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

Effects of lisinopril on NMDA receptor subunits 2A and 2B levels in the hippocampus of rats with L-NAME-induced hypertension

Hypertension is major risk factor leading to cerebrovascular pathologies. N-methyl D-aspartate receptors (NMDARs) and renin-angiotensin system are involved in neuronal plasticity, as well as cognitive functions in the hippocampus. In this study, we examined the effects of lisinopril, an ACE inhibitor, on the levels of hippocampal NMDAR subunits; NR2A and NR2B in L-NAME (N(ε)-nitro-L-arginine Methyl Ester)-induced hypertensive rats. In addition, malondialdehyde (MDA) levels were measured as a marker for lipid peroxidation. Compared with the control group, the MDA level was significantly increased after 8 weeks in the L-NAME-treated group. Rats treated with lisinopril and L-NAME plus lisinopril were found to have significantly decreased hippocampal MDA levels. Regarding the hippocampal concentrations of NR2A and NR2B, there were no statistically significant differences between groups. We demonstrated that lisinopril treatment has no direct regulatory effect on the levels of NR2A and NR2B in the rat hippocampus. Our results showed that Lisinopril could act as an antioxidant agent against hypertension-induced oxidative stress in rat hippocampus. The findings support that the use of lisinopril may offer a good alternative in the treatment of hypertension by reducing not only blood pressure but also prevent hypertensive complications in the brain.

Intranasal administration of TAT-haFGF(₁₄₋₁₅₄) attenuates disease progression in a mouse model of Alzheimer's disease

Human acidic fibroblast growth factor (haFGF), a neurotrophin-like growth factor in the brain, plays important roles in the development, differentiation and regeneration of brain neurons, which makes it potential to treat Alzheimer's disease (AD). In this study, haFGF(14-154) and TAT-haFGF(14-154) (haFGF(14-154) fused with the cell-penetrating peptide transactivator of transcription protein transduction domain (TAT-PTD)) were intranasally administrated for 5 weeks to investigate the effects on senescence-accelerated mouse prone-8 (SAMP8) mice (a mouse model of AD). Results showed that TAT-PTD could increase the concentration of haFGF in the brain significantly, and TAT-haFGF(14-154) was more effective than haFGF(14-154) in the same dosage (300 μg/kg). Importantly, TAT-haFGF(14-154) improved the learning and memory abilities of SAMP8 mice in the behavioral test, and promoted the function of cholinergic system by measuring the relevant biomarkers (acetylcholine (ACh) level, acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) activities). TAT-haFGF(14-154) also significantly reduced β-amyloid protein(1-42) (Aβ(1-42)) deposits as well as the levels of Aβ soluble forms in the mice brains and prevented the neurons from apoptosis. Besides, the oxidative stress impairment in the brain and serum was also ameliorated. The results suggest that TAT-haFGF(14-154) could attenuate the disease progression of SAMP8 AD mice, and the mechanism is related to the regulation of neurons microenvironment including neurotransmitters, Aβ pathology and oxidative stress.

Oxidative lipid modification of nicastrin enhances amyloidogenic γ-secretase activity in Alzheimer's disease

The cause of elevated level of amyloid β-peptide (Aβ42) in common late-onset sporadic [Alzheimer's disease (AD)] has not been established. Here, we show that the membrane lipid peroxidation product 4-hydroxynonenal (HNE) is associated with amyloid and neurodegenerative pathologies in AD and that it enhances γ-secretase activity and Aβ42 production in neurons. The γ-secretase substrate receptor, nicastrin, was found to be modified by HNE in cultured neurons and in brain specimens from patients with AD, in which HNE-nicastrin levels were found to be correlated with increased γ-secretase activity and Aβ plaque burden. Furthermore, HNE modification of nicastrin enhanced its binding to the γ-secretase substrate, amyloid precursor protein (APP) C99. In addition, the stimulation of γ-secretase activity and Aβ42 production by HNE were blocked by an HNE-scavenging histidine analog in a 3xTgAD mouse model of AD. These findings suggest a specific molecular mechanism by which oxidative stress increases Aβ42 production in AD and identify HNE as a novel therapeutic target upstream of the γ-secretase cleavage of APP.

Inhibition of aminoacylase 3 protects rat brain cortex neuronal cells from the toxicity of 4-hydroxy-2-nonenal mercapturate and 4-hydroxy-2-nonenal

4-Hydroxy-2-nonenal (4HNE) and acrolein (ACR) are highly reactive neurotoxic products of lipid peroxidation that are implicated in the pathogenesis and progression of Alzheimer's and Parkinson's diseases. Conjugation with glutathione (GSH) initiates the 4HNE and ACR detoxification pathway, which generates the mercapturates of 4HNE and ACR that can be excreted. Prior work has shown that the efficiency of the GSH-dependent renal detoxification of haloalkene derived mercapturates is significantly decreased upon their deacetylation because of rapid transformation of the deacetylated products into toxic compounds mediated by β-lyase. The enzymes of the GSH-conjugation pathway and β-lyases are expressed in the brain, and we hypothesized that a similar toxicity mechanism may be initiated in the brain by the deacetylation of 4HNE- and ACR-mercapturate. The present study was performed to identify an enzyme(s) involved in 4HNE- and ACR-mercapturate deacetylation, characterize the brain expression of this enzyme and determine whether its inhibition decreases 4HNE and 4HNE-mercapturate neurotoxicity. We demonstrated that of two candidate deacetylases, aminoacylases 1 (AA1) and 3 (AA3), only AA3 efficiently deacetylates both 4HNE- and ACR-mercapturate. AA3 was further localized to neurons and blood vessels. Using a small molecule screen we generated high-affinity AA3 inhibitors. Two of them completely protected rat brain cortex neurons expressing AA3 from the toxicity of 4HNE-mercapturate. 4HNE-cysteine (4HNE-Cys) was also neurotoxic and its toxicity was mostly prevented by a β-lyase inhibitor, aminooxyacetate. The results suggest that the AA3 mediated deacetylation of 4HNE-mercapturate may be involved in the neurotoxicity of 4HNE.

