Toxic effects of dopamine metabolism in Parkinson's disease

Levodopa is the most effective medication for Parkinson's disease (PD). In contrast, there is evidence that levodopa and its metabolites such as dopa/dopamine quinone are toxic for nigral neurons based on in vitro studies. Moreover, there is growing evidence that oxidative stress and mitochondrial dysfunction contribute the pathogenesis of PD. Thus, studies for oxidative stress give us good information for elucidating the pathogenesis of PD. In this regard, it is mandatory to develop markers such as 4-hydroxy-nonenal (HNE). HNE is a product of lipid peroxidation. Indeed, immunohistochemical studies have revealed that HNE-modified proteins accumulate within ragged red fibers (RRFs). This finding indicated that mitochondrial impairment may be linked to oxidative stress. Moreover, HNE-modified proteins accumulate in nigral neurons. In PD, mitochondrial dysfunction such as complex I deficiency has also been reported. In addition, HNE can modify α-synuclein (SNCA). Subsequently, this modification may trigger the aggregation of this protein. At a minimum, this modification could be associated with oligomer formation or fibrillation of SNCA.     

Oxidative damage and progression to Alzheimer's disease in patients with mild cognitive impairment

Recent studies show that most of the oxidative changes found in Alzheimer's disease (AD) are already present in mild cognitive impairment (MCI) patients. The question arises as to whether oxidative stress has a role in the progression of MCI to AD. We conducted a longitudinal study on 70 MCI patients, and the peripheral blood levels of a broad spectrum of non-enzymatic and enzymatic antioxidant defenses, as well as lipid and protein oxidation markers and nitrogen oxidative species were determined. At baseline, there were no differences in any of the indexes of oxidative damage between stable MCI patients (MCI-MCI) and patients that progressed to AD (MCI-AD). Cellular levels of lipid peroxidation markers increased in both groups and this was accompained in MCI-AD, but not in MCI-MCI patients, by a significant decrease in cellular antioxidant defenses (oxidyzed/reduced glutathione ratio and vitamin E). Among MCI-AD patients, the longitudinal decrease in cellular vitamin E was associated with the deterioration in cognitive performance. These results suggest that accumulation of oxidative damage may start in pre-symptomatic phases of AD pathology and that progression to AD might be related to depletion of antioxidant defenses.     

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.     

Loss of phospholipid asymmetry and elevated brain apoptotic protein levels in subjects with amnestic mild cognitive impairment and Alzheimer disease

Oxidative stress, a hallmark of Alzheimer disease (AD), has been shown to induce lipid peroxidation and apoptosis disrupting cellular homeostasis. Normally, the aminophospholipid phosphatidylserine (PtdSer) is asymmetrically distributed on the cytosolic leaflet of the lipid bilayer. Under oxidative stress conditions, asymmetry is altered, characterized by the appearance of PtdSer on the outer leaflet, to initiate the first stages of an apoptotic process. PtdSer asymmetry is actively maintained by the ATP-dependent translocase flippase, whose function is inhibited if covalently bound by lipid peroxidation products, 4-hydroxynonenal (HNE) and acrolein, within the membrane bilayer in which they are produced. Additionally, pro-apoptotic proteins Bax and caspase-3 have been implemented in the oxidative modification of PtdSer resulting in subsequent asymmetric collapse, while anti-apoptotic protein Bcl-2 has been found to prevent this process.The current investigation focused on detection of PtdSer on the outer leaflet of the bilayer in synaptosomes from brain of subjects with AD and amnestic mild cognitive impairment (MCI), as well as expression levels of apoptosis-related proteins Bcl-2, Bax, and caspase-3. Fluorescence and Western blot analysis suggest PtdSer exposure on the outer leaflet is significantly increased in brain from subjects with MCI and AD contributing to early apoptotic elevation of pro- and anti-apoptotic proteins and finally neuronal loss. MCI is considered a possible transition point between normal cognitive aging and probable AD. Brain from subjects with MCI is reported to have increased levels of tissue oxidation; therefore, the results of this study could mark the progression of patients with MCI into AD. This study contributes to a model of apoptosis-specific oxidation of phospholipids consistent with the notion that PtdSer exposure is required for apoptotic-cell death.     

