Oxidative stress as a crucial factor in liver diseases

Redox state constitutes an important background of numerous liver disorders. The redox state participates in the course of inflammatory, metabolic and proliferative liver diseases. Reactive oxygen species (ROS) are primarily produced in the mitochondria and in the endoplasmic reticulum of hepatocytes via the cytochrome P450 enzymes. Under the proper conditions, cells are equipped with special molecular strategies that control the level of oxidative stress and maintain a balance between oxidant and antioxidant particles. Oxidative stress represents an imbalance between oxidant and antioxidant agents. Hepatocytic proteins, lipids and DNA are among the cellular structures that are primarily affected by ROS and reactive nitrogen species. The process results in structural and functional abnormalities in the liver. Thus, the phenomenon of oxidative stress should be investigated for several reasons. First, it may explain the pathogenesis of various liver disorders. Moreover, monitoring oxidative markers among hepatocytes offers the potential to diagnose the degree of liver damage and ultimately to observe the response to pharmacological therapies. The present report focuses on the role of oxidative stress in selected liver diseases.

Hypertension and physical exercise: The role of oxidative stress

Oxidative stress is associated with the pathogenesis of hypertension. Decreased bioavailability of nitric oxide (NO) is one of the mechanisms involved in the pathogenesis. It has been suggested that physical exercise could be a potential non-pharmacological strategy in treatment of hypertension because of its beneficial effects on oxidative stress and endothelial function. The aim of this review is to investigate the effect of oxidative stress in relation to hypertension and physical exercise, including the role of NO in the pathogenesis of hypertension. Endothelial dysfunction and decreased NO levels have been found to have the adverse effects in the correlation between oxidative stress and hypertension. Most of the previous studies found that aerobic exercise significantly decreased blood pressure and oxidative stress in hypertensive subjects, but the intense aerobic exercise can also injure endothelial cells. Isometric exercise decreases normally only systolic blood pressure. An alternative exercise, Tai chi significantly decreases blood pressure and oxidative stress in normotensive elderly, but the effect in hypertensive subjects has not yet been studied. Physical exercise and especially aerobic training can be suggested as an effective intervention in the prevention and treatment of hypertension and cardiovascular disease via reduction in oxidative stress.

Caloric restriction and the aging process: a critique

The main objective of this review is to provide an appraisal of the current status of the relationship between energy intake and the life span of animals. The concept that a reduction in food intake, or caloric restriction (CR), retards the aging process, delays the age-associated decline in physiological fitness, and extends the life span of organisms of diverse phylogenetic groups is one of the leading paradigms in gerontology. However, emerging evidence disputes some of the primary tenets of this conception. One disparity is that the CR-related increase in longevity is not universal and may not even be shared among different strains of the same species. A further misgiving is that the control animals, fed ad libitum (AL), become overweight and prone to early onset of diseases and death, and thus may not be the ideal control animals for studies concerned with comparisons of longevity. Reexamination of body weight and longevity data from a study involving over 60,000 mice and rats, conducted by a National Institute on Aging-sponsored project, suggests that CR-related increase in life span of specific genotypes is directly related to the gain in body weight under the AL feeding regimen. Additionally, CR in mammals and "dietary restriction" in organisms such as Drosophila are dissimilar phenomena, albeit they are often presented to be the very same. The latter involves a reduction in yeast rather than caloric intake, which is inconsistent with the notion of a common, conserved mechanism of CR action in different species. Although specific mechanisms by which CR affects longevity are not well understood, existing evidence supports the view that CR increases the life span of those particular genotypes that develop energy imbalance owing to AL feeding. In such groups, CR lowers body temperature, rate of metabolism, and oxidant production and retards the age-related pro-oxidizing shift in the redox state.

Procyanidin B2 ameliorates free fatty acids-induced hepatic steatosis through regulating TFEB-mediated lysosomal pathway and redox state

