope of preload recruitable stroke work, which is a load-independent inotropic parameter, were observed at either dose. In conclusion, trastuzumab-induced little inotropic effect but induced negative chronotropic or lusitropic effects in monkeys, which might be associated with impaired left ventricular diastolic function.

Pharmacodynamics and Pharmacokinetics of Injectable Pimobendan and Its Metabolite, O-Desmethyl-Pimobendan, in Healthy Dogs

Objectives: This study was designed to thoroughly evaluate the effects of bolus pimobendan at a dose of 0.15 mg/kg on cardiac functions, hemodynamics, and electrocardiographic parameters together with the pharmacokinetic profile of pimobendan and its active metabolite, o-desmethyl-pimobendan (ODMP), in anesthetized dogs.

Methods: Nine beagle dogs were anesthetized and instrumented to obtain left ventricular pressures, aortic pressures, cardiac outputs, right atrial pressures, pulmonary arterial pressures, pulmonary capillary wedge pressures, electrocardiograms. After baseline data were collected, dogs were given a single bolus of pimobendan, and the pharmacodynamic parameters were obtained at 10, 20, 30, 60, and 120 min. Meanwhile, the venous blood was collected at baseline and 2, 5, 10, 20, 30, 60, 120, 180, 360, and 1,440 min after administration for the determination of pharmacokinetic parameters.

Results: Compared with baseline measurements, the left ventricular inotropic indices significantly increased in response to intravenous pimobendan, as inferred from the maximum rate of rise in the left ventricular pressure and the contractility index. Conversely, the left ventricular lusitropic parameters significantly decreased, as inferred from the maximum rate of fall in the left ventricular pressure and the left ventricular relaxation time constant. Significant increases were also noted in cardiac output and systolic blood pressure. Decreases were observed in the systemic vascular resistance, pulmonary vascular resistance, left ventricular end-diastolic pressure, pulmonary capillary wedge pressure, right atrial pressure, and pulmonary arterial pressure. The heart rate increased, but the PQ interval decreased. There was no arrhythmia during the observed period (2 h). The mean maximum plasma concentration (in μg/L) for ODMP was 30.0 ± 8.8. Pimobendan exerted large volume of distribution ~9 L/kg.

Conclusions: Intravenous pimobendan at the recommended dose for dogs increased cardiac contraction and cardiac output, accelerated cardiac relaxation but decreased both vascular resistances. These mechanisms support the use of injectable pimobendan in acute heart failure.

RGFP966 inactivation of the YAP pathway attenuates cardiac dysfunction induced by prolonged hypothermic preservation

Oxidative stress and apoptosis are the key factors that limit the hypothermic preservation time of donor hearts to within 4-6 h. The aim of this study was to investigate whether the histone deacetylase 3 (HDAC3) inhibitor RGFP966 could protect against cardiac injury induced by prolonged hypothermic preservation. Rat hearts were hypothermically preserved in Celsior solution with or without RGFP966 for 12 h followed by 60 min of reperfusion. Hemodynamic parameters during reperfusion were evaluated. The expression and phosphorylation levels of mammalian STE20-like kinase-1 (Mst1) and Yes-associated protein (YAP) were determined by western blotting. Cell apoptosis was measured by the terminal deoxynucleotidyl-transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) method. Addition of RGFP966 in Celsior solution significantly inhibited cardiac dysfunction induced by hypothermic preservation. RGFP966 inhibited the hypothermic preservation-induced increase of the phosphorylated (p)-Mst1/Mst1 and p-YAP/YAP ratios, prevented a reduction in total YAP protein expression, and increased the nuclear YAP protein level. Verteporfin (VP), a small molecular inhibitor of YAP-transcriptional enhanced associate domain (TEAD) interaction, partially abolished the protective effect of RGFP966 on cardiac function, and reduced lactate dehydrogenase activity and malondialdehyde content. RGFP966 increased superoxide dismutase, catalase, and glutathione peroxidase gene and protein expression, which was abolished by VP. RGFP966 inhibited hypothermic preservation-induced overexpression of B-cell lymphoma protein 2 (Bcl-2)-associated X (Bax) and cleaved caspase-3, increased Bcl-2 mRNA and protein expression, and reduced cardiomyocyte apoptosis. The antioxidant and anti-apoptotic effects of RGFP966 were cancelled by VP. The results suggest that supplementation of Celsior solution with RGFP966 attenuated prolonged hypothermic preservation-induced cardiac dysfunction. The mechanism may involve inhibition of oxidative stress and apoptosis via inactivation of the YAP pathway.

