Synergistic effects of selegiline and donepezil on cognitive impairment induced by amyloid beta (25-35)

Protective effects of selegiline against amyloid beta-induced anxiety-like behavior and memory impairment

BACKGROUND

Alzheimer's disease (AD) is a complex and common neurodegenerative disorder. The present study aimed to investigate the potential effects of selegiline (SEL) on various aspects of memory performance, anxiety, and oxidative stress in an AD rat model induced by intracerebroventricular injection of amyloid beta1-42 (Aβ1-42).

METHODS

Oral administration of SEL at a dose of 0.5 mg/kg/day was performed for 30 consecutive days. Following the 30 days, several tests, including the open-field, elevated plus-maze, novel object recognition, Morris water maze, and passive avoidance learning were conducted to assess locomotor activity, anxiety-like behavior, recognition memory, spatial memory, and passive avoidance memory, respectively.

RESULTS

The results indicate that the induction of AD in rats led to recognition memory, spatial memory, and passive avoidance memory impairments, as well as increased anxiety. Additionally, the AD rats exhibited a decrease in total antioxidant capacity and an increase in total oxidant status levels, suggesting an imbalance in oxidative-antioxidant status. However, the administration of SEL improved memory performance, reduced anxiety, and modulated oxidative-antioxidant status in AD rats.

CONCLUSIONS

These findings provide evidence that SEL may alleviate anxiety-like behavior and cognitive deficits induced by Aβ through modulation of oxidative-antioxidant status.

The role of dopamine in NLRP3 inflammasome inhibition: Implications for neurodegenerative diseases

In the Central Nervous System (CNS), neuroinflammation orchestrated by microglia and astrocytes is an innate immune response to counteract stressful and dangerous insults. One of the most important and best characterized players in the neuroinflammatory response is the NLRP3 inflammasome, a multiproteic complex composed by NOD-like receptor family Pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein (ASC) and pro-caspase-1. Different stimuli mediate NLRP3 activation, resulting in the NLRP3 inflammasome assembly and the pro-inflammatory cytokine (IL-1β and IL-18) maturation and secretion. The persistent and uncontrolled NLRP3 inflammasome activation has a leading role during the pathophysiology of neuroinflammation in age-related neurodegenerative diseases such as Parkinson's (PD) and Alzheimer's (AD). The neurotransmitter dopamine (DA) is one of the players that negatively modulate NLRP3 inflammasome activation through DA receptors expressed in both microglia and astrocytes. This review summarizes recent findings linking the role of DA in the modulation of NLRP3-mediated neuroinflammation in PD and AD, where early deficits of the dopaminergic system are well characterized. Highlighting the relationship between DA, its glial receptors and the NLRP3-mediated neuroinflammation can provide insights to novel diagnostic strategies in early disease phases and new pharmacological tools to delay the progression of these diseases.

Naringin enhances long-term potentiation and recovers learning and memory deficits of amyloid-beta induced Alzheimer's disease-like behavioral rat model

Alzheimer's disease (AD), as the most typical type of dementia, is a chronic neurodegenerative disorder characterized by progressive learning and memory impairment. It is known that the main causes of AD are the accumulation of β-amyloid (Aβ) plaques and neurofibrillary tangles (NFT) containing hyperphosphorylated tau protein. Naringin is a flavonoid from citrus fruits, especially in grapefruit, which has anti-inflammatory, antioxidant, anti-apoptotic, and neuroprotective activities. However, the effect of naringin in AD caused by Aβ has not been clearly studied, and there are few studies on the electrophysiological aspect. Thus, we investigated the ex vivo neuroprotective effect of naringin through the long-term potentiation (LTP) on organotypic hippocampal slice cultures. We evaluated the in vivo effects of naringin (100 mg/kg/day) orally treated for 20 days on learning, memory, and cognition which was impaired by bilateral CA1 subregion injection of Aβ. Cognitive behaviors were measured 2 weeks after Aβ injection using behavioral tests and the hippocampal expression of apoptotic and neurotrophic regulators were measured by immunoblotting. In hippocampal tissue slices, naringin dose-dependently increased the field excitatory postsynaptic potential (fEPSP) after theta burst stimulation and attenuated Aβ-induced blockade of fEPSP in the hippocampal CA1 area. In Aβ injected rats, naringin improved object recognition memory in the novel object test, avoidance memory in the passive avoidance test and spatial recognition memory in the Morris water maze test. In the hippocampus, naringin attenuated the Aβ-induced cyclooxygenase-2, Bax activation and Bcl-2, CREB, BDNF and TrkB inhibition. These results suggest that naringin has therapeutic potential to reduce neuronal inflammation and apoptosis induced by Aβ related with the BDNF/TrkB/CREB signaling.

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.

Honey and Alzheimer's Disease-Current Understanding and Future Prospects

Alzheimer's disease (AD), a leading cause of dementia, has been a global concern. AD is associated with the involvement of the central nervous system that causes the characteristic impaired memory, cognitive deficits, and behavioral abnormalities. These abnormalities caused by AD is known to be attributed by extracellular aggregates of amyloid beta plaques and intracellular neurofibrillary tangles. Additionally, genetic factors such as abnormality in the expression of APOE, APP, BACE1, PSEN-1, and PSEN-2 play a role in the disease. As the current treatment aims to treat the symptoms and to slow the disease progression, there has been a continuous search for new nutraceutical agent or medicine to help prevent and cure AD pathology. In this quest, honey has emerged as a powerful nootropic agent. Numerous studies have demonstrated that the high flavonoids and phenolic acids content in honey exerts its antioxidant, anti-inflammatory, and neuroprotective properties. This review summarizes the effect of main flavonoid compounds found in honey on the physiological functioning of the central nervous system, and the effect of honey intake on memory and cognition in various animal model. This review provides a new insight on the potential of honey to prevent AD pathology, as well as to ameliorate the damage in the developed AD.

Cholinergic regulation of object recognition memory

Object recognition memory refers to a basic memory mechanism to identify and recall various features of objects. This memory has been investigated by numerous studies in human, primates and rodents to elucidate the neuropsychological underpinnings in mammalian memory, as well as provide the diagnosis of dementia in some neurological diseases, such as Alzheimer's disease and Parkinson's disease. Since Alzheimer's disease at the early stage is reported to be accompanied with cholinergic cell loss and impairment in recognition memory, the central cholinergic system has been studied to investigate the neural mechanism underlying recognition memory. Previous studies have suggested an important role of cholinergic neurons in the acquisition of some variants of object recognition memory in rodents. Cholinergic neurons in the medial septum and ventral diagonal band of Broca that project mainly to the hippocampus and parahippocampal area are related to recognition memory for object location. Cholinergic projections from the nucleus basalis magnocellularis innervating the entire cortex are associated with recognition memory for object identification. Especially, the brain regions that receive cholinergic projections, such as the perirhinal cortex and prefrontal cortex, are involved in recognition memory for object-in-place memory and object recency. In addition, experimental studies using rodent models for Alzheimer's disease have reported that neurodegeneration within the central cholinergic system causes a deficit in object recognition memory. Elucidating how various types of object recognition memory are regulated by distinct cholinergic cell groups is necessary to clarify the neuronal mechanism for recognition memory and the development of therapeutic treatments for dementia.

