High oxide ion and proton conductivity in a disordered hexagonal perovskite.

Oxide ion and proton conductors, which exhibit high conductivity at intermediate temperature, are necessary to improve the performance of ceramic fuel cells. The crystal structure plays a pivotal role in defining the ionic conduction properties, and the discovery of new materials is a challenging research focus. Here, we show that the undoped hexagonal perovskite Ba7Nb4MoO20 supports pure ionic conduction with high proton and oxide ion conductivity at 510 °C (the bulk conductivity is 4.0 mS cm-1), and hence is an exceptional candidate for application as a dual-ion solid electrolyte in a ceramic fuel cell that will combine the advantages of both oxide ion and proton-conducting electrolytes. Ba7Nb4MoO20 also showcases excellent chemical and electrical stability. Hexagonal perovskites form an important new family of materials for obtaining novel ionic conductors with potential applications in a range of energy-related technologies.

WWOX suppresses autophagy for inducing apoptosis in methotrexate-treated human squamous cell carcinoma.

Squamous cell carcinoma (SCC) cells refractory to initial chemotherapy frequently develop disease relapse and distant metastasis. We show here that tumor suppressor WW domain-containing oxidoreductase (WWOX) (also named FOR or WOX1) regulates the susceptibility of SCC to methotrexate (MTX) in vitro and cure of SCC in MTX therapy. MTX increased WWOX expression, accompanied by caspase activation and apoptosis, in MTX-sensitive SCC cell lines and tumor biopsies. Suppression by a dominant-negative or small interfering RNA targeting WWOX blocked MTX-mediated cell death in sensitive SCC-15 cells that highly expressed WWOX. In stark contrast, SCC-9 cells expressed minimum amount of WWOX protein and resisted MTX-induced apoptosis. Transiently overexpressed WWOX sensitized SCC-9 cells to apoptosis by MTX. MTX significantly downregulated autophagy-related Beclin-1, Atg12-Atg5 and LC3-II protein expression and autophagosome formation in the sensitive SCC-15, whereas autophagy remained robust in the resistant SCC-9. Mechanistically, WWOX physically interacted with mammalian target of rapamycin (mTOR), which potentiated MTX-increased phosphorylation of mTOR and its downstream substrate p70 S6 kinase, along with dramatic downregulation of the aforementioned proteins in autophagy, in SCC-15. When WWOX was knocked down in SCC-15, MTX-induced mTOR signaling and autophagy inhibition were blocked. Thus, WWOX renders SCC cells susceptible to MTX-induced apoptosis by dampening autophagy, and the failure in inducing WWOX expression leads to chemotherapeutic drug resistance.

Neutrophil-mediated formation of carcinogenic N-nitroso compounds in an in vitro model for intestinal inflammation.

In order to study neutrophil-mediated formation of carcinogenic N-nitroso compounds as a mechanism of inflammation-related colon carcinogenesis, we designed an in vitro model for intestinal inflammation, consisting of a coincubation system with human colon cells (Caco-2 cells) and activated human neutrophils (PMN), as important immunoreactive cells. We investigated whether nitrosamines and nitrosamides could be formed upon addition of dimethylamine, morpholine and methylurea to the coincubations as nitrosatable precursors, which are known to produce carcinogenic N-nitroso compounds. Incubations of pure nitric oxide with dimethylamine and morpholine showed that NO-mediated formation of nitrosodimethylamine and nitrosomorpholine is possible under the incubation conditions. During the coincubations of activated PMN and Caco-2 cells, 0.34 nmol nitrite/10(6) PMN was produced. Dose-dependent formation of NMOR was observed in this PMN/Caco-2 system; addition of 5mM morpholine resulted in a significantly increased NMOR formation of 4.2 nM. However, no detectable NDMA and methylnitrosourea were formed in this coincubation system. These results suggest that activated human neutrophils are able to synthesize carcinogenic N-nitrosamines, e.g. NMOR, which implies a risk of colon carcinogenesis during chronic inflammation. However, the observed relatively low level of nitrosation suggests that also other risk factors are contributing to the association between chronic inflammation and colon cancer risk.

