Functional abdominal pain and discomfort (IBS) is not associated with faecal microbiota composition in the general population

Glaucoma Patients Have a Lower Abundance of Butyrate-Producing Taxa in the Gut

Purpose

Glaucoma is an eye disease that is the most common cause of irreversible blindness worldwide. It has been suggested that gut microbiota can produce reactive oxygen species and pro-inflammatory cytokines that may travel from the gastric mucosa to distal sites, for example, the optic nerve head or trabecular meshwork. There is evidence for a gut-eye axis, as microbial dysbiosis has been associated with retinal diseases. We investigated the microbial composition in patients with glaucoma and healthy controls. Moreover, we analyzed the association of the gut microbiome with intraocular pressure (IOP; risk factor of glaucoma) and vertical cup-to-disc ratio (VCDR; quantifying glaucoma severity).

Methods

The discovery analyses included participants of the Rotterdam Study and the Erasmus Glaucoma Cohort. A total of 225 patients with glaucoma and 1247 age- and sex-matched participants without glaucoma were included in our analyses. Stool samples were used to generate 16S rRNA gene profiles. We assessed associations with 233 genera and species. We used data from the TwinsUK and the Study of Health in Pomerania (SHIP) to replicate our findings.

Results

Several butyrate-producing taxa (e.g. Butyrivibrio, Caproiciproducens, Clostridium sensu stricto 1, Coprococcus 1, Ruminococcaceae UCG 007, and Shuttleworthia) were less abundant in people with glaucoma compared to healthy controls. The same taxa were also associated with lower IOP and smaller VCDR. The replication analyses confirmed the findings from the discovery analyses.

Conclusions

Large human studies exploring the link between the gut microbiome and glaucoma are lacking. Our results suggest that microbial dysbiosis plays a role in the pathophysiology of glaucoma.

The Role of the FODMAP Diet in IBS

The low FODMAP (fermentable oligosaccharide, disaccharide, monosaccharide, and polyol) diet is a beneficial therapeutic approach for patients with irritable bowel syndrome (IBS). However, how the low FODMAP diet works is still not completely understood. These mechanisms encompass not only traditionally known factors such as luminal distension induced by gas and water but also recent evidence on the role of FOMAPs in the modulation of visceral hypersensitivity, increases in intestinal permeability, the induction of microbiota changes, and the production of short-chain fatty acids (SCFAs), as well as metabolomics and alterations in motility. Although most of the supporting evidence is of low quality, recent trials have confirmed its effectiveness, even though the majority of the evidence pertains only to the restriction phase and its effectiveness in relieving abdominal bloating and pain. This review examines potential pathophysiological mechanisms and provides an overview of the existing evidence on the effectiveness of the low FODMAP diet across various IBS subtypes. Key considerations for its use include the challenges and disadvantages associated with its practical implementation, including the need for professional guidance, variations in individual responses, concerns related to microbiota, nutritional deficiencies, the development of constipation, the necessity of excluding an eating disorder before commencing the diet, and the scarcity of long-term data. Despite its recognized efficacy in symptom management, acknowledging these limitations becomes imperative for a nuanced comprehension of the role of a low FODMAP diet in managing IBS. By investigating its potential mechanisms and evidence across IBS subtypes and addressing emerging modulations alongside limitations, this review aims to serve as a valuable resource for healthcare practitioners, researchers, and patients navigating the intricate landscape of IBS.

Multi-omics for biomarker approaches in the diagnostic evaluation and management of abdominal pain and irritable bowel syndrome: what lies ahead

Reliable biomarkers for common disorders of gut-brain interaction characterized by abdominal pain, including irritable bowel syndrome (IBS), are critically needed to enhance care and develop individualized therapies. The dynamic and heterogeneous nature of the pathophysiological mechanisms that underlie visceral hypersensitivity have challenged successful biomarker development. Consequently, effective therapies for pain in IBS are lacking. However, recent advances in modern omics technologies offer new opportunities to acquire deep biological insights into mechanisms of pain and nociception. Newer methods for large-scale data integration of complementary omics approaches have further expanded our ability to build a holistic understanding of complex biological networks and their co-contributions to abdominal pain. Here, we review the mechanisms of visceral hypersensitivity, focusing on IBS. We discuss candidate biomarkers for pain in IBS identified through single omics studies and summarize emerging multi-omics approaches for developing novel biomarkers that may transform clinical care for patients with IBS and abdominal pain.

Immune activation in irritable bowel syndrome: what is the evidence?

Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder that is characterized by abdominal pain and an altered defecation pattern. It affects between 5 and 20% of the general population and can seriously impact quality of life. The pathophysiology of IBS is rather complex and multifactorial including, for example, altered signalling by the gut-brain axis, dysbiosis, abnormal visceral pain signalling and intestinal immune activation. The latter has gained particular interest in recent years, with growing insight into the bidirectional communication between the nervous system and the immune system. In this Review, we detail the current evidence suggesting that immune activation contributes to the pathology seen in patients with IBS and discuss the potential mechanisms involved. Moreover, we describe how immune mediators, particularly those released by mast cells, can directly activate or sensitize pain-transmitting nerves, leading to increased pain signalling and abdominal pain. Finally, we discuss the potential of interventions targeting immune activation as a new therapeutic strategy for patients suffering from IBS.

