Changes In Fractional Shortening Research Articles

Umbilical Vein Flows and Cardiac Size, Shape, and Ventricular Contractility in Fetuses With Estimated Weight Less-Than 10th Centile.

In a cohort of patients with estimated fetal weights (EFWs) <10th centile, we aimed 1) to compare the prevalence of abnormalities of fetal 4-chamber view (4CV) cardiac size, shape, and ventricular contractility in fetal growth restricted (FGR) and small-for-gestational-age (SGA) fetuses and 2) to compare umbilical vein flow (UVF) measurements to standard Doppler surveillance in predicting abnormalities of cardiac function. Prospective observational cohort study of fetuses with EFW <10th percentile. Measurements of size and shape used were 4CV transverse width, 4CV cardiac area, 4CV global sphericity index, and right-to-left ventricular mid-chamber width ratio. Variables of contractility used were fractional shortening change at the mid-ventricle chamber, global longitudinal strain, fractional area change, and left ventricular cardiac output. The UVF and standard Doppler surveillance including umbilical artery (UA), middle cerebral artery, and cerebroplacental ratio (CPR) were collected. Control data were from previously published studies. A total of 95 fetuses with EFWs <10th centile were included in the study. The rates of abnormalities of cardiac size and shape and ventricular contractility were all significantly elevated compared with normally grown control fetuses but similar between FGR and SGA fetuses. In a subset of 76 patients with UVF data, evaluation UVF identified more patients with any abnormality of contractility compared with UA (37.9 vs 17.2%, P = .02). The addition of UVF doubled the detection rate of ventricular contractility abnormalities. The addition of UVF should be considered in the surveillance of FGR and SGA fetuses to further stratify the severity of hypoxemia and to identify those at greater risk for future cardiovascular dysfunction.

Biventricular Interaction During Acute Left Ventricular Ischemia in Mice: A Combined In-Vivo and In-Silico Approach

Computational models provide an efficient paradigm for integrating and linking multiple spatial and temporal scales. However, these models are difficult to parameterize and match to experimental data. Recent advances in both data collection and model analyses have helped overcome this limitation. Here, we combine a multiscale, biventricular interaction model with mouse data before and after left ventricular (LV) ischemia. Sensitivity analyses are used to identify the most influential parameters on pressure and volume predictions. The subset of influential model parameters are calibrated to biventricular pressure–volume loop data (n = 3) at baseline. Each mouse underwent left anterior descending coronary artery ligation, during which changes in fractional shortening and RV pressure–volume dynamics were recorded. Using the calibrated model, we simulate acute LV ischemia and contrast outputs at baseline and in simulated ischemia. Our baseline simulations align with the LV and RV data, and our predictions during ischemia complement recorded RV data and prior studies on LV function during myocardial infarction. We show that a model with both biventricular mechanical interaction and systems-level cardiovascular dynamics can quantitatively reproduce in-vivo data and qualitatively match prior findings from animal studies on LV ischemia.

Cardiorespiratory adaptation to low-dose dexamethasone for lung disease in extremely preterm infants: A prospective echocardiographic study.

The cardiovascular impact of dexamethasone (Dex) is not well understood. Most data are obtained from a 6week, high-dose regimen, and are limited to findings of hypertension and cardiac hypertrophy. The present study ascertained the impact of low-dose Dex on cardiac indices when administered to extremely preterm infants for lung disease. A pre-post intervention prospective echocardiographic (Echo) study was undertaken, with cardiac assessments performed before and within 24h after completion of first course of therapy (10day regimen, cumulative 0.89mgkg-1 ). Thirty infants with a gestational age of 24.6±1.1weeks and birthweight of 612±125g, respectively, were studied. The age at Dex administration was 20±9days. Fractional inspired oxygen decreased from 0.7±0.23 to 0.35±0.14 (P<0.001). Patent ductus arteriosus was noted in 20 infants at Echo1. At Echo2, the ductal diameter decreased from 2.16±0.8 to 1.1±0.8mm (P= 0.0003), with complete closure in 7/20 (35%). A reduction in left pulmonary artery end-diastolic velocity was noted (17±12 to 9±10cms-1 , P<0.001). Pulmonary vascular resistance decreased (increased time to peak velocity/right ventricular ejection time, 0.2±0.03 to 0.23 ±0.03, P= 0.0001) and right ventricular systolic performance improved (tricuspid annular plane systolic excursion, 4.9±0.8 to 5.5±0.9mm, P= 0.02). No significant changes in fractional shortening and left ventricular mass were noted. A significant increase in blood pressure was noted. As a percentage of pre-treatment baseline, the mean increase for systolic blood pressure was 20.3% (95% confidence interval=14-26) on day 2 (P= 0.008). Low-dose Dex influenced cardiovascular parameters related to pulmonary circulation. KEY POINTS: Corticosteroid therapy is frequently used in preterm infants who are dependent on ventilator support. Echocardiographic studies in infants administered a 6week course of steroids have noted left ventricular hypertrophy, outlet obstruction and hypertension, but no information is available on right heart indices. The cardiopulmonary effects of the current, significantly lesser cumulative dose (10day regimen, commonly described as 'DART') have not been evaluated. The present study noted a significant influence on ductal and pulmonary circulation indices. Left heart architecture and function was maintained, whereas a significant but transient increase in blood pressure was noted.

