Altered mitochondrial function, iron metabolism and glutathione levels in Parkinson's disease

Transcriptome-based biomarker prediction for Parkinson's disease using genome-scale metabolic modeling

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world. Identification of PD biomarkers is crucial for early diagnosis and to develop target-based therapeutic agents. Integrative analysis of genome-scale metabolic models (GEMs) and omics data provides a computational approach for the prediction of metabolite biomarkers. Here, we applied the TIMBR (Transcriptionally Inferred Metabolic Biomarker Response) algorithm and two modified versions of TIMBR to investigate potential metabolite biomarkers for PD. To this end, we mapped thirteen post-mortem PD transcriptome datasets from the substantia nigra region onto Human-GEM. We considered a metabolite as a candidate biomarker if its production was predicted to be more efficient by a TIMBR-family algorithm in control or PD case for the majority of the datasets. Different metrics based on well-known PD-related metabolite alterations, PD-associated pathways, and a list of 25 high-confidence PD metabolite biomarkers compiled from the literature were used to compare the prediction performance of the three algorithms tested. The modified algorithm with the highest prediction power based on the metrics was called TAMBOOR, TrAnscriptome-based Metabolite Biomarkers by On-Off Reactions, which was introduced for the first time in this study. TAMBOOR performed better in terms of capturing well-known pathway alterations and metabolite secretion changes in PD. Therefore, our tool has a strong potential to be used for the prediction of novel diagnostic biomarkers for human diseases.

Abscisic acid ameliorates motor disabilities in 6-OHDA-induced mice model of Parkinson's disease

Parkinson's disease (PD) is characterized by a myriad of symptoms, encompassing both motor disabilities and cognitive impairments. Recent research has shown that abscisic acid (ABA) is a phytohormone found in various brain regions of several mammals and exhibits neuroprotective properties. To investigate the effects of ABA on cognitive and motor disorders, a mouse model of PD was utilized. The administration of 6-hydroxydopamine (6-OHDA) to the lateral ventricles was conducted, with ABA (10 and 15 μg/mouse, i. c.v.) being administered for one week after the 6-OHDA injection for 4 days. Motor and cognitive performance were evaluated through the use of open field, rotarod, wire grip, and shuttle box tests. The results indicated that cognitive function and motor disorders were significantly impaired in 6-OHDA-treated animals. However, in mice treated with 6-OHDA, ABA (15 μg/mouse) significantly reversed balance and muscle strength deficits. It should be noted that the administration of ABA did not significantly improve cognitive impairment or rearing in Parkinsonism mice. Therefore, the findings suggest that ABA plays a crucial role in protecting mice from motor disabilities caused by 6-OHDA.

Quantitation of Brain and Blood Glutathione and Iron in Healthy Age Groups Using Biophysical and In Vivo MR Spectroscopy: Potential Clinical Application

The antioxidant glutathione (GSH) and pro-oxidant iron levels play a balancing role in the modulation of oxidative stress (OS). There is a significant depletion of GSH in the left hippocampus (LH) in patients with Alzheimer's disease (AD) with concomitant elevation of iron level. However, the correlation of GSH and iron distribution patterns between the brain and the peripheral system (blood) is not yet known. We measured GSH and magnetic susceptibility (e.g., iron) in the LH region along with GSH in plasma and iron in serum across four age groups consisting of healthy volunteers (age range 18-72 y, n = 70). We report non-variability of the mean GSH in the plasma and LH region across mentioned age groups. The mean iron level in the LH region does not change, but the iron level in the serum in the 51-72 y age group increases non-significantly. Regression analysis of our data indicated that GSH and iron levels (both in blood and in brain) are not related to age. This research pave the way for the identification of a risk/susceptibility biomarker for AD and Parkinson's disease from the evaluation of GSH (in plasma) and iron (in serum) levels concomitantly.

Unveiling new secrets in Parkinson's disease: The glycatome

We are witnessing a considerable increase in the incidence of Parkinson's disease (PD), which may be due to the general ageing of the population. While there is a plethora of therapeutic strategies for this disease, they still fail to arrest disease progression as they do not target and prevent the neurodegenerative process. The identification of disease-causing mutations allowed researchers to better dissect the underlying causes of this disease, highlighting, for example, the pathogenic role of alpha-synuclein. However, most PD cases are sporadic, which is making it hard to unveil the major causative mechanisms of this disease. In the recent years, epidemiological evidence suggest that type-2 diabetes mellitus (T2DM) individuals have higher risk and worst outcomes of PD, allowing to raise the hypothesis that some dysregulated processes in T2DM may contribute or even trigger the neurodegenerative process in PD. One major consequence of T2DM is the unprogrammed reaction between sugars, increased in T2DM, and proteins, a reaction named glycation. Pre-clinical reports show that alpha-synuclein is a target of glycation, and glycation potentiates its pathogenicity which contributes for the neurodegenerative process. Moreover, it triggers, anticipates, or aggravates several PD-like motor and non-motor complications. A given profile of proteins are differently glycated in diseased conditions, altering the brain proteome and leading to brain dysfunction and neurodegeneration. Herein we coin the term Glycatome as the profile of glycated proteins. In this review we report on the mechanisms underlying the association between T2DM and PD, with particular focus on the impact of protein glycation.

Reflections of an Aging Free Radical Part 2: Meeting Inspirational People

Significance: During my long career in the field of redox biology, I met many inspiring people, especially Lester Packer. Recent Advances: This special issue of Antioxidants & Redox Signaling is dedicated to Lester Packer. Critical Issues: In this short review, I explore how Lester and other pioneers helped to develop the redox biology field and how I interacted with them. Future Directions: In our research to advance the field of redox biology, we stand on the shoulders of giants, including Lester Packer.

Pyruvate Prevents Dopaminergic Neurodegeneration and Motor Deficits in the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Model of Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the selective loss of dopamine(DA)rgic neurons in the substantia nigra of the midbrain, and primarily causes motor symptoms. While the pathological cause of PD remains uncertain, oxidative damage, neuroinflammation, and energy metabolic perturbation have been implicated. Pyruvate has been shown neuroprotective in animal models for many neurological disorders, presumably owing to its potent anti-oxidative, anti-inflammatory, and energy metabolic properties. We therefore investigated whether exogenous pyruvate could also protect nigral DA neurons from degeneration and reverse the associated motor deficits in an animal model of PD using the DA neuron-specific toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP (20 mg/kg) was injected four times every 2 h into the peritoneum of mice, which resulted in a massive loss of DA neurons as well as an increase in neuronal death and cytosolic labile zinc overload. There were rises in inflammatory and oxidative responses, a drop in the striatal DA level, and the emergence of PD-related motor deficits. In comparison, when sodium pyruvate was administered intraperitoneally at a daily dose of 250 mg/kg for 7 days starting 2 h after the final MPTP treatment, significant relief in the MPTP-induced neuropathology, neurodegeneration, DA depletion, and motor symptoms was observed. Equiosmolar dose of NaCl had no neuroprotective effect, and lower doses of sodium pyruvate did not have any statistically significant effects. These findings suggest that pyruvate has therapeutic potential for the treatment of PD and related neurodegenerative diseases.

