N-acetyl-serotonin offers neuroprotection through inhibiting mitochondrial death pathways and autophagic activation in experimental models of ischemic injury

Enhanced In Vitro Plant Morphogenesis of Tobacco: Unveiling Indoleamine-Modulated Adaptogenic Properties of Tulsi (Ocimum sanctum L.)

The medicinal plant tulsi (Ocimum sanctum L.) is acknowledged for its invigorating and healing properties that enhance resilience to stress in various human and animal models by modulating antioxidant compounds. While extensive research has documented these effects in humans, the adaptogenic potential of tulsi in stressful in vitro plant systems has not been explored. This study aimed to elucidate the adaptogenic properties of tulsi leaf extract on the in vitro regeneration of tobacco leaf explants through an investigation of the indoleamines at different developmental stages. Shoot regeneration from leaf explants on the medium supplemented with tulsi extract (20%) was compared to the control, and the differences in indoleamine compounds were analyzed using ultra-performance liquid chromatography. Treatment of the explants with the extract resulted in an almost two-fold increase in the number of regenerants after four weeks of culture, and 9% of the regenerants resembled somatic embryo-like structures. The occurrence of browning in the extract-treated explants stopped on day 10, shoots began to develop, and a significant concentration of tryptamine and N-acetyl-serotonin accumulated. A comparative analysis of indoleamine compounds in intact and cut tobacco leaves also revealed the pivotal role of melatonin and 2-hydroxymelatonin functioning as antioxidants during stress adaptation. This study demonstrates that tulsi is a potent adaptogen that is capable of modulating plant morphogenesis in vitro, paving the way for further investigations into the role of adaptogens in plant stress biology.

Tryptophan Metabolism in Alzheimer's Disease with the Involvement of Microglia and Astrocyte Crosstalk and Gut-Brain Axis

Alzheimer's disease (AD) is an age-dependent neurodegenerative disease characterized by extracellular Amyloid Aβ peptide (Aβ) deposition and intracellular Tau protein aggregation. Glia, especially microglia and astrocytes are core participants during the progression of AD and these cells are the mediators of Aβ clearance and degradation. The microbiota-gut-brain axis (MGBA) is a complex interactive network between the gut and brain involved in neurodegeneration. MGBA affects the function of glia in the central nervous system (CNS), and microbial metabolites regulate the communication between astrocytes and microglia; however, whether such communication is part of AD pathophysiology remains unknown. One of the potential links in bilateral gut-brain communication is tryptophan (Trp) metabolism. The microbiota-originated Trp and its metabolites enter the CNS to control microglial activation, and the activated microglia subsequently affect astrocyte functions. The present review highlights the role of MGBA in AD pathology, especially the roles of Trp per se and its metabolism as a part of the gut microbiota and brain communications. We (i) discuss the roles of Trp derivatives in microglia-astrocyte crosstalk from a bioinformatics perspective, (ii) describe the role of glia polarization in the microglia-astrocyte crosstalk and AD pathology, and (iii) summarize the potential of Trp metabolism as a therapeutic target. Finally, we review the role of Trp in AD from the perspective of the gut-brain axis and microglia, as well as astrocyte crosstalk, to inspire the discovery of novel AD therapeutics.

The MT1 receptor as the target of ramelteon neuroprotection in ischemic stroke

Stroke is the leading cause of death and disability worldwide. Novel and effective therapies for ischemic stroke are urgently needed. Here, we report that melatonin receptor 1A (MT1) agonist ramelteon is a neuroprotective drug candidate as demonstrated by comprehensive experimental models of ischemic stroke, including a middle cerebral artery occlusion (MCAO) mouse model of cerebral ischemia in vivo, organotypic hippocampal slice cultures ex vivo, and cultured neurons in vitro; the neuroprotective effects of ramelteon are diminished in MT1-knockout (KO) mice and MT1-KO cultured neurons. For the first time, we report that the MT1 receptor is significantly depleted in the brain of MCAO mice, and ramelteon treatment significantly recovers the brain MT1 losses in MCAO mice, which is further explained by the Connectivity Map L1000 bioinformatic analysis that shows gene-expression signatures of MCAO mice are negatively connected to melatonin receptor agonist like Ramelteon. We demonstrate that ramelteon improves the cerebral blood flow signals in ischemic stroke that is potentially mediated, at least, partly by mechanisms of activating endothelial nitric oxide synthase. Our results also show that the neuroprotection of ramelteon counteracts reactive oxygen species-induced oxidative stress and activates the nuclear factor erythroid 2-related factor 2/heme oxygenase-1 pathway. Ramelteon inhibits the mitochondrial and autophagic death pathways in MCAO mice and cultured neurons, consistent with gene set enrichment analysis from a bioinformatics perspective angle. Our data suggest that Ramelteon is a potential neuroprotective drug candidate, and MT1 is the neuroprotective target for ischemic stroke, which provides new insights into stroke therapy. MT1-KO mice and cultured neurons may provide animal and cellular models of accelerated ischemic damage and neuronal cell death.

N-Acetylserotonin Alleviates Retinal Autophagy via TrkB/AKT/Nrf2 Signaling Pathway in Retinal Ischemia-Reperfusion Injury Rats

INTRODUCTION

The objective of this study was to investigate the impact of N-acetylserotonin (NAS) on the autophagy of retinal cells in rats with retinal ischemia-reperfusion injury (RIRI) and to explore the mechanisms by which NAS administration can alleviate RIRI through the tropomyosin-related kinase receptor B (TrkB)/protein kinase B (Akt)/nuclear factor erythroid-derived factor 2-related factor (Nrf2) signaling pathway.

METHODS

Healthy adult male rats were randomly assigned to four groups: sham, RIRI, RIRI+NAS, and RIRI+NAS+ANA-12. The RIRI group was induced by elevating intraocular pressure, and changes in retinal structure and edema were assessed using H&E staining. The RIRI+NAS and RIRI+NAS+ANA-12 groups received intraperitoneal injections of NAS before and after modeling. The RIRI+NAS+ANA-12 group was also administered ANA-12, a TrkB antagonist. Immunohistochemical staining and Western blot analysis were used to evaluate phosphorylated TrkB (p-TrkB), phosphorylated Akt (p-Akt), Nrf2, sequestosome 1 (P62), and microtubule-associated protein 1 light chain 3 (LC3-II) levels in the retinas of each group. Electroretinogram was recorded to detect retinal function in each group of rats 24 h after modeling.

RESULTS

The RIRI+NAS group had a thinner retina and more retinal ganglion cells (RGCs) than RIRI and RIRI+NAS+ANA-12 groups (p < 0.05). Immunohistochemical staining and Western blot results showed that p-TrkB, p-Akt, n-Nrf2, and P62 levels in the RIRI+NAS group were higher compared with those in RIRI and RIRI+NAS+ANA-12 groups (p < 0.05). Also, lower LC3-II levels were observed in the RIRI+NAS group compared with that in RIRI and RIRI+NAS+ANA-12 groups (p < 0.05). Electroretinogram recording results showed that 24 h after retinal ischemia-reperfusion, the magnitude of b-wave changes was attenuated in the RIRI+NAS group compared with the RIRI group (p < 0.05).

CONCLUSION

The administration of NAS activates the TrkB/Akt/Nrf2 signaling pathway, reduces autophagy, alleviates retinal edema, promotes the survival of retinal ganglion cells (RGCs), and provides neuroprotection against retinal injury.

The Dual Role of Autophagy in Postischemic Brain Neurodegeneration of Alzheimer's Disease Proteinopathy

Autophagy is a self-defense and self-degrading intracellular system involved in the recycling and elimination of the payload of cytoplasmic redundant components, aggregated or misfolded proteins and intracellular pathogens to maintain cell homeostasis and physiological function. Autophagy is activated in response to metabolic stress or starvation to maintain homeostasis in cells by updating organelles and dysfunctional proteins. In neurodegenerative diseases, such as cerebral ischemia, autophagy is disturbed, e.g., as a result of the pathological accumulation of proteins associated with Alzheimer's disease and their structural changes. Postischemic brain neurodegeneration, such as Alzheimer's disease, is characterized by the accumulation of amyloid and tau protein. After cerebral ischemia, autophagy was found to be activated in neuronal, glial and vascular cells. Some studies have shown the protective properties of autophagy in postischemic brain, while other studies have shown completely opposite properties. Thus, autophagy is now presented as a double-edged sword with possible therapeutic potential in brain ischemia. The exact role and regulatory pathways of autophagy that are involved in cerebral ischemia have not been conclusively elucidated. This review aims to provide a comprehensive look at the advances in the study of autophagy behavior in neuronal, glial and vascular cells for ischemic brain injury. In addition, the importance of autophagy in neurodegeneration after cerebral ischemia has been highlighted. The review also presents the possibility of modulating the autophagy machinery through various compounds on the development of neurodegeneration after cerebral ischemia.

