Glutathione peroxidase-2 protects from allergen-induced airway inflammation in mice

Evolutionary expansion, functional diversification, and transcript profiling of plant Glutathione Peroxidases

Glutathione peroxidases (GPXs) play a crucial role in combating activated oxygen species and have been widely studied for their involvement in stress responses. In addition to their stress-related functions, GPXs exhibit diverse roles such as immunological response, and involvement in growth and development. These enzymes are found in both animals and plants, with multiple families identified in the evolutionarily diverse species. These families consist of conserved genes as well as unique members, highlighting the evolutionary diversification of GPX members. While animals have eight GPX families, plants possess five families. Notably, plant genomes undergo duplication and expansion events, leading to an increase in the number of GPX genes and the overall size of the GPX superfamily. This expansion suggests a wide range of functional roles for GPX. In this study, the evolutionary diversification, family expansion, and diverse functional roles of GPX enzymes have been investigated. Additionally, the expression profile of Arabidopsis and Oryza sativa GPX genes were analyzed in different developmental stages, tissues, and abiotic stress conditions. Further extensive research has been required to unravel the intricate interplay between GPX and other proteins, to gain the comprehensive mechanism governing the physiological and developmental roles of GPX.

Biological and Catalytic Properties of Selenoproteins

Selenocysteine is a catalytic residue at the active site of all selenoenzymes in bacteria and mammals, and it is incorporated into the polypeptide backbone by a co-translational process that relies on the recoding of a UGA termination codon into a serine/selenocysteine codon. The best-characterized selenoproteins from mammalian species and bacteria are discussed with emphasis on their biological function and catalytic mechanisms. A total of 25 genes coding for selenoproteins have been identified in the genome of mammals. Unlike the selenoenzymes of anaerobic bacteria, most mammalian selenoenzymes work as antioxidants and as redox regulators of cell metabolism and functions. Selenoprotein P contains several selenocysteine residues and serves as a selenocysteine reservoir for other selenoproteins in mammals. Although extensively studied, glutathione peroxidases are incompletely understood in terms of local and time-dependent distribution, and regulatory functions. Selenoenzymes take advantage of the nucleophilic reactivity of the selenolate form of selenocysteine. It is used with peroxides and their by-products such as disulfides and sulfoxides, but also with iodine in iodinated phenolic substrates. This results in the formation of Se-X bonds (X = O, S, N, or I) from which a selenenylsulfide intermediate is invariably produced. The initial selenolate group is then recycled by thiol addition. In bacterial glycine reductase and D-proline reductase, an unusual catalytic rupture of selenium-carbon bonds is observed. The exchange of selenium for sulfur in selenoproteins, and information obtained from model reactions, suggest that a generic advantage of selenium compared with sulfur relies on faster kinetics and better reversibility of its oxidation reactions.

Importance of Microminerals for Maintaining Antioxidant Function After COVID-19-induced Oxidative Stress

Background

COVID-19 is caused by the Severe Acute Respiratory Distress Syndrome Coronavirus 2. Since the antioxidant mechanisms such as glutathione peroxidase or superoxide dismutase are downregulated during infection by the virus, there is an imbalance in the oxidant-antioxidant system. In this study we aimed to identify the effect of COVID-19 on the antioxidant defense mechanism by comparing the concentrations of antioxidants and microminerals in COVID-19 patients and healthy controls.

Methods

This cross-sectional analytical study involved 200 patients at Kasturba Hospital, Manipal University. The serum concentrations of antioxidants and minerals were determined to establish the impact of COVID-19 on antioxidants mechanism and nutrient status in COVID-19 patients.

Results

The serum concentrations of GPX (10.36 ± 2.70 ≥ 5.82 ± 1.64 mKAT/L, p < 0.0001) and copper (2192.5 ± 449.8 ≥ 782.15 ± 106.5 µg/dL, p < 0.0001) were significantly greater, and zinc (34.78 ± 4.5 ≤ 81.07 ± 10.13 µg/dL, p < 0.0001) was significantly less, in the study group than in controls. The Pearson correlation between serum SOD and zinc was significant (r = 0.491, p < 0.0001) indicating the importance of zinc in maintaining and improving SOD activity. No significant correlations were observed between copper and SOD (r = -0.089) or iron and CAT (r = -0.027).

Conclusion

Our study demonstrated the expected increase in oxidant-radical production during COVID-19 by estimating the altered concentrations of antioxidants and the minerals required to neutralize the elevated ROS. This finding is not novel but adds to the existing literature, which recommends nutritional supplementation of microminerals and antioxidants.

The beginning of GPX2 and 30 years later

We published the first paper to characterize GPX2 (aka GSHPx-GI) as a selenoenzyme with glutathione peroxidase activity in 1993. Among the four Se-GPX isozymes, GPX1-4, GPX1 and GPX2 are closely related in terms of structure, substrate specificities, and subcellular localization. What sets them apart are distinct patterns of gene regulation, tissue distribution and response to selenium. While we identified the digestive tract epithelium as the main site of GPX2 expression, later work has shown GPX2 is found more widely in epithelial tissues with concentration of expression in stem cell and proliferative compartments. GPX2 expression is regulated over a wide range of levels by many pathways, including NRF2, WNT, p53, RARE and this often results in attaching undue significance to GPX2 as GPX2 is only a part of a system of hydroperoxidase activities, including GPX1, peroxiredoxins and catalase. These other activities may play equal or greater roles, particularly in cell lines cultured without selenium supplementation and often with very low GPX2 levels. This could be assessed by examining levels of mRNA and protein among these various peroxidases at the outset of studies. As an example, it was found that GPX1 responds to the absence of GPX2 in mouse ileum and colon epithelium with higher expression. As such, both Gpx1 and Gpx2 had to be knocked out in mice to produce ileocolitis. However, we note that the actual role of GPX1 and GPX2 in relation to peroxiredoxin function is unclear. There may be an interdependence that requires only low amounts of GPX1 and/or GPX2 in a supporting role to maintain proper peroxiredoxin function. GPX2 levels may be prognostic for cancer progression in colon, breast, prostate and liver, however, there is no consistent trend for higher or lower levels to be favorable.

