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Aims: Coronary microvascular dysfunction (CMD) is common in patients with non-obstructive coronary arteries but has not been described in low-risk symptomatic patients. We therefore assessed the prevalence and characteristics of CMD in low to moderate risk patients with chest pain in an emergency department. Methods and results: We used three-dimensional Rb82 cardiac positron emission tomography/computed tomography to diagnose coronary artery disease (known or new regional defect, any coronary calcification) and CMD (low coronary flow reserve without coronary artery disease) in chest pain patients after being ruled out for acute myocardial infarction. Exclusions included age 30 years or less, acute myocardial infarction, hemodynamic instability, heart failure and dialysis. Among 195 participants undergoing cardiac positron emission tomography/computed tomography, 42% had CMD, 36% had coronary artery disease and 22% had normal flows; 70% were women and 84% were obese. Patients with CMD and coronary artery disease had significantly lower coronary flow reserve than normal patients (mean coronary flow reserve 1.6 and 1.9 vs. 2.6, respectively, PConclusions: Despite their low-risk profile, nearly one half of symptomatic and mostly obese emergency department patients without evidence of myocardial infarction or coronary artery disease had CMD. The results could explain the high rates of return visits associated with chest pain, although their application to the general emergency department population require validation.

Radionuclide myocardial perfusion imaging (MPI) is among the most commonly performed diagnostic tests in cardiology. Although the diagnostic and prognostic applications of radionuclide MPI are supported by a wealth of observational and clinical trial data, its performance is limited by two

There is a lack of consensus to guide which breast cancer patients require left ventricular function assessment (LVEF) prior to anthracycline therapy; the cost-effectiveness of screening this patient population has not been previously evaluated. We performed a retrospective analysis of the Yale Nuclear Cardiology Database, including 702 patients with baseline equilibrium radionuclide angiography (ERNA) scan prior to anthracycline and/or trastuzumab therapy. We sought to examine associations between abnormal baseline LVEF and potential cardiac risk factors. Additionally, we designed a Markov model to determine the incremental cost-effectiveness ratio (ICER) of ERNA screening for women aged 55 with stage I–III breast cancer from a payer perspective over a lifetime horizon. An abnormal LVEF was observed in 2% (n = 14) of patients. There were no significant associations on multivariate analysis performed on self-reported risk factors. Our analysis showed LVEF screening is cost-effective with ICER of $45,473 per QALY gained. For a willingness-to-pay threshold of $100,000/ QALY, LVEF screening had an 81.9% probability of being cost-effective. Under the same threshold, screening was cost-effective for non-anthracycline cardiotoxicity risk of RR ≤ 0.58, as compared to anthracycline regimens. Age, preexisting cardiac risk factors and coronary artery disease did not predict a baseline abnormal LVEF. While the prevalence of an abnormal baseline LVEF is low in patients with breast cancer, our results suggest that cardiac screening prior to anthracycline is cost-effective.

Background: It is unclear if all breast cancer (BC) patients require baseline left ventricular function (LVEF) assessment prior to anthracycline based chemotherapy (ABC), and the approach is variable in clinical practice. Our objective is to determine the cost effectiveness of obtaining a baseline LVEF assessment prior to (neo) adjuvant ABC in clinical practice. Methods: We performed a retrospective analysis of the Yale Equilibrium Radionuclide Angiography (ERNA) database for 701 breast cancer patients who had a baseline ERNA scan prior to systemic therapy for an initial diagnosis of stages I-IV BC between July 2003 and May 2013. We found that 14 of 701 (2%) patients had a baseline LVEF < 50%. Age, pre-existing cardiac risk factors and coronary artery disease did not predict an abnormal baseline LVEF Results: Assuming that 20% of the unscreened patients with a LVEF < 50% will develop CHF if treated with ABC regimen without management of baseline cardiac dysfunction, the base case incremental cost effectiveness ratio (ICER) was determined to be 18,520 $USD/QALY. Sensitivity analysis suggested that the cost-effectiveness of baseline LVEF assessment is primarily driven by the prevalence of patients with LVEF < 50%, the incidence of CHF in this high-risk patient group if treated with ABC regimen, and time to CHF development. While our analysis did not reveal risk factors predictive of low baseline LVEF, our model's dependence on prevalence of LVEF < 50% demonstrates the importance of risk factor stratification. A hypothetical predictive marker which enriches the prevalence of an abnormal baseline LVEF 5-fold to 10% would result in a cost-effectiveness of 10,990 $USD/QALY. The model is less sensitive to the cost of baseline echocardiogram testing. Conclusion: Baseline LVEF assessment was found to be cost-effective under a willingness-to-pay threshold of $50,000/QALY. Our sensitivity analysis suggests that risk factor-guided LVEF baseline LVEF screening may increase the number of high-risk patients in the treatment population, thus further increasing the cost-effectiveness of baseline LVEF assessment. Citation Format: Safonov A, Hatzis C, Stratton J, Gross CP, Russell R, Pusztai L, Abu-Khalaf MM. A cost effectiveness analysis of baseline left ventricular function assessment for breast cancer patients undergoing anthracycline chemotherapy. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-11-03.

AMP-activated kinase (AMPK) is a stress responsive kinase that regulates cellular metabolism and protects against cardiomyocyte injury during ischemia-reperfusion (IR). Mitochondria play an important role in cell survival, but the specific actions of activated AMPK in maintaining mitochondrial integrity and function during reperfusion are unknown. Thus, we assessed the consequences of AMPK inactivation on heart mitochondrial function during reperfusion. Mouse hearts expressing wild type (WT) or kinase-dead (KD) AMPK were studied. Mitochondria isolated from KD hearts during reperfusion had intact membrane integrity, but demonstrated reduced oxidative capacity, increased hydrogen peroxide production and decreased resistance to mitochondrial permeability transition pore opening compared to WT. KD hearts showed increased activation of the mitogen activated protein kinase kinase 4 (MKK4) and downstream c-Jun terminal kinase (JNK) and greater necrosis during reperfusion after coronary occlusion. Transgenic expression of mitochondrial catalase (MCAT) prevented the excessive cardiac JNK activation and attenuated the increased myocardial necrosis observed during reperfusion in KD mice. Inhibition of JNK increased the resistance of KD hearts to mPTP opening, contractile dysfunction and necrosis during IR. Thus, intrinsic activation of AMPK is critical to prevent excess mitochondrial reactive oxygen production and consequent JNK signaling during reperfusion, thereby protecting against mPTP opening, irreversible mitochondrial damage and myocardial injury.

