Chapter 7 Protein Oxidation Processes in Aging Brain

Detection of carbonylated proteins in two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis separations

Protein carbonyls are an index of protein oxidation which, in turn, reflects the interplay of oxidative stress and degradation of oxidatively modified proteins. Protein carbonyls are increased in brain proteins in aging and age-related neurodegenerative disorders, including Alzheimer's disease. In this chapter, we outline methods to detect protein carbonyls following two dimensional-based separation of brain proteins.

Roles of amyloid beta-peptide-associated oxidative stress and brain protein modifications in the pathogenesis of Alzheimer's disease and mild cognitive impairment

Oxidative stress has been implicated to play a crucial role in the pathogenesis of a number of diseases, including neurodegenerative disorders, cancer, and ischemia, just to name a few. Alzheimer disease (AD) is an age-related neurodegenerative disorder that is recognized as the most common form of dementia. AD is histopathologically characterized by the presence of extracellular amyloid plaques, intracellular neurofibrillary tangles, the presence of oligomers of amyloid beta-peptide (Abeta), and synapse loss. In this review we discuss the role of Abeta in the pathogenesis of AD and also the use of redox proteomics to identify oxidatively modified brain proteins in AD and mild cognitive impairment. In addition, redox proteomics studies in in vivo models of AD centered around human Abeta(1-42) are discussed.

Proteomic identification of nitrated brain proteins in amnestic mild cognitive impairment: a regional study

Oxidative stress is an imbalance between the level of antioxidants and oxidants in a cell. Oxidative stress has been shown in brain of subjects with mild cognitive impairment (MCI) as well Alzheimer's disease (AD). MCI is considered as a transition phase between control and AD. The focus of the current study was to identify nitrated proteins in the hippocampus and inferior parietal lobule (IPL) brain regions of subjects with amnestic MCI using proteomics. The identified nitrated proteins in MCI brain were compared to those previously reported to be nitrated and oxidatively modified in AD brain, a comparison that might provide an invaluable insight into the progression of the disease.

Acrolein induces selective protein carbonylation in synaptosomes

Acrolein, the most reactive of the alpha,beta-unsaturated aldehydes, is endogenously produced by lipid peroxidation, and has been found increased in the brain of patients with Alzheimer's disease. Although it is known that acrolein increases total protein carbonylation and impairs the function of selected proteins, no study has addressed which proteins are selectively carbonylated by this aldehyde. In this study we investigated the effect of increasing concentrations of acrolein (0, 0.005, 0.05, 0.5, 5, 50 microM) on protein carbonylation in gerbil synaptosomes. In addition, we applied proteomics to identify synaptosomal proteins that were selectively carbonylated by 0.5 microM acrolein. Acrolein increased total protein carbonylation in a dose-dependent manner. Proteomic analysis (two-dimensional electrophoresis followed by mass spectrometry) revealed that tropomyosin-3-gamma isoform 2, tropomyosin-5, beta-actin, mitochondrial Tu translation elongation factor (EF-Tu(mt)) and voltage-dependent anion channel (VDAC) were significantly carbonylated by acrolein. Consistent with the proteomics studies that have identified specifically oxidized proteins in Alzheimer's disease (AD) brain, the proteins identified in this study are involved in a wide variety of cellular functions including energy metabolism, neurotransmission, protein synthesis, and cytoskeletal integrity. Our results suggest that acrolein may significantly contribute to oxidative damage in AD brain.

Oxidative stress in the aging murine olfactory bulb: redox proteomics and cellular localization

A recent proteomics analysis from our laboratory demonstrated that several oxidative stress response proteins showed significant changes in steady-state levels in olfactory bulbs (OBs) of 20- vs. 1.5-month-old mice. Oxidative stress may result in protein oxidation. In this study, we investigated two forms of protein oxidative modification in murine OBs: carbonylation and nitration. Redox proteomics with two-dimensional gel electrophoresis, Western blotting, protein digestion, and mass spectrometry was used to quantify total and specific protein carbonylation and to identify differentially carbonylated proteins and determine the carbonylation status of previously identified proteins in OBs of 1.5- and 20-month-old mice. Immunohistochemistry was used to demonstrate the relative intensity and localization of protein nitration in OBs of 1.5-, 6-, and 20-month-old mice. Total protein carbonylation was significantly greater in OBs of 20- vs. 1.5-month-old mice. Aldolase 1 (ALDO1) showed significantly more carbonylation in OBs from 20- vs. 1.5-month-old mice; heat shock protein 9A and dihydropyrimidinase-like 2 showed significantly less. Several previously investigated proteins were also carbonylated, including ferritin heavy chain (FTH). Nitration, identified by 3-nitrotyrosine immunoreactivity, was least abundant at 1.5 months, intermediate at 6 months, and greatest at 20 months and was localized primarily in blood vessels. Proteins that were specific targets of oxidation were also localized: ALDO1 in astrocytes of the granule cell layer and FTH in mitral/tufted cells. These results indicate that specific carbonylated proteins, including those in astrocytes and mitral/tufted neurons, and nitrated proteins in the vasculature are molecular substrates of age-related olfactory dysfunction.

Difluoromethylornithine decreases long-lasting protein oxidation induced by neonatal ethanol exposure in the hippocampus of adolescent rats

BACKGROUND

Ethanol exposure and withdrawal during central nervous system development can cause oxidative stress and produce severe and long-lasting behavioral and morphological alterations in which polyamines seem to play an important role. However, it is not known if early ethanol exposure causes long-lasting protein oxidative damage and if polyamines play a role in such a deleterious effect of ethanol.

METHODS

In this study we investigated the effects of early ethanol exposure (6 g/kg/d, by gavage), from postnatal day (PND) 1 to 8, and of the administration of difluoromethylornithine (DFMO, 500 mg/kg, i.p., on PND 8), a polyamine biosynthesis inhibitor, on the extent of oxidative modification of proteins. Indices of oxidative modification of proteins included protein carbonyls, 3-nitrotyrosine (3-NT), and protein bound 4-hydroxynonenal (HNE) in the hippocampus, cerebellum, hypothalamus, striatum, and cerebral cortex of Sprague-Dawley rats at PND 40.

RESULTS

Both ethanol and DFMO administration alone increased protein carbonyl immunoreactivity in the hippocampus at PND 40, but the combination of DFMO and ethanol resulted in no effect on protein carbonyl levels. No alterations in the content of protein-bound HNE, 3-NT, or carbonyl were found in any other cerebral structure.

CONCLUSIONS

These results suggest that the hippocampus is selectively affected by early ethanol exposure and by polyamine synthesis inhibition. In addition, the results suggest a role for polyamines in the long-lasting increase of protein carbonyls induced by ethanol exposure and withdrawal.

Extensive feeding versus oleic acid and tocopherol enriched mixed diets for the production of Iberian dry-cured hams: Effect on chemical composition, oxidative status and sensory traits

The present study aimed to analyse the chemical composition and oxidative status of Iberian dry-cured hams from pigs fed different finishing diets: extensive feeding on acorns and pasture in a "Montanera" traditional system (MON), fed in confinement with a mixed diet containing high-oleic sunflower oil (115g/kg of diet) and supplemented with 250mg/kg α-tocopherol (HOVE), and fed in confinement control mixed diet (CON) without added tocopherol and oleic acid fat. Muscles from MON dry-cured hams contained significantly (p<0.05) higher amounts of intramuscular fat (IMF) than those from HOVE and CON hams. The feeding background affected the tocopherol levels in dry-cured hams as those from MON and HOVE pigs had significantly higher levels of α-tocopherol than those from CON pigs whereas the extensive feeding provided muscles from MON pigs with significantly higher levels of γ-tocopherol than the experimental diets did to CON and HOVE pigs. The HOVE diet significantly increased the levels of oleic acid in Iberian dry-cured hams with these levels being similar to the oleic acid levels found in MON hams and significantly higher than those in CON hams. Compared to dry-cured hams from CON pigs, those from MON and HOVE pigs exhibited a higher oxidative stability as a likely result of a most favourable fatty acid composition and the presence of higher tocopherol levels. The principal component analysis (PCA) successfully discriminated between dry-cured hams from pigs fed different finishing diets.

