Myocardial contractile dysfunction contributes to the development of heart failure in rats with aortic stenosis

Effects of early exercise on cardiac function and lipid metabolism pathway in heart failure

We employed an early training exercise program, immediately after recovery from surgery, and before severe cardiac hypertrophy, to study the underlying mechanism involved with the amelioration of cardiac dysfunction in aortic stenosis (AS) rats. As ET induces angiogenesis and oxygen support, we aimed to verify the effect of exercise on myocardial lipid metabolism disturbance. Wistar rats were divided into Sham, trained Sham (ShamT), AS and trained AS (AST). The exercise consisted of 5-week sessions of treadmill running for 16 weeks. Statistical analysis was conducted by anova or Kruskal-Wallis test and Goodman test. A global correlation between variables was also performed using a two-tailed Pearson's correlation test. AST rats displayed a higher functional capacity and a lower cardiac remodelling and dysfunction when compared to AS, as well as the myocardial capillary rarefaction was prevented. Regarding metabolic properties, immunoblotting and enzymatic assay raised beneficial effects of exercise on fatty acid transport and oxidation pathways. The correlation assessment indicated a positive correlation between variables of angiogenesis and FA utilisation, as well as between metabolism and echocardiographic parameters. In conclusion, early exercise improves exercise tolerance and attenuates cardiac structural and functional remodelling. In parallel, exercise attenuated myocardial capillary and lipid metabolism derangement in rats with aortic stenosis-induced heart failure.

Aerobic Exercise Training Improves Calcium Handling and Cardiac Function in Rats with Heart Failure Resulting from Aortic Stenosis

Aerobic exercise training (AET) has been used to manage heart disease. AET may totally or partially restore the activity and/or expression of proteins that regulate calcium (Ca2+) handling, optimize intracellular Ca2+ flow, and attenuate cardiac functional impairment in failing hearts. However, the literature presents conflicting data regarding the effects of AET on Ca2+ transit and cardiac function in rats with heart failure resulting from aortic stenosis (AoS). This study aimed to evaluate the impact of AET on Ca2+ handling and cardiac function in rats with heart failure due to AoS. Wistar rats were distributed into two groups: control (Sham; n = 61) and aortic stenosis (AoS; n = 44). After 18 weeks, the groups were redistributed into: non-exposed to exercise training (Sham, n = 28 and AoS, n = 22) and trained (Sham-ET, n = 33 and AoS-ET, n = 22) for 10 weeks. Treadmill exercise training was performed with a velocity equivalent to the lactate threshold. The cardiac function was analyzed by echocardiogram, isolated papillary muscles, and isolated cardiomyocytes. During assays of isolated papillary muscles and isolated cardiomyocytes, the Ca2+ concentrations were evaluated. The expression of regulatory proteins for diastolic Ca2+ was assessed via Western Blot. AET attenuated the diastolic dysfunction and improved the systolic function. AoS-ET animals presented an enhanced response to post-rest contraction and SERCA2a and L-type Ca2+ channel blockage compared to the AoS. Furthermore, AET was able to improve aspects of the mechanical function and the responsiveness of the myofilaments to the Ca2+ of the AoS-ET animals. AoS animals presented an alteration in the protein expression of SERCA2a and NCX, and AET restored SERCA2a and NCX levels near normal values. Therefore, AET increased SERCA2a activity and myofilament responsiveness to Ca2+ and improved the cellular Ca2+ influx mechanism, attenuating cardiac dysfunction at cellular, tissue, and chamber levels in animals with AoS and heart failure.

Cenário Disfuncional dos Principais Componentes Responsáveis pelo Equilíbrio do Trânsito de Cálcio Miocárdico na Insuficiência Cardíaca Induzida por Estenose Aórtica

Fundamento

O remodelamento cardíaco patológico se caracteriza por disfunção diastólica e sistólica, levando à insuficiência cardíaca. Neste contexto, o cenário disfuncional do trânsito de cálcio miocárdico (Ca²⁺) tem sido pouco estudado. Um modelo experimental de estenose aórtica tem sido extensamente utilizado para aprimorar os conhecimentos sobre os principais mecanismos do remodelamento patológico cardíaco.

