A selective TrkB agonist with potent neurotrophic activities by 7,8-dihydroxyflavone

Comprehensive characterization of the neurogenic and neuroprotective action of a novel TrkB agonist using mouse and human stem cell models of Alzheimer's disease

BACKGROUND

Neural stem cell (NSC) proliferation and differentiation in the mammalian brain decreases to minimal levels postnatally. Nevertheless, neurogenic niches persist in the adult cortex and hippocampus in rodents, primates and humans, with adult NSC differentiation sharing key regulatory mechanisms with development. Adult neurogenesis impairments have been linked to Alzheimer's disease (AD) pathology. Addressing these impairments by using neurotrophic factors is a promising new avenue for therapeutic intervention based on neurogenesis. However, this possibility has been hindered by technical difficulties of using in-vivo models to conduct screens, including working with scarce NSCs in the adult brain and differences between human and mouse models or ethical limitations.

METHODS

Here, we use a combination of mouse and human stem cell models for comprehensive in-vitro characterization of a novel neurogenic compound, focusing on the brain-derived neurotrophic factor (BDNF) pathway. The ability of ENT-A011, a steroidal dehydroepiandrosterone derivative, to activate the tyrosine receptor kinase B (TrkB) receptor was tested through western blotting in NIH-3T3 cells and its neurogenic and neuroprotective action were assessed through proliferation, cell death and Amyloid-β (Aβ) toxicity assays in mouse primary adult hippocampal NSCs, mouse embryonic cortical NSCs and neural progenitor cells (NPCs) differentiated from three human induced pluripotent stem cell lines from healthy and AD donors. RNA-seq profiling was used to assess if the compound acts through the same gene network as BDNF in human NPCs.

RESULTS

ENT-A011 was able to increase proliferation of mouse primary adult hippocampal NSCs and embryonic cortical NSCs, in the absence of EGF/FGF, while reducing Aβ-induced cell death, acting selectively through TrkB activation. The compound was able to increase astrocytic gene markers involved in NSC maintenance, protect hippocampal neurons from Αβ toxicity and prevent synapse loss after Aβ treatment. ENT-A011 successfully induces proliferation and prevents cell death after Aβ toxicity in human NPCs, acting through a core gene network shared with BDNF as shown through RNA-seq.

CONCLUSIONS

Our work characterizes a novel BDNF mimetic with preferable pharmacological properties and neurogenic and neuroprotective actions in Alzheimer's disease via stem cell-based screening, demonstrating the promise of stem cell systems for short-listing competitive candidates for further testing.

Intranasal delivery of liposome encapsulated flavonoids ameliorates l-DOPA induced dyskinesia in hemiparkinsonian mice

In the present study, we explored the development of a novel noninvasive liposomal drug delivery material for use in intranasal drug delivery applications in human diseases. We used drug entrapment into liposomal nanoparticle assembly to efficiently deliver the drugs to the nasal mucosa to be delivered to the brain. The naturally occurring flavonoid 7,8-dihydroxyflavone (7,8-DHF) has previously been shown to have beneficial effects in ameliorating Parkinson's disease (PD). We used both naturally occurring 7,8-DHF and the chemically modified form of DHF, the DHF-ME, to be used as a drug candidate for the treatment of PD and l-DOPA induced dyskinesia (LID), which is the debilitating side effect of l-DOPA therapy in PD. The ligand-protein interaction behavior for 7,8-DHF and 6,7-DHF-ME was found to be more effective with molecular docking and molecular stimulation studies of flavonoid compounds with TrkB receptor. Our study showed that 7,8-DHF delivered via intranasal route using a liposomal formulation ameliorated LID in hemiparkinsonian mice model when these mice were chronically administered with l-DOPA, which is the only current medication for relieving the clinical symptoms of PD. The present study also demonstrated that apart from reducing the LID, 7,8-DHF delivery directly to the brain via the intranasal route also corrected some long-term signaling adaptations involving ΔFosB and α Synuclein in the brain of dopamine (DA) depleted animals.

7,8-Dihydroxyflavone is a direct inhibitor of human and murine pyridoxal phosphatase

Vitamin B6 deficiency has been linked to cognitive impairment in human brain disorders for decades. Still, the molecular mechanisms linking vitamin B6 to these pathologies remain poorly understood, and whether vitamin B6 supplementation improves cognition is unclear as well. Pyridoxal 5'-phosphate phosphatase (PDXP), an enzyme that controls levels of pyridoxal 5'-phosphate (PLP), the co-enzymatically active form of vitamin B6, may represent an alternative therapeutic entry point into vitamin B6-associated pathologies. However, pharmacological PDXP inhibitors to test this concept are lacking. We now identify a PDXP and age-dependent decline of PLP levels in the murine hippocampus that provides a rationale for the development of PDXP inhibitors. Using a combination of small-molecule screening, protein crystallography, and biolayer interferometry, we discover, visualize, and analyze 7,8-dihydroxyflavone (7,8-DHF) as a direct and potent PDXP inhibitor. 7,8-DHF binds and reversibly inhibits PDXP with low micromolar affinity and sub-micromolar potency. In mouse hippocampal neurons, 7,8-DHF increases PLP in a PDXP-dependent manner. These findings validate PDXP as a druggable target. Of note, 7,8-DHF is a well-studied molecule in brain disorder models, although its mechanism of action is actively debated. Our discovery of 7,8-DHF as a PDXP inhibitor offers novel mechanistic insights into the controversy surrounding 7,8-DHF-mediated effects in the brain.

TrkB transmembrane domain: bridging structural understanding with therapeutic strategy

TrkB (neuronal receptor tyrosine kinase-2, NTRK2) is the receptor for brain-derived neurotrophic factor (BDNF) and is a critical regulator of activity-dependent neuronal plasticity. The past few years have witnessed an increasing understanding of the structure and function of TrkB, including its transmembrane domain (TMD). TrkB interacts with membrane cholesterol, which bidirectionally regulates TrkB signaling. Additionally, TrkB has recently been recognized as a binding target of antidepressant drugs. A variety of different antidepressants, including typical and rapid-acting antidepressants, as well as psychedelic compounds, act as allosteric potentiators of BDNF signaling through TrkB. This suggests that TrkB is the common target of different antidepressant compounds. Although more research is needed, current knowledge suggests that TrkB is a promising target for further drug development.

TrkB-mediated neuroprotection in female hippocampal neurons is autonomous, estrogen receptor alpha-dependent, and eliminated by testosterone: a proposed model for sex differences in neonatal hippocampal neuronal injury

BACKGROUND

Neonatal hypoxia ischemia (HI) related brain injury is one of the major causes of learning disabilities and memory deficits in children. In both human and animal studies, female neonate brains are less susceptible to HI than male brains. Phosphorylation of the nerve growth factor receptor TrkB has been shown to provide sex-specific neuroprotection following in vivo HI in female mice in an estrogen receptor alpha (ERα)-dependent manner. However, the molecular and cellular mechanisms conferring sex-specific neonatal neuroprotection remain incompletely understood. Here, we test whether female neonatal hippocampal neurons express autonomous neuroprotective properties and assess the ability of testosterone (T) to alter this phenotype.

METHODS

We cultured sexed hippocampal neurons from ERα+/+ and ERα-/- mice and subjected them to 4 h oxygen glucose deprivation and 24 h reoxygenation (4-OGD/24-REOX). Sexed hippocampal neurons were treated either with vehicle control (VC) or the TrkB agonist 7,8-dihydroxyflavone (7,8-DHF) following in vitro ischemia. End points at 24 h REOX were TrkB phosphorylation (p-TrkB) and neuronal survival assessed by immunohistochemistry. In addition, in vitro ischemia-mediated ERα gene expression in hippocampal neurons were investigated following testosterone (T) pre-treatment and TrkB antagonist therapy via q-RTPCR. Multifactorial analysis of variance was conducted to test for significant differences between experimental conditions.

RESULTS

Under normoxic conditions, administration of 3 µM 7,8-DHF resulted an ERα-dependent increase in p-TrkB immunoexpression that was higher in female, as compared to male neurons. Following 4-OGD/24-REOX, p-TrkB expression increased 20% in both male and female ERα+/+ neurons. However, with 3 µM 7,8-DHF treatment p-TrkB expression increased further in female neurons by 2.81 ± 0.79-fold and was ERα dependent. 4-OGD/24-REOX resulted in a 56% increase in cell death, but only female cells were rescued with 3 µM 7,8-DHF, again in an ERα dependent manner. Following 4-OGD/3-REOX, ERα mRNA increased ~ 3 fold in female neurons. This increase was blocked with either the TrkB antagonist ANA-12 or pre-treatment with T. Pre-treatment with T also blocked the 7,8-DHF- dependent sex-specific neuronal survival in female neurons following 4-OGD/24-REOX.

