Fecal microbiota transplantation and short-chain fatty acids protected against cognitive dysfunction in a rat model of chronic cerebral hypoperfusion

Elucidating the specific mechanisms of the gut-brain axis: the short-chain fatty acids-microglia pathway

In recent years, the gut microbiota has been increasingly recognized for its influence on various central nervous system diseases mediated by microglia, yet the underlying mechanisms remain unclear. As key metabolites of the gut microbiota, short-chain fatty acids (SCFAs) have emerged as a focal point in understanding microglia-related interactions. In this review, we further refine the connection between the gut microbiota and microglia by introducing the concept of the "SCFAs-microglia" pathway. We summarize current knowledge on this pathway, recent discoveries regarding its role in neurological diseases, and potential pharmacological strategies targeting it. Finally, we outlined the current challenges and limitations in this field of research. We hope this review provides new insights into the role of the gut microbiota in neuroimmune regulation.

Extracellular vesicles from Lacticaseibacillus paracasei reduce neuroinflammation in hippocampus and restore some cognitive functions in hyperammonemic rats

Cirrhotic patients may show minimal hepatic encephalopathy (MHE) which impairs life quality and span. There is a need of new safe treatments for MHE. Hyperammonemia is a main contributor to MHE. Hyperammonemic rats reproduce the cognitive impairment present in patients with MHE, which is mediated by neuroinflammation and altered glutamatergic neurotransmission in hippocampus. Probiotics induce positive effects in MHE patients, which could be mediated by bacterial extracellular vesicles (EVs). The aims of this work were to evaluate in hyperammonemic rats: 1) if intravenous administration of EVs from L. paracasei improves memory and learning and 2) reduces neuroinflammation in hippocampus and 3) to study the mechanisms involved using an ex vivo approach. It is shown that intravenous injection of EVs from L. paracasei reverses glial activation in hippocampus and cognitive impairment in hyperammonemic rats. Ex vivo studies in hippocampal slices show that hyperammonemia increases TNFα and TNFR1 and S1PR2 membrane expression and activation, leading to increased IL-1β content and activation of IL-1 receptor and of Src. This increases CCL2 and BDNF and TrkB activation. This leads to increased membrane expression of the NR2B subunit of the NMDA receptor and of the GluA2 subunit of AMPA receptors and reduced membrane expression of the GluA1 subunit, leading to cognitive impairment. EVs from L. paracasei reduce neuroinflammation in hyperammonemic rats and restore the function of the TNFα-TNFR1-S1PR2-IL-1β-CCL2-BDNF-TrkB pathway, glutamatergic neurotransmission and cognitive function in rats with hyperammonemia and MHE. This suggests that these EVs could also improve cognitive function in cirrhotic patients with MHE.

The role of fecal microbiota transplantation on the NLRP3-Caspase 1 pathway and anxiety like behavioral in the ulcerative colitis model in rats

The purpose of this study was to investigate the function of the NLRP3-Caspase 1 signaling pathway in the colon during fecal microbiota transplantation (FMT) in colitis induced by acetic acid. Additionally, the study aimed to determine the impact of FMT on anxiety behaviors by analyzing the function of the NLRP3-Caspase 1 signaling pathway in the hippocampus. A total of twenty-four rats were selected randomly for the study and divided into two groups, a control group, and an acid acetic-induced colitis group. The acid acetic-induced colitis group further consisted of three subgroups: untreated acid acetic-induced colitis group, mesalazine 0.3 gr/kg group, and FMT group. After 6 days, the colon was evaluated for macroscopic and microscopic damage, and the signaling pathway NLRP3-Caspase1-related genes in the colon and hippocampus were analyzed. Additionally, anxiety-related behaviors of the rats were observed. FMT decreased colonic mRNA expression levels of NLRP3, NF-кB, and Caspase1 and pro-inflammatory cytokines (IL-1β and IL-18). Also, FMT reduced the expression of NLRP3, NF-κB, and Caspase1 protein levels as well as pro-inflammatory cytokines IL-1β and IL-18 in the hippocampus, resulting in a reduction of anxiety behaviors in the open field and elevated plus maze tests in the colitis model. FMT may improve acetic acid-induced colitis by regulating the NLRP3-Caspase1 signaling pathway in the colon. It also reduced colitis-induced anxiety behavior by regulating the expression of proteins related to the NLRP3-Caspase 1 pathway in the hippocampus.

