Neurotransmitter and Intestinal Interactions: Focus on the Microbiota-Gut-Brain Axis in Irritable Bowel Syndrome

Innovations in the diagnosis, treatment, and management of disorders of gut-brain interaction (DGBI)

INTRODUCTION

Functional dyspepsia (FD) and irritable bowel syndrome (IBS) are the most prevalent disorders of gut-brain interaction (DGBI), frequently overlapping and associated with complex pathophysiological mechanisms. Increasing evidence implicates gut microbiota alterations in driving symptoms via immune activation, altered motility, gut vascular barrier and gut-brain axis disruption.

AREAS COVERED

This review explores the role of gut microbiota in FD and IBS pathogenesis and symptomatology. A comprehensive literature search was conducted using PubMed, EMBASE, and Google Scholar databases, including studies published between January 2013 and March 2025. Particular focus is given to microbiota-targeted therapies such as prebiotics, probiotics, synbiotics, postbiotics, and fecal microbiota transplantation (FMT). The review also discusses multidimensional treatment strategies combining dietary and lifestyle modification, cognitive-behavioral therapy, and pharmacological neuromodulation. Recent advances in diagnostic methods, including capsule-based microbiota sampling and digital tools for remote psychogastroenterology care, are highlighted.

EXPERT OPINION

Despite scientific progress, current DGBI management remains insufficiently personalized. Future approaches should integrate individualized microbiota profiling with targeted interventions and utilize innovative diagnostic and digital health technologies to enhance clinical outcomes in FD and IBS.

Multi-omics technology reveals the changes in gut microbiota to stimulate aromatic amino acid metabolism in children with allergic rhinitis and constipation

Background

Comorbid allergic rhinitis and constipation (ARFC) in children are associated with gut microbiota (GM) dysbiosis and metabolic perturbations; however, the underlying mechanistic interplay remains unclear.

Objective

This multi-omics study aimed to characterize GM and fecal metabolomic signatures in preschool ARFC children and elucidate microbial-metabolite interactions driving dual symptomatology.

Methods

Fecal samples from 16 ARFC and 15 healthy control (HC) children underwent high-throughput absolute quantification 16S rRNA sequencing and untargeted metabolomics. Differential taxa and metabolites were identified via LEfSe and OPLS-DA (VIP > 1, false discovery rate (FDR) q < 0.05). Microbial-metabolite networks were reconstructed using genome-scale metabolic modeling and KEGG pathway analysis.

Results

The ARFC group exhibited distinct β-diversity (P = 0.031), marked by elevated Hungatella, Tyzzerella, and Bifidobacterium longum (P < 0.05). Metabolomics revealed upregulated aromatic amino acids (AAAs), neurotransmitters, and bile acids (FDR q < 0.05), with enrichment in tryptophan/tyrosine pathways (P < 0.01). Bioinformatic modeling linked Hungatella to tryptophan hydroxylase (EC:1.14.16.4), driving serotonin synthesis, and Tyzzerella to indoleamine 2,3-dioxygenase (EC:1.13.11.52), promoting kynurenine production. Bifidobacterium longum correlated with phenylalanine hydroxylase (EC:1.14.16.1), enhancing phenylalanine derivatives. A combined GM-metabolite diagnostic model demonstrated robust accuracy (AUC = 0.8).

Conclusion

GM dysbiosis in ARFC children activates AAA metabolism, generating neuroactive and pro-inflammatory metabolites that may exacerbate allergic and gastrointestinal symptoms. These findings highlight microbial-metabolite axes as therapeutic targets. Study limitations include cohort size and lack of disease-specific controls, necessitating validation in expanded cohorts.

Mechanisms and implications of histamine-induced reactions and complications

Histamine, classified as a biogenic amine, plays a crucial role in both pro-inflammatory and immune regulatory processes, thereby establishing itself as a key mediator in allergic diseases and immune responses. This review provides an exhaustive analysis of the structure, function, and regulation of histamine, with particular emphasis on its interaction with four receptor subtypes: histamine H1 receptor (H1R), histamine H2 receptor (H2R), histamine H3 receptor (H3R), and histamine H4 receptor (H4R), all of which are instrumental in mediating a variety of physiological processes, including neurotransmitter release, modulation of immune responses, and gastric acid secretion. The review explores intracellular signaling pathways mediated by the activation of these receptors, highlighting the complex cascades involved in immediate- and delayed-type hypersensitivity reactions. It also examines the broad spectrum of histamine-induced complications, focusing on their effects on the gastrointestinal, cardiovascular, respiratory, and central nervous systems, and emphasizes histamine's potential to cause vascular dysfunction and other pathological changes. Furthermore, the role of histamine in inflammation and immune responses is explored, particularly in the context of allergic diseases such as asthma, allergic rhinitis, and atopic dermatitis. The review also covers pharmacological interventions targeting histamine receptors, including the use of antihistamines and mast cell stabilizers, which are critical for the treatment of symptoms and the inhibition of the progression of histamine-related conditions. Finally, the review addresses emerging research and future directions, identifying potential areas for innovation and improved therapeutic strategies. This comprehensive overview not only deepens understanding of histamine's multifaceted roles in health and disease, but also underscores the importance of developing advanced diagnostic tools and targeted treatments for histamine-associated disorders.

Small intestine bacterial overgrowth (SIBO) breath test does not predict symptom severity in gut-brain interaction disorders: role of anxiety, depression, and inflammatory biomarkers

BACKGROUND

The high prevalence of disorders of the gut-brain interaction (DGBI), the availability of breath tests for the diagnosis of small intestine bacterial overgrowth (SIBO) together with some confusion about the concept of SIBO are leading to an increase in the number of SIBO diagnoses.

OBJECTIVE

We aimed to analyze the factors associated with the severity of gastrointestinal symptoms in patients undergoing a SIBO breath test.

METHODS

A cross-sectional observational study including 70 patients who underwent a SIBO test with lactitol and completed questionnaires including the ROME IV criteria for Irritable Bowel Syndrome (IBS), the Irritable Bowel Syndrome Severity Score (IBSSS), and the HAD anxiety and depression scales. Additionally, blood levels of histamine, citrulline, ghrelin, Intestinal-Fatty Acid Binding Protein (I-FABP) and Transient Receptor Potential Cation Channel Subfamily V, Member 1 (TRPV-1) were measured.

RESULTS

The mean age was 45±16 years and 70% were women. Abdominal pain and/or abdominal distension were present in 85% of patients. 44% met IBS Rome IV criteria. IBSSS total score had a correlation with age (-0.354, p<0.001), HAD-A (0.391, p<0.001) and HAD-D (0.409, p<0.001) scores, and histamine levels (0.279, p=0.019). Abdominal pain correlated with levels of histamine (0.320, p<0.05; 0.282, p<0.05) and ghrelin (0.252, p<0.05, 0.347, p<0.05), while abdominal distension correlated with I-FABP levels (0.314, p<0.05). The SIBO test was positive in 75% but did not correlate with symptom severity.

CONCLUSION

We hereby unveiled some factors associated with the severity of abdominal pain and distension such as age, auto-perceived anxiety and depression and some biomarkers but not SIBO test result.

Gut Microbiota: A New Challenge in Mood Disorder Research

The gut microbiome has emerged as a novel and intriguing focus in mood disorder research. Emerging evidence demonstrates the significant role of the gut microbiome in influencing mental health, suggesting a bidirectional communication between the gut and the brain. This review examines the latest findings on the gut-microbiota-brain axis and elucidates how alterations in gut microbiota composition can influence this axis, leading to changes in brain function and behavior. Although dietary interventions, prebiotics, probiotics, and fecal microbiota transplantation have yielded encouraging results, significant advances are needed to establish next-generation approaches that precisely target the neurobiological mechanisms of mood disorders. Future research must focus on developing personalized treatments, facilitated by innovative therapies and technological progress, which account for individual variables such as age, sex, drug history, and lifestyle. Highlighting the potential therapeutic implications of targeting the gut microbiota, this review emphasizes the importance of integrating microbiota research into psychiatric studies to develop more effective and personalized treatment strategies for mood disorders.

