Melatonin receptor stimulation by agomelatine prevents Aβ-induced tau phosphorylation and oxidative damage in PC12 cells

GSK3: A potential target and pending issues for treatment of Alzheimer's disease

Glycogen synthase kinase-3 (GSK3), consisting of GSK3α and GSK3β subtypes, is a complex protein kinase that regulates numerous substrates. Research has observed increased GSK3 expression in the brains of Alzheimer's disease (AD) patients and models. AD is a neurodegenerative disorder with diverse pathogenesis and notable cognitive impairments, characterized by Aβ aggregation and excessive tau phosphorylation. This article provides an overview of GSK3's structure and regulation, extensively analyzing its relationship with AD factors. GSK3 overactivation disrupts neural growth, development, and function. It directly promotes tau phosphorylation, regulates amyloid precursor protein (APP) cleavage, leading to Aβ formation, and directly or indirectly triggers neuroinflammation and oxidative damage. We also summarize preclinical research highlighting the inhibition of GSK3 activity as a primary therapeutic approach for AD. Finally, pending issues like the lack of highly specific and affinity-driven GSK3 inhibitors, are raised and expected to be addressed in future research. In conclusion, GSK3 represents a target in AD treatment, filled with hope, challenges, opportunities, and obstacles.

The Role of Dietary Antioxidants and Their Potential Mechanisms in Alzheimer’s Disease Treatment

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder associated with cognitive decline and characterized by amyloid-β plaques and neurofibrillary tau tangles. Although AD’s exact pathophysiology remains unclear, oxidative stress is known to play a role in the neurodegenerative process. Since no curative treatment exists, antioxidants represent a potential treatment for AD due to their ability to modulate oxidative stress. Therefore, this review aims to examine the impact of antioxidant supplementation and its potential mechanisms on cognitive function. The review primarily discusses research articles published between 2012 and 2022 reporting the results of clinical trials involving antioxidant supplementation on cognitive function in individuals with AD. Antioxidant supplementation included probiotics, selenium, melatonin, resveratrol, rosmarinic acid, carotenoids, curcumin, vitamin E, and coenzyme Q. While the studies included in this review did not provide much evidence for the beneficial role of antioxidant supplements on cognitive function in AD, the results varied from antioxidant to antioxidant and among trials examining the same antioxidant. Furthermore, many of the studies’ findings face several limitations, including short trial durations, small sample sizes, and a lack of diversity among study participants. As a result, more research is required to examine the impact of antioxidant supplementation on cognitive function in AD.

Brain washing and neural health: role of age, sleep, and the cerebrospinal fluid melatonin rhythm

The brain lacks a classic lymphatic drainage system. How it is cleansed of damaged proteins, cellular debris, and molecular by-products has remained a mystery for decades. Recent discoveries have identified a hybrid system that includes cerebrospinal fluid (CSF)-filled perivascular spaces and classic lymph vessels in the dural covering of the brain and spinal cord that functionally cooperate to remove toxic and non-functional trash from the brain. These two components functioning together are referred to as the glymphatic system. We propose that the high levels of melatonin secreted by the pineal gland directly into the CSF play a role in flushing pathological molecules such as amyloid-β peptide (Aβ) from the brain via this network. Melatonin is a sleep-promoting agent, with waste clearance from the CNS being highest especially during slow wave sleep. Melatonin is also a potent and versatile antioxidant that prevents neural accumulation of oxidatively-damaged molecules which contribute to neurological decline. Due to its feedback actions on the suprachiasmatic nucleus, CSF melatonin rhythm functions to maintain optimal circadian rhythmicity, which is also critical for preserving neurocognitive health. Melatonin levels drop dramatically in the frail aged, potentially contributing to neurological failure and dementia. Melatonin supplementation in animal models of Alzheimer's disease (AD) defers Aβ accumulation, enhances its clearance from the CNS, and prolongs animal survival. In AD patients, preliminary data show that melatonin use reduces neurobehavioral signs such as sundowning. Finally, melatonin controls the mitotic activity of neural stem cells in the subventricular zone, suggesting its involvement in neuronal renewal.

