Supplementation of Low- and High-fat Diets with Fermentable Fiber Exacerbates Severity of DSS-induced Acute Colitis

Dietary fibers boost gut microbiota-produced B vitamin pool and alter host immune landscape

BACKGROUND

Dietary fibers can alter microbial metabolic output in support of healthy immune function; however, the impact of distinct fiber sources and immunomodulatory effects beyond short-chain fatty acid production are underexplored. In an effort to discern the effects of diverse fibers on host immunity, we employed five distinct rodent diets with varying fiber content and source in specific-pathogen-free, gnotobiotic (containing a 14-member synthetic human gut microbiota), and germ-free mice.

RESULTS

Broad-scale metabolomics analysis of cecal contents revealed that fiber deprivation consistently reduced the concentrations of microbiota-produced B vitamins. This phenomenon was not always explained by reduced biosynthesis, rather, metatranscriptomic analyses pointed toward increased microbial usage of certain B vitamins under fiber-free conditions, ultimately resulting in a net reduction of host-available B vitamins. Broad immunophenotyping indicated that the local gut effector immune populations and activated T cells accumulate in a microbiota-dependent manner. Supplementation with the prebiotic inulin recovered the availability of microbially produced B vitamins and restored immune homeostasis.

CONCLUSIONS

Our findings highlight the potential to use defined fiber polysaccharides to boost microbiota-derived B vitamin availability in an animal model and to regulate local innate and adaptive immune populations of the host. Video abstract.

Cocoa and Polyphenol-Rich Cocoa Fractions Fail to Improve Acute Colonic Inflammation in Dextran Sulfate Sodium-Treated Mice

SCOPE

A study is conducted to determine the anti-inflammatory effects of cocoa and polyphenol-rich cocoa fractions in the dextran sulfate sodium (DSS)-induced mouse model of acute colonic inflammation.

METHODS AND RESULTS

Male C57BL/6J mice are treated with dietary cocoa powder, an extractable cocoa polyphenol fraction, or a non-extractable cocoa polyphenol fraction for 2 weeks prior to treatment with 2.5% DSS in the drinking water for 7 days to induce colonic inflammation. Cocoa treatment continues during the DSS period. Cocoa and/or cocoa fractions exacerbate DSS-induced weight loss and fail to mitigate DSS-induced colon shortening but do improve splenomegaly. Cocoa/cocoa fraction treatment fails to mitigate DSS-induced mRNA and protein markers of inflammation. Principal component analysis shows overlap between cocoa or cocoa fraction-treated mice and DSS-induced controls, but separation from mice not treated with DSS.

CONCLUSION

The results suggest cocoa and cocoa polyphenols may not be useful in mitigating acute colonic inflammation.

Let food be your medicine - dietary fiber

Dietary fiber (DF) cannot be digested and absorbed by the digestive tract, nor can it provide the energy needed to be burned for metabolic activities. Therefore, from the 1950s to the 1980s, DF received little attention in nutrition studies. With in-depth research and developments in global nutrition, people have gradually paid attention to the fact that DF occupies an essential position in the structure of nutrition, and it can ensure the healthy development of human beings. As early as 390 B.C., the ancient Greek physician Hippocrates proposed, "Let your food be your medicine, and your medicine be your food". This concept has been more systematically validated in modern scientific research, with numerous epidemiological studies showing that the dietary intake of DF-rich foods such as whole grains, root vegetables, legumes, and fruits has the potential to regulate the balance of the gut microbiota and thereby prevent diseases. However, the crosstalk between different types of DF and the gut microbiota is quite complex, and the effects on the organism vary. In this paper, we discuss research on DF and the gut microbiota and related diseases, aiming to understand the relationship between all three better and provide a reference basis for the risk reduction of related diseases.

Colorectal cancer and inulin supplementation: the good, the bad, and the unhelpful

The prebiotic inulin has been vaunted for its potential to reduce the risk of colorectal cancer. Inulin fermentation resulting in the production of short-chain fatty acids, primarily butyrate, has been reported to be associated with properties that are beneficial for gut health and has led to an increased consumption of inulin in the Western population through processed food and over-the-counter dietary supplements. However, in clinical trials, there is limited evidence of the efficacy of inulin in preventing colorectal cancer. Moreover, recent data suggest that improper inulin consumption may even be harmful for gastro-intestinal health under certain circumstances. The main objective of this review is to provide insight into the beneficial and potentially detrimental effects of inulin supplementation in the context of colorectal cancer prevention and enhancement of treatment efficacy.

Dietary fiber is a critical determinant of pathologic ILC2 responses and intestinal inflammation

Innate lymphoid cells (ILCs) can promote host defense, chronic inflammation, or tissue protection and are regulated by cytokines and neuropeptides. However, their regulation by diet and microbiota-derived signals remains unclear. We show that an inulin fiber diet promotes Tph1-expressing inflammatory ILC2s (ILC2INFLAM) in the colon, which produce IL-5 but not tissue-protective amphiregulin (AREG), resulting in the accumulation of eosinophils. This exacerbates inflammation in a murine model of intestinal damage and inflammation in an ILC2- and eosinophil-dependent manner. Mechanistically, the inulin fiber diet elevated microbiota-derived bile acids, including cholic acid (CA) that induced expression of ILC2-activating IL-33. In IBD patients, bile acids, their receptor farnesoid X receptor (FXR), IL-33, and eosinophils were all upregulated compared with controls, implicating this diet-microbiota-ILC2 axis in human IBD pathogenesis. Together, these data reveal that dietary fiber-induced changes in microbial metabolites operate as a rheostat that governs protective versus pathologic ILC2 responses with relevance to precision nutrition for inflammatory diseases.

The emergence of inflammatory microglia during gut inflammation is not affected by FFAR2 expression in intestinal epithelial cells or peripheral myeloid cells

Gut inflammation can trigger neuroinflammation and is linked to mood disorders. Microbiota-derived short-chain fatty acids (SCFAs) can modulate microglia, yet the mechanism remains elusive. Since microglia do not express free-fatty acid receptor (FFAR)2, but intestinal epithelial cells (IEC) and peripheral myeloid cells do, we hypothesized that SCFA-mediated FFAR2 activation within the gut or peripheral myeloid cells may impact microglia inflammation. To test this hypothesis, we developed a tamoxifen-inducible conditional knockout mouse model targeting FFAR2 exclusively on IEC and induced intestinal inflammation with dextran sodium sulfate (DSS), a well-established colitis model. Given FFAR2's high expression in myeloid cells, we also investigated its role by selectively deleting it in these populations of cells. In an initial study, male and female wild-type mice received 0 or 2% DSS for 5d and microglia were isolated 3d later to assess inflammatory status. DSS induced intestinal inflammation and upregulated inflammatory gene expression in microglia, indicating inflammatory signaling via the gut-brain axis. Despite the lack of significant effects of sex in the intestinal phenotype, male mice showed higher microglial inflammatory response than females. Subsequent studies using FFAR2 knockout models revealed that FFAR2 expression in IECs or immune myeloid cells did not affect DSS-induced colonic pathology (i.e. clinical and histological scores and colon length), or colonic expression of inflammatory genes. However, FFAR2 knockout led to an upregulation of several microglial inflammatory genes in control mice and downregulation in DSS-treated mice, suggesting that FFAR2 may constrain neuroinflammatory gene expression under healthy homeostatic conditions but may permit it during intestinal inflammation. No interactions with sex were observed, suggesting sex does not play a role on FFAR2 potential function in gut-brain communication in the context of colitis. To evaluate the role of FFAR2 activated by microbiota-derived SCFAs, we employed the same knockout and DSS models adding fermentable dietary fiber (0 or 2.5% inulin for 8 wks). Despite no genotype or fiber main effects, contrary to our hypothesis, inulin feeding augmented DSS-induced inflammation and signs of colitis, suggesting context-dependent effects of fiber. These findings highlight microglial involvement in colitis-associated neuroinflammation and advance our understanding of FFAR2's role in the gut-brain axis. Although not integral, we observed that the role of FFAR2 differs between homeostatic and inflammatory conditions, underscoring the need to consider different inflammatory conditions and disease contexts when investigating the role of FFAR2 and SCFAs in the gut-brain axis.

