Oxygen, Volume 2, Issue 3 (September 2022) – 10 articles

For most living beings, oxygen is an essential molecule for survival, being the basis of biological oxidations, which satisfy most of the energy needs of aerobic organisms. Oxygen can also behave as a toxic agent posing a threat to the existence of living beings since it can give rise to reactive oxygen species (ROS) that can oxidise biological macromolecules, among which proteins and lipids are the preferred targets. Oxidative damage can induce cell, tissue, and organ dysfunction, which leads to severe body damage and even death. The survival of the aerobic organism depends on the development of an elaborate antioxidant defence system adapted to the normal level of atmospheric oxygen. The production of ROS in the aerobic organism can occur accidentally from exposure to pollutants or radiation, but occurs constantly during normal metabolic reactions. Cells have evolved using ROS to their advantage. Indeed, ROS are used as signalling molecules in numerous physiological processes, including muscle contraction, regulation of insulin release, and adaptation to environmental changes. Therefore, supplementation with antioxidants must be used wisely. A low level of ROS is essential for adaptation processes, so an excess of antioxidants can be harmful. Conversely, in conditions where ROS production increases, antioxidants can be useful to avoid cellular dysfunction. Full article

This narrative paper reviews the current knowledge of Home Oxygen Therapy (HOT) in stable Chronic Obstructive Pulmonary Disease (COPD) and Interstitial Lung Disease (ILD), two major causes of Long-Term Oxygen Therapy (LTOT) prescription. There is evidence that LTOT improves survival in COPD subjects with chronic severe respiratory failure. HOT is also used to contrast exercise and sleeping hypoxemia and to improve Quality of Life (QoL) and symptoms. Ambulatory Oxygen Therapy (AOT) did not assure generalized improvements in symptoms and Quality of Life (QoL) of COPD subjects. There is short-term evidence in a real-life study that AOT may improve QoL in ILD subjects with Exercise Oxygen Desaturation (EOD) and exertional dyspnea. There are some differences between guidelines and practices, which translate into variations in characteristics and rates of ILD and COPD subjects admitted to LTOT and AOT. Indications on titration of oxygen flow and the best oxygen delivery device for optimal management of AOT in COPD and ILD subjects are often vague or lacking. More work is needed for optimizing and customizing HOT in COPD and ILD subjects. Full article

Many environmental stresses cause an increase in reactive oxygen species in plants and alter their nutritional value. Plants respond to many stresses by producing increased amounts of compounds with antioxidant properties including vitamins, phenylpropanoids and carotenoids. Such compounds have wide-ranging health-promoting effects in humans that are partly due to their antioxidant function because oxidative stress underlies many human diseases. Some of these compounds have complex interactions with the gut, promoting gut health and changing the gut microbiome, whereas the gut influences the bioavailability of the ingested compounds and may metabolize them into products with different effects on health than the original compound. Substantial efforts have been made to increase the nutritional value of crops through breeding or transgenic approaches, but comparatively little effort has been directed towards increasing nutritional value through crop management and environment, which may present another approach to enhance the nutritional quality. Full article

This review deals with the production of oxygen by photo-oxidation of water, which is a topic fitting a journal devoted to oxygen. Most of the present biosphere, including mankind, depends on oxygen. Elucidating the mechanism is of importance for solving the present energy crisis. Photosynthesis evolved in bacteria, first in a form that did not produce oxygen. The oxygen-producing version arose with the advent of cyanobacteria about three billion years ago. The production of oxygen by photo-oxidation of water requires the co-operative action of four photons. These are harvested from daylight by chlorophyll and other pigments (e.g., phycobiliproteins) and are channeled to photosystem II and photosystem I. The oxygen-evolving complex resides in photosystem II, surrounded by protein subunits, and contains one ion of calcium, four ions of manganese, and a number of oxygen atoms. For each quantum of energy it receives from absorbed light, it proceeds one step through a cycle of states known as the Kok–Joliot cycle. For each turn of the cycle, one molecule of oxygen (O₂) is produced. Full article

In Nuclear Magnetic Resonance (NMR) spectroscopy, the isotropic chemical shift ${\delta }_{iso}$ is a measure of the electron density around the observed nuclide. For characterization of solid materials and compounds, it is desirable to find correlations between ${\delta }_{iso}$ and structural parameters such as coordination numbers and distances to neighboring atoms. Correlations of good quality are easier to find when the coordination sphere is formed by only one element, as the electron density is obviously strongly dependent on the atomic number. The current study is therefore restricted to nuclides in pure oxygen coordination. It is shown that the isotropic shift ${\delta }_{iso}$ correlates well with the average oxygen distances (as defined by the coordination sphere) for the nuclides ${}^{23}$Na (with spin $I=3/2$), ${}^{27}$Al ($I=5/2$), and ${}^{43}$Ca ($I=7/2$), using literature data for a range of periodic solids. It has been previously suggested for ${}^{207}$Pb ($I=1/2$) that ${\delta }_{iso}$ may alternatively be related to the shortest oxygen distance in the structure, and our study corroborates this also for the nuclides considered here. While the correlation with the minimal distance is not always better, it has the advantage of being uniquely defined. In contrast, the average distance is strongly dependent on the designation of the oxygen coordination sphere, which may be contentious in some crystal structures. Full article

