Hydroperoxyl, superoxide and pH gradients in the mitochondrial matrix: a theoretical assessment

Mitochondria Play Essential Roles in Intracellular Protection against Oxidative Stress-Which Molecules among the ROS Generated in the Mitochondria Can Escape the Mitochondria and Contribute to Signal Activation in Cytosol?

Questions about which reactive oxygen species (ROS) or reactive nitrogen species (RNS) can escape from the mitochondria and activate signals must be addressed. In this study, two parameters, the calculated dipole moment (debye, D) and permeability coefficient (Pm) (cm s-1), are listed for hydrogen peroxide (H2O2), hydroxyl radical (•OH), superoxide (O2•-), hydroperoxyl radical (HO2•), nitric oxide (•NO), nitrogen dioxide (•NO2), peroxynitrite (ONOO-), and peroxynitrous acid (ONOOH) in comparison to those for water (H2O). O2•- is generated from the mitochondrial electron transport chain (ETC), and several other ROS and RNS can be generated subsequently. The candidates which pass through the mitochondrial membrane include ROS with a small number of dipoles, i.e., H2O2, HO2•, ONOOH, •OH, and •NO. The results show that the dipole moment of •NO2 is 0.35 D, indicating permeability; however, •NO2 can be eliminated quickly. The dipole moments of •OH (1.67 D) and ONOOH (1.77 D) indicate that they might be permeable. This study also suggests that the mitochondria play a central role in protecting against further oxidative stress in cells. The amounts, the long half-life, the diffusion distance, the Pm, the one-electron reduction potential, the pKa, and the rate constants for the reaction with ascorbate and glutathione are listed for various ROS/RNS, •OH, singlet oxygen (1O2), H2O2, O2•-, HO2•, •NO, •NO2, ONOO-, and ONOOH, and compared with those for H2O and oxygen (O2). Molecules with negative electrical charges cannot directly diffuse through the phospholipid bilayer of the mitochondrial membranes. Short-lived molecules, such as •OH, would be difficult to contribute to intracellular signaling. Finally, HO2• and ONOOH were selected as candidates for the ROS/RNS that pass through the mitochondrial membrane.

Molecular Dynamics Study of the Effect of Charge and Glycosyl on Superoxide Anion Distribution near Lipid Membrane

To examine the effects of membrane charge, the electrolyte species and glycosyl on the distribution of negatively charged radical of superoxide anion (·O₂^-) around the cell membrane, different phospholipid bilayer systems containing ·O₂^- radicals, different electrolytes and phospholipid bilayers were constructed through Charmm-GUI and Amber16. These systems were equilibrated with molecular dynamics by using Gromacs 5.0.2 to analyze the statistical behaviors of ·O₂^- near the lipid membrane under different conditions. It was found that in the presence of potassium rather than sodium, the negative charge of the phospholipid membrane is more likely to rarefy the superoxide anion distribution near the membrane surface. Further, the presence of glycosyl significantly reduced the density of ·O₂^- near the phospholipid bilayer by 78.3% compared with that of the neutral lipid membrane, which may have a significant contribution to reducing the lipid peroxidation from decreasing the ·O₂^- density near the membrane.

OXIDATIVE STRESS AND REPRODUCTIVE FUNCTION: The impact of oxidative stress on reproduction: a focus on gametogenesis and fertilization

In brief

Many aspects of the reproductive process are impacted by oxidative stress. This article summarizes the chemical nature of reactive oxygen species and their role in both the physiological regulation of reproductive processes and the pathophysiology of infertility.

Abstract

This article lays out the fundamental principles of oxidative stress. It describes the nature of reactive oxygen species (ROS), the way in which these potentially toxic metabolites interact with cells and how they impact both cellular function and genetic integrity. The mechanisms by which ROS generation is enhanced to the point that the cells' antioxidant defence mechanisms are overwhelmed are also reviewed taking examples from both the male and female reproductive system, with a focus on gametogenesis and fertilization. The important role of external factors in exacerbating oxidative stress and impairing reproductive competence is also examined in terms of their ability to disrupt the physiological redox regulation of reproductive processes. Developing diagnostic and therapeutic strategies to cope with oxidative stress within the reproductive system will depend on the development of a deeper understanding of the nature, source, magnitude, and location of such stress in order to fashion personalized treatments that meet a given patient's clinical needs.

Importance of Locations of Iron Ions to Elicit Cytotoxicity Induced by a Fenton-Type Reaction

The impact of the site of the Fenton reaction, i.e., hydroxyl radical (^•OH) generation, on cytotoxicity was investigated by estimating cell lethality in rat thymocytes. Cells were incubated with ferrous sulfate (FeSO₄) and hydrogen peroxide (H₂O₂), or pre-incubated with FeSO₄ and then H₂O₂ was added after medium was replaced to remove iron ions or after the medium was not replaced. Cell lethality in rat thymocytes was estimated by measuring cell sizes using flow cytometry. High extracellular concentrations of FeSO₄ exerted protective effects against H₂O₂-induced cell death instead of enhancing cell lethality. The pre-incubation of cells with FeSO₄ enhanced cell lethality induced by H₂O₂, whereas a pre-incubation with a high concentration of FeSO₄ exerted protective effects. FeSO₄ distributed extracellularly or on the surface of cells neutralized H₂O₂ outside cells. Cytotoxicity was only enhanced when the Fenton reaction, i.e., the generation of ^•OH, occurred inside cells. An assessment of plasmid DNA breakage showed that ^•OH induced by the Fenton reaction system did not break DNA. Therefore, the main target of intracellularly generated ^•OH does not appear to be DNA.

