Extracellular redox state: refining the definition of oxidative stress in aging

Glutathione redox control of asthma: from molecular mechanisms to therapeutic opportunities

Asthma is a chronic inflammatory disorder of the airways associated with airway hyper-responsiveness and airflow limitation in response to specific triggers. Whereas inflammation is important for tissue regeneration and wound healing, the profound and sustained inflammatory response associated with asthma may result in airway remodeling that involves smooth muscle hypertrophy, epithelial goblet-cell hyperplasia, and permanent deposition of airway extracellular matrix proteins. Although the specific mechanisms responsible for asthma are still being unraveled, free radicals such as reactive oxygen species and reactive nitrogen species are important mediators of airway tissue damage that are increased in subjects with asthma. There is also a growing body of literature implicating disturbances in oxidation/reduction (redox) reactions and impaired antioxidant defenses as a risk factor for asthma development and asthma severity. Ultimately, these redox-related perturbations result in a vicious cycle of airway inflammation and injury that is not always amenable to current asthma therapy, particularly in cases of severe asthma. This review will discuss disruptions of redox signaling and control in asthma with a focus on the thiol, glutathione, and reduced (thiol) form (GSH). First, GSH synthesis, GSH distribution, and GSH function and homeostasis are discussed. We then review the literature related to GSH redox balance in health and asthma, with an emphasis on human studies. Finally, therapeutic opportunities to restore the GSH redox balance in subjects with asthma are discussed.

Evidence of oxidative damage and inflammation associated with low glutathione redox status in the autism brain

Despite increasing evidence of oxidative stress in the pathophysiology of autism, most studies have not evaluated biomarkers within specific brain regions, and the functional consequences of oxidative stress remain relatively understudied. We examined frozen samples from the cerebellum and temporal cortex (Brodmann area 22 (BA22)) from individuals with autism and unaffected controls (n=15 and n=12 per group, respectively). Biomarkers of oxidative stress, including reduced glutathione (GSH), oxidized glutathione (GSSG) and glutathione redox/antioxidant capacity (GSH/GSSG), were measured. Biomarkers of oxidative protein damage (3-nitrotyrosine; 3-NT) and oxidative DNA damage (8-oxo-deoxyguanosine; 8-oxo-dG) were also assessed. Functional indicators of oxidative stress included relative levels of 3-chlorotyrosine (3-CT), an established biomarker of a chronic inflammatory response, and aconitase activity, a biomarker of mitochondrial superoxide production. Consistent with previous studies on plasma and immune cells, GSH and GSH/GSSG were significantly decreased in both autism cerebellum (P<0.01) and BA22 (P<0.01). There was a significant increase in 3-NT in the autism cerebellum and BA22 (P<0.01). Similarly, 8-oxo-dG was significantly increased in autism cerebellum and BA22 (P<0.01 and P=0.01, respectively), and was inversely correlated with GSH/GSSG in the cerebellum (P<0.01). There was a significant increase in 3-CT levels in both brain regions (P<0.01), whereas aconitase activity was significantly decreased in autism cerebellum (P<0.01), and was negatively correlated with GSH/GSSG (P=0.01). Together, these results indicate that decreased GSH/GSSG redox/antioxidant capacity and increased oxidative stress in the autism brain may have functional consequence in terms of a chronic inflammatory response, increased mitochondrial superoxide production, and oxidative protein and DNA damage.

MicroRNA-23b downregulates peroxiredoxin III in human prostate cancer

To investigate the mechanism by which peroxiredoxin III (PRDX3) is altered in human prostate cancer (PCa), we used microRNA (miRNA) target prediction program and miRNA microarray to predict and identify miR-23b as a candidate miRNA that targets PRDX3. We showed that miR-23b suppresses PRDX3 protein expression in human DU145 cells under normal and hypoxic conditions. Additionally, the clinical significance of miR-23b and PRDX3 expression in PCa patients was also confirmed. In conclusion, our data suggest that the effects of PRDX3 in PCa progression may be caused by the regulation function of miR-23b, and consequently, miR-23b may be involved in the response of PCa cells to hypoxia stress.

Melatonin protects lung mitochondria from aging

We assessed whether melatonin administration would prevent the hyperoxidative status that occurs in lung mitochondria with age. Mitochondria from lungs of male and female senescent prone mice at 5 and 10 months of age were studied. Age-dependent mitochondrial oxidative stress was evaluated by measuring the levels of lipid peroxidation and nitrite, glutathione/glutathione disulfide ratio, and glutathione peroxidase and reductase activities. Mitochondrial respiratory chain and oxidative phosphorylation capability were also measured. Age induces a significant oxidative/nitrosative status in lung mitochondria, which exhibited a significantly reduced activity of the respiratory chain and ATP production. These manifestations of age were more pronounced in males than in females. After 9 months of melatonin administration in the drinking water, the hyperoxidative status and functional deficiency of aged lung mitochondria were totally counteracted, and had increased ATP production. The beneficial effects of melatonin were generally similar in both mice genders. Thus, melatonin administration, as a single therapy, maintained fully functioning lung mitochondria during aging, a finding with important consequences in the pathophysiology of lung aging. In view of these data melatonin, the production of which decreases with age, should be considered a preventive therapy against the hyperoxidative status of the aged lungs, and its use may lead to the avoidance of respiratory complications in the elderly.

Abnormal lung aging in chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis

Aging is a natural process characterized by progressive functional impairment and reduced capacity to respond appropriately to environmental stimuli and injury. The incidence of two common chronic respiratory diseases (chronic obstructive pulmonary disease [COPD] and idiopathic pulmonary fibrosis [IPF]) increases with advanced age. It is plausible, therefore, that abnormal regulation of the mechanisms of normal aging may contribute to the pathobiology of both COPD and IPF. This review discusses the available evidence supporting a number of aging mechanisms, including oxidative stress, telomere length regulation, cellular and immunosenescence, as well as changes in a number of antiaging molecules and the extracellular matrix, which are abnormal in COPD and/or IPF. A better understanding of these abnormalities may help in the design of novel and better therapeutic interventions for these patients.

Alzheimer's disease: redox dysregulation as a common denominator for diverse pathogenic mechanisms

Alzheimer's disease (AD) is the most common cause of dementia and a progressive neurodegeneration that appears to result from multiple pathogenic mechanisms (including protein misfolding/aggregation, involved in both amyloid β-dependent senile plaques and tau-dependent neurofibrillary tangles), metabolic and mitochondrial dysfunction, excitoxicity, calcium handling impairment, glial cell dysfunction, neuroinflammation, and oxidative stress. Oxidative stress, which could be secondary to several of the other pathophysiological mechanisms, appears to be a major determinant of the pathogenesis and progression of AD. The identification of oxidized proteins common for mild cognitive impairment and AD suggests that key oxidation pathways are triggered early and are involved in the initial progression of the neurodegenerative process. Abundant data support that oxidative stress, also considered as a main factor for aging, the major risk factor for AD, can be a common key element capable of articulating the divergent nature of the proposed pathogenic factors. Pathogenic mechanisms influence each other at different levels. Evidence suggests that it will be difficult to define a single-target therapy resulting in the arrest of progression or the improvement of AD deterioration. Since oxidative stress is present from early stages of disease, it appears as one of the main targets to be included in a clinical trial. Exploring the articulation of AD pathogenic mechanisms by oxidative stress will provide clues for better understanding the pathogenesis and progression of this dementing disorder and for the development of effective therapies to treat this disease.

