Metformin treatment prevents amyloid plaque deposition and memory impairment in APP/PS1 mice

Impairment of the autophagy-lysosomal pathway in Alzheimer's diseases: Pathogenic mechanisms and therapeutic potential

Alzheimer's disease (AD), the most common neurodegenerative disorder, is characterized by memory loss and cognitive dysfunction. The accumulation of misfolded protein aggregates including amyloid beta (Aβ) peptides and microtubule associated protein tau (MAPT/tau) in neuronal cells are hallmarks of AD. So far, the exact underlying mechanisms for the aetiologies of AD have not been fully understood and the effective treatment for AD is limited. Autophagy is an evolutionarily conserved cellular catabolic process by which damaged cellular organelles and protein aggregates are degraded via lysosomes. Recently, there is accumulating evidence linking the impairment of the autophagy–lysosomal pathway with AD pathogenesis. Interestingly, the enhancement of autophagy to remove protein aggregates has been proposed as a promising therapeutic strategy for AD. Here, we first summarize the recent genetic, pathological and experimental studies regarding the impairment of the autophagy–lysosomal pathway in AD. We then describe the interplay between the autophagy–lysosomal pathway and two pathological proteins, Aβ and MAPT/tau, in AD. Finally, we discuss potential therapeutic strategies and small molecules that target the autophagy–lysosomal pathway for AD treatment both in animal models and in clinical trials. Overall, this article highlights the pivotal functions of the autophagy–lysosomal pathway in AD pathogenesis and potential druggable targets in the autophagy–lysosomal pathway for AD treatment.

Mechanistic insight into the role of metformin in Alzheimer's disease

Alzheimer's disease (AD), a type of dementia, is characterized by progressive memory decline and cognition impairment. Despite the considerable body of evidence regarding AD pathophysiology, current therapies merely slow down the disease progression, and a comprehensive therapeutic approach is unavailable. Accordingly, finding an efficient multifunctional remedy is necessary to blunt the increasing rate of AD incidence in the upcoming years. AD shares pathophysiological similarities (e.g., impairment of cognitive functions, insulin sensitivity, and brain glucose metabolism) with noninsulin-dependent diabetes mellitus (NIDDM), which offers the utilization of metformin, a biguanide hypoglycemic agent, as an alternative therapeutic approach in AD therapy. Emerging evidence has revealed the impact of metformin in patients suffering from AD. It has been described that metformin employs multiple mechanisms to improve cognition and memory impairment in pre-clinical AD models, including reduction of hippocampal amyloid-beta (Aβ) plaque and neurofibrillary tangles (NFTs) load, suppression of inflammation, amelioration of mitochondrial dysfunction and oxidative stress, restriction of apoptotic neuronal death, and induction of neurogenesis. This review discusses the pre-clinical evidence, which may shed light on the role of metformin in AD and provide a more comprehensive mechanistic insight for future studies in this area of research.

Deciphering the Roles of Metformin in Alzheimer's Disease: A Snapshot

Alzheimer’s disease (AD) is a prevalent neurodegenerative disease predominantly affecting millions of elderly people. To date, no effective therapy has been identified to reverse the progression of AD. Metformin, as a first-line medication for Type 2 Diabetes Mellitus (T2DM), exerts multiple beneficial effects on various neurodegenerative disorders, including AD. Evidence from clinical studies has demonstrated that metformin use contributes to a lower risk of developing AD and better cognitive performance, which might be modified by interactors such as diabetic status and APOE-ε4 status. Previous mechanistic studies have gradually unveiled the effects of metformin on AD pathology and pathophysiology, including neuronal loss, neural dysfunction, amyloid-β (Aβ) depositions, tau phosphorylation, chronic neuroinflammation, insulin resistance, impaired glucose metabolism and mitochondrial dysfunction. Current evidence remains ambiguous and even conflicting. Herein, we review the current state of knowledge concerning the mechanisms of metformin in AD pathology while summarizing current evidence from clinical studies.

Autophagy system as a potential therapeutic target for neurodegenerative diseases

Autophagy is an evolutionally conserved process by which cytoplasmic contents including protein aggregates and damaged organelles such as mitochondria and lysosomes, are sequestered by double-membrane structure, autophagosomes, and delivered to the lysosomes for degradation. Recently, considerable efforts have been made to reveal the role of autophagy in neurodegenerative diseases like Alzheimer's disease, Parkinson's disease and Huntington's disease. Impairment of autophagy aggravates the accumulation of misfolded protein and damaged organelles in neurons, while sufficient autophagic activity reduces such accumulation in nervous system and ameliorates the pathology. Here we summarize recent progress regarding the role of autophagy in several neurodegenerative diseases and the potential autophagy-associated therapies for them.

Metformin attenuated sepsis-associated liver injury and inflammatory response in aged mice

Sepsis-associated liver injury is with poor survival in intensive care units. Metformin is well known for its therapeutic effects; however, its impact on treating liver injury due to sepsis remains poorly understood. This study investigated the therapeutic effects of metformin on aged mice suffering from sepsis-associated liver injury. Male C57BL/6 J mice aged (18–19 months) were divided into 3 groups: 1) intraperitoneal injection of sterile normal saline (C group), 12.5 mg/kg lipopolysaccharide (LPS) to induce sepsis-associated liver injury (LPS group), and 25 mg/kg metformin (MET) at 1 h after LPS injection (MET group). After 24 h, blood samples and liver tissue were collected for biochemical analysis. Histological assays revealed significantly elevated inflammatory infiltration and apoptosis in the liver, while metformin was found to relieve these aberrant features. The percentage of apoptotic cells decreased after metformin treatment (P < 0.05). Additionally, MET group had significantly reduced plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels compared to the LPS group (P < 0.05). Furthermore, in the MET group, the mRNA levels of chemokines and inflammatory factors, TNF-α, IL-6, caspase-1, decreased markedly (P < 0.05). Metformin notably reversed the decreased phosphorylated AMP-activated protein kinase (p-AMPK) and PGC-1α expressions in the liver of septic rats. Metformin also inhibited PDK1, HIF-1α expression, including downstream inflammatory mediators, HMGB1 and TNF-α. Metformin attenuated inflammation and liver injury in septic aged mice. Most importantly, we report the effect of metformin on liver injury via the AMPK–PGC1α axis in septic aged mice for the first time.

Neuroprotective effects of liraglutide against inflammation through the AMPK/NF-κB pathway in a mouse model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease with increasing incidence in aged populations, second only to Alzheimer's disease. Increasing evidence has shown that inflammation plays an important role in the occurrence and development of Parkinson's disease. Growing evidence has shown that AMP-activated protein kinase (AMPK) and NF-κB are closely related to inflammation. Glucagon-like peptide 1 (GLP-1) is a hormone that is primarily secreted by intestinal endocrine L cells, and it has a variety of physiology through binding to GLP-1 receptor. GLP-1can be used for treatment of type 2 diabetes. In addition, GLP-1 also has anti-neuroinflammation activity. However, the exact mechanism behind how GLP-1 regulates neuroinflammation remains unclear. This study was designed to examine the effect of liraglutide on 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP)-induced injury in mice and its potential mechanism of action. Results showed that liraglutide dose-dependently ameliorated mouse behavior including swimming time and locomotor activity, increased the number of tyrosine hydroxylase (TH)-positive neurons and protein level, and reduced Iba1 and GFAP expression in the substantia nigra (SN). Liraglutide treatment also increased p-AMPK expression and reduced NF-κB protein level. Applying the AMPK inhibitor Dorsomorphin (Compound C) reversed the effect of liraglutide-reducing p-AMPK and increasing NF-κB expression. Finally, GFAP protein level increased, along with a decrease in TH expression. In conclusion, these results suggest that liraglutide can suppress neuroinflammation. Moreover, this effect is mediated through the AMPK/NF-κB signaling pathway.

