A. N. Klimov

On the Ability of High Density Lipoproteins to Remove Phospholipid Peroxidation Products from Erythrocyte Membranes

To study the transfer of oxidized phospholipids from cell membranes to high-density lipoproteins (HDL), human Cu2+-oxidized erythrocyte membranes were incubated with HDL3 subfraction for 17 h at 37°C followed by isolation of the supernatant, precipitation from it of HDL3, and determination of lipid peroxide products (LPP) in them. The incubation increased the content of lipid hydroperoxides in HDL3 significantly (by 32 and 40% calculated per ml of sample or mg of protein) and of malondialdehyde (by 27 and 34%, respectively) compared to control (incubation of HDL3 alone). The content of conjugated dienes did not change significantly. Fluorescence analyses of isolated HDL3 particles showed that the content of fluorescent products (λex = 365 nm, λem = 430 nm) in them was 2.5 times higher than in control, and the number of binding sites for the 1-anilinonaphthalene-8-sulfonic acid probe decreased by 22%. This also confirms accumulation of LPP in the lipoprotein subfraction. It seems likely that an increase in LPP (at least hydroperoxides) in HDL3 after their incubation with oxidized membranes occurs via transport of phospholipids containing LPP from erythrocyte membranes to lipoproteins. The data on the ability of HDL3 to accept LPP from erythrocyte membranes in vitro suggest that HDL3 may have a protective action on cell membranes undergoing oxidation in vivo as well.

Antioxidant effect of high-density lipoproteins in peroxidation of low-density lipoproteins

It has been shown that in the solution of low density lipoproteins (LDL) during their incubation at 37 degrees C the turbidity and concentration of malondialdehyde was increased, as compared to that observed at 4 degrees C. Both parameters were slowed down by the addition of high density lipoproteins (HDL) into the medium. The protective effect of HDL depended on the time of incubation and the concentration of HDL added. Delipidated HDL had no effect. Similar action of HDL was established in the experiments where the peroxidation in LDL was induced by the xanthine-xanthine oxidase. The data obtained demonstrate that HDL possess an antioxidant property that may play an important role in their antiatherogenic action.

“Essential” phospholipids versus nicotinic acid in the treatment of patients with type IIb hyperlipoproteinemia and ischemic heart disease

SummaryIn patients with moderate, dietary noncorrigible hyperlipoproteinemia type IIb and ischemic heart disease, treatment with nicotinic acid is limited by the side effects of the drug. In 100 patients, 6-month treatment with nicotinic acid (n=50) or “essential” phospholipids (EPL); Lipostabil®, manufacturer: Rhône-Poulenc Rorer) (n=50) indicated comparable efficacy for both substances: Significant (p<.001) reductions of serum total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglyceride values were similar in both groups, while nicotinic acid increased high-density lipoprotein (HDL) cholesterol significantly (p<.01) better than Lipostabil. A detailed analysis of ultracentrifugal lipoprotein profiles, hydroperoxide concentrations in LDL, and cholesterol-accepting properties of HDL in a small number of Lipostabil- and nicotinic acid-treated patients revealed favorable shifts in the lipoprotein profile, significant (p<.05) reductions of LDL hydroperoxides, and favorable increases of the most antiatherogenic HDL2b subfraction only in the Lipostabil-treated group. Clinically, both medications reduced the intensity and number of angina pectoris attacks per week (p<.05), but only Lipostabil-treated patients significantly (p<.05) increased their working capacity in the veloergometric test. Since in the nicotinic acid-treated group dropouts (nine patients, eight related to the drug) and side effects [14] exceeded those in the Lipostabil-treated group (two dropouts not related to the drug, no side effects), it is suggested that Lipostabil is a preferable alternative in the treatment of patients with moderate, dietary noncorrigible hyperlipoproteinemia IIb and ischemic heart disease.

On the mechanism of cholesterol interaction with apolipoproteins A-I and E

It is shown that cholesterol may interact with some substances containing the guanidine group (guanidine itself, arginine, metformin and dodecylguanidine bromide) and with arginine-rich proteins--apoproteins A-I and E. In the latter case the interaction produces the formation of cholesterol-apoprotein complexes. Analysis of such complexes has shown that one apo A-I molecule binds 17-22 and one apo E molecule binds 30-35 sterol molecules, which approximately corresponds to the amount of arginine residues in these proteins. Formation of cholesterol-apoprotein complexes has been suggested to occur due to: (1) formation of hydrogen bond and/or ion-dipole interaction between cholesterol hydroxyl and guanidine groups of the apoprotein arginine residues and (2) hydrophobic interaction of the cholesterol aliphatic chain with nonpolar side chains of the amino acids occupying the third position from arginine in the protein molecule.

Comparative characteristics of fatty-acid composition of lipoproteins from human blood plasma and aortic wall

The fatty-acid composition of lipid fractions in lipoproteins of very low, low, and high density from blood plasma and the aortic wall of patients with atherosclerosis was investigated. A close similarity was found in the fatty-acid composition of phospholipids, triglycerides, and cholesterol esters in all classes of lipoproteins from the vascular wall and blood plasma. The composition of the fatty acids of the fractions was very similar in all classes of lipoproteins. Lipids from the vascular wall not included in the composition of lipoproteins differed considerably in their fatty-acid composition from lipids isolated from lipoproteins: the content of unsaturated fatty acids in the lipids of the aortic wall was much smaller than in lipoproteins.

Hydroperoxides of ApoB-lipoproteins isolated by immunoaffinity chromatography

Studies using affinity chromatography and ultracentrifugation indicate that in human blood 40–50% of lipid hydroperoxides are transported by apoB-lipoproteins, 20% by high-density lipoproteins, and 30–40% by albumins and other proteins. Affinity-isolated apoB-lipoproteins from umbilical blood contain smaller amounts of lipid hydroperoxides than do those from the blood of healthy adults, while the content of lipid hydroperoxides in apoB-lipoproteins from the blood of patients with ischemic heart disease is often higher. Aortal apoB-lipoproteins are considerably enriched in these hydroperoxides.

Unusual route of protein discharge from the cell

A protein-secreting plasma cell is revealed in atherosclerotic intima of the rabbit aorta by electron microscopy. Protein is secreted together with rough endoplasmic reticulum by budding of preformed processes. Mast cells also release α-granules by the budding of cell processes. It is suggested that the ability of intimal cells to export synthesized substances by this route is realized during atherogenesis.

Nonreceptor interaction of low density lipoproteins with human fibroblasts

An analysis was made of catabolism of low density lipids (LDL) labeled in the protein or lipid moieties with cultivated human fibroblasts under inhibition of receptor-mediated endocytosis of LDL. The results have shown that under these conditions, only part of LDL uptaken by the cells are catabolized in the cells for 24 h. A considerable part account for a slow-metabolized intracellular pool. LDL of the latter may leave the cells by exocytosis (regurgitation), appearing in the culture medium. On the whole, the data obtained agree with the basic regularities of LDL transport in the cell within the structure of uncoated vesicles.