Cardiac transthyretin amyloidosis (ATTR) is an underrecognized and underdiagnosed entity. With increasing clinical awareness and availability of non-invasive diagnostic testing, more patients are being identified early and can benefit from treatment. Our study examines the positive testing rate for

Cardio-oncology focuses increased effort to decrease cancer treatment-related cardiotoxicity while continuing to improve outcomes. We sought to synthesize the latest in nuclear cardiology as it pertains to the assessment of left ventricular function in preventative guidelines and comparison to other modalities, novel molecular markers of pre-clinical cardiotoxicity, and its role in cardiac amyloid diagnosis.Planar ERNA (equilibrium radionuclide angiocardiography) provides a reliable and proven means of monitoring and preventing anthracycline cardiotoxicity, and SPECT ERNA using solid-state gamma cameras may provide reproducible assessments of left ventricular function with reduced radiation exposure. While certain chemotherapeutics have vascular side effects, the use of stress perfusion imaging has still not been adequately studied for routine use. Similarly, markers of apoptosis, inflammation, and sympathetic nerve dysfunction are promising, but are still not ready for uniform usage. SPECT tracers can assist in nonbiopsy diagnosis of cardiac amyloid. Nuclear cardiology is a significant contributor to the multimodality approach to cardio-oncology.

BACKGROUND: Prior studies indicate that an elevated creatinine kinase (CK)-MB imparts poor prognosis in patients with acute coronary syndrome despite a normal troponin. Its prognosis in the undifferentiated chest pain observation unit (CPU) population remains undefined. OBJECTIVE: To compare rates and predictors of 30-day adverse cardiac events in 2 cohorts (CK ±/MB+ vs. normal [CK ±/MB-]) in low-moderate-risk CPU patients. METHODS: Consecutive CPU patients were followed in a retrospective cohort study for primary outcome (acute coronary syndrome, percutaneous transluminal coronary angioplasty, coronary artery bypass graft, abnormal stress test, cardiac hospitalization, or death within 30 days) by using standardized chart reviews and national death registry. Exclusions were: those aged 30 years or younger, positive troponin, ischemic electrocardiogram, hemodynamic instability, heart failure, or dialysis. RESULTS: Between January 2006 and April 2009, 2979 patients were eligible, of which 350 excluded and 2629 analyzed. MB+ compared with normal patients were more likely to be: older (mean, 53.4 ± 14 vs. 51.5 ± 12 years; P = 0.04); male (71% vs. 40%; P = 0.01); renal insufficient (5% vs. 2%; P = 0.01); hypertensive (50% vs. 44%; P = 0.04); dyslipidemic (44% vs. 33%; P = 0.01) obese (55% vs. 43%; P = 0.01); and with known coronary artery disease (14% vs. 5%; P < 0.01). Composite adverse events were 213 (8%) and did not significantly differ for either initial MB+ vs. normal (9.1%, 8.0%; odds ratio, 1.1, 0.7-1.9) or serial MB+ vs. normal (7.5%, 7.4%; odds ratio, 1.0, 0.5-1.8). In a multiple logistic regression model, male sex, diabetes, and prior CAD predicted adverse events, whereas CK-MB along with race, hypertension, smoking, dyslipidemia, family history, and obesity did not. CONCLUSIONS: Elevated CK-MB does not add value to serial troponin testing in low-moderate-risk CPU patients.

Although intimately positioned between metabolic substrates in the bloodstream and the tissue parenchymal cells that require these substrates, a major role of the vascular endothelium in the regulation of tissue metabolism has not been widely appreciated. We hypothesized that via control of transendothelial glucose transport and contributing paracrine mechanisms the endothelium plays a major role in regulating organ and tissue glucose metabolism. We further hypothesized that the hypoxia-inducible factor -1α (HIF-1α) plays an important role in coordinating these endothelial functions. To test these hypotheses, we generated mice with endothelial cell-specific deletion of HIF-1α. Loss of HIF in the endothelium resulted in significantly increased fasting blood glucose levels, a blunted insulin response with delayed glucose clearance from the blood after i.v. loading, and significantly decreased glucose uptake into the brain and heart. Endothelial HIF-1α knockout mice also exhibited a reduced cerebrospinal fluid/blood glucose ratio, a finding consistent with reduced transendothelial glucose transport and a diagnostic criterion for the Glut1 deficiency genetic syndrome. Endothelial cells from these mice demonstrated decreased Glut1 levels and reduced glucose uptake that was reversed by forced expression of Glut1. These data strongly support an important role of the vascular endothelium in determining whole-organ glucose metabolism and indicate that HIF-1α is a critical mediator of this function.

Anthracyclines, such as doxorubicin and idarubicin, remain an important class of chemotherapeutic agents. Unfortunately, their efficacy in treating cancer is limited by a cumulative dose-dependent cardiotoxicity, which can cause irreversible heart failure. In this review, we discuss the pathogenesis and incidence of anthracycline-induced cardiotoxicity as well as methods to detect, prevent and treat the condition.

