[Apolipoprotein A-I stimulates secretion of insulin and matrix metalloproteinases by islets of Langerhans]. / Apolipoprotein A-I stimuliruet sekretsiiu insulina i matriksnykh metalloproteinaz ostrovkami Langergansa podzheludochnoi zhelezy.

The development of type 2 diabetes mellitus (DM2) is accompanied by disturbances in lipid metabolism. These include the increase in serum levels of atherogenic fractions of very low-density (VLDL) and low-density lipoproteins (LDL), total cholesterol, triglycerides and apo B. In contrast, the level of antiatherogenic high density lipoproteins (HDL) and the content of apolipoprotein A-I (apoA-I) decreased. To study the effect of the observed metabolic changes on insulin secretion in vitro, we used the islets of Langerhans isolated from the rat pancreas. It has been found that incubation of the islets in the presence of serum of the obese patients and patients with decompensated DM2 leads to a decrease in insulin secretion by 2.4 and 5.0 times, respectively. On the contrary, the addition of HDL to the incubation medium increased the insulin secretion by 3.4 times. A similar effect was observed in the presence of apoA-I, the main protein component of HDL. In the presence of apoA-I, the extracellular activity of matrix metalloproteinases (MMPs) demonstrated a 10-fold increase. The addition of LDL and VLDL to the islets did not change the secretion of insulin and activity of MMP. Our results testify to the important role of HDL and apoA-I in regulation of the insulin secretion by b-cells and the activity of MMPs in the islets of Langerhans.

Production and Analysis of Biological Properties of Recombinant Human Apolipoprotein A-I.

Production of recombinant human apolipoprotein A-I (apoA-I) in E. coli cells is described and its biological properties are compared with those of natural protein. Recombinant apoA-I was isolated as a chimeric polypeptide and then processed to a mature form apoA-I (rapo-I). We studied the ability of the resulting protein to penetrate into hepatocyte nuclei and regulate the rate of DNA biosynthesis in complex with estriol. Penetration of rapoA-I conjugated with FITC into hepatocyte nuclei was demonstrated. rapoA-I-estriol and apoA-I-estriol complexes induced similar increase in DNA biosynthesis rate in isolated hepatocytes, which confi rms functional similarity of the obtained recombinant mature protein (rapoA-I) and native human apoA-I.

Content of circulating extracellular DNA, plasma activities of matrix metalloproteinases, and ultrastructure of the myocardium in hypothyroid rats with hypercholesterolemia.

Free circulating extracellular DNA, plasma activities of matrix metalloproteinases in hypothyroid rats, and ultrastructural changes in the myocardium were studied under conditions of experimental hypercholesterolemia. For suppression of thyroid function, the animals received antithyroid drug mercazolyl under conditions of cholesterol diet. Hypercholesterolemia in hypothyroid rats (thyroxine concentration 2-fold below the normal) was paralleled by a pronounced increase of the concentration of free circulating extracellular DNA and total matrix metalloproteinases 2 and 7 activity. These changes were associated with lytic and destructive changes in cardiomyocytes and blood capillary endotheliocytes. Changes in the cardiomyocyte and endotheliocyte ultrastructure were more pronounced in hypothyroid rats.

Structural changes in the myocardium and serum lipid spectrum in experimental hypercholesterolemia and hypothyroidism.

We studied the peculiarities of lipid spectrum of the blood and structural reorganization of the myocardium in experimental hypercholesterolemia with and without hypothyroidism. It was found that alimentary hypercholesterolemia accompanied by elevated total cholesterol, LDL, HDL, and triglyceride concentrations led to a decrease in body weight, heart weight, number of cardiomyocytes in the heart and induced pronounced lytic changes in cardiomyocytes, circulation disorders (sludge syndrome, echinocytosis of erythrocytes, lymphostasis), diffuse fibrosis of the stroma, and appearance of foam cells among diffuse mononuclear infiltrate cells. The combination of hypercholesterolemia with hypothyroid status caused more pronounced changes in the lipid spectrum and atherogenic index and more pronounced lytic and necrobiotic changes in cardiomyocytes. These findings suggest that elevated cholesterol concentrations in the blood, especially against the background of suppressed thyroid function, can directly induce considerable damage to cardiomyocytes, intramural vessels, and erythrocytes without the development of myocardial ischemia and in the absence of atherosclerotic plaques.

Apolipoprotein A-I as a carrier of lipopolysaccharide into rat hepatocytes.