Gastrointestinal microbiota-directed nutritional and therapeutic interventions for inflammatory bowel disease: opportunities and challenges

Evidence-based research has confirmed the role of gastrointestinal microbiota in regulating intestinal inflammation. These data have generated interest in developing microbiota-based therapies for the prevention and management of inflammatory bowel disease (IBD). Despite in-depth understanding of the etiology of IBD, it currently lacks a cure and requires ongoing management. Accumulating data suggest that an aberrant gastrointestinal microbiome, often referred to as dysbiosis, is a significant environmental instigator of IBD. Novel microbiome-targeted interventions including prebiotics, probiotics, fecal microbiota transplant, and small molecule microbiome modulators are being evaluated as therapeutic interventions to attenuate intestinal inflammation by restoring a healthy microbiota composition and function. In this review, the effectiveness and challenges of microbiome-centered interventions that have the potential to alleviate intestinal inflammation and improve clinical outcomes of IBD are explored.

Nutritional regulation of microbiota-derived metabolites: Implications for immunity and inflammation

Nutrition profoundly shapes immunity and inflammation across the lifespan of mammals, from pre- and post-natal periods to later life. Emerging insights into diet-microbiota interactions indicate that nutrition has a dominant influence on the composition-and metabolic output-of the intestinal microbiota, which in turn has major consequences for host immunity and inflammation. Here, we discuss recent findings that support the concept that dietary effects on microbiota-derived metabolites potently alter immune responses in health and disease. We discuss how specific dietary components and metabolites can be either pro-inflammatory or anti-inflammatory in a context- and tissue-dependent manner during infection, chronic inflammation, and cancer. Together, these studies emphasize the influence of diet-microbiota crosstalk on immune regulation that will have a significant impact on precision nutrition approaches and therapeutic interventions for managing inflammation, infection, and cancer immunotherapy.

Restricted intake of sulfur-containing amino acids reversed the hepatic injury induced by excess Desulfovibrio through gut-liver axis

Diet is a key player in gut-liver axis. However, the effect of different dietary patterns on gut microbiota and liver functions remains unclear. Here, we used rodent standard chow and purified diet to mimic two common human dietary patterns: grain and plant-based diet and refined-food-based diet, respectively and explored their impacts on gut microbiota and liver. Gut microbiota experienced a great shift with notable increase in Desulfovibrio, gut bile acid (BA) levels elevated significantly, and liver inflammation was observed in mice fed with the purified diet. Liver inflammation and elevated gut BA levels also occurred in mice fed with the chow diet after receiving Desulfovibrio desulfuricans ATCC 29,577 (DSV). Restriction of sulfur-containing amino acids (SAAs) prevented liver injury mainly through higher hepatic antioxidant and detoxifying ability and reversed the elevated BA levels due to excess Desulfovibrio. Ex vivo fermentation of human fecal microbiota with primary BAs demonstrated that DSV enhanced production of secondary BAs. Higher concentration of both primary and secondary BAs were found in the gut of germ-free mice after receiving DSV. In conclusion, Restriction of SAAs in diet may become an effective dietary intervention to prevent liver injury associated with excess Desulfovibrio in the gut.

Gut microbiota-mediated polyphenol metabolism is restrained by parasitic whipworm infection and associated with altered immune function in mice

Polyphenols are phytochemicals commonly found in plant-based diets which have demonstrated immunomodulatory and anti-inflammatory properties. However, the interplay between polyphenols and pathogens at mucosal barrier surfaces has not yet been elucidated in detail. Here, we show that proanthocyanidin (PAC) polyphenols interact with gut parasites to influence immune function and gut microbial-derived metabolites in mice. PAC intake inhibited mastocytosis during infection with the small intestinal roundworm Heligmosomoides polygyrus, and altered the host tissue transcriptome at the site of infection with the large intestinal whipworm Trichuris muris, with a notable enhancement of type-1 inflammatory and interferon-driven gene pathways. In the absence of infection, PAC intake promoted the expansion of Turicibacter within the gut microbiota, increased fecal short chain fatty acids, and enriched phenolic metabolites such as phenyl-γ-valerolactones in the cecum. However, these putatively beneficial effects were reduced in PAC-fed mice infected with T. muris, suggesting concomitant parasite infection can attenuate gut microbial-mediated PAC catabolism. Collectively, our results suggest an inter-relationship between a phytonutrient and infection, whereby PAC may augment parasite-induced inflammation (most prominently with the cecum dwelling T. muris), and infection may abrogate the beneficial effects of health-promoting phytochemicals.

Metastatic Colon Cancer in an Individual Following Prolonged Daily Inulin Consumption

Studies in rodents suggest that inulin supplements may be carcinogenic. We present a case implicating that this risk extends to humans. A healthy male from a family lacking history of cancer had his first cancer-screening colonoscopy at age 56. No intestinal polyps/abnormalities were detected. A second colonoscopy, performed 7 years later, revealed a tumor in the cecum, with evidence of metastasis to lymph nodes. The only known change in patient's lifestyle during that seven-year period was the addition of 4g of inulin powder as a daily supplement during the last 2 years. Such inulin consumption is a plausible contributor to his disease.

Immunomodulatory effects of inulin and its intestinal metabolites

"Dietary fiber" (DF) refers to a type of carbohydrate that cannot be digested fully. DF is not an essential nutrient, but it plays an important part in enhancing digestive capacity and maintaining intestinal health. Therefore, DF supplementation in the daily diet is highly recommended. Inulin is a soluble DF, and commonly added to foods. Recently, several studies have found that dietary supplementation of inulin can improve metabolic function and regulate intestinal immunity. Inulin is fermented in the colon by the gut microbiota and a series of metabolites is generated. Among these metabolites, short-chain fatty acids provide energy to intestinal epithelial cells and participate in regulating the differentiation of immune cells. Inulin and its intestinal metabolites contribute to host immunity. This review summarizes the effect of inulin and its metabolites on intestinal immunity, and the underlying mechanisms of inulin in preventing diseases such as type 2 diabetes mellitus, inflammatory bowel disease, chronic kidney disease, and certain cancer types.

Dietary non-starch polysaccharides impair immunity to enteric nematode infection

BACKGROUND

The influence of diet on immune function and resistance to enteric infection and disease is becoming ever more established. Highly processed, refined diets can lead to inflammation and gut microbiome dysbiosis, whilst health-promoting dietary components such as phytonutrients and fermentable fibres are thought to promote a healthy microbiome and balanced mucosal immunity. Chicory (Cichorium intybus) is a leafy green vegetable rich in fibres and bioactive compounds that may promote gut health.

RESULTS

Unexpectedly, we here show that incorporation of chicory into semisynthetic AIN93G diets renders mice susceptible to infection with enteric helminths. Mice fed a high level of chicory leaves (10% dry matter) had a more diverse gut microbiota, but a diminished type-2 immune response to infection with the intestinal roundworm Heligmosomoides polygyrus. Furthermore, the chicory-supplemented diet significantly increased burdens of the caecum-dwelling whipworm Trichuris muris, concomitant with a highly skewed type-1 immune environment in caecal tissue. The chicory-supplemented diet was rich in non-starch polysaccharides, particularly uronic acids (the monomeric constituents of pectin). In accordance, mice fed pectin-supplemented AIN93G diets had higher T. muris burdens and reduced IgE production and expression of genes involved in type-2 immunity. Importantly, treatment of pectin-fed mice with exogenous IL-25 restored type-2 responses and was sufficient to allow T. muris expulsion.