Resistant Potato Starch Alters the Cecal Microbiome and Gene Expression in Mice Fed a Western Diet Based on NHANES Data

Several studies indicate that the four major types of resistant starch (RS1-4) are fermented in the cecum and colon to produce short-chain fatty acids (SCFAs) and can alter the microbiome and host physiology. However, nearly all these studies were conducted in rodents fed with a diet that does not approximate what is typically consumed by humans. To address this, mice were fed a Total Western Diet (TWD) based on National Health and Nutrition Examination Survey (NHANES) data that mimics the macro and micronutrient composition of a typical American diet for 6 weeks and then supplemented with 0, 2, 5, or 10% of the RS2, resistant potato starch (RPS), for an additional 3 weeks. The cecal microbiome was analyzed by 16S sequencing. The alpha-diversity of the microbiome decreased with increasing consumption of RPS while a beta-diversity plot showed four discreet groupings based on the RPS level in the diet. The relative abundance of various genera was altered by feeding increasing levels of RPS. In particular, the genus Lachnospiraceae NK4A136 group was markedly increased. Cecal, proximal, and distal colon tissue mRNA abundance was analyzed by RNASeq. The cecal mRNA abundance principal component analysis showed clear segregation of the four dietary groups whose separation decreased in the proximal and distal colon. Differential expression of the genes was highest in the cecum, but substantially decreased in the proximal colon (PC) and distal colon (DC). Most differentially expressed genes were unique to each tissue with little overlap in between. The pattern of the observed gene expression suggests that RPS, likely through metabolic changes secondary to differences in microbial composition, appears to prime the host to respond to a range of pathogens, including viruses, bacteria, and parasites. In summary, consumption of dietary RPS led to significant changes to the microbiome and gene expression in the cecum and to a lesser extent in the proximal and distal colon.

Clinical significance of serum GPX2 levels in patients with osteoarthritis was suppressed and reduced inflammation of osteoarthritis through STAT3 function

The main alterations of osteoarthritis are degenerative lesions of articular cartilage and secondary hyperostosis. Despite the unclear pathogenic mechanism, experimental studies have confirmed that the incidence of osteoarthritis is closely associated with inflammation-related substances. In this study, we explored the significance of serum GPX2 levels in patients with osteoarthritis and the mechanism of GPX2 in the anti-inflammation effects in osteoarthritis. As a result, serum GPX2 level was down-regulated and there was a negative correlation between GPX2 levels and IL-1β levels in patients with osteoarthritis. Over-expression of GPX2 decreased the inflammatory levels and down-regulation of GPX2 increased inflammatory levels in vitro. In contrast, GPX2 combined and regulated STAT3 protein expression. Over-expression of GPX2 promoted ubiquitination-STAT3 protein expression to decrease p-STAT3 protein expression in vitro. The inhibition of STAT3 attenuated the anti-inflammation effects of GPX2 in osteoarthritis. Thus, we proposed that GPX2 was down-regulated in patients with osteoarthritis and GPX2 played vital roles in osteoarthritis for clinical diagnosis or therapy.

Infant Iodine and Selenium Status in Relation to Maternal Status and Diet During Pregnancy and Lactation

Iodine and selenium are essential trace elements. Recent studies indicate that pregnant and lactating women often have insufficient intake of iodine and selenium, but the impact on fetal and infant status is unclear. Here, we assessed iodine and selenium status of infants in relation to maternal intake and status of these trace elements in the birth cohort NICE, conducted in northern Sweden (n = 604). Iodine was measured in urine (UIC) in gestational week 29, and in breast milk and infant urine 4 months postpartum, while selenium was measured in maternal plasma and erythrocytes in gestational week 29, and in breast milk and infant erythrocytes 4 months postpartum, in both cases using ICP-MS. Maternal intake was assessed with semi-quantitative food frequency questionnaires in gestational week 34 and at 4 months postpartum. The median intake of iodine and selenium during pregnancy (98 and 40 μg/d, respectively) and lactation (108 and 39 μg/d, respectively) was below recommended intakes, reflected in insufficient status (median UIC of 113 μg/L, median plasma selenium of 65 μg/L). Also, breast milk concentrations (median iodine 77 μg/L, median selenium 9 μg/L) were unlikely to meet infant requirements. Median UIC of the infants was 114 μg/L and median erythrocyte selenium 96 μg/kg, both similar to the maternal concentrations. Infant UIC correlated strongly with breast milk levels (rho = 0.64, p < 0.001). Their erythrocyte selenium correlated with maternal erythrocyte selenium in pregnancy (rho = 0.38, p < 0.001), but not with breast milk selenium, suggesting formation of prenatal reserves. Our results indicate that the transport of iodine and selenium to the fetus and infant is prioritized. Still, it is uncertain whether most infants had sufficient intakes. Further, the results might indicate an involvement of iodine in asthma development during the first year of life, which is essential to follow up. The low maternal and infant dietary intake of both iodine and selenium, especially when the mothers did not use supplements or iodized table salt, suggest a need for a general screening of women and young children.

The phytonutrient cinnamaldehyde limits intestinal inflammation and enteric parasite infection

Phytonutrients such as cinnamaldehyde (CA) have been studied for their effects on metabolic diseases, but their influence on mucosal inflammation and immunity to enteric infection are not well documented. Here, we show that consumption of CA in mice significantly down-regulates transcriptional pathways connected to inflammation in the small intestine, and alters T-cell populations in mesenteric lymph nodes. During infection with the enteric helminth Heligomosomoides polygyrus, CA treatment attenuated infection-induced changes in biological pathways connected to cell cycle and mitotic activity, and tended to reduce worm burdens. Mechanistically, CA did not appear to exert activity through a prebiotic effect, as CA treatment did not significantly change the composition of the gut microbiota. Instead, in vitro experiments showed that CA directly induced xenobiotic metabolizing pathways in intestinal epithelial cells and suppressed endotoxin-induced inflammatory responses in macrophages. Collectively, our results show that CA down-regulates inflammatory pathways in the intestinal mucosa and can limit the pathological response to enteric infection. These properties appear to be largely independent of the gut microbiota, and instead connected to the ability of CA to induce antioxidant pathways in intestinal cells. Our results encourage further investigation into the use of CA and related phytonutrients as functional food components to promote intestinal health in humans and animals.

Glutathione S-transferases and their implications in the lung diseases asthma and chronic obstructive pulmonary disease: Early life susceptibility?

