M. Dimitrova

Bulgarian Academy of Sciences, Ulpia Serdica, Sofia-Capital, Bulgaria

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Publications (28)15.16 Total impact

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    ABSTRACT: Tripeptidyl peptidase I (TPPI) localization and activity levels are studied in MIA PaCa-2 cells (human pancreatic adenocarcinoma) using immunofluores- cence, enzyme cytochemistry and biochemistry methods. The enzyme is highly active and co-localized with the lysosomal marker acridine orange in the cell line. Application of 40 μg/ml oxaliplatin exerts cytotoxic effect in 31% of the cells and starts the mechanisms of apoptosis in 62% of the cells. As a result from the use of the anti-tumour drug, TPPI activity increases twice and the enzyme is released into the cytosol as revealed by confocal microscopy. Thus, TPPI activity is necessary for initiation of apoptosis/necrosis in these cells. The enzyme could be studied in cases of pancreatic carcinoma in order to evaluate its applicability as diagnostic/prognostic marker for these types of tumour.
    No preview · Article · Jan 2011
  • Mashenka Dimitrova · Ivaylo Ivanov · Denislava Deleva
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    ABSTRACT: Distribution of tripeptidyl peptidase I (TPP I) in the brain and spinal cord of mature Wistar rats was studied using enzyme histochemistry with the recently developed specific TPP I substrate Gly-Pro-Met-2-anthraquinonyl hydrazide. The histochemical method was chosen in order to reveal the functional expression of the enzyme. The sites of TPP I activity largely coincided with those of acid phosphatase - a known marker for lysosomes. TPP I was shown to possess high activity in the neurons of the brain (cerebrum, cerebellum, medulla oblongata) and spinal cord (cervical region). Thus, TPP I could be considered as very important for the proper function of the neurons. This is the first enzyme histochemical study of TPP I in the nervous tissue of laboratory rats.
    No preview · Article · Jan 2009 · Comptes rendus de l'Académie bulgare des sciences: sciences mathématiques et naturelles
  • Mashenka Dimitrova · Denislava Deleva
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    ABSTRACT: Developmental changes in tripeptidyl peptidase I (TPP I) functional expression were studied by enzyme histochemistry in the cerebral cortex, cerebellar cortex, medulla oblongata at the level of hypoglossal nerve and cervical part of the spinal cord of Wistar rats during the main age periods - infancy (41st postnatal day), puberty (64th postnatal day), maturity(6th month) and old animals (19th month). In rat brain TPP I became active at the 41st postnatal day. Then, the enzyme activity gradually increased to reach highest levels in maturity and remained practically unchanged at old age. At 64th day after birth the enzyme distribution pattern started to resemble the one of mature rats. In the spinal cord TPP I was functionally expressed late in puberty and remained unaffected in old rats. Thus far, histochemical studies of TPP I have not been performed in developing rat brain and the spinal cord. Since TPP I is recognized as very important for neuronal function, the results obtained might be useful in view of application of animal models of different neurodegenerative diseases.
    No preview · Article · Jan 2009 · Comptes rendus de l'Académie bulgare des sciences: sciences mathématiques et naturelles
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    Full-text · Article · Jan 2009 · Biotechnology & Biotechnological Equipment
  • Mashenka Dimitrova · Ivaylo Ivanov · Lillia Georgieva · Elena Nikolova
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    ABSTRACT: A novel procedure for the simultaneous visualization of cell differentiation antigens (CD) by immunocytochemistry and CD26/ Dipeptidyl peptidase IV (DPP IV) activity by fluorescent enzyme cytochemistry was developed. This procedure was used for the determination of the percentage of DPP IV-positive cells from different subpopulations of human peripheral blood lymphocytes at rest and after mitogen stimulation. The number of DPP IV+T and B cells increased after application of mitogenic stimuli. These results might help for elucidation of the role of CD26 proteolytic activity in the exertion of its costimulatory effect upon the immune response.