CONCLUSIONS

OGD/REOX results in sex-dependent TrkB phosphorylation in female neurons that increases further with 7,8-DHF treatment. TrkB phosphorylation by 7,8-DHF increased ERα mRNA expression and promoted cell survival preferentially in female hippocampal neurons. The sex-dependent neuroprotective actions of 7,8-DHF were blocked by either ANA-12 or by T pre-treatment. These results are consistent with a model for a female-specific neuroprotective pathway in hippocampal neurons in response to hypoxia. The pathway is activated by 7,8-DHF, mediated by TrkB phosphorylation, dependent on ERα and blocked by pre-exposure to T.

Seasonal fluctuations in BDNF regulate hibernation and torpor in golden-mantled ground squirrels

Aphagic hibernators such as the golden-mantled ground squirrel (GMGS; Callospermophilus lateralis) can fast for months and exhibit profound seasonal fluctuations in body weight, food intake, and behavior. Brain-derived neurotrophic factor (BDNF) regulates cellular and systemic metabolism via mechanisms that are conserved across mammalian species. In this study, we characterized regional changes in BDNF with hibernation, hypothermia, and seasonal cycle in GMGS. Analysis of BDNF protein concentrations by ELISA revealed overlapping seasonal patterns in the hippocampus and hypothalamus, where BDNF levels were highest in summer and lowest in winter. BDNF is the primary ligand for receptor tyrosine kinase B (TrkB), and BDNF/TrkB signaling in the brain potently regulates energy expenditure. To examine the functional relevance of seasonal variation in BDNF, hibernating animals were injected with the small molecule TrkB agonist 7,8-dihydroxyflavone (DHF) daily for 2 wk. When compared with vehicle, DHF-treated animals exhibited fewer torpor bouts and shorter bout durations. These results suggest that activating BDNF/TrkB disrupts hibernation and raise intriguing questions related to the role of BDNF as a potential regulatory mechanism or downstream response to seasonal changes in body temperature and environment.NEW & NOTEWORTHY Golden-mantled ground squirrels exhibit dramatic seasonal fluctuations in metabolism and can fast for months while hibernating. Brain-derived neurotrophic factor is an essential determinant of cellular and systemic metabolism, and in this study, we characterized seasonal fluctuations in BDNF expression and then administered the small molecule BDNF mimetic 7,8-dihydroxyflavone (DHF) in hibernating squirrels. The results indicate that activating BDNF/TrkB signaling disrupts hibernation, with implications for synaptic homeostasis in prolonged hypometabolic states.

Exercise-induced BDNF promotes PPARδ-dependent reprogramming of lipid metabolism in skeletal muscle during exercise recovery

Post-exercise recovery is essential to resolve metabolic perturbations and promote long-term cellular remodeling in response to exercise. Here, we report that muscle-generated brain-derived neurotrophic factor (BDNF) elicits post-exercise recovery and metabolic reprogramming in skeletal muscle. BDNF increased the post-exercise expression of the gene encoding PPARδ (peroxisome proliferator-activated receptor δ), a transcription factor that is a master regulator of lipid metabolism. After exercise, mice with muscle-specific Bdnf knockout (MBKO) exhibited impairments in PPARδ-regulated metabolic gene expression, decreased intramuscular lipid content, reduced β-oxidation, and dysregulated mitochondrial dynamics. Moreover, MBKO mice required a longer period to recover from a bout of exercise and did not show increases in exercise-induced endurance capacity. Feeding naïve mice with the bioavailable BDNF mimetic 7,8-dihydroxyflavone resulted in effects that mimicked exercise-induced adaptations, including improved exercise capacity. Together, our findings reveal that BDNF is an essential myokine for exercise-induced metabolic recovery and remodeling in skeletal muscle.

Recent Research Trends in Neuroinflammatory and Neurodegenerative Disorders

Neuroinflammatory and neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD), traumatic brain injury (TBI) and Amyotrophic lateral sclerosis (ALS) are chronic major health disorders. The exact mechanism of the neuroimmune dysfunctions of these disease pathogeneses is currently not clearly understood. These disorders show dysregulated neuroimmune and inflammatory responses, including activation of neurons, glial cells, and neurovascular unit damage associated with excessive release of proinflammatory cytokines, chemokines, neurotoxic mediators, and infiltration of peripheral immune cells into the brain, as well as entry of inflammatory mediators through damaged neurovascular endothelial cells, blood-brain barrier and tight junction proteins. Activation of glial cells and immune cells leads to the release of many inflammatory and neurotoxic molecules that cause neuroinflammation and neurodegeneration. Gulf War Illness (GWI) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are chronic disorders that are also associated with neuroimmune dysfunctions. Currently, there are no effective disease-modifying therapeutic options available for these diseases. Human induced pluripotent stem cell (iPSC)-derived neurons, astrocytes, microglia, endothelial cells and pericytes are currently used for many disease models for drug discovery. This review highlights certain recent trends in neuroinflammatory responses and iPSC-derived brain cell applications in neuroinflammatory disorders.

3-Amino-5,6,7,8-tetrahydrothieno[2,3-b]quinoline-2-carbonitrile: A fluorescent molecule that induces differentiation in PC12 cells

Neural differentiation is triggered by the activation of multiple signaling pathways initiated by various neurotrophic factors. An elucidation of these mechanisms is anticipated to facilitate the prevention of diseases and the development of novel therapeutic approaches. Alternative small-molecule inducers for neuroscience studies are required instead of protein-based reagents for more efficient and convenient experiments. We demonstrated that small molecules of thieno[2,3-b]pyridine derivatives that induce neural differentiation, compounds 3a and 9a in particular, exhibited significant neuritogenic activity in rat pheochromocytoma (PC12) cells. Moreover, 3a displayed pronounced fluorescence and a discernible Stokes shift. Furthermore, the outcome of the experiment conducted on the NGF-insensitive clones of rat PC12 cells, and the results of the intercellular uptake analyses suggested that the 3a-mediated activation of neural differentiation occurred independently of the TrkA receptor. Therefore, 3a portrays potential applicability both as a small molecule reagent to replace novel neurotrophic factors and as a potent fluorescent reagent for various techniques, including bioimaging.

Natural flavonoids as potential therapeutics in the management of Alzheimer's disease: a review

Alzheimer's disease (AD) is an age-dependent neurodegenerative disorder which is associated with the accumulation of proteotoxic Aβ peptides, and pathologically characterized by the deposition of Aβ-enriched plaques and neurofibrillary tangles. Given the social and economic burden caused by the rising frequency of AD, there is an urgent need for the development of appropriate therapeutics. Natural compounds are gaining popularity as alternatives to synthetic drugs due to their neuroprotective properties and higher biocompatibility. While natural compound's therapeutic effects for AD have been recently investigated in numerous in vitro and in vivo studies, only few have developed to clinical trials. The present review aims to provide a brief overview of the therapeutic effects, new insights, and upcoming perspectives of the preclinical and clinical trials of flavonoids for the treatment of Alzheimer's disease.

An Interaction between Brain-Derived Neurotrophic Factor and Stress-Related Glucocorticoids in the Pathophysiology of Alzheimer's Disease

Both the brain-derived neurotrophic factor (BDNF) and glucocorticoids (GCs) play multiple roles in various aspects of neurons, including cell survival and synaptic function. BDNF and its receptor TrkB are extensively expressed in neurons of the central nervous system (CNS), and the contribution of the BDNF/TrkB system to neuronal function is evident; thus, its downregulation has been considered to be involved in the pathogenesis of Alzheimer's disease (AD). GCs, stress-related molecules, and glucocorticoid receptors (GRs) are also considered to be associated with AD in addition to mental disorders such as depression. Importantly, a growing body of evidence suggests a close relationship between BDNF/TrkB-mediated signaling and the GCs/GR system in the CNS. Here, we introduce the current studies on the interaction between the neurotrophic system and stress in CNS neurons and discuss their involvement in the pathophysiology of AD.

Brain-Derived Neurotrophic Factor - The Protective Agent Against Neurological Disorders

The burden of neurological illnesses on global health is significant. Our perception of the molecular and biological mechanisms underlying intellectual processing and behavior has significantly advanced over the last few decades, laying the groundwork for potential therapies for various neurodegenerative diseases. A growing body of literature reveals that most neurodegenerative diseases could be due to the gradual failure of neurons in the brain's neocortex, hippocampus, and various subcortical areas. Research on various experimental models has uncovered several gene components to understand the pathogenesis of neurodegenerative disorders. One among them is the brain-derived neurotrophic factor (BDNF), which performs several vital functions, enhancing synaptic plasticity and assisting in the emergence of long-term thoughts. The pathophysiology of some neurodegenerative diseases, including Alzheimer's, Parkinson's, Schizophrenia, and Huntington's, has been linked to BDNF. According to numerous research, high levels of BDNF are connected to a lower risk of developing a neurodegenerative disease. As a result, we want to concentrate on BDNF in this article and outline its protective role against neurological disorders.

