Respiration-dependent H2O2 removal in brain mitochondria via the thioredoxin/peroxiredoxin system

Nicotinamide nucleotide transhydrogenase is required for brain mitochondrial redox balance under hampered energy substrate metabolism and high-fat diet

Among mitochondrial NADP-reducing enzymes, nicotinamide nucleotide transhydrogenase (NNT) establishes an elevated matrix NADPH/NADP⁺ by catalyzing the reduction of NADP⁺ at the expense of NADH oxidation coupled to inward proton translocation across the inner mitochondrial membrane. Here, we characterize NNT activity and mitochondrial redox balance in the brain using a congenic mouse model carrying the mutated Nnt gene from the C57BL/6J strain. The absence of NNT activity resulted in lower total NADPH sources activity in the brain mitochondria of young mice, an effect that was partially compensated in aged mice. Nonsynaptic mitochondria showed higher NNT activity than synaptic mitochondria. In the absence of NNT, an increased release of H₂ O₂ from mitochondria was observed when the metabolism of respiratory substrates occurred with restricted flux through relevant mitochondrial NADPH sources or when respiratory complex I was inhibited. In accordance, mitochondria from Nnt^-/- brains were unable to sustain NADP in its reduced state when energized in the absence of carbon substrates, an effect aggravated after H₂ O₂ bolus metabolism. These data indicate that the lack of NNT in brain mitochondria impairs peroxide detoxification, but peroxide detoxification can be partially counterbalanced by concurrent NADPH sources depending on substrate availability. Notably, only brain mitochondria from Nnt^-/- mice chronically fed a high-fat diet exhibited lower activity of the redox-sensitive aconitase, suggesting that brain mitochondrial redox balance requires NNT under the metabolic stress of a high-fat diet. Overall, the role of NNT in the brain mitochondria redox balance especially comes into play under mitochondrial respiratory defects or high-fat diet.

Mitochondria can act as energy-sensing regulators of hydrogen peroxide availability

Mitochondria are widely recognized as sources of reactive oxygen species in animal cells, with H₂O₂ being of particular note because it can act not only in oxidative stress but also is important to several signalling pathways. Lesser recognized is that mitochondria can have far greater capacity to consume H₂O₂ than to produce it; however, the consumption of H₂O₂ may be kinetically constrained by H₂O₂ availability especially at the low nanomolar (or lower) concentrations that occur in vivo. The production of H₂O₂ is a function of many factors, not the least of which are respiratory substrate availability and the protonmotive force (Δp). The Δp, which is predominantly membrane potential (ΔΨ), can be a strong indicator of mitochondrial energy status, particularly if respiratory substrate supply is either not meeting or exceeding demand. The notion that mitochondria may functionally act in regulating H₂O₂ concentrations may be somewhat implicit but little evidence demonstrating this is available. Here we demonstrate key assumptions that are required for mitochondria to act as regulators of H₂O₂ by an integrated system of production and concomitant consumption. In particular we show the steady-state level of H₂O₂ mitochondria approach is a function of both mitochondrial H₂O₂ consumption and production capacity, the latter of which is strongly influenced by ΔΨ. Our results are consistent with mitochondria being able to manipulate extramitochondrial H₂O₂ as a means of signalling mitochondrial energetic status, in particular the Δp or ΔΨ. Such a redox-based signal could operate with some independence from other energy sensing mechanisms such as those that transmit information using the cytosolic adenylate pool.

H2O2 metabolism in liver and heart mitochondria: Low emitting-high scavenging and high emitting-low scavenging systems

Although mitochondria are presumed to emit and consume reactive oxygen species (ROS), the quantitative interplay between the two processes in ROS regulation is not well understood. Here, we probed the role of mitochondrial bioenergetics in H₂O₂ metabolism using rainbow trout liver and heart mitochondria. Both liver and heart mitochondria emitted H₂O₂ at rates that depended on their metabolic state, with the emission rates (free radical leak) constituting 0.8-2.9% and 0.2-2.5% of the respiration rate in liver and heart mitochondria, respectively. When presented with exogenous H₂O₂, liver and heart mitochondria consumed it by first order reactions with half-lives (s) of 117 and 210, and rate constants of 5.96 and 3.37 (× 10^-3 s^-1), respectively. The mitochondrial bioenergetic status greatly affected the rate of H₂O₂ consumption in heart but not liver mitochondria. Moreover, the activities and contribution of H₂O₂ scavenging systems varied between liver and heart mitochondria. The significance of the scavenging systems ranked by the magnitude (%) of inhibition of H₂O₂ removal after correcting for emission were, liver (un-energized and energized): catalase > glutathione (GSH) ≥ thioredoxin reductase (TrxR); un-energized heart mitochondria: catalase > TrxR > GSH and energized heart mitochondria: GSH > TrxR > catalase. Notably, depletion of GSH evoked a massive surge in H₂O₂ emission that grossly masked the contribution of this pathway to H₂O₂ scavenging in heart mitochondria. Irrespective of the organ of their origin, mitochondria behaved as H₂O₂ regulators that emitted or consumed it depending on the ambient H₂O₂ concentration, mitochondrial bioenergetic state and activity of the scavenging enzyme systems. Indeed, manipulation of mitochondrial bioenergetics and H₂O₂ scavenging systems caused mitochondria to switch from being net consumers to net emitters of H₂O₂. Overall, our data suggest that the low levels of H₂O₂ typically present in cells would favor emission of this metabolite but the scavenging systems would prevent its accumulation.

Genetic Alterations in Oxidant and Anti-Oxidant Enzymes in the Vascular System

Cardiovascular diseases (CVD) are one of the prime causes of mortality worldwide. Experimental animal models have become a valuable tool to investigate and further advance our knowledge on etiology, pathophysiology and intervention. They also provide a great opportunity to understand the contribution of different genes and effector molecules in the pathogenesis and development of diseases at the sub-cellular levels. High levels of reactive oxygen species (ROS) have been associated with the progression of CVD such as ischemic heart disease (IHD), myocardial infarction, hypertension, atherosclerosis, aortic aneurysm, aortic dissection and others. On the contrary, low levels of antioxidants were associated with exacerbated cardiovascular event. Major focus of this review is on vascular pathogenesis that leads to CVD, with special emphasis on the roles of oxidant/antioxidant enzymes in health and disease progression in vascular cells including vascular endothelium. The major oxidant enzymes that have been implicated with the progression of CVD include NADPH Oxidase, nitric oxide synthase, monoamine oxidase, and xanthine oxidoreductase. The major antioxidant enzymes that have been attributed to normalizing the levels of oxidative stress include superoxide dismutases, catalase and glutathione peroxidases (GPx), and thioredoxin. Cardiovascular phenotypes of major oxidants and antioxidants knockout and transgenic animal models are discussed here.

Mechanism Underlying the Effectiveness of Deferiprone in Alleviating Parkinson's Disease Symptoms

Elevation in iron content as well as severe depletion of dopamine (DA) as a result of iron-induced loss of dopaminergic neurons has been recognized to accompany the progression of Parkinson's disease (PD). To better understand the mechanism of the mitigating effect of the iron chelator deferiprone (DFP) on PD, the interplay between iron and DFP was investigated both in the absence and presence of DA. The results show that DFP was extremely efficient in scavenging both aqueous iron and iron that was loosely bound to DA with the entrapment of iron in Fe-DFP complexed form critical to halting the iron catalyzed degradation of DA and associated generation of toxic metabolites. The DFP related scavenging of dopamine semiquinone (DA^•-) and superoxide (O₂^•-) may also contribute to its positive effects in the treatment of PD.

