Evidence of oxidative stress in the neocortex in incidental Lewy body disease

Protein targets of oxidative damage in human neurodegenerative diseases with abnormal protein aggregates

Human neurodegenerative diseases with abnormal protein aggregates are associated with aberrant post-translational modifications, solubility, aggregation and fibril formation of selected proteins which cannot be degraded by cytosolic proteases, ubiquitin-protesome system and autophagy, and, therefore, accumulate in cells and extracellular compartments as residual debris. In addition to the accumulation of "primary" proteins, several other mechanisms are involved in the degenerative process and probably may explain crucial aspects such as the timing, selective cellular vulnerability and progression of the disease in particular individuals. One of these mechanisms is oxidative stress, which occurs in the vast majority of, if not all, degenerative diseases of the nervous system. The present review covers most of the protein targets that have been recognized as modified proteins mainly using bidimensional gel electrophoresis, Western blotting with oxidative and nitrosative markers, and identified by mass spectrometry in Alzheimer disease; certain tauopathies such as progressive supranuclear palsy, Pick disease, argyrophilic grain disease and frontotemporal lobar degeneration linked to mutations in tau protein, for example, FTLD-tau, Parkinson disease and related alpha-synucleinopathies; Huntington disease; and amyotrophic lateral sclerosis, together with related animal and cellular models. Vulnerable proteins can be mostly grouped in defined metabolic pathways covering glycolysis and energy metabolism, cytoskeletal, chaperoning, cellular stress responses, and members of the ubiquitin-proteasome system. Available information points to the fact that vital metabolic pathways are hampered by protein oxidative damage in several human degenerative diseases and that oxidative damage occurs at very early stages of the disease. Yet parallel functional studies are limited and further work is needed to document whether protein oxidation results in loss of activity and impaired performance. A better understanding of proteins susceptible to oxidation and nitration may serve to define damaged metabolic networks at early stages of disease and to advance therapeutic interventions to attenuate disease progression.

Ribosylation rapidly induces alpha-synuclein to form highly cytotoxic molten globules of advanced glycation end products

Background

Alpha synuclein (α-Syn) is the main component of Lewy bodies which are associated with several neurodegenerative diseases such as Parkinson's disease. While the glycation with D-glucose that results in α-Syn misfold and aggregation has been studied, the effects of glycation with D-ribose on α-Syn have not been investigated.

Methodology/Principal Findings

Here, we show that ribosylation induces α-Syn misfolding and generates advanced glycation end products (AGEs) which form protein molten globules with high cytotoxcity. Results from native- and SDS-PAGE showed that D-ribose reacted rapidly with α-Syn, leading to dimerization and polymerization. Trypsin digestion and sequencing analysis revealed that during ribosylation the lysinyl residues (K₅₈, K₆₀, K₈₀, K₉₆, K₉₇ and K₁₀₂) in the C-terminal region reacted more quickly with D-ribose than those of the N-terminal region. Using Western blotting, AGEs resulting from the glycation of α-Syn were observed within 24 h in the presence of D-ribose, but were not observed in the presence of D-glucose. Changes in fluorescence at 410 nm demonstrated again that AGEs were formed during early ribosylation. Changes in the secondary structure of ribosylated α-Syn were not clearly detected by CD spectrometry in studies on protein conformation. However, intrinsic fluorescence at 310 nm decreased markedly in the presence of D-ribose. Observations with atomic force microscopy showed that the surface morphology of glycated α-Syn looked like globular aggregates. thioflavin T (ThT) fluorescence increased during α-Syn incubation regardless of ribosylation. As incubation time increased, ribosylation of α-Syn resulted in a blue-shift (∼100 nm) in the fluorescence of ANS. The light scattering intensity of ribosylated α-Syn was not markedly different from native α-Syn, suggesting that ribosylated α-Syn is present as molten protein globules. Ribosylated products had a high cytotoxicity to SH-SY5Y cells, leading to LDH release and increase in the levels of reactive oxygen species (ROS).

