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

Aging: A mitochondrial DNA perspective, critical analysis and an update

The mitochondrial theory of aging, a mainstream theory of aging which once included accumulation of mitochondrial DNA (mtDNA) damage by reactive oxygen species (ROS) as its cornerstone, has been increasingly losing ground and is undergoing extensive revision due to its inability to explain a growing body of emerging data. Concurrently, the notion of the central role for mtDNA in the aging process is being met with increased skepticism. Our progress in understanding the processes of mtDNA maintenance, repair, damage, and degradation in response to damage has largely refuted the view of mtDNA as being particularly susceptible to ROS-mediated mutagenesis due to its lack of “protective” histones and reduced complement of available DNA repair pathways. Recent research on mitochondrial ROS production has led to the appreciation that mitochondria, even in vitro, produce much less ROS than previously thought, automatically leading to a decreased expectation of physiologically achievable levels of mtDNA damage. New evidence suggests that both experimentally induced oxidative stress and radiation therapy result in very low levels of mtDNA mutagenesis. Recent advances provide evidence against the existence of the “vicious” cycle of mtDNA damage and ROS production. Meta-studies reveal no longevity benefit of increased antioxidant defenses. Simultaneously, exciting new observations from both comparative biology and experimental systems indicate that increased ROS production and oxidative damage to cellular macromolecules, including mtDNA, can be associated with extended longevity. A novel paradigm suggests that increased ROS production in aging may be the result of adaptive signaling rather than a detrimental byproduct of normal respiration that drives aging. Here, we review issues pertaining to the role of mtDNA in aging.

Redox control of microglial function: molecular mechanisms and functional significance

Neurodegenerative diseases are characterized by chronic microglial over-activation and oxidative stress. It is now beginning to be recognized that reactive oxygen species (ROS) produced by either microglia or the surrounding environment not only impact neurons but also modulate microglial activity. In this review, we first analyze the hallmarks of pro-inflammatory and anti-inflammatory phenotypes of microglia and their regulation by ROS. Then, we consider the production of reactive oxygen and nitrogen species by NADPH oxidases and nitric oxide synthases and the new findings that also indicate an essential role of glutathione (γ-glutamyl-l-cysteinylglycine) in redox homeostasis of microglia. The effect of oxidant modification of macromolecules on signaling is analyzed at the level of oxidized lipid by-products and sulfhydryl modification of microglial proteins. Redox signaling has a profound impact on two transcription factors that modulate microglial fate, nuclear factor kappa-light-chain-enhancer of activated B cells, and nuclear factor (erythroid-derived 2)-like 2, master regulators of the pro-inflammatory and antioxidant responses of microglia, respectively. The relevance of these proteins in the modulation of microglial activity and the interplay between them will be evaluated. Finally, the relevance of ROS in altering blood brain barrier permeability is discussed. Recent examples of the importance of these findings in the onset or progression of neurodegenerative diseases are also discussed. This review should provide a profound insight into the role of redox homeostasis in microglial activity and help in the identification of new promising targets to control neuroinflammation through redox control of the brain.

Low-dose estrogen is as effective as high-dose treatment in rats with postmenopausal hypertension

: This study was conducted to test the hypothesis that 17β-estradiol therapy improves redox balance by decreasing reactive oxygen species production and increasing nitric oxide (NO) bioavailability, favoring Akt pathway activation and resulting in a better autonomic vascular control. Ovariectomized female Wistar rats were divided into 4 groups: (1) vehicle (VL) and animals treated with a pellet of 17β-estradiol for 21 days; (2) low dose (LE; 0.05 mg); (3) medium dose (ME; 0.2 mg); and (4) high dose (HE; 0.5 mg). Arterial pressure and its sympathetic nervous system modulation were evaluated by spectral analysis. Nitric oxide synthase and NADPH oxidase (Nox) activities, H2O2 concentration, redox status (GSH/GSSG), protein expression of Trx-1 and p-Akt/Akt were evaluated in the aorta, whereas NO metabolites were measured in the serum. Estrogen-treated groups showed a significant decrease in arterial pressure and sympathetic vascular drive. Redox status was significantly improved and NADPH oxidase and H2O2 were decreased in all estrogen-treated groups. Estrogen also induced an enhancement in NO metabolites, nitric oxide synthase activity, and Akt phosphorylation. This study demonstrated that estrogen treatment to ovariectomized rats induced cardioprotection, which was evidenced by reduced blood pressure variability and vascular sympathetic drive. These effects were associated with an improved redox balance and Akt activation, resulting in an enhanced NO bioavailability.

Scavenging of H2O2 by mouse brain mitochondria

Mitochondrial reactive oxygen species (ROS) metabolism is unique in that mitochondria both generate and scavenge ROS. Recent estimates of ROS scavenging capacity of brain mitochondria are surprisingly high, ca. 9-12 nmol H2O2/min/mg, which is ~100 times higher than the rate of ROS generation. This raises a question whether brain mitochondria are a source or a sink of ROS. We studied the interaction between ROS generation and scavenging in mouse brain mitochondria by measuring the rate of removal of H2O2 added at a concentration of 0.4 μM, which is close to the reported physiological H2O2 concentrations in tissues, under conditions of low and high levels of mitochondrial H2O2 generation. With NAD-linked substrates, the rate of H2O2 generation by mitochondria was ~50-70 pmol/min/mg. The H2O2 scavenging dynamics was best approximated by the first order reaction equation. H2O2 scavenging was not affected by the uncoupling of mitochondria, phosphorylation of added ADP, or the genetic ablation of glutathione peroxidase 1, but decreased in the absence of respiratory substrates, in the presence of thioredoxin reductase inhibitor auranofin, or in partially disrupted mitochondria. With succinate, the rate of H2O2 generation was ~2,200-2,900 pmol/min/mg; the scavenging of added H2O2 was masked by a significant accumulation of generated H2O2 in the assay medium. The obtained data were fitted into a simple model that reasonably well described the interaction between H2O2 scavenging and production. It showed that mitochondria are neither a sink nor a source of H2O2, but can function as both at the same time, efficiently stabilizing exogenous H2O2 concentration at a level directly proportional to the ratio of the H2O2 generation rate to the rate constant of the first order scavenging reaction.

Neuroprotection of antioxidant enzymes against transient global cerebral ischemia in gerbils

Experimentally transient global cerebral ischemia using animal models have been thoroughly studied and numerous reports suggest the involvement of oxidative stress in the pathogenesis of neuronal death in ischemic lesions. In animal models, during the reperfusion period after ischemia, increased oxygen supply results in the overproduction of reactive oxygen species (ROS), which are involved in the process of cell death. ROS, such as superoxide anions, hydroxyl free radicals, hydrogen peroxide and nitric oxide are produced as a consequence of metabolic reactions and central nervous system activity. These reactive species are directly involved in the oxidative damage of cellular macromolecules such as nucleic acids, lipids and proteins in ischemic tissues, which can lead to cell death. Antioxidant enzymes are believed to be among the major mechanisms by which cells counteract the deleterious effect of ROS after cerebral ischemia. Consequently, antioxidant strategies have been long suggested as a therapy for experimental ischemic stroke; however, clinical trials have not yet been able to promote the translation of this concept into patient treatment regimens. This article focuses on the contribution of oxidative stress or antioxidants to the post-ischemic neuronal death following transient global cerebral ischemia by using a gerbil model.