Thioredoxin-Interacting Protein (TXNIP) in Cerebrovascular and Neurodegenerative Diseases: Regulation and Implication

Neurological diseases, including acute attacks (e.g., ischemic stroke) and chronic neurodegenerative diseases (e.g., Alzheimer's disease), have always been one of the leading cause of morbidity and mortality worldwide. These debilitating diseases represent an enormous disease burden, not only in terms of health suffering but also in economic costs. Although the clinical presentations differ for these diseases, a growing body of evidence suggests that oxidative stress and inflammatory responses in brain tissue significantly contribute to their pathology. However, therapies attempting to prevent oxidative damage or inhibiting inflammation have shown little success. Identification and targeting endogenous "upstream" mediators that normalize such processes will lead to improve therapeutic strategy of these diseases. Thioredoxin-interacting protein (TXNIP) is an endogenous inhibitor of the thioredoxin (TRX) system, a major cellular thiol-reducing and antioxidant system. TXNIP regulating redox/glucose-induced stress and inflammation, now is known to get upregulated in stroke and other brain diseases, and represents a promising therapeutic target. In particular, there is growing evidence that glucose strongly induces TXNIP in multiple cell types, suggesting possible physiological roles of TXNIP in glucose metabolism. Recently, a significant body of literature has supported an essential role of TXNIP in the activation of the NOD-like receptor protein (NLRP3)-inflammasome, a well-established multi-molecular protein complex and a pivotal mediator of sterile inflammation. Accordingly, TXNIP has been postulated to reside centrally in detecting cellular damage and mediating inflammatory responses to tissue injury. The majority of recent studies have shown that pharmacological inhibition or genetic deletion of TXNIP is neuroprotective and able to reduce detrimental aspects of pathology following cerebrovascular and neurodegenerative diseases. Conspicuously, the mainstream of the emerging evidences is highlighting TXNIP link to damaging signals in endothelial cells. Thereby, here, we keep the trend to present the accumulative data on CNS diseases dealing with vascular integrity. This review aims to summarize evidence supporting the significant contribution of regulatory mechanisms of TXNIP with the development of brain diseases, explore pharmacological strategies of targeting TXNIP, and outline obstacles to be considered for efficient clinical translation.

The neuronal protection of a zinc-binding protein isolated from oyster

Mitochondrial function is applied as oxidative stress and neuronal damage index. In this study, d-galactose was used to induce free radicals production and neuronal damage in HN-h cells, and the effect of novel 43 kDa protein isolated from oyster on anti-mitochondrial dysfunction and zinc-binding ability were evaluated. Crystal violet stain results indicated zinc-binding protein of oyster (ZPO) attenuated neuronal cell death induced by 100 mM of d-galactose on HN-h cells in a dose-dependent manner. ZPO alleviated mitochondrial inactivation, mitochondrial membrane potential decreasing, oxidative stress, and fusion/fission state in non-cytotoxic concentration of d-galactose (50 mM)-treated HN-h cells. ZPO treatment recovered metallathionein-3 (MT-3) decrease and inhibited β- and γ-secretase as well as amyloid beta (Aβ) accumulation in HN-h cells caused by d-galactose induction. These results suggest ZPO could avoid oxidative stress and is a functional protein for zinc concentration maintainability, which has potential for development of functional foods for neuronal protection.

Metabolic Dysfunction and Oxidative Stress in Epilepsy

The epilepsies are a heterogeneous group of disorders characterized by the propensity to experience spontaneous recurrent seizures. Epilepsies can be genetic or acquired, and the underlying mechanisms of seizure initiation, seizure propagation, and comorbid conditions are incompletely understood. Metabolic changes including the production of reactive species are known to result from prolonged seizures and may also contribute to epilepsy development. In this review, we focus on the evidence that metabolic and redox disruption is both cause and consequence of epileptic seizures. Additionally, we discuss the promise of targeting redox processes as a therapeutic option in epilepsy.

Redox Signaling Mediated by Thioredoxin and Glutathione Systems in the Central Nervous System

SIGNIFICANCE

The thioredoxin (Trx) and glutathione (GSH) systems play important roles in maintaining the redox balance in the brain, a tissue that is prone to oxidative stress due to its high-energy demand. These two disulfide reductase systems are active in various areas of the brain and are considered to be critical antioxidant systems in the central nervous system (CNS). Various neuronal disorders have been characterized to have imbalanced redox homeostasis. Recent Advances: In addition to their detrimental effects, recent studies have highlighted that reactive oxygen species/reactive nitrogen species (ROS/RNS) act as critical signaling molecules by modifying thiols in proteins. The Trx and GSH systems, which reversibly regulate thiol modifications, regulate redox signaling involved in various biological events in the CNS.

CRITICAL ISSUES

In this review, we focus on the following: (i) how ROS/RNS are produced and mediate signaling in CNS; (ii) how Trx and GSH systems regulate redox signaling by catalyzing reversible thiol modifications; (iii) how dysfunction of the Trx and GSH systems causes alterations of cellular redox signaling in human neuronal diseases; and (iv) the effects of certain small molecules that target thiol-based signaling pathways in the CNS.

FUTURE DIRECTIONS

Further study on the roles of thiol-dependent redox systems in the CNS will improve our understanding of the pathogenesis of many human neuronal disorders and also help to develop novel protective and therapeutic strategies against neuronal diseases. Antioxid. Redox Signal. 27, 989-1010.

Progress in understanding the molecular oxygen paradox - function of mitochondrial reactive oxygen species in cell signaling

The molecular oxygen (O2) paradox was coined to describe its essential nature and toxicity. The latter characteristic of O2 is associated with the formation of reactive oxygen species (ROS), which can damage structures vital for cellular function. Mammals are equipped with antioxidant systems to fend off the potentially damaging effects of ROS. However, under certain circumstances antioxidant systems can become overwhelmed leading to oxidative stress and damage. Over the past few decades, it has become evident that ROS, specifically H2O2, are integral signaling molecules complicating the previous logos that oxyradicals were unfortunate by-products of oxygen metabolism that indiscriminately damage cell structures. To avoid its potential toxicity whilst taking advantage of its signaling properties, it is vital for mitochondria to control ROS production and degradation. H2O2 elimination pathways are well characterized in mitochondria. However, less is known about how H2O2 production is controlled. The present review examines the importance of mitochondrial H2O2 in controlling various cellular programs and emerging evidence for how production is regulated. Recently published studies showing how mitochondrial H2O2 can be used as a secondary messenger will be discussed in detail. This will be followed with a description of how mitochondria use S-glutathionylation to control H2O2 production.

A radical shift in perspective: mitochondria as regulators of reactive oxygen species

Mitochondria are widely recognized as a source of reactive oxygen species (ROS) in animal cells, where it is assumed that over-production of ROS leads to an overwhelmed antioxidant system and oxidative stress. In this Commentary, we describe a more nuanced model of mitochondrial ROS metabolism, where integration of ROS production with consumption by the mitochondrial antioxidant pathways may lead to the regulation of ROS levels. Superoxide and hydrogen peroxide (H₂O₂) are the main ROS formed by mitochondria. However, superoxide, a free radical, is converted to the non-radical, membrane-permeant H₂O₂; consequently, ROS may readily cross cellular compartments. By combining measurements of production and consumption of H₂O₂, it can be shown that isolated mitochondria can intrinsically approach a steady-state concentration of H₂O₂ in the medium. The central hypothesis here is that mitochondria regulate the concentration of H₂O₂ to a value set by the balance between production and consumption. In this context, the consumers of ROS are not simply a passive safeguard against oxidative stress; instead, they control the established steady-state concentration of H₂O₂ By considering the response of rat skeletal muscle mitochondria to high levels of ADP, we demonstrate that H₂O₂ production by mitochondria is far more sensitive to changes in mitochondrial energetics than is H₂O₂ consumption; this concept is further extended to evaluate how the muscle mitochondrial H₂O₂ balance should respond to changes in aerobic work load. We conclude by considering how differences in the ROS consumption pathways may lead to important distinctions amongst tissues, along with briefly examining implications for differing levels of activity, temperature change and metabolic depression.