Procyanidin B2, a naturally occurring phenolic compound, has been reported to exert multiple beneficial functions. However, the effect of procyanidin B2 on free fatty acids (FFAs)-induced hepatic steatosis remains obscure. The present study is therefore aimed to elucidate the protective effect of procyanidin B2 against hepatic steatosis and its underlying mechanism. Herein, we reported that procyanidin B2 attenuated FFAs-induced lipid accumulation and its associated oxidative stress by scavenging excessive ROS and superoxide anion radicals, blocking loss of mitochondrial membrane potential, restoring glutathione content, and increasing activity of antioxidant enzymes (GPx, SOD and CAT) in hepatocytes. Procyanidin B2 mechanistically promoted lipid degradation via modulation of transcription factor EB (TFEB), a master regulator of lysosomal pathway. Molecular docking analysis indicated a possible ligand-binding position of procyanidin B2 with TFEB. In addition, administration of procyanidin B2 resulted in a significant reduction of hepatic fat accumulation in high-fat diet (HFD)-induced obese mice, and also ameliorated HFD-induced metabolic abnormalities, including hyperlipidemia and hyperglycemia. It was confirmed that procyanidin B2 prevented HFD-induced hepatic fat accumulation through down-regulating lipogenesis-related gene expressions (PPARγ, C/EBPα and SREBP-1c), inhibiting pro-inflammatory cytokines production (IL-6 and TNF-α) and increasing antioxidant enzymes activity (GPx, SOD and CAT). Moreover, hepatic fatty acids analysis indicated that procyanidin B2 caused a significant increase in the levels of palmitic acid, oleic acid and linoleic acid. Intriguingly, procyanidin B2 restored the decreased nuclear TFEB expression in HFD-induced liver steatosis and up-regulated its target genes involved in lysosomal pathway (Lamp1, Mcoln, Uvrag), which suggested a previously unrecognized mechanism of procyanidin B2 on ameliorating HFD-induced hepatic steatosis. Taken together, our results demonstrated that procyanidin B2 attenuated FFAs-induced hepatic steatosis through regulating TFEB-mediated lysosomal pathway and redox state, which had important implications that modulation of TFEB might be a potential therapeutic strategy for hepatic steatosis and procyanidin B2 could represent a promising novel agent in the prevention and treatment of non-alcoholic fatty liver disease (NAFLD).

The redox state of the alarmin HMGB1 is a pivotal factor in neuroinflammatory and microglial priming: A role for the NLRP3 inflammasome

The alarmin high mobility group box-1 (HMGB1) has been implicated as a key factor mediating neuroinflammatory processes. Recent findings suggest that the redox state of HMGB1 is a critical molecular feature of HMGB1 such that the reduced form (fr-HMGB1) is chemotactic, while the disulfide form (ds-HMGB1) is pro-inflammatory. The present study examined the neuroinflammatory effects of these molecular forms as well as the ability of these forms to prime the neuroinflammatory and microglial response to an immune challenge. To examine the neuroinflammatory effects of these molecular forms in vivo, animals were administered intra-cisterna magna (ICM) a single dose of fr-HMGB1 (10μg), ds-HMGB1 (10μg) or vehicle and basal pro-inflammatory effects were measured 2 and 24h post-injection in hippocampus. Results of this initial experiment demonstrated that ds-HMGB1 increased hippocampal pro-inflammatory mediators at 2h (NF-κBIα mRNA, NLRP3 mRNA and IL-1β protein) and 24h (NF-κBIα mRNA, TNFα mRNA, and NLRP3 protein) after injection. fr-HMGB1 had no effect on these mediators. These neuroinflammatory effects of ds-HMGB1 suggested that ds-HMGB1 may function to prime the neuroinflammatory response to a subsequent immune challenge. To assess the neuroinflammatory priming effects of these molecular forms, animals were administered ICM a single dose of fr-HMGB1 (10μg), ds-HMGB1 (10μg) or vehicle and 24h after injection, animals were challenged with LPS (10μg/kg IP) or vehicle. Neuroinflammatory mediators and the sickness response (3, 8 and 24h after injection) were measured 2h after immune challenge. We found that ds-HMGB1 potentiated the neuroinflammatory (NF-κBIα mRNA, TNFα mRNA, IL-1β mRNA, IL-6 mRNA, NLRP3 mRNA and IL-1β protein) and sickness response (reduced social exploration) to LPS challenge. fr-HMGB1 failed to potentiate the neuroinflammatory response to LPS. To examine whether these molecular forms of HMGB1 directly induce neuroinflammatory effects in isolated microglia, whole brain microglia were isolated and treated with fr-HMGB1 (0, 1, 10, 100, or 1000ng/ml) or ds-HMGB1 (0, 1, 10, 100, or 1000ng/ml) for 4h and pro-inflammatory mediators measured. To assess the effects of these molecular forms on microglia priming, whole brain microglia were pre-exposed to these forms of HMGB1 (0, 1, 10, 100, or 1000ng/ml) and subsequently challenged with LPS (10ng/ml). We found that ds-HMGB1 increased expression of NF-κBIα mRNA and NLRP3 mRNA in isolated microglia, and potentiated the microglial pro-inflammatory response (TNFα mRNA, IL-1β mRNA and IL-1β protein) to LPS. fr-HMGB1 failed to potentiate the microglial pro-inflammatory response to LPS. Consistent with prior reports, the present findings demonstrate that the disulfide form of HMGB1 not only potentiates the neuroinflammatory response to a subsequent immune challenge in vivo, but also potentiates the sickness response to that challenge. Moreover, the present findings demonstrate for the first time that ds-HMGB1 directly potentiates the microglia pro-inflammatory response to an immune challenge, a finding that parallels the effects of ds-HMGB1 in vivo. In addition, ds-HMGB1 induced expression of NLRP3 and NF-κBIα in vivo and in vitro suggesting that the NLRP3 inflammasome may play role in the priming effects of ds-HMGB1. Taken together, the present results suggest that the redox state of HMGB1 is a critical determinant of the priming properties of HMGB1 such that the disulfide form of HMGB1 induces a primed immunophenotype in the CNS, which may result in an exacerbated neuroinflammatory response upon exposure to a subsequent pro-inflammatory stimulus.

