Frequency of antibodies to the cholesterol transport protein apolipoprotein A1 in patients with SLE.

In examining reasons for premature atherosclerosis in systemic lupus erythematosus (SLE), we previously reported low levels of the cholesterol transport protein apolipoprotein A1 (apoA1) in these patients, and specific antibodies to purified apoA1 were identified in the sera of 5 out of 30 lupus patients. The current study was initiated to determine whether these antibodies are common in lupus patients. 520 serum samples from 175 patients with SLE or primary antiphospholipid syndrome (PAPS) were tested for antibodies to purified apoA1. Positive sera were retested for binding to apolipoprotein incorporated into reconstructed nascent or mature high-density lipoprotein (HDL). Autoantibodies to apoA1 were found in 32.5% of patients with SLE and 22.9% of patients with PAPS, associated with the presence of aPL (anti-beta2 glycoprotein-1, anti-beta2 GP1) antibodies. When reconstructed, nascent and mature HDL molecules were compared as antigen-containing environments, positive sera reacted best to apoA1 embedded in mature HDL molecules. This report confirms the high prevalence of antibodies to apoA1 in patients with systemic lupus and suggests a high affinity of these antibodies for mature HDL.

Immunoreactivity of apolipoprotein B-100 in oxidatively modified low density lipoprotein.

Thirteen monoclonal antibodies (MAbs) against apolipoprotein B-100 (apo B) were used to analyze changes in immunoreactivity of human LDL resulting from oxidation mediated by cupric ions and oxygen. Decrease in immunoreactivity of oxidized LDL was demonstrated by competitive ELISA with MAbs 5F8, BL3, Mb43, 2G8, B3, B5, and BL7 for which the epitopes are located within residues 1-1297, 4235-4355, 4027-4081, 3728-4306, 2239-2331, 1854-1878, and in the vicinity of residue 2331, respectively. Immunoreactivity of the epitope B6 (2239-2331) increased during first 4 hours of oxidation and then diminished gradually. Epitope B1 (405-539) had slightly reduced immunoreactivity during first 8 h of LDL oxidation and then its minor increase was observed. MAb 12G10, specific to the epitope within apo B thrombin-digest fragment T4 (1-1297), displayed either weak or strong binding to LDL. LDL with weak binding pattern demonstrated significant increase in immunoreactivity upon oxidation. In contrast, LDL with strong binding pattern showed little to no change. Epitopes Mb47 (3441-3569) and 8G4 (1-1297) remained unchanged in oxidized LDL. Immunoreactivity of apo B-100 epitope recognized by MAb 4C11 (residues 2377-2658) was shown to be a function of oxidation time: it increased progressively up to 16 h and was stabilized for another 24 h of LDL oxidation. This epitope may be unmasked by LDL oxidation and may provide a useful immunochemical marker to monitor the extent of LDL oxidation.

Does a HDL injection reduce the development of serum hyperlipidemia and progression of fatty streaks in cholesterol fed rabbits?

The influences of homologous (rabbit) or heterologous (human) high density lipoprotein (HDL) on the development of serum hyperlipidemia and progression of fatty streaks were studied in cholesterol fed rabbits. Three groups of New Zealand rabbits were fed a 0.5% cholesterol rich diet for 8 weeks. Additionally into these animals the following solutions were injected intravenously two times per week: group 1 (control): saline; group 2: human HDL dissolved in saline; group 3: rabbit HDL dissolved in saline. The animals of group 2 had lower serum cholesterol levels during the dietary period than rabbits of group 1 (p < 0.05) but the surface of intima covered with fatty streaks was the same as in group 1. On the other hand, the serum cholesterol level in rabbits of group 3 was the same as in group 1 during the whole experimental period, but the surface of aorta covered with fatty streaks was significantly lower (p < 0.05) in group 3 than in group 1. The results of this study support the hypothesis of an antiatherogenic action of HDL, which seems to be independent of the influence of HDL on the serum lipids but depends on the source of HDL.

[Immobilization of phospholipid micelles on modified apoHDL-Sepharose]. / Immobilizatsiia fosfolipidnykh mitsell na modifitsirovannoi apoLVP- Sefarose.

There was developed a procedure for immobilization of phosphatidyl cholines (Egg yolk phosphatidyl choline and polyunsaturated soya beams phosphatidyl choline) on the modified apoHDL-Sepharose. The formation of phospholipid micelles was proved by linear dependence of the content of the sorbed phosphatidyl choline versus, the content of apoHDL bound to Sepharose. Incubation of apoHDL/PC-Sepharose with human plasma was shown to change the plasma lipid composition. The apoHDL/PC-Sepharose might be used for correction of the plasma lipid composition on vitro experiments.

[Metabolism of phosphatidylcholine in model lipoproteins. Use of phospholipid micelles immobilized on apoHDL-Sepharose]. / Obmen fosfatidilkholina v model'nykh lipoproteinakh. Ispol'zovanie fosfolipidnykh mitsell, immobilizovannykh na apo-LVP-Sefarose.

