Effect of Dietary Fibers on Cecal Microbiota and Intestinal Tumorigenesis in Azoxymethane Treated A/J Min/+ Mice

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.

Interactions between diet and gut microbiota in cancer

Dietary patterns and specific dietary components, in concert with the gut microbiota, can jointly shape susceptibility, resistance and therapeutic response to cancer. Which diet-microbial interactions contribute to or mitigate carcinogenesis and how they work are important questions in this growing field. Here we interpret studies of diet-microbial interactions to assess dietary determinants of intestinal colonization by opportunistic and oncogenic bacteria. We explore how diet-induced expansion of specific gut bacteria might drive colonic epithelial tumorigenesis or create immuno-permissive tumour milieus and introduce recent findings that provide insight into these processes. Additionally, we describe available preclinical models that are widely used to study diet, microbiome and cancer interactions. Given the rising clinical interest in dietary modulations in cancer treatment, we highlight promising clinical trials that describe the effects of different dietary alterations on the microbiome and cancer outcomes.

Eating away cancer: the potential of diet and the microbiome for shaping immunotherapy outcome

The gut microbiome (GMB) plays a substantial role in human health and disease. From affecting gut barrier integrity to promoting immune cell differentiation, the GMB is capable of shaping host immunity and thus oncogenesis and anti-cancer therapeutic response, particularly with immunotherapy. Dietary patterns and components are key determinants of GMB composition, supporting the investigation of the diet-microbiome-immunity axis as a potential avenue to enhance immunotherapy response in cancer patients. As such, this review will discuss the role of the GMB and diet on anti-cancer immunity. We demonstrate that diet affects anti-cancer immunity through both GMB-independent and GMB-mediated mechanisms, and that different diet patterns mold the GMB's functional and taxonomic composition in distinctive ways. Dietary modulation therefore shows promise as an intervention for improving cancer outcome; however, further and more extensive research in human cancer populations is needed.

Western diet influences on microbiome and carcinogenesis

The intestinal microbiota composition and associated bioactivities are sensitive to various modifier cues such as stress, inflammation, age, life-style and nutrition, which in turn are associated with susceptibility to developing cancer. Among these modifiers, diet has been shown to influence both microbiota composition as well as being an important source of microbial-derived compounds impacting the immunological, neurological and hormonal systems. Thus, it is necessary to take a holistic view when considering effect of diet on health and diseases. In this review, we focus on the interplay between western diet, the microbiota and cancer development by dissecting key components of the diet and leveraging data from human interventions and pre-clinical studies to better understand this relationship. We highlight key progress as well as stressing limitations in this field of research.

Inulin impacts tumorigenesis promotion by colibactin-producing Escherichia coli in ApcMin/+ mice

Introduction

The prebiotic inulin has previously shown both protective and tumor-promoting effects in colorectal cancer (CRC). These inconsistencies may be due to the gut microbial composition as several bacteria have been associated with CRC. Specifically, polyketide synthase-positive (pks+) Escherichia coli promotes carcinogenesis and facilitates CRC progression through the production of colibactin, a genotoxin that induces double-strand DNA breaks (DSBs). We investigated whether colibactin-producing Escherichia coli changed the protection conferred by inulin against tumor growth and progression using the Apc^Min/+ mouse model of CRC.

Methods

Mice received a 2% dextran sodium sulfate (DSS) solution followed by oral gavage with the murine pks + E. coli strain NC101 (EcNC101) and were fed a diet supplemented with 10% cellulose as control or 10% inulin for 4 weeks.

Results

Inulin supplementation led to increase EcNC101 colonization compared to mice receiving the control diet. The increased colonization of EcNC101 resulted in more DSBs, tumor burden, and tumor progression in Apc^Min/+ mice. The tumorigenic effect of EcN101 in Apc^Min/+ mice mediated by inulin was dependent on colibactin production. Pasteurized E. coli Nissle 1917 (EcN), a probiotic, suppressed the inulin-driven EcNC101 expansion and impacted tumor progression.

Discussion

Our results suggest that the presence of pks + E. coli influences the outcome of inulin supplementation in CRC and that microbiota-targeted interventions may mitigate this effect. Given the prevalence of pks + E. coli in both healthy and CRC populations and the importance of a fiber-rich diet, inulin supplementation in individuals colonized with pks + bacteria should be considered with caution.

The Pleiotropic Effects of Gut Microbiota in Colorectal Cancer Progression: How to Turn Foes into Friends

Colorectal Cancer (CRC) is one of most frequent malignant cancers, showing high lethality worldwide [...].