Superoxide Dismutase-Loaded Nanoparticles Attenuate Myocardial Ischemia-Reperfusion Injury and Protect Against Chronic Adverse Ventricular Remodeling

Early revascularization is critical to reduce morbidity after myocardial infarction, although reperfusion incites additional oxidative injury. Superoxide dismutase (SOD) is an antioxidant that scavenges reactive oxygen species (ROS) but has low endogenous expression and rapid myocardial washout when administered exogenously. This study utilizes a novel nanoparticle carrier to improve exogeneous SOD retention while preserving enzyme function. Its role is assessed in preserving cardiac function after myocardial ischemia-reperfusion (I/R) injury. Here, nanoparticle-encapsulated SOD (NP-SOD) exhibits similar enzyme activity as free SOD, measured by ferricytochrome-c assay. In an in vitro I/R model, free and NP-SOD reduce active ROS, preserve mitochondrial integrity and improve cell viability compared to controls. In a rat in vivo I/R injury model, NP-encapsulation of fluorescent-tagged SOD improves intramyocardial retention after direct injection. Intramyocardial NP-SOD administration in vivo improves left ventricular contractility at 3-hours post-reperfusion by echocardiography and 4-weeks by echocardiography and invasive pressure-volume catheter analysis. These findings suggest that NP-SOD mitigates ROS damage in cardiac I/R injury in vitro and maximizes retention in vivo. NP-SOD further attenuates acute injury and protects against myocyte loss and chronic adverse ventricular remodeling, demonstrating potential for translating NP-SOD as a therapy to mitigate myocardial I/R injury.

Isolation of Redox-Active Endosomes (Redoxosomes) and Assessment of NOX Activity

Reactive oxygen species (ROS) convey signals essential for proliferation, maintenance, and senescence of a growing list of cell types. Compartmentalization of these signals is integral to cell viability as well as the signaling pathways ROS direct. Redox-active endosomes (redoxosomes) are formed downstream of several ligand-activated receptors. NADPH oxidase (NOX) is a main component of redoxosomes, which recruits multiple proteins (Rac1, NOX2, p67^phox, SOD1). Isolation of redoxosomes and evaluation of how superoxide (O₂˙^-) production directs receptor signaling at the level of the endosome have enabled a better understanding of biologic processes controlled by ROS. In this chapter, we will first review the major signaling pathways that utilize redoxosomes and components that control its redox-dependent functions. We will then outline biochemical and biophysical methods for the isolation and characterization of redoxosome properties.

Toxic target of trans-crotonaldehyde in mitochondria altered by diallyl disulfides for anti-myocardial ischemia

The purposes of this study were to probe spectral behaviors of the toxic targets in trans-crotonaldehyde (TCA) in mitochondria altered by diallyl disulfides (DADS) derived from garlic. Ultraviolet absorption spectra showed that when ethanol as a solvent, the DADS blue shifted the peak of TCA from 318 nm to 312 nm. In mitochondria, the DADS further blue displaced the peak of TCA from 312 nm to 308 nm. Raman spectra displayed that the SS of DADS directly interacted with the CC toxic target of TCA, then the CCC of DADS interacted with the CHO toxic target of TCA. When DADS to TCA was 1:2, the DADS was the most powerful for the removal of the CC and CHO toxic targets of TCA. Study suggested that the SS of DADS altered the CC toxic target of TCA, while the CCC of DADS eliminated the CHO toxic target of TCA via local electron delocalization. The above two together clearly depicted the spectral behaviors of the toxic targets of TCA in mitochondria altered by DADS. These results are of great significance and value to elucidate the effects of garlic organic polysulfide on myocardial ischemia for the extensive development and use of garlic extracts.

Redox Signaling by Reactive Electrophiles and Oxidants

The concept of cell signaling in the context of nonenzyme-assisted protein modifications by reactive electrophilic and oxidative species, broadly known as redox signaling, is a uniquely complex topic that has been approached from numerous different and multidisciplinary angles. Our Review reflects on five aspects critical for understanding how nature harnesses these noncanonical post-translational modifications to coordinate distinct cellular activities: (1) specific players and their generation, (2) physicochemical properties, (3) mechanisms of action, (4) methods of interrogation, and (5) functional roles in health and disease. Emphasis is primarily placed on the latest progress in the field, but several aspects of classical work likely forgotten/lost are also recollected. For researchers with interests in getting into the field, our Review is anticipated to function as a primer. For the expert, we aim to stimulate thought and discussion about fundamentals of redox signaling mechanisms and nuances of specificity/selectivity and timing in this sophisticated yet fascinating arena at the crossroads of chemistry and biology.

