SIRT1 as a therapeutic target for Alzheimer's disease

The SIRT-1/Nrf2/HO-1 axis: Guardians of neuronal health in neurological disorders

SIRT1 (Sirtuin 1) is a NAD+-dependent deacetylase that functions through nucleoplasmic transfer and is present in nearly all mammalian tissues. SIRT1 is believed to deacetylate its protein substrates, resulting in neuroprotective actions, including reduced oxidative stress and inflammation, increased autophagy, increased nerve growth factors, and preserved neuronal integrity in aging or neurological disease. Nrf2 is a transcription factor that regulates the genes responsible for oxidative stress response and substance detoxification. The activation of Nrf2 guards cells against oxidative damage, inflammation, and carcinogenic stimuli. Several neurological abnormalities and inflammatory disorders have been associated with variations in Nrf2 activation caused by either pharmacological or genetic factors. Recent evidence indicates that Nrf2 is at the center of a complex cellular regulatory network, establishing it as a transcription factor with genuine pleiotropy. HO-1 is most likely a component of a defense mechanism in cells under stress, as it provides negative feedback for cell activation and mediator synthesis. This mediator is upregulated by Nrf2, nitric oxide (NO), and other factors in various inflammatory states. HO-1 or its metabolites, such as CO, may mitigate inflammation by modulating signal transduction pathways. Neurological diseases may be effectively treated by modulating the activity of HO-1. Multiple studies have demonstrated that SIRT1 and Nrf2 share an important connection. SIRT1 enhances Nrf2, activates HO-1, protects against oxidative injury, and decreases neuronal death. This has been associated with numerous neurodegenerative and neuropsychiatric disorders. Therefore, activating the SIRT1/Nrf2/HO-1 pathway may help treat various neurological disorders. This review focuses on the current understanding of the SIRT1 and Nrf2/HO-1 neuroprotective processes and the potential therapeutic applications of their target activators in neurodegenerative and neuropsychiatric disorders.

Interaction between resveratrol and SIRT1: role in neurodegenerative diseases

Neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Huntington's disease, pose significant health challenges and economic burdens worldwide. Recent studies have emphasized the potential therapeutic value of activating silent information regulator-1 (SIRT1) in treating these conditions. Resveratrol, a compound known for its ability to potently activate SIRT1, has demonstrated promising neuroprotective effects by targeting the underlying mechanisms of neurodegeneration. In this review, we delve into the crucial role of resveratrol-mediated SIRT1 upregulation in improving neurodegenerative diseases. The role of the activation of SIRT1 by resveratrol was reviewed. Moreover, network pharmacology was used to elucidate the possible mechanisms of resveratrol in these diseases. Activation of SIRT1 by resveratrol had positive effects on neuronal function and survival and alleviated the hallmark features of these diseases, such as protein aggregation, oxidative stress, neuroinflammation, and mitochondrial dysfunction. In terms of network pharmacology, the signaling pathways by which resveratrol protects against different neurodegenerative diseases were slightly different. Although the precise mechanisms underlying the neuroprotective effects of resveratrol and SIRT1 activation remain under investigation, these findings offer valuable insights into potential therapeutic strategies for neurodegenerative diseases.

Ameliorative Effects of Raisin Polyphenol Extract on Oxidative Stress and Aging In Vitro and In Vivo via Regulation of Sirt1-Nrf2 Signaling Pathway

Raisins are an important source of polyphenolic compounds in plant foods, and polyphenols are associated with antioxidant and anti-aging activity. In this work, 628 polyphenols in raisin extracts were characterized using UPLC-MS/MS, mainly including tricetin 3'-glucuronide, diisobutyl phthalate, butyl isobutyl phthalate, isoquercitrin and 6-hydroxykaempferol-7-O-glucoside. The oxidative stress in H2O2-induced HepG2 cells and D-gal-induced aging mice was alleviated by raisin polyphenols (RPs) via increases in the cellular levels of superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH), along with decreases in malonaldehyde (MDA), reactive oxygen species (ROS) and advanced glycosylation end-products (AGEs) levels. In addition, it was observed that RPs enhanced Sirt1 and Sirt3 expression, initiating the Keap1-Nrf2 signaling pathway, by upregulating the levels of nuclear Nrf2, facilitating the expressions of the antioxidant proteins NQO1 and HO-1, and downregulating Keap1 and cytoplasmic Nrf2 protein levels in H2O2-induced HepG2 cells and D-gal-induced aging mice. In summary, RP exerted antioxidant and anti-aging effects via regulating the Sirt1-Nrf2 signaling pathway in vitro and in vivo.

Neuroprotective Potential of Aminonaphthoquinone Derivatives Against Amyloid Beta-Induced Neuronal Cell Death Through Modulation of SIRT1 and BACE1

Alzheimer's disease (AD) is characterized by the accumulation of tau protein tangles and amyloid-β (Aβ) plaques in the central nervous system (CNS), leading to progressive neurodegeneration. Hence, the discovery of disease-modifying agents capable of delaying the progression is essential for effective management. Aminonaphthoquinone (ANQ) is an attractive pharmacophore with various biological effects. This study explores the neuroprotective potentials of ANQ derivatives (1-18) using in vitro models of AD pathology (i.e., Aβ42-induced SH-SY5Y cells). Findings demonstrated that all compounds mitigated Aβ42-induced cellular damage by preserving cell viability and morphology. Among all, four compounds (10, 12, 16, and 18) showed potent antioxidant activities as well as abilities to minimize AD-related damages (i.e. decreasing intracellular reactive oxygen species (ROS) production, preserving mitochondrial membrane potential (MMP), protecting membrane damage, and modulating beta-secretase 1 (BACE1) activity) with comparable protective effects to the well-known neuroprotectant, resveratrol (RSV). A molecular docking study indicated these compounds could suitably bind to sirtuin 1 (SIRT1) protein with preferable affinity. Key amino acid residues and key functional groups essential for binding interactions were revealed. Target prediction identified a list of possible AD-related targets of these compounds offering insights into their mechanisms of action and suggesting their multifunctional potentials. Additionally, in silico predictions revealed that these candidates showed favorable drug-like properties. Overall, this study highlighted the therapeutic potential of ANQ derivatives in AD treatment, emphasizing the need for further experimental validation and comprehensive investigations to fully realize their therapeutic benefits.

