Evolution of Metastable Defects and Its Effect on the Electronic Properties of MoS2 Films.

We report on structural and electronic properties of defects in chemical vapor-deposited monolayer and few-layer MoS2 films. Scanning tunneling microscopy, Kelvin probe force microscopy, and transmission electron microscopy were used to obtain high resolution images and quantitative measurements of the local density of states, work function and nature of defects in MoS2 films. We track the evolution of defects that are formed under heating and electron beam irradiation. We observe formation of metastable domains with different work function values after annealing the material in ultra-high vacuum to moderate temperatures. We attribute these metastable values of the work function to evolution of crystal defects forming during the annealing. The experiments show that sulfur vacancies formed after exposure to elevated temperatures diffuse, coalesce, and migrate bringing the system from a metastable to equilibrium ground state. The process could be thermally or e-beam activated with estimated energy barrier for sulfur vacancy migration of 0.6 eV in single unit cell MoS2. Even at equilibrium conditions, the work function and local density of states values are strongly affected near grain boundaries and edges. The results provide initial estimates of the thermal budgets available for reliable fabrication of MoS2-based integrated electronics and indicate the importance of defect control and layer passivation.

Comet assay on thawed embryos: An optimized technique to evaluate DNA damage in mouse embryos.

Our objective was to optimize the CA technique on mammal embryos. MATERIALS AND METHODS: 1000 frozen 2-cell embryos from B6CBA mice were used. Based on a literature review, and after checking post-thaw embryo viability, the main outcome measures included: 1) comparison of the embryo recovery rate between 2 CA protocols (2 agarose layers and 3 agarose layers); 2) comparison of DNA damage by the CA on embryos with (ZP+) and without (ZP-) zona pellucida; and 3) comparison of DNA damage in embryos exposed to 2 genotoxic agents (H2O2 and simulated sunlight irradiation (SSI)). DNA damage was quantified by the % tail DNA. RESULTS: 1) The recovery rate was 3,3% (n=5/150) with the 2 agarose layers protocol and 71,3% (n=266/371) with the 3 agarose layers protocol. 2) DNA damage did not differ statistically significantly between ZP- and ZP+ embryos (12.60±2.53% Tail DNA vs 11.04±1.50 (p=0.583) for the control group and 49.23±4.16 vs 41.13±4.31 (p=0.182) for the H2O2 group); 3) H2O2 and SSI induced a statistically significant increase in DNA damage compared with the control group (41.13±4.31% Tail DNA, 36.33±3.02 and 11.04±1.50 (p<0.0001)). The CA on mammal embryos was optimized by using thawed embryos, by avoiding ZP removal and by the adjunction of a third agarose layer.

Observation of superconducting vortex clusters in S/F hybrids.

While Abrikosov vortices repel each other and form a uniform vortex lattice in bulk type-II superconductors, strong confinement potential profoundly affects their spatial distribution eventually leading to vortex cluster formation. The confinement could be induced by the geometric boundaries in mesoscopic-size superconductors or by the spatial modulation of the magnetic field in superconductor/ferromagnet (S/F) hybrids. Here we study the vortex confinement in S/F thin film heterostructures and we observe that vortex clusters appear near magnetization inhomogeneities in the ferromagnet, called bifurcations. We use magnetic force microscopy to image magnetic bifurcations and superconducting vortices, while high resolution scanning tunneling microscopy is used to obtain detailed information of the local electronic density of states outside and inside the vortex cluster. We find an intervortex spacing at the bifurcation shorter than the one predicted for the same superconductor in a uniform magnetic field equal to the thermodynamical upper critical field Hc2. This result is due to a local enhanced stray field and a competition between vortex-vortex repulsion and Lorentz force. Our findings suggest that special magnetic topologies could result in S/F hybrids that support superconductivity even when locally the vortex density exceeds the thermodynamic critical threshold value beyond which the superconductivity is destroyed.

Ferromagnetism and Conductivity in Hydrogen Irradiated Co-Doped ZnO Thin Films.

