Model Of Diastolic Dysfunction Research Articles

Soft robotic patient-specific hydrodynamic model of aortic stenosis and ventricular remodeling.

Aortic stenosis (AS) affects about 1.5 million people in the United States and is associated with a 5-year survival rate of 20% if untreated. In these patients, aortic valve replacement is performed to restore adequate hemodynamics and alleviate symptoms. The development of next-generation prosthetic aortic valves seeks to provide enhanced hemodynamic performance, durability, and long-term safety, emphasizing the need for high-fidelity testing platforms for these devices. We propose a soft robotic model that recapitulates patient-specific hemodynamics of AS and secondary ventricular remodeling which we validated against clinical data. The model leverages 3D-printed replicas of each patient's cardiac anatomy and patient-specific soft robotic sleeves to recreate the patients' hemodynamics. An aortic sleeve allows mimicry of AS lesions due to degenerative or congenital disease, whereas a left ventricular sleeve recapitulates loss of ventricular compliance and diastolic dysfunction (DD) associated with AS. Through a combination of echocardiographic and catheterization techniques, this system is shown to recreate clinical metrics of AS with greater controllability compared with methods based on image-guided aortic root reconstruction and parameters of cardiac function that rigid systems fail to mimic physiologically. Last, we leverage this model to evaluate the hemodynamic benefit of transcatheter aortic valves in a subset of patients with diverse anatomies, etiologies, and disease states. Through the development of a high-fidelity model of AS and DD, this work demonstrates the use of soft robotics to recreate cardiovascular disease, with potential applications in device development, procedural planning, and outcome prediction in industrial and clinical settings.

Abstract 14365: Interrogating Diastolic Dysfunction Using a Novel Stem Cell Model of Restrictive Cardiomyopathy

Introduction: Diastolic dysfunction is an important cause of morbidity and mortality in both children and adults. Unfortunately, investigation of new therapies is limited by a lack of in vitro models of diastolic dysfunction. Idiopathic Restrictive Cardiomyopathy (RCM) is a serious genetic condition in which children have an isolated defect in myocardial relaxation. Though some of the genetic lesions have been identified, there is still an incomplete understanding of the mechanisms that lead to diastolic dysfunction in this condition. Hypothesis: Cardiomyocytes from human induced pluripotent stem cells (hiPSC-CMs) derived from patients with RCM will provide an in vitro model of diastolic dysfunction and will allow elucidation of cellular and molecular pathways involved in myocardial relaxation. Methods: Patients with RCM and a known pathogenic sarcomeric mutation were identified through speaking with providers in our heart failure and cardiac transplant program. hiPSCs were derived from patient blood samples and differentiated into cardiomyocytes. Isogenic controls were generated using CRISPR-mediated homologous directed repair. Calcium handling, contraction kinetics, and resting tension of RCM hiPSC-CMs were compared to control hiPSC-CMs on substrates with defined stiffness using high-throughput quantitative imaging techniques. Results: hiPSC-CMs derived from a patient with a pathogenic mutation in troponin T (TNNT2) display prolonged calcium kinetics and relaxation times compared to controls, as well as increased resting tension. Conclusions: RCM hiPSC-CMs represent a novel model of diastolic dysfunction that can be interrogated on a high-throughput platform. We plan to use these cells to perform proteome-scale functional screens, providing a novel opportunity to discover previously unknown contributors to diastolic dysfunction.

HDAC Inhibition Reverses Preexisting Diastolic Dysfunction and Blocks Covert Extracellular Matrix Remodeling.

