Functional and bioenergetic consequences of postinfarction left ventricular remodeling in a new porcine model. MRI and 31 P-MRS study

Assessing the Feasibility of Dynamic 31P Spectroscopy for Metabolic Studies with a 1.0T Extremity Scanner

Objective: The feasibility of conducting in vivo non-localized ³¹P Magnetic Resonance Spectroscopy (MRS) with a 1.0T extremity scanner and the potential to increase accessibility of this important diagnostic tool for low cost applications is revisited. Methods: This work presents a custom transmit-only quadrature birdcage, four-element receive coil array, and spectrometer interfaced to a commercial ONI 1.0T magnet for enabling multi-channel, non-1H frequency capabilities. A custom, magnetic resonance compatible plantar flexion-extension exercise device was also developed to enable exercise protocols. The coils were assessed with bench measurements and ³¹P phantom studies before an in vivo demonstration. Results: In pulse and acquire spectroscopy of a phantom, the array was found to improve the signal-to-noise ratio (SNR) by a factor of 1.31 and reduce the linewidth by 13.9% when compared to a large loop coil of the same overall size. In vivo testing results show that two averages and a four second repetition time for a temporal resolution of eight seconds was sufficient to obtain phosphocreatine recovery values and baseline pH levels aligned with expected literature values. Conclusion: Initial in vivo human skeletal muscle ³¹P MRS allowed successful monitoring of metabolic changes during an 18-minute exercise protocol. Significance: Adding an array coil and multinuclear capability to a commercial low-cost 1.0T extremity scanner enabled the observation of characteristic ³¹P metabolic information, such as the phosphocreatine recovery rate and underlying baseline pH.

Exosomes secreted by hiPSC-derived cardiac cells improve recovery from myocardial infarction in swine

Cell therapy treatment of myocardial infarction (MI) is mediated, in part, by exosomes secreted from transplanted cells. Thus, we compared the efficacy of treatment with a mixture of cardiomyocytes (CMs; 10 million), endothelial cells (ECs; 5 million), and smooth muscle cells (SMCs; 5 million) derived from human induced pluripotent stem cells (hiPSCs), or with exosomes extracted from the three cell types, in pigs after MI. Female pigs received sham surgery; infarction without treatment (MI group); or infarction and treatment with hiPSC-CMs, hiPSC-ECs, and hiPSC-SMCs (MI + Cell group); with homogenized fragments from the same dose of cells administered to the MI + Cell group (MI + Fra group); or with exosomes (7.5 mg) extracted from a 2:1:1 mixture of hiPSC-CMs:hiPSC-ECs:hiPSC-SMCs (MI + Exo group). Cells and exosomes were injected into the injured myocardium. In vitro, exosomes promoted EC tube formation and microvessel sprouting from mouse aortic rings and protected hiPSC-CMs by reducing apoptosis, maintaining intracellular calcium homeostasis, and increasing adenosine 5'-triphosphate. In vivo, measurements of left ventricular ejection fraction, wall stress, myocardial bioenergetics, cardiac hypertrophy, scar size, cell apoptosis, and angiogenesis in the infarcted region were better in the MI + Cell, MI + Fra, and MI + Exo groups than in the MI group 4 weeks after infarction. The frequencies of arrhythmic events in animals from the MI, MI + Cell, and MI + Exo groups were similar. Thus, exosomes secreted by hiPSC-derived cardiac cells improved myocardial recovery without increasing the frequency of arrhythmogenic complications and may provide an acellular therapeutic option for myocardial injury.

Large Animal Models of Heart Failure: A Translational Bridge to Clinical Success

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Preclinical large animal models play a critical and expanding role in translating basic science findings to the development and clinical approval of novel cardiovascular therapeutics.

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This state-of-the-art review outlines existing methodologies and physiological phenotypes of several HF models developed in large animals. A comprehensive list of porcine, ovine, and canine models of disease are presented, and the translational importance of these studies to clinical success is highlighted through a brief overview of recent devices approved by the FDA alongside associated clinical trials and preclinical animal reports.

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Increasing the use of large animal models of HF holds significant potential for identifying new mechanisms underlying this disease and providing valuable information regarding the safety and efficacy of new therapies, thus, improving physiological and economical translation of animal research to the successful treatment of human HF.

Preclinical large animal models of heart failure (HF) play a critical and expanding role in translating basic science findings to the development and clinical approval of novel therapeutics and devices. The complex combination of cardiovascular events and risk factors leading to HF has proved challenging for the development of new treatments for these patients. This state-of-the-art review presents historical and recent studies in porcine, ovine, and canine models of HF and outlines existing methodologies and physiological phenotypes. The translational importance of large animal studies to clinical success is also highlighted with an overview of recent devices approved by the Food and Drug Administration, together with preclinical HF animal studies used to aid both development and safety and/or efficacy testing. Increasing the use of large animal models of HF holds significant potential for identifying the novel mechanisms underlying the clinical condition and to improving physiological and economical translation of animal research to successfully treat human HF.

Feasibility of Using a 1T Extremity Scanner with a Four-Element Array to Detect 31P in the Human Calf

The feasibility of conducting in vivo non-localized skeletal muscle ³¹P Magnetic Resonance Spectroscopy (MRS) with a low-cost extremity 1 Tesla magnet is demonstrated. We designed and built a transmit-only quadrature birdcage, four-element receive coil array, and employed a home-built spectrometer interfaced with a commercial ONI 1.0T magnet. In phantom comparison tests with a large loop coil of comparable size, the array was found to improve the SNR by a factor of 1.8 and the linewidth from 0.72 ppm to 0.45 ppm. Phantom and in vivo testing results show only 6 averages with a 4 second repetition time are required to obtain quantifiable ³¹P spectra. Initial in vivo human skeletal muscle ³¹P spectra successfully allowed for peak characterization. A low-cost approach to MRS could enable more widespread use of this tool in clinical diagnosis and in vivo metabolic research.

FGF23 impairs peripheral microvascular function in renal failure

Cardiovascular diseases account for ~50% of mortality in patients with chronic kidney disease (CKD). Fibroblast growth factor 23 (FGF23) is independently associated with endothelial dysfunction and cardiovascular mortality. We hypothesized that CKD impairs microvascular endothelial function and that this can be attributed to FGF23. Mice were subjected to partial nephrectomy (5/6Nx) or sham surgery. To evaluate the functional role of FGF23, non-CKD mice received FGF23 injections and CKD mice received FGF23-blocking antibodies after 5/6Nx surgery. To examine microvascular function, myocardial perfusion in vivo and vascular function of gracilis resistance arteries ex vivo were assessed in mice. 5/6Nx surgery blunted ex vivo vasodilator responses to acetylcholine, whereas responses to sodium nitroprusside or endothelin were normal. In vivo FGF23 injections in non-CKD mice mimicked this endothelial defect, and FGF23 antibodies in 5/6Nx mice prevented endothelial dysfunction. Stimulation of microvascular endothelial cells with FGF23 in vitro did not induce ERK phosphorylation. Increased plasma asymmetric dimethylarginine concentrations were increased by FGF23 and strongly correlated with endothelial dysfunction. Increased FGF23 concentration did not mimic impaired endothelial function in the myocardium of 5/6Nx mice. In conclusion, impaired peripheral endothelium-dependent vasodilatation in 5/6Nx mice is mediated by FGF23 and can be prevented by blocking FGF23. These data corroborate FGF23 as an important target to combat cardiovascular disease in CKD. NEW & NOTEWORTHY In the present study, we provide the first evidence that fibroblast growth factor 23 (FGF23) is a cause of peripheral endothelial dysfunction in a model of early chronic kidney disease (CKD) and that endothelial dysfunction in CKD can be prevented by blockade of FGF23. This pathological effect on endothelial cells was induced by long-term exposure of physiological levels of FGF23. Mechanistically, increased plasma asymmetric dimethylarginine concentrations were strongly associated with this endothelial dysfunction in CKD and were increased by FGF23.

