Dysregulation of GABAergic Signalling Contributes in the Pathogenesis of Diarrhea-predominant Irritable Bowel Syndrome

The Power of Psychobiotics in Depression: A Modern Approach through the Microbiota-Gut-Brain Axis: A Literature Review

The microbiota-gut-brain (MGB) axis is a complex communication network linking the gut, microbiota, and brain, influencing various aspects of health and disease. Dysbiosis, a disturbance in the gut microbiome equilibrium, can significantly impact the MGB axis, leading to alterations in microbial composition and function. Emerging evidence highlights the connection between microbiota alterations and neurological and psychiatric disorders, including depression. This review explores the potential of psychobiotics in managing depressive disorders, emphasizing their role in restoring microbial balance and influencing the MGB axis. Psychobiotics exhibit positive effects on the intestinal barrier, immune response, cortisol levels, and the hypothalamic-pituitary-adrenal (HPA) axis. Studies suggest that probiotics may serve as an adjunct therapy for depression, especially in treatment-resistant cases. This review discusses key findings from studies on psychobiotics interventions, emphasizing their impact on the gut-brain axis and mental health. The increasing acceptance of the expanded concept of the MGB axis underscores the importance of microorganisms in mental well-being. As our understanding of the microbiome's role in health and disease grows, probiotics emerge as promising agents for addressing mental health issues, providing new avenues for therapeutic interventions in depressive disorders.

Experimental colitis-induced visceral hypersensitivity is attenuated by GABA treatment in mice

Ulcerative colitis (UC) is linked with inflammation of the large intestine due to an overactive response of the colon-immune system. UC is associated with weight loss, rectal bleeding, diarrhea, and abdominal pain. Given that γ-amino butyric acid (GABA) suppresses immune cell activity and the excitability of colonic afferents, and that there is a decrease in colonic GABA during UC, we hypothesized that UC pain is due to a decrease in the inhibition of colonic afferents. Thus, restoring GABA in the colon will attenuate inflammatory hypersensitivity. We tested this hypothesis in a mouse model of colitis. Colon inflammation was induced with seven days of dextran sodium sulfate (DSS, 3%) in the drinking water. GABA (40 mg/kg) was administered orally for the same period as DSS, and body weight, colon length, colon permeability, clinical progression of colitis (disease activity index or DAI), and colon histological score (HS) were assessed to determine the effects of GABA on colitis. A day after the end of GABA treatment, visceral sensitivity was assessed with balloon distention (of the colon)-evoked visceromotor response and colon samples were collected for the measurement of GABA and cytokines. Treatment with GABA reduced the DSS-induced increase in the colon permeability, DAI, HS, and decrease in body weight and colon length. Furthermore, GABA inhibited the DSS-induced increase in the proinflammatory cytokines tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), interleukin-12 (IL-12), and increased the expression of the anti-inflammatory cytokine IL-10 in the colon tissue. Importantly, GABA reduced DSS-induced visceral hypersensitivity. These data suggest that increasing gastrointestinal levels of GABA may be useful for the treatment of colitis.NEW & NOTEWORTHY GABA treatment reduces the severity of colitis and inflammation and produces inhibition of visceral hypersensitivity in colon-inflamed mice. These results raise the promising possibility that GABA treatment may be an effective therapeutic strategy for the management of symptoms associated with colitis. However, clinical studies are required to corroborate whether this mouse-model data translates to human colon.

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.

The many faces of gastrointestinal dysfunction in stiff person syndrome spectrum disorders

Introduction

The effect of stiff person syndrome spectrum disorders (SPSD) on the gastrointestinal tract (GIT) is unknown. This case series aims to characterize the prevalence and types of GI dysfunction in individuals with SPSD.

Methods

A retrospective chart review included individuals diagnosed with SPSD with descriptors of GI symptoms in their medical records. SPSD phenotypes, type of motility test performed, and dysmotility pattern (upper, lower, or diffuse) were assessed. Descriptive statistics and univariate chi-square analyses were utilized.

Results

Of 240 individuals with SPSD, 32% reported GI symptoms, most were female (83.1%), and white (74%), with a median age at time of GI symptom onset of 50 ± 13 years. Most common symptoms reported were dysphagia (45%), constipation (40%), and nausea/vomiting (23%). Most individuals had classic SPS (47%) followed by SPS-plus (29%) and 82.9% were positive for serum antiGAD65 antibodies. Of 36 patients that underwent at least one GI motility test, 26 had evidence of upper, lower, or diffuse GI dysmotility (44.4%, 17%, and 4%, respectively). The group who did not undergo testing had a higher proportion of patients with DM.

