Broad and Specific Caspase Inhibitor-Induced Acute Repression of Apoptosis in Atherosclerotic Lesions Evaluated by Radiolabeled Annexin A5 Imaging

ObjectivesThe purpose of this study was to evaluate the role of caspase inhibitors on acute resolution of apoptosis in atherosclerotic lesions as evaluated by imaging with annexin A5.BackgroundExtensive apoptosis of macrophages has been reported at the site of plaque rupture in patients dying of acute coronary syndrome.MethodsOf 31 New Zealand White atherosclerotic rabbits, 6 received broad caspase, 3 received caspase-1, 3 received caspase-3, 3 received caspase-8, and 4 received caspase-9 inhibitors; 12 animals did not receive any caspase inhibitors (treatment control group). Six unmanipulated rabbits were used for comparison (disease control group). Technetium-99m–labeled annexin A5 was used for imaging atherosclerotic lesions; 6 of the 12 uninhibited atherosclerotic rabbits received 99mTc-labeled mutant annexin A5 (radiotracer control group). Gamma images were obtained, and quantitative radiotracer uptake was compared with pathologic findings.ResultsAtherosclerotic lesions were best visible in untreated atherosclerotic rabbits. Quantitative annexin uptake, defined as the percent of injected dose per g of abdominal aorta tissue, was significantly higher in untreated atherosclerotic animals (mean ± SD = 0.0515 ± 0.0099) compared with the normal rabbits (0.0065 ± 0.0008; p < 0.0001) or atherosclerotic rabbits receiving mutant annexin (0.014 ± 0.0024; p < 0.0001). Among all caspase inhibitor-treated rabbits, uptake was 39% lower (0.0314 ± 0.0151) than in untreated atherosclerotic animals (p < 0.01). Uptake was also significantly lower in rabbits receiving broad caspase (0.0206 ± 0.0058; p < 0.0001) or caspase-1, -3, or -9 (0.0272 ± 0.0088, p < 0.01; 0.0286 ± 0.0095, p < 0.01; 0.0300 ± 0.0021, p < 0.01, respectively) inhibitors. Caspase-8 inhibitor did not affect apoptosis (0.0618 ± 0.0047; p = NS). Upon histologic characterization, a substantial decrease in macrophage apoptosis was observed in caspase-inhibited animals.ConclusionsMolecular imaging, using radiolabeled annexin A5, allows the detection of acute resolution of apoptosis as a result of caspase inhibition in experimental atherosclerosis. If proven clinically, this may allow development of novel intervention strategies in acute vascular events.