Mitochondrial- and endoplasmic reticulum-associated oxidative stress in Alzheimer's disease: from pathogenesis to biomarkers

Alzheimer's disease (AD) is the most common cause of dementia in the elderly, affecting several million of people worldwide. Pathological changes in the AD brain include the presence of amyloid plaques, neurofibrillary tangles, loss of neurons and synapses, and oxidative damage. These changes strongly associate with mitochondrial dysfunction and stress of the endoplasmic reticulum (ER). Mitochondrial dysfunction is intimately linked to the production of reactive oxygen species (ROS) and mitochondrial-driven apoptosis, which appear to be aggravated in the brain of AD patients. Concomitantly, mitochondria are closely associated with ER, and the deleterious crosstalk between both organelles has been shown to be involved in neuronal degeneration in AD. Stimuli that enhance expression of normal and/or folding-defective proteins activate an adaptive unfolded protein response (UPR) that, if unresolved, can cause apoptotic cell death. ER stress also induces the generation of ROS that, together with mitochondrial ROS and decreased activity of several antioxidant defenses, promotes chronic oxidative stress. In this paper we discuss the critical role of mitochondrial and ER dysfunction in oxidative injury in AD cellular and animal models, as well as in biological fluids from AD patients. Progress in developing peripheral and cerebrospinal fluid biomarkers related to oxidative stress will also be summarized.

Alzheimer's disease: redox dysregulation as a common denominator for diverse pathogenic mechanisms

Alzheimer's disease (AD) is the most common cause of dementia and a progressive neurodegeneration that appears to result from multiple pathogenic mechanisms (including protein misfolding/aggregation, involved in both amyloid β-dependent senile plaques and tau-dependent neurofibrillary tangles), metabolic and mitochondrial dysfunction, excitoxicity, calcium handling impairment, glial cell dysfunction, neuroinflammation, and oxidative stress. Oxidative stress, which could be secondary to several of the other pathophysiological mechanisms, appears to be a major determinant of the pathogenesis and progression of AD. The identification of oxidized proteins common for mild cognitive impairment and AD suggests that key oxidation pathways are triggered early and are involved in the initial progression of the neurodegenerative process. Abundant data support that oxidative stress, also considered as a main factor for aging, the major risk factor for AD, can be a common key element capable of articulating the divergent nature of the proposed pathogenic factors. Pathogenic mechanisms influence each other at different levels. Evidence suggests that it will be difficult to define a single-target therapy resulting in the arrest of progression or the improvement of AD deterioration. Since oxidative stress is present from early stages of disease, it appears as one of the main targets to be included in a clinical trial. Exploring the articulation of AD pathogenic mechanisms by oxidative stress will provide clues for better understanding the pathogenesis and progression of this dementing disorder and for the development of effective therapies to treat this disease.

Molecular neuropathogenesis of Alzheimer's disease: an interaction model stressing the central role of oxidative stress

Alzheimer's disease (AD) exhibits a complex etiology that simultaneously manifests as a complex cellular, neurobiological, molecular, anatomic-physiological and clinical entity. Other significant psychiatric conditions, such as depression and schizophrenia, may also present with complex and concurrent clinical and/or molecular phenotypes. These neuropsychiatric pathologies also originate from both environmental and genetic factors. We analyzed the molecular phenotypes of AD and discuss them with respect to the classical theories, which we integrated into mechanisms that share molecular and/or anatomical connections. Based on these mechanisms, we propose an interaction model and discuss the model in light of studies that refute or support it. Given the spectrum of AD phenotypes, we limit the scope of our discussion to a few, which facilitates concrete analysis. In addition, the study of specific, individual pathogenic phenotypes may be critical to defining the complex mechanisms leading to AD, thereby improving strategies for developing novel therapies.

The earliest stage of cognitive impairment in transition from normal aging to Alzheimer disease is marked by prominent RNA oxidation in vulnerable neurons

Although neuronal RNA oxidation is a prominent and established feature in age-associated neurodegenerative disorders such as Alzheimer disease (AD), oxidative damage to neuronal RNA in aging and in the transitional stages from normal elderly to the onset of AD has not been fully examined. In this study, we used an in situ approachto identify an oxidized RNA nucleoside 8-hydroxyguanosine (8OHG) in the cerebral cortex of 65 individuals without dementia ranging in age from 0.3 to 86 years. We also examined brain samples from 20 elderly who were evaluated for their premortem clinicaldementia rating score and postmortem brain pathologic diagnoses to investigate preclinical AD and mild cognitive impairment. Relative density measurements of 8OHG-immunoreactivity revealed a statistically significant increase in neuronal RNA oxidation during aging in the hippocampus and the temporal neocortex. In subjects with mild cognitive impairment but not preclinical AD, neurons of the temporal cortex showed a higher burden of oxidized RNA compared to age-matched controls. These results indicate that, although neuronal RNA oxidation fundamentally occurs as an age-associated phenomenon, more prominent RNA damage than in normal aging correlates with the onset of cognitive impairment in the prodromal stage of AD.

Dietary omega 3 polyunsaturated fatty acids and Alzheimer's disease: interaction with apolipoprotein E genotype

Epidemiological studies suggest a protective role of omega-3 poly-unsaturated fatty acids (n-3 PUFA) against Alzheimer's disease (AD). However, most intervention studies of supplementation with n-3 PUFA have yielded disappointing results. One reason for such discordant results may result from inadequate targeting of individuals who might benefit from the supplementation, in particular because of their genetic susceptibility to AD. The ε4 allele of the apolipoprotein E gene (ApoE) is a genetic risk factor for late-onset AD. ApoE plays a key role in the transport of cholesterol and other lipids involved in brain composition and functioning. The action of n-3 PUFA on the aging brain might therefore differ according to ApoE polymorphism. The aim of this review is to examine the interaction between dietary fatty acids and ApoE genotype on the risk for AD. Carriers of the ε4 allele tend to be the most responsive to changes in dietary fat and cholesterol. Conversely, several epidemiological studies suggest a protective effect of long-chain n-3 PUFA on cognitive decline only in those who do not carry ε4 but with inconsistent results. An intervention study showed that only non-carriers had increased concentrations of long-chain n-3 PUFA in response to supplementation. The mechanisms underlying this gene-by-diet interaction on AD risk may involve impaired fatty acids and cholesterol transport, altered metabolism of n-3 PUFA, glucose or ketones, or modification of other risk factors of AD in ε4 carriers. Further research is needed to explain the differential effect of n-3 PUFA on AD according to ApoE genotype.

