Ischemia induces translocation of the insulin-responsive glucose transporter GLUT4 to the plasma membrane of cardiac myocytes

Anthracycline-induced cardiotoxicity: From pathobiology to identification of molecular targets for nuclear imaging

Anthracyclines are a widely used class of chemotherapy in pediatric and adult cancers, however, their use is hampered by the development of cardiotoxic side-effects and ensuing complications, primarily heart failure. Clinically used imaging modalities to screen for cardiotoxicity are mostly echocardiography and occasionally cardiac magnetic resonance imaging. However, the assessment of diastolic and global or segmental systolic function may not be sensitive to detect subclinical or early stages of cardiotoxicity. Multiple studies have scrutinized molecular nuclear imaging strategies to improve the detection of anthracycline-induced cardiotoxicity. Anthracyclines can activate all forms of cell death in cardiomyocytes. Injury mechanisms associated with anthracycline usage include apoptosis, necrosis, autophagy, ferroptosis, pyroptosis, reactive oxygen species, mitochondrial dysfunction, as well as cardiac fibrosis and perturbation in sympathetic drive and myocardial blood flow; some of which have been targeted using nuclear probes. This review retraces the pathobiology of anthracycline-induced cardiac injury, details the evidence to date supporting a molecular nuclear imaging strategy, explores disease mechanisms which have not yet been targeted, and proposes a clinical strategy incorporating molecular imaging to improve patient management.

Intrapatient repeatability of background 18F-FDG uptake on PET/CT

Background

Background activity is often used as a reference to assess tumor treatment response on positron emission tomography with 2-deoxy-2-[fluorine-18] fluoro-D-glucose integrated with computed tomography (18F-FDG PET/CT). Our objective was to find the preferred background by assessing the repeatability of its activity. The activity was expressed by a standardized uptake value normalized to lean body mass (SUL).

Methods

Patients who received repeat ¹⁸F-FDG PET/CT scans within 1 to 4 days were selected. The indications included cancer screening, tumor staging, or treatment response evaluation. Background SULs from the aortic blood pool (ABP), liver, and muscle were recorded. Intraclass correlation coefficients (ICCs), the coefficient of variation (CV), and Bland-Altman plots for repeated measures were used to evaluate the degree of repeatability between the two scans. Intrapatient variation in SULs and factors, including the blood glucose level (BGL), tracer uptake period, and dose, were calculated as relative changes between the two scans. A linear regression model was used to analyze all relative changes to identify the correlation between factors and SULs.

Results

Thirty patients were included. The SUL ICCs for the ABP, liver, and muscle were 0.65 (95% CI, 0.38-0.81), 0.47 (95% CI, 0.15-0.70), and 0.82 (95% CI, 0.65-0.91), respectively. The SUL coefficients of variation (CVs) were 9% for the ABP, 12% for the liver, and 10% for muscle. Similar results were obtained from the Bland-Altman plots. There was a positive correlation between the variations in the liver SUL and the BGL (b=0.60, P<0.01). A similar result was found between the variations in muscle SUL and the BGL (b=0.45, P<0.01). The variation in muscle SUL showed a positive correlation with the variation in the tracer uptake period (b=0.58, P<0.01).

Conclusions

The SUL of the liver is more sensitive to BGLs and, therefore, may not be suitable as a referential background. Activities within the ABP and muscle are more stable than those of the liver and should be used as the preferred background for sequential patient evaluation.

Mesenchymal Stem Cell Transplantation for Ischemic Diseases: Mechanisms and Challenges

Ischemic diseases are conditions associated with the restriction or blockage of blood supply to specific tissues. These conditions can cause moderate to severe complications in patients, and can lead to permanent disabilities. Since they are blood vessel-related diseases, ischemic diseases are usually treated with endothelial cells or endothelial progenitor cells that can regenerate new blood vessels. However, in recent years, mesenchymal stem cells (MSCs) have shown potent bioeffects on angiogenesis, thus playing a role in blood regeneration. Indeed, MSCs can trigger angiogenesis at ischemic sites by several mechanisms related to their trans-differentiation potential. These mechanisms include inhibition of apoptosis, stimulation of angiogenesis via angiogenic growth factors, and regulation of immune responses, as well as regulation of scarring to suppress blood vessel regeneration when needed. However, preclinical and clinical trials of MSC transplantation in ischemic diseases have shown some limitations in terms of treatment efficacy. Such studies have emphasized the current challenges of MSC-based therapies. Treatment efficacy could be enhanced if the limitations were better understood and potentially resolved. This review will summarize some of the strategies by which MSCs have been utilized for ischemic disease treatment, and will highlight some challenges of those applications as well as suggesting some strategies to improve treatment efficacy.

DRD4 Mitigates Myocardial Ischemia/Reperfusion Injury in Association With PI3K/AKT Mediated Glucose Metabolism

Ischemia-reperfusion (I/R) could cause heart irreversible damage, which is tightly combined with glucose metabolism disorder. It is demonstrated that GLUT4 (glucose transporter 4) translocation is critical for glucose metabolism in the cardiomyocytes under I/R injury. Moreover, DRD4 (dopamine receptor D4) modulate glucose metabolism, and protect neurocytes from anoxia/reoxygenation (A/R) injury. Thus, DRD4 might regulate myocardial I/R injury in association with GLUT4-mediated glucose metabolism. However, the effects and mechanisms are largely unknown. In the present study, the effect of DRD4 in heart I/R injury were studied ex vivo and in vitro. For I/R injury ex vivo, DRD4 agonist (PD168077) was perfused by Langendorff system in the isolated rat heart. DRD4 activated by PD168077 improved cardiac function in the I/R-injured heart as determined by the left ventricular developed pressure (LVDP), +dp/dt, and left ventricular end diastolic pressure (LVEDP), and reduced heart damage evidenced by infarct size, the release of troponin T (TNT) and lactate dehydrogenase (LDH). DRD4 activation diminished I/R injury induced apoptosis and enhanced cell viability impaired by I/R injury in cardiomyocyte, showed by TUNEL staining, flow cytometer and CCK8 assay. Furthermore, DRD4 activation did not change total GULT4 protein expression level but increased the membrane GULT4 localization determined by western blot. In terms of mechanism, DRD4 activation increased pPI3K/p-AKT but not the total PI3K/AKT during anoxia/reoxygenation (A/R) injury in vitro. Interestingly, PI3K inhibitor, Wortmannin, blocked PI3K/AKT pathway and depleted the membrane GULT4, and further promoted apoptosis showed by TUNEL staining, flow cytometer, western blot of cleaved caspase 3, BAX and BCL2 expression. Thus, DRD4 activation exerted a protective effect against I/R injury by promoting GLUT4 translocation depended on PI3K/AKT pathway, which enhanced the ability of glucose uptake, and ultimately reduced the apoptosis in cardiomyocytes.

