Dietary fat, bile acid metabolism and colorectal cancer.

Colorectal cancer (CRC) risk is predominantly driven by environmental factors, in particular diet. A high intake of dietary fat has been implicated as a risk factor inducing the formation of pre-neoplastic lesions (e.g., adenomatous polyps) and/or exacerbating colonic tumorigenesis. Recent data attributed the tumor-promoting activity of high-fat diets to their effects on gut microbiota composition and metabolism, in particular with regard to bile acids. Bile acids are synthesized in the liver in response to dietary fat and facilitate lipid absorption in the small intestine. The majority of bile acids is re-absorbed during small intestinal transit and subjected to enterohepatic circulation. Bile acids entering the colon undergo complex biotransformation performed by gut bacteria, resulting in secondary bile acids that show tumor-promoting activity. Excessive dietary fat leads to high levels of secondary bile acids in feces and primes the gut microbiota to bile acid metabolism. This promotes an altered overall bile acid pool, which activates or restricts intestinal and hepatic cross-signaling of the bile acid receptor, farnesoid X receptor (FXR). Recent studies provided evidence that FXR is a main regulator of bile acid-mediated effects on intestinal tumorigenesis integrating dietary, microbial and genetic risk factors for CRC. Selective FXR agonist or antagonist activity by specific bile acids depends on additional factors (e.g., bile acid concentration, composition of bile acid pool, genetic instability of cells) and, thus, may differ in healthy and tumorigenic conditions in the intestine. In conclusion, fat-mediated alterations of the gut microbiota link bile acid metabolism to CRC risk and colonic tumorigenesis, exemplifying how gut microbial co-metabolism affects colon health.

Bile acids, bile pigments and colorectal cancer risk.

PURPOSE OF REVIEW: The gut microbial co-metabolism of bile-derived compounds (e.g. bile acids and bile pigments) affects colorectal cancer (CRC) risk. Here, we review recent findings with focus on selected novel aspects of bile-associated effects with interesting but unclear implications on CRC risk. RECENT FINDINGS: Numerous studies demonstrated novel biotransformation of bile acids by gut bacteria (e.g. microbial conjugation of bile acids), resulting in diverse bile acid compounds that show complex interactions with host receptors (e.g. FXR, TGR5). In addition, YAP-associated signalling in intestinal epithelial cells is modulated via bile acid receptor TGR5 and contributes to colonic tumorigenesis. Finally, studies indicate that serum levels of the bile pigment bilirubin are inversely associated with CRC risk or intestinal inflammation and that bilirubin affects gut microbiota composition. SUMMARY: Bile acids and bile pigments have multiple effects on intestinal microbe-host interactions, which may collectively modulate long-term CRC risk of the host.

Interactions between the environmental and human microbiota in the preservation of health and genesis of disease: symposium report.

PURPOSE OF REVIEW: The purpose of this symposium was to bring thought leaders in the microbiome from the west to Africa to share their unique experiences with African investigators in order to build the foundations for scientifically rigorous explorations into the African human and environmental microbiome that may explain why disease patterns are different in Africa where the chief killers are infectious diseases, whereas noncommunicable diseases (NCDs) are the major threat to healthcare resources in the developed world. RECENT FINDINGS: The application of new high throughput technologies to the investigation of the microbiome and its metabolome has revealed mechanisms whereby a traditional African high fiber diet can suppress NCDs which include colon cancer, inflammatory bowel diseases, obesity, type 2 diabetes and atherosclosis. There is concern that with migration and westernization, NCDs are becoming more common in Africa and that food security is becoming impaired by unbalanced obesogenic foods rather than inadequate food intake. SUMMARY: There is an urgent need for the formation of combined African-Western research programs to identify what is good and bad in the African diet-microbiome axis to develop strategies to prevent the incidence of NCDs rising to western levels in Africa, at the same time offering novel prevention strategies against the #1 healthcare threat in the developed world.

Diet and the Human Gut Microbiome: An International Review.