Humulus lupulus L. extract and its active constituent xanthohumol attenuate oxidative stress and nerve injury induced by iron overload via activating AKT/GSK3β and Nrf2/NQO1 pathways

Hops, the dried female clusters from Humulus lupulus L., have traditionally been used as folk medicines for treating insomnia, neuralgia, and menopausal disorders. However, its pharmacological action on iron overload induced nerve damage has not been investigated. This study aims to evaluate the protective effects of hops extract (HLE) and its active constituent xanthohumol (XAN) on nerve injury induced by iron overload in vivo and in vitro, and to explore its underlying mechanism. The results showed that HLE and XAN significantly improved the memory impairment of iron overload mice, mainly manifested as shortened latency time, increased crossing platform times and spontaneous alternation ratio, and increased the expression of related proteins. Additionally, HLE and XAN significantly increased superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX) activities, and remarkably decreased malondialdehyde (MDA) level in hippocampus. Also, HLE and XAN apparently reduced reactive oxygen species (ROS) content of PC12 cells induced by iron dextran (ID), and improved the oxidative stress level. Moreover, HLE and XAN significantly upregulated the expression of nuclear factor E2-related factor (Nrf2), NAD(P)H quinone oxidoreductase (NQO1), heme oxygenase-1 (HO-1), SOD, phosphorylated AKT (p-AKT), and phosphorylated GSK3β (p-GSK3β) both in hippocampus and PC12 cells. These findings demonstrated the protective effect of HLE and XAN against iron-induced memory impairment, which is attributed to its antioxidant profile by activation of AKT/GSK3β and Nrf2/NQO1 pathways. Also, it was suggested that hops could be a potential candidate for iron overload-related neurological diseases treatment.

Design, Synthesis, and Bioactivity of Novel Bifunctional Small Molecules for Alzheimer's disease

The abnormal phosphorylation of the τ-protein is a typical early pathological feature of Alzheimer's disease (AD). The excessive phosphorylation of the τ-protein in the brain causes the formation of neurofibrillary tangles (NFTs) and increases the neurotoxicity of amyloid-β (Aβ). Thus, targeting the τ-protein is considered a promising strategy for treating AD. Herein, we designed and synthesized a series of molecules containing bifunctional groups to recognize the τ-protein and the E3 ligase. The molecules were examined in vitro, and their effects were tested on PC12 cells. In addition, we further studied the pharmacokinetics of compound I3 in healthy rats. Our data showed that compound I3 could effectively degrade τ-protein, reduce Aβ-induced cytotoxicity, and regulate the uneven distribution of mitochondria, which may open a new therapeutic strategy for the treatment of AD.

Ube2c-inhibition alleviated amyloid pathology and memory deficits in APP/PS1 mice model of AD

Autophagy is a major intracellular degradation pathway for the clearance of damaged organelles and misfolded peptides. Previous studies have indicated that autophagy is involved in the pathogenesis of neurodegenerative disease including Alzheimer's disease (AD). Defective autophagy and highly expressed ubiquitin-conjugating enzyme 2C (Ube2c) have been found in AD patients and mouse. However, little is known about the regulation of autophagy in AD. The association of Ube2c with autophagy, amyloid pathology and cognitive deficits in AD remains unclear. In the present study, we characterized over expression of Ube2c and declined autophagy in amyloid β (Aβ)-treated microglia and demonstrated the protective effects of agomelatine (AGO) in APP/PS1 mice. We found that knockdown of Ube2c with AAV2 encoding shUbe2c resulted in an obvious enhancement of autophagy in BV2 microglia cells, and an alleviation of Aβ pathology and memory deficits in APP/PS1 mice. Further, pharmacological inhibition of Ube2c by AGO significantly reduced Aβ plaques, improved synaptic plasticity and cognitive behaviors in APP/PS1 mice, as well as promoted autophagy in microglia. Our findings uncover a potent role of Ube2c over-expression and autophagy decline in the pathogenesis of AD, and suggest that regulation of Ube2c and autophagy may provide an important clue and a potential target for the novel therapeutics of AD.

Agomelatine rescues lipopolysaccharide-induced neural injury and depression-like behaviors via suppression of the Gαi-2-PKA-ASK1 signaling pathway

BACKGROUND

Agomelatine has been shown to be effective in the treatment of depression, but the molecular mechanisms underlying its antidepressant effects have yet to be elucidated. Identification of these molecular mechanisms would not only offer new insights into the basis for depression but also provide the foundation for the development of novel treatments for this disorder.

METHODS

Intraperitoneal injection of LPS was used to induce depression-like behaviors in rats. The interactions of the 5-HT2C reporter and Gαi-2 were verified by immunoprecipitation or immunofluorescence assay. Inflammatory related proteins, autophagy related proteins and apoptosis markers were verified by immunoblotting or immunofluorescence assay. Finally, electron microscopy analysis was used to observe the synapse and ultrastructural pathology.

