Review: Alzheimer's amyloid beta-peptide-associated free radical oxidative stress and neurotoxicity

Tripeptide GGH as the Inhibitor of Copper-Amyloid-β-Mediated Redox Reaction and Toxicity

The Aβ complexes of some redox-active species, such as Cu, cause oxidative stress and induce severe toxicity by generating reactive oxygen species (ROS). Thus, Cu chelation therapy should be considered as a valuable strategy for the treatment of Alzheimer's disease (AD). However, more attention should be paid to the specific chelating ability of these chelating agents. Herein, a tripeptide GGH was used to selectively chelate the Cu(2+) in Aβ-Cu complex in the presence of other metal ions (e.g., K(+), Ca(2+), Ni(2+), Mg(2+), and Zn(2+)) as shown by isothermal titration calorimetry results. GGH decreased the level of HO(•) radicals by preventing the formation of intermediate Cu(I) ion. Thus, the Cu species completely lost its catalytic activity at a superequimolar GGH/Cu(II) ratio (4:1) as observed by UV-visible spectroscopy, coumarin-3-carboxylic acid fluorescence, and BCA assay. Moreover, (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT) assay indicates that GGH increased PC-12 cell viability from 36% to 63%, and neurotoxicity partly triggered by ROS decreased. These results indicate potential development of peptide chelation therapy for AD treatment.

Chronic oxidative damage together with genome repair deficiency in the neurons is a double whammy for neurodegeneration: Is damage response signaling a potential therapeutic target?

A foremost challenge for the neurons, which are among the most oxygenated cells, is the genome damage caused by chronic exposure to endogenous reactive oxygen species (ROS), formed as cellular respiratory byproducts. Strong metabolic activity associated with high transcriptional levels in these long lived post-mitotic cells render them vulnerable to oxidative genome damage, including DNA strand breaks and mutagenic base lesions. There is growing evidence for the accumulation of unrepaired DNA lesions in the central nervous system (CNS) during accelerated aging and progressive neurodegeneration. Several germ line mutations in DNA repair or DNA damage response (DDR) signaling genes are uniquely manifested in the phenotype of neuronal dysfunction and are etiologically linked to many neurodegenerative disorders. Studies in our lab and elsewhere revealed that pro-oxidant metals, ROS and misfolded amyloidogenic proteins not only contribute to genome damage in CNS, but also impede their repair/DDR signaling leading to persistent damage accumulation, a common feature in sporadic neurodegeneration. Here, we have reviewed recent advances in our understanding of the etiological implications of DNA damage vs. repair imbalance, abnormal DDR signaling in triggering neurodegeneration and potential of DDR as a target for the amelioration of neurodegenerative diseases.

Guanosine and its role in neuropathologies

Guanosine is a purine nucleoside thought to have neuroprotective properties. It is released in the brain under physiological conditions and even more during pathological events, reducing neuroinflammation, oxidative stress, and excitotoxicity, as well as exerting trophic effects in neuronal and glial cells. In agreement, guanosine was shown to be protective in several in vitro and/or in vivo experimental models of central nervous system (CNS) diseases including ischemic stroke, Alzheimer's disease, Parkinson's disease, spinal cord injury, nociception, and depression. The mechanisms underlying the neurobiological properties of guanosine seem to involve the activation of several intracellular signaling pathways and a close interaction with the adenosinergic system, with a consequent stimulation of neuroprotective and regenerative processes in the CNS. Within this context, the present review will provide an overview of the current literature on the effects of guanosine in the CNS. The elucidation of the complex signaling events underlying the biochemical and cellular effects of this nucleoside may further establish guanosine as a potential therapeutic target for the treatment of several neuropathologies.

Design, synthesis, and evaluation of Trolox-conjugated amyloid-β C-terminal peptides for therapeutic intervention in an in vitro model of Alzheimer's disease

Two hallmarks of Alzheimer's disease (AD) observed in the brains of patients with the disease include oxidative injury and deposition of protein aggregates comprised of amyloid-β (Aβ) variants. To inhibit these toxic processes, we synthesized antioxidant-conjugated peptides comprised of Trolox and various C-terminal motifs of Aβ variants, TxAβx-n (x=34, 36, 38, 40; n=40, 42, 43). Most of these compounds were found to exhibit anti-aggregation activities. Among them, TxAβ36-42 significantly inhibited Aβ1-42 aggregation, showed potent antioxidant activity, and protected SH-SY5Y cells from Aβ1-42-induced cytotoxicity. Thus, this method represents a promising strategy for developing multifunctional AD therapeutic agents.

Interaction of Aβ(25-35) fibrillation products with mitochondria: Effect of small-molecule natural products

The 25-35 fragment of the amyloid β (Aβ) peptide is a naturally occurring proteolytic by-product that retains the pathophysiology of its larger parent molecule, whose deposition has been shown to involve mitochondrial dysfunction. Hence, disruption of Aβ(25-35) aggregates could afford an effective remedial strategy for Alzheimer's disease (AD). In the present study, the effect of a number of selected small-molecule natural products (polyphenols: resveratrol, quercetin, biochanin A, and indoles: indole-3-acetic acid, indole-3-carbinol (I3C)) on Aβ(25-35) fibrillogenesis was explored under physiological conditions, and interaction of the resulting structures with rat brain mitochondria was investigated. Several techniques, including fluorescence, circular dichroism, and transmission electron microscopy were utilized to characterize the aggregation products, and possible mitochondrial membrane permeabilization was determined following release of marker enzymes. Results demonstrate the capacity of Aβ(25-35) fibrils to damage mitochondria and suggest how small molecules may afford protection. While I3C appeared more effective in inhibiting the fibrillation process, all natural products behaved similarly in destabilizing preformed aggregates. It is concluded that elucidation of such protection may provide important insights into the development of preventive and therapeutic agents for AD.