TrkB/BDNF signaling pathway and its small molecular agonists in CNS injury

As one of the most prevalent neurotrophic factors in the central nervous system (CNS), brain-derived neurotrophic factor (BDNF) plays a significant role in CNS injury by binding to its specific receptor Tropomyosin-related kinase receptor B (TrkB). The BDNF/TrkB signaling pathway is crucial for neuronal survival, structural changes, and plasticity. BDNF acts as an axonal growth and extension factor, a pro-survival factor, and a synaptic modulator in the CNS. BDNF also plays an important role in the maintenance and plasticity of neuronal circuits. Several studies have demonstrated the importance of BDNF in the treatment and recovery of neurodegenerative and neurotraumatic disorders. By undertaking in-depth study on the mechanism of BDNF/TrkB function, important novel therapeutic strategies for treating neuropsychiatric disorders have been discovered. In this review, we discuss the expression patterns and mechanisms of the TrkB/BDNF signaling pathway in CNS damage and introduce several intriguing small molecule TrkB receptor agonists produced over the previous several decades.

7,8-dihydroxyflavone displayed antioxidant effect through activating HO-1 expression and inhibiting caspase-3/PARP activation in RAW264.7 cells

Flavonoids, which contain a benzo-γ-pyrone (C6-C3-C6) skeleton, have been reported to exhibit effective antioxidant ability. This study aimed to compare the antioxidant activities of 7,8-dihydroxyflavone (7,8-DHF) and 7-hydroxyflavone (7-HF) in H2 O2 , lipopolysaccharide (LPS), or tert-butyl hydroperoxide (t-BHP)-induced RAW264.7 cells, respectively. The antioxidant capacities of 7,8-DHF and 7-HF were firstly evaluated by 2,2-azinobis-3-ethyl-benzothiazoline-6-sulphonic acid (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays. Then, reactive oxygen species (ROS), super oxide dismutase (SOD), and malondialdehyde (MDA) productions in H2 O2 , LPS, or t-BHP-induced RAW264.7 cells were tested and compared, respectively. Finally, the antioxidant mechanisms of 7-HF and 7,8-DHF were initially investigated by western blot. Our results showed that 7,8-DHF possessed stronger free-radical scavenging capacity than 7-HF. Both 7,8-DHF and 7-HF suppressed MDA production and ROS accumulation, improved the activity of SOD in H2 O2 , LPS, or t-BHP-induced RAW264.7 cells, respectively. And 7,8-DHF exerted a better antioxidant effect than 7-HF, especially in t-BHP-induced oxidative stress. Mechanically, 7,8-DHF prevented the activation of poly ADP-ribosepolymerase and caspase-3, meanwhile markedly upregulated the expression of HO-1 protein in t-BHP-induced oxidative stress. These results suggested that 7,8-DHF might serve as a potential pharmaceutical drug against oxidative stress injury.

Targeting synapse function and loss for treatment of neurodegenerative diseases

Synapse dysfunction and loss are hallmarks of neurodegenerative diseases that correlate with cognitive decline. However, the mechanisms and therapeutic strategies to prevent or reverse synaptic damage remain elusive. In this Review, we discuss recent advances in understanding the molecular and cellular pathways that impair synapses in neurodegenerative diseases, including the effects of protein aggregation and neuroinflammation. We also highlight emerging therapeutic approaches that aim to restore synaptic function and integrity, such as enhancing synaptic plasticity, preventing synaptotoxicity, modulating neuronal network activity and targeting immune signalling. We discuss the preclinical and clinical evidence for each strategy, as well as the challenges and opportunities for developing effective synapse-targeting therapeutics for neurodegenerative diseases.

7,8-Dihydroxyflavone ameliorates cognitive impairment induced by repeated neonatal sevoflurane exposures in mice through increasing tau O-GlcNAcylation

BACKGROUND

Sevoflurane, one of the most commonly used general anesthetics for pediatric anesthesia, has recently gained significant attention in both preclinical and clinical settings due to its potential neurotoxicity in the developing brain. Tau phosphorylation, induced by sevoflurane, is recognized as one of the major causes of neurotoxicity. 7,8-dihydroxyflavone (DHF), a TrkB receptor agonist, has been reported to exhibit potential neuroprotective effects against tauopathies. In this study, our objective was to investigate whether DHF could provide neuroprotective effects against sevoflurane-induced neurotoxicity and explore the underlying molecular mechanisms.

METHODS

Six-day-old mice were subjected to 2 h of anesthesia with 3 % sevoflurane, with or without pretreatment of DHF (5 mg/kg/day, i.p.) for 3 consecutive days. Autonomic motor ability was assessed by open-field test, while learning and memory abilities were evaluated by the fear conditioning test. Western blotting was conducted to measure the levels of t-TrkB, p-TrkB, tau, and phosphorylated tau. Additionally, a co-immunoprecipitation assay was performed to investigate the interaction between O-GlcNAcylation and tau.

RESULTS

Repeated neonatal sevoflurane exposures resulted in reduced freezing time during the context and cued fear conditioning tests in adulthood. However, pretreatment with DHF restored the freezing time to the level of the control group, indicating that DHF effectively alleviated cognitive impairments induced by neonatal sevoflurane exposure. We also observed that repeated neonatal sevoflurane exposures increased tau phosphorylation while decreasing tau O-GlcNAcylation. However, DHF pretreatment rebalanced the tau O-GlcNAcylation/phosphorylation ratio by enhancing the interaction between tau and O-GlcNAcylation.

CONCLUSION

Our findings demonstrate that DHF effectively ameliorates sevoflurane-induced cognitive impairment in developing mice by restoring the balance between tau O-GlcNAcylation and phosphorylation. Therefore, this study suggests that DHF has the potential to be a therapeutic agent for treating cognitive impairment associated with anesthetics, such as sevoflurane.

Are TrkB receptor agonists the right tool to fulfill the promises for a therapeutic value of the brain-derived neurotrophic factor?

Brain-derived neurotrophic factor signaling via its receptor tropomyosin receptor kinase B regulates several crucial physiological processes. It has been shown to act in the brain, promoting neuronal survival, growth, and plasticity as well as in the rest of the body where it is involved in regulating for instance aspects of the metabolism. Due to its crucial and very pleiotropic activity, reduction of brain-derived neurotrophic factor levels and alterations in the brain-derived neurotrophic factor/tropomyosin receptor kinase B signaling have been found to be associated with a wide spectrum of neurological diseases. However, because of its poor bioavailability and pharmacological properties, brain-derived neurotrophic factor itself has a very low therapeutic value. Moreover, the concomitant binding of exogenous brain-derived neurotrophic factor to the p75 neurotrophin receptor has the potential to elicit several unwanted and deleterious side effects. Therefore, developing tools and approaches to specifically promote tropomyosin receptor kinase B signaling has become an important goal of translational research. Among the newly developed tools are different categories of tropomyosin receptor kinase B receptor agonist molecules. In this review, we give a comprehensive description of the different tropomyosin receptor kinase B receptor agonist drugs developed so far and of the results of their application in animal models of several neurological diseases. Moreover, we discuss the main benefits of tropomyosin receptor kinase B receptor agonists, concentrating especially on the new tropomyosin receptor kinase B agonist antibodies. The benefits observed both in vitro and in vivo upon application of tropomyosin receptor kinase B receptor agonist drugs seem to predominantly depend on their general neuroprotective activity and their ability to promote neuronal plasticity. Moreover, tropomyosin receptor kinase B agonist antibodies have been shown to specifically bind the tropomyosin receptor kinase B receptor and not p75 neurotrophin receptor. Therefore, while, based on the current knowledge, the tropomyosin receptor kinase B receptor agonists do not seem to have the potential to reverse the disease pathology per se, promoting brain-derived neurotrophic factor/tropomyosin receptor kinase B signaling still has a very high therapeutic relevance.

The role of natural flavonoids on neuroinflammation as a therapeutic target for Alzheimer's disease: a narrative review

Alzheimer's disease is a neurodegenerative disease that affects a large proportion of older adult people and is characterized by memory loss, progressive cognitive impairment, and various behavioral disturbances. Although the pathological mechanisms underlying Alzheimer's disease are complex and remain unclear, previous research has identified two widely accepted pathological characteristics: extracellular neuritic plaques containing amyloid beta peptide, and intracellular neurofibrillary tangles containing tau. Furthermore, research has revealed the significant role played by neuroinflammation over recent years. The inflammatory microenvironment mainly consists of microglia, astrocytes, the complement system, chemokines, cytokines, and reactive oxygen intermediates; collectively, these factors can promote the pathological process and aggravate the severity of Alzheimer's disease. Therefore, the development of new drugs that can target neuroinflammation will be a significant step forward for the treatment of Alzheimer's disease. Flavonoids are plant-derived secondary metabolites that possess various bioactivities. Previous research found that multiple natural flavonoids could exert satisfactory treatment effects on the neuroinflammation associated with Alzheimer's disease. In this review, we describe the pathogenesis and neuroinflammatory processes of Alzheimer's disease, and summarize the effects and mechanisms of 13 natural flavonoids (apigenin, luteolin, naringenin, quercetin, morin, kaempferol, fisetin, isoquercitrin, astragalin, rutin, icariin, mangiferin, and anthocyanin) derived from plants or medicinal herbs on neuroinflammation in Alzheimer's disease. As an important resource for the development of novel compounds for the treatment of critical diseases, it is essential that we focus on the exploitation of natural products. In particular, it is vital that we investigate the effects of flavonoids on the neuroinflammation associated with Alzheimer's disease in greater detail.

