Intraneuronal amyloid beta accumulation and oxidative damage to nucleic acids in Alzheimer disease

Insights into Dysregulated Neurological Biomarkers in Cancer

The link between neurodegenerative diseases (NDs) and cancer has generated greater interest in biomedical research, with decades of global studies investigating neurodegenerative biomarkers in cancer to better understand possible connections. Tau, amyloid-β, α-synuclein, SOD1, TDP-43, and other proteins associated with nervous system diseases have also been identified in various types of solid and malignant tumors, suggesting a potential overlap in pathological processes. In this review, we aim to provide an overview of current evidence on the role of these proteins in cancer, specifically examining their effects on cell proliferation, apoptosis, chemoresistance, and tumor progression. Additionally, we discuss the diagnostic and therapeutic implications of this interconnection, emphasizing the importance of further research to completely comprehend the clinical implications of these proteins in tumors. Finally, we explore the challenges and opportunities in targeting these proteins for the development of new targeted anticancer therapies, providing insight into how to integrate knowledge of NDs in oncology research.

Oxidative damage in neurodegeneration: roles in the pathogenesis and progression of Alzheimer disease

Alzheimer disease (AD) is associated with multiple etiologies and pathological mechanisms, among which oxidative stress (OS) appears as a major determinant. Intriguingly, OS arises in various pathways regulating brain functions, and it seems to link different hypotheses and mechanisms of AD neuropathology with high fidelity. The brain is particularly vulnerable to oxidative damage, mainly because of its unique lipid composition, resulting in an amplified cascade of redox reactions that target several cellular components/functions ultimately leading to neurodegeneration. The present review highlights the "OS hypothesis of AD," including amyloid beta-peptide-associated mechanisms, the role of lipid and protein oxidation unraveled by redox proteomics, and the antioxidant strategies that have been investigated to modulate the progression of AD. Collected studies from our groups and others have contributed to unraveling the close relationships between perturbation of redox homeostasis in the brain and AD neuropathology by elucidating redox-regulated events potentially involved in both the pathogenesis and progression of AD. However, the complexity of AD pathological mechanisms requires an in-depth understanding of several major intracellular pathways affecting redox homeostasis and relevant for brain functions. This understanding is crucial to developing pharmacological strategies targeting OS-mediated toxicity that may potentially contribute to slow AD progression as well as improve the quality of life of persons with this severe dementing disorder.

Ameliorative effects of pine nut peptide-zinc chelate (Korean pine) on a mouse model of Alzheimer's disease

In this study, 50 SD adult male mice were used to create an Alzheimer's disease model. The mice's learning and memory abilities were evaluated using an eight-arm radial maze experiment, and changes in body weight and food intake were noted. This helped to better validate the improvement of Alzheimer's disease caused by pine nut peptide-zinc chelate (Korean pine). For a more thorough investigation, mice's brains were dissected, Endogenous mercaptan antioxidants (enzymes), which are markers of brain tissue, were assessed, and mouse gut flora was analyzed. The findings demonstrated that pine nut peptide-zinc chelate (Korean pine) can improve learning and memory, stop brain aging and damage, and control gut flora in mice. It may exert its effects by ameliorating decreased AChE levels and increased ChAT levels in the central cholinergic system, endogenous thiol antioxidants (enzymes) in the cerebral cortex, and by controlling the bacterial flora in the gut.

Neuroprotective effects of novel pyrrolidine-2-one derivatives on scopolamine-induced cognitive impairment in mice: Behavioral and biochemical analysis

Alzheimer's disease (AD) is a long-term neurodegenerative condition that impairs cognitive abilities. Brain acetylcholine deficit and oxidative stress may be considered the key pathogenic causes for AD, even though the basic etiology is still unknown. The effects of some novel pyrrolidine-2-one derivatives on the learning and memory deficits caused by scopolamine in mice were examined in the current study. The learning and memory parameters were assessed using the morris water maze test, rota rod test the and locomotor activity. A number of biochemical factors were also evaluated, including acetylcholinesterase (AChE), lipid peroxidation (LPO), reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CA), and nitrite oxide (NO) assay. The current study shows that these derivatives were more effective and comparable to donepezil at treating the behavioral and biochemical changes brought on by scopolamine. The observed results showed pyrrolidine-2-one derivatives as a promising candidate for diseases associated with cognitive deficits.

Effect of amyloid-β on the redox system activity in SH-SY5Y cells preincubated with lipopolysaccharide or co-cultured with microglia cells

Amyloid deposits and hyperphosphorylation of the tau protein are still believed to be the two main causes of Alzheimer's disease. However, newer studies show the beneficial (including antiradical and antimicrobial) effects of amyloid at physiological concentrations. Therefore, this study aimed to investigate the impact of three amyloid fragments - 25-35, 1-40, and 1-42 at concentrations close to physiological levels on the oxidative stress induced by the administration of lipopolysaccharide (LPS) or co-culturing with microglia cells. Differentiated SH-SY5Y cells were used, constituting a model of neuronal cells that were preincubated with LPS or supernatant collected from THP-1 cell culture. The cells were treated with amyloid-β fragments at concentrations of 0.001, 0.1, and 1.0 µM, and then biological assays were carried out. The results of the study support the antioxidant properties of Aβ, which may protect neurons from the damaging effects of neuroinflammation. All tested amyloid-β fragments reduced oxidative stress and increased the levels of enzymatic stress parameters - the activity of SOD, GPx and catalase. In addition, the administration of amyloid-β at low physiological concentrations also increased reduced glutathione (GSH) levels and the ratio between reduced and oxidized glutathione (GSH/GSSG), which is considered a good indicator of maintaining cellular redox balance. Furthermore, a stronger antioxidant effect of 1-40 fragment was observed, occurring in a wider range of concentrations, compared to the other tested fragments 25-35 and 1-42.

Biology of aging: Oxidative stress and RNA oxidation

The prevalence of aged people has increased rapidly in recent years and brings profound demographic changes worldwide. The multi-level progression of aging occurs at diverse stages of complexity, from cell to organ systems and eventually to the human as a whole. The cellular and molecular damages are usually regulated by the cells; repair or degrade mechanisms. However, these mechanisms are not entirely functional; their effectiveness decreases with age due to influence from endogenous sources like oxidative stress, which all contribute to the aging process. The hunt for novel strategies to increase the man's longevity since ancient times needs better understandings of the biology of aging, oxidative stress, and their roles in RNA oxidation. The critical goal in developing new strategies to increase the man's longevity is to compile the novel developed knowledge on human aging into a single picture, preferably able to understand the biology of aging and the contributing factors. This review discusses the biology of aging, oxidative stress, and their roles in RNA oxidation, leading to aging in humans.