RESULTS

Here, we found that the capacity for agomelatine to ameliorate depression and anxiety in a lipopolysaccharide (LPS)-induced rat model of depression was associated with an alleviation of neuroinflammation, abnormal autophagy and neuronal apoptosis as well as the promotion of neurogenesis in the hippocampal dentate gyrus (DG) region of these rats. We also found that the 5-HT2C receptor is coupled with G alphai (2) (Gαi-2) protein within hippocampal neurons and, agomelatine, acting as a 5-HT2C receptor antagonist, can up-regulate activity of the Gαi-2-cAMP-PKA pathway. Such events then suppress activation of the apoptosis signal-regulating kinase 1 (ASK1) pathway, a member of the mitogen-activated protein kinase (MAPK) family involved in pathological processes of many diseases.

CONCLUSION

Taken together, these results suggest that agomelatine plays a neuroprotective role in regulating neuroinflammation, autophagy disorder and apoptosis in this LPS-induced rat model of depression, effects which are associated with the display of antidepressant behaviors. These findings provide evidence for some of the potential mechanisms for the antidepressant effects of agomelatine.

Role of melatonin in Alzheimer's disease: From preclinical studies to novel melatonin-based therapies

Melatonin and novel melatonin-based therapies such as melatonin-containing hybrid molecules, melatonin analogues, and melatonin derivatives have been investigated as potential therapeutics against Alzheimer's disease (AD) pathogenesis. In this review, we examine the developmental trends of melatonin therapies for AD from 1997 to 2021. We then highlight the neuroprotective mechanisms of melatonin therapy derived from preclinical studies. These mechanisms include the alleviation of amyloid-related burden, neurofibrillary tangle accumulation, oxidative stress, neuroinflammation, apoptosis, mitochondrial dysfunction, and impaired neuroplasticity and neurotransmission. We further illustrate the beneficial effects of melatonin on behavior in animal models of AD. Next, we discuss the clinical effects of melatonin on sleep, cognition, behavior, psychiatric symptoms, electroencephalography findings, and molecular biomarkers in patients with mild cognitive impairment and AD. We then explore the effectiveness of novel melatonin-based therapies. Lastly, we discuss the limitations of current melatonin therapies for AD and suggest two emerging research themes for future study.

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.

Naturally Occurring Antioxidant Therapy in Alzheimer's Disease

It is estimated that the prevalence rate of Alzheimer's disease (AD) will double by the year 2040. Although currently available treatments help with symptom management, they do not prevent, delay the progression of, or cure the disease. Interestingly, a shared characteristic of AD and other neurodegenerative diseases and disorders is oxidative stress. Despite profound evidence supporting the role of oxidative stress in the pathogenesis and progression of AD, none of the currently available treatment options address oxidative stress. Recently, attention has been placed on the use of antioxidants to mitigate the effects of oxidative stress in the central nervous system. In preclinical studies utilizing cellular and animal models, natural antioxidants showed therapeutic promise when administered alone or in combination with other compounds. More recently, the concept of combination antioxidant therapy has been explored as a novel approach to preventing and treating neurodegenerative conditions that present with oxidative stress as a contributing factor. In this review, the relationship between oxidative stress and AD pathology and the neuroprotective role of natural antioxidants from natural sources are discussed. Additionally, the therapeutic potential of natural antioxidants as preventatives and/or treatment for AD is examined, with special attention paid to natural antioxidant combinations and conjugates that are currently being investigated in human clinical trials.

The effects of agomelatine on endoplasmic reticulum stress related to mitochondrial dysfunction in hippocampus of aging rat model

BACKGROUND

Agomelatine, a novel antidepressant, is a melatonin MT receptor agonist and serotonin 5HT2C receptor antagonist. In this study, agomelatine was used to investigate the molecular mechanisms of hippocampal aging associated with endoplasmic reticulum (ER) stress, mitochondrial dysfunction, and apoptosis, all of which led to short-term memory impairment.

METHOD

Hippocampal aging was induced in male Wistar rats by d-galactose (D-gal) intraperitoneal injection (100 mg/kg) for 14 weeks. During the last 4 weeks of D-gal treatment, rats were treated with agomelatine (40 mg/kg) or melatonin (10 mg/kg). At the end of the experiment, all rats were assessed for short-term memory by using the Morris water maze test. Subsequently, rats were sacrified and the hippocampus was removed from each rat for determination of reactive oxygen species (ROS), malondialdehyde (MDA), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays; and immunohistochemistry related to ER stress, mitochondrial dysfunction, and apoptosis.

