Specks of insight into Alzheimer’s disease

Microglia and Astrocytes in Alzheimer's Disease: Significance and Summary of Recent Advances

Alzheimer's disease, one of the most common forms of dementia, is characterized by a slow progression of cognitive impairment and neuronal loss. Currently, approved treatments for AD are hindered by various side effects and limited efficacy. Despite considerable research, practical treatments for AD have not been developed. Increasing evidence shows that glial cells, especially microglia and astrocytes, are essential in the initiation and progression of AD. During AD progression, activated resident microglia increases the ability of resting astrocytes to transform into reactive astrocytes, promoting neurodegeneration. Extensive clinical and molecular studies show the involvement of microglia and astrocyte-mediated neuroinflammation in AD pathology, indicating that microglia and astrocytes may be potential therapeutic targets for AD. This review will summarize the significant and recent advances of microglia and astrocytes in the pathogenesis of AD in three parts. First, we will review the typical pathological changes of AD and discuss microglia and astrocytes in terms of function and phenotypic changes. Second, we will describe microglia and astrocytes' physiological and pathological role in AD. These roles include the inflammatory response, "eat me" and "don't eat me" signals, Aβ seeding, propagation, clearance, synapse loss, synaptic pruning, remyelination, and demyelination. Last, we will review the pharmacological and non-pharmacological therapies targeting microglia and astrocytes in AD. We conclude that microglia and astrocytes are essential in the initiation and development of AD. Therefore, understanding the new role of microglia and astrocytes in AD progression is critical for future AD studies and clinical trials. Moreover, pharmacological, and non-pharmacological therapies targeting microglia and astrocytes, with specific studies investigating microglia and astrocyte-mediated neuronal damage and repair, may be a promising research direction for future studies regarding AD treatment and prevention.

New Tiaoxin Recipe Alleviates Energy Metabolism Disorders in an APPswe/PS1DE9 Mouse Model of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is a typical neurodegenerative disease with a complex etiology. Until now, there has been no effective treatment available for AD; however, improving energy dysmetabolism, the key pathological event in the early stage of AD, can effectively delay the progression of AD.

OBJECTIVE

This paper aims to investigate the therapeutic effect and potential mechanism of the new Tiaoxin recipe on early AD.

METHODS

APP/PS1 mice were divided into a model group, a new Tiaoxin recipe group, and a donepezil group, and C57/BL mice were used for the control group. Mouse cognitive and learning abilities were tested using the Morris water maze test and a new object-recognition experiment. The 42 amino acid form of amyloid β peptide (Aβ1-42) content was detected by enzyme-linked immunosorbent assay, the senile plaque area was detected by thioflavin S staining, and the senescence- associated β-galactosidase (SA-β-gal)-positive area was detected by chemical staining. Also, the adenosine triphosphate (ATP), nicotinamide adenine dinucleotide (NAD+), and nicotinamide adenine dinucleotide hydride (NADH) contents were detected using a biochemical method, and the cluster of differentiation 38 (CD38) and silent mating-type information regulation 2 homolog 3 (SIRT3) protein expression levels were detected by immunofluorescence and Western blot analysis.

RESULTS

Compared with those of the control group, the learning and memory abilities of the model group were impaired; the senile plaque deposition, Aβ1-42 content, and SA-βgal-positive staining area were increased; the ATP concentration, NAD+ concentration, and NAD+/NADH ratio were decreased; the CD38 protein expression level was increased; and the SIRT3 protein expression level was decreased. Following intervention with the new Tiaoxin recipe, the learning and memory abilities were improved; the senile plaque deposition, Aβ1-42 content, and SA-βgal-positive area were reduced; the ATP concentration, NAD+ concentration, and NAD+/NADH ratio were increased; CD38 protein expression was decreased, and SIRT3 protein expression was increased.

CONCLUSION

This study shows that the new Tiaoxin Recipe can improve cognitive ability and reduce the Aβ1-42 content and senile plaque deposition in APP/PS1 mice, which may occur through the downregulation of CD38 protein expression, upregulation of SIRT3 protein expression, restoration of the NAD+ level, promotion of ATP synthesis, mitigation of energy metabolism disorders.

Evidence of Flavonoids on Disease Prevention

A growing body of evidence highlights the properties of flavonoids in natural foods for disease prevention. Due to their antioxidative, anti-inflammatory, and anti-carcinogenic activities, flavonoids have been revealed to benefit skeletal muscle, liver, pancreas, adipocytes, and neural cells. In this review, we introduced the basic classification, natural sources, and biochemical properties of flavonoids, then summarize the experimental results and underlying molecular mechanisms concerning the effects of flavonoid consumption on obesity, cancers, and neurogenerative diseases that greatly threaten public health. Especially, the dosage and duration of flavonoids intervening in these diseases are discussed, which might guide healthy dietary habits for people of different physical status.