Background— Removal of cardiac endothelial cells (EC) has been shown to produce significant detrimental effects on the function of adjacent cardiac myocytes, suggesting that EC play a critical role in autocrine/paracrine regulation of the heart. Despite this important observation, the mediators of the protective function of EC remain obscure. Neuregulin (NRG, a member of the epidermal growth factor family) is produced by EC and cardiac myocytes contain receptors (erbB) for this ligand. We hypothesized that NRG is an essential factor produced by EC, which promotes cardioprotection against ischemic injury. Methods and Results— We demonstrate that human cardiac EC express and release NRG in response to hypoxia–reoxygenation. Under conditions where hypoxia–reoxygenation causes significant cardiac myocyte cell death, NRG can significantly decrease apoptosis of isolated adult ventricular myocytes. Coculturing adult murine myocytes with human umbilical vein, murine lung microvascular, or human coronary artery EC can also protect myocytes against hypoxia–reoxygenation–induced apoptosis. These protective effects are abolished by NRG gene deletion or silencing of NRG expression in EC. Finally, endothelium-selective deletion of NRG in vivo leads to significantly decreased tolerance to ischemic insult, as demonstrated by impaired postischemic contractile recovery in a perfused whole-organ preparation and larger infarct sizes after coronary artery ligation. Conclusion— Together, these data demonstrate that EC-derived NRG plays an important role in cardiac myocyte protection against ischemic injury in the heart and supports the idea that manipulation of this signaling pathway may be an important clinical target in this setting.

Aims Doxorubicin (DOX) is a highly effective chemotherapeutic agent; however, cumulative dose-dependent cardiotoxicity is a significant side effect of this therapy. Because DOX is a polyaromatic hydrocarbon, we hypothesized that it will be metabolized by the activation of the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor that is involved in the metabolism of numerous xenobiotic agents. These studies were performed to determine whether DOX activates AhR and whether this activation modulates the toxicity of DOX in cardiomyocytes. Methods and results Treatment with DOX induced AhR migration to the nucleus, increased AhR binding with its co-factor, aryl hydrocarbon receptor nuclear translocator-1 (ARNT1), and increased the expression of AhR-regulated phase I (CYP1A1) and phase II (GSTA1) drug-metabolizing enzymes in both cardiomyocytes and in the intact heart. Knockdown of AhR in H9C2 cells abolished DOX-induced increases in CYP1A1 and GSTA1 expression. Similar results were obtained by treating adult rat ventricular myocytes with the AhR antagonist, CH-223191. Taken together, these findings indicate that DOX-induced upregulation of CYP1A1 and GSTA1 expression is AhR dependent. AhR null mice treated with 10 mg/kg DOX did not show any activation of CYP1A1 or GSTA1 expression. Moreover, lack of AhR in vivo resulted in a significant decrease in left ventricular function compared with wild-type animals, and increased p53 activation and apoptosis in the heart after treatment with DOX. Conclusions These findings indicate that AhR plays an important role in DOX metabolism by the heart and further demonstrate that AhR is cardioprotective against DOX-induced cardiotoxicity.

Doxorubicin-based chemotherapy is limited by the development of dose-dependent left ventricular dysfunction and congestive heart failure caused by reactive oxygen species (ROS). Uncoupling proteins (UCP) can inhibit mitochondrial ROS production as well as decrease myocyte damage from exogenous ROS. Prior studies have shown that cardiac UCP2 and UCP3 mRNA expression is decreased with acute doxorubicin treatment. However, the expression of UCP protein in hearts with doxorubicin cardiotoxicity and the resultant changes in mitochondrial function and oxidant stress have not been determined.Heart failure was induced in Sprague-Dawley rats with intraperitoneal injections of doxorubicin (2 mg/kg t.i.w., total dose: 18 mg/kg). Mitochondria were isolated from mice receiving doxorubicin or saline injections for determination of UCP2 and UCP3 expression. In addition, mitochondrial respiration, ATP synthesis and ROS production were determined.Doxorubicin-induced heart failure was associated with significant decreases in UCP2 and UCP3 protein expression compared with nonfailing hearts (P0.05). While the rates of state 3 and state 4 respiration and ATP synthesis were lower in mitochondria isolated from failing hearts, the respiratory control ratio was 15% higher (P0.05), and the ratio of ATP production to oxygen consumption was 25% higher (P0.05) in mitochondria from failing hearts, indicating greater coupling between citric acid cycle flux and mitochondrial ATP synthesis. However, the decrease in UCP expression was associated with 50% greater mitochondrial ROS generation (P0.05).Downregulation of myocardial UCP2 and UCP3 in the setting of doxorubicin-induced heart failure is associated with improved efficiency of ATP synthesis, which might compensate for abnormal energy metabolism. However, this beneficial effect is counterbalanced by greater oxidant stress.

Inflammation is often accompanied by robust angiogenesis. Vascular endothelial cells (ECs) express erbB receptors and their ligand, neuregulin-1, and can respond to neuregulin by proliferation and angiogenesis. We hypothesized that some growth factor-like responses of ECs to inflammatory cytokines can be explained by cleavage of transmembrane neuregulin with subsequent release of its extracellular epidermal growth factor-like-containing domain and autocrine activation. Using a model of cultured human ECs, we found that interleukin-6 or interferon-γ causes rapid cleavage and release of transmembrane neuregulin. Inhibitors of metalloproteinases abolish this effect. The addition of an inhibitor of tumor necrosis factor-α converting enzyme (TACE) blocks cytokine-induced neuregulin release. Silencing of TACE expression increases the amount of basal proneuregulin present in ECs but does not block neuregulin release in response to phorbol myristate acetate (PMA), suggesting that other proteinases are responsible for mediating protein kinase C-dependent cleavage. Cytokines capable of inducing neuregulin cleavage stimulated ERK activation and in vitro angiogenesis (Matrigel cord formation). This effect is blocked by inhibitors that block neuregulin cleavage, erbB protein tyrosine kinase inhibitors, or antineuregulin-neutralizing antibodies. Cytokine-activated metalloproteinase cleavage of neuregulin may play an important role in autocrine activation of EC signaling pathways, contributing to key biological effects, perhaps including inflammation-associated angiogenesis.—Kalinowski, A., Plowes, N. J. R., Huang, Q., Berdejo-Izquierdo, C., Russell, R. R., Russell, K. S. Metalloproteinase-dependent cleavage of neuregulin and autocrine stimulation of vascular endothelial cells.

