Persistent changes in myocardial glucose metabolism in vivo during reperfusion of a limited-duration coronary occlusion

The cardioprotective effects of carvedilol on ischemia and reperfusion injury by AMPK signaling pathway

Carvedilol, a third generation beta blocker, is in clinical use for heart failure patients. However, besides adrenergic receptor blockade, the pharmacological effects of carvedilol on cardiomyocytes remain unknown. AMP-activated protein kinase (AMPK) is an emerging target recognized for heart failure treatment. The mechanical properties and intracellular Ca²⁺ properties were measured in isolated cardiomyocyte contractile functions in response to ischemic stress. Treatment of cardiomyocytes with carvedilol augmented phosphorylation of AMPK and downstream acetyl CoA carboxylase (ACC), and ameliorated hypoxia-induced impairment in maximal velocity of shortening (+dL/dt) and relengthening (-dL/dt), and the impaired peak height and peak shortening (PS) amplitude caused by hypoxia. Carvedilol treatment improved calcium homeostasis with rescuing the peak Ca²⁺ signal, the maximum rate of Ca²⁺ change during contraction (+dF/dt) and the maximum rate of Ca²⁺ change during relaxation (-dF/dt) under hypoxia conditions. In mouse hearts perfused ex vivo with carvedilol, the function of post-ischemia left ventricle was improved and an augmentation in myocardial glucose uptake and glucose oxidation, and inhibition of fatty acid oxidation during ischemia and reperfusion. The protective effect of carvedilol was further supported in an in vivo regional ischemia model by ligation of left anterior descending coronary artery (LAD), mice treated with carvedilol followed by LAD occlusion and reperfusion showed significant size reduction in infarcted myocardium and improved cardiac functions. Therefore, Carvedilol as a clinical drug can modulate cardiac AMPK signaling pathway to reduce ischemic insults by ischemia and reperfusion.

Cardiac Radionuclide Imaging in Rodents: A Review of Methods, Results, and Factors at Play

The interest around small-animal cardiac radionuclide imaging is growing as rodent models can be manipulated to allow the simulation of human diseases. In addition to new radiopharmaceuticals testing, often researchers apply well-established probes to animal models, to follow the evolution of the target disease. This reverse translation of standard radiopharmaceuticals to rodent models is complicated by technical shortcomings and by obvious differences between human and rodent cardiac physiology. In addition, radionuclide studies involving small animals are affected by several extrinsic variables, such as the choice of anesthetic. In this paper, we review the major cardiac features that can be studied with classical single-photon and positron-emitting radiopharmaceuticals, namely, cardiac function, perfusion and metabolism, as well as the results and pitfalls of small-animal radionuclide imaging techniques. In addition, we provide a concise guide to the understanding of the most frequently used anesthetics such as ketamine/xylazine, isoflurane, and pentobarbital. We address in particular their mechanisms of action and the potential effects on radionuclide imaging. Indeed, cardiac function, perfusion, and metabolism can all be significantly affected by varying anesthetics and animal handling conditions.

Use of resting myocardial 18F-FDG imaging in the detection of unstable angina

OBJECTIVE

Increased myocardial glucose metabolism occurs with the onset of myocardial ischemia and may persist even after the restoration of blood flow, termed as 'ischemic memory'. Previous studies have demonstrated that 18F-fluorodeoxyglucose (18F-FDG) is a sensitive marker of myocardial ischemia and may have potential utility in diagnosing unstable angina (UA). This study aimed to explore the value of F-FDG PET/CT in diagnosing UA.

PATIENTS AND METHODS

Thirty-four patients (17 male patients; mean age, 59 ± 6 years) with suspected UA were prospectively recruited. Resting myocardial F-FDG PET/CT imaging was performed 21 ± 9 h (2-46 h) after the latest onset of angina pectoris. Resting or exercise myocardial perfusion imaging (MPI) and coronary angiography were performed. 'Focal' or 'focal on diffuse' myocardial F-FDG uptake was defined as abnormal, whereas other patterns of myocardial uptake, including 'focal' uptake on the basal segments, were considered as normal. The final diagnosis of UA was based on a comprehensive analysis of ECG, MPI, and coronary angiography.

RESULTS

Of the 21 patients with a final diagnosis of UA, 18 had increased 18F-FDG uptake (sensitivity 85.7%), whereas, of the 13 patients without UA, only one had abnormal 18F-FDG uptake (specificity 92.3%). The sensitivity of resting 18F-FDG imaging was higher than that of resting MPI (85.7 vs. 52.4%, P=0.016). Moreover, six UA patients with only exercise-induced ischemia showed abnormal F-FDG uptake at rest.

CONCLUSION

This pilot study demonstrated that resting 18F-FDG PET/CT imaging is an accurate and sensitive technique for the identification of UA.

Comparison of Tc-99m tetrofosmin myocardial perfusion scintigraphy and exercise F18-FDG imaging in detection of myocardial ischemia in patients with coronary artery disease

BACKGROUND

Direct ischemia imaging with F18-FDG can potentially overcome many limitations of SPECT-MPS inherent to "cold imaging". We compared SPECT-MPS with exercise F18-FDG PET in detection of ischemia in patients with suspected CAD.

