G. Kellnerweibel et al., EFFECTS OF INTRACELLULAR FREE-CHOLESTEROL ACCUMULATION ON MACROPHAGE VIABILITY - A MODEL FOR FOAM CELL-DEATH, Arteriosclerosis, thrombosis, and vascular biology, 18(3), 1998, pp. 423-431
This study was designed to identify cellular responses associated with
free cholesterol (FC) accumulation in model macrophage foam cells. Mo
use peritoneal macrophages (MPMs) or J774 macrophages were loaded with
cholesteryl esters using acetylated LDL and FC/phospholipid dispersio
ns and were subsequently exposed to an acyl coenzyme A:cholesterol acy
ltransferase (ACAT) inhibitor. This treatment produced a rapid accumul
ation of cellular FC. The FC that accumulated due to ACAT inhibition w
as more readily available for efflux to 2-hydroxypropyl-beta-cyclodest
rin (which removes cholesterol from the plasma membrane) than FC in un
treated control cells. After a 3-hour exposure to an ACAT inhibitor, a
significant increase in phospholipid synthesis was seen, followed by
the leakage of LDH after 12 hours of treatment. We also observed, by e
lectron and fluorescence microscopy, morphological indications of both
apoptosis and necrosis in cells treated with an ACAT inhibitor, In ad
dition, inhibition of ACAT for 48 hours resulted in the formation of F
C crystals in MPMs but not in J774 cells. If compound 3 beta-[2-(dieth
ylamino)ethoxyl]androst-5-en-17-one (U18666A), which modulates intrace
llular trafficking of cholesterol, was added together with the ACAT in
hibitor, each of the metabolic changes elicited by the accumulation of
excess FC was either diminished or eliminated. The protective affect
of U18666A was not due to a decrease in cellular FC concentrations, be
cause cells treated with an ACAT inhibitor accumulated similar amounts
of FC in the presence or absence of U18666A. Thus, treatment with U18
666A results in the sequestering of FC in a pool that prevents it from
causing various responses to FC deposition in macrophages. The metabo
lic changes that were produced when these model foam cells were treate
d with the ACAT inhibitor parallel the pathological events that have b
een shown to occur in the developing atherosclerotic plaque.