CONCLUSIONS

Collectively, our data suggest that increasing levels of fermentable, non-starch polysaccharides in refined diets compromises immunity to helminth infection in mice. This diet-infection interaction may inform new strategies for manipulating the gut environment to promote resistance to enteric parasites.

Inulin diet uncovers complex diet-microbiota-immune cell interactions remodeling the gut epithelium

BACKGROUND

The continuous proliferation of intestinal stem cells followed by their tightly regulated differentiation to epithelial cells is essential for the maintenance of the gut epithelial barrier and its functions. How these processes are tuned by diet and gut microbiome is an important, but poorly understood question. Dietary soluble fibers, such as inulin, are known for their ability to impact the gut bacterial community and gut epithelium, and their consumption has been usually associated with health improvement in mice and humans. In this study, we tested the hypothesis that inulin consumption modifies the composition of colonic bacteria and this impacts intestinal stem cells functions, thus affecting the epithelial structure.

METHODS

Mice were fed with a diet containing 5% of the insoluble fiber cellulose or the same diet enriched with an additional 10% of inulin. Using a combination of histochemistry, host cell transcriptomics, 16S microbiome analysis, germ-free, gnotobiotic, and genetically modified mouse models, we analyzed the impact of inulin intake on the colonic epithelium, intestinal bacteria, and the local immune compartment.

RESULTS

We show that the consumption of inulin diet alters the colon epithelium by increasing the proliferation of intestinal stem cells, leading to deeper crypts and longer colons. This effect was dependent on the inulin-altered gut microbiota, as no modulations were observed in animals deprived of microbiota, nor in mice fed cellulose-enriched diets. We also describe the pivotal role of γδ T lymphocytes and IL-22 in this microenvironment, as the inulin diet failed to induce epithelium remodeling in mice lacking this T cell population or cytokine, highlighting their importance in the diet-microbiota-epithelium-immune system crosstalk.

CONCLUSION

This study indicates that the intake of inulin affects the activity of intestinal stem cells and drives a homeostatic remodeling of the colon epithelium, an effect that requires the gut microbiota, γδ T cells, and the presence of IL-22. Our study indicates complex cross kingdom and cross cell type interactions involved in the adaptation of the colon epithelium to the luminal environment in steady state. Video Abstract.

The diet-microbiota axis: a key regulator of intestinal permeability in human health and disease

The intestinal barrier orchestrates selective permeability to nutrients and metabolites while excluding noxious stimuli. Recent scientific advances establishing a causal role for the gut microbiota in human health outcomes have generated a resurgent interest toward intestinal permeability. Considering the well-established role of the gut barrier in protection against foreign antigens, there is mounting evidence for a causal link between gut permeability and the microbiome in regulating human health. However, an understanding of the dynamic host-microbiota interactions that govern intestinal barrier functions remains poorly defined. Furthermore, the system-level mechanisms by which microbiome-targeted therapies, such as probiotics and prebiotics, simultaneously promote intestinal barrier function and host health remain an area of active investigation. This review summarizes the recent advances in understanding the dynamics of intestinal permeability in human health and its integration with gut microbiota. We further summarize mechanisms by which probiotics/prebiotics influence the gut microbiota and intestinal barrier functions.

The high dose of inulin exacerbated food allergy through the excess accumulation of short-chain fatty acids in a BABL/c mouse model

Inulin dietary supplement is conventionally beneficial to gut health and can potentially prevent food allergy (FA). This study aimed to determine how dietary inulin interventions at different doses affect the OVA-induced FA in a BALB/c mouse model. Although the middle dose of inulin (50 mg per mouse) showed the best therapeutic effect on FA, high-inulin supplementation (80 mg per mouse) provoked severe allergic and intestinal inflammatory responses, which were characterized by elevated serum allergic inflammation-related factor levels, dysfunctional gut barrier, unbalanced luminal pH value, decrease in intestinal antioxidant capacity, and disordered gut microecology. Moreover, profiling of SCFAs indicated that the high-inulin-induced excess accumulation of SCFAs in the colon was responsible for the gut immune disorders. Spearman correlation analysis unraveled that the featured bacterial taxa in the high-inulin-treated mice were Ruminococcaceae and Bifidobacterium, of which the relative abundance was negatively correlated with expression of tight junction proteins and improvement of T cell homeostasis, and positively correlated with levels of allergic inflammation-related indexes. Our work suggested that high-inulin dietary supplementation can be detrimental to allergic individuals and highlighted the importance for personalized use of inulin-type dietary supplements to safely improve human health.

Psyllium Fiber Protects Against Colitis Via Activation of Bile Acid Sensor Farnesoid X Receptor

BACKGROUND & AIMS

Fiber-rich foods promote health, but mechanisms by which they do so remain poorly defined. Screening fiber types, in mice, revealed psyllium had unique ability to ameliorate 2 chronic inflammatory states, namely, metabolic syndrome and colitis. We sought to determine the mechanism of action of the latter.

METHODS

Mice were fed grain-based chow, which is naturally rich in fiber or compositionally defined diets enriched with semi-purified fibers. Mice were studied basally and in models of chemical-induced and T-cell transfer colitis.

RESULTS

Relative to all diets tested, mice consuming psyllium-enriched compositionally defined diets were markedly protected against both dextran sulfate sodium- and T-cell transfer-induced colitis, as revealed by clinical-type, histopathologic, morphologic, and immunologic parameters. Such protection associated with stark basal changes in the gut microbiome but was independent of fermentation and, moreover, maintained in mice harboring a minimal microbiota (ie, Altered Schaedler Flora). Transcriptomic analysis revealed psyllium induced expression of genes mediating bile acids (BA) secretion, suggesting that psyllium's known ability to bind BA might contribute to its ability to prevent colitis. As expected, psyllium resulted in elevated level of fecal BA, reflecting their removal from enterohepatic circulation but, in stark contrast to the BA sequestrant cholestyramine, increased serum BA levels. Moreover, the use of BA mimetics that activate the farnesoid X receptor (FXR), as well as the use of FXR-knockout mice, suggested that activation of FXR plays a central role in psyllium's protection against colitis.

CONCLUSIONS

Psyllium protects against colitis via altering BA metabolism resulting in activation of FXR, which suppresses pro-inflammatory signaling.

Maternal prebiotic supplementation impacts colitis development in offspring mice

Background and aims

Maternal diet plays a key role in preventing or contributing to the development of chronic diseases, such as obesity, allergy, and brain disorders. Supplementation of maternal diet with prebiotics has been shown to reduce the risk of food allergies and affect the intestinal permeability in offspring later in life. However, its role in modulating the development of other intestinal disorders, such as colitis, remains unknown. Therefore, we investigated the effects of prebiotic supplementation in pregnant mice on the occurrence of colitis in their offspring.

Materials and methods

Offspring from mothers, who were administered prebiotic galacto-oligosaccharides and inulin during gestation or fed a control diet, were subjected to three cycles of dextran sulphate sodium (DSS) treatment to induce chronic colitis, and their intestinal function and disease activity were evaluated. Colonic remodelling, gut microbiota composition, and lipidomic and transcriptomic profiles were also assessed.

