Beta-amyloidolysis and glutathione in Alzheimer's disease

Beneficial effects of levetiracetam in streptozotocin-induced rat model of Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder among the elderly. In the light of increasing AD prevalence and lack of effective treatment, new strategies to prevent or reverse this condition are needed. Levetiracetam (LEV) is a newer antiepileptic drug that is commonly used to treat certain types of seizures. Researches indicated that LEV has several other pharmacological activities, including improvement of cognitive function. In this study, the recovery effects of chronic (28 days) administration of LEV (50, 100, and 150 mg/kg, ip) on cognitive deficits caused by the intracerebroventricular (icv) injection of streptozotocin (STZ), as a model for sporadic AD, were evaluated in rats. We also considered the protective effects of LEV against hippocampal cell loss, oxidative damage, acetylcholinesterase (AChE) activity, neuroinflammation, and tauopathy caused by STZ. LEV (100 and 150 mg/kg) significantly attenuated the STZ-induced learning and memory impairments in the passive avoidance and Morris water maze (MWM) tasks. In addition, LEV suppressed STZ-induced hippocampal neuronal loss, while restored alterations in the redox status (lipid peroxides and glutathione), AChE activity, proinflammatory cytokines (IL-1β, IL-6, TNF-α), and hyperphosphorylation of tau linked to STZ administration. In conclusion, our study demonstrated that LEV alleviated hippocampal cell death and memory deficits in STZ-AD rats, through mitigating oxidative damage, suppression of proinflammatory cytokines expression, and inhibition of abnormal tau hyperphosphorylation.

Plasma Glutathione Levels Decreased with Cognitive Decline among People with Mild Cognitive Impairment (MCI): A Two-Year Prospective Study

Glutathione (GSH) is a major endogenous antioxidant. Several studies have shown GSH redox imbalance and altered GSH levels in Alzheimer’s disease (AD) patients. Early detection is crucial for the outcome of AD. However, whether GSH can serve as a biomarker during the very early-phase of AD, such as mild cognitive impairment (MCI), remains unknown. The current prospective study aimed to examine the longitudinal change in plasma GSH concentration and its influence on cognitive decline in MCI. Overall, 49 patients with MCI and 16 healthy individuals were recruited. Plasma GSH levels and cognitive function, measured by the Mini-Mental Status Examination (MMSE) and Alzheimer’s disease assessment scale-cognitive subscale (ADAS-cog), were monitored every 6 months. We employed multiple regressions to examine the role of GSH level in cognitive decline in the 2 years period. The MCI patients showed significant decline in plasma GSH levels and cognitive function from baseline to endpoint (month 24). In comparison, the healthy individuals’ GSH concentration and cognitive function did not change significantly. Further, both GSH level at baseline and GSH level change from baseline to endpoint significantly influenced cognitive decline among the MCI patients. To our knowledge, this is the first study to demonstrate that both plasma GSH levels and cognitive function declined 2 years later among the MCI patients in a prospective manner. If replicated by future studies, blood GSH concentration may be regarded as a biomarker for monitoring cognitive change in MCI.

All roads lead to Rome - a review of the potential mechanisms by which exerkines exhibit neuroprotective effects in Alzheimer's disease

Age-related neurodegenerative disorders such as Alzheimer’s disease (AD) have become a critical public health issue due to the significantly extended human lifespan, leading to considerable economic and social burdens. Traditional therapies for AD such as medicine and surgery remain ineffective, impractical, and expensive. Many studies have shown that a variety of bioactive substances released by physical exercise (called “exerkines”) help to maintain and improve the normal functions of the brain in terms of cognition, emotion, and psychomotor coordination. Increasing evidence suggests that exerkines may exert beneficial effects in AD as well. This review summarizes the neuroprotective effects of exerkines in AD, focusing on the underlying molecular mechanism and the dynamic expression of exerkines after physical exercise. The findings described in this review will help direct research into novel targets for the treatment of AD and develop customized exercise therapy for individuals of different ages, genders, and health conditions.

Assessment and Validation of Globodera pallida as a Novel In Vivo Model for Studying Alzheimer's Disease

BACKGROUND

Whole transgenic or non-transgenic organism model systems allow the screening of pharmacological compounds for protective actions in Alzheimer's disease (AD).

AIM

In this study, a plant parasitic nematode, Globodera pallida, which assimilates intact peptides from the external environment, was investigated as a new potential non-transgenic model system of AD. Methods: Fresh second-stage juveniles of G. pallida were used to measure their chemosensory, perform immunocytochemistry on their neurological structures, evaluate their survival rate, measure reactive oxygen species, and determine total oxidized glutathione to reduced glutathione ratio (GSSG/GSH) levels, before and after treatment with 100 µM of various amyloid beta (Aβ) peptides (1-40, 1-42, 17-42, 17-40, 1-28, or 1-16). Wild-type N2 C. elegans (strain N2) was cultured on Nematode Growth Medium and directly used, as control, for chemosensory assays.

