Uptake of radioiodinated cardiac specific troponin-I antibodies in myocardial infarction

Study objective – To examine the potential diagnostic value of the cardiac myofibrillar protein troponin-I as a target for radiolabelled antibodies in detecting heart damage, the uptake of 131I labelled polyclonal cardiac troponin-I Fab was investigated in necrotic myocardial cells in canine myocardial infarction. Design – Cardiac specific troponin-I Fab was prepared by immunoaffinity chromatography and injected 5 h after coronary artery ligation. Whole body gamma camera scintigraphic images were taken after the injection, and heart slices were examined for the presence of labelled antibody. Subjects – Adult dogs of either sex (n=6) were used. Measurements and main results – Scintigraphic whole body images at 24 and 40 h after troponin-I Fab injection showed increased 131I localisation over the apical region of the heart which corresponded to the infarcted areas. Localisation in infarcted tissue was confirmed in isolated heart and histochemically stained heart slice images. Uptake of 131I Fab was up to 24 times greater in necrotic than in normal myocardium and was inversely related to regional blood flow as determined by 141cerium microsphere distribution. Confirmation that 131I Fab uptake was due to direct binding to troponin-I in necrotic cells was obtained by coinjection of non-immune 125I labelled Fab. Conclusions – Results indicate that troponin-I could act as a suitable target for detecting myocardial necrosis.