Diastolic dysfunction (DD) is associated with the development of heart failure and contributes to the pathogenesis of other cardiac maladies, including atrial fibrillation. Inhibition of histone deacetylases (HDACs) has been shown to prevent DD by enhancing myofibril relaxation. We addressed the therapeutic potential of HDAC inhibition in a model of established DD with preserved ejection fraction. Four weeks after uninephrectomy and implantation with deoxycorticosterone acetate pellets, when DD was clearly evident, 1 cohort of mice was administered the clinical-stage HDAC inhibitor ITF2357/Givinostat. Echocardiography, blood pressure measurements, and end point invasive hemodynamic analyses were performed. Myofibril mechanics and intact cardiomyocyte relaxation were assessed ex vivo. Cardiac fibrosis was evaluated by picrosirius red staining and second harmonic generation microscopy of left ventricle (LV) sections, RNA sequencing of LV mRNA, mass spectrometry-based evaluation of decellularized LV biopsies, and atomic force microscopy determination of LV stiffness. Mechanistic studies were performed with primary rat and human cardiac fibroblasts. HDAC inhibition normalized DD without lowering blood pressure in this model of systemic hypertension. In contrast to previous models, myofibril relaxation was unimpaired in uninephrectomy/deoxycorticosterone acetate mice. Furthermore, cardiac fibrosis was not evident in any mouse cohort on the basis of picrosirius red staining or second harmonic generation microscopy. However, mass spectrometry revealed induction in the expression of >100 extracellular matrix proteins in LVs of uninephrectomy/deoxycorticosterone acetate mice, which correlated with profound tissue stiffening based on atomic force microscopy. ITF2357/Givinostat treatment blocked extracellular matrix expansion and LV stiffening. The HDAC inhibitor was subsequently shown to suppress cardiac fibroblast activation, at least in part, by blunting recruitment of the profibrotic chromatin reader protein BRD4 (bromodomain-containing protein 4) to key gene regulatory elements. These findings demonstrate the potential of HDAC inhibition as a therapeutic intervention to reverse existing DD and establish blockade of extracellular matrix remodeling as a second mechanism by which HDAC inhibitors improve ventricular filling. Our data reveal the existence of pathophysiologically relevant covert or hidden cardiac fibrosis that is below the limit of detection of histochemical stains such as picrosirius red, highlighting the need to evaluate fibrosis of the heart using diverse methodologies.

Biomechanics of diastolic dysfunction: a one-dimensional computational modeling approach.

Diastolic dysfunction (DD) is a major component of heart failure with preserved ejection fraction (HFpEF). Accordingly, a profound understanding of the underlying biomechanical mechanisms involved in DD is needed to elucidate all aspects of HFpEF. In this study, we have developed a computational model of DD by leveraging the power of an advanced one-dimensional arterial network coupled to a four-chambered zero-dimensional cardiac model. The two main pathologies investigated were linked to the active relaxation of the myocardium and the passive stiffness of the left ventricular wall. These pathologies were quantified through two parameters for the biphasic delay of active relaxation, which simulate the early and late-phase relaxation delay, and one parameter for passive stiffness, which simulates the increased nonlinear stiffness of the ventricular wall. A parameter sensitivity analysis was conducted on each of the three parameters to investigate their effect in isolation. The three parameters were then concurrently adjusted to produce the three main phenotypes of DD. It was found that the impaired relaxation phenotype can be replicated by mainly manipulating the active relaxation, the pseudo-normal phenotype was replicated by manipulating both the active relaxation and passive stiffness, and, finally, the restricted phenotype was replicated by mainly changing the passive stiffness. This article presents a simple model producing a holistic and comprehensive replication of the main DD phenotypes and presents novel biomechanical insights on how key parameters defining the relaxation and stiffness properties of the myocardium affect the development and manifestation of DD.NEW & NOTEWORTHY This study uses a complete and validated computational model of the cardiovascular system to simulate the two main pathologies involved in diastolic dysfunction (DD), i.e., abnormal active relaxation and increased ventricular diastolic stiffness. The three phenotypes of DD were successfully replicated according to literature data. We elucidate the biomechanical effect of the relaxation pathologies involved and how these pathologies interact to create the various phenotypes of DD.