NADPH-dependent thioredoxin reductase A (NTRA) confers elevated tolerance to oxidative stress and drought

NADPH-dependent thioredoxin reductases (NTRs) are key-regulatory enzymes determining the redox state of the thioredoxin (Trx) system that provides reducing power to peroxidases or oxidoreductases. Moreover, it also plays an essential function in the direct reduction of ROS and acquiring stress tolerance in plant. Cytoplasmic NTRA, mitochondrial NTRB, and chloroplastic NTRC are the three conserved NTRs which cooperate with specific sub-cellularly localized Trxs in Arabidopsis. However, cytosolic NTRs such as NTRA in Arabidopsis have not previously been identified in plants or mammals as a source of functional redundancy with mitochondrial NTRs. Here, we show the involvement of NTRA in the plant stress response counteracting oxidative and drought stresses. Methyl viologen (MV), an inducer of oxidative stress in plants, enhanced the NTRA transcripts. To identify the physiological role of NTRA influencing ROS homeostasis by stress, NTRA overexpression (NTRAOX) and knock-out mutants (ntra-ko) were generated. After exposure to oxidative stress, wild-type and ntra-ko plants were sensitive, but NTRAOX plants tolerant. ROS range was increased by MV in wild-type and ntra-ko plants, but not in NTRAOX. Investigating the involvement of Arabidopsis NTRA in drought, NTRAOX plants exhibited extreme drought tolerance with high survival rates, lower water loss and reduced ROS compared to wild-type and ntra-ko plants. Transcripts of drought-responsive genes, such as RD29A and DREB2A, were highly expressed under drought and antioxidant genes, namely CuZnSOD and APX1 were enhanced in the absence of drought in NTRAOX plants. The results suggest that NTRA overexpression confers oxidative and drought tolerance by regulation of ROS amounts.

Short time exposure to hydrogen peroxide induces sustained glutathione export from cultured neurons

Hydrogen peroxide is a normal by-product of cellular metabolism that in higher concentrations can cause oxidative stress. Cultured cerebellar granule neurons efficiently disposed of micromolar concentrations of hydrogen peroxide with half-times in the minute range in a process that predominately involved catalase. Application of up to 100 µM hydrogen peroxide did not affect the cell viability for up to 4h, but caused a time- and concentration-dependent increase in the extracellular glutathione (GSH) content that was accompanied by a matching decrease in the cellular GSH content. Hydrogen peroxide at 100 µM stimulated maximally the GSH export from viable neurons, but did not affect GSH export from cultured astrocytes. The peroxide-induced extracellular GSH accumulation from neurons was lowered by 70% in the presence of MK571, an inhibitor of multidrug resistance protein (Mrp) 1. The extracellular GSH content determined after 4h of incubation was already significantly increased after a 5-min exposure of neurons to hydrogen peroxide and became maximal after 15 min of peroxide application. These data demonstrate that just a short exposure of viable cerebellar granule neurons to micromolar concentrations of hydrogen peroxide stimulates a prolonged Mrp1-mediated export of cellular GSH. This process may compromise the antioxidative potential of neurons and increase their sensitivity toward drugs and toxins.

Brain mitochondria from DJ-1 knockout mice show increased respiration-dependent hydrogen peroxide consumption

Mutations in the DJ-1 gene have been shown to cause a rare autosomal-recessive genetic form of Parkinson's disease (PD). The function of DJ-1 and its role in PD development has been linked to multiple pathways, however its exact role in the development of PD has remained elusive. It is thought that DJ-1 may play a role in regulating reactive oxygen species (ROS) formation and overall oxidative stress in cells through directly scavenging ROS itself, or through the regulation of ROS scavenging systems such as glutathione (GSH) or thioredoxin (Trx) or ROS producing complexes such as complex I of the electron transport chain. Previous work in this laboratory has demonstrated that isolated brain mitochondria consume H2O2 predominantly by the Trx/Thioredoxin Reductase (TrxR)/Peroxiredoxin (Prx) system in a respiration dependent manner (Drechsel et al., Journal of Biological Chemistry, 2010). Therefore we wanted to determine if mitochondrial H2O2 consumption was altered in brains from DJ-1 deficient mice (DJ-1(-/-)). Surprisingly, DJ-1(-/-) mice showed an increase in mitochondrial respiration-dependent H2O2 consumption compared to controls. To determine the basis of the increased H2O2 consumption in DJ1(-/-) mice, the activities of Trx, Thioredoxin Reductase (TrxR), GSH, glutathione disulfide (GSSG) and glutathione reductase (GR) were measured. Compared to control mice, brains from DJ-1(-/-) mice showed an increase in (1) mitochondrial Trx activity, (2) GSH and GSSG levels and (3) mitochondrial glutaredoxin (GRX) activity. Brains from DJ-1(-/-) mice showed a decrease in mitochondrial GR activity compared to controls. The increase in the enzymatic activities of mitochondrial Trx and total GSH levels may account for the increased H2O2 consumption observed in the brain mitochondria in DJ-1(-/-) mice perhaps as an adaptive response to chronic DJ-1 deficiency.

Nicotinamide nucleotide transhydrogenase (Nnt) links the substrate requirement in brain mitochondria for hydrogen peroxide removal to the thioredoxin/peroxiredoxin (Trx/Prx) system

Mitochondrial reactive oxygen species are implicated in the etiology of multiple neurodegenerative diseases, including Parkinson disease. Mitochondria are known to be net producers of ROS, but recently we have shown that brain mitochondria can consume mitochondrial hydrogen peroxide (H2O2) in a respiration-dependent manner predominantly by the thioredoxin/peroxiredoxin system. Here, we sought to determine the mechanism linking mitochondrial respiration with H2O2 catabolism in brain mitochondria and dopaminergic cells. We hypothesized that nicotinamide nucleotide transhydrogenase (Nnt), which utilizes the proton gradient to generate NADPH from NADH and NADP(+), provides the link between mitochondrial respiration and H2O2 detoxification through the thioredoxin/peroxiredoxin system. Pharmacological inhibition of Nnt in isolated brain mitochondria significantly decreased their ability to consume H2O2 in the presence, but not absence, of respiration substrates. Nnt inhibition in liver mitochondria, which do not require substrates to detoxify H2O2, had no effect. Pharmacological inhibition or lentiviral knockdown of Nnt in N27 dopaminergic cells (a) decreased H2O2 catabolism, (b) decreased NADPH and increased NADP(+) levels, and (c) decreased basal, spare, and maximal mitochondrial oxygen consumption rates. Nnt-deficient cells possessed higher levels of oxidized mitochondrial Prx, which rendered them more susceptible to steady-state increases in H2O2 and cell death following exposure to subtoxic levels of paraquat. These data implicate Nnt as the critical link between the metabolic and H2O2 antioxidant function in brain mitochondria and suggests Nnt as a potential therapeutic target to improve the redox balance in conditions of oxidative stress associated with neurodegenerative diseases.