Mapping the phenotypic repertoire of the cytoplasmic 2-Cys peroxiredoxin - Thioredoxin system. 1. Understanding commonalities and differences among cell types

The system (PTTRS) formed by typical 2-Cys peroxiredoxins (Prx), thioredoxin (Trx), Trx reductase (TrxR), and sulfiredoxin (Srx) is central in antioxidant protection and redox signaling in the cytoplasm of eukaryotic cells. Understanding how the PTTRS integrates these functions requires tracing phenotypes to molecular properties, which is non-trivial. Here we analyze this problem based on a model that captures the PTTRS' conserved features. We have mapped the conditions that generate each distinct response to H2O2 supply rates (vsup), and estimated the parameters for thirteen human cell types and for Saccharomyces cerevisiae. The resulting composition-to-phenotype map yielded the following experimentally testable predictions. The PTTRS permits many distinct responses including ultra-sensitivity and hysteresis. However, nearly all tumor cell lines showed a similar response characterized by limited Trx-S- depletion and a substantial but self-limited gradual accumulation of hyperoxidized Prx at high vsup. This similarity ensues from strong correlations between the TrxR, Srx and Prx activities over cell lines, which contribute to maintain the Prx-SS reduction capacity in slight excess over the maximal steady state Prx-SS production. In turn, in erythrocytes, hepatocytes and HepG2 cells high vsup depletes Trx-S- and oxidizes Prx mainly to Prx-SS. In all nucleated human cells the Prx-SS reduction capacity defined a threshold separating two different regimes. At sub-threshold vsup the cytoplasmic H2O2 concentration is determined by Prx, nM-range and spatially localized, whereas at supra-threshold vsup it is determined by much less active alternative sinks and μM-range throughout the cytoplasm. The yeast shows a distinct response where the Prx Tsa1 accumulates in sulfenate form at high vsup. This is mainly due to an exceptional stability of Tsa1's sulfenate. The implications of these findings for thiol redox regulation and cell physiology are discussed. All estimates were thoroughly documented and provided, together with analytical approximations for system properties, as a resource for quantitative redox biology.

Redox homeostasis and age-related deficits in neuromuscular integrity and function

Skeletal muscle is a major site of metabolic activity and is the most abundant tissue in the human body. Age-related muscle atrophy (sarcopenia) and weakness, characterized by progressive loss of lean muscle mass and function, is a major contributor to morbidity and has a profound effect on the quality of life of older people. With a continuously growing older population (estimated 2 billion of people aged >60 by 2050), demand for medical and social care due to functional deficits, associated with neuromuscular ageing, will inevitably increase. Despite the importance of this 'epidemic' problem, the primary biochemical and molecular mechanisms underlying age-related deficits in neuromuscular integrity and function have not been fully determined. Skeletal muscle generates reactive oxygen and nitrogen species (RONS) from a variety of subcellular sources, and age-associated oxidative damage has been suggested to be a major factor contributing to the initiation and progression of muscle atrophy inherent with ageing. RONS can modulate a variety of intracellular signal transduction processes, and disruption of these events over time due to altered redox control has been proposed as an underlying mechanism of ageing. The role of oxidants in ageing has been extensively examined in different model organisms that have undergone genetic manipulations with inconsistent findings. Transgenic and knockout rodent studies have provided insight into the function of RONS regulatory systems in neuromuscular ageing. This review summarizes almost 30 years of research in the field of redox homeostasis and muscle ageing, providing a detailed discussion of the experimental approaches that have been undertaken in murine models to examine the role of redox regulation in age-related muscle atrophy and weakness.

Luminal flow induces NADPH oxidase 4 translocation to the nuclei of thick ascending limbs

Superoxide (O₂⁻) exerts its physiological actions in part by causing changes in gene transcription. In thick ascending limbs flow‐induced O₂⁻ production is mediated by NADPH oxidase 4 (Nox4) and is dependent on protein kinase C (PKC). Polymerase delta interacting protein 2 (Poldip2) increases Nox4 activity, but it is not known whether Nox4 translocates to the nucleus and whether Poldip2 participates in this process. We hypothesized that luminal flow causes Nox4 translocation to the nuclei of thick ascending limbs in a PKC‐dependent process facilitated by Poldip2. To test our hypothesis, we studied the subcellular localization of Nox4 and Poldip2 using confocal microscopy and O₂⁻ production in the absence and presence of luminal flow. Luminal flow increased the ratio of nuclear to cytoplasmic intensity of Nox4 (N/C) from 0.3 ± 0.1 to 0.7 ± 0.1 (P < 0.01) and O₂⁻ production from 89 ± 15 to 231 ± 16 AU/s (P < 0.001). In the presence of flow PKC inhibition reduced N/C from 0.5 ± 0.1 to 0.2 ± 0.1 (P < 0.01). Flow‐induced O₂⁻ production was also blocked (flow: 142 ± 20 AU/s; flow plus PKC inhibition 26 ± 12 AU/s; P < 0.01). The cytoskeleton disruptor cytochalasin D (1 μmol/L) decreased flow‐induced Nox4 translocation by 0.3 ± 0.01 (P < 0.01); however, it did not reduce flow‐induced O₂⁻. Flow did not alter Poldip2 localization. We conclude that: (1) luminal flow elicits Nox4 translocation to the nucleus in a PKC‐ and cytoskeleton‐dependent process; (2) Nox4 activation occurs before translocation; and (3) Poldip2 is not involved in Nox4 nuclear translocation. Flow‐induced Nox4 translocation to the nucleus may play a role in O₂⁻‐dependent changes in thick ascending limbs.