Gene expression of selenoproteins can be regulated by thioredoxin(Txn) silence in chicken cardiomyocytes

Thioredoxin (Txn) system is the most crucial antioxidant defense mechanism in myocardium. The aim of this study was to clarify the effect of Txn low expression on 25 selenoproteins in chicken cardiomyocytes. We developed a Se-deficient model (0.033mg/kg) and Txn knock down cardiomyocytes model (siRNA) studies. Western Blot, Quantitative Real-time PCR (qPCR) were performed, and correlation analysis, heat map were used for further analysis. Both low expression of Txn models are significantly decreased (P<0.05) the mRNA levels of Deiodinase 1, 2 (Dio 1, 2), Glutathione Peroxidase 1, 2, 3, 4 (Gpx 1, 2, 3, 4), Thioredoxin Reductase 1, 2, 3 (TR 1, 2, 3), Selenoprotein t (Selt), Selenoprotein w (Selw), Selenoprotein k (Selk), selenoprotein x1 (Sepx1), and significantly increased (P<0.05) the mRNA levels of the rest of selenoproteins. Correlation analysis showed that Deiodinase 3 (Dio 3), Selenoprotein m (Selm), 15-kDa Selenoprotein (Selp15), Selenoprotein h (Selh), Selenoprotein u (Selu), Selenoprotein i (Seli), Selenoprotein n (Seln), Selenoprotein p1 (Sepp1), Selenoprotein o (Selo), Selenoprotein s (Sels), Selenoprotein synthetase 2 (Sels2) and Selenoprotein p (Selp) had a negative correlation with Txn, while the rest of selenoproteins had a positive correlation with Txn. Combined in vivo and in vitro we can know that hamper Txn expression can inhibit Gpx 1, 2, 3, 4, TR 1, 2, 3, Dio 1, 2, Selt, Selw, Selk, Sepx1, meanwhile, over expression the rest of selenoproteins. In conclusion, the different selenoproteins possess and exhibit distinct responses to silence of Txn in chicken cardiomyocytes.

Mitochondrial Dysfunction in Parkinson’s Disease

Parkinson’s disease (PD) is one of the most common neurodegenerative disorders where oxidative stress and mitochondrial dysfunction have been implicated as etiological factors. Mitochondria are the major producers of reactive oxygen species (ROS) that can have damaging effects to cellular macromolecules leading to neurodegeneration. The most compelling evidence for the role of mitochondria in the pathogenesis of PD has been derived from toxicant-induced models of parkinsonism. Over the years, epidemiological studies have suggested a link between exposure to environmental toxins such as pesticides and the risk of developing PD. Data from human and experimental studies involving the use of chemical agents like paraquat, diquat, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, rotenone and maneb have provided valuable insight into the underlying mitochondrial mechanisms contributing to PD and associated neurodegeneration. In this review, we have discussed the role of mitochondrial ROS and dysfunction in the pathogenesis of PD with a special focus on environmental agent-induced parkinsonism. We have described the various mitochondrial mechanisms by which such chemicals exert neurotoxicity, highlighting some landmark epidemiological and experimental studies that support the role of mitochondrial ROS and oxidative stress in contributing to these effects. Finally, we have discussed the significance of these studies in understanding the mechanistic underpinnings of PD-related dopaminergic neurodegeneration.

Selenium deficiency-induced thioredoxin suppression and thioredoxin knock down disbalanced insulin responsiveness in chicken cardiomyocytes through PI3K/Akt pathway inhibition

Thioredoxin (Txn) system is the most crucial antioxidant defense mechanism in cell consisting of Txn, thioredoxin reductase (TR) and Nicotinamide Adenine Dinucleotide Phosphate (NADPH). Perturbations in Txn system may compromise cell survival through oxidative stress induction. Metabolic activity of insulin plays important roles in fulfilling the stable and persistent demands of heart through glucose metabolism. However, the roles of Txn and Txn system in insulin modulated cardiac energy metabolism have been less reported. Therefore, to investigate the role of Txn in myocardial metabolism, we developed a Se-deficient chicken model (0.033mg/kg) for in-vivo and Txn knock down cardiomyocytes culture model (siRNA) for in-vitro studies. Quantitative real time PCR and western blotting was performed. Se deficiency suppressed Txn and TR in cardiac tissues. Significant increases in ROS (P<0.05) levels signify the onset of oxidative stress and in both models. Se deficiency-induced Txn suppression model and Txn knock down cardiomyocytes models significantly decreased (P<0.05), the mRNA and protein levels of insulin-like growth factors (IGF1, IGF2), IGF-binding proteins (IGFBP2, IGFBP4), insulin receptor (IR), insulin receptor substrates (IRS1, IRS2), and glucose transporters (GLUT1, GLUT3, GLUT8), however, IGFBP3 expression increased in Txn knock down cardiomyocytes. In addition, in contrast to their respective controls, Se deficiency-induced Txn depleted tissues and Txn deleted cardiomyocytes showed suppression in mRNA and protein levels of PI3K, AKT, P-PI3K, and repression in FOX, P-FOX JNK genes. Combing the in vitro and in vivo experiments, we demonstrate that Txn gene suppression can cause dysfunction of insulin-modulated cardiac energy metabolism and increase insulin resistance through PI3K-Akt pathway inhibition. Herein, we conclude that inactivation of Txn system can alter cellular insulin response through IRS/PI3K/Akt pathway repression and JNK and FOX expression. These findings point out that Txn system can redox regulate the insulin dependent glucose metabolism in heart and is essential for cell vitality. Moreover, the increased expression of IGFBP3 indicates that it can be a potential negative modulator of metabolic activity of insulin in Txn deficient cells.

Reductions in the mitochondrial enzyme α-ketoglutarate dehydrogenase complex in neurodegenerative disease - beneficial or detrimental?

Reductions in metabolism and excess oxidative stress are prevalent in multiple neurodegenerative diseases. The activity of the mitochondrial enzyme α-ketoglutarate dehydrogenase complex (KGDHC) appears central to these abnormalities. KGDHC is diminished in multiple neurodegenerative diseases. KGDHC can not only be rate limiting for NADH production and for substrate level phosphorylation, but is also a source of reactive oxygen species (ROS). The goal of these studies was to determine how changes in KGDHC modify baseline ROS, the ability to buffer ROS, baseline glutathionylation, calcium modulation and cell death in response to external oxidants. In vivo, reducing KGDHC with adeno virus diminished neurogenesis and increased oxidative stress. In vitro, treatments of short duration increased ROS and glutathionylation and enhanced the ability of the cells to diminish the ROS from added oxidants. However, long-term reductions lessened the ability to diminish ROS, diminished glutathionylation and exaggerated oxidant-induced changes in calcium and cell death. Increasing KGDHC enhanced the ability of the cells to diminish externally added ROS and protected against oxidant-induced changes in calcium and cell death. The results suggest that brief periods of diminished KGDHC are protective, while prolonged reductions are harmful. Furthermore, elevated KGDHC activities are protective. Thus, mitogenic therapies that increase KGDHC may be beneficial in neurodegenerative diseases. Read the Editorial Highlight for this article on Page 689.