    No preview · Article · Jan 2009 · Comptes rendus de l'Académie bulgare des sciences: sciences mathématiques et naturelles
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    ABSTRACT: After oxygen, silicon is the second most abundant element in the environment and is present as an impurity in most materials. The widespread occurrence of siliceous biominerals as structural elements in lower plants and animals suggests that Si plays a role in the production and maintenance of connective tissue in higher organisms. It has been shown that the presence of Si is necessary in bones, cartilage and in the formation of connective tissue, as well as in some important metabolic processes. In this work, polycrystalline silicon layers are tested in terms of bioactivity, i.e., their ability to induce hydroxyapatite formation from simulated body fluid. Hydroxyapatite is a biologically compatible material with chemical similarity to the inorganic part of bones and teeth. Polycrystalline silicon layers are obtained by aluminum induced crystallization of Al and amorphous Si thin films deposited sequentially on glass substrates by radio-frequency magnetron sputtering and subsequently annealed in different atmospheres. The hydroxyapatite formation is induced by applying a method of laser-liquid-solid interaction. The method consists of irradiating the samples with laser light while immersed in a solution that is supersaturated with respect to Ca and P. As a result, heterogeneous porous sponge-like carbonate-containing hydroxyapatite is grown on the polysilicon surfaces. Crystals that are spherical in shape, containing Ca, P and O, Na, Cl, Mg, Al, Si and S, as well as well-faceted NaCl crystals are embedded in the hydroxyapatite layer. Enhancement of the hydroxyapatite growth and increased crystallinity is observed due to the applied laser-liquid-solid interaction.
    Full-text · Article · Mar 2008 · Journal of Nanoscience and Nanotechnology
  • M. Dimitrova · I. Ivanov · R. Todorova · V. Tzenova
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    ABSTRACT: A fluorogenic histochemical substrate for tripeptidyl peptidase I (TPP I) - Gly-pro-Met-4-hydrazido-N-hexyl-1,8-naphthalimide (Gly-Pro-Met-HHNI) is developed and used to study the enzyme distribution in mice reproductive organs. The specificity of the substrate is proved by inhibition tests. High enzyme activity is found in the ovary, fallopian tube, uterus, testis and epididymis. It decreases in the seminal vesicle and is not detected in the prostate. Hitherto, TPP I has not been studied in these organs by activity histochemistry. Presented data and the fluorescent histochemical method might be valuable for future studies on the enzyme.
    No preview · Article · Jan 2008
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    ABSTRACT: Hydroxyapatite/detonation nanodiamond composites are created on silica glass and cover glass by simple soaking process in an open deposition type set-up. The supersaturated solution (simulated body fluid, SBF) is prepared in a way to resemble the composition of human blood plasma. The composite growth is carried out through the addition of detonation nanodiamond particles to the SBF. Scanning electron microscopy, X-ray diffraction and FTIR spectroscopy are used to determine the surface morphology and the structure of the hydroxyapatite /detonation nanodiamond composite layers. The applied methods provide evidence that the nanodiamond surface functional groups interact strongly with the biological solution. The detonation nanodiamond surface is chemically multifunctional (surface OH, C-O-H, C = C, C-O-C and C = O groups exist), so that the hydroxyapatite is grown both by physical adsorption and chemical interaction. The OH- groups are regarded to play an important role in the hydroxyapatite growth on a diamond's surface from SBF, as they charge it negatively and attract Ca2+ ions, which in turn attract PO43- ions, thus forming apatite nuclei.