Noradrenaline in Alzheimer's Disease: A New Potential Therapeutic Target

A growing body of evidence demonstrates the important role of the noradrenergic system in the pathogenesis of many neurodegenerative processes, especially Alzheimer’s disease, due to its ability to control glial activation and chemokine production resulting in anti-inflammatory and neuroprotective effects. Noradrenaline involvement in this disease was first proposed after finding deficits of noradrenergic neurons in the locus coeruleus from Alzheimer’s disease patients. Based on this, it has been hypothesized that the early loss of noradrenergic projections and the subsequent reduction of noradrenaline brain levels contribute to cognitive dysfunctions and the progression of neurodegeneration. Several studies have focused on analyzing the role of noradrenaline in the development and progression of Alzheimer’s disease. In this review we summarize some of the most relevant data describing the alterations of the noradrenergic system normally occurring in Alzheimer’s disease as well as experimental studies in which noradrenaline concentration was modified in order to further analyze how these alterations affect the behavior and viability of different nervous cells. The combination of the different studies here presented suggests that the maintenance of adequate noradrenaline levels in the central nervous system constitutes a key factor of the endogenous defense systems that help prevent or delay the development of Alzheimer’s disease. For this reason, the use of noradrenaline modulating drugs is proposed as an interesting alternative therapeutic option for Alzheimer’s disease.

Neuroprotective Effects of Cholinesterase Inhibitors: Current Scenario in Therapies for Alzheimer’s Disease and Future Perspectives

Alzheimer’s disease (AD) is a slowly progressive neurodegenerative disease conceptualized as a continuous process, ranging from mild cognitive impairment (MCI), to the mild, moderate, and severe clinical stages of AD dementia. AD is considered a complex multifactorial disease. Currently, the use of cholinesterase inhibitors (ChEI), such as tacrine, donepezil, rivastigmine, and galantamine, has been the main treatment for AD patients. Interestingly, there is evidence that ChEI also promotes neuroprotective effects, bringing some benefits to AD patients. The mechanisms by which the ChEI act have been investigated in AD. ChEI can modulate the PI3K/AKT pathway, which is an important signaling cascade that is capable of causing a significant functional impact on neurons by activating cell survival pathways to promote neuroprotective effects. However, there is still a huge challenge in the field of neuroprotection, but in the context of unravelling the details of the PI3K/AKT pathway, a new scenario has emerged for the development of more efficient drugs that act on multiple protein targets. Thus, the mechanisms by which ChEI can promote neuroprotective effects and prospects for the development of new drug candidates for the treatment of AD are discussed in this review.

The VTA dopaminergic system as diagnostic and therapeutical target for Alzheimer's disease

Neuropsychiatric symptoms (NPS) occur in nearly all patients with Alzheimer's Disease (AD). Most frequently they appear since the mild cognitive impairment (MCI) stage preceding clinical AD, and have a prognostic importance. Unfortunately, these symptoms also worsen the daily functioning of patients, increase caregiver stress and accelerate the disease progression from MCI to AD. Apathy and depression are the most common of these NPS, and much attention has been given in recent years to understand the biological mechanisms related to their appearance in AD. Although for many decades these symptoms have been known to be related to abnormalities of the dopaminergic ventral tegmental area (VTA), a direct association between deficits in the VTA and NPS in AD has never been investigated. Fortunately, this scenario is changing since recent studies using preclinical models of AD, and clinical studies in MCI and AD patients demonstrated a number of functional, structural and metabolic alterations affecting the VTA dopaminergic neurons and their mesocorticolimbic targets. These findings appear early, since the MCI stage, and seem to correlate with the appearance of NPS. Here, we provide an overview of the recent evidence directly linking the dopaminergic VTA with NPS in AD and propose a setting in which the precocious identification of dopaminergic deficits can be a helpful biomarker for early diagnosis. In this scenario, treatments of patients with dopaminergic drugs might slow down the disease progression and delay the impairment of daily living activities.

Early derailment of firing properties in CA1 pyramidal cells of the ventral hippocampus in an Alzheimer's disease mouse model

Gradual decline in cognitive and non-cognitive functions are considered clinical hallmarks of Alzheimer's Disease (AD). Post-mortem autoptic analysis shows the presence of amyloid β deposits, neuroinflammation and severe brain atrophy. However, brain circuit alterations and cellular derailments, assessed in very early stages of AD, still remain elusive. The understanding of these early alterations is crucial to tackle defective mechanisms. In a previous study we proved that the Tg2576 mouse model of AD displays functional deficits in the dorsal hippocampus and relevant behavioural AD-related alterations. We had shown that these deficits in Tg2576 mice correlate with the precocious degeneration of dopamine (DA) neurons in the Ventral Tegmental Area (VTA) and can be restored by L-DOPA treatment. Due to the distinct functionality and connectivity of dorsal versus ventral hippocampus, here we investigated neuronal excitability and synaptic functionality in the ventral CA1 hippocampal sub-region of Tg2576 mice. We found an age-dependent alteration of cell excitability and firing in pyramidal neurons starting at 3 months of age, that correlates with reduced levels in the ventral CA1 of tyrosine hydroxylase - the rate-limiting enzyme of DA synthesis. Additionally, at odds with the dorsal hippocampus, we found no alterations in basal glutamatergic transmission and long-term plasticity of ventral neurons in 8-month old Tg2576 mice compared to age-matched controls. Last, we used computational analysis to model the early derailments of firing properties observed and hypothesize that the neuronal alterations found could depend on dysfunctional sodium and potassium conductances, leading to anticipated depolarization-block of action potential firing. The present study depicts that impairment of cell excitability and homeostatic control of firing in ventral CA1 pyramidal neurons is a prodromal feature in Tg2576 AD mice.

Early postnatal inhibition of GLAST causes abnormalities of psychobehaviors and neuronal morphology in adult mice

The importance of glutamate transporters in learning, memory, and emotion remains poorly understood; hence, in the present study, we investigated whether deficiency of pharmacological GLAST in neurodevelopmental processes affects cognitive and/or emotional behaviors in mice. The mice were injected with a glutamate transporter inhibitor, dl-threo-β-benzyloxyaspartate (dl-TBOA), during the early postnatal period. At 8 weeks of age, they showed impairments in cognitive or emotional behaviors; dysfunction of glutamatergic neurotransmission (increased expressions of GLAST, GLT-1, or GFAP protein, and decreased ability of glutamate release) in the cortex or hippocampus; morphological changes (decreased cell size in the cortex and thickness of the pyramidal neuronal layer of the CA1 area in the hippocampus). Such behavioral and morphological changes were not observed in adult mice injected with dl-TBOA. These results suggest that GLAST plays an important role in the regulation of cognitive and emotional behaviors. Early postnatal glutamatergic facilitation by GLAST dysfunction leads to cognitive and emotional abnormalities due to neurodevelopmental abnormalities such as morphological changes.