Examination of the superoxide/hydrogen peroxide forming and quenching potential of mouse liver mitochondria

Pyruvate dehydrogenase (PDHC) and α-ketoglutarate dehydrogenase complex (KGDHC) are important sources of reactive oxygen species (ROS). In addition, it has been found that mitochondria can also serve as sinks for cellular hydrogen peroxide (H₂O₂). However, the ROS forming and quenching capacity of liver mitochondria has never been thoroughly examined. Here, we show that mouse liver mitochondria use catalase, glutathione (GSH), and peroxiredoxin (PRX) systems to quench ROS. Incubation of mitochondria with catalase inhibitor 3-amino-1,2,4-triazole (triazole) induced a significant increase in pyruvate or α-ketoglutarate driven O₂^-/H₂O₂ formation. 1-Choro-2,4-dinitrobenzene (CDNB), which depletes glutathione (GSH), elicited a similar effect. Auranofin (AF), a thioredoxin reductase-2 (TR2) inhibitor which disables the PRX system, did not significantly change O₂^-/H₂O₂ formation. By contrast catalase, GSH, and PRX were all required to scavenging extramitochondrial H₂O₂. In this study, the ROS forming potential of PDHC, KGDHC, Complex I, and Complex III was also profiled. Titration of mitochondria with 3-methyl-2-oxovaleric acid (KMV), a specific inhibitor for O₂^-/H₂O₂ production by KGDHC, induced a ~86% and ~84% decrease in ROS production during α-ketoglutarate and pyruvate oxidation. Titration of myxothiazol, a Complex III inhibitor, decreased O₂^-/H₂O₂ formation by ~45%. Rotenone also lowered ROS production in mitochondria metabolizing pyruvate or α-ketoglutarate indicating that Complex I does not contribute to ROS production during forward electron transfer from NADH. Taken together, our results indicate that KGDHC and Complex III are high capacity sites for O₂^-/H₂O₂ production in mouse liver mitochondria. We also confirm that catalase plays a role in quenching either exogenous or intramitochondrial H₂O₂.

Homozygous mutation in TXNRD1 is associated with genetic generalized epilepsy

Increased oxidative stress has been widely implicated in the pathogenesis in various forms of human epilepsy. Here, we report a homozygous mutation in TXNRD1 (thioredoxin reductase 1) in a family with genetic generalized epilepsy. TXNRD1 is an essential selenium-containing enzyme involved in detoxification of reactive oxygen species (ROS) and redox signaling. The TXNRD1 mutation p.Pro190Leu affecting a highly conserved amino acid residue was identified by whole-exome sequencing of blood DNA from the index patient. The detected mutation and its segregation within the family - all siblings of the index patient were homozygous and the parents heterozygous - were confirmed by Sanger sequencing. TXNRD1 activity was determined in subcellular fractions from a skeletal muscle biopsy and skin fibroblasts of the index patient and the expression levels of the mutated protein were assessed by ⁷⁵Se labeling and Western blot analysis. As result of the mutation, the activity of TXNRD1 was reduced in the patient's fibroblasts and skeletal muscle (to 34±3% and 16±8% of controls, respectively). In fibroblasts, we detected reduced ⁷⁵Se-labeling of the enzyme (41±3% of controls). An in-depth in vitro kinetic analysis of the recombinant mutated TXNRD1 indicated 30-40% lowered k_cat/Se values. Therefore, a reduced activity of the enzyme in the patient's tissue samples is explained by (i) lower enzyme turnover and (ii) reduced abundance of the mutated enzyme as confirmed by Western blotting and ⁷⁵Se labeling. The mutant fibroblasts were also found to be less resistant to a hydrogen peroxide challenge. Our data agree with a potential role of insufficient ROS detoxification for disease manifestation in genetic generalized epilepsy.

Simplified qPCR method for detecting excessive mtDNA damage induced by exogenous factors

Damage to mitochondrial DNA (mtDNA) is a meaningful biomarker for evaluating genotoxicity of drugs and environmental toxins. Existing PCR methods utilize long mtDNA fragments (∼8-10kb), which complicates detecting exact sites of mtDNA damage. To identify the mtDNA regions most susceptible to damage, we have developed and validated a set of primers to amplify ∼2kb long fragments, while covering over 95% of mouse mtDNA. We have modified the detection method by greatly increasing the enrichment of mtDNA, which allows us solving the problem of non-specific primer annealing to nuclear DNA. To validate our approach, we have determined the most damage-susceptible mtDNA regions in mice treated in vivo and in vitro with rotenone and H₂O₂. The GTGR-sequence-enriched mtDNA segments located in the D-loop region were found to be especially susceptible to damage. Further, we demonstrate that H₂O₂-induced mtDNA damage facilitates the relaxation of mtDNA supercoiled conformation, making the sequences with minimal damage more accessible to DNA polymerase, which, in turn, results in a decrease in threshold cycle value. Overall, our modified PCR method is simpler and more selective to the specific sites of damage in mtDNA.

High Expression Levels of NADPH Oxidase 3 in the Cerebrum of Ten-Week-Old Stroke-Prone Spontaneously Hypertensive Rats

We previously demonstrated that the high levels of oxidative stress in the brains of ten-week-old stroke-prone hypertensive rats (SHRSP) were attributable to intrinsic, not extrinsic factors (Biol. Pharm. Bull., 33, 2010, Michihara et al.). The aim of the present study was to determine whether increases in the enzymes producing reactive oxygen species (ROS), reductions in the enzymes and proteins removing ROS, or increases in an enzyme and transporter removing antioxidants promoted oxidative stress in the SHRSP cerebrum. No significant decreases were observed in the mRNA levels of enzymes that remove ROS between SHRSP and normotensive Wistar Kyoto rats. The activity of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) and the protein and mRNA levels of NOX3, an enzyme that produces ROS, were significantly increased in the SHRSP cerebrum. These results suggested that the high expression levels of NOX3 increased oxidative stress in the SHRSP cerebrum.

Energy metabolism and inflammation in brain aging and Alzheimer's disease

The high energy demand of the brain renders it sensitive to changes in energy fuel supply and mitochondrial function. Deficits in glucose availability and mitochondrial function are well-known hallmarks of brain aging and are particularly accentuated in neurodegenerative disorders such as Alzheimer's disease. As important cellular sources of H₂O₂, mitochondrial dysfunction is usually associated with altered redox status. Bioenergetic deficits and chronic oxidative stress are both major contributors to cognitive decline associated with brain aging and Alzheimer's disease. Neuroinflammatory changes, including microglial activation and production of inflammatory cytokines, are observed in neurodegenerative diseases and normal aging. The bioenergetic hypothesis advocates for sequential events from metabolic deficits to propagation of neuronal dysfunction, to aging, and to neurodegeneration, while the inflammatory hypothesis supports microglia activation as the driving force for neuroinflammation. Nevertheless, growing evidence suggests that these diverse mechanisms have redox dysregulation as a common denominator and connector. An independent view of the mechanisms underlying brain aging and neurodegeneration is being replaced by one that entails multiple mechanisms coordinating and interacting with each other. This review focuses on the alterations in energy metabolism and inflammatory responses and their connection via redox regulation in normal brain aging and Alzheimer's disease. Interaction of these systems is reviewed based on basic research and clinical studies.

Evaluation of Protective Immune Responses Induced by Recombinant TrxLp and ENO2 Proteins against Toxoplasma gondii Infection in BALB/c Mice

Toxoplasma gondii is an obligate intracellular parasitic protozoan that can infect almost all species of warm-blooded animals. As any chemical-based drugs could not act against the tissue cyst stage of T. gondii, vaccination may be one of the ideal control strategies. In the present study, two new vaccine candidates, named TgENO2 and TgTrxLp, were purified from Escherichia coli with pET-30a(+) expression system and then were injected into BALB/c mice to evaluate the protective efficacy against acute and chronic toxoplasmosis. The results showed that both the recombinant proteins, either alone or in combination, could elicit strong humoral and cellular immune responses with a higher level of IgG antibodies, IFN-γ, IL-2, CD4⁺, and CD8⁺ T cells as compared to those in mice from control groups. After acute challenge with tachyzoites of the GJS strain, mice immunized with rTgTrxLp (8 ± 2.77 d), rTgENO2 (7.4 ± 1.81 d), and rTgTrxLp + rTgENO2 (8.38 ± 4.57 d) proteins showed significantly longer survival time than those that received Freund's adjuvant (6.78 ± 2.08 d) and PBS (6.38 ± 4.65 d) (χ² = 9.687, df = 4, P = 0.046). The protective immunity of rTgTrxLp, rTgENO2, and rTgTrxLp + rTgENO2 proteins against chronic T. gondii infection showed 69.77%, 58.14%, and 20.93% brain cyst reduction as compared to mice that received PBS. The present study suggested that both TgENO2 and TgTrxLp were potential candidates for the development of multicomponent vaccines against toxoplasmosis.

