The chemical potential of the oxygen molecule relies on its electron structure two unpaired electrons in its basic triplet state. It promotes one-electron reactions that form the basis for respiration reduction of oxygen molecules in four single-electron reactions , microsomal electron transport chains ETC via cytochrome P CYP , and oxidative burst activity in macrophages [ 3 ].

The high dynamics of the chemical processes that are achieved in elementary single-electron reactions are desirable and are the source of reactive molecules, which are either undesirable side products respiration and metabolism or in excess of the established requirements defense process.

These reactive molecules are known as reactive oxygen species ROS and reactive nitrogen species RNS. This is caused by the high reactivity of ROS and RNS with lipids, proteins, carbohydrates, and nucleic acids. OS can be triggered by radicals produced by either exogenous processes e.

Generation of reactive species based on [ — ]. ROS production as a side effect of aerobic respiration occurs on the inner membrane of the mitochondrion [ 6 ] Fig.

The final acceptor of electrons and protons, an oxygen molecule, undergoes four-electron reduction, which can lead to the production of water molecules. Source of radical and OS biomarkers. Because of its high consumption of oxygen and its high lipid content, the brain is particularly vulnerable to damage caused by ROS and RNS.

The extent of the damage varies, depending on, among other factors, the source and type of the reactive species. In mitochondria, NO is produced from l -arginine and l -citrulline in a reaction that is catalyzed by nitric oxide synthase NOS , which has three isoforms with different tissue localizations.

NO is involved in many important processes within the central nervous system, such as the regulation of cerebral blood flow and memory. In addition, it plays a significant role in the regulation of the immune system, including the modulation of cytokine production.

The released NO acts on neighboring cells, leading to somatic mutations and affecting cell cycle regulatory proteins, apoptosis, and DNA repair [ 11 ].

RNS are important for the generation of OS. All of these can damage nerve cells [ 12 ]. These highly reactive compounds induce changes in the structure and function of cell membranes, proteins, lipoproteins, enzymes, hormones, and genetic material.

In particular, membranes are a primary target for ROS. Conversion products of lipid peroxidation lead to the decomposition of polyunsaturated fatty acids and the formation of the final products, i.

These compounds react with DNA or protein molecules and modify their structure and functions [ 13 , 14 ]. There are several mechanisms designed to protect the organism from the harmful effects of ROS and RNS. The production of ROS- and RNS-induced damage the final effect of OS in tissue can be confirmed by the presence of tissue-specific and non-specific biomarkers [ 15 — 20 ].

Several markers of OS and antioxidant activity are presented in Fig. The cellular antioxidant system, designed to prevent damage to tissue, is composed of antioxidant enzymes and other non-enzymatic compounds that have the ability to reduce different chemical structures [ 21 ].

These compounds are responsible for maintaining the balance between pro- and antioxidant agents and alleviating OS see Table 1. The essential components of the enzymatic antioxidant defense are superoxide dismutase SOD , catalase CAT , glutathione peroxidase GPx , and glutathione reductase GR , while the non-enzymatic antioxidants include glutathione GSH , thioredoxin Trx , vitamins A, E, and C, flavonoids, trace elements, and proteins, e.

A large body of evidence confirms a relationship between OS and the development of neurodegenerative diseases. The increased neuronal ROS production and accumulation of oxidative damage that occurs with age correlate well with the extent of neurodegeneration.

In the following sections of this article, we present the current knowledge on the relationships between the intensity of OS and the initiation and progression of the major neurodegenerative diseases AD, PD, and ALS. This results in spasticity, muscle wasting, and weakness, leading finally to paralysis and difficulties with speech, swallowing, and breathing.

There is currently no cure for ALS and only riluzole, which acts on glutamate signaling, has been registered for the treatment of the disease. Riluzole was shown to slow disease progression and to improve limb function; however, the survival of patients was prolonged by only 2—3 months and death due to respiratory failure occurred in most cases within 3—5 years of the diagnosis [ 26 ].

The main pathological hallmark of ALS is the formation of cytoplasmic aggregates in degenerating motor neurons and surrounding oligodendrocytes, but those inclusions are also present in the frontal and temporal cortices, hippocampus, and cerebellum [ 27 ].

Studies concerning the mechanisms of ALS development indicate that many factors, including excitotoxicity, mitochondrial dysfunction, endoplasmic reticulum stress, neuroinflammation, and OS, can be involved in this process. The two forms of the disease are clinically indistinguishable because the symptoms and pathological changes in SALS and FALS are similar.

FALS is caused by mutations in some genes, such as those coding for SOD1, FUS RNA binding protein, TAR DNA binding protein, vesicle-associated membrane protein B, valosin-containing protein, optineurin, alsin, senataxin, spatascin, angiogenin, or ubiquilin-2 [ 24 , 26 ].

Some of these gene mutations have also been found in SALS patients [ 28 , 29 ]. The most common known genetic mutation for ALS is the recently described expanded GGGGCC hexanucleotide repeat in the non-coding region of the C9Orf72 gene, on chromosome 9p21 [ 30 ].

Another common mutation is localized in SOD1. Pathogenic mutations of SOD1 enzyme can be present in different regions of the enzyme, e. Mutated SOD1 can form cytotoxic protein aggregates alone or with other proteins what possibly leads to loss of the enzymatic function or to acquiring the toxic properties [ 32 , 33 ].

Then, the remaining wild-type SOD1 may become itself a target of oxidative modification after which it dissociates from dimers to monomers and further forms aggregates with toxic properties of mutant forms of SOD1.

That was shown in in vitro studies [ 34 , 35 ]. Accumulation of abnormal SOD1 was also confirmed in the spinal cord [ 34 ] in animal studies [ 36 , 37 ] as well as in ALS patients [ 38 ].

Post - mortem studies on tissue samples from SALS and FALS patients support the hypothesis of oxidative damage of proteins, lipids, and DNA. However, no correlation between these markers and the severity or duration of the disease has been found [ 43 ].

Raised levels of thiobarbituric acid reactive substances TBARS and advanced oxidation protein products AOPP and decreased ferric-reducing ability of plasma FRAP were detected in the plasma or erythrocytes of SALS patients [ 44 — 46 ], but plasma protein carbonyl PC levels surprisingly did not differ between SALS patients and control subjects [ 16 ].

More conclusive results came from a study where urine from SALS patients contained a higher level of isoprostanoids IsoPs and 8-OHdG compared to a control group [ 16 , 47 ], suggesting that IsoPs and 8-OHdG could be considered markers of OS in ALS.