Importance of Toll-like receptor 2 in mitochondrial dysfunction during polymicrobial sepsis

BACKGROUND

Toll-like receptor 2 (TLR2) contributes to sepsis pathogenesis such as deleterious systemic inflammation, cardiac dysfunction, and high mortality in animal studies. Mitochondrial dysfunction is a key molecular event that is associated with organ injury in sepsis. The role of TLR2 in sepsis-induced mitochondrial dysfunction remains unclear.

METHODS

Intracellular hydrogen peroxide (H2O2), mitochondrial superoxide (O2), mitochondrial membrane potential (ΔΨm), and intracellular adenosine triphosphate (ATP) were measured in peritoneal leukocytes. A mouse model of polymicrobial sepsis was generated by cecum ligation and puncture (CLP). Wild-type and TLR2-deficient (TLR2) mice were subjected to sham or CLP. Mitochondrial functions including reactive oxygen species (ROS), ΔΨm, intracellular ATP, and complex III activity were measured.

RESULTS

TLR2/1 activation by Pam3Cys enhanced intracellular H2O2 and mitochondrial O2 production in leukocytes, but had no effect on mitochondrial ΔΨm and ATP production. The effect was specific for TLR2/1 as TLR3 or TLR9 ligands did not induce ROS production. Polymicrobial sepsis induced mitochondrial dysfunction in leukocytes, as demonstrated by increased H2O2 and mitochondrial O2- production (CLP vs. sham; H2O2: 3,173±498, n=5 vs. 557±38, n=4; O2-: 707±66, n=35 vs. 485±35, n=17, mean fluorescence intensity, mean±SEM), attenuated complex III activity (13±2, n=16 vs. 30±3, n=7, millioptical densities/min), loss of mitochondrial ΔΨm, and depletion of intracellular ATP (33±6, n=11 vs. 296±29, n=4, nmol/mg protein). In comparison, there was significant improvement in mitochondrial function in septic TLR2-/- mice as evidenced by attenuated mitochondrial ROS production, better-maintained mitochondrial ΔΨm, and higher cellular ATP production.

CONCLUSIONS

TLR2 signaling plays a critical role in mediating mitochondrial dysfunction in peritoneal leukocytes during polymicrobial sepsis.

Hydrogen peroxide metabolism and sensing in human erythrocytes: a validated kinetic model and reappraisal of the role of peroxiredoxin II

Hydrogen peroxide (H2O2) metabolism in human erythrocytes has been thoroughly investigated, but unclear points persist. By integrating the available data into a mathematical model that accurately represents the current understanding and comparing computational predictions to observations we sought to (a) identify inconsistencies in present knowledge, (b) propose resolutions, and (c) examine their functional implications. The systematic confrontation of computational predictions with experimental observations of the responses of intact erythrocytes highlighted the following important discrepancy. The high rate constant (10(7)-10(8) M(-1) s(-1)) for H2O2 reduction determined for purified peroxiredoxin II (Prx2) and the high abundance of this protein indicate that under physiological conditions it consumes practically all the H2O2. However, this is inconsistent with extensive evidence that Prx2's contribution to H2O2 elimination is comparable to that of catalase. Models modified such that Prx2's effective peroxidase activity is just 10(5) M(-1) s(-1) agree near quantitatively with extensive experimental observations. This low effective activity is probably due to a strong but readily reversible inhibition of Prx2's peroxidatic activity in intact cells, implying that the main role of Prx2 in human erythrocytes is not to eliminate peroxide substrates. Simulations of the responses to physiological H2O2 stimuli highlight that a design combining abundant Prx2 with a low effective peroxidase activity spares NADPH while improving potential signaling properties of the Prx2/thioredoxin/thioredoxin reductase system.

Rho GTPases, oxidation, and cell redox control

While numerous studies support regulation of Ras GTPases by reactive oxygen and nitrogen species, the Rho subfamily has received considerably less attention. Over the last few years, increasing evidence is emerging that supports the redox sensitivity of Rho GTPases. Moreover, as Rho GTPases regulate the cellular redox state by controlling enzymes that generate and convert reactive oxygen and nitrogen species, redox feedback loops likely exist. Here, we provide an overview of cellular oxidants, Rho GTPases, and their inter-dependence.

Overview on how oncogenic Kras promotes pancreatic carcinogenesis by inducing low intracellular ROS levels

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease without clearly known disease causes. Recent epidemiological and animal studies suggest that the supplementation of dietary antioxidants (e.g., vitamins C and E) decreases cancer risk, implying that increased reactive oxygen species (ROS) may play a role in pancreatic carcinogenesis. However, oncogenic Kras mutations (e.g., Kras^G12D), which are present in more than 90% of PDAC, have been proven to foster low intracellular ROS levels. Here, oncogenic Kras activates expression of a series of anti-oxidant genes via Nrf2 (nuclear factor, erythroid derived 2, like 2) and also mediates an unusual metabolic pathway of glutamine to generate NADPH. This can then be used as the reducing power for ROS detoxification, leading collectively to low ROS levels in pancreatic pre-neoplastic cells and in cancer cells. In adult stem cells and cancer stem cells, low ROS levels have been associated with the formation of a proliferation-permissive intracellular environment and with perseverance of self-renewal capacities. Therefore, it is conceivable that low intracellular ROS levels may contribute significantly to oncogenic Kras-mediated PDAC formation.