Cancer surgery in the elderly

The proportions both of elderly patients in the world and of elderly patients with cancer are both increasing. In the evaluation of these patients, physiologic age, and not chronologic age, should be carefully considered in the decision-making process prior to both cancer screening and cancer treatment in an effort to avoid ageism. Many tools exist to help the practitioner determine the physiologic age of the patient, which allows for more appropriate and more individualized risk stratification, both in the pre- and postoperative periods as patients are evaluated for surgical treatments and monitored for surgical complications, respectively. During and after operations in the oncogeriatric populations, physiologic changes occuring that accompany aging include impaired stress response, increased senescence, and decreased immunity, all three of which impact the risk/benefit ratio associated with cancer surgery in the elderly.

Thiols stabilize cobblestone morphology of cultured mesothelial cells

Cellular thiols including GSH (glutathione) and L-Cys (L-cysteine) are essential for cell signalling, growth and differentiation. L-Cys is derived from the extracellular thiol pool and is the rate-limiting compound for intracellular GSH biosynthesis. The present study investigated the effect of thiol-supplemented medium on cell growth, phenotype and total GSH of cultured hPMCs (human peritoneal mesothelial cells). Cells were cultured in medium M199 supplemented with 2% serum, with 'plus' or without 'minus' L-Cys and compared with medium supplemented with either β-ME (β-mercaptoethanol) (0.25 mmol/l) or the receptor tyrosine kinase ligand EGF (epidermal growth factor, 100 ng/ml). β-ME produced a disproportionate increase in total GSH compared with L-Cys and other thiols tested [(procysteine (2-oxothiazolidine-4-carboxylic acid) or NAC (N-acetyl-L-cysteine)], while growth and morphology were identical. Cell behaviour of primary hPMCs is characterized by the transition of fibroblastoid to cobblestone morphology during early passage. L-Cys and β-ME promoted a rapid MET (mesenchymal-to-epithelial transition) within 3 days of culture, confirmed by the presence of cobblestone cells, intact organelles, abundant microvilli, primary cilia and cortical actin. In contrast, EGF produced a biphasic response consisting of delayed growth and retention of a fibroblastoid morphology. During a rapid log phase of growth, MET was accompanied by rapid catch-up growth. Thiols may stabilize the epithelial phenotype by engaging redox-sensitive receptors and transcription factors that modulate differentiation. These data may benefit researchers working on thiol-mediated cell differentiation and strategies to regenerate damage to serosal membranes.

Redox outside the box: linking extracellular redox remodeling with intracellular redox metabolism

Aerobic organisms generate reactive oxygen species as metabolic side products and must achieve a delicate balance between using them for signaling cellular functions and protecting against collateral damage. Small molecule (e.g. glutathione and cysteine)- and protein (e.g. thioredoxin)-based buffers regulate the ambient redox potentials in the various intracellular compartments, influence the status of redox-sensitive macromolecules, and protect against oxidative stress. Less well appreciated is the fact that the redox potential of the extracellular compartment is also carefully regulated and is dynamic. Changes in intracellular metabolism alter the redox poise in the extracellular compartment, and these are correlated with cellular processes such as proliferation, differentiation, and death. In this minireview, the mechanism of extracellular redox remodeling due to intracellular sulfur metabolism is discussed in the context of various cell-cell communication paradigms.

Intracellular and extracellular redox status and free radical generation in primary immune cells from children with autism

The modulation of the redox microenvironment is an important regulator of immune cell activation and proliferation. To investigate immune cell redox status in autism we quantified the intracellular glutathione redox couple (GSH/GSSG) in resting peripheral blood mononuclear cells (PBMCs), activated monocytes and CD4 T cells and the extracellular cysteine/cystine redox couple in the plasma from 43 children with autism and 41 age-matched control children. Resting PBMCs and activated monocytes from children with autism exhibited significantly higher oxidized glutathione (GSSG) and percent oxidized glutathione equivalents and decreased glutathione redox status (GSH/GSSG). In activated CD4 T cells from children with autism, the percent oxidized glutathione equivalents were similarly increased, and GSH and GSH/GSSG were decreased. In the plasma, both glutathione and cysteine redox ratios were decreased in autistic compared to control children. Consistent with decreased intracellular and extracellular redox status, generation of free radicals was significantly elevated in lymphocytes from the autistic children. These data indicate primary immune cells from autistic children have a more oxidized intracellular and extracellular microenvironment and a deficit in glutathione-mediated redox/antioxidant capacity compared to control children. These results suggest that the loss of glutathione redox homeostasis and chronic oxidative stress may contribute to immune dysregulation in autism.

Pathways to aging: the mitochondrion at the intersection of biological and psychosocial sciences

Compelling evidence suggests that both biological and psychosocial factors impact the process of aging. However, our understanding of the dynamic interplay among biological and psychosocial factors across the life course is still fragmentary. For example, it needs to be established how the interaction of individual factors (e.g., genetic and epigenetic endowment and personality), behavioral factors (e.g., physical activity, diet, and stress management), and psychosocial experiences (e.g., social support, well-being, socioeconomic status, and marriage) in perinatal, childhood, and adulthood influence health across the aging continuum. This paper aims to outline potential intersection points serving as an interface between biological and psychosocial factors, with an emphasis on the mitochondrion. Mitochondria are cellular organelles which play a critical role in cellular senescence. Both chronic exposure to psychosocial stress and genetic-based mitochondrial dysfunction have strikingly similar biological consequences; both predispose individuals to adverse age-related health disorders and early mortality. Exploring the interactive nature of the factors resulting in pathways to normal healthy aging, as well as those leading to morbidity and early mortality, will continue to enhance our ability to translate research into effective practices that can be implemented throughout the life course to optimise the aging process.

Absence of SOD1 leads to oxidative stress in peripheral nerve and causes a progressive distal motor axonopathy

Oxidative stress is commonly implicated in the pathogenesis of motor neuron disease. However, the cause and effect relationship between oxidative stress and motor neuron degeneration is poorly defined. We recently identified denervation at the neuromuscular junction in mice lacking the antioxidant enzyme, Cu,Zn-superoxide dismutase (SOD1) (Fischer et al., 2011). These mice show a phenotype of progressive muscle atrophy and weakness in the setting of chronic oxidative stress. Here, we investigated further the extent of motor neuron pathology in this model, and the relationship between motor pathology and oxidative stress. We report preferential denervation of fast-twitch muscles beginning between 1 and 4 months of age, with relative sparing of slow-twitch muscle. Motor axon terminals in affected muscles show widespread sprouting and formation of large axonal swellings. We confirmed, as was previously reported, that spinal motor neurons and motor and sensory nerve roots in these mice are preserved, even out to 18 months of age. We also found preservation of distal sensory fibers in the epidermis, illustrating the specificity of pathology in this model for distal motor axons. Using HPLC measurement of the glutathione redox potential, we quantified oxidative stress in peripheral nerve and muscle at the onset of denervation. SOD1 knockout tibial nerve, but not gastrocnemius muscle, showed significant oxidation of the glutathione pool, suggesting that axonal degeneration is a consequence of impaired redox homeostasis in peripheral nerve. We conclude that the SOD1 knockout mouse is a model of oxidative stress-mediated motor axonopathy. Pathology in this model primarily affects motor axon terminals at the neuromuscular junction, demonstrating the vulnerability of this synapse to oxidative injury.

