Observation of electron neutrino appearance in a muon neutrino beam

The T2K experiment has observed electron neutrino appearance in a muon neutrino beam produced 295 km from the Super-Kamiokande detector with a peak energy of 0.6 GeV. A total of 28 electron neutrino events were detected with an energy distribution consistent with an appearance signal, corresponding to a significance of 7.3σ when compared to 4.92±0.55 expected background events. In the Pontecorvo-Maki-Nakagawa-Sakata mixing model, the electron neutrino appearance signal depends on several parameters including three mixing angles θ12, θ23, θ13, a mass difference Δm(32)(2) and a CP violating phase δ(CP). In this neutrino oscillation scenario, assuming |Δm(32)(2)|=2.4×10(-3)  eV(2), sin(2)θ(23)=0.5, and Δm322>0 (Δm(32)(2)<0), a best-fit value of sin(2)2θ(13)=0.140(-0.032)(+0.038) (0.170(-0.037)(+0.045)) is obtained at δ(CP)=0. When combining the result with the current best knowledge of oscillation parameters including the world average value of θ(13) from reactor experiments, some values of δ(CP) are disfavored at the 90% C.L.

Measurement of neutrino oscillation parameters from muon neutrino disappearance with an off-axis beam

The T2K Collaboration reports a precision measurement of muon neutrino disappearance with an off-axis neutrino beam with a peak energy of 0.6 GeV. Near detector measurements are used to constrain the neutrino flux and cross section parameters. The Super-Kamiokande far detector, which is 295 km downstream of the neutrino production target, collected data corresponding to 3.01×10(20) protons on target. In the absence of neutrino oscillations, 205±17 (syst) events are expected to be detected while only 58 muon neutrino event candidates are observed. A fit to the neutrino rate and energy spectrum, assuming three neutrino flavors and normal mass hierarchy yields a best-fit mixing angle sin2(θ23)=0.514±0.082 and mass splitting |Δm(32)(2)|=2.44(-0.15)(+0.17)×10(-3) eV2/c4. Our result corresponds to the maximal oscillation disappearance probability.

Synergistic increase in cell lethality by dieldrin and H2O2 in rat thymocytes: effect of dieldrin on the cells exposed to oxidative stress

Dieldrin, one of persistent pesticides, is highly resistant to biotic and abiotic degradation. It is accumulated in organisms. Recent studies suggest that dieldrin exerts a potent cytotoxic action on cells exposed to oxidative stress. In this study, the effect of dieldrin on rat thymocytes exposed to hydrogen peroxide (H2O2)-induced oxidative stress was examined. Dieldrin at 5μM and H2O2 at 300μM slightly increased cell lethality from a control value of 5.4±0.5% (mean±standard deviation of four experiments) to 7.8±1.3% and 9.0±0.3%, respectively. Simultaneous application of dieldrin and H2O2 significantly increased cell lethality to 46.2±1.8%. The synergistic increase in cell lethality was dependent on dieldrin concentration (0.3-5μM) but not on H2O2 concentration (30-300μM). Dieldrin accelerated H2O2-induced cell death, which was estimated with the help of annexin V-FITC and propidium iodide. Presence of either dieldrin or H2O2 decreased the cellular content of nonprotein thiol and increased intracellular Zn(2+) concentration. The combination of dieldrin and H2O2 further pronounced these effects. TPEN, a chelator of intracellular Zn(2+), significantly attenuated the synergistic increase in cell lethality induced by dieldrin and H2O2. It is, therefore, suggested that dieldrin augments the cytotoxicity of H2O2 in a Zn(2+)-dependent manner.

Nanomolar concentration of triclocarban increases the vulnerability of rat thymocytes to oxidative stress

It was recently reported that triclocarban was absorbed significantly from soap used during showering in human subjects and that its C(max) in their whole blood ranged from 23 nM to 530 nM. We revealed that a nanomolar concentration (300 nM) of triclocarban potentiated the cytotoxicity of 300 µM H(2)O(2) in rat thymocytes by using cytometric techniques with appropriate fluorescent probes. Although 300 nM triclocarban did not itself increase the population of dead cells (cell lethality), it facilitated the process of cell death induced by H(2)O(2), resulting in a further increase in the population of dead cells. Nanomolar concentrations (300 nM or higher) of triclocarban significantly decreased the cellular content of nonprotein thiol (glutathione), which has a protective role against oxidative stress. Triclocarban at 300 nM or higher increased the cell vulnerability to oxidative stress. The results may suggest that nanomolar concentration (300 nM or higher) of triclocarban affects some cellular functions although there is no evidence for adverse effects of triclocarban in humans at present.