PCSK9 Promotes Hypoxia-Induced EC Pyroptosis by Regulating Smac Mitochondrion-Cytoplasm Translocation in Critical Limb Ischemia

Hypoxia-induced endothelial cell death and impaired angiogenesis are the main pathophysiological features of critical limb ischemia. Mechanistically, proprotein convertase subtilisin/kexin type 9 (PCSK9) promoted Smac translocation from mitochondria to the cytoplasm. Inhibition of Smac release into the cytoplasm attenuated PCSK9-mediated hypoxia-induced pyroptosis. Functionally, PCSK9 overexpression impaired angiogenesis in vitro and reduced blood perfusion in mice with lower limb ischemia, but the effect was reversed by PCSK9 inhibition. This study demonstrates that PCSK9 aggravates pyroptosis by regulating Smac mitochondrion-cytoplasm translocation in the vascular endothelium, providing novel insights into PCSK9 as a potential therapeutic target in critical limb ischemia.

Current and future therapeutic strategies for Alzheimer's disease: an overview of drug development bottlenecks

Alzheimer's disease (AD) is the most common chronic neurodegenerative disease worldwide. It causes cognitive dysfunction, such as aphasia and agnosia, and mental symptoms, such as behavioral abnormalities; all of which place a significant psychological and economic burden on the patients' families. No specific drugs are currently available for the treatment of AD, and the current drugs for AD only delay disease onset and progression. The pathophysiological basis of AD involves abnormal deposition of beta-amyloid protein (Aβ), abnormal tau protein phosphorylation, decreased activity of acetylcholine content, glutamate toxicity, autophagy, inflammatory reactions, mitochondria-targeting, and multi-targets. The US Food and Drug Administration (FDA) has approved five drugs for clinical use: tacrine, donepezil, carbalatine, galantamine, memantine, and lecanemab. We have focused on the newer drugs that have undergone clinical trials, most of which have not been successful as a result of excessive clinical side effects or poor efficacy. Although aducanumab received rapid approval from the FDA on 7 June 2021, its long-term safety and tolerability require further monitoring and confirmation. In this literature review, we aimed to explore the possible pathophysiological mechanisms underlying the occurrence and development of AD. We focused on anti-Aβ and anti-tau drugs, mitochondria-targeting and multi-targets, commercially available drugs, bottlenecks encountered in drug development, and the possible targets and therapeutic strategies for future drug development. We hope to present new concepts and methods for future drug therapies for AD.

Mechanistic insights on impact of Adenosine monophosphate-activated protein kinase (AMPK) mediated signalling pathways on cerebral ischemic injury

Cerebral ischemia is the primary cause of morbidity and mortality worldwide due to the perturbations in the blood supply to the brain. The brain triggers a cascade of complex metabolic and cellular defects in response to ischemic stress. However, due to the disease heterogeneity and complexity, ischemic injury's metabolic and cellular pathologies remain elusive, and the link between various pathological mechanisms is difficult to determine. Efforts to develop effective treatments for these disorders have yielded limited efficacy, with no proper cure available to date. Recent clinical and experimental research indicates that several neuronal diseases commonly coexist with metabolic dysfunction, which may aggravate neurological symptoms. As a result, it stands to a reason that metabolic hormones could be a potential therapeutic target for major NDDs. Moreover, fasting signals also influence the circadian clock, as AMPK phosphorylates and promotes the degradation of the photo-sensing receptor (cryptochrome). Here, the interplay of AMPK signaling between metabolic regulation and neuronal death and its role for pathogenesis and therapeutics has been studied. We have also highlighted a significant signaling pathway, i.e., the adenosine monophosphate-activated protein kinase (AMPK) involved in the relationship between the metabolism and ischemia, which could be used as a target for future studies therapeutics, and review some of the clinical progress in this area.

Neuroprotective Effects of N-acetylserotonin and Its Derivative

N-acetylserotonin (NAS) is a chemical intermediate in melatonin biosynthesis. NAS and its derivative N-(2-(5-hydroxy-1H-indol-3-yl) ethyl)-2-oxopiperidine-3-carboxamide (HIOC) are potential therapeutic agents for traumatic brain injury, autoimmune encephalomyelitis, hypoxic-ischemic encephalopathy, and other diseases. Evidence shows that NAS and its derivative HIOC have neuroprotective properties, and can exert neuroprotective effects by inhibiting oxidative stress, anti-apoptosis, regulating autophagy dysfunction, and anti-inflammatory. In this review, we discussed the neuroprotective effects and related mechanisms of NAS and its derivative HIOC to provide a reference for follow-up research and applications.

Environmental microplastic accumulation exacerbates liver ischemia-reperfusion injury in rat: Protective effects of melatonin

Ischemia-reperfusion (IR) injury is an inevitable complication of liver transplantation and partial hepatectomy. Although the hazards of environmental microplastics (EMPs) have been well explored, data underlying their impact on IR-induced hepatotoxicity and how to alleviate these damages remain largely undefined. In this study, the involvement of melatonin (MT) in modulating EMPs toxicity in the liver undergoing ischemia-reperfusion injury was investigated. Male Wistar rats were exposed to MPs for 7 days and then subjected to 1 h of partial warm ischemia (70 %) followed by 24 h of reperfusion. We analyzed some parameters as the oxidative stress, the stability of cytoskeleton as well as inflammation, and autophagy. Our data suggested that EMPs elicited liver injury in ischemic animals. Data revealed several histological alterations caused by EMP and IRI, including cellular disorientation, cell necrosis, and microvacuolar steatosis, as well as inflammatory cell infiltration. EMPs increased blood transaminase (AST and ALT) and oxidative stress levels in the ischemic liver. In addition, RT-qPCR, immunofluorescence, and western blot analyses highlighted an increased expression of α-tubulin, IL-18, NFkB, and LC3. However, the ability of MT to reduce MPs and IRI toxicity was consistent with a significant decrease in the evaluated markers. The combined data not only document that melatonin is an effective agent to protect against hepatic IRI but also reduces cellular dysfunction caused by EMPs.

Chromium exposure altered metabolome and microbiome-associated with neurotoxicity in zebrafish

In recent years, chromium (Cr) has been found to induce neurotoxicity. However, the underlying mechanism remains unclear. This study aimed to investigate the effects of chromium exposure on the metabolome and microbiome that may contribute to neurotoxicity in juvenile zebrafish. Zebrafish embryos were exposed to 1 mg/L Cr (III) and 1 mg/L Cr (VI) for 7 days, respectively. Swimming distance and locomotor behavior was decreased, and acetylcholinesterase activity was reduced in Cr-exposed groups. Total cholesterol levels were decreased in Cr-exposed groups. The differential-expressed metabolites due to Cr exposure were mainly enriched in primary bile acid biosynthesis, which indicated that Cr exposure may promote cholesterol conversion. The abundance of Bacteroidetes decreased and the abundance of Actinomycetes increased in Cr-exposed groups, as compared with that in the control group. At the genus level, the abundance of Acinetobacter, Acidophorax, Mycobacterium, Aeromonas, Hydrophagophaga, and Brevundimonas increased, whereas Chryseobacterium, Pseudomonas, Delftia, and Ancylobacter decreased in the Cr-exposed groups. Analysis of the correlation between gut microbiota and bile acid metabolites showed that changes of gut microbial community due to Cr exposure may be related to secondary bile acid metabolism. Collectively, chromium exposure may disturb cholesterol metabolism, including primary bile acid and microbiota-related secondary bile acid metabolism. This study provides potential mechanism of the effects of chromium on neurotoxicity based on modulation of metabolome and gut microbiota diversity, which needs further verification.

