Atherosclerosis 154 2001 79 – 86
Expression of adhesion molecules by human endothelial cells exposed to oxidized low density lipoprotein
Influences of degree of oxidation and location of oxidized LDL
Akira Takei
a
, Yan Huang
b,c
, Maria F. Lopes-Virella
b,c,
a
Department of Medicine, Kgusha Uni6ersity, Fukuoka, JPN
b
Ralph H. Johnson Veterans Administration Medical Center, Charleston, SC, USA
c
Department of Medicine, Di6ison of Endocrinology, Diabetes and Medical Genetics, Medical Uni6ersity of South Cardina, Charleston, SC
29403
, USA Received 5 August 1999; received in revised form 20 January 2000; accepted 2 March 2000
Abstract
The main objective of this study was to determine the influence of the degree of low density lipoprotein LDL oxidation and the location of oxidized LDL oxLDL on expression of adhesion molecules on endothelial cells EC. OxLDL preparations 1 – 4
with different degrees of oxidative modification were studied. All preparations of oxLDL, after addition to the medium, stimulated the expression of intercellular adhesion molecule-1 ICAM-1 by human umbilical vein endothelial cells HUVEC as
determined by cell-ELISA. Concentration-dependent studies examining ICAM-1 expression by HUVEC showed that the minimal concentration of oxLDL which significantly stimulated ICAM-1 expression was 5 mgml, suggesting that the predicted physiolog-
ical concentration of oxLDL in plasma may be not high enough to elicit a substantial increase of ICAM-1 expression in EC. In contrast, very small amounts 0.15 mgwell of oxLDL-3 and 4, the more heavily oxidized LDL preparations, stimulated effectively
ICAM-1 expression by HUVEC when located below the endothelial cell monolayer by immobilizing to type I collagen. The results suggest that the increased expression of ICAM-1 induced by accumulated oxLDL may be one of the mechanisms by which
oxLDL contributes to atherogenesis. © 2001 Elsevier Science Ireland Ltd. All rights reserved.
Keywords
:
Oxidized low-density lipoproteins; Intercellular adhesion molecule-1; Endothelial cells; Atherosclerosis www.elsevier.comlocateatherosclerosis
1. Introduction
During the last decade, evidence that oxidized low density lipoproteins oxLDL play a critical role in
atherogenesis has been steadily accumulating [1,2]. OxLDL contributes to the development of atheroscle-
rosis by several mechanisms. One of them is the stimu- lation of endothelial cells EC to releaseexpress
leukocyte chemoattractants and adhesion molecules [3 – 6]. Adhesion molecules mediate the attachment of cir-
culating mononuclear cells to the endothelium and facilitate their migration into the subendothelial space
thus contributing to accumulation of mononuclear cells in the vascular wall, one of the initial steps in the
development of atherosclerosis [7]. Thus it is not sur- prising that several studies have shown increased ex-
pression of adhesion molecules in the endothelium overlaying atherosclerotic lesions but not in the normal
endothelium [8 – 11].
Thus far, all in vitro studies investigating the effect of oxLDL on the expression of adhesion molecules by
endothelial cells have been performed by adding oxLDL to the culture medium [3 – 6]. However, the
presence of circulating plasma oxLDL, even in small amounts, is debatable and the concentrations of
oxLDL used in the above studies 25 – 100 mgml have always been higher than the levels of oxLDL reported
predicted to be present in human plasma [12,13]. The expression of adhesion molecules in the endothelium
may however be induced by oxLDL located in the subendothelial space, likely in atherosclerotic lesions. It
is well accepted that oxLDL becomes trapped in the
Corresponding author. Tel.: + 1-843-5775011, ext. 6823; fax: +
1-843-9536480. E-mail address
:
virellammusc.edu M.F. Lopes-Virella. 0021-915001 - see front matter © 2001 Elsevier Science Ireland Ltd. All rights reserved.
PII: S0021-91500000465-2
extracellular matrix during the formation of atheroma- tous plaques and, therefore, it is likely that larger
amounts of oxLDL than those circulating in plasma accumulate in these regions [14]. Furthermore the LDL
is likely more heavily oxidized since the entrapment of LDL by the extracellular matrix together with the
presence of microenvironment conditions excluding plasma soluble anti-oxidants in the subendothelial
space creates ideal conditions for oxidation of LDL. Studies showing that LDL eluted from atherosclerotic
lesions has characteristics similar to those of copper-ox- idized LDL support this hypothesis [14].
In this study it was proposed to determine whether or not the expression of adhesion molecules by endothelial
cells is influenced by the degree of LDL oxidation. It was also determined whether or not the expression of
adhesion molecules by endothelial cells can be elicited by oxLDL located in the subendothelial space by im-
mobilizing oxLDL to type I collagen, one of the main components of the subendothelial matrix.
2. Material and methods
