Indoleamine 2,3-Dioxygenase-Dependent Neurotoxic Kynurenine Metabolism Contributes to Poststroke Depression Induced in Mice by Ischemic Stroke along with Spatial Restraint Stress

Therapeutic effects of exercise on depression: The role of microglia

Major depressive disorderadversely affects mental health. Traditional therapeutic approaches, including medication, psychological intervention, and physical therapy, exert beneficial effects on depression. However, these approaches are associated with some limitations, such as high cost, adverse reactions, recurrent episodes, and low patient adherence. Previous studies have demonstrated that exercise therapy can effectively mitigate depressive symptoms, although the underlying mechanism has not been elucidated. Recent studies have suggested that depression is a microglial disease. Microglia regulate the inflammatory response, synaptic plasticity, neurogenesis, kynurenine pathway and the activation of hypothalamic-pituitary-adrenal axis, all of which affect depression. Exercise therapy is reported to shift the balance of microglial M1/M2 polarization in the hippocampus, frontal lobe, and striatum, suppressing the release of pro-inflammatory factors and consequently alleviating behavioral deficits in animal models of depression. Further studies are needed to examine the specific effects of different exercise regimens on microglia to identify the exercise regimen with the best therapeutic effect.

Effects of E2 on the IDO1-mediated metabolic KYN pathway in OVX female mice

The aim of this study was to investigate the role of 17β-estradiol (E2)-mediated oestrogen receptor (ER) in modulating the depressive-like behaviours of ovariectomy (OVX) mice and the associated mechanisms. E2 was administrated in OVX mice. The behaviour and physiological changes of OVX mice including immobility time in tail suspension test (TST) and forced swimming test (FST), levels of serum E2, inflammatory mediators, oxidative stress factors, indoleamine2,3-dioxygenase 1 (IDO1) and the neurotransmitters mediated by IDO1 activation were then recorded. Cell injury models established by lipopolysaccharide (LPS) or H2O2 stimulation in HT22 and BV2 cells were employed to further explore the mechanisms of E2's function. E2 treatment improved OVX-induced increase of immobility time in FST and TST. Meanwhile, E2 ameliorated the changes of inflammatory factors (NF-κB, TNF-α and IL-6), IDO1, IDO1-mediated TRP/KYN pathway and oxidative stress factors (iNOS, MDA, GSH and SOD) in the hippocampus of OVX mice. Interestingly, ERβ inhibitor abolished E2's inhibitory effects on the inflammation and IDO1-mediated TRP/KYN pathway; ERβ inhibitor also abolished E2's anti-oxidative stress effect. In cell experiments, ERβ small interfering RNA (siRNA) pretreatment reversed E2's anti-inflammatory effect on LPS-treated HT22 and BV2 cells and E2's inhibitory effect on IDO1 expression in LPS-treated BV2 cells. ERβ siRNA pretreatment also reversed E2's anti-oxidation effect on H2O2-treated HT22 cells. E2 exert the antidepressant function in OVX mice via ERβ-modulated suppression of NF-κB-mediated inflammatory pathway, oxidative stress factors and IDO1-mediated TRP/KYN pathway in the hippocampus.

Blueberry extract for the treatment of ischaemic stroke through regulating the gut microbiota and kynurenine metabolism

Although the gut microbiota and kynurenine (KYN) metabolism have significant protective effects against ischaemic stroke (IS), the exact mechanism has yet to be fully elucidated. Combined serum metabolomics and 16S rRNA gene sequencing were used to reveal the differences between the gut microbiota and metabolites in rats treated with or without blueberry extract. Faecal microbiota transplantation (FMT) was employed to validate the protective role of the gut microbiota in IS. Furthermore, the interaction between Prevotella and IS was also confirmed in patients. Rats with IS experienced neurological impairments accompanied by an impaired intestinal barrier and disturbed intestinal flora, which further contributed to heightened inflammatory responses. Furthermore, Prevotella played a critical role in IS pathophysiology, and a positive correlation between Prevotella and KYN was detected. The role of KYN metabolism in IS was further demonstrated by the finding that IDO was significantly upregulated and that the use of the IDO inhibitor, attenuated KYN metabolic pathway activity and ameliorated neurological damage in rats with IS. Prevotella intervention also significantly improved stroke symptoms and decreasing KYN levels in rats with IS. FMT showed that the beneficial effects of blueberry extract on IS involve gut bacteria, especially Prevotella, which were confirmed by microbiological analyses conducted on IS patients. Moreover, blueberry extract led to significant changes in kynurenic acid levels and tryptophan and IDO levels through interactions with Prevotella. Our study demonstrates for the first time that blueberry extract could modulate "intestinal microecology-KYN metabolism" to improve IS.