These studies included only 50 participants with SALS compared to 46 control subjects. Thus, these results should be confirmed in larger cohorts. The presence of OS biomarkers in regions of the CNS that are critical for ALS suggests that they are implicated in motor neuron degeneration.

This fact is supported by very recent positron emission tomography PET imaging data in humans, which confirmed that OS were enhanced in the motor cortex in ALS patients compared with controls. Moreover, the observed OS increase in the mild stage of the disease led to the conclusion that OS may be an important factor associated with the development of neurodegeneration in ALS patients [ 48 ].

Most studies concerning antioxidant defense biomarkers in ALS patients have shown changes in peripheral tissues or in CSF but rarely in the brain.

For example, GSH levels were reduced in erythrocytes in ALS patients [ 45 ]. Very recent in vivo imaging studies have shown decreased GSH levels in the motor cortex of ALS patients by using the J-editing technique or 62 copper-diacetyl-bis N4-methylthiosemicarbazone 62 CU-ATSM PET technique [ 25 , 48 ].

The activity of SOD decreased in red blood cells and the CSF of FALS- and SALS-diagnosed patients [ 42 , 50 — 52 ]. Interestingly, the reduction in the SOD1 protein concentration in erythrocytes of FALS patients correlated with SOD1 gene mutations [ 42 ].

However, SALS patients displayed enhanced activity of SOD1 in CSF [ 53 ], indicating that this different outcome may depend on either the ALS type, the disease duration, or the sampling time [ 54 ]. Apart from SOD, the activity of CAT, another antioxidant defense enzyme, was also found to be diminished in red blood cells in FALS [ 51 ] and SALS [ 51 , 52 ] patients.

Another study revealed that CAT activity decreased in erythrocytes with disease progression, which may suggest a link between this parameter and ALS duration [ 45 ].

Results regarding GPx or GR activity in ALS patients are controversial. GPx type 3 also known as plasma GPx and GR levels were lower in the serum or in red blood cells, respectively, in ALS patients [ 45 , 55 ].

In contrast, another study showed enhanced GPx in the serum and CSF of ALS patients [ 56 ], while GR activity was elevated in the erythrocytes in both SALS and FALS patients [ 51 , 52 ]. One study reported no change in GR activity in red blood cells in SALS patients [ 57 ].

These divergent results could be explained by the heterogeneity of ALS [ 60 ]. In fact, ALS-diagnosed patients vary in their rate of disease progression and may differ in the number of years of survival.

Moreover, a study from Cova et al. All of these results support the hypothesis that ALS has many variants or mimic syndromes that differ in their pathogenic mechanisms and in their profile of enzymatic and non-enzymatic antioxidant responses [ 57 ].

Several pharmacotherapeutic agents with antioxidant properties have been attempted to slow ALS progression; however, most of them failed to do so Table 2. Vitamin E, when combined with riluzole, diminished TBARS levels, enhanced GPx activity in the plasma, and prolonged the milder stages of the ALS Health State scale, but it did not affect survival and motor function [ 61 ].

On the other hand, another study showed that intake of a combination of polyunsaturated fatty acids and vitamin E reduced the risk of developing ALS [ 63 ]. Edavarone MCI is another free radical scavenger that is already approved to treat cerebral infarction and to investigate ALS.

It eliminates lipid peroxide and hydroxyl radicals by transferring an electron to the radical and thereby exerting a protective effect on neurons. In ALS patients, edavarone was shown to diminish nitrosative stress NS in CSF [ 64 ] and is now being tested in a phase III clinical trial in Japan for ALS treatment [ 65 ].

This study also determined 8-OHdG levels in the plasma; however, according to the authors, the results for this measure will only be available later [ 66 ]. Other antioxidant medications, i. In these studies, the influence on antioxidant defense biomarkers and oxidant damage was not evaluated.

In another study, melatonin was used as a potential neuroprotective compound and, when normalized to control values, was found to elevate the level of PC in the serum of 31 SALS patients [ 70 ].

The novel antioxidant AEOL , which is a small molecule that catalytically consumes ROS and RNS, is considered to be the most promising compound under evaluation in a clinical trial [ 71 ]. In a small, open-label study in ALS patients, AEOL was shown to be a safe and well-tolerated drug [ 71 ].

However, neither efficacy nor measurement of oxidative biomarkers in ALS patients who were on AEOL has been published. The antioxidant medications used in ALS clinical trials have so far been unable to slow the progression of the disease. Moreover, a limited number of clinical studies have investigated oxidative damage or changes in the antioxidant defense status after antioxidant therapy.

for more details, see [ 72 ]. Changes in oxidative biomarkers have been detected in ALS models in rodents Table 3. For example, free radical levels were elevated in the spinal cord of SOD1 G93A mice post-mortem [ 74 , 75 ], and trapped radical adducts were also recently detected in the spinal cord of these mice in vivo [ 76 ].

In line with this latter observation, increased levels of PC in the spinal cord and in the motor cortex [ 77 , 78 ], MDA and 4-HDA in the brain and CSF [ 79 ], and HNE, HNE-adducts, and 8-OHdG in the spinal cord [ 80 , 81 ] have been observed in several ALS animal models see Table 3.

It has been established that enhanced nitration processes are also present in animal models of ALS. For example, 3-NT was found in the spinal cords of aged SOD1 G93A mice together with the presence of overnitrated proteins actin or ATPase in the spinal cord [ 82 ], in the motor and sensory cortices [ 78 ], and in the peripheral blood mononuclear cells [ 83 ] in transgenic mouse models of ALS and that these were observed even before the onset of the disease.

OS and NS are widely present in ALS, and in vitro studies suggest that this mechanism can facilitate the formation of protein aggregates [ 84 ].

In support of this conclusion, recent studies have revealed that a selective nNOS inhibitor increased survival in SOD1 transgenic mice [ 85 ]. In general, transgenic mouse models overexpressing mutant human SOD1 showed increased activity by the enzyme [ 32 ].

However, in the end stage of the disease, SOD1 activity in SOD1 G93A mice remained at the same level as wild-type SOD in non-transgenic mice [ 86 ].

What is interesting is that SOD1 knockout mice did not show an ALS-like phenotype [ 32 ]. Other antioxidant biomarkers, including GSH, GPx, and GR, are also changed during the course of ALS.

The levels of GSH differed in mice carrying different SOD1 mutations. A recent study by Vargas et al. The mechanism of GSH reduction is linked to the nuclear transcription factor Nrf2 because its transfection into the SOD G93A mouse brain led to the up-regulation of GSH synthesis in astrocytes and reduced the most apparent neurological and biochemical symptoms of the disease [ 89 ].