Activities of key glycolytic enzymes in the brains of patients with Alzheimer's disease

Summary. The activities of hexokinase, aldolase, pyruvate kinase, lactate dehydrogenase and glucose 6-phosphate dehydrogenase were determined in brains of patients with Alzheimer's disease (AD) and in age matched controls. For pyruvate kinase and lactate dehydrogenase a significant increase in specific activity was found in frontal and temporal cortex of AD brains, while the activities of aldolase and hexokinase are not changed. Glucose 6-phosphate dehydrogenase activity was significantly reduced in hippocampus. The increase of some glycolytic enzyme activities is correlated with increased contents of lactate dehydrogenase and glial fibrillary acidic protein (GFAP) in homogenates of frontal and temporal cortex and elevated phosphofructokinase (PFK) and GFAP in astrocytes from the same brain areas. The data extend previous findings on an increase in brain PFK specific activity in AD and suggest that the increased activity of some glycolytic enzymes may be, at least in part, the result of the reactive astrocytosis developing in the course of AD. Received August 3, 1998; accepted November 2, 1998     

Expression and activities of aldo-keto oxidoreductases in Alzheimer disease.

A reactive intermediate generated by lipid peroxidation, 4-hydroxy-2-nonenal (HNE), has received considerable attention as a potential effector of oxidative damage and Abeta peptide-mediated neurotoxicity in Alzheimer disease (AD). However, little is known about aldo-keto oxidoreductases, a group of enzymes that constitute a major detoxifying pathway for HNE and related reactive aldehydes in human brain. We have determined the regional, cellular, and class distribution in human brain of the 4 major aldo-keto oxidoreductases that detoxify HNE: aldehyde dehydrogenase (ALDH): aldose reductase; aldehyde reductase: and alcohol dehydrogenase (ADH). Of these 4 enzymes, only ALDH and aldose reductase were expressed in cerebral cortex. hippocampus, basal ganglia, and midbrain: all 4 enzymes were present in cerebellum. In cerebrum and hippocampus, aldose reductase was localized to pyramidal neurons and mitochondrial class 2 ALDH was localized to glia and senile plaques. ALDH, but not aldose reductase, activity was significantly increased in temporal cortex from patients with AD compared to age-matched controls. These results suggest that in brain regions involved in AD, neurons and glia utilize different mechanisms to detoxify HNE, and that increased ALDH activity is a protective response of cerebral cortex to AD.     

Peripheral oxidative stress biomarkers in mild cognitive impairment and Alzheimer's disease

Oxidative stress has been associated with normal aging and Alzheimer's disease (AD). However, little is known about oxidative stress in mild cognitive impairment (MCI) patients who present a high risk for developing AD. The aim of this study was to investigate plasma production of the lipid peroxidation marker, malonaldehyde (MDA) and to determine, in erythrocytes, the enzymatic antioxidant activity of catalase, glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione S-transferase (GST) in 33 individuals with MCI, 29 with mild probable AD and 26 healthy aged subjects. GR/GPx activity ratio was calculated to better assess antioxidant defenses. The relationship between oxidative stress and cognitive performance was also evaluated by the Mini Mental State Examination (MMSE). AD patients showed higher MDA levels than both MCI and healthy elderly subjects. MCI subjects also exhibited higher MDA levels compared to controls. Catalase and GPx activity were similar in MCI and healthy individuals but higher in AD. GR activity was lower in MCI and AD patients than in healthy aged subjects. Additionally, GR/GPx ratio was higher in healthy aged subjects, intermediate in MCI and lower in AD patients. No differences in GST activity were detected among the groups. MMSE was negatively associated with MDA levels (r = -0.31, p = 0.028) and positively correlated with GR/GPx ratio in AD patients (r = 0.68, p < 0.001). MDA levels were also negatively correlated to GR/GPx ratio (r = -0.31, p = 0.029) in the AD group. These results suggest that high lipid peroxidation and decreased antioxidant defenses may be present early in cognitive disorders.     