A Three-Day Intervention With Granola Containing Cereal Beta-Glucan Improves Glycemic Response and Changes the Gut Microbiota in Healthy Individuals: A Crossover Study

Intake of soluble fibers including beta-glucan, is known to improve post-prandial glycemic response. The mechanisms have been attributed to the viscous gel forming in the stomach and small intestine, giving a longer absorption time. However, recent evidence suggests a link between intake of beta-glucan and improved glycemic regulation at subsequent meals through the gut microbiota. We investigated the short-term effect of granola with different amounts of cereal beta-glucan on glycemic response and gut microbiota. After a two-week run-in period (baseline), fourteen healthy, normal weight adults completed a dose-response dietary crossover study. Different amounts of cereal beta-glucan (low: 0.8 g, medium: 3.2 g and high: 6.6 g) were provided in granola and eaten with 200 ml low-fat milk as an evening meal for three consecutive days. Blood glucose and insulin were measured fasted and after an oral glucose tolerance test (OGTT) the following day, in addition to peptide YY (PYY) and glucagon-like peptide (GLP-2), fasting short chain fatty acids (SCFA) in blood, breath H2, and gut microbiota in feces. Only the intervention with medium amounts of beta-glucan decreased blood glucose and insulin during OGTT compared to baseline. Fasting PYY increased with both medium and high beta-glucan meal compared to the low beta-glucan meal. The microbiota and SCFAs changed after all three interventions compared to baseline, where acetate and butyrate increased, while propionate was unchanged. Highest positive effect size after intake of beta-glucan was found with Haemophilus, followed by Veillonella and Sutterella. Furthermore, we found several correlations between different bacterial taxa and markers of glycemic response. In summary, intake of granola containing 3.2 g cereal beta-glucan as an evening meal for three consecutive days reduced the glycemic response after an OGTT 0-180 min and changed gut microbiota composition. Since we cannot rule out that other fiber types have contributed to the effect, more studies are needed to further explore the effect of cereal beta-glucan on glycemic regulation.

Clinical Trial Registration

[www.clinicaltrials.gov], identifier [NCT03293693].

The effect of inulin-type fructans on the intestinal immune function of antibiotic-treated mice

This study aimed to evaluate the effect of supplementation with inulin-type fructans (ITFs) on the intestinal immune function in the context of dysbiosis resulting from antibiotic cocktail (ABx) treatment. BALB/c mice (8-9 weeks of age) were treated with an ABx for 3 weeks and then allowed to recover spontaneously or with ITF supplementation (5%) for 4 weeks. Our results showed that ABx treatment can induce gut microbiota dysbiosis and intestinal inflammation in mice. After 4 weeks of recovery, ITF supplementation restored the composition of the intestinal microbial community. However, compared with spontaneous recovery, ITF supplementation delayed inflammation recovery in the intestine and upregulated diamine oxidase (DAO) activity and increased lipopolysaccharide (LPS) content in serum. In addition, ITF supplementation delayed the regulatory T (Treg) cell and B cell recovery in the lamina propria (LP). Furthermore, compared with spontaneous recovery, ITF supplementation inhibited the relative expression of certain proinflammatory genes, such as for inducible nitric oxide synthase (iNOS) and tumour necrosis factor α (Tnf-α), in the colon, but it reduced the secretion of the anti-inflammatory mediator transforming growth factor β1 (TGF-β1) in serum, reduced the secretion of secretory immunoglobulin A (SIgA) in the colon and promoted the secretion of the proinflammatory cytokine interleukin (IL)-17A. In conclusion, these data supported the hypothesis that the influence of ITFs on the host's intestinal status is not always beneficial in the context of ABx-induced biological disorder. However, the significance of these findings needs to be determined by advanced studies KEY POINTS: • ITFs did not promote the recovery of microbial community composition. • ITFs delayed the recovery of ABx-induced colonic inflammation. • ITFs reduced the secretion of TGF-β1 and SIgA. • ITFs delayed the recovery of Treg and B cells in the LP.

Analysing microbiome intervention design studies: Comparison of alternative multivariate statistical methods

The diet plays a major role in shaping gut microbiome composition and function in both humans and animals, and dietary intervention trials are often used to investigate and understand these effects. A plethora of statistical methods for analysing the differential abundance of microbial taxa exists, and new methods are constantly being developed, but there is a lack of benchmarking studies and clear consensus on the best multivariate statistical practices. This makes it hard for a biologist to decide which method to use. We compared the outcomes of generic multivariate ANOVA (ASCA and FFMANOVA) against statistical methods commonly used for community analyses (PERMANOVA and SIMPER) and methods designed for analysis of count data from high-throughput sequencing experiments (ALDEx2, ANCOM and DESeq2). The comparison is based on both simulated data and five published dietary intervention trials representing different subjects and study designs. We found that the methods testing differences at the community level were in agreement regarding both effect size and statistical significance. However, the methods that provided ranking and identification of differentially abundant operational taxonomic units (OTUs) gave incongruent results, implying that the choice of method is likely to influence the biological interpretations. The generic multivariate ANOVA tools have the flexibility needed for analysing multifactorial experiments and provide outputs at both the community and OTU levels; good performance in the simulation studies suggests that these statistical tools are also suitable for microbiome data sets.