RESULTS

Agomelatine suppressed the expression of the aging-related proteins P16 and receptor for advanced glycation endproducts (RAGE), the expression of NADPH oxidase (NOX) 2 and 4, and ROS production. This treatment also shifted the morphology of astrocytes and microglia toward homeostasis. Furthermore, agomelatine decreased inositol-requiring enzyme 1 (pIRE1), protein kinase R-like endoplasmic reticulum kinase (pPERK), and chaperone binding immunoglobulin protein (BiP), leading to suppression of ER stress markers C/EBP homologous protein (CHOP) and caspase-12. Agomelatine reduced Ca2+ from the ER and stabilized the mitochondrial membrane stability, which was denoted by the BCL2 Associated X (Bax)/B-cell lymphoma 2 (Bcl2) balance. Agomelatine decreased cleaved caspase-3 production and the Terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL)-positive area, and glutamate excitotoxicity was prevented via suppression of N-methyl-d-aspartate (NMDA) receptor subunit expression. Agomelatine exhibited effects that were similar to melatonin.

CONCLUSION

Agomelatine improved neurodegeneration in a rat model of hippocampal aging by attenuating ROS production, ER stress, mitochondrial dysfunction, excitotoxicity, and apoptosis.

Melatonin: Regulation of Biomolecular Condensates in Neurodegenerative Disorders

Biomolecular condensates are membraneless organelles (MLOs) that form dynamic, chemically distinct subcellular compartments organizing macromolecules such as proteins, RNA, and DNA in unicellular prokaryotic bacteria and complex eukaryotic cells. Separated from surrounding environments, MLOs in the nucleoplasm, cytoplasm, and mitochondria assemble by liquid-liquid phase separation (LLPS) into transient, non-static, liquid-like droplets that regulate essential molecular functions. LLPS is primarily controlled by post-translational modifications (PTMs) that fine-tune the balance between attractive and repulsive charge states and/or binding motifs of proteins. Aberrant phase separation due to dysregulated membrane lipid rafts and/or PTMs, as well as the absence of adequate hydrotropic small molecules such as ATP, or the presence of specific RNA proteins can cause pathological protein aggregation in neurodegenerative disorders. Melatonin may exert a dominant influence over phase separation in biomolecular condensates by optimizing membrane and MLO interdependent reactions through stabilizing lipid raft domains, reducing line tension, and maintaining negative membrane curvature and fluidity. As a potent antioxidant, melatonin protects cardiolipin and other membrane lipids from peroxidation cascades, supporting protein trafficking, signaling, ion channel activities, and ATPase functionality during condensate coacervation or dissolution. Melatonin may even control condensate LLPS through PTM and balance mRNA- and RNA-binding protein composition by regulating N6-methyladenosine (m6A) modifications. There is currently a lack of pharmaceuticals targeting neurodegenerative disorders via the regulation of phase separation. The potential of melatonin in the modulation of biomolecular condensate in the attenuation of aberrant condensate aggregation in neurodegenerative disorders is discussed in this review.

Melatonin Promotes In Vitro Maturation of Vitrified-Warmed Mouse Germinal Vesicle Oocytes, Potentially by Reducing Oxidative Stress through the Nrf2 Pathway

Simple Summary

Cryopreservation of oocytes can cause high oxidative stress, reduce the quality of vitrified-warmed oocytes, and seriously hinder the application of oocyte cryopreservation technology in production and medicine. In this work, we found for the first time that melatonin can exert antioxidant effects through receptors and regulate the Nrf2 antioxidant pathway to respond to oxidative stress of vitrified-warmed oocytes, thereby improving both oocyte quality and the potential for subsequent development. The results illustrated the molecular mechanism of melatonin’s antioxidant effect in vitrified-warmed oocytes and provided a theoretical basis for the application of melatonin in the cryopreservation of oocytes. These findings are of great significance for the further application of oocyte cryopreservation technology to production and assisted reproduction in the future.

Abstract

Previously it was reported that melatonin could mitigate oxidative stress caused by oocyte cryopreservation; however, the underlying molecular mechanisms which cause this remain unclear. The objective was to explore whether melatonin could reduce oxidative stress during in vitro maturation of vitrified-warmed mouse germinal vesicle (GV) oocytes through the Nrf2 signaling pathway or its receptors. During in vitro maturation of vitrified-warmed mouse GV oocytes, there were decreases (p < 0.05) in the development rates of metaphase I (MI) oocytes and metaphase II (MII) and spindle morphology grades; increases (p < 0.05) in the reactive oxygen species (ROS) levels; and decreases (p < 0.05) in expressions of Nrf2 signaling pathway-related genes (Nrf2, SOD1) and proteins (Nrf2, HO-1). However, adding 10⁻⁷ mol/L melatonin to both the warming solution and maturation solutions improved (p < 0.05) these indicators. When the Nrf2 protein was specifically inhibited by Brusatol, melatonin did not increase development rates, spindle morphology grades, genes, or protein expressions, nor did it reduce vitrification-induced intracellular oxidative stress in GV oocytes during in vitro maturation. In addition, when melatonin receptors were inhibited by luzindole, the ability of melatonin to scavenge intracellular ROS was decreased, and the expressions of genes (Nrf2, SOD1) and proteins (Nrf2, HO-1) were not restored to control levels. Therefore, we concluded that 10⁻⁷ mol/L melatonin acted on the Nrf2 signaling pathway through its receptors to regulate the expression of genes (Nrf2, SOD1) and proteins (Nrf2, HO-1), and mitigate intracellular oxidative stress, thereby enhancing in vitro development of vitrified-warmed mouse GV oocytes.