Because of the high metabolic cost of maintaining an adequate cardiac output, the heart possesses the ability to utilize a wide variety of metabolic substrates, including fatty acids, glucose, lactate, amino acids, and ketone bodies. The relative contribution of each of these substrates is regulated by multiple factors, including substrate concentration, presence of adequate blood flow and oxygen, the action of a variety of hormones, and the influences of disease states that can alter the metabolic machinery of the heart. This review summarizes the biochemical and cellular basis of myocardial substrate selection, as well as the changes in the metabolic phenotype of the heart in response to cardiac diseases. Based on this background, this review also illustrates the nuclear-based imaging techniques that can be used to assess myocardial metabolism and their current and future applications to patient care.

The 12th annual Scientific Sessions of the American Society of Nuclear Cardiology (ASNC) (chaired by Dr. Brian Abbott) were held in San Diego, California, from September 6 through 9, 2007. The meeting, entitled “Cardiac Imaging: Imagine the Future,” attracted over 1,700 attendees. The scientific

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.

The American Society of Nuclear Cardiology (ASNC) now consists of more than 4,700 nuclear cardiology professionals. The 10th Annual Scientific Session (chaired by Dr. Diwakar Jain) was held from September 29 through October 2, 2005 in Seattle Washington, with more than 1,500 registrants in

AMP-activated protein kinase (AMPK) is an important regulator of diverse cellular pathways in the setting of energetic stress. Whether AMPK plays a critical role in the metabolic and functional responses to myocardial ischemia and reperfusion remains uncertain. We examined the cardiac consequences of long-term inhibition of AMPK activity in transgenic mice expressing a kinase dead (KD) form of the enzyme. The KD mice had normal fractional shortening and no heart failure, cardiac hypertrophy, or fibrosis, although the in vivo left ventricular (LV) dP/dt was lower than that in WT hearts. During low-flow ischemia and postischemic reperfusion in vitro, KD hearts failed to augment glucose uptake and glycolysis, although glucose transporter content and insulin-stimulated glucose uptake were normal. KD hearts also failed to increase fatty acid oxidation during reperfusion. Furthermore, KD hearts demonstrated significantly impaired recovery of LV contractile function during postischemic reperfusion that was associated with a lower ATP content and increased injury compared with WT hearts. Caspase-3 activity and TUNEL-staining were increased in KD hearts after ischemia and reperfusion. Thus, AMPK is responsible for activation of glucose uptake and glycolysis during low-flow ischemia and plays an important protective role in limiting damage and apoptotic activity associated with ischemia and reperfusion in the heart.

The heart responds to energetic stress with both acute and chronic changes in substrate metabolism. Recent work has demonstrated that the metabolic stress kinase AMP-activated protein kinase (AMPK) plays an important role in the acute regulation of carbohydrate and fatty acid metabolism in the setting of acute energetic stressors, such as ischemia/reperfusion, or increased workload, through covalent and noncovalent regulation of enzymes involved in intermediary metabolism. In addition, chronic activation of AMPK has been shown to affect the expression of key proteins regulating carbohydrate and fatty acid metabolism. Characterizing the effects of AMPK will provide important insights into its function in the normal heart and might provide new metabolic therapies for ischemic heart disease and heart failure.

The Centers for Medicare & Medicaid Services will require physicians to adopt appropriate use criteria, which promote using diagnostic tests of proven value based on the clinical context and avoid ...

Activation of AMP-activated protein kinase (AMPK) with 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) increases glucose transport in skeletal muscle via an insulin-independent pathway. To examine the effects of AMPK activation on skeletal muscle glucose transport activity and whole-body carbohydrate and lipid metabolism in an insulin-resistant rat model, awake obese Zucker fa/fa rats (n = 26) and their lean (n = 23) littermates were infused for 90 min with AICAR, insulin, or saline. The insulin infusion rate (4 mU · kg−1 · min−1) was selected to match the glucose requirements during AICAR (bolus, 100 mg/kg; constant, 10 mg · kg−1 · min−1) isoglycemic clamps in the lean rats. The effects of these identical AICAR and insulin infusion rates were then examined in the obese Zucker rats. AICAR infusion increased muscle AMPK activity more than fivefold (P < 0.01 vs. control and insulin) in both lean and obese rats. Plasma triglycerides, fatty acid concentrations, and glycerol turnover, as assessed by [2-13C]glycerol, were all decreased in both lean and obese rats infused with AICAR (P < 0.05 vs. basal), whereas insulin had no effect on these parameters in the obese rats. Endogenous glucose production rates, measured by [U-13C]glucose, were suppressed by >50% during AICAR and insulin infusions in both lean and obese rats (P < 0.05 vs. basal). In lean rats, rates of whole-body glucose disposal increased by more than twofold (P < 0.05 vs. basal) during both AICAR and insulin infusion; [3H]2-deoxy-d-glucose transport activity increased to a similar extent, by >2.2-fold (both P < 0.05 vs. control), in both soleus and red gastrocnemius muscles of lean rats infused with either AICAR or insulin. In the obese Zucker rats, neither AICAR nor insulin stimulated whole-body glucose disposal or soleus muscle glucose transport activity. However, AICAR increased glucose transport activity by ∼2.4-fold (P < 0.05 vs. control) in the red gastrocnemius from obese rats, whereas insulin had no effect. In summary, acute infusion of AICAR in an insulin-resistant rat model activates skeletal muscle AMPK and increases glucose transport activity in red gastrocnemius muscle while suppressing endogenous glucose production and lipolysis. Because type 2 diabetes is characterized by diminished rates of insulin-stimulated glucose uptake as well as increased basal rates of endogenous glucose production and lipolysis, these results suggest that AICAR-related compounds may represent a new class of antidiabetic agents.

