Intestinal dysbiosis contributes to the delayed gastrointestinal transit in high-fat diet fed mice

Influence of bacterial components on the developmental programming of enteric neurons

BACKGROUND

Intestinal bacteria have been increasingly shown to be involved in early postnatal development. Previous work has shown that intestinal bacteria are necessary for the structural development and intrinsic function of the enteric nervous system in early postnatal life. Furthermore, colonization with a limited number of bacteria appears to be sufficient for the formation of a normal enteric nervous system. We tested the hypothesis that common bacterial components could influence the programming of developing enteric neurons.

METHODS

The developmental programming of enteric neurons was studied by isolating enteric neural crest-derived cells from the fetal gut of C57Bl/6 mice at embryonic day 15.5. After the establishment of the cell line, cultured enteric neuronal precursors were exposed to increasing concentrations of a panel of bacterial components including lipopolysaccharide, flagellin, and components of peptidoglycan.

KEY RESULT

Exposure to bacterial components consistently affected proportions of enteric neuronal precursors that developed into nitrergic neurons. Furthermore, flagellin and D-gamma-Glu-mDAP were found to promote the development of serotonergic neurons. Proportions of dopaminergic neurons remained unchanged. Proliferation of neuronal precursor cells was significantly increased upon exposure to lipopolysaccharide and flagellin, while no significant changes were observed in the proportion of apoptotic neuronal precursors compared to baseline with exposure to any bacterial component.

CONCLUSIONS AND INTERFACES

These findings suggest that bacterial components may influence the development of enteric neurons.

Early life interaction between the microbiota and the enteric nervous system

Recent studies on humans and their key experimental model, the mouse, have begun to uncover the importance of gastrointestinal (GI) microbiota and enteric nervous system (ENS) interactions during developmental windows spanning from conception to adolescence. Disruptions in GI microbiota and ENS during these windows by environmental factors, particularly antibiotic exposure, have been linked to increased susceptibility of the host to several diseases. Mouse models have provided new insights to potential signaling factors between the microbiota and ENS. We review very recent work on maturation of GI microbiota and ENS during three key developmental windows: embryogenesis, early postnatal, and postweaning periods. We discuss advances in understanding of interactions between the two systems and highlight research avenues for future studies.

Enteric Nervous System Remodeling in a Rat Model of Spinal Cord Injury: A Pilot Study

The physiopathology of digestive disorders in patients with spinal cord injury (SCI) remains largely unknown, particularly the involvement of the enteric nervous system (ENS). We aimed in a rat model of chronic thoracic SCI to characterize (1) changes in the neurochemical coding of enteric neurons and their putative consequences upon neuromuscular response, and (2) the inflammatory response of the colon. Ex vivo motility of proximal and distal colon segments of SCI and control (CT) rats were studied in an organ chamber in response to electrical field stimulation (EFS) and bethanechol. Immunohistochemical analysis of proximal and distal segments was performed using antibodies again Hu, neuronal nitric oxide synthase, (nNOS), and choline acetyltransferase. Colonic content of acetylcholine and acetylcholinesterase was measured; messenger RNA (mRNA) expression of inflammatory cytokines was measured using reverse transcription quantitative polymerase chain reaction (RT-qPCR) approaches. Compared with the CT rats, the contractile response to bethanechol was significantly decreased in the proximal colon of SCI rats but not in the distal colon. The proportion of nNOS immunoreactive (IR) neurons was significantly reduced in the proximal but not distal colon of SCI rats. No change in proportion of choline acetyltransferase (ChAT)-IR was reported; the tissue concentration of acetylcholine was significantly decreased in the proximal colon of SCI rats. The expression of tumor necrosis factor alpha (TNF-α) and intercellular adhesion molecule-1 (ICAM-1) was significantly reduced in the proximal and distal colon of SCI rats. This study demonstrates that functional motor and enteric neuroplastic changes affect preferentially the proximal colon compared with the distal colon. The underlying mechanisms and factors responsible for these changes remain to be discovered.

Intestinal Bacteria Maintain Adult Enteric Nervous System and Nitrergic Neurons via Toll-like Receptor 2-induced Neurogenesis in Mice

BACKGROUND & AIMS

The enteric nervous system (ENS) exists in close proximity to luminal bacteria. Intestinal microbes regulate ENS development, but little is known about their effects on adult enteric neurons. We investigated whether intestinal bacteria or their products affect the adult ENS via toll-like receptors (TLRs) in mice.

METHODS

We performed studies with conventional C57/BL6, germ-free C57/BL6, Nestin-creERT2:tdTomato, Nestin-GFP, and ChAT-cre:tdTomato. Mice were given drinking water with ampicillin or without (controls). Germ-free mice were given drinking water with TLR2 agonist or without (controls). Some mice were given a blocking antibody against TLR2 or a TLR4 inhibitor. We performed whole gut transit, bead latency, and geometric center studies. Feces were collected and analyzed by 16S ribosomal RNA gene sequencing. Longitudinal muscle myenteric plexus (LMMP) tissues were collected, analyzed by immunohistochemistry, and levels of nitric oxide were measured. Cells were isolated from colonic LMMP of Nestin-creERT2:tdTomato mice and incubated with agonists of TLR2 (receptor for gram-positive bacteria), TLR4 (receptor for gram-negative bacteria), or distilled water (control) and analyzed by flow cytometry.

RESULTS

Stool from mice given ampicillin had altered composition of gut microbiota with reduced abundance of gram-positive bacteria and increased abundance of gram-negative bacteria, compared with mice given only water. Mice given ampicillin had reduced colon motility compared with mice given only water, and their colonic LMMP had reduced numbers of nitrergic neurons, reduced neuronal nitric oxide synthase production, and reduced colonic neurogenesis. Numbers of colonic myenteric neurons increased after mice were switched from ampicillin to plain water, with increased markers of neurogenesis. Nestin-positive enteric neural precursor cells expressed TLR2 and TLR4. In cells isolated from the colonic LMMP, incubation with the TLR2 agonist increased the percentage of neurons originating from enteric neural precursor cells to approximately 10%, compared with approximately 0.01% in cells incubated with the TLR4 agonist or distilled water. Mice given an antibody against TLR2 had prolonged whole gut transit times; their colonic LMMP had reduced total neurons and a smaller proportion of nitrergic neurons per ganglion, and reduced markers of neurogenesis compared with mice given saline. Colonic LMMP of mice given the TLR4 inhibitor did not have reduced markers of neurogenesis. Colonic LMMP of germ-free mice given TLR2 agonist had increased neuronal numbers compared with control germ-free mice.