METHODS

45 patients with clinical suspicion of CAD without the history of myocardial infarction were prospectively included. All patients underwent Tc-99m tetrofosmin SPECT-MPS and exercise F18-FDG PET imaging within 7 days of SPECT-MPS, and both modalities were compared with coronary angiography for detecting ischemia.

RESULTS

27 patients had an abnormal coronary angiography (at least one coronary artery with stenosis >50%). Exercise F18-FDG performed better than SPECT-MPS in LAD and LCX territory with comparably good performance in RCA territory. Exercise F18-FDG performed better in single-vessel disease and equally good in multi-vessel disease compared to SPECT-MPS. Performance of exercise 18F-FDG study was significantly better than SPECT-MPS (P = .0014) in the analysis of the 81 vascular territories in the 27 patients with abnormal coronary angiography. Performance of exercise F18-FDG was significantly better than SPECT-MPS in detecting ischemia in suspected CAD patients.

CONCLUSION

Exercise F18-FDG imaging is a potentially useful ischemia imaging modality which offers the advantages of direct ischemia imaging in CAD patients.

Direct myocardial ischemia imaging: a new cardiovascular nuclear imaging paradigm

Myocardial perfusion imaging (MPI), using radiotracers, has been in routine clinical use for over 40 years. This modality is used for the detection of coronary artery disease (CAD), risk stratification, optimizing therapy, and follow-up of patients with CAD. Molecular cardiovascular imaging using targeted radiotracers provides a unique opportunity for imaging biochemical and metabolic processes, and cell membrane transporter and receptor functions at a cellular and molecular level in experimental animal models as well as in humans. Cardiac imaging using radiolabeled free fatty acid analogues and glucose analogues enable us to image myocardial ischemia directly as an alternative to stress-rest MPI. Direct ischemia imaging techniques can avoid and overcome some of the limitations of standard stress-rest MPI. This article describes recent studies using (18) F-fluorodeoxyglucose ((18) FDG) for myocardial ischemia imaging.

Comparison of methods to reduce myocardial 18F-FDG uptake in mice: calcium channel blockers versus high-fat diets

Purpose

Besides its application in oncology, ¹⁸F-FDG PET-CT imaging is also useful in the diagnosis of certain lung infections, inflammatory diseases, and atherosclerotic plaques. Myocardial uptake of ¹⁸F-FDG may hamper visualization of the lesions caused by these diseases. Two approaches have been proposed for reducing myocardial uptake in preclinical studies, namely, calcium channel blockers (verapamil) and high-fat diets such as commercial ketogenic diets and sunflower seed diets. The objective of this study was to compare the efficacy of these approaches in reducing myocardial uptake of ¹⁸F-FDG in mice.

Methods

We performed two experiments. In experiment A, each animal underwent four ¹⁸F-FDG PET/CT scans in the following order: baseline, after administration of verapamil, after two days on ketogenic diet and after two days on sunflower seeds. PET scans were performed 60 minutes after injection of 18.5 MBq of ¹⁸F-FDG. In experiment B, the best protocol of the three (ketogenic diet) was evaluated in a lung inflammation model to assess the efficacy of reducing myocardial uptake of ¹⁸F-FDG.

Results

Compared with baseline (SUV 2.03±1.21); the greatest reduction in uptake of ¹⁸F-FDG was with ketogenic diet (SUV 0.79±0.16; p = 0.008), followed by sunflower seeds (SUV 0.91±0.13; p = 0.015); the reduction in myocardial uptake produced by verapamil was not statistically significant (SUV 1.78±0.79; p = NS). In experiment B, complete suppression of myocardial uptake noticeably improved the visualization of inflamed areas near the heart, while in the case of null or partial myocardial suppression, it was much harder to distinguish lung inflammation from myocardial spillover.

Conclusion

A high-fat diet appeared to be the most effective method for decreasing myocardial uptake of ¹⁸F-FDG in healthy mice, outperforming verapamil. Our findings also demonstrate that ketogenic diet actually improves visualization of inflammatory lesions near the heart.

Ischaemic memory imaging using metabolic radiopharmaceuticals: overview of clinical settings and ongoing investigations

"Ischaemic memory" is defined as a prolonged functional and/or biochemical alteration remaining after a particular episode of severe myocardial ischaemia. The biochemical alteration has been reported as metabolic stunning. Metabolic imaging has been used to detect the footprint left by previous ischaemic episodes evident due to delayed recovery of myocardial metabolism (persistent dominant glucose utilization with suppression of fatty acid oxidation). β-Methyl-p-[(123)I]iodophenylpentadecanoic acid (BMIPP) is a single-photon emission computed tomography (SPECT) radiotracer widely used for metabolic imaging in clinical settings in Japan. In patients with suspected coronary artery disease but no previous myocardial infarction, BMIPP has shown acceptable diagnostic accuracy. In particular, BMIPP plays an important role in the identification of prior ischaemic insult in patients arriving at emergency departments with acute chest pain syndrome. Recent data also show the usefulness of (123)I-BMIPP SPECT for predicting cardiovascular events in patients undergoing haemodialysis. Similarly, SPECT or PET imaging with (18)F-FDG injected during peak exercise or after exercise under fasting conditions shows an increase in FDG uptake in postischaemic areas. This article will overview the roles of ischaemic memory imaging both under established indications and in ongoing investigations.