Lipopolysaccharide Preconditioning Restricts Microglial Overactivation and Alleviates Inflammation-Induced Depressive-like Behavior in Mice

Overactive microglia and severe neuroinflammation play crucial roles in the development of major depressive disorder. Preconditioning with lipopolysaccharide (LPS) provides protection against severe neuroinflammation. However, administering high doses of LPS to mice triggers depressive symptoms. Therefore, the optimal dose of LPS preconditioning needs to be determined by further experiments. LPS preconditioning is an effective agent in anti-inflammation and neuroprotection, but the mechanism by which LPS preconditioning acts in depression remain unclear. This study finds that the anti-inflammation mechanism of low-dose LPS preconditioning is mainly dependent on G-protein-coupled receptor 84 (GPR84). We use low-dose LPS for preconditioning and re-challenged mice or BV2 microglia with high-dose LPS. In addition, RNA-seq is used to explore underlying changes with LPS preconditioning. Low-dose LPS preconditioning reduces the expression of pro-inflammatory mediators and inhibits microglial activation, as well as suppresses the depressive-like behavior when the mice are re-challenged with high-dose LPS. Further investigation reveals that the tolerance-like response in microglia is dependent on the GPR84. Here, we show that low-dose LPS preconditioning can exert anti-inflammation effects and alleviates inflammation-induced depressive-like behavior in mice. As a potential therapeutic target for depression, LPS preconditioning needs to be given further attention regarding its effectiveness and safety.

Subanesthetic dose of S-ketamine improved cognitive dysfunction via the inhibition of hippocampal astrocytosis in a mouse model of post-stroke chronic stress

Post-stroke chronic stress (PSCS) is generally associated with the poorer recovery and more pronounced cognitive dysfunction. Recent evidence has implied that S-ketamine can reduce suicidal ideation in treatment-resistant depression. In this current study, we aimed to investigate whether the administration of S-ketamine ameliorated cognitive deficits under PSCS conditions, which was established by a model combining middle cerebral artery occlusion (MCAO) and chronic restraint stress. Our data suggested that mice exposed to PSCS exhibited depression-like behavior and cognitive impairment, which coincided with astrocytosis as indicated by increased GFAP-positive cells and impairment of long-time potentiation (LTP) in the hippocampal CA1. Subanesthetic doses (10 mg/kg) of S-ketamine have significantly mitigated depression-like behaviors, cognitive deficits and LTP impairment, reduced astrocytosis, excessive GABA, and inflammatory factors, including NLRP3 and IL-18 in astrocytes in the CA1. Besides, neuroprotective effects induced by S-ketamine administration were found in vitro but could be partially reversed by an agonist of the NLRP3 nigericin. Our current data also suggests that the subanesthetic doses of S-ketamine improved cognitive dysfunction via the inhibition of hippocampal astrocytosis in a mouse model of PSCS.

The role of indoleamine 2,3-dioxygenase 1 in early-onset post-stroke depression

Background

The immune-inflammatory response has been widely considered to be involved in the pathogenesis of post-stroke depression (PSD), but there is ambiguity about the mechanism underlying such association.

Methods

According to Diagnostic and Statistical Manual of Mental Disorders (5th edition), depressive symptoms were assessed at 2 weeks after stroke onset. 15 single nucleotide polymorphisms (SNPs) in genes of indoleamine 2,3-dioxygenase (IDO, including IDO1 and IDO2) and its inducers (including pro-inflammatory cytokines interferon [IFN]-γ, tumor necrosis factor [TNF]-α, interleukin [IL]-1β, IL-2 and IL-6) were genotyped using SNPscan™ technology, and serum IDO1 levels were detected by double-antibody sandwich enzyme-linked immune-sorbent assay.

Results

Fifty-nine patients (31.72%) were diagnosed with depression at 2 weeks after stroke onset (early-onset PSD). The IDO1 rs9657182 T/T genotype was independently associated with early-onset PSD (adjusted odds ratio [OR] = 3.008, 95% confidence interval [CI] 1.157-7.822, p = 0.024) and the frequency of rs9657182 T allele was significantly higher in patients with PSD than that in patients with non-PSD (χ2 = 4.355, p = 0.037), but these results did not reach the Bonferroni significance threshold (p > 0.003). Serum IDO1 levels were also independently linked to early-onset PSD (adjusted OR = 1.071, 95% CI 1.002-1.145, p = 0.044) and patients with PSD had higher serum IDO1 levels than patients with non-PSD in the presence of the rs9657182 T allele but not homozygous C allele (t = -2.046, p = 0.043). Stroke patients with the TNF-α rs361525 G/G genotype had higher serum IDO1 levels compared to those with the G/A genotype (Z = -2.451, p = 0.014).

Conclusions

Our findings provided evidence that IDO1 gene polymorphisms and protein levels were involved in the development of early-onset PSD and TNF-α polymorphism was associated with IDO1 levels, supporting that IDO1 which underlie strongly regulation by cytokines may be a specific pathway for the involvement of immune-inflammatory mechanism in the pathophysiology of PSD.