Objetivo

Entender o processo disfuncional dos principais componentes responsáveis pelo equilíbrio do cálcio miocárdico e sua influência sobre a função cardíaca na insuficiência cardíaca induzida pela estenose aórtica.

Métodos

Ratos Wistar de 21 dias de idade foram distribuídos em dois grupos: controle (placebo; n=28) e estenose aórtica (EaO; n=18). A função cardíaca foi analisada com o ecocardiograma, músculo papilar isolado e cardiomiócitos isolados. No ensaio do músculo papilar, SERCA2a e a atividade do canal de Ca²⁺ do tipo L foram avaliados. O ensaio de cardiomiócitos isolados avaliou o trânsito de cálcio. A expressão proteica da proteínas do trânsito de cálcio foi analisada com o western blot. Os resultados foram estatisticamente significativos quando p <0,05.

Resultados

Os músculos papilares e cardiomiócitos dos corações no grupo EaO demonstraram falhas mecânicas. Os ratos com EaO apresentaram menor tempo de pico do Ca²⁺, menor sensibilidade das miofibrilas do Ca²⁺, prejuízos nos processos de entrada e recaptura de cálcio pelo retículo sarcoplasmático, bem como disfunção no canal de cálcio do tipo L (CCTL). Além disso, os animais com EaO apresentaram maior expressão de SERCA2a, CCTL e trocador de Na⁺/Ca²⁺.

Conclusão

Insuficiência cardíaca sistólica e diastólica devido à estenose aórtica supravalvular acarretou comprometimento da entrada de Ca²⁺ celular e inibição da recaptura de cálcio pelo retículo sarcoplasmático devido à disfunção no CCTL e SERCA2a, assim como mudanças no trânsito de cálcio e na expressão das principais proteínas responsáveis pela homeostase de Ca²⁺ celular.

Congestive heart failure model representing aortic banding induced hypertrophy: A study to analyse extent of pressure overload and alteration in myocardial structure and function

Congestive Heart failure (CHF) is a severe pathology representing a major public health problem in industrialized nations which is increasing in prevalence and incidence. The aortic banding rat model provides steady progression of cardiac dysfunction under chronic pressure overload. Present study evaluated two abdominal aortic constriction techniques including constriction of aorta above renal arteries and between renal arteries. The extent of constriction was varied with 22 G and 24 G needles and the duration for evaluation of CHF was also varied by terminating the banded animals after 6 and 8 weeks of banding. Various hemodynamic, ECG and tissue parameters were evaluated after banding to see the progression of CHF. The findings revealed that the constriction of the aorta above both renal arteries with 24 G needle is a better technique amongst other tested banding techniques as the rate of progression of CHF was found to be maximum with it. On the basis of above study, it was concluded that, aortic banding above both renal arteries with 24 G needle is a better technique for induction of pressure overload and for further observation in transition of the cardiac compensatory to decompensatory phase, the duration of the model needs to be prolonged.

Cardiac function and intracellular Ca2+ handling proteins are not impaired by high-saturated-fat diet-induced obesity