The role of thioredoxin in the regulation of cellular processes by S-nitrosylation

BACKGROUND

S-nitrosylation (or S-nitrosation) by Nitric Oxide (NO), i.e., the covalent attachment of a NO group to a cysteine thiol and formation of S-nitrosothiols (R-S-N=O or RSNO), has emerged as an important feature of NO biology and pathobiology. Many NO-related biological functions have been directly associated with the S-nitrosothiols and a considerable number of S-nitrosylated proteins have been identified which can positively or negatively regulate various cellular processes including signaling and metabolic pathways.

SCOPE OF THE REVIEW

Taking account of the recent progress in the field of research, this review focuses on the regulation of cellular processes by S-nitrosylation and Trx-mediated cellular homeostasis of S-nitrosothiols.

MAJOR CONCLUSIONS

Thioredoxin (Trx) system in mammalian cells utilizes thiol and selenol groups to maintain a reducing intracellular environment to combat oxidative/nitrosative stress. Reduced glutathione (GSH) and Trx system perform the major role in denitrosylation of S-nitrosylated proteins. However, under certain conditions, oxidized form of mammalian Trx can be S-nitrosylated and then it can trans-S-nitrosylate target proteins, such as caspase 3.

GENERAL SIGNIFICANCE

Investigations on the role of thioredoxin system in relation to biologically relevant RSNOs, their functions, and the mechanisms of S-denitrosylation facilitate the development of drugs and therapies. This article is part of a Special Issue entitled Regulation of Cellular Processes.

S-allylmercapto-N-acetylcysteine up-regulates cellular glutathione and protects vascular endothelial cells from oxidative stress

Oxidative stress and/or low cellular glutathione (GSH) levels are associated with the development and progression of numerous pathological conditions. Cells possess various antioxidant protection mechanisms, including GSH and phase II detoxifying enzymes. N-acetylcysteine (NAC) supplies cells with cysteine to increase GSH level but its efficacy is relatively low because of its limited tissue penetration. Allicin (diallyl thiosulfinate), a reactive sulfaorganic compound, increases cellular GSH and phase II detoxifying enzymes in vascular endothelial cells (EC). A novel compound was designed: S-allylmercapto-N-acetylcysteine (ASSNAC), a conjugate of S-allyl mercaptan (a component of allicin) and NAC. Both ASSNAC and NAC increased cellular GSH of ECs, reaching a maximum of up to four- and threefold increase after exposure for 24 or 6 h at a concentration of 0.2 or 1 mM, respectively. ASSNAC induced nuclear translocation of the activated transcription factor Nrf2 and expression of phase II detoxifying enzymes. EC exposure to tBuOOH resulted in 75% cytotoxicity, and pretreatment of cultures with 0.2 mM ASSNAC or 2mM NAC reduced cytotoxicity to 20 and 42%, respectively. In conclusion, ASSNAC is superior to NAC in protecting cells from oxidative stress because of its ability to up-regulate both GSH and the expression of phase II detoxifying enzymes.

The redox state of human serum albumin in eye diseases with and without complications

PURPOSE

To investigate the redox state of human serum albumin concerning cysteine-34 as a possible systemic redox marker in patients with different eye diseases with and without complications and with consideration of possible effects of age.

METHODS

Cataract (CAT), glaucoma, age-related macular degeneration (AMD), diabetes mellitus (DM), diabetic retinopathy and hypertension were the pathologies investigated. Albumin redox state concerning cysteine-34 was measured by high-performance liquid chromatography with fluorescence detection. The separation gives three fractions: the fully reduced form containing a thiol group, the disulphide form and a higher oxidized form. Statistical analysis was done by Student's t-test, analysis of variance and stepwise regression analysis.

RESULTS

Albumin as a systemic marker for oxidative stress was shifted to a more oxidized state by DM. An even stronger shift to the oxidized form was observed in patients with proliferative diabetic retinopathy. Notably, these effects were independent from age. In contrast, CAT and AMD had no influence on serum albumin redox state.

CONCLUSION

Serum albumin is not shifted to more oxidized forms by localized oxidative stress, but it is in systemic diseases like DM.

Low molecular mass thiols, disulfides and protein mixed disulfides in rat tissues: influence of sample manipulation, oxidative stress and ageing

Most of the data in studies investigating the contribution of oxidative stress to some human diseases and to ageing derive from measurements carried out in blood, on the basis of the assumption that any alteration of the hematic thiol/disulfide balance should reflect a corresponding alteration in other less accessible tissues. But it is evident that the information that can be gleaned from a direct analysis in specific tissues is largely greater. Nevertheless, the accurate measurement of disulfides is frequently hampered by the artifactual oxidation occurring during sample manipulation as a consequence of the presence of heme-proteins. Therefore, the levels of disulfide forms of low molecular mass thiols in tissues are still poorly investigated, even if their measurements could represent a powerful index of the oxidative status. Here we have used an artifact-free procedure to measure low molecular mass thiols and their disulfides in different rat tissues. Our findings suggest that disulfides are a reliable biomarker of even slight oxidative damage. In tissues of aged rats we observed that either oxidative stress or glutathione depletion alone can occur in different tissues during ageing. Interestingly, among the investigated thiols, only homocysteine showed a tendency to increase in some organs with ageing.

Environmentally induced oxidative stress in aquatic animals

Reactive oxygen species (ROS) are an unenviable part of aerobic life. Their steady-state concentration is a balance between production and elimination providing certain steady-state ROS level. The dynamic equilibrium can be disturbed leading to enhanced ROS level and damage to cellular constituents which is called "oxidative stress". This review describes the general processes responsible for ROS generation in aquatic animals and critically analyses used markers for identification of oxidative stress. Changes in temperature, oxygen levels and salinity can cause the stress in natural and artificial conditions via induction of disbalance between ROS production and elimination. Human borne pollutants can also enhance ROS level in hydrobionts. The role of transition metal ions, such as copper, chromium, mercury and arsenic, and pesticides, namely insecticides, herbicides, and fungicides along with oil products in induction of oxidative stress is highlighted. Last years the research in biology of free radicals was refocused from only descriptive works to molecular mechanisms with particular interest to ones enhancing tolerance. The function of some transcription regulators (Keap1-Nrf2 and HIF-1α) in coordination of organisms' response to oxidative stress is discussed. The future directions in the field are related with more accurate description of oxidative stress, the identification of its general characteristics and mechanisms responsible for adaptation to the stress have been also discussed. The last part marks some perspectives in the study of oxidative stress in hydrobionts, which, in addition to classic use, became more and more popular to address general biological questions such as development, aging and pathologies.

Pyruvate-enriched cardioplegia suppresses cardiopulmonary bypass-induced myocardial inflammation

BACKGROUND

Cardiopulmonary bypass-induced oxidative stress initiates inflammation that can damage the myocardium. This study tested whether cardioplegia enriched with the intermediary metabolite and antioxidant pyruvate dampens postbypass myocardial inflammation.

METHODS

Pigs were maintained on cardiopulmonary bypass while their hearts were arrested for 60 minutes with 4:1 blood:crystalloid cardioplegia, in which the crystalloid contained 188 mM glucose ± 24 mM pyruvate. Pigs were weaned from bypass after 30 minutes of whole blood reperfusion and recovered for 4 hours. Glutathione (GSH) and glutathione disulfide (GSSG) were measured in coronary sinus plasma to indirectly monitor myocardial GSH redox state (GSH/GSSG). Left ventricular myocardium was sampled 4 hours after cardiopulmonary bypass for analyses of C-reactive protein, matrix metalloproteinases 2 and 9 and tissue inhibitor of metalloproteinase-2 (TIMP-2), and to assess neutrophil infiltration by histology and myeloperoxidase assay.

