The microbiota-gut-brain axis in gastrointestinal disorders: stressed bugs, stressed brain or both?

Specialized metabolites from the microbiome in health and disease

The microbiota, and the genes that comprise its microbiome, play key roles in human health. Host-microbe interactions affect immunity, metabolism, development, and behavior, and dysbiosis of gut bacteria contributes to disease. Despite advances in correlating changes in the microbiota with various conditions, specific mechanisms of host-microbiota signaling remain largely elusive. We discuss the synthesis of microbial metabolites, their absorption, and potential physiological effects on the host. We propose that the effects of specialized metabolites may explain present knowledge gaps in linking the gut microbiota to biological host mechanisms during initial colonization, and in health and disease.

Altered erythrocyte membrane fatty acid profile in typical Rett syndrome: effects of omega-3 polyunsaturated fatty acid supplementation

This study mainly aims at examining the erythrocyte membrane fatty acid (FAs) profile in Rett syndrome (RTT), a genetically determined neurodevelopmental disease. Early reports suggest a beneficial effects of omega-3 polyunsaturated fatty acids (ω-3 PUFAs) on disease severity in RTT. A total of 24 RTT patients were assigned to ω-3 PUFAs-containing fish oil for 12 months in a randomized controlled study (average DHA and EPA doses of 72.9, and 117.1mg/kgb.w./day, respectively). A distinctly altered FAs profile was detectable in RTT, with deficient ω-6 PUFAs, increased saturated FAs and reduced trans 20:4 FAs. FAs changes were found to be related to redox imbalance, subclinical inflammation, and decreased bone density. Supplementation with ω-3 PUFAs led to improved ω-6/ω-3 ratio and serum plasma lipid profile, decreased PUFAs peroxidation end-products, normalization of biochemical markers of inflammation, and reduction of bone hypodensity as compared to the untreated RTT group. Our data indicate that a significant FAs abnormality is detectable in the RTT erythrocyte membranes and is partially rescued by ω-3 PUFAs.

The past 10 years of gastroenterology and hepatology-reflections and predictions

In November 2004, the very first issue of this journal featured articles on the pathogenesis of ulcerative colitis, mechanisms leading to chronic pancreatitis, and treatment of recurrent Clostridium-difficile-associated diarrhoea. Although those topics might seem familiar, much has changed in the intervening years in our understanding, diagnosis and treatment of many different diseases across the field of gastroenterology and hepatology. Nonetheless, many challenges remain. Here, we have asked five of our Advisory Board members-international experts across different subspecialties in gastroenterology and hepatology-to reflect on the progress and frustrations of the past 10 years. They also comment on where effort and money should be invested now, as well as their predictions for progress in the next 10 years.

Probiotics normalize the gut-brain-microbiota axis in immunodeficient mice

The gut-brain-microbiota axis is increasingly recognized as an important regulator of intestinal physiology. Exposure to psychological stress causes activation of the hypothalamic-pituitary-adrenal (HPA) axis and causes altered intestinal barrier function, intestinal dysbiosis, and behavioral changes. The primary aim of this study was to determine whether the effects of psychological stress on intestinal physiology and behavior, including anxiety and memory, are mediated by the adaptive immune system. Furthermore, we wanted to determine whether treatment with probiotics would normalize these effects. Here we demonstrate that B and T cell-deficient Rag1(-/-) mice displayed altered baseline behaviors, including memory and anxiety, accompanied by an overactive HPA axis, increased intestinal secretory state, dysbiosis, and decreased hippocampal c-Fos expression. Both local (intestinal physiology and microbiota) and central (behavioral and hippocampal c-Fos) changes were normalized by pretreatment with probiotics, indicating an overall benefit on health conferred by changes in the microbiota, independent of lymphocytes. Taken together, these findings indicate a role for adaptive immune cells in maintaining normal intestinal and brain health in mice and show that probiotics can overcome this immune-mediated deficit in the gut-brain-microbiota axis.

Cyclic dipeptides: from bugs to brain

Cyclic dipeptides (CDPs) are a group of hormone-like molecules that are evolutionarily conserved from bacteria to humans. In bacteria, CDPs are used in quorum sensing (QS) to communicate information about population size and to regulate a behavioural switch from symbiosis with their host to virulence. In mammals, CDPs have been shown to act on glial cells (macrophage-like cells) to control a conceptually homologous behavioural switch between homeostatic and inflammatory modes, with implications for the control of neurodegenerative disease. Here we argue that, because of their capacity to regulate inflammation via glial cells and induce a protective response in neuronal cells, CDPs have potential therapeutic utility in an array of inflammatory diseases.

Direct Detection and Quantification of Bacterial Genes Associated with Inflammation in DNA Isolated from Stool

Although predominantly associated with health benefits, the gut microbiota has also been shown to harbor genes that promote inflammation. In this work, we report a method for the direct detection and quantification of these pro-inflammatory bacterial genes by PCR and qPCR in DNA extracted from human stool samples. PCR reactions were performed to detect (i) the pks island genes, (ii) tcpC, which is present in some strains of Escherichia coli and (iii) gelE presented in some strains of Enterococcus faecalis. Additionally, we screened for the presence of the following genes encoding cyclomodulins that disrupted mammalian cell division: (iv) cdt (which encodes the cytolethal distending toxin) and (v) cnf-1 (which encodes the cytotoxic necrotizing factor-1). Our results show that 20% of the samples (N = 41) tested positive for detectable amounts of pks island genes, whereas 10% of individuals were positive for tcpC or gelE and only one individual was found to harbor the cnf-1 gene. Of the 13 individuals that were positive for at least one of the pro-inflammatory genes, 5 were found to harbor more than one. A quantitative version of the assay, which used real-time PCR, revealed the pro-inflammatory genes to be in high copy numbers: up to 1.3 million copies per mg of feces for the pks island genes. Direct detection of specific genes in stool could prove useful toward screening for the presence of pro-inflammatory bacterial genes in individuals with inflammatory bowel diseases or colorectal cancer.