Lipid peroxidation and neurodegenerative disease

Lipid peroxidation is a complex process involving the interaction of oxygen-derived free radicals with polyunsaturated fatty acids, resulting in a variety of highly reactive electrophilic aldehydes. Since 1975, lipid peroxidation has been extensively studied in a variety of organisms. As neurodegenerative diseases became better understood, research establishing a link between this form of oxidative damage, neurodegeneration, and disease has provided a wealth of knowledge to the scientific community. With the advent of proteomics in 1995, the identification of biomarkers for neurodegenerative disorders became of paramount importance to better understand disease pathogenesis and develop potential therapeutic strategies. This review focuses on the relationship between lipid peroxidation and neurodegenerative diseases. It also demonstrates how findings in current research support the common themes of altered energy metabolism and mitochondrial dysfunction in neurodegenerative disorders.

Neuroprotective strategies involving ROS in Alzheimer disease

Alzheimer disease (AD) is a neurodegenerative disorder in which oxidative stress is a key hallmark. It occurs early in disease pathogenesis and can exacerbate its progression. Several causes of oxidative stress have been determined over the years. First, mitochondria play an important role in the generation and accumulation of free radicals. In addition to mitochondria, inflammation can also induce oxidative damage, especially via microglia, and microglia are also important for Aβ clearance. In AD, both mitochondrial function and inflammatory response are affected, leading to increased ROS formation and oxidative damage to lipid, proteins, and nucleic acids. Some other sources have also been identified. From these findings, various neuroprotective strategies against ROS-mediated damages have been elaborated in AD research. This review recapitulates some of the major strategies used to prevent oxidative stress and disease progression. Outcomes from in vitro and in vivo studies using models of AD are encouraging. However, only a few clinical trials have provided positive results in terms of slowing down cognitive decline. Nonetheless, there is still hope for improved compounds that would better target pathways implicated in ROS production. In fact, facilitating the endogenous antioxidant system by modulating transcription has great promise for AD therapy.

Evaluation of respiratory chain activity in lymphocytes of patients with Alzheimer disease

Alzheimer disease (AD) is a progressive neurodegenerative disease associated with cognitive impairment in multiple domains, such as memory and executive functions. Studies reveal damage in the electron transport chain of patients with AD, suggesting that this mitochondrial dysfunction plays an important role in the pathophysiology of the disease. Blood samples were taken from patients with AD (n = 20) and older subjects without dementia (n = 40) to evaluate the activity of complexes I, II, II-III, and IV of the mitochondrial respiratory chain in isolated lymphocytes. Results from the patient and control groups were compared. The activity of complexes II and IV was increased among patients compared to the control group. No significant difference was observed between controls who were not using psychotropic medication and patients. Our findings point out a mechanism of cellular compensation in which the mitochondrial respiratory chain requires an increase in electron transport to supply the energy needed for cellular functioning. Additional studies are needed to better clarify the mechanisms involved in the mitochondrial dynamics of AD.

Dietary lipids and their oxidized products in Alzheimer's disease

Alzheimer's disease (AD) is the commonest form of dementia in the elderly, characterized by memory dysfunction, loss of lexical access, spatial and temporal disorientation, and impaired judgment. A growing body of scientific literature addresses the implication of dietary habits in the pathogenesis of AD. This review reports recent findings concerning the modulation of AD development by dietary lipids, in animals and humans, focusing on the pathogenetic role of lipid oxidation products. Oxidative breakdown products of ω-6 polyunsaturated fatty acids (ω-6 PUFAs), and cholesterol oxidation products (oxysterols), might play a role in favoring β-amyloid deposition, a hallmark of AD's onset and progression. Conversely, ω-3 PUFAs appear to contribute to preventing and treating AD. However, high concentrations of ω-3 PUFAs can also produce oxidized derivatives reacting with important functions of nervous cells. Thus, altered balances between cholesterol and oxysterols, and between ω-3 and ω-6 PUFAs must be considered in AD's pathophysiology. The use of a diet with an appropriate ω-3/ω-6 PUFA ratio, rich in healthy oils, fish and antioxidants, such as flavonoids, but low in cholesterol-containing foods, can be a beneficial component in the clinical strategies of prevention of AD.

Oxidatively modified nucleic acids in preclinical Alzheimer's disease (PCAD) brain

Previous studies show increased oxidative DNA and RNA damage and diminished 8-oxoguanine glycosylase (OGG1) mediated base excision repair in vulnerable brain regions of mild cognitive impairment and late-stage Alzheimer's disease (LAD) subjects compared to normal control (NC) subjects. Recently, a preclinical stage of AD (PCAD) has been described in which subjects show no overt clinical manifestations of AD but demonstrate significant AD pathology at autopsy. To determine if DNA or RNA oxidation are significantly elevated in PCAD brain we quantified 8-hydroxyguanine (8-OHG) in sections of hippocampus/parahippocamapal gyri in PCAD and NC subjects using immunohistochemistry and confocal microscopy and in superior and middle temporal gyri (SMTG) using gas chromatography/mass spectrometry. To determine if increased DNA oxidation is associated with altered repair capacity, levels of OGG1 protein in HPG were measured by immunohistochemistry and levels of OGG1 mRNA were measured in SMTG using quantitative PCR. Results show significantly increased (p<0.05) 8-OHG immunostaining in DNA and RNA of PCAD HPG and significantly increased 8-OHG in PCAD SMTG. Quantification of OGG1 showed significantly elevated mRNA in PCAD SMTG and a trend toward elevated protein immunostaining in PCAD HPG. Overall, the data suggest oxidative damage to nucleic acids and a compensatory increase in OGG1 expression occur early in the pathogenesis of AD.