Targeting whole body metabolism and mitochondrial bioenergetics in the drug development for Alzheimer's disease

Aging is by far the most prominent risk factor for Alzheimer's disease (AD), and both aging and AD are associated with apparent metabolic alterations. As developing effective therapeutic interventions to treat AD is clearly in urgent need, the impact of modulating whole-body and intracellular metabolism in preclinical models and in human patients, on disease pathogenesis, have been explored. There is also an increasing awareness of differential risk and potential targeting strategies related to biological sex, microbiome, and circadian regulation. As a major part of intracellular metabolism, mitochondrial bioenergetics, mitochondrial quality-control mechanisms, and mitochondria-linked inflammatory responses have been considered for AD therapeutic interventions. This review summarizes and highlights these efforts.

Recent Neurotherapeutic Strategies to Promote Healthy Brain Aging: Are we there yet?

Owing to the global exponential increase in population ageing, there is an urgent unmet need to develop reliable strategies to slow down and delay the ageing process. Age-related neurodegenerative diseases are among the main causes of morbidity and mortality in our contemporary society and represent a major socio-economic burden. There are several controversial factors that are thought to play a causal role in brain ageing which are continuously being examined in experimental models. Among them are oxidative stress and brain inflammation which are empirical to brain ageing. Although some candidate drugs have been developed which reduce the ageing phenotype, their clinical translation is limited. There are several strategies currently in development to improve brain ageing. These include strategies such as caloric restriction, ketogenic diet, promotion of cellular nicotinamide adenine dinucleotide (NAD+) levels, removal of senescent cells, 'young blood' transfusions, enhancement of adult neurogenesis, stem cell therapy, vascular risk reduction, and non-pharmacological lifestyle strategies. Several studies have shown that these strategies can not only improve brain ageing by attenuating age-related neurodegenerative disease mechanisms, but also maintain cognitive function in a variety of pre-clinical experimental murine models. However, clinical evidence is limited and many of these strategies are awaiting findings from large-scale clinical trials which are nascent in the current literature. Further studies are needed to determine their long-term efficacy and lack of adverse effects in various tissues and organs to gain a greater understanding of their potential beneficial effects on brain ageing and health span in humans.

Agomelatine Prevents Amyloid Plaque Deposition, Tau Phosphorylation, and Neuroinflammation in APP/PS1 Mice

Agomelatine, an agonist of melatonergic MT1 and MT2 receptors and a selective 5-hydroxytryptamine 2C receptor antagonist, is widely applied in treating depression and insomnia symptoms in several neurogenerative diseases. However, the neuroprotective effect of agomelatine in Alzheimer’s disease (AD) is less known. In this study, a total of 30 mice were randomly divided into three groups, namely, wild type (WT), APP/PS1, and agomelatine (50 mg/kg). After 30 days, the Morris water maze was performed to test the cognitive ability of mice. Then, all mice were sacrificed, and the hippocampus tissues were collected for ELISA, Western blot, and immunofluorescence analysis. In this study, we found that agomelatine attenuated spatial memory deficit, amyloid-β (Aβ) deposition, tau phosphorylation, and neuroinflammation in the hippocampus of APP/PS1 mice. Further study demonstrated that agomelatine treatment upregulated the protein expression of DHCR24 and downregulated P-Akt, P-mTOR, p-p70s6k, Hes1, and Notch1 expression. In summary, our results identified that agomelatine could improve cognitive impairment and ameliorate AD-like pathology in APP/PS1 mice via activating DHCR24 signaling and inhibiting Akt/mTOR and Hes1/Notch1 signaling pathway. Agomelatine may become a promising drug candidate in the therapy of AD.

Exploring the dual character of metformin in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease, which results in dementia typically in the elderly. The disease is mainly characterized by the deposition of amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs) in the brain. However, only few drugs are available for AD because of its unknown pathological mechanism which limits the development of new drugs. Therefore, it is urgent to identify potential therapeutic strategies for AD. Moreover, research have showed that there is a significant association between Type 2 diabetes mellites (T2DM) and AD, suggesting that the two diseases may share common pathophysiological mechanisms. Such mechanisms include impaired insulin signaling, altered glucose metabolism, inflammation, oxidative stress, and premature aging, which strongly affect cognitive function and increased risk of dementia. Consequently, as a widely used drug for T2DM, metformin also has therapeutic potential for AD in vivo. It has been confirmed that metformin is beneficial on the brain of AD animal models. The mechanisms underlying the effects of metformin in Alzheimer's disease are complex and multifaceted. Metformin may work through mechanisms involving homeostasis of glucose metabolism, decrease of amyloid plaque deposition, normalization of tau protein phosphorylation and enhancement of autophagy. However, in clinical trials, metformin had little effects on patients with mild cognitive impairment or mild AD. Pathological effects and negative clinical results of metformin on AD make the current topic quite controversial. By reviewing the latest progress of related research, this paper summarizes the possible role of metformin in AD. The purpose of this study is not only to determine the potential treatment of AD, but also other related neurodegenerative diseases.

Gadd45g, a novel antidepressant target, mediates metformin-induced neuronal differentiation of neural stem cells via DNA demethylation

Increased neurogenesis elicits antidepressive-like effects. The antidiabetic drug metformin (Met) reportedly promotes hippocampal neurogenesis, which ameliorates spatial memory deficits and depression-like behaviors. However, the precise molecular mechanisms underpinning Met-induced neuronal differentiation of neural stem cells (NSCs) remain unclear. We showed that Met enhanced neuronal differentiation of NSCs via Gadd45g but not Gadd45a and Gadd45b. We further found that Gadd45g increased demethylation of neurogenic differentiation 1 (NeuroD1) promoter by regulating the activity of passive and active DNA demethylation enzymes through an AMPK-independent mechanism in Met-treated NSCs. Importantly, genetic deficiency of Gadd45g decreased hippocampal neurogenesis, which could contribute to spatial memory decline, and depression-like behaviors in the adult mice, whereas forced expression of Gadd45g alleviated the depressive-like behaviors. Our findings provide a model that Gadd45g-mediated DNA demethylation contributes to Met-induced neuronal genesis and its antidepressant-like effects, and propose the concept that targeting Gadd45g regulation of neurogenesis might serve as a novel antidepressant strategy.

Avicularin Attenuates Memory Impairment in Rats with Amyloid Beta-Induced Alzheimer's Disease

Amyloid-beta-induced Alzheimer's disease (AD) and its further complications are well-established models in preclinical studies and demonstrated by many researchers. Intracerebroventricular injection of Aβ produces brain malfunction, including neurodegeneration and memory impairment. Avicularin is a bioactive flavonoid that has been found to prevent oxidative stress and proinflammatory cytokines. Alzheimer's disease treatment may benefit from inhibiting amyloid-beta and its related complications. Hence, by considering multiple actions of avicularin, including antioxidant and anti-inflammatory, we demonstrated the neuroprotective action of avicularin against amyloid beta-induced neurotoxicity. Aβ_1-42 (1 µg/µl) was dissolved in phosphate buffer solution (pH7.4) and incubated at 37 °C for 3 days to induce aggregation. A single intracerebroventricular (i.c.v.) injection of the Aβ_1-42 was given to the animals utilizing stereotaxic equipment. Avicularin was dissolved in 0.5% sodium carboxymethyl cellulose (CMC), and treatment was given to the animals for 21 days at a dose of (25, 50, and 100 mg/kg, p.o.) after Aβ_1-42 peptide (i.c.v.) injection. Several behavioral studies, acetylcholinesterase activity, oxidative stress, TNFα, IL-6, IL-1β, and expression of BDNF and amyloid-beta were measured. Avicularin treatment (50 and 100 mg/kg) showed cognition enhancement activity in behavioral studies and could reverse the effects of amyloid beta-induced inflammatory response and excessive oxidative stress. Furthermore, the findings reveal that avicularin can halt AD progression by targeting BDNF and amyloid-beta levels in the brain, suggesting that avicularin could be used for Alzheimer's disease treatment.