Oxidatively-modified and glycated proteins as candidate pro-inflammatory toxins in uremia and dialysis patients

End stage renal disease (ESRD) patients accumulate blood hallmarks of protein glycation and oxidation. It is now well established that these protein damage products may represent a heterogeneous class of uremic toxins with pro-inflammatory and pro-oxidant properties. These toxins could be directly involved in the pathogenesis of the inflammatory syndrome and vascular complications, which are mainly sustained by the uremic state and bioincompatibility of dialysis therapy. A key underlying event in the toxicity of these proteinaceous solutes has been identified in scavenger receptor-dependent recognition and elimination by inflammatory and endothelial cells, which once activated generate further and even more pronounced protein injuries by a self-feeding mechanism based on inflammation and oxidative stress-derived events. This review examines the literature and provides original information on the techniques for investigating proteinaceous pro-inflammatory toxins. We have also evaluated therapeutic - either pharmacological or dialytic - strategies proposed to alleviate the accumulation of these toxins and to constrain the inflammatory and oxidative burden of ESRD.

Elevated levels of 3-nitrotyrosine in brain from subjects with amnestic mild cognitive impairment: implications for the role of nitration in the progression of Alzheimer's disease

A number of studies reported that oxidative and nitrosative damage may be important in the pathogenesis of Alzheimer's disease (AD). However, whether oxidative damage precedes, contributes directly, or is secondary to AD pathogenesis is not known. Amnestic mild cognitive impairment (MCI) is a clinical condition that is a transition between normal aging and dementia and AD, characterized by a memory deficit without loss of general cognitive and functional abilities. Analysis of nitrosative stress in MCI could be important to determine whether nitrosative damage directly contributes to AD. In the present study, we measured the level of total protein nitration to determine if excess protein nitration occurs in brain samples from subjects with MCI compared to that in healthy controls. We demonstrated using slot blot that protein nitration is higher in the inferior parietal lobule (IPL) and hippocampus in MCI compared to those regions from control subjects. Immunohistochemistry analysis of hippocampus confirmed this result. These findings suggest that nitrosative damage occurs early in the course of MCI, and that protein nitration may be important for conversion of MCI to AD.

Actin Cys374 as a nucleophilic target of alpha,beta-unsaturated aldehydes

We have recently shown that actin can be modified by the Michael addition of 4-hydroxynonenal to Cys374. Here, we have exposed purified actin at increasing acrolein concentrations and have identified the sites of acrolein addition using LC-ESI-MS/MS. Acrolein reacted with Cys374, His87, His173, and, minimally, His40. Cys374 adduction by both 4-hydroxynonenal and acrolein negligibly affected the polymerization of aldehyde-modified (carbonylated) actin, as shown by fluorescence measurements. Differently, acrolein binding at histidine residues, when Cys374 was completely saturated, inhibited polymerization in a dose-dependent manner. Molecular modeling analyses indicated that structural distortions of the ATP-binding site, induced by four acrolein-Michael adducts, could explain the changes in the polymerization process. Aldehyde binding to Cys374 does not alter significantly actin polymerization because this residue is located in a very flexible region, whose covalent modifications do not alter the protein folding. These data demonstrate that Cys374 represents the primary target site of alpha,beta-unsaturated aldehyde addition to actin in vitro. As Cys374 is a preferential target for various oxidative/nitrosative modifications, and actin is one of the main carbonylated proteins in vivo, these findings also suggest that the highly reactive Cys374 could serve as a carbonyl scavenger of reactive alpha,beta-unsaturated aldehydes and other electrophilic lipids.

Adriamycin-mediated nitration of manganese superoxide dismutase in the central nervous system: insight into the mechanism of chemobrain

Adriamycin (ADR), a potent anti-tumor agent, produces reactive oxygen species (ROS) in cardiac tissue. Treatment with ADR is dose-limited by cardiotoxicity. However, the effect of ADR in the other tissues, including the brain, is unclear because ADR does not pass the blood-brain barrier. Some cancer patients receiving ADR treatment develop a transient memory loss, inability to handle complex tasks etc., often referred to by patients as chemobrain. We previously demonstrated that ADR causes CNS toxicity, in part, via systemic release of cytokines and subsequent generation of reactive oxygen and nitrogen species (RONS) in the brain. Here, we demonstrate that treatment with ADR led to an increased circulating level of tumor necrosis factor-alpha in wild-type mice and in mice deficient in the inducible form of nitric oxide (iNOSKO). However, the decline in mitochondrial respiration and mitochondrial protein nitration after ADR treatment was observed only in wild-type mice, not in the iNOSKO mice. Importantly, the activity of a major mitochondrial antioxidant enzyme, manganese superoxide dismutase (MnSOD), was reduced and the protein was nitrated. Together, these results suggest that NO is an important mediator, coupling the effect of ADR with cytokine production and subsequent activation of iNOS expression. We also identified the mitochondrion as an important target of ADR-induced NO-mediated CNS injury.

An increase in S-glutathionylated proteins in the Alzheimer's disease inferior parietal lobule, a proteomics approach

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by neurofibrillary tangles, senile plaques, and loss of synapses. Many studies support the notion that oxidative stress plays an important role in AD pathogenesis. Previous studies from our laboratory employed redox proteomics to identify oxidatively modified proteins in the AD inferior parietal lobule (IPL) and hippocampus. The proteins were consistent with biochemical or pathological alterations in AD and have been central to further investigations of the disease. The present study focused on the identification of specific targets of protein S-glutathionylation in AD and control IPL by using a redox proteomics approach. For AD IPL, we identified deoxyhemoglobin, alpha-crystallin B, glyceraldehyde phosphate dehydrogenase (GAPDH), and alpha-enolase as significantly S-glutathionylated relative to these brain proteins in control IPL. GAPDH and alpha-enolase were also shown to have reduced activity in the AD IPL. This study demonstrates that specific proteins are sensitive to S-glutathionylation, which most likely is due to their sensitivity to cysteine oxidation initiated by the increase in oxidative stress in the AD brain.

