Donepezil ameliorates Aβ pathology but not tau pathology in 5xFAD mice

Enhanced prefrontal nicotinic signaling as evidence of active compensation in Alzheimer's disease models

BACKGROUND

Cognitive reserve allows for resilience to neuropathology, potentially through active compensation. Here, we examine ex vivo electrophysiological evidence for active compensation in Alzheimer's disease (AD) focusing on the cholinergic innervation of layer 6 in prefrontal cortex. Cholinergic pathways are vulnerable to neuropathology in AD and its preclinical models, and their modulation of deep layer prefrontal cortex is essential for attention and executive function.

METHODS

We functionally interrogated cholinergic modulation of prefrontal layer 6 pyramidal neurons in two preclinical models: a compound transgenic AD mouse model that permits optogenetically-triggered release of endogenous acetylcholine and a transgenic AD rat model that closely recapitulates the human trajectory of AD. We then tested the impact of therapeutic interventions to further amplify the compensated responses and preserve the typical kinetic profile of cholinergic signaling.

RESULTS

In two AD models, we found potentially compensatory upregulation of functional cholinergic responses above non-transgenic controls after onset of pathology. To identify the locus of this enhanced cholinergic signal, we dissected key pre- and post-synaptic components with pharmacological strategies. We identified a significant and selective increase in post-synaptic nicotinic receptor signalling on prefrontal cortical neurons. To probe the additional impact of therapeutic intervention on the adapted circuit, we tested cholinergic and nicotinic-selective pro-cognitive treatments. Inhibition of acetylcholinesterase further enhanced endogenous cholinergic responses but greatly distorted their kinetics. Positive allosteric modulation of nicotinic receptors, by contrast, enhanced endogenous cholinergic responses and retained their rapid kinetics.

CONCLUSIONS

We demonstrate that functional nicotinic upregulation occurs within the prefrontal cortex in two AD models. Promisingly, this nicotinic signal can be further enhanced while preserving its rapid kinetic signature. Taken together, our work suggests that compensatory mechanisms are active within the prefrontal cortex that can be harnessed by nicotinic receptor positive allosteric modulation, highlighting a new direction for cognitive treatment in AD neuropathology.

Modulation of Amyloid and Tau Aggregation to Alleviate Cognitive Impairment in a Transgenic Mouse Model of Alzheimer's Disease

Aggregation of misfolded amyloid-β (Aβ) and hyperphosphorylated tau proteins to plaques and tangles, respectively, is the major drug target of Alzheimer's disease (AD), as the former is an onset biomarker and the latter is associated with neurodegeneration. Thus, we report a small molecule drug candidate, DN5355, with a dual-targeting function toward aggregates of both Aβ and tau. DN5355 was selected through a series of four screenings assessing 52 chemicals for their functions to inhibit and reverse the aggregation of Aβ and tau by utilizing thioflavin T. When orally administered to AD transgenic mouse model 5XFAD, DN5355 significantly reduced cerebral Aβ plaques and hyperphosphorylated tau tangles. In Y-maze spontaneous alteration and contextual fear conditioning tests, 5XFAD mice showed amelioration of cognitive deficits upon the oral administration of DN5355.

Tailored Melatonin- and Donepezil-Based Hybrids Targeting Pathognomonic Changes in Alzheimer's Disease: An In Vitro and In Vivo Investigation

A plethora of pathophysiological events have been shown to play a synergistic role in neurodegeneration, revealing multiple potential targets for the pharmacological modulation of Alzheimer's disease (AD). In continuation to our previous work on new indole- and/or donepezil-based hybrids as neuroprotective agents, the present study reports on the beneficial effects of lead compounds of the series on key pathognomonic features of AD in both cellular and in vivo models. An enzyme-linked immunosorbent assay (ELISA) was used to evaluate the anti-fibrillogenic properties of 15 selected derivatives and identify quantitative changes in the formation of neurotoxic β-amyloid (Aβ42) species in human neuronal cells in response to treatment. Among the most promising compounds were 3a and 3c, which have recently shown excellent antioxidant and anticholinesterase activities, and, therefore, have been subjected to further in vivo investigation in mice. An acute toxicity study was performed after intraperitoneal (i.p.) administration of both compounds, and 1/10 of the LD50 (35 mg/kg) was selected for subacute treatment (14 days) with scopolamine in mice. Donepezil (DNPZ) and/or galantamine (GAL) were used as reference drugs, aiming to establish any pharmacological superiority of the multifaceted approach in battling hallmark features of neurodegeneration. Our promising results give first insights into emerging disease-modifying strategies to combine multiple synergistic activities in a single molecule.