Oral Dysbiosis and Neurodegenerative Diseases: Correlations and Potential Causations

Biofilms are a heterogenous complex community of vegetative cells and extracellular polymeric substances that can adhere to various surfaces and are responsible for a variety of chronic and acute diseases. The impact of bacterial biofilms on oral and intestinal health is well studied, but the correlation and causations of biofilms and neurodegenerative diseases are still in their infancy. However, the correlations between biofilms and diseases such as Alzheimer’s Disease, Multiple Sclerosis, and even Parkinson’s Disease are starting to demonstrate the role bacterial biofilms have in promoting and exasperating various illnesses. The review article provides insight into the role bacterial biofilms may have on the development and progression of various neurodegenerative diseases and hopefully shine a light on this very important area of research.

Evidence That Substantia Nigra Pars Compacta Dopaminergic Neurons Are Selectively Vulnerable to Oxidative Stress Because They Are Highly Metabolically Active

There are 400–500 thousand dopaminergic cells within each side of the human substantia nigra pars compacta (SNpc) making them a minuscule portion of total brain mass. These tiny clusters of cells have an outsized impact on motor output and behavior as seen in disorders such as Parkinson’s disease (PD). SNpc dopaminergic neurons are more vulnerable to oxidative stress compared to other brain cell types, but the reasons for this are not precisely known. Here we provide evidence to support the hypothesis that this selective vulnerability is because SNpc neurons sustain high metabolic rates compared to other neurons. A higher baseline requirement for ATP production may lead to a selective vulnerability to impairments in oxidative phosphorylation (OXPHOS) or genetic insults that impair Complex I of the electron transport chain. We suggest that the energy demands of the unique morphological and electrophysiological properties of SNpc neurons may be one reason these cells produce more ATP than other cells. We further provide evidence to support the hypothesis that transcription factors (TFs) required to drive induction, differentiation, and maintenance of midbrain dopaminergic neural progenitor cells which give rise to terminally differentiated SNpc neurons are uniquely involved in both developmental patterning and metabolism, a dual function unlike other TFs that program neurons in other brain regions. The use of these TFs during induction and differentiation may program ventral midbrain progenitor cells metabolically to higher ATP levels, allowing for the development of those specialized cell processes seen in terminally differentiated cells. This paper provides a cellular and developmental framework for understanding the selective vulnerability of SNpc dopaminergic cells to oxidative stress.

Computational Modeling of Mitochondria to Understand the Dynamics of Oxidative Stress

Mitochondria are complex organelles that use catabolic metabolism to produce ATP which is the critical energy source for cell function. Oxidative phosphorylation by the electron transport chain, which receives reducing equivalents (NADH and FADH₂) from the tricarboxylic acid cycle, also produces reactive oxygen species (ROS) as a by-product at complex I and III. ROS play a significant role in health and disease. In order to better understand this process, a computational model of mitochondrial energy metabolism and the production of ROS has been developed. The model demonstrates the process regulating ROS production and removal and how different energy substrates can affect ROS production.

Plasma Glutathione and Prodromal Parkinson's Disease Probability

BACKGROUND

A decrease in glutathione (GSH) levels is considered one of the earliest biochemical changes in Parkinson's disease (PD).

OBJECTIVE

The authors explored the potential role of plasma GSH as a risk/susceptibility biomarker for prodromal PD (pPD) by examining its longitudinal associations with pPD probability trajectories.

METHODS

A total of 405 community-dwelling participants (median age [interquartile range] = 73.2 [7.41] years) without clinical features of parkinsonism were followed for a mean (standard deviation) of 3.0 (0.9) years.

RESULTS

A 1 μmol/L increase in plasma GSH was associated with 0.4% (95% confidence interval [CI], 0.1%-0.7%; P = 0.017) less increase in pPD probability for 1 year of follow-up. Compared with participants in the lowest GSH tertile, participants in the highest GSH tertile had a 12.9% (95% CI, 22.4%-2.2%; P = 0.020) slower rate of increase of pPD probability for 1 year of follow-up.

CONCLUSION

Plasma GSH was associated with pPD probability trajectories; therefore, it might assist in the identification of individuals who are likely to reach the threshold for pPD diagnosis more rapidly. © 2021 International Parkinson and Movement Disorder Society.

Raman Imaging of Individual Membrane Lipids and Deoxynucleoside Triphosphates in Living Neuronal Cells during Neurite Outgrowth

Recent developments in Raman imaging at the microscopic scale were exploited here with the specific purpose of locating spectral fingerprints of individual membrane lipids and deoxynucleoside triphosphates during neuronal cell networking and separation. After carefully screening the Raman spectra of isolated lipid components, we located an in situ mapped specific Raman fingerprints from individual phospholipids at the micrometric level in comparison with the total lipid distribution within single living cells. We concurrently examined silent zones of lipid emissions and exploited those peculiar spectral ranges for mapping both abundance and localization of individual DNA nucleoside triphosphates. This work represents a first step toward label-free/molecular-selective Raman patterning with high spectral resolution of the relevant chemical species involved with the functionality of neuronal cells.

Role of Ionizing Radiation in Neurodegenerative Diseases

Ionizing radiation (IR) from terrestrial sources is continually an unprotected peril to human beings. However, the medical radiation and global radiation background are main contributors to human exposure and causes of radiation sickness. At high-dose exposures acute radiation sickness occurs, whereas chronic effects may persist for a number of years. Radiation can increase many circulatory, age related and neurodegenerative diseases. Neurodegenerative diseases occur a long time after exposure to radiation, as demonstrated in atomic bomb survivors, and are still controversial. This review discuss the role of IR in neurodegenerative diseases and proposes an association between neurodegenerative diseases and exposure to IR.

