Glyceraldehyde-3-phosphate dehydrogenase inactivation by peroxynitrite

Oxidation of the active site cysteine residue of glyceraldehyde-3-phosphate dehydrogenase to the hyper-oxidized sulfonic acid form is favored under crowded conditions

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a key cellular enzyme, with major roles in both glycolysis, and 'moonlighting' activities in the nucleus (uracil DNA glycosylase activity, nuclear protein nitrosylation), as a regulator of mRNA stability, a transferrin receptor, and as an antimicrobial agent. These activities are dependent, at least in part, on the integrity of an active site Cys residue, and a second neighboring Cys. These residues are differentially sensitive to oxidation, and determine both its catalytic activity and the redox signaling capacity of the protein. Such Cys modification is critical to cellular adaptation to oxidative environments by re-routing metabolic pathways to favor NADPH generation and antioxidant defenses. Despite the susceptibility of GAPDH to oxidation, it remains a puzzle as to how this enzyme acts as a redox signaling hub for oxidants such as hydrogen peroxide (H2O2) in the presence of high concentrations of specialized high-efficiency peroxide-removing enzymes. One possibility is that crowded environments, such as the cell cytosol, alter the oxidation pathways of GAPDH. In this study, we investigated the role of crowding (induced by dextran) on H2O2- and SIN-1-induced GAPDH oxidation, with data for crowded and dilute conditions compared. LC-MS/MS data revealed a lower extent of modification of the catalytic Cys under crowded conditions (i.e. less monomer units modified), but enhanced formation of the sulfonic acid resulting from hyper-oxidation. This effect was not observed with SIN-1. These data indicate that molecular crowding can modulate the oxidation pathways of GAPDH and its extent of oxidation and inactivation.

Cysteine thiol sulfinic acid in plant stress signaling

Cysteine thiols are susceptible to various oxidative posttranslational modifications (PTMs) due to their high chemical reactivity. Thiol-based PTMs play a crucial role in regulating protein functions and are key contributors to cellular redox signaling. Although reversible thiol-based PTMs, such as disulfide bond formation, S-nitrosylation, and S-glutathionylation, have been extensively studied for their roles in redox regulation, thiol sulfinic acid (-SO2 H) modification is often perceived as irreversible and of marginal significance in redox signaling. Here, we revisit this narrow perspective and shed light on the redox regulatory roles of -SO2 H in plant stress signaling. We provide an overview of protein sulfinylation in plants, delving into the roles of hydrogen peroxide-mediated and plant cysteine oxidase-catalyzed formation of -SO2 H, highlighting the involvement of -SO2 H in specific regulatory signaling pathways. Additionally, we compile the existing knowledge of the -SO2 H reducing enzyme, sulfiredoxin, offering insights into its molecular mechanisms and biological relevance. We further summarize current proteomic techniques for detecting -SO2 H and furnish a list of experimentally validated cysteine -SO2 H sites across various species, discussing their functional consequences. This review aims to spark new insights and discussions that lead to further investigations into the functional significance of protein -SO2 H-based redox signaling in plants.

The enzymes of the oxidative phase of the pentose phosphate pathway as targets of reactive species: consequences for NADPH production

The pentose phosphate pathway (PPP) is a key metabolic pathway. The oxidative phase of this process involves three reactions catalyzed by glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconolactonase (6PGL) and 6-phosphogluconate dehydrogenase (6PGDH) enzymes. The first and third steps (catalyzed by G6PDH and 6PGDH, respectively) are responsible for generating reduced nicotinamide adenine dinucleotide phosphate (NAPDH), a key cofactor for maintaining the reducing power of cells and detoxification of both endogenous and exogenous oxidants and electrophiles. Despite the importance of these enzymes, little attention has been paid to the fact that these proteins are targets of oxidants. In response to oxidative stimuli metabolic pathways are modulated, with the PPP often up-regulated in order to enhance or maintain the reductive capacity of cells. Under such circumstances, oxidation and inactivation of the PPP enzymes could be detrimental. Damage to the PPP enzymes may result in a downward spiral, as depending on the extent and sites of modification, these alterations may result in a loss of enzymatic activity and therefore increased oxidative damage due to NADPH depletion. In recent years, it has become evident that the three enzymes of the oxidative phase of the PPP have different susceptibilities to inactivation on exposure to different oxidants. In this review, we discuss existing knowledge on the role that these enzymes play in the metabolism of cells, and their susceptibility to oxidation and inactivation with special emphasis on NADPH production. Perspectives on achieving a better understanding of the molecular basis of the oxidation these enzymes within cellular environments are given.

Neutrophil metabolomics in severe COVID-19 reveal GAPDH as a suppressor of neutrophil extracellular trap formation

Severe COVID-19 is characterized by an increase in the number and changes in the function of innate immune cells including neutrophils. However, it is not known how the metabolome of immune cells changes in patients with COVID-19. To address these questions, we analyzed the metabolome of neutrophils from patients with severe or mild COVID-19 and healthy controls. We identified widespread dysregulation of neutrophil metabolism with disease progression including in amino acid, redox, and central carbon metabolism. Metabolic changes in neutrophils from patients with severe COVID-19 were consistent with reduced activity of the glycolytic enzyme GAPDH. Inhibition of GAPDH blocked glycolysis and promoted pentose phosphate pathway activity but blunted the neutrophil respiratory burst. Inhibition of GAPDH was sufficient to cause neutrophil extracellular trap (NET) formation which required neutrophil elastase activity. GAPDH inhibition increased neutrophil pH, and blocking this increase prevented cell death and NET formation. These findings indicate that neutrophils in severe COVID-19 have an aberrant metabolism which can contribute to their dysfunction. Our work also shows that NET formation, a pathogenic feature of many inflammatory diseases, is actively suppressed in neutrophils by a cell-intrinsic mechanism controlled by GAPDH.

The metabolic adaptation evoked by arginine enhances the effect of radiation in brain metastases

Selected patients with brain metastases (BM) are candidates for radiotherapy. A lactatogenic metabolism, common in BM, has been associated with radioresistance. We demonstrated that BM express nitric oxide (NO) synthase 2 and that administration of its substrate l-arginine decreases tumor lactate in BM patients. In a placebo-controlled trial, we showed that administration of l-arginine before each fraction enhanced the effect of radiation, improving the control of BM. Studies in preclinical models demonstrated that l-arginine radiosensitization is a NO-mediated mechanism secondary to the metabolic adaptation induced in cancer cells. We showed that the decrease in tumor lactate was a consequence of reduced glycolysis that also impacted ATP and NAD⁺ levels. These effects were associated with NO-dependent inhibition of GAPDH and hyperactivation of PARP upon nitrosative DNA damage. These metabolic changes ultimately impaired the repair of DNA damage induced by radiation in cancer cells while greatly sparing tumor-infiltrating lymphocytes.

