Susann Eriksson

Sensitive protein detection via triple-binder proximity ligation assays

The detection of weakly expressed proteins and protein complexes in biological samples represents a fundamental challenge. We have developed a new proximity-ligation strategy named 3PLA that uses three recognition events for the highly specific and sensitive detection of as little as a hundred molecules of the vascular endothelial growth factor (VEGF), the biomarkers troponin I, and prostate-specific antigen (PSA) alone or in complex with an inhibitor—demonstrating the versatility of 3PLA.

Autoantibodies against Cardiac Troponins

To the Editor: Cardiac troponins are preferred markers of tissue injury in acute coronary syndromes. Their specificity and the fact that only very minute amounts or none are normally found in the c...

Negative Interference in Cardiac Troponin I Immunoassays from a Frequently Occurring Serum and Plasma Component

BACKGROUND Cardiac troponin I (cTnI) is a sensitive marker of cardiac injury, but cTnI assays, like other immunoassays, are susceptible to interferences. We evaluated the presence of interfering substances by measuring the recovery of cTnI added to samples from volunteers and from patients with acute coronary syndromes (ACS). METHODS We added a ternary complex of human cardiac troponin (30-500 microg/L) or cTnI from serum to samples from healthy volunteers and ACS patients. We measured cTnI with a two-site sandwich time-resolved immunofluorometric assay using two antibodies against epitopes in the central stable part of cTnI. We also analyzed 108 heparin-plasma samples from 16 ACS patients with this assay, with an assay based on four antibodies, and with two commercial cTnI assays, AxSYM and ACS:180. RESULTS In samples from both healthy persons and ACS patients, recoveries for our assay were 1-167% (range). Recoveries were increased by addition of an antibody with an epitope in the N-terminal region of cTnI to the solid phase and an antibody with an epitope in the C-terminal region as a second detection antibody. In 2 of 16 patients with ACS, normal cTnI concentrations found when measured with the original assay demonstrated clinically abnormal (up to 10-fold higher) results with the additional N- and C-terminal antibodies in the early phase of infarction. Both commercial cTnI assays also demonstrated clinically misleading, falsely low cTnI concentrations. CONCLUSIONS Some yet unidentified, variable component, present in the blood from healthy volunteers and ACS patients, interferes with the binding of antibodies against epitopes in the central part of cTnI used in two commercial assays. Our approach to supplement the mid-fragment cTnI antibodies with antibodies in the N- and C-terminal parts of the molecule in an experimental assay represents a step in resolving this interferent.

Release Patterns of Pregnancy Associated Plasma Protein A (PAPP-A) in Patients with Acute Coronary Syndromes

Objective : Pregnancy associated plasma protein A (PAPP-A) has recently been shown to be associated with acute coronary syndromes (ACS). The goal of this study was to investigate its release patterns in patients with ACS. Design : PAPP-A concentrations in plasma samples serially collected after admissions from 15 patients with ACS were measured. The levels of PAPP-A were compared with a reference range determined from 80 normal subjects. The associations between PAPP-A and myoglobin (Mb), C-reactive protein (CRP), fatty-acid-binding protein (FABP) and creatine kinase MB (CK-MB) were determined. Results : Various release patterns were observed with 2-10-fold changes of PAPP-A in the different patients. Increases in PAPP-A levels above the reference range could appear early at 2 h or late at 30 h after onset of chest pain. Only in 4 of the 15 cases were significantly elevated PAPP-A levels detected before 6 h after onset. Elevations early after admission showed rapid decline whereas later elevations were more persistent. No associations between PAPP-A and Mb, CRP, FABP and CK-MB were found. However, a weak but significant association to cardiac troponin I (cTn I) was found. Conclusion : PAPP-A is an additional marker for ACS, but does not seem to be a useful early marker for acute myocardial infarction (AMI). The possible clinical utility of PAPP-A calls for extensive studies of chest pain patients using serial sampling combined with short- and long-term outcome studies.