PHARMACOLOGIC ACTIVATION OF THE ALTERNATIVE RAS ATTENUATES DEVELOPMENT OF PULMONARY ARTERIAL HYPERTENSION IN MONOCROTALINE TREATED RATS

Objective: Pulmonary arterial hypertension (PAH) is a rare, chronic and debilitating disease characterized by increased pulmonary arterial pressure leading to right heart failure and – eventually death. Several drugs are approved for the treatment of PAH, but due to ongoing disease progression only half of the patients survive more than 7 years after diagnosis. A novel therapeutic approach based on pharmacologic activation of the alternative RAS was investigated in monocrotaline induced PAH in rats. Design and method: PAH was induced in 12 week-old Wistar rats by an injection of monocrotaline (60 mg/kg). Immediately after PAH induction, the rats (n = 11-12 in each group) were treated for 4 weeks with either a) vehicle, b) the novel peptidase inhibitor ALT001, or c) the endothelin receptor antagonist bosentan – representing the standard of care. Vehicle-treated sham rats served as healthy controls. Analysis included tissue and plasma equilibrium levels of angiotensin metabolites, echocardiography determined right ventricular function and structure, pulmonary arterial pressure, systemic blood pressure and histomorphometrical evaluations. Results: Ang II was significantly increased in lungs of monocrotaline treated animals concomitant with a profound increase in pulmonary arterial pressure (mPAP), reduced fractional shortening, dilated pulmonary valve diameter and a thickened and enlarged right ventricle. ALT001 treatment resulted in increased Ang 1–7 levels while Ang II levels were normalized. Bosentan treatment did not affect angiotensin peptide levels. The PAH induced increase in mPAP was almost completely abolished by ALT001 treatment, while systemic blood pressure remained unaffected. Right ventricular structure and function was effectively preserved under ALT001 treatment and pathological changes in fractional shortening (FS) were significantly reduced. Conclusions: Small molecule based modulation of the RAS might represent a promising novel therapeutic approach in treating RAS-related diseases, including PAH. (Partly supported by VEGA 1/0127/17, FFG 872313)

Abstract 267: Safety and Efficacy of a Combinatorial CCN5/SERCA2a Gene Delivery Approach for Arrhythmia Suppression in a Chronic Model of Angiotensin II (ANG) Induced Cardiac Hypertrophy and Failure