Acetaminophen reactive intermediates target hepatic thioredoxin reductase

Acetaminophen (APAP) is metabolized in the liver to N-acetyl-p-benzoquinone imine (NAPQI), an electrophilic metabolite known to bind liver proteins resulting in hepatotoxicity. Mammalian thioredoxin reductase (TrxR) is a cellular antioxidant containing selenocysteine (Sec) in its C-terminal redox center, a highly accessible target for electrophilic modification. In the present study, we determined if NAPQI targets TrxR. Hepatotoxicity induced by APAP treatment of mice (300 mg/kg, i.p.) was associated with a marked inhibition of both cytosolic TrxR1 and mitochondrial TrxR2 activity. Maximal inhibition was detected at 1 and 6 h post-APAP for TrxR1 and TrxR2, respectively. In purified rat liver TrxR1, enzyme inactivation was correlated with the metabolic activation of APAP by cytochrome P450, indicating that enzyme inhibition was due to APAP-reactive metabolites. NAPQI was also found to inhibit TrxR1. NADPH-reduced TrxR1 was significantly more sensitive to NAPQI (IC50 = 0.023 μM) than the oxidized enzyme (IC50 = 1.0 μM) or a human TrxR1 Sec498Cys mutant enzyme (IC50 = 17 μM), indicating that cysteine and selenocysteine residues in the redox motifs of TrxR are critical for enzyme inactivation. This is supported by our findings that alkylation of reduced TrxR with biotin-conjugated iodoacetamide, which selectively reacts with selenol or thiol groups on proteins, was inhibited by NAPQI. LC-MS/MS analysis confirmed that NAPQI modified cysteine 59, cysteine 497, and selenocysteine 498 residues in the redox centers of TrxR, resulting in enzyme inhibition. In addition to disulfide reduction, TrxR is also known to mediate chemical redox cycling. We found that menadione redox cycling by TrxR was markedly less sensitive to NAPQI than disulfide reduction, suggesting that TrxR mediates these reactions via distinct mechanisms. These data demonstrate that APAP-reactive metabolites target TrxR, suggesting an additional mechanism by which APAP induces oxidative stress and hepatotoxicity.

Mitochondrial respiratory chain complexes as sources and targets of thiol-based redox-regulation

The respiratory chain of the inner mitochondrial membrane is a unique assembly of protein complexes that transfers the electrons of reducing equivalents extracted from foodstuff to molecular oxygen to generate a proton-motive force as the primary energy source for cellular ATP-synthesis. Recent evidence indicates that redox reactions are also involved in regulating mitochondrial function via redox-modification of specific cysteine-thiol groups in subunits of respiratory chain complexes. Vice versa the generation of reactive oxygen species (ROS) by respiratory chain complexes may have an impact on the mitochondrial redox balance through reversible and irreversible thiol-modification of specific target proteins involved in redox signaling, but also pathophysiological processes. Recent evidence indicates that thiol-based redox regulation of the respiratory chain activity and especially S-nitrosylation of complex I could be a strategy to prevent elevated ROS production, oxidative damage and tissue necrosis during ischemia-reperfusion injury. This review focuses on the thiol-based redox processes involving the respiratory chain as a source as well as a target, including a general overview on mitochondria as highly compartmentalized redox organelles and on methods to investigate the redox state of mitochondrial proteins. This article is part of a Special Issue entitled: Thiol-Based Redox Processes.

Selenium protects neonates against neurotoxicity from prenatal exposure to manganese

Manganese (Mn) exposure can affect brain development. Whether Selenium (Se) can protect neonates against neurotoxicity from Mn exposure remains unclear. We investigated this issue in 933 mother-newborn pairs in Shanghai, China, from 2008 through 2009. Umbilical cord serum concentrations of Mn and Se were measured and Neonatal Behavioral Neurological Assessment (NBNA) tests were conducted. The scores <37 were defined as the low NBNA. The median concentrations of cord serum Mn and Se were 4.0 µg/L and 63.1 µg/L, respectively. After adjusting for potential confounders, the interaction between Se and Mn was observed. Cord blood Mn levels had different effects on NBNA scores stratified by different cord blood Se levels. With Se Collapse

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MESH Headings

• Analysis of Variance
• Female
• Humans
• Infant, Newborn
• Male
• Manganese/toxicity
• Maternal Exposure/adverse effects
• Neuroprotective Agents/pharmacology
• Pregnancy
• Prenatal Exposure Delayed Effects/prevention & control
• Selenium/pharmacology

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Affiliation(s)

Xin Yang MOE-Shanghai Key Lab of Children’s Environmental Health, Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China
YiXiao Bao Department of Pediatrics, Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China
HuanHuan Fu MOE-Shanghai Key Lab of Children’s Environmental Health, Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China
LuanLuan Li MOE-Shanghai Key Lab of Children’s Environmental Health, Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China
TianHong Ren MOE-Shanghai Key Lab of Children’s Environmental Health, Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China
XiaoDan Yu MOE-Shanghai Key Lab of Children’s Environmental Health, Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China

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Mitochondrial energy metabolism and redox signaling in brain aging and neurodegeneration

SIGNIFICANCE

The mitochondrial energy-transducing capacity is essential for the maintenance of neuronal function, and the impairment of energy metabolism and redox homeostasis is a hallmark of brain aging, which is particularly accentuated in the early stages of neurodegenerative diseases.

RECENT ADVANCES

The communications between mitochondria and the rest of the cell by energy- and redox-sensitive signaling establish a master regulatory device that controls cellular energy levels and the redox environment. Impairment of this regulatory devise is critical for aging and the early stages of neurodegenerative diseases.

CRITICAL ISSUES

This review focuses on a coordinated metabolic network-cytosolic signaling, transcriptional regulation, and mitochondrial function-that controls the cellular energy levels and redox status as well as factors which impair this metabolic network during brain aging and neurodegeneration.

FUTURE DIRECTIONS

Characterization of mitochondrial function and mitochondria-cytosol communications will provide pivotal opportunities for identifying targets and developing new strategies aimed at restoring the mitochondrial energy-redox axis that is compromised in brain aging and neurodegeneration.

Morphological changes and altered expression of antioxidant proteins in a heterozygous dynein mutant; a mouse model of spinal muscular atrophy

OBJECTIVE

There is increased evidence that oxidative stress is involved in exacerbations of neurodegenerative diseases and spinal muscular atrophies.

METHODS

We examined changes in morphology and expression of antioxidant proteins and peroxiredoxins in motor neurons of lumbar spinal cord, dorsal root ganglion sensory neurons, macroglial cells and quadriceps muscles of newborn heterozygous Loa/+ mice ("legs at odd angles"), a mouse model for early onset of the spinal muscular atrophy with lower extremity predominance (SMA-LED).

RESULTS

Our data indicate that newborn Loa-mice develop: neuroinflammation of the sensory and motor neurons; muscular inflammation with atrophic and denervated myofibers; increased expression of neuronal mitochondrial peroxiredoxins (Prxs) 3, 5 and cytoplasmic Prx 6 in motor and sensory neurons, myofibers, fibroblasts of perimysium and chondrocytes of cartilage; and decreased expression of Prx 6 by glial cells and in extracellular space surrounding motor neurons.

CONCLUSION

The decrease in expression of Prx 6 by glial cells and extracellular Prx 6 secretion in early stages of the pathological conditions is consistent with the hypothesis that chronic oxidative stress may lead to neurodegeneration of motor neurons and exacerbation of the pathology.

Lymphocyte mitochondria: toward identification of peripheral biomarkers in the progression of Alzheimer disease

Alzheimer disease (AD) is an age-related neurodegenerative condition. AD is histopathologically characterized by the presence of three main hallmarks: senile plaques (rich in amyloid-β peptide), neuronal fibrillary tangles (rich in phosphorylated tau protein), and synapse loss. However, definitive biomarkers for this devastating disease in living people are still lacking. In this study, we show that levels of oxidative stress markers are significantly increased in the mitochondria isolated from lymphocytes of subjects with mild cognitive impairment (MCI) compared to cognitively normal individuals. Further, an increase in mitochondrial oxidative stress in MCI is associated with MMSE score, vitamin E components, and β-carotene. Further, a proteomics approach showed that alterations in the levels of thioredoxin-dependent peroxide reductase, myosin light polypeptide 6, and ATP synthase subunit β might be important in the progression and pathogenesis of AD. Increased understanding of oxidative stress and protein alterations in easily obtainable peripheral tissues will be helpful in developing biomarkers to combat this devastating disorder.