CONCLUSIONS

In the adult mouse colon, TLR2 promotes colonic neurogenesis, regulated by intestinal bacteria. Our findings indicate that colonic microbiota help maintain the adult ENS via a specific signaling pathway. Pharmacologic and probiotic approaches directed towards specific TLR2 signaling processes might be developed for treatment of colonic motility disorders related to use of antibiotics or other factors.

Caspase-11-mediated enteric neuronal pyroptosis underlies Western diet-induced colonic dysmotility

Enteric neuronal degeneration, as seen in inflammatory bowel disease, obesity, and diabetes, can lead to gastrointestinal dysmotility. Pyroptosis is a novel form of programmed cell death but little is known about its role in enteric neuronal degeneration. We observed higher levels of cleaved caspase-1, a marker of pyroptosis, in myenteric ganglia of overweight and obese human subjects compared with normal-weight subjects. Western diet-fed (WD-fed) mice exhibited increased myenteric neuronal pyroptosis, delayed colonic transit, and impaired electric field stimulation-induced colonic relaxation responses. WD increased TLR4 expression and cleaved caspase-1 in myenteric nitrergic neurons. Overactivation of nitrergic neuronal NF-κB signaling resulted in increased pyroptosis and delayed colonic motility. In caspase-11-deficient mice, WD did not induce nitrergic myenteric neuronal pyroptosis and colonic dysmotility. To understand the contributions of saturated fatty acids and bacterial products to the steps leading to enteric neurodegeneration, we performed in vitro experiments using mouse enteric neurons. Palmitate and lipopolysaccharide (LPS) increased nitrergic, but not cholinergic, enteric neuronal pyroptosis. LPS gained entry to the cytosol in the presence of palmitate, activating caspase-11 and gasdermin D, leading to pyroptosis. These results support a role of the caspase-11-mediated pyroptotic pathway in WD-induced myenteric nitrergic neuronal degeneration and colonic dysmotility, providing important therapeutic targets for enteric neuropathy.

High-fat diet-induced alterations to gut microbiota and gut-derived lipoteichoic acid contributes to the development of enteric neuropathy

BACKGROUND

High-fat diet, microbial alterations and lipopolysaccharide (LPS) are thought to cause enteric diabetic neuropathy and intestinal dysmotility. However, the role of the gut microbiota, lipoteichoic acid (LTA) from Gram-positive bacteria and short-chain fatty acids (SCFAs) in the development of diabetic enteric neuropathy and intestinal dysmotility is not well understood. Our aim was to examine the role of the gut microbiota, LTA and SCFAs in the development of diabetic enteric neuropathy and intestinal dysmotility.

METHODS

We fed germ-free (GF) and conventionally raised (CR) mice either a high-fat (HFD) or standard chow diet (SCD) for 8 weeks. We analyzed the microbial community composition in CR mice using 16S rRNA sequencing and damage to myenteric neurons using immunohistochemistry. We also studied the effects of LPS, LTA, and SCFAs on duodenal muscularis externa contractions and myenteric neurons using cultured preparations.

KEY RESULTS

High-fat diet ingestion reduced the total number and the number of nitrergic myenteric neurons per ganglion in the duodenum of CR but not in GF-HFD mice. GF mice had fewer neurons per ganglion compared with CR mice. CR mice fed a HFD had increased abundance of Gram-positive bacteria. LTA and LPS did not affect the frequency of duodenal muscularis contractions after 24 hours of cultured but reduced the density of nitrergic myenteric neurons and increased oxidative stress and TNFα production in myenteric ganglia. SCFAs did not affect muscularis contractions or injure myenteric neurons.

CONCLUSIONS & INFERENCES

Gut microbial alterations induced increase in Gram-positive bacterial LTA may contribute to enteric neuropathy.

Gut Epithelial Metabolism as a Key Driver of Intestinal Dysbiosis Associated with Noncommunicable Diseases

In high-income countries, the leading causes of death are noncommunicable diseases (NCDs), such as obesity, cancer, and cardiovascular disease. An important feature of most NCDs is inflammation-induced gut dysbiosis characterized by a shift in the microbial community structure from obligate to facultative anaerobes such as Proteobacteria This microbial imbalance can contribute to disease pathogenesis by either a depletion in or the production of microbiota-derived metabolites. However, little is known about the mechanism by which inflammation-mediated changes in host physiology disrupt the microbial ecosystem in our large intestine leading to disease. Recent work by our group suggests that during gut homeostasis, epithelial hypoxia derived from peroxisome proliferator-activated receptor γ (PPAR-γ)-dependent β-oxidation of microbiota-derived short-chain fatty acids limits oxygen availability in the colon, thereby maintaining a balanced microbial community. During inflammation, disruption in gut anaerobiosis drives expansion of facultative anaerobic Enterobacteriaceae, regardless of their pathogenic potential. Therefore, our research group is currently exploring the concept that dysbiosis-associated expansion of Enterobacteriaceae can be viewed as a microbial signature of epithelial dysfunction and may play a greater role in different models of NCDs, including diet-induced obesity, atherosclerosis, and inflammation-associated colorectal cancer.

Development of the gut microbiota in early life: The impact of cystic fibrosis and antibiotic treatment

OBJECTIVES

Patients with Cystic Fibrosis (CF) suffer from pancreatic insufficiency, lipid malabsorption and gastrointestinal complaints, next to progressive pulmonary disease. Altered mucosal homoeostasis due to malfunctioning chloride channels results in an adapted microbial composition of the gastrointestinal and the respiratory tract. Additionally, antibiotic treatment has the potential to distort resident microbial communities dramatically. This study aims to investigate early life development of the gut microbial community composition of children with CF compared to healthy infants and to study the independent effects of antibiotics taking into account other clinical and lifestyle factors.

STUDY DESIGN

Faecal samples from 20 infants with CF and 45 healthy infants were collected regularly during the first 18 months of life and microbial composition was determined using 16S rRNA based sequencing.

RESULTS

We observed significant differences in the overall microbiota composition between infants with CF and healthy infants (p<0.001). Akkermansia and Anaerostipes were significantly more abundant in control infants, whereas Streptococci and E. coli were significantly more abundant in infants with CF, also after correction for several clinical factors (p<0.05). Antibiotic use in infants with CF was associated with a lower alpha diversity, a reduced abundance of Bifidobacterium and Bacteroides, and a higher abundance of Enterococcus.

CONCLUSION

Microbial development of the gut is different in infants with CF compared to healthy infants from the first months of life on, and further deviates over time, in part as a result of antibiotic treatment. The resulting dysbiosis may have significant functional consequences for the microbial ecosystem in CF patients.