Our lungs are exposed daily to airborne pollutants, particulate matter, pathogens as well as lung allergens and irritants. Exposure to these substances can lead to inflammatory responses and may induce endogenous oxidant production, which can cause chronic inflammation, tissue damage and remodeling. Notably, the development of asthma and Chronic Obstructive Pulmonary Disease (COPD) is linked to the aforementioned irritants. Some inhaled foreign chemical compounds are rapidly absorbed and processed by phase I and II enzyme systems critical in the detoxification of xenobiotics including the glutathione-conjugating enzymes Glutathione S-transferases (GSTs). GSTs, and in particular genetic variants of GSTs that alter their activities, have been found to be implicated in the susceptibility to and progression of these lung diseases. Beyond their roles in phase II metabolism, evidence suggests that GSTs are also important mediators of normal lung growth. Therefore, the contribution of GSTs to the development of lung diseases in adults may already start in utero, and continues through infancy, childhood, and adult life. GSTs are also known to scavenge oxidants and affect signaling pathways by protein-protein interaction. Moreover, GSTs regulate reversible oxidative post-translational modifications of proteins, known as protein S-glutathionylation. Therefore, GSTs display an array of functions that impact the pathogenesis of asthma and COPD.

In this review we will provide an overview of the specific functions of each class of mammalian cytosolic GSTs. This is followed by a comprehensive analysis of their expression profiles in the lung in healthy subjects, as well as alterations that have been described in (epithelial cells of) asthmatics and COPD patients. Particular emphasis is placed on the emerging evidence of the regulatory properties of GSTs beyond detoxification and their contribution to (un)healthy lungs throughout life. By providing a more thorough understanding, tailored therapeutic strategies can be designed to affect specific functions of particular GSTs.

Airways glutathione S-transferase omega-1 and its A140D polymorphism are associated with severity of inflammation and respiratory dysfunction in cystic fibrosis

BACKGROUND

Glutathione S-transferase omega-1 (GSTO1-1) is a cytosolic enzyme that modulates the S-thiolation status of intracellular factors involved in cancer cell survival or in the inflammatory response. Studies focusing on chronic obstructive pulmonary disease (COPD) have demonstrated that GSTO1-1 is detectable in alveolar macrophages, airway epithelium and in the extracellular compartment, where its functions have not been completely understood. Moreover GSTO1-1 polymorphisms have been associated with an increased risk to develop COPD. Against this background, the aim of this study was to evaluate GSTO1-1 levels and its polymorphisms in cystic fibrosis (CF) patients.

METHODS

Clinical samples from a previous study published by our groups were analyzed for GSTO1-1 levels and polymorphisms. For comparison, a model of lung inflammation in CFTR-knock out mice was also used.

RESULTS

Our data document that soluble GSTO1-1 can be found in the airways of CF patients and correlates with inflammatory parameters such as neutrophilic elastase and the chemokine IL-8. A negative correlation was found between GSTO1-1 levels and the spirometric parameter FEV1 and the FEV1/FVC ratio. Additionally, the A140D polymorphism of GSTO1-1 was associated with lower levels of the antiinflammatory mediators PGE2 and 15(S)-HETE, and with lower values of the FEV1/FVC ratio in CF subjects with the homozygous CFTR ΔF508 mutation.

CONCLUSIONS

Our data suggest that extracellular GSTO1-1 and its polymorphysms could have a biological and clinical significance in CF. Pathophysiological functions of GSTOs are far from being completely understood, and more studies are required to understand the role(s) of extracellular GSTO1-1 in inflamed tissues.

Regulatory Phenomena in the Glutathione Peroxidase Superfamily

Significance: The selenium-containing Glutathione peroxidases (GPxs)1-4 protect against oxidative challenge, inhibit inflammation and oxidant-induced regulated cell death. Recent Advances: GPx1 and GPx4 dampen phosphorylation cascades predominantly via prevention of inactivation of phosphatases by H₂O₂ or lipid hydroperoxides. GPx2 regulates the balance between regeneration and apoptotic cell shedding in the intestine. It inhibits inflammation-induced carcinogenesis in the gut but promotes growth of established cancers. GPx3 deficiency facilitates platelet aggregation likely via disinhibition of thromboxane biosynthesis. It is also considered a tumor suppressor. GPx4 is expressed in three different forms. The cytosolic form proved to inhibit interleukin-1-driven nuclear factor κB activation and leukotriene biosynthesis. Moreover, it is a key regulator of ferroptosis, because it reduces hydroperoxy groups of complex lipids and silences lipoxygenases. By alternate substrate use, the nuclear form contributes to chromatin compaction. Mitochondrial GPx4 forms the mitochondrial sheath of spermatozoa and, thus, guarantees male fertility. Out of the less characterized GPxs, the cysteine-containing GPx7 and GPx8 are unique in contributing to oxidative protein folding in the endoplasmic reticulum by reacting with protein isomerase as an alternate substrate. A yeast 2-Cysteine glutathione peroxidase equipped with CP and CR was reported to sense H₂O₂ for inducing an adaptive response. Critical Issues: Most of the findings compiled are derived from tissue culture and/or animal studies only. Their impact on human physiology is sometimes questionable. Future Directions: The expression of individual GPxs and GPx-dependent regulatory phenomena are to be further investigated, in particular in respect to human health.

Tempol reduces inflammation and oxidative damage in cigarette smoke-exposed mice by decreasing neutrophil infiltration and activating the Nrf2 pathway

Cigarette smoke is a complex mixture capable of triggering inflammation and oxidative damage in animals at pulmonary and systemic levels. Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl) reduces tissue injury associated with inflammation in vivo by mechanisms that are not completely understood. Here we evaluated the effect of tempol on inflammation and oxidative damage induced by acute exposure to cigarette smoke in vivo. Male C57BL/6 mice (n = 32) were divided into 4 groups (n = 8 each): 1) control group exposed to ambient air (GC), 2) animals exposed to cigarette smoke for 5 days (CSG), mice treated 3) prior or 4) concomitantly with tempol (50 mg/kg/day) and exposed to cigarette smoke for 5 days. The results showed that the total number of leukocytes and neutrophils increased in the respiratory tract and lung parenchyma of mice exposed to cigarette smoke. Likewise, MPO levels and activity as well as lipid peroxidation and lung protein nitration and carbonylation also increased. Administration of tempol before or during exposure to cigarette smoke inhibited all the above parameters. Tempol also reduced the pulmonary expression of the inflammatory cytokines Il-6, Il-1β and Il-17 to basal levels and of Tnf-α by approximately 50%. In contrast, tempol restored Il-10 and Tgf-β levels and enhanced the expression of Nrf2-associated genes, such as Ho-1 and Gpx2. Accordingly, total GPx activity increased in lung homogenates of tempol-treated animals. Taken together, our results show that tempol protects mouse lungs from inflammation and oxidative damage resulting from exposure to cigarette smoke, likely through reduction of leukocyte infiltration and increased transcription of some of the Nrf2-controlled genes.