In animal models of ALS, motor neurons have displayed overexpression of Prx2 and glutathione peroxidase-1 GPx1. The number of neurons containing Prx2 and GPx1 decreased in the terminal stage of ALS [ 90 ], suggesting a breakdown of this redox system at the advanced stages of the disease.

As discussed by Kato et al. Similarly, GPx3 protein levels in the serum of SOD1 H46R rats were increased in the pre-symptomatic stage and decreased gradually with disease progression [ 55 ]. However, another study did not reveal significance for the role of GPx in ALS [ 92 ], and further investigation is therefore necessary to clarify this problem.

Because enhanced SOD activity in ALS animal models remains enhanced in most of the disease stages and decreases only to the control level of non-transgenic mice in the end stage of the disease, this raises the question of whether these ALS animal models are suitable to study ALS antioxidant defense biomarkers because an ALS key enzyme, SOD, is decreased in ALS patients.

These contradictory results, obtained in animals and humans, do not allow researchers to draw conclusions regarding the significance of these biomarkers in animal ALS models. Many substances possessing antioxidant properties have been proposed as ALS treatment strategies Table 4.

For example, coenzyme Q10 was shown recently to be unable to prolong survival when given after ALS onset [ 93 ]. As coenzyme Q10 is characterized by rather poor CNS availability which possibly explains its small pharmacological effects , its reduced form, ubiquinol, has better bioavailability and antioxidant properties and was also investigated.

However, similar to its parent drug, ubiquinol did not prolong lifespan. Nevertheless, it was noted that poor CNS availability after oral dosing was observed in this study, which possibly explains the lack of pharmacological effects, similar to the case with its parent drug [ 93 ].

Creatine was the next drug that extended survival, but not age of onset, in ALS animals [ 94 — 96 ]. It has neuroprotective properties and buffers against ATP depletion in mitochondria. Its dysfunction can lead to ATP decreases, which may contribute to cell death [ 97 ].

Because mitochondrial swelling and vacuolization are among the earliest pathological features in ALS mice with the SOD mutations [ 98 ], creatine could be useful for protecting mitochondria and for disease treatment in such a preclinical model.

In addition to its effect of prolonging the lifespan in a mouse ALS model, creatine also improved motor performance [ 96 ] and provided protection from motor neuron loss at days of age in these mice [ 98 ]. Moreover, creatine was shown to prevent the rise of 3-NT in the spinal cord and ROS production in the dialysate from microdialysis in ALS animals [ 98 ], and it also had a positive effect on weight retention [ 99 ].

However, one study found that creatine administration had no effect on the disturbed muscle function [ ]. Other antioxidants that extended survival in ALS mice include EUK-8 and EUK On the other hand, treatment with vitamin E significantly delayed ALS onset with no effect on survival but with a diminishing effect on 8-hydroxyguanine 8-OHG levels in the spinal cord [ ].

Drugs that shared both effects ALS onset delay and lifespan extension were melatonin, ammonium tetrathiomolybdate a copper-chelating drug , and resveratrol a substance that originates in plants and is found in highest amounts in red wine and the skin of red grapes [ 86 , — ]. However, in case of melatonin, the data were not clear as it was given in a dose range of 2.

in the same animal model and also produced a surprisingly shortened survival, accelerated disease onset, enhanced lipid peroxidation in the spinal cord, and increased spinal motoneuron loss [ ]. Such a hypothesis needs to be tested in future studies. Other substances used in preclinical ALS models, i.

The latter compound also ameliorated ALS-like symptoms in SOD1 G93A mice, probably by chelating the copper ions from the Cys site in the SOD-1 enzyme, which is important because various SOD-1 mutations affect Cu and Zn metal-binding, thereby promoting toxic protein aggregation [ 86 ].

Moreover, successful effects were achieved from treatment with ammonium tetrathiomolybdate when it was given after disease onset, which is satisfactory because this regime of administration closely reflects clinical practice.

Edaravone and AEOL are recently studied drugs for ALS that were administered at ALS onset. Although edaravone did not prolong survival in an ALS mouse model, it diminished SOD1 deposition in the anterior horn of the spinal cord and slowed disease progression and motor neuron degeneration [ 36 ].

Another substance that gave more promising results is AEOL , which, when administered to ALS mice, decreased 3-NT and MDA levels in the spinal cord, extended animal survival [ ], provided better preservation of motor neuron architecture, and diminished the level of astrogliosis [ ].

In conclusion, according to animal studies, antioxidants may become putative ALS therapies because many of them extend the lifespan and diminish OS in ALS animals. However, it must be remembered that many of them, when tested in humans, have not yet shown benefits for survival time and motor function amelioration.

Riluzole was shown to extend the lifespan in mice in the SOD1 G93A ALS animal model, but it did not change the disease onset [ ] or have a satisfactory effect on the latter parameter [ ]. No studies concerning oxidative defense or oxidative damage biomarkers were conducted; however, in vitro studies showed that riluzole had antioxidant properties in cultured cortical neurons [ ].

PD is a progressive degenerative disorder that is characterized by the loss of dopamine-producing neurons in the substantia nigra SN and by the presence of Lewy bodies in the SN and locus coeruleus.

Clinical manifestations of PD include resting tremor, muscle rigidity, slowing of voluntary movements bradykinesia , a tendency to fall postural instability , and a mask-like facial expression [ ].

The pathological hallmarks of PD, Lewy bodies, contain various proteins, including α-synuclein, ubiquitin, Parkin, and neurofilaments. Mutations in the α-synuclein gene cause one of the familial forms of PD via autosomal dominant inheritance [ ].

Many studies have demonstrated the presence of OS and its markers in the brain and CSF in PD patients. Cholesterol lipid hydroperoxide and MDA were found to be up to fold higher in SN in post-mortem brains of PD patients compared with other brain regions and age-matched controls [ ].

In contrast, a recent paper demonstrated lower levels of MDA in the caudate nucleus and putamen and increased MDA levels in the frontal cortex in the post-mortem analyses of PD brains compared to healthy age-matched controls.

Those results suggested that the non-SN regions, such as the caudate nucleus or the putamen, may have different compensatory mechanisms against OS could protect them from oxidative damage [ ].

Moreover, HNE and acrolein-modified proteins were found in the neocortex and brainstem and in the SN, respectively, of PD patients [ — ]. According to in vitro studies, HNE modification of α-synuclein has been shown to trigger oligomerization and fibrillization of unmodified α-synuclein in the nervous system, which might lead to dopaminergic neuron injury.