Beneficial effect of etazolate on depression-like behavior and, learning, and memory impairment in a model of Parkinson's disease

The aim of this study was to evaluate etazolate against depression-like behavior and, learning and memory impairment induced by 6- hydroxydopamine (6-OHDA) rat model of Parkinson's disease (PD). This aim was achieved through comparing 6-OHDA lesioned rats in the presence and absence of etazolate. The 6-OHDA was used to induce lesion as a model of PD. Etazolate was administered at a dose of 1 mg/kg/day for 14 days, starting 7 days after lesion induction. Apomorphine-induced rotation test was used to evaluate 6-OHDA-induced motor deficits, tail suspension test was used to assess depression-like symptoms, and the radial arms water maze (RAWM) was used to evaluate special learning and memory functions. Antioxidant biomarkers and BDNF protein levels were assessed in the hippocampus. Results revealed that etazolate administration significantly improved 6-OHDA-induced PD related symptoms including motor deficits, depression-like behavior and impairment of both short- and long- term memory. Moreover, etazolate significantly prevented 6-OHDA-induced reduction in oxidative stress biomarkers (GSH/GSSG ratio, GPx) and BDNF levels. In conclusion, motor dysfunction, depressive- like behavior, and learning and memory deficits in the 6-OHDA rat model of PD can be significantly prevented by etazolate. This prevention could be attributed to etazolate's ability to prevent reduction in antioxidative stress biomarkers and BDNF levels.

Astrocytes, Microglia, and Parkinson's Disease

Astrocytes and microglia support well-being and well-function of the brain through diverse functions in both intact and injured brain. For example, astrocytes maintain homeostasis of microenvironment of the brain through up-taking ions and neurotransmitters, and provide growth factors and metabolites for neurons, etc. Microglia keep surveying surroundings, and remove abnormal synapses or respond to injury by isolating injury sites and expressing inflammatory cytokines. Therefore, their loss and/or functional alteration may be directly linked to brain diseases. Since Parkinson's disease (PD)-related genes are expressed in astrocytes and microglia, mutations of these genes may alter the functions of these cells, thereby contributing to disease onset and progression. Here, we review the roles of astrocytes and microglia in intact and injured brain, and discuss how PD genes regulate their functions.

Repeated-Dose Oral N-Acetylcysteine in Parkinson's Disease: Pharmacokinetics and Effect on Brain Glutathione and Oxidative Stress

Parkinson's disease (PD) is associated with oxidative stress and decreased nigral glutathione (GSH), suggesting that therapies that boost GSH may have a disease-modifying effect. Intravenous administration of a high dose of N-acetylcysteine (NAC), a well-known antioxidant and GSH precursor, increases blood and brain GSH in individuals with PD and with Gaucher disease and in healthy controls. To characterize the pharmacokinetics of repeated high oral doses of NAC and their effect on brain and blood oxidative stress measures, we conducted a 4-week open-label prospective study of oral NAC in individuals with PD (n = 5) and in healthy controls (n = 3). Brain GSH was measured in the occipital cortex using ¹ H-MRS at 3 and 7 tesla before and after 28 days of 6000 mg NAC/day. Blood was collected prior to dosing and at predetermined collection times before and after the last dose to assess NAC, cysteine, GSH, catalase, malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) concentrations and the reduced-to-oxidized GSH ratio (GSH/ glutathione disulfide [GSSG]). Symptomatic adverse events were reported by 3 of the 5 subjects with PD. NAC plasma concentration-time profiles were described by a first-order absorption, 1-compartment pharmacokinetic model. Although peripheral antioxidant measures (catalase and GSH/GSSG) increased significantly relative to baseline, indicators of oxidative damage, that is, measures of lipid peroxidation (4-HNE and MDA) were unchanged. There were no significant increases in brain GSH, which may be related to low oral NAC bioavailability and small fractional GSH/GSSG blood responses. Additional studies are needed to further characterize side effects and explore the differential effects of NAC on measures of antioxidant defense and oxidative damage.

Metabolic Dysfunction in Parkinson's Disease: Bioenergetics, Redox Homeostasis and Central Carbon Metabolism

The loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the accumulation of protein inclusions (Lewy bodies) are the pathological hallmarks of Parkinson's disease (PD). PD is triggered by genetic alterations, environmental/occupational exposures and aging. However, the exact molecular mechanisms linking these PD risk factors to neuronal dysfunction are still unclear. Alterations in redox homeostasis and bioenergetics (energy failure) are thought to be central components of neurodegeneration that contribute to the impairment of important homeostatic processes in dopaminergic cells such as protein quality control mechanisms, neurotransmitter release/metabolism, axonal transport of vesicles and cell survival. Importantly, both bioenergetics and redox homeostasis are coupled to neuro-glial central carbon metabolism. We and others have recently established a link between the alterations in central carbon metabolism induced by PD risk factors, redox homeostasis and bioenergetics and their contribution to the survival/death of dopaminergic cells. In this review, we focus on the link between metabolic dysfunction, energy failure and redox imbalance in PD, making an emphasis in the contribution of central carbon (glucose) metabolism. The evidence summarized here strongly supports the consideration of PD as a disorder of cell metabolism.

Insulin-like growth factor 1 (IGF-1) therapy: Mitochondrial dysfunction and diseases

This review resumes the association between mitochondrial function and diseases, especially neurodegenerative diseases. Additionally, it summarizes the major role of IGF-1 as a mitochondrial protector, as studied in several experimental models (cirrhosis, aging …). The contribution of mitochondrial dysfunction to impairments in insulin metabolic signaling is also suggested by gene array analysis showing that reductions in gene expression, that regulates mitochondrial ATP production, are associated with insulin resistance and type 2 diabetes mellitus. Moreover, reductions in oxidative capacity of mitochondrial electron transport chain are manifested in obese, insulin-resistant and diabetic patients. Genetic and environmental factors, oxidative stress, and alterations in mitochondrial biogenesis can adversely affect mitochondrial function, leading to insulin resistance and several pathological conditions, such as type 2 diabetes. Finally, it remains essential to know the exact mechanisms involved in mitochondrial generation and metabolism, mitophagy, apoptosis, and oxidative stress to establish new targets in order to develop potentially effective therapies. One of the newest targets to recover mitochondrial dysfunction could be the administration of IGF-1 at low doses. In the last years, it has been observed that IGF-1 therapy has several beneficial effects: restores physiological IGF-1 levels; improves insulin resistance and lipid metabolism; exerts mitochondrial protection; and has hepatoprotective, neuroprotective, antioxidant and antifibrogenic effects. In consequence, treatment of mitochondrial dysfunctions with low doses of IGF-1 could be a powerful and useful effective therapy to restore normal mitochondrial functions.