Tsg101 Is Involved in the Sorting and Re-Distribution of Glucose Transporter-4 to the Sarcolemma Membrane of Cardiac Myocytes

Cardiac cells can adapt to pathological stress-induced energy crisis by shifting from fatty acid oxidation to glycolysis. However, the use of glucose-insulin-potassium (GIK) solution in patients undergoing cardiac surgery does not alleviate ischemia/reperfusion (I/R)-induced energy shortage. This indicates that insulin-mediated translocation of glucose transporter-4 (Glut-4) is impaired in ischemic hearts. Indeed, cardiac myocytes contain two intracellular populations of Glut-4: an insulin-dependent non-endosomal pool (also referred to as Glut-4 storage vesicles, GSVs) and an insulin-independent endosomal pool. Tumor susceptibility gene 101 (Tsg101) has been implicated in the endosomal recycling of membrane proteins. In this study, we aimed to examine whether Tsg101 regulated the sorting and re-distribution of Glut-4 to the sarcolemma membrane of cardiomyocytes under basal and ischemic conditions, using gain- and loss-of-function approaches. Forced overexpression of Tsg101 in mouse hearts and isolated cardiomyocytes could promote Glut-4 re-distribution to the sarcolemma, leading to enhanced glucose entry and adenosine triphosphate (ATP) generation in I/R hearts which in turn, attenuation of I/R-induced cardiac dysfunction. Conversely, knockdown of Tsg101 in cardiac myocytes exhibited opposite effects. Mechanistically, we identified that Tsg101 could interact and co-localize with Glut-4 in the sarcolemma membrane of cardiomyocytes. Our findings define Tsg101 as a novel regulator of cardiac Glut-4 trafficking, which may provide a new therapeutic strategy for the treatment of ischemic heart disease.

An Inhibitor of the Sodium-Hydrogen Exchanger-1 (NHE-1), Amiloride, Reduced Zinc Accumulation and Hippocampal Neuronal Death after Ischemia

Acidosis in the brain plays an important role in neuronal injury and is a common feature of several neurological diseases. It has been reported that the sodium–hydrogen exchanger-1 (NHE-1) is a key mediator of acidosis-induced neuronal injury. It modulates the concentration of intra- and extra-cellular sodium and hydrogen ions. During the ischemic state, excessive sodium ions enter neurons and inappropriately activate the sodium–calcium exchanger (NCX). Zinc can also enter neurons through voltage-gated calcium channels and NCX. Here, we tested the hypothesis that zinc enters the intracellular space through NCX and the subsequent zinc accumulation induces neuronal cell death after global cerebral ischemia (GCI). Thus, we conducted the present study to confirm whether inhibition of NHE-1 by amiloride attenuates zinc accumulation and subsequent hippocampus neuronal death following GCI. Mice were subjected to GCI by bilateral common carotid artery (BCCA) occlusion for 30 min, followed by restoration of blood flow and resuscitation. Amiloride (10 mg/kg, intraperitoneally (i.p.)) was immediately injected, which reduced zinc accumulation and neuronal death after GCI. Therefore, the present study demonstrates that amiloride attenuates GCI-induced neuronal injury, likely via the prevention of intracellular zinc accumulation. Consequently, we suggest that amiloride may have a high therapeutic potential for the prevention of GCI-induced neuronal death.

Psoas muscle fluorine-18-labelled fluoro-2-deoxy-d-glucose uptake associated with the incidence of existing and incipient metabolic derangement

BACKGROUND

Skeletal muscle glucose utilization is an important component of whole-body glucose consumption in normal humans. Fluorine-18-labelled fluoro-2-deoxy-d-glucose (¹⁸ F-FDG) is a non-invasive molecular imaging probe for evaluating tissue glucose utilization. It remains unclear whether or not ¹⁸ F-FDG uptake by skeletal muscle has utility as a biomarker for metabolic derangement. We investigated the utility of measurement of muscle ¹⁸ F-FDG positron emission tomography/computed tomography uptake as a surrogate marker for existing and incipient metabolic abnormalities.

METHODS

Fluorine-18-labelled fluoro-2-deoxy-d-glucose (¹⁸ F-FDG) uptakes of insulin-sensitive organs (liver, pancreas, mesenteric visceral fat, psoas muscle, and abdominal subcutaneous fat) and their association with metabolic abnormalities were evaluated in an experimental group comprising 91 men and 66 women (mean age 49.9 ± 11.1 years). In this cross-sectional cohort, we assessed the predictive power of the optimal cut-off ¹⁸ F-FDG uptake [maximum standardized uptake value (SUV_max )]. We confirmed its feasibility and reliability for diagnosis of existing and incipient metabolic derangement in the validation group (longitudinal cohort comprising 91 men and 67 women; mean age 52.6 ± 7.9 years).

RESULTS

Fluorine-18-labelled fluoro-2-deoxy-d-glucose (¹⁸ F-FDG) uptake (SUV_max ) of psoas muscle was strongly correlated with clinical metabolic parameters in the experimental group. It was positively correlated with waist circumference, body mass index, fasting glucose, triglyceride, systolic and diastolic pressure, and negatively correlated with high-density lipoprotein cholesterol levels (for all, P < 0.05). SUV_max of the psoas muscle also showed the best area under the curve value (0.779) as a predictor of metabolic syndrome (MetS) in the experimental group. Using the optimal cut-off SUV_max of 1.34, the sensitivity, specificity, accuracy, positive, and negative predictive value for predicting existing MetS in the experimental group were 70.0%, 84.6%, 80.9%, 60.9%, and 89.2%, respectively. In the validation group, corresponding values were 47.6%, 92.3%, 86.1%, 50.0%, and 91.6%, respectively. Existing and incipient MetS were significantly higher in subjects with high ¹⁸ F-FDG uptake by the psoas muscle (SUV_max  > 1.34). Subjects with higher psoas muscle SUV_max had a 3.3-fold increased risk of developing MetS (P = 0.017).

CONCLUSIONS

Fluorine-18-labelled fluoro-2-deoxy-d-glucose (¹⁸ F-FDG) uptake of psoas muscle is a promising surrogate marker for existing and incipient metabolic derangement.

Macrophage migration inhibitory factor plays an essential role in ischemic preconditioning-mediated cardioprotection

Ischemic preconditioning (IPC) is an endogenous protection strategy against myocardial ischemia-reperfusion (I/R) injury. Macrophage migration inhibitory factor (MIF) released from the myocardium subjected to brief periods of ischemia confers cardioprotection. We hypothesized that MIF plays an essential role in IPC-induced cardioprotection. I/R was induced either ex vivo or in vivo in male wild-type (WT) and MIF knockout (MIFKO) mice with or without proceeding IPC (three cycles of 5-min ischemia and 5-min reperfusion). Indices of myocardial injury, regional inflammation and cardiac function were determined to evaluate the extent of I/R injury. Activations of the reperfusion injury salvage kinase (RISK) pathway, AMP-activated protein kinase (AMPK) and their downstream components were investigated to explore the underlying mechanisms. IPC conferred prominent protection in WT hearts evidenced by reduced infarct size (by 33-35%), myocyte apoptosis and enzymatic markers of tissue injury, ROS production, inflammatory cell infiltration and MCP1/CCR2 expression (all P<0.05). IPC also ameliorated cardiac dysfunction both ex vivo and in vivo These protective effects were abolished in MIFKO hearts. Notably, IPC mediated further activations of RISK pathway, AMPK and the membrane translocation of GLUT4 in WT hearts. Deletion of MIF blunted these changes in response to IPC, which is the likely basis for the absence of protective effects of IPC against I/R injury. In conclusion, MIF plays a critical role in IPC-mediated cardioprotection under ischemic stress by activating RISK signaling pathway and AMPK. These results provide an insight for developing a novel therapeutic strategy that target MIF to protect ischemic hearts.

