99mTc-annexin V and 111In-antimyosin antibody uptake in experimental myocardial infarction in rats

Purpose: Tc-annexin V (ANX) allows scintigraphic detection of apoptotic cells via specific binding to exposed phosphatidylserine. In myocardial infarction, apoptosis of myocytes is variable and depends especially on the presence or absence of coronary reperfusion. In this study, ANX uptake in non-reperfused experimental myocardial infarcts was compared with uptake of a marker of myocyte necrosis (In-111-antimyosin antibodies, AM) and an immunohistochemical marker of apoptosis (Apostain). Methods: The left anterior coronary artery was ligated in 47 Wistar rats, which were then injected with ANX (n=20), AM (n=21) or both (n=6). Myocardial uptake of ANX and AM was determined at 2 h (n=14), 4 h (n=14) and 24 h (n=19) after coronary ligation (CL), by quantitative autoradiography with (n=23) or without (n=24) gamma imaging. Heart-to-lung ratios (HLRs) and infarct-to-remote myocardium activity ratios (INRs) were calculated on the scintigrams and autoradiograms respectively. Cardiac sections were stained with haematoxylin-eosin and Apostain. The above studies were repeated in 12 normal rats. Results: All rats with CL showed increased ANX and AM uptake in cardiac areas on scintigrams 24 h after CL, with HLRs higher than in controls: 3.1 +/- 0.6 versus 1.5 +/- 0.3 (p=0.001) for ANX and 1.99 +/- 0.44 versus 1.01 +/- 0.05 (p < 0.0005) for AM. Autoradiography showed intense ANX and AM uptake in infarcts, with comparable topography and INRs at 2 h, 4 h and 24 h after CL (4.6 +/- 0.9 versus 5.0 +/- 1.8 at 24 h), while Apostain staining was very low (0.06 +/- 0.06% of cells). Conclusion: In this model of persistent CL, we observed increased ANX uptake in injured myocardium, comparable in intensity, topography and kinetics to that of AM. There was only minimal Apostain staining in the same areas.