Metformin Alleviates Neuroinflammation Following Intracerebral Hemorrhage in Mice by Regulating Microglia/Macrophage Phenotype in a Gut Microbiota-Dependent Manner

The gut microbiota plays a key role in regulating intracerebral hemorrhage (ICH)-induced neuroinflammation. The anti-neuroinflammatory effects of metformin (Met) have been reported in many central nervous system (CNS) diseases. However, whether Met regulates neuroinflammation through the gut microbiota in ICH-induced brain injury remains unknown. We found that Met treatment substantially alleviated neurological dysfunction and reduced neuroinflammation by inhibiting pro-inflammatory polarization of microglia/macrophages in mice with ICH. Moreover, Met treatment altered the microbiota composition and improved intestinal barrier function. The expression of lipopolysaccharide-binding protein (LBP), a biomarker of intestinal barrier damage, was also significantly reduced by Met treatment. Neuroinflammation was also potently ameliorated after the transplantation of fecal microbiota from Met-treated ICH mice. The neuroprotective effects of fecal microbiota transplantation (FMT) were similar to those of oral Met treatment. However, suppression of the gut microbiota negated the neuroprotective effects of Met in ICH mice. Therefore, Met is a promising therapeutic agent for neuroinflammation owing to ICH-induced imbalance of the gut microbiota.

Adult Hippocampal Neurogenesis in Alzheimer’s Disease: An Overview of Human and Animal Studies with Implications for Therapeutic Perspectives Aimed at Memory Recovery

The mammalian hippocampal dentate gyrus is a niche for adult neurogenesis from neural stem cells. Newborn neurons integrate into existing neuronal networks, where they play a key role in hippocampal functions, including learning and memory. In the ageing brain, neurogenic capability progressively declines while in parallel increases the risk for developing Alzheimer's disease (AD), the main neurodegenerative disorder associated with memory loss. Numerous studies have investigated whether impaired adult neurogenesis contributes to memory decline in AD. Here, we review the literature on adult hippocampal neurogenesis (AHN) and AD by focusing on both human and mouse model studies. First, we describe key steps of AHN, report recent evidence of this phenomenon in humans, and describe the specific contribution of newborn neurons to memory, as evinced by animal studies. Next, we review articles investigating AHN in AD patients and critically examine the discrepancies among different studies over the last two decades. Also, we summarize researches investigating AHN in AD mouse models, and from these studies, we extrapolate the contribution of molecular factors linking AD-related changes to impaired neurogenesis. Lastly, we examine animal studies that link impaired neurogenesis to specific memory dysfunctions in AD and review treatments that have the potential to rescue memory capacities in AD by stimulating AHN.

Fighting fire with fire: the immune system might be key in our fight against Alzheimer's disease

The ultimate cause of Alzheimer's disease (AD) is still unknown and no disease-modifying treatment exists. Emerging evidence supports the concept that the immune system has a key role in AD pathogenesis. This awareness leads to the idea that specific parts of the immune system must be engaged to ward off the disease. Immunotherapy has dramatically improved the management of several previously untreatable cancers and could hold similar promise as a novel therapy for treating AD. However, before potent immunotherapies can be rationally designed as treatment against AD, we need to fully understand the dynamic interplay between AD and the different parts of our immune system. Accordingly, here we review the most important aspects of both the innate and adaptive immune system in relation to AD pathology. Teaser: Emerging results support the concept that Alzheimer's disease is affected by the inability of the immune system to contain the pathology of the brain. Here, we discuss how we can engage our immune system to fight this devastating disease.

Novel Insight into Functions of Transcription Factor EB (TFEB) in Alzheimer’s Disease and Parkinson’s Disease

A key pathological feature of neurodegenerative diseases (NDs) such as Alzheimer's disease (AD) and Parkinson's disease (PD) is the accumulation of aggregated and misfolded protein aggregates with limited effective therapeutic agents. TFEB (transcription factor EB), a key regulator of lysosomal biogenesis and autophagy, plays a pivotal role in the degradation of protein aggregates and has thus been regarded as a promising therapeutic target for these NDs. Here, we systematically summarize the molecular mechanisms and function of TFEB regulation. We then discuss the roles of TFEB and autophagy-lysosome pathways in major neurodegenerative diseases including AD and PD. Finally, we illustrate small molecule TFEB activators with protective roles in NDs animal models, which show great potential for being further developed into novel anti-neurodegenerative agents. Overall, targeting TFEB for enhancing lysosomal biogenesis and autophagy may represent a promising opportunity for the discovery of disease-modifying therapeutics for neurodegenerative disorders though more in-depth basic and clinical studies are required in the future.

Pretreatment with metformin prevents microcystin-LR-induced tau hyperphosphorylation via mTOR-dependent PP2A and GSK-3β activation

Microcystin-leucine-arginine (MC-LR) is a toxin secreted by freshwater cyanobacteria that is considered a potential environmental risk factor for Alzheimer's disease (AD). A previous study indicated that tau protein hyperphosphorylation via protein phosphatase 2A (PP2A) and GSK-3β inhibition was the mechanism by which MC-LR induces neurotoxicity; however, how MC-LR-induced neurotoxicity can be effectively prevented remains unclear. In this study, the reversal effect of metformin on MC-LR-induced neurotoxicity was investigated. The results showed that metformin effectively prevented tau hyperphosphorylation at Ser202 caused by MC-LR through PP2A and GSK-3b activity. The effect of metformin on PP2A activity was dependent on the inhibition of mTOR in MC-LR-treated SH-SY5Y cells. Metformin prevented spatial memory deficits in rats caused by intrahippocampal MC-LR administration. In sum, the results suggested that metformin can ameliorate the MC-LR-induced AD-like phenotype by preventing tau phosphorylation at Ser202, which was mainly mediated by mTOR-dependent PP2A and GSK-3β activation.

Autophagy and apoptosis cascade: which is more prominent in neuronal death?

Autophagy and apoptosis are two crucial self-destructive processes that maintain cellular homeostasis, which are characterized by their morphology and regulated through signal transduction mechanisms. These pathways determine the fate of cellular organelle and protein involved in human health and disease such as neurodegeneration, cancer, and cardiovascular disease. Cell death pathways share common molecular mechanisms, such as mitochondrial dysfunction, oxidative stress, calcium ion concentration, reactive oxygen species, and endoplasmic reticulum stress. Some key signaling molecules such as p53 and VEGF mediated angiogenic pathway exhibit cellular and molecular responses resulting in the triggering of apoptotic and autophagic pathways. Herein, based on previous studies, we describe the intricate relation between cell death pathways through their common genes and the role of various stress-causing agents. Further, extensive research on autophagy and apoptotic machinery excavates the implementation of selective biomarkers, for instance, mTOR, Bcl-2, BH3 family members, caspases, AMPK, PI3K/Akt/GSK3β, and p38/JNK/MAPK, in the pathogenesis and progression of neurodegenerative diseases. This molecular phenomenon will lead to the discovery of possible therapeutic biomolecules as a pharmacological intervention that are involved in the modulation of apoptosis and autophagy pathways. Moreover, we describe the potential role of micro-RNAs, long non-coding RNAs, and biomolecules as therapeutic agents that regulate cell death machinery to treat neurodegenerative diseases. Mounting evidence demonstrated that under stress conditions, such as calcium efflux, endoplasmic reticulum stress, the ubiquitin-proteasome system, and oxidative stress intermediate molecules, namely p53 and VEGF, activate and cause cell death. Further, activation of p53 and VEGF cause alteration in gene expression and dysregulated signaling pathways through the involvement of signaling molecules, namely mTOR, Bcl-2, BH3, AMPK, MAPK, JNK, and PI3K/Akt, and caspases. Alteration in gene expression and signaling cascades cause neurotoxicity and misfolded protein aggregates, which are characteristics features of neurodegenerative diseases. Excessive neurotoxicity and misfolded protein aggregates lead to neuronal cell death by activating death pathways like autophagy and apoptosis. However, autophagy has a dual role in the apoptosis pathways, i.e., activation and inhibition of the apoptosis signaling. Further, micro-RNAs and LncRNAs act as pharmacological regulators of autophagy and apoptosis cascade, whereas, natural compounds and chemical compounds act as pharmacological inhibitors that rescue neuronal cell death through inhibition of apoptosis and autophagic cell death.

