Evidence for lipid regression in humans in vivo performed by 123iodine-low-density lipoprotein scintiscanning.

Abstract

Radiolabeling of autologous LDL allows in vivo characterization of arterial wall lipid metabolism and LDL receptor imaging. Different kinetic types of arterial wall LDL entry reflect the de-, re-, and endothelialized segments in both animals and humans. In 36 male cholesterol-fed rabbits being treated with the calcium channel blocker isradipine (0.3 mg/kg daily), the retention of the radiolabeled (125I-LDL) was reduced, being related to the reduction in arterial wall cholesterol ester content and the decreased extent of Sudan III-positive areas. In parallel, a significant (p < 0.01) increase in vascular prostaglandin I2 (PGI2) generation was seen in endothelialized and reendothelialized segments of the abdominal aorta. These effects were completely abolished by concomitant treatment with acetylicsalicylic acid (ASA). These data could be confirmed in humans, too: a 4-week treatment with prostaglandin E1 (PGE1:5 ng/kg/min iv, 5 days/week, 6 h/day for 6 weeks) and isradipine (2 x 2.5 mg po daily for 4 weeks) did not change arterial 123I-LDL influx kinetics, which were examined over a total of 60 (PGE1) and 96 (isradipine) vascular regions. In contrast to this, the retention of the tracer was significantly diminished in different arterial segments. In isradipine-treated patients, 20 hours after reinjection of radiolabeled LDL, the quantitative LDL entry was reduced by at least 4.7% with a maximum of 23.5% (p < 0.01) in type I (n = 50 lesions) or type II lesions (n = 41). PGE1 treatment induced a 16.9% to 30.7% (p < 0.01) decrease of LDL retention in type I (n = 36 lesions) or type II lesions (n = 24), respectively. These findings support the hypothesis derived from earlier experimental studies that the antiatherosclerotic effects are likely to be due to the increase in PGE1 and/or PGI2 availability mediated by an increase in cAMP. The results demonstrate the potential of 123I-LDL scintigraphy for the characterization of vascular LDL kinetics and the monitoring of functional lipid lesion regression.