Gut hormones in microbiota-gut-brain cross-talk. Chin Med J (Engl). 2020;133:826-833. [PMID: 32132364 PMCID: PMC7147657 DOI: 10.1097/cm9.0000000000000706]

Regulation of the intestinal flora: A potential mechanism of natural medicines in the treatment of type 2 diabetes mellitus

Diabetes mellitus comprises a group of heterogeneous disorders, which are usually subdivided into type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). Both genetic and environmental factors have been implicated in the onset of diabetes. Type 1 diabetes primarily involves autoimmune insulin deficiency. In comparison, type 2 diabetes is contributed by the pathological state of insulin deficiency and insulin resistance. In recent years, significant differences were found in the abundance of microflora, intestinal barrier, and intestinal metabolites in diabetic subjects when compared to normal subjects. To further understand the relationship between diabetes mellitus and intestinal flora, this paper summarizes the interaction mechanism between diabetes mellitus and intestinal flora. Furthermore, the natural compounds found to treat diabetes through intestinal flora were classified and summarized. This review is expected to provide a valuable resource for the development of new diabetic drugs and the applications of natural compounds.

Roles of gastrointestinal polypeptides in intestinal barrier regulation

The intestinal barrier is a dynamic entity that is organized as a multilayer system and includes various intracellular and extracellular elements. The gut barrier functions in a coordinated manner to impede the passage of antigens, toxins, and microbiome components and simultaneously preserves the balanced development of the epithelial barrier and the immune system and the acquisition of tolerance to dietary antigens and intestinal pathogens.Numerous scientific studies have shown a significant association between gut barrier damage and gastrointestinal and extraintestinal diseases such as inflammatory bowel disease, celiac disease and hepatic fibrosis. Various internal and external factors regulate the intestinal barrier. Gastrointestinal peptides originate from enteroendocrine cells in the luminal digestive tract and are critical gut barrier regulators. Recent studies have demonstrated that gastrointestinal peptides have a therapeutic effect on digestive tract diseases, enhancing epithelial barrier activity and restoring the gut barrier. This review demonstrates the roles and mechanisms of gastrointestinal polypeptides, especially somatostatin (SST) and vasoactive intestinal peptide (VIP), in intestinal barrier regulation.

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.

The Impact of Probiotic Bacillus subtilis on Injurious Behavior in Laying Hens

Simple Summary

Injurious behavior prevention is a critical issue in the poultry industry due to increasing social stress, leading to negative effects on bird production and survivability, consequently enhancing gut microbiota dysbiosis and neuroinflammation via the microbiota–gut–brain axis. Probiotics have been used as potential therapeutic psychobiotics to treat or improve neuropsychiatric disorders or symptoms by boosting cognitive and behavioral processes and reducing stress reactions in humans and various experimental animals. The current data will first report that probiotic Bacillus subtilis reduces stress-induced injurious behavior in laying hens via regulating microbiota–gut–brain function with the potential to be an alternative to beak trimming during poultry egg production.

Abstract

Intestinal microbiota functions such as an endocrine organ to regulate host physiological homeostasis and behavioral exhibition in stress responses via regulating the gut–brain axis in humans and other mammals. In humans, stress-induced dysbiosis of the gut microbiota leads to intestinal permeability, subsequently affecting the clinical course of neuropsychiatric disorders, increasing the frequency of aggression and related violent behaviors. Probiotics, as direct-fed microorganism, have been used as dietary supplements or functional foods to target gut microbiota (microbiome) for the prevention or therapeutic treatment of mental diseases including social stress-induced psychiatric disorders such as depression, anxiety, impulsivity, and schizophrenia. Similar function of the probiotics may present in laying hens due to the intestinal microbiota having a similar function between avian and mammals. In laying hens, some management practices such as hens reared in conventional cages or at a high stocking density may cause stress, leading to injurious behaviors such as aggressive pecking, severe feather pecking, and cannibalism, which is a critical issue facing the poultry industry due to negative effects on hen health and welfare with devastating economic consequences. We discuss the current development of using probiotic Bacillus subtilis to prevent or reduce injurious behavior in laying hens.