Effect of metformin treatment on memory and hippocampal neurogenesis decline correlated with oxidative stress induced by methotrexate in rats

Metformin is currently used as a first-line drug to treat patients with type 2 diabetes. Previous studies have demonstrated that metformin has antioxidant properties and reduces neuroinflammation and hippocampal neuronal cell loss, which eventually improves memory. Methotrexate (MTX) is an antimetabolite chemotherapeutic agent reported to activate cognitive impairment found in many patients. Moreover, MTX negatively affects the spatial working memory, related to neurogenesis reduction in animal models. Therefore, the present study aimed to investigate the antioxidant effect of metformin on the reduction of memory and neurogenesis caused by MTX. Male Sprague-Dawley rats were divided into four groups: control, MTX, metformin, and MTX+metformin. MTX (75 mg/kg, i.v.) was administered on days 7 and 14. Rats were administered metformin (200 mg/kg, i.p.) for 14 days. Memory was determined using novel object location (NOL) and novel object recognition (NOR) tests. Furthermore, cell cycle arrest was quantified by p21 immunostaining. Levels of neuronal protein expression, scavenging enzymes activity, and malondialdehyde (MDA) level changes in the hippocampus and prefrontal cortex were investigated. Rats receiving only MTX showed memory impairment. Decreases in scavenging enzyme activity and BDNF, DCX, and Nrf2 protein expressions levels were detected in the MTX-treated rats. In addition, MTX significantly increased p21-positive cell numbers and MDA levels. However, these adverse MTX effects were counteracted by co-administration with metformin. These results demonstrate that metformin can improve memory impairments, increase BDNF, DCX and Nrf2 protein expressions and antioxidant capacities, and decrease MDA levels in MTX-treated rats.

Nanotechnology-Based Drug Delivery Strategies to Repair the Mitochondrial Function in Neuroinflammatory and Neurodegenerative Diseases

Mitochondria are vital organelles in eukaryotic cells that control diverse physiological processes related to energy production, calcium homeostasis, the generation of reactive oxygen species, and cell death. Several studies have demonstrated that structural and functional mitochondrial disturbances are involved in the development of different neuroinflammatory (NI) and neurodegenerative (ND) diseases (NI&NDDs) such as multiple sclerosis, Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Remarkably, counteracting mitochondrial impairment by genetic or pharmacologic treatment ameliorates neurodegeneration and clinical disability in animal models of these diseases. Therefore, the development of nanosystems enabling the sustained and selective delivery of mitochondria-targeted drugs is a novel and effective strategy to tackle NI&NDDs. In this review, we outline the impact of mitochondrial dysfunction associated with unbalanced mitochondrial dynamics, altered mitophagy, oxidative stress, energy deficit, and proteinopathies in NI&NDDs. In addition, we review different strategies for selective mitochondria-specific ligand targeting and discuss novel nanomaterials, nanozymes, and drug-loaded nanosystems developed to repair mitochondrial function and their therapeutic benefits protecting against oxidative stress, restoring cell energy production, preventing cell death, inhibiting protein aggregates, and improving motor and cognitive disability in cellular and animal models of different NI&NDDs.

A Tale of Two Diseases: Exploring Mechanisms Linking Diabetes Mellitus with Alzheimer's Disease

Dementias, including the type associated with Alzheimer's disease (AD), are on the rise worldwide. Similarly, type 2 diabetes mellitus (T2DM) is one of the most prevalent chronic diseases globally. Although mechanisms and treatments are well-established for T2DM, there remains much to be discovered. Recent research efforts have further investigated factors involved in the etiology of AD. Previously perceived to be unrelated diseases, commonalities between T2DM and AD have more recently been observed. As a result, AD has been labeled as "type 3 diabetes". In this review, we detail the shared processes that contribute to these two diseases. Insulin resistance, the main component of the pathogenesis of T2DM, is also present in AD, causing impaired brain glucose metabolism, neurodegeneration, and cognitive impairment. Dysregulation of insulin receptors and components of the insulin signaling pathway, including protein kinase B, glycogen synthase kinase 3β, and mammalian target of rapamycin are reported in both diseases. T2DM and AD also show evidence of inflammation, oxidative stress, mitochondrial dysfunction, advanced glycation end products, and amyloid deposition. The impact that changes in neurovascular structure and genetics have on the development of these conditions is also being examined. With the discovery of factors contributing to AD, innovative treatment approaches are being explored. Investigators are evaluating the efficacy of various T2DM medications for possible use in AD, including but not limited to glucagon-like peptide-1 receptor agonists, and peroxisome proliferator-activated receptor-gamma agonists. Furthermore, there are 136 active trials involving 121 therapeutic agents targeting novel AD biomarkers. With these efforts, we are one step closer to alleviating the ravaging impact of AD on our communities.

Comparing anti-aging hallmark activities of Metformin and Nano-PSO in a mouse model of genetic Creutzfeldt-Jakob Disease

Advanced age is the main risk factor for the manifestation of late onset neurodegenerative diseases. Metformin, an anti-diabetic drug, was shown to extend longevity, and to ameliorate the activity of recognized aging hallmarks. Here, we compared the clinical, pathologic and biochemical effects of Metformin to those of Nano-PSO (Granagard), a brain targeted anti-oxidant shown by us to delay disease advance in transgenic mice mimicking for genetic Creutzfeldt Jacob disease (CJD) linked to the E200KPrP mutation. We demonstrate that both Metformin and Nano-PSO reduced aging hallmarks activities such as activated AMPK, the main energy sensor of cells as well as Nrf2 and COX IV1, regulators of oxidation, and mitochondrial activity. Both compounds reduced inflammation and increased stem cells production, however did not decrease PrP accumulation. As opposed to Nano-PSO, Metformin neither delayed clinical disease advance in these mice nor reduced the accumulation of sulfated glycosaminoglycans, a pathologic feature of prion disease. We conclude that elevation of anti-aging markers may not be sufficient to delay the fatal advance of genetic CJD.

Molecular and Biochemical Pathways Encompassing Diabetes Mellitus and Dementia

Diabetes mellitus is a major metabolic disorder that has now emerged as an epidemic, and it affects the brain through an array of pathways. Diabetes mellitus patients can develop pathological changes in the brain, which eventually take the shape of mild cognitive impairment progressing to Alzheimer's Disease. A number of preclinical and clinical studies demonstrate this fact, and it comes out to be those molecular pathways such as amyloidogenesis, oxidative stress, inflammation, and impaired insulin signaling are identical in diabetes mellitus and dementia. However, the critical player involved in the vicious cycle of diabetes mellitus and dementia is insulin, whose signaling, when impaired in diabetes mellitus (both type 1 and 2), leads to a decline in cognition, although other pathways are also essential contributors. Moreover, it is not only that diabetes mellitus patients indicate cognitive decline at a later stage; many Alzheimer's Disease patients also reflect symptoms of diabetes mellitus, thus creating a vicious cycle inculcating a web of complex molecular mechanisms and hence categorizing Alzheimer's Disease as 'brain diabetes'. Thus, it is practical to suggest that anti-diabetic drugs are beneficial in Alzheimer's Disease; but only smaller trials, not the larger ones, have showcased positive outcomes mainly because of the late onset of therapy. Therefore, it is extremely important to develop more of such molecules that target insulin in dementia patients along with such methods that diagnose impaired insulin signaling and the associated cognitive decline so that early therapy may be initiated and the progression of the disease be prevented.

Adverse Effects of Metformin From Diabetes to COVID-19, Cancer, Neurodegenerative Diseases, and Aging: Is VDAC1 a Common Target?

Metformin has been used for treating diabetes mellitus since the late 1950s. In addition to its antihyperglycemic activity, it was shown to be a potential drug candidate for treating a range of other diseases that include various cancers, cardiovascular diseases, diabetic kidney disease, neurodegenerative diseases, renal diseases, obesity, inflammation, COVID-19 in diabetic patients, and aging. In this review, we focus on the important aspects of mitochondrial dysfunction in energy metabolism and cell death with their gatekeeper VDAC1 (voltage-dependent anion channel 1) as a possible metformin target, and summarize metformin’s effects in several diseases and gut microbiota. We question how the same drug can act on diseases with opposite characteristics, such as increasing apoptotic cell death in cancer, while inhibiting it in neurodegenerative diseases. Interestingly, metformin’s adverse effects in many diseases all show VDAC1 involvement, suggesting that it is a common factor in metformin-affecting diseases. The findings that metformin has an opposite effect on various diseases are consistent with the fact that VDAC1 controls cell life and death, supporting the idea that it is a target for metformin.