Associations of changes in body mass index with all-cause and cardiovascular mortality in healthy middle-aged adults

Background

Conflicting data exist regarding the association of body mass index (BMI) changes with all-cause and cardiovascular (CV) mortality. The current study investigated the association between changes in BMI and all-cause, CV, and non-CV mortality in a large cohort of middle-aged adults.

Methods

A total of 379,535 adults over 40 years of age without pre-existing CV disease or cancer at baseline were enrolled to undergo a series of at least three health examinations of biennial intervals. Changes in BMI between baseline, midpoint follow-up, and final health examination during mean 9.3 years were defined according to the pattern of BMI change as follows: stable, sustained gain, sustained loss, and fluctuation. The relationship between BMI change category and mortality was assessed by multivariate Cox regression reporting hazard ratio (HR) with 95% confidence interval (95% CI).

Results

During a mean follow-up of 10.7 years for mortality, 12,378 deaths occurred from all causes, of which 2,114 were CV and 10,264 were non-CV deaths. Sustained BMI gain was associated with the lower risk of all-cause (HR 0.89, 95% CI: 0.83–0.95), CV (HR 0.84, 95% CI 0.72–0.98), and non-CV mortality (HR 0.90, 95% CI 0.84–0.96) compared with stable BMI. Conversely, sustained BMI loss (HR 1.25, 95% CI 1.19–1.32) and fluctuation (HR 1.13, 95% CI 1.08–1.19) displayed a higher risk of all-cause mortality compared with stable BMI, which was mainly attributable to the increase in non-CV mortality.

Conclusion

Sustained BMI gains were associated with reduced risk of all-cause, CV, and non-CV mortality in middle-aged healthy adults.

Evaluation of cardiac energetics by non-invasive 31P magnetic resonance spectroscopy

Alterations in myocardial energy metabolism have been implicated in the pathophysiology of cardiac diseases such as heart failure and diabetic cardiomyopathy. ³¹P magnetic resonance spectroscopy (MRS) is a powerful tool to investigate cardiac energetics non-invasively in vivo, by detecting phosphorus (³¹P)-containing metabolites involved in energy supply and buffering. In this article, we review the historical development of cardiac ³¹P MRS, the readouts used to assess cardiac energetics from ³¹P MRS, and how ³¹P MRS studies have contributed to the understanding of cardiac energy metabolism in heart failure and diabetes. This article is part of a Special issue entitled Cardiac adaptations to obesity, diabetes and insulin resistance, edited by Professors Jan F.C. Glatz, Jason R.B. Dyck and Christine Des Rosiers.

Myocardial contrast echocardiography in mice: technical and physiological aspects

Myocardial contrast echocardiography (MCE) offers the opportunity to study myocardial perfusion defects in mice in detail. The value of MCE compared with single-photon emission computed tomography, positron emission tomography, and computed tomography consists of high spatial resolution, the possibility of quantification of blood volume, and relatively low costs. Nevertheless, a number of technical and physiological aspects should be considered to ensure reproducibility among research groups. The aim of this overview is to describe technical aspects of MCE and the physiological parameters that influence myocardial perfusion data obtained with this technique. First, technical aspects of MCE discussed in this technical review are logarithmic compression of ultrasound data by ultrasound systems, saturation of the contrast signal, and acquisition of images during different phases of the cardiac cycle. Second, physiological aspects of myocardial perfusion that are affected by the experimental design are discussed, including the anesthesia regimen, systemic cardiovascular effects of vasoactive agents used, and fluctuations in body temperature that alter myocardial perfusion. When these technical and physiological aspects of MCE are taken into account and adequately standardized, MCE is an easily accessible technique for mice that can be used to study the control of myocardial perfusion by a wide range of factors.

Quantitative Proteomics and Immunohistochemistry Reveal Insights into Cellular and Molecular Processes in the Infarct Border Zone One Month after Myocardial Infarction

Postinfarction remodeling and expansion of the peri-infarct border zone (BZ) directly correlate with mortality following myocardial infarction (MI); however, the cellular and molecular mechanisms underlying remodeling processes in the BZ remain unclear. Herein, we utilized a label-free quantitative proteomics approach in combination with immunohistochemical analyses to gain a better understanding of processes contributing to postinfarction remodeling of the peri-infarct BZ in a swine model of MI with reperfusion. Our analysis uncovered a significant down-regulation of proteins involved in energy metabolism, indicating impaired myocardial energetics and possibly mitochondrial dysfunction, in the peri-scar BZ. An increase in endothelial and vascular smooth muscles cells, as well as up-regulation of proteins implicated in vascular endothelial growth factor (VEGF) signaling and marked changes in the expression of extracellular matrix and subendothelial basement membrane proteins, is indicative of active angiogenesis in the infarct BZ. A pronounced increase in macrophages in the peri-infarct BZ was also observed, and proteomic analysis uncovered evidence of persistent inflammation in this tissue. Additional evidence suggested an increase in cellular proliferation that, concomitant with increased nestin expression, indicates potential turnover of endogenous stem cells in the BZ. A marked up-regulation of pro-apoptotic proteins, as well as the down-regulation of proteins important for adaptation to mechanical, metabolic, and oxidative stress, likely contributes to increased apoptosis in the peri-infarct BZ. The cellular processes and molecular pathways identified herein may have clinical utility for therapeutic intervention aimed at limiting remodeling and expansion of the BZ myocardium and preventing the development of heart failure post-MI.

Magnetic resonance-compatible model of isolated working heart from large animal for multimodal assessment of cardiac function, electrophysiology, and metabolism

To provide a model close to the human heart, and to study intrinsic cardiac function at the same time as electromechanical coupling, we developed a magnetic resonance (MR)-compatible setup of isolated working perfused pig hearts. Hearts from pigs (40 kg, n = 20) and sheep (n = 1) were blood perfused ex vivo in the working mode with and without loaded right ventricle (RV), for 80 min. Cardiac function was assessed by measuring left intraventricular pressure and left ventricular (LV) ejection fraction (LVEF), aortic and mitral valve dynamics, and native T1 mapping with MR imaging (1.5 Tesla). Potential myocardial alterations were assessed at the end of ex vivo perfusion from late-Gadolinium enhancement T1 mapping. The ex vivo cardiac function was stable across the 80 min of perfusion. Aortic flow and LV-dP/dtmin were significantly higher (P < 0.05) in hearts perfused with loaded RV, without differences for heart rate, maximal and minimal LV pressure, LV-dP/dtmax, LVEF, and kinetics of aortic and mitral valves. T1 mapping analysis showed a spatially homogeneous distribution over the LV. Simultaneous recording of hemodynamics, LVEF, and local cardiac electrophysiological signals were then successfully performed at baseline and during electrical pacing protocols without inducing alteration of MR images. Finally, (31)P nuclear MR spectroscopy (9.4 T) was also performed in two pig hearts, showing phosphocreatine-to-ATP ratio in accordance with data previously reported in vivo. We demonstrate the feasibility to perfuse isolated pig hearts in the working mode, inside an MR environment, allowing simultaneous assessment of cardiac structure, mechanics, and electrophysiology, illustrating examples of potential applications.

Transmurally differentiated measurement of ATP hydrolysis rates in the in vivo porcine hearts

PURPOSE

Compare the transmural distribution of forward creatine kinase reaction (kf,CK ) and ATP hydrolysis rate (kr,ATPase ) in the myocardium of normal porcine heart. Rate constants were extracted from partially relaxed spectra by applying the T1nom method, effectively reducing data acquisition time by up to an order of magnitude.

THEORY AND METHODS

T1nom method for double saturation of PCr and Pi is introduced and validated through simulations. Bioenergetics was measured in vivo utilizing one-dimensional chemical shift imaging (1D-CSI) magnetic resonance (31) P spectroscopy.

RESULTS

At basal conditions, there was no significant difference between subepicardial layers (EPI) vs. the subendocardial layers (ENDO) for both fluxf,CK and fluxr,ATPase . At high cardiac workload (HWL), where the rate pressure product increased 2.6-fold, PCr/ATP ratio and fluxf,CK showed no significant change in both EPI and ENDO layers, while fluxr,ATPase increased significantly (baseline: 1.11 ± 0.12 and 1.12 ± 0.13 μmol/g/s, EPI and ENDO, respectively; to HWL: 2.35 ± 0.27 and 2.21 ± 0.08 μmol/g/s, EPI and ENDO, respectively, each P < 0.01 vs. baseline).

