[Dysfunctional high-density lipoproteins in diabetes mellitus].

The risk of cardiovascular disease (CVD) in persons with type 2 diabetes mellitus (DM2) increases two to four times. One of the main factors increasing cardiovascular risk is dyslipidemia, which includes abnormalities in all lipoproteins, including high-density lipoproteins (HDL). The development of DM2 is accompanied not only by a decrease in the level of HDL, but also by significant changes in their structure. This leads to the transformation of native HDL into so-called dysfunctional or diabetic HDL, which loses their antiatherogenic, cardioprotective, anti-inflammatory and anti-diabetic properties. In poorly controlled diabetes mellitus HDL can not only lose its beneficial functions, but also acquire proatherogenic, proinflammatory ones. Diabetic HDL can contribute to the accumulation of such unfavorable qualities as increased proliferation, migration, and invasion of cancer cells. Given that HDL, in addition to participation in cholesterol transport, performs important regulatory functions in the body, there is reason to assume that structural modifications of HDL (oxidation, glycation, triglyceride enrichment, loss of HDL-associated enzymes, etc.) are one of the causes of vascular complications of diabetes.

High-density lipoproteins: from quantitative measures to functional assessment and therapy (review of literature).

The antiatherogenic role of high-density lipoproteins (HDL) is associated primarily with their participation in the reverse transport of excess cholesterol from peripheral tissues to the liver. The efficiency of this mechanism depends on the ability of apolipoprotein A-I (apoA-I), the main protein component of HDL, to capture cholesterol from cells. It is known that the acceptor properties of this protein can change under the influence of various factors. This review discusses modern approaches aimed both at increasing the plasma level of HDL and preserving their native functional properties. As one of the key criteria of HDL functionality it is proposed to determine the ability of HDL to accept labeled cholesterol from macrophages. Studies have shown that injection of recombinant HDL or apoA-I mimetic peptides accelerates cholesterol efflux from peripheral tissues, improves vascular endothelial state, and leads to regression of atherosclerotic plaque. Thus, therapy with recombinant HDL/apoA-I may become an effective way to treat cardiovascular diseases caused by cholesterol accumulation in the vascular wall.

[Molecular mechanisms of action and physiological effects of the proinsulin C-peptide (a systematic review)]. / Molekuliarnye mekhanizmy deistviia i fiziologicheskie éffekty S-peptida proinsulina (sistematicheskii obzor).

The C-peptide is a fragment of proinsulin, the cleavage of which forms active insulin. In recent years, new information has appeared on the physiological effects of the C-peptide, indicating its positive effect on many organs and tissues, including the kidneys, nervous system, heart, vascular endothelium and blood microcirculation. Studies on experimental models of diabetes mellitus in animals, as well as clinical trials in patients with diabetes, have shown that the C-peptide has an important regulatory effect on the early stages of functional and structural disorders caused by this disease. The C-peptide exhibits its effects through binding to a specific receptor on the cell membrane and activation of downstream signaling pathways. Intracellular signaling involves G-proteins and Ca2+-dependent pathways, resulting in activation and increased expression of endothelial nitric oxide synthase, Na+/K+-ATPase and important transcription factors involved in apoptosis, anti-inflammatory and other intracellular defense mechanisms. This review gives an idea of the C-peptide as a bioactive endogenous peptide that has its own biological activity and therapeutic potential.

[Diagnostics value and regulatory functions of roinsulin.]

Proinsulin is one of the indicators reflecting the functional activity of the pancreas. In insulin-independent diabetes mellitus the ratio proinsulin / insulin is increased. The review examined the causes of hyperproinsulinemia and the diagnostic value of proinsulin in patients with diabetes mellitus type 1 and 2. The role of proinsulin in the regulation of metabolic pathways and the preservation of the functional activity of cells under physiological conditions, during aging and during pathological processes is discussed. Studies in these areas justify the inclusion of proinsulin in the superfamily of signaling factors. The neuroprotective activity of proinsulin and its potential as a therapeutic tool for neurodegenerative diseases and retinal dystrophy are considered.

[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.

Changes in Activity of Matrix Metalloproteinases and Serum Concentrations of Proinsulin and C-Peptide Depending on the Compensation Stage of Type 2 Diabetes Mellitus.

In patients with type 2 diabetes mellitus, serum activities of MMP-2 and MMP-7 were substantially decreased in comparison with apparently healthy individuals. At the decompensation stage, along with the increased content of glucose and glycated hemoglobin, a pronounced (3-fold) increase in proinsulin concentration was observed. On the contrary, MMP activity and C-peptide concentration decreased at this stage. The ratio of proinsulin concentration to MMP activity at the stages of diabetes mellitus compensation and subcompensation was approximately 1:50, while at the stage of decompensation it was 1:12. Thus, the ratio of these blood serum parameters can be used as an additional diagnostic marker of diabetes decompensation and severity of its complications.