Conclusions/Significance

α-Syn is rapidly glycated in the presence of D-ribose generating molten globule-like aggregations which cause cell oxidative stress and result in high cytotoxicity.

Molecular insights into the interaction between alpha-synuclein and docosahexaenoic acid

alpha-Synuclein (alpha-syn) is a 140-residue protein of unknown function, involved in several neurodegenerative disorders, such as Parkinson's disease. Recently, the possible interaction between alpha-syn and polyunsaturated fatty acids has attracted a strong interest. Indeed, lipids are able to trigger the multimerization of the protein in vitro and in cultured cells. Docosahexaenoic acid (DHA) is one of the main fatty acids (FAs) in cerebral gray matter and is dynamically released following phospholipid hydrolysis. Moreover, it has been found in high levels in brain areas containing alpha-syn inclusions in patients affected by Parkinson's disease. Debated and unsolved questions regard the nature of the molecular interaction between alpha-syn and DHA and the effect exerted by the protein on the aggregated state of the FA. Here, we show that alpha-syn is able to strongly interact with DHA and that a mutual effect on the structure of the protein and on the physical state of the lipid derives from this interaction. alpha-Syn acquires an alpha-helical conformation in a simple two-state transition. The binding of the protein to the FA leads to a reduction of the size of the spontaneously formed aggregated species of DHA as well as of the critical aggregate concentration of the lipid. Specifically, biophysical methods and electron microscopy observations indicated that the FA forms oil droplets in the presence of alpha-syn. Limited proteolysis experiments showed that, when the protein is bound to the FA oil droplets, it is initially cleaved in the 89-102 region, suggesting that this chain segment is sufficiently flexible or unfolded to be protease-sensitive. Subsequent proteolytic events produce fragments corresponding to the first 70-80 residues that remain structured and show high affinity for the lipid. The fact that a region of the polypeptide chain remains accessible to proteases, when interacting with the lipid, suggests that this region could be involved in other interactions, justifying the ambivalent propensity of alpha-syn towards folding or aggregation in the presence of FAs.

Human brain cortex: mitochondrial oxidative damage and adaptive response in Parkinson disease and in dementia with Lewy bodies

Frontal cortex samples from frozen human brains were used to assess tissue respiration; content of mitochondria; mitochondrial oxygen uptake; activity of respiratory complexes and of mitochondrial nitric oxide synthase (mtNOS); content of cytochromes a, b, and c; oxidative damage (protein carbonyls and TBARS); and expression of Mn-SOD in patients with Parkinson disease (PD) and with dementia with Lewy bodies (DLB) in comparison with those of normal healthy controls. Brain cortex and mitochondrial O(2) uptake and complex I activity were significantly lower in PD and DLB, whereas mtNOS activity, cytochrome content, expression of Mn-SOD, mitochondrial mass, and oxidative damage were significantly higher in the frontal cortex in PD and DLB. The decreases in tissue and mitochondrial O(2) uptake and in complex I activity are considered the consequences of mitochondrial oxidative damage. The increases in mtNOS activity and in mitochondrial mass are interpreted as an adaptive response of the frontal cortex that involves increased NO signaling for mitochondrial biogenesis. The adaptive response would partially compensate for mitochondrial dysfunction in these neurodegenerative diseases and would afford a human evolutionary response to shortage of ATP in the frontal cortex.

Dissembled DJ-1 high molecular weight complex in cortex mitochondria from Parkinson's disease patients

The PARK7 gene encodes a protein, DJ-1, with several functions such as protection of cells from oxidative stress, sperm maturation and fertilization, and chaperone activity. Mutations in the PARK7 gene are associated with autosomal recessive early-onset Parkinson's disease (PD). DJ-1 has been reported to be expressed in multiple cells in the central nerve system. Here, by using both native and denatured Western blots, we examined levels of total DJ-1 and high molecular weight complexes of DJ-1 (HMW) in both the substantia nigra and cortex from rapidly autopsied 18 PD and 9 non-pathological control (NPC) brains. We have discovered that the level of total DJ-1 protein is significantly reduced in the substantia nigra in brains of sporadic PD patients. Moreover, in the PD cortex mitochondria fraction, the HMW DJ-1 complex is significantly lower than in the NPC. These results suggest abnormal DJ-1 expression levels and DJ-1 complex changes may contribute to PD pathogenesis.