Target identification for the diagnosis and intervention of vulnerable atherosclerotic plaques beyond 18F-fluorodeoxyglucose positron emission tomography imaging: promising tracers on the horizon

Cardiovascular disease is the major cause of morbidity and mortality in developed countries and atherosclerosis is the major cause of cardiovascular disease. Atherosclerotic lesions obstruct blood flow in the arterial vessel wall and can rupture leading to the formation of occlusive thrombi. Conventional diagnostic tools are still of limited value for identifying the vulnerable arterial plaque and for predicting its risk of rupture and of releasing thromboembolic material. Knowledge of the molecular and biological processes implicated in the process of atherosclerosis will advance the development of imaging probes to differentiate the vulnerable plaque. The development of imaging probes with high sensitivity and specificity in identifying high-risk atherosclerotic vessel wall changes and plaques is crucial for improving knowledge-based decisions and tailored individual interventions. Arterial PET imaging with ¹⁸F-FDG has shown promising results in identifying inflammatory vessel wall changes in numerous studies and clinical trials. However, due to its limited specificity in general and its intense physiological uptake in the left ventricular myocardium that impair imaging of the coronary arteries, different PET tracers for the molecular imaging of atherosclerosis have been evaluated. This review describes biological, chemical and medical expertise supporting a translational approach that will enable the development of new or the evaluation of existing PET tracers for the identification of vulnerable atherosclerotic plaques for better risk prediction and benefit to patients.

Heart failure patients with prediabetes and newly diagnosed diabetes display abnormalities in myocardial metabolism

BACKGROUND

In type 2 diabetes, a decrease in myocardial glucose uptake (MGU) may lower glucose oxidation and contribute to progression of chronic heart failure (CHF). However, it is unsettled whether CHF patients with prediabetes have abnormal MGU and myocardial blood flow (MBF) during normal physiological conditions.

METHODS AND RESULTS

We studied 35 patients with CHF and reduced left ventricular ejections fraction (34 ± 9%) without overt T2D (mean HbA1c: 40 ± 4 mmol/mol) using echocardiography and quantitative measurements of MGU by 18F-FDG-PET and perfusion by 15O-H2O-PET. An oral glucose tolerance test (OGTT) was performed during the FDG-PET, which identified 17 patients with abnormal and 18 patients with normal glucometabolic response. Global MGU was higher in patients with normal OGTT response (0.31 ± 0.09 µmol/g/min) compared with patients with abnormal OGTT response (0.25 ± 0.09 µmol/g/min) (P = 0.05). MBF (P = 0.22) and myocardial flow reserve (MFR) (P = 0.83) were similar in the study groups. The reduced MGU in prediabetic patients was attributable to reduced MGU in viable myocardium with normal MFR (P < 0.001).

CONCLUSION

CHF patients with prediabetes have reduced MGU in segments with preserved MFR as compared to CHF patients with normal glucose tolerance. Whether reversal of these myocardial abnormalities can improve outcome needs to be investigated in large-scale studies.

Sestrin2 prevents age-related intolerance to ischemia and reperfusion injury by modulating substrate metabolism

A novel stress-inducible protein, Sestrin2 (Sesn2), declines in the heart with aging. AMPK has emerged as a pertinent stress-activated kinase that has been shown to have cardioprotective capabilities against myocardial ischemic injury. We identified the interaction between Sesn2 and AMPK in the ischemic heart. To determine whether ischemic AMPK activation-modulated by the Sesn2-AMPK complex in the heart-is impaired in aging that sensitizes the heart to ischemic insults, young C57BL/6 mice (age 3-4 mo), middle-aged mice (age 10-12 mo), and aged mice (age 24-26 mo) were subjected to left anterior descending coronary artery occlusion for in vivo regional ischemia. The ex vivo working heart system was used for measuring substrate metabolism. The protein level of Sesn2 in hearts was gradually decreased with aging. Of interest, ischemic AMPK activation was blunted in aged hearts compared with young hearts (P < 0.05); the AMPK downstream glucose uptake and the rate of glucose oxidation were significantly impaired in aged hearts during ischemia and reperfusion (P < 0.05 vs. young hearts). Myocardial infarction size was larger in aged hearts (P < 0.05 vs. young hearts). Immunoprecipitation with Sesn2 Ab revealed that cardiac Sesn2 forms a complex with AMPK and upstream liver kinase B1 (LKB1) during ischemia. Of interest, the binding affinity between Sesn2 and AMPK upstream LKB1 is impaired in aged hearts during ischemia (P < 0.05 vs. young hearts). Furthermore, Sesn2-knockout hearts demonstrate a cardiac phenotype and response to ischemic stress that is similar to wild-type aged hearts (i.e., impaired ischemic AMPK activation and higher sensitivity to ischemia- and reperfusion- induced injury). Adeno-associated virus-Sesn2 was delivered to aged hearts via a coronary delivery approach and significantly rescued the protein level of Sesn2 and the ischemic tolerance of aged hearts; therefore, Sesn2 is a scaffold protein that mediates AMPK activation in the ischemic myocardium via an interaction with AMPK upstream LKB1. Decreased Sesn2 levels in aging lead to a blunted ischemic AMPK activation, alterations in substrate metabolism, and an increased sensitivity to ischemic insults-Quan, N., Sun, W., Wang, L., Chen, X., Bogan, J. S., Zhou, X., Cates, C., Liu, Q., Zheng, Y., Li J. Sestrin2 prevents age-related intolerance to ischemia and reperfusion injury by modulating substrate metabolism.

Development of GLUT4-selective antagonists for multiple myeloma therapy

Cancer cells consume more glucose to fuel metabolic programs fundamental to sustaining their survival, growth and proliferation. Among the fourteen SLC2A family members, GLUTs 1 and 4 are high-affinity glucose transporters. GLUT4 (SLC2A4) is highly expressed in muscle and adipose tissue. Basally retained within the cell, GLUT4 traffics to the plasma membrane (PM) in response to insulin and exercise-stimulation. The plasma cell malignancy multiple myeloma (MM) exhibits increased constitutive expression of GLUT4 on the PM, co-opting use of GLUT4 for survival and proliferation. GLUT4 inhibition by knockdown or treatment with the FDA-approved HIV protease inhibitor ritonavir leads to cytostatic and/or cytotoxic and chemosensitizing effects in tumor cells both in vitro and in vivo. We recently reported our generation of GLUT4 homology models and virtual high-throughput screening (vHTS) to identify multiple series of novel GLUT4 antagonists. In this report, we describe our initial hit-to-lead optimization to synthesize new analogs with improved potency and selectivity for GLUT4, and the biological characterization of these compounds in a variety of assays. We show that our lead compound (compound 20) decreases glucose uptake and cell proliferation as well as inhibits the expression of pro-survival MCL-1 in MM similar to the effect observed via knockdown of GLUT4 expression. Compound 20 is also effective at chemosensitizing multiple myeloma cell lines and patient samples to venetoclax, dexamethasone and melphalan. In sum, we report development of selective GLUT4 inhibitors lacking inhibitory activity against GLUT1 and GLUT8. We show that selective pharmacological inhibition of GLUT4 is feasible and this may represent a novel strategy for the treatment and chemosensitization of multiple myeloma to standard therapeutics.

