M Dimitrova

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

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Publications (23)23.39 Total impact

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    ABSTRACT: Lithium is extensively used in psychiatric practice for the prevention and treatment of manic-depressive disorders. However, neurotoxicity attributed to lithium salts within therapeutic doses was also reported in patients, manifested by transient or persistent neurological deficits. In this study, morphological changes were examined in rats treated acutely and chronically with lithium. Pathological changes were observed in different brain regions including cerebral cortex, cerebellum, medulla oblongata, mesencephalon, thalamus, and pons, using a silver-copper impregnation technique for neurodegeneration. Vacuolization of brain tissue with subsequent formation of spongiosis was the prominent morphological feature following lithium administration. The zones of spongiosis were irregularly distributed throughout the brain. More intensive compact areas with spongiform changes were found in the cerebral cortex and medulla oblongata. Less pronounced vacuolization was noted in the pons and thalamic region. The cerebellum and mesencephalon appeared least affected. Vacuolization in the cerebellar cortex was found at loci with Purkinje cells, but the classical picture of spongiosis was not apparent. Data indicate that both acute and chronic lithium intoxication accelerated neurodegenerative changes normally seen with normal brain aging.
    Journal of Toxicology and Environmental Health Part A 02/2013; 76(4-5):304-10. DOI:10.1080/15287394.2013.757268 · 1.83 Impact Factor
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    ABSTRACT: The development of red solid-state fluorochromes is important for different applications. The influence of the electronic effects of substituents on the chemical shifts in the 1H NMR spectra and solid-state fluorescent properties of aryl hydrazones of 4-hydrazino-N-hexyl-1,8-naphthalimide is evaluated. The main fragmentation pathway of hydrazones is determined using electrospray ionization mass spectrometry and high resolution MS/MS. A possible application of these fluorochromes for the in situ imaging of enzyme activities is presented.
    Tetrahedron 01/2013; 69(2):712–721. DOI:10.1016/j.tet.2012.10.093 · 2.82 Impact Factor
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    ABSTRACT: Dipeptidyl peptidase IV (DPPIV) was studied in three human lung cells - P (fetal lung-derived cells), A549 (lung adenocarcinoma) and SK-MES-1 (squamous cell carcinoma) using a fluorescent cytochemical procedure developed on the basis of the substrate 4-(glycyl-L-prolyl hydrazido)-N-hexyl-1,8-naphthalimide. The observed differences in the enzyme expression were confirmed by measuring the enzyme hydrolysis of glycyl-L-prolyl-para-nitroanilide. The surface and total dipeptidyl peptidase activities of P cells were correspondingly 7-8 and 3-10 times higher than those of SK-MES-1 and A549 cells. The ratio surface per total activity showed that in P (95%) and A549 (93%) cells the enzyme is associated with the plasmalemma while in SK-MES-1 cells (35%) it is bound to intracellular membranes. In order to compare the results from cell cultures with those in human tumor, the enzyme activity was investigated in cryo-sections of three cases of diagnosed squamous lung carcinoma. DPPIV activity was restricted to the connective tissue stroma surrounding the DPPIV-negative tumor foci.
    Tissue and Cell 12/2011; 44(2):74-9. DOI:10.1016/j.tice.2011.11.003 · 1.05 Impact Factor
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    ABSTRACT: Tripeptidyl peptidase I (TPPI) - a lysosomal serine protease - is encoded by the CLN2 gene, mutations that cause late-infantile neuronal ceroid lipofuscinosis (LINCL) connected with profound neuronal loss, severe clinical symptoms and early death at puberty. Developmental studies of TPPI activity levels and distribution have been done in the human and rat central nervous systems (CNS) and visceral organs. Similar studies have not been performed in mouse. In this paper, we follow up on the developmental changes in the enzyme activity and localization pattern in the CNS and visceral organs of mouse over the main periods of life - embryonic, neonate, suckling, infantile, juvenile, adult and aged - using biochemical assays and enzyme histochemistry. In the studied peripheral organs (liver, kidney, spleen, pancreas and lung) TPPI is present at birth but further its pattern is not consistent in different organs over different life periods. TPPI activity starts to be expressed in the brain at the 10th embryonic day but in most neuronal types it appears at the early infantile period, increases during infancy, reaches high activity levels in the juvenile period and is highest in adult and aged animals. Thus, in mice TPPI activity becomes crucial for the neuronal functions later in development (juvenile period) than in humans and does not decrease with aging. These results are essential as a basis for comparison between normal and pathological TPPI patterns in mice. They can be valuable in view of the use of animal models for studying LINCL and other neurodegenerative disorders.