The Beneficial Effects of Antioxidants in Health And Diseases

Reactive oxygen and nitrogen species can be generated endogenously (by mitochondria, peroxisomes, and phagocytic cells) and exogenously (by pollutions, UV exposure, xenobiotic compounds, and cigarette smoke). The negative effects of free radicals are neutralized by antioxidant molecules synthesized in our body, like glutathione, uric acid, or ubiquinone, and those obtained from the diet, such as vitamins C, E, and A, and flavonoids. Different microelements like selenium and zinc have no antioxidant action themselves but are required for the activity of many antioxidant enzymes. Furthermore, circulating blood proteins are suggested to account for more than 50% of the combined antioxidant effects of urate, ascorbate, and vitamin E. Antioxidants together constitute a mutually supportive defense against reactive oxygen and nitrogen species to maintain the oxidant/antioxidant balance. This article outlines the oxidative and anti-oxidative molecules involved in the pathogenesis of chronic obstructive lung disease. The role of albumin and alpha-1 antitrypsin in antioxidant defense is also discussed.

Selenium and selenoproteins in prostanoid metabolism and immunity

Selenium (Se) is an essential trace element that functions in the form of the 21st amino acid, selenocysteine (Sec) in a defined set of proteins. Se deficiency is associated with pathological conditions in humans and animals, where incorporation of Sec into selenoproteins is reduced along with their expression and catalytic activity. Supplementation of Se-deficient population with Se has shown health benefits suggesting the importance of Se in physiology. An interesting paradigm to explain, in part, the health benefits of Se stems from the observations that selenoprotein-dependent modulation of inflammation and efficient resolution of inflammation relies on mechanisms involving a group of bioactive lipid mediators, prostanoids, which orchestrate a concerted action toward maintenance and restoration of homeostatic immune responses. Such an effect involves the interaction of various immune cells with these lipid mediators where cellular redox gatekeeper functions of selenoproteins further aid in not only dampening inflammation, but also initiating an effective and active resolution process. Here we have summarized the current literature on the multifaceted roles of Se/selenoproteins in the regulation of these bioactive lipid mediators and their immunomodulatory effects.

Oral administration of 3,3'-diselenodipropionic acid prevents thoracic radiation induced pneumonitis in mice by suppressing NF-kB/IL-17/G-CSF/neutrophil axis

The incidence of symptomatic radiation induced lung pneumonitis (RILP), a major dose limiting side effect of thoracic radiotherapy, is in the range of 15-40%. Therapeutic options for the prevention and treatment of RILP are limited. Hence there is a need for developing novel radioprotectors to prevent RILP which can be patient compliant. This study sought to evaluate the efficacy of oral 3,3'-diselenodipropionic acid (DSePA), a novel selenocystine derivative to prevent RILP. C3H/HeJ (pneumonitis responding) mice received a single dose of 18 Gy, whole thorax irradiation and a subset were treated with DSePA orally (2.5 mg/kg), three times per week beginning 2 h post irradiation and continued till 6 months. DSePA delayed onset of grade ≥ 2 RILP by 45 days compared to radiation control (~105 versus ~60 days). It also reversed the severity of pneumonitis in 3/10 radiation treated mice leading to significant improvement in asymptomatic survival compared to radiation control (~180 versus ~102 days). DSePA significantly (p < 0.05) reduced the radiation-mediated infiltration of polymorphonuclear neutrophils (PMN) and elevation in levels of cytokines such as IL1-β, ICAM-1, E-selectin, IL-17 and TGF-β in the bronchoalveolar lavage fluid. Moreover DSePA lowered PMN-induced oxidants, maintained glutathione peroxidase activity and suppressed NF-kB/IL-17/G-CSF/neutrophil axis in the lung of irradiated mice. Additionally, this compound did not protect A549 (lung cancer) derived xenograft tumor from radiation exposure in SCID mice. DSePA offers protection to normal lung against RILP without affecting radiation sensitivity of tumors. It has the potential to be developed as an oral agent for preventing RILP.

Oxidative Stress Mechanisms in the Pathogenesis of Environmental Lung Diseases

Globally, respiratory diseases are major cause of disability and mortality, and more alarmingly, it disproportionately affects developing countries, which is largely attributed to poor quality of air. Tobacco smoke and emissions from combustion of fossil fuel and biomass fuel are the major airborne pollutants affecting human lung health. Oxidative stress is the dominant driving force by which the airborne pollutants exert their toxicity in lungs and cause respiratory diseases. Most airborne pollutants are associated with intrinsic oxidative potential and, additionally, stimulate endogenous production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). Elevated ROS and RNS in lungs modulate redox signals and cause irreversible damage to critical biomolecules (lipids, proteins and DNA) and initiate various pathogenic cellular process. This chapter provides an insight into oxidative stress-linked pathogenic cellular process such as lipid peroxidation, inflammation, cell death, mitochondrial dysfunction, endoplasmic reticulum stress, epigenetic changes, profibrotic signals and mucus hypersecretion, which drive the development and progression of lung diseases. Lungs are associated with robust enzymatic and non-enzymatic (GSH, ascorbic acid, uric acid, vitamin E) antioxidant defences. However, sustained production of free radicals due to continuous exposures to airborne pollutants overwhelms lung antioxidant defences and causes oxidative injury. Preclinical studies have demonstrated the critical roles and therapeutic potential of upregulating lung antioxidants for intervention of respiratory diseases; however, so far clinical benefits in antioxidant supplementation trials have been minimal and conflicting. Antioxidants alone may not be effective in treatment of respiratory diseases; however it could be a promising adjunctive therapy.