In vitro investigations into the interaction of beta-carotene with DNA: evidence for the role of carbon-centered free radicals.

Supplementation by beta-carotene has unexpectedly appeared to increase lung cancer risk among smokers. In order to explain this it has been suggested that at high serum levels of beta-carotene, prooxidant characteristics of beta-carotene may become manifest, yielding reactive oxygen species (ROS) and inducing oxidative DNA damage. It has further been hypothesized that cigarette smoke carcinogens such as benzo[a]pyrene (B[a]P) and/or B[a]P metabolites, may directly react with beta-carotene. Furthermore, beta-carotene oxidation products may have a role in the bioactivation of B[a]P analogous to the peroxide shunt pathway of cytochrome P450 supported by cumene hydroperoxide. The aim of this study was to assess the effects of beta-carotene on the formation of B[a]P-DNA adducts and oxidative DNA damage in vitro in isolated DNA, applying as metabolizing systems rat liver and lung metabolizing fractions and lung metabolizing fractions from smoking and non-smoking humans. We established that beta-carotene in the presence of various metabolizing systems was unable to induce oxidative DNA damage (8-oxo-dG), although beta-carotene is capable of generating ROS spontaneously in the absence of metabolizing fractions. We also could not find an effect of beta-carotene on DNA adduct formation induced by B[a]P upon metabolic activation. We could, however, provide evidence of the occurrence of a carbon-centered beta-carotene radical which was found to be able to interact with B[a]P and to intercalate in DNA.

Generation of free radicals and induction of DNA adducts by activation of heterocyclic aromatic amines via different metabolic pathways in vitro.

Food-derived heterocyclic aromatic amines (HCAs) have proved to be carcinogenic in both rodents and nonhuman primates. Two different metabolic pathways are suggested for the metabolic activation of HCA. The hepatic pathway proceeds via a two-step process involving N-hydroxylation by cytochrome P4501A2 and subsequent O-acetylation by N-acetyltransferase-2. An alternative pathway may be of particular interest in extrahepatic tissues and proceeds via one-electron oxidation catalyzed by prostaglandin H synthase (PHS), rendering free-radical metabolites. In this study, we investigated the metabolic activation of two HCAs, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), by two different enzyme systems in vitro, generating different primary and secondary reactive metabolites. Rat liver S9 mix and PHS were used as the activating system and represent the hepatic and extrahepatic pathways, respectively. Electron-spin resonance spectroscopy showed that both IQ and PhIP exerted inhibiting effects on PHS-mediated formation of hydroxyl radicals during the conversion of arachidonic acid to prostaglandins. Evidence for the formation of HCA free radicals was presented in an indirect way by the formation of glutathione-derived thiyl radicals, with purified PHS as the activating system. Activation by S9 mix did not result in the formation of detectable radical metabolites, showing that the two metabolic routes primarily led to the formation of different metabolites. In all electron-spin resonance experiments, IQ appeared to be more effective than PhIP. In contrasts, DNA adduct analysis by means of (32)P-postlabeling showed similar adduct patterns for S9 and PHS in single-stranded and double-stranded salmon testes DNA after incubation with PhIP, indicating the ultimate formation of a common reactive intermediate. For IQ, activation by PHS led to an additional adduct spot that was not present after S9 activation. Furthermore, activation of IQ resulted in higher adduct levels compared with PhIP for both activation pathways. Overall, adduct levels were higher in single-stranded DNA than double-stranded DNA. Our results showed that the hepatic and extrahepatic pathways resulted in different primary metabolites, while the ultimate formation of a similar reactive intermediate for PhIP, possibly an arylnitrenium ion, suggested that both pathways could play an important role in the onset of carcinogenesis.

In vivo staphylococcal enterotoxin B (SEB)-primed murine splenocytes secrete mediators which suppress CD25(hi) expression and cell cycle progression of naive splenocytes in response to SEB in vitro.