Impressive changes in the transport and ferromagnetic properties of Co-doped ZnO thin films have been obtained by postgrowth hydrogen irradiation at temperatures of 400 °C. Hydrogen incorporation increases the saturation magnetization by one order of magnitude (up to ∼1.50 µB/Co) and increases the carrier density and mobility by about a factor of two. In addition to the magnetic characterization, the transport and structural properties of hydrogenated ZnO:Co have been investigated by Hall effect, local probe conductivity measurements, micro-Raman, and X-ray absorption spectroscopy. Particular care has been given to the detection of Co oxides and metal Co nanophases, whose influence on the increase in the transport and ferromagnetic properties can be excluded on the ground of the achieved results. The enhancement in ferromagnetism is directly related to the dose of H introduced in the samples. On the contrary, despite the shallow donor character of H atoms, the increase in carrier density n is not related to the H dose. These apparently contradictory effects of H are fully accounted for by a mechanism based on a theoretical model involving Co-VO (Co-O vacancy) pairs.

In vitro and in vivo antimutagenic effects of DIG, a herbal preparation of Berberis vulgaris, Taraxacum officinale and Arctium lappa, against mitomycin C.

DIG, a liquid herbal preparation made from a mixture of diluted mother tinctures of Berberis vulgaris, Taraxacum officinale and Arctium lappa, was assessed for its antimutagenic properties against mitomycin C. The micronucleus assay on Chinese hamster ovary (CHO)-K1 cells was used to evaluate the in vitro anticlastogenic activity of DIG compared to those of separately diluted mother tinctures. The micronucleus assay was performed on mouse erythrocytes and the comet assay was performed on mouse liver, kidney, lung, brain and testicles to assess the protective effects of DIG (0.2 and 2 % at libitum) against an intraperitoneal injection of mitomycin C (1 mg Kg(-1)) in mice. DIG exerted a powerful anticlastogenic activity, under both pretreatment and simultaneous treatment conditions as assessed by the micronucleus assay in CHO-K1 cells. Its protective activity was greater than that observed for each mother tincture. DIG reduced micronuclei levels in mouse erythrocytes and suppressed >80 % of DNA strand breaks in the liver, kidney, lung, brain and testicles of mice exposed to mitomycin C.

Genotoxicity of mixtures of glyphosate and atrazine and their environmental transformation products before and after photoactivation.

The photo-inducible cytogenetic toxicity of glyphosate, atrazine, aminomethyl phosphoric acid (AMPA), desethyl-atrazine (DEA), and their various mixtures was assessed by the in vitro micronucleus assay on CHO-K1 cells. Results demonstrated that the cytogenetic potentials of pesticides greatly depended on their physico-chemical environment. The mixture made with the four pesticides exhibited the most potent cytogenetic toxicity, which was 20-fold higher than those of the most active compound AMPA, and 100-fold increased after light-irradiation. Intracellular ROS assessment suggested the involvement of oxidative stress in the genotoxic impact of pesticides and pesticide mixtures. This study established that enhanced cytogenetic activities could be observed in pesticide mixtures containing glyphosate, atrazine, and their degradation products AMPA and DEA. It highlighted the importance of cocktail effects in environmental matrices, and pointed out the limits of usual testing strategies based on individual molecules, to efficiently estimate environmental risks.

Genotoxic and clastogenic activity of saponins extracted from Nauclea bark as assessed by the micronucleus and the comet assays in Chinese Hamster Ovary cells.

ETHNOPHARMACOLOGICAL RELEVANCE: Bark extracts of Nauclea latifolia, Nauclea diderrichii, Nauclea pobeguinii and Nauclea vandergutchii are used in traditional medicine in West and South Africa for the treatment of fevers, diarrhea and malaria. AIM OF THE STUDY: To estimate the possible long-term toxicity and genotoxicity of plant extracts (dichloromethane, methanol, water/methanol, water) and saponins. MATERIALS AND METHODS: The clastogenicity of plant extracts and saponins was assessed by the micronucleus assay performed on Chinese Hamster Ovary cells. The DNA-damaging activity of saponin mixture was assessed by the comet assay on Chinese Hamster ovary cells. RESULTS: Hydromethanolic extracts from Nauclea latifolia, Nauclea diderrichii and Nauclea pobeguinii exhibited a significant clastogenic/aneugenic activity without S9 mix. The hydromethanolic extract from Nauclea diderrichii was the most clastogenic/aneugenic fraction with a Minimal Active Concentration (MAC) of 23.1 µgm L(-1). It was submitted to a separation step leading to six main saponins identified as quinovic acid glycosides (saponins A, D, E, G, J, K). None of the isolated saponins exerted a significant clastogenic/aneugenic activity by the micronucleus assay, however a mixture made with equal quantities of each of the six saponins exhibited a direct genotoxic/clastogenic activity as assessed by both the micronucleus assay and the comet assay on Chinese Hamster Ovary cells. CONCLUSION: Saponins present in the hydromethanolic extracts of Nauclea induced synergistic in vitro DNA-damage and chromosome mutations in mammalian cells. This genotoxic activity was probably due to the capacity of Nauclea saponins to reduce cell defense against oxidative stress through the inhibition of glutathione-S-transferase activity.

