Clinical assessment of serum myosin light chains in the diagnosis of acute myocardial infarction

Clinical Biochemistry of Serum Troponin

Accurate measurement and interpretation of serum levels of troponin (Tn) is a central part of the clinical workup of a patient presenting with chest pain suspicious for acute coronary syndrome (ACS). Knowledge of the molecular characteristics of the troponin complex and test characteristics of troponin measurement assays allows for a deeper understanding of causes of false positive and false negative test results in myocardial injury. In this review, we discuss the molecular structure and functions of the constituent proteins of the troponin complex (TnT, TnC, and TnI); review the different isoforms of Tn and where they are from; survey the evolution of clinical Tn assays, ranging from first-generation to high-sensitivity (hs); provide a primer on statistical interpretation of assay results based on different clinical settings; and discuss potential causes of false results. We also summarize the advances in technologies that may lead to the development of future Tn assays, including the development of point of care assays and wearable Tn sensors for real-time continuous measurement.

Novel blood coagulation molecules: Skeletal muscle myosin and cardiac myosin

Essentials Striated muscle myosins can promote prothrombin activation by FXa or FVa inactivation by APC. Cardiac myosin and skeletal muscle myosin are pro-hemostatic in murine tail cut bleeding models. Infused cardiac myosin exacerbates myocardial injury caused by myocardial ischemia reperfusion. Skeletal muscle myosin isoforms that circulate in human plasma can be grouped into 3 phenotypes. ABSTRACT: Two striated muscle myosins, namely skeletal muscle myosin (SkM) and cardiac myosin (CM), may potentially contribute to physiologic mechanisms for regulation of thrombosis and hemostasis. Thrombin is generated from activation of prothrombin by the prothrombinase (IIase) complex comprising factor Xa, factor Va, and Ca++ ions located on surfaces where these factors are assembled. We discovered that SkM and CM, which are abundant motor proteins in skeletal and cardiac muscles, can provide a surface for thrombin generation by the prothrombinase complex without any apparent requirement for phosphatidylserine or lipids. These myosins can also provide a surface that supports the inactivation of factor Va by activated protein C/protein S, resulting in negative feedback downregulation of thrombin generation. Although the physiologic significance of these reactions remains to be established for humans, substantive insights may be gleaned from murine studies. In mice, exogenously infused SkM and CM can promote hemostasis as they are capable of reducing tail cut bleeding. In a murine myocardial ischemia-reperfusion injury model, exogenously infused CM exacerbates myocardial infarction damage. Studies of human plasmas show that SkM antigen isoforms of different MWs circulate in human plasma, and they can be used to identify three plasma SkM phenotypes. A pilot clinical study showed that one SkM isoform pattern appeared to be linked to isolated pulmonary embolism. These discoveries enable multiple preclinical and clinical studies of SkM and CM, which should provide novel mechanistic insights with potential translational relevance for the roles of CM and SkM in the pathobiology of hemostasis and thrombosis.

Plasma skeletal muscle myosin phenotypes identified by immunoblotting are associated with pulmonary embolism occurrence in young adults

BACKGROUND

Purified skeletal muscle myosin (SkM) binds factor Xa and is procoagulant. The molecular forms of SkM in human plasma have not been characterized.

METHOD

Human plasma SkM heavy chain (HC) isoforms of different molecular weights were detected by a newly developed immunoblotting protocol. In this pilot study, the distribution of SkM HC antigen isoforms in plasmas of healthy subjects and young adult patients with venous thrombosis was analyzed.

RESULTS

Multiple SkM HC antigen bands were detected in human plasmas, corresponding to full-length SkM HC, heavy meromyosin, or the S1 fragment. Plasma immunoblots of healthy subjects displayed three major phenotypes: Type I with two primary bands for full-length SkM and heavy meromyosin, and two lesser bands including S1 fragment (54%); Type II with bands primarily for full-length SkM HC (34%); and Type III with only a band for the S1 fragment (12%). Plasma SkM HC antigen Type II phenotype was associated with an increased occurrence of isolated pulmonary embolism in younger patients, respectively (≤50 years old).

CONCLUSIONS

Three SkM HC antigen phenotypes were identified in human plasma by immunoblotting, and Type II phenotype was correlated with the occurrence of isolated pulmonary embolisms in younger patients.

Cardiac Myosin Promotes Thrombin Generation and Coagulation In Vitro and In Vivo

OBJECTIVE

Cardiac myosin (CM) is structurally similar to skeletal muscle myosin, which has procoagulant activity. Here, we evaluated CM's ex vivo, in vivo, and in vitro activities related to hemostasis and thrombosis. Approach and Results: Perfusion of fresh human blood over CM-coated surfaces caused thrombus formation and fibrin deposition. Addition of CM to blood passing over collagen-coated surfaces enhanced fibrin formation. In a murine ischemia/reperfusion injury model, exogenous CM, when administered intravenously, augmented myocardial infarction and troponin I release. In hemophilia A mice, intravenously administered CM reduced tail-cut-initiated bleeding. These data provide proof of concept for CM's in vivo procoagulant properties. In vitro studies clarified some mechanisms for CM's procoagulant properties. Thrombin generation assays showed that CM, like skeletal muscle myosin, enhanced thrombin generation in human platelet-rich and platelet-poor plasmas and also in mixtures of purified factors Xa, Va, and prothrombin. Binding studies showed that CM, like skeletal muscle myosin, directly binds factor Xa, supporting the concept that the CM surface is a site for prothrombinase assembly. In tPA (tissue-type plasminogen activator)-induced plasma clot lysis assays, CM was antifibrinolytic due to robust CM-dependent thrombin generation that enhanced activation of TAFI (thrombin activatable fibrinolysis inhibitor).