Discussion

There is a high prevalence of GI symptoms and transit abnormalities in patients with SPSD. Future prospective, longitudinal studies are warranted to further assess GI symptoms in the context of SPSD and to determine if individuals with GI symptoms differ in prognosis or treatment response from those without GI symptoms. In the meantime, there should be a low threshold for motility testing in patients with SPSD.

Indian consensus statements on irritable bowel syndrome in adults: A guideline by the Indian Neurogastroenterology and Motility Association and jointly supported by the Indian Society of Gastroenterology

The Indian Neurogastroenterology and Motility Association (INMA), earlier named the Indian Motility and Functional Diseases Association developed this evidence-based practice guidelines for the management of irritable bowel syndrome (IBS). A modified Delphi process was used to develop this consensus containing 28 statements, which were concerning diagnostic criteria, epidemiology, etiopathogenesis and comorbidities, investigations, lifestyle modifications and treatments. Owing to the Coronavirus disease-19 (COVID-19) pandemic, lockdowns and mobility restrictions, web-based meetings and electronic voting were the major tools used to develop this consensus. A statement was regarded as accepted when the sum of "completely accepted" and "accepted with minor reservation" voted responses were 80% or higher. Finally, the consensus was achieved on all 28 statements. The consensus team members are of the view that this work may find use in teaching, patient care, and research on IBS in India and other nations.

Anti-Helicobacter pylori activity of potential probiotic Lactiplantibacillus pentosus SLC13

BACKGROUND

Here, we aimed to evaluate and compare the anti-Helicobacter pylori activity of potential probiotic Lactiplantibacillus pentosus SLC13 to Lactobacillus gasseri BCRC 14619 T and Lacticaseibacillus rhamnosus LGG. Phenotypic assays including growth curve, cell adhesion, and cellular cytotoxicity were performed to characterize SLC13. Anti-H. pylori activity of lactobacilli was determined by the disk diffusion method and co-culture assay. Exopolysaccharide (EPS) was extracted from lactobacilli to test its immune modulation activity, and IL-8 expression in AGS and GES-1 was determined by RT-qPCR.

RESULTS

All three lactobacilli strains were tolerant to the simulated gastrointestinal conditions. SLC13 showed the highest adhesion ability to AGS and GES-1 cells, compared to LGG and BCRC 14619 T. The coculture assays of SLC13, LGG, and BCRC 14619 T with cells for 4 h showed no significant cytotoxic effects on cells. All tested strains exhibited an inhibitory effect against H. pylori J99. The cell-free supernatant (CFS) of three strains showed activity to inhibit H. pylori urease activity in a dose-dependent manner and the CFS of SLC13 had the highest urease inhibitory activity, compared to LGG and BCRC 14619 T. Only the treatment of AGS cells with SLC13 EPS significantly decreased the IL-8 expression induced by H. pylori infection as compared to cells treated with LGG and BCRC 14619 T EPS.

CONCLUSIONS

SLC13 possesses potent antimicrobial activity against H. pylori growth, infection, and H. pylori-induced inflammation. These results suggest that SLC13 and its derivatives have the potential as alternative agents against H. pylori infection and alleviate inflammatory response.

Metabolomics: The Key to Unraveling the Role of the Microbiome in Visceral Pain Neurotransmission

Inflammatory bowel disease (IBD), comprising Crohn’s disease and Ulcerative colitis, is a relapsing and remitting disease of the gastrointestinal tract, presenting with chronic inflammation, ulceration, gastrointestinal bleeding, and abdominal pain. Up to 80% of patients suffering from IBD experience acute pain, which dissipates when the underlying inflammation and tissue damage resolves. However, despite achieving endoscopic remission with no signs of ongoing intestinal inflammation or damage, 30–50% of IBD patients in remission experience chronic abdominal pain, suggesting altered sensory neuronal processing in this disorder. Furthermore, effective treatment for chronic pain is limited such that 5–25% of IBD outpatients are treated with narcotics, with associated morbidity and mortality. IBD patients commonly present with substantial alterations to the microbial community structure within the gastrointestinal tract, known as dysbiosis. The same is also true in irritable bowel syndrome (IBS), a chronic disorder characterized by altered bowel habits and abdominal pain, in the absence of inflammation. An emerging body of literature suggests that the gut microbiome plays an important role in visceral hypersensitivity. Specific microbial metabolites have an intimate relationship with host receptors that are highly expressed on host cell and neurons, suggesting that microbial metabolites play a key role in visceral hypersensitivity. In this review, we will discuss the techniques used to analysis the metabolome, current potential metabolite targets for visceral hypersensitivity, and discuss the current literature that evaluates the role of the post-inflammatory microbiota and metabolites in visceral hypersensitivity.

