Oxygen, Volume 2, Issue 2 (June 2022) – 13 articles

Red-eared slider turtles face natural changes in oxygen availability throughout the year. This includes long-term anoxic brumation where they reduce their metabolic rate by ~90% for months at a time, which they survive without apparent tissue damage. This metabolic rate depression (MRD) is underlaid by various regulatory mechanisms, including messenger RNA (mRNA) silencing via microRNA (miRNA), leading to mRNA decay or translational inhibition in processing bodies (P-bodies) and stress granules. Regulation of miRNA biogenesis was assessed in red-eared slider turtle liver and skeletal muscle via immunoblotting. Hepatic miRNA biogenesis was downregulated in early processing steps, while later steps were upregulated. These contradictory findings indicate either overall decreased miRNA biogenesis, or increased biogenesis if sufficient pre-miRNA stores were produced in early anoxia. Conversely, muscle showed clear upregulation of multiple biogenesis steps indicating increased miRNA production. Additionally, immunoblotting indicated that P-bodies may be favoured by the liver for mRNA storage/decay during reoxygenation with a strong suppression of stress granule proteins in anoxia and reoxygenation. Muscle however showed downregulation of P-bodies during anoxia and reoxygenation, and upregulation of stress granules for mRNA storage during reoxygenation. This study advances our understanding of how these champion anaerobes regulate miRNA biogenesis to alter miRNA expression and mRNA fate during prolonged anoxia. Full article

Sustainable long-term space missions require regenerative life support from plants. Traditional crop plants lack some features desirable for use in space environments. The aquatic plant family Lemnaceae (duckweeds) has enormous potential as a space crop, featuring (i) fast growth, with very high rates of O₂ production and CO₂ sequestration, (ii) an exceptional nutritional quality (with respect to radiation-fighting antioxidants and high-quality protein), (iii) easy propagation and high productivity in small spaces, and (iv) resilience to the stresses (radiation, microgravity, and elevated CO₂) of the human-inhabited space environment. These traits of Lemnaceae are placed into the context of their unique adaptations to the aquatic environment. Furthermore, an overview is provided of the challenges of galactic cosmic radiation to plant and human physiology and the mechanisms involved in oxidative injury and the prevention/mitigation of such effects by antioxidant micronutrients. A focus is placed on the carotenoid zeaxanthin accumulated by Lemnaceae in unusually high amounts and its role in counteracting system-wide inflammation, cognitive dysfunction, and other oxidative injuries in humans. Full article

Oxidative stress (OS) represents one of the main mechanisms of toxicity induced by environmental pollutants such as cadmium (Cd). OS is a natural physiological process where the presence of oxidants, such as reactive oxygen-derived species (ROS), outweighs the strategy of antioxidant defenses, culminating in the interruption of signaling and redox control. It has been suggested that Cd increases ROS mainly by inducing damage to the electron transport chain and by increasing the activity of nicotinamide adenine dinucleotide hydrogen phosphate (NADPH) oxidase (NOX) and the concentration of free iron (Fe), as well as causing a decrease in antioxidant defense. On the other hand, OS has been related to changes in the biology of the epigenome, causing adverse health effects. Recent studies show that Cd generates alterations in deoxyribonucleic acid (DNA) methylation, histone modifications, and noncoding RNA (ncRNA) expression. However, the role of OS in Cd-induced epigenetic modifications is still poorly explored. Therefore, this review provides an update on the basic concepts of OS and its relationship with Cd-induced epigenetic changes. Furthermore, the use of antioxidant compounds is proposed to mitigate Cd-induced epigenetic alterations. Full article

Before fertilization, spermatozoa must undergo a process called capacitation in order to fulfill their fertilization potential. This includes a series of structural, biochemical, and functional changes before a subsequent acrosome reaction and fusion with the oocyte. However, low temperatures during cryopreservation may induce a premature activation of capacitation-like changes, also known as cryocapacitation, immediately after thawing, which may lead to a decreased viability, motility, and fertilization ability of cryopreserved spermatozoa. Furthermore, cryopreservation is responsible for the overgeneration of reactive oxygen species (ROS) such as superoxide, hydrogen peroxide, and hydroxyl radicals, which may result in the development of oxidative stress, cell membrane damage, and lipid peroxidation. Despite that, both capacitation and cryocapacitation are considered to be oxidative events; however, potential beneficial or detrimental effects of ROS depend on a wide array of circumstances. This review summarizes the available information on the role of free radicals in the process of capacitation and cryocapacitation of spermatozoa. Full article