The Gut-Brain Axis in Irritable Bowel Syndrome: Implementing the Role of Microbiota and Neuroimmune Interaction in Personalized Prevention-A Narrative Review

Background and Purpose

Irritable bowel syndrome (IBS) is a disorder characterized by microbiota-neuroimmune interaction resulting in disturbance to the gut-brain axis (GBA). The purpose of this review is to garner an overview of the different pathophysiological mechanisms indicated in the development of IBS and the associated sequalae on gut microbiota alongside its role in the GBA. Moreover, we aim to provide an insight into the possibility of utilizing personalized medicine when managing said affected populations.

Methods

A comprehensive review was performed of the relevant literature pertaining to the current state of GBA alteration implicated in IBS, comprising microbiota-neuroimmune interaction alongside disturbance and activation, respectively. Different search databases were utilized, including PubMed/MEDLINE and ScienceDirect.

Results

The review demonstrated the most evident etiologies of IBS being the imbalance of microbiota and the alteration to the GBA. Furthermore, the interrelation between microbiota and neuroimmunity was discussed. Promising avenues for IBS prevention and management are offered through emerging research on the pathophysiological mechanisms indicated in IBS-associated GBA alteration. This entails a role for the involved interactions between microbiota modification and neuroimmunity activation.

Conclusion

Promising prospects for symptom prevention and management are signaled by the possibility of personalized therapy specifically designed to address the GBA dysfunction indicated in IBS. Policymakers and developers should encourage further study and allocate available resources to aid researchers in the implementation and identification of novel preventive therapeutics. Furthermore, physicians should advocate and integrate the use of personalized medical approaches of IBS to help ensure a better quality of life.

Association of rotating shift work with incident irritable bowel syndrome: a large population-based prospective cohort study

Objectives

Limited epidemiological study has examined the association between rotating shift work and risk of irritable bowel syndrome (IBS). This study aimed to investigate the association between shift work and risk of IBS and explore the potential mediating factors for the association.

Methods

A total of 268,290 participants from the UK Biobank were included. Cox proportional hazards model was used to examine the associations between shift work and the incidence of IBS. The mediation analyses were performed to investigate the mediating effects.

Results

Participants engaged in always/usually shift work showed a significantly increased risk of developing IBS (HR: 1.12, 95% CI: 1.03-1.23). Joint analysis indicated that, participants with both always/usually shift work and inadequate sleep duration had a 54% increased risk of IBS (HR: 1.54, 95% CI: 1.35-1.82) compared to those with adequate sleep duration and never/rarely shift work; while participants with both always/usually shift work and insomnia-always had a 65% increased risk of IBS (HR: 1.65, 95% CI: 1.43-1.90) compared to those with never/rarely shift work and never/sometimes insomnia. Mediation analysis revealed that sleep quality and anxiety/depression partially mediated the relationship between shift work and IBS incidence, contributing 16.1% (6.8-25.4%) and 3.6% (0.4-6.8%) of the mediation effect, respectively.

Conclusion

This study found that participants with always/usually shiftwork status had significantly increased risk of IBS, and this association may partially be mediated by anxiety/depression and sleep quality. Moreover, inadequate sleep duration and usually insomnia may intensify the effect of rotating shift work on the risk of incident IBS.

Effects of Lactococcus cremoris PS133 in 5-Hydroxytryptophan-Induced Irritable Bowel Syndrome Model Rats

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder marked by abdominal pain and irregular bowel habits. Recently, more and more evidence supports gut microbiota imbalance in IBS and highlights the potential of probiotics in restoring gut health and reducing symptoms. In this study, we explored the effects of Lactococcus cremoris PS133 (PS133) on an IBS-like condition in rats triggered by 5-hydroxytryptophan (5-HTP), a serotonin precursor. Eight-week-old Sprague Dawley rats received either PS133 or saline for 14 days, followed by 5-HTP to induce IBS-like symptoms. Colorectal distension tests showed that PS133 reduced visceral hypersensitivity. PS133 also protected intestinal mucin against 5-HTP-induced degradation, as seen in alcian blue staining, and increased the levels of tight junction proteins (occludin and zonula occludens-1) in the colon, indicating improved gut barrier integrity. Additionally, PS133 normalized the levels of substance P (a neuropeptide) in the spinal cord and altered 5-hydroxyindoleacetic acid (a serotonin metabolite) in the brain. Gut microbiota analysis revealed PS133 regulated specific bacterial groups, including [Eubacterium]_coprostanoligenes_group and Lactococcus. Overall, PS133 improved gut function, reduced IBS-like symptoms, and modulated gut microbiota, neurotransmitters, and intestinal barrier health in this IBS model.

Psycho-gastroenterological profile of an Italian population of children with disorders of gut-brain interaction: A case-control study

BACKGROUND

Disorders of gut-brain interaction (DGBI) are common, but knowledge about their physiopathology is still poor, nor valid tools have been used to evaluate them in childhood.

AIM

To develop a psycho-gastroenterological questionnaire (PGQ) to assess the psycho-gastroenterological profile and social characteristics of a pediatric population with and without DGBI.

METHODS

One hundred and nineteen Italian children (age 11-18) were included: 28 outpatient patients with DGBI (Rome IV criteria) and 91 healthy controls. They filled the PGQ, faces pain scale revised (FPS-R), Bristol stool chart, gastrointestinal symptoms rating scale, state-trait anxiety inventory, Toronto alexithymia scale 20, perceived self-efficacy in the management of negative emotions and expression of positive emotions (APEN-G, APEP-G), irritable bowel syndrome-quality of life questionnaire, school performances, tobacco use, early life events, degree of digitalization.

RESULTS

Compared to controls, patients had more medical examinations (35% of them went to the doctor more than five times), a higher school performance (23% vs 13%, P < 0.05), didn't use tobacco (never vs 16%, P < 0.05), had early life events (28% vs 1% P < 0.05) and a higher percentage of pain classified as 4 in the FPS-R during the examination (14% vs 7%, P < 0.05).

CONCLUSION

Pediatric outpatients with DGBI had a higher prevalence of early life events, a lower quality of life, more medical examinations rising health care costs, lower anxiety levels.

Periodic Changes in the Gut Microbiome in Women with the Mixed Type of Irritable Bowel Syndrome

Background: The mixed type of irritable bowel syndrome (IBS-M) is characterized by recurrent constipation and diarrhea. The cause of the variability of these symptoms is not sufficiently understood. The aim of this study was to perform metagenomic and metabolic assessment of the gut microbiome in constipation and diarrheal period of IBS-M. Methods: This study included 30 women, aged 28-47 years old, with the symptoms which aligned with those of IBS-M, according to the Rome IV Criteria. Results: In both periods of the disease, the dysbiosis index (DI), the Shannon diversity index (SDI), the hydrogen-methane and ammonia breath tests, as well as the selected bacterial metabolites (-p-hydroxyphenyl acetic acid (HPA), 3-indoxyl sulfate (Indican, 3-IS)), and hippuric acid (A) in urine, were determined. The dysbiosis index (DI) in the period of constipation was 3.73 ± 0.90 points, and in the diarrheal period it did not change significantly 3.93 ± 0.75 points (p > 0.05). During the diarrheal period, the diversity of bacteria increases from 2.16 ± 0.59 to 2.74 ± 0.50 points on the Shannon dietary index (p < 0.001). The gut microbiome profile also changed, especially during the diarrheal period where an abundance of Bifidobacterium spp. and Lactobacillus spp. decreased significantly. In addition, during this period, the levels of hydrogen and ammonia in breath air increased, while the methane level decreased. The differences also concern the results of urinary metabolites, especially related to hippuric acid and indican. During the diarrheal period, the levels of hydrogen and ammonia ions increased, while the methane level decreased. The differences also concern the results of urinary metabolites, especially related to hippuric acid and indican. Conclusions: In patients with IBS-M, periodic changes in the profile and metabolism of the gut microbiome occur, which coexist with recurrent symptoms such as constipation and diarrhea.

