Evaluation and targeting of amyloid precursor protein (APP)/amyloid beta (Aβ) axis in amyloidogenic and non-amyloidogenic pathways: A time outside the tunnel

In Alzheimer disease (AD), amyloid precursor protein (APP) and production of amyloid beta (Aβ) which is generated by amyloidogenic pathway is implicated in neurotoxicity and neuronal cell deaths. However, physiological Aβ level is essential to improves neuronal survival, attenuates neuronal apoptosis and has neuroprotective effect. In addition, physiological APP level has neurotrophic effect on the central nervous system (CNS). APP has a critical role in the brain growth and development via activation of long-term potentiation (LTP) and acceleration of neurite outgrowth. Moreover, APP is cleaved by α secretase to form a neuroprotective soluble APP alpha (sAPPα) in non-amyloidogenic pathway. Consequently, this mini-review purposes to highlight the possible beneficial role of APP and Aβ. In addition, this mini-review discussed the modulation of APP processing and Aβ production.

Ketamine promotes the amyloidogenic pathway by regulating endosomal pH

Ketamine is an anesthetic and addictive drug that can cause cognitive dysfunction and neuroinflammation. Studies have shown that carboxy-terminal fragment derived from β-secretase (CTF-β) and amyloid beta (Aβ), the amyloidogenic products of amyloid precursor protein (APP), can also induce neuroinflammation and impair cognitive function. However, it remains unclear whether ketamine regulates the amyloidogenic pathway. In the endosome, APP is cleaved by beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), whose activity is influenced by pH. Endosomal acidification is mainly regulated by sodium hydrogen exchanger 6 (NHE6), which leaks protons out of endosomes, and vacuolar proton translocating ATPases (V-ATPase), which pump protons into endosomes. Therefore, we hypothesized that ketamine lowers the endosomal pH by reducing the endosomal NHE6 protein level, and this hyperacidification promotes the amyloidogenic pathway. We set up C57BL/6 J mouse models using 10, 20, 40, 80, and 100 mg/kg ketamine administration and SH-SY5Y cell models using 1, 10, 100, and 1000 μM ketamine administration to investigate its effects on the amyloidogenic pathway at different doses. Western blotting results showed that 100 mg/kg ketamine treatment in vivo and 1000 μM ketamine treatment in vitro increased endosomal BACE1 and CTF-β protein levels and reduced endosomal NHE6 and APP protein levels. The endosomal accumulation of BACE1 caused by ketamine administration was also observed using confocal imaging. Moreover, flow cytometry indicated that ketamine treatment lowered the endosomal pH value of SH-SY5Y cells. Later, cells were pretreated with monensin to restore the endosomal pH. Monensin did not affect amyloidogenic-related proteins or NHE6 directly; therefore, ketamine-promoted endosomal amyloidogenic processing and BACE1 accumulation were depleted by restoring endosomal acidity through monensin pretreatment. Finally, knockdown of NHE6 promoted the amyloidogenic pathway similarly and prevented further enhancement by ketamine. These results indicated that the effects of ketamine on the amyloidogenic pathway were dependent on the reduction of NHE6 and endosomal pH.

Protective effects of octylseleno-xylofuranoside in a streptozotocin-induced mouse model of Alzheimer's disease