Role of the excessive amounts of circulating catecholamines and glucocorticoids in stress-induced heart disease

Various stressful stimuli are known to activate the sympathetic nervous system to release catecholamines and the hypothalamic-pituitary-adrenal axis to release glucocorticoids in the circulation. Although initial actions of both catecholamines and glucocorticoids are beneficial for the function of the cardiovascular system, their delayed effects on the heart are deleterious. Glucocorticoids not only increase plasma levels of catecholamines by inhibiting their extraneuronal uptake, but they have also been shown to induce supersensitivity to catecholamines in the heart by upregulating different components of the betta-adrenoceptor signal transduction system. Low concentrations of catecholamines stimulate the heart by promoting Ca2+ movements, whereas excessive amounts of catecholamines produce cardiac dysfunction by inducing intracellular Ca2+ overload in cardiomyocytes. Several studies have shown, however, that under stressful conditions high concentrations of catecholamines become oxidized to form aminolutins and generate oxyradicals. These oxidation products of catecholamines have been demonstrated to produce coronary spasm, arrhythmias, and cardiac dysfunction by inducing Ca2+-handling abnormalities in both sarcolemmal and sarcoplasmic reticulum, defects in energy production by mitochondria, and myocardial cell damage. In this article we have focused the discussion to highlight the interrelationship between catecholamines and glucocorticoids and to emphasize the role of oxidation products of catecholamines in the development of stress-induced heart disease.

Functional alterations of cardiac proteasomes under physiological and pathological conditions

The cardiac proteasome is a complex, heterogeneous, and dynamic organelle. Its function is regulated by its molecular organization, post-translational modifications, and associated partner proteins. Pressure overload, ischaemic heart disease, or genetic mutations in contractile proteins can cause heart failure, during which misfolded protein levels are elevated. At the same time, numerous interconnected signal transduction pathways are activated that may modulate any of the three proteasomal regulatory mechanisms mentioned above, resulting in functional changes in cardiac proteasomes. Many lines of evidence support the important role of the ubiquitin-proteasome system (UPS) in the development of heart diseases. Many researchers have focused on the UPS, applying new drug discovery methods not only in the field of cancer research but also in cardiovascular fields such as cardiac hypertrophy and ischaemic heart diseases. More understanding of UPS in the pathophysiology of heart diseases will lead to new routes for therapy.

Myocardial 18F-FDG uptake after exercise-induced myocardial ischemia in patients with coronary artery disease

We have recently demonstrated the potential of (18)F-FDG as an imaging marker of myocardial ischemia if injected at peak exercise. However, how long increased (18)F-FDG uptake can be observed after an episode of exercise-induced myocardial ischemia is not known. We performed the current study to determine whether increased regional myocardial (18)F-FDG uptake at exercise in patients with coronary artery disease (CAD) persists on rest imaging (24 h later), after an episode of exercise-induced myocardial ischemia.

METHODS

Twenty-four patients with suspected CAD underwent exercise (99m)Tc-sestamibi and (18)F-FDG imaging. Repeated (18)F-FDG imaging was performed 24 h after exercise imaging, after an injection of a second dose of (18)F-FDG at rest in 20 patients. Perfusion imaging with (99m)Tc-sestamibi was simultaneously performed with (18)F-FDG imaging. All patients underwent coronary angiography.

RESULTS

Eighteen patients had greater than or equal to 70% luminal narrowing of 1 or more coronary vessels. Fifteen patients (83%) showed increased regional (18)F-FDG uptake on exercise imaging, but only 11 patients (61%) had perfusion abnormalities. Of these 15 patients with increased regional (18)F-FDG uptake on exercise imaging, 8 (53%) had no discernible (18)F-FDG uptake, 5 (33%) had decreased (18)F-FDG uptake, and only 2 (13%) had persistent (18)F-FDG uptake on rest (18)F-FDG images. The summed (18)F-FDG uptake score significantly decreased, from 14.4 +/- 10.3 at exercise to 6.7 +/- 9.2 at rest (P = 0.01). Patients with persistent (18)F-FDG uptake at rest had more (18)F-FDG uptake and lower peak rate-pressure product at exercise, compared with patients with no residual (18)F-FDG uptake at rest.

CONCLUSION

Exercise-induced regional myocardial (18)F-FDG uptake is highly specific and sensitive for exercise-induced myocardial ischemia. Regional myocardial (18)F-FDG uptake may persist 24 h after an episode of exercise-induced myocardial ischemia in some patients.

