Antidepressant-like effects of sodium butyrate and its possible mechanisms of action in mice exposed to chronic unpredictable mild stress

The Gut Microbiome and Symptom Burden After Kidney Transplantation: An Overview and Research Opportunities

Many kidney transplant recipients continue to experience high symptom burden despite restoration of kidney function. High symptom burden is a significant driver of quality of life. In the post-transplant setting, high symptom burden has been linked to negative outcomes including medication non-adherence, allograft rejection, graft loss, and even mortality. Symbiotic bacteria (microbiota) in the human gastrointestinal tract critically interact with the immune, endocrine, and neurological systems to maintain homeostasis of the host. The gut microbiome has been proposed as an underlying mechanism mediating symptoms in several chronic medical conditions including irritable bowel syndrome, chronic fatigue syndrome, fibromyalgia, and psychoneurological disorders via the gut-brain-microbiota axis, a bidirectional signaling pathway between the enteric and central nervous system. Post-transplant exposure to antibiotics, antivirals, and immunosuppressant medications results in significant alterations in gut microbiota community composition and function, which in turn alter these commensal microorganisms' protective effects. This overview will discuss the current state of the science on the effects of the gut microbiome on symptom burden in kidney transplantation and future directions to guide this field of study.

Unraveling the Role of the Blood-Brain Barrier in the Pathophysiology of Depression: Recent Advances and Future Perspectives

Depression is a highly prevalent psychological disorder characterized by persistent dysphoria, psychomotor retardation, insomnia, anhedonia, suicidal ideation, and a remarkable decrease in overall well-being. Despite the prevalence of accessible antidepressant therapies, many individuals do not achieve substantial improvement. Understanding the multifactorial pathophysiology and the heterogeneous nature of the disorder could lead the way toward better outcomes. Recent findings have elucidated the substantial impact of compromised blood-brain barrier (BBB) integrity on the manifestation of depression. BBB functions as an indispensable defense mechanism, tightly overseeing the transport of molecules from the periphery to preserve the integrity of the brain parenchyma. The dysfunction of the BBB has been implicated in a multitude of neurological disorders, and its disruption and consequent brain alterations could potentially serve as important factors in the pathogenesis and progression of depression. In this review, we extensively examine the pathophysiological relevance of the BBB and delve into the specific modifications of its components that underlie the complexities of depression. A particular focus has been placed on examining the effects of peripheral inflammation on the BBB in depression and elucidating the intricate interactions between the gut, BBB, and brain. Furthermore, this review encompasses significant updates on the assessment of BBB integrity and permeability, providing a comprehensive overview of the topic. Finally, we outline the therapeutic relevance and strategies based on BBB in depression, including COVID-19-associated BBB disruption and neuropsychiatric implications. Understanding the comprehensive pathogenic cascade of depression is crucial for shaping the trajectory of future research endeavors.

Microbial short-chain fatty acids regulate drug seeking and transcriptional control in a model of cocaine seeking

Cocaine use disorder represents a public health crisis with no FDA-approved medications for its treatment. A growing body of research has detailed the important connections between the brain and the resident population of bacteria in the gut, the gut microbiome, in psychiatric disease models. Acute depletion of gut bacteria results in enhanced reward in a mouse cocaine place preference model, and repletion of bacterially-derived short-chain fatty acid (SCFA) metabolites reverses this effect. However, the role of the gut microbiome and its metabolites in modulating cocaine-seeking behavior after prolonged abstinence is unknown. Given that relapse prevention is the most clinically challenging issue in treating substance use disorders, studies examining the effects of microbiome manipulations in relapse-relevant models are critical. Here, male Sprague-Dawley rats received either untreated water or antibiotics to deplete the gut microbiome and its metabolites. Rats were trained to self-administer cocaine and subjected to either within-session threshold testing to evaluate motivation for cocaine or 21 days of abstinence followed by a cue-induced cocaine-seeking task to model relapse behavior. Microbiome depletion did not affect cocaine acquisition on an fixed-ratio 1 schedule. However, microbiome-depleted rats exhibited significantly enhanced motivation for low dose cocaine on a within-session threshold task. Similarly, microbiome depletion increased cue-induced cocaine-seeking following prolonged abstinence and altered transcriptional regulation in the nucleus accumbens. In the absence of a normal microbiome, repletion of bacterially-derived SCFA metabolites reversed the behavioral and transcriptional changes associated with microbiome depletion. These findings suggest that gut bacteria, via their metabolites, are key regulators of drug-seeking behaviors, positioning the microbiome as a potential translational research target.

Mechanisms for the biological activity of Gastrodia elata Blume and its constituents: A comprehensive review on sedative-hypnotic, and antidepressant properties

BACKGROUND

Insomnia and depressive disorder are two common symptoms with a reciprocal causal relationship in clinical practice, which are usually manifested in comorbid form. Several medications have been widely used in the treatment of insomnia and depression, but most of these drugs show non-negligible side effects. Currently, many treatments are indicated for insomnia and depressive symptom, including Chinese herbal medicine such as Gastrodia elata Blume (G. elata), which has excellent sedative-hypnotic and antidepressant effects in clinical and animal studies.

PURPOSE

To summarize the mechanisms of insomnia and depression and the structure-activity mechanism for G. elata to alleviate these symptoms, particularly by hypothalamic-pituitary-adrenal (HPA) axis and intestinal flora, aiming to discover new approaches for the treatment of insomnia and depression.

METHODS

The following electronic databases were searched from the beginning to November 2023: PubMed, Web of Science, Google Scholar, Wanfang Database, and CNKI. The following keywords of G. elata were used truncated with other relevant topic terms, such as depression, insomnia, antidepressant, sedative-hypnotic, neuroprotection, application, safety, and toxicity.

RESULTS

Natural compounds derived from G. elata could alleviate insomnia and depressive disorder, which is involved in monoamine neurotransmitters, inflammatory response, oxidative stress, and gut microbes, etc. Several clinical trials showed that G. elata-derived natural compounds that treat depression and insomnia have significant and safe therapeutic effects, but further well-designed clinical and toxicological studies are needed.

CONCLUSION

G. elata exerts a critical role in treating depression and insomnia due to its multi-targeting properties and fewer side effects. However, more clinical and toxicological studies should be performed to further explore the sedative-hypnotic and antidepressant mechanisms of G. elata and provide more evidence and recommendations for its clinical application. Our review provides an overview of G. elata treating insomnia with depression for future research direction.

Microbiota-Induced Epigenetic Alterations in Depressive Disorders Are Targets for Nutritional and Probiotic Therapies

Major depressive disorder (MDD) is a complex disorder and a leading cause of disability in 280 million people worldwide. Many environmental factors, such as microbes, drugs, and diet, are involved in the pathogenesis of depressive disorders. However, the underlying mechanisms of depression are complex and include the interaction of genetics with epigenetics and the host immune system. Modifications of the gut microbiome and its metabolites influence stress-related responses and social behavior in patients with depressive disorders by modulating the maturation of immune cells and neurogenesis in the brain mediated by epigenetic modifications. Here, we discuss the potential roles of a leaky gut in the development of depressive disorders via changes in gut microbiota-derived metabolites with epigenetic effects. Next, we will deliberate how altering the gut microbiome composition contributes to the development of depressive disorders via epigenetic alterations. In particular, we focus on how microbiota-derived metabolites such as butyrate as an epigenetic modifier, probiotics, maternal diet, polyphenols, drugs (e.g., antipsychotics, antidepressants, and antibiotics), and fecal microbiota transplantation could positively alleviate depressive-like behaviors by modulating the epigenetic landscape. Finally, we will discuss challenges associated with recent therapeutic approaches for depressive disorders via microbiome-related epigenetic shifts, as well as opportunities to tackle such problems.

Promising new pharmacological targets for depression: The search for efficacy

Pharmacological treatment of major depressive disorder (MDD) still relies on the use of serotonergic drugs, despite their limited efficacy. A few mechanistically new drugs have been developed in recent years, but many fail in clinical trials. Several hypotheses have been proposed to explain MDD pathophysiology, indicating that physiological processes such as neuroplasticity, circadian rhythms, and metabolism are potential targets. Here, we review the current state of pharmacological treatments for MDD, as well as the preclinical and clinical evidence for an antidepressant effect of molecules that target non-serotonergic systems. We offer some insights into the challenges facing the development of new antidepressant drugs, and the prospect of finding more effectiveness for each target discussed.