Aronia melanocarpa polysaccharide ameliorates inflammation and aging in mice by modulating the AMPK/SIRT1/NF-κB signaling pathway and gut microbiota

Aronia melanocarpa is a natural medicinal plant that has a variety of biological activities, its fruit is often used for food and medicine. Aronia melanocarpa polysaccharide (AMP) is the main component of the Aronia melanocarpa fruit. This research evaluated the delay and protection of AMP obtained from Aronia melanocarpa fruit on aging mice by D-Galactose (D-Gal) induction and explored the effect of supplementing AMP on the metabolism of the intestinal flora of aging mice. The aging model was established by intraperitoneal injection of D-Gal (200 mg/kg to 1000 mg/kg) once per 3 days for 12 weeks. AMP (100 and 200 mg/kg) was given daily by oral gavage after 6 weeks of D-Gal-induced. The results showed that AMP treatment significantly improved the spatial learning and memory impairment of aging mice determined by the eight-arm maze test. H&E staining showed that AMP significantly reversed brain tissue pathological damage and structural disorders. AMP alleviated inflammation and oxidative stress injury in aging brain tissue by regulating the AMPK/SIRT1/NF-κB and Nrf2/HO-1 signaling pathways. Particularly, AMP reduced brain cell apoptosis and neurological deficits by activating the PI3K/AKT/mTOR signaling pathway and its downstream apoptotic protein family. Importantly, 16S rDNA analysis indicated the AMP treatment significantly retarded the aging process by improving the composition of intestinal flora and abundance of beneficial bacteria. In summary, this study found that AMP delayed brain aging in mice by inhibiting inflammation and regulating intestinal microbes, which providing the possibility for the amelioration and treatment of aging and related metabolic diseases.

AMPK activators for the prevention and treatment of neurodegenerative diseases

INTRODUCTION

As the global population ages at an unprecedented rate, the burden of neurodegenerative diseases is expected to grow. Given the profound impact illness like dementia exert on individuals and society writ large, researchers, physicians, and scientific organizations have called for increased investigation into their treatment and prevention. Both metformin and aspirin have been associated with improved cognitive outcomes. These agents are related in their ability to stimulate AMP kinase (AMPK). Momordica charantia, another AMPK activator, is a component of traditional medicines and a novel agent for the treatment of cancer. It is also being evaluated as a nootropic agent.

AREAS COVERED

This article is a comprehensive review which examines the role of AMPK activation in neuroprotection and the role that AMPK activators may have in the management of dementia and cognitive impairment. It evaluates the interaction of metformin, aspirin, and Momordica charantia, with AMPK, and reviews the literature characterizing these agents' impact on neurodegeneration.

EXPERT OPINION

We suggest that AMPK activators should be considered for the treatment and prevention of neurodegenerative diseases. We identify multiple areas of future investigation which may have a profound impact on patients worldwide.

Thioperamide attenuates neuroinflammation and cognitive impairments in Alzheimer's disease via inhibiting gliosis

Alzheimer's disease (AD) is an age-related neurodegenerative disease, which characterized by deposition of amyloid-β (Aβ) plaques, neurofibrillary tangles, neuronal loss, and accompanied by neuroinflammation. Neuroinflammatory processes are well acknowledged to contribute to the progression of AD pathology. Histamine H3 receptor (H3R) is a presynaptic autoreceptor regulating histamine release via negative feedback way. Recently, studies show that H3R are highly expressed not only in neurons but also in microglia and astrocytes. H3R antagonist has been reported to have anti-inflammatory efficacy. However, whether inhibition of H3R is responsible for the anti-neuroinflammation in glial cells and neuroprotection on APPswe, PSEN1dE9 (APP/PS1 Tg) mice remain unclear. In this study, we found that inhibition of H3R by thioperamide reduced the gliosis and induced a phenotypical switch from A1 to A2 in astrocytes, and ultimately attenuated neuroinflammation in APP/PS1 Tg mice. Additionally, thioperamide rescued the decrease of cyclic AMP response element-binding protein (CREB) phosphorylation and suppressed the phosphorylated P65 nuclear factor kappa B (p-P65 NF-κB) in APP/PS1 Tg mice. H89, an inhibitor of CREB signaling, abolished these effects of thioperamide to suppress gliosis and proinflammatory cytokine release. Lastly, thioperamide alleviated the deposition of amyloid-β (Aβ) and cognitive dysfunction in APP/PS1 mice, which were both reversed by administration of H89. Taken together, these results suggested the H3R antagonist thioperamide improved cognitive impairment in APP/PS1 Tg mice via modulation of the CREB-mediated gliosis and inflammation inhibiting, which contributed to Aβ clearance. This study uncovered a novel mechanism involving inflammatory regulating behind the therapeutic effect of thioperamide in AD.

The protective effects of Agomelatine against Aβ1-42 oligomers-induced cellular senescence mediated by SIRT6 and Agomelatine's potential in AD treatment

Alzheimer's disease (AD) is a vicious degenerative disease commonly observed in the elderly population, and the deposition of Amyloid β (Aβ) is regarded as the principal pathological inducement of AD. Severe oxidative stress, inflammatory reactions, and cell senescence in neurons can be induced by Aβ1-42 oligomers, which further contribute to the damage on neurons. Agomelatine is an antidepressant that is recently claimed to have promising anti-oxidative stress and anti-inflammatory effects. The present study aims to explore the potential therapeutic function of Agomelatine on AD and the possible mechanism. Aβ1-42 oligomers were used to induce an in vitro injury model in SH-SY5Y neuronal cells. First, we found that exposure to Aβ1-42 oligomers significantly exacerbated oxidative stress by increasing hydrogen peroxide production and reducing glutathione peroxidase (GPx), which were partially rescued by Agomelatine. Also, Agomelatine attenuated Aβ1-42 oligomers-induced inflammatory response by decreasing the expression of TNF-α and IL-1β. Notably, Agomelatine improved cellular senescence by reducing senescence-associated β-galactosidase (SA-β-Gal) staining and mitigating Aβ1-42 oligomers-induced reduction of telomerase activity. In addition, the upregulated p16^INK4A and p21^CIP1 and the suppressed expression of SIRT6 in Aβ1-42 oligomers-treated cells were reversed by Agomelatine. Lastly, after the knockdown of SIRT6, the protective effect of Agomelatine against Aβ1-42 oligomers-induced cellular senescence was significantly eliminated. In conclusion, our data indicated that Agomelatine ameliorated Aβ1-42 oligomers-induced cellular senescence mediated by SIRT6, and thus, Agomelatine could be effective in treating AD.

Is resveratrol a prospective therapeutic strategy in the co-association of glucose metabolism disorders and neurodegenerative diseases?

Objectives: The mechanism behind the progression of Mild Cognitive Impairment (MCI) to Alzheimer's disease (AD) remains poorly understood. However some evidence pointed out that the co-occurrence of metabolic conditions affecting glucose homeostasis, as type 2 diabetes mellitus (T2DM), may be an important catalyst in this context. Notably, candidate drugs which modulate common pathways in the development of MCI-to-AD mediated by T2DM may offer likely therapy for AD. Nonetheless, limited pharmacological alternatives that modulate common pathways in T2DM, MCI, and AD are available. In the recent decades, studies have shown that resveratrol may act as a neuroprotective compound, but little is known about its potential in improving cognitive and metabolic aspects associated with AD progression mediated by the co-association between TDM2-MCI.Methods: In this review, we discuss possible protective mechanisms of resveratrol on shared pathways associated with AD progression mediated by T2DM-MCI co-occurrence.Results: Some studies indicated that insulin resistance and hyperglycemia may be also a T2DM risk factor for the progression of MCI-to-AD, promoting alterations in metabolic pathways associated with neuronal plasticity, and increasing pro-inflammatory environment. Interestingly, basic research and clinical trials indicate that resveratrol may modulate those pathways, showing a potential neuroprotective effect of this polyphenol.Conclusion: Therefore, there is not enough clinical data supporting the translational therapeutic use of resveratrol in this scenario.