Apolipoprotein A-I Stimulates Cell Proliferation in Bone Marrow Cell Culture.

Culturing of bone marrow cells in serum-free RPMI-1640 medium led to a decrease in the rate of DNA biosynthesis. Addition of HDL or their main protein component apolipoprotein A-I to the culture medium dose-dependently increased the rate of [3H]-thymidine incorporation into DNA. The maximum stimulation was achieved at HDL concentration of 80 µg/ml and apolipoprotein A-I concentration of 20 µg/ml. To identify the target-cells of apolipoprotein A-I, we used thymidine analogue 5-ethynyl-2'-deoxyuridine (EdU) that incorporates into cell DNA at the stage of replicative DNA synthesis (S phase) and can be detected by fluorescence microscopy. In bone marrow cell culture, apolipoprotein A-I stimulates the proliferation of monocyte (monoblasts, promonocytes) and granulocyte (myeloblasts, promyelocytes) progenitor cells, as well as bone marrow stromal cells.

[Antidiabetic role of high density lipoproteins]. / Antidiabeticheskaia rol' lipoproteinov vysokoi plotnosti.

Disturbance in lipid metabolism can be both a cause and a consequence of the development of diabetes mellitus (DM). One of the most informative indicator of lipid metabolism is the ratio of atherogenic and antiatherogenic fractions of lipoproteins and their protein components. The review summarizes literature data and own results indicating the important role of high-density lipoprotein (HDL) and their main protein component, apolipoprotein A-I (apoA-I), in the pathogenesis of type 2 DM. On the one hand, HDL are involved in the regulation of insulin secretion by b-cells and insulin-independent absorption of glucose. On the other hand, insulin resistance and hyperglycemia lead to a decrease in HDL levels and cause modification of their protein component. In addition, HDL, possessing anti-inflammatory and mitogenic properties, provide anti-diabetic protection through systemic mechanisms. Thus, maintaining a high concentration of HDL and apoA-I in blood plasma and preventing their modification are important issues in the context of prevention and treatment of diabetes.

Effect of Native and Modified Apolipoprotein A-I on DNA Synthesis in Cultures of Different Cells.

Culturing of bone marrow cells in serum-free RPMI-1640 medium for 24 h was accompanied by a decrease in the rate of [3H]-thymidine incorporation into DNA. Addition of native apolipoprotein A-I (apoA-I) or plasma LDL and HDL to the culture medium increased this parameter. In contrast to native apoA-I, its modified form decelerated DNA synthesis in bone marrow cells. A similar inhibitory effect of modified protein was observed in cultures of human embryonic kidney cells (HEK293) and in rapidly proliferating mouse macrophage cell line ANA-1. The only exclusion was human myeloid cell line U937: neither native nor modified apoA-I affected DNA synthesis in these cells. Thus, the regulatory effects of apoA-I are tissue-specific; this protein can produce either stimulatory or inhibitory effect on DNA biosynthesis in cells depending on its conformation.

[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.

Mechanisms determining phenotypic heterogeneity of hepatocytes.

This review summarizes results of biochemical and immunohistochemical studies indicating the existence of functional heterogeneity of hepatocytes depending on their localization in the hepatic acinus; this determines characteristic features of metabolism of carbohydrates, lipids, and xenobiotics. The physiological significance of hepatocyte heterogeneity is discussed. According to the proposed model of intercellular communication, the metabolic specialization of hepatocytes is determined by secretory activity of hepatic resident macrophages (Kupffer cells) localized mainly in the periportal zone of the liver acinus. Macrophages participate in secretion of a wide spectrum of intercellular mediators (cytokines, prostaglandins, growth factors) and also in metabolism of numerous blood metabolites and biologically active substances (hormones, lipoproteins, etc.). In the sinusoid and in the space of Disse (also known as perisinusoidal space) they form a concentration gradient of regulatory factors and metabolites inducing the phenotypic differences between hepatocytes.

Role of glucocorticoids and resident liver macrophages in induction of tyrosine aminotransferase.

Administration of cortisol to an animal induces tyrosine aminotransferase (TAT) in the liver. A similar effect was observed after stimulation of resident liver macrophages (Kupffer cells) by dextran sulfate. Actinomycin D completely blocks enzyme induction both by cortisol and dextran sulfate, whereas their combined effect gives an additive result. In primary culture of hepatocytes, dextran sulfate inhibits TAT activity, but conditioned macrophage medium reliably increases enzyme activity in hepatocytes. However, incubation of isolated macrophages in the presence of dextran sulfate and such medium transfer into hepatocyte culture results in even more pronounced increase in TAT activity. In a combined culture of hepatocytes and non-parenchymal liver cells, reproducing intercellular interactions in vitro, cortisol and non-parenchymal cells exhibit an additive effect on TAT activity. These results show that liver macrophages release a factor of unknown nature launching the mechanism of TAT induction independently of cortisol, a classic TAT inducer.

