Association of glycogenolysis with cardiac sarcoplasmic reticulum: II. Effect of glycogen depletion, deoxycholate solubilization and cardiac ischemia: evidence for a phorphorylase kinase membrane complex

Role of AMP deaminase in diabetic cardiomyopathy

Diabetes mellitus is one of the major causes of ischemic and nonischemic heart failure. While hypertension and coronary artery disease are frequent comorbidities in patients with diabetes, cardiac contractile dysfunction and remodeling occur in diabetic patients even without comorbidities, which is referred to as diabetic cardiomyopathy. Investigations in recent decades have demonstrated that the production of reactive oxygen species (ROS), impaired handling of intracellular Ca2+, and alterations in energy metabolism are involved in the development of diabetic cardiomyopathy. AMP deaminase (AMPD) directly regulates adenine nucleotide metabolism and energy transfer by adenylate kinase and indirectly modulates xanthine oxidoreductase-mediated pathways and AMP-activated protein kinase-mediated signaling. Upregulation of AMPD in diabetic hearts was first reported more than 30 years ago, and subsequent studies showed similar upregulation in the liver and skeletal muscle. Evidence for the roles of AMPD in diabetes-induced fatty liver, sarcopenia, and heart failure has been accumulating. A series of our recent studies showed that AMPD localizes in the mitochondria-associated endoplasmic reticulum membrane as well as the sarcoplasmic reticulum and cytosol and participates in the regulation of mitochondrial Ca2+ and suggested that upregulated AMPD contributes to contractile dysfunction in diabetic cardiomyopathy via increased generation of ROS, adenine nucleotide depletion, and impaired mitochondrial respiration. The detrimental effects of AMPD were manifested at times of increased cardiac workload by pressure loading. In this review, we briefly summarize the expression and functions of AMPD in the heart and discuss the roles of AMPD in diabetic cardiomyopathy, mainly focusing on contractile dysfunction caused by this disorder.

Brain-Type Glycogen Phosphorylase (PYGB) in the Pathologies of Diseases: A Systematic Review

Glycogen metabolism is a form of crucial metabolic reprogramming in cells. PYGB, the brain-type glycogen phosphorylase (GP), serves as the rate-limiting enzyme of glycogen catabolism. Evidence is mounting for the association of PYGB with diverse human diseases. This review covers the advancements in PYGB research across a range of diseases, including cancer, cardiovascular diseases, metabolic diseases, nervous system diseases, and other diseases, providing a succinct overview of how PYGB functions as a critical factor in both physiological and pathological processes. We present the latest progress in PYGB in the diagnosis and treatment of various diseases and discuss the current limitations and future prospects of this novel and promising target.

A Pathophysiological Approach To Current Biomarkers

Biomarkers are necessary for screening and diagnosing numerous diseases, predicting the prognosis of patients, and following-up treatment and the course of the patient. Everyday new biomarkers are being used in clinics for these purposes. This section will discuss the physiological roles of the various current biomarkers in a healthy person and the pathophysiological mechanisms underlying the release of these biomarkers. This chapter aims to gain a new perspective for evaluating and interpreting the most current biomarkers.

Diagnostic accuracy of glycogen phosphorylase BB for myocardial infarction: A systematic review and meta-analysis

PURPOSE

We tried to investigate the diagnostic accuracy of glycogen phosphorylase BB as a cardiac marker for myocardial infarction.

METHODS

We searched through different electronic databases (PubMed, Google-scholar, Embase, and Cochrane Library) to locate relevant articles. Studies, with sufficient data to reconstruct a 2 × 2 contingency table, met our inclusion criteria were included. Three reviewers independently screened the articles. Discrepancies were resolved by other reviewers. Unpublished data were requested from the authors of the study via email. Subsequently, data extraction was done using a standardized form and quality assessment of studies using the QUADAS-2 tool. Meta-analysis was done using a bivariate model using R software.

RESULTS

Fourteen studies were selected for the final evaluation, which yielded the summary points: pooled sensitivity 87.77% (77.52%-93.72%, I2  = 86%), pooled specificity 88.45% (75.59%-94.99%, I2  = 88%), pooled DOR 49.37(14.53-167.72, I2  = 89%), and AUC of SROC was 0.923. The lambda value of the HSROC curve was 3.670. The Fagan plot showed that GPBB increases the pretest probability of myocardial infarction from 46% to 81% when positive, and it lowers the same probability to 12% when negative.

CONCLUSION

With these results, we can conclude that GPBB has modest accuracy in screening myocardial infarction, but the limitations of the study warrant further high-quality studies to confirm its usefulness in predicting myocardial infarction (MI).

Heart failure in diabetes

Heart failure and cardiovascular disorders represent the leading cause of death in diabetic patients. Here we present a systematic review of the main mechanisms underlying the development of diabetic cardiomyopathy. We also provide an excursus on the relative contribution of cardiomyocytes, fibroblasts, endothelial and smooth muscle cells to the pathophysiology of heart failure in diabetes. After having described the preclinical tools currently available to dissect the mechanisms of this complex disease, we conclude with a section on the most recent updates of the literature on clinical management.

Mitochondrial calcium handling and heart disease in diabetes mellitus

Diabetes mellitus-induced heart disease, including diabetic cardiomyopathy, is an important medical problem and is difficult to treat. Diabetes mellitus increases the risk for heart failure and decreases cardiac myocyte function, which are linked to changes in cardiac mitochondrial energy metabolism. The free mitochondrial calcium concentration ([Ca²⁺]_m) is fundamental in activating the mitochondrial respiratory chain complexes and ATP production and is also known to regulate the activity of key mitochondrial dehydrogenases. The mitochondrial calcium uniporter complex (MCUC) plays a major role in mediating mitochondrial Ca²⁺ import, and its expression and function therefore may have a marked impact on cardiac myocyte metabolism and function. Here, we summarize the pathophysiological role of [Ca²⁺]_m handling and MCUC in the diabetic heart. In addition, we evaluate potential therapeutic targets, directed to the machinery that regulates mitochondrial calcium handling, to alleviate diabetes-related cardiac disease.