Mitochondrial biology in airway pathogenesis and the role of NRF2

A constant improvement in understanding of mitochondrial biology has provided new insights into mitochondrial dysfunction in human disease pathogenesis. Impaired mitochondrial dynamics caused by various stressors are characterized by structural abnormalities and leakage, compromised turnover, and reactive oxygen species overproduction in mitochondria as well as increased mitochondrial DNA mutation frequency, which leads to modified energy production and mitochondria-derived cell signaling. The mitochondrial dysfunction in airway epithelial, smooth muscle, and endothelial cells has been implicated in diseases including chronic obstructive lung diseases and acute lung injury. Increasing evidence indicates that the NRF2-antioxidant response element (ARE) pathway not only enhances redox defense but also facilitates mitochondrial homeostasis and bioenergetics. Identification of functional or potential AREs further supports the role for Nrf2 in mitochondrial dysfunction-associated airway disorders. While clinical reports indicate mixed efficacy, NRF2 agonists acting on respiratory mitochondrial dynamics are potentially beneficial. In lung cancer, growth advantage provided by sustained NRF2 activation is suggested to be through increased cellular antioxidant defense as well as mitochondria reinforcement and metabolic reprogramming to the preferred pathways to meet the increased energy demands of uncontrolled cell proliferation. Further studies are warranted to better understand NRF2 regulation of mitochondrial functions as therapeutic targets in airway disorders.

Role of glutathione peroxidase 1 in glucose and lipid metabolism-related diseases

Glutathione peroxidase 1 (GPX1) is a selenium-dependent enzyme that reduces intracellular hydrogen peroxide and lipid peroxides. While past research explored regulations of gene expression and biochemical function of this selenoperoxidase, GPX1 has recently been implicated in the onset and development of chronic diseases. Clinical data have shown associations of human GPX1 gene variants with elevated risks of diabetes. Knockout and overexpression of Gpx1 in mice may induce types 1 and 2 diabetes-like phenotypes, respectively. This review assembles the latest advances in this new field of selenium biology, and attempts to postulate signal and molecular mechanisms mediating the role of GPX1 in glucose and lipid metabolism-related diseases. Potential therapies by harnessing the beneficial effects of this ubiquitous redox-modulating enzyme are briefly discussed.

Oxidative stress in chronic lung disease: From mitochondrial dysfunction to dysregulated redox signaling

The lung is a delicate organ with a large surface area that is continuously exposed to the external environment, and is therefore highly vulnerable to exogenous sources of oxidative stress. In addition, each of its approximately 40 cell types can also generate reactive oxygen species (ROS), as byproducts of cellular metabolism and in a more regulated manner by NOX enzymes with functions in host defense, immune regulation, and cell proliferation or differentiation. To effectively regulate the biological actions of exogenous and endogenous ROS, various enzymatic and non-enzymatic antioxidant defense systems are present in all lung cell types to provide adequate protection against their injurious effects and to allow for appropriate ROS-mediated biological signaling. Acute and chronic lung diseases are commonly thought to be associated with increased oxidative stress, evidenced by altered cellular or extracellular redox status, increased irreversible oxidative modifications in proteins or DNA, mitochondrial dysfunction, and altered expression or activity of NOX enzymes and antioxidant enzyme systems. However, supplementation strategies with generic antioxidants have been minimally successful in prevention or treatment of lung disease, most likely due to their inability to distinguish between harmful and beneficial actions of ROS. Recent studies have attempted to identify specific redox-based mechanisms that may mediate chronic lung disease, such as allergic asthma or pulmonary fibrosis, which provide opportunities for selective redox-based therapeutic strategies that may be useful in treatment of these diseases.

Selenium-Dependent Glutathione Peroxidases During Tumor Development

Five out of eight human glutathione peroxidases (GPxes) are selenoproteins and thus their expression depends on the selenium (Se) supply. Most Se-dependent GPxes are downregulated in tumor cells, while only GPx2 is considerably upregulated. Whether expression profiles of GPxes predict tumor development and patient survival is controversially discussed. Also, results from in vitro and in vivo studies modulating the expression of GPx isoforms provide evidence for both anti- and procarcinogenic mechanisms. GPxes are able to reduce hydroperoxides, which otherwise would damage DNA, possibly resulting in DNA mutations, modulate redox-sensitive signaling pathways affecting proliferation, differentiation, and cellular metabolism or initiate cell death. Considering these different processes, the role and functions of individual Se-dependent GPx isoforms will be discussed herein in the context of tumorigenesis.

Parasites, nutrition, immune responses and biology of metabolic tissues

Nutritional immunology, immunometabolism and identification of novel immunotherapeutic targets are areas of active investigation in parasitology. There is a well-documented crosstalk among immune cells and cells in metabolically active tissues that is important for homeostasis. The numbers and function of these cells are altered by obesity leading to inflammation. A variety of helminths spend some part of their life cycle in the gastrointestinal tract and even entirely enteral nematode infections exert beneficial effects on glucose and lipid metabolism. The foundation of this review is the ability of enteric nematode infections to improve obesity-induced type 2 diabetes and the metabolic syndrome, which are significant health issues in developed areas. It considers the impact of nutrition and specific nutritional deficiencies, which are occur in both undeveloped and developed areas, on the host's ability mount a protective immune response against parasitic nematodes. There are a number of proposed mechanisms by which parasitic nematodes can impact metabolism including effects gastrointestinal hormones, altering epithelial function and changing the number and/or phenotype of immune cells in metabolic tissues. Nematodes can also exert their beneficial effects through Th2 cytokines that activate the transcription factor STAT6, which upregulates genes that regulate glucose and lipid metabolism.

Investigation of anti-asthmatic potential of dried fruits of Vitis vinifera L. in animal model of bronchial asthma

Background

Fruits of Vitis vinifera L., commonly known as grapes, are largely consumed worldwide because of their high nutritional and medicinal benefits.

Context and purpose

The present study investigated effects of V. vinifera fruits in ovalbumin-induced animal model of bronchial asthma.