Redox dynamics of manganese as a mitochondrial life-death switch

Sten Orrenius, M.D., Ph.D., pioneered many areas of cellular and molecular toxicology and made seminal contributions to our knowledge of oxidative stress and glutathione (GSH) metabolism, organellar functions and Ca+2-dependent mechanisms of cell death, and mechanisms of apoptosis. On the occasion of his 80th birthday, we summarize current knowledge on redox biology of manganese (Mn) and its role in mechanisms of cell death. Mn is found in all organisms and has critical roles in cell survival and death mechanisms by regulating Mn-containing enzymes such as manganese superoxide dismutase (SOD2) or affecting expression and activity of caspases. Occupational exposures to Mn cause "manganism", a Parkinson's disease-like condition of neurotoxicity, and experimental studies show that Mn exposure leads to accumulation of Mn in the brain, especially in mitochondria, and neuronal cell death occurs with features of an apoptotic mechanism. Interesting questions are why a ubiquitous metal that is essential for mitochondrial function would accumulate to excessive levels, cause increased H2O2 production and lead to cell death. Is this due to the interactions of Mn with other essential metals, such as iron, or with toxic metals, such as cadmium? Why is the Mn loading in the human brain so variable, and why is there such a narrow window between dietary adequacy and toxicity? Are non-neuronal tissues similarly vulnerable to insufficiency and excess, yet not characterized? We conclude that Mn is an important component of the redox interface between an organism and its environment and warrants detailed studies to understand the role of Mn as a mitochondrial life-death switch.

Inhibition of extracellular HMGB1 attenuates hyperoxia-induced inflammatory acute lung injury

Prolonged exposure to hyperoxia results in acute lung injury (ALI), accompanied by a significant elevation in the levels of proinflammatory cytokines and leukocyte infiltration in the lungs. However, the mechanisms underlying hyperoxia-induced proinflammatory ALI remain to be elucidated. In this study, we investigated the role of the proinflammatory cytokine high mobility group box protein 1 (HMGB1) in hyperoxic inflammatory lung injury, using an adult mouse model. The exposure of C57BL/6 mice to ≥99% O₂ (hyperoxia) significantly increased the accumulation of HMGB1 in the bronchoalveolar lavage fluids (BALF) prior to the onset of severe inflammatory lung injury. In the airways of hyperoxic mice, HMGB1 was hyperacetylated and existed in various redox forms. Intratracheal administration of recombinant HMGB1 (rHMGB1) caused a significant increase in leukocyte infiltration into the lungs compared to animal treated with a non-specific peptide. Neutralizing anti-HMGB1 antibodies, administrated before hyperoxia significantly attenuated pulmonary edema and inflammatory responses, as indicated by decreased total protein content, wet/dry weight ratio, and numbers of leukocytes in the airways. This protection was also observed when HMGB1 inhibitors were administered after the onset of the hyperoxic exposure. The aliphatic antioxidant, ethyl pyruvate (EP), inhibited HMGB1 secretion from hyperoxic macrophages and attenuated hyperoxic lung injury. Overall, our data suggest that HMGB1 plays a critical role in mediating hyperoxic ALI through the recruitment of leukocytes into the lungs. If these results can be translated to humans, they suggest that HMGB1 inhibitors provide treatment regimens for oxidative inflammatory lung injury in patients receiving hyperoxia through mechanical ventilation.

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Exposure to hyperoxia results in accumulation of high levels of airway HMGB1 that precede inflammatory acute lung injury (ALI).

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Airway HMGB1 is critical in mediating hyperoxia-induced inflammatory ALI via recruiting leukocytes including neutrophils.

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Extracellular HMGB1-accumulated upon prolonged exposure to hyperoxia is hyperacetylated, existing in different redox states.

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Small molecule EP, administrated even after the onset of hyperoxic exposure, can mitigate hyperoxia-induced inflammatory ALI by inhibiting HMGB1 release into the extracellular milieu.