This review summarizes the key results of recently published studies on the effects of dietary change and nutritional intervention on the human microbiome from around the world, focusing on the USA, Canada, Europe, Asia, and Africa. It first explores mechanisms that might explain the ability of fiber-rich foods to suppress the incidence and mortality from westernized diseases, notably cancers of the colon, breast, liver, cardiovascular, infectious, and respiratory diseases, diabetes, and obesity (O'Keefe in Lancet Gastroenterol Hepatol 4(12):984-996, 2019; Am J Clin Nutr 110:265-266, 2019). It summarizes studies from Africa which suggest that disturbance of the colonic microbiome may exacerbate chronic malnutrition and growth failure in impoverished communities and highlights the importance of breast feeding. The American section discusses the role of the microbiome in the swelling population of patients with obesity and type 2 diabetes and examines the effects of race, ethnicity, geography, and climate on microbial diversity and metabolism. The studies from Europe and Asia extoll the benefits of whole foods and plant-based diets. The Asian studies examine the worrying changes from low-fat, high-carbohydrate diets to high-fat, low-carbohydrate ones and the increasing appearance of westernized diseases as in Africa and documents the ability of high-fiber traditional Chinese diets to reverse type 2 diabetes and control weight loss. In conclusion, most of the studies reviewed demonstrate clear changes in microbe abundances and in the production of fermentation products, such as short-chain fatty acids and phytochemicals following dietary change, but the significance of the microbiota changes to human health, with the possible exception of the stimulation of butyrogenic taxa by fiber-rich foods, is generally implied and not measured. Further studies are needed to determine how these changes in microbiota composition and metabolism can improve our health and be used to prevent and treat disease.

Fiber, Fat, and Colorectal Cancer: New Insight into Modifiable Dietary Risk Factors.

PURPOSE OF REVIEW: To review recent data on the role and interactions of fiber and fat as dietary risk factors associated with colorectal cancer (CRC) risk in humans. RECENT FINDINGS: Fiber intake shows convincing and linear dose-response negative correlation with CRC risk. Dietary fiber stimulates butyrogenic activity of the gut microbiota, providing high amounts of butyrate that shows extensive anti-neoplastic effects. A high-fat diet promotes CRC risk through stimulated bile acid metabolism, facilitating bile acid conversion by the gut microbiota to tumor-promoting deoxycholic acid. Comprehensive interactions of these microbial metabolites are likely to underlie mechanisms driving diet-dependent CRC risk in different populations, but require further experimental investigation. Dietary fiber and fat shape the composition and metabolic function of the gut microbiota, resulting in altered amounts of butyrate and deoxycholic acid in the colon. Fiber supplementation and restriction of fat intake represent promising strategies to reduce CRC risk in healthy individuals.

Surface-Associated Lipoproteins Link Enterococcus faecalis Virulence to Colitogenic Activity in IL-10-Deficient Mice Independent of Their Expression Levels.

The commensal Enterococcus faecalis is among the most common causes of nosocomial infections. Recent findings regarding increased abundance of enterococci in the intestinal microbiota of patients with inflammatory bowel diseases and induction of colitis in IL-10-deficient (IL-10-/-) mice put a new perspective on the contribution of E. faecalis to chronic intestinal inflammation. Based on the expression of virulence-related genes in the inflammatory milieu of IL-10-/- mice using RNA-sequencing analysis, we characterized the colitogenic role of two bacterial structures that substantially impact on E. faecalis virulence by different mechanisms: the enterococcal polysaccharide antigen and cell surface-associated lipoproteins. Germ-free wild type and IL-10-/- mice were monoassociated with E. faecalis wild type OG1RF or the respective isogenic mutants for 16 weeks. Intestinal tissue and mesenteric lymph nodes (MLN) were collected to characterize tissue pathology, loss of intestinal barrier function, bacterial adhesion to intestinal epithelium and immune cell activation. Bone marrow-derived dendritic cells (BMDC) were stimulated with bacterial lysates and E. faecalis virulence was additionally investigated in three invertebrate models. Colitogenic activity of wild type E. faecalis (OG1RF score: 7.2±1.2) in monoassociated IL-10-/- mice was partially impaired in E. faecalis lacking enterococcal polysaccharide antigen (ΔepaB score: 4.7±2.3; p<0.05) and was almost completely abrogated in E. faecalis deficient for lipoproteins (Δlgt score: 2.3±2.3; p<0.0001). Consistently both E. faecalis mutants showed significantly impaired virulence in Galleria mellonella and Caenorhabditis elegans. Loss of E-cadherin in the epithelium was shown for all bacterial strains in inflamed IL-10-/- but not wild type mice. Inactivation of epaB in E. faecalis reduced microcolony and biofilm formation in vitro, altered bacterial adhesion to intestinal epithelium of germ-free Manduca sexta larvae and impaired penetration into the colonic mucus layer of IL-10-/- mice. Lipoprotein-deficient E. faecalis exhibited an impaired TLR2-mediated activation of BMDCs in vitro despite their ability to fully reactivate MLN cells as well as MLN-derived colitogenic T cells ex vivo. E. faecalis virulence factors accounting for bacterial adhesion to mucosal surfaces as well as intestinal barrier disruption partially contribute to colitogenic activity of E. faecalis. Beyond their well-known role in infections, cell surface-associated lipoproteins are essential structures for colitogenic activity of E. faecalis by mediating innate immune cell activation.

Endoplasmic reticulum stress response promotes cytotoxic phenotype of CD8αß+ intraepithelial lymphocytes in a mouse model for Crohn's disease-like ileitis.