Methods

Male wistar rats (except group 1) were sensitized with allergen (ovalbumin, 40 mg/rat + aluminum hydroxide, 2 mg/rat). Groups of sensitized animals were treated orally with either vehicle (0.4 mL/kg), standard dexamethasone (2.5 mg/kg) or alcoholic extract of V. vinifera dried fruits (31 and 42.5 mg/kg) from day 1 to 28 (n = 6 for all groups). Inflammatory markers including cell counts, cytokines such as interleukin (IL)-4, IL-5, IL-1β, tumor necrosis factor, immunoglobulin E (IgE), leukotrienes and nitrite levels in both blood/serum and bronchoalveolar fluid were analysed. Breathing rate and tidal volume as lung function parameters were examined by spirometer. Lung tissues were studied for histamine content and histopathology.

Results

Treatment of sensitized animals with dexamethasone or two doses of V. vinifera fruits extract inhibited recruitment of inflammatory cytokines, IgE, nitrites and circulating cells particularly eosinophils in blood/serum and bronchoalveolar fluid (p < 0.001, p < 0.01 and p < 0.05). Dexamethasone and V. vinifera fruits extract treatment also normalized lung functions and histamine levels compared to ovalbumin-sensitized controls (p < 0.05 and p < 0.01). Moreover, both drugs exhibited protection against airway inflammation in lung histology.

Conclusion

Results of study demonstrate the effectiveness of V. vinifera fruits in allergic asthma possibly related to its ability to inhibit cellular response and subsequent production of inflammatory cytokines.

Electronic supplementary material

The online version of this article (doi:10.1186/s13223-016-0145-x) contains supplementary material, which is available to authorized users.

Structure, function and disease relevance of Omega-class glutathione transferases

The Omega-class cytosolic glutathione transferases (GSTs) have distinct structural and functional attributes that allow them to perform novel roles unrelated to the functions of other GSTs. Mammalian GSTO1-1 has been found to play a previously unappreciated role in the glutathionylation cycle that is emerging as significant mechanism regulating protein function. GSTO1-1-catalyzed glutathionylation or deglutathionylation of a key signaling protein may explain the requirement for catalytically active GSTO1-1 in LPS-stimulated pro-inflammatory signaling through the TLR4 receptor. The observation that ML175 a specific GSTO1-1 inhibitor can block LPS-stimulated inflammatory signaling has opened a new avenue for the development of novel anti-inflammatory drugs that could be useful in the treatment of toxic shock and other inflammatory disorders. The role of GSTO2-2 remains unclear. As a dehydroascorbate reductase, it could contribute to the maintenance of cellular redox balance and it is interesting to note that the GSTO2 N142D polymorphism has been associated with multiple diseases including Alzheimer's disease, Parkinson's disease, familial amyotrophic lateral sclerosis, chronic obstructive pulmonary disease, age-related cataract and breast cancer.

Thiol redox chemistry: role of protein cysteine oxidation and altered redox homeostasis in allergic inflammation and asthma

Asthma is a pulmonary disorder, with an estimated 300 million people affected worldwide. While it is thought that endogenous reactive oxygen species (ROS) and reactive nitrogen species (RNS) such as hydrogen peroxide and nitric oxide, are important mediators of natural physiological processes, inflammatory cells recruited to the asthmatic airways have an exceptional capacity for producing a variety of highly reactive ROS and RNS believed to contribute to tissue damage and chronic airways inflammation. Antioxidant defense systems form a tightly regulated network that maintains the redox environment of the intra- as well as extracellular environment. Evidence for an oxidant-antioxidant imbalance in asthmatic airways is demonstrated in a number of studies, revealing decreased total antioxidant capacity as well as lower levels of individual antioxidants. Thiols in the form of GSH and sulfhydryl groups of proteins are among the most susceptible oxidant-sensitive targets, and hence, studies investigating protein thiol redox modifications in biology and disease have emerged. This perspective offers an overview of the combined efforts aimed at the elucidation of mechanisms whereby cysteine oxidations contribute to chronic inflammation and asthma, as well as insights into potential cysteine thiol-based therapeutic strategies.

Plant glutathione peroxidases: emerging role of the antioxidant enzymes in plant development and stress responses

The plant glutathione peroxidase (GPX) family consists of multiple isoenzymes with distinct subcellular locations which exhibit different tissue-specific expression patterns and environmental stress responses. Contrary to most of their counterparts in animal cells, plant GPXs contain cysteine instead of selenocysteine in their active site and while some of them have both glutathione peroxidase and thioredoxin peroxidase functions, the thioredoxin regenerating system is much more efficient in vitro than the glutathione system. At present, the function of these enzymes in plants is not completely understood. The occurrence of thiol-dependent activities of plant GPX isoenzymes suggests that - besides detoxification of H2O2 and organic hydroperoxides - they may be involved in regulation of the cellular redox homeostasis by maintaining the thiol/disulfide or NADPH/NADP(+) balance. GPXs may represent a link existing between the glutathione- and the thioredoxin-based system. The various thiol buffers, including Trx, can affect a number of redox reactions in the cells most probably via modulation of thiol status. It is still required to identify the in vivo reductant for particular GPX isoenzymes and partners that GPXs interact with specifically. Recent evidence suggests that plant GPXs does not only protect cells from stress induced oxidative damage but they can be implicated in plant growth and development. Following a more general introduction, this study summarizes present knowledge on plant GPXs, highlighting the results on gene expression analysis, regulation and signaling of Arabidopsis thaliana GPXs and also suggests some perspectives for future research.

Expression microarray as a tool to identify differentially expressed genes in horses suffering from inflammatory airway disease

BACKGROUND

Inflammatory airway disease (IAD) affects performance and well-being of horses. Diagnosis is primarily reached by bronchoalveolar lavage (BAL) cytology which is invasive and requires sedation.

OBJECTIVES

The purpose of this study was to identify differential gene expression in peripheral blood of horses with IAD using species-specific expression microarrays.

METHODS

Equine gene expression microarrays were used to investigate global mRNA expression in circulating leukocytes from healthy, IAD-affected, and low-performing Standardbred and endurance horses.

RESULTS

Nine genes in Standardbred and 61 genes in endurance horses were significantly differentially regulated (P < .001). These genes were related to inflammation (eg, ALOX15B, PLA2G12B, and PENK), oxidant/antioxidant balance (eg, DUOXA2 and GSTO1-1), and stress (eg, V1aR, GRLF1, Homer-2, and MAOB). All these genes were up-regulated, except down-regulated Homer-2 and MAOB. DUOXA2, ALOX15B, PLA2G12B, MAOB, and GRLF1 expression was further validated by RT-qPCR. An increase in glutathione peroxidase (GPx) activity in heparinized whole blood of IAD-affected Standardbred (P = .0025) and endurance horses (P = .0028) also suggests a deregulation of the oxidant/antioxidant balance. There was good correlation (r = .7354) between BAL neutrophil percentage and whole blood GPx activity in all horses.