Manganese superoxide dismutase (SOD2/MnSOD)/catalase and SOD2/GPx1 ratios as biomarkers for tumor progression and metastasis in prostate, colon, and lung cancer

The role of manganese-dependent superoxide dismutase (SOD2/MnSOD) during tumor progression has been studied for several decades with controversial results. While SOD2 downregulation was initially associated with tumor initiation and was proposed as a tumor suppressor gene, recent studies have reported that SOD2 might favor tumor progression and dissemination. To our knowledge this is the first time that changes in SOD2 expression in three different types of tumors, i.e., prostate, lung, and colon cancer, are studied by analyzing both SOD2 mRNA and protein levels in a total of 246 patients' samples. In prostate samples, SOD2 protein levels were also increased, especially in middle stage tumors. In the case of colon and lung tumors both mRNA and protein SOD2 levels were increased in malignant tissues compared to those in nontumor samples. More importantly, all metastases analyzed showed increased levels of SOD2 when compared to those of normal primary tissue and healthy adjacent tissue. Together, these results suggest that a common redox imbalance in these three types of tumor occurs at intermediate stages which then might favor migration and invasion, leading to a more aggressive cancer type. Consequently, the ratios SOD2/catalase and SOD2/Gpx1 could be considered as potential markers during progression from tumor growth to metastasis.

Biochemical methods for monitoring protein thiol redox states in biological systems

Oxidative post-translational modifications of proteins resulting from events that increase cellular oxidant levels play important roles in physiological and pathophysiological processes. Evaluation of alterations to protein redox states is increasingly common place because of methodological advances that have enabled detection, quantification and identification of such changes in cells and tissues. This mini-review provides a synopsis of biochemical methods that can be utilized to monitor the array of different oxidative and electrophilic modifications that can occur to protein thiols and can be important in the regulatory or maladaptive impact oxidants can have on biological systems. Several of the methods discussed are valuable for monitoring the redox state of established redox sensing proteins such as Keap1.

Integration of metabolism and virulence in Clostridium difficile

Synthesis of the major toxin proteins of the diarrheal pathogen, Clostridium difficile, is dependent on the activity of TcdR, an initiation (sigma) factor of RNA polymerase. The synthesis of TcdR and the activation of toxin gene expression are responsive to multiple components in the bacterium's nutritional environment, such as the presence of certain sugars, amino acids, and fatty acids. This review summarizes current knowledge about the mechanisms responsible for repression of toxin synthesis when glucose or branched-chain amino acids or proline are in excess and the pathways that lead to synthesis of butyrate, an activator of toxin synthesis. The regulatory proteins implicated in these mechanisms also play key roles in modulating bacterial metabolic pathways, suggesting that C. difficile pathogenesis is intimately connected to the bacterium's metabolic state.

Different molecular weights chitosan coatings delay the senescence of postharvest nectarine fruit in relation to changes of redox state and respiratory pathway metabolism

The aim of this study is to investigate the impact of different molecular weights of chitosan treatment (LM 30 kDa; HM 120 kDa) on fruit senescence related to redox state and respiratory pathway metabolism in postharvest nectarine fruit stored at 25 °C for 8 days. The treatments of LM and HM chitosan both delayed senescence, which are due to inhibition of respiration rate, and enhanced the antioxidant system, as evidenced by the improvement of ASA-GSH cycle and total phenolics and flavonoids contents and decrease in H₂O₂ and MDA accumulation. Meanwhile, fruit treated with HM chitosan manifested better quality and redox state than LM. It is noteworthy that the results showed that HM chitosan notably suppressed the activity of SDH enzyme and increased the total activity of G-6-PDH and 6-PGDH. Accordingly, changed respiratory pathways by HM chitosan coating contributed to senescence retardation and modification of redox status in postharvest nectarine fruit.

Effect of severe environmental thermal stress on redox state in salmon

Fish are exposed to many kinds of environmental stressors and the chances of succumbing to infectious diseases may be increased a result. For example, an acute increase in temperature can induce numerous physiological changes in the body. In the present study, we examined the redox state in response to a severe acute stress resulting from heat shock in teleost coho salmon (Oncorhynchus kisutch). The plasma lipid peroxides levels in fish gradually increased after heat shock treatment. By 2.5 h post-heat stress, plasma glutathione (GSH) levels had decreased, but they had returned to basal levels by 17.5 h post-stress. Plasma superoxide dismutase activities in stressed fish were significantly increased compared with those in control fish at 17.5 h post-stress, but had returned to basal levels by 48 h post-stress. Expression levels of hepatic GSH and heat shock protein 70 gradually increased after heat shock treatment. These results concerning the changing patterns of multiple important redox-related biomarkers suggest that severe thermal stressors can affect the redox state and induce oxidative stress in ectothermal animals, such as fish, in vivo. Hence, manipulation of appropriate thermal treatment may possibly be useful to control fish fitness.

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The plasma lipid peroxides levels gradually increased after heat shock.