Role of oxidative stress in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of disability in individuals aged >65 years worldwide. AD is characterized by the abnormal deposition of amyloid β (Aβ) peptide, and intracellular accumulation of neurofibrillary tangles of hyperphosphorylated τ protein and dementia. The neurotoxic oligomer Aβ peptide, which is the neuropathological diagnostic criterion of the disease, together with τ protein, are mediators of the neurodegeneration that is among the main causative factors. However, these phenomena are mainly initiated and enhanced by oxidative stress, a process referring to an imbalance between antioxidants and oxidants in favour of oxidants. This imbalance can occur as a result of increased free radicals or a decrease in antioxidant defense, free radicals being a species that contains one or more unpaired electrons in its outer shell. The major source of potent free radicals is the reduction of molecular oxygen in water, that initially yields the superoxide radical, which produces hydrogen peroxide by the addition of an electron. The reduction of hydrogen peroxide produces highly reactive hydroxyl radicals, termed reactive oxygen species (ROS) that can react with lipids, proteins, nucleic acids, and other molecules and may also alter their structures and functions. Thus, tissues and organs, particularly the brain, a vulnerable organ, are affected by ROS due to its composition. The brain is largely composed of easily oxidizable lipids while featuring a high oxygen consumption rate. The current review examined the role of oxidative stress in AD.

High-affinity Anticalins with aggregation-blocking activity directed against the Alzheimer β-amyloid peptide

Anticalins engineered for high affinity and specificity towards the central VFFAED epitope in Aβ peptides potently inhibit their aggregation, thus providing novel reagents to study the molecular pathology of Alzheimer's disease (AD) and alternative drug candidates compared with current biopharmaceutical treatments.

Amyloid beta (Aβ) peptides, in particular Aβ42 and Aβ40, exert neurotoxic effects and their overproduction leads to amyloid deposits in the brain, thus constituting an important biomolecular target for treatments of Alzheimer's disease (AD). We describe the engineering of cognate Anticalins as a novel type of neutralizing protein reagent based on the human lipocalin scaffold. Phage display selection from a genetic random library comprising variants of the human lipocalin 2 (Lcn2) with mutations targeted at 20 exposed amino acid positions in the four loops that form the natural binding site was performed using both recombinant and synthetic target peptides and resulted in three different Anticalins. Biochemical characterization of the purified proteins produced by periplasmic secretion in Escherichia coli revealed high folding stability in a monomeric state, with T_m values ranging from 53.4°C to 74.5°C, as well as high affinities for Aβ40, between 95 pM and 563 pM, as measured by real-time surface plasmon resonance analysis. The central linear VFFAED epitope within the Aβ sequence was mapped using a synthetic peptide array on membranes and was shared by all three Anticalins, despite up to 13 mutual amino acid differences in their binding sites. All Anticalins had the ability–with varying extent–to inhibit Aβ aggregation in vitro according to the thioflavin-T fluorescence assay and, furthermore, they abolished Aβ42-mediated toxicity in neuronal cell culture. Thus, these Anticalins provide not only useful protein reagents to study the molecular pathology of AD but they also show potential as alternative drug candidates compared with antibodies.

Cassia obtusifolia seed ameliorates amyloid β-induced synaptic dysfunction through anti-inflammatory and Akt/GSK-3β pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Tea infused with the seed of Cassia obtusifolia has been traditionally used as an herbal remedy for liver, eye, and acute inflammatory diseases. Recent pharmacological reports have indicated that Cassiae semen has neuroprotective effects, attributable to its anti-inflammatory actions, in ischemic stroke and Parkinson's disease models.

AIM OF THE STUDY

Previously, the ethanol extract of C. obtusifolia seeds (COE) was reported to have memory enhancing properties. However, the effects of COE in an Alzheimer's disease (AD) model are currently unknown. In this study, we investigated the effect(s) of COE on aberrant synaptic plasticity and memory impairment induced by amyloid β (Aβ), a key toxic component found in the AD brain.

MATERIALS AND METHODS

To determine the effect of COE on Aβ-induced aberrant synaptic plasticity, we used acute mouse hippocampal slices and delivered theta burst stimulation to induce long-term potentiation (LTP). Western blots were used to detect Aβ- and/or COE-induced changes in signaling proteins. The novel object location recognition test was conducted to determine the effect of COE on Aβ-induced recognition memory impairment.

RESULTS

COE was found to ameliorate Aβ-induced LTP impairment in the acute hippocampal slices. Glycogen synthase kinase-3β (GSK-3β), a key molecule in LTP impairment, was activated by Aβ. However, this process was inhibited by COE via Akt signaling. Moreover, COE was found to attenuate Aβ-induced microglia, inducible nitric oxide synthase (iNOS), and cyclooxygenase (COX) activation. In the in vivo studies performed, COE ameliorated the Aβ-induced object recognition memory impairment.

CONCLUSION

These results suggest that COE exhibits neuroprotective activities against Aβ-induced brain disorders.