Irritable bowel syndrome remains a complex disorder of gut-brain interaction: Too many actors on stage

The recent study published in the World Journal of Gastroenterology examines the interplay among the neuroendocrine axis, gut microbiota, inflammatory markers, and gastrointestinal symptoms in irritable bowel syndrome (IBS). By integrating all these factors into a single study, this approach reflects the modern concept of functional gastrointestinal disorders as disorders of the gut-brain interaction to be approached in a multiparametric manner, also incorporating non-gastroenterological elements and extending evaluations to parameters related to the neuroendocrine axis. This invited letter to the editor summarizes the main results of the aforementioned study and highlights its multiparametric approach, including variables not strictly gastroenterological, in the study of IBS, and discusses its strengths and limitations.

Multifluid Metabolomics Identifies Novel Biomarkers for Irritable Bowel Syndrome

Background/Objectives: Irritable bowel syndrome (IBS) is a complex disorder affecting 10% of the global population, but the underlying mechanisms remain poorly understood. By integrating multifluid metabolomics, we aimed to identify metabolite markers of IBS in a large population-based cohort. Methods: We included individuals from TwinsUK with and without IBS, ascertained using the Rome III criteria, and analysed serum (232 cases, 1707 controls), urine (185 cases, 1341 controls), and stool (186 cases, 1284 controls) metabolites (Metabolon Inc.). Results: After adjusting for covariates, and multiple testing, 44 unique metabolites (25 novel) were associated with IBS, including lipids, amino acids, and xenobiotics. Androsterone sulphate, a sulfated steroid hormone precursor, was associated with lower odds of IBS in both urine (0.69 [95% confidence interval = 0.56-0.85], p = 2.34 × 10-4) and serum (0.75 [0.63-0.90], p = 1.54 × 10-3. Moreover, suberate (C8-DC) was associated with higher odds of IBS in serum (1.36 [1.15-1.61]; p = 1.84 × 10-4) and lower odds of IBS in stool (0.76 [0.63-0.91]; p = 2.30 × 10-3). On the contrary, 32 metabolites appeared to be fluid-specific, including indole, 13-HODE + 9-HODE, pterin, bilirubin (E,Z or Z,Z), and urolithin. The remaining 10 metabolites were associated with IBS in one fluid with suggestive evidence (p < 0.05) in another fluid. Finally, we identified androgenic signalling, dicarboxylates, haemoglobin, and porphyrin metabolism to be significantly over-represented in individuals with IBS compared to controls. Conclusions: Our results highlight the utility of a multi-fluid approach in IBS research, revealing distinct metabolic signatures across biofluids.

Gut-brain axis mediated by intestinal content microbiota was associated with Zhishi Daozhi decoction on constipation

Background

Constipation is a common digestive system disorder, which is closely related to the intestinal flora. Zhishi Daozhi decoction (ZDD) is a traditional Chinese medicine prescription used to treat constipation caused by indigestion. This study is to evaluate the efficacy of ZDD in treating constipation and to elucidate the underlying mechanism.

Methods

In this study, Kunming mice were administered a high-protein diet (HFHPD) and loperamide hydrochloride injections to induce constipation. The mice then received varying doses (2.4, 4.7, and 9.4 mg/kg) of ZDD for seven days. Following the sampling process, we measured fecal microbial activity. The levels of 5-hydroxytryptamine (5-HT), vasoactive intestinal peptide (VIP), and aquaporin-3 (AQP3) were quantified using enzyme-linked immunosorbent assay. Changes in the gut microbiota were evaluated through 16S rRNA gene sequencing. Additionally, we investigated the correlation between specific microbiota features and the levels of 5-HT, VIP, and AQP3.

Results

The fecal surface of the mice in the model group (CMM) was rough and dry. The stool of mice in the low-dose ZDD group (CLD), medium-dose ZDD group (CMD), and high-dose ZDD group (CHD) exhibited a smoother texture, closely resembling that of the normal group (CNM). 5-HT levels in the CMM group were significantly lower than in the CNM, CLD, and CHD. VIP levels in the CMD were lower than in the other four groups, and AQP3 levels in CMM showed a decreasing trend. The fecal microbial activity of the CMM group was significantly higher than that of the other groups. Diversity analysis indicated that CMD and CHD treatments were more effective in restoring the intestinal microbiota structure. Potential pathogenic bacteria, including Clostridium, Aerococcus, Jeotgalicoccus, and Staphylococcus were enriched in CMM. In contrast, beneficial bacteria such as Faecalibacterium, Bacillaceae, and Bacillus were more prevalent in the CLD, CMD, and CHD. Correlation analysis revealed that Streptococcus and Enterococcus were positively correlated with VIP, while Succinivibrio showed a negative correlation with 5-HT.

Conclusions

Constipation induced by HFHPD and loperamide hydrochloride disrupts the structure of the intestinal microbiota. ZDD appears to alleviate constipation, potentially through mechanisms linked to the brain-gut axis and its interaction with the intestinal microbiota. Among the treatment groups, the medium dose of ZDD demonstrated the most effective results.

Relationship Between High Frequency Component of Heart Rate Variability and Delta EEG Power During Sleep in Women With Irritable Bowel Syndrome Compared to Healthy Women

OBJECTIVE

To explore the relationship between the high frequency (HF) heart rate variability (HRV) and electroencephalogram (EEG) delta band power in women with irritable bowel syndrome (IBS) versus healthy control women.

MATERIALS AND METHODS

Twenty women with IBS and twenty healthy controls were studied over three consecutive nights using polysomnography in a sleep laboratory. To avoid the first night effect, only second-night data were analyzed. Power spectral analysis was applied to HRV and EEG recordings. The linear system coherence/phase analysis assessed the relationship between normalized HF power of HRV and normalized delta band power of EEG during the first four NREM-REM sleep cycles.

RESULTS

Women with IBS exhibited a significantly higher percentage of NREM sleep, higher normalized HF, lower normalized low frequency (LF) and decreased LF/HF ratio of HRV in the first four NREM-REM sleep cycles compared to controls. Additionally, their normalized delta band power was significantly lower in these sleep cycles and over the whole night. The phase shift between HF and delta band power was significantly longer in the IBS group. While the coherence between normalized HF and normalized delta band power was lower in the IBS group, the difference was not statistically significant.

CONCLUSIONS

The coherence/phase analysis showed a dysregulated interaction between autonomic and central nervous systems in women with IBS, manifested by increased lag time between cardiac and EEG delta band power compared to healthy controls. Whether this dysregulation contributes to the pathophysiology of IBS remains to be determined.

D, Rajendran P, N H, Singh S A. Exploring the potential of probiotics in Alzheimer's disease and gut dysbiosis

Alzheimer's disease is a fatal neurodegenerative disorder that causes memory loss and cognitive decline in older people. There is increasing evidence suggesting that gut microbiota alteration is a cause of Alzheimer's disease pathogenesis. This review explores the link between gut dysbiosis and the development of Alzheimer's disease contributing to neuroinflammation, amyloid β accumulation, and cognitive decline. We examine the recent studies that illustrate the gut-brain axis (GBA) as a bidirectional communication between the gut and brain and how its alteration can influence neurological health. Furthermore, we discuss the potential of probiotic supplementation as a management approach to restore gut microbiota balance, and ultimately improve cognitive function in AD patients. Based on current research findings, this review aims to provide insights into the promising role of probiotics in Alzheimer's disease management and the need for further investigation into microbiota-targeted interventions.

Taurine Supplementation Alleviates Blood Pressure via Gut-Brain Communication in Spontaneously Hypertensive Rats

OBJECTS

Taurine exhibits protective effects in the context of cardiovascular pathophysiology. A range of evidence suggests that hypertension activates inflammatory responses and oxidative stress in the paraventricular nucleus (PVN), elevating the arterial tone and sympathetic activity, while it induces gut-brain axis dysfunction in the context of hypertension. However, the mechanism underlying taurine's anti-hypertensive effects via the gut-brain axis remains unclear.