Role of enzymatic and non-enzymatic processes in H2O2 removal by rat liver and heart mitochondria

We compared the capacity of rat liver and heart mitochondria to remove exogenously produced H2O2, determining their ability to decrease fluorescence generated by H2O2 detector system. In the absence of substrates, liver and heart mitochondria removed H2O2 at similar rates. Respiratory substrate addition increased removal rates, indicating a respiration-dependent process. Moreover, the rates were higher with pyruvate/malate than with succinate and in heart than in liver mitochondria. Generally, the changes in H2O2 removal rates mirrored those of H2O2 release rates excluding the possibility that endogenous and exogenous H2O2 competed for the removing system. This idea was supported by the observation that the heaviest of three liver mitochondrial fractions exhibited the highest rates of both H2O2 release and removal. Pharmacological inhibition showed tissue-linked differences in antioxidant enzyme contribution to H2O2 removal which were consistent with the differences in antioxidant system activities. The enzymatic processes accounted only in part for net H2O2 removal and the non-enzymatic ones participated to H2O2 scavenging to a degree that was higher for heart than for liver mitochondria. The idea that non-enzymatic scavenging was due in great part to hemoproteins action was consistent with observation that the concentration of cytochromes, in particular cytochrome c, was higher in heart mitochondria. Indirect support was also obtained by a technique of enhanced luminescence, utilizing the capacity of cytochrome c/H2O2 to catalyze the luminol oxidation, which showed that luminescence response to an oxidative challenge was higher in heart mitochondria.

A single amino acid residue controls ROS production in the respiratory Complex I from Escherichia coli

Reactive oxygen species (ROS) production by respiratory Complex I from Escherichia coli was studied in bacterial membrane fragments and in the isolated and purified enzyme, either solubilized or incorporated in proteoliposomes. We found that the replacement of a single amino acid residue in close proximity to the nicotinamide adenine dinucleotide (NADH)-binding catalytic site (E95 in the NuoF subunit) dramatically increases the reactivity of Complex I towards dioxygen (O2 ). In the E95Q variant short-chain ubiquinones exhibit strong artificial one-electron reduction at the catalytic site, also leading to a stronger increase in ROS production. Two mechanisms can contribute to the observed kinetic effects: (a) a change in the reactivity of flavin mononucleotide (FMN) towards dioxygen at the catalytic site, and (b) a change in the population of the ROS-generating state. We propose the existence of two (closed and open) states of the NAD(+) -bound enzyme as one feature of the substrate-binding site of Complex I. The analysis of the kinetic model of ROS production allowed us to propose that the population of Complex I with reduced FMN is always low in the wild-type enzyme even at low ambient redox potentials, minimizing the rate of reaction with O2 in contrast to E95Q variant.

A spontaneous mutation in the nicotinamide nucleotide transhydrogenase gene of C57BL/6J mice results in mitochondrial redox abnormalities

NADPH is the reducing agent for mitochondrial H2O2 detoxification systems. Nicotinamide nucleotide transhydrogenase (NNT), an integral protein located in the inner mitochondrial membrane, contributes to an elevated mitochondrial NADPH/NADP(+) ratio. This enzyme catalyzes the reduction of NADP(+) at the expense of NADH oxidation and H(+) reentry to the mitochondrial matrix. A spontaneous Nnt mutation in C57BL/6J (B6J-Nnt(MUT)) mice arose nearly 3 decades ago but was only discovered in 2005. Here, we characterize the consequences of the Nnt mutation on the mitochondrial redox functions of B6J-Nnt(MUT) mice. Liver mitochondria were isolated both from an Nnt wild-type C57BL/6 substrain (B6JUnib-Nnt(W)) and from B6J-Nnt(MUT) mice. The functional evaluation of respiring mitochondria revealed major redox alterations in B6J-Nnt(MUT) mice, including an absence of transhydrogenation between NAD and NADP, higher rates of H2O2 release, the spontaneous oxidation of NADPH, the poor ability to metabolize organic peroxide, and a higher susceptibility to undergo Ca(2+)-induced mitochondrial permeability transition. In addition, the mitochondria of B6J-Nnt(MUT) mice exhibited increased oxidized/reduced glutathione ratios as compared to B6JUnib-Nnt(W) mice. Nonetheless, the maximal activity of NADP-dependent isocitrate dehydrogenase, which is a coexisting source of mitochondrial NADPH, was similar between both groups. Altogether, our data suggest that NNT functions as a high-capacity source of mitochondrial NADPH and that its functional loss due to the Nnt mutation results in mitochondrial redox abnormalities, most notably a poor ability to sustain NADP and glutathione in their reduced states. In light of these alterations, the potential drawbacks of using B6J-Nnt(MUT) mice in biomedical research should not be overlooked.

Redox modification of proteins as essential mediators of CNS autophagy and mitophagy

Production of cellular reactive oxygen species (ROS) is typically associated with protein and DNA damage, toxicity, and death. However, ROS are also essential regulators of signaling and work in concert with redox-sensitive proteins to regulate cell homeostasis during stress. In this review, we focus on the redox regulation of mitophagy, a process that contributes to energetic tone as well as mitochondrial form and function. Mitophagy has been increasingly implicated in diseases including Parkinson's, Amyotrophic Lateral Sclerosis, and cancer. Although these disease states employ different genetic mutations, they share the common factors of redox dysregulation and autophagic signaling. This review highlights key redox sensitive signaling molecules which can enhance neuronal survival by promoting temporally and spatially controlled autophagic signaling and mitophagy.

Stromal response to prostate cancer: nanotechnology-based detection of thioredoxin-interacting protein partners distinguishes prostate cancer associated stroma from that of benign prostatic hyperplasia

Histological staining of reactive stroma has been shown to be a predictor of biochemical recurrence in prostate cancer, however, molecular markers of the stromal response to prostate cancer have not yet been fully delineated. The objective of this study was to determine whether or not the stromal biomarkers detected with a thioredoxin-targeted nanodevice could be used to distinguish the stroma associated with benign prostatic hyperplasia from that associated with PCA. In this regard, we recently demonstrated that a thioredoxin-targeted nanodevice selectively binds to reactive stroma in frozen prostate tumor tissue sections. To accomplish this, random frozen prostate tissue sections from each of 35 patients who underwent resection were incubated with the nanodevice and graded for fluorescent intensity. An adjacent section from each case was stained with Hematoxylin & Eosin to confirm the diagnosis. Select cases were stained with Masson's Trichrome or immunohistochemically using antibodies to thioredoxin reductase 1, thioredoxin reductase 2 or peroxiredoxin 1. Our results demonstrate that the graded intensity of nanodevice binding to the stroma associated with PCA was significantly higher (p = 0.0127) than that of benign prostatic hyperplasia using the t-test. Immunohistochemical staining of adjacent sections in representative cases showed that none of the two commonly studied thioredoxin interacting protein partners mirrored the fluorescence pattern seen with the nanodevice. However, thioredoxin reductase 2 protein was clearly shown to be a biomarker of prostate cancer-associated reactive stroma whose presence distinguishes the stroma associated with benign prostatic hyperplasia from that associated with prostate cancer. We conclude that the signal detected by the nanodevice, in contrast to individual targets detected with antibodies used in this study, originates from multiple thioredoxin interacting protein partners that distinguish the M2 neutrophil and macrophage associated inflammatory response in prostate cancer-associated stroma from the CD4+ T-Lymphocyte linked inflammation in benign prostatic hyperplasia.