The Application of High-Throughput Technologies for the Study of Microbiome and Cancer

Human gut microbiome research, especially gut microbiome, has been developing at a considerable pace over the last decades, driven by a rapid technological advancement. The emergence of high-throughput technologies, such as genomics, transcriptomics, and others, has afforded the generation of large volumes of data, and in relation to specific pathologies such as different cancer types. The current review identifies high-throughput technologies as they have been implemented in the study of microbiome and cancer. Four main thematic areas have emerged: the characterization of microbial diversity and composition, microbial functional analyses, biomarker prediction, and, lastly, potential therapeutic applications. The majority of studies identified focus on the microbiome diversity characterization, which is reaching technological maturity, while the remaining three thematic areas could be described as emerging.

A comprehensive review for gut microbes: technologies, interventions, metabolites and diseases

Gut microbes have attracted much more attentions in the recent decade since their essential roles in the development of metabolic diseases, cancer and neurological diseases. Considerable evidence indicates that the metabolism of gut microbes exert influences on intestinal homeostasis and human diseases. Here, we first reviewed two mainstream sequencing technologies involving 16s rRNA sequencing and metagenomic sequencing for gut microbes, and data analysis methods assessing alpha and beta diversity. Next, we introduced some observational studies reflecting that many factors, such as lifestyle and intake of diets, drugs, contribute to gut microbes' quantity and diversity. Then, metabolites produced by gut microbes were presented to understand that gut microbes exert on host homeostasis in the intestinal epithelium and immune system. Finally, we focused on the molecular mechanism of gut microbes on the occurrence and development of several common diseases. In-depth knowledge of the relationship among interventions, gut microbes and diseases might provide new insights in to disease prevention and treatment.

Cage bedding modifies metabolic and gut microbiota profiles in mouse studies applying dietary restriction

Experiments involving food restriction are common practice in metabolic research. Under fasted conditions, mice supplement their diet with cage bedding. We aimed at identifying metabolic and microbiota-related parameters affected by the bedding type. We exposed mice housed with wooden, cellulose, or corncob cage beddings to ad libitum feeding, caloric restriction (CR), or over-night (ON) fasting. Additionally, two subgroups of the ON fast group were kept without any bedding or on a metal grid preventing coprophagy. Mice under CR supplemented their diet substantially with bedding; however, the amount varied depending on the kind of bedding. Bedding-related changes in body weight loss, fat loss, cecum size, stomach weight, fecal output, blood ghrelin levels as well as a response to glucose oral tolerance test were recorded. As fiber is fermented by the gut bacteria, the type of bedding affects gut bacteria and fecal metabolites composition of CR mice. CR wood and cellulose groups showed distinct cecal metabolite and microbiome profiles when compared to the CR corncob group. While all ad libitum fed animal groups share similar profiles. We show that restriction-related additional intake of bedding-derived fiber modulates multiple physiological parameters. Therefore, the previous rodent studies on CR, report the combined effect of CR and increased fiber consumption.

Prebiotic effect of inulin-type fructans on faecal microbiota and short-chain fatty acids in type 2 diabetes: a randomised controlled trial

PURPOSE

Compared to a healthy population, the gut microbiota in type 2 diabetes presents with several unfavourable features that may impair glucose regulation. The aim of this study was to evaluate the prebiotic effect of inulin-type fructans on the faecal microbiota and short-chain fatty acids (SCFA) in patients with type 2 diabetes.

METHODS

The study was a placebo controlled crossover study, where 25 patients (15 men) aged 41-71 years consumed 16 g of inulin-type fructans (a mixture of oligofructose and inulin) and 16-g placebo (maltodextrin) for 6 weeks in randomised order. A 4-week washout separated the 6 weeks treatments. The faecal microbiota was analysed by high-throughput 16S rRNA amplicon sequencing and SCFA in faeces were analysed using vacuum distillation followed by gas chromatography.

RESULTS

Treatment with inulin-type fructans induced moderate changes in the faecal microbiota composition (1.5%, p = 0.045). A bifidogenic effect was most prominent, with highest positive effect on operational taxonomic units (OTUs) of Bifidobacterium adolescentis, followed by OTUs of Bacteroides. Significantly higher faecal concentrations of total SCFA, acetic acid and propionic acid were detected after prebiotic consumption compared to placebo. The prebiotic fibre had no effects on the concentration of butyric acid or on the overall microbial diversity.

CONCLUSION

Six weeks supplementation with inulin-type fructans had a significant bifidogenic effect and induced increased concentrations of faecal SCFA, without changing faecal microbial diversity. Our findings suggest a moderate potential of inulin-type fructans to improve gut microbiota composition and to increase microbial fermentation in type 2 diabetes.