RESULTS

We demonstrated that: (i) G. pallida (unlike Caenorhabditis elegans) assimilates amyloid-β (Aβ) peptides which co-localise with its neurological structures; (ii) pre-treatment with various Aβ isoforms (1-40, 1-42, 17-42, 17-40, 1-28, or 1-16) impairs G. pallida's chemotaxis to differing extents; (iii) Aβ peptides reduced survival, increased the production of ROS, and increased GSSG/GSH levels in this model; (iv) this unique model can distinguish differences between different treatment concentrations, durations, and modalities, displaying good sensitivity; (v) clinically approved neuroprotective agents were effective in protecting G. pallida from Aβ (1-42) exposure. Taken together, the data indicate that G. pallida is an interesting in vivo model with strong potential for discovery of novel bioactive compounds with anti-AD activity.

Role of reactive oxygen species in the progression of Alzheimer's disease

The pathogenesis of Alzheimer's disease (AD) involves neurodegeneration following the deposition of β-amyloid (Aβ) plaques and neurofibrillary tangles in vulnerable brain regions. The vulnerability of the brain to reactive oxygen species (ROS) is now emerging as a key detrimental factor driving AD pathogenesis. Oxidative stress (OS) irreversibly damages cellular biomolecules and perturbs neuronal functions. Scientific evidence is emerging that supports the therapeutic effects of antioxidants in preventing the onset and delaying the progression of AD pathology. In this review, we highlight the role of the OS in AD and the importance of antioxidants in its treatment.

Antia, a Natural Antioxidant Product, Attenuates Cognitive Dysfunction in Streptozotocin-Induced Mouse Model of Sporadic Alzheimer's Disease by Targeting the Amyloidogenic, Inflammatory, Autophagy, and Oxidative Stress Pathways

Background

Many neurodegenerative diseases such as Alzheimer's disease are associated with oxidative stress. Therefore, antioxidant therapy has been suggested for the prevention and treatment of neurodegenerative diseases.

Objective

We investigated the ability of the antioxidant Antia to exert a protective effect against sporadic Alzheimer's disease (SAD) induced in mice. Antia is a natural product that is extracted from the edible yamabushitake mushroom, the gotsukora and kothala himbutu plants, diosgenin (an extract from wild yam tubers), and amla (Indian gooseberry) after treatment with MRN-100.

Methods

Single intracerebroventricular (ICV) injection of streptozotocin (STZ) (3 mg/kg) was used for induction of SAD in mice. Antia was injected intraperitoneally (i.p.) in 3 doses (25, 50, and 100 mg/kg/day) for 21 days. Neurobehavioral tests were conducted within 24 h after the last day of injection. Afterwards, mice were sacrificed and their hippocampi were rapidly excised, weighed, and homogenized to be used for measuring biochemical parameters.

Results

Treatment with Antia significantly improved mice performance in the Morris water maze. In addition, biochemical analysis showed that Antia exerted a protective effect for several compounds, including GSH, MDA, NF-κB, IL-6, TNF-α, and amyloid β. Further studies with western blot showed the protective effect of Antia for the JAK2/STAT3 pathway.

Conclusions

Antia exerts a significant protection against cognitive dysfunction induced by ICV-STZ injection. This effect is achieved through targeting of the amyloidogenic, inflammatory, and oxidative stress pathways. The JAK2/STAT3 pathway plays a protective role for neuroinflammatory and neurodegenerative diseases such as SAD.

Neuroprotective Effect of New Nanochelating-Based Nano Complex, ALZc3, Against Aβ (1-42)-Induced Toxicity in Rat: a Comparison with Memantine

PURPOSE

The current drugs for Alzheimer's disease (AD) are only used to slow or delay the progression of the pathology. So using a novel technology is a necessity to synthesize more effective medications to control this most common cause of dementia. In this study, using nanochelating technology, ALZc3 was synthesized and its therapeutic effects were evaluated in comparison with memantine on a well-known rat model of AD, which is based on Amyloid-βeta (Aβ) injection into the brain.

MATERIALS AND METHODS

Aβ (1-42) was injected bilaterally into the CA1 area of the hippocampus of male rats and then animals were treated daily by oral administration of Alz-C3, memantine or their vehicles. Activities of antioxidant enzymes catalase and superoxide dismutase (SOD), glutathione (GSH) and malondialdehyde (MDA) levels, as well as Bax/Bcl-2 ratio, caspase-3 activation, and TNF-α expression were evaluated 7 days after Aβ injection. Finally, learning and memory of the rats were assessed by Morris water maze test.