A study on UHPLC-MS/MS analyses of DNA and RNA oxidative damage metabolites in patients with cervical carcinoma: 8-oxoG in urine as a potential biomarker of cervical carcinoma

Objective

Methods

Results

Conclusions

Mitochondrial Targeting of Amyloid-β Protein Precursor Intracellular Domain Induces Hippocampal Cell Death via a Mechanism Distinct from Amyloid-β

BACKGROUND

Amyloid-β (Aβ) is a principal cleavage product of amyloid-β protein precursor (AβPP) and is widely recognized as a key pathogenic player in Alzheimer's disease (AD). Yet, there is increasing evidence of a neurotoxic role for the AβPP intracellular domain (AICD) which has been proposed to occur through its nuclear function. Intriguingly, there is a γ-secretase resident at the mitochondria which could produce AICD locally.

OBJECTIVE

We examined the potential of AICD to induce neuronal apoptosis when targeted specifically to the mitochondria and compared its mechanism of neurotoxicity to that of Aβ.

METHODS

We utilized transient transfection of HT22 neuronal cells with bicistronic plasmids coding for DsRed and either empty vector (Ires), Aβ, AICD59, or mitochondrial-targeted AICD (mitoAICD) in combination with various inhibitors of pathways involved in apoptosis.

RESULTS

AICD induced significant neuronal apoptosis only when targeted to the mitochondria. Apoptosis required functional mitochondria as neither Aβ nor mitoAICD induced significant toxicity in cells devoid of mitochondrial DNA. Both glutathione and a Bax inhibitor protected HT22 cells from either peptide. However, inhibition of the mitochondrial permeability transition pore only protected from Aβ, while pan-caspase inhibitors uniquely rescued cells from mitoAICD.

CONCLUSION

Our results show that AICD displays a novel neurotoxic function when targeted to mitochondria. Moreover, mitoAICD induces apoptosis via a mechanism that is distinct from that of Aβ. These findings suggest that AICD produced locally at mitochondria via organelle-specific γ-secretase could act in a synergistic manner with Aβ to cause mitochondrial dysfunction and neuronal death in AD.

Impact of NMDA receptor activation on DNA damage in PC12 neuron-like cell cultures in the presence of β-amyloid peptides

OBJECTIVE

This study aimed to investigate the effect of low nanomolar concentrations of Aβ1-40 and Aβ25-35 on DNA double-strand breaks following NMDA activation of cells.

MATERIALS AND METHODS

After incubating the differentiated PC12 cells with Aβ_25-35, Aβ_1-40 or Aβ_1-42 for 24 h, the culture was washed and stimulated for 15 min with NMDA. Then, tests were performed at four-time intervals from stimulation to assess the viability of the culture, the level of oxygen free radicals, and the γH2AX and pATM kinase. NMDAR1 expression was also evaluated by performing immunocytochemical staining.

RESULTS

It was found that amyloid peptides in nanomolar concentrations reduce double-stranded DNA breaks after NMDA neuron activation. A slight antioxidant effect was also demonstrated when measured 120 min after NMDA cell activation.

CONCLUSION

The NMDA stimulation of PC12 cells led to a rapid increase in the number of double-stranded DNA breaks in the cells and is assumed to be the initial step in IEG activation and LTP induction. The effect of Aβ on the reduction of double-strand breaks after NMDA cell stimulation indicates that at concentrations similar to physiological amyloid peptides, it may reduce the mobilization of the neuronal response to stimuli, leading to inhibition of LTP induction and decreasing synaptic plasticity in the early stages of Alzheimer's disease.

A Review of Oxidative Stress Products and Related Genes in Early Alzheimer's Disease

Oxidative stress is associated with the progression of Alzheimer’s disease (AD). Reactive oxygen species can modify lipids, DNA, RNA, and proteins in the brain. The products of their peroxidation and oxidation are readily detectable at incipient stages of disease. Based on these oxidation products, various biomarker-based strategies have been developed to identify oxidative stress levels in AD. Known oxidative stress-related biomarkers include lipid peroxidation products F2-isoprostanes, as well as malondialdehyde and 4-hydroxynonenal which both conjugate to specific amino acids to modify proteins, and DNA or RNA oxidation products 8-hydroxy-2’-deoxyguanosine (8-OHdG) and 8-hydroxyguanosine (8-OHG), respectively. The inducible enzyme heme oxygenase type 1 (HO-1) is found to be upregulated in response to oxidative stress-related events in the AD brain. While these global biomarkers for oxidative stress are associated with early-stage AD, they generally poorly differentiate from other neurodegenerative disorders that also coincide with oxidative stress. Redox proteomics approaches provided specificity of oxidative stress-associated biomarkers to AD pathology by the identification of oxidatively damaged pathology-specific proteins. In this review, we discuss the potential combined diagnostic value of these reported biomarkers in the context of AD and discuss eight oxidative stress-related mRNA biomarkers in AD that we newly identified using a transcriptomics approach. We review these genes in the context of their reported involvement in oxidative stress regulation and specificity for AD. Further research is warranted to establish the protein levels and their functionalities as well as the molecular mechanisms by which these potential biomarkers are involved in regulation of oxidative stress levels and their potential for determination of oxidative stress and disease status of AD patients.

Evidence for the Role of Mitochondrial DNA Release in the Inflammatory Response in Neurological Disorders

Mitochondria are regarded as the metabolic centers of cells and are integral in many other cell processes, including the immune response. Each mitochondrion contains numerous copies of mitochondrial DNA (mtDNA), a small, circular, and bacterial-like DNA. In response to cellular damage or stress, mtDNA can be released from the mitochondrion and trigger immune and inflammatory responses. mtDNA release into the cytosol or bloodstream can occur as a response to hypoxia, sepsis, traumatic injury, excitatory cytotoxicity, or drastic mitochondrial membrane potential changes, some of which are hallmarks of neurodegenerative and mood disorders. Released mtDNA can mediate inflammatory responses observed in many neurological and mood disorders by driving the expression of inflammatory cytokines and the interferon response system. The current understanding of the role of mtDNA release in affective mood disorders and neurodegenerative diseases will be discussed.

Neuropathology of Aging in Cats and its Similarities to Human Alzheimer’s Disease

Elderly cats develop age-related behavioral and neuropathological changes that ultimately lead to cognitive dysfunction syndrome (CDS). These neuropathologies share similarities to those seen in the brains of humans with Alzheimer’s disease (AD), including the extracellular accumulation of ß-amyloid (Aβ) and intraneuronal deposits of hyperphosphorylated tau, which are considered to be the two major hallmarks of AD. The present study assessed the presence and distribution of Aβ and tau hyperphosphorylation within the cat brain (n = 55 cats), and how the distribution of these proteins changes with age and the presence of CDS. For this, immunohistochemistry was performed on seven brain regions from cats of various ages, with and without CDS (n = 10 with CDS). Cats accumulate both intracytoplasmic and extracellular deposits of Aβ, as well as intranuclear and intracytoplasmic hyperphosphorylated tau deposits. Large extracellular aggregates of Aβ were found in elderly cats, mainly in the cortical brain areas, with occasional hippocampal aggregates. This may suggest that these aggregates start in cortical areas and later progress to the hippocampus. While Aβ senile plaques in people with AD have a dense core, extracellular Aβ deposits in cats exhibited a diffuse pattern, similar to the early stages of plaque pathogenesis. Intraneuronal Aβ deposits were also observed, occurring predominantly in cortical brain regions of younger cats, while older cats had few to no intraneuronal Aβ deposits, especially when extracellular aggregates were abundant. Intracytoplasmic hyperphosphorylated tau was found within neurons in the brains of elderly cats, particularly in those with CDS. Due to their ultrastructural features, these deposits are considered to be pre-tangles, which are an early stage of the neurofibrillary tangles seen in AD. The largest numbers of pre-tangles are found mainly in the cerebral cortex of elderly cats, whereas lower numbers were found in other regions (i.e., entorhinal cortex and hippocampus). For the first time, intranuclear tau was found in both phosphorylated and non-phosphorylated states within neurons in the cat brain. The highest numbers of intranuclear deposits were found in the cortex of younger cats, and this tended to decrease with age. In contrast, elderly cats with pre-tangles had only occasional or no nuclear labelling.