CONCLUSIONS

This study showed that circulating blood cell gene expression reflects inflammatory responses in tissues. Whether any of the genes have potential for diagnostic applications in the future remains to be investigated. Although not specific for IAD, whole blood GPx activity appears to be correlated with BAL neutrophil percentage. This finding should be further assessed by testing a larger number of horses.

Glutathione peroxidases

BACKGROUND

With increasing evidence that hydroperoxides are not only toxic but rather exert essential physiological functions, also hydroperoxide removing enzymes have to be re-viewed. In mammals, the peroxidases inter alia comprise the 8 glutathione peroxidases (GPx1-GPx8) so far identified.

SCOPE OF THE REVIEW

Since GPxs have recently been reviewed under various aspects, we here focus on novel findings considering their diverse physiological roles exceeding an antioxidant activity.

MAJOR CONCLUSIONS

GPxs are involved in balancing the H2O2 homeostasis in signalling cascades, e.g. in the insulin signalling pathway by GPx1; GPx2 plays a dual role in carcinogenesis depending on the mode of initiation and cancer stage; GPx3 is membrane associated possibly explaining a peroxidatic function despite low plasma concentrations of GSH; GPx4 has novel roles in the regulation of apoptosis and, together with GPx5, in male fertility. Functions of GPx6 are still unknown, and the proposed involvement of GPx7 and GPx8 in protein folding awaits elucidation.

GENERAL SIGNIFICANCE

Collectively, selenium-containing GPxs (GPx1-4 and 6) as well as their non-selenium congeners (GPx5, 7 and 8) became key players in important biological contexts far beyond the detoxification of hydroperoxides. This article is part of a Special Issue entitled Cellular functions of glutathione.

Sex-specific perinatal expression of glutathione peroxidases during mouse lung development

Reports indicate that antioxidant enzymes like the glutathione peroxidases (GPx) can be regulated by sex steroids. The GPx, a major class of antioxidants involved in H(2)O(2) and lipid hydroperoxides neutralization, showed an age- and sex-specific expression in many adult organs including the lung. High levels of androgens in the male lung are known to delay the surge of surfactant synthesis during gestation in several species. However, the impact of male androgens on antioxidant GPx early in life remains to be determined. The objective was to study the lung sex-specific expression of GPx during BALB/c mouse perinatal development. The mRNA expression of four seleno-dependent Gpx (Gpx1 to 4) in the lung of both sexes was characterized by real-time PCR from gestational day 15 to postnatal day 30, covering the entire canalicular, saccular and alveolar stages. Immunohistochemistry of GPx-1, -3 and -4, and seleno-dependent GPx enzymatic assays were also performed in the lung. We found a transient lower Gpx1 mRNA level in male than in female lungs during the first 5 days after birth, corresponding to the saccular phase. This dimorphic expression was concomitant to a sex difference in GPx enzymatic activity corrected for blood. It is, to our knowledge, the first report of a sex dimorphism for murine lung enzymatic antioxidant defenses during the perinatal period.

The role of selenium in inflammation and immunity: from molecular mechanisms to therapeutic opportunities

Dietary selenium (]Se), mainly through its incorporation into selenoproteins, plays an important role in inflammation and immunity. Adequate levels of Se are important for initiating immunity, but they are also involved in regulating excessive immune responses and chronic inflammation. Evidence has emerged regarding roles for individual selenoproteins in regulating inflammation and immunity, and this has provided important insight into mechanisms by which Se influences these processes. Se deficiency has long been recognized to negatively impact immune cells during activation, differentiation, and proliferation. This is related to increased oxidative stress, but additional functions such as protein folding and calcium flux may also be impaired in immune cells under Se deficient conditions. Supplementing diets with above-adequate levels of Se can also impinge on immune cell function, with some types of inflammation and immunity particularly affected and sexually dimorphic effects of Se levels in some cases. In this comprehensive article, the roles of Se and individual selenoproteins in regulating immune cell signaling and function are discussed. Particular emphasis is given to how Se and selenoproteins are linked to redox signaling, oxidative burst, calcium flux, and the subsequent effector functions of immune cells. Data obtained from cell culture and animal models are reviewed and compared with those involving human physiology and pathophysiology, including the effects of Se levels on inflammatory or immune-related diseases including anti-viral immunity, autoimmunity, sepsis, allergic asthma, and chronic inflammatory disorders. Finally, the benefits and potential adverse effects of intervention with Se supplementation for various inflammatory or immune disorders are discussed.

Mouse Models of Oxidative Stress Indicate a Role for Modulating Healthy Aging

Aging is a complex process that affects every major system at the molecular, cellular and organ levels. Although the exact cause of aging is unknown, there is significant evidence that oxidative stress plays a major role in the aging process. The basis of the oxidative stress hypothesis is that aging occurs as a result of an imbalance between oxidants and antioxidants, which leads to the accrual of damaged proteins, lipids and DNA macromolecules with age. Age-dependent increases in protein oxidation and aggregates, lipofuscin, and DNA mutations contribute to age-related pathologies. Many transgenic/knockout mouse models over expressing or deficient in key antioxidant enzymes have been generated to examine the effect of oxidative stress on aging and age-related diseases. Based on currently reported lifespan studies using mice with altered antioxidant defense, there is little evidence that oxidative stress plays a role in determining lifespan. However, mice deficient in antioxidant enzymes are often more susceptible to age-related disease while mice overexpressing antioxidant enzymes often have an increase in the amount of time spent without disease, i.e., healthspan. Thus, by understanding the mechanisms that affect healthy aging, we may discover potential therapeutic targets to extend human healthspan.