Medicinal Herbs and Their Derived Ingredients Protect against Cognitive Decline in In Vivo Models of Alzheimer’s Disease

Alzheimer’s disease (AD) has pathological hallmarks including amyloid beta (Aβ) plaque formation. Currently approved single-target drugs cannot effectively ameliorate AD. Medicinal herbs and their derived ingredients (MHDIs) have multitarget and multichannel properties, engendering exceptional AD treatment outcomes. This review delineates how in in vivo models MHDIs suppress Aβ deposition by downregulating β- and γ-secretase activities; inhibit oxidative stress by enhancing the antioxidant activities and reducing lipid peroxidation; prevent tau hyperphosphorylation by upregulating protein phosphatase 2A expression and downregulating glycogen synthase kinase-3β expression; reduce inflammatory mediators partly by upregulating brain-derived neurotrophic factor/extracellular signal-regulated protein kinase 1/2-mediated signaling and downregulating p38 mitogen-activated protein kinase (p38 MAPK)/c-Jun N-terminal kinase (JNK)-mediated signaling; attenuate synaptic dysfunction by increasing presynaptic protein, postsynaptic protein, and acetylcholine levels and preventing acetylcholinesterase activity; and protect against neuronal apoptosis mainly by upregulating Akt/cyclic AMP response element-binding protein/B-cell lymphoma 2 (Bcl-2)-mediated anti-apoptotic signaling and downregulating p38 MAPK/JNK/Bcl-2-associated x protein (Bax)/caspase-3-, Bax/apoptosis-inducing factor-, C/EBP homologous protein/glucose-regulated protein 78-, and autophagy-mediated apoptotic signaling. Therefore, MHDIs listed in this review protect against Aβ-induced cognitive decline by inhibiting Aβ accumulation, oxidative stress, tau hyperphosphorylation, inflammation, synaptic damage, and neuronal apoptosis in the cortex and hippocampus during the early and late AD phases.

Involvement of the gut-brain axis in vascular depression via tryptophan metabolism: A benefit of short chain fatty acids

Cerebral hemodynamic dysfunction and hypoperfusion have been found to underlie vascular depression, but whether the gut-brain axis is involved remains unknown. In this study, a rat model of bilateral common carotid artery occlusion (BCCAO) was adopted to mimic chronic cerebral hypoperfusion. A reduced sucrose preference ratio, increased immobility time in the tail suspension test and forced swim test, and compromised gut homeostasis were found. A promoted conversion of tryptophan (Trp) into kynurenine (Kyn) instead of 5-hydroxytryptamine (5-HT) was observed in the hippocampus and gut of BCCAO rats. Meanwhile, 16S ribosomal RNA gene sequencing suggested a compromised profile of the gut SCFA-producing microbiome, with a decreased serum level of SCFAs revealed by targeted metabolomics analysis. With SCFA supplementation, BCCAO rats exhibited ameliorated depressive-like behaviors and improved gut dysbiosis, compared with the salt-matched BCCAO group. Enzyme-linked immunosorbent assays and quantitative RT-PCR suggested that SCFA supplementation suppressed the conversion of Trp to Kyn and rescued the reduction in 5-HT levels in the hippocampus and gut. In addition to inhibiting the upregulation of inflammatory cytokines, SCFA supplementation ameliorated the activated oxidative stress and reduced the number of microglia and the expression of its proinflammatory markers in the hippocampus post BCCAO. In conclusion, our data suggested the participation of the gut-brain axis in vascular depression, shedding light on the neuroprotective potential of treatment with gut-derived SCFAs.

Microglia Involves in the Immune Inflammatory Response of Poststroke Depression: A Review of Evidence

Poststroke depression (PSD) does not exist before and occurs after the stroke. PSD can appear shortly after the onset of stroke or be observed in the weeks and months after the acute or subacute phase of stroke. The pathogenesis of PSD is unclear, resulting in poor treatment effects. With research advancement, immunoactive cells in the central nervous system, particularly microglia, play a role in the occurrence and development of PSD. Microglia affects the homeostasis of the central nervous system through various factors, leading to the occurrence of depression. The research progress of microglia in PSD has been summarized to review the evidence regarding the pathogenesis and treatment target of PSD in the future.

CysLT2R Antagonist HAMI 3379 Ameliorates Post-Stroke Depression through NLRP3 Inflammasome/Pyroptosis Pathway in Gerbils

Post-stroke depression (PSD) is a kind of prevalent emotional disorder following stroke that usually results in slow functional recovery and even increased mortality. We had reported that the cysteinyl leukotriene receptor 2 (CysLT₂R) antagonist HAMI3379 (HM3379) contributes to the improvement of neurological injury. The present study was designed to investigate the role of HM3379 in PSD-induced chronic neuroinflammation and related mechanisms in gerbils. The gerbils were subjected to transient global cerebral ischemia (tGCI) and spatial restraint stress to induce the PSD model. They were randomized to receive the vehicle or HM3379 (0.1 mg/kg, i.p.) for a consecutive 14 days. In the PSD-treated gerbils, HM3379 had noteworthy efficacy in improving the modified neurological severity score (mNSS) and depression-like behaviors, including the sucrose preference test and the forced swim test. HM3379 administration significantly mitigated neuron loss, lessened TUNEL-positive neurons, and reduced the activation of microglia in the cerebral cortex. Importantly, HM3379 downregulated protein expressions of the NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome and pyroptosis including NLRP3, cleaved caspase-1, interleukin-1β (IL-1β), IL-18, cleaved gasdermin-N domain (GSDMD-N), and apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC). Mechanistically, HM3379 could repress pyroptosis via inhibiting NLRP3 inflammasome activation under oxygen-glucose deprivation (OGD) stimulation. Knockdown of CysLT₂R by short hairpin RNA (shRNA) or overexpression of CysLT₂R by lentivirus (LV)-CysLT₂R could abolish or restore the anti-depression effect of HM3379. Our results demonstrated that the selective CysLT₂R antagonist HM3379 has beneficial effects on PSD, partially by suppressing the NLRP3 inflammasome/pyroptosis pathway.