Mitochondrial compartmentalization of redox processes

Knowledge of location and intracellular subcompartmentalization is essential for the understanding of redox processes, because oxidants, owing to their reactive nature, must be generated close to the molecules modified in both signaling and damaging processes. Here we discuss known redox characteristics of various mitochondrial microenvironments. Points covered are the locations of mitochondrial oxidant generation, characteristics of antioxidant systems in various mitochondrial compartments, and diffusion characteristics of oxidants in mitochondria. We also review techniques used to measure redox state in mitochondrial subcompartments, antioxidants targeted to mitochondrial subcompartments, and methodological concerns that must be addressed when using these tools.

Cellular dysfunction in diabetes as maladaptive response to mitochondrial oxidative stress

Oxidative stress has been implicated in diabetes long-term complications. In this paper, we summarize the growing evidence suggesting that hyperglycemia-induced overproduction of superoxide by mitochondrial electron transport chain triggers a maladaptive response by affecting several metabolic and signaling pathways involved in the pathophysiology of cellular dysfunction and diabetic complications. In particular, it is our goal to describe physiological mechanisms underlying the mitochondrial free radical production and regulation to explain the oxidative stress derived from a high intracellular glucose concentration and the resulting maladaptive response that leads to a cellular dysfunction and pathological state. Finally, we outline potential therapies for diabetes focused to the prevention of mitochondrial oxidative damage.

Emerging roles of ROS/RNS in muscle function and fatigue

Reactive oxygen and nitrogen species (ROS/RNS) are involved in numerous aspects of cellular signaling. Classically ROS/RNS have been associated with cellular dysfunction and disease, but it is now clear that they are also of integral importance under normal conditions. In this review, we discuss ROS/RNS effects in skeletal muscle, with special focus on changes in contractile function. The review deals with the tentative roles of ROS/RNS for acute changes that can occur during strenuous exercise resulting in muscle fatigue, for the recovery from fatigue, and for the effects of training/overtraining. We also discuss two groups of inherited diseases; muscle dystrophies, where recent data suggest that ROS/RNS may be of unexpectedly large importance, and mitochondrial myopathies, where the role of ROS seems more limited than originally thought.

Reactive oxygen species: impact on skeletal muscle

It is well established that contracting muscles produce both reactive oxygen and nitrogen species. Although the sources of oxidant production during exercise continue to be debated, growing evidence suggests that mitochondria are not the dominant source. Regardless of the sources of oxidants in contracting muscles, intense and prolonged exercise can result in oxidative damage to both proteins and lipids in the contracting myocytes. Further, oxidants regulate numerous cell signaling pathways and modulate the expression of many genes. This oxidant-mediated change in gene expression involves changes at transcriptional, mRNA stability, and signal transduction levels. Furthermore, numerous products associated with oxidant-modulated genes have been identified and include antioxidant enzymes, stress proteins, and mitochondrial electron transport proteins. Interestingly, low and physiological levels of reactive oxygen species are required for normal force production in skeletal muscle, but high levels of reactive oxygen species result in contractile dysfunction and fatigue. Ongoing research continues to explore the redox-sensitive targets in muscle that are responsible for both redox regulation of muscle adaptation and oxidant-mediated muscle fatigue.

Potential therapeutic benefits of strategies directed to mitochondria

The mitochondrion is the most important organelle in determining continued cell survival and cell death. Mitochondrial dysfunction leads to many human maladies, including cardiovascular diseases, neurodegenerative disease, and cancer. These mitochondria-related pathologies range from early infancy to senescence. The central premise of this review is that if mitochondrial abnormalities contribute to the pathological state, alleviating the mitochondrial dysfunction would contribute to attenuating the severity or progression of the disease. Therefore, this review will examine the role of mitochondria in the etiology and progression of several diseases and explore potential therapeutic benefits of targeting mitochondria in mitigating the disease processes. Indeed, recent advances in mitochondrial biology have led to selective targeting of drugs designed to modulate and manipulate mitochondrial function and genomics for therapeutic benefit. These approaches to treat mitochondrial dysfunction rationally could lead to selective protection of cells in different tissues and various disease states. However, most of these approaches are in their infancy.