Modifiable, Non-Modifiable, and Clinical Factors Associated with Progression of Alzheimer's Disease

There is an extensive literature relating to factors associated with the development of Alzheimer's disease (AD), but less is known about factors which may contribute to its progression. This review examined the literature with regard to 15 factors which were suggested by PubMed search to be positively associated with the cognitive and/or neuropathological progression of AD. The factors were grouped as potentially modifiable (vascular risk factors, comorbidities, malnutrition, educational level, inflammation, and oxidative stress), non-modifiable (age at clinical onset, family history of dementia, gender, Apolipoprotein E ɛ4, genetic variants, and altered gene regulation), and clinical (baseline cognitive level, neuropsychiatric symptoms, and extrapyramidal signs). Although conflicting results were found for the majority of factors, a positive association was found in nearly all studies which investigated the relationship of six factors to AD progression: malnutrition, genetic variants, altered gene regulation, baseline cognitive level, neuropsychiatric symptoms, and extrapyramidal signs. Whether these or other factors which have been suggested to be associated with AD progression actually influence the rate of decline of AD patients is unclear. Therapeutic approaches which include addressing of modifiable factors associated with AD progression should be considered.

Alzheimer's Disease as a Membrane Disorder: Spatial Cross-Talk Among Beta-Amyloid Peptides, Nicotinic Acetylcholine Receptors and Lipid Rafts

Biological membranes show lateral and transverse asymmetric lipid distribution. Cholesterol (Chol) localizes in both hemilayers, but in the external one it is mostly condensed in lipid-ordered microdomains (raft domains), together with saturated phosphatidyl lipids and sphingolipids (including sphingomyelin and glycosphingolipids). Membrane asymmetries induce special membrane biophysical properties and behave as signals for several physiological and/or pathological processes. Alzheimer’s disease (AD) is associated with a perturbation in different membrane properties. Amyloid-β (Aβ) plaques and neurofibrillary tangles of tau protein together with neuroinflammation and neurodegeneration are the most characteristic cellular changes observed in this disease. The extracellular presence of Aβ peptides forming senile plaques, together with soluble oligomeric species of Aβ, are considered the major cause of the synaptic dysfunction of AD. The association between Aβ peptide and membrane lipids has been extensively studied. It has been postulated that Chol content and Chol distribution condition Aβ production and posterior accumulation in membranes and, hence, cell dysfunction. Several lines of evidence suggest that Aβ partitions in the cell membrane accumulate mostly in raft domains, the site where the cleavage of the precursor AβPP by β- and γ- secretase is also thought to occur. The main consequence of the pathogenesis of AD is the disruption of the cholinergic pathways in the cerebral cortex and in the basal forebrain. In parallel, the nicotinic acetylcholine receptor has been extensively linked to membrane properties. Since its transmembrane domain exhibits extensive contacts with the surrounding lipids, the acetylcholine receptor function is conditioned by its lipid microenvironment. The nicotinic acetylcholine receptor is present in high-density clusters in the cell membrane where it localizes mainly in lipid-ordered domains. Perturbations of sphingomyelin or cholesterol composition alter acetylcholine receptor location. Therefore, Aβ processing, Aβ partitioning, and acetylcholine receptor location and function can be manipulated by changes in membrane lipid biophysics. Understanding these mechanisms should provide insights into new therapeutic strategies for prevention and/or treatment of AD. Here, we discuss the implications of lipid-protein interactions at the cell membrane level in AD.

Alpha 7 nicotinic acetylcholine receptor and its effects on Alzheimer's disease

Alzheimer's disease (AD) is one of the major disabling and lethal diseases for aged individuals worldwide. To date, there are more than 10 hypotheses proposed for AD pathology. The beta-amyloid (Aβ) cascade hypothesis is the most widely accepted and proposes that the accumulation of Aβ in the brain is one potential mechanism for AD pathogenesis. Because some Aβ-overloaded patients do not have AD syndrome, this hypothesis is challenged from time to time. More recently, it has been shown that intracellular Aβ plays a key role in AD pathology. Aβ is internalized by receptors distributed on the cell membrane. Among these receptors, the alpha7 nicotinic acetylcholine receptor (α7 nAChR) has been shown to play an important role in AD. The α7 nAChR is a ligand-gated ion channel and is expressed in pivotal brain regions (e.g., the cerebral cortex and hippocampus) responsible for cognitive functions. The α7 nAChR is localized both presynaptically and postsynaptically, where it activates intracellular signaling cascades. Its agonist has been investigated in clinical studies to improve cognitive functions in AD. Although many studies have shown the importance of the α7 nAChR in AD, little is known regarding its role in AD pathology. Therefore, in the current review, we summarized the basic information regarding the structures and functions of the α7 nAChR, the distribution and expression of the α7 nAChR, and the role of the α7 nAChR in mediating Aβ internalization. We subsequently focused on introducing the comprehensive α7 nAChR related signaling pathways and how these signaling pathways are integrated with the α7 nAChR to play a role in AD. Finally, we stressed the AD therapy that targets the α7 nAChR.

Protective effect of chloroform extract of Stereospermum chelonoides bark against amyloid beta42 induced cell death in SH-SY5Y cells and against inflammation in Swiss albino mice

Background This study was designed to evaluate the free radical scavenging property of chloroform extract of the bark of Stereospermum chelonoides (SCBC) and to investigate its potential in Alzheimer's disease and inflammation, two oxidative stress related disorders. Methods Preliminary phytochemical analysis and in vitro antioxidant potential of SCBC were evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, ferric reducing antioxidant power (FRAP) assay, cupric reducing antioxidant capacity (CUPRAC) and total antioxidant capacity determination assay. Total phenol and total flavonoid contents were also determined. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) based cytotoxicity and cyto-protective assays were performed on human neuroblastoma SH-SY5Y cells. Thioflavin-T assay and caspase activation measurement assay were carried out to elucidate the mechanism of cytoprotection of SCBC observed here. In vivo anti-inflammatory potential was measured using croton oil and xylene induced ear edema tests. Results Phytochemical screening of SCBC revealed the presence of various phytoconstituents. Dose-dependent in vitro antioxidant activity was observed. The extract was enriched in flavonoids and polyphenolic compounds too. SCBC was found to inhibit amyloid-β peptide 1-42 (Aβ42) induced cell death in a dose-dependent manner. Encouraged by the cyto-protective effect, its effects on Aβ42 fibrillogenesis and caspase-3 activated apoptosis were observed. SCBC significantly slowed down the Aβ42 fibrillogenesis and caspase-3 activation in a concentration-dependent manner indicating its probable mechanism of rendering cyto-protection. SCBC has been able to reduce inflammation significantly in croton oil induced ear edema in both doses. Conclusions Thus, this study could form the basis for further study for the potential use of SCBC in oxidative stress associated cell death and inflammation.

