Hemodynamic changes and neurohumoral regulation during development of congestive heart failure in a model of epinephrine-induced cardiomyopathy in conscious rabbits

The Effect of Molecular Hydrogen on Functional States of Erythrocytes in Rats with Simulated Chronic Heart Failure

Molecular hydrogen has an anti-inflammatory and cardioprotective effect, which is associated with its antioxidant properties. Erythrocytes are subjected to oxidative stress in pathologies of the cardiovascular system, which is the cause of a violation of the gas transport function of blood and microcirculation. Therefore, our aim was to investigate the effects of H₂ inhalation on the functional states of red blood cells (RBCs) in chronic heart failure (CHF) in rats. The markers of lipid peroxidation, antioxidant capacity, electrophoretic mobility of erythrocytes (EPM), aggregation, levels of adenosine triphosphate (ATP) and 2,3-diphosphoglyceric acid (2,3-DPG), hematological parameters were estimated in RBCs. An increase in EPM and a decrease in the level of aggregation were observed in groups with multiple and single H₂ application. The orientation of lipoperoxidation processes in erythrocytes was combined with the dynamics of changes in oxidative processes in blood plasma, it was observed with both single and multiple exposures, although the severity of the changes was greater with multiple H₂ inhalations. Probably, the antioxidant effects of molecular hydrogen mediate its metabolic action. Based on these data, we conclude the use of H₂ improves microcirculation and oxygen transport function of blood and can be effective in the treatment of CHF.

Low-Dose Propranolol Prevents Functional Decline in Catecholamine-Induced Acute Heart Failure in Rats

Severe hyper-catecholaminergic states likely cause heart failure and cardiac fibrosis. While previous studies demonstrated the effects of beta-blockade in experimental models of single-catecholamine excess states, the detailed benefits of beta-blockade in more realistic models of hyper-adrenergic states are less clearly understood. In this study, we examined different therapeutic dosages and the effects of propranolol in rats with hyper-acute catecholamine-induced heart failure, and subsequent cardiopulmonary changes. Rats (n = 41) underwent a 6 h infusion of epinephrine and norepinephrine alone, with additional low-dose (1 mg/kg) or high-dose propranolol (10 mg/kg) at hour 1. Cardiac and pulmonary tissues were examined after 6 h. Catecholamine-only groups had the lowest survival rate. Higher doses of propranolol (15 mg/kg) caused similarly low survival rates and were not further analyzed. All low-dose propranolol rats survived, with a modest survival improvement in the high-dose propranolol groups. Left ventricular (LV) systolic pressure and LV end-diastolic pressure improved maximally with low-dose propranolol. Cardiac immunohistochemistry revealed an LV upregulation of FGF-23 in the catecholamine groups, and this improved in low-dose propranolol groups. These results suggest catecholamine-induced heart failure initiates early pre-fibrotic pathways through FGF-23 upregulation. Low-dose propranolol exerted cardio-preventative effects through FGF-23 downregulation and hemodynamic-parameter improvement in our model of hyper-acute catecholamine-induced heart failure.

Evaluation of β-adrenergic ligands for development of pharmacological heart failure and transparency models in zebrafish

Cardiovascular toxicity represents one of the most common reasons for clinical trial failure. Consequently, early identification of novel cardioprotective strategies could prevent the later-stage drug-induced cardiac side effects. The use of zebrafish (Danio rerio) in preclinical studies has greatly increased. High-throughput and low-cost of assays make zebrafish model ideal for initial drug discovery. A common strategy to induce heart failure is a chronic β-adrenergic (βAR) stimulation. Herein, we set out to test a panel of βAR agonists to develop a pharmacological heart failure model in zebrafish. We assessed βAR agonists with respect to the elicited mortality, changes in heart rate, and morphological alterations in zebrafish larvae according to Fish Embryo Acute Toxicity Test. Among the tested βAR agonists, epinephrine elicited the most potent onset of heart stimulation (EC₅₀ = 0.05 mM), which corresponds with its physiological role as catecholamine. However, when used at ten-fold higher dose (0.5 mM), the same compound caused severe heart rate inhibition (-28.70 beats/min), which can be attributed to its cardiotoxicity. Further studies revealed that isoetharine abolished body pigmentation at the sublethal dose of 7.50 mM. Additionally, as a proof of concept that zebrafish can mimic human cardiac physiology, we tested βAR antagonists (propranolol, carvedilol, metoprolol, and labetalol) and verified that they inhibited fish heart rate in a similar fashion as in humans. In conclusion, we proposed two novel pharmacological models in zebrafish; i.e., epinephrine-dependent heart failure and isoetharine-dependent transparent zebrafish. We provided strong evidence that the zebrafish model constitutes a valuable tool for cardiovascular research.