CX3CR1 is a prerequisite for the development of cardiac hypertrophy and left ventricular dysfunction in mice upon transverse aortic constriction

The CX3CL1/CX3CR1 axis mediates recruitment and extravasation of CX3CR1-expressing subsets of leukocytes and plays a pivotal role in the inflammation-driven pathology of cardiovascular disease. The cardiac immune response differs depending on the underlying causes. This suggests that for the development of successful immunomodulatory therapy in heart failure due to chronic pressure overload induced left ventricular (LV) hypertrophy, the underlying immune patterns must be examined. Here, the authors demonstrate that Fraktalkine-receptor CX3CR1 is a prerequisite for the development of cardiac hypertrophy and left ventricular dysfunction in a mouse model of transverse aortic constriction (TAC). The comparison of C57BL/6 mice with CX3CR1 deficient mice displayed reduced LV hypertrophy and preserved cardiac function in response to pressure overload in mice lacking CX3CR1. Moreover, the normal immune response following TAC induced pressure overload which is dominated by Ly6C^low macrophages changed to an early pro-inflammatory immune response driven by neutrophils, Ly6C^high macrophages and altered cytokine expression pattern in CX3CR1 deficient mice. In this early inflammatory phase of LV hypertrophy Ly6C^high monocytes infiltrated the heart in response to a C-C chemokine ligand 2 burst. CX3CR1 expression impacts the immune response in the development of LV hypertrophy and its absence has clear cardioprotective effects. Hence, suppression of CX3CR1 may be an important immunomodulatory therapeutic target to ameliorate pressure-overload induced heart failure.

Semi-mechanistic modelling platform to assess cardiac contractility and haemodynamics in preclinical cardiovascular safety profiling of new molecular entities

BACKGROUND AND PURPOSE

Cardiovascular safety is one of the most frequent causes of safety-related attrition both preclinically and clinically. Preclinical cardiovascular safety is routinely assessed using dog telemetry monitoring key cardiovascular functions. The present research was to develop a semi-mechanistic modelling platform to simultaneously assess changes in contractility (dPdt_max ), heart rate (HR) and mean arterial pressure (MAP) in preclinical studies.

EXPERIMENTAL APPROACH

Data from dPdt_max , HR, preload (left ventricular end-diastolic pressure [LVEDP]) and MAP were available from dog telemetry studies after dosing with atenolol (n = 27), salbutamol (n = 5), L-N^G -nitroarginine methyl ester (L-NAME; n = 4), milrinone (n = 4), verapamil (n = 12), dofetilide (n = 8), flecainide (n = 4) and AZ001 (n = 14). Literature model for rat CV function was used for the structural population pharmacodynamic model development. LVEDP was evaluated as covariate to account for the effect of preload on dPdt_max .

KEY RESULTS

The model was able to describe drug-induced changes in dPdt_max , HR and MAP for all drugs included in the developed framework adequately, by incorporating appropriate drug effects on dPdt_max , HR and/or total peripheral resistance. Consistent with the Starling's law, incorporation of LVEDP as a covariate on dPdt_max to correct for the preload effect was found to be statistically significant.

CONCLUSIONS AND IMPLICATIONS

The contractility and haemodynamics semi-mechanistic modelling platform accounts for diurnal variation, drug-induced changes and inter-animal variation. It can be used to hypothesize and evaluate pharmacological effects and provide a holistic cardiovascular safety profile for new drugs.

Reducing Aortic Barotrauma and Vascular Extracellular Matrix Degradation by Pacemaker-Mediated QRS Widening

Background

The extent of pressure‐related damage might be related to acceleration rate of the applied pressure (peak dP/dt) in the vascular system. In this study, we sought to determine whether dP/dt applied to the aortic wall (aortic dP/dt) and in turn vascular extracellular matrix degradation can be mitigated via modulation of left ventricular (LV) contractility (LV dP/dt) by pacemaker‐mediated desynchronization.