Results

DSS-treated offspring from prebiotic-fed mothers presented a higher disease score, increased weight loss, and increased faecal humidity than those from standard diet-fed mothers. DSS-treated offspring from prebiotic-fed mothers also showed increased number of colonic mucosal lymphocytes and macrophages than the control group, associated with the increased colonic concentrations of resolvin D5, protectin DX, and 14-hydroxydocosahexaenoic acid, and modulation of colonic gene expression. In addition, maternal prebiotic supplementation induced an overabundance of eight bacterial families and a decrease in the butyrate caecal concentration in DSS-treated offspring.

Conclusion

Maternal prebiotic exposure modified the microbiota composition and function, lipid content, and transcriptome of the colon of the offspring. These modifications did not protect against colitis, but rather sensitised the mice to colitis development.

Inulin increases the beneficial effects of rhubarb supplementation on high-fat high-sugar diet-induced metabolic disorders in mice: impact on energy expenditure, brown adipose tissue activity, and microbiota

Consumption of prebiotics and plant-based compounds have many beneficial health effects through modulation of gut microbiota composition and are considered as promising nutritional strategy for the treatment of metabolic diseases. In the present study, we assessed the separated and combined effects of inulin and rhubarb on diet-induced metabolic disease in mice. We showed that supplementation with both inulin and rhubarb abolished the total body and fat mass gain upon high-fat and high-sucrose diet (HFHS) as well as several obesity-associated metabolic disorders. These effects were associated with increased energy expenditure, lower whitening of the brown adipose tissue, higher mitochondria activity and increased expression of lipolytic markers in white adipose tissue. Despite modifications of intestinal gut microbiota and bile acid compositions by inulin or rhubarb alone, combination of both inulin and rhubarb had minor additional impact on these parameters. However, the combination of inulin and rhubarb increased the expression of several antimicrobial peptides and higher goblet cell numbers, thereby suggesting a reinforcement of the gut barrier. Together, these results suggest that the combination of inulin and rhubarb in mice potentiates beneficial effects of separated rhubarb and inulin on HFHS-related metabolic disease and could be considered as nutritional strategy for the prevention and treatment of obesity and related pathologies.

Inflammatory bowel disease therapeutic strategies by modulation of the microbiota: how and when to introduce pre-, pro-, syn-, or postbiotics?

Inflammatory bowel diseases (IBD), a heterogeneous group of inflammatory conditions that encompass both ulcerative colitis and Crohn's disease, represent a major public health concern. The etiology of IBD is not yet fully understood and no cure is available, with current treatments only showing long-term effectiveness in a minority of patients. A need to increase our knowledge on IBD pathophysiology is growing, to define preventive measures, to improve disease outcome, and to develop new effective and lasting treatments. IBD pathogenesis is sustained by aberrant immune responses, associated with alterations of the intestinal epithelial barrier (IEB), modifications of the enteric nervous system, and changes in microbiota composition. Currently, most of the treatments target the inflammation and the immune system, but holistic approaches targeting lifestyle and diet improvements are emerging. As dysbiosis is involved in IBD pathogenesis, pre-, pro-, syn-, and postbiotics are used/tested to reduce the inflammation or strengthen the IEB. The present review will resume these works, pointing out the stage of life, the duration, and the environmental conditions that should go along with microbiota or microbiota-derived treatments.

The Role of Dietary Fibers in the Management of IBD Symptoms

Inflammatory bowel diseases (IBDs) are chronic, progressive, immune-mediated diseases of the intestinal tract. The main subtypes of IBDs are Chron's disease (CD) and ulcerative colitis (UC). The etiology is still unclear, but there are genetic, environmental and host-related factors that contribute to the development of these diseases. Recent literature has shown that dietary therapy is the cornerstone of IBD treatment in terms of management of symptoms, relapse and care of the pathology. IBD patients show that microbiota dysbiosis and diet, especially dietary fiber, can modulate its composition. These patients are more at risk of energy protein malnutrition than the general population and are deficient in micronutrients. So far, no dietary component is considered responsible for IBD and there is not a specific therapeutic diet for it. The aim of this review is to evaluate the role of dietary fibers in CD and UC and help health professionals in the nutritional management of these pathologies. Further studies are necessary to determine the appropriate amount and type of fiber to suggest in the case of IBD to ameliorate psychosocial conditions and patients' quality of life.

Pretreatment with millet-derived selenylated soluble dietary fiber ameliorates dextran sulfate sodium-induced colitis in mice by regulating inflammation and maintaining gut microbiota balance

Inflammatory activation and intestinal flora imbalance play key roles in the development and progression of inflammatory bowel disease (IBD). Soluble dietary fiber (SDF) and selenium have been proven to be effective for preventing and relieving IBD. This study investigated and compared the therapeutic efficacy of millet-derived selenylated-soluble dietary fiber (Se-SDF) against dextran sulfate sodium (DSS)-induced colitis in mice alone or through the synergistic interaction between selenium and SDF. In female mice, Se-SDF markedly alleviated body weight loss, decreased colon length, reduced histological damage scores, and enhanced IL-10 expression to maintain the barrier function of intestinal mucosa compared to male mice. The 16S rRNA sequence analysis further indicated that pretreatment with Se-SDF restored the gut microbiota composition in female mice by increasing the relative abundance of Lactobacillus and the Firmicutes/Bacteroidetes ratio. In conclusion, these findings demonstrated that Se-SDF can protect against DSS-induced colitis in female mice by regulating inflammation and maintaining gut microbiota balance. This study, therefore, provides new insights into the development of Se-SDF as a supplement for the prevention and treatment of colitis.

Dietary Inulin Supplementation Affects Specific Plasmalogen Species in the Brain

Plasmalogens (Pls) are glycerophospholipids that play critical roles in the brain. Evidence supports the role of diet and that of the gut microbiota in regulating brain lipids. We investigated the impact of dietary intake of inulin—a soluble fiber used as prebiotic—on the Pl content of the cortex in mice. No global modification in the Pl amounts was observed when evaluated by gas chromatographic analysis of dimethyl acetals (DMAs). However, the analysis of individual molecular species of Pls by liquid chromatography revealed a reduced abundance of major species of ethanolamine Pls (PlsEtn)―PE(P-18:0/22:6) and PE(P-34:1)―in the cortex of mice fed a diet supplemented with inulin. DMA and expression levels of genes (Far-1, Gnpat, Agps, Pla2g6 and Tmem86b) encoding key enzymes of Pl biosynthesis or degradation were not altered in the liver and in the cortex of mice exposed to inulin. In addition, the fatty acid profile and the amount of lyso forms derived from PlsEtn were not modified in the cortex by inulin consumption. To conclude, inulin affects the brain levels of major PlsEtn and further investigation is needed to determine the exact molecular mechanisms involved.

Dysregulation of intestinal flora: excess prepackaged soluble fibers damage the mucus layer and induce intestinal inflammation

Soluble fiber is commonly used as a dietary supplement to improve intestinal flora, and many prepackaged products are sold in the market. However, whether these prepared soluble fibers are harmless for intestinal flora has not been systematically evaluated. Here, we assessed the dose-effect of fructooligosaccharides (FOSs) on obesity and intestinal flora using a mouse model. Gavage of low- and medium-dose FOS improved the microbiota in high-fat diet fed mice, but high-dose FOS leads to intestinal flatulence, diarrhea and flora disorders, including an increase in Akkermansia muciniphila and Clostridium difficile, which disrupt the mucus barrier and cause intestinal inflammation. Besides, a high dose of xylooligosaccharide by gavage induces symptoms similar to those of FOS in mice. These adverse effects can be alleviated by regulating intestinal flora. In addition, we experimentally proved that supplementary probiotics protect against the negative effects of FOS in obese mice. Therefore, prepackaged soluble fiber supplements need to be taken with caution, and excessive consumption of soluble fibers results in intestinal dysfunction and even induces intestinal inflammation. Combining probiotics and soluble fiber can be considered if necessary.