Microglia in depression: an overview of microglia in the pathogenesis and treatment of depression

Major depressive disorder is a highly debilitating psychiatric disorder involving the dysfunction of different cell types in the brain. Microglia are the predominant resident immune cells in the brain and exhibit a critical role in depression. Recent studies have suggested that depression can be regarded as a microglial disease. Microglia regulate inflammation, synaptic plasticity, and the formation of neural networks, all of which affect depression. In this review, we highlighted the role of microglia in the pathology of depression. First, we described microglial activation in animal models and clinically depressed patients. Second, we emphasized the possible mechanisms by which microglia recognize depression-associated stress and regulate conditions. Third, we described how antidepressants (clinical medicines and natural products) affect microglial activation. Thus, this review aimed to objectively analyze the role of microglia in depression and focus on potential antidepressants. These data suggested that regulation of microglial actions might be a novel therapeutic strategy to counteract the adverse effects of devastating mental disorders.

The effects of okadaic acid-treated SH-SY5Y cells on microglia activation and phagocytosis

The activation of microglia is found to be associated with neurodegenerative disorders including Alzheimer's disease (AD). Several studies have shown that okadaic acid (OA) induced deposition of tau hyperphosphorylation, and subsequent neuronal degeneration, loss of synapses, and memory impairment, all of which resemble the pathology of AD. Although OA is a powerful tool available for mechanisms of the neurotoxicity associated with AD, the exact mechanism underlying the activation of microglial cells remains unrevealed. The aim of this study was to determine the effect of both OA and OA-treated neuroblastoma SH-SY5Y cells on microglial HAPI cell viability, activation, and phagocytosis. The results showed that both OA and OA-treated neurons did not induce any detectable cytotoxicity of microglial cells. Furthermore, incubation with OA-treated SH-SY5Y cells could increase the expression of ionized calcium-binding adapter molecule 1 (Iba1) on microglial HAPI cells. This result indicated that OA may induce microglial activation through the toxicity of neurons. Moreover, we also demonstrated that OA-treated SH-SY5Y cells were engulfed by CD11b/c-labeled microglial HAPI cells, which were abolished after treatment with 10 mM O-phospho- l-serine ( L-SOP) for 30 min before co-culture with OA-treated SH-SY5Y cells, indicating cells experiencing phagocytic activity. We also confirmed that OA treatment for 24 h significantly increased tau hyperphosphorylation at S396 in SH-SY5Y cells. In conclusion, our findings indicate that OA is a potential toxic inducer underlying the role of microglia in AD pathogenesis.

Tryptophan plays an important role in yeast's tolerance to isobutanol

BACKGROUND

Isobutanol is considered a potential biofuel, thanks to its high-energy content and octane value, limited water solubility, and compatibility with gasoline. As its biosynthesis pathway is known, a microorganism, such as Saccharomyces cerevisiae, that inherently produces isobutanol, can serve as a good engineering host. Isobutanol's toxicity, however, is a major obstacle for bioproduction. This study is to understand how yeast tolerates isobutanol.

RESULTS

A S. cerevisiae gene-deletion library with 5006 mutants was used to screen genes related to isobutanol tolerance. Image recognition was efficiently used for high-throughput screening via colony size on solid media. In enrichment analysis of the 161 isobutanol-sensitive clones identified, more genes than expected were mapped to tryptophan biosynthesis, ubiquitination, and the pentose phosphate pathway (PPP). Interestingly, adding exogenous tryptophan enabled both tryptophan biosynthesis and PPP mutant strains to overcome the stress. In transcriptomic analysis, cluster analysis of differentially expressed genes revealed the relationship between tryptophan and isobutanol stress through some specific cellular functions, such as biosynthesis and transportation of amino acids, PPP, tryptophan metabolism, nicotinate/nicotinamide metabolism (e.g., nicotinamide adenine dinucleotide biosynthesis), and fatty acid metabolism.

CONCLUSIONS

The importance of tryptophan in yeast's tolerance to isobutanol was confirmed by the recovery of isobutanol tolerance in defective strains by adding exogenous tryptophan to the growth medium. Transcriptomic analysis showed that amino acid biosynthesis- and transportation-related genes in a tryptophan biosynthesis-defective host were up-regulated under conditions similar to nitrogen starvation. This may explain why ubiquitination was required for the protein turnover. PPP metabolites may serve as precursors and cofactors in tryptophan biosynthesis to enhance isobutanol tolerance. Furthermore, the tolerance mechanism may also be linked to tryptophan downstream metabolism, including the kynurenine pathway and nicotinamide adenine dinucleotide biosynthesis. Both pathways are responsible for cellular redox balance and anti-oxidative ability. Our study highlights the central role of tryptophan in yeast's isobutanol tolerance and offers new clues for engineering a yeast host with strong isobutanol tolerance.