A high-fat diet induces a microbiota-dependent increase in stem cell activity in the Drosophila intestine

Over-consumption of high-fat diets (HFDs) is associated with several pathologies. Although the intestine is the organ that comes into direct contact with all diet components, the impact of HFD has mostly been studied in organs that are linked to obesity and obesity related disorders. We used Drosophila as a simple model to disentangle the effects of a HFD on the intestinal structure and physiology from the plethora of other effects caused by this nutritional intervention. Here, we show that a HFD, composed of triglycerides with saturated fatty acids, triggers activation of intestinal stem cells in the Drosophila midgut. This stem cell activation was transient and dependent on the presence of an intestinal microbiota, as it was completely absent in germ free animals. Moreover, major components of the signal transduction pathway have been elucidated. Here, JNK (basket) in enterocytes was necessary to trigger synthesis of the cytokine upd3 in these cells. This ligand in turn activated the JAK/STAT pathway in intestinal stem cells. Chronic subjection to a HFD markedly altered both the microbiota composition and the bacterial load. Although HFD-induced stem cell activity was transient, long-lasting changes to the cellular composition, including a substantial increase in the number of enteroendocrine cells, were observed. Taken together, a HFD enhances stem cell activity in the Drosophila gut and this effect is completely reliant on the indigenous microbiota and also dependent on JNK signaling within intestinal enterocytes.

High-fat diets have been associated with a plethora of morbidities. The major research focus has been on its effects on obesity related disorders, mostly omitting the intestine, although it is the organ that makes the first contact with all diet components. Here, we aimed to understand the effects of HFD on the intestine itself. Using Drosophila as a model, we showed that a HFD and more specifically, trigylcerides with saturated fatty acids, induced a transient activation of intestinal stem cells. This response completely depended on the presence of an intestinal microbiota, as in germ free flies this reaction was completely abolished. Mechanistically, we found that HFD induces JNK signaling in enterocytes, which triggers production of the cytokine upd3. This ligand of the JAK/STAT pathway, in turn activates STAT signaling in intestinal stem cells, leading to their activation. All these components of the JNK- and JAK/STAT-pathways are necessary for a HFD to lead to increased stem cell production. Moreover, HFD changed both, composition and abundance of the microbiota. As fecal transfer experiments failed to recapitulate the HFD phenotype, we assume that the increased bacterial load is the major cause for the HFD triggered stem cell activation in the intestine.

Gut Microbiota, Its Role in Induction of Alzheimer's Disease Pathology, and Possible Therapeutic Interventions: Special Focus on Anthocyanins

The human gut is a safe environment for several microbes that are symbiotic and important for the wellbeing of human health. However, studies on gut microbiota in different animals have suggested that changes in the composition and structure of these microbes may promote gut inflammation by releasing inflammatory cytokines and lipopolysaccharides, gut-wall leakage, and may affect systemic inflammatory and immune mechanisms that are important for the normal functioning of the body. There are many factors that aid in the gut’s dysbiosis and neuroinflammation, including high stress levels, lack of sleep, fatty and processed foods, and the prolonged use of antibiotics. These neurotoxic mechanisms of dysbiosis may increase susceptibility to Alzheimer’s disease (AD) and other neurodegenerative conditions. Therefore, studies have recently been conducted to tackle AD-like conditions by specifically targeting gut microbes that need further elucidation. It was suggested that gut dyshomeostasis may be regulated by using available options, including the use of flavonoids such as anthocyanins, and restriction of the use of high-fatty-acid-containing food. In this review, we summarize the gut microbiota, factors promoting it, and possible therapeutic interventions especially focused on the therapeutic potential of natural dietary polyflavonoid anthocyanins. Our study strongly suggests that gut dysbiosis and systemic inflammation are critically involved in the development of neurodegenerative disorders, and the natural intake of these flavonoids may provide new therapeutic opportunities for preclinical or clinical studies.

Routine disaccharidase testing: are we there yet?

PURPOSE OF REVIEW

Disaccharidase testing, as applied to the evaluation of gastrointestinal disturbances is available but it is not routinely considered in the diagnostic work-up. The purpose of this review was to determine if disaccharidase testing is clinically useful and to consider how the results could alter patient management.

RECENT FINDINGS

Indicate that carbohydrate maldigestion could contribute functional bowel disorders and negatively impact the fecal microbiome. Diagnostic techniques include enzyme activity assays performed on random endoscopically obtained small intestinal biopsies, immunohistochemistry, stable isotope tracer and nonenriched substrate load breath testing, and genetic testing for mutations. More than 40 sucrase--isomaltase gene variants coding for defective or reduced enzymatic activity have been reported and deficiency conditions are more common than previously thought.

SUMMARY

The rationale for disaccharidase activity testing relates to a need to fully assess unexplained recurrent abdominal discomfort and associated symptoms. All disaccharidases share the same basic mechanism of mucosal expression and deficiency has far reaching consequences. Testing for disaccharidase expression appears to have an important role in symptom evaluation, but there are accuracy and logistical issues that should be considered. It is likely that specific recommendations for patient management, dietary modification, and enzyme supplementation would come from better testing methods.

Colonic dysmotility associated with high-fat diet-induced obesity: Role of enteric glia

The present study was designed to examine the role of enteric glial cells (EGCs) in colonic neuromuscular dysfunctions in a mouse model of high-fat diet (HFD)-induced obesity. C57BL/6J mice were fed with HFD or standard diet (SD) for 1, 2, or 8 weeks. Colonic interleukin (IL)-1β, IL-6, and malondialdehyde (MDA) levels were measured. Expression of occludin in colonic tissues was examined by western blot. Substance P (SP), S100β, GFAP, and phosphorylated mitogen-activated protein kinase 1 (pERK) were assessed in whole mount specimens of colonic plexus by immunohistochemistry. Colonic tachykininergic contractions, elicited by electrical stimulation or exogenous SP, were recorded in the presence or absence of fluorocitrate (FC). To mimic exposure to HFD, cultured EGCs were incubated with palmitate (PA) and/or lipopolysaccharide (LPS). SP and IL-1β levels were assayed in the culture medium by ELISA. HFD mice displayed an increase in colonic IL-1β and MDA, and a reduction of occludin at week 2. These changes occurred to a greater extent at week 8. In vitro electrically evoked tachykininergic contractions were enhanced in HFD mice after 2 or 8 weeks, and they were blunted by FC. Colonic IL-6 levels as well as substance P and S100β density in myenteric ganglia of HFD mice were increased at week 8, but not at week 1 or 2. In cultured EGCs, co-incubation with palmitate plus LPS led to a significant increase in both SP and IL-1β release. HFD-induced obesity is characterized by a hyperactivation of EGCs and is involved in the development of enteric motor disorders through an increase in tachykininergic activity and release of pro-inflammatory mediators.

