TRANSFERABLE LIPIDS IN OXIDIZED LOW-DENSITY-LIPOPROTEIN STIMULATE PLASMINOGEN-ACTIVATOR INHIBITOR-1 AND INHIBIT TISSUE-TYPE PLASMINOGEN-ACTIVATOR RELEASE FROM ENDOTHELIAL-CELLS

Decreased fibrinolytic activity has been reported in atherosclerotic cardiovascular diseases. To determine whether oxidized low-density lipoprotein (Ox-LDL), which accumulates in atherosclerotic arteries, modulates the endothelial fibrinolytic system, cultures of human umbilical vein endothelial cells were incubated with low-density lipoproteins or lipids, and levels of plasminogen activator inhibitor-1 (PAI-1) and tissue-type plasminogen activator (t-PA) antigens in the conditioned medium were measured by enzyme-linked immunosorbent assay. Ox-LDL (30 mug protein/mL) and its extracted lipid (50 mug cholesterol/mL) stimulated PAI-1 release by 42+/-3% and 29+/-3% of control cultures, respectively, whereas Ox-LDL and its lipid inhibited t-PA release by 42+/-4% and 53+/-3% of control cultures, respectively. Native LDL and its lipid were inactive on their release. OX-LDL depleted of hydrophilic lipids, which was prepared by the incubation with defatted albumin (an acceptor for hydrophilic lipids), lost both the stimulatory action on PAI-1 and the inhibitory action on t-PA. The extracted lipid from the incubated albumin, which has been found to accept the hydrophilic lipids from Ox-LDL, gained the stimulatory action on PAI-1 and the inhibitory action on t-PA. Ox-LDL depleted of lysophosphatidylcholine (LPC), which was prepared by the incubation with phospholipase B, lost the stimulatory effect on PAI-1, whereas the inhibitory effect on t-PA remained present in the Ox-LDL depleted of LPC. The incubation with synthetic palmitoyl LPC (10 muM) stimulated PAI-I release by 85+/-7% of control. 25-Hydroxycholesterol (50 muM) and 7-ketocholesterol (50 muM), both of which were generated in Ox-LDL and were found to be transferable from Ox-LDL to defatted albumin by the analysis using gas chromatography-mass spectrometry, inhibited t-PA release by 26+/-3% and 31+/-3% of control cultures, respectively. The level of PAI activity in the conditioned medium also increased after the incubation with Ox-LDL or LPC but not native LDL. The results indicate that Ox-LDL stimulates PAI-1 release by the transferable hydrophilic lipid(s), especially LPC, whereas Ox-LDL inhibits t-PA release by oxysterols or other transferable lipid(s) from Ox-LDL to albumin rather than LPC. Lipid products in Ox-LDL may impair endothelial fibrinolysis.