Obesity is often associated with changes in cardiac function; however, the mechanisms responsible for functional abnormalities have not yet been fully clarified. Considering the lack of information regarding high-saturated-fat diet-induced obesity, heart function, and the proteins involved in myocardial calcium (Ca²⁺) handling, the aim of this study was to test the hypothesis that this dietary model of obesity leads to cardiac dysfunction resulting from alterations in the regulatory proteins of intracellular Ca²⁺ homeostasis. Male Wistar rats were distributed into two groups: control (C, n=18; standard diet) and obese (Ob, n=19; high-saturated-fat diet), which were fed for 33 weeks. Cardiac structure and function were evaluated using echocardiographic and isolated papillary muscle analyses. Myocardial protein expressions of sarcoplasmic reticulum Ca²⁺-ATPase, phospholamban (PLB), PLB serine-16 phosphorylation, PLB threonine-17 phosphorylation, ryanodine receptor, calsequestrin, Na⁺/Ca²⁺ exchanger, and L-type Ca²⁺ channel were assessed by western blot. Obese rats presented 104% increase in the adiposity index (C: 4.5±1.4 vs Ob: 9.2±1.5%) and obesity-related comorbidities compared to control rats. The left atrium diameter (C: 5.0±0.4 vs Ob: 5.5±0.5 mm) and posterior wall shortening velocity (C: 36.7±3.4 vs Ob: 41.8±3.8 mm/s) were higher in the obese group than in the control. The papillary muscle function was similar between the groups at baseline and after inotropic and lusitropic maneuvers. Obesity did not lead to changes in myocardial Ca²⁺ handling proteins expression. In conclusion, the hypothesis was not confirmed, since the high-saturated-fat diet-induced obese rats did not present cardiac dysfunction or impaired intracellular Ca²⁺ handling proteins.

Heart remodeling produced by aortic stenosis promotes cardiomyocyte apoptosis mediated by collagen V imbalance

Cardiac remodeling (CR) is a structural change of the heart due to chronic hemodynamic overload related to changes in both myocyte and extracellular matrix (ECM). We investigated that the imbalance of collagen V promotes cardiomyocyte apoptosis that contributes to heart failure and cell death. Aortic stenosis was induced surgically and male Wistar rats were randomized to 18 weeks (Sham 18 w, n = 12; AoS 18 w, n = 12) and severe of heart failure (Sham HF, n = 12; AoS HF, n = 12) groups. Functional and structural echocardiogram, immunohistochemistry for Ki-67, TUNEL assay and Immunofluorescence for collagen were performed. Our main results were: (1) Progressive reduction of cardiac functional capacity due to cardiac remodeling with decreased eject fraction in heart failure; (2) Imbalance of collagen deposition with increased, crowded and irregular collagen I in situ expression; (3) Dysregulation of dynamic control of collagen fibers with exposed epitopes of collagen V; (4) Additional apoptosis that are dependent to cardiac injury. The collagen V expression in cardiac remodeling is for the first time described and may be related to additional apoptosis and autoimmune response. Our findings suggest a critical role of collagen V in cardiac remodeling to modulate and promote heart failure and death.

Pathological hypertrophy and cardiac dysfunction are linked to aberrant endogenous unsaturated fatty acid metabolism

Pathological cardiac hypertrophy leads to derangements in lipid metabolism that may contribute to the development of cardiac dysfunction. Since previous studies, using high saturated fat diets, have yielded inconclusive results, we investigated whether provision of a high-unsaturated fatty acid (HUFA) diet was sufficient to restore impaired lipid metabolism and normalize diastolic dysfunction in the pathologically hypertrophied heart. Male, Wistar rats were subjected to supra-valvar aortic stenosis (SVAS) or sham surgery. After 6 weeks, diastolic dysfunction and pathological hypertrophy was confirmed and both sham and SVAS rats were treated with either normolipidic or HUFA diet. At 18 weeks post-surgery, the HUFA diet failed to normalize decreased E/A ratios or attenuate measures of cardiac hypertrophy in SVAS animals. Enzymatic activity assays and gene expression analysis showed that both normolipidic and HUFA-fed hypertrophied hearts had similar increases in glycolytic enzyme activity and down-regulation of fatty acid oxidation genes. Mass spectrometry analysis revealed depletion of unsaturated fatty acids, primarily linoleate and oleate, within the endogenous lipid pools of normolipidic SVAS hearts. The HUFA diet did not restore linoleate or oleate in the cardiac lipid pools, but did maintain body weight and adipose mass in SVAS animals. Overall, these results suggest that, in addition to decreased fatty acid oxidation, aberrant unsaturated fatty acid metabolism may be a maladaptive signature of the pathologically hypertrophied heart. The HUFA diet is insufficient to reverse metabolic remodeling, diastolic dysfunction, or pathologically hypertrophy, possibly do to preferentially partitioning of unsaturated fatty acids to adipose tissue.