Colonic neuronal loss and delayed motility induced by high-fat diet occur independently of changes in the major groups of microbiota in Swiss mice

BACKGROUND

Obesity has been linked to gastrointestinal disorders, and the loss of myenteric neurons in the intestine caused by high-fat diets (HFD) has been attributed to changes in microbiota and lipotoxicity. We investigated whether the prebiotic inulin modulates bacterial populations and alleviates neuronal loss in mice fed HFD.

METHODS

Swiss mice were fed purified rodent diet or HFD (59% kcal fat), or both diets supplemented with inulin for 17 weeks. Intestinal motility was assessed and a metagenome analysis of the colonic microbiota was performed. The gene expression of inflammatory markers was evaluated, and immunofluorescence was performed for different types of myenteric neurons and glial cells in the distal colon.

KEY RESULTS

The HFD caused obesity and delayed colonic motility. The loss of myenteric neurons and glial cells in obese mice affected all of the studied neuronal populations, including neurons positive for myosin-V, neuronal nitric oxide synthase, vasoactive intestinal peptide, and calretinin. Although obese mice supplemented with inulin exhibited improvements in colonic motility, neuronal, and glial cell loss persisted. The HFD did not altered the expression levels of inflammatory cytokines in the intestine or the prevalence of the major groups in microbiota, but inulin increased the proportion of the genus Akkermansia in the obese mice.

CONCLUSIONS AND INFERENCES

In Swiss mice, the HFD-induced neuronal loss but did not change the major groups in microbiota. This suggests that, despite the increase in the beneficial bacteria, other factors that are directly linked to excess dietary lipid intake affect the enteric nervous system.

Impairment of Nrf2- and Nitrergic-Mediated Gastrointestinal Motility in an MPTP Mouse Model of Parkinson's Disease

BACKGROUND

Gastrointestinal (GI) motility dysfunction is the most common non-motor symptom of Parkinson's disease (PD). Studies have indicated that GI motility functions are impaired before the onset of PD.

AIMS

To investigate the underlying mechanism of PD-induced GI dysmotility in MPTP (1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine)-induced animal model.

METHODS

C57BL/6 mice were administered with or without a selective dopamine neurotoxin, MPTP, to induce parkinsonian symptoms. In addition to in vivo studies, in vitro experiments were also conducted in colon specimens using l-methyl-4-phenylpyridinium (MPP+), a metabolic product of MPTP. Gastric emptying, colon motility, nitrergic relaxation, and western blot experiments were performed as reported.

RESULTS

MPTP-induced PD mice showed decreased expression of nuclear factor erythroid 2-related factor (Nrf2) and its target phase II genes in gastric and colon neuromuscular tissues. Decreased levels of tetrahydrobiopterin (BH4, a critical cofactor for nNOS dimerization) associated with uncoupling of nNOS in gastric and colon tissues exposed to MPTP. Impaired enteric nitrergic system led to delayed gastric emptying and slower colonic motility compared to the control mice. In vitro results in colon specimens confirm that activation of Nrf2 restored MPP+-induced suppression of alpha-synuclein, tyrosine hydroxylase (TH), Nrf2, and heme oxygenase-1. In vitro exposure to L-NAME [N(w)-nitro-L-arginine methyl ester], a NOS synthase inhibitor, reduced protein expression of TH in colon tissue homogenates.

CONCLUSIONS

Loss of Nrf2/BH4/nNOS expression in PD impairs antioxidant gene expression, which deregulates NO synthesis, thereby contributing to the development of GI dysmotility and constipation. Nitric oxide appears to be important to maintain dopamine synthesis in the colon.

Regulation of Gut Microbiota and Metabolic Endotoxemia with Dietary Factors

Metabolic endotoxemia is a condition in which blood lipopolysaccharide (LPS) levels are elevated, regardless of the presence of obvious infection. It has been suggested to lead to chronic inflammation-related diseases such as obesity, type 2 diabetes mellitus, non-alcoholic fatty liver disease (NAFLD), pancreatitis, amyotrophic lateral sclerosis, and Alzheimer’s disease. In addition, it has attracted attention as a target for the prevention and treatment of these chronic diseases. As metabolic endotoxemia was first reported in mice that were fed a high-fat diet, research regarding its relationship with diets has been actively conducted in humans and animals. In this review, we summarize the relationship between fat intake and induction of metabolic endotoxemia, focusing on gut dysbiosis and the influx, kinetics, and metabolism of LPS. We also summarize the recent findings about dietary factors that attenuate metabolic endotoxemia, focusing on the regulation of gut microbiota. We hope that in the future, control of metabolic endotoxemia using dietary factors will help maintain human health.

Gut Microbiota-Produced Tryptamine Activates an Epithelial G-Protein-Coupled Receptor to Increase Colonic Secretion

Tryptamine, a tryptophan-derived monoamine similar to 5-hydroxytryptamine (5-HT), is produced by gut bacteria and is abundant in human and rodent feces. However, the physiologic effect of tryptamine in the gastrointestinal (GI) tract remains unknown. Here, we show that the biological effects of tryptamine are mediated through the 5-HT₄ receptor (5-HT₄R), a G-protein-coupled receptor (GPCR) uniquely expressed in the colonic epithelium. Tryptamine increases both ionic flux across the colonic epithelium and fluid secretion in colonoids from germ-free (GF) and humanized (ex-GF colonized with human stool) mice, consistent with increased intestinal secretion. The secretory effect of tryptamine is dependent on 5-HT₄R activation and is blocked by 5-HT₄R antagonist and absent in 5-HT₄R^-/- mice. GF mice colonized by Bacteroides thetaiotaomicron engineered to produce tryptamine exhibit accelerated GI transit. Our study demonstrates an aspect of host physiology under control of a bacterial metabolite that can be exploited as a therapeutic modality. VIDEO ABSTRACT.

Obesity, Motility, Diet, and Intestinal Microbiota-Connecting the Dots

PURPOSE OF REVIEW

The goal of the present review is to explore the relationship between dietary changes and alterations in gut microbiota that contribute to disorders of gut motility and obesity.

