In vitro and in vivo protein oxidation induced by Alzheimer's disease amyloid beta-peptide (1-42)

An intracerebroventricular injection of amyloid-beta peptide (1-42) aggregates modifies daily temporal organization of clock factors expression, protein carbonyls and antioxidant enzymes in the rat hippocampus

Alzheimer disease (AD) is the most frequent form of dementia in the elderly. It is characterized by the deterioration of memory and learning. The histopathological hallmarks of AD include the presence of extracellular deposits of amyloid beta peptide, intracellular neurofibrillary tangles, neuron and synapse loss, in the brain, including the hippocampus. Accumulation of Aβ peptide causes an increase in intracellular reactive oxygen species (ROS) and free radicals associated to a deficient antioxidant defense system. Besides oxidative stress and cognitive deficit, AD patients show alterations in their circadian rhythms. The objective of this work was to investigate the effects of an intracerebroventricular injection of amyloid beta peptide Aβ(1-42) aggregates on temporal patterns of protein oxidation, antioxidant enzymes and clock factors in the rat hippocampus. Four-month-old male Holtzman rats divided into the groups control (CO) and Aβ-injected (Aβ), were maintained under 12 h-light12h-dark conditions and received water and food ad-libitum. Hippocampus samples were isolated every 6 h during a 24 h period. Our results showed daily patterns of protein carbonyls, catalase (CAT) and glutathione peroxidase (GPx) expression and activity, as well as Rorα and Rev-erbß mRNA, in the rat hippocampus. Interestingly, an intracerebroventricular injection of Aβ aggregates modified daily oscillation of protein carbonyls levels, phase-shifted daily rhythms of clock genes and had a differential effect on the daily expression and activity of CAT and GPx. Thus, Aβ aggregates might affect clock-mediated transcriptional regulation of antioxidant enzymes, by affecting the formation of BMAL1:CLOCK heterodimer, probably, as a consequence of the alteration of the redox state observed in rats injected with Aβ.

Redox proteomics and amyloid β-peptide: insights into Alzheimer disease

Alzheimer disease (AD) is a progressive neurodegenerative disorder associated with aging and characterized pathologically by the presence of senile plaques, neurofibrillary tangles, and neurite and synapse loss. Amyloid beta-peptide (1-42) [Aβ(1-42)], a major component of senile plaques, is neurotoxic and induces oxidative stress in vitro and in vivo. Redox proteomics has been used to identify proteins oxidatively modified by Aβ(1-42) in vitro and in vivo. In this review, we discuss these proteins in the context of those identified to be oxidatively modified in animal models of AD, and human studies including familial AD, pre-clinical AD (PCAD), mild cognitive impairment (MCI), early AD, late AD, Down syndrome (DS), and DS with AD (DS/AD). These redox proteomics studies indicate that Aβ(1-42)-mediated oxidative stress occurs early in AD pathogenesis and results in altered antioxidant and cellular detoxification defenses, decreased energy yielding metabolism and mitochondrial dysfunction, excitotoxicity, loss of synaptic plasticity and cell structure, neuroinflammation, impaired protein folding and degradation, and altered signal transduction. Improved access to biomarker imaging and the identification of lifestyle interventions or treatments to reduce Aβ production could be beneficial in preventing or delaying the progression of AD. This article is part of the special issue "Proteomics".

Proteomics in Traditional Chinese Medicine with an Emphasis on Alzheimer's Disease

In recent years, there has been an increasing worldwide interest in traditional Chinese medicine (TCM). This increasing demand for TCM needs to be accompanied by a deeper understanding of the mechanisms of action of TCM-based therapy. However, TCM is often described as a concept of Chinese philosophy, which is incomprehensible for Western medical society, thereby creating a gap between TCM and Western medicine (WM). In order to meet this challenge, TCM research has applied proteomics technologies for exploring the mechanisms of action of TCM treatment. Proteomics enables TCM researchers to oversee various pathways that are affected by treatment, as well as the dynamics of their interactions with one another. This review discusses the utility of comparative proteomics to better understand how TCM treatment may be used as a complementary therapy for Alzheimer's disease (AD). Additionally, we review the data from comparative AD-related TCM proteomics studies and establish the relevance of the data with available AD hypotheses, most notably regarding the ubiquitin proteasome system (UPS).

