Echocardiographic assessment of left ventricular midwall mechanics in spontaneously hypertensive rats

Combined cardiovascular effects of ovariectomy and high-intensity interval training in female spontaneously hypertensive rats

Hypertensive postmenopausal women are more likely to develop adverse cardiac remodeling and respond less effectively to drug treatment than men. High-intensity interval exercise (HIIE) is a nonpharmacological strategy for the treatment of hypertension; however, the effectiveness in women remains uncertain. This study was designed to evaluate 1) the effects of HIIE training upon morphological and functional markers of cardiovascular health in female SHR and 2) to determine whether the hormonal shift induced by ovariectomy could influence cardiovascular responses to HIIE. Thirty-six SHR were randomly assigned to four groups: ovariectomized sedentary, ovariectomized trained, sham-operated sedentary, and sham-operated trained. The trained rats performed HIIE 5 days/wk for 8 wk. Blood pressure and echocardiographic measurements were performed before and after training in animals. Cardiac response to β-adrenergic stimulation and the expression of calcium regulatory proteins and estrogen receptors in heart samples were assessed. Endothelium-dependent vasorelaxation in response to acetylcholine was evaluated in aortic rings as well as the expression of nitric oxide synthase isoforms (eNOS and P-eNOS) by Western blotting. In both groups of trained SHR, HIIE induced eccentric cardiac remodeling with greater inotropic and chronotropic effects, as well as an increase in SERCA and β1AR expression. However, although the trained rats showed improved endothelial function and expression of eNOS and P-eNOS in the aorta, there was no demonstrated effect on blood pressure. In addition, the responses to HIIE training were not affected by ovariectomy. This work highlights the importance of assessing the cardiovascular efficacy and safety of different exercise modalities in women.NEW & NOTEWORTHY This study reports the effects of high-intensity interval exercise (HIIE) training on cardiac and endothelial function in female hypertensive rats. Despite a lack of effect on blood pressure (BP), HIIE training induces eccentric cardiac remodeling with greater functionals effects. Furthermore, training has beneficial effects on endothelial function. However, ovarian hormones do not seem to modulate cardiac and aortic adaptations to this training modality. All this underlines the need to consider training modalities on the cardiovascular system in women.

Ultrasonographic assessment of pulmonary and Central venous congestion in experimental heart failure

Pulmonary and systemic congestion as a consequence of heart failure are clinically recognized as alarm signals for clinical outcome and mortality. Although signs and symptoms of congestion are well detectable in patients, monitoring of congestion in small animals with heart failure lacks adequate noninvasive methodology yet. Here, we developed a novel ultrasonography-based scoring system to assess pulmonary and systemic congestion in experimental heart failure, by using lung ultrasound (LUS) and imaging of the inferior vena cava (Cava), termed CavaLUS. CavaLUS was established and tested in a rat model of supracoronary aortic banding and a mouse model of myocardial infarction, providing high sensitivity and specificity while correlating to numerous parameters of cardiac performance and disease severity. CavaLUS, therefore, provides a novel comprehensive tool for experimental heart failure in small animals to noninvasively assess congestion.NEW & NOTEWORTHY As thorough, noninvasive assessment of congestion is not available in small animals, we developed and validated an ultrasonography-based research tool to evaluate pulmonary and central venous congestion in experimental heart failure models.

Polyunsaturated ω3 fatty acids prevent the cardiac hypertrophy in hypertensive rats

It has been demonstrated that supplementation with the two main omega 3 polyunsaturated fatty acids (ω3 FAs), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), leads to modifications in the cardiac physiology. ω3 FAs can affect the membrane's lipid composition, as well as proteins' location and/or function. The Na⁺/H⁺ exchanger (NHE1) is an integral membrane protein involved in the maintenance of intracellular pH and its hyperactivity has been associated with the development of various cardiovascular diseases such as cardiac hypertrophy. Our aim was to determine the effect of ω3 FAs on systolic blood pressure (SBP), lipid profiles, NHE1 activity, and cardiac function in spontaneously hypertensive rats (SHR) using Wistar rats (W) as normotensive control. After weaning, the rats received orally ω3 FAs (200 mg/kg body mass/day/ 4 months). We measured SBP, lipid profiles, and different echocardiography parameters, which were used to calculate cardiac hypertrophy index, systolic function, and ventricular geometry. The rats were sacrificed, and ventricular cardiomyocytes were obtained to measure NHE1 activity. While the treatment with ω3 FAs did not affect the SBP, lipid analysis of plasma revealed a significant decrease in omega-6/omega-3 ratio, correlated with a significant reduction in left ventricular mass index in SHR. The NHE1 activity was significantly higher in SHR compared with W. While in W the NHE1 activity was similar in both groups, a significant decrease in NHE1 activity was detected in SHRs supplemented with ω3 FAs, reaching values comparable with W. Altogether, these findings revealed that diet supplementation with ω3 FAs since early age prevents the development of cardiac hypertrophy in SHR, perhaps by decreasing NHE1 activity, without altering hemodynamic overload.