Octylseleno-xylofuranoside (OSX) is an organic selenium compound which has previously shown antioxidant and antidepressant-like activities, trough the modulation of monoaminergic system and synaptic plasticity pathways. Since recent studies have suggested Major Depressive Disorder (MDD) as a potential risk factor or condition that precedes and correlates with Alzheimer's Disease (AD), this study aimed to evaluate the protective effects of OSX in an AD mouse model induced by intracerebroventricular injection of streptozotocin (STZ). To address this protective effect, mice were pre-treated with intragastrical OSX (0.1 mg/kg) or vehicle for 20 days. After the pre-treatment, mice were submitted to two alternated intracerebroventricular infusions of STZ (days 21 and 23) or saline. 15 days after the last STZ injection, cognitive and memory skills of the treated mice were evaluated on object recognition test, Y-maze, stepdown passive avoidance and social recognition paradigms. Added to that, measurements of oxidative stress markers and gene expression were evaluated in brain samples of the same mice groups. Mice pre-treatment with OSX protected mice from cognitive and memory decline elicited by STZ. This effect was attributed to the prevention of lipid peroxidation and modulation of acetylcholinesterase and monoamine oxidase activities in cerebral cortices and hippocampi by OSX treatment. Furthermore, OSX treatment demonstrated reduction of amyloidogenic pathway genes expression when compared to the control groups. Besides that, OSX treatment showed no hepatic and renal toxicity in the protocol used for treatment. Considering the antidepressant-like effect of OSX, together with the ability to prevent memory and cognitive impairment, this new compound may be an interesting strategy for targeting the comorbidity between MDD and AD, in a multitarget drug paradigm.

Developmental Perfluorooctanesulfonic acid (PFOS) exposure as a potential risk factor for late-onset Alzheimer's disease in CD-1 mice and SH-SY5Y cells

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that accounts for approximately 60-80% of dementia cases worldwide and is characterized by an accumulation of extracellular senile plaques composed of β-amyloid (Aβ) peptide and intracellular neurofibrillary tangles (NFTs) containing hyperphosphorylated tau protein. Sporadic or late-onset AD (LOAD) represents 95 % of the AD cases and its etiology does not appear to follow Mendelian laws of inheritance, thus, implicating the role of epigenetic programming and environmental factors. Apolipoprotein allele 4 (ApoE4), the only established genetic risk factor for LOAD, is suggested to accelerate the pathogenesis of AD by increasing tau hyperphosphorylation, inhibiting the clearance of amyloid-β (Aβ), and promoting Aβ aggregation. Perfluorooctanesulfonic acid (PFOS) is a persistent organic pollutant, with potential neurotoxic effects, that poses a major threat to the ecosystem and human health. By employing in vivo and in vitro models, the present study investigated PFOS as a potential risk factor for LOAD by assessing its impact on amyloidogenesis, tau pathology, and rodent behavior. Our behavioral analysis revealed that developmentally exposed male and female mice exhibited a strong trend of increased rearing and significantly increased distance traveled in the open field test. Biochemically, GSK3β and total ApoE were increased following developmental exposure, in vivo. Furthermore, in vitro, low concentrations of PFOS elevated protein levels of APP, tau, and its site-specific phosphorylation. Differentiated SH-SY5Y cells exposed to a series of PFOS concentrations, also, had elevated protein expression of GSK3β. These data suggest that total ApoE is inducible by environmental exposure to PFOS.

Ameliorative effects of astaxanthin on brain tissues of alzheimer's disease-like model: cross talk between neuronal-specific microRNA-124 and related pathways

Alzheimer's disease (AD) is a chronic, progressive, multifactorial, and the most common neurodegenerative disease which causes dementia and mental deterioration in the elderly. The available treatments for AD are not disease-modifying drugs and only provide symptomatic relief. Astaxanthin (ATX), a second-generation antioxidant, is a dark red carotenoid and exhibits the highest antioxidant capacity, anti-inflammatory, neuroprotective, and antiapoptotic effects. In this study, we investigated the therapeutic effect of different doses of ATX on the cerebral cortex and hippocampus of AD-like rats. The AD-like model was induced in rats using hydrated aluminum chloride (AlCl₃.6H₂O) solution that was given orally at a dose of 75 mg/kg daily for 6 weeks. Morris water maze (MWM) behavioral test was performed to confirm the cognitive dysfunction then AD-like rats were orally treated with different doses of ATX (5, 10, and 15 mg/kg) dissolved in dimethyl sulfoxide (DMSO) for six weeks. The results indicated that ATX significantly and dose-dependently improved the performance of AD-like rats treated with ATX during MWM and suppress the accumulation of amyloid β_1-42 and malondialdehyde. Also, significantly inhibit acetylcholinesterase and monoamine oxidase activities and the expression of β-site amyloid precursor protein cleaving enzyme 1 (BACE 1). ATX also significantly elevated the content of acetylcholine, serotonin, and nuclear factor erythroid-2-related factor 2 (Nrf2) and miRNA-124 expression. The effect of ATX treatment was confirmed by histopathological observations using H&E stain and morphometric tissue analysis. From this study, we concluded that ATX may be a promising therapeutic agent for AD through targeting different pathogenic pathways.