Endothelial Dysfunction, and A Prothrombotic, Proinflammatory Phenotype Is Caused by Loss of Mitochondrial Thioredoxin Reductase in Endothelium

Objective—

Although the investigation on the importance of mitochondria-derived reactive oxygen species (ROS) in endothelial function has been gaining momentum, little is known on the precise role of the individual components involved in the maintenance of a delicate ROS balance. Here we studied the impact of an ongoing dysregulated redox homeostasis by examining the effects of endothelial cell–specific deletion of murine thioredoxin reductase 2 (Txnrd2), a key enzyme of mitochondrial redox control.

Approach and Results—

We analyzed the impact of an inducible, endothelial cell–specific deletion of Txnrd2 on vascular remodeling in the adult mouse after femoral artery ligation. Laser Doppler analysis and histology revealed impaired angiogenesis and arteriogenesis. In addition, endothelial loss of Txnrd2 resulted in a prothrombotic, proinflammatory vascular phenotype, manifested as intravascular cellular deposits, as well as microthrombi. This phenotype was confirmed by an increased leukocyte response toward interleukin-1 in the mouse cremaster model. In vitro, we could confirm the attenuated angiogenesis measured in vivo, which was accompanied by increased ROS and an impaired mitochondrial membrane potential. Ex vivo analysis of femoral arteries revealed reduced flow-dependent vasodilation in endothelial cell Txnrd2-deficient mice. This endothelial dysfunction could be, at least partly, ascribed to inadequate nitric oxide signaling.

Conclusions—

We conclude that the maintenance of mitochondrial ROS via Txnrd2 in endothelial cells is necessary for an intact vascular homeostasis and remodeling and that Txnrd2 plays a vitally important role in balancing mitochondrial ROS production in the endothelium.

Targeting Oxidative Stress in Central Nervous System Disorders

There is widespread recognition that reactive oxygen species (ROS) play key roles in normal brain function and pathology in the context of neurological disease. Oxidative stress continues to be a key therapeutic target for neurological diseases. In developing antioxidant therapies for neurological disease, special attention should be given to the brain's unique vulnerability to oxidative insults and its architecture. Consideration of antioxidant therapy should be guided by a strong rationale for oxidative stress in a given neurological disease. This review provides an overview of processes that can guide the development of antioxidant therapies in neurological diseases, such as knowledge of basic redox mechanisms, unique features of brain pathophysiology, mechanisms and classes of antioxidants, and desirable properties of drug candidates.

GL-V9, a new synthetic flavonoid derivative, ameliorates DSS-induced colitis against oxidative stress by up-regulating Trx-1 expression via activation of AMPK/FOXO3a pathway

GL-V9, a new synthesized flavonoid derivative, has been reported to possess anti-cancer properties in our previous studies. Uncontrolled overproduction of reactive oxygen species (ROS) has been implicated in oxidative damage of inflammatory bowel disease (IBD). In this study, we aimed to investigate the protective effect of GL-V9 against dextran sulfate sodium (DSS)-induced colitis. GL-V9 attenuated DSS-induced body weight loss, colon length shortening and colonic pathological damage. GL-V9 also inhibited inflammatory cells infiltration and decreased myeloperoxidase (MPO) and inducible nitric oxide synthase (iNOS) activities. Moreover, GL-V9 inhibited ROS and malondialdehyde (MDA) generation, but enhanced superoxide dismutase (SOD), glutathione (GSH) and total antioxidant capacity. GL-V9 reduced pro-inflammatory cytokines production in serum and colon as well. Mechanically, GL-V9 could increase Trx-1 via activation of AMPK/FOXO3a to suppress DSS-induced colonic oxidative stress. Furthermore, GL-V9 decreased pro-inflammatory cytokines and ROS production and increased the antioxidant defenses in the mouse macrophage cells RAW264.7 by promoting Trx-1 expression. In conclusion, our study demonstrated that GL-V9 attenuated DSS-induced colitis against oxidative stress by up-regulating Trx-1 via activation of AMPK/FOXO3a pathway, suggesting that GL-V9 might be a potential effective drug for colitis.

The thioredoxin and glutathione-dependent H2O2 consumption pathways in muscle mitochondria: Involvement in H2O2 metabolism and consequence to H2O2 efflux assays

The most common methods of measuring mitochondrial hydrogen peroxide production are based on the extramitochondrial oxidation of a fluorescent probe such as amplex ultra red (AUR) by horseradish peroxidase (HRP). These traditional HRP-based assays only detect H2O2 that has escaped the matrix, raising the potential for substantial underestimation of production if H2O2 is consumed by matrix antioxidant pathways. To measure this underestimation, we characterized matrix consumers of H2O2 in rat skeletal muscle mitochondria, and developed specific means to inhibit these consumers. Mitochondria removed exogenously added H2O2 (2.5µM) at rates of 4.7 and 5.0nmol min(-1) mg protein(-1) when respiring on glutamate+malate and succinate+rotenone, respectively. In the absence of respiratory substrate, or after disrupting membranes by cycles of freeze-thaw, rates of H2O2 consumption were negligible. We concluded that matrix consumers are respiration-dependent (requiring respiratory substrates), suggesting the involvement of either the thioredoxin (Trx) and/or glutathione (GSH)-dependent enzymatic pathways. The Trx-reductase inhibitor auranofin (2µM), and a pre-treatment of mitochondria with 35µM of 1-chloro-2,4-dintrobenzene (CDNB) to deplete GSH specifically compromise these two consumption pathways. These inhibition approaches presented no undesirable "off-target" effects during extensive preliminary tests. These inhibition approaches independently and additively decreased the rate of consumption of H2O2 exogenously added to the medium (2.5µM). During traditional HRP-based H2O2 efflux assays, these inhibition approaches independently and additively increased apparent efflux rates. When used in combination (double inhibition), these inhibition approaches allowed accumulation of (endogenously produced) H2O2 in the medium at a comparable rate whether it was measured with an end point assay where 2.5µM H2O2 is initially added to the medium or with traditional HRP-based efflux assays. This finding confirms that a high degree of inhibition of all matrix consumers is attained with the double inhibition. Importantly, this double inhibition of the matrix consumers allowed revealing that a large part of the H2O2 produced in muscle mitochondria is consumed before escaping the matrix during traditional HRP-based efflux assays. The degree of this underestimation was substrate dependent, reaching >80% with malate, which complicates comparisons of substrates for their capacity to generate H2O2 in normal conditions i.e. when matrix consumers are active. Our results also urge caution in interpreting changes in H2O2 efflux in response to a treatment; when HRP-based assays are used, large changes in apparent H2O2 efflux may come from altered capacity of the matrix consumers.

Succinate, an intermediate in metabolism, signal transduction, ROS, hypoxia, and tumorigenesis

Succinate is an important metabolite at the cross-road of several metabolic pathways, also involved in the formation and elimination of reactive oxygen species. However, it is becoming increasingly apparent that its realm extends to epigenetics, tumorigenesis, signal transduction, endo- and paracrine modulation and inflammation. Here we review the pathways encompassing succinate as a metabolite or a signal and how these may interact in normal and pathological conditions.(1).

Mitochondrial ROS Metabolism: 10 Years Later

The role of mitochondria in oxidative stress is well recognized, but many questions are still to be answered. This article is intended to update our comprehensive review in 2005 by highlighting the progress in understanding of mitochondrial reactive oxygen species (ROS) metabolism over the past 10 years. We review the recently identified or re-appraised sources of ROS generation in mitochondria, such as p66(shc) protein, succinate dehydrogenase, and recently discovered properties of the mitochondrial antioxidant system. We also reflect upon some controversies, disputes, and misconceptions that confound the field.