Tryptophan: From Diet to Cardiovascular Diseases

Cardiovascular disease (CVD) is one of the major causes of mortality worldwide. Inflammation is the underlying common mechanism involved in CVD. It has been recently related to amino acid metabolism, which acts as a critical regulator of innate and adaptive immune responses. Among different metabolites that have emerged as important regulators of immune and inflammatory responses, tryptophan (Trp) metabolites have been shown to play a pivotal role in CVD. Here, we provide an overview of the fundamental aspects of Trp metabolism and the interplay between the dysregulation of the main actors involved in Trp metabolism such as indoleamine 2, 3-dioxygenase 1 (IDO) and CVD, including atherosclerosis and myocardial infarction. IDO has a prominent and complex role. Its activity, impacting on several biological pathways, complicates our understanding of its function, particularly in CVD, where it is still under debate. The discrepancy of the observed IDO effects could be potentially explained by its specific cell and tissue contribution, encouraging further investigations regarding the role of this enzyme. Thus, improving our understanding of the function of Trp as well as its derived metabolites will help to move one step closer towards tailored therapies aiming to treat CVD.

Effect of repetitive transcranial magnetic stimulation on the kynurenine pathway in stroke patients

OBJECTIVE

Repetitive transcranial magnetic stimulation (rTMS) improves depressive symptoms and motor function in stroke patients. While metabolic derangement of the kynurenine pathway has been reported in stroke patients, the effect of rTMS on this pathway remains unknown. This study was performed to investigate the effect of rTMS on serum levels of kynurenine and tryptophan in stroke patients.

METHODS

Sixty-two stroke patients received rTMS in addition to intensive rehabilitation and 33 stroke patients received intensive rehabilitation alone for 14 days. The rTMS involved low-frequency stimulation (at 1 Hz) of the primary motor cortex on the unaffected side of the cerebrum. The depressive state of the patients was evaluated with the Beck Depression Inventory (BDI) before and after treatment. Motor function of the patients was evaluated with Fugl-Meyer Assessment (FMA). Serum levels of kynurenine and tryptophan levels were also measured before and after treatment.

RESULTS

The serum tryptophan level decreased in the group receiving rTMS to the right brain and increased in the group receiving rTMS to the left brain. The serum kynurenine/tryptophan ratio was elevated in the group receiving rTMS to the right brain. The BDI indicated improvement of depressive symptoms in the rehabilitation alone group and the group receiving rTMS to the right brain plus rehabilitation. The FMA improved in all groups.

CONCLUSIONS

The effect of low-frequency rTMS on the kynurenine pathway may differ depending on whether it is applied to the right or left cerebral hemisphere.

Changes in Gene Expression and Neuroinflammation in the Hippocampus after Focal Brain Ischemia: Involvement in the Long-Term Cognitive and Mental Disorders

Ischemic brain injuries are accompanied by the long-term changes in gene expression in the hippocampus, the limbic system structure, involved in the regulation of key aspects of the higher nervous activity, such as cognitive functions and emotions. The altered expression of genes and proteins encoded by them may be related to the development of post-ischemic psycho-emotional and cognitive disturbances. Activation of neuroinflammation following stroke in the hippocampus has been suggested to play an essential role in induction of long-lasting consequences. Identification of changes in the gene expression patterns after ischemia and investigation of the dynamics of these changes in the hippocampus are the necessary first steps toward understanding molecular pathways responsible for the development of post-stroke cognitive impairments and mental pathologies.

Infections at the nexus of metabolic-associated fatty liver disease

Metabolic-associated fatty liver disease (MAFLD) is a chronic liver disease that affects about a quarter of the world population. MAFLD encompasses different disease stadia ranging from isolated liver steatosis to non-alcoholic steatohepatitis (NASH), fibrosis, cirrhosis and hepatocellular carcinoma. Although MAFLD is considered as the hepatic manifestation of the metabolic syndrome, multiple concomitant disease-potentiating factors can accelerate disease progression. Among these risk factors are diet, lifestyle, genetic traits, intake of steatogenic drugs, male gender and particular infections. Although infections often outweigh the development of fatty liver disease, pre-existing MAFLD could be triggered to progress towards more severe disease stadia. These combined disease cases might be underreported because of the high prevalence of both MAFLD and infectious diseases that can promote or exacerbate fatty liver disease development. In this review, we portray the molecular and cellular mechanisms by which the most relevant viral, bacterial and parasitic infections influence the progression of fatty liver disease and steatohepatitis. We focus in particular on how infectious diseases, including coronavirus disease-19, hepatitis C, acquired immunodeficiency syndrome, peptic ulcer and periodontitis, exacerbate MAFLD. We specifically underscore the synergistic effects of these infections with other MAFLD-promoting factors.

