Transferable Lipids in Oxidized Low-Densit 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 ,ug protein/mL) and its extracted lipid (50 ,g 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 PAIT1, whereas the inhibitory effect on t-PA remained present in the Ox-LDL depleted of LPC. The incubation with synthetic palmitoyl LPC (10 ,uM) stimulated PAI-1 release by 85±7% of control. 25-Hydroxycholesterol (50 ,uM) and 7-ketocholesterol (50 ,uM), 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. (Circulation Research 1993;73:335-343)