Apolipoprotein A-I-mediated transport of LPS into isolated rat hepatocytes was demonstrated by means of fluorescent microscopy and spectrofluorometry. The efficiency of intracellular endotoxin transport in a complex with apolipoprotein A-I significantly exceeded the absorption of LPS without this carrier. Our results suggest that the mechanism of the anti-inflammatory effect of HDL and apolipoprotein A-I can be related to alternative pathway for metabolic degradation of this endotoxin with the involvement of lipoprotein receptors.

Plasma lipoproteins as a transport form of extracellular DNA.

We showed DNA-binding activity of different classes of plasma lipoproteins in rats and humans. Experiments with fluorescent dye Hoechst 33258 showed that about 12% extracellular plasma DNA is present in circulating lipoproteins complexes; 7-8% of them with HDL. Structural HDL protein apoA-I probably plays the major role in the interaction between extracellular DNA and lipoprotein particle. Participation of lipoproteins in the transport of extracellular DNA can be considered as an important mechanism for elimination of nucleic acids from blood plasma.

Activity of matrix metalloproteinases during antimycobacterial therapy in mice with simulated tuberculous inflammation.

Matrix metalloproteinases are shown to be involved in the pathogenesis of tuberculosis inflammation. In the early stages of BCG-granuloma formation in mouse liver and lungs, the serum levels of matrix metalloproteinases 2 and 7 increased by 4.5 times and remained unchanged while the pathology developed. Antimycobacterial therapy with isoniazid reduced enzyme activity almost to the level of intact control. The decrease in activity of matrix metalloproteinases 2 and 7 that play the most prominent role in the development of destructive forms of tuberculosis is of great therapeutic importance.

Effect of apolipoprotein a-I complex with tetrahydrocortisone on protein biosynthesis and glucose absorption by rat hepatocytes.

We studied the effect of apolipoprotein A-I-tetrahydrocortisone complex on (14)C glucose absorption and lactate accumulation and on the rate of protein biosynthesis in isolated rat hepatocytes. The presence of apolipoprotein A-I-tetrahydrocortisone complex in the incubation medium increased absorption of labeled glucose by hepatocytes by 52%, while lactate content in the conditioning medium increased 4-fold. The rate of protein biosynthesis increased by 80% in comparison with control cells. It is hypothesized that the increase in protein biosynthesis rate in hepatocytes under the effect of apolipoprotein A-I-tetrahydrocortisone complex is due to stimulation of energy metabolism, specifically, of its glycolytic component.

Effect of plasma lipoproteins and their complexes with polysaccharides on interleukin-1beta concentration in macrophages of mice with HA-1 ascitic hepatoma.

Experiments on cultured peritoneal macrophage from mice with HA-1 ascitic hepatoma showed that plasma lipoproteins present in the incubation medium decreased intracellular concentration of interleukin-1beta. These changes were most pronounced for high-density lipoproteins (alone or in combination with cortisol). Bacterial and yeast polysaccharides had little effect on interleukin-1beta concentration in macrophages. Addition of polysaccharides in combination with lipoproteins was followed by a 2-3-fold decrease in interleukin-1beta concentration. A combination of polysaccharides and high-density lipoproteins had the strongest effect. These properties of plasma lipoproteins should be taken into account in the correction of macrophage function during tumor growth.

[Effect of a complex of corticosteroids with apolipoprotein A-I on protein biosynthesis in cultured hepatocytes].

A complex of apolipoprotein A-I with steroid hormones containing reduced Δ4, 3-ketogroup in the A ring was shown to increase the rate of protein synthesis in the cultured rat hepatocytes. The biological activity of the hormones depends on the position of the oxygroup of the third carbonic atom and hydrogen at the fifth position of a carbonic atom. The cis-position is more preferable for the biological effect. The oxygroup at the third position of the A-ring may be replaced by the sulfo-group. The complex of dehydroepiandrosterone sulphate with apolipoprotein A-I increases the rate of protein biosynthesis in the cultured rat hepatocytes, which confirms the involvement of this hormone in the regulation of gene expression.

Modification and clearance of low density lipoproteins during the formation of endotoxin-lipoprotein complexes.

Changes in electrical charge and clearance rate of LDL after the formation of their complexes with bacterial LPS were studied in experiments on Wistar rats. It was found that binding of S. minnesota R595 LPS with (125)I-LDL sharply accelerated clearance of the greater part of LDL complexes, but on the other hand induced the appearance of an LDL-LPS subfraction with slower elimination rate compared to free LDL. Electrophoresis showed that after binding of LPS, LDL acquired a negative charge. These data suggest that the formation of LDL-LPS complexes is accompanied by modification of LDL due to which they acquire atherogenic properties.