Scopolamine-Induced Memory Impairment Is Alleviated by Xanthotoxin: Role of Acetylcholinesterase and Oxidative Stress Processes

Xanthotoxin, popularly occurring furanocoumarin, which can be found in plants from the Apiaceae family, was isolated from fruits of Pastinaca sativa L. by mean of high-performance countercurrent chromatography, and its effects on the scopolamine-induced cognitive deficits in male Swiss mice using the passive avoidance (PA) test were evaluated. To measure the acquisition of memory processes, xanthotoxin (1, 2.5, 5 mg/kg) was administered 30 min before PA test and scopolamine was administered 10 min after xanthotoxin. To measure the consolidation of memory processes, xanthotoxin (1 and 2.5 mg/kg) was injected immediately after removing the mouse from the apparatus and 10 min after scopolamine was administered. In subchronic experiments, mice were injected with xanthotoxin (1 mg/kg) or saline, 6 days, twice daily. At 24 h after the last injection of the drugs, the hippocampus and the prefrontal cortex were removed for biochemical assays. The results demonstrated that either single (2.5 and 5 mg/kg) or repeatable (1 mg/kg) administration of xanthotoxin significantly increased index of latency (IL) in both acquisition and consolidation of memory processes, showing some procognitive effects. The behavioral tests also showed that an acute (2.5 mg/kg) and subchronic (1 mg/kg) administration of xanthotoxin prevent memory impairment induced by injection of scopolamine (1 mg/kg). Observed effects could be due to the inhibition of acetylcholinesterase activities and amelioration of oxidative stress processes in the hippocampus and the prefrontal cortex. It was suggested that xanthotoxin could show neuroprotective effect in scopolamine-induced cognitive impairment connected to cholinergic neurotransmission and oxidative stress in the brain structures.

Bombesin attenuated ischemia-induced spatial cognitive and synaptic plasticity impairment associated with oxidative damage

The dysfunction of spatial cognition is a character to various neurological disorders and therapeutic strategy. However, it is limited to known risk factors clinically so far. Gastrin releasing peptide (GRP) signaling is a neuropeptide system mediating emotional memory events. However, the effects of GRP agonist on spatial cognition and hippocampal synaptic plasticity are rarely investigated, especially in pathologic condition. This study was designed to investigate the long-term effects of GRPR agonist, bombesin, against cognitive impairment induced by chronic cerebral ischemia in rats and its possible mechanisms. Our results revealed that bombesin administration (30 μg/kg/day, for 14 continuous days) significantly protected the cognitive and synaptic plasticity impairments as assessed by the Morris water maze and long-term potentiation tests. The mechanism studies demonstrated that bombesin significantly alleviated the decreased activity of total superoxide dismutase (T-SOD), catalase (CAT) and altered the increased the content of malondialdehyde (MDA). Besides, the decreased expression of synapse plasticity-related proteins, calcium- calmodulin- dependent protein kinase II (CaMKII) and synaptophysin (SYP) in the hippocampus were increased with drug treatment. In conclusion, bombesin could protect the oxidative stress and expression of proteins, which were important for synaptic plasticity and cognitive function impairment induced by chronic cerebral ischemia. Our study is presented to provide novel insights into the effects of bombesin on spatial learning and memory, which should be further explored as a potential drug in disorders involving deficits in cognitive function.

Biophysical properties, thermal stability and functional impact of 8-oxo-7,8-dihydroguanine on oligonucleotides of RNA-a study of duplex, hairpins and the aptamer for preQ1 as models

A better understanding of the effects that oxidative lesions have on RNA is of importance to understand their role in the development/progression of disease. 8-oxo-7,8-dihydroguanine was incorporated into RNA to understand its structural and functional impact on RNA:RNA and RNA:DNA duplexes, hairpins and pseudoknots. One to three modifications were incorporated into dodecamers of RNA [AAGAGGGAUGAC] resulting in thermal destabilization (ΔT_m – 10°C per lesion). Hairpins with tetraloops c-UUCG*-g* (8-10), a-ACCG-g* (11-12), c-UUG*G*-g* (13-16) and c-ACG*G*-g* (17-20) were modified and used to determine thermal stabilities, concluding that: (i) modifying the stem leads to destabilization unless adenosine is the opposing basepair of 8-oxoGua; (ii) modification at the loop is position- and sequence-dependent and varies from slight stabilization to large destabilization, in some cases leading to formation of other secondary structures (hairpin→duplex). Functional effects were established using the aptamer for preQ₁ as model. Modification at G5 disrupted the stem P1 and inhibited recognition of the target molecule 7-methylamino-7-deazaguanine (preQ₁). Modifying G11 results in increased thermal stability, albeit with a K_d 4-fold larger than its canonical analog. These studies show the capability of 8-oxoG to affect structure and function of RNA, resulting in distinct outcomes as a function of number and position of the lesion.

Potential application of the oxidative nucleic acid damage biomarkers in detection of diseases

Reactive oxygen species (ROS) are generated after exposure to harmful environmental factors and during normal cellular metabolic processes. The balance of the generating and scavenging of ROS plays a significant role in living cells. The accumulation of ROS will lead to oxidative damage to biomolecules including nucleic acid. Although many types of oxidative nucleic acid damage products have been identified, 8-oxo-7,8-dihydro-2’-deoxyguanosine (8-oxodG) and 8-oxo-7,8-dihydroguanosine (8-oxoG) has been commonly chosen as the biomarkers of oxidative damage to DNA and RNA, respectively. It has been demonstrated that oxidative damage to nucleic acid is an initiator in pathogenesis of numerous diseases. Thus, oxidative nucleic acid damage biomarkers have the potential to be utilized for detection of diseases. Herein, we reviewed the relationship of oxidative nucleic acid damage and development of various diseases including cancers (colorectal cancer, gastrointestinal cancer, breast cancer, lung cancer, epithelial ovarian carcinoma, esophageal squamous cell carcinoma), neurodegenerative disorders and chronic diseases (diabetes and its complications, cardiovascular diseases). The potential of oxidative nucleic acid damage biomarkers for detection of diseases and drug development were described. Moreover, the approaches for detection of these biomarkers were also summarized.