Administration of bacterial superantigen results in clonal activation of T cells followed by a state of hyporesponsiveness to subsequent antigen stimulation. Using a coculture system, we showed that the splenocytes from staphylococcal enterotoxin B (SEB)-injected BALB/c mice suppressed the proliferative response of naive splenocytes to SEB stimulation. The suppressive effect also occurred in Fas-deficient MRL-lpr/lpr mice. When naive responder cells were separated by a semipermeable membrane from SEB-primed effector cells, the suppressive effect remained apparent. The hyporesponsiveness of responder cells did not result from excessive induction of apoptosis, but rather from prevention of entering the S and G2/M phases of the cell cycle. The IL-2 levels in culture supernatants were low with the presence of SEB-primed effector cells. However, addition of IL-2 to the cocultures only partially reversed the inhibitory effect. Further studies revealed a reduced level of the CD25(hi) subpopulation in responder cells when cultured in the transwell with the presence of SEB-primed effector cells compared to that with saline-primed controls. This inhibitory effect was not observed for SEB-induced activation of CD25(int) and CD69 expression. Taken together, using a transwell culture system, we show in this study an inhibition of CD25(hi) expression and cell cycle arrest in target cells, which may serve at least in part the mechanisms of SEB-induced hyporesponsiveness.

alpha-Difluoromethylornithine blocks thymocyte apoptosis via a reduction in tyrosine phosphorylation.

The effect of alpha-difluoromethylornithine on cell apoptosis was investigated. Freshly isolated mouse thymocytes were cultured in the medium alone or with dexamethasone, and apoptotic cell death was monitored after 6 h. A correlation was seen between cell apoptosis and a reduction in the polyamine levels of thymocytes. Addition of exogenous polyamines decreased the levels of apoptosis induced spontaneously in the culture medium or by dexamethasone. However, addition of alpha-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase, to the cultures did not enhance apoptosis but rather caused inhibition of thymocyte apoptosis. Analysis of the mechanism of alpha-difluoromethylornithine-mediated inhibition of apoptosis indicated that alpha-difluoromethylornithine treatment blocked protein tyrosine phosphorylation, which was elevated drastically during the first hour of thymocyte cultivation. Treatment with the phosphotyrosine phosphatase inhibitor phenylarsine oxide reversed this inhibitory effect of alpha-difluoromethylornithine on apoptotic cell death. Our results provide an alternative mechanism for alpha-difluoromethylornithine showing the inhibition of apoptosis via reduction of protein tyrosine phosphorylation.

Bad overexpression sensitizes NIH/3T3 cells to undergo apoptosis which involves caspase activation and ERK inactivation.

The effect of Bad overexpression on apoptosis was demonstrated by a mouse Bad transgene stably expressed in NIH/3T3 cells. The cells overexpressing Bad treated with either serum starvation or ceramide showed apoptotic characteristics evident at 18 and 8 h, respectively. Whether serum deprivation and ceramide utilize a common death pathway requires further investigation. The time for the first apoptosis detection was shortened to 2 h and was prominent at 4 h, while above that time cells were maintained under serum-depleted conditions in the presence of ceramide (40 microM). Further investigation revealed that the activity of caspase-3 (CPP32) was elevated after ceramide treatment in Bad-transfected cells compared to that of the cells without Bad transfection, indicating the involvement of caspase cascade. Furthermore, the Bad-transfected cells showed reduced phosphorylation of extracellular signal-regulated kinase (ERK). Taken together, we hypothesize that Bad-overexpressing NIH/3T3 cells in the presence of ceramide undergo apoptosis by activating caspase cascade. Simultaneously, the cell survival pathway was blocked possibly by inactivation of the MAPK pathway such as the down-regulation of ERK.

Is green fluorescent protein toxic to the living cells?

