Oxygen

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

Although there has been some controversy surrounding exactly when oxygen was first discovered, it is likely that that accolade should go to Carl Wilhelm Scheele, who isolated oxygen in 1772, or even a year earlier. Others since then have been given the credit for the instrumental work leading to the discovery including Joseph Priestley in 1774 and Antoine-Laurent Lavoisier. Oxygen, a paramagnetic, diradical gaseous (at room temperature) molecule, is instrumental to life as we know it. It is also crucial to some medical therapies, used in multiple industries and has even been found on other planets. The importance of oxygen cannot be overplayed. Now, 250 years since oxygen was discovered, it is timely to revisit some of the history, the controversies and look at how oxygen has evolved during that time. Here, a few of the highlights in oxygen research are discussed. Full article

Mammalian cell culture is widely used for discovery and development. Recently, increasing attention has been paid to the importance of maintaining physiologically-relevant conditions in cell culture. Although oxygen level is a particularly important consideration, it is rarely regulated by experimentalists. The atmospheric O₂ levels commonly used in cell culture are significantly higher than those experienced by most mammalian cells in vivo, leaving cells susceptible to oxidative damage, senescence, transformation, and otherwise aberrant physiology. A barrier to incorporating O₂ regulation into most cell culture workflows has been the expense of investing in new equipment, as the vast majority of laboratory CO₂ incubators do not regulate O₂. Here, we describe an inexpensive (<CAD 1000), portable and user-friendly O₂/CO₂ incubator that can establish and maintain physiological O₂, CO₂, and temperature values within their physiological ranges. We used an Arduino-based approach to add O₂ and CO₂ control to a temperature-regulating egg incubator. Our incubator was tested against a commercial laboratory O₂/CO₂ incubator. Using Presens OxoDish technology, we demonstrate that at a setpoint value of 5% gas-phase incubator O₂, media O₂ averaged 5.03 (SD = 0.03) with a range of 4.98–5.09%. MCF7, LNCaP and C2C12 cell lines cultured in the incubator displayed normal morphology, proliferation, and viability. Culture for up to one week produced no contamination. Thus, our incubator provides an inexpensive means of maintaining physioxia in routine mammalian cell culture. Full article

Uterine transplantation may be a solution for infertility of uterine origin. Nevertheless, only three pregnancies with a live birth have so far been possible involving a uterine transplant from a brain-dead donor. Particularly, the impact of ischemia needs a better understanding. Analysis of mitochondrial respiration and production of reactive oxygen species (ROS) in muscle are of interest since they are pertinent markers of the harmful effects of ischemia. We therefore studied both uterine fundus and horn muscle mitochondrial use of oxygen and ROS production in eight women needing hysterectomy. High resolution respirometry and electron paramagnetic resonance allowed the determination of, respectively, myometrium oxidative capacity, hydrogen peroxide, mitochondrial free radical leak and superoxide anion production early (2 and 7 h) and late (24 h) following surgery. Mitochondrial oxygen consumption of the uterine fundus and horn tended to decrease with time but this was not statistically significant. Concerning ROS production, globally, we observed no significant change for H₂O₂, superoxide anion and free radical leak. In conclusion, a long period of cold ischemia did not impair myometrium mitochondrial respiration, only generating a transient H₂O₂ increase in uterine fundus. These data support that cold ischemia, even when prolonged, does not significantly alter uterine muscle oxidative capacity. Full article

Background: Infertility, defined as the failure to conceive after one year of regular, unprotected intercourse, affects 50–80 million people worldwide. A male factor is involved in approximately 20–30% of cases. In the etiology of male infertility, the association between poor semen quality and oxidative stress (OS) is well known. High levels of reactive oxygen species (ROS) allow the oxidation of DNA, proteins, and lipids of sperm cells, modifying their vitality, motility, and morphology. Methods: To evaluate the effects of antioxidants on sperm in infertile men, we queried the MEDLINE database (via the PubMed interface) for published studies in the last 10 years (2011–2021). The following keywords were used: “infertility” and -“inositol”, -“alpha-lipoic acid”, -“zinc”, -“folate”, -“coenzyme Q10”, -“selenium”, and -“vitamin”. Results: Inositol regulates OS levels in sperm cells thanks to its role in mitochondrial reactions and is involved in several processes favoring sperm–oocyte interactions. Alpha-lipoic acid (ALA) reduces ROS damage and improves semen parameters in terms of spermatozoa’s motility, morphology, and count. Poor zinc nutrition may be related to low quality of sperm. Supplementation of folate plus zinc has a positive effect on the sperm concentration and morphology. Supplementation with CoQ10 increases sperm concentration, total and progressive motility. Selenium (Se) supplementation improves the overall semen quality and is related to a higher ejaculated volume. Among vitamins, only vitamin B12 shows a positive effect on semen quality; it increases sperm count and motility and reduces sperm DNA damage. Conclusions: In men showing low-quality semen, diet supplementation with antioxidants may improve the sperm quality by alleviating OS-induced sperm damage and enhancing hormone synthesis and spermatozoa concentration, motility, and morphology. Future clinical trials should be focused on the possible association of several antioxidants to take advantage of combined mechanisms of action. Full article