Gut feelings: the relations between depression, anxiety, psychotropic drugs and the gut microbiome

The gut microbiome is involved in the bi-directional relationship of the gut - brain axis. As most studies of this relationship are small and do not account for use of psychotropic drugs (PTDs), we explored the relations of the gut microbiome with several internalizing disorders, while adjusting for PTDs and other relevant medications, in 7,656 Lifelines participants from the Northern Netherlands (5,522 controls and 491 participants with at least one internalizing disorder). Disorders included dysthymia, major depressive disorder (MDD), any depressive disorder (AnyDep: dysthymia or MDD), generalized anxiety disorder (GAD) and any anxiety disorder (AnyAnx: GAD, social phobia and panic disorder). Compared to controls, 17 species were associated with depressive disorders and 3 were associated with anxiety disorders. Around 90% of these associations remained significant (FDR <0.05) after adjustment for PTD use, suggesting that the disorders, not PTD use, drove these associations. Negative associations were observed for the butyrate-producing bacteria Ruminococcus bromii in participants with AnyDep and for Bifidobacterium bifidum in AnyAnx participants, along with many others. Tryptophan and glutamate synthesis modules and the 3,4-Dihydroxyphenylacetic acid synthesis module (related to dopamine metabolism) were negatively associated with MDD and/or dysthymia. After additional adjustment for functional gastrointestinal disorders and irritable bowel syndrome, these relations remained either statistically (FDR <0.05) or nominally (P < 0.05) significant. Overall, multiple bacterial species and functional modules were associated with internalizing disorders, including gut - brain relevant components, while associations to PTD use were moderate. These findings suggest that internalizing disorders rather than PTDs are associated with gut microbiome differences relative to controls.

Short-chain-fatty acid valerate reduces voluntary alcohol intake in male mice

Background

Despite serious health and social consequences, effective intervention strategies for habitual alcohol binge drinking are lacking. Development of novel therapeutic and preventative approaches is highly desirable. Accumulating evidence in the past several years has established associations between the gut microbiome and microbial metabolites with drinking behavior, but druggable targets and their underlying mechanism of action are understudied.

Results

Here, using a drink-in-the-dark mouse model, we identified a microbiome metabolite-based novel treatment (sodium valerate) that can reduce excessive alcohol drinking. Sodium valerate is a sodium salt of valeric acidshort-chain-fatty-acid with similar structure as γ-aminobutyric acid (GABA). Ten days of oral sodium valerate supplementation attenuates excessive alcohol drinking by 40%, reduces blood ethanol concentration by 53%, and improves anxiety-like or approach-avoidance behavior in male mice, without affecting overall food and water intake. Mechanistically, sodium valerate supplementation increases GABA levels across stool, blood, and amygdala. It also significantly increases H4 acetylation in the amygdala of mice. Transcriptomics analysis of the amygdala revealed that sodium valerate supplementation led to changes in gene expression associated with functional pathways including potassium voltage-gated channels, inflammation, glutamate degradation, L-DOPA degradation, and psychological behaviors. 16S microbiome profiling showed that sodium valerate supplementation shifts the gut microbiome composition and decreases microbiome-derived neuroactive compounds through GABA degradation in the gut microbiome.

Conclusion

Our findings suggest that the sodium valerate holds promise as an innovative therapeutic avenue for the reduction of habitual binge drinking, potentially through multifaceted mechanisms.

Attenuation of Chronic Stress-Induced Depressive-like Symptoms by Fish Oil via Alleviating Neuroinflammation and Impaired Tryptophan Metabolism in Aging Rats

The prevalence of depression is increasing, and geriatric depression, in particular, is difficult to recognize and treat. Depression in older adults is often accompanied by neuroinflammation in the central nervous system (CNS). Neuroinflammation affects the brain's physiological and immune functions through several pathways and induces depressive symptoms. This study investigated the relationship among depression, neuroinflammation, and fish oil supplementation. Thirty-six male Sprague-Dawley rats were used in an aging-related depression animal model to simulate geriatric depression. Cognitive function, depressive-like symptoms, peripheral nervous system and CNS inflammation status, and the tryptophan-related metabolic pathway were analyzed. The geriatric depression animal model was associated with depressive-like behaviors and cognitive impairment. The integrity of the blood-brain barrier was compromised, resulting in increased expression of ionized calcium-binding adapter molecule 1 and the glial fibrillary acidic protein in the brain, indicating increased neuroinflammation. Tryptophan metabolism was also negatively affected. The geriatric-depressive-like rats had high levels of neurotoxic 5-hydroxyindoleacetic acid and kynurenine in their hippocampus. Fish oil intake improved depressive-like symptoms and cognitive impairment, reduced proinflammatory cytokine expression, activated the brain's glial cells, and increased the interleukin-10 level in the prefrontal cortex. Thus, fish oil intervention could ameliorate abnormal neurobehaviors and neuroinflammation and elevate the serotonin level in the hippocampus.

The Role of Short-Chain Fatty Acids in Microbiota-Gut-Brain Cross-Talk with a Focus on Amyotrophic Lateral Sclerosis: A Systematic Review

Amyotrophic lateral sclerosis is a devastating neurodegenerative disease characterized by the gradual loss of motor neurons in the brain and spinal cord, leading to progressive motor function decline. Unfortunately, there is no effective treatment, and its increasing prevalence is linked to an aging population, improved diagnostics, heightened awareness, and changing lifestyles. In the gastrointestinal system, the gut microbiota plays a vital role in producing metabolites, neurotransmitters, and immune molecules. Short-chain fatty acids, of interest for their potential health benefits, are influenced by a fiber- and plant-based diet, promoting a diverse and balanced gut microbiome. These fatty acids impact the body by binding to receptors on enteroendocrine cells, influencing hormones like glucagon-like peptide-1 and peptide YY, which regulate appetite and insulin sensitivity. Furthermore, these fatty acids impact the blood-brain barrier, neurotransmitter levels, and neurotrophic factors, and directly stimulate vagal afferent nerves, affecting gut-brain communication. The vagus nerve is a crucial link between the gut and the brain, transmitting signals related to appetite, inflammation, and various processes. Dysregulation of this pathway can contribute to conditions like obesity and irritable bowel syndrome. Emerging evidence suggests the complex interplay among these fatty acids, the gut microbiota, and environmental factors influences neurodegenerative processes via interconnected pathways, including immune function, anti-inflammation, gut barrier, and energy metabolism. Embracing a balanced, fiber-rich diet may foster a diverse gut microbiome, potentially impacting neurodegenerative disease risk. Comprehensive understanding requires further research into interventions targeting the gut microbiome and fatty acid production and their potential therapeutic role in neurodegeneration.

Post-stroke depression: epigenetic and epitranscriptomic modifications and their interplay with gut microbiota

Epigenetic and epitranscriptomic modifications that regulate physiological processes of an organism at the DNA and RNA levels, respectively, are novel therapeutic candidates for various neurological diseases. Gut microbiota and its metabolites are known to modulate DNA methylation and histone modifications (epigenetics), as well as RNA methylation especially N6-methyladenosine (epitranscriptomics). As gut microbiota as well as these modifications are highly dynamic across the lifespan of an organism, they are implicated in the pathogenesis of stroke and depression. The lack of specific therapeutic interventions for managing post-stroke depression emphasizes the need to identify novel molecular targets. This review highlights the interaction between the gut microbiota and epigenetic/epitranscriptomic pathways and their interplay in modulating candidate genes that are involved in post-stroke depression. This review further focuses on the three candidates, including brain-derived neurotrophic factor, ten-eleven translocation family proteins, and fat mass and obesity-associated protein based on their prevalence and pathoetiologic role in post-stroke depression.

The role of gut microbiota in the pathogenesis and treatment of postpartum depression

Postpartum depression (PPD) is a common complication of pregnancy in women, and its pathogenesis mainly involves disturbances of the neuroendocrine regulation, immune system, neurotransmitters, hormone secretion, and the gut microbiome. Gut microbes play essential physiological and pathological roles in the gut-brain axis' pathways which are involved in various central nervous system (CNS) and psychiatric disorders, including PPD. Numerous studies have identified the fundamental role of the gut-brain axis in the pathogenesis and treatment of PPD patients and also correlates with other pathogenic mechanisms of PPD. Disturbances in gut microbes are associated with the disruption of multiple signaling pathways and systems that ultimately lead to PPD development. This review aimed to elucidate the potential connections between gut microbes and the established PPD network, and this might serve as a guide for the development of new efficient diagnostic, therapeutic, and prognostic strategies in the management of PPD.

