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

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.

Markers of maternal cardiac dysfunction in pre-eclampsia and superimposed pre-eclampsia

AUTHORS

Frances Conti-Ramsden MBBS Academic Clinical Fellow¹, Carolyn Gill PhD BRC Research Assistant¹, Paul T Seed MSc CStat Senior Lecturer in Medical Statistics¹, Kate Bramham PhD Clinical Senior Lecturer in Nephrology^2, Lucy C Chappell PhD NIHR Research Professor in Obstetrics¹, Fergus P McCarthy PhD Clinical Senior Lecturer in Obstetrics and Gynaecology^1,3.

OBJECTIVES

To determine whether glycogen phosphorylase isoenzyme B (GPBB) and/or brain natriuretic peptide (BNP) concentrations are elevated in pre-eclampsia and superimposed pre-eclampsia (SPE), demonstrating cardiac ischaemia and strain.

STUDY DESIGN

A nested case-control study was performed using samples and clinical data available from a prospective pregnancy cohort. Four groups were selected: healthy pregnant controls (n = 21), pre-eclampsia (n = 19), pre-existing chronic hypertension (CHT) and/or chronic kidney disease (CKD) without (n = 20) or with superimposed pre-eclampsia (SPE) (n = 19). Plasma samples were taken at time of disease or the third trimester in controls.

MAIN OUTCOME MEASURES

Plasma concentrations of GPBB and BNP.

RESULTS

There was no significant difference in GPBB plasma concentrations between controls and pre-eclampsia (geometric mean (GM) [95% CI]: 4.74 [2.54-8.84]ng/mL vs 5.01 [2.58-9.74]ng/mL, p = 0.90)), or between CHT and/or CKD and SPE (GM [95% CI]: 9.49 [4.93-18.25]ng/mL vs 10.24 [5.27-19.92]ng/mL, p = 0.87). BNP plasma concentrations were significantly raised in women with pre-eclampsia compared to controls (GM [95% CI]: 31.83 [20.18-50.22]pg/mL vs 11.33 [7.34-17.51]pg/mL, p = 0.001). Women with CKD, but not CHT, who developed SPE had elevated BNP concentrations. There were no significant differences in BNP concentration between women with comorbidity (CHT and/or CKD) and controls.

CONCLUSIONS

GPBB has a limited role as a biomarker in hypertensive disorders of pregnancy. BNP concentrations were elevated in pre-eclampsia compared to controls. This suggests cardiac strain at the time of pre-eclampsia. Further studies are needed to examine whether BNP can identify women at increased risk of cardiovascular disease.

New biomarker for acute ischaemic stroke: plasma glycogen phosphorylase isoenzyme BB

BACKGROUND

Glycogen phosphorylase is the key enzyme that breaks down glycogen to yield glucose-1-phosphate in order to restore depleted energy stores during cerebral ischaemia. We sought to determine whether plasma levels of glycogen phosphorylase BB (GPBB) isoform increased in patients with acute ischaemic stroke (AIS).

METHODS

We studied plasma GPBB levels within 12 hours and again at 48±24 hours of symptom onset in 172 patients with imaging-confirmed AIS and 133 stroke-free individuals. We determined the ability of plasma GPBB to discriminate between cases and controls and examined the predictive value of plasma GPBB for 90-day functional outcome, 90-day survival and acute lesion volumes on neuroimaging.

RESULTS

The mean (SD) GPBB levels were higher in cases (46.3±38.6 ng/mL at first measurement and 38.6±36.5 ng/mL at second measurement) than in controls (4.1±7.6 ng/mL, p<0.01 for both). The area under the receiver operating characteristic (ROC) curve for case-control discrimination based on first GPBB measurement was 0.96 (95% CI 0.93 to 0.98). The sensitivity and specificity based on optimal operating point on the ROC curve (7.0 ng/mL) were both 93%. GPBB levels increased in 90% of patients with punctate infarcts (<1.5 mL) and in all patients admitted within the first 4.5 hours of onset. There was no correlation between GPBB concentration and either clinical outcome or acute infarct volume.

CONCLUSION

GPBB demonstrates robust response to acute ischaemia and high sensitivity for small infarcts. If confirmed in more diverse populations that also include stroke mimics, GPBB could find utility as a stand-alone marker for acute brain ischaemia.