Methods and Results

First, in 34 patients, changes in aortic dP/dt values in 3 aortic segments in response to pacemaker‐mediated stepwise QRS widening leading to gradual desynchronization of the LV contraction by means of steadily changed atrioventricular delay (AVD) with temporary dual‐chamber pacing was examined before and after beta‐blocker (15 mg IV metoprolol) administration. Second, serum matrix metalloproteinase‐9 levels were measured in the 20 patients with permanent pacemaker while they were on sinus rhythm with normal QRS width and 3 weeks after wide QRS rhythm ensured by dual pacing, dual sensing, and dual response to sensing with short AVD. LV dP/dt substantially correlated with dP/dt measured in ascending (r=0.83), descending (r=0.89), and abdominal aorta (r=0.96). QRS width strongly correlated with dP/dt measured in ascending (r=−0.95), descending (r=−0.92), and abdominal (r=−0.96) aortic segments as well. In patients with permanent pacemaker, wide QRS rhythm led to a significant reduction in serum matrix metalloproteinase‐9 levels (from 142.5±32.9 pg/mL to 87.5±32.4 pg/mL [P<0.001]) at the end of 3 weeks follow‐up.

Conclusions

QRS prolongation by short AVD dual pacing, dual sensing, and dual response to sensing results in concomitant decreases in peak dP/dt values in the LV and in all aortic segments with or without background beta‐blocker administration, which in turn led to a significant reduction in circulating matrix metalloproteinase‐9 levels.

Registration

URL: https://www.clini​caltr​ials.gov; Unique identifier: NCT03665558.

Exenatide promotes cardiac lncRNAs HOX transcript antisense RNA (HOTAIR) in Wistar rats with liver cirrhosis; a novel role of GLP-1 receptor agonists in cirrhotic cardiomyopathy

Long acting non-coding RNAs lncRNAs HOX Transcript Antisense RNA (HOTAIR) is cardioprotective and mediates its effect through sirtulin 1 (SIRT1). The decrease in HOTAIR expression predisposes to various types of cardiomyopathy. We aimed to investigate whether decrease HOTAIR expression is involved in cirrhotic cardiomyopathy or not and the role of glucagon like peptide 1 receptor (GLP-1 receptor) in facilitating its effect through studying the effect of a exenatide (EXA), on cardiac function as well as the expression of some relevant bio-molecules. Rats were used and divided into: naïve, EXA, Thioacetamide (TAA) and TAA + EXA groups. ECG, dobutamine stress test (DST) were done. AST, ALT, fasting blood glucose, troponin I were measured. Cardiac HOTAIR & SIRT1, hepatic and cardiac GLP-1 receptor expression levels were investigated in addition to histological studies. Our results showed that EXA administration in control rats produced no significant changes. TAA induced cirrhosis with insulin resistance and significant changes in cardiac functions. GLP-1 receptor, HOTAIR and SIRT1 expression in cardiac tissue were significantly decreased with a significant increase in troponin I. EXA + TAA group showed a restoration of the hepatic architecture and function. EXA treatment produced significant improvement in cardiac parameters and was associated with increasing the expression of cardiac GLP-1 receptor, HOTAIR. The cardiac muscle showed an apparent decrease in collagen fibers. So we can conclude that EXA promotes the protective effect of HOTAIR on cardiac structure and function in rat model of cirrhosis which may introduce a new therapeutic strategy in cirrhotic cardiomyopathy.

Chemically synthesized Secoisolariciresinol diglucoside (LGM2605) improves mitochondrial function in cardiac myocytes and alleviates septic cardiomyopathy

