Low-density lipoproteins (
LDL) were radiolabeled in
atherosclerosis studies. The aim was to investigate the biodistribution and uptake of 99mTc-labeled
LDL by
atherosclerotic plaques in experimentally induced
hyperlipidemia. Rabbits were fed a diet containing 2%
cholesterol for 60 days to develop
hyperlipidemia and atheromatous aortic plaques. A combination of preparative and analytical ultracentrifugation was used to investigate human
LDL aliquots, to prepare radioactive-labeled
lipoproteins and in rabbits with induced
hyperlipidemia. Preparative density gradient centrifugation was applied for the simultaneous isolation of the major
lipoprotein density classes, which form discrete bands of
lipoproteins in the preparative tubes. The
cholesterol and
protein levels in the
lipoprotein fractions were determined.
LDL was subsequently dialysed against physiological
solution and sterilized and
apolipoprotein fragments and aggregates were eliminated by passage through a 0.22-micron filter.
LDL was radiolabeled with 99mTc by using
sodium dithionite as a
reducing agent. Radiochemical purity and in vitro stability were controlled by paper chromatography in
acetone. The labelling efficiency was 85-90% for human
LDL. Two months after the start of
cholesterol feeding, the total
cholesterol in the blood serum had increased approximately 33-fold in comparison with the basal
cholesterol content of hypercholesterolemic rabbits. Investigation of
LDL was performed by Schlieren analysis after adjustment of the density of serum and underlayering by
salt solution in a spinning ultracentrifugation capillary band-forming cell. Quantitative results were obtained by measuring the Schlieren areas between the sample curves and the reference baseline curve by means of computerized numerical and graphic techniques. In this manner we measured the concentrations of human
LDL and analyzed rabbit
LDL levels in induced
hyperlipidemia. Gamma
scintillation camera scanning of the rabbits was performed. Overnight fasted rabbits were injected in the marginal ear vein with 99mTc-labeled human
LDL (4-10 mCi, 0.5-1.5 mg
protein). The initial scintigram showing a typical blood-pool scan, gradually changing with time to an image of specific organ uptake of radioactivity by the liver, kidneys and brain and in the bladder.
Gamma camera in vivo scintigraphy on rabbits revealed visible signals corresponding to
atherosclerotic plaques in the aorta and carotid arteries. Our results show that
99mTc-LDL can be used to assess the organ distribution pattern of
LDL in the rabbit, and to detect and localize areas of arterial atherosclerotic lesions.