High Oxygen Conditions Research Articles

Palaeoceanographic and palaeoenvironmental controls on late Quaternary benthic foraminifera of the western continental slope of South Africa

Benthic foraminifera from two gravity cores recovered on the western continental slope (3522 and 3631 m water depth) of South Africa were studied to determine bottom water conditions and benthic environments over late Quaternary glacial-interglacial cycles. Benthic foraminifera assemblages and the carbon isotopic composition (δ13C) of Cibicidoides wuellerstorfi and Globoconella inflata were used to reconstruct palaeoenvironmental conditions. The assemblages reflect influences from substrate, productivity (seasonal and annual variations in the flux of organic matter, such as phytodetritus to the seafloor) and bottom water oxygenation. Uvigerinid forms were found to be distributed along bathymetric depths that also reflect oxygenation of bottom waters, where hispid and hispidocostate forms were more abundant at depths of oxygen-enriched bottom waters on the lower slope. These uvigerinids and other benthic species such as Epistominella exigua were also found to benefit from periods of high productivity. Palaeoproductivity increased during glacial periods but decreased sharply by a difference of ∼1‰ in δ13C during glacial terminations, reflecting a less nutrient-rich bottom water signal. During interglacial periods, epifaunal foraminifera and taxa adapted to oxygen-enriched environments, such as Cibicidoides spp. and high oxygen assemblages increased in abundance and were correlated to the less radiogenic regional εNd signals, while the abundance of high-productivity fauna and assemblages, associated with the nutrient-rich Southern Component Water, and that are adapted to a high organic matter flux and low oxygen conditions, decreased. Interglacial periods were reflected to exhibit benthic environments that are more oligotrophic, while glacial periods were interpreted to reflect more eutrophic conditions.

Impact of annealing on the growth dynamics of indium sulphide buffer layers

Thin films of Indium sulphide are deposited on corning glass substrate by thermal evaporation at room temperature (300 K). The as-deposited films were annealed from 373 to 723 K under vacuum ∼1 × 10−3 mbar. An amorphous phase is obtained from 300 to 473 K; the polycrystalline β-In2S3 emerges at 523 K, and In2O3 is grown at 723 K. The intermediary phases of β-In2S3 and In2O3 are perceived from 573 to 673 K. A clear distinction between the morphology of β-In2S3 and In2O3 was observed in the micrographs of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The β-In2S3 dominated films provide absorption coefficient (α) from 18 to 25 × 104 cm−1, while α values of In2O3 layers lie within 1–5 × 104 cm−1. The bandgap (Eg) of β-In2S3 thin films is low (2.34 eV), and that of In2O3 is high (3.47 eV); however, the intermediary phases of β-In2S3 and In2O3 exhibit bandgap tunning from 2.30 to 3.14 eV. Moreover, the β-In2S3 shows the highest carrier concentration (Nd; 3.25 × 1018 cm−3), In2O3 provides the highest mobility (μ; 228 Cm2/V.s), and intermediary phases exhibit the lowest resistivity (ρ; 1.27 × 103 Ω/cm) within the existing forms. The thin films β-In2S3 phase grown at 523 and 573 K meet its stoichiometric ratio. In comparison, the In2O3 phase emerges under high oxygen and sulphur deficit conditions. The films are suitable for photo-conduction devices and in the buffer/window layer of PV solar cell design.

Predominance of comammox bacteria among ammonia oxidizers under low dissolved oxygen condition

Although low-oxygen nitrification can significantly cut down the aeration demand in wastewater treatment plants, little is known about the community dynamics of relevant microorganisms under different oxygen concentrations. Here, by conducting a series of bioreactors with oxygen concentrations of 0%, 2%, 5%, 10%, 20%, 40%, and 70%, we provided a comprehensive investigation on the behaviors and performances of comammox bacteria (CMX), ammonia-oxidizing bacteria (AOB) and archaea (AOA) during the nitrification process. Quantitative PCR analysis demonstrated that CMX was the dominant ammonia-oxidizer under low oxygen condition (10%) after the four-month operation with the abundance increased by 8.65 times higher than the initial operation, whereas the growth of AOA and AOB was inhibited. Moreover, Nitrospira nitrosa dominated the CMX species (relative abundance >96%) in low dissolved oxygen concentrations, while Nitrospira nitrificans (3.39%) seemed to prefer high oxygen conditions. Our study indicates the long-term effects of oxygen concentrations on the niche differentiation of ammonia oxidizers, and highlights the significance of CMX in low-oxygen nitrification for reducing global carbon emission and energy consumption.