Regulation of Melatonin and Neurotransmission in Alzheimer's Disease

Alzheimer’s disease is a neurodegenerative disorder associated with age, and is characterized by pathological markers such as amyloid-beta plaques and neurofibrillary tangles. Symptoms of AD include cognitive impairments, anxiety and depression. It has also been shown that individuals with AD have impaired neurotransmission, which may result from the accumulation of amyloid plaques and neurofibrillary tangles. Preclinical studies showed that melatonin, a monoaminergic neurotransmitter released from the pineal gland, is able to ameliorate AD pathologies and restore cognitive impairments. Theoretically, inhibition of the pathological progression of AD by melatonin treatment should also restore the impaired neurotransmission. This review aims to explore the impact of AD on neurotransmission, and whether and how melatonin can enhance neurotransmission via improving AD pathology.

The neuroprotective effects of alpha-lipoic acid on an experimental model of Alzheimer's disease in PC12 cells

With the growth of the aging population, the prevalence of Alzheimer's disease (AD) has increased and influenced the work and daily life of AD patients, imposing a heavy burden on society and the patients' families. AD is a progressive disease with a long duration, and the pathogenesis is very complicated. Here, we found that alpha-lipoic acid (LA), an endogenous, naturally synthesized compound, could attenuate amyloid beta fragment (Aβ_25-35 )-induced PC12 cell toxicity. Aβ_25-35 treatment largely decreased the viability of PC12 cells, increased reactive oxygen species (ROS) levels, and increased the percentage of apoptotic cells, which were accompanied by changes in the expression of the apoptosis-related genes. Further, the Wnt pathway was inactivated, and the expression of Wnt pathway-related proteins such as Frizzled2, GSK3β, and phosphorylated GSK3β were dysregulated after Aβ_25-35 treatment. LA efficiently attenuated Aβ_25-35 -induced PC12 cell apoptosis and downregulated the phosphorylation-mediated degradation of β-catenin as well as GSK3β. Our results demonstrate that LA rescues Aβ_25-35 -induced neurocytotoxicity through the Wnt-β-catenin pathway.

Agomelatine prevents macrophage infiltration and brain endothelial cell damage in a stroke mouse model

Background and purpose: Ischemic/reperfusions are regarded as the clinical consensus for stroke treatment, which results in secondary injury of brain tissues. Increased blood-brain barrier (BBB) permeability and infiltration of inflammatory cells are responsible for the ischemic/reperfusion injury. In the present study, we aimed to investigate the effects of Agomelatine on brain ischemic/reperfusions injury and the underlying mechanism.

Methods: MCAO model was established in mice. The expressions of CD68 and claudin-5 in the cerebral cortex were determined using an immunofluorescence assay. Brain permeability was evaluated using Evans blue staining assay. A two-chamber and two-cell trans-well assay was used to detect the migration ability of macrophages through endothelial cells. The expression levels of claudin-5 and MCP-1 in the endothelial cells were determined using qRT-PCR and ELISA.

Results: CD68 was found to be up-regulated in the cerebral cortex of MCAO mice but was down-regulated by treatment with Agomelatine. The expression level of down-regulated claudin-5 in the cerebral cortex of MCAO mice was significantly suppressed by Agomelatine. Deeper staining of Evans blue was found in the MCAO group, which was however faded significantly in the Agomelatine treated MCAO mice. The migrated macrophages were significantly increased by hypoxia incubation but were greatly suppressed by the introduction of Agomelatine. The down-regulated claudin-5 by hypoxic incubation in endothelial cells was up-regulated by treatment with Agomelatine. Furthermore, the increased expression of MCP-1 in endothelial cells under hypoxic conditions was significantly inhibited by Agomelatine.

Conclusion: Agomelatine prevents macrophage infiltration and brain endothelial cell damage in a stroke mouse model.