Glycation in Parkinson's disease and Alzheimer's disease

Glycation is a spontaneous age-dependent posttranslational modification that can impact the structure and function of several proteins. Interestingly, glycation can be detected at the periphery of Lewy bodies in the brain in Parkinson's disease. Moreover, α-synuclein can be glycated, at least under experimental conditions. In Alzheimer's disease, glycation of amyloid β peptide exacerbates its toxicity and contributes to neurodegeneration. Recent studies establish diabetes mellitus as a risk factor for several neurodegenerative disorders, including Parkinson's and Alzheimer's diseases. However, the mechanisms underlying this connection remain unclear. We hypothesize that hyperglycemia might play an important role in the development of these disorders, possibly by also inducing protein glycation and thereby dysfunction, aggregation, and deposition. Here, we explore protein glycation as a common player in Parkinson's and Alzheimer's diseases and propose it may constitute a novel target for the development of strategies for neuroprotective therapeutic interventions. © 2016 International Parkinson and Movement Disorder Society.

Cerebrospinal fluid concentrations of N-acetylcysteine after oral administration in Parkinson's disease

INTRODUCTION

Depletion of neuronal glutathione may contribute to the pathogenesis of Parkinson's disease (PD). N-acetylcysteine (NAC) can restore neuronal glutathione levels, but it has not been established whether NAC can cross the blood-brain barrier in humans.

METHODS

Twelve patients with PD were given oral NAC twice daily for 2 days. Three doses were compared: 7 mg/kg, 35 mg/kg, and 70 mg/kg. NAC, cysteine, and glutathione were measured in the cerebrospinal fluid (CSF) at baseline and 90 min after the last dose. Cognitive and motor functions were assessed pre- and post-NAC administration using the Montreal Cognitive Assessment (MoCA) and the Unified Parkinson's Disease Rating Scale part III motor subscore (UPDRS-III).

RESULTS

Oral NAC produced a dose-dependent increase in CSF NAC concentrations (p < 0.001), with the highest dose producing a CSF concentration of 9.26 ± 1.62 μM. There were no significant adverse events. NAC had no acute effect on motor or cognitive function.

CONCLUSION

Orally administered NAC produces biologically relevant CSF NAC concentrations at doses that are well tolerated. The findings support the feasibility of NAC as a potential disease-modifying therapy for PD.

Complex deregulation and expression of cytokines and mediators of the immune response in Parkinson's disease brain is region dependent

Neuroinflammation is common in neurodegenerative diseases including Parkinson disease (PD). Expression of 25 mRNAs was assessed with TaqMan-PCR including members of the complement system, colony stimulating factors, Toll family, cytokines IL-8, IL-6, IL-6ST, IL-1B, TNF-α family, IL-10, TGFβ family, cathepsins and integrin family, in the substantia nigra pars compacta, putamen, frontal cortex area 8 and angular gyrus area 39, in a total of 43 controls and 56 cases with PD-related pathology covering stages 1-6 of Braak. Up-regulation of IL-6ST was the only change in the substantia nigra at stages 1-2. Down-regulation of the majority of members examined occurred in the substantia nigra from stage 4 onwards. However, region-dependent down- and up-regulation of selected mRNAs occurred in the putamen and frontal cortex, whereas only mRNA up-regulated mRNAs were identified in the angular cortex from stage 3 onwards in PD cases. Protein studies in frontal cortex revealed increased IL6 expression and reduced IL-10 with ELISA, and increased IL-6 with western blotting in PD. Immunohistochemistry revealed localization of IL-5, IL-6 and IL-17 receptors in glial cells, mainly microglia; IL-5, IL-10 and M-CSF in neurons; TNF-α in neurons and microglia; and active NF-κB in the nucleus of subpopulations of neurons and glial cells in PD. Distinct inflammatory responses, involving pro- and anti-inflammatory cytokines, and variegated mediators of the immune response occur in different brain regions at the same time in particular individuals. Available information shows that altered α-synuclein solubility and aggregation, Lewy body formation, oxidative damage and neuroinflammation converge in the pathogenesis of PD.

Neuroprotection by 6-(methylsulfinyl)hexyl isothiocyanate in a 6-hydroxydopamine mouse model of Parkinson׳s disease

A number of pathogenic factors have been implicated in the progression of Parkinson׳s disease (PD), including oxidative stress, mitochondrial dysfunction, inflammation, excitotoxicity, and signals mediating apoptosis cascade. 6-(methylsulfinyl)hexyl isothiocyanate (6-MSITC) is a major component in wasabi, a very popular spice in Japan and a member of the Brassica family of vegetables. This study was designed to investigate the neuroprotective effects of 6-MSITC in a PD mouse model. Mice were treated with 6-MSITC (5mg/kg twice a week) for four weeks after the unilateral intrastriatal injection of 6-hydroxydopamine (6-OHDA). On the 28th day, 6-OHDA-injected mice showed behavioral impairments, a significant decrease in tyrosine hydroxylase (TH) and an increase in apoptosis. In addition, lesioned mice showed reduced glutathione levels and glutathione-S-transferase and glutathione reductase activities. Notably, 6-MSITC demonstrated neuroprotective effects in our experimental model strongly related to the preservation of functional nigral dopaminergic neurons, which contributed to the reduction of motor dysfunction induced by 6-OHDA. Furthermore, this study provides evidence that the beneficial effects of 6-MSITC could be attributed to the decrease of apoptotic cell death and to the activation of glutathione-dependent antioxidant systems. These findings may render 6-MSITC as a promising molecule for further pharmacological studies on the investigation for disease-modifying treatment in PD.

Glutathione metabolism and Parkinson's disease

It has been established that oxidative stress, defined as the condition in which the sum of free radicals in a cell exceeds the antioxidant capacity of the cell, contributes to the pathogenesis of Parkinson disease. Glutathione is a ubiquitous thiol tripeptide that acts alone or in concert with enzymes within cells to reduce superoxide radicals, hydroxyl radicals, and peroxynitrites. In this review, we examine the synthesis, metabolism, and functional interactions of glutathione and discuss how these relate to the protection of dopaminergic neurons from oxidative damage and its therapeutic potential in Parkinson disease.

