Alzheimer's disease (AD) therapeutics - 2: Beyond amyloid - Re-defining AD and its causality to discover effective therapeutics

Neuroprotective Effects of Vapreotide on Tau Transfection-Induced Neurodegeneration

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by loss of neurons and synapses. The aim of this study was to investigate the effect of somatostatin analogue Vapreotide in an in vitro Alzheimer's model and its effects based on the relationship between somatostatinergic transmission and neurodegenerative functions. In this study, tau transfection was performed using the MAPT gene cloned into the pcDNA3.1 vector and transfection reagent into the SH-SY5Y cell line. In viability experiments using 10 µM Memantine as a positive control, it was observed that Vapreotide at 50 µM (p < 0.0001) and 100 µM (p < 0.05) had a protective effect on cell viability, 100 µM CYN154806 was found to decrease (p < 0.05) cell viability. It was determined that Vapreotide, decreased the expression levels (50 µM-p < 0.001; 100 µM-p < 0.001; 200 µM-p < 0.0001) and phosphorylation of Tau and p-Tau proteins by western blots. With the qRT-PCR method, it was found that Vapreotide, decreased the BAX/BCL2 (50 µM-p < 0.001; 100 µM-p < 0.01; 200 µM-p < 0.001) expression level and decreased the expression level (50 µM-p < 0.01; 100 µM-p < 0.01; 200 µM-p < 0.001) of the APOE4 gene, which constitutes a genetic risk for AD. This study demonstrates a potential therapeutic role for a somatostatin analogue Vapreotide in Alzheimer's disease.

Cerebral Organoids for Modeling of HSV-1-Induced-Amyloid β Associated Neuropathology and Phenotypic Rescue

Herpes simplex virus type I (HSV-1) infection is a potential risk factor involved in the Amyloid β (Aβ) associated neuropathology. However, further understanding of the neuropathological effects of the HSV-1 infection is hampered by the limitations of existing infection models due to the distinct differences between human brains and other mammalians’ brains. Here we generated cerebral organoid models derived from pluripotent stem cells to investigate the HSV-induced Aβ associated neuropathology and the role of antiviral drugs in the phenotypic rescue. Our results identified that the HSV-1-infected cerebral organoids recapitulated Aβ associated neuropathology including the multicellular Aβ deposition, dysregulated endogenous AD mediators, reactive gliosis, neuroinflammation, and neural loss, indicating that cerebral organoids offer an opportunity for modeling the interaction of HSV-1 with the complex phenotypes across the genetic, cellular, and tissue levels of the human Alzheimer’s disease (AD). Furthermore, we identified that two antiviral drugs, namely Ribavirin (RBV) and Valacyclovir (VCV), inhibited HSV-1 replication and rescued the neuropathological phenotypes associated with AD in the HSV-1-infected cerebral organoids, implying their therapeutic potential to slow down the progression of AD. Our study provides a high-fidelity human-relevant in-vitro HSV-1 infection model to reconstitute the multiscale neuropathological features associated with AD and discover therapeutic drug candidates relevant to the AD viral hypothesis.

Gardenia jasminoides J.Ellis extract GJ-4 alleviated cognitive deficits of APP/PS1 transgenic mice

BACKGROUND

Accumulating evidence demonstrates that traditional Chinese medicines that act on multiple targets could effectively treat various multi-etiological diseases, including cerebrovascular diseases, Alzheimer's disease (AD), Parkinson's disease (PD) and so on. Previous studies have shown that crocin richments (GJ-4), Gardenia jasminoides J.Ellis extract, provide neuroprotective effects on cognitive impairments in AD mouse models. However, the mechanism how GJ-4 improves cognition remains still unclear.

PURPOSE

The aim of this study was to uncover the protective effects and underlying mechanism of GJ-4 on PrP-hAβPPswe/PS1^ΔE9 (APP/PS1) transgenic mice.