TrkB agonist N-acetyl serotonin promotes functional recovery after traumatic brain injury by suppressing ferroptosis via the PI3K/Akt/Nrf2/Ferritin H pathway

Ferroptosis is a form of regulated cell death that is mainly triggered by iron-dependent lipid peroxidation. A growing body of evidence suggests that ferroptosis is involved in the pathophysiology of traumatic brain injury (TBI), and tropomyosin-related kinase B (TrkB) deficiency would mediate TBI pathologies. As an agonist of TrkB and an immediate precursor of melatonin, N-acetyl serotonin (NAS) exerts several beneficial effects on TBI, but there is no information regarding the role of NAS in ferroptosis after TBI. Here, we examined the effect of NAS treatment on TBI-induced functional outcomes and ferroptosis. Remarkably, the administration of NAS alleviated TBI-induced neurobehavioral deficits, lesion volume, and neurodegeneration. NAS also rescued TBI-induced mitochondrial shrinkage, the changes in ferroptosis-related molecule expression, and iron accumulation in the ipsilateral cortex. Similar results were obtained with a well-established ferroptosis inhibitor, liproxstatin-1. Furthermore, NAS activated the TrkB/PI3K/Akt/Nrf2 pathway in the mouse model of TBI, while inhibition of PI3K and Nrf2 weakened the protection of NAS against ferroptosis both in vitro and in vivo, suggesting that a possible pathway linking NAS to the action of anti-ferroptosis was TrkB/PI3K/Akt/Nrf2. Given that ferritin H (Fth) is a known transcription target of Nrf2, we then investigated the effects of NAS on neuron-specific Fth knockout (Fth-KO) mice. Strikingly, Fth deletion almost abolished the protective effects of NAS against TBI-induced ferroptosis and synaptic damage, although Fth deletion-induced susceptibility toward ferroptosis after TBI was reversed by an iron chelator, deferoxamine. Taken together, these data indicate that the TrkB agonist NAS treatment appears to improve brain function after TBI by suppressing ferroptosis, at least in part, through activation of the PI3K/Akt/Nrf2/Fth pathway, providing evidence that NAS is likely to be a promising anti-ferroptosis agent for further treatment for TBI.

N-Acetylserotonin is an oxidation-responsive activator of Nrf2 ameliorating colitis in rats

N-Acetylserotonin (NAS) is an intermediate in the melatonin biosynthetic pathway. We investigated the anti-inflammatory activity of NAS by focusing on its chemical feature oxidizable to an electrophile. NAS was readily oxidized by reaction with HOCl, an oxidant produced in the inflammatory state. HOCl-reacted NAS (Oxi-NAS), but not NAS, activated the anti-inflammatory nuclear factor erythroid 2-related factor 2 (Nrf2)-heme oxygenase (HO)-1 pathway in cells. Chromatographic and mass analyses demonstrated that Oxi-NAS was the iminoquinone form of NAS and could react with N-acetylcysteine possessing a nucleophilic thiol to form a covalent adduct. Oxi-NAS bound to Kelch-like ECH-associated protein 1, resulting in Nrf2 dissociation. Moreover, rectally administered NAS increased the levels of nuclear Nrf2 and HO-1 proteins in the inflamed colon of rats. Simultaneously, NAS was converted to Oxi-NAS in the inflamed colon. Rectal NAS mitigated colonic damage and inflammation. The anticolitic effects were significantly compromised by the coadministration of an HO-1 inhibitor.

Cornin protects against cerebral ischemia/reperfusion injury by preventing autophagy via the PI3K/Akt/mTOR pathway

Background

Ischemia stroke is the leading cause of disability, which is a consequence of vascular occlusion. The purpose of this study is to investigate the effect of cornin which is isolated from the fruit of Verbena officinalis L, against astrocytes autophagy induced by cerebral ischemia/reperfusion (CI/R) injury in vitro and in vivo and its potential mechanism.

Methods

Cornin at dose of 2.5, 5 and 10 mg/kg were intravenously injected to MCAO rats at 15 min after reperfusion. The infarction volume, blood–brain barrier (BBB), neurological severity score (mNSS), and autophagy related protein were used to evaluated the protective effects and potential mechanism of cornin in autophagy with or without phosphoinositide-3 kinase (PI3K)inhibitor LY294002 and mammalian target of rapamycin (mTOR) small interfering RNA (siRNA) at 24 h after CI/R injury. The potential protective effects and mechanism of cornin at concention of 10 ~ 1000 nM were also evaluated in oxygen glucose deprivation/reperfusion (OGD/R) in U87 cells.

Results

The results suggest that cornin at dose of 5 or 10 mg/kg significantly reduce the cerebral infarction volume and blood–brain barrier (BBB) leakage, and improve neurological recovery in MCAO rats. Cleaved caspase-3 and Bax levels were significantly decreased, while B-cell lymphoma-2 (Bcl-2) and the apoptosis regulator ratio (Bcl-2/Bax) were markedly increased when treated with 2.5–10 mg/kg cornin. The obvious decreased expressions of glial fibrillary acidic protein (GFAP), myosin-like BCL2 interacting protein (Beclin-1) and microtubule-associated protein light chain 3 II (LC3-II) and increased of neuronal nuclei (NeuN), sequestosome-1 (p62), phosphorylated mTOR (p-mTOR), and phosphorylated Akt (p-Akt) were observed in MCAO rats treated with 10 mg/kg cornin, which was counteracted by LY294002. The expression of autophagy-related proteins with or without LY294002 and mTOR siRNA presented the similar results as in vitro in OGD/R in U87 cells.

Conclusions

These results indicate that cornin improved neurological recovery after cerebral ischemia injury by preventing astrocytes autophagy induced by CI/R via the PI3K/Akt/mTOR signaling pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40360-022-00620-3.

Recent progresses in novel in vitro models of primary neurons: A biomaterial perspective

Central nervous system (CNS) diseases have been a growing threat to the health of humanity, emphasizing the urgent need of exploring the pathogenesis and therapeutic approaches of various CNS diseases. Primary neurons are directly obtained from animals or humans, which have wide applications including disease modeling, mechanism exploration and drug development. However, traditional two-dimensional (2D) monoculture cannot resemble the native microenvironment of CNS. With the increasing understanding of the complexity of the CNS and the remarkable development of novel biomaterials, in vitro models have experienced great innovation from 2D monoculture toward three-dimensional (3D) multicellular culture. The scope of this review includes the progress of various in vitro models of primary neurons in recent years to provide a holistic view of the modalities and applications of primary neuron models and how they have been connected with the revolution of biofabrication techniques. Special attention has been paid to the interaction between primary neurons and biomaterials. First, a brief introduction on the history of CNS modeling and primary neuron culture was conducted. Next, detailed progress in novel in vitro models were discussed ranging from 2D culture, ex vivo model, spheroid, scaffold-based model, 3D bioprinting model, and microfluidic chip. Modalities, applications, advantages, and limitations of the aforementioned models were described separately. Finally, we explored future prospects, providing new insights into how basic science research methodologies have advanced our understanding of the CNS, and highlighted some future directions of primary neuron culture in the next few decades.

N-acetylserotonin protects PC12 cells from hydrogen peroxide induced damage through ROS mediated PI3K / AKT pathway

N-acetylserotonin (NAS) exerts neuroprotective, antioxidant, and anti-apoptotic effects. Oxidative stress and apoptosis are the primary causes of spinal cord injury (SCI). Herein, we explored potential protective effects and mechanisms of NAS in a neuron oxidative damage model in vitro. We established an oxidative damage model in PC12 cells induced by hydrogen peroxide (H₂O₂) and treated these cells with NAS. NAS enhanced the activity of superoxide dismutase and halted the increase in reactive oxygen species (ROS) and the expression of inducible nitric oxide synthase. Additionally, NAS promoted protein expression of Bcl-2, but inhibited protein expressions of Fas, FADD, cytochrome c, Bax, cleaved caspase-9, and cleaved caspase-3, namely, decreasing protein expression of the Fas and mitochondrial pathways. Furthermore, it reduced the rate of apoptosis and necroptosis-related protein expressions of MLKL and p-MLKL. Moreover, NAS promoted the protein expression of p-PI3K and p-AKT, and the addition of the PI3K inhibitor LY294002 partially attenuated the antioxidant stress and anti-apoptotic effects of NAS in H₂O₂ stimulated PC12 cells. In conclusion, NAS protected PC12 cells from apoptosis and oxidative stress induced by H₂O₂ by inhibiting ROS activity and activating the PI3K/AKT signaling pathway.

Naoluo Xintong Decoction Ameliorates Cerebral Ischemia-Reperfusion Injury by Promoting Angiogenesis through Activating the HIF-1α/VEGF Signaling Pathway in Rats

Background

Naoluo Xintong decoction (NLXTD) is a traditional Chinese medicine (TCM) formula which has been used to improve neuronal functional recovery after cerebral ischemic stroke. However, the molecular mechanism underlying NLXTD's amelioration of ischemic stroke remains unclear. The present study was designed to explore the effect and mechanism of NLXTD on brain angiogenesis in a rat model with cerebral ischemia-reperfusion (I/R) injury targeting the hypoxia-inducible factor-1α (HIF-1α)/vascular endothelial growth factor (VEGF) pathway.