Oral zinc supplementation does not improve oxidative stress or vascular function in patients with type 2 diabetes with normal zinc levels

OBJECTIVE

There is considerable controversy about what constitutes optimal zinc intakes in patients with type 2 diabetes mellitus. Several studies suggest that higher zinc intakes improve vascular function and decrease oxidative damage. We aimed to assess the effects of zinc supplementation using a range of reliable biomarkers of oxidative damage and vascular function in patients with type 2 diabetes.

METHODS

Forty male type 2 diabetic patients were supplemented either with 240 mg/day of zinc as zinc gluconate (n=20) or with placebo (n=20) for 3 months. Blood and spot urine samples were taken at baseline, days 3 and 7, months 1, 2 and 3 during supplementation and 1 month after cessation. Serum zinc, reliable biomarkers of oxidative damage (F(2)-isoprostanes, neuroprostanes, cholesterol oxidation products, allantoin) as well as hydroxyeicosatetraenoic acid products and vascular-related indices (augmentation index, pulse wave velocity and aortic pressure) were measured.

RESULTS

Despite significantly higher levels of serum zinc in the treatment group, markers of oxidative damage, levels of hydroxyeicosatetraenoic acid products and vascular indices were unchanged by zinc supplementation during the four-month study period.

CONCLUSION

Improving the zinc status in patients with type 2 diabetes with normal zinc levels did not have any impact on oxidative damage and vascular function, and such supplementation may not be generally beneficial in these individuals.

Biomarkers of oxidative damage in cigarette smokers: which biomarkers might reflect acute versus chronic oxidative stress?

Cigarette smoking predisposes to the development of multiple diseases involving oxidative damage. We measured a range of oxidative damage biomarkers to understand which differ between smokers and nonsmokers and if the levels of these biomarkers change further during the act of smoking itself. Despite overnight abstinence from smoking, smokers had higher levels of plasma total and esterified F(2)-isoprostanes, hydroxyeicosatetraenoic acid products (HETEs), F(4)-neuroprostanes, 7-ketocholesterol, and 24- and 27-hydroxycholesterol. Levels of urinary F(2)-isoprostanes, HETEs, and 8-hydroxy-2'-deoxyguanosine were also increased compared with age-matched nonsmokers. Several biomarkers (plasma free F(2)-isoprostanes, allantoin, and 7β-hydroxycholesterol and urinary F(2)-isoprostane metabolites) were not elevated. The smokers were then asked to smoke a cigarette; this acute smoking elevated plasma and urinary F(2)-isoprostanes, plasma allantoin, and certain cholesterol oxidation products compared to presmoking levels, but not plasma HETEs or urinary 8-hydroxy-2'-deoxyguanosine. Smokers showed differences in plasma fatty acid composition. Our findings confirm that certain oxidative damage biomarkers are elevated in smokers even after a period of abstinence from smoking, whereas these plus some others are elevated after acute smoking. Thus, different biomarkers do not measure identical aspects of oxidative stress.

Methionine-35 of aβ(1-42): importance for oxidative stress in Alzheimer disease

Alzheimer disease (AD) is an age-related progressive neurodegenerative disorder. This devastating disease is characterized by the presence of senile plaques (SP), neurofibrillary tangles (NFTs), and loss of synapses. Amyloid beta-peptide 1-42 (Aβ(1-42)) is the main component of SP and is pivotal to AD pathogenesis. Brain of subjects with AD and arguably its earliest manifestation, mild cognitive impairment (MCI), demonstrate increased levels of oxidative stress markers. Our laboratory combined these two aspects of AD and MCI and proposed the Aβ(1-42)-associated free radical oxidative stress hypothesis to explain oxidative stress under which the MCI and AD brain exist and the loss of synapses in both disorders. A large number of in vitro and in vivo studies showed that Aβ causes protein oxidation, lipid peroxidation, reactive oxygen species formation, and cell death in neuronal and synaptosomal systems. Methionine located at residue 35 of Aβ(1-42) is an important contributor to the oxidative stress associated with this neurotoxic peptide. In this paper, we summarize studies involving Met-35 of Aβ(1-42). Understanding the role of the single methionine residue of Aβ(1-42) may help in understanding underlying disease mechanisms in AD and MCI.

Identification of the oxidative stress proteome in the brain

The redox proteomics technique normally combines two-dimensional gel electrophoresis, mass spectrometry, and protein databases to analyze the cell proteome from various samples, thereby leading to the identification of specific targets of oxidative modification. Oxidative stress that occurs because of increased levels of reactive oxygen species and reactive nitrogen species can target most biomolecules, consequently leading to altered physiological function of the cells. Redox proteomics has identified oxidatively modified protein targets in various pathological conditions, consequently providing insight into the pathways involved in the pathogenesis of these conditions. This approach also can be used to identify possible protective mechanisms to prevent or delay these disorders.

Trans-4-oxo-2-nonenal potently alters mitochondrial function

Alzheimer disease elevates lipid peroxidation in the brain and data indicate that the resulting lipid-aldehydes are pathological effectors of lipid peroxidation. The disposition of 4-substituted nonenals derived from arachidonate (20:4, n-6) and linoleate (18:2, n-6) oxidation is modulated by their protein adduction targets, their metabolism, and the nature of the 4-substitutent. Trans-4-oxo-2-nonenal (4-ONE) has a higher toxicity in some systems than the more commonly studied trans-4-hydroxy-2-nonenal (HNE). In this work, we performed a structure-function analysis of 4-hydroxy/oxoalkenal upon mitochondrial endpoints. We tested the hypotheses that 4-ONE, owing to a highly reactive nature, is more toxic than HNE and that HNE toxicity is enantioselective. We chose to study freshly isolated brain mitochondria because of the role of mitochondrial dysfunction in neurodegenerative disorders. Whereas there was little effect related to HNE chirality, our data indicate that in the mitochondrial environment, the order of toxic potency under most conditions was 4-ONE>HNE. 4-ONE uncoupled mitochondrial respiration at a concentration of 5μM and inhibited aldehyde dehydrogenase 2 (ALDH2) activity with an IC(50) of approximately 0.5μM. The efficacy of altering mitochondrial endpoints was ALDH2 inhibition>respiration=mitochondrial swelling=ALDH5A inhibition>GSH depletion. Thiol-based alkenal scavengers, but not amine-based scavengers, were effective in blocking the effects of 4-ONE upon respiration. Quantum mechanical calculations provided insights into the basis for the elevated reactivity of 4-ONE>HNE. Our data demonstrate that 4-ONE is a potent effector of lipid peroxidation in the mitochondrial environment.

