The goal of this thesis was to develop an animal model which would provide a means of assessing the severity of atherosclerosis in vivo. A nonhydrolyzable radioiodinated cholesteryl ester, 125I-cholesteryl iopanoate (125I-CI), was found to accumulate in high concentrations in atherosclerotic aortas of cholesterol-fed rabbits after intravenous administration. Aortas from normal chow-fed rabbits did not exhibit significant 125I-CI accumulation. When cholesterol-fed rabbits were intravenously administered Tween-solubilized 125I-CI and simultaneously treated with either of two anti-atherogenic compounds, estradiol 17(beta)-cypionate or colestipol, the extent of aortic atherosclerosis was found to dramatically decrease as determined by measurement of either aortic total cholesterol or aortic surface area covered by atheroma. Measurement of aortic radioactivity (from accumulated 125I-CI) was found to strongly correlate with the severity of atherosclerosis. Although the specificity of 125I-CI for atheromatous lesions was very good, gamma-camera scintigraphy of the abdomens of these rabbits 6 days after cessation of 125I-CI administration was not able to consistently predict the severity of atherosclerosis. Tissue distribution studies suggested that high blood and spinal column bone marrow radioactivity produced aorta:nontarget radioactivity ratios unfavorable with respect to imaging. To improve this ratio so as to permit noninvasive imaging, attempts were made to incorporate 125I-CI into serum lipoproteins. Labelling of either rabbit LDL by in vivo incorporation or human LDL by transfer of 125I-CI from liposomes using cholesteryl ester transfer protein resulted in lipoproteins with low specific activity. Higher specific activity was achieved by reconstituting delipidated human LDL with a mixture of 125I-CI and unlabelled cholesteryl oleate. These particles were taken up in high amounts by monolayers of human fibroblasts but not by fibroblasts deficient in LDL receptors or by normal fibroblasts during competition with unlabelled native LDL. However, polyacrylamide gel electrophoresis (PAGE), SDS-PAGE, and agarose column chromatography showed this procedure to form at least two populations of labelled particles having apolipoprotein B subspecies different from each other and from native LDL. Fibroblast uptake studies with these two preparations showed differences in their rate of uptake by human fibroblasts. Further studies are required to determine if the influx of LDL reconstituted with 125I-CI correlates with the influx of serum lipoproteins into the rabbit arterial wall in vivo.Ph.D.PharmacologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161376/1/8712093.pd
