Detection of myocardial ischemic memory using 99mTc-fucoidan: preclinical validation

Objectives The retrospective identification of a remote acute coronary syndrome is a diagnostic challenge. Because adhesion molecules such as selectins persist on the endothelial surface after ischemia has resolved, they represent a tissue imprint of the prior ischemic event, referred to as ischemic memory. The aim of this study was to assess whether 99mTc-fucoidan SPECT, a P-and E-selectin targeting agent, allows to detect myocardial ischemic memory in a rat model of ischemia-reperfusion.

Methods Transient myocardial ischemia was induced in male Wistar rats by coronary ligation. Ischemia duration ranged from 5 min to 20 min and reperfusion duration ranged from 2 to 24 hours. SPECT/CT acquisitions were performed 2 hours after intravenous injection of 70 MBq 99mTc-Fucoidan. Images were visually assessed for the presence of a focal tracer uptake in the cardiac area, and quantified by use of the heart-to-bloodpool ratio (HBR). The animals were then sacrificed and the heart explanted, frozen and cut in slices for autoradiography (quantified using the uptake ratio between the area at risk and remote myocardium) and histology/immunostaining (P-/E-selectin expression).

Results For a constant delay of 2 hours of reperfusion, myocardial uptake of 99mTc-Fucoidan was detected after ischemia duration ranging from 20 minutes (8/8 rats, HBR: 2.4 +/- 0.9 [2.0-4.7]), 10 minutes (10/10 rats, HBR: 3.6 +/- 1.7 [1.5-7.5]) and 5 minutes (8/12 rats, HBR: 2.6 +/- 1.8 [1.9-7.1]). On autoradiography, the uptake ratio of 99mTc-Fucoidan was 4.5 +/- 1.9 [3.2-9.3] at 20 min, 7.4 +/- 3.1 [2.8-12.1] at 10 min and 5.6 +/- 2.1 [3.4-8.6] at 5 min. Areas of 99mTc-Fucoidan increased uptake matched with endothelial expression of P-selectin. After 6 hours of reperfusion, 99mTc-Fucoidan uptake was detected after 20 min ischemia (7/7, HBR: 3.0 +/- 0.6 [2.8-4.5]), 10 min ischemia (8/8 rats, HBR: 2.9 +/- 0.4 [2.5-3.3]) and 5 min ischemia (6/8 rats; HBR: 2.7 +/- 0.4 [2.1-3.1]). After 24 hours of reperfusion duration, 99mTc-Fucoidan uptake was detected after 20 min ischemia (8/8 rats, 3.1 +/- 0.7 [2.0-4.2]), 10 min ischemia (6/8 rats, HBR: 3.0 +/- 0.6 [2.5-3.9]) and 5 min ischemia (5/8 rats, HBR: 3.1 +/-0.8 [2.0-4.2]). On autoradiography, 99mTc-Fucoidan was co-localized with selectins expression.

Conclusions This study shows that brief coronary occlusions followed by reperfusion durations up to 24 hours are associated with P- and E-selectin endothelial expression, detectable in vivo by 99mTc-Fucoidan SPECT. These data support the clinical translation of 99mTc-Fucoidan in the detection of ischemic memory.