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

Assessing Water Content of the Human Colonic Chyme Using the MRI Parameter T1: A Key Biomarker of Colonic Function

BACKGROUND

The human colon receives 2 L of fluid daily. Small changes in the efficacy of absorption can lead to altered stool consistency with diarrhea or constipation. Drugs and formulations can also alter colonic water, which can be assessed using the magnetic resonance imaging (MRI) longitudinal relaxation time constant, T1. We explore the use of regional T1 assessment in evaluating disorders of colonic function.

METHODS

Individual participant data analysis of data from 12 studies from a single center of patients with constipation, irritable bowel syndrome with diarrhea (IBS-D), and healthy volunteers (HV). T1 was quantified by measuring the signal from the tissue at different times after a pulse which inverts the magnetization.

KEY RESULTS

When diarrhea was induced by a macrogol laxative T1 in the ascending colon, T1AC was negatively correlated with stool bacterial content, r2 = 0.78, p < 0.001. T1AC was increased by another laxative, rhubarb. Patients with IBS-D had elevated fasting T1AC (0.78 ± 0.28 s, N = 67) compared to HV (0.62 ± 0.21 s, N = 92) while those with constipation lay within the normal range (HV 10-90th centiles 0.33-0.91 s). Fasting T1AC in IBS-D was reduced by mesalazine treatment. T1 in the descending colon was consistently lower than T1AC, with a bigger reduction in patients with constipation than HV. Pre-feeding dietary fiber (bran, nopal, and psyllium) was associated with fasting T1AC at or above the normal 90th centile.

CONCLUSIONS AND INFERENCES

T1 is an MRI parameter which could be used to monitor effectiveness of novel agents designed to alter colonic water content and stool consistency.

Effects of opium tincture on gastrointestinal function and motility in healthy volunteers: A magnetic resonance imaging study

BACKGROUND

Opioids inhibit motility and secretion of the gut and have been used for antidiarrheal treatment for centuries. However, the underlying mechanisms of opium tincture are not evident.

AIM

To investigate the effects of opium tincture on gastrointestinal motility, intestinal volumes, and water content of different gut segments assessed by magnetic resonance imaging (MRI).

METHODS

Twenty healthy volunteers were included in a randomized, placebo-controlled, crossover study of 9 days of treatment with 30 drops of opium tincture per day. MRI was performed on day 1 (before treatment) and day 9 (during treatment). Measurements included assessments of gastric volume, gastric emptying, gastric motility, small bowel volume, small bowel water content, small bowel motility, colon volume, colon water content, and whole gut transit.

KEY RESULTS

Opium tincture delayed gastric emptying by a mean difference of 5.6 min [95% CI: 1.8-9.4], p = 0.004, and increased postprandial gastric meal volume (17-21%, p = 0.02). Small bowel endpoints did not change. Opium tincture delayed whole gut transit time (p = 0.027) and increased ascending colon volume by 59 mL [95% CI: 15-103], p = 0.004, and transverse colon volume by 48 mL [95% CI: 4-92], p = 0.027. T1-relaxation time of the descending colon chyme was decreased during opium treatment, indicating dryer feces (difference: -173 ms [95% CI: -336 -11], p = 0.03).

CONCLUSION AND INFERENCES

Opium tincture induced changes in the stomach and colon in healthy volunteers. An improved understanding of how opioids affect gut functions may lead to a better understanding and optimized management of diarrhea.

Structuring white rice with gellan gum reduces the glycemic response in healthy humans