Preserving cognitive function in patients with Alzheimer's disease: The Alzheimer's disease neuroprotection research initiative (ADNRI)

The global trend toward aging populations has resulted in an increase in the occurrence of Alzheimer's disease (AD) and associated socioeconomic burdens. Abnormal metabolism of amyloid-β (Aβ) has been proposed as a significant pathomechanism in AD, supported by results of recent clinical trials using anti-Aβ antibodies. Nonetheless, the cognitive benefits of the current treatments are limited. The etiology of AD is multifactorial, encompassing Aβ and tau accumulation, neuroinflammation, demyelination, vascular dysfunction, and comorbidities, which collectively lead to widespread neurodegeneration in the brain and cognitive impairment. Hence, solely removing Aβ from the brain may be insufficient to combat neurodegeneration and preserve cognition. To attain effective treatment for AD, it is necessary to (1) conduct extensive research on various mechanisms that cause neurodegeneration, including advances in neuroimaging techniques for earlier detection and a more precise characterization of molecular events at scales ranging from cellular to the full system level; (2) identify neuroprotective intervention targets against different neurodegeneration mechanisms; and (3) discover novel and optimal combinations of neuroprotective intervention strategies to maintain cognitive function in AD patients. The Alzheimer's Disease Neuroprotection Research Initiative's objective is to facilitate coordinated, multidisciplinary efforts to develop systemic neuroprotective strategies to combat AD. The aim is to achieve mitigation of the full spectrum of pathological processes underlying AD, with the goal of halting or even reversing cognitive decline.

Role of brain-derived neurotrophic factor in endotoxaemia-induced acute lung injury

Acute lung injury (ALI) or acute respiratory distress syndrome (ARDS), which is a pulmonary manifestation of a systemic reactive inflammatory syndrome, is a serious disease with high mortality, and sepsis is an important risk factor in the development of ALI. Brain-derived neurotrophic factor (BDNF) is a member of the nerve growth factor family. It plays an essential role in the regulation of the modification of synaptic efficacy and brain metabolic activity and enhances neuronal survival. However, the role and underlying mechanism of BDNF in sepsis-induced ALI remain unclear. Here, we sought to observe the expression of BDNF in the lung tissues of mice. C57BL/6J mice were divided randomly into two groups: saline (n = 4) and lipopolysaccharide (LPS) (n = 4). We found that BDNF expression was elevated in the lung tissues of septic mice. Furthermore, we found that BDNF colocalized with aquaporin 5, a marker for type I alveolar epithelial cells, by immunofluorescence staining. In addition, we also found that tropomyosin-related kinase B, the specific receptor of BDNF, colocalized with surfactant protein C, a marker for type II alveolar epithelial cells, by immunofluorescence staining. Finally, the present study indicated that BDNF may alleviate excessive LPS-induced autophagy in alveolar epithelial cells. Overall, we hypothesize that BDNF expression increases in the lung tissues of septic mice as a compensatory mechanism to ameliorate sepsis-induced ALI by inhibiting excessive alveolar epithelial cell autophagy.

Impact of dietary plant flavonoids on 7,8-dihydroxyflavone transepithelial transport in human intestinal Caco-2 cells

7,8-dihydroxyflavone (7,8-DHF) is a biologically active flavone with various physiological activities, including neuroprotection, anti-inflammation, and weight loss. Previous studies have found that the efflux protein P-glycoprotein (P-gp) significantly affects the transepithelial transport of 7,8-DHF in the intestine, resulting in its low oral bioavailability. Based on this, in this study, a Caco-2 monolayer cell model was used to investigate 14 dietary plant flavonoids as potential P-gp inhibitors, and their effects on the transepithelial transport and in vitro digestion of 7,8-DHF were explored. The results showed that among the 14 plant flavonoids, hesperetin, epigallocatechin gallate, fisetin, kaempferol, quercetin, and isoorientin increased and the apparent permeability coefficients (P app) of 7,8-DHF at AP → BL direction and lowered P app value at BL → AP direction to varying degrees, reducing the efflux ratio of 7,8-DHF less than 1.5. In particular, kaempferol and quercetin exhibited the best effect on promoting the transepithelial transport of 7,8-DHF, especially when used at molar concentration ratios of 1:1 and 1:2 with 7,8-DHF. This is beneficial for improving the oral bioavailability of 7,8-DHF. Meanwhile, 7,8-DHF was found to maintain structural stability in simulated saliva, gastric juice, and intestinal juice, and its stability was not affected by the coexistence of quercetin and kaempferol. Overall, this study provided a theoretical basis for seeking natural and safe P-gp inhibitors to improve the oral absorption of natural products.

The efficacy of a TrkB monoclonal antibody agonist in preserving the auditory nerve in deafened guinea pigs

The auditory nerve typically degenerates following loss of cochlear hair cells or synapses. In the case of hair cell loss neural degeneration hinders restoration of hearing through a cochlear implant, and in the case of synaptopathy suprathreshold hearing is affected, potentially degrading speech perception in noise. It has been established that neurotrophins such as brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) can mitigate auditory nerve degeneration. Several potential BDNF mimetics have also been investigated for neurotrophic effects in the cochlea. A recent in vitro study showed favorable effects of M3, a TrkB monoclonal antibody agonist, when compared with BDNF. In the present study we set out to examine the effect of M3 on auditory nerve preservation in vivo. Thirty-one guinea pigs were bilaterally deafened, and unilaterally treated with a single 3-µl dose of 7 mg/ml, 0.7 mg/ml M3 or vehicle-only by means of a small gelatin sponge two weeks later. During the experiment and analyses the experimenters were blinded to the three treatment groups. Four weeks after treatment, we assessed the treatment effect (1) histologically, by quantifying survival of SGCs and their peripheral processes (PPs); and (2) electrophysiologically, with two different paradigms of electrically evoked compound action potential (eCAP) recordings shown to be indicative of neural health: single-pulse stimulation with varying inter-phase gap (IPG), and pulse-train stimulation with varying inter-pulse interval. We observed a consistent and significant preservative effect of M3 on SGC survival in the lower basal turn (approximately 40% more survival than in the untreated contralateral cochlea), but also in the upper middle and lower apical turn of the cochlea. This effect was similar for the two treatment groups. Survival of PPs showed a trend similar to that of the SGCs, but was only significantly higher for the highest dose of M3. The protective effect of M3 on SGCs was not reflected in any of the eCAP measures: no statistically significant differences were observed between groups in IPG effect nor between the M3 treatment groups and the control group using the pulse-train stimulation paradigm. In short, while a clear effect of M3 was observed on SGC survival, this was not clearly translated into functional preservation.

Thirty years of BDNF study in central myelination: From biology to therapy

Being the highest expressed neurotrophin in the mammalian brain, the brain-derived neurotrophic factor (BDNF) is essential to neural development and plasticity in both health and diseases. Following the discovery of BDNF by Yves-Alain Barde in 1982, the main feature of BDNF's activity in myelination was first described by Cellerino et al. in 1997. Since then, genetic manipulation of the BDNF-encoding gene and its receptors in murine models has revealed the contribution of BDNF to the myelinating process in the central nervous system (CNS). The series of BDNF or receptor mouse mutants as well as the BDNF polymorphism in humans have provided new insights into the roles that BDNF signaling plays in myelination in a complex manner. 2024 marks the 30th year of BDNF's research in myelination. Here, we share our perspective on the 30-year history of BDNF in the field of CNS myelination from phenotyping to therapeutic development, focusing on genetic evidence regarding the mechanism by which BDNF regulates myelin formation and repair in the CNS. This review also discusses the current hypotheses of BDNF's action on CNS myelination: axonal- and oligodendroglial-driven mechanisms, which may be ultimately activity-dependent. Last, this review raises the challenges and opportunities of developing BDNF-based therapies for neurodegenerative diseases, opening unanswered questions for future investigation.

Tyrosine kinase receptor B attenuates liver fibrosis by inhibiting TGF-β/SMAD signaling

BACKGROUND AND AIMS

Liver fibrosis is a leading indicator for increased mortality and long-term comorbidity in NASH. Activation of HSCs and excessive extracellular matrix production are the hallmarks of liver fibrogenesis. Tyrosine kinase receptor (TrkB) is a multifunctional receptor that participates in neurodegenerative disorders. However, paucity of literature is available about TrkB function in liver fibrosis. Herein, the regulatory network and therapeutic potential of TrkB were explored in the progression of hepatic fibrosis.