Mechanisms of NLRP3 activation and pathology during neurodegeneration

Inflammasomes are multiprotein complexes that are mainly present in resident and infiltrating immune cells in the central nervous system. Inflammasomes function as intracellular sensors of immunometabolic stress, infection and changes in the local microenvironment. Inflammasome assembly in response to these 'danger signals', triggers recruitment and cluster-dependent activation of caspase-1 and the subsequent proteolytic activation of inflammatory cytokines such as interleukin-1β and interleukin-18. This is typically followed by a form of inflammatory cell death through pyroptosis. Since the discovery of inflammasomes in 2002, they have come to be recognized as central regulators of acute and chronic inflammation, a hallmark of progressive neurological diseases. Indeed, over the last decade, extensive inflammasome activation has been found at the sites of neuropathology in all progressive neurodegenerative diseases. Disease-specific misfolded protein aggregates which accumulate in neurodegenerative diseases, such as alpha synuclein or beta amyloid, have been found to be important triggers of NLRP3 inflammasome activation in the central nervous system. Together, these discoveries have transformed our understanding of how chronic inflammation is triggered and sustained in the central nervous system, and how it can contribute to neuronal death and disease progression in age-related neurodegenerative diseases. Therapeutic strategies around inhibition of NLRP3 activation in the central nervous system are already being evaluated to determine their effectiveness to slow progressive neurodegeneration. This review summarizes current understanding of inflammasomes in the most prevalent neurodegenerative diseases and discusses current knowledge gaps and inflammasome inhibition as a therapeutic strategy.

Aβ promotes CD38 expression in senescent microglia in Alzheimer's disease

Background

In Alzheimer’s disease (AD), the neuroinflammatory response mediated by the activation of senescent microglia is closely related to energy dysmetabolism. However, the mechanism underlying the interaction between the energy metabolism of aging microglia and neuroinflammation remains unclear.

Methods

We used biochemical methods, enzyme-linked immunosorbent assay (ELISA), immunofluorescence, and western blot to determine the effects and mechanism of CD38 knockdown on energy metabolism and neuroinflammation in Aβ1-40 injured BV2 cells. Using AD model mice, we detected CD38 enzyme activity, energy metabolism factors (ATP, NAD +, and NAD + /NADH), and neuroinflammatory factors (IL-1β, IL-6, and TNF-α) following the addition of CD38 inhibitor. Using a combination of biochemical analysis and behavioral testing, we analyzed the effects of the CD38 inhibitor on energy metabolism disorder, the neuroinflammatory response, and the cognition of AD mice.

Results

Following Aβ1-40 injury, SA-β-Gal positive cells and senescence-related proteins P16 and P21 increased in BV2 cells, while energy-related molecules (ATP, NAD +, and NAD + /NADH) and mitochondrial function (mitochondrial ROS and MMP) decreased. Further studies showed that CD38 knockdown could improve Aβ1-40-induced BV2 cells energy dysmetabolism and reduce the levels of IL-1β, IL-6, and TNF-α. In vivo results showed an increase in senile plaque deposition and microglial activation in the hippocampus and cortex of 34-week-old APP/PS1 mice. Following treatment with the CD38 inhibitor, senile plaque deposition decreased, the number of Iba1 + BV2 cells increased, the energy metabolism disorder was improved, the proinflammatory cytokines were reduced, and the spatial learning ability was improved.

Conclusions

Our results confirm that senescent microglia appeared in the brain of 34-week-old APP/PS1 mice, and that Aβ1-40 can induce senescence of BV2 cells. The expression of CD38 increases in senescent BV2 cells, resulting in energy metabolism disorder. Therefore, reducing CD38 expression can effectively improve energy metabolism disorder and reduce proinflammatory cytokines. Following intervention with the CD38 inhibitor in APP/PS1 mice, the energy metabolism disorder was improved in the hippocampus and cortex, the level of proinflammatory cytokines was reduced, and cognitive impairment was improved.

High-density lipoprotein in Alzheimer's disease: From potential biomarkers to therapeutics

The inverse correlation between high-density lipoprotein (HDL) levels in vivo and the risk of Alzheimer's disease (AD) has become an inspiration for HDL-inspired AD therapy, including plain HDL and various intelligent HDL-based drug delivery systems. In this review, we will focus on the two endogenous HDL subtypes in the central nervous system (CNS), apolipoprotein E-based HDL (apoE-HDL) and apolipoprotein A-I-based HDL (apoA-I-HDL), especially their influence on AD pathophysiology to reveal HDL's potential as biomarkers for risk prediction, and summarize the relevant therapeutic mechanisms to propose possible treatment strategies. We will emphasize the latest advances of HDL as therapeutics (plain HDL and HDL-based drug delivery systems) to discuss the potential for AD therapy and review innovative techniques in the preparation of HDL-based nanoplatforms to provide a basis for the rational design and future development of anti-AD drugs.