Neuronal response in Alzheimer's and Parkinson's disease: the effect of toxic proteins on intracellular pathways

Accumulation of protein aggregates is the leading cause of cellular dysfunction in neurodegenerative disorders. Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease, Prion disease and motor disorders such as amyotrophic lateral sclerosis, present with a similar pattern of progressive neuronal death, nervous system deterioration and cognitive impairment. The common characteristic is an unusual misfolding of proteins which is believed to cause protein deposition and trigger degenerative signals in the neurons. A similar clinical presentation seen in many neurodegenerative disorders suggests the possibility of shared neuronal responses in different disorders. Despite the difference in core elements of deposits in each neurodegenerative disorder, the cascade of neuronal reactions such as activation of glycogen synthase kinase-3 beta, mitogen-activated protein kinases, cell cycle re-entry and oxidative stress leading to a progressive neurodegeneration are surprisingly similar. This review focuses on protein toxicity in two neurodegenerative diseases, AD and PD. We reviewed the activated mechanisms of neurotoxicity in response to misfolded beta-amyloid and α-synuclein, two major toxic proteins in AD and PD, leading to neuronal apoptosis. The interaction between the proteins in producing an overlapping pathological pattern will be also discussed.

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).

β-Amyloid: the key peptide in the pathogenesis of Alzheimer's disease

The amyloid β peptide (Aβ) is a critical initiator that triggers the progression of Alzheimer's Disease (AD) via accumulation and aggregation, of which the process may be caused by Aβ overproduction or perturbation clearance. Aβ is generated from amyloid precursor protein through sequential cleavage of β- and γ-secretases while Aβ removal is dependent on the proteolysis and lysosome degradation system. Here, we overviewed the biogenesis and toxicity of Aβ as well as the regulation of Aβ production and clearance. Moreover, we also summarized the animal models correlated with Aβ that are essential in AD research. In addition, we discussed current immunotherapeutic approaches targeting Aβ to give some clues for exploring the more potentially efficient drugs for treatment of AD.

Natural lignans from Arctium lappa as antiaging agents in Caenorhabditis elegans

Arctium lappa is a well-known traditional medicinal plant in China (TCM) and Europe that has been used for thousands of years to treat arthritis, baldness or cancer. The plant produces lignans as secondary metabolites, which have a wide range of bioactivities. Yet, their antiaging potential has not been explored. In this study, we isolated six lignans from A. lappa seeds, namely arctigenin, matairesinol, arctiin, (iso)lappaol A, lappaol C, and lappaol F. The antioxidant and antiaging properties of the isolated lignans were studied using Caenorhabditis elegans as a relevant animal model. All lignans at concentrations of 10 and 100 μM significantly extended the mean life span of C. elegans. The strongest effect was observed with matairesinol, which at a concentration of 100 μM extended the life span of worms by 25%. Additionally, we observed that five lignans are strong free radical-scavengers in vitro and in vivo and all lignans can improve survival of C. elegans under oxidative stress. Furthermore, the lignans can induce the nuclear translocation of the transcription factor DAF-16 and up-regulate its expression, suggesting that a possible underlying mechanism of the observed longevity-promoting activity of lignans depends on DAF-16 mediated signaling pathway. All lignans up-regulated the expression of jnk-1, indicating that lignans may promote the C. elegans longevity and stress resistance through a JNK-1-DAF-16 cascade. Our study reports new antiaging activities of lignans, which might be candidates for developing antiaging agents.

Effect of methionine-35 oxidation on the aggregation of amyloid-β peptide

Aggregation of Aβ peptides into amyloid plaques is considered to trigger the Alzheimer’s disease (AD), however the mechanism behind the AD onset has remained elusive. It is assumed that the insoluble Aβ aggregates enhance oxidative stress (OS) by generating free radicals with the assistance of bound copper ions. The aim of our study was to establish the role of Met35 residue in the oxidation and peptide aggregation processes. Met35 can be readily oxidized by H₂O₂. The fibrillization of Aβ with Met35 oxidized to sulfoxide was three times slower compared to that of the regular peptide. The fibrils of regular and oxidized peptides looked similar under transmission electron microscopy. The relatively small inhibitory effect of methionine oxidation on the fibrillization suggests that the possible variation in the Met oxidation state should not affect the in vivo plaque formation. The peptide oxidation pattern was more complex when copper ions were present: addition of one oxygen atom was still the fastest process, however, it was accompanied by multiple unspecific modifications of peptide residues. Addition of copper ions to the Aβ with oxidized Met35 in the presence of H₂O₂, resulted a similar pattern of nonspecific modifications, suggesting that the one-electron oxidation processes in the peptide molecule do not depend on the oxidation state of Met35 residue. Thus, it can be concluded that Met35 residue is not a part of the radical generating mechanism of Aβ–Cu(II) complex.

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Aβ peptides with oxidized Met35 residue fibrillize three times slower than the reduced peptide.

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Met35 is the only residue in Aβ peptide that is oxidized by H₂O₂ in the absent of copper ions.

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In the presence of copper ions as catalyst multiple unspecific oxidative processes occur in Aβ.

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Previous oxidation of Met35 does not affect the unspecific oxidation in the presence of copper ions.