The role of sirtuin 1 in ageing and neurodegenerative disease: A molecular perspective

Sirtuin 1 (SIRT1), an NAD+-dependent deacetylase, has emerged as a key regulator of cellular processes linked to ageing and neurodegeneration. SIRT1 modulates various signalling pathways, including those involved in autophagy, oxidative stress, and mitochondrial function, which are critical in the pathogenesis of neurodegenerative diseases. This review explores the therapeutic potential of SIRT1 in several neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and Amyotrophic Lateral Sclerosis (ALS). Preclinical studies have demonstrated that SIRT1 activators, such as resveratrol, SRT1720, and SRT2104, can alleviate disease symptoms by reducing oxidative stress, enhancing autophagic flux, and promoting neuronal survival. Ongoing clinical trials are evaluating the efficacy of these SIRT1 activators, providing hope for future therapeutic strategies targeting SIRT1 in neurodegenerative diseases. This review explores the role of SIRT1 in ageing and neurodegenerative diseases, with a particular focus on its molecular mechanisms, therapeutic potential, and clinical applications.

Deep Learning-Driven Exploration of Pyrroloquinoline Quinone Neuroprotective Activity in Alzheimer's Disease

Alzheimer's disease (AD) is a pressing concern in neurodegenerative research. To address the challenges in AD drug development, especially those targeting Aβ, this study uses deep learning and a pharmacological approach to elucidate the potential of pyrroloquinoline quinone (PQQ) as a neuroprotective agent for AD. Using deep learning for a comprehensive molecular dataset, blood-brain barrier (BBB) permeability is predicted and the anti-inflammatory and antioxidative properties of compounds are evaluated. PQQ, identified in the Mediterranean-DASH intervention for a diet that delays neurodegeneration, shows notable BBB permeability and low toxicity. In vivo tests conducted on an Aβ₁₋₄₂-induced AD mouse model verify the effectiveness of PQQ in reducing cognitive deficits. PQQ modulates genes vital for synapse and anti-neuronal death, reduces reactive oxygen species production, and influences the SIRT1 and CREB pathways, suggesting key molecular mechanisms underlying its neuroprotective effects. This study can serve as a basis for future studies on integrating deep learning with pharmacological research and drug discovery.

Neuroprotective effects of vitamin D in an Alzheimer's disease rat model: Improvement of mitochondrial dysfunction via calcium/calmodulin-dependent protein kinase kinase 2 activation of Sirtuin1 phosphorylation

Mitochondrial dysfunction is an early event in Alzheimer's disease (AD) pathogenesis. To assess the impact of vitamin D3 (Vit.D) on neurogenesis, we investigated its role in mitigating cognitive impairment and mitochondrial dysfunction through calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2)-mediated phosphorylation of Sirtuin1 (SIRT1) in an aluminum-chloride-D-galactose (AlCl3-D-gal)-induced AD rat model. Rats were distributed into four groups: control, AlCl3 + D-gal (10 + 60 mg/kg, ip), Vit.D (500 IU/kg, po), and AlCl3 + D-gal+Vit.D. Novel object recognition (NOR), Morris Water Maze, and passive avoidance (PA) tests were used to measure memory abilities. The hippocampal tissue was used to assess vitamin D3 receptor (VDR) and peroxisome-proliferator-activated-receptor-γ-coactivator-1α (PGC-1α) expression by quantitative real-time polymerase chain reaction (qRT-PCR), CAMKK2, p-SIRT1, phosphorylated-AMP-activated protein kinase (p-AMPK), dynamin-related-protein-1 (Drp1), and mitofusin-1 (Mnf1) proteins by western blot and Ca2+ levels, endothelial nitic oxide synthase (eNOS), superoxide dismutase (SOD), amyloid beta (Aβ), and phospho tau (p-Tau) via enzyme-linked immunosorbent assay(ELISA) in addition to histological and ultrastructural examination of rat's brain tissue. Vit.D-attenuated hippocampal injury reversed the cognitive decline and Aβ aggregation, and elevated p-Tau levels in the AlCl3 + D-gal-induced AD rat model. In AlCl3 + D-gal-exposed rats, Vit.D induced VDR expression, normalized Ca2+ levels, elevated CAMKK2, p-AMPK, p-SIRT1, and PGC-1α expression. Vit.D reduced Drp1, induced Mnf1, increased mitochondrial membrane potential, preserved mitochondrial structure, restored normal mitochondrial function, and retained normal eNOS level and SOD activity in AlCl3 + D-gal rats. In conclusion, our findings proved that Vit.D may ameliorate cognitive deficits in AlCl3 + D-gal-induced AD by restoring normal mitochondrial function and reducing inflammatory and oxidative stress via CAMKK2-AMPK/SIRT1 pathway upregulation.

Targeting Sirtuin 1 for therapeutic potential: Drug repurposing approach integrating docking and molecular dynamics simulations

Identifying novel therapeutic agents is a fundamental challenge in contemporary drug development, especially in the context of complex diseases like cancer, neurodegenerative disorders, and metabolic syndromes. Here, we present a comprehensive computational study to identify potential inhibitors of SIRT1 (Sirtuin 1), a critical protein involved in various cellular processes and disease pathways. Leveraging the concept of drug repurposing, we employed a multifaceted approach that integrates molecular docking and molecular dynamics (MD) simulations to predict the binding affinities and dynamic behavior of a diverse set of FDA-approved drugs from DrugBank against the SIRT1. Initially, compounds were shortlisted based on their binding affinities and interaction analyses to identify safe and promising binding partners for SIRT1. Among these candidates, Doxercalciferol and Timiperone emerged as potential candidates, displaying notable affinity, efficiency, and specificity towards the binding pocket of SIRT1. Extensive evaluation revealed that these identified compounds boast a range of favorable biological properties and prefer binding to the active site of SIRT1. To delve deeper into the interactions, all-atom MD simulations were conducted for 500 nanoseconds (ns). These simulations assessed the conformational dynamics, stability, and interaction mechanism of the SIRT1-Doxercalciferol and SIRT1-Timiperone complexes. The MD simulations illustrated that the SIRT1-Doxercalciferol and SIRT1-Timiperone complexes maintain stability over a 500 ns trajectory. These insightful outcomes propose that Doxercalciferol and Timiperone hold promise as viable scaffolds for developing potential SIRT1 inhibitors, with implications for tackling complex diseases such as cancer, neurodegenerative disorders, and metabolic syndromes.

