Clinical assessment of specific enzyme immunoassay for the human cardiac myosin light chain II (MLC II) with use of monoclonal antibodies

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.

Candidate-based proteomics in the search for biomarkers of cardiovascular disease

The key concept of proteomics (looking at many proteins at once) opens new avenues in the search for clinically useful biomarkers of disease, treatment response and ageing. As the number of proteins that can be detected in plasma or serum (the primary clinical diagnostic samples) increases towards 1000, a paradoxical decline has occurred in the number of new protein markers approved for diagnostic use in clinical laboratories. This review explores the limitations of current proteomics protein discovery platforms, and proposes an alternative approach, applicable to a range of biological/physiological problems, in which quantitative mass spectrometric methods developed for analytical chemistry are employed to measure limited sets of candidate markers in large sets of clinical samples. A set of 177 candidate biomarker proteins with reported associations to cardiovascular disease and stroke are presented as a starting point for such a 'directed proteomics' approach.

Biochemical markers of myocardial damage

OBJECTIVE

To assess various biochemical markers of myocardial damage.

METHODS AND RESULTS

Before routinely using any test as a biochemical marker of myocardial damage, the published evidence for its diagnostic utility must be critically assessed. Such assessment includes receiver operator curve (ROC) curve analyses, confidence interval estimates of claimed sensitivity and specificity values, and the effects of testing in serial and parallel modes. It is also necessary to establish the test's rule-in (high specificity) and rule-out (high sensitivity) decision thresholds that may vary with time after the onset of symptoms. The spectrum of ischemic heart disease includes acute (sudden death, non-Q- and Q-wave infarctions) and chronic (stable, unstable, and variant angina) conditions. Biochemical markers of myocardial damage are of most value in the diagnosis of acute ischemic heart disease, although increasingly some of these markers are being found to possess a prognostic value in chronic ischemic heart disease. The markers of enzymatic activity include aspartate aminotransferase, creatine kinase (together with isoenzymes and isoforms), and lactate dehydrogenase and isoenzymes. Creatine kinase isoenzyme-2 may also be measured immunologically, and this type of assay is in increasing use both because of its speed and because its blood levels rise earlier than the corresponding activities. The commercially available nonenzymatic markers are myoglobin and troponin T; troponin I is expected to become available in late 1995. While myoglobin is a nonspecific indicator of myocardial damage, its diagnostic value is due to its early appearance in blood. Troponin T is more cardiac specific, but the published data appears to suggest that the cardiac specificity of troponin I is superior. Troponin levels become abnormal at about the same time after the onset of symptoms as mass assays of creatine kinase isoenzyme-2; therefore, they are not useful as early markers of myocardial damage.

CONCLUSION

The availability of these nonenzymatic markers of myocardial damage must force a reassessment of the continued use of the enzymatic markers. Are they necessary, and if so, which ones should be retained?