Nitrite consumption in ischemic rat heart catalyzed by distinct blood-borne and tissue factors

Nitric oxide (NO) may limit myocardial ischemia-reperfusion injury by slowing the mitochondrial metabolism. We examined whether rat heart contains catalysts potentially capable of reducing nitrite to NO during an episode of regional myocardial ischemia produced by temporary coronary artery occlusion. In intact Sprague-Dawley rats, a 15-min coronary occlusion lowered the nitrite concentration of the myocardial regions exhibiting ischemic glucose metabolism to approximately 50% that of nonischemic regions (185 +/- 223 vs. 420 +/- 203 nmol/l). Nitrite was rapidly repleted during subsequent reperfusion. The heart tissue tested in vitro acquired a substantial ability to consume nitrite when made hypoxic at neutral pH, and this ability was slightly enhanced by simultaneously lowering the pH to 5.5. More than 70% of this activity could be abolished by flushing the coronary circulation with crystalloid to remove trapped erythrocytes. Correspondingly, erythrocytes demonstrated the ability to reduce exogenous nitrite to NO under hypoxic conditions in vitro. In erythrocyte-free heart tissue, the nitrite consumption increased fivefold when the pH was lowered to 5.5. Approximately 40% of this pH-sensitive increase in nitrite consumption could be blocked by the xanthine oxidoreductase inhibitor allopurinol, whereas lowering the Po(2) sufficiently to desaturate myoglobin accelerated it further. We conclude that rat heart contains several factors capable of catalyzing ischemic nitrite reduction; the most potent is contained within erythrocytes and activated by hypoxia, whereas the remainder includes xanthine oxidoreductase and other pH-sensitive factors endogenous to heart tissue, including deoxymyoglobin.

Glucose-insulin therapy, plasma substrate levels and cardiac recovery after cardiac ischemic events

Introduction

The potential usefulness of glucose-insulin therapy relies to a large extent on the premise that it prevents hyperglycemia and hyperlipidemia following cardiac ischemic events.

Methods

In this review we evaluate the literature concerning plasma glucose and free fatty acids levels during and following cardiac ischemic events.

Results

The data indicate that hyperlipidemia and hyperglycemia most likely occur during acute coronary ischemic syndromes in the conscious state (e.g. acute myocardial infarction) and less so during reperfusion following CABG reperfusion. This is in accordance with observations that glucose-insulin therapy during early reperfusion post CABG may actually cause hypolipidemia, because substantial hyperlipidemia does not appear to occur during that stage of cardiac surgery.

Discussion

Considering recent data indicating that hypolipidemia may be detrimental for cardiac function, we propose that free fatty acid levels during reperfusion post CABG with the adjunct glucose-insulin therapy need to be closely monitored.

Conclusion

From a clinical point of view, a strategy directed at monitoring and thereafter maintaining plasma substrate levels in the normal range for both glucose (4–6 mM) and FFA (0.2–0.6 mM) as well as stimulation of glucose oxidation, promises to be the most optimal metabolic reperfusion treatment following cardiac ischemic episodes. Future (preclinical and subsequently clinical) investigations are required to investigate whether the combination of glucose-insulin therapy with concomitant lipid administration may be beneficial in the setting of reperfusion post CABG.

Noninvasive assessment of myocardial viability in a small animal model: comparison of MRI, SPECT, and PET

Acute myocardial infarction (AMI) research relies increasingly on small animal models and noninvasive imaging methods such as MRI, single-photon emission computed tomography (SPECT), and positron emission tomography (PET). However, a direct comparison among these techniques for characterization of perfusion, viability, and infarct size is lacking. Rats were studied within 18-24 hr post AMI by MRI (4.7 T) and subsequently (40-48 hr post AMI) by SPECT ((99)Tc-MIBI) and micro-PET ((18)FDG). A necrosis-specific MRI contrast agent was used to detect AMI, and a fast low angle shot (FLASH) sequence was used to acquire late enhancement and functional images contemporaneously. Infarcted regions showed late enhancement, whereas corresponding radionuclide images had reduced tracer uptake. MRI most accurately depicted AMI, showing the closest correlation and agreement with triphenyl tetrazolium chloride (TTC), followed by SPECT and PET. In some animals a mismatch of reduced uptake in normal myocardium and relatively increased (18)FDG uptake in the infarct border zone precluded conventional quantitative analysis. We performed the first quantitative comparison of MRI, PET, and SPECT for reperfused AMI imaging in a small animal model. MRI was superior to the other modalities, due to its greater spatial resolution and ability to detect necrotic myocardium directly. The observed (18)FDG mismatch likely represents variable metabolic conditions between stunned myocardium in the infarct border zone and normal myocardium and supports the use of a standardized glucose load or glucose clamp technique for PET imaging of reperfused AMI in small animals.

[18F]Fluorodeoxyglucose as a memory marker of transient myocardial ischaemia

BACKGROUND

Experimental data have shown that glucose utilization increases during acute myocardial ischaemia, and may persist for up to 24 h. Whether fluorodeoxyglucose (FDG) uptake can be imaged as a memory marker of ischaemia in humans is unknown.