Restoring mitochondrial calcium uniporter expression in diabetic mouse heart improves mitochondrial calcium handling and cardiac function

Diabetes mellitus is a growing health care problem, resulting in significant cardiovascular morbidity and mortality. Diabetes also increases the risk for heart failure (HF) and decreased cardiac myocyte function, which are linked to changes in cardiac mitochondrial energy metabolism. The free mitochondrial calcium level ([Ca²⁺] _m ) is fundamental in activating the mitochondrial respiratory chain complexes and ATP production and is also known to regulate pyruvate dehydrogenase complex (PDC) activity. The mitochondrial calcium uniporter (MCU) complex (MCUC) plays a major role in mediating mitochondrial Ca²⁺ import, and its expression and function therefore have a marked impact on cardiac myocyte metabolism and function. Here, we investigated MCU's role in mitochondrial Ca²⁺ handling, mitochondrial function, glucose oxidation, and cardiac function in the heart of diabetic mice. We found that diabetic mouse hearts exhibit altered expression of MCU and MCUC members and a resulting decrease in [Ca²⁺] _m , mitochondrial Ca²⁺ uptake, mitochondrial energetic function, and cardiac function. Adeno-associated virus-based normalization of MCU levels in these hearts restored mitochondrial Ca²⁺ handling, reduced PDC phosphorylation levels, and increased PDC activity. These changes were associated with cardiac metabolic reprogramming toward normal physiological glucose oxidation. This reprogramming likely contributed to the restoration of both cardiac myocyte and heart function to nondiabetic levels without any observed detrimental effects. These findings support the hypothesis that abnormal mitochondrial Ca²⁺ handling and its negative consequences can be ameliorated in diabetes by restoring MCU levels via adeno-associated virus-based MCU transgene expression.

The dynamic life of the glycogen granule

Glycogen, the primary storage form of glucose, is a rapid and accessible form of energy that can be supplied to tissues on demand. Each glycogen granule, or "glycosome," is considered an independent metabolic unit composed of a highly branched polysaccharide and various proteins involved in its metabolism. In this Minireview, we review the literature to follow the dynamic life of a glycogen granule in a multicompartmentalized system, i.e. the cell, and how and where glycogen granules appear and the factors governing its degradation. A better understanding of the importance of cellular compartmentalization as a regulator of glycogen metabolism is needed to unravel its role in brain energetics.

The regulation of sarco(endo)plasmic reticulum calcium-ATPases (SERCA)

The sarco(endo)plasmic reticulum calcium ATPase (SERCA) is responsible for transporting calcium (Ca(2+)) from the cytosol into the lumen of the sarcoplasmic reticulum (SR) following muscular contraction. The Ca(2+) sequestering activity of SERCA facilitates muscular relaxation in both cardiac and skeletal muscle. There are more than 10 distinct isoforms of SERCA expressed in different tissues. SERCA2a is the primary isoform expressed in cardiac tissue, whereas SERCA1a is the predominant isoform expressed in fast-twitch skeletal muscle. The Ca(2+) sequestering activity of SERCA is regulated at the level of protein content and is further modified by the endogenous proteins phospholamban (PLN) and sarcolipin (SLN). Additionally, several novel mechanisms, including post-translational modifications and microRNAs (miRNAs) are emerging as integral regulators of Ca(2+) transport activity. These regulatory mechanisms are clinically relevant, as dysregulated SERCA function has been implicated in the pathology of several disease states, including heart failure. Currently, several clinical trials are underway that utilize novel therapeutic approaches to restore SERCA2a activity in humans. The purpose of this review is to examine the regulatory mechanisms of the SERCA pump, with a particular emphasis on the influence of exercise in preventing the pathological conditions associated with impaired SERCA function.

Glycogen phosphorylase BB in myocardial infarction

Early experimental and clinical reports on glycogen phosphorylase BB (GPBB) kinetics following myocardial ischemic injury suggested that it could be a useful diagnostic marker for early detection of acute myocardial infarction (AMI). After more than two decades of investigation, there is now overwhelming body of evidence that do not support the use of GPBB measurement in diagnosis of acute AMI in patients presenting with acute chest pain. Currently, GPBB cannot be recommended as a diagnostic marker of AMI either as a stand-alone test or as an addition to (high-sensitive) troponin testing. It should be noted that these considerations apply to the early diagnosis of AMI, not to the prognostic stratification, which is also suggested but it warrants further investigation. The aim of this review is to summarize available evidence of GPBB measurement in early diagnosis of myocardial infarction.

Cardiac metabolism in heart failure: implications beyond ATP production

The heart has a high rate of ATP production and turnover that is required to maintain its continuous mechanical work. Perturbations in ATP-generating processes may therefore affect contractile function directly. Characterizing cardiac metabolism in heart failure (HF) revealed several metabolic alterations called metabolic remodeling, ranging from changes in substrate use to mitochondrial dysfunction, ultimately resulting in ATP deficiency and impaired contractility. However, ATP depletion is not the only relevant consequence of metabolic remodeling during HF. By providing cellular building blocks and signaling molecules, metabolic pathways control essential processes such as cell growth and regeneration. Thus, alterations in cardiac metabolism may also affect the progression to HF by mechanisms beyond ATP supply. Our aim is therefore to highlight that metabolic remodeling in HF not only results in impaired cardiac energetics but also induces other processes implicated in the development of HF such as structural remodeling and oxidative stress. Accordingly, modulating cardiac metabolism in HF may have significant therapeutic relevance that goes beyond the energetic aspect.