A personalized diet intervention improves depression symptoms and changes microbiota and metabolite profiles among community-dwelling older adults

Introduction

The impact of diet on mental well-being and gut microorganisms in humans is well recognized. However, research on the connections between food nutrients, gut microbiota, and mental health remains limited. To address this, the present study aimed to assess the effects of a personalized diet, based on individual needs and aligned with the Mediterranean diet principles, on depression symptoms, quality of life, nutritional intake, and gut microbiota changes among older adults living in the community.

Methods

The intervention involved regular visits from a registered dietitian, who provided tailored dietary recommendations. During the 6-month study, participants completed questionnaires to evaluate their depression levels, quality of life, and dietary habits. Additionally, they provided stool samples for analysis of gut microbiota and metabolites.

Results

The results demonstrated that the personalized dietary intervention reduced depression symptoms and improved the quality of life among older adults. Furthermore, significant changes in the intake of certain nutrients, such as folate, lutein, zeaxanthin, EPA, and DHA, were observed following the intervention. Moreover, the intervention was associated with increased diversity in the gut microbiome and reduced total short-chain fatty acids, the main metabolites produced by gut microorganisms. The study also revealed correlations between food nutrients, gut microbiota, and mental health parameters.

Discussion

In conclusion, this research highlights the potential advantages of personalized dietary interventions in managing depression and enhancing overall well-being among older populations. It also sheds light on the role of gut microbiota and its metabolites in these effects. The findings offer valuable insights into the significance of nutrition and gut health for mental well-being in older adults.

Enterogenic metabolomics signatures of depression: what are the possibilities for the future

INTRODUCTION

An increasing number of studies indicate that the microbiota-gut-brain axis is an important pathway involved in the onset and progression of depression. The responses of the organism (or its microorganisms) to external cues cannot be separated from a key intermediate element: their metabolites.

AREAS COVERED

In recent years, with the rapid development of metabolomics, an increasing amount of metabolites has been detected and studied, especially the gut metabolites. Nevertheless, the increasing amount of metabolites described has not been reflected in a better understanding of their functions and metabolic pathways. Moreover, our knowledge of the biological interactions among metabolites is also incomplete, which limits further studies on the connections between the microbial-entero-brain axis and depression.

EXPERT OPINION

This paper summarizes the current knowledge on depression-related metabolites and their involvement in the onset and progression of this disease. More importantly, this paper summarized metabolites from the intestine, and defined them as enterogenic metabolites, to further clarify the function of intestinal metabolites and their biochemical cross-talk, providing theoretical support and new research directions for the prevention and treatment of depression.

The Muscle-Gut-Brain Axis and Psychiatric Illness

The microbiota-gut-brain axis (MGBA) has been the subject of much research over the past decade, offering an exciting new paradigm for the treatment of psychiatric disorders. In this review, the MGBA is extended to include skeletal muscle and the potential role of an expanded "muscle-gut-brain axis" (MuGBA) in conditions such as anxiety and depression is discussed. There is evidence, from both preclinical and human studies, of bidirectional links between the gut microbiome and skeletal muscle function and structure. The therapeutic role of exercise in reducing depressive and anxiety symptoms is widely recognised, and the potential role of the gut microbiota-skeletal muscle link is discussed within this context. Potential pathways of communication involved in the MuGBA including the tryptophan-kynurenine pathway, intestinal permeability, immune modulation, and bacterial metabolites such as short-chain-fatty-acids are explored.

Maternal high-fat diet alters the neurobehavioral, biochemical and inflammatory parameters of their adult female rat offspring

BACKGROUND

Lipid metabolism dysregulations have been associated with depressive and anxious behaviors which can affect pregnant and lactating individuals, with indications that such changes extend to the offspring. Therefore, the aim of this study was to evaluate the effect of a maternal high-fat diet on the neurobehavioral, biochemical and inflammatory parameters of their adult female offspring.

METHODS

Wistar rats ± 90 days old were mated. The dams were allocated to consume a control (CTL) or high-fat (HFD) diet during pregnancy and lactation. After weaning, the female offspring from the CTL (N=10) and HFD (N=10) groups received standard chow. The offspring behavioral tests were started at 120 days old. Then, the somatic measures were evaluated followed by euthanasia, histological and biochemical analyses.

RESULTS

The HFD group had less ambulation and longer immobility time in the open field test compared to the CTL. The HFD group had lower HDL (48.4%) and a higher adiposity (71.8%) and LDL (62.2%) than the CTL. The CTL had a higher organic acid concentration in the intestine, mainly acetic and butyric acids, however the HFD had a higher citric and acetic acid concentration in the brain and ischemic lesion in the hippocampus with a higher NF-κB concentration.

CONCLUSION

The results demonstrate deleterious effects of a maternal HFD on the neurobehavioral and biochemical parameters of their offspring which may be associated with the role of organic acids and NF-κB in fetal programming.

Synergistic antidepressant-like effect of n-3 polyunsaturated fatty acids and probiotics through the brain-gut axis in rats exposed to chronic mild stress

N-3 polyunsaturated fatty acids (PUFA) and probiotics have antidepressant-like effects, but the underlying mechanisms are unclear. We hypothesized that n-3 PUFA combined with live and dead probiotics synergistically improves depression by modulating the hypothalamic-pituitary-adrenal (HPA) axis and serotonergic pathways through the brain-gut axis. Rats were randomly divided into seven groups (n = 8/group): non-chronic mild stress (CMS) with n-6 PUFA, CMS with n-3 PUFA, n-6 PUFA, live probiotics, dead probiotics, n-3 PUFA and live probiotics, and n-3 PUFA and dead probiotics. Diets of n-6 and n-3 PUFA and oral supplementation of live and dead probiotics were provided for 12 weeks, and CMS was performed for the last 5 weeks. N-3 PUFA and probiotics improved depressive behaviors and modulated the brain and gut HPA axis by synergistically increasing glucocorticoid receptor expression and decreasing corticotropin-releasing factor expression and blood levels of adrenocorticotropic hormone and corticosterone. N-3 PUFA and probiotics upregulated the brain serotonergic pathway through serotonin levels and expression of brain-derived neurotrophic factor, phosphorylated cAMP response binding protein, and 5-hydroxytryptamine 1A receptor while downregulating the gut serotonergic pathway. Furthermore, n-3 PUFA and probiotics increased the abundance of Ruminococcaceae, brain and gut short chain fatty acid levels, and occludin expression while decreasing the expression of tumor necrosis factor-α, interleukin-1β, and prostaglandin E₂ and blood lipopolysaccharides levels. There was no significant difference between the live and dead probiotics. In conclusion, n-3 PUFA and probiotics had synergistic antidepressant-like effects on the HPA axis and serotonergic pathways of the brain and gut through the brain-gut axis.

Emotional-Single Prolonged Stress: A promising model to illustrate the gut-brain interaction

Excessive stress can precipitate depression and anxiety diseases, and damage gastrointestinal functionality and microbiota changes, favoring the development of functional gastrointestinal disorders (FGIDs) - defined by dysregulation in the brain-gut interaction. Therefore, the present study investigated if Emotional-Single Prolonged Stress (E-SPS) induces depressive/anxiety-like phenotype and gut dysfunction in adult Swiss male mice. For this, mice of the E-SPS group were subjected to three stressors sequential exposure: immobilization, swimming, and odor of the predator for 7 days (incubation period). Next, animals performed behavior tests and 24 h later, samples of feces, blood, and colon tissue were collected. E-SPS increased the plasma corticosterone levels, immobility time in the tail suspension and forced swim test, decreased the grooming time in the splash test, OAT%, and OAE% in the elevated plus-maze test, as well as increased anxiety index. Mice of E-SPS had increased % of intestinal transit rate, % of fecal moisture content, and fecal pellets number, and decreased Claudin1 content in the colon. E-SPS decreased the relative abundance of Bacteroidetes phylum, Bacteroidia class, Bacteroidales order, Muribaculaceae and Porphyromonadaceae family, Muribaculum, and Duncaniella genus. However, E-SPS increased Firmicutes and Actinobacteria phylum, Coriobacteriales order, and the ratio of Firmicutes/Bacteroidetes, and demonstrated Mucispirillum genus presence. The present study showed that E-SPS induced depressive/anxiety-like phenotype, predominant diarrhea gut dysfunction, and modulated the gut bacterial microbiota profile in male adult Swiss mice. E-SPS might be a promising model for future studies on the brain-gut interaction and the development of FGIDs with psychological comorbidities.