Endoplasmic reticulum (ER) unfolded protein responses (UPR) are implicated in the pathogenesis of inflammatory bowel disease. Cytotoxic CD8αß(+) intraepithelial lymphocytes (IEL) contribute to the development of Crohn's disease-like ileitis in TNF(ΔARE/+) mice. In this study, we characterized the role of ER-UPR mechanisms in contributing to the disease-associated phenotype of cytotoxic IEL under conditions of chronic inflammation. Inflamed TNF(ΔARE/+) mice exhibited increased expression of Grp78, ATF6, ATF4, and spliced XBP1 in CD8αß(+) IEL but not in CD8αα(+) IEL or in lamina propria lymphocytes. Chromatin immunoprecipitation analysis in CD8αß(+) T cells showed selective recruitment of ER-UPR transducers to the granzyme B gene promoter. Heterozygous Grp78(-/+) mice exhibited an attenuated granzyme B-dependent cytotoxicity of CD8αß(+) T cells against intestinal epithelial cells, suggesting a critical activity of this ER-associated chaperone in maintaining a cytotoxic T cell phenotype. Granzyme B-deficient CD8αß(+) T cells showed a defect in IL-2-mediated proliferation in Grp78(-/+) mice. Adoptively transferred Grp78(-/+) CD8αß(+) T cells had a decreased frequency of accumulation in the intestine of RAG2(-/-) recipient mice. The tissue pathology in TNF(ΔARE/+) × Grp78(-/+) mice was similar to TNF(ΔARE/+) mice, even though the cytotoxic effector functions of CD8αß(+) T cells were significantly reduced. In conclusion, ER stress-associated UPR mechanisms promote the development and maintenance of the pathogenic cytotoxic CD8αß(+) IEL phenotype in the mouse model of Crohn's disease-like ileitis.

Ketogenic Diet Has Moderate Effects on the Fecal Microbiota of Wild-Type Mice.

The ketogenic diet (KD) is a high-fat, low-carbohydrate diet that has been reported to have neuroprotective effects. The health effects of KD might be linked to an altered gut microbiome, which plays a major role in host health, leading to neuroprotective effects via the gut-brain axis. However, results from different studies, most often based on the 16S rRNA gene and metagenome sequencing, have been inconsistent. In this study, we assessed the effect of a 4-week KD compared to a western diet (WD) on the colonic microbiome of female C57Bl/6J mice by analyzing fecal samples using fluorescence in situ hybridization. Our results showed distinct changes in the total number of gut bacteria following the 4-week KD, in addition to changes in the composition of the microbiome. KD-fed mice showed higher absolute numbers of Actinobacteria (especially Bifidobacteria spp.) and lower absolute levels of Proteobacteria, often linked to gut inflammation, in comparison with WD-fed mice. Furthermore, an increased abundance of the typically rare genus Atopobium was observed. These changes may indicate the possible anti-inflammatory effects of the KD. However, since the overall changes in the microbiota seem low, the KD effects might be linked to the differential abundance of only a few key genera in mice.

A non-coding variant linked to metabolic obesity with normal weight affects actin remodelling in subcutaneous adipocytes.

Recent large-scale genomic association studies found evidence for a genetic link between increased risk of type 2 diabetes and decreased risk for adiposity-related traits, reminiscent of metabolically obese normal weight (MONW) association signatures. However, the target genes and cellular mechanisms driving such MONW associations remain to be identified. Here, we systematically identify the cellular programmes of one of the top-scoring MONW risk loci, the 2q24.3 risk locus, in subcutaneous adipocytes. We identify a causal genetic variant, rs6712203, an intronic single-nucleotide polymorphism in the COBLL1 gene, which changes the conserved transcription factor motif of POU domain, class 2, transcription factor 2, and leads to differential COBLL1 gene expression by altering the enhancer activity at the locus in subcutaneous adipocytes. We then establish the cellular programme under the genetic control of the 2q24.3 MONW risk locus and the effector gene COBLL1, which is characterized by impaired actin cytoskeleton remodelling in differentiating subcutaneous adipocytes and subsequent failure of these cells to accumulate lipids and develop into metabolically active and insulin-sensitive adipocytes. Finally, we show that perturbations of the effector gene Cobll1 in a mouse model result in organismal phenotypes matching the MONW association signature, including decreased subcutaneous body fat mass and body weight along with impaired glucose tolerance. Taken together, our results provide a mechanistic link between the genetic risk for insulin resistance and low adiposity, providing a potential therapeutic hypothesis and a framework for future identification of causal relationships between genome associations and cellular programmes in other disorders.

CD39 and CD326 Are Bona Fide Markers of Murine and Human Plasma Cells and Identify a Bone Marrow Specific Plasma Cell Subpopulation in Lupus.