METHODS AND RESULTS

The protein level of TrkB was decreased in mouse models of CDAHFD feeding or carbon tetrachloride-induced hepatic fibrosis. TrkB suppressed TGF-β-stimulated proliferation and activation of HSCs in 3-dimensional liver spheroids and significantly repressed TGF-β/SMAD signaling pathway either in HSCs or in hepatocytes. The cytokine, TGF-β, boosted Nedd4 family interacting protein-1 (Ndfip1) expression, promoting the ubiquitination and degradation of TrkB through E3 ligase Nedd4-2. Moreover, carbon tetrachloride intoxication-induced hepatic fibrosis in mouse models was reduced by adeno-associated virus vector serotype 6 (AAV6)-mediated TrkB overexpression in HSCs. In addition, in murine models of CDAHFD feeding and Gubra-Amylin NASH (GAN), fibrogenesis was reduced by adeno-associated virus vector serotype 8 (AAV8)-mediated TrkB overexpression in hepatocytes.

CONCLUSION

TGF-β stimulated TrkB degradation through E3 ligase Nedd4-2 in HSCs. TrkB overexpression inhibited the activation of TGF-β/SMAD signaling and alleviated the hepatic fibrosis both in vitro and in vivo . These findings demonstrate that TrkB could be a significant suppressor of hepatic fibrosis and confer a potential therapeutic target in hepatic fibrosis.

Anti-Neurodegenerating Activity: Structure-Activity Relationship Analysis of Flavonoids

An anti-neurodegeneration activity study was carried out for 80 flavonoid compounds. The structure-activity analysis of the structures was carried out by performing three different anti-neurodegeneration screening tests, showing that in these structures, the presence of a hydroxy substituent group at position C3' as well as C5' of ring B and a methoxy substituent group at the C7 position of ring A play a vital role in neuroprotective and antioxidant as well as anti-inflammatory activity. Further, we found structure (5) was the top-performing active structure out of 80 structures. Subsequently, a molecular docking study was carried out for the 3 lead flavonoid compounds (4), (5), and (23) and 21 similar hypothetical proposed structures to estimate the binding strength between the tested compounds and proteins potentially involved in disease causation. Ligand-based pharmacophores were generated to guide future drug design studies.

Peripheral Levels of the Brain-Derived Neurotrophic Factor in Coronary Artery Disease: A Systematic Review and Meta-Analysis

Background

Among its functions, brain-derived neurotrophic factor (BDNF) regulates endothelial and macrophage activation, possibly playing a role in atherosclerotic plaque pathophysiology. Given contradicting reports, this study sought to investigate whether blood levels of BDNF differed between patients with coronary heart disease (CHD) and controls.

Methods

We explored PubMed, Embase, Web of Science, and Cochrane Library for studies comparing BDNF blood levels in patients with CHD and controls. Random-effect meta-analysis was conducted to calculate the standardized mean differences (SMD) and 95% confidence intervals (CI). The Newcastle-Ottawa scale was used to evaluate the quality of included articles, and statistical analyses were conducted using R version 4.0.4.

Results

The final analysis comprised 12 investigations covering 1422 CHD cases and 929 controls with mean ages of 59.66±13.56 and 53.78±13.61 years, respectively. The initial analyses revealed a tendency toward low levels of BDNF in the CHD group compared with the control group (SMD= -0.41; 95% CI, -1.12 to 0.30; P=0.26). After the removal of outliers, the difference achieved statistical difference (SMD= -0.56; 95% CI, -0.93 to -0.19; P<0.01). Subgroup analysis demonstrated no significant difference between serum and plasma BDNF levels (P=0.54); however, subgroup analyses of studies investigating plasma BDNF showed that patients with CHD had significantly lower BDNF levels.

Conclusion

Serum and plasma BDNF concentrations were considerably lower in patients with CHD than in healthy controls. Further studies of higher quality are required on the potential role of BDNF as a biomarker of CHD pathophysiology and severity.

7,8-Dihydroxy Flavone Induces Apoptosis via Upregulation of Caspase-3 in Human Hepatocarcinoma Cell

OBJECTIVE

7,8-Dihydroxyflavone, a tyrosine kinase receptor agonist, is a flavonoid that has recently gained the attention of researchers due to its anticancer properties. Nevertheless, molecular pathways of 7,8-dihydroxyflavone for hepatocarcinoma are uncertain. Our aim was to identify the impact of 7,8-dihydroxyflavone on human hepatocarcinoma.

MATERIAL AND METHODS

Human hepatocarcinoma cell line-7 cells were used as human hepatocarcinoma cells, and 7,8-dihydroxyflavone was applied to the cells at various doses. The cytotoxic and apoptotic effects of 7,8-dihydroxyflavone were determined with Alamar Blue and flow cytometry. The properties of 7,8-dihydroxyflavone on the mRNA expressions related with Bcl-2, Bax, cleaved-caspase-3 genes, and protein expressions were determined via quantitative real-time polymerase chain reaction and western blot analysis, respectively.

RESULTS

7,8-Dihydroxyflavone-enhanced cell death in human hepatocarcinoma cell line-7 via the overexpression of cleaved-caspase-3 (P=.003) and decreased Bcl-2 (P=.038) protein levels. Furthermore, cleavedcaspase-3 mRNA overexpression (P=.001) markedly led to 7,8-dihydroxyflavone-induced apoptosis.

CONCLUSION

7,8-Dihydroxyflavone could promote apoptotic cell death by modulating caspase pathways and suppressing antiapoptotic protein. These characteristics may mediate to clinical practice of 7,8-dihydroxyflavone for prevention and therapy of hepatocarcinoma.

The BDNF mimetic R-13 attenuates TBI pathogenesis using TrkB-related pathways and bioenergetics

Traumatic brain injury (TBI) is major neurological burden globally, and effective treatments are urgently needed. TBI is characterized by a reduction in energy metabolism and synaptic function that seems a primary cause of neuronal dysfunction. R13, a small drug and BDNF mimetic showed promising results in improving spatial memory and anxiety-like behavior after TBI. Additionally, R13 was found to counteract reductions in molecules associated with BDNF signaling (p-TrkB, p-PI3K, p-AKT), synaptic plasticity (GluR2, PSD95, Synapsin I) as well as bioenergetic components such as mitophagy (SOD, PGC-1α, PINK1, Parkin, BNIP3, and LC3) and real-time mitochondrial respiratory capacity. Behavioral and molecular changes were accompanied by adaptations in functional connectivity assessed using MRI. Results highlight the potential of R13 as a therapeutic agent for TBI and provide valuable insights into the molecular and functional changes associated with this condition.

Linking Hypothermia and Altered Metabolism with TrkB Activation

Many mechanisms have been proposed to explain acute antidepressant drug-induced activation of TrkB neurotrophin receptors, but several questions remain. In a series of pharmacological experiments, we observed that TrkB activation induced by antidepressants and several other drugs correlated with sedation, and most importantly, coinciding hypothermia. Untargeted metabolomics of pharmacologically dissimilar TrkB activating treatments revealed effects on shared bioenergetic targets involved in adenosine triphosphate (ATP) breakdown and synthesis, demonstrating a common perturbation in metabolic activity. Both activation of TrkB signaling and hypothermia were recapitulated by administration of inhibitors of glucose and lipid metabolism, supporting a close relationship between metabolic inhibition and neurotrophic signaling. Drug-induced TrkB phosphorylation was independent of electroencephalography slow-wave activity and remained unaltered in knock-in mice with the brain-derived neurotrophic factor (BDNF) Val66Met allele, which have impaired activity-dependent BDNF release, alluding to an activation mechanism independent from BDNF and neuronal activity. Instead, we demonstrated that the active maintenance of body temperature prevents activation of TrkB and other targets associated with antidepressants, including p70S6 kinase downstream of the mammalian target of rapamycin (mTOR) and glycogen synthase kinase 3β (GSK3β). Increased TrkB, GSK3β, and p70S6K phosphorylation was also observed during recovery sleep following sleep deprivation, when a physiological temperature drop is known to occur. Our results suggest that the changes in bioenergetics and thermoregulation are causally connected to TrkB activation and may act as physiological regulators of signaling processes involved in neuronal plasticity.

Zein-Based Nanoparticles Improve the Therapeutic Efficacy of a TrkB Agonist toward Alzheimer's Disease

The brain-derived neurotrophic factor (BDNF)/TrkB pathway plays a crucial role in neural plasticity and neuronal survival but is often deficient in neurodegenerative diseases like Alzheimer's disease (AD). CF3CN acts as a specific TrkB agonist that displays therapeutic effects in the AD mouse model, but its brain/plasma ratio (B/P ratio) distribution is not satisfactory. To increase its brain exposure, we synthesized several derivatives and employed nanoparticle (NP) formulation to optimize the most potent #2 derivative's in vivo PK profiles. We generated stable #2-loaded zein/lactoferrin composite NPs (#2/zein/LF) using the antisolvent co-precipitation method. In vivo PK studies revealed that nanoencapsulation improved #2's oral bioavailability by approximately 2-fold and significantly enhanced its plasma Cmax and t1/2, but the brain profiles were comparable. Pharmacodynamics showed that #2/zein/LF activates TrkB signaling that phosphorylates asparagine endopeptidase (AEP) T322 and decreases its enzymatic activity, resulting in reduced AEP-cleaved amyloid precursor protein and Tau fragments in the brains of AD mice, correlating with its PK profiles. After 3 months of treatment in 3xTg mice, #2/zein/LF decreased AD pathologies and alleviated cognitive dysfunction. Hence, zein/LF composite nanoencapsulation is a promising drug delivery method for improving the PK profiles of a potential preclinical candidate for treating neurodegenerative diseases.