Glycogen phosphorylase isoenzyme BB plasma kinetics is not related to myocardial ischemia induced by exercise stress echo test

BACKGROUND

Glycogen phosphorylase BB (GPBB) is released from cardiac cells during myocyte damage. Previous studies have shown contradictory results regarding the relation of enzyme release and reversible myocardial ischemia. The aim of this study was to determine the plasma kinetics of GPBB as a response to the exercise stress echocardiographic test (ESET), and to define the relationship between myocardial ischemia and enzyme plasma concentrations.

METHODS

We studied 46 consecutive patients undergoing ESET, with recent coronary angiography. In all patients, a submaximal stress echo test according to Bruce protocol was performed. Concentration of GPBB was measured in peripheral blood that was sampled 5 min before and 10, 30 and 60 min after ESET.

RESULTS

There was significant increase of GPBB concentration after the test (p=0.021). Significant increase was detected 30 min (34.9% increase, p=0.021) and 60 min (34.5% increase, p=0.016) after ESET. There was no significant effect of myocardial ischemia on GPBB concentrations (p=0.126), and no significant interaction between sampling intervals and myocardial ischemia, suggesting a similar release profile of GPBB in ischemic and non-ischemic conditions (p=0.558). Patients in whom ESET was terminated later (stages 4 or 5 of standard Bruce protocol; n=13) had higher GPBB concentrations than patients who terminated ESET earlier (stages 1, 2 or 3; n=33) (p=0.049). Baseline GPBB concentration was not correlated to any of the patients' demographic, clinical and hemodynamic characteristics.

CONCLUSIONS

GPBB plasma concentration increases after ESET, and it is not related to inducible myocardial ischemia. However, it seems that GPBB release during ESET might be related to exercise load/duration.

Limited effects of exogenous glucose during severe hypoxia and a lack of hypoxia-stimulated glucose uptake in isolated rainbow trout cardiac muscle

We examined whether exogenous glucose affects contractile performance of electrically paced ventricle strips from rainbow trout under conditions known to alter cardiomyocyte performance, ion regulation and energy demands. Physiological levels of d-glucose did not influence twitch force development for aerobic preparations (1) paced at 0.5 or 1.1 Hz, (2) at 15 or 23°C, (3) receiving adrenergic stimulation or (4) during reoxygenation with or without adrenaline after severe hypoxia. Contractile responses to ryanodine, an inhibitor of Ca(2+) release from the sarcoplasmic reticulum, were also not affected by exogenous glucose. However, glucose did attenuate the fall in twitch force during severe hypoxia. Glucose uptake was assayed in non-contracting ventricle strips using 2-[(3)H] deoxy-d-glucose (2-DG) under aerobic and hypoxic conditions, at different incubation temperatures and with different inhibitors. Based upon a lack of saturation of 2-DG uptake and incomplete inhibition of uptake by cytochalasin B and d-glucose, 2-DG uptake was mediated by a combination of facilitated transport and simple diffusion. Hypoxia stimulated lactate efflux sixfold to sevenfold with glucose present, but did not increase 2-DG uptake or reduce lactate efflux in the presence of cytochalasin B. Increasing temperature (14 to 24°C) also did not increase 2-DG uptake, but decreasing temperature (14 to 4°C) reduced 2-DG uptake by 45%. In conclusion, exogenous glucose improves mechanical performance under hypoxia but not under any of the aerobic conditions applied. The extracellular concentration of glucose and cold temperature appear to determine and limit cardiomyocyte glucose uptake, respectively, and together may help define a metabolic strategy that relies predominantly on intracellular energy stores.

Nitric oxide/reactive oxygen species generation and nitroso/redox imbalance in heart failure: from molecular mechanisms to therapeutic implications

Adaptation of the heart to intrinsic and external stress involves complex modifications at the molecular and cellular levels that lead to tissue remodeling, functional and metabolic alterations, and finally to failure depending upon the nature, intensity, and chronicity of the stress. Reactive oxygen species (ROS) have long been considered as merely harmful entities, but their role as second messengers has gradually emerged. At the same time, our comprehension of the multifaceted role of nitric oxide (NO) and the related reactive nitrogen species (RNS) has been upgraded. The tight interlay between ROS and RNS suggests that their imbalance may implicate the impairment in physiological NO/redox-based signaling that contributes to the failing of the cardiovascular system. This review initially provides basic concepts on the role of nitroso/oxidative stress in the pathophysiology of heart failure with a particular focus on sources of ROS/RNS, their downstream targets, and endogenous modulators. Then, the role of NO/redox regulation of cardiomyocyte function, including calcium homeostasis, electrogenesis, and insulin signaling pathways, is described. Finally, an overview of old and emerging therapeutic opportunities in heart failure is presented, focusing on modulation of NO/redox mechanisms and discussing benefits and limitations.

Analytical and clinical performance of a fully automated cardiac multi-markers strategy based on protein biochip microarray technology

OBJECTIVES

The analytical and clinical performance of the Evidence Cardiac Panel were evaluated.

DESIGN AND METHODS

The Evidence Cardiac Panel, an automated protein biochip microarray system, allows the simultaneous determination of creatine kinase MB (CK-MB), myoglobin (MYO), glycogen phosphorylase BB (GPBB), heart-type fatty acid-binding protein (H-FABP), carbonic anhydrase III (CA III), cardiac troponin I (cTnI). Precision: 3 levels of quality control (QC) and 2 in house pools (P) were assayed. Method comparison: MYO and cTnI concentrations measured on Evidence (E) and on Dimension RxL (D) analyzers were compared. Clinical study: 132 non-consecutive patients admitted to the Emergency Department for chest pain were enrolled.