CONCLUSIONS

CM in vitro is procoagulant and prothrombotic. CM in vivo can augment myocardial damage and can be prohemostatic in the presence of bleeding. CM's procoagulant and antifibrinolytic activities likely involve, at least in part, its ability to bind factor Xa and enhance thrombin generation. Future work is needed to clarify CM's pathophysiology and its mechanistic influences on hemostasis or thrombosis.

Diagnosis of acute myocardial infarction: CK-MB versus cTn-T in Indian patients

The comparative diagnostic efficacy of two cardiac markers: CK-MB and cTn-T, has scarcely been investigated in Indian patients of acute myocardial infarction. The present study was conducted for the same objective. The present study comprised of 59 patients. Males were 44 (75%) and females were 15 (25 %). The age of patients ranged from 32-84 years with mean age of 62.8 yrs. The mean age of males and females were 60 and 63 yrs respectively. All patients presented with history of chest pain with a 12 leads ECG proven MI (ST Elevation, discordant T-waves). CK-MB was estimated in peripheral blood samples at 0,24,48 and 72 hours by an autoanalyzer. Following 12 hours of admission bed side Troponin-T test was done employing cTn-T marker kit. Initially (0 hr), in 50% patients CK-MB was elevated. By end of 24 hours all the patients were CKMB positive and peak level was attained at 24 hrs. Then it tended to decline over next 48 hrs. There were no false positive or negative results. The cTn-T test was positive only in 22 % of ECG positive infarctions. However, the cTn-T positive cases were always accompanied by a higher CK-MB levels. A significantly lower cTn-T positive cases in Indian patients can only be attributed to some difference in amino acid sequence of Indian cTn-T and occidental cTn-T. A larger study from other Indian cardiac centers can either substantiate or contradict our results.

Soluble elastin fragments in serum are elevated in acute aortic dissection

OBJECTIVE

We aimed to establish an enzyme-linked immunosorbent assay for measuring soluble elastin fragments (sELAF) in serum and to reveal its usefulness in diagnosing acute aortic dissection (AAD).

METHODS AND RESULTS

An enzyme-linked immunosorbent assay to measure sELAF in serum was developed by using the newly created double monoclonal antibodies, which recognize the different epitopes of human aortic elastin. Twenty-five AAD patients, 50 patients with acute myocardial infarction (AMI), and 474 healthy individuals were enrolled in the study. The sELAF levels from healthy subjects gradually increased with aging. When the cutoff point for positivity was set at the mean+3 SD (ie, 3 SD above the mean in healthy subjects at each age), 16 AAD patients (64.0%) were found be positive, whereas only 1 AMI patient was found to be positive (2.0%). AAD patients with either an open or a partially open pseudolumen were found be 88.9% positive for sELAF, whereas those with its early closure were 0% positive. The difference in the sELAF levels between AAD patients with and without a thrombotic closure of false lumen was significant (60.3+/-15.6 versus 135.4+/-53.2 ng/mL, respectively; P<0.005).

CONCLUSIONS

The sELAF level in serum may be a useful marker for helping in the diagnosis and screening of AAD and may also help to distinguish AAD from AMI.

Biochemical diagnosis of aortic dissection: from bench to bedside

Aortic dissection is an acute cardiovascular disease associated with high mortality and morbidity. Although uncommon, recent studies have shown that the incidence of this catastrophic disease is steadily increasing. Unfortunately, the disease is still not well recognized on clinical presentation due to lack of specific signs and symptoms. As early diagnosis and initial management are critical for survival, we focused on developing a biochemical diagnostic approach for this disease given its meritorious properties in use in the acute clinical situation and additional projected combined use with established imaging modalities. Studies using an assay developed against smooth muscle myosin heavy chain, a protein which is released from the aortic medial smooth muscle cells on insult to the aortic wall, showed promising results for use of this assay in the diagnosis of aortic dissection. The background of this pioneering assay in addition to its clinical use are discussed in this review.