Diffusion tensor imaging based white matter changes and antioxidant enzymes status for early identification of mild cognitive impairment

Mild cognitive impairment (MCI) is an early stage of dementia. The changes in white matter integrity and antioxidant enzymes levels are crucial in onset and progression to Alzheimer’s disease (AD). To elucidate the changes in cognitive performance, white matter integrity, oxidative stress marker, for early detection of prodromal state of AD. Fifty cases of MCI and controls (55-75 years) were subjected to Mini Mental State Examination (MMSE), diffusion tensor imaging (DTI) followed by estimation of superoxide dismutase, glutathione peroxidase and lipid peroxidation in serum of MCI and control population. The MMSE scores of MCI subjects were (28±2 - 22.6±1) as compared with controls (28±1- 29±1). DTI metrics fractional anisotropy (FA) values in right and left frontal lobe, fornix, corpus callosum, while apparent diffusion coefficient (ADC) values in right temporal lobe, hippocampus head, corpus callosum right, and forcep major were significantly altered in MCI as compared with controls. Superoxide dismutase, glutathione peroxidase level were lower while lipid peroxidation marker malondialdehyde (MDA) was increased in patients with MCI as compared with controls. The study emphasized that changes in neuro-psychological performance, white matter integrity and antioxidant enzymes level provide early signature for diagnosis of MCI.     

Lipid peroxidation is an early event in the brain in amnestic mild cognitive impairment

Multiple studies demonstrate that the brain in Alzheimer's disease (AD) contains extensive oxidative damage. Most of these studies used advanced-stage AD patients raising the question of whether oxidative damage is a late effect of neurodegeneration or precedes and contributes to the pathogenesis of AD. Here we describe F(2)-isoprostane (F(2)-IsoP) and F(4)-neuroprostane (F(4)-NP) levels in longitudinally followed, well documented autopsied normal control subjects and patients with amnestic mild cognitive impairment (MCI), and late-stage AD. Gas chromatography/negative ion chemical ionization/mass spectrometry was used to determine F(2)-IsoP and F(4)-NP levels. Significant increases in F(2)-IsoP levels were found in frontal, parietal and occipital lobes in MCI and late AD compared to controls but no significant differences were present between MCI and late AD. A significant increase in F(4)-NPs was present in parietal and occipital lobes in MCI compared to controls and a significant increase was present in these regions and hippocampus in late AD compared to controls. The only difference between MCI and late AD was significantly increased F(4)-NP in hippocampus in late AD. Our data indicate that lipid peroxidation is present in the brain of MCI patients and suggest that oxidative damage may play a role in the pathogenesis of AD.     

Elevation of 12/15 lipoxygenase products in AD and mild cognitive impairment

The 12/15 lipoxygenase (12/15LOX) enzyme is increased in pathologically affected frontal and temporal regions of Alzheimer's disease (AD) brains compared with controls. Herein, we measured 12(S)-HETE and 15(S)-HETE levels, products of 12/15LOX, in cerebrospinal fluid (CSF) of normal individuals, subjects with mild cognitive impairment (MCI) and AD. Compared with controls, there was a significant increase of both metabolites in CSF from AD and MCI, which correlated with lipid peroxidation and tau protein levels. These results suggest that the activation of this enzyme occurs early in the course of AD, before the onset of overt dementia, thereby implicating 12/15LOX-mediated lipid peroxidation in the pathogenesis of AD.     

