Preferential influx and decreased fractional loss of lipoprotein(a) in atherosclerotic compared with nonlesioned rabbit aorta.

Abstract

The aim was to investigate the atherogenic potential of lipoprotein(a) (Lp(a)) and to further our understanding of the atherogenic process by measuring rates of transfer into the intima-inner media (i.e., intimal clearance) and rates of loss from the intima-inner media (i.e., fractional loss) of Lp(a) and LDL using cholesterol-fed rabbits with nonlesioned ( n ϭ 13) or atherosclerotic aortas ( n ϭ 12). In each rabbit,

Increased Degradation of Lipoprotein(a) in Atherosclerotic Compared With Nonlesioned Aortic Intima–Inner Media of Rabbits

“…After determining radioactivity, lipids in aortic intima-inner media were extracted over a 24-hour period with chloroform/methanol (2:1 vol/vol) followed by two further extractions with chloroform/methanol (1:1, vol/vol) before the combined lipid extract was washed by the procedure of Folch et al 36 Total cholesterol content was determined by an enzymatic method (CHOD-PAP, Boehringer Mannheim) after evaporation of the chloroform/methanol and solubilization of the extract in isopropanol. 22 In control experiments, the addition of half-strength Karnowsky's fixative to plasma samples did not interfere with subsequent extraction and quantification of cholesterol, supporting the idea that fixation of aortic tissues before lipid extraction did not affect the cholesterol measurement (data not shown). Nondenaturing polyacrylamide gradient gel electrophoresis, gradient density ultracentrifugation, and a two-tier rocket immunoelectrophoresis assay were used to evaluate the intactness of labeled Lp(a) and LDL in labeled preparations used for injections and in plasma after intravenous injection into the rabbits.…”

“…To induce atherosclerosis in the aorta, 17 rabbits were fed a 0.25% to 1% cholesterol-enriched chow for 5 to 6 months; the chow was prepared as described elsewhere. 22 The amount of cholesterol in the chow was adjusted regularly to maintain a plasma cholesterol level of about 50 mmol/L. Sixteen other rabbits were fed a 1% cholesterol-enriched chow for 6 days; this short cholesterol-feeding period was chosen to increase the plasma cholesterol concentration without inducing atherosclerosis.…”

“…22,23 After fixed-density ultracentrifugation, the dϽ1.12-g/mL fraction was passed over a lysine Sepharose column. Purified Lp(a) was eluted with ⑀-amino-n-caproic acid.…”

“…33 The aorta was divided into the aortic arch, thoracic aorta, and abdominal aorta, and each of these three segments were then subdivided into a proximal and distal part of similar size, as previously described. 22,26 The intima-inner media was separated from the outer media in each of these six aortic segments. There was no difference in the weight of aortic tissues from rabbits used for studying Lp(a) or for studying LDL.…”

“…22 Briefly, the initial model included all main effects and all possible two-factor interactions. Using a step-down procedure, the model was then reduced as much as possible to include only significant (PϽ.05) main effects and interactions.…”