The therapeutic effects and mechanisms of glucagon-like peptide-1 receptor agonists in neurocognitive disorders

Chronic cerebral hypoperfusion (CCH) represents a key pathogenic contributor to neurocognitive disorders. It can lead to multifaceted pathological alterations including neuroinflammation, neuronal apoptosis, blood-brain barrier disruption, synaptic plasticity deficits, and mitochondrial dysfunction. The glucagon-like peptide-1 receptor (GLP-1R), ubiquitously expressed across multiple organ systems, exerts neuroprotective effects by maintaining intracellular homeostasis and mitigating neuronal damage triggered by oxidative stress, inflammatory cascades, apoptotic signaling, and ischemic insults. Furthermore, GLP-1R activity is modulated by gut microbiota composition and short-chain fatty acid abundance, implicating the gut-brain axis in its regulatory influence on neurological function. This review systematically examines the pathophysiological mechanisms underlying CCH and highlights the therapeutic potential of GLP-1R activation. Specifically, GLP-1R-targeted interventions attenuate hypoperfusion-induced damage through pleiotropic pathways and gut-brain crosstalk, thereby offering novel perspectives for advancing both fundamental research and clinical management of neurocognitive disorders.

Short-chain fatty acids in Huntington's disease: Mechanisms of action and their therapeutic implications

Huntington's disease (HD) is a progressive neurodegenerative disorder characterized by motor dysfunction, cognitive decline, and emotional instability, primarily resulting from the abnormal accumulation of mutant huntingtin protein. Growing research highlights the role of intestinal microbiota and their metabolites, particularly short-chain fatty acids (SCFAs), in modulating HD progression. SCFAs, including acetate, propionate, and butyrate, are produced by gut bacteria through dietary fiber fermentation and are recognized for their neuroprotective properties. Evidence suggests that SCFAs regulate neuroinflammation, neuronal communication, and metabolic functions within the central nervous system (CNS). In HD, these compounds may support neuronal health, reduce oxidative stress, and enhance blood-brain barrier (BBB) integrity. Their mechanisms of action involve binding to G-protein-coupled receptors (GPCRs) and modulating gene expression through epigenetic pathways, underscoring their therapeutic potential. This analysis examines the significance of SCFAs in HD, emphasizing the gut-brain axis and the benefits of dietary interventions aimed at modifying gut microbiota composition and promoting SCFA production. Further research into these pathways may pave the way for novel HD management strategies and improved therapeutic outcomes.

The impact of gut microbiota on the occurrence, treatment, and prognosis of ischemic stroke

Ischemic stroke (IS) is a cerebrovascular disease that predominantly affects middle-aged and elderly populations, exhibiting high mortality and disability rates. At present, the incidence of IS is increasing annually, with a notable trend towards younger affected individuals. Recent discoveries concerning the "gut-brain axis" have established a connection between the gut and the brain. Numerous studies have revealed that intestinal microbes play a crucial role in the onset, progression, and outcomes of IS. They are involved in the entire pathophysiological process of IS through mechanisms such as chronic inflammation, neural regulation, and metabolic processes. Although numerous studies have explored the relationship between IS and intestinal microbiota, comprehensive analyses of specific microbiota is relatively scarce. Therefore, this paper provides an overview of the typical changes in gut microbiota following IS and investigates the role of specific microorganisms in this context. Additionally, it presents a comprehensive analysis of post-stroke microbiological therapy and the relationship between IS and diet. The aim is to identify potential microbial targets for therapeutic intervention, as well as to highlight the benefits of microbiological therapies and the significance of dietary management. Overall, this paper seeks to provide key strategies for the treatment and management of IS, advocating for healthy diets and health programs for individuals. Meanwhile, it may offer a new perspective on the future interdisciplinary development of neurology, microbiology and nutrition.

Short-chain fatty acids mediate gut microbiota-brain communication and protect the blood-brain barrier integrity

The human gut, with a complex community of microbes, is essential for maintaining overall health. This gut microbiota engages in two-way communication with the central nervous system, collectively known as the gut microbiota-brain axis. Alterations in gut microbiota have been associated with various neurological disorders, and disruptions to the blood-brain barrier (BBB) may be crucial, though the exact mechanisms remain unknown. In the current study, we investigated the impacts of short-chain fatty acids (SCFAs) on the integrity of the BBB, which was compromised by orally administered antibiotics in rhesus monkeys and C57BL/6n mice. Our results showed that SCFA supplementation notably enhanced BBB integrity in rhesus monkeys with gut dysbiosis. Similar outcomes were observed in mice with gut dysbiosis, accompanied by decreased cortical claudin-5 mRNA levels. In particular, propionate, but not acetate or butyrate, could reverse the antibiotic-induced BBB permeability increase in mice. Additionally, in vitro studies demonstrated that propionate boosted the expression of tight junction proteins in brain endothelial cells. These results suggest that the propionate can maintain BBB integrity through a free fatty acid receptor 2-dependent mechanism. This study offers new insights into the gut-brain axis and underscores potential therapeutic targets for interventions based on gut microbiota.