Selenium, selenoproteins and the thyroid gland: interactions in health and disease

The trace element selenium is an essential micronutrient that is required for the biosynthesis of selenocysteine-containing selenoproteins. Most of the known selenoproteins are expressed in the thyroid gland, including some with still unknown functions. Among the well-characterized selenoproteins are the iodothyronine deiodinases, glutathione peroxidases and thioredoxin reductases, enzymes involved in thyroid hormone metabolism, regulation of redox state and protection from oxidative damage. Selenium content in selenium-sensitive tissues such as the liver, kidney or muscle and expression of nonessential selenoproteins, such as the glutathione peroxidases GPx1 and GPx3, is controlled by nutritional supply. The thyroid gland is, however, largely independent from dietary selenium intake and thyroid selenoproteins are preferentially expressed. As a consequence, no explicit effects on thyroid hormone profiles are observed in healthy individuals undergoing selenium supplementation. However, low selenium status correlates with risk of goiter and multiple nodules in European women. Some clinical studies have demonstrated that selenium-deficient patients with autoimmune thyroid disease benefit from selenium supplementation, although the data are conflicting and many parameters must still be defined. The baseline selenium status of an individual could constitute the most important parameter modifying the outcome of selenium supplementation, which might primarily disrupt self-amplifying cycles of the endocrine-immune system interface rectifying the interaction of lymphocytes with thyroid autoantigens. Selenium deficiency is likely to constitute a risk factor for a feedforward derangement of the immune system-thyroid interaction, while selenium supplementation appears to dampen the self-amplifying nature of this derailed interaction.

Selenium and asthma

Se is a potent nutritional antioxidant important for various aspects of human health. Because asthma has been demonstrated to involve increased oxidative stress, levels of Se intake have been hypothesized to play an important role in the pathogenesis of asthma. However, significant associations between Se status and prevalence or severity of asthma have not been consistently demonstrated in human studies. This highlights both the complex etiology of human asthma and the inherent problems with correlative nutritional studies. In this review, the different findings in human studies are discussed along with results from limited intervention studies. Mouse models of asthma have provided more definitive results suggesting that the benefits of Se supplementation may depend on an individual's initial Se status. This likely involves T helper cell differentiation and the mechanistic studies that have provided important insight into the effects of Se levels on immune cell function are summarized. Importantly, the benefits and adverse effects of Se supplementation must both be considered in using this nutritional supplement for treating asthma. With this in mind new approaches are discussed that may provide more safe and effective means for using Se supplementation for asthma or other disorders involving inflammation or immunity.

Adaptive dysfunction of selenoproteins from the perspective of the triage theory: why modest selenium deficiency may increase risk of diseases of aging

The triage theory proposes that modest deficiency of any vitamin or mineral (V/M) could increase age-related diseases. V/M-dependent proteins required for short-term survival and/or reproduction (i.e., "essential") are predicted to be protected on V/M deficiency over other "nonessential" V/M-dependent proteins needed only for long-term health. The result is accumulation of insidious damage, increasing disease risk. We successfully tested the theory against published evidence on vitamin K. Here, we review about half of the 25 known mammalian selenoproteins; all of those with mouse knockout or human mutant phenotypes that could be used as criteria for a classification of essential or nonessential. Five selenoproteins (Gpx4, Txnrd1, Txnrd2, Dio3, and Sepp1) were classified as essential and 7 (Gpx1, Gpx 2, Gpx 3, Dio1, Dio2, Msrb1, and SelN) nonessential. On modest selenium (Se) deficiency, nonessential selenoprotein activities and concentrations are preferentially lost, with one exception (Dio1 in the thyroid, which we predict is conditionally essential). Mechanisms include the requirement of a special form of tRNA sensitive to Se deficiency for translation of nonessential selenoprotein mRNAs except Dio1. The same set of age-related diseases and conditions, including cancer, heart disease, and immune dysfunction, are prospectively associated with modest Se deficiency and also with genetic dysfunction of nonessential selenoproteins, suggesting that Se deficiency could be a causal factor, a possibility strengthened by mechanistic evidence. Modest Se deficiency is common in many parts of the world; optimal intake could prevent future disease.

Mitochondrial Dysfunction and Oxidative Stress in Asthma: Implications for Mitochondria-Targeted Antioxidant Therapeutics

Asthma is a complex, inflammatory disorder characterized by airflow obstruction of variable degrees, bronchial hyper-responsiveness, and airway inflammation. Asthma is caused by environmental factors and a combination of genetic and environmental stimuli. Genetic studies have revealed that multiple loci are involved in the etiology of asthma. Recent cellular, molecular, and animal-model studies have revealed several cellular events that are involved in the progression of asthma, including: increased Th2 cytokines leading to the recruitment of inflammatory cells to the airway, and an increase in the production of reactive oxygen species and mitochondrial dysfunction in the activated inflammatory cells, leading to tissue injury in the bronchial epithelium. Further, aging and animal model studies have revealed that mitochondrial dysfunction and oxidative stress are involved and play a large role in asthma. Recent studies using experimental allergic asthmatic mouse models and peripheral cells and tissues from asthmatic humans have revealed antioxidants as promising treatments for people with asthma. This article summarizes the latest research findings on the involvement of inflammatory changes, and mitochondrial dysfunction/oxidative stress in the development and progression of asthma. This article also addresses the relationship between aging and age-related immunity in triggering asthma, the antioxidant therapeutic strategies in treating people with asthma.

Glutathione biochemistry in asthma

BACKGROUND

Oxidative stress in an important hallmark of asthma and much research has therefore focused on the predominant antioxidant in the lungs, namely the tripeptide glutathione.

MAJOR CONCLUSIONS

In lung samples of patients with asthma increased levels of glutathione are typically observed, which appear to relate to the level of pulmonary inflammation and are therefore regarded as an adaptive response to the associated oxidative stress. Also in blood samples increased total GSH levels have been reported, representing the systemic inflammatory component of the disease. In addition, a number of the antioxidant enzymes involved in the maintenance of the GSH/GSSG ratio as well as enzymes that utilize GSH have been found to be altered in the lungs and blood of asthmatics and will be summarized in this review. Very few studies have however linked enzymatic alterations to GSH levels or found that either of these correlated with disease severity. Some animal studies have started to investigate the pathophysiological role of GSH biochemistry in asthma and have yielded surprising results. Important in this respect is the physiological role of the GSH redox equilibrium in determining the outcome of immune responses, which could be deregulated in asthmatics and contribute to the disease.

SCOPE OF REVIEW

Clinical data as well as animal and cell culture studies regarding these aspects of GSH in the context of asthma will be summarized and discussed in this review. This article is part of a Special Issue entitled: Biochemistry of Asthma.