Amyloid-beta(25-35) impairs memory and increases NO in the temporal cortex of rats

Galectin-9 and Tim-3 are upregulated in response to microglial activation induced by the peptide Amyloid-β (25-35)

Galectins are a group of β-galactoside-binding lectins associated with regulating immunological response. In the brains of AD patients and 5xFAD (familial AD) mice, galectin-3 (Gal-3) was highly upregulated and found to be expressed in microglia associated with Aβ plaques. However, the participation of other galectins, specifically galectin-9 (Gal-9) and T-cell immunoglobulin and mucin domain 3 (Tim-3) receptors, are unknown in the inflammatory response. The experimental model of the Aβ25-35 peptide will allow us to study the mechanisms of neuroinflammation and describe the changes in the expression of the Gal-9 and Tim-3 receptor. This study aimed to evaluate whether Aβ25-35 peptide administration into the lateral ventricles of rats upregulated Gal-9 and Tim-3 implicated in the modulation of neuroinflammation. The vehicle or Aβ25-35 peptide (1 μg/μL) was bilaterally administered into the lateral ventricles of the rat, and control group. After the administration of the Aβ25-35 peptide, animals were tested for learning (day 29) and spatial memory (day 30) in the novel object recognition test (NOR). On day 31, hippocampus was examined for morphological changes by Nilss stain, biochemical changes by NO2 and MDA, immunohistochemical analysis by astrocytes (GFAP), microglia (Iba1), Gal-9 and Tim-3, and western blot. Our results show the administration of the Aβ25-35 peptide into the lateral ventricles of rats induce memory impairment in the NOR by increases the oxidative stress and inflammatory response. This result is associated with an upregulation of Gal-9 and Tim-3 predominantly detected in the microglia cells of Aβ25-35-treated rats with respect to the control group. Gal-9 and Tim-3 are upregulated in activated microglia that could modulate the inflammatory response and damage in neurodegenerative processes induced by the Aβ25-35 peptide. Therefore, we suggest that Gal-9 and Tim-3 participate in the inflammatory process induced by the administration of the Aβ25-35 peptide.

Palmatine Protects PC12 Cells and Mice from Aβ25-35-Induced Oxidative Stress and Neuroinflammation via the Nrf2/HO-1 Pathway

Alzheimer's disease is a common degenerative disease which has a great impact on people's daily lives, but there is still a certain market gap in the drug research about it. Palmatine, one of the main components of Huangteng, the rattan stem of Fibraurea recisa Pierre (Menispermaceae), has potential in the treatment of Alzheimer's disease. The aim of this study was to evaluate the neuroprotective effect of palmatine on amyloid beta protein 25-35-induced rat pheochromocytoma cells and AD mice and to investigate its mechanism of action. CCK8 assays, ELISA, the Morris water maze assay, fluorescent probes, calcein/PI staining, immunofluorescent staining and Western blot analysis were used. The experimental results show that palmatine can increase the survival rate of Aβ25-35-induced PC12 cells and mouse hippocampal neurons, reduce apoptosis, reduce the content of TNF-α, IL-1β, IL-6, GSH, SOD, MDA and ROS, improve the learning and memory ability of AD mice, inhibit the expression of Keap-1 and Bax, and promote the expression of Nrf2, HO-1 and Bcl-2. We conclude that palmatine can ameliorate oxidative stress and neuroinflammation produced by Aβ25-35-induced PC12 cells and mice by modulating the Nrf2/HO-1 pathway. In conclusion, our results suggest that palmatine may have a potential therapeutic effect on AD and could be further investigated as a promising therapeutic agent for AD. It provides a theoretical basis for the development of related drugs.

The Neuroprotective Effects of Dendropanax morbifera Water Extract on Scopolamine-Induced Memory Impairment in Mice

This study investigated the neuroprotective effects of Dendropanax morbifera leaves and stems (DMLS) water extract on scopolamine (SCO)-induced memory impairment in mice. First, we conducted experiments to determine the protective effect of DMLS on neuronal cells. Treatment with DMLS showed a significant protective effect against neurotoxicity induced by Aβ(25-35) or H2O2. After confirming the neuroprotective effects of DMLS, we conducted animal studies. We administered DMLS orally at concentrations of 125, 250, and 375 mg/kg for 3 weeks. In the Y-maze test, SCO decreased spontaneous alternation, but treatment with DMLS or donepezil increased spontaneous alternation. In the Morris water-maze test, the SCO-treated group showed increased platform reach time and decreased swim time on the target platform. The passive avoidance task found that DMLS ingestion increased the recognition index in short-term memory. Furthermore, memory impairment induced by SCO reduced the ability to recognize novel objects. In the Novel Object Recognition test, recognition improved with DMLS or donepezil treatment. In the mouse brain, except for the cerebellum, acetylcholinesterase activity increased in the SCO group and decreased in the DMLS and donepezil groups. We measured catalase and malondialdehyde, which are indicators of antioxidant effectiveness, and found that oxidative stress increased with SCO but was mitigated by DMLS or donepezil treatment. Thus, our findings suggest that ingestion of DMLS restored memory impairment by protecting neuronal cells from Aβ(25-35) or H2O2-induced neurotoxicity, and by reducing oxidative stress.

The pathomimetic oAβ25–35 model of Alzheimer's disease: Potential for screening of new therapeutic agents

Alzheimer's disease (AD) is the most common form of dementia in the elderly, currently affecting more than 40 million people worldwide. The two main histopathological hallmarks of AD were identified in the 1980s: senile plaques (composed of aggregated amyloid-β (Aβ) peptides) and neurofibrillary tangles (composed of hyperphosphorylated tau protein). In the human brain, both Aβ and tau show aggregation into soluble and insoluble oligomers. Soluble oligomers of Aβ include their most predominant forms - Aβ_1-40 and Aβ_1-42 - as well as shorter peptides such as Aβ_25-35 or Aβ_25-35/40. Most animal models of AD have been developed using transgenesis, based on identified human mutations. However, these familial forms of AD represent less than 1% of AD cases. In this context, the idea emerged in the 1990s to directly inject the Aβ_25-35 fragment into the rodent brain to develop an acute model of AD that could mimic the disease's sporadic forms (99% of all cases). This review aims to: (1) summarize the biological activity of Aβ_25-35, focusing on its impact on the main structural and functional alterations observed in AD (cognitive deficits, APP misprocessing, tau system dysfunction, neuroinflammation, oxidative stress, cholinergic and glutamatergic alterations, HPA axis dysregulation, synaptic deficits and cell death); and (2) confirm the interest of this pathomimetic model in AD research, as it has helped identify and characterize many molecules (marketed, in clinical development, and in preclinical testing), and to the development of alternative approaches for AD prevention and therapy. Today, the Aβ_25-35 model appears as a first-intent choice model to rapidly screen the symptomatic or neuroprotective potencies of new compounds, chemical series, or innovative therapeutic strategies.