Age-related differences of γ-aminobutyric acid (GABA)ergic transmission in human colonic smooth muscle

BACKGROUND

Enteric neurons undergo to functional changes during aging. We investigated the possible age-associated differences in enteric γ-aminobutyric acid (GABA)ergic transmission evaluating function and distribution of GABAergic receptors in human colon.

METHODS

Mechanical responses to GABA and GABA receptor agonists on slow phasic contractions were examined in vitro as changes in isometric tension in colonic muscle strips from young (<65 years old) and aged patients (>65 years old). GABAergic receptor expression was assessed by quantitative RT-PCR.

KEY RESULTS

In both preparations GABA induced an excitatory effect, consisting in an increase in the basal tone, antagonized by the GABAA receptor antagonist, bicuculline, and potentiated by phaclofen, GABAB receptor antagonist.Tetrodotoxin (TTX) and atropine-sensitive contractile responses to GABA and GABAA receptor agonist, muscimol, were more pronounced in old compared to young subjects. Baclofen, GABAB receptor agonist, induced a TTX-sensitive reduction of the amplitude of the spontaneous. Nω-nitro-l-arginine methyl ester (L-NAME), nitric oxide (NO) synthase inhibitor abolished the inhibitory responses in old preparations, but a residual responses persisted in young preparations, which in turn was abolished by suramin, purinergic receptor antagonist. α3-GABAA receptor subunit expression tends to change in an age-dependent manner.

CONCLUSIONS AND INFERENCES

Our results reveal age-related differences in GABAergic transmission in human colon. At all the age tested GABA regulates muscular contractility modulating the activity of the intrinsic neurons. Activation of GABAA receptor, through acetylcholine release, induces contraction, which increases in amplitude with age. GABAB receptor activation leads to neural release of NO and purines, being a loss of purinergic-component in aged group.

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

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder of unknown etiology. IBS is caused by a disruption in the gut-brain axis. Given the importance of the gut microbiota in maintaining local and systemic homeostasis of immunity, endocrine, and other physiological processes, the microbiota-gut-brain axis has been proposed as a key regulator in IBS. Neurotransmitters have been shown to affect blood flow regulation, intestinal motility, nutrient absorption, the gastrointestinal immune system, and the microbiota in recent studies. It has the potential role to play a function in the pathophysiology of the gastrointestinal and neurological systems. Transmitters and their receptors, including 5-hydroxytryptamine, dopamine, γ-aminobutyric acid, and histamine, play an important role in IBS, especially in visceral sensitivity and gastrointestinal motility. Studies in this field have shed light on revealing the mechanism by which neurotransmitters act in the pathogenesis of IBS and discovering new therapeutic strategies based on traditional pharmacological approaches that target the nervous system or novel therapies that target the microbiota.

Gut feelings: the microbiota-gut-brain axis on steroids

The intricate connection between central and enteric nervous systems is well established with emerging evidence linking gut microbiota function as a significant new contributor to gut-brain axis signaling. Several microbial signals contribute to altered gut-brain communications, with steroids representing an important biological class that impacts central and enteric nervous system function. Neuroactive steroids contribute pathologically to neurological disorders, including dementia and depression, by modulating the activity of neuroreceptors. However, limited information is available on the influence of neuroactive steroids on the enteric nervous system and gastrointestinal function. In this review, we outline how steroids can modulate enteric nervous system function by focusing on their influence on different receptors that are present in the intestine in health and disease. We also highlight the potential role of the gut microbiota in modulating neuroactive steroid signaling along the gut-brain axis.

Gut Microbiota-Derived Metabolites in Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is the most common functional bowel disorder worldwide and is associated with visceral hypersensitivity, gut motility, immunomodulation, gut microbiota alterations, and dysfunction of the brain-gut axis; however, its pathophysiology remains poorly understood. Gut microbiota and its metabolites are proposed as possible etiological factors of IBS. The aim of our study was to investigate specific types of microbiota-derived metabolites, especially bile acids, short-chain fatty acids, vitamins, amino acids, serotonin and hypoxanthine, which are all implicated in the pathogenesis of IBS. Metabolites-focused research has identified multiple microbial targets relevant to IBS patients, important roles of microbiota-derived metabolites in the development of IBS symptoms have been established. Thus, we provide an overview of gut microbiota and their metabolites on the different subtypes of IBS (constipation-predominant IBS-C, diarrhea-predominant IBS-D) and present controversial views regarding the role of microbiota in IBS.