Metformin a Potential Pharmacological Strategy in Late Onset Alzheimer's Disease Treatment

Alzheimer's disease (AD) is one of the most devastating brain disorders. Currently, there are no effective treatments to stop the disease progression and it is becoming a major public health concern. Several risk factors are involved in the progression of AD, modifying neuronal circuits and brain cognition, and eventually leading to neuronal death. Among them, obesity and type 2 diabetes mellitus (T2DM) have attracted increasing attention, since brain insulin resistance can contribute to neurodegeneration. Consequently, AD has been referred to "type 3 diabetes" and antidiabetic medications such as intranasal insulin, glitazones, metformin or liraglutide are being tested as possible alternatives. Metformin, a first line antihyperglycemic medication, is a 5'-adenosine monophosphate (AMP)-activated protein kinase (AMPK) activator hypothesized to act as a geroprotective agent. However, studies on its association with age-related cognitive decline have shown controversial results with positive and negative findings. In spite of this, metformin shows positive benefits such as anti-inflammatory effects, accelerated neurogenesis, strengthened memory, and prolonged life expectancy. Moreover, it has been recently demonstrated that metformin enhances synaptophysin, sirtuin-1, AMPK, and brain-derived neuronal factor (BDNF) immunoreactivity, which are essential markers of plasticity. The present review discusses the numerous studies which have explored (1) the neuropathological hallmarks of AD, (2) association of type 2 diabetes with AD, and (3) the potential therapeutic effects of metformin on AD and preclinical models.

Metformin attenuates vascular pathology by increasing expression of insulin-degrading enzyme in a mixed model of cerebral amyloid angiopathy and type 2 diabetes mellitus

Sporadic cerebral amyloid angiopathy (CAA), which is characterized by cerebrovascular amyloid β (Aβ) deposits, causes cerebral hemorrhages and dementia in elderly people. Metformin has been used to treat patients with type 2 diabetes mellitus (T2DM), and animal and clinical studies have reported therapeutic effects of metformin in Alzheimer's disease (AD). However, the therapeutic effects of metformin in CAA are unclear. Here, we used a mixed mouse model of CAA and T2DM (APP23-ob/ob) to investigate whether metformin has therapeutic effects on cerebrovascular Aβ deposits. We dissolved metformin hydrochloride in water and administered it orally at 350 mg/kg/day. Treatments started when mice were 6 weeks old and continued until they were 15 months old. After we treated APP23-ob/ob mice with metformin, we counted the numbers of vessels with Aβ and measured levels of Aβ40 and Aβ42 (soluble and insoluble), amyloid precursor protein (APP), APP-processing enzymes (α-, β-, and γ-secretases), and Aβ-degrading enzymes (insulin-degrading enzyme [IDE], neprilysin). Metformin significantly reduced cerebrovascular Aβ deposits in APP23-ob/ob mice (p < .05). Compared with controls, metformin-treated APP23-ob/ob mice had significantly reduced Aβ levels in the cerebral cortex (p < .05) and hippocampus (p < .05) and increased levels of IDE in the hippocampus (p < .01). Our results indicate that metformin attenuates the severity of CAA by enhancing Aβ-cleaving IDE expression. The clinical application of metformin may lead to a novel therapeutic strategy in CAA treatment, especially in patients with T2DM.

Metformin prevents p-tau and amyloid plaque deposition and memory impairment in diabetic mice

Insulin deficiency or resistance can promote dementia and hallmarks of Alzheimer's disease (AD). The formation of neurofibrillary tangles of p-TAU protein, extracellular Aβ plaques, and neuronal loss is related to the switching off insulin signaling in cognition brain areas. Metformin is a biguanide antihyperglycemic drug used worldwide for the treatment of type 2 diabetes. Some studies have demonstrated that metformin exerts neuroprotective, anti-inflammatory, anti-oxidant, and nootropic effects. This study aimed to evaluate metformin's effects on long-term memory and p-Tau and amyloid β modulation, which are hallmarks of AD in diabetic mice. Swiss Webster mice were distributed in the following experimental groups: control; treated with streptozotocin (STZ) that is an agent toxic to the insulin-producing beta cells; STZ + metformin 200 mg/kg (M200). STZ mice showed significant augmentation of time spent to reach the target box in the Barnes maze, while M200 mice showed a significant time reduction. Moreover, the M200 group showed reduced GFAP immunoreactivity in hippocampal dentate gyrus and CA1 compared with the STZ group. STZ mice showed high p-Tau levels, reduced p-CREB, and accumulation of β-amyloid (Aβ) plaque in hippocampal areas and corpus callosum. In contrast, all these changes were reversed in the M200 group. Protein expressions of p-Tau, p-ERK, pGSK3, iNOS, nNOS, PARP, Cytochrome c, caspase 3, and GluN2A were increased in the parietal cortex of STZ mice and significantly counteracted in M200 mice. Moreover, M200 mice also showed significantly high levels of eNOS, AMPK, and p-AKT expression. In conclusion, metformin improved spatial memory in diabetic mice, which can be associated with reducing p-Tau and β-amyloid (Aβ) plaque load and inhibition of neuronal death.

Mammalian/mechanistic target of rapamycin (mTOR) complexes in neurodegeneration

Novel targets to arrest neurodegeneration in several dementing conditions involving misfolded protein accumulations may be found in the diverse signaling pathways of the Mammalian/mechanistic target of rapamycin (mTOR). As a nutrient sensor, mTOR has important homeostatic functions to regulate energy metabolism and support neuronal growth and plasticity. However, in Alzheimer's disease (AD), mTOR alternately plays important pathogenic roles by inhibiting both insulin signaling and autophagic removal of β-amyloid (Aβ) and phospho-tau (ptau) aggregates. It also plays a role in the cerebrovascular dysfunction of AD. mTOR is a serine/threonine kinase residing at the core in either of two multiprotein complexes termed mTORC1 and mTORC2. Recent data suggest that their balanced actions also have implications for Parkinson's disease (PD) and Huntington's disease (HD), Frontotemporal dementia (FTD) and Amyotrophic Lateral Sclerosis (ALS). Beyond rapamycin; an mTOR inhibitor, there are rapalogs having greater tolerability and micro delivery modes, that hold promise in arresting these age dependent conditions.

Diabetes, insulin and new therapeutic strategies for Parkinson's disease: Focus on glucagon-like peptide-1 receptor agonists

Parkinson's disease and diabetes mellitus are two chronic disorders associated with aging that are becoming increasingly prevalent worldwide. Parkinson is a multifactorial progressive condition with no available disease modifying treatments at the moment. Over the last few years there is growing interest in the relationship between diabetes (and impaired insulin signaling) and neurodegenerative diseases, as well as the possible benefit of antidiabetic treatments as neuroprotectors, even in non-diabetic patients. Insulin regulates essential functions in the brain such as neuronal survival, autophagy of toxic proteins, synaptic plasticity, neurogenesis, oxidative stress and neuroinflammation. We review the existing epidemiological, experimental and clinical evidence that supports the interplay between insulin and neurodegeneration in Parkinson's disease, as well as the role of antidiabetic treatments in this disease.