Neuroprotective Effects of a Multi-Herbal Extract on Axonal and Synaptic Disruption in Vitro and Cognitive Impairment in Vivo

Background

Alzheimer's disease (AD) is a multifactorial disorder characterized by cognitive decline. Current available therapeutics for AD have limited clinical benefit. Therefore, preventive therapies for interrupting the development of AD are critically needed. Molecules targeting multifunction to interact with various pathlogical components have been considered to improve the therapeutic efficiency of AD. In particular, herbal medicines with multiplicity of actions produce cognitive benefits on AD. Bugu-M is a multi-herbal extract composed of Ganoderma lucidum (Antler form), Nelumbo nucifera Gaertn., Ziziphus jujuba Mill., and Dimocarpus longan, with the ability of its various components to confer resilience to cognitive deficits.

Objective

To evaluate the potential of Bugu-M on amyloid-β (Aβ) toxicity and its in vitro mechanisms and on in vivo cognitive function.

Methods

We illustrated the effect of Bugu-M on Aβ_25-35-evoked toxicity as well as its possible mechanisms to diminish the pathogenesis of AD in rat cortical neurons. For cognitive function studies, 2-month-old female 3×Tg-AD mice were administered 400 mg/kg Bugu-M for 30 days. Behavioral tests were performed to assess the efficacy of Bugu-M on cognitive impairment.

Results

In primary cortical neuronal cultures, Bugu-M mitigated Aβ-evoked toxicity by reducing cytoskeletal aberrations and axonal disruption, restoring presynaptic and postsynaptic protein expression, suppressing mitochondrial damage and apoptotic signaling, and reserving neurogenic and neurotrophic factors. Importantly, 30-day administration of Bugu-M effectively prevented development of cognitive impairment in 3-month-old female 3×Tg-AD mice.

Conclusion

Bugu-M might be beneficial in delaying the progression of AD, and thus warrants consideration for its preventive potential for AD.

Amyloid-β (25-35) induces the morphological alteration of dendritic spines and decreases NR2B and PSD-95 expression in the hippocampus

Research on the memory impairment caused by the Amyloid-β 25-35 (Aβ25-35) peptide in animal models has provided an understanding of the causes that occurs in Alzheimer's disease. However, it is uncertain whether this cognitive impairment occurs due to disruption of information encoding and consolidation or impaired retrieval of stored memory. The aim of this study was to determine the effect of the Aβ25-35 peptide on the morphology of dendritic spines and the changes in the expression of NR2B and PSD-95 in the hippocampus associated with learning and memory deficit. Vehicle or Aβ25-35 peptide (0.1 µg/µL) was bilaterally administered into the CA1 subfield of the rat hippocampus, then tested for spatial learning and memory in the Morris Water Maze. On Day 39, the morphological changes in the CA1 of the hippocampus and dentate gyrus were examined via Golgi-Cox stain. It was observed that the Aβ25-35 peptide administered in the CA1 region of the rat hippocampus induced changes to the morphology of dendritic spines and the expression of the NR2B subunit of the NMDA receptor co-localized with both the spatial memory and PSD-95 protein in the hippocampus of learning rats. We conclude that, in soluble form, the Aβ25-35 peptide perturbs synaptic plasticity, specifically in the formation of new synapses, thus promoting the progression of memory impairment.

Cirsium japonicum var. Maackii Improves Cognitive Impairment under Amyloid Beta25-35-Induced Alzheimer’s Disease Model

Abnormal production and degradation of amyloid beta (Aβ) in the brain lead to oxidative stress and cognitive impairment in Alzheimer’s disease (AD). Cirsium japonicum var. maackii (CJM) is widely used as an herbal medicine and has antibacterial and anti-inflammatory properties. This study focused on the protective effect of the ethyl acetate fraction from CJM (ECJM) on Aβ25-35-induced control mice. In the T-maze and novel object recognition test, ECJM provided higher spatial memory and object recognition compared to Aβ25-35 treatment alone. In the Morris water maze test, ECJM-administered mice showed greater learning and memory abilities than Aβ25-35-induced control mice. Additionally, ECJM-administered mice experienced inhibited lipid peroxidation and nitric oxide production in a dose-dependent manner. The present study indicates that ECJM improves cognitive impairment by inhibiting oxidative stress in Aβ25-35-induced mice. Therefore, CJM may be useful for the treatment of AD and may be a potential material for functional foods.

Daily oscillation of cognitive factors is modified in the temporal cortex of an amyloid β(1-42)-induced rat model of Alzheimer's disease

Alzheimer's disease (AD) is a devastating disease characterized by loss of synapses and neurons in the elderly. Accumulation of the β-amyloid peptide (Aβ) in the brain is thought to be central to the pathogenesis of AD. ApoE plays a key role in normal and physiological clearance of Aß, since it facilitates the peptide intra- and extracellular proteolytic degradation. Besides the cognitive deficit, AD patients also show alterations in their circadian rhythms. The objective of this study was to investigate the effects of an i.c.v. injection of Aβ (1-42) peptide on the 24 h rhythms of Apo E, BMAL1, RORα, Bdnf and trkB mRNA and Aβ levels in the rat temporal cortex. We found that an i.c.v. injection of Aβ aggregates phase shifts daily Bdnf expression as well as Apo E, BMAL1, RORα, Aβ and decreased the mesor of TrkB rhythms. Thus, elevated Aβ peptide levels might modify the temporal patterns of cognition-related factors, probably; by affecting the clock factors rhythms as well as in the 24 h rhythms of Apo E.

Interleukin-4-Mediated Oxidative Stress Is Harmful to Hippocampal Neurons of Prothrombin Kringle-2-Lesioned Rat In Vivo

The present study investigated the effects of reactive microglia/macrophages-derived interleukin-4 (IL-4) on hippocampal neurons in prothrombin kringle-2 (pKr-2)-lesioned rats. pKr-2 was unilaterally injected into hippocampus in the absence or presence of IL-4 neutralizing antibody (IL-4Nab). Immunohistochemical analysis showed a significant loss of Nissl⁺ and NeuN⁺ cells and activation of microglia/macrophages (increase in reactive OX-42⁺ and OX-6⁺ cells) in the hippocampus at 7 days after pKr-2 injection. The levels of IL-4 expression were upregulated in the reactive OX-42⁺ microglia/macrophages as early as 1 day, maximal at 3 days and maintained up to 7 days after pKr-2 injection. Treatment with IL-4Nab significantly increased neuronal survival in pKr-2-treated CA1 layer of hippocampus in vivo. Accompanying neuroprotection, IL-4 neutralization inhibited activation of microglia/macrophages, reactive oxygen species-derived oxidative damages, production of myeloperoxidase- and inducible nitric oxide synthase-derived reactive nitrogen species and nitrosative damages as analyzed by immunohistochemistry and hydroethidine histochemistry. These results suggest that endogenous IL-4 expressed on reactive microglia/macrophages mediates oxidative/nitrosative stress and play a critical role on neurodegeneration of hippocampal CA1 layer in vivo.