Background: Structural &amp; electromechanical remodeling promotes the incidence of ventricular tachycardia (VT) during progression from compensated hypertrophy to heart failure. The multifactorial nature of VT during disease progression presents a major challenge for conventional anti-arrhythmic approaches. Objective: To determine the safety &amp; efficacy of the antifibrotic matricellular protein CCN5 and a novel combinatorial vector carrying CCN5 and SERCA2a (CCN5/S2a) for prevention of VT. Methods: Adult mice (N=15) underwent chronic ANG infusion (3mg/kg/d) for 2 wk. Mice were subsequently randomized for treatment with AAV9 vectors carrying CCN5, CCN5/S2a, or an empty vector and were maintained for another 2 wk. Age matched mice served as controls (Ctrl). Cardiac function was serially assessed by echocardiography. Optical mapping was performed in perfused hearts before &amp; after challenge with isoproterenol and rapid pacing. VT threshold (VT-t) was defined as the pacing frequency required for induction of sustained VT. Results: ANG infusion resulted in a biphasic change in fractional shortening (FS) consistent with an early phase of compensated hypertrophy followed by decompensation. Late decompensation was associated with adverse electrophysiological (EP) remodeling, including action potential prolongation (21.3±2.4ms in ANG vs 17.5±1.9ms in Ctrl), conduction slowing (0.43±0.04m/s in ANG vs 0.57±0.08m/s in Ctrl) and susceptibility for pacing induced VT (VT-t 21.3±1.2Hz in ANG vs 25.8±1.4Hz in Ctrl). At a cut-off frequency of 22Hz, 5/5 ANG vs 0/7 Ctrl heart were prone to VT. Treatment of ANG mice with CCN5 and the combinatorial CCN5/S2a vector suppressed VT susceptibility by increasing VT-t (25.9±2.9Hz for CCN5, 28.4±2.6Hz for CCN5/S2a). Mechanistically, CCN5/S2a delivery reversed EP and structural remodeling, which in turn prevented the formation of the critical lines of block that maintained VT circuits. In addition, CCN5/S2a fully abrogated the late decrease in FS. Conclusion: Delivery of a combinatorial AAV9 vector carrying CCN5/S2a during the early phase of compensated hypertrophy prevents the progression of electrical and structural remodeling, thereby suppressing the incidence of VT while preserving mechanical function.

Speckle tracking echocardiography assessment of global and regional contraction dysfunction in the mice model of pressure overload.

Speckle tracking echocardiography (STE) has been applied to the evaluation of cardiac contraction dysfunction. However, there were few studies on alteration of global and regional STE parameters in the process of myocardial hypertrophy and heart failure. In this study, STE was applied to evaluate the global and regional cardiac function under heart failure and hypertrophy in the mice model of pressure overload. Adult mice were subjected to mild or severe aortic banding with a 25 Gauge (G) or 27 G needle. After surgery, STE and conventional echocardiography were used in the sham group (n=10), mild trans-aortic banding (TAB) group (n=14) and severe TAB group (n=10) for 8 weeks. The results showed that the mice subjected to severe TAB showed a significant change in fractional shortening (FS), left ventricular (LV) mass, and left ventricular end diastolic diameter (LVEDD) (P<0.05 for each). Meanwhile, there were no significant differences in FS and LVEDD between the sham group and mild TAB group during the experimental procedures (P>0.05 for both). STE analysis revealed that longitudinal strain (LS) was significantly decreased in the severe TAB group as compared with the sham and mild TAB groups (P<0.05 for both) from the postoperative week 1. LS in the mild TAB group was reduced as compared to the sham group (P<0.05). Radial strain (RS) and circumferential strain (CS) were significantly decreased in the severe TAB group as compared to the sham group and the mild TAB group (P<0.05 for both) from the postoperative week 1 (P<0.05 for both). Compared to the sham group, CS in the mild TAB group maintained unchanged during the test period, and RS was reduced only on the postoperative week 6 (P<0.05). Finally, regional contraction dysfunction was analyzed in both hypertrophic and failing myocardium in longitudinal and radial directions. It was found that LS was largest in the apex region and RS was smallest in the apex region in the healthy and hypertrophic myocardium. It was also found that compared to the sham group, only base longitudinal strain in the mild TAB group was decreased. Each of regional strain in the severe TAB group was uniformly depressed in radial and longitudinal directions. It is concluded that STE has provided a non-invasive and highly feasible way to explore the global and regional contraction dysfunction in hypertrophic and heart failure myocardium in the murine model of pressure overload.

Nigella sativa: A potential natural protective agent against cardiac dysfunction in patients with type 2 diabetes mellitus.