The microbiota-gut-brain axis: pathways to better brain health. Perspectives on what we know, what we need to investigate and how to put knowledge into practice

The gut and brain link via various metabolic and signalling pathways, each with the potential to influence mental, brain and cognitive health. Over the past decade, the involvement of the gut microbiota in gut-brain communication has become the focus of increased scientific interest, establishing the microbiota-gut-brain axis as a field of research. There is a growing number of association studies exploring the gut microbiota's possible role in memory, learning, anxiety, stress, neurodevelopmental and neurodegenerative disorders. Consequently, attention is now turning to how the microbiota can become the target of nutritional and therapeutic strategies for improved brain health and well-being. However, while such strategies that target the gut microbiota to influence brain health and function are currently under development with varying levels of success, still very little is yet known about the triggers and mechanisms underlying the gut microbiota's apparent influence on cognitive or brain function and most evidence comes from pre-clinical studies rather than well controlled clinical trials/investigations. Filling the knowledge gaps requires establishing a standardised methodology for human studies, including strong guidance for specific focus areas of the microbiota-gut-brain axis, the need for more extensive biological sample analyses, and identification of relevant biomarkers. Other urgent requirements are new advanced models for in vitro and in vivo studies of relevant mechanisms, and a greater focus on omics technologies with supporting bioinformatics resources (training, tools) to efficiently translate study findings, as well as the identification of relevant targets in study populations. The key to building a validated evidence base rely on increasing knowledge sharing and multi-disciplinary collaborations, along with continued public-private funding support. This will allow microbiota-gut-brain axis research to move to its next phase so we can identify realistic opportunities to modulate the microbiota for better brain health.

What Is the Role of Gut Microbiota in Obesity Prevalence? A Few Words about Gut Microbiota and Its Association with Obesity and Related Diseases

Obesity is becoming the most dangerous lifestyle disease of our time, and its effects are already being observed in both developed and developing countries. The aim of this study was to investigate the impact of gut microbiota on the prevalence of obesity and associated morbidities, taking into consideration underlying molecular mechanisms. In addition to exploring the relationship between obesity and fecal microorganisms with their metabolites, the study also focused on the factors that would be able to stimulate growth and remodeling of microbiota. Assessed articles were carefully classified according to a predetermined criterion and were critically appraised and used as a basis for conclusions. The considered articles and reviews acknowledge that intestinal microbiota forms a multifunctional system that might significantly affect human homeostasis. It has been proved that alterations in the gut microbiota are found in obese and metabolically diseased patients. The imbalance of microbiome composition, such as changes in Bacteroidetes/Firmicutes ratio and presence of different species of genus Lactobacillus, might promote obesity and comorbidities (type 2 diabetes mellitus, hypertension, dyslipidemia, depression, obstructive sleep apnea). However, there are also studies that contradict this theory. Therefore, further well-designed studies are needed to improve the knowledge about the influence of microbiota, its metabolites, and probiotics on obesity.

Gut Bacteria and Neuropsychiatric Disorders

Bacteria in the gut microbiome plays an intrinsic part in immune activation, intestinal permeability, enteric reflex, and entero-endocrine signaling. Apart from physiological and structural changes brought about by gut bacteria on entero-epithelial cells and mucus layers, a vast number of signals generated in the gastro-intestinal tract (GIT) reaches the brain via the vagus nerve. Research on the gut–brain axis (GBA) has mostly been devoted to digestive functions and satiety. Less papers have been published on the role gut microbiota play in mood, cognitive behavior and neuropsychiatric disorders such as autism, depression and schizophrenia. Whether we will be able to fully decipher the connection between gut microbiota and mental health is debatable, especially since the gut microbiome is diverse, everchanging and highly responsive to external stimuli. Nevertheless, the more we discover about the gut microbiome and the more we learn about the GBA, the greater the chance of developing novel therapeutics, probiotics and psychobiotics to treat gastro-intestinal disorders such as inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), but also improve cognitive functions and prevent or treat mental disorders. In this review we focus on the influence gut bacteria and their metabolites have on neuropsychiatric disorders.

Alterations in Metabolome and Microbiome Associated with an Early Stress Stage in Male Wistar Rats: A Multi-Omics Approach

Stress disorders have dramatically increased in recent decades becoming the most prevalent psychiatric disorder in the United States and Europe. However, the diagnosis of stress disorders is currently based on symptom checklist and psychological questionnaires, thus making the identification of candidate biomarkers necessary to gain better insights into this pathology and its related metabolic alterations. Regarding the identification of potential biomarkers, omic profiling and metabolic footprint arise as promising approaches to recognize early biochemical changes in such disease and provide opportunities for the development of integrative candidate biomarkers. Here, we studied plasma and urine metabolites together with metagenomics in a 3 days Chronic Unpredictable Mild Stress (3d CUMS) animal approach that aims to focus on the early stress period of a well-established depression model. The multi-omics integration showed a profile composed by a signature of eight plasma metabolites, six urine metabolites and five microbes. Specifically, threonic acid, malic acid, alpha-ketoglutarate, succinic acid and cholesterol were proposed as key metabolites that could serve as key potential biomarkers in plasma metabolome of early stages of stress. Such findings targeted the threonic acid metabolism and the tricarboxylic acid (TCA) cycle as important pathways in early stress. Additionally, an increase in opportunistic microbes as virus of the Herpesvirales was observed in the microbiota as an effect of the primary stress stages. Our results provide an experimental biochemical characterization of the early stage of CUMS accompanied by a subsequent omic profiling and a metabolic footprinting that provide potential candidate biomarkers.