METHODS

Patients with mild-to-moderate ischaemia on exercise single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) underwent repeat exercise testing within 1-2 weeks. Positron emission tomography (PET) was performed after injection of FDG 60 min post-exercise. SPECT and PET images were assessed visually, aided by circumferential profile-based analysis modified for 'hot-spot' imaging.

RESULTS

Twelve men with stress SPECT ischaemia (mean age, 69 years; nine with known coronary artery disease) were studied. The mean rate-pressure products for the first (SPECT) and second (FDG PET) exercise tests were similar (22,841+/-7321 vs. 22,680+/-7393 mmHg x bpm, P=NS). Overall, six of 12 patients studied had evidence of FDG uptake. The extent of ischaemia on SPECT was similar in FDG positive and FDG negative patients (summed difference score 10.6+/-6.9 vs. 8.0+/-1.6, P=NS). All patients with a positive FDG scan had uptake in either an ischaemic SPECT region or in a territory with known CAD by angiography.

CONCLUSION

Regional myocardial uptake of FDG is enhanced even when injected 1 h post-exercise stress in a subset of patients with ischaemia on exercise SPECT MPI. The ability to image FDG uptake injected 1 h after an ischaemic episode suggests the potential utility of FDG as a memory marker of transient ischaemia.

Nuclear Cardiology: Present and Future

Nuclear cardiology has made significant advances since the first reports of planar scintigraphy for the evaluation of left ventricular perfusion and function. While the current "state of the art" of gated myocardial perfusion single-photon emission computed tomographic (SPECT) imaging offers invaluable diagnostic and prognostic information for the evaluation of patients with suspected or known coronary artery disease (CAD), advances in the cellular and molecular biology of the cardiovascular system have helped to usher in a new modality in nuclear cardiology, namely, molecular imaging. In this review, we will discuss the current state of the art in nuclear cardiology, which includes SPECT and positron emission tomographic evaluation of myocardial perfusion, evaluation of left ventricular function by gated myocardial perfusion SPECT and gated blood pool SPECT, and the evaluation of myocardial viability with PET and SPECT methods. In addition, we will discuss the future of nuclear cardiology and the role that molecular imaging will play in the early detection of CAD at the level of the vulnerable plaque, the evaluation of cardiac remodeling, and monitoring of important new therapies including gene therapy and stem cell therapy.

Noninvasive cardiac imaging in the evaluation of suspected acute coronary syndromes

Optimal management of patients presenting with chest pain to the emergency department is a major challenge, both in terms of a diagnostic dilemma and consumption of resources. The triage of such patients can be aided vastly by the appropriate use of noninvasive imaging. Noninvasive imaging modalities such as echocardiogram, radionuclide perfusion studies, positron emission tomography, cardiac magnetic resonance imaging and computed tomography have all been demonstrated to have favorable diagnostic and prognostic value, with an enhanced sensitivity to detect acute ischemia. A normal noninvasive evaluation in the appropriate clinical setting presents a strong argument against acute ischemia as an etiology of the chest pain. Randomized trials of both rest and stress imaging in the emergency department have confirmed a reduction in unnecessary hospitalizations and cost savings without compromising the safety of the patient. Cardiac magnetic resonance and computed tomography would provide an insight into subendocardial ischemia, the detection of which has previously been difficult, using single-photon emission tomography and echocardiography. In this review, novel hot-spot imaging modalities are discussed including infarct-avid imaging agents and ischemia-avid imaging agents, thus elucidating the pathophysiology of reperfusion-induced cell death. These agents represent work in evolution and are likely to be used routinely in the future as understanding of coronary syndromes and coronary artery disease becomes clearer.

The ubiquitin-proteasome system in cardiac physiology and pathology

The ubiquitin-proteasome system (UPS) is the major nonlysosomal pathway for intracellular protein degradation, generally requiring a covalent linkage of one or more chains of polyubiquitins to the protein intended for degradation. It has become clear that the UPS plays major roles in regulating many cellular processes, including the cell cycle, immune responses, apoptosis, cell signaling, and protein turnover under normal and pathological conditions, as well as in protein quality control by removal of damaged, oxidized, and/or misfolded proteins. This review will present an overview of the structure, biochemistry, and physiology of the UPS with emphasis on its role in the heart, if known. In addition, evidence will be presented supporting the role of certain muscle-specific ubiquitin protein ligases, key regulatory components of the UPS, in regulation of sarcomere protein turnover and cardiomyocyte size and how this might play a role in induction of the hypertrophic phenotype. Moreover, this review will present the evidence suggesting that proteasomal dysfunction may play a role in cardiac pathologies such as myocardial ischemia, congestive heart failure, and myofilament-related and idiopathic-dilated cardiomyopathies, as well as cardiomyocyte loss in the aging heart. Finally, certain pitfalls of proteasome studies will be described with the intent of providing investigators with enough information to avoid these problems. This review should provide current investigators in the field with an up-to-date analysis of the literature and at the same time provide an impetus for new investigators to enter this important and rapidly changing area of research.

