Conditions Of Low Oxygen Availability Research Articles

Multiple-day high-dose beetroot juice supplementation does not improve pulmonary or muscle deoxygenation kinetics of well-trained cyclists in normoxia and hypoxia

Dietary nitrate (NO3−) supplementation via beetroot juice (BR) has been reported to lower oxygen cost (i.e., increased exercise efficiency) and speed up oxygen uptake (VO2) kinetics in untrained and moderately trained individuals, particularly during conditions of low oxygen availability (i.e., hypoxia). However, the effects of multiple-day, high dose (12.4 mmol NO3− per day) BR supplementation on exercise efficiency and VO2 kinetics during normoxia and hypoxia in well-trained individuals are not resolved. In a double-blinded, randomized crossover study, 12 well-trained cyclists (66.4 ± 5.3 ml min−1∙kg−1) completed three transitions from rest to moderate-intensity (~70% of gas exchange threshold) cycling in hypoxia and normoxia with supplementation of BR or nitrate-depleted BR as placebo. Continuous measures of VO2 and muscle (vastus lateralis) deoxygenation (ΔHHb, using near-infrared spectroscopy) were acquired during all transitions. Kinetics of VO2 and deoxygenation (ΔHHb) were modeled using mono-exponential functions. Our results showed that BR supplementation did not alter the primary time constant for VO2 or ΔHHb during the transition from rest to moderate-intensity cycling. While BR supplementation lowered the amplitude of the VO2 response (2.1%, p = 0.038), BR did not alter steady state VO2 derived from the fit (p = 0.258), raw VO2 data (p = 0.231), moderate intensity exercise efficiency (p = 0.333) nor steady state ΔHHb (p = 0.224). Altogether, these results demonstrate that multiple-day, high-dose BR supplementation does not alter exercise efficiency or oxygen uptake kinetics during normoxia and hypoxia in well-trained athletes.

Reconfiguration of N Metabolism upon Hypoxia Stress and Recovery: Roles of Alanine Aminotransferase (AlaAT) and Glutamate Dehydrogenase (GDH).

In the context of climatic change, more heavy precipitation and more frequent flooding and waterlogging events threaten the productivity of arable farmland. Furthermore, crops were not selected to cope with flooding- and waterlogging-induced oxygen limitation. In general, low oxygen stress, unlike other abiotic stresses (e.g., cold, high temperature, drought and saline stress), received little interest from the scientific community and less financial support from stakeholders. Accordingly, breeding programs should be developed and agronomical practices should be adapted in order to save plants’ growth and yield—even under conditions of low oxygen availability (e.g., submergence and waterlogging). The prerequisite to the success of such breeding programs and changes in agronomical practices is a good knowledge of how plants adapt to low oxygen stress at the cellular and the whole plant level. In the present paper, we summarized the recent knowledge on metabolic adjustment in general under low oxygen stress and highlighted thereafter the major changes pertaining to the reconfiguration of amino acids syntheses. We propose a model showing (i) how pyruvate derived from active glycolysis upon hypoxia is competitively used by the alanine aminotransferase/glutamate synthase cycle, leading to alanine accumulation and NAD+ regeneration. Carbon is then saved in a nitrogen store instead of being lost through ethanol fermentative pathway. (ii) During the post-hypoxia recovery period, the alanine aminotransferase/glutamate dehydrogenase cycle mobilizes this carbon from alanine store. Pyruvate produced by the reverse reaction of alanine aminotransferase is funneled to the TCA cycle, while deaminating glutamate dehydrogenase regenerates, reducing equivalent (NADH) and 2-oxoglutarate to maintain the cycle function.

A genetic screen reveals a periplasmic copper chaperone required for nitrite reductase activity in pathogenic Neisseria.

Under conditions of low oxygen availability, Neisseria meningitidis and Neisseria gonorrhoeae are able to respire via a partial denitrification pathway in which nitrite is converted to nitrous oxide. In this process, nitrite reductase (AniA), a copper (Cu)-containing protein converts nitrite to NO, and this product is converted to nitrous oxide by nitric oxide reductase (NorB). NorB also confers protection against toxic NO, and so we devised a conditional lethal screen, using a norB mutant, to identify mutants that were resistant to nitrite-dependent killing. After random-deletion mutagenesis of N. meningitidis, this genetic screen identified a gene encoding a Cu chaperone that is essential for AniA function, AccA. Purified AccA binds one Cu (I) ion and also possesses a second binding site for Cu (II). This novel periplasmic Cu chaperone (AccA) appears to be essential for provision of Cu ions to AniA of pathogenic Neisseria to generate an active nitrite reductase. Apart from the Neisseria genus, AccA is distributed across a wide range of environmental Proteobacteria species.