Review

Production of superoxide anion O2*- by the membrane-bound enzyme NADPH oxidase of phagocytes is a long-known phenomenon; it is generally assumed that O2*-helps phagocytes kill bacterial intruders. The details and the chemistry of the killing process have, however, remained a mystery. Isoforms of NADPH oxidase exist in membranes of nearly every cell, suggesting that reactive oxygen species (ROS) participate in intra- and intercellular signaling processes. What the nature of the signal is exactly, how it is transmitted, and what structural characteristics a receptor of a "radical message" must have, have not been addressed convincingly. This review discusses how the action of messengers is in agreement with radical-specific behavior. In search for the smallest common denominator of cellular free radical activity we hypothesize that O2*- and its conjugate acid, HO2*, may have evolved under primordial conditions as regulators of membrane mechanics and that isoprostanes, widely used markers of "oxidative stress", may be an adventitious correlate of this biologic activity of O2*-/HO2*. An overall picture is presented that suggests that O2*-/HO2* radicals, by modifying cell membranes, help other agents gain access to the hydrophobic region of phospholipid bilayers and hence contribute to lipid-dependent signaling cascades. With this, O2*-/HO2* are proposed as indispensable adjuvants for the generation of cellular signals, for membrane transport, channel gating and hence, in a global sense, for cell viability and growth. We also suggest that many of the allegedly O2*- dependent bacterial pathologies and carcinogenic derailments are due to membrane-modifying activity rather than other chemical reactions of O2*-/HO2*. A consequence of this picture is the potential evolution of the "radical theory of ageing" to a "lipid theory of aging".

Redox modifier genes and pathways in amyotrophic lateral sclerosis

Enhanced redox-stress caused by neuroinflammation, mitochondria, and NADPH oxidases has been hypothesized to play critical roles in disease progression of amyotrophic lateral sclerosis (ALS). However, distinguishing whether the redox-stress observed in ALS is due to a primary defect in cellular reactive oxygen species metabolism/catabolism, or is a secondary consequence of neuroinflammation, has been difficult and the issue remains a matter of debate. Emerging evidence suggests that defects in genes that regulate NADPH oxidases may account for at least some forms of ALS. NADPH oxidases are key signaling complexes that influence cellular responses to growth factors and cytokines. In this context, NADPH oxidase-derived reactive oxygen species exert spatial control over the redox-dependent activation of certain pro-inflammatory receptors. Understanding the biology of how NADPH oxidases control cell signaling may help to clarify how genetic determinants of ALS lead to dysregulated pro-inflammatory signaling. This review provides a framework for understanding endosomal signaling through NADPH oxidases and potential mechanisms whereby gene defects in various forms of ALS may influence this cellular process and lead to motor neuron degeneration. Lastly, this review discusses past and current efforts to treat ALS using antioxidant therapies, as well as the limitations and advantages of each of these approaches.

Exercise-induced oxidative stress: cellular mechanisms and impact on muscle force production

The first suggestion that physical exercise results in free radical-mediated damage to tissues appeared in 1978, and the past three decades have resulted in a large growth of knowledge regarding exercise and oxidative stress. Although the sources of oxidant production during exercise continue to be debated, it is now well established that both resting and contracting skeletal muscles produce reactive oxygen species and reactive nitrogen species. Importantly, intense and prolonged exercise can result in oxidative damage to both proteins and lipids in the contracting myocytes. Furthermore, oxidants can modulate a number of cell signaling pathways and regulate the expression of multiple genes in eukaryotic cells. This oxidant-mediated change in gene expression involves changes at transcriptional, mRNA stability, and signal transduction levels. Furthermore, numerous products associated with oxidant-modulated genes have been identified and include antioxidant enzymes, stress proteins, DNA repair proteins, and mitochondrial electron transport proteins. Interestingly, low and physiological levels of reactive oxygen species are required for normal force production in skeletal muscle, but high levels of reactive oxygen species promote contractile dysfunction resulting in muscle weakness and fatigue. Ongoing research continues to probe the mechanisms by which oxidants influence skeletal muscle contractile properties and to explore interventions capable of protecting muscle from oxidant-mediated dysfunction.

Evidence for a superoxide permeability pathway in endosomal membranes

The compartmentalized production of superoxide (*O(2)(-)) by endosomal NADPH oxidase is important in the redox-dependent activation of NF-kappaB following interleukin 1beta (IL-1beta) stimulation. It remains unclear how *O(2)(-) produced within endosomes facilitates redox-dependent signaling events in the cytoplasm. We evaluated *O(2)(-) movement out of IL-1beta-stimulated endosomes and whether SOD1 at the endosomal surface mediates redox-signaling events required for NF-kappaB activation. The relative outward permeability of NADPH-dependent *O(2)(-) from fractionated endosomes was assessed using membrane-permeable (luminol and lucigenin) and -impermeable (isoluminol) luminescent probes for *O(2)(-). In these studies, approximately 60% of *O(2)(-) efflux out of endosomes was inhibited by treatment with either of two anion channel blockers, 4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS) or niflumic acid (NFA). Furthermore, radioisotopic electrodiffusion flux assays on endomembrane proteoliposomes suggested that *O(2)(-) and Cl(-) are transported through the same DIDS-sensitive channel(s). Rab5-based immunoaffinity isolation of IL-1beta-stimulated early endosomes demonstrated SOD1 recruitment to endosomes harboring the IL-1 receptor. Finally, SOD1-deficient cells were found to be defective in their ability to activate NF-kappaB following IL-1beta stimulation. Together, these results suggest that *O(2)(-) exits endosomes through a DIDS-sensitive chloride channel(s) and that SOD1-mediated dismutation of *O(2)(-) at the endosomal surface may produce the localized H(2)O(2) required for redox-activation of NF-kappaB.

