AJP - Endocrinology and Metabolism, Vol 250, Issue 3 265-E268, Copyright © 1986 by American Physiological Society
Generation of plasma free cholesterol from circulating lipoprotein-associated cholesteryl ester
I. J. Goldberg, R. S. Rosenfeld, I. Paul and B. Leeman
Studies were performed to investigate the contribution of
lipoprotein-associated cholesteryl ester (CE) in the monkey to circulating
free cholesterol (FC). Monkey plasma was incubated with [14C]- or
[3H]cholesteryl ester, and radiolabeled low-density lipoproteins (LDL) and
high-density lipoproteins (HDL) were isolated by ultracentrifugation.
Animals received labeled LDL or HDL. A rapid transfer of CE between
lipoproteins was observed, consistent with an active CE transfer protein
activity in the monkey. Within 4 h the percent of plasma radioactivity in
FC after injection of CE-labeled LDL or HDL was, respectively, 30 and 7% of
that of the ester. To determine whether the generation of FC was due to a
circulating plasma cholesteryl ester hydrolase, monkey plasma was incubated
with CE-labeled lipoproteins with and without 5,5'-dithiobis(2-nitrobenzoic
acid) (DTNB). A small amount of FC (less than 3% of the radioactivity) was
generated during this incubation but most of the FC production was
inhibited by DTNB. Although a small amount of FC can be produced by a
plasma cholesteryl esterase (perhaps via reverse action of
lecithin-cholesterol acyltransferase), most of the FC in plasma derived
from lipoprotein-associated CE is probably due to tissue uptake of
lipoproteins and subsequent intracellular hydrolysis of the CE to produce
FC.
