n-type charge transport in heavily p-doped polymers.

It is commonly assumed that charge-carrier transport in doped π-conjugated polymers is dominated by one type of charge carrier, either holes or electrons, as determined by the chemistry of the dopant. Here, through Seebeck coefficient and Hall effect measurements, we show that mobile electrons contribute substantially to charge-carrier transport in π-conjugated polymers that are heavily p-doped with strong electron acceptors. Specifically, the Seebeck coefficient of several p-doped polymers changes sign from positive to negative as the concentration of the oxidizing agents FeCl3 or NOBF4 increase, and Hall effect measurements for the same p-doped polymers reveal that electrons become the dominant delocalized charge carriers. Ultraviolet and inverse photoelectron spectroscopy measurements show that doping with oxidizing agents results in elimination of the transport gap at high doping concentrations. This approach of heavy p-type doping is demonstrated to provide a promising route to high-performance n-type organic thermoelectric materials.

Cadmium induces carcinogenesis in BEAS-2B cells through ROS-dependent activation of PI3K/AKT/GSK-3ß/ß-catenin signaling.

Cadmium has been widely used in industry and is known to be carcinogenic to humans. Although it is widely accepted that chronic exposure to cadmium increases the incidence of cancer, the mechanisms underlying cadmium-induced carcinogenesis are unclear. The main aim of this study was to investigate the role of reactive oxygen species (ROS) in cadmium-induced carcinogenesis and the signal transduction pathways involved. Chronic exposure of human bronchial epithelial BEAS-2B cells to cadmium induced cell transformation, as evidenced by anchorage-independent growth in soft agar and clonogenic assays. Chronic cadmium treatment also increased the potential of these cells to invade and migrate. Injection of cadmium-stimulated cells into nude mice resulted in the formation of tumors. In contrast, the cadmium-mediated increases in colony formation, cell invasion and migration were prevented by transfection with catalase, superoxide dismutase-1 (SOD1), or SOD2. In particular, chronic cadmium exposure led to activation of signaling cascades involving PI3K, AKT, GSK-3ß, and ß-catenin and transfection with each of the above antioxidant enzymes markedly inhibited cadmium-mediated activation of these signaling proteins. Inhibitors specific for AKT or ß-catenin almost completely suppressed the cadmium-mediated increase in total and active ß-catenin proteins and colony formation. Moreover, there was a marked induction of AKT, GSK-3ß, ß-catenin, and carcinogenic markers in tumor tissues formed in mice after injection with cadmium-stimulated cells. Collectively, our findings suggest a direct involvement of ROS in cadmium-induced carcinogenesis and implicate a role of AKT/GSK-3ß/ß-catenin signaling in this process.

NADPH oxidase activation is required in reactive oxygen species generation and cell transformation induced by hexavalent chromium.

Hexavalent chromium [Cr(VI)] is a well-known human carcinogen associated with the incidence of lung cancer. Although overproduction of reactive oxygen species (ROS) has been suggested to play a major role in its carcinogenicity, the mechanisms of Cr(VI)-induced ROS production remain unclear. In this study, we investigated the role of NADPH oxidase (NOX), one of the major sources of cellular ROS, in Cr(VI)-induced oxidative stress and carcinogenesis. We found that short-term exposure to Cr(VI) (2µM) resulted in a rapid increase in ROS generation in Beas-2B cells, and concomitantly increased NOX activity and expression of NOX members (NOX1-3 and NOX5) and subunits (p22(phox), p47(phox), p40(phox), and p67(phox)). Cr(VI) also induced phosphorylation of p47(phox) and membrane translocation of p47(phox) and p67(phox), further confirming NOX activation. Knockdown of p47(phox) with a short hairpin RNA attenuated the ROS production induced by Cr(VI). Chronic exposure (up to 3 months) to low doses of Cr(VI) (0.125, 0.25, and 0.5µM) also promoted ROS generation and the expression of NOX subunits, such as p47(phox) and p67(phox), but inhibited the expression of main antioxidant enzymes, such as superoxidase dismutase (SOD) and glutathione peroxidase (GPx). Chronic Cr(VI) exposure resulted in transformation of Beas-2B cells, increasing cell proliferation, anchorage independent growth in soft agar, and forming aggressive tumors in nude mice. Stable knockdown of p47(phox) or overexpression of SOD1, SOD2, or catalase (CAT) eliminated Cr(VI)-induced malignant transformation. Our results suggest that NOX plays an important role in Cr(VI)-induced ROS generation and carcinogenesis.

Cr(VI) induces mitochondrial-mediated and caspase-dependent apoptosis through reactive oxygen species-mediated p53 activation in JB6 Cl41 cells.

