The gut microbiome acts as an integral part of the gastrointestinal tract (GIT) that has the largest and vulnerable surface with desirable features to observe foods, nutrients, and environmental factors, as well as to differentiate commensals, invading pathogens, and others. It is well-known that the gut has a strong connection with the central nervous system (CNS) in the context of health and disease. A healthy gut with diverse microbes is vital for normal brain functions and emotional behaviors. In addition, the CNS controls most aspects of the GI physiology. The molecular interaction between the gut/microbiome and CNS is complex and bidirectional, ensuring the maintenance of gut homeostasis and proper digestion. Besides this, several mechanisms have been proposed, including endocrine, neuronal, toll-like receptor, and metabolites-dependent pathways. Changes in the bidirectional relationship between the GIT and CNS are linked with the pathogenesis of gastrointestinal and neurological disorders; therefore, the microbiota/gut-and-brain axis is an emerging and widely accepted concept. In this review, we summarize the recent findings supporting the role of the gut microbiota and immune system on the maintenance of brain functions and the development of neurological disorders. In addition, we highlight the recent advances in improving of neurological diseases by probiotics/prebiotics/synbiotics and fecal microbiota transplantation via the concept of the gut–brain axis.

The gut–liver axis plays important roles in both the maintenance of a healthy liver and the pathogenesis of liver diseases, where the gut microbiota acts as a major determinant of this relationship. Gut bacteria-derived metabolites and cellular components are key molecules that affect the function of the liver and modulate the pathology of liver diseases. Accumulating evidence showed that gut microbiota produces a myriad of molecules, including lipopolysaccharide, lipoteichoic acid, peptidoglycan, and DNA, as well as short-chain fatty acids, bile acids, trimethylamine, and indole derivatives. The translocation of these components to the liver exerts beneficial or pathogenic effects by interacting with liver immune cells. This is a bidirectional relationship. Therefore, the existence of crosstalk between the gut and liver and its implications on host health and diseases are essential for the etiology and treatment of diseases. Several mechanisms have been proposed for the pathogenesis of liver diseases, but still, the mechanisms behind the pathogenic role of gut-derived components on liver pathogenesis remain elusive and not understandable. This review discusses the current progress on the gut microbiota and its components in terms of the progression of liver diseases, and in turn, how liver diseases indirectly affect the intestinal function and induce intestinal inflammation. Moreover, this paper highlights the current therapeutic and preventive strategies used to restore the gut microbiota composition and improve host health.

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Background: Alzheimer’s disease (AD) is a lethal progressive neurodegenerative disorder. Currently, many acetylcholinesterase inhibitors, such as donepezil, is widely used for the treatment of AD. However, the efficacy of long-term donepezil use is limited. SIP3, a mixture of Santalum album, Illicium verum, and Polygala tenuifolia, a new formula derived from traditional Korean herbal medicine. In this study, SIP3 were assessed the survival of Drosophila AD model and synergistic effect of SIP3, donepezil co-treatment of AD using APP/PS1 transgenic mice. Methods: In Drosophila AD models, we analyzed the survival, climbing ability and acridine orange (AO) staining. In APP/PS1 mice, at six months of age were randomized into four groups. Then, these groups were orally administered vehicle (for the control), donepezil, low and high doses SIP3 plus Donepezil respectively for six months. The passive avoidance test (PAT) and the Morris water maze (MWM) were analyzed cognitive behavioral changes. In addition, the forced swimming test (FST) and the tail suspension test (TST) were assessed depression-like behavior. To investigate the molecular and cellular mechanisms underlying positive effects of SIP3 on AD, the cerebral cortex transcriptomes were analyzed by RNA sequencing.Results: Using the passive avoidance test (PAT), we analyzed the combination of SIP3 and donepezil improved the learning capabilities and memory of APP/PS1 mice, compared with the group treated with donepezil only, in late stage of AD. In addition, using the Morris water maze (MWM) test, co-treatment with donepezil and a low concentration of SIP3 significantly ameliorated cognitive impairment. Co-administration of SIP3 and donepezil effectively reduced depression-like behavior in the forced swimming and tail suspension tests. Furthermore, RNA sequencing of cerebral cortex transcriptome revealed that gene expression profiles after low dose of SIP3 co-treatment are slightly similar to those of normal phenotype mice than those obtained after donepezil treatment alone. Gene ontology (GO) along with Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway have demonstrated that differentially expressed genes were involved in locomotor behavior and neuroactive ligand-receptor interactions. Collectively: our results suggest that co-treatment of low dose of SIP3 and donepezil improves impaired learning, memory, and depression in late stage of AD in mice.

