Zoran Nikolić

Metformin reduces cisplatin-mediated apoptotic death of cancer cells through AMPK-independent activation of Akt.

Metformin is an antidiabetic drug with anticancer properties, which mainly acts through induction of AMP-activated protein kinase (AMPK). In the present study we investigated the influence of metformin on the in vitro anticancer activity of the well-known chemotherapeutic agent cisplatin. Cell viability was determined by MTT and LDH release assay, oxidative stress and apoptosis (caspase activation, DNA fragmentation, and phosphatidylserine exposure) were assessed by flow cytometry, while activation of AMPK and Akt was analyzed by immunoblotting. Although metformin reduced the number of tumour cells when applied alone, it surprisingly antagonized the cytotoxicity of cisplatin towards U251 human glioma, C6 rat glioma, SHSY5Y human neuroblastoma, L929 mouse fibrosarcoma and HL-60 human leukemia cell lines. Only in B16 mouse melanoma cells metformin augmented the cytotoxicity of cisplatin. In U251 glioma cells metformin suppressed cisplatin-induced apoptotic cell death through inhibition of oxidative stress and caspase activation. The observed cytoprotection was apparently AMPK-independent, as metformin did not further increase cisplatin-induced AMPK activation in U251 cells and other pharmacological AMPK activators failed to block cisplatin-mediated apoptosis. On the other hand, metformin induced Akt activation in cisplatin-treated cells and Akt inhibitor 10-DEBC hydrochloride or phosphoinositide 3-kinase/Akt inhibitor LY294002 abolished metformin-mediated antioxidant and antiapoptotic effects. In conclusion, the antidiabetic drug metformin reduces cisplatin in vitro anticancer activity through AMPK-independent upregulation of Akt survival pathway. These data warrant caution when considering metformin for treatment of diabetic cancer patients receiving cisplatin or as a potential adjuvant in cisplatin-based chemotherapeutic regimens.

Modulation of Tumor Necrosis Factor-mediated Cell Death by Fullerenes

PurposeThe fullerene (C60/C70 mixture—C60/70) nanocrystalline suspension prepared by solvent exchange method using tetrahydrofyran (THF/nC60/70) and polyhydroxylated C60/70 [C60/70(OH)n] were compared for their ability to modulate cytotoxicity of the proinflammatory cytokine tumor necrosis factor (TNF).Materials and MethodsTNF-induced cytotoxicity was assessed in L929 fibrosarcoma cells by crystal violet assay. The type of cell death (apoptosis/necrosis), production of reactive oxygen species, mitochondrial depolarization and caspase activation were determined by flow cytometry using the appropriate reporter dyes.ResultsTHF/nC60/70 augmented, while C60/70(OH)n reduced the cytotoxicity of TNF. The numbers of cells undergoing apoptosis/necrosis, as well as of those displaying the activation of apoptosis-inducing enzymes of caspase family, were respectively increased or reduced by THF/nC60/70 or C60/70(OH)n. The antioxidant N-acetylcysteine and mitochondrial permeability transition inhibitor cyclosporin A each partly blocked the cytotoxic action of TNF, indicating the involvement of oxidative stress and mitochondrial dysfunction in the TNF cytotoxicity. Accordingly, THF/nC60/70 or C60/70(OH)n potentiated or suppressed, respectively, TNF-triggered oxidative stress and mitochondrial depolarization.ConclusionThe ability of different fullerene preparations to modulate TNF-induced oxidative stress and subsequent cell death suggests their potential value in the TNF-based cancer therapy or prevention of TNF-dependent tissue damage.

Taxol activates inducible nitric oxide synthase in rat astrocytes: the role of MAP kinases and NF-κB

Taxol is a microtubule-stabilizing agent that has recently been shown effective in the treatment of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. As astrocytes could modulate central nervous system (CNS) autoimmunity through inducible nitric oxide synthase (iNOS)-mediated production of immunoregulatory free radical nitric oxide (NO), we investigated the effect of taxol on NO synthesis in rat astrocytes. Taxol, either alone or in combination with interferon-γ, induced NO generation in primary astrocytes and astrocytoma C6 cells in a dose- and time-dependent manner. Accordingly, the drug markedly up-regulated the expression of both iNOS mRNA and protein in astrocytes. The observed effect of taxol was mediated through induction of iNOS transcription factors NF-κB and IRF-1, and required the activation of p38 MAP kinase and JNK. Finally, NO release by taxol-stimulated astrocytes was blocked with the microtubule-depolymerizing agent colchicine, suggesting the involvement of a microtubule-stabilizing activity of taxol in the observed effect.

Antiglioma action of xanthones from Gentiana kochiana: Mechanistic and structure–activity requirements

The present study identifies xanthones gentiakochianin and gentiacaulein as the active principles responsible for the in vitro antiglioma action of ether and methanolic extracts of the plant Gentiana kochiana. Gentiakochianin and gentiacaulein induced cell cycle arrest in G(2)/M and G(0)/G(1) phases, respectively, in both C6 rat glioma and U251 human glioma cell lines. The more efficient antiproliferative action of gentiakochianin was associated with its ability to induce microtubule stabilization in a cell-free assay. Both the xanthones reduced mitochondrial membrane potential and increased the production of reactive oxygen species in glioma cells, but only the effects of gentiakochianin were pronounced enough to cause caspase activation and subsequent apoptotic cell death. The assessment of structure-activity relationship in a series of structurally related xanthones from G. kochiana and Gentianella austriaca revealed dihydroxylation at positions 7, 8 of the xanthonic nucleus as the key structural feature responsible for the ability of gentiakochianin to induce microtubule-associated G(2)/M cell block and apoptotic cell death in glioma cells.