Roles of 3-nitrotyrosine- and 4-hydroxynonenal-modified brain proteins in the progression and pathogenesis of Alzheimer's disease

Proteins play an important role in normal structure and function of the cells. Oxidative modification of proteins may greatly alter the structure and may subsequently lead to loss of normal physiological cell functions and may lead to abnormal function of cell and eventually to cell death. These modifications may be reversible or irreversible. Reversible protein modifications, such as phosphorylation, can be overcome by specific enzymes that cause a protein to 'revert' back to its original protein structure, while irreversible protein modifications cannot. Several important irreversible protein modifications include protein nitration and HNE modification, both which have been extensively investigated in research on the progression of Alzheimer's disease (AD). From the earliest stage of AD throughout the advancement of the disorder there is evidence of increased protein nitration and HNE modification. These protein modifications lead to decreased enzymatic activity, which correlates directly to protein efficacy and provides support for several common themes in AD pathology, namely altered energy metabolism, mitochondrial dysfunction and reduced cholinergic neurotransmission. The current review summarized some of the findings on protein oxidation related to different stages of Alzheimer's disease (AD) that will be helpful in understanding the role of protein oxidation in the progression and pathogenesis of AD.

Plasma F2-isoprostane level and cognitive function over eight years in non-demented older adults: Findings from the Health ABC Study

F2-isoprostanes (F2-IsoP) are reportedly increased in dementia patients, and are considered a reliable biomarker of oxidation. However, few studies have examined the predictive value of peripheral F2-IsoP levels in non-demented older adults. This study assesses the association between plasma F2-IsoP and change in cognitive function in non-demented elderly over eight years. Plasma F2-IsoP was measured by gas chromatography-mass spectrometry in a biracial cohort of 726 elderly men and women. Digit Symbol Substitution test and the Modified Mini-Mental State Exam were administered over time. No association was found between F2-IsoP tertile and baseline or change (slope) in cognitive function over eight years. Plasma F2-IsoP is not a valuable biomarker in predicting cognitive change over years in non-demented older adults.

Why docosahexaenoic acid and aspirin supplementation could be useful in women as a primary prevention therapy against Alzheimer's disease?

The assumption that disease specific risk factors are similar or the same in men and women may lead to incorrect primary prevention strategies. This study focused on the evaluation of gender-specific Alzheimer's disease (AD) risk factors. In AD, female gender appears to be an important risk factor associated with the aberrant production of beta amyloid (βA) peptides. Although decreased levels in plasma DHA concentration are associated with cognitive decline in healthy elderly and Alzheimer's patients, pre-treatment with DHA significantly reduced the survival of cortical neurons incubated with beta amyloid (βA). Hence, in the presence of an increasing amount of βA, paradoxically women - who have higher plasma levels of DHA - are more likely to develop AD. Aspirin (ASA) converts cyclooxygenase (COX)-2 into a form that generates new neuroprotective docosanoids from DHA; therefore, ASA might positively resolve the paradoxical effect of the concomitant presence of DHA and βA.

Hypothesis: soluble aβ oligomers in association with redox-active metal ions are the optimal generators of reactive oxygen species in Alzheimer's disease

Considerable evidence points to oxidative stress in the brain as an important event in the early stages of Alzheimer's disease (AD). The transition metal ions of Cu, Fe, and Zn are all enriched in the amyloid cores of senile plaques in AD. Those of Cu and Fe are redox active and bind to Aβ in vitro. When bound, they can facilitate the reduction of oxygen to hydrogen peroxide, and of the latter to the hydroxyl radical. This radical is very aggressive and can cause considerable oxidative damage. Recent research favours the involvement of small, soluble oligomers as the aggregating species responsible for Aβ neurotoxicity. We propose that the generation of reactive oxygen species (i.e., hydrogen peroxide and hydroxyl radicals) by these oligomers, in association with redox-active metal ions, is a key molecular mechanism underlying the pathogenesis of AD and some other neurodegenerative disorders.

Oxidative damage is present in the fatal brain edema of diabetic ketoacidosis

Oxidative stress is implicated as a pathogenic factor in a spectrum of chronic diseases, notably, neurodegenerative disease. Noteworthy in this regard is that type 1 diabetes mellitus (T1DM) results in oxidative stress, leading to systemic complications of T1DM. We hypothesized that oxidative stress associated with diabetic ketoacidosis (DKA) of T1DM might have measurable brain sequelae. Consistent with this hypothesis are neurohistology and neuroradiologic studies of T1DM that suggest oxidative insults are involved in the chronic complications of diabetic encephalopathy. To further address the role of oxidative stress in an acute setting, specifically in fatal brain edema (BE) associated with DKA, we studied neuronal localization and levels of oxidative stress markers reported to be increased in other neurodegenerative conditions. We demonstrated increased levels of 8-hydroxyguanosine (8OHG), 4-hydroxynonenal (HNE), and heme oxygenase-1 (HO-1) in the pyramidal neurons of the hippocampus of DKA BE in comparison to controls. However, in the cerebellum, only 8OHG was increased in the Purkinje cells and other cells of the molecular layer. These results indicate a role for oxidative stress in the pathogenesis of T1DM encephalopathy.