Lactobacillus rhamnosus Strain LRH05 Intervention Ameliorated Body Weight Gain and Adipose Inflammation via Modulating the Gut Microbiota in High-Fat Diet-Induced Obese Mice

SCOPE

This study aims to investigate the underlying mechanism of a specific probiotic strain on suppression of adipogenesis and inflammatory response in white adipose tissue (WAT) of high-fat diet (HFD)-fed mice.

METHODS AND RESULTS

Eight strains are screened in vitro for candidates of potential probiotics. Lactobacillus rhamnosus LRH05 (LRH05) and Lactobacillus reuteri LR47 (LR47) are screened out with lower triglyceride expression in vitro. The mice are fed a control diet (CD), HFD, or HFD supplemented with a dose of LRH05 or LR47 at 10⁹ CFU per mouse per day for 10 weeks (n = 8), respectively. The results demonstrate that LRH05, but not LR47, significantly reduce body weight gain and the weight of WAT, as well as improve hepatic steatosis and glucose intolerance. LRH05 regulates the Mogat1, Igf-1, Mcp-1, and F4/80 mRNA expression and decreases macrophage infiltration in WAT. LRH05 shows an increase in butyric and propionic acid-producing bacteria, including Lachnoclostridium, Romboutsia, and Fusobacterium that is coincident with the increased fecal propionic acid and butyric acid levels.

CONCLUSION

LRH05 shows a strain-specific effect on ameliorating the pro-inflammatory process by reducing inflammatory macrophage infiltration and the expression of inflammation-related genes in mice. Thus, LRH05 can be considered a potential probiotic strain to prevent obesity.

Gut Hormones as Potential Therapeutic Targets or Biomarkers of Response in Depression: The Case of Motilin

Recent research has identified the gut–brain axis as a key mechanistic pathway and potential therapeutic target in depression. In this paper, the potential role of gut hormones as potential treatments or predictors of response in depression is examined, with specific reference to the peptide hormone motilin. This possibility is explored through two methods: (1) a conceptual review of the possible links between motilin and depression, including evidence from animal and human research as well as clinical trials, based on a literature search of three scientific databases, and (2) an analysis of the relationship between a functional polymorphism (rs2281820) of the motilin (MLN) gene and cross-national variations in the prevalence of depression based on allele frequency data after correction for potential confounders. It was observed that (1) there are several plausible mechanisms, including interactions with diet, monoamine, and neuroendocrine pathways, to suggest that motilin may be relevant to the pathophysiology and treatment of depression, and (2) there was a significant correlation between rs2281820 allele frequencies and the prevalence of depression after correcting for multiple confounding factors. These results suggest that further evaluation of the utility of motilin and related gut peptides as markers of antidepressant response is required and that these molecular pathways represent potential future mechanisms for antidepressant drug development.

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.

Going with the grain: Fiber, cognition, and the microbiota-gut-brain-axis

Healthy dietary intake has been acknowledged for decades as one of the main contributors to health. More recently, the field of nutritional psychiatry has progressed our understanding regarding the importance of nutrition in supporting mental health and cognitive function. Thereby, individual nutrients, including omega-3 fatty acids and polyphenols, have been recognized to be key drivers in this relationship. With the progress in appreciating the influence of dietary fiber on health, increasingly research is focusing on deciphering its role in brain processes. However, while the importance of dietary fiber in gastrointestinal and metabolic health is well established, leading to the development of associated health claims, the evidence is not conclusive enough to support similar claims regarding cognitive function. Albeit the increasing knowledge of the impact of dietary fiber on mental health, only a few human studies have begun to shed light onto the underexplored connection between dietary fiber and cognition. Moreover, the microbiota-gut-brain axis has emerged as a key conduit for the effects of nutrition on the brain, especially fibers, that are acted on by specific bacteria to produce a variety of health-promoting metabolites. These metabolites (including short chain fatty acids) as well as the vagus nerve, the immune system, gut hormones, or the kynurenine pathway have been proposed as underlying mechanisms of the microbiota-brain crosstalk. In this minireview, we summarize the evidence available from human studies on the association between dietary fiber intake and cognitive function. We provide an overview of potential underlying mechanisms and discuss remaining questions that need to be answered in future studies. While this field is moving at a fast pace and holds promise for future important discoveries, especially data from human cohorts are required to further our understanding and drive the development of public health recommendations regarding dietary fiber in brain health.