Nannochloropsis oceanica (Eustigmatophyceae) mutants resistant to rose bengal demonstrate high tolerance to oxygen

ABSTRACT The genus Nannochloropsis (Eustigmatophyceae), including N. oceanica, has attracted considerable interest, due to its ability to accumulate high levels of lipids. Under large-scale cultivation outdoors, cells are exposed to a combination of high oxygen and light irradiance conditions that may promote photoinhibition, so selecting strains able to tolerate oxidative stress is desirable. Rose bengal (RB) reacts with oxygen to form singlet oxygen in the presence of light. Therefore, RB can be a very useful tool for testing the sensitivity of algae to oxidative stress and thus identify strains capable of photosynthesis under oxidative stress. In this study, two mutants of N. oceanica, RB2 and RB113, which are resistant to high concentrations of rose bengal, were phenotypically characterized for their sensitivity to high oxygen concentrations. Both strains exhibited levels of catalase and ascorbate peroxidase 1.5- and 3-fold higher, respectively, than the wild type. In addition, the synthesis of carotenoids was lower than in the wild type, indicating lower oxidative stress. These results were confirmed by chlorophyll fluorescence measurements, which indicated a lower sensitivity of the photosynthetic apparatus of the mutants, especially of RB2, even in the presence of H2O2. The results support the hypothesis that resistance to rose bengal may also induce resistance to high dissolved oxygen stress. The ability shown by the mutants to perform photosynthesis more efficiently under high oxygen stress than the wild type makes them promising candidates for outdoor cultures.

CO2-elevated cell-free protein synthesis

Gases are the vital nutrition of all organisms as the precursor of metabolism pathways. As a potential biological process, protein synthesis is inevitably regulated by gas transport and utilization. However, the effect of carbon dioxide (CO2) present in many metabolic pathways on protein synthesis has not been studied well. In this work, carbon dioxide combined with oxygen was employed for cell-free protein synthesis (CFPS) in the tube-in-tube reactor with precise control of gas concentration. In this in vitro system, gases could directly affect the protein synthesis process without transmembrane transport. Varied concentrations of carbon dioxide (0–1%) and constant oxygen concentration (21%) were employed for CFPS to assess the effects. The cell-free reactions with 0.3% CO2 and 21% O2 showed the highest protein yields. The combined effect of CO2 and O2 also resulted in relatively high protein expression under high oxygen conditions (0.3% CO2 and 100% O2). Moreover, metabolomics assays were performed to gain insight into metabolic changes, which showed that CO2 slightly improved energy metabolism and redox balance. In particular, the extra supplied CO2 activated the decarboxylating reactions and removed toxic metabolites to recover the protein synthesis activity. The exploration of CO2 on protein synthesis could provide guiding implications for basic studies and biomanufacturing.

Experimental and modeling investigation on char combustion and char-nitrogen evolution characteristics under different conditions

The proper description of char combustion and char-nitrogen (char-N) evolution characteristics are imperative to analyze the operating performance of decoupling combustion systems. The char-O2 combustion and char-CO2 gasification reactivity of three typical coal chars, including lignite, bituminous, and anthracite, was tested in a lab-scale fixed-bed reactor in the temperature range of 1023 K–1223 K. The relevant chemical kinetic parameters were determined by applying a one-dimensional packed-bed reactor model embedded with a lumped particle model. Meanwhile, a 1-dimensional spherical particle model is necessary for describing the char-N conversion behaviors. Experimental results show that the conversion rate of char-N in the entire bed to NO (XNO, bed) gradually decreases with increasing temperature, and the decrease of coal rank leads to a decline in the NOx emission. Further simulation results indicate that for a single char particle in the initial combustion stage, if the char particle size increases (0–1000 μm), the external gas mass transfer coefficient decreases (0–5 m·s−1), or the oxygen content decreases (0–20%), the char-N conversion to NO (XNO, p) will gradually decrease. However, due to the complicated effects of temperature on multiple factors, involving reactivity, CO/CO2 ratio in products, and dual nature of CO influence on char-NO reaction, the relationship between char-N conversion and temperature for a single particle is not fixed. When the oxygen concentration is low, the XNO, p increases as temperature rising; while, an opposite trend may be formed under high oxygen conditions.