RECENT FINDINGS

We review the microbiota changes that are seen in obesity, diarrhea, and constipation and look at potential mechanisms of how dysbiosis can predispose to these. We find that microbial metabolites, particularly short chain fatty acids, can lead to signaling changes in the host enterocytes. Microbial alteration leading to both motility disorders and obesity may be mediated by the release of hormones including glucagon-like peptides 1 and 2 (GLP-1, GLP-2) and polypeptide YY (PYY). These pathways provide avenues for microbiota-targeted interventions that can treat both disorders of motility and obesity. In summary, multiple mechanisms contribute to the interplay between the microbial dysbiosis, obesity, and dysmotility.

Metabolic Modeling of Clostridium difficile Associated Dysbiosis of the Gut Microbiota

Recent in vitro experiments have demonstrated the ability of the pathogen Clostridium difficile and commensal gut bacteria to form biofilms on surfaces, and biofilm development in vivo is likely. Various studies have reported that 3%–15% of healthy adults are asymptomatically colonized with C. difficile, with commensal species providing resistance against C. difficile pathogenic colonization. C. difficile infection (CDI) is observed at a higher rate in immunocompromised patients previously treated with broad spectrum antibiotics that disrupt the commensal microbiota and reduce competition for available nutrients, resulting in imbalance among commensal species and dysbiosis conducive to C. difficile propagation. To investigate the metabolic interactions of C. difficile with commensal species from the three dominant phyla in the human gut, we developed a multispecies biofilm model by combining genome-scale metabolic reconstructions of C. difficile, Bacteroides thetaiotaomicron from the phylum Bacteroidetes, Faecalibacterium prausnitzii from the phylum Firmicutes, and Escherichia coli from the phylum Proteobacteria. The biofilm model was used to identify gut nutrient conditions that resulted in C. difficile-associated dysbiosis characterized by large increases in C. difficile and E. coli abundances and large decreases in F. prausnitzii abundance. We tuned the model to produce species abundances and short-chain fatty acid levels consistent with available data for healthy individuals. The model predicted that experimentally-observed host-microbiota perturbations resulting in decreased carbohydrate/increased amino acid levels and/or increased primary bile acid levels would induce large increases in C. difficile abundance and decreases in F. prausnitzii abundance. By adding the experimentally-observed perturbation of increased host nitrate secretion, the model also was able to predict increased E. coli abundance associated with C. difficile dysbiosis. In addition to rationalizing known connections between nutrient levels and disease progression, the model generated hypotheses for future testing and has the capability to support the development of new treatment strategies for C. difficile gut infections.

Compositional changes to the ileal microbiome precede the onset of spontaneous ileitis in SHIP deficient mice

Inflammatory bowel disease, encompassing both ulcerative colitis and Crohn's disease, is characterized by chronic, relapsing-remitting gastrointestinal inflammation of unknown etiology. SHIP deficient mice develop fully penetrant, spontaneous ileitis at 6 weeks of age, and thus offer a tractable model of Crohn's disease-like inflammation. Since disruptions to the microbiome are implicated in the pathogenesis of Crohn's disease, we conducted a 16S rRNA gene survey of the ileum, cecum, colon, and stool contents of SHIP^+/+ and SHIP^-/- mice. We predicted that diversity and compositional changes would occur after, and possibly prior to, the onset of overt disease. No differences were found in alpha diversity, but significant changes in beta diversity and specific commensal populations were observed in the ileal compartment of SHIP deficient mice after the onset of overt disease. Specifically, reductions in the Bacteroidales taxa, Muribaculum intestinale, and an expansion in Lactobacillus were most notable. In contrast, expansions to bacterial taxa previously associated with inflammation, including Bacteroides, Parabacteroides, and Prevotella were observed in the ilea of SHIP deficient mice prior to the onset of overt disease. Finally, antibiotic treatment reduced the development of intestinal inflammation in SHIP^-/- mice. Thus, our findings indicate that SHIP is involved in maintaining ileal microbial homeostasis. These results have broader implications for humans, since reduced SHIP protein levels have been reported in people with Crohn's disease.

Advances in Enteric Neurobiology: The "Brain" in the Gut in Health and Disease

The enteric nervous system (ENS) is a large, complex division of the peripheral nervous system that regulates many digestive, immune, hormonal, and metabolic functions. Recent advances have elucidated the dynamic nature of the mature ENS, as well as the complex, bidirectional interactions among enteric neurons, glia, and the many other cell types that are important for mediating gut behaviors. Here, we provide an overview of ENS development and maintenance, and focus on the latest insights gained from the use of novel model systems and live-imaging techniques. We discuss major advances in the understanding of enteric glia, and the functional interactions among enteric neurons, glia, and enteroendocrine cells, a large class of sensory epithelial cells. We conclude by highlighting recent work on muscularis macrophages, a group of immune cells that closely interact with the ENS in the gut wall, and the importance of neurological-immune system communication in digestive health and disease.

Inflammasome: A Double-Edged Sword in Liver Diseases

Inflammasomes have emerged as critical innate sensors of host immune that defense against pathogen infection, metabolism syndrome, cellular stress and cancer metastasis in the liver. The assembly of inflammasome activates caspase-1, which promotes the maturation of interleukin-1β (IL-1β) and interleukin-18 (IL-18), and initiates pyroptotic cell death (pyroptosis). IL-18 exerts pleiotropic effects on hepatic NK cells, priming FasL-mediated cytotoxicity, and interferon-γ (IFN-γ)-dependent responses to prevent the development of liver diseases. However, considerable attention has been attracted to the pathogenic role of inflammasomes in various acute and chronic liver diseases, including viral hepatitis, nanoparticle-induced liver injury, alcoholic and non-alcoholic steatohepatitis. In this review, we summarize the latest advances on the physiological and pathological roles of inflammasomes for further development of inflammasome-based therapeutic strategies for human liver diseases.