Heart-type fatty acid-binding protein (H-FABP) and highly sensitive troponin T (hsTnT) as markers of myocardial injury and cardiovascular events in elective percutaneous coronary intervention (PCI)

BACKGROUND/INTRODUCTION

Type 4a myocardial infarction (MI) occurs when myocardial injury is combined with either symptoms suggestive of myocardial ischaemia, new left bundle branch block, angiographic loss of patency of a major artery or imaging suggestive of new loss of myocardium. Myocardial injury is defined as a rise of >5 x 99th upper reference limit (URL) of 14 ng/l (i.e. >70 ng/l) for highly sensitive troponin T (hsTnT) at 6 h if hsTnT was normal at baseline or >20% rise from 0 to 6 h if hsTnT was >14 ng/l at baseline.

AIM

To assess the prognostic value of biomarkers of myocardial injury following elective percutaneous coronary intervention (PCI).

DESIGN

A cohort of 209 patients were included of whom 144 (68.9%) were male, mean age was 68.8 years, 28 (13.4%) were smokers, 31 (14.8%) were diabetic, 199 (95.2%) had hypercholesterolaemia and 138 (66.0%) had hypertension.

METHODS

We evaluated hsTnT, heart-type fatty acid-binding protein (H-FABP), troponin I (TnI), creatine kinase MB type (CKMB), myoglobin, glycogen phosphorylase BB (GPBB) and carbonic anhydrase III (CA III) at 0, 4, 6 and 24 h following elective PCI. Patients were followed up at 1 year to assess for major adverse clinical events (MACE).

RESULTS

Myocardial injury was observed in 37 (17.7%) patients. Median hsTnT/H-FABP at 4 h were most predictive. MACE was noted in 6 (2.9%) patients, 3 had type 4a MI post PCI, P = 0.036.

DISCUSSION/CONCLUSIONS

Median 4 h hsTnT/H-FABP were most predictive of myocardial injury following PCI. H-FABP and hsTnT were predictive of MACE.

Cost-Effectiveness of Introducing Point-of-Care Test for Detection of Level of Glycogen Phosphorylase in Early Diagnostic Algorithm of Acute Coronary Syndrome

BACKGROUND

The detection of specific biomarkers in the early phase of acute coronary syndrome (ACS) is important for the early diagnosis and appropriate management of patients with ACS.

OBJECTIVES

To estimate the cost-effectiveness of introducing a diagnostic point-of-care (POC) test for determining the levels of glycogen phosphorylase BB isoform (GPBB) in a standard diagnostic algorithm for the early diagnosis of ACS within the health system of the Republic of Serbia.

METHODS

The probabilistic decision-tree model was constructed for patients with nontraumatic chest pain comparing the use of standard diagnostic procedure, physical examination, and electrocardiogram monitoring with the use of a diagnostic test for the detection of the levels of specific biomarkers. The perspective of the health care services purchaser (the Republic Institute for Health Insurance, Serbia) was used in the model, and only direct costs were taken into account. The time horizon was set at one treatment episode of ACS, and the discount rate was not included because of the short length of the time horizon.

RESULTS

Using the GPBB POC test in comparison with not using it in the early diagnosis of ACS results in a significant reduction in the cost per treatment episode (10,034.48 ± 7,283.80 Serbian dinar [RSD]), increase in the number of survivors per 1000 treatment episodes (16 ± 18), decrease in the number of hospitalizations per 1000 treatment episodes (104 ± 44), and decrease in the number of performed coronarographies per 1000 treatment episodes (22 ± 19). The costs per hospitalization avoided (incremental cost-effectiveness ratio) were -145,887.57 ± 5,271.54 RSD, and the costs per coronarography avoided were -137,295.68 ± 4,681.05 RSD.

CONCLUSIONS

In the circumstances of limited health resources, reducing hospitalizations and decreasing unnecessary treatments and invasive diagnostic procedures by a GPBB POC test could be an effective way to improve the economic status of other Balkan countries with limited health care budgets.

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.

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.