Materials and Methods

Cerebral I/R model was established by the classical middle cerebral artery occlusion (MCAO) method. Sprague-Dawley (SD) male rats (n = 80) were randomly divided into the sham-operation group, the model group, the HIF-1α inhibitor 2-methoxyestradiol (2ME2) group, the 2ME2 with NLXTD group, and the NLXTD group. Neurological deficit test, TTC staining, H&E staining, TUNEL staining, immunohistochemistry (IH), immunofluorescence (IF), western blot, and quantitative RT-PCR were performed to evaluate the effect of NLXTD after MCAO.

Results

Administration of NLXTD significantly decreased neuron deficiency scores, reduced brain infarct volume, and lowered damaged and apoptotic cells after brain I/R injury in rats. Meanwhile, NLXTD had a protective effect on angiogenesis by increasing the MVD and the expressions of BrdU and CD34, which enhanced the number of endothelial cells in the ischemic penumbra brain. NLXTD treatment significantly raised the protein and mRNA levels of HIF-1α, VEGF, VEGFR2, and Notch1 compared with the model treatment. In contrast, a specific HIF-1α inhibitor, 2ME2, inhibited the improvement of neurological function and angiogenesis in NLXTD-induced rats with cerebral I/R injury, suggesting that NLXTD played a positive role in ischemic brain injury by activating the HIF-1α/VEGF signaling pathway.

Conclusions

NLXTD exerts neuroprotection targeting angiogenesis by upregulating the HIF-1α/VEGF signaling pathway on cerebral I/R injury rats.

Melatonin ameliorates cerebral ischemia-reperfusion injury in diabetic mice by enhancing autophagy via the SIRT1-BMAL1 pathway

Diabetic brains are more vulnerable to ischemia-reperfusion injury. Previous studies have proved that melatonin could protect against cerebral ischemia-reperfusion (CIR) injury in non-diabetic stroke models; however, its roles and the underlying mechanisms against CIR injury in diabetic mice remain unknown. Streptozotocin-induced diabetic mice and high-glucose-cultured HT22 cells were exposed to melatonin, with or without administration of the autophagy inhibitor 3-methyladenine (3-MA) and the specifically silent information regulator 1 (SIRT1) inhibitor EX527, and then subjected to CIR or oxygen-glucose deprivation/reperfusion operation. We found that diabetic mice showed aggravated brain damage, increased apoptosis and oxidative stress, and deficient autophagy following CIR compared with non-diabetic counterparts. Melatonin treatment exhibited improved histological damage, neurological outcomes, and cerebral infarct size. Intriguingly, melatonin markedly increased cell survival, anti-oxidative and anti-apoptosis effects, and significantly enhanced autophagy. However, these effects were largely attenuated by 3-MA or EX527. Additionally, our cellular experiments demonstrated that melatonin increased the SIRT1-BMAL1 pathway-related proteins' expression in a dose-dependent manner. In conclusion, these results indicate that melatonin treatment can protect against CIR-induced brain damage in diabetic mice, which may be achieved by the autophagy enhancement mediated by the SIRT1-BMAL1 pathway.

Potentiating the Benefits of Melatonin through Chemical Functionalization: Possible Impact on Multifactorial Neurodegenerative Disorders

Although melatonin is an astonishing molecule, it is possible that chemistry will help in the discovery of new compounds derived from it that may exceed our expectations regarding antioxidant protection and perhaps even neuroprotection. This review briefly summarizes the significant amount of data gathered to date regarding the multiple health benefits of melatonin and related compounds. This review also highlights some of the most recent directions in the discovery of multifunctional pharmaceuticals intended to act as one-molecule multiple-target drugs with potential use in multifactorial diseases, including neurodegenerative disorders. Herein, we discuss the beneficial activities of melatonin derivatives reported to date, in addition to computational strategies to rationally design new derivatives by functionalization of the melatonin molecular framework. It is hoped that this review will promote more investigations on the subject from both experimental and theoretical perspectives.

Neuroprotective Effect of Alpha-asarone on the Rats Model of Cerebral Ischemia-Reperfusion Stroke via Ameliorating Glial Activation and Autophagy

Alpha-asarone, a major active component isolated from Acorus gramineus, can affect brain functions and behaviors by multiple mechanisms. However, the effect of alpha-asarone on cerebral ischemia-reperfusion (CIR) stroke has not been reported. The present study aimed to investigate the neuroprotective effect of alpha-asarone and the involved mechanisms against CIR stroke. Rats were subjected to middle cerebral occlusion (MCAO) for 2 h. Then the drug or drug-free vehicle was intravenously injected to corresponding groups. After reperfusion for 24 h, the infarct volume was evaluated by Triphenyl Tetrazolium Chloride (TTC) staining. The neurofunctional recovery and post-stroke epilepsy were evaluated. Nissl and Hematoxylin-Eosin (H&E) staining were used for histological observation. We investigated the protective mechanism of alpha-asarone against the stroke. The results showed that alpha-asarone exhibited a desirable neuroprotective effect, manifested as reducing infarct volume and post-stroke epilepsy and improving neurological function. Histological and flow cytometry analysis revealed that alpha-asarone treatment alleviated cell injury and apoptosis in vivo and in vitro. Furthermore, alpha-asarone decreased GFAP, Iba-1, and LC3II/LC3I expression and increased the expression of p62. These results suggested that alpha-asarone attenuated the CIR stroke injury via ameliorating glial activation and autophagy.

Autophagy Elicits Neuroprotection at the Subacute Phase of Transient Cerebral Ischaemia but Has Few Effects on Neurological Outcomes After Permanent Ischaemic Stroke in Rats

OBJECTIVE

Autophagy was prominently activated by cerebral ischaemia. This study was to investigate the exact role of autophagy in ischaemic stroke.

METHODS

Two rat models of transient middle cerebral artery occlusion (tMCAO) and permanent MCAO (pMCAO) were prepared. The brain tissues in the penumbra were obtained to observe the dynamic variations of autophagy activity with Beclin1 and LC3 antibodies by Western blotting. At the characteristic time points, when autophagy activity was markedly elevated or reduced, the autophagy activation signaling was intervened with rapamycin and 3-methyladenine, respectively. Thereafter, key proteins in the autopahgic/lysosomal pathway were detected with the antibodies of LC3, p62, ubiquitin, LAMP-1 and cathepsin B. Meanwhile, TTC staining, neurological score and immunofluorescence were performed to evaluate brain infarct volume, neurological deficit and neuron survival, respectively.

RESULTS

Both Beclin1 and LC3 expression levels were remarkably altered at 6 h, 12 h, 2 days and 7 days after tMCAO. Interestingly, the dynamic changes of autophagy activity following pMCAO were identical to those after tMCAO. Neither autophagy induction nor autophagy inhibition was able to ameliorate the pMCAO-induced neurological injury due to lysosomal dysfunction, as indicated by low levels of LAMP-1 and cathepsin B, accompanied with the accumulation of LC3-II, ubiquitin and insoluble p62. Comparatively, autophagy induction elicited overt neuroprotection at 2 and 7 days after tMCAO, and this neuroprotection might be elicited by the enhancement of autophagy flux.

CONCLUSION

Our study suggests that autophagy confers neuroprotection at the subacute phase of tMCAO but has few effects on neurological outcomes after pMCAO.

Protective effects of antidepressant citalopram against abnormal APP processing and amyloid beta-induced mitochondrial dynamics, biogenesis, mitophagy and synaptic toxicities in Alzheimer's disease

The purpose of this study is to study the neuroprotective role of selective serotonin reuptake inhibitor (SSRI), citalopram, against Alzheimer's disease (AD). Multiple SSRIs, including citalopram, are reported to treat patients with depression, anxiety and AD. However, their protective cellular mechanisms have not been studied completely. In the current study, we investigated the protective role of citalopram against impaired mitochondrial dynamics, defective mitochondrial biogenesis, defective mitophagy and synaptic dysfunction in immortalized mouse primary hippocampal cells (HT22) expressing mutant APP (SWI/IND) mutations. Using quantitative RT-PCR, immunoblotting, biochemical methods and transmission electron microscopy methods, we assessed mutant full-length APP/C-terminal fragments and Aβ levels and mRNA and protein levels of mitochondrial dynamics, biogenesis, mitophagy and synaptic genes in mAPP-HT22 cells and mAPP-HT22 cells treated with citalopram. Increased levels of mRNA levels of mitochondrial fission genes, decreased levels of fusion biogenesis, autophagy, mitophagy and synaptic genes were found in mAPP-HT22 cells relative to WT-HT22 cells. However, mAPP-HT22 cells treated with citalopram compared to mAPP-HT22 cells revealed reduced levels of the mitochondrial fission genes, increased fusion, biogenesis, autophagy, mitophagy and synaptic genes. Our protein data agree with mRNA levels. Transmission electron microscopy revealed significantly increased mitochondrial numbers and reduced mitochondrial length in mAPP-HT22 cells; these were reversed in citalopram-treated mAPP-HT22 cells. Cell survival rates were increased in citalopram-treated mAPP-HT22 relative to citalopram-untreated mAPP-HT22. Further, mAPP and C-terminal fragments werealso reduced in citalopram-treated cells. These findings suggest that citalopram reduces mutant APP and Aβ and mitochondrial toxicities and may have a protective role of mutant APP and Aβ-induced injuries in patients with depression, anxiety and AD.