The nexus between redox state and intermediary metabolism

Reactive oxygen species (ROS) are not just a by-product of cellular metabolic processes but act as signalling molecules that regulate both physiological and pathophysiological processes. A close connection exists in cells between redox homeostasis and cellular metabolism. In this review, we describe how intracellular redox state and glycolytic intermediary metabolism are closely coupled. On the one hand, ROS signalling can control glycolytic intermediary metabolism by direct regulation of the activity of key metabolic enzymes and indirect regulation via redox-sensitive transcription factors. On the other hand, metabolic adaptation and reprogramming in response to physiological or pathological stimuli regulate intracellular redox balance, through mechanisms such as the generation of reducing equivalents. We also discuss the impact of these intermediary metabolism-redox circuits in physiological and disease settings across different tissues. A better understanding of the mechanisms regulating these intermediary metabolism-redox circuits will be crucial to the development of novel therapeutic strategies.

Reactive Species from Two-Signal Activated Macrophages Interfere with Their Oxygen Consumption Measurements

Metabolic modulation of macrophage activation has emerged as a promising strategy lately in immunotherapeutics. However, macrophages have a broad spectrum of functions and thus, understanding the exact metabolic changes that drive a particular immune response, is of major importance. In our previous work, we have reported a key role of nitric oxide (NO^●) in two(2)-signal activated macrophages [M(2-signals)]. Further characterization using metabolic analysis in intact cells, showed that the basal and maximal respiration levels of M(2-signals) were comparable, with cells being unresponsive to the injections-inducd mitochondrial stress. Here, we show that excessive NO^● secretion by the M(2-signals) macrophages, interferes with the oxygen (O₂) consumption measurements on cells using the seahorse metabolic analyzer. This is attributed mainly to the consumption of ambient oxygen by NO^● to form NO₂⁻ and/or NO₃⁻ but also to the reduction of O₂ to superoxide anion (O₂^●−) by stray electrons from the electron transport chain, leading to the formation of peroxynitrite (ONOO⁻). We found that reactive species-donors in the absence of cells, produce comparable oxygen consumption rates (OCR) with M(2-signals) macrophages. Furthermore, inhibition of NO^● production, partly recovered the respiration of activated macrophages, while external addition of NO^● in non-activated macrophages downregulated their OCR levels. Our findings are crucial for the accurate metabolic characterization of cells, especially in cases where reactive nitrogen or oxygen species are produced in excess.

Targeting oxidative stress, a crucial challenge in renal transplantation outcome

Disorders characterized by ischemia/reperfusion (I/R) are the most common causes of debilitating diseases and death in stroke, cardiovascular ischemia, acute kidney injury or organ transplantation. In the latter example the I/R step defines both the amplitude of the damages to the graft and the functional recovery outcome. During transplantation the kidney is subjected to blood flow arrest followed by a sudden increase in oxygen supply at the time of reperfusion. This essential clinical protocol causes massive oxidative stress which is at the basis of cell death and tissue damage. The involvement of both reactive oxygen species (ROS) and nitric oxides (NO) has been shown to be a major cause of these cellular damages. In fact, in non-physiological situations, these species escape endogenous antioxidant control and dangerously accumulate in cells. In recent years, the objective has been to find clinical and pharmacological treatments to reduce or prevent the appearance of oxidative stress in ischemic pathologies. This is very relevant because, due to the increasing success of organ transplantation, clinicians are required to use limit organs, the preservation of which against oxidative stress is crucial for a better outcome. This review highlights the key actors in oxidative stress which could represent new pharmacological targets.

Carbonyl Stress in Red Blood Cells and Hemoglobin

The paper overviews the peculiarities of carbonyl stress in nucleus-free mammal red blood cells (RBCs). Some functional features of RBCs make them exceptionally susceptible to reactive carbonyl compounds (RCC) from both blood plasma and the intracellular environment. In the first case, these compounds arise from the increased concentrations of glucose or ketone bodies in blood plasma, and in the second-from a misbalance in the glycolysis regulation. RBCs are normally exposed to RCC-methylglyoxal (MG), triglycerides-in blood plasma of diabetes patients. MG modifies lipoproteins and membrane proteins of RBCs and endothelial cells both on its own and with reactive oxygen species (ROS). Together, these phenomena may lead to arterial hypertension, atherosclerosis, hemolytic anemia, vascular occlusion, local ischemia, and hypercoagulation phenotype formation. ROS, reactive nitrogen species (RNS), and RCC might also damage hemoglobin (Hb), the most common protein in the RBC cytoplasm. It was Hb with which non-enzymatic glycation was first shown in living systems under physiological conditions. Glycated HbA1c is used as a very reliable and useful diagnostic marker. Studying the impacts of MG, ROS, and RNS on the physiological state of RBCs and Hb is of undisputed importance for basic and applied science.

Formation of protein cross-links by singlet oxygen-mediated disulfide oxidation

Cross-links formed within and between proteins are a major cause of protein dysfunction, and are postulated to drive the accumulation of protein aggregates in some human pathologies. Cross-links can be formed from multiple residues and can be reversible (usually sulfur-sulfur bonds) or irreversible (typically carbon-carbon or carbon-heteroatom bonds). Disulfides formed from oxidation of two Cys residues are widespread, with these formed both deliberately, via enzymatic reactions, or as a result of unintended oxidation reactions. We have recently demonstrated that new protein-glutathione mixed disulfides can be formed through oxidation of a protein disulfide to a thiosulfinate, and subsequent reaction of this species with glutathione. Here we investigate whether similar reactions occur between an oxidized protein disulfide, and a Cys residues on a second protein, to give novel protein cross-links. Singlet oxygen (¹O₂)-mediated oxidation of multiple proteins (α-lactalbumin, lysozyme, beta-2-microglobulin, C-reactive protein), and subsequent incubation with the Cys-containing protein glyceraldehyde-3-phosphate dehydrogenase (GAPDH), generates inter-protein cross-links as detected by SDS-PAGE, immunoblotting and mass spectrometry (MS). The cross-link yield is dependent on the ¹O₂ concentration, the presence of the original protein disulfide bond, and the free Cys on GAPDH. MS with ¹⁸O-labeling has allowed identification of the residues involved in some cases (e.g. Cys25 from the Cys25-Cys80 disulfide in beta-2-microglobulin, with Cys149 or Cys244 of GAPDH). The formation of these cross-links results in a loss of GAPDH enzymatic activity. These data provide 'proof-of-concept' for a novel mechanism of protein cross-link formation which may help rationalize the accumulation of cross-linked proteins in multiple human pathologies.