METHODS

APP/PS1 mice were given GJ-4 (10, 20, and 50 mg/kg), donepezil (5 mg/kg) and memantine (5 mg/kg) orally at eight months of age for 12 consecutive weeks. Morris water maze and novel object recognition were conducted to assess the cognitive ability of mice. The release of inflammatory cytokines was determined by RT-PCR assay, and the pathological features of neurons and microglia were assayed by immunohistochemistry and immunofluorescence assay. The expression of Aβ-related proteins and signaling pathways were determined by Western blot.

RESULTS

The behavioral results revealed that GJ-4 ameliorated the cognitive deficits of APP/PS1 mice measured by Morris water maze and novel object recognition tests. Mechanism studies indicated that GJ-4 significantly decreased β-amyloid (Aβ) level through reducing Aβ production and promoting Aβ degradation. It has been reported that Aβ plaques trigger the hyper-phosphorylation of tau protein in APP/PS1 mice. Consistent with previous studies, hyper-phosphorylation of tau was also occurred in APP/PS1 mice in the present study, and GJ-4 inhibited Tau phosphorylation at different sites. Overwhelming evidence indicates that neuroinflammation stimulated by Aβ and hyperphosphorylated tau is involved in the pathological progression of AD. We found that GJ-4 suppressed neuroinflammatory responses in the brain through regulating phosphatidylinositide 3-kinase/AKT (PI3K/AKT) signaling pathway activation, and subsequent expression of inflammatory proteins and release of inflammatory cytokines.

CONCLUSION

Altogether, GJ-4 ameliorated cognition of APP/PS1 transgenic mice through multiple targets, including Aβ, tau and neuroinflammation. This study provides a solid research basis for further development of GJ-4 as a potential candidate for the treatment of AD.

Utilization of Human Induced Pluripotent Stem Cells-Derived In vitro Models for the Future Study of Sex Differences in Alzheimer's Disease

Alzheimer’s disease (AD) is an aging-dependent neurodegenerative disease that impairs cognitive function. Although the main pathologies of AD are the aggregation of amyloid-beta (Aβ) and phosphorylated Tau protein, the mechanisms that lead to these pathologies and their effects are believed to be heterogeneous among patients. Many epidemiological studies have suggested that sex is involved in disease prevalence and progression. The reduction of sex hormones contributes to the pathogenesis of AD, especially in females, suggesting that the supplementation of sex hormones could be a therapeutic intervention for AD. However, interventional studies have revealed that hormone therapy is beneficial under limited conditions in certain populations with specific administration methods. Thus, this suggests the importance of identifying crucial factors that determine hormonal effects in patients with AD. Based on these factors, it is necessary to decide which patients will receive the intervention before starting it. However, the long observational period and many uncontrollable environmental factors in clinical trials made it difficult to identify such factors, except for the APOE ε4 allele. Induced pluripotent stem cells (iPSCs) derived from patients can differentiate into neurons and recapitulate some aspects of AD pathogenesis. This in vitro model allows us to control non-cell autonomous factors, including the amount of Aβ aggregates and sex hormones. Hence, iPSCs provide opportunities to investigate sex-dependent pathogenesis and predict a suitable population for clinical trials of hormone treatment.

Age- and sex-dependent alterations in the peripheral immune system in the 3xTg-AD mouse model of Alzheimer's disease: Increased proportion of CD3+CD4-CD8- double-negative T cells in the blood

It is well documented that sporadic Alzheimer's disease (AD) is a multifactorial disease and considered to be a result of several pathological events, both in the periphery and in the brain. The role of the peripheral immune system in the etiology and/or progression of the disease is not fully understood yet, and the results in humans are contradictory so far. Several animal models of AD have been generated and thoroughly characterized to elucidate disease mechanisms and evaluate numerous therapeutic strategies in preclinical studies. In the present study, we carried out a longitudinal evaluation of blood lymphocytes from male and female 3xTg-AD mice to document important immunological abnormalities in the periphery. We documented the age-dependent decrease in the percentage of CD3+ and CD4+ lymphocytes and an increase in the percentage CD3+CD4-CD8- (DN T) cells in the blood of 3xTg-AD mice compared with non-transgenic animals. Severe splenomegaly was observed in 3xTg-AD mice in contrast to wild-type animals. Importantly, all these abnormalities in the peripheral immune system appeared earlier and were more pronounced in males compared with females of the same age, which may account for the shorter lifespan of male mice. We suggest that future research should include the measurement of CD3+ and DN T cells as a potential immunological marker of disease progression in AD patients.