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The plasma glutathione levels had decreased, but they had returned to basal levels.

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The plasma superoxide dismutase activities were increased.

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The hepatic glutathione and heat shock protein 70 levels gradually increased.

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Severe thermal stressors can affect the redox state and might induce oxidative stress.

Reactive oxygen species in development and infection processes

Reactive oxygen species (ROS) are important signaling molecules that affect vegetative and pathogenic processes in pathogenic fungi. There is growing evidence that ROS are not only secreted during the interaction of host and pathogen but also involved in tightly controlled intracellular processes. The major ROS producing enzymes are NADPH oxidases (Nox). Recent investigations in fungi revealed that Nox-activity is responsible for the formation of infection structures, cytoskeleton architecture as well as interhyphal communication. However, information about the localization and site of action of the Nox complexes in fungi is limited and signaling pathways and intracellular processes affected by ROS have not been fully elucidated. This review focuses on the role of ROS as signaling molecules in fungal "model" organisms: it examines the role of ROS in vegetative and pathogenic processes and gives special attention to Nox complexes and their function as important signaling hubs.

Light acclimation in diatoms: from phenomenology to mechanisms

This review summarizes the current knowledge about light acclimation processes in diatoms. Against the background of the phenomenological description of the process in the 70s-80s, the recent progress in diatom genetics has generated new information about the underlying mechanisms. Although the general responses of diatoms to changes in the light climate are comparable to the green algal lineage, many differences in the underlying mechanisms have been observed in the last ten years, yielding clear evidence that the regulatory network in diatoms has unique traits that might explain their ecological success.

In vivo evaluation of different alterations of redox status by studying pharmacokinetics of nitroxides using magnetic resonance techniques

Free radicals, particularly reactive oxygen species (ROS), are involved in various pathologies, injuries related to radiation, ischemia-reperfusion or ageing. Unfortunately, it is virtually impossible to directly detect free radicals in vivo, but the redox status of the whole organism or particular organ can be studied in vivo by using magnetic resonance techniques (EPR and MRI) and paramagnetic stable free radicals - nitroxides. Here we review results obtained in vivo following the pharmacokinetics of nitroxides on experimental animals (and a few in humans) under various conditions. The focus was on conditions where the redox status has been altered by induced diseases or harmful agents, clearly demonstrating that various EPR/MRI/nitroxide combinations can reliably detect metabolically induced changes in the redox status of organs. These findings can improve our understanding of oxidative stress and provide a basis for studying the effectiveness of interventions aimed to modulate oxidative stress. Also, we anticipate that the in vivo EPR/MRI approach in studying the redox status can play a vital role in the clinical management of various pathologies in the years to come providing the development of adequate equipment and probes.

A novel role for endothelial tetrahydrobiopterin in mitochondrial redox balance

The redox co-factor tetrahydrobiopterin (BH4) regulates nitric oxide (NO) and reactive oxygen species (ROS) production by endothelial NOS (eNOS) and is an important redox-dependent signalling molecule in the endothelium. Loss of endothelial BH4 is observed in cardiovascular disease (CVD) states and results in decreased NO and increased superoxide (O2-) generation via eNOS uncoupling. Genetic mouse models of augmented endothelial BH4 synthesis have shown proof of concept that endothelial BH4 can alter CVD pathogenesis. However, clinical trials of BH4 therapy in vascular disease have been limited by systemic oxidation, highlighting the need to explore the wider roles of BH4 to find novel therapeutic targets. In this study, we aimed to elucidate the effects of BH4 deficiency on mitochondrial function and bioenergetics using targeted knockdown of the BH4 synthetic enzyme, GTP Cyclohydrolase I (GTPCH). Knockdown of GTPCH by >90% led to marked loss of cellular BH4 and a striking induction of O2- generation in the mitochondria of murine endothelial cells. This effect was likewise observed in BH4-depleted fibroblasts devoid of NOS, indicating a novel NOS-independent role for BH4 in mitochondrial redox signalling. Moreover, this BH4-dependent, mitochondria-derived ROS further oxidised mitochondrial BH4, concomitant with changes in the thioredoxin and glutathione antioxidant pathways. These changes were accompanied by a modest increase in mitochondrial size, mildly attenuated basal respiratory function, and marked changes in the mitochondrial proteome and cellular metabolome, including the accumulation of the TCA intermediate succinate. Taken together, these data reveal a novel NOS-independent role for BH4 in the regulation of mitochondrial redox signalling and bioenergetic metabolism.