N-acetylserotonin alleviated the expression of interleukin-1β in retinal ischemia-reperfusion rats via the TLR4/NF-κB/NLRP3 pathway

This study aimed to explore the effects of N-acetylserotonin (NAS) on the expression of interleukin-1β (IL-1β) in the retina of retinal ischemia-reperfusion injury (RIRI) rats via the toll-like receptor 4 (TLR4)/nuclear factor-kappa B (NF-κB)/nod-like receptor pyrin domain containing 3 (NLRP3) signaling pathway. In this study, adult male Sprague Dawley rats were randomly divided into the sham, RIRI, RIRI + NAS and RIRI + TAK-242 + NAS groups. The rats in the RIRI + NAS and RIRI + TAK-242 + NAS groups were intraperitoneally injected with NAS 30 min before and after modeling. TAK-242, a selective TLR4 inhibitor, was administered by intraperitoneal injection in RIRI + TAK-242 + NAS group. The RIRI rat model was established by elevating the intraocular pressure to 110 mmHg for 60 min. The retinal structure and edema were assessed by H&E staining. The expression levels of TLR4, phosphorylated NF-κB (p-NF-κB), NLRP3, cleaved Caspase-1, and IL-1β in the retina of each group were detected using immunohistochemistry and Western blot. The correlations of the differences of TLR4⁺ and cleaved Caspase-1⁺ with IL-1β⁺ cells (between the NAS and the RIRI groups) were analyzed, using linear regression in the RIRI + NAS group. Results showed that thinner retina, more RGCs, and less TLR4⁺, p-NF-κB⁺, NLRP3⁺, cleaved Caspase-1⁺, and IL-1β⁺ cells in the retina were observed in the RIRI + NAS and RIRI + TAK-242 + NAS groups compared with the RIRI group 12 h after RIRI (all P < 0.01). Western blot analysis results showed that the expression of IL-1β in the RIRI + NAS group began to increase 6 h after RIRI, and it reached a high level 12 h after RIRI, and then decreased. And it was lower at each time point in the RIRI + NAS group than in the RIRI group, and there existed significant difference (all P < 0.01). Besides, the expression levels of TLR4, p-NF-κB, NLRP3, and cleaved Caspase-1 proteins in the RIRI + NAS and RIRI + TAK-242 + NAS groups decreased 12 h after RIRI compared with those in the RIRI group (all P < 0.01). The difference in IL-1β⁺ cells was significantly correlated with those of TLR4⁺ and cleaved Caspase-1⁺ cells in the RIRI + NAS group (r² = 0.9054 or 0.7431, P < 0.01). In conclusion, NAS could attenuate the expression of IL-1β by inhibiting the TLR4/NF-κB/NLRP3 signaling pathway, reduce the retina edema, and promote the survival of RGCs, thereby alleviating the retinal injury and exert its neuroprotective effect.

The Intestinal Fatty Acid-Enteroendocrine Interplay, Emerging Roles for Olfactory Signaling and Serotonin Conjugates

Intestinal enteroendocrine cells (EECs) respond to fatty acids from dietary and microbial origin by releasing neurotransmitters and hormones with various paracrine and endocrine functions. Much has become known about the underlying signaling mechanisms, including the involvement of G-protein coupled receptors (GPCRs), like free fatty acids receptors (FFARs). This review focusses on two more recently emerging research lines: the roles of odorant receptors (ORs), and those of fatty acid conjugates in gut. Odorant receptors belong to a large family of GPCRs with functional roles that only lately have shown to reach beyond the nasal-oral cavity. In the intestinal tract, ORs are expressed on serotonin (5-HT) and glucagon-like-peptide-1 (GLP-1) producing enterochromaffin and enteroendocrine L cells, respectively. There, they appear to function as chemosensors of microbiologically produced short-, and branched-chain fatty acids. Another mechanism of fatty acid signaling in the intestine occurs via their conjugates. Among them, conjugates of unsaturated long chain fatty acids and acetate with 5-HT, N-acyl serotonins have recently emerged as mediators with immune-modulatory effects. In this review, novel findings in mechanisms and molecular players involved in intestinal fatty acid biology are highlighted and their potential relevance for EEC-mediated signaling to the pancreas, immune system, and brain is discussed.

An updated review of autophagy in ischemic stroke: From mechanisms to therapies

Stroke is a leading cause of mortality and morbidity worldwide. Understanding the underlying mechanisms is important for developing effective therapies for treating stroke. Autophagy is a self-eating cellular catabolic pathway, which plays a crucial homeostatic role in the regulation of cell survival. Increasing evidence shows that autophagy, observed in various cell types, plays a critical role in brain pathology after ischemic stroke. Therefore, the regulation of autophagy can be a potential target for ischemic stroke treatment. In the present review, we summarize the recent progress that research has made regarding autophagy and ischemic stroke, including common signaling pathways, the role of autophagic subtypes (e.g. mitophagy, pexophagy, aggrephagy, endoplasmic reticulum-phagy, and lipophagy) in ischemic stroke, as well as the current methods for autophagy detection and potential therapeutic strategy.

N-acetylserotonin Derivative Exerts a Neuroprotective Effect by Inhibiting the NLRP3 Inflammasome and Activating the PI3K/Akt/Nrf2 Pathway in the Model of Hypoxic-Ischemic Brain Damage

Neonatal hypoxic-ischemic encephalopathy (HIE) is one of the main causes of neonatal disability and death. As a derivative of N-acetylserotonin, N-[2-(5-hydroxy-1H-indol-3-yl) ethyl]-2-oxopiperidine-3-carboxamide (HIOC) can easily cross the blood-brain barrier and have a long half-life in the brain. In this study, the hypothesis was verified that HIOC plays a neuroprotective role in the HIE model and its potential mechanism was evaluated. Firstly, an HIE rat model was established to deliver HIOC, revealing that it can reduce cerebral infarction volume, cerebral edema, and neuronal apoptosis. The results of immunofluorescence staining, Western blots and RT-PCR further showed that HIOC could inhibit the activation of the NLRP3 inflammasome and the expression of related proteins. Finally, the activation of the phosphatidylinositol-3-kinase (PI3K)/Akt/nuclear factor erythroid 2-related factor 2 (Nrf2) pathway by HIOC was verified in vitro and in vivo. It was discovered that HIOC could increase the nuclear translocation of Nrf2, and that this induction can be reversed by the PI3K/Akt pathway inhibitor LY294002. In general terms, the neuroprotective effect of HIOC was confirmed in the HIE model, which is related to the activation of the Pi3k/Akt/Nrf2 signal pathway and the inhibition of the NLRP3 inflammasome.

Melatonin and Autophagy in Aging-Related Neurodegenerative Diseases

With aging, the nervous system gradually undergoes degeneration. Increased oxidative stress, endoplasmic reticulum stress, mitochondrial dysfunction, and cell death are considered to be common pathophysiological mechanisms of various neurodegenerative diseases (NDDs) such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), organophosphate-induced delayed neuropathy (OPIDN), and amyotrophic lateral sclerosis (ALS). Autophagy is a cellular basic metabolic process that degrades the aggregated or misfolded proteins and abnormal organelles in cells. The abnormal regulation of neuronal autophagy is accompanied by the accumulation and deposition of irregular proteins, leading to changes in neuron homeostasis and neurodegeneration. Autophagy exhibits both a protective mechanism and a damage pathway related to programmed cell death. Because of its "double-edged sword", autophagy plays an important role in neurological damage and NDDs including AD, PD, HD, OPIDN, and ALS. Melatonin is a neuroendocrine hormone mainly synthesized in the pineal gland and exhibits a wide range of biological functions, such as sleep control, regulating circadian rhythm, immune enhancement, metabolism regulation, antioxidant, anti-aging, and anti-tumor effects. It can prevent cell death, reduce inflammation, block calcium channels, etc. In this review, we briefly discuss the neuroprotective role of melatonin against various NDDs via regulating autophagy, which could be a new field for future translational research and clinical studies to discover preventive or therapeutic agents for many NDDs.