Cell Cycle Proteins in Brain in Mild Cognitive Impairment: Insights into Progression to Alzheimer Disease

Recent studies have demonstrated the re-emergence of cell cycle proteins in brain as patients progress from the early stages of mild cognitive impairment (MCI) into Alzheimer's disease (AD). Oxidative stress markers present in AD have also been shown to be present in MCI brain suggesting that these events occur in early stages of the disease. The levels of key cell cycle proteins, such as CDK2, CDK5, cyclin G1, and BRAC1 have all been found to be elevated in MCI brain compared to age-matched control. Further, peptidyl prolyl cis-trans isomerase (Pin1), a protein that plays an important role in regulating the activity of key proteins, such as CDK5, GSK3-β, and PP2A that are involved in both the phosphorylation state of Tau and in the cell cycle, has been found to be oxidatively modified and downregulated in both AD and MCI brain. Hyperphosphorylation of Tau then results in synapse loss and the characteristic Tau aggregation as neurofibrillary tangles, an AD hallmark. In this review, we summarized the role of cell cycle dysregulation in the progression of disease from MCI to AD. Based on the current literature, it is tempting to speculate that a combination of oxidative stress and cell cycle dysfunction conceivably leads to neurodegeneration.     

Peripheral oxidative damage in mild cognitive impairment and mild Alzheimer's disease

Oxidative stress has been shown to be a triggering event in the pathogenesis of Alzheimer's disease (AD). However, little evidence exists on the role of oxidative imbalance in Mild Cognitive Impairment (MCI), a group with a high risk of progression to AD. We therefore assessed the peripheral blood levels of a broad spectrum of non-enzymatic and enzymatic antioxidant defenses, as well as lipid and protein oxidation markers and nitrogen oxidative species in 85 MCI patients, 42 mild AD patients and 37 age-matched controls. In mild AD patients, the plasma levels of vitamin E were significantly decreased, while the plasma concentration of oxidized glutathione was increased in both MCI and mild AD patients. An increase in plasmatic and erythrocytes oxidative markers was also observed in MCI and mild AD patients as compared to controls. In both patients groups, increased levels of plasma antioxidants were found in females, whereas apolipoprotein E epsilon4 allele carriers showed higher indices of intracellular oxidative markers. Moreover, in MCI patients, cognitive function positively correlates with antioxidant levels. This study shows that most of the oxidative changes found in mild AD patients are already present in the MCI group, and that progression to AD might be accompanied by antioxidant depletion.     

Increase of brain oxidative stress in mild cognitive impairment: a possible predictor of Alzheimer disease

BACKGROUND: The isoprostane 8,12-iso-iPF(2alpha)-VI, a specific marker of in vivo lipid peroxidation, is increased in Alzheimer disease (AD). The pathological changes associated with AD have a long silent phase before the appearance of clinical symptoms. Several studies have shown that AD is preceded by a prodromal phase characterized by mild cognitive impairment (MCI). OBJECTIVE: To investigate levels of this biomarker in subjects with MCI. DESIGN AND MAIN OUTCOME MEASURES: Using gas chromatography-mass spectrometry analysis, we measured 8,12-iso-iPF(2alpha)-VI levels in urine, plasma, and cerebrospinal fluid of patients with AD, subjects with MCI, and cognitively normal elderly subjects. SETTING AND PATIENTS: Subjects attending the Memory Disorders Clinic. RESULTS: We found significantly higher 8,12-iso-iPF(2alpha)-VI levels in cerebrospinal fluid, plasma, and urine of subjects with MCI compared with cognitively normal elderly subjects. CONCLUSIONS: These results imply that individuals with MCI have increased brain oxidative damage before the onset of symptomatic dementia. Measurement of this isoprostane may identify a subgroup of patients with MCI with increased lipid peroxidation who are at increased risk to progress to symptomatic AD.     