Role of Nrf2 in Synaptic Plasticity and Memory in Alzheimer's Disease

Nuclear factor erythroid 2-related factor 2 (Nrf2) is an important transcription factor that reduces oxidative stress. When reactive oxygen species (ROS) or reactive nitrogen species (RNS) are detected, Nrf2 translocates from the cytoplasm into the nucleus and binds to the antioxidant response element (ARE), which regulates the expression of antioxidant and anti-inflammatory genes. Nrf2 impairments are observed in the majority of neurodegenerative disorders, including Alzheimer’s disease (AD). The classic hallmarks of AD include β-amyloid (Aβ) plaques, and neurofibrillary tangles (NFTs). Oxidative stress is observed early in AD and is a novel therapeutic target for the treatment of AD. The nuclear translocation of Nrf2 is impaired in AD compared to controls. Increased oxidative stress is associated with impaired memory and synaptic plasticity. The administration of Nrf2 activators reverses memory and synaptic plasticity impairments in rodent models of AD. Therefore, Nrf2 activators are a potential novel therapeutic for neurodegenerative disorders including AD.

Exploring the Role of Monoamine Oxidase Activity in Aging and Alzheimer's Disease

Monoamine oxidases (MAOs) are a family of flavin adenine dinucleotide-dependent enzymes that exert a crucial role in the metabolism of neurotransmitters of the central nervous system. The impaired function of MAOs is associated with copious brain diseases. The alteration of monoamine metabolism is a characteristics feature of aging. MAO plays a crucial role in the pathogenesis of Alzheimer's disease (AD) - a progressive neurodegenerative disorder associated with an excessive accumulation of amyloid-beta (Aβ) peptide and neurofibrillary tangles (NFTs). Activated MAO has played a critical role in the development of amyloid plaques from Aβ, as well as the formation of the NFTs. In the brain, MAO mediated metabolism of monoamines is the foremost source of reactive oxygen species formation. The elevated level of MAO-B expression in astroglia has been reported in the AD brains adjacent to amyloid plaques. Increased MAO-B activity in the cortical and hippocampal regions is associated with AD. This review describes the pathogenic mechanism of MAOs in aging as well as the development and propagation of Alzheimer's pathology.

Neural stem cell-conditioned medium ameliorates Aβ25-35-induced damage in SH-SY5Y cells by protecting mitochondrial function

Inhibition of amyloid β (Aβ)-induced mitochondrial damage is considered crucial for reducing the pathological damage in Alzheimer’s disease (AD). We evaluated the effect of neural stem cell-conditioned medium (NSC-CDM) on Aβ_25–35-induced damage in SH-SY5Y cells. An in vitro model of AD was established by treating SH-SY5Y cells with 40 μM Aβ_25–35 for 24 h. SH-SY5Y cells were divided into control, Aβ_25–35 (40 μM), Aβ_25–35 (40 μM) + NSC-CDM, and Aβ_25–35 (40 μM) + neural stem cell-complete medium (NSC-CPM) groups. Cell viability was detected by CCK-8 assay. Apoptosis, reactive oxygen species (ROS) production, and mitochondrial membrane potential (MMP) were detected by flow cytometry. Malondialdehyde content was detected by ELISA assay. Western blot analysis was used to detect cytochrome c release and apoptosis-related proteins. Transmission electron microscopy was used to observe mitochondrial morphology. Cell viability significantly decreased and apoptosis significantly increased in SH-SY5Y cells treated with Aβ_25–35, and both effects were rescued by NSC-CDM. In addition, NSC-CDM reduced ROS production and significantly inhibited the reduction of MMP caused by Aβ_25–35. Furthermore, NSC-CDM ameliorated Aβ_25–35-induced reduction in Bcl-2 expression levels and increased the expression levels of cytochrome c, caspase-9, caspase-3, and Bax. Moreover, Aβ_25–35 induced the destruction of mitochondrial ultrastructure and this effect was reversed by NSC-CDM. Collectively, our findings demonstrated the protective effect of NCS-CDM against Aβ_25–35-induced SH-SY5Y cell damage and clarified the mechanism of action of Aβ_25–35 in terms of mitochondrial maintenance and mitochondria-associated apoptosis signaling pathways, thus providing a theoretical basis for the development of novel anti-AD treatments.

Nilotinib restores memory function by preventing dopaminergic neuron degeneration in a mouse model of Alzheimer's Disease

What happens precociously to the brain destined to develop Alzheimer's Disease (AD) still remains to be elucidated and this is one reason why effective AD treatments are missing. Recent experimental and clinical studies indicate that the degeneration of the dopaminergic (DA) neurons in the Ventral Tegmental Area (VTA) could be one of the first events occurring in AD. However, the causes of the increased vulnerability of DA neurons in AD are missing. Here, we deeply investigate the physiology of DA neurons in the VTA before, at the onset, and after onset of VTA neurodegeneration. We use the Tg2576 mouse model of AD, overexpressing a mutated form of the human APP, to identify molecular targets that can be manipulated pharmacologically. We show that in Tg2576 mice, DA neurons of the VTA at the onset of degeneration undergo slight but functionally relevant changes in their electrophysiological properties and cell morphology. Importantly, these changes are associated with accumulation of autophagosomes, suggestive of a dysfunctional autophagy, and with enhanced activation of c-Abl, a tyrosine kinase previously implicated in the pathogenesis of neurodegenerative diseases. Chronic treatment of Tg2576 mice with Nilotinib, a validated c-Abl inhibitor, reduces c-Abl phosphorylation, improves autophagy, reduces Aβ levels and - more importantly - prevents degeneration as well as functional and morphological alterations in DA neurons of the VTA. Interestingly, the drug prevents the reduction of DA outflow to the hippocampus and ameliorates hippocampal-related cognitive functions. Our results strive to identify early pathological brain changes in AD, to provide a rational basis for new therapeutic interventions able to slow down the disease progression.