Identification and potential functions of tRNA-derived small RNAs (tsRNAs) in irritable bowel syndrome with diarrhea

IBS-D is a functional bowel disease without clear diagnostic markers and exact pathogenesis. Studies have proved that non-coding RNAs participate in IBS-D. However, tRNA-derived small RNAs (tsRNAs), as a new type of non-coding RNAs that are more suitable as markers, remain to be clarified in IBS-D. Hence, we focused on the identification and potential functions of tsRNAs in IBS-D. Intestinal biopsies were obtained from IBS-D patients and healthy volunteers, and twenty-eight differential tsRNAs were screened by high-throughput sequencing. The changes of tiRNA-His-GTG-001, tRF-Ser-GCT-113, and tRF-Gln-TTG-035 by q-PCR in expanded samples were consistent with the sequencing results. Meanwhile, target gene prediction and bioinformatics showed that the three differential tsRNAs may be involved in some key signal pathways, such as GABAergic synapse, tumor necrosis factor-α (TNF-α), etc. Their regulation on target genes were demonstrated through cell experiments and luciferase reporter assays. In addition, the receiver-operating characteristic (ROC) analysis showed that the three tsRNAs all could be used as candidate markers of IBS-D. The correlation analysis indicated they were related to the degree of abdominal pain, abdominal distension, and stool morphology. So, we believe that the abnormal tiRNA-His-GTG-001, tRF-Ser-GCT-113, and tRF-Gln-TTG-035 are related to the clinical symptoms of IBS-D, and can target regulate the important molecules of the brain-gut axis, even could be expected as potential biomarkers for the diagnosis and treatment of IBS-D.

Cytokine-specific autoantibodies shape the gut microbiome in autoimmune polyendocrine syndrome type 1

BACKGROUND

Gastrointestinal dysfunction is a frequent and disabling manifestation of autoimmune polyendocrine syndrome type 1 (APS-1), a rare monogenic multiorgan autoimmune disease caused by the loss of central AIRE-controlled immune tolerance.

OBJECTIVES

This study aimed to understand the role of the gut microbiome in APS-1 symptoms and potentially alleviate common gastrointestinal symptoms by probiotic intervention.

METHODS

This study characterized the fecal microbiomes of 28 patients with APS-1 and searched for associations with gastrointestinal symptoms, circulating anti-cytokine autoantibodies, and tryptophan-related metabolites. Additionally, daily doses of the probiotic Lactobacillus rhamnosus GG were administered for 3 months.

RESULTS

Of 581 metagenomic operational taxonomic units (mOTUs) characterized in total, 14 were significantly associated with patients with APS-1 compared with healthy controls, with 6 mOTUs depleted and 8 enriched in patients with APS-1. Four overabundant mOTUs were significantly associated with severity of constipation. Phylogenetically conserved microbial associations with autoantibodies against cytokines were observed. After the 3-month intervention with the probiotic L rhamnosus GG, a subset of gastrointestinal symptoms were alleviated. L rhamnosus GG abundance was increased postintervention and corresponded with decreased abundances of Alistipes onderdonkii and Collinsella aerofaciens, 2 species positively associated with severity of diarrhea in patients with APS-1.

CONCLUSIONS

The APS-1 microbiome correlates with several APS-1 symptoms, some of which are alleviated after a 3-month L rhamnosus GG intervention. Autoantibodies against cytokines appear to shape the gut microbiome by positively correlating with a taxonomically consistent group of bacteria.

Neurotransmitter Dysfunction in Irritable Bowel Syndrome: Emerging Approaches for Management

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder whose aetiology is still unknown. Most hypotheses point out the gut-brain axis as a key factor for IBS. The axis is composed of different anatomic and functional structures intercommunicated through neurotransmitters. However, the implications of key neurotransmitters such as norepinephrine, serotonin, glutamate, GABA or acetylcholine in IBS are poorly studied. The aim of this review is to evaluate the current evidence about neurotransmitter dysfunction in IBS and explore the potential therapeutic approaches. IBS patients with altered colorectal motility show augmented norepinephrine and acetylcholine levels in plasma and an increased sensitivity of central serotonin receptors. A decrease of colonic mucosal serotonin transporter and a downregulation of α2 adrenoceptors are also correlated with visceral hypersensitivity and an increase of 5-hydroxyindole acetic acid levels, enhanced expression of high affinity choline transporter and lower levels of GABA. Given these neurotransmitter dysfunctions, novel pharmacological approaches such as 5-HT₃ receptor antagonists and 5-HT₄ receptor agonists are being explored for IBS management, for their antiemetic and prokinetic effects. GABA-analogous medications are being considered to reduce visceral pain. Moreover, agonists and antagonists of muscarinic receptors are under clinical trials. Targeting neurotransmitter dysfunction could provide promising new approaches for IBS management.

