Anneke Rijnierse

Mechanisms underlying immune effects of dietary oligosaccharides

The WHO refers to human milk as the nutritional gold standard for term infants. Human milk contains many immunomodulatory compounds, including oligosaccharides. Human-milk oligosaccharides can serve as prebiotics because the nondigestible oligosaccharides present in human milk show a clear bifidogenic effect on the gut microbiota. Dietary oligosaccharide structures that have prebiotic effects similar to human-milk oligosaccharides include galacto-oligosaccharides, fructo-oligosaccharides, and pectin-derived acidic oligosaccharides. Both animal studies and human clinical trials showed that dietary intervention with these dietary oligosaccharides in early life could lead to the prevention of atopic dermatitis, food allergy, and allergic asthma. The immune-modulating effects of these oligosaccharides are likely assisted via alteration of the intestinal microbiota or in a microbiota-independent manner by direct interaction on immune cells or both. In this review, an overview of the prebiotic role of dietary oligosaccharides on the microbiota and the microbiota-independent immune modulation by these prebiotics is provided. In addition, recent publications that report on the pathways by which the oligosaccharides might exert their direct immunomodulatory effect are summarized.

Dietary Heme Alters Microbiota and Mucosa of Mouse Colon without Functional Changes in Host-Microbe Cross-Talk

Colon cancer is a major cause of cancer deaths in Western countries and is associated with diets high in red meat. Heme, the iron-porphyrin pigment of red meat, induces cytotoxicity of gut contents which injures surface cells leading to compensatory hyperproliferation of crypt cells. This hyperproliferation results in epithelial hyperplasia which increases the risk of colon cancer. In humans, a high red-meat diet increases Bacteroides spp in feces. Therefore, we simultaneously investigated the effects of dietary heme on colonic microbiota and on the host mucosa of mice. Whole genome microarrays showed that heme injured the colonic surface epithelium and induced hyperproliferation by changing the surface to crypt signaling. Using 16S rRNA phylogenetic microarrays, we investigated whether bacteria play a role in this changed signaling. Heme increased Bacteroidetes and decreased Firmicutes in colonic contents. This shift was most likely caused by a selective susceptibility of Gram-positive bacteria to heme cytotoxic fecal water, which is not observed for Gram-negative bacteria, allowing expansion of the Gram-negative community. The increased amount of Gram-negative bacteria most probably increased LPS exposure to colonocytes, however, there is no appreciable immune response detected in the heme-fed mice. There was no functional change in the sensing of the bacteria by the mucosa, as changes in inflammation pathways and Toll- like receptor signaling were not detected. This unaltered host-microbe cross-talk indicates that the changes in microbiota did not play a causal role in the observed hyperproliferation and hyperplasia.

Neuro-immune interactions in inflammatory bowel disease and irritable bowel syndrome: Future therapeutic targets

The gastro-intestinal tract is well known for its largest neural network outside the central nervous system and for the most extensive immune system in the body. Research in neurogastroenterology implicates the involvement of both enteric nervous system and immune system in symptoms of inflammatory bowel disease and irritable bowel syndrome. Since both disorders are associated with increased immune cell numbers, nerve growth and activation of both immune cells and nerves, we focus in this review on the involvement of immune cell-nerve interactions in inflammatory bowel disease and irritable bowel syndrome. Firstly, the possible effects of enteric nerves, especially of the nonadrenergic and noncholinergic nerves, on the intestinal immune system and their possible role in the pathogenesis of chronic intestinal inflammatory diseases are described. Secondly, the possible effects of immunological factors, from the innate (chemokines and Toll-like receptors) as well as the adaptive (cytokines and immunoglobulins) immune system, on gastro-intestinal nerves and its potential role in the development of inflammatory bowel disease and irritable bowel syndrome are reviewed. Investigations of receptor-mediated and intracellular signal pathways in neuro-immune interactions might help to develop more effective therapeutic approaches for chronic inflammatory intestinal diseases.