Activation of TrkB signaling mitigates cerebellar anomalies caused by Rbm4-Bdnf deficiency

A molecular and functional link between neurotrophin signaling and cerebellar foliation is lacking. Here we show that constitutive knockout of two homologous genes encoding the RNA binding protein RBM4 results in foliation defects at cerebellar lobules VI-VII and delayed motor learning in mice. Moreover, the features of Rbm4 double knockout (dKO), including impaired differentiation of cerebellar granule cells and dendritic arborization of Purkinje cells, are reminiscent of neurotrophin deficiency. Loss of RBM4 indeed reduced brain-derived neurotrophic factor (BDNF). RBM4 promoted the expression of BDNF and full-length TrkB, implicating RBM4 in efficient BDNF-TrkB signaling. Finally, prenatal supplementation with 7,8-dihydroxyflavone, a TrkB agonist, restored granule cell differentiation, Purkinje cell dendritic complexity and foliation-the intercrural fissure in particular-in the neonatal cerebellum of Rbm4dKO mice, which also showed improved motor learning in adulthood. This study provides evidence that prenatal activation of TrkB signaling ameliorates cerebellar malformation caused by BDNF deficiency.

BDNF/TrkB pathway activation in D1 receptor-expressing striatal projection neurons plays a protective role against L-DOPA-induced dyskinesia

L-DOPA-induced dyskinesia (LID) is a frequent adverse side effect of L-DOPA treatment in Parkinson's disease (PD). Understanding the mechanisms underlying the development of these motor disorders is needed to reduce or prevent them. We investigated the role of TrkB receptor in LID, in hemiparkinsonian mice treated by chronic L-DOPA administration. Repeated L-DOPA treatment for 10 days specifically increased full-length TrkB receptor mRNA and protein levels in the dopamine-depleted dorsal striatum (DS) compared to the contralateral non-lesioned DS or to the DS of sham-operated animals. Dopamine depletion alone or acute L-DOPA treatment did not significantly increase TrkB protein levels. In addition to increasing TrkB protein levels, chronic L-DOPA treatment activated the TrkB receptor as evidenced by its increased tyrosine phosphorylation. Using specific agonists for the D1 or D2 receptors, we found that TrkB increase is D1 receptor-dependent. To determine the consequences of these effects, the TrkB gene was selectively deleted in striatal neurons expressing the D1 receptor. Mice with TrkB floxed gene were injected with Cre-expressing adeno-associated viruses or crossed with Drd1-Cre transgenic mice. After unilateral lesion of dopamine neurons in these mice, we found an aggravation of axial LID compared to the control groups. In contrast, no change was found when TrkB deletion was induced in the indirect pathway D2 receptor-expressing neurons. Our study suggests that BDNF/TrkB signaling plays a protective role against the development of LID and that agonists specifically activating TrkB could reduce the severity of LID.

Growth factors and their peptide mimetics for treatment of traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of disability in adults, caused by a physical insult damaging the brain. Growth factor-based therapies have the potential to reduce the effects of secondary injury and improve outcomes by providing neuroprotection against glutamate excitotoxicity, oxidative damage, hypoxia, and ischemia, as well as promoting neurite outgrowth and the formation of new blood vessels. Despite promising evidence in preclinical studies, few neurotrophic factors have been tested in clinical trials for TBI. Translation to the clinic is not trivial and is limited by the short in vivo half-life of the protein, the inability to cross the blood-brain barrier and human delivery systems. Synthetic peptide mimetics have the potential to be used in place of recombinant growth factors, activating the same downstream signalling pathways, with a decrease in size and more favourable pharmacokinetic properties. In this review, we will discuss growth factors with the potential to modulate damage caused by secondary injury mechanisms following a traumatic brain injury that have been trialled in other indications including spinal cord injury, stroke and neurodegenerative diseases. Peptide mimetics of nerve growth factor (NGF), hepatocyte growth factor (HGF), glial cell line-derived growth factor (GDNF), brain-derived neurotrophic factor (BDNF), platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF) will be highlighted, most of which have not yet been tested in preclinical or clinical models of TBI.

Natural flavonoids disrupt bacterial iron homeostasis to potentiate colistin efficacy

In the face of the alarming rise in global antimicrobial resistance, only a handful of novel antibiotics have been developed in recent decades, necessitating innovations in therapeutic strategies to fill the void of antibiotic discovery. Here, we established a screening platform mimicking the host milieu to select antibiotic adjuvants and found three catechol-type flavonoids-7,8-dihydroxyflavone, myricetin, and luteolin-prominently potentiating the efficacy of colistin. Further mechanistic analysis demonstrated that these flavonoids are able to disrupt bacterial iron homeostasis through converting ferric iron to ferrous form. The excessive intracellular ferrous iron modulated the membrane charge of bacteria via interfering the two-component system pmrA/pmrB, thereby promoting the colistin binding and subsequent membrane damage. The potentiation of these flavonoids was further confirmed in an in vivo infection model. Collectively, the current study provided three flavonoids as colistin adjuvant to replenish our arsenals for combating bacterial infections and shed the light on the bacterial iron signaling as a promising target for antibacterial therapies.

3D printed elastic hydrogel conduits with 7,8-dihydroxyflavone release for peripheral nerve repair

Nerve guide conduit is a promising treatment for long gap peripheral nerve injuries, yet its efficacy is limited. Drug-releasable scaffolds may provide reliable platforms to build a regenerative microenvironment for nerve recovery. In this study, an elastic hydrogel conduit encapsulating with prodrug nanoassemblies is fabricated by a continuous 3D printing technique for promoting nerve regeneration. The bioactive hydrogel is comprised of gelatin methacryloyl (GelMA) and silk fibroin glycidyl methacrylate (SF-MA), exhibiting positive effects on adhesion, proliferation, and migration of Schwann cells. Meanwhile, 7,8-dihydroxyflavone (7,8-DHF) prodrug nanoassemblies with high drug-loading capacities are developed through self-assembly of the lipophilic prodrug and loaded into the GelMA/SF-MA hydrogel. The drug loading conduit could sustainedly release 7,8-DHF to facilitate neurite elongation. A 12 ​mm nerve defect model is established for therapeutic efficiency evaluation by implanting the conduit through surgical suturing with rat sciatic nerve. The electrophysiological, morphological, and histological assessments indicate that this conduit can promote axon regeneration, remyelination, and function recovery by providing a favorable microenvironment. These findings implicate that the GelMA/SF-MA conduit with 7,8-DHF release has potentials in the treatment of long-gap peripheral nerve injury.

Conjugation, Prodrug, and Co-Administration Strategies in Support of Nanotechnologies to Improve the Therapeutic Efficacy of Phytochemicals in the Central Nervous System

Phytochemicals, produced as secondary plant metabolites, have shown interesting potential therapeutic activities against neurodegenerative diseases and cancer. Unfortunately, poor bioavailability and rapid metabolic processes compromise their therapeutic use, and several strategies are currently proposed for overcoming these issues. The present review summarises strategies for enhancing the central nervous system's phytochemical efficacy. Particular attention has been paid to the use of phytochemicals in combination with other drugs (co-administrations) or administration of phytochemicals as prodrugs or conjugates, particularly when these approaches are supported by nanotechnologies exploiting conjugation strategies with appropriate targeting molecules. These aspects are described for polyphenols and essential oil components, which can improve their loading as prodrugs in nanocarriers, or be part of nanocarriers designed for targeted co-delivery to achieve synergistic anti-glioma or anti-neurodegenerative effects. The use of in vitro models, able to simulate the blood-brain barrier, neurodegeneration or glioma, and useful for optimizing innovative formulations before their in vivo administration via intravenous, oral, or nasal routes, is also summarised. Among the described compounds, quercetin, curcumin, resveratrol, ferulic acid, geraniol, and cinnamaldehyde can be efficaciously formulated to attain brain-targeting characteristics, and may therefore be therapeutically useful against glioma or neurodegenerative diseases.