Acetylcholinesterase and butyrylcholinesterase inhibitory activities of khellactone coumarin derivatives isolated from Peucedanum japonicum Thurnberg

Cholinesterase (ChE) and monoamine oxidase (MAO) inhibitors have been attracted as candidate treatments for Alzheimer's disease (AD). Fifteen khellactone-type coumarins from the roots of Peucedanum japonicum Thunberg were tested for acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and MAO inhibitory activities. Compound 3′-angeloyl-4′-(2-methylbutyryl)khellactone (PJ13) most potently inhibited AChE (IC₅₀ = 9.28 µM), followed by 3′-isovaleryl-4′-(2-methylbutyroyl)khellactone (PJ15) (IC₅₀ = 10.0 μM). Compound senecioyl-4′-angeloyl-khellactone (PJ5) most potently inhibited BChE (IC₅₀ = 7.22 μM) and had the highest selectivity index (> 5.54), followed by 3′-senecioyl-4′-(2-methylbutyryl)khellactone (PJ10) and 3′,4′-disenecioylkhellactone (PJ4) (IC₅₀ = 10.2 and 10.7 μM, respectively). Compounds PJ13, PJ15, and PJ5 showed reversible and mixed-types of inhibition with K_i values of 5.98, 10.4 (for AChE), and 4.16 µM (for BChE), respectively. However, all 15 compounds weakly inhibited MAO-A and MAO-B. Molecular docking simulation revealed that PJ13 had a higher binding affinity (− 9.3 kcal/mol) with AChE than PJ15 (− 7.8 kcal/mol) or PJ5 (− 5.4 kcal/mol), due to the formation of a hydrogen bond with Tyr121 (distance: 2.52 Å). On the other hand, the binding affinity of PJ5 (− 10.0 kcal/mol) with BChE was higher than for PJ13 (− 7.7 kcal/mol) or PJ15 (− 8.1 kcal/mol), due to the formation of a hydrogen bond with Ser198 (distance: 2.05 Å). These results suggest that PJ13 and PJ5 are potential reversible selective inhibitors of AChE and BChE, respectively, for the treatment of AD.

Microglial TonEBP mediates LPS-induced inflammation and memory loss as transcriptional cofactor for NF-κB and AP-1

BACKGROUND

Microglia are brain-resident myeloid cells involved in the innate immune response and a variety of neurodegenerative diseases. In macrophages, TonEBP is a transcriptional cofactor of NF-κB which stimulates the transcription of pro-inflammatory genes in response to LPS. Here, we examined the role of microglial TonEBP.

METHODS

We used microglial cell line, BV2 cells. TonEBP was knocked down using lentiviral transduction of shRNA. In animals, TonEBP was deleted from myeloid cells using a line of mouse with floxed TonEBP. Cerulenin was used to block the NF-κB cofactor function of TonEBP.

RESULTS

TonEBP deficiency blocked the LPS-induced expression of pro-inflammatory cytokines and enzymes in association with decreased activity of NF-κB in BV2 cells. We found that there was also a decreased activity of AP-1 and that TonEBP was a transcriptional cofactor of AP-1 as well as NF-κB. Interestingly, we found that myeloid-specific TonEBP deletion blocked the LPS-induced microglia activation and subsequent neuronal cell death and memory loss. Cerulenin disrupted the assembly of the TonEBP/NF-κB/AP-1/p300 complex and suppressed the LPS-induced microglial activation and the neuronal damages in animals.

CONCLUSIONS

TonEBP is a key mediator of microglial activation and neuroinflammation relevant to neuronal damage. Cerulenin is an effective blocker of the TonEBP actions.

GnRH protective effects against amyloid β-induced cognitive decline: A potential role of the 17β-estradiol

INTRODUCTION

The 17β-estradiol (E2) enhances hippocampal dendritic spine synapses, facilitates learning processes, and exerts neuroprotection. Brain estrogen decline has been reported in Alzheimer's disease. The role of GnRH in modulating steroid biosynthesis convinced us to examine whether hippocampal GnRH administration could enhance the local E2 levels and overcome the development of cognition decline in amyloid β (Aβ) neurotoxicity. To explore if GnRH acts through regulating E2 synthesis, letrozole, an aromatase inhibitor, has been applied in combination with GnRH.

METHODS

Female rats received an intracerebroventricular injection of Aβ. The GnRH and, or letrozole were injected into the CA1 for 14 consecutive days. Working memory, novel object recognition memory, and anxiety-like behavior were evaluated. Serum and hippocampal E2 levels were measured. Hippocampal mRNA expression of GnRH (GnRH-R) and E2 (ERα and ERβ) receptors was assessed. GnRH effect on the excitability of pyramidal cells was studied by in vivo single-unit recording.

RESULTS

GnRH increased hippocampal E2 levels, evoked an increase in the spontaneous firing of pyramidal neurons, and caused mRNA overexpression of hippocampal GnRH receptors. GnRH prevented the adverse effects of Aβ on working memory, NOR index, and anxiogenic behavior. Letrozole did not reverse GnRH modulatory effects on hippocampal E2 levels and neuroprotection.

CONCLUSION

GnRH prevented the Aβ-induced memory deficit, which may be mediated through hippocampal E2 levels enhancement. The electrophysiological analysis revealed the enhanced neuronal excitability in the CA1 region. All these data suggest that GnRH might be a promising candidate that reduces anxiety and improves memory indices in the context of Aβ neurotoxicity.

Effects of the fermented Zizyphus jujuba in the amyloid β25-35-induced Alzheimer's disease mouse model

BACKGROUD/OBJECTIVES

Alzheimer's disease (AD) is the most common cause of dementia in the elderly. Due to the increased incidence of dementia, there is a corresponding increase concerning the importance of AD. In this study, we investigated the protective effects conferred by Zizyphus jujuba (Zj) and Zizyphus jujuba fermented by yeast (Zj-Y), on cognitive impairment in an AD mouse model.

MATERIALS/METHODS

AD was induced by injecting amyloid beta_25-35 (Aβ_25-35) in ICR mice, and subsequently 200 mg/kg Zj or Zj-Y was administered daily for 14 days. The cognitive ability of AD mice was observed through behavioral experiments in T-maze, novel object recognition, and Morris water maze tests. We subsequently measured the levels of malondialdehyde (MDA), nitric oxide (NO), aspartate aminotransferase, and alanine aminotransferase in either tissues or serum.

RESULTS

In behavioral tests, deterioration was revealed in the short- and long-term learning and memory functions in the Aβ_25-35-injected control group compared to the normal group, indicating that Aβ_25-35 injection impairs cognitive functions. However, administration of Zj and Zj-Y improved cognitive function in mice, as compared to the Aβ_25-35-injected control mice. In addition, the Aβ_25-35 induced elevations of MDA and NO in the brain, kidney, and liver were suppressed after exposure to Zj and Zj-Y. Especially, Zj-Y showed stronger scavenging effect against MDA and NO, as compared to Zj.

CONCLUSIONS

Results of the present study indicate that Zj-Y exerts a protective effect on cognitive impairment and memory dysfunction, which is exerted by attenuating the oxidative stress induced by Aβ_25-35.