Histamine 2 receptor antagonism elicits protection against doxorubicin-induced cardiotoxicity in rodent model

Doxorubicin (DOX), an anthracycline-based antibiotic, is regularly used in the management of carcinomas, and haematological malignancies have been downplayed in chemotherapy because of its ability to induce dilated cardiomyopathy (DCM). Dexrazoxane is approved to combat the cardiotoxicity, but limited by its adverse effects. Redox imbalance and reactive oxygen species generation plays major role in DOX-induced cardiotoxicity. Histamine, known to mediate various cardiovascular effects, but nevertheless the role of histamine or its receptors in DOX-induced DCM is remained obscure. Hence, this study is aimed to examine the effect of Famotidine (FAM), a H2 receptor antagonist on DOX-induced DCM in Wistar rats. Myocardial antioxidant status, stress and apoptosis markers, myocardial morphology and function were evaluated as the end points. Treatment with FAM has alleviated DOX doxorubicin-induced cardiotoxicity by reducing oxidative and nitrosative stress evident from lipid peroxidation and total nitrate-to-nitrite ratio, and enhanced the activity of super oxide dismutase. Cardiac stress markers like LDH and Na⁺-K⁺ATPase activities as well as CK-MB and Cardiac troponin levels were reduced by FAM treatment. It also normalised the myocardial function as assessed by 2D echocardiography and myocardial index. Treatment imparted anti-apoptotic effect as evident from decrease in myocardial caspase 3 and 9 activity and cleaved PARP expression. Effect of FAM is found to be comparable to the standard ACE inhibitor Captopril (CAP). The results from this study collectively suggest H2 receptor antagonism as a novel therapeutic strategy to impart biochemical, structural and functional improvement indicating its cardio-protective activity.

Cardiac hypertrophy reduction in SHR by specific silencing of myocardial Na+/H+ exchanger

We examined the effect of specific and local silencing of sodium/hydrogen exchanger isoform 1 (NHE1) with a small hairpin RNA delivered by lentivirus (L-shNHE1) in the cardiac left ventricle (LV) wall of spontaneously hypertensive rats, to reduce cardiac hypertrophy. Thirty days after the lentivirus was injected, NHE1 protein expression was reduced 53.3 ± 3% in the LV of the L-shNHE1 compared with the control group injected with L-shSCR (NHE1 scrambled sequence), without affecting its expression in other organs, such as liver and lung. Hypertrophic parameters as LV weight-to-body weight and LV weight-to-tibia length ratio were significantly reduced in animals injected with L-shNHE1 (2.32 ± 0.5 and 19.30 ± 0.42 mg/mm, respectively) compared with L-shSCR-injected rats (2.68 ± 0.06 and 21.53 ± 0.64 mg/mm, respectively). Histochemical analysis demonstrated a reduction of cardiomyocytes cross-sectional area in animals treated with L-shNHE1 compared with L-shSCR (309,81 ± 20,86 vs. 424,52 ± 21 μm2, P < 0.05). Echocardiography at the beginning and at the end of the treatment showed that shNHE1 expression for 30 days induced 9% reduction of LV mass. Also, animals treated with L-shNHE1 exhibited a reduced LV wall thickness without changing LV diastolic dimension and arterial pressure, indicating an increased parietal stress. In addition, midwall shortening was not modified, despite the increased wall tension, suggesting an improvement of cardiac function. Chronic shNHE1 expression in the heart emerges as a possible methodology to reduce pathological cardiac hypertrophy, avoiding potentially undesired effects caused from a body-wide inhibition of NHE1.