ATP release from erythrocytes: A role of adenosine1.

The oxygen required to meet metabolic needs of all tissues is delivered by the red blood cell (RBC), a small, flexible cell which, in mammals, is devoid of a nucleus and mitochondria. Despite its simple appearance, this cell has an important role in its own distribution, enabling the delivery of oxygen to precisely meet localized metabolic need. When red blood cells enter in hypoxic area, a signalling pathway is activated within the cell, resulting in the release of ATP in amounts adequate to activate purinergic receptors on vascular endothelium, which trigger secretion of nitric oxide and other factors resulting in vasodilatation. The present study investigates the effect of adenosine exposure on this molecular mechanism. We report that RBC in the presence of adenosine in low oxygen conditions, ATP release increase after 24 h exposure. Adenosine induced-ATP release in deoxygenated red blood cell show data similar to that of RBC in high oxygen conditions: (1) RBC after band 3 modification by 4,4'- diisothio-cyanatostilbene- 2,2'-disulphonic acid; (2) CO-treated RBC. In the presence of Sphingosine kinase (SphK1) inhibitor, adenosine mediated effects on ATP release were abolished. Activity of adenylate cyclase increase following to adenosine exposure, on the contrary red cell phosphofructokinase is not modified within the RBC in the presence of adenosine. Our data support involvement of band 3/deoxyHb binding and adenylate cyclase in the pathway responsible for ATP release from RBC following exposure to adenosine.

Dynamic Oxygen Conditions Promote the Translocation of HIF-1α to the Nucleus in Mouse Blastocysts.

Oxygen tension is one of the most critical factors for mammalian embryo development and its survival. The HIF protein is an essential transcription factor that activated under hypoxic conditions. In this study, we evaluated the effect of dynamic oxygen conditions on the expression of embryonic genes and translocation of hypoxia-inducible factor-1α (HIF-1α) in cultured mouse blastocysts. Two-pronuclear (2PN) zygotes harvested from ICR mice were subjected to either high oxygen (HO; 20%), low oxygen (LO; 5%), or dynamic oxygen (DO; 5% to 2%) conditions. In the DO group, PN zygotes were cultured in 5% O2 from days 1 to 3 and then in 2% O2 till day 5 after hCG injection. On day 5, the percentage of blastocysts in the cultured embryos from each group was estimated, and the embryos were also subjected to immunocytochemical and gene expression analysis. We found that the percentage of blastocysts was similar among the experimental groups; however, the percentage of hatching blastocysts in the DO and LO groups was significantly higher than that in the HO group. The total cell number of blastocysts in the DO group was significantly higher than that of both the HO and LO groups. Further, gene expression analysis revealed that the expression of genes related to the embryonic development was significantly higher in the DO group than that in the HO and LO groups. Interestingly, HIF-1α mRNA expression did not significantly differ; however, HIF-1α protein translocation from the cytoplasm to the nucleus was significantly higher in the DO group than in the HO and LO groups. Our study suggests that dynamic oxygen concentrations increase the developmental capacity in mouse preimplantation embryos through activation of the potent transcription factor HIF-1α.