A recent observation suggests that HNE-modified proteins should be considered to be important players in PD pathophysiology [ ]. Despite a number of studies supporting lipid peroxidation in the brains of PD patients, the levels of F2-isoprostanes were not elevated in the SN of PD patients [ ], and the reason for this observed difference needs to be explained.

PCs are present not only in the brain regions specific for PD the SN, caudate nucleus, and putamen but also in other brain areas not directly linked with PD.

Interestingly, brain regions from individuals with putative presymptomatic PD incidental Lewy body disease showed no PC rise.

Oxidative damage to proteins in PD also occurred through nitration, and 3-NT was found to be increased within Lewy bodies in the SN pars compacta SNpc of PD patients [ ]. Another pathology found in PD brains is DNA and RNA damage [ , ].

The factors 8-OHG and 8-OHdG were elevated in various parts of the PD brain compared to controls; however, the most striking rise was detected in the SN [ , ].

Similarly, increased levels of 8-OHG and 8-OHdG were observed in CSF [ , ]. However, these studies came to opposite conclusions with respect for the correlation between 8-OHG levels and disease duration.

In the CSF of living PD patients, enhanced levels of HNE and MDA have been shown as well [ — ], but different results were obtained by Shukla et al. Moreover, markers of oxidative damage in PD patients were also detected in the serum and urine [ — ], but their use as indicators of the course of the disease is far from being useful for clinical practice because the existing data are contradictory [ — ].

As has been suggested [ — ], these differences may be due to the variability in methods used to measure OS markers.

The results of many studies have demonstrated the presence of OS in the brain, CSF, serum, and urine of PD patients; however, none of the OS markers has been established as a specific biomarker for PD disease or as a marker for PD disease progression.

This decrease is one of the earliest biochemical changes that has been observed in the disease [ — ], and it results in a selective drop in mitochondrial complex I activity, another hallmark of PD [ ]. On the other hand, a substantial rise in SOD levels has been observed in the SN and basal ganglia in PD patients [ ], while no change in activities of CAT, GPx, and GR was found compared to age-matched controls [ ].

Another study showed some deficiency in GPx in the SN in Parkinsonian patients [ ], but the weak ca. This suggests that PD medications may play a disadvantageous role that leads to enhanced peripheral oxidative stress; however, the small sample size excludes a final conclusion [ ].

One of the possible strategies was to supplement GSH. As shown by Sechi et al. infusion [ ]. Unfortunately, no results concerning the clinical status of PD patients have been described.

Magnetic resonance imaging MRI studies showed a rise in iron concentrations in the SN in PD patients [ ]. Because iron can lead to ROS production in PD patients, an iron-binding compound, deferiprone, has been tested in a pilot study in PD patients FAIRPARK trial, registered as ClinicalTrials.

gov NCT The earlier therapy start diminished SN iron deposits to a greater extent than the delayed-start paradigm and improved motor performance vs. placebo and vs. Moreover, in deferiprone-treated patients, GPx and SOD activity in the CSF increased, which supports the connection between the chelator treatment and the antioxidant response.

Vitamin E α-tocopherol was also suggested as a way to diminish the OS and to reduce clinical symptoms in PD. It is of note that no analysis of OS biomarkers was performed in that trial [ , ]. Since DATATOP, no clinical trials using vitamin E as a potential PD medication have been conducted.

In fact, vitamin E was only used in PD clinical trials as a supplement for coenzyme Q10 or as a placebo [ ] or a control [ ]. Another potent antioxidant, coenzyme Q10 mg a day , in the first reported multicenter, randomized, placebo-controlled, and double-blind trial slowed functional declines compared to placebo [ ].

Lower doses or different formulations of coenzyme Q10 displayed no symptomatic effects on midstage PD [ ]. In September , the NINDS discontinued the NET-PD LS-1 study phase III clinical trial with a total of 1, planned participants, ClinicalTrials.

gov identifier: NCT that started in because the results obtained from a study of creatine used for the treatment of early stage PD did not demonstrate a statistically significant difference between the active substance and placebo [ ]. In conclusion, although evidence for the link between OS and damage in PD is overwhelming, suggesting the potential efficacy of antioxidant drugs, most clinical trials have so far failed to support this statement.

Administration of zonisamide, an anticonvulsant drug prescribed to treat resting tremor in PD, inhibited the rise of 8-OHdG levels in the urine of PD patients. As the 8-OHdG rise correlates with disease progression and aging, it can be presumed that zonisamide could be helpful in defending against OS-evoked DNA modifications in PD patients.

Other drugs used for treatment of PD i. Interesting findings were reported in a study that measured GSH levels in venous blood in PD subjects who were on- and off-medication while performing acute physical exercises, because we know that this type of physical activity leads to GSH depletion and GSSG rise [ ].

Surprisingly, the off-medication patients had a lower drop in GSH level than the on-medication group. This finding suggests that patients in the off-medication state handled acute stress better than those in the on-medication state, indicating that medication may impede the ability to tolerate acute OS [ ].

Similar conclusions were obtained in a very recent study by Nikolova et al. The most popular animal models of PD include pharmacological 6-hydroxydopamine 6-OHDA , 1-methylphenyl-1,2,3,6-tetrahydropyridine MPTP , rotenone, and paraquat as well as several genetic with mutations in the α-synuclein, PINK1, Parkin, or LRRK2 genes models [ ].

The 6-OHDA model Table 5 , wherein the toxin is injected directly into the SNpc, medial forebrain bundle, or striatum, was the first animal model of PD associated with dopaminergic neuronal death within the SNpc [ ].

Another PD model utilizes MPTP, a highly lipophilic molecule that rapidly crosses the blood—brain barrier, leading to an irreversible and selective loss of dopaminergic neurons in the SN in non-human primates [ , ] and in rodents [ , ], although the latter species was less sensitive to MPTP than primates [ ].

Other chemical models are based on an insecticide, rotenone, or paraquat, an herbicide. Rotenone, when given i. in a low dose to rats, produces selective degeneration of SN dopaminergic neurons that is accompanied by α synuclein-positive LB-like inclusions [ ].

Paraquat is used less widely than MPTP, rotenone, or 6-OHDA models and is used instead as an addition to other toxic agents, such as the fungicide maneb [ ]. It was reported to cause selective degeneration of nigrostriatal dopaminergic neurons in mice [ ].