Oxygen is a unique molecule that possesses a spin quantum number $S=1$. In the condensed phases of oxygen, the delicate balance between the antiferromagnetic interaction and van der Waals force results in the various phases with different crystal structures. By applying ultrahigh magnetic fields, the antiferromagnetic coupling between O${}_2$ molecules breaks, and novel high-field phases can appear. We have investigated the physical properties of condensed oxygen under ultrahigh magnetic fields and have found that the stable crystal structure of solid oxygen changes around 100 T. Even in liquid oxygen, we observed a strong acoustic attenuation, which indicates the fluctuation of local molecular arrangements. These results demonstrate that magnetic fields can modulate the packing structure of oxygen through spin-lattice coupling. Our study implies the possibility of controlling oxygen-related (bio-)chemical processes by using an external magnetic field. Full article

Carbon monoxide (CO) is one of the most common causes of inhalation poisoning worldwide. However, it is also well known that CO is produced endogenously in the heme degradation reaction catalyzed by heme oxygenase (HO) enzymes. HO catalyzes the degradation of heme to equimolar quantities of CO, iron ions (Fe²⁺), and biliverdin. Three oxygen molecules (O₂) and the electrons provided by NADPH-dependent cytochrome P450 reductase are used in the reaction. HO enzymes comprise three distinct isozymes: the inducible form, heme oxygenase-1 (HO-1); the constitutively expressed isozyme, heme oxygenase-2 (HO-2); and heme oxygenase-3 (HO-3), which is ubiquitously expressed but possesses low catalytic activity. According to some authors, HO-3 is rather a pseudogene originating from the HO-2 transcript, and it has only been identified in rats. Therefore, cellular HO activity is provided by two major isoforms—the inducible HO-1 and the constitutively expressed HO-2. For many years, endogenously generated CO was treated as a by-product of metabolism without any serious physiological or biochemical significance, while exogenous CO was considered only as an extremely toxic gas with lethal effects. Research in recent years has proven that endogenous and exogenous CO (which may be surprising, given public perceptions) acts not only as an agent that affects many intracellular pathways, but also as a therapeutic molecule. Hence, the modulation of the HO/CO system may be one option for a potential therapeutic strategy. Another option is the administration of CO by exogenous inhalation. As alternatives to gas administration, compounds known as CO-releasing molecules (CORMs) can be administered, since they can safely release CO in the body. The aim of this article is to provide a brief overview of the physiological and biochemical properties of CO and its therapeutic potential. Full article

The last 20–30 years, the oxygen exposure of newborn infants has been substantially reduced. This is mainly due to a dramatic reduction in the use of oxygen in the delivery room in newborn infants in need of positive pressure ventilation (PPV) and the better control of oxygen saturation with clearly defined targets in immature infants in need of supplemental oxygen during treatment in neonatal intensive care units. Term and near-term infants in need of IPPV in the delivery room should start with a FiO₂ of 0.21. Between 28 and 31 weeks of gestation, an initial FiO₂ of 0.21–0.30 is generally recommended. For immature infants, a higher FiO₂ than 0.3 may be needed, although the optimal initial level is not defined. For all groups, it is recommended to adjust the FiO₂ according to oxygen saturation (SpO₂) and heart rate response. For immature infants, the combination of prolonged bradycardia and an SpO₂ not reaching 80% within 5 min of life is associated with a substantially increased risk of death. For immature infants beyond the delivery room, an SpO₂ target between 91 and 95% is recommended. Full article

Simulated stable oxygen isotopic composition (δ¹⁸O) of precipitation from isotope-enabled GCMs (iGCMs) have gained significant visibility nowadays. This study evaluates bias correction techniques to reduce the systematic and dispersion biases of the modelled δ¹⁸O by the ECHAM5-wiso model compared to the Global Network of Isotopes in Precipitation (GNIP) observations over Central Europe. mean bias error (MBE) and Root Mean Square Error (RMSE) are substantially reduced by more than 70% and 10%, respectively, depending on the bias correction scheme, with better results for Generalized Additive Model (GAM) and linear scaling approach (SCL) methods. The bias-corrected δ¹⁸O_ECHAM5-wiso values successfully describe the long-term isotopic composition of precipitation and the isotopic amplitude with the best performances for the EQM method. The necessity of applying bias correction algorithms is verified by the excellent agreement between the corrected δ¹⁸O_ECHAM5-wiso with GNIP in high-altitude areas where ECHAM5-wiso fails to reproduce the observed isotopic variability. The results are expected to bring valuable insights into the utilization of iGCMs’ relationships in climate studies for understanding the present and past water cycle under the isotopic perspective. Full article