Effect of complexes of apolipoprotein A-I with tetrahydrocortisol and pregnenolone on protein biosynthesis in rat hepatocytes culture.

Complexes of apolipoprotein A-I with tetrahydrocortisol and pregnenolone exhibit high biological activity and increase the rate of protein biosynthesis in the culture of rat hepatocytes. An important role in this process is played by reduced delta44-3-keto group in the A-ring of steroid hormones. A complex of apolipoprotein A-I and pregnenolone modulated the rate of protein biosynthesis in liver cells. Hence, the observed changes are not organ-specific for this steroid. Our results suggest that this mechanism of regulation play an important role in intracellular regeneration and proliferation.

Interaction of apolipoproteins A-I and E in the regulation of DNA, RNA, and protein biosynthesis in cultured rat hepatocytes.

Experiments on hepatocyte culture showed that apolipoprotein A-I-tetrahydrocortisol complex increases the rate of DNA, RNA, and protein biosynthesis measured by radioactive label incorporation. Apolipoprotein E acted as competitor of the apolipoprotein A-I-tetrahydrocortisol complex and abolished biological activity of the latter. We hypothesize that this mechanism of regulation plays an important role in processes of intracellular regeneration and proliferation.

Effect of polysaccharides and human plasma lipoproteins on the secretion of cystatin C by peritoneal macrophages from normal and tumor bearing mice.

Intact peritoneal macrophages in vitro secreted the cysteine proteinase inhibitor cystatin C. Polysaccharides stimulated cystatin C secretion: lipopolysaccharide < carboxymethylated beta-D-glucan < sulfoethylated beta-D-glucan. Human plasma low-density- (LDL) and high-density lipoproteins (HDL) are still more potent inducers of cystatin C secretion by macrophages. Peritoneal macrophages from mice with experimental HA-1 hepatoma compared to those from intact mice secreted more cystatin C with maximum polysaccharide-stimulated secretion after 30 min of incubation. LDL and HDL induced cystatin C secretion by tumor macrophages also.

Involvement of adenine nucleotide carrier in the mechanism of the apolipoprotein C induced decrease of membrane potential in rat liver mitochondria.

Apolipoprotein C (apo C) was shown to decrease the Ca2+ capacity and membrane potential of mitochondria isolated from rat liver. The specific ligands of adenine nucleotide carrier, ADP and carboxyatractyloside (CAT), inhibited the effect of apo C on the mitochondrial membrane potential. The effect of ADP and CAT was revealed in the absence of Ca2+. We conclude that in the presence of apo C, adenine nucleosides carrier transforms into a pore, and this causes the decrease in the membrane potential of the mitochondria. ADP and CAT support the primary conformation of the carrier and therefore inhibit the effect of apolipoprotein C.

Detection of apolipoprotein A-I, B, and E immunoreactivity in the nuclei of various rat tissue cells.

Proteins with apolipoprotein A-I immunoreactivity were detected in the fraction of non-histone acidic proteins isolated from nuclei of various rat tissue cells. These proteins were detected in the brain, liver, kidney, lung, heart, skeletal muscle, testis, spleen, and bone marrow. In the same fraction from liver nuclei, proteins with apoB and apoE immunoreactivity were also detected. The composition of these proteins was studied by immunoblotting. ApoA-I immunoreactivity in the liver nuclei is due to two proteins. One 28-kD protein corresponds to the mature form of the plasma pool of apoA-I and another 14-kD protein is the product of limited proteolysis of apoA-I. The highest content of apoA-I immunoreactivity was detected in transcriptionally active chromatin and nuclear matrix. ApoB immunoreactivity is due to six proteins with molecular weights from 15 to 100 kD. ApoE immunoreactivity is due to a single protein corresponding to the 35-kD form of plasma apoE. Proteins with apoA-I, apoB, and apoE immunoreactivity may be involved in the regulation of transcriptional activity of chromatin.

Effects of apolipoproteins C on oxidative phosphorylation in rat liver mitochondria.