Abundant neuroprotective chaperone Lipocalin-type prostaglandin D synthase (L-PGDS) disassembles the Amyloid-β fibrils

Misfolding of Amyloid β (Aβ) peptides leads to the formation of extracellular amyloid plaques. Molecular chaperones can facilitate the refolding or degradation of such misfolded proteins. Here, for the first time, we report the unique ability of Lipocalin-type Prostaglandin D synthase (L-PGDS) protein to act as a disaggregase on the pre-formed fibrils of Aβ(1-40), abbreviated as Aβ40, and Aβ(25-35) peptides, in addition to inhibiting the aggregation of Aβ monomers. Furthermore, our proteomics results indicate that L-PGDS can facilitate extraction of several other proteins from the insoluble aggregates extracted from the brain of an Alzheimer's disease patient. In this study, we have established the mode of binding of L-PGDS with monomeric and fibrillar Aβ using Nuclear Magnetic Resonance (NMR) Spectroscopy, Small Angle X-ray Scattering (SAXS), and Transmission Electron Microscopy (TEM). Our results confirm a direct interaction between L-PGDS and monomeric Aβ40 and Aβ(25-35), thereby inhibiting their spontaneous aggregation. The monomeric unstructured Aβ40 binds to L-PGDS via its C-terminus, while the N-terminus remains free which is observed as a new domain in the L-PGDS-Aβ40 complex model.

The Acute Activation of the CB1 Receptor in the Hippocampus Decreases Neurotoxicity and Prevents Spatial Memory Impairment in Rats Lesioned with β-Amyloid 25-35

Given their anti-inflammatory properties, cannabinoids have been shown to be neuroprotective agents and to reduce excitotoxicity, through the activation of the Cannabinoid receptor type 1 (CB1r). These properties have led to CB1r being proposed as pharmacological targets for the treatment of various neurodegenerative diseases. Amyloid-β 25-35 (Aβ_25-35) induces the expression of inducible nitric oxide synthase (iNOS) and increases nitric oxide (NO●) levels. It has been observed that increased NO● concentrations trigger biochemical pathways that contribute to neuronal death and cognitive damage. This study aimed to evaluate the neuroprotective effect of an acute activation of CB1r on spatial memory and its impact on iNOS protein expression, NO● levels, gliosis and the neurodegenerative process induced by the injection of Aβ_(25-35) into the CA1 subfield of the hippocampus. ACEA [1 μM/1 μL] and Aβ_(25-35) [100 μM/1 μL] and their respective vehicle groups were injected into the CA1 subfield of the hippocampus. The animals were tested for spatial learning and memory in the eight-arm radial maze, with the results revealing that the administration of ACEA plus Aβ_(25-35) improves learning and memory processes, in contrast with the Aβ_(25-35) group. Moreover, ACEA plus Aβ_(25-35) prevented both the increase in iNOS protein and NO● levels and the reactive gliosis induced by Aβ_(25-35). Importantly, neurodegeneration was significantly reduced by the administration of ACEA plus Aβ_(25-35) in the CA1 subfield of the hippocampus. The data obtained in the present research suggest that the acute early activation of CB1r is crucial for neuroprotection.

De novo aggregation of Alzheimer's Aβ25-35 peptides in a lipid bilayer

A potential mechanism of cytotoxicity attributed to Alzheimer’s Aβ peptides postulates that their aggregation disrupts membrane structure causing uncontrollable permeation of Ca²⁺ ions. To gain molecular insights into these processes, we have performed all-atom explicit solvent replica exchange with solute tempering molecular dynamics simulations probing aggregation of the naturally occurring Aβ fragment Aβ25-35 within the DMPC lipid bilayer. To compare the impact produced on the bilayer by Aβ25-35 oligomers and monomers, we used as a control our previous simulations, which explored binding of Aβ25-35 monomers to the same bilayer. We found that compared to monomeric species aggregation results in much deeper insertion of Aβ25-35 peptides into the bilayer hydrophobic core causing more pronounced disruption in its structure. Aβ25-35 peptides aggregate by incorporating monomer-like structures with stable C-terminal helix. As a result the Aβ25-35 dimer features unusual helix head-to-tail topology supported by a parallel off-registry interface. Such topology affords further growth of an aggregate by recruiting additional peptides. Free energy landscape reveals that inserted dimers represent the dominant equilibrium state augmented by two metastable states associated with surface bound dimers and inserted monomers. Using the free energy landscape we propose the pathway of Aβ25-35 binding, aggregation, and insertion into the lipid bilayer.

Neuroinflammation induced by the peptide amyloid-β (25-35) increase the presence of galectin-3 in astrocytes and microglia and impairs spatial memory

Galectins are animal lectins that bind to β-galactosides, such as lactose and N-acetyllactosamine, contained in glycoproteins or glycolipids. Galectin-1 (Gal-1) and Galectin-3 (Gal-3) are involved in pathologies associated with the inflammatory process, cell proliferation, adhesion, migration, and apoptosis. Recent evidence has shown that the administration of Amyloid-β 25-35 (Aβ_25-35) into the hippocampus of rats increases the inflammatory response that is associated with memory impairment and neurodegeneration. Galectins could participate in the modulation of the neuroinflammation induced by the Aβ_25-35. The aim of this study was to evaluate the presence of Gal-1 and Gal-3 in the neuroinflammation induced by administration of Aβ_25-35 into the hippocampus and to examine spatial memory in the Morris water maze. After the administration of Aβ_25-35, animals were tested for learning and spatial memory in the Morris water maze. Behavioral performance showed that Aβ_25-35 didn't affect spatial learning but did impair memory, with animals taking longer to find the platform. On the day 32, hippocampus was examined for astrocytes (GFAP), microglia (Iba1), Gal-1 and Gal-3 via immunohistochemical analysis, and the cytokines IL-1β, TNF-α, IFN-γ by ELISA. This study's results showed a significant increase in the expression of Gal-3 in the microglia and astrocytes, while Gal-1 didn't increase in the dorsal hippocampus. The expression of galectins is associated with increased cytokines in the hippocampal formation of Aβ_25-35 treated rats. These findings suggest that Gal-3 could participate in the inflammation induced by administration of Aβ_25-35 and could be involved in the neurodegeneration progress and memory impairment.

Melatonin receptor stimulation by agomelatine prevents Aβ-induced tau phosphorylation and oxidative damage in PC12 cells

Purpose

As a novel antidepressant drug, agomelatine has good therapeutic effect on the mood disorder and insomnia in Alzheimer's disease (AD). Recent studies have shown the neuroprotective function of agomelatine, including anti-oxidative and anti-apoptosis effect. However, it remains unclear whether agomelatine exerts neuroprotection in AD. Thus, the neuroprotective effect of agomelatine against amyloid beta _25-35 (Aβ_25-35)-induced toxicity in PC12 cells was evaluated in this study.