As has been demonstrated in numerous studies, OS is widely present in all of these toxin-based models see Table 5. Similarly, in the MPTP and in the rotenone models, elevated levels of lipid peroxidation products [ — ] and oxidatively modified proteins [ , ] were observed in various parts of the brain striatum, cortex, SN, hippocampus, cerebellum, and midbrain.

In addition to lipid damage, increased 3-NT levels were also detected following the use of MPTP in the SN, striatum, and ventral midbrain [ , ]. MPTP or rotenone-treated animals also showed oxidatively modified RNA or DNA in the SN or striatum [ , , ]. In the paraquat and maneb PD models, enhanced lipid peroxidation in the nigrostriatal areas of animal brains was also shown [ ] Table 5.

A very recent report from Kumar et al. This interesting result regarding α-synuclein radical formation was obtained by using the immuno-spin trapping method in combination with immunoprecipitation [ ]. Moreover, it was noted that protein radicals such as α-synuclein radical may trigger protein aggregation, which plays a causal role in dopaminergic neuronal death [ ].

For review of genetic models and OS, see the excellent paper [ ]. All toxin-based models share common characteristics, including the ability to produce ROS and further oxidative damage, which causes death in dopaminergic neurons and reflects part of the pathology observed in PD.

Although all of those models have drawbacks, they are useful for testing neuroprotective therapies. A characteristic shared feature observed in all toxin-based models is a drop in GSH level in key PD structures [ , — , — ] Table 5.

Importantly, lower GSH levels make nigrostriatal neurons more susceptible to oxidative damage and further degeneration. Studies using 6-OHDA also showed a reduction in activity by SOD, CAT, and glutathione S -transferase GST in striatum and SN [ , , ].

On the other hand, results from the MPTP model are inconclusive regarding SOD and CAT activity. Moreover, some of the MPTP studies showed increased SOD activity in the SN [ ] and striatum [ ], while others reported diminished SOD activity in these regions [ , ].

These differences may have resulted from the use of different doses of the toxin, varied routes of drug administration intracranial versus i.

Similar to SOD activity, CAT activity cannot be considered a biomarker of OS in rodent PD models as its activity was both diminished [ , , , , , ] and enhanced [ ]. Moreover, GPx activity was diminished in striatum in an MPTP model [ ], while GST activity was found to be elevated in a maneb and paraquat PD animal model [ ] Table 5.

All of these reports on the enhanced activities of SOD, CAT, and GST suggest the presence of mechanisms in brain areas that defend against exposure to PD toxin models. On the other hand, diminished activities or levels of antioxidant enzymes may indicate that these defense mechanisms were overcome and that the degeneration process had begun.

Several agents, such as valproic acid [ ] and melatonin [ ], effectively reversed changes in antioxidant defense biomarkers and oxidative damage in the 6-OHDA rat model of PD Table 6. There are also data in the literature showing that other agents and drugs have antioxidant activity i.

Ibuprofen a non-steroidal anti-inflammatory drug [ ] , acetyl- l -carnitine a natural compound reported to prevent mitochondrial injury deriving from oxidative damage in vivo , α-lipoic acid given alone or in combination with acetyl- l -carnitine [ ] , and centrophenoxine a potent nootropic agent that acts as an antioxidant [ ] were demonstrated to enhance GSH levels and CAT and SOD activity and to decrease lipid peroxidation in investigated brain regions in a rat rotenone model Table 6.

Prevention of oxidative damage and the presence of antioxidant defense biomarkers have been documented following treatment with natural compounds, such as lycopene [ ], aqueous extract of tomato seeds TSE [ ], and melatonin [ ].

Many different agents may improve antioxidant brain status in different PD models. However, it should be noted that most of these agents were given before or concomitantly with rotenone, MPTP, or other PD-causing toxins. To definitively answer whether these agents can also show efficacy in reducing the consequences of exposure to prior administration of PD-inducing toxins, further studies are required.

This is especially true because the latter type of drug administration would be a better model for evaluating any pharmacological strategy for reducing OS in PD patients.

Most anti-parkinsonian drugs may improve brain antioxidant status in PD preclinical tests Table 7. Ropinirole, a second-generation, non-ergoline dopamine receptor agonist with D2-like receptor selectivity and a chemical structure similar to that of dopamine was found to enhance GSH levels and CAT [ ] activity and to diminish nitrate levels [ ] in the striatum in MPTP-lesioned animals.

Other anti-parkinsonian drugs, such as selegiline a selective irreversible MAO-B inhibitor [ ], deferoxamine [ ], and pramipexole a non-ergoline dopamine agonist [ ], increased GSH levels in the striatum, SN, or cortex. Deferoxamine also decreased a protein oxidative damage biomarker [ ] and enhanced SOD activity in the striatum, while selegiline reduced superoxide anion generation SAG and increased CAT activity in midbrain regions and the cortex [ ].

Interestingly, l -DOPA, the most commonly used drug in PD treatment, did not restore the reduced GSH levels in the SN in the MPTP mouse model [ ]. The above studies suggest that antiparkinsonian drugs, with the exception of l -DOPA, display some antioxidant properties, which may be considered as part of their mode of action and efficacy in PD treatment.

AD is the most common neurodegenerative disease and is characterized by memory loss, dysfunctions in cognitive abilities e. The pathogenesis of AD is not yet clearly understood.

The aggregation of extracellular insoluble protein plaques composed of beta amyloid Aβ and intracellular neurofibrillary tangles NFTs, composed of tau protein are critical hallmarks of AD [ , ]. However, many ongoing pathological processes lead to regional neuron loss, beginning in the medial temporal lobe [ ] and following in other brain regions, such as the hippocampus and cerebral cortex [ ].

Many clinical trials and animal studies have recognized free radicals as mediators of injury in AD patients and AD models. The first report of the involvement of OS in AD pathology came from a paper by Martins et al. The latter increase was proposed to be a response to enhanced brain peroxide metabolism.

Other post-mortem studies on brains and CSF from AD patients showed ROS-mediated injuries. For instance, AD patients had increased levels of MDA and HNE, iso- and neuroprostanes, and acrolein compared to controls [ ]. It was suggested that these peroxidated lipids formed adducts with proteins and that they might thereby play a role in AD pathogenesis [ ].

In addition to lipids, protein damage due to OS has also been reported in AD. In fact, increased PC levels in the frontal and parietal cortices and the hippocampus were found in post-mortem studies of the brains of AD patients, while PC was absent in the cerebellum, where no AD pathology was present [ ].