The role of short-chain fatty acid in metabolic syndrome and its complications: focusing on immunity and inflammation

Metabolic syndrome (Mets) is an important contributor to morbidity and mortality in cardiovascular, liver, neurological, and reproductive diseases. Short-chain fatty acid (SCFA), an organismal energy donor, has recently been demonstrated in an increasing number of studies to be an important molecule in ameliorating immuno-inflammation, an important causative factor of Mets, and to improve lipid distribution, blood glucose, and body weight levels in animal models of Mets. This study reviews recent research advances on SCFA in Mets from an immune-inflammatory perspective, including complications dominated by chronic inflammation, as well as the fact that these findings also contribute to the understanding of the specific mechanisms by which gut flora metabolites contribute to metabolic processes in humans. This review proposes an emerging role for SCFA in the inflammatory Mets, followed by the identification of major ambiguities to further understand the anti-inflammatory potential of this substance in Mets. In addition, this study proposes novel strategies to modulate SCFA for the treatment of Mets that may help to mitigate the prognosis of Mets and its complications.

The Role of Gut Microbiota-Derived Trimethylamine N-Oxide in the Pathogenesis and Treatment of Mild Cognitive Impairment

Mild cognitive impairment (MCI) represents a transitional stage between normal aging and dementia, often considered critical for dementia prevention. Despite its significance, no effective clinical treatment for MCI has yet been established. Emerging evidence has demonstrated a strong association between trimethylamine-N-oxide (TMAO), a prominent metabolite derived from the gut microbiota, and MCI, highlighting its potential as a biomarker and therapeutic target. TMAO has been implicated in increasing MCI risk through its influence on factors such as hypertension, cardiovascular disease, depression, diabetes, and stroke. Moreover, it contributes to MCI by promoting oxidative stress, disrupting the blood-brain barrier, impairing synaptic plasticity, inducing inflammation, causing mitochondrial metabolic disturbances, and facilitating abnormal protein aggregation. This review further explores therapeutic strategies targeting TMAO to mitigate MCI progression.

Extracellular vesicles from L. paracasei improve neuroinflammation, GABA neurotransmission and motor incoordination in hyperammonemic rats

Patients with liver cirrhosis may show minimal hepatic encephalopathy (MHE) with motor incoordination and cognitive impairment that reduce life quality and span. Motor incoordination is due to neuroinflammation and enhanced GABAergic neurotransmission in cerebellum. Recent reports support that probiotics, including L. casei, may improve cognitive function in different pathologies and MHE in cirrhotic patients. Extracellular vesicles (EV) are small cell-derived membrane vesicles that carry bioactive molecules released from cells, including bacteria. We hypothesized that EV from Lacticaseibacillus paracasei (LC-EV) could improve neuroinflammation, GABAergic neurotransmission and motor function in MHE. We show that LC-EV treatment reverses glial activation and neuroinflammation in cerebellum and restore motor coordination in hyperammonemic rats. Moreover, ex vivo treatment of cerebellar slices from hyperammonemic rats with LC-EV also reverses glial activation and neuroinflammation, and the enhancement of the TNFR1-S1PR2-BDNF-TrkB and TNFR1-TrkB-pAKT-NFκB-glutaminase-GAT3 pathways and of GABAergic neurotransmission. The results reported support that LC-EV may be used as a therapeutic tool to improve motor incoordination in patients with MHE.

