Radiolabeled cholesteryl iopanoate/acetylated low density lipoprotein as a potential probe for visualization of early atherosclerotic lesions in rabbits

Visualizing the atherosclerotic plaque: a chemical perspective

Atherosclerosis is the major underlying pathologic cause of coronary artery disease. An early detection of the disease can prevent clinical sequellae such as angina, myocardial infarction, and stroke. The different imaging techniques employed to visualize the atherosclerotic plaque provide information of diagnostic and prognostic value. Furthermore, the use of contrast agents helps to improve signal-to-noise ratio providing better images. For nuclear imaging techniques and optical imaging these agents are absolutely necessary. We report on the different contrast agents that have been used, are used or may be used in future in animals, humans, or excised tissues for the distinct imaging modalities for atherosclerotic plaque imaging.

Modified lipoproteins as contrast agents for imaging of atherosclerosis

The ability to detect and characterize atherosclerosis with targeted contrast agents may enable initiation of therapy for atherosclerotic lesions prior to becoming symptomatic. Since lipoproteins such as high-density lipoprotein (HDL) and low-density lipoprotein (LDL) play a critical role in the regulation of plaque biology through the transport of lipids into and out of atherosclerotic lesions, modifying HDL and LDL with radioisotopes for nuclear imaging, chelates for magnetic resonance imaging (MRI) or other possible contrast agents for computed tomography imaging techniques may aid in the detection and characterization of atherosclerosis. This review focuses on the literature employing lipoproteins as contrast agents for imaging atherosclerosis and the feasibility of this approach.

Ex vivo evaluation of a novel polyiodinated compound for early detection of atherosclerosis

Atherosclerosis is a primary cause of heart disease and stroke; it is the underlying cause of about 50% of all deaths in Western countries. It is known that early detection of atherosclerotic lesions would significantly reduce the risk of mortality. The objective of this study was to develop a radioimaging method for early detection of atherosclerotic plaques. A novel polyiodinated cholesterol analog, cholesteryl 1,3-diiopanoate glyceryl ether (C2I, patent pending), was synthesized and radiolabeled with 125I. 125I-C2I was incorporated into acetylated low-density lipoprotein (AcLDL), which is considered to be an atherosclerotic plaque-seeking carrier. 125I-C2I was also prepared as a chylomicron-like emulsion. Transgenic mice deficient in apoE and low-density lipoprotein receptors (LDLR), known as apoE/LDLR double knockout, were used as an animal model of early atherosclerosis. 125I-C2I/AcLDL or 125I-C2I emulsion was injected into the apoE/LDLR knockout mice via the tail vein, and the mice were killed humanely 24 h after injection. Various tissues including aorta were removed and radioactivity was determined. The aorta samples were also imaged to determine the accumulation of radioactivity from C2I. The images were compared to the atherosclerotic lesions revealed by histological studies. It was found that both 125I-C2I/AcLDL and 125I-C2I emulsion resulted in accumulation of radioactivity at the site of early atherosclerotic lesions, and they therefore may be useful for early detection of atherosclerosis.

Inhibitory effect of acyl-CoA:cholesterol acyltransferase inhibitor-low density lipoprotein complex on experimental atherosclerosis

KV-2920 is a novel acyl-CoA: cholesterol acyltransferase (ACAT) inhibitor. To confirm the efficacy of KV-2920-low density lipoprotein (LDL) complex (KV-LDL complex) as a drug-carrier complex on experimental atherosclerosis, we examined its inhibitory effects in vitro and in vivo. LDL was isolated from human plasma and the KV-LDL complex was prepared by incubation in the presence of Celite 545. The complex contained about 800 mol KV-2920 in 1 mol LDL. The cholesterol levels in the serum and aorta of atherogenic mice after 14 weeks of feeding were significantly higher than those of nonatherogenic mice. With the intravenous injection of KV-LDL complex, although the cholesterol levels in the serum were not influenced, the level of cholesterol ester in the aorta of atherogenic mice was significantly reduced. The concentration of cholesterol ester in the macrophages derived from ICR mice was predominantly increased by incubation with LDL for 48 h, this increase was significantly inhibited by incubation with KV-LDL complex. Moreover, the complex also inhibited the increase of cholesterol ester in macrophages following incubation with oxidized LDL. These findings suggest that KV-LDL complex inhibits the foam cell formation of macrophages though action of KV-2920 as an ACAT inhibitor, and prevents the accumulation of cholesterol ester in the aorta of atherogenic mice. Therefore, KV-LDL complex may be useful as a drug-carrier complex in antiatherosclerotic therapy.

Effect of dexamethasone palmitate-low density lipoprotein complex on cholesterol ester accumulation in aorta of atherogenic model mice

In order to confirm the efficacy of dexamethasone palmitate (DP)-low density lipoprotein (LDL) complex on experimental atherosclerosis in vivo, we examined whether DP-LDL complex could be effective for cholesterol ester accumulation in the aorta of atherogenic mice. Nonatherogenic and atherogenic mice were fed with normal and atherogenic diet for 14 weeks, respectively. Dexamethasone (DEX), lipid emulsion containing DP (DP-LE), or DP-LDL complex was intravenously injected once a week from 8 to 14 weeks. Cholesterol levels in serum and aorta in the atherogenic mice were significantly higher than those of nonatherogenic mice. Injection of DP-LDL complex significantly reduced cholesterol ester (CE) accumulation in the aorta of atherogenic mice. The reduction of CE accumulation in aorta treated with DP-LDL complexes was 10 and 100 times more potent than that with DP-LE and DEX, respectively. The radioactivity in the aorta of atherogenic mice treated with 3H-DP-LDL complex was significantly higher than that with 3H-DP-LE and 3H-DEX at 24 h after injection. Even 7 d after injection, a significant amount of radioactivity was present only in the aorta of atherogenic mice treated with DP-LDL complex. This result suggests that DP-LDL complex is selectively delivered to the atherogenic lesions in the aorta of atherogenic mice, and then DP released from the complex inhibits CE accumulation in the aortic intima. Therefore, DP-LDL complex may be a good drug-carrier in drug delivery system for atherosclerosis.