Physiological cardiac hypertrophy: critical role of AKT in the prevention of NHE-1 hyperactivity

BACKGROUND

The involvement of NHE-1 hyperactivity, critical for pathological cardiac hypertrophy (CH), in physiological CH has not been elucidated yet. Stimulation of NHE-1 increases intracellular Na(+) and Ca(2+) favouring calcineurin activation. Since myocardial stretch, an activator of NHE-1, is common to both types of CH, we speculate that NHE-1 hyperactivity may also happen in physiological CH. However, calcineurin activation is characteristic only for pathological hypertrophy. We hypothesize that an inhibitory AKT-dependent mechanism prevents NHE-1 hyperactivity in the setup of physiological CH.

METHODS

Physiological CH was induced in rats by swimming (90 min/day, 12 weeks) or in cultured isolated cardiomyocytes with IGF-1 (10 nmol/L).

RESULTS

Training induced eccentric CH development (left ventricular weight/tibial length: 22.0±0.3 vs. 24.3±0.7 mg/mm; myocyte cross sectional area: 100±3.2 vs. 117±4.1 %; sedentary (Sed) and swim-trained (Swim) respectively; p<0.05] with decreased myocardial stiffness and collagen deposition [1.7±0.05 % (Sed) vs. 1.4±0.09 % (Swim); p<0.05]. Increased phosphorylation of AKT, ERK1/2, p90(RSK) and NHE-1 at the consensus site for ERK1/2-p90(RSK) were detected in the hypertrophied hearts (P-AKT: 134±10 vs. 100±5; P-ERK1/2: 164±17 vs. 100±18; P-p90(RSK): 160±18 vs. 100±9; P-NHE-1 134±10 vs. 100±10; % in Swim vs. Sed respectively; p<0.05). No significant changes were detected neither in calcineurin activation [calcineurin Aβ 100±10 (Sed) vs. 96±12 (Swim)], nor NFAT nuclear translocation [100±3.11 (Sed) vs. 95±9.81 % (Swim)] nor NHE-1 expression [100±8.5 (Sed) vs. 95±6.7 % (Swim)]. Interestingly, the inhibitory phosphorylation of the NHE-1 consensus site for AKT was increased in the hypertrophied myocardium (151.6±19.4 (Swim) vs. 100±9.5 % (Sed); p<0.05). In isolated cardiomyocytes 24 hours IGF-1 increased cell area (114±1.3 %; p<0.05) and protein/DNA content (115±3.9 %, p<0.05), effects not abolished by NHE-1 inhibition with cariporide (114±3 and 117±4.4 %, respectively). IGF-1 significantly decreased NHE-1 activity during pHi recovery from sustained intracellular acidosis (JH+ at pHi 6.8: 4.08±0.74 and 9.09±1.21 mmol/L/min, IGF-1 vs. control; p<0.05), and abolished myocardial slow force response, the mechanical counterpart of stretch-induced NHE-1 activation.

CONCLUSIONS

NHE-1 hyperactivity seems not to be involved in physiological CH development, contrary to what characterizes pathological CH. We propose that AKT, through an inhibitory phosphorylation of the NHE-1, prevents its stretch-induced activation. This posttranslational modification emerges as an adaptive mechanism that avoids NHE-1 hyperactivity preserving its housekeeping functioning.

Sitagliptin reduces cardiac apoptosis, hypertrophy and fibrosis primarily by insulin-dependent mechanisms in experimental type-II diabetes. Potential roles of GLP-1 isoforms

Background

Myocardial fibrosis is a key process in diabetic cardiomyopathy. However, their underlying mechanisms have not been elucidated, leading to a lack of therapy. The glucagon-like peptide-1 (GLP-1) enhancer, sitagliptin, reduces hyperglycemia but may also trigger direct effects on the heart.

Methods

Goto-Kakizaki (GK) rats developed type-II diabetes and received sitagliptin, an anti-hyperglycemic drug (metformin) or vehicle (n=10, each). After cardiac structure and function assessment, plasma and left ventricles were isolated for biochemical studies. Cultured cardiomyocytes and fibroblasts were used for invitro assays.