Cardiac myofibrillar proteins: biochemical markers to estimate myocardial injury

Ischaemic heart disease represents the most common of the serious health problems in the contemporary society and acute myocardial infarction (AMI) is the major cause of cardiovascular morbidity and death. The accurate localization and determination of the infarct size and the volume of myocardium at risk at the time of insult is crucial and vital for the choice of treatment. Initially the ischaemic cells are reversibly injured. However, if these changes are not reverted at the earliest, it results in the death of the myocyte. This irreversible myocyte necrosis travels transmurally towards epicardium in the form of a wavefront. A timely intervention during evolving infarct could reduce and delimit the infarct and preserve the left ventricular function. Enzyme analysis and electrocardiography (ECG) along with the clinical history of the patient is still considered to constitute a reliable triad in the diagnosis of myocardial infarction (MI). Efforts have been made to relate infarct size with the serum enzyme level changes without much success. In addition, a number of specialist techniques such as planar radioisotope imaging, single photon emission computed tomography (SPECT), positron emission tomography (PET), Echocardiography, Ventriculography and nuclear magnetic resonance (NMR) imaging have been devised to support diagnosis in the patients who show ambiguous symptoms and ECG findings. However most of these procedures are unavailable to the patients due to economic reasons while others have suffered due to non-availability of ideal radiopharmaceuticals. Major advances have been made in the methods based on immunological techniques to improve the detection and estimation of infarct. These methods are exclusively based upon the production and availability of specific antibodies against intracellular, cardiac specific components.

Perioperative myocardial cell damage assessed by immunoradiometric assay of beta-myosin heavy chain serum levels in patients undergoing coronary bypass surgery

In order to investigate myocardial cell damage in patients undergoing coronary bypass surgery, serum levels of cardiac myosin fragments, using monoclonal antibodies to myosin beta heavy chains, were measured in serial blood samples of 85 patients, 79 male and 6 female, 43-66 years old, after a total of 86 internal mammary artery and 137 saphenous vein graft implants. Eight patients had perioperative acute myocardial infarction (MI), detected by abnormal Q waves and a rise of CK-MB levels. After surgery, beta-myosin levels increased from post-operative day 3 and reached peak values on day 5 in patients without and in day 7 in patients with perioperative MI, in these 8 patients, myosin peak levels were greater as compared to 77 patients without perioperative MI (3452 +/- 1596 vs. 761 +/- 494; P < 0.01). There was a correlation between myosin peak levels and creatine kinase (CK) (r = 0.71; P < 0.05) and CK-MB peak levels (r = 0.74; P < 0.05) only in the patients with perioperative MI, but not in the patients without MI. There was no correlation between myosin peak levels and the times of aortic cross clamping or cardiopulmonary bypass. Peak myosin levels over 75% confidence limits of the mean were found in 23 patients; post-operative low output syndrome occurred in 10 of these 23 patients and in 7 out of 62 patients with peak myosin levels within 75% of the mean (P < 0.005). The increase in beta-myosin heavy chain serum levels observed in almost all patients undergoing coronary surgery suggests lesser perioperative damage of the contractile apparatus, which could be detected by the usual enzyme and ECG criteria. The higher prevalence of low output syndrome in patients with higher increases in myosin levels suggests more pronounced damage to the contractile apparatus in these patients. The higher myosin levels clearly indicate the presence of perioperative MI.

Novel biochemical diagnostic method for aortic dissection. Results of a prospective study using an immunoassay of smooth muscle myosin heavy chain

BACKGROUND

Aortic dissection is one of the most common aortic catastrophes. Although newer diagnostic methods as exemplified by image diagnostic techniques have greatly improved the diagnosis of aortic dissection, the diagnosis is still frequently missed today because the signs and symptoms of the disease are at times obscure. A reliable biochemical diagnostic method for aortic dissection would be beneficial.

METHODS AND RESULTS

A novel biochemical diagnostic method for diagnosis of aortic dissection was developed that uses an immunoassay of monoclonal antibodies to smooth muscle myosin heavy chain. A prospective study was conducted to ascertain the usefulness of the method in the diagnosis of aortic dissection. Twenty-seven patients with aortic dissection admitted within the first 24 hours after onset were enrolled. Serial assay of serum smooth muscle myosin heavy chain showed significant elevations within the first 24 hours after onset of aortic dissection, with levels exceeding 10 ng/mL, with subsequent rapid reductions. The sensitivity of the assay within the first 12 hours was 90% with a specificity of 97%. Analysis of 65 patients with acute myocardial infarction showed that the method could accurately differentiate myocardial infarction from aortic dissection.

CONCLUSIONS

The immunoassay of serum smooth muscle myosin heavy chain is a rapid and reliable biochemical method in the diagnosis of aortic dissection. The potential use of the method in clinical medicine is promising.

A novel immunoassay of smooth muscle myosin heavy chain in serum

We have developed a double monoclonal sandwich enzyme immunoassay to measure smooth muscle myosin heavy chain (MHC). Analytical performance of the assay showed reliable detection of smooth muscle MHC in human sera. The mean of the smooth muscle MHC level in normal human sera was 0.9 +/- 0.9 ng/ml. In sera of patients with aortic dissection, the smooth muscle MHC level sharply elevated at the onset and rapidly decreased to normal levels. Immunoassay of smooth muscle MHC in serum is a promising method for biochemical diagnosis of smooth muscle disorders.