Effect of reduced humic acid on the transport of ferrihydrite nanoparticles under anoxic conditions

Humic acid (HA) occurs ubiquitously in the subsurface environments and is well-known to play a critical role in the fate and transport of ferrihydrite nanoparticles (NPs) and NPs-associated contaminants. Under anoxic conditions, HA can readily be reduced by microorganisms or geochemical reducing species, and the mechanisms and kinetics of ferrihydrite reduction by reduced HA (HA_red) are well-documented; however, the role of these redox reactions on the transport of ferrihydrite NPs is largely underestimated. This study provides new knowledge regarding the role of HA (both reduced HA (HA_red) and oxidized HA (HA_ox)) of environmentally relevant concentrations (0-50 mg C/L) on the transport of ferrihydrite NPs in anoxic sand columns. Our findings show that, regardless of the redox state, the presence of a low concentration of HA (3 mg C/L) inhibited ferrihydrite NP's transport due to enhanced aggregation (and deposition) between positively charged ferrihydrite NPs and negatively charged HA molecules. In contrast, higher HA (both HA_red and HA_ox) concentration (≥10 mg C/L) significantly enhanced the mobility of ferrihydrite NPs, primarily due to the enhanced electrostatic and steric stabilization originating from excessively adsorbed HA molecules. Interestingly, the transport of ferrihydrite NPs is substantially lower in the presence of HA_red than in the presence of HA_ox. This distinct effect (HA_red vs. HA_ox) on the particle transport is attributed to the fact that reductive dissolution of ferrihydrite NPs occurs in the presence of HA_red (ferrihydrite dissolves and thus total breakthrough decreases), but not in the presence of HA_ox. Furthermore, the abatement extent of ferrihydrite NPs transport triggered by the presence of HA_red is dependent on dissolved HA_red concentration. Taken together, our findings provide direct, and much needed insights into the distinct roles of redox state of HA on the transport of redox-sensitive metal-bearing NPs in porous media.

H2O2 mediates ALA-induced glutathione and ascorbate accumulation in the perception and resistance to oxidative stress in Solanum lycopersicum at low temperatures

BACKGROUND

Low temperature is a crucial factor influencing plant growth and development. The chlorophyll precursor, 5-aminolevulinic acid (ALA) is widely used to improve plant cold tolerance. However, the interaction between H₂O₂ and cellular redox signaling involved in ALA-induced resistance to low temperature stress in plants remains largely unknown. Here, the roles of ALA in perceiving and regulating low temperature-induced oxidative stress in tomato plants, together with the roles of H₂O₂ and cellular redox states, were characterized.

RESULTS

Low concentrations (10-25 mg·L^- 1) of ALA enhanced low temperature-induced oxidative stress tolerance of tomato seedlings. The most effective concentration was 25 mg·L^- 1, which markedly increased the ratio of reduced glutathione and ascorbate (GSH and AsA), and enhanced the activities of superoxide dismutase, catalase, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase. Furthermore, gene expression of respiratory burst oxidase homolog1 and H₂O₂ content were upregulated with ALA treatment under normal conditions. Treatment with exogenous H₂O₂, GSH, and AsA also induced plant tolerance to oxidative stress at low temperatures, while inhibition of GSH and AsA syntheses significantly decreased H₂O₂-induced oxidative stress tolerance. Meanwhile, scavenging or inhibition of H₂O₂ production weakened, but did not eliminate, GSH- or AsA- induced tomato plant tolerance to oxidative stress at low temperatures.

CONCLUSIONS

Appropriate concentrations of ALA alleviated the low temperature-induced oxidative stress in tomato plants via an antioxidant system. The most effective concentration was 25 mg·L^- 1. The results showed that H₂O₂ induced by exogenous ALA under normal conditions is crucial and may be the initial step for perception and signaling transmission, which then improves the ratio of GSH and AsA. GSH and AsA may then interact with H₂O₂ signaling, resulting in enhanced antioxidant capacity in tomato plants at low temperatures.

Redox state of microbial extracellular polymeric substances regulates reduction of selenite to elemental selenium accompanying with enhancing microbial detoxification in aquatic environments

In nature, many microorganisms show resistance to toxic selenite by reducing selenite to non-soluble and low toxic elemental selenium. Extracellular polymeric substances (EPS), a high-molecular-weight biopolymers originated from microbial metabolism, contain many reducing groups and can induce reductive transformation of pollutants. However, the roles of EPS and its redox state in reductive detoxification or reduction removal of selenite, respectively, remain unknown yet. Herein, the reduction of selenite by different sources of EPS was investigated. Selenite was proved to be reduced by EPS and partly transformed to elemental selenium. The formed elemental selenium was mainly selenium nanoparticles confirmed by transmission electron microscopy coupled with energy dispersive spectroscopy. The redox state of EPS governed selenite reduction and elemental selenium formation, and the reduced state of EPS was in favor of selenite reduction. Dissolved oxygen concentration in water regulated EPS redox state and influenced selenite reduction. The thiols, aldehyde and phenolic groups in EPS were responsible for selenite reduction. Under selenite stress, EPS was capable of increasing cell survivability by enhancing microorganisms-mediated selenite reduction. This work revealed the previously undiscovered roles of EPS in selenite reduction and elemental selenium formation in aquatic environments and also suggested a possible crucial role of EPS in selenium biogeochemical cycle.