Efficacy of THN201, a Combination of Donepezil and Mefloquine, to Reverse Neurocognitive Deficits in Alzheimer's Disease

Donepezil (DPZ) is an acetylcholinesterase inhibitor used in Alzheimer’s disease to restore cognitive functions but is endowed with limited efficacy. Recent studies pointed out the implication of astroglial networks in cognitive processes, notably via astrocyte connexins (Cxs), proteins involved in gap junction intercellular communications. Hence, we investigated the impact on cognition of pharmacological or genetic modulations of those astrocyte Cxs during DPZ challenge in two rodent models of Alzheimer’s disease–like memory deficits. We demonstrated that the Cx modulator mefloquine (MEF) significantly enhanced the procognitive effect of DPZ in both models. In parallel, we determined that MEF potentiated DPZ-induced release of acetylcholine in hippocampus. Finally, local genetic silencing of astrocyte Cxs in the hippocampus was also found to enhance the procognitive effect of DPZ, pointing out the importance of Cx-dependent astrocyte networks in memory processes.

The role of dopaminergic midbrain in Alzheimer's disease: Translating basic science into clinical practice

Mammalian brain cortical functions, from executive and motor functioning to memory and emotional regulation, are strictly regulated by subcortical projections. These projections terminate in cortical areas that are continuously influenced by released neurotransmitters and neuromodulators. Among the subcortical structures, the dopaminergic midbrain plays a pivotal role in tuning cortical functions that commonly result altered in many neurological and psychiatric disorders. Incidentally, extensive neuropathological observations support a strong link between structural alterations of the dopaminergic midbrain and significant behavioural symptomatology observed in patients suffering from Alzheimer 's disease(AD). Here, we will review recent progress on the involvement of the dopaminergic system in the pathophysiology of AD as well as the current therapeutic strategies targeting this system.

Identification of 5-(1-Methyl-5-(trifluoromethyl)-1H-pyrazol-3-yl)thiophene-2-Carboxamides as Novel and Selective Monoamine Oxidase B Inhibitors Used to Improve Memory and Cognition

Initial work in Drosophila and mice demonstrated that the transcription factor cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) is a master control gene for memory formation. The relationship between CREB and memory has also been found to be true in other species, including aplysia and rats. It is thus well-established that CREB activation plays a central role in memory enhancement and that CREB is activated during memory formation. On the basis of these findings, a phenotypic high-throughput screening campaign utilizing a CRE-luciferase (CRE-Luci) SK-N-MC cell line was performed to identify compounds that enhance transcriptional activation of the CRE promoter with a suboptimal dose of forskolin. A number of small-molecule hits of unknown mechanisms of action were identified in the screening campaign, including HT-0411. Follow-up studies suggested that the CREB activation by HT-0411 is attributed to its specific and selective inhibition of monoamine oxidase B (MAO-B). Further, HT-0411 was shown to improve 24 h memory in rodents in a contextual fear conditioning model. This report describes the lead optimization of a series of 5-(1-methyl-5-(trifluoromethyl)-1H-pyrazol-3-yl) thiophene-2-carboxamides that were identified as novel, potent, and selective inhibitors of MAO-B. Extensive SAR studies and in vivo behavioral evaluations of this and other related analogue series identified a number of potential clinical development candidates; ultimately, compound 8f was identified as a candidate molecule with high selectivity toward MAO-B (29-56 nM) over MAO-A (19% inhibition at a screening concentration of 50 μM), an excellent profile against a panel of other enzymes and receptors, good pharmacokinetic properties in rodents and dogs, and efficacy in multiple rodent memory models.

Inhibitory effects of Tabernaemontana divaricata root extract on oxidative stress and neuronal loss induced by amyloid β25-35 peptide in mice

In Alzheimer's disease, there are numerous amyloid plaques, neurofibrillary tangles, and neuronal loss in several brain areas. Oxidative stress is involved in the mechanisms of Aβ-peptide induced neurotoxicity by the generation of free radical oxidative stress that may lead to neurodegeneration. Tabernaemontana divaricata has various medical properties in Thai folklore medicine including prevent forgetfulness or improve memory. The present study aimed to investigate the effects of T. divaricata root extract (TDE) on Aβ_25-35 peptides induced neuronal loss and oxidative stress in mice. Male ICR mice were administered with vehicle or TDE (250, 500, and 1000 mg/kg b.w., p.o.) for 28 consecutive days. Then, these mice were given a single intracerebroventricular (i.c.v.) injection of Aβ_25-35 or phosphate buffer saline (PBS) (10 μg/mouse). The novel object recognition (NOR) test was used to determine memory disturbance. In addition, the neuronal cells in the cerebral cortex and hippocampus were measured by using crystal violet staining and lipid peroxidation was determined by measuring the formation of thiobarbituric acid reactive substances. An i.c.v. injection of Aβ_25-35 peptides could significantly induce memory impairment, increase level of lipid peroxidation including the neuronal loss in CA3 of hippocampus. However, the mice pretreated with TDE could prevent the memory loss, neuronal loss and decrease lipid peroxidation. These results suggest the potential therapeutic value in dementia of TDE through its antioxidant property.

YY-1224, a terpene trilactone-strengthened Ginkgo biloba, attenuates neurodegenerative changes induced by β-amyloid (1-42) or double transgenic overexpression of APP and PS1 via inhibition of cyclooxygenase-2

BACKGROUND

Ginkgo biloba has been reported to possess free radical-scavenging antioxidant activity and anti-inflammatory properties. In our pilot study, YY-1224, a terpene trilactone-strengthened extract of G. biloba, showed anti-inflammatory, neurotrophic, and antioxidant effects.

RESULTS

We investigated the pharmacological potential of YY-1224 in β-amyloid (Aβ) (1-42)-induced memory impairment using cyclooxygenase-2 (COX-2) knockout (-/-) and APPswe/PS1dE9 transgenic (APP/PS1 Tg) mice. Repeated treatment with YY-1224 significantly attenuated Aβ (1-42)-induced memory impairment in COX-2 (+/+) mice, but not in COX-2 (-/-) mice. YY-1224 significantly attenuated Aβ (1-42)-induced upregulation of platelet-activating factor (PAF) receptor gene expression, reactive oxygen species, and pro-inflammatory factors. In addition, YY-1224 significantly inhibited Aβ (1-42)-induced downregulation of PAF-acetylhydrolase-1 (PAF-AH-1) and peroxisome proliferator-activated receptor γ (PPARγ) gene expression. These changes were more pronounced in COX-2 (+/+) mice than in COX-2 (-/-) mice. YY-1224 significantly attenuated learning impairment, Aβ deposition, and pro-inflammatory microglial activation in APP/PS1 Tg mice, whereas it significantly enhanced PAF-AH and PPARγ expression. A preferential COX-2 inhibitor, meloxicam, did not affect the pharmacological activity by YY-1224, suggesting that the COX-2 gene is a critical mediator of the neuroprotective effects of YY-1224. The protective activity of YY-1224 appeared to be more efficacious than a standard G. biloba extract (Gb) against Aβ insult.

CONCLUSIONS

Our results suggest that the protective effects of YY-1224 against Aβ toxicity may be associated with its PAF antagonistic- and PPARγ agonistic-potential as well as inhibition of the Aβ-mediated pro-inflammatory switch of microglia phenotypes through suppression of COX-2 expression.