RESULTS

Coronary sinus GSH/GSSG fell 70% after cardiopulmonary bypass with control cardioplegia, but pyruvate cardioplegia produced a robust increase in coronary sinus GSH/GSSG that persisted for 4 hours after bypass. Myocardial C-reactive protein content increased 5.6-fold after control bypass, and neutrophil infiltration and myeloperoxidase activity also increased, but pyruvate-fortified cardioplegia prevented these inflammatory effects. Control cardioplegia lowered myocardial TIMP-2 content by 59% and increased matrix metalloproteinase-9 activity by 35% versus nonbypass sham values, but pyruvate cardioplegia increased TIMP-2 content ninefold versus control cardioplegia and prevented the increase in matrix metalloproteinase-9. Matrix metalloproteinase-2 was not affected by bypass ± pyruvate.

CONCLUSIONS

Pyruvate-enriched cardioplegia dampens cardiopulmonary bypass-induced myocardial inflammation. Increased GSH/GSSG and TIMP-2 may mediate pyruvate's effects.

Redox control systems in the nucleus: mechanisms and functions

Proteins with oxidizable thiols are essential to many functions of cell nuclei, including transcription, chromatin stability, nuclear protein import and export, and DNA replication and repair. Control of the nuclear thiol-disulfide redox states involves both the elimination of oxidants to prevent oxidation and the reduction of oxidized thiols to restore function. These processes depend on the common thiol reductants, glutathione (GSH) and thioredoxin-1 (Trx1). Recent evidence shows that these systems are controlled independent of the cytoplasmic counterparts. In addition, the GSH and Trx1 couples are not in redox equilibrium, indicating that these reductants have nonredundant functions in their support of proteins involved in transcriptional regulation, nuclear protein trafficking, and DNA repair. Specific isoforms of glutathione peroxidases, glutathione S-transferases, and peroxiredoxins are enriched in nuclei, further supporting the interpretation that functions of the thiol-dependent systems in nuclei are at least quantitatively distinct, and probably also qualitatively distinct, from similar processes in the cytoplasm. Elucidation of the distinct nuclear functions and regulation of the thiol redox pathways in nuclei can be expected to improve understanding of nuclear processes and also to provide the basis for novel approaches to treat aging and disease processes associated with oxidative stress in the nuclei.

A network perspective on metabolism and aging

Aging affects a myriad of genetic, biochemical, and metabolic processes, and efforts to understand the underlying molecular basis of aging are often thwarted by the complexity of the aging process. By taking a systems biology approach, network analysis is well-suited to study the decline in function with age. Network analysis has already been utilized in describing other complex processes such as development, evolution, and robustness. Networks of gene expression and protein-protein interaction have provided valuable insight into the loss of connectivity and network structure throughout lifespan. Here, we advocate the use of metabolic networks to expand the work from genomics and proteomics. As metabolism is the final fingerprint of functionality and has been implicated in multiple theories of aging, metabolomic methods combined with metabolite network analyses should pave the way to investigate how relationships of metabolites change with age and how these interactions affect phenotype and function of the aging individual. The metabolomic network approaches highlighted in this review are fundamental for an understanding of systematic declines and of failure to function with age.

Inhibitory effect of gallic acid and its esters on 2,2'-azobis(2-amidinopropane)hydrochloride (AAPH)-induced hemolysis and depletion of intracellular glutathione in erythrocytes

The protective effect of gallic acid and its esters, methyl, propyl, and lauryl gallate, against 2,2'-azobis(2-amidinopropane)hydrochloride (AAPH)-induced hemolysis and depletion of intracellular glutathione (GSH) in erythrocytes was studied. The inhibition of hemolysis was dose-dependent, and the esters were significantly more effective than gallic acid. Gallic acid and its esters were compared with regard to their reactivity to free radicals, using the DPPH and AAPH/pyranine free-cell assays, and no significant difference was obtained. Gallic acid and its esters not only failed to inhibit the depletion of intracellular GSH in erythrocytes induced by AAPH but exacerbated it. Similarly, the oxidation of GSH by AAPH or horseradish peroxidase/H(2)O(2) in cell-free systems was exacerbated by gallic acid or gallates. This property could be involved in the recent findings on pro-apoptotic and pro-oxidant activities of gallates in tumor cells. We provide evidence that lipophilicity and not only radical scavenger potency is an important factor regarding the efficiency of antihemolytic substances.

Effect of bone marrow-derived mesenchymal stem cells on endotoxin-induced oxidation of plasma cysteine and glutathione in mice

Bone marrow-derived mesenchymal stem cells (BMDMSC) are emerging as a therapeutic modality in various inflammatory disease states, including acute lung injury (ALI). A hallmark of inflammation, and a consistent observation in patients with ALI, is a perturbation in the systemic redox environment. However, little is known about the effects of BMDMSC on the systemic redox status. The objective of the present study was to determine whether exogenously infused BMDMSC protect against endotoxin-induced oxidation of plasma cysteine (Cys) and glutathione (GSH) redox states. To determine the effect on the redox state if BMDMSC, mice received endotoxin intraperitoneally (1 mg/kg), followed by intravenous infusion of either 5 × 10⁵ BMDMSC or an equal volume of saline solution. Control mice received intraperitoneal endotoxin followed by 5 × 10⁵ lung fibroblasts given intravenously. Cys, cystine (CySS), GSH, and glutathione disulfide (GSSG) concentrations were determined by HPLC. Results showed sequential preservation of plasma Cys and GSH levels in response to BMDMSC infusion. The data show that BMDMSC infusion leads to a more reducing Cys and GSH redox state. The findings are the first to demonstrate that BMDMSC have antioxidant effects in vivo, and add to our understanding of the systemic effects of BMDMSC in lung injury.

Markers of oxidative stress in erythrocytes and plasma during aging in humans

Aging is an inevitable universal biological process, which can be characterized by a general decline in physiological function with the accumulation of diverse adverse changes and increased probability of death. Among several theories, oxidative stress/free radical theory offers the best mechanistic elucidation of the aging process and other age -related phenomenon. In the present paper , we discuss the aging process and have focused on the importance of some reliable markers of oxidative stress which may be used as biomarkers of the aging process.

Extracellular redox status regulates Nrf2 activation through mitochondrial reactive oxygen species

The redox status of the extracellular compartment has only just been elucidated as a mechanism controlling intracellular signal transduction and correlates with aging, diabetes, heart disease and lung fibrosis. In the present paper, we describe a mechanism by which oxidizing extracellular environments, as maintained by the cysteine/cystine (Cys/CySS) redox couple, induce mitochondria-derived ROS (reactive oxygen species) generation and cause the activation of Nrf2 (nuclear factor-erythroid 2-related factor 2), inducing an antioxidant response. NIH 3T3 cells were cultured in medium with extracellular Cys/CySS redox potentials (Eh), ranging from 0 to -150 mV. Cellular and mitochondrial ROS production significantly increased in cells incubated under more oxidizing extracellular conditions (0 and -46 mV). Trx2 (thioredoxin-2) is a mitochondrial-specific oxidoreductase and antioxidant and became oxidized in cells incubated at 0 or -46 mV. MEFs (mouse embryonic fibroblasts) from Trx2-overexpressing transgenic (Trx2 Tg) mice produced less intracellular ROS compared with WT (wild-type) MEFs at the more oxidizing extracellular conditions. Nrf2 activity was increased in WT MEFs at the 0 or -46 mV conditions, but was inhibited in Trx2 Tg MEFs under the same conditions. Furthermore, Nrf2-regulated gene expression was significantly increased in the WT MEFs, but not in the Trx2 Tg MEFs. These results show that the Cys/CySS redox status in the extracellular compartment regulates intracellular ROS generated primarily in the mitochondria, which play an important role in the activation of Nrf2 and up-regulation of antioxidant and detoxification systems.