RESULTS

ALZc3 and memantine improved memory impairment and antioxidant activity and reduced TNF-α expression, caspase-3 activity and Bax/Bcl-2 ratio in the rat's hippocampus. The results showed a superiority of ALZC3 compared to memantine in reducing caspase-3, increasing CAT activity in Aβ (1-42)-injected groups and improving apoptosis factor in healthy mice.

CONCLUSION

These results indicated that ALZc3 could significantly prevent the memory impairment and Aβ (1-42) toxicity. Thus, ALZc3 could be a promising novel anti-AD agent.

Mechanisms of action of amyloid-beta and its precursor protein in neuronal cell death

Extracellular senile plaques and intracellular neurofibrillary tangles are the neuropathological findings of the Alzheimer's disease (AD). Based on the amyloid cascade hypothesis, the main component of senile plaques, the amyloid-beta (Aβ) peptide, and its derivative called amyloid precursor protein (APP) both have been found to place their central roles in AD development for years. However, the recent therapeutics have yet to reverse or halt this disease. Previous evidence demonstrates that the accumulation of Aβ peptides and APP can exert neurotoxicity and ultimately neuronal cell death. Hence, we discuss the mechanisms of excessive production of Aβ peptides and APP serving as pathophysiologic stimuli for the initiation of various cell signalling pathways including apoptosis, necrosis, necroptosis and autophagy which lead to neuronal cell death. Conversely, the activation of such pathways could also result in the abnormal generation of APP and Aβ peptides. An elucidation of actions of APP and its metabolite, Aβ, could be vital in suggesting novel therapeutic opportunities.

The synthesis of thiol-stabilized silver nanoparticles and their application towards the nanomolar-level colorimetric recognition of glutathione

The synthesis and characterization of 5-methyl-1,3,4-thiadiazole-2-thiol fabricated silver nanoparticles and their application to detect glutathione.

Mitochondrial GSH Systems in CA1 Pyramidal Cells and Astrocytes React Differently during Oxygen-Glucose Deprivation and Reperfusion

Pyramidal cells and astrocytes have differential susceptibility to oxygen-glucose deprivation and reperfusion (OGD-RP). It is known that excessive reactive oxygen species (ROS) in mitochondria initiates cell death, while glutathione (GSH) is one of the major defenses against ROS. Although it is known that astrocytes contain a higher concentration of GSH than neurons, and that astrocytes can provide neurons with GSH, we are unaware of a detailed and quantitative examination of the dynamic changes in the mitochondrial GSH system in the two cell types during OGD-RP. Here, we determined mitochondrial membrane potential and the degrees of oxidation of the mitochondrially targeted roGFP-based sensors for hydrogen peroxide (OxD_P) and GSH (OxD_G). We also developed a method to estimate the mitochondrial GSH (mGSH) concentration in single cells in the CA1 region of organotypic hippocampal slice cultures at several time-points during OGD-RP. We find that mitochondrial membrane potential drops in pyramidal cells during OGD while it is relatively stable in astrocytes. In both types of cell, the mitochondrial membrane potential decreases during RP. During OGD-RP, mitochondrial peroxide levels are the same. Astrocytic mGSH is more than four times higher than pyramidal cell mGSH (3.2 vs 0.7 mM). Astrocytic mGSH is drained from mitochondria during OGD, whereas in pyramidal cells it remains fairly constant. OxD_GSH prior to and during OGD is lower (less oxidized) in pyramidal cells than in astrocytes, but the two nearly converge during RP. The larger changes of redox status in the GSH system in pyramidal cells than astrocytes is an upstream sign of the higher mortality of the pyramidal cells after facing an insult. The pattern of [mGSH] changes in the two cell types could be recognized as another mechanism by which astrocytes protect neurons from transient, extreme conditions.

HBT-based turn-on fluorescent probe for discrimination of homocysteine from glutathione/cysteine and its bioimaging applications

In this work, we firstly reported a new type of turn-on fluorescent probe HBTI for Hcy over GSH/Cys based on ESIPT and heavy atom effect strategy.

A gold nanoparticle-mediated rapid in vitro assay of anti-aggregation reagents for amyloid β and its validation

A rapidin vitrocolorimetric method for screening anti-aggregation reagents of amyloid β is reported by using gold nanoparticles.