Aerobic exercise combined with chlorogenic acid exerts neuroprotective effects and reverses cognitive decline in Alzheimer's disease model mice (APP/PS1) via the SIRT1/ /PGC-1α/PPARγ signaling pathway

Alzheimer's disease (AD) is a prevalent neurodegenerative disease account for 60-80% of the total number of people with dementia, but its treatment and prevention strategies are still in a long process of exploration. It has been reported that a healthy lifestyle may be an effective non-pharmacological intervention for the prevention and treatment of AD, including increased physical activity and the consumption of polyphenol-rich foods. This study, therefore, investigated the effects of 8 weeks of moderate-intensity aerobic exercise (EX), administration of chlorogenic acid administration (GCA), and a combination of both (EX+GCA) on β-amyloid (Aβ) deposition, inflammatory factors, oxidative stress markers, neuronal damage, and cognitive performance in the brains of AD model mice (APP/PS1) and which signaling pathways may be responsible for these effects. The study used Western blot to detect the expression of signaling pathway-related proteins, enzyme-linked immunosorbent assay to detect the expression of inflammatory factors, hematoxylin-eosin staining to detect hippocampal neuronal morphology, immunohistochemistry to detect changes in Aβ deposition in the hippocampus, an oxidative stress marker kit to detect oxidative stress status and the Morris water maze to detect changes in cognitive performance. This study showed that an 8-week intervention (EX/GCA/EX+GCA) activating the SIRT1/PGC-1α signaling pathway improved oxidative stress, neuroinflammation, Aβ deposition, and cognitive performance in mice. However, there was no obvious difference between the EX and GCA groups. In contrast, the combined EX+GCA intervention was significantly better than phase EX or GCA. Our study suggests that although relief of Aβ deposition, neuroinflammation, oxidative stress, neuronal damage, and cognitive decline could also be achieved with EX or GCA, the combined EX+GCA intervention showed better results. These relief effects on AD-related conditions may be obtained by mediating the activation of the SIRT1/PGC-1α signaling pathway. This study is the first to explore the improvement of AD-related conditions with a combined lifestyle of EX+GCA. This healthy lifestyle could be a candidate option for the treatment of AD.

Acetyl-11-keto-beta boswellic acid(AKBA) modulates CSTC-pathway by activating SIRT-1/Nrf2-HO-1 signalling in experimental rat model of obsessive-compulsive disorder: Evidenced by CSF, blood plasma and histopathological alterations

Obsessive-Compulsive disorder (OCD) is a long-term and persistent mental illness characterised by obsessive thoughts and compulsive behaviours. Numerous factors can contribute to the development or progression of OCD. These factors may result from the dysregulation of multiple intrinsic cellular pathways, including SIRT-1, Nrf2, and HO-1. Inhibitors of selective serotonin reuptake (SSRIs) are effective first-line treatments for OCD. In our ongoing research, we have investigated the role of SIRT-1, Nrf2, and HO-1, as well as the neuroprotective potential of Acetyl-11-keto-beta boswellic acid (AKBA) against behavioural and neurochemical changes in rodents treated with 8-OH-DPAT. In addition, the effects of AKBA were compared to those of fluvoxamine (FLX), a standard OCD medication. Injections of 8-OH-DPAT into the intra-dorso raphe nuclei (IDRN) of rats for seven days induced repetitive and compulsive behaviour accompanied by elevated oxidative stress, inflammatory processes, apoptosis, and neurotransmitter imbalances in CSF, blood plasma, and brain samples. Chronic administration of AKBA at 50 mg/kg and 100 mg/kg p.o. restored histopathological alterations in the cortico-striatal-thalamo-cortical (CSTC) pathway, including the cerebral cortex, striatum, and hippocampal regions. Our investigation revealed that when AKBA and fluvoxamine were administered together, the alterations were restored to a greater degree than when administered separately. These findings demonstrate that the neuroprotective effect of AKBA can serve as an effective basis for developing a novel OCD treatment.

Zinc Ortho Methyl Carbonodithioate Improved Pre and Post-Synapse Memory Impairment via SIRT1/p-JNK Pathway against Scopolamine in Adult Mice

Alzheimer's disease (AD) is globally recognized as a prominent cause of dementia for which efficient treatment is still lacking. New candidate compounds that are biologically potent are regularly tested. We, therefore, hypothesized to study the neuroprotective potential of Zinc Ortho Methyl Carbonodithioate (thereafter called ZOMEC) against Scopolamine (SCOP) induced Alzheimer's disease (AD) model using adult albino mice. We post-administered ZOMEC (30 mg/Kg) into two group of mice for three weeks on daily basis that received either 0.9% saline or SCOP (1 mg/Kg) for initial two weeks. The other two groups of mice received 0.9% saline and SCOP (1 mg/Kg) respectively. After memory related behavioral analysis the brain homogenates were evaluated for the antioxidant potential of ZOMEC and multiple protein markers were examined through western blotting. Our results provide enough evidences that ZOMEC decrease oxidative stress by increasing catalase (CAT) and glutathione S transferase (GST) and decreasing the lipid peroxidation (LPO). The SIRT1 and pre and post synaptic marker proteins, synaptophysin (SYP) as well as post synaptic density protein (PSD-95) expression were also enhanced upon ZOMEC treatment. Furthermore, memory impairment was rescued and ZOMEC appreciably abrogated the Aβ accumulation, BACE1 expression C and the p-JNK pathway. The inflammatory protein markers, NF-kβ and IL-1β in ZOMEC treated mice were also comparable with control group. The predicted interaction of ZOMEC with SIRT1 was further confirmed by molecular docking. These findings thus provide initial reports on efficacy of ZOMEC in SCOP induced AD model.