Microglial cell dysregulation in brain aging and neurodegeneration

Aging is the main risk factor for neurodegenerative diseases. In aging, microglia undergoes phenotypic changes compatible with their activation. Glial activation can lead to neuroinflammation, which is increasingly accepted as part of the pathogenesis of neurodegenerative diseases, including Alzheimer’s disease (AD). We hypothesize that in aging, aberrant microglia activation leads to a deleterious environment and neurodegeneration. In aged mice, microglia exhibit an increased expression of cytokines and an exacerbated inflammatory response to pathological changes. Whereas LPS increases nitric oxide (NO) secretion in microglia from young mice, induction of reactive oxygen species (ROS) predominates in older mice. Furthermore, there is accumulation of DNA oxidative damage in mitochondria of microglia during aging, and also an increased intracellular ROS production. Increased ROS activates the redox-sensitive nuclear factor kappa B, which promotes more neuroinflammation, and can be translated in functional deficits, such as cognitive impairment. Mitochondria-derived ROS and cathepsin B, are also necessary for the microglial cell production of interleukin-1β, a key inflammatory cytokine. Interestingly, whereas the regulatory cytokine TGFβ1 is also increased in the aged brain, neuroinflammation persists. Assessing this apparent contradiction, we have reported that TGFβ1 induction and activation of Smad3 signaling after inflammatory stimulation are reduced in adult mice. Other protective functions, such as phagocytosis, although observed in aged animals, become not inducible by inflammatory stimuli and TGFβ1. Here, we discuss data suggesting that mitochondrial and endolysosomal dysfunction could at least partially mediate age-associated microglial cell changes, and, together with the impairment of the TGFβ1-Smad3 pathway, could result in the reduction of protective activation and the facilitation of cytotoxic activation of microglia, resulting in the promotion of neurodegenerative diseases.

Inactivation of brain Cofilin-1 by age, Alzheimer's disease and γ-secretase

Rapid remodeling of the actin cytoskeleton in the pre- and/or post-synaptic compartments is responsible for the regulation of neuronal plasticity,which is an important process for learning and memory. Cofilin1 plays an essential role in these processes and a dysregulation of its activity was associated with the cognitive decline observed during normal aging and Alzheimer's disease (AD). To understand the mechanism(s) regulating Cofilin1 activity we evaluated changes occurring with regard to Cofilin1 and its up-stream regulators Lim kinase-1 (LIMK1) and Slingshot phosphatase-1 (SSH1) in (i) human AD brain, (ii) 1-, 4-, and 10-months old APP/PS1 mice, (iii) wildtype 3-, 8-, 12-, 18- and 26-months old mice, as well as in cellular models including (iv) mouse primary cortical neurons (PCNs, cultured for 5, 10, 15 and 20 days in vitro) and (v) mouse embryonic fibroblasts (MEF). Interestingly,we found an increased Cofilin1 phosphorylation/inactivation with age and AD pathology, both in vivo and in vitro. These changes were associated with a major inactivation of SSH1. Interestingly, inhibition of ã-secretase activity with Compound-E (10 ìM) prevented Cofilin1 phosphorylation/inactivation through an increase of SSH1 activity in PCNs. Similarly, MEF cells double knock-out for ã-secretase catalytic subunits presenilin-1 and -2(MEFDKO) showed a strong decrease of both Cofilin1 and SSH1 phosphorylation,which were rescued by the over expression of human ã-secretase. Together, these results shed new light in understanding the molecular mechanisms promoting Cofilin1 dysregulation, both during aging and AD. They further have the potential to impact the development of therapies to safely treat AD.

Pharmacological and neuroprotective profile of an essential oil derived from leaves of Aloysia citrodora Palau

OBJECTIVES

The Jordanian 'Melissa', (Aloysia citrodora) has been poorly studied both pharmacologically and in the clinic. Essential oils (EO) derived from leaves of A. citrodora were obtained by hydrodistillation, analysed by gas chromatography-mass spectrometry (GC-MS) and were investigated for a range of neurobiological and pharmacological properties, as a basis for potential future use in drug discovery.

METHODS

A selection of central nervous system (CNS) receptor-binding profiles was carried out. Antioxidant activity and ferrous iron-chelating assays were adopted, and the neuroprotective properties of A. citrodora EO assessed using hydrogen peroxide-induced and β-amyloid-induced neurotoxicity with the CAD (Cath.-a-differentiated) neuroblastoma cell line.

KEY FINDINGS

The major chemical components detected in the A. citrodora EOs, derived from dried and fresh leaves, included limonene, geranial, neral, 1, 8-cineole, curcumene, spathulenol and caryophyllene oxide, respectively. A. citrodora leaf EO inhibited [(3) H] nicotine binding to well washed rat forebrain membranes, and increased iron-chelation in vitro. A. citrodora EO displays effective antioxidant, radical-scavenging activities and significant protective properties vs both hydrogen peroxide- and β-amyloid-induced neurotoxicity.

CONCLUSIONS

A. citrodora EO displays a range of pharmacological properties worthy of further investigation to isolate the compounds responsible for the observed neuroactivities, to further analyse their mode of action and determine their clinical potential in neurodegenerative diseases.

Long-term dietary supplementation of pomegranates, figs and dates alleviate neuroinflammation in a transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a devastating age-related neurodegenerative disease with no specific treatment at present. The APPsw/Tg2576 mice exhibit age-related deterioration in memory and learning as well as amyloid-beta (Aβ) accumulation, and this mouse strain is considered an effective model for studying the mechanism of accelerated brain aging and senescence. The present study was aimed to investigate the beneficial effects of dietary supplements pomegranate, figs, or the dates on suppressing inflammatory cytokines in APPsw/Tg2576 mice. Changes in the plasma cytokines and Aβ, ATP, and inflammatory cytokines were investigated in the brain of transgenic mice. Significantly enhanced levels of inflammatory cytokines IL-1β, IL-2, IL-3, IL-4, IL-5, IL-6, IL-9, IL-10, TNF-α and Eotaxin activity were decreased by administration of the diet supplements containing pomegranates, figs, or dates. In addition, putative delays in the formation of senile plaques, as indicated by a decreasing tendency of brain Aβ1-40 and Aβ1-42 contents, were observed. Thus, novel results mediated by reducing inflammatory cytokines during aging may represent one mechanism by which these supplements exert their beneficial effects against neurodegenerative diseases such as AD.