Antibody-secreting cells (ASCs) contribute to immunity through production of antibodies and cytokines. Identification of specific markers of ASC would allow selective targeting of these cells in several disease contexts. Here, we performed an unbiased, large-scale protein screening, and identified twelve new molecules that are specifically expressed by murine ASCs. Expression of these markers, particularly CD39, CD81, CD130, and CD326, is stable and offers an improved resolution for ASC identification. We accessed their expression in germ-free conditions and in T cell deficient mice, showing that at least in part their expression is controlled by microbial- and T cell-derived signals. Further analysis of lupus mice revealed the presence of a subpopulation of LAG-3- plasma cells, co-expressing high amounts of CD39 and CD326 in the bone marrow. This population was IgM+ and correlated with IgM anti-dsDNA autoantibodies in sera. Importantly, we found that CD39, CD81, CD130, and CD326 are also expressed by human peripheral blood and bone marrow ASCs. Our data provide innovative insights into ASC biology and function in mice and human, and identify an intriguing BM specific CD39++CD326++ ASC subpopulation in autoimmunity.

A prospective cohort analysis of gut microbial co-metabolism in Alaska Native and rural African people at high and low risk of colorectal cancer.

BACKGROUND: Alaska Native (AN) people have the world's highest recorded incidence of sporadic colorectal cancer (CRC) (∼91:100,000), whereas rural African (RA) people have the lowest risk (<5:100,000). Previous data supported the hypothesis that diet affected CRC risk through its effects on the colonic microbiota that produce tumor-suppressive or -promoting metabolites. OBJECTIVES: We investigated whether differences in these metabolites may contribute to the high risk of CRC in AN people. METHODS: A cross-sectional observational study assessed dietary intake from 32 AN and 21 RA healthy middle-aged volunteers before screening colonoscopy. Analysis of fecal microbiota composition by 16S ribosomal RNA gene sequencing and fecal/urinary metabolites by 1H-NMR spectroscopy was complemented with targeted quantification of fecal SCFAs, bile acids, and functional microbial genes. RESULTS: Adenomatous polyps were detected in 16 of 32 AN participants, but not found in RA participants. The AN diet contained higher proportions of fat and animal protein and less fiber. AN fecal microbiota showed a compositional predominance of Blautia and Lachnoclostridium, higher microbial capacity for bile acid conversion, and low abundance of some species involved in saccharolytic fermentation (e.g., Prevotellaceae, Ruminococcaceae), but no significant lack of butyrogenic bacteria. Significantly lower concentrations of tumor-suppressive butyrate (22.5 ± 3.1 compared with 47.2 ± 7.3 SEM µmol/g) coincided with significantly higher concentrations of tumor-promoting deoxycholic acid (26.7 ± 4.2 compared with 11 ± 1.9 µmol/g) in AN fecal samples. AN participants had lower quantities of fecal/urinary metabolites than RA participants and metabolite profiles correlated with the abundance of distinct microbial genera in feces. The main microbial and metabolic CRC-associated markers were not significantly altered in AN participants with adenomatous polyps. CONCLUSIONS: The low-fiber, high-fat diet of AN people and exposure to carcinogens derived from diet or environment are associated with a tumor-promoting colonic milieu as reflected by the high rates of adenomatous polyps in AN participants.

Traditional medicinal plants used for the treatment of diabetes in rural and urban areas of Dhaka, Bangladesh--an ethnobotanical survey.

BACKGROUND: The usage of medicinal plants is traditionally rooted in Bangladesh and still an essential part of public healthcare. Recently, a dramatically increasing prevalence brought diabetes mellitus and its therapy to the focus of public health interests in Bangladesh. We conducted an ethnobotanical survey to identify the traditional medicinal plants being used to treat diabetes in Bangladesh and to critically assess their anti-diabetic potentials with focus on evidence-based criteria. METHODS: In an ethnobotanical survey in defined rural and urban areas 63 randomly chosen individuals (health professionals, diabetic patients), identified to use traditional medicinal plants to treat diabetes, were interviewed in a structured manner about their administration or use of plants for treating diabetes. RESULTS: In total 37 medicinal plants belonging to 25 families were reported as being used for the treatment of diabetes in Bangladesh. The most frequently mentioned plants were Coccinia indica, Azadirachta indica, Trigonella foenum-graecum, Syzygium cumini, Terminalia chebula, Ficus racemosa, Momordica charantia, Swietenia mahagoni. CONCLUSION: Traditional medicinal plants are commonly used in Bangladesh to treat diabetes. The available data regarding the anti-diabetic activity of the detected plants is not sufficient to adequately evaluate or recommend their use. Clinical intervention studies are required to provide evidence for a safe and effective use of the identified plants in the treatment of diabetes.