TRIAL REGISTRATION

The trial is registered at clinicaltrials.gov (NCT02569684).

Effects of prebiotic dietary fibers and probiotics on human health: With special focus on recent advancement in their encapsulated formulations

Background

Dietary fibers (DFs) are known as potential formulations in human health due to their beneficial effects in control of life-threatening chronic diseases including cardiovascular disease (CVD), diabetes mellitus, obesity and cancer. In recent decades scientists around the globe have shown tremendous interest to evaluate the interplay between DFs and gastrointestinal (GIT) microbiota. Evidences from various epidemiological and clinical trials have revealed that DFs modulate formation and metabolic activities of the microbial communities residing in the human GIT which in turn play significant roles in maintaining health and well-being. Furthermore, interestingly, a rapidly growing literature indicates success of DFs being prebiotics in immunomodulation, namely the stimulation of innate, cellular and humoral immune response, which could also be linked with their significant roles in modulation of the probiotics (live beneficial microorganisms).

Scope and approach

The main focus of the current review is to expressively highlight the importance of DFs being prebiotics in human health in association with their influence on gut microbiota. Now in order to significantly achieve the promising health benefits from these prebiotics, it is aimed to develop novel formulations to enhance and scale up their efficacy. Therefore, finally, herein unlike previously published articles, we highlighted different kinds of prebiotic and probiotic formulations which are being regarded as hot research topics among the scientific community now a days.

Conclusion

The information in this article will specifically provide a platform for the development of novel functional foods the demands for which has risen drastically in recent years.

The Role of the Gut Microbiome in Colorectal Cancer Development and Therapy Response

Colorectal cancer (CRC) is the third most common cancer worldwide and the leading cause of cancer-related deaths. Recently, several studies have demonstrated that gut microbiota can alter CRC susceptibility and progression by modulating mechanisms such as inflammation and DNA damage, and by producing metabolites involved in tumor progression or suppression. Dysbiosis of gut microbiota has been observed in patients with CRC, with a decrease in commensal bacterial species (butyrate-producing bacteria) and an enrichment of detrimental bacterial populations (pro-inflammatory opportunistic pathogens). CRC is characterized by altered production of bacterial metabolites directly involved in cancer metabolism including short-chain fatty acids and polyamines. Emerging evidence suggests that diet has an important impact on the risk of CRC development. The intake of high-fiber diets and the supplementation of diet with polyunsaturated fatty acids, polyphenols and probiotics, which are known to regulate gut microbiota, could be not only a potential mechanism for the reduction of CRC risk in a primary prevention setting, but may also be important to enhance the response to cancer therapy when used as adjuvant to conventional treatment for CRC. Therefore, a personalized modulation of the pattern of gut microbiome by diet may be a promising approach to prevent the development and progression of CRC and to improve the efficacy of antitumoral therapy.

The Effects of Cellulose on AOM/DSS-Treated C57BL/6 Colorectal Cancer Mice by Changing Intestinal Flora Composition and Inflammatory Factors

Chronic intestinal inflammation is a key risk factor of colorectal cancer (CRC). It is known that microbial dysbiosis induces increased inflammatory factors which promote tumorigenesis and cellulose can be beneficial to CRC. In the present study, we investigated the regulatory effects of cellulose on intestinal flora composition and colorectal carcinogenesis in an azoxymethane (AOM)/dextran sulfate sodium (DSS)-induced CRC mouse model. Supplementation of cellulose significantly attenuated inflammation and tumor formation in AOM/DSS-treated CRC mice. The survival rate and the tumor inhibition rate were higher in the medium-dose cellulose group (MCEG) and high-dose cellulose group (HCEG) than in the model group (MG; P < 0.05). Cellulose supplementation stimulated shifts in the intestinal flora in AOM/DSS-treated CRC mice. Additionally, levels of inflammatory mediators involved in colorectal carcinogenesis, such as IL-6, IL-1β, and TNF-α, were lower in the serum of the low-dose cellulose group, MCEG, and HCEG when compared with the MG (P < 0.05). Whereas the abundance of differential bacteria was correlated with the concentration of IL-6, IL-1β, and TNF-α. These results showed cellulose changed the composition of intestinal flora and inhibited colon inflammation and neoplasm formation caused by the AOM/DSS treatment.