Glutamate receptors function as scaffolds for the regulation of β-amyloid and cellular prion protein signaling complexes

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that affects 36 million people worldwide, but currently has no effective treatment options. One of the original hallmarks of AD are plaques comprised of beta amyloid (Aβ) and neurofibrillary tangles comprised of phosphorylated Tau protein. However, it is soluble oligomeric Aβ which is more closely correlated with cognitive decline and is therefore considered to be the neurotoxic species. Oligomeric Aβ has recently been shown to form complexes with the glycosylphosphatidylinositol (GPI)-anchored membrane protein, cellular prion protein (PrP(c)), and these complexes are believed to play an important role in the progression of AD pathogenesis. Glutamate, the major excitatory neurotransmitter is responsible for mediating learning and memory under normal physiological conditions. However, the dysregulation of glutamatergic signaling has also been implicated in a number of neurodegenerative diseases including AD. Glutamate acts via both ionotropic glutamate receptors (iGluR) and metabotropic glutamate receptors (mGluR), each of which have been implicated in AD. There is now growing evidence to suggest that mGluR5 may contribute the AD pathogenesis by acting as scaffolds for the PrP(c)/Aβ oligomer complex, enabling the propagation of neurotoxic signaling in AD. In addition, PrP(c) and Aβ oligomer signaling via NMDARs may also contribute to AD pathology. The current review overviews our current understanding of the role of PrP(c) and Aβ oligomers in regulating glutamate receptor signaling, as well as highlights the importance of understanding these signaling complexes to develop more effective therapeutic strategies to treat AD.

Aβ induces oxidative stress in senescence-accelerated (SAMP8) mice

According to the amyloid hypothesis, amyloid β accumulates in brains with Alzheimer's disease (AD) and triggers cell death and memory deficit. Previously, we developed a rice Aβ vaccine expressing Aβ, which reduced brain Aβ levels in the Tg2576 mouse model of familial AD. We used senescence-accelerated SAMP8 mice as a model of sporadic AD and investigated the relationship between Aβ and oxidative stress. Insoluble Aβ and 4-hydroxynonenal (4-HNE) levels tended to be reduced in SAMP8 mice-fed the rice Aβ vaccine. We attempted to clarify the relationship between oxidative stress and Aβ in vitro. Addition of Aβ peptide to the culture medium resulted in an increase in 4-HNE levels in SH-SY5Y cells. Tg2576 mice, which express large amounts of Aβ in their brain, also exhibited increased 4-HNE levels; this increase was inhibited by the Aβ vaccine. These results indicate that Aβ induces oxidative stress in cultured cells and in the mouse brain.

The protein oxidation repair enzyme methionine sulfoxide reductase a modulates Aβ aggregation and toxicity in vivo

AIMS

To examine the role of the enzyme methionine sulfoxide reductase A-1 (MSRA-1) in amyloid-β peptide (Aβ)-peptide aggregation and toxicity in vivo, using a Caenorhabditis elegans model of the human amyloidogenic disease inclusion body myositis.

RESULTS

MSRA-1 specifically reduces oxidized methionines in proteins. Therefore, a deletion of the msra-1 gene was introduced into transgenic C. elegans worms that express the Aβ-peptide in muscle cells to prevent the reduction of oxidized methionines in proteins. In a constitutive transgenic Aβ strain that lacks MSRA-1, the number of amyloid aggregates decreases while the number of oligomeric Aβ species increases. These results correlate with enhanced synaptic dysfunction and mislocalization of the nicotinic acetylcholine receptor ACR-16 at the neuromuscular junction (NMJ).

INNOVATION

This approach aims at modulating the oxidation of Aβ in vivo indirectly by dismantling the methionine sulfoxide repair system. The evidence presented here shows that the absence of MSRA-1 influences Aβ aggregation and aggravates locomotor behavior and NMJ dysfunction. The results suggest that therapies which boost the activity of the Msr system could have a beneficial effect in managing amyloidogenic pathologies.

CONCLUSION

The absence of MSRA-1 modulates Aβ-peptide aggregation and increments its deleterious effects in vivo.

Assessment of the therapeutic potential of hesperidin and proteomic resolution of diabetes-mediated neuronal fluctuations expediting Alzheimer’s disease

Alzheimer’s disease (AD) has been proposed as type III diabetes mellitus. Prognosis and early stage diagnosis of AD is essentially required in diabetes to avoid extensive irreversible neuronal damage.

An investigation into the ameliorating effect of black soybean extract on learning and memory impairment with assessment of neuroprotective effects

BACKGROUND

The physiological effects of the non-anthocyanin fraction (NAF) in a black soybean seed coat extract on Aβ-induced oxidative stress were investigated to confirm neuroprotection. In addition, we examined the preventive effect of NAF on cognitive defects induced by the intracerebroventricular (ICV) injection of Aβ.

METHODS

Levels of cellular oxidative stress were measured using 2',7'-dichlorofluorescein diacetate (DCF-DA). Neuronal cell viability was investigated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assay. To investigate in vivo anti-amnesic effects of NAF by using Y-maze and passive avoidance tests, the learning and memory impairment in mice was induced by Aβ. After in vivo assays, acetylcholinesterase (AChE) activity and level of malondialdehyde (MDA) in the mouse brain were determined to confirm the cognitive effect. Individual phenolics of NAF were qualitatively analyzed by using an ultra-performance liquid chromatography (UPLC) Accurate-Mass Quadrupole Time of-Flight (Q-TOF) UPLC/MS.