Abstract 333: Cardiomyocyte Hypercontractility is an Adaptational Response to Stiffness in High-Fat Diet Mice

Diabetic heart disease typically features a restrictive/ hypertrophic cardiac phenotype characterised by diastolic dysfunction with preserved systolic performance. Little is known about the early adaptational mechanisms that underpin maintenance of systolic performance in diabetic diastolic dysfunction and how this may contribute to disease progression. This study aimed to evaluate cardiomyocyte contractility in a high-fat diet (HFD) mouse model of diastolic dysfunction. Echocardiography (GE Vivid 9) was performed in 33 wk old male C57Bl/6 mice fed a high-fat diet (HFD, 43% kcal fat, 24 wks duration). Isolated cardiomyocytes (paced 2Hz, 2.0mM Ca 2+ , 37C) were subjected to progressive axial stretch. Sarcomere length/ shortening, tension and intracellular calcium transients (Fura-2AM, 5μM) were simultaneously measured (Myostretcher, Ionoptix). HFD hearts displayed in vivo (22.2±1.4 vs 16.7±1.0 E/E’; p<0.05) and in vitro diastolic dysfunction (0.244±0.039 vs 0.075±0.017 nN/pl/ %cell stretch; p<0.05). HFD cardiomyocytes exhibited length-dependent hypercontractility with augmented developed tension amplitude at maximal stretch (4.891±0.942 vs 2.484±0.677 nN/pl; p<0.05), but not basal stretch. Hypercontractility could not be attributed to a difference in Ca 2+ transient amplitude but was correlated with length dependence of Ca 2+ sensitivity (n=17 cells, R 2 =0.4039 p<0.05). During progressive cardiomyocyte stretch, systolic tension slopes were strongly correlated with diastolic tension slopes (cardiomyocyte stiffness) (n=30 cells; R 2 =0.8442, p<0.05) while there was no difference in the ratio of systolic/diastolic tension slopes indicating maintained length-dependent activation. These findings provide the first evidence that cardiomyocyte hypercontractility and stiffness are strongly linked. High-fat diet cardiomyocytes may operate near maximal contractile capacity to maintain basal cardiac output, potentially limiting capacity for cardiac output increase in response to physiological stressors. An aberrant myofilament post-translational modification profile represents a potential mechanism through which cardiac dysfunction arises during the development of diabetes.

Ischemia-Induced Model of Diastolic Dysfunction in Sheep

ABSTRACTBackground: Ischemic heart failure with normal ejection fraction (HFNEF) is an increasingly recognized entity that carries similar morbidity and mortality than low ejection fraction heart failure. Animal models of diastolic dysfunction mimicking this condition are lacking and are essential for the development of therapeutic strategies. Methods and Results: Eight Corriedale sheep, 18 ± 5 months old, were included in the study. Basal echocardiography and myocardial perfusion evaluation (SPECT) was performed. Acute myocardial infarction (AMI) was made by occlusion (90 min) and reperfusion of the second diagonal branch of the anterior descending coronary artery. Two months after AMI, echocardiography and SPECT evaluation were performed prior to sacrifice. Basal and 2 months echocardiography showed similar fractional shortening and ventricular dimensions in each animal except for an increase in left atrial diameter. No mitral regurgitation was evidenced. SPECT imaging and pathology confirmed infarction in the apical, apico-anterior, and apico-septal segments. Conclusion: A novel model of ischemia-induced diastolic dysfunction with preserved ventricular thickness and ejection fraction is described. This model opens the possibility of testing therapeutic options for patients with this condition.

CCR5 Inhibition Prevents Cardiac Dysfunction in the SIV/Macaque Model of HIV

BackgroundDiastolic dysfunction is a highly prevalent cardiac abnormality in asymptomatic as well as ART‐treated human immunodeficiency virus (HIV) patients. Although the mechanisms underlying depressed cardiac function remain obscure, diastolic dysfunction in SIV‐infected rhesus macaques is highly correlated with myocardial viral load. As cardiomyocytes are not productively infected, damage may be an indirect process attributable to a combination of pro‐inflammatory mediators and viral proteins.Methods and ResultsGiven the diverse roles of CCR5 in mediating recruitment of leukocytes to inflammatory sites and serving as a receptor for HIV entry into cells, we investigated the role of CCR5 in the SIV/macaque model of diastolic dysfunction. We found that in SIV‐infected macaques, CCR5 inhibition dramatically impacted myocardial viral load measured by qRT‐PCR and prevented diastolic dysfunction measured by echocardiography. Complementary in vitro experiments using fluorescence microscopy showed that CCR5 ligands impaired contractile function of isolated cardiomyocytes, thus identifying CCR5 signaling as a novel mediator of impaired cardiac mechanical function.ConclusionsTogether, these findings incriminate SIV/HIV gp120‐CCR5 as well as chemokine‐CCR5 interactions in HIV‐associated cardiac dysfunction. These findings also have important implications for the treatment of HIV‐infected individuals: in addition to antiviral properties and reduced chemokine‐mediated recruitment and activation of inflammatory cells, CCR5 inhibition may provide a cardioprotective benefit by preventing cardiomyocyte CCR5 signaling.