Aging in vertebrates, and the effect of caloric restriction: a mitochondrial free radical production-DNA damage mechanism?

Oxygen is toxic to aerobic animals because it is univalently reduced inside cells to oxygen free radicals. Studies dealing with the relationship between oxidative stress and aging in different vertebrate species and in caloric-restricted rodents are discussed in this review. Healthy tissues mainly produce reactive oxygen species (ROS) at mitochondria. These ROS can damage cellular lipids, proteins and, most importantly, DNA. Although antioxidants help to control this oxidative stress in cells in general, they do not decrease the rate of aging, because their concentrations are lower in long- than in short-lived animals and because increasing antioxidant levels does not increase vertebrate maximum longevity. However, long-lived homeothermic vertebrates consistently have lower rates of mitochondrial ROS production and lower levels of steady-state oxidative damage in their mitochondrial DNA than short-lived ones. Caloric-restricted rodents also show lower levels of these two key parameters than controls fed ad libitum. The decrease in mitochondrial ROS generation of the restricted animals has been recently localized at complex I and the mechanism involved is related to the degree of electronic reduction of the complex I ROS generator. Strikingly, the same site and mechanism have been found when comparing a long- with a short-lived animal species. It is suggested that a low rate of mitochondrial ROS generation extends lifespan both in long-lived and in caloric-restricted animals by determining the rate of oxidative attack and accumulation of somatic mutations in mitochondrial DNA.

Copper−Zinc Superoxide Dismutase: Theoretical Insights into the Catalytic Mechanism

The mechanism for the toxic superoxide radical disproportionation to molecular oxygen and hydrogen peroxide by copper-zinc superoxide dismutase (CuZnSOD) has been studied using the B3LYP hybrid density functional. On the basis of the X-ray structure of the enzyme, the molecular system investigated includes the first-shell protein ligands of the two metal centers as well as the second-shell ligand Asp122. The substrates of the model reaction are two superoxide radical anions, approaching the copper center at the beginning of two half-reactions: the first part of the catalytic cycle involving Cu+ oxidation and the second part reducing Cu2+ back to its initial state. The quantitative free energy profile of the reaction is obtained and discussed in connection with the experimental data on the reduction potentials and CuZnSOD kinetics. The optimized structures are analyzed and compared to the experimental ones. The two transition states alternate the protonation state of His61 and correspond to histidine Cu-His61-Zn bridge rupture/reformation. Modifications applied to the initial model allow the importance of Asp122 for catalysis to be estimated.

Role of oxygen radicals in DNA damage and cancer incidence

The development of cancer in humans and animals is a multistep process. The complex series of cellular and molecular changes participating in cancer development are mediated by a diversity of endogenous and exogenous stimuli. One type of endogenous damage is that arising from intermediates of oxygen (dioxygen) reduction - oxygen-free radicals (OFR), which attacks not only the bases but also the deoxyribosyl backbone of DNA. Thanks to improvements in analytical techniques, a major achievement in the understanding of carcinogenesis in the past two decades has been the identification and quantification of various adducts of OFR with DNA. OFR are also known to attack other cellular components such as lipids, leaving behind reactive species that in turn can couple to DNA bases. Endogenous DNA lesions are genotoxic and induce mutations. The most extensively studied lesion is the formation of 8-OH-dG. This lesion is important because it is relatively easily formed and is mutagenic and therefore is a potential biomarker of carcinogenesis. Mutations that may arise from formation of 8-OH-dG involve GC --> TA transversions. In view of these findings, OFR are considered as an important class of carcinogens. The effect of OFR is balanced by the antioxidant action of non-enzymatic antioxidants as well as antioxidant enzymes. Non-enzymatic antioxidants involve vitamin C, vitamin E, carotenoids (CAR), selenium and others. However, under certain conditions, some antioxidants can also exhibit a pro-oxidant mechanism of action. For example, beta-carotene at high concentration and with increased partial pressure of dioxygen is known to behave as a pro-oxidant. Some concerns have also been raised over the potentially deleterious transition metal ion-mediated (iron, copper) pro-oxidant effect of vitamin C. Clinical studies mapping the effect of preventive antioxidants have shown surprisingly little or no effect on cancer incidence. The epidemiological trials together with in vitro experiments suggest that the optimal approach is to reduce endogenous and exogenous sources of oxidative stress, rather than increase intake of anti-oxidants. In this review, we highlight some major achievements in the study of DNA damage caused by OFR and the role in carcinogenesis played by oxidatively damaged DNA. The protective effect of antioxidants against free radicals is also discussed.