Latent abnormal fatty acid metabolism in apparently normal perfusion during stress in patients with restenosis after coronary angioplasty: assessment by exercise stress thallium-201 and iodine-123-labeled 15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid-dual myocardial single-photon emission computed tomography

Restenosis is a major problem in patients undergoing coronary angioplasty. Reduced uptake of iodine-123-labeled 15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid (I-BMIPP-123) relatively to thallium-201 (Tl-201) has been attributed to the metabolic damage in the myocardium in patients with coronary artery disease. Therefore, we performed exercise stress Tl-201 and I-BMIPP-123 dual myocardial single-photon emission computed tomography (SPECT) to detect coronary restenosis in 48 patients (35 men and 13 women, mean age 66 +/- 8 years), followed by coronary angiography at follow-up. Patients were divided into 2 groups: those with (n = 24) and without (n = 24) restenosis. Redistribution of Tl-201 was seen more frequently in the restenosis group than in no-restenosis group (58% [14 of 24] vs 8% [2 of 24], p <0.05). Five of 10 patients (50%) with restenosis but without Tl-201 redistribution had Tl-201/I-BMIPP-123 discrepancy during stress. In patients without restenosis, only 1 patient had this discrepancy during stress. Incorporation of Tl-201/I-BMIPP-123 uptake discrepancy during stress significantly improved the sensitivity (58% [14 of 24] to 79% [19 of 24]) with preserved specificity (92% [22 of 24] to 88% [21 of 24]). Exercise stress Tl-201 and I-BMIPP-123 dual myocardial SPECT revealed that latent abnormal fatty acid metabolism may exist in apparently normal perfusion during stress in patients with restenosis after coronary angioplasty. Use of I-BMIPP-123 together with Tl-201 during stress SPECT substantially improved the diagnostic accuracy of restenosis based on Tl-201 redistribution (from 75% to 83%).

Metabolic engineering: advances in modeling and intervention in health and disease

The field of metabolic engineering encompasses a powerful set of tools that can be divided into (a) methods to model complex metabolic pathways and (b) techniques to manipulate these pathways for a desired metabolic outcome. These tools have recently seen increased utility in the medical arena, and this paper aims to review significant accomplishments made using these approaches. The modeling of metabolic pathways has been applied to better understand disease-state physiology in a variety of cellar, subcellular, and organ systems, including the liver, heart, mitochondria, and cancerous cells. Metabolic pathway engineering has been used to generate cells with novel biochemical functions for therapeutic use, and specific examples are provided in the areas of glycosylation engineering and dopamine-replacement therapy. In order to document the potential of applying both metabolic modeling and pathway manipulation, we describe pertinent advances in the field of diabetes research. Undoubtedly, as the field of metabolic engineering matures and is applied to a wider array of problems, new advances and therapeutic strategies will follow.

Serial changes in BMIPP uptake in relation to thallium uptake in the rat myocardium after ischaemia

Several clinical studies have shown that iodine-123 labelled 15-(p-iodophenyl)-3-(R, S)-methylpentadecanoic acid (BMIPP) uptake is often lower than the uptake of perfusion tracers in patients with ischaemic heart disease. However, BMIPP accumulation may not decrease during the acute phase of a stunned myocardium in patients with acute coronary syndrome. We evaluated serial changes in BMIPP and perfusion tracer uptake in the myocardium after ischaemia. We performed a 20-min left coronary artery occlusion followed by reperfusion in male Wistar rats. One hour after the reperfusion, echocardiography was performed. Intravenous injection of iodine-125 labelled BMIPP and thallium-201 was performed 1 day (acute group) and 5 days (subacute group) after the operation. To determine the myocardial distribution of 125I-BMIPP and 201Tl, dual-tracer autoradiography was conducted. We identified regions of interest in the anterolateral wall as an area at risk and in the inferoseptum as a remote control area. The anterolateral wall/inferoseptum ratio (A/I ratio) was calculated to compare the distributions of 125I-BMIPP and 201Tl. Coronary occlusion induced hypokinesia in the anterolateral region 1 h after the reperfusion. The A/I ratio of 125I-BMIPP was significantly higher than that of 201Tl in the acute group (1.01 +/- 0.15 vs 0.80 +/- 0.23, P<0.001). On the other hand, there was no significant difference between the A/I ratios of 125I-BMIPP and 201Tl in the subacute group (0.88 +/- 0.18 vs 0.85 +/- 0.18). Two rats showed a significantly lower A/I ratio of 125I-BMIPP than 201Tl in the subacute phase. These data suggest that BMIPP uptake is preserved despite a decrease in perfusion in the acute phase after ischaemia. In the subacute phase, on the other hand, BMIPP uptake is similar to or even lower than thallium uptake. Since BMIPP uptake may change with time after ischaemia, careful interpretation of BMIPP uptake after ischaemia is required in a clinical setting.