Connective tissue growth factor and cardiac diastolic dysfunction: human data from the Taiwan Diastolic Heart Failure Registry and molecular basis by cellular and animal models

Connective tissue growth factor (CTGF) is an emerging marker for tissue fibrosis. We investigated the association between CTGF and cardiac diastolic function using cellular and animal models and clinical human data. A total of 125 patients with a diagnosis of diastolic heart failure (DHF) were recruited from 1283 patients of the Taiwan Diastolic Heart Failure Registry. The severity of DHF was determined by tissue Doppler imaging (E/e'). Cardiac magnetic resonance imaging (CMRI) was used to evaluate myocardial fibrosis in some of the patients (n = 25). Stretch of cardiomyocytes on a flexible membrane base serves as a cellular phenotype of cardiac diastolic dysfunction (DD). A canine model of DD was induced by aortic banding. A significant correlation was found between plasma CTGF and E/e' in DHF patients. The severity of cardiac fibrosis evaluated by CMRI also correlated with CTGF. In the cell model, stretch increased secretion of CTGF from cardiomyocytes. In the canine model, myocardial tissue CTGF expression and fibrosis significantly increased after 2 weeks of aortic banding. Notably, the expression of CTGF paralleled the severity of LV DD (r = 0.40, P < 0.001 for E/e') and haemodynamic changes (r = 0.80, P < 0.001). After adjusting for confounding factors, CTGF levels still correlated with diastolic parameters in both human and canine models (human plasma CTGF, P < 0.001; canine tissue CTGF, P = 0.04). Plasma CTGF level correlated with the severity of DD and tissue fibrosis in DHF patients. The mechanism may be through myocardial stretch. Our study indicated that CTGF may serve as an early marker for DHF.

Abstract 19116: Efficacy of a Small Molecule HDAC Inhibitor in a Model of Diastolic Dysfunction with Preserved Ejection Fraction

Heart failure (HF) is a major health problem and growing economic burden worldwide. Of the patients with HF, ∼50% suffer from heart failure with preserved ejection fraction (HFpEF), also known as diastolic HF. Current standards-of-care for systolic HF provide little to no benefit to patients with HFpEF. Histone deacetylase inhibitors (HDACi) have been shown to improve systolic function in a variety of rodent models of HF. However, the impact of HDACi on diastolic function remains poorly understood. This study assessed the efficacy of an HDACi in a rat model of HFpEF. Dahl salt-sensitive (DSS) rats were fed low salt (LS, 0.4% NaCl) or high salt (HS, 4.0% NaCl) diets for 10 weeks. Rats were treated either with vehicle (LS and HS groups) or the pan-HDAC inhibitor, ITF2357, at 3 and 30 mg/kg (HS groups). Serial echocardiography was performed to assess left ventricle (LV) dimensions and function. At study endpoint, pressure-volume analyses were performed to further quantify effects of HS and HDACi on hemodynamic properties. HS feeding caused hypertension, cardiac hypertrophy and diastolic dysfunction, as shown by a 30% reduction of E/A and E’/A’ from baseline (measured by flow and tissue Doppler), a 27% increase of isovolumic relaxation time (IVRT), and a significant increase in LV end-diastolic pressure (LVEDP). EF was preserved in HS fed animals. ITF2357 was well tolerated and did not cause hematological side effects. ITF2357 dose-dependently prevented diastolic dysfunction of the heart; E/A and E’/A’ decreased 14% and 5% from baseline with low and high doses of ITF2357, respectively. Efficacy of ITF2357 was also observed at the level of IVRT and LVEDP. HDAC inhibition-mediated improvement in cardiac function and hemodynamics occurred independently of effects on cardiac hypertrophy and systemic hypertension. These data suggest that HDACs play a critical role in the pathogenesis of diastolic HF and that small molecule HDAC inhibitor have potential as novel therapeutics for HFpEF