Critical Role for Mast Cells in the Pathogenesis of 2,4-Dinitrobenzene-Induced Murine Colonic Hypersensitivity Reaction

The immunological mechanisms underlying the role of mast cells in the pathogenesis of inflammatory bowel disease (IBD) are poorly defined. In this study, non-IgE mediated colonic hypersensitivity responses in BALB/c mice induced by skin sensitization with dinitrofluorobenzene (DNFB) followed by an intrarectal challenge with dinitrobenzene sulfonic acid featured as a model to study the role of mast cells in the development of IBD. Vehicle- or DNFB-sensitized mice were monitored for clinical symptoms and inflammation 72 h after dinitrobenzene sulfonic acid challenge. DNFB-sensitized mice developed diarrheic stool, increased colonic vascular permeability, hypertrophy of colonic lymphoid follicles (colonic patches), and showed cellular infiltration at the microscopic level. Increased numbers of mast cells were found in the colon of DNFB-sensitized mice located in and around colonic patches associated with elevated levels of mouse mast cell protease-1 in plasma indicating mast cell activation. Colonic patches of DNFB mice, stimulated in vitro with stem cell factor indicated that an increase in TNF-α levels in the colon is mainly mast cell originated. Finally, neutrophil infiltration was observed in the colon of DNFB-sensitized mice. Induction of this model in mast cell-deficient WBB6F1 W/Wv mice shows a profound reduction of characteristics of the colonic hypersensitivity reaction. Reconstitution with bone marrow-derived mast cells in WBB6F1 W/Wv mice fully restored the inflammatory response. This study demonstrates the importance of mast cells in the development of clinical symptoms and inflammation in the presented murine model for IBD.

Dietary heme induces acute oxidative stress, but delayed cytotoxicity and compensatory hyperproliferation in mouse colon

Red meat consumption is associated with an increased colon cancer risk. Heme, present in red meat, injures the colon surface epithelium by generating cytotoxic and oxidative stress. Recently, we found that this surface injury is compensated by hyperproliferation and hyperplasia of crypt cells, which was induced by a changed surface to crypt signaling. It is unknown whether this changed signaling is caused by cytotoxic stress and/or oxidative stress, as these processes were never studied separately. The aim of this study was to determine the possible differential effects of dietary heme on these luminal stressors and their impact on the colonic mucosa after 2, 4, 7 and 14 days of heme feeding. Mice received a purified, humanized, control diet or the diet supplemented with 0.2 µmol heme/g. Oxidative and cytotoxic stress were measured in fecal water. Proliferation was determined by Ki67-immunohistochemistry and mucosal responses by whole-genome transcriptomics. After heme ingestion, there was an acute increase in reactive oxygen species (ROS) leading to increased levels of lipid peroxidation products. Mucosal gene expression showed an acute antioxidant response, but no change in cell turnover. After day 4, cytotoxicity of the colonic contents was increased and this coincided with differential signaling and hyperproliferation, indicating that cytotoxicity was the causal factor. Simultaneously, several oncogenes were activated, whereas the tumor suppressor p53 was inhibited. In conclusion, luminal cytotoxicity, but not ROS, caused differential surface to crypt signaling resulting in mucosal hyperproliferation and the differential expression of oncogenes and tumor suppressor genes.

Dietary haem stimulates epithelial cell turnover by downregulating feedback inhibitors of proliferation in murine colon

Objective Colon cancer is a leading cause of cancer deaths in Western countries and is associated with diets high in red meat. Haem, the iron-porphyrin pigment of red meat, induces cytotoxicity of gut contents and damages the colon surface epithelium. Compensatory hyperproliferation leads to epithelial hyperplasia which increases the risk of colon cancer. The aim of this study was to identify molecules signalling from the surface epithelium to the crypt to initiate hyperproliferation upon stress induced by haem. Methods C57Bl6/J mice (n=9/group) received a ‘westernised’ control diet (40 en% fat) with or without 0.5 μmol/g haem for 14 days. Colon mucosa was used to quantify cell proliferation and for microarray transcriptome analysis. Gene expression profiles of surface and crypt cells were compared using laser capture microdissection. Protein levels of potential signalling molecules were quantified. Results Haem-fed mice showed epithelial hyperproliferation and decreased apoptosis, resulting in hyperplasia. Microarray analysis of the colon mucosa showed 3710 differentially expressed genes (false discovery rate (q) <0.01), with many involved in the cell cycle. Expression levels of haem- and stress-related genes showed that haem affected surface cells but did not directly affect crypt cells. Injured surface cells should therefore signal to crypt cells to induce compensatory hyperproliferation. Haem downregulated the inhibitors of proliferation, Wnt inhibitory factor 1, Indian Hedgehog and bone morphogenetic protein 2. Interleukin-15 was also downregulated. Haem upregulated amphiregulin, epiregulin and cyclo-oxygenase-2 mRNA in surface cells. Their protein/metabolite levels were, however, not increased as haem induced surface-specific inhibition of translation by increasing 4E-BP1. Conclusions Haem induces colonic hyperproliferation and hyperplasia by inhibiting the surface to crypt signalling of feedback inhibitors of proliferation.