The functional role of peroxiredoxin 3 in reactive oxygen species, apoptosis, and chemoresistance of cancer cells

PURPOSE

The mammalian peroxiredoxin (PRX) family contains six members that provide antioxidant defense in different cell types by removing reactive oxygen species (ROS) through conserved active cysteines. Different from other members, PRX3 is predominantly located in mitochondria, a major apoptosis mediator. The purpose of this review is to summarize the findings on PRX3 concerning its role in ROS removal, apoptosis, and chemoresistance of cancer cells.

METHODS

The relevant literature from PubMed and Medline databases is reviewed in this article (1994-2014).

RESULTS

Because of fast growth and relatively low supply of oxygen in cancer cells, ROS production from mitochondria is exaggerated to an extent that overwhelms cellular antioxidant defenses resulting in oxidative stress. As an active responder to oxidative stress, PRX3 is accordingly up-regulated in cancer cells to remove cellular ROS and inhibit apoptosis, which provides a favorable microenvironment for cell proliferation.

CONCLUSION

Since most of chemotherapy or radiotherapy for cancers is through ROS increase and apoptotic induction, PRX3 might be involved in the chemotherapeutic resistance of cancers.

Blockade of metabotropic glutamate receptor 5 protects against DNA damage in a rotenone-induced Parkinson's disease model

Glutamate excitotoxicity contributes to the development of Parkinson's disease (PD) and pharmacological blockade of metabotropic glutamate receptor 5 (mGluR5) has beneficial anti-akinetic effects in animal models of PD; however, the mechanism by which these antagonists alleviate PD symptoms is largely unknown. In our study, the effects of mGluR5 inhibition on DNA damage were investigated in a rotenone-induced model of PD. We first found that the selective mGluR5 antagonist, 2-methyl-6- (phenylethynyl) pyridine, prevented rotenone-induced DNA damage in MN9D dopaminergic neurons through a mechanism involving the downregulation of intracellular calcium release which was associated with a reduction in endoplasmic reticulum stress and reactive oxygen species (ROS)-related mitochondrial dysfunction. Interestingly, the ROS-related mitochondrial dysfunction was accompanied by an increase in expression of the antioxidant protein, Trx2. Treatment of cells with the calcium chelating agent 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid or the ROS scavenger N-acetyl-L-cysteine, also reduced rotenone-induced DNA damage, while transfection of a dominant-negative form of Trx2 increased it. In addition, mGluR5 inhibition altered the expression profiles of proteins involved in DNA repair activity. Specifically, the expression of phosphorylated ERK (p-ERK) and CREB, as well as APE1 and Rad51 were elevated after rotenone stimulation and were subsequently downregulated following blockade of mGluR5. These findings were confirmed in vivo in a rotenone-induced rat model of PD. Inhibition of mGluR5 protected against neurotoxicity by mitigating oxidative stress-related DNA damage associated with 8-hydroxy-2'-deoxyguanosine production and also reduced p-ERK activity and Trx2 expression. These findings provide a novel link between mGluR5 and DNA damage in a model of PD, and reveal a potential mechanism by which mGluR5 mediates DNA damage in neurodegenerative diseases.

Embryonic oxidative stress results in reproductive impairment for adult zebrafish

Exposure to environmental stressors during embryo development can have long-term effects on the adult organism. This study used the thioredoxin reductase inhibitor auranofin to investigate the consequences of oxidative stress during zebrafish development. Auranofin at low doses triggered upregulation of the antioxidant genes gstp1 and prdx1. As the dose was increased, acute developmental abnormalities, including cerebral hemorrhaging and jaw malformation, were observed. To determine whether transient disruption of redox homeostasis during development could have long-term consequences, zebrafish embryos were exposed to a low dose of auranofin from 6–24 hours post fertilization, and then raised to adulthood. The adult fish were outwardly normal in their appearance with no gross physical differences compared to the control group. However, these adult fish had reduced odds of breeding and a lower incidence of egg fertilization. This study shows that a suboptimal early life environment can reduce the chances of reproductive success in adulthood.

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We exposed zebrafish embryos to the oxidative stress-inducing compound auranofin.

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Embryos showed a dose-dependent increase in developmental abnormalities.

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Exposed embryos responded by upregulating oxidative stress-responsive genes.

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Embryos transiently exposed to a low dose of auranofin were raised into adults.

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The resulting adults had reduced fertility compared with controls.

Differentiating between apparent and actual rates of H2O2 metabolism by isolated rat muscle mitochondria to test a simple model of mitochondria as regulators of H2O2 concentration

Mitochondria are often regarded as a major source of reactive oxygen species (ROS) in animal cells, with H2O2 being the predominant ROS released from mitochondria; however, it has been recently demonstrated that energized brain mitochondria may act as stabilizers of H2O2 concentration (Starkov et al. [1]) based on the balance between production and the consumption of H2O2, the later of which is a function of [H2O2] and follows first order kinetics. Here we test the hypothesis that isolated skeletal muscle mitochondria, from the rat, are able to modulate [H2O2] based upon the interaction between the production of ROS, as superoxide/H2O2, and the H2O2 decomposition capacity. The compartmentalization of detection systems for H2O2 and the intramitochondrial metabolism of H2O2 leads to spacial separation between these two components of the assay system. This results in an underestimation of rates when relying solely on extramitochondrial H2O2 detection. We find that differentiating between these apparent rates found when using extramitochondrial H2O2 detection and the actual rates of metabolism is important to determining the rate constant for H2O2 consumption by mitochondria in kinetic experiments. Using the high rate of ROS production by mitochondria respiring on succinate, we demonstrate that net H2O2 metabolism by mitochondria can approach a stable steady-state of extramitochondrial [H2O2]. Importantly, the rate constant determined by extrapolation of kinetic experiments is similar to the rate constant determined as the [H2O2] approaches a steady state.

Mitochondrial Respiratory Chain Inhibitors Involved in ROS Production Induced by Acute High Concentrations of Iodide and the Effects of SOD as a Protective Factor

A major source of reactive oxygen species (ROS) generation is the mitochondria. By using flow cytometry of the mitochondrial fluorescent probe, MitoSOX Red, western blot of mitochondrial ROS scavenger Peroxiredoxin (Prx) 3 and fluorescence immunostaining, ELISA of cleaved caspases 3 and 9, and TUNEL staining, we demonstrated that exposure to 100 μM KI for 2 hours significantly increased mitochondrial superoxide production and Prx 3 protein expression with increased expressions of cleaved caspases 3 and 9. Besides, we indicated that superoxide dismutase (SOD) at 1000 unit/mL attenuated the increase in mitochondrial superoxide production, Prx 3 protein expression, and lactate dehydrogenase (LDH) release and improved the relative cell viability at 100 μM KI exposure. However, SOD inhibitor diethyldithiocarbamic acid (DETC) (2 mM), Rotenone (0.5 μM), a mitochondrial complex I inhibitor, and Antimycin A (10 μM), a complex III inhibitor, caused an increase in mitochondrial superoxide production, Prx 3 protein expression, and LDH release and decreased the relative cell viability. We conclude that the inhibitors of mitochondrial respiratory chain complex I or III may be involved in oxidative stress caused by elevated concentrations of iodide, and SOD demonstrates its protective effect on the Fischer rat thyroid cell line (FRTL) cells.

Transcriptomic Analysis Reveals Possible Influences of ABA on Secondary Metabolism of Pigments, Flavonoids and Antioxidants in Tomato Fruit during Ripening

Abscisic acid (ABA) has been proven to be involved in the regulation of climacteric fruit ripening, but a comprehensive investigation of its influence on ripening related processes is still lacking. By applying the next generation sequencing technology, we conducted a comparative analysis of the effects of exogenous ABA and NDGA (Nordihydroguaiaretic acid, an inhibitor of ABA biosynthesis) on tomato fruit ripening. The high throughput sequencing results showed that out of the 25728 genes expressed across all three samples, 10388 were identified as significantly differently expressed genes. Exogenous ABA was found to enhance the transcription of genes involved in pigments metabolism, including carotenoids biosynthesis and chlorophyll degradation, whereas NDGA treatment inhibited these processes. The results also revealed the crucial role of ABA in flavonoids synthesis and regulation of antioxidant system. Intriguingly, we also found that an inhibition of endogenous ABA significantly enhanced the transcriptional abundance of genes involved in photosynthesis. Our results highlighted the significance of ABA in regulating tomato ripening, which provided insight into the regulatory mechanism of fruit maturation and senescence process.