Objectives:To study the effect of Nigella sativa supplementation on cardiac functions in Type 2 diabetic patients treated with oral hypoglycemic agents.Background:Diabetes mellitus is associated with a high risk of cardiovascular morbidity and mortality. A number of reported beneficial effects of N. sativa on cardiovascular function were the inspiration for this study.Materials and Methods:Sixty patients with uncontrolled diabetes (hemoglobin A1c [HbA1c] >7%) and with no known cardiovascular complications were recruited from the outpatient diabetes clinic. They were assigned, by convenience, to two groups; the control group received activated charcoal as placebo while the test group received 2 g/day of powdered N. sativa for 1-year. All patients continued with their standard oral hypoglycemic agents. Echocardiography was used to evaluate the diastolic function, systolic function, and left ventricular mass (LVM) before the intervention and after 6 and 12 months of the treatment.Results:HbA1c decreased significantly in the N. sativa group but did not change in the control group. Echocardiographic assessment in the control group showed impairment in diastolic function after 12 months, but there were no significant changes in fractional shortening (FS) or ejection fraction (EF). Furthermore, left ventricular (LV) dimensions at diastole and systole, LVM, and LVM index were significantly increased. In N. sativa group, no significant changes were found in diastolic function or LVM. LV dimension at systole was decreased while FS and EF were significantly increased after 6 and 12 months.Conclusion:N. sativa supplementation may protect the hearts of type 2 diabetic patients from diastolic dysfunction while improving LV systolic function.

Natural history of arrhythmogenic right ventricular cardiomyopathy in the boxer dog: a prospective study.

BackgroundBoxer arrhythmogenic right ventricular cardiomyopathy (ARVC) is a disease that may result in sudden death or heart failure.Hypothesis/objectivesTo prospectively study the natural history of Boxer ARVC.Animals72 dogs (49 ARVC, 23 controls).MethodsBoxers >1 year of age were recruited for annual reevaluation. Controls were defined as being ≥6 years of age and having <50 ventricular premature complex (VPCs)/24 h. ARVC was defined as ≥300 VPCs/24 h in the absence of other disease. Dogs were genotyped for the striatin deletion when possible. Descriptive statistics were determined for age; VPC number; annual change in VPC number; and left ventricular (LV) echocardiographic dimensions. Survival time was calculated.Results Controls: median age of 7 years (range, 6–10); number of VPCs 12 (range, 4–32). Median time in study of 6 years (range, 2–9). Seventeen of 23 were genotyped (5 positive, 12 negative). ARVC: median age of diagnosis of 6 (range, 1–11). Median time in study 5 years (range, 3–8). A total of 33% were syncopal and 43/49 were genotyped (36 positive, 7 negative). Yearly change in VPCs was 46 (range, −7,699 to 33,524). Annual percentage change in LV dimensions was 0, and change in fractional shortening (FS%) was 2%. Two dogs had FS% <20%. Although ARVC dogs died suddenly, there was no difference in survival time between groups. ARVC median age of survival was 11 years, and for controls was 10 years.Conclusions/Clinical ImportanceArrhythmogenic right ventricular cardiomyopathy is a disease of middle age and frequently is associated with the striatin deletion. Syncope occurs in approximately 1/3 of affected dogs; systolic dysfunction is uncommon. The prognosis in many affected dogs is good.

Left ventricular structure and function in the aging naked mole‐rat, the longest‐lived rodent (879.1)

The extraordinarily long‐lived mouse‐sized naked mole‐rat (NMR) shows an attenuated age‐related decline in diastolic function compared to mice and humans, despite having a maximum lifespan of &gt;31 years. Using echocardiography, we have examined the left ventricles (LVs) of young (2‐5 years), middle‐aged (8‐10 years) and old (16‐22 years) NMRs (n=10/cohort). Young NMRs displayed low LV contractility, as measured by fractional shortening (~28%), which was not significantly changed with age. LV wall thicknesses were significantly greater in young NMRs when compared with physiologically age‐matched mice, and NMR LV wall thickness did not decline with age as has been reported for mice. Dobutamine stress echocardiography (3 μg/g body weight i.p.) elicited similar percent changes in fractional shortening, ejection fraction, and cardiac output in each cohort, indicating that cardiac reserve in the NMR is maintained with age. This is in contrast to reports to age‐related declines in cardiac reserve in both mice and humans. Interestingly, cardiac reserve in NMRs of all ages studied here was considerably greater than cardiac reserve we and others have observed in young adult mice. Further studies will investigate the mechanisms by which the NMR may attenuate declines in cardiovascular composition and function commonly observed during aging in other species.