Intranasal 15d-PGJ2 ameliorates brain glucose hypometabolism via PPARγ-dependent activation of PGC-1α/GLUT4 signalling in APP/PS1 transgenic mice

Targeting the common molecular mechanism of type 2 diabetes mellitus and Alzheimer's disease (AD), including dysregulation of glucose metabolism, insulin resistance, and neuroinflammation, might be an efficient treatment strategy for AD. Previous studies have shown that 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2), an endogenous PPARγ agonist, has anti-inflammatory, insulin sensitizing and anti-diabetic effects. However, whether 15d-PGJ2 has beneficial effects on AD remains to be elucidated. In the present study, we found that intranasal administration of 15d-PGJ2 (300 ng/30 μL/day) for 3 months significantly inhibited Aβ plaques, suppressed neuroinflammation, and attenuated cognitive deficits in APP/PS1 transgenic mice. Interestingly, 15d-PGJ2 treatment could increase brain glucose uptake, as detected by ¹⁸F-FDG microPET imaging, and co-localization of GLUT4 and NeuN in the hippocampus of APP/PS1 mice. Furthermore, 15d-PGJ2 markedly increased the expression of PPARγ and PGC-1α, upregulated GLUT4, and decreased the phosphorylation of IRS-1 (Ser616) in the hippocampus of APP/PS1 mice. Importantly, co-administration of a PPARγ antagonist GW9662 abrogated these protective effects of 15d-PGJ2. Collectively, intranasal 15d-PGJ2 conferred protective effects against AD by activating PPARγ-dependent PGC-1α/GLUT4 signalling. The PPARγ agonist 15d-PGJ2 might be a potential therapeutic drug for AD.

Sex-Independent Cognition Improvement in Response to Kaempferol in the Model of Sporadic Alzheimer's Disease

Alzheimer's disease (AD) is associated with neural oxidative stress and inflammation, and it is assumed to affect more women than men with unknown mechanisms. Kaempferol (KMP) as a potent natural antioxidant has been known to exhibit various biological and pharmacological functions, including antioxidant and anti-inflammatory. We aimed here to evaluate the role of gender difference in response to KMP on the rat model of sporadic AD. Forty-six female and male Wistar rats were divided into six groups of sham, streptozotocin (STZ) + saline (SAL), STZ + KMP. Female rats were ovariectomized, and then all animals received an intracerebroventricular bilateral injection of STZ (3 mg/kg) to induce the AD model. KMP (10 mg/kg) was intraperitoneally administered for 21 consecutive days. Afterward, spatial learning and memory were assessed via the Morris water maze task (MWM). Finally, the hippocampus level of superoxide dismutase (SOD), glutathione, and malondialdehyde were measured using calorimetric kits. Data showed a significant cognition deficit in STZ + SAL compared with the sham. To sum up, we reported that chronic KMP treatment increase significantly improved acquisition and retrieval of spatial memory as evident by longer TTS (total time spent) and short-latency to the platform in MWM. In addition, KMP increased the levels of SOD and glutathione in the hippocampus of rats. Also, KMP decreased hippocampal levels of malondialdehyde in both genders. In conclusion, KMP successfully restores spatial memory impairment independent of gender difference. This memory restoration may at least in part be mediated through boosting the hippocampal level of SOD and glutathione.

Deletion of Dcf1 Reduces Amyloid-β Aggregation and Mitigates Memory Deficits

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disease. One of the pathologies of AD is the accumulation of amyloid-β (Aβ) to form senile plaques, leading to a decline in cognitive ability and a lack of learning and memory. However, the cause leading to Aβ aggregation is not well understood. Dendritic cell factor 1 (Dcf1) shows a high expression in the entorhinal cortex neurons and neurofibrillary tangles in AD patients.

OBJECTIVE

Our goal is to investigate the effect of Dcf1 on Aβ aggregation and memory deficits in AD development.

METHODS

The mouse and Drosophila AD model were used to test the expression and aggregation of Aβ, senile plaque formation, and pathological changes in cognitive behavior during dcf1 knockout and expression. We finally explored possible drug target effects through intracerebroventricular delivery of Dcf1 antibodies.

RESULTS

Deletion of Dcf1 resulted in decreased Aβ42 level and deposition, and rescued AMPA Receptor (GluA2) levels in the hippocampus of APP-PS1-AD mice. In Aβ42 AD Drosophila, the expression of Dcf1 in Aβ42 AD flies aggravated the formation and accumulation of senile plaques, significantly reduced its climbing ability and learning-memory. Data analysis from all 20 donors with and without AD patients aged between 80 and 90 indicated a high-level expression of Dcf1 in the temporal neocortex. Dcf1 contributed to Aβ aggregation by UV spectroscopy assay. Intracerebroventricular delivery of Dcf1 antibodies in the hippocampus reduced the area of senile plaques and reversed learning and memory deficits in APP-PS1-AD mice.

CONCLUSION

Dcf1 causes Aβ-plaque accumulation, inhibiting dcf1 expression could potentially offer therapeutic avenues.

Dimethyl fumarate abridged tauo-/amyloidopathy in a D-Galactose/ovariectomy-induced Alzheimer's-like disease: Modulation of AMPK/SIRT-1, AKT/CREB/BDNF, AKT/GSK-3β, adiponectin/Adipo1R, and NF-κB/IL-1β/ROS trajectories

Since the role of estrogen in postmenauposal-associated dementia is still debatable, this issue urges the search for other medications. Dimethyl fumarate (DMF) is a drug used for the treatment of multiple sclerosis and has shown a neuroprotective effect against other neurodegenerative diseases. Accordingly, the present study aimed to evaluate the effect of DMF on an experimental model of Alzheimer disease (AD) using D-galactose (D-Gal) administered to ovariectomized (OVX) rats, resembling a postmenopausal dementia paradigm. Adult 18-month old female Wistar rats were allocated into sham-operated and OVX/D-Gal groups that were either left untreated or treated with DMF for 56 days starting three weeks after sham-operation or ovariectomy. DMF succeeded to ameliorate cognitive (learning/short- and long-term memory) deficits and to enhance the dampened overall activity (NOR, Barnes-/Y-maze tests). These behavioral upturns were associated with increased intact neurons (Nissl stain) and a reduction in OVX/D-Gal-mediated hippocampal CA1 neurodegeneration and astrocyte activation assessed as GFAP immunoreactivity. Mechanistically, DMF suppressed the hippocampal contents of AD-surrogate markers; viz., apolipoprotein (APO)-E1, BACE1, Aβ42, and hyperphosphorylated Tau. Additionally, DMF has augmented the neuroprotective parameters p-AKT, its downstream target CREB and BDNF. Besides, it activated AMPK, and enhanced SIRT-1, as well as antioxidant defenses (SOD, GSH). On the other hand, DMF inhibited the transcription factor NF-κB, IL-1β, adiponectin/adiponectin receptor type (AdipoR)1, GSK-3β, and MDA. Accordingly, in this postmenopausal AD model, DMF treatment by pursuing the adiponectin/AdipoR1, AMPK/SIRT-1, AKT/CREB/BDNF, AKT/GSK-3β, and APO-E1 quartet hampered the associated tauo-/amyloidopathy and NF-κB-mediated oxidative/inflammatory responses to advance insights into its anti-amnesic effect.

Metformin: A Growing Journey from Glycemic Control to the Treatment of Alzheimer's Disease and Depression

Metabolic stress, transduced as an altered cellular redox and energy status, presents as the main culprit in many diseases, including diabetes. However, its role in the pathology of neurological disorders is still not fully elucidated. Metformin, a biguanide compound, is an FDA approved antidiabetic drug generally used for the treatment of type 2 diabetes. The recently described wide spectrum of action executed by this drug suggests a potential therapeutic benefit in a panoply of disorders. Current studies imply that metformin could play a neuroprotective role by reversing hallmarks of brain injury (metabolic dysfunction, neuronal dystrophy and cellular loss), in addition to cognitive and behavioral alterations that accompany the onset of certain brain diseases such as Alzheimer's disease (AD) and depression. However, the mechanisms by which metformin exerts its protective effect in neurodegenerative disorders are not yet fully elucidated. The aim of this review is to reexamine the mechanisms through which metformin performs its function while concentrating on its effect on reestablishing homeostasis in a metabolically disturbed milieu. We will also highlight the importance of metabolic stress, not only as a component of many neurological disorders, but also as a primary driving force for neural insult. Of interest, we will explore the involvement of metabolic stress in the pathobiology of AD and depression. The derangement in major metabolic pathways, including AMPK, insulin and glucose transporters, will be explored and the potential therapeutic effects of metformin administration on the reversal of brain injury in such metabolism dependent diseases will be exposed.