RESULTS

A NAF showed cell protective effects against oxidative stress-induced cytotoxicity. Intracellular ROS accumulated through Aβ1-40 treatment was significantly reduced in comparison to cells only treated with Aβ1-40. In MTT and LDH assay, the NAF also presented neuroprotective effects on Aβ1-40-treated cytotoxicity. Finally, the administration of this NAF in mice significantly reversed the Aβ1-40-induced cognitive defects in in vivo behavioral tests. After behavioral tests, the mice brains were collected in order to examine lipid peroxidation and AChE activity. AChE, preparation was inhibited by NAF in a dose-dependent manner. MDA generation in the brain homogenate of mice treated with the NAF was decreased. Q-TOF UPLC/MS analyses revealed three major phenolics from the non-anthocyanin fraction; epicatechin, procyanidin B1, and procyanidin B2.

CONCLUSIONS

The results suggest that the NAF in black soybean seed coat extracts may improve the cytotoxicity of Aβ in PC12 cells, possibly by reducing oxidative stress, and also have an anti-amnesic effect on the in vivo learning and memory deficits caused by Aβ. Q-TOF UPLC/MS analyses showed three major phenolics; (-)-epicatechin, procyanidin B1, and procyanidin B2. Above results suggest that (-)-epicatechins are the major components, and contributors to the anti-amnesic effect of the NAF from black soybean seed coat.

Neuroprotective effect of purple rice extract and its constituent against amyloid beta-induced neuronal cell death in SK-N-SH cells

This study evaluated the protective effects of purple rice (Oryza sativa L.) extract (PRE) and its major constituent, cyanidin, and their underlying mechanisms against Aβ 25-35-induced neuronal cell death in SK-N-SH cells. Aβ 25-35-induced neuronal toxicity is characterized by decrease in cell viability, the release of lactate dehydrogenase (LDH), decrease superoxide dismutase (SOD) activity, increase in reactive oxygen species (ROS) production, morphological alteration, and activation of mitochondrial death pathway. Pretreatment with PRE and cyanidin significantly attenuated Aβ 25-35-induced loss of cell viability, apoptosis, and increase in ROS and RNS production in a dose-dependent manner. In addition, PRE and cyanidin also helped to bring about the downregulation of the expression of Bax, cytochrome c, cleavage caspase-9, and cleavage caspase-3 proteins, and the upregulation of the Bcl-XL protein in cascade. Therefore, it is evident that PRE and its major constituent, cyanidin, were successful in protecting from the cytotoxic effect of Aβ 25-35 through attenuation ROS and RNS production and modulation of mitochondrial death pathway in SK-N-SH cells. This result suggests that PRE and its major constituent, cyanidin, might be beneficial as potential therapeutic agents in preventing neurodegenerative diseases.

The 2013 SFRBM discovery award: selected discoveries from the butterfield laboratory of oxidative stress and its sequela in brain in cognitive disorders exemplified by Alzheimer disease and chemotherapy induced cognitive impairment

This retrospective review on discoveries of the roles of oxidative stress in brain of subjects with Alzheimer disease (AD) and animal models thereof as well as brain from animal models of chemotherapy-induced cognitive impairment (CICI) results from the author receiving the 2013 Discovery Award from the Society for Free Radical Biology and Medicine. The paper reviews our laboratory's discovery of protein oxidation and lipid peroxidation in AD brain regions rich in amyloid β-peptide (Aβ) but not in Aβ-poor cerebellum; redox proteomics as a means to identify oxidatively modified brain proteins in AD and its earlier forms that are consistent with the pathology, biochemistry, and clinical presentation of these disorders; how Aβ in in vivo, ex vivo, and in vitro studies can lead to oxidative modification of key proteins that also are oxidatively modified in AD brain; the role of the single methionine residue of Aβ(1-42) in these processes; and some of the potential mechanisms in the pathogenesis and progression of AD. CICI affects a significant fraction of the 14 million American cancer survivors, and due to diminished cognitive function, reduced quality of life of the persons with CICI (called "chemobrain" by patients) often results. A proposed mechanism for CICI employed the prototypical ROS-generating and non-blood brain barrier (BBB)-penetrating chemotherapeutic agent doxorubicin (Dox, also called adriamycin, ADR). Because of the quinone moiety within the structure of Dox, this agent undergoes redox cycling to produce superoxide free radical peripherally. This, in turn, leads to oxidative modification of the key plasma protein, apolipoprotein A1 (ApoA1). Oxidized ApoA1 leads to elevated peripheral TNFα, a proinflammatory cytokine that crosses the BBB to induce oxidative stress in brain parenchyma that affects negatively brain mitochondria. This subsequently leads to apoptotic cell death resulting in CICI. This review outlines aspects of CICI consistent with the clinical presentation, biochemistry, and pathology of this disorder. To the author's knowledge this is the only plausible and self-consistent mechanism to explain CICI. These two different disorders of the CNS affect millions of persons worldwide. Both AD and CICI share free radical-mediated oxidative stress in brain, but the source of oxidative stress is not the same. Continued research is necessary to better understand both AD and CICI. The discoveries about these disorders from the Butterfield Laboratory that led to the 2013 Discovery Award from the Society of Free Radical and Medicine provide a significant foundation from which this future research can be launched.

