99mTc-Annexin A5 for noninvasive characterization of atherosclerotic lesions: imaging and histological studies in myocardial infarction-prone Watanabe heritable hyperlipidemic rabbits.
OBJECTIVE
Apoptosis is commonly observed in advanced atherosclerotic lesions. 99mTc-annexin A5 (99mTc-annexin V) has been proposed as a potential tracer for imaging apoptosis in atherosclerotic plaques. Accordingly, we determined the usefulness of 99mTc-annexin A5 as an atherosclerosis imaging tracer in a rabbit model (myocardial infarction-prone Watanabe heritable hyperlipidemic rabbits; WHHLMI rabbits) of spontaneous atherosclerosis.


METHODS
The WHHLMI and control rabbits were injected intravenously with 99mTc-annexin A5. After in vivo planar imaging, the radioactivity in the aorta was measured. Autoradiography, TUNEL staining, Azan-Mallory staining and immunohistological studies were performed serially throughout the aorta.


RESULTS
99mTc-Annexin A5 accumulation in the aorta of the WHHLMI rabbits was 5.6-fold higher than in that of control rabbits. Autoradiography showed heterogeneous multifocal accumulation of 99mTc-annexin A5 in WHHLMI rabbits. 99mTc-Annexin A5 accumulation was highest in the atheromatous lesions (6.2+/-2.5, %IDxBW/mm2x10(3)), followed in decreasing order by neointimal (4.9+/-1.3), fibroatheromatous (4.5+/-1.9), and collagen-rich lesions (3.3+/-1.4). The regional 99mTc-annexin A5 accumulation was significantly correlated with the TUNEL-positive cell density, macrophage density and "vulnerability index," an index of the morphological destabilized characteristics. The in vivo imaging clearly visualized the atherosclerotic lesions in WHHLMI rabbits.


CONCLUSIONS
The present study in WHHLMI rabbits showed higher 99mTc-annexin A5 accumulation in grade IV atheroma than in other more stable lesions. 99mTc-Annexin A5 may be useful in identifying atheroma that is at higher risk for rupture and possibly in assessing the response to anti-atherosclerotic therapy.
Ishino
Seigo
S
Department of Patho-Functional Bioanalysis, Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida Shimoadachi-cho, Sakyo-ku, Kyoto, 606-8501, Japan.
Kuge
Yuji
Y
Takai
Nozomi
N
Tamaki
Nagara
N
Strauss
H William
HW
Blankenberg
Francis G
FG
Shiomi
Masashi
M
Saji
Hideo
H
D000818:Animals; D017304:Annexin A5 / Q000737:chemistry*; D017209:Apoptosis; D001161:Arteriosclerosis / Q000175:diagnosis / Q000000981:diagnostic imaging*; D050197:Atherosclerosis / Q000000981:diagnostic imaging / Q000378:metabolism*; D001345:Autoradiography / Q000379:methods; D005260:Female; D006949:Hyperlipidemias / Q000000981:diagnostic imaging / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism; D009203:Myocardial Infarction / Q000175:diagnosis / Q000000981:diagnostic imaging*; D011817:Rabbits; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000494:pharmacology*; D012044:Regression Analysis; D013667:Technetium / Q000494:pharmacology*
D017304:Annexin A5; D019275:Radiopharmaceuticals; D013667:Technetium