Correlations between gene expression and mercury levels in blood of boys with and without autism

Gene expression in blood was correlated with mercury levels in blood of 2- to 5-year-old boys with autism (AU) compared to age-matched typically developing (TD) control boys. This was done to address the possibility that the two groups might metabolize toxicants, such as mercury, differently. RNA was isolated from blood and gene expression assessed on whole genome Affymetrix Human U133 expression microarrays. Mercury levels were measured using an inductively coupled plasma mass spectrometer. Analysis of covariance (ANCOVA) was performed and partial correlations between gene expression and mercury levels were calculated, after correcting for age and batch effects. To reduce false positives, only genes shared by the ANCOVA models were analyzed. Of the 26 genes that correlated with mercury levels in both AU and TD boys, 11 were significantly different between the groups (P(Diagnosis*Mercury) ≤ 0.05). The expression of a large number of genes (n = 316) correlated with mercury levels in TD but not in AU boys (P ≤ 0.05), the most represented biological functions being cell death and cell morphology. Expression of 189 genes correlated with mercury levels in AU but not in TD boys (P ≤ 0.05), the most represented biological functions being cell morphology, amino acid metabolism, and antigen presentation. These data and those in our companion study on correlation of gene expression and lead levels show that AU and TD children display different correlations between transcript levels and low levels of mercury and lead. These findings might suggest different genetic transcriptional programs associated with mercury in AU compared to TD children.

Age-related deficiencies in complex I endogenous substrate availability and reserve capacity of complex IV in cortical neuron electron transport

Respiratory enzyme complex dysfunction is mechanistically involved in mitochondrial failure leading to neurodegenerative disease, but the pathway is unclear. Here, age-related differences in mitochondrial respiration were measured in both whole and permeabilized neurons from 9-month and 24-month adult rat cortex cultured in common conditions. After permeabilization, respiration increased in both ages of neurons with excess substrates. To dissect specific deficiencies in the respiratory chain, inhibitors for each respiratory chain complex were used to isolate their contributions. Relative to neurons from 9-month rats, in neurons isolated from 24-month rats, complexes I, III, and IV were more sensitive to selective inhibition. Flux control point analysis identified complex I in neurons isolated from 24-month rats as the most sensitive to endogenous substrate availability. The greatest age-related deficit in flux capacity occurred at complex IV with a 29% decrease in neurons isolated from 24-month rats relative to those from 9-month rats. The deficits in complexes I and III may contribute to a redox shift in the quinone pool within the electron transport chain, further extending these age-related deficits. Together these changes could lead to an age-related catastrophic decline in energy production and neuronal death.

Rejuvenation in distinct cell populations - What does it mean?

Rejuvenation represents a well organized and tightly regulated cellular process in vitro and in vivo, whereby senescent and/or certain differentiated cells revert specific properties acquired during previous steps of maturation to restore again a younger phenotype. Effects of the microenvironment and cellular mechanisms including asymmetric mitosis or retrodifferentiation can contribute to rejuvenation during a dynamic cellular development in contrast to terminally differentiated cells like unicellular organisms, which appear unable to retrodifferentiate and to rejuvenate. The process of rejuvenation is observed in distinct cell populations and includes a coordinated multistep network of transduction cascades with extracellular signaling and cell-to-cell communication to relay intracellular pathways. This provides a certain tissue homeostasis by a regenerative potential and renewal upon tissue-specific repair requirements in addition to residual stem cells, which can vary among different organs and species to extend their life span. However, dysfunctions within a rejuvenation program may also include the risk of neoplastic growth during such a retrograde development. In contrast to rejuvenation in certain cell types, a life span extension - also termed longevity - does not represent a retrograde development but an overall prolonged function of tissues, organs and/or whole organisms. Thus, rejuvenation of a distinct cell population could contribute to longevity of the corresponding organism but may not necessarily be required since longevity could also be achieved mechanistically by inhibition of the mTOR-mediated signaling pathway or by sufficient supply of anti-oxidative defence compounds, physiologically by nutrient restrictions, genetically by the induction of longevity genes or environmentally by the inhibition of aging.

Antioxidant activity of sulfur and selenium: a review of reactive oxygen species scavenging, glutathione peroxidase, and metal-binding antioxidant mechanisms

It is well known that oxidation caused by reactive oxygen species (ROS) is a major cause of cellular damage and death and has been implicated in cancer, neurodegenerative, and cardiovascular diseases. Small-molecule antioxidants containing sulfur and selenium can ameliorate oxidative damage, and cells employ multiple antioxidant mechanisms to prevent this cellular damage. However, current research has focused mainly on clinical, epidemiological, and in vivo studies with little emphasis on the antioxidant mechanisms responsible for observed sulfur and selenium antioxidant activities. In addition, the antioxidant properties of sulfur compounds are commonly compared to selenium antioxidant properties; however, sulfur and selenium antioxidant activities can be quite distinct, with each utilizing different antioxidant mechanisms to prevent oxidative cellular damage. In the present review, we discuss the antioxidant activities of sulfur and selenium compounds, focusing on several antioxidant mechanisms, including ROS scavenging, glutathione peroxidase, and metal-binding antioxidant mechanisms. Findings of several recent clinical, epidemiological, and in vivo studies highlight the need for future studies that specifically focus on the chemical mechanisms of sulfur and selenium antioxidant behavior.

Sulfur amino acid deficiency upregulates intestinal methionine cycle activity and suppresses epithelial growth in neonatal pigs

We recently showed that the developing gut is a significant site of methionine transmethylation to homocysteine and transsulfuration to cysteine. We hypothesized that sulfur amino acid (SAA) deficiency would preferentially reduce mucosal growth and antioxidant function in neonatal pigs. Neonatal pigs were enterally fed a control or an SAA-free diet for 7 days, and then whole body methionine and cysteine kinetics were measured using an intravenous infusion of [1-(13)C;methyl-(2)H(3)]methionine and [(15)N]cysteine. Body weight gain and plasma methionine, cysteine, homocysteine, and taurine and total erythrocyte glutathione concentrations were markedly decreased (-46% to -85%) in SAA-free compared with control pigs. Whole body methionine and cysteine fluxes were reduced, yet methionine utilization for protein synthesis and methionine remethylation were relatively preserved at the expense of methionine transsulfuration, in response to SAA deficiency. Intestinal tissue concentrations of methionine and cysteine were markedly reduced and hepatic levels were maintained in SAA-free compared with control pigs. SAA deficiency increased the activity of methionine metabolic enzymes, i.e., methionine adenosyltransferase, methionine synthase, and cystathionine beta-synthase, and S-adenosylmethionine concentration in the jejunum, whereas methionine synthase activity increased and S-adenosylmethionine level decreased in the liver. Small intestine weight and protein and DNA mass were lower, whereas liver weight and DNA mass were unchanged, in SAA-free compared with control pigs. Dietary SAA deficiency induced small intestinal villus atrophy, lower goblet cell numbers, and Ki-67-positive proliferative crypt cells in association with lower tissue glutathione, especially in the jejunum. We conclude that SAA deficiency upregulates intestinal methionine cycle activity and suppresses epithelial growth in neonatal pigs.