Cardiac biomarkers - the old and the new: a review

Biomarkers are biological parameters that can be objectively measured and quantified as indicators of normal biologic processes, pathogenic processes, or responses to a therapeutic intervention. Typically thought of as disease process screening, diagnosing, or monitoring tools, biomarkers may also be used to determine disease susceptibility and eligibility for specific therapies. Cardiac biomarkers are protein components of cell structures that are released into circulation when myocardial injury occurs. They play a pivotal role in the diagnosis, risk stratification, and treatment of patients with chest pain and suspected acute coronary syndrome and those with acute exacerbations of heart failure. Cardiac markers are central to the new definition of acute myocardial infarction put forward by the American College of Cardiology and the European Society of Cardiology. Active investigation has brought forward an increasingly large number of novel candidate markers but few have withstood the test of time and become integrated into contemporary clinical care because of their readily apparent diagnostic, prognostic, or therapeutic utility.

Quick identification of acute chest pain patients study (QICS)

Background

Patients with acute chest pain are often referred to the emergency ward and extensively investigated. Investigations are costly and could induce unnecessary complications, especially with invasive diagnostics. Nevertheless, chest pain patients have high mortalities. Fast identification of high-risk patients is crucial. Therefore several strategies have been developed including specific symptoms, signs, laboratory measurements, and imaging.

Methods/Design

The Quick Identification of acute Chest pain Study (QICS) will investigate whether a combined use of specific symptoms and signs, electrocardiography, routine and new laboratory measures, adjunctive imaging including electron beam (EBT) computed tomography (CT) and contrast multislice CT (MSCT) will have a high diagnostic yield for patients with acute chest pain. All patients will be investigated according a standardized protocol in the Emergency Department. Serum and plasma will be frozen for future analysis for a wide range of biomarkers at a later time point. The primary endpoint is the safe recognition of low-risk chest pain patients directly at presentation. Secondary endpoint is the identification of a wide range of sensitive predictive clinical markers, chemical biomarkers and radiological markers in acute chest pain patients. Chemical biomarkers will be compared to quantitative CT measurements of coronary atherosclerosis as a surrogate endpoint. Chemical biomarkers will also be compared in head to head comparison and for their additional value.

Discussion

This will be a very extensive investigation of a wide range of risk predictors in acute chest pain patients. New reliable fast and cheap diagnostic algorithm resulting from the test results might improve chest pain patients' prognosis, and reduce unnecessary costs and diagnostic complications.

Use of glycogen phosphorylase BB measurement with POCT in the diagnosis of acute coronary syndromes. A comparison with the ELISA method

BACKGROUND

Glycogen Phosphorylase BB (GPBB) is considered an early and specific marker of myocardial necrosis and ischemia. A POCT kit GPBB for diagnostic use has recently been approved.

AIM

an evaluation of the correspondence of qualitative POCT GBPP measurements with ELISA test results.

MATERIAL AND METHODOLOGY

20 individuals with non-ST elevation myocardial infarction (non-STEMI) and 20 probands without acute coronary syndrome (ACS) were tested. GPBB (POCT, ELISA) in venous plasma (lithium-heparin) was assayed in all probands.

RESULTS

individuals with non-STEMI had significantly higher GPBB ELISA values (32.3 vs. 6.1 microg/l; p < 0.01). GPBB sensitivity and specificity for non-STEMI presence 6 hours after chest pain generation were 100 %. No proband was classified in a different subgroup with POCT of GPBB (positive/negative). GPBB POCT correlate with a non- STEMI diagnosis (chi(2) 36.1; p <0.01).

CONCLUSION

GPBB POCT measurement is comparable with ELISA test results. GPBB analysis could expand the diagnostic palette in the first hours after the onset of acute coronary syndrome.

Biochemical markers of myocardial injury

The serum markers of myocardial injury are used to help in establishing the diagnosis of myocardial infarction. The older markers like aspartate amino-transferase, creatine kinase, lactate dehydrogenase etc. lost their utility due to lack of specificity and limited sensitivities. Among the currently available markers cardiac troponins are the most widely used due to their improved sensitivity specificity, efficiency and low turn around time. Studies have shown that cardiac troponins should replace CKMB as the diagnostic 'gold standard' for the diagnosis of myocardial injury. The combination of myoglobin with cardiac troponins has further improved the accuracy in the diagnosis of acute coronary syndromes and thereby reducing the hospital stay and patients' money. Among the other new markers of early detection of myocardial damage, heart fatty acid binding protein, glycogen phosphorylase BB and myoglobin/carbonic anhydrase III ratio seem to be the most promising. But the search for the most ideal marker of myocardial injury is still on.