Nucleic acid oxidative damage in Alzheimer's disease-explained by the hepcidin-ferroportin neuronal iron overload hypothesis?

There is strong literature support for brain metal dysregulation, oxidative stress and oxidative damage to neurons in Alzheimer's disease (AD); these processes begin early and continue throughout the disease. Here, we review current knowledge on metal dysregulation and nucleic acid oxidative damage in AD (we also include new data demonstrating increased RNA and DNA oxidative damage in hippocampus from individuals having suffered from degenerative (e.g. AD) and psychological diseases: 8-oxo-7,8-dihydroguanine (8-oxoGua) levels as determined by HPLC-EC-UV were particularly elevated in RNA and heterogeneously distributed among adjacent regions versus the control). Whereas neuronal iron accumulation occurs in aging, neuronal iron levels further increase in AD accompanied by oxidative damage, decreased copper levels, amyloid plaque formation and brain inflammation. The 'hepcidin-ferroportin iron overload' AD hypothesis links these processes together and is discussed here. Moreover, we find that most existing transgenic animal AD models only partly involve these processes, rather they are often limited to expression of mutated amyloid beta protein precursor (AbetaPP), presenilin, tau or apolipoprotein E proteins although a few models appear more relevant than others. Relevant models are likely to be crucial for refining and testing this hypothesis as well as developing new drugs.

Increased DNA and RNA damage by oxidation in patients with bipolar I disorder

The mechanisms underlying bipolar disorder (BD) and the associated medical burden are unclear. Damage generated by oxidation of nucleosides may be implicated in BD pathophysiology; however, evidence from in vivo studies is limited and the extent of state-related alterations is unclear. This prospective study investigated for we believe the first time the damage generated by oxidation of DNA and RNA strictly in patients with type I BD in a manic or mixed state and subsequent episodes and remission compared with healthy control subjects. Urinary excretion of 8-oxo-deoxyguanosine (8-oxodG) and 8-oxo-guanosine (8-oxoGuo), valid markers of whole-body DNA and RNA damage by oxidation, respectively, was measured in 54 patients with BD I and in 35 healthy control subjects using a modified ultraperformance liquid chromatography and mass spectrometry assay. Repeated measurements were evaluated in various affective phases during a 6- to 12-month period and compared with repeated measurements in healthy control subjects. Independent of lifestyle and demographic variables, a 34% (P<0.0001) increase in RNA damage by oxidation across all affective states, including euthymia, was found in patients with BD I compared with healthy control subjects. Increases in DNA and RNA oxidation of 18% (P<0.0001) and 8% (P=0.02), respectively, were found in manic/hypomanic states compared with euthymia, and levels of 8-oxodG decreased 15% (P<0.0001) from a manic or mixed episode to remission. The results indicate a role for DNA and RNA damage by oxidation in BD pathophysiology and a potential for urinary 8-oxodG and 8-oxoGuo to function as biological markers of diagnosis, state and treatment response in BD.

Dendritic Spine Pathology in Neurodegenerative Diseases

Substantial progress has been made toward understanding the neuropathology, genetic origins, and epidemiology of neurodegenerative diseases, including Alzheimer's disease; tauopathies, such as frontotemporal dementia; α-synucleinopathies, such as Parkinson's disease or dementia with Lewy bodies; Huntington's disease; and amyotrophic lateral sclerosis with dementia, as well as prion diseases. Recent evidence has implicated dendritic spine dysfunction as an important substrate of the pathogenesis of dementia in these disorders. Dendritic spines are specialized structures, extending from the neuronal processes, on which excitatory synaptic contacts are formed, and the loss of dendritic spines correlates with the loss of synaptic function. We review the literature that has implicated direct or indirect structural alterations at dendritic spines in the pathogenesis of major neurodegenerative diseases, focusing on those that lead to dementias such as Alzheimer's, Parkinson's, and Huntington's diseases, as well as frontotemporal dementia and prion diseases. We stress the importance of in vivo studies in animal models.

Amyloid beta modulation of neuronal network activity in vitro

In vitro assays offer a means of screening potential therapeutics and accelerating the drug development process. Here, we utilized neuronal cultures on planar microelectrode arrays (MEA) as a functional assay to assess the neurotoxicity of amyloid-β 1-42 (Aβ42), a biomolecule implicated in the Alzheimer׳s disease (AD). In this approach, neurons harvested from embryonic mice were seeded on the substrate-integrated microelectrode arrays. The cultured neurons form a spontaneously active network, and the spiking activity as a functional endpoint could be detected via the MEA. Aβ42 oligomer, but not monomer, significantly reduced network spike rate. In addition, we demonstrated that the ionotropic glutamate receptors, NMDA and AMPA/kainate, play a role in the effects of Aβ42 on neuronal activity in vitro. To examine the utility of the MEA-based assay for AD drug discovery, we tested two model therapeutics for AD, methylene blue (MB) and memantine. Our results show an almost full recovery in the activity within 24h after administration of Aβ42 in the cultures pre-treated with either MB or memantine. Our findings suggest that cultured neuronal networks may be a useful platform in screening potential therapeutics for Aβ induced changes in neurological function.

Analyzing dendritic spine pathology in Alzheimer's disease: problems and opportunities

Synaptic failure is an immediate cause of cognitive decline and memory dysfunction in Alzheimer’s disease. Dendritic spines are specialized structures on neuronal processes, on which excitatory synaptic contacts take place and the loss of dendritic spines directly correlates with the loss of synaptic function. Dendritic spines are readily accessible for both in vitro and in vivo experiments and have, therefore, been studied in great detail in Alzheimer’s disease mouse models. To date, a large number of different mechanisms have been proposed to cause dendritic spine dysfunction and loss in Alzheimer’s disease. For instance, amyloid beta fibrils, diffusible oligomers or the intracellular accumulation of amyloid beta have been found to alter the function and structure of dendritic spines by distinct mechanisms. Furthermore, tau hyperphosphorylation and microglia activation, which are thought to be consequences of amyloidosis in Alzheimer’s disease, may also contribute to spine loss. Lastly, genetic and therapeutic interventions employed to model the disease and elucidate its pathogenetic mechanisms in experimental animals may cause alterations of dendritic spines on their own. However, to date none of these mechanisms have been translated into successful therapeutic approaches for the human disease. Here, we critically review the most intensely studied mechanisms of spine loss in Alzheimer’s disease as well as the possible pitfalls inherent in the animal models of such a complex neurodegenerative disorder.