Sleep disorders related to nutrition and digestive diseases: a neglected clinical condition

Sleep disturbances often result from inappropriate lifestyles, incorrect dietary habits, and/or digestive diseases. This clinical condition, however, has not been sufficiently explored in this area. Several studies have linked the circadian timing system to the physiology of metabolism control mechanisms, energy balance regulation, and nutrition. Sleep disturbances supposedly trigger digestive disorders or conversely represent specific clinical manifestation of gastrointestinal (GI) diseases. Poor sleep may worsen the symptoms of GI disorders, affecting the quality of life. Conversely, short sleep may influence dietary choices, as well as meal timing, and the circadian system drives temporal changes in metabolic patterns. Emerging evidence suggests that patients with inappropriate dietary habits and chronic digestive disorders often sleep less and show lower sleep efficiency, compared with healthy individuals. Sleep disturbances may thus represent a primary symptom of digestive diseases. Further controlled trials are needed to fully understand the relationship between sleep disturbances, dietary habits, and GI disorders. It may be also anticipated that the evaluation of sleep quality may prove useful to drive positive interventions and improve the quality of life in a proportion of patients. This review summarizes data linking sleep disorders with diet and a series of disease including gastro-esophageal reflux disease, peptic disease, functional gastrointestinal disorders, inflammatory bowel diseases, gut microbiota alterations, liver and pancreatic diseases, and obesity. The evidence supporting the complex interplay between sleep dysfunction, nutrition, and digestive diseases is discussed.

Does Gut-Microbiome Interaction Protect against Obesity and Obesity-Associated Metabolic Disorders?

More research has recently focused on the role of the gut microbiota in the development or course of numerous diseases, including non-communicable diseases. As obesity remains prevalent, the question arises as to what microbial changes are associated with increased obesity prevalence and what kind of prevention and treatment approaches it could provide. Moreover, the influence of the gut-brain axis on obesity is also crucial, since it can affect metabolism and food intake. The quantitative and qualitative changes in the microbiota composition are called dysbiosis; however, in view of the current knowledge, it is difficult to conclude which microbial imbalances are adverse or beneficial. Increased numbers of pathological microorganisms were observed among patients with obesity and comorbidities associated with it, such as diabetes, cardiovascular disease, and insulin resistance. Our review provides current knowledge regarding changes in the intestinal microbiota associated with obesity and obesity-associated comorbidities. Nevertheless, given that dietary patterns and nutrients are two of the factors affecting the intestinal microbiota, we also discuss the role of different dietary approaches, vitamins, and minerals in the shaping of the intestinal microbiota.

Effects of microbiota transplantation and the role of the vagus nerve in gut-brain axis in animals subjected to chronic mild stress

INTRODUCTION

Currently, there is a growing emphasis on the study of intestinal signaling as an influencer in the pathophysiology of neuropsychiatric diseases, and the gut-brain axis is recognized as a communication route through endocrine, immune, and neural pathways (vagus nerve). Studies have shown that diets that modify the microbiota can reduce stress-related behavior and hypothalamic-pituitary-adrenal axis activation. Investigators have used fecal microbiota transplantation (FMT) approaches to demonstrate that stress-related microbiota composition plays a causal role in behavioral changes.

AIM

We hypothesized that FMT may present immunomodulatory, biochemical, endocrine, cognitive, and behavioral benefits in stress situations and that these changes can be mediated via the vagus nerve.

METHODS

Animals were subjected to a chronic mild stress (CMS) protocol. In one experiment, animals were divided into five groups: control, control + FMT, control + FMT + CMS, CMS + saline, and CMS + FMT. The animals received FMT, and behavioral tests were performed; cytokine and carbonyl levels were measured. In a second experiment, animals were submitted to vagotomy and divided into two groups: CMS + FMT and CMS + vagotomy + FMT.

RESULTS

Animals submitted to the CMS protocol or that received FMT from stressed animals showed behavioral changes and changes in neuroactive substances (increased IL-6 and TNF-α levels and carbonyl proteins). The FMT of healthy donors improved the analyzed parameters. In addition, vagotomy influenced beneficial FMT results, confirmed by behavioral testing and protein carbonyl in the hippocampus.