Increased oxidation of certain glycolysis and energy metabolism enzymes in the frontal cortex in Lewy body diseases

Lipoxidative damage of aldolase A, enolase 1, and glyceraldehyde dehydrogenase (GAPDH) was found in the frontal cortex in a percentage of aged controls by bidimensional gel electrophoresis, Western blot test, in-gel digestion, and mass spectrometry. Aldolase A and enolase 1 were altered in 12 of 19 cases, whereas oxidation of GAPDH was found in 6 of 19 controls. The three enzymes were oxidized in the frontal cortex in the majority of cases of incidental Parkinson's disease (iPD), PD, and dementia with Lewy bodies (DLB). Differences were statistically significant (chi(2) test) for GAPDH in PD and DLB. Densitometric studies have shown that the ratio of oxidized protein per spot is higher in iPD, PD, and DLB compared with controls. These findings show oxidation of three enzymes linked with glycolysis and energy metabolism in the adult human brain as well as increased oxidation of aldolase A, enolase 1, and GAPDH in the frontal cortex in Lewy body diseases. Modifications of these enzymes may result in decreased activity and may partly account for impaired metabolism and function of the frontal lobe in PD.

The coenzyme Q10 status of the brain regions of Parkinson's disease patients

There is increasing evidence that impairment of mitochondrial function and oxidative damage are contributing factors to the pathophysiology of Parkinson's disease (PD). Studies have reported decreased levels of the mitochondrial electron transport chain carrier, coenzyme Q(10) (CoQ(10)) in plasma and platelets from PD patients. Although a deficit in peripheral CoQ(10) has been reported no studies have assessed the CoQ(10) status of the PD brain. In this study we investigated the CoQ(10) status of the substantia nigra, cerebellum, cortex and striatum brain regions of both PD patients and age-matched controls. The results of this study indicate a significant reduction (p=0.007) in CoQ(10) concentration in the cortex region of the brain. In conclusion, the results of this study indicate evidence of a deficit in brain CoQ(10) status may be involved in the pathophysiology of PD.

Advanced glycation end products induce in vitro cross-linking of alpha-synuclein and accelerate the process of intracellular inclusion body formation

Cross-linking of alpha-synuclein and Lewy body formation have been implicated in the dopaminergic neuronal cell death observed in Parkinson's disease (PD); the mechanisms responsible, however, are not clear. Reactive oxygen species and advanced glycation end products (AGEs) have been found in the intracellular, alpha-synuclein-positive Lewy bodies in the brains of both PD as well as incidental Lewy body disease patients, suggesting a role for AGEs in alpha-synuclein cross-linking and Lewy body formation. The aims of the present study were to determine 1) whether AGEs can induce cross-linking of alpha-synuclein peptides, 2) the progressive and time-dependent intracellular accumulation of AGEs and inclusion body formation, and 3) the effects of extracellular or exogenous AGEs on intracellular inclusion formation. We first investigated the time-dependent cross-linking of recombinant human alpha-synuclein in the presence of AGEs in vitro, then used a cell culture model based on chronic rotenone treatment of human dopaminergic neuroblastoma cells (SH-SY5Y) over a period of 1-4 weeks, in the presence of different doses of AGEs. Cells (grown on coverslips) and cell lysates, collected at the end of every week, were analyzed for the presence of intracellular reactive oxygen species, AGEs, alpha-synuclein proteins, and intracellular alpha-synuclein- and AGE-positive inclusion bodies by using immunocytochemical, biochemical, and Western blot techniques. Our results show that AGEs promote in vitro cross-linking of alpha-synuclein, that intracellular accumulation of AGEs precedes alpha-synuclein-positive inclusion body formation, and that extracellular AGEs accelerate the process of intracellular alpha-synuclein-positive inclusion body formation.