Concurrent Low Brain and High Liver Uptake on FDG PET Are Associated with Cardiovascular Risk Factors

Objective

Concurrent low brain and high liver uptake are sometimes observed on fluorine-18-labeled fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET). We investigated the potential clinical significance of this uptake pattern related to metabolic syndrome (MS).

Materials and Methods

We retrospectively reviewed data from 264 consecutive males who had undergone general health check-ups, including FDG PET/CT scans. After an overnight fast, the men had their peripheral blood drawn and the levels of various laboratory parameters measured; an FDG PET/CT scan was performed on the same day. We measured the maximum standardized uptake values of the brain and liver from regions of interest manually placed over the frontal cortex at the level of the centrum semiovale and the right lobe of the liver parenchyma, respectively.

Results

Fasting blood glucose (FBG; odds ratio [OR] = 1.063, p < 0.001) and glycated hemoglobin (HbA1c; OR = 3.634, p = 0.010) were the strongest predictive factors for low brain FDG uptake, whereas waist circumference (OR = 1.200, p < 0.001) and γ-glutamyl transpeptidase (OR = 1.012, p = 0.001) were the strongest predictive factors for high liver uptake. Eleven subjects (4.2%) showed concurrent low brain and high liver FDG uptake, and all but one of these subjects (90.9%) had MS. Systolic blood pressure, waist circumference, FBG, triglyceride, alanine aminotransferase, insulin resistance (measured by homeostasis model assessment), insulin, HbA1c, and body mass index were higher in subjects with this FDG uptake pattern than in those without (all, p < 0.001).

Conclusion

Concurrent low brain and high liver FDG uptake were closely associated with MS. Moreover, subjects with this pattern had higher values for various cardiovascular risk factors than did those without.

Cardiac Metabolism in Perspective

The heart is a biological pump that converts chemical to mechanical energy. This process of energy conversion is highly regulated to the extent that energy substrate metabolism matches energy use for contraction on a beat-to-beat basis. The biochemistry of cardiac metabolism includes the biochemistry of energy transfer, metabolic regulation, and transcriptional, translational as well as posttranslational control of enzymatic activities. Pathways of energy substrate metabolism in the heart are complex and dynamic, but all of them conform to the First Law of Thermodynamics. The perspectives expand on the overall idea that cardiac metabolism is inextricably linked to both physiology and molecular biology of the heart. The article ends with an outlook on emerging concepts of cardiac metabolism based on new molecular models and new analytical tools. © 2016 American Physiological Society. Compr Physiol 6:1675-1699, 2016.

Glucagon-Like Peptide-1: A Promising Agent for Cardioprotection During Myocardial Ischemia

Glucagon-like peptide-1-(7-36) amide (GLP-1) is a human incretin hormone responsible for the release of insulin in response to food. Pre-clinical and human physiological studies have demonstrated cardioprotection from ischemia-reperfusion injury. It can reduce infarct size, ischemic left ventricular dysfunction, and myocardial stunning. GLP-1 receptor agonists have also been shown to reduce infarct size in myocardial infarction. The mechanism through which this protection occurs is uncertain but may include hijacking the subcellular pathways of ischemic preconditioning, modulation of myocardial metabolism, and hemodynamic effects including peripheral, pulmonary, and coronary vasodilatation. This review will assess the evidence for each of these mechanisms in turn. Challenges remain in successfully translating cardioprotective interventions from bench-to-bedside. The window of cardioprotection is short and timing of cardioprotection in the appropriate clinical setting is critically important. We will emphasize the need for high-quality, well-designed research to evaluate GLP-1 as a cardioprotective agent for use in real-world practice.

Targeted Modification of Mitochondrial ROS Production Converts High Glucose-Induced Cytotoxicity to Cytoprotection: Effects on Anesthetic Preconditioning

Contradictory reports on the effects of diabetes and hyperglycemia on myocardial infarction range from cytotoxicity to cytoprotection. The study was designed to investigate acute effects of high glucose-driven changes in mitochondrial metabolism and osmolarity on adaptive mechanisms and resistance to oxidative stress of isolated rat cardiomyocytes. We examined the effects of high glucose on several parameters of mitochondrial bioenergetics, including changes in oxygen consumption, mitochondrial membrane potential, and NAD(P)H fluorometry. Effects of high glucose on the endogenous cytoprotective mechanisms elicited by anesthetic preconditioning (APC) and the mediators of cell injury were also tested. These experiments included real-time measurements of reactive oxygen species (ROS) production and mitochondrial permeability transition pore (mPTP) opening in single cells by laser scanning fluorescence confocal microscopy, and cell survival assay. High glucose rapidly enhanced mitochondrial energy metabolism, observed by increase in NAD(P)H fluorescence intensity, oxygen consumption, and mitochondrial membrane potential. This substantially elevated production of ROS, accelerated opening of the mPTP, and decreased survival of cells exposed to oxidative stress. Abrogation of high glucose-induced mitochondrial hyperpolarization with 2,4 dinitrophenol (DNP) significantly, but not completely, attenuated ROS production to a level similar to hyperosmotic mannitol control. DNP treatment reversed high glucose-induced cytotoxicity to cytoprotection. Hyperosmotic mannitol treatment also induced cytoprotection. High glucose abrogated APC-induced mitochondrial depolarization, delay in mPTP opening and cytoprotection. In conclusion, high glucose-induced mitochondrial hyperpolarization abolishes APC and augments cell injury. Attenuation of high glucose-induced ROS production by eliminating mitochondrial hyperpolarization protects cardiomyocytes. J. Cell. Physiol. 232: 216-224, 2017. © 2016 Wiley Periodicals, Inc.

Fuel availability and fate in cardiac metabolism: A tale of two substrates

The heart's extraordinary metabolic flexibility allows it to adapt to normal changes in physiology in order to preserve its function. Alterations in the metabolic profile of the heart have also been attributed to pathological conditions such as ischemia and hypertrophy; however, research during the past decade has established that cardiac metabolic adaptations can precede the onset of pathologies. It is therefore critical to understand how changes in cardiac substrate availability and use trigger events that ultimately result in heart dysfunction. This review examines the mechanisms by which the heart obtains fuels from the circulation or from mobilization of intracellular stores. We next describe experimental models that exhibit either an increase in glucose use or a decrease in FA oxidation, and how these aberrant conditions affect cardiac metabolism and function. Finally, we highlight the importance of alternative, relatively under-investigated strategies for the treatment of heart failure. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.