Stress cardiomyopathy: Is it limited to Takotsubo syndrome? Problems of definition

In 2006, Takotsubo syndrome (TTC) was described as a distinct type of stress-induced cardiomyopathy (stress cardiomyopathy). However, when thinking about Takotsubo cardiomyopathy from the viewpoints of the AHA and ESC classifications, 2 possible problems may arise. The first potential problem is that a forecast of disease outcome is lacking in the ESC classification, whereas the AHA only states that 'outcome is favorable with appropriate medical therapy'. However, based on the literature data, one can make a general conclusion that occurrence of myocardial lesions in TTC (i.e., myocardial fibrosis and contraction-band necrosis) causes the same effects as in other diseases with similar levels of myocardial damage and should not be considered to have a lesser impact on mortality. To summarise, TTC can cause not only severe complications such as pulmonary oedema, cardiogenic shock, and dangerous ventricular arrhythmias, but also damage to the myocardium, which can result in the development of potentially fatal conditions even after the disappearance of LV apical ballooning. The second potential problem arises from the definition of TTC as a stress cardiomyopathy in the AHA classification. In fact, the main factors leading to TTC are stress and microvascular anginas, since, as has been already discussed, coronary spasm can cause myocardium stunning, resulting in persistent apical ballooning. Thus, based on this review, 3 distinct types of stress cardiomyopathies exist (variant angina, microvascular angina, and TTC), with poor prognosis. Adding these diseases to the classification of cardiomyopathies will facilitate diagnosis and preventive prolonged treatment, which should include intensive anti-stress therapy.

Clinical management of takotsubo cardiomyopathy

The clinical management of takotsubo cardiomyopathy is challenging. Its diagnosis must be made on clinical grounds and differentiated from alternative diagnoses with echocardiography, serum biomarkers, cardiac catheterization, and cardiac magnetic resonance imaging. Acute therapy includes supportive care, targeting the precipitating trigger if known, b-blockade, inhibitors of the renin-angiotensin system, and consideration of systemic anticoagulation in all patients. Recovery of left ventricular function to normal is expected regardless of early therapy. Although the prognosis is generally favorable, monitoring for early dangerous complications is essential. There is no evidence to support use of long-term medical therapy to reduce the risk of recurrence.

Effects of metoprolol on epinephrine-induced takotsubo-like left ventricular dysfunction in non-human primates

Takotsubo cardiomyopathy, alternatively known as stress cardiomyopathy, is an increasingly recognized clinical syndrome characterized by acute reversible apical ventricular dysfunction. To elucidate the mechanism, we tried to make a new model of takotsubo-like cardiomyopathy in non-human primates. Echocardiography revealed that repeated intravenous infusion of epinephrine overdose in cynomolgus monkeys induced takotsubo-like cardiomyopathy, which is characterized by progressive left ventricle and depressed systolic function with severe hypokinesis in apical regions and hyperkinesis in the basal region. Although this cardiac dysfunction almost normalized after a month even without any treatment, metoprolol, a beta-blocker, improved the decreased ejection fraction earlier than in the control. Luxol fast blue staining, which is useful for estimating myocytolysis, showed that increased myocytolysis was observed in the apical ventricle of the epinephrine-infused heart. Metoprolol diminished epinephrine-induced cardiomyocytolysis. To explain the mechanism of takotsubo myopathy and the effect of metoprolol, gene expressions in apical or basal ventricle were compared. Heart failure-related genes, such as brain natriuretic peptide, connective tissue growth factor and osteopontin; calcium signaling-related genes, such as ryanodine receptor 2, sarcoendoplasmic reticulum Ca(2+)-ATPase 2A2 and adenylate cyclase 7; renin-angiotensin system-related genes, such as angiotensinogen, angiotensin II receptor, type 1 and type 2; and mitochondria-related genes, such as peroxisome proliferator-activated receptor-gamma co-activator-1alpha, cytochrome c and transcription factor A mitochondrial, were significantly changed at the apical ventricle rather than at the basal ventricle. The changes of some genes improved with metoprolol treatment. These results indicate that this model is valuable in understanding the pathogenesis of takotsubo cardiomyopathy and the effectivity of beta-blockers.

Rabbit models of heart disease

Human heart disease is a major cause of death and disability. A variety of animal models of cardiac disease have been developed to better understand the etiology, cellular and molecular mechanisms of cardiac dysfunction and novel therapeutic strategies. The animal models have included large animals (e.g. pig and dog) and small rodents (e.g. mouse and rat) and the advantages of genetic manipulation in mice have appropriately encouraged the development of novel mouse models of cardiac disease. However, there are major differences between rodent and human hearts that raise cautions about the extrapolation of results from mouse to human. The rabbit is a medium-sized animal that has many cellular and molecular characteristics very much like human, and is a practical alternative to larger mammals. Numerous rabbit models of cardiac disease are discussed, including pressure or volume overload, ischemia, rapid-pacing, doxorubicin, drug-induced arrhythmias, transgenesis and infection. These models also lead to the assessment of therapeutic strategies which may become beneficial in human cardiac disease.

Ju Chen – University of California, San Diego, Department of Medicine, La Jolla, CA, USA

Robert Ross – University of California, San Diego, Cardiology Section, San Diego, CA, USA

Beneficial Effects of Chronic Pharmacological Manipulation of β-Adrenoreceptor Subtype Signaling in Rodent Dilated Ischemic Cardiomyopathy

Background— Studies in isolated cardiac myocytes have demonstrated that signaling via specific β 1 -adrenergic receptor subtypes (β 1 ARs) promotes but that signaling via β 2 ARs protects from cell death. We hypothesized that prolonged β 2 AR stimulation or β 1 AR blockade would each protect myocytes from death and thereby ameliorate cardiac remodeling in chronic heart failure.