Differential expression of alpha-synuclein, parkin, and synphilin-1 isoforms in Lewy body disease

Alpha-synuclein, parkin, and synphilin-1 are proteins mainly involved in the pathogenesis of Lewy body (LB) diseases. mRNAs of all three undergo alternative splicing, so that the existence of various isoforms has been described. Since increasing evidence supports the importance of differential isoform-expression changes in disease development, we have established isoform-expression profiles in frontal cortices of LB disease brains in comparison with those of Alzheimer disease (AD) and control frontal cortices. The differential expression of four alpha-synuclein, seven parkin, and four synphilin-1 isoforms was ascertained by the use of isoform-specific primers and relative expression analysis with SybrGreen and beta-actin as an internal standard. The establishment of isoform-expression profiles revealed that these are disease specific. Moreover, isoform-expression deregulation of mainly one gene in each disease could be observed. All four alpha-synuclein isoforms were affected in the case of the pure form of dementia with LB, most parkin transcript variants in common LB disease, and all synphilin-1 isoforms in Parkinson disease. Only minor involvement was detected in AD. Finally, the existence of a proprietary isoform-expression profile in common LB disease indicates that this disease develops as a result of its own molecular mechanisms, and so, at the molecular level, it does not exactly share changes found in pure dementia with LB and AD. In conclusion, isoform-expression profiles in LB diseases represent additional evidence for the direct involvement of isoform-expression deregulation in the development of neurodegenerative disorders.

Early α-synuclein lipoxidation in neocortex in Lewy body diseases

Previous studies in Lewy body diseases (LBDs), including Parkinson's disease (PD) and Dementia with Lewy bodies (DLB), have shown oxidative stress damage more extended than the expected for the distribution of Lewy pathology. Since malondialdehyde (MDA) can form adducts with lysine residues of proteins, MDA-Lys immunoprecipitation and alpha-synuclein immunoblotting has been carried out in frontal cortex and substantia nigra homogenates from five patients with PD, five DLB, three iPD and seven aged-matched controls to decipher the extent of lipoxidized alpha-synuclein in LBDs. MDA-Lys-lipoxidation of alpha-synuclein in the substantia nigra and frontal cortex has been found in all DLB and PD cases examined, but also in the frontal cortex in 3/3 and in the substantia nigra in 2/3 cases with iPD. In addition, one control case had MDA-Lys-modified alpha-synuclein in the frontal cortex, and another in the substantia nigra. This work provides evidence of extended lipoxidative modification of alpha-synuclein in LBDs. Moreover, it demonstrates that alpha-synuclein lipoxidation is an early event in LBDs which precedes alpha-synuclein solubility modification and aggregation, and formation of Lewy bodies and neurites.

Methionine restriction decreases endogenous oxidative molecular damage and increases mitochondrial biogenesis and uncoupling protein 4 in rat brain

Aging plays a central role in the occurrence of neurodegenerative diseases. Caloric restriction (CR) mitigates oxidative stress by decreasing the rate of generation of endogenous damage, a mechanism that can contribute to the slowing of the aging rate induced by this intervention. Various reports have recently linked methionine to aging, and methionine restriction (MetR) without energy restriction also increases life span. We have thus hypothesized that MetR can be responsible, at least in part, for the decrease in endogenous oxidative damage in CR. In this investigation we subjected male rats to exactly the same dietary protocol of MetR that is known to increase their life span. We have found that MetR: (1) decreases the mitochondrial complex I content and activity, as well as complex III content, while the complex II and IV, the mitochondrial flavoprotein apoptosis-inducing factor (AIF) and ATP content are unchanged; (2) increases the mitochondrial biogenesis factor PGC-1alpha; (3) increases the resistance of brain to metabolic and oxidative stress by increasing mitochondrial uncoupling protein 4 uncoupling protein 4 (UCP4); and (4) decreases mitochondrial oxidative DNA damage and all five different markers of protein oxidation measured and lowers membrane unsaturation in rat brain. No changes were detected for protein amino acid composition. These beneficial MetR-induced changes likely derived from metabolic reprogramming at the cellular and tissue level can play a key role in the protection against aging-associated neurodegenerative disorders.