Ranolazine Improves Diastolic Function in the Stress-Tested Spontaneously Hypertensive Rat

<h3>Background</h3> Delayed left ventricular relaxation impairs diastolic function, mostly at high heart rates; thus, exercise or dobutamine stress tests are often used in clinical diagnosis. Ranolazine, a late I_Na inhibitor, can reverse diastolic dysfunction <i>in vitro</i> and <i>in vivo</i>. However, mechanisms other than late I_Na inhibition have been suggested. In this study, we tested the hypothesis that late I_Na is elevated in spontaneously hypertensive rat hearts (SHR), a model of diastolic dysfunction, and that ranolazine can improve diastolic function <i>in vivo</i> when heart rate is increased. <h3>Methods</h3> SHR and Wistar Kyoto (WKY) rats aged 10 months were used for all experiments. Late I_Na was measured from isolated SHR and WKY rat ventricular myocytes using a voltage-ramp protocol. Diastolic function was evaluated <i>in vivo</i> by echocardiography and left ventricular pressure–volume (LVPV) catheter techniques. Effects of ranolazine (R, 30 mg/kg) or saline (S) pretreatment on the response to dobutamine (β-agonist) were measured in SHR. In echo experiments (n = 5/group), the dose of dobutamine was titrated (∼40 μg/kg/min to achieve a heart rate of 450 bpm, whereas the dose response to 10, 20, and 40 μg/kg/min (n = 2/group) was measured by PV loop analysis. <h3>Results</h3> Baseline echo and LVPV loop analysis confirmed diastolic dysfunction in SHR. Late I_Na current density was larger in SHR ventricular myocytes (–0.69 pA/pF, n=7) compared with WKY (0.32 pA/pF, n=9, <i>P</i> <.05). Whereas ranolazine alone did not alter isovolumic relaxation time (IVRT) (S: 13 ± 8% vs R: –4 ± 7% change from baseline, NS), pretreatment with ranolazine prevented an increase in IVRT during dobutamine infusion in SHR (S: 89 ± 27% vs R: 8 ± 14% change from baseline, <i>P</i> <.05), despite the matched increase in heart rate (<i>P</i> >.05). Ranolazine pretreatment also prevented the dose-dependent increase in end-diastolic pressure in response to dobutamine in SHR, although the heart rate increased dose-dependently in both groups. At 40 μg/kg/min, the change (Δ) from baseline was (S) 8 ± 3 mm Hg vs (R) –1 ± 1 mm Hg (<i>P</i> <.01). <h3>Conclusions</h3> Our data indicate that ranolazine may protect against heart rate-dependent worsening of diastolic dysfunction. Inhibition of late I_Na, which is enhanced in this model, may underlie this effect.

Ranolazine prevents heart failure with preserved ejection fraction, diastolic dysfunction, and left ventricular hypertrophy in a hypertensive murine model