Metallothionein-I/II Knockout Mice Aggravate Mitochondrial Superoxide Production and Peroxiredoxin 3 Expression in Thyroid after Excessive Iodide Exposure

Purpose. We aim to figure out the effect of metallothioneins on iodide excess induced oxidative stress in the thyroid. Methods. Eight-week-old MT-I/II knockout (MT-I/II KO) mice and background-matched wild-type (WT) mice were used. Mitochondrial superoxide production and peroxiredoxin (Prx) 3 expression were measured. Results. In in vitro study, more significant increases in mitochondrial superoxide production and Prx 3 expression were detected in the MT-I/II KO groups. In in vivo study, significantly higher concentrations of urinary iodine level were detected in MT-I/II KO mice in 100 HI group. Compared to the NI group, there was no significant difference existing in serum thyroid hormones level in either groups (P > 0.05), while the mitochondrial superoxide production was significantly increased in 100 HI groups with significantly increased LDH activity and decreased relative cell viability. Compared to WT mice, more significant changes were detected in MT-I/II KO mice in 100 HI groups. No significant differences were detected between the NI group and 10 HI group in both the MT-I/II KO and WT mice groups (P > 0.05). Conclusions. Iodide excess in a thyroid without MT I/II protection may result in strong mitochondrial oxidative stress, which further leads to the damage of thyrocytes.

Differences in the protein expression levels of Trx2 and Prx3 in the hippocampal CA1 region between adult and aged gerbils following transient global cerebral ischemia

The thioredoxin (Trx) and peroxiredoxin (Prx) redox system is associated with neuronal damage and neuroprotective effects via the regulation of oxidative stress in brain ischemia. In the present study, ischemia-induced changes in the protein expression levels of Trx2 and Prx3 in the stratum pyramidale (SP) of the hippocampal CA1 region were investigated in adult and aged gerbils, subjected to 5 min of transient global cerebral ischemia, using immunohistochemistry and western blot analysis. In the adult ischemia-group, minimal Trx2 immunoreactivity was detected in the SP 2 days after ischemia-reperfusion. In the aged animals, the Trx2 immunoreactivity in the sham-group was marginally lower compared with that in the adult sham-group. In the aged ischemia-group, Trx2 immunoreactivity in the SP was significantly higher 1, 2 and 4 days post-ischemia, compared with that in the adult ischemia-group and, in the 5 days post-ischemia group, Trx2 immunoreactivity was significantly decreased in the SP. Prx3 immunoreactivity in the SP of the adult ischemia-group was significantly decreased from 4 days after ischemia-reperfusion. In the aged animals, Prx3 immunoreactivity in the sham-group was also marginally lower compared with that in the adult sham-group. Prx3 immunoreactivity in the aged ischemia-group was also significantly higher 1, 2 and 4 days post-ischemia, compared with the adult ischemia-group; however, the Prx3 immunoreactivity was significantly decreased 5 days post-ischemia. The western blot analyses revealed that the pattern of changes in the protein levels of Trx2 and Prx3 in the adult and aged hippocampal CA1 region following ischemic damage were similar to the results obtained in the immunohistochemical data. These findings indicated that cerebral ischemia lead to different protein expression levels of Trx2 and Prx3 in the hippocampal CA1 region between adult and aged gerbils, and these differences may be associated with more delayed neuronal death in the aged gerbil hippocampus following transient global cerebral ischemia.

Thiol redox homeostasis in neurodegenerative disease

This review provides an overview of the biochemistry of thiol redox couples and the significance of thiol redox homeostasis in neurodegenerative disease. The discussion is centred on cysteine/cystine redox balance, the significance of the x_c⁻ cystine–glutamate exchanger and the association between protein thiol redox balance and neurodegeneration, with particular reference to Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and glaucoma. The role of thiol disulphide oxidoreductases in providing neuroprotection is also discussed.

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An overview of the biochemistry of thiol redox couples.

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The significance of thiol redox homoeostasis in neurodegenerative disease.

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The association between the x_c⁻ cystine–glutamate exchanger and glutamate-mediated toxicity.

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The role of thiol disulphide oxidoreductases in neuroprotection.

Knockout of mitochondrial thioredoxin reductase stabilizes prolyl hydroxylase 2 and inhibits tumor growth and tumor-derived angiogenesis

AIMS

Mitochondrial thioredoxin reductase (Txnrd2) is a central player in the control of mitochondrial hydrogen peroxide (H2O2) abundance by serving as a direct electron donor to the thioredoxin-peroxiredoxin axis. In this study, we investigated the impact of targeted disruption of Txnrd2 on tumor growth.

RESULTS

Tumor cells with a Txnrd2 deficiency failed to activate hypoxia-inducible factor-1α (Hif-1α) signaling; it rather caused PHD2 accumulation, Hif-1α degradation and decreased vascular endothelial growth factor (VEGF) levels, ultimately leading to reduced tumor growth and tumor vascularization. Increased c-Jun NH2-terminal Kinase (JNK) activation proved to be the molecular link between the loss of Txnrd2, an altered mitochondrial redox balance with compensatory upregulation of glutaredoxin-2, and elevated PHD2 expression.

INNOVATION

Our data provide compelling evidence for a yet-unrecognized mitochondrial Txnrd-driven, regulatory mechanism that ultimately prevents cellular Hif-1α accumulation. In addition, simultaneous targeting of both the mitochondrial thioredoxin and glutathione systems was used as an efficient therapeutic approach in hindering tumor growth.

CONCLUSION

This work demonstrates an unexpected regulatory link between mitochondrial Txnrd and the JNK-PHD2-Hif-1α axis, which highlights how the loss of Txnrd2 and the resulting altered mitochondrial redox balance impairs tumor growth as well as tumor-related angiogenesis. Furthermore, it opens a new avenue for a therapeutic approach to hinder tumor growth by the simultaneous targeting of both the mitochondrial thioredoxin and glutathione systems.

Mitochondrial mechanisms of redox cycling agents implicated in Parkinson's disease

Environmental agents have been implicated in Parkinson's disease (PD) based on epidemiological studies and the ability of toxicants to replicate features of PD. However, the precise mechanisms by which toxicants induce dopaminergic toxicity observed in the idiopathic form of PD remain to be fully understood. The roles of ROS and mitochondria are strongly suggested in the mechanisms by which these toxicants exert dopaminergic toxicity. There are marked differences and similarities shared by the toxicants in increasing steady-state levels of mitochondrial ROS. Furthermore, toxicants increase steady-state mitochondrial ROS levels by stimulating the production, inhibiting the antioxidant pathways of both. This review will focus on the role of mitochondria and ROS in PD associated with environmental exposures to redox-based toxicants.

