Interactions between vascular endothelium and low density lipoprotein (LDL) have been implicated in the development of atherosclerosis. The effect of normal and oxidized LDL (Ox-LDL) on prostaglandin release by cultured adult human saphenous vein endothelial cells was investigated. Ox-LDL induced a rapid release of prostacyclin (PGI 2 ) to levels which were several-fold higher than those observed with control LDL. PGI 2 release was concentration-dependent and was biphasic, with a first peak occurring within 30 minutes (followed by a decrease), and a second peak occurring after several hours of incubation. PGI 2 production was inhibited by lipoproteindepleted serum and by indomethacin, an antagonist of cyclooxygenase activity. These cells produced mainly PGF^, with some PGE 2 and PGI 2 when stimulated by the ionophore A23187 at confluency. However, among these prostanoids, mainly PGI 2 was produced in response to Ox-LDL. The data indicate that Ox-LDL induces the production of PGI 2 by human vascular endothelial cells. Since Ox-LDL is cytotoxic, this phenomenon may be a manifestation of an early response to injury. (Arteriosclerosis 8:810-818, November/December 1988) T he interaction of low density lipoprotein (LDL) with endothelial cells is of significant interest to researchers in the field of atherosclerosis. LDL is toxic to endothelial cells cultured in serum-free medium.1 -2 LDL cytotoxicity is due to oxidation of its lipid moiety, and oxidized LDL (Ox-LDL) cytotoxicity is prevented by the use of antioxidants in vitro.3 -6 Endothelial cells, smooth muscle cells,' and leukocytes oxidize LDL in vitro in a manner similar to the oxidation catalyzed by transition metals.
5789Ox-LDL inhibits macrophage mobility, is metabolized via the scavenger receptor, and induces cholesterol ester accumulation in the macrophage.9 -12 Ox-LDL may thus promote atherosclerosis.3 " 12 Prostacyclin (PGI 2 ) is a potent vasodilator and decreases platelet aggregation.13 PGI 2 is produced by endothelial cells, and increased levels of 2,3-dinor-6-keto-PGF 1(I , a major urinary metabolite of PGI 2 , have been observed in patients with atherosclerosis.141516 When endothelial cells are subjected to various forms of injury such as balloon catheter trauma, radiation, shear stress, or exposure to mellitin, PGI 2 is released. 17 -20 We tested the hypothesis that adult human vascular endothelial cells produce PGI 2 in response to Ox-LDL. The data presented support this hypothesis.
Methods
Tissue CultureHuman saphenous vein endothelial cell (HSVEC) cultures were prepared by collagenase digestion of unused saphenous vein sections obtained during coronary artery bypass surgery. 21 The use of normally discarded human tissues was approved by the Human Investigation Review Committee of the New England Medical Center, Boston, MA. The cells were grown on human fibronectin-coated dishes (1.5 /xg/cm 2 ) in Morgan's M-199 medium containing 25 mM HEPES, and supplemented with 5% fetal bovine serum (FBS), 50 /Ag/ml bovine endothelial cell growth factor, 10...