Assessment of the genotoxicity of three cryoprotectants used for human oocyte vitrification: dimethyl sulfoxide, ethylene glycol and propylene glycol.

Vitrification requires high concentrations of cryoprotectants that may induce long-term toxic effects on cells. The aim of this study was to evaluate the possible genotoxicity of three cryoprotectants extensively used for oocyte vitrification: dimethyl sulfoxide (DMSO), ethylene glycol (EG) and propylene glycol (PROH). For this purpose, a Chinese Hamster Ovary cell line (CHO), commonly used in genetic toxicology, was selected as an in vitro biological model to assess both the induction of DNA strand-breaks as identifiable by the alkaline comet assay and the persistence of chromosomal damages (micronuclei) as analyzed by the micronucleus assay. Results showed that DMSO was not genotoxic. EG did not exert direct genotoxic activity, however EG exhibited significant genotoxic and clastogenic activities in the presence of an external cytochrome-based P450 oxidation system (S9 Mix). PrOH produced in vitro DNA-damage leading to chromosome mutations in the presence and absence of the S9 Mix. These results showed that high concentrations of EG and PrOH could induce in vitro chromosomal damage in eukaryotic cells.

Activity of benzothiazoles and chemical derivatives on Plasmodium falciparum.

Malaria is a major health concern particularly in Africa which has about 90% of the worldwide annual clinical cases. The increasing number of drug-resistant Plasmodium falciparum justifies the search for new drugs in this field. Antimalarial activity of 2-substituted 6-nitro- and 6-amino-benzothiazoles and their anthranilic acids has been tested. An in vitro study has been performed on W2 and 3D7 strains of P. falciparum and on clinical isolates from malaria-infected patients. Toxicity has been assessed on THP1 human monocytic cells. For the most active drug candidates, the in vitro study was followed by in vivo assays on P. berghei-infected mice and by in vitro assays in order to determine the stage-dependency and the mechanism of action. Of 39 derivatives tested in vitro, 2 had specific antimalarial properties. Each compound was active on all stages of the parasite, but one was markedly active on mature schizonts, while the other was more active on young schizont forms. Both drugs were also active on mitochondrial membrane potential. In vivo data confirmed efficiency with a sustained decrease of parasitaemia. Products A12 and C7 may be considered as potential antimalarial worthy of further chemical and biological research.

In vitro activity of the beta-carboline alkaloids harmane, harmine, and harmaline toward parasites of the species Leishmania infantum.

Harmane, harmine, and harmaline were investigated for their in vitro antileishmanial activity toward parasites of the species Leishmania infantum. Harmane and Harmine displayed a moderate antiproliferative activity toward human monocytes and exerted a weak antileishmanial activity toward both the promastigote and the amastigote forms of the parasite. Their mechanism of action on the promastigote form of the parasite involved interactions with DNA metabolism leading to an accumulation of parasites in the S-G(2)M phases of the cell-cycle. Harmaline, at the contrary, was deprived from toxicity toward human cells and Leishmania promastigotes, however it exerted a strong antileishmanial activity toward the intracellular amastigote form of the parasite. This property was shown to partly result from the capacity of the molecule to prevent parasite internalization within macrophages by inhibiting Leishmania PKC activity.

Antimalarial activity of extracts and alkaloids isolated from six plants used in traditional medicine in Mali and Sao Tome.

Methanol and chloroform extracts were prepared from various parts of four plants collected in Mali: Guiera senegalensis (Gmel.) Combretaceae, Feretia apodanthera (Del.) Rubiaceae, Combretum micranthum (Don.) Combretaceae, Securidaca longepedunculata (Fres.) Polygalaceae and two plants -collected in Sao Tome: Pycnanthus angolensis (Welw.) Myristicaceae and Morinda citrifolia (Benth.) Rubiaceae were assessed for their in vitro antimalarial activity and their cytotoxic effects on human monocytes (THP1 cells) by flow cytometry. The methanol extract of leaves of Feretia apodanthera and the chloroform extract of roots of Guiera senegalensis exhibited a pronounced antimalarial activity. Two alkaloids isolated from the active extract of Guiera senegalensis, harman and tetrahydroharman, showed antimalarial activity (IC(50) lower than 4 microg/mL) and displayed low toxicity against THP1. Moreover, the decrease of THP1 cells in S phase of the cell cycle, after treatment with harman and tetrahydroharman, was probably due to an inhibition of total protein synthesis.

