Diana Petkova

• Ph.D and Dr.Sci
• Professor (Full) at Institute of Biophysocs and Biomedical Engeniring, Bulgarian Academy of Sciences

A generalized net model of acute respiratory distress syndrome is described. This net model could be used for investigation of blood parameters after HCL administration, after inhalation of liposomes for improvement of lung functions as well as for training medical students to take decisions in case of ARDS pathology after HCl - inhalation or other...

Biological neurons and their connection in neural networks have motivated the creation of the architecture of artificial neural networks. In the previously considered cases, the description of the neural networks and their connections are described with standard matrices where the values for the weighting coefficients and biases are placed. By reca...

The polyphenol quercetin is associated with numerous beneficial health effects in various pathologies such as oxidative stress, neurodegenerative disorders, inflammation, neoplastic processes, age-related diseases, and so on. However, the molecular mechanisms underlying the effects of quercetin and its implication in the pharmaceutical practice req...

A number of neurological diseases are related to autoimmune pathogenesis. These are multiple sclerosis, Guillain–Barre syndrome, chronic inflammatory demyelinating polyneuropathy, monoclonal gammopathy, myasthenia, polymyositis, and others. The mentioned diseases are characterized by autoantibodies from immunocompetent cells connected to myelin of...

The phase separation of aminophospholipids in glycerophospholipid matrix and the effect of cholesterol were studied by means of fluorescence microscopy of giant unilamellar vesicles (GUV). GUVs were composed of binary mixtures, egg yolk phosphatidylcholine (eggPC)/egg yolk phosphatidylethanolamine (eggPE) and egg yolk phosphatidylcholine (eggPC)/br...

The aim of this study is to evaluate the application of phospholipid liposomes in HCl -induced acute respiratory distress syndrome (ARDS) in rabbits. ARDS was induced by administration of 0.2 N HCl via intratracheal instillation for 45 min. After inducing of ARDS, the rabbits under artificial lung ventilation were retreated with liposomes for 60 mi...

A weekly administration of 1,2 -dimethylhidrazine (DMH) for 30, 60 and 90 days for stimulation of sphingomyelin metabolism was used in this study and the behaviour of protein kinase A and C has been investigated under these conditions. DMH—treatment caused two-fold increase of the membrane cholesterol and of the percent participation of phosphatidy...

Investigations were performed on the effect of xylooligosaccharide (XOS) intake on the phospholipid and fatty acid composition of rat liver plasma membranes. The results showed that phosphatidylcholine was elevated and lysophosphatidylcholine was reduced in liver plasma membranes of XOS-fed rats and these alterations were due to decrease of phospho...

Investigations were carried out on the changes in the alveolar surfactant lipids induced by administration of the antioxidant ascorbic acid in patients with adult respiratory distress syndrome (ARDS). The pulmonary surfactant phospholipids play an essential role in the maintenance of the alveolar surface activity and in the general physiological fu...

The effect of beta-glucan intake on cholesterol content and susceptibility to oxidative damage has been investigated in rat liver plasma membranes. The obtained results demonstrated that all tested membrane lipids remained almost unchanged except cholesterol, which was reduced as a result of beta-glucan intake. Since cholesterol (CH) is the only ma...

The antioxidant n-propyl gallate (nPG) is widely used in the food industry, pharmaceutics and cosmetics. Therefore, we should be well acquainted with its exact mechanism of action and its effects on the human organism, especially at the molecular level. Because of its slight solubility in water, it could be expected that, in cells, nPG would enter...

Xylooligosaccharides (XOS) are non-digestible carbohydrate prebiotics that beneficially affect the host by selective stimulation of specific bacteria in the gastro-intestinal tract. The impact of XOS on gastrointestinal microflora and blood lipids is well known but the exact mechanism of action on liver membranes is still unclear. The organization...

The influence of the prebiotic inulin on the level and sensitivity to oxida- tive attack has been investigated in rat liver plasma membranes. The obtained results showed that the oral administration of inulin in experimental animals induced a slight decrease of the content of cholesterol in liver plasma mem- branes. In addition, the susceptibility...

Investigations were carried out on the applicability of L-buthionine-S, R-sulfoximine (BSO) for experimental development of a model of senescent cells in laboratory conditions. The obtained results showed that some of the typical alterations of the membrane lipids such as decrease of sphingomyelin and reduced glutathione, as well as elevation of ce...

The aim of this study was to investigate the effects of testosterone replacement therapy (TRT) on erythrocyte membrane (EM) lipid composition and physico-chemical properties in hypogonadal men. EM isolated from three patients before and after TRT with injectable testosterone undecanoate or testosterone gel were used for analysis of the phospholipid...