Sepsis is the overwhelming systemic immune response to infection, which can result in multiple organ dysfunction and septic shock. Myocardial dysfunction during sepsis is associated with advanced disease and significantly increased in-hospital mortality. Our group has shown that energetic failure and excess reactive oxygen species (ROS) generation constitute major components of myocardial dysfunction in sepsis. Because ROS production is central to cellular metabolic health, we tested if the synthetic anti-oxidant lignan secoisolariciresinol diglucoside (SDG; LGM2605) would alleviate septic cardiac dysfunction and investigated the underlying mechanism. Using the cecal ligation and puncture (CLP) mouse model of peritonitis-induced sepsis, we observed impairment of cardiac function beginning at 4 h post-CLP surgery. Treatment of mice with LGM2605 (100 mg/kg body weight, i.p.) 6 h post-CLP surgery reduced cardiac ROS accumulation and restored cardiac function. Assessment of mitochondrial respiration (Seahorse XF) in primary cardiomyocytes obtained from adult C57BL/6 mice that had undergone CLP and treatment with LGM2605 showed restored basal and maximal respiration, as well as preserved oxygen consumption rate (OCR) associated with spare capacity. Further analyses aiming to identify the cellular mechanisms that may account for improved cardiac function showed that LGM2605 restored mitochondria abundance, increased mitochondrial calcium uptake and preserved mitochondrial membrane potential. In addition to protecting against cardiac dysfunction, daily treatment with LGM2605 and antibiotic ertapenem (70 mg/kg) protected against CLP-associated mortality and reversed hypothermia when compared against mice receiving ertapenem and saline. Therefore, treatment of septic mice with LGM2605 emerges as a novel pharmacological approach that reduces cardiac ROS accumulation, protects cardiac mitochondrial function, alleviates cardiac dysfunction, and improves survival.

Exploring the putative role of TRPV1 -dependent CGRP release in remote hind preconditioning-induced cardioprotection

BACKGROUND

Remote ischemic preconditioning (RIPC) is a phenomenon whereby transient nonlethal ischemia and reperfusion episodes confer protection against prolonged ischemia reperfusion-induced injury. However, the underlying intracellular signaling has not been extensively explored.

OBJECTIVE

This study aimed to inspect the putative involvement of TRPV₁ -dependent CGRP release in mediating remote hind limb preconditioning-induced cardioprotection.

METHODS

In this study, remote hind limb preconditioning stimulus was delivered (four consecutive episodes of 5 minutes of ischemia reperfusion) using a blood pressure cuff tied at the inguinal level of the rat. The isolated rat hearts were perfused on the Langendorff's system and were subjected to 30-minutes global ischemia and 120-minutes reperfusion. Prolonged ischemia and subsequent reperfusion led to myocardial injury that was evaluated in terms of infarct size, LDH release, CK release, LVDP, +dp/dt_max , -dp/dt_min , and coronary flow rate. The pharmacological agents used in this study included capsaicin as TRPV₁ channel activator, sumatriptan and CGRP8-37 as CGRP blockers.

RESULTS

Remote hind limb and capsaicin preconditioning (10 mg/kg^-1 ) significantly reduced the infarct size, LDH release, CK release and significantly improved LVDP, +dp/dt_max , -dp/dt_min , and coronary flow rate. However, remote hind limb and capsaicin preconditioning-induced cardioprotective effects were remarkably reduced in the presence of sumatriptan (8 mg/kg^-1 ) and CGRP8-37 (1 mg/kg^-1 ).

CONCLUSION

This indicates that remote hind limb preconditioning stimulus probably activates TRPV₁ channels which subsequently induces CGRP release to produce cardioprotective effects.

Effect of Transmural Differences in Excitation-Contraction Delay and Contraction Velocity on Left Ventricle Isovolumic Contraction: A Simulation Study

Recent studies have shown that left ventricle (LV) exhibits considerable transmural differences in active mechanical properties induced by transmural differences in electrical activity, excitation-contraction coupling, and contractile properties of individual myocytes. It was shown that the time between electrical and mechanical activation of myocytes (electromechanical delay: EMD) decreases from subendocardium to subepicardium and, on the contrary, the myocyte shortening velocity (MSV) increases in the same direction. To investigate the physiological importance of this inhomogeneity, we developed a new finite element model of LV incorporating the observed transmural gradients in EMD and MSV. Comparative simulations with the model showed that when EMD or MSV or both were set constant across the LV wall, the LV contractility during isovolumic contraction (IVC) decreased significantly ((dp/dt)max⁡  was reduced by 2 to 38% and IVC was prolonged by 18 to 73%). This was accompanied by an increase of transmural differences in wall stress. These results suggest that the transmural differences in EMD and MSV play an important role in physiological contractility of LV by synchronising the contraction of individual layers of ventricular wall during the systole. Reduction or enhancement of these differences may therefore impair the function of LV and contribute to heart failure.