Background: Recent in vitro studies on failing human heart muscle has suggested that ranolazine (RAN), a novel antianginal drug known to inhibit late sodium current, may improve diastolic dysfunction (DD) caused by hypertension (HTN)-induced oxidative stress. By improving DD, RAN can improve heart failure with preserved ejection fraction (HFPEF). Methods: Amouse model of DDwas developed by inducing mild HTN by unilateral nephrectomy, deoxycorticosterone acetate (DOCA) pellet implantation, and substituting drinking water with 1% NaCl. Control animals underwent sham operation and drank regular tap water. RAN 50 (mg/kg) was given orally twice a day. Weekly blood pressures (BPs) and heart rates (HRs) were measured using tail-cuff plethysmography. Cardiac function and left ventricular posterior wall thickness (LVPWd) were measured by echocardiogram under light anesthesia using isoflurane. Treatment durationwas for 3weeks and 7weeks. Pulmonary congestion was assessed by lung to body weight (L/BW) ratio. Results: Compared to controls, DOCA mice were hypertensive (BP 112 ±4 vs. 89±2 mmHg) and had DD evidenced by a low LV inflow propagation velocity Vp (28.1±0.5 vs. 47.2±1 cm/s⁎), a low mitral annulus early longitudinal velocity E' (2.70 vs. 4.40 cm/s⁎), and a high E/E' ratio (29.3±1.5 vs. 18.0±0⁎). DOCA mice had LVH as evidenced by high heart/BW ratio (6.22±0.15 vs. 4.90±0.22 mg/g⁎) and increased LVPWd (0.82±0.22 vs. 0.74±0.01 mm⁎). There was no systolic dysfunction in either group. RAN pretreatment effectively prevented DD and LVH in DOCA mice as evidenced by high E' (3.9 Vs 2.70 cm/s⁎), low E/E' (18.8±1.0⁎), high Vp (41±2Vs 28.1±0.5 cm/s⁎), lowheart/BW ratio (4.79±0.11 mg/g⁎), and low LVPWd thickness (0.76±0.01 vs. 0.82±0.02 mm⁎). RAN had no effect on HR [625±18 vs. 630±20 bpm, P=not significant (NS)]. RAN pretreatment effectively prevented development of heart failure in DOCA mice at 7 weeks as evidenced by significantly lower L/BW ratios when compared with untreated DOCA mice (0.41±0.002 vs. 0.52±0.02 mg/g⁎). Conclusions: RANhas prevented DD, LVH, and HFPEF in a hypertensive murine model of DD. Prevention of heart failure in our model warrants additional animal andhuman studies to further evaluate the therapeutic potential of RAN in HFPEF (Mean±S.E.M., ⁎Pb.05).

PLATINUM Japan SV: platinum chromium everolimus-eluting stent in small vessels

Background: Recent in vitro studies on failing human heart muscle has suggested that ranolazine (RAN), a novel antianginal drug known to inhibit late sodium current, may improve diastolic dysfunction (DD) caused by hypertension (HTN)-induced oxidative stress. By improving DD, RAN can improve heart failure with preserved ejection fraction (HFPEF). Methods: Amouse model of DDwas developed by inducing mild HTN by unilateral nephrectomy, deoxycorticosterone acetate (DOCA) pellet implantation, and substituting drinking water with 1% NaCl. Control animals underwent sham operation and drank regular tap water. RAN 50 (mg/kg) was given orally twice a day. Weekly blood pressures (BPs) and heart rates (HRs) were measured using tail-cuff plethysmography. Cardiac function and left ventricular posterior wall thickness (LVPWd) were measured by echocardiogram under light anesthesia using isoflurane. Treatment durationwas for 3weeks and 7weeks. Pulmonary congestion was assessed by lung to body weight (L/BW) ratio. Results: Compared to controls, DOCA mice were hypertensive (BP 112 ±4 vs. 89±2 mmHg) and had DD evidenced by a low LV inflow propagation velocity Vp (28.1±0.5 vs. 47.2±1 cm/s⁎), a low mitral annulus early longitudinal velocity E' (2.70 vs. 4.40 cm/s⁎), and a high E/E' ratio (29.3±1.5 vs. 18.0±0⁎). DOCA mice had LVH as evidenced by high heart/BW ratio (6.22±0.15 vs. 4.90±0.22 mg/g⁎) and increased LVPWd (0.82±0.22 vs. 0.74±0.01 mm⁎). There was no systolic dysfunction in either group. RAN pretreatment effectively prevented DD and LVH in DOCA mice as evidenced by high E' (3.9 Vs 2.70 cm/s⁎), low E/E' (18.8±1.0⁎), high Vp (41±2Vs 28.1±0.5 cm/s⁎), lowheart/BW ratio (4.79±0.11 mg/g⁎), and low LVPWd thickness (0.76±0.01 vs. 0.82±0.02 mm⁎). RAN had no effect on HR [625±18 vs. 630±20 bpm, P=not significant (NS)]. RAN pretreatment effectively prevented development of heart failure in DOCA mice at 7 weeks as evidenced by significantly lower L/BW ratios when compared with untreated DOCA mice (0.41±0.002 vs. 0.52±0.02 mg/g⁎). Conclusions: RANhas prevented DD, LVH, and HFPEF in a hypertensive murine model of DD. Prevention of heart failure in our model warrants additional animal andhuman studies to further evaluate the therapeutic potential of RAN in HFPEF (Mean±S.E.M., ⁎Pb.05).