Protein modification by the lipid peroxidation product 4-hydroxynonenal in the spinal cords of amyotrophic lateral sclerosis patients

We report increased modification of proteins by 4-hydroxynoneal (HNE), a product of membrane lipid peroxidation, in the lumbar spinal cord of sporadic amyotrophic lateral sclerosis (ALS) patients versus that of neurologically normal controls. By immunohistochemistry, HNE-protein modification was detected in ventral horn motor neurons, and immunoprecipitation analysis revealed that one of the proteins modified by HNE was the astrocytic glutamate transporter EAAT2. Given that the function of proteins modified by HNE can be severely compromised as previously demonstrated for glutamate transporters in cortical synaptosome preparatations, our findings suggest a scenario in which oxidative stress leads to the production of HNE, impairment of gluatmate transport, and excitotoxic motor neuron degeneration in ALS.     

Redox proteomics identification of oxidatively modified brain proteins in Alzheimer's disease and mild cognitive impairment: insights into the progression of this dementing disorder

Alzheimer disease is a common age-related neurodegenerative disease characterized pathologically by senile plaques, neurofibrillary tangles, synaptic disruption, and progressive neuronal deficits. The senile plaques contain amyloid-beta (1-42) and amyloid-beta (1-40), that has been shown by a number of laboratories to induce oxidative stress and as well as neurodegeneration, although the exact mechanisms remained to be defined. Our laboratory showed an increased oxidative stress in AD and MCI brain as indexed by protein oxidation and lipid peroxidation. In the present review, we summarize our finding of oxidatively modified proteins using a redox proteomics approach in AD and MCI brain to investigate the mechanism that may be involved in MCI and AD pathogenesis and discuss our findings in terms of AD progression and pathogenesis.     

Oxidative damage in mild cognitive impairment and early Alzheimer's disease

Increasing evidence supports a role for oxidative damage in the pathogenesis of Alzheimer's disease (AD). Multiple studies show significantly increased levels of lipid peroxidation and protein, DNA, and RNA oxidation in vulnerable regions of the brain of patients with late-stage AD (LAD). More recent studies of patients with amnestic mild cognitive impairment (MCI), the earliest clinical manifestation of AD, show similar patterns of oxidative damage. These observations suggest that oxidative damage to critical biomolecules occurs early in the pathogenesis of AD and precedes pronounced neuropathologic alterations. Because oxidative damage begins early in the progress of the disease, it represents a potential therapeutic target for slowing the onset and progression of AD.     

The neurofilament heavy chain (NfH) in the cerebrospinal fluid diagnosis of Alzheimer's disease

BACKGROUND/AIMS: Attempting to improve the cerebrospinal fluid (CSF) diagnosis of Alzheimer's disease (AD), the neurofilament heavy chain isoform, NfH(SMI35) was compared to other CSF markers [total tau, phospho-tau, amyloid beta 1-42 (Abeta42), the ratio of amyloid beta fragments Abeta42/Abeta40 (Abeta ratio)]. METHODS: CSF levels were determined in patients with AD (n = 109), mild cognitive impairment (MCI, n = 25), frontotemporal dementia (n = 15), vascular dementia (VD, n = 41), and controls (n = 58). RESULTS: CSF NfH(SMI35) was elevated in AD and VD as compared to controls (p < 0.05). Total tau was higher in AD as compared to controls (p < 0.05). CSF phospho-tau was elevated in AD as compared to controls and VD (p < 0.05 each). CSF Abeta42 and Abeta ratios in AD were lower than in MCI and controls (p < 0.05 each). CONCLUSION: The diagnostic potential of NfH(SMI35) is not superior to that of other CSF markers.     