Maternal Gut Microbiome-Mediated Epigenetic Modifications in Cognitive Development and Impairments: A New Frontier for Therapeutic Innovation

Cognitive impairment in various mental illnesses, particularly neuropsychiatric disorders, has adverse functional and clinical consequences. While genetic mutations and epigenetic dysregulations of several genes during embryonic and adult periods are linked to cognitive impairment in mental disorders, the composition and diversity of resident bacteria in the gastrointestinal tract-shaped by environmental factors-also influence the brain epigenome, affecting behavior and cognitive functions. Accordingly, many recent studies have provided evidence that human gut microbiota may offer a potential avenue for improving cognitive deficits. In this review, we provide an overview of the relationship between cognitive impairment, alterations in the gut microbiome, and epigenetic alterations during embryonic and adult periods. We examine how various factors beyond genetics-such as lifestyle, age, and maternal diet-impact the composition, diversity, and epigenetic functionality of the gut microbiome, consequently influencing cognitive performance. Additionally, we explore the potential of maternal gut microbiome signatures and epigenetic biomarkers for predicting cognitive impairment risk in older adults. This article also explores the potential roles of nutritional deficiencies in programming cognitive disorders during the perinatal period in offspring, as well as the promise of gut microbiome-targeted therapeutics with epigenetic effects to prevent or alleviate cognitive dysfunctions in infants, middle-aged adults, and older adults. Unsolved challenges of gut microbiome-targeted therapeutics in mitigating cognitive dysfunctions for translation into clinical practice are discussed, lastly.

Natural products: Harnessing the power of gut microbiota for neurological health

BACKGROUND

Neurological diseases are the primary cause of disability and death and impose substantial financial burdens. However, existing treatments only relieve symptoms and may cause many adverse effects. Natural products are a promising source of neurological therapeutic agents due to their excellent neuroprotective effect and safety. The gut microbiota has an essential impact on maintaining brain homeostasis via the gut-brain axis. Multiple investigations show that natural products offer neuroprotective effects by regulating gut microbiota-driven signaling networks.

OBJECTIVES

This review aims to provide a systematic review of how natural products promote neurological health by harnessing the power of gut microbiota.

METHODS

The pre-January 1, 2024 literature was gathered from several databases, including Scopus, PubMed, Google Scholar, and Web of Science, utilizing appropriate keywords. The gathered publications underwent a review process and were classified based on their study content, specifically focusing on the impact of natural products on gut microbiota and neurological health.

RESULTS

Here, we review how natural products promote neurological health by regulating the gut microbiota-brain axis. Specifically, we focus on the following areas. (1) Altering microorganism community structure, including increasing α-diversity and altering β-diversity. (2) Regulating the population of certain bacteria, including enriching beneficial microorganisms Akkermansia and Bifidobacterium, and inhibiting potentially hazardous microorganisms Bilophila, Klebsiella, and Helicobacter. (3) Regulating microbial neuroactive metabolites levels, including short-chain fatty acids, tryptophan and its derivatives, trimethylamine N-oxide, dopa/dopamine, γ-aminobutyric acid, and lipopolysaccharide. Furthermore, we review how natural products promote neurological health by regulating intestinal barrier homeostasis.

CONCLUSION

Natural products promote neurological health by harnessing the power of gut microbiota. This review will contribute to understanding how natural products promote neurological health by orchestrating the gut microbiota-brain axis.

Single-cell RNA Sequencing Identifies a Novel Subtype of Microglia with High Cd74 Expression that Facilitates White Matter Inflammation During Chronic Cerebral Hypoperfusion

Vascular dementia (VaD) causes progressive cognitive decline in the elderly population, but there is short of available therapeutic measures. Microglia-mediated neuroinflammation is vigorously involved in the pathogenesis of VaD, but the traditional classification of microglial M1/M2 phenotypes remains restrictive and controversial. This study aims to investigate whether microglia transform into novel subtypes in VaD. Chronic cerebral hypoperfusion (CCH) rat model was constructed to mimic VaD. Microglia were isolated via magnetic-activated cell sorting and analyzed by single-cell RNA sequencing (scRNA-seq) and bioinformatics. The findings inferred from scRNA-seq and bioinformatics were further validated through in vivo experiments. In this study, microglia were divided into eight clusters. The proportion of MG5 cluster was significantly increased in the white matter of the CCH group compared with the Sham group and was named chronic ischemia-associated microglia (CIAM). Immunity- and inflammation-related genes, including RT1-Db1, RT1-Da, RT1-Ba, Cd74, Spp1, C3, and Cd68, were markedly upregulated in CIAM. Enrichment analysis illustrated that CIAM possessed the function of evoking neuroinflammation. Further studies unveiled that Cd74 is associated with the most abundant GO terms involved in inflammation as well as cell proliferation and differentiation. In addition, microglia-specific Cd74 knockdown mediated by adeno-associated virus decreased the abundance of CIAM in the white matter, thereby mitigating inflammatory cytokine levels, alleviating white matter lesions, and improving cognitive impairment for CCH rats. These findings indicate that Cd74 is the core molecule of CIAM to trigger neuroinflammation and induce microglial differentiation to CIAM, suggesting that Cd74 may be a potential therapeutic target for VaD.