Neuroinflammation related to the blood-brain barrier and sphingosine-1-phosphate in a pre-clinical model of periodontal diseases and depression in rats

AIM

To explore the potential mechanisms of neuroinflammation (microglia, blood-brain barrier [BBB] permeability, and the sphingosine-1-phosphate [S1P] pathways) resulting from the association between periodontitis and depression in rats.

MATERIALS AND METHODS

This pre-clinical in vivo experimental study used Wistar rats, in which experimental periodontitis (P) was induced by using oral gavages with Porphyromonas gingivalis and Fusobacterium nucleatum. Then, a chronic mild stress (CMS) model was implemented to induce a depressive-like behaviour, resulting in four groups: P with CMS (P+CMS+), P without CMS (P+CMS-), CMS without P (P-CMS+), and control (P-CMS-). After harvesting brain samples, protein/mRNA expression analyses and fluorescence immunohistochemistry were performed in the frontal cortex (FC). Results were analysed by ANOVA.

RESULTS

CMS exposure increased the number of microglia (an indicator of neuroinflammation) in the FC. In the combined model (P+CMS+), there was a decrease in the expression of tight junction proteins (zonula occludens-1 [ZO-1], occludin) and an increase in intercellular and vascular cell adhesion molecules (ICAM-1, VCAM-1) and matrix metalloproteinase 9 (MMP9), suggesting a more severe disruption of the BBB. The enzymes and receptors of S1P were also differentially regulated.

CONCLUSIONS

Microglia, BBB permeability, and S1P pathways could be relevant mechanisms explaining the association between periodontitis and depression.

Graves' disease as a driver of depression: a mechanistic insight

Graves' disease (GD) is characterized by diffuse enlargement and overactivity of the thyroid gland, which may be accompanied by other physical symptoms. Among them, depression can dramatically damage patients' quality of life, yet its prevalence in GD has not received adequate attention. Some studies have established a strong correlation between GD and increased risk of depression, though the data from current study remains limited. The summary of mechanistic insights regarding GD and depression has underpinned possible pathways by which GD contributes to depression. In this review, we first summarized the clinical evidence that supported the increased prevalence of depression by GD. We then concentrated on the mechanistic findings related to the acceleration of depression in the context of GD, as mounting evidence has indicated that GD promotes the development of depression through various mechanisms, including triggering autoimmune responses, inducing hormonal disorders, and influencing the thyroid-gut-microbiome-brain axis. Finally, we briefly presented potential therapeutic approaches to decreasing the risk of depression among patients with GD.

Reviewing the role of gut microbiota in the pathogenesis of depression and exploring new therapeutic options

The relationship between gut microbiota (GM) and mental health is one of the focuses of psychobiology research. In recent years, the microbial-gut-brain axis (MGBA) concept has gradually formed about this bidirectional communication between gut and brain. But how the GM is involved in regulating brain function and how they affect emotional disorders these mechanisms are tenuous and limited to animal research, and often controversial. Therefore, in this review, we attempt to summarize and categorize the latest advances in current research on the mechanisms of GM and depression to provide valid information for future diagnoses and therapy of mental disorders. Finally, we introduced some antidepressant regimens that can help restore gut dysbiosis, including classic antidepressants, Chinese materia medica (CMM), diet, and exogenous strains. These studies provide further insight into GM's role and potential pathways in emotion-related diseases, which holds essential possible clinical outcomes for people with depression or related psychiatric disorders. Future research should focus on clarifying the causal role of GM in disease and developing microbial targets, applying these findings to the prevention and treatment of depression.

Anthocyanins from Opuntia ficus-indica Modulate Gut Microbiota Composition and Improve Short-Chain Fatty Acid Production

Opuntia ficus-indica is rich in a variety of active substances, such as anthocyanins, flavonoids, and polysaccharides. Some studies have shown that anthocyanins extracted from natural plants can regulate intestinal flora. The fruit was used as raw material, and anthocyanins were extracted from it. In vivo experiments were used to study the effect of Opuntia ficus-indica anthocyanins on the mouse intestine by 16S rRNA high-throughput sequencing (NovaSeq 6000 platform) and gas chromatography (hydrogen flame ionization detector (FID)) methods. Microbiota and effects of short-chain fatty acids (SCFAs). The results showed that after feeding anthocyanins, the diversity of intestinal microorganisms in mice was significantly increased (p < 0.05), the ratio of Firmicutes/Bacteroidetes (F/B value) was significantly decreased (p < 0.05), the relative abundances of beneficial bacteria Lactobacillus, Bifidobacterium, Prevotella, and Akkermansia in the intestinal tract of mice were significantly increased (p < 0.05), and the relative abundance of pathogenic bacteria Escherichia-Shigella and Desulfovibrio decreased significantly (p < 0.05). Furthermore, anthocyanins significantly increased the content of short-chain fatty acids in the cecum of mice, among which the content of acetic acid, propionic acid, and butyric acid increased the most. Opuntia ficus-indica anthocyanins can change the microbial diversity and flora composition of the mouse gut and promote the production of short-chain fatty acids. The findings provide a theoretical basis for the use of Opuntia ficus-indica anthocyanins as dietary supplements to regulate human intestinal flora.

Sodium butyrate attenuated diet-induced obesity, insulin resistance and inflammation partly by promoting fat thermogenesis via intro-adipose sympathetic innervation

Emerging evidence suggests that butyrate, a short-chain fatty acid, may have beneficial effects on obesity and its associated metabolic comorbidities, but the related molecular mechanism is largely unknown. This study aims to investigate the role of butyrate in diet-induced obesity and metabolic disorders and the relevant regulatory mechanisms. Here, dietary supplementation with Sodium butyrate (NaB) was carried out in mice fed with a high-fat diet (HFD) or chow diet. At week 14, mice on HFD displayed an obese phenotype and down-regulated expression of thermogenic regulators including Ucp-1 and Pgc-1α in adipose tissue. Excitingly, NaB add-on treatment abolished these detrimental effects. Moreover, the obesity-induced insulin resistance, inflammation, fatty liver, and intestinal dysfunction were also attenuated by NaB administration. Mechanistically, NaB can promote fat thermogenesis via the increased local sympathetic innervation of adipose tissue, and blocking the β3-adrenergic signaling pathway by 6-hydroxydopamine abolished NaB-induced thermogenesis. Our study reveals a potential pharmacological target for NaB to combat obesity and metabolic disorders.

The gut microbiome and Alzheimer's disease: Complex and bidirectional interactions

Structural and functional alterations to the gut microbiome, referred to as gut dysbiosis, have emerged as potential key mediators of neurodegeneration and Alzheimer disease (AD) pathogenesis through the "gut -brain" axis. Emerging data from animal and clinical studies support an important role for gut dysbiosis in mediating neuroinflammation, central and peripheral immune dysregulation, abnormal brain protein aggregation, and impaired intestinal and brain barrier permeability, leading to neuronal loss and cognitive impairment. Gut dysbiosis has also been shown to directly influence various mechanisms involved in neuronal growth and repair, synaptic plasticity, and memory and learning functions. Aging and lifestyle factors including diet, exercise, sleep, and stress influence AD risk through gut dysbiosis. Furthermore, AD is associated with characteristic gut microbial signatures which offer value as potential markers of disease severity and progression. Together, these findings suggest the presence of a complex bidirectional relationship between AD and the gut microbiome and highlight the utility of gut modulation strategies as potential preventative or therapeutic strategies in AD. We here review the current literature regarding the role of the gut-brain axis in AD pathogenesis and its potential role as a future therapeutic target in AD treatment and/or prevention.