Amyloid and Tau in Alzheimer's Disease: Biomarkers or Molecular Targets for Therapy? Are We Shooting the Messenger?

Alzheimer's disease is a neuropsychiatric disorder with devastating clinical and socioeconomic consequences. Since the original description of the neuropathological correlates of the disorder, neuritic plaques and neurofibrillary tangles have been presumed to be critical to the underlying pathophysiology of the illness. The authors review the clinical and neuropathological origins of Alzheimer's disease and trace the evolution of modern biomarkers from their historical roots. They describe how technological innovations such as neuroimaging and biochemical assays have been used to measure and quantify key proteins and lipids in the brain, cerebrospinal fluid, and blood and advance their role as biomarkers of Alzheimer's disease. Together with genomics, these approaches have led to the development of a thematic and focused science in the area of degenerative disorders. The authors conclude by drawing distinctions between legitimate biomarkers of disease and molecular targets for therapeutic intervention and discuss future approaches to this complex neurobehavioral illness.

Glutamate and GABA in Microglia-Neuron Cross-Talk in Alzheimer's Disease

The physiological balance between excitation and inhibition in the brain is significantly affected in Alzheimer’s disease (AD). Several neuroactive compounds and their signaling pathways through various types of receptors are crucial in brain homeostasis, among them glutamate and γ-aminobutyric acid (GABA). Activation of microglial receptors regulates the immunological response of these cells, which in AD could be neuroprotective or neurotoxic. The novel research approaches revealed the complexity of microglial function, including the interplay with other cells during neuroinflammation and in the AD brain. The purpose of this review is to describe the role of several proteins and multiple receptors on microglia and neurons, and their involvement in a communication network between cells that could lead to different metabolic loops and cell death/survival. Our review is focused on the role of glutamatergic, GABAergic signaling in microglia–neuronal cross-talk in AD and neuroinflammation. Moreover, the significance of AD-related neurotoxic proteins in glutamate/GABA-mediated dialogue between microglia and neurons was analyzed in search of novel targets in neuroprotection, and advanced pharmacological approaches.

4-Phenethyl-1-Propargylpiperidine-Derived Dual Inhibitors of Butyrylcholinesterase and Monoamine Oxidase B

The multi-target-directed ligands (MTDLs) strategy is encouraged for the development of novel modulators targeting multiple pathways in the neurodegenerative cascade typical for Alzheimer’s disease (AD). Based on the structure of an in-house irreversible monoamine oxidase B (MAO-B) inhibitor, we aimed to introduce a carbamate moiety on the aromatic ring to impart cholinesterase (ChE) inhibition, and to furnish multifunctional ligands targeting two enzymes that are intricately involved in AD pathobiology. In this study, we synthesized three dual hMAO-B/hBChE inhibitors 13–15, with compound 15 exhibiting balanced, low micromolar inhibition of hMAO-B (IC₅₀ of 4.3 µM) and hBChE (IC₅₀ of 8.5 µM). The docking studies and time-dependent inhibition of hBChE confirmed the initial expectation that the introduced carbamate moiety is responsible for covalent inhibition. Therefore, dual-acting compound 15 represents an excellent starting point for further optimization of balanced MTDLs

Defining early changes in Alzheimer's disease from RNA sequencing of brain regions differentially affected by pathology