The Effects of Neuregulin on Cardiac Myosin Light Chain Kinase Gene-Ablated Hearts

BackgroundActivation of ErbB2/4 receptor tyrosine kinases in cardiomyocytes by neuregulin treatment is associated with improvement in cardiac function, supporting its use in human patients with heart failure despite the lack of a specific mechanism. Neuregulin infusion in rodents increases cardiac myosin light chain kinase (cMLCK) expression and cardiac myosin regulatory light chain (RLC) phosphorylation which may improve actin-myosin interactions for contraction. We generated a cMLCK knockout mouse to test the hypothesis that cMLCK is necessary for neuregulin-induced improvement in cardiac function by increasing RLC phosphorylation.Principal FindingsThe cMLCK knockout mice have attenuated RLC phosphorylation and decreased cardiac performance measured as fractional shortening. Neuregulin infusion for seven days in wildtype mice increased cardiac cMLCK protein expression and RLC phosphorylation while increasing Akt phosphorylation and decreasing phospholamban phosphorylation. There was no change in fractional shortening. In contrast, neuregulin infusion in cMLCK knockout animals increased cardiac performance in the absence of cMLCK without increasing RLC phosphorylation. In addition, CaMKII signaling appeared to be enhanced in neuregulin-treated knockout mice.ConclusionsThus, Neuregulin may improve cardiac performance in the failing heart without increasing cMLCK and RLC phosphorylation by activating other signaling pathways.

874 Chronic measurement of left ventricular pressure and dP/dt in freely moving rats during the development of heart failure following myocardial infarction

Background: Understanding the mechanisms involved in the progression from cardiac injury to heart failure is essential in order to develop better treatment strategies. Using a rat model of heart failure following myocardial infarction (MI) we can study the development of heart failure. Recently we have developed a method to chronically measure left ventricular pressure (LVP) in conscious rats allowing the use of the maximum rate of change of LVP (dP/dt) as an index of contractility of the heart. Methods: High-fidelity dual-pressure telemetry units were surgically implanted, with pressure sensors continuously monitoring arterial pressure and LVP (through the apex of the heart). After a two-week baseline period the rats underwent either sham surgery, or MI (ligation of the left anterior descending coronary artery). Data were then continuously recorded for a further 6 weeks. Results: Results indicate that we can reliably record baseline arterial pressure and LVP data in conscious rats for at least 10 weeks. Ultrasound results have shown ventricular function to be maintained following LVP sensor implantation, with no change in fractional shortening before and 4 weeks post implantation. After MI, maximum dP/dt was shown to closely follow the changes in ventricular function as assessed by ultrasound. Conclusions: These results demonstrate that the use of the high-fidelity telemetry units can reliably assess dP/dt in the conscious animal without adverse affects on ventricular function. We propose that the chronic measurement of LVP in conscious rats can provide a valuable tool in following the progression of heart failure following MI.

A novel secretagogue increases cardiac contractility by enhancement of L-type Ca2+ current

N′1-(3,3,6,8-tetramethyl-1-oxo-1,2,3,4-tetrahydronaphthalen-2-yliden)-2-cyanoethanohydrazide (TTYC) increases secretion of glucagon-like peptide-1 and intracellular Ca2+ concentration in GLUTag cells. The purpose of the present study was to examine if TTYC exerts positive inotropic effects on isolated rabbit ventricular myocytes and in vivo heart in anesthetized rats, and if so to further define the potential mechanism of action. Contractility was assessed in vitro using changes in fractional shortening (FS) of myocyte sarcomere length and in vivo using changes in the velocity of left ventricular pressure. Changes in L-type Ca2+ current of ventricular myocytes were evaluated using whole-cell voltage-clamp techniques. TTYC increased FS of myocyte sarcomere length in a concentration-dependent manner. The positive inotropic effect was not abrogated by β-adrenergic blockade (propranolol) or protein kinase A inhibition. TTYC enhanced peak L-type Ca2+ current in a voltage-dependent manner (current amplitudes increased by 4.0-fold at -10mV and 1.5-fold at +10mV). Voltage-dependence of steady-state activation of L-type Ca2+ current was shifted by 15mV in the negative direction. Inactivation time course of the L-type Ca2+ currents at voltages of −10 to 20mV was significantly slowed by 0.3μM TTYC. In vivo studies demonstrated that TTYC increased cardiac contractility in a dose-dependent manner. In conclusion, TTYC is a novel L-type Ca2+ current activator with positive cardiac inotropic effects. Negative shifting of the voltage-dependence of L-type Ca2+ current activation and reduced inactivation are two mechanisms responsible for the enhanced L-type Ca2+ current that contribute to the positive inotropic effects.