Importance of SERCA2a on early isolated diastolic dysfunction induced by supravalvular aortic stenosis in rats

Cardiac remodeling is defined as changes in shape and function of the heart in response to aggression (pressure overload). The sarcoplasmic reticulum calcium ATPase cardiac isoform 2a (SERCA2a) is a known factor that influences function. A wide spectrum of studies report a decrease in SERCA2a in heart failure, but none evaluate it's the role in early isolated diastolic dysfunction in supravalvular aortic stenosis (AoS). Our hypothesis was that SERCA2a participates in such dysfunction. Thirty-day-old male Wistar rats (60-80 g) were divided into AoS and Sham groups, which were submitted to surgery with or without aorta clipping, respectively. After 6 weeks, the animals were submitted to echocardiogram and functional analysis by isolated papillary muscle (IPM) in basal condition, hypoxia, and SERCA2a blockage with cyclopiazonic acid at calcium concentrations of 0.5, 1.5, and 2.5 mM. Western-blot analyses were used for SERCA2a and phospholamban detection. Data analysis was carried out with Student's t-test and ANOVA. AoS enhanced left atrium and E and A wave ratio, with preserved ejection fraction. Basal condition in IPM showed similar increases in developed tension (DT) and resting tension (RT) in AoS, and hypoxia was similar between groups. After cyclopiazonic acid blockage, final DT was equally decreased and RT was similar between groups, but the speed of relaxation was decreased in the AoS group. Western-blot was uniform in all evaluations. The hypothesis was confirmed, since functional parameters regarding SERCA2a were changed in the AoS group.

Multivariate analysis for animal selection in experimental research

BACKGROUND

Several researchers seek methods for the selection of homogeneous groups of animals in experimental studies, a fact justified because homogeneity is an indispensable prerequisite for casualization of treatments. The lack of robust methods that comply with statistical and biological principles is the reason why researchers use empirical or subjective methods, influencing their results.

OBJECTIVE

To develop a multivariate statistical model for the selection of a homogeneous group of animals for experimental research and to elaborate a computational package to use it.

METHODS

The set of echocardiographic data of 115 male Wistar rats with supravalvular aortic stenosis (AoS) was used as an example of model development. Initially, the data were standardized, and became dimensionless. Then, the variance matrix of the set was submitted to principal components analysis (PCA), aiming at reducing the parametric space and at retaining the relevant variability. That technique established a new Cartesian system into which the animals were allocated, and finally the confidence region (ellipsoid) was built for the profile of the animals' homogeneous responses. The animals located inside the ellipsoid were considered as belonging to the homogeneous batch; those outside the ellipsoid were considered spurious.

RESULTS

The PCA established eight descriptive axes that represented the accumulated variance of the data set in 88.71%. The allocation of the animals in the new system and the construction of the confidence region revealed six spurious animals as compared to the homogeneous batch of 109 animals.

CONCLUSION

The biometric criterion presented proved to be effective, because it considers the animal as a whole, analyzing jointly all parameters measured, in addition to having a small discard rate.

Diabetes mellitus activates fetal gene program and intensifies cardiac remodeling and oxidative stress in aged spontaneously hypertensive rats

Background

The combination of systemic arterial hypertension and diabetes mellitus (DM) induces greater cardiac remodeling than either condition alone. However, this association has been poorly addressed in senescent rats. Therefore, this study aimed to analyze the influence of streptozotocin-induced DM on ventricular remodeling and oxidative stress in aged spontaneously hypertensive rats (SHR).

