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

Abstract

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.