GABA-producing Lactobacillus plantarum inhibits metastatic properties and induces apoptosis of 5-FU-resistant colorectal cancer cells via GABAB receptor signaling

5-Fluorouracil (5-FU) is an essential drug in systemic chemotherapy treatments for colorectal cancer (CRC). Despite the development of several treatment strategies over the past decades, the patient benefits of 5-FU-based therapies have been compromised by the development of chemoresistance. Differences in treatment responses among CRC patients may be due to genetic and epigenetic factors unique to individuals. Therefore, important factors for realizing personalized medicine are to accurately understand the causes and mechanisms of drug resistance to 5-FU-based therapies and to identify and validate prognostic biomarkers. Gut microbes that interact directly with the host contribute to human health and cancer control. Lactobacillus plantarum, in particular, has the potential to be a therapeutic agent by producing bioactive compounds that may benefit the host. Here, we investigated the gamma-aminobutyric acid (GABA) and GABAB receptor (GABABR)-dependent signaling pathway as a treatment option for 5-FU-resistant HT-29 cells. GABA-producing L. plantarum activates anti-proliferative, anti-migration, and anti-invasion effects against 5-FU-resistant HT-29 cells. The inhibitory effects of GABA-producing L. plantarum are mediated via GABABR. Activated GABABR induces apoptosis through the inhibition of cAMP-dependent signaling pathways and cellular inhibitor of apoptosis protein 2 (cIAP2) expression. Thus, the GABAergic system has potential in 5-FU-resistant HT-29 cells as a predictive biomarker. In addition, GABA-producing L. plantarum is promising as an adjuvant treatment for 5-FU-resistant CRC, and its intervention in neurobiological signaling imply new possibilities for chemoprevention and the treatment of colon cancer-related diseases.

Molecular Mechanisms of Microbiota-Mediated Pathology in Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is one of the most prevalent functional gastrointestinal disorders, and accumulating evidence gained in both preclinical and clinical studies indicate the involvement of enteric microbiota in its pathogenesis. Gut resident microbiota appear to influence brain activity through the enteric nervous system, while their composition and function are affected by the central nervous system. Based on these results, the term “brain–gut–microbiome axis” has been proposed and enteric microbiota have become a potential therapeutic target in IBS cases. However, details regarding the microbe-related pathophysiology of IBS remain elusive. This review summarizes the existing knowledge of molecular mechanisms in the pathogenesis of IBS as well as recent progress related to microbiome-derived neurotransmitters, compounds, metabolites, neuroendocrine factors, and enzymes.

Gut Microbial Metabolites and Biochemical Pathways Involved in Irritable Bowel Syndrome: Effects of Diet and Nutrition on the Microbiome

The food we consume and its interactions with the host and their gut microbiota affect normal gut function and health. Functional gut disorders (FGDs), including irritable bowel syndrome (IBS), can result from negative effects of these interactions, leading to a reduced quality of life. Certain foods exacerbate or reduce the severity and prevalence of FGD symptoms. IBS can be used as a model of perturbation from normal gut function with which to study the impact of foods and diets on the severity and symptoms of FGDs and understand how critical processes and biochemical mechanisms contribute to this impact. Analyzing the complex interactions between food, host, and microbial metabolites gives insights into the pathways and processes occurring in the gut which contribute to FGDs. The following review is a critical discussion of the literature regarding metabolic pathways and dietary interventions relevant to FGDs. Many metabolites, for example bile acids, SCFAs, vitamins, amino acids, and neurotransmitters, can be altered by dietary intake, and could be valuable for identifying perturbations in metabolic pathways that distinguish a "normal, healthy" gut from a "dysfunctional, unhealthy" gut. Dietary interventions for reducing symptoms of FGDs are becoming more prevalent, but studies investigating the underlying mechanisms linked to host, microbiome, and metabolite interactions are less common. Therefore, we aim to evaluate the recent literature to assist with further progression of research in this field.