Fermentable Dietary Fiber Promotes Helminth Infection and Exacerbates Host Inflammatory Responses

Fermentable dietary fibers promote the growth of beneficial bacteria, can enhance mucosal barrier integrity, and reduce chronic inflammation. However, effects on intestinal type 2 immune function remain unclear. In this study, we used the murine whipworm Trichuris muris to investigate the effect of the fermentable fiber inulin on host responses to infection regimes that promote distinct Th1 and Th2 responses in C57BL/6 mice. In uninfected mice, dietary inulin stimulated the growth of beneficial bacteria, such as Bifidobacterium (Actinobacteria) and Akkermansia (Verrucomicrobia). Despite this, inulin prevented worm expulsion in normally resistant mice, instead resulting in chronic infection, whereas mice fed an equivalent amount of nonfermentable fiber (cellulose) expelled worms normally. Lack of expulsion in the mice fed inulin was accompanied by a significantly Th1-skewed immune profile characterized by increased T-bet⁺ T cells and IFN-γ production in mesenteric lymph nodes, increased expression of Ido1 in the cecum, and a complete absence of mast cell and IgE production. Furthermore, the combination of dietary inulin and high-dose T. muris infection caused marked dysbiosis, with expansion of the Firmicutes and Proteobacteria phyla, near elimination of Bacteroidetes, and marked reductions in cecal short-chain fatty acids. Neutralization of IFN-γ during infection abrogated Ido1 expression and was sufficient to restore IgE production and worm expulsion in inulin-fed mice. Our results indicate that, whereas inulin promoted gut health in otherwise healthy mice, during T. muris infection, it exacerbated inflammatory responses and dysbiosis. Thus, the positive effects of fermentable fiber on gut inflammation appear to be context dependent, revealing a novel interaction between diet and infection.

Food matrix and the microbiome: considerations for preclinical chronic disease studies

Animal models of chronic disease are continuously being refined and have evolved with the goal of increasing the translation of results to human populations. Examples of this progress include transgenic models and germ-free animals conventionalized with human microbiota. The gut microbiome is involved in the etiology of several chronic diseases. Therefore, consideration of the experimental conditions that may affect the gut microbiome in preclinical disease is very important. Of note, diet plays a large role in shaping the gut microbiome and can be a source of variation between animal models and human populations. Traditionally, nutrition researchers have focused on manipulating the macronutrient profile of experimental diets to model diseases such as metabolic syndrome. However, other dietary components found in human foods, but not in animal diets, can have sizable effects on the composition and metabolic capacity of the gut microbiome and, as a consequence, manifestation of the chronic disease being modeled. The purpose of this review is to describe how food matrix food components, including diverse fiber sources, oxidation products from cooking, and dietary fat emulsifiers, shape the composition of the gut microbiome and influence gut health.

Deficiency of Dietary Fiber in Slc5a8-Null Mice Promotes Bacterial Dysbiosis and Alters Colonic Epithelial Transcriptome towards Proinflammatory Milieu

Inflammatory bowel disease (IBD) is characterized by chronic inflammation in the intestinal tract due to disruption of the symbiotic relationship between the host immune system and microbiota. Various factors alter the gut microbiota which lead to dysbiosis; in particular, diet and dietary fibers constitute important determinants. Dietary fiber protects against IBD; bacteria ferment these dietary fibers in colon and generate short-chain fatty acids (SCFAs), which mediate the anti-inflammatory actions of dietary fibers. SLC5A8 is a high-affinity transporter in the apical membrane of colonic epithelium which mediates the entry of SCFAs from the lumen into cells in Na⁺-coupled manner. Due to the unique transport kinetics, the function of the transporter becomes important only under conditions of low dietary fiber intake. Here, we have examined the impact of dietary fiber deficiency on luminal microbial composition and transcriptomic profile in colonic epithelium in wild-type (WT) and Slc5a8-null (KO) mice. We fed WT and KO mice with fiber-containing diet (FC-diet) or fiber-free diet (FF-diet) and analyzed the luminal bacterial composition by sequencing 16S rRNA gene in feces. Interestingly, results showed significant differences in the microbial community depending on dietary fiber content and on the presence or absence of Slc5a8. There were also marked differences in the transcriptomic profile of the colonic epithelium depending on the dietary fiber content and on the presence or absence of Slc5a8. We conclude that absence of fiber in diet in KO mice causes bacterial dysbiosis and alters gene expression in the colon that is conducive for inflammation.

Comparison of the fecal, cecal, and mucus microbiome in male and female mice after TNBS-induced colitis