Microbiome-based interventions to modulate gut ecology and the immune system

The gut microbiome lies at the intersection between the environment and the host, with the ability to modify host responses to disease-relevant exposures and stimuli. This is evident in how enteric microbes interact with the immune system, e.g., supporting immune maturation in early life, affecting drug efficacy via modulation of immune responses, or influencing development of immune cell populations and their mediators. Many factors modulate gut ecosystem dynamics during daily life and we are just beginning to realise the therapeutic and prophylactic potential of microbiome-based interventions. These approaches vary in application, goal, and mechanisms of action. Some modify the entire community, such as nutritional approaches or faecal microbiota transplantation, while others, such as phage therapy, probiotics, and prebiotics, target specific taxa or strains. In this review, we assessed the experimental evidence for microbiome-based interventions, with a particular focus on their clinical relevance, ecological effects, and modulation of the immune system.

Inulin fructans in diet: Role in gut homeostasis, immunity, health outcomes and potential therapeutics

Inulin consumption in both humans and animal models is recognized for its prebiotic action with the most consistent change that lies in enhancing the growth and functionality of Bifidobacterium bacteria, as well as its effect on host gene expression and metabolism. Further, inulin-type fructans are utilized in the colon by bacterial fermentation to yield short-chain fatty acids (SCFAs), which play important role in its biological effects both locally inside the gut and in systemic actions. The gut symbiosis sustained by inulin supplementation among other dietary fibers exerts preventive and/or therapeutic options for many metabolic disorders including obesity, type 2 diabetes mellitus, cardiometabolic diseases, kidney diseases and hyperuricemia. Although, gastrointestinal negative effects due to inulin consumption were reported, such as gastrointestinal symptoms in humans and exacerbated inflammatory bowel disease (IBD) in mice. This comprehensive review aims to present the whole story of how inulin functions as a prebiotic at cellular levels and the interplay between physiological, functional and immunological responses inside the animal or human gut as influenced by inulin in diets, in context to its structural composition. Such review is of importance to identify management and feed strategies to optimize gut health, for instance, consumption of the tolerated doses to healthy adults of 10 g/day of native inulin or 5 g/day of naturally inulin-rich chicory extract. In addition, inulin-drug interactions should be further clarified particularly if used as a supplement for the treatment of degenerative diseases (e.g., diabetes) over a long period. The combined effect of probiotics and inulin appears more effective, and more research on this synergy is still needed.

Structural Characteristics of Inulin and Microcrystalline Cellulose and Their Effect on Ameliorating Colitis and Altering Colonic Microbiota in Dextran Sodium Sulfate-Induced Colitic Mice

Several studies have reported that dietary fibers (DFs) from plants may exert beneficial effects on inflammatory bowel disease. In the present study, we investigated the structural differences of soluble DF (inulin) and insoluble DF (microcrystalline cellulose, MCC) and their effects on the intestinal barrier integrity, gut microbiota community, and inflammation response in mice with dextran sodium sulfate (DSS)-induced colitis. Mice were fed for 21 days with diets containing inulin or MCC (2.5 g/kg body weight), and colitis was induced by administration of DSS (4% w/v) in drinking water during the last 8 days of experimentation. The results showed that inulin and MCC differ in morphology and structure. MCC exhibited a smaller particle size, a larger specific surface area, and higher thermal stability than inulin. In addition, both inulin and MCC restored various physical signs (body weight, colon weight and length, disease activity index score, and infiltration of inflammatory cells), gut barrier function (as evidenced by the increased expression of claudin-3, claudin-7, ZO-2, occludin, JAM-2, and MUC-3 and the decreased activity of myeloperoxidase activity), downregulation of mRNA expression of proinflammatory cytokines (caspase-1, NLPR3, TLR4, TNF-α, and IL-1β), and modulation of colon microbiota community. Taken together, the present study demonstrates that DFs differ in morphology and structure and ameliorate DSS-induced colitis in mice by blocking proinflammatory cytokines, reinforcing gut barrier integrity, and modulating gut microbiota. Therefore, DFs, especially inulin, are promising dietary supplements to alleviate intestinal inflammation.

Long-term maternal intake of inulin exacerbated the intestinal damage and inflammation of offspring rats in a DSS-induced colitis model

This study aimed to investigate the effects of long-term maternal intake of inulin on intestinal morphology, permeability, inflammation and microbiota of offspring rats treated with dextran sulfate sodium (DSS). Sixteen female adult Sprague-Dawley rats were assigned to two groups receiving the fiber-free diet (FFD) or inulin diet (INU, 5% inulin) for three parities. The offspring weaned rats (third-parity) were fed with the same diet for four weeks until receiving 6% DSS for 7 days; the four groups were as follows: FFD, FFD + DSS, INU and INU + DSS. The results showed that maternal intake of inulin increased the histopathology score and activity of diamine oxidase (DAO) in serum, and the highest histopathology scores and activity of DAO were observed in INU + DSS rats. Maternal intake of inulin increased the activity of myeloperoxidase (MPO), mRNA expressions of inflammatory factors and protein expression of IL-1β in colonic tissues. Likewise, INU + DSS rats had the highest activity of MPO and mRNA expressions of inflammatory factors in colonic tissues. Maternal intake of inulin increased the abundances of Bacteroidetes, Bacteroides and Parasutterella, which were the highest enriched in INU + DSS rats. The level of acetate in the colonic digesta of INU + DSS rats was lower than that in FFD and INU rats. These results indicated that long-term maternal intake of inulin exacerbated the intestinal damage and inflammation of DSS-induced offspring rats, associated with the decreased level of acetate and altered intestinal microbiota.

Dietary Fiber Intake and Femoral Bone Mineral Density in Middle-Aged and Older US Adults: A Cross-Sectional Study of National Health and Nutrition Examination Survey 2013-2014

Sufficient dietary fiber intake (DFI) is considered necessary for human health. However, the association between DFI and bone mineral density (BMD) remains unclear. Therefore, this study aimed to investigate the association between DFI and BMD and to determine whether sex modifies the association between DFI and BMD. Participants aged ≥ 40 years from the 2013-2014 National Health and Nutrition Examination Survey were included in the final analysis. The association between DFI and BMD was evaluated using a multivariate linear regression model. The non-linear relationship between DFI and BMD was characterized by smooth curve fittings and generalized additive models. Finally, 1,935 participants with a mean age of 58.12 ± 11.84 years were included in the final analysis. The results revealed that DFI was positively associated with femoral BMD in the unadjusted model. However, no correlation was observed between DFI and femoral BMD after adjusting for covariates. Moreover, the results showed an inverted U-shaped association between total DFI and femoral BMD among men but not women for the nonlinear relationship between DFI and femoral BMD. In conclusion, our results indicate that DFI might not follow a linear relationship with femoral BMD, and sex factors might modify the association between DFI and BMD. Particularly, high total DFI might contribute to lower femoral neck BMD. However, more studies are needed to investigate whether the negative effect of high DFI on femoral BMD does exist and whether high DFI has clear biological effects on bone metabolism, such as increasing the risk of osteoporosis.

Effect of diet on pathogen performance in the microbiome

Intricate interactions among commensal bacteria, dietary substrates and immune responses are central to defining microbiome community composition, which plays a key role in preventing enteric pathogen infection, a dynamic phenomenon referred to as colonisation resistance. However, the impact of diet on sculpting microbiota membership, and ultimately colonisation resistance has been overlooked. Furthermore, pathogens have evolved strategies to evade colonisation resistance and outcompete commensal microbiota by using unique nutrient utilisation pathways, by exploiting microbial metabolites as nutrient sources or by environmental cues to induce virulence gene expression. In this review, we will discuss the interplay between diet, microbiota and their associated metabolites, and how these can contribute to or preclude pathogen survival.