Highly aerated cultures boost gluconic acid production by the yeast-like fungus Aureobasidium pullulans

The ability of Aureobasidium pullulans NCYC 4012 to produce gluconic acid (GA) was firstly studied in flask batch cultures and it was found that GA productivity was not affected by initial glucose concentration, but highest substrate uptake rate was observed at glucose concentration of 80 g L−1. The effect of oxygen mass transfer, varied by changing agitation and aeration rates or total air pressure, was evaluated in batch cultures of A. pullulans in stirred tank bioreactors. Higher productivities were attained in conditions of high oxygen mass transfer and it was proven that the use of increased total pressure of 4 bar is an effective means of oxygen supply to A. pullulans cultures. At increased pressure, cells induced the antioxidant intracellular enzyme superoxide dismutase to cope with oxidative stress due to high oxygenation conditions. On the other hand, extracellular glucose oxidase activity was reduced by highly oxygenated conditions, suggesting opposite effects of oxygen on this enzyme secretion and GA production.

Exploration and characterization of hypoxia-inducible endogenous promoters in Aspergillus niger.

Aspergillus niger is widely used for the efficient production of organic acids and enzyme preparations. However, this organism lacks basic genetic elements for dynamic control, especially inducible promoters that can respond to specific environmental signals. Since these are desirable for better adaptation of fermentation to large-scale industrial production, herein, we have identified the two first hypoxia-inducible promoters in A. niger, PsrbB and PfhbA. Their performance under high or low oxygen conditions was monitored using two reporter proteins, green fluorescent protein (EGFP) and β-glucuronidase (GUS). For comparison, basal expression of the general strong promoter PgpdA was lower than PsrbB but higher than PfhbA. However, under hypoxia, both promoters showed higher expression than under hyperoxia, and these values were also higher than those observed for PgpdA. For PsrbB, strength under hypoxia was ~2-3 times higher than under hyperoxia (for PfhbA, 3-9 times higher) and ~2.5-5 times higher than for PgpdA (for PfhbA, 2-3 times higher). Promoter truncation analysis showed that the PsrbB fragment -1024 to -588 bp is the core region that determines hypoxia response. KEY POINTS: The first identification of two hypoxia-inducible promoters in A. niger is a promising tool for modulation of target genes under hypoxia. Two reporter genes revealed a different activity and responsiveness to hypoxia of PfhbA and PsrbB promoters, which is relevant for the development of dynamic metabolic regulation of A. niger fermentation. PsrbB promoter truncation and bioinformatics analysis is the foundation for further research.

Hypoxia profoundly alters Natural Killer cell phenotype and function: implications for immunotherapy within the solid tumor microenvironment

Abstract For Natural Killer (NK) cell-based immunotherapy to succeed against solid tumors, NK cells need to enter a highly immunosuppressive tumor microenvironment (TME) and retain functionality. The objective of this study is to evaluate how hypoxia exerts an immunosuppressive effect on NK cells. We used the novel AVATAR™ system to model oxygen levels of three key tissues that NK cells inhabit in vivo: the peripheral blood (12% O2), the bone marrow (5% O2) and the TME (1% O2). NK cells incubated at 1% O2 have decreased proliferation and cytotoxicity compared to NK cells incubated at higher oxygen conditions. To assess what contributes to these changes, we conducted a mass cytometry (CyTOF) analysis, real time imaging assays, metabolic assays and gene expression (RNA-seq and ATAC-seq) analysis. We observed oxygen dependent changes in expression of activating receptors, Ki-67, perforin and granzyme. Hypoxia impacts aggregation of perforin and granzyme granules at the immune synapse. Under hypoxic conditions, NK cell metabolism resembles cancer cell metabolism with increased glycolysis, amino acid synthesis and central carbon metabolism. These changes are accompanied by mitochondrial defects. Gene expression analysis revealed that changes in NK cell metabolism and function are mediated at the epigenetic level by histone demethylases. Treatment with histone demethylase inhibitors rescued NK cell cytotoxicity as measured using an IncuCyte machine. These results indicate that NK cells who enter the TME are fundamentally different than those in the bone marrow or blood stream. The insights gained from this study will be leveraged to overcome hypoxia induced immune suppression in the TME to enhance NK cell-based immunotherapy for solid tumors.

Manipulation of the Regulatory Genes ppsR and prrA in Rhodobacter sphaeroides Enhances Lycopene Production.