Redox control of platelet function

There has recently been a dramatic expansion in research in the area of redox biology with systems that utilize thiols to perform redox chemistry being central to redox control. Thiol-based reactions occur in proteins involved in platelet function, including extracellular platelet proteins. The alphaIIbbeta3 fibrinogen receptor contains free thiols that are required for the activation of this receptor to a fibrinogen-binding conformation. This process is under enzymatic control, with protein disulfide isomerase playing a central role in the activation of alphaIIbbeta3. Other integrins, such as the alpha2beta1 collagen receptor on platelets, are also regulated by protein disulfide isomerase and thiol metabolism. Low molecular weight thiols that are found in blood regulate these processes by converting redox sensitive disulfide bonds to thiols and by providing the appropriate redox potential for these reactions. Additional mechanisms of redox control of platelets involve nitric oxide that inhibits platelet responses, and reactive oxygen species that potentiate platelet thrombus formation. Specific nitrosative or oxidative modifications of thiol groups in platelets may modulate platelet function. Since many biologic processes are regulated by redox reactions that involve surface thiols, the extracellular redox state can have an important influence on health and disease status and may be a target for therapeutic intervention.

Catalytic mechanisms and specificities of glutathione peroxidases: variations of a basic scheme

Kinetics and molecular mechanisms of GPx-type enzymes are reviewed with emphasis on structural features relevant to efficiency and specificity. In Sec-GPxs the reaction takes place at a single redox centre with selenocysteine as redox-active residue (peroxidatic Sec, U(P)). In contrast, most of the non-vertebrate GPx have the U(P) replaced by a cysteine (peroxidatic Cys, C(P)) and work with a second redox centre that contains a resolving cysteine (C(R)). While the former type of enzymes is more or less specific for GSH, the latter are reduced by "redoxins". The common denominator of the GPx family is the first redox centre comprising the (seleno)cysteine, tryptophan, asparagine and glutamine. In this architectural context the rate of hydroperoxide reduction by U(P) or C(P), respectively, is enhanced by several orders of magnitude compared to that of free selenolate or thiolate. Mammalian GPx-1 dominates H(2)O(2) metabolism, whereas the domain of GPx-4 is the reduction of lipid hydroperoxides with important consequences such as counteracting 12/15-lipoxygenase-induced apoptosis and regulation of inflammatory responses. Beyond, the degenerate GSH specificity of GPx-4 allows selenylation and oxidation to disulfides of protein thiols. Heterodimer formation of yeast GPx with a transcription factor is discussed as paradigm of a redox sensing that might also be valid in vertebrates.

Cellular and mitochondrial glutathione redox imbalance in lymphoblastoid cells derived from children with autism

Research into the metabolic phenotype of autism has been relatively unexplored despite the fact that metabolic abnormalities have been implicated in the pathophysiology of several other neurobehavioral disorders. Plasma biomarkers of oxidative stress have been reported in autistic children; however, intracellular redox status has not yet been evaluated. Lymphoblastoid cells (LCLs) derived from autistic children and unaffected controls were used to assess relative concentrations of reduced glutathione (GSH) and oxidized disulfide glutathione (GSSG) in cell extracts and isolated mitochondria as a measure of intracellular redox capacity. The results indicated that the GSH/GSSG redox ratio was decreased and percentage oxidized glutathione increased in both cytosol and mitochondria in the autism LCLs. Exposure to oxidative stress via the sulfhydryl reagent thimerosal resulted in a greater decrease in the GSH/GSSG ratio and increase in free radical generation in autism compared to control cells. Acute exposure to physiological levels of nitric oxide decreased mitochondrial membrane potential to a greater extent in the autism LCLs, although GSH/GSSG and ATP concentrations were similarly decreased in both cell lines. These results suggest that the autism LCLs exhibit a reduced glutathione reserve capacity in both cytosol and mitochondria that may compromise antioxidant defense and detoxification capacity under prooxidant conditions.

The thioredoxin-like protein rod-derived cone viability factor (RdCVFL) interacts with TAU and inhibits its phosphorylation in the retina

Rod-derived cone viability factor (RdCVF) is produced by the Nxnl1 gene that codes for a second polypeptide, RdCVFL, by alternative splicing. Although the role of RdCVF in promoting cone survival has been described, the implication of RdCVFL, a putative thioredoxin enzyme, in the protection of photoreceptors is presently unknown. Using a proteomics approach we identified 90 proteins interacting with RdCVFL including the microtubule-binding protein TAU. We demonstrate that the level of phosphorylation of TAU is increased in the retina of the Nxnl1(-/-) mice as it is hyperphosphorylated in the brain of patients suffering from Alzheimer disease, presumably in some cases through oxidative stress. Using a cell-based assay, we show that RdCVFL inhibits TAU phosphorylation. In vitro, RdCVFL protects TAU from oxidative damage. Photooxidative stress is implicated in retinal degeneration, particularly in retinitis pigmentosa, where it is considered to be a contributor to secondary cone death. The functional interaction between RdCVFL and TAU described here is the first characterization of the RdCVFL signaling pathway involved in neuronal cell death mediated by oxidative stress.

Activation of c-Jun-N-terminal kinase and decline of mitochondrial pyruvate dehydrogenase activity during brain aging

Mitochondrial dysfunction is often associated with aging and neurodegeneration. c-Jun-N-terminal kinase (JNK) phosphorylation and its translocation to mitochondria increased as a function of age in rat brain. This was associated with a decrease of pyruvate dehydrogenase (PDH) activity upon phosphorylation of the E(1alpha) subunit of PDH. Phosphorylation of PDH is likely mediated by PDH kinase, the protein levels and activity of which increased with age. ATP levels were diminished, whereas lactic acid levels increased, thus indicating a shift toward anaerobic glycolysis. The energy transduction deficit due to impairment of PDH activity during aging may be associated with JNK signaling.

Aging and lung injury repair: a role for bone marrow derived mesenchymal stem cells

The incidence of lung fibrosis increases with age. Aging is associated with modifications in the intracellular and extracellular environment including alteration of the extracellular matrix, imbalance of the redox state, accumulation of senescent cells and potential alteration of the recruitment of bone marrow mesenchymal stem cells. The combination of these senescence-related alterations in the lung and in bone marrow progenitor cells might be responsible of the higher susceptibility to lung fibrosis in elderly individuals. The understanding of these age related changes must be considered in the rationale for the development of therapeutic interventions to control lung injury and fibrosis.

Association between adherence to the Mediterranean diet and oxidative stress

BACKGROUND

The cardioprotective property of the Mediterranean diet has been attributed to its antioxidant capacity, but direct investigation of this mechanism has been limited.

OBJECTIVE

We examined the association between the Mediterranean diet and an established plasma marker of oxidative stress, the ratio of reduced to oxidized glutathione (GSH/GSSG), in a well-controlled study of twins.