Abeta, oxidative stress in Alzheimer disease: evidence based on proteomics studies

The initiation and progression of Alzheimer disease (AD) is a complex process not yet fully understood. While many hypotheses have been provided as to the cause of the disease, the exact mechanisms remain elusive and difficult to verify. Proteomic applications in disease models of AD have provided valuable insights into the molecular basis of this disorder, demonstrating that on a protein level, disease progression impacts numerous cellular processes such as energy production, cellular structure, signal transduction, synaptic function, mitochondrial function, cell cycle progression, and proteasome function. Each of these cellular functions contributes to the overall health of the cell, and the dysregulation of one or more could contribute to the pathology and clinical presentation in AD. In this review, foci reside primarily on the amyloid β-peptide (Aβ) induced oxidative stress hypothesis and the proteomic studies that have been conducted by our laboratory and others that contribute to the overall understanding of this devastating neurodegenerative disease.

Mass spectrometry and redox proteomics: applications in disease

Proteomics techniques are continuously being developed to further understanding of biology and disease. Many of the pathways that are relevant to disease mechanisms rely on the identification of post-translational modifications (PTMs) such as phosphorylation, acetylation, and glycosylation. Much attention has also been focused on oxidative PTMs which include protein carbonyls, protein nitration, and the incorporation of fatty acids and advanced glycation products to amino acid side chains, amongst others. The introduction of these PTMs in the cell can occur due to the attack of reactive oxygen and nitrogen species (ROS and RNS, respectively) on proteins. ROS and RNS can be present as a result of normal metabolic processes as well as external factors such as UV radiation, disease, and environmental toxins. The imbalance of ROS and RNS with antioxidant cellular defenses leads to a state of oxidative stress, which has been implicated in many diseases. Redox proteomics techniques have been used to characterize oxidative PTMs that result as a part of normal cell signaling processes as well as oxidative stress conditions. This review highlights many of the redox proteomics techniques which are currently available for several oxidative PTMs and brings to the reader's attention the application of redox proteomics for understanding disease pathogenesis in neurodegenerative disorders and others such as cancer, kidney, and heart diseases.

Hypoxia-induced tau phosphorylation and memory deficit in rats

Hypoxia was shown to be associated with an increased risk of Alzheimer's disease (AD). The effects of hypoxia on the development of AD pathology and spatial memory ability and the possible molecular mechanisms remain poorly understood. In this study, we demonstrate that rats exposed to a hypoxic condition (10% oxygen concentration) for 1, 2, 4 and 8 weeks (6 h each day) displayed spatial memory impairment and increased tau phosphorylation at Ser198/199/202, Thr205, Ser262, Ser396 and Ser404 in the hippocampus. Concomitantly, the levels of Tyr216-phosphorylated glycogen synthase kinase (GSK)-3β (activated form of GSK-3β) and Tyr307-phosphorylated protein phosphatase 2A (inactivated form of PP2A) were significantly increased in the hippocampus of the rats with 1, 2, 4 and 8 weeks of hypoxia exposure, while the levels of methylated PP2A (activated form of PP2A) were significantly decreased in the hippocampus of the rats with 4 and 8 weeks of hypoxia exposure. In addition, the content of malondialdehyde, an indicator of oxidative stress, was elevated, whereas the activity of superoxide dismutase was not significantly changed in the hippocampus of the rats exposed to hypoxia. Taken together, these data demonstrated that hypoxia induced tau hyperphosphorylation and memory impairment in rats, and that the increased tau phosphorylation could be attributed to activation of GSK-3β and inactivation of PP2A. These data suggest that interventions to improve hypoxia may be helpful to prevent the development of AD pathology and cognitive impairment.

Chronic dietary supplementation of 4% figs on the modification of oxidative stress in Alzheimer's disease transgenic mouse model

We assessed the changes in the plasma Aβ, oxidative stress/antioxidants, and membrane bound enzymes in the cerebral cortex and hippocampus of Alzheimer's disease (AD) transgenic mice (Tg2576) after dietary supplementation of Omani figs fruits for 15 months along with spatial memory and learning test. AD Tg mice on control diet without figs showed significant impairment in spatial learning ability compared to the wild-type mice on same diet and figs fed Tg mice as well. Significant increase in oxidative stress and reduced antioxidant status were observed in AD Tg mice. 4% figs treated AD Tg mice significantly attenuated oxidative damage, as evident by decreased lipid peroxidation and protein carbonyls and restoration of antioxidant status. Altered activities of membrane bound enzymes (Na(+) K(+) ATPase and acetylcholinesterase (AChE)) in AD Tg mice brain regions and was restored by figs treatment. Further, figs supplementation might be able to decrease the plasma levels of Aβ (1-40, 1-42) significantly in Tg mice suggesting a putative delay in the formation of plaques, which might be due to the presence of high natural antioxidants in figs. But this study warrants further extensive investigation to find a novel lead for a therapeutic target for AD from figs.

Agmatine improves cognitive dysfunction and prevents cell death in a streptozotocin-induced Alzheimer rat model

PURPOSE

Alzheimer's disease (AD) results in memory impairment and neuronal cell death in the brain. Previous studies demonstrated that intracerebroventricular administration of streptozotocin (STZ) induces pathological and behavioral alterations similar to those observed in AD. Agmatine (Agm) has been shown to exert neuroprotective effects in central nervous system disorders. In this study, we investigated whether Agm treatment could attenuate apoptosis and improve cognitive decline in a STZ-induced Alzheimer rat model.

MATERIALS AND METHODS

We studied the effect of Agm on AD pathology using a STZ-induced Alzheimer rat model. For each experiment, rats were given anesthesia (chloral hydrate 300 mg/kg, ip), followed by a single injection of STZ (1.5 mg/kg) bilaterally into each lateral ventricle (5 μL/ventricle). Rats were injected with Agm (100 mg/kg) daily up to two weeks from the surgery day.