Central and peripheral regulations mediated by short-chain fatty acids on energy homeostasis

The human gut microbiota influences obesity, insulin resistance, and the subsequent development of type 2 diabetes (T2D). The gut microbiota digests and ferments nutrients resulting in the production of short-chain fatty acids (SCFAs), which generate various beneficial metabolic effects on energy and glucose homeostasis. However, their roles in the central nervous system (CNS)-mediated outputs on the metabolism have only been minimally studied. Here, we explore what is known and future directions that may be worth exploring in this emerging area. Specifically, we searched studies or data in English by using PubMed, Google Scholar, and the Human Metabolome Database. Studies were filtered by time from 1978 to March 2022. As a result, 195 studies, 53 reviews, 1 website, and 1 book were included. One hundred and sixty-five of 195 studies describe the production and metabolism of SCFAs or the effects of SCFAs on energy homeostasis, glucose balance, and mental diseases through the gut-brain axis or directly by a central pathway. Thirty of 195 studies show that inappropriate metabolism and excessive of SCFAs are metabolically detrimental. Most studies suggest that SCFAs exert beneficial metabolic effects by acting as the energy substrate in the TCA cycle, regulating the hormones related to satiety regulation and insulin secretion, and modulating immune cells and microglia. These functions have been linked with AMPK signaling, GPCRs-dependent pathways, and inhibition of histone deacetylases (HDACs). However, the studies focusing on the central effects of SCFAs are still limited. The mechanisms by which central SCFAs regulate appetite, energy expenditure, and blood glucose during different physiological conditions warrant further investigation.

Depression and antidepressant effects of ketamine and its metabolites: The pivotal role of gut microbiota

The discovery of the robust antidepressant actions of ketamine is regarded as one of the greatest advancements in depression treatment in the past 60 years. Recent findings have provided strong evidence for the presence of bidirectional communication networks between the gastrointestinal tract and the brain in depression. Moreover, increasing evidence supports the antidepressant role of ketamine in regulating the gut microbiome and microbiota-derived molecules; however, the mechanisms underpinning such effects are still ambiguous. This review summarizes the current understanding of the anti-depressant mechanisms of ketamine and its metabolites regarding the bidirectional regulation by microbiota-gut-brain axis. We review the relationship between gut microbiota and the antidepressant mechanisms of ketamine, and discuss the role of stress response, brain-derived neurotrophic factor (BDNF)-mediated neurogenesis, anti-inflammatory effect and neurotransmitters.

Remodeling of microbiota gut-brain axis using psychobiotics in depression

Depression is a multifaceted psychiatric disorder mainly orchestrated by dysfunction of neuroendocrine, neurochemical, immune, and metabolic systems. The interconnection of gut microbiota perturbation with the central nervous system disorders has been well documented in recent times. Indeed, alteration of commensal intestinal microflora is noted in several psychiatric disorders such as anxiety and depression, which are presumed to be routed through the enteric nervous system, autonomic nervous system, endocrine, and immune system. This review summarises the new mechanisms underlying the crosstalk between gut microbiota and brain involved in the management of depression. Depression-induced changes in the commensal intestinal microbiota are majorly linked with the disruption of gut integrity, hyperinflammation, and modulation of short-chain fatty acids, neurotransmitters, kynurenine metabolites, endocannabinoids, brain-derived neurotropic factors, hypothalamic-pituitary-adrenal axis, and gut peptides. The restoration of gut microbiota with prebiotics, probiotics, postbiotics, synbiotics, and fermented foods (psychobiotics) has gained a considerable attention for the management of depression. Recent evidence also propose the role of gut microbiota in the process of treatment-resistant depression. Thus, remodeling of the microbiota-gut-brain axis using psychobiotics appears to be a promising therapeutic approach for the reversal of psychiatric disorders, and it is imperative to decipher the underlying mechanisms for gut-brain crosstalk.

Role of Short Chain Fatty Acids in Epilepsy and Potential Benefits of Probiotics and Prebiotics: Targeting “Health” of Epileptic Patients

The WHO’s definition of health transcends the mere absence of disease, emphasizing physical, mental, and social well-being. As this perspective is being increasingly applied to the management of chronic diseases, research on gut microbiota (GM) is surging, with a focus on its potential for persistent and noninvasive dietary therapeutics. In patients with epilepsy (PWE), a chronic lack of seizure control along with often neglected psychiatric comorbidities greatly disrupt the quality of life. Evidence shows that GM-derived short chain fatty acids (SCFAs) may impact seizure susceptibility through modulating (1) excitatory/inhibitory neurotransmitters, (2) oxidative stress and neuroinflammation, and (3) psychosocial stress. These functions are also connected to shared pathologies of epilepsy and its two most common psychiatric consequences: depression and anxiety. As the enhancement of SCFA production is enabled through direct administration, as well as probiotics and prebiotics, related dietary treatments may exert antiseizure effects. This paper explores the potential roles of SCFAs in the context of seizure control and its mental comorbidities, while analyzing existing studies on the effects of pro/prebiotics on epilepsy. Based on currently available data, this study aims to interpret the role of SCFAs in epileptic treatment, extending beyond the absence of seizures to target the health of PWE.

Differences in cognition, short-chain fatty acids and related metabolites in pregnant versus non-pregnant women: a cross-sectional study

Background

Pregnancy induces cognitive reorganization which can lead to mental disorders. The aim of this study is to determine differences in cognitive scores, short-chain fatty acids (SCFAs) and related metabolites between pregnant and non-pregnant participants.

Methods

This cross-sectional study included 67 full-term pregnant women and 31 non-pregnant women. We compared scores of mental state and cognitive assessment tests, as well as serum concentrations of SCFAs, hormones, inflammatory factors, and neurotransmitters between these groups.

Results

Scores for information processing speed, immediate visual memory, motor response speed and accuracy, execution ability and verbal use ability in the pregnant group were lower than those in the non-pregnant group (p < 0.05 for all tests). Total serum SCFAs in the pregnant group were significantly lower than those in the non-pregnant group (P = 0.031). Among them, acetate and propionate were significantly decreased (P = 0.013 and 0.037, respectively) whereas butyrate was significantly increased (P = 0.035). Serum peptide YY, glucagon-like peptide-1, γ-aminobutyric acid, and dopamine showed no differences between the two groups. However, cortisol, adrenocorticotropic hormone, and acetylcholine were significantly increased in the pregnant group as compared with the non-pregnant group (P = 0.039, 0.016, and 0.012, respectively). Tumor necrosis factor-α was increased and interleukin-10 significantly decreased in the pregnant group (P = 0.045 and 0.019, respectively).

Conclusion

According to our study findings, cognitive reorganization in the third trimester of pregnancy showed that both the passive storage capacity of working memory and the executive function of online information processing were decreased to varying degrees. At the same time, the changes in total SCFAs, the proportions of SCFAs and related metabolites were also detected. These changes in the internal environment may be increasing the risk of perinatal mental illness.

Repeated testing modulates chronic unpredictable mild stress effects in male rats

Depression is a highly prevalent, debilitating mental disorder. Chronic unpredictable mild stress (CUMS) is the most widely applied model to study this affliction in rodents. While studies incorporating CUMS prior to an intervention often require long-lasting stress effects that persist after exposure is ceased, the longevity of these effects is rarely studied. Additionally, it is unclear whether behavioural assessments can be performed before and after interventions without repeated testing effects. In rats, we investigated CUMS effects on components of depressive-like behaviour both acutely after stress cessation and after a recovery period, as well as effects of repeated testing. We observed acute disruptions of the circadian locomotor rhythm and a reduced sucrose preference immediately after CUMS exposure. While circadian locomotor rhythm effects persisted up until four weeks after stress cessation, independently of repeated testing, sucrose preference effects did not. Interestingly, CUMS animals tested once after a recovery period of four weeks showed reduced anxiety-like behaviour in the open field and elevated plus maze compared to their control group and repeatedly-tested CUMS animals. These findings suggest that distinct CUMS-induced components of depressive-like behaviour are affected differentially by recovery time and repeated testing; these aspects should be considered carefully in future study designs.

Mechanistic Insights into the Link between Gut Dysbiosis and Major Depression: An Extensive Review

Depression is a highly common mental disorder, which is often multifactorial with sex, genetic, environmental, and/or psychological causes. Recent advancements in biomedical research have demonstrated a clear correlation between gut dysbiosis (GD) or gut microbial dysbiosis and the development of anxiety or depressive behaviors. The gut microbiome communicates with the brain through the neural, immune, and metabolic pathways, either directly (via vagal nerves) or indirectly (via gut- and microbial-derived metabolites as well as gut hormones and endocrine peptides, including peptide YY, pancreatic polypeptide, neuropeptide Y, cholecystokinin, corticotropin-releasing factor, glucagon-like peptide, oxytocin, and ghrelin). Maintaining healthy gut microbiota (GM) is now being recognized as important for brain health through the use of probiotics, prebiotics, synbiotics, fecal microbial transplantation (FMT), etc. A few approaches exert antidepressant effects via restoring GM and hypothalamus–pituitary–adrenal (HPA) axis functions. In this review, we have summarized the etiopathogenic link between gut dysbiosis and depression with preclinical and clinical evidence. In addition, we have collated information on the recent therapies and supplements, such as probiotics, prebiotics, short-chain fatty acids, and vitamin B12, omega-3 fatty acids, etc., which target the gut–brain axis (GBA) for the effective management of depressive behavior and anxiety.