Tau pathology in Alzheimer’s disease (AD) spreads in a predictable pattern that corresponds with disease symptoms and severity. At post-mortem there are cortical regions that range from mildly to severely affected by tau pathology and neuronal loss. A comparison of the molecular signatures of these differentially affected areas within cases and between cases and controls may allow the temporal modelling of disease progression. Here we used RNA sequencing to explore differential gene expression in the mildly affected primary visual cortex and moderately affected precuneus of ten age-, gender- and RNA quality-matched post-mortem brains from AD patients and healthy controls. The two regions in AD cases had similar transcriptomic signatures but there were broader abnormalities in the precuneus consistent with the greater tau load. Both regions were characterised by upregulation of immune-related genes such as those encoding triggering receptor expressed on myeloid cells 2 and membrane spanning 4-domains A6A and milder changes in insulin/IGF1 signalling. The precuneus in AD was also characterised by changes in vesicle secretion and downregulation of the interneuronal subtype marker, somatostatin. The ‘early’ AD transcriptome is characterised by perturbations in synaptic vesicle secretion on a background of neuroimmune dysfunction. In particular, the synaptic deficits that characterise AD may begin with the somatostatin division of inhibitory neurotransmission.

MRI characterization of early CNS transport kinetics post intrathecal gadolinium injection: Trends of subarachnoid and parenchymal distribution in healthy volunteers

PURPOSE

To quantify CSF transport kinetics and brain glymphatic distribution using MRI following intrathecal injection of gadolinium contrast in healthy adults.

SUBJECTS AND METHODS

Eight completely healthy volunteer subjects underwent intrathecal injection of gadolinium via image guided lumbar puncture and serial MRI's at six subsequent time points up to 11 h post-injection. Rate of enhancement and deposition were calculated for various regions and lobes of the brain.

RESULTS

Normalized cranial data revealed that gadolinium in the intracranial CSF spaces peaked within 1-3 h and started to decrease at 7 h. In some regions of the brain parenchyma, such as the cerebral cortex and white matter, enhancement was increasing after 11 h. Differential rates of uptake between the parietal and frontal (p = 0.0003), cingulate (p = 0.002) and temporal (p = 0.018) lobes were shown as well as a several fold change between various cortical regions. Lastly, a linear regression comparing laterality between 35 cortical regions yielded (R² = 0.90, p < 0.001) with a slope of 1.01 showing symmetry in uptake.

CONCLUSIONS

Gadolinium enhancement after lumbar intrathecal injection demonstrated differential CSF flow and brain parenchymal penetration, which illustrated the distributory function of the glymphatic system.

Rationale for the development of an Alzheimer's disease vaccine

Vaccination traditionally has targeted infectious agents and thus has not heretofore been used to prevent neurodegenerative illness. However, amyloid β (Aβ) or tau, which can act like infectious proteins, or prions, might induce Alzheimer's disease (AD). Furthermore, evidence suggests that traditional infectious agents, including certain viruses and bacteria, may trigger AD. It is therefore worth exploring whether removing such targets could prevent AD. Although failing to treat AD patients who already display cognitive impairment, Aβ monoclonal antibodies are being tested in pre-symptomatic, at-risk individuals to prevent dementia. These antibodies might become the first AD therapeutics. However, their high cost will keep them out of the arms of the vast majority of patients, who increasingly live in developing countries. Because vaccines produce antibodies internally at much lower cost, vaccination might be the most promising approach to reducing the global burden of dementia.