β-Hydroxybutyrate Oxidation Promotes the Accumulation of Immunometabolites in Activated Microglia Cells

Metabolic regulation of immune cells has arisen as a critical set of processes required for appropriate response to immunological signals. While our knowledge in this area has rapidly expanded in leukocytes, much less is known about the metabolic regulation of brain-resident microglia. In particular, the role of alternative nutrients to glucose remains poorly understood. Here, we use stable-isotope (¹³C) tracing strategies and metabolomics to characterize the oxidative metabolism of β-hydroxybutyrate (BHB) in human (HMC3) and murine (BV2) microglia cells and the interplay with glucose in resting and LPS-activated BV2 cells. We found that BHB is imported and oxidised in the TCA cycle in both cell lines with a subsequent increase in the cytosolic NADH:NAD⁺ ratio. In BV2 cells, stimulation with LPS upregulated the glycolytic flux, increased the cytosolic NADH:NAD⁺ ratio and promoted the accumulation of the glycolytic intermediate dihydroxyacetone phosphate (DHAP). The addition of BHB enhanced LPS-induced accumulation of DHAP and promoted glucose-derived lactate export. BHB also synergistically increased LPS-induced accumulation of succinate and other key immunometabolites, such as α-ketoglutarate and fumarate generated by the TCA cycle. Finally, BHB upregulated the expression of a key pro-inflammatory (M1 polarisation) marker gene, NOS2, in BV2 cells activated with LPS. In conclusion, we identify BHB as a potentially immunomodulatory metabolic substrate for microglia that promotes metabolic reprogramming during pro-inflammatory response.

Ionizing Radiation-induced Proteomic Oxidation in Escherichia coli

Recent work has begun to investigate the role of protein damage in cell death because of ionizing radiation (IR) exposure, but none have been performed on a proteome-wide basis, nor have they utilized MS (MS) to determine chemical identity of the amino acid side chain alteration. Here, we use Escherichia coli to perform the first MS analysis of IR-treated intact cells on a proteome scale. From quintuplicate IR-treated (1000 Gy) and untreated replicates, we successfully quantified 13,262 peptides mapping to 1938 unique proteins. Statistically significant, but low in magnitude (<2-fold), IR-induced changes in peptide abundance were observed in 12% of all peptides detected, although oxidative alterations were rare. Hydroxylation (+15.99 Da) was the most prevalent covalent adduct detected. In parallel with these studies on E. coli, identical experiments with the IR-resistant bacterium, Deinococcus radiodurans, revealed orders of magnitude less effect of IR on the proteome. In E. coli, the most significant target of IR by a wide margin was glyceraldehyde 3'-phosphate dehydrogenase (GAPDH), in which the thiol side chain of the catalytic Cys residue was oxidized to sulfonic acid. The same modification was detected in IR-treated human breast carcinoma cells. Sensitivity of GAPDH to reactive oxygen species (ROS) has been described previously in microbes and here, we present GAPDH as an immediate, primary target of IR-induced oxidation across all domains of life.

The molecular mechanisms associated with the physiological responses to inflammation and oxidative stress in cardiovascular diseases

The complex physiological signal transduction networks that respond to the dual challenges of inflammatory and oxidative stress are major factors that promote the development of cardiovascular pathologies. These signaling networks contribute to the development of age-related diseases, suggesting crosstalk between the development of aging and cardiovascular disease. Inhibition and/or attenuation of these signaling networks also delays the onset of disease. Therefore, a concept of targeting the signaling networks that are involved in inflammation and oxidative stress may represent a novel treatment paradigm for many types of heart disease. In this review, we discuss the molecular mechanisms associated with the physiological responses to inflammation and oxidative stress especially in heart failure with preserved ejection fraction and emphasize the nature of the crosstalk of these signaling processes as well as possible therapeutic implications for cardiovascular medicine.

Short-chain lipid peroxidation products form covalent adducts with pyruvate kinase and inhibit its activity in vitro and in breast cancer cells

Pyruvate kinase catalyses the last step in glycolysis and has been suggested to contribute to the regulation of aerobic glycolysis in cancer cells. It can be inhibited by oxidation of cysteine residues in vitro and in vivo, which is relevant to the more pro-oxidant state in cancer and proliferating tissues. These conditions also favour lipid peroxidation and the formation of electrophilic fragmentation products, including short-chain aldehydes that can covalently modify proteins. However, as yet few studies have investigated their interactions with pyruvate kinase, so we investigated the effects of three different aldehydes, acrolein, malondialdehyde and 4-hydroxy-2(E)-hexenal (HHE), on the structure and activity of the enzyme. Analysis by LC-MS/MS showed unique modification profiles for each aldehyde, but Cys152, Cys423 and Cys474 were the residues most susceptible to electrophilic modification. Analysis of enzymatic activity under these conditions showed that acrolein was the strongest inhibitor, and at incubation times longer than 2 h, pathophysiological concentrations induced significant effects. Treatment of MCF-7 cells with the aldehydes caused similar losses of pyruvate kinase activity to those observed in vitro, and at lower concentrations than those required to cause cell death, with time and dose-dependent effects; acrolein adducts on Cys152 and Cys358 were detected. Cys358 and Cys474 are located at or near the allosteric or active sites, and formation of adducts on these residues probably contributes to loss of activity at low treatment concentrations. This study provides the first detailed analysis of the structure-activity relationship of C3 and C6 aldehydes with pyruvate kinase, and suggests that reactive short-chain aldehydes generated in diseases with an oxidative aetiology or from environmental exposure such as smoking could be involved in the metabolic alterations observed in cancer cells, through alteration of pyruvate kinase activity.

Synthesis and metabolism of methylglyoxal, S-D-lactoylglutathione and D-lactate in cancer and Alzheimer's disease. Exploring the crossroad of eternal youth and premature aging

Both cancer and Alzheimer's disease (AD) are emerging as metabolic diseases in which aberrant/dysregulated glucose metabolism and bioenergetics occur, and play a key role in disease progression. Interestingly, an enhancement of glucose uptake, glycolysis and pentose phosphate pathway occurs in both cancer cells and amyloid-β-resistant neurons in the early phase of AD. However, this metabolic shift has its adverse effects. One of them is the increase in methylglyoxal production, a physiological cytotoxic by-product of glucose catabolism. Methylglyoxal is mainly detoxified via cytosolic glyoxalase route comprising glyoxalase 1 and glyoxalase 2 with the production of S-D-lactoylglutathione and D-lactate as intermediate and end-product, respectively. Due to the existence of mitochondrial carriers and intramitochondrial glyoxalase 2 and D-lactate dehydrogenase, the transport and metabolism of both S-D-lactoylglutathione and D-lactate in mitochondria can contribute to methylglyoxal elimination, cellular antioxidant power and energy production. In this review, it is supposed that the different ability of cancer cells and AD neurons to metabolize methylglyoxal, S-D-lactoylglutathione and D-lactate scores cell fate, therefore being at the very crossroad of the "eternal youth" of cancer and the "premature death" of AD neurons. Understanding of these processes would help to elaborate novel metabolism-based therapies for cancer and AD treatment.