White rice has a high glycemic index and its consumption has been linked to an increased risk of developing type-2 diabetes mellitus, increased diabetes associated complications and obesity. In recent in vitro studies we have shown that addition of food hydrocolloids, such as low acyl gellan gum (LAGG), when cooking white rice potentially modifies starch digestion kinetics. The impact in vivo remains to be investigated. We aimed to determine the effect of adding LAGG to white rice on postprandial glycemic, gastrointestinal and appetitive responses in humans. Following LAGG in vitro characterisation, 12 healthy adults participated in a randomised, controlled, crossover study. They consumed isoenergetic meals of jasmine white rice (232 kcal) cooked with (Rice + LAGG) and without (Rice control) 3 % w/dry rice w LAGG. Blood glucose, intragastric meal appearance, meal volume and appetite were assessed serially for 2 h. The incremental area under the curve over two hours (iAUC2h) for blood glucose for the Rice + LAGG meal (93 ± 16 mmol/L·min) was significantly lower than that for the Rice control meal (160 ± 18 mmol/L·min), P=0.0007. Blood glucose rose postprandially to a peak at T=30 min, with the Rice control meal peak (7.3 ± 0.2 mmol/L) significantly higher than that for the Rice + LAGG meal (6.5 ± 0.2 mmol/L), P < 0.01. MRI images showed that for Rice + LAGG there were multiple rice boluses persisting intragastrically throughout the digestion time. There were no significant differences in appetite between meals. The addition of LAGG to the cooking process was effective in reducing postprandial blood glucose responses in healthy humans. If confirmed, this could potentially provide a simple and relatively inexpensive intervention to reduce the post prandial glycemic response to white rice.

Impact of extended Elexacaftor/Tezacaftor/Ivacaftor therapy on the gut microbiome in cystic fibrosis

BACKGROUND

There is a paucity of knowledge on the longer-term effects of CF transmembrane conductance regulator (CFTR) modulator therapies upon the gut microbiome and associated outcomes. In a pilot study, we investigated longitudinal Elexacaftor/Tezacaftor/Ivacaftor (ETI) therapy on the gut microbiota, metabolomic functioning, and clinical outcomes in people with CF (pwCF).

STUDY DESIGN

Faecal samples from 20 pwCF were acquired before and then following 3, 6, and 17+ months of ETI therapy. Samples were subjected to microbiota sequencing and targeted metabolomics to profile and quantify short-chain fatty acid composition. Ten healthy matched controls were included for comparison. Clinical data, including markers of intestinal function were integrated to investigate relationships.

RESULTS

Extended ETI therapy increased core microbiota diversity and composition, which translated to gradual shifts in whole microbiota composition towards that observed in healthy controls. Despite becoming more similar over time, CF microbiota and functional metabolite compositions remained significantly different to healthy controls. Antibiotic treatment for pulmonary infection significantly explained a relatively large degree of variation within the whole microbiota and rarer satellite taxa. Clinical outcomes were not significantly different following ETI.

CONCLUSIONS

Whilst differences persisted, a positive trajectory towards the microbiota observed in healthy controls was found. We posit that progression was predominately impeded by pulmonary antibiotics administration. We recommend future studies use integrated omics approaches within a combination of long-term longitudinal patient studies and model experimental systems. This will deepen our understanding of the impacts of CFTR modulator therapy and respiratory antibiotic interventions upon the gut microbiome and gastrointestinal pathophysiology in CF.

A longitudinal study assessing the impact of elexacaftor/tezacaftor/ivacaftor on gut transit and function in people with cystic fibrosis using magnetic resonance imaging (MRI)

BACKGROUND

Gastrointestinal (GI) symptoms in cystic fibrosis (CF) are common and disruptive. The effect of cystic fibrosis transmembrane conductance regulator (CFTR) modulators on the GI tract is not fully understood. The aim was to use magnetic resonance imaging (MRI) to determine if elexacaftor/tezacaftor/ivacaftor (ETI) changed GI function and transit.

METHODS

This was an 18 month prospective, longitudinal, observational study. We enrolled 24 people with CF aged 12 years or older to undergo MRI scans before starting ETI and 3, 6, and 18 months after starting ETI. The primary outcome measure was change in oro-caecal transit time (OCTT) at 6 and 18 months. Secondary outcome measures included change in small bowel water content (SBWC), change in the reduction in small bowel water content following a meal (DeltaSBWC) and change in total colonic volume (TCV).

RESULTS

A total of 21 participants completed MRI scans at 6 months and 11 completed at 18 months. After 18 months of ETI, median OCTT significantly reduced, from >360 min [IQR 240->360] to 240 min [IQR 180-300] (p = 0.02, Wilcoxon signed-rank). Both SBWC and DeltaSBWC increased after starting ETI. TCV reduced significantly after 18 months (p = 0.005, Friedman).

CONCLUSIONS

Our findings suggest an improvement in small bowel transit, small bowel response to food and a reduction in colonic volume after starting ETI. These effects may relate to CFTR activation in the small bowel. To our knowledge this is the first study to show a physiological change in GI transit and function in response to CFTR modulator use through imaging 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.