Methods

Fifty 18 month old male SHR were divided into two groups: control (SHR, n = 25) and diabetic (SHR-DM, n = 25). DM was induced by streptozotocin (40 mg/kg, i.p.). After nine weeks, the rats underwent echocardiography and myocardial functional study in left ventricular (LV) isolated papillary muscle preparations. LV samples were obtained to measure myocyte diameters, interstitial collagen fraction, and hydroxyproline concentration. Gene expression of atrial natriuretic peptide (ANP) and α- and β-myosin heavy chain (MyHC) isoforms was evaluated by RT-PCR. Serum oxidative stress was assessed by measuring lipid hydroperoxide concentration and superoxide dismutase and glutathione peroxidase activities. Statistics: Student’s t test or Mann-Whitney test, p < 0.05.

Results

SHR-DM presented higher blood glucose (487 ± 29 vs. 89.1 ± 21.1 mg/dL) and lower body weight (277 ± 26 vs. 339 ± 38 g). Systolic blood pressure did not differ between groups. Echocardiography showed LV and left atrial dilation, LV diastolic and relative wall thickness decrease, and LV systolic and diastolic function impairment in SHR-DM. Papillary muscle study showed decreased myocardial contractility and contractile reserve in SHR-DM. Myocyte diameters and myocardial interstitial collagen fraction and hydroxyproline concentration did not differ between groups. Increased serum pro-oxidant activity and gene expression of ANP and β/α-MyHC ratio were observed in DM.

Conclusion

Diabetes mellitus induces cardiac dilation and functional impairment, increases oxidative stress and activates fetal gene program in aged spontaneously hypertensive rats.

Influence of AIN-93 diet on mortality and cardiac remodeling after myocardial infarction in rats

BACKGROUND

The AIN-93 diet was proposed by the American Institute of Nutrition with the objective of standardising studies in experimental nutrition. Our objective was to analyze the effects of AIN-93 diet after myocardial infarction in rats.

METHODS

Post weaning, the animals were divided into two groups: control (C, n=62), fed the standard diet of our laboratory (Labina); AIN-93 Group (n=70), fed the AIN-93 diet. Achieving 250 g, the animals were subjected to myocardial infarction.

RESULTS

Early mortality was increased in AIN-93 animals, associated with lower serum levels of calcium, magnesium, potassium, sodium, and phosphorus. On the other hand, after 90 days, AIN-93 showed smaller normalized left ventricular dimensions. The caloric and carbohydrate intake was smaller, but the fat intake was higher in AIN-93 rats. AIN-93 group also showed increased levels of β-hydroxyacylcoenzyme A dehydrogenase and citrate synthase. In addition, serum levels of insulin and cardiac levels of malondialdehyde, metalloproteinases-2 and -9, and TNF-α and IFN-γ were decreased in the AIN-93 group.

CONCLUSION

AIN-93 diet increased early mortality, while attenuated the chronic remodeling process after experimental coronary occlusion. Therefore, this diet has biological effects and should be use with attention in this model.

Cardiac fibroblast: the renaissance cell

The permanent cellular constituents of the heart include cardiac fibroblasts, myocytes, endothelial cells, and vascular smooth muscle cells. Previous studies have demonstrated that there are undulating changes in cardiac cell populations during embryonic development, through neonatal development and into the adult. Transient cell populations include lymphocytes, mast cells, and macrophages, which can interact with these permanent cell types to affect cardiac function. It has also been observed that there are marked differences in the makeup of the cardiac cell populations depending on the species, which may be important when examining myocardial remodeling. Current dogma states that the fibroblast makes up the largest cell population of the heart; however, this appears to vary for different species, especially mice. Cardiac fibroblasts play a critical role in maintaining normal cardiac function, as well as in cardiac remodeling during pathological conditions such as myocardial infarct and hypertension. These cells have numerous functions, including synthesis and deposition of extracellular matrix, cell-cell communication with myocytes, cell-cell signaling with other fibroblasts, as well as with endothelial cells. These contacts affect the electrophysiological properties, secretion of growth factors and cytokines, as well as potentiating blood vessel formation. Although a plethora of information is known about several of these processes, relatively little is understood about fibroblasts and their role in angiogenesis during development or cardiac remodeling. In this review, we provide insight into the various properties of cardiac fibroblasts that helps illustrate their importance in maintaining proper cardiac function, as well as their critical role in the remodeling heart.