Ig-Free Light Chains Play a Crucial Role in Murine Mast Cell-Dependent Colitis and Are Associated with Human Inflammatory Bowel Diseases

Traditionally, mast cells were regarded as key cells orchestrating type I hypersensitivity responses. However, it is now recognized that mast cells are widely involved in nonallergic (non-IgE) chronic diseases. Also, in inflammatory bowel disease (IBD), a disease not associated with increased IgE concentrations, clear signs of activation of mast cells have been found. In this study, we investigated if Ig-free L chain-induced hypersensitivity-like responses through activation of mast cells could contribute to the pathophysiology of IBD. As a mast cell-dependent model for IBD, mice were skin-sensitized with dinitrofluorobenzene followed by intrarectal application of the hapten. In this murine IBD model, F991 prevented mast cell activation and also abrogated the development of diarrhea, cellular infiltration, and colonic lymphoid follicle hyperplasia. Furthermore, passive immunization with Ag-specific Ig-free L chains (IgLCs) and subsequent rectal hapten challenge elicited local mast cell activation and increased vascular permeability in the colon of mice. Clinical support is provided by the observation that serum concentrations of IgLCs of patients suffering from Crohn’s disease are greatly increased. Moreover, increased presence of IgLCs was evident in tissue specimens from colon and ileum tissue of patients with IBD. Our data suggest that IgLCs may play a role in the pathogenesis of IBD, which provides novel therapeutic means to prevent or ameliorate the adverse gastrointestinal manifestations of IBD.

Food-derived oligosaccharides exhibit pharmaceutical properties

Breast feeding is considered as the best nutrition for growth and development of an infant. Human milk consists of a unique combination of nutritional components each with different characteristics. Oligosaccharides or non-digestible carbohydrates as one of these components, are generally accepted to have a beneficial effect by selectively stimulating the growth and/or activity of one or a limited number of bacterial species. Recently more evidence is rising for direct effects of oligosaccharides on the immune system. Oligosaccharides often used as dietary supplements for their beneficial effects on the host and its immune system, are derived from nutritional sources. In this review we aim to summarize the pharmaceutical properties of these food-borne oligosaccharides early in life.

Prebiotic‐supplemented partially hydrolysed cow's milk formula for the prevention of eczema in high‐risk infants: a randomized controlled trial

Prevention guidelines for infants at high risk of allergic disease recommend hydrolysed formula if formula is introduced before 6 months, but evidence is mixed. Adding specific oligosaccharides may improve outcomes.

Dietary calcium decreases but short-chain fructo-oligosaccharides increase colonic permeability in rats

An increased intestinal permeability is associated with several diseases. Nutrition can influence gut permeability. Previously, we showed that dietary Ca decreases whereas dietary short-chain fructo-oligosaccharides (scFOS) increase intestinal permeability in rats. However, it is unknown how and where in the gastrointestinal tract Ca and scFOS exert their effects. Rats were fed a Western low-Ca control diet, or a similar diet supplemented with either Ca or scFOS. Lactulose plus mannitol and Cr-EDTA were added to the diets to quantify small and total gastrointestinal permeability, respectively. Additionally, colonic tissue was mounted in Ussing chambers and exposed to faecal water of these rats. Dietary Ca immediately decreased urinary Cr-EDTA excretion by 24 % in Ca-fed rats compared with control rats. Dietary scFOS increased total Cr-EDTA permeability gradually with time, likely reflecting relatively slow gut microbiota adaptations, which finally resulted in a 30 % increase. The lactulose:mannitol ratio was 15 % higher for Ca-fed rats and 16 % lower for scFOS-fed rats compared with control rats. However, no dietary effect was present on individual urinary lactulose and mannitol excretion. The faecal waters did not influence colonic permeability in Ussing chambers. In conclusion, despite effects on the lactulose:mannitol ratio, individual lactulose values did not alter, indicating that diet did not influence small-intestinal permeability. Therefore, both nutrients affect permeability only in the colon: Ca decreases, while scFOS increase colonic permeability. As faecal water did not influence permeability in Ussing chambers, probably modulation of mucins and/or microbiota is important for the in vivo effects of dietary Ca and scFOS.