Effects of passive static stretching on blood glucose levels in patients with type 2 diabetes mellitus

[Purpose] This study determined the effects of passive static stretching on blood glucose levels in patients with type 2 diabetes. [Subjects] Fifteen patients (8 males and 7 females) with type 2 diabetes were recruited and randomly assigned to the control group or passive static stretching group. [Methods] Glycated hemoglobin was measured before and after the 8-week training period. [Results] Glycated hemoglobin levels decreased significantly in the passive static stretching group, and there were significant differences in blood glucose levels between the 2 groups. [Conclusion] Passive static stretching of the skeletal muscles may be an alternative to exercise to help regulate blood glucose levels in diabetes patients.

Targeting caveolin-3 for the treatment of diabetic cardiomyopathy

Diabetes is a global health problem with more than 550 million people predicted to be diabetic by 2030. A major complication of diabetes is cardiovascular disease, which accounts for over two-thirds of mortality and morbidity in diabetic patients. This increased risk has led to the definition of a diabetic cardiomyopathy phenotype characterised by early left ventricular dysfunction with normal ejection fraction. Here we review the aetiology of diabetic cardiomyopathy and explore the involvement of the protein caveolin-3 (Cav3). Cav3 forms part of a complex mechanism regulating insulin signalling and glucose uptake, processes that are impaired in diabetes. Further, Cav3 is key for stabilisation and trafficking of cardiac ion channels to the plasma membrane and so contributes to the cardiac action potential shape and duration. In addition, Cav3 has direct and indirect interactions with proteins involved in excitation-contraction coupling and so has the potential to influence cardiac contractility. Significantly, both impaired contractility and rhythm disturbances are hallmarks of diabetic cardiomyopathy. We review here how changes to Cav3 expression levels and altered relationships with interacting partners may be contributory factors to several of the pathological features identified in diabetic cardiomyopathy. Finally, the review concludes by considering ways in which levels of Cav3 may be manipulated in order to develop novel therapeutic approaches for treating diabetic cardiomyopathy.

Pyrrolidinyl caffeamide against ischemia/reperfusion injury in cardiomyocytes through AMPK/AKT pathways

Background

Coronary heart disease is a leading cause of death in the world and therapy to reduce injury is still needed. The uncoupling of glycolysis and glucose oxidation induces lactate accumulation during myocardial ischemia/reperfusion (I/R) injury. Cell death occurs and finally leads to myocardial infarction. Caffeic acid, one of the major phenolic constituents in nature, acts as an antioxidant. Pyrrolidinyl caffeamide (PLCA), a new derivative of caffeic acid, was synthesized by our team. We aimed to investigate the effect of PLCA on hypoxia/reoxygenation (H/R) in neonatal rat ventricular myocytes (NRVM) and on myocardial I/R in rats.

Results

Cardiomyocytes were isolated and subjected to 6 h hypoxia followed by 18 h reperfusion. PLCA (0.1 to 3 μM) and metformin (30 μM) were added before hypoxia was initiated. PLCA at 1 μM and metformin at 30 μM exerted similar effects on the improvement of cell viability and the alleviation of cell apoptosis in NRVM after H/R. PLCA promoted p-AMPK, p-AKT, and GLUT4 upregulation to induce a cardioprotective effect in both cell and animal model. The accumulation of cardiac lactate was attenuated by PLCA during myocardial I/R, and infarct size was smaller in rats treated with PLCA (1 mg/kg) than in those treated with caffeic acid (1 mg/kg).

Conclusions

AMPK and AKT are synergistically activated by PLCA, which lead facilities glucose utilization, thereby attenuating lactate accumulation and cell death. The cardioprotective dose of PLCA was lower than those of metformin and caffeic acid. We provide a new insight into this potential drug for the treatment of myocardial I/R injury.

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.

Advanced glycation end products: role in pathology of diabetic cardiomyopathy

Increasing evidence demonstrates that advanced glycation end products (AGEs) play a pivotal role in the development and progression of diabetic heart failure, although there are numerous other factors that mediate the disease response. AGEs are generated intra- and extracellularly as a result of chronic hyperglycemia. Then, following the interaction with receptors for advanced glycation end products (RAGEs), a series of events leading to vascular and myocardial damage are elicited and sustained, which include oxidative stress, increased inflammation, and enhanced extracellular matrix accumulation resulting in diastolic and systolic dysfunction. Whereas targeting glycemic control and treating additional risk factors, such as obesity, dyslipidemia, and hypertension, are mandatory to reduce chronic complications and prolong life expectancy in diabetic patients, drug therapy tailored to reducing the deleterious effects of the AGE-RAGE interactions is being actively investigated and showing signs of promise in treating diabetic cardiomyopathy and associated heart failure. This review shall discuss the formation of AGEs in diabetic heart tissue, potential targets of glycation in the myocardium, and underlying mechanisms that lead to diabetic cardiomyopathy and heart failure along with the use of AGE inhibitors and breakers in mitigating myocardial injury.

Impact of glucagon-like peptide-1 on myocardial glucose metabolism revisited

The gut hormone glucagon-like peptide-1 (GLP-1) is an insulinotropic incretin with significant cardiovascular impact. Two classes of medication, GLP-1 analogues and DPP-4 inhibitors, have been developed that circumvent the rapid degradation of GLP-1 by the enzyme dipeptidyl peptidase-4 (DPP-4), both enhance the incretin effect and were developed for the treatment of type 2 diabetes. Several mechanisms suggesting that DPP-4 inhibitors, GLP-1, and analogues could have a protective effect on the cardiovascular risk profile have been forwarded; e.g., reductions of blood glucose, body weight, blood pressure, improvement in left ventricular ejection fraction, myocardial perfusion, atherosclerosis development, and endothelial function. Despite this, the reasons for a decreased risk of developing cardiovascular disease and reduced post-ischaemia damage are still poorly understood. The potentially beneficial effect of GLP-1 stimulation may rely on, among others, improved myocardial glucose metabolism. This review focuses on the dogma that GLP-1 receptor stimulation may provide beneficial cardiovascular effects, possibly due to enhanced myocardial energetic efficiency, by increasing myocardial glucose uptake. The published literature was systematically reviewed and the applied models evaluated since the outcomes of varying studies differ substantially. Reports on the effect of GLP-1R stimulation on myocardial metabolism are conflicting and should be evaluated carefully. There is limited and conflicting information on the impact of these agents in real life patients and while clinical outcome studies investigating the cardiovascular effects of GLP-1 based therapies have been initiated, the first two studies, both on DPP-4 inhibitors, designed specifically to evaluate cardiac safety reported largely neutral outcomes.

JAK-STAT signaling and myocardial glucose metabolism

JAK-STAT signaling occurs in virtually every tissue of the body, and so does glucose metabolism. In this review, we summarize the regulation of glucose metabolism in the myocardium and ponder whether JAK-STAT signaling participates in this regulation. Despite a paucity of data directly pertaining to cardiac myocytes, we conclude that JAK-STAT signaling may contribute to the development of insulin resistance in the myocardium in response to various hormones and cytokines.

Twenty minutes of passive stretching lowers glucose levels in an at-risk population: an experimental study

QUESTION

Can passive static stretching lower blood glucose in an at-risk population?

DESIGN

Randomised, within-participant experimental study.

PARTICIPANTS

22 adults (17 males) either at increased risk of Type 2 diabetes or with Type 2 diabetes.