Detecting the effect of genetic diversity on brain composition in an Alzheimer's disease mouse model

Alzheimer's disease (AD) is broadly characterized by neurodegeneration, pathology accumulation, and cognitive decline. There is considerable variation in the progression of clinical symptoms and pathology in humans, highlighting the importance of genetic diversity in the study of AD. To address this, we analyze cell composition and amyloid-beta deposition of 6- and 14-month-old AD-BXD mouse brains. We utilize the analytical QUINT workflow- a suite of software designed to support atlas-based quantification, which we expand to deliver a highly effective method for registering and quantifying cell and pathology changes in diverse disease models. In applying the expanded QUINT workflow, we quantify near-global age-related increases in microglia, astrocytes, and amyloid-beta, and we identify strain-specific regional variation in neuron load. To understand how individual differences in cell composition affect the interpretation of bulk gene expression in AD, we combine hippocampal immunohistochemistry analyses with bulk RNA-sequencing data. This approach allows us to categorize genes whose expression changes in response to AD in a cell and/or pathology load-dependent manner. Ultimately, our study demonstrates the use of the QUINT workflow to standardize the quantification of immunohistochemistry data in diverse mice, - providing valuable insights into regional variation in cellular load and amyloid deposition in the AD-BXD model.

Optimizing drug-like properties of selective butyrylcholinesterase inhibitors for cognitive improvement: Enhancing aqueous solubility by disrupting molecular plane

Most recently, worldwide interest in butyrylcholinesterase (BChE) as a potential target for treating Alzheimer's disease (AD) has increased. In this study, the previously obtained selective BChE inhibitors with benzimidazole-oxadiazole scaffold were further structurally modified to increase their aqueous solubility and pharmacokinetic (PK) characteristics. S16-1029 showed improved solubility (3280 μM, upgraded by 14 times) and PK parameters, including plasma exposure (AUC0-inf = 1729.95 ng/mL*h, upgraded by 2.6 times) and oral bioavailability (Fpo = 48.18%, upgraded by 2 times). S16-1029 also displayed weak or no inhibition against Cytochrome P450 (CYP450) and human ether a-go-go related gene (hERG) potassium channel. In vivo experiments on tissue distribution revealed that S16-1029 could cross the blood-brain barrier (BBB) and reach the central nervous system (CNS). In vivo cognitive improvement efficacy and good in vitro target inhibitory activity (eqBChE IC50 = 11.35 ± 4.84 nM, hBChE IC50 = 48.1 ± 11.4 nM) were also assured. The neuroprotective effects against several AD pathology characteristics allowed S16-1029 to successfully protect the CNS of progressed AD patients. According to the findings of this study, altering molecular planarity might be a viable strategy for improving the drug-like property of CNS-treating drugs.

Star power: harnessing the reactive astrocyte response to promote remyelination in multiple sclerosis

Astrocytes are indispensable for central nervous system development and homeostasis. In response to injury and disease, astrocytes are integral to the immunological- and the, albeit limited, repair response. In this review, we will examine some of the functions reactive astrocytes play in the context of multiple sclerosis and related animal models. We will consider the heterogeneity or plasticity of astrocytes and the mechanisms by which they promote or mitigate demyelination. Finally, we will discuss a set of biomedical strategies that can stimulate astrocytes in their promyelinating response.

Urolithin A Inhibits Anterior Basolateral Amygdala to Ventral Hippocampal CA1 Circuit to Ameliorate Amyloid-β-Impaired Social Ability

Background

Anxiety and social withdrawal are highly prevalent among patients with Alzheimer's disease (AD). However, the neural circuit mechanisms underlying these symptoms remain elusive, and there is a need for effective prevention strategies.

Objective

This study aims to elucidate the neural circuitry mechanisms underlying social anxiety in AD.

Methods

We utilized 5xFAD mice and conducted a series of experiments including optogenetic manipulation, Tandem Mass Tag-labeled proteome analysis, behavioral assessments, and immunofluorescence staining.

Results

In 5xFAD mice, we observed significant amyloid-β (Aβ) accumulation in the anterior part of basolateral amygdala (aBLA). Behaviorally, 6-month-old 5xFAD mice displayed excessive social avoidance during social interaction. Concurrently, the pathway from aBLA to ventral hippocampal CA1 (vCA1) was significantly activated and exhibited a disorganized firing patterns during social interaction. By optogenetically inhibiting the aBLA-vCA1 pathway, we effectively improved the social ability of 5xFAD mice. In the presence of Aβ accumulation, we identified distinct changes in the protein network within the aBLA. Following one month of administration of Urolithin A (UA), we observed significant restoration of the abnormal protein network within the aBLA. UA treatment also attenuated the disorganized firings of the aBLA-vCA1 pathway, leading to an improvement in social ability.

Conclusions

The aBLA-vCA1 circuit is a vulnerable pathway in response to Aβ accumulation during the progression of AD and plays a crucial role in Aβ-induced social anxiety. Targeting the aBLA-vCA1 circuit and UA administration are both effective strategies for improving the Aβ-impaired social ability.