Optimized real-time monitoring of glutathione redox status in single pyramidal neurons in organotypic hippocampal slices during oxygen-glucose deprivation and reperfusion

A redox-sensitive Grx1-roGFP2 fusion protein was introduced by transfection into single pyramidal neurons in the CA1 subfield of organotypic hippocampal slice cultures (OHSCs). We assessed changes in the GSH system in neuronal cytoplasm and mitochondria during oxygen-glucose deprivation and reperfusion (OGD/RP), an in vitro model of stroke. Pyramidal cells in a narrow range of depths below the surface of the OHSC were transfected by gene gun or single-cell electroporation with cyto- or mito-Grx1-roGFP2. To mimic the conditions of acute stroke, we developed an optimized superfusion system with the capability of rapid and reproducible exchange of the solution bathing the OHSCs. Measurements of pO2 as a function of tissue depth show that in the region containing the transfected cells, the pO2 is well-controlled. We also found that the pO2 changes on the same time scale as changes in intracranial pressure, cerebral blood flow, and pO2 during acute stroke. Determining the reduction potential, EGSH, from the ratiometric fluorescence signal requires an absolute intensity measurement during calibration of the Grx1-roGFP2. Using the signal from cotransfected tdTomato as an internal standard during calibration improves quantitative measurements of Grx1-roGFP2 redox status and allows EGSH to be determined. EGSH becomes more reducing during OGD and more oxidizing during RP in mitochondria while changes in cytoplasm are not significant compared with controls.

Neuroprotective effect of neuroserpin in oxygen-glucose deprivation- and reoxygenation-treated rat astrocytes in vitro

Neuroserpin (NSP) reportedly exerts neuroprotective effects in cerebral ischemic animal models and patients; however, the mechanism of protection is poorly understood. We thus attempted to confirm neuroprotective effects of NSP on astrocytes in the ischemic state and then explored the relative mechanisms. Astrocytes from neonatal rats were treated with oxygen-glucose deprivation (OGD) followed by reoxygenation (OGD/R). To confirm the neuroprotective effects of NSP, we measured the cell survival rate, relative lactate dehydrogenase (LDH) release; we also performed morphological methods, namely Hoechst 33342 staining and Annexin V assay. To explore the potential mechanisms of NSP, the release of nitric oxide (NO) and TNF-α related to NSP administration were measured by enzyme-linked immunosorbent assay. The proteins related to the NF-κB, ERK1/2, and PI3K/Akt pathways were investigated by Western blotting. To verify the cause-and-effect relationship between neuroprotection and the NF-κB pathway, a NF-κB pathway inhibitor sc3060 was employed to observe the effects of NSP-induced neuroprotection. We found that NSP significantly increased the cell survival rate and reduced LDH release in OGD/R-treated astrocytes. It also reduced NO/TNF-α release. Western blotting showed that the protein levels of p-IKKBα/β and P65 were upregulated by the OGD/R treatment and such effects were significantly inhibited by NSP administration. The NSP-induced inhibition could be significantly reversed by administration of the NF-κB pathway inhibitor sc3060, whereas, expressions of p-ERK1, p-ERK2, and p-AKT were upregulated by the OGD/R treatment; however, their levels were unchanged by NSP administration. Our results thus verified the neuroprotective effects of NSP in ischemic astrocytes. The potential mechanisms include inhibition of the release of NO/TNF-α and repression of the NF-κB signaling pathways. Our data also indicated that NSP has little influence on the MAPK and PI3K/Akt pathways.

Glutathione redox imbalance in brain disorders

PURPOSE OF REVIEW

Glutathione (GSH) is a major endogenous antioxidant. Several studies have implicated GSH redox imbalance in brain disorders. Here, we summarize current evidence on how GSH depletion and GSH-related enzyme deficit are involved in the pathology of brain disorders such as autism, schizophrenia, bipolar disorder, Alzheimer's disease, and Parkinson's disease.

RECENT FINDINGS

Many studies with animal models of various brain disorders and/or with clinical samples from humans with neurodegenerative and neuropsychiatric disorders have demonstrated altered levels of GSH and oxidized glutathione (GSSG), decreased ratio of GSH/GSSG, and/or impaired expressions or activities of GSH-related enzymes in the blood or brain of these individuals. GSH depletion can lead to abnormalities in methylation metabolism and mitochondrial function. A few studies showed that a GSH deficit occurs prior to neuropathological abnormalities in these diseases. The potential therapeutic agents for brain disorders include N-acetylcysteine, liposomes encapsulated with GSH, and whey protein supplement, which can increase the GSH levels in the brain and alleviate oxidative stress-associated damage and may improve the behavior of individuals with brain diseases.

SUMMARY

GSH plays an important role during the onset and progression of neuropsychiatric and neurodegenerative diseases. GSH redox imbalance may be a primary cause of these brain disorders and may be used as a biomarker for diagnosis of these diseases. N-acetylcysteine and other agents that can increase the concentration of GSH in the brain are promising approaches for the treatment of these brain disorders.