Tc-99m-labeled endothelin derivative for imaging of experimentally induced atherosclerosis

doi:10.1016/S0021-9150(00)00753-X

Atherosclerosis

Volume 157, Issue 2, August 2001, Pages 383-392

https://doi.org/10.1016/S0021-9150(00)00753-X Get rights and content

Abstract

Objective: to characterize the potential of an endothelin derivative labeled with technetium-99m (Tc-99m) for the imaging of experimentally induced atherosclerosis. Methods: neointima of different cellularity and severity of stenosis was induced in 32 rabbits by balloon denudation followed by distinct dietary regimens and drug application. Angiograms and scintigrams after injection of the Tc-99m-labeled endothelin derivative were obtained. The aorta was dissected for autoradiography, sudan-III-staining, morphometry, and immunohistology. Results: the lesions induced could be detected in vivo (whole body scintigram) in all the animals 15 min after the injection of the Tc-99m endothelin derivative. Autoradiography revealed a strong relationship between tracer accumulation and sudan-III-staining of lesions. Accumulation of the endothelin derivative correlated with the number of neointimal smooth muscle cells (SMC), but not with the number of medial SMC, neointimal macrophages, and neointimal area. Conclusions: the results indicate that in vivo imaging of atherosclerosis with an endothelin derivative is a feasible method of detecting and characterizing atherosclerotic arterial wall lesions at early stages.

Introduction

Atherosclerosis is the principal cause of heart attack, stroke and gangrene of the extremities and is responsible for approximately 50% of all mortality in USA, Europe and Japan [1]. The approaches to the treatment of atherosclerosis are bypass grafting, endarterectomy and percutaneous transluminal angioplasty. The failure rate due to restenosis after these approaches presents a major problem with an incidence rate of 30–40% [1], [2], [3]. Vascular stenotic lesions can be diagnosed either by conventional angiography, ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI). These techniques are based mainly on the changes in the cross-sectional area of the vascular lumen. However, these changes provide only little information on plaque pathophysiology. The mechanisms involved in the process of restenosis include elastic vessel recoil and release of biochemical mediators resulting in smooth muscle cell (SMC) proliferation [2], [3], [4], [5], [6]. Endothelin has been shown to be involved in the process of atherosclerosis and restenosis [7], [8], [9], [10]. Temporary expression of ET_A and ET_B receptor mRNAs after balloon angioplasty, especially in SMC, has been reported in rats [9]. Lerman et al. demonstrated a significant increase in the endothelin levels measured distally of the dilated stenosis in patients undergoing PTCA [10]. mRNA for ET_A and ET_B-receptors has been detected in human atherosclerotic plaques [11], [12]. Recently we reported development of an endothelin derivative for scintigraphic visualization of experimentally induced atherosclerosis [13]. In animal models of restenosis we found a significant correlation between the labeled activity and the number of neointimal smooth muscle cells in eight rabbits. The aim of the present study was to evaluate the diagnostic potential of this endothelin derivative for imaging of experimentally induced atherosclerosis depending on neointima formation with different severity of stenosis and cellularity.

Section snippets

Endothelin derivative

The Tc-99m endothelin derivative is a tridecapeptide with the primary sequence of Asp-Gly-Gly-Cys-Gly-Cys-Phe-(D-Trp)-Leu-Asp-Ile-Ile-Trp [14]. The C-terminal heptapeptide Phe-(D-Trp)-Leu-Asp-Ile-Ile-Trp of this endothelin derivative is a modified sequence of the C-terminal hexapeptide of the endothelin family His-Leu-Asp-Ile-Ile-Trp. The C-terminal hexapeptide of the endothelin family, as well as the derivatives thereof have a micro- to nanomolar affinity to endothelin A- and B-receptors [15].

Animal model

Thirty-two male New Zealand White rabbits (3.0–3.5 kg body weight) were used in this study. The investigation conforms with the Guide for the Care and Use of Laboratory animals published by the US National Institutes of Health (NIH Publication No. 85-23, revised 1996). Interventions and imaging procedures were done under general anesthesia (22 mg ketamine/kg body weight, 4.5 mg xylazine/kg body weight, and 0.7 μg atropine sulfate/kg body weight). All of the animals underwent balloon denudation

Angiography

Biplanar transvenous digital subtraction angiograms were obtained after 6 weeks (groups 1–4), and after 12 weeks (groups 2–4). After 6 weeks n=18 animals were rated 0 points, n=12 one point and n=2 two points. After 12 weeks six rabbits scored 0 points, 14 animals scored one point, and four animals scored two points. Although considerable neointima formation could be detected histologicaly in all the animals, no animal received a score ≥3 at angiography. There were no significant differences

Discussion

The purpose of this study was to characterize the potential of an endothelin derivative labeled with Tc-99m for imaging of experimentally induced atherosclerosis in vivo. A noninvasive screening technique for disease-specific localization and quantification of early stages of neointima formation could be of importance. If a patient with risk factors for the development of atherosclerosis, such as an increased serum cholesterol level, develops an atherosclerotic lesion, the progression of early

Acknowledgements

We gratefullyj acknowledge the excellent technical assistance of Eva Maria Bickel and Ingolf Weber. This paper is dedicated to Prof. M.K. Grieshaber on the occasion of the 20th anniversary of the Institute for Zoo-Physiology, Dusseldorf, Germany.

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Tc-99m-labeled endothelin derivative for imaging of experimentally induced atherosclerosis

Abstract

Introduction

Section snippets

Endothelin derivative

Animal model

Angiography

Discussion

Acknowledgements

J. Am. Coll. Cardiol.

Biochem. Biophys. Res. Comm.

Appl. Radiat. Isot.

J Am Coll Cardiol.

Atherosclerosis

Progr. Cardiovasc. Dis.

Eur. J. Pharmacol.

Atherosclerosis

Atherosclerosis

The pathogenesis of atherosclerosis: a perspective for the 1990s

Nature

The intima: soil for atherosclerosis and restenosis

Circ Res.

Coronary stenting decreases restenosis in lesions with early loss in luminal diameter 24 hours after successful PTCA

Circulation

Covered stents for prevention of restenosis — experimental and clinical results with different stent designs

Invest. Radiol.

Diagnosis of arterial disease of lower extremities with duplex ultrasonography

Br. J. Surg.

Primary structure, synthesis, and biological activity of rat endothelin, an endothelium derived vasoconstrictor peptide

Proc. Natl. Acad. Sci.

Endothelin and restenosis

Cardiovasc. Res.

Expression of endothelin-1, endothelin-3, endothelin-converting enzyme-1, and endothelin-A and endothelin-B receptor mRNA after angioplasty-induced neointimal formation in the rat

Circ. Res.

Local release of endothelin in human coronary arteries in response to balloon angioplasty

J. Am. Coll. Cardiol.

Clinical significance of endothelin in cardiovascular disease

Hypertension

Molecular imaging of atherosclerosis using a technetium-99m-labeled endothelin derivative

J. Nucl. Med.

Structure-activity relationships of C-terminal endothelin hexapeptide antagonists

J. Med. Chem.