The Gut Microbiome in Patients With Chronic Pancreatitis Is Characterized by Significant Dysbiosis and Overgrowth by Opportunistic Pathogens

Exocrine pancreatic function is a critical host factor in determining the intestinal microbiota composition. Diseases affecting the exocrine pancreas could therefore influence the gut microbiome. We investigated the changes in gut microbiota of patients with chronic pancreatitis (CP).

Long-term instability of the intestinal microbiome is associated with metabolic liver disease, low microbiota diversity, diabetes mellitus and impaired exocrine pancreatic function

OBJECTIVE

The intestinal microbiome affects the prevalence and pathophysiology of a variety of diseases ranging from inflammation to cancer. A reduced taxonomic or functional diversity of the microbiome was often observed in association with poorer health outcomes or disease in general. Conversely, factors or manifest diseases that determine the long-term stability or instability of the microbiome are largely unknown. We aimed to identify disease-relevant phenotypes associated with faecal microbiota (in-)stability.

DESIGN

A total of 2564 paired faecal samples from 1282 participants of the population-based Study of Health in Pomerania (SHIP) were collected at a 5-year (median) interval and microbiota profiles determined by 16S rRNA gene sequencing. The changes in faecal microbiota over time were associated with highly standardised and comprehensive phenotypic data to determine factors related to microbiota (in-)stability.

RESULTS

The overall microbiome landscape remained remarkably stable over time. The greatest microbiome instability was associated with factors contributing to metabolic syndrome such as fatty liver disease and diabetes mellitus. These, in turn, were associated with an increase in facultative pathogens such as Enterobacteriaceae or Escherichia/Shigella. Greatest stability of the microbiome was determined by higher initial alpha diversity, female sex, high household income and preserved exocrine pancreatic function. Participants who newly developed fatty liver disease or diabetes during the 5-year follow-up already displayed significant microbiota changes at study entry when the diseases were absent.

CONCLUSION

This study identifies distinct components of metabolic liver disease to be associated with instability of the intestinal microbiome, increased abundance of facultative pathogens and thus greater susceptibility toward dysbiosis-associated diseases.

Self-reported bowel symptoms are associated with differences in overall gut microbiota composition and enrichment of Blautia in a population-based cohort

BACKGROUND AND AIM

Altered gut microbiota have been suggested as part of an etiology of irritable bowel syndrome (IBS), but studies have shown contrasting results. Our aim was to examine gut microbiota composition in a large population-based cohort, with respect to presence and severity of bowel symptoms.

METHODS

The study cohort consisted of 1988 participants of the Malmö Offspring Study (mean age 40 years, 53% women). From a questionnaire, 19% reported having bowel symptoms the last 2 weeks and 15% reported having IBS. Bowel symptoms were assessed by a validated set of questions with visual analog scales. Gut microbiota was assessed by 16S rRNA gene sequencing (300 bp*2 in V1-V3 region) from fecal samples. The association between abundance of bacteria at genus level and bowel symptoms was calculated by logistic regression or general linear model, adjusted for false discovery rate (q < 0.05).

RESULTS

Self-reported bowel symptoms (P = 0.003) and IBS (P = 0.031) were associated with difference in overall gut microbiota composition (beta-diversity). Additionally, bowel symptoms and IBS were associated with increased abundance of Blautia, and bowel symptoms also with a genus in the SHA98 order and Butyricimonas. Pain was associated with increased abundance of Fusobacterium. Diarrhea was associated positively with [Prevotella] and Blautia and negatively with a genus in the SHA98 order and a genus in the Christensenellaceae family.

CONCLUSION

Self-reported bowel symptoms are associated with differences in overall gut microbiota composition and abundancy of a few specific bacteria at genus level in a population-based cohort. Diarrhea is the individual symptom with most associations.

The Role of Intestinal Microbiota and Mast Cell in a Rat Model of Visceral Hypersensitivity

Background/Aims

To explore the role of intestinal flora and mast cells in visceral hypersensitivity (VH).

Methods

The experimental animals were divided into 4 groups: control group, VH group, VH + VSL#3 group, and VH + ketotifen group. Stool samples were collected from each group (n = 3) for a further analysis using 16S ribosomal DNA gene sequence. Visceral sensitivity was evaluated by abdominal withdrawal reflex (AWR) score. Colon tissues of rats were obtained from each group. Mast cells were detected by toluidine blue staining. The degranulation of mast cells was assessed by transmission electron microscopy.

Results

VH rat model could successfully be induced by acetic acid enema combined with partial limb restraint method. Compared with rats in the control group, AWR score, number of mast cells, and degranulation of mast cells were increased in the VH rats, which could be reduced by administration of ketotifen or probiotic VSL#3. Clostridium sensu stricto 1 abundance was higher in the VH group compared to the control group, which could be restored by application of probiotic VSL#3.

