Coeliac disease (CD) is a lifelong immune-mediated enteropathy manifested as gluten intolerance. Gluten intolerance arises in a small fraction of gluten-exposed genetically higher risk individuals (carrying specific human leukocyte antigen (HLA) haplotypes) and its incidence seems to be rising globally.
There are indications that the gut microbiome may play a role in CD pathogenesis, progression, and clinical presentation. Several studies have reported imbalances in the gut microbiome of patients with CD, leading to dysbiosis. Studies in those with established CD are, however, prone to reverse causation, meaning it is unclear whether these alterations are a symptom of the disease or a contributing factor.
Probiotics have been suggested as a potential adjunctive therapy for CD but most of the trials have focussed on ongoing CD. The authors of the current study, from Czech University of Life Sciences, Prague, and Lund University, Sweden, note that changes in the gut environment may occur before the CD diagnosis, thus potentially allowing prevention.
Faecal metabolites are primary products of microbial metabolism, but also reflect factors such as bile and enzyme activity, gut barrier function, transit time, and diet of the host.
The most studied metabolites are short-chain fatty acids (SCFAs), end-products of bacterial saccharolytic activity. Especially in CD, SCFAs are of major interest due to their involvement in immunomodulatory functions such as the production of regulatory T-cells. Other metabolites with altered amounts in CD are glutamine and tryptophan, which also impact the immune system.
In this study, which utilised data from the Celiac disease Prevention with Probiotics (CiPP) study, researchers aimed to describe the composition of the faecal metabolome in Children With Celiac Disease Autoimmunity and test its changes associated with the probiotic intervention.
They conclude that thhe combination of Lactiplantibacillus plantarum HEAL9 and Lacticaseibacillus paracasei 8700:2 showed marginal, though significant changes in the levels of numerous stool metabolites after six months of intervention, mainly consisting of differences in amino acids profiles, indicating a shift towards known healthier metabolic patterns.
The study
The CiPP study recruited 78 children aged 2–11 years with ongoing CD autoimmunity - positivity for tTGA in two consecutive samples - enrolled between March 2012 and August 2015. The enrolled children were identified among carriers of HLA-genotypes associated with CD.
Participating children were invited to a randomisation and baseline visit (visit 0) and scheduled for follow-up visits ~3 (visit 1) and 6 (visit 2) months later. Participants were randomised at a 1:1 ratio to either placebo or intervention group. Among the 78 enrolled children (placebo, n = 38; intervention, n = 40), 63 (81%) provided faeces samples for all three visits.
The study product was an equal mixture of Lactiplantibacillus plantarum HEAL9, formerly classified as Lactobacillus plantarum, and Lacticaseibacillus paracasei 8700:2, formerly classified as Lactobacillus paracasei, in a total bacterial dose of 1 × 1010 CFU/sachet in maltodextrin (1.0 g). The placebo product consisted of maltodextrin only. The combination of the two Lactobacillus strains was chosen due to their different physiological effects, i.e., Lactiplantibacillus plantarum HEAL9 targets the permeability of the mucosa, and Lactocaseibacillus paracasei 8700:2 targets the immune system. All enrolled children followed a regular gluten-containing diet during the study.
Stool sample collection was carried out at home by the study participant's caregiver. Nuclear magnetic resonance (NMR) was used for the analysis of metabolites present in the faecal samples .
The resulting data indicated the metabolomes of those supplemented with the probiotic strains had a reduction in threonine and a rise in 4-hydroxyphenylacetate compared to the placebo group. There was also a tendency for other amino acids, such as valine, leucine, isoleucine, aspartate, methionine, and phenylalanine, together with fumarate, to decrease after the intervention. Their changes were borderline significant, though not after the adjustment for multiple comparisons.
The authors note that all these metabolites are linked to protein breakdown and imply an effect on proteolytic fermentation in the gut.
"In the gastrointestinal tract, there is a delicate equilibrium between saccharolytic and proteolytic fermentation, and disturbances in this balance can be associated with various disease conditions.
"Proteolytic fermentation, in general, leads to a protein, and peptides breakdown into amino acids, mainly resulting in the production of branched-chain fatty acids, polyamines, etc., while saccharolytic fermentation degrades dietary fibre to simple carbohydrates to generate primarily SCFA and other organic acids.
"However, the suppression of the proteolytic pathway observed in our study was not translated into an increase in saccharolytic fermentation," the report explains.
"Proteolysis was previously shown to increase in disease states such as gut inflammation, where tissue damage occurs, and cells and cell exudates are released to the intestinal lumen and are subject to bacterial hydrolysis...
"In this light, our results may suggest a preventive nature of the probiotics and their potential ability to shape microbial metabolism towards a balanced state."
The authors point out that the decreased threonine concentration was the major change in the metabolome.
"Threonine synthesis by the human digestive system is limited, but it can be synthesised from glucose and aspartate by gut microbiota members. Additionally, we have seen a reduction in aspartate levels, and although we have not observed any alterations in glucose levels, the findings imply the regulation of this pathway. Furthermore, the pathway analysis confirmed an effect on threonine metabolism."
In a previous study by this team, which was based on this same sample set examined using 16S rDNA sequencing, they noted an increase in abundance of the Prevotella, Akkermansia, Streptococcus, and Bifidobacterium genera. They noted that Akkermansia is a prominent degrader of mucus, mucus is a protective layer in the gut, and threonine is a highly abundant amino acid in the mucin protein core.
They therefore hypothesise that Akkermansia may indirectly influence the threonine levels in the gut by degrading the mucus. They say subsequent research on this finding is highly desirable."
In conclusion, the authors state: "The combination of Lactiplantibacillus plantarum HEAL9 and Lacticaseibacillus paracasei 8700:2 showed marginal, though significant changes in the levels of numerous stool metabolites in children genetically predisposed to CD after 6 months of intervention, mainly consisting of differences in amino acids profiles, indicating a shift towards known healthier metabolic patterns. The observed reduction in threonine levels is also worth emphasising, as threonine is an amino acid closely associated with gut mucus. The metabolic pathway related to threonine appears to be impacted by probiotic the intervention."
Source: Frontiers in Nutrition
https://doi.org/10.3389/fnut.2023.1183963
"Effects of Lactiplantibacillus plantarum and Lacticaseibacillus paracasei supplementation on the faecal metabolome in children with coeliac disease autoimmunity: a randomised, double-blinded placebo-controlled clinical trial"
Authors: Jenickova, E.,Aronsson, C. A., Bergo, A. M. Cinek, O., Havlik.J., and Agardh, D.,