The piperine derivative HJ105 inhibits Aβ1-42-induced neuroinflammation and oxidative damage via the Keap1-Nrf2-TXNIP axis

BACKGROUND

Piperine is a great lead compound, as a phytopharmaceutical with reported neuroprotective effects in neurodegenerative diseases. HJ105, a piperine derivative with high affinity to Keap1 receptor, attracts increasing attention in Alzheimer's disease (AD) treatment.

PURPOSE

This work mainly aimed to study HJ105's therapeutic effects on Aβ_1-42-associated AD and the underpinning mechanisms.

METHODS

In the in vivo part, a rat model of AD was established by bilateral intra-hippocampal administration of aggregated Aβ_1-42, followed by a month of intragastric HJ105 or donepezil administration. Spatial and learning memories were detected by the Morris water maze assay, passive avoidance learning as well as Y-maze test. The morphology of hippocampal neurons was assessed by hematoxylin-eosin (H&E) staining. In addition, the amounts of the IL-1β and TNF-α were obtained with specific ELISA kits. More importantly, apoptosis-related proteins and factors involved in Nrf2/TXNIP/NLPR3 pathways were detected by Western blot, while the interaction between Keap1 and Nrf2 was assessed by co-immunoprecipitation. In the in vitro part, human neuroblastoma (SH-SY5Y) cells were applied to evaluate the role of HJ105 on Aβ_1-42-induced neuronal damage.

RESULTS

Treatment of HJ105 not only reversed memory impairment, but also protected neurons in the hippocampus by inhibiting Bax/Bcl2 ratio increase. HJ105 decreased TXNIP expression, suppressing NLRP3 inflammasome activation in the hippocampus, which in turn counteracted the upregulation of IL-1β and TNF-α. Notably, HJ105 exerted an inhibitory effect on Keap1-Nrf2 interaction and upregulated nuclear Nrf2, which conversely increased the expression levels of superoxide dismutase, catalase and glutathione peroxidase and downregulated malondialdehyde. Additionally, neurotoxicity induced by Aβ_1-42 in SH-SY5Y cells was alleviated by HJ105.

CONCLUSION

Overall, HJ105 exerts neuroprotective effects in SH-SY5Y cells induced by Aβ_1-42 as well as in experimental rats with AD by decreasing apoptosis, oxidative stress and neuroinflammation, partly via suppression of Keap1-Nrf2 complex generation. HJ105 might represent a promising compound for AD treatment.

ROS-associated immune response and metabolism: a mechanistic approach with implication of various diseases

The immune system plays a pivotal role in maintaining the defense mechanism against external agents and also internal danger signals. Metabolic programming of immune cells is required for functioning of different subsets of immune cells under different physiological conditions. The field of immunometabolism has gained ground because of its immense importance in coordination and balance of immune responses. Metabolism is very much related with production of energy and certain by-products. Reactive oxygen species (ROS) are generated as one of the by-products of various metabolic pathways. The amount, localization of ROS and redox status determine transcription of genes, and also influences the metabolism of immune cells. This review discusses ROS, metabolism of immune cells at different cellular conditions and sheds some light on how ROS might regulate immunometabolism.

HJ22, a Novel derivative of piperine, Attenuates ibotenic acid-induced cognitive impairment, oxidativestress, apoptosis and inflammation via inhibiting the protein-protein interaction of Keap1-Nrf2

Kelch-like ECH-associated protein (Keap1)-nuclear factor erythroid-2-related factor 2 (Nrf2) protein-protein interaction has become an important drug target for the treatment of Alzheimer's disease. In this study, we found a novel piperine derivative (HJ22) synthesized by our group with great ability to bind to Keap-1 and activate Keap1-Nrf2-ARE signaling pathway in vitro, driving us to investigate the beneficial effects of HJ22 on ibotenic acid (IBO)-induced neurological disorders in rats and underlying mechanisms. Interestingly, HJ22 significantly ameliorated IBO-induced cognitive impairment in Morris water maze, Y-maze and passive avoidance tests. Moreover, HJ22 significantly attenuated cholinergic dysfunction and neuronal morphological changes via inhibiting apoptotic cell death induced by IBO. Notably, HJ22 inhibited the interaction between Keap1 and Nrf2, and subsequently up-regulated nuclear Nrf2 expression, thereby inhibiting oxidative stress and Thioredoxin-interacting protein (TXNIP)-mediated Nod-like receptor protein 3 (NLRP3) inflammasome activation. These findings demonstrated that HJ22 exhibited potent therapeutic effects against IBO-induced cognitive impairment by alleviating cholinergic damage, oxidative stress, apoptosis and neuroinflammation, which might be partly attributed to its inhibitory activity on Keap1-Nrf2 protein-protein interaction.