Dopamine neuronal loss contributes to memory and reward dysfunction in a model of Alzheimer's disease

Alterations of the dopaminergic (DAergic) system are frequently reported in Alzheimer's disease (AD) patients and are commonly linked to cognitive and non-cognitive symptoms. However, the cause of DAergic system dysfunction in AD remains to be elucidated. We investigated alterations of the midbrain DAergic system in the Tg2576 mouse model of AD, overexpressing a mutated human amyloid precursor protein (APPswe). Here, we found an age-dependent DAergic neuron loss in the ventral tegmental area (VTA) at pre-plaque stages, although substantia nigra pars compacta (SNpc) DAergic neurons were intact. The selective VTA DAergic neuron degeneration results in lower DA outflow in the hippocampus and nucleus accumbens (NAc) shell. The progression of DAergic cell death correlates with impairments in CA1 synaptic plasticity, memory performance and food reward processing. We conclude that in this mouse model of AD, degeneration of VTA DAergic neurons at pre-plaque stages contributes to memory deficits and dysfunction of reward processing.

Dopaminergic dysfunction occurs in Alzheimer's disease (AD). The authors show that in a mouse model of AD, loss of dopaminergic neurons in the ventral tegmental area, but not the substantia nigra, occurs at early pre-plaque stages, and may contribute to impaired cognition and reward processing.

Echinacoside ameliorates the memory impairment and cholinergic deficit induced by amyloid beta peptides via the inhibition of amyloid deposition and toxicology

This study investigates the role of the amyloid cascade and central neuronal function on the protective effects of echinacoside in amyloid β peptide 1-42 (Aβ 1-42)-treated SH-SY5Y cells and an Aβ 1-42-infused rat.

Olfactory Ensheathing Cell-Conditioned Medium Reverts Aβ25-35-Induced Oxidative Damage in SH-SY5Y Cells by Modulating the Mitochondria-Mediated Apoptotic Pathway

Olfactory ensheathing cells (OECs) are a type of glia from the mammalian olfactory system, with neuroprotective and regenerative properties. β-Amyloid peptides are a major component of the senile plaques characteristic of the Alzheimer brain. The amyloid beta (Aβ) precursor protein is cleaved to amyloid peptides, and Aβ_25-35 is regarded to be the functional domain of Aβ, responsible for its neurotoxic properties. It has been reported that Aβ_25-35 triggers reactive oxygen species (ROS)-mediated oxidative damage, altering the structure and function of mitochondria, leading to the activation of the mitochondrial intrinsic apoptotic pathway. Our goal is to investigate the effects of OECs on the toxicity of aggregated Aβ_25-35, in human neuroblastoma SH-SY5Y cells. For such purpose, SH-SY5Y cells were incubated with Aβ_25-35 and OEC-conditioned medium (OECCM). OECCM promoted the cell viability and reduced the apoptosis, and decreased the intracellular ROS and the lipid peroxidation. In the presence of OECCM, mRNA and protein levels of antioxidant enzymes (SOD1 and SOD2) were upregulated. Concomitantly, OECCM decreased mRNA and the protein expression levels of cytochrome c, caspase-9, caspase-3, and Bax in SH-SY5Y cells, and increased mRNA and the protein expression level of Bcl-2. However, OECCM did not alter intracellular Ca²⁺ concentration in SH-SY5Y cells. Taken together, our data suggest that OECCM ameliorates Aβ_25-35-induced oxidative damage in neuroblastoma SH-SY5Y cells by inhibiting the mitochondrial intrinsic pathway. These data provide new insights into the functional actions of OECCM on oxidative stress-induced cell damage.

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.

Amyloid-β peptide absence in short term effects on kinase activity of energy metabolism in mice hippocampus and cerebral cortex

Considering that Alzheimer's disease is a prevalent neurodegenerative disease worldwide, we investigated the activities of three key kinases: creatine kinase, pyruvate kinase and adenylate kinase in the hippocampus and cerebral cortex in Alzheimer's disease model. Male adult Swiss mice received amyloid-β or saline. One day after, mice were treated with blank nanocapsules (17 ml/kg) or meloxicam-loaded nanocapsules (5 mg/kg) or free meloxicam (5 mg/kg). Treatments were performed on alternating days, until the end of the experimental protocol. In the fourteenth day, kinases activities were performed. Amyloid-β did not change the kinases activity in the hippocampus and cerebral cortex of mice. However, free meloxicam decrease the creatine kinase activity in mitochondrial-rich fraction in the group induced by amyloid-β, but for the cytosolic fraction, it has raised in the activity of pyruvate kinase activity in cerebral cortex. Further, meloxicam-loaded nanocapsules administration reduced adenylate kinase activity in the hippocampus of mice injected by amyloid-β. In conclusion we observed absence in short-term effects in kinases activities of energy metabolism in mice hippocampus and cerebral cortex using amyloid-β peptide model. These findings established the foundation to further study the kinases in phosphoryltransfer network changes observed in the brains of patients post-mortem with Alzheimer's disease.

SOD3 Ameliorates Aβ25-35-Induced Oxidative Damage in SH-SY5Y Cells by Inhibiting the Mitochondrial Pathway

This study was designed to investigate the protective effects of extracellular superoxide dismutase (SOD3) against amyloid beta (Aβ_25-35)-induced damage in human neuroblastoma SH-SY5Y cells and to elucidate the mechanisms responsible for this beneficial effect. SH-SY5Y cells overexpressing SOD3 were generated by adenoviral vector-mediated infection and Aβ_25-35 was then added to the cell culture system to establish an in vitro model of oxidative stress. Cell viability, the generation of intracellular reactive oxygen species (ROS), the expression and activity of antioxidant enzymes, the levels of lipid peroxidation malondialdehyde (MDA), the expression of mitochondrial apoptosis-related genes and calcium images were examined. Following Aβ_25-35 exposure, SOD3 overexpression promoted the survival of SH-SY5Y cells, decreased the production of ROS, decreased MDA and calcium levels, and decreased cytochrome c, caspase-3, caspase-9 and Bax gene expression. Furthermore, SOD3 overexpression increased the expression and activity of antioxidant enzyme genes and Bcl-2 expression. Together, our data demonstrate that SOD3 ameliorates Aβ_25-35-induced oxidative damage in neuroblastoma SH-SY5Y cells by inhibiting the mitochondrial pathway. These data provide new insights into the functional actions of SOD3 on oxidative stress-induced cell damage.

Piromelatine ameliorates memory deficits associated with chronic mild stress-induced anhedonia in rats

RATIONALE

Previous studies have demonstrated that piromelatine (a melatonin and serotonin 5-HT1A and 5-HT1D agonist) exerts an antidepressant activity in rodent models of acute stress and improves cognitive impairments in a rat model of Alzheimer's disease (AD). However, the role of piromelatine in chronic stress-induced memory dysfunction remains unclear.