    Cell and Tissue Research 11/2011; 346(2):141-9. DOI:10.1007/s00441-011-1252-0 · 3.33 Impact Factor
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    ABSTRACT: Absorption and fluorescence spectra in acetonitrile for a series of substituted aryl hydrazones of N-hexyl-1,8-naphthalimide are studied with the aim of potential application of the compounds for enzyme activity localization. The influence of the substituents on the spectral characteristics has been evaluated. The absorption and fluorescence energies of substituted aryl-1,8-naphthalimide hydrazones have been calculated with the PCM TDDFT formalism. The M06 and PBE0 functionals, combined with the 6-31+G(d) atomic basis set, have been found to accurately model the excited state properties of the present set of solvated fluorophores. Absorption and fluorescence spectral characteristics have been rationalized in terms of experimental and theoretical electronic indices in order to assess their predictive abilities for application in designing analogues with good emitting properties. An excellent linear dependence is established between the experimental fluorescence and Hammett σ(p)(+) substituent constants and on the other hand σ(p)(+) constants correlate with the theoretically calculated values for the electrostatic potential at nuclei (EPN). A model for predicting the fluorescence properties of substituted hydrazones by means of EPN is drawn, including the polysubstituted derivatives, where Hammett constants are not applicable.
    Physical Chemistry Chemical Physics 09/2011; 13(41):18530-8. DOI:10.1039/c1cp21756a · 4.20 Impact Factor
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    ABSTRACT: Gamma-glutamyl transpeptidase (EC 2.3.2.2, GGT) is a membrane-associated enzyme, hydrolysing peptide bonds at the γ-carboxyl group of glutamic acid and transferring γ-Glu moiety to other amino acids or peptides. The main function of GGT is to regulate extracellular levels of glutathione, thus participating in the mechanisms involved in the cell resistance against oxidative stress. The enzyme is up-regulated during pathogenesis of a number of malignant diseases including non-small cell lung carcinomas. GGT activity in cultured normal (P) and tumor (A549 and SK-MES-1) human lung-derived cells were studied using both a recently developed fluorescent cytochemical procedure with the substrate γ-Glu-4-hydrazido-N-hexyl-1,8-naphthalimide (γ-Glu-HHNI) and the standard biochemical evaluation of the surface enzyme activity by γ-Glu-para-nitroanilide (γ-Glu-pNA). In the second phase of incubation, the enzyme activity was higher in tumor cell lines comparing with normal lung cells, pointing out to a possible role of GGT in the tumorogenesis of lung cancers. The fluorogenic GGT substrate γ-Glu-HHNI failed to reveal the enzyme activity in normal P cells but showed moderate activity of the enzyme in tumor cells. Thus, the novel GGT substrate could be tested for application for diagnostic purposes in cases of non-small cell lung carcinomas on the principle detectable/not-detectable GGT activity.
    Scientific Youth Conference “Kliment’s days” – Proceedings; 11/2010
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    Biotechnology & Biotechnological Equipment 01/2009; BIOTECHNOL. & BIOTECHNOL. EQ.:577. DOI:10.1080/13102818.2009.10818491 · 0.38 Impact Factor
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    ABSTRACT: Gly-Pro-, Gly-Pro-Met- and Ala-Ala-Phe-N'-(2-hexyl-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl)-hydrazides are synthesized by guanidinium/uronium type condensing reagent and used as fluorogenic substrates to localize dipeptidyl peptidase IV and tripeptidyl peptidase I activities in mammalian tissue sections. Enzyme hydrolysis releases 2-hexyl-6-hydrazino-1H-benzo[de]isoquinoline-1,3(2H)-dione, which couples with piperonal to form insoluble fluorescent hydrazone, precipitating on the enzyme locations and marking them. The fluorescent technique reveals precisely the enzymes locations at the lack of background noise in a single incubation step. It avoids most of the drawbacks of the previously proposed fluorescent histochemical techniques and can be valuable for the in situ studies of these enzymes in norm and pathology.
    European Journal of Medicinal Chemistry 04/2008; 44(1):384-92. DOI:10.1016/j.ejmech.2008.02.036 · 3.43 Impact Factor
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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.
    General Physiology and Biophysics 01/2006; 24(4):381-96. · 0.88 Impact Factor