Elevated 4-hydroxyhexenal in Alzheimer's disease (AD) progression

Multiple studies have demonstrated elevations of α, β-unsaturated aldehydes including 4-hydroxynonenal (HNE) and acrolein, in vulnerable regions of mild cognitive impairment (MCI), preclinical Alzheimer's disease (PCAD), and late stage Alzheimer's disease (LAD) brain. However, there has been limited study of a third member, 4-hydroxyhexenal (HHE), a diffusible lipid peroxidation product of the ω-3 polyunstataturated fatty acids (PUFAs). In the present study levels of extractable and protein-bound HHE were quantified in the hippocampus/parahippocampal gyrus (HPG), superior and middle temporal gyri (SMTG), and cerebellum (CER) of MCI, PCAD, LAD, and normal control (NC) subjects. Levels of extractable and protein-bound HHE were increased in multiple regions in the progression of Alzheimer's disease (AD). Extractable HHE was significantly elevated in the hippocampus/parahippocampal gyrus (HPG) of PCAD and LAD subjects and protein-bound HHE was significantly higher in MCI, PCAD, and LAD HPG. A time- and concentration-dependent decrease in survival and a concentration-dependent decrease in glucose uptake were observed in primary cortical cultures treated with HHE. Together these data support a role for lipid peroxidation in the progression of Alzheimer's disease.

Transferrin and HFE genes interact in Alzheimer's disease risk: the Epistasis Project

Iron overload may contribute to the risk of Alzheimer's disease (AD). In the Epistasis Project, with 1757 cases of AD and 6295 controls, we studied 4 variants in 2 genes of iron metabolism: hemochromatosis (HFE) C282Y and H63D, and transferrin (TF) C2 and -2G/A. We replicated the reported interaction between HFE 282Y and TF C2 in the risk of AD: synergy factor, 1.75 (95% confidence interval, 1.1-2.8, p = 0.02) in Northern Europeans. The synergy factor was 3.1 (1.4-6.9; 0.007) in subjects with the APOEε4 allele. We found another interaction, between HFE 63HH and TF -2AA, markedly modified by age. Both interactions were found mainly or only in Northern Europeans. The interaction between HFE 282Y and TF C2 has now been replicated twice, in altogether 2313 cases of AD and 7065 controls, and has also been associated with increased iron load. We therefore suggest that iron overload may be a causative factor in the development of AD. Treatment for iron overload might thus be protective in some cases.

Cerebrospinal fluid biomarkers in mild cognitive impairment and dementia

Given the magnitude of the public health problem of dementia in the elderly, there is a pressing need for research, development, and timely application of biomarkers that will identify latent and prodromal illness as well as dementia. Although identification of risk factors and neuroimaging measures will remain key to these efforts, this review focuses on recent progress in the discovery, validation, and standardization of cerebrospinal fluid (CSF) biomarkers, small molecules and macromolecules whose CSF concentration can aid in diagnosis at different stages of disease as well as in assessment of disease progression and response to therapeutics. A multimodal approach that brings independent information from risk factor assessment, neuroimaging, and biomarkers may soon guide physicians in the early diagnosis and management of cognitive impairment in the elderly.

The plasma membrane redox system is impaired by amyloid β-peptide and in the hippocampus and cerebral cortex of 3xTgAD mice

Membrane-associated oxidative stress has been implicated in the synaptic dysfunction and neuronal degeneration that occurs in Alzheimer's disease (AD), but the underlying mechanisms are unknown. Enzymes of the plasma membrane redox system (PMRS) provide electrons for energy metabolism and recycling of antioxidants. Here, we show that activities of several PMRS enzymes are selectively decreased in plasma membranes from the hippocampus and cerebral cortex of 3xTgAD mice, an animal model of AD. Our results that indicate the decreased PMRS enzyme activities are associated with decreased levels of coenzyme Q(10) and increased levels of oxidative stress markers. Neurons overexpressing the PMRS enzymes (NQO1 or cytochrome b5 reductase) exhibit increased resistance to amyloid β-peptide (Aβ). If and to what extent Aβ is the cause of the impaired PMRS enzymes in the 3xTgAD mice is unknown. Because these mice also express mutant tau and presenilin-1, it is possible that one or more of the PMRS could be adversely affected by these mutations. Nevertheless, the results of our cell culture studies clearly show that exposure of neurons to Aβ1-42 is sufficient to impair PMRS enzymes. The impairment of the PMRS in an animal model of AD, and the ability of PMRS enzyme activities to protect neurons against Aβ-toxicity, suggest enhancement PMRS function as a novel approach for protecting neurons against oxidative damage in AD and related disorders.

Increased levels of 4-hydroxynonenal and acrolein in the brain in preclinical Alzheimer disease

Previous studies demonstrate increased levels of 4-hydroxynonenal (HNE) and acrolein in vulnerable brain regions of subjects with mild cognitive impairment and late-stage Alzheimer disease (LAD). Recently preclinical AD (PCAD) subjects, who demonstrate normal antemortem neuropsychological test scores but abundant AD pathology at autopsy, have become the focus of increased study. Levels of extractable HNE and acrolein were quantified by gas chromatography-mass spectrometry with negative chemical ionization, and protein-bound HNE and acrolein were quantified by dot-blot immunohistochemistry in the hippocampus/parahippocampal gyrus (HPG), superior and middle temporal gyri (SMTG), and cerebellum (CER) of 10 PCAD and 10 age-matched normal control (NC) subjects. Results of the analyses show a significant (P<0.05) increase in levels of extractable acrolein in the HPG of PCAD subjects compared to age-matched NC subjects and a significant decrease in extractable acrolein in PCAD CER. Significant increases in protein-bound HNE in HPG and a significant decrease in CER of PCAD subjects compared to NC subjects were observed. No significant alterations were observed in either extractable or protein-bound HNE or acrolein in the SMTG of PCAD subjects. Additionally, no significant differences in levels of protein carbonyls were observed in the HPG, SMTG, or CER of PCAD subjects compared to NC subjects.

Interplay between oxidative damage, protein synthesis, and protein degradation in Alzheimer's disease

Protein synthesis and protein degradation are highly regulated cellular processes that are essential to maintaining cell viability. Numerous studies now indicate that protein synthesis and protein degradation are significantly altered in Alzheimer's disease (AD), with impairments in these two processes potentially contributing to AD pathogenesis. Alterations in steady state protein regulation may be a particularly important factor in regulating whether cells maintain homeostasis in response to oxidative damage, or conversely whether oxidative stress is induced by oxidative damage. The focus of this review is to discuss recent findings on each of these topics, and to discuss their importance to the onset and progression of AD.