INTERVENTION

The participants reported to the laboratory 2hr after eating a meal, and drank 355ml of fruit juice (∼43g carbohydrate). Thirty minutes later, they underwent either a 40min passive static stretching regimen or a mock passive stretching regimen. Stretching consisted of six lower body and four upper body static passive stretches. For the mock stretches, the same positions were adopted, but no tension was applied to the musculature.

OUTCOME MEASURES

Blood glucose levels for both the stretching and mock stretching were analysed from a finger prick sample using a hand-held glucometer. Values were obtained at baseline (0min), during the regimen (20min), and after the regimen (40min) on both study days.

RESULTS

Compared to mock stretch, stretching resulted in a significantly greater drop in blood glucose at 20min (mean difference 28mg/dL, 95% CI 13 to 43; or 1.57mmol/L, 95% CI 0.72 to 2.39). This effect was also statistically significant at 40min (mean difference 24mg/dL, 95% CI 9 to 39; or 1.35mmol/L, 95% CI 0.50 to 2.17).

CONCLUSION

These results suggest that passive static stretching of the skeletal muscles may be an alternative to exercise to help lower blood glucose levels.

Diabetic cardiomyopathy: understanding the molecular and cellular basis to progress in diagnosis and treatment

Diabetes mellitus is an important and prevalent risk factor for congestive heart failure. Diabetic cardiomyopathy has been defined as ventricular dysfunction that occurs in diabetic patients independent of a recognized cause such as coronary artery disease or hypertension. The disease course consists of a hidden subclinical period, during which cellular structural insults and abnormalities lead initially to diastolic dysfunction, later to systolic dysfunction, and eventually to heart failure. Left ventricular hypertrophy, metabolic abnormalities, extracellular matrix changes, small vessel disease, cardiac autonomic neuropathy, insulin resistance, oxidative stress, and apoptosis are the most important contributors to diabetic cardiomyopathy onset and progression. Hyperglycemia is a major etiological factor in the development of diabetic cardiomyopathy. It increases the levels of free fatty acids and growth factors and causes abnormalities in substrate supply and utilization, calcium homeostasis, and lipid metabolism. Furthermore, it promotes excessive production and release of reactive oxygen species, which induces oxidative stress leading to abnormal gene expression, faulty signal transduction, and cardiomyocytes apoptosis. Stimulation of connective tissue growth factor, fibrosis, and the formation of advanced glycation end-products increase the stiffness of the diabetic hearts. Despite all the current information on diabetic cardiomyopathy, translational research is still scarce due to limited human myocardial tissue and most of our knowledge is extrapolated from animals. This paper aims to elucidate some of the molecular and cellular pathophysiologic mechanisms, structural changes, and therapeutic strategies that may help struggle against diabetic cardiomyopathy.

AMPK signalling and the control of substrate use in the heart

All mammalian cells rely on adenosine triphosphate (ATP) to maintain function and for survival. The heart has the highest basal ATP demand of any organ due to the necessity for continuous contraction. As such, the ability of the cardiomyocyte to monitor cellular energy status and adapt the supply of substrates to match the energy demand is crucial. One important serine/threonine protein kinase that monitors cellular energy status in the heart is adenosine monophosphate activated protein kinase (AMPK). AMPK is also a key enzyme that controls multiple catabolic and anabolic biochemical pathways in the heart and indirectly plays a crucial role in regulating cardiac function in both physiological and pathophysiological conditions. Herein, we review the involvement of AMPK in myocardial fatty acid and glucose transport and utilization, as it relates to basal cardiac function. We also assess the literature amassed on cardiac AMPK and discuss the controversies surrounding the role of AMPK in physiological and pathophysiological processes in the heart. The work reviewed herein also emphasizes areas that require further investigation for the purpose of eventually translating this information into improved patient care.

Impact of blood glucose, diabetes, insulin, and obesity on standardized uptake values in tumors and healthy organs on 18F-FDG PET/CT

INTRODUCTION

Chronically altered glucose metabolism interferes with (18)F-FDG uptake in malignant tissue and healthy organs and may therefore lower tumor detection in (18)F-FDG PET/CT. The present study assesses the impact of elevated blood glucose levels (BGL), diabetes, insulin treatment, and obesity on (18)F-FDG uptake in tumors and biodistribution in normal organ tissues.

METHODS

(18)F-FDG PET/CT was analyzed in 90 patients with BGL ranging from 50 to 372 mg/dl. Of those, 29 patients were diabetic and 21 patients had received insulin prior to PET/CT; 28 patients were obese with a body mass index >25. The maximum standardized uptake value (SUV(max)) of normal organs and the main tumor site was measured. Differences in SUV(max) in patients with and without elevated BGLs, diabetes, insulin treatment, and obesity were compared and analyzed for statistical significance.

RESULTS

Increased BGLs were associated with decreased cerebral FDG uptake and increased uptake in skeletal muscle. Diabetes and insulin diminished this effect, whereas obesity slightly enhanced the outcome. Diabetes and insulin also increased the average SUV(max) in muscle cells and fat, whereas the mean cerebral SUV(max) was reduced. Obesity decreased tracer uptake in several healthy organs by up to 30%. Tumoral uptake was not significantly influenced by BGL, diabetes, insulin, or obesity.

CONCLUSIONS

Changes in BGLs, diabetes, insulin, and obesity affect the FDG biodistribution in muscular tissue and the brain. Although tumoral uptake is not significantly impaired, these findings may influence the tumor detection rate and are therefore essential for diagnosis and follow-up of malignant diseases.

S100B: role in cardiac remodeling and function following myocardial infarction in diabetes

AIM

S100B plays a role in cardiac remodeling following myocardial infarction (MI) and in diabetic vascular complications but not examined in diabetic myocardium. We thus examined the effects of targeted deletion of S100B gene on post-MI hearts.

MAIN METHODS

Coronary artery ligation or sham was performed 15 weeks after streptozotocin (STZ) or vehicle injection in wild-type (WT) and S100B knock-out (BKO) mice. Left ventricular (LV) structural and functional remodeling was studied 35 days after induction of MI.

KEY FINDINGS

In diabetes, post-MI remodeling exhibited an attenuated increase in LV mass, dilation, and myocyte hypertrophy in association with increased apoptosis and fibrosis and reduced matrix metalloproteinase-2 (MMP-2) activity. Despite reduced LV dilation, impairment of cardiac function was similar to non-diabetic controls. Both diabetes and MI alone induced myocardial S100B and its canonical receptor for advanced glycation end product (RAGE) expression. By contrast, in post-MI diabetic myocardium, S100B expression was attenuated. Diabetic BKO, following MI demonstrated increased ventricular dilation compared to WT, in association with greater impairment of cardiac function, GLUT4 expression and systemic AGE levels.

SIGNIFICANCE

These data suggest that S100B expression may serve to modulate cardiac metabolism and adverse consequences of AGE in diabetic post-MI remodeling and function.