Myocardial glucose utilization increases in response to the energetic stress imposed on the heart by exercise, pressure overload, and myocardial ischemia. Recruitment of glucose transport proteins is the cellular mechanism by which the heart increases glucose transport for subsequent metabolism. Moderate regional ischemia leads to the translocation of both glucose transporters, GLUT4 and GLUT1, to the sarcolemma in vivo. Myocardial ischemia also stimulates 5'-adenosine monophosphate-activated protein kinase, which may be a fuel gauge in the heart and other tissues signaling the need to turn on energy-generating metabolic pathways. Pharmacologic stimulation of this kinase increases cardiac glucose uptake and transporter translocation, suggesting that it may play an important role in augmenting glucose entry in the setting of ischemic or energetic stress. Thus, recent work has provided insight into the cellular and molecular mechanisms responsible for glucose uptake during energetic stress, which may lead to new approaches to the treatment of patients with coronary artery disease.

Overexpression of mitochondrial uncoupling proteins (UCPs) attenuates ischemia-reperfusion (I/R) injury in cultured cardiomyocytes. However, it is not known whether UCPs play an essential role in cardioprotection in the intact heart. This study evaluated the cardioprotective efficacy of UCPs against I/R injury and characterized the mechanism of UCP-mediated protection in addition to the role of UCPs in ischemic preconditioning (IPC). Cardiac UCP3 knockout (UCP3−/−) and wild-type (WT) mice hearts were subjected to ex vivo and in vivo models of I/R injury and IPC. Isolated UCP3−/−mouse hearts were retrogradely perfused and found to have poorer recovery of left ventricular function compared with WT hearts under I/R conditions. In vivo occlusion of the left coronary artery resulted in twofold larger infarcts in UCP3−/−mice compared with WT mice. Moreover, the incidence of in vivo I/R arrhythmias was higher in UCP3−/−mice. Myocardial energetics were significantly impaired with I/R, as reflected by a decreased ATP content and an increase in the AMP-to-ATP ratio. UCP3−/−hearts generated more reactive oxygen species (ROS) than WT hearts during I/R. Pretreatment of UCP3−/−hearts with the pharmacological uncoupling agent carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone improved postischemic functional recovery. Also the protective efficacy of IPC was abolished in UCP3−/−mice. We conclude that UCP3 plays a critical role in cardioprotection against I/R injury and the IPC phenomenon. There is increased myocardial vulnerability to I/R injury in hearts lacking UCP3. The mechanisms of UCP3-mediated cardioprotection include regulation of myocardial energetics and ROS generation by UCP3 during I/R.

Chronic kidney disease (CKD) leads to an 18-fold increase in cardiovascular complications not fully explained by traditional risk factors. Levels of renalase, a recently discovered oxidase that metabolizes catecholamines, are decreased in CKD. Here we show that renalase deficiency in a mouse knockout model causes increased plasma catecholamine levels and hypertension. Plasma blood urea nitrogen, creatinine, and aldosterone were unaffected. However, knockout mice had normal systolic function and mild ventricular hypertrophy but tolerated cardiac ischemia poorly and developed myocardial necrosis threefold more severe than that found in wild-type mice. Treatment with recombinant renalase completely rescued the cardiac phenotype. To gain insight into the mechanisms mediating this cardioprotective effect, we tested if gene deletion affected nitrate and glutathione metabolism, but found no differences between hearts of knockout and wild-type mice. The ratio of oxidized (NAD) to reduced (NADH) nicotinamide adenine dinucleotide in cardiac tissue, however, was significantly decreased in the hearts of renalase knockout mice, as was plasma NADH oxidase activity. In vitro studies confirmed that renalase metabolizes NADH and catecholamines. Thus, renalase plays an important role in cardiovascular pathology and its replacement may reduce cardiac complications in renalase-deficient states such as CKD.

To determine the temporal relationship between changes in contractile performance and flux through the citric acid cycle in hearts oxidizing acetoacetate, we perfused isolated working rat hearts with either glucose or acetoacetate (both 5 mM) and freeze-clamped the tissue at defined times. After 60 min of perfusion, hearts utilizing acetoacetate exhibited lower systolic and diastolic pressures and lower cardiac outputs. The oxidation of acetoacetate increased the tissue content of 2-oxoglutarate and glutamate and decreased the content of succinyl-CoA suggesting inhibition of citric acid cycle flux through 2-oxoglutarate dehydrogenase. Whereas hearts perfused with either acetoacetate or glucose were similar with respect to their function for the first 20 min, changes in tissue metabolites were already observed within 5 min of perfusion at near-physiological workloads. The addition of lactate or propionate, but not acetate, to hearts oxidizing acetoacetate improved contractile performance, although inhibition of 2-oxoglutarate dehydrogenase was probably not diminished. If lactate or propionate were added, malate and citrate accumulated indicating utilization of anaplerotic pathways for the citric acid cycle. We conclude that a decreased rate of flux through 2-oxoglutarate dehydrogenase in hearts oxidizing acetoacetate precedes, and may be responsible for, contractile failure and is not the result of decreased cardiac work. Further, anaplerosis play an important role in the maintenance of contractile function in hearts utilizing acetoacetate.

The stress-signaling protein, adenosine monophosphate-activated protein kinase (AMPK), regulates a variety of pathways in cells that 1) increase the provision and utilization of energy-providing substrates such as glucose and fatty acids, 2) inhibit energy-requiring pathways such as cholesterol biosynthesis and protein synthesis, and 3) increase the transcription of genes involved in energy metabolism and mitochondrial biogenesis. In the heart, AMPK therefore becomes very important in protecting against ischemia-reperfusion injury and regulating substrate metabolism in the face of changes in workload. This review summarizes the regulation of AMPK activity in the heart and discusses the effects of AMPK activation.