Lactiplantibacillus plantarum P9 for chronic diarrhea in young adults: a large double-blind, randomized, placebo-controlled trial

Current treatments for chronic diarrhea have limited efficacy and several side effects. Probiotics have the potential to alleviate symptoms of diarrhea. This randomized, double-blind, placebo-controlled trial evaluates the effects of administering the probiotic Lactiplantibacillus plantarum P9 (P9) strain in young adults with chronic diarrhea (Clinical Trial Registration Number: ChiCTR2000038410). The intervention period lasts for 28 days, followed by a 14-day post-intervention period. Participants are randomized into the P9 (n = 93) and placebo (n = 96) groups, with 170 individuals completing the double-blind intervention phase (n = 85 per group). The primary endpoint is the diarrhea symptom severity score. Both intention-to-treat (n = 189) and per-protocol (n = 170) analyses reveal a modest yet statistically significant reduction in diarrhea severity compared to the placebo group (20.0%, P = 0.050; 21.4%, P = 0.048, respectively). In conclusion, the results of this study support the use of probiotics in managing chronic diarrhea in young adults. However, the lack of blood parameter assessment and the short intervention period represent limitations of this study.

The interplay between mitochondria, the gut microbiome and metabolites and their therapeutic potential in primary mitochondrial disease

The various roles of the mitochondria and the microbiome in health and disease have been thoroughly investigated, though they are often examined independently and in the context of chronic disease. However, the mitochondria and microbiome are closely connected, namely, through their evolution, maternal inheritance patterns, overlapping role in many diseases and their importance in the maintenance of human health. The concept known as the "mitochondria-microbiome crosstalk" is the ongoing bidirectional crosstalk between these two entities and warrants further exploration and consideration, especially in the context of primary mitochondrial disease, where mitochondrial dysfunction can be detrimental for clinical manifestation of disease, and the role and composition of the microbiome is rarely investigated. A potential mechanism underlying this crosstalk is the role of metabolites from both the mitochondria and the microbiome. During digestion, gut microbes modulate compounds found in food, which can produce metabolites with various bioactive effects. Similarly, mitochondrial metabolites are produced from substrates that undergo biochemical processes during cellular respiration. This review aims to provide an overview of current literature examining the mitochondria-microbiome crosstalk, the role of commonly studied metabolites serve in signaling and mediating these biochemical pathways, and the impact diet has on both the mitochondria and the microbiome. As a final point, this review highlights the up-to-date implications of the mitochondria-microbiome crosstalk in mitochondrial disease and its potential as a therapeutic tool or target.

Gut Microbiota Mediate the Neuroprotective Effect of Oolong Tea Polyphenols in Cognitive Impairment Induced by Circadian Rhythm Disorder

Oolong tea polyphenols (OTP) have attracted wide attention due to their ability to reduce inflammatory response, regulate gut microbiota, and improve cognitive function. However, exactly how the gut microbiota modulates nervous system activity is still an open question. We previously expounded that supplementing with OTP alleviated neuroinflammation in circadian rhythm disorder (CRD) mice. Here, we showed that OTP can relieve microglia activation by reducing harmful microbial metabolites lipopolysaccharide (LPS) that alleviate CRD-induced cognitive decline. Mechanistically, OTP suppressed the inflammation response by regulating the gut microbiota composition, including upregulating the relative abundance of Muribaculaceae and Clostridia_UCG-014 and downregulating Desulfovibrio, promoting the production of short-chain fatty acids (SCFAs). Moreover, the use of OTP alleviated intestinal barrier damage and decreased the LPS transport to the serum. These results further inhibited the activation of microglia, thus alleviating cognitive impairment by inhibiting neuroinflammation, neuron damage, and neurotoxicity metabolite glutamate elevation. Meanwhile, OTP upregulated the expression of synaptic plasticity-related protein postsynaptic density protein 95 (PSD-95) and synaptophysin (SYN) by elevating the brain-derived neurotrophic factor (BDNF) level. Taken together, our findings suggest that the OTP has the potential to prevent CRD-induced cognition decline by modulating gut microbiota and microbial metabolites.