Intake of high-purity insoluble dietary fiber from Okara for the amelioration of colonic environment disturbance caused by acute ulcerative colitis

High-purity insoluble dietary fiber from okara (okara-HPIDF) is a raw material with a potentially positive effect on colon health. However, the mechanisms of the effect are far from clear. In this study, okara-HPIDF and low-purity dietary fiber from okara (okara-LPDF) were fed to C57BL/6 mice with acute ulcerative colitis induced by DSS. The levels of inflammatory factors, bacterial 16S rDNA sequencing, short-chain fatty acids (SCFAs), and bioinformatics were analyzed with the colonic tissue status. The results showed that the intake of HPIDF affected the proliferation of the key bacteria Shigella, Lactobacillus, and Peptostreptococcaceae in the PWY-2941 pathway and AEROBACTINSYN-PWY pathway, and then affected the synthesis of SCFAs, providing a positive role for colon health. However, the intake of HPIDF was unable to repair colonic injury caused by DSS-induced acute ulcerative colitis mainly owing to the abundance of Shigella in the colon. This study demonstrates that the recommended intake content of HPIDF can ameliorate colonic environment disturbance caused by acute ulcerative colitis, but not enough to relieve it.

A High-Fat Western Diet Attenuates Intestinal Changes in Mice with DSS-Induced Low-Grade Inflammation

BACKGROUND

A Western diet (WD) is associated with increased inflammation in the large intestine, which is often ascribed to the high dietary fat content. Intestinal inflammation in rodents can be induced by oral administration of dextran sodium sulfate (DSS). However, most studies investigating effects of WD and DSS have not used appropriate low-fat diets (LFDs) as control.

OBJECTIVES

To compare the effects of a WD with those of an LFD on colon health in a DSS-induced low-grade colonic inflammation mouse model.

METHODS

Six-week-old male C57BL/6JRj mice were fed an LFD (fat = 10.3% energy, n = 24) or a WD (fat = 41.2% energy, n = 24) for 15 wk [Experiment 1 (Exp.1)]. Half the mice on each diet (n = 12) then received 1% DSS in water for 6 d with the remainder (n = 12 in each diet) administered water. Disease activity, proinflammatory genes, inflammatory biomarkers, and fecal microbiota (16S rRNA) were assessed (Exp.1). Follow-up experiments (Exp.2 and Exp.3) were performed to investigate whether fat source (milk or lard; Exp.2) affected outcomes and whether a shift from LFD to WD 1 d prior to 1% DSS exposure caused an immediate effect on DSS-induced inflammation (Exp.3).

RESULTS

In Exp.1, 1% DSS treatment significantly increased disease score in the LFD group compared with the WD group (2.7 compared with 0.8; P < 0.001). Higher concentrations of fecal lipocalin (11-fold; P < 0.001), proinflammatory gene expression (≤82-fold), and Proteobacteria were observed in LFD-fed mice compared with the WD group. The 2 fat sources in WDs (Exp.2) revealed the same low inflammation in WD+DSS mice compared with LFD+DSS mice. Finally, the switch from LFD to WD just before DSS exposure resulted in reduced colonic inflammation (Exp.3).

CONCLUSIONS

Herein, WDs (with milk or lard) protected mice against DSS-induced colonic inflammation compared with LFD-fed mice. Whether fat intake induces protective mechanisms against DSS-mediated inflammation or inhibits establishment of the DSS-induced colitis model is unclear.

The gut microbiota in retinal diseases

The gut microbiota is a complex ecosystem that inhabits the gastrointestinal tract and consists of archaea, fungi, viruses, and bacteria, with bacteria being dominant. From birth onwards, it coevolves dynamically together with the host. The composition of the gut microbiota is under the influence of a complex interplay between both host and environmental factors. Scientific advances in the past few decades have shown that it is essential in maintaining homeostasis and tipping the balance between health and disease. In addition to its role in food digestion, the gut microbiota is implicated in regulating multiple physiological processes in the host gut mucosa and in distant organs such as the brain. Persistent imbalance between gut microbial communities, termed "dysbiosis," has been associated with several inflammatory and metabolic diseases as well as with central nervous system disorders. In this review, we present the state of the art of current knowledge on an emerging concept, the microbiota-retina axis, and the potential role of its disturbance in the development of retinopathies. We also describe several microbiota-targeting strategies that could constitute preventive and therapeutic tools for retinopathies.

Long-Term Overconsumption of Fat and Sugar Causes a Partially Reversible Pre-inflammatory Bowel Disease State

Nutrition appears to be an important environmental factor involved in the onset of inflammatory bowel diseases (IBD) through yet poorly understood biological mechanisms. Most studies focused on fat content in high caloric diets, while refined sugars represent up to 40% of caloric intake within industrialized countries and contribute to the growing epidemics of inflammatory diseases. Herein we aim to better understand the impact of a high-fat-high-sucrose diet on intestinal homeostasis in healthy conditions and the subsequent colitis risk. We investigated the early events and the potential reversibility of high caloric diet-induced damage in mice before experimental colitis. C57BL/6 mice were fed with a high-fat or high-fat high-sucrose or control diet before experimental colitis. In healthy mice, a high-fat high-sucrose diet induces a pre-IBD state characterized by gut microbiota dysbiosis with a total depletion of bacteria belonging to Barnesiella that is associated with subclinical endoscopic lesions. An overall down-regulation of the colonic transcriptome converged with broadly decreased immune cell populations in the mesenteric lymph nodes leading to the inability to respond to tissue injury. Such in-vivo effects on microbiome and transcriptome were partially restored when returning to normal chow. Long-term consumption of diet enriched in sucrose and fat predisposes mice to colitis. This enhanced risk is preceded by gut microbiota dysbiosis and transcriptional reprogramming of colonic genes related to IBD. Importantly, diet-induced transcriptome and microbiome disturbances are partially reversible after switching back to normal chow with persistent sequelae that may contribute to IBD predisposition in the general population.

Changes of High-Purity Insoluble Fiber from Soybean Dregs (Okara) after Being Fermented by Colonic Flora and Its Adsorption Capacity

In order to explore the changes and properties of high-purity insoluble dietary fiber from okara (HPIDF) after entering the colon and be fermented by colonic flora, fermented high-purity insoluble dietary fiber (F-HPIDF) was obtained by simulated fermentation in vitro by HPIDF and colonic flora from C57BL/6 mice. For exploring the differences of HPIDF and F-HPIDF, the changes of structure (SEM. FTIR, XRD, particle size, specific surface area, monosaccharide composition) and adsorption properties (water, oil, heavy metal irons, harmful substances) of HPIDF/F-HPIDF were explored. The results showed that F-HPIDF had a higher water-holding capacity (19.17 g/g), water-swelling capacity (24.83 mL/g), heavy metals-adsorption capacity (Cd²⁺: 1.82 μmol/g; Pb²⁺: 1.91 μmol/g; Zn²⁺: 1.30 μmol/g; Cu²⁺: 0.68 μmol/g), and harmful substances-adsorption capacity (GAC: 0.23 g/g; CAC: 14.80 mg/g; SCAC: 0.49 g/g) than HPIDF due to the changes of structure caused by fermentation. In addition, with the fermentation of HPIDF, some beneficial substances were produced, which might be potential intestinal prebiotics. The study of F-HPIDF strengthens the speculation that HPIDF may have potential bioactivities after entering the colon, which proved that okara-HPIDF may have potential functionality.