Neuroprotective effect of EGb761® and low-dose whole-body γ-irradiation in a rat model of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. The present study was undertaken to investigate the pretreatment effects of standardized Ginkgo biloba extract (EGb761(®)) and low-dose whole-body γ-irradiation on the neurological dysfunction in the reserpine model of PD. Male Wistar rats were pretreated orally with EGb761 or fractionated low-dose whole-body γ-irradiation or their combination, then subjected to intraperitoneal injection of reserpine (5 mg/kg body weight) 24 h after the final dose of EGb761 or radiation. Reserpine injection resulted in the depletion of striatal dopamine (DA) level, increased catalepsy score, increased oxidative stress indicated via depletion of glutathione (GSH), increased malondialdehyde (MDA) and iron levels, decreased DA metabolites metabolizing enzymes; indicated by inhibition by glutathione-S-transferase, and nicotinamide adenine dinucleotide phosphate (NADPH)-quinone oxidoreductase (NQO) activities, mitochondrial dysfunction; indicated by declined complex I activity, and adenosine triphosphate (ATP) level and increased apoptosis; indicated by decreased mitochondrial B cell lymphoma-2 (Bcl-2) protein level and by transmission electron microscope. EGb761 and low-dose γ-radiation ameliorated the reserpine-induced state of oxidative stress, mitochondrial dysfunction, and apoptosis in brain. It can be concluded that EGb761, a widely used herbal medicine and low dose of γ-irradiation have protective effects for combating Parkinsonism possibly via replenishment of GSH levels.

Long-term effects of ionising radiation on the brain: cause for concern?

There is no clear evidence proving or disproving that ionising radiation is causally linked with neurodegenerative diseases such as Parkinson's and Alzheimer's. However, it is known that high doses of ionising radiation to the head (20-50 Gy) lead to severe learning and memory impairment which is characteristical for Alzheimer's. The cumulative doses of ionising radiation to the Western population are accruing, mostly due to the explosive growth of medical imaging procedures. Children are in particular prone to ionising radiation as the molecular processes within the brain are not completely finished. Furthermore, they have a long lifespan under risk. We wish to open a debate if such low doses of radiation exposure may lead to delayed long-term cognitive and other defects, albeit at a lower frequency than those observed during application of high doses. Further, we want to sensitise the society towards the risks of ionising radiation. To achieve these aims, we will recapitulate the known symptoms of Parkinson's and Alzheimer's on the molecular level and incorporate data of mainly low- and moderate-ionising radiation (<5 Gy). Thus, we want to highlight in general the potential similarities of both the neurodegenerative and radiation-induced pathways. We will propose a mechanistic model for radiation-induced neurodegeneration pointing out mitochondria as a key element. This includes effects of oxidative stress and neuroinflammation-all fundamental players of neurodegenerative diseases.

Glutaredoxin 1 protects dopaminergic cells by increased protein glutathionylation in experimental Parkinson's disease

AIMS

Chronic exposure to environmental toxicants, such as paraquat, has been suggested as a risk factor for Parkinson's disease (PD). Although dopaminergic cell death in PD is associated with oxidative damage, the molecular mechanisms involved remain elusive. Glutaredoxins (GRXs) utilize the reducing power of glutathione to modulate redox-dependent signaling pathways by protein glutathionylation. We aimed to determine the role of GRX1 and protein glutathionylation in dopaminergic cell death.

RESULTS

In dopaminergic cells, toxicity induced by paraquat or 6-hydroxydopamine (6-OHDA) was inhibited by GRX1 overexpression, while its knock-down sensitized cells to paraquat-induced cell death. Dopaminergic cell death was paralleled by protein deglutathionylation, and this was reversed by GRX1. Mass spectrometry analysis of immunoprecipitated glutathionylated proteins identified the actin binding flightless-1 homolog protein (FLI-I) and the RalBP1-associated Eps domain-containing protein 2 (REPS2/POB1) as targets of glutathionylation in dopaminergic cells. Paraquat induced the degradation of FLI-I and REPS2 proteins, which corresponded with the activation of caspase 3 and cell death progression. GRX1 overexpression reduced both the degradation and deglutathionylation of FLI-I and REPS2, while stable overexpression of REPS2 reduced paraquat toxicity. A decrease in glutathionylated proteins and REPS2 levels was also observed in the substantia nigra of mice treated with paraquat.

INNOVATION

We have identified novel protein targets of glutathionylation in dopaminergic cells and demonstrated the protective role of GRX1-mediated protein glutathionylation against paraquat-induced toxicity.

CONCLUSIONS

These results demonstrate a protective role for GRX1 and increased protein glutathionylation in dopaminergic cell death induced by paraquat, and identify a novel protective role for REPS2.

Thiol-redox signaling, dopaminergic cell death, and Parkinson's disease

SIGNIFICANCE

Parkinson's disease (PD) is characterized by the selective loss of dopaminergic neurons of the substantia nigra pars compacta, which has been widely associated with oxidative stress. However, the mechanisms by which redox signaling regulates cell death progression remain elusive.

RECENT ADVANCES

Early studies demonstrated that depletion of glutathione (GSH), the most abundant low-molecular-weight thiol and major antioxidant defense in cells, is one of the earliest biochemical events associated with PD, prompting researchers to determine the role of oxidative stress in dopaminergic cell death. Since then, the concept of oxidative stress has evolved into redox signaling, and its complexity is highlighted by the discovery of a variety of thiol-based redox-dependent processes regulating not only oxidative damage, but also the activation of a myriad of signaling/enzymatic mechanisms.

CRITICAL ISSUES

GSH and GSH-based antioxidant systems are important regulators of neurodegeneration associated with PD. In addition, thiol-based redox systems, such as peroxiredoxins, thioredoxins, metallothioneins, methionine sulfoxide reductases, transcription factors, as well as oxidative modifications in protein thiols (cysteines), including cysteine hydroxylation, glutathionylation, and nitrosylation, have been demonstrated to regulate dopaminergic cell loss.

FUTURE DIRECTIONS

In this review, we summarize major advances in the understanding of the role of thiol-redox signaling in dopaminergic cell death in experimental PD. Future research is still required to clearly understand how integrated thiol-redox signaling regulates the activation of the cell death machinery, and the knowledge generated should open new avenues for the design of novel therapeutic approaches against PD.

Increased oxidative damage and decreased antioxidant function in aging human substantia nigra compared to striatum: implications for Parkinson's disease

Parkinson's disease (PD) is characterized by selective degeneration and loss of dopaminergic neurons in the substantia nigra (SN) of the ventral mid brain leading to dopamine depletion in the striatum. Oxidative stress and mitochondrial damage have been implicated in the death of SN neurons during the evolution of PD. In our previous study on human PD brains, we observed that compared to SN, striatum was significantly protected against oxidative damage and mitochondrial dysfunction. To understand whether brain aging contributes to the vulnerability of midbrain to neurodegeneration in PD compared to striatum, we assessed the status of oxidant and antioxidant markers, glutathione metabolic enzymes, glial fibrillary acidic protein (GFAP) expression and mitochondrial complex I(CI) activity in SN (n = 23) and caudate nucleus (n = 24) during physiological aging in human brains. We observed a significant increase in protein oxidation (P < 0.001), loss of CI activity (P = 0.04) and increased astrocytic proliferation indicated by GFAP expression (P < 0.001) in SN compared to CD with increasing age. These changes were attributed to significant decrease in antioxidant function represented by superoxide dismutase (SOD) (P = 0.03), glutathione (GSH) peroxidase (GPx) (P = 0.02) and GSH reductase (GR) (P = 0.03) and a decreasing trend in total GSH and catalase with increasing age. However, these parameters were relatively unaltered in CD. We propose that SN undergoes extensive oxidative damage, loss of antioxidant and mitochondrial function and increased GFAP expression during physiological aging which might make it more vulnerable to neurotoxic insults thus contributing to selective degeneration during evolution of PD.

