Full-Size Cardiac Troponin I and Its Proteolytic Fragments in Blood of Patients with Acute Myocardial Infarction: Antibody Selection for Assay Development

Abstract BACKGROUND In the blood of patients with acute myocardial infarction (AMI), cardiac troponin I (cTnI) presents as an intact molecule with a repertoire of proteolytic fragments. The degradation of cTnI might negatively influence its precise immunodetection. In this study we identified cTnI fragments and calculated their ratio in the blood of patients at different times after AMI to discriminate the most stable part(s) of cTnI. METHODS Serial serum samples were collected from AMI patients within 1 to 36 h after the onset of chest pain both before and after stenting. cTnI and its fragments were immunoextracted from serum samples and analyzed by Western blotting with monoclonal antibodies (mAbs) specific to the different epitopes of cTnI and by 2 in-house immunoassays specific to the central and terminal portions of cTnI. RESULTS Intact cTnI and its 11 major fragments were detected in blood of AMI patients. The ratio of the fragments in serial samples did not show large changes in the period 1–36 h after AMI. mAbs specific to the epitopes located approximately between amino acid residues (aar) 34 and 126 stained all extracted cTnI. mAbs specific to aar 23–36 and 126–196 recognized approximately 80% to 90% (by abundance) of cTnI. CONCLUSIONS In addition to mAbs specific to the central part of cTnI (approximately aar 34–126), antibodies specific to the adjacent epitopes (approximately aar 23–36 and 126–196) could be used in assays because they recognize ≥80% of cTnI in patients' blood samples within the first 36 h after AMI.

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Faculty Opinions recommendation of One-hour rule-in and rule-out of acute myocardial infarction using high-sensitivity cardiac troponin I.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.725420089.793507697 ◽

2015 ◽

Author(s):

Patrick Ray

Keyword(s):

Myocardial Infarction ◽

Acute Myocardial Infarction ◽

Cardiac Troponin ◽

Troponin I ◽

High Sensitivity ◽

Cardiac Troponin I ◽

Rule Out

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Abstract 2425: Absence of Auto-Antibodies against Cardiac Troponin I Predicts Improvement of Left Ventricular Function after Acute Myocardial Infarction

Circulation ◽

10.1161/circ.118.suppl_18.s_724-b ◽

2008 ◽

Vol 118 (suppl_18) ◽

Author(s):

Florian Leuschner ◽

Jin Li ◽

Stefan Göser ◽

Lars Reinhardt ◽

Renate Öttl ◽

...

Keyword(s):

Myocardial Infarction ◽

Acute Myocardial Infarction ◽

Stroke Volume ◽

Antibody Titer ◽

Cardiac Troponin ◽

Troponin I ◽

Cardiac Troponin I ◽

Igg Antibody ◽

Follow Up Study

Application of antibodies against cardiac troponin I (cTnI-Ab) can induce dilation and dysfunction of the heart in mice. Recently, we demonstrated that immunization with cTnI induces inflammation and fibrosis in myocardium of mice. Others have shown that autoanti-bodies to cTnI are present in patients with acute coronary syndrome. But little is known about the clinical relevance of detected cTnI-Ab. First, anti-cTnI and anti-cTnT antibody titers were measured in sera from 272 patients with dilated- (DCM) and 185 with ischemic- (ICM) cardiomyopathy. Secondly, 108 patients with acute myocardial infarction (AMI) were included for a follow-up study. Heart characteristics were determined by magnetic resonance imaging 4 days and 6 –9 months after AMI. Altogether, in 7,0% of patients with DCM and in 9,2% with ICM an anti-cTnI IgG antibody titer ≥1:160 was measured. In contrast, only in 1,7% of patients with DCM and in 0,5% with ICM an anti-cTnT IgG antibody titer ≥1:160 was detected. Ten out of 108 patients included in the follow-up study were tested positive for cTnI-Ab with IgG Ab titers ≥1:160. TnI-Ab negative patients showed a significant increase in LVEF and stroke volume 6 –9 months after AMI. In contrast, there was no significant increase in LVEF and stroke volume in TnI-Ab positive patients. We demonstrate for the first time that the prevalence of cTnI-Abs in patients with AMI has an impact on the improvement of the LVEF over a study period of 6 –9 months.