OBJECTIVE

The aim of this study was to determine whether piromelatine ameliorates chronic mild stress (CMS)-induced memory deficits and explore the underlying mechanisms.

METHODS

Rats were exposed randomly to chronic mild stressors for 7 weeks to induce anhedonia (reflected by a significant decrease in sucrose intake), which was used to select rats vulnerable (CMS-anhedonic, CMSA) or resistant (CMS-resistant, CMSR) to stress. Piromelatine (50 mg/kg) was administered daily during the last 2 weeks of CMS. The tail suspension and forced swimming tests were adopted to further characterize vulnerable and resilient rats. The Y-maze and novel object recognition (NOR) tests were used to evaluate memory performance. Brain-derived neurotrophic factor (BDNF), cAMP response element-binding protein (CREB), phosphorylated CREB (pCREB), and cytogenesis were measured in the hippocampus.

RESULTS

We found that only CMSA rats displayed significant increases in immobility time in the tail suspension and forced swimming tests; memory deficits in the Y-maze and NOR tests; significant decreases in hippocampal BDNF, CREB, and pCREB expression; and cytogenesis. All these anhedonia-associated effects were reversed by piromelatine.

CONCLUSIONS

Piromelatine ameliorates memory deficits associated with CMS-induced anhedonia in rats and this effect may be mediated by restoring hippocampal BDNF, CREB, and cytogenesis deficits.

Effects of HIV/TAT protein expression and chronic selegiline treatment on spatial memory, reversal learning and neurotransmitter levels in mice

Neurotoxic viral protein TAT may contribute to deficits in dopaminergic and cognitive function in individuals infected with human immunodeficiency virus. Transgenic mice with brain-specific doxycycline-induced TAT expression (TAT+, TAT- control) show impaired cognition. However, previously reported TAT-induced deficits in reversal learning may be compromised by initial learning deficits. We investigated the effects of TAT expression on memory retention/recall and reversal learning, and neurotransmitter function. We also investigated if TAT-induced effects can be reversed by improving dopamine function with selegiline, a monoamine oxidase inhibitor. Mice were tested in the Barnes maze and TAT expression was induced after the task acquisition. Selegiline treatment continued throughout behavioral testing. Dopamine, serotonin and glutamate tissue levels in the prefrontal/orbitofrontal cortex, hippocampus and caudate putamen were measured using high performance liquid chromatography. Neither TAT expression nor selegiline altered memory retention. On day 2 of reversal learning testing, TAT+ mice made fewer errors and used more efficient search strategies than TAT- mice. TAT expression decreased dopamine turnover in the caudate putamen, increased serotonin turnover in the hippocampus and tended to increase the conversion of glutamate to glutamine in all regions. Selegiline decreased dopamine and serotonin metabolism in all regions and increased glutamate levels in the caudate putamen. In the absence of impaired learning, TAT expression does not impair spatial memory retention/recall, and actually facilitates reversal learning. Selegiline-induced increases in dopamine metabolism did not affect cognitive function. These findings suggest that TAT-induced alterations in glutamate signaling, but not alterations in monoamine metabolism, may underlie the facilitation of reversal learning.

Water-soluble ferulic acid derivatives improve amyloid-β-induced neuronal cell death and dysmnesia through inhibition of amyloid-β aggregation

Ferulic acid (FA) has been reported to exhibit protective effects against amyloid-β (Aβ)-induced neurodegeneration in vitro and in vivo. Recently, we developed two water-soluble FA derivatives: 1-feruloyl glycerol and 1-feruloyl diglycerol. In this study, we examined the neuroprotective effects of these water-soluble FA derivatives on Aβ-induced neurodegeneration both in vitro and in vivo. FA and water-soluble FA derivatives inhibited Aβ aggregation and destabilized pre-aggregated Aβ to a similar extent. Furthermore, water-soluble FA derivatives, as well as FA, inhibited Aβ-induced neuronal cell death in cultured neuronal cells. In in vivo experiments, oral administration of water-soluble FA derivatives to mice improved Aβ-induced dysmnesia assessed by contextual fear conditioning test and protected hippocampal neurons against Aβ-induced neurotoxicity. This study provides useful evidence suggesting that water-soluble FA derivatives are expected to be effective neuroprotective agents.

Propargylamine as functional moiety in the design of multifunctional drugs for neurodegenerative disorders: MAO inhibition and beyond

Much progress has been made in designing analogues that can potentially confer neuroprotection against debilitating neurodegenerative disorders, yet the multifactorial pathogenesis of this cluster of diseases remains a stumbling block for the successful design of an 'ultimate' drug. However, with the growing popularity of the "one drug, multiple targets" paradigm, many researchers have successfully synthesized and evaluated drug-like molecules incorporating a propargylamine function that shows potential to serve as multifunctional drugs or multitarget-directed ligands. It is the aim of this review to highlight the reported activities of these propargylamine derivatives and their prospect to serve as drug candidates for the treatment of neurodegenerative disorders.

EPPS rescues hippocampus-dependent cognitive deficits in APP/PS1 mice by disaggregation of amyloid-β oligomers and plaques

Alzheimer's disease (AD) is characterized by the transition of amyloid-β (Aβ) monomers into toxic oligomers and plaques. Given that Aβ abnormality typically precedes the development of clinical symptoms, an agent capable of disaggregating existing Aβ aggregates may be advantageous. Here we report that a small molecule, 4-(2-hydroxyethyl)-1-piperazinepropanesulphonic acid (EPPS), binds to Aβ aggregates and converts them into monomers. The oral administration of EPPS substantially reduces hippocampus-dependent behavioural deficits, brain Aβ oligomer and plaque deposits, glial γ-aminobutyric acid (GABA) release and brain inflammation in an Aβ-overexpressing, APP/PS1 transgenic mouse model when initiated after the development of severe AD-like phenotypes. The ability of EPPS to rescue Aβ aggregation and behavioural deficits provides strong support for the view that the accumulation of Aβ is an important mechanism underlying AD.

Amyloid-beta deposits are a pathological hallmark of Alzheimer's disease, and have previously been targeted in immunisation therapies. Here, the authors show that oral administration of the small molecule EPPS reduces Aß plaque and oligomer load in APP/PS1 mice and improves learning and memory performance.

Protective role of caffeic acid in an Aβ25-35-induced Alzheimer's disease model

BACKGROUND/OBJECTIVES

Alzheimer's disease (AD) is characterized by deficits in memory and cognitive functions. The accumulation of amyloid beta peptide (Aβ) and oxidative stress in the brain are the most common causes of AD.

MATERIALS/METHODS

Caffeic acid (CA) is an active phenolic compound that has a variety of pharmacological actions. We studied the protective abilities of CA in an Aβ_25-35-injected AD mouse model. CA was administered at an oral dose of 10 or 50 mg/kg/day for 2 weeks. Behavioral tests including T-maze, object recognition, and Morris water maze were carried out to assess cognitive abilities. In addition, lipid peroxidation and nitric oxide (NO) production in the brain were measured to investigate the protective effect of CA in oxidative stress.