Intraneuronal APP and extracellular Aβ independently cause dendritic spine pathology in transgenic mouse models of Alzheimer's disease

Alzheimer’s disease (AD) is thought to be caused by accumulation of amyloid-β protein (Aβ), which is a cleavage product of amyloid precursor protein (APP). Transgenic mice overexpressing APP have been used to recapitulate amyloid-β pathology. Among them, APP23 and APPswe/PS1deltaE9 (deltaE9) mice are extensively studied. APP23 mice express APP with Swedish mutation and develop amyloid plaques late in their life, while cognitive deficits are observed in young age. In contrast, deltaE9 mice with mutant APP and mutant presenilin-1 develop amyloid plaques early but show typical cognitive deficits in old age. To unveil the reasons for different progressions of cognitive decline in these commonly used mouse models, we analyzed the number and turnover of dendritic spines as important structural correlates for learning and memory. Chronic in vivo two-photon imaging in apical tufts of layer V pyramidal neurons revealed a decreased spine density in 4–5-month-old APP23 mice. In age-matched deltaE9 mice, in contrast, spine loss was only observed on cortical dendrites that were in close proximity to amyloid plaques. In both cases, the reduced spine density was caused by decreased spine formation. Interestingly, the patterns of alterations in spine morphology differed between these two transgenic mouse models. Moreover, in APP23 mice, APP was found to accumulate intracellularly and its content was inversely correlated with the absolute spine density and the relative number of mushroom spines. Collectively, our results suggest that different pathological mechanisms, namely an intracellular accumulation of APP or extracellular amyloid plaques, may lead to spine abnormalities in young adult APP23 and deltaE9 mice, respectively. These distinct features, which may represent very different mechanisms of synaptic failure in AD, have to be taken into consideration when translating results from animal studies to the human disease.

D-beta-hydroxybutyrate extends lifespan in C. elegans

The ketone body beta-hydroxybutyrate (βHB) is a histone deacetylase (HDAC) inhibitor and has been shown to be protective in many disease models, but its effects on aging are not well studied. Therefore we determined the effect of βHB supplementation on the lifespan of C. elegans nematodes. βHB supplementation extended mean lifespan by approximately 20%. RNAi knockdown of HDACs hda-2 or hda-3 also increased lifespan and further prevented βHB-mediated lifespan extension. βHB-mediated lifespan extension required the DAF-16/FOXO and SKN-1/Nrf longevity pathways, the sirtuin SIR-2.1, and the AMP kinase subunit AAK-2. βHB did not extend lifespan in a genetic model of dietary restriction indicating that βHB is likely functioning through a similar mechanism. βHB addition also upregulated βHB dehydrogenase activity and increased oxygen consumption in the worms. RNAi knockdown of F55E10.6, a short chain dehydrogenase and SKN-1 target gene, prevented the increased lifespan and βHB dehydrogenase activity induced by βHB addition, suggesting that F55E10.6 functions as an inducible βHB dehydrogenase. Furthermore, βHB supplementation increased worm thermotolerance and partially prevented glucose toxicity. It also delayed Alzheimer's amyloid-beta toxicity and decreased Parkinson's alpha-synuclein aggregation. The results indicate that D-βHB extends lifespan through inhibiting HDACs and through the activation of conserved stress response pathways.

Neuronal amyloid-β accumulation within cholinergic basal forebrain in ageing and Alzheimer's disease

The mechanisms that contribute to selective vulnerability of the magnocellular basal forebrain cholinergic neurons in neurodegenerative diseases, such as Alzheimer's disease, are not fully understood. Because age is the primary risk factor for Alzheimer's disease, mechanisms of interest must include age-related alterations in protein expression, cell type-specific markers and pathology. The present study explored the extent and characteristics of intraneuronal amyloid-β accumulation, particularly of the fibrillogenic 42-amino acid isoform, within basal forebrain cholinergic neurons in normal young, normal aged and Alzheimer's disease brains as a potential contributor to the selective vulnerability of these neurons using immunohistochemistry and western blot analysis. Amyloid-β1-42 immunoreactivity was observed in the entire cholinergic neuronal population regardless of age or Alzheimer's disease diagnosis. The magnitude of this accumulation as revealed by optical density measures was significantly greater than that in cortical pyramidal neurons, and magnocellular neurons in the globus pallidus did not demonstrate a similar extent of amyloid immunoreactivity. Immunoblot analysis with a panel of amyloid-β antibodies confirmed accumulation of high concentration of amyloid-β in basal forebrain early in adult life. There was no age- or Alzheimer-related alteration in total amyloid-β content within this region. In contrast, an increase in the large molecular weight soluble oligomer species was observed with a highly oligomer-specific antibody in aged and Alzheimer brains when compared with the young. Similarly, intermediate molecular weight oligomeric species displayed an increase in aged and Alzheimer brains when compared with the young using two amyloid-β42 antibodies. Compared to cortical homogenates, small molecular weight oligomeric species were lower and intermediate species were enriched in basal forebrain in ageing and Alzheimer's disease. Regional and age-related differences in accumulation were not the result of alterations in expression of the amyloid precursor protein, as confirmed by both immunostaining and western blot. Our results demonstrate that intraneuronal amyloid-β accumulation is a relatively selective trait of basal forebrain cholinergic neurons early in adult life, and increases in the prevalence of intermediate and large oligomeric assembly states are associated with both ageing and Alzheimer's disease. Selective intraneuronal amyloid-β accumulation in adult life and oligomerization during the ageing process are potential contributors to the degeneration of basal forebrain cholinergic neurons in Alzheimer's disease.

Icariin upregulates phosphorylated cyclic adenosine monophosphate response element binding protein levels in the hippocampus of the senescence- accelerated mouse

At 8 weeks after intragastric administration of icariin to senescence-accelerated mice (P8 strain), Morris water maze results showed that escape latency was shortened, and the number of platform crossings was increased. Immunohistochemical staining and western blot assay detected significantly increased levels of cyclic adenosine monophosphate response element binding protein. These results suggest that icariin upregulates phosphorylated cyclic adenosine monophosphate response element binding protein levels and improves learning and memory functions in hippocampus of the senescence-accelerated mouse.

Oxidative stress in Alzheimer's disease

Oxidative stress plays a significant role in the pathogenesis of Alzheimer's disease (AD), a devastating disease of the elderly. The brain is more vulnerable than other organs to oxidative stress, and most of the components of neurons (lipids, proteins, and nucleic acids) can be oxidized in AD due to mitochondrial dysfunction, increased metal levels, inflammation, and β-amyloid (Aβ) peptides. Oxidative stress participates in the development of AD by promoting Aβ deposition, tau hyperphosphorylation, and the subsequent loss of synapses and neurons. The relationship between oxidative stress and AD suggests that oxidative stress is an essential part of the pathological process, and antioxidants may be useful for AD treatment.

Involvement of peroxisome proliferator-activated receptor β/δ (PPAR β/δ) in BDNF signaling during aging and in Alzheimer disease: possible role of 4-hydroxynonenal (4-HNE)

Aging and many neurological disorders, such as AD, are linked to oxidative stress, which is considered the common effector of the cascade of degenerative events. In this phenomenon, reactive oxygen species play a fundamental role in the oxidative decomposition of polyunsaturated fatty acids, resulting in the formation of a complex mixture of aldehydic end products, such as malondialdehyde, 4-hydroxynonenal, and other alkenals. Interestingly, 4-HNE has been indicated as an intracellular agonist of peroxisome proliferator-activated receptor β/δ. In this study, we examined, at early and advanced AD stages (3, 9, and 18 months), the pattern of 4-HNE and its catabolic enzyme glutathione S-transferase P1 in relation to the expression of PPARβ/δ, BDNF signaling, as mRNA and protein, as well as on their pathological forms (i.e., precursors or truncated forms). The data obtained indicate a novel detrimental age-dependent role of PPAR β/δ in AD by increasing pro-BDNF and decreasing BDNF/TrkB survival pathways, thus pointing toward the possibility that a specific PPARβ/δ antagonist may be used to counteract the disease progression.