CONCLUSION

In the normal heart, increase of cardiac work state is accompanied by an increase in ATP hydrolysis rate with no changes in CK flux rate. There are no significant differences between EPI vs. ENDO concerning the ATP hydrolysis rate or CK flux rate in both baseline and high cardiac work states.

What can we learn about treating heart failure from the heart's response to acute exercise? Focus on the coronary microcirculation

Coronary microvascular function and cardiac function are closely related in that proper cardiac function requires adequate oxygen delivery through the coronary microvasculature. Because of the close proximity of cardiomyocytes and coronary microvascular endothelium, cardiomyocytes not only communicate their metabolic needs to the coronary microvasculature, but endothelium-derived factors also directly modulate cardiac function. This review summarizes evidence that the myocardial oxygen balance is disturbed in the failing heart because of increased extravascular compressive forces and coronary microvascular dysfunction. The perturbations in myocardial oxygen balance are exaggerated during exercise and are due to alterations in neurohumoral influences, endothelial function, and oxidative stress. Although there is some evidence from animal studies that the myocardial oxygen balance can partly be restored by exercise training, it is largely unknown to what extent the beneficial effects of exercise training include improvements in endothelial function and/or oxidative stress in the coronary microvasculature and how these improvements are impacted by risk factors such as diabetes, obesity, and hypercholesterolemia.

The role of large animal studies in cardiac regenerative therapy concise review of translational stem cell research

Animal models have long been developed for cardiovascular research. These animal models have been helpful in understanding disease, discovering potential therapeutics, and predicting efficacy. Despite many efforts, however, translational study has been underestimated. Recently, investigations have identified stem cell treatment as a potentially promising cell therapy for regenerative medicine, largely because of the stem cell's ability to differentiate into many functional cell types. Stem cells promise a new era of cell-based therapy for salvaging the heart. However, stem cells have the potential risk of tumor formation. These properties of stem cells are considered a major concern over the efficacy of cell therapy. The translational/preclinical study of stem cells is essential but only at the beginning stages. What types of heart disease are indicated for stem cell therapy, what type of stem cell, what type of animal model, how do we deliver stem cells, and how do we improve heart function? These may be the key issues that the settlement of which would facilitate the transition of stem cell research from bench to bedside. In this review article, we discuss state-of-the-art technology in stem cell therapies for cardiovascular diseases.

Functional consequences of human induced pluripotent stem cell therapy: myocardial ATP turnover rate in the in vivo swine heart with postinfarction remodeling

BACKGROUND

The use of cells derived from human induced pluripotent stem cells as cellular therapy for myocardial injury has yet to be examined in a large-animal model.

METHODS AND RESULTS

Immunosuppressed Yorkshire pigs were assigned to 1 of 3 groups: A myocardial infarction group (MI group; distal left anterior descending coronary artery ligation and reperfusion; n=13); a cell-treatment group (MI with 4×10(6) vascular cells derived from human induced pluripotent stem cells administered via a fibrin patch; n=14); and a normal group (n=15). At 4 weeks, left ventricular structural and functional abnormalities were less pronounced in hearts in the cell-treated group than in MI hearts (P<0.05), and these improvements were accompanied by declines in scar size (10.4±1.6% versus 8.3±1.1%, MI versus cell-treatment group, P<0.05). The cell-treated group displayed a significant increase in vascular density and blood flow (0.83±0.11 and 1.05±0.13 mL·min(-1)·g(-1), MI versus cell-treatment group, P<0.05) in the periscar border zone (BZ), which was accompanied by improvements in systolic thickening fractions (infarct zone, -10±7% versus 5±5%; BZ, 7±4% versus 23±6%; P<0.05). Transplantation of vascular cells derived from human induced pluripotent stem cells stimulated c-kit(+) cell recruitment to BZ and the rate of bromodeoxyuridine incorporation in both c-kit(+) cells and cardiomyocytes (P<0.05). Using a magnetic resonance spectroscopic saturation transfer technique, we found that the rate of ATP hydrolysis in BZ of MI hearts was severely reduced, and the severity of this reduction was linearly related to the severity of the elevations of wall stresses (r=0.82, P<0.05). This decline in BZ ATP utilization was markedly attenuated in the cell-treatment group.

CONCLUSIONS

Transplantation of vascular cells derived from human induced pluripotent stem cells mobilized endogenous progenitor cells into the BZ, attenuated regional wall stress, stimulated neovascularization, and improved BZ perfusion, which in turn resulted in marked increases in BZ contractile function and ATP turnover rate.

Myocardial infarction and intramyocardial injection models in swine

Sustainable and reproducible large animal models that closely replicate the clinical sequelae of myocardial infarction (MI) are important for the translation of basic science research into bedside medicine. Swine are well accepted by the scientific community for cardiovascular research, and they represent an established animal model for preclinical trials for US Food and Drug Administration (FDA) approval of novel therapies. Here we present a protocol for using porcine models of MI created with a closed-chest coronary artery occlusion-reperfusion technique. This creates a model of MI encompassing the anteroapical, lateral and septal walls of the left ventricle. This model infarction can be easily adapted to suit individual study design and enables the investigation of a variety of possible interventions. This model is therefore a useful tool for translational research into the pathophysiology of ventricular remodeling and is an ideal testing platform for novel biological approaches targeting regenerative medicine. This model can be created in approximately 8-10 h.

Cardiac AAV9-S100A1 gene therapy rescues post-ischemic heart failure in a preclinical large animal model

As a prerequisite for clinical application, we determined the long-term therapeutic effectiveness and safety of adeno-associated virus (AAV)-S100A1 gene therapy in a preclinical large animal model of heart failure. S100A1, a positive inotropic regulator of myocardial contractility, becomes depleted in failing cardiomyocytes in humans and animals, and myocardial-targeted S100A1 gene transfer rescues cardiac contractile function by restoring sarcoplasmic reticulum calcium (Ca(2+)) handling in acutely and chronically failing hearts in small animal models. We induced heart failure in domestic pigs by balloon occlusion of the left circumflex coronary artery, resulting in myocardial infarction. After 2 weeks, when the pigs displayed significant left ventricular contractile dysfunction, we administered, by retrograde coronary venous delivery, AAV serotype 9 (AAV9)-S100A1 to the left ventricular, non-infarcted myocardium. AAV9-luciferase and saline treatment served as control. At 14 weeks, both control groups showed significantly decreased myocardial S100A1 protein expression along with progressive deterioration of cardiac performance and left ventricular remodeling. AAV9-S100A1 treatment prevented and reversed these functional and structural changes by restoring cardiac S100A1 protein levels. S100A1 treatment normalized cardiomyocyte Ca(2+) cycling, sarcoplasmic reticulum calcium handling, and energy homeostasis. Transgene expression was restricted to cardiac tissue, and extracardiac organ function was uncompromised. This translational study shows the preclinical feasibility of long-term therapeutic effectiveness of and a favorable safety profile for cardiac AAV9-S100A1 gene therapy in a preclinical model of heart failure. Our results present a strong rationale for a clinical trial of S100A1 gene therapy for human heart failure that could potentially complement current strategies to treat end-stage heart failure.