Treadmill Exercise Improves PINK1/Parkin-Mediated Mitophagy Activity Against Alzheimer's Disease Pathologies by Upregulated SIRT1-FOXO1/3 Axis in APP/PS1 Mice

Although treadmill exercise is effective against Alzheimer's disease (AD), the molecular mechanisms underlying these effects are not fully understood. Recent literature has linked the accumulation of damaged mitochondria and defective mitophagy to AD progression. Here, we determined that abnormally activated PINK1/Parkin pathway-mediated mitophagy plays an important role in AD progression and pathogenesis in 6-month-old APP/PS1 mice. We used the lysosomal inhibitor chloroquine and demonstrated that a 12-week treadmill exercise program improved mitochondrial function, decreased accumulation of β-amyloid plaques, and ameliorated loss of learning and memory ability by enhancing PINK1/Parkin-mediated mitophagy activity in the hippocampus of APP/PS1 mice. Moreover, using the SIRT1 inhibitor EX527, we found that 12 weeks of treadmill exercise rescued PINK1/Parkin-mediated mitophagy by activating the SIRT1-FOXO1/3 axis in the hippocampus of APP/PS1 mice. These findings reveal that activating PINK1/Parkin-mediated mitophagy is a promising strategy for AD treatment, and that the SIRT1-FOXO1/3 axis is a potential candidate for the development of mitophagy enhancers.

Dysregulated miRNAs in Progression and Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive degeneration of neurons due to the accumulation of amyloid-β peptide (Aβ) and hyper-phosphorylation of tau protein in the neuronal milieu leading to increased oxidative stress and apoptosis. Numerous factors contribute towards the progression of AD, including miRNA, which are 22-24 nucleotides long sequence which acts as critical regulators of cellular processes by binding to 3' UTR of mRNA, regulating its expression post-transcriptionally. This review aims to determine the miRNA with the most significant dysregulation in the brain and cerebrospinal fluid (CSF) of human patients. A systemized inclusion/exclusion criterion has been utilized based on selected keywords followed by screening of those articles to conclude a list of 8 highly dysregulated miRNAs based on the fold change of AD vs control patients, which could be used in clinical testing as these miRNAs play central role in the pathophysiology of AD. Furthermore, a network study of highly dysregulated miRNA estimated the association of these miRNA in the mediation of Aβ generation and aggregation, inhibition of autophagy, reduction of Aβ clearance, microglial and astrocytic activation, neuro-inflammation, tau hyper-phosphorylation, and synaptic loss.

Hippocampal SIRT1 improves cognitive impairment by deacetylating tau protein in diabetic models

Diabetes mellitus (DM) is associated with accelerated cognitive decline. However, the mechanism of diabetic cognitive impairment remains poorly understood. In this study, we found that the expression of Sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide (NAD+)-dependent histone deacetylase, was downregulated significantly in the hippocampus of streptozotocin (STZ)-induced diabetic cognitive impairment rats. Viral overexpression of hippocampal SIRT1 ameliorated cognitive impairment in diabetic rats, but viral knockdown of hippocampal SIRT1 mimicked the diabetic effect, eliciting the cognitive decline in normal animals. Further study showed that the decreased level of SIRT1 may result in the increase of acetylated tau protein in the hippocampus, which may mediate the development of diabetic cognitive impairment. These results suggest that SIRT1 may be a key epigenetic regulator that guards against the development of diabetic cognitive impairment by deacetylating the tau protein. SIRT1 activator may serve as a new therapeutic approach for the treatment of diabetic cognitive impairment.

Hypoglycemia, Vascular Disease and Cognitive Dysfunction in Diabetes: Insights from Text Mining-Based Reconstruction and Bioinformatics Analysis of the Gene Networks

Hypoglycemia has been recognized as a risk factor for diabetic vascular complications and cognitive decline, but the molecular mechanisms of the effect of hypoglycemia on target organs are not fully understood. In this work, gene networks of hypoglycemia and cardiovascular disease, diabetic retinopathy, diabetic nephropathy, diabetic neuropathy, cognitive decline, and Alzheimer's disease were reconstructed using ANDSystem, a text-mining-based tool. The gene network of hypoglycemia included 141 genes and 2467 interactions. Enrichment analysis of Gene Ontology (GO) biological processes showed that the regulation of insulin secretion, glucose homeostasis, apoptosis, nitric oxide biosynthesis, and cell signaling are significantly enriched for hypoglycemia. Among the network hubs, INS, IL6, LEP, TNF, IL1B, EGFR, and FOS had the highest betweenness centrality, while GPR142, MBOAT4, SLC5A4, IGFBP6, PPY, G6PC1, SLC2A2, GYS2, GCGR, and AQP7 demonstrated the highest cross-talk specificity. Hypoglycemia-related genes were overrepresented in the gene networks of diabetic complications and comorbidity; moreover, 14 genes were mutual for all studied disorders. Eleven GO biological processes (glucose homeostasis, nitric oxide biosynthesis, smooth muscle cell proliferation, ERK1 and ERK2 cascade, etc.) were overrepresented in all reconstructed networks. The obtained results expand our understanding of the molecular mechanisms underlying the deteriorating effects of hypoglycemia in diabetes-associated vascular disease and cognitive dysfunction.

5,6,7,4'-Tetramethoxyflavanone attenuates NADPH oxidase 1/4 and promotes sirtuin-1 to inhibit cell stress, senescence and apoptosis in Aß25-35-mediated SK-N-SH dysfunction