AMP-activated protein kinase (AMPK) promotes glucose transport, maintains ATP stores, and prevents injury and apoptosis during ischemia. AMPK has several direct molecular targets in the heart but also may interact with other stress-signaling pathways. This study examined the role of AMPK in the activation of the p38 mitogen-activated protein kinase (MAPK). In isolated heart muscles, the AMPK activator 5-aminoimidazole-4-carboxy-amide-1-β- d -ribofuranoside (AICAR) increased p38 MAPK activation. In AMPK-deficient mouse hearts, expressing a kinase-dead (KD) α 2 catalytic subunit, p38 MAPK activation was markedly reduced during low-flow ischemia (2.3- versus 7-fold in wild-type hearts, P P −/− mouse hearts. Ischemia increased p38 MAPK recruitment to transforming growth factor-β-activated protein kinase 1–binding protein 1 (TAB1), a scaffold protein that promotes p38 MAPK autophosphorylation. Moreover, TAB1 was associated with the α 2 catalytic subunit of AMPK. p38 MAPK recruitment to TAB1/AMPK complexes required AMPK activation and was reduced in ischemic AMPK-deficient transgenic mouse hearts. The potential role of p38 MAPK in mediating the downstream action of AMPK to promote glucose transport was also assessed. The p38 MAPK inhibitor SB203580 partially inhibited both AICAR- and hypoxia-stimulated glucose uptake and GLUT4 translocation. Activation of p38 MAPK by anisomycin also increased glucose transport in heart muscles. Thus, AMPK has an important role in promoting p38 MAPK activation in the ischemic heart by inducing p38 MAPK autophosphorylation through interaction with the scaffold protein TAB1.

AMP-activated protein kinase (AMPK) is activated during exercise and ischemia and is emerging as an important regulatory mechanism in the heart. AMPK promotes adenosine triphosphate-generating pathways, including glucose transport, glycolysis, and fatty acid oxidation, while inhibiting energy-consuming anabolic pathways. After ischemia-reperfusion, AMPK-deficient hearts from transgenic mice have severe left ventricular contractile dysfunction with increased apoptosis and necrosis. Mutations in the AMPKgamma(2) subunit lead to cardiac glycogen overload, Wolff-Parkinson-White syndrome, arrhythmias, and heart failure. This review focuses on the molecular mechanisms of activation and cardiovascular actions of AMPK in the heart.

test the natu thou reac with com seco ofte of m stre dise coro infu of S in p Case presentation. A 44-year-old man with no history of coronary artery disease was referred for cardial stress testing. He presented to the emergency artment with a single episode of exertional rightd chest pain associated with breathlessness. He had a ative helical computed tomography scan to evaluate pulmonary embolism and was ruled out for myocarinfarction by serial cardiac biomarkers as well as ing electrocardiograms (ECGs), which showed no ges diagnostic for ischemia. Two weeks before this entation, he had undergone abdominal surgery for a ll bowel obstruction, which was complicated by a nd infection. Because of his nonhealed abdominal nd, he was scheduled for a pharmacologic myocarperfusion test with adenosine infused at 140 g · 1 · min . He tolerated the 4.5-minute infusion of osine with only mild atypical chest pain and no ECG ges. He had received a 559-mBq (15.1-mCi) injecof technetium 99m sestamibi 1.5 minutes into the osine infusion. Three minutes after the end of osine infusion, severe, substernal chest discomfort ciated with profound diaphoresis suddenly develd. The ECG at that time showed ST elevations riorly with reciprocal ST depressions laterally ure 1A). He was treated with sublingual nitroglyc, aspirin, and oxygen. His chest pain resolved within inutes, and his ECG reverted back to baseline ure 1B). The patient was admitted and taken to the cardiac eterization laboratory. Coronary angiography reed a right-dominant coronary tree without any evice of atherosclerosis (Figure 2). Left ventriculograperformed in orthogonal views demonstrated no onal wall motion abnormalities. As a result of the rvening catheterization, the patient’s nuclear imaging

AMP-activated protein kinase (AMPK) is a serine-threonine kinase that regulates cellular metabolism and has an essential role in activating glucose transport during hypoxia and ischemia. The mechanisms responsible for AMPK stimulation of glucose transport are uncertain, but may involve interaction with other signaling pathways or direct effects on GLUT vesicular trafficking. One potential downstream mediator of AMPK signaling is the nitric oxide pathway. The aim of this study was to examine the extent to which AMPK mediates glucose transport through activation of the nitric oxide (NO)-signaling pathway in isolated heart muscles. Incubation with 1 mM 5-amino-4-imidazole-1-β-carboxamide ribofuranoside (AICAR) activated AMPK ( P < 0.01) and stimulated glucose uptake ( P < 0.05) and translocation of the cardiomyocyte glucose transporter GLUT4 to the cell surface ( P < 0.05). AICAR treatment increased phosphorylation of endothelial NO synthase (eNOS) ∼1.8-fold ( P < 0.05). eNOS, but not neuronal NOS, coimmunoprecipitated with both the α2 and α1 AMPK catalytic subunits in heart muscle. NO donors also increased glucose uptake and GLUT4 translocation ( P < 0.05). Inhibition of NOS with Nω-nitro-l-arginine and Nω-methyl-l-arginine reduced AICAR-stimulated glucose uptake by 21 ± 3% ( P < 0.05) and 25 ± 4% ( P < 0.05), respectively. Inhibition of guanylate cyclase with ODQ and LY-83583 reduced AICAR-stimulated glucose uptake by 31 ± 4% ( P < 0.05) and 22 ± 3% ( P < 0.05), respectively, as well as GLUT4 translocation to the cell surface ( P < 0.05). Taken together, these results indicate that activation of the NO-guanylate cyclase pathway contributes to, but is not the sole mediator of, AMPK stimulation of glucose uptake and GLUT4 translocation in heart muscle.

e11501 Background: Aromatase inhibitors (AIs) have been reported to increase the risk of cardiotoxicity in women with early stage breast cancer (BC). This study was performed to further elucidate t...

