Effect of isoproterenol on myocardial perfusion, function, energy metabolism and nitric oxide pathway in the rat heart - a longitudinal MR study

Beta-adrenergic agonism protects mitochondrial metabolism in the pancreatectomised rat heart

The diabetic heart is characterised by functional, morphological and metabolic alterations predisposing it to contractile failure. Chronic sympathetic activation is a feature of the pathogenesis of heart failure, however the type 1 diabetic heart shows desensitisation to β-adrenergic stimulation. Here, we sought to understand the impact of repeated isoprenaline-mediated β-stimulation upon cardiac mitochondrial respiratory capacity and substrate metabolism in the 90% pancreatectomy (Px) rat model of type 1 diabetes. We hypothesised these hearts would be relatively protected against the metabolic impact of stress-induced cardiomyopathy. We found that individually both Px and isoprenaline suppressed cardiac mitochondrial respiration, but that this was preserved in Px rats receiving isoprenaline. Px and isoprenaline had contrasting effects on cardiac substrate metabolism, with increased reliance upon cardiac fatty acid oxidation capacity and altered ketone metabolism in the hearts of Px rats, but enhanced capacity for glucose uptake and metabolism in isoprenaline-treated rats. Moreover, Px rats were protected against isoprenaline-induced mortality, whilst isoprenaline elevated cGMP and protected myocardial energetic status in Px rat hearts. Our work suggests that adrenergic stimulation may be protective in the type 1 diabetic heart, and underlines the importance of studying pathological features in combination when modeling complex disease in rodents.

Multiple organs injury and myocardial energy metabolism disorders induced by isoproterenol

The study sought to assess the detrimental effects of isoproterenol (ISO) on major organs and investigate the potential reversibility of these adverse reactions in mice. Male mice were divided into normal control, 0.2 mg/kg.d and 3.0 mg/kg.d ISO groups, and were subcutaneously administered of the respective doses for 14 consecutive days. Subsequently, a recovery period experiment was conducted, replicating the aforementioned procedure, followed by an additional 2-week recovery period for the mice. Following 14 consecutive days of administration, mice treated with ISO exhibited notable cardiac damage manifested by abnormal ECG patterns, dysregulated energy metabolism, elevated cardiac hypertrophy, and increased heart pathological score. Additionally, the administration of ISO resulted in liver and kidney damage, as evidenced by increased pathological score, serum albumin level, and urea level. Lung damage was also observed, indicated by an increase in lung pathological score. Furthermore, the administration of ISO at a dosage of 3.0 mg/kg.d resulted in a decrease in liver mass index, serum iron content, and an increase in lung mass index. After a 2-week recovery period, mice treated with ISO showed abnormalities in ECG patterns and dysregulated myocardial energy metabolism, accompanied by a decrease in serum iron content. Histopathological examinations revealed continued pathological changes in the heart and lung, as well as significant hemosiderin deposition in the spleen. Furthermore, the group treated with ISO at a dosage of 3.0 mg/kg.d showed an increase in serum AST and TP levels. In summary, the study demonstrates that both 0.2 mg/kg.d and 3.0 mg/kg.d doses of ISO can induce damage to the heart, liver, lung, kidney, and spleen, with the higher dose causing more severe injuries. After a 2-week withdrawal period, the liver, kidney, and thymus injuries caused by 0.2 mg/kg ISO shows signs of recovery, while damage to the heart, lung, and spleen persists. The thymus injury mostly recovers, with minimal kidney pathology, but significant damage to the heart, liver, and lung remains even after the withdrawal period for the 3.0 mg/kg ISO dose.

L-carnitine attenuated hyperuricemia-associated left ventricular remodeling through ameliorating cardiomyocytic lipid deposition

Hyperuricemia (HUA) is associated with left ventricular remodeling (LVR) and thereby causes the initiation and development of a large number of cardiovascular diseases. LVR is typically accompanied by cardiomyocyte energy metabolic disorder. The energy supply of cardiomyocytes is provided by glucose and fatty acid (FA) metabolism. Currently, the effect of HUA on cardiomyocytic FA metabolism is unclear. In this study, we demonstrate that UA-induced cardiomyocyte injury is associated with cytoplasmic lipid deposition, which can be ameliorated by the FA metabolism-promoting drug L-carnitine (LC). UA suppresses carnitine palmitoyl transferase 1B (CPT1B), thereby inhibiting FA transport into the mitochondrial inner matrix for elimination. LC intervention can ameliorate HUA-associated left ventricular anterior wall thickening in mice. This study showed that FA transport dysfunction plays is a critical mechanism in both cardiomyocytic injury and HUA-associated LVR and promoting cytoplasmic FA transportation through pharmacological treatment by LC is a valid strategy to attenuate HUA-associated LVR.