Investigations were carried out on the effect of cholesterol reduction on the antioxidant potential of the avonoid quercetin in rat liver plasma membranes. The results showed that the accumulation of reactive oxygen species in intact membranes was significantly lower, compared to membranes with reduced content of cholesterol in the presence of quer...

Prebiotic intake is generally associated with alterations in the gastrointestinal microflora and blood serum lipids. However, less attention has been paid to the effect of prebiotics on the liver membrane lipids. We hypothesized that the reported alterations in the serum lipids might be related to changes in the liver membrane phospholipids in anim...

The PhD education in Bulgaria is the third degree of high education after bachelor and MC degrees. Every year Bulgarian Academy of Sciences and Universities educate about 1000 PhD students. From them about 120 are in Health sciences and biomedicine. The main Universities which educate PhD students are Medical Universities in Sofia, Varna, Plovdiv a...

The effect oftumor necrosis factor-α (TNF-α) on sphingomyelin (SM) turnover in human skin fibroblasts (HFS) was investigated. The activation of SM hydrolysis was observed to follow two different pathways depending on the concentration of TNF-α. Treatment of cells with 2 nM TNF-α induced the activation of phospholipase A3 with subsequent stimulation...

The three-dimensional (3D) cell culture approach offers a means to study cells under conditions that mimic an in vivo environment, thus avoiding the limitations imposed by the conventional two-dimensional (2D) monolayer cell cultures. By using this approach we demonstrated significant differences in the plasma membrane phospholipid composition and...

Fatty acids are essential for normal cell functioning because they influence the membrane structure and function. The investigation of the incorporation of short chain fatty acids in fibroblast cells cultured in three-dimensional matrix show two different molecular mechanisms depending of the structure of the fatty acid. Palmitic acid is incorporat...

Investigations were carried out on the alterations in the lipid peroxide level in control and ras-transformed fibroblasts enriched with two polyunsaturated fatty acids with different degree of unsaturation (linoleic acid (LA) and eicosaheptoenoic acid (EPA)) before and after exposure to oxidative stress induced by hydrogen peroxide. The obtained re...

The alterations in the lipid composition and the raft microdomain content in plasma membranes of fibroblasts exposed to oxidative attack have been investigated. The results show that treatment of cells with hydrogen peroxide induces reduction of the raft microdomain lipid components, sphingomyelin and cholesterol, as well as of some of the most uns...

Investigations were performed on the alterations of membrane-bound phospholipase A2 in plasma membranes of fibroblasts cultured as a monolayer (2D) and in three-dimensional (3D) environment. Since previous studies have shown that 2D and 3D cells exhibit different susceptibility to oxidative damage and also have different phospholipid acyl chains, w...

Most in vitro studies use 2-dimensional (2D) monolayer cultures, where cells are forced to adjust to unnatural substrates that differ significantly from the natural 3-dimensional (3D) extracellular matrix that surrounds cells in living organisms. Our analysis demonstrates significant differences in the cholesterol and sphingomyelin content, structu...

The dependence of membrane-bound alkaline phosphatase on the content of membrane sphingomyelin has been investigated. The level of membrane sphingomyelin has been manipulated by means of exogenous sphingomyelinase, which hydrolysed sphingomyelin molecules, yielding ceramide as a product. The results showed that the reduction of the level of membran...

The aim of this study is to evaluate the application of phospholipid liposomes in HCl--induced RDS in rabbits. Acute respiratory distress syndrome was induced by administration of 0.2 N HCl via intratracheal instillation for 45 min. After induced ARDS animals under artificial lung ventilation were retreated with liposomes for 60 min. Arterial blood...

The aim of this study is to evaluate the application of phospholipid liposomes in HCl - induced ARDS in rabbits. Acute respiratory distress syndrome was induced by administration of 0.2 N HCl via intratracheal instillation for 45 min. After induced ARDS animals under artificial lung ventilation were retreated with liposomes for 60 min. Arterial blo...

The aim of this study was to investigate the correlation between changes in alveolar surfactant biochemical and biophysical characteristics and pulmonary function of mechanically ventilated patients with ARDS. Phospholipid, cholesterol and specific surfactant protein content of bronchoalveolar lavage fluid (BALF) was detected. The equilibrium surfa...

The possibility of using multilamellar 99mTc-labelled li posomes at 2:1 phosphatidylcholine-to-cholesterol ratio for testing pulmonary perfusion and ventilation was investigated. For the purpose an experimental model of pulmonary embolism by iv injection of air into the rabbit ear vein is used. Comparative assessment is done of pulmonary perfusion...