Abstract P143: Activation of GPR30 Attenuates Diastolic Dysfunction and LV Remodeling in Oophorectomized mRen2.Lewis Rats

The incidence of diastolic dysfunction increases in women after menopause but the mechanisms involved are not completely understood. GPR30 is a novel estrogen receptor expressed in various tissues including the heart. Studies have shown that activation of GPR30 by its agonist G1, improves contractile function and reduces infarct size in isolated rat and mouse hearts subjected to ischemia/reperfusion injury and attenuates diastolic dysfunction in a salt-sensitive rat model of hypertension. We hypothesized that the activation of GPR30 by G1 protects against the development of diastolic dysfunction and cardiac hypertrophy in oophorectomized mRen2.Lewis rats, an established model that emulates the cardiac phenotype of the postmenopausal woman. Surgical bilateral oophorectomy (OVX) was performed in female mRen2.Lewis rats at 4 weeks of age, and G1 (50 or 100 µg/kg/day) was given subcutaneously via minipump starting at 13 weeks of age for 2 weeks. Both doses of G1 significantly improved lusitropic function and structure, independent of changes in blood pressure. Compared to vehicle-treated OVX rats, G1 reduced the tissue Doppler-derived index of left ventricular filling pressure (E/e’), left ventricle mass, wall thickness, and the biomarkers of hypertrophy, ANF and BNP mRNA levels. Using cultured H9c2 cardiomyocytes, in vitro studies further showed that 1) G1 inhibited angiotensin (ANG) II-induced hypertrophy, evidenced by reductions in cell size, and ANF and BNP gene expression; 2) the antagonist of GPR30, G15, inhibited estrogen’s protective effects on ANG II-induced hypertrophy; and 3) G1 induced phosphorylation of Erk and Akt. These data demonstrate the protective role of GPR30 in a model of diastolic dysfunction and cardiac hypertrophy, and provide insight into the underlying mechanisms.

NO Way to Relax

The roles of nitric oxide (NO) in the heart have been studied intensely ever since the first report nearly 2 decades ago showing that endogenous NO modulates cardiac myocyte function.1 All 3 NO synthase (NOS) isoforms have been found in mammalian heart tissues (see reviews in Massion et al2 and Belge et al3). A complex array of myocyte and nonmyocyte cells in the heart express NOS isoforms, and the local generation of NO2,3 and reactive oxygen species (ROS)4 may exert both autocrine and paracrine effects on cellular function. Not only is the endothelial isoform of NOS (eNOS, or NOS3) robustly expressed in the endothelial cells of the cardiac vasculature, but eNOS is also present within cardiac myocytes, where the enzyme associates with the scaffolding/regulatory protein caveolin-3 in T tubules in plasmalemmal caveolae.5 The neuronal NOS (nNOS, or NOS1) is also expressed in cardiac myocytes, where the enzyme appears to be localized in the sarcoplasmic reticulum and modulates phospholamban phosphorylation.6 Although both eNOS and nNOS appear to be physiologically expressed in cardiac tissues, the inflammation-related NOS isoform (iNOS, or NOS2) only appears in the heart after immunoactivation; iNOS may modulate the decline in myocardial function seen in sepsis.7 There have been innumerable studies of the cardiac effects of various NOS inhibitors, NO-donating drugs, and NO itself.2 The cardiac phenotypes of NOS “knockout” mouse models have been characterized extensively, and mice lacking 1, 2, or all 3 NOS isoforms have been generated and characterized.8 In addition, the roles of NOS substrates, cofactors, and allosteric modulators have been explored exhaustively in diverse cardiac model systems. Emerging from this broad range of experimental evidence is an increasingly clear view that NO and NOS are key determinants of cardiac function. Yet the molecular mechanisms and …

Uncoupling between left ventricular contractility and relaxation after direct-current counter shocks.