Melatonin receptor agonist ramelteon attenuates mouse acute and chronic ischemic brain injury

Melatonin receptors (MTs) are potential drug targets for stroke therapy. Ramelteon is a selective melatonin receptor agonist used to treat insomnia. In this study we investigated whether ramelteon could attenuate cerebral ischemia in mice. Acute focal cerebral ischemia was induced in mice via middle cerebral artery occlusion (MCAO). We found oral administration of ramelteon (3.0 mg/kg) significantly attenuated ischemic injury even when it was given 4 h after the onset of ischemia. We showed that administration of ramelteon (3.0 mg/kg) displayed comparable protective efficacy and length of effective time window as administration of edaravone (10 mg/kg, i.p.), which was used in clinic to treat ischemic stroke. Chronic ischemic brain injury was induced in mice using photothrombosis. Oral administration of ramelteon (3.0 mg · kg^-1 · d^-1) for 7 days after ischemia significantly attenuated functional deficits for at least 15 days. The neuroprotection of ramelteon was blocked by 4-P-PDOT, a specific MT antagonist. We further revealed that ramelteon significantly inhibited autophagy in the peri-infarct cortex in both the mouse ischemia models via regulating AMPK/mTOR signaling pathway. Intracerebroventricular injection of rapamycin, an autophagy activator, compromised the neuroprotection of ramelteon, suggesting ramelteon might attenuate ischemic injury by counteracting autophagic cell death. These data demonstrate for the first time the potential benefits of ramelteon in the treatment of both acute and chronic ischemic brain injury and provide the rationale for the application of ramelteon in stroke therapy.

MTMR14 protects against cerebral stroke through suppressing PTEN-regulated autophagy

The phosphoinositide phosphatase, myotubularinrelated protein 14 (MTMR14), plays a critical role in the regulating autophagy. However, its functional contribution to neuronal autophagy is still unclear. In the present study, we attempted to explore the effects of MTMR14 on ischemic stroke progression, as well as the underlying molecular mechanisms. Oxygen-glucose deprivation/reoxygenation (OGDR)-induced primary cortical neurons and pheochromocytoma (PC12) cells, and middle cerebral artery occlusion (MCAO)-operated mice were used to establish cerebral ischemia/reperfusion (I/R) injury in vitro and in vivo, respectively. OGDR treatment markedly decreased the expression of MTMR14 expression from mRNA and protein levels in the cultured primary neurons and PC12 cells. Functional analysis showed that OGDR-reduced cell viability was further accelerated by MTMR14 knockdown. On the contrary, MTMR14 over-expression significantly rescued the cell survival in OGDR-exposed cells. Moreover, autophagic markers including LC3BII and Beclin 1 were highly up-regulated in OGDR-incubated neurons and PC12 cells, while being further exacerbated by MTMR14 deletion. However, promoting MTMR14 dramatically alleviated LC3BII and Beclin 1 expression levels stimulated by OGDR. Importantly, we found that MTMR14-regulated autophagy was through its interactions with phosphatase and tensin homolog (PTEN). MTMR14 negatively modulated PTEN protein expression levels in OGDR-exposed cells. In vivo, MCAO-operated mice exhibited significantly reduced expression of MTMR14 in the ischemic penumbra tissues. After MCAO operation, MTMR14 over-expression effectively reduced infarct volume and neurological deficits scores, along with decreased activation of LC3B in neurons. Consistently, MCAO-increased PTEN, LC3BII and Beclin 1 were repressed by MTMR14 in mice. An interaction between MTMR14 and PTEN in response to MCAO was confirmed in vivo. Together, these results indicated the neuroprotective effects of MTMR14 on modulating PTEN-dependent excessive autophagy during cerebral I/R injury. Thus, targeting MTMR14 may provide feasible therapy for ischemic stroke onset and progression.

Mitochondria as a promising target for developing novel agents for treating Alzheimer's disease

The mitochondria-targeting drugs can be conventionally divided into the following groups: those compensating for the energy deficit involved in neurodegeneration, including stimulants of mitochondrial bioenergetics and activators of mitochondrial biogenesis; and neuroprotectors, that are compounds increasing the resistance of mitochondria to opening of mitochondrial permeability transition (MPT) pores. Although compensating for the energy deficit and inhibition of MPT are obvious targets for drugs used in the very early stages of Alzheimer-like pathology, but their use as the monotherapy for patients with severe symptoms is unlikely to be sufficiently effective. It would be optimal to combine targets that would provide the cognitive-stimulating, the neuroprotective effects and the ability to affect specific disease-forming mechanisms. In the design of such drugs, assessment of their potential mitochondrial-targeted effects is of particular importance. The possibility of targeted drug design for simultaneous action on mitochondrial and neurotransmitter's receptors targets is, in particularly, based on the known interplay of various cellular pathways and the presence of common structural components. Of particular interest is directed search for multitarget drugs that would act simultaneously on mitochondrial calcium-dependent functions, the targets (receptors, enzymes, etc.) facilitating neurotransmission, and the molecular targets related to the action of so-called disease-modifying factors, in particular, the formation and overcoming of the toxicity of β-amyloid or hyperphosphorylated tau protein. The examples of such approaches realized on the level of preclinical and clinical trials are presented below.

Kynurenines in the Pathogenesis of Multiple Sclerosis: Therapeutic Perspectives

Over the past years, an increasing amount of evidence has emerged in support of the kynurenine pathway’s (KP) pivotal role in the pathogenesis of several neurodegenerative, psychiatric, vascular and autoimmune diseases. Different neuroactive metabolites of the KP are known to exert opposite effects on neurons, some being neuroprotective (e.g., picolinic acid, kynurenic acid, and the cofactor nicotinamide adenine dinucleotide), while others are toxic to neurons (e.g., 3-hydroxykynurenine, quinolinic acid). Not only the alterations in the levels of the metabolites but also disturbances in their ratio (quinolinic acid/kynurenic acid) have been reported in several diseases. In addition to the metabolites, the enzymes participating in the KP have been unearthed to be involved in modulation of the immune system, the energetic upkeep of neurons and have been shown to influence redox processes and inflammatory cascades, revealing a sophisticated, intertwined system. This review considers various methods through which enzymes and metabolites of the kynurenine pathway influence the immune system, the roles they play in the pathogenesis of neuroinflammatory diseases based on current evidence with a focus on their involvement in multiple sclerosis, as well as therapeutic approaches.

NMMHC IIA triggers neuronal autophagic cell death by promoting F-actin-dependent ATG9A trafficking in cerebral ischemia/reperfusion

Previous findings have shown that non-muscle myosin heavy-chain IIA (NMMHC IIA) is involved in autophagy induction triggered by starvation in D. melanogaster; however, its functional contribution to neuronal autophagy remains unclear. The aim of this study is to explore the function of NMMHC IIA in cerebral ischemia-induced neuronal autophagy and the underlying mechanism related to autophagy-related gene 9A (ATG9A) trafficking. Functional assays and molecular mechanism studies were used to investigate the role of NMMHC IIA in cerebral ischemia-induced neuronal autophagy in vivo and in vitro. A middle cerebral artery occlusion (MCAO) model in mice was used to evaluate the therapeutic effect of blebbistatin, a myosin II ATPase inhibitor. Herein, either depletion or knockdown of NMMHC IIA led to increased cell viability in both primary cultured cortical neurons and pheochromocytoma (PC12) cells exposed to oxygen–glucose deprivation/reoxygenation (OGD/R). In addition, NMMHC IIA and autophagic marker LC3B were upregulated by OGD/R, and inhibition of NMMHC IIA significantly reduced OGD-induced neuronal autophagy. Furthermore, NMMHC IIA-induced autophagy is through its interactions with F-actin and ATG9A in response to OGD/R. The NMMHC IIA–actin interaction contributes to ATG9A trafficking and autophagosome formation. Inhibition of the NMMHC IIA–actin interaction using blebbistatin and the F-actin polymerization inhibitor cytochalasin D significantly suppressed ATG9A trafficking and autophagy induction. Furthermore, blebbistatin significantly improved neurological deficits and infarct volume after ischemic attack in mice, accompanied by ATG9A trafficking and autophagy inhibition. These findings demonstrate neuroprotective effects of NMMHC IIA inhibition on regulating ATG9A trafficking-dependent autophagy activation in the context of cerebral ischemia/reperfusion.

