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L M Poliakov

Publications and source records attributed to L M Poliakov.

35 records · Page 2Linked to original sources
PubMedDate not supplied

[Anomalous change in the specific conductivity in lipoproteins at around physiologic temperatures].

Studying the temperature dependence of conductivity sigma of rat and human lipoproteins and apoprotein A-I fractions revealed an anomalous region in the range of temperatures (35-38) +/- 0.5 degree C. The activation energy delta H and temperature coefficient sigma (delta sigma/delta T) on both sides of Tc and the heat of transition (delta H of transition) were calculated. In high-density human lipoproteins and apoA-I, the delta H value was found to be very low. Some mechanisms of interaction of hydrocortizone with high-density lipoproteins and apoA-I were studied by using IR-spectroscopy and conductometry were studied. It was found that the hormone considerably increases the portion of alpha-helices and beta-structures in these proteins (coil<-->alpha-helix and coil<-->beta-structure transitions). In this case, delta H value of the transition increases 13-fold; in addition, the abnormal region in apoA-I shifts 1-2 degrees C downwards. The anomalous changes in conductivity in the range of physiological temperatures in all lipoprotein fractions including apoA-I are probably related to structural phase transitions both in proteins and in phospholipids. Since the delta H value of the transition in human high-density lipoproteins is small, it is assumed that, in phospholipids of these particles, an orientation transition of the A<-->C smectic type takes place, which is assigned to the second-order phase transition. The structural transition in apoA-I can probably also be assigned to the second-order phase transition since the enthalpia of the transition is very small; presumably, this transition is related to changes in symmetry due to changes in the secondary structure (coil<-->beta-tructure transition).

Animals↗
PubMedDate not supplied

[Interaction of eukaryotic DNA with apolipoprotein A-I and its complexes with glucocorticoids].

A biochemically active complex of apolipoprotein A-I with tetrahydrocortisol was revealed, which increases gene expression in hepatocytes. It was shown by the method of fluorescent probe that titration of rat liver DNA by the apolipoprotein A-I-tetrahydrocortisol complex leads to the appearance of single-stranded fragments. The effect of the complex on the secondary structure of native DNA was confirmed by the method of small-angle X-ray scattering. It was shown that approximately 54 apolipoprotein A-I molecules carrying tetrahydrocortisol as a ligand bind to one molecule of isolated native DNA, inducing a break of hydrogen bonds between the pair of nitrous bases. It is concluded that the cooperative effect of high-density lipoproteins and cortisol in the regulation of gene expression in hepatocytes with the participation of resident liver macrophages is accomplished by a new biochemical mechanism. This mechanism makes itself evident as a result of the interaction of DNA with the apolipoprotein A-I-tetrahydrocortisol complex, the appearance of single-stranded DNA regions in binding sites, and subsequent initiation of gene transcription.

Animals↗
PubMedDate not supplied

[Interaction of tetrahydrocortisol-apolipoprotein A-I complex with eukaryotic DNA and with single-stranded oligonucleotides].

The complex formed by tetrahydrocortisol (THC) and apolipoprotein A-I (ApoAI) specifically interacts with eukaryotic DNA from rat liver. Taken together, physical and chemical data and the results of small-angle X-ray scattering analysis show that interaction of the THC-ApoAI complex with eukaryotic DNA results in deformation of the DNA double helix. Single-stranded fragments were demonstrated to cause deformation of the double helix. In this state DNA forms complexes with DNA-dependent RNA polymerase. This interaction is cooperative and of saturating type; up to six enzyme molecules bind with one DNA molecule. The putative site of complex binding with DNA is the sequence CC(GCC)n found in many genes including the human ApoAI gene. An oligonucleotide of this type was synthesized. Its association constant (Ka) was 1.66 x 10(6) M-1. Substitution of THC with cortysol considerably decreases the Ka. We suggest that THC interacting with GC pairs of the binding site forms hydrogen bonds with cytosine, inducing rupture of the bonds within the complementary nucleic base pair.

Animals↗
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[Determination of apoprotein A-1 by immunoenzyme analysis].

Indirect solid-phase immunoenzymatic assay was improved and adapted for quantitative estimation of apo A-I in blood serum. Immunochemical identification of apo A-I was carried out and specific antibodies were obtained. Various procedures of blood serum pretreatment affected dissimilarly the detection of antigenic determinants in apo A-I. Presence of tetramethyl urea in blood serum increased by 30% the latent antigenic determinants accessibility.