H2O2 Signalling Pathway: A Possible Bridge between Insulin Receptor and Mitochondria

This review is focused on the mechanistic aspects of the insulin-induced H2O2 signalling pathway in neurons and the molecules affecting it, which act as risk factors for developing central insulin resistance. Insulin-induced H2O2 promotes insulin receptor activation and the mitochondria act as the insulin-sensitive H2O2 source, providing a direct molecular link between mitochondrial dysfunction and irregular insulin receptor activation. In this view, the accumulation of dysfunctional mitochondria during chronological ageing and Alzheimer's disease (AD) is a risk factor that may contribute to the development of dysfunctional cerebral insulin receptor signalling and insulin resistance. Due to the high significance of insulin-induced H2O2 for insulin receptor activation, oxidative stress-induced upregulation of antioxidant enzymes, e.g., in AD brains, may represent another risk factor contributing to the development of insulin resistance. As insulin-induced H2O2 signalling requires fully functional mitochondria, pharmacological strategies based on activating mitochondria biogenesis in the brain are central to the treatment of diseases associated with dysfunctional insulin receptor signalling in this organ.

The pH sensitivity of H2O2 metabolism in skeletal muscle mitochondria

Mitochondria have the capacity to produce and consume H2O2. We examined H2O2 metabolism in isolated rat skeletal muscle mitochondria and found that the substrate-dependent capacity to consume extramitochondrial H2O2 was markedly higher than the observed rate of H2O2 efflux from mitochondria under the same conditions. The substrate-dependent capacity to consume H2O2 was sensitive to the pH of the medium and we propose that pH related differences in H2O2 consumption pathways may explain inconsistencies we observed between H2O2 efflux rate and the reduction state of the matrix NADH pool.

A conceptually new treatment approach for relapsed glioblastoma: coordinated undermining of survival paths with nine repurposed drugs (CUSP9) by the International Initiative for Accelerated Improvement of Glioblastoma Care

To improve prognosis in recurrent glioblastoma we developed a treatment protocol based on a combination of drugs not traditionally thought of as cytotoxic chemotherapy agents but that have a robust history of being well-tolerated and are already marketed and used for other non-cancer indications. Focus was on adding drugs which met these criteria: a) were pharmacologically well characterized, b) had low likelihood of adding to patient side effect burden, c) had evidence for interfering with a recognized, well-characterized growth promoting element of glioblastoma, and d) were coordinated, as an ensemble had reasonable likelihood of concerted activity against key biological features of glioblastoma growth. We found nine drugs meeting these criteria and propose adding them to continuous low dose temozolomide, a currently accepted treatment for relapsed glioblastoma, in patients with recurrent disease after primary treatment with the Stupp Protocol. The nine adjuvant drug regimen, Coordinated Undermining of Survival Paths, CUSP9, then are aprepitant, artesunate, auranofin, captopril, copper gluconate, disulfiram, ketoconazole, nelfinavir, sertraline, to be added to continuous low dose temozolomide. We discuss each drug in turn and the specific rationale for use- how each drug is expected to retard glioblastoma growth and undermine glioblastoma's compensatory mechanisms engaged during temozolomide treatment. The risks of pharmacological interactions and why we believe this drug mix will increase both quality of life and overall survival are reviewed.

Neuroprotective mechanisms of the standardized extract of Bacopa monniera in a paraquat/diquat-mediated acute toxicity

Parkinson's disease (PD) is one of the most common age related neurodegenerative disease and affects millions of people worldwide. Strong evidence suggests a role for oxidative stress and mitochondrial dysfunctions in the pathogenesis of PD. Recent epidemiologic and toxicological studies have shown that environmental factors, especially herbicides such as paraquat and diquat represent one of the primary classes of neurotoxic agents associated with PD. The objective of our study was to investigate the neuroprotective effects of the standardized extract of Bacopa monniera (BM) against paraquat/diquat-induced toxicity and to elucidate the mechanisms underlying this protection. Our results showed that a pre-treatment with the BM extract, from 20.0μg/ml, protected the rat dopaminergic PC12 cell line against paraquat/diquat-induced toxicity in various cell survival assays. We demonstrated that BM pre-treatment, from 5.0μg/ml, could prevent the generation of intracellular reactive oxygen species (ROS), decreased mitochondrial superoxide levels and depolarized the mitochondria. BM pre-treatment also increased tyrosine hydroxylase (TH) levels and antioxidant defense systems such as γ-glutamylcysteine synthetase (γ-GCS) and thioredoxin1 (Trx1) levels. Furthermore, BM pre-treatment prevented the activation of Akt and heat shock protein90 (HSP90) proteins. Thus, our findings demonstrated that BM can protect PC12 cells through modulating cellular redox pathways which are altered in PD and could have a therapeutic application in the prevention of PD.

Mitochondrial peroxiredoxin-5 as potential modulator of mitochondria-ER crosstalk in MPP+-induced cell death

Peroxiredoxin-5 (PRDX5) is an antioxidant enzyme which differs from the other peroxiredoxins with regards to its enzymatic mechanism, its high affinity for organic peroxides and peroxynitrite and its wide subcellular distribution. In particular, the mitochondrial isoform of PRDX5 confers a remarkable cytoprotection toward oxidative stress to mammalian cells. Mitochondrial dysfunction and disruption of Ca²⁺ homeostasis are implicated in neurodegeneration. Growing evidence supports that endoplasmic reticulum (ER) could operate in tandem with mitochondria to regulate intracellular Ca²⁺ fluxes in neurodegenerative processes. Here, we overexpressed mitochondrial PRDX5 in SH-SY5Y cells to dissect the role of this enzyme in 1-methyl-4-phenylpyridinium (MPP)⁺-induced cell death. Our data show that mitochondria-dependent apoptosis triggered by MPP⁺, assessed by the measurement of caspase-9 activation and mitochondrial DNA damage, is prevented by mitochondrial PRDX5 overexpression. Moreover, PRDX5 overexpression blocks the increase in intracellular Ca²⁺, Ca²⁺-dependent activation of calpains and Bax cleavage. Finally, using Ca²⁺ channel inhibitors (Nimodipine, Dantrolene and 2-APB), we show that Ca²⁺ release arises essentially from ER stores through 1,4,5-inositol-trisphosphate receptors (IP3 R). Altogether, our results suggest that the MPP⁺ mitochondrial pathway of apoptosis is regulated by mitochondrial PRDX5 in a process that could involve redox modulation of Ca²⁺ transporters via a crosstalk between mitochondria and ER.

Superoxide generation by complex III: from mechanistic rationales to functional consequences

Apart from complex I (NADH:ubiquinone oxidoreductase) the mitochondrial cytochrome bc1 complex (complex III; ubiquinol:cytochrome c oxidoreductase) has been identified as the main producer of superoxide and derived reactive oxygen species (ROS) within the mitochondrial respiratory chain. Mitochondrial ROS are generally linked to oxidative stress, aging and other pathophysiological settings like in neurodegenerative diseases. However, ROS produced at the ubiquinol oxidation center (center P, Qo site) of complex III seem to have additional physiological functions as signaling molecules during cellular processes like the adaptation to hypoxia. The molecular mechanism of superoxide production that is mechanistically linked to the electron bifurcation during ubiquinol oxidation is still a matter of debate. Some insight comes from extensive kinetic studies with mutated complexes from yeast and bacterial cytochrome bc1 complexes. This review is intended to bridge the gap between those mechanistic studies and investigations on complex III ROS in cellular signal transduction and highlights factors that impact superoxide generation. This article is part of a Special Issue entitled: Respiratory complex III and related bc complexes.