Anticoagulants for Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a multifactorial syndrome with a plethora of progressive, degenerative changes in the brain parenchyma, but also in the cerebrovascular and hemostatic system. A therapeutic approach for AD is reviewed, which is focused on the role of amyloid-β protein (Aβ) and fibrin in triggering intra-brain vascular dysfunction and connected, cognitive decline. It is proposed that direct oral anticoagulants (DOACs) counteract Aβ-induced pathological alterations in cerebral blood vessels early in AD, a condition, known as cerebral amyloid angiopathy (CAA). By inhibiting thrombin for fibrin formation, anticoagulants can prevent accumulations of proinflammatory thrombin and fibrin, and deposition of degradation-resistant, Aβ-containing fibrin clots. These fibrin-Aβ clots are found in brain parenchyma between neuron cells, and in and around cerebral blood vessels in areas of CAA, leading to decreased cerebral blood flow. Consequently, anticoagulant treatment could reduce hypoperfusion and restricted supply of brain tissue with oxygen and nutrients. Concomitantly, hypoperfusion-enhanced neurodegenerative processes, such as progressive Aβ accumulation via synthesis and reduced perivascular clearance, neuroinflammation, and synapse and neuron cell loss, could be mitigated. Given full cerebral perfusion and reduced Aβ- and fibrin-accumulating and inflammatory milieu, anticoagulants could be able to decrease vascular-driven progression in neurodegenerative and cognitive changes, present in AD, when treated early, therapeutically, or prophylactically.

Computational Studies Applied to Flavonoids against Alzheimer's and Parkinson's Diseases

Neurodegenerative diseases, such as Parkinson's and Alzheimer's, are understood as occurring through genetic, cellular, and multifactor pathophysiological mechanisms. Several natural products such as flavonoids have been reported in the literature for having the capacity to cross the blood-brain barrier and slow the progression of such diseases. The present article reports on in silico enzymatic target studies and natural products as inhibitors for the treatment of Parkinson's and Alzheimer's diseases. In this study we evaluated 39 flavonoids using prediction of molecular properties and in silico docking studies, while comparing against 7 standard reference compounds: 4 for Parkinson's and 3 for Alzheimer's. Osiris analysis revealed that most of the flavonoids presented no toxicity and good absorption parameters. The Parkinson's docking results using selected flavonoids as compared to the standards with four proteins revealed similar binding energies, indicating that the compounds 8-prenylnaringenin, europinidin, epicatechin gallate, homoeriodictyol, capensinidin, and rosinidin are potential leads with the necessary pharmacological and structural properties to be drug candidates. The Alzheimer's docking results suggested that seven of the 39 flavonoids studied, being those with the best molecular docking results, presenting no toxicity risks, and having good absorption rates (8-prenylnaringenin, europinidin, epicatechin gallate, homoeriodictyol, aspalathin, butin, and norartocarpetin) for the targets analyzed, are the flavonoids which possess the most adequate pharmacological profiles.

Preventive Effects of Dairy Products on Dementia and the Underlying Mechanisms

Alongside the rapid population aging occurring worldwide, the prevention of age-related memory decline and dementia has become a high priority. Dairy products have many physiological effects owing to their contents of lactic acid bacteria and the fatty acids and peptides generated during their fermentation. In particular, several recent studies have elucidated the effects of fermented dairy products on cognitive function. Epidemiological and clinical evidence has indicated that fermented dairy products have preventive effects against dementia, including Alzheimer’s disease. Recent preclinical studies have identified individual molecules generated during fermentation that are responsible for those preventive effects. Oleamide and dehydroergosterol have been identified as the agents responsible for reducing microglial inflammatory responses and neurotoxicity. In this review, the protective effects of fermented dairy products and their components on cognitive function, the mechanisms underlying those effects, and the prospects for their future clinical development will be discussed.

Positive Feedback Loops in Alzheimer's Disease: The Alzheimer's Feedback Hypothesis

The dominant model for Alzheimer's disease (AD) is the amyloid cascade hypothesis, in which the accumulation of excess amyloid-β (Aβ) leads to inflammation, excess glutamate and intracellular calcium, oxidative stress, tau hyperphosphorylation and tangle formation, neuronal loss, and ultimately dementia. In a cascade, AD proceeds in a unidirectional fashion, with events only affecting downstream processes. Compelling evidence now exists for the presence of positive feedback loops in AD, however, involving oxidative stress, inflammation, glutamate, calcium, and tau. The pathological state of AD is thus a system of positive feedback loops, leading to amplification of the initial perturbation, rather than a linear cascade. Drugs may therefore be effective by targeting numerous points within the loops, rather than concentrating on upstream processes. Anti-inflammatories and anti-oxidants may be especially valuable, since these processes are involved in many loops and hence would affect numerous processes in AD.