RESULTS AND CONCLUSIONS

The between-day imprecision was CK-MB=6.80-10.08%; MYO=5.36-16.50%; GPBB=6.51-12.12%; H-FABP=6.26-12.63%; CA III=6.98-13.61%; cTnI=6.02-9.80%. Method comparison: E-MYO vs. D-MYO, Bias=-29.22, 95% CI from -40.25 to -18.18; E-cTnI vs. D-cTnI, Bias=-2.75, 95% CI from -4.04 to -1.46. In patients studied (at discharge: AMI, acute myocardial infarction n=42; non-AMI, n=90) H-FABP showed the highest accuracy (ROC analysis, AUC=0.92) and "cTnI+H-FABP" the greatest diagnostic efficacy (89.4%) in AMI diagnosis.

The impact of diabetes on heart failure: opportunities for intervention

The pathophysiologic processes of diabetes mellitus and heart failure are likely interrelated. In particular, hyperglycemia and insulin resistance can induce myocardial contractile systolic and diastolic abnormalities at the cellular level. Furthermore, patients with heart failure and concomitant diabetes mellitus are more likely to have underlying comorbid conditions resulting in greater vulnerability to adverse consequences. It is reassuring that the majority of patients with diabetes mellitus and heart failure respond to standard heart failure medical regimens comparable to their nondiabetes counterparts. However, the safety profiles of current antidiabetic medications are far from ideal when used in patients with heart failure. Emerging novel therapies that reverse the metabolic and structural changes induced by the diabetic milieu are currently under clinical development, and their potential benefits may even extend beyond the diabetic population.

Deranged energy substrate metabolism in the failing heart

Control of energy metabolism in the heart is closely linked to cardiac performance. Dysregulation of energy-generating pathways occurs in many forms of heart disease, including heart failure. Uncertainty exists as to whether these alterations in the way adenosine triphosphate (ATP) is produced serve to protect the heart from excessive oxygen demands or have untoward long-term consequences. Regulation of fatty acid beta-oxidation (FAO), the principal source of ATP in the healthy heart, occurs at multiple levels, including a strong gene transcriptional component. In the heart, members of the peroxisome proliferator-activated receptor (PPAR) family of transcription factors are the primary regulators of FAO gene expression. PPARs are ligand activated by endogenous lipids and synthetic small molecules, thus providing attractive targets for pharmaceutical intervention. This article discusses controversies surrounding our understanding of cardiac energy metabolism in heart failure and the role that PPAR family members may play, either as contributors to or as potential adjunctive therapy for cardiac disease.

Role of changes in cardiac metabolism in development of diabetic cardiomyopathy

In patients with diabetes, an increased risk of symptomatic heart failure usually develops in the presence of hypertension or ischemic heart disease. However, a predisposition to heart failure might also reflect the effects of underlying abnormalities in diastolic function that can occur in asymptomatic patients with diabetes alone (termed diabetic cardiomyopathy). Evidence of cardiomyopathy has also been demonstrated in animal models of both Type 1 (streptozotocin-induced diabetes) and Type 2 diabetes (Zucker diabetic fatty rats and ob/ob or db/db mice). During insulin resistance or diabetes, the heart rapidly modifies its energy metabolism, resulting in augmented fatty acid and decreased glucose consumption. Accumulating evidence suggests that this alteration of cardiac metabolism plays an important role in the development of cardiomyopathy. Hence, a better understanding of this dysregulation in cardiac substrate utilization during insulin resistance and diabetes could provide information as to potential targets for the treatment of cardiomyopathy. This review is focused on evaluating the acute and chronic regulation and dysregulation of cardiac metabolism in normal and insulin-resistant/diabetic hearts and how these changes could contribute toward the development of cardiomyopathy.

Myocardial substrate metabolism in the normal and failing heart

The alterations in myocardial energy substrate metabolism that occur in heart failure, and the causes and consequences of these abnormalities, are poorly understood. There is evidence to suggest that impaired substrate metabolism contributes to contractile dysfunction and to the progressive left ventricular remodeling that are characteristic of the heart failure state. The general concept that has recently emerged is that myocardial substrate selection is relatively normal during the early stages of heart failure; however, in the advanced stages there is a downregulation in fatty acid oxidation, increased glycolysis and glucose oxidation, reduced respiratory chain activity, and an impaired reserve for mitochondrial oxidative flux. This review discusses 1) the metabolic changes that occur in chronic heart failure, with emphasis on the mechanisms that regulate the changes in the expression of metabolic genes and the function of metabolic pathways; 2) the consequences of these metabolic changes on cardiac function; 3) the role of changes in myocardial substrate metabolism on ventricular remodeling and disease progression; and 4) the therapeutic potential of acute and long-term manipulation of cardiac substrate metabolism in heart failure.

Glycogen phosphorylase BB in acute coronary syndromes

The diagnosis of myocardial damage is preferably based on measurement of the cardiac-specific troponins. However, there is an emerging need for early, specific cardiac markers. One potential candidate is the glycogen phosphorylase BB isoenzyme (GPBB). We investigated the use of a new, commercially available GPBB ELISA assay in 61 patients presenting with an acute coronary syndrome (37 acute myocardial infarction, 24 unstable angina pectoris) in comparison to established cardiac markers such as troponin T, creatine kinase isoenzyme MB (CKMB) mass, and myoglobin. Blood samples were obtained on arrival, as well as 1, 2, 3, 4, 8, 12 and 24h later. GPBB plasma concentrations were elevated in 90.9% of patients 1h after onset of chest pain and increased to 100% at 4–5h. Within the first 6h, GPBB showed the highest sensitivity (95.5–100%) and high specificity (94–96%) compared to myoglobin (85–95% sensitivity) and CKMB mass (71.4–91.3% sensitivity). As expected, troponin T showed high specificity (100%) and sensitivity >95% later in the time course (≥3h). In un-stable angina pectoris patients, a very high rate of elevated GPBB was observed (93.9% at 3h) compared to myoglobin (66.7%). Cardiac troponin T and CKMB were only elevated in 33.8% and 55.0% of these patients, respectively. In conclusion, GPBB is a promising marker for the early diagnosis of acute coronary syndromes and could probably act as a marker of ischemia. However, further studies on specificity and development of a fast, automated assay are necessary before GPBB can be recommended as a routine diagnostic tool.