Crohn’s Disease and Ulcerative Colitis are chronic, inflammatory conditions of the digestive tract, collectively known as Inflammatory Bowel Disease (IBD). The combined influence of lifestyle factors, genetics, and the gut microbiome contribute to IBD pathogenesis. Studies of the gut microbiome have shown significant differences in its composition between healthy individuals and those with IBD. Due to the high inter-individual microbiome variation seen in humans, mouse models of IBD are often used to investigate potential IBD mechanisms and their interplay between host, microbial, and environmental factors. While fecal samples are the predominant material used for microbial community analysis, they may not be the ideal sample to use for analysis of the microbiome of mice with experimental colitis, such as that induced by 2, 4, 6 trinitrobenzesulfonic acid (TNBS). As TNBS is administered intrarectally to induce colitis and inflammation is confined to the colon in this model, we hypothesized that the microbiome of the colonic mucus would most closely correlate with TNBS colitis severity. Based on our previous research, we also hypothesized that sex would be associated with both disease severity and microbial differences in mice with chronic TNBS colitis. We examined and compared the fecal, cecal content, and colonic mucus microbiota of 8-week old male and female C57BL/6J wild-type mice prior to and after the induction of TNBS colitis via 16S rRNA gene sequencing. We found that the colonic mucus microbiome was more closely correlated with disease severity than were alterations in the fecal and cecal microbiomes. We also found that the microbiomes of the feces, cecum, and mucus were distinct, but found no significant differences that were associated with sex in either compartment. Our findings highlight the importance of sampling colonic mucus in TNBS-induced colitis. Moreover, consideration of the differential impact of sex on the microbiome across mouse strains may be critical for the appropriate application of TNBS colitis models and robust comparisons across studies in the future.

Traditional Processed Meat Products Re-designed Towards Inulin-rich Functional Foods Reduce Polyps in Two Colorectal Cancer Animal Models

Inulin-rich foods exert a prebiotic effect, as this polysaccharide is able to enhance beneficial colon microbiota populations, giving rise to the in situ production of short-chain fatty acids (SCFAs) such as propionic and butyric acids. These SCFAs are potent preventive agents against colorectal cancer due to their histone deacetylases inhibitory properties, which induce apoptosis in tumor colonocytes. As colorectal cancer is the fourth most common neoplasia in Europe with 28.2 new cases per 100,000 inhabitants, a cost-effective preventive strategy has been tested in this work by redesigning common porcine meat products (chorizo sausages and cooked ham) consumed by a substantial proportion of the population towards potential colorectal cancer preventive functional foods. In order to test the preventive effect of these inulin-rich meat products against colorectal cancer, an animal model (Rattus norvegicus F344) was used, involving two doses of azoxymethane (10 mg/kg) and two treatments with dextran sodium sulfate (DSS) during a 20-week assay period. Control feed, control sausages, functional sausages (15.7% inulin), control cooked ham and functional cooked ham (10% inulin) were used to feed the corresponding animal cohorts. Then, the animals were sacrificed and their digestive tract tissues were analyzed. The results showed a statistically significant 49% reduction in the number of colon polyps in the functional meat products cohorts with respect to the control meat products animals, as well as an increase in the cecum weight (an indicator of a diet rich in prebiotic fiber), a 51.8% increase in colon propionate production, a 39.1% increase in colon butyrate concentrations, and a reduction in the number of hyperplastic Peyer's patches. Metagenomics studies also demonstrated colon microbiota differences, revealing a significant increase in Bacteroidetes populations in the functional meat products (mainly due to an increase in Bacteroidaceae and Prevotellaceae families, which include prominent propionate producers), together with a reduction in Firmicutes (especially due to lower Lachnospiraceae populations). However, functional meat products showed a remarkable increase in the anti-inflammatory and fiber-fermentative Blautia genus, which belongs to this Lachnospiraceae family. The functional meat products cohorts also presented a reduction in important pro-inflammatory bacterial populations, such as those of the genus Desulfovibrio and Bilophila. These results were corroborated in a genetic animal model of CRC (F344/NSlc-Apc1588/kyo) that produced similar results. Therefore, processed meat products can be redesigned towards functional prebiotic foods of interest as a cost-effective dietary strategy for preventing colorectal cancer in human populations.

Beneficial Effect of Intestinal Fermentation of Natural Polysaccharides

With the rapid development of modern society, many chronic diseases are increasing including diabetes, obesity, cardiovascular diseases, etc., which further cause an increased death rate worldwide. A high caloric diet with reduced natural polysaccharides, typically indigestible polysaccharides, is considered a health risk factor. With solid evidence accumulating that indigestible polysaccharides can effectively prevent and/or ameliorate symptoms of many chronic diseases, we give a narrative review of many natural polysaccharides extracted from various food resources which mainly contribute their health beneficial functions via intestinal fermentation.

Effects of Prebiotic Fiber Xylooligosaccharide in Adenine-Induced Nephropathy in Mice

SCOPE

This study evaluates the effect of the prebiotic fiber xylooligosaccharide (XOS) on kidney function and gut microbiome in mice with adenine-induced chronic kidney disease (CKD).