In vivo administration of D609 leads to protection of subsequently isolated gerbil brain mitochondria subjected to in vitro oxidative stress induced by amyloid beta-peptide and other oxidative stressors: relevance to Alzheimer's disease and other oxidative stress-related neurodegenerative disorders

Tricyclodecan-9-yl-xanthogenate (D609) has in vivo and in vitro antioxidant properties. D609 mimics glutathione (GSH) and has a free thiol group, which upon oxidation forms a disulfide. The resulting dixanthate is a substrate for glutathione reductase, regenerating D609. Recent studies have also shown that D609 protects brain in vivo and neuronal cultures in vitro against the potential Alzheimer's disease (AD) causative factor, Abeta(1-42)-induced oxidative stress and cytotoxicity. Mitochondria are important organelles with both pro- and antiapoptotic factor proteins. The present study was undertaken to test the hypothesis that intraperitoneal injection of D609 would provide neuroprotection against free radical-induced, mitochondria-mediated apoptosis in vitro. Brain mitochondria were isolated from gerbils 1 h post injection intraperitoneally (ip) with D609 and subsequently treated in vitro with the oxidants Fe(2+)/H(2)O(2) (hydroxyl free radicals), 2,2-azobis-(2-amidinopropane) dihydrochloride (AAPH, alkoxyl and peroxyl free radicals), and AD-relevant amyloid beta-peptide 1-42 [Abeta(1-42)]. Brain mitochondria isolated from the gerbils previously injected ip with D609 and subjected to these oxidative stress inducers, in vitro, showed significant reduction in levels of protein carbonyls, protein-bound hydroxynonenal [a lipid peroxidation product], 3-nitrotyrosine, and cytochrome c release compared to oxidant-treated brain mitochondria isolated from saline-injected gerbils. D609 treatment significantly maintains the GSH/GSSG ratio in oxidant-treated mitochondria. Increased activity of glutathione S-transferase, glutathione peroxidase, and glutathione reductase in brain isolated from D609-injected gerbils is consistent with the notion that D609 acts like GSH. These antiapoptotic findings are discussed with reference to the potential use of this brain-accessible glutathione mimetic in the treatment of oxidative stress-related neurodegenerative disorders, including AD.

Increase in Mrp1 expression and 4-hydroxy-2-nonenal adduction in heart tissue of Adriamycin-treated C57BL/6 mice

Multidrug resistance-associated protein 1 (MRP1) mediates the ATP-dependent efflux of endobiotics and xenobiotics, including estradiol 17-(beta-d-glucuronide), leukotriene C(4), and the reduced glutathione conjugate of 4-hydroxy-2-nonenal (HNE), a highly reactive product of lipid peroxidation. Adriamycin is an effective cancer chemotherapeutic drug whose use is limited by cardiotoxicity. Adriamycin induces oxidative stress and production of HNE in cardiac tissue, which may contribute to cardiomyopathy. We investigated the role of Mrp1 in Adriamycin-induced oxidative stress in cardiac tissue. Mice were treated with Adriamycin (20 mg/kg, i.p.), and heart homogenate and sarcolemma membranes were assayed for Mrp1 expression and ATP-dependent transport activity. Expression of Mrp1 was increased at 6 and 24 hours after Adriamycin treatment compared with saline treatment. HNE-adducted proteins were significantly increased (P < 0.001) in the homogenates at 6 hours after Adriamycin treatment and accumulated further with time; HNE adduction of a 190-kDa protein was evident 3 days after Adriamycin treatment. Mrp1 was localized predominately in sarcolemma as shown by confocal and Western blot analysis. Sarcolemma membrane vesicles transported leukotriene C(4) with a K(m) and V(max) of 51.8 nmol/L and 94.1 pmol/min/mg, respectively, and MK571 (10 micromol/L) inhibited the transport activity by 65%. Exposure of HEK(Mrp1) membranes to HNE (10 micromol/L) significantly decreased the V(max) for estradiol 17-(beta-d-glucuronide) transport by 50%. These results show that expression of Mrp1 in the mouse heart is localized predominantly in sarcolemma. Adriamycin treatment increased Mrp1 expression and HNE adduction of Mrp1. Cardiac Mrp1 may play a role in protecting the heart from Adriamycin-induced cardiomyopathy by effluxing HNE conjugates.

Oxidative stress and toxicity induced by the nucleoside reverse transcriptase inhibitor (NRTI)--2',3'-dideoxycytidine (ddC): relevance to HIV-dementia

Human immunodeficiency virus dementia (HIVD) is the most common form of dementia occurring among young adults. In HIVD, neuronal cell loss occurs in the absence of neuronal infection. With the advent of highly active anti-retroviral therapy (HAART), the incidence of HIVD has drastically reduced, though prevalence of milder forms of HIVD continues to rise. Though these agents have been used successfully in suppressing viral production, they have also been associated with a number of side effects. Here we examine the possible role of NRTIs, in particular 2',3'-dideoxycytidine (ddC), in the neuropathology of HIVD. Synaptosomes and isolated mitochondria treated and incubated for 6 h with CSF-achievable concentrations of ddC, i.e., 6-11 ng/ml, were found to show a significant increase in oxidative stress with 40 nM ddC as measured by protein carbonyls and 3-nitrotyrosine (3NT), effects that were not observed in the more tolerable NRTI, 3TC. Protection against protein oxidation induced by ddC was observed when brain mitochondria were isolated from gerbils 1 h after injection i.p. with the brain accessible antioxidant and glutathione mimetic, tricyclodecan-9-yl-xanthogenate (D609). In addition, there is a significant reduction in the levels of anti-apoptotic protein Bcl-2 and a significant increase in cytochrome c release and also a significant increase in the expression of pro-apoptotic protein caspase-3 after mitochondria were treated with 40 nM ddC. The results reported here show that ddC at 40 nM can induce oxidative stress, cause the release of cytochrome c, and in addition, reduce the levels of anti-apoptotic proteins, increase the levels of pro-apoptotic proteins, thereby increasing the possibility for induction of apoptosis. These findings are consistent with the notion of a possible role of the NRTIs, and in particular, ddC, in the mechanisms involved in HIVD.

Proteomic identification of brain proteins in the canine model of human aging following a long-term treatment with antioxidants and a program of behavioral enrichment: relevance to Alzheimer's disease

Aging and age-related disorders such as Alzheimer's disease (AD) are usually accompanied by oxidative stress as one of the main mechanisms contributing to neurodegeneration and cognitive decline. Aging canines develop cognitive dysfunction and neuropathology similar to those seen in humans, and the use of antioxidants results in reductions in oxidative damage and in improvement in cognitive function in this canine model of human aging. In the present study, the effect of a long-term treatment with an antioxidant-fortified diet and a program of behavioral enrichment on oxidative damage was studied in aged canines. To identify the neurobiological mechanisms underlying these treatment effects, the parietal cortex from 23 beagle dogs (8.1-12.4 years) were treated for 2.8 years in one of four treatment groups: i.e., control food-control behavioral enrichment (CC); control food-behavioral enrichment (CE); antioxidant food-control behavioral enrichment (CA); enriched environment-antioxidant-fortified food (EA). We analyzed the levels of the oxidative stress biomarkers, i.e., protein carbonyls, 3-nitrotyrosine (3-NT), and the lipid peroxidation product, 4-hydroxynonenal (HNE), and observed a decrease in their levels on all treatments when compared to control, with the most significant effects found in the combined treatment, EA. Since EA treatment was most effective, we also carried out a comparative proteomics study to identify specific brain proteins that were differentially expressed and used a parallel redox proteomics approach to identify specific brain proteins that were less oxidized following EA. The specific protein carbonyl levels of glutamate dehydrogenase [NAD (P)], glyceraldehyde-3-phosphate dehydrogenase (GAPDH), alpha-enolase, neurofilament triplet L protein, glutathione-S-transferase (GST) and fascin actin bundling protein were significantly reduced in brain of EA-treated dogs compared to control. We also observed significant increases in expression of Cu/Zn superoxide dismutase, fructose-bisphosphate aldolase C, creatine kinase, glutamate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase. The increased expression of these proteins and in particular Cu/Zn SOD correlated with improved cognitive function. In addition, there was a significant increase in the enzymatic activities of glutathione-S-transferase (GST) and total superoxide dismutase (SOD), and significant increase in the protein levels of heme oxygenase (HO-1) in EA treated dogs compared to control. These findings suggest that the combined treatment reduces the levels of oxidative damage and improves the antioxidant reserve systems in the aging canine brain, and may contribute to improvements in learning and memory. These observations provide insights into a possible neurobiological mechanism underlying the effects of the combined treatment. These results support the combination treatments as a possible therapeutic approach that could be translated to the aging human population who are at risk for age-related neurodegenerative disorders, including Alzheimer's disease.