Regulation and dysregulation of glucose transport in cardiomyocytes

The ability of the heart muscle to derive energy from a wide variety of substrates provides the myocardium with remarkable capacity to adapt to the ever-changing metabolic environment depending on factors including nutritional state and physical activity. There is increasing evidence that loss of metabolic flexibility of the myocardium contributes to cardiac dysfunction in disease conditions such as diabetes, ischemic heart disease and heart failure. At the level of glucose metabolism reduced metabolic adaptation in most cases is characterized by impaired stimulation of transarcolemmal glucose transport in the cardiomyocytes in response to insulin, referred to as insulin resistance, or to other stimuli such as energy deficiency. This review discusses cellular mechanisms involved in the regulation of glucose uptake in cardiomyocytes and their potential implication in impairment of stimulation of glucose transport under disease conditions. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.

Targeting myocardial substrate metabolism in heart failure: potential for new therapies

The incidence and prevalence of heart failure have increased significantly over the past few decades. Available data suggest that patients with heart failure independent of the aetiology have viable but dysfunctional myocardium that is potentially salvageable. Although a great deal of research effort has focused on characterizing the molecular basis of heart failure, cardiac metabolism in this disorder remains an understudied discipline. It is known that many aspects of cardiomyocyte energetics are altered in heart failure. These include a shift from fatty acid to glucose as a preferred substrate and a decline in the levels of ATP. Despite these demonstrated changes, there are currently no approved drugs that target metabolic enzymes or proteins in heart failure. This is partly due to our limited knowledge of the mechanisms and pathways that regulate cardiac metabolism. Better characterization of these pathways may potentially lead to new therapies for heart failure. Targeting myocardial energetics in the viable and potentially salvageable tissue may be particularly effective in the treatment of heart failure. Here, we will review metabolic changes that occur in fatty acid and glucose metabolism and AMP-activated kinase in heart failure. We propose that cardiac energetics should be considered as a potential target for therapy in heart failure and more research should be done in this area.

Intensive management of hyperglycaemia in acute coronary syndromes. Study design and rationale of the BIOMArCS 2 glucose trial

BACKGROUND

Elevated admission plasma glucose is associated with increased mortality in patients who are admitted with an acute coronary syndrome. This may be mediated by increased inflammation, apoptosis and coagulation, and by a disturbed endothelial function that can be found in hyperglycaemic patients. Insulin has several characteristics that may potentially counteract these mechanisms.

METHODS

The BIOMArCS programme is a multi-centre initiative and currently consists of three different studies. The effects of acute coronary syndrome on acute biomarkers washout are studied in the BIOMArCS pilot and the value of biomarkers in predicting upcoming acute coronary syndrome events is studied in BIOMArCS 1. The third study (BIOMArCS 2 glucose), which will be presented here, investigates the effectiveness and safety of intensive glucose level control compared with conventional glucose management in patients with acute coronary syndrome and an admission plasma glucose of 7.8-16 mmol/l. In BIOMArCS 2 glucose, a total of 300 patients without insulin-treated diabetes mellitus will be randomized in a 1:1 ratio to either intensive or conventional glucose management on top of standard medical care. The primary endpoint is infarct size as expressed by the cardiac troponin T level 72 h after admission. To study the metabolic effects of insulin administration, we will investigate biomarker washout patterns of various metabolic mechanisms up to 7 days after admission. These markers will address inflammation, oxidative stress, hypercoagulability, endothelial activation and vasodilatation.

IMPLICATIONS

Current acute coronary syndrome guidelines lack a clear strategy for hyperglycaemia treatment. This study will extend our knowledge on this matter as it may clarify mechanisms and generate hypotheses of if and how myocardial infarct size may be limited by glucose management at admission.

Inhibition of mitochondrial respiration by phosphoenolpyruvate

The cytosolic factors that influence mitochondrial oxidative phosphorylation rates are relatively unknown. In this report, we examine the effects of phosphoenolpyruvate (PEP), a glycolytic intermediate, on mitochondrial function. It is reported here that in rat heart mitochondria, PEP delays the onset of state 3 respiration in mitochondria supplied with either NADH-linked substrates or succinate. However, the maximal rate of state 3 respiration is only inhibited when oxidative phosphorylation is supported by NADH-linked substrates. The capacity of PEP to delay and/or inhibit state 3 respiration is dependent upon the presence or absence of ATP. Inhibition of state 3 is exacerbated in uncoupled mitochondria, with a 40% decrease in respiration seen with 0.1mM PEP. In contrast, ATP added exogenously or produced by oxidative phosphorylation completely prevents PEP-mediated inhibition. Mechanistically, the results support the conclusion that the main effects of PEP are to impede ADP uptake and inhibit NADH oxidation. By altering the NADH/NAD(+) status of mitochondria, it is demonstrated that PEP enhances succinate dehydrogenase activity and increase free radical production. The results of this study indicate PEP may be an important modulator of mitochondrial function under conditions of decreased ATP.

Myocardial AKT: the omnipresent nexus

One of the greatest examples of integrated signal transduction is revealed by examination of effects mediated by AKT kinase in myocardial biology. Positioned at the intersection of multiple afferent and efferent signals, AKT exemplifies a molecular sensing node that coordinates dynamic responses of the cell in literally every aspect of biological responses. The balanced and nuanced nature of homeostatic signaling is particularly essential within the myocardial context, where regulation of survival, energy production, contractility, and response to pathological stress all flow through the nexus of AKT activation or repression. Equally important, the loss of regulated AKT activity is primarily the cause or consequence of pathological conditions leading to remodeling of the heart and eventual decompensation. This review presents an overview compendium of the complex world of myocardial AKT biology gleaned from more than a decade of research. Summarization of the widespread influence that AKT exerts upon myocardial responses leaves no doubt that the participation of AKT in molecular signaling will need to be reckoned with as a seemingly omnipresent regulator of myocardial molecular biological responses.

Comparison of quantity of left ventricular scarring and remodeling by magnetic resonance imaging in patients with versus without diabetes mellitus and with coronary artery disease

Diabetic patients with coronary artery disease (CAD) are more likely to develop heart failure (HF) than nondiabetic patients, but the mechanism responsible is unclear. Evidence suggests that infarct size and accompanying remodeling may not explain this difference. We used cardiac magnetic resonance (CMR) imaging to compare degree of left ventricular (LV) myocardial scar and remodeling in diabetic and nondiabetic patients with CAD. We evaluated 85 patients (39 diabetic, 46 nondiabetic) who underwent coronary angiography showing obstructive CAD and CMR imaging within 6 months of each other. Myocardial scar was measured by late gadolinium enhancement on CMR imaging and was graded according to spatial and transmural extents on a semiquantitative scale. More diabetic than nondiabetic patients had HF (69% vs 43%, p <0.03); however, groups did not differ in total scar burden (0.94 ± 0.60 vs 1.17 ± 0.74, p = NS), spatial extent of scar, or extent of transmural scar. Diabetes remained an independent predictor of HF after adjustment for CAD and other variables. LV ejection fraction (36 ± 12% vs 37 ± 14%, p = NS) and end-diastolic volume (215 ± 56 vs 217 ± 76 ml, p = NS) were similar for diabetic and nondiabetic patients, respectively. In conclusion, although diabetic patients with CAD had a higher prevalence of HF than nondiabetic patients, there was no difference in myocardial scar, LV volume, or LV ejection fraction. These findings support the theory that mechanisms other than extent of myocardial injury and negative remodeling play a significant role in the development of HF in diabetic patients with CAD.