A phosphatidyl choline (PC) exchange between apoHDL/PC micellar complexes in solution and the same complexes immobilized on Sepharose was studied. The PC exchange in buffer was represented in terms of pseudo first order reversible process. The first order constants for the unidirectional efflux of PC from apoHDL/PC-Sepharose (k1) and for the unidirectional efflux of PC from apoHDL/PC complexes (k2) were equal to (0.45 +/- 0.2) x 10(-3) and (1.35 +/- 0.2) x 10(-3) min-1, respectively. The k1 values showed the Arrhenius dependence on the temperature within range 278-323 K. Plasma serum proteins facilitated the PC efflux from apoHDL/PC-Sepharose being additional acceptors of PC. These data allow use of apoHDL/PC-Sepharose for correcting lipid plasma composition in vitro.

[Study of HDL2-dependent synthesis of bile acids in culture of rabbit hepatocytes: effects of oxidized cholesterol derivatives]. / Izuchenie LVP2-zavisimogo sinteza zhelchnykh kislot v kul'ture gepatotsitov krolika: éffekty oksiproizvodnykh kholesterina.

The effect of individual oxysterols--products of auto-oxidation of cholesterol on bile acid synthesis by cultivated rabbit hepatocytes was studied. Relative rates of bile acid synthesis were measured as the conversion of 4-14C cholesterol-HDL2 into total 4-14C labeled bile acids. 7 beta-hydroxycholesterol and 3,5-cholestane-7-dione strongly inhibited bile acid synthesis at concentrations 1-10 micrograms/ml. These data support the hypothesis that oxidized cholesterol derivatives accelerate the development of hypercholesterolemia in rabbits fed on cholesterol containing diet.

[Detergent properties of apolipoprotein A1 in micellar complexes with dimyristoyl phosphatidylcholine]. / Detergentnye svoistva apolipoproteina A1 v mitselliarnykh kompleksakhs dimiristoilfosfatidilkholinom.

Bilayer micellar complexes of the human plasma apolipoprotein A1 with dimyristoyl phosphatidylcholine were prepared under kinetically controlled conditions. Detergent-like properties of Apo A1 in the complexes were expressed in terms of delta SA1 parameter (surface area of mixed micelle per an Apo A1 molecule). Analysis of our and earlier published data showed the correlation of the delta SA1 parameter with the stoichiometry of complexes. Changes of detergent-like properties were caused by cross-linking or proteolysis of Apo A1.

[Formation of micellar complexes of apolipoprotein A-I with dimyristoylphosphatidylcholine]. / Obrazovanie mitselliarnykh kompleksov apolipoproteina A-I s dimiristoilfosfatidilkholinom.

Structural changes of apolipoprotein AI from human plasma high density lipoproteins in 2-chloroethanol solutions were studied using spin label and fluorescence techniques. Reversible changes in spectral parameters occur in 2-chloroethanol concentration range 0-40% and are affected by dimyristoylphosphatidylcholine, of 2-chloroethanol concentration does not exceed 30%. Dialysis experiments demonstrated the absence of binding of monomer phosphatidylcholine with apolipoprotein AI. It thus follows that formation of complexes of apolipoprotein AI with dimyristoylphosphatidylcholine is caused by lipid micella aggregation.

[Interaction of plasma lipoproteins and apolipoproteins with lipid bilayer membranes]. / Izuchenie vzaimodeistviia lipoproteidov plazmy krovi i apolipoproteinov s bisloinymi lipidnymi membranami.

It was shown that the interaction of lipoproteins (LP) with bilayer lipid membranes (BLM) resulted in some changes in the physical-chemical properties of the membranes. Adsorption of very low and low density lipoproteins (VLDL and LDL) at concentrations of 5-8 g protein/ml increased the surface potential difference and decreased transversal elasticity module of the bilayer. LP concentrations higher than the mentioned ones increased BLM conductance and caused instability and disruption of the membranes. The same effects were revealed for high density lipoproteins (HDL) at higher concentrations--15-20 micrograms protein/ml. The effect of apolipoproteins in the interaction of LP with BLM was investigated. It is proposed that apolipoproteins and especially apo B are the main factor which affects the nonreceptor interactions of LP with the membranes.

Recombinant models of lipoproteins. Apolipoprotein A-I/phosphatidylcholine/cholesterol complexes formed in a 2-chloroethanol-water mixture.

Apolipoprotein A-I can spontaneously associate with phosphatidylcholine and cholesterol in 2-chloroethanol-water mixture. It was demonstrated, using a spin label technique, that dissolved molecules participate in complex formation. The apolipoprotein A-I/phosphatidylcholine/cholesterol complexes were isolated by gel chromatography. Complexes of three types were prepared and characterized: type A, large heterogeneous aggregates with molecular weight 600 000, sedimentation coefficient 10 S and the following molar composition - protein/phosphatidylcholine/cholesterol, 1:(70-100):(10-12); types B and C, with weight average molecular weights 140 000 and 110 000, average sedimentation coefficients 3.6 S and 1.7 S, respectively. Both types have the same molar composition - protein/phosphatidylcholine/cholesterol, 1:25:8. The dissimilar sedimentation coefficients between complexes B and C may be explained by the difference in the monomer/tetramer ratio (monomer molecular weight 50 000). The spin label sn-1-O-stearoyl-2-O-9'-spiro(4'',4''-dimethyloxazolidine-3''-oxyl) heptadecanoylglycero-3-phosphocholine introduced into the complexes A and B showed different thermal properties of these complexes, which may be due to differences in the lipid-protein interactions.