Interplay of human gastrointestinal microbiota metabolites: Short-chain fatty acids and their correlation with Parkinson's disease

Short-chain fatty acids (SCFAs) are, the metabolic byproducts of intestinal microbiota that, are generated through anaerobic fermentation of undigested dietary fibers. SCFAs play a pivotal role in numerous physiological functions within the human body, including maintaining intestinal mucosal health, modulating immune functions, and regulating energy metabolism. In recent years, extensive research evidence has indicated that SCFAs are significantly involved in the onset and progression of Parkinson disease (PD). However, the precise mechanisms remain elusive. This review comprehensively summarizes the progress in understanding how SCFAs impact PD pathogenesis and the underlying mechanisms. Primarily, we delve into the synthesis, metabolism, and signal transduction of SCFAs within the human body. Subsequently, an analysis of SCFA levels in patients with PD is presented. Furthermore, we expound upon the mechanisms through which SCFAs induce inflammatory responses, oxidative stress, abnormal aggregation of alpha-synuclein, and the intricacies of the gut-brain axis. Finally, we provide a critical analysis and explore the potential therapeutic role of SCFAs as promising targets for treating PD.

Exertional heat stroke-induced changes in gut microbiota cause cognitive impairment in mice

BACKGROUND

The incidence of exertional heat stroke (EHS) escalates during periods of elevated temperatures, potentially leading to persistent cognitive impairment postrecovery. Currently, effective prophylactic or therapeutic measures against EHS are nonexistent.

METHODS

The selection of days 14 and 23 postinduction for detailed examination was guided by TEM of neuronal cells and HE staining of intestinal villi and the hippocampal regions. Fecal specimens from the ileum and cecum at these designated times were analyzed for changes in gut microbiota and metabolic products. Bioinformatic analyses facilitated the identification of pivotal microbial species and metabolites. The influence of supplementing these identified microorganisms on behavioral outcomes and the expression of functional proteins within the hippocampus was subsequently assessed.

RESULTS

TEM analyses of neurons, coupled with HE staining of intestinal villi and the hippocampal region, indicated substantial recovery in intestinal morphology and neuronal injury on Day 14, indicating this time point for subsequent microbial and metabolomic analyses. Notably, a reduction in the Lactobacillaceae family, particularly Lactobacillus murinus, was observed. Functional annotation of 16S rDNA sequences suggested diminished lipid metabolism and glycan biosynthesis and metabolism in EHS models. Mice receiving this intervention (EHS + probiotics group) exhibited markedly reduced cognitive impairment and increased expression of BDNF/TrKB pathway molecules in the hippocampus during behavioral assessment on Day 28.

CONCLUSION

Probiotic supplementation, specifically with Lactobacillus spp., appears to mitigate EHS-induced cognitive impairment, potentially through the modulation of the BDNF/TrKB signaling pathway within the hippocampus, illustrating the therapeutic potential of targeting the gut-brain axis.

Relationship Between Short-chain Fatty Acids and Parkinson's Disease: A Review from Pathology to Clinic

Parkinson's disease (PD) is a complicated neurodegenerative disease, characterized by the accumulation of α-synuclein (α-syn) in Lewy bodies and neurites, and massive loss of midbrain dopamine neurons. Increasing evidence suggests that gut microbiota and microbial metabolites are involved in the development of PD. Among these, short-chain fatty acids (SCFAs), the most abundant microbial metabolites, have been proven to play a key role in brain-gut communication. In this review, we analyze the role of SCFAs in the pathology of PD from multiple dimensions and summarize the alterations of SCFAs in PD patients as well as their correlation with motor and non-motor symptoms. Future research should focus on further elucidating the role of SCFAs in neuroinflammation, as well as developing novel strategies employing SCFAs and their derivatives to treat PD.

[Modulating gut microbiota improves neurological function and depressive symptoms in rats with post-stroke depression]

OBJECTIVE

To evaluate the effect of modulating gut microbiota for improving brain injury in rats with post-stroke depression.

METHODS

Adult SD rats were randomized into normal control, middle cerebral artery occlusion (MCAO), post-stroke depression (PSD), PSD with fecal transplantation, PSD with antibiotics (rifaximin), PSD with probiotics (lactobacilli), and PSD with fluoxetine treatment groups (n=9). Neurological function scores of the rats were determined, and the changes in sugar water preference and immobility time in forced swimming test were observed; plasma levels of trimethylamine N-oxide (TMAO) and hydrogen sulfide (H2S) were detected with ELISA, Occludin, and the expressions of occludin, caudin-5 and IgG proteins Ⅰ the brain tissues were determined using Western blotting.