Evaluation of markers of oxidative stress, antioxidant function and astrocytic proliferation in the striatum and frontal cortex of Parkinson's disease brains

Dopaminergic neurons die in Parkinson's disease (PD) due to oxidative stress and mitochondrial dysfunction in the substantia nigra (SN). We evaluated if oxidative stress occurs in other brain regions like the caudate nucleus (CD), putamen (Put) and frontal cortex (FC) in human postmortem PD brains (n = 6). While protein oxidation was elevated only in CD (P < 0.05), lipid peroxidation was increased only in FC (P < 0.05) and protein nitration was unchanged in PD compared to controls. Interestingly, mitochondrial complex I (CI) activity was unaffected in PD compared to controls. There was a 3-5 fold increase in the total glutathione (GSH) levels in the three regions (P < 0.01 in FC and CD; P < 0.05 in Put) but activities of antioxidant enzymes catalase, superoxide dismutase, glutathione reductase and glutathione-s-tranferase were not increased. Total GSH levels were elevated in these areas because of decreased activity of gamma glutamyl transpeptidase (γ-GT) (P < 0.05) activity suggesting a decreased breakdown of GSH. There was an increase in expression of glial fibrillary acidic protein (GFAP) (P < 0.001 in FC; P < 0.05 in CD) and glutathione peroxidase (P < 0.05 in CD and Put) activity due to proliferation of astrocytes. We suggest that increased GSH and astrocytic proliferation protects non-SN brain regions from oxidative and mitochondrial damage in PD.

Quantitative mapping of reversible mitochondrial Complex I cysteine oxidation in a Parkinson disease mouse model

Differential cysteine oxidation within mitochondrial Complex I has been quantified in an in vivo oxidative stress model of Parkinson disease. We developed a strategy that incorporates rapid and efficient immunoaffinity purification of Complex I followed by differential alkylation and quantitative detection using sensitive mass spectrometry techniques. This method allowed us to quantify the reversible cysteine oxidation status of 34 distinct cysteine residues out of a total 130 present in murine Complex I. Six Complex I cysteine residues were found to display an increase in oxidation relative to controls in brains from mice undergoing in vivo glutathione depletion. Three of these residues were found to reside within iron-sulfur clusters of Complex I, suggesting that their redox state may affect electron transport function.

Mitochondrial abnormalities in the putamen in Parkinson's disease dyskinesia

Prolonged treatment of Parkinson's disease (PD) with levodopa leads to disabling side effects collectively referred to as 'dyskinesias'. We hypothesized that bioenergetic function in the putamen might play a crucial role in the development of dyskinesias. To test this hypothesis, we used post mortem samples of the human putamen and applied real time-PCR approaches and gene expression microarrays. We found that mitochondrial DNA (mtDNA) levels are decreased in patients who have developed dyskinesias, and mtDNA damage is concomitantly increased. These pathologies were not observed in PD subjects without signs of dyskinesias. The group of nuclear mRNA transcripts coding for the proteins of the mitochondrial electron transfer chain was decreased in patients with dyskinesias to a larger extent than in patients who had not developed dyskinesias. To examine whether dopamine fluctuations affect mtDNA levels in dopaminoceptive neurons, rat striatal neurons in culture were repeatedly exposed to levodopa, dopamine or their metabolites. MtDNA levels were reduced after treatment with dopamine, but not after treatment with dopamine metabolites. Levodopa led to an increase in mtDNA levels. We conclude that mitochondrial susceptibility in the putamen plays a role in the development of dyskinesias.

Alpha-synuclein deficiency leads to increased glyoxalase I expression and glycation stress

The presynaptic protein alpha-synuclein has received much attention because its gain-of-function is associated with Parkinson's disease. However, its physiological function is still poorly understood. We studied brain regions of knock-out mice at different ages with regard to consistent upregulations of the transcriptome and focused on glyoxalase I (GLO1). The microarray data were confirmed in qPCR, immunoblot, enzyme activity, and behavior analyses. GLO1 induction is a known protective cellular response to glucose stress, representing efforts to decrease toxic levels of methylglyoxal (MG), glyoxal and advanced glycation endproducts (AGEs). Mass spectrometry quantification demonstrated a ubiquitous increase in MG and fructosyl-lysine as consequences of glucose toxicity, and consistent enhancement of certain AGEs. Thus, GLO1 induction in KO brain seems insufficient to prevent AGE formation. In conclusion, the data demonstrate GLO1 expression and glycation damage to be induced by alpha-synuclein ablation. We propose that wild-type alpha-synuclein modulates brain glucose metabolism.

Lactacystin requires reactive oxygen species and Bax redistribution to induce mitochondria-mediated cell death

BACKGROUND AND PURPOSE

The proteasome inhibitor model of Parkinson's disease (PD) appears to reproduce many of the important behavioural, imaging, pathological and biochemical features of the human disease. However, the mechanisms involved in the lactacystin-induced, mitochondria-mediated apoptotic pathway remain poorly defined.

EXPERIMENTAL APPROACH

We have used lactacystin as a specific inhibitor of the 20S proteasome in the dopaminergic neuroblastoma cell line SH-SY5Y. We over-expressed a green fluorescent protein (GFP)-Bax fusion protein in these cells to study localization of Bax. Free radical scavengers were used to assess the role of reactive oxygen species (ROS) in these pathways.

KEY RESULTS

Lactacystin triggered a concentration-dependent increase in cell death mediated by the mitochondrial apoptotic pathway, and induced a change in mitochondrial membrane permeability accompanied by cytochrome c release. The participation of Bax protein was more critical than the formation of the permeability transition pore in mitochondria. GFP-Bax over-expression demonstrated Bax redistribution from the cytosol to mitochondria after the addition of lactacystin. ROS, but not p38 mitogen-activated protein kinase, participated in lactacystin-induced mitochondrial Bax translocation. Lactacystin disrupted the intracellular redox state by increasing ROS production and depleting endogenous antioxidant systems such as glutathione (GSH). Pharmacological depletion of GSH, using L-buthionine sulphoxide, potentiated lactacystin-induced cell death. Lactacystin sensitized neuroblastoma cells to oxidative damage, induced by subtoxic concentrations of 6-hydroxydopamine.