Serotonin 2 Receptors, Agomelatine, and Behavioral and Psychological Symptoms of Dementia in Alzheimer's Disease

There are nearly 50 million Alzheimer's disease (AD) patients worldwide, 90% of whom develop behavioral and psychological symptoms of dementia (BPSD), which increase the mortality rate of patients, and impose an economic and care burden on families and society. As a neurotransmitter and neuromodulator, serotonin is involved in the regulation of psychoemotional, sleep, and feeding functions. Accumulating data support the importance of serotonin in the occurrence and development of BPSD. Studies have shown that reduction of serotonin receptors can increase depression and mental symptoms in AD patients. At present, there is no drug treatment for AD approved by the US Food and Drug Administration. Among them, agomelatine, as a new type of antidepressant, can act on serotonin 2 receptors to improve symptoms such as depression and anxiety. At present, research on BPSD is still in the preliminary exploratory stage, and there are still a lot of unknowns. This review summarizes the relationship between serotonin 2 receptors, agomelatine, and BPSD. It provides a new idea for the study of the pathogenesis and treatment of BPSD.

Agomelatine confers neuroprotection against cisplatin-induced hippocampal neurotoxicity

Neurotoxicity caused by cisplatin is a major obstacle during chemotherapy. Oxidative stress and inflammation are considered the primary mechanism behind neuronal damage which affects the continuing chemotherapy regimen. Agomelatine was recently described as a neuroprotective compound against toxic insults in the nervous systems. It is an analog of the well-known antioxidant and anti-inflammatory compound melatonin and currently used for depression and sleep disturbances. In the current study, we investigated the possible neuroprotective role of agomelatine against cisplatin-induced oxidative, inflammatory, and behavioral alterations in male rats. Our results show that agomelatine prevented cisplatin-induced neurotoxicity in the HT-22 mouse hippocampal neuronal cell line. Additionally, agomelatine treatment inhibited cisplatin-induced behavioral deficits and neuronal integrity in vivo. For the evaluation of the effect of agomelatine on oxidative stress and inflammation, GSH, MDA, TNF, and IL-6 levels were analyzed in HT-22 cells and hippocampal tissues. Agomelatine significantly attenuated oxidative stress and inflammation due to the cisplatin insult in vitro and in vivo. Also, agomelatine treatment ameliorated the neuronal pathology in the hippocampus, which is strongly related to cognition and memory. Taken together, our results indicate that in males, the neuroprotective effect of agomelatine is mediated through its antioxidant and anti-inflammatory actions abrogating functional deficits.

Agomelatine Attenuates Isoflurane-Induced Inflammation and Damage in Brain Endothelial Cells

Background and Purpose

Neurotoxicity of anesthetics has been widely observed by clinicians. It is reported that inflammation and oxidative stress are involved in the pathological process. In the present study, we aimed to assess the therapeutic effects of agomelatine against isoflurane-induced inflammation and damage to brain endothelial cells.

Materials and Methods

MTT assay was used to detect cell viability in order to determine the optimized concentration of agomelatine. The bEnd.3 brain endothelial cells were treated with 2% isoflurane in the presence or absence of agomelatine (5, 10 μM) for 24 h. LDH release was evaluated and the ROS levels were checked using DHE staining assay. The expressions of IL-6, IL-8, TNF-α, VEGF, TF, VCAM-1, and ICAM-1 were evaluated using real-time PCR and ELISA. Real-time PCR and Western blot analysis were used to determine the expression level of Egr-1.

Results

The decreased cell viability promoted LDH release and elevated ROS levels induced by isoflurane were significantly reversed by the introduction of agomelatine in a dose-dependent manner. The expression levels of IL-6, IL-8, TNF-α, VEGF, TF, VCAM-1, and ICAM-1 were elevated by stimulation with isoflurane, which were significantly suppressed by the administration of agomelatine. The up-regulation of transcriptional factor Egr-1 induced by isoflurane was down-regulated by agomelatine.

Conclusion

Agomelatine might attenuate isoflurane-induced inflammation and damage via down-regulating Egr-1 in brain endothelial cells.

Protective Activity of Aβ on Cell Cultures (PC12 and THP-1 after Differentiation) Preincubated with Lipopolysaccharide (LPS)

Amyloid-β (Aβ), the influence of which is considered the pathomechanism of Alzheimer’s disease, is also present in healthy people. The microbiome’s impact is also taken into account, where bacterial lipopolysaccharide (LPS) activates inflammatory processes and stimulates microglia via TLRs. Molecules of bacterial origin can co-create senile plaques with Aβ. This study evaluated the activity of physiological Aβ concentrations on neuronal and microglial cells after preincubation with LPS. Two cell lines were used in the study: PC12 cells differentiated with NGF and THP-1 cells differentiated with phorbol 12-myristate 13-acetate (PMA). Cells were incubated with LPS at concentrations of 1–100 μM for 24 h and then with Aβ_25–35 at a concentration of 0.001 μM or 1.0 μM for another 24 h. The viability of the culture and free oxygen radicals and the number of DNA strand breaks in both cell lines were evaluated. Additionally, for PC12 cells, neural features were assessed. Stimulation of repair processes in the presence of Aβ was observed for both studied cell lines. There was a decrease in free radical level and DNA damage number compared to control cultures (cells treated with LPS and without Aβ). The neurotrophic activity of Aβ was observed—the effect on neurites’ growth even after the preincubation of PC12 cells with LPS. At the lowest concentration of LPS used, the increase in neurite length was about 50% greater than in the negative control. At low concentrations, Aβ has a protective effect on neuron-like PC12 cells pretreated with LPS.