It is shown that apoC-III, but not other apoC proteins, components of very low density lipoproteins (apoC-I, apoC-II, apoC-III), reduced the rate of mitochondrial respiration in various metabolic states. This effect depended on the dose of apoprotein, type of oxidized substrate, and the presence of Ca ions in the incubation medium. ApoC-III completely blocked oxidative phosphorylation during oxidation of palmitoyl carnitine by mitochondria, while the respiration rate in metabolic state 4 remained unchanged.

Distribution of tocopherol and apolipoprotein A-I immunoreactivity in rat liver chromatin.

[125I]Labelled lipoproteins (HDL, LDL, and VLDL) are actively taken up by the rat liver. The uptake rate in nonparenchymal liver cells was significantly higher than that in hepatocytes. Analysis of the distribution of the labelled lipoproteins in liver subcellular structures showed the presence of these compounds in the nuclei. The presence of apoA-I, apoB and apoE immunoreactivity in liver cell nuclei was demonstrated by immunochemical methods (ELISA and dot immunoassay). The nuclear matrix and transcriptionally active chromatin displayed the highest apoA-I levels, which considerably exceeded those in the total and transcriptionally inactive chromatins. A similar distribution pattern was observed for alpha-tocopherol. It is concluded that blood serum lipoproteins, primarily HDL, may transport tocopherol and other lipids into cell nuclei.

Soluble glucan protects against endotoxin shock in the rat: the role of the scavenger receptor.

Soluble carboxymethyl-b-1,3-glucan (CMG), a possible ligand for scavenger receptors, has macrophage-activating action but lacks the granulomatose inflammatory side effect: it is a promising immunomodulator that may mitigate the severity of sepsis. This motivated us to study in rats the effect of CMG (25 mg/kg), injected into the tail vein at 48 and 24 h prior to the administration of 5 mg/kg Escherichia coli 0127.B8 endotoxin on survival, hemodynamic condition, and, in vitro, on the chemiluminescence of PMNs and macrophages, and on macrophagal tumor necrosis factor (TNF) production. Acetylated low density lipoprotein (AcLDL) clearance in vivo and in vitro binding to macrophages was used to study scavenger receptor function. In the nonpretreated group 9 of 10 rats died during the first 24 h after endotoxin, but all CMG-pretreated rats survived. CMG-pretreatment prevented severe decreases in cardiac output and blood pressure after endotoxin. Chemiluminescence of macrophages and PMNs from CMG-pretreated rats was about two times less (p < .05) than that from nonpretreated ones; the endotoxin induced TNF production by macrophages also decreased. Pretreatment with CMG increased, but coinjection of CMG and AcLDL decreased the AcLDL clearance, while coinjection of endotoxin and AcLDL decreased the survival rate. In vitro AcLDL uptake by macrophages decreased after coinjection with CMG. Our results thus showed that CMG was protective in rat endotoxin shock, which seemed partly connected with enhancement of endotoxin clearance through scavenger receptors and to decreased TNF production.

Binding and transport of benzo[a]pyrene by blood plasma lipoproteins: the possible role of apolipoprotein B in this process.

The role of plasma lipoproteins as carriers in the transport of benzo[a]pyrene was assessed in in vitro and in vivo studies. Addition of [3H]benzo[a]pyrene to rat plasma resulted in binding of the xenobiotic to lipoproteins. Studies of labeled benzo[a]pyrene distribution in rat blood plasma by the method of ultracentrifugation have given the following results: high-density lipoproteins, 40%; low-density lipoproteins, 14%; very-low-density lipoproteins, 23%; other plasma proteins, 23%. Complexes of benzo[a]pyrene-lipoproteins were isolated by gel filtration with Sephadex G-25 and used for intravenous injection in rats. Biodistribution studies have shown different localization of benzo[a]pyrene in rat organs and tissues depending on lipoprotein classes. A high amount or radioactivity was bound by the liver and adrenals when all classes of lipoproteins were used, but especially with high-density lipoproteins. High levels of benzo[a]pyrene were measured in the kidneys. Equilibrium dissociation constants for complexes of benzo[a]pyrene with high-density lipoproteins and low-density lipoproteins were obtained (Kd 4.1 x 10(-5) and 1.5 x 10(-5) M, respectively). Binding and distribution of the protein component of lipoproteins were studied by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. More than 80% of the radioactivity recovered from the gel was localized in the area of apolipoprotein B. After isolation and purification of apolipoprotein B, the equilibrium dissociation constant for complexes of benzo[a]pyrene with apolipoprotein B was obtained, and its value indicated that apolipoprotein B might be the main protein carrier for benzo[a]pyrene.