NADPH oxidase-derived superoxide impairs calcium transients and contraction in aged murine ventricular myocytes

Since aging increases oxidative stress, we analyzed the contribution of reactive oxygen species (ROS) to the contractile dysfunction of aged ventricular myocytes and investigated whether short-term interference with ROS formation could normalize contractile performance. Isolated ventricular myocytes from young (2–4 months) and aged (24–26 months) male mice (C57BL/6) were used. We analyzed sarcomere shortening and calcium transients (Indo-1 fluorescence) of voltage clamped ventricular myocytes and myofilament ATPase activity (malachite green assay). Expression of calcium handling proteins (Western blots) and NADPH oxidase subunits (real-time PCR) was quantified, as well as NADPH oxidase activity (lucigenin chemiluminescence). We found that aged myocytes showed decelerated shortening/relengthening without changes in fractional shortening. Calcium transient decay was similarly decelerated, but the amplitude of calcium transients was increased with aging. Calcium sensitivity of myofilaments of aged myocytes was reduced. These age-dependent changes occurred without altered calcium handling protein expression but were reversed by the superoxide scavenger tiron. Aged myocytes showed increased NADPH oxidase expression and activity. Pharmacological inhibition of NADPH oxidase (diphenylene iodonium; apocynin) normalized age-dependent deceleration of shortening/relengthening. In summary, we show that increased superoxide formation by upregulated NADPH oxidase contributes significantly to age-dependent alterations in calcium handling and contractility of murine ventricular myocytes.

Minimally invasive transverse aortic banding as a model to study heart disease in SD, SS and Mas−/− rat strains

Minimally invasive transverse aortic banding (MTAB) is a model for inducing ventricular dysfunction that has been used exclusively in mice. Our objective was to test the efficacy of the MTAB model in rats by using the Sprague Dawley, Dahl salt‐sensitive hypertensive and the recently developed Mas receptor knock out rat. The Mas receptor mediates the physiological effects of the angiotensin peptide ANG1‐7 and thus modulates cardiovascular function. A rat knockout of the Mas1 receptor was generated using zinc‐finger nuclease (ZFN) mediated engineering on the SS genetic background. A 10‐bp deletion in exon1 of the Mas1 gene led to a severely truncated protein and a loss of function. Cardiac function was assessed following MTAB using cardiac ultrasound, PV loop analysis, and histology.Weekly echocardiography showed rat MTAB resulted in significant LV hypertrophy associated with a biphasic change in fractional shortening compared to sham controls. Six weeks after banding, acute measurements of LV pressures and volumes revealed significant changes in systolic and diastolic function associated with decreases in ventricular contractility and compliance. Histology showed increases in fibrosis. Differences in severity of disease between rat strains were observed suggesting MTAB combined with ZFN engineering can reveal functional cardiac effects and supports the role of the Mas1 receptor in cardiac fibrosis.HL082798

Resistance to cardiac doxorubicin damage in a Gsta4 knockout mouse

4‐hydroxynonenal (4‐HNE) mediates both pathological effects of oxidative stress and signaling from mitochondrion to nucleus to elicit transcriptional responses that are largely controlled by Nrf2. As elevated levels of 4‐HNE are associated with several cardiovascular diseases, metabolism of 4‐HNE is critical. The murine glutathione transferase A4–4 (GSTA4–4) exhibits very high levels of 4‐HNE‐conjugating activity, which is reduced in the hearts of Gsta4 knockout (KO) mice. KO mice exhibited no cardiac pathology; cardiac 4‐HNE levels were no different in WT and KO mice. We examined how Gsta4 KO mice react to high cardiac 4‐HNE accumulation following chronic administration of doxorubicin (DOX) (5 mg/kg, 4 weekly injections). Cardiac function was assessed by echocardiography. While untreated mice exhibited similar basal cardiac function, WT mice were more sensitive to DOX, resulting in a significantly higher mortality rate. Ejection Fraction (EF) fell in both groups after the first DOX injection. At day 21, EF was significantly lower in WT mice as compared to baseline whereas EF in KO mice recovered to the basal value. Changes in fractional shortening correlated with EF in both groups. We concluded that Gsta4 KO mice exhibited resistance to DOX cardiomyopathy and will explore how Nrf2‐induction of SOD and catalase may contribute to a cardioprotective effect. Supported by a College of Medicine Pilot Study Grant.