Identification of a novel BACE1 inhibitor, timosaponin A-III, for treatment of Alzheimer's disease by a cell extraction and chemogenomics target knowledgebase-guided method

BACKGROUND

Rhizoma Anemarrhenae (RA) has been conventionally used for treatment of Alzheimer's disease (AD) in Traditional Chinese Medicine, and thus, the active components from RA can be screened.

PURPOSE

This research aimed to identify the active components of RA and their targets and further clarify the molecular mechanisms underlying its anti-AD activity.

METHODS

First, the potential active compounds from RA were screened by neurocyte extraction and micro-dialysis methods. Second, the potential targets were predicted by a chemogenomics target knowledgebase and further explored by surface plasmon resonance and enzyme activity assays. Third, the pharmacological effects were evaluated by employing APP/PS1 transgenic mice and SH-SY5Y-APP cells. ELISAs and Western blot analyses were used to evaluate the expression of key molecules in the amyloidogenic and NMDAR/ERK pathways.

RESULTS

Timosaponin A-III (TA-III) was screened and identified as a potential active component for the anti-AD activity, and BACE1 was proven to be a potential high-affinity target. Enzyme kinetic analysis showed that TA-III had strong noncompetitive inhibitory activity against BACE1. The in vitro and in vivo assays indicated that TA-III had pharmacological effects through improving memory impairment, reducing Aβ aggregation via the amyloidogenic pathway and preventing neuronal impairment through downregulating the NMDAR/ERK signaling pathway.

CONCLUSION

TA-III targets BACE1 to reduce Aβ aggregation through down-regulating the NMDAR/ERK pathway for treating AD.

Novel small molecule therapeutic agents for Alzheimer disease: Focusing on BACE1 and multi-target directed ligands

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder that effects 50 million people worldwide. In this review, AD pathology and the development of novel therapeutic agents targeting AD were fully discussed. In particular, common approaches to prevent Aβ production and/or accumulation in the brain including α-secretase activators, specific γ-secretase modulators and small molecules BACE1 inhibitors were reviewed. Additionally, natural-origin bioactive compounds that provide AD therapeutic advances have been introduced. Considering AD is a multifactorial disease, the therapeutic potential of diverse multi target-directed ligands (MTDLs) that combine the efficacy of cholinesterase (ChE) inhibitors, MAO (monoamine oxidase) inhibitors, BACE1 inhibitors, phosphodiesterase 4D (PDE4D) inhibitors, for the treatment of AD are also reviewed. This article also highlights descriptions on the regulator of serotonin receptor (5-HT), metal chelators, anti-aggregants, antioxidants and neuroprotective agents targeting AD. Finally, current computational methods for evaluating the structure-activity relationships (SAR) and virtual screening (VS) of AD drugs are discussed and evaluated.

The amyloid precursor protein (APP) processing as a biological link between Alzheimer's disease and cancer

Aging is a risk factor for several illnesses, such as Alzheimer's Disease and various cancers. However, an inverse correlation between malignancies and Alzheimer's Disease has been suggested. This review addressed the potential role of non-amyloidogenic and amyloidogenic pathways of amyloid precursor protein processing as a relevant biochemical mechanism to clarify this association. Amyloidogenic and non-amyloidogenic pathways have been related to Alzheimer's Disease and certain malignancies, respectively. Several known molecules involved in APP processing, including its regulation and final products, were summarized. Among them some candidate mechanisms emerged, such as extracellular-regulated kinase (Erk) and protein kinase C (PKC). Therefore, the imbalance of APP processing may be involved with the negative correlation between cancer and Alzheimer Disease.