Evolution of β-catenin-independent Wnt-GSK3-mTOR signalling in regulation of energy metabolism in isoproterenol-induced cardiotoxicity model

OBJECTIVE

Isoproterenol (ISO) is widely used agent to study the effects of interventions which could prevent or attenuate the development of myocardial infarction. The sequence of pathological event's revealed that increased myocardial tissue oxygen demand and energy dysregulation exist early during Iso-induced cardiac toxicity. Later, tissue hypoxia results in increased oxidative stress, inflammation and fibrosis along with cardiac dysfunction in this model. The canonical Wnt/β-catenin pathway has been reported to directly implicate in inducing cardiomyocyte hypertrophy and remodelling. However, less is known about the role of non-canonical Wnt signalling in cardiac diseases.

METHOD

Certain evidences have suggested that the activation of Wnt could up-regulate key energy sensor and cell growth regulator mTOR (Mechanistic target of rapamycin) by inhibition of GSK-3β mediator.

RESULT

The GSK-3β could negatively influence the mTOR activity and produce energy dysregulation during stress or hypoxic conditions. This suggests that the inhibition of GSK-3β by Wnt signalling could up-regulate mTOR levels and thereby restore early myocardial tissue energy balance and prevent cardiac toxicity in rodents.

CONCLUSION

We hereby discuss a novel therapeutic role of the β-catenin independent, Wnt-GSK3-mTOR axis in attenuation of Iso-induced cardiotoxicity in rodents.

M3, a 1,4-Dihydropyridine Derivative and Mixed L-/T-Type Calcium Channel Blocker, Attenuates Isoproterenol-Induced Toxicity in Male Wistar Rats

Recent evidence indicates that Ca²⁺ dysregulation is involved in the pathogenesis of isoproterenol (ISP)-induced biochemical toxicity and associated oxidative stress. In this study, we investigated the chemopreventive benefit of M3, a 1,4-dihydropyridine calcium channel blocker, against ISP-induced toxicity in male Wistar rats. Adult rats were divided into eight groups of six rats/group. Groups 1-5 received normal saline (control, 10 mL/kg/day, p.o.), ISP (85 mg/kg/day, s.c.), M3 lower dose (M3LD, 5 mg/kg, p.o.), M3 upper dose (M3UD, 20 mg/kg/day, p.o.), and Nifedipine (NFD, 20 mg/kg/day, p.o.), respectively. Others (groups 6-8) were pretreated with either M3LD, M3UD or NFD one hour before ISP administration. All rats were sacrificed 24 h after the last administration and changes in biochemical, hematological, and antioxidant parameters were assessed. Histologic examination of the heart, liver and kidney was also conducted. ISP elevated (p < 0.05) Ca²⁺, alanine aminotransferase, lactate dehydrogenase, triglycerides, and low-density lipoprotein levels when compared with control. Similarly, ISP increased levels of markers of renal function (p < 0.01), C-reactive protein (148.1%) and myocardial malondialdehyde (MDA, 88.7%) and tumor necrosis factor-alpha (109.2%). Platelet level was reduced (p < 0.05) in the ISP-intoxicated control rats. M3 exhibited antioxidant property, reduced levels of triglycerides, MDA and improved biochemical and hematological alterations associated with ISP toxicity. M3, however, was not effective in restoring histological changes that characterized ISP toxicity at the doses used. M3 offers chemopreventive benefits against ISP toxicity possibly through L-/T-type calcium channels blockade and modulatory actions on biochemical and antioxidant homeostasis.

Sex-Mediated Response to the Beta-Blocker Landiolol in Sepsis: An Experimental, Randomized Study

OBJECTIVES

To investigate any gender effect of the beta-1 adrenergic blocker, landiolol, on cardiac performance and energy metabolism in septic rats, and to explore the expression of genes and proteins involved in this process.

DESIGN

Randomized animal study.

SETTING

University research laboratory.

SUBJECTS

Male and female Wistar rats.

INTERVENTIONS

One hour after cecal ligation and puncture, male and female rats were randomly allocated to the following groups: sham male, cecal ligation and puncture male, cecal ligation and puncture + landiolol male, sham female, cecal ligation and puncture female, and cecal ligation and puncture + landiolol female. Cardiac MRI was carried out 18 hours after cecal ligation and puncture to assess in vivo cardiac function. Ex vivo cardiac function measurement and P magnetic resonance spectroscopy were subsequently performed using an isovolumic isolated heart preparation. Finally, we assessed cardiac gene and protein expression.