Impacts of chlorothalonil on denitrification and N2O emission in riparian sediments: Microbial metabolism mechanism

Riparian zones can receive large amounts of nitrate, potentially contributing to water pollution. Denitrification is a major pathway to remove nitrate. Previous research on riparian denitrification focused on natural factors, but frequently neglected the roles of human activity, such as pesticide accumulations. Here, we combined field investigations and exposure experiments to reveal the responses of denitrification and N₂O emission to chlorothalonil (CTN, a common pesticide) in column experiments with riparian sediments. In this study, CTN inhibited denitrification and led to nitrate accumulation in sediments. Furthermore, CTN significantly increased N₂O emission by 208-377%, and this response was regulated by N₂O reductase (NOS) activity rather than nosZ abundance. A mechanistic study indicated that the critical step (glyceraldehyde-3-phosphate to 3-phosphogylcerate) catalyzed by glyceraldehyde-3-phosphate dehydrogenase during microbial metabolism greatly influenced denitrification in CTN-polluted sediments. Our data also revealed that CTN declined electron donor NADH, electron transport system, and denitrifying enzyme activities during denitrification. Such responses suggested that CTN deteriorated sediment denitrification by inhibiting electron production, transport and consumption in denitrifiers. Additionally, structure equation modeling indicated that NOS was the key factor in predicting denitrification rate in CTN-polluted sediments. Overall, this is the first study to explore the effects of pesticide on denitrification and N₂O emission in riparian zones at microbial metabolism level. Our results suggest that the safety threshold of CTN accumulation for inhibiting sediment denitrification is approximately 2 mg kg^-1, and imply that the wide presence of pesticides in riparian zones could impact eutrophication control of aquatic ecosystems.

Fluorescence and chemiluminescence approaches for peroxynitrite detection

In the last two decades, there has been a significant advance in understanding the biochemistry of peroxynitrite, an endogenously-produced oxidant and nucleophile. Its relevance as a mediator in several pathologic states and the aging process together with its transient character and low steady-state concentration, motivated the development of a variety of techniques for its unambiguous detection and estimation. Among these, fluorescence and chemiluminescence approaches have represented important tools with enhanced sensitivity but usual limited specificity. In this review, we analyze selected examples of molecular probes that permit the detection of peroxynitrite by fluorescence and chemiluminescence, disclosing their mechanism of reaction with either peroxynitrite or peroxynitrite-derived radicals. Indeed, probes have been divided into 1) redox probes that yield products by a free radical mechanism, and 2) electrophilic probes that evolve to products secondary to the nucleophilic attack by peroxynitrite. Overall, boronate-based compounds are emerging as preferred probes for the sensitive and specific detection and quantitation. Moreover, novel strategies involving genetically-modified fluorescent proteins with the incorporation of unnatural amino acids have been recently described as peroxynitrite sensors. This review analyzes the most commonly used fluorescence and chemiluminescence approaches for peroxynitrite detection and provides some guidelines for appropriate experimental design and data interpretation, including how to estimate peroxynitrite formation rates in cells.

Functional consequences of piceatannol binding to glyceraldehyde-3-phosphate dehydrogenase

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is one of the key redox-sensitive proteins whose activity is largely affected by oxidative modifications at its highly reactive cysteine residue in the enzyme’s active site (Cys149). Prolonged exposure to oxidative stress may cause, inter alia, the formation of intermolecular disulfide bonds leading to accumulation of GAPDH aggregates and ultimately to cell death. Recently these anomalies have been linked with the pathogenesis of Alzheimer’s disease. Novel evidences indicate that low molecular compounds may be effective inhibitors potentially preventing the GAPDH translocation to the nucleus, and inhibiting or slowing down its aggregation and oligomerization. Therefore, we decided to establish the ability of naturally occurring compound, piceatannol, to interact with GAPDH and to reveal its effect on functional properties and selected parameters of the dehydrogenase structure. The obtained data revealed that piceatannol binds to GAPDH. The ITC analysis indicated that one molecule of the tetrameric enzyme may bind up to 8 molecules of polyphenol (7.3 ± 0.9). Potential binding sites of piceatannol to the GAPDH molecule were analyzed using the Ligand Fit algorithm. Conducted analysis detected 11 ligand binding positions. We indicated that piceatannol decreases GAPDH activity. Detailed analysis allowed us to presume that this effect is due to piceatannol ability to assemble a covalent binding with nucleophilic cysteine residue (Cys149) which is directly involved in the catalytic reaction. Consequently, our studies strongly indicate that piceatannol would be an exceptional inhibitor thanks to its ability to break the aforementioned pathologic disulfide linkage, and therefore to inhibit GAPDH aggregation. We demonstrated that by binding with GAPDH piceatannol blocks cysteine residue and counteracts its oxidative modifications, that induce oligomerization and GAPDH aggregation.

Neurovascular-neuroenergetic coupling axis in the brain: master regulation by nitric oxide and consequences in aging and neurodegeneration

The strict energetic demands of the brain require that nutrient supply and usage be fine-tuned in accordance with the specific temporal and spatial patterns of ever-changing levels of neuronal activity. This is achieved by adjusting local cerebral blood flow (CBF) as a function of activity level - neurovascular coupling - and by changing how energy substrates are metabolized and shuttled amongst astrocytes and neurons - neuroenergetic coupling. Both activity-dependent increase of CBF and O₂ and glucose utilization by active neural cells are inextricably linked, establishing a functional metabolic axis in the brain, the neurovascular-neuroenergetic coupling axis. This axis incorporates and links previously independent processes that need to be coordinated in the normal brain. We here review evidence supporting the role of neuronal-derived nitric oxide (^•NO) as the master regulator of this axis. Nitric oxide is produced in tight association with glutamatergic activation and, diffusing several cell diameters, may interact with different molecular targets within each cell type. Hemeproteins such as soluble guanylate cyclase, cytochrome c oxidase and hemoglobin, with which ^•NO reacts at relatively fast rates, are but a few of the key in determinants of the regulatory role of ^•NO in the neurovascular-neuroenergetic coupling axis. Accordingly, critical literature supporting this concept is discussed. Moreover, in view of the controversy regarding the regulation of catabolism of different neural cells, we further discuss key aspects of the pathways through which ^•NO specifically up-regulates glycolysis in astrocytes, supporting lactate shuttling to neurons for oxidative breakdown. From a biomedical viewpoint, derailment of neurovascular-neuroenergetic axis is precociously linked to aberrant brain aging, cognitive impairment and neurodegeneration. Thus, we summarize current knowledge of how both neurovascular and neuroenergetic coupling are compromised in aging, traumatic brain injury, epilepsy and age-associated neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease, suggesting that a shift in cellular redox balance may contribute to divert ^•NO bioactivity from regulation to dysfunction.