A fibrin patch-based enhanced delivery of human embryonic stem cell-derived vascular cell transplantation in a porcine model of postinfarction left ventricular remodeling

It is unknown how to use human embryonic stem cell (hESC) to effectively treat hearts with postinfarction left ventricular (LV) remodeling. Using a porcine model of postinfarction LV remodeling, this study examined the functional improvement of enhanced delivery of combined transplantation of hESC-derived endothelial cells (ECs) and hESC-derived smooth muscle cells (SMCs) with a fibrin three-dimensional (3D) porous scaffold biomatrix. To facilitate tracking the transplanted cells, the hESCs were genetically modified to stably express green fluorescent protein and luciferase (GFP/Luc). Myocardial infarction (MI) was created by ligating the first diagonal coronary artery for 60 minutes followed by reperfusion. Two million each of GFP/Luc hESC-derived ECs and SMCs were seeded in the 3D porous biomatrix patch and applied to the region of ischemia/reperfusion for cell group (MI+P+C, n = 6), whereas biomatrix without cell (MI+P, n = 5), or saline only (MI, n = 5) were applied to control group hearts with same coronary artery ligation. Functional outcome (1 and 4 weeks follow-up) of stem cell transplantation was assessed by cardiac magnetic resonance imaging. The transplantation of hESC-derived vascular cells resulted in significant LV functional improvement. Significant engraftment of hESC-derived cells was confirmed by both in vivo and ex vivo bioluminescent imaging. The mechanism underlying the functional beneficial effects of cardiac progenitor transplantation is attributed to the increased neovascularization. These findings demonstrate a promising therapeutic potential of using these hESC-derived vascular cell types and the mode of patch delivery.

The rate of ATP export in the extramitochondrial phase via the adenine nucleotide translocator changes in aging in mitochondria isolated from heart left ventricle of either normotensive or spontaneously hypertensive rats

To find out whether and how deficit of cellular energy supply from mitochondria to cytosol occurs in aging and hypertension, we used mitochondria isolated from 5 to 72 week-old heart left ventricle of either normotensive (WKY) or spontaneous hypertensive (SH) rats as a model system. Measurements were made of the rate of ATP appearance outside mitochondria, due to externally added ADP, as an increase of NADPH absorbance which occurs when ATP is produced in the presence of glucose, hexokinase and glucose-6-phosphate dehydrogenase. Such a rate proved to mirror the function of the adenine nucleotide translocator (ANT) rather than other processes linked to the both oxidative and substrate level phosphorylation. The changes in both Ki for atractyloside and Km for ADP suggest the occurrence of modification of the ANT conformation during aging in which the ANT Vmax was found to decrease in normotensive but to increase under spontaneously hypertension in 24 week-old rats with a subsequent decrease in both cases. ANT function, as investigated in the ADP physiological range (20-60μM), is expected to decrease in normotensive, but to increase in hypertensive rats up to 48 weeks. Later a decrease in the ATP rate of export outside mitochondria should occur in both cases.

Myocardial energetics in left ventricular hypertrophy

The heart carries out its pumping function by converting the chemical energy stored in fatty acids and glucose into the mechanical energy of actin-myosin interaction of myofibrils. Development of congestive heart failure is usually preceded by a period of compensated left ventricular hypertrophy (LVH) and alterations in myocardial bioenergetics have been considered to play an important role in this transition. Myocardial energetic state that is reflected by the ratio of Phosphocreatine to Adenosine Triphosphate (PCr/ATP) is significantly decreased in hearts with LVH. The severity of this abnormality is linearly related to the severity of cardiac hypertrophy as well as left ventricular (LV) dysfunction, and is independent of a persistent myocardial ischemia. The decrease in PCr/ATP is accompanied by a decrease in creatine kinase flux and alterations in substrate utilization in LVH hearts. Moreover, there is a profound heterogeneity in alterations in myocardial energy metabolism in hearts with post-infarction hypertrophy with the most severe abnormality present in the inner layers of the periscar border zone (BZ). This review will discuss various aspects of myocardial energetics in animal models of three different types of LVH (pressure-overload, volume overload and post-infarction) with a brief description of myocardial energetics in humans with LVH.

ATP production rate via creatine kinase or ATP synthase in vivo: a novel superfast magnetization saturation transfer method

RATIONALE

³¹P magnetization saturation transfer (MST) experiment is the most widely used method to study ATP metabolism kinetics. However, its lengthy data acquisition time greatly limits the wide biomedical applications in vivo, especially for studies requiring high spatial and temporal resolutions.

OBJECTIVE

We aimed to develop a novel superfast MST method that can accurately quantify ATP production rate constants (k(f)) through creatine kinase (CK) or ATP synthase (ATPase) with 2 spectra.

METHODS AND RESULTS

The T₁(nom) (T₁ nominal) method uses a correction factor to compensate the partially relaxed MST experiments, thus allowing measurement of enzyme kinetics with an arbitrary repetition time and flip angle, which consequently reduces the data acquisition time of a transmurally differentiated CK k(f) measurement by 91% as compared with the conventional method with spatial localization. The novel T₁(nom) method is validated theoretically with numeric simulation, and further verified with in vivo swine hearts, as well as CK and ATPase activities in rat brain at 9.4 Tesla. Importantly, the in vivo data from swine hearts demonstrate, for the first time, that within an observation window of 30 minutes, the inhibition of CK activity by iodoacetamide does not limit left ventricular chamber contractile function.

CONCLUSIONS

A novel MST method for superfast examination of enzyme kinetics in vivo has been developed and verified theoretically and experimentally. In the in vivo normal heart, redundant multiple supporting systems of myocardial ATP production, transportation, and utilization exist, such that inhibition of one mechanism does not impair the normal left ventricular contractile performance.

Long-term preservation of myocardial energetic in chronic hibernating myocardium

We previously reported that the myocardial energetic state, as defined by the ratio of phosphocreatine to ATP (PCr/ATP), was preserved at baseline (BL) in a swine model of chronic myocardial ischemia with mild reduction of myocardial blood flow (MBF) 10 wk after the placement of an external constrictor on the left anterior descending coronary artery. It remains to be seen whether this stable energetic state is maintained at a longer-term follow-up. Hibernating myocardium (HB) was created in minipigs (n = 7) by the placement of an external constrictor (1.25 mm internal diameter) on the left anterior descending coronary artery. Function was assessed with MRI at regular intervals until 6 mo. At 6 mo, myocardial energetic in the HB was assessed by (31)P-magnetic resonance spectrometry and myocardial oxygenation was examined from the deoxymyoglobin signal using (1)H-magnetic resonance spectrometry during BL, coronary vasodilation with adenosine, and high cardiac workload with dopamine and dobutamine (DpDb). MBF was measured with radiolabeled microspheres. At BL, systolic thickening fraction was significantly lower in the HB compared with remote region (34.4 ± 9.4 vs. 50.1 ± 10.7, P = 0.006). This was associated with a decreased MBF in the HB compared with the remote region (0.73 ± 0.08 vs. 0.97 ± 0.07 ml · min(-1) · g, P = 0.03). The HB PCr/ATP at BL was normal. DpDb resulted in a significant increase in rate pressure product, which caused a twofold increase in MBF in the HB and a threefold increase in the remote region. The systolic thickening fraction increased with DpDb, which was significantly higher in the remote region than HB (P < 0.05). The high cardiac workload was associated with a significant reduction in the HB PCr/ATP (P < 0.02), but this response was similar to normal myocardium. Thus HB has stable BL myocardial energetic despite the reduction MBF and regional left ventricular function. More importantly, HB has a reduced contractile reserve but has a similar energetic response to high cardiac workload like normal myocardium.

