Enhanced photocatalytic performance of MoS_2 modified by AgVO_3 from improved generation of reactive oxygen species

In this work, an efficient AgVO3/MoS 2 composite photocatalyst was successfully synthesized via a hydrothermal method. The photocatalytic activity of the as-prepared photocatalyst was evaluated by using it for assessing the degradation of different organic pollutants under visible-light irradiation. The composite 3%-AgVO3/MoS 2 catalyst demonstrated a significantly enhanced photocatalytic activity compared to the pure compounds（AgVO3 and MoS2）. The reason behind the excellent photocatalytic performance was the modification of MoS 2 by AgVO3 to facilitate O2 adsorption/activation. In addition, the composite catalyst facilitates the two-electron oxygen reduction reaction whereby H2O2 is generated on the surface of MoS 2 to produce additional reactive oxygen species（ROSs）. ESR coupled with the POPHA fluorescence detection method and a free radical capture experiment were used to elucidate the mechanism of formation of the ROSs, including ·OH, ·O2- and H2O2. Furthermore, the generation of additional ROSs could accelerate electron consumption, leaving behind more holes for the oxidation of organic pollutants. A possible photocatalytic mechanism of the composite is also discussed.

Cytotoxicity and Apoptosis Induction in Human HepG2 Hepatoma Cells by Decabromodiphenyl Ethane

Abstract Objective To investigate the toxic effects of decabromodiphenyl ethane （DBDPE）, used as an alternative to decabromodiphenyl ether in vitro. Methods HepG2 cells were cultured in the presence of DBDPE at various concentrations （3.125-100.0 mg/L） for 24, 48, and 72 h respectively and the toxic effect of DBDPE was studied. Results As evaluated by the 3-（4,5-dimethylthiazol-2-yl）-2,5-diphenyl tetrazolium bromide and lactate dehydrogenase assays and nuclear morphological changes, DBDPE inhibited HepG2 viability in a time- and dose-dependent manner within a range of 12.5 mg/L to 100 mg/L and for 48 h and 72 h. Induction of apoptosis was detected at 12.5-100 mg/L at 48 h and 72 h by propidium iodide staining, accompanied with overproduction of reactive oxygen species （ROS）. Furthermore, N-acetyI-L-cysteine, a widely used ROS scavenger, significantly reduced DBDPE-induced ROS levels and increased HepG2 cells viability. Conclusion DBDPE has cytotoxic and anti-proliferation effect and can induce apoptosis in which ROS plays an important role

Inhibitory effect of metformin on the proliferation of human hepatoma HepG2 cells and its potential mechanism

Objective： This work aimed to study the inhibitory effect and the related mechanism of metformin （MET） on the proliferation of human hepatoma HepG2 cells. Methods： Human hepatoma HepG2 cells were treated with MET （0, 2, 10, and 50 mM）. The inhibitory effect of MET on the proliferation of HepG2 cells was determined by MTT method. The apoptosis of HepG2 cells was detected by flow cytornetry. The expression of cyclin D1 in HepG2 cells was examined by Western blot. ROS-DHE fluorescence probe was used to stain the reactive oxygen species （ROS） generated by HepG2 cells after treat- ment. Results： MET could inhibit the proliferation of HepG2 cells in a dose and time dependent manner. MET promoted the apoptosis of HepG2 cells. In addition, MET suppressed the expression of cell cycle protein cyclin D1 and induced the produc- tion of ROS in HepG2 cells. Conclusion： MET can inhibit the proliferation of human hepatoma HepG2 cells and induce cell apoptosis. Meanwhile, MET has the ability to decrease the expression of cyclin D1 and induce ROS generation, which may be involved in the mechanism of inhibiting hepatoma cells proliferation.

Extracellular ATP Promotes Stomatal Opening of Arabidopsis thaliana through Heterotrimeric G Protein α Subunit and Reactive Oxygen Species

In recent years, adenosine tri-phosphate （ATP） has been reported to exist in apoplasts of plant cells as a signal molecule. Extracellular ATP （eATP） plays important roles in plant growth, development, and stress tolerance. Here, extra- cellular ATP was found to promote stomatal opening of Arabidopsis thaliana in light and darkness. ADP, GTP, and weakly hydrolyzable ATP analogs （ATPγS, Bz-ATP, and 2meATP） showed similar effects, whereas AMP and adenosine did not affect stomatal movement. Apyrase inhibited stomatal opening. ATP-promoted stomatal opening was blocked by an NADPH oxidase inhibitor （diphenylene iodonium） or deoxidizer （dithiothreitol）, and was impaired in null mutant of NADPH ox- idase （atrbohD/F）. Added ATP triggered ROS generation in guard cells via NADPH oxidase. ATP also induced Ca^2＋ influx and H ＋ efflux in guard cells. In atrbohD/F, ATP-induced ion flux was strongly suppressed. In null mutants of the heterotrimeric G protein α subunit, ATP-promoted stomatal opening, cytoplasmic ROS generation, Ca^2＋ influx, and ^H＋ efflux were all sup- pressed. These results indicated that eATP-promoted stomatal opening possibly involves the heterotrimeric G protein, ROS, cytosolic Ca^2＋, and plasma membrane H＋-ATPase.