METHOD

Male spontaneously hypertensive rats (SHRs) were administered 3% taurine in their drinking water for eight weeks, with their arterial pressure measured weekly. Molecular techniques were employed to investigate taurine's effects on the hypertensive gut and PVN. Additionally, 16S rRNA gene sequencing was used to analyze the gut microbiota composition, and untargeted metabolomics was applied to assess the fecal metabolites following taurine supplementation.

RESULTS

Taurine supplementation not only reduced the blood pressure, sympathetic activity, and inflammatory and oxidative stress in the PVN but also improved the cardiac pathology and microbiota composition while alleviating gut inflammation in hypertensive rats. The untargeted metabolite analysis indicated that the primary effect of the taurine intervention in SHRs was exerted on tryptophan metabolism. The levels of serum metabolites such as kynurenine, L-tryptophan, serotonin (5-HT), and 5-hydroxyindole-3-acetic acid (5-HIAA) were altered in hypertensive rats following taurine treatment.

CONCLUSIONS

Taurine supplementation restored the microbiota balance, strengthened the mucosal barrier, reduced intestinal inflammation, and stimulated tryptophan metabolism. The metabolites derived from the gut microbiota likely crossed the brain barrier and reached the paraventricular nucleus, thereby reducing the inflammatory responses and oxidative stress in the PVN via gut-brain communication, leading to decreased sympathetic nerve activity and blood pressure in the studied hypertensive rats.

The emerging roles of neuroactive components produced by gut microbiota

BACKGROUND

As a multifunctional ecosystem, the human digestive system contains a complex network of microorganisms, collectively known as gut microbiota. This consortium composed of more than 1013 microorganisms and Firmicutes and Bacteroidetes are the dominant microbes. Gut microbiota is increasingly recognized for its critical role in physiological processes beyond digestion. Gut microbiota participates in a symbiotic relationship with the host and takes advantage of intestinal nutrients and mutually participates in the digestion of complex carbohydrates and maintaining intestinal functions.

METHOD AND RESULT

We reviewed the neuroactive components produced by gut microbiota. Interestingly, microbiota plays a crucial role in regulating the activity of the intestinal lymphatic system, regulation of the intestinal epithelial barrier, and maintaining the tolerance to food immunostimulating molecules. The gut-brain axis is a two-way communication pathway that links the gut microbiota to the central nervous system (CNS) and importantly is involved in neurodevelopment, cognition, emotion and synaptic transmissions. The connections between gut microbiota and CNS are via endocrine system, immune system and vagus nerve.

CONCLUSION

The gut microbiota produces common neurotransmitters and neuromodulators of the nervous system. These compounds play a role in neuronal functions, immune system regulation, gastrointestinal homeostasis, permeability of the blood brain barrier and other physiological processes. This review investigates the essential aspects of the neurotransmitters and neuromodulators produced by gut microbiota and their implications in health and disease.

Early-Life Stress Induced by Neonatal Maternal Separation Leads to Intestinal 5-HT Accumulation and Causes Intestinal Dysfunction

Background

The early childhood period is a critical development stage, and experiencing stress during this time may increase the risk of gastrointestinal disorders, including irritable bowel syndrome (IBS). Neonatal maternal separation (NMS) in rodent models has been shown to cause bowel dysfunctions similar to IBS, and 5-HT is considered to be a key regulator regulating intestinal function, but the precise underlying mechanisms remain unclear.

Results

We established a maternal separation stress mouse model to simulate early-life stress, exploring the expression patterns of 5-HT under chronic stress and its mechanisms affecting gut function. We observed a significant increase in 5-HT expression due to NMS, leading to disruptions in intestinal structure and function. However, inhibiting 5-HT reversed these effects, suggesting its potential as a therapeutic target. Furthermore, our research revealed that excess 5-HT in mice with early life stress increased intestinal neural network density and promoted excitatory motor neuron expression. Mechanistically, 5-HT activated the Wnt signaling pathway through the 5-HT4 receptor, promoting neurogenesis within the intestinal nervous system.

Conclusion

These findings shed light on the intricate changes induced by early life stress in the intestines, confirming the regulatory role of 5-HT in the enteric nervous system and providing potential insights for the development of novel therapies for gastrointestinal disorders.

The Role of the Gut Microbiota in Individuals with Irritable Bowel Syndrome: A Scoping Review

Irritable bowel syndrome (IBS) represents the most prevalent disorder of brain-gut interaction, affecting approximately 10% of the global population. The objective of this study was to examine the mechanisms by which the gut microbiota contributes to the development of IBS. To this end, a review of articles that examined the gut microbiota of IBS patients was conducted. A search was conducted using PubMed and J-STAGE for articles published over the past five years that relate to the gut microbiota in patients with IBS. Individuals diagnosed with IBS display a reduction in alpha diversity and a decline in butyrate-producing bacteria, which collectively indicate a state of dysbiosis within their gut microbiota. Butyrate plays a dual role in the body, acting as a source of nutrition for the intestinal epithelium while also regulating the expression of dopamine transporters and D2 receptors in the central nervous system through epigenetic mechanisms. These characteristics may be linked to dysfunction of the central dopamine D2 pathway and play a role in the formation of various symptoms in IBS.

Gut microbiota and irritable bowel syndrome: status and prospect

Irritable bowel syndrome (IBS) is a very common gastrointestinal disease that, although not as aggressive as tumors, affects patients' quality of life in different ways. The cause of IBS is still unclear, but more and more studies have shown that the characteristics of the gut microbiota, such as diversity, abundance, and composition, are altered in patients with IBS, compared to the healthy population, which confirms that the gut microbiota plays a crucial role in the development of IBS. This paper aims to identify the commonalities by reviewing a large body of literature. Changes in the characteristics of gut microbiota in patients with different types of IBS are discussed, relevant mechanisms are described, and the treatment modalities of gut microbiota in IBS are summarized. Although there are more clinical trials that have made good progress, more standardized, more generalized, larger-scale, multi-omics clinical studies are what is missing. Overall, gut microbiota plays a crucial role in the development of IBS, and there is even more potential for treating IBS by modulating gut microbiota.

The Association of the Oral Microbiota with Cognitive Functioning in Adolescence

Background: A growing body of research supports the role of the microbial communities residing in the digestive system in the host's cognitive functioning. Most of these studies have been focused on the gut microbiome and its association with clinical phenotypes in middle-aged and older adults. There is an insufficiency of population-based research exploring the association of normative cognitive functioning with the microbiome particularly with the oral microbiota. Methods: In this study, using metagenomics and metabolomics, we characterized the salivary microbiome diversity in a sample of 51 males of Hispanic and African American origin aged 12-18 years and explored the associations between the microbiome and the youths' cognitive performance captured with the Kaufman Assessment Battery for Children II (KABC-II). Results: Several bacterial species of the oral microbiota and related metabolic pathways were associated with cognitive function. In particular, we found negative associations between indicators of general intelligence and the relative abundance of Bacteroidetes and Lachnospiraceae and positive associations with Bifidobacteriaceae and Prevotella histicola sp. Among metabolic pathways, the super pathways related to bacterial cell division and GABA metabolism were linked to cognitive function. Conclusions: The results of our work are consistent with the literature reporting on the association between microbiota and cognitive function and support further population work to elucidate the potential for a healthy oral microbiome to improve cognitive health.

Correlation between the neuroendocrine axis, microbial species, inflammatory response, and gastrointestinal symptoms in irritable bowel syndrome

BACKGROUND

This study examines the complex relationships among the neuroendocrine axis, gut microbiome, inflammatory responses, and gastrointestinal symptoms in patients with irritable bowel syndrome (IBS). The findings provide new insights into the pathophysiology of IBS and suggest potential therapeutic targets for improving patient outcomes.

AIM

To investigate the interactions between the neuroendocrine axis, gut microbiome, inflammation, and gastrointestinal symptoms in patients with IBS.