Molecular cloning and characterization of peroxiredoxin 4 involved in protection against oxidative stress in the silkworm Bombyx mori

Peroxiredoxins (Prxs) are a ubiquitous family of proteins that play important roles in insects in protection against oxidative stress through the detoxification of cellular peroxides. Here, we describe the cloning and characterization of a Prx4 cDNA of the silkworm Bombyx mori (BmPrx4). The BmPrx4 gene has an open reading frame of 744 bp encoding 248 amino acids and a conserved motif, VCP, involved in its presumed redox functions. The heterologously expressed proteins of the gene in Escherichia coli showed antioxidant activity, removed hydrogen peroxide and protected DnA. Western blotting analysis showed the presence of BmPrx4 in the haemolymph, suggesting that the protein is secretable. Moreover, BmPrx4 was expressed at all developmental stages. The expression level of BmPrx4 was relatively low during the feeding stage but high at the wandering stage. BmPrx4 was induced by quercetin or temperature stress. Immunohistochemical analysis revealed that BmPrx4 is present in the brain, neurones and olfactory organ of the head in silkworms. Overall, our results indicate that the expression profile of BmPrx4 correlates well with protection from oxidative damage. Our data provide clues for the development of control technology for agricultural and forestry pests as the silkworm is a representative of lepidopteran pests.

Thioredoxin reductase deficiency potentiates oxidative stress, mitochondrial dysfunction and cell death in dopaminergic cells

Mitochondria are considered major generators of cellular reactive oxygen species (ROS) which are implicated in the pathogenesis of neurodegenerative diseases such as Parkinson's disease (PD). We have recently shown that isolated mitochondria consume hydrogen peroxide (H₂O₂) in a substrate- and respiration-dependent manner predominantly via the thioredoxin/peroxiredoxin (Trx/Prx) system. The goal of this study was to determine the role of Trx/Prx system in dopaminergic cell death. We asked if pharmacological and lentiviral inhibition of the Trx/Prx system sensitized dopaminergic cells to mitochondrial dysfunction, increased steady-state H₂O₂ levels and death in response to toxicants implicated in PD. Incubation of N27 dopaminergic cells or primary rat mesencephalic cultures with the Trx reductase (TrxR) inhibitor auranofin in the presence of sub-toxic concentrations of parkinsonian toxicants paraquat; PQ or 6-hydroxydopamine; 6OHDA (for N27 cells) resulted in a synergistic increase in H₂O₂ levels and subsequent cell death. shRNA targeting the mitochondrial thioredoxin reductase (TrxR2) in N27 cells confirmed the effects of pharmacological inhibition. A synergistic decrease in maximal and reserve respiratory capacity was observed in auranofin treated cells and TrxR2 deficient cells following incubation with PQ or 6OHDA. Additionally, TrxR2 deficient cells showed decreased basal mitochondrial oxygen consumption rates. These data demonstrate that inhibition of the mitochondrial Trx/Prx system sensitizes dopaminergic cells to mitochondrial dysfunction, increased steady-state H₂O₂, and cell death. Therefore, in addition to their role in the production of cellular H₂O₂ the mitochondrial Trx/Prx system serve as a major sink for cellular H₂O₂ and its disruption may contribute to dopaminergic pathology associated with PD.

Glutathione and glutaredoxin act as a backup of human thioredoxin reductase 1 to reduce thioredoxin 1 preventing cell death by aurothioglucose

Thioredoxin reductase 1 (TrxR1) in cytosol is the only known reductant of oxidized thioredoxin 1 (Trx1) in vivo so far. We and others found that aurothioglucose (ATG), a well known active-site inhibitor of TrxR1, inhibited TrxR1 activity in HeLa cell cytosol but had no effect on the viability of the cells. Using a redox Western blot analysis, no change was observed in redox state of Trx1, which was mainly fully reduced with five sulfhydryl groups. In contrast, auranofin killed cells and oxidized Trx1, also targeting mitochondrial TrxR2 and Trx2. Combining ATG with ebselen gave a strong synergistic effect, leading to Trx1 oxidation, reactive oxygen species accumulation, and cell death. We hypothesized that there should exist a backup system to reduce Trx1 when only TrxR1 activity was lost. Our results showed that physiological concentrations of glutathione, NADPH, and glutathione reductase reduced Trx1 in vitro and that the reaction was strongly stimulated by glutaredoxin1. Simultaneous depletion of TrxR activity by ATG and glutathione by buthionine sulfoximine led to overoxidation of Trx1 and loss of HeLa cell viability. In conclusion, the glutaredoxin system and glutathione have a backup role to keep Trx1 reduced in cells with loss of TrxR1 activity. Monitoring the redox state of Trx1 shows that cell death occurs when Trx1 is oxidized, followed by general protein oxidation catalyzed by the disulfide form of thioredoxin.

Glutathione/thioredoxin systems modulate mitochondrial H2O2 emission: an experimental-computational study

The net emission of hydrogen peroxide (H(2)O(2)) from mitochondria results from the balance between reactive oxygen species (ROS) continuously generated in the respiratory chain and ROS scavenging. The relative contribution of the two major antioxidant systems in the mitochondrial matrix, glutathione (GSH) and thioredoxin (Trx), has not been assessed. In this paper, we examine this key question via combined experimental and theoretical approaches, using isolated heart mitochondria from mouse, rat, and guinea pig. As compared with untreated control mitochondria, selective inhibition of Trx reductase with auranofin along with depletion of GSH with 2,4-dinitrochlorobenzene led to a species-dependent increase in H(2)O(2) emission flux of 17, 11, and 6 fold in state 4 and 15, 7, and 8 fold in state 3 for mouse, rat, and guinea pig mitochondria, respectively. The maximal H(2)O(2) emission as a percentage of the total O(2) consumption flux was 11%/2.3% for mouse in states 4 and 3 followed by 2%/0.25% and 0.74%/0.29% in the rat and guinea pig, respectively. A minimal computational model accounting for the kinetics of GSH/Trx systems was developed and was able to simulate increase in H(2)O(2) emission fluxes when both scavenging systems were inhibited separately or together. Model simulations suggest that GSH/Trx systems act in concert. When the scavenging capacity of either one of them saturates during H(2)O(2) overload, they relieve each other until complete saturation, when maximal ROS emission occurs. Quantitatively, these results converge on the idea that GSH/Trx scavenging systems in mitochondria are both essential for keeping minimal levels of H(2)O(2) emission, especially during state 3 respiration, when the energetic output is maximal. This suggests that the very low levels of H(2)O(2) emission observed during forward electron transport in the respiratory chain are a result of the well-orchestrated actions of the two antioxidant systems working continuously to offset ROS production.

Rapid generation of mitochondrial superoxide induces mitochondrion-dependent but caspase-independent cell death in hippocampal neuronal cells that morphologically resembles necroptosis

Studies in recent years have revealed that excess mitochondrial superoxide production is an important etiological factor in neurodegenerative diseases, resulting from oxidative modifications of cellular lipids, proteins, and nucleic acids. Hence, it is important to understand the mechanism by which mitochondrial oxidative stress causes neuronal death. In this study, the immortalized mouse hippocampal neuronal cells (HT22) in culture were used as a model and they were exposed to menadione (also known as vitamin K(3)) to increase intracellular superoxide production. We found that menadione causes preferential accumulation of superoxide in the mitochondria of these cells, along with the rapid development of mitochondrial dysfunction and cellular ATP depletion. Neuronal death induced by menadione is independent of the activation of the MAPK signaling pathways and caspases. The lack of caspase activation is due to the rapid depletion of cellular ATP. It was observed that two ATP-independent mitochondrial nucleases, namely, AIF and Endo G, are released following menadione exposure. Silencing of their expression using specific siRNAs results in transient suppression (for ~12h) of mitochondrial superoxide-induced neuronal death. While suppression of the mitochondrial superoxide dismutase expression markedly sensitizes neuronal cells to mitochondrial superoxide-induced cytotoxicity, its over-expression confers strong protection. Collectively, these findings showed that many of the observed features associated with mitochondrial superoxide-induced cell death, including caspase independency, rapid depletion of ATP level, mitochondrial release of AIF and Endo G, and mitochondrial swelling, are distinctly different from those of apoptosis; instead they resemble some of the known features of necroptosis.