Amyloidogenesis is a fundamental step of amyloid beta (Aβ) generation-induced toxicity that is commonly reported to disrupt neuronal circuits, function and survival in Alzheimer's disease (AD). The neuroprotective effect of 5,6,7,4'-tetramethoxyflavanone (TMF) from Chormolaela odorata extract on brain degeneration and amyloidogenesis has previously been demonstrated. However, the mechanistic evidence for TMF's effects is still unclear. In this study, we evaluated the neuroprotective effect of TMF in Aβ_25-35-induced toxicity in SK-N-SH neuroblastoma cells. Herein, we demonstrated that TMF exhibited potent antioxidant activity and significantly increased cell viability and decreased ROS production in a dose-dependent manner. Moreover, TMF reversed the effect of Aβ_25-35, which caused energy deprivation and apoptosis, by decreasing the ratio of Bax/Bcl-x_L and reducing mitochondrial membrane potential (Δψ_m), caspase-3 expression, apoptotic cells, and attenuating glucose transporter (Glut-3) expression. In addition, TMF protected against Aβ_25-35-induced cellular senescence by attenuating β-galactosidase, p-21 and p-53 expression and promoted the expression of Sirt-1 and p-Rb. In addition, the effects of TMF on Aβ_25-35 toxicity were related to the upregulation of phase II antioxidant and nuclear factor erythroid 2-related factor-2 (Nrf2) signaling, including superoxide dismutase (SOD), heme oxygenase (HO)-1, and nuclear translocation of Nrf2. Finally, we also found that TMF attenuated Aβ_25-35-reduced synaptic plasticity by increasing the expression of synaptophysin and PSD-95, which was correlated with a decrease in acetylcholine esterase (AChE). Importantly, we found that the protective effects of TMF on Aβ_25-35 were bidirectional, including marked inhibition of NADPH oxidase (NOX)-4 activity and partial activation of Sirt-1, which occurred prior to a reduction in the negative responses. Therefore, TMF may be useful for treating Aβ toxicity in AD.

Icariin ameliorate Alzheimer's disease by influencing SIRT1 and inhibiting Aβ cascade pathogenesis

Of all types of dementia, Alzheimer's disease is the type that has the highest proportion of cases and is the cause of substantial medical and economic burden. The mechanism of Alzheimer's disease is closely associated with the aggregation of amyloid-β protein and causes neurotoxicity and extracellular accumulation in the brain and to intracellular neurofibrillary tangles caused by tau protein hyperphosphorylation in the brain tissue. Previous studies have demonstrated that sirtuin1 downregulation is involved in the pathological mechanism of Alzheimer's disease. The decrease of sirtuin1 level would cause Alzheimer's disease by means of promoting the amyloidogenic pathway to generate amyloid-β species and thereby triggering amyloid-β cascade reaction, such as tau protein hyperphosphorylation, neuron autophagy, neuroinflammation, oxidative stress, and neuron apoptosis. Currently, there is no effective treatment for Alzheimer's disease, it is necessary to develop new treatment strategies. According to the theory of traditional Chinese medicine and based on the mechanism of the disease, tonifying the kidneys is one of the principles for the treatment of Alzheimer's disease and Epimedium is a well-known Chinese medicine for tonifying kidney. Therefore, investigating the influence of the components of Epimedium on the pathological characteristics of Alzheimer's disease may provide a reference for the treatment of Alzheimer's disease in the future. In this article, we summarise the effects and mechanism of icariin, the main ingredient extracted from Epimedium, in ameliorating Alzheimer's disease by regulating sirtuin1 to inhibit amyloid-β protein and improve other amyloid-β cascade pathogenesis.

SIRT1-Dependent Upregulation of BDNF in Human Microglia Challenged with Aβ: An Early but Transient Response Rescued by Melatonin

Microglia represent a first-line defense in the brain. However, in pathological conditions such as Alzheimer’s disease (AD), a pro-inflammatory switch may occur, leading to loss of protective functions. Using the human microglial cell line HMC3, we showed that exposure to low concentrations of β-amyloid peptide 1-42 (Aβ42; 0.2 μM) initially (6 h) upregulated anti-inflammatory markers interleukin (IL)-4, IL-13, and brain-derived neurotrophic factor (BDNF). BDNF increase was prevented by selective inhibition of SIRT1 with EX527 (2 μM). Accordingly, these early effects were accompanied by a significant Aβ42-induced increase of SIRT1 expression, nuclear localization, and activity. SIRT1 modulation involved adenosine monophosphate-regulated kinase (AMPK), which was promptly (30 min) phosphorylated by Aβ42, while the AMPK inhibitor BML-275 (2 μM) attenuated Aβ42-induced SIRT1 increase. Initially observed microglial responses appeared transient, as microglial features changed when exposure to Aβ42 was prolonged (0.2 μM for 72 h). While SIRT1 and BDNF levels were reduced, the expression of inflammatory markers IL-1β and tumor necrosis factor (TNF)-α increased. This coincided with a rise in NF-kB nuclear localization. The effects of melatonin (1 μM) on prolonged microglial exposure to Aβ42 were analyzed for their protective potential. Melatonin was able to prolong SIRT1 and BDNF upregulation, as well as to prevent NF-kB nuclear translocation and acetylation. These effects were sensitive to the melatonin receptor antagonist, luzindole (25 μM). In conclusion, our data define an early microglial defensive response to Aβ42, featuring SIRT1-mediated BDNF upregulation that can be exogenously modulated by melatonin, thus identifying an important target for neuroprotection.

Sowing the Seeds of Discovery: Tau-Propagation Models of Alzheimer's Disease

The propagation of pathological proteins throughout the brain is the primary physiological hallmark of the progression of Alzheimer's Disease (AD). A growing body of evidence indicates that hyperphosphorylated Tau proteins are spread transcellularly between neurons in a prionlike fashion, inducing misfolding and aggregation into neurofibrillary tangles which accumulate along specific connectivity pathways. Earlier transgenic rodent AD models did not capture this disease-relevant spread, and therefore, seeded Tau-propagation models have been developed. Here, mutant human Tau (as isolated protein or packaged into an adeno-associated virus (AAV) viral vector) is stereotaxically injected into select brain regions and its histopathological propagation to downstream neurons quantified. These models offer a faster and more direct mechanism to evaluate genetic components and therapeutic approaches which attenuate Tau spreading in vivo. Recently, these Tau-seeding models have revealed several new targets for AD drug discovery, including nSMase2, SIRT1, p300/CBP, LRP1, and TYROBP, as well as the potential therapeutics based on melatonin and chondroitinase ABC. Importantly, these Tau-propagation rodent models more closely phenocopy the progression of AD in humans and are therefore likely to improve preclinical studies and derisk future moves into clinical trials.