Methods

The concentration of malondialdehyde (MDA), LDH, and ROS was investigated to evaluate oxidative damage. The expression of P-tau, tau, PTEN, P-Akt, Akt, P-GSK3β, and GSK3β proteins was assessed by Western blotting. Our results demonstrated that Aβ_25-35 significantly increased the content of MDA, LDH, and ROS. Meanwhile, Aβ_25-35 upregulated the expression of P-tau and PTEN as well as downregulated P-Akt and P-GSK3β expression. These effects could be blocked by agomelatine pretreatment. Furthermore, luzindole, the melatonin receptor (MT) antagonist, could reverse the neuroprotective effect of agomelatine.

Conclusion

The results demonstrated that antidepressant agomelatine might prevent the tau protein phosphorylation and oxidative damage induced by Aβ_25-35 in PC12 cells by activating MT-PTEN/Akt/GSK3β signaling. This study provided a novel therapeutic target for AD in the future.

Association of cerebrovascular dysfunction with the development of Alzheimer's disease-like pathology in OXYS rats

Background

Cerebrovascular dysfunction plays a critical role in the pathogenesis of Alzheimer’s disease (AD): the most common cause of dementia in the elderly. The involvement of neurovasculature disorders in the progression of AD is now increasingly appreciated, but whether they represent initial factors or late-stage pathological changes during the disease is unclear. Using senescence-accelerated OXYS rats, which simulate key characteristics of sporadic AD, we evaluated contributions of cerebrovascular alterations to the disease development. At preclinical, early, and advanced stages of AD-like pathology, in the hippocampus of OXYS and Wistar (control) rats, we evaluated (i) the blood vessel state by histological and electron-microscopic analyses; (ii) differences in gene expression according to RNA sequencing (RNA-Seq) to identify the metabolic processes and pathways associated with blood vessel function; (iii) the amount of vascular endothelial growth factor (VEGF) by western blot and immunohistochemical analysis.

Results

We observed a loss of hippocampal blood vessel density and ultrastructural changes of those blood vessels in OXYS rats at the early stage of AD-like pathology. There were significant alterations in the vessels and downregulation of VEGF with an increased amount of amyloid β_1–42 there at the advanced stage of the disease. According to RNA-Seq data analysis, major alterations in cerebrovascular processes of OXYS rats were associated with blood vessel development, circulatory system processes, the VEGF signaling pathway, and vascular smooth muscle contraction. At preclinical and early stages of the AD-like pathology, these processes were upregulated and then downregulated with age. At the advanced stage in OXYS rats, differentially expressed genes (DEGs) were associated with downregulation of cerebrovascular function as compared to Wistar rats. Among the 46 DEGs at the preclinical stage of the disease, 28 DEGs at the early stage, and among 85 DEGs at the advanced stage, using functional analysis and gene network construction, we identified genes (Nos1, P2rx4, Pla2g6, and Bdkrb2) probably playing a significant role in the development of cerebrovascular dysfunction in OXYS rats.

Conclusions

Changes in expression of the genes functionally associated with cerebrovascular processes already in the early period of life may contribute to the development of AD-like pathology in OXYS rats.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4480-9) contains supplementary material, which is available to authorized users.

Neurogenesis and morphological-neural alterations closely related to amyloid β-peptide (25-35)-induced memory impairment in male rats

Memory impairment by the Amyloid-β 25-35 (Aβ_25-35) peptide in animal models has provided an understanding of the causes behind the similar deterioration that occurs in Alzheimer's disease. However, it is uncertain if a decrease of dendritic spines and neurogenesis conduces to cognitive impairment by an impairment in the retrieval of stored memory. The aim of this study was to evaluate the consequences of impairment on spatial memory caused by the administration of the Aβ_25-35 peptide in the hippocampus, which is associated whit morphological changes and neurogenesis in the dentate gyrus (DG). The vehicle or Aβ_25-35 peptide (0.1μg/μL) were bilaterally administered in the CA1 subfield of the rat hippocampus. The animals were tested for spatial learning and memory in the Morris Water Maze. In the day's 11, 18 and 32 after administration of the Aβ_25-35 peptide were examined the morphological changes in the DG using a Golgi-Cox stain. In the day 32, the neurogenesis was evaluated by the immunoreactivity to 5-bromo-2'-deoxyuridine (BrdU; 100mg/kg, i.p.) that corresponding to cellular proliferation post damage, the neuronal specific nuclear protein (NeuN) and doublecortin (DCX). This study found a memory retrieval impairment occurring at day 17, a cognitive deficit which had increased significantly at day 31 after the administration of Aβ_25-35 peptide. These results are related to morphological changes in the granular cells of the DG, such as a shorter dendritic length and a decrease in the number of dendritic spines. In neurogenesis, the total number of cells positive to BrdU, NeuN and DCX in the hippocampal granule cell layer was found to have declined in animals treated with Aβ_25-35. The results suggest that the Aβ_25-35 peptide impairs memory retrieval by decreasing the number of dendritic spines and altering neurogenesis in the DG.

Neurotropin® alleviates hippocampal neuron damage through a HIF-1α/MAPK pathway

AIMS

The main purpose was to verify the potent capacity of Neurotropin® against neuronal damage in hippocampus and to explore its underlying mechanisms.

METHODS

HT22 cells were treated with 40 μmol/L Aβ_25-35 in the presence of various concentrations of Neurotropin® or in its absence. The cell viability was assessed with a CCK-8 assay, and flow cytometry was used to measure cell apoptosis, intracellular ROS levels, and mitochondrial membrane potential. Aβ plaques were examined by Bielschowsky silver staining, and the activities of antioxidants were detected in hippocampus of APP/PS1 mice after Neurotropin® treatment. The expression of proteins, including HIF-1α, Bcl-2, Bax, and MAPKs signaling molecules was evaluated by Western blot.

RESULTS

Neurotropin® significantly reversed the cell injury induced by Aβ_25-35 through increasing cell viability and mitochondrial membrane potential, decreasing intracellular ROS and cell apoptosis of HT22 cells (P<.05). Furthermore, Neurotropin® markedly reduced the formation of Aβ plaques and upregulated the activities of antioxidants (P<.05). Additionally, the protein expression of HIF-1α, p-ERK1/2, p-JNK, and p-P38 was significantly inhibited in hippocampus of APP/PS1 mice.

CONCLUSIONS

Neurotropin® exhibited a potent neuroprotective effect on inhibiting Aβ-induced oxidative damage and alleviating Aβ deposition in hippocampus via modulation of HIF-1α/MAPK signaling pathway.