Early markers of myocardial injury: cTnI is enough☆

BACKGROUND We compared the early diagnostic and prognostic performance of a highly sensitive cardiac troponin I (cTnI) assay with heart-type fatty acid binding protein (H-FABP), in the early hours of acute coronary syndrome. METHODS Serum samples of 293 patients were studied using the Abbott Architect cTnI assay and the H-FABP assay. Special attention was paid to the diagnostic and prognostic value of admission blood samples taken <24 h after symptom onset. The prognostic endpoint was total mortality and reinfarction at 6 months. RESULTS To detect forthcoming myocardial injury, admission samples gave receiver operating curve (ROC) areas (AUC) of 0.908 for cTnI and 0.855 for H-FABP (p=0.068) when the delay from symptom onset was <6 h (60.4% of all patients). When the delay was 6-24 h, the corresponding AUC values were 0.995 for cTnI and 0.849 for H-FABP (p=0.002). In multivariate analysis cTnI but not H-FABP predicted adverse events in all 293 patients (RR 3.02, 95% CI 1.62-5.63) and in those with delays <6 h (RR 2.92, 95% CI 1.47-5.81). CONCLUSION In the era of highly sensitive cTnI assays, H-FABP appears to give no additional information even in patients who present within the first 6 h after acute MI.

Autoantibodies to Cardiac Troponin Associate with Higher Initial Concentrations and Longer Release of Troponin I in Acute Coronary Syndrome Patients

BACKGROUND Cardiac troponin (cTn) is an established marker of myocardial infarction. Pronounced heterogeneity and the minute amounts released into the circulation constitute significant challenges for cTn detection. Recently, autoantibody formation to cTn was shown to be common and to interfere with immunoassay performance. In this study, we investigated cTn autoantibodies and cardiac troponin I (cTnI) in acute coronary syndrome (ACS) patients over a 1-year period after the index event. METHODS We used a second-generation cTnI assay designed to reduce the interference of cTn autoantibodies. The assay for cTn autoantibodies used 2 anti-cTnI antibodies to capture the ternary cTnI-complex, enabling unrestricted binding of the autoantibodies, which were detected with a labeled antihuman IgG antibody. We analyzed serum samples from 81 non-ST-elevation ACS patients taken at admission and after 1 week and 3 and 12 months. RESULTS We found 14 cTn autoantibody-positive patients (21%) among the 67 cTnI-positive and none among the 14 cTnI-negative patients. Nine were autoantibody-positive at admission, and 5 became positive at 1 week. Autoantibody signals significantly increased in the 1-week and 3-month samples. At all time points, cTnI was significantly increased in the autoantibody-positive group relative to the negative group. Persistent cTnI elevations at 3 and 12 months were seen in the patients already autoantibody positive at admission. CONCLUSIONS During ACS, patients with cTn autoantibodies have higher cTnI release and therefore larger myocardial damage than patients without autoantibodies. Their cTnI release also lasts longer, at least months. The possible prognostic impact of these observations must be evaluated in larger clinical cohorts.

Improved early risk stratification and diagnosis of myocardial infarction, using a novel troponin I assay concept

Background  We evaluated the clinical performance of a novel cardiac troponin I (cTnI) assay specifically designed to improve the very early risk stratification in acute coronary syndromes.

Present and Future Biochemical Markers for Detection of Acute Coronary Syndrome

The use of biochemical markers in the diagnosis and management of patients with acute coronary syndrome has increased continually in recent decades. The development of highly sensitive and cardiac-specific troponin assays has changed the view on diagnosis of myocardial infarction and also extended the role of biochemical markers of necrosis into risk stratification and guidance for treatment. The consensus definition of myocardial infarction places increased emphasis on cardiac marker testing, with cardiac troponin replacing creatine kinase MB as the “gold standard” for diagnosis of myocardial infarction. Along with advances in the use of more cardiac-specific markers of myocardial necrosis, biochemical markers that are involved in the progression of atherosclerotic plaques to the vulnerable state or that signal the presence of vulnerable plaques have recently been identified. These markers have variable abilities to predict the risk of an individual for acute coronary syndrome. The aim of this review is to provide an overview of the well-established markers of myocardial necrosis, with a special focus on cardiac troponin I, together with a summary of some of the potential future markers of inflammation, plaque instability, and ischemia.

Development of troponin autoantibodies in experimental coxsackievirus B3 myocarditis

Background  Autoantibodies against various endogenous proteins are found in myocarditis. Troponin autoantibodies are detected in patients with chronic dilated cardiomyopathy, but their presence in myocarditis remains unknown. We set out to study the presence of troponin autoantibodies in experimental viral myocarditis.