Effects of protein kinase A inhibition on rat diaphragm force generation

Although protein kinases are known to play a role in modulating a variety of intracellular functions, the direct effect of inhibition of these enzymes on skeletal muscle force production has not been studied. The purpose of the present study was to examine this issue by determining the effects produced on diaphragm force generation by two protein kinase inhibitors: (a) H7, an inhibitor of both cAMP-dependent protein kinase (PKA) and of protein kinase C, and (b) H89, a selective inhibitor of PKA. Experiments (n=15) were performed using isolated, arterially perfused, electrically stimulated rat diaphragms. Perfusate temperature was adjusted to maintain muscle temperature at 27 degrees C and arterial pressure was kept at 150 Torr. Animals were divided into three groups: (a) a control group perfused with Krebs-Henselheit solution equilibrated with 95% O(2)/5% CO(2), (b) a group in which H7 (2 microM) was added to the perfusate, and (c) a group perfused with solution containing H89 (4 microM). In all three groups, we assessed diaphragm twitch kinetics, force-frequency relationships and in vitro fatiguability. We found that both H7 and H89 administration slowed twitch relaxation, augmented force generation in response to low frequency stimulation, and increased the rate of development of fatigue. Specifically, for control, H7 and H89 groups, respectively, we found: (a) 1/2 relaxation time averaged 64+/-2 S.E.M., 87+/-6 and 90+/-2 ms, P<0. 003, (b) force production during 10-Hz stimulation averaged 12.6+/-1. 1, 20.1+/-2.3, and 20.3+/-2.1 N/cm(2), P<0.035, and (c) force fell to 14.3+/-2.0, 9.5+/-0.5 and 8.7+/-0.2% of its initial value after 20 min of fatiguing stimulation, P<0.035. These data show that it is possible to produce large increases in low frequency skeletal muscle force generation by directly inhibiting PKA. We speculate that it may be possible to pharmacologically augment respiratory muscle force and pressure generation in clinical medicine by administration of PKA inhibitors.

Glycogen phosphorylase isoenzyme BB to diagnose ischaemic myocardial damage

Glycogen phosphorylase isoenzyme BB (GPBB) is a key enzyme of glycogenolysis. Its degree of association with the sarcoplasmatic reticulum glycogenolysis complex depends essentially on the metabolic state of the myocardium. With the onset of tissue hypoxia, when glycogen is broken down, GPBB is converted from a structurally bound into a cytoplasmatic form. Considerable amounts of GPBB are only found in human heart and brain. In the first clinical studies GPBB was the most sensitive marker for the diagnosis of acute myocardial infarction within 4 h of chest pain onset. GPBB also increases early in patients with unstable angina and reversible ST-T alterations in the resting electrocardiogram at hospital admission, which could be useful for risk stratification. GPBB is sensitive for the detection of perioperative ischaemic myocardial damage and infarction in patients undergoing coronary artery bypass grafting. The diagnostic specificity of GPBB in non-traumatic chest pain patients was comparable to creatine kinase MB. These results indicate that GPBB is a sensitive marker for ischaemic myocardial damage.

Can clonidine, enoximone, and enalaprilat help to protect the myocardium against ischaemia in cardiac surgery?

OBJECTIVE

To evaluate whether clonidine, enoximone, and enalaprilat reduce ischaemia-related myocardial cell damage in cardiac surgery.

DESIGN

Prospective randomised controlled trial.

SETTING

Clinical investigation in a cardiac anaesthesia department of a university hospital.

PATIENTS

88 consecutive patients undergoing coronary artery bypass surgery.

INTERVENTIONS

After induction of anaesthesia patients continuously received the alpha 2 agonist clonidine (group 1, n = 22), the phosphodiesterase (PDE) III inhibitor enoximone (group 2, n = 22), the angiotensin converting enzyme (ACE) inhibitor enalaprilat (group 3, n = 22), or saline solution as placebo (control group, n = 22). The infusion was stopped immediately before the start of cardiopulmonary bypass.

MAIN OUTCOME MEASURES

The ST segment was analysed and the activity of creatine kinase isoenzyme MB (CKMB), cardiac troponin T (TnT), and the BB isoenzyme of glycogen phosphorylase (GPBB) were measured before the start of infusion (baseline), after weaning from cardiopulmonary bypass (CPB), at the end of surgery, 5 h after CPB, and on the morning of the first and third postoperative days.

RESULTS

Biometric data and time of cross-clamping were not significantly different in the four groups. Changes in the ST segment indicating ischaemia were least common in the enalaprilat group (P < 0.05). Postoperatively, CKMB activity was significantly higher in the clonidine and the control groups. Both new markers of myocardial cell damage increased more after CPB and postoperatively in the control patients (TnT peak: (mean (SD)) 3.99 (0.35) microgram/1; GPBB peak: 82 (15) ng/ml) and the clonidine-treated group (TnT peak: 3.80 (0.3) microgram/1; GPBB peak: 85 (14) ng/ml). Enalaprilat-treated patients showed the smallest overall changes in standard (CKMB) and new serological markers of myocardial ischaemia (TnT peak: 0.71 (0.1) microgram/1; GPBB peak: 44 (14) ng/ml).

CONCLUSIONS

In patients treated with enalaprilat before CPB, both new, more sensitive markers of ischaemic myocardial tissue damage increased significantly less than in an untreated control group. Those treated with enoximone also had lower plasma concentration of TnT and GPBB than the control group, whereas clonidine did not reduce the concentration of these markers of myocardial ischaemia. Pharmacological interventions, such as the continuous infusion of the ACE inhibitor enalaprilat, before start of CPB may help to protect the heart against ischaemia/reperfusion injury.