Determination of Reduced and Total Glutathione Content in Extremophilic Microalga Galdieria phlegrea

Glutathione is an important molecule involved in the primary and secondary metabolism of all organisms. The Glutathione redox status is an indicator of the cellular redox state. Therefore, it is important to have precise methods on hand to determine the glutathione redox status in the cell. In this protocol, we describe an improved spectrophotometric method to estimate the content of reduced (GSH) and oxidized (GSSG) forms of glutathione in the extremophilic microalga Galdieria phlegrea.

Aluminum resistance in wheat involves maintenance of leaf Ca(2+) and Mg(2+) content, decreased lipid peroxidation and Al accumulation, and low photosystem II excitation pressure

The phytotoxic aluminum species (Al(3+)) is considered as the primary factor limiting crop productivity in over 40 % of world's arable land that is acidic. We evaluated the responses of two wheat cultivars (Triticum aestivum L.) with differential Al resistance, cv. Yecora E (Al-resistant) and cv. Dio (Al-sensitive), exposed to 0, 37, 74 and 148 μM Al for 14 days in hydroponic culture at pH 4.5. With increasing Al concentration, leaf Ca(2+) and Mg(2+) content decreased, as well as the effective quantum yield of photosystem II (PSII) photochemistry (Φ PSII ), while a gradual increase in leaf membrane lipid peroxidation, Al accumulation, photoinhibition (estimated as F v /F m ), and PSII excitation pressure (1 - q p ) occurred. However, the Al-resistant cultivar with lower Al accumulation, retained larger concentrations of Ca(2+) and Mg(2+) in the leaves and kept a larger fraction of the PSII reaction centres (RCs) in an open configuration, i.e. a higher ratio of oxidized to reduced quinone A (QA), than plants of the Al-sensitive cultivar. Four times higher Al concentration in the nutrient solution was required for Al-resistant plants (148 μM Al) than for Al-sensitive (37 μM Al), in order to establish the same closed RCs. Yet, the decline in photosynthetic efficiency in the cultivar Dio was not only due to closure of PSII RCs but also to a decrease in the quantum yield of the open RCs. We suggest that Al(3+) toxicity may be mediated by nutrient deficiency and oxidative stress, and that Al-resistance of the wheat cultivar Yecora E, may be due at least partially, from the decreased Al accumulation that resulted to decreased reactive oxygen species (ROS) formation. However, under equal internal Al accumulation (exposure Al concentration: Dio 74 μM, Yecora E 148 μM) that resulted to the same oxidative stress, the reduced PSII excitation pressure and the better PSII functioning of the Al-resistant cultivar was probably due to the larger concentrations of Ca(2+) and Mg(2+) in the leaves. We propose that the different sensitivities of wheat cultivars to Al(3+) toxicity can be correlated to differences in the redox state of QA. Thus, chlorophyll fluorescence measurements can be a promising tool for rapid screening of Al resistance in wheat cultivars.

Contribution of pristine and reduced microbial extracellular polymeric substances of different sources to Cu(II) reduction

Microbial extracellular polymeric substances (EPS) significantly influence metal behavior in the environment, but the electron transfer reaction between EPS and copper that determine the speciation and fate of copper is lacking. Here, we investigated the role of EPS from Shewanella oneidensis MR-1, Bacillus subtilis, and Saccharomyces cerevisiae and its redox state in the Cu(II) reduction under anoxic conditions. Both pristine and reduced EPS mediated copper transformation from Cu(II) to Cu(I) within 10 min. The Cu(II) reduction efficiency by the reduced EPS was ten times higher than that by the pristine EPS, which could be ascribed to the varied electron transfer ability of EPS. Multiple spectroscopic results indicated that c-type cytochromes and O-/N-containing groups were effective redox moieties responsible for copper transformation. The c-type cytochromes contributed for about 80% to the overall electron flux in S. oneidensis MR-1 EPS, which was significantly higher than in B. subtilis (27%) and S. cerevisiae EPS (22%). In contrast, functional groups such as phenolic and amide, dominated Cu(II) reduction for the B. subtilis and S. cerevisiae EPS. This study emphasizes the significant contribution of microbial EPS that serve as reducing agents and electron transfer mediators for cupric reduction and cuprous formation in the natural environments.