Carbonyl Stress in Bacteria: Causes and Consequences

Pathways of synthesis of the α-reactive carbonyl compound methylglyoxal (MG) in prokaryotes are described in this review. Accumulation of MG leads to development of carbonyl stress. Some pathways of MG formation are similar for both pro- and eukaryotes, but there are reactions specific for prokaryotes, e.g. the methylglyoxal synthase reaction. This reaction and the glyoxalase system constitute an alternative pathway of glucose catabolism - the MG shunt not associated with the synthesis of ATP. In violation of the regulation of metabolism, the cell uses MG shunt as well as other glycolysis shunting pathways and futile cycles enabling stabilization of its energetic status. MG was first examined as a biologically active metabolic factor participating in the formation of phenotypic polymorphism and hyperpersistent potential of bacterial populations. The study of carbonyl stress is interesting for evolutionary biology and can be useful for constructing highly effective producer strains.

Nitrosative stress by peroxynitrite impairs ATP production in human spermatozoa

The most toxic species in live systems include reactive nitrogen species such as peroxynitrite, which at high levels induces nitrosative stress. In human spermatozoa, the negative effect of peroxynitrite on motility and mitochondrial membrane potential was recently demonstrated, and the hypothesis of this work is that impairment of ATP production could be one cause of the effect on motility. Therefore, the aim here was to evaluate ATP production by both glycolysis and oxidative phosphorylation (OXPHOS) in spermatozoa exposed to peroxynitrite in vitro. Human spermatozoa were incubated with SIN-1, a molecule which generates peroxynitrite, and the ATP level was evaluated. Then, to inactivate glycolysis or OXPHOS, spermatozoa were incubated with pharmacological inhibitors of these pathways. Spermatozoa treated for inactivating one or the other pathway were exposed to SIN-1, and the ATP level was compared to the control without SIN-1 in each condition. The ATP level fell after peroxynitrite exposure. The ATP in spermatozoa treated for inactivating one or the other metabolic pathway and subsequently exposed to peroxynitrite was reduced compared with the control. These results show for the first time that an important mechanism by which peroxynitrite reduces sperm function is the inhibition of ATP production, affecting both glycolysis and OXPHOS.

Interplay between oxidant species and energy metabolism

It has long been recognized that energy metabolism is linked to the production of reactive oxygen species (ROS) and critical enzymes allied to metabolic pathways can be affected by redox reactions. This interplay between energy metabolism and ROS becomes most apparent during the aging process and in the onset and progression of many age-related diseases (i.e. diabetes, metabolic syndrome, atherosclerosis, neurodegenerative diseases). As such, the capacity to identify metabolic pathways involved in ROS formation, as well as specific targets and oxidative modifications is crucial to our understanding of the molecular basis of age-related diseases and for the design of novel therapeutic strategies.

Herein we review oxidant formation associated with the cell's energetic metabolism, key antioxidants involved in ROS detoxification, and the principal targets of oxidant species in metabolic routes and discuss their relevance in cell signaling and age-related diseases.

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Energy metabolism is both a source and target of oxidant species.

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Reactive oxygen species are formed in redox reactions in catabolic pathways.

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Sensitive targets of oxidant species regulate the flux of metabolic pathways.

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Metabolic pathways and antioxidant systems are regulated coordinately.

One- and two-electron oxidation of thiols: mechanisms, kinetics and biological fates

The oxidation of biothiols participates not only in the defense against oxidative damage but also in enzymatic catalytic mechanisms and signal transduction processes. Thiols are versatile reductants that react with oxidizing species by one- and two-electron mechanisms, leading to thiyl radicals and sulfenic acids, respectively. These intermediates, depending on the conditions, participate in further reactions that converge on different stable products. Through this review, we will describe the biologically relevant species that are able to perform these oxidations and we will analyze the mechanisms and kinetics of the one- and two-electron reactions. The processes undergone by typical low-molecular-weight thiols as well as the particularities of specific thiol proteins will be described, including the molecular determinants proposed to account for the extraordinary reactivities of peroxidatic thiols. Finally, the main fates of the thiyl radical and sulfenic acid intermediates will be summarized.

Organic Nitrate Therapy, Nitrate Tolerance, and Nitrate-Induced Endothelial Dysfunction: Emphasis on Redox Biology and Oxidative Stress

Organic nitrates, such as nitroglycerin (GTN), isosorbide-5-mononitrate and isosorbide dinitrate, and pentaerithrityl tetranitrate (PETN), when given acutely, have potent vasodilator effects improving symptoms in patients with acute and chronic congestive heart failure, stable coronary artery disease, acute coronary syndromes, or arterial hypertension. The mechanisms underlying vasodilation include the release of •NO or a related compound in response to intracellular bioactivation (for GTN, the mitochondrial aldehyde dehydrogenase [ALDH-2]) and activation of the enzyme, soluble guanylyl cyclase. Increasing cyclic guanosine-3',-5'-monophosphate (cGMP) levels lead to an activation of the cGMP-dependent kinase I, thereby causing the relaxation of the vascular smooth muscle by decreasing intracellular calcium concentrations. The hemodynamic and anti-ischemic effects of organic nitrates are rapidly lost upon long-term (low-dose) administration due to the rapid development of tolerance and endothelial dysfunction, which is in most cases linked to increased intracellular oxidative stress. Enzymatic sources of reactive oxygen species under nitrate therapy include mitochondria, NADPH oxidases, and an uncoupled •NO synthase. Acute high-dose challenges with organic nitrates cause a similar loss of potency (tachyphylaxis), but with distinct pathomechanism. The differences among organic nitrates are highlighted regarding their potency to induce oxidative stress and subsequent tolerance and endothelial dysfunction. We also address pleiotropic effects of organic nitrates, for example, their capacity to stimulate antioxidant pathways like those demonstrated for PETN, all of which may prevent adverse effects in response to long-term therapy. Based on these considerations, we will discuss and present some preclinical data on how the nitrate of the future should be designed.