Microbial Changes and Host Response in F344 Rat Colon Depending on Sex and Age Following a High-Fat Diet

Gut microbiota, an important component that affects host health, change rapidly and directly in response to altered diet composition. Recently, the role of diet–microbiome interaction on the development of colon cancer has been the focus of interest. Colon cancer occurs more frequently in an aged population, and in males. However, the effect of dietary changes on the gut microbiome has been studied mainly in young males, even though it may vary with age and sex. The aim of this study was to investigate microbial changes and host response in the colons of male and female 6-week-old (young) and 2-year-old (old) Fisher-344 rats exposed to a high-fat diet (HFD). Our results showed that exposure to HFD for 8 weeks decreased the species richness of microbiota (Chao1) and increased Firmicutes/Bacteroidetes ratio only in aged rats, and not in young rats. Sex differences underlying the alteration by HFD in the gut microbiome were observed in the microbiome of aged rats. For instance, the abundance ratio of Akkermansia muciniphila and Desulfovibrio spp. increased in response to HFD in young rats and female aged rats, but not in male aged rats. Histological inflammation and cell proliferation of colon mucosa (indexed by Ki67) were significantly increased by HFD even in young rats; aged rats showed significantly higher cell proliferation in the HFD group than in the control. The HFD-induced decrease of species richness and the increase in specific species (Desulfovibrio spp. and Clostridium lavalense), which produce carcinogenic compounds such as H₂S and N-nitroso compounds, were significantly correlated with Ki67 index. In colon mucosa, the concentration of myeloperoxidase was increased by HFD only in males, and not in females. In conclusion, the results suggest a link between HFD-induced gut dysbiosis (particularly the low species richness and high abundance ratios of Desulfovibrio spp. and C. lavalense) and cell proliferation of colon mucosa (indicated by Ki67 IHC). In addition, sex differences influence the response of gut microbiome to HFD particularly in old age. Such sex differences in the gut microbiota might be related to sex differences in inflammation in the colon mucosa.

Interplay between colonic inflammation and tachykininergic pathways in the onset of colonic dysmotility in a mouse model of diet-induced obesity

BACKGROUND

The murine model of high fat diet (HFD)-induced obesity is characterized by an increment of intestinal permeability, secondary to an impairment of mucosal epithelial barrier and enteric inflammation, followed by morphofunctional rearrangement of the enteric nervous system. The present study investigated the involvement of abdominal macrophages in the mechanisms underlying the development of enteric dysmotility associated with obesity.

METHODS

Wild type C57BL/6J mice were fed with HFD (60% kcal from fat) or normocaloric diet (NCD, 18% kcal from fat) for 8 weeks. Groups of mice fed with NCD or HFD were treated with clodronate encapsulated into liposomes to deplete abdominal macrophages. Tachykininergic contractions, elicited by electrical stimulation or exogenous substance P (SP), were recorded in vitro from longitudinal muscle colonic preparations. Substance P distribution was examined by confocal immunohistochemistry. The density of macrophages in the colonic wall was examined by immunohistochemical analysis. Malondialdehyde (MDA, colorimetric assay) and IL-1β (ELISA assay) levels were also evaluated.

RESULTS

MDA and IL-1β levels were increased in colonic tissues from HFD-treated animals. In colonic preparations, electrically evoked tachykininergic contractions were enhanced in HFD mice. Immunohistochemistry displayed an increase in substance P immunoreactivity in myenteric ganglia, as well as in the muscular layers of colonic cryosections from obese mice. Macrophage depletion in HFD mice was associated with a significant reduction of colonic inflammation. In addition, the decrease in macrophage density attenuated the morphofunctional alterations of tachykininergic pathways observed in obese mice.

CONCLUSION

Obesity elicited by HFD determines a condition of colonic inflammation, followed by a marked rearrangement of motor excitatory tachykininergic enteric nerves. Macrophage depletion counteracted the morphofunctional changes of colonic neuromuscular compartment, suggesting a critical role for these immune cells in the onset of enteric dysmotility associated with obesity.

Dietary flavonoids as a potential intervention to improve redox balance in obesity and related co-morbidities: a review

Obesity represents one of major health problems strongly linked to other co-morbidities, such as type 2 diabetes, CVD, gastrointestinal disorders and cognitive impairment. In this context, nutritional stress, such as an excess of fat intake, promotes a systemic oxidative stress, characterised by hyperproduction of reactive oxygen species, leading to cellular alterations that include impaired energy metabolism, altered cell signalling and cell cycle control, impaired cell transport mechanisms and overall dysfunctional biological activity. Flavonoids, dietary components of plant foods, are endowed with a wide spectrum of biological activities, including antioxidant activity, and have been proposed to reduce the risk of major chronic diseases. The present review intends to highlight and critically discuss the current scientific evidence on the possible effects of flavonoids in counteracting obesity and related co-morbidities (i.e. type 2 diabetes mellitus, CVD, gastrointestinal disorders and cognitive impairment) through a decrease in oxidative stress and related inflammatory conditions.

The flavonoid compound apigenin prevents colonic inflammation and motor dysfunctions associated with high fat diet-induced obesity

Background and purpose

Apigenin can exert beneficial actions in the prevention of obesity. However, its putative action on obesity-associated bowel motor dysfunctions is unknown. This study examined the effects of apigenin on colonic inflammatory and motor abnormalities in a mouse model of diet-induced obesity.

Experimental approach

Male C57BL/6J mice were fed with standard diet (SD) or high-fat diet (HFD). SD or HFD mice were treated with apigenin (10 mg/Kg/day). After 8 weeks, body and epididymal fat weight, as well as cholesterol, triglycerides and glucose levels were evaluated. Malondialdehyde (MDA), IL-1β and IL-6 levels, and let-7f expression were also examined. Colonic infiltration by eosinophils, as well as substance P (SP) and inducible nitric oxide synthase (iNOS) expressions were evaluated. Motor responses elicited under blockade of NOS and tachykininergic contractions were recorded in vitro from colonic longitudinal muscle preparations.

Key results

When compared to SD mice, HFD animals displayed increased body weight, epididymal fat weight and metabolic indexes. HFD mice showed increments in colonic MDA, IL-1β and IL-6 levels, as well as a decrease in let-7f expression in both colonic and epididymal tissues. HFD mice displayed an increase in colonic eosinophil infiltration. Immunohistochemistry revealed an increase in SP and iNOS expression in myenteric ganglia of HFD mice. In preparations from HFD mice, electrically evoked contractions upon NOS blockade or mediated by tachykininergic stimulation were enhanced. In HFD mice, Apigenin counteracted the increase in body and epididymal fat weight, as well as the alterations of metabolic indexes. Apigenin reduced also MDA, IL-1β and IL-6 colonic levels as well as eosinophil infiltration, SP and iNOS expression, along with a normalization of electrically evoked tachykininergic and nitrergic contractions. In addition, apigenin normalized let-7f expression in epididymal fat tissues, but not in colonic specimens.

Conclusions and implications

Apigenin prevents systemic metabolic alterations, counteracts enteric inflammation and normalizes colonic dysmotility associated with obesity.