Polysaccharides from the leaves of Polygonatum sibiricum Red. regulate the gut microbiota and affect the production of short-chain fatty acids in mice

Polysaccharides from the rhizome of Polygonatum sibiricum display a variety of biological activities, including the regulation of intestinal microbiota, but the polysaccharides from the leaves of P. sibiricum have not been studied extensively. Here, we extracted crude polysaccharides from the leaves of P. sibiricum and further separated and purified them to study the effects of P. sibiricum polysaccharides (PsPs) on intestinal microbes and short-chain fatty acids (SCFAs). The PsPs had a total sugar content of 97.48% and a monosaccharide composition comprising mannose, rhamnose, galacturonic acid, glucose, xylose, and arabinose, with molar ratios of 6.6:15.4:4.5:8.8:40.7:24, respectively. The effects of PsPs on intestinal microflora in mice were also studied, with 16S sequencing results showing an increase in the relative abundance of Firmicutes and a decrease in Bacteroidetes at the phylum level. The abundance of Lactobacillus increased, while those of Lachnospiraceae and Bacteroides reduced (at the genus level) by PsPs treatment. The composition of microbes changed. Levels of SCFAs in the PsPs group were significantly increased compared with control mice, including acetic acid, propionic acid, and butyric acid. These results suggest that PsPs can act as prebiotics, regulating the intestinal tract probiotics.

The Microbiota-Gut-Brain Axis and Epilepsy

Honoured as the second genome in humans, the gut microbiota is involved in a constellation of physiological and pathological processes, including those related to the central nervous system. The communication between the gut microbiota and the brain is realized by a complex bidirectional connection, known as the "microbiota-gut-brain axis", via neuroendocrine, immunological, and direct neural mechanisms. Recent studies indicate that gut dysfunction/dysbiosis is presumably involved in the pathogenesis of and susceptibility to epilepsy. In addition, the reconstruction of the intestinal microbiome through, for example, faecal microbiota transplantation, probiotic intervention, and a ketogenic diet, has exhibited beneficial effects on drug-resistant epilepsy. The purposes of this review are to provide a brief overview of the microbiota-gut-brain axis and to synthesize what is known about the involvement of the gut microbiota in the pathogenesis and treatment of epilepsy, to bring new insight into the pathophysiology of epilepsy and to present a preliminary discussion of novel therapeutic options for epilepsy based on the gut microbiota.

Dextran sulfate sodium-induced colitis in C57BL/6J mice increases their susceptibility to chronic unpredictable mild stress that induces depressive-like behavior

AIMS

In patients with colitis, the high comorbidity of depressive disorders is well-known, but the detailed mechanisms remain unresolved. In this study, we examined whether colitis induced by dextran sulfate sodium (DSS) increased the susceptibility to chronic unpredictable mild stress (CUMS) in C57BL/6J mice with resilience to CUMS.

MAIN METHODS

To induce experimental colitis and depressive-like behaviors, male 7-weeks old C57BL/6J mice were administered ad libitum 1% DSS solution for 11 days, and subjected to various mild stressors in a chronic, inevitable and unpredictable way according to a random schedule for 21 days, respectively.

KEY FINDINGS

In naïve mice exposed to CUMS, their immobility times in a forced swim (FS) test were almost equal to those in control mice. The DSS administration to naïve mice induced colitis without depressive-like behavior, and at 18 days after termination of the DSS administration, the colitis had recovered to control levels, while altered diversity and composition of bacterial genera such as Bacteroides spp., Alistipes spp., etc., were found in the gut microbiota. Exposure of mice with DSS-induced colitis to CUMS (DSS + CUMS) significantly increased the immobility times in the FS test. In the gut microbiota of DSS + CUMS mice, the alteration profile of the relative abundance of bacterial genera differed from in the DSS ones.

SIGNIFICANCE

These findings indicate that mice with colitis exhibit increased susceptibility to psychological stress, resulting in induction of depressive-like behavior, and this might be due, at least in part, to altered characteristics of the gut microbiota.

Effect of Coffee against MPTP-Induced Motor Deficits and Neurodegeneration in Mice Via Regulating Gut Microbiota

The mechanisms of coffee against Parkinson disease (PD) remained incompletely elucidated. Numerous studies suggested that gut microbiota played a crucial role in the pathogenesis of PD. Here, we explored the further mechanisms of coffee against PD via regulating gut microbiota. C57BL/6 mice were intraperitoneally injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to induce a PD mouse model, then treated with coffee for 4 consecutive weeks. Behavioral tests consisting of the pole test and beam-walking test were conducted to evaluate the motor function of mice. The levels of tyrosine hydroxylase (TH) and α-synuclein (α-syn) were assessed for dopaminergic neuronal loss. The levels of occludin, glial fibrillary acidic protein (GFAP), Bcl-2, Bax, cleaved caspase-3, and cytochrome c (Cyt c) were detected. Moreover, microbial components were measured by 16s rRNA sequencing. Our results showed that coffee significantly improved the motor deficits and TH neuron loss, and reduced the level of α-syn in the MPTP-induced mice. Moreover, coffee increased the level of BBB tight junction protein occludin and reduced the level of astrocyte activation marker GFAP in the MPTP-induced mice. Furthermore, coffee significantly decreased the levels of proapoptotic proteins, including Bax, cleaved caspase-3, and cytochrome c, while it increased the level of antiapoptotic protein Bcl-2, consequently preventing MPTP-induced apoptotic cascade. Moreover, coffee improved MPTP-induced gut microbiota dysbiosis. These findings suggested that the neuroprotective effects of coffee on PD were involved in the regulation of gut microbiota, which might provide a novel option to elucidate the effects of coffee on PD.

Alzheimer's disease and depression in the elderly: A trajectory linking gut microbiota and serotonin signaling

The occurrence of neuropsychiatric symptoms in the elderly is viewed as an early sign of subsequent cognitive deterioration and conversion from mild cognitive impairment to Alzheimer's disease. The prognosis in terms of both the severity and progression of clinical dementia is generally aggravated by the comorbidity of neuropsychiatric symptoms and decline in cognitive function. Undeniably, aging and in particular unhealthy aging, is a silent "engine of neuropathology" over which multiple changes take place, including drastic alterations of the gut microbial ecosystem. This narrative review evaluates the role of gut microbiota changes as a possible unifying concept through which the comorbidity of neuropsychiatric symptoms and Alzheimer's disease can be considered. However, since the heterogeneity of neuropsychiatric symptoms, it is improbable to describe the same type of alterations in the bacteria population observed in patients with Alzheimer's disease, as well as it is improbable that the variety of drugs used to treat neuropsychiatric symptoms might produce changes in gut bacterial diversity similar to that observed in the pathophysiology of Alzheimer's disease. Depression seems to be another very intriguing exception, as it is one of the most frequent neuropsychiatric symptoms in dementia and a mood disorder frequently associated with brain aging. Antidepressants (i.e., serotonin reuptake inhibitors) or tryptophan dietary supplementation have been shown to reduce Amyloid β-loading, reinstate microbial diversity and reduce the abundance of bacterial taxa dominant in depression and Alzheimer's disease. This review briefly examines this trajectory by discussing the dysfunction of gut microbiota composition, selected bacterial taxa, and alteration of tryptophan and serotonin metabolism/neurotransmission as overlapping in-common mechanisms involved with depression, Alzheimer's disease, and unhealthy aging.

Gut Microbiome, Inflammation, and Cerebrovascular Function: Link Between Obesity and Cognition

Obesity affects 13% of the adult population worldwide and this number is only expected to increase. Obesity is known to have a negative impact on cardiovascular and metabolic health, but it also impacts brain structure and function; it is associated with both gray and white matter integrity loss, as well as decreased cognitive function, including the domains of executive function, memory, inhibition, and language. Especially midlife obesity is associated with both cognitive impairment and an increased risk of developing dementia at later age. However, underlying mechanisms are not yet fully revealed. Here, we review recent literature (published between 2010 and March 2021) and discuss the effects of obesity on brain structure and cognition, with a main focus on the contributions of the gut microbiome, white adipose tissue (WAT), inflammation, and cerebrovascular function. Obesity-associated changes in gut microbiota composition may cause increased gut permeability and inflammation, therewith affecting cognitive function. Moreover, excess of WAT in obesity produces pro-inflammatory adipokines, leading to a low grade systemic peripheral inflammation, which is associated with decreased cognition. The blood-brain barrier also shows increased permeability, allowing among others, peripheral pro-inflammatory markers to access the brain, leading to neuroinflammation, especially in the hypothalamus, hippocampus and amygdala. Altogether, the interaction between the gut microbiota, WAT inflammation, and cerebrovascular integrity plays a significant role in the link between obesity and cognition. Future research should focus more on the interplay between gut microbiota, WAT, inflammation and cerebrovascular function to obtain a better understanding about the complex link between obesity and cognitive function in order to develop preventatives and personalized treatments.

