sodium-pertechnetate-tc-99m and Atherosclerosis

Annexin V recognizes apoptotic cells by specific molecular interaction with phosphatidyl serine, a lipid that is normally sequestered in the inner leaflet of the cell membrane, but is translocated to the outer leaflet in apoptotic cells, such as foam cells of atherosclerotic plaque. Annexin V could potentially deliver carried materials (such as superparamagnetic contrast agents for magnetic resonance imaging) to sites containing apoptotic cells, such as high grade atherosclerotic lesions, so we administered biochemically-derivatized (annexin V) superparmagnetic iron oxide particles (SPIONs) parenterally to two related rabbit models of human atherosclerosis. We observe development of negative magnetic resonance imaging (MRI) contrast in atheromatous lesions and but not in healthy artery. Vascular targeting by annexin V SPIONs is atheroma-specific (i.e., does not occur in healthy control rabbits) and requires active annexin V decorating the SPION surface. Targeted SPIONs produce negative contrast at doses that are 2,000-fold lower than reported for non-specific atheroma uptake of untargeted superparamagnetic nanoparticles in plaque in the same animal model. Occlusive and mural plaques are differentiable. While most of the dose accumulates in liver, spleen, kidneys and bladder, annexin V SPIONs also partition rapidly and deeply into early apoptotic foamy macrophages in plaque. Contrast in plaque decays within 2 months, allowing MRI images to be replicated with a subsequent, identical dose of annexin V SPIONs. Thus, biologically targeted superparamagnetic contrast agents can contribute to non-invasive evaluation of cardiovascular lesions by simultaneously extracting morphological and biochemical data from them.

Topics: Animals; Annexin A5; Aorta, Abdominal; Atherosclerosis; Contrast Media; Dextrans; Disease Models, Animal; Ferrosoferric Oxide; Humans; Iron; Magnetic Resonance Imaging; Magnetite Nanoparticles; Metal Nanoparticles; Oxides; Particle Size; Rabbits; Sodium Pertechnetate Tc 99m; Tissue Distribution; Tomography, Emission-Computed, Single-Photon; Tomography, X-Ray Computed

Chemotactic peptides, such as Monocyte Chemotactic Protein 1 (MCP-1), play a key role in transendothelial migration of mononuclear cells during the development and progression of atherosclerotic disease. Because atherosclerotic plaques that are precursors of acute coronary events harbor abundant macrophage infiltration, we hypothesized that the detection of a high concentration of MCP-1 receptors on inflammatory cells should noninvasively identify vulnerable plaques.. Atherosclerotic lesions were induced by balloon deendothelialization of the abdominal aorta, which was followed by a 0.5% cholesterol diet for 16 wk in 7 New Zealand White rabbits; 5 unmanipulated rabbits, fed normal chow for 16 wk, were used as controls. Radionuclide imaging was performed immediately after intravenous (99m)Tc-labeled MCP-1 administration and 3 h later. At the end of imaging session, aortas were explanted and submitted for estimation of quantitative MCP-1 uptake (in percentage injected dose per gram, %ID/g) and pathologic characterization.. Atherosclerotic lesions were clearly visible in all hyperlipidemic animal gamma-imaging. No tracer uptake was seen in the control rabbits. The mean quantitative MCP-1 uptake in atherosclerotic lesions was 4-fold higher than that of the aortic specimens from the control rabbits (0.065 +/- 0.005 vs. 0.016 +/- 0.006; P < 0.0001). Histology confirmed a strong correlation between MCP-1 uptake and the number of macrophages in American Heart Association type II-IV lesions (r = 0.87, P < 0.0001).. Noninvasive radionuclide imaging of inflammation is feasible by MCP-1 in experimentally induced atherosclerosis. It is proposed that detection of the extent of inflammation in advanced atherosclerotic plaques may allow identification of unstable plaques.

Topics: Animals; Atherosclerosis; Chemokine CCL2; Diet, Atherogenic; Humans; Inflammation; Macrophages; Rabbits; Radionuclide Imaging; Radiopharmaceuticals; Recombinant Proteins; Sodium Pertechnetate Tc 99m

The 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.. Extensive apoptosis of macrophages has been reported at the site of plaque rupture in patients dying of acute coronary syndrome.. Of 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 (99m)Tc-labeled mutant annexin A5 (radiotracer control group). Gamma images were obtained, and quantitative radiotracer uptake was compared with pathologic findings.. Atherosclerotic 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.. Molecular 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.

Topics: Animals; Annexin A5; Apoptosis; Atherosclerosis; Caspase Inhibitors; Enzyme Inhibitors; Male; Rabbits; Radionuclide Imaging; Radiopharmaceuticals; Sodium Pertechnetate Tc 99m