MEASUREMENTS AND MAIN RESULTS

In males, landiolol increased indexed stroke volume by reversing the indexed end-diastolic volume reduction without affecting left ventricle ejection fraction. In females, landiolol did not increase indexed stroke volume and indexed end-diastolic volume but decreased left ventricle ejection fraction. Landiolol had no effect on ex vivo cardiac function and on high-energy phosphate compounds. The effect of landiolol on the gene expression of natriuretic peptide receptor 3 and on protein expression of phosphorylated-AKT:AKT ratio and endothelial nitric oxide synthase was different in males and females.

CONCLUSIONS

Landiolol improved the in vivo cardiac performance of septic male rats while deleterious effects were reported in females. Expression of natriuretic peptide receptor 3, phosphorylated-AKT:AKT, and endothelial nitric oxide synthase are signaling pathways to investigate to better understand the sex differences in sepsis.

Comprehensive Analysis of Animal Models of Cardiovascular Disease using Multiscale X-Ray Phase Contrast Tomography

Cardiovascular diseases (CVDs) affect the myocardium and vasculature, inducing remodelling of the heart from cellular to whole organ level. To assess their impact at micro and macroscopic level, multi-resolution imaging techniques that provide high quality images without sample alteration and in 3D are necessary: requirements not fulfilled by most of current methods. In this paper, we take advantage of the non-destructive time-efficient 3D multiscale capabilities of synchrotron Propagation-based X-Ray Phase Contrast Imaging (PB-X-PCI) to study a wide range of cardiac tissue characteristics in one healthy and three different diseased rat models. With a dedicated image processing pipeline, PB-X-PCI images are analysed in order to show its capability to assess different cardiac tissue components at both macroscopic and microscopic levels. The presented technique evaluates in detail the overall cardiac morphology, myocyte aggregate orientation, vasculature changes, fibrosis formation and nearly single cell arrangement. Our results agree with conventional histology and literature. This study demonstrates that synchrotron PB-X-PCI, combined with image processing tools, is a powerful technique for multi-resolution structural investigation of the heart ex-vivo. Therefore, the proposed approach can improve the understanding of the multiscale remodelling processes occurring in CVDs, and the comprehensive and fast assessment of future interventional approaches.

Comparison between Radionuclide Ventriculography and Echocardiography for Quantification of Left Ventricular Systolic Function in Rats Exposed to Doxorubicin

Background

Radionuclide ventriculography (RV) is a validated method to evaluate the left ventricular systolic function (LVSF) in small rodents. However, no prior study has compared the results of RV with those obtained by other imaging methods in this context.

Objectives

To compare the results of LVSF obtained by RV and echocardiography (ECHO) in an experimental model of cardiotoxicity due to doxorubicin (DXR) in rats.

Methods

Adult male Wistar rats serving as controls (n = 7) or receiving DXR (n = 22) in accumulated doses of 8, 12, and 16 mg/kg were evaluated with ECHO performed with a Sonos 5500 Philips equipment (12-MHz transducer) and RV obtained with an Orbiter-Siemens gamma camera using a pinhole collimator with a 4-mm aperture. Histopathological quantification of myocardial fibrosis was performed after euthanasia.

Results

The control animals showed comparable results in the LVSF analysis obtained with ECHO and RV (83.5 ± 5% and 82.8 ± 2.8%, respectively, p > 0.05). The animals that received DXR presented lower LVSF values when compared with controls (p < 0.05); however, the LVSF values obtained by RV (60.6 ± 12.5%) were lower than those obtained by ECHO (71.8 ± 10.1%, p = 0.0004) in this group. An analysis of the correlation between the LVSF and myocardial fibrosis showed a moderate correlation when the LVSF was assessed by ECHO (r = -0.69, p = 0.0002) and a stronger correlation when it was assessed by RV (r = -0.79, p < 0.0001). On multiple regression analysis, only RV correlated independently with myocardial fibrosis.

Conclusion

RV is an alternative method to assess the left ventricular function in small rodents in vivo. When compared with ECHO, RV showed a better correlation with the degree of myocardial injury in a model of DXR-induced cardiotoxicity.