Gut microbiota, innate immune pathways, and inflammatory control mechanisms in patients with major depressive disorder

Although alterations in the gut microbiota have been linked to the pathophysiology of major depressive disorder (MDD), including through effects on the immune response, our understanding is deficient about the straight connection patterns among microbiota and MDD in patients. Male and female MDD patients were recruited: 46 patients with a current active MDD (a-MDD) and 22 in remission or with only mild symptoms (r-MDD). Forty-five healthy controls (HC) were also recruited. Psychopathological states were assessed, and fecal and blood samples were collected. Results indicated that the inducible nitric oxide synthase expression was higher in MDD patients compared with HC and the oxidative stress levels were greater in the a-MDD group. Furthermore, the lipopolysaccharide (an indirect marker of bacterial translocation) was higher in a-MDD patients compared with the other groups. Fecal samples did not cluster according to the presence or the absence of MDD. There were bacterial genera whose relative abundance was altered in MDD: Bilophila (2-fold) and Alistipes (1.5-fold) were higher, while Anaerostipes (1.5-fold) and Dialister (15-fold) were lower in MDD patients compared with HC. Patients with a-MDD presented higher relative abundance of Alistipes and Anaerostipes (1.5-fold) and a complete depletion of Dialister compared with HC. Patients with r-MDD presented higher abundance of Bilophila (2.5-fold) compared with HC. Thus, the abundance of bacterial genera and some immune pathways, both with potential implications in the pathophysiology of depression, appear to be altered in MDD, with the most noticeable changes occurring in patients with the worse clinical condition, the a-MDD group.

Butyrate Rescues Oxidative Stress-Induced Transport Deficits of Tryptophan: Potential Implication in Affective or Gut-Brain Axis Disorders

INTRODUCTION

Butyrate is a short-chain fatty acid metabolite produced by microbiota in the colon. With its antioxidant properties, butyrate has also been shown to alter the neurological functions in affective disorder models, suggesting it as a key mediator in gut-brain interactions.

OBJECTIVE

Here, we evaluated the negative effect of oxidative stress on the transport of the serotonin precursor tryptophan as present in affective disorders. Butyrate was hypothesized to be able to rescue these deficits due to its antioxidative capacities and its effect on transmembrane transport of tryptophan. Human skin-derived fibroblasts were used as cellular models to address these objectives.

METHODS

Human fibroblasts were treated with hydrogen peroxide to induce oxidative stress. Stressed as well as control cells were treated with different concentrations of butyrate. Tryptophan (3H) was used as a tracer to measure the transport of tryptophan across the cell membranes (n = 6). Furthermore, gene expression profiles of different amino acid transporters were analyzed (n = 2).

RESULTS

As hypothesized,oxidative stress significantly decreased the uptake of tryptophan in fibroblast cells, while butyrate counteracted this effect. Oxidative stress did not alter the gene expression profile of amino acid transporters. However, treatment of stressed and control cells with different concentrations of butyrate differentially regulated the gene expression of large amino acid transporters 1 and 2, which are the major transporters of tryptophan.

CONCLUSIONS

Gut microbiota-derived butyrate may have therapeutic potential in affective disorders characterized by either aberrant serotonergic activity or neuroinflammation due to its role in rescuing the oxidative stress-induced perturbations of tryptophan transport.

Microbiome therapeutics: exploring the present scenario and challenges

Human gut-microbiome explorations have enriched our understanding of microbial colonization, maturation, and dysbiosis in health-and-disease subsets. The enormous metabolic potential of gut microbes and their role in the maintenance of human health is emerging, with new avenues to use them as therapeutic agents to overcome human disorders. Microbiome therapeutics are aimed at engineering the gut microbiome using additive, subtractive, or modulatory therapy with an application of native or engineered microbes, antibiotics, bacteriophages, and bacteriocins. This approach could overcome the limitation of conventional therapeutics by providing personalized, harmonized, reliable, and sustainable treatment. Its huge economic potential has been shown in the global therapeutics market. Despite the therapeutic and economical potential, microbiome therapeutics is still in the developing stage and is facing various technical and administrative issues that require research attention. This review aims to address the current knowledge and landscape of microbiome therapeutics, provides an overview of existing health-and-disease applications, and discusses the potential future directions of microbiome modulations.

Increased efficacy of combining prebiotic and postbiotic in mouse models relevant to autism and depression

The Microbiota-Gut-Brain axis (MGBA) is a bidirectional communication pathway between gut bacteria and the central nervous system (CNS) (including the intestine) that exerts a profound influence on neural development, neuroinflammation, activation of stress response and neurotransmission, in addition to modulating complex behaviours, such as sociability and anxiety. Several MGBA modulating approaches are possible, such as probiotic administration. A reasonable pharmacological approach would also be the contemporarily administration of both prebiotics and postbiotics. To test this hypothesis, we probed the effects of α-lactalbumin (ALAC; a prebiotic in the dose range of 125-500 mg/kg) and sodium butyrate (NaB; a postbiotic in the dose range of 30-300 mg/kg) alone and in combination. We used two animal behavioural models of idiopathic autism, (BTBR mice) and anxiety/depression (chronic unexpected mild stress - CUMS mice) respectively, using several standard behavioural paradigms such as Three-chamber social interaction test, Marble burying assay, depression-, anxiety- and memory-tests. In BTBR autistic mice, we found that both ALAC and NaB improve animal sociability, and memory in the passive avoidance (PA); drug combination was more effective in almost all tests also reducing immobility time in the forced swimming test (FST), which was not affected by single drug administration. Similarly, in the CUMS mice, single drug administration was effective in improving: 1) depressive-like behaviour in the FST and sucrose preference test; 2) memory and learning in the PA, novel object recognition and Morris water maze tests. Drug combination was again more effective than single drug administration in most cases; however, in the CUMS model, neither single drug or combination was effective in the elevated plus maze test for anxiety. Our results suggest that in both models, ALAC and NaB combination is more effective in improving some pathological aspects of animal behaviour than single administration and that the prebiotic/postbiotic approach should be considered a reasonable approach for the manipulation of the MGBA to improve efficacy.

The gut microbiota and microbial metabolites are associated with tail biting in pigs

Tail biting is an abnormal behaviour that causes stress, injury and pain. Given the critical role of the gut-microbiota in the development of behavioural problems in humans and animals, the aim of this study was to determine whether pigs that are biters, victims of tail biting or controls (nine matched sets of pigs) have a different microbiota composition, diversity and microbial metabolite profile. We collected faecal and blood samples from each individual for analysis. The gut microbiota composition was most different between the biter and the control pigs, with a higher relative abundance of Firmicutes in tail biter pigs than the controls. Furthermore, we detected differences in faecal and plasma short chain fatty acids (SCFA) profiles between the biter and victim pigs, suggesting physiological differences even though they are kept in the same pen. Thus, in addition to supporting an association between the gut microbiota and tail biting in pigs, this study also provides the first evidence of an association between tail biting and SCFA. Therefore, further research is needed to confirm these associations, to determine causality and to study how the SCFA profiles of an individual play a role in the development of tail biting behaviour.