METHOD AND RESULTS

Mice are fed the control diet containing adenine for 3 weeks to induce CKD and are switched to XOS supplemented (2 or 7%) or control diets for another 3 weeks. Mice with CKD exhibit increased blood urea nitrogen (BUN), creatinine, and kidney histopathology. XOS significantly reverses kidney injuries in CKD mice. Analysis of cecum microbiota reveales that adenine-induced CKD does not change alpha diversity, and XOS induces a decrease of alpha diversity in control mice and mice with CKD. Beta diversity analysis shows significant clustering according to experimental groups. Six out of the nine bacterial genera enriched in CKD are significantly reduced with XOS intervention. Furthermore, XOS increases cecal short-chain fatty acid (SCFA) production in both control and CKD mice. Cecal SCFAs and blood propionate are negatively correlated with BUN. XOS also decreases blood p-cresol sulfate in CKD mice, likely resulting from altered microbial tyrosine metabolism.

CONCLUSION

These results show that XOS intervention improves kidney function in mice with CKD, and is associated with profound changes in microbial composition and metabolism.

Short-chain fatty acids administration is protective in colitis-associated colorectal cancer development

Reduced short-chain fatty acids (SCFAs) have been reported in patients with ulcerative colitis, and increased intake of dietary fiber has shown to be clinically beneficial for colitis. Whether SCFAs suppress tumorigenesis in colitis-associated colorectal cancer remains unknown. The chemopreventive effect of SCFAs in colitis-associated colorectal cancer was evaluated in this study. Model of colitis-associated colorectal cancer in male BALB/c mice was induced by azoxymethane (AOM) and dextran sodium sulfate (DSS). SCFAs mix (67.5 mM acetate, 40 mM butyrate, 25.9 mM propionate) was administered in drink water during the study period. Macroscopic and histological studies were performed to examine the colorectal inflammation and tumorigenesis in AOM/DSS-induced mice treated with or without SCFA mix. The effects of SCFAs mix on colonic epithelial cellular proliferation were also assessed using Ki67 immunohistochemistry and TUNEL staining. The administration of SCFAs mix significantly reduced the tumor incidence and size in mice with AOM/DSS-induced colitis associated colorectal cancer. SCFAs mix protected from AOM/DSS-induced colorectal cancer by improving colon inflammation and disease activity index score as well as suppressing the expression of proinflammatory cytokines including IL-6, TNF-α and IL-17. A decrease in cell proliferation markers and an increase in TUNEL-positive tumor epithelial cells were also demonstrated in AOM/DSS mice treated with SCFAs mix. SCFAs mix administration prevented development of tumor and attenuated the colonic inflammation in a mouse model of colitis-associated colorectal cancer. SCFAs mix may be a potential agent in the prevention and treatment of colitis-associated colorectal cancer.

Dietary fiber and health outcomes: an umbrella review of systematic reviews and meta-analyses

Background

Several studies have suggested that higher consumption of dietary fiber is beneficial for a variety of health outcomes. However, many results have been inconclusive and, to our knowledge, there has been no attempt to systematically capture the breadth of outcomes associated with dietary fiber intake or to systematically assess the quality and the strength of the evidence on the associations of dietary fiber intake and different health outcomes or medical conditions.

Objective

The aim of this study was to describe the diverse health outcomes convincingly associated with dietary fiber consumption.

Design

This was an umbrella review of systematic reviews with meta-analysis of observational studies. For each association, random-effects summary effect size, 95% CIs, and 95% prediction intervals were estimated. We also assessed heterogeneity, evidence for small-study effect, and evidence for excess significance bias. We used these metrics to evaluate the credibility of the identified evidence.

Results

Our literature search identified 1351 abstracts. Of these, 18 meta-analyses including a total of 298 prospective observational studies and 21 outcomes were included. Outcomes studied included cancer and precancer lesions (n = 12), cardiovascular diseases (CVDs; n = 3), all-cause and specific-cause mortality (n = 4), type 2 diabetes (n = 1), and Crohn disease (n = 1). Overall, 6 (29%) of the 21 eligible outcomes reported highly significant summary results (P < 1 × 10-6); these included CVD and CVD mortality, coronary artery disease, pancreatic cancer, and gastric cancer. Overall, 3 of 21 (14%) outcomes presented convincing evidence (pancreatic cancer, CVD mortality, and all-cause mortality), but only CVD and all-cause mortality were based on prospective studies. Two other outcomes (10%), CVD and coronary artery disease, presented highly suggestive evidence based on prospective studies.

Conclusion

Our results support dietary recommendations that promote higher fiber intake as part of a healthy diet.