RESULTS

Agm suppressed the accumulation of amyloid beta and enhanced insulin signal transduction in STZ-induced Alzheimer rats [experimetal control (EC) group]. Upon evaluation of cognitive function by Morris water maze testing, significant improvement of learning and memory dysfunction in the STZ-Agm group was observed compared with the EC group. Western blot results revealed significant attenuation of the protein expressions of cleaved caspase-3 and Bax, as well as increases in the protein expressions of Bcl2, PI3K, Nrf2, and γ-glutamyl cysteine synthetase, in the STZ-Agm group.

CONCLUSION

Our results showed that Agm is involved in the activation of antioxidant signaling pathways and activation of insulin signal transduction. Accordingly, Agm may be a promising therapeutic agent for improving cognitive decline and attenuating apoptosis in AD.

Neuroprotective properties of the marine carotenoid astaxanthin and omega-3 fatty acids, and perspectives for the natural combination of both in krill oil

The consumption of marine fishes and general seafood has long been recommended by several medical authorities as a long-term nutritional intervention to preserve mental health, hinder neurodegenerative processes, and sustain cognitive capacities in humans. Most of the neurological benefits provided by frequent seafood consumption comes from adequate uptake of omega-3 and omega-6 polyunsaturated fatty acids, n-3/n-6 PUFAs, and antioxidants. Optimal n-3/n-6 PUFAs ratios allow efficient inflammatory responses that prevent the initiation and progression of many neurological disorders. Moreover, interesting in vivo and clinical studies with the marine antioxidant carotenoid astaxanthin (present in salmon, shrimp, and lobster) have shown promising results against free radical-promoted neurodegenerative processes and cognition loss. This review presents the state-of-the-art applications of n-3/n-6 PUFAs and astaxanthin as nutraceuticals against neurodegenerative diseases associated with exacerbated oxidative stress in CNS. The fundamental “neurohormesis” principle is discussed throughout this paper. Finally, new perspectives for the application of a natural combination of the aforementioned anti-inflammatory and antioxidant agents (found in krill oil) are also presented herewith.

Soluble beta-amyloid peptides, but not insoluble fibrils, have specific effect on neuronal microRNA expression

Recent studies indicate that soluble β-amyloid (sAβ) oligomers, rather than their fibrillar aggregates, contribute to the pathogenesis of Alzheimer's disease (AD), though the mechanisms of their neurotoxicity are still elusive. Here, we demonstrate that sAβ derived from 7PA2 cells exert a much stronger effect on the regulation of a set of functionally validated microRNAs (miRNAs) in primary cultured neurons than the synthetic insoluble Aβ fibrils (fAβ). Synthetic sAβ peptides at a higher concentration present comparable effect on these miRNAs in our neuronal model. Further, the sAβ-induced miR-134, miR-145 and miR-210 expressions are fully reversed by two selective N-methyl-d-aspartate (NMDA) receptor inhibitors, but are neither reversed by insulin nor by forskolin, suggesting an NMDA receptor-dependent, rather than PI3K/AKT or PKA/CREB signaling dependent regulatory mechanism. In addition, the repression of miR-107 expression by the sAβ containing 7PA2 CM is likely involved multiple mechanisms and multiple players including NMDA receptor, N-terminally truncated Aβ and reactive oxygen species (ROS).

Cocoa powder triggers neuroprotective and preventive effects in a human Alzheimer's disease model by modulating BDNF signaling pathway

The molecular mechanisms linking Aβ to the onset of neurotoxicity are still largely unknown, but several lines of evidence point to reactive oxygen species, which are produced even under the effect of nanomolar concentrations of soluble Aβ-oligomers. The consequent oxidative stress is considered as the mediator of a cascade of degenerative events in many neurological disorders. Epidemiological studies indicate that dietary habits and antioxidants from diet can influence the incidence of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. In the recent years, a number of reviews have reported on neuroprotective effects of polyphenols in cell and animal models. However, the majority of these studies have focused only on the anti-oxidant properties of these compounds and less on the mechanism/s of action at cellular level. In this work we investigated the effect of cocoa polyphenolic extract on a human AD in vitro model. The results obtained, other than confirming the anti-oxidant properties of cocoa, demonstrate that cocoa polyphenols triggers neuroprotection by activating BDNF survival pathway, both on Aβ plaque treated cells and on Aβ oligomers treated cells, resulting in the counteraction of neurite dystrophy. On the light of the results obtained the use of cocoa powder as preventive agent for neurodegeneration is further supported.

Amyloid beta: multiple mechanisms of toxicity and only some protective effects?

Amyloid beta (Aβ) is a peptide of 39–43 amino acids found in large amounts and forming deposits in the brain tissue of patients with Alzheimer's disease (AD). For this reason, it has been implicated in the pathophysiology of damage observed in this type of dementia. However, the role of Aβ in the pathophysiology of AD is not yet precisely understood. Aβ has been experimentally shown to have a wide range of toxic mechanisms in vivo and in vitro, such as excitotoxicity, mitochondrial alterations, synaptic dysfunction, altered calcium homeostasis, oxidative stress, and so forth. In contrast, Aβ has also shown some interesting neuroprotective and physiological properties under certain experimental conditions, suggesting that both physiological and pathological roles of Aβ may depend on several factors. In this paper, we reviewed both toxic and protective mechanisms of Aβ to further explore what their potential roles could be in the pathophysiology of AD. The complete understanding of such apparently opposed effects will also be an important guide for the therapeutic efforts coming in the future.