METHODS

Patients diagnosed with IBS between January 2022 and January 2023 were selected for the study. Healthy individuals undergoing routine check-ups during the same period served as the control group. Data were collected on neuroendocrine hormone levels, gut microbiome profiles, inflammatory biomarkers, and gastrointestinal symptomatology to analyze their interrelations and their potential roles in IBS pathogenesis.

RESULTS

IBS patients exhibited significant dysregulation of the neuroendocrine axis, with altered levels of cortisol, serotonin, and neuropeptides compared to healthy controls. The gut microbiome of IBS patients showed reduced diversity and specific alterations in bacterial genera, including Bifidobacterium, Lactobacillus, and Faecalibacterium, which were associated with neuroendocrine disturbances. Additionally, elevated levels of inflammatory markers, such as C-reactive protein, interleukin-6, and tumor necrosis factor-α, were observed and correlated with the severity of gastrointestinal symptoms like abdominal pain, bloating, and altered bowel habits.

CONCLUSION

The findings suggest that targeting the neuroendocrine axis, gut microbiome, and inflammatory pathways may offer novel therapeutic strategies to alleviate symptoms and improve the quality of life in IBS patients.

Assessment of Urinary Dopamine and Serotonin Metabolites in Relation to Dysbiosis Indicators in Patients with Functional Constipation

BACKGROUND

The causes of functional constipation (FC) in adults are unclear, but changes in the gut microbiome may play an important role. The present study aimed to assess the relationship between urinary metabolites of dopamine and serotonin and some dysbiosis indicators in patients with FC. The study included 40 healthy women and 40 women with FC aged 21-46 years.

METHODS

Urinary levels of homovanillic acid (HVA), 5-hydoxyindoleacetic acid (5-HIAA), p-hydroxyphenylacetic acid (PhAc), and 3-indoxyl sulfate, as final metabolites of dopamine, serotonin, and indole pathway, respectively, were determined using the LC-Ms/Ms method. However, hydrogen-methane and ammonia breath tests were performed. The GA-map Dysbiosis Test was used to identify and characterize the dysbiosis index (DI).

RESULTS

In patients with FC, the DI was significantly higher than in the control group: 4.05 ± 0.53 vs. 1.52 ± 0.81 points (p < 0.001), but the number of many types of bacteria varied among individuals. The levels of HVA were higher, while 5-HIAA levels were lower in patients. Moreover, the HVA/5-HIAA ratio had a positive correlation with DI as well as with the severity of symptoms.

CONCLUSIONS

In patients with functional constipation, the balance in dopamine and serotonin secretion is disturbed, which is associated with changes in the gut microbiome.

Shared Pathophysiology of Inflammatory Bowel Disease and Psoriasis: Unraveling the Connection

Inflammatory bowel disease (IBD) and psoriasis are both chronic autoimmune diseases with a unique set of characteristics. Interestingly, both conditions share considerable overlap in their pathophysiological mechanisms and immune dysregulation. Epidemiological studies validate the relationship by showing a greater prevalence of co-occurrence of the two disorders. At the genetic level, there is a confirmation of a link between shared susceptibility loci and DNA polymorphism, particularly interleukin-23 receptor (IL23R), interleukin-12 subunit beta (IL12B), tumor necrosis factor (ligand) superfamily member 15 (TNFSF15), and signal transducer and activator of transcription 3 (STAT3). In addition, epigenetic factors have a role in genetic predisposition in the development and progression through processes such as DNA methylation and histone modification adding another layer of genetic susceptibility. The relationship between psoriasis and IBD is emphasized by a comparable immunopathogenesis, which involves delicate relationships between the innate and adaptive immune responses. The primary interest is on the T-helper 17 (Th17) cell pathway and the cytokines interleukin-17 (IL-17), interleukin-23 (IL-23), and tumor necrosis factor-alpha (TNF-α). Consequently, both disorders exhibit chronic inflammation and tissue restructuring, resulting from similar cellular and molecular processes. The presence of overlapping pathophysiology highlights the significance of implementing integrated management strategies and employing multidisciplinary techniques for both diagnosis and therapy. Hence, understanding the mutual processes might facilitate the advancement of precise biologic treatments that aim at these commonly shared inflammatory pathways.

The GABAergic pathway from anterior cingulate cortex to lateral hypothalamus area regulates irritable bowel syndrome in mice and its underlying mechanism

Irritable bowel syndrome (IBS), which is characterized by chronic abdominal pain, has a high global prevalence. The anterior cingulate cortex (ACC), which is a pivotal region involved in pain processing, should be further investigated regarding its role in the regulation of visceral sensitivity and mental disorders. A C57BL/6J mouse model for IBS was established using chronic acute combining stress (CACS). IBS-like symptoms were assessed using behavioral tests, intestinal motility measurements, and abdominal withdrawal reflex scores. Fluoro-Gold retrograde tracing and immunohistochemistry techniques were employed to investigate the projection of ACC gamma-aminobutyric acid-producing (GABAergic) neurons to the lateral hypothalamus area (LHA). Chemogenetic approaches enabled the selective activation or inhibition of the ACC-LHA GABAergic pathway. Enzyme-linked immunosorbent assay (ELISA) and western blot analyses were conducted to determine the expression of histamine, 5-hydroxytryptamine (5-HT), and transient receptor potential vanilloid 4 (TRPV4). Our findings suggest that CACS induced IBS-like symptoms in mice. The GABA type A receptors (GABAAR) within LHA played a regulatory role in modulating IBS-like symptoms. The chemogenetic activation of ACC-LHA GABAergic neurons elicited anxiety-like behaviors, intestinal dysfunction, and visceral hypersensitivity in normal mice; however, these effects were effectively reversed by the administration of the GABAAR antagonist Bicuculline. Conversely, the chemogenetic inhibition of ACC-LHA GABAergic neurons alleviated anxiety-like behaviors, intestinal dysfunction, and visceral hypersensitivity in the mouse model for IBS. These results highlight the crucial involvement of the ACC-LHA GABAergic pathway in modulating anxiety-like behaviors, intestinal motility alterations, and visceral hypersensitivity, suggesting a potential therapeutic strategy for alleviating IBS-like symptoms.

Macrophages and Gut Barrier Function: Guardians of Gastrointestinal Health in Post-Inflammatory and Post-Infection Responses

The gut barrier is essential for protection against pathogens and maintaining homeostasis. Macrophages are key players in the immune system, are indispensable for intestinal health, and contribute to immune defense and repair mechanisms. Understanding the multifaceted roles of macrophages can provide critical insights into maintaining and restoring gastrointestinal (GI) health. This review explores the essential role of macrophages in maintaining the gut barrier function and their contribution to post-inflammatory and post-infectious responses in the gut. Macrophages significantly contribute to gut barrier integrity through epithelial repair, immune modulation, and interactions with gut microbiota. They demonstrate active plasticity by switching phenotypes to resolve inflammation, facilitate tissue repair, and regulate microbial populations following an infection or inflammation. In addition, tissue-resident (M2) and infiltration (M1) macrophages convert to each other in gut problems such as IBS and IBD via major signaling pathways mediated by NF-κB, JAK/STAT, PI3K/AKT, MAPK, Toll-like receptors, and specific microRNAs such as miR-155, miR-29, miR-146a, and miR-199, which may be good targets for new therapeutic approaches. Future research should focus on elucidating the detailed molecular mechanisms and developing personalized therapeutic approaches to fully harness the potential of macrophages to maintain and restore intestinal permeability and gut health.

Emerging role of gut microbiota in autoimmune diseases

Accumulating studies have indicated that the gut microbiota plays a pivotal role in the onset of autoimmune diseases by engaging in complex interactions with the host. This review aims to provide a comprehensive overview of the existing literatures concerning the relationship between the gut microbiota and autoimmune diseases, shedding light on the complex interplay between the gut microbiota, the host and the immune system. Furthermore, we aim to summarize the impacts and potential mechanisms that underlie the interactions between the gut microbiota and the host in autoimmune diseases, primarily focusing on systemic lupus erythematosus, rheumatoid arthritis, Sjögren's syndrome, type 1 diabetes mellitus, ulcerative colitis and psoriasis. The present review will emphasize the clinical significance and potential applications of interventions based on the gut microbiota as innovative adjunctive therapies for autoimmune diseases.