H_2O_2-induced Leaf Cell Death and the Crosstalk of Reactive Nitric/Oxygen Species

In plants, the chloroplast is the main reactive oxygen species （ROS） producing site under high light stress. Catalase （CAT）, which decomposes hydrogen peroxide （H2O2）, is one of the controlling enzymes that maintains leaf redox homeostasis. The catalase mutants with reduced leaf catalase activity from different plant species exhibit an H2O2-induced leaf cell death phenotype. This phenotype was differently affected by light intensity or photoperiod, which may be caused by plant species, leaf redox status or growth conditions. In the rice CAT mutant nitric oxide excess 1 （noe1）, higher H2O2 levels induced the generation of nitric oxide （NO） and higher S-nitrosothiol （SNO） levels, suggesting that NO acts as an important endogenous mediator in H2O2-induced leaf cell death. As a free radical, NO could also react with other intracellular and extracellular targets and form a series of related molecules, collectively called reactive nitrogen species （RNS）. Recent studies have revealed that both RNS and ROS are important partners in plant leaf cell death. Here, we summarize the recent progress on H2O2-induced leaf cell death and the crosstalk of RNS and ROS signals in the plant hypersensitive response （HR）, leaf senescence, and other forms of leaf cell death triggered by diverse environmental conditions.

Shielding of the geomagnetic field reduces hydrogen peroxide production in human neuroblastoma cell and inhibits the activity of CuZn superoxide dismutase

Accumulative evidence has shown the adverse effects of a geomagnetic field shielded condition, so called a hypomagnetic field （HMF）, on the metabolic processes and oxidative stress in animals and cells. However, the underlying mechanism remains unclear. In this study, we evaluate the role of HMF on the regulation of cellular reactive oxygen species （ROS） in human neuroblastoma SH-SY5Y cells. We found that HMF exposure led to ROS decrease, and that restoring the decrease by additional H2O2 rescued the HMF-enhanced cell proliferation. The measurements on ROS related indexes, including total anti-oxidant capacity, H2O2 and superoxide anion levels, and superoxide dismutase （SOD） activity and expres- sion, indicated that the HMF reduced H2O2 production and inhibited the activity of CuZn-SOD. Moreover, the HMF accelerated the denaturation of CuZn-SOD as well as enhanced aggregation of CuZn-SOD protein, in vitro. Our findings indicate that CuZn-SOD is able to response to the HMF stress and suggest it a mediator of the HMF effect.

Loss of IKB kinase βpromotes myofibroblast transformation and senescence through activation of the ROS-TGFβ autocrine loop

Using forward and reverse genetics and global gene expression analyses, we explored the crosstalk between the IKB kinase β （IKKβ） and the transforming growth factor β （TGFβ） signaling pathways. We show that in vitro ablation of Ikkβ in fibroblasts led to progressive ROS accumulation and TGFβ activation, and ultimately accelerated cell migration, fibroblast-myofibroblast transformation and senescence. Mechanistically, the basal IKKβ activity was required for anti-oxidant gene expression and redox homeostasis. Lacking this activity, IKKβ-null cells showed ROS accumulation and activation of stress-sensitive transcription factor AP-1/c- Jun. AP-1/c-Jun activation led to up-regulation of the Tgfβ2 promoter, which in turn further potentiated intracellular ROS through the induction of NADPH oxidase （NOX）. These data suggest that by blocking the autocrine amplification of a ROS-TGFβ loop IKKβ plays a crucial role in the prevention of fibroblast-myofibroblast transformation and senescence.

Comparative study of oxidative stress induced by sand flower and schistose nanosized layered double hydroxides in N2a cells

Magnesium-aluminum layered double hydroxide （Mg/ALLDH） nanoparticles have strong potential application as drug delivery systems because of their low toxicity and suitable biocompatibility. However, few studies have described the morphological effects of these hydroxides on nerve cells. The present study compares the oxidative stress induced by different concentrations （i.e., 0, 50, 100, 200, 400, and 800 μg/mL） of sand flower and flake nano-Mg/ AI-LDHs in mouse neuroblastoma cells （N2a） when these cells were exposed for 24 and 48 h. Cell viability was detected by MTT assay, and production of reactive oxygen species （ROS）, glutathione （GSH）, and malondialdehyde （MDA） were monitored to evaluate oxidative damage. Results suggested that sand flower nano-LDHs, at the appropriate concentrations （less than 200 μg/mL）, especially those of about 100-200 nm in size, induce no harmful effects on N2a cells.