Anti-apoptotic PI3K/Akt signaling by sodium/glucose transporter 1 reduces epithelial barrier damage and bacterial translocation in intestinal ischemia

Intestinal ischemia/reperfusion (I/R) causes mucosal barrier damage and bacterial translocation (BT), leading to septic complications. Previous in vitro studies showed that activation of sodium/glucose transporter 1 (SGLT1) prevented the epithelial apoptosis and permeability rise induced by microbial products. Our aim was to investigate whether luminal glucose uptake by SGLT1 protects against ischemia-induced epithelial cell death and barrier dysfunction, and to explore the glucose-mediated cellular survival pathways in vivo. Rat jejunum was luminally instilled with either vehicle, a pancaspase inhibitor ZVAD, or glucose prior to I/R challenge (occlusion of the superior mesenteric artery for 20 min and reperfusion for 60 min). Histopathology and apoptosis in the jejunum were examined by TUNEL staining and caspase-3 cleavage. Intestinal permeability was evaluated using in vivo assays measuring luminal-to-blood passage of fluorescein-dextran and portal drainage of enterally administered gadodiamide by magnetic resonance imaging. BT was determined by culturing liver and spleen homogenates. Immunofluorescent analysis and kinase assay were used to study PI3K/Akt signaling pathways. Intestinal I/R caused enterocyte apoptosis and villous destruction. Intestinal infusion with ZVAD decreased the I/R-triggered gut permeability rise and BT, suggesting that the barrier damage was partly dependent on cell apoptosis. Enteral instillation of glucose attenuated the epithelial apoptosis, barrier damage, and mucosal inflammation caused by I/R. Phloridzin (a SGLT1 inhibitor) reduced the protective effect of glucose in a dose-dependent manner. Enteral glucose increased the mucosal Akt kinase activity as evidenced by the augmented phosphorylation of exogenous GSK3. Enhanced membrane translocation and phosphorylation of Akt in epithelial cells were associated with elevated phosphorylation of mTOR, Bad, and FoxO1/3a following glucose uptake. Inhibition of PI3K/Akt signaling by LY294002 and wortmannin partially blocked the glucose-mediated rescue of cell apoptosis and barrier damage. In conclusion, SGLT1 glucose uptake alleviated I/R-induced barrier dysfunction and BT, partly by inhibiting epithelial apoptosis via activation of PI3K/Akt signaling.

Insulin effect on glucose transport in thymocytes and splenocytes from rats with metabolic syndrome

Metabolic syndrome (MS) may comprise several clinical conditions such as obesity, diabetes and inflammatory disorders, which are characterized by metabolic imbalances. The study of glucose transport and regulation by insulin in lymphocytes is important, since the way they increase inflammation and susceptibility to infections are common in MS. We studied glucose internalization in isolated thymocytes and splenocytes, its regulation by insulin, and the role of three glucose transporters (Gluts) in control and in MS rats. Control glucose internalization and insulin responses were lower in splenocytes than in thymocytes. Control and insulin-induced glucose internalization in thymocytes declined with age, while transport by splenocyte continued to respond to insulin. Control thymocyte glucose internalization was blocked by antibodies against Glut 1 and 4, while the insulin response also was blocked by an anti-Glut 3 antibody. On four month old control and insulin-induced response, splenocyte transport was only blocked by Glut 1 and 4 antibodies. At six months splenocyte glucose internalization depended on Glut 1 and was less sensitive to the effects of an anti-Glut 4 antibody. In MS splenocytes the capacity of anti-Glut 1 antibodies to inhibit control and insulin-dependent glucose transport was less significant, and we found that in MS rats, glucose internalization was dependent on Glut 3 and Glut 4. In summary, the altered metabolic state present in MS rats shows signs of modulation of glucose internalization by the Glut1, Glut 3 and Glut 4 transporters, compared with its own age control.

Myocardial fatty acid metabolism in health and disease

There is a constant high demand for energy to sustain the continuous contractile activity of the heart, which is met primarily by the beta-oxidation of long-chain fatty acids. The control of fatty acid beta-oxidation is complex and is aimed at ensuring that the supply and oxidation of the fatty acids is sufficient to meet the energy demands of the heart. The metabolism of fatty acids via beta-oxidation is not regulated in isolation; rather, it occurs in response to alterations in contractile work, the presence of competing substrates (i.e., glucose, lactate, ketones, amino acids), changes in hormonal milieu, and limitations in oxygen supply. Alterations in fatty acid metabolism can contribute to cardiac pathology. For instance, the excessive uptake and beta-oxidation of fatty acids in obesity and diabetes can compromise cardiac function. Furthermore, alterations in fatty acid beta-oxidation both during and after ischemia and in the failing heart can also contribute to cardiac pathology. This paper reviews the regulation of myocardial fatty acid beta-oxidation and how alterations in fatty acid beta-oxidation can contribute to heart disease. The implications of inhibiting fatty acid beta-oxidation as a potential novel therapeutic approach for the treatment of various forms of heart disease are also discussed.

Anti-hypoxic effect of ginsenoside Rbl on neonatal rat cardiomyocytes is mediated through the specific activation of glucose transporter-4 ex vivo

AIM

The aim of this study was to investigate whether Gs-Rbl relieves the CoCl(2)-induced apoptosis of hypoxic neonatal rat cardiomyocytes and in which the role of glucose transporter-4 (GLUT-4).

METHODS

Gs-Rbl (0, 10, 50, 100, 200, 400, and 500 micromol/L), adenine 9-beta-D-arabinofuranoside (ara A, 500 micromol/L; AMPK inhibitor) and wortmannin (0.5 micromol/L; PI3K inhibitor) only in combination with 200 micromol/L Gs-Rbl were administered in hypoxic cardiomyocytes, which were induced by 500 micromol/L CoCl(2) for 12 h. Then, the apoptotic rate (AR), 2-[(3)H]-deoxy-D-glucose (2-[(3)H]-DG) uptake, and the expression of GLUT-4 (including in plasma membrane, PM), phospho-AMPKalpha (Thr172), AMPKalpha and Akt in cells were assayed.

RESULTS

Compared with simple hypoxia (0 micromol/L Gs-Rbl), Gs-Rb1 greater than 10 micromol/L significantly decreased the apoptotic rate (P<0.01) and significantly increased 2-[(3)H]-DG uptake (P<0.01), GLUT-4 content in cells and PM (P<0.01), AMPK activity (P<0.01) and Akt (P<0.01) levels in a dose-dependent manner. AMPK activity was completely suppressed by ara-A, just as Akt was suppressed by wortmannin. The AR, glucose uptake and GLUT-4 levels in cells and PM were partly down-regulated by ara-A or wortmannin.

CONCLUSION

Gs-Rb1 may protect neonatal rat cardiomyocytes from apoptosis induced by CoCl(2). The anti-apoptotic effect of Gs-Rb1 may occur by improving glucose uptake, in which GLUT-4 translocation and expression played a key role. Both the AMPK and the PI3K/Akt pathways may take part in the anti-hypoxic efficacy of Gs-Rb1.