CONCLUSIONS AND IMPLICATIONS

The lactacystin-induced, mitochondrial-mediated apoptotic pathway involved interactions between ROS, GSH and Bax. Lactacystin could constitute a potential factor in the development of sporadic PD.

A disruption in iron-sulfur center biogenesis via inhibition of mitochondrial dithiol glutaredoxin 2 may contribute to mitochondrial and cellular iron dysregulation in mammalian glutathione-depleted dopaminergic cells: implications for Parkinson's disease

Parkinson's disease (PD) is characterized by early glutathione depletion in the substantia nigra (SN). Among its various functions in the cell, glutathione acts as a substrate for the mitochondrial enzyme glutaredoxin 2 (Grx2). Grx2 is involved in glutathionylation of protein cysteine sulfhydryl residues in the mitochondria. Although monothiol glutathione-dependent oxidoreductases (Grxs) have previously been demonstrated to be involved in iron-sulfur (Fe-S) center biogenesis, including that in yeast, here we report data suggesting the involvement of mitochondrial Grx2, a dithiol Grx, in iron-sulfur biogenesis in a mammalian dopaminergic cell line. Given that mitochondrial dysfunction and increased cellular iron levels are two important hallmarks of PD, this suggests a novel potential mechanism by which glutathione depletion may affect these processes in dopaminergic neurons. We report that depletion of glutathione as substrate results in a dose-dependent Grx2 inhibition and decreased iron incorporation into a mitochondrial complex I (CI) and aconitase (m-aconitase). Mitochondrial Grx2 inhibition through siRNA results in a corresponding decrease in CI and m-aconitase activities. It also results in significant increases in iron-regulatory protein (IRP) binding, likely as a consequence of conversion of Fe-S-containing cellular aconitase to its non-Fe-S-containing IRP1 form. This is accompanied by increased transferrin receptor, decreased ferritin, and subsequent increases in mitochondrial iron levels. This suggests that glutathione depletion may affect important pathologic cellular events associated with PD through its effects on Grx2 activity and mitochondrial Fe-S biogenesis.

Expression of human uncoupling protein-3 in Drosophila insulin-producing cells increases insulin-like peptide (DILP) levels and shortens lifespan

Uncoupling proteins (UCPs) can dissipate mitochondrial protonmotive force by increasing the proton conductance of the inner membrane and through this effect could decrease ROS production, ameliorate oxidative stress and extend lifespan. We investigated whether ubiquitous, pan-neuronal or neurosecretory cell-specific expression of human UCP3 (hUCP3) in adult Drosophila melanogaster affected lifespan. Low, ubiquitous expression of hUCP3 at levels found in rodent skeletal muscle mitochondria did not affect proton conductance in mitochondria isolated from whole flies, but high pan-neuronal expression of hUCP3 increased the proton conductance of mitochondria isolated from fly heads. Expression of hUCP3 at moderate levels in adult neurons led to a marginal lifespan-extension in males. However, high expression of hUCP3 in neuronal tissue shortened lifespan. The life-shortening effect was replicated when hUCP3 was expressed specifically in median neurosecretory cells (mNSC), which express three of the Drosophila insulin-like peptides (DILPs). Expression of hUCP3 in the mNSC did not alter expression of dilp2, dilp3 or dilp5 mRNA, but led to increased amounts of DILP2 in fly heads. These data suggest that lowering mitochondrial coupling by high expression of hUCP3 alters mNSC function in a way that appears to increase DILP-levels in fly heads and lead to a concomitant decrease in lifespan.

Modifying effects of the HFE polymorphisms on the association between lead burden and cognitive decline

BACKGROUND

As iron and lead promote oxidative damage, and hemochromatosis (HFE) gene polymorphisms increase body iron burden, HFE variant alleles may modify the lead burden and cognitive decline relationship.

OBJECTIVE

Our goal was to assess the modifying effects of HFE variants on the lead burden and cognitive decline relation in older adults.

METHODS

We measured tibia and patella lead using K-X-ray fluorescence (1991-1999) among participants of the Normative Aging Study, a longitudinal study of community-dwelling men from greater Boston. We assessed cognitive function with the Mini-Mental State Examination (MMSE) twice (1993-1998 and 1995-2000) and genotyped participants for HFE polymorphisms. We estimated the adjusted mean differences in lead-associated annual cognitive decline across HFE genotype groups (n = 358).

RESULTS

Higher tibia lead was associated with steeper cognitive decline among participants with at least one HFE variant allele compared with men with only wild-type alleles (p interaction = 0.03), such that a 15 microg/g increase in tibia lead was associated with a 0.2 point annual decrement in MMSE score among HFE variant allele carriers. This difference in scores among men with at least one variant allele was comparable to the difference in baseline MMSE scores that we observed among men who were 4 years apart in age. Moreover, the deleterious association between tibia lead and cognitive decline appeared progressively worse in participants with increasingly more copies of HFE variant alleles (p-trend = 0.008). Results for patella lead were similar.

CONCLUSION

Our findings suggest that HFE polymorphisms greatly enhance susceptibility to lead-related cognitive impairment in a pattern consistent with allelelic dose.

Sequential opening of mitochondrial ion channels as a function of glutathione redox thiol status

Mitochondrial membrane potential (DeltaPsi(m)) depolarization contributes to cell death and electrical and contractile dysfunction in the post-ischemic heart. An imbalance between mitochondrial reactive oxygen species production and scavenging was previously implicated in the activation of an inner membrane anion channel (IMAC), distinct from the permeability transition pore (PTP), as the first response to metabolic stress in cardiomyocytes. The glutathione redox couple, GSH/GSSG, oscillated in parallel with DeltaPsi(m) and the NADH/NAD(+) redox state. Here we show that depletion of reduced glutathione is an alternative trigger of synchronized mitochondrial oscillation in cardiomyocytes and that intermediate GSH/GSSG ratios cause reversible DeltaPsi(m) depolarization, although irreversible PTP activation is induced by extensive thiol oxidation. Mitochondrial dysfunction in response to diamide occurred in stages, progressing from oscillations in DeltaPsi(m) to sustained depolarization, in association with depletion of GSH. Mitochondrial oscillations were abrogated by 4'-chlorodiazepam, an IMAC inhibitor, whereas cyclosporin A was ineffective. In saponin-permeabilized cardiomyocytes, the thiol redox status was systematically clamped at GSH/GSSG ratios ranging from 300:1 to 20:1. At ratios of 150:1-100:1, DeltaPsi(m) depolarized reversibly, and a matrix-localized fluorescent marker was retained; however, decreasing the GSH/GSSG to 50:1 irreversibly depolarized DeltaPsi(m) and induced maximal rates of reactive oxygen species production, NAD(P)H oxidation, and loss of matrix constituents. Mitochondrial GSH sensitivity was altered by inhibiting either GSH uptake, the NADPH-dependent glutathione reductase, or the NADH/NADPH transhydrogenase, indicating that matrix GSH regeneration or replenishment was crucial. The results indicate that GSH/GSSG redox status governs the sequential opening of mitochondrial ion channels (IMAC before PTP) triggered by thiol oxidation in cardiomyocytes.