Fecal imaging demonstrates that low-methoxyl pectin supplementation normalizes gastro-intestinal transit in mice given a liquid diet

This study has the following aims: (1) to confirm a methodology for a fecal indocyanine green (ICG) imaging test for measuring gastro-intestinal transit time (GITT); and (2) to compare GITT in mice given a liquid diet in which viscosity increases under acidic conditions to that in mice given stable liquid diets with comparable viscosity or regular chow. To address Aim 1, mice received ICG orally along with intraperitoneal injection of atropine in Study 1, and mice were given ICG orally with concurrent carmine red for Study 2. Fluorescence imaging of feces collected for 8 h thereafter was used to detect the first feces with fluorescence and thereby determine GITT. To address Aim 2, mice were fed ad libitum for 1 week with either liquid diet or regular chow for Study 3, or with liquid diet containing low-methoxyl (LM) pectin or high-methoxyl (HM) pectin, or regular chow for Study 4. GITT was then determined by fecal ICG imaging. Atropine delayed GITT in a dose-dependent manner. The GITT of ICG completely corresponded to that of carmine red (correlation coefficient, 1.00). The first ICG excretion in the loose/some diarrheal feces of mice given a liquid diet was seen at 170 min. Feces of mice given liquid diet were loose with LM pectin and loose/some diarrhea with HM pectin. GITT of mice given liquid diet with HM pectin was significantly delayed (280 min) compared to that of mice given liquid diet with LM pectin (111 min) or regular chow (130 min). Fecal imaging of ICG enables measurements of GITT. LM pectin supplementation in a liquid diet may normalize GITT in mice to that of a normal meal and may be associated with changes in fecal properties.

Stool Immune Profiles Evince Gastrointestinal Inflammation in Parkinson's Disease

BACKGROUND

Gastrointestinal symptoms are common in Parkinson's disease and frequently precede the development of motor impairments. Intestinal inflammation has been proposed as a driver of disease pathology, and evaluation of inflammatory mediators in stool could possibly identify valuable early-stage biomarkers. We measured immune- and angiogenesis-related proteins in human stool to examine inflammatory profiles associated with Parkinson's disease.

METHODS

Stool samples and subjects' self-reported metadata were obtained from 156 individuals with Parkinson's disease and 110 without, including spouse and nonhousehold controls. Metadata were probed for disease-associated differences, and levels of 37 immune and angiogenesis factors in stool homogenates were measured by multiplexed immunoassay and compared across experimental groups.

RESULTS

Parkinson's disease patients reported greater incidence of intestinal disease and digestive problems than controls. Direct comparison of levels of stool analytes in patients and controls revealed elevated vascular endothelial growth factor receptor 1, interleukin-1α, and CXCL8 in patients' stool. Paired comparison of patients and spouses suggested higher levels of multiple factors in patients, but this was complicated by sex differences. Sex, body mass index, a history of smoking, and use of probiotics were found to strongly influence levels of stool analytes. Multivariate analysis accounting for these and other potential confounders confirmed elevated levels of interleukin-1α and CXCL8 and also revealed increased interleukin-1β and C-reactive protein in stool in Parkinson's disease. These differences were not dependent on subject age or disease duration.

CONCLUSIONS

Levels of stool immune factors indicate that intestinal inflammation is present in patients with Parkinson's disease. © 2018 International Parkinson and Movement Disorder Society.

Prevalence of Functional Constipation and Relationship with Dietary Habits in 3- to 8-Year-Old Children in Japan

Objectives

To determine the prevalence and effect of dietary habits on functional constipation in preschool and early elementary school children in Japan.

Study Design

A total of 3595 children aged 3 to 8 years from 28 nursery schools and 22 elementary schools in Yokohama City, Kanagawa Prefecture, Japan, were evaluated. The subjects were divided into a functional constipation group and a nonfunctional constipation group according to the Rome III criteria. Dietary intake data were collected using a brief-type, self-administered, diet-history questionnaire validated for Japanese preschool-aged children.

Results

Of the 3595 subjects evaluated, 718 (20.0%) had functional constipation. The association between functional constipation and gender was not statistically significant (p = 0.617). A decrease in bowel frequency was observed in 15.9% of those with functional constipation. There was no significant difference in the proportion of participants in the constipation group by age (p = 0.112). Binomial logistic regression analysis indicated that only fat per 100 kcal positively correlated with functional constipation [odds ratio = 1.216, 95% confidence interval: 1.0476–1.412].

Conclusions

Functional constipation is common among children in preschool and early elementary school in urban areas of Japan. Parents should pay attention to constipation-related symptoms other than defecation frequency. A high-fat diet should be avoided to prevent functional constipation.

Feeding Immunity: Physiological and Behavioral Responses to Infection and Resource Limitation

Resources are a core currency of species interactions and ecology in general (e.g., think of food webs or competition). Within parasite-infected hosts, resources are divided among the competing demands of host immunity and growth as well as parasite reproduction and growth. Effects of resources on immune responses are increasingly understood at the cellular level (e.g., metabolic predictors of effector function), but there has been limited consideration of how these effects scale up to affect individual energetic regimes (e.g., allocation trade-offs), susceptibility to infection, and feeding behavior (e.g., responses to local resource quality and quantity). We experimentally rewilded laboratory mice (strain C57BL/6) in semi-natural enclosures to investigate the effects of dietary protein and gastrointestinal nematode (Trichuris muris) infection on individual-level immunity, activity, and behavior. The scale and realism of this field experiment, as well as the multiple physiological assays developed for laboratory mice, enabled us to detect costs, trade-offs, and potential compensatory mechanisms that mice employ to battle infection under different resource conditions. We found that mice on a low-protein diet spent more time feeding, which led to higher body fat stores (i.e., concentration of a satiety hormone, leptin) and altered metabolite profiles, but which did not fully compensate for the effects of poor nutrition on albumin or immune defenses. Specifically, immune defenses measured as interleukin 13 (IL13) (a primary cytokine coordinating defense against T. muris) and as T. muris-specific IgG1 titers were lower in mice on the low-protein diet. However, these reduced defenses did not result in higher worm counts in mice with poorer diets. The lab mice, living outside for the first time in thousands of generations, also consumed at least 26 wild plant species occurring in the enclosures, and DNA metabarcoding revealed that the consumption of different wild foods may be associated with differences in leptin concentrations. When individual foraging behavior was accounted for, worm infection significantly reduced rates of host weight gain. Housing laboratory mice in outdoor enclosures provided new insights into the resource costs of immune defense to helminth infection and how hosts modify their behavior to compensate for those costs.