Neurovascular uncoupling in the triple transgenic model of Alzheimer's disease: Impaired cerebral blood flow response to neuronal-derived nitric oxide signaling

Nitric oxide (NO)-dependent pathways and cerebrovascular dysfunction have been shown to contribute to the cognitive decline and neurodegeneration observed in Alzheimer's disease (AD) but whether they represent initial factors or later changes of the disease is still a matter of debate. In this work, we aimed at investigating whether and to what extent neuronal-derived NO signaling and related neurovascular coupling are impaired along aging in the hippocampus of the triple transgenic mouse model of Alzheimer's Disease (3xTg-AD). We performed a longitudinal study combining behavior studies, in vivo simultaneous measurements of NO concentration gradients and cerebral blood flow (CBF), along with detection of NO synthase (NOS) and markers of nitroxidative stress. Our results revealed an impairment in the neurovascular coupling along aging in the 3xTg-AD mice which preceded obvious cognitive decline. This impairment was characterized by diminished CBF changes in response to normal or even increased NO signals and associated with markers of nitroxidative stress. The results suggest that impairment in neurovascular coupling is primarily due to cerebrovascular dysfunction, rather than due to dysfunctional NO signaling from neurons to blood vessels. Overall, this work supports cerebrovascular dysfunction as a fundamental underlying process in AD pathology.

Hydrogen sulfide ameliorates learning memory impairment in APP/PS1 transgenic mice: A novel mechanism mediated by the activation of Nrf2

Beta-amyloid (Aβ) plaques and oxidative stress are associated with the pathogenesis of Alzheimer's disease (AD). Hydrogen sulfide (H₂S) has been recognized as a cytoprotectant, which improves learning memory impairment and exerts antioxidant effects in neurodegenerative disorders, including AD. The experiment was projected to explore the effects of H₂S on cognitive deficits, Aβ levels and possible antioxidant mechanisms. Here, APP/PS1 transgenic mice were injected sodium hydrosulfide (NaHS, a H₂S donor, 2.8mg/kg) once a day for three months. It was found that APP/PS1 transgenic mice exhibited cognitive deficits and a large number of senile plaques, along with neurons decrease and Aβ increase. However, intraperitoneal (i.p.) injection of NaHS improved learning memory deficits, decreased the number of senile plaques, Aβ_1-40 and Aβ_1-42 levels, suppressed neurons loss, together with up-regulated the levels of cystathionine-β-synthase (CBS) and 3-mercaptopyruvate-sulfurtransferase (3MST). Furthermore, the protein levels of beta-amyloid precursor (APP) and beta-secretase 1 (BACE1) were dramatically restrained after administration of H₂S. In addition, H₂S exerted antioxidant effects via up-regulation nuclear factor erythroid-2-related factor 2 (Nrf2), heme oxygenase-1(HO-1) and glutathione S-transferase (GST). Taken together, these findings suggest that H₂S ameliorates learning memory impairment, decreases the number of senile plaques in APP/PS1 mice possibly through inhibition of Aβ production and activation of Nrf2/antioxidant response element (ARE) pathway.

Meloxicam-loaded nanocapsules as an alternative to improve memory decline in an Alzheimer's disease model in mice: involvement of Na(+), K(+)-ATPase

The objective of this study was to investigate the effect of meloxicam-loaded nanocapsules (M-NC) on the treatment of the memory impairment induced by amyloid β-peptide (aβ) in mice. The involvement of Na(+), K(+)-ATPase and cyclooxygenase-2 (COX-2) activities in the hippocampus and cerebral cortex was also evaluated. Mice received aβ (3 nmol/ 3 μl/ per site, intracerebroventricular) or vehicle (3 μl/ per site, i.c.v.). The next day, the animals were treated with blank nanocapsules (17 mL/kg) or M-NC (5 mg/kg) or free meloxicam (M-F) (5 mg/kg). Treatments were performed every other day, until the twelfth day. Animals were submitted to the behavioral tasks (open-field, object recognition, Y-maze and step-down inhibitory avoidance tasks) from the twelfth day. Na(+), K(+)-ATPase and COX-2 activities were performed in hippocampus and cerebral cortex. aβ caused a memory deficit, an inhibition of the hippocampal Na(+), K(+)-ATPase activity and an increase in the hippocampal COX-2 activity. M-NC were effective against all behavioral and biochemical alterations, while M-F restored only the COX-2 activity. In conclusion, M-NC were able to reverse the memory impairment induced by aβ, and Na(+), K(+)-ATPase is involved in the effect of M-NC.

Acute Exposure of the Mediobasal Hypothalamus to Amyloid-β25-35 Perturbs Hepatic Glucose Metabolism

Patients with Alzheimer's disease (AD) have a higher risk for developing insulin resistance and diabetes. Amyloid plaques, a hallmark of AD, are composed of amyloid-β (Aβ). Because the mediobasal hypothalamus controls hepatic glucose production, we examined the hypothesis that its exposure to Aβ perturbs the regulation of glucose metabolism. The infusion of Aβ25-35, but not its scrambled counterpart, into the mediobasal hypothalamus of young rats, increased circulating glucose as a consequence of enhanced hepatic glucose production during pancreatic clamp studies. These findings suggest a link between AD and alterations of glucose metabolism.

Age-dependent changes in the glutamate-nitric oxide pathway in the hippocampus of the triple transgenic model of Alzheimer's disease: implications for neurometabolic regulation

Age-dependent changes in nitric oxide ((•)NO) concentration dynamics may play a significant role in both decaying synaptic and metabolic functions in Alzheimer's disease (AD). This neuromodulator acts presynaptically to increase vesicle release and glutamatergic transmission and also regulates mitochondrial function. Under conditions of altered intracellular redox environment, (•)NO may react and produce reactive species such as peroxynitrite. Using the triple transgenic mouse model of AD (3xTgAD), we investigated age-dependent changes in the glutamate-(•)NO axis in the hippocampus. Direct measurement of (•)NO concentration dynamics revealed a significant increase in N-methyl-D-aspartate type receptor-evoked peak (•)NO in the 3xTgAD model at an early age. Aging produced a decrease in peak (•)NO accompanied by significant decrease in production and decay rates in the transgenic model. Evaluation of energy metabolism revealed age-dependent decrease in basal oxygen consumption rate, a general decrease in mitochondrial oxidative phosphorylation parameters, and loss in mitochondrial sparing capacity in both genotypes. Finally, we observed age-dependent increase in 3-nitrotyrosine residues in the hippocampus, consistent with a putative shift in (•)NO bioactivity toward oxidative chemistry associated with neurotoxicity.

A potential therapeutic effect of saikosaponin C as a novel dual-target anti-Alzheimer agent

Alzheimer's disease (AD) is a chronic neurodegenerative disease and the risk of developing it increases with advancing age. In this study, we investigated the protective effects of saikosaponin C (SSc), one of the main bioactive components produced by the traditional Chinese herb, radix bupleuri, the root of Bupleurum falcatum, against AD in various neuronal models. Interestingly, we found that SSc has dual effects on AD by targeting amyloid beta (Aβ) and tau, two key proteins in AD. SSc significantly suppressed the release of both Aβ peptides 1-40 and 1-42 into cell culture supernatants, though it does not affect BACE1 activity and expression. SSc also inhibited abnormal tau phosphorylation at multiple AD-related residues. Moreover, SSc seems to have beneficial effects on cellular tau function; it accelerated nerve growth factor-mediated neurite outgrowth and increased the assembly of microtubules. In addition, SSc increased synaptic marker proteins such as synaptophysin and PSD-95. Considering its various biological activities, our results suggest that SSc might be a novel therapeutic tool for treating human AD and other neurodegenerative diseases. Tau and amyloid beta are two key features in Alzheimer's disease. Saikosaponin C, an active component of Bupleuri Radix, inhibits abnormal tau phosphorylation and amyloid beta production, thereby promoting synaptic integrity. Saikosaponin C also prevents amyloid beta-induced apoptosis in brain vascular endothelial cells. Therefore, Saikosaponin C may provide a new therapeutic strategy for treatment of neurodegenerative diseases, including Alzheimer's disease.