The function of astrocytes and their role in neurological diseases

Astrocytes have countless links with neurons. Previously, astrocytes were only considered a scaffold of neurons; in fact, astrocytes perform a variety of functions, including providing support for neuronal structures and energy metabolism, offering isolation and protection and influencing the formation, function and elimination of synapses. Because of these functions, astrocytes play an critical role in central nervous system (CNS) diseases. The regulation of the secretiory factors, receptors, channels and pathways of astrocytes can effectively inhibit the occurrence and development of CNS diseases, such as neuromyelitis optica (NMO), multiple sclerosis, Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease. The expression of aquaporin 4 in AS is directly related to NMO and indirectly involved in the clearance of Aβ and tau proteins in AD. Connexin 43 has a bidirectional effect on glutamate diffusion at different stages of stroke. Interestingly, astrocytes reduce the occurrence of PD through multiple effects such as secretion of related factors, mitochondrial autophagy and aquaporin 4. Therefore, this review is focused on the structure and function of astrocytes and the correlation between astrocytes and CNS diseases and drug treatment to explore the new functions of astrocytes with the astrocytes as the target. This, in turn, would provide a reference for the development of new drugs to protect neurons and promote the recovery of nerve function.

Ginkgolide attenuates memory impairment and neuroinflammation by suppressing the NLRP3/caspase-1 pathway in Alzheimer's disease

The NLRP3 inflammasome is involved in the neuroinflammatory pathway of Alzheimer's disease (AD). The aim of this study is to explore the roles and underlying mechanisms of ginkgolide (Baiyu®) on amyloid precursor protein (APP)/presenilin 1 (PS1) transgenic mice and a murine microglial cell line, BV-2. In the present study, the APP/PS1 mice were administered with ginkgolide, followed by a Morris water maze test. The mice were then euthanized to obtain brain tissue for histological and Aβ analysis. Additionally, BV-2 cells were pretreated with ginkgolide and then incubated with Aβ1-42 peptide. NLRP3, ASC, and caspase-1 mRNA and protein expression in brain tissue of mice and BV-2 cells were quantified by real-time PCR and western blotting, as well as reactive oxygen species (ROS) production, interleukin (IL)-1β and IL-18 levels by lucigenin technique and ELISA. Compared with the APP/PS1 mice, ginkgolide-treated mice demonstrated the shortened escape latency, reduced plaques, less inflammatory cell infiltration and neuron loss in the hippocampi of APP/PS1 mice. The levels of NLRP3, ASC, caspase-1, ROS, IL-1β, and IL-18 were also decreased in the brain tissue of APP/PS1 mice or Aβ1-42-treated BV-2 cells following ginkgolide treatment. Ginkgolide exerted protective effects on AD, at least partly by inactivating the NLRP3/caspase-1 pathway.

The past and present of therapeutic strategy for Alzheimer's diseases: potential for stem cell therapy

Alzheimer's disease (AD), a progressive neurodegenerative disease characterized by cognitive dysfunction and neuropsychiatric symptoms, is the most prevalent form of dementia among the elderly. Amyloid aggregation, tau hyperphosphorylation, and neural cell loss are the main pathological features. Various hypotheses have been proposed to explain the development of AD. Some therapeutic agents have shown clinical benefits in patients with AD; however, many of these agents have failed. The degree of neural cell loss is associated with the severity of AD. Adult neurogenesis, which governs cognitive and emotional behaviors, occurs in the hippocampus, and some research groups have reported that neural cell transplantation into the hippocampus improves cognitive dysfunction in AD model mice. Based on these clinical findings, stem cell therapy for patients with AD has recently attracted attention. This review provides past and present therapeutic strategies for the management and treatment of AD.

Polyphenols from Conyza dioscoridis (L.) ameliorate Alzheimer’s disease- like alterations through multi-targeting activities in two animal models

Background

Recent investigations suggested that anticancer agents may inhibit the progression of Alzheimer's disease (AD) pathology. Conyza dioscoridis (L.) was demonstrated to have anticancer, antioxidant, anti-inflammatory and antidiabetic effects. This study was carried out to investigate the efficacy of polyphenols from Conyza dioscoridis (L.) extract (PCDE) on AD.

Methods

Impacts of 3 doses of PCDE and donepezil, a reference drug, on the features of Alzheimer's disease in two animal models were investigated.

Results

PCDE ameliorated the memory and learning impairment shown in rats following a single dose of scopolamine (scopolamine model) or 17 weeks of high-fat/high-fructose(HF/Hfr) diet coupled with a single dose of streptozotocin, (25 mg/kg) (T2D model). They reduced significantly the high hippocampal cholinesterase activity in the two models of rats. Administration of PCDE for 8 weeks in the T2D model showed a significant reduction in hippocampal GSK-3β, caspase-3 activity and increase in the inhibited glutamate receptor expression (AMPA GluR1 subunit and NMDA receptor subunits NR1, NR2A, NR2B). A significant reduction of HOMA-insulin resistance and serum hypercholesterolemia was observed. The Tau hyperphosphorylation and Aβ 1–42 generation in the hippocampal of T2D rats were significantly decreased by PCDE. Modulation of the oxidative stress markers, (rise in GH and SOD; decrease in MDA levels) and a significant reduction of TNF-α and IL-1β in the hippocampus of T2D rats treated by PCDE extract were important findings in this study. The highest dose tested was 4% of the highest safe dose.

Conclusion

Our study suggests that PCDE is multi-targeting agent with multiple beneficial activities in combating features of AD. This study may provide a novel therapeutic strategy for AD treatment that warrants clinical studies.