[Effect of tetrahydrocortisol-apolipoprotein A-I complex on RNA polymerase interaction with eukaryotic DNA and the rate of protein biosynthesis in hepatocytes]. / Vliianie kompleksa tetragidrokortizol-apolipoprotein A-I na vzaimodeistvie RNK polimerazy s éukarioticheskoi DNK i na skorost' biosinteza belka v gepatotsitakh.

A mechanism of activation of protein biosynthesis in hepatocytes was proposed as effected by the conditioned medium of nonparenchymal liver cells incubated in the presence of high density lypoproteins, cortisol, and lypopolysaccharides. It was found that the increase in the biosynthesis rate was associated with the formation of the tetrahydrocortisol-apolipoprotein A-I (THC-apoA-I) complex in macrophages, which display 5 alpha- and 5 beta-reductase activity and are constituents of nonparenchymal liver hepatocytes. Using the small-angle X-ray scattering technique, it was shown that the THC-apoA-I-eukaryotic DNA interaction may break hydrogen bonds between pairs of complementary nucleic bases and cause the formation of single-stranded DNA fragments capable of binding to DNA-dependent RNA polymerase. The interaction is highly cooperative and has a saturating mode, up to six enzyme molecules being bound per DNA molecule.

Role of apolipoprotein A-I in steroid-induced activation of DNA and protein synthesis in hepatocytes.

It is demonstrated that anabolic effect of steroid hormones is produced by steroid-apolipoprotein A-I complexes. These complexes accelerate not only protein, but also DNA synthesis and produce both cell hypertrophy and hyperplasia. For realization of their anabolic effect steroid hormones are modified by alpha- and beta-reductases in resident macrophages.

Gadolinium chloride-induced Kupffer cell blockade increases uptake of oxidized low-density lipoproteins by rat heart and aorta.

Oxidized low-density lipoproteins (LDL) play a key role in the formation of atherosclerotic lesions of arteries. We analyzed the effect of hepatic resident macrophage (Kupffer cell) blockade on oxidized [125I]LDL accumulation in different organs and tissues of the rat. Kupffer cell blockade was induced by gadolinium chloride (GdCl3) which was injected intravenously 24 h prior to injection of oxidized [125I]LDL into the rats. Ten minutes after administration to intact animals, oxidized [125I]LDL was accumulated in the liver (86.8% of the dose administered), muscles (4.7%), spleen (2.1%), lungs (0.8%), kidney (0.6%), adrenal glands (0.2%), heart (0.15%), and thymus (0.04%). Kupffer cell blockade significantly decreased the clearance rate of oxidized [125I]LDL from the blood. Specific radioactivity (per g tissue) decreased in the liver (1.3-fold compared to control), but increased in the aorta (2.5-fold), heart (2-fold), lungs (1.6-fold), and kidney (1.3-fold). The results indicate that the accumulation of oxidized LDL in heart and aorta significantly depends on the functional state of the mononuclear phagocyte system in the liver.

Macrophage stimulation and antitumor effect of Ukrain.

It has previously been demonstrated that Ukrain administration (0.5 mg in mice of 20 g, five times) to A/Sn mice results in retardation of HA-1 tumor growth in the liver and a prolongation of lifespan compared with untreated controls. In the present study Ukrain was tested as a macrophage stimulator in intact mice and animals with HA-1 hepatoma. There were no changes to the carbon particles phagocytosis rate in the case of a single administration of Ukrain to intact mice. Significant secretion of procathepsin B into ascitic fluid was shown in tumor mice as well as marker enzyme of macrophages beta-hexosaminidase activity, suggesting an influx of macrophages into ascites. Single Ukrain administration increased this index, and repeated drug injections were followed by a tendency to normalization of secretion. The cytolytic effect of Ukrain against tumor cells (as a result of macrophage stimulation) is the most probable mechanism of its antitumor action, but this suggestion needs further experimental evidence with special attention paid to the balance of proteinases and endogenous proteinase inhibitors.

[The role of the mononuclear phagocyte system in regulating protein biosynthesis in rat organs and tissues in ontogeny]. / Rol' sistemy mononuklearnykh fagotsitov v reguliatsii biosinteza belka v organakh i tkaniakh krys v ontogeneze.

In experiments on Wistar rats, we demonstrate that activation of mononuclear phagocytes by a lipopolysaccharide (prodigiosin) results in a marked increase of protein biosynthesis in various organs and tissues. This control mechanism is most distinct in mature rats and undergoes involution in older rats. Cell elements in the mononuclear phagocytes (resident macrophages) originate from the bone marrow. Decrease in the reserve capacity of the bone marrow with age in response to prodigiosin administration suggests an important role of this mechanism during aging.