Antibodies↗
PubMedDate not supplied

[Cholesterol esterification in tissues and change in the apoprotein spectrum in rat blood under the effect of auto-oxidized cholesterol].

Influence of autooxidized cholesterol (Ch) products on accumulation of cholesterol esters (ChE) in liver and aorta tissues as well as alteration of the apolipoprotein spectrum in low density and very low density (LDL and VLDL) lipoproteins in blood plasma was studied in rats treated with purified Ch (ChP-rats) and with oxidized Ch containing 5% 25-hydroxyCh and 3% 7-ketoCh (ChO-rats). Increase of ChE content in liver tissue of ChO-rats resulted in two-fold activation of acyl-CoA-cholesterol-O-acyltransferase (ACAT) in liver microsomes as compared with the enzymatic activity rate in ChP-rats. As shown by polyacrylamide gel electrophoresis content of apoE in VLDL and LDL of ChO-rats was 1,5-fold higher as compared with that of ChP-rats. Content of apoIV was increased in LDL and VLDL of ChP-rats as compared with controls; this effect was not observed in ChO-rats. LDL and VLDL from ChO-rats stimulated incorporation of 14C-oleate into ChE of cultivated macrophages. Increase in content of ChE found in aorta of ChO-rats appears to occur due to activation of Ch esterification. Intensification of ChE synthesis in tissues and alterations in the spectrum of LDL and VLDL apolipoproteins caused by oxidized products of cholesterol may be one of the mechanisms involved in atherogenesis.

Animals↗
PubMedDate not supplied

[Interaction of lipoproteins in blood serum with steroid hormones].

Interaction of human and serum lipoproteins with steroid hormones (corticosterone and cortisol) was studied. Methods of fluorescence quenching titration and equilibrium dialysis were used for quantitative evaluation of VLDL, LDL and HDL glucocorticoid-binding ability. Association constants were found to be 0.6-2.0 x 10(6) M-1 for corticosterone and 4.0-8.0 x 10(6) M-1 for cortisol. The number of binding sites varied from 3 to 300 for different classes of lipoproteins.

Hormones↗
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[Use of circadian rhythms for analysis of the interrelationships between the concentration of glucocorticoids in the blood and the activity of key enzymes for gluconeogenesis in the liver and kidney of rats].

Circadian rhythms of alterations in content of 11-hydroxycorticosteroids and glucose in blood as well as in the activity of phosphoenolpyruvate carboxykinase, fructose-1,6-diphosphatase and glucose-6-phosphatase in liver and kidney tissues were studied under normal and inverted luminous regimens in summer and winter seasons. These patterns were distinctly altered depending on circadian rhythms in the above-mentioned conditions. The maximal content of 11-hydroxycorticosteroids in blood did not correlate with the highest activity of the gluconeogenesis key enzymes in the periods studied. Daily alterations in the activity of phosphoemolpyruvate carboxykinase were shown to be similar to that of the fructose-1,6-diphosphatase in various tissues at different seasons. But glucose-6-phosphatase differed distinctly from these enzymes by the daily rhythm of activity. This suggests that glucose-6-phosphatase has the other mechanism for regulation of its daily rhythm.

11-Hydroxycorticosteroids↗
PubMedDate not supplied

[Evaluation of the binding of benzo-a-pyrene by blood serum lipoproteins using the cellulose disk method].

A simple and convenient method has been developed for evaluation binding capacity of lipophilic ligands with lipoproteins or other transport proteins. For this purpose cellulose discs (Whatman 3 MM) were loaded with the constant quantity of 3H-benzopyrene and increasing amounts of unlabelled benzo[a]pyrene in dimethylsulfoxide, dried up and incubated in solution of lipoproteins. Dissociation constants were deduced from the remained disk radioactivity using the Scatchard plot method. The obtained values of the dissociation constants were: HDL--4.1 x 10(-5) M; LDL--1.5 x 10(-6) M; VLDL--8.8 x 10(-6) M.

Animals↗
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[Transport of steroid hormones by serum lipoproteins].

Binding and distribution of glucocorticoids as well as of some of their precursors in lipoprotein fractions of human and rat blood serum were studied. Binding of the corticosteroids with blood serum lipoproteins was shown by ultracentrifugation and gel filtration. The binding of corticosteroids with lipoproteins was accompanied by alterations in the apoprotein conformation, detected by means of quenching of tryptophane fluorescence. The data obtained suggest that the lipoproteins are involved in transport of corticosteroids.

Animals↗
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[Absorption of iodinated plasma lipoproteins by subpopulations of hepatocytes and sinusoid cells of the rat liver].