Neuroinflammation is an inflammatory response in the nervous system that is associated with various neurological diseases including Alzheimer's diseases and others. Many studies evaluated the anti‐inflammatory potential of Santalum album (S. album) extract, but none of them analyzed its effects against neuroinflammatory response in vitro. In addition, the precise mechanism underlying the anti‐inflammatory effect of the extract has not yet been elucidated. Therefore, in this study, we investigated the effect of S. album extract on modulation of toll‐like receptor 3 (TLR3) agonist polyinosnic‐polycytidylic acid (PolyI:C)‐induced neuroinflammatory response in human neuroblastoma cells. The TLR3‐mediated immune response was differentially modulated by S. album extract in SH‐SY5Y cells. In addition, treatment of cells with the conditioned medium (CM) of S. album extract significantly increased the mRNA levels of IFN‐β, IFN‐α, MxA and OAS‐1 and decreased IL‐6, CXCL8, CCL2 and IP‐10. S. album extract has indirectly affected the expression of IFNs and inflammatory cytokines in SH‐SY5Y cells. Furthermore, the extract was able to modulate PolyI:C‐induced inflammatory response in Caco2 cells. Overall, S. album was capable to attenuate PolyI:C‐induced neuroinflammatory effect through the induction of TLR2, TLR4 and the modulation of TLR negative regulators of the TRAF3, IRF3 and NF‐κB pathways.

Background: Alzheimer’s disease (AD) is a lethal, progressive neurodegenerative disorder that has been linked to a deficiency of the neurotransmitter, acetylcholine. Currently, many acetylcholinesterase inhibitors, such as donepezil, are widely used for the treatment of AD. On the other hand, the efficacy of long-term donepezil use is limited. SIP3, a mixture of three herbal extracts from Santalum album, Illicium verum, and Polygala tenuifolia, is a new formula derived from traditional Korean herbal medicine. Objective: We assessed the synergistic effect of SIP3 and donepezil co-treatment on symptoms of AD using APP/PS1 transgenic mice. Methods: In this study, a Drosophila AD model and SH-SY5Y clles was were used to assess the toxicity of SIP3, and APPswe/PS1dE9 (APP/PS1) transgenic mice were used to evaluate the cognitivebehavioral and depression-like behavior effect of SIP3 and donepezil co-treatment on symptoms of AD. The cerebral cortex or hippocampus transcriptomes were analyzed by RNA sequencing and miRNA to investigate the molecular and cellular mechanisms underlying the positive effects of SIP3 on AD. Results: In the passive avoidance test (PAT) and Morris water maze (MWM) test, the combination of SIP3 and donepezil improved the learning capabilities and memory of APP/PS1 mice in the mid-stage of AD compared to the group treated with donepezil only. In addition, co-administration of SIP3 and donepezil effectively reduced the depression-like behavior in the forced swimming and tail suspension tests. Furthermore, RNA sequencing of the cerebral cortex transcriptome and miRNA of the hippocampus showed that the gene expression profiles after a low dose SIP3 co-treatment were more similar to those of the normal phenotype mice than those obtained after the donepezil treatment alone. The Gene ontology Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, showed that differentially expressed genes were involved in the locomotor behavior and neuroactive ligand-receptor interactions. These results suggest that a co-treatment of low dose SIP3 and donepezil improves impaired learning, memory, and depression in the mid-stage of AD in mice. Conclusion: Co-treatment of low dose SIP3 and donepezil improves impaired learning, memory, and depression in the mid-stage of AD in mice.

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Background: Alzheimer’s disease (AD) is the most general, chronic, and progressive neurodegenerative senile disorder characterized clinically by progressive cognitive deterioration and memory impairment. Neoline is effective against neuropathic pain models, but the effects of neoline against AD-like phenotypes have not been investigated. Objective: We offer the investigation of the effects of neoline in AD. Methods: In this study, a Tg-APPswe/PS1dE9 AD mouse model was treated orally with neoline at a concentration of 0.5 mg/kg or 0.1 mg/kg starting at 7.5 months and administered for three months, and its anti-AD effects were evaluated. Results: Neoline improved memory and cognition impairments and reduced the number of amyloid-beta plaque and the amount of amyloid-β in the brain of AD mice. Furthermore, neoline reduced the anxiety behavior in the AD mouse model. The chronic administration of neoline also induced AMPK phosphorylation and decreased tau, amyloid-β, and BACE1 expression in the hippocampus. These findings indicate that chronic administration of neoline has therapeutic effects via AMPK activation, and BACE1 downregulation resulted in a decrease in the amyloid-β levels in the brain of Tg-APPswe/PS1dE9 AD mice. Conclusion: Our results suggest that neoline is a therapeutic agent for the cure of neurodegenerative diseases like AD.