Left ventricular (LV) contractility and relaxation are physiologically coupled on the basis of intracellular calcium cycling. The relation has been reported to be unique. However, this may not be always true if relaxation is predominantly impaired. Direct current counter (DC) shocks develop myocardial interstitial edema, inducing diastolic heart failure. Thus, we hypothesized that LV contractility-relaxation coupling would be altered in an experimental model of diastolic dysfunction by DC shocks. The relation between Emax (LV contractility index) and the time constant of LV pressure decay (tau) was evaluated in isovolumic contraction of seven isolated, blood perfused dog hearts. There existed a hyperbolic relation between Emax and tau in control (= pre-DC) hearts. After the application of five consecutive 80 J DC shocks, Emax was unchanged (from 4.6 +/- 1.0 to 5.2 +/- 0.8 mmHg x ml(-1) x 100 g) but tau was markedly prolonged (from 36 +/- 12 to 74 +/- 38 ms, P < 0.01). Thus, DC shocks induced a strikingly upward displacement of the hyperbolic curve compared with the control. The slope of the linear relation between Emax and the reciprocal of tau (= a relaxation velocity index normalized for contractility) significantly decreased after DC shocks. We conclude that the coupling between LV contractility and relaxation is not unique, but can be altered acutely by DC shocks. A dissociation of contractility-relaxation coupling may be of help for distinguishing diastolic heart failure and exploring its pathogenesis.

Chronic inhibition of fatty acid oxidation: new model of diastolic dysfunction

This study was designed to determine the changes in the heart that result from inhibition of long-chain fatty acid oxidation with 2-tetradecylglycidic acid (TDGA). Male Sprague-Dawley rats (n = 64) were treated with TDGA (20 mg.kg-1.day-1) or a comparable volume of vehicle by gavage feeding for 7 or 21 days. In conscious rats TDGA produced no changes in heart rate, left ventricular systolic or end-diastolic pressures, left ventricular pressure development (dP/dt), or the time constant of left ventricular relaxation. Left ventricular developed pressure was not changed at 21 days. TDGA increased left ventricular weight, left ventricular weight-to-body weight ratio, and total heart weight-to-body weight ratio. Left ventricular endocardial and epicardial myocyte volumes were increased by 53 and 65%, respectively. Myocardial triglyceride content was increased threefold. Left ventricular chamber stiffness constants between end-diastolic pressures of 0 and 30 mmHg were increased, and left ventricular end-diastolic volumes at operating end-diastolic pressures were decreased at both 7 and 21 days. The myocardial stiffness constant was also increased at 7 and 21 days. Thus inhibition of long-chain fatty acid oxidation with TDGA increased left ventricular mass and altered left ventricular chamber and muscle stiffness without changing left ventricular relaxation or systolic function. We conclude that inhibition of long-chain fatty acid oxidation produced an unusual model of left ventricular hypertrophy and diastolic dysfunction characterized by abnormalities of passive-elastic properties but preserved relaxation.

Chronic inhibition of fatty acid oxidation: New model of diastolic dysfunction

The proportion of cardiac energy derived from fatty acid oxidation decreases and that derived from glucose increases during ischemia. This biochemical profile of cardiac energy production is achieved in rats and mice without ischemia by pharmacological agents such as tetradecylglycidic acid. Chronically this leads to increased cardiac stiffness, and hypertrophy in the rodent models. Elements of human cardiac dysfunction are hypothesized to develop from and/or cause similar changes in substrate utilization for energy production. For some individuals treatment that would prevent or reverse these changes may be appropriate.