DESIGN

We administered the Willett food-frequency questionnaire to 138 monozygotic and dizygotic twin pairs and to 21 unpaired twins and derived a score measuring adherence to the Mediterranean diet. Fasting plasma GSH and GSSG concentrations were measured to calculate the GSH/GSSG ratio. The higher the ratio, the lower the oxidative stress. Mixed-effect regression analysis was used to partition the association into between- and within-twin pair differences. When within-pair effects are examined, twins are matched for sociodemographic and familial factors.

RESULTS

A one-unit increment in the diet score was associated with a 7% higher GSH/GSSG ratio (P = 0.03) after adjustment for energy intake, other nutritional factors, cardiovascular disease risk factors, and medication use. The association persisted within twin pairs: a one-unit within-pair absolute difference in the diet score was associated with a 10% (95% CI: 2.7, 18.0) higher GSH/GSSG ratio in the twin with the higher score than in the co-twin with the lower score (P = 0.007). Results were similar in monozygotic and dizygotic twin pairs.

CONCLUSIONS

The association between the Mediterranean diet and plasma oxidative stress is robust and is not confounded by genetic or shared environmental factors. Decreased oxidative stress is a plausible mechanism linking the Mediterranean diet to reduced cardiovascular disease risk.

Oxidation of extracellular cysteine/cystine redox state in bleomycin-induced lung fibrosis

Several lines of evidence indicate that depletion of glutathione (GSH), a critical thiol antioxidant, is associated with the pathogenesis of idiopathic pulmonary fibrosis (IPF). However, GSH synthesis depends on the amino acid cysteine (Cys), and relatively little is known about the regulation of Cys in fibrosis. Cys and its disulfide, cystine (CySS), constitute the most abundant low-molecular weight thiol/disulfide redox couple in the plasma, and the Cys/CySS redox state (E(h) Cys/CySS) is oxidized in association with age and smoking, known risk factors for IPF. Furthermore, oxidized E(h) Cys/CySS in the culture media of lung fibroblasts stimulates proliferation and expression of transitional matrix components. The present study was undertaken to determine whether bleomycin-induced lung fibrosis is associated with a decrease in Cys and/or an oxidation of the Cys/CySS redox state and to determine whether these changes were associated with changes in E(h) GSH/glutathione disulfide (GSSG). We observed distinct effects on plasma GSH and Cys redox systems during the progression of bleomycin-induced lung injury. Plasma E(h) GSH/GSSG was selectively oxidized during the proinflammatory phase, whereas oxidation of E(h) Cys/CySS occurred at the fibrotic phase. In the epithelial lining fluid, oxidation of E(h) Cys/CySS was due to decreased food intake. Thus the data show that decreased precursor availability and enhanced oxidation of Cys each contribute to the oxidation of extracellular Cys/CySS redox state in bleomycin-induced lung fibrosis.

Excess dietary L-cysteine causes lethal metabolic acidosis in chicks

A 72-h time-course study was conducted to elucidate the physiological mechanism underlying cysteine (Cys) toxicity in chicks beginning at 8-d posthatch. Biochemical markers quantified in plasma and liver samples collected from chicks receiving 30 g/kg excess dietary Cys were compared with baseline measurements from chicks receiving an unsupplemented corn-soybean meal diet over a 72-h feeding period. Concomitant with chick mortality were indices of acute metabolic acidosis, including a rapid increase (P < 0.001) in anion gap that resulted from a reduction (P < 0.001) in plasma HCO(3)(-) of approximately 40% and a 2.8-fold increase (P < 0.001) in plasma sulfate in chicks receiving excess Cys. Additionally, provision of 30 g/kg excess Cys resulted in a 1.5-fold increase (P < 0.05) in hepatic oxidized glutathione compared with the 0-h control time-point. Excess dietary Cys did not affect plasma free Met, but plasma free Cys increased (P < 0.05) from 89 to 107 mumol/L at 12 h and remained elevated through 36 h. Strikingly, ingestion of 30 g/kg excess Cys caused more than a doubling (P < 0.001) of plasma free cystine, the oxidized form of Cys, beginning 12 h after initiating the study, and it remained elevated throughout the 72-h feeding period. Taken together, these data suggest that ingestion of 30 g/kg excess l-Cys causes both acute metabolic acidosis and oxidative stress in young chicks when fed a nutritionally adequate, corn-soybean meal diet.

Prospective type 1 and type 2 disulfides of Keap1 protein

Experiments were carried out to detect cysteine residues on human Keap1 protein that may be sensors of oxidative stress that gives rise to changes in the GSH/GSSG redox couple. Human Keap1 protein, at a final concentration of 6 microM, was incubated for two hours in aqueous buffer containing 0.010 M GSH, pH 8, in an argon atmosphere. Subsequently, excess iodoacetamide and trypsin were added to generate a peptide map effected by LCMS analysis. Peptides containing all 27 carboxamidomethylated cysteines were identified. Replacement of GSH by 0.010 M GSSG yielded a map in which 13 of the original carboxamidomethylated peptides were unperturbed, while other caboxamidomethylated cysteine-containing peptides were undetected, and a number of new cysteine-containing peptide peaks were observed. By mass analysis, and in some cases, by isolation, reduction, carboxamidomethylation, and reanalysis, these were identified as S-glutathionylated (Type 1) or Cys-Cys (Type 2) disulfides. Such peptides derived from the N-terminal, dimerization, central linker, Kelch repeat and C-terminal domains of Keap1. Experiments were carried out in which Keap1 was incubated similarly but in the presence of various GSH/GSSG ratios between 100 and 1 ([GSH + GSSG] = 0.010 M), with subsequent caraboxamidomethylation and trypsinolysis to determine differences in sensitivities of the different cysteines to the type 1 and type 2 modifications. Cysteines most sensitive to S-glutathionylation include Cys77, Cys297, Cys319, Cys368, and Cys434, while cysteine disulfides most readily formed are Cys23-Cys38 and Cys257-Cys297. The most reducing conditions at which these modifications are at GSH/GSSG = 10, which computes to an oxidation potential of E h = -268.5 mV, a physiologically relevant value. Under somewhat more oxidizing, but still physiologically relevant, conditions, GSH/GSSG = 1 ( E h = -231.1 mV), a Cys319-Cys319 disulfide is detected far from the dimerization domain of the Keap1 homodimer. The potential impact on protein structure of the glutathionylation of Cys434 and Cys368, the two modified residues in the Kelch repeat domain, was analyzed by docking and energy minimizations of glutathione residues attached to the Kelch repeat domain, whose coordinates are known. The energy minimizations indicated marked alterations in structure with a substantial constriction of Neh2 binding domain of the Keap1 Kelch repeat domain. This alteration appears to be enforced by an extended hydrogen-bonding network between residues on the glutathione moiety attached to Cys434 and amino acid side chains that have been shown to be essential for repression of Nrf2 by Keap1. The modifications of Keap1 detected in the present study are discussed in the context of previous work of others who have examined the sensitivity of cysteines on Keap1 to electrophile assault.

Oxidative damage to extracellular matrix and its role in human pathologies

The extracellular compartments of most biological tissues are significantly less well protected against oxidative damage than intracellular sites and there is considerable evidence for such compartments being subject to a greater oxidative stress and an altered redox balance. However, with some notable exceptions (e.g., plasma and lung lining fluid) oxidative damage within these compartments has been relatively neglected and is poorly understood. In particular information on the nature and consequences of damage to extracellular matrix is lacking despite the growing realization that changes in matrix structure can play a key role in the regulation of cellular adhesion, proliferation, migration, and cell signaling. Furthermore, the extracellular matrix is widely recognized as being a key site of cytokine and growth factor binding, and modification of matrix structure might be expected to alter such behavior. In this paper we review the potential sources of oxidative matrix damage, the changes that occur in matrix structure, and how this may affect cellular behavior. The role of such damage in the development and progression of inflammatory diseases is discussed.