Attenuation of skeletal muscle reperfusion injury with intravenous 12 amino acid peptides that bind to pathogenic IgM

BACKGROUND

The injury sustained by reperfused skeletal muscle is inflammatory and is initiated by binding of pre-formed IgM to involved tissue, followed by local complement activation and further inflammation. A clone of natural IgM has been described that initiates this injury, suggesting that specific antigens are exposed on ischemic tissues that act as ligands for this pathogenic antibody. In these experiments, we examine the properties of short peptide sequences, and their homologues, that bind to the antigen-combining site of this pathogenic IgM clone.

METHODS

A 12-mer phage display library was biopanned with the pathogenic IgM clone and then negatively selected against an inactive natural IgM clone. All 8 clones that bound specifically to the pathogenic IgM had closely related amino acid sequences. P8 is the clone that bound most avidly. Tissue lysates from ischemic tissue were reacted with pathogenic IgM, and immune complexes isolated and analyzed on SDS-PAGE. Bands were excised and sequenced, identifying non-muscle myosin as the protein reacting with pathogenic antibody in ischemic gut and glycogen phosphorylase as the counterpart in ischemic skeletal muscle. Both proteins contain sequence homologous to P8; N2 and GP1 are the natural 12-mers homologues that are contained within non-muscle myosin and glycogen phosphorylase, respectively. Wild-type C57/Bl6 mice, divided into groups receiving saline, P8, N2, GP1, or a random peptide at the start of the experiment, were subjected to 2 hours of tourniquet induced hind limb ischemia and 3 hours of reperfusion. Muscle was assessed for injury with histology and for immune activation with histochemistry.

RESULTS

Intravenous administration of P8, N2, and GP1 led to significant attenuation of muscle injury (13 +/- 1.8 injured fibers/50 counted, 12 +/- 0.81, 8.0 +/- 0.73 respectively) after reperfusion injury compared to animals receiving saline (26 +/- 2.3) or the same mass of a random peptide (22 +/- 2.3), P less than .05. This level of protection from injury is comparable to that seen in the absence of antibody altogether. As well, P8-treated animals exhibited a marked decrease in deposition of IgM (as well as C3) in comparison to saline treated controls.

CONCLUSIONS

Specific peptide blockade of an injury-inducing IgM clone decreased the local consequences of skeletal muscle ischemia/reperfusion injury in wild-type animals that have the full repertoire of IgM specificities. This indicates that the antibodies that initiate reperfusion injury have specificity only for P8-related antigens. This could also indicate that the variety of relevant ischemic antigens is quite restricted.

Proteomic approach to the diagnosis of acute coronary syndrome: Preliminary results

BACKGROUND

Cardiac multimarker strategy is recommended by the IFCC, ESC and the ACC for an early risk stratification in non-ST-segment elevation (NSTE) ECG patients with chest pain. A new approach, based on protein biochip array technology, performs simultaneously: cTnI, CK-MB, myoglobin, CAIII, GFBB and FABP using a single chip.

METHODS

We evaluated the analytical performance of the Randox-Evidence Investigator -biochip cardiac panel according to IFCC recommendations and NCCLS guidelines; a preliminary clinical evaluation was carried out on chest pain NSTE ECG patients, to evaluate the accuracy of the multimarker approach in an early diagnosis of AMI, related to the final diagnosis (ACC/ESC criteria).

RESULTS

Troponin, CK-MB and FABP methods provide reproducible within-run and between-day results (total % CVs from 5.9% to 9.7%), and myoglobin and CAIII methods showed the total % CVs from 16.4% to 25.8%. Our preliminary clinical data suggests that FABP had a better diagnostic performance (sensibility = 100%) than myoglobin (sensibility = 75%) to detect AMI in the first hours after the onset of the chest pain and myoglobin/CAIII ratio (specificity = 92.9%) improved the myoglobin specificity.

CONCLUSIONS

Cardiac markers have different diagnostic roles and, in this contest, biochip technology could be an interesting approach supporting clinical expectations.