Preserved postischemic heart function in sucrose-fed type 2 diabetic OLETF rats

Cardiovascular disease is one of the most important causes of morbidity and mortality in diabetes mellitus, but there has been controversy over functional impairment of diabetic hearts and their tolerance to ischemia. We studied ischemic heart function in type 2 diabetic rats with different degrees of hyperglycemia and its relationship with cardiac norepinephrine release. Otsuka Long-Evans Tokushima Fatty rats (OLETF) and age-matched Long-Evans Tokushima Otsuka normal rats (LETO) were used. One group of OLETF rats was given 30% sucrose in drinking water (OLETF-S). Hearts were isolated and perfused in a working heart preparation and subjected to 30 min ischemia followed by 40 min reperfusion at age of 12 months. Hemodynamics and coronary norepinephrine overflow were examined. Fasting plasma glucose in OLETF increased markedly at 12 months and sucrose administration exacerbated hyperglycemia in diabetic rats (LETO 6.6 +/- 0.5, OLETF 8.3 +/- 0.7, OLETF-S 15.0 +/- 1.7 mmol/L, P < 0.01). Basic cardiac output in OLETF was decreased as compared with LETO and OLETF-S (LETO 29.4 +/- 2.5, OLETF 24.0 +/- 2.4, OLETF-S 27.0 +/- 0.9 ml/min/g, P < 0.05) and remained very low after ischemia, while in OLETF-S it was well preserved (OLETF 4.2 +/- 2.1, OLETF-S 13.7 +/- 2.6 ml/min/g, P < 0.01). Correspondently, cardiac norepinephrine released during ischemia and reperfusion was lower in OLETF-S (OLETF 2.3 +/- 1.0, OLETF-S 0.7 +/- 0.1 pmol/ml, P < 0.01). Thus, OLETF hearts were more vulnerable to ischemia but sucrose feeding rendered their hearts resistant to ischemia. Less norepinephrine release may play a role in preventing postischemic functional deterioration in sucrose-fed diabetic hearts.

Use of radionuclide imaging in acute coronary syndromes

The triage of patients presenting to the emergency department (ED) with acute chest pain is a diagnostic challenge. Radionuclide myocardial perfusion imaging has been shown to have favorable diagnostic and prognostic value in this setting, with an excellent early sensitivity to detect acute myocardial infarction (MI) not achieved by other testing modalities. A normal resting perfusion imaging study has been shown to have a negative predictive value of over 99% to exclude MI. Observational and randomized trials of both rest and stress imaging in the ED evaluation of patients with chest pain have demonstrated reductions in unnecessary hospitalizations and cost savings compared with routine care. Perfusion imaging has also been used in risk stratification after MI, and for measurement of infarct size to evaluate reperfusion therapies. Novel "hot spot" imaging radiopharmaceuticals that visualize infarction or ischemia are currently undergoing evaluation and hold promise for future imaging of acute coronary syndromes.

Intraoperative insulin therapy does not reduce the need for inotropic or antiarrhythmic therapy after cardiopulmonary bypass

OBJECTIVE

To determine whether attempted glucose control through intraoperative insulin therapy reduces the need for inotropic or antiarrhythmic therapy after cardiopulmonary bypass (CPB).

DESIGN

Post hoc analysis of a randomized, masked clinical trial of insulin therapy for prevention of neurobehavioral deficits.

SETTING

Single university hospital.

PARTICIPANTS

Nondiabetic patients undergoing elective coronary artery bypass graft surgery (n = 381).

INTERVENTIONS

Patients received either insulin infusions in an attempt to maintain blood glucose at 80 to 120 mg/dL (n = 188) or placebo (saline; n = 193). Inotropic therapy was defined as the initiation of vasoactive support with epinephrine or amrinone infusions or mechanical support with the initiation of an intra-aortic balloon pump in the operating room or within 12 hours postoperatively. Antiarrhythmic therapy was defined as cardioversion, antiarrhythmic medications, or pacing.

MEASUREMENTS AND MAIN RESULTS

Of patients, 64 in the placebo group and 71 in the insulin group required inotropic support after CPB (p = not significant). The use of cardioversion (55 in placebo group v 61 in insulin group), antiarrhythmic medications (64 in placebo group v 76 in insulin group), and pacing (118 in placebo group v 117 in insulin group) was similar between groups. Inotropic drug support was associated with age >60 years, female gender, reduced preoperative ejection fraction, history of angina, and increased duration of CPB.

CONCLUSION

Intraoperative insulin therapy did not reduce the use of inotropic or antiarrhythmic support after cardiac surgery with CPB. The lack of benefit may be due to the inability to prevent hyperglycemia during the physiologic stress of CPB or a tribute to the effectiveness of modern myocardial preservation techniques.