Lymphocyte mitochondria: toward identification of peripheral biomarkers in the progression of Alzheimer disease

Alzheimer disease (AD) is an age-related neurodegenerative condition. AD is histopathologically characterized by the presence of three main hallmarks: senile plaques (rich in amyloid-β peptide), neuronal fibrillary tangles (rich in phosphorylated tau protein), and synapse loss. However, definitive biomarkers for this devastating disease in living people are still lacking. In this study, we show that levels of oxidative stress markers are significantly increased in the mitochondria isolated from lymphocytes of subjects with mild cognitive impairment (MCI) compared to cognitively normal individuals. Further, an increase in mitochondrial oxidative stress in MCI is associated with MMSE score, vitamin E components, and β-carotene. Further, a proteomics approach showed that alterations in the levels of thioredoxin-dependent peroxide reductase, myosin light polypeptide 6, and ATP synthase subunit β might be important in the progression and pathogenesis of AD. Increased understanding of oxidative stress and protein alterations in easily obtainable peripheral tissues will be helpful in developing biomarkers to combat this devastating disorder.

Nucleic acid oxidation: an early feature of Alzheimer's disease

Studies of oxidative damage during the progression of Alzheimer's disease (AD) suggest its central role in disease pathogenesis. To investigate levels of nucleic acid oxidation in both early and late stages of AD, levels of multiple base adducts were quantified in nuclear and mitochondrial DNA from the superior and middle temporal gyri (SMTG), inferior parietal lobule (IPL), and cerebellum (CER) of age-matched normal control subjects, subjects with mild cognitive impairment, preclinical AD, late-stage AD, and non-AD neurological disorders (diseased control; DC) using gas chromatography/mass spectrometry. Median levels of multiple DNA adducts in nuclear and mitochondrial DNA were significantly (p ≤ 0.05) elevated in the SMTG, IPL, and CER in multiple stages of AD and in DC subjects. Elevated levels of fapyguanine and fapyadenine in mitochondrial DNA suggest a hypoxic environment early in the progression of AD and in DC subjects. Overall, these data suggest that oxidative damage is an early event not only in the pathogenesis of AD but is also present in neurodegenerative diseases in general. Levels of oxidized nucleic acids in nDNA and mtDNA were found to be significantly elevated in mild cognitive impairment (MCI), preclinical Alzheimer's disease (PCAD), late-stage AD (LAD), and a pooled diseased control group (DC) of frontotemporal dementia (FTD) and dementia with Lewy bodies (DLB) subjects compared to normal control (NC) subjects. Nucleic acid oxidation peaked early in disease progression and remained elevated. The study suggests nucleic acid oxidation is a general event in neurodegeneration.

The airbag problem-a potential culprit for bench-to-bedside translational efforts: relevance for Alzheimer's disease

For the last 20 years, the "amyloid cascade hypothesis" has dominated research aimed at understanding, preventing, and curing Alzheimer's disease (AD). During that time researchers have acquired an enormous amount of data and have been successful, more than 300 times, in curing the disease in animal model systems by treatments aimed at clearing amyloid deposits. However, to date similar strategies have not been successful in human AD patients. Hence, before rushing into further clinical trials with compounds that aim at lowering amyloid-beta (Aβ) levels in increasingly younger people, it would be of highest priority to re-assess the initial assumption that accumulation of Aβ in the brain is the primary pathological event driving AD. Here we question this assumption by highlighting experimental evidence in support of the alternative hypothesis suggesting that APP and Aβ are part of a neuronal stress/injury system, which is up-regulated to counteract inflammation/oxidative stress-associated neurodegeneration that could be triggered by a brain injury, chronic infections, or a systemic disease. In AD, this protective program may be overridden by genetic and other risk factors, or its maintenance may become dysregulated during aging. Here, we provide a hypothetical example of a hypothesis-driven correlation between car accidents and airbag release in analogy to the evolution of the amyloid focus and as a way to offer a potential explanation for the failure of the AD field to translate the success of amyloid-related therapeutic strategies in experimental models to the clinic.

Oxidative stress and the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease that causes dementia in the elderly. Patients with AD suffer a gradual deterioration of memory and other cognitive functions, which eventually leads to a complete incapacity and death. A complicated array of molecular events has been implicated in the pathogenesis of AD. The major pathological characteristics of AD brains are the presence of senile plaques, neurofibrillary tangles, and neuronal loss. Growing evidence has demonstrated that oxidative stress is an important factor contributing to the initiation and progression of AD. However, the mechanisms that lead to the disruption of redox balance and the sources of free radicals remain elusive. The excessive reactive oxygen species may be generated from mechanisms such as mitochondria dysfunction and/or aberrant accumulation of transition metals, while the abnormal accumulation of Abeta and tau proteins appears to promote the redox imbalance. The resulted oxidative stress has been implicated in Abeta- or tau-induced neurotoxicity. In addition, evidence has suggested that oxidative stress may augment the production and aggregation of Abeta and facilitate the phosphorylation and polymerization of tau, thus forming a vicious cycle that promotes the initiation and progression of AD.

Markers of oxidant stress that are clinically relevant in aging and age-related disease

Despite the long held hypothesis that oxidant stress results in accumulated oxidative damage to cellular macromolecules and subsequently to aging and age-related chronic disease, it has been difficult to consistently define and specifically identify markers of oxidant stress that are consistently and directly linked to age and disease status. Inflammation because it is also linked to oxidant stress, aging, and chronic disease also plays an important role in understanding the clinical implications of oxidant stress and relevant markers. Much attention has focused on identifying specific markers of oxidative stress and inflammation that could be measured in easily accessible tissues and fluids (lymphocytes, plasma, serum). The purpose of this review is to discuss markers of oxidant stress used in the field as biomarkers of aging and age-related diseases, highlighting differences observed by race when data is available. We highlight DNA, RNA, protein, and lipid oxidation as measures of oxidative stress, as well as other well-characterized markers of oxidative damage and inflammation and discuss their strengths and limitations. We present the current state of the literature reporting use of these markers in studies of human cohorts in relation to age and age-related disease and also with a special emphasis on differences observed by race when relevant.

Association between urinary markers of nucleic acid oxidation and mortality in type 2 diabetes: a population-based cohort study

OBJECTIVE

We recently showed that RNA oxidation, estimated by urinary excretion of 8-oxo-7,8-dihydroguanosine (8-oxoGuo), independently predicted mortality in a cohort of 1,381 treatment-naive patients with newly diagnosed type 2 diabetes. In the present investigation, we analyzed urine collected 6 years after the diagnosis to assess the association between urinary markers of nucleic acid oxidation and mortality in patients with established and treated diabetes.