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Acceptable Analytical Variation May Exceed High-Sensitivity Cardiac Troponin I Cutoffs in Early Rule-Out and Rule-In Acute Myocardial Infarction Algorithms

Clinical Chemistry ◽

10.1373/clinchem.2016.255448 ◽

2016 ◽

Vol 62 (6) ◽

pp. 887-889 ◽

Cited By ~ 36

Author(s):

Peter A Kavsak ◽

Andrew C Don-Wauchope ◽

Stephen A Hill ◽

Andrew Worster

Keyword(s):

Myocardial Infarction ◽

Acute Myocardial Infarction ◽

Cardiac Troponin ◽

Troponin I ◽

High Sensitivity ◽

Cardiac Troponin I ◽

Analytical Variation ◽

Rule Out

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Characterization of cardiac troponin subunit release into serum after acute myocardial infarction and comparison of assays for troponin T and I

Clinical Chemistry ◽

10.1093/clinchem/44.6.1198 ◽

1998 ◽

Vol 44 (6) ◽

pp. 1198-1208 ◽

Cited By ~ 88

Author(s):

Alan H B Wu ◽

Yue-Jin Feng ◽

Robert Moore ◽

Fred S Apple ◽

Paul H McPherson ◽

...

Keyword(s):

Myocardial Infarction ◽

Acute Myocardial Infarction ◽

Cardiac Troponin ◽

Troponin I ◽

Troponin T ◽

Cross Reactivity ◽

Binary Complex ◽

Serum Samples ◽

Binary And Ternary Complexes ◽

The Cross

Abstract We examined the release of cardiac troponin T (cTnT) and I (cTnI) into the blood of patients after acute myocardial infarction (AMI). Three postAMI serum samples were applied in separate analytical runs onto a calibrated gel filtration column (Sephacryl S-200), and the proteins were separated by molecular weight. Using commercial cTnT and cTnI assays measured on collected fractions, we found that troponin was released into blood as a ternary complex of cTnT-I-C, a binary complex of cTnI-C, and free cTnT, with no free cTnI within the limits of the analytical methodologies. The serum samples were also examined after incubation with EDTA and heparin. EDTA broke up troponin complexes into individual subunits, whereas heparin had no effect on the assays tested. We added free cTnC subunits to 24 AMI serum samples and found no marked increase in the total cTnI concentrations, using an immunoassay that gave higher values for the cTnI-C complex than free cTnI. To characterize the cross-reactivity of cTnT and cTnI assays, purified troponin standards in nine different forms were prepared, added to serum and plasma pools, and tested in nine quantitative commercial and pre-market assays for cTnI and one approved assay for cTnT. All nine cTnI assays recognized each of the troponin I forms (complexed and free). In five of these assays, the relative responses for cTnI were nearly equimolar. For the remainder, the response was substantially greater for complexed cTnI than for free cTnI. Moreover, there was a substantial difference in the absolute concentration of results between cTnI assays. The commercial cTnT assay recognized binary and ternary complexes of troponin on a near equimolar basis. We conclude that all assays are useful for detection of cardiac injury. However, there are differences in absolute cTnI results due to a lack of mass standardization and heterogeneity in the cross-reactivities of antibodies to various troponin I forms.

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Comparable detection of acute myocardial infarction by creatine kinase MB isoenzyme and cardiac troponin I

Clinical Chemistry ◽

10.1093/clinchem/40.7.1291 ◽

1994 ◽

Vol 40 (7) ◽

pp. 1291-1295 ◽

Cited By ~ 197

Author(s):

J E Adams ◽

K B Schechtman ◽

Y Landt ◽

J H Ladenson ◽

A S Jaffe

Keyword(s):

Myocardial Infarction ◽

Acute Myocardial Infarction ◽

Creatine Kinase ◽

Cardiac Troponin ◽

Troponin I ◽

Characteristic Curve ◽

Cardiac Injury ◽

Cardiac Troponin I ◽

Creatine Kinase Mb ◽

Coronary Care

Abstract Although measurement of cardiac troponin I (cTnI) is, in some situations, more specific for detection of cardiac injury than is measurement of the MB isoenzyme of creatine kinase (MBCK), its sensitivity and specificity relative to MBCK for detection of myocardial infarction has not been established. Accordingly, we studied prospectively 199 consecutive patients admitted to the coronary care unit. Values of MBCK and cTnI mass were determined in all samples. Of the 188 patients admitted with a suspicion of acute myocardial ischemia, 89 were diagnosed as having an acute myocardial infarction on the basis of the patterns of MBCK values. Eighty-six of these patients also had increased cTnI (concordance, 96.6%); three did not. Of the patients diagnosed as without infarction, five with unstable angina and symptoms in the day(s) prior to admission had increased cTnI, for a cTnI specificity of 94.9%. Receiver operating characteristic curve analysis indicated that cTnI and MBCK had statistically indistinguishable diagnostic accuracies for the detection of acute myocardial infarction.

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