Insulin-induced hypoglycemia occurs commonly in intensively treated patients with type 1 diabetes, but the cardiovascular consequences of hypoglycemia in these patients are not known. We studied left ventricular systolic [left ventricular ejection fraction (LVEF)] and diastolic [peak filling rate (PFR)] function by equilibrium radionuclide angiography during insulin infusion (12 pmol · kg−1 · min−1) under either hypoglycemic (∼2.8 mmol/l) or euglycemic (∼5 mmol/l) conditions in intensively treated patients with type 1 diabetes and healthy nondiabetic subjects ( n = 9 for each). During hypoglycemic hyperinsulinemia, there were significant increases in LVEF (ΔLVEF = 11 ± 2%) and PFR [ΔPFR = 0.88 ± 0.18 end diastolic volume (EDV)/s] in diabetic subjects as well as in the nondiabetic group (ΔLVEF = 13 ± 2%; ΔPFR = 0.79 ± 0.17 EDV/s). The increases in LVEF and PFR were comparable overall but occurred earlier in the nondiabetic group. A blunted increase in plasma catecholamine, cortisol, and glucagon concentrations occurred in response to hypoglycemia in the diabetic subjects. During euglycemic hyperinsulinemia, LVEF also increased in both the diabetic (ΔLVEF = 7 ± 1%) and nondiabetic (ΔLVEF = 4 ± 2%) groups, but PFR increased only in the diabetic group. In the comparison of the responses to hypoglycemic and euglycemic hyperinsulinemia, only the nondiabetic group had greater augmentation of LVEF, PFR, and cardiac output in the hypoglycemic study ( P < 0.05 for each). Thus intensively treated type 1 diabetic patients demonstrate delayed augmentation of ventricular function during moderate insulin-induced hypoglycemia. Although diabetic subjects have a more pronounced cardiac response to hyperinsulinemia per se than nondiabetic subjects, their response to hypoglycemia is blunted.

Tremendous advances have recently been achieved in our understanding of the cellular and molecular mechanisms regulating glucose transport in the heart and other tissues. An intricate network of signaling molecules and intracellular proteins trigger and mediate the vesicular movement of GLUT vesicles, targeting them to the sarcolemma. Ongoing research in this area promises to further define these mechanisms in the heart, which may lead to potential targets for pharmacologic or gene therapy to modulate glucose transport in the heart.

The effect of AMP-activated protein kinase (AMPK) activation on skeletal muscle glucose metabolism was examined in awake rats by infusing them with 5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside (AICAR; 40 mg/kg bolus and 7.5 mg ⋅ kg−1⋅ min−1constant infusion) along with a variable infusion of glucose (49.1 ± 2.4 μmol ⋅ kg−1⋅ min−1) to maintain euglycemia. Activation of AMPK by AICAR caused 2-deoxy-d-[1,2-3H]glucose (2-DG) uptake to increase more than twofold in the soleus and the lateral and medial gastrocnemius compared with saline infusion and occurred without phosphatidylinositol 3-kinase activation. Glucose uptake was also assessed in vitro by use of the epitrochlearis muscle incubated either with AICAR (0.5 mM) or insulin (20 mU/ml) or both in the presence or absence of wortmannin (1.0 μM). AICAR and insulin increased muscle 2-DG uptake rates by ∼2- and 2.7-fold, respectively, compared with basal rates. Combining AICAR and insulin led to a fully additive effect on muscle glucose transport activity. Wortmannin inhibited insulin-stimulated glucose uptake. However, neither wortmannin nor 8-(p-sulfophenyl)-theophylline (10 μM), an adenosine receptor antagonist, inhibited the AICAR-induced activation of glucose uptake. Electrical stimulation led to an about threefold increase in glucose uptake over basal rates, whereas no additive effect was found when AICAR and contractions were combined. In conclusion, the activation of AMPK by AICAR increases skeletal muscle glucose transport activity both in vivo and in vitro. This cellular pathway may play an important role in exercise-induced increase in glucose transport activity.

Background —Myocardial ischemia increases glucose uptake through the translocation of GLUT1 and GLUT4 from an intracellular compartment to the sarcolemma. The present study was performed to determine whether hyperinsulinemia causes translocation of myocardial GLUT1 as well as GLUT4 in vivo and whether there are additive effects of insulin and ischemia on GLUT1 and GLUT4 translocation. Methods and Results —Myocardial glucose uptake and transporter distribution were assessed by arteriovenous measurements, cell fractionation, and immunofluorescence. In fasted anesthetized dogs, hyperinsulinemia increased myocardial glucose extraction 3-fold ( P P P P Conclusions —Insulin stimulates myocardial glucose utilization through translocation of GLUT1 as well as GLUT4. Insulin and ischemia have additive effects to increase in vivo glucose utilization and augment glucose transporter translocation. We conclude that recruitment of both GLUT1 and GLUT4 contributes to increased myocardial glucose uptake during moderate reductions in coronary blood flow under insulin-stimulated conditions.

To examine the effects of a physiological increase in plasma epinephrine concentration (∼800 pg/ml) on muscle glycogenolysis and insulin-stimulated glycogenesis, we infused epinephrine [1.2 μg ⋅ (m2body surface)−1⋅ min−1] for 2 h and monitored muscle glycogen and glucose 6-phosphate (G-6- P) concentrations with13C/31P nuclear magnetic resonance (NMR) spectroscopy. Epinephrine caused an increase in plasma glucose (Δ ∼50 mg/dl), lactate (Δ ∼1.4 mM), free fatty acids (Δ ∼1,200 μM at peak), and whole body glucose oxidation (Δ ∼0.85 mg ⋅ kg−1⋅ min−1) compared with levels in a group of control subjects ( n = 4) in the presence of slight hyperinsulinemia (∼13 μU/ml, n = 8) or basal insulin (∼7 μU/ml, n = 7). However, epinephrine did not induce any detectable changes in glycogen or G-6- P concentrations, whereas muscle inorganic phosphate (Pi) decreased by 35%. Epinephrine infusion during a euglycemic-hyperinsulinemic clamp ( n = 8) caused a 45% decrease in the glucose infusion rate that could be mostly attributed to a 73% decrease in muscle glycogen synthesis rate. After an initial increase to ∼160% of basal values, G-6- Plevels decreased by ∼30% with initiation of the epinephrine infusion. We conclude that a physiological increase in plasma epinephrine concentration 1) has a negligible effect on muscle glycogenolysis at rest, 2) decreases muscle Pi, which may maintain phosphorylase activity at a low level, and 3) causes a major impairment in insulin-stimulated muscle glycogen synthesis, possibly due to inhibition of glucose transport-phosphorylation activity.