Long-term functional improvement and gene expression changes after bone marrow-derived multipotent progenitor cell transplantation in myocardial infarction

The study examined the long-term outcome of cardiac stem cell transplantation in hearts with postinfarction left ventricular (LV) remodeling. Myocardial infarction (MI) was created by ligating the first and second diagonal branches of the left anterior descending coronary artery in miniature swine. Intramyocardial injections of 50 million LacZ-labeled bone marrow-derived multipotent progenitor cells (MPC) were performed in the periscar region (Cell, n = 7) immediately after MI, whereas, in control animals (Cont, n = 7), saline was injected. Functional outcome was assessed monthly for 4 mo with MRI and (31)P-magnetic resonance spectroscopy. Engraftment was studied on histology, and gene chip (Affymetrix) array analysis was used to study differential expression of genes in the two groups. MPC treatment resulted in improvement of ejection fraction as early as 10 days after MI (Cell, 43.4 +/- 5.1% vs. Cont, 32.2 +/- 5.5%; P < 0.05). This improvement was seen each month and persisted to 4 mo (Cell, 51.2 +/- 4.8% vs. Cont, 35.7 +/- 5.0%; P < 0.05). PCr-to-ATP ratio (PCr/ATP) improved with MPC transplantation, which was most pronounced at high cardiac work states (subendocardial PCr/ATP was 1.70 +/- 0.10 vs. 1.34 +/- 0.14, P < 0.05). There was no significant difference in scar size (scar/LV area * 100) at 10 days postinfarction. However, at 4 mo, there was a significant decrease in scar size in the Cell group (Cell, 4.6 +/- 1.0% vs. Cont, 8.6 +/- 2.4%; P < 0.05). No significant engraftment of MPC was observed. MPC transplantation was associated with a downregulation of mitochondrial oxidative enzymes and increased levels of myocyte enhancer factor 2a and zinc finger protein 91. In conclusion, MPC transplantation leads to long-term functional and bioenergetic improvement in a porcine model of postinfarction LV remodeling, despite no significant engraftment of stem cells in the heart. MPC transplantation reduces regional wall stresses and infarct size and mitigates the adverse effects of LV remodeling, as seen by a reduction in LV hypertrophy and LV dilatation, and is associated with differential expression of genes relating to metabolism and apoptosis.

Mice over-expressing the myocardial creatine transporter develop progressive heart failure and show decreased glycolytic capacity

The metabolic phenotype of the failing heart includes a decrease in phosphocreatine and total creatine concentration [Cr], potentially contributing to contractile dysfunction. Surprisingly, in 32- week-old mice over-expressing the myocardial creatine transporter (CrT-OE), we previously demonstrated that elevated [Cr] correlates with left ventricular (LV) hypertrophy and failure. The aim of this study was to determine the temporal relationship between elevated [Cr] and the onset of cardiac dysfunction and to screen for potential molecular mechanisms. CrT-OE mice were compared with wild-type (WT) littermate controls longitudinally using cine-MRI to measure cardiac function and single-voxel (1)H-MRS to measure [Cr] in vivo at 6, 16, 32, and 52 weeks of age. CrT-OE mice had elevated [Cr] at 6 weeks (mean 1.9-fold), which remained constant throughout life. Despite this increased [Cr], LV dysfunction was not apparent until 16 weeks and became more pronounced with age. Additionally, LV tissue from 12 to 14 week old CrT-OE mice was compared to WT using 2D difference in-gel electrophoresis (DIGE). These analyses detected a majority of the heart's metabolic enzymes and identified seven proteins that were differentially expressed between groups. The most pronounced protein changes were related to energy metabolism: alpha- and beta-enolase were selectively decreased (p<0.05), while the remaining enzymes of glycolysis were unchanged. Consistent with a decrease in enolase content, its activity was significantly lower in CrT-OE hearts (in WT, 0.59+/-0.02 micromol ATP produced/microg protein/min; CrT-OE, 0.31+/-0.06; p<0.01). Additionally, anaerobic lactate production was decreased in CrT-OE mice (in WT, 102+/-3 micromol/g wet myocardium; CrT-OE, 78+/-13; p=0.02), consistent with decreased glycolytic capacity. Finally, we found that enolase may be regulated by increased expression of the beta-enolase repressor transcription factor, which was significantly increased in CrT-OE hearts. This study demonstrates that chronically increased myocardial [Cr] in the CrT-OE model leads to the development of progressive hypertrophy and heart failure, which may be mediated by a compromise in glycolytic capacity at the level of enolase.

Novel strategy for measuring creatine kinase reaction rate in the in vivo heart

In the heart, the creatine kinase (CK) system plays an important role in the cascade of ATP production, transportation, and utilization. The forward pseudo-first-order rate constant for the CK reaction can be measured noninvasively by the (31)P-magnetic resonance (MR) spectroscopy magnetization saturation transfer (MST) techniques. However, the measurement of MST in the in vivo heart is limited by the lengthy data acquisition time, especially for studies requiring spatial localization. This technical report presents a new method for measuring ATP production rate via CK that can reduce the MST data acquisition time by 82%. This method is validated using an in vivo pig model to evaluate the forward pseudo-first-order rate constant of myocardial CK reaction noninvasively.

Effect of ATP-sensitive potassium channel agonists on sympathetic hyperinnervation in postinfarcted rat hearts

Although the acute administration of ATP-sensitive potassium (KATP) channel agonists provides a neuroprotection, it is unclear whether similar benefits are found by modulating sympathetic innervation in chronic settings after myocardial infarction. We assessed whether KATP channel agonists can attenuate the sprouting of cardiac sympathetic nerves after infarction. Male Wistar rats after ligating coronary artery were randomized to either saline, nicorandil, pinacidil, glibenclamide, or a combination of 1) nicorandil and glibenclamide or 2) pinacidil and glibenclamide for 4 wk. To elucidate the role of mitochondrial KATP channels in modulating nerve growth factor, 5-hydroxydecanoate was assessed in an in vitro model. The measurement of myocardial norepinephrine levels revealed a significant elevation in saline-treated infarcted rats compared with sham-operated rats, consistent with excessive sympathetic innervation. Excessive sympathetic innervation was blunted after giving the rats either nicorandil or pinacidil, compared with saline, as assessed by the immunohistochemical analysis of tyrosine hydroxylase, growth associated protein-43, and neurofilament and Western blot analysis and real-time quantitative RT-PCR of nerve growth factor. The arrhythmic scores during programmed stimulation in the saline- or glibenclamide-treated infarcted rats were significantly higher than those of rats treated with KATP channel agonists. In contrast, the beneficial effects of nicorandil and pinacidil were abolished by administering either glibenclamide or 5-hydroxydecanoate. The sympathetic hyperinnervation after infarction is attenuated by the activation of mitochondrial KATP channels. The chronic use of mitochondrial KATP channel agonists after infarction may attenuate the arrhythmogenic response to programmed electrical stimulation.

Enhancing efficacy of stem cell transplantation to the heart with a PEGylated fibrin biomatrix

Bone marrow-derived mononuclear cell (BMNC) transplantation provides the possibility of rescue or regeneration of myocardium lost during acute myocardial infarction (AMI). The extensive death of transplanted cells and the lack of sustained engraftment may limit its application. We investigated whether delivery of BMNCs by an injectable PEGylated fibrin biomatrix that covalently binds hepatocyte growth factor (HGF) would enhance the rate of cell engraftment and improve cardiac function. Balb/C female mice with AMI secondary to left anterior descending coronary ligation were randomly assigned to one of six groups: the Saline control group (n = 8) received a myocardial injection of saline (50 microL); the Cell group (n = 10) received a myocardial injection in the peri-infarct and infarct zones consisting of 500,000 murine BMNCs suspended in 50 microL saline; and the Biomatrix + HGF (n = 9) and Biomatrix + HGF + Cell (n = 9) group hearts received the HGF-loaded injectable biomatrix (identical volume) with or without entrapped BMNCs. Control groups consisting of the biomatrix alone (n = 9) and Biomatrix + Cells (n = 9) without HGF were also included for comparison. The left ventricular (LV) function was measured by echocardiography at days 14 and 28 post-MI. All animals were euthanized 4 weeks after AMI and transplantation for evaluation of angiogenesis, apoptosis, and fibrosis by immunohistochemistry. Cell prevalence rate at 4 weeks increased 15-fold in hearts receiving the Biomatrix + HGF + Cell delivery (p < 0.01), which was accompanied by the lowest levels of apoptosis and the highest LV function recovery among the treated groups.

The use of magnetic resonance methods in translational cardiovascular research

Magnetic resonance methods are widely applicable to research questions posed in translational cardiovascular studies. The main intent of this review was to offer the cardiovascular translational research scientist a "menu" of magnetic resonance (MR) approaches that can be applied to answering research questions posed in a variety of experimental situations including those involving the use of human subjects. Obviously, this menu is not comprehensive and many other topics could have been selected for emphasis. However, we hope that the material presented encompasses a broad enough slice of the field to stimulate thinking about the possible applications of MR methods to specific research questions.