Bisabololoxide A, one of the constituents in German chamomile extract, attenuates cell death induced by calcium overload

Bisabololoxide A (BSBO), main constituents in German chamomile extract, is responsible for antipruritic effect. In previous study, the incubation with 30-100 μM BSBO for 24 h exerted cytotoxic and proapoptotic effects on rat thymocytes. To further characterize BSBO cytotoxicity, the effect on the cells suffering from calcium overload by calcium ionophore A23187 was examined. A23187 induced Ca(2+) -dependent cell death. Contrary to our expectation, 1-10 μM BSBO inhibited A23187-induced increase in cell lethality of rat thymocytes. BSBO attenuated A23187-induced increases in populations of shrunken living cells, phosphatidylserine-exposed living cells, and dead cells, without affecting the increase in intracellular Ca(2+) concentration and the Ca(2+) -dependent hyperpolarization. The effect of BSBO on A23187-treated cells may be unique because the activation of Ca(2+) -dependent K(+) channels is required for cell shrinkage, externalization of phosphatidylserine, and cell death in some cells. The cell death induced by A23187 was not inhibited by Z-VAD-FMK, a pan-inhibitor of caspases. Thus, the cell death may be a necrosis with some features observed during an early stage of apoptosis. These results suggest that BSBO at low micromolar concentrations is cytoprotective against calcium overload.

Evidence for the appearance of atmospheric tau neutrinos in super-Kamiokande

Super-Kamiokande atmospheric neutrino data were fit with an unbinned maximum likelihood method to search for the appearance of tau leptons resulting from the interactions of oscillation-generated tau neutrinos in the detector. Relative to the expectation of unity, the tau normalization is found to be 1.42 ± 0.35(stat)(-0.12)(+0.14)(syst) excluding the no-tau-appearance hypothesis, for which the normalization would be zero, at the 3.8σ level. We estimate that 180.1 ± 44.3(stat)(-15.2)(+17.8) (syst) tau leptons were produced in the 22.5 kton fiducial volume of the detector by tau neutrinos during the 2806 day running period. In future analyses, this large sample of selected tau events will allow the study of charged current tau neutrino interaction physics with oscillation produced tau neutrinos.

Elevation of intracellular Zn2+ level by nanomolar concentrations of triclocarban in rat thymocytes

It was recently reported that nanomolar concentrations of triclocarban, an antimicrobial agent, were detected in human blood after the use of soap containing triclocarban. Due to the widespread use of triclocarban in adult and infant personal care products, the report prompted us to study its cytotoxicity. The cytotoxicity of triclocarban was examined in rat thymocytes by using a cytometric technique with propidium iodide for examining cell lethality, FluoZin-3-AM for monitoring the intracellular Zn(2+) level, and 5-chloromethylfluorescencein diacetate for estimating the cellular content of non-protein thiol. The incubation with triclocarban at nanomolar concentrations (50-500nM) for 1h did not affect cell lethality but significantly elevated the intracellular Zn(2+) level. The elevation of the intracellular Zn(2+) level by triclocarban was not significantly dependent on external Zn(2+) level. There was a negative correlation (r=-0.9225) between the effect on the intracellular Zn(2+) level and that on the cellular content of non-protein thiol. These results suggest that nanomolar concentrations of triclocarban decrease the cellular content of non-protein thiol, leading to intracellular Zn(2+) release. Since zinc plays physiological roles in mammalian cells, the percutaneous absorption of triclocarban from soap may, therefore, affect some cellular functions.

Yttrium decreases the intracellular Zn2+ concentration in rat thymocytes by attenuating a temperature-sensitive Zn2+ influx

Yttrium is used in the production of various electronic devices because the alloy it contains enhances or modifies the properties of other elements. In order to study the cytotoxic action of yttrium, the effect of yttrium chloride (YCl(3)) on the intracellular Zn(2+) level was examined in rat thymocytes using a flow cytometer with FluoZin-3-AM and propidium iodide. The application of YCl(3) significantly decreased the intensity of the FluoZin-3 fluorescence, suggesting a decrease in the intracellular Zn(2+) level or quenching of the FluoZin-3 fluorescence by Y(3+). However, since Y(3+) did not attenuate the FluoZin-3 fluorescence under cell-free conditions, the latter suggestion was ruled out. Rat thymocytes possess a temperature-sensitive membrane pathway that carries Zn(2+) into the cells. The application of YCl(3) attenuated the FluoZin-3 fluorescence augmented by externally applied ZnCl(2) in a concentration-dependent manner. This suggested that Y(3+) inhibited the Zn(2+) influx, resulting in the decrease in the intracellular Zn(2+) level. Yttrium may induce dyshomeostasis of intracellular Zn(2+), leading to some cytotoxic actions.