The Ubiquitin-Proteasome System and Molecular Chaperone Deregulation in Alzheimer's Disease

One of the shared hallmarks of neurodegenerative diseases is the accumulation of misfolded proteins. Therefore, it is suspected that normal proteostasis is crucial for neuronal survival in the brain and that the malfunction of this mechanism may be the underlying cause of neurodegenerative diseases. The accumulation of amyloid plaques (APs) composed of amyloid-beta peptide (Aβ) aggregates and neurofibrillary tangles (NFTs) composed of misfolded Tau proteins are the defining pathological markers of Alzheimer's disease (AD). The accumulation of these proteins indicates a faulty protein quality control in the AD brain. An impaired ubiquitin-proteasome system (UPS) could lead to negative consequences for protein regulation, including loss of function. Another pivotal mechanism for the prevention of misfolded protein accumulation is the utilization of molecular chaperones. Molecular chaperones, such as heat shock proteins (HSPs) and FK506-binding proteins (FKBPs), are highly involved in protein regulation to ensure proper folding and normal function. In this review, we elaborate on the molecular basis of AD pathophysiology using recent data, with a particular focus on the role of the UPS and molecular chaperones as the defensive mechanism against misfolded proteins that have prion-like properties. In addition, we propose a rational therapy approach based on this mechanism.

The redox chemistry of the Alzheimer's disease amyloid beta peptide

There is a growing body of evidence to support a role for oxidative stress in Alzheimer's disease (AD), with increased levels of lipid peroxidation, DNA and protein oxidation products (HNE, 8-HO-guanidine and protein carbonyls respectively) in AD brains. The brain is a highly oxidative organ consuming 20% of the body's oxygen despite accounting for only 2% of the total body weight. With normal ageing the brain accumulates metals ions such iron (Fe), zinc (Zn) and copper (Cu). Consequently the brain is abundant in antioxidants to control and prevent the detrimental formation of reactive oxygen species (ROS) generated via Fenton chemistry involving redox active metal ion reduction and activation of molecular oxygen. In AD there is an over accumulation of the Amyloid beta peptide (Abeta), this is the result of either an elevated generation from amyloid precursor protein (APP) or inefficient clearance of Abeta from the brain. Abeta can efficiently generate reactive oxygen species in the presence of the transition metals copper and iron in vitro. Under oxidative conditions Abeta will form stable dityrosine cross-linked dimers which are generated from free radical attack on the tyrosine residue at position 10. There are elevated levels of urea and SDS resistant stable linked Abeta oligomers as well as dityrosine cross-linked peptides and proteins in AD brain. Since soluble Abeta levels correlate best with the degree of degeneration [C.A. McLean, R.A. Cherny, F.W. Fraser, S.J. Fuller, M.J. Smith, K. Beyreuther, A.I. Bush, C.L. Masters, Soluble pool of Abeta amyloid as a determinant of severity of neurodegeneration in Alzheimer's disease, Ann. Neurol. 46 (1999) 860-866] we suggest that the toxic Abeta species corresponds to a soluble dityrosine cross-linked oligomer. Current therapeutic strategies using metal chelators such as clioquinol and desferrioxamine have had some success in altering the progression of AD symptoms. Similarly, natural antioxidants curcumin and ginkgo extract have modest but positive effects in slowing AD development. Therefore, drugs that target the oxidative pathways in AD could have genuine therapeutic efficacy.

Amyloid-beta metal interaction and metal chelation

Alzheimer's disease (AD) is associated with the abnormal aggregation of amyloid-beta (Abeta) protein. Abeta and its precursor protein (APP) interact with metal ions such as zinc, copper and iron. Evidence shows that these metals play a role in the precipitation and cytotoxicity of Abeta. Despite recent advances in AD research, there is a lack of therapeutic agents to hinder the apparent aggregation and toxicity of Abeta. Recent studies show that drugs with metal chelating properties could produce a significant reversal of amyloid-beta plaque deposition in vitro and in vivo. Here we discuss the interaction of Abeta with metals, metal dyshomeostasis in the CNS of patients with AD, and the potential therapeutic effects of metal chelators.