The mechanism of accumulation of 99mmTclabeled liposomes (phosphatidylcholine: phosphatidic acid: cholesterol 30:20:50 mol/mol) (Lp 2) into lung and alveolar surfactant was investigated. Partially purified lipid transfer proteins - pH 5.1 were isolated from lung and alveolar surfactant. The lung protein as well as the alveolar surfactant protein ac...

Removal of small chylomicron remnants by perfused rat livers closely correlates with the LDL-receptor mRNA modulated by various interventions. In contrast, removal of remnants of large chylomicrons is not appreciably influenced by the activity of the hepatic LDL-receptor. Their primary removal depends on a heparinase-sensitive binding site. Transie...

The changes in phospholipid compositions, membrane fluidity and protein kinase A, protein kinase C, tyrosine and casein kinase activities in chick embryo liver plasma membranes during development have been investigated. The percentage participation of sphingomyelin increased while that of phosphatidylserine decreased during chick embryo development...

The role of rat liver plasma membrane phospholipids in the regulation of protein kinase A, protein kinase C and tyrosine kinase activities was investigated. Plasma membrane composition was modified by phospholipase A2, phospholipase C and phospholipase D treatment and subsequent incorporation of various phospholipids. Phospholipase A2 deactivated t...

Cholesterol oxidase was used to investigate the distribution of free cholesterol between plasma membrane and intracellular pools in cultured neonatal rat heart myocytes. Only 20% of the total unesterified cholesterol was converted to delta 4-cholestenone by cholesterol oxidase in intact cells. With increasing age in culture and concurrent hypertrop...

The mechanism leading to accumulation of cholesterol in hypertrophic cultures of neonatal rat heart myocytes was investigated in light of its relevance to aging-related hypertrophy of myocardial tissue. Lipoprotein turnover was low in young cells (days 4-6) and further depressed in older cells (days 12-14), and therefore could not account for the i...

1. The effect of a sunflower oil-enriched diet on plasma membrane-bound protein kinase C, protein kinase A, casein and tyrosine kinase activities was studied. 2. The diet induced an increase in the content of linoleic acid and a decrease in the content of palmitic acid. The anisotropy parameter (rs) of the fluorescence probe DPH and SDPH decreased...

The effect of cholesterol-supplemented diet on the activities of rat liver plasma membrane sphingomyelin-metabolizing enzymes and protein kinase C was studied. Protein kinase C, phosphatidylcholine:ceramide-phosphocholine transferase, and phosphatidylethanolamine:ceramide-phosphoethanolamine transferase activities were found to increase continuousl...

1. Plasma membranes were treated with phospholipase A2, phospholipase C or phospholipase D. The phosphatidylethanolamine:ceramide-phosphorylethanolamine transferase was deactivated by phospholipase C treatment, whereas phospholipase A2 and phospholipase D did not affect the enzyme. 2. Incorporation of phosphatidylethanolamine and phosphatidylglycer...

1. The effects of age-dependent or liposome-induced alterations in the phospholipid composition of rat liver plasma and microsomal membranes on the phosphatidylethanolamine:ceramide-phosphoethanolamine (PE:Cer-PEt) and phosphatidylcholine:ceramide-phosphocholine (PC:Cer-PCh) transferase activities were studied. 2. In all cases under study the PE:Ce...

The age-induced changes in the liver cytosol phospholipid transfer activity of male and female rats have been investigated. These changes were found to be closely related to the age-induced alterations in the two major microsomal phospholipids--phosphatidylcholine and phosphatidylethanolamine. Regression analysis indicated a linear correlation betw...

1. The influence of insulin on rat liver membrane lipid composition, fluidity, some enzyme activities and asymmetry of microsomal phospholipids were investigated. 2. The total phospholipids and cholesterol were increased in microsomes and reduced in plasma membranes from insulin-treated rats. 3. Of all the investigated enzymes participating in the...

The changes in the phospholipid composition of spermatozoa plasma membranes after freezing were determined by thin-layer chromatography. The results showed an augmentation of the diphosphatidylglycerol and a diminution of phosphatidylglycerol, phosphatidylserine, and phosphatidylethanolamine in sperm plasma membranes after freezing. In intact sperm...

1. The possibility for sphingomyelin and ceramide: phosphoethanolamine synthesis in ram spermatozoa plasma membranes has been established. 2. Ceramide: phosphoethanolamine formation appears to be higher than the synthesis of sphingomyelin. 3. The pH optimum of the phosphatidylethanolamine: ceramide-phosphoethanolamine transferase is about 7.0. An i...