In Vitro Cardiac Safety Profiling of a Novel Benzyl-Ethylamine Compound

When developing novel compounds for any clinical indication, the possibility of untoward cardiovascular effects must be addressed. To evaluate the cardiac electrophysiologic effects of A-674563 ((S)-1-benzyl-2-[5-(3-methyl-1H-indazol-5-yl)-pyridin-3-yloxy]-ethylamine), a novel benzyl-ethylamine, we profiled the compound in a series of cellular and tissue assays. In canine Purkinje fibers (30 min exposure; 2 sec BCL), A-674563 elicited concentration dependent depolarization with shouldering of the terminal repolarization phase (20 μM) and increased abnormal automaticity (60 μM). In papillary muscles, concentration dependent depolarization was also seen, but the effect was much less potent; 60 μM induced shouldering of the terminal phase of repolarization. Contractility was assessed using percent changes in fractional shortening of sarcomere length (FS) in rabbit left ventricular myocytes. A-674563 reduced FS in a concentration dependent manner; 10% at 2 μM and 47% at 20 μM. Effects on ionic currents were further evaluated using heterologously expressed cardiac ion channel cell lines. A-674563 inhibited Cav1.2, expressed in HEK cells, with an IC50 of 20 μM, suggesting that the decreased contractility seen in native cells is due to L-type calcium channel block. The compound reduced Nav1.5 (HEK cells) by 50% at 20 μM and inhibited Kir2.1 (tSA201 cells) with an IC50 of 35 μM. Block of these channels would be expected to reduce the upstroke velocity, depolarize the cellular membrane and lead to abnormal automaticity as was seen in the tissue assays. Although A-674563 caused minimal prolongation of action potential duration in tissues up to 60 μM, it inhibited hERG (HEK cells) with an IC50 of 0.7 μM. This potent block was most likely offset by the concomitant block of multiple cardiac ion channels. In conclusion, A-674563 affects multiple cardiac ion channels to elicit depolarization and increased automaticity in native cardiac tissues.

The delivery of superoxide dismutase encapsulated in polyketal microparticles to rat myocardium and protection from myocardial ischemia-reperfusion injury

Oxidative stress is increased in the myocardium following infarction and plays a significant role in death of cardiac myocytes, leading to cardiac dysfunction. Levels of the endogenous antioxidant Cu/Zn-superoxide dismutase (SOD1) decrease following myocardial infarction. While SOD1 gene therapy studies show promise, trials with SOD1 protein have had little success due to poor pharmacokinetics and thus new delivery vehicles are needed. In this work, polyketal particles, a recently developed delivery vehicle, were used to make SOD1-encapsulated-microparticles (PKSOD). Our studies with cultured macrophages demonstrated that PKSOD treatment scavenges both intracellular and extracellular superoxide, suggesting efficient delivery of SOD1 protein to the inside of cells. In a rat model of ischemia/reperfusion (IR) injury, injection of PKSOD, and not free SOD1 or empty particles was able to scavenge IR-induced excess superoxide 3 days following infarction. In addition, only PKSOD treatment significantly reduced myocyte apoptosis. Further, PKSOD treatment was able to improve cardiac function as measured by acute changes in fractional shortening from baseline echocardiography, suggesting that sustained delivery of SOD1 is critical during the early phase of cardiac repair. These data demonstrate that delivery of SOD1 with polyketals is superior to free SOD1 protein therapy and may have potential clinical implications.

Chronic β-adrenergic activation-induced left ventricular systolic dysfunction is associated with systemic release of TNF-α and IL-1-β in rats

The relationship between systemic cytokine release and chronic β-adrenergic activation-induced left ventricular dysfunction (LVSD) has not been widely reported in the literature. In the present study, we examined changes in the serum levels of inflammatory cytokines (IL-l-β, IL-6 and TNF-α) following chronic β-adrenergic activation-induced LVSD. Male Wistar rats were administered isoproterenol (ISO, 5mg/kg,sc once daily) for 4 weeks (ISO 4) or 12 weeks (ISO 12). Echocardiography was done and serum levels of IL - 1- β, IL-6 and TNF-α were estimated at the end of each protocol. In the ISO 4 group there was a significant increase in relative wall thickness (p<0.01) and heart weight: body weight ratio (p<0.001) without any significant changes in fractional shortening (FS) or serum cytokine levels. However, in the ISO 12 group, there was a 32% decrease in FS along with increased serum levels of IL-l-β and TNF-α. The present findings indicate that LVSD induced by chronic β-adrenergic activation in rats is accompanied by increased serum cytokine levels.