Antisense directed at the Abeta region of APP decreases brain oxidative markers in aged senescence accelerated mice

Amyloid beta-peptide (Abeta) is known to induce free radical-mediated oxidative stress in the brain. Free radical-mediated damage to the neuronal membrane components has been implicated in the etiology of Alzheimer's disease (AD). Abeta is produced by proteolytic processing of the amyloid precursor protein (APP). The senescence accelerated mouse prone 8 (SAMP8) strain was developed by phenotypic selection from a common genetic pool. The SAMP8 strain exhibits age-related deterioration in memory and learning as well as Abeta accumulation, and it is considered an effective model for studying brain aging in accelerated senescence. Previous research has shown that a phosphorothiolated antisense oligonucleotide directed against the Abeta region of APP decreases the expression of APP and reverses deficits in learning and memory in aged SAMP8 mice. Consistent with other reports, our previous study showed that 12-month-old SAMP8 mice have increased levels of oxidative stress markers in the brain compared with that in brains from 4-month-old SAMP8 mice. In the current study, 12-month-old SAMP8 mice were treated with antisense oligonucleotide directed against the Abeta region of APP, and the oxidative markers in brain were decreased significantly. Therefore, we conclude that Abeta may contribute to the oxidative stress found in aged SAMP8 mice that have learning and memory impairments. These results are discussed in reference to AD.

Cerebrometabolic abnormalities in Alzheimer's disease

Extensive, replicated evidence in patients in vivo and in Alzheimer (AD) tissues in vitro indicates that impaired brain metabolism is one of the cardinal and essentially invariable events in AD. The degree of impairment in brain metabolism is proportional to the degree of clinical disability, both in vivo and in vitro. The 'cerebrometabolic lesion' cannot be attributed to 'slower thinking' or 'brain atrophy', because of quantitative considerations and because the metabolic lesion precedes the development of neuropsychological abnormalities or decreases in brain mass detectable by modern imaging techniques. The causes of the cerebrometabolic lesion in AD are not well defined. Free radicals seem likely to be involved, including free radicals generated from Alzheimer amyloid. Thus, the importance of the cerebrometabolic lesion is entirely compatible with most versions of the widely accepted 'amyloid cascade hypothesis' of AD. A variety of plausible, redundantly documented mechanisms are compatible with the proposal that the cerebrometabolic lesion is a proximate cause of the clinical disability in AD. In agreement with these findings, recent attempts to treat the cerebrometabolic lesion in AD have given encouraging preliminary results. The cerebrometabolic lesion in AD deserves further study.

Endothelial dysfunction precedes C-fiber abnormalities in primary (AL) amyloidosis

Primary (AL; immunoglobulin light-chain associated) amyloidosis is characterized by the deposition of pathological proteins in the extracellular matrix of tissues and organs. Autonomic and sensory peripheral neuropathy is a common feature of this disorder. The pathogenesis of the neuropathy is poorly defined. The aims of this study were to investigate vascular and neural function in the cutaneous microcirculation of AL amyloidosis patients. Seven patients with AL amyloidosis and controls were studied. Acetylcholine and sodium nitroprusside were iontophoresed into the forearm skin. Endothelial, smooth muscle, and C-fiber-mediated cutaneous blood flow (CuBF) were recorded by laser Doppler flowmetry. Endothelial vasodilation in the forearm skin was attenuated in AL amyloidosis patients (p = 0.007). Maximum endothelium-mediated CuBF in the patient group was reduced (p = 0.047). No group differences could be detected in the C-fiber response or smooth muscle vasodilation (p value not significant). Maximum C-fiber and endothelium-independent CuBF did not differ between the two groups (p value not significant). Early in the disease, AL amyloidosis patients present with impaired endothelial function. At this stage, C-fiber and smooth muscle function are still preserved. These data suggest that endothelial abnormalities precede and may contribute to the pathogenesis of the neuropathy associated with AL amyloidosis.

Amyloid-beta and tau serve antioxidant functions in the aging and Alzheimer brain

Historically, amyloid-beta and tau (tau), the major components of senile plaques and neurofibrillary tangles, respectively, have been considered central mediators of the pathogenesis of Alzheimer disease. Therefore, efforts to understand disease mechanisms have concentrated on understanding either the processes involved in amyloid-beta deposition as senile plaques or on the phosphorylation and aggregation of tau as neurofibrillary tangles. However, in light of recent evidence, such "lesion-centric" approaches look to be inappropriate. In fact, rather than initiators of disease pathogenesis, the lesions occur consequent to oxidative stress and function as a primary line of antioxidant defense. Given this, it is perhaps not surprising that the increased sensitivity to oxidative stress in the aged brain, even in control individuals, is invariably marked by the appearance of both amyloid-beta and tau. Additionally, in Alzheimer disease, where chronic oxidative stress persists and is superimposed upon an age-related vulnerable environment, one would predict, and there is, an increased lesion load. The notion that amyloid-beta and tau function as protective components brings into serious question the rationale of current therapeutic efforts targeted toward lesion removal.