Nitric oxide diffusion to red blood cells limits extracellular, but not intraphagosomal, peroxynitrite formation by macrophages

Macrophage-derived nitric oxide ((•)NO) participates in cytotoxic mechanisms against diverse microorganisms and tumor cells. These effects can be mediated by (•)NO itself or (•)NO-derived species such as peroxynitrite formed by its diffusion-controlled reaction with NADPH oxidase-derived superoxide radical anion (O(2)(•-)). In vivo, the facile extracellular diffusion of (•)NO as well as different competing consumption routes limit its bioavailability for the reaction with O(2)(•-) and, hence, peroxynitrite formation. In this work, we evaluated the extent by which (•)NO diffusion to red blood cells (RBC) can compete with activated macrophages-derived O(2)(•-) and affect peroxynitrite formation yields. Macrophage-dependent peroxynitrite production was determined by boron-based probes that react directly with peroxynitrite, namely, coumarin-7-boronic acid (CBA) and fluorescein-boronate (Fl-B). The influence of (•)NO diffusion to RBC on peroxynitrite formation was experimentally analyzed in co-incubations of (•)NO and O(2)(•-)-forming macrophages with erythrocytes. Additionally, we evaluated the permeation of (•)NO to RBC by measuring the intracellular oxidation of oxyhemoglobin to methemoglobin. Our results indicate that diluted RBC suspensions dose-dependently inhibit peroxynitrite formation, outcompeting the O(2)(•-) reaction. Computer-assisted kinetic studies evaluating peroxynitrite formation by its precursor radicals in the presence of RBC are in accordance with experimental results. Moreover, the presence of erythrocytes in the proximity of (•)NO and O(2)(•-)-forming macrophages prevented intracellular Fl-B oxidation pre-loaded in L1210 cells co-cultured with activated macrophages. On the other hand, Fl-B-coated latex beads incorporated in the macrophage phagocytic vacuole indicated that intraphagosomal probe oxidation by peroxynitrite was not affected by nearby RBC. Our data support that in the proximity of a blood vessel, (•)NO consumption by RBC will limit the extracellular formation (and subsequent cytotoxic effects) of peroxynitrite by activated macrophages, while the intraphagosomal yield of peroxynitrite will remain unaffected.

Oxidised low density lipoprotein causes human macrophage cell death through oxidant generation and inhibition of key catabolic enzymes

Oxidised low density lipoprotein (oxLDL) is thought to be a significant contributor to the death of macrophage cells observed in advanced atherosclerotic plaques. Using human-derived U937 cells we have examined the effect of cytotoxic oxLDL on oxidative stress and cellular catabolism. Within 3h of the addition of oxLDL, there was a rapid, concentration dependent rise in cellular reactive oxygen species followed by the loss of cellular GSH, and the enzyme activity of both glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and aconitase. The loss of these catabolic enzymes was accompanied by the loss of cellular ATP and lower lactate generation. Addition of the macrophage antioxidant 7,8-dihydroneopterin inhibited the ROS generation, glutathione loss and catabolic inactivation. NOX was shown to be activated by oxLDL addition while apocynin inhibited the loss of GSH and cell viability. The data suggests that oxLDL triggers an excess of ROS production through NOX activation, and catabolic failure through thiol oxidation resulting in cell death.

Possible role of NAD-dependent glyceraldehyde-3-phosphate dehydrogenase in growth promotion of Arabidopsis seedlings by low levels of selenium

We explored functional significance of selenium (Se) in Arabidopsis physiology. Se at very low concentrations in cultivation exerted a considerable positive effect on Arabidopsis growth with no indication of oxidative stress, whereas Se at higher concentrations significantly suppressed the growth and brought serious oxidative damage. Respiration, ATP levels, and the activity of NAD-dependent glyceraldehyde-3-phosphate dehydrogenase (NAD-GAPDH) were enhanced in Arabidopsis grown in the medium containing 1.0 μM Se. Addition of an inhibitor of glutathione (GSH) synthesis to the medium abolished both of the Se-dependent growth promotion and NAD-GAPDH up-regulation. Assay of NAD-GAPDH purified from seedlings subjected to Se interventions raised the possibility of a direct connection between the activity of this enzyme and Arabidopsis growth. These results reveal that trace amounts of Se accelerate Arabidopsis growth, and suggest that this pro-growth effect of Se arises enhancing mitochondrial performance in a GSH-dependent manner, in which NAD-GAPDH may serve as a key regulator.

Ex vivo effects of ibogaine on the activity of antioxidative enzymes in human erythrocytes

ETHNOPHARMACOLOGICAL RELEVANCE

Ibogaine is a naturally occurring alkaloid with psychotropic and metabotropic effects, derived from the bark of the root of the West African Tabernanthe iboga plant. The tribes of Kongo basin have been using iboga as a stimulant, for medicinal purposes, and in rite of passage ceremonies, for centuries. Besides, it has been found that this drug has anti-addictive effects.

AIM OF THE STUDY

Previous studies have demonstrated that ibogaine changed the quantity of ATP and energy related enzymes as well as the activity of antioxidant enzymes in cells thus altering redox equilibrium in a time manner. In this work, the mechanism of its action was further studied by measuring the effects of ibogaine in human erythrocytes in vitro on ATP liberation, membrane fluidity and antioxidant enzymes activity.

MATERIALS AND METHODS

Heparinized human blood samples were incubated with ibogaine (10 and 20 μM) at 37°C for 1h. Blood plasma was separated by centrifugation and the levels of ATP and uric acid were measured 10 min after the addition of ibogaine using standard kits. The activity of copper-zinc superoxide dismutase (SOD1), catalase (CAT), glutathione peroxidase (GSH-Px) and glutathione reductase (GR) were measured in erythrocytes after incubation period. The stability of SOD1 activity was further tested through in vitro incubation with H2O2 and scanning of its electrophoretic profiles. Membrane fluidity was determined using an electron paramagnetic resonance spin-labelling method.

RESULTS

Results showed that ibogaine treatment of erythrocytes in vitro increased ATP concentration in the blood plasma without changes in neither erythrocytes membrane fluidity nor uric acid concentration. Ibogaine also increased SOD1 activity in erythrocytes at both doses applied here. Treatment with 20 μM also elevated GR activity after in vitro incubation at 37°C. Electrophoretic profiles revealed that incubation with ibogaine mitigates H2O2 mediated suppression of SOD1 activity.

CONCLUSION

Some of the effects of ibogaine seem to be mediated through its influence on energy metabolism, redox active processes and the effects of discrete fluctuations of individual reactive oxygen species on different levels of enzyme activities. Overall, ibogaine acts as a pro-antioxidant by increasing activity of antioxidative enzymes and as an adaptagene in oxidative distress.

The many roads to mitochondrial dysfunction in neuroimmune and neuropsychiatric disorders

BACKGROUND

Mitochondrial dysfunction and defects in oxidative metabolism are a characteristic feature of many chronic illnesses not currently classified as mitochondrial diseases. Examples of such illnesses include bipolar disorder, multiple sclerosis, Parkinson's disease, schizophrenia, depression, autism, and chronic fatigue syndrome.

DISCUSSION

While the majority of patients with multiple sclerosis appear to have widespread mitochondrial dysfunction and impaired ATP production, the findings in patients diagnosed with Parkinson's disease, autism, depression, bipolar disorder schizophrenia and chronic fatigue syndrome are less consistent, likely reflecting the fact that these diagnoses do not represent a disease with a unitary pathogenesis and pathophysiology. However, investigations have revealed the presence of chronic oxidative stress to be an almost invariant finding in study cohorts of patients afforded each diagnosis. This state is characterized by elevated reactive oxygen and nitrogen species and/or reduced levels of glutathione, and goes hand in hand with chronic systemic inflammation with elevated levels of pro-inflammatory cytokines.