N-Acetyl Serotonin Alleviates Oxidative Damage by Activating Nuclear Factor Erythroid 2-Related Factor 2 Signaling in Porcine Enterocytes

Apoptosis of intestinal epithelial cells following oxidative stress is a major cause of mucosal barrier dysfunction and is associated with the pathogenesis of various gastrointestinal diseases. Although L-tryptophan (Trp) is known to improve intestinal integrity and function, a beneficial effect of N-acetyl serotonin (NAS), a metabolite of Trp, on the apoptosis of enterocytes and the underlying mechanisms remain largely unknown. In the present study, we showed that porcine enterocytes treated with 4-hydroxy-2-nonenal (4-HNE), a metabolite of lipid peroxidation, led to upregulation of apoptotic proteins, including Bax and cleaved caspase-3, and reduction of tight junction proteins. These effects of 4-HNE were significantly abrogated by NAS. In addition, NAS reduced ROS accumulation while increasing the intracellular concentration of glutathione (GSH), and the abundance of the Nrf2 protein in the nucleus and its downstream target proteins. Importantly, these protective effects of NAS were abrogated by Atra, an inhibitor of Nrf2, indicating a dependence on Nrf2 signaling. Taken together, we demonstrated that NAS attenuated oxidative stress-induced cellular injury in porcine enterocytes by regulating Nrf2 signaling. These findings provide new insights into a functional role of NAS in maintaining intestinal homeostasis.

Neuromodulation of the Pineal Gland via Electrical Stimulation of Its Sympathetic Innervation Pathway

Stimulation of the pineal gland via its sympathetic innervation pathway results in the production of N-acetylserotonin and melatonin. Melatonin has many therapeutic roles and is heavily implicated in the regulation of the sleep-wake cycle. In addition, N-acetylserotonin has recently been reported to promote neurogenesis in the brain. Upregulation of these indoleamines is possible via neuromodulation of the pineal gland. This is achieved by electrical stimulation of structures or fibres in the pineal gland sympathetic innervation pathway. Many studies have performed such pineal neuromodulation using both invasive and non-invasive methods. However, the effects of various experimental variables and stimulation paradigms has not yet been reviewed and evaluated. This review summarises these studies and presents the optimal experimental protocols and stimulation parameters necessary for maximal upregulation of melatonin metabolic output.

Cell Death Pathways in Ischemic Stroke and Targeted Pharmacotherapy

Ischemic stroke is one of the significant causes of morbidity and mortality, affecting millions of people across the globe. Cell injury in the infarct region is an inevitable consequence of focal cerebral ischemia. Subsequent reperfusion exacerbates the harmful effect and increases the infarct volume. These cellular injuries follow either a regulated pathway involving tightly structured signaling cascades and molecularly defined effector mechanisms or a non-regulated pathway, also known as accidental cell death, where the process is biologically uncontrolled. Classical cell death pathways are long established and well reported in several articles that majorly define apoptotic cell death. A recent focus on cell death study also considers investigation on non-classical pathways that are tightly regulated, may or may not involve caspases, but non-apoptotic. Pathological cell death is a cardinal feature of different neurodegenerative diseases. Although ischemia cannot be classified as a neurodegenerative disease, it is a cerebrovascular event where the infarct region exhibits aberrant cell death. Over the past few decades, several therapeutic options have been implicated for ischemic stroke. However, their use has been hampered owing to the number of limitations that they possess. Ischemic penumbral neurons undergo apoptosis and become dysfunctional; however, they are salvageable. Thus, understanding the role of different cell death pathways is crucial to aid in the modern treatment of protecting apoptotic neurons.

Positive allosteric modulation of indoleamine 2,3-dioxygenase 1 restrains neuroinflammation

l-tryptophan (Trp), an essential amino acid for mammals, is the precursor of a wide array of immunomodulatory metabolites produced by the kynurenine and serotonin pathways. The kynurenine pathway is a paramount source of several immunoregulatory metabolites, including l-kynurenine (Kyn), the main product of indoleamine 2,3-dioxygenase 1 (IDO1) that catalyzes the rate-limiting step of the pathway. In the serotonin pathway, the metabolite N-acetylserotonin (NAS) has been shown to possess antioxidant, antiinflammatory, and neuroprotective properties in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). However, little is known about the exact mode of action of the serotonin metabolite and the possible interplay between the 2 Trp metabolic pathways. Prompted by the discovery that NAS neuroprotective effects in EAE are abrogated in mice lacking IDO1 expression, we investigated the NAS mode of action in neuroinflammation. We found that NAS directly binds IDO1 and acts as a positive allosteric modulator (PAM) of the IDO1 enzyme in vitro and in vivo. As a result, increased Kyn will activate the ligand-activated transcription factor aryl hydrocarbon receptor and, consequently, antiinflammatory and immunoregulatory effects. Because NAS also increased IDO1 activity in peripheral blood mononuclear cells of a significant proportion of MS patients, our data may set the basis for the development of IDO1 PAMs as first-in-class drugs in autoimmune/neuroinflammatory diseases.

Tartary buckwheat extract alleviates alcohol-induced acute and chronic liver injuries through the inhibition of oxidative stress and mitochondrial cell death pathway

Alcohol use disorder (AUD) is an enormous public health problem that poses significant social, medical, and economic burdens. Under AUD, the liver is one of the most adversely affected organs. As current therapies and protective drugs for AUD-mediated liver injury are very limited, the prevention and therapy of alcoholic liver disease are urgently needed. The present study aims to investigate the beneficial effects of tartary buckwheat extract (TBE), the important component of Maopu tartary buckwheat liquor, on both alcoholic-induced acute and chronic liver injuries. We show that the TBE administration, similar to curcumin, significantly reduces the elevated serum aspartate aminotransferase and alanine aminotransferase levels, improves liver index, alleviates the elevated contents of hepatic malondialdehye, and restores the decreased contents of hepatic glutathione both in acute and chronic liver injuries in alcohol-exposed rats. Furthermore, histopathological analyses show that a medium dose of TBE (16.70 ml/kg body weight) alleviates hepatocyte morphology changes in both acute and chronic alcohol exposure models. We also show the protective effects of TBE on the cell death rates of alcohol-exposed primary cultured hepatocytes, HepG2 hepatoma, and Huh 7 hepatoma cells. Furthermore, we demonstrate that TBE exerts hepatoprotection partly through inhibiting the mitochondrial cell death pathway by reducing cytochrome c release, caspase-9 and -3 activities, and the number of TUNEL-positive cells. These effects of TBE were accompanied by enhanced levels of Bcl-2 and Bcl-xL and autophagic cell death pathway by reducing Beclin-1 expression, as well as through promoting its anti-oxidant capacity by suppressing reactive oxygen species production. This study demonstrates, for the first time, the protective effect of TBE against alcohol-induced acute and chronic liver injury in vivo and in vitro. Given the dietary nature of tartary buckwheat, pueraria, lycium barbarum, and hawthorn, the oral intake of TBE or liquor contained TBE, e.g., Maopu Tartary buckwheat liquor, compared with pure liquor consumption alone, may have the potential to alleviate alcoholic-induced liver injuries.

Global metabolomics analysis of serum from humans at risk of thrombotic stroke

We aimed to determine the serum concentrations of altered compounds to understand the changes in metabolism and pathophysiology that occur prior to thrombotic stroke.

Melatonin and Multiple Sclerosis: From Plausible Neuropharmacological Mechanisms of Action to Experimental and Clinical Evidence

Multiple sclerosis (MS) is a devastating chronic autoimmune demyelinating disease of the central nervous system (CNS), thought to affect more than 2.5 million people worldwide. Regulation of the sleep-wake cycle might influence disease activity and the frequency of relapses in patients. As melatonin (or sleep hormone) involves the regulation of circadian rhythms, much attention has been paid to the management of MS symptoms with melatonin. This review describes the pharmacological mechanisms underlying the neuroprotective effects of melatonin and recent clinical evidence from MS patients. Apparent risks and benefits of melatonin therapies are also discussed. Various in vivo and clinical data presented in this up-to-date review suggest that melatonin may possibly possess a protective role against the behavioral deficits and neuropathological characteristics of MS. Multiple mechanisms of the neuroprotective effects of melatonin such as mitochondrial protection and antioxidant, anti-inflammatory, and anti-apoptotic properties, as well as its anti-demyelinating function are also discussed. A large body of evidence shows that melatonin potently regulates the immune system, demyelination, free radical generation, and inflammatory responses in neural tissue, which are mediated by multiple signal transduction cascades. In the present article, we focus on different pathways that are targeted by melatonin to prevent the development and progression of MS.