Rhodobacter sphaeroides is a non-sulfur purple bacterium with great metabolic versatility, capable of producing a variety of valuable compounds that include carotenoids and CoQ10. In order to enhance lycopene production, we deleted the photosynthetic gene cluster repressor ppsR from a lycopene-producing Rb. sphaeroides strain (RL1) constructed in a previous study to break the control of carotenoid synthesis by the oxygen level. Also, lycopene production was further increased by overexpression of the activator prrA. The superior lycopene producer DppsR/OprrA thus obtained had a high growth rate and a lycopene production of 150.15 mg/L with a yield of 21.45 mg/g dry cell weight (DCW) under high oxygen conditions; these values were ≥6.85-fold higher than those of RL1 (19.13 mg/L; 3.32 mg/g DCW). Our findings indicate that elimination of oxygen repression led to more efficient lycopene production by DppsR/OprrA and that its increased productivity under high oxygen conditions makes it a potentially useful strain for industrial-scale lycopene production.

Hydroperiod and Salinity Interactions Control Mangrove Root Dynamics in a Karstic Oceanic Island in the Caribbean Sea (San Andres, Colombia)

Mangroves sustain high soil accretion and carbon sequestration rates, yet it is still unknown if they can keep pace with increasing sea level rise (SLR) across a wider range of coastal geomorphic settings. Because accretion rates are controlled by mineral sediment inputs and organic matter accumulation, it is paramount to assess the relative contribution of root productivity to soil formation. Here, we evaluated root biomass, production, and turnover in three mangrove ecotypes to evaluate the role of soil nutrient limitation, stressors, and hydroperiod in controlling root dynamics in San Andres Island (SAI), a karstic oceanic island in the Caribbean Sea. Root production was modulated by soil stress conditions and not by nutrient availability as it has been reported for other karstic environments. The lowest root biomass allocation, and both production and turnover of fine roots were measured under low flooding duration, and low salinity (<20 PSU) and sulfide concentrations (0.84 ± 0.4 mM). Yet, when soil stress conditions increased during high flooding duration (6207 h y–1) and low oxygen conditions (Eh), root tissues reached the highest biomass and production values, including a relative fast turnover of fine roots (<2 mm; 0.75 y–1). Our results follow the predictions of the plant root longevity cost-benefit hypothesis where plants maintain roots only until the efficiency of resource acquisition is maximized by water and nutrient acquisition. Because of the importance of groundwater in controlling porewater salinity and mangrove root productivity in karstic oceanic islands such as SAI, water use and coastal development should be regulated in the short term to avoid the loss of mangrove area and concomitant ecosystem services.

Investigation on ignition behaviors of pulverized coal particles in a tubular swirl burner

This paper intensively investigated the ignition of turbulent coal flames in a novel fully-mixed tubular swirl burner. The Nikon D300s digital camera was used to capture the statistical ignition behavior of dispersed coal particle streams in different ambiences. Meanwhile, the combustion dynamics of individual coal particles were also recorded by means of high-speed photography. Two low-rank coal samples, Hulunbel lignite and Zhundong coal, were tested in this study. The ignition delay times of coal particles in the swirl burner were compared with those in a flat-flame burner. In contrast to previous work on a laminar flat-flame burner, the current experimental results show that the turbulent ambience significantly enhances the ignition of all coal samples, which is exceptionally pronounced under high temperature and low oxygen conditions. In addition, the sensitivity analysis suggests that both the enhanced heat and mass transfer contribute to the early ignition in turbulence. The effect of elevated mass transfer coefficient turns prominent in low oxygen fraction ambience, wherein the volatile barrier effect is suppressed by the enhanced mixing process. The combined effect of turbulence favors the shifting of ignition modes to the heterogeneous-dominant region. Last but not least, the ceased volatile flame that visualized in turbulent low oxygen ambience further confirms the important role of heterogeneous ignition.