XPS Analysis of Ti6Al4V Oxidation Under UHV Conditions

Oxidation of Ti6Al4V is studied by X-ray photoelectron spectroscopy (XPS). Oxide layer growth was monitored on the Ti6Al4V surface for 24 hours. The surface was previously etched with Ar+ ions under ultra-high vacuum conditions. XPS spectra show that TiO and Ti2O3, together with Al2O3, were the earliest oxides formed. Vanadium, despite being detected in its elementary form in the bulk, was not found in any of its oxidized states. TiO2, directly related to the good performance of Ti6Al4V for biomedical applications, did not contribute significantly to the passive layer at the beginning; nevertheless, it was identified after the oxidation process progressed to a more advanced stage. This behavior indicates that reoxidation of Ti6Al4V permits auto-healing of its passive layer, with the presence of TiO2, even in conditions of low oxygen availability.

A Scanning Kelvin Probe Investigation of the Interaction of PEDOT:PSS Films with Metal Surfaces

The study of conducting polymers (CPs) is of significant current interest due to their incorporation in a range of applications, including optical and electronic devices. Poly(3,4-Ethylenedioxythiophene)-Poly(Styrene Sulphonate) (PEDOT:PSS) is considered one of the most electrochemically and thermally stable CPs available at present 1. In many applications there is a requirement for electrical contact to be made between an organic PEDOT:PSS layer and a metallic substrate and therefore it highly important to understand the interaction between the CP and various metals, in order to gauge the long term stability of the metal-ICP interface. In this work an in-situ scanning Kelvin probe (SKP) technique is employed to measure the Volta potential differences of various PEDOT:PSS coated metal surfaces to identify instances where a reaction may be taking place at the buried interface. Previous studies have demonstrated the capability of SKP in elucidating the nature of the interaction of polyaniline and polypyrrole coatings with various metal surfaces 2- 4.Experiments have been carried out on a range of metals spanning a significant part of the electrochemical series. A threshold thickness of PEDOT:PSS of 3 μm was determined for more reactive metals (i.e. Ni, Zn, Al and Mg), at or above which a consistent Kelvin probe potential (EKP) value of ca. -0.15 V vs. SHE was measured. A potential of -0.4 V vs. SCE (ca. -0.156 V vs. SHE) has been reported previously by Ghilane et al, at which a PEDOT:PSS polymer film converts from the oxidized form to the reduced form 5. The constant value of -0.15V vs SHE measured for coated Ni, Zn, Al and Mg surfaces strongly suggests that these metals are polarized to this potential by a PEDOT:PSS(ox)/PEDOT:PSS(red) redox couple, where (ox) and (red) refer to the oxidized and reduced form of the CP respectively. This in turn implies that each of these metals enters into a galvanic interaction with the PEDOT:PSS, causing oxidation at the metal-coating interface and the reduction of a fraction of the CP.For a selection of more noble metals, (i.e. Pt, Ag and Cu) no consistent EKP values are observed (see Figure 1) and this is attributed to the fact that no redox reaction with PEDOT:PSS occurs. In such a case the PEDOT:PSS coating remains fully oxidised, resulting in potentials that are consistently higher than Eo(PEDOT:PSS(ox)) /(PEDOT:PSS(red)). The current investigation also demonstrates that cyclic re-oxidation of a PEDOT:PSS coating applied to a Al surface by atmospheric oxygen can occur. Previous studies have reported that sustained substrate ennoblement with other conducting polymers, such as Polyaniline emeraldine salt 2 occurs on ferrous metals by this mechanism. Upon removal of oxygen, EKP values measured for PEDOT:PSS coated Al decrease to ca. -0.38 V vs. SHE, a value similar to that that measured for uncoated Al. Upon the reintroduction of air, EKP values return to the values recorded initially. Therefore it seems that the presence of oxygen is important in maintaining the PEDOT:PSS redox state. Under conditions of low oxygen availability, complete reduction of PEDOT:PSS by the underlying Al is possible. This is confirmed by colorimetric observations of the thin PEDOT:PSS layer adherent to the Al surface.