Effect of early acute high concentrations of iodide exposure on mitochondrial superoxide production in FRTL cells

Excessive oxidative stress has been suggested as one of the underlying mechanisms in the development of thyroid cytotoxicity. Although the involvement of mitochondria has been hypothesized, the effect of early acute high concentrations of iodide on mitochondrial superoxide production remains largely unknown, especially within a 24 h time frame. By using a novel fluorescent probe, MitoSOX Red, we demonstrated the concentration response and time-course response of KI-induced mitochondrial superoxide production in the Fischer rat thyroid cell line (FRTL). A strong increase of MitoSOX Red fluorescence intensity in FRTL cells can be seen at 2 h following high concentrations of iodide exposure. Besides, we indicated that 6-propyl-2-thiouracil (PTU, 300 μM), thyroid-stimulating hormone (TSH, 10 mU/ml), and perchlorate (KClO(4), 30 μM) can inhibit excessive iodide-induced strong mitochondrial superoxide production; however, diethyldithiocarbamic acid (DETC, 2 mM) can further increase excessive iodide-induced mitochondrial superoxide production. By using transmission electron microscopy (TEM), we noted accumulated myelinoid bodies with lipid droplets and numerous apoptotic nuclear bodies at 24 h in FRTL cells. In addition, we demonstrated a significant decrease in cytochrome c (cyt c) content in the mitochondria by enzyme linked immunosorbent assay (ELISA), and DNA fragments and significant increases in lactate dehydrogenase (LDH) activity were detected. We propose a sequence of events mediated by a strong mitochondrial superoxide production at 2 h, followed by lipid peroxidation, cell membrane damage with significant cyt c release, culminating in DNA fragmentation and apoptotic nuclear formation at 24 h, which may partly contribute to the underlying mechanisms of early acute iodide excess.

Birds and longevity: does flight driven aerobicity provide an oxidative sink?

Birds generally age slower and live longer than similar sized mammals. For birds this occurs despite elevated blood glucose levels that for mammals would in part define them as diabetic. However these data were acquired in respiration states that have little resemblance to conditions in healthy tissues and mitochondrial RS production is probably minimal in healthy animals. Indeed mitochondria probably act as net consumers rather than producers of RS. Here we propose that (1) if mitochondria are antioxidant systems, the greater mitochondrial mass in athletic species, such as birds, is advantageous as it should provide a substantial sink for RS. (2) The intense drive for aerobic performance and decreased body density to facilitate flight may explain the relative insensitivity of birds to insulin, as well as depressed insulin levels and apparent sensitization to glucagon. Glucagon also associates with the sirtuin protein family, most of which are associated with caloric restriction regulated pathways, mitochondrial biogenesis and life span extension. (3) We note that telomeres, which appear to be unusually long in birds, bind Sirtuins 2 and 4 and therefore may stabilize and protect nuclear DNA. Ultimately these flight driven responses may suppress somatic growth and protect DNA from oxidative damage that would otherwise lead to ageing and non-viral cancers.

Peroxiredoxin distribution in the mouse brain with emphasis on neuronal populations affected in neurodegenerative disorders

Redox changes are observed in neurodegenerative diseases, ranging from increased levels of reactive oxygen/nitrogen species and disturbance of antioxidant systems, to nitro-oxidative damage. By reducing hydrogen peroxide, peroxynitrite, and organic hydroperoxides, peroxiredoxins (Prdxs) represent a major potential protective barrier against nitro-oxidative insults in the brain. While recent works have investigated the putative role of Prdxs in neurodegenerative disorders, less is known about their expression in the healthy brain. Here we used immunohistochemistry to map basal expression of Prdxs throughout C57BL/6 mouse brain. We first confirmed the neuronal localization of Prdx2-5 and the glial expression of Prdx1, Prdx4, and Prdx6. Then we performed an in-depth analysis of neuronal Prdx distribution in the brain. Our results show that Prdx2-5 are widely detected in the different neuronal populations, and especially well expressed in the olfactory bulb, in the cerebral cortex, in pons nuclei, in the red nucleus, in all cranial nerve nuclei, in the cerebellum, and in motor neurons of the spinal cord. In contrast, Prdx expression is very low in the dopaminergic neurons of substantia nigra pars compacta and in the CA1/2 pyramidal cells of hippocampus. This low basal expression may contribute to the vulnerability of these neurons to nitro-oxidative attacks occurring in Parkinson's disease and Alzheimer's disease. In addition, we found that Prdx expression levels are unevenly distributed among neurons of a determined region and that distinct regional patterns of expression are observed between isoforms, reinforcing the hypothesis of the nonredundant function of Prdxs.

α-Haemoglobin regulates sympathoadrenal cell metabolism to maintain a catecholaminergic phenotype

Discovery of haemoglobin A expression outside of the erythroid cell lineage suggests that oxygen transport is the main, but not the unique, function of adult haemoglobin chains in mammals. The contribution of haemoglobin A to antioxidant defences has been proposed in the territories where it is expressed. Catecholaminergic cells rely on an active oxidative metabolism to accomplish their biological function, but are exposed to strong oxidative stress due to metabolism of catecholaminergic transmitters. We show in the present study that peripheral catecholaminegic cells express the α- and not the β-haemoglobin A chains, and that α-haemoglobin expression could modulate the antioxidant capabilities of these cells. We also show that α-haemoglobin overexpression in PC12 cells leads to a selective increase of tyrosine hydroxylase synthesis and activity. This is achieved by means of a reorganization of antioxidant defences, decreasing cytoplasmic glutathione peroxidase and superoxide dismutase, and increasing mitochondrial peroxidase. Moreover, α-haemoglobin induces a decrease in lipogenesis and increase in lipid degradation, situations that help save NAD(P)H and favour supply of acetyl-CoA to the tricarboxylic acid cycle and production of reducing equivalents in the cell. All of these results point to a role for α-haemoglobin as a regulator of catecholaminergic cell metabolism required for phenotype acquisition and maintenance.

The contribution of thioredoxin-2 reductase and glutathione peroxidase to H(2)O(2) detoxification of rat brain mitochondria

Brain mitochondria are not only major producers of reactive oxygen species but they also considerably contribute to the removal of toxic hydrogen peroxide by the glutathione (GSH) and thioredoxin-2 (Trx2) antioxidant systems. In this work we estimated the relative contribution of both systems and catalase to the removal of intrinsically produced hydrogen peroxide (H(2)O(2)) by rat brain mitochondria. By using the specific inhibitors auranofin and 1-chloro-2,4-dinitrobenzene (DNCB), the contribution of Trx2- and GSH-systems to reactive oxygen species (ROS) detoxification in rat brain mitochondria was determined to be 60±20% and 20±15%, respectively. Catalase contributed to a non-significant extent only, as revealed by aminotriazole inhibition. In digitonin-treated rat hippocampal homogenates inhibition of Trx2- and GSH-systems affected mitochondrial hydrogen peroxide production rates to a much higher extent than the endogenous extramitochondrial hydrogen peroxide production, pointing to a strong compartmentation of ROS metabolism. Imaging experiments of hippocampal slice cultures showed on single cell level substantial heterogeneity of hydrogen peroxide detoxification reactions. The strongest effects of inhibition of hydrogen peroxide removal by auranofin or DNCB were detected in putative interneurons and microglial cells, while pyramidal cells and astrocytes showed lower effects. Thus, our data underline the important contribution of the Trx2-system to hydrogen peroxide detoxification in rat hippocampus. This article is part of a Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012).