    Full-text · Article · Dec 2007 · Journal of Physics Conference Series
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    ABSTRACT: One example for the medical application of nanodiamonds is their use in orthopedic implants. Detonation generated nanodiamonds (DND) are of great interest, because they are able to strengthen bone tissue, producing tougher and more flexible artificial bone implants. Carbon-based materials can be used to replace natural collagen in bone, in which the main inorganic ingredient is the calcium phosphate (CaP) phase, namely hydroxyapatite (HA). Collagen is the organic part of bone that is based on carbon and is of the same size as DND. In this work, we present the deposition of CaP through DND on TiCu alloys by their immersion in a mixture of simulated body fluid (SBF) and a suspension of DND. The layers were characterized by SEM, EDX, coherence probe microscopy and Raman spectroscopy. It was found that DND produced a stable aqueous suspension in SBF, and was able to stimulate the growth of CaP layers on the surfaces of TiCu substrates.
    Full-text · Article · Jan 2007 · Journal of Optoelectronics and Advanced Materials
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    Full-text · Article · Jan 2007
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    ABSTRACT: A calcium phosphate layer was grown on glass by a laser-liquid-solid interaction (LLSI) process in simulated body fluid (SBF). Glass samples with a layer grown by simple soaking in the SBF (i.e. without laser irradiation) were prepared for comparison. Formation of an inhomogeneous calcium phosphate (CaP) layer on both laser-treated and non-treated samples was observed. The results showed that the laser irradiation did not change the layer structure and morphology but yielded the growth of a thicker CaP layer. With increasing load the elasticity and the hardness increased for both laser-treated and non-treated samples. Furthermore, we tested the osteoblast cell activity of the CaP layers grown on the laser-treated and non-treated samples. Toxicity test showed that the viability of the cells on the layer grown by the LLSI process was over 95%. A permanent increase in the cell number was observed for both groups of samples, and it was more stable on the laser-treated surfaces. The latter showed a higher cell number after 7 days of cell culturing. A slower increase, resulting in a lower cell numbers was observed for the samples untreated with laser irradiation.
    Full-text · Article · Jan 2007 · Journal of Optoelectronics and Advanced Materials
  • F. Riesz · L. Pramatarova · E.V. Pecheva · M. Dimitrova
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    ABSTRACT: The use of Makyoh (magic-mirror) topography (MT), an optical surface characterisation tool, is demonstrated in the research of artificial biomineralisation. The method is based on the defocused detection of the whole-sample reflection of collimated light. The sample surface morphology is revealed in the form of dark/bright contrast regions in the reflected image, due to the focusing/defocusing action of the morphological features of the surface. It is shown that MT can be used for the quick, qualitative assessment of the mm and sub-mm scale morphology of the substrates used for deposition of hydroxyapatite layers. In particular, we show the roughening effect in stainless steel substrates due to Ca+P implantation.
    No preview · Article · Jan 2007

  • No preview · Article · Oct 2006
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    ABSTRACT: Continuous activity of isolated frog gastrocnemius muscle fibres provoked by repetitive stimulation of 5 Hz was used as an experimental model for fatigue development in different fibre types. Parameter changes of the elicited intracellular action potentials and mechanical twitches during the period of uninterrupted activity were used as criteria for fatigue evaluation. Slow fatigable muscle fibre (SMF) and fast fatigable muscle fibre (FMF) types were distinguished depending on the duration of their uninterrupted activity, which was significantly longer in SMFs than in FMFs. The normalized changes of action potential amplitude and duration were significantly smaller in FMFs than in SMFs. The average twitch force and velocity of contraction and relaxation were significantly higher in FMFs than in SMFs. Myosin ATPase (mATPase) and succinate dehydrogenase activity were studied by histochemical assessment in order to validate the fibre type classification based on their electrophysiological characteristics. Based on the relative mATPase reactivity, the fibres of the studied muscle were classified as one of five different types (1-2, 2, 2-3, 3 and tonic). Smaller sized fibres (tonic and type 3) expressed higher succinate dehydrogenase activity than larger sized fibres (type 1-2, 2), which is related to the fatigue resistance. The differences between fatigue development in SMFs and FMFs during continuous activity were associated with fibre-type specific mATPase and succinate dehydrogenase activity.