Comparison of biochemical markers for the detection of minimal myocardial injury: superior sensitivity of cardiac troponin--T ELISA

OBJECTIVES

Patients with minimal myocardial injuries who present clinically with unstable angina, early stages of myocardial infarction or myocarditis require different therapy strategies to those without. The newer diagnostic assays for detecting myocardial lesions (cardiac Troponin T and cardiac Troponin I [cTnT, cTnI], glycogenphosphorylase - BB [GPBB]) are reported to be more sensitive and specific than common biochemical markers such as CK and myoglobin. Our study tested whether the recently developed four assays cTnT-ELISA (in vitro), cTnT rapid bedside assay, cTnI rapid bedside assay, and GPBB (Immunoenzymetric assay) are effective in detecting minimal myocardial injuries caused by endomyocardial biopsy. We compared them with CK activity (CK-cat), CK-MB activity (CK-MBcat), CK-MB-concentration (CK-MB-mass) and Myoglobin concentration (Myo-conc.).

PATIENTS AND METHODS

Twenty-four patients [six female, 18 male, age (mean): 47 years (20-65)] underwent diagnostic endomyocardial biopsy. Between four and six biopsies were taken from the mid-right ventricular aspect of the interventricular septum of the heart. Blood was drawn before catheterization (baseline), 10 min after the biopsy, in the next morning, and in the morning of the second day after (days 1 and 2).

RESULTS AND CONCLUSION

Because of very low CKcat it was not possible to analyse CK-MBcat with reliable precision. The assay for GPBB and cTnI rapid bedside assay did not indicate this minimal myocardial injury. The CK cat, CK-MB mass, and myoglobin assays indicated significant increase at 10 min after biopsy but remained within reference range. cTnT rapid bedside assay indicated this minimal myocardial injury in 50% (P < 0.05). cTnT-ELISA (in vitro) was increased above the reference limit in 54%. This increase was 3. 6-fold the upper reference limit (P < 0.01). In our study, due to superior discriminating power, cTnT-ELISA (in vitro) was the most sensitive assay for minimal myocardial injuries.

New markers for early diagnosis of acute myocardial infarction

The availability of 'new' biochemical markers of myocardial injury such as creatine kinase isoforms and troponins has renewed the interest for rapid confirmation/exclusion of myocardial infarction in patients presented to the hospital for suspected acute myocardial ischemia. Many of these protein markers have the potential to allow the diagnosis of acute myocardial infarction at a time from the onset of symptoms when the activity of creatine kinase MB is still within the reference range. However, the exclusion of classical myocardial infarction as defined by WHO criteria does not allow to conclude that the patient is at low-risk and can be safely sent home since he may have high-risk unstable angina. The sensitivity for the detection of myocardial damage of troponins is such that a substantial proportion of patients with unstable angina develop elevations of troponins in the absence of creatine kinase MB increases. It is now clear that such patients have an increased risk of cardiac events over the short and long-term similar to that of patients with definite myocardial infarction. Such finding may help in developing selective admission policies and deciding which patients deserve aggressive treatment.

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.

Biochemical markers of myocardial injury during cardiac operations

The evaluation of myocardial damage in relation to cardiac operation from a clinical and a research perspective is of great importance, particularly for the evaluation of different cardioprotective strategies. Although measurements of serum biochemical markers have often been used, their value has been limited by their lack of sensitivity and specificity in the presence of skeletal muscle damage. A newer range of markers are now available that may reliably indicate both perioperative myocardial infarction, as well as more subtle degrees of subclinical myocyte injury. In this review, the application of biochemical markers for clinical and research purposes during cardiac operation is considered.

Cardiac troponin I and troponin T: are enzymes still relevant as cardiac markers?

Creatine kinase (CK) MB and lactate dehydrogenase (LDH) isoenzyme 1 are not heart-specific. By contrast, the regulatory proteins troponin I and troponin T are expressed in three different isoforms, one for slow-twitch skeletal muscle fibers, one for fast-twitch skeletal muscle fibers, and one for cardiac muscle (cTnI, cTnT). cTnI and cTnT are usually not detectable in patients without myocardial damage, which is a prerequisite for high diagnostic performance. After acute myocardial infarction (AMI) cTnI, cTnT, and CKMB mass have a comparable early sensitivity. cTnI and cTnT usually peak in parallel except for patients without reperfusion in whom cTnI peaks about 1 day and cTnT approximately 3-4 days after onset of AMI. Both stay increased for at least 4-5 days. cTnT tends to stay increased longer than cTnI. Because the sensitivities of cTnI and cTnT for myocardial injury are comparable, their specificities are the main topic of current debate. Recent reports on mismatches of cTnI and cTnT in patients with renal failure and myopathy without other evidence for myocardial injury suggest that cTnT could be reexpressed similar to CKMB and LDH-1 in chronically damaged human skeletal muscle. In contrast to cTnT, CKMB, and LDH-1, cTnI is not expressed in skeletal muscle during fetal development. So far, an increase in cTnI has been reported only after myocardial damage. Because of currently higher costs, troponin measurement should be restricted at present to clinical settings that really require their high specificity. Based on its distinct functional association with the metabolism of acute ischemic myocardium and according to initial clinical results, glycogen phosphorylase isoenzyme BB is a promising enzyme for the early detection of ischemic myocardial damage.