Proteasome Inhibition Induces Glutathione Synthesis and Protects Cells from Oxidative Stress

The cause of selective dopaminergic neuronal degeneration in Parkinson disease has still not been resolved, but it has been hypothesized that oxidative stress and the ubiquitin-proteasome system are important in the pathogenesis. In this report, we investigated the effect of proteasome inhibition on oxidative stress-induced cytotoxicity in PC12 cells, an in vitro model of Parkinson disease. Treatment with proteasome inhibitors provided significant protection against toxicity by 6-hydroxydopamine and H(2)O(2) in a concentration-dependent manner. The measurement of intracellular reactive oxygen species using 2',7'-dichlorofluorescein diacetate demonstrated that lactacystin, a proteasome inhibitor, significantly reduced 6-hydroxydopamineand H(2)O(2)-induced reactive oxygen species production. Proteasome inhibitors elevated the amount of glutathione and phosphorylated p38 mitogen-activated protein kinase (MAPK) prior to glutathione elevation. The treatment with lactacystin induced the nuclear translocation of NF-E2-related factor 2 (Nrf2) and increased the level of mRNA for gamma-glutamylcysteine synthetase, a rate-limiting enzyme in glutathione synthesis. Furthermore, SB203580, an inhibitor of p38 MAPK, abolished glutathione elevation and cytoprotection by lactacystin. These data suggest that proteasome inhibition afforded cytoprotection against oxidative stress by the elevation of glutathione content, and its elevation was mediated by p38 MAPK phosphorylation.

Glutaredoxin 2 Catalyzes the Reversible Oxidation and Glutathionylation of Mitochondrial Membrane Thiol Proteins

The redox poise of the mitochondrial glutathione pool is central in the response of mitochondria to oxidative damage and redox signaling, but the mechanisms are uncertain. One possibility is that the oxidation of glutathione (GSH) to glutathione disulfide (GSSG) and the consequent change in the GSH/GSSG ratio causes protein thiols to change their redox state, enabling protein function to respond reversibly to redox signals and oxidative damage. However, little is known about the interplay between the mitochondrial glutathione pool and protein thiols. Therefore we investigated how physiological GSH/GSSG ratios affected the redox state of mitochondrial membrane protein thiols. Exposure to oxidized GSH/GSSG ratios led to the reversible oxidation of reactive protein thiols by thiol-disulfide exchange, the extent of which was dependent on the GSH/GSSG ratio. There was an initial rapid phase of protein thiol oxidation, followed by gradual oxidation over 30 min. A large number of mitochondrial proteins contain reactive thiols and most of these formed intraprotein disulfides upon oxidation by GSSG; however, a small number formed persistent mixed disulfides with glutathione. Both protein disulfide formation and glutathionylation were catalyzed by the mitochondrial thiol transferase glutaredoxin 2 (Grx2), as were protein deglutathionylation and the reduction of protein disulfides by GSH. Complex I was the most prominent protein that was persistently glutathionylated by GSSG in the presence of Grx2. Maintenance of complex I with an oxidized GSH/GSSG ratio led to a dramatic loss of activity, suggesting that oxidation of the mitochondrial glutathione pool may contribute to the selective complex I inactivation seen in Parkinson's disease. Most significantly, Grx2 catalyzed reversible protein glutathionylation/deglutathionylation over a wide range of GSH/GSSG ratios, from the reduced levels accessible under redox signaling to oxidized ratios only found under severe oxidative stress. Our findings indicate that Grx2 plays a central role in the response of mitochondria to both redox signals and oxidative stress by facilitating the interplay between the mitochondrial glutathione pool and protein thiols.

Reversible glutathionylation of complex I increases mitochondrial superoxide formation

Increased production of reactive oxygen species (ROS) by mitochondria is involved in oxidative damage to the organelle and in committing cells to apoptosis or senescence, but the mechanisms of this increase are unknown. Here we show that ROS production by mitochondrial complex I increases in response to oxidation of the mitochondrial glutathione pool. This correlates with thiols on the 51- and 75-kDa subunits of complex I forming mixed disulfides with glutathione. Glutathionylation of complex I increases superoxide production by the complex, and when the mixed disulfides are reduced, superoxide production returns to basal levels. Within intact mitochondria oxidation of the glutathione pool to glutathione disulfide also leads to glutathionylation of complex I, which correlates with increased superoxide formation. In this case, most of this superoxide is converted to hydrogen peroxide, which can then diffuse into the cytoplasm. This mechanism of reversible mitochondrial ROS production suggests how mitochondria might regulate redox signaling and shows how oxidation of the mitochondrial glutathione pool could contribute to the pathological changes that occur to mitochondria during oxidative stress.

Oxidation of biological systems: oxidative stress phenomena, antioxidants, redox reactions, and methods for their quantification

Reactive oxygen species (ROS) and other radicals are involved in a variety of biological phenomena, such as mutation, carcinogenesis, degenerative and other diseases, inflammation, aging, and development. ROS are well recognized for playing a dual role as deleterious and beneficial species. The objectives of this review are to describe oxidative stress phenomena, terminology, definitions, and basic chemical characteristics of the species involved; examine the biological targets susceptible to oxidation and the defense mechanisms of the organism against these reactive metabolites; and analyze methodologies, including immunohistochemical markers, used in toxicological pathology in the visualization of oxidative stress phenomena. Direct detection of ROS and other free radicals is difficult, because these molecules are short-lived and highly reactive in a nonspecific manner. Ongoing oxidative damage is, thus, generally analyzed by measurement of secondary products including derivatives of amino acids, nuclei acids, and lipid peroxidation. Attention has been focused on electrochemical methods based on voltammetry measurements for evaluating the total reducing power of biological fluids and tissues. This approach can function as a tool to assess the antioxidant-reducing profile of a biological site and follow changes in pathological situations. This review thus includes different topics essential for understanding oxidative stress phenomena and provides tools for those intending to conduct study and research in this field.