A catheter based chronic porcine model of post-infarct dilated heart failure

OBJECTIVES

New surgical treatments for post-infarct antero-septal myocardial akinesia have been developed but evaluation of their mode of function is hampered by absence of suitable large animal heart failure models. We aimed to develop and evaluate a human compatible model for chronic post-infarct left ventricular (LV) remodeling.

DESIGN

Fourteen female 50 kg pigs underwent catheter-based coronary artery occlusion (one hour) distal to the first LAD diagonal. Eight weight- and age-matched healthy animals served as controls. LV geometry and function were assessed after 6 weeks with cardiovascular MRI.

RESULTS

All animals recovered from interventions. Three animals died during follow-up. All intervention animals had antero-septal akinetic infarcts (mean 26.5% of LV myocardium). Intervention animals had significantly increased end-diastolic and end-systolic volumes, and decreased stroke volume, ejection fraction and cardiac output. Detailed functional analysis showed significant systolic- and diastolic-dysfunction in intervention animals.

CONCLUSIONS

We have established a feasible model of post-infarct LV remodeling, which accurately simulates human pathogenesis and pathophysiology. The model may be suitable for evaluation of novel surgical alleviations for heart failure.

Alterations in vasomotor control of coronary resistance vessels in remodelled myocardium of swine with a recent myocardial infarction

The mechanism underlying the progressive deterioration of left ventricular (LV) dysfunction after myocardial infarction (MI) towards overt heart failure remains incompletely understood, but may involve impairments in coronary blood flow regulation within remodelled myocardium leading to intermittent myocardial ischemia. Blood flow to the remodelled myocardium is hampered as the coronary vasculature does not grow commensurate with the increase in LV mass and because extravascular compression of the coronary vasculature is increased. In addition to these factors, an increase in coronary vasomotor tone, secondary to neurohumoral activation and endothelial dysfunction, could also contribute to the impaired myocardial oxygen supply. Consequently, we explored, in a series of studies, the alterations in regulation of coronary resistance vessel tone in remodelled myocardium of swine with a 2 to 3-week-old MI. These studies indicate that myocardial oxygen balance is perturbed in remodelled myocardium, thereby forcing the myocardium to increase its oxygen extraction. These perturbations do not appear to be the result of blunted β-adrenergic or endothelial NO-mediated coronary vasodilator influences, and are opposed by an increased vasodilator influence through opening of K_ATP channels. Unexpectedly, we observed that despite increased circulating levels of noradrenaline, angiotensin II and endothelin-1, α-adrenergic tone remained negligible, while the coronary vasoconstrictor influences of endogenous endothelin and angiotensin II were virtually abolished. We conclude that, early after MI, perturbations in myocardial oxygen balance are observed in remodelled myocardium. However, adaptive alterations in coronary resistance vessel control, consisting of increased vasodilator influences in conjunction with blunted vasoconstrictor influences, act to minimize the impairments of myocardial oxygen balance.

Magnetic resonance imaging in the assessment of ventricular remodeling and viability

Cardiovascular MRI has effectively become a reference standard for quantifying ventricular volumes and function and for measuring the myocardial scar burden after myocardial infarction. Imaging of late gadolinium enhancement and microvascular obstruction carries strong prognostic information for identifying patients who would benefit from anti-remodeling therapy. The combination of gadolinium enhancement, perfusion, and cine imaging should make MRI the modality of choice in the assessment of left ventricular dysfunction and remodeling. The use of MRI in clinical trials of heart failure could help reduce sample size requirements because of its accuracy and reproducibility. This review describes the use of MRI in assessing ventricular remodeling and viability and summarizes the few studies that have relied on MRI for image-based markers of ventricular remodeling.

Phosphate metabolite concentrations and ATP hydrolysis potential in normal and ischaemic hearts

To understand how cardiac ATP and CrP remain stable with changes in work rate - a phenomenon that has eluded mechanistic explanation for decades - data from (31)phosphate-magnetic resonance spectroscopy ((31)P-MRS) are analysed to estimate cytoplasmic and mitochondrial phosphate metabolite concentrations in the normal state, during high cardiac workstates, during acute ischaemia and reactive hyperaemic recovery. Analysis is based on simulating distributed heterogeneous oxygen transport in the myocardium integrated with a detailed model of cardiac energy metabolism. The model predicts that baseline myocardial free inorganic phosphate (P(i)) concentration in the canine myocyte cytoplasm - a variable not accessible to direct non-invasive measurement - is approximately 0.29 mm and increases to 2.3 mm near maximal cardiac oxygen consumption. During acute ischaemia (from ligation of the left anterior descending artery) P(i) increases to approximately 3.1 mm and ATP consumption in the ischaemic tissue is reduced quickly to less than half its baseline value before the creatine phosphate (CrP) pool is 18% depleted. It is determined from these experiments that the maximal rate of oxygen consumption of the heart is an emergent property and is limited not simply by the maximal rate of ATP synthesis, but by the maximal rate at which ATP can be synthesized at a potential at which it can be utilized. The critical free energy of ATP hydrolysis for cardiac contraction that is consistent with these findings is approximately -63.5 kJ mol(-1). Based on theoretical findings, we hypothesize that inorganic phosphate is both the primary feedback signal for stimulating oxidative phosphorylation in vivo and also the most significant product of ATP hydrolysis in limiting the capacity of the heart to hydrolyse ATP in vivo. Due to the lack of precise quantification of P(i) in vivo, these hypotheses and associated model predictions remain to be carefully tested experimentally.

Relationships between regional myocardial wall stress and bioenergetics in hearts with left ventricular hypertrophy

This study utilized porcine models of postinfarction left ventricular (LV) remodeling [myocardial infarction (MI); n = 8] and concentric LV hypertrophy secondary to aortic banding (AoB; n = 8) to examine the relationships between regional myocardial contractile function (tagged MRI), wall stress (MRI and LV pressure), and bioenergetics ((31)P-magnetic resonance spectroscopy). Physiological assessments were conducted at a 4-wk time point after MI or AoB surgery. Comparisons were made with size-matched normal animals (normal; n = 8). Both MI and AoB instigated significant LV hypertrophy. Ejection fraction was not significantly altered in the AoB group, but significantly decreased in the MI group (P < 0.01 vs. normal and AoB). Systolic and diastolic wall stresses were approximately two times greater than normal in the infarct region and border zone. Wall stress in the AoB group was not significantly different from that in normal hearts. The infarct border zone demonstrated profound bioenergetic abnormalities, especially in the subendocardium, where the ratio of PCr/ATP decreased from 1.98 +/- 0.16 (normal) to 1.06 +/- 0.30 (MI; P < 0.01). The systolic radial thickening fraction and the circumferential shortening fraction in the anterior wall were severely reduced (MI, P < 0.01 vs. normal). The radial thickening fraction and circumferential shortening fraction in the AoB group were not significantly different from normal. The severely elevated wall stress in the infarct border zone was associated with a significant increase in chemical energy demand and abnormal myocardial energy metabolism. Such severe metabolic perturbations cannot support normal cardiac function, which may explain the observed regional contractile abnormalities in the infarct border zone.

MR diffusion tensor imaging study of postinfarct myocardium structural remodeling in a porcine model

This study aimed to investigate postinfarct left ventricular (LV) fiber structural alterations by ex vivo diffusion tensor imaging (DTI) in a porcine heart model. In vivo cardiac MR imaging was first performed to measure ventricular function in six adult pigs with septal infarction near apex induced by the LAD ligation 13 weeks earlier. Hearts were then excised from the infarct pigs (n = 6) and six intact controls (n = 6) and fixed in formalin. High-resolution DTI was employed to examine changes in fractional anisotropy (FA), apparent diffusion coefficient (ADC), and transmural helix angle distribution in the infarct, adjacent and remote regions as compared to the sham regions in the controls. FA values were found to decrease in the infarct and differ between the adjacent and remote regions. ADC increase in the infarct region was substantial, while changes in the adjacent and remote regions were insignificant. Structurally, the double-helix myocardial structure shifted toward more left-handed around the infarcted myocardium. Accordingly, the histological analysis revealed clear fiber structural degradation in the adjacent region. These findings confirmed the subtle alterations in the myocardial fiber quality and structure not only in the infarcted but also in the surrounding noninfarcted myocardium or borderzone.