Proteome analysis of human substantia nigra in Parkinson's disease

Background

Parkinson's disease (PD) is the most common neurodegenerative disorder involving the motor system. Although not being the only region involved in PD, affection of the substantia nigra and its projections is responsible for some of the most debilitating features of the disease. To further advance a comprehensive understanding of nigral pathology, we conducted a tissue based comparative proteome study of healthy and diseased human substantia nigra.

Results

The gross number of differentially regulated proteins in PD was 221. In total, we identified 37 proteins, of which 16 were differentially expressed. Identified differential proteins comprised elements of iron metabolism (H-ferritin) and glutathione-related redox metabolism (GST M3, GST P1, GST O1), including novel redox proteins (SH3BGRL). Additionally, many glial or related proteins were found to be differentially regulated in PD (GFAP, GMFB, galectin-1, sorcin), as well as proteins belonging to metabolic pathways sparsely described in PD, such as adenosyl homocysteinase (methylation), aldehyde dehydrogenase 1 and cellular retinol-binding protein 1 (aldehyde metabolism). Further differentially regulated proteins included annexin V, beta-tubulin cofactor A, coactosin-like protein and V-type ATPase subunit 1. Proteins that were similarly expressed in healthy or diseased substantia nigra comprised housekeeping proteins such as COX5A, Rho GDI alpha, actin gamma 1, creatin-kinase B, lactate dehydrogenase B, disulfide isomerase ER-60, Rab GDI beta, methyl glyoxalase 1 (AGE metabolism) and glutamine synthetase. Interestingly, also DJ-1 and UCH-L1 were expressed similarly. Furthermore, proteins believed to serve as internal standards were found to be expressed in a constant manner, such as 14-3-3 epsilon and hCRMP-2, thus lending further validity to our results.

Conclusion

Using an approach encompassing high sensitivity and high resolution, we show that alterations of SN in PD include many more proteins than previously thought. The results point towards a heterogeneous aetiopathogenesis of the disease, including alterations of GSH-related proteins as well as alterations of proteins involved in retinoid metabolism, and they indicate that proteins involved in familial PD may not be differentially regulated in idiopathic Parkinson's disease.

Maillard reaction versus other nonenzymatic modifications in neurodegenerative processes

Nonenzymatic protein modifications are generated from direct oxidation of amino acid side chains and from reaction of the nucleophilic side chains of specific amino acids with reactive carbonyl species. These reactions give rise to specific markers that have been analyzed in different neurodegenerative diseases sharing protein aggregation, such as Alzheimer's disease, Pick's disease, Parkinson's disease, dementia with Lewy bodies, Creutzfeldt-Jakob disease, and amyotrophic lateral sclerosis. Collectively, available data demonstrate that oxidative stress homeostasis, mitochondrial function, and energy metabolism are key factors in determining the disease-specific pattern of protein molecular damage. In addition, these findings suggest the lack of a "gold marker of oxidative stress," and, consequently, they strengthen the need for a molecular dissection of the nonenzymatic reactions underlying neurodegenerative processes.

Advanced glycation and lipoxidation end products--amplifiers of inflammation: the role of food

BACKGROUND

High levels of glycated and lipoxidated proteins and peptides in the body are repeatedly associated with chronic diseases. These molecules are strongly associated with activation of a specific receptor called RAGE and a long-lasting exaggerated level of inflammation in the body.

METHODS

PubMed reports over 5000 papers plus >13,500 articles about the related HbA(1c), most of them published in the past 5 years. Most of the available abstracts have been read and approximately 800 full papers have been studied.