Progress in myocardial damage detection: new biochemical markers for clinicians

New clinical requirements for triaging chest pain patients challenge the abilities of the current cardiac markers. Serial measurements of myoglobin, creatine kinase (CK) isoenzyme MB (CKMB) mass, or CK isoforms in emergency rooms help to rapidly rule out acute myocardial infarction (AMI). However, within the first 3 to 4 h from chest pain onset, their sensitivities are too low to contribute significantly to AMI diagnosis during this period. CKMB and lactate dehydrogenase (LDH) isoenzyme 1 are not heart-specific, which hampers reliable diagnosis in patients with concomitant skeletal muscle damage. By contrast, the regulatory proteins troponin I and troponin T are expressed in three different isoforms: one for slow-twitch skeletal muscle fibers, one for fast-twitch skeletal muscle fibers, and one for cardiac muscle (cTnI, cTnT); cardiac-specific cTnI and cTnT assays are already available for routine use. cTnT and cTnI are the most promising markers for risk stratification in patients with unstable angina pectoris. Recent reports on increased cTnT in patients with renal failure or myopathy without evidence of myocardial injury and undetectable cTnI suggest that cTnT could be reexpressed similar to CKMB and LDH-1 in chronically damaged human skeletal muscle. Therefore, cTnI is probably the most heart-specific marker. Among the recently proposed new markers for early AMI diagnosis: glycogen phosphorylase isoenzyme BB (GPBB), fatty acid binding protein, phosphoglyceric acid mutase isoenzyme MB, enolase isoenzyme alpha beta, S100a0, and annexin V, GPBB is the most promising because it increases as early as 1 to 4 h from chest pain onset and its early release appears to be essentially dependent on ischemic myocardial injury.

Cardiac markers in the early hours of acute myocardial infarction: clinical performance of creatine kinase, creatine kinase MB isoenzyme (activity and mass concentration), creatine kinase MM and MB subform ratios, myoglobin and cardiac troponin T

We compared early markers of acute myocardial infarction (AMI) in the first 6 h from the onset of symptoms in 133 non-traumatized patients arriving at the emergency department with chest pain suggestive of AMI. Clinical performance parameters were calculated on the basis of 45 patients with AMI and 88 patients with a non-AMI diagnosis. At admission and in the first 0-3 h after the onset of chest pain the creatine kinase-MB (CK-MB) subform ratio was the most sensitive test at a comparable specificity level of 0.95. In the time interval of 3-5 h, myoglobin, the CK-MB mass concentration and the CK-MB subform ratio were associated with the greatest areas under receiver operating characteristic (ROC) curves, but differences between these tests were small and non-significant. At 6 h from the onset of pain, differences in clinical performance between the same three tests were even smaller whether or not samples drawn after the start of thrombolytic treatment were included in the test comparison. For confirmation of AMI at 6 h after onset of pain, CK-MB (activity and mass concentration) demonstrated the highest positive likelihood ratio, and for exclusion of AMI at 6 h the CK-MB subform ratio was associated with the highest negative likelihood ratio. However, differences between the CK-MB subform ratio, CK-MB mass concentration and myoglobin were not significant as estimated by the substantial overlap between the confidence intervals of the likelihood ratios and the ROC areas at 6 h. Cardiac troponin T (cTnT) demonstrated an ROC area equal to the CK-MB isoform ratio and myoglobin at 6 h. However, the likelihood ratio for ruling out AMI was lower, mostly due to the elevated cTnT in unstable coronary disease not defined as AMI. We conclude that the CK-MB subform ratio, CK-MB mass concentration and myoglobin do not demonstrate any significant differences in clinical performance for ruling in or ruling out acute myocardial infarction at 6 h after the onset of chest pain.

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.