Energetic differences between viable and non-viable myocardium in patients with recent myocardial infarction are not an effect of differences in wall thinning- a multivoxel (31)P-MR-spectroscopy and MRI study

To evaluate multivoxel (31)P-MR spectroscopy (MRS) for assessment of energy metabolism in patients with myocardial infarction (MI) in correlation to left ventricular (LV) wall thickness and the outcome of revascularization. Thirty patients with subacute anterior myocardial infarction and planned revascularization were enrolled. 3D-chemical shift imaging was applied to determine PCr/ATP ratios in two areas: infarcted/anterior and noninfarcted/septal myocardium. MRI was used to evaluate LV function and wall thickness, and was repeated 6 months after revascularization to assess myocardial viability. Fifteen volunteers were controls. Fifteen patients showed normalization of wall motion abnormalities after revascularization (Group 1; viable), 15 not (Group 2; non-viable). Regarding infarcted/anterior myocardium, Group 2 had lower PCr/ATP ratios (0.81 +/- 0.60 vs 1.17 +/- 0.25), and PCr/ATP ratios were reduced in both groups compared to controls (1.45 +/- 0.29). Regarding noninfarcted/septal myocardium, again Group 2 had lower ratios (0.93 +/- 0.53 vs 1.31 +/- 0.38); however, compared to controls (1.51 +/- 0.32) a reduction of PCr/ATP ratios was only found in Group 2. For both myocardial regions, no correlations between PCr/ATP ratios and LV wall thickness were detected. The more severe energetic alteration in irreversibly damaged myocardium is not an effect of differences of wall thinning. Additional alterations of noninfarcted, adjacent myocardium can be detected.

Hemodynamic Support With the Pulsatile Catheter Pump in a Sheep Model of Acute Heart Failure

This study was aimed to mimic clinical heart failure (HF) conditions and to assess the effect of pulsatile catheter (PUCA) pump support on hemodynamics and tissue perfusion in a sheep model of acute HF. In 14 sheep, HF was induced by partial occluding the middle left circumflex coronary artery combined with pacemaker-induced tachycardia. PUCA pump was then activated to support the HF for 3 h. Hemodynamic parameters were recorded at baseline, HF, and then every 30 min during experiments. Blood samples were taken in carotid artery (CA), pulmonary artery (PA), and coronary sinus (CS) for the determination of oxygen saturation (SO2) and lactate concentration as markers of tissue perfusion. Results showed that HF model was induced successfully in 10 sheep and failed in four sheep due to refractory ventricular fibrillation. PUCA pump support was successful in seven out of 10 sheep for 3 h. Three cases failed due to technical problems. After HF (n = 10), cardiac output (CO) was decreased from 3.7 +/- 0.5 to 2.0 +/- 0.5 L/min (P < 0.001). Mean arterial pressure (MAP) was lowered from 116.1 +/- 14.2 to 68.1 +/- 14.7 mm Hg (P < 0.001). In seven sheep supported with PUCA pump, MAP rose from 68.9 +/- 15.2 to 94.7 +/- 14.7 mm Hg (P = 0.005), systolic blood pressure increased from 86.6 +/- 17.0 to 112.6 +/- 17.1 mm Hg (P = 0.009), and diastolic blood pressure increased from 57.7 +/- 12.6 to 79.9 +/- 13.9 mm Hg (P = 0.011). CO remained at about 2.0 L/min. SO2 in CA, PA, and CS decreased significantly after HF (P < 0.001), with an increase after support (compared with HF, P < 0.001, 0.066 and 0.114, respectively). Lactate concentrations increased gradually in CA, PA, and CS toward the end of experiments without difference among different sampling sites. This HF model in sheep is simple, easy to manipulate, reproducible and reflecting clinical HF conditions. PUCA pump can maintain the hemodynamic status for 3 h in this acute HF model.

Acute Effects of Febuxostat, a Nonpurine Selective Inhibitor of Xanthine Oxidase, in Pacing Induced Heart Failure

We investigated whether xanthine oxidase inhibition with febuxostat enhances left ventricular (LV) function and improves myocardial high energy phosphates (HEP) in dogs with pacing-induced heart failure (CHF). Febuxostat (2.2 mg/kg over 10 minutes followed by 0.06 mg/kg/min) caused no change of LV function or myocardial oxygen consumption (MVO2) at rest or during treadmill exercise in normal dogs. In dogs with CHF, febuxostat increased LV dP/dtmax at rest and during heavy exercise (P < 0.05), indicating improved LV function with no change of MVO2. Myocardial adenosine triphosphate (ATP) and phosphocreatine (PCr) were examined using 31P nuclear magnetic resonance spectroscopy in the open chest state. In normal dogs, febuxostat increased PCr/ATP during basal conditions and during high workload produced by dobutamine + dopamine (P < 0.05). PCr/ATP was decreased in animals with CHF; in these animals, febuxostat (given after completing basal and high workload measurements with vehicle) tended to increase PCr/ATP during basal conditions with no effect during catecholamine stimulation. Thus, febuxostat improved LV performance in awake dogs with CHF, but caused only a trend toward increased PCr/ATP in the open chest state. It is possible that the antecedent high workload condition prior to drug administration blunted the effect of febuxostat on HEP in the CHF animals. Alternatively, beneficial effects of febuxostat on LV performance in the failing heart may not involve HEP.

Coronary vasoconstrictor influence of angiotensin II is reduced in remodeled myocardium after myocardial infarction

The renin-angiotensin system plays an important role in cardiovascular homeostasis by contributing to the regulation of blood volume, blood pressure, and vascular tone. Because AT(1) receptors have been described in the coronary microcirculation, we investigated whether ANG II contributes to the regulation of coronary vascular tone and whether its contribution is altered during exercise. Since the renin-angiotensin system is activated after myocardial infarction, resulting in an increase in circulating ANG II, we also investigated whether the contribution of ANG II to the regulation of vasomotor tone is altered after infarction. Twenty-six chronically instrumented swine were studied at rest and while running on a treadmill at 1-4 km/h. In 13 swine, myocardial infarction was induced by ligation of the left circumflex coronary artery. Blockade of AT(1) receptors (irbesartan, 1 mg/kg iv) had no effect on myocardial O(2) consumption but resulted in an increase in coronary venous O(2) tension and saturation both at rest and during exercise, reflecting coronary vasodilation. Despite increased plasma levels of ANG II after infarction and maintained coronary arteriolar AT(1) receptor levels, the vasodilation evoked by irbesartan was significantly reduced both at rest and during exercise. In conclusion, despite elevated plasma levels, the vasoconstrictor influence of ANG II on the coronary circulation in vivo is reduced after myocardial infarction. This reduction in ANG II-induced coronary vasoconstriction may serve to maintain perfusion of the remodeled myocardium.

Functional and Bioenergetic Consequences of AT1 Antagonist Olmesartan Medoxomil in Hearts With Postinfarction LV Remodeling

The structural left ventricular (LV) remodeling and contractile dysfunction of hearts with postinfarction LV remodeling are benefited by angiotensin II type 1 receptor (AT1) blocker. However, the myocardial bioenergetic consequences of AT1 blocker in these hearts are not known. To investigate, we used a porcine model of postinfarction LV remodeling produced by ligation of the left circumflex coronary artery. After infarction, 7 pigs received olmesartan medoxomil (2 mg/kg) for comparison against 9 untreated and 10 normal pigs. Measurements of hemodynamics, myocardial perfusion, and myocardial bioenergetics were taken 7 weeks postinfarction. The treated group had an LV-to-body weight ratio significantly lower than the untreated group (2.69 +/- 0.70, 2.96 +/- 0.51, 3.66 +/- 0.60 g/kg for control, treated, and untreated groups, respectively). The untreated group had a mean aortic pressure significantly higher than the control (73 +/- 16, 86 +/- 14, and 94 +/- 20 mm Hg, respectively). The subendocardial phosphocreatine-to-ATP ratios of the treated group were significantly higher than that of the untreated group. The untreated group, but not the treated group, had significant reductions in mitochondrial F0F1-ATPase subunits compared with controls. Congestive heart failure as evidenced by significant ascites (100 to 2000 mL) developed in 4 of the 9 untreated animals, but was absent in the treated group. Animals with heart failure demonstrated reductions in both mitochondrial F0F1-ATPase expression and myocardial high-energy phosphate levels. Thus, severe LV dysfunction and accompanying abnormal myocardial bioenergetic phenotype were prevented by the AT1 antagonist olmesartan medoxomil.