Oxygen free radical burst is a prominent early event in the pathogenesis of Alzheimer’s disease (AD). Posttranslational modifications of Tau protein, primarily hyper-phosphorylation and truncation, are indicated as critical mediators of AD pathology. This finding is confirmed by the high levels of oxidative stress markers and by the increased susceptibility to oxygen radicals found in cultured neurons and in brains from transgenic animal models expressing toxic Tau forms, in concomitance with a dramatic reduction in their viability/survival. Here, we collect the latest progress in research focused on the reciprocal and dynamic interplay between oxygen radicals and pathological Tau, discussing how these harmful species cooperate and/or synergize in the progression of AD. In this context, a better understanding of the role of oxidative stress in determining Tau pathology, and vice versa, primarily could be able to define novel biomarkers of early stages of human tauopathies, including AD, and then to develop therapeutic strategies aimed at attenuating, halting, or reversing disease progression. Full article

Reactive oxygen species comprise oxygen-based free radicals and non-radical species such as peroxynitrite and electronically excited (singlet) oxygen. These reactive species often have short lifetimes, and much of our understanding of their formation and reactivity in biological and especially medical environments has come from complimentary fast reaction methods involving pulsed lasers and high-energy radiation techniques. These and related methods, such as EPR, are discussed with particular reference to singlet oxygen, hydroxy radicals, the superoxide radical anion, and their roles in medical aspects, such as cancer, vision and skin disorders, and especially pro- and anti-oxidative processes. Full article

Epitaxial SrTiO₃ (STO) thin films were grown on (001)-oriented LaAlO₃ (LAO) substrates at 800 °C by an ion beam sputter deposition (IBSD). Oxygen partial pressure (PO₂) was varied at 1.5 × 10⁻⁵, 1.5 × 10⁻⁴, and 1.5 × 10⁻³ Torr during the growth. The effects of PO₂ on crystal structure, oxygen vacancy, and surface morphology of the STO films were investigated and are discussed to understand their correlation. It was found that PO₂ played a significant role in influencing the crystal structure, oxygen vacancy, and surface morphology of the STO films. All STO films grew on the LAO substrates under a compressive strain along an in-plane direction (a- and b-axes) and a tensile strain along the growth direction (c-axis). The crystalline quality of STO films was slightly improved at higher PO₂. Oxygen vacancy was favorably created in the STO lattice grown at low PO₂ due to a lack of oxygen during growth and became suppressed at high PO₂. The existence of oxygen vacancy could result in a lattice expansion in both out-of-plane and in-plane directions due to the presence of Ti³⁺ instead of Ti⁴⁺ ions. The surface roughness of the STO films gradually decreased and was nearly close to that of the bare LAO substrate at high PO₂, indicating a two-dimensional (2D) growth mode. The results presented in this work provide a correlation among crystal structure, oxygen vacancy, and surface morphology of the epitaxial STO films grown by IBSD, which form a useful guideline for further study. Full article

Many cells in the human body strongly react on decreased oxygen concentrations, generally defined as hypoxia. Therefore, inducing hypoxia in vitro is essential for research. Classically, hypoxia is induced using a hypoxia chamber, but alternative methods exist that do not require special equipment. Here, we compared three different methods to induce hypoxia without a hypoxia chamber: the chemical stabilization of HIF-1α by CoCl₂, the decrease in pericellular oxygen concentrations by increased media height, and the consumption of oxygen by an enzymatic system. Hypoxia induction was further analyzed within three different cell culture systems: 2D (adherent) osteoprogenitor cells, monocytic (suspension) cells, and in a 3D in vitro fracture hematoma model. The different methods were analyzed within the scope of fracture healing regarding inflammation and differentiation. We could show that all three induction methods were feasible for hypoxia induction within adherent cells. Increased media heights did not stimulate a hypoxic response within suspension cells and in the 3D system. Chemical stabilization of HIF-1α showed limitations when looking at the expression of cytokines in osteoprogenitors and monocytes. Enzymatic reduction of oxygen proofed to be most effective within all three systems inducing inflammation and differentiation. Full article