RESEARCH DESIGN AND METHODS

We used data from the 970 patients who attended the screening for diabetes complications 6 years after the diagnosis. Cox proportional hazards regression was used to examine the relationship between urinary markers of DNA oxidation (8-oxo-7,8-dihydro-2'-deoxyguanosine [8-oxodG] [n = 938]) and RNA oxidation (8-oxoGuo [n = 936]) and mortality.

RESULTS

During a median of 9.8 years of follow-up, 654 patients died. Urinary 8-oxoGuo assessed 6 years after the diagnosis was significantly associated with mortality. The multivariate-adjusted hazard ratios for all-cause and diabetes-related mortality of patients with 8-oxoGuo levels in the highest quartile compared with those in the lowest quartile were 1.86 (95% CI 1.34-2.58) and 1.72 (1.11-2.66), respectively. Conversely, 8-oxodG was not associated with mortality. In addition, we found an association between changes in 8-oxoGuo from diagnosis to 6-year follow-up and mortality, with increased risk in patients with an increase and decreased risk in patients with a decrease in 8-oxoGuo.

CONCLUSIONS

The RNA oxidation marker 8-oxoGuo is an independent predictor of mortality in patients with established and treated type 2 diabetes, and changes in 8-oxoGuo during the first 6 years after diagnosis are associated with mortality.

Oxidative stress in Alzheimer's disease: Primary villain or physiological by-product?

The prevalence of Alzheimer's disease (AD) is increasing rapidly worldwide due to an ageing population and largely ineffective treatments. In AD cognitive decline is due to progressive neuron loss that begins in the medial temporal lobe and spreads through many brain regions. Despite intense research the pathogenesis of the common sporadic form of AD remains largely unknown. The popular amyloid cascade hypothesis suggests that the accumulation of soluble oligomers of beta amyloid peptides (Aβ) initiates a series of events that cause neuronal loss. Among their putative toxic effects, Aβ oligomers are thought to act as pro-oxidants combining with redox-active metals to produce excessive reactive oxygen and nitrogen species. However, to date the experimental therapies that reduce Aβ load in AD have failed to halt cognitive decline. Another hypothesis proposed by the late Mark Smith and colleagues is that oxidative stress, rather than Aβ, precipitates the pathogenesis of AD. That is, Aβ and microtubule-associated protein tau are upregulated to address the redox imbalance in the AD brain. As the disease progresses, excess Aβ and tau oligomerise to further accelerate the disease process. Here, we discuss redox balance in the human brain and how this balance is affected by ageing. We then discuss where oxidative stress is most likely to act in the disease process and the potential for intervention to reduce its effects.

Alzheimer's disease-associated neurotoxic peptide amyloid-β impairs base excision repair in human neuroblastoma cells

Alzheimer's disease (AD) is the leading cause of dementia in developed countries. It is characterized by two major pathological hallmarks, one of which is the extracellular aggregation of the neurotoxic peptide amyloid-β (Aβ), which is known to generate oxidative stress. In this study, we showed that the presence of Aβ in a neuroblastoma cell line led to an increase in both nuclear and mitochondrial DNA damage. Unexpectedly, a concomitant decrease in basal level of base excision repair, a major route for repairing oxidative DNA damage, was observed at the levels of both gene expression and protein activity. Moreover, the addition of copper sulfate or hydrogen peroxide, used to mimic the oxidative stress observed in AD-affected brains, potentiates Aβ-mediated perturbation of DNA damage/repair systems in the "Aβ cell line". Taken together, these findings indicate that Aβ could act as double-edged sword by both increasing oxidative nuclear/mitochondrial damage and preventing its repair. The synergistic effects of increased ROS production, accumulated DNA damage and impaired DNA repair could participate in, and partly explain, the massive loss of neurons observed in Alzheimer's disease since both oxidative stress and DNA damage can trigger apoptosis.

Toxicity in rat primary neurons through the cellular oxidative stress induced by the turn formation at positions 22 and 23 of Aβ42

The 42-mer amyloid β-protein (Aβ42) aggregates to form soluble oligomers that cause memory loss and synaptotoxicity in Alzheimer's disease (AD). Oxidative stress is closely related to the pathogenesis of AD. We previously identified the toxic conformer of Aβ42 with a turn at positions 22 and 23 ("toxic turn") by solid-state NMR and demonstrated that a monoclonal antibody (11A1) against the toxic turn in Aβ42 mainly detected the oligomer in the brains of AD patients. Our recent study suggested that oxidative stress is a key factor of the oligomerization and cognitive impairment induced by Aβ overproduction in vivo. However, the involvement of the toxic conformer in Aβ42-induced oxidative damage remains unclear. To investigate this mechanism, we examined the levels of intracellular reactive oxygen species (ROS) and neurotoxicity in rat primary neurons using E22P-Aβ42, a mutant that induces a turn at positions 22 and 23, and E22V-Aβ42, a turn-preventing mutant. E22P-Aβ42, but not E22V-Aβ42, induced greater ROS production than Wt-Aβ42 in addition to potent neurotoxicity. Interestingly, the formation of the toxic conformer in both E22P-Aβ42 and Wt-Aβ42 probed by the 11A1 antibody preceded Aβ42-induced neurotoxicity. Trolox (a radical scavenger) and Congo red (an aggregation inhibitor) significantly prevented the neurotoxicity and intracellular ROS induced by E22P-Aβ42 and Wt-Aβ42, respectively. These results suggest that Aβ42-mediated toxicity is caused by the turn that favors toxic oligomers, which increase generation of ROS.

Melamine induced cognitive impairment associated with oxidative damage in rat's hippocampus

Previous studies reported that melamine could affect hippocampal function and cause spatial cognition impairment. Moreover, some evidences implied that there might be an oxidative damage pathway linking melamine to the function of hippocampus in vitro, but there was a paucity of data about this adverse effect in vivo. The aim of this study was to investigate the toxicology of melamine induced by oxidative damage in hippocampus in vivo. Male Wistar rats were randomly divided into two groups: control group (n=8) and melamine group (n=8). The animals were treated with melamine at a dose of 300 mg/kg/day in 1% carboxymethylcellulose (CMC) solution as a suspension by oral administration, while rats received the same dose of solution of 1% CMC in control group. Melamine was given once a day and for 28 consecutive days. The MWM experiment and histopathological examination were performed. MWM results showed that there were significant deficits of spatial learning and memory in melamine group. The levels of superoxide anion radical, hydroxyl free radical and malonaldehyde (MDA) were significantly increased by melamine, which also reduced the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). The analysis of hippocampal energy metabolism showed that melamine caused significant decrease in the content of adenosine-triphosphate (ATP), implying the reduction of energy synthesis in hippocampal neurocytes. The results suggest that the selective neurotoxicity of melamine in hippocampus may be in part associated with oxidative damage.