Genes and Gut Bacteria Involved in Luminal Butyrate Reduction Caused by Diet and Loperamide

Unbalanced dietary habits and gut dysmotility are causative factors in metabolic and functional gut disorders, including obesity, diabetes, and constipation. Reduction in luminal butyrate synthesis is known to be associated with gut dysbioses, and studies have suggested that restoring butyrate formation in the colon may improve gut health. In contrast, shifts in different types of gut microbiota may inhibit luminal butyrate synthesis, requiring different treatments to restore colonic bacterial butyrate synthesis. We investigated the influence of high-fat diets (HFD) and low-fiber diets (LFD), and loperamide (LPM) administration, on key bacteria and genes involved in reduction of butyrate synthesis in mice. MiSeq-based microbiota analysis and HiSeq-based differential gene analysis indicated that different types of bacteria and genes were involved in butyrate metabolism in each treatment. Dietary modulation depleted butyrate kinase and phosphate butyryl transferase by decreasing members of the Bacteroidales and Parabacteroides. The HFD also depleted genes involved in succinate synthesis by decreasing Lactobacillus. The LFD and LPM treatments depleted genes involved in crotonoyl-CoA synthesis by decreasing Roseburia and Oscilllibacter. Taken together, our results suggest that different types of bacteria and genes were involved in gut dysbiosis, and that selected treatments may be needed depending on the cause of gut dysfunction.

Lack of NLRP3-inflammasome leads to gut-liver axis derangement, gut dysbiosis and a worsened phenotype in a mouse model of NAFLD

Non-Alcoholic Fatty Liver Disease (NAFLD) represents the most common form of chronic liver injury and can progress to cirrhosis and hepatocellular carcinoma. A "multi-hit" theory, involving high fat diet and signals from the gut-liver axis, has been hypothesized. The role of the NLRP3-inflammasome, which senses dangerous signals, is controversial. Nlrp3-/- and wild-type mice were fed a Western-lifestyle diet with fructose in drinking water (HFHC) or a chow diet. Nlrp3-/--HFHC showed higher hepatic expression of PPAR γ2 (that regulates lipid uptake and storage) and triglyceride content, histological score of liver injury and greater adipose tissue inflammation. In Nlrp3-/--HFHC, dysregulation of gut immune response with impaired antimicrobial peptides expression, increased intestinal permeability and the occurrence of a dysbiotic microbiota led to bacterial translocation, associated with higher hepatic expression of TLR4 (an LPS receptor) and TLR9 (a receptor for double-stranded bacterial DNA). After antibiotic treatment, gram-negative species and bacterial translocation were reduced, and adverse effects restored both in liver and adipose tissue. In conclusion, the combination of a Western-lifestyle diet with innate immune dysfunction leads to NAFLD progression, mediated at least in part by dysbiosis and bacterial translocation, thus identifying new specific targets for NAFLD therapy.

Adult enteric nervous system in health is maintained by a dynamic balance between neuronal apoptosis and neurogenesis

According to current dogma, there is little or no ongoing neurogenesis in the fully developed adult enteric nervous system. This lack of neurogenesis leaves unanswered the question of how enteric neuronal populations are maintained in adult guts, given previous reports of ongoing neuronal death. Here, we confirm that despite ongoing neuronal cell loss because of apoptosis in the myenteric ganglia of the adult small intestine, total myenteric neuronal numbers remain constant. This observed neuronal homeostasis is maintained by new neurons formed in vivo from dividing precursor cells that are located within myenteric ganglia and express both Nestin and p75NTR, but not the pan-glial marker Sox10. Mutation of the phosphatase and tensin homolog gene in this pool of adult precursors leads to an increase in enteric neuronal number, resulting in ganglioneuromatosis, modeling the corresponding disorder in humans. Taken together, our results show significant turnover and neurogenesis of adult enteric neurons and provide a paradigm for understanding the enteric nervous system in health and disease.

Western diet induces colonic nitrergic myenteric neuropathy and dysmotility in mice via saturated fatty acid- and lipopolysaccharide-induced TLR4 signalling

KEY POINTS

A high-fat diet (60% kcal from fat) is associated with motility disorders inducing constipation and loss of nitrergic myenteric neurons in the proximal colon. Gut microbiota dysbiosis, which occurs in response to HFD, contributes to endotoxaemia. High levels of lipopolysaccharide lead to apoptosis in cultured myenteric neurons that express Toll-like receptor 4 (TLR4). Consumption of a Western diet (WD) (35% kcal from fat) for 6 weeks leads to gut microbiota dysbiosis associated with altered bacterial metabolites and increased levels of plasma free fatty acids. These disorders precede the nitrergic myenteric cell loss observed in the proximal colon. Mice lacking TLR4 did not exhibit WD-induced myenteric cell loss and dysmotility. Lipopolysaccharide-induced in vitro enteric neurodegeneration requires the presence of palmitate and may be a result of enhanced NO production. The present study highlights the critical role of plasma saturated free fatty acids that are abundant in the WD with respect to driving enteric neuropathy and colonic dysmotility.

ABSTRACT

The consumption of a high-fat diet (HFD) is associated with myenteric neurodegeneration, which in turn is associated with delayed colonic transit and constipation. We examined the hypothesis that an inherent increase in plasma free fatty acids (FFA) in the HFD together with an HFD-induced alteration in gut microbiota contributes to the pathophysiology of these disorders. C57BL/6 mice were fed a Western diet (WD) (35% kcal from fat enriched in palmitate) or a purified regular diet (16.9% kcal from fat) for 3, 6, 9 and 12 weeks. Gut microbiota dysbiosis was investigated by fecal lipopolysaccharide (LPS) measurement and metabolomics (linear trap quadrupole-Fourier transform mass spectrometer) analysis. Plasma FFA and LPS levels were assessed, in addition to colonic and ileal nitrergic myenteric neuron quantifications and motility. Compared to regular diet-fed control mice, WD-fed mice gained significantly more weight without blood glucose alteration. Dysbiosis was exhibited after 6 weeks of feeding, as reflected by increased fecal LPS and bacterial metabolites and concomitant higher plasma FFA. The numbers of nitrergic myenteric neurons were reduced in the proximal colon after 9 and 12 weeks of WD and this was also associated with delayed colonic transit. WD-fed Toll-like receptor 4 (TLR4)^-/- mice did not exhibit myenteric cell loss or dysmotility. Finally, LPS (0.5-2 ng·ml^-1 ) and palmitate (20 and 30 μm) acted synergistically to induce neuronal cell death in vitro, which was prevented by the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester. In conclusion, WD-feeding results in increased levels of FFA and microbiota that, even in absence of hyperglycaemia or overt endotoxaemia, synergistically induce TLR4-mediated neurodegeneration and dysmotility.