Localization of (99m)Tc-Labeled ApoB Synthetic Peptide in Arterial Lesions of an Experimental Model of Spontaneous Atherosclerosis.
We have previously shown that after administration of (123)I-SP-4 (a synthetic ApoB peptide fragment) to Watanabe heritable hyperlipidemic (WHHL) rabbits that foci of tracer uptake can be identified by external gamma camera imaging which correspond to regions of the aortas found to contain abundant atherosclerotic lesions at postmortem evaluation. Because (99m)Tc is preferred over (123)I for scintigraphic imaging, we prepared a (99m)Tc-labeled form of the SP-4 peptide, designated (99m)Tc-P199. To assess the feasibility of detecting atherosclerotic lesions using (99m)Tc-P199 and to compare the relative uptake of the (99m)Tc-labeled and radioiodinated peptides by such lesions, an admixture of (99m)Tc-199 and (125)I-SP-4 was administered to 11 WHHL and 2 normal rabbits. These animals were imaged for up to 3 h and were sacrificed 3--4 h after injection. The extent of aortic lesion involvement and radiotracer uptake were quantitatively compared by planimetric analysis of photographs of the endothelial surface, (99m)Tc-P199 ex vivo images and (125)I-SP-4 autoradiograms of the excised aortas. Pairwise correlation coefficients for planimetric analysis were as follows: photographs versus ex vivo images, r = 0.83, p = 0.003; photographs versus autoradiograms, r = 0.87, p = 0.001; ex vivo images versus autoradiograms, r = 0.83, p = 0.003. (99m)Tc-199 in vivo gamma camera images revealed relatively weak focal aortic uptake in 8 of 11 WHHL rabbits manifesting aortic lesions, and focal carotid artery uptake in 4 of 6 WHHL rabbits manifesting carotid lesions. Neither aortic nor carotid foci were visualized in the normal rabbits. We conclude that (99m)Tc-199 localizes specifically in atherosclerotic lesions and may be useful for external imaging of atherosclerosis.