Effects of microplastic exposure on the early developmental period and circadian rhythm of zebrafish (Danio rerio): A comparative study of polylactic acid and polyglycolic acid

Polyglycolic acid (PGA) is an emerging biodegradable plastic material. Together with polylactic acid (PLA), PGA is considered a suitable alternative to conventional plastics and has been widely used in biomedical and food packaging industries. However, degradable plastics continue to face the drawbacks of harsh degradation environment and long degradation time, and may harm the environment and the human body. Therefore, our study focused on assessing the effects of degradable microplastics PGA and PLA on the development and neurobehavior of zebrafish. The results showed that PGA and PLA had little effect on 3-10 hpf embryos. However, developmental stunting was observed in a100 mg/L PGA and PLA-exposed group at 24 hpf. In addition, PGA and PLA exposure decreased the survival and hatching rates, increased wakefulness, and reduced sleep in zebrafish. This indicates that PGA and PLA may affect the circadian behavior of zebrafish by affecting the brain-derived neurotrophic factor (BDNF). Therefore, our results suggest that PGA and PLA exposure induces developmental toxicity, reduces voluntary locomotion, induces of anxiety-like behaviors, and impairs sleep/wake behaviors in zebrafish larvae. This also suggests that the potentially toxic effects of degradable plastics cannot be ignored and that the biological effects of PGA require further research.

Exploring the Therapeutic Effect of Neurotrophins and Neuropeptides in Neurodegenerative Diseases: at a Glance

Neurotrophins and neuropeptides are the essential regulators of peripheral nociceptive nerves that help to induce, sensitize, and maintain pain. Neuropeptide has a neuroprotective impact as it increases trophic support, regulates calcium homeostasis, and reduces excitotoxicity and neuroinflammation. In contrast, neurotrophins target neurons afflicted by ischemia, epilepsy, depression, and eating disorders, among other neuropsychiatric conditions. Neurotrophins are reported to inhibit neuronal death. Strategies maintained for "brain-derived neurotrophic factor (BDNF) therapies" are to upregulate BDNF levels using the delivery of protein and genes or compounds that target BDNF production and boosting BDNF signals by expanding with BDNF mimetics. This review discusses the mechanisms of neurotrophins and neuropeptides against acute neural damage as well as highlighting neuropeptides as a potential therapeutic agent against Parkinson's disease (PD), Huntington's disease (HD), Alzheimer's disease (AD), and Machado-Joseph disease (MJD), the signaling pathways affected by neurotrophins and their receptors in both standard and diseased CNS systems, and future perspectives that can lead to the potent application of neurotrophins and neuropeptides in neurodegenerative diseases (NDs).

High throughput assay for compounds that boost BDNF expression in neurons

Deficiencies in brain-derived neurotrophic factor (BDNF) have been linked to several brain disorders, making compounds that can boost neuronal BDNF synthesis attractive as potential therapeutics. However, a sensitive and quantitative BDNF assay for high-throughput screening (HTS) is still missing. Here we report the generation of a new mouse Bdnf allele, BdnfNLuc, in which the sequence encoding nano luciferase (NLuc) is inserted into the Bdnf locus immediately before the stop codon so that the allele will produce a BDNF-NLuc fusion protein. BDNF-NLuc protein appears to function like BDNF as BdnfNLuc/NLuc homozygous mice grew and behaved almost normally. We were able to establish and optimize cultures of cortical and hippocampal BdnfNLuc/+ neurons isolated from mouse embryos in 384-well plates. We used the cultures as a phenotypic assay to detect the ability of 10 mM KCl to stimulate BDNF synthesis and achieved a reproducible Z' factor > 0.50 for the assay, a measure considered suitable for HTS. We successfully scaled up the assay to screen the 1280-compound LOPAC library (Library of Pharmacologically Active Compounds). The screen identified several BDNF-boosting compounds, one of which is Bay K8644, a L-type voltage-gated calcium channel (L-VGCC) agonist, which was previously shown to stimulate BDNF synthesis. These results indicate that our phenotypic neuronal assay is ready for HTS to identify novel BDNF-boosting compounds.

Autophagy regulates the release of exercise factors and their beneficial effects on spatial memory recall

Exercise promotes learning and memory recall as well as rescues cognitive decline associated with aging. The positive effects of exercise are mediated by circulatory factors that predominantly increase Brain Derived Neurotrophic Factor (BDNF) signaling in the hippocampus. Identifying the pathways that regulate the release of the circulatory factors by various tissues during exercise and that mediate hippocampal Mus musculus Bdnf expression will allow us to harness the therapeutic potential of exercise. Here, we report that two weeks of voluntary exercise in male mice activates autophagy in the hippocampus by increasing LC3B protein levels (p = 0.0425) and that autophagy is necessary for exercise-induced spatial learning and memory retention (p < 0.001; exercise + autophagy inhibitor chloroquine CQ versus exercise). We place autophagy downstream of hippocampal BDNF signaling and identify a positive feedback activation between the pathways. We also assess whether the modulation of autophagy outside the nervous system is involved in mediating exercise's effect on learning and memory recall. Indeed, plasma collected from young exercise mice promote spatial learning (p = 0.0446; exercise versus sedentary plasma) and memory retention in aged inactive mice (p = 0.0303; exercise versus sedentary plasma), whereas plasma collected from young exercise mice that received the autophagy inhibitor chloroquine diphosphate failed to do so. We show that the release of exercise factors that reverse the symptoms of aging into the circulation is dependent on the activation of autophagy in young animals. Indeed, we show that the release of the exercise factor, beta-hydroxybutyrate (DBHB), into the circulation, is autophagy-dependent and that DBHB promotes spatial learning and memory formation (p = 0.0005) by inducing hippocampal autophagy (p = 0.0479). These results implicate autophagy in peripheral tissues and in the hippocampus in mediating the effects of exercise on learning and memory recall and identify DBHB as a candidate endogenous exercise factor whose release and positive effects are autophagy-dependent.

Myocardial brain-derived neurotrophic factor regulates cardiac bioenergetics through the transcription factor Yin Yang 1

AIMS

Brain-derived neurotrophic factor (BDNF) is markedly decreased in heart failure patients. Both BDNF and its receptor, tropomyosin-related kinase receptor (TrkB), are expressed in cardiomyocytes; however, the role of myocardial BDNF signalling in cardiac pathophysiology is poorly understood. Here, we investigated the role of BDNF/TrkB signalling in cardiac stress response to exercise and pathological stress.

METHODS AND RESULTS

We found that myocardial BDNF expression was increased in mice with swimming exercise but decreased in a mouse heart failure model and human failing hearts. Cardiac-specific TrkB knockout (cTrkB KO) mice displayed a blunted adaptive cardiac response to exercise, with attenuated upregulation of transcription factor networks controlling mitochondrial biogenesis/metabolism, including peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α). In response to pathological stress (transaortic constriction, TAC), cTrkB KO mice showed an exacerbated heart failure progression. The downregulation of PGC-1α in cTrkB KO mice exposed to exercise or TAC resulted in decreased cardiac energetics. We further unravelled that BDNF induces PGC-1α upregulation and bioenergetics through a novel signalling pathway, the pleiotropic transcription factor Yin Yang 1.

CONCLUSION

Taken together, our findings suggest that myocardial BDNF plays a critical role in regulating cellular energetics in the cardiac stress response.

7,8-Dihydroxyflavone induces mitochondrial apoptosis and down-regulates the expression of ganglioside GD3 in malignant melanoma cells

Malignant melanoma is a skin cancer with poor prognosis and high resistance to conventional treatment. 7,8-dihydroxyflavone (7,8-DHF) has shown anti-carcinogenic, anti-inflammatory, anti-oxidant, and pharmacological effects in several types of cancer. However, the relationship between ganglioside expression and the anti-cancer effects of 7,8-DHF in melanoma is not fully understood. In the present study, 7,8-DHF exhibits specific anti-proliferation, anti-migration, and G2/M phase cell-cycle arrest effects on both melanoma cancer cell lines, and induces mitochondrial dysfunction and apoptosis, making it a potent candidate for anti-melanoma treatment. Furthermore, we confirmed that 7,8-DHF significantly reduces the expression levels of ganglioside GD3 and its synthase, which are known to be closely involved in carcinogenesis. Taken together, our findings suggest that 7,8-DHF may be a potent anti-cancer drug candidate for the treatment of malignant melanoma.

7,8-dihydroxyflavone enhances long-term spatial memory and alters brain volume in wildtype mice

Introduction: 7,8-dihydroxyflavone (7,8-DHF) is a low molecular weight compound that can cross the blood brain barrier and has been implicated in numerous functions and behaviours. It is thought to have neuroprotective capability and has been shown to alleviate symptoms in a wide range of diseases.

Methods: 7,8-DHF was administered systemically to wildtype mice during Morris water maze training. Long-term spatial memory was assessed 28 days later. Ex-vivo T2-weighted (T2w) imaging was undertaken on a subset of these mice to assess brain-wide changes in volume.

Results: We found that systemic 7,8-DHF administration during the training period enhanced spatial memory 28 days later. Volumetric changes were observed in numerous brain regions associated with a broad range of functions including cognition, sensory, and motor processing.

Discussion: Our findings give the first whole brain overview of long-term anatomical changes following 7,8-DHF administration providing valuable information for assessing and understanding the widespread effects this drug has been shown to have in behaviour and disease.

