Small bowel water content assessed by MRI in health and disease: a collation of single-centre studies

Is there a fast track ("Darmstrasse") for fluids in the small intestine? Evidence from magnetic resonance imaging

BACKGROUND

The transit and distribution pattern of fluids in the small intestine is a key parameter for the dissolution and absorption of drugs. Although some information is known about the small intestinal water content after administration of fluid volumes and meals, the intestinal transit of orally ingested fluids and solutions has been barely investigated. The aim of this three-arm, cross-over, 9-subject human study was to investigate the transit of orally ingested water in the small intestine under fasting and postprandial conditions using MRI. To identify the ingested water, manganese gluconate, which can be identified with T1-weighted MRI sequences, was added as a marker. Using Horos (DICOM software), quantification of the distribution of Mn2+ ions in the gastrointestinal tract in fasted versus fed state (standard meal by FDA guidance and a light meal) was possible. The distribution and approximate wetted intestinal length was very similar in the fasting and postprandial states, suggesting rapid transport of water ingested after a meal through the chyme-filled small intestine in continuation of the "Magenstrasse" (stomach road). In some subjects, manganese gluconate reached deeper parts of the small intestine even more quickly in the postprandial state than in the fasting arm of the study. A deeper understanding of the behaviour of solutes in the gastrointestinal tract is fundamental to a mechanistic explanation for the kinetic interaction between food and drug intake (food effects).

The Role of the FODMAP Diet in IBS

The low FODMAP (fermentable oligosaccharide, disaccharide, monosaccharide, and polyol) diet is a beneficial therapeutic approach for patients with irritable bowel syndrome (IBS). However, how the low FODMAP diet works is still not completely understood. These mechanisms encompass not only traditionally known factors such as luminal distension induced by gas and water but also recent evidence on the role of FOMAPs in the modulation of visceral hypersensitivity, increases in intestinal permeability, the induction of microbiota changes, and the production of short-chain fatty acids (SCFAs), as well as metabolomics and alterations in motility. Although most of the supporting evidence is of low quality, recent trials have confirmed its effectiveness, even though the majority of the evidence pertains only to the restriction phase and its effectiveness in relieving abdominal bloating and pain. This review examines potential pathophysiological mechanisms and provides an overview of the existing evidence on the effectiveness of the low FODMAP diet across various IBS subtypes. Key considerations for its use include the challenges and disadvantages associated with its practical implementation, including the need for professional guidance, variations in individual responses, concerns related to microbiota, nutritional deficiencies, the development of constipation, the necessity of excluding an eating disorder before commencing the diet, and the scarcity of long-term data. Despite its recognized efficacy in symptom management, acknowledging these limitations becomes imperative for a nuanced comprehension of the role of a low FODMAP diet in managing IBS. By investigating its potential mechanisms and evidence across IBS subtypes and addressing emerging modulations alongside limitations, this review aims to serve as a valuable resource for healthcare practitioners, researchers, and patients navigating the intricate landscape of IBS.

Novel food drug interaction mechanism involving acyclovir, chitosan and endogenous mucus

Drug absorption from drug products may be affected by pharmaceutical excipients and/or food additives through different mechanisms. Chitosan is a recognized nutraceutical, with potential as an excipient due to its permeability enhancer properties. While chitosan properties have been evaluated in in vitro and pre-clinical models, studies in humans are scarce. Unexpectedly, a controlled clinical trial showed chitosan actually reduced acyclovir bioavailability. The effect seems to be related to an interaction with gastrointestinal mucus that prevents further absorption, although more in depth research is needed to unravel the mechanism. In this paper, we propose a mechanism underlying this excipient effect. The mucus - chitosan interaction was characterized and its effect on acyclovir diffusion, permeation and bioaccessibility was investigated. Further, pharmacokinetic modeling was used to assess the clinical relevance of our findings. Results suggest that in situ coacervation between endogenous mucus and chitosan rapidly entrap 20-30% of acyclovir dissolved dose in the intestinal lumen. This local reduction of acyclovir concentration together with its short absorption window in the small intestine would explain the reduction in acyclovir C_max and AUC. This study highlights the importance of considering mucus in any biorelevant absorption model attempting to anticipate the effect of chitosan on drug absorption.

Mechanisms underlying food-related symptoms in disorders of gut-brain interaction: Course ahead in research and clinical practice

A subgroup of patients with a disorder of gut-brain interaction (DGBI) report symptoms such as abdominal pain, gas-related symptoms, dyspeptic symptoms and loose stool or urgency after meal intake. Therefore, the effect of several dietary therapies including fibre-rich or restrictive diets have already been studied in patients with irritable bowel syndrome, functional abdominal bloating or distention, and functional dyspepsia. However, there is a paucity of studies in the literature on the mechanisms underlying food-related symptoms. Therefore, this review focuses on these potential mechanisms and explains the role of nutrient sensing and tasting, physical considerations, malabsorption or allergy-like reaction to food and its interaction with microbiota. In addition, it emphasizes the importance of future research and clinical practice regarding food-related symptoms in patients with a DGBI.

Mechanisms Underlying Food-Triggered Symptoms in Disorders of Gut-Brain Interactions

There has been a dramatic increase in clinical studies examining the relationship between disorders of gut-brain interactions and symptoms evoked by food ingestion in the upper and lower gastrointestinal tract, but study design is challenging to verify valid endpoints. Consequently, mechanistic studies demonstrating biological relevance, biomarkers and novel therapeutic targets are greatly needed. This review highlights emerging mechanisms related to nutrient sensing and tasting, maldigestion, physical effects with underlying visceral hypersensitivity, allergy and immune mechanisms, food-microbiota interactions and gut-brain signaling, with a focus on patients with functional dyspepsia and irritable bowel syndrome. Many patients suffering from disorders of gut-brain interactions exhibit these mechanism(s) but which ones and which specific properties may vary widely from patient to patient. Thus, in addition to identifying these mechanisms and the need for further studies, biomarkers and novel therapeutic targets are identified that could enable enriched patient groups to be studied in future clinical trials examining the role of food in the generation of gut and non-gut symptoms.