Propionic acid induces convulsions and protein carbonylation in rats

Propionic acid (PA) accumulates in patients with propionic acidemia, an inherited metabolic disorder caused by the deficiency of propionyl-CoA carboxylase activity that is clinically characterized by neurological dysfunction, including seizures. However, it is not known whether PA causes seizures in experimental animals. In the current study, we investigated whether intrastriatal injection of PA (0.6-6 micromol) causes seizures and alters protein carbonyl content in the striatum of adult rats. The injection of PA caused the appearance of seizures and increased protein carbonyl content in injected and noninjected striata. PA-induced seizures and increased protein carbonylation in the striatum were prevented by the injection of MK-801 (3 nmol/0.5 microL). Our results suggest that PA causes seizures and oxidative damage by NMDA receptor-mediated mechanisms. The involvement of NMDA receptors in the pathogenesis of propionic acidemia is suggested.

Proteomic identification of proteins specifically oxidized in Caenorhabditis elegans expressing human Aβ(1–42): Implications for Alzheimer's disease

Protein oxidation has been shown to lead to loss of protein function, increased protein aggregation, decreased protein turnover, decreased membrane fluidity, altered cellular redox poteintial, loss of Ca2+ homeostaisis, and cell death. There is increasing evidence that protein oxidation is involved in the pathogenesis of Alzheimer's disease and amyloid beta-peptide (1-42) has been implicated as a mediator of oxidative stress in AD. However, the specific implications of the oxidation induced by Abeta(1-42) on the neurodegeneration evident in AD are unknown. In this study, we used proteomic techniques to identify specific targets of oxidation in transgenic Caenorhabditis elegans (C. elegans) expressing human Abeta(1-42). We identified 16 oxidized proteins involved in energy metabolism, proteasome function, and scavenging of oxidants that are more oxidized compared to control lines. These results are discussed with reference to Alzheimer's disease.

Dopaminergic marker proteins in the substantia nigra of human immunodeficiency virus type 1-infected brains

With the advent of highly active antiretroviral therapy, human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) is becoming a more chronic, manageable disease; nevertheless, the prevalence of neurological complications of AIDS is increasing. In this study, protein levels of tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the substantia nigra of HIV-infected brains and -seronegative controls were determined by immunoblotting. The immunoreactivity of neuronal specific enolase (NSE) was used to assess cell loss. Although there were no changes in levels of immunoreactive DAT or NSE proteins in HIV brains, levels of immunoreactive TH were significantly reduced, relative to controls. These results suggest that decreases in TH, the rate-limiting enzyme of dopamine synthesis, may be a factor in the neurological manifestations of HIV infection.

Modification by vitamin E and exercise of oxidative stress in regions of aging rat brain: Studies on superoxide dismutase isoenzymes and protein oxidation status

This study was aimed at determining the effect of exercise and vitamin E on age-associated changes in the superoxide dismutase (SOD), lipid (LPO) and protein oxidations (PO) in the cerebral cortex (CC), cerebellum (CB) and hippocampus (HC) of rat brain. For this, male Wistar albino rats of 4- (adult), 12- (middle-age) and 18-month (old) of age were orally supplemented with vitamin E and swim trained at 3% intensity for 30 min/day, 5 days/week, and for a period of 30 days. Reduced total SOD was evident with age in the CC while it was highest in the HC of old rats. Vitamin E elevated SOD in the old trainees. Mn-SOD increased in the middle-age and old trainees and Cu Zn-SOD increased in the supplemented and trained adults. Age-related and region-specific increase in protein carbonyl (PrC) content with decreased sulphydryl (P-SH) was seen. Vitamin E reduced PrC and advanced oxidation of protein products (AOPP) in all ages, and appreciably in the HC and CB. Our study emphasizes a correlation between mitochondrial H(2)O(2) generation, Mn-SOD activity and MDA level, and reveals in part an age-related increase in lipid peroxidation and protein oxidation, and that may occur under conditions such as vitamin E deficiency.

Oxidative modification and down-regulation of Pin1 in Alzheimer's disease hippocampus: A redox proteomics analysis

Alzheimer disease (AD) is characterized neuropathologically by intracellular neurofibrillary tangles (NFT) and of extracellular senile plaques (SP), the central core of which is amyloid beta-peptide (Abeta) derived from amyloid precursor protein (APP), a transmembrane protein. AD brain has been reported to be under oxidative stress that may play an important role in the pathogenesis and progression of AD. The present proteomics study is focused on identification of a specific target of protein oxidation in AD hippocampus that has relevance to the role of oxidative stress in AD. Here, we report that the protein, Pin1, is significantly down-regulated and oxidized in AD hippocampus. The identity of Pin1 was confirmed immunochemically. Analysis of Pin1 activity in AD brain and separately as oxidized pure Pin1 demonstrated that oxidation of Pin1 led to loss of activity. Pin1 has been implicated in multiple aspects of cell cycle regulation and dephosphorylation of tau protein as well as in AD. The in vivo oxidative modification of Pin1 as found by proteomics in AD hippocampus in the present study suggests that oxidative modification may be related to the known loss of Pin1 isomerase activity that could be crucial in AD neurofibrillary pathology. Taken together, these results provide evidence supporting a direct link between oxidative damage to neuronal Pin1 and the pathobiology of AD.

Proteomics analysis provides insight into caloric restriction mediated oxidation and expression of brain proteins associated with age-related impaired cellular processes: Mitochondrial dysfunction, glutamate dysregulation and impaired protein synthesis

Age-related impairment of functionality of the central nervous system (CNS) is associated with increased susceptibility to develop many neurodegenerative diseases. Increased oxidative stress in the CNS of aged animals is manifested by increased protein oxidation, which is believed to contribute to the age-related learning and memory deficits. Glutamate dysregulation, mitochondrial dysfunction and impaired protein synthesis are observed in aged brains, along with increased protein oxidation. Interestingly, all of these age-related cellular alterations can be improved by caloric restriction (CR), which can also improve the plasticity and recovery of the CNS. Although the beneficial effects of CR on brains are well established, the mechanism(s) of its action remains unclear. In order to gain insight into the mechanism of CR in the brain, we located the brain regions that are benefited the most from reduced oxidative stress by CR. Along with other brain regions, striatum (ST) showed significantly decreased bulk protein carbonyl levels and hippocampus (HP) showed decreased bulk protein 3-nitrotyrosine (3-NT) levels in CR aged rats when compared to those of age matched controls. To determine which proteins were oxidatively modified in these brain regions, we used parallel proteomics approach to identify the proteins that are altered in oxidation and expression. The specific carbonyl levels of pyruvate kinase M2 (PKM2), alpha-enolase (ENO1), inositol monophosphatase (INSP1), and F1-ATPase Chain B (ATP-F1B) were significantly decreased in ST of aged CR rats. In contrast, the expression levels of phosphoglycerate kinase 1 (PKG1), inosine monophosphate cyclohydrolase (IMPCH) and F1-ATPase Chain A (ATP-F1A) were significantly increased in the ST of CR rats. In the hippocampus of CR rats, the specific 3-NT levels of malate dehydrogenase (MDH), phosphoglycerate kinase 1 (PKG1) and 14-3-3 zeta protein were significantly decreased and expression levels of DLP1 splice variant 1 (DLP1), mitochondrial aconitase (ACO2), dihydrolipoamide dehydrogenase (DLDH), neuroprotective peptide H3 (NPH3), and eukaryotic translation initiation factor 5A (eIF-5A) are increased. Moreover, an unnamed protein product (UNP1) with similar sequence to initiation factor 2 (IF-2) was decreased in the HP of CR rats. Our data support the hypothesis that CR induces a mild metabolic stress response by increasing the production of neurotrophic proteins, therefore, priming neurons against apoptosis. Moreover, our study shows that the improvement of glutamate dysregulation, mitochondrial dysfunction and protein synthesis by CR is, at least partially, due to the CR-mediated alteration of the oxidation or the expression of PKM2, ENO1, INSP1, ATP-F1B, PKG1, IMPCH, ATP-F1A MDH, PKG1 and 14-3-3 zeta protein, DLP1, ACO2, DLDH, NPH3, eIF-5A and UNP1. This study provides valuable insights into the mechanisms of the beneficial factors on brain aging by CR.