The melatonin receptor antagonist luzindole induces the activation of cellular stress responses and decreases viability of rat pancreatic stellate cells

In this study, we have examined the effects of luzindole, a melatonin receptor-antagonist, on cultured pancreatic stellate cells. Intracellular free-Ca²⁺ concentration, production of reactive oxygen species (ROS), activation of mitogen-activated protein kinases (MAPK), endoplasmic reticulum stress and cell viability were analyzed. Stimulation of cells with the luzindole (1, 5, 10 and 50 μm) evoked a slow and progressive increase in intracellular free Ca²⁺ ([Ca²⁺ ]_i ) towards a plateau. The effect of the compound on Ca²⁺ mobilization depended on the concentration used. Incubation of cells with the sarcoendoplasmic reticulum Ca²⁺ -ATPase inhibitor thapsigargin (1 μm), in the absence of Ca²⁺ in the extracellular medium, induced a transient increase in [Ca²⁺ ]_i . In the presence of thapsigargin, the addition of luzindole to the cells failed to induce further mobilization of Ca²⁺ . Luzindole induced a concentration-dependent increase in ROS generation, both in the cytosol and in the mitochondria. This effect was smaller in the absence of extracellular Ca²⁺ . In the presence of luzindole the phosphorylation of p44/42 and p38 MAPKs was increased, whereas no changes in the phosphorylation of JNK could be noted. Moreover, the detection of the endoplasmic reticulum stress-sensor BiP was increased in the presence of luzindole. Finally, viability was decreased in cells treated with luzindole. Because cellular membrane receptors for melatonin have not been detected in pancreatic stellate cells, we conclude that luzindole could exert direct effects that are not mediated through its action on melatonin membrane receptors.

Effect of (m)RVD-hemopressin against Aβ1-42-induced apoptosis and inhibition of neurite outgrowth in SH-SY5Y cells

Alzheimer's disease (AD) is a serious neurodegenerative disease. Senile plaques (SPs) in the extracellular space and neurofibrillary tangles (NFTs) in the intracellular areas of the brain are two typical features of AD. SPs and NFTs are composed of amyloid-β (Aβ) aggregates and hyperphosphorylated Tau, respectively. (m)RVD-hemopressin (RVD), which is derived from mouse brain peptide, binds to the cannabinoid 1 receptor (CB1R) as an agonist. Our previous study indicated that RVD reversed Aβ1-42-induced memory impairment in mice. Here, we investigated the underlying molecular mechanism of RVD on Aβ1-42-induced neurotoxicity in retinoic acid-differentiated human neuroblastoma SH-SY5Y cells. Cell viability and neurite outgrowth were investigated by live cell imaging and analysis instrument. We found that RVD reversed Aβ1-42-induced Tau phosphorylation, apoptosis and suppression of neurite outgrowth and the synapse-associated protein postsynaptic density protein 95 (PSD-95) by inhibiting the activity of protein kinase A (PKA) and glycogen synthase kinase 3β (GSK-3β). Combined treatment with AM251 (a CB1R antagonist) blocked the effects of RVD. In conclusion, RVD may be a potential therapeutic agent for the treatment of cognitive dysfunctions, such as Alzheimer's disease.

Phytochemicals and bioactive analysis of different sweet tea (Lithocarpus litseifolius [Hance] Chun) varieties

This paper aims to investigate the constituent phytochemicals and biological activities of six Lithocarpus litseifolius (Hance) Chun (L. litseifolius) cultivars. Processed by UPLC-MS/MS and untargeted metabolomics analysis software (MS-DIAL and MS-FINDER), components of different L. litseifolius cultivars were analyzed qualitatively and quantitatively. By conducting a comprehensive analysis of spectra, MS/MS fragmentation, and retention time, 40 compounds (including 6 phenolic glycosides and 34 flavonoids) were identified rapidly and accurately. Moreover, the total phenolic content (TPC), total flavonoid content (TFC), antioxidant, antimicrobial effects, and pheochromocytoma (PC12) cell viability of different L. litseifolius varieties were evaluated. Purple small leaf (PSL) was found to be the most superior variety with the highest antioxidant activities (8.27, 10.09, and 10.80 mg TE/g for DPPH, ABTS, and FRAP assays, respectively), broad-spectrum antimicrobial activity, and lowest cell cytotoxicity. The results showed that these bioactivities were closely related to phytochemicals among the six cultivars. PRACTICAL APPLICATIONS: L. litseifolius is well known as an important folk drink in the Southern China folklore for its specific efficacy in preventing diabetes. However, there is still a paucity of information on L. litseifolius, as other active components and bioactivities of it remain to be investigated. The wide range of flavonoids discovered in L. litseifolius provides abundant natural health-promoting agents for further applications in medicine and functional food.