Protein Homeostasis Networks and the Use of Yeast to Guide Interventions in Alzheimer's Disease

Alzheimer's Disease (AD) is a progressive multifactorial age-related neurodegenerative disorder that causes the majority of deaths due to dementia in the elderly. Although various risk factors have been found to be associated with AD progression, the cause of the disease is still unresolved. The loss of proteostasis is one of the major causes of AD: it is evident by aggregation of misfolded proteins, lipid homeostasis disruption, accumulation of autophagic vesicles, and oxidative damage during the disease progression. Different models have been developed to study AD, one of which is a yeast model. Yeasts are simple unicellular eukaryotic cells that have provided great insights into human cell biology. Various yeast models, including unmodified and genetically modified yeasts, have been established for studying AD and have provided significant amount of information on AD pathology and potential interventions. The conservation of various human biological processes, including signal transduction, energy metabolism, protein homeostasis, stress responses, oxidative phosphorylation, vesicle trafficking, apoptosis, endocytosis, and ageing, renders yeast a fascinating, powerful model for AD. In addition, the easy manipulation of the yeast genome and availability of methods to evaluate yeast cells rapidly in high throughput technological platforms strengthen the rationale of using yeast as a model. This review focuses on the description of the proteostasis network in yeast and its comparison with the human proteostasis network. It further elaborates on the AD-associated proteostasis failure and applications of the yeast proteostasis network to understand AD pathology and its potential to guide interventions against AD.

Molecular Crosstalk Between Circadian Rhythmicity and the Development of Neurodegenerative Disorders

Neurodegenerative disorders have been shown to exhibit substantial interconnectedness with circadian rhythmicity. Alzheimer's patients exhibit high degradation of the suprachiasmatic nucleus (SCN), the central endogenous circadian timekeeper, and Parkinson's patients have highly disrupted peripheral clock gene expression. Disrupted sleep patterns are highly evident in patients with neurodegenerative diseases; fragmented sleep has been shown to affect tau-protein accumulation in Alzheimer's patients, and rapid eye movement (REM) behavioral disorder is observed in a significant amount of Parkinson's patients. Although numerous studies exist analyzing the mechanisms of neurodegeneration and circadian rhythm function independently, molecular mechanisms establishing specific links between the two must be explored further. Thus, in this review, we explore the possible intersecting molecular mechanisms between circadian rhythm and neurodegeneration, with a particular focus on Parkinson's disease. We provide evidence for potential influences of E3 ligase and poly adenosine diphosphate (ADP-ribose) polymerase 1 (PARP1) activity on neurodegenerative pathology. The cellular stress and subsequent DNA damage signaling imposed by hyperactivity of these multiple molecular systems in addition to aberrant circadian rhythmicity lead to extensive protein aggregation such as α-synuclein pre-formed fibrils (α-Syn PFFs), suggesting a specific molecular pathway linking circadian rhythmicity, PARP1/E3 ligase activity, and Parkinson's disease.

SIRT1 activation by resveratrol reverses atrophy of apical dendrites of hippocampal CA1 pyramidal neurons and neurobehavioral impairments in moderate grade hepatic encephalopathy rats

A preliminary observation about resveratrol (RSV) dependent normalization of inflammatory and apoptotic factors in the cortex of hyperammonemic rat model of moderate grade hepatic encephalopathy (MoHE) led us to evaluate whether RSV is ultimately able to confer neuroprotection against MoHE pathogenesis and that it does so by activating its bonafide molecular target SIRT1. The present study compared the profile of relevant neurobehavioral pattern vs neuromorphometry of hippocampal CA1 neurons and SIRT1 activity in the hippocampus of the chronic liver failure (CLF) model of moderate grade HE (MoHE) rats induced by administration of 100 mg/kg body weight of thioacetamide i.p. for 10 days and in the CLF/MoHE rats treated with 10 mg/kg body weight RSV i.p. for 7 days. As compared to the control group rats, the MoHE rats showed significantly deranged pattern of memory and motor functions on MWM and rota rod tests, respectively. These behavioural deficits were associated with a significant reduction in apical dendrite length and number of branching points in the CA1 pyramidal neurons. Interestingly, all these parameters were found to be recovered back to their normal levels in the MoHE rats treated with RSV. Concordantly, MoHE associated declined SIRT1 activity in the hippocampus could be normalized back due to RSV treatment to those MoHE rats. Our findings suggest that RSV is able to normalize MoHE associated memory impairments and motor deficits vis a vis reversal of CA1 dendritic atrophy via SIRT1 activation.

Molecular Pathogenesis and Interventional Strategies for Alzheimer's Disease: Promises and Pitfalls

Alzheimer's disease (AD) is a debilitating disorder characterized by age-related dementia, which has no effective treatment to date. β-Amyloid depositions and hyperphosphorylated tau proteins are the main pathological hallmarks, along with oxidative stress, N-methyl-d-aspartate (NMDA) receptor-mediated excitotoxicity, and low levels of acetylcholine. Current pharmacotherapy for AD only provides symptomatic relief and limited improvement in cognitive functions. Many molecules have been explored that show promising outcomes in AD therapy and can regulate cellular survival through different pathways. To have a vivid approach to strategize the treatment regimen, AD physiopathology should be better explained considering diverse etiological factors in conjunction with biochemical disturbances. This Review attempts to discuss different disease modification approaches and address the novel therapeutic targets of AD that might pave the way for new drug discovery using the well-defined targets for therapy of the disease.

Enhancing α-secretase Processing for Alzheimer's Disease-A View on SFRP1

Amyloid β (Aβ) peptides generated via sequential β- and γ-secretase processing of the amyloid precursor protein (APP) are major etiopathological agents of Alzheimer's disease (AD). However, an initial APP cleavage by an α-secretase, such as the a disintegrin and metalloproteinase domain-containing protein ADAM10, precludes β-secretase cleavage and leads to APP processing that does not produce Aβ. The latter appears to underlie the disease symptom-attenuating effects of a multitude of experimental therapeutics in AD animal models. Recent work has indicated that an endogenous inhibitor of ADAM10, secreted-frizzled-related protein 1 (SFRP1), is elevated in human AD brains and associated with amyloid plaques in mouse AD models. Importantly, genetic or functional attenuation of SFRP1 lowered Aβ accumulation and improved AD-related histopathological and neurological traits. Given SFRP1's well-known activity in attenuating Wnt signaling, which is also commonly impaired in AD, SFRP1 appears to be a promising therapeutic target for AD. This idea, however, needs to be addressed with care because of cancer enhancement potentials resulting from a systemic loss of SFRP1 activity, as well as an upregulation of ADAM10 activity. In this focused review, I shall discuss α-secretase-effected APP processing in AD with a focus on SFRP1, and explore the contrasting perspectives arising from the recent findings.