The earliest diagnosis of acute myocardial infarction

Acute myocardial infarction results from the cessation of myocardial blood flow caused by thrombotic occlusion of a coronary artery. Rapid restoration of blood flow to the ischemic myocardium minimizes cardiac damage and improves early and long-term morbidity and mortality. Chest pain is the first symptom of myocardial infarction, but in some patients with silent ischemia, the disease can be diagnosed only in retrospect. In symptomatic patients, myocardial infarction should be accurately and promptly diagnosed so that reperfusion therapy can begin immediately. Electrocardiography is the simplest diagnostic modality. Although regional ST-segment elevation is specific, it is not sensitive. In contrast, new computerized algorithms for electrocardiographic analysis and serial monitoring increase sensitivity without decreasing specificity. In the emergency room, echocardiography is used to diagnose patients with no prior history of coronary artery disease whose electrocardiograms proved nondiagnostic. Time-consuming perfusion nuclear studies are inferior to echocardiography but may nevertheless enable physicians to diagnose myocardial infarction in the emergency room. Although the presence of excess creatine kinase is a sign of myocardial necrosis, its increase is delayed for a few hours after coronary occlusion. Doctors can diagnose myocardial infarction as early as two hours after coronary occlusion with the help of simpler automatic assays of MB-creatine kinase mass that use monoclonal antibodies. Other investigational markers of myocardial necrosis include myoglobin and troponin. Elevation of a circulating protein marker also signifies established necrosis, but physicians hope to achieve reperfusion through therapy before irreversible damage occurs.

Circulating alpha-actin protein in acute myocardial infarction

We used Western-blot analysis to investigate the possible presence in the bloodstream of the contractile protein alpha-actin in 70 patients diagnosed with acute myocardial infarction on the basis of clinical, electrocardiographic and laboratory (creatine kinase and lactate dehydrogenase) criteria. Circulating protein was identified with a monoclonal antibody specific for cardiac alpha-actin. Of the 70 control samples of blood, the immunoblot results were negative for alpha-actin in 98% of the cases. Of the 30 patients with skeletal muscle damage caused by surgery, 26 were negative for circulating alpha-actin. Of the 70 patients with acute myocardial infarction, circulating alpha-actin was found in 67 (95%) as a 43 kDa band in immunoblots; the highest circulating concentrations (0.0580 micrograms/microliters) were found in those with anterior acute myocardial infarction. Circulating alpha-actin was detected in samples taken between 1 and 180 h after the onset of pain, and showed a biphasic pattern of appearance. Our findings for serum alpha-actin, together with the relationship between serum concentrations of this protein and sex (p = 0.001), tobacco use (p = 0.007) and postepisode complications (p = 0.002), should make it possible to gain a deeper understanding of acute myocardial infarction as a clinical entity.

Increase in serum cardiac myosin light chain I associated with elective percutaneous transluminal coronary angioplasty in patients with ischemic heart disease

Changes in serum myosin light chain I (MLCI) due to elective percutaneous transluminal coronary angioplasty (PTCA) were studied after PTCA (0, 8 and 48 hours) in 57 patients with old myocardial infarction (MI group) and 20 patients with angina pectoris (AP group). The AP group showed no increase after PTCA. In contrast, in the MI group there were 16 patients in whom MLCI at 48 hours was increased by 1.0 ng/ml or more (MI1 group) and another group of 41 patients who showed no increase in MLCI (MI2 group). The MI1 group had a significantly higher incidence of (1) non-Q wave myocardial infarction (62.5% vs. 17.1%, p < 0.01), (2) 99% stenosis of a coronary artery (50.0% vs. 12.2%, p < 0.01), and (3) redistribution in a hypoperfusion area found in the delayed image of resting thallium-201 (201Tl) myocardial scintigraphy (85.7% vs. 15.8%, p < 0.01). The left ventricular ejection fraction (LVEF) was significantly improved in the MI1 group, 3 to 4 months later (from 0.49 +/- 0.12 to 0.58 +/- 0.11, p < 0.01), in contrast to the patient of MI2 group who did not show any improvement. The AP group was not considered to have a bulk of myocardium impaired enough to show a release of MLCI due to PTCA-associated transient coronary occlusion. In the MI1 group, however, MLCI was probably released from the chronically under-perfused, but still salvageable, portion of the myocardium. This is consistent with the improvement in LVEF observed 3 to 4 months after the relief of severe coronary stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Circulating myosin light chain I levels after coronary reperfusion: a comparison with myocardial necrosis evaluated from single photon emission computed tomography with pyrophosphate

This study was performed to assess the influence of coronary reperfusion on the serial serum myosin light chain (LC)I levels and to evaluate the relationship between the peak LCI level and the infarct size calculated from single photon emission computed tomography (SPECT) with technetium-99m pyrophosphate (Tc-99m PYP) in 11 patients who underwent coronary reperfusion. Blood was drawn before reperfusion, immediately after reperfusion, and once a day for 14 days, to estimate the time course of serum LCI release. The infarct size estimated by Tc-99m PYP ranged from 7.3 to 62.4 ml. The LCI levels obtained before reperfusion were less than 2.5 ng/ml but those obtained immediately after reperfusion were much higher. The value ranged from 2.7 to 9.7 ng/ml and that expressed as a percentage of peak LCI (% peak LCI) ranged from 19 to 83%. Collateral circulation, reperfusion arrhythmia and the degree of residual stenosis had no influence upon the % peak LCI. The correlation between peak LCI levels and SPECT-determined infarct size was good, with a correlation of 0.76 (p less than 0.01, regression line by least squares method y = 3.31 + 1.53x). Early serum LCI might be influenced by coronary reperfusion but the peak LCI value reflected acute myocardial necrosis in patients who underwent coronary reperfusion.