RESULTS

RAGE, a member of the immunoglobulin superfamily of cell surface molecules and receptor for advanced glycation end products, known since 1992, functions as a master switch, induces sustained activation of nuclear factor kappaB (NFkappaB), suppresses a series of endogenous autoregulatory functions, and converts long-lasting proinflammatory signals into sustained cellular dysfunction and disease. Its activation is associated with high levels of dysfunctioning proteins in body fluids and tissues, and is strongly associated with a series of diseases from allergy and Alzheimers to rheumatoid arthritis and urogenital disorders. Heat treatment, irradiation, and ionization of foods increase the content of dysfunctioning molecules.

CONCLUSIONS

More than half of the studies are performed in diabetes and chronic renal diseases; there are few studies in other diseases. Most of our knowledge is based on animal studies and in vitro studies. These effects are worth further exploration both experimentally and clinically. An avoidance of foods rich in deranged proteins and peptides, and the consumption of antioxidants, especially polyphenols, seem to counteract such a development.

Site-specific Effects of Peptide Lipidation on β-Amyloid Aggregation and Cytotoxicity

Beta-amyloid (Abeta) aggregates at low concentrations in vivo, and this may involve covalently modified forms of these peptides. Modification of Abeta by 4-hydroxynonenal (4-HNE) initially increases the hydrophobicity of these peptides and subsequently leads to additional reactions, such as peptide cross-linking. To model these initial events, without confounding effects of subsequent reactions, we modified Abeta at each of its amino groups using a chemically simpler, close analogue of 4-HNE, the octanoyl group: K16-octanoic acid (OA)-Abeta, K28-OA-Abeta, and Nalpha-OA-Abeta. Octanoylation of these sites on Abeta-(1-40) had strikingly different effects on fibril formation. K16-OA-Abeta and K28-OA-Abeta, but not Nalpha-OA-Abeta, had increased propensity to aggregate. The type of aggregate (electron microscopic appearance) differed with the site of modification. The ability of octanoyl-Abeta peptides to cross-seed solutions of Abeta was the inverse of their ability to form fibrils on their own (i.e. Abeta approximately Nalpha-OA-Abeta>>K16-OA-Abeta>>K28-OA-Abeta). By CD spectroscopy, K16-OA-Abeta and K28-OA-Abeta had increased beta-sheet propensity compared with Abeta-(1-40) or Nalpha-OA-Abeta. K16-OA-Abeta and K28-OA-Abeta were more amphiphilic than Abeta-(1-40) or Nalpha-OA-Abeta, as shown by lower "critical micelle concentrations" and higher monolayer collapse pressures. Finally, K16-OA-Abeta and K28-OA-Abeta are much more cytotoxic to N2A cells than Abeta-(1-40) or Nalpha-OA-Abeta. The greater cytotoxicity of K16-OA-Abeta and K28-OA-Abeta may reflect their greater amphiphilicity. We conclude that lipidation can make Abeta more prone to aggregation and more cytotoxic, but these effects are highly site-specific.

ELISA reveals a difference in the structure of substantia nigra ferritin in Parkinson's disease and incidental Lewy body compared to control

Iron released from ferritin may trigger oxidative stress leading to progressive neurodegeneration of substantia nigra resulting in Parkinson's disease (PD). Change in the structure of ferritin may allow an easier efflux of iron. We compared with the use of ELISA the structure of ferritin (concentrations of H and L ferritins) in substantia nigra (SN) in ten cases of PD, six of incidental Lewy body (ILB) cases and 20 controls. SN concentration of L ferritin in ILB (50.6+/-11.5 ng/mg) and in PD (52.5+/-26.0) was lower than in control (97.9+/-54.9). H ferritin in PD (534.2+/-223.1) was higher than in ILB (336.9+/-87.7) and control (374.8+/-169.3). The decrease of L ferritin in SN in PD and ILB may suggest that the whole process of neurodegeneration starts with a higher availability of free iron, which is released from the ferritin shell.