Quantitative proteomics analysis of differential protein expression and oxidative modification of specific proteins in the brains of old mice

The brain is susceptible to oxidative stress, which is associated with age-related brain dysfunction, because of its high content of peroxidizable unsaturated fatty acids, high oxygen consumption per unit weight, high content of key components for oxidative damage, and the relative scarcity of antioxidant defense systems. Protein oxidation, which results in functional disruption, is not random but appears to be associated with increased oxidation in specific proteins. By using a proteomics approach, we have compared the protein levels and specific protein carbonyl levels, an index of oxidative damage in the brains of old mice, to these parameters in the brains of young mice and have identified specific proteins that are altered as a function of aging. We show here that the expression levels of dihydropyrimidinase-like 2 (DRP2), alpha-enolase (ENO1), dynamin-1 (DNM1), and lactate dehydrogenase 2 (LDH2) were significantly increased in the brains of old versus young mice; the expression levels of three unidentified proteins were significantly decreased. The specific carbonyl levels of beta-actin (ACTB), glutamine synthase (GS), and neurofilament 66 (NF-66) as well as a novel protein were significantly increased, indicating protein oxidation, in the brains of old versus young mice. These results were validated by immunochemistry. In addition, enzyme activity assays demonstrated that oxidation was associated with decreased GS activity, while the activity of lactate dehydrogenase was unchanged in spite of an up-regulation of LDH2 levels. Several of the up-regulated and oxidized proteins in the brains of old mice identified in this report are known to be oxidized in neurodegenerative diseases as well, suggesting that these proteins may be particularly susceptible to processes associated with neurodegeneration. Our results establish an initial basis for understanding protein alterations that may lead to age-related cellular dysfunction in the brain.

REVIEW: Pin1 in Alzheimer's disease

Proteolytic processing and phosphorylation of amyloid precursor protein (APP), and hyperphosphorylation of tau protein, have been shown to be increased in Alzheimer's disease (AD) brains, leading to increased production of beta-amyloid (Abeta) peptides and neurofibrillary tangles, respectively. These observations suggest that phosphorylation events are critical to the understanding of the pathogenesis and treatment of this devastating disease. Pin-1, one of the peptidyl-prolyl isomerases (PPIase), catalyzes the isomerization of the peptide bond between pSer/Thr-Pro in proteins, thereby regulating their biological functions which include protein assembly, folding, intracellular transport, intracellular signaling, transcription, cell cycle progression and apoptosis. A number of previous studies have shown that Pin1 is co-localized with phosphorylated tau in AD brain, and shows an inverse relationship to the expression of tau. Pin1 protects neurons under in vitro conditions. Moreover, recent studies demonstrate that APP is a target for Pin1 and thus, in Abeta production. Furthermore, Pin1 was found to be oxidatively modified and to have reduced activity in the hippocampus in mild cognitive impairment (MCI) and AD. Because of the diverse functions of Pin1, and the discovery that this protein is one of the oxidized proteins common to both MCI and AD brain, the question arises as to whether Pin1 is one of the driving forces for the initiation or progression of AD pathogenesis, finally leading to neurodegeneration and neuronal apoptosis. In the present review, we discuss the role of Pin1 with respect to Alzheimer's disease.

Mutations in amyloid precursor protein and presenilin-1 genes increase the basal oxidative stress in murine neuronal cells and lead to increased sensitivity to oxidative stress mediated by amyloid beta-peptide (1-42), HO and kainic acid: implications for Alzheimer's disease

Oxidative stress is observed in Alzheimer's disease (AD) brain, including protein oxidation and lipid peroxidation. One of the major pathological hallmarks of AD is the brain deposition of amyloid beta-peptide (Abeta). This 42-mer peptide is derived from the beta-amyloid precursor protein (APP) and is associated with oxidative stress in vitro and in vivo. Mutations in the PS-1 and APP genes, which increase production of the highly amyloidogenic amyloid beta-peptide (Abeta42), are the major causes of early onset familial AD. Several lines of evidence suggest that enhanced oxidative stress, inflammation, and apoptosis play important roles in the pathogenesis of AD. In the present study, primary neuronal cultures from knock-in mice expressing mutant human PS-1 and APP were compared with those from wild-type mice, in the presence or absence of various oxidizing agents, viz, Abeta(1-42), H2O2 and kainic acid (KA). APP/PS-1 double mutant neurons displayed a significant basal increase in oxidative stress as measured by protein oxidation, lipid peroxidation, and 3-nitrotyrosine when compared with the wild-type neurons (p < 0.0005). Elevated levels of human APP, PS-1 and Abeta(1-42) were found in APP/PS-1 cultures compared with wild-type neurons. APP/PS-1 double mutant neuron cultures exhibited increased vulnerability to oxidative stress, mitochondrial dysfunction and apoptosis induced by Abeta(1-42), H2O2 and KA compared with wild-type neuronal cultures. The results are consonant with the hypothesis that Abeta(1-42)-associated oxidative stress and increased vulnerability to oxidative stress may contribute significantly to neuronal apoptosis and death in familial early onset AD.

Redox proteomics identification of oxidatively modified hippocampal proteins in mild cognitive impairment: Insights into the development of Alzheimer's disease

Mild cognitive impairment (MCI) is generally referred to the transitional zone between normal cognitive function and early dementia or clinically probable Alzheimer's disease (AD). Oxidative stress plays a significant role in AD and is increased in the superior/middle temporal gyri of MCI subjects. Because AD involves hippocampal-resident memory dysfunction, we determined protein oxidation and identified the oxidized proteins in the hippocampi of MCI subjects. We found that protein oxidation is significantly increased in the hippocampi of MCI subjects when compared to age- and sex-matched controls. By using redox proteomics, we determined the oxidatively modified proteins in MCI hippocampus to be alpha-enolase (ENO1), glutamine synthetase (GLUL), pyruvate kinase M2 (PKM2) and peptidyl-prolyl cis/trans isomerase 1 (PIN1). The interacteome of these proteins revealed that these proteins functionally interact with SRC, hypoxia-inducible factor 1, plasminogen (PLG), MYC, tissue plasminogen activator (PLAT) and BCL2L1. Moreover, the interacteome indicates the functional involvement of energy metabolism, synaptic plasticity and mitogenesis/proliferation. Therefore, oxidative inactivation of ENO1, GLUL and PIN1 may alter these cellular processes and lead to the development of AD from MCI. We conclude that protein oxidation plays a significant role in the development of AD from MCI and that the oxidative inactivation of ENO1, GLUL, PKM2 and PIN1 is involved in the progression of AD from MCI. The current study provides a framework for future studies on the development of AD from MCI relevant to oxidative stress.