On the Sn I and Sn II Stark broadening

The Stark widths (W) of 12 neutral and 16 singly ionized tin (Sn I and Sn II, respectively) spectral lines have been measured in a laboratory helium plasma at 13 000 K electron temperature and 5.1 × 1022 m−3 electron density. Many of them are the first data in the literature. At mentioned plasma conditions, the Stark broadening has been found to be the dominant mechanism in line shape formation. The modified version of the linear, low-pressure, pulsed arc was used as a plasma source operated in helium with tin atoms, as impurities, evaporated from tin cylindrical plates located in the homogeneous part of the discharge, providing conditions free of self-absorption. Our Sn II W values are compared to the recent theoretical data calculated on the basis of the modified semi-empirical approach and, also, to the existing experimental W values. Our normalized Stark widths are much smaller (up to a factor of 4, on average) than those measured in a laser-produced plasma and in a plasma created by the shock-wave tubes. An agreement, within the accuracy of the experiment and uncertainties of the used theoretical approach, with the recent calculated W data was found. Our normalized Sn I Stark widths are much smaller than those observed in the mentioned plasma sources.

Defensive Secretions in Three Ground-Beetle Species (Insecta: Coleoptera: Carabidae)

The adults of three ground-beetle species were induced to discharge defensive secretions into vials. The secretions were obtained by CH2Cl2 extraction. Altogether 11 compounds were identified by GC-MS analysis. Calosoma sycophanta possesses 10 defensive compounds, Carabus ullrichii seven, while Abax parallelepipedus has six compounds. Methacrylic, tiglic and isobutyric acids were present in all samples. The first two organic compounds were predominant in the extracts of Abax parallelepipedus. Methacrylic acid and salicylaldehyde were the major compounds in extracts of Calosoma sycophanta. Methacrylic and angelic acids were the major components in extracts of Carabus ullrichii. Propanoic acid was detected for the first time in the family Carabidae and in all animals. 2-Methyl butyric, angelic and benzoic acids were found for the first time in the subfamily Carabinae. Our finding of butyric acid is its first precise identification in the Carabinae subfamily. 2-Methyl butyric, angelic, crotonic, senecioic and benzoic acids were found for the first time in a European groundbeetle species. The compounds detected in the defensive secretions serve as protection against predators.

RF thermal plasma processing of fullerenes

This paper presents results on fullerene formation during the processing of different graphite powders in an RF thermal plasma reactor. Graphite powders of different particle size and purity were fed into the reactor (Aldrich, KS4). Optical emission spectroscopy of atomic and molecular species is used as a diagnostic tool of the RF plasma flame. It was found that rotational and vibrational temperatures of C2 radicals depend on the feed rate of the precursor used. The volumes of RF plasma flame during processing of graphite powders have been calculated. By analysing scanning electron microscopy micrographs of soot, the evaporation rate of the precursors used has been evaluated as well. Based on the obtained values of volumes of plasma flame and evaporation rate of starting powders, the concentration of C2 radicals has been calculated.

Phase Transformations and Thermal Effects of Mechanically Activated BaCO 3 -TiO 2 System

Phase transformations and thermal effects of BaTiO 3 ceramics due to influence of mechanical activation were investigated. Equimolar mixture of BaCO 3 and TiO 2 powders was activated in high energy vibromill for various grinding times. Specific surface area determinations of initial and activated powders were carried out. The phase composition and crystallographic data of initial and thermal treated powders was determined using X-ray powder diffraction method. Heating process was investigated using differential thermal analysis.

Multiple Charged Nitrogen Ion Beam Irradiation of Fullerene Thin Films

Abstract In this work, the results of structural modification of fullerene thin films bombarded by multiple charged nitrogen ions have been reported. The properties of as‐deposited and irraditated fullerene thin films have been investigated by Raman and FTIR spectroscopy and AFM analysis. After irradiation by multiple charged nitrogen ions (N2+, N5+) new bondings in fullerene films have been formed and the amorphicity has been enhanced at higher doses. Raman and FTIR spectra showed structural changes of deposited films depending on the energy and implantation dose. AFM analysis showed that the ion beam had destroyed the surface ordering. At lower doses the surface order has been characterized by carbon clusters of 500 nm. At higher doses significantly smaller clusters have been formed (200 nm).

Optical diagnostics of fullerene synthesis in the RF thermal plasma process

In this work, the results of an optical emission study of fullerene synthesis in an inductively coupled radio frequency thermal plasma reactor are presented. The emis- sion spectroscopy studies, based on the use of the Swan C 2 (0,1) and CN (0,0) vibra- tional emission spectra, were carried out to determine the plasma temperature. The evaporation process of graphite powder was observed by scanning electron microscopy.