Resource Competition and Host Feedbacks Underlie Regime Shifts in Gut Microbiota

AbstractThe spread of an enteric pathogen in the human gut depends on many interacting factors, including pathogen exposure, diet, host gut environment, and host microbiota, but how these factors jointly influence infection outcomes remains poorly characterized. Here we develop a model of host-mediated resource competition between mutualistic and pathogenic taxa in the gut that aims to explain why similar hosts, exposed to the same pathogen, can have such different infection outcomes. Our model successfully reproduces several empirically observed phenomena related to transitions between healthy and infected states, including (1) the nonlinear relationship between pathogen inoculum size and infection persistence, (2) the elevated risk of chronic infection during or after treatment with broad-spectrum antibiotics, (3) the resolution of gut dysbiosis with fecal microbiota transplants, and (4) the potential protection from infection conferred by probiotics. We then use the model to explore how host-mediated interventions-namely, shifts in the supply rates of electron donors (e.g., dietary fiber) and respiratory electron acceptors (e.g., oxygen)-can potentially be used to direct gut community assembly. Our study demonstrates how resource competition and ecological feedbacks between the host and the gut microbiota can be critical determinants of human health outcomes. We identify several testable model predictions ready for experimental validation.

Western-style diet impedes colonization and clearance of Citrobacter rodentium

Western-style diet (WSD), which is high in fat and low in fiber, lacks nutrients to support gut microbiota. Consequently, WSD reduces microbiota density and promotes microbiota encroachment, potentially influencing colonization resistance, immune system readiness, and thus host defense against pathogenic bacteria. Here we examined the impact of WSD on infection and colitis in response to Citrobacter rodentium. We observed that, relative to mice consuming standard rodent grain-based chow (GBC), feeding WSD starkly altered the dynamics of Citrobacter infection, reducing initial colonization and inflammation but frequently resulting in persistent infection that associated with low-grade inflammation and insulin resistance. WSD's reduction in initial Citrobacter virulence appeared to reflect that colons of GBC-fed mice contain microbiota metabolites, including short-chain fatty acids, especially acetate, that drive Citrobacter growth and virulence. Citrobacter persistence in WSD-fed mice reflected inability of resident microbiota to out-compete it from the gut lumen, likely reflecting the profound impacts of WSD on microbiota composition. These studies demonstrate potential of altering microbiota and their metabolites by diet to impact the course and consequence of infection following exposure to a gut pathogen.

Soluble Fiber Inulin Consumption Limits Alterations of the Gut Microbiota and Hepatic Fatty Acid Metabolism Caused by High-Fat Diet

Diet shapes the gut microbiota which impacts hepatic lipid metabolism. Modifications in liver fat content are associated with metabolic disorders. We investigated the extent of dietary fat and fiber-induced alterations in the composition of gut microbiota and hepatic fatty acids (FAs). Mice were fed a purified low-fat diet (LFD) or high-fat diet (HFD) containing non-soluble fiber cellulose or soluble fiber inulin. HFD induced hepatic decreases in the amounts of C14:0, C16:1n-7, C18:1n-7 and increases in the amounts of C17:0, C20:0, C16:1n-9, C22:5n-3, C20:2n-6, C20:3n-6, and C22:4n-6. When incorporated in a LFD, inulin poorly affected the profile of FAs. However, when incorporated in a HFD, it (i) specifically led to an increase in the amounts of hepatic C18:0, C22:0, total polyunsaturated FAs (PUFAs), total n-6 PUFAs, C18:3n-3, and C18:2n-6, (ii) exacerbated the HFD-induced increase in the amount of C17:0, and (iii) prevented the HFD-induced increases in C16:1n-9 and C20:3n-6. Importantly, the expression/activity of some elongases and desaturases, as well as the gut microbiota composition, were impacted by the dietary fat and fiber content. To conclude, inulin modulated gut microbiota and hepatic fatty acid composition, and further investigations will determine whether a causal relationship exists between these two parameters.

Replacing Animal Protein with Soy-Pea Protein in an "American Diet" Controls Murine Crohn Disease-Like Ileitis Regardless of Firmicutes: Bacteroidetes Ratio

BACKGROUND

The current nutritional composition of the "American diet" (AD; also known as Western diet) has been linked to the increasing incidence of chronic diseases, including inflammatory bowel disease (IBD), namely Crohn disease (CD).

OBJECTIVES

This study investigated which of the 3 major macronutrients (protein, fat, carbohydrates) in the AD has the greatest impact on preventing chronic inflammation in experimental IBD mouse models.

METHODS

We compared 5 rodent diets designed to mirror the 2011-2012 "What We Eat in America" NHANES. Each diet had 1 macronutrient dietary source replaced. The formulated diets were AD, AD-soy-pea (animal protein replaced by soy + pea protein), AD-CHO ("refined carbohydrate" by polysaccharides), AD-fat [redistribution of the ω-6:ω-3 (n-6:n-3) PUFA ratio; ∼10:1 to 1:1], and AD-mix (all 3 "healthier" macronutrients combined). In 3 separate experiments, 8-wk-old germ-free SAMP1/YitFC mice (SAMP) colonized with human gut microbiota ("hGF-SAMP") from CD or healthy donors were fed an AD, an AD-"modified," or laboratory rodent diet for 24 wk. Two subsequent dextran sodium sulfate-colitis experiments in hGF-SAMP (12-wk-old) and specific-pathogen-free (SPF) C57BL/6 (20-wk-old) mice, and a 6-wk feeding trial in 24-wk-old SPF SAMP were performed. Intestinal inflammation, gut metagenomics, and MS profiles were assessed.

RESULTS

The AD-soy-pea diet resulted in lower histology scores [mean ± SD (56.1% ± 20.7% reduction)] in all feeding trials and IBD mouse models than did other diets (P < 0.05). Compared with the AD, the AD-soy-pea correlated with increased abundance in Lactobacillaceae and Leuconostraceae (1.5-4.7 log2 and 3.0-5.1 log2 difference, respectively), glutamine (6.5 ± 0.8 compared with 3.9 ± 0.3 ng/μg stool, P = 0.0005) and butyric acid (4:0; 3.3 ± 0.5 compared with 2.54 ± 0.4 ng/μg stool, P = 0.006) concentrations, and decreased linoleic acid (18:2n-6; 5.4 ± 0.4 compared with 8.6 ± 0.3 ng/μL plasma, P = 0.01).

CONCLUSIONS

Replacement of animal protein in an AD by plant-based sources reduced the severity of experimental IBD in all mouse models studied, suggesting that similar, feasible adjustments to the daily human diet could help control/prevent IBD in humans.

Not All Fibers Are Born Equal; Variable Response to Dietary Fiber Subtypes in IBD

Diet provides a safe and attractive alternative to available treatment options in a variety of diseases; however, research has only just begun to elucidate the role of diet in chronic diseases, such as the inflammatory bowel diseases (IBD). The chronic and highly debilitating IBDs, Crohn disease and ulcerative colitis, are hallmarked by intestinal inflammation, immune dysregulation, and dysbiosis; and evidence supports a role for genetics, microbiota, and the environment, including diet, in disease pathogenesis. This is true especially in children with IBD, where diet-based treatments have shown excellent results. One interesting group of dietary factors that readily links microbiota to gut health is dietary fibers. Fibers are not digested by human cells, but rather fermented by the gut microbes within the bowel. Evidence has been mounting over the last decade in support of the importance of dietary fibers in the maintenance of gut health and in IBD; however, more recent studies highlight the complexity of this interaction and importance of understanding the role of each individual dietary fiber subtype, especially during disease. There are roughly ten subtypes of dietary fibers described to date, categorized as soluble or insoluble, with varying chemical structures, and large differences in their fermentation profiles. Many studies to date have described the benefits of the byproducts of fermentation in healthy individuals and the potential health benefits in select disease models. However, there remains a void in our understanding of how each of these individual fibers affect human health in dysbiotic settings where appropriate fermentation may not be achieved. This review highlights the possibilities for better defining the role of individual dietary fibers for use in regulating inflammation in IBD.