RESULTS

Compared with those in the control group, the rats in MCAO and PSD groups had significantly increased neurological function scores, TMAO level, the ratio of TMAO/H2S, and immobility time in forced swimming test with a lowered level of H2S (P < 0.05). These changes were more obvious in PSD rats, which also exhibited a reduced sugar water preference with increased IgG protein and decreased occluding and caudin-5 expressions in the brain tissue (P < 0.05). TMAO/H2S ratio in PSD rats was positively correlated with neurological function score (R2=0.3235, P=0.0269) and immobility time in swimming (R2=0.6290, P=0.0004) and negatively with sugar water preference (R2=-0.4534, P=0.0059). Treatment with fecal transplantation, antibiotics, probiotics and fluoxetine all significantly reduced neurological function scores, immobility time in forced swimming, TMAO/H2S ratio, and IgG protein expression and increased sugar water preference and brain occludin and caudin-5 expressions of the PSD rats (P < 0.05).

CONCLUSION

In PSD rats, TMAO/H2S ratio is correlated with neurological function score, immobility time in forced swimming and sugar water preference, and modulating intestinal flora can improve neurological function and depressive symptoms and improve the integrity of the blood-brain barrier.

Gut microbiota-derived short-chain fatty acids and depression: deep insight into biological mechanisms and potential applications

The gut microbiota is a complex and dynamic ecosystem known as the 'second brain'. Composing the microbiota-gut-brain axis, the gut microbiota and its metabolites regulate the central nervous system through neural, endocrine and immune pathways to ensure the normal functioning of the organism, tuning individuals' health and disease status. Short-chain fatty acids (SCFAs), the main bioactive metabolites of the gut microbiota, are involved in several neuropsychiatric disorders, including depression. SCFAs have essential effects on each component of the microbiota-gut-brain axis in depression. In the present review, the roles of major SCFAs (acetate, propionate and butyrate) in the pathophysiology of depression are summarised with respect to chronic cerebral hypoperfusion, neuroinflammation, host epigenome and neuroendocrine alterations. Concluding remarks on the biological mechanisms related to gut microbiota will hopefully address the clinical value of microbiota-related treatments for depression.

Combined VEGF and bFGF loaded nanofiber membrane protects against neuronal injury and hypomyelination in a rat model of chronic cerebral hypoperfusion

Currently, there are no effective therapeutic targets for the treatment of chronic cerebral hypoperfusion(CCH)-induced cerebral ischemic injury. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) are discovered as the inducers of neurogenesis and angiogenesis. We previously made a nanofiber membrane (NFM), maintaining a long-term release of VEGF and bFGF up to 35 days, which might make VEGF and bFGF NFM as the potential protective agents against cerebral ischemic insult. In this study, the effects of VEGF and bFGF delivered by NFM into brain were investigated as well as their underlying mechanismsin a rat model of CCH. VEGF + bFGF NFM application increased the expressions of tight junction proteins, maintained BBB integrity, and alleviated vasogenic cerebral edema. Furthermore, VEGF + bFGF NFM sticking enhanced angiogenesis and elevated CBF. Besides, VEGF + bFGF NFM treatment inhibited neuronal apoptosis and decreased neuronal loss. Moreover, roofing of VEGF + bFGF NFM attenuated microglial activation and blocked the launch of NLRP3/caspase-1/IL-1β pathway. In addition, VEGF + bFGF NFM administration prevented disruption to the pre/postsynaptic membranes and loss of myelin sheath, relieving synaptic injury and demyelination. Oligodendrogenesis, neurogenesis and PI3K/AKT/mTOR pathway were involved in the treatment of VEGF + bFGF NFM against CCH-induced neuronal injury and hypomyelination. These findings supported that VEGF + bFGF NFM application constitutes a neuroprotective strategy for the treatment of CCH, which may be worth further clinical translational research as a novel neuroprotective approach, benifiting indirect surgical revascularization.

The immunometabolic reprogramming of microglia in Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder (NDD). In the central nervous system (CNS), immune cells like microglia could reprogram intracellular metabolism to alter or exert cellular immune functions in response to environmental stimuli. In AD, microglia could be activated and differentiated into pro-inflammatory or anti-inflammatory phenotypes, and these differences in cellular phenotypes resulted in variance in cellular energy metabolism. Considering the enormous energy requirement of microglia for immune functions, the changes in mitochondria-centered energy metabolism and substrates of microglia are crucial for the cellular regulation of immune responses. Here we reviewed the mechanisms of microglial metabolic reprogramming by analyzing their flexible metabolic patterns and changes that occurred in their metabolism during the development of AD. Further, we summarized the role of drugs in modulating immunometabolic reprogramming to prevent neuroinflammation, which may shed light on a new research direction for AD treatment.