Green fluorescent protein (GFP) has become more popular to be used as a living marker for positively transfected clones in many studies. To establish stable cell lines constitutively expressing GFP, three GFPs expressed from plasmid pBIEGFP, pSG5GFP, and pRSGFP were introduced into NIH/3T3, BHK-21, Huh-7, and HepG2 cells. All the GFPs we used are the mutant forms of a common wild phenotype. The pBIEGFP expressed enhanced GFP (EGFP). The pRSGFP and pSG5GFP expressed red shift GFP (RSGFP). The RSGFP gene in pSG5GFP was driven by a strong SV40 promoter and showed at least 20-fold higher RSGFP expression by western blot analysis. Despite of the variation in the levels of GFP expression, many GFP expressing cells contracted, rounded-up, and died, which was confirmed by decreasing luciferase activity. CPP32 activity and flow cytometric analyses further demonstrate that cells expressing GFP underwent apoptosis. Our observation is contradictory to other reports that GFP is nontoxic to the cells. Most importantly, this paper shows for the first time the link between expression of GFP and induction of apoptosis. This finding should promote studies of GFP cytotoxicity and attempts to isolate new non-toxic mutants of GFP.

Selective activation of Ha-ras(val12) oncogene increases susceptibilityof NIH/3T3 cells to TNF-alpha.

This is the first report demonstrating that NIH/3T3 fibroblasts utilize the Raf-1/MAPK pathway to sensitize themselves to tumor necrosis factor-alpha (TNF-alpha) cytotoxicity under Ha-rasVal12 oncogene-overexpressed conditions. This paper clearly shows that the sensitivity of NIH/3T3 cells to TNF-alpha cytotoxicity positively correlated with the expression level of activated Ha-ras transgene, which was manipulated either positively by isopropyl-beta-d-thiogalactoside (IPTG) induction or negatively by a ribozyme or a dominant negative Ras suppression. Further analysis revealed that after TNF-alpha treatment, Ha-ras-overexpressed transformants underwent apoptosis. Overexpression of dominant negative Raf-1, Rac1, or RhoA in the Ha-ras transformants clarified that among these factors, only dominant negative Raf-1 could reverse the cell sensitivity to TNF-alpha, indicating that Raf-1, as a proapoptotic factor, indeed participates in TNF-alpha cytotoxicity. The anti-apoptotic roles of Bcl-2 and PI(3) kinase are also demonstrated by the Ha-ras transformants which became more resistant to TNF-alpha while overexpressing Bcl-2 or the activated p110 catalytic subunit. The analyses of the cell cycle and nuclear transcription factor activities revealed that TNF-alpha treatment caused the Ha-ras overexpressed transformants to shift from S to G0/G1 phase and increased the responses of AP-1, c-fos, and c-myc. Taken together, we suggest that the possible action of Ha-ras overexpression to sensitize TNF-alpha-treated fibroblasts is predominantly through the Ras/Raf-1/MAPK pathway to increase the responses of AP-1, c-fos, and c-myc, which are possibly involved in the aberration of cell cycle machinery, and subsequently to turn on the death program.

Requirement of I-E molecule for thymocyte apoptosis induced by staphylococcal enterotoxin B in vivo.

In vivo administration of bacterial superantigen staphylococcal enterotoxin B (SEB) to BALB/c mice led to thymus atrophy resulting from thymocyte apoptosis. In this study, we demonstrated that SEB induced a substantial reduction in thymocyte numbers in BALB/c, B10. D2 (H-2(d) haplotype), B10.BR, C3H/HeJ, C3H/HeN (H-2(k)), and (BALB/c x B6)F1 (H-2(dxb)), but caused little or no effect in I-E- strains such as B6, B10, A.BY (H-2(b)), and A.SW (H-2(s)) mice. Elimination of CD4(+)CD8(+) cells predominantly accounted for the thymocyte loss, although the numbers of other subpopulations may also be reduced. Thymocyte apoptosis was shown by an increase in the level of DNA fragmentation in BALB/c but not in B6 mice after SEB administration. Treatment with anti-I-Ed monoclonal antibody to BALB/c mice blocked SEB-induced thymocyte apoptosis when anti-I-Ad exerted less effect. In contrast to SEB, staphylococcal enterotoxin A led to comparable levels of thymus atrophy in BALB/c and B6 mice. Studies on the surface marker expression indicated that CD25 expression was upregulated on BALB/c mouse thymocytes but with only a moderate increase in B6 mice. The CD4(+)CD8(+) cells were the major (>90%) population that expressed elevated levels of CD25 in BALB/c mice. An increase in the expression of TCRalphabeta, CD3, and CD69 surface markers was also observed on thymocytes from BALB/c mice, but not from I-E- strains. The differential response of I-E+ and I-E- mice to SEB may be exploited as a model for the study of apoptosis in the thymus.