Inulin Supplementation Disturbs Hepatic Cholesterol and Bile Acid Metabolism Independent from Housing Temperature

Dietary fibers are fermented by gut bacteria into the major short chain fatty acids (SCFAs) acetate, propionate, and butyrate. Generally, fiber-rich diets are believed to improve metabolic health. However, recent studies suggest that long-term supplementation with fibers causes changes in hepatic bile acid metabolism, hepatocyte damage, and hepatocellular cancer in dysbiotic mice. Alterations in hepatic bile acid metabolism have also been reported after cold-induced activation of brown adipose tissue. Here, we aim to investigate the effects of short-term dietary inulin supplementation on liver cholesterol and bile acid metabolism in control and cold housed specific pathogen free wild type (WT) mice. We found that short-term inulin feeding lowered plasma cholesterol levels and provoked cholestasis and mild liver damage in WT mice. Of note, inulin feeding caused marked perturbations in bile acid metabolism, which were aggravated by cold treatment. Our studies indicate that even relatively short periods of inulin consumption in mice with an intact gut microbiome have detrimental effects on liver metabolism and function.

Dietary Emulsifiers Directly Impact Adherent-Invasive E. coli Gene Expression to Drive Chronic Intestinal Inflammation

Dietary emulsifiers carboxymethylcellulose (CMC) and polysorbate-80 (P80) disturb gut microbiota, promoting chronic inflammation. Mice with minimal microbiota are protected against emulsifiers’ effects, leading us to hypothesize that these compounds might provoke select pathobionts to promote inflammation. Gnotobiotic wild-type (WT) and interleukin-10 (IL-10)^−/− mice were colonized with Crohn’s-disease-associated adherent-invasive E. coli (AIEC) and subsequently administered CMC or P80. AIEC colonization of GF and altered Schaedler flora (ASF) mice results in chronic intestinal inflammation and metabolism dysregulations when consuming the emulsifier. In IL-10^−/− mice, AIEC mono-colonization results in severe intestinal inflammation in response to emulsifiers. Exposure of AIEC to emulsifiers in vitro increases its motility and ability to adhere to intestinal epithelial cells. Transcriptomic analysis reveals that emulsifiers directly induce expression of clusters of genes that mediate AIEC virulence and promotion of inflammation. To conclude, emulsifiers promote virulence and encroachment of pathobionts, providing a means by which these compounds may drive inflammation in hosts carrying such bacteria.

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Dietary emulsifiers alter the intestinal microbiota, promoting chronic inflammation

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Select pathobionts are required to mediate the detrimental effects of emulsifiers

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Emulsifiers directly induce the expression of bacterial virulence genes

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Microbiota-based dietary intervention appears warranted

Resistant Maltodextrin Alleviates Dextran Sulfate Sodium-Induced Intestinal Inflammatory Injury by Increasing Butyric Acid to Inhibit Proinflammatory Cytokine Levels

Inflammatory bowel disease (IBD), one kind of intestinal chronic inflammatory disease, is characterized by colonic epithelial barrier injury, overproduction of proinflammatory cytokines, and fewer short-chain fatty acids (SCFAs). The present study is aimed at testing the hypothesis that resistant maltodextrin (RM), a soluble dietary fiber produced by starch debranching, alleviated dextran sulfate sodium- (DSS-) induced colitis in mice. Female C57BL/6 mice with or without oral administration of 50 mg/kg RM for 19 days were challenged with 3% DSS in drinking water to induce colitis (from day 14 to day 19). Although RM could not reverse DSS-induced weight loss or colon shortening, it reduced inflammatory cell infiltration and epithelial damage in colon tissue, as well as the transfer of intestinal permeability indicators including serum diamine oxidase (DAO) and D-lactic acid (D-LA). ELISA analysis indicated that RM significantly suppressed the increase of Th1 cytokines induced by DSS in the colon such as tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ). The levels of proinflammatory cytokines interleukin-1β (IL-1β), IL-17, and IL-8 in the DSS group were significantly higher than those in the control group and RM group, but no significant difference was observed in the RM-DSS group compared with the RM group. Interestingly, IL-10 levels of the DSS group were significantly higher than those of the other groups. With respect to SCFAs, DSS administration significantly decreased the concentration of faecal butyric acid while the RM-DSS group showed a tendency to increase (P = 0.08). In general, RM alleviated dextran sulfate sodium-induced intestinal inflammation through increasing the level of butyric acid and subsequently inhibiting the expression of proinflammatory cytokines.

Effects of the prebiotic inulin-type fructans on post-antibiotic reconstitution of the gut microbiome

AIMS

Interventions using prebiotic inulin-type fructans (ITFs) are widely prescribed to modulate the gut microbiota composition and activity to promote health. However, the impacts of ITFs on post-antibiotic reconstitution of the gut microbiome remain incompletely understood. The aim of the present study was to investigate the effects of ITFs supplementation on intestinal inflammation, the composition of the intestinal microbiota and the colonic transcriptome after antibiotic treatment.

METHODS AND RESULTS

Male BALB/c mice were subjected to an antibiotic cocktail (ABx) treatment for 7 days, and their microbiomes were then reconstituted either spontaneously or with ITFs supplementation (5%) for 14 days. Our data showed that ITFs supplementation delayed the recovery of antibiotic-induced colitis compared with the spontaneous recovery. Neither ITFs supplementation nor spontaneous recovery could restore the microbial community composition at the genus level back to its initial composition. ITFs supplementation increased the relative abundance of some beneficial bacteria and butyrate levels, but resulted in selective blooms of some opportunistic pathogens and elevated the pathways associated with diseases linked to gut microbiota function. Both ITFs supplementation and spontaneous recovery could restore the colonic transcriptome nearly to the initial profile to a certain extent; however, ITFs supplementation delayed the restoration of the immunoglobulin genes compared to spontaneous recovery.

CONCLUSION

These data showed that post-antibiotic ITFs consumption did not always lead to beneficial effects but might lead to potential adverse effects in the context of dysbiosis.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings highlighted that caution is required when supplementing ITFs to restore intestinal homeostasis in the context of dysbiosis resulting from broad-spectrum antibiotics.

Polysaccharides isolated from Cordyceps Sinensis contribute to the progression of NASH by modifying the gut microbiota in mice fed a high-fat diet

Various dietary fibers are considered to prevent obesity by modulating the gut microbiota. Cordyceps sinensis polysaccharide (CSP) is a soluble dietary fiber known to have protective effects against obesity and related diseases, but whether these effects induce any side effects remains unknown. The function and safety of CSP were tested in high-fat diet (HFD)-feding C57BL/6J mice. The results revealed that even though CSP supplementation could prevent an increase in body weight, it aggravated liver fibrosis and steatosis as evidenced by increased inflammation, lipid metabolism markers, insulin resistance (IR) and alanine aminotransferase (ALT) in HFD-induced obesity. 16S rDNA gene sequencing was used to analyze the gut microbiota composition, and the relative abundance of the Actinobacteria phylum, including the Olsenella genus, was significantly higher in CSP-treated mice than in HFD-fed mice. CSP supplementation may increase the proportion of Actinobacteria, which can degrade CSP. The high level of Actinobacteria aggravated the disorder of the intestinal flora and contributed to the progression from obesity to nonalcoholic steatohepatitis (NASH) and related diseases.