Citrus peel residues are of great interest due to the use of their extracted compounds in the food, pharmaceutical and cosmetic industries, mainly due to their antioxidant properties. The flavedo of this peel is especially relevant in modern culinary uses. The antioxidant capacity of the water and ethanolic extracts of the flavedos of ten peels was measured by a spectrophotometric assay and two electrochemical assays. The Folin–Ciocalteu values and ascorbic acid contents were also determined. From the results, it was concluded that the polyphenols extracted from the flavedos have antioxidant activities that occur through single-electron-transfer (SET) mechanisms rather than SET+ hydrogen atom transfer mechanisms. The polyphenols with high polarities extracted in the water constituted the least abundant fraction, and were better antioxidants than those with lower polarity extracted in the ethanol, which constituted the most abundant fraction. Full article

Polyphenols are an important class of compounds, due to their excellent antioxidant properties. Lately, much effort has been placed into developing new extraction techniques and optimizing them, so that polyphenols can be retrieved more efficiently from the plant materials. One of the most recent advances in extraction techniques is pulsed electric field extraction (PEF). This new technique is environmentally friendly and has the potential to maximize the recovery of compounds from plant tissues. Although the efficiency of PEF depends, among others, on the nature of the solvent used, up to date, there are no reports on the optimization of the PEF extraction of polyphenols, using hydroethanolic solutions of varying content in ethanol. In this study, three hydroethanolic solutions, water, and ethanol were used for the PEF-based extraction of total polyphenols from Sideritis raiseri. Results were conclusive that the 1:1 mixture of ethanol and water can increase by up to 146% the yield of polyphenols in the extract, highlighting the need to study more extensively, in the future, mixtures of solvents and not just plain water. Full article

Reactive Oxygen Species (ROS) are compounds derived from oxygen with important implications in biological processes in plants, some of them related to reproduction. Among ROS, superoxide is the primary oxidant, since an array of other ROS are eventually derived from this anion. Therefore, analysis of the molecular systems able to generate this molecule and the cellular compartmentalization of these events is of paramount importance. We have used the fluorochrome DCFH₂-DA and the chromogenic substrate NBT in association with DPI (a specific inhibitor of Rboh enzymes generating superoxide in plants) in combination with confocal microscopy and stereomicroscopy, respectively to identify cell localization of ROS in general, and superoxide accumulation in olive reproductive tissues. A significant production of both ROS and superoxide has been described, showing a fairly precise spatial and temporal location throughout olive flower development. The reduction of the NBT signal after the addition of DPI suggests that the generation of superoxide is largely due to Rboh or other flavin oxidase activity. At the subcellular level, accumulation of O₂^●− has been located in the plasma membrane of mature pollen and germinated pollen, as well as in the rough endoplasmic reticulum and in mitochondria. Full article

Free radicals have acquired growing importance in the fields of biology and medicine. They are produced during many different endogenous and exogenous processes. Mitochondria are the main source of endogenous reactive oxygen species (ROS) produced at cell level. The overproduction of free radicals can damage macromolecules such as nucleic acids, proteins and lipids. This leads to tissue damage in various chronic and degenerative diseases. Antioxidants play a crucial role in the body’s defense against free radicals. This review concerns the main properties of free radicals, their sources and deleterious effects. It highlights the potential role of the dietary supplementation of antioxidants and discusses unsolved problems regarding antioxidant supplements in the prevention and therapy of diseases. Full article

Exposure to hyperoxic conditions can induce pulmonary oxygen toxicity (POT). Divers of the Special Operations Forces (SOF) use oxygen rebreather systems during dives, and therefore are frequently exposed to hyperoxic conditions. Few studies have reported on POT in this population. This study reports on long-term pulmonary function tests (PFTs) and diffusing capacity in SOF divers to test the hypothesis that these measures of pulmonary function do not change clinically significantly during their career. The Royal Netherlands Navy performs yearly medical assessments of its military divers. All PFT and diffusing capacity data of SOF divers between the years 2000 and 2020 were analyzed using generalized estimating equations. The study included 257 SOF divers (median age, 27; interquartile range, 24–32), with 1612 dive medical assessments and a maximum follow-up time of 18.8 years. Alveolar volume (V_A) and the diffusing capacity of carbon monoxide (TL_CO) were significantly lower at baseline in smokers. Although these parameters were within the normal range, they declined over time and were significantly associated with age and years of diving. Smoking additionally affected TL_CO and the transfer coefficient for carbon monoxide (K_CO). TL_CO and K_CO were reduced by years of diving with oxygen rebreathers, albeit over clinically insignificant ranges, but smoking increased these changes by factors of 10 and 15, respectively. Full article