Cr(VI) compounds are known to cause serious toxic and carcinogenic effects. Cr(VI) exposure can lead to a severe damage to the skin, but the mechanisms involved in the Cr(VI)-mediated toxicity in the skin are unclear. The present study examined whether Cr(VI) induces cell death by apoptosis or necrosis using mouse skin epidermal cell line, JB6 Cl41 cells. We also investigated the cellular mechanisms of Cr(VI)-induced cell death. This study showed that Cr(VI) induced apoptotic cell death in a dose-dependent manner, as demonstrated by the appearance of cell shrinkage, the migration of cells into the sub-G1 phase, the increase of Annexin V positively stained cells, and the formation of nuclear DNA ladders. Cr(VI) treatment resulted in the increases of mitochondrial membrane depolarization and caspases activation. Electron spin resonance (ESR) and fluorescence analysis revealed that Cr(VI) increased intracellular levels of reactive oxygen species (ROS) such as hydrogen peroxide and superoxide anion radical in dose-dependent manner. Blockage of p53 by si-RNA transfection suppressed mitochondrial changes of Bcl-2 family composition, mitochondrial membrane depolarization, caspase activation and PARP cleavage, leading to the inhibition of Cr(VI)-induced apoptosis. Further, catalase treatment prevented p53 phosphorylation stimulated by Cr(VI) with the concomitant inhibition of caspase activation. These results suggest that Cr(VI) induced a mitochondrial-mediated and caspase-dependent apoptosis in skin epidermal cells through activation of p53, which are mainly mediated by reactive oxidants generated by the chemical.

Differential sensitivity of CYP1A to 3,3',4',4-tetrachlorobiphenyl and benzo(a)pyrene in two Lepomis species.

Although Lepomis species are abundant in a wide variety of habitats throughout North America and could serve as potentially valuable biomonitoring tools, few studies have examined the induction of pollutant biomarkers in this genus. We hypothesized that the induction of cytochrome P-450 1A (CYP1A), a sensitive and widely used indicator of response to aquatic contaminants, would serve as an effective biomarker of organic pollutant exposure in Lepomis species. We examined the response of CYP1A and two of the major pollutant-responsive phase II enzymes, glutathione S-transferase (GST), and uridine diphosphate glucuronyltransferase (UDPGT), in Lepomis exposed to organic pollutants under laboratory and field conditions. Two Lepomis species (longear sunfish, Lepomis megalottis and bluegill, Lepomis macrochirus) were exposed in the laboratory via intraperitoneal injection to corn oil (vehicle), benzo(a)pyrene (BaP) (10 and 50mg/kg), a polynuclear aromatic hydrocarbon (PAH) or 3,4,3',4'-tetrachlorobiphenyl (PCB 77) (0.1 and 1.0mg/kg), a dioxin-like planar halogenated aromatic hydrocarbon (HAH), and sacrificed 2 (BaP) or 7 (corn oil, PCB77) days later. Lepomis hepatic CYP1A exhibited differential sensitivity to these two classes of environmental contaminants. CYP1A activity was weakly induced in bluegill exposed to 1.0mg/kg PCB 77 (3 fold induction over controls) but strongly induced in both bluegill and longear sunfish exposed to 50mg/kg BaP (37 and 15 fold induction over controls, respectively). In contrast, hepatic GST activity in both species remained unchanged following the treatment with either compound and hepatic UDPGT activity, which was assessed only in BaP-treated longear sunfish, was unaffected by that chemical, indicating these phase II enzymes may not be sensitive pollutant biomarkers in this genus. Further, longear sunfish collected from a PCB contaminated site displayed relatively low levels of CYP1A activity despite PCB body burdens associated with strong induction of CYP1A activity in other fish species. The strong induction of CYP1A by BaP with much weaker CYP1A response to PCB indicates that CYP1A in Lepomis sp. could be an excellent biomarker for PAH pollution, but may not be a reliable indicator of site contamination by halogenated hydrocarbons. We conclude that Lepomis species provide a useful model for examining the regulation and potential consequences of differential pollutant sensitivity, but that CYP1A in these species should be used with caution as an indicator of halogenated contaminants.

Cadmium induces intracellular Ca2+- and H2O2-dependent apoptosis through JNK- and p53-mediated pathways in skin epidermal cell line.

Cadmium is a toxic heavy metal and has been widely used in industry. The skin is an important target for this metal. The mechanisms by which cadmium leads to damage to the skin are unclear at present. The aims of this study were to examine whether cadmium induces apoptosis in mouse skin epidermal cell line, JB6 Cl41 cells, and to investigate the cellular mechanisms by which cadmium causes cytotoxicity in the cells. The present study showed that cadmium induced cell death by apoptosis in a dose-dependent manner, as proven by the appearance of cell shrinkage, the increase of Annexin V positively stained cells, and the formation of nuclear DNA ladders. Cadmium-induced apoptosis involved a mitochondria-mediated mechanism but not caspase-dependent pathway in that the critical apoptotic events induced by cadmium, such as the decrease of Bcl-2/Bcl-xL, the increase of GADD45alpha, and the nuclear translocation of apoptosis inducing factor, were not affected by the inhibition of executive caspases. In contrast, blockage of p53 and JNK by pharmacological inhibitors or small interference RNA transfection suppressed the cadmium-induced apoptosis with the concomitant inhibition of antiapoptotic Bcl-2 family proteins and GADD45alpha, respectively. Furthermore, the activation of p53 and JNK and their downstream proteins in cadmium-exposed cells were inhibited by individual treatment with catalase and Bapta-acetoxymethyl. These results suggest that cadmium induces apoptosis via the activation of JNK- and p53-mediated signaling, where calcium ion and hydrogen peroxide act as the pivotal mediators of the apoptotic signaling.