Repurposing of Anti-Diabetic Agents as a New Opportunity to Alleviate Cognitive Impairment in Neurodegenerative and Neuropsychiatric Disorders

Cognitive impairment is a shared abnormality between type 2 diabetes mellitus (T2DM) and many neurodegenerative and neuropsychiatric disorders, such as Alzheimer’s disease (AD) and schizophrenia. Emerging evidence suggests that brain insulin resistance plays a significant role in cognitive deficits, which provides the possibility of anti-diabetic agents repositioning to alleviate cognitive deficits. Both preclinical and clinical studies have evaluated the potential cognitive enhancement effects of anti-diabetic agents targeting the insulin pathway. Repurposing of anti-diabetic agents is considered to be promising for cognitive deficits prevention or control in these neurodegenerative and neuropsychiatric disorders. This article reviewed the possible relationship between brain insulin resistance and cognitive deficits. In addition, promising therapeutic interventions, especially current advances in anti-diabetic agents targeting the insulin pathway to alleviate cognitive impairment in AD and schizophrenia were also summarized.

Immunization with Aβ3-10-KLH vaccine improves cognitive function and ameliorates mitochondrial dysfunction and reduces Alzheimer's disease-like pathology in Tg-APPswe/PSEN1dE9 mice

Alzheimer's disease is a common cause of dementia, for which no disease-modifying therapy is yet available. Aβ3-10-KLH, a vaccine for active immunization, has been shown to prevent pathological changes in young transgenic models of AD, but the effects of treatment with it and its effects on mitochondrial dysfunction remain unclear. We immunized 6-month-old Tg-APPswe/PSEN1dE9 mice with Aβ3-10-KLH to analyze whether it is capable of eliminating amyloid-β after its appearance. The vaccine effectively decreased amyloid-β deposits, improved cognitive function and ameliorated mitochondrial dysfunction. These results indicate the potential of Aβ3-10-KLH as a vaccine to treat AD.

Systemic Actions of SGLT2 Inhibition on Chronic mTOR Activation as a Shared Pathogenic Mechanism between Alzheimer's Disease and Diabetes

Alzheimer's disease (AD) affects tens of millions of people worldwide. Despite the advances in understanding the disease, there is an increased urgency for pharmacological approaches able of impacting its onset and progression. With a multifactorial nature, high incidence and prevalence in later years of life, there is growing evidence highlighting a relationship between metabolic dysfunction related to diabetes and subject's susceptibility to develop AD. The link seems so solid that sometimes AD and type 3 diabetes are used interchangeably. A candidate for a shared pathogenic mechanism linking these conditions is chronically-activated mechanistic target of rapamycin (mTOR). Chronic activation of unrestrained mTOR could be responsible for sustaining metabolic dysfunction that causes the breakdown of the blood-brain barrier, tau hyperphosphorylation and senile plaques formation in AD. It has been suggested that inhibition of sodium glucose cotransporter 2 (SGLT2) mediated by constant glucose loss, may restore mTOR cycle via nutrient-driven, preventing or even decreasing the AD progression. Currently, there is an unmet need for further research insight into molecular mechanisms that drive the onset and AD advancement as well as an increase in efforts to expand the testing of potential therapeutic strategies aimed to counteract disease progression in order to structure effective therapies.

Targeting impaired nutrient sensing with repurposed therapeutics to prevent or treat age-related cognitive decline and dementia: A systematic review

BACKGROUND

Dementia is a debilitating syndrome that significantly impacts individuals over the age of 65 years. There are currently no disease-modifying treatments for dementia. Impairment of nutrient sensing pathways has been implicated in the pathogenesis of dementia, and may offer a novel treatment approach for dementia.

AIMS

This systematic review collates all available evidence for Food and Drug Administration (FDA)-approved therapeutics that modify nutrient sensing in the context of preventing cognitive decline or improving cognition in ageing, mild cognitive impairment (MCI), and dementia populations.

METHODS

PubMed, Embase and Web of Science databases were searched using key search terms focusing on available therapeutics such as 'metformin', 'GLP1', 'insulin' and the dementias including 'Alzheimer's disease' and 'Parkinson's disease'. Articles were screened using Covidence systematic review software (Veritas Health Innovation, Melbourne, Australia). The risk of bias was assessed using the Cochrane Risk of Bias tool v 2.0 for human studies and SYRCLE's risk of bias tool for animal studies.

RESULTS

Out of 2619 articles, 114 were included describing 31 different 'modulation of nutrient sensing pathway' therapeutics, 13 of which specifically were utilized in human interventional trials for normal ageing or dementia. Growth hormone secretagogues improved cognitive outcomes in human mild cognitive impairment, and potentially normal ageing populations. In animals, all investigated therapeutic classes exhibited some cognitive benefits in dementia models. While the risk of bias was relatively low in human studies, this risk in animal studies was largely unclear.

CONCLUSIONS

Modulation of nutrient sensing pathway therapeutics, particularly growth hormone secretagogues, have the potential to improve cognitive outcomes. Overall, there is a clear lack of translation from animal models to human populations.

Inflammation and Insulin Resistance as Risk Factors and Potential Therapeutic Targets for Alzheimer's Disease

Overnutrition and modern diets containing high proportions of saturated fat are among the major factors contributing to a low-grade state of inflammation, hyperglycemia and dyslipidemia. In the last decades, the global rise of type 2 diabetes and obesity prevalence has elicited a great interest in understanding how changes in metabolic function lead to an increased risk for premature brain aging and the development of neurodegenerative disorders such as Alzheimer's disease (AD). Cognitive impairment and decreased neurogenic capacity could be a consequence of metabolic disturbances. In these scenarios, the interplay between inflammation and insulin resistance could represent a potential therapeutic target to prevent or ameliorate neurodegeneration and cognitive impairment. The present review aims to provide an update on the impact of metabolic stress pathways on AD with a focus on inflammation and insulin resistance as risk factors and therapeutic targets.

Ginkgolide B‑induced AMPK pathway activation protects astrocytes by regulating endoplasmic reticulum stress, oxidative stress and energy metabolism induced by Aβ1‑42

Ginkgolide B (GB), the diterpenoid lactone compound isolated from the extracts of Ginkgo biloba leaves, significantly improves cognitive impairment, but its potential pharmacological effect on astrocytes induced by β-amyloid (Aβ)_1-42 remains to be elucidated. The present study aimed to investigate the protective effect and mechanism of GB on astrocytes with Aβ_1-42-induced apoptosis in Alzheimer's disease (AD). Astrocytes obtained from Sprague Dawley rats were randomly divided into control, Aβ, GB and GB + compound C groups. Cell viability and apoptosis were analyzed using Cell Counting Kit-8 and flow cytometry assays, respectively. Protein and mRNA expression levels were analyzed using western blotting and reverse transcription-quantitative PCR, respectively. The levels of superoxide dismutase (SOD), malondialdehyde (MDA), glutathione peroxidase (GSH-Px), reactive oxygen species (ROS) and ATP were determined using the corresponding commercial kits. The findings revealed that GB attenuated Aβ_1-42-induced apoptosis and the 5′ adenosine monophosphate- activated protein kinase (AMPK) inhibitor compound C reversed the protective effects of GB. In addition, GB reversed Aβ_1-42-induced oxidative damage and energy metabolism disorders, including decreases in the levels of SOD, GSH-Px and ATP and increased the levels of MDA and ROS in astrocytes, while compound C reversed the anti-oxidative effect and the involvement of GB in maintaining energy metabolism in astrocytes. Finally, GB decreased the expression levels of the endoplasmic reticulum stress (ERS) proteins and the apoptotic protein CHOP and increased both mRNA and protein expression of the components of the energy metabolism-related AMPK/peroxisome proliferator-activated receptor γ coactivator 1α/peroxisome proliferator-activated receptor α and anti-oxidation-related nuclear respiratory factor 2/heme oxygenase 1/NAD(P)H dehydrogenase (quinone 1) pathways and downregulated the expression of β-secretase 1. However, compound C could antagonize these effects. In conclusion, the findings demonstrated that GB protected against Aβ_1-42-induced apoptosis by inhibiting ERS, oxidative stress, energy metabolism disorders and Aβ_1-42 production probably by activating AMPK signaling pathways. The findings provided an innovative insight into the treatment using GB as a therapeutic in Aβ_1-42-related AD.