Gut Microbiota #18
By Pr. Satu Pekkala
Academy of Finland Research Fellow, Faculty of Sport and Health Sciences, University of Jyväskylä, Finland
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Created
07 June 2023
Updated
13 September 2023
DIET-INDUCED MODIFICATIONS TO HUMAN MICROBIOME RESHAPE COLONIC HOMEOSTASIS IN IRRITABLE BOWEL SYNDROME
Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that can be classified to different subtypes: diarrheaor constipation-predominant IBS (IBS-D and IBS-C, respectively), IBS with mixed bowel habits, and unclassified IBS. Many IBS patients benefit from low-fermentable oligo-, di- and monosaccharides as well as polyols (FODMAP) diet. However, only about 60-70% of patients clinically respond to the diet. This study examined the effects of 6-weeks low-FODMAP diet on the gut microbiota in therapy-naive patients with IBS-D. The diet led to an increase in the abundance of Acutalibacter timonensis and Oscillibacter species, as well as a decrease in Bifidobacterium adolescentis, Eubacterium ventriosum, and Clostridium disporicum. Seventy percent of the patients showed improvements in disease manifestations. The authors then studied using ex vivo gut organ cultures how the fecal samples affected gene expression. The post-diet microbiota induced expression of genes implicated in enteric neuronal and muscle functions and suppressed the expression of many genes encoding pro-inflammatory proteins. Gene ontology analysis revealed that post-diet microbiota increased pathways related to extracellular matrix organization, cellular adhesion, and junction assembly. Because many pathways and genes associated with the abundance of B. adolescentis, the authors co-cultured colonic epithelial cells with B. adolescentis and administered mice with the bacterium to find a mechanistic link between the bacterium and gut health. Both in vitro and in vivo, B. adolescentis disrupted epithelial tight junction integrity and gut barrier functions. Ultimately, using in vitro cultures it was found that fructose avoidance under low-FODMAP diet explained the reduced B. adolescentis levels in patients’ postdiet microbiota. The study provides a mechanistic link between diet, microbiome and intestinal functions which will help, in the future, the development of personalized microbiome-based therapies for human diseases.
ALTERED FUNCTIONAL CONNECTIVITY STRENGTH IN CHRONIC INSOMNIA ASSOCIATED WITH GUT MICROBIOTA COMPOSITION AND SLEEP EFFICIENCY
Little is known about the link between the gut microbiota and resting-state brain activity in patients with chronic insomnia (CI). CI manifests with, for instance, difficulties in initiating or maintaining sleep, obtaining refreshing sleep, and a hyperarousal state. Moreover, CI can impair social, cognitive, and behavioral functioning of the patients. This study investigated associations between the brain functions, gut microbiota composition and neuropsychological performance in patients with CI. The gut microbiota composition strongly associated with neuropsychological performance in CI patients. Specifically, the abundance of Intestinibacter, Lachnospiraceae UCG-003 and Faecalicoccus correlated with the functional connectivity strength (FCS) in the left superior parietal gyrus. This part of the brain is involved in aspects of attention and visuospatial perception, including the representation and manipulation of objects. As expected, the FCS was lower in CI patients than in healthy controls. At the genus level, Alloprevotella, members of Lachnospiraceae family and Faecalicoccus associated with mood and sleep assessment scores. Because Alloprevotella and members of Lachnospiraceae are producers of short chain fatty acids (SCFA), the authors hypothesized that these genera could affect brain functions by modulating SCFA metabolism in CI patients. However, no mechanistic link was established in the study. While the findings of the study were interesting, longitudinal studies are needed to determine whether interventions could affect the gut microbiota of the CI patients and whether the gut microbiota could be targeted, e.g., with probiotic interventions to improve the brain functions in insomnia patients.
MODE OF DELIVERY MODULATES THE INTESTINAL MICROBIOTA AND IMPACTS THE RESPONSE TO VACCINATION
Various factors influence infant’s vaccine responses, such as genetics, birth weight, maternal antibodies, and feeding type. Less is known on the role of gut microbiota in immune responses to vaccination though the microbes importantly affect the development of the immune system early in life. This study determined whether the mode of delivery-induced differences in gut microbial colonization patterns in early life are associated with antigen-specific IgG responses to the pneumococcal 10-valent PCV (PCV-10) and the meningococcal MenC conjugate vaccine. Among many variables studied, the mode of delivery and feeding type were the only early life factors significantly associated with IgG responses against one or more serotypes. The diversity of the gut microbiota was not associated with the PSV or MenC IgG responses. The infants, whose gut microbiota was characterized by low abundances of Bifidobacterium and Escherichia coli had the lowest IgG concentrations against both vaccines. Contrarily, anti-MenC IgG concentrations in infants with high abundance of E. coli were ~2-fold higher, which was also associated with vaginal birth. However, at the age of one year, the gut microbiota did not associate with vaccine responses, confirming that early life microbiota is more related to vaccine responses than the microbiota close to the time of vaccination. Regarding the early life gut microbiota, higher abundances of E. coli and Bifidobacterium associated with high anti-pneumococcal responses, while Clostridium, Prevotella and Streptococcus pyogenes associated with low responses. In high anti-MenC responders, higher abundances of many low abundant OTUs belonging to the Lachnospiraceae family were observed. The study proves that understanding the microbial factors driving immune maturation and vaccine immunogenicity is key to improve vaccine performance in children.