Electrophoresis of serum isoenzymes and proteins following acute myocardial infarction

The clinical significance of the serum enzymes creatine kinase (CK, EC 2.7.3.2), lactate dehydrogenase (LD, EC 1.1.1.27) and aspartate aminotransferase (EC 2.6.1.1), and the isoenzymes CK 1-3 and LD 1-5, in acute myocardial infarction (AMI) is reviewed. Particular attention is given to electrophoretic analysis of the isoenzymes (and the CK isoforms/subforms) following AMI and thrombolytic therapy. Other protein markers for the monitoring of AMI, including myoglobin and muscle contractile proteins, are also discussed and the potential for the detection of new marker proteins using high-resolution two-dimensional electrophoretic methods is demonstrated. Whilst emphasis is placed upon electrophoretic methods the value of complementary immunoassays is acknowledged in order to maintain a balanced perspective.

Early detection of acute myocardial infarction in patients presenting with chest pain and nondiagnostic ECGs: serial CK-MB sampling in the emergency department

STUDY OBJECTIVES

Patients presenting to the emergency department with chest discomfort are a difficult problem for emergency physicians. Nearly 50% of patients with acute myocardial infarction (AMI) will initially have nondiagnostic ECGs on ED presentation. The purpose of this study was to determine if patients with AMI having nondiagnostic ECGs could be identified using new immunochemical assays for serial CK-MB sampling in the ED.

DESIGN

Chest pain patients, more than 30 years old, with pain not caused by trauma or explained by radiographic findings, were eligible for the study. Serial serum samples were drawn on ED presentation (zero hours) and three hours after presentation, then analyzed for CK-MB using four immunochemical methods and electrophoresis. Standard World Health Organization criteria were used to establish the diagnosis of AMI, including new Q-wave formation or elevation of standard in-hospital serum cardiac enzyme markers.

SETTING

A tertiary cardiac care community hospital.

MEASUREMENTS AND MAIN RESULTS

The serum from 183 patients hospitalized for possible ischemic chest pain was collected and analyzed. Thirty-one of 183 patients (17%) were found to have AMI by standard in-hospital criteria. Sixteen of the 31 patients (52%) with AMI had nondiagnostic ECGs on presentation. Immunochemical determination of serial CK-MB levels provided a sensitive and specific method for detecting AMI in patients within three hours after ED presentation compared with standard electrophoresis. The four immunochemical methods demonstrated a range in sensitivity from 50% to 62.1% on ED presentation versus 92% to 96.7% three hours later. The immunochemical tests demonstrated specificities ranging from 83.0% to 96.4% at three hours, with three of the four tests having specificities of 92% or greater. Electrophoresis had a sensitivity of 34.5% on ED presentation, increasing to 76.9% at three hours, with a specificity of 98.6%.

CONCLUSIONS

Immunochemical CK-MB methods allowed rapid, sensitive detection of AMI in the ED. Early detection of AMI offers many potential advantages to the emergency physician. Early detection of AMI, while the patient is in the ED, could direct disposition of this potentially unstable patient to an intensive care setting. Such information may prevent the ED discharge of patients with AMI having nondiagnostic ECGs. The diagnosis of AMI within a six-hour period after symptom onset may allow thrombolytic therapy to be given to patients with AMI not having diagnostic ECGs. This study served as a pilot trial for a multicenter study of the Emergency Medicine Cardiac Research Group, which is currently ongoing.

Assay of serum cardiac myosin heavy chain fragments in patients with acute myocardial infarction: determination of infarct size and long-term follow-up

To evaluate the correlation between myosin heavy chain release and the necrosis mass, serum levels of myosin heavy chain fragments were determined serially in 55 patients with acute myocardial infarction. Eight of these patients were successfully treated with thrombolytic agents: the others were not treated. The same myosin titration was applied to the sera of 25 dogs with an experimental myocardial infarction. Six of the dogs were successfully treated with thrombolytic agents. The time courses of the myosin concentrations are typical and monophasic for all patients with a noncomplex myocardial infarction. The values for the kinetic parameters of myosin release are comparable to those previously reported. We have now determined that cumulative myosin release significantly correlates with cumulative creatine kinase (CK), CK-MB, and lactate dehydrogenase release, as well as with thallium-201 distribution, as determined for different patient groups. Thrombolytic treatment does not seem to qualitatively upset myosin kinetics. The results obtained in dogs with or without thrombolysis conclusively indicate that myosin release is a quantitative index of the necrosis mass. From a practical point of view, a few serial determinations of serum levels of myosin heavy chains are enough to estimate the necrosed mass in patients with acute myocardial infarction. More generally, serum myosin titration could be useful in detecting any cardiac disturbance involving myocardial injury resulting in membrane leakage of cardiac cells.