Neuroprotective Potential of Non-Digestible Oligosaccharides: An Overview of Experimental Evidence

Non-digestible oligosaccharides (NDOs) from dietary sources have the potential as prebiotics for neuroprotection. Globally, diverse populations suffering from one or the other forms of neurodegenerative disorders are on the rise, and NDOs have the potential as supportive complementary therapeutic options against these oxidative-linked disorders. Elevated levels of free radicals cause oxidative damage to biological molecules like proteins, lipids, and nucleic acids associated with various neurological disorders. Therefore, investigating the therapeutic or prophylactic potential of prebiotic bioactive molecules such as NDOs as supplements for brain and cognitive health has merits. Few prebiotic NDOs have shown promise as persuasive therapeutic solutions to counter oxidative stress by neutralizing free radicals directly or indirectly. Furthermore, they are also known to modulate through brain-derived neurotrophic factors through direct and indirect mechanisms conferring neuroprotective and neuromodulating benefits. Specifically, NDOs such as fructo-oligosaccharides, xylo-oligosaccharides, isomalto-oligosaccharides, manno-oligosaccharides, pectic-oligosaccharides, and similar oligosaccharides positively influence the overall health via various mechanisms. Increasing evidence has suggested that the beneficial role of such prebiotic NDOs is not only directed towards the colon but also distal organs including the brain. Despite the wide applications of these classes of NDOs as health supplements, there is limited understanding of the possible role of these NDOs as neuroprotective therapeutics. This review provides important insights into prebiotic NDOs, their source, and production with special emphasis on existing direct and indirect evidence of their therapeutic potential in neuroprotection.

Potential gut-brain mechanisms behind adverse mental health outcomes of bariatric surgery

Bariatric surgery induces sustained weight loss and metabolic benefits via notable effects on the gut-brain axis that lead to alterations in the neuroendocrine regulation of appetite and glycaemia. However, in a subset of patients, bariatric surgery is associated with adverse effects on mental health, including increased risk of suicide or self-harm as well as the emergence of depression and substance use disorders. The contributing factors behind these adverse effects are not well understood. Accumulating evidence indicates that there are important links between gut-derived hormones, microbial and bile acid profiles, and disorders of mood and substance use, which warrant further exploration in the context of changes in gut-brain signalling after bariatric surgery. Understanding the basis of these adverse effects is essential in order to optimize the health and well-being of people undergoing treatment for obesity.

Gut Microbiota in Psychiatric Disorders: A Systematic Review

OBJECTIVE

This systematic review sought to comprehensively summarize gut microbiota research in psychiatric disorders following PRISMA guidelines.

METHODS

Literature searches were performed on databases using keywords involving gut microbiota and psychiatric disorders. Articles in English with human participants up until February 13, 2020, were reviewed. Risk of bias was assessed using a modified Newcastle-Ottawa Scale for microbiota studies.

RESULTS

Sixty-nine of 4231 identified studies met the inclusion criteria for extraction. In most studies, gut microbiota composition differed between individuals with psychiatric disorders and healthy controls; however, limited consistency was observed in the taxonomic profiles. At the genus level, the most replicated findings were higher abundance of Bifidobacterium and lower abundance of Roseburia and Faecalibacterium among patients with psychiatric disorders.

CONCLUSIONS

Gut bacteria that produce short-chain fatty acids, such as Roseburia and Faecalibacterium, could be less abundant in patients with psychiatric disorders, whereas commensal genera, for example, Bifidobacterium, might be more abundant compared with healthy controls. However, most included studies were hampered by methodological shortcomings including small sample size, unclear diagnostics, failure to address confounding factors, and inadequate bioinformatic processing, which might contribute to inconsistent results. Based on our findings, we provide recommendations to improve quality and comparability of future microbiota studies in psychiatry.

Gut microbiome in serious mental illnesses: A systematic review and critical evaluation

Schizophrenia and bipolar disorder (BD) are associated with debilitating psychiatric and cognitive dysfunction, worse health outcomes, and shorter life expectancies. The pathophysiological understanding of and therapeutic resources for these neuropsychiatric disorders are still limited. Humans harbor over 1000 unique bacterial species in our gut, which have been linked to both physical and mental/cognitive health. The gut microbiome is a novel and promising avenue to understand the attributes of psychiatric diseases and, potentially, to modify them. Building upon our previous work, this systematic review evaluates the most recent evidence of the gut microbiome in clinical populations with serious mental illness (SMI). Sixteen articles that met our selection criteria were reviewed, including cross-sectional cohort studies and longitudinal treatment trials. All studies reported alterations in the gut microbiome of patients with SMI compared to non-psychiatric comparison subjects (NCs), and beta-diversity was consistently reported to be different between schizophrenia and NCs. Ruminococcaceae and Faecalibacterium were relatively decreased in BD, and abundance of Ruminococcaceae was reported across several investigations of SMI to be associated with better clinical characteristics. Lactic acid bacteria were relatively more abundant in SMI and associated with worse clinical outcomes. There was very limited evidence for the efficacy of probiotic or prebiotic interventions in SMI. As microbiome research in psychiatry is still nascent, the extant literature has several limitations. We critically evaluate the current data, including experimental approaches. There is a need for more unified methodological standards in order to arrive at robust biological understanding of microbial contributions to SMI.

Diet and the Microbiota-Gut-Brain Axis: Sowing the Seeds of Good Mental Health

Over the past decade, the gut microbiota has emerged as a key component in regulating brain processes and behavior. Diet is one of the major factors involved in shaping the gut microbiota composition across the lifespan. However, whether and how diet can affect the brain via its effects on the microbiota is only now beginning to receive attention. Several mechanisms for gut-to-brain communication have been identified, including microbial metabolites, immune, neuronal, and metabolic pathways, some of which could be prone to dietary modulation. Animal studies investigating the potential of nutritional interventions on the microbiota-gut-brain axis have led to advancements in our understanding of the role of diet in this bidirectional communication. In this review, we summarize the current state of the literature triangulating diet, microbiota, and host behavior/brain processes and discuss potential underlying mechanisms. Additionally, determinants of the responsiveness to a dietary intervention and evidence for the microbiota as an underlying modulator of the effect of diet on brain health are outlined. In particular, we emphasize the understudied use of whole-dietary approaches in this endeavor and the need for greater evidence from clinical populations. While promising results are reported, additional data, specifically from clinical cohorts, are required to provide evidence-based recommendations for the development of microbiota-targeted, whole-dietary strategies to improve brain and mental health.

Tight junction proteins in the small intestine and prefrontal cortex of female rats exposed to stress of chronic isolation starting early in life

BACKGROUND

Simultaneous evaluation of barrier protein expression in the gut and the brain and their modulation under stress conditions have not been studied before now. As the permeability and function of the gut and blood-brain barrier are different and both express the MRs, we hypothesized that stress of post-weaning social isolation induces changes in tight junction protein expression in the gut which are (1) independent of changes in the brain and (2) are mediated via the mineralocorticoid receptor (MR).

METHODS

First, using UPLC-MS/MS we have successfully validated and selected a dose (1.2 mg/rat/day) of the MR antagonist spironolactone to treat female rats exposed to stress of chronic isolation or control conditions from postnatal day 21 for 9 weeks.

KEY RESULTS

Isolation stress caused an enhancement of gene expression of occludin and ZO-1 and a decrease in claudin-5 and MR expression in both the small intestine and prefrontal cortex. Isolation stress failed to decrease claudin-5 (small intestine) and MR (prefrontal cortex) gene expression in spironolactone-treated rats. MR blockade resulted in a decrease in claudin-15 expression in the small intestine. Anxiogenic effect of chronic stress, measured in elevated plus-maze test, was partly prevented by spironolactone treatment.

CONCLUSIONS & INFERENCES

Claudins, the main regulators of intestinal barrier permeability responded to chronic stress of social isolation and/or simultaneous blockade of MR in female rats by alterations independent of changes in the brain cortex. The results suggest a physiological role of MR in the control of claudin expression in the small intestine, but not in the brain cortex.

Roles and Mechanisms of Gut Microbiota in Patients With Alzheimer's Disease

Alzheimer’s disease (AD) is the most common age-related progressive neurodegenerative disease, characterized by a decline in cognitive function and neuronal loss, and is caused by several factors. Numerous clinical and experimental studies have suggested the involvement of gut microbiota dysbiosis in patients with AD. The altered gut microbiota can influence brain function and behavior through the microbiota–gut–brain axis via various pathways such as increased amyloid-β deposits and tau phosphorylation, neuroinflammation, metabolic dysfunctions, and chronic oxidative stress. With no current effective therapy to cure AD, gut microbiota modulation may be a promising therapeutic option to prevent or delay the onset of AD or counteract its progression. Our present review summarizes the alterations in the gut microbiota in patients with AD, the pathogenetic roles and mechanisms of gut microbiota in AD, and gut microbiota–targeted therapies for AD. Understanding the roles and mechanisms between gut microbiota and AD will help decipher the pathogenesis of AD from novel perspectives and shed light on novel therapeutic strategies for AD.