SUMMARY

This paper details mechanisms by which elevated levels of reactive oxygen and nitrogen species together with elevated pro-inflammatory cytokines could conspire to pave a major road to the development of mitochondrial dysfunction and impaired oxidative metabolism seen in many patients diagnosed with these disorders.

Cancer cell metabolism and the modulating effects of nitric oxide

Altered metabolic phenotype has been recognized as a hallmark of tumor cells for many years, but this aspect of the cancer phenotype has come into greater focus in recent years. NOS2 (inducible nitric oxide synthase of iNOS) has been implicated as a component in many aggressive tumor phenotypes, including melanoma, glioblastoma, and breast cancer. Nitric oxide has been well established as a modulator of cellular bioenergetics pathways, in many ways similar to the alteration of cellular metabolism observed in aggressive tumors. In this review we attempt to bring these concepts together with the general hypothesis that one function of NOS2 and NO in cancer is to modulate metabolic processes to facilitate increased tumor aggression. There are many mechanisms by which NO can modulate tumor metabolism, including direct inhibition of respiration, alterations in mitochondrial mass, oxidative inhibition of bioenergetic enzymes, and the stimulation of secondary signaling pathways. Here we review metabolic alterations in the context of cancer cells and discuss the role of NO as a potential mediator of these changes.

ROS and energy metabolism in cancer cells: alliance for fast growth

In normal cells, the cellular reactive oxygen species (ROS) level is proportional to the activity of mitochondrial electron transport and tightly controlled by endogenous antioxidant system. However, energy metabolism and ROS homeostasis in cancer cells are much different from those in normal cells. For example, a majority of cellular glucose is metabolized through aerobic glycolysis ("Warburg effect") and the pentose phosphate pathway. Cancer cells harbor functional mitochondria, but many mutations in nuclear DNA-encoded mitochondrial genes and mitochondrial genome result in the mitochondrial metabolic reprogramming. The other characteristic of cancer cells is to maintain much higher ROS level than normal cells. Ironically, cancer cells overexpress the ROS-producing NADPH oxidase and the ROS-eliminating antioxidant enzymes, both of which enzyme systems share NADPH as a reducing power source. In this article, we review the complex connection between ROS and energy metabolisms in cancer cells.

Glutathione-garlic sulfur conjugates: slow hydrogen sulfide releasing agents for therapeutic applications

Natural organosulfur compounds (OSCs) from Allium sativum L. display antioxidant and chemo-sensitization properties, including the in vitro inhibition of tumor cell proliferation through the induction of apoptosis. Garlic water- and oil-soluble allyl sulfur compounds show distinct properties and the capability to inhibit the proliferation of tumor cells. In the present study, we optimized a new protocol for the extraction of water-soluble compounds from garlic at low temperatures and the production of glutathionyl-OSC conjugates during the extraction. Spontaneously, Cys/GSH-mixed-disulfide conjugates are produced by in vivo metabolism of OSCs and represent active molecules able to affect cellular metabolism. Water-soluble extracts, with (GSGaWS) or without (GaWS) glutathione conjugates, were here produced and tested for their ability to release hydrogen sulfide (H₂S), also in the presence of reductants and of thiosulfate:cyanide sulfurtransferase (TST) enzyme. Thus, the TST catalysis of the H₂S-release from garlic OSCs and their conjugates has been investigated by molecular in vitro experiments. The antiproliferative properties of these extracts on the human T-cell lymphoma cell line, HuT 78, were observed and related to histone hyperacetylation and downregulation of GAPDH expression. Altogether, the results presented here pave the way for the production of a GSGaWS as new, slowly-releasing hydrogen sulfide extract for potential therapeutic applications.

Biochemical methods for monitoring protein thiol redox states in biological systems

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

Oxidative and Nitrosative Stress and Immune-Inflammatory Pathways in Patients with Myalgic Encephalomyelitis (ME)/Chronic Fatigue Syndrome (CFS)

Myalgic Encephalomyelitis (ME) / Chronic Fatigue Syndrome (CFS) has been classified as a disease of the central nervous system by the WHO since 1969. Many patients carrying this diagnosis do demonstrate an almost bewildering array of biological abnormalities particularly the presence of oxidative and nitrosative stress (O&NS) and a chronically activated innate immune system. The proposal made herein is that once generated chronically activated O&NS and immune-inflammatory pathways conspire to generate a multitude of self-sustaining and self-amplifying pathological processes which are associated with the onset of ME/CFS. Sources of continuous activation of O&NS and immune-inflammatory pathways in ME/CFS are chronic, intermittent and opportunistic infections, bacterial translocation, autoimmune responses, mitochondrial dysfunctions, activation of the Toll-Like Receptor Radical Cycle, and decreased antioxidant levels. Consequences of chronically activated O&NS and immune-inflammatory pathways in ME/CFS are brain disorders, including neuroinflammation and brain hypometabolism / hypoperfusion, toxic effects of nitric oxide and peroxynitrite, lipid peroxidation and oxidative damage to DNA, secondary autoimmune responses directed against disrupted lipid membrane components and proteins, mitochondrial dysfunctions with a disruption of energy metabolism (e.g. compromised ATP production) and dysfunctional intracellular signaling pathways. The interplay between all of these factors leads to self-amplifying feed forward loops causing a chronic state of activated O&NS, immune-inflammatory and autoimmune pathways which may sustain the disease.

Peroxynitrite, a potent macrophage-derived oxidizing cytotoxin to combat invading pathogens

Macrophages are among the first cellular actors facing the invasion of microorganisms. These cells are able to internalize pathogens and destroy them by means of toxic mediators, many of which are produced enzymatically and have strong oxidizing capacity. Indeed, macrophages count on the NADPH oxidase complex activity, which is triggered during pathogen invasion and leads to the production of superoxide radical inside the phagosome. At the same time, the induction of nitric oxide synthase results in the production of nitric oxide in the cytosol which is able to readily diffuse to the phagocytic vacuole. Superoxide radical and nitric oxide react at diffusion controlled rates with each other inside the phagosome to yield peroxynitrite, a powerful oxidant capable to kill micro-organisms. Peroxynitrite toxicity resides on oxidations and nitrations of biomolecules in the target cell. The central role of peroxynitrite as a key effector molecule in the control of infections has been proven in a wide number of models. However, some microorganisms and virulent strains adapt to survive inside the potentially hostile oxidizing microenvironment of the phagosome by either impeding peroxynitrite formation or rapidly detoxifying it once formed. In this context, the outcome of the infection process is a result of the interplay between the macrophage-derived oxidizing cytotoxins such as peroxynitrite and the antioxidant defense machinery of the invading pathogens.