Tropisetron protects against brain aging via attenuating oxidative stress, apoptosis and inflammation: The role of SIRT1 signaling

AIMS

The aim of this study was to elucidate the signaling pathway involved in the anti-aging effect of tropisetron and to clarify whether it affects mitochondrial oxidative stress, apoptosis and inflammation in the aging mouse brain by upregulating Sirtuin 1 or silent information regulator 1 (SIRT1).

MATERIALS AND METHODS

Aging was induced by d-galactose (DG) at the dose of 200 mg/kg body weight/day subcutaneously injected to male mice for six weeks. Tropisetron was simultaneously administered intraperitoneally once a day at three various doses (1, 3 and 5 mg/kg body weight). Oxidative stress and mitochondrial dysfunction markers were evaluated. Nitric oxide (NO) and pro-inflammatory cytokines levels including tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) were studied. Besides, the expressions of apoptosis-associated genes (Bax and Bcl-2) and the aging-related gene (SIRT1) were determined by the real time polymerase chain reaction (RT-PCR). In addition, histopathological alterations were assessed.

KEY FINDINGS

Tropisetron reversed the induction of oxidative damage, mitochondrial dysfunction and overproduction of inflammatory mediators induced by DG in the brain tissue. In addition, tropisetron suppressed DG-induced apoptosis and found to significantly elevate SIRT1 gene expression. Besides, tropisetron could markedly alleviate DG-induced abnormal changes in the brain morphology.

SIGNIFICANCE

Tropisetron exhibited anti-aging effects in the context of DG-induced senescence in mouse brain through various pathways. Our results suggest that tropisetron may attenuate DG-induced brain aging via SIRT1 signaling activation.

The Bewildering Effect of AMPK Activators in Alzheimer's Disease: Review of the Current Evidence

Alzheimer's disease is a multifactorial neurodegenerative disease characterized by progressive cognitive dysfunction. It is the most common form of dementia. The pathologic hallmarks of the disease include extracellular amyloid plaque, intracellular neurofibrillary tangles, and oxidative stress, to mention some of them. Despite remarkable progress in the understanding of the pathogenesis of the disease, drugs for cure or disease-modifying therapy remain somewhere in the distance. From recent time, the signaling molecule AMPK is gaining enormous attention in the AD drug research. AMPK is a master regulator of cellular energy metabolism, and recent pieces of evidence show that perturbation of its function is highly ascribed in the pathology of AD. Several drugs are known to activate AMPK, but their effect in AD remains to be controversial. In this review, the current shreds of evidence on the effect of AMPK activators in Aβ accumulation, tau aggregation, and oxidative stress are addressed. Positive and negative effects are reported with regard to Aβ and tauopathy but only positive in oxidative stress. We also tried to dissect the molecular interplays where the bewildering effects arise from.

Pharmacological Targets and the Biological Mechanisms of Formononetin for Alzheimer's Disease: A Network Analysis

BACKGROUND This study aimed to identify the pharmacological targets and mechanisms of action of the traditional Chinese medicine, formononetin, in the treatment of Alzheimer's disease (AD) using network pharmacological analysis. MATERIAL AND METHODS Targets of AD were obtained by using DisGeNET gene discovery platform, the herbal ingredients target (HIT) database, the SuperPred, and the SwissTargetPrediction compound target prediction platforms. Pathogenic and therapeutic targets were imported to the STRING biological database, and Cytoscape network integration software was used to construct component-target and disease-target interaction networks. Core targets were identified by topological analysis and were further tested to identify the biological processes and signaling pathways. RESULTS Seven key target genes for formononetin in the treatment of patients with AD were identified, including estrogen receptor alpha (ESR1), peroxisome proliferator-activated receptor gamma (PPARG), tumor protein p53 (TP53), sirtuin 1 (SIRT1), tumor necrosis factor (TNF), cytochrome P450 19A1 (CYP19A1), and nuclear factor (erythroid-derived 2)-like 2 (NFE2L2). The biological processes included hormone metabolism, regulation of nucleoside, nucleotide and nucleic acid metabolism, apoptosis, energy pathways, metabolism, cell communication, and signal transduction. The signaling pathways included histone acetylation and deacetylation (HDAC) class I, regulation of p38-alpha/beta, p38 mitogen-activated protein kinase (MAPK) signaling pathway, bone morphogenetic protein (BMP) receptor signaling, interleukin-1 (IL1) mediated signaling events, the tumor necrosis factor (TNF) receptor signaling pathway, and cytoplasmic and nuclear Smad2/3 signaling. CONCLUSIONS Pharmacological network analysis was used to identify the gene targets and mechanisms of formononetin treatment in patients with AD.

Sirtuins in Alzheimer's Disease: SIRT2-Related GenoPhenotypes and Implications for PharmacoEpiGenetics

Sirtuins (SIRT1-7) are NAD⁺-dependent protein deacetylases/ADP ribosyltransferases with important roles in chromatin silencing, cell cycle regulation, cellular differentiation, cellular stress response, metabolism and aging. Sirtuins are components of the epigenetic machinery, which is disturbed in Alzheimer’s disease (AD), contributing to AD pathogenesis. There is an association between the SIRT2-C/T genotype (rs10410544) (50.92%) and AD susceptibility in the APOEε4-negative population (SIRT2-C/C, 34.72%; SIRT2-T/T 14.36%). The integration of SIRT2 and APOE variants in bigenic clusters yields 18 haplotypes. The 5 most frequent bigenic genotypes in AD are 33CT (27.81%), 33CC (21.36%), 34CT (15.29%), 34CC (9.76%) and 33TT (7.18%). There is an accumulation of APOE-3/4 and APOE-4/4 carriers in SIRT2-T/T > SIRT2-C/T > SIRT2-C/C carriers, and also of SIRT2-T/T and SIRT2-C/T carriers in patients who harbor the APOE-4/4 genotype. SIRT2 variants influence biochemical, hematological, metabolic and cardiovascular phenotypes, and modestly affect the pharmacoepigenetic outcome in AD. SIRT2-C/T carriers are the best responders, SIRT2-T/T carriers show an intermediate pattern, and SIRT2-C/C carriers are the worst responders to a multifactorial treatment. In APOE-SIRT2 bigenic clusters, 33CC carriers respond better than 33TT and 34CT carriers, whereas 24CC and 44CC carriers behave as the worst responders. CYP2D6 extensive metabolizers (EM) are the best responders, poor metabolizers (PM) are the worst responders, and ultra-rapid metabolizers (UM) tend to be better responders that intermediate metabolizers (IM). In association with CYP2D6 genophenotypes, SIRT2-C/T-EMs are the best responders. Some Sirtuin modulators might be potential candidates for AD treatment.