Elevated protein-bound levels of the lipid peroxidation product, 4-hydroxy-2-nonenal, in brain from persons with mild cognitive impairment

Oxidative damage is a feature of many age-related neurodegenerative diseases, including Alzheimer's disease (AD). 4-Hydroxy-2-nonenal (HNE) is a highly reactive product of the free radical-mediated lipid peroxidation of unsaturated lipids, particularly arachidonic acid, in cellular membranes. In the present study we show for the first time in brain obtained at short postmortem intervals that the levels of HNE are elevated in mild cognitive impairment (MCI) hippocampus and inferior parietal lobules compared to those of control brain. Thus, increased levels of HNE in MCI brain implicate lipid peroxidation as an early event in AD pathophysiology and also suggest that the pharmacologic intervention to prevent lipid peroxidation at the MCI stage or earlier may be a promising therapeutic strategy to delay or prevent progression to AD.

Proteomics analyses of specific protein oxidation and protein expression in aged rat brain and its modulation by L-acetylcarnitine: insights into the mechanisms of action of this proposed therapeutic agent for CNS disorders associated with oxidative stress

Impaired function of the central nervous system (CNS) in aged animals is associated with increased susceptibility to the development of many neurodegenerative diseases. Age-related functional deterioration in brain is consistent with the free radical theory of aging that predicts, among other things, that free radical reactions with and damage to biomolecules, such as proteins and membrane lipid bilayers, leads to loss of neurons and subsequently diminished cognition. These oxidatively modified biomolecules are believed to contribute to the decreased antioxidant content, mitochondrial dysfunction, and impaired plasticity in aged brains. Treatment of rodents with L-acetylcarnitine (LAC; gamma-trimethyl-beta-acetylbutyrobetaine) can improve these functional losses. Although it is well established that administration of LAC can decrease protein oxidation in aged brains, it is not clear which proteins are decreased in their level of oxidation in the brains of aged rats treated with LAC. The current study used a parallel redox proteomics approach to identify the proteins that are oxidized in aged rat cortex and hippocampus of aged rats. Moreover, those proteins that are reduced in oxidation status were identified in aged brains from rats treated in vivo with LAC. The findings are discussed in reference to brain aging and age-related cognitive impairment.

Redox modulation of heat shock protein expression by acetylcarnitine in aging brain: relationship to antioxidant status and mitochondrial function

There is significant evidence to show that aging is characterized by a stochastic accumulation of molecular damage and by a progressive failure of maintenance and repair processes. Protective mechanisms exist in the brain which are controlled by vitagenes and include members of the heat shock system, heme oxygenase-I, and Hsp70 as critical determinants of brain stress tolerance. Given the broad cytoprotective properties of the heat shock response, molecules inducing this defense mechanism appear to be possible candidates for novel cytoprotective strategies. Acetyl-L-carnitine is proposed as a therapeutic agent for several neurodegenerative disorders, and the present study reports that treatment for 4 months of senescent rats with acetyl-L-carnitine induces heme oxygenase-1 as well as Hsp70 and SOD-2. This effect was associated with upregulation of GSH levels, prevention of age-related changes in mitochondrial respiratory chain complex expression, and decrease in protein carbonyls and HNE formation. We hypothesize that maintenance or recovery of the activity of vitagenes may delay the aging process and decrease the risk of age-related diseases. Particularly, modulation of endogenous cellular defense mechanisms via acetyl-L-carnitine may represent an innovative approach to therapeutic intervention in diseases causing tissue damage, such as neurodegeneration.

Protective effect of carnosine during nitrosative stress in astroglial cell cultures

Formation of nitric oxide by astrocytes has been suggested to contribute, via impairment of mitochondrial function, to the neurodegenerative process. Mitochondria under oxidative stress are thought to play a key role in various neurodegenerative disorders; therefore protection by antioxidants against oxidative stress to mitochondria may prove to be beneficial in delaying the onset or progression of these diseases. Carnosine has been recently proposed to act as antioxidant in vivo. In the present study, we demonstrate its neuroprotective effect in astrocytes exposed to LPS- and INFgamma-induced nitrosative stress. Carnosine protected against nitric oxide-induced impairment of mitochondrial function. This effect was associated with decreased formation of oxidatively modified proteins and with decreased up-regulation oxidative stress-responsive genes, such as Hsp32, Hsp70 and mt-SOD. Our results sustain the possibility that carnosine might have anti-ageing effects to brain cells under pathophysiological conditions leading to degenerative damage, such as aging and neurodegenerative disorders.

Low molecular weight thiol amides attenuate MAPK activity and protect primary neurons from Abeta(1-42) toxicity

Oxidative stress caused by various stimuli lead to oxidation of glutathione (GSH), the major redox power of the cell. Amyloid beta [Abeta(1-42)] is one of the key components of senile plaques and is involved in the progress initiation and triggers of Alzheimer's disease (AD). Lower GSH levels correlated with the activation of mitogen-activated proteins kinases (MAPK) have been demonstrated in AD, Parkinson's disease (PD) and other neurodegenerative disorders and have been proposed to play a central role in the deterioration of the aging and neurodegenerative brain. In this study, we evaluated the ability of low molecular weight thiol amides, N-acetyl cysteine amide (AD4) that replenishes GSH levels, N-acetyl glycine cysteine amide (AD7) and N-acetyl-Cys-Gly-Pro-Cys-amide (CB4) to protect primary neuronal culture against the oxidative and neurotoxic effects of Abeta(1-42) and to inhibit cisplatin- and hydrogen-peroxide-induced phosphorylation of two MAP kinases (MAPK), p38 and ERK1/2, in NIH3T3 cells. Cell death induced by Abeta(1-42) in primary neuronal cells was reversed by the thiol amides. Likewise, protein oxidation, loss of mitochondrial function and DNA fragmentation all returned to control levels by pretreatment with the three thiol amides. Elevated phosphorylation of ERK1/2 and p38 induced by cisplatin or H2O2 in NIH3T3 cells was lowered by AD4, AD7 and CB4 in a dose-dependent manner. Taken together, these results suggest that the thiol amides AD4, AD7 and CB4 protect neuronal cells against Abeta(1-42) toxicity by attenuating oxidative stress in correlation with inhibiting the MAPK phosphorylation cascade. These results are consistent with the notion that these small molecular thiol amides may play a viable protective role in the oxidative and neurotoxicity induced by Abeta(1-42) in AD brain.

In vivo protection of synaptosomes by ferulic acid ethyl ester (FAEE) from oxidative stress mediated by 2,2-azobis(2-amidino-propane)dihydrochloride (AAPH) or Fe(2+)/H(2)O(2): insight into mechanisms of neuroprotection and relevance to oxidative stress-related neurodegenerative disorders

Ferulic acid ethyl ester (FAEE) is an ester derivative of ferulic acid, the latter known for its anti-inflammatory and antioxidant properties. Previous studies from our laboratory have shown that ferulic acid protects synaptosomal membrane system and neuronal cell culture systems against hydroxyl and peroxyl radical oxidation. FAEE is lipophilic and is able to penetrate lipid bilayer. Previous studies reported that FAEE reduces Alzheimer's amyloid beta peptide Abeta(1-42)-induced oxidative stress and cytotoxicity in neuronal cell culture by direct radical scavenging and by inducing certain antioxidant proteins. In the present study we tested the hypothesis that FAEE would provide neuroprotection against free radical oxidative stress in vivo. Synaptosomes were isolated from the gerbils that were previously injected intraperitoneally (i.p.) with FAEE or DMSO and were treated with oxidants, Fe(2+)/H(2)O(2) or 2,2-azobis(2-amidino-propane)dihydrochloride (AAPH). Synaptosomes isolated from the gerbil previously injected i.p. with FAEE and treated with Fe(2+)/H(2)O(2) and AAPH showed significant reduction in reactive oxygen species (ROS), levels of protein carbonyl, protein bound 4-hydroxynonenal (HNE, a lipid peroxidation product), and 3-nitrotyrosine (3-NT, another marker of protein oxidation formed by reaction of tyrosine residues with peroxynitrite) compared to Fe(2+)/H(2)O(2) or AAPH induced oxidative stress in synapotosomes isolated from the brain of gerbils that were previously injected with DMSO. The synaptosomes isolated from gerbil pre-injected with FAEE and subsequently treated with AAPH or Fe(2+)/H(2)O(2) showed induction of heme oxygenase (HO-1) and heat shock protein 70 (HSP-70) but reduced inducible nitric oxide synthase (iNOS) levels. These results are discussed with reference to potential use of this lipophilic antioxidant phenolic compound in the treatment of oxidative stress-related neurodegenerative disorders.