Two-dimensional differential in-gel electrophoresis-based proteomics of male gametes in relation to oxidative stress

OBJECTIVE

To identify the relative abundance of proteins in pooled reactive oxygen species (ROS)-positive (ROS+) and ROS-negative (ROS-) semen samples with the use of two-dimensional differential in-gel electrophoresis (2D-DIGE).

DESIGN

Spermatozoa suspensions from ROS+ and ROS- groups by 2D-DIGE analysis.

SETTING

Tertiary hospital.

PATIENT(S)

20 donors and 32 infertile men.

INTERVENTION(S)

Seminal ejaculates evaluated for semen and proteomic analysis.

MAIN OUTCOME MEASURE(S)

Semen samples from 20 donors and 32 infertile men were pooled, divided into ROS+ and ROS- groups based on the cutoff value of <20 relative light units/s/10(6) sperm and frozen. From each pooled group, spermatozoa were labeled with Cy3/Cy5 fluorescent dye. Duplicate 2D-DIGE gels were run. Image analysis was performed with the use of Decider software. Protein spots exhibiting ≥1.5-fold difference in intensity were excised from the preparatory gel and identified by liquid chromatography-mass spectrometry. Data were analyzed with the use of Sequest and Blast programs.

RESULT(S)

A total of 1,343 protein spots in gel 1 (ROS-) and 1,265 spots in gel 2 (ROS+) were detected. The majority of protein spots had similar expression, with 31 spots were differentially expressed. Six spots were significantly decreased and 25 increased in the ROS- sample compared with the ROS+ sample.

CONCLUSION(S)

Significantly different expression of protective proteins against oxidative stress was found in ROS-compared with ROS+ samples. These differences may explain the role of oxidation species in the pathology of male infertility.

Functional diversity

There is increasing evidence to support a gene economy model that is fully based on the principles of evolution in which a limited number of proteins does not necessarily reflect a finite number of biochemical processes. The concept of 'gene sharing' proposes that a single protein can have alternate functions that are typically attributed to other proteins. GAPDH appears to play this role quite well in that it exhibits more than one function. GAPDH represents the prototype for this new paradigm of protein multi-functionality. The chapter discusses the diverse functions of GAPDH among three broad categories: cell structure, gene expression and signal transduction. Protein function is curiously re-specified given the cell's unique needs. GAPDH provides the cell with the means of linking metabolic activity to various cellular processes. While interpretations may often lead to GAPDH's role in meeting focal energy demands, this chapter discusses several other very distinct GAPDH functions (i.e. membrane fusogenic properties) that are quite different from its ability to catalyze oxidative phosphorylation of the triose, glyceraldehyde 3-phosphate. It is suggested that a single protein participates in multiple processes in the structural organization of the cell, controls the transmission of genetic information (i.e. GAPDH's involvement may not be finite) and mediates intracellular signaling.

Target for diverse chemical modifications

The chapter begins with an historical perspective of GAPDH isozymes that is juxtaposed to the fact that there is only one somatic functional gene in humans that is virtually identical among the mammalian species. Over the many years of GAPDH research, dozens of labs have reported the existence of multiple forms of GAPDH, which mostly vary as a function of charge with an occasional report of truncated forms. These observations are in part due to GAPDH being a substrate for many enzymatically-controlled post-translational modifications. While target residues have been identified and predictive algorithms have implicated certain residues, this area of research appears to be in its infancy regarding GAPDH. Equally fascinating, the uniquely susceptible nature of GAPDH to non-enzymatic reactions, that typically are associated with cell stress, such as oxidation and nitration, is also discussed. Two metabolic gases, nitric oxide and hydrogen sulfide, which are enzymatically produced, appear to exert their signaling properties through non-enzymatic reaction with GAPDH. Models of cellular decline are also proposed, including the compelling hypothesis that states cell compromise occurs by the physically blocking the function of chaperonins (i.e. dual-ring multiple-subunit molecular chaperones) by the attachment of misfolded GAPDH.

Formation of 3-nitrotyrosines in carbonic anhydrase III is a sensitive marker of oxidative stress in skeletal muscle

Oxidation of skeletal muscle proteins has been reported to occur following contractions, with ageing, and with a variety of disease states, but the nature of the oxidised proteins has not been identified. A proteomics approach was utilised to identify major proteins that contain carbonyls and/or 3-nitrotyrosine (3-NT) groups in the gastrocnemius (GTN) muscles of adult (5-11 months of age) and old (26-28 months of age) wild type (WT) mice and adult mice lacking copper, zinc superoxide dismutase (Sod1(-/-) mice), manganese superoxide dismutase (Sod2(+/-) mice) or glutathione peroxidase 1 (GPx1(-/-) mice). In quiescent GTN muscles of adult and old WT mice, protein carbonylation and/or formation of 3-NT occurred in several proteins involved in glycolysis, as well as creatine kinase and carbonic anhydrase III. Following contractions, the 3-NT intensity was increased in specific protein bands from GTN muscles of both adult and old WT mice. In quiescent GTN muscles from adult Sod1(-/-) , Sod2(+/-) or GPx1(-/-) mice compared with age-matched WT mice only carbonic anhydrase III showed a greater 3-NT content. We conclude that formation of 3-NT occurs readily in response to oxidative stress in carbonic anhydrase III and this may provide a sensitive measure of oxidative damage to muscle proteins.

Selective vulnerability of synaptic signaling and metabolism to nitrosative stress

SIGNIFICANCE

Nitric oxide (NO) plays diverse physiological roles in the central nervous system, where it modulates neuronal communication, regulates blood flow, and contributes to the innate immune responses. In a number of brain pathologies, the excessive production of NO also leads to the formation of reactive and toxic intermediates generically termed reactive nitrogen species (RNS). RNS cause irreversible or poorly reversible damage to brain cells.

RECENT ADVANCES

Recent work in the field focused on the ability of NO and RNS to yield protein modifications, including the S-nitrosation of cysteine residues, which, in many instances, impact cellular functions and viability.

CRITICAL ISSUES

The vast majority of neuropathological studies focus on the loss of cell viability, but nitrosative stress may also strongly impair the functions of neuronal processes: axonal projections and dendritic trees. The functional integrity of axons and dendrites critically depends on local metabolism and effective delivery of metabolic enzymes and organelles. Here, we summarize the existing literature describing the effects of nitrosative stress on the major pathways of energetic metabolism: glycolysis, tricarboxylic acid cycle, and mitochondrial respiration, with the emphasis on modifications of protein thiols.

FUTURE DIRECTIONS

We propose that axons and dendrites are highly vulnerable to nitrosative stress because of their low glycolytic capacity and high dependence on timely delivery of metabolic enzymes and organelles from the cell body. Thus, supplementation with the end products of glycolysis, pyruvate or lactate, may help preserve metabolism in distal neuronal processes and protect or restore synaptic function in the ailing brain.