Ha-rasVal12 oncogene increases susceptibility of NIH/3T3 cells to lovastatin.

This study demonstrates that Ha-rasVal12 oncogene overexpression sensitizes NIH/3T3 fibroblasts to lovastatin (LOV) cytotoxicity. This sensitization is through apoptosis, which was characterized by increasing CPP32 (caspase-3) activity and DNA fragmentation. Bcl-2 overexpression increased the resistance of the Ha-ras transformants to LOV and rescued the cells from apoptosis, further confirming that the LOV-sensitive cells died of apoptosis. Further analysis showed that Ha-ras activity inversely correlated with WAF1 activity. LOV treatment suppressed Ha-ras activity but induced WAF1 activity and disrupted the cell population in G0/G1 and S phases. The Ha-ras transformants expressing either dominant negative RasAsn17 or Raf-1CB4 showed reverted susceptibility to LOV. These data confirm the involvement of Ras and demonstrate that Raf-1 signalling is required for LOV-induced cell death. Taken together, the possible action of LOV-induced apoptosis is through suppressing Ha-ras activity and increasing WAF1 activity, which alters cell cycle progression and finally activates suppressed apoptotic pathway in a Fas/Fas-L- and p53-independent fashion.

Changes of protein kinase C subspecies in staphylococcal enterotoxin-B-induced thymocyte apoptosis.

Our previous studies demonstrated that intravenous administration of staphylococcal enterotoxin B (SEB) to BALB/c mice resulted in thymocyte apoptosis. In the present study, we evaluated the role of protein kinase C (PKC) in thymocyte apoptosis induced by SEB. Our results showed that the level of protein phosphorylation in the thymocytes was reduced after the in vivo SEB treatment for 24 h. The activity of classical PKC subspecies was decreased in both cytosolic and membrane fractions of thymocytes following SEB administration. The lowest level of PKC activity was reached by 24 and 48 h, then was recovered gradually after 72 h. Furthermore, the mRNA expression of PKC-beta and, to a much less extent, PKC-alpha, but not PKC-sigma, in thymocytes was reduced by SEB. The decrease of mRNA level of PKC-beta showed good correlation with the pattern of PKC activity. These results provide direct evidence showing the changes in PKC subspecies mRNA expression during the process of apoptosis.

Immunomodulatory effects of acute exercise bout in sedentary and trained rats.

The immune response to acute exercise after long-term training was evaluated in rats. After 10 wk of exercise training on a drum exerciser, both sedentary control and trained groups ran with the intensity of 70% of peak oxygen consumption (VO2peak) for 10 min immediately before sacrifice. The mitogenic activity of spleen lymphocytes in trained group to staphylococcal enterotoxin B, a polyclonal T cell activator, decreased as compared to the sedentary control following acute exercise. However, proliferative response to lipopolysaccharide, a B cell mitogen, was augmented. Furthermore, the interleukin-2 production was reduced in the trained group. The lymphocyte subpopulations in the spleen and the peripheral blood lymphocytes were analyzed by flow cytometry. Although the tendency of changes in some populations was observed in trained vs untrained groups, no statistically significant difference was manifested. The serum levels of both norepinephrine and epinephrine increased immediately after acute exercise. The increase in serum lactate concentration was observed following acute exercise in sedentary control, but less prominent in the trained group.