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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.
    Cryo letters 01/2005; 26(2):131-6. · 0.64 Impact Factor
  • 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.
    Cellular and molecular biology 02/2004; 50 Online Pub:OL565-8. · 0.69 Impact Factor
  • 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.
    Cellular and molecular biology 02/2004; 50 Online Pub:OL553-8. · 0.69 Impact Factor
  • A. Dikov, M. Dimitrova
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    A. Dikov, M. Dimitrova
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    ABSTRACT: A new method for the histochemical visualization of lysosomal aminopeptidase dipeptidyl peptidase II activity (DPP II) is developed. The substrate L-Lys-L-Ala-5-chloro-1-anthraquinonylhydrazide-2HBr (Lys-Ala-CAH) is readily hydrolyzed by the enzyme to release 5-Cl-1-anthraquinonylhydrazine (CAH). The last compound is simultaneously coupled to an aromatic aldehyde, e.g. 4-nitrobenzaldehyde (p-NBA) or piperonal (3,4-methylenedioxybenzaldehyde; PPL), to form a highly insoluble deeply colored hydrazone, marking the enzyme locations. Using the new method, DPP II is successfully localyzed in tissue sections from different rat organs.
    Cellular and molecular biology 12/2000; 46(7):1213-8. · 0.69 Impact Factor
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    ABSTRACT: The original histochemical method for the visualization of tripeptidyl aminopeptidase I (TPP I, EC 3.4.14.9) is developed. The method is based on the new synthetic substrates Gly-L-Pro-L-Met(or L-Ala)-5-chloro-1-anthraquinonyl hydrazide (Gly-Pro-Met[Ala]-CAH). The final reaction product is represented as tripeptidyl-5-chloro-1 anthraquinonyl hydrazides (TPP-CAH). Upon the enzyme action the practically in aqueous media insoluble brown-reddish dye 5-chloro-1-anthraquinonyl hydrazine (CAH) is released, which reacts simultaneously with aromatic aldehydes as e.g. 4-anisaldehyde (p-AA) or 4-nitrobenzaldehyde (p-NBA), resulting in microcrystalline or amorphous deeply colored hydrazones. The last compounds mark accurately the locations of enzymatic activity. The biochemically suggested lysosomal localization of this collagen-degrading exopeptidase is thus confirmed on tissue sections. More information about the distribution of TPP I in different rat organs is presented as well.
    Cellular and molecular biology 12/2000; 46(7):1219-25. · 0.69 Impact Factor
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    ABSTRACT: A new method for the histochemical localization of dipeptidyl aminopeptidase I (DPP I, cathepsin C), based on a newly synthesized substrate-Gly-L-Phe-5-chloro-1-anthraquinoyl hydrazide.HCl (Gly-Phe-CAH), is proposed. The enzyme activity liberates 5-chloro-1-anthraquinoyl hydrazine (CAH)--a water-insoluble brown-reddish compound, which precipitates on the enzyme locations. The primary reaction product reacts simultaneously or, otherwise, by post-coupling with p-anisaldehyde (p-AA), thus converting to the reddish-violet amorphous hydrazone--the final reaction product. The validity of enzyme localization is thus assured by the insolubility of the primary reaction product and does not depend on the rate of the second reaction step. The enzyme studied is successfully localized in different rat organs using the newly proposed technique.
    Cellular and molecular biology 01/2000; 45(8):1229-35. · 0.69 Impact Factor
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    D. Nikolova, A. Dikov, E. Marinova, M. Dimitrova
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    ABSTRACT: New tetrazolium method for the histochemical localization of dipeptidyl peptidase IV (DPP IV), based on a newly synthesized substrate Gly-L-Pro-1-hydroxy-4-naphthylamide is proposed. Upon the enzyme hydrolysis of the substrate a strong reducing agent, i.e. 4-amino-1-naphthol is released, which reduces tetrazolium salts to water-insoluble, deeply colored formazans, that precipitate on the sites of enzyme activity, marking them accurately. No auxiliary electron acceptor is needed for the redox reaction. The incubation is performed at the optimal pH of the enzyme. Precise enzyme localization is achieved in all organs studied. Thus, the new method avoids most of the disadvantages of the methods in use and might open new possibilities in peptidases histochemistry.
    Cellular and molecular biology 04/1999; 45(2):225-31. · 0.69 Impact Factor

Publication Stats

37 Citations
23.39 Total Impact Points

Institutions

  • 1993–2013
    • Bulgarian Academy of Sciences
      • • Institute of Experimental Morphology, Pathology and Anthropology with Museum
      • • Department of Excitable Structures
      Ulpia Serdica, Sofia-Capital, Bulgaria
  • 2004
    • Friedrich-Schiller-University Jena
      • Institute of Anatomy
      Jena, Thuringia, Germany