Results

Untreated GK rats exhibited hyperglycemia, hyperlipidemia, plasma GLP-1 decrease, and cardiac cell-death, hypertrophy, fibrosis and prolonged deceleration time. Moreover, cardiac pro-apoptotic/necrotic, hypertrophic and fibrotic factors were up-regulated. Importantly, both sitagliptin and metformin lessened all these parameters. In cultured cardiomyocytes and cardiac fibroblasts, high-concentration of palmitate or glucose induced cell-death, hypertrophy and fibrosis. Interestingly, GLP-1 and its insulinotropic-inactive metabolite, GLP-1(9-36), alleviated these responses. In addition, despite a specific GLP-1 receptor was only detected in cardiomyocytes, GLP-1 isoforms attenuated the pro-fibrotic expression in cardiomyocytes and fibroblasts. In addition, GLP-1 receptor signalling may be linked to PPARδ activation, and metformin may also exhibit anti-apoptotic/necrotic and anti-fibrotic direct effects in cardiac cells.

Conclusions

Sitagliptin, via GLP-1 stabilization, promoted cardioprotection in type-II diabetic hearts primarily by limiting hyperglycemia e hyperlipidemia. However, GLP-1 and GLP-1(9-36) promoted survival and anti-hypertrophic/fibrotic effects on cultured cardiac cells, suggesting cell-autonomous cardioprotective actions.

Mechanoelectrical remodeling and arrhythmias during progression of hypertrophy

Despite a clear association between left ventricular (LV) mechanical dysfunction in end-stage heart failure and the incidence of arrhythmias, the majority of sudden cardiac deaths occur at earlier stages of disease development. The mechanisms by which structural, mechanical, and molecular alterations predispose to arrhythmias at the tissue level before the onset of LV dysfunction remain unclear. In a rat model of pressure overload hypertrophy (PoH) produced by ascending aortic banding, we correlated mechanical and structural changes measured in vivo with key electrophysiological changes measured ex vivo in the same animals. We found that action potential prolongation, a hallmark of electrical remodeling at the tissue level, is highly correlated with changes in LV wall thickness but not mechanical function. In contrast, conduction delays are not predicted by either mechanical or structural changes during disease development. Moreover, disrupted Cx43 phosphorylation at intermediate (increased) and late (decreased) stages of PoH are associated with moderate and severe conduction delays, respectively. Interestingly, the level of interaction between Cx43 and the cytoskeletal protein ZO-1 is exclusively decreased at the late stage of PoH. Closely coupled action potentials consistent with afterdepolarization-mediated triggered beats were readily observed in 6 of 15 PoH hearts but never in controls. Similarly, PoH (8/15) but not control hearts exhibited sustained episodes of ventricular tachycardia after rapid stimulation. The initiation and early maintenance of arrhythmias in PoH were formed by rapid and highly uniform activation wavefronts emanating from sites distal to the former site of stimulation. In conclusion, repolarization but not conduction delays are predicted by structural remodeling in PoH. Cx43 phosphorylation is disrupted at intermediate (increased) and late (decreased) stages, which are associated with conduction delays. Dephosphorylation of Cx43 is associated with loss of interaction with ZO-1 and severe conduction delays. Remodeling at all stages of PoH predisposes to triggers and focal arrhythmias.

Effect of preload reduction on sonographic myocardial integrated backscatter

PURPOSE

Sonographic myocardial tissue characterization with integrated backscatter (IBS) is affected by both structural and functional properties of the myocardium. The aim of the present study was to investigate the effect of preload reduction by hemodialysis (HD) on IBS measurements.

METHODS

Fifty-two patients on maintenance HD underwent echocardiography before and after a routine HD session. Measurements included the variation of IBS during the cardiac cycle (CV-IBS) and calibrated IBS (cal-IBS).

RESULTS

After HD, there were significant reductions in left ventricular end-diastolic and end-systolic dimensions and left atrial diameter. There was a reduction in stroke volume and LV ejection fraction consistent with a reduction in preload. Furthermore, CV-IBS was significantly lower after HD (7.9 +/- 2.2 versus 6.9 +/- 1.8 dB, 7.0 +/- 2.1 versus 6.2 +/- 1.9 dB, and 9.0 +/- 2.6 versus 8.1 +/- 2.0 dB [p < 0.01], respectively, in the left anterior, lateral, and inferior wall of the ventricle). Cal-IBS remained unchanged after dialysis compared with baseline. CV-IBS and ultrafiltration volume were significantly correlated.