Dietary Fiber Treatment Corrects the Composition of Gut Microbiota, Promotes SCFA Production, and Suppresses Colon Carcinogenesis

Epidemiological studies propose a protective role for dietary fiber in colon cancer (CRC). One possible mechanism of fiber is its fermentation property in the gut and ability to change microbiota composition and function. Here, we investigate the role of a dietary fiber mixture in polyposis and elucidate potential mechanisms using TS4Cre × cAPC^l°^x468 mice. Stool microbiota profiling was performed, while functional prediction was done using PICRUSt. Stool short-chain fatty acid (SCFA) metabolites were measured. Histone acetylation and expression of SCFA butyrate receptor were assessed. We found that SCFA-producing bacteria were lower in the polyposis mice, suggesting a decline in the fermentation product of dietary fibers with polyposis. Next, a high fiber diet was given to polyposis mice, which significantly increased SCFA-producing bacteria as well as SCFA levels. This was associated with an increase in SCFA butyrate receptor and a significant decrease in polyposis. In conclusion, we found polyposis to be associated with dysbiotic microbiota characterized by a decline in SCFA-producing bacteria, which was targetable by high fiber treatment, leading to an increase in SCFA levels and amelioration of polyposis. The prebiotic activity of fiber, promoting beneficial bacteria, could be the key mechanism for the protective effects of fiber on colon carcinogenesis. SCFA-promoting fermentable fibers are a promising dietary intervention to prevent CRC.

Epigenetic Regulation of Gene Expression Induced by Butyrate in Colorectal Cancer: Involvement of MicroRNA

Colorectal cancer (CRC) is the third most common cause of cancer mortality globally. Development of CRC is closely associated with lifestyle, and diet may modulate risk. A Western-style diet is characterised by a high intake of red meat but low consumption of fruit, vegetables, and whole cereals. Such a diet is associated with CRC risks. It has been demonstrated that butyrate, produced by the fermentation of dietary plant fibre, can alter both genetic and epigenetic expressions. MicroRNAs (miRNAs) are small non-coding RNAs that are commonly present in both normal and tumour cells. Aberrant miRNA expression is associated with CRC initiation, progression, and metastasis. In addition, butyrate can modulate cell proliferation, differentiation, apoptosis, and miRNA expression in CRC. In this review, the effects of butyrate on modulating miRNA expression in CRC will be discussed. Furthermore, evidence on the effect of butyrate on CRC risk through reducing oncogenic miRNA expression will be presented.

A study of the prebiotic-like effects of tomato juice consumption in rats with diet-induced non-alcoholic fatty liver disease (NAFLD)

Tomato juice intake partially ameliorated high-fat diet-induced disturbances of gut microbiota, particularly by increasingLactobacillusabundance and diminishing the acetate to propionate ratio.

Cecal microbiota association with tumor load in a colorectal cancer mouse model

Background: Colorectal cancer (CRC) is one of the most common cancer types worldwide. The role of the intestinal microbiota in CRC, however, is not well established. In particular, the co-variation between age, tumor progression and microbiota remains largely unknown.

Objective and design: We therefore used a recently developed A/J Min/+ mouse model resembling human CRC to investigate how microbial composition in cecum correlates with tumor progression, butyrate and age.

Results: We found that the association between the gut microbiota and tumor load was stronger, by far, than the association with both butyrate and age. The strongest direct tumor association was found for mucosal bacteria, with nearly 60% of the significantly correlating operational taxonomic units being correlated with CRC tumor load alone.

Conclusion: We favor a systemic association between tumor load and microbiota, since the correlations are associated with tumor load in gut segments other than the cecum (both small and large intestine).

Light/Dark Shifting Promotes Alcohol-Induced Colon Carcinogenesis: Possible Role of Intestinal Inflammatory Milieu and Microbiota

Background: Colorectal cancer (CRC) is associated with the modern lifestyle. Chronic alcohol consumption—a frequent habit of majority of modern societies—increases the risk of CRC. Our group showed that chronic alcohol consumption increases polyposis in a mouse mode of CRC. Here we assess the effect of circadian disruption—another modern life style habit—in promoting alcohol-associated CRC. Method: TS4Cre × adenomatous polyposis coli (APC)^lox468 mice underwent (a) an alcohol-containing diet while maintained on a normal 12 h light:12 h dark cycle; or (b) an alcohol-containing diet in conjunction with circadian disruption by once-weekly 12 h phase reversals of the light:dark (LD) cycle. Mice were sacrificed after eight weeks of full alcohol and/or LD shift to collect intestine samples. Tumor number, size, and histologic grades were compared between animal groups. Mast cell protease 2 (MCP2) and 6 (MCP6) histology score were analyzed and compared. Stool collected at baseline and after four weeks of experimental manipulations was used for microbiota analysis. Results: The combination of alcohol and LD shifting accelerated intestinal polyposis, with a significant increase in polyp size, and caused advanced neoplasia. Consistent with a pathogenic role of stromal tryptase-positive mast cells in colon carcinogenesis, the ratio of mMCP6 (stromal)/mMCP2 (intraepithelial) mast cells increased upon LD shifting. Baseline microbiota was similar between groups, and experimental manipulations resulted in a significant difference in the microbiota composition between groups. Conclusions: Circadian disruption by Light:dark shifting exacerbates alcohol-induced polyposis and CRC. Effect of circadian disruption could, at least partly, be mediated by promoting a pro-tumorigenic inflammatory milieu via changes in microbiota.