Growth hormone and heart failure: oxidative stress and energetic metabolism in rats

Several evidences point for beneficial effects of growth hormone (GH) in heart failure (HF). Taking into account that HF is related with changes in myocardial oxidative stress and in energy generation from metabolic pathways, it is important to clarify whether GH increase or decrease myocardial oxidative stress and what is its effect on energetic metabolism in HF condition. Thus, this study investigated the effects of two different doses of GH on energetic metabolism and oxidative stress in myocardium of rats with HF. Male Wistar rats (n=25) were submitted to aortic stenosis (AS). The HF was evidenced by tachypnea and echocardiographic criteria around 28 weeks of AS. The rats were then randomly divided into three groups: (HF) with HF, treated with saline (0.9% NaCl); (HF-GH1), treated with 1 mk/kg/day recombinant human growth hormone (rhGH), and (HF-GH2) treated with 2 mg/kg/day rhGH. GH was injected, subcutaneously, daily for 2 weeks. A control group (sham; n=12), with the same age of the others rats was evaluated to confirm data for AS. HF had lower IGF-I (insulin-like growth factor-I) than sham-operated rats, and both GH treatments normalized IGF-I level. HF-GH1 animals had lower lipid hydroperoxide (LH), LH/total antioxidant substances (TAS) and glutathione-reductase than HF. Glutathione peroxidase (GSH-Px), hydroxyacyl coenzyme-A dehydrogenase, lactate dehydrogenase(LDH) were higher in HF-GH1 than in HF. HF-GH2 compared with HF, had increased LH/TAS ratio, as well as decreased oxidized glutathione and LDH activity. Comparing the two GH doses, GSH-Px, superoxide dismutase and LDH were lower in HF-GH2 than in HF-GH1. In conclusion, GH effects were dose-dependent and both tested doses did not aggravate the heart dysfunction. The higher GH dose, 2 mg/kg exerted detrimental effects related to energy metabolism and oxidative stress. The lower dose, 1mg/kg GH exerted beneficial effects enhancing antioxidant defences, reducing oxidative stress and improving energy generation in myocardium of rats with heart failure.

Determination of cell types and numbers during cardiac development in the neonatal and adult rat and mouse

Cardiac fibroblasts, myocytes, endothelial cells, and vascular smooth muscle cells are the major cellular constituents of the heart. The aim of this study was to observe alterations in myocardial cell populations during early neonatal development in the adult animal and to observe any variations of the cardiac cell populations in different species, specifically, the rat and mouse. Whole hearts were isolated from either mice or rats during the neonatal and adult stages of development, and single cell suspensions were prepared via sequential collagenase digestion. Heterogeneous cell populations were immunolabeled for specific cell types and analyzed using fluorescence-activated cell sorting (FACS). In addition, the left ventricle, right ventricle, and septa were isolated, fixed, and sectioned for morphometric analyses. These same cardiac regions were also analyzed using FACS. We observed that the adult murine myocardium is composed of approximately 56% myocytes, 27% fibroblasts, 7% endothelial cells, and 10% vascular smooth muscle cells. Moreover, our morphometric and FACS data demonstrated similar percentages in the three regions examined. During murine neonatal cardiac development, we observed a marked increase in numbers of cardiac fibroblasts and a resultant decrease in percentages of myocytes in late neonatal development (day 15). Finally, FACS analyses of the rat heart during development displayed similar results in relation to increases in cardiac fibroblasts during development; however, cell populations in the rat differed markedly from those observed in the mouse. Taken together, these data enabled us to establish a homeostatic model for the myocardium that can be compared with genetic and cardiac disease models.