Neurotoxicity and metabolism of the catecholamine-derived 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde: the role of aldehyde dehydrogenase

Aldehydes are highly reactive molecules formed during the biotransformation of numerous endogenous and exogenous compounds, including biogenic amines. 3,4-Dihydroxyphenylacetaldehyde is the aldehyde metabolite of dopamine, and 3,4-dihydroxyphenylglycolaldehyde is the aldehyde metabolite of both norepinephrine and epinephrine. There is an increasing body of evidence suggesting that these compounds are neurotoxic, and it has been recently hypothesized that neurodegenerative disorders may be associated with increased levels of these biogenic aldehydes. Aldehyde dehydrogenases are a group of NAD(P)+ -dependent enzymes that catalyze the oxidation of aldehydes, such as those derived from catecholamines, to their corresponding carboxylic acids. To date, 19 aldehyde dehydrogenase genes have been identified in the human genome. Mutations in these genes and subsequent inborn errors in aldehyde metabolism are the molecular basis of several diseases, including Sjögren-Larsson syndrome, type II hyperprolinemia, gamma-hydroxybutyric aciduria, and pyridoxine-dependent seizures, most of which are characterized by neurological abnormalities. Several pharmaceutical agents and environmental toxins are also known to disrupt or inhibit aldehyde dehydrogenase function. It is, therefore, possible to speculate that reduced detoxification of 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde from impaired or deficient aldehyde dehydrogenase function may be a contributing factor in the suggested neurotoxicity of these compounds. This article presents a comprehensive review of what is currently known of both the neurotoxicity and respective metabolism pathways of 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde with an emphasis on the role that aldehyde dehydrogenase enzymes play in the detoxification of these two aldehydes.

Effect of 4-hydroxy-2-nonenal modification on alpha-synuclein aggregation

Several observations have implicated oxidative stress and aggregation of the presynaptic protein alpha-synuclein in the pathogenesis of Parkinson disease. alpha-Synuclein has been shown to have affinity for unsaturated fatty acids and membranes enriched in polyunsaturated fatty acids, which are especially sensitive to oxidation under conditions of oxidative stress. One of the most important products of lipid oxidation is 4-hydroxy-2-nonenal (HNE), which has been implicated in the pathogenesis of Parkinson disease. Consequently, we investigated the effects of the interaction of HNE with alpha-synuclein. Incubation of HNE with alpha-synuclein at pH 7.4 and 37 degrees C resulted in covalent modification of the protein, with up to six HNE molecules incorporated as Michael addition products. Fourier transform infrared and CD spectra indicated that HNE modification of alpha-synuclein resulted in a major conformational change involving increased beta-sheet. HNE modification of alpha-synuclein led to inhibition of fibrillation in an HNE concentration-dependent manner. This inhibition of fibrillation was shown to be due to the formation of soluble oligomers based on size exclusion high pressure liquid chromatography and atomic force microscope data. Small angle x-ray scattering analysis indicated that the HNE-induced oligomers were compact and tightly packed. Treatment with guanidinium chloride demonstrated that the HNE-induced oligomers were very stable with an extremely slow rate of dissociation. Addition of 5 mum HNE-modified oligomers to primary mesencephalic cultures caused marked neurotoxicity because the integrity of dopaminergic and GABAergic neurons was reduced by 95 and 85%, respectively. Our observations indicate that HNE modification of alpha-synuclein prevents fibrillation but may result in toxic oligomers, which could therefore contribute to the demise of neurons subjected to oxidative damage.