Background Myocardial ischemia increases heart glucose utilization in vivo. However, whether low-flow ischemia leads to the translocation of glucose transporter (GLUT)-4 and/or GLUT-1 to the sarcolemma in vivo is unknown. Methods and Results In a canine model, we evaluated myocardial glucose metabolism in vivo and the distribution of GLUT-4 and GLUT-1 by use of immunoblotting of sarcolemma and intracellular membranes and immunofluorescence localization with confocal microscopy. In vivo glucose extraction increased fivefold ( P P P Conclusions Translocation of the insulin-responsive GLUT-4 transporter from an intracellular storage pool to the sarcolemma occurs in vivo during acute low-flow ischemia. GLUT-1 is also present in an intracellular storage pool from which it undergoes translocation to the sarcolemma in response to ischemia. These results indicate that both GLUT-1 and GLUT-4 are important in ischemia-mediated myocardial glucose uptake in vivo.

Background: It is unclear if all breast cancer patients require baseline left ventricular function (LVEF) assessment prior to anthracycline chemotherapy, and the approach is variable in clinical practice. While some oncologist do not obtain baseline LVEF assessment in breast cancer patients under the age of 65 without known cardiac risk factors, others continue to perform baseline LVEF assessment in all breast cancer patients who will be receiving adjuvant anthracycline chemotherapy. We sought to determine the prevalence of left ventricular dysfunction in breast cancer patients prior to anthracycline and /or trastuzumab therapy, and to identify the cardiac risk factors associated with a low LVEF. Methods: We performed a retrospective analysis of the Yale Equilibrium Radionuclide Angiography (ERNA) database, which also included self-reported cardiac risk factors. We identified 702 patients who had a baseline ERNA scan prior to anthracycline and/or trastuzumab therapy for an initial diagnosis of stages I-IV BC between July 2003 and May 2013. Our objective was to determine the prevalence rate of an abnormal baseline LVEF defined as Results: Median age was 51(range 26-86); 637 (91%) patients were 65 years of age or younger. BMI Conclusion: The prevalence of abnormal baseline LVEF in patients being considered for anthracycline and/or trastuzumab therapy is small. Age, BMI, pre-existing cardiac risk factors and coronary artery disease were not associated with LVEF Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-06-09.

Radiolabeled analogues of 2-deoxyglucose are widely used to trace glucose metabolism in cell cultures, whole organs, and intact animals, although kinetic differences in transport and phosphorylation between these compounds and glucose exist. The present studies were undertaken to determine the effects of insulin stimulation on the phosphorylation of 2-deoxyglucose compared to glucose in the intact, saline-perfused working rat heart. Rates of glucose utilization determined from tritiated glucose differed from rates estimated from the accumulation of [14C]2-deoxyglucose in a nonconstant manner when comparing rates in the absence or presence of physiologic levels of insulin (13 microU/ml). The fraction of monophosphorylated hexoses that was accounted for by [14C]2-deoxyglucose 6-phosphate was dramatically decreased in hearts perfused in the presence of insulin. Additionally, hexokinase activity associated with the mitochondrial fraction of tissue extracts was increased in hearts stimulated by insulin. While this redistribution of hexokinase to the mitochondria did not affect the apparent affinity constant for glucose, hexokinase bound to mitochondria exhibited an 8.5-fold decrease in the affinity for 2-deoxyglucose when compared with hexokinase present in the cytosolic fraction. The findings are consistent with an insulin-mediated preferential uptake and phosphorylation of glucose compared to deoxyglucose. The results also imply that the redistribution of hexokinase and the differential effect of insulin on its affinity for tracer and tracee are responsible for changes in the "lumped constant" (i.e., the correction factor used to equate 2-deoxyglucose to glucose uptake). These changes must be taken into account when regional myocardial glucose metabolism is assessed by the 2-deoxyglucose method.

Insulin increases glucose uptake through the translocation of GLUT-4 via a pathway mediated by phosphatidylinositol 3-kinase (PI3K). In contrast, myocardial glucose uptake during ischemia and hypoxia is stimulated by the translocation of GLUT-4 to the surface of cardiac myocytes through a PI3K-independent pathway that has not been characterized. AMP-activated protein kinase (AMPK) activity is also increased by myocardial ischemia, and we examined whether AMPK stimulates glucose uptake and GLUT-4 translocation. In isolated rat ventricular papillary muscles, 5-aminoimidazole-4-carboxyamide-1-β-d-ribofuranoside (AICAR), an activator of AMPK, as well as cyanide-induced chemical hypoxia and insulin, increased 2-[3H]deoxyglucose uptake two- to threefold. Wortmannin, a PI3K inhibitor, did not affect either the AICAR- or the cyanide-stimulated increase in deoxyglucose uptake but eliminated the insulin-stimulated increase in deoxyglucose uptake. Immunofluorescence studies demonstrated translocation of GLUT-4 to the myocyte sarcolemma in response to stimulation with AICAR, cyanide, or insulin. Preincubation of papillary muscles with the kinase inhibitor iodotubercidin or adenine 9-β-d-arabinofuranoside (araA), a precursor of araATP (a competitive inhibitor of AMPK), decreased AICAR- and cyanide-stimulated glucose uptake but did not affect basal or insulin-stimulated glucose uptake. In vivo infusion of AICAR caused myocardial AMPK activation and GLUT-4 translocation in the rat. We conclude that AMPK activation increases cardiac muscle glucose uptake through translocation of GLUT-4 via a pathway that is independent of PI3K. These findings suggest that AMPK activation may be important in ischemia-induced translocation of GLUT-4 in the heart.