Triptolide attenuated injury via inhibiting oxidative stress in Amyloid-Beta25-35-treated differentiated PC12 cells

BACKGROUND

Recently, an abnormal deposition of Amyloid-Beta (Aβ) was considered the primary cause of the pathogenesis of Alzheimer's disease (AD). And how to inhibit the cytotoxicity is considered an important target for the treatment of AD. Triptolide (TP), a purified diterpenoid from the herb Tripterygium wilfordii Hook.f. (TWHF), has potential neuroprotective effects pertinent to disease of the nervous system. However, whether triptolide and its specific mechanisms have protective functions in differentiated PC12 cells treated with Aβ25-35 remain unclear.

AIMS

The purpose is to investigate the protective functions of triptolide in Aβ25-35-stimulated differentiated PC12 cells.

MAIN METHODS

In the study, we use 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, lactate dehydrogenase (LDH) assay, flow cytometry assay, immunohistochemical staining and Western blot to observe the effects of triptolide on cytotoxicity induced by Aβ25-35 and its mechanism of oxidative stress.

KEY FINDINGS

The result of MTT and LDH assay indicates that triptolide protected PC12 cells against Aβ25-35-induced cytotoxicity. The flow cytometry assay shows that triptolide attenuated Aβ25-35-induced apoptosis in differentiated PC12 cells. Meanwhile, the results give a clear indication that triptolide could downregulate generation of reactive oxygen species (ROS), hydrogen peroxide (H2O2) and malondialdehyde (MDA) induced by Aβ25-35. The apoptotic process triggered by triptolide involved the up-regulation of the activity of superoxide dismutase (SOD).

SIGNIFICANCE

The results suggest that triptolide may serve as an important role in the inhibition of the cell apoptosis induced by Aβ and the decreased oxidative stress is a key mechanism in the protective effect of triptolide in AD.

Nitrosative and cognitive effects of chronic L-DOPA administration in rats with intra-nigral 6-OHDA lesion

Besides motor disturbances, other symptoms found in the early stage of Parkinson's disease (PD) are deficits in both learning and memory. The nigro-striatal-cortical pathway is affected in this pathology, with this neuronal circuit involved in cognitive processes such as spatial working memory (SWM). However, cognitive dysfunction appears even when the patients are receiving L-DOPA treatment. There is evidence that the dopamine metabolism formed by L-DOPA generates free radicals such as nitric oxide, which may cause damage through the nitrosative stress (NS). The aim of this study was to evaluate both the effects of chronic L-DOPA administration on SWM and the production of NS in rats using an intra-nigral lesion caused by 6-hydroxydopamine (6-OHDA). Post-lesion, the animals were administered orally with L-DOPA/Carbidopa (100-mg/kg) for 20 days. An SWM task in a Morris water maze was conducted post-treatment. Nitrite levels and immunoreactivity of 3-Nitrotyrosine (3-NT), Inducible Nitric Oxide Synthase (iNOS), Glial Fibrillary Acidic Protein (GFAP), and Tyrosine Hydroxylase (TH) were evaluated in the substantia nigra pars compacta, the dorsal striatum and the medial prefrontal cortex. Our results show that chronic L-DOPA administration in rats with intra-nigral 6-OHDA-lesion caused significant increases in SWM deficit, nitrite levels and the immunoreactivity of 3-NT, iNOS and GFAP in the nigro-striatal-cortical pathway. These facts suggest that as L-DOPA can induce NS in rats with dopaminergic intra-nigral lesion, it could play a key role in the impairment of the SWM, and thus can be considered as a toxic mechanism that induces cognitive deficit in PD patients.

17-AAG improves cognitive process and increases heat shock protein response in a model lesion with Aβ25-35

Molecular chaperones, or heat shock proteins (HSP), have been implicated in numerous neurodegenerative disorders characterized by the accumulation of protein aggregates, such as Alzheimer disease. The agglomeration of insoluble structures of Aβ is thought to be responsible for neuronal death, which in turn leads to the loss of cognitive functions. Recent findings have shown that the induction of HSP decreases the level of abnormal protein aggregates, as well as demonstrating that 17-(allylamino)-17-demethoxygeldanamycin (17-AAG), an analogue of geldanamycin (GA), increases Aβ clearance through the induction of molecular chaperones in cell culture. In light of this discovery that HSP overexpression can be neuroprotective, the search for a way to pharmacologically induce the overexpression of HSP and other associated chaperones may lead to a promising approach for the treatment of neurodegenerative diseases. The aim of our study was to evaluate both the effect of 17-AAG on the cognitive process and the HSP response in rats injected with Aβ25-35 into the CA1 of the hippocampus. The results show that the injection of Aβ caused a significant increase in the expression of the HSP involved in the regulation of cellular proteostasis. While the HSP did not reverse excitotoxic damage, given that experimental subjects showed learning and memory deficits, the administration of 17-AAG prior to the injection of Aβ25-35 did show an improvement in the behavioral assessment that correlated with the upregulation of HSP70 in subjects injured with Aβ. Overall, our data shows that the pharmacological induction of HSP using 17-AAG may be an alternative treatment of neurodegenerative diseases.

Aminoguanidine treatment ameliorates inflammatory responses and memory impairment induced by amyloid-beta 25-35 injection in rats

Alzheimer disease (AD) is a neurodegenerative disorder caused by accumulation of the amyloid-beta peptide (Aβ) in neuritic plaques. Its neurotoxic mechanisms are associated with inflammatory responses and nitrosative stress generation that promote expression of inducible nitric oxide synthase (iNOS) and increased nitric oxide causing neuronal death and memory impairment. Studies suggest that treatment with anti-inflammatory and anti-oxidant agents decreases the risk of developing AD. Aminoguanidine (AG) is an iNOS inhibitor with anti-inflammatory and anti-oxidant effects. In this study, we evaluated the effects of systemic administration of AG (100 mg/kg/day for 4 days) on spatial memory and inflammatory responses induced by an injection of Aβ(25-35) [100 μM] into the temporal cortex (TCx) of rats. A significant improvement of spatial memory was evident in the Aβ(25-35)-treated group at day 30 post-injection subjected to AG treatment; this effect was correlated with decreases in reactive gliosis, IL-1β, TNF-α, and nitrite levels, as well as a reduction in neurodegeneration in the TCx and hippocampus (Hp). These results suggest that AG treatment inhibited glia activation and cytokine release, which may help to counteract neurodegenerative events induced by the toxicity of Aβ.