Neuroinflammation and the Kynurenine Pathway in CNS Disease: Molecular Mechanisms and Therapeutic Implications

Diseases of the central nervous system (CNS) remain a significant health, social and economic problem around the globe. The development of therapeutic strategies for CNS conditions has suffered due to a poor understanding of the underlying pathologies that manifest them. Understanding common etiological origins at the cellular and molecular level is essential to enhance the development of efficacious and targeted treatment options. Over the years, neuroinflammation has been posited as a common link between multiple neurological, neurodegenerative and neuropsychiatric disorders. Processes that precipitate neuroinflammatory conditions including genetics, infections, physical injury and psychosocial factors, like stress and trauma, closely link dysregulation in kynurenine pathway (KP) of tryptophan metabolism as a possible pathophysiological factor that 'fuel the fire' in CNS diseases. In this study, we aim to review emerging evidence that provide mechanistic insights between different CNS disorders, neuroinflammation and the KP. We provide a thorough overview of the different branches of the KP pertinent to CNS disease pathology that have therapeutic implications for the development of selected and efficacious treatment strategies.

Ginsenoside Rg1 improves cognitive capability and affects the microbiota of large intestine of tree shrew model for Alzheimer's disease

Ginsenoside Rg1 (Rg1) is traditional Chinese medicine with neuroprotective activity. Previous studies have demonstrated that Rg1 improves Alzheimer's disease (AD) and alters gut microbiology, but its mechanism remains to be elucidated, and thus far, its use in the treatment of AD has not been satisfactory. The present study investigated the improvement effects of Rg1 and its association with the microbiota of the large intestine. Following treatment with Rg1 in AD tree shrews, the treatment group demonstrated significantly shorter escape latency and crossed a platform more frequently in a water maze test. Western blotting demonstrated that Rg1 inhibited the expression of β-secretase 1, while increasing microtubule-associated protein 2 and Fox-3 in the hippocampus. Immunohistochemical analysis revealed that Rg1 decreased the expression of amyloid β, tau phosphorylated at serine 404 and pro-apoptotic factor Bax, while increasing the expression of Bcl-2 in the hippocampus and cortex. High throughput sequencing of 16S rRNA demonstrated that Rg1 altered the microbiota abundance of the large intestine. In conclusion, Rg1 affected the expression of apoptosis proteins, possessed a neuroprotective effect and may have a close association with the microbiota of large intestine by significantly reducing the abundance of Bacteroidetes and increasing the energy requirement of tree shrews.

Neuroendocrine, neuroinflammatory and pathological outcomes of chronic stress: A story of microglial remodeling

Microglia, the resident macrophage cells of the central nervous system (CNS), are involved in a myriad of processes required to maintain CNS homeostasis. These cells are dynamic and can adapt their phenotype and functions to the physiological needs of the organism. Microglia rapidly respond to changes occurring in their microenvironment, such as the ones taking place during stress. While stress can be beneficial for the organism to adapt to a situation, it can become highly detrimental when it turns chronic. Microglial response to prolonged stress may lead to an alteration of their beneficial physiological functions, becoming either maladaptive or pro-inflammatory. In this review, we aim to summarize the effects of chronic stress exerted on microglia through the neuroendocrine system and inflammation at adulthood. We also discuss how these effects of chronic stress could contribute to microglial involvement in neuropsychiatric and sleep disorders, as well as neurodegenerative diseases.

Nicotinamide Improves Cognitive Function in Mice With Chronic Cerebral Hypoperfusion

Normal brain function requires steady blood supply to maintain stable energy state. When blood supply to the brain becomes suboptimal for a long period of time, chronic cerebral hypoperfusion (CCH) and a variety of brain changes may occur. CCH causes white matter injury and cognitive impairment. The present study investigated the effect of nicotinamide (NAM) on CCH-induced cognitive impairment and white matter damage in mice. Male C57Bl/6J mice aged 10–12 weeks (mean age = 11 ± 1 weeks) and weighing 24 - 29 g (mean weight = 26.5 ± 2.5 g) were randomly assigned to three groups (eight mice/group): sham group, CCH group and NAM group. Chronic cerebral hypoperfusion (CCH) was induced using standard methods. The treatment group mice received intraperitoneal injection of NAM at a dose of 200 mg/kg body weight (bwt) daily for 30 days. Learning, memory, anxiety, and depression-like behaviors were measured using Morris water maze test (MWMT), open field test (OFT), sucrose preference test (SPT), and forced swim test (FST), respectively. White matter damage and remodeling were determined via histological/ immunohistochemical analyses, and western blotting, respectively. The results showed that the time spent in target quadrant, number of crossings and escape latency were significantly lower in CCH group than in sham group, but they were significantly increased by NAM (p < 0.05). Mice in NAM group moved significantly faster and covered longer distances, when compared with those in CCH group (p < 0.05). The percentage of time spent in open arms and the number of entries to the open arms were significantly lower in CCH group than in NAM group (p < 0.05). Moreover, anhedonia and histologic scores (index of myelin injury) were significantly higher in CCH group than in sham group, but they were significantly reduced by NAM (p < 0.05). The results of immunohistochemical staining and Western blotting showed that the protein expressions of 2′, 3′-cyclic-nucleotide 3′-phosphodiesterase (CNPase) and synaptophysin were significantly downregulated in CCH group, relative to sham group, but they were significantly upregulated by NAM (p < 0.05). These results indicate that NAM improves cognitive function in mice with CCH.