Investigating the involvement of glycogen synthase kinase-3β and gap junction signaling in TRPV1 and remote hind preconditioning-induced cardioprotection

Remote ischemic preconditioning (RIPC) is the phenomenon that harnesses the body's endogenous protective mechanisms against prolonged ischemia-reperfusion-induced injury. The present study aimed to explore the involvement of glycogen synthase kinase-3β and gap junction signaling in TRPV₁ and remote hind preconditioning-induced cardioprotection. In the present study, four consecutive cycles (5min of ischemia-reperfusion) of remote hind limb preconditioning stimulus were delivered using a blood pressure cuff fastened at the inguinal level of the rat. The isolated rat hearts were mounted on the Langendorff's apparatus and were exposed to 30min of global ischemia-120min of reperfusion. Sustained ischemia-reperfusion led to cardiac injury that was assessed in terms of infarct size, LDH release, CK release, LVDP, +dp/dt_max, -dp/dt_min, heart rate and coronary flow rate. The pharmacological agents employed in the present study included capsaicin (10mg/kg) as TRPV₁ channel activator, AR-A014418 (1 and 3mg/kg) as glycogen synthase kinase-3β inhibitor and carbenoxolone disodium (50 and 100mg/kg) as gap junction blocker. Remote hind limb, capsaicin and AR-A014418 preconditioning led to significant reduction in the infarct size, LDH release, CK release and improved LVDP, +dp/dt_max, -dp/dt_min, heart rate and coronary flow rate. However, remote hind limb, capsaicin and AR-A014418 preconditioning-induced cardioprotective effects were remarkably reduced in the presence of carbenoxolone (100mg/kg). This indicates that remote preconditioning stimulus probably activates TRPV₁ channels that may inhibit glycogen synthase kinase-3β activity which subsequently enhances gap junction coupling to produce cardioprotective effects.

Gadolinium and ruthenium red attenuate remote hind limb preconditioning-induced cardioprotection: possible role of TRP and especially TRPV channels

Remote ischemic preconditioning is a well reported therapeutic strategy that induces cardioprotective effects but the underlying intracellular mechanisms have not been widely explored. The current study was designed to investigate the involvement of TRP and especially TRPV channels in remote hind limb preconditioning-induced cardioprotection. Remote hind limb preconditioning stimulus (4 alternate cycles of inflation and deflation of 5 min each) was delivered using a blood pressure cuff tied on the hind limb of the anesthetized rat. Using Langendorff's system, the heart was perfused and subjected to 30-min ischemia and 120-min reperfusion. The myocardial injury was assessed by measuring infarct size, lactate dehydrogenase (LDH), creatine kinase (CK), LVDP, +dp/dtmax, -dp/dtmin, heart rate, and coronary flow rate. Gadolinium, TRP blocker, and ruthenium red, TRPV channel blocker, were employed as pharmacological tools. Remote hind limb preconditioning significantly reduced the infarct size, LDH release, CK release and improved coronary flow rate, hemodynamic parameters including LVDP, +dp/dtmax, -dp/dtmin, and heart rate. However, gadolinium (7.5 and 15 mg kg(-1)) and ruthenium red (4 and 8 mg kg(-1)) significantly attenuated the cardioprotective effects suggesting the involvement of TRP especially TRPV channels in mediating remote hind limb preconditioning-induced cardioprotection. Remote hind limb preconditioning stimulus possibly activates TRPV channels on the heart or sensory nerve fibers innervating the heart to induce cardioprotective effects. Alternatively, remote hind limb preconditioning stimulus may also activate the mechanosensitive TRP and especially TRPV channels on the sensory nerve fibers innervating the skeletal muscles to trigger cardioprotective neurogenic signaling cascade. The cardioprotective effects of remote hind limb preconditioning may be mediated via activation of mechanosensitive TRP and especially TRPV channels.