The effect of chronic and acute exercise on immunity in rats.

The effects of exercise training and acute exercise on the immune system were investigated in rats. For chronic exercise training, the rats ran on a drum exerciser at the intensity of about 60-70% of maximal oxygen consumption (VO2max) for 30 min and then extended up to 60 min per day, 5 days per week for 10 weeks. The rats were at rest for 3 days before sacrifice. The mitogenic activity of spleen lymphocytes to concanavalin A (Con A) and staphylococcal enterotoxin B (SEB) decreased as compared to the sedentary control, while proliferative response to lipopolysaccharide (LPS) increased. The interleukin-2 (IL-2) production in the training group was reduced. The immunomodulatory effect after acute exercise has also been investigated and it showed profound enhancement of cell proliferation to Con A, SEB and LPS in mild (50% VO2max for 10 min) and moderate (70% VO2max for 10 min) exercise groups. The enhancing activity was less prominent after severe exercise (> 75%) VO2max until exhaustion). The IL2 production increased in all of these acute exercise groups. Nevertheless, there was no significant variation between exercise and control groups in the cell number per spleen and the percentages of various lymphocyte populations, i.e., total T, CD4+, CD8+ and IL-2R+ T cells as well as B cells. In summary, this study indicates that chronic exercise training may cause the reduction of T cell activity while acute exercise manifests an enhancing effect. However, B cell proliferation was elevated in both chronic and acute exercise groups.

In vivo induction of apoptosis in immature thymocytes by staphylococcal enterotoxin B.

Staphylococcal enterotoxins are potent T cell mitogens. Recent studies have shown that the binding of these toxins to class II MHC molecules on accessory cells is essential for the stimulation of T cells which bear specific V beta segment of TCR. In the present study we show that i.v. administration of staphylococcal enterotoxin B (SEB) results in an enlargement of spleen and lymph nodes but causes thymus atrophy. Elimination of CD4+CD8+ cells predominantly accounted for the shrinkage of thymus, and the lowest level of this cell population was reached 4 days after SEB injection. Furthermore, this decrease in CD4+CD8+ cells was accompanied by a relative increase in the percentages of CD4+CD8-, CD4-CD8+ and CD4-CD8- cells, whereas their absolute numbers actually reduced on day 4. The thymus shrinkage involved apoptosis which was characterized by DNA fragmentation and morphologic changes. The depletion of Thy-1 high, TCR-alpha beta low and TCR-alpha beta intermediate cells also occurred with a kinetic correlated to the reduction of CD4+CD8+ cells. Our results further showed that the percentages of V beta 8+ cells reduced 12 h post SEB injection, increased after 2 days, and decreased again thereafter. SEB thus causes both apoptotic and stimulative effects in the thymus. Apparently, the tremendous loss of double-positive cells (greater than 90% in cell number on day 4) is not simply due to the reduction of V beta 8+ cells, the possible modulatory effect of other factors or hormones which may play a role in the cell death is discussed.

Inhibition of the delayed-type hypersensitivity response by staphylococcal enterotoxin B-induced suppressor T cells.

Staphylococcal enterotoxin B (SEB) is a member of a family of gram-positive bacterial exotoxins which act as superantigens in both mouse and man. The administration of this toxin has been shown to inhibit antibody responses in vivo. We have previously shown that SEB is a potent inducer in vitro of multiple T suppressor cell populations. The present studies show that administration of microgram quantities of this toxin result in a reduced capacity to manifest a delayed-type hypersensitivity (DTH) response. In addition, we find that the failure to generate a normal DTH response appears to be due to the generation of a T suppressor cell population following SEB administration. Adoptive transfer studies show that the suppressor cells bear the CD5+ I-J+ CD4- CD8- Thy 1+ surface phenotype. The relationship of these cells to suppressor T cell populations generated following in vitro activation by SEB is discussed.