Wildfire during deposition of the \u201cIllinger Fl\xf6zzone\u201d (Heusweiler-Formation, \u201cStephanian B\u201d, Kasimovian\u2013Ghzelian) in the Saar-Nahe Basin (SW-Germany)

Wildfires occurred more or less regularly in many Pennsylvanian ecosystems, not only in seasonally dry regions but also in the ever wet tropics. One of the reasons for this was probably the relatively high atmospheric oxygen conditions prevailing during this period. The present study reports evidence for the occurrence of wildfires during deposition of the Upper Pennsylvanian Heusweiler Formation (“Stephanian B”, Kasimovian–Gzhelian) in the intramontane Saar-Nahe (or Saar-Lorraine) Basin in SW-Germany. Based on anatomical features of the charcoal, as well as the co-occurring adpression flora, it seems possible that some of the fires occurred in an ecosystem inhabited by Cordaites. Some of the charcoal fragments exhibit traces of pre-charring decay by fungi, indicating either the consumption of litter by ground or surface fires, or of still standing (partly) dead trees by crown fires.

How fructophilic lactic acid bacteria may reduce the FODMAPs content in wheat-derived baked goods: a proof of concept

BackgroundFODMAPs (Fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) intake is associated with the onset of irritable bowel syndrome symptoms. FODMAPs in wheat-derived baked goods may be reduced via bioprocessing by endogenous enzymes and/or microbial fermentation. Because of the inherent enzyme activities, bread made by baker’s yeast and sourdough may result in decreased levels of FODMAPs, whose values are, however, not enough low for people sensitive to FODMAPs.ResultsOur study investigated the complementary capability of targeted commercial enzymes and metabolically strictly fructophilic lactic acid bacteria (FLAB) to hydrolyze fructans and deplete fructose during wheat dough fermentation. FLAB strains displayed higher fructose consumption rate compared to conventional sourdough lactic acid bacteria. Fructose metabolism by FLAB was faster than glucose. The catabolism of mannitol with the goal of its reuse by FLAB was also investigated. Under sourdough conditions, higher fructans breakdown occurred in FLAB inoculated doughs compared to conventional sourdough bacteria. Preliminary trials allowed selecting Apilactobacillus kunkeei B23I and Fructobacillus fructosus MBIII5 as starter candidates, which were successfully applied in synergy with commercial invertase for low FODMAPs baking.ConclusionsResults of this study clearly demonstrated the potential of selected strictly FLAB to strongly reduce FODMAPs in wheat dough, especially under liquid-dough and high oxygenation conditions.

Energetics of Acidianus ambivalens growth in response to oxygen availability.

All life requires energy to drive metabolic reactions such as growth and cell maintenance; therefore, fluctuations in energy availability can alter microbial activity. There is a gap in our knowledge concerning how energy availability affects the growth of extreme chemolithoautotrophs. Toward this end, we investigated the growth of thermoacidophile Acidianus ambivalens during sulfur oxidation under aerobic to microaerophilic conditions. Calorimetry was used to measure enthalpy (ΔHinc ) of microbial activity, and chemical changes in growth media were measured to calculate Gibbs energy change (ΔGinc ) during incubation. In all experiments, Gibbs energy was primarily dissipated through the release of heat, which suggests enthalpy-driven growth. In microaerophilic conditions, growth was significantly more efficient in terms of biomass yield (defined as C-mol biomass per mole sulfur consumed) and resulted in lower ΔGinc and ΔHinc . ΔGinc in oxygen-limited (OL) and oxygen- and CO2 -limited (OCL) microaerophilic growth conditions resulted in averages of -1.44×103 kJ/C-mol and -7.56×102 kJ/C-mol, respectively, and average ΔHinc values of -1.11×105 kJ/C-mol and -4.43×104 kJ/C-mol, respectively. High-oxygen experiments resulted in lower biomass yield values, an increase in ΔGinc to -1.71×104 kJ/C-mol, and more exothermic ΔHinc values of -4.71×105 kJ/C-mol. The observed inefficiency in high-oxygen conditions may suggest larger maintenance energy demands due to oxidative stresses and a preference for growth in microaerophilic environments.