Sixteen years (July 2003–July 2019) of ground-based measurements of total ozone in the urban environment of Athens, Greece, are analyzed in this work. Measurements were acquired with a single Brewer monochromator operating on the roof of the Biomedical Research Foundation of the Academy of Athens since July 2003. We estimate a 16-year climatological mean of total ozone in Athens of about 322 DU, with no significant change since 2003. Ozone data from the Brewer spectrophotometer were compared with TOMS, OMI, and GOME-2A satellite retrievals. The results reveal excellent correlations between the ground-based and satellite ozone measurements greater than 0.9. The variability of total ozone over Athens related to the seasonal cycle, the quasi biennial oscillation (QBO), the El Nino Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), the 11-year solar cycle, and tropopause pressure variability is presented. Full article

Epigenetics contains various mechanisms by which cells employ to regulate the transcription of many DNAs. Histone acetylation is an obvious example of the epigenetic mechanism regulating the expression of several genes by changing chromatin accessibility. Histone deacetylases (HDACs) are a class of enzymes that play a critical role in the epigenetic regulation by deacetylation of histone proteins. Inhibitors of the histone deacetylase could result in hyperacetylation of histones, which eventually induce various cellular consequences such as generation of reactive oxygen species (ROS), activation of apoptotic pathways, and initiating autophagy. In particular, excessive levels of ROS have been proposed to contribute to the pathophysiology of various diseases including cancer. Cancers are, as it were, a class of redox diseases. Low levels of ROS are beneficial for cells, however, cancer cells generally have high levels of ROS, which makes them more susceptible than normal cells to the further increases of ROS levels. Cancer cells exhibit metabolic alterations for managing to sustain these oxidative stresses. There is a growing interest in the use of HDAC inhibitors as promising cancer therapeutics with potentiating the activity of established therapeutic applications. Therefore, it should be important to understand the underlying relationship between the regulation of HDACs, ROS production, and cancer cell biology. Full article

A lithium superionic conductor of Li₁₀GeP₂S₁₂ that exhibits the highest lithium ionic conductivity among the sulfide electrolytes and the most promising oxide electrolytes, namely, Li_6.6La₃Sr_0.06Zr_1.6Sb_0.4O₁₂ and Li_6.6La₃Zr_1.6Sb_0.4O₁₂, are successfully synthesized. Novel hybrid electrolytes with a weight ratio of Li_6.6La₃Zr_1.6Sb_0.4O₁₂ to Li₁₀GeP₂S₁₂ from 1/1 to 1/3 with the higher Li-ion conductivity than that of the pure Li₁₀GeP₂S₁₂ electrolyte are developed for the fabrication of the advanced all-solid-state Li batteries. Full article

Control of cellular function is extremely complex, being reliant on a wide range of components. Several of these are small oxygen-based molecules. Although reactive compounds containing oxygen are usually harmful to cells when accumulated to relatively high concentrations, they are also instrumental in the control of the activity of a myriad of proteins, and control both the upregulation and downregulation of gene expression. The formation of one oxygen-based molecule, such as the superoxide anion, can lead to a cascade of downstream generation of others, such as hydrogen peroxide (H₂O₂) and the hydroxyl radical (^∙OH), each with their own reactivity and effect. Nitrogen-based signaling molecules also contain oxygen, and include nitric oxide (NO) and peroxynitrite, both instrumental among the suite of cell signaling components. These molecules do not act alone, but form part of a complex interplay of reactions, including with several sulfur-based compounds, such as glutathione and hydrogen sulfide (H₂S). Overaccumulation of oxygen-based reactive compounds may alter the redox status of the cell and lead to programmed cell death, in processes referred to as oxidative stress, or nitrosative stress (for nitrogen-based molecules). Here, an overview of the main oxygen-based molecules involved, and the ramifications of their production, is given. Full article