Gut microbiota and intestinal immunity-A crosstalk in irritable bowel syndrome

Irritable bowel syndrome (IBS), one of the most prevalent functional gastrointestinal disorders, is characterized by recurrent abdominal pain and abnormal defecation habits, resulting in a severe healthcare burden worldwide. The pathophysiological mechanisms of IBS are multi-factorially involved, including food antigens, visceral hypersensitivity reactions, and the brain-gut axis. Numerous studies have found that gut microbiota and intestinal mucosal immunity play an important role in the development of IBS in crosstalk with multiple mechanisms. Therefore, based on existing evidence, this paper elaborates that the damage and activation of intestinal mucosal immunity and the disturbance of gut microbiota are closely related to the progression of IBS. Combined with the application prospect, it also provides references for further in-depth exploration and clinical practice.

The Profound Influence of Gut Microbiome and Extracellular Vesicles on Animal Health and Disease

The animal gut microbiota, comprising a diverse array of microorganisms, plays a pivotal role in shaping host health and physiology. This review explores the intricate dynamics of the gut microbiome in animals, focusing on its composition, function, and impact on host-microbe interactions. The composition of the intestinal microbiota in animals is influenced by the host ecology, including factors such as temperature, pH, oxygen levels, and nutrient availability, as well as genetic makeup, diet, habitat, stressors, and husbandry practices. Dysbiosis can lead to various gastrointestinal and immune-related issues in animals, impacting overall health and productivity. Extracellular vesicles (EVs), particularly exosomes derived from gut microbiota, play a crucial role in intercellular communication, influencing host health by transporting bioactive molecules across barriers like the intestinal and brain barriers. Dysregulation of the gut-brain axis has implications for various disorders in animals, highlighting the potential role of microbiota-derived EVs in disease progression. Therapeutic approaches to modulate gut microbiota, such as probiotics, prebiotics, microbial transplants, and phage therapy, offer promising strategies for enhancing animal health and performance. Studies investigating the effects of phage therapy on gut microbiota composition have shown promising results, with potential implications for improving animal health and food safety in poultry production systems. Understanding the complex interactions between host ecology, gut microbiota, and EVs provides valuable insights into the mechanisms underlying host-microbe interactions and their impact on animal health and productivity. Further research in this field is essential for developing effective therapeutic interventions and management strategies to promote gut health and overall well-being in animals.

Fecal microbiota transplantation for treatment of irritable bowel syndrome: Current advances and future perspectives

Irritable bowel syndrome (IBS) is a kind of functional gastroin-testinal disorder, characterized by recurrent abdominal pain and altered bowel habits. IBS adversely affects the quality of life of patients for the lack of effective treatment. The etiology of IBS remains poorly known. Previous studies suggested a possible role of gut dysbiosis in IBS pathogenesis. Fecal microbiota transplantation (FMT), which aims to reverse the gut dysbiosis, is a promising strategy in IBS management. In this review, we summarize the role of the gut microbiota in IBS pathogenesis from different aspects. We also review recent studies on efficacy evaluation of FMT in IBS. Besides, we discuss factors affecting the efficacy of FMT, hoping to provide a reference for future IBS treatment strategies targeting the gut microbiota.

Modulation of GABA by sodium butyrate ameliorates hypothalamic inflammation in experimental model of PCOS

Polycystic ovarian syndrome (PCOS) is a known endocrine disorder that has affected many women of childbearing age, and is accompanied by various neurodegenerative conditions. Hence, this study investigates the impact of butyrate in reversing hypothalamic-related disorder, possibly through γ aminobutyric acid (GABA) in a rat model of PCOS. Eight-week-old female Wistar rats were allotted into four groups (n = 5), which include control, butyrate, letrozole, and letrozole + butyrate groups. PCOS was induced by administering 1 mg/kg of letrozole (oral gavage) for 21 days. After confirmation of PCOS, 200 mg/kg of butyrate (oral gavage) was administered for 6 weeks. Rats with PCOS were characterized by elevated levels of plasma insulin and testosterone. Increases in plasma and hypothalamic triglyceride levels, inflammatory biomarker (SDF-1), apoptotic marker (caspase-6), and decreased plasma GnRH were observed. Additionally, a decrease in hypothalamic GABA was revealed. Nevertheless, the administration of butyrate attenuated these alterations. The present study suggests that butyrate ameliorates hypothalamic inflammation in an experimental model of PCOS, a beneficial effect that is accompanied by enhanced GABA production.

Pharmacological Management for Pediatric Irritable Bowel Syndrome: A Review

Irritable bowel syndrome is a multifactorial disease with chronic symptoms that interfere with the quality of life of patients. It represents one of the most common causes of functional abdominal pain in the pediatric population. Various theses with little evidence tried to explain the pathophysiology of the disease. Neurological origin was one of the theories explaining the disease, either by the disturbance of neurotransmitters like dopamine, noradrenaline, and serotonin, which have some evidence of their relation to GI tract functions. Other factors like bio-psycho-social factors that affect the pediatric population are represented in bullying, unrealistic academic expectations from the parents, continuous educational stress, and difficult relationships with peers. Other factors may be genetic abnormalities of the receptors or visceral hypersensitivity. Treatment strategies for the disease varied from physical activity like yoga to a diet like a low-FODMAP diet. Pharmacological treatment of the disease targets the presenting symptoms, represented by antispasmodic drugs treating abdominal pain/discomfort, antipsychotics that regulate the disturbance in the brain-gut axis, and other drugs targeting diarrhea or constipation that present with the patient according to the type of IBS and the condition of the patient.

Targeting the gut-microbiota-brain axis in irritable bowel disease to improve cognitive function - recent knowledge and emerging therapeutic opportunities

The brain-gut axis forms a bidirectional communication system between the gastrointestinal (GI) tract and cognitive brain areas. Disturbances to this system in disease states such as inflammatory bowel disease have consequences for neuronal activity and subsequent cognitive function. The gut-microbiota-brain axis refers to the communication between gut-resident bacteria and the brain. This circuits exists to detect gut microorganisms and relay information to specific areas of the central nervous system (CNS) that in turn, regulate gut physiology. Changes in both the stability and diversity of the gut microbiota have been implicated in several neuronal disorders, including depression, autism spectrum disorder Parkinson's disease, Alzheimer's disease and multiple sclerosis. Correcting this imbalance with medicinal herbs, the metabolic products of dysregulated bacteria and probiotics have shown hope for the treatment of these neuronal disorders. In this review, we focus on recent advances in our understanding of the intricate connections between the gut-microbiota and the brain. We discuss the contribution of gut microbiota to neuronal disorders and the tangible links between diseases of the GI tract with cognitive function and behaviour. In this regard, we focus on irritable bowel syndrome (IBS) given its strong links to brain function and anxiety disorders. This adds to the growing body of evidence supporting targeted therapeutic strategies to modulate the gut microbiota for the treatment of brain/mental-health-related disease.

Early life stress induces irritable bowel syndrome from childhood to adulthood in mice

Background

Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorder. Traditionally, early life stress (ELS) is predisposed to IBS in adult. However, whether ELS induces IBS in early life remains unclear.

Methods

Separated cohort studies were conducted in neonatal male pups of C57BL/6 mice by maternal separation (MS) model. MS and non-separation mice were scheduled to be evaluated for prime IBS-phenotypes, including visceral hypersensitivity, intestinal motility, intestinal permeability, and anxiety-like behavior. Ileal contents and fecal samples were collected and analyzed by 16S rRNA gene sequencing and bacterial community analyses. Subcellular structures of intestinal epithelial, such as epithelial tight junctions and mitochondria, were observed under transmission electron microscopy.

Results

MS induced visceral hypersensitivity and decreased total intestinal transit time from childhood to adulthood. In addition, MS induced intestinal hyperpermeability and anxiety-like behavior from adolescence to adulthood. Besides, MS affected intestinal microbial composition from childhood to adulthood. Moreover, MS disrupted intestinal mitochondrial structure from childhood to adulthood.