RESULTS

In the T-maze and object recognition tests, novel route awareness and novel object recognition were improved by oral administration of CA compared with the Aβ_25-35-injected control group. These results indicate that administration of CA improved spatial cognitive and memory functions. The Morris water maze test showed that memory function was enhanced by administration of CA. In addition, CA inhibited lipid peroxidation and NO formation in the liver, kidney, and brain compared with the Aβ_25-35-injected control group. In particular, CA 50 mg/kg/day showed the stronger protective effect from cognitive impairment than CA 10 mg/kg/day.

CONCLUSIONS

The present results suggest that CA improves Aβ_25-35-induced memory deficits and cognitive impairment through inhibition of lipid peroxidation and NO production.

Reversal by aqueous extracts of Cistanche tubulosa from behavioral deficits in Alzheimer's disease-like rat model: relevance for amyloid deposition and central neurotransmitter function

Background

Cistanche tubulosa (Schenk) R. Wight (CT) is commonly used to treat forgetfulness by traditional Chinese physicians. This study presents the ameliorating effects of CT extract which was quantified with three phenylpropanoid glycosides in Alzheimer’s disease (AD)-like rat model.

Methods

Amyloid β peptide 1-42 (Aβ 1-42) intracisternally infused to rats by osmotic pump (Alzet 2002) was used as an AD-like rat model. The major pathological makers were measured including Aβ 1-42 immunohistochemical stain, behavioral tests (inhibitory avoidance task and Morris water maze) and central neurotransmitter functions.

Results

Aβ 1-42 caused the cognitive deficits, the increase in the amyloid deposition and acetylcholinesterase activities, and the decrease in the levels of brain’s acetylcholine and dopamine. Daily administration of CT extract throughout Aβ 1-42 infusion periods ameliorated the cognitive deficits, decreased amyloid deposition and reversed cholinergic and hippocampal dopaminergic dysfunction caused by Aβ 1-42. Donepezil also ameliorated the cognitive dysfunction, but only blocked the amyloid deposition and cholinergic dysfunction caused by Aβ 1-42.

Conclusions

We suggest that CT extract, containing enough echinacoside and acteoside, ameliorated the cognitive dysfunction caused by Aβ 1-42 via blocking amyloid deposition, reversing cholinergic and hippocampal dopaminergic neuronal function.

Behavioral assays with mouse models of Alzheimer's disease: practical considerations and guidelines

In Alzheimer's disease (AD) basic research and drug discovery, mouse models are essential resources for uncovering biological mechanisms, validating molecular targets and screening potential compounds. Both transgenic and non-genetically modified mouse models enable access to different types of AD-like pathology in vivo. Although there is a wealth of genetic and biochemical studies on proposed AD pathogenic pathways, as a disease that centrally features cognitive failure, the ultimate readout for any interventions should be measures of learning and memory. This is particularly important given the lack of knowledge on disease etiology - assessment by cognitive assays offers the advantage of targeting relevant memory systems without requiring assumptions about pathogenesis. A multitude of behavioral assays are available for assessing cognitive functioning in mouse models, including ones specific for hippocampal-dependent learning and memory. Here we review the basics of available transgenic and non-transgenic AD mouse models and detail three well-established behavioral tasks commonly used for testing hippocampal-dependent cognition in mice - contextual fear conditioning, radial arm water maze and Morris water maze. In particular, we discuss the practical considerations, requirements and caveats of these behavioral testing paradigms.

Monoamine oxidase inhibitors: promising therapeutic agents for Alzheimer's disease (Review)

Activated monoamine oxidase (MAO) has a critical role in the pathogenesis of Alzheimer's disease (AD), including the formation of amyloid plaques from amyloid β peptide (Aβ) production and accumulation, formation of neurofibrillary tangles, and cognitive impairment via the destruction of cholinergic neurons and disorder of the cholinergic system. Several studies have indicated that MAO inhibitors improve cognitive deficits and reverse Aβ pathology by modulating proteolytic cleavage of amyloid precursor protein and decreasing Aβ protein fragments. Thus, MAO inhibitors may be considered as promising therapeutic agents for AD.

Silymarin effect on amyloid-β plaque accumulation and gene expression of APP in an Alzheimer's disease rat model

Background

The deposition of amyloid peptides is associated with Alzheimer’s disease (AD). These amyloid peptides are derived from the amyloid protein precursor (APP). Silymarin, a standardized extract of milk thistle, which is currently used in liver diseases, may be effective in the inhibition of amyloid formation. However, its effect has not been assessed on APP expression.

Results

In this study, first, the effect of silymarin was examined on the passive avoidance learning in a rat model of AD. This model was induced by the intracerebroventricular injection of Aβ peptide (Aβ_1–42) in Wistar rats. Rats were treated with 70 and 140 mg/kgof the extract, once a day, for 4 weeks. Memory function that was evaluated in a shuttle-cage test, showed improvement upon administration of this extract. Brain amyloid plaques had also decreased upon administration of the extract. Furthermore, APP gene expression was compared in treated and untreated groups. The result showed that silymarin was able to suppress APP expression.

Conclusion

Our results are in accordance with the in vitro tests concerning the positive antiamyloidogenic property of the main component of silymarin, namely silibinin. We suggest that the beneficial effect of sylimarin in the AD model is related to its capacity to disaggregate amyloid plaques and to suppress APP expression. Considering the limited side effects of silymarin, this compound could be of use in AD therapy.

Evaluation of cognitive behaviors in young offspring of C57BL/6J mice after gestational nicotine exposure during different time-windows

Gestational nicotine exposure is associated with cognitive abnormalities in young offspring. However, practical strategies for prevention or treatment of impaired cognitive behaviors of offspring are not available due to the lack of systematic investigation of underlying mechanism. Therefore, this study aimed at examining the effects of gestational and/or perinatal nicotine exposure (GPNE) on cognitive behaviors in offspring of C57BL/6J mice to provide systematic behavioral data. Pregnant mice were exposed to nicotine via sweetened drinking water during six time-windows, including gestational day 0 to day 13 (G0-G13), G14-postnatal day 0 (P0), G0-P0, G14-P7, G0-P7, and P0-P7. During P42-P56 days, both male and female offspring were given a battery of behavioral tests. Depending on the time of exposure, GPNE impaired working memory, object-based attention, and prepulse inhibition in male and female offspring to different extents. Nicotine exposure during G14-P0 also decreased norepinephrine turnover in the prefrontal cortex on P28 and P56. Overall results indicate that nicotine exposure during any time-windows of development impairs cognitive behaviors in offspring, and suggest that certain time-windows, e.g., G14-P0, should be selected for further studies on the underlying neurochemical or molecular mechanisms.