Glycogen phosphorylase isoenzyme BB in diagnosis of myocardial ischaemic injury and infarction

This review deals with glycogen phosphorylase (GP) and its isoenzyme BB in the diagnosis of ischaemic myocardial injury. Early identification and confirmation of acute myocardial infarction is essential for correct patient care and disposition decision in the emergency department. In this respect, glycogen phosphorylase isoenzyme BB (GPBB) based on its metabolic function is an enzyme for early laboratory detection of ischaemia. In the aerobic heart muscle GPBB together with glycogen is tightly associated with the vesicles of the sarcoplasmic reticulum. Release of GPBB, the main isoform in the human myocardium, essentially depends on the degradation of glycogen, which is catalyzed by GP. Ischaemia is known to favour the conversion of bound GP in the b form into GP a, thereby accelerating glycogen breakdown, which is the ultimate prerequisite for getting GP into a soluble form being able to move freely in the cytosol. The efflux of GPBB into the extracellular fluid follows if ischaemia-induced structural alterations in the cell membrane become manifest. The clinical application of GPBB as a marker of ischaemic myocardial injury is a very promising tool for extending our knowledge of the severity of myocardial ischaemic events in the various coronary syndromes. The rational roots of this development were originated from Albert Wollenberger's research work on the biochemistry of cardiac ischaemia and the transient acceleration of glycogenolysis mainly brought about by GP activation.

Crucial role of intracellular effectors on glycogenolysis in the isolated rat heart: potential consequences on the myocardial tolerance to ischemia

The role played by glycogenolysis in the ischemic heart has been recently put into question because it is suspected that a slowing down of this process could be beneficial for the tolerance of the myocardium to ischemia. The role of the intracellular effectors that control the rate of glycogenolysis has therefore regained interest. We aimed to understand the role played by those intracellular effectors which are directly related to the energy balance of the heart. To this end, we review some of the previously published data on this subject and we present new data obtained from P-31 and C-13 NMR spectroscopic measurement on isolated rat heart. Two conditions of ischemia were studied: 15 min global no-flow and 25 min low-flow ischemia. The hearts were isolated either from control animals or from rats pre-treated with isoproterenol (5 mg.kg-1 b.w. i.p.) 1 h before the perfusion in order to C-13 label glycogen stores. Our main results are as follows: (1) the biochemically determined glycogenolysis rate during the early phase of ischemia (up to 10-15 min) was larger in no-flow ischemia than in low-flow conditions for both groups, (2) direct measurement of the glycogenolysis rate, as determined by C-13 NMR, after labelling of the glycogen pool in the hearts from isoproterenol-treated rats, confirms the estimations from the biochemical data, (3) glycogenolysis was slower in the hearts from pre-treated animals than in control hearts for both conditions of ischemia, (4) the total activity of glycogen phosphorylase (a + b) increased, by 50%, after 5 min no-flow ischemia, whereas it decreased by 42% after the same time of low-flow ischemia. However, the ratio phosphorylase a/a + b was not altered, whatever the conditions, (5) the concentration of inorganic phosphate (Pi) increased sharply during the first minutes of ischemia, to values above 8-10 mM, under all conditions studied. The rate of increase was larger during no-flow ischemia than during low-flow ischemia. The concentration of Pi was thereafter higher in controls than in the hearts from isoproterenol-treated animals. The calculated cytosolic concentration of free 5'AMP increased sharply at the onset on ischemia, reaching in a few minutes values above 30 microM in controls and significantly lower values around 15 microM, in the hearts from isoproterenol-treated rats. (6) The hearts from isoproterenol-treated rats displayed a reduced intracellular acidosis, when compared to controls, under both conditions of ischemia. We conclude that the intracellular effectors, mainly free AMP, play an essential role in the control of glycogenolysis via allosteric control of phosphorylase b activity. The alteration in the concentration of free Pi, the substrate of both forms of phosphorylase, can be considered as determinant in the control of the rate of glycogenolysis. The attenuation of ischemia-induced intracellular acidosis in the hearts from isoproterenol-treated rats could be a consequence of a reduced glycogenolytic rate and is likely to be related to a better resumption of the mechanical function on reperfusion.

Myocardial oxygen consumption, cardiac work, and myocardial efficiency in children

Few reports on human cardiac functional development exist, although this information is important for managing paediatric heart disease. The work and the energy usage of the heart was measured in children. A total of 58 patients (aged 1-19 years) with a history of Kawasaki disease without coronary sequelae underwent cardiac catheterization to obtain haemodynamic data and to measure myocardial oxygen consumption. Myocardial oxygen consumption (ml/min) (y = 0.63 x + 3.6, r = 0.86, P < 0.0001, x = age) and left ventricular minute work (kg m/min) (y = 0.46 x 2.4, r = 0.84, P < 0.0001, x = age) correlated positively with age. However, left ventricular minute work per body surface area (age: 2-5 years, 5.8 +/- 0.34 kg m/min/m2; age: 6-10 years, 6.9 +/- 0.59 kg m/min/m2; age: 11-15 years, 5.9 +/- 0.51 kg m/min/m2; age 16-19 years, 6.5 +/- 0.29 kg m/min/m2; and myocardial efficiency (age: 2-5 years, 40.1 +/- 4.4%; age: 6-10 years, 42.4 +/-3.9%; age: 11-15 years, 45.9 +/- 4.1%; age: 15-19 years, 42.3 +/- 6.6%) remained constant throughout childhood.

CONCLUSION

In spite of the structural immaturity of the developing heart, the myocardial oxygen consumption per body surface area and myocardial efficiency led by the cardiac work are the same in adults and in children older than 1 year of age.