Conclusion

The study showed for the first time that MS induced IBS from early life to adulthood in mice. The disrupted intestinal mitochondrial structure and the significant dysbiosis of intestinal microbiota in early life may contribute to the initiation and progress of IBS from early life to adulthood.

IBS randomized study: FODMAPs alter bile acids, phenolic- and tryptophan metabolites, while gluten modifies lipids

Diet is considered a culprit for symptoms in irritable bowel syndrome (IBS), although the mechanistic understanding of underlying causes is lacking. Metabolomics, i.e., the analysis of metabolites in biological samples may offer a diet-responsive fingerprint for IBS. Our aim was to explore alterations in the plasma metabolome after interventions with fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) or gluten versus control in IBS, and to relate such alterations to symptoms. People with IBS (n = 110) were included in a double-blind, randomized, crossover study with 1-wk provocations of FODMAPs, gluten, or placebo. Symptoms were evaluated with the IBS severity scoring system (IBS-SSS). Untargeted metabolomics was performed on plasma samples using LC-qTOF-MS. Discovery of metabolite alterations by treatment was performed using random forest followed by linear mixed modeling. Associations were studied using Spearman correlation. The metabolome was affected by FODMAP [classification rate (CR) 0.88, P < 0.0001], but less by gluten intake CR 0.72, P = 0.01). FODMAP lowered bile acids, whereas phenolic-derived metabolites and 3-indolepropionic acid (IPA) were higher compared with placebo. IPA and some unidentified metabolites correlated weakly to abdominal pain and quality of life. Gluten affected lipid metabolism weakly, but with no interpretable relationship to IBS. FODMAP affected gut microbial-derived metabolites relating to positive health outcomes. IPA and unknown metabolites correlated weakly to IBS severity. Minor symptom worsening by FODMAP intake must be weighed against general positive health aspects of FODMAP. The gluten intervention affected lipid metabolism weakly with no interpretable association to IBS severity. Registration: www.clinicaltrials.gov as NCT03653689.NEW & NOTEWORTHY In irritable bowel syndrome (IBS), fermentable oligo-, di-, monosaccharides, and polyols (FODMAPs) affected microbial-derived metabolites relating to positive health outcomes such as reduced risk of colon cancer, inflammation, and type 2 diabetes, as shown in previous studies. The minor IBS symptom induction by FODMAP intake must be weighed against the positive health aspects of FODMAP consumption. Gluten affected lipids weakly with no association to IBS severity.

Association between gut microbiota and psychiatric disorders: a systematic review

Introduction

In recent years, it has been described that the dysbiosis of the intestinal microbiota plays a transcendental role in several pathologies. In this sense, the importance of the gut microbiota in the gut-brain axis, with a bidirectional communication, has been demonstrated. Furthermore, the gut microbiota has been linked with mood disorders and neuropsychiatric disorders.

Methods

A systematic review of two databases - PubMed and Scopus - was carried out following PRISMA guidelines. We included original studies in humans with a control group published in the last 11 years, which were assessed by the Critical Appraisal Skills Program (CASP) to confirm their quality. Eighteen articles met all the selection criteria.

Results

A review of the articles revealed an association between psychiatric disorders and different bacterial phyla. The studies we have reviewed have demonstrated differences between subjects with psychiatric disorders and controls and highlight a clear relationship between depression, stress, autism spectrum disorder (ASD), psychotic episodes, eating disorders, anxiety and brain function and the gut microbiota composition.

Conclusion

A reduction of fermentative taxa has been observed in different psychiatric disorders, resulting in a decrease in the production of short-chain fatty acids (SCFAs) and an increase in pro-inflammatory taxa, both of which may be consequences of the exacerbation of these pathologies.

Effects of Fructose and Palmitic Acid on Gene Expression in Drosophila melanogaster Larvae: Implications for Neurodegenerative Diseases

One of the largest health problems worldwide is the development of chronic noncommunicable diseases due to the consumption of hypercaloric diets. Among the most common alterations are cardiovascular diseases, and a high correlation between overnutrition and neurodegenerative diseases has also been found. The urgency in the study of specific damage to tissues such as the brain and intestine led us to use Drosophila melanogaster to study the metabolic effects caused by the consumption of fructose and palmitic acid in specific tissues. Thus, third instar larvae (96 ± 4 h) of the wild Canton-S strain of D. melanogaster were used to perform transcriptomic profiling in brain and midgut tissues to test for the potential metabolic effects of a diet supplemented with fructose and palmitic acid. Our data infer that this diet can alter the biosynthesis of proteins at the mRNA level that participate in the synthesis of amino acids, as well as fundamental enzymes for the dopaminergic and GABAergic systems in the midgut and brain. These also demonstrated alterations in the tissues of flies that may help explain the development of various reported human diseases associated with the consumption of fructose and palmitic acid in humans. These studies will not only help to better understand the mechanisms by which the consumption of these alimentary products is related to the development of neuronal diseases but may also contribute to the prevention of these conditions.

Regulation of the central amygdala on intestinal motility and behavior via the lateral hypothalamus in irritable bowel syndrome model mice

BACKGROUND

Impaired bidirectional communication between the gastrointestinal tract and the central nervous system (CNS) is closely related to the development of irritable bowel syndrome (IBS). Studies in patients with IBS have also shown significant activation of the hypothalamus and amygdala. However, how neural circuits of the CNS participate in and process the emotional and intestinal disorders of IBS remains unclear.

METHODS

The GABAergic neural pathway projecting from the central amygdala (CeA) to the lateral hypothalamus (LHA) in mice was investigated by retrograde tracking combined with fluorescence immunohistochemistry. Anxiety, depression-like behavior, and intestinal motility were observed in the water-immersion restraint stress group and the control group. Furthermore, the effects of the chemogenetic activation of the GABAergic neural pathway of CeA-LHA on behavior and intestinal motility, as well as the co-expression of orexin-A and c-Fos in the LHA, were explored.

KEY RESULTS

In our study, Fluoro-Gold retrograde tracking combined with fluorescence immunohistochemistry showed that GABAergic neurons in the CeA were projected to the LHA. The microinjection of the gamma-aminobutyric acid (GABA) receptor antagonist into the LHA relieved anxiety, depression-like behavior, and intestinal motility disorder in the IBS mice. The chemogenetic activation of GABAergic neurons in the CeA-LHA pathway led to anxiety, depression-like behavior, and intestinal motility disorder. In addition, GABAergic neurons in the CeA-LHA pathway inhibited the expression of orexin-A in the LHA, and orexin-A was co-expressed with GABAA receptors.

CONCLUSIONS & INFERENCES

The CeA-LHA GABAergic pathway might participate in the occurrence and development of IBS by regulating orexin-A neurons.

Pharmacokinetic and Permeation Studies in Rat Brain of Natural Compounds Led to Investigate Eugenol as Direct Activator of Dopamine Release in PC12 Cells

Eugenol, cinnamaldehyde and D-limonene, the main components of natural essential oils, are endowed with antioxidant and anti-inflammatory properties which allow them to induce beneficial effects on intestinal, cardiac and neuronal levels. In order to characterize their pharmacokinetic profiles and aptitude to permeate in the central nervous system after intravenous and oral administration to rats, new analytical procedures, easily achievable with HPLC-UV techniques, were developed. The terminal half-lives of these compounds range from 12.4 ± 0.9 (D-limonene) and 23.1 ± 1.6 min (cinnamaldehyde); their oral bioavailability appears relatively poor, ranging from 4.25 ± 0.11% (eugenol) to 7.33 ± 0.37% (cinnamaldehyde). Eugenol evidences a marked aptitude to permeate in the cerebrospinal fluid (CSF) of rats following both intravenous and oral administrations, whereas cinnamaldehyde appears able to reach the CSF only after intravenous administration; limonene is totally unable to permeate in the CSF. Eugenol was therefore recruited for in vitro studies of viability and time-/dose-dependent dopamine release in neuronal differentiated PC12 cells (a recognized cellular model mimicking dopaminergic neurons), evidencing its ability to increase cell viability and to induce dopamine release according to a U-shaped time-course curve. Moreover, concentration-response data suggest that eugenol may induce beneficial effects against Parkinson's disease after oral administration.