Ganoderma lucidum Triterpenoids (GLTs) Reduce Neuronal Apoptosis via Inhibition of ROCK Signal Pathway in APP/PS1 Transgenic Alzheimer's Disease Mice

Alzheimer's disease (AD) is the most common cause of dementia among senior citizen. Ganoderma lucidum triterpenoids (GLTs) have nutritional health benefits and has been shown to promote health and longevity, but a protective effect of GLTs on AD damage has not yet been reported. The objective of this research was to elucidate the phylactic effect of GLTs on AD model mice and cells and to explore its underlying mechanisms. Morris water maze (MWM) test was conducted to detect changes in the cognitive function of mice. Hematoxylin-eosin (HE) staining was applied to observe pathological changes in the hippocampus. Silver nitrate staining was applied to observe the hippocampal neuronal tangles (NFTs). Apoptosis of the hippocampal neurons in mouse brain tissue was determined by TUNEL staining. The expression levels of apoptosis-related protein Bcl2, Bax, and caspase 3/cleaved caspase 3; antioxidative protein Nrf2, NQO1, and HO1; and ROCK signaling pathway-associated proteins ROCK2 and ROCK1 were measured by western blot. In vivo experiments show that 5-month-old APP/PS1 mice appeared to have impaired acquisition of spatial learning and GLTs could reduce cognitive impairment in AD mice. Compared to normal mice, the hippocampus of APP/PS1 mouse's brains was severely damaged, while GLTs could alleviate this symptom by inhibiting apoptosis, relieving oxidative damage, and inactivating the ROCK signaling pathway. In in vitro cell experiments, Aβ _25-35 was applied to induce hippocampal neurons into AD model cells. GLTs promoted cell proliferation, facilitated superoxide dismutase (SOD) expression, and inhibited malondialdehyde (MDA) and lactic dehydrogenase (LDH) expression of neurons. Our study highlights that GLTs improve cognitive impairment, alleviate neuronal damage, and inhibit apoptosis in the hippocampus tissues and cells in AD through inhibiting the ROCK signaling pathway.

Sleep and β-Amyloid Deposition in Alzheimer Disease: Insights on Mechanisms and Possible Innovative Treatments

The growing interest in the preclinical stage of Alzheimer's disease (AD) led investigators to identify modifiable risk and predictive factors useful to design early intervention strategies. The preclinical stage of AD is characterized by β-amyloid (Aβ) aggregation into amyloid plaques and tau phosphorylation and aggregation into neurofibrillary tangles. There is a consensus on the importance of sleep within this context: the bidirectional relationship between sleep and AD pathology is supported by growing evidence that proved that the occurrence of sleep changes starting from the preclinical stage of AD, many years before the onset of cognitive decline. Hence, we review the most recent studies on sleep disturbances related to Aβ and the effects of sleep deprivation on Aβ accumulation in animal and human models. We also discuss evidence on the role of sleep in clearing the brain of toxic metabolic by-products, with original findings of the clearance activity of the glymphatic system stimulated by sleep. Furthermore, starting from new recent advances about the relationship between slow-wave sleep (SWS) and Aβ burden, we review the results of recent electroencephalographic (EEG) studies in order to clarify the possible role of SWS component disruption as a novel mechanistic pathway through which Aβ pathology may contribute to cognitive decline and, conversely, the eventual useful role of SWS in facilitating Aβ clearance. Finally, we discuss some promising innovative, effective, low-risk, non-invasive interventions, although empirical evidence on the efficacy of sleep interventions in improving the course of AD is at the very beginning.

Mitochondrial dynamics and transport in Alzheimer's disease

Mitochondrial dysfunction is now recognized as a contributing factor to the early pathology of multiple human conditions including neurodegenerative diseases. Mitochondria are signaling organelles with a multitude of functions ranging from energy production to a regulation of cellular metabolism, energy homeostasis, stress response, and cell fate. The success of these complex processes critically depends on the fidelity of mitochondrial dynamics that include the ability of mitochondria to change shape and location in the cell, which is essential for the maintenance of proper function and quality control, particularly in polarized cells such as neurons. This review highlights several aspects of alterations in mitochondrial dynamics in Alzheimer's disease, which may contribute to the etiology of this debilitating condition. We also discuss therapeutic strategies to improve mitochondrial dynamics and function that may provide an alternative approach to failed amyloid-directed interventions.