Cellular responses to reactive oxygen species-induced DNA damage and aging

Oxidative stress in cells and tissues can occur during pathophysiological developments, e.g., during inflammatory and allergic diseases or during ischemic or toxic and hyperglycemic conditions via the generation of reactive oxygen species (ROS). Moreover, ROS can be generated by radiation (UV, X-rays) and pharmacologically, e.g., by anthracyclins as chemotherapeutic compounds for treatment of a variety of tumors to induce 'stress or aberrant signaling-inducing senescence' (STASIS). Although STASIS is distinguished from intracellular replicative senescence, a variety of cellular mechanisms appear similar in both aging pathways. It is generally accepted that oxidative stress and ROS eventually cause DNA damage, whereby insufficient cellular repair mechanisms may contribute to premature aging and apoptosis. Conversely, ROS-induced imbalances of the signaling pathways for metabolic protein turnover may also result in opposite effects to recruit malfunctioning aberrant proteins and compounds that trigger tumorigenic processes. Consequently, DNA damage plays a role in the development of carcinogenesis, but is also associated with an aging process in cells and organisms.

The rate of cellular hydrogen peroxide removal shows dependency on GSH: mathematical insight into in vivo H2O2 and GPx concentrations

Although its concentration is generally not known, glutathione peroxidase-1 (GPx-1) is a key enzyme in the removal of hydrogen peroxide (H₂O₂) in biological systems. Extrapolating from kinetic results obtained in vitro using dilute, homogenous buffered solutions, it is generally accepted that the rate of elimination of H₂O₂in vivo by GPx is independent of glutathione concentration (GSH). To examine this doctrine, a mathematical analysis of a kinetic model for the removal of H₂O₂ by GPx was undertaken to determine how the reaction species (H₂O₂, GSH, and GPx-1) influence the rate of removal of H₂O₂. Using both the traditional kinetic rate law approximation (classical model) and the generalized kinetic expression, the results show that the rate of removal of H₂O₂ increases with initial GPx_r, as expected, but is a function of both GPx_r and GSH when the initial GPx_r is less than H₂O₂. This simulation is supported by the biological observations of Li et al.. Using genetically altered human glioma cells in in vitro cell culture and in an in vivo tumour model, they inferred that the rate of removal of H₂O₂ was a direct function of GPx activity × GSH (effective GPx activity). The predicted cellular average GPx_r and H₂O₂ for their study are approximately GPx_r ≤ 1 μm and H₂O₂ ≈ 5 μm based on available rate constants and an estimation of GSH. It was also found that results from the accepted kinetic rate law approximation significantly deviated from those obtained from the more generalized model in many cases that may be of physiological importance.

A cystine-cysteine shuttle mediated by xCT facilitates cellular responses toS-nitrosoalbumin

We have shown previously that extracellular cysteine is necessary for cellular responses to S-nitrosoalbumin. In this study we have investigated mechanisms involved in accumulation of extracellular cysteine outside vascular smooth muscle cells and characterized the role of cystine-cysteine release in transfer of nitric oxide (NO)-bioactivity. Incubation of cells with cystine led to cystine uptake, reduction, and cysteine release. The process was inhibitable by extracellular glutamate, suggesting a role for system xc−amino acid transporters. Smooth muscle cells express this transporter constitutively and induction of the light chain component (xCT) by either diethyl maleate or 3-morpholino-sydnonimine (SIN-1) led to glutamate-inhibitable cystine uptake and an increased rate of cysteine release from cells. Likewise, overexpression of xCT in smooth muscle cells or endothelial cells led to glutamate-inhibitable cysteine release. The resulting extracellular cysteine was found to be required for transfer of NO from extracellular S-nitrosothiols into cells via system L transporters leading to formation of cellular S-nitrosothiols. Cysteine release coupled to cystine uptake was also found to be required for cellular responses to S-nitrosoalbumin and facilitated S-nitrosoalbumin-mediated inhibition of epidermal growth factor signaling. These data show that xCT expression can constitute a cystine-cysteine shuttle whereby cystine uptake drives cysteine release. Furthermore, we show that extracellular cysteine provided by this shuttle mechanism is necessary for transfer of NO equivalents and cellular responses to S-nitrosoablumin.

Aberrant insulin receptor signaling and amino acid homeostasis as a major cause of oxidative stress in aging

The mechanisms leading to the increase in free radical-derived oxidative stress in "normal aging" remains obscure. Here we present our perspective on studies from different fields that reveal a previously unnoticed vicious cycle of oxidative stress. The plasma cysteine concentrations during starvation in the night and early morning hours (the postabsorptive state) decreases with age. This decrease is associated with a decrease in tissue concentrations of the cysteine derivative and quantitatively important antioxidant glutathione. The decrease in cysteine reflects changes in the autophagic protein catabolism that normally ensures free amino acid homeostasis during starvation. Autophagy is negatively regulated by the insulin receptor signaling cascade that is enhanced by oxidative stress in the absence of insulin. This synopsis of seemingly unrelated processes reveals a novel mechanism of progressive oxidative stress in which decreasing antioxidant concentrations and increasing basal (postabsorptive) insulin receptor signaling activity compromise not only the autophagic protein catabolism but also the activity of FOXO transcription factors (i.e., two functions that were found to have an impact on lifespan in several animal models of aging). In addition, the aging-related decrease in glutathione levels is likely to facilitate certain "secondary" disease-related mechanisms of oxidative stress. Studies on cysteine supplementation show therapeutic promise.

Mutation in G6PD gene leads to loss of cellular control of protein glutathionylation: mechanism and implication

More than 400 million people are susceptible to oxidative stress due to glucose-6-phosphate dehydrogenase (G6PD) deficiency. Protein glutathionylation is believed to be responsible for loss of protein function and/or cellular signaling during oxidative stress. To elucidate the implications of G6PD deficiency specifically in cellular control of protein glutathionylation, we used hydroxyethyldisulfide (HEDS), an oxidant which undergoes disulfide exchange with existing thiols. G6PD deficient (E89) cells treated with HEDS showed a significant increase in protein glutathionylation compared to wild-type (K1) cells. In order to determine whether increase in global protein glutathionylation by HEDS leads to loss of function of an important protein, we compared the effect of HEDS on global protein glutathionylation with that of Ku protein function, a multifunctional DNA repair protein, using a novel ELISA. E89 cells treated with HEDS showed a significant loss of Ku protein binding to DNA. Cellular protein thiol and GSH, whose disulfide is involved in protein glutathionylation, were decreased by HEDS in E89 cells with no significant effect in K1 cells. E89 cells showed lower detoxification of HEDS, that is, conversion of disulfide HEDS to free sulfhydryl mercaptoethanol (ME), compared to K1 cells. K1 cells maintained their NADH level in the presence of HEDS but that of E89 cells decreased by tenfold following a similar exposure. NADPH, a cofactor required to maintain reduced form of the thiols, was decreased more in E89 than K1 cells. The specific role of G6PD in the control of such global protein glutathionylation and Ku function was further demonstrated by reintroducing the G6PD gene into E89 (A1A) cells, which showed a normal phenotype.