Current and Emerging Pharmacological Targets for the Treatment of Alzheimer's Disease

No cure or disease-modifying therapy for Alzheimer's disease (AD) has yet been realized. However, a multitude of pharmacological targets have been identified for possible engagement to enable drug discovery efforts for AD. Herein, we review these targets comprised around three main therapeutic strategies. First is an approach that targets the main pathological hallmarks of AD: amyloid-β (Aβ) oligomers and hyperphosphorylated tau tangles which primarily focuses on reducing formation and aggregation, and/or inducing their clearance. Second is a strategy that modulates neurotransmitter signaling. Comprising this strategy are the cholinesterase inhibitors and N-methyl-D-aspartate receptor blockade treatments that are clinically approved for the symptomatic treatment of AD. Additional targets that aim to stabilize neuron signaling through modulation of neurotransmitters and their receptors are also discussed. Finally, the third approach comprises a collection of 'sensitive targets' that indirectly influence Aβ or tau accumulation. These targets are proteins that upon Aβ accumulation in the brain or direct Aβ-target interaction, a modification in the target's function is induced. The process occurs early in disease progression, ultimately causing neuronal dysfunction. This strategy aims to restore normal target function to alleviate Aβ-induced toxicity in neurons. Overall, we generally limit our analysis to targets that have emerged in the last decade and targets that have been validated using small molecules in in vitro and/or in vivo models. This review is not an exhaustive list of all possible targets for AD but serves to highlight the most promising and critical targets suitable for small molecule drug intervention.

Reduced expression of SIRT1 and SOD-1 and the correlation between these levels in various regions of the brains of patients with Alzheimer's disease

AIMS

This study was designed to explore the expression and distribution of silent information regulator 1 (SIRT1) and superoxide dismutase 1 (SOD-1) in various regions of the brains of patients with Alzheimer's disease (AD), as well as to assess potential correlations between the levels of these proteins and also between these proteins and the Braak stage of AD.

METHODS

In the temporal and frontal cortices, hippocampus and cerebellum of 10 patients with AD and 10 age-matched control subjects, expression of SIRT1 and SOD-1, together with histopathology, were assessed by immunohistochemical and immunofluorescent stainings. Relationships between variables were examined with the Pearson correlation test.

RESULTS

The numbers of both SIRT1-positive and SOD-1-positive neurons and integrated optical density of immunohistochemical staining for these proteins in the temporal and frontal cortices, and hippocampus of patients with AD were significantly decreased than those in corresponding controls. In the case of the cerebellum, very weak expression of SIRT1 and obvious expression of SOD-1 were observed in granule cells, with no significant difference between AD and the control group. Interestingly, the protein levels between SIRT1 and SOD-1, as well as the level of SIRT1 or SOD-1 and Braak stage, were significantly correlated in neurons in all regions of the AD brains investigated except for the cerebellum.

CONCLUSIONS

These findings indicate that the reduced level of SIRT1 in the brains of patients with AD may be related to the decline in SOD-1 and neuropathological changes of this disorder.

Molecular Imaging of Sirtuin1 Expression-Activity in Rat Brain Using Positron-Emission Tomography-Magnetic-Resonance Imaging with [18F]-2-Fluorobenzoylaminohexanoicanilide

Sirtuin 1 (SIRT1) is a class III histone deacetylase that plays significant roles in the regulation of lifespan, metabolism, memory, and circadian rhythms and in the mechanisms of many diseases. However, methods of monitoring the pharmacodynamics of SIRT1-targeted drugs are limited to blood sampling because of the invasive nature of biopsies. For the noninvasive monitoring of the spatial and temporal dynamics of SIRT1 expression-activity in vivo by PET-CT-MRI, we developed a novel substrate-type radiotracer, [¹⁸F]-2-fluorobenzoylaminohexanoicanilide (2-[¹⁸F]BzAHA). PET-CT-MRI studies in rats demonstrated increased accumulation of 2-[¹⁸F]BzAHA-derived radioactivity in the hypothalamus, hippocampus, nucleus accumbens, and locus coeruleus, consistent with autoradiographic and immunofluorescent (IMF) analyses of brain-tissue sections. Pretreatment with the SIRT1 specific inhibitor, EX-527 (5 mg/kg, ip), resulted in about a 20% reduction of 2-[¹⁸F]BzAHA-derived-radioactivity accumulation in these structures. In vivo imaging of SIRT1 expression-activity should facilitate studies that improve the understanding of SIRT1-mediated regulation in the brain and aid in the development and clinical translation of SIRT1-targeted therapies.

Could Sirtuin Activities Modify ALS Onset and Progression?

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with a complex etiology. Sirtuins have been implicated as disease-modifying factors in several neurological disorders, and in the past decade, attempts have been made to check if manipulating Sirtuin activities and levels could confer benefit in terms of neuroprotection and survival in ALS models. The efforts have largely focused on mutant SOD1, and while limited in scope, the results were largely positive. Here, the body of work linking Sirtuins with ALS is reviewed, with discussions on how Sirtuins and their activities may impact on the major etiological mechanisms of ALS. Moving forward, it is important that the potentially beneficial effect of Sirtuins in ALS disease onset and progression are assessed in ALS models with TDP-43, FUS, and C9orf72 mutations.