Antioxidant and Anti-inflammatory Mechanisms of Neuroprotection by Ursolic Acid: Addressing Brain Injury, Cerebral Ischemia, Cognition Deficit, Anxiety, and Depression

Ursolic acid (UA) is a pentacyclic triterpene which is found in common herbs and medicinal plants that are reputed for a variety of pharmacological effects. Both as an active principle of these plants and as a nutraceutical ingredient, the pharmacology of UA in the CNS and other organs and systems has been extensively reported in recent years. In this communication, the antioxidant and anti-inflammatory axis of UA's pharmacology is appraised for its therapeutic potential in some common CNS disorders. Classic examples include the traumatic brain injury (TBI), cerebral ischemia, cognition deficit, anxiety, and depression. The pharmacological efficacy for UA is demonstrated through the therapeutic principle of one drug → multitargets → one/many disease(s). Both specific enzymes and receptor targets along with diverse pharmacological effects associated with oxidative stress and inflammatory signalling are scrutinised.

Salvation of the fallen angel: Reactivating mutant p53

The transcription factor p53 is known as the guardian of the genome for its powerful anti-tumour capacity. However, mutations of p53 that undermine their protein structure, resulting in loss of tumour suppressor function and gain of oncogenic function, have been implicated in more than half of human cancers. The crucial role of mutant forms of p53 in cancer makes it an attractive therapeutic target. A large number of candidates, including low MW compounds, peptides, and nucleic acids, have been identified or designed to rescue p53 mutants and reactivate their anti-tumour capacity through a variety of mechanisms. In this review, we summarize the progress made in the reactivation of mutant forms of p53, focusing on the pharmacological mechanisms of the reactivators of p53 mutants.

Preclinical Models of Alzheimer's Disease: Relevance and Translational Validity

The only drugs currently approved for the treatment of Alzheimer's Disease (AD) are four acetylcholinesterase inhibitors and the NMDA antagonist memantine. Apart from these drugs, which have minimal to no clinical benefit, the 40-year search for effective therapeutics to treat AD has resulted in a clinical failure rate of 100% not only for compounds that prevent brain amyloid deposition or remove existing amyloid plaques but also those acting by a variety of other putative disease-associated mechanisms. This indicates that the preclinical data generated from current AD targets to support the selection, optimization, and translation of new chemical entities (NCEs) and biologics to clinical trials is seriously compromised. While many of these failures reflect flawed hypotheses or a lack of adequate characterization of the preclinical pharmacodynamic and pharmacokinetic (PD/PK) properties of lead NCEs-including their bioavailability and toxicity-the conceptualization, validation, and interrogation of the current animal models of AD represent key limitations. The overwhelming majority of these AD models are transgenic, based on aspects of the amyloid hypothesis and the genetics of the familial form of the disease. As a result, these generally lack construct and predictive validity for the sporadic form of the human disease. The 170 or so transgenic models, perhaps the largest number ever focused on a single disease, use rodents, mainly mice, and in addition to amyloid also address aspects of tau causality with more complex multigene models including other presumed causative factors together with amyloid. This overview discusses the current animal models of AD in the context of both the controversies surrounding the causative role of amyloid in the disease and the need to develop validated models of cognitive function/dysfunction that more appropriately reflect the phenotype(s) of human aged-related dementias. © 2019 by John Wiley & Sons, Inc.

The de-Alzheimerization of age-related dementias: implications for drug targets and approaches to effective therapeutics

Alzheimer's disease (AD) was differentiated from senile dementia (SD) in 1910 due to its early onset and pathological severity. In 1976, this distinction was upended when SD was redesignated as AD to focus efforts and funding in dementia-related research. AD then became conflated with amyloid plaques and, to a lesser degree, neurofibrillary tangles complicating efforts in understanding dementia causality and its treatment. The resultant four-decade search for therapies-based almost exclusively on amyloid was an exercise in futility. While dementia is a complex, multifactorial syndrome, AD is viewed as a homogeneous, linear disease. An amyloid-agnostic approach is necessary to discover therapeutics for age-related dementias.