7,8-Dihydroxiflavone protects retinal ganglion cells and promotes axonal regeneration through TrkB signaling pathway followed by AKT and ERK activation

The aim of this study was to investigate the effects of 7,8-dihydroxyflavone (7,8-DHF) in protecting retinal ganglion cells (RGCs) and promoting axonal regeneration, and to explore its potential molecular mechanisms. We used three-dimensional retinal culture system and optic nerve crush (ONC) rat models in this study. The pro-axonal regenerative effect of 7,8-DHF was determined with light microscopy observation and immunofluorescence staining of Thy1.1 and GAP43. The RGC protective function of 7,8-DHF was detected by RBPMS immunofluorescent staining and TUNEL staining. The inhibition effect of 7,8-DHF on astrocyte activation was measured using GFAP immunofluorescence and Western blotting. The protein levels of p-TrkB, p-AKT and p-ERK was examined by Western blotting and immunohistochemistry. Our results revealed that 7,8-DHF significantly promoted the average density and length of regenerated neurites and suppressed the apoptosis of GCL cells in three-dimensional culture system and significantly increased the number of RBPMS-positive cells and inhibited the GFAP expression and apoptosis of GCL cells in ONC rats. Our results also revealed that 7,8-DHF activates TrkB, AKT and ERK proteins in vivo, however, these activations can be inhibited byANA-12. In conclusion, 7,8-DHF protects RGCs and promotes axonal regeneration through the TrkB signaling pathway followed by AKT and ERK activation.

Neurotrophins and Other Growth Factors in the Pathogenesis of Alzheimer’s Disease

The involvement of the changed expression/function of neurotrophic factors in the pathogenesis of neurodegenerative diseases, including Alzheimer’s disease (AD), has been suggested. AD is one of the age-related dementias, and is characterized by cognitive impairment with decreased memory function. Developing evidence demonstrates that decreased cell survival, synaptic dysfunction, and reduced neurogenesis are involved in the pathogenesis of AD. On the other hand, it is well known that neurotrophic factors, especially brain-derived neurotrophic factor (BDNF) and its high-affinity receptor TrkB, have multiple roles in the central nervous system (CNS), including neuronal maintenance, synaptic plasticity, and neurogenesis, which are closely linked to learning and memory function. Thus, many investigations regarding therapeutic approaches to AD, and/or the screening of novel drug candidates for its treatment, focus on upregulation of the BDNF/TrkB system. Furthermore, current studies also demonstrate that GDNF, IGF1, and bFGF, which play roles in neuroprotection, are associated with AD. In this review, we introduce data demonstrating close relationships between the pathogenesis of AD, neurotrophic factors, and drug candidates, including natural compounds that upregulate the BDNF-mediated neurotrophic system.

Dysfunction of NG2 glial cells affects neuronal plasticity and behavior

NG2 glia represents a distinct type of macroglial cells in the CNS and is unique among glia because they receive synaptic input from neurons. They are abundantly present in white and gray matter. While the majority of white matter NG2 glia differentiates into oligodendrocytes, the physiological impact of gray matter NG2 glia and their synaptic input are still ill defined. Here, we asked whether dysfunctional NG2 glia affect neuronal signaling and behavior. We generated mice with inducible deletion of the K⁺ channel Kir4.1 in NG2 glia and performed comparative electrophysiological, immunohistochemical, molecular and behavioral analyses. Kir4.1 was deleted at postnatal day 23-26 (recombination efficiency about 75%) and mice were investigated 3-8 weeks later. Notably, these mice with dysfunctional NG2 glia demonstrated improved spatial memory as revealed by testing new object location recognition while working and social memory remained unaffected. Focussing on the hippocampus, we found that loss of Kir4.1 potentiated synaptic depolarizations of NG2 glia and stimulated the expression of myelin basic protein while proliferation and differentiation of hippocampal NG2 glia remained largely unaffected. Mice with targeted deletion of the K⁺ channel in NG2 glia showed impaired long-term potentiation at CA3-CA1 synapses, which could be fully rescued by extracellular application of a TrkB receptor agonist. Our data demonstrate that proper NG2 glia function is important for normal brain function and behavior.

7,8-Dihydroxyflavone Attenuates Inflammatory Response and Insulin Resistance Induced by the Paracrine Interaction between Adipocytes and Macrophages

Obesity-induced inflammation and insulin resistance are mediated by macrophage infiltration into adipose tissue. We investigated the effects of 7,8-dihydroxyflavone (7,8-DHF), a flavone found in plants, on the inflammatory response and insulin resistance induced by the interaction between adipocytes and macrophages. Hypertrophied 3T3-L1 adipocytes were cocultured with RAW 264.7 macrophages and treated with 7,8-DHF (3.12, 12.5, and 50 μM). The inflammatory cytokines and free fatty acid (FFA) release were evaluated by assay kits, and signaling pathways were determined by immunoblotting. Coculture of adipocytes and macrophages increased inflammatory mediators, such as nitric oxide (NO), monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6) and FFA secretion but suppressed the production of anti-inflammatory adiponectin. 7,8-DHF counteracted the coculture-induced changes (p < 0.001). 7,8-DHF also inhibited c-Jun N-terminal kinase (JNK) activation and blocked nuclear factor kappa B (NF-κB) nuclear translocation in the coculture system (p < 0.01). In addition, adipocytes cocultured with macrophages did not increase glucose uptake and Akt phosphorylation in response to insulin. However, 7,8-DHF treatment recovered the impaired responsiveness to insulin (p < 0.01). These findings show that 7,8-DHF alleviates inflammation and adipocyte dysfunction in the coculture of hypertrophied 3T3-L1 adipocytes and RAW 264.7 macrophages, indicating its potential as a therapeutic agent for obesity-induced insulin resistance.

The potential neuroprotective effects of stingless bee honey

Tropical Meliponini bees produce stingless bee honey (SBH). Studies have shown beneficial properties, including antibacterial, bacteriostatic, anti-inflammatory, neurotherapeutic, neuroprotective, wound, and sunburn healing capabilities. High phenolic acid and flavonoid concentrations offer SBH its benefits. SBH can include flavonoids, phenolic acids, ascorbic acid, tocopherol, organic acids, amino acids, and protein, depending on its botanical and geographic origins. Ursolic acid, p-coumaric acid, and gallic acid may diminish apoptotic signals in neuronal cells, such as nuclear morphological alterations and DNA fragmentation. Antioxidant activity minimizes reactive oxygen species (ROS) formation and lowers oxidative stress, inhibiting inflammation by decreasing enzymes generated during inflammation. Flavonoids in honey reduce neuroinflammation by decreasing proinflammatory cytokine and free radical production. Phytochemical components in honey, such as luteolin and phenylalanine, may aid neurological problems. A dietary amino acid, phenylalanine, may improve memory by functioning on brain-derived neurotrophic factor (BDNF) pathways. Neurotrophin BDNF binds to its major receptor, TrkB, and stimulates downstream signaling cascades, which are crucial for neurogenesis and synaptic plasticity. Through BDNF, SBH can stimulate synaptic plasticity and synaptogenesis, promoting learning and memory. Moreover, BDNF contributes to the adult brain's lasting structural and functional changes during limbic epileptogenesis by acting through the cognate receptor tyrosine receptor kinase B (TrkB). Given the higher antioxidants activity of SBH than the Apis sp. honey, it may be more therapeutically helpful. There is minimal research on SBH's neuroprotective effects, and the related pathways contribute to it is unclear. More research is needed to elucidate the underlying molecular process of SBH on BDNF/TrkB pathways in producing neuroprotective effects.

Dose-dependent manner of luteolin in the modulation of spatial memory with respect to the hippocampal level of HSP70 and HSP90 in sleep-deprived rats

Sleep deprivation (SD) induces a variety of deleterious effects on different cognitive functions such as memory. Elevated neuroinflammation, oxidative stress, and apoptosis, and decreased synaptic plasticity and antioxidant capacity are involved in the deleterious effects of SD on memory. On the other hand, luteolin (a flavonoid compound) has antioxidant, neuroprotective, and anti-inflammatory properties. Also, Heat shock protein 70 (HSP70) and Heat shock protein 90 (HSP90) can be involved in modulating memory. In this study, we aimed to assess the effects of SD and luteolin on spatial learning and memory using Morris Water Maze apparatus in rats, with respect to the level of HSP70 and HSP90 in the hippocampus. Luteolin was injected intracerebroventricular (i.c.v.) at the doses of 0.5, 1, and 2 µg/rat. The results showed that SD impaired spatial memory, while luteolin dose-dependently restored SD-induced spatial memory impairment. SD increased the expression level of HSP90 in the hippocampus, whereas luteolin dose-dependently reversed the effect of SD. Furthermore, SD decreased the expression level of HSP70 protein in the hippocampus, while luteolin dose-dependently reversed the effect of SD. In conclusion, HSP70 and HSP90 may be involved in the deleterious effect of SD on memory, and in the improvement effect of luteolin on memory. This is a novel study reporting novel data and we suggest further detailed studies to better understand the interactions between SD, luteolin, and Heat shock proteins.