Electroacupuncture Ameliorates Depressive-Like Behaviors in Poststroke Rats via Activating the tPA/BDNF/TrkB Pathway

BACKGROUND

Electroacupuncture (EA) is a form of physical therapy that has been widely used in clinical practice in China. Post-stroke depression (PSD) is the most common neuropsychiatric complication after stroke. EA has been shown to have beneficial effects on PSD patients. However, the potential mechanism underlying the protective effects of EA on PSD remains unclear. Here, we investigated whether tissue plasminogen activator (tPA)/brain-derived neurotrophic factor (BDNF)/tyrosine kinase receptor B (TrkB) signaling pathway participates in the therapeutic effects of EA in a rat PSD model.

METHODS

Experimental PSD was induced by combining middle cerebral artery occlusion (MCAO) with chronic unpredictable mild stimulation (CUMS) in adult male rats. Bodyweight gain, neurological score, sucrose preference, and open field test were determined at 0, 7, 14, and 35 days after completing MCAO. The protein expressions of tPA, precursor BDNF (proBDNF), mature BDNF (mBDNF), and TrkB were measured by immunofluorescence and Western blot analysis. The tPA inhibitor plasminogen inhibitor-1 (PAI-1) was used to explore whether tPA plays a crucial role in the protective effects of EA on PSD.

RESULTS

Compared with the sham rats, the PSD rats showed decreased bodyweight, deteriorated neurological score, and significant depressive-like behaviors. EA remarkably reversed bodyweight loss, neurological deficit, and depressive-like behaviors in PSD rats. Immunofluorescence staining and Western blot analysis showed that PSD-induced decreased expression of tPA, mBDNF, and TrkB were prevented by EA. Furthermore, we found that the effects of EA against PSD-induced depressive-like behaviors were abolished by PAI-1, the specific inhibitor of tPA.

CONCLUSION

Our results suggest that the improvement in depressive-like behaviors induced by EA is likely achieved via activation of the tPA/BDNF/TrkB pathway.

Oxidative Stress at the Crossroads of Aging, Stroke and Depression

Epidemiologic studies have shown that in the aging society, a person dies from stroke every 3 minutes and 42 seconds, and vast numbers of people experience depression around the globe. The high prevalence and disability rates of stroke and depression introduce enormous challenges to public health. Accumulating evidence reveals that stroke is tightly associated with depression, and both diseases are linked to oxidative stress (OS). This review summarizes the mechanisms of OS and OS-mediated pathological processes, such as inflammation, apoptosis, and the microbial-gut-brain axis in stroke and depression. Pathological changes can lead to neuronal cell death, neurological deficits, and brain injury through DNA damage and the oxidation of lipids and proteins, which exacerbate the development of these two disorders. Additionally, aging accelerates the progression of stroke and depression by overactive OS and reduced antioxidant defenses. This review also discusses the efficacy and safety of several antioxidants and antidepressants in stroke and depression. Herein, we propose a crosstalk between OS, aging, stroke, and depression, and provide potential therapeutic strategies for the treatment of stroke and depression.

The Effect of IDO on Neural Progenitor Cell Survival Under Oxygen Glucose Deprivation

Objective: Indoleamine 2,3-dioxygenase (IDO) activity plays an important role in many neurological disorders in the central nervous system, which may be associated with immunomodulation or anti-inflammatory activity. However, the action of IDO in the ischemic condition is still poorly understood. The purpose of the present study is to explore the expression and action of IDO in stem cell culture under oxygen and glucose deprivation.

Methods: Neural progenitor cells were obtained from the human embryonic stem cell line BG01. These cells underwent oxygen and glucose deprivation. We examined the IDO expression at 3 and 8 h of oxygen and glucose deprivation and then examined neuronal progenitor cell viability in the normal and oxygen and glucose deprivation condition using the [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. In addition, we studied the effect of IDO inhibition and the expression of TNF-α, IGF-1, VEGF, IL-6, FGFβ, TGFβ, EGF, and Leptin to explore the mechanism of IDO under the oxygen and glucose deprivation.

Results: IDO expression in neural progenitor cells increased under oxygen and glucose deprivation, which is closely associated with cell death (p < 0.05). Inhibiting IDO did not affect cell survival in normal neural progenitor cells. However, inhibiting IDO could attenuate cell viability under oxygen and glucose deprivation (p < 0.05). Further study demonstrated that IDO expression was closely associated to the growth factor’s leptin expression.

Conclusions: Our results demonstrated that an increase of IDO under oxygen and glucose deprivation was associated with cell death, suggesting that inhibiting IDO could be a target for neuroprotection.