Furthermore, evidence of oxidative DNA modification was found in AD patients as an increase in 8-OHG in human brain homogenates [ ]. In AD patients, ROS production seems to be enhanced; furthermore, increases in RNS were also detected. Such evidence of RNS modification was identified both in astrocytes and in neurons in AD patient brains examined post-mortem [ ].

The changes in astrocytes were found to co-localize with an increase in iNOS, eNOS, and nNOS expression. The latter increases were noted specifically in cortical pyramidal cells [ ].

In another study, increased expression of iNOS and eNOS was observed to be directly associated with Aβ deposits, showing that beta amyloid might induce NOS to produce NO, which might lead to 3-NT formation [ ]. The presence of 3-NT was also reported in the cerebral blood vessels of AD patients post-mortem [ ].

These findings were associated with reduced NO bioavailability in plasma and further hypoperfusion in AD patients because NO promotes vascular smooth muscle relaxation and thereby regulates blood flow.

Another set of oxidative damage biomarkers, 8-OHdG and 8-OHG, were elevated in AD ventricular CSF [ ] and in brains in both mitochondrial and nuclear DNA compared with age-matched controls [ ]. Consistent data showing enhanced levels of MDA, HNE, iso- and neuroprostanes, acrolein, PC, 8-OHG, 8-OHdG, and 3-NT in the CNS of AD patients can be considered to be proof that OS and NOS are significant contributors to brain damage.

Pivotal antioxidant enzymes, including GPx, CAT, and SOD, display changed levels in the brains of AD patients [ , ]. However, the data are not consistent. For instance, elevated levels of antioxidant enzymes mainly SOD in the hippocampus and amygdala of AD patients have been reported [ ].

On the other hand, in AD patients, decreased levels of SOD, GPx, and CAT were found in the frontal and temporal cortex [ ], while decreases in GSH were observed in the brain and erythrocytes of AD patients [ , ].

Evidence in support of changes in antioxidant enzymes comes from a recent study that identified genetic polymorphisms in the GPx - 1 and GST genes that were positive risk factors for AD [ , ]. The GSH levels were reduced not only in AD but also in mild cognitive impairment MCI , which is considered to be a preclinical stage of AD [ ].

The plasma levels of antioxidants, such as albumin, bilirubin, uric acid, lycopene, vitamin A, vitamin C, and vitamin E, are decreased in AD patients [ , ], although there are some reports indicating the opposite direction of these changes [ ].

Differences in results might be caused by measurement of antioxidants at different disease stages fully developed disease vs. subclinical stage of the disease [ — ].

As OS is present in AD patients, some clinical studies have aimed to test the ability of antioxidant substances to diminish ROS production and to alleviate or to slow the course of the disorder Table 8. Most studies on the effects of the administration of vitamins that possess antioxidant activity have provided inconclusive information showing that they diminished lipid peroxidation in CSF but had no positive effects on cognitive or functional aspects.

Although the latter study suggests that vitamin E can have a positive influence on AD, no OS biomarkers have been measured in parallel in the AD patients who participated in that trial, which limits the final conclusion. Administration of other antioxidants, including coenzyme Q10 as well as its synthetic analogue, idebenone which possesses a better ability to pass the blood—brain barrier , in AD patients did not provide any positive results with regards to the volume of ROS-dependent tissue damage or cognitive function improvements [ , ].

Different results were reported in a recent study, where month ω-3 fatty acid supplementation caused a delay in progression of functional impairment in AD patients, while combined supplementation of ω-3 and α-lipoic acid resulted in slowing global cognitive declines MMSE [ ].

Although positive cognitive outcomes were obtained, no changes after ω-3 or ω-3 plus α-lipoic acid supplementation were observed in OS biomarkers, suggesting a different mechanism for their actions that lead to improved cognitive and functional measures [ ].

Curcumin, which is a natural polyphenolic compound and an in vitro blocker of Aβ aggregation, did not diminish the enhancement of F2-isoprostane levels in the CSF [ ] or plasma [ ], or the Aβ 1—40 level in plasma [ ], and it did not ameliorate neuropsychological test results in AD patients [ , ].

As suggested by Ringman et al. There is some hope that curcumin efficacy can be improved through the use of its lipidated forms, which are predicted to have better uptake compared to the nonlipidated form [ ]. More promising results came from a study using resveratrol.

The Copenhagen City Heart Study reported that monthly or weekly consumption of red wine was associated with a lower risk of dementia [ ]. gov record accessed 15 May , the study has been completed, but no results have yet been published.

Acetylcholinesterase AChE inhibitors donepezil, rivastigmine, galantamine, and tacrine and the NMDA receptor antagonist memantine are the most commonly used drugs in AD pharmacotherapy.

Only some clinical studies that have investigated the influence of these drugs on oxidative balance in AD patients are currently available see Table 9. One of them showed no positive effects of AChE inhibitors on OS parameters CAT and GR levels in the blood of AD patients compared with AD drug-naïve patients [ ].

In another study, donepezil enhanced GSH levels, while rivastigmine diminished advanced glycation end products AGEs in the plasma of AD patients. However, other examined parameters, namely total antioxidant capacity TAC and PC, have not been improved by those drugs [ ].

Combined therapy with memantine and donepezil failed to improve GSH, TAC, PC, or AGEs [ ]. A very recent study revealed that 6-month treatment with memantine decreased the oxidation rate of plasma lipids in AD patients compared with untreated patients [ ].

The above clinical trials included small sample sizes and should initiate future examinations evaluating the effect of different types of AD medications on OS markers in AD patients. AD can be modeled by several procedures in animal. Injection with scopolamine i. For detailed descriptions of AD animal models, see [ — ].

In both pharmacological and genetic models of AD, disordered OS biomarkers are present in animal brains Table Oxidative modification of proteins has also been demonstrated in the cortex and whole brain homogenate of transgenic AD mice [ , ] and in the cerebral cortex and hippocampus of an Aβ mouse model [ ].

In addition to OS due to oxygen, there is also proof of the presence of NS in whole brain lysates from the APP23 transgenic AD mouse model [ ]. Antioxidant defense biomarkers have been found to be changed in AD models see Table Diminished levels of GSH in the cerebral cortex or hippocampus or in whole brain lysates have been demonstrated in pharmacologically induced AD animal models [ , , , , , , , ].