Synergistic in vitro antimalarial activity of plant extracts used as traditional herbal remedies in Mali.

In Mali, where malaria is endemic, plants are extensively used for treating periodic fevers and malaria. According to the advice of traditional medicine, plants are often mixed during the preparation of febrifugal decoctions. In previous studies, we demonstrated the potent in vitro antimalarial activity of extracts isolated from four plants commonly used in traditional remedies: Mitragyna inermis (Willd.) O. Kuntze, Rubiaceae, Nauclea latifolia (Sm.), Rubiaceae, Guiera senegalensis (Gmel.), Combretaceae, and Feretia apodanthera (Del.), Rubiaceae. In the present work, we evaluate the potent in vitro synergistic antimalarial interaction between these extracts, using standard isobologram analysis. Then, we evaluate their cytotoxicity on human monocytes and their mutagenic activity on an in vitro system of two beta-carboline alkaloids isolated from Guiera senegalensis (harman and tetrahydroharman). Three combinations demonstrate a strong, synergistic, inhibitory effect on in vitro plasmodial development and are devoid of cytotoxicity towards human cells. These results justify their use in association in traditional medicine. Moreover, tetrahydroharman, isolated from G. senegalensis, presents interesting antimalarial activity, no cytotoxicity and is not genotoxic in the Salmonella Ames test with and without metabolic activation.

In vitro and in vivo antileishmanial activity of 2-amino-4,6-dimethylpyridine derivatives against Leishmania mexicana.

Leishmania mexicana promastigote and intracellular amastigote growths were inhibited by the water-soluble furan-2-carboxamide issued from the pharmacophore 2-amino-4,6-dimethylpyridine with IC50 values of 69 +/- 2 and 89 +/- 9 microM, respectively. This compound was also tested against established L. mexicana infection in susceptible BALB/c mice; an intraperitoneal administration of 10 mg/Kg/day during five consecutive days induced a high reduction in the amastigote burden of the poplitea lymph node (81 +/- 6.4%), the spleen (80 +/- 1.6%) and the liver (73 +/- 9%). Approach of the mechanism of antileishmanial activity of this compound, assessed by the flow cytometry, showed a reduction in the protein and DNA synthesis. Finally, an actual increase of the in vitro antileishmanial activity was obtained by replacement of the amidic function by an imidazolidin-2-one moiety. In this new series, two of the N-substituted derivatives showed IC50 values of 13 +/- 0.5 and 7 +/- 3 microM in intracellular amastigotes constituting new promising compounds for further studies.

Molecular umbrella-assisted transport of glutathione across a phospholipid membrane.

A di-walled molecular umbrella (1a) has been synthesized by acylation of the terminal amino groups of spermidine with cholic acid, followed by condensation with bis(3-O-[N-1,2,3-benzotriazin-4(3H)-one]yl)-5,5'-dithiobis-2-nitrobenzoate (BDTNB), and displacement with glutathione (gamma-Glu-Cys-Gly, GSH). Replacement of the sterol hydroxyls with sulfate groups, prior to displacement with GSH, afforded a hexasulfate analogue 1b. Both conjugates have been found to enter large unilamellar vesicles (200 nm diameter, extrusion) of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and to react with entrapped GSH to form oxidized glutathione (GSSG). Evidence for vesicular entry has come from the formation of oxidized glutathione (GSSG) within the interior of the vesicle, the appearance of the thiol form of the umbrella (USH), and the absence of release of GSH into the external aqueous phase. Results that have been obtained from monolayer experiments, together with the fact that the heavily sulfated conjugate is able to cross the phospholipid bilayer, have yielded strong inferential evidence for an "umbrella-like" action of these molecules as they cross the lipid bilayer.

In vitro antileishmanial activity of three saponins isolated from ivy, alpha-hederin, beta-hederin and hederacolchiside A(1), in association with pentamidine and amphotericin B.