Tau Ser262 phosphorylation is critical for Abeta42-induced tau toxicity in a transgenic Drosophila model of Alzheimer's disease

The amyloid-beta 42 (Abeta42) peptide has been suggested to promote tau phosphorylation and toxicity in Alzheimer's disease (AD) pathogenesis; however, the underlying mechanisms are not fully understood. Using transgenic Drosophila expressing both human Abeta42 and tau, we show here that tau phosphorylation at Ser262 plays a critical role in Abeta42-induced tau toxicity. Co-expression of Abeta42 increased tau phosphorylation at AD-related sites including Ser262, and enhanced tau-induced neurodegeneration. In contrast, formation of either sarkosyl-insoluble tau or paired helical filaments was not induced by Abeta42. Co-expression of Abeta42 and tau carrying the non-phosphorylatable Ser262Ala mutation did not cause neurodegeneration, suggesting that the Ser262 phosphorylation site is required for the pathogenic interaction between Abeta42 and tau. We have recently reported that the DNA damage-activated Checkpoint kinase 2 (Chk2) phosphorylates tau at Ser262 and enhances tau toxicity in a transgenic Drosophila model. We detected that expression of Chk2, as well as a number of genes involved in DNA repair pathways, was increased in the Abeta42 fly brains. The induction of a DNA repair response is protective against Abeta42 toxicity, since blocking the function of the tumor suppressor p53, a key transcription factor for the induction of DNA repair genes, in neurons exacerbated Abeta42-induced neuronal dysfunction. Our results demonstrate that tau phosphorylation at Ser262 is crucial for Abeta42-induced tau toxicity in vivo, and suggest a new model of AD progression in which activation of DNA repair pathways is protective against Abeta42 toxicity but may trigger tau phosphorylation and toxicity in AD pathogenesis.

Preclinical Alzheimer disease: brain oxidative stress, Abeta peptide and proteomics

Alzheimer disease (AD) is a neurodegenerative disorder characterized clinically by progressive memory loss and subsequent dementia and neuropathologically by senile plaques, neurofibrillary tangles, and synapse loss. Interestingly, a small percentage of individuals with normal antemortem psychometric scores meet the neuropathological criteria for AD (termed 'preclinical' AD (PCAD)). In this study, inferior parietal lobule (IPL) from PCAD and control subjects was compared for oxidative stress markers by immunochemistry, amyloid beta peptide by ELISA, and identification of protein expression differences by proteomics. We observed a significant increase in highly insoluble monomeric Abeta42, but no significant differences in oligomeric Abeta nor in oxidative stress measurements between controls and PCAD subjects. Expression proteomics identified proteins whose trends in PCAD are indicative of cellular protection, possibly correlating with previous studies showing no cell loss in PCAD. Our analyses may reveal processes involved in a period of protection from neurodegeneration that mimic the clinical phenotype of PCAD.

Omega-3 fatty acids: potential role in the management of early Alzheimer's disease

Omega-3 fatty acids are essential for brain growth and development. They play an important role throughout life, as critical modulators of neuronal function and regulation of oxidative stress mechanisms, in brain health and disease. Docosahexanoic acid (DHA), the major omega-3 fatty acid found in neurons, has taken on a central role as a target for therapeutic intervention in Alzheimer’s disease (AD). A plethora of in vitro, animal model, and human data, gathered over the past decade, highlight the important role DHA may play in the development of a variety of neurological and psychiatric disorders, including AD. Cross sectional and prospective cohort data have demonstrated that reduced dietary intake or low brain levels of DHA are associated with accelerated cognitive decline or the development of incipient dementia, including AD. Several clinical trials investigating the effects of omega-3 fatty acid supplementation in AD have been completed and all failed to demonstrate its efficacy in the treatment of AD. However, these trials produced intriguing data suggesting that the beneficial effects of omega-3 fatty acid supplementation may depend on the stage of disease, other dietary mediators, and apolipoprotein E status.

Fourier transform infrared imaging showing reduced unsaturated lipid content in the hippocampus of a mouse model of Alzheimer's disease

Polyunsaturated fatty acids are essential to brain functions such as membrane fluidity, signal transduction, and cell survival. It is also thought that low levels of unsaturated lipid in the brain may contribute to Alzheimer's disease (AD) risk or severity. However, it is not known how accumulation of unsaturated lipids is affected in different regions of the hippocampus, which is a central target of AD plaque pathology, during aging. In this study, we used Fourier transform infrared imaging (FTIRI) to visualize the unsaturated lipid content in specific regions of the hippocampus in the PSAPP mouse model of AD as a function of plaque formation. Specifically, the unsaturated lipid content was imaged using the olefinic =CH stretching mode at 3012 cm(-1). The axonal, dendritic, and somatic layers of the hippocampus were examined in the mice at 13, 24, 40, and 56 weeks old. Results showed that lipid unsaturation in the axonal layer was significantly increased with normal aging in control (CNT) mice (p < 0.01) but remained low and relatively constant in PSAPP mice. Thus, these findings indicate that unsaturated lipid content is reduced in hippocampal white matter during amyloid pathogenesis and that maintaining unsaturated lipid content early in the disease may be critical in avoiding progression of the disease.

Oxidative stress in the progression of Alzheimer disease in the frontal cortex

We investigated oxidative stress in human postmortem frontal cortexfrom individuals characterized as mild cognitive impairment (n= 8), mild/moderate Alzheimer disease (n = 4), and late-stage Alzheimer disease (n = 9). Samples from subjects with no cognitive impairment (n = 10) that were age- and postmortem interval-matched with these cases were used as controls. The short postmortem intervalbrain samples were processed for postmitochondrial supernatant, nonsynaptic mitochondria, and synaptosome fractions. Samples were analyzed for several antioxidants (glutathione, glutathione peroxidase, glutathione reductase, glutathione-S-transferase, glucose-6-phosphate dehydrogenase, superoxide dismutase, catalase) and the oxidative marker, thiobarbituric acid reactive substances. The tissue was also analyzed for possible changes in protein damage using neurochemical markers for protein carbonyls, 3-nitrotyrosine, 4-hydroxynonenal, andacrolein. All 3 neuropil fractions (postmitochondrial supernatant, mitochondrial, and synaptosomal) demonstrated significant disease-dependent increases in oxidative markers. The highest changes were observed in the synaptosomal fraction. Both mitochondrial and synaptosomal fractions had significant declines in antioxidants (glutathione, glutathione peroxidase, glutathione-S-transferase, and superoxide dismutase). Levels of oxidative markers significantly correlated with Mini-Mental Status Examination scores. Oxidative stress was more localized to the synapses, with levels increasing in a disease-dependent fashion. These correlations implicate an involvement of oxidative stress in Alzheimer disease-related synaptic loss.