Mitochondrial dysfunction, peroxidation damage and changes in glutathione metabolism in PARK6

Oxidative stress and protein aggregation are biochemical hallmarks of Parkinson's disease (PD), a frequent sporadic late-onset degenerative disorder particularly of dopaminergic neurons in the substantia nigra, resulting in impaired spontaneous movement. PARK6 is a rare autosomal-recessively inherited disorder, mimicking the clinical picture of PD with earlier onset and slower progression. Genetic data demonstrated PARK6 to be caused by mutations in the protein PINK1, which is localized to mitochondria and has a serine-threonine kinase domain. To study the effect of PINK1 mutations on oxidative stress, we used primary fibroblasts and immortalized lymphoblasts from three patients homozygous for G309D-PINK1. Oxidative stress was evident from increases in lipid peroxidation and in antioxidant defenses by mitochondrial superoxide dismutase and glutathione. Elevated levels of glutathione reductase and glutathione-S-transferase were also observed. As a putative cause of oxidation, a mild decrease in complex I activity and a trend to superoxide elevation were detectable. These data indicate that PINK1 function is critical to prevent oxidative damage and that peripheral cells may be useful for studies of progression and therapy of PARK6.

Glial fibrillary acidic protein is a major target of glycoxidative and lipoxidative damage in Pick's disease

Pick's disease is a subset of fronto-temporal dementia characterised by severe atrophy of the temporal and frontal lobes due to marked neuronal loss accompanied by astrocytic gliosis enriched in glial acidic protein. The remaining neurones have intracytoplasmic inclusions composed of hyperphosphorylated tau, called Pick bodies, in addition to hyperphosphorylated tau in astrocytes and oligodendrocytes. Gel electrophoresis and western blotting using markers of glycoxidation (advanced glycation end products, N-carboxyethyl-lysine and N-carboxymethyl-lysine: AGE, CEL, CML, respectively) and lipoxidation (4-hydroxy-2-nonenal: HNE, and malondialdehyde-lysine: MDAL) were used in the frontal and occipital cortex in three Pick's disease cases and three age-matched controls. In Pick's disease, increased AGE, CML, CEL, HNE and MDAL bands of about 50 kDa were observed in the frontal cortex (but not in the occipital cortex) in association with increased density of glial acidic protein bands. Bi-dimensional gel electrophoresis and western blotting also disclosed increased amounts and numbers of glial acidic protein isoforms in the frontal cortex in Pick's disease. Moreover, redox proteomics showed glycoxidation, as revealed with anti-CEL antibodies and lipoxidation using anti-HNE antibodies, of at least three glial acidic protein isoforms. The present results demonstrate that glial acidic protein is a target of oxidative damage in the frontal cortex in Pick's disease.

Oxidation, glycoxidation, lipoxidation, nitration, and responses to oxidative stress in the cerebral cortex in Creutzfeldt-Jakob disease

Gel electrophoresis and Western blotting of frontal cortex homogenates have been carried out in sporadic Creutzfeldt-Jakob disease (CJD) cases and age-matched controls to gain understanding of the expression of glycation-end products (AGEs). N-Carboxymethyl-lysine (CML) and N-carboxyethyl-lysine (CEL) were used as markers of glycoxidation; 4-hydroxynonenal (4-HNE) and malondialdehyde-lysine (MDAL) as markers of lipoxidation; and nitrotyrosine (N-tyr) and neuronal, endothelial and inducible nitric oxide synthase (nNOS, eNos and iNos) as markers of protein nitration and as sources of NO production, respectively. Age receptor (RAGE) and Cu/Zn superoxide dismutase (SOD1) and Mn superoxide dismutase (SOD2) expression levels were also examined. The results showed a significant increase in the expression levels of AGE (p<0.05), CEL (p<0.001), RAGE (p<0.05), HNE-modified proteins (p<0.01), nNOS, iNOS and eNOS (p<0.01 and p<0.05, respectively), N-tyr (p<0.05), and SOD1 (p<0.05) and SOD2 (p<0.05). No relationship was observed between PrP genotype, PrP type, PrP burden, and expression levels of oxidative stress markers. The present findings demonstrate oxidative, glycoxidative, lipoxidative and nitrative protein damage, accompanied by increased oxidative responses, in the cerebral cortex in sporadic CJD. These results provide support for the concept that oxidative stress may have important implications in the pathogenesis of prion diseases.