Disruption of alternative NAD(P)H dehydrogenases leads to decreased mitochondrial ROS in Neurospora crassa

Mitochondria are a main providers of high levels of energy, but also a major source of reactive oxygen species (ROS) during normal oxidative metabolism. The involvement of Neurospora crassa alternative NAD(P)H dehydrogenases in mitochondrial ROS production was evaluated. The growth responses of a series of respiratory mutants to several stress conditions revealed that disrupting alternative dehydrogenases leads to an increased tolerance to the redox cycler paraquat, with a mutant devoid of the external NDE1 and NDE2 enzymes being significantly more resistant. The nde1nde2 mutant mitochondria show a significant decrease in ROS generation in the presence and absence of paraquat, regardless of the respiratory substrate used, and an intrinsic increase in catalase activity. Analysis of ROS production by a complex I mutant (nuo51) indicates that, as in other organisms, paraquat-derived ROS in Neurospora mitochondria occur mainly at the level of complex I. We propose that disruption of the external NAD(P)H dehydrogenases NDE1 and NDE2 leads to a synergistic effect diminishing ROS generation by the mitochondrial respiratory chain. This, in addition to a robust increase in scavenging capacity, provides the mutant strain with an improved ability to withstand paraquat treatment.

Molecular mechanisms of superoxide production by the mitochondrial respiratory chain

The mitochondrial respiratory chain is a major source of reactive oxygen species (ROS) in eukaryotic cells. Mitochondrial ROS production associated with a dysfunction of respiratory chain complexes has been implicated in a number of degenerative diseases and biological aging. Recent findings suggest that mitochondrial ROS can be integral components of cellular signal transduction as well. Within the respiratory chain, complexes I (NADH:ubiquinone oxidoreductase) and III (ubiquinol:cytochrome c oxidoreductase; cytochrome bc (1) complex) are generally considered as the main producers of superoxide anions that are released into the mitochondrial matrix and the intermembrane space, respectively. The primary function of both respiratory chain complexes is to employ energy supplied by redox reactions to drive the vectorial transfer of protons into the mitochondrial intermembrane space. This process involves a set of distinct electron carriers designed to minimize the unwanted leak of electrons from reduced cofactors onto molecular oxygen and hence ROS generation under normal circumstances. Nevertheless, it seems plausible that superoxide is derived from intermediates of the normal catalytic cycles of complexes I and III. Therefore, a detailed understanding of the molecular mechanisms driving these enzymes is required to understand mitochondrial ROS production during oxidative stress and redox signalling. This review summarizes recent findings on the chemistry and control of the reactions within respiratory complexes I and III that result in increased superoxide generation. Regulatory contributions of other components of the respiratory chain, especially complex II (succinate:ubiquinone oxidoreductase) and the redox state of the ubiquinone pool (Q-pool) will be briefly discussed.

Deletion of thioredoxin-interacting protein in mice impairs mitochondrial function but protects the myocardium from ischemia-reperfusion injury

Classic therapeutics for ischemic heart disease are less effective in individuals with the metabolic syndrome. As the prevalence of the metabolic syndrome is increasing, better understanding of cardiac metabolism is needed to identify potential new targets for therapeutic intervention. Thioredoxin-interacting protein (Txnip) is a regulator of metabolism and an inhibitor of the antioxidant thioredoxins, but little is known about its roles in the myocardium. We examined hearts from Txnip-KO mice by polony multiplex analysis of gene expression and an independent proteomic approach; both methods indicated suppression of genes and proteins participating in mitochondrial metabolism. Consistently, Txnip-KO mitochondria were functionally and structurally altered, showing reduced oxygen consumption and ultrastructural derangements. Given the central role that mitochondria play during hypoxia, we hypothesized that Txnip deletion would enhance ischemia-reperfusion damage. Surprisingly, Txnip-KO hearts had greater recovery of cardiac function after an ischemia-reperfusion insult. Similarly, cardiomyocyte-specific Txnip deletion reduced infarct size after reversible coronary ligation. Coordinated with reduced mitochondrial function, deletion of Txnip enhanced anaerobic glycolysis. Whereas mitochondrial ATP synthesis was minimally decreased by Txnip deletion, cellular ATP content and lactate formation were higher in Txnip-KO hearts after ischemia-reperfusion injury. Pharmacologic inhibition of glycolytic metabolism completely abolished the protection afforded the heart by Txnip deficiency under hypoxic conditions. Thus, although Txnip deletion suppresses mitochondrial function, protection from myocardial ischemia is enhanced as a result of a coordinated shift to enhanced anaerobic metabolism, which provides an energy source outside of mitochondria.

Novel metabolic biomarkers related to sulfur-dependent detoxification pathways in autistic patients of Saudi Arabia

BACKGROUND

Xenobiotics are neurotoxins that dramatically alter the health of the child. In addition, an inefficient detoxification system leads to oxidative stress, gut dysbiosis, and immune dysfunction. The consensus among physicians who treat autism with a biomedical approach is that those on the spectrum are burdened with oxidative stress and immune problems. In a trial to understand the role of detoxification in the etiology of autism, selected parameters related to sulfur-dependent detoxification mechanisms in plasma of autistic children from Saudi Arabia will be investigated compared to control subjects.

METHODS

20 males autistic children aged 3-15 years and 20 age and gender matching healthy children as control group were included in this study. Levels of reduced glutathione (GSH), total (GSH+GSSG), glutathione status (GSH/GSSG), glutathione reductase (GR), glutathione- s-transferase (GST), thioredoxin (Trx), thioredoxin reductase (TrxR) and peroxidoxins (Prxs I and III) were determined.

RESULTS

Reduced glutathione, total glutathione, GSH/GSSG and activity levels of GST were significantly lower, GR shows non-significant differences, while, Trx, TrxR and both Prx I and III recorded a remarkably higher values in autistics compared to control subjects.

CONCLUSION

The impaired glutathione status together with the elevated Trx and TrxR and the remarkable over expression of both Prx I and Prx III, could be used as diagnostic biomarkers of autism.

Brain mitochondrial drug delivery: influence of drug physicochemical properties

PURPOSE

To determine the influence of drug physicochemical properties on brain mitochondrial delivery of 20 drugs at physiological pH.

METHODS

The delivery of 8 cationic drugs (beta-blockers), 6 neutral drugs (corticosteroids), and 6 anionic drugs (non-steroidal anti-inflammatory drugs, NSAIDs) to isolated rat brain mitochondria was determined with and without membrane depolarization. Multiple linear regression was used to determine whether lipophilicity (Log D), charge, polarizability, polar surface area (PSA), and molecular weight influence mitochondrial delivery.

RESULTS

The Log D for beta-blockers, corticosteroids, and NSAIDs was in the range of -1.41 to 1.37, 0.72 to 2.97, and -0.98 to 2, respectively. The % mitochondrial uptake increased exponentially with an increase in Log D for each class of drugs, with the uptake at a given lipophilicity obeying the rank order cationic>anionic>neutral. Valinomycin reduced membrane potential and the delivery of positively charged propranolol and betaxolol. The best equation for the combined data set was Log % Uptake = 0.333 Log D + 0.157 Charge - 0.887 Log PSA + 2.032 (R(2) = 0.738).

CONCLUSIONS

Drug lipopohilicity, charge, and polar surface area and membrane potential influence mitochondrial drug delivery, with the uptake of positively charged, lipophilic molecules being the most efficient.