Conclusions

Probiotic VSL#3 decreases visceral sensitivity in VH rats. The mechanism may be related to mast cell and intestinal flora. Change of Clostridium sensu stricto 1 abundance may be a basis for VH observed in irritable bowel syndrome and may be prevented by specific probiotic administration.

Mucosal Tuft Cell Density Is Increased in Diarrhea-Predominant Irritable Bowel Syndrome Colonic Biopsies

Tuft cells are rare chemosensory sentinels found in the gut epithelium. When triggered by helminth infection, tuft cells secrete interleukin-25 (IL-25) basolaterally and subsequently evoke an immune response. Irritable bowel syndrome (IBS) is a common and heterogeneous disorder characterized by bowel dysfunction and visceral pain sensitivity. Dysfunctional gut-brain communication and immune activation contribute to the pathophysiology of this disorder. The study aims were to investigate changes in tuft cell density in non-post-infectious IBS patients. Immunofluorescent labeling of DCLK1-positive tuft cells was carried out in mucosal biopsies from the distal colons of diarrhea and constipation-predominant IBS patients and healthy controls. Tuft cell numbers were also assessed in animal models. Concentrations of interleukin-25 (IL-25) secreted from colonic biopsies and in plasma samples were analyzed using an immunoassay. The density of tuft cells was increased in diarrhea-but not constipation-predominant IBS patient colonic biopsies. Biopsy secretions and plasma concentrations of IL-25 were elevated in diarrhea-but not constipation-predominant IBS participants. Tuft cell hyperplasia was detected in a rat model of IBS but not in mice exposed to chronic stress. Tuft cell hyperplasia is an innate immune response to helminth exposure. However, the patients with diarrhea-predominant IBS have not reported any incidents of enteric infection. Moreover, rats exhibiting IBS-like symptoms displayed increased tuft cell density but were not exposed to helminths. Our findings suggest that factors other than helminth exposure or chronic stress lead to tuft cell hyperplasia in IBS colonic biopsies.

Polymicrobial interactions involving fungi and their importance for the environment and in human disease

Understanding polymicrobial interactions involving fungi in the environment and the human mycobiome is necessary to address environmental and medically related problems such as drought or antimicrobial resistance. The diversity of these interactions highlights the complexity of fungi, considering how some interactions can be antagonistic, while others synergistic. Over the years, an increase in studies on the mycobiome have revealed similarities between the human and environmental hosts. More recently, studies have focused on microbial commensal relationships and identifying causative agents of human disease. The overlap of some of these interactions is impossible to ignore, indicating that there are areas for medical exploitation that need to be further investigated. This review provides the latest advances in polymicrobial interactions involving fungi and discusses the importance of the fungal lifestyle in the environment and in human disease.

Improvement of subsoil physicochemical and microbial properties by short-term fallow practices

Fallow management can improve the soil nutrients in the topsoil and upper subsoil. However, little is known about the effects of short-term (one year) fallowing with different treatments, such as vegetation and fertilization, on subsoil (20–40 cm) properties. We conducted field trials to explore the changes in subsoil properties in response to such treatments in the Yellow River Delta region in China. Different vegetation and fertilization treatments were applied, and we measured the carbon and nitrogen contents, microbial biomass and microbial community structure in the subsoil. Fallowing without manure resulted in the storage of more total nitrogen (16.38%) than fallowing with manure, and meadow vegetation improved the ammonium nitrogen content (45.71%) relative to spontaneous vegetation. Spontaneous vegetation with manure improved the microbial biomass nitrogen (P < 0.05). Although the impact of short-term fallowing on microbial community structure was low, an effect of management was observed for some genera. Blastopirellula, Lysobacter, and Acidobacteria Gp6 showed significant differences among fallow treatments by the end of the year (P < 0.05). Blastopirellula abundance was related to the microbial biomass nitrogen and nitrogen mineralization rate in the subsoil. Manure retained a high abundance of Lysobacter, which may strengthen soil-borne disease resistance. The response of Acidobacteria Gp6 showed that meadow vegetation without manure may not benefit future crops. Although the treatments did not significantly improve microbial community structure in the one-year period, annual fallowing improved certain subsoil properties and increased the number of functional genera, which may enhance crop productivity in the future.

The Potential Role of Gut Mycobiome in Irritable Bowel Syndrome

The human gut is inhabited by diverse microorganisms that play crucial roles in health and disease. Gut microbiota dysbiosis is increasingly considered as a vital factor in the etiopathogenesis of irritable bowel syndrome (IBS), which is a common functional gastrointestinal disorder with a high incidence all over the world. However, investigations to date are primarily directed to the bacterial community, and the gut mycobiome, another fundamental part of gut ecosystem, has been underestimated. Intestinal fungi have important effects on maintaining gut homeostasis just as bacterial species. In the present article, we reviewed the potential roles of gut mycobiome in the pathogenesis of IBS and the connections between the fungi and existing mechanisms such as chronic low-grade inflammation, visceral hypersensitivity, and brain-gut interactions. Moreover, possible strategies targeted at the gut mycobiome for managing IBS were also described. This review provides a basis for considering the role of the mycobiome in IBS and offers novel treatment strategies for IBS patients; moreover, it adds new dimensions to researches on microorganism.