Microcompartmentation, metabolic channelling and carbohydrate metabolism

The inter-organelle cytoplasm of eukaryotic cells was once considered to be a homogeneous solution in which many of the enzymes of intermediary metabolism are soluble; however, advances in cell biology have revealed an intricate picture at the microscopic level of cytoplasm structure. Consequently, a great deal of constraint is required when extrapolating to the intact cell from enzyme studies in vitro, a point made frequently in the literature of the last decade or so. The idea of spatial organization is now accepted and covers a wide variety of local microenvironments and possibly localized metabolic channelling. The latter, although accepted as a phenomenon, is controversial in terms of its physiological significance. This review covers evidences showing that both glycolytic and glycogenolytic enzymes are microcompartmentalized. The potential significance of this compartmentation appears to involve metabolic chanelling, a process by which rearrangement of enzymes on a dynamic cytomatrix leads to "channels" in which metabolic substrates are passed from one enzyme to the next. The combined effects of such enzyme proximity and their activation as a result of the altered kinetic properties conferred upon the enzymes by their cytoskeletal associations favours maximal rate of reaction. These and other aspects of microcompartmentation and metabolic channelling are discussed.

Early release of glycogen phosphorylase in patients with unstable angina and transient ST-T alterations

OBJECTIVE

To determine whether transient ST-T alterations in patients with unstable angina are associated with an increase in plasma glycogen phosphorylase BB concentrations on admission to hospital.

DESIGN

Prospective screening of patients with unstable angina for markers of myocardial cell damage.

SETTING

Accident and emergency department of university hospital.

PATIENTS

48 consecutive patients admitted for angina pectoris (18 with transient ST-T alterations). None of the patients had acute myocardial infarction according to standard criteria.

MAIN OUTCOME MEASURES

Creatine kinase and creatine kinase MB activities, creatine kinase MB mass concentration, and myoglobin, cardiac troponin T, and glycogen phosphorylase BB concentrations on admission.

RESULTS

All variables except for creatine kinase and creatine kinase MB activities were significantly higher on admission in patients with unstable angina and transient ST-T alterations than in patients without. However, glycogen phosphorylase BB concentration was the only marker that was significantly (p = 0.0001) increased above its discriminator value in most patients (16). In the 18 patients with transient ST-T alterations creatine kinase MB mass concentration and troponin T and myoglobin concentrations were significantly (p = 0.0001) less commonly increased on admission (in five, three, and two patients, respectively).

CONCLUSIONS

The early release of glycogen phosphorylase BB may help to identify high risk patients with unstable angina even on admission to an emergency department. Glycogen phosphorylase BB concentrations could help to guide decisions about patient management.

Glucose flux rate regulates onset of ischemic contracture in globally underperfused rat hearts

This study analyzes the importance of the source and rate of ATP production (glucose flux, glycogenolysis, and oxidative phosphorylation) in the prevention of ischemic contracture in isolated rat hearts. Ischemic contracture was initiated at about 10 minutes by buffer perfusion with nonglycolytic substrates whereas the addition of 11 mM glucose prevented contracture for 2 hours. Tissue values of ATP, phosphocreatine, and lactate could be dissociated from onset of ischemic contracture. In hearts perfused with acetate or free fatty acid, with 11 mM glucose, glycolytic ATP production was 2.3-2.8 mumol/g fresh wt/min; as initial rates of glycogenolysis fell, glycolysis was maintained by a steady increase of glucose flux to values in excess of 2 mumol ATP/g fresh wt/min. Decreasing the glucose flux by lowering the perfusate glucose or by the addition of 2-deoxyglucose precipitated ischemic contracture. When oxidative phosphorylation was further reduced by hypoxia, glucose still prevented ischemic contracture; however, when oxidative phosphorylation dropped to near zero (near-anoxic) rates, glycolysis was inhibited, and glucose could only delay ischemic contracture to about 45 minutes. Combined ATP production rates could be dissociated from contracture. The metabolic parameter that correlated best with prevention or delay of ischemic contracture was the rate of glycolytic flux from glucose, which in this model of global low-flow ischemia had to accelerate to provide a rate of ATP production from glucose in excess of 2 mumol/g fresh wt/min within 30 minutes of the start of ischemia to prevent ischemic contracture.

Binding of phosphorylase a and b to skeletal muscle thin filament proteins

Phosphorylase plays an important role in energy generation during muscle contraction. We have demonstrated that purified rabbit skeletal muscle phosphorylase a and phosphorylase b bind to rabbit muscle F-actin, F-actin-tropomyosin, F-actin-tropomyosin-troponin, and myofibrils. Neither phosphorylase a nor phosphorylase b binds to myosin. Phosphorylase a and b bind to F-actin with S0.5 values of 1.5 X 10(-6) and 2.1 X 10(-6) M, respectively. At saturation, 0.035 mol of phosphorylase a and b is bound for every seven G-actin monomers in the F-actin polymer. Using the F-actin-tropomyosin-troponin complex as opposed to F-actin as a binding target, there are five- and threefold increases in the maximal binding capacity for phosphorylase a and phosphorylase b, respectively, without a significant change in the S0.5 value for either form of the enzyme. A similar stoichiometry and affinity of phosphorylase binding are observed when myofibrils are used as the binding target. Ca2+ ions and AMP increase the maximal binding capacity for phosphorylase a to myofibrils while ATP decreases the Bmax. Our study suggests that in skeletal muscle, phosphorylase a and phosphorylase b may interact with the thin filament, and that this binding to thin filament proteins may be controlled by changes in sarcoplasmic concentration of Ca2+ and ligands of phosphorylase during muscle contraction.