Furthermore, the activities of enzymes connected with GSH metabolism, such as GPx and GR, and the enzymes involved in antioxidant defense SOD and CAT were reduced in the hippocampus and cerebral cortex in pharmacological and genetic models [ , , , , , — ]. It should be noted that some studies demonstrated no change in CAT and SOD activity in whole brain lysates in Wistar rats in the streptozotocin model [ ], while enhanced SOD, GPx, and GR were observed in the mouse cerebral cortex and hippocampus following i.

Aβ injection [ ]. It is also important to mention that in transgenic models, the changes depend on animal age. Several preclinical studies on AD have shown that many antioxidants can both diminish OS and improve cognitive impairments Table Among different compounds of special interest are vitamin E, vitamin C, and α-lipoic acid.

Vitamin E given 7 days before Aβ decreased MDA and protein carbonyls in the mouse hippocampus and cortex [ ].

Similarly, α-lipoic acid enrichment decreased HNE levels in AbPP Tg mouse brains but did not decrease 3-NT levels [ ]. In AbPP Tg mice that overexpress a mutant form of APP beta amyloid βA , an A4 precursor protein and show impaired learning, an R-α-lipoic acid-enriched diet, administered for 10 months, decreased HNE levels in total brain homogenates and also attenuated HNE protein adducts that accumulated around amyloid deposits in the hippocampal and cortical region, but it had little effect on cognitive performance and brain Aβ load.

This latter study seems to suggest that a long-term antioxidant therapy that reduced oxidative modifications provided a limited benefit [ ].

The lack of effect of vitamin C on Aβ plaque deposits seems to result from the late introduction of medication in this test because Aβ plaques, considered an end point in the disease process, are detectable in these mice at 4—5 months, which was before the beginning of the test [ ].

It is also possible that ascorbate had an effect on soluble Aβ [ ]. This latter observation led to the conclusion that vitamin C may not be an anti-OS medication per se, but its deficiency in AD patients may lead to oxidative damage.

Interestingly, another study showed that the long-lasting incretin hormone analogue d -Ala 2 GIP glucose-dependent insulinotropic polypeptide was able to decrease OS biomarkers i. Many natural compounds that possess antioxidant properties have been tested in animal models as AD treatments.

Imperatorin and hesperidin diminished brain damage due to OS, and most of them enhanced the power of oxidative defenses [ — , ]. Moreover, meloxicam an anti-inflammatory drug and selegiline, given alone or in combination, inhibited lipid peroxidation, prevented a decrease in CAT activity, and showed memory-enhancing capacity in a scopolamine AD model [ ].

Another compound, S -allyl cysteine, which is a sulfur-containing amino acid that was reported to have antioxidant and neurotrophic activity, prevented cognitive and neurobehavioral impairments, prevented ROS damage in the hippocampus, and augmented endogenous antioxidant enzymes in a streptozocin AD model [ ].

Similar results were obtained when melatonin was given chronically to a genetic AD mouse model, as the drug alleviated OS and enhanced GSH levels [ , ].

Moreover, results from Feng et al. As shown above, results from animal AD models that have used various pharmacological compounds to reduce OS and to alleviate memory deficits in AD are promising but do not yet parallel the results obtained in clinical trials.

For example, tacrine, the first anticholinesterase inhibitor approved by the Food and Drug Administration FDA , was shown to suppress OS in an animal AD model [ ].

The effect of tacrine may therefore be considered to be positive when this drug is used in doses that stimulate the antioxidant system without inducing oxidative damage in brain tissue [ ].

However, donepezil, when given in a similar dose of 2. Those contradictory results come from studies using non-transgenic and transgenic animal AD models, which means that the multiple adaptations developed for use in these transgenic animals could be the reason for the observed difference in outcomes.

Another medication used in AD treatment is rivastigmine. This drug neither attenuated lipid peroxidation nor restored GSH depletion in the brains of rats in an AD model [ ], although an older study indicated antioxidant properties for rivastigmine when AD was induced in rats by aluminum chloride administration [ ].

Such differences in the effects of rivastigmine might be caused either by differences in the AD model used in the study aluminum chlorate p. colchicine i. models or by differences in the rivastigmine dose regimen 0.

for 28 days. Based on the above scant reports, it is too soon to either confirm or exclude rivastigmine as an effective OS scavenger in AD. A single report showed the ability of another AChE inhibitor, galantamine, to reduce OS. In a cognitive impairment animal model, galantamine decreased lipid peroxidation, nitrate, and GSSG levels, enhanced SOD activity, and impaired GSH levels following kainic acid intrahippocampal injection, and it restored cognitive deficits as well [ ].

Memantine has also been widely studied in preclinical AD models. For example, it was shown that memantine reduced oxidative damage to proteins in the cortex and hippocampus but not in the striatum, resulting in the reversal of concomitant age-induced recognition memory deficits in aged rats [ ].

Other studies found that memantine diminished the level of inducible forms of NOS in an Αβ 25—35 AD model [ ] and ROS and nitrate levels in the hippocampus and cortex in a streptozotocin AD model [ ] and in a kainic acid-induced model of dementia [ ].

However, memantine was shown to have neuroprotective properties not only in AD models but also in 3-nitropropionic acid [ ], rotenone [ ], and diisopropylphosphorofluoridate DFP toxicity models [ ]. There is a wide range of evidence showing that several drugs used to treat AD have antioxidant properties, suggesting that at least part of their efficacy in animal models may come from that action.

In general, the presence of OS in the pathophysiology of many neurodegenerative disorders, including ALS, PD, and AD, is a well-recognized phenomenon. The results of many in vitro and in vivo preclinical and clinical studies have consistently demonstrated that OS is one of the crucial players in the degeneration that occurs in the nervous system.

The imbalance between OS and antioxidant defense systems seems to be a universal condition in neurodegeneration.

However, what can be surprising is that the results of many studies often provide different results when trying to determine the exact mechanisms that underlie OS and to determine which of the markers of OS could be clinically useful.

What has been shown to be elevated in one study does not necessarily have to rise in another. In preclinical studies, these divergent results could be explained by the use of different models, different species, or different methodologies. As for the clinical setting, it must be stressed that the number of patients available for study is usually small because they are in different stages of their diseases, there are often coexisting comorbidities, and, last but not least, they often take many other medications with different pro- or antioxidant properties.

The analysis of potential biomarkers under these conditions is extremely difficult. Therefore, assessing the real efficacy of potential antioxidant drugs is a challenge. However, there are some data, if even modest, that some of the existing drugs possess anti-oxidant properties and that they could slow down neurodegenerative processes and improve our understanding of the significance of OS in the pathobiology of these untreatable conditions.