    Full-text · Article · Jan 2006 · General Physiology and Biophysics
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    A. NERONOV · P. GIUROV · M. CHOLAKOVA · M. DIMITROVA · E. NIKOLOVA
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    ABSTRACT: Porcine corneas were frozen with Me 2 SO, glycerol, 1,2-propanediol and PEG-400. The effects of the range of concentrations (5% and 10%) and temperature regimen (1 degrees C/min and 5 degrees C/min) were investigated. The integrity of corneal endothelial cells was evaluated by scanning electron microscopy and trypan blue staining. The presence of 5-10% PEG-400 in the protective medium was the most effective in minimizing changes in the integrity of the corneal endothelium during freezing-thawing procedures.
    Preview · Article · May 2005 · Veterinární medicína
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    ABSTRACT: The aim of the present study was to elaborate an optimal method for cryopreservation of human donor cornea for transplantation and to follow the morphological changes in the structure of the endothelial cell layer using scanning electron microscopy (SEM). Sixteen groups, with four donor cornea each, were cryopreserved at cooling rates of 1 degree C per min and 5 degree C per min. Four cryoprotectants (glycerol, dimethyl sulfoxide, 1,2-propanediol, polyethylene glycol-400) in two concentrations (5% and 10% v/v) were prepared on the bases of medium Optisol GS supplied with 20% v/v human serum albumin. Four additional human cornea were used as controls. Endothelial cell recovery of the cornea after thawing and 24 hours culture, was calculated as a percent of the preserved recovered cells. Sufficient recovery of the endothelial cell layer, making the cornea suitable for transplantation was obtained using the cryoprotectants dimethyl sulfoxide and especially polyethylene glycol-400.
    Preview · Article · Mar 2005 · Cryo letters
  • A Dikov · M Dimitrova · R Krieg · K J Halbhuber
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    ABSTRACT: A new substrate for tripeptidyl peptidase I (TPP I; E.C.3.4.14.9)-Gly-L-Pro-L-Met-2-anthraquinonyl hydrazide (Gly-Pro-Met-2-AH) is synthesized and used for the fluorescent histochemical detection of the enzyme. The enzyme liberates low soluble 2-anthraquinonylhydrazine, which-couples quickly with 3-nitrobenzaldehyde (3-NBA) yielding a highly fluorescent water-insoluble hydrazone--3-nitrobenzylidene-2-anthraquinonylhydrazone. The latter compound is localized precisely at sites of enzymatic activity and marks them with a very bright and stable orange-red fluorescence after excitation with conventional monochromatic andlaser green light (lambda(exc)=520-580 nm). The new technique is used successfully for the visualization of the enzyme in tissue sections of different rat organs - and represent the first fluorescent histochemical method for that peptidase.
    No preview · Article · Feb 2004 · Cellular and molecular biology
  • A Dikov · M Dimitrova · R Krieg · K J Halbhuber
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    ABSTRACT: Glycyl-4-prolyl-2-anthraquinonylhydrazide (Gly-Pro-2-AH) was synthesized and used as a new fluorogenic substrate for the histochemical detection of dipeptidyl peptidase IV activity (DPP IV). The enzymatic hydrolysis liberates 2-anthraquinonyl hydrazine (2-AH). Further on, the primary reaction product reacts with an aromatic aldehyde to give an insoluble hydrazone. The final reaction product fluoresces orange-red when exited by green light (lambda(exc)=520-580 nm) and marks sites of enzymatic activity by an intensive fluorescence. This fluorescent method permits highly sensitive enzyme detection and causes only very low background tissue fluorescence. Thus enzyme locations in the capillary bed endothelium properly and sensitively stained, which has not been achieved by now. The new method is used successfully to demonstrate the enzyme in cryotome tissue sections from several rat organs.
    No preview · Article · Feb 2004 · Cellular and molecular biology
  • D. Dimitrova · S. Tashkova · A. Dikov · M. Dimitrova · E. Nikolova

    No preview · Article · Jan 2002
  • A. Dikov · M. Dimitrova

    No preview · Article · Jan 2002