Myocardial uptake of 99mTc-annexin-V and 111In-antimyosin-antibodies after ischemia-reperfusion in rats

Abstract

Objectives: Phosphatidylserin exposure on cell surfaces occurs early during apoptosis and is detected in vivo by using (99m)Tc-annexin-V (ANX). Cardiomyocyte membrane disruption is detected in vivo by using (111)In-antimyosin-antibodies (AM). We aimed to determine if ANX and AM allow evaluation of the time-course of these two distinct cell death events after myocardial ischemia-reperfusion.

Methods: Coronary tying (20 min) followed by reperfusion (IR) was performed in 31 rats. Twelve of the rats were injected with ANX, 11 with AM, and eight with both tracers. Myocardial uptake of tracers was studied 1-2 h, 4 h, or 24 h after IR by scintigraphy (ANX, n = 14) and autoradiography (all cases), and compared to histology and Apostain staining.

Results: Scintigraphy was positive in all rats 2 h after IR and in three of five rats at 24 h. On autoradiography, ANX activity was intense in myocardial lesions as early as 1 h post-IR, whereas AM activity was mild at 2 h then increased at 4 h post-IR. ANX and AM uptakes evolved from mid-myocardium to endocardial and epicardial regions from 2 h to 24 h post-IR. Apostain staining was significant in myocardial lesions (p < 10(6) compared to six sham-operated rats). On histology, myocardial lesion was characterized by interstitial oedema, myocytes necrosis, and dramatic thinning at 24 h.

Conclusion: These data suggest that ANX and AM allow temporal and regional evaluations of PS exposure and membrane disruption, respectively, during myocytes death after 20-min myocardial ischemia followed by reperfusion. Also, (i) apoptosis starts very early in injured myocardium, (ii) myocyte necrosis occurs later (3-4 h post-reperfusion), and (iii) most dead cells are removed from mid-myocardium between 6 h and 24 h after reperfusion.