Effect of thyroid state on enzymatic and non-enzymatic processes in H2O2 removal by liver mitochondria of male rats

We investigated thyroid state effect on capacity of rat liver mitochondria to remove exogenously produced H2O2, determining their ability to decrease fluorescence generated by an H2O2 detector system. The rate of H2O2 removal by both non respiring and respiring mitochondria was increased by hyperthyroidism and decreased by hypothyroidism. However, the rate was higher in the presence of respiratory substrates, in particular pyruvate/malate, indicating a respiration-dependent process. Generally, the changes in H2O2 removal rates mirrored those in H2O2 release rates excluding the possibility that endogenous and exogenous H2O2 competed for the removing system. Pharmacological inhibition revealed thyroid state-linked differences in antioxidant enzyme contribution to H2O2 removal which were consistent with those in antioxidant system activities. The H2O2 removal was only in part due to enzymatic systems and that imputable to non-enzymatic processes was higher in hyperthyroid and lower in hypothyroid mitochondria. The levels of cytochrome c and the light emissions, due to luminol oxidation catalyzed by cytochrome/H2O2, exhibited similar changes with thyroid state supporting the idea that non-enzymatic scavenging was mainly due to hemoprotein action, which produces hydroxyl radicals. Further support was obtained showing that the whole antioxidant capacity, which provides an evaluation of capacity of the systems, different from cytochromes, assigned to H2O2 scavenging, was lower in hyperthyroid than in hypothyroid state. In conclusion, our results show that mitochondria from hyperthyroid liver have a high capacity for H2O2 removal, which, however, leading in great part to more reactive oxygen species, results harmful for such organelles.

Changes in the mitochondrial antioxidant systems in neurodegenerative diseases and acute brain disorders

Oxidative and nitrosative stress (ONS) contributes to the pathogenesis of most brain maladies, and the magnitude of ONS is related to the ability of cellular antioxidants to neutralize the accumulating reactive oxygen and nitrogen species (ROS/RNS). While the major ROS/RNS scavengers and regenerators of bio-oxidized molecules, superoxide dysmutases (SODs), glutathione (GSH), thioredoxin (Trx) and peroxiredoxin (Prx), are distributed in all cellular compartments. This review specifically focuses on the role of the systems operating in mitochondria. There is a growing consensus that the mitochondrial SOD isoform - SOD2 and GSH are critical for the cellular antioxidant defense. Variable changes of the expression or activities of one or more of the mitochondrial antioxidant systems have been documented in the brains derived from human patients and/or in animal models of neurodegenerative diseases (Alzheimer's disease, Parkinson's disease), cerebral ischemia, toxic brain cell damage associated with overexposure to mercury or excitotoxins, or hepatic encephalopathy. In many cases, ambiguity of the responses of the different antioxidant systems in one and the same disease needs to be more conclusively evaluated before the balance of the changes is viewed as beneficial or detrimental. Modulation of the mitochondrial antioxidant systems may in the future become a target of antioxidant therapy.

Toxicity assessment of 2,4-D and MCPA herbicides in primary culture of fish hepatic cells

In this study, we used primary cultures of fish hepatic cells as a tool for evaluating the effects of environmental contamination. Primary hepatic cell cultures derived from the subtropical fish Metynnis roosevelti were exposed to different concentrations (0.275, 2.75 and 27.5 μg L(-1)) of the herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA). Cellular respiratory activity was evaluated by polarography using three substrates: 0.5 M glucose, 0.5 M succinate and 0.5 M α-ketoglutarate. Significant changes were observed in cellular oxygen consumption with 0.5 M α-ketoglutarate. Even at low concentrations, 2,4-D and MCPA were potent uncouplers of oxidative phosphorylation. Primary cultures of M. roosevelti liver cells may provide a useful tool for the evaluation of environmental contaminant effects. A review of regulations regarding permitted concentrations of these herbicides is needed.

Dyclonine rescues frataxin deficiency in animal models and buccal cells of patients with Friedreich's ataxia

Inherited deficiency in the mitochondrial protein frataxin (FXN) causes the rare disease Friedreich's ataxia (FA), for which there is no successful treatment. We identified a redox deficiency in FA cells and used this to model the disease. We screened a 1600-compound library to identify existing drugs, which could be of therapeutic benefit. We identified the topical anesthetic dyclonine as protective. Dyclonine increased FXN transcript and FXN protein dose-dependently in FA cells and brains of animal models. Dyclonine also rescued FXN-dependent enzyme deficiencies in the iron-sulfur enzymes, aconitase and succinate dehydrogenase. Dyclonine induces the Nrf2 [nuclear factor (erythroid-derived 2)-like 2] transcription factor, which we show binds an upstream response element in the FXN locus. Additionally, dyclonine also inhibited the activity of histone methyltransferase G9a, known to methylate histone H3K9 to silence FA chromatin. Chronic dosing in a FA mouse model prevented a performance decline in balance beam studies. A human clinical proof-of-concept study was completed in eight FA patients dosed twice daily using a 1% dyclonine rinse for 1 week. Six of the eight patients showed an increase in buccal cell FXN levels, and fold induction was significantly correlated with disease severity. Dyclonine represents a novel therapeutic strategy that can potentially be repurposed for the treatment of FA.

Mitochondrial function and energy metabolism in neuronal HT22 cells resistant to oxidative stress

BACKGROUND AND PURPOSE

The hippocampal cell line HT22 is an excellent model for studying the consequences of endogenous oxidative stress. Extracellular glutamate depletes cellular glutathione by blocking the glutamate/cystine antiporter system xc-. Glutathione depletion induces a well-defined programme of cell death characterized by an increase in reactive oxygen species and mitochondrial dysfunction.

EXPERIMENTAL APPROACH

We compared the mitochondrial shape, the abundance of mitochondrial complexes and the mitochondrial respiration of HT22 cells, selected based on their resistance to glutamate, with those of the glutamate-sensitive parental cell line.

KEY RESULTS

Glutamate-resistant mitochondria were less fragmented and displayed seemingly contradictory features: mitochondrial calcium and superoxide were increased while high-resolution respirometry suggested a reduction in mitochondrial respiration. This was interpreted as a reverse activity of the ATP synthase under oxidative stress, leading to hydrolysis of ATP to maintain or even elevate the mitochondrial membrane potential, suggesting these cells endure ineffective energy metabolism to protect their membrane potential. Glutamate-resistant cells were also resistant to oligomycin, an inhibitor of the ATP synthase, but sensitive to deoxyglucose, an inhibitor of hexokinases. Exchanging glucose with galactose rendered resistant cells 1000-fold more sensitive to oligomycin. These results, together with a strong increase in cytosolic hexokinase 1 and 2, a reduced lactate production and an increased activity of glucose-6-phosphate dehydrogenase, suggest that glutamate-resistant HT22 cells shuttle most available glucose towards the hexose monophosphate shunt to increase glutathione recovery.

CONCLUSIONS AND IMPLICATIONS

These results indicate that mitochondrial and metabolic adaptations play an important role in the resistance of cells to oxidative stress.

Enhanced hydrogen peroxide generation accompanies the beneficial bioenergetic effects of methylene blue in isolated brain mitochondria

The redox dye methylene blue (MB) is proven to have beneficial effects in various models of neurodegenerative diseases. Here we investigated the effects of MB (100 nM, 300 nM, and 1 μM) on key bioenergetic parameters and on H2O2 production/elimination in isolated guinea pig brain mitochondria under normal as well as respiration-impaired conditions. As measured by high-resolution Oxygraph the rate of resting oxygen consumption was increased, but the ADP-stimulated respiration was unaffected by MB with any of the substrates (glutamate malate, succinate, or α-glycerophosphate) used for supporting mitochondrial respiration. In mitochondria treated with inhibitors of complex I or complex III MB moderately but significantly increased the rate of ATP production, restored ΔΨm, and increased the rate of Ca(2+) uptake. The effects of MB are consistent with transferring electrons from upstream components of the electron transport chain to cytochrome c, which is energetically favorable when the flow of electrons in the respiratory chain is compromised. On the other hand, MB significantly increased the production of H2O2 measured by Amplex UltraRed fluorimetry under all conditions, in resting, ATP-synthesizing, and respiration-impaired mitochondria, with each substrate combination supporting respiration. Furthermore, it also decreased the elimination of H2O2. Generation of H2O2 without superoxide formation, observed in the presence of MB, is interpreted as a result of reduction of molecular oxygen to H2O2 by the reduced MB. The elevated generation and impaired elimination of H2O2 should be considered for the overall oxidative state of mitochondria treated with MB.