DNMT3a epigenetic program regulates the HIF-2α oxygen-sensing pathway and the cellular response to hypoxia.

Epigenetic regulation of gene expression by DNA methylation plays a central role in the maintenance of cellular homeostasis. Here we present evidence implicating the DNA methylation program in the regulation of hypoxia-inducible factor (HIF) oxygen-sensing machinery and hypoxic cell metabolism. We show that DNA methyltransferase 3a (DNMT3a) methylates and silences the HIF-2α gene (EPAS1) in differentiated cells. Epigenetic silencing of EPAS1 prevents activation of the HIF-2α gene program associated with hypoxic cell growth, thereby limiting the proliferative capacity of adult cells under low oxygen tension. Naturally occurring defects in DNMT3a, observed in primary tumors and malignant cells, cause the unscheduled activation of EPAS1 in early dysplastic foci. This enables incipient cancer cells to exploit the HIF-2α pathway in the hypoxic tumor microenvironment necessary for the formation of cellular masses larger than the oxygen diffusion limit. Reintroduction of DNMT3a in DNMT3a-defective cells restores EPAS1 epigenetic silencing, prevents hypoxic cell growth, and suppresses tumorigenesis. These data support a tumor-suppressive role for DNMT3a as an epigenetic regulator of the HIF-2α oxygen-sensing pathway and the cellular response to hypoxia.

Dietary nitrate supplementation and exercise performance.

Dietary nitrate is growing in popularity as a sports nutrition supplement. This article reviews the evidence base for the potential of inorganic nitrate to enhance sports and exercise performance. Inorganic nitrate is present in numerous foodstuffs and is abundant in green leafy vegetables and beetroot. Following ingestion, nitrate is converted in the body to nitrite and stored and circulated in the blood. In conditions of low oxygen availability, nitrite can be converted into nitric oxide, which is known to play a number of important roles in vascular and metabolic control. Dietary nitrate supplementation increases plasma nitrite concentration and reduces resting blood pressure. Intriguingly, nitrate supplementation also reduces the oxygen cost of submaximal exercise and can, in some circumstances, enhance exercise tolerance and performance. The mechanisms that may be responsible for these effects are reviewed and practical guidelines for safe and efficacious dietary nitrate supplementation are provided.

Potential of Inga sp. (Inga uruguensis Hook. and Arn.) in the Phytoremediation of Oily Compounds

Plant survival under conditions of low oxygen availability is an important aspect of the phytoremediation of oily compounds, as one of the problems associated with environmental contamination by such compounds is anaerobic stress. Since Inga spp. presents adaptation mechanisms to conditions of partial and total submersion, it would be useful in the phytoremediation of petroleum wastes. The aim of this work was to verify the efficiency of a phytoremediation system using1 Inga uruguensis Hook. and Arn. to degrade organic compounds such as semisolid petroleum waste (SSPW) and used cooking oil (UCO). A greenhouse study was conducted with plants grown in pots containing 3.1 kg substrate (soil + organic waste) that contained 10.15% SSPW or 5.56% UCO. Plants were grown for 84 days, and the system was evaluated by measuring changes in the oil and grease content (OGC), plant development, and abundance of microorganisms in substrate. Treatment of the SSPW with Inga sp. yielded a 40.7% reduction in OGC, whereas there was no significant change in the OGC in unplanted systems. Conversely, there was no significant plant effect on the OGC in the UCO-treated systems. Furthermore, we found evidence that the plant effect is associated with microbial community changes. Considering the high dose of SSPW and the high rate of degradation within an experiment of short duration, it was concluded that Inga uruguensis Hook. and Arn. holds potential for the phytoremediation of recalcitrant oily residues in soil.