CONCLUSION

HD leads to a decrease in CV-IBS that appears to be preload-dependent. This finding is in concordance with diminished left ventricular performance during HD.

Normalization of the calcineurin pathway underlies the regression of hypertensive hypertrophy induced by Na+/H+exchanger-1 (NHE-1) inhibitionThis paper is one of a selection of papers published in this Special Issue, entitled The Cellular and Molecular Basis of Cardiovascular Dysfunction, Dhalla 70th Birthday Tribute

Na+/H+exchanger-1 (NHE-1) inhibition induces cardiac hypertrophy regression and (or) prevention in several experimental models, although the intracellular events involved remain unclarified. We aimed to determine whether the calcineurin/NFAT pathway mediates this effect of NHE-1 inhibitors. Spontaneously hypertensive rats (SHR) with cardiac hypertrophy were treated with the NHE-1 inhibitors cariporide and BIIB723 for 30 days. Wistar rats served as normotensive controls. Their hearts were studied by echocardiography, immunoblotting, and real-time RT-PCR. Cytoplasmic Ca2+and calcineurin Aβ expression were measured in cultured neonatal rat ventricular myocytes (NRVM) stimulated with endothelin-1 for 24 h. NHE-1 blockade induced cardiac hypertrophy regression (heart mass/body mass = 3.63 ± 0.07 vs. 3.06 ± 0.05 and 3.02 ± 0.13 for untreated vs. cariporide- and BIIB723-treated SHR, respectively; p < 0.05) and decreased myocardial brain natriuretic peptide, calcineurin Aβ, and nuclear NFAT expressions. Echocardiographic evaluation demonstrated a reduction in left ventricular wall thickness without changes in cavity dimensions or a significant decrease in blood pressure. NHE-1-inhibitor treatment did not affect myocardial stiffness or endocardial shortening, but increased mid-wall shortening, suggesting that a positive inotropic effect develops after hypertrophy regression. Cariporide normalized the increased diastolic Ca2+and calcineurin Aβ expression observed in ET-1-stimulated NRVM. In conclusion, our data suggest that inactivation of calcineurin/NFAT pathway may underlie the regression of cardiac hyper-trophy induced by NHE-1 inhibition.

Aldosterone receptor blockade prevents the transition to cardiac pump dysfunction induced by beta-adrenoreceptor activation

The transition from compensated to decompensated left ventricular hypertrophy (LVH) in hypertension involves excessive beta-adrenoreceptor (beta-AR) stimulation. To explore whether aldosterone receptor activation contributes toward beta-AR-induced left ventricular (LV) decompensation in hypertensive LVH, the effect of spironolactone (SPIRO; 80 mg x kg(-1) x day(-1)) on LV cavity dimensions, function, and chamber remodeling mechanisms was evaluated in spontaneously hypertensive rats (SHR) receiving a low dose of the beta-AR agonist isoproterenol (ISO) at 0.02 to 0.04 mg x kg(-1) . day for 4.5 months. ISO administered to SHR resulted in an increased 24-hour urinary aldosterone excretion and LV cavity dimensions, a right shift in LV diastolic pressure-volume relations, a decreased LV relative wall thickness, and increased total, noncross-linked, type I and type III myocardial collagen concentrations without further enhancing increased myocardial norepinephrine (NE) release. ISO reduced pump function without modifying intrinsic myocardial systolic function or inducing further myocyte necrosis or apoptosis. ISO only increased LV cavity volumes after prolonged periods of administration. SPIRO abolished ISO-induced chamber dilatation, wall thinning, and pump dysfunction and reduced total, noncross-linked, type I and type III myocardial collagen concentrations but failed to modify blood pressure, volume preloads, intrinsic myocardial systolic function, myocardial NE release, or the degree of necrosis or apoptosis. In conclusion, these results suggest that aldosterone receptor blockade, through load-independent effects, may be useful in preventing the transition from compensated LVH to dilatation and pump dysfunction mediated by chronic beta-AR activation.