Cisplatin-induced acute kidney injury (AKI) is the main factor restraining the clinical application of cisplatin. The AKI is associated with high mortality and morbidity, but no effective pharmacological treatment is available at present. As increased levels of reactive oxygen species (ROS) may promote the progression of the injury, the elimination of ROS has been considered as an effective method to prevent the cisplatin-induced AKI. In addition, it has been revealed that an inducer of autophagy could protect kidney cells in the autophagy dependent manner. Induction of autophagy could also modulate the production of ROS in cases of renal injury. Therefore, kidney-targeted antioxidants and/or autophagy are urgently required for the better treatment of AKI. Accumulating evidence has indicated the important roles of gut microbiota in the pathogenesis of AKI. In addition, there is a scientific basis for considering future clinical applications of probiotics and/or prebiotics to treat cisplatin-induced AKI. Thus, gut microbiota might be a promising therapeutic target via the alteration of autophagy for the cancer therapy-induced nephrotoxicity. Full article

Molecular oxygen (O₂) is the perfect probe molecule for membrane studies carried out using the saturation recovery EPR technique. O₂ is a small, paramagnetic, hydrophobic enough molecule that easily partitions into a membrane’s different phases and domains. In membrane studies, the saturation recovery EPR method requires two paramagnetic probes: a lipid-analog nitroxide spin label and an oxygen molecule. The experimentally derived parameters of this method are the spin–lattice relaxation times (T₁s) of spin labels and rates of bimolecular collisions between O₂ and the nitroxide fragment. Thanks to the long T₁ of lipid spin labels (from 1 to 10 µs), the approach is very sensitive to changes of the local (around the nitroxide fragment) O₂ diffusion-concentration product. Small variations in the lipid packing affect O₂ solubility and O₂ diffusion, which can be detected by the shortening of T₁ of spin labels. Using O₂ as a probe molecule and a different lipid spin label inserted into specific phases of the membrane and membrane domains allows data about the lateral arrangement of lipid membranes to be obtained. Moreover, using a lipid spin label with the nitroxide fragment attached to its head group or a hydrocarbon chain at different positions also enables data about molecular dynamics and structure at different membrane depths to be obtained. Thus, the method can be used to investigate not only the lateral organization of the membrane (i.e., the presence of membrane domains and phases), but also the depth-dependent membrane structure and dynamics and, hence, the membrane properties in three dimensions. Full article

Tzatziki is a deli salad widely consumed in the Eastern Mediterranean and Balkan countries, and it is acknowledged for its health benefits. So far, it is proved to exhibit extreme resistance to microbial spoilage by (pathogenic) microorganisms and microbial self-stabilization, but no research was carried out regarding its oxidative stability despite the fact that it contains a large amount of lipids. In this study, the factor that affects the oxidative stability of tzatziki was exploited. Different samples of tzatziki salad were prepared and stored for 16 or 27 days, depending on the conducted experiment. They varied in the type of yogurt (set yogurt or traditional Greek-style yogurt), the type of oil (olive oil or soybean oil), and the addition or not of preservatives, garlic, and cucumber. Samples were analyzed in terms of oxidative stability (by the Rancimat method), colony-forming units, and tocopherol content throughout the storage period. Among the examined parameters, no correlation between the tocopherol content and oxidative stability was recorded. However, a strong correlation between the microbial population and the oxidative stability was recorded. Therefore, this correlation can be used to prepare tzatziki salads with increased shelf life and decreased flavor deterioration (due to oxidation). Moreover, such correlations should be further exploited for other foods so as to promote their stability. Full article

In the history of life, cooperation between biological units has led to increased complexity, e.g., eukaryotic cells and multicellular organisms. Cooperation requires limiting the gains of “defectors” in favor of the cooperative higher-level unit. Early in an evolutionary transition, bioenergetics and reactive oxygen species (ROS) may play a large role in managing these evolutionary conflicts. Chemiosmosis can be thought of as a poorly insulated wire—when supply exceeds demand, electrons are cast off and can form ROS. ROS signaling may thus lead to the dispersal of the excess products into the environment. These products may lead to groups and the formation of higher-level units that can subsequently be targeted by selection. Examining modern symbioses such as those between corals and photosynthetic dinoflagellates provides useful insight in this context. While ROS are an important factor in coral bleaching, little is known of the function of ROS under other circumstances, although some data suggest that ROS may modulate cooperation. ROS may have functioned similarly in the origin of eukaryotes, involving chemiosmotic mitochondria and chloroplasts. ROS may act as “arbiters” of evolutionary conflict, leading to cooperation via signaling pathways that favor the emergence of the higher-level unit. Full article

The rising prevalence of chronic metabolic disorders, such as obesity and type 2 diabetes, most notably associated with cardiovascular diseases, has emerged as a major global health concern. Reactive oxygen species (ROS) play physiological functions by maintaining normal cellular redox signaling. By contrast, a disturbed balance occurring between ROS production and detoxification of reactive intermediates results in excessive oxidative stress. Oxidative stress is a critical mediator of endothelial dysfunction in obesity and diabetes. Under a hyperglycemic condition, the antioxidant enzymes are downregulated, resulting in an increased generation of ROS. Increases in ROS lead to impairment of endothelium-dependent vasodilatations by reducing NO bioavailability. Chronic treatments with antioxidants were reported to prevent the development of endothelial dysfunction in diabetic patients and animals; however, the beneficial effects of antioxidant treatment in combating vascular complications in diabetes remain controversial as antioxidants do not always reverse endothelial dysfunction in clinical settings. In this review, we summarize the latest progress in research focused on the role of ROS in vascular complications of diabetes and the antioxidant properties of bioactive compounds from medicinal plants and food in animal experiments and clinical studies to provide insights for the development of therapeutic strategies. Full article