Redox proteomic analysis of carbonylated brain proteins in mild cognitive impairment and early Alzheimer's disease

Previous studies indicated increased levels of protein oxidation in brain from subjects with Alzheimer's disease (AD), raising the question of whether oxidative damage is a late effect of neurodegeneration or precedes and contributes to the pathogenesis of AD. Hence, in the present study we used a parallel proteomic approach to identify oxidatively modified proteins in inferior parietal lobule (IPL) from subjects with mild cognitive impairment (MCI) and early stage-AD (EAD). By comparing to age-matched controls, we reasoned that such analysis could help in understanding potential mechanisms involved in upstream processes in AD pathogenesis. We have identified four proteins that showed elevated levels of protein carbonyls: carbonic anhydrase II (CA II), heat shock protein 70 (Hsp70), mitogen-activated protein kinase I (MAPKI), and syntaxin binding protein I (SBP1) in MCI IPL. In EAD IPL we identified three proteins: phosphoglycerate mutase 1 (PM1), glial fibrillary acidic protein, and fructose bisphospate aldolase C (FBA-C). Our results imply that some of the common targets of protein carbonylation correlated with AD neuropathology and suggest a possible involvement of protein modifications in the AD progression.

Involvements of the lipid peroxidation product, HNE, in the pathogenesis and progression of Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder. A number of hypotheses have been proposed to explain AD pathogenesis. One such hypothesis proposed to explain AD pathogenesis is the oxidative stress hypothesis. Increased levels of oxidative stress markers including the markers of lipid peroxidation such as acrolein, 4-hydroxy-2-trans-nonenal (HNE), malondialdehyde, etc. are found in brains of AD subjects. In this review, we focus principally on research conducted in the area of HNE in the central nervous system (CNS) of AD and mild cognitive impairment (MCI), and further, we discuss likely consequences of lipid peroxidation with respect to AD pathogenesis and progression. Based on the research conducted so far in the area of lipid peroxidation, it is suggested that lipid accessible antioxidant molecules could be a promising therapeutic approach to treat or slow progression of MCI and AD.

A DNA damage-activated checkpoint kinase phosphorylates tau and enhances tau-induced neurodegeneration

Hyperphosphorylation of the microtubule associated protein tau is detected in the brains of individuals with a range of neurodegenerative diseases including Alzheimer's disease (AD). An imbalance in phosphorylation and/or dephosphorylation of tau at disease-related sites has been suggested to initiate the abnormal metabolism and toxicity of tau in disease pathogenesis. However, the mechanisms underlying abnormal phosphorylation of tau in AD are not fully understood. Here, we show that the DNA damage-activated Checkpoint kinase 2 (Chk2) is a novel tau kinase and enhances tau toxicity in a transgenic Drosophila model. Overexpression of Drosophila Chk2 increases tau phosphorylation at Ser262 and enhances tau-induced neurodegeneration in transgenic flies expressing human tau. The non-phosphorylatable Ser262Ala mutation abolishes Chk2-induced enhancement of tau toxicity, suggesting that the Ser262 phosphorylation site is involved in the enhancement of tau toxicity by Chk2. In vitro kinase assays revealed that human Chk2 and a closely related checkpoint kinase 1 (Chk1) directly phosphorylate human tau at Ser262. We also demonstrate that Drosophila Chk2 does not modulate the activity of the fly homolog of microtubule affinity regulating kinase, which has been shown to be a physiological tau Ser262 kinase. Since accumulation of DNA damage has been detected in the brains of AD patients, our results suggest that the DNA damage-activated kinases Chk1 and Chk2 may be involved in tau phosphorylation and toxicity in the pathogenesis of AD.

L-methylfolate, methylcobalamin, and N-acetylcysteine in the treatment of Alzheimer's disease-related cognitive decline

Neuroinflammatory oxidative stress occurs early in AD pathology. Elevated blood Hcy is a useful marker for such neuroinflammation. Hcy contributes to pathological cascades involving AP and NFTs. In AD, Hcy should be lowered by B-vitamin supplements and NAC.

Current Challenges for the Early Detection of Alzheimer's Disease: Brain Imaging and CSF Studies

The development of prevention therapies for Alzheimer's disease (AD) would greatly benefit from biomarkers that are sensitive to the subtle brain changes that occur in the preclinical stage of the disease. Reductions in the cerebral metabolic rate of glucose (CMRglc), a measure of neuronal function, have proven to be a promising tool in the early diagnosis of AD. In vivo brain 2-[¹⁸F]fluoro-2-Deoxy-D-glucose-positron emission tomography (FDG-PET) imaging demonstrates consistent and progressive CMRglc reductions in AD patients, the extent and topography of which correlate with symptom severity. There is increasing evidence that hypometabolism appears during the preclinical stages of AD and can predict decline years before the onset of symptoms. This review will give an overview of FDG-PET results in individuals at risk for developing dementia, including: presymptomatic individuals carrying mutations responsible for early-onset familial AD; patients with Mild Cognitive Impairment (MCI), often a prodrome to late-onset sporadic AD; non-demented carriers of the Apolipoprotein E (ApoE) ε4 allele, a strong genetic risk factor for late-onset AD; cognitively normal subjects with a family history of AD; subjects with subjective memory complaints; and normal elderly followed longitudinally until they expressed the clinical symptoms and received post-mortem confirmation of AD. Finally, we will discuss the potential to combine different PET tracers and CSF markers of pathology to improve the early detection of AD.