Individual hepatocytes and sinusoid cells were isolated from rat liver tissue within various periods after intravenous administration of 125I-lipoproteins of very low (VLDL), low (LDL) and high density (HDL). Estimation of the radioactivity per 1 mg of the cell protein showed that within 30 min absorption of VLDL was 6-fold, LDL--4-fold and HDL--14-fold as high as compared with hepatocytes. Within the first 30 min sinusoid cells accumulated 54% of 125I-HDL, while hepatocytes contained 46% of the labelled lipoprotein, absorbed in liver tissue. On the other hand, within 6 hrs and 12 hrs hepatocytes contained 80-88% and sinusoid cells--17-20% of the label. After fractionation of hepatocytes in Ficoll density gradient all the populations of hepatocytes were shown to absorb effectively VLDL fraction, while HDL and LDL were accumulated in "heavy" (centrolobular) hepatocytes. Penetration of the lipoproteins in hepatocytes appears to be carried out by means of intracellular transport from sinusoid cells.

Animals↗
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[Plasma lipoprotein absorption by steroid-producing organs in the rat].

A study was made of the blood plasma iodinated lipoprotein (LP) absorption by the organs and tissues of rats following i.v. injection. The adrenals and ovaries were shown to effectively absorb high density lipoproteins (HDL) as compared to the liver, spleen, kidneys, heart and lungs. HDL absorption reached its maximum 30 min after LP injection. Six hours later the adrenal tissue radioactivity level decreased by 30% and after 12 h 3-fold. The time-course of HDL absorption by the ovaries was characterized by a slow increase in radioactivity after 6 h and a gradual decrease of the label index after 12 h. Differences in HDL absorption by the adrenals and ovaries reflected some functional features of these steroid producing organs.

Absorption↗
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[Lipoprotein absorption and intracellular distribution in the adrenals of rats under physical load].

Intravenous injections of the blood plasma iodinated lipoproteins (LP) to rats led to the marker binding and penetration into the adrenal cells. The most intensive absorption was specific to LPs of high density (LPHD) and, to a lesser degree, to LPs of low and very low density (LPLD, LPVLD). Intensive exercises produced an enhanced LPHD accumulation and a reduced LPLD level in the adrenal tissues. During subcellular fractionation of the adrenals LPVLDs were uniformly distributed among cellular organelles, LPLDs were accumulated in lysosomes and cytosol, whereas a large LPHD amount was collected in the small cytoplasmic membranes. The exercises led to an increase in LPHD binding with the fraction of small cytoplasmic membranes. The role of different LP classes in steroidogenesis processes is discussed. The differences, found in the absorption extent and localization of LP labelled, allowed one to suggest that the pathways of intracellular metabolism of several LP classes in the rat adrenals are distinctive.

Absorption↗
PubMedDate not supplied

[Physiological mechanisms of the regulation of lipoprotein biosynthesis in liver during physical exercise and in different phases of the restoration period].

Changes in serum lipoprotein pattern and in total content of low density lipoproteins (LDL) and very low density lipoproteins (VLDL) were studied in blood and liver tissues of rats during physical exercise and restoration. Physical training induced synthesis of liver lipoproteins, in particular of their protein components. An initial period of lipoprotein synthesis in the liver tissue was preceded by transient activation of lysosomes in hepatocytes and their translocation towards nuclei. When lysosome translocation was depressed by vinblastine or colchicine injected 1 h before the physical exercise, an increase in total amount of LDL and VLDL fractions in liver and blood could not be observed. The inhibition of lysosomal proteolytic activity by hordox also impaired an increase in blood and liver lipoproteins. The data obtained suggest that activation of lysosomes and their translocation towards nuclei are important for induction of lipoprotein synthesis in liver tissue during physical exercise.

Animals↗
PubMedDate not supplied

[Use of direct spectrophotometry for the quantitative analysis of corticosteroids on thin-layer chromatograms].

Direct densimetry at 252.5 microns of cortisol on chromatographic plates with a thin silica gel layer provides the best results in comparison with fluorimetry, that includes pretreatment of plates with tetrazole reagent. Accuracy, sensitivity and reproducibility of the method were examined with reference to quantitative determination of the blood serum corticosterone of rats. Owing to a high sensitivity the direct densimetry technique in reflected light at 252.5 microns proved suitable for quantitative evaluation of the steroid spectrum in extracts from the rat adrenal incubate sections and the human blood serum. 3 ml of the blood serum is required for analysis performance.

Adrenal Cortex Hormones↗