Serotonin regulates mitochondrial biogenesis and function in rodent cortical neurons via the 5-HT2A receptor and SIRT1-PGC-1α axis

Neuronal mitochondria are crucial organelles that regulate bioenergetics and also modulate survival and function under environmental challenges. Here, we show that the neurotransmitter serotonin (5-HT) plays an important role in the making of new mitochondria (mitochondrial biogenesis) in cortical neurons, through the 5-HT_2A receptor and via master regulators of mitochondrial biogenesis, SIRT1 and PGC-1α. Mitochondrial function is also enhanced by 5-HT, increasing cellular respiration and ATP, the energy currency of the cell. We found 5-HT reduces cellular reactive oxygen species and exerts potent neuroprotective action in neurons challenged with stress, an effect that requires SIRT1. These findings highlight a role for the mitochondrial effects of 5-HT in the facilitation of stress adaptation and identify drug targets to ameliorate mitochondrial dysfunction in neurons.

Mitochondria in neurons, in addition to their primary role in bioenergetics, also contribute to specialized functions, including regulation of synaptic transmission, Ca²⁺ homeostasis, neuronal excitability, and stress adaptation. However, the factors that influence mitochondrial biogenesis and function in neurons remain poorly elucidated. Here, we identify an important role for serotonin (5-HT) as a regulator of mitochondrial biogenesis and function in rodent cortical neurons, via a 5-HT_2A receptor-mediated recruitment of the SIRT1–PGC-1α axis, which is relevant to the neuroprotective action of 5-HT. We found that 5-HT increased mitochondrial biogenesis, reflected through enhanced mtDNA levels, mitotracker staining, and expression of mitochondrial components. This resulted in higher mitochondrial respiratory capacity, oxidative phosphorylation (OXPHOS) efficiency, and a consequential increase in cellular ATP levels. Mechanistically, the effects of 5-HT were mediated via the 5-HT_2A receptor and master modulators of mitochondrial biogenesis, SIRT1 and PGC-1α. SIRT1 was required to mediate the effects of 5-HT on mitochondrial biogenesis and function in cortical neurons. In vivo studies revealed that 5-HT_2A receptor stimulation increased cortical mtDNA and ATP levels in a SIRT1-dependent manner. Direct infusion of 5-HT into the neocortex and chemogenetic activation of 5-HT neurons also resulted in enhanced mitochondrial biogenesis and function in vivo. In cortical neurons, 5-HT enhanced expression of antioxidant enzymes, decreased cellular reactive oxygen species, and exhibited neuroprotection against excitotoxic and oxidative stress, an effect that required SIRT1. These findings identify 5-HT as an upstream regulator of mitochondrial biogenesis and function in cortical neurons and implicate the mitochondrial effects of 5-HT in its neuroprotective action.

Protective effects of leptin against cerebral ischemia/reperfusion injury

In recent years, the use of thrombolytic therapy for treating ischemia/reperfusion injury has resulted in damage to the self-regulatory mechanisms of the brain. This is due to the increased production of free radicals, excitatory amino acids and pro-inflammatory cytokines causing secondary damage to the brain. Simple thrombolytic therapy has not been the best approach for treating ischemia/reperfusion injury. Excessive perfusion leads to failure of the body's self-regulatory functions, which in turn increases the area of cerebral edema and aggravates cerebral ischemia. Previous studies have evaluated the satiety hormone leptin as a link between energy expenditure and obesity. Of note, leptin, which is involved in brain development, synaptic transmission and angiogenesis following ischemia/reperfusion injury, has been considered an important factor for treating ischemia/reperfusion injury. The present review outlines the discovery of leptin and discusses its association with cerebral ischemia/reperfusion.

Novel therapeutic strategies for stroke: The role of autophagy

Autophagy is an important biological mechanism involved in the regulation of numerous fundamental cellular processes that are mainly associated with cellular growth and differentiation. Autophagic pathways are vital for maintaining cellular homeostasis by enhancing the turnover of nonfunctional proteins and organelles. Neuronal cells, like other eukaryotic cells, are dependent on autophagy for neuroprotection in response to stress, but can also induce cell death in cerebral ischemia. Recent studies have demonstrated that autophagy may induce neuroprotection following acute brain injury, including ischemic stroke. However in some special circumstances, activation of autophagy can induce cell death, playing a deleterious role in the etiology and progression of ischemic stroke. Currently, there are no therapeutic options against stroke that demonstrate efficient neuroprotective abilities. In the present work, we will review the significance of autophagy in the context of ischemic stroke by first outlining its role in ischemic neuronal death. We will also highlight the potential therapeutic applications of pharmacological modulators of autophagy, including some naturally occurring polyphenolic compounds that can target this catabolic process. Our findings provide renewed insight on the mechanism of action of autophagy in stroke together with potential neuroprotective compounds, which may partially exert their function through enhancing mitochondrial function and attenuating damaging autophagic processes.

RETRACTED: Placental serotonin systems in pregnancy metabolic complications associated with maternal obesity and gestational diabetes mellitus

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). The publication was retracted by request of the authors following an investigation by Monash University performed following its Procedures for Investigating Code Breaches and in accordance with the Australian Code for the Responsible Conduct of Research. The University concluded on the balance of probability that a significant part of the text in the paper was included without knowledge, without consent and without correct attribution of the original author who, at the time, was a student at the University. The results discussed in the review article are still scientifically valid. ☆ This article is part of a Special Issue entitled: Membrane Transporters and Receptors in Pregnancy Metabolic Complications edited by Luis Sobrevia.

Monogenic, Polygenic, and MicroRNA Markers for Ischemic Stroke

Ischemic stroke (IS) is a leading disease with high mortality and disability, as well as with limited therapeutic window. Biomarkers for earlier diagnosis of IS have long been pursued. Family and twin studies confirm that genetic variations play an important role in IS pathogenesis. Besides DNA mutations found previously by genetic linkage analysis for monogenic IS (Mendelian inheritance), recent studies using genome-wide associated study (GWAS) and microRNA expression profiling have resulted in a large number of DNA and microRNA biomarkers in polygenic IS (sporadic IS), especially in different IS subtypes and imaging phenotypes. The present review summarizes genetic markers discovered by clinical studies and discusses their pathogenic molecular mechanisms involved in developmental or regenerative anomalies of blood vessel walls, neuronal apoptosis, excitotoxic death, inflammation, neurogenesis, and angiogenesis. The possible impact of environment on genetics is addressed as well. We also include a perspective on further studies and clinical application of these IS biomarkers.

The multiple protective roles and molecular mechanisms of melatonin and its precursor N-acetylserotonin in targeting brain injury and liver damage and in maintaining bone health

Melatonin is a neurohormone associated with sleep and wakefulness and is mainly produced by the pineal gland. Numerous physiological functions of melatonin have been demonstrated including anti-inflammation, suppressing neoplastic growth, circadian and endocrine rhythm regulation, and its potent antioxidant activity as well as its role in regeneration of various tissues including the nervous system, liver, bone, kidney, bladder, skin, and muscle, among others. In this review, we summarize the recent advances related to the multiple protective roles of melatonin receptor agonists, melatonin and N-acetylserotonin (NAS), in brain injury, liver damage, and bone health. Brain injury, including traumatic brain injury, ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, and newborn perinatal hypoxia-ischemia encephalopathy, is a major cause of mortality and disability. Liver disease causes serious public health problems and various factors including alcohol, chemical pollutants, and drugs induce hepatic damage. Osteoporosis is the most common bone disease in humans. Due in part to an aging population, both the cost of care of fracture patients and the annual fracture rate have increased steadily. Despite the discrepancy in the pathophysiological processes of these disorders, time frames and severity, they may share several common molecular mechanisms. Oxidative stress is considered to be a critical factor in these pathogeneses. We update the current state of knowledge related to the molecular processes, mainly including anti-oxidative stress, anti-apoptosis, autophagy dysfunction, and anti-inflammation as well as other properties of melatonin and NAS. Particularly, the abilities of melatonin and NAS to directly scavenge oxygen-centered radicals and toxic reactive oxygen species, and indirectly act through antioxidant enzymes are disscussed. In this review, we summarize the similarities and differences in the protection provided by melatonin and/or NAS in brain, liver and bone damage. We analyze the involvement of melatonin receptor 1A (MT1), melatonin receptor 1B (MT2), and melatonin receptor 1C (MT3) in the protection of melatonin and/or NAS. Additionally, we evaluate their potential clinical applications. The multiple mechanisms of action and multiple organ-targeted properties of melatonin and NAS may contribute to development of promising therapies for clinical trials.