CONCLUSION

Manipulation of the microbiota reversed the behavioral and biochemical changes induced by the CMS protocol, and the vagus nerve influenced the gut-brain axis response.

Awareness and attitude of fecal microbiota transplantation through transendoscopic enteral tubing among inflammatory bowel disease patients

BACKGROUND

Transendoscopic enteral tubing (TET) has been used in China as a novel delivery route for fecal microbiota transplantation (FMT) into the whole colon with a high degree of patient satisfaction among adults.

AIM

To explore the recognition and attitudes of FMT through TET in patients with inflammatory bowel disease (IBD).

METHODS

An anonymous questionnaire, evaluating their awareness and attitudes toward FMT and TET was distributed among IBD patients in two provinces of Eastern and Southwestern China. Question formats included single-choice questions, multiple-choice questions and sorting questions. Patients who had not undergone FMT were mainly investigated for their cognition and acceptance of FMT and TET. Patients who had experience of FMT, the way they underwent FMT and acceptance of TET were the main interest. Then all the patients were asked whether they would recommend FMT and TET. This study also analyzed the preference of FMT delivery in IBD patients and the patient-related factors associated with it.

RESULTS

A total of 620 eligible questionnaires were included in the analysis. The survey showed that 44.6% (228/511) of patients did not know that FMT is a therapeutic option in IBD, and 80.6% (412/511) of them did not know the concept of TET. More than half (63.2%, 323/511) of the participants stated that they would agree to undergo FMT through TET. Of the patients who underwent FMT via TET [62.4% (68/109)], the majority [95.6% (65/68)] of them were satisfied with TET. Patients who had undergone FMT and TET were more likely to recommend FMT than patients who had not (94.5% vs 86.3%, P = 0.018 and 98.5% vs 87.8%, P = 0.017). Patients' choice for the delivery way of FMT would be affected by the type of disease and whether the patient had the experience of FMT. When compared to patients without experience of FMT, Crohn's disease and ulcerative colitis patients who had experience of FMT preferred mid-gut TET (P < 0.001) and colonic TET (P < 0.001), respectively.

CONCLUSION

Patients' experience of FMT through TET lead them to maintain a positive attitude towards FMT. The present findings highlighted the significance of patient education on FMT and TET.

Potential contribution of the gut microbiota to hypoglycemia after gastric bypass surgery

Obesity has become a global health problem. Lifestyle modification and medical treatment only appear to yield short-term weight loss. Roux-en-Y gastric bypass (RYGB) is the most popular bariatric procedure, and it sustains weight reduction and results in the remission of obesity-associated comorbidities for obese individuals. However, patients who undergo this surgery may develop hypoglycemia. To date, the diagnosis is challenging and the prevalence of post-RYGB hypoglycemia (PRH) is unclear. RYGB alters the anatomy of the upper gastrointestinal tract and has a combined effect of caloric intake restriction and nutrient malabsorption. Nevertheless, the physiologic changes after RYGB are complex. Although hyperinsulinemia, incretin effects, dysfunction of β-cells and α-cells, and some other factors have been widely investigated and are reported to be possible mediators of PRH, the pathogenesis is still not completely understood. In light of the important role of the gut microbiome in metabolism, we hypothesized that the gut microbiome might also be a critical link between RYGB and hypoglycemia. In this review, we mainly highlight the current possible factors predisposing individuals to PRH, particularly related to the gut microbiota, which may yield significant insights into the intestinal regulation of glucose metabolic homeostasis and provide novel clues to improve the treatment of type 2 diabetes mellitus.

The HPA Axis under Stress and Aging: Individual Vulnerability is Associated with Behavioral Patterns and Exposure Time

With aging, incidence of severe stress-related diseases increases. However, mechanisms, underlying individual vulnerability to stress and age-related diseases are not clear. The goal of this review is to analyze finding from the recent literature on age-related characteristics of the hypothalamic-pituitary-adrenal (HPA) axis associated with stress reactivity in animals that show behavioral signs of anxiety and depression under mild stress, and in human patients with anxiety disorders and depression with emphasis on the impact of the circadian rhythm and the negative feedback mechanisms involved in the stress response. One can conclude that HPA axis reaction to psycho-emotional stress, at least acute stress, increases in the aged individuals with anxiety and depression behavior. Elevated stress reactivity is associated with disruption of the circadian rhythm and the mineralocorticoid receptor-mediated glucocorticoid negative feedback. The disordered function of the HPA axis in individuals with anxiety and depression behavior can contribute to aging-related pathology.