Effect of (m)VD-hemopressin against Aβ1-42-induced oxidative stress and apoptosis in mouse hippocampal neurons

Alzheimer's disease (AD) is a serious neurodegenerative disease. Senile plaques (SPs) composed of amyloid-β (Aβ) are typical features of AD. Aβ plays a key role in the disease and has the ability to induce other pathological characteristics of AD, including oxidative stress injury. (m)VD-hemopressin (VD), a peptide derived from mouse brain extracts, can bind cannabinoid 1 receptor (CB1R) as an agonist. Our previous report indicated that VD reverses memory impairment induced by Aβ1-42 in mice. This study aimed to clarify the mechanism by which VD protects hippocampal neurons against Aβ1-42-induced impairment. Our results showed that VD inhibited oxidative stress injury induced by Aβ1-42, as demonstrated by the VD-induced reversal of the upregulation of reactive oxygen species (ROS) and the intracellular lipid peroxidation product malondialdehyde (MDA) and the downregulation of the activities of the antioxidative enzymes catalase (CAT) and glutathione peroxidase (GSH-PX) in mouse hippocampal neurons. We also found that VD restored the decrease in cell growth and viability induced by Aβ1-42 and reversed Aβ1-42-induced apoptosis mediated by the apoptosis-associated proteins Bcl-2 and Bax. However, cotreatment with AM251 (an antagonist of CB1R) blocked the effects of VD. In brief, this study suggested that through CB1R, VD reversed the impairment of cell growth and viability, oxidative stress injury and apoptosis induced by Aβ1-42. Therefore, VD may be a promising agent for the treatment of diseases that involve oxidative stress injury and apoptosis induced by Aβ1-42, such as AD.

Antioxidants and Neuron-Astrocyte Interplay in Brain Physiology: Melatonin, a Neighbor to Rely on

This manuscript is a review focused onto the role of astrocytes in the protection of neurons against oxidative stress and how melatonin can contribute to the maintenance of brain homeostasis. The first part of the review is dedicated to the dependence of neurons on astrocytes by terms of survival under oxidative stress conditions. Additionally, the effects of melatonin against oxidative stress in the brain and its putative role in the protection against diseases affecting the brain are highlighted. The effects of melatonin on the physiology of neurons and astrocytes also are reviewed.

Diagnostic value of miR-193a-3p in Alzheimer's disease and miR-193a-3p attenuates amyloid-β induced neurotoxicity by targeting PTEN

OBJECTIVE

Many microRNAs (miRNAs) have been reported to be aberrantly expressed in Alzheimer's disease (AD) patients. The present study aimed to explore the diagnostic value and neuroprotective role of miR-193a-3p in AD.

METHODS

108 sporadic AD patients and 93 healthy controls were included. An Aβ25-35 insult cellular AD model of PC12 and SH-SY5Y was established. The relative expression levels of miR-193a-3p were calculated using qRT-PCR. Receiver operating characteristic (ROC) curve was applied to evaluate the usefulness of miR-193a-3p for detecting AD. Cell viability and apoptotic rates were calculated. Luciferase reporter assay was performed to confirm the interaction between miR-193a-3p and PTEN.

RESULTS

miR-193a-3p expression was downregulated in both AD patients and the cellular AD model (all P < 0.001). Remarkable positive association was detected between serum miR-193a-3p level and MMSE score in AD patients (r = 0.5889, P < 0.0001). The diagnostic sensitivity and specificity were 89.8% and 77.4%, respectively, and the area under the curve (AUC) was 0.914. Overexpression of miR-193a-3p weakened Aβ25-35 induced cell viability inhibition, and reduced Aβ25-35 induced cell apoptosis in PC12 cells (all P < 0.01). Downregulation of miR-193a-3p intensified the effect of Aβ25-35 PTEN was proved to be the target gene of miR-193a-3p.

CONCLUSION

MiR-193a-3p could be a novel biomarker for AD diagnosis, and may protect against neurotoxicity in AD by targeting PTEN.