Glucose uptake and glycogen levels are increased in pig heart after repetitive ischemia

Repetitive myocardial ischemia increases glucose uptake, but the effect on glycogen is unclear. Thirteen swine instrumented with a hydraulic occluder on the circumflex (Cx) artery underwent 10-min occlusions twice per day for 4 days. After 24 h postfinal ischemia and in the fasted state, echocardiogram and positron emission tomography imaging for blood flow ([(13)N]-ammonia) and 2-[(18)F]fluoro-2-deoxy-D-glucose (FDG) uptake were obtained. Tissue was then collected for ATP, creatine phosphate (CP), glycogen, and glucose transporter-4 content, and hexokinase activity. After reperfusion, regional function and CP-to-ATP ratios in the Cx and remote regions were similar. Despite the absence of stunning, the Cx region demonstrated higher glycogen levels (33 +/- 11 vs. 24 +/- 11 micromol/g; P < 0.05), and this increase correlated well with the increase in FDG uptake (r(2) = 0.78; P < 0.01). Hexokinase activity was also increased relative to remote regions (0.62 +/- 0.29 vs. 0.37 +/- 0.19 IU/g; P < 0.05), with no difference in GLUT-4 content. In summary, 24 h after repetitive ischemia, glucose uptake and glycogen levels are increased at a time that functional and bioenergetic markers of stunning have recovered. The significant correlation between glycogen content and FDG accumulation in the postischemic region suggests that increased rates of glucose transport and/or phosphorylation are linked to increased glycogen levels in hearts subjected to repetitive bouts of ischemia.

Suppression of fatty acid metabolism after exercise stress in patients with no electrocardiographic ST segment shift during balloon angioplasty

Although ST segment shift is a marker of myocardial ischemia, some patients have no ST segment shift during percutaneous transluminal coronary angioplasty (PTCA). The aim of this study is to investigate myocardial perfusion and metabolism in adaptation for ischemia using 201TI and 123I-BMIPP dual exercise stress myocardial single photon emission computed tomography (SPECT) (dual stress SPECT). In 28 patients with coronary artery disease, dual stress SPECT was performed 3 weeks before PTCA. Early and delayed images were obtained at 5 minutes and at 3 hours after termination of ergometer stress, respectively. During PTCA, 12-lead ECG was recorded, and a significant ST segment shift was defined as more than 1 mm elevation or a depression of the J-point at the first ballooning. No collateral circulation on the coronary angiogram or 201TI filling on the delayed images were observed on any of the target regions of PTCA. Patients were divided into 2 groups: with (Group A: n = 15) and without (Group B: n = 13) significant ST segment shift during PTCA. A redistribution of TI was observed in 14 (93%) of Group A and 10 (77%) of Group B patients. Incidence of BMIPP redistribution was significantly higher in Group B (11 [85%]) than in Group A (3 [20%]) (p < 0.05). Redistribution of BMIPP means suppression of fatty acid metabolism during exercise stress. Augmentation of glucose metabolism is speculated to be an energy source in ischemic preconditioning.

Lipid metabolism in the heart--contribution of BMIPP to the diseased heart

Lipid contributes greatly in cardiac metabolism to produce high energy ATPs, and is suggested to be related to the progression and deterioration of heart disease. It is fortunate that the I-123-betamethyliodophenylpentadecanoic acid (BMIPP) imaging technique is now available in determining heart condition, but we must be cautious about the interpretation of images obtained with this new tracer. From the uptake of BMIPP into the cell to breakdown and catabolism of it, there exist so many critical enzymatical pathways relating to the modification of BMIPP imaging. In clinical evaluation, the image will be translated as the integral effects of these pathways. In other words, we must be aware of these critical pathways regulating lipid metabolism and modifying factors in order to correctly understand BMIPP imaging. Lipid transport is affected by the albumin/FFA ratio in the blood, and extraction with membrane transporter proteins. Fatty acid binding protein (FABP) in the cytosole will play an important role in regulating lipid flux and following metabolism. Lipid will be utilized either for oxidation, triglyceride or phospholipid formation. For oxidation, carnitine palmitoil transferase is the key enzyme for the entrance of lipid into mitochondria, and oxidative enzymes such as acyl CoA dehydrogenase (MCAD, LCAD, HAD) will determine lipid use for the TCA cycle. ATPs produced in the mitochondria again limit the TG store. It is well known that BMIPP imaging completely changes in the ischemic condition, and is also shown that lipid metabolical regulation completely differs from normal in the very early phase of cardiac hypertrophy. In the process of deteriorating heart failure, metabolical switching of lipid with glucose will take place. In such a different heart disease conditions, it is clear that lipid metabolical regulation, including many lipid enzymes, works differently from in the healthy condition. These lipid enzymes are regulated by nuclear factor peroxisome proliferator-activated receptors (PPAR) just like a conductor of an orchestra. Most of the regulating mechanisms of the PPAR are still unknown, but reduction of this nuclear factor is shown in the process of decompensated heart failure. This review is based by mostly on our fundamental and Japanese clinical data. BMIPP has been used clinically in abundant cases in Japan. In such situations, further correct information on lipid metabolism, including BMIPP, will contribute to the understanding of deteriorating heart disease and its prognosis.