Evaluation of the Effects of Low Oxygen Concentration on Stable Isotope Fractionation during Aerobic MTBE Biodegradation

Laboratory experiments were performed with two aerobic MTBE degrading strains ( Methylibium sp. PM1 and Aquincola tertiaricarbonaris L108) in order to determine whether conditions of low oxygen availability, typically found in fuel-contaminated aquifers, can influence stable isotope fractionation of MTBE. Although single carbon and hydrogen enrichment factors of the two strains were not significantly or were only slightly (L108) affected by low oxygen concentrations (fully oxic incubation with initial 21% O2 in the headspace tested versus hypoxic conditions always <2% O2), the experiments showed indirect effects caused by competition interactions in mixed cultures. In a mixed culture of PM1 and L108 under oxic and even more so under hypoxic conditions, the total observed carbon isotope enrichment factor was significantly reduced, while hydrogen fractionation was not detectable. This indicates that the low fractionating model strain L108 is more competitive in degrading MTBE compared to strain PM1. Consistently, higher oxygen affinities during MTBE degradation were observed for strain L108. These first studies, conducted with resting cells, may explain the low isotope fractionation observed in some field studies that are not necessarily related to a lack of biodegradation.

Leaching of a low-grade, copper–nickel sulfide ore. 3. Interactions of Cu with selected sulfide minerals

Interactions between copper ions and selected sulfide mineral concentrates were investigated in flask and column tests under conditions relevant to heap leaching in order to understand why copper recovery from a copper–nickel complex sulfide ore was significantly less than nickel recovery. Both pyrrhotite and pyrite were found to play roles in copper deposition from sulfate solutions in the range pH 1–5. The non-oxidative dissolution of pyrrhotite, previously reported to occur under acidic conditions of low oxygen availability, was also found to occur in a well-aerated system. Soluble copper reacted with the generated hydrogen sulfide to form copper sulfide, mainly covellite at pH > 2.3 and its re-dissolution required acid, oxygen and a strong oxidant such as ferric ion. While significant copper also precipitated from copper sulfate solutions pH > 3 in the presence of pyrite, the brochantite which was formed was readily re-dissolved at pH < 3. The poor recovery of copper experienced in a test heap of copper–nickel sulfide ore was attributed to the presence of pyrrhotite and the rise in pH as the leachate percolated through the heap bed. The copper would only be recovered if acidic, oxidising conditions were restored in the heap.

Reactions of ferrous neuroglobin and cytoglobin with nitrite under anaerobic conditions

Recent evidence suggests that the reaction of nitrite with deoxygenated hemoglobin and myoglobin contributes to the generation of nitric oxide and S-nitrosothiols in vivo under conditions of low oxygen availability. We have investigated whether ferrous neuroglobin and cytoglobin, the two hexacoordinate globins from vertebrates expressed in brain and in a variety of tissues, respectively, also react with nitrite under anaerobic conditions. Using absorption spectroscopy, we find that ferrous neuroglobin and nitrite react with a second-order rate constant similar to that of myoglobin, whereas the ferrous heme of cytoglobin does not react with nitrite. Deconvolution of absorbance spectra shows that, in the course of the reaction of neuroglobin with nitrite, ferric Fe(III) heme is generated in excess of nitrosyl Fe(II)–NO heme as due to the low affinity of ferrous neuroglobin for nitric oxide. By using ferrous myoglobin as scavenger for nitric oxide, we find that nitric oxide dissociates from ferrous neuroglobin much faster than previously appreciated, consistently with the decay of the Fe(II)–NO product during the reaction. Both neuroglobin and cytoglobin are S-nitrosated when reacting with nitrite, with neuroglobin showing higher levels of S-nitrosation. The possible biological significance of the reaction between nitrite and neuroglobin in vivo under brain hypoxia is discussed.

Staphylococcus epidermidis Polysaccharide Intercellular Adhesin Production Significantly Increases during Tricarboxylic Acid Cycle Stress

Staphylococcal polysaccharide intercellular adhesin (PIA) is important for the development of a mature biofilm. PIA production is increased during growth in a nutrient-replete or iron-limited medium and under conditions of low oxygen availability. Additionally, stress-inducing stimuli such as heat, ethanol, and high concentrations of salt increase the production of PIA. These same environmental conditions are known to repress tricarboxylic acid (TCA) cycle activity, leading us to hypothesize that altering TCA cycle activity would affect PIA production. Culturing Staphylococcus epidermidis with a low concentration of the TCA cycle inhibitor fluorocitrate dramatically increased PIA production without impairing glucose catabolism, the growth rate, or the growth yields. These data lead us to speculate that one mechanism by which staphylococci perceive external environmental change is through alterations in TCA cycle activity leading to changes in the intracellular levels of biosynthetic intermediates, ATP, or the redox status of the cell. These changes in the metabolic status of the bacteria result in the attenuation or augmentation of PIA production.

