Abstract
A large part of serum lipid peroxides (LPO) are believed to be carried in lipoproteins. It has been reported that serum LPO levels increase at the time of vascular accidents. Little is known about the distribution of LPOs in lipoproteins, however, or the relationship between LPOs and thrombus formation.
We studied LPOs in oxidatively modified lipoproteins and their effect on platelet aggregation. Lipoproteins were isolated from 20 patients with arteriosclerotic diseases. The lipoproteins were oxidized by dialysis against tap water and against water containing Cu++. LPO was measured using a thiobarbituric acid reacting substance (TBARS) assay. Platelet aggregation was measured by the Born method, and lipid constituents of the lipoproteins were analyzed using thin layer chromatography (TLC).
1) TBARS levels of very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL) increased after dialysis. After tap water dialysis, the profile of lipid peroxide levels of LDL was almost the same as that of VLDL, and much higher than that of HDL. After dialysis against Cu++, lipid peroxide in the LDLs was higher than that in the VLDLs and much higher than that in the HDLs.
2) Tap-water-dialyzed lipoproteins which were preincubated with platelet-rich plasma potentiated adenosine diphosphate (ADP)-induced platelet aggregation. Among tap water dialyzed lipoproteins with the same LPO levels, LDLs had the strongest potentiation affect.
3) Using TLC, new spots were detected between triglycerides (TG) and free fatty acids (FFA) and between FFA and free cholesterol (FC) in tap-water-dialyzed lipoproteins. These spots were not detected when ethylenediamine tetraacetate or butylated hydroxytoluene was added to the dialysate. The spot between TG and FFA was detected only with oxidized LDLs and HDLs. Spots of the same rate of flow as these were identified in oxidized products of cholesterol esters in native LDLs, but they were not detected in oxidized products of other lipid constituents.These spots were made of oxidized products of cholesteryl linoleate.
Our data suggest the following: 1) oxidized lipoproteins have different biological activities; 2) the oxidized cholesteryl linoleate product plays an important role in the potentiation of platelet aggregation by oxidatively modified LDLs.