The physiology and pathophysiology of nitric oxide in the brain

Nitric oxide (NO) is a molecule with pleiotropic effects in different tissues. NO is synthesized by NO synthases (NOS), a family with four major types: endothelial, neuronal, inducible and mitochondrial. They can be found in almost all the tissues and they can even co-exist in the same tissue. NO is a well-known vasorelaxant agent, but it works as a neurotransmitter when produced by neurons and is also involved in defense functions when it is produced by immune and glial cells. NO is thermodynamically unstable and tends to react with other molecules, resulting in the oxidation, nitrosylation or nitration of proteins, with the concomitant effects on many cellular mechanisms. NO intracellular signaling involves the activation of guanylate cyclase but it also interacts with MAPKs, apoptosis-related proteins, and mitochondrial respiratory chain or anti-proliferative molecules. It also plays a role in post-translational modification of proteins and protein degradation by the proteasome. However, under pathophysiological conditions NO has damaging effects. In disorders involving oxidative stress, such as Alzheimer's disease, stroke and Parkinson's disease, NO increases cell damage through the formation of highly reactive peroxynitrite. The paradox of beneficial and damaging effects of NO will be discussed in this review.

HIV-dementia, Tat-induced oxidative stress, and antioxidant therapeutic considerations

Oxidative stress is thought to play a role in the onset of dementia. HIV-dementia has recently been demonstrated to be associated with oxidative stress as indexed by increased protein and lipid peroxidation in the brain and cerebrospinal fluid compared to HIV non-demented patients. The HIV protein Tat induces neurotoxicity, and, more recently, Tat was found to induce oxidative stress directly and indirectly. The role of Tat in HIV-dementia and possible therapeutic strategies involving endogenous and exogenous antioxidants are discussed.

Protein oxidation by the cytochrome P450 mixed-function oxidation system

This mini-review summarizes results of studies on the oxidation of proteins and low-density lipoprotein (LDL) by various mixed-function oxidation (MFO) systems. Oxidation of LDL by the O2/FeCl3/H2O2/ascorbate MFO system is dependent on all four components and is much greater when reactions are carried out in the presence of a physiological bicarbonate/CO2 buffer system as compared to phosphate buffer. However, FeCl3 in this system could be replaced by hemin or the heme-containing protein, hemoglobin, or cytochrome c. Oxidation of LDL by the O2/cytochrome P450 cytochrome c reductase/NADPH/FeCl3 MFO system is only slightly higher (25%) in the bicarbonate/CO2 buffer as compared to phosphate buffer, but is dependent on all components except FeCl3. Omission of FeCl3 led to a 60% loss of activity. These results suggest that peroxymonobicarbonate and/or free radical derivatives of bicarbonate ion and/or CO2 might contribute to LDL oxidation by these MFO systems.

Proteomic identification of proteins specifically oxidized by intracerebral injection of amyloid beta-peptide (1-42) into rat brain: implications for Alzheimer's disease

Protein oxidation has been shown to result in loss of protein function. There is increasing evidence that protein oxidation plays a role in the pathogenesis of Alzheimer's disease (AD). Amyloid beta-peptide (1-42) [Abeta(1-42)] has been implicated as a mediator of oxidative stress in AD. Additionally, Abeta(1-42) has been shown to induce cholinergic dysfunction when injected into rat brain, a finding consistent with cholinergic deficits documented in AD. In this study, we used proteomic techniques to examine the regional in vivo protein oxidation induced by Abeta(1-42) injected into the nucleus basalis magnocellularis (NBM) of rat brain compared with saline-injected control at 7 days post-injection. In the cortex, we identified glutamine synthetase and tubulin beta chain 15/alpha, while, in the NBM, we identified 14-3-3 zeta and chaperonin 60 (HSP60) as significantly oxidized. Extensive oxidation was detected in the hippocampus where we identified 14-3-3 zeta, beta-synuclein, pyruvate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, and phosphoglycerate mutase 1. The results of this study suggest that a single injection of Abeta(1-42) into NBM can have profound effects elsewhere in the brain. The results further suggest that Abeta(1-42)-induced oxidative stress in rat brain mirrors some of those proteins oxidized in AD brain and leads to oxidized proteins, which when inserted into their respective biochemical pathways yields insight into brain dysfunction that can lead to neurodegeneration in AD.

Protection against amyloid beta-peptide (1–42)-induced loss of phospholipid asymmetry in synaptosomal membranes by tricyclodecan-9-xanthogenate (D609) and ferulic acid ethyl ester: Implications for Alzheimer's disease

Amyloid-beta (1-42) [Abeta (1-42)] deposition in the brain is a hallmark of Alzheimer's disease (AD) and has been shown to induce apoptosis and disrupt cellular ion homeostasis. Abeta (1-42) induces membrane lipid peroxidation, and 4-hydroxynonenal (HNE) and 2-propenal (acrolein) are the two reactive products of lipid peroxidation, which structurally modify proteins by covalent interaction and inhibit enzyme function. Phosphatidylserine (PS), an aminophospholipid, is sequestered in the inner leaflet of the plasma membrane in nonstimulated cells. An early signal of synaptosomal apoptosis is the loss of phospholipid asymmetry and the appearance of phosphatidylserine in the outer leaflet of the membrane. The ATP-requiring enzyme, flippase, maintains phospholipid asymmetry of PS. Here, we have investigated the inactivation of the transmembrane enzyme aminophospholipid-translocase (or flippase) by Abeta (1-42). Flippase activity depends on a critical cysteine residue, a putative site of covalent modification by the Abeta (1-42)-induced lipid peroxidation products, HNE or acrolein. The present study is aimed to investigate the protective effects of tricyclodecan-9-xanthogenate (D609) and ferulic acid ethyl ester (FAEE) on Abeta (1-42) induced modulation in phospholipid asymmetry in the synaptosomal membranes. Pretreatment of synaptosomes with D609 and FAEE significantly protected Abeta (1-42)-induced loss of phospholipid asymmetry in synaptosomal membranes. Our results suggest that D609 and FAEE exert protective effects against Abeta (1-42) induced apoptosis. The increase in intracellular Ca(2+) might not be the sole cause for the loss of flippase activity. Rather, other mechanisms that could modulate the function of flippase might be important in the modulation of phospholipid asymmetry. The results of this study are discussed with relevance to neuronal loss in the AD brain.