The results of clinical and preclinical studies have demonstrated the presence of elevated levels of OS biomarkers as well as impairments to antioxidant defenses in the brain and peripheral tissues in PD, AD, and ALS. As the currently available therapies for these neurodegenerative diseases are not sufficiently effective for treating disease symptoms, novel substances are searched for.

Most such drugs have so far failed to slow down the progression of the disease or to prolong the lives of patients. Some exceptions within these anti-neurodegenerative drugs exist, and they give hope and inspire further research.

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focus on protein-centered radicals. Biochim Biophys Acta - Gen Subj — Cozzolino M, Carrì MT Mitochondrial dysfunction in ALS. Prog Neurobiol — GAPDH plays a crucial role in glycolysis, the metabolic pathway that produces energy by metabolising glucose molecules to generate adenosine triphosphate ATP molecules, the main carrier of energy in cells.

GAPDH is widely distributed in tissues and, in addition to its metabolic function, it plays a role in other vital tasks, including DNA repair, regulation of gene expression, and controlled cell death, or apoptosis. All enzymes are polymeric chains of amino acids, arranged according to a specific sequence known as primary structure.

Through electrostatic and covalent bonding, these chains acquire a characteristic three-dimensional shape, which includes secondary structures, such as alpha helices and beta sheets. The overall three-dimensional shape is known as the tertiary structure. Proteins can also form complexes with other protein chains quaternary structure.

The cellular environment and selective modifications influence the tertiary structure of each component. These modifications enable interactions with other proteins, promoting essential communication and signalling functions within and between cells. GAPDH is a tetramer, a group of four identical subunits each of which contains one active site — where the enzyme reaction takes place.

If the ability of GAPDH to carry out this chemical reaction is compromised, the cell looses its functionality. When a neurone is under stress, GAPDH can undergo chemical modifications, such as oxidation and nitrosylation, which shift its physiological function from a metabolic enzyme to a signalling molecule.

These modifications promote the interaction of GAPDH with chaperone proteins, which assist its translocation from the cytoplasm to key intracellular organelles such as the nucleus [2] and mitochondria [3].

The nucleus is responsible for orchestrating maintenance and repair of cell structures and function, while mitochondria produce the cells energy supply in the form of ATP. As we age, apoptosis slowly diminishes our complement of neurones.

At present, the molecular signals that trigger neurodegeneration are poorly understood, and is the subject of intense research into identifying probable causes at the molecular level to target with novel pharmaceuticals.

Although translocation of oxidised GAPDH to cellular organelles is known to play a crucial role in apoptosis, we do not know to what extent dysregulation of this process contributes to neurodegenerative diseases. To address this question, it is first necessary to study and understand how GAPDH is conformationally modified by oxidation to trigger binding to its molecular chaperones.

Using a combination of experimental techniques and computer simulations, Hyslop and Chaney have investigated the details of the mechanism through which H 2 O 2 influences both the ability of GAPDH to supply energy to neurons via the metabolism of glucose, and to bind to signalling chaperone proteins.

Their approach starts from careful biochemical measurements resulting from chemical modifications following H 2 O 2 oxidation of commercially purified GAPDH, and then applying these modifications directly to the native GAPDH crystal structure. Based on the work of others, oxidation of GAPDH and its translocation to the mitochondria also promotes the production of H 2 O 2 , further increasing the level of cellular oxidative stress.

Cells use antioxidants to counteract the destructive effects of reactive oxygen species. Glutathione is one such molecule that can protect the GAPDH catalytic cysteine residue from oxidation by H 2 O 2 , forming S-glutathionylated GAPDH.

The process is reversible, allowing fully functional GAPDH to be regenerated with the help of a second glutathione molecule directly or with the help of glutathione transferase enzymes.

Figure 1. Cartoon representation of GAPDH enzyme subunit using the crystal structures modified by both H 2 O 2 oxidation and S—glutathionylation.

The S-loop region is a potential site for binding of oxidised GAPDH with other cellular proteins to form complexes involved in cell signalling events. B The same analysis was performed as in panel A , except that the native subunit was superposed with S-glutathionylated subunit.

Importantly, there are clear differences between the structural features between the H 2 O 2 -oxidised and S-glutathionylated structures, indicating that the two modifications to GAPDH potentially interact with different cellular proteins that mediate different signalling events.

In both cardiovascular and neurodegenerative diseases S-glutathionylated GAPDH has been shown to accumulate in tissue and blood.

It is also known that following either ischaemic injury or oxidative stress to isolated cells, GAPDH function is inhibited and can account for the inhibition of metabolic energy available to the cell from glucose.

Hyslop and collaborators were puzzled by this observation, and how it might tie into the role of GAPDH as an integral participant in both providing cells with metabolic energy, available to the cell from glucose, and its role in apoptosis.

In a recently published companion study, they discovered important clues to this question. When the active site cysteine of GAPDH is S-glutathionylated, S-glutathione binds tightly with neighbouring amino acids within the active site pocket, effectively inhibiting its removal and reactivation of and its role in apoptosis, providing insights to its role in inhibition of glucose metabolism and its accumulation in cardiovascular and neurodegenerative diseases.

Using the same techniques of molecular dynamic simulation, the energy minimised structure of S-glutathionylated GAPDH shows that H 2 O 2 oxidation of both the catalytic and neighbouring cysteines glycolysis block and apoptosis and S-glutathionylation of the H 2 O 2 oxidised catalytic cysteine glycolysis block affect the structure of GAPDH in subtly different ways.

However, the final structure of the two modified GAPDH subunits are significantly different in the two cases. A superposition of the structure of a subunits of native and H 2 O 2 oxidised GAPDH figure 1A and native and S-glutathionylated GAPDH figure 1B with the native enzyme structure shows substantial differences in the orientation of the S-loop.

As a visual guide the colour-coded tryptophane residue side-chain is added to the subunit backbone to illustrate change in the overall conformation of the protein. On one hand, only in the case of GAPDH with both catalytic and neighbouring cysteines oxidised, do these binding events lead to apoptosis.

S-glutathionylated GAPDH on the other hand could signal to the cell nucleus that a condition of oxidative stress exists, and countermeasures to promote neuronal survival are activated.

The conclusions of these findings are that GAPDH is key to understanding the intersection of oxidative stress, energy metabolism, and apoptosis and how cell fate decisions are guided. These findings provide novel insight into the biochemical phenomena leading to neurodegeneration in the brain.

The use of computer simulations also makes it possible to study in silico how chemical modification of GAPDH can increase its resistance to oxidative stress.

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