Overexpression myocardial inducible nitric oxide synthase exacerbates cardiac dysfunction and beta-adrenergic desensitization in experimental hypothyroidism

BACKGROUND

Altered nitric oxide synthase (NOS) has been implicated in the pathophysiology of heart failure (HF). Recent evidence links hypothyroidism to the pathology of HF. However, the precise mechanisms are incompletely understood. The alterations and functional effects of cardiac NOS in hypothyroidism are unknown. We tested the hypothesis that hypothyroidism increases cardiomyocyte inducible NOS (iNOS) expression, which plays an important role in hypothyroidism-induced depression of cardiomyocyte contractile properties, [Ca(2+)]i transient ([Ca(2+)]iT), and β-adrenergic hyporesponsiveness.

METHODS AND RESULTS

We simultaneously evaluated LV functional performance and compared myocyte three NOS, β-adrenergic receptors (AR) and SERCA2a expressions and assessed cardiomyocyte contractile and [Ca(2+)]iT responses to β-AR stimulation with and without pretreatment of iNOS inhibitor (1400 W, 10(-5)mol/L) in 26 controls and 26 rats with hypothyroidism induced by methimazole (~30 mg/kg/day for 8 weeks in the drinking water). Compared with controls, in hypothyroidism, total serum T3 and T4 were significantly reduced followed by significantly decreased LV contractility (EES) with increased LV time constant of relaxation. These LV abnormalities were accompanied by concomitant significant decreases in myocyte contraction (dL/dtmax), relaxation (dR/dtmax), and [Ca(2+)]iT. In hypothyroidism, isoproterenol (10(-8)M) produced significantly smaller increases in dL/dtmax, dR/dtmax and [Ca(2+)]iT. These changes were associated with decreased β1-AR and SERCA2a, but significantly increased iNOS. Moreover, only in hypothyroidism, pretreatment with iNOS inhibitor significantly improved basal and isoproterenol-stimulated myocyte contraction, relaxation and [Ca(2+)]iT.

CONCLUSIONS

Hypothyroidism produces intrinsic defects of LV myocyte force-generating capacity and relaxation with β-AR desensitization. Up-regulation of cardiomyocyte iNOS may promote progressive cardiac dysfunction in hypothyroidism.

Acute effects of intravenous dronedarone on electrocardiograms, hemodynamics and cardiac functions in anesthetized dogs

Dronedarone is a class III antiarrhythmic that has been used for management of atrial fibrillation in humans, but limited information was found in dogs. The objective of this study was to determine the acute effects of escalating concentrations of dronedarone on electrocardiograms (ECG), hemodynamics and cardiac mechanics in healthy dogs. A total of 7 beagle dogs were anesthetized with isoflurane and instrumented to obtain lead II ECG, pressures at ascending aorta, right atrium, pulmonary artery and left ventricle, and left ventricular pressure-volume relationship. Five dogs were given vehicle and followed by escalating doses of dronedarone (0.5, 1.0 and 2.5 mg/kg, 15 min for each dose), and two dogs were used as a vehicle-treated control. All parameters were measured at 15 min after the end of each dose. The results showed that all parameters in vehicle-treated dogs were unaltered. Dronedarone at 2.5 mg/kg significantly lengthened PQ interval (P<0.01), reduced cardiac output (P<0.01) and increased systemic vascular resistance (P<0.01). Dronedarone produced negative inotropy assessed by significantly lowered end-systolic pressure-volume relationship, preload recruitable stroke work, contractility index and dP/dtmax. It also impaired diastolic function by significantly increased end-diastolic pressure-volume relationship, tau and dP/dtmin. These results suggested that acute effects of dronedarone produced negative dromotropy, inotropy and lusitropy in anesthetized dogs. Care should be taken when given dronedarone to dogs, especially when the patients have impaired cardiac function.

Cardiovascular safety risk assessment for new candidate drugs from functional and pathological data: Conference report

This is a report on a 2-day joint meeting between the British Society of Toxicological Pathology (BSTP) and the Safety Pharmacology Society (SPS) held in the UK in November 2013. Drug induced adverse effects on the cardiovascular system are associated with the attrition of more marketed and candidate drugs than any other safety issue. The objectives of this meeting were to foster inter-disciplinary approaches to address cardiovascular risk assessment, improve understanding of the respective disciplines, and increase awareness of new technologies. These aims were achieved. This well attended meeting covered both 'purely functional' cardiovascular adverse effects of drugs (e.g., electrophysiological and haemodynamic changes) as well as adverse effects encompassing both functional and pathological changes. Most of the presentations focused on nonclinical safety data, with information on translation to human where known. To reflect the content of the presentations we have cited key references and review articles.