The role of the sca-1+/CD31- cardiac progenitor cell population in postinfarction left ventricular remodeling

Cardiac stem cell-like populations exist in adult hearts, and their roles in cardiac repair remain to be defined. Sca-1 is an important surface marker for cardiac and other somatic stem cells. We hypothesized that heart-derived Sca-1(+)/CD31(-) cells may play a role in myocardial infarction-induced cardiac repair/remodeling. Mouse heart-derived Sca-1(+)/CD31(-) cells cultured in vitro could be induced to express both endothelial cell and cardiomyocyte markers. Immunofluorescence staining and fluorescence-activated cell sorting analysis indicated that endogenous Sca-1(+)/CD31(-) cells were significantly increased in the mouse heart 7 days after myocardial infarction (MI). Western blotting confirmed elevated Sca-1 protein expression in myocardium 7 days after MI. Transplantation of Sca-1(+)/CD31(-) cells into the acutely infarcted mouse heart attenuated the functional decline and adverse structural remodeling initiated by MI as evidenced by an increased left ventricular (LV) ejection fraction, a decreased LV end-diastolic dimension, a decreased LV end-systolic dimension, a significant increase of myocardial neovascularization, and modest cardiomyocyte regeneration. Attenuation of LV remodeling was accompanied by remarkably improved myocardial bioenergetic characteristics. The beneficial effects of cell transplantation appear to primarily depend on paracrine effects of the transplanted cells on new vessel formation and native cardiomyocyte function. Sca-1(+)/CD31(-) cells may hold therapeutic possibilities with regard to the treatment of ischemic heart disease.

Bioenergetic and functional consequences of stem cell-based VEGF delivery in pressure-overloaded swine hearts

In an established swine model of severe left ventricular (LV) hypertrophy (LVH), the bioenergetic and functional consequences of transplanting autologous mesenchymal stem cells (MSCs) overexpressing vascular endothelial growth factor (VEGF-MSCs) into the LV were evaluated; transplantation was accomplished by infusion of VEGF-MSCs into the interventricular cardiac vein. Specifically, the hypertrophic response to aortic banding was compared in seven pigs treated with 30 million VEGF-MSCs, eight pigs treated with 30 million MSCs without VEGF modification, and 19 untreated LVH pigs. Eight pigs without banding or cell transplantation (normal) were also studied. Four weeks postbanding, LV wall thickening (MRI), myocardial blood flow (MBF), high-energy phosphate levels (31P magnetic resonance spectroscopy), and hemodynamic measurements were obtained under basal conditions and during a catecholamine-induced high cardiac workstate (HCW). Although 9 of 19 untreated banded pigs developed clinical evidence of biventricular failure, no MSCs-treated animal developed heart failure. MSCs engraftment was present in both cell transplant groups, and both baseline and HCW MBF values were significantly increased in hearts receiving VEGF-MSCs compared with other groups ( P < 0.05). During HCW, cardiac inotropic reserve (defined as the percent increase of rate pressure product at HCW relative to baseline) was normal in the VEGF-MSCs group and significantly decreased in all other banded groups. Additionally, during HCW, the myocardial energetic state [reflected by the phosphocreatine-to-ATP ratio (PCr/ATP)] of VEGF-MSCs-treated hearts remained stable, whereas in all other groups, PCr/ATP decreased significantly from baseline values ( P < 0.05, each group). Myocardial von Willebrand factor and VEGF mRNA expressions and myocardial capillary density were significantly increased in VEGF-MSCs-treated hearts ( P < 0.05). Hence, in the pressure-overloaded LV, transplantation of VEGF-MSCs prevents LV decompensation, induces neovascularization, attenuates hypertrophy, and improves MBF, myocardial bioenergetic characteristics, and contractile performance.

Profound bioenergetic abnormalities in peri-infarct myocardial regions

Regions of myocardial infarct (MI) are surrounded by a border zone (BZ) of normally perfused but dysfunctional myocardium. Although systolic dysfunction has been attributed to elevated wall stress in this region, there is evidence that intrinsic abnormalities of contractile performance exist in BZ myocardium. This study examined whether decreases of high-energy phosphates (HEP) and mitochondrial F(1)F(0)-ATPase (mtATPase) subunits typical of failing myocardium exist in BZ myocardium of compensated postinfarct remodeled hearts. Eight pigs were studied 6 wk after MI was produced by ligation of the left anterior descending coronary artery (LAD) distal to the second diagonal. Animals developed compensated LV remodeling with a decrease of ejection fraction from 54.6 +/- 5.4% to 31 +/- 2.1% (MRI) 5 wk after LAD occlusion. The remote zone (RZ) myocardium demonstrated modest decreases of ATP and mtATPase components. In contrast, BZ myocardium demonstrated profound abnormalities with ATP levels decreased to 42% of normal, and phosphocreatine-to-ATP ratio ((31)P-magnetic resonance spectroscopy) decreased from 2.06 +/- 0.19 in normal hearts to 1.07 +/- 0.10, with decreases in alpha-, beta-, OSCP, and IF(1) subunits of mtATPase, especially in the subendocardium. The reduction of myocardial creatine kinase isoform protein expression was also more severe in the BZ relative to the RZ myocardium. These abnormalities were independent of a change in mitochondrial content because the mitochondrial citrate synthase protein level was not different between the BZ and RZ. This regional heterogeneity of ATP content and expression of key enzymes in ATP production suggests that energetic insufficiency in the peri-infarct region may contribute to the transition from compensated LV remodeling to congestive heart failure.

Contribution of KATP+ channels to coronary vasomotor tone regulation is enhanced in exercising swine with a recent myocardial infarction

Previous studies demonstrated a decreased flow reserve in the hypertrophied myocardium early after myocardial infarction (MI). Previously, we reported that exacerbation of hemodynamic abnormalities and neurohumoral activation during exercise caused slight impairment of myocardial O(2) supply in swine with a recent MI. We hypothesized that increased metabolic coronary vasodilation [via ATP-sensitive K(+) (K(ATP)(+)) channels and adenosine] may have partially compensated for the increased extravascular compressive forces and increased vasoconstrictor neurohormones, thereby preventing a more severe impairment of myocardial O(2) balance. Chronically instrumented swine were exercised on a treadmill up to 85% of maximum heart rate. Under resting conditions, adenosine receptor blockade [8-phenyltheophylline (8-PT), 5 mg/kg i.v.] and K(ATP)(+) channel blockade (glibenclamide, 3 mg/kg i.v.) produced similar decreases in myocardial O(2) supply in normal and MI swine. However, while glibenclamide's effect waned in normal swine during exercise (P < 0.05), it was maintained in MI swine. 8-PT's effect was maintained during exercise and was not different between normal and MI swine. Finally, in normal swine combined treatment with 8-PT and glibenclamide produced a vasoconstrictor response that equaled the sum of the responses to blockade of the individual pathways. In contrast, in MI swine the vasoconstrictor response to 8-PT and glibenclamide was similar to that produced by glibenclamide alone. In conclusion, despite significant hemodynamic abnormalities in swine with a recent MI, myocardial O(2) supply and O(2) consumption in remodeled myocardium are still closely matched during exercise. This close matching is supported by increased K(ATP)(+) channel-mediated coronary vasodilation. Although the net vasodilator influence of adenosine was unchanged in remodeled myocardium, it became exclusively dependent on K(ATP)(+) channel opening.