Push‐up response of stonefly larvae in low‐oxygen conditions

Under conditions of low oxygen availability, the larvae of the stonefly Oyamia lugubris McLachlan demonstrate a ‘push‐up’ behavior that is thought to enhance respiratory efficiency. We conducted an experiment to investigate the effect of the oxygen supply on this behavior in winter and summer by using a lotic chamber and natural water. From the experiment, we determined the critical oxygen supply level below which the stonefly larvae are compelled to do push‐ups. There was a small difference in the critical oxygen supply level between the seasons. This result emphasizes that a novel measurement of the oxygen availability, that is, the oxygen supply, could be an important determinant of the distribution of aquatic insects.

Effect of hypoxia on buried weed seed germination

SummaryTrials were carried out in order to investigate the effect of hypoxia on seed germination of Datura stramonium L. in Petri dishes and when buried at various depths in soil. Hypoxia was found to cause a decrease in germination capacity and germination rate. This inhibition was partially alleviated by daily exchange of hypoxic gas surrounding the seeds during incubation. Similarly, seed scarification allowed maintenance of a higher germination capacity under conditions of low oxygen availability, showing that the seed coat was only partially gas permeable. Oxygen deficiency led to a decrease in respiratory capacity. However, this was probably compensated for by induction of fermentation metabolism. The possibility of removing the final products of fermentation exerts a decisive influence on seed germination, especially in an environment such as soil, where their diffusion into the surrounding environment is restricted. Thus daily nitrogen flushing partially eliminated this inhibition, even under conditions of low external oxygen availability. It was therefore postulated that the main depth–derived inhibition was not caused directly by oxygen deficiency but by the increasing difficulty in eliminating toxic fermentation products, which was found to be proportional to the degree of hypoxia. Finally, incubation for several days under completely anaerobic conditions induced secondary dormancy. This was probably due to an ecological adaptation mechanism that prevents germination under conditions that are unfavourable for survival.

Thyroid function during intermittent exposure to hypobaric hypoxia

Circulatory levels of triiodothyronine (T3) and thyroxine (T4) and their kinetics were studied in rabbits exposed to intermittent hypobaric hypoxia (5200 m, 395 mm Hg, PO2 83 mm Hg) 6 h daily for 5 weeks in a decompression chamber maintained at room temperature of 22 degrees-24 degrees C. Kinetics of T3 and T4 were studied on days 21 and 28 of hypoxic exposure. The T3 and T4 values were found to be significantly lower on day 8 of exposure to hypoxia compared to the pre-exposure values. The decreased levels were maintained throughout the entire period of hypoxic stress. The metabolic clearance rate, production rate, distribution space and extrathyroidal T3 and T4 pools were significantly decreased in animals under hypoxic stress compared to the control animals. The decline in thyroid hormone levels and their production in rabbits under hypoxic stress indicate an adaptive phenomenon under conditions of low oxygen availability.

Continuous culture studies on the production of staphylocoagulase by Staphylococcus aureus.

The production of staphylocoagulase was studied with continuous cultures of various S. aureus strains in a simple salts medium supplemented with mannitol, casein hydrolysate and three vitamins. Conditions of low oxygen availability and magnesium-limitation were required for optimal steady-state staphylocoagulase production. It was demonstrated that the specific rate of staphylocoagulase production was dependent on the growth rate. In two bovine strains, the production rate pattern was similar to that of an inducible enzyme sensitive to catabolite repression, although no specific inductor suppressor could be demonstrated. The human strain, on the other hand, produced staphylocoagulase constitutively. In all strains the specific rate of production of total extracellular protein was strictly proportional to the growth rate. The bovine strains produced 6 times more staphylocoagulase in chemostat culture as compared with batch cultures of the same organisms. It is likely that mannitol functioned as an energy source rather than as a carbon source because it was converted for a major part to acetate and for a minor part to lactate and not to new cell material. Repression and staphylocoagulase production by mannitol, acetate or lactate was not observed. The probable nature of the regulating mechanism(s) underlying staphylocoagulase production is discussed.