A sensitive mass spectrometric assay for mitochondrial CoQ pool redox state in vivo

Coenzyme Q (CoQ) is an essential cofactor, primarily found in the mitochondrial inner membrane where it functions as an electron carrier in the respiratory chain, and as a lipophilic antioxidant. The redox state of the CoQ pool is the ratio of its oxidised (ubiquinone) and reduced (ubiquinol) forms, and is a key indicator of mitochondrial bioenergetic and antioxidant status. However, the role of CoQ redox state in vivo is poorly understood, because determining its value is technically challenging due to redox changes during isolation, extraction and analysis. To address these problems, we have developed a sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay that enables us to extract and analyse both the CoQ redox state and the magnitude of the CoQ pool with negligible changes to redox state from small amounts of tissue. This will enable the physiological and pathophysiological roles of the CoQ redox state to be investigated in vivo.

Cadmium as an endocrine disruptor: correlation with anterior pituitary redox and circadian clock mechanisms and prevention by melatonin

To examine the effect of a low dose of cadmium (Cd) as an endocrine disruptor, male Wistar rats received CdCl2 (5ppm Cd) in drinking water or drinking water alone. After 1 month, the rats were euthanized at one of six time intervals around the clock and the 24-h pattern of adenohypophysial prolactin (PRL) synthesis and release, lipid peroxidation, and redox enzyme and metallothionein (MT) gene expression was examined. Cd suppressed 24-h rhythmicity in expression of the PRL gene and in circulating PRL by increasing them at early photophase only, in correlation with an augmented pituitary lipid peroxidation and redox enzyme expression. CdCl2 treatment effectively disrupted the 24-h variation in expression of every pituitary parameter tested except for MT-3. In a second experiment the effect of melatonin (3μg/ml in drinking water) was assessed at early photophase, the time of maximal endocrine-disrupting effect of Cd. Melatonin treatment blunted the effect of Cd on PRL synthesis and release, decreased Cd-induced lipid peroxidation, and counteracted the effect of Cd on expression of most redox enzymes. A third experiment was performed to examine whether melatonin could counteract Cd-induced changes in the 24-h pattern of pituitary circadian clock gene expression and plasma PRL, luteinizing hormone (LH), thyrotropin (TSH), and corticosterone levels. Rats receiving CdCl2 exhibited a suppressed daily rhythm of Clock expression and a significant disruption in daily rhythms of pituitary Bmal1, Per1, Per2, Cry1, and Cry2. The coadministration of melatonin restored rhythmicity in Clock and Bmal1 expression but shifted the maxima in pituitary Per1, Cry1, and Cry2 expression to the scotophase. Melatonin also counteracted the effect of Cd on 24-h rhythmicity of circulating PRL, LH, TSH, and corticosterone. The results highlight the occurrence of a significant endocrine disruptor effect of a low dose of Cd. Generally melatonin counteracted the effects of Cd and ameliorated partially the circadian disruption caused by the pollutant.

Extracellular redox state shift: A novel approach to target prostate cancer invasion

AIM

Extracellular superoxide dismutase (ECSOD) and the cysteine/glutamate transporter (Cys)/(xCT) are tumor microenvironment (TME) redox state homeostasis regulators. Altered expression of ECSOD and xCT can lead to imbalance of the TME redox state and likely have a profound effect on cancer invasion. In the present study, we investigated whether ECSOD and xCT could be therapeutic targets for prostate cancer (PCa) invasion.

RESULTS

Immunohistochemistry of tumor microarray PCa tissues (N = 165) with high Gleason scores indicated that xCT protein expression is significantly increased while ECSOD protein expression is significantly decreased. Metastatic PCa indicated ECSOD protein expression is significantly decreased in epithelial area whereas xCT protein expression is significantly increased in stromal area. Furthermore, inhibition of extracellular O₂^•- by overexpression of ECSOD or alteration of the extracellular Cys/CySS ratio by knockdown of xCT protein inhibited PCa cell invasion. Simultaneous overexpression of ECSOD and knockdown xCT inhibited PCa cell invasion more than overexpression of ECSOD or knockdown of xCT alone. In the co-culturing system, simultaneous overexpression of ECSOD and knockdown of xCT in prostate stromal WPMY-1 cells inhibited PCa cell invasiveness more than overexpression of ECSOD alone. The decrease in PCa invasion correlated with increased of extracellular H₂O₂ levels. Notably, overexpression of catalase in TME reversed the inhibitory effect of ECSOD on cancer cell invasion.

CONCLUSION

Impaired ECSOD activity and an upregulated of xCT protein expression may be clinical features of an aggressive PCa, particularly metastatic cancers and/or those with a high Gleason score. Therefore, shifting the extracellular redox state toward an oxidizing status by targeted modulation of ECSOD and xCT, in both cancer and stromal cells, may provide a greater strategy for potential therapeutic interventions of aggressive PCa.