Two-dimensional electrophoresis of human serum proteins following acute myocardial infarction

Serum proteins associated with acute myocardial infarction (AMI) have been monitored by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and high resolution two-dimensional electrophoresis (2-DE) under nonreducing conditions. Proteins a, b, c (Mr 13,000; pI6.2, 6.7 and 7.5, respectively) and e(Mr27,000; pI5.2) appear simultaneously approximately 30 h after infarction, reach maximum intensity after 48 h and progressively decline thereafter. Protein d (Mr15,000; pI7-8.5; identified as hemoglobin) sometimes appears within 18 h of infarction. Proteins a-c are not detected in the 2-DE patterns of healthy myocardium, infarcted myocardium, pectoral muscle or tongue, but e is present in all and tentatively identified as myosin light chain. Other myocardial proteins which are either reduced in amount following infarction or more specifically associated with myocardium than pectoral muscle are not detected in the serum of AMI patients. Analysis of unconcentrated urine by SDS-PAGE and silver staining does not reveal proteins specific to AMI.

LC2 involvement in the assembly of skeletal myosin filaments

The assembly of LC2-deficient myosin was studied under conditions where control and LC2-reassociated myosin assemble around the native length of about 1.5 microns. The aim of this work was to determine how loss of LC2 affects the assembly characteristics. The findings of this study can be summarized as follows: (a) LC2-deficient myosin assembles into two populations of filaments, one around 0.5 micron in length and the other around 1 micron in length. This suggests that loss of the LC2 perturbs the length-determining mechanism. (b) The population of filaments around 0.5 micron has a diameter around 14 nm and that around 1 micron a diameter around 22 nm. Neither diameter corresponds to the 18 nm obtained with the control and LC2-reassociated myosins, suggesting that the presence of LC2 may have a role in regulating the side-to-side assembly of the myosin rods. (c) Filaments assembled from LC2-deficient myosin tend to aggregate side-by-side, but not those assembled from control and LC2-reassociated myosin. (d) The presence of MgATP has no effect on the length distribution of LC2-deficient myosin filaments in contrast to the sharpening of the distribution observed with control and reassociated myosin.

Influence of reperfusion on serum concentrations of cytosolic creatine kinase and structural myosin light chains in acute myocardial infarction

The kinetics of cytosolic and structural marker protein release from myocardium were studied in 44 patients with acute myocardial infarction. After intracoronary infusion of streptokinase, there was early recanalization of the infarct-related artery in 8 patients and late recanalization in 18. In 18 patients the infarct-related artery remained occluded. Creatine kinase (CK) level peaked and normalized significantly earlier in patients with early reperfusion than in patients with late reperfusion, and in patients with late reperfusion earlier than in patients with permanent occlusion. Thus, the interval of absolute diagnostic sensitivity of CK depends on early infarct perfusion. In contrast, release of myosin light chains was not significantly changed by recanalization of the infarct-related artery compared with that in nonreperfused myocardial infarction. Thus, in patients with acute myocardial infarction, myosin light chains may be superior to CK as a diagnostic means and for estimation of infarct size.

Cardiac-specific troponin-I radioimmunoassay in the diagnosis of acute myocardial infarction

The cardiac isotype of the myofibrillar contractile protein, troponin-I, is located specifically in the mammalian heart. A sensitive radioimmunoassay has been developed to detect human and nonhuman primate cardiac troponin-I in serum down to 10 ng/ml. Immunochemical cross reactivity with skeletal troponin-I was only 2% and was species nonspecific. Normal patient levels of cardiac troponin-I are about 10 ng/ml. In patients with acute myocardial infarction (n = 32), serum cardiac troponin-I was elevated within 4 to 6 hours, reached a mean peak level of 112 ng/ml (range 20 to 550 ng/ml) at 18 hours, and remained above normal for up to 6 to 8 days following infarction. Peak cardiac troponin-I correlated with peak creatine kinase (CK) MB isoenzyme (r = 0.75). In subjects (n = 34) with skeletal muscle damage (total CK = 338 to 5384 IU/L), cardiac troponin-I levels were not elevated above normal, although CK-MB isoenzyme was elevated in some patients. Cardiac troponin-I levels were normal or slightly elevated in patients with ischemic heart disease and were normal in patients with chest pain of noncardiac origin. Immunoassay of cardiac troponin-I could be a valuable diagnostic aid in the cardiac-specific detection of cell necrosis.

Use of cardiac enzymes in the evaluation of acute chest pain

Diagnosis of acute myocardial infarction (AMI) rests upon detailed clinical evaluation of the patient, careful examination of the ECG, and utilization of cardiac enzymes only in those patients admitted to rule out this diagnosis. Any tendency by physicians to diminish emphasis on either of these first two diagnostic criteria, or to inappropriately utilize cardiac enzymes as a screening device, contributes to costly and inefficient errors in diagnosis and disposition of patients with chest pain. Utilization of recently developed mathematical models may prove effective in enhancing clinical judgment and presenting such errors.