Cardiac Catheterization in Mice to Measure the Pressure Volume Relationship: Investigating the Bowditch Effect

Animal models that mimic human cardiac disorders have been created to test potential therapeutic strategies. A key component to evaluating these strategies is to examine their effects on heart function. There are several techniques to measure in vivo cardiac mechanics (e.g., echocardiography, pressure/volume relations, etc.). Compared to echocardiography, real-time left ventricular (LV) pressure/volume analysis via catheterization is more precise and insightful in assessing LV function. Additionally, LV pressure/volume analysis provides the ability to instantaneously record changes during manipulations of contractility (e.g., β-adrenergic stimulation) and pathological insults (e.g., ischemia/reperfusion injury). In addition to the maximum (+dP/dt) and minimum (-dP/dt) rate of pressure change in the LV, an accurate assessment of LV function via several load-independent indexes (e.g., end systolic pressure volume relationship and preload recruitable stroke work) can be attained. Heart rate has a significant effect on LV contractility such that an increase in the heart rate is the primary mechanism to increase cardiac output (i.e., Bowditch effect). Thus, when comparing hemodynamics between experimental groups, it is necessary to have similar heart rates. Furthermore, a hallmark of many cardiomyopathy models is a decrease in contractile reserve (i.e., decreased Bowditch effect). Consequently, vital information can be obtained by determining the effects of increasing heart rate on contractility. Our and others data has demonstrated that the neuronal nitric oxide synthase (NOS1) knockout mouse has decreased contractility. Here we describe the procedure of measuring LV pressure/volume with increasing heart rates using the NOS1 knockout mouse model.

The evaluation of drug-induced changes in cardiac inotropy in dogs: Results from a HESI-sponsored consortium

INTRODUCTION

Drug-induced effects on the cardiovascular system remain a major cause of drug attrition. While hemodynamic (blood pressure (BP) and heart rate (HR)) and electrophysiological methods have been used in testing drug safety for years, animal models for assessing myocardial contractility are used less frequently and their translation to humans has not been established. The goal of these studies was to determine whether assessment of contractility and hemodynamics, when measured across different laboratories using the same protocol, could consistently detect drug-induced changes in the inotropic state of the heart using drugs known to have clinically relevant positive and negative effects on myocardial contractility.

METHODS

A 4×4 double Latin square design (n=8) design using Beagle dogs was developed. Drugs were administrated orally. Arterial blood pressure, left ventricular pressure (LVP) and the electrocardiogram were assessed. Each of the six laboratories studied at least 2 drugs (one positive inotrope (pimobendan or amrinone) and one negative inotrope) (itraconazole or atenolol) at 3 doses selected to match clinical exposure data and a vehicle control. Animals were instrumented with an ITS telemetry system, DSI's D70-PCTP system or DSI's Physiotel Digital system. Data acquisition and analysis systems were Ponemah, Notocord or EMKA.

RESULTS

Derived parameters included: diastolic, systolic and mean arterial BP, peak systolic LVP, HR, end-diastolic LVP, and LVdP/dtmax as the primary contractility index. Blood samples were drawn to confirm drug exposures predicted from independent pharmacokinetic studies. Across the laboratories, a consistent change in LVdP/dtmax was captured despite some differences in the absolute values of some of the hemodynamic parameters prior to treatment.

DISCUSSION

These findings indicate that this experimental model, using the chronically instrumented conscious dog, can accurately and consistently detect changes in cardiac contractility, across multiple sites and instrumentation systems, and that data obtained in this model may also translate to clinical outcomes.