Methods and Results— A large myocardial infarction (MI) induced in rats by coronary artery ligation resulted in a dilated cardiomyopathy (DCM) characterized by infarct expansion and a progressive increase in left ventricular (LV) end-diastolic volume, accompanied by a reduction in ejection fraction (EF), as assessed by repeated echocardiography. Pressure-volume analysis at 8 weeks after ligation showed that diastolic stiffness (Eed) and arterial elastance (Ea) were increased, end-systolic elastance (Ees) was decreased, and arterioventricular (AV) coupling (Ea/Ees) had deteriorated. Apoptosis was present in both peri-infarct and remote myocardium. Chronic (6-week) administration of the β 2 AR agonists fenoterol or zinterol, starting at 2 weeks after MI, reduced the extent of LV dilation, infarct expansion, and EF decline. The β 1 AR blocker metoprolol did not affect the former and preserved EF to a lesser extent than did the β 2 AR agonists. At 8 weeks after ligation, apoptosis was reduced by all drugs but to a greater extent by β 2 AR agonists than by the β 1 AR blocker. Both β 2 AR agonists and the β 1 AR blocker improved AV coupling, the former mainly by reducing Ea and the latter mainly by increasing Ees. Only the β 2 AR agonists reduced the Eed and the MI size by reducing infarct expansion.

Conclusions— These results provide proof of concept for the efficacy of chronic β 2 AR stimulation in this DCM model.

A novel gene IC53 stimulates ECV304 cell proliferation and is upregulated in failing heart

C53, cloned from rat brain cDNA library, can bind to p35, the precursor of activator of Cdk5. A novel gene with 84% homolog to C53, named IC53, was cloned from our 5300 EST database of human aorta cDNA library (GenBank Accession No. AF110322). Computational analysis showed that IC53 cDNA is 2538 bp long, encoding 419 amino acids, mapped to chromosome 17q21.31 with 12 exons, ubiquitously expressed in 12 tested normal tissues and 8 tumor cell lines from MTN membranes and vascular endothelial cells by Northern blot and in situ hybridization, and upregulated in the rat models of subacute heart failure and chronic ischemic heart failure by left coronary ligation. Stable transfection of IC53 stimulates ECV304 cell proliferation by 2.1-fold compared to cells with empty vector (P<0.05). The results support that IC53 is a novel gene, mainly expressed in vascular endothelial cells and mediates cell proliferation.

Alterations in myocardial creatinine kinase (CK) and lactate dehydrogenase (LDH) isoenzyme-distribution in a model of left ventricular dysfunction

The purpose of the current study was to evaluate myocardial creatinine kinase (CK) and lactate dehydrogenase (LDH) systems in a model of epinephrine-induced cardiomyopathy in rabbits. Eight rabbits received four repetitive epinephrine infusions (300 mg/kg/60 min, i.v.) in 12-day intervals and eight untreated rabbits served as controls (CTRL). Echocardiography demonstrated a significant deterioration of LV function as well as increased LV-diameter and -mass index in catecholamine-induced cardiomyopathy. Histological examination revealed that repetitive catecholamine infusion resulted in LV fibrous areas with collagenous content and an increase in myocyte width (16.9+/-0.8 microm vs. CTRL 12.9+/-0.9; P<0.05). LV dysfunction was associated with a decreased total LV lactate dehydrogenase activity (LDH; 0.43+/-0.03 IU/mg protein vs. CTRL 0.52+/-0.04; P<0.05) whereas total creatinine kinase activity was unchanged (CK; 7.30+/-0.63 IU/mg protein vs. CTRL 9.20+/-0.49, n.s.). Furthermore, myocardial LDH isoenzymes were shifted with a decrease in LDH(1) and an increase in LDH2 and LDH3 (LDH(1): 84.90+/-2.60% vs. CTRL 94.50+/-0.40; LDH2: 7.30+/-1.20% vs. 1.50+/-0.13; LDH3: 5.40+/-0.90% vs. 3.20+/-0.25; all P<0.05). Foetal B-CK isoenzymes were significantly increased (CK-MB 5.30+/-0.66 vs. 2.20+/-0.35%; P<0.05). The current study demonstrates changes in cardiac energy metabolism including an impaired LDH activity with a shift towards anaerobic isoenzymes as well as a more efficient CK system in a model of catecholamine-induced LV dysfunction.

Animal models of chronic heart failure

Chronic heart failure is associated with multiple pathophysiological alterations and adaptations, such as marked anatomic and biochemical changes of the myocardium, left ventricular dysfunction and dilatation, increased systemic vascular resistance, and activation of neurohumoral and cytokine systems. The use of animal models has provided a new insight into the complex pathogenesis of this syndrome and supplemented clinical experience. However, all of the animal models used have advantages and limitations, and the transfer from experimental to human heart failure needs critical evaluation. The current review will focus upon new aspects of rat and rabbit models of heart failure.