Release of unassembled rat cardiac myosin light chain 1 following the calcium paradox

To determine the intracellular source and release kinetics of myosin light chain 1 immediately following irreversible myocytic injury, we perfused rat hearts in a Langendorff apparatus under control conditions (20 minutes), or during global cellular injury produced by oxygenated, calcium-free perfusion (5 minutes), followed by reperfusion with buffer containing 2.5 mM calcium (15 minutes). Light chain 1 concentration (double antibody radioimmunoassay) and creatine kinase activity were measured in both the coronary effluent and the 140,000 g supernatant extract of perfused ventricular tissue (after homogenization and ultracentrifugation). Calcium reperfusion caused the rapid release of both light chain 1 and creatine kinase activity (peak light chain 1 = 1.09 +/- 0.19 micrograms/g; peak creatine kinase = 74.9 +/- 10.7 IU/ g at 1 minute, mean +/- SD, n = 3); 28.5 +/- 13.5% of total light chain 1 and 86.5 +/- 0.6% of total creatine kinase activity were depleted from the tissue extract during the 15-minute reperfusion. No light chain 1 or creatine kinase was detected in the effluents of control-perfused hearts. Dodecyl sulfate polyacrylamide gel electrophoresis and immunodetection with specific antibody to myosin heavy chain and light chain 1 showed that the effluent light chain 1 was of similar molecular weight (mol wt = 27,000) to the subunit bound to myofibrils. In addition, light chain 1 was released in the absence of myosin heavy chain. Thus, a small soluble pool of unassembled myosin light chain 1 subunits exists in the cytoplasm of cardiac myocytes that is released from irreversibly injured cells. This pool demonstrates initial washout kinetics similar to creatine kinase.

Levels of ventricular myosin fragments in human sera after myocardial infarction, determined with monoclonal antibodies to myosin heavy chains

Serum levels of ventricular myosin heavy chains were quantitated in patients with acute myocardial infarction using a competitive radioimmunoassay involving monoclonal antibodies to the b-type myosin heavy chains of a human ventricle. Among the seven antibodies selected for their higher affinity for ventricular myosin heavy chains, only four antibodies detected significant and variable myosin amounts in the serum samples of nineteen patients with acute myocardial infarction; the same antibodies occasionally detected, if at all, low myosin amounts in the sera of patients with no clinical sign of myocardial infarction, and no myosin in the serum of the healthy control subjects. The peak levels of myosin release were observed 4.6 +/- 0.5 days (n = 13, P less than 0.01) after myocardial infarction and correlated rather well with the measured creatine kinase peak levels (the correlation coefficients were between 0.75 and 0.81, P less than 0.01, depending on the monoclonal antibody used for myosin determination). The time courses of myosin release varied according to the complexity of the heart attack observed. It was concluded that the titration of serum myosin was probably of little clinical value for therapeutic intervention during the acute phase of myocardial infarction; it could, however be an effective tool for retroactive detection of an infarct and for late estimation of infarct size.

Diagnosis of acute myocardial infarction by detection of circulating cardiac myosin light chains

A radioimmunoassay for human cardiac myosin light chains (CM-LC) was developed and evaluated as a selective diagnostic test for acute myocardial infarction (AMI). The assay had a sensitivity of 1.0 ng/ml (+/- 2 standard deviations) in serum. Eighty-three patients with confirmed AMI all showed an elevated plasma concentration of CM-LC at some time during the course of their illness. Of 9 patients from whom early blood samples were obtained, 7 had diagnostic concentrations within 6 hours from the onset of chest pain. Only 2 had an elevated total creatine kinase level at this time. CM-LC concentrations peaked on days 2 to 4, but remained elevated in patients with large AMIs for more than 1 week. In preinfarction syndrome, 8 of 15 patients had elevated CM-LC levels at least once. Of 15 patients with stable angina pectoris, only 1 patient, who had congestive heart failure, showed elevated light chain levels. CM-LC levels were not detectable by this method in the sera of healthy persons (n = 72), patients with recent intramuscular injection (n = 3), or those with a variety of systemic illnesses (n = 14). In initial studies using an antiserum having 25% cross-reactivity between cardiac and skeletal muscle myosin light chains, 3 patients who had extensive skeletal muscle damage appeared to have elevated concentrations. Patients with this finding have not yet been examined with a more specific antiserum (8% cross-reactivity).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of steroid treatment on release of cardiac myosin light chain II in acute myocardial infarction in dogs