Plasma antioxidants and brain glucose metabolism in elderly subjects with cognitive complaints

PURPOSE

The role of oxidative stress is increasingly recognized in cognitive disorders of the elderly, notably Alzheimer's disease (AD). In these subjects brain(18)F-FDG PET is regarded as a reliable biomarker of neurodegeneration. We hypothesized that oxidative stress could play a role in impairing brain glucose utilization in elderly subjects with increasing severity of cognitive disturbance.

METHODS

The study group comprised 85 subjects with cognitive disturbance of increasing degrees of severity including 23 subjects with subjective cognitive impairment (SCI), 28 patients with mild cognitive impairment and 34 patients with mild AD. In all subjects brain FDG PET was performed and plasma activities of extracellular superoxide dismutase (eSOD), catalase and glutathione peroxidase were measured. Voxel-based analysis (SPM8) was used to compare FDG PET between groups and to evaluate correlations between plasma antioxidants and glucose metabolism in the whole group of subjects, correcting for age and Mini-Mental State Examination score.

RESULTS

Brain glucose metabolism progressively decreased in the bilateral posterior temporoparietal and cingulate cortices across the three groups, from SCI to mild AD. eSOD activity was positively correlated with glucose metabolism in a large area of the left temporal lobe including the superior, middle and inferior temporal gyri and the fusiform gyrus.

CONCLUSION

These results suggest a role of oxidative stress in the impairment of glucose utilization in the left temporal lobe structures in elderly patients with cognitive abnormalities, including AD and conditions predisposing to AD. Further studies exploring the oxidative stress-energy metabolism axis are considered worthwhile in larger groups of these patients in order to identify pivotal pathophysiological mechanisms and innovative therapeutic opportunities.

Afobazole activation of σ-1 receptors modulates neuronal responses to amyloid-β25-35

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a continual decline of cognitive function. No therapy has been identified that can effectively halt or reverse its progression. One hallmark of AD is accumulation of the amyloid-β peptide (Aβ), which alone induces neuronal injury via various mechanisms. Data presented here demonstrate that prolonged exposure (1-24 hours) of rat cortical neurons to Aβ25-35 results in an increase in basal intracellular Ca(2+) concentration ([Ca(2+)]i), and that coincubation with the compound afobazole inhibits these [Ca(2+)]i increases. The effect of afobazole on [Ca(2+)]i is due to activation of σ-1 receptors but could not be mimicked by a second pan-selective σ receptor agonist, 1,3-di-o-tolylguanidine (DTG). Afobazole was also found to lessen nitric oxide (NO) production in response to Aβ25-35 application but did not affect elevations in reactive oxygen species elicited by the Aβ fragment. The reductions in [Ca(2+)]i and NO perturbation produced by afobazole were associated with a decrease in neuronal cell death, whereas DTG failed to enhance cell survival. Examining the molecular mechanisms involved in the increased neuronal survival demonstrates that afobazole incubation results in lower expression of the proapoptotic protein Bax and the death protease caspase-3, while at the same time increasing expression of the antiapoptotic protein, Bcl-2. Given the importance of Aβ neurotoxicity in AD etiology, the findings reported here suggest that afobazole may be an effective AD therapeutic agent. Furthermore, σ-1 receptors may represent a useful target for AD treatment, although not all σ ligands appear to be equally beneficial.

Involvement of opioidergic and nitrergic systems in memory acquisition and exploratory behaviors in cholestatic mice

Bile duct ligation (BDL) is an animal model used in cholestatic disease research. Both opioidergic and nitrergic systems are known to be involved in cholestasis. The aim of this study was to investigate the possible interaction between these two systems in BDL-induced memory formation and exploratory behaviors in mice. Male mice weighing 25-30 g were divided into nonoperated controls, sham-operated, and BDL groups. One-trial step-down and hole-board paradigms were used to assess memory acquisition and exploratory behaviors, respectively. Cholestasis did not alter memory acquisition while increasing exploratory behaviors 7 days after BDL. A pretraining intraperitoneal injection of L-arginine (50, 100, and 200 mg/kg), L-NG-nitroarginine methyl ester (L-NAME) (5, 10, 20, and 40 mg/kg), or naloxone (0.125, 0.25, and 0.5 mg/kg) did not alter memory acquisition or exploratory behaviors, whereas morphine (5 and 7.5 mg/kg) decreased memory acquisition in sham-operated animals. Moreover, although injection of L-NAME and naloxone exerted no effect on memory acquisition in the 7 days post-BDL mice, L-arginine (100 and 200 mg/kg) and morphine (2.5, 5, and 7.5 mg/kg) injection reduced it. In contrast, L-NAME and naloxone, but not morphine or L-arginine, reduced the BDL-induced exploratory behaviors. Coadministration of subthreshold doses of morphine (1.25 mg/kg) and L-arginine (50 mg/kg) caused a memory deficit in 7 days post-BDL mice. However, the memory deficit induced by the effective doses of morphine (2.5 mg/kg) or L-arginine (200 mg/kg) in these mice was restored by the administration of either naloxone (0.5 mg/kg) or L-NAME (40 mg/kg). In addition, naloxone and L-NAME reduced the exploratory behaviors in L-arginine-pretreated mice but not in morphine-pretreated mice. We conclude that there appears to be a synergistic effect between opioidergic and nitrergic systems on memory acquisition and exploratory behaviors in cholestatic mice.

Potential prevention and treatment of maifanite for Alzheimer's disease based on behavior test, oxidative stress assay, and trace element analysis in hippocampus of Aβ(₂₅₋₃₅)-induced AD rats

This study aimed to assess whether maifanite can improve the learning and memory, and antioxidant abilities of Alzheimer's disease (AD) rats. The 70 rats were divided into seven groups: [A] normal control group, [B] AD model group, [C] sham group, [D] positive control group (donepezil), [E] low-dose maifanite group, [F] middle-dose maifanite group, [G] high-dose maifanite group. For [B], [D], [E], [F], and [G] groups, Aβ(25-35) ventricle injection was carried out, then respective medicine were administered once a day for 60 consecutive days. The step-down and step-through test were used to measure learning and memory ability. The hippocampus levels of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) were assayed. The hippocampus contents of Al, Fe, Cu, Zn, Se, and Mn were analyzed by inductively coupled plasma-atomic emission spectrometer. Maifanite decreased the acquisition errors and the retention errors while prolonging the step-down latency, and decreased the number of electric shocks while prolonging the first latency of AD rats. Aβ(25-35) ventricle injection initiated the decrease of SOD and GSH-Px activities and the increase of MDA content, and triggered the rise of Al, Fe, and Cu levels and the decline of Mn, Zn, and Se levels. The SOD and GSH-Px activities were enhanced followed by reduced MDA level, and the levels of Mn, Zn, and Se increased accompanied by Al, Fe, and Cu decreased in the maifanite treat groups. Maifanite could improve the learning and memory, and the antioxidant abilities of AD rats. Maifanite had the potential prevention and treatment for AD.