Role of oxidative stress and antioxidants in neurodegenerative diseases

Neurodegenerative diseases (NDD) are a group of illness with diverse clinical importance and etiologies. NDD include motor neuron disease such as amyotrophic lateral sclerosis (ALS), cerebellar disorders, Parkinson's disease (PD), Huntington's disease (HD), cortical destructive Alzheimer's disease (AD) and Schizophrenia. Numerous epidemiological and experimental studies provide many risk factors such as advanced age, genetic defects, abnormalities of antioxidant enzymes, excitotoxicity, cytoskeletal abnormalities, autoimmunity, mineral deficiencies, oxidative stress, metabolic toxicity, hypertension and other vascular disorders. Growing body of evidence implicates free radical toxicity, radical induced mutations and oxidative enzyme impairment and mitochondrial dysfunction due to congenital genetic defects in clinical manifestations of NDD. Accumulation of oxidative damage in neurons either primarily or secondarily may account for the increased incidence of NDD such as AD, ALS and stroke in aged populations. The molecular mechanisms of neuronal degeneration remain largely unknown and effective therapies are not currently available. Recent interest has focused on antioxidants such as carotenoids and in particular lycopene, a potent antioxidant in tomatoes and tomato products, flavonoids and vitamins as potentially useful agents in the management of human NDD. The pathobiology of neurodegenerative disorders with emphasis on genetic origin and its correlation with oxidative stress of neurodegenerative disorders will be reviewed and the reasons as to why brain constitutes a vulnerable site of oxidative damage will be discussed. The article will also discuss the potential free radical scavenger, mechanism of antioxidant action of lycopene and the need for the use of antioxidants in the prevention of NDD.

Oxidation of methionine 35 attenuates formation of amyloid beta -peptide 1-40 oligomers

Amyloid plaques formed by aggregation of the amyloid beta-peptide (Abeta) are an intrinsic component of Alzheimer disease pathogenesis. It has been suggested that oxidation of methionine 35 in Abeta has implications for Alzheimer disease, and it has been shown that oxidation of Met-35 significantly inhibits aggregation in vitro. In this study, the aggregational properties of Abeta-(1-40) before and after Met-35 oxidation were investigated using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The results show that Abeta-(1-40)Met-35(O) trimer and tetramer formation is significantly attenuated as compared with Abeta-(1-40). This suggests that oxidation of Met-35 inhibits a conformational switch in Abeta-(1-40) necessary for trimer but not dimer formation. Random incorporation of Abeta-(1-40) and Abeta-(1-40)Met-35(O) in homo- and heterooligomers could also be observed. This is the first report of an early rate-limiting step in Abeta-(1-40) aggregation. Slowing of the fibrillization process at this early step is likely to support prolonged solubility and clearance of Abeta from brain and may reduce disease progression.

Proteome and proteomics for the research on protein alterations in aging

Functional decline of tissues in aged animals is a result of cellular aging. Though any process of somatic cell aging basically depends on genomic instructions, phenotypes of aged cells are expressed in a given internal environment of each cell type that was made with translated proteins and post-translationally modified products. Therefore, research on age-dependent protein alterations in each cell type is very important in clarifying mechanisms of aging. The novel term "proteome" is a compound of "protein" and "genome," which means constitutive whole proteins including post-translationally modified products in a cell type. Proteomics is a novel strategy for analyzing proteomes. In proteomics, high resolution two-dimensional electrophoresis is exclusively performed for isolation of proteins followed by mass spectrometry for identification of proteins and determination of modifications. Thus, proteomics is becoming appreciated as a powerful tool to find out proteins responsible for cellular aging, symptoms of senility and geriatric diseases.

The mitochondrial spiral. An adequate cause of dementia in the Alzheimer's syndrome

A variety of chronic, relatively low-grade injuries to the brain occur in Alzheimer's disease (AD). The extent to which each of these contributes to the clinical syndrome is unclear. Several of the abnormalities that occur in AD brain can cause dementia by themselves, even in people who do not have the neuropathological hallmarks of AD. Prominent among these abnormalities is a deleterious "mitochondrial spiral," which consists of reduced brain metabolism, oxidative stress, and calcium dysregulation. The hypothesis presented in this paper is that the mitochondrial spiral contributes to dementia in AD and presents a reasonable target for the development of new approaches to the treatment of this syndrome.