The in vitro antileishmanial activity of three saponins isolated from ivy, alpha-hederin, beta-hederin and hederacolchiside A(1), was investigated on parasites of the species Leishmania mexicana, in their promastigote and amastigote forms compared with their toxicity versus human monocytes. The results showed that saponins exhibited a strong antiproliferative activity on all stages of development of the parasite but demonstrated a strong toxicity versus human cells. Association of subtoxic concentrations of saponins with antileishmanial drugs such as pentamidine and amphotericin B demonstrated that saponins could enhance the efficiency of conventional drugs on both the promastigote and the amastigote stages of development of the parasite. The results demonstrated moreover that the action of saponins on promastigote membrane was cumulative with those of amphotericin B.

No evidence of oxidant events in amphotericin B cytotoxicity versus L. infantum promastigotes.

Amphotericin B is used for the treatment of systemic mycoses and visceral leishmaniasis. The objective of our study was to evaluate the impact of catalase, ascorbic acid and ketoconazole on the amphotericin B toxicity towards Leishmania promastigotes membrane by two flow cytometric tests, the membrane potential assay using a cationic dye, [DiOC5(3)], and the membrane permeability test using propidium iodide. The collapse of membrane potential appeared at amphotericin B concentrations weaker than those assessed by the membrane permeability test. The binding of amphotericin B to membrane sterol was not modified by catalase or ascorbic acid whereas amphotericin B-induced growth inhibition could be modulated by these products. The permeabilizing effect of amphotericin B on parasite membrane was strongly reduced in the presence of ketoconazole. These results confirmed the pore hypothesis of amphotericin B action and suggested that flow cytometric methods constituted a valuable alternative to conventional methods for assessing the effect of drugs on cellular membrane and evaluating parasite susceptibility to polyene antibiotics.

Toxicity and genotoxicity of antimalarial alkaloid rich extracts derived from Mitragyna inermis O. Kuntze and Nauclea latifolia.

The toxicity and the genotoxicity of antimalarial alkaloid rich extracts derived from two plants used in traditional medicine in Mali (Mitragyna inermis (Willd.) O. Kuntze Rubiaceae and Nauclea latifolia (Sm.) Rubiaceae) were evaluated on in vitro and in vivo systems. The results demonstrated that an alkaloid rich extract derived from M. inermis induced a strong inhibition of protein synthesis in mammalian cells but did not exhibit mutagenic or genotoxic activity. An alkaloid rich extract derived from N. latifolia could interact in vitro with DNA of bacteria and mammalian cells, leading to G2-M cell cycle arrest and heritable DNA-damage, as well as inducing in vivo single-strand breaks in liver, kidney and blood cells.

Flow cytometric detection of Leishmania parasites in human monocyte-derived macrophages: application to antileishmanial-drug testing.

A flow cytometric technique was developed for detection of amastigotes of the protozoan Leishmania infantum in human nonadherent monocyte-derived macrophages. The cells were fixed and permeabilized with paraformaldehyde-ethanol, and intracellular amastigotes were labeled with Leishmania lipophosphoglycan-specific monoclonal antibody. Results showed that flow cytometry provided accurate quantification of the infection rates in human macrophages compared to the rates obtained by the conventional microscopic technique, with the advantage that a large number of cells could be analyzed rapidly. The results demonstrated, moreover, that labeling of intracellular amastigotes could reliably be used to evaluate the antileishmanial activities of conventional drugs such as meglumine antimoniate, amphotericin B, pentamidine, and allopurinol. They also established that various Leishmania species (L. mexicana, L. donovani) could be detected by this technique in other host-cell models such as mouse peritoneal macrophages and suggested that the flow cytometric method could be a valid alternative to the conventional method.

Antileishmanial activity of three saponins isolated from ivy, alpha-hederin, beta-hederin and hederacolchiside A1, as compared to their action on mammalian cells cultured in vitro.

The in vitro antileishmanial activity of three saponins isolated from ivy, alpha-hederin, beta-hederin and hederacolchiside A1, was investigated on Leishmania infantum. The assessment of possible targets (membrane integrity, membrane potential, DNA synthesis and protein content) was performed in both Leishmania promastigotes and human monocytes (THP1 cells). Results observed in Leishmania showed that the saponins exhibited a strong antiproliferative activity on all stages of development of the parasite by altering membrane integrity and potential: hederacolchiside A1 appeared to be the most active compound against both promastigotes and amastigotes. Results observed in THP1 cells demonstrated that the saponins exerted also a potent antiproliferative activity against human monocytes, by producing a significant DNA synthesis inhibition. The ratio between antileishmanial activity on amastigotes and toxicity to human cells suggested that the saponins could be considered as possible antileishmanial drugs.