A 23000 year old record of paleoclimatic and environmental changes from the eastern Arabian Sea

Abstract Climate of the eastern Arabian Sea is highly influenced by both global climate and Indian monsoon. We produced multi-proxy records of benthic foraminiferal biofacies and stable isotope ratio (δ13C and δ18O), planktic foraminifera and total organic carbon (wt%) content of sediments from core SK291/GC11 in the upper continental shelf off Mangalore, off eastern Arabian Sea (EAS) to decipher paleoenvironmental and paleoclimatic changes during the past ~23,000 years. The monsoon was weak during the Last Glacial Maximum ~23,000–18,000 calibrated years before Present (cal yr BP) when sea level was lower. Globigerinoides ruber populations fluctuate from 30 to 60% in the studied interval with a maximum during ~6000–5000 cal yr BP and a minimum during 19,000–17,000 cal yr BP. The δ18O values of benthic foraminifer Ammonia gaimardii suggest pronounced cooling phases during ~23,000–18,000 cal yr BP, and a short-term cooling at ~6000 cal yr BP. Several intervals of high organic productivity and low oxygen conditions were identified based on benthic foraminiferal biofacies during 23,247–682 cal yr BP. Wind-induced surface mixing was intense during 3200–530 cal yr BP as evidenced by high Globigerina bulloides abundances. The core was affected by moderate chemical weathering and solar variability appears to have been an important forcing factor in shaping climate of the region.

Hypoxia/reoxygenation exacerbates drug-induced cytotoxicity by opening mitochondrial permeability transition pore: Possible application for toxicity screening

Recently, mitochondrial dysfunction is thought of as an important factor leading to a drug-induced liver injury. Our previous reports show that mitochondria-related toxicity, including respiratory chain inhibition (RCI) and reactive oxygen species (ROS) induction, can be detected by the modification of sugar resource substitution and high oxygen condition. However, this in vitro model does not detect mitochondrial permeability transition (MPT)-induced toxicity. Another study with a lipopolysaccharide-pre-administered rodent model showed that ischemia/reperfusion induced ROS, sensitized the susceptibility of MPT pore opening and, finally developed drug-induced liver toxicity. Based on this result, the present study investigated the effect of hypoxia/reoxygenation (H/R) treatment mimicking the ischemia/reperfusion on MPT-dependent toxicity, aiming to construct a system that can evaluate MPT by drugs in hepatocytes. Mitochondrial ROS were enhanced by H/R treatment only in the galactose culture condition. Amiodarone, benzbromarone, flutamide and troglitazone which induced MPT pore opening led to hepatocyte death only in combination with H/R and galactose. Moreover, this alteration was significantly suppressed in hepatocytes lacking cyclophilin D. In conclusion, MPT-induced cytotoxicity can be detected by activating mitochondrial function and H/R. This cell-based assay system could evaluate MPT induced-cytotoxicity by drugs, besides RCI and ROS induction.

Effects of Ambient Parameters and Sample Width on Upward Flame Spread over Thermally Thin Solids

Upward flame spread is the most rapid and hazardous of the different modes of flame spread. Moreover, studies on the effects of ambient parameters on flame spread are very important for fire safety on spacecraft systems. Therefore, the effects of pressure (0 kPa to 70 kPa), oxygen mole fraction (0.30 to 0.90) and sample width (0.3 cm to 2 cm) on upward flame spread over thin papers were studied. A flame break-off phenomenon over papers was firstly observed, which occurred more likely at high oxygen and high pressure conditions. Upward flame spread reached a steady state by varying the ambient parameters and using narrow samples. The smaller sample width narrowed the flammability limits. Differences in upward and downward flame spread were discussed. We found that a power law relationship between flame spread rate and pressure remained valid near the extinction limit for upward spread, while the power law broke down in the extinction region for downward spread. The controlling mechanism of upward spread was revealed by a pressure modeling method showing that the upward flame spread rate was proportional to the Grashof number raised to an exponent of 0.257. For upward flame spread over narrow solids, the gas phase kinetics and radiation effects are less important compared to the heat convection in the flame spread process, which is quite different from the downward spread. This study contributes to the fire safety of space vehicles and enhances the understanding of the controlling mechanism of flame spread.