1. A decrease of the alkenyl-acyl derivatives and an increase of the diacyl derivatives of PC and PE were observed after cryoconservation. 2. A diminution of membrane-bound phospholipase A2 activity was observed after cryoconservation. The activity of neutral sphingomyelinase remained unchanged. 3. The enrichment of plasma membranes with DPPC as we...

The age-induced changes of some phospholipid fractions, membrane fluidity and neutral membrane-bound sphingomyelinase (EC 3.1.4.12) activity in rat liver plasma membranes have been investigated. Alterations in the percentage participation of phosphatidylcholine and sphingomyelin with aging have been established. Regression analysis indicated a posi...

Investigations have been carried out on the influence of the phospholipid composition and the physicochemical properties of rat liver plasma membranes on the endogenous activity of membrane-bound phospholipase A2. The membrane phospholipid composition was modified by the incorporation of different phospholipids in the lipid bilayer by the aid of li...

A highly active neutral sphingomyelinase was observed for the first time in ram spermatozoal plasma membranes. The optimal conditions for the enzyme activity are pH 7.4, 40 mM MgCl2, 40 min of incubation, and 267 nmol sphingomyelin. Ca2+ and cholesterol were found to inhibit sphingomyelinase activity.

A highly active phospholipase A2 in ram spermatozoa plasma membranes has been established. Phospholipase A2 was optimally active at pH 7.4 and was Ca2+ dependent. Low concentrations of K+ (25 mM) were found to inhibit phospholipase A2 activity, whereas higher concentrations induced enzyme reactivation. An inhibitory effect of Zn2+ has also been obs...

The influence of D-galactosamine administration on rat liver plasma membranes lipid composition, fluidity and some enzyme activities was investigated. D-Galactosamine was found to induce an increase of the total phospholipids, the cholesterol level and membrane rigidity. In liver plasma membranes of D-galactosamine-treated rats the exogenous phosph...

Investigations have been carried out on the influence of the phospholipid composition of rat liver plasma membranes and of their physico-chemical properties on the activity of membrane-bound neutral sphingomyelinase. The membrane phospholipid composition was modified by the incorporation of different phospholipids into the membrane bilayer by means...

The alterations of the lipid composition and fluidity of liver plasma membranes as well as the activity of membrane-bound phospholipase A2 (EC 3.1.1.4) in male and female rats of different ages are investigated. An age-induced increase of the protein/phospholipid and cholesterol/phospholipid ratios is observed, as well as a decrease in the unsatura...

The influence of the phospholipid composition and the physico-chemical properties of rat liver plasma membranes on the activity of membrane-bound phospholipase A2 has been investigated. The plasma membrane composition was modified by the aid of exogenous phospholipases A2, C and D, and by butanol treatment. The partially delipidated membranes thus...

The influence of the physical state and the lipid composition on microsomal membrane-bound phospholipase A2 activity has been investigated. It was established that the decrease of membrane fluidity expressed by the alterations of the steady-state fluorescent anisotropy (rs) and the structural order parameter for DPH (SDPH) leads to augmentation of...

The changes in the phospholipid and fatty acid composition of liver plasma membranes isolated from rats, fed two different diets, containing either saturated or unsaturated fatty acids, were investigated. We established that dietary treatment can considerably modify the fatty acid as well as the phospholipid composition of liver plasma membranes. L...

The effects of the phospholipid composition of rat liver microsomes on the differential binding spectra of cytochrome P-450 with type I and II substrates (hexobarbital and aniline) were studied. Lysophosphatidylcholine was found to decrease the binding of both type substrates. These changes were reversible, and the spectra were restored by exchangi...

The lipid dependence of hydroxylase and demethylase activities of microsomal cytochrome P-450 was studied, using purified phosphatidylcholine transfer protein from bovine liver. In the presence of this protein exogeneous phosphatidylcholine was shown to reactivate cytochrome P-450 inactivated earlier with lysophosphatidylcholine.

Modification of membrane lipid composition by lipid exchange proteins was used to study the lipid dependence of cytochrome P-450 activity in rat liver microsomes. The introduction of exogenous lysophosphatidylcholine into microsomal membranes decreased the capacity of cytochrome P-450 to demethylate dimethylaniline and dimethylaminoantipyrine and t...

The article presents part of the researches on extrasolar planets, which we recently performed. This newly discovered phenomenon attracted many astronomers 'attention over the past years. More than 170 planets systems have been already mapped and a significant quantity of observation material has been accumulated. These results allow us to build qu...