Novel ketone diet enhances physical and cognitive performance

Ketone bodies are the most energy-efficient fuel and yield more ATP per mole of substrate than pyruvate and increase the free energy released from ATP hydrolysis. Elevation of circulating ketones via high-fat, low-carbohydrate diets has been used for the treatment of drug-refractory epilepsy and for neurodegenerative diseases, such as Parkinson's disease. Ketones may also be beneficial for muscle and brain in times of stress, such as endurance exercise. The challenge has been to raise circulating ketone levels by using a palatable diet without altering lipid levels. We found that blood ketone levels can be increased and cholesterol and triglycerides decreased by feeding rats a novel ketone ester diet: chow that is supplemented with (R)-3-hydroxybutyl (R)-3-hydroxybutyrate as 30% of calories. For 5 d, rats on the ketone diet ran 32% further on a treadmill than did control rats that ate an isocaloric diet that was supplemented with either corn starch or palm oil (P < 0.05). Ketone-fed rats completed an 8-arm radial maze test 38% faster than did those on the other diets, making more correct decisions before making a mistake (P < 0.05). Isolated, perfused hearts from rats that were fed the ketone diet had greater free energy available from ATP hydrolysis during increased work than did hearts from rats on the other diets as shown by using [31P]-NMR spectroscopy. The novel ketone diet, therefore, improved physical performance and cognitive function in rats, and its energy-sparing properties suggest that it may help to treat a range of human conditions with metabolic abnormalities.-Murray, A. J., Knight, N. S., Cole, M. A., Cochlin, L. E., Carter, E., Tchabanenko, K., Pichulik, T., Gulston, M. K., Atherton, H. J., Schroeder, M. A., Deacon, R. M. J., Kashiwaya, Y., King, M. T., Pawlosky, R., Rawlins, J. N. P., Tyler, D. J., Griffin, J. L., Robertson, J., Veech, R. L., Clarke, K. Novel ketone diet enhances physical and cognitive performance.

Myocardial arterial spin labeling

Arterial spin labeling (ASL) is a cardiovascular magnetic resonance (CMR) technique for mapping regional myocardial blood flow. It does not require any contrast agents, is compatible with stress testing, and can be performed repeatedly or even continuously. ASL-CMR has been performed with great success in small-animals, but sensitivity to date has been poor in large animals and humans and remains an active area of research. This review paper summarizes the development of ASL-CMR techniques, current state-of-the-art imaging methods, the latest findings from pre-clinical and clinical studies, and future directions. We also explain how successful developments in brain ASL and small-animal ASL-CMR have helped to inform developments in large animal and human ASL-CMR.

Small animal cardiovascular MR imaging and spectroscopy

The use of MR imaging and spectroscopy for studying cardiovascular disease processes in small animals has increased tremendously over the past decade. This is the result of the remarkable advances in MR technologies and the increased availability of genetically modified mice. MR techniques provide a window on the entire timeline of cardiovascular disease development, ranging from subtle early changes in myocardial metabolism that often mark disease onset to severe myocardial dysfunction associated with end-stage heart failure. MR imaging and spectroscopy techniques play an important role in basic cardiovascular research and in cardiovascular disease diagnosis and therapy follow-up. This is due to the broad range of functional, structural and metabolic parameters that can be quantified by MR under in vivo conditions non-invasively. This review describes the spectrum of MR techniques that are employed in small animal cardiovascular disease research and how the technological challenges resulting from the small dimensions of heart and blood vessels as well as high heart and respiratory rates, particularly in mice, are tackled.

Manganese-enhanced MRI detection of impaired calcium regulation in a mouse model of cardiac hypertrophy

The aim of this study was to use manganese (Mn)-enhanced MRI (MEMRI) to detect changes in calcium handling associated with cardiac hypertrophy in a mouse model, and to determine whether the impact of creatine kinase ablation is detectable using this method. Male C57BL/6 (C57, n = 11) and male creatine kinase double-knockout (CK-M/Mito(-/-) , DBKO, n = 12) mice were imaged using the saturation recovery Look-Locker T1 mapping sequence before and after the development of cardiac hypertrophy. Hypertrophy was induced via subcutaneous continuous 3-day infusion of isoproterenol, and sham mice not subjected to cardiac hypertrophy were also imaged. During each scan, the contrast agent Mn was administered and the resulting change in R1 (=1/T1) was calculated. Two anatomical regions of interest (ROIs) were considered, the left-ventricular free wall (LVFW) and the septum, and one ROI in an Mn-containing standard placed next to the mouse. We found statistically significant (p < 0.05) decreases in the uptake of Mn in both the LVFW and septum following the induction of cardiac hypertrophy. No statistically significant decreases were detected in the standard, and no statistically significant differences were found among the sham mice. Using a murine model, we successfully demonstrated that changes in Mn uptake as a result of cardiac hypertrophy are detectable using the functional contrast agent and calcium mimetic Mn. Our measurements showed a decrease in the relaxivity (R1) of the myocardium following cardiac hypertrophy compared with normal control mice.