Nanomolar concentrations of zinc pyrithione increase cell susceptibility to oxidative stress induced by hydrogen peroxide in rat thymocytes

Zinc pyrithione is used as an antifouling agent. However, the environmental impacts of zinc pyrithione have recently been of concern. Zinc induces diverse actions during oxidative stress; therefore, we examined the effect of zinc pyrithione on rat thymocytes suffering from oxidative stress using appropriate fluorescent probes. The cytotoxicity of zinc pyrithione was not observed when the cells were incubated with 3 μM zinc pyrithione for 3 h. However, zinc pyrithione at nanomolar concentrations (10 nM or more) significantly increased the lethality of cells suffering from oxidative stress induced by 3 mM H(2)O(2). The application of zinc pyrithione alone at nanomolar concentrations increased intracellular Zn(2+) level and the cellular content of superoxide anions, and decreased the cellular content of nonprotein thiols. The simultaneous application of nanomolar zinc pyrithione and micromolar H(2)O(2) synergistically increased the intracellular Zn(2+) level. Therefore, zinc pyrithione at nanomolar concentrations may exert severe cytotoxic action on cells simultaneously exposed to chemicals that induce oxidative stress. If so, zinc pyrithione leaked from antifouling materials into surrounding environments would be a risk factor for aquatic ecosystems. Alternatively, zinc pyrithione under conditions of oxidative stress may become more potent antifouling ingredient.

Triclosan, an antibacterial agent, increases intracellular Zn(2+) concentration in rat thymocytes: its relation to oxidative stress

Triclosan is used as an antibacterial agent in household items and personal care products. Since this compound is found in maternal milk of humans and bodies of wild animals, there is growing concern among some consumer groups and scientific community that triclosan is adverse for humans and wild animals. In order to estimate adverse actions of triclosan, the effects of triclosan on intracellular Zn(2+) concentration and cellular thiol content were studied in rat thymocytes by the use of flow cytometer with appropriate fluorescent probes. Triclosan at 1-3 μM (sublethal concentrations) increased the intensity of FluoZin-3 fluorescence (intracellular Zn(2+) concentration) and decreased the intensity of 5-chloromethylfluorescein (5-CMF) fluorescence (cellular thiol content). Negative correlation (r=-0.985) between triclosan-induced changes in FluoZin-3 and 5-CMF fluorescences was found. Removal of external Zn(2+) did not significantly affect the triclosan-induced augmentation of FluoZin-3 fluorescence, suggesting an intracellular Zn(2+) release by triclosan. These actions of triclosan were similar to those of H(2)O(2) and triclosan significantly potentiated the cytotoxicity of H(2)O(2). Therefore, the results may suggest that triclosan at sublethal concentrations induces oxidative stress that decreases cellular thiol content, resulting in an increase in intracellular Zn(2+) concentration by Zn(2+) release from intracellular store(s). Since recent studies show many physiological roles of intracellular Zn(2+) in cellular functions, the triclosan-induced disturbance of cellular Zn(2+) homeostasis may induce adverse actions on the cells.

Search for differences in oscillation parameters for atmospheric neutrinos and antineutrinos at Super-Kamiokande

We present a search for differences in the oscillations of antineutrinos and neutrinos in the Super-Kamiokande-I, -II, and -III atmospheric neutrino sample. Under a two-flavor disappearance model with separate mixing parameters between neutrinos and antineutrinos, we find no evidence for a difference in oscillation parameters. Best-fit antineutrino mixing is found to be at (Δm2,sin2 2θ)=(2.0×10(-3)  eV2, 1.0) and is consistent with the overall Super-K measurement.

Putative role of intracellular Zn(2+) release during oxidative stress: a trigger to restore cellular thiol content that is decreased by oxidative stress

Although the ability of zinc to retard the oxidative process has been recognized for many years, zinc itself has been reported to induce oxidative stress. In order to give some insights into elucidating the role of intracellular Zn(2+) in cells suffering from oxidative stress, the effects of N-ethylmaleimide (NEM) and ZnCl(2) on cellular thiol content and intracellular Zn(2+) concentration were studied by use of 5-chloromethylfluorescein diacetate (5-CMF-DA) and FluoZin-3 pentaacetoxymethyl ester (FluoZin-3-AM) in rat thymocytes. The treatment of cells with NEM attenuated 5-CMF fluorescence and augmented FluoZin-3 fluorescence in a dose-dependent manner. These NEM-induced phenomena were observed under external Zn(2+)-free conditions. Results suggest that NEM decreases cellular thiol content and induces intracellular Zn(2+) release. Micromolar ZnCl(2) dose-dependently augmented both FluoZin-3 and 5-CMF fluorescences, suggesting that the elevation of intracellular Zn(2+) concentration increases cellular thiol content. Taken together, it is hypothesized that intracellular Zn(2+) release during oxidative stress is a trigger to restore cellular thiol content that is decreased by oxidative stress.

Indication of electron neutrino appearance from an accelerator-produced off-axis muon neutrino beam

The T2K experiment observes indications of ν(μ) → ν(e) appearance in data accumulated with 1.43×10(20) protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with |Δm(23)(2)| = 2.4×10(-3)  eV(2), sin(2)2θ(23) = 1 and sin(2)2θ(13) = 0, the expected number of such events is 1.5±0.3(syst). Under this hypothesis, the probability to observe six or more candidate events is 7×10(-3), equivalent to 2.5σ significance. At 90% C.L., the data are consistent with 0.03(0.04) < sin(2)2θ(13) < 0.28(0.34) for δ(CP) = 0 and a normal (inverted) hierarchy.