Electroacupuncture on Trigeminal Nerve-Innervated Acupoints Ameliorates Poststroke Cognitive Impairment in Rats with Middle Cerebral Artery Occlusion: Involvement of Neuroprotection and Synaptic Plasticity

Poststroke cognitive impairment (PSCI) is a severe sequela of stroke. There are no effective therapeutic options for it. In this study, we evaluated whether electroacupuncture (EA) on the trigeminal nerve-innervated acupoints could alleviate PSCI and identified the mechanisms in an animal model. The male Sprague-Dawley rat middle cerebral artery occlusion (MCAO) model was used in our study. EA was conducted on the two scalp acupoints, EX-HN3 (Yintang) and GV20 (Baihui), innervated by the trigeminal nerve, for 14 sessions, daily. Morris water maze and novel object recognition were used to evaluate the animal's cognitive performance. Neuroprotection and synaptic plasticity biomarkers were analyzed in brain tissues. Ischemia-reperfusion (I/R) injury significantly impaired spatial and cognition memory, while EA obviously reversed cognitive deterioration to the control level in the two cognitive paradigms. Moreover, EA reversed the I/R injury-induced decrease of brain-derived neurotrophic factor, tyrosine kinase B, N-methyl-D-aspartic acid receptor 1, α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor, γ-aminobutyric acid type A receptors, Ca²⁺/calmodulin-dependent protein kinase II, neuronal nuclei, and postsynaptic density protein 95 expression in the prefrontal cortex and hippocampus. These results suggest that EA on the trigeminal nerve-innervated acupoints is an effective therapy for PSCI, in association with mediating neuroprotection and synaptic plasticity in related brain regions in the MCAO rat model.

Urinary kynurenine as a biomarker for Parkinson's disease

OBJECTIVE

To examine whether urine kynurenine (KYN) levels were associated with early-stage Parkinson's disease (PD), as well as the value of urine KYN as a potential biomarker in early-stage PD.

METHOD

Eighty-two participants including 41 PD patients and 41 healthy controls were enrolled into this study. Urine KYN levels were measured with a KYN enzyme-linked immunoassay kit. In order to explore the correlation between some clinical parameters and urine KYN, the clinical parameters for these participants were recorded. Diagnostic value and clinical relevance of urine KYN were assessed by using receiver operator characteristic (ROC) curve and correlation analysis.

RESULTS

Urine KYN levels were significantly higher in the PD group than in the healthy group (891.95 ± 276.65 pg/ml vs. 640.11 ± 122.37 pg/ml, p = 0.000). The correlations between urine KYN levels and clinical parameters are as follows: Hoehn-Yahr stage (r = 0.676, p = 0.000), disease duration (r = 0.772, p = 0.000), Mini-Mental State Examination scores (r = -0.434, p = 0.005). There was no statistically significant correlation between urine KYN with age, low-density cholesterol (LDL), triglycerides (TG), cholesterol (TC), homocysteine (HCY), uric acid (UA), and glomerular filtration rate (GFR). The ROC analysis showed that urine KYN optimal cutoff value of 751.88 pg/ml had a sensitivity of 65.9% and a specificity of 90.2% for distinguishing between PD and controls, with an area under the curve (AUC) of 0.776.

CONCLUSION

Urine KYN were significantly associated with PD severity and mild cognitive impairment. Urine KYN may be a new biomarker for early-stage PD.

Glucocorticoid-Driven NLRP3 Inflammasome Activation in Hippocampal Microglia Mediates Chronic Stress-Induced Depressive-Like Behaviors

Chronic stress is a key risk factor for depression, and microglia have been implicated in the pathogenesis of the disease. Recent studies show that the Nod-like receptor protein 3 (NLRP3) inflammasome is expressed in microglia and may play a crucial role in depression. However, the mechanism of NLRP3 inflammasome activation in hippocampal microglia and its role in depressive-like behaviors remain poorly understood. In this study, rats were subjected to 6 h of restraint stress per day for 21 days to produce a model of stress-induced depression. Behavioral tests and serum corticosterone were used to assess the success of the model. Furthermore, HAPI cells were pretreated with dexamethasone (5 × 10^-7 M) to assess stress-induced changes in microglial cells in culture. The microglial marker Iba-1, reactive oxygen species (ROS), nuclear factor kappa B (NF-κB) and key components of the NLRP3 inflammasome and its downstream inflammatory effectors (IL-1β and IL-18) were measured. Chronic stress induced depressive-like behavior, increased serum corticosterone levels and produced hippocampal structural changes. Chronic stress and dexamethasone both increased Iba-1 expression and ROS formation and also elevated levels of NF-κB, NLRP3, cleaved caspase-1, IL-1β and IL-18. After use of the NF-κB inhibitor BAY 117082 and knocked out NLRP3 in vitro decreased ROS formation and the expression of Iba-1, NF-κB and NLRP3 as well as levels of cleaved caspase-1, IL-1β and IL-18. These findings suggest that activation of the glucocorticoid receptor-NF-κB-NLRP3 pathway in hippocampal microglia mediates chronic stress-induced hippocampal neuroinflammation and depression-like behavior.