Role of β-hairpin formation in aggregation: the self-assembly of the amyloid-β(25-35) peptide

The amyloid-β(25-35) peptide plays a key role in the etiology of Alzheimer's disease due to its extreme toxicity even in the absence of aging. Because of its high tendency to aggregate and its low solubility in water, the structure of this peptide is still unknown. In this work, we sought to understand the early stages of aggregation of the amyloid-β(25-35) peptide by conducting simulations of oligomers ranging from monomers to tetramers. Our simulations show that although the monomer preferentially adopts a β-hairpin conformation, larger aggregates have extended structures, and a clear transition from compact β-hairpin conformations to extended β-strand structures occurs between dimers and trimers. Even though β-hairpins are not present in the final architecture of the fibril, our simulations indicate that they play a critical role in fibril growth. Our simulations also show that β-sheet structures are stabilized when a β-hairpin is present at the edge of the sheet. The binding of the hairpin to the sheet leads to a subsequent destabilization of the hairpin, with part of the hairpin backbone dangling in solution. This free section of the peptide can then recruit an extra monomer from solution, leading to further sheet extension. Our simulations indicate that the peptide must possess sufficient conformational flexibility to switch between a hairpin and an extended conformation in order for β-sheet extension to occur, and offer a rationalization for the experimental observation that overstabilizing a hairpin conformation in the monomeric state (for example, through chemical cross-linking) significantly hampers the fibrillization process.

Neuroprotective effect of sinapic acid in a mouse model of amyloid β(1-42) protein-induced Alzheimer's disease

Sinapic acid (SA) is a phenylpropanoid compound with anti-inflammatory and neuroprotective activities. The neuroprotective effects of SA in a mouse model of amyloid β (Aβ)(1-42) protein-induced Alzheimer's disease (AD) were investigated. Mice received a bilateral injection of Aβ(1-42) protein into the hippocampus to verify the efficacy of SA. Mice were treated with SA (10mg/kg/day, p.o.) for 7days beginning immediately after Aβ(1-42) protein injection, and an acquisition trial of the passive avoidance task was conducted 1h after the last administration of SA. Retention trial was conducted 24h after the acquisition trial, and mice were sacrificed for immunohistochemistry immediately after the retention trial. SA rescued neuronal cell death in the hippocampal CA1 region and also attenuated the increase of iNOS expression, glial cell activations and nitrotyrosine expressions induced by Aβ(1-42) protein. SA significantly attenuated memory impairment in the passive avoidance task. These results suggest that SA ameliorated Aβ(1-42) protein-related pathology including neuronal cell death and cognitive dysfunction via its anti-oxidative and anti-inflammatory activities, and may be an efficacious treatment for AD.

Nitric oxide inactivation mechanisms in the brain: role in bioenergetics and neurodegeneration

During the last decades nitric oxide ((•)NO) has emerged as a critical physiological signaling molecule in mammalian tissues, notably in the brain. (•)NO may modify the activity of regulatory proteins via direct reaction with the heme moiety, or indirectly, via S-nitrosylation of thiol groups or nitration of tyrosine residues. However, a conceptual understanding of how (•)NO bioactivity is carried out in biological systems is hampered by the lack of knowledge on its dynamics in vivo. Key questions still lacking concrete and definitive answers include those related with quantitative issues of its concentration dynamics and diffusion, summarized in the how much, how long, and how far trilogy. For instance, a major problem is the lack of knowledge of what constitutes a physiological (•)NO concentration and what constitutes a pathological one and how is (•)NO concentration regulated. The ambient (•)NO concentration reflects the balance between the rate of synthesis and the rate of breakdown. Much has been learnt about the mechanism of (•)NO synthesis, but the inactivation pathways of (•)NO has been almost completely ignored. We have recently addressed these issues in vivo on basis of microelectrode technology that allows a fine-tuned spatial and temporal measurement (•)NO concentration dynamics in the brain.

Integrating cytosolic phospholipase A₂ with oxidative/nitrosative signaling pathways in neurons: a novel therapeutic strategy for AD

The pathophysiology of Alzheimer's disease (AD) is comprised of complex metabolic abnormalities in different cell types in the brain. To date, there are not yet effective drugs that can completely inhibit the pathophysiological event, and efforts have been devoted to prevent or minimize the progression of this disease. Much attention has focused on studies to understand aberrant functions of the ionotropic glutamate receptors, perturbation of calcium homeostasis, and toxic effects of oligomeric amyloid beta peptides (Aβ) which results in production of reactive oxygen and nitrogen species and signaling pathways, leading to mitochondrial dysfunction and synaptic impairments. Aberrant phospholipase A(2) (PLA(2)) activity has been implicated to play a role in the pathogenesis of many neurodegenerative diseases, including AD. However, mechanisms for their modes of action and their roles in the oxidative and nitrosative signaling pathways have not been firmly established. In this article, we review recent studies providing a metabolic link between cytosolic PLA(2) (cPLA(2)) and neuronal excitation due to stimulation of ionotropic glutamate receptors and toxic Aβ peptides. The requirements for Ca(2+) binding together with its posttranslational modifications by protein kinases and possible by the redox-based S-nitrosylation, provide strong support for a dynamic role of cPLA(2) in serving multiple functions to neurons and glial cells under abnormal physiological and pathological conditions. Therefore, understanding mechanisms for cPLA(2) in the oxidative and nitrosative pathways in neurons will allow the development of novel therapeutic targets to mitigate the detrimental effects of AD.

Alteration of the sialylation pattern and memory deficits by injection of Aβ(25-35) into the hippocampus of rats

Sialic acid in glycoconjugates participates in important cellular functions associated with normal development, growth, and communication. Therefore we evaluated the sialylation pattern and memory deficits caused by the injection of Aβ((25-35)) into the hippocampus (Hp) of rats. The eight-arm maze spatial-learning and memory test indicated that the injection of Aβ((25-35)) into subfield CA1 of the Hp impaired both learning and memory. The sialylation pattern was examined using sialic acid-specific lectins. Our results showed that Maackia amurensis agglutinin (MAA, specific for Neu5Acα2,3Gal) showed reactivity in the CA1 and dentate gyrus (DG) subfields of the Hp mainly in the group injected with vehicle, whereas Macrobrachium rosenbergii lectin (MRL, specific for Neu5,9,7Ac) and Sambucus nigra agglutinin (SNA, specific for Neu5Acα2,6Gal-GalNAc) had increased reactivity in the CA1 and DG subfields of the Hp in the Aβ((25-35))-injected group. The staining pattern of the antibody specific for polysialic acid (a linear homopolymer of α-2,8-linked sialic acid) increased in the CA1 and DG subfields of the Hp of the Aβ((25-35)) group compared to the control group. Our results suggest that injection of Aβ((25-35)) causes impairment in spatial memory and alters the sialylation pattern in response to compensatory reorganization and-or sprouting of dendrites and axons of the surviving neurons.