Lipid peroxidation during human cerebral myelination

The critical period of human cerebral myelination is characterized by rapid production of cellular membranes. We hypothesize that this period is subject to the "physiological" generation of free radicals resulting in lipid peroxidation (LPO). In this study, oxidative markers were examined in developing human parietal white matter using 4-hydroxy-2-nonenal (HNE) protein adducts as an indicator of LPO. Immunocytochemistry showed an increase in HNE-positive glia from 40 gestational weeks to 1.5 postnatal years encompassing the peak period of myelin sheath synthesis at this site. Western blots showed a distinct pattern of HNE-modified proteins at fetal/term ages 26 to 42 gestational weeks and a second, different pattern at 45 gestational weeks to 2.5 postnatal years. Proteins modified by HNE in the latter period, corresponding to active myelination, were identified using mass spectrometry. The most prominent category of HNE modification included cytoskeletal proteins such as tubulins and neurofilaments. Other categories included cell type-specific proteins for mature oligodendrocytes and astrocytes and proteins involved in cell cycle and energy metabolism. We conclude that human brain development involves basal levels of oxidative stress and resulting LPO and that these processes target different proteins in an age-specific manner, thereby likely playing distinct roles during different periods of brain maturation.     

Potential in vivo amelioration by N‐acetyl‐L‐cysteine of oxidative stress in brain in human double mutant APP/PS‐1 knock‐in mice: Toward therapeutic modulation of mild cognitive impairment

Alzheimer's disease (AD) is the most prevalent form of dementia among the elderly. Although the underlying cause has yet to be established, numerous data have shown that oxidative stress is implicated in AD as well as in preclinical stages of AD, such as mild cognitive impairment (MCI). The oxidative stress observed in brains of subjects with AD and MCI may be due, either fully or in part, to increased free radicals mediated by amyloid‐β peptide (Aβ). By using double human mutant APP/PS‐1 knock‐in mice as the AD model, the present work demonstrates that the APP/PS‐1 double mutation results in elevated protein oxidation (as indexed by protein carbonyls), protein nitration (as indexed by 3‐nitrotyrosine), as well as lipid peroxidation (as indexed by protein‐bound 4‐hydroxy‐2‐nonenal) in brains of mice aged 9 months and 12 months. APP/PS‐1 mice also exhibited lower levels of brain glutathione peroxidase (GPx) in both age groups studied, whereas glutathione reductase (GR) levels in brain were unaffected by the mutation. The activities of both of these antioxidant enzymes were significantly decreased in APP/PS‐1 mouse brains, whereas the activity of glucose‐6‐phosphate dehydrogenase (G6PDH) was increased relative to controls in both age groups. Levels of peptidyl prolyl isomerase 1 (Pin1) were significantly decreased in APP/PS‐1 mouse brain aged 9 and 12 months. Administration of N‐acetyl‐L‐cysteine (NAC), a glutathione precursor, to APP/PS‐1 mice via drinking water suppressed increased protein oxidation and nitration and also significantly augmented levels and activity of GPx in brain from both age groups. Oral administration of NAC also increased the diminished activity of GR and protected against lipid peroxidation in brains of 9‐month‐old APP/PS‐1 mice only. Pin1 levels, GR levels, and G6PDH activity in brain were unaffected by oral administration of NAC in both age groups. These results are discussed with reference to the therapeutic potential of this brain‐accessible glutathione precursor in the treatment of MCI and AD. © 2010 Wiley‐Liss, Inc.     

Overexpression of aldehyde dehydrogenase 1A1 reduces oxidation‐induced toxicity in SH‐SY5Y neuroblastoma cells

Oxidative stress leading to lipid peroxidation is a problem in neurodegenerative diseases, because the brain is rich in polyunsaturated fatty acids and low in endogenous antioxidants. One of the most toxic byproducts of lipid peroxidation, 4‐hydroxynonenal (HNE), is implicated in oxidative stress‐induced damage in neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). In this study, the human neuroblastoma cell line SH‐SY5Y was used to test the protective effects of increasing the detoxification of HNE by overexpressing the HNE‐detoxifying enzyme aldehyde dehydrogenase 1A1 (ALDH1). Overexpression of ALDH1 in the SH‐SY5Y cells acts to reduce production of protein–HNE adducts and activation of caspase‐3. Our data suggest that detoxification of HNE could be therapeutic in preventing some of the toxic disruptions of the brain's redox systems found in many neurodegenerative diseases. © 2009 Wiley‐Liss, Inc.