Intermittent Fasting on Neurologic Diseases: Potential Role of Gut Microbiota

As the global population ages, the prevalence of neurodegenerative diseases is surging. These disorders have a multifaceted pathogenesis, entwined with genetic and environmental factors. Emerging research underscores the profound influence of diet on the development and progression of health conditions. Intermittent fasting (IF), a dietary pattern that is increasingly embraced and recommended, has demonstrated potential in improving neurophysiological functions and mitigating pathological injuries with few adverse effects. Although the precise mechanisms of IF's beneficial impact are not yet completely understood, gut microbiota and their metabolites are believed to be pivotal in mediating these effects. This review endeavors to thoroughly examine current studies on the shifts in gut microbiota and metabolite profiles prompted by IF, and their possible consequences for neural health. It also highlights the significance of dietary strategies as a clinical consideration for those with neurological conditions.

Fecal microbiota transplantation and short-chain fatty acids protected against cognitive dysfunction in a rat model of chronic cerebral hypoperfusion

AIMS

Clear roles and mechanisms in explaining gut microbial dysbiosis and microbial metabolites short-chain fatty acids (SCFAs) alterations in chronic cerebral ischemic pathogenesis have yet to be explored. In this study, we investigated chronic cerebral hypoperfusion (CCH)-induced gut microbiota and metabolic profiles of SCFAs as well as the effects and mechanisms of fecal microbiota transplantation (FMT) and SCFAs treatment on CCH-induced hippocampal neuronal injury.

METHODS

Bilateral common carotid artery occlusion (BCCAo) was used to establish the CCH model. Gut microbiota and SCFAs profiles in feces and hippocampus were evaluated by 16S ribosomal RNA sequencing and gas chromatography-mass spectrometry. RNA sequencing analysis was performed in hippocampal tissues. The potential molecular pathways and differential genes were verified through western blot, immunoprecipitation, immunofluorescence, and ELISA. Cognitive function was assessed via the Morris water maze test. Ultrastructures of mitochondria and synapses were tested through a transmission electron microscope.

RESULTS

Chronic cerebral hypoperfusion induced decreased fecal acetic and propionic acid and reduced hippocampal acetic acid, which were reversed after FMT and SCFAs administration by changing fecal microbial community structure and compositions. Furthermore, in the hippocampus, FMT and SCFAs replenishment exerted anti-neuroinflammatory effects through inhibiting microglial and astrocytic activation as well as switching microglial phenotype from M1 toward M2. Moreover, FMT and SCFAs treatment alleviated neuronal loss and microglia-mediated synaptic loss and maintained the normal process of synaptic vesicle fusion and release, resulting in the improvement of synaptic plasticity. In addition, FMT and SCFAs supplement prevented oxidative phosphorylation dysfunction via mitochondrial metabolic reprogramming. The above effects of FMT and SCFAs treatment led to the inhibition of CCH-induced cognitive impairment.

CONCLUSION

Our findings highlight FMT and SCFAs replenishment would be the feasible gut microbiota-based strategy to mitigate chronic cerebral ischemia-induced neuronal injury.

Acoustic Stress Induces Opposite Proliferative/Transformative Effects in Hippocampal Glia

The hippocampus is a brain region crucially involved in regulating stress responses and highly sensitive to environmental changes, with elevated proliferative and adaptive activity of neurons and glial cells. Despite the prevalence of environmental noise as a stressor, its effects on hippocampal cytoarchitecture remain largely unknown. In this study, we aimed to investigate the impact of acoustic stress on hippocampal proliferation and glial cytoarchitecture in adult male rats, using environmental noise as a stress model. After 21 days of noise exposure, our results showed abnormal cellular proliferation in the hippocampus, with an inverse effect on the proliferation ratios of astrocytes and microglia. Both cell lineages also displayed atrophic morphologies with fewer processes and lower densities in the noise-stressed animals. Our findings suggest that, stress not only affects neurogenesis and neuronal death in the hippocampus, but also the proliferation ratio, cell density, and morphology of glial cells, potentially triggering an inflammatory-like response that compromises their homeostatic and repair functions.