The effect of methylprednisolone sodium succinate (MP) on release of myosin light chain II (LCII) from the myocardium was studied in experimental myocardial infarction (MI). Acute MI was produced in conscious, closed-chest dogs by ligating the left anterior descending coronary artery beyond the first diagonal branch. MP, 30 mg/kg, was administered intravenously just before and 24 hours after MI. After MI, LCII levels in the serum were determined serially up to 240 hours. MI size was determined histologically 10 days after MI. In the MP group, LCII levels in the serum within 72 hours were lower than in the control, and cumulative LCII release for 3 days decreased from 530 +/- 159 to 310 +/- 101 ng/ml (mean +/- standard deviation) (p less than 0.001). However, the peak LCII level appeared later (control vs MP, 63 +/- 27 vs 122 +/- 25 hours, p less than 0.001), and the peak LCII level and cumulative LCII release for 10 days were not decreased by MP treatment. MI size also was not reduced by MP (11.0 +/- 4.4% vs 11.8% +/- 4.5% of the left ventricle, difference not significant). Since the rate of disappearance of LCII is rapid and was not affected by MP, these results suggest that MP treatment early after acute MI delays breakdown of myosin filaments, but cannot prevent it.

Serum levels of acute phase and cardiac proteins after myocardial infarction, surgery, and infection

C-reactive protein and four other acute phase reactant proteins of non-cardiac, origin (orosomucoid, alpha 1- antitrypsin, heptoglobin, and alpha 2- macroglobulin) were studied serially by laser immunonephelometric assay in sera from 17 patients with myocardial infarction. A similar comparison was made in 57 patients undergoing surgery and 72 patients with acute infection. C-reactive protein was consistently the most sensitive acute phase reactant in all three conditions. After myocardial infarction, a raised serum C-reactive protein level was found on admission in four patients before a rise in creatine kinase MB isoenzyme (CK MB). The peak C-reactive protein level was reached on the third post-infarct day and it then declined over seven days with a half-life similar to myocardial tropomyosin. Serial monitoring of serum C-reactive protein, in parallel with cardiac proteins of short half-life (CK MB) and long half-life (tropomyosin), provides maximal information for diagnosis and for detecting post-infarct complications.

Increased specificity in human cardiac-myosin radioimmunoassay utilizing two monoclonal antibodies in a double sandwich assay

In some instances, even the increased resolution that may be afforded in immunoassays by the use of monoclonal antibodies fails to effect resolution among molecules that share many epitopes. An immunoradiometric assay that simultaneously measured two different epitopes on the same molecule was devised to overcome this difficulty in the differentiation between cardiac- and skeletal-myosin light chains. Three monoclonal antibodies were examined that were 100% (1C5), 25% (2B9) and 17% (4F10) cross reactive, respectively, between the two antigens. One antibody of the pair to be studied was immobilized to cyanogen bromide-activated Sepharose 4B while the other was iodinated with 125I using the lactoperoxidase method. The antigen was mixed with the immobilized antibody, the labeled antibody was added and the precipitate then washed and counted in a gamma counter. When both antibodies of the pair to be studied (immobilized and labeled) were the same (2B9), no radioactivity above background was bound to the precipitate, indicating that the second antibody could not bind to an already occupied epitope. When two different antibodies were employed, the specificity of the assay increased over that of a single antibody. The cross reactivity of a pair approximated the product of the cross reactivities of the individual antibodies. Thus, 1C5 and 2B9 were 25% cross reactive together, 1C5 and 4F10 17% cross reactive, and 2B9 and 4F10 4.3% cross reactive.

Detection of serum cardiac myosin light chains in acute experimental myocardial infarction: radioimmunoassay of cardiac myosin light chains

To develop a more specific plasma test for myocardial infarction, antibodies specific for cardiac myosin light chains (CM-LC) were elicited that showed less than 3% cross-reactivity with skeletal muscle light chains. These antibodies were used to develop a radioimmunoassay for CM-LC that had a sensitivity of 20 ng (+/- 4 SD; P less than 0.001). Normal dog plasma showed no measurable concentrations of CM-LC (n = 6). Plasma samples from 10 dogs with experimental myocardial infarction produced by persistent left anterior descending coronary artery (LAD) occlusion were obtained at 0, 2, 4, 6, 24, 48 and 72 hours. CM-LC were first detectable in all 10 animals 6 hours after occlusion (97.98 +/- 14 ng/ml [mean +/- SEM]; P less than 0.001). Maximal CM-LC levels were usually obtained between 24 and 48 hours. Sham-operated open chest dogs (0--48 hours, n = 3) showed no measurable CM-LC in the plasma samples. Another group of 10 dogs were subjected to 5 hours of LAD occlusion, followed by reperfusion. In four dogs, CM-LC were detectable as early as 1 hour after reperfusion (81.88 +/- 37.75 ng/ml serum). Sera from all 10 dogs showed elevated levels of CM-LC (199.75 +/- 24.0 ng/ml) by 24 hours. Peak CM-LC concentrations were obtained in five dogs at 24 hours (247.0 +/- 35.28 ng/ml) and in another dog at 120 hours (245 ng/ml). Histochemical infarct size was determined to be 0.5--10% of the left ventricular mass at seven days by triphenyltetrazolium chloride staining. The specificity and sensitivity of this radioimmunoassay for detection of CM-LC, unique proteins to the heart, may be valuable in the diagnosis of myocardial infarction.