Haemodynamic Assessment in Safety Pharmacology

Evaluation of the effects of a drug on arterial blood pressure is important in nonclinical safety pharmacology assessment. Detecting large and obvious changes in blood pressure is an unchallenging task. Detecting small changes is more difficult, and interpretation of findings requires careful risk/benefit evaluation. Detecting subtle and small changes in blood pressure is important in particular with respect to increases, since blood pressure above the normal range is associated with increased risk of stroke and sudden cardiac death. Cardiovascular safety pharmacology has been preoccupied with drug-induced changes in the electrocardiogram, and by comparison, there has been little in the way of contemporaneous improvements in the level of complexity and sophistication involved in blood pressure assessment. Thus, it is important to understand the nature of drug-induced changes in blood pressure, appreciate the plethora of agents currently used clinically (and over the counter) that alter blood pressure and understand safety pharmacology study design in order to optimize assessment of a new chemical entity (NCE) or biologic agent in this context.

Drug-induced effects on cardiovascular function in pentobarbital anesthetized guinea-pigs: invasive LVP measurements versus the QA interval

INTRODUCTION

Evaluation of drug-related effects on cardiovascular function is part of the core battery described in the ICH S7A guideline. Anesthetized guinea-pigs are excellent models for the evaluation of drug-induced prolongation of ventricular repolarization; however less information is available regarding other cardio-hemodynamic parameters in this model. The current study aimed to document cardio-hemodynamic responses in anesthetized guinea-pigs after administration of a number of reference drugs with known pharmacological actions.

METHODS

Experiments were carried out in closed chest pentobarbital anesthetized female guinea-pigs. Compounds were administered intravenously while arterial blood pressure, left ventricular pressure (LVP) and the electrocardiogram were measured continuously. The rate of LVP contraction (LV dP/dt(max)) was used to evaluate cardiac performance; and was compared to the QA interval; which has previously been proposed as an indirect measurement of cardiac function.

RESULTS

Baseline values for heart rate and blood pressure were lower in anesthetized animals compared to literature data of conscious guinea-pigs. Heart rate increased after administration of adrenaline, isoprenaline and salbutamol, but not after L-phenylephrine. Verapamil and amiodarone decreased heart rate and blood pressure. Zatebradine infusion led to a decrease in heart rate with minimal effects on blood pressure. Sodium nitroprusside (SNP) caused a reduction in mean blood pressure at higher doses followed by reflex tachycardia. Both adrenaline and L-phenylephrine increased arterial blood pressure. Furthermore, adrenaline, isoprenaline and salbutamol increased LV dP/dt(max) and decreased the QA interval. L-phenylephrine increased LV dP/dt(max), but transiently prolonged the QA interval. Both verapamil and amiodarone decreased LV dP/dt(max) and prolonged the QA interval, whereas zatebradine did not affect this parameter.

DISCUSSION

In addition to its utility for the assessment of test compounds on ventricular repolarization the pentobarbital anesthetized guinea-pig model shows promise for early stage cardio-hemodynamic screening. Furthermore, the QA interval shows potential for prediction of adverse effects on cardiac contractility.

Methodological innovations expand the safety pharmacology horizon

Almost uniquely in pharmacology, drug safety assessment is driven by the need for elaboration and validation of methods for detecting drug actions. This is the 9th consecutive year that the Journal of Pharmacological and Toxicological Methods (JPTM) has published themed issues arising from the annual meeting of the Safety Pharmacology Society (SPS). The SPS is now past its 10th year as a distinct (from pharmacology to toxicology) discipline that integrates safety pharmacologists from industry with those in academia and the various global regulatory authorities. The themes of the 2011 meeting were (i) the bridging of safety assessment of a new chemical entity (NCE) between all the parties involved, (ii) applied technologies and (iii) translation. This issue of JPTM reflects these themes. The content is informed by the regulatory guidance documents (S7A and S7B) that apply prior to first in human (FIH) studies, which emphasize the importance of seeking model validation. The manuscripts encompass a broad spectrum of safety pharmacology topics including application of state-of-the-art techniques for study conduct and data processing and evaluation. This includes some exciting novel integrated core battery study designs, refinements in hemodynamic assessment, arrhythmia analysis algorithms, and additionally an overview of safety immunopharmacology, and a brief survey discussing similarities and differences in business models that pharmaceutical companies employ in safety pharmacology, together with SPS recommendations on 'best practice' for the conduct of a non-clinical cardiovascular assessment of a NCE.