Transferable lipids in oxidized low-density lipoprotein stimulate plasminogen activator inhibitor-1 and inhibit tissue-type plasminogen activator release from endothelial cells.

Abstract

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.

Influence of Glycation on LDL-Induced Generation of Fibrinolytic Regulators in Vascular Endothelial Cells

“…10,11,13 The results of the present study indicate that oxidized LDL also reduces tPA generation in HUVECs. Glycated LDL may be more susceptible to oxidation than is native LDL.…”

Effects of Native, Triglyceride-Enriched, and Oxidatively Modified LDL on Plasminogen Activator Inhibitor-1 Expression in Human Endothelial Cells

“…13,15 In contrast, variable effects have been reported for native and oxidatively modified LDL. Native LDL (nLDL) has generally been shown not to induce PAI-1 synthesis, 14,16,17 unless high concentrations or prolonged incubation times (48 hours) are used. 12,18 LDL oxidized by UV light (uvLDL) stimulates the synthesis and secretion of PAI-1 from cultured endothelial cells, 16 whereas either stimulation, 17 no effect, 12 or reversal of nLDL-induced effects 18 has been obtained with more drastic peroxidation using copper.…”

Hypertriglyceridemic VLDL Downregulates Tissue Plasminogen Activator Gene Transcription Through cis -Repressive Region(s) in the Tissue Plasminogen Activator Promoter in Cultured Human Endothelial Cells

“…These findings complement previous in vitro and clinical observations. For example, it is known that other atherogenic lipoproteins decrease tPA secretion and tPA-mediated Pmg activation in cultured ECs 8,10,43 and that compared with control subjects, patients with CAD and elevated Lp(a) levels have a marked reduction in their ability to release tPA in response to venous occlusion. 1 Whether this type of regula- …”

“…4,5 Therefore, it is conceivable that perturbation of the expression or activity of Ն1 of these fibrinolytic proteins may alter the hemostatic balance on the EC surface, thus promoting early initiation of fibrin deposition, atherogenesis, CAD, and eventual MI. 1 Several atherogenic lipoproteins may cause such a perturbation; eg, Lp(a), 6 oxidized LDL, 7,8 and acetylated LDL 9 increase PAI-1 levels and decrease tPA expression in cultured human ECs. 8,10 In addition, abnormal triglyceride-rich lipoproteins, including VLDL (hypertriglyceridemic VLDL [HTG-VLDL]), have been shown to increase PAI levels 11,12 and decrease surface localized plasmin generation.…”

“…1 Several atherogenic lipoproteins may cause such a perturbation; eg, Lp(a), 6 oxidized LDL, 7,8 and acetylated LDL 9 increase PAI-1 levels and decrease tPA expression in cultured human ECs. 8,10 In addition, abnormal triglyceride-rich lipoproteins, including VLDL (hypertriglyceridemic VLDL [HTG-VLDL]), have been shown to increase PAI levels 11,12 and decrease surface localized plasmin generation. 13 Conversely, normotriglyceridemic VLDL (NTG-VLDL) has been shown to be less potent in creating a prothrombotic state.…”