Augmented efficacy of tamoxifen in rat breast tumorigenesis when gavaged along with riboflavin, niacin, and CoQ10: Effects on lipid peroxidation and antioxidants in mitochondria

Reactive oxygen species (ROS) play a major role in causing mitochondrial changes linked to cancer and metastasis. Uptake of antioxidants by tissue to reduce the ROS production could be instrumental in controlling cancer. Tamoxifen (TAM), a nonsteroidal anti-estrogen drug most used in the chemotherapy and chemoprevention of breast cancer. Riboflavin, niacin and coenzyme Q10 (CoQ10) are proved to be potent antioxidants and protective agents against many diseases including cancer. The objective of this research is to determine the therapeutic efficacy of combinatorial therapy on mammary carcinoma bearing rats in terms of the mitochondrial lipid peroxidation and antioxidant status especially MnSOD. Female albino rats of Sprague-Dawley strain were selected for the investigation. Mammary carcinoma was induced with 7,12-dimethyl benz(a)anthracene (DMBA: 25 mg), and the treatment was started by the oral administration of TAM (10 mg/kg body weight/day) along with riboflavin (45 mg/kg body weight/day), niacin (100 mg/kg body weight/day) and CoQ10 (40 mg/kg body weight/day) for 28 days. The levels of lipid peroxides, activities of enzymic and non-enzymic antioxidants were measured in the mitochondria isolated from the mammary gland and liver of control and experimental rats. Rats treated with DMBA showed an increase in mitochondrial lipid peroxidation (mammary gland 52.3%; liver 25.1%) accompanied by high malondialdehyde levels along with lowered activities of mitochondrial enzymic antioxidants [superoxide dismutase (mammary gland 19.9%; liver 24.8%), catalase (mammary gland 50%; liver 19.7%), glutathione peroxidase (mammary gland 47.8%; liver 31.1%)] and non-enzymic antioxidants [reduced glutathione (mammary gland 14.3%; liver 13.3%), Vitamin C (mammary gland 6.49%; liver 21.4%) and E (mammary gland 20.3%; liver 22.2%)]. Administration of combinatorial therapy restored lipid peroxide level and the activities of enzymic and non-enzymic antioxidants to near normalcy. In addition, antitumour activity was also found to be enhanced which is evident from the increased expression of tumour suppressor gene MnSOD thereby preventing cancer cell proliferation. These results suggested that TAM treatment is the most effective during co-administration of riboflavin, niacin and CoQ10 in terms of mitochondrial antioxidant and antitumour activity.

Characterization of the peroxidase system at low H2O2 concentrations in isolated neonatal rat islets

B cell destruction during the onset of diabetes mellitus is associated with oxidative stress. In this work, we attempted to further trace the fate of H2O2 inside the pancreatic islets and determine whether it is mediated by enzymatic (peroxidase) activity or by chemical reaction with thiols from any protein chain. Our results suggest that the islet cells have a very similar peroxidase activity at the hydrophilic (cytoplasm) and hydrophobic compartments (organelles and nucleus), independent of the catalase content of the samples. This activity is composed of sacrificial thiols and by proteins with Fe3+/Mn3+ ions at non-heme catalytic sites. The capacity of the hydrophobic fraction to scavenge O2- was increased in the presence of high concentrations of NADP* and RS* and was highly dependent on RSH. On the contrary, the hydrophilic fraction exhibited a low RSH-dependent activity where the O2- scavenging is related to metal Cu2+/Fe3+/Mn3+ ions attached to the protein molecules.

Functional specialization of maize mitochondrial aldehyde dehydrogenases

The maize (Zea mays) rf2a and rf2b genes both encode homotetrameric aldehyde dehydrogenases (ALDHs). The RF2A protein was shown previously to accumulate in the mitochondria. In vitro import experiments and ALDH assays on mitochondrial extracts from rf2a mutant plants established that the RF2B protein also accumulates in the mitochondria. RNA gel-blot analyses and immunohistolocation experiments revealed that these two proteins have only partially redundant expression patterns in organs and cell types. For example, RF2A, but not RF2B, accumulates to high levels in the tapetal cells of anthers. Kinetic analyses established that RF2A and RF2B have quite different substrate specificities; although RF2A can oxidize a broad range of aldehydes, including aliphatic aldehydes and aromatic aldehydes, RF2B can oxidize only short-chain aliphatic aldehydes. These two enzymes also have different pH optima and responses to changes in substrate concentration. In addition, RF2A, but not RF2B or any other natural ALDHs, exhibits positive cooperativity. These functional specializations may explain why many species have two mitochondrial ALDHs. This study provides data that serve as a basis for identifying the physiological pathway by which the rf2a gene participates in normal anther development and the restoration of Texas cytoplasm-based male sterility. For example, the observations that Texas cytoplasm anthers do not accumulate elevated levels of reactive oxygen species or lipid peroxidation and the kinetic features of RF2A make it unlikely that rf2a restores fertility by preventing premature programmed cell death.

Determination of mitochondrial reactive oxygen species: methodological aspects

The generation of Reactive Oxygen Species (ROS) as by-products in mitochondria Electron Transport Chain (ETC) has long been admitted as the cost of aerobic energy metabolism with oxidative damages as consequence. The purpose of this methodological review is to present some of the most widespread methods of ROS generation and to underline the limitations as well as some problems, identified with some experiments as examples, in the interpretation of such results. There is now no doubt that besides their pejorative role, ROS are involved in a variety of cellular processes for the continuous adaptation of the cell to its environment. Because ROS metabolism is a complex area (low production, instability of species, efficient antioxidant defense system, several places of production...) bias, variances and limitations in ROS measurements must be recognized in order to avoid artefactual conclusions, and especially to improve our understanding of physiological and pathophysiological mechanisms of such phenomenon.