In Vivo Metabolic Phenotyping of Myocardial Substrate Metabolism in Rodents

Background— Cardiovascular disease is the leading cause of death among diabetic patients, with alteration in myocardial substrate metabolism being a likely contributor. We aimed to assess noninvasively the efficacy of metformin and rosiglitazone monotherapy in normalizing myocardial substrate metabolism in an animal model of type 2 diabetes mellitus. Methods and Results— The study used 18 male ZDF rats (fa/fa) with 6 rats in each group: an untreated group; a group treated with metformin (16.6 mg/kg/d), and a group treated with rosiglitazone (4 mg/kg). Each rat was scanned at age 14 weeks (baseline) and subsequently at 19 weeks with small-animal positron emission tomography to estimate myocardial glucose utilization (MGU) and myocardial utilization (MFAU), oxidation (MFAO), and esterification (MFAE). Treatment lasted for 5 weeks after baseline imaging. At week 19, rats were euthanized and hearts were extracted for expression analysis of select genes encoding for GLUT transporters and fatty acid transport and oxidation genes. In addition, echocardiography measurements were obtained at weeks 13 and 18 to characterize cardiac function. Metformin had no significant effect on either MGU or MFAU and MFAO. In contrast, rosiglitazone tended to enhance MGU and significantly reduced MFAU and MFAO. Rosiglitazone-induced increase in glucose uptake correlated significantly with increased expression of GLUT4, whereas diminished MFAO correlated significantly with decreased expression of FATP-1 and MCAD. Finally, changes in fractional shortening as a measure of cardiac function were unchanged throughout the study. Conclusions— Treatment with rosiglitazone enhanced glucose utilization and diminished MFAO, thus reversing the metabolic phenotype of the diabetic heart.

Abstract 2673: Myoblast Transplantation Improves Cardiac Function Whether the Cells are Implanted Early or Late After Coronary Ligation

Background: The inability of skeletal myoblasts to transdifferentiate into cardiomyocytes supports the hypothesis that their beneficial effects on cardiac function after a myocardial infarction (MI) are mediated by paracrine effects. In order to explore the role of the timing of cell therapy on the resultant angiogenesis and matrix remodeling, we compared the effects of myoblast transplantation early or late after MI. Methods: MI was generated in Lewis rats by coronary artery ligation. Skeletal myoblasts (5X10 6 ) or control media were injected into the scar and border zone either 5 days (early; n=33) or 30 days (late; n=29) after ligation. Function was assessed by echocardiography before transplantation (Tx), and 14 and 30 days thereafter. Invasive hemodynamics were measured with a Millar catheter at 30 days after Tx, following which explanted hearts were processed to assess LV volumes (computerized planimetry), fibrillar collagen (confocal microscopy), and myoblast engraftment, angiogenesis and extra-cellular matrix characteristics (immunohistochemistry). Results: Load-independent indices of left ventricular (LV) function (Emax, preload recruitable stroke work) were significantly increased in myoblast recipients compared with controls regardless of whether cells were implanted early (p=0.003, p=0.03, respectively) or late (p=0.003, p=0.0007, respectively) after MI. Changes in fractional shortening (by echocardiography) followed a similar pattern. These changes were associated with a significant reduction in LV volume (p=0.04, p=0.01 for early and late Tx groups vs. controls, respectively), and an increase in angiogenesis (p=0.02) whether the myoblasts were injected early or late after MI. The length and width of collagen fibers both in the scar and remote myocardium were also significantly increased (p&lt;0.001) regardless of the timing of myoblast injection. Conclusions: The data suggest that myoblast transplantation improved cardiac function whether cells were injected early or late after MI. In each case, functional recovery was associated with enhanced angiogenesis, favourable effects on extracellular matrix remodeling, and improved LV geometry, supporting the paracrine hypothesis for myoblast transplantation.