Evaluation of two laboratory model methods for diarrheal irritable bowel syndrome

BACKGROUND

Diarrheal irritable bowel syndrome (IBS-D) is a common chronic functional gastrointestinal disorder, and the underlying pathogenic mechanism is still unclear. Animal models that mimic the pathological state of IBS-D patients were constructed to provide a reference for later drug research and model development.

METHODS

The IBS-D model was induced using restraint stress and chemical stimulation (rhubarb), and rats were divided into normal control group (NC), chemically stimulated group (CS), and restraint stress group (RS). Visceral motility responses to Colorectal Balloon Dilation (CRD) were measured by Abdominal Withdrawal Reflex (AWR); evaluation of faecal properties and water content; determination of colonic tissue tight junction (TJ) mRNA expression by RT-PCR; measurement of inflammatory cytokines by ELISA; and intestinal flora and short chain fatty acids.

RESULTS

Compared to NC group, CS and RS group rats showed increased intestinal sensitivity and Bristol stool score, significant diarrheal symptoms and weight loss. Mucin 2, ZO-1, OCLN, CLDN4 mRNA expression was reduced and the intestinal mucosal barrier function was diminished. In addition, the levels of inflammatory factors IL-1β, IL-6, IL-8, IL-10 and TNF-α increased, the abundance and diversity of intestinal flora decreased, the content of beneficial bacteria such as Bifidobacteria decreased, and SCFAs such as acetic acid, propionic acid and butyric acid decreased to different degrees. Although, no significant difference was observed for any molecular and inflammatory marker, but compared to CS group, RS group had less water in the stool, higher visceral sensitivity, and higher relative abundance of beneficial intestinal bacteria such as Actinobacteria.

CONCLUSION

In conclusion, restraint stress combined with chemical stimulation can mimic the pathological state of diarrhoea symptoms, visceral hypersensitivity, reduced intestinal mucosal barrier permeability, immune regulatory dysfunction and dysbiosis in IBS-D patients. However, herbs with antibacterial effects such as rhubarb and senna, for example, are not suitable as the first choice for chemical stimulation, as they may lead to a decrease in harmful bacteria and an increase in beneficial bacteria in the intestinal fraction and do not perfectly mimic the imbalanced state of intestinal flora in IBS-D patients, while restraint stress may be a key factor in modelling.

Gut Inflammation Induced by Finasteride Withdrawal: Therapeutic Effect of Allopregnanolone in Adult Male Rats

The treatment with finasteride (i.e., an inhibitor of 5α-reductase) may be associated with different side effects (i.e., depression, anxiety, cognitive impairment and sexual dysfunction) inducing the so-called post finasteride syndrome (PFS). Moreover, previous observations in PFS patients and an experimental model showed alterations in gut microbiota populations, suggesting an inflammatory environment. To confirm this hypothesis, we have explored the effect of chronic treatment with finasteride (i.e., for 20 days) and its withdrawal (i.e., for 1 month) on the levels of steroids, neurotransmitters, pro-inflammatory cytokines and gut permeability markers in the colon of adult male rat. The obtained data demonstrate that the levels of allopregnanolone (ALLO) decreased after finasteride treatment and after its withdrawal. Following the drug suspension, the decrease in ALLO levels correlates with an increase in IL-1β and TNF-α, serotonin and a decrease in dopamine. Importantly, ALLO treatment is able to counteract some of these alterations. The relation between ALLO and GABA-A receptors and/or pregnenolone (ALLO precursor) could be crucial in their mode of action. These observations provide an important background to explore further the protective effect of ALLO in the PFS experimental model and the possibility of its translation into clinical therapy.

Heart Rate Variability-An Index of the Efficacy of Complementary Therapies in Irritable Bowel Syndrome: A Systematic Review

Irritable bowel syndrome (IBS), as a functional and psychosomatic disease, reduces the quality of life and increases the risk of developing mental disorders. Deregulation of the autonomic nervous system (ANS) is one of the main causes of the disease. The objective of the present study was to identify the studies in which measurements of heart rate variability (HRV) were performed before and after therapeutic intervention, and to evaluate the effectiveness of IBS therapy in terms of a reduction of IBS symptoms and changes in autonomic tone. A systematic review of the literature was carried out in accordance with PRISMA standards. Six databases were searched for articles published before 2022: PubMed®, MEDLINE®, EBSCO, Cochrane, Scopus, and Web of Science. Inclusion criteria were experimental design, diagnosis of IBS (medical and/or diagnosis in accordance with the Rome Criteria), non-pharmacological intervention, and HRV measurement before and after the intervention. The quality of the studies was assessed by JBI Critical appraisal. In total, 455 studies were identified, of which, sixwere included in the review. Expected changes in HRV (increase in parasympathetic activity) were observed in four of the six studies (interventions studied: ear acupressure, transcutaneous auricular vagusnerve stimulation, cognitive behavioral therapy with relaxation elements, yoga). In the same studies, therapeutic interventions significantly reduced the symptoms of IBS. The present review indicated that interventions under investigation improve the efficiency of the ANS and reduce the symptoms of IBS. It is advisable to include HRV measurements as a measure of the effectiveness of interventions in IBS therapy, and to assess autonomic changes as a moderator of the effectiveness of IBS therapy.

Effects and Mechanisms of Acupuncture on Diarrhea-Predominant Irritable Bowel Syndrome: A Systematic Review

Background

Irritable bowel syndrome (IBS) is a common disorder of gut-brain interaction with challenging treatment. According to evidence-based studies, acupuncture is likely to be a promising therapy and subservient adjunct for IBS. Mechanism study of acupuncture based on related clinical trials of high quality, nevertheless, is still vacant.

Aim

This study aims to assess the results and qualities of current clinical evidence and conclude the relevant pathophysiological mechanisms and therapeutic effects of acupuncture on IBS with diarrhea (IBS-D).

Methods

Literature from four databases, namely, PubMed, Cochrane Library, EMBASE, and Web of Science, was systematically searched to obtain eligible randomized controlled trials (RCTs), which contained mechanism research of acupuncture treatment in IBS-D patients. Two independent reviewers completed data extraction and quality evaluation using the RevMan 5.4.1 software.

Results

Ten trials that covered 19 items related to mechanism research were included in this review. Acupuncture was reported to improve IBS-D symptoms and quality of life, with positive effects in regulating brain-gut peptides, cerebral activities, neuroendocrine functions, psychological state, and inflammatory GI and hypersensitive intestinal tracts.

Conclusion

Acupuncture has potential influence on pathophysiology alterations such as regulating brain-gut peptides, altering cerebral connectivity and activity, promoting neuroendocrine functions and mental state, and mitigating inflammation as well as hypersensitivity of bowels in IBS-D patients, but further studies of high quality are still necessary.

Systematic Review Registration

[https://www.crd.york.ac.uk/PROSPERO], identifier [CRD42022320331].

Gut Microbes and Neuropathology: Is There a Causal Nexus?

The gut microbiota is a virtual organ which produces a myriad of molecules that the brain and other organs require. Humans and microbes are in a symbiotic relationship, we feed the microbes, and in turn, they provide us with essential molecules. Bacteroidetes and Firmicutes phyla account for around 80% of the total human gut microbiota, and approximately 1000 species of bacteria have been identified in the human gut. In adults, the main factors influencing microbiota structure are diet, exercise, stress, disease and medications. In this narrative review, we explore the involvement of the gut microbiota in Parkinson’s disease, Alzheimer’s disease, multiple sclerosis and autism, as these are such high-prevalence disorders. We focus on preclinical studies that increase the understanding of disease pathophysiology. We examine the potential for targeting the gut microbiota in the development of novel therapies and the limitations of the currently published clinical studies. We conclude that while the field shows enormous promise, further large-scale studies are required if a causal link between these disorders and gut microbes is to be definitively established.