Cytochemical studies of a glycogen-sarcoplasmic reticulum complex

Enzymatically active cardiac sarcoplasmic reticulum (SR) fractions contain glycogen. Previous biochemical and morphological studies indicate that the glycogen particles are membrane associated. In the present study, further evidence for membrane-associated glycogen particles in these cardiac SR fractions is presented: (1) morphological parameters, (2) enzymatic digestion by glucoamylase and alpha-amylase and (3) cytochemical staining by two different methods. Dense granules comparable in size (20-30 nm diameter), electron density and substructure to glycogen particles observed in intact cardiac muscle and in glycogen preparations isolated from skeletal muscle were seen. Most of these glycogen particles were removed by amylase digestion except for glycogen particles closely adhering to vesicle membranes. Two different cytochemical techniques (bismuth subnitrate and silver proteinate) revealed a positive reaction product over the glycogen particles. These findings provide further support for the biochemical finding of a structured enzyme complex involving the SR, glycogenolytic enzymes and glycogen.

The association of phosphorylase kinase with rabbit muscle T-tubules

Evidence is presented for the association of a phosphorylase kinase activity with transverse tubules as well as terminal cisternae in triads isolated from rabbit skeletal muscle. This activity remained associated with T-tubules throughout the purification of triad junctions by one cycle of dissociation and reassociation. The possibility that the presence of phosphorylase kinase in these highly purified membrane vesicle preparations was due to its association with glycogen was eliminated by digestion of the latter with alpha-amylase. The phosphorylase kinase activity associated with the T-tubule membranes was similar to that reported for other membrane-bound phosphorylase kinases. The enzyme had a high pH 6.8/pH 8.2 activity ratio (0.4-0.7) and a high level of Ca2+ independent activity (EGTA/Ca2+ = 0.3-0.5). The kinase activated and phosphorylated exogenous phosphorylase b with identical time courses. When mechanically disrupted triads were centrifuged on continuous sucrose gradients, the distribution of phosphorylase kinase activity was correlated with the distribution of a Mr 128,000 polypeptide in the gradients. This polypeptide and a Mr 143,000 polypeptide were labeled with 32P by endogenous and exogenous protein kinases. These findings suggest that the membrane-associated phosphorylase kinase may be similar to the cytosolic enzyme. Markers employed for the isolated organelles included a Mr 102,000 membrane polypeptide which followed the distribution of Ca2+-stimulated 3-O-methylfluorescein phosphatase activity, which is specific for the sarcoplasmic reticulum. A Mr 72,000 polypeptide was confirmed to be a T-tubule-specific protein. Several proteins of the triad component organelle were phosphorylated by the endogenous kinase in a Ca2+/calmodulin-stimulated manner, including a Mr ca. 72,000 polypeptide found only in the transverse tubule.

Membrane-glycogen complexes in rabbit extraocular muscle

Analysis of 432 electron micrographs of membrane-glycogen complexes revealed that: (1) Golgi apparatus is closely associated with 4.2% of the complexes, such associations occurring irrespective of the degree of glycogen loading in the complex. (2) Apparent ribosomes are seen in association with about 30% of the complexes, either attached to membranes or enclosed between cisternae. (3) In longitudinal sections of the muscle fibers, complexes may form columns which extend for as much as 40 microns along the fiber. (4) Various cytoplasmic organelles may become enclosed within a complex. (5) Some cisternae of a complex may assume the form of randomly oriented tubules, in contrast to the typical systematic array of flattened cisternae. (6) Some cisternae of a complex may become distended in a wide and uneven manner, in contrast to the typical narrow and even distension.

The effects of insulin on myocardial metabolism and acidosis in normoxia and ischaemia. A 31P-NMR study

1. The effect of insulin on the perfused rat heart during normoxia and total ischaemia was studied by 31P-NMR. 2. During normoxic perfusion, insulin increased the phosphocreatine to ATP ratio at the expense of Pi, when glucose was the substrate. No change was observed when acetate was used as the sole substrate. the intracellular pH (as measured from the position of the 2-deoxyglucose 6-phosphate resonance peak) was unaffected by insulin treatment. 3. Infusion of insulin prior to ischaemia caused an increase in the rate and extent of acidosis during the period of no flow while the rate of ATP depletion was decreased. 4. Freeze-clamped studies showed an increase in glycogen levels upon insulin treatment of the glucose perfused rat heart. During ischaemia, a decrease in glycogen content concomitant with an increase in lactate was observed. The accessibility of glycogen to phosphorylase during ischaemia is increased as a result of insulin treatment. The control of glycolysis during ischaemia is discussed with respect to the content and structure of glycogen in heart tissue.

[Changes in functional and metabolic characteristics of isolated rat heart during initial phase and long lasting perfusion]

Mechanical performance, tissue content of high-energy phosphates (ATP and CP), glycogen and phosphorylase activity were measured in isolated rat hearts either just after excision (hearts arrested by plunging in ice-cold perfusate) or during long time perfusions (6 h) at 37 degrees C. Arrested hearts exhibited : (1) higher total phosphorylase activity (a + b); (2) higher percentage of phosphorylase a; (3) lower CP content. During perfusion, high energy phosphates appeared well maintained whereas glycogen content and phosphorylase activity decreased with a significant correlation between these two parameters. The validity of this isolated heart model and possible implications of the variations in phosphorylase activity are discussed.

Modification by liposomes of the adenosine triphosphate-activating effect on adenylate deaminase from pig heart

Adenylate deaminase (AMP deaminase, EC 3.5.4.6) of a high substrate specificity was purified from pig heart by chromatography on cellulose phosphate. The enzyme shows a co-operative binding of AMP [h (Hill coefficient) 2.35, with SO.5 (half-saturating substrate concentration) 5mM]. ATP and ADP act as positive effectors, lowering h to 1.55 and SO.5 to 1 mM. The addition of liposomes (phospholipid bilayers) to ATP-activated or ADP-activated enzyme causes a further shift of the h value to 1.04 and SO.5 to 0.5 mM. For ATP-activated enzyme the addition of liposomes increases Vmax. by about 100%, and for ADP-activated enzyme by 50%. Liposomes have no effect on the kinetics of AMP deaminase in the absence of ATP and ADP, and neither do they influence the inhibitory effect of orthophosphate on heart muscle AMP deaminase. Metabolic implications of these findings are discussed.