Overview of molecular, cellular, and genetic neurotoxicology

It has become increasingly evident that the field of neurotoxicology is not only rapidly growing but also rapidly evolving, especially over the last 20 years. As the number of drugs and environmental and bacterial/viral agents with potential neurotoxic properties has grown, the need for additional testing has increased. Only recently has the technology advanced to a level that neurotoxicologic studies can be performed without operating in a "black box." Examination of the effects of agents that are suspected of being toxic can occur on the molecular (protein-protein), cellular (biomarkers, neuronal function), and genetic (polymorphisms) level. Together, these areas help to elucidate the potential toxic profiles of unknown (and in some cases, known) agents. The area of proteomics is one of the fastest growing areas in science and particularly applicable to neurotoxicology. Lubec et al, provide a review of the potential and limitations of proteomics. Proteomics focuses on a more comprehensive view of cellular proteins and provides considerably more information about the effects of toxins on the CNS. Proteomics can be classified into three different focuses: post-translational modification, protein-expression profiling, and protein-network mapping. Together, these methods represent a more complete and powerful image of protein modifications following potential toxin exposure. Cellular neurotoxicology involves many cellular processes including alterations in cellular energy homeostasis, ion homeostasis, intracellular signaling function, and neurotransmitter release, uptake, and storage. The greatest hurdle in cellular neurotoxicology has been the discovery of appropriate biomarkers that are reliable, reproducible, and easy to obtain. There are biomarkers of exposure effect, and susceptibility. Finding the appropriate biomarker for a particular toxin is a daunting task. The appropriate biomarker for a particular toxin is a daunting task. The advantage to biomarker/toxin combinations is they can be detected and measured shortly following exposure and before overt neuroanatomic damage or lesions. Intervention at this point, shortly following exposure, may prevent or at least attenuate further damage to the individual. The use of peripheral biomarkers to assess toxin damage in the CNS has numerous advantages: time-course analysis may be performed, ethical concerns with the use of human subjects can partially be avoided, procedures to acquire samples are less invasive, and in general, peripheral studies are easier to perform. Genetic neurotoxicology comprises two focuses--toxin-induced alterations in genetic expression and genetic alterations that affect toxin metabolism, distribution, and clearance. These differences can be beneficial or toxic. Polymorphisms have been shown to result in altered metabolism of certain toxins (paraoxonase and paraoxon). Conversely, it is possible that some polymorphisms may be beneficial and help prevent the formation of a toxic by-product of an exogenous agent (resistance to ozone-induced lung inflammation). It has also become clear that interactions of potential toxins are not straightforward as interactions with DNA, causing mutations. There are numerous agents that cause epigenetic responses (cellular alterations that are not mutagenic or cytotoxic). This finding suggests that many agents that may originally have been thought of as nontoxic should be re-examined for potential "indirect" toxicity. With the advancement of the human genome project and the development of a human genome map, the effects of potential toxins on single or multiple genes can be identified. Although collectively, the field of neurotoxicology has recently come a long way, it still has a long way to go reach its full potential. As technology and methodology advances continue and cooperation with other disciplines such as neuroscience, biochemistry, neurophysiology, and molecular biology is improved, the mechanisms of toxin action will be further elucidated. With this increased understanding will come improved clinical interventions to prevent neuronal damage following exposure to a toxin.

Gamma-glutamylcysteine ethyl ester protection of proteins from Abeta(1-42)-mediated oxidative stress in neuronal cell culture: a proteomics approach

Protein oxidation mediated by amyloid beta-peptide (1-42) (Abeta[1-42]) has been proposed to play a central role in the pathogenesis of Alzheimer's disease (AD), a neurodegenerative disorder associated with aging and the loss of cognitive function. The specific mechanism by which Abeta(1-42), the primary component of the senile plaque and a pathologic hallmark of AD, contributes to the oxidative damage evident in AD brain is unknown. Moreover, the specific proteins that are vulnerable to oxidative damage induced by Abeta(1-42) are unknown. Identification of such proteins could contribute to our understanding of not only the role of Abeta(1-42) in the pathogenesis of AD, but also provide insight into the mechanisms of neurodegeneration at the protein level in AD. We report the proteomic identification of two proteins found to be oxidized significantly in neuronal cultures treated with Abeta(1-42): 14-3-3zeta and glyceraldehyde-3-phosphate dehydrogenase. We also report that pretreatment of neuronal cultures with gamma-glutamylcysteine ethyl ester, a compound that supplies the limiting substrate for the synthesis of glutathione and results in the upregulation of glutathione in neuronal cultures, protects both proteins against Abeta(1-42)-mediated protein oxidation.

Gamma-glutamylcysteine ethyl ester-induced up-regulation of glutathione protects neurons against Abeta(1-42)-mediated oxidative stress and neurotoxicity: implications for Alzheimer's disease

Glutathione (GSH) is an important endogenous antioxidant found in millimolar concentrations in the brain. GSH levels have been shown to decrease with aging. Alzheimer's disease (AD) is a neurodegenerative disorder associated with aging and oxidative stress. Abeta(1-42) has been shown to induce oxidative stress and has been proposed to play a central role in the oxidative damage detected in AD brain. It has been shown that administration of gamma-glutamylcysteine ethyl ester (GCEE) increases cellular levels of GSH, circumventing the regulation of GSH biosynthesis by providing the limiting substrate. In this study, we evaluated the protective role of up-regulation of GSH by GCEE against the oxidative and neurotoxic effects of Abeta(1-42) in primary neuronal culture. Addition of GCEE to neurons led to an elevated mean cellular GSH level compared with untreated control. Inhibition of gamma-glutamylcysteine synthetase by buthionine sulfoximine (BSO) led to a 98% decrease in total cellular GSH compared with control, which was returned to control levels by addition of GCEE. Taken together, these results suggest that GCEE up-regulates cellular GSH levels which, in turn, protects neurons against protein oxidation, loss of mitochondrial function, and DNA fragmentation induced by Abeta(1-42). These results are consistent with the notion that up-regulation of GSH by GCEE may play a viable protective role in the oxidative and neurotoxicity induced by Abeta(1-42) in AD brain.

Protective effect of antioxidants on brain oxidative damage caused by proline administration

We have previously demonstrated that acute and chronic hyperprolinemia induce oxidative stress in cerebral cortex of rats. In the present study, we investigated the action of Vitamins E and C on the oxidative damage elicited by acute and chronic administration of proline (Pro) in rat cerebral cortex. Results showed that treatment with Vitamins E and C prevented the alterations caused by acute and chronic administration of proline on chemiluminescence, total radical-trapping antioxidant potential (TRAP) and on the activities of catalase and glutathione peroxidase. If these effects also occur in the human condition, it is possible that antioxidant administration might serve as a potential adjuvant therapy to avoid the progression of the neuropsychiatric dysfunction observed in hyperprolinemic patients.

Searching for the role and the most suitable biomarkers of oxidative stress in Alzheimer's disease and in other neurodegenerative diseases

The contribution of oxidative stress to neurodegeneration is not peculiar of a specific neurodegenerative disease, oxidative stress has been found implicated in a number of neurodegenerative disorders among which Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS). Even increasing are studies dealing with the search for peripheral biomarkers of oxidative stress in biological fluids or even in peripheral tissues themselves such as fibroblasts or blood cells. The application of the modified version of the comet assay for the detection of oxidised purines and pyrimidines in peripheral blood leukocytes results particularly useful if the study requires repeated blood drawn from the same individual, for instance if a clinical trial is performed with a preventive therapy. Likely damage occurs to every category of biological macromolecules and we consider, in the context of neurodegenerative diseases, particularly critical the proteic level. The identification of subjects at risk to develop AD or with pre-pathogenic conditions, the possibility to use "a battery of assays" for the detection of oxidative damage at peripheral level, together with recent advances in brain imaging, will allow to better address studies aimed not only to therapeutic purposes but also mainly to primary prevention.