Novel intervention may improve outcomes for malnourished children (Aug 2026, mice) Microbiota-derived isovalerate ameliorates sex-specific gut barrier dysfunction in malnutrition Other

[Michael Harrop]

https://bioengineer.org/novel-intervention-may-improve-outcomes-for-malnourished-children/
https://www.pnas.org/doi/10.1073/pnas.2611392123

Significance​

Malnutrition weakens the intestinal barrier, allowing bacteria to translocate from the gut and cause invasive infections. Clinical guidelines for malnutrition do not address dysfunction of the gut barrier, which is regulated in part by the microbiota via mechanisms that are incompletely understood.

Using human-derived organoid and mouse models, we show that malnutrition induces colonic barrier failure with mucus layer thinning, and that low-protein, low-fat diet depletes intestinal branched-chain fatty acids, which are microbial fermentation products of dietary amino acids. The branched-chain fatty acid isovalerate or its fermentation substrate, leucine, restores protein localization within colonic epithelial junctions and improves barrier function in malnourished mice.

Supplying gut microbiota with prebiotic leucine warrants further study as an adjunct precision nutrition therapy for malnutrition.

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Abstract​

Malnutrition increases intestinal permeability and the risk of sepsis, yet mechanisms underlying malnutrition-induced gut barrier dysfunction are poorly defined.

Here, we aimed to determine how the gut microbiome and microbiota-derived metabolites influence intestinal barrier function in the malnourished host. We induced malnutrition in specific pathogen-free (SPF) and germ-free (GF) mice using a low-protein, low-fat diet. Colonic permeability was quantified in Ussing chambers and invasive bacteria were cultured from liver and spleen. Targeted metabolomics identified microbial metabolites depleted in malnutrition. Candidate metabolites were screened in human-derived colonoid monolayers and administered to malnourished mice to determine whether gut barrier dysfunction can be rescued.

Malnutrition thinned the colonic mucus layer, increased gut barrier permeability, and facilitated bacterial translocation in male, but not female, SPF mice. Malnourished GF mice exhibited normal barrier function. In the malnourished intestine, a subset of microbial short-chain fatty acids, the branched-chain fatty acids (BCFAs), was depleted in SPF mice of both sexes.

Treating human-derived colonoid monolayers with BCFAs, especially isovalerate, increased transepithelial electrical resistance and altered the expression of genes associated with epithelial junction complexes. In malnourished male SPF mice, either enemas with isovalerate or gavages with its branched-chain amino acid fermentation substrate, leucine, restored the localization of the integral membrane protein claudin-8 within the colonic crypt and reduced barrier permeability.

Together, these findings identify BCFAs, including isovalerate, as microbiota-derived regulators of intestinal junction complexes and barrier integrity. We propose the branched-chain amino acid leucine as a microbiota-directed precision nutrition therapy that could target intestinal barrier dysfunction in malnutrition.

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[SFBayFMT5]

Malnutrition thinned the colonic mucus layer, increased gut barrier permeability, and facilitated bacterial translocation in male, but not female, SPF mice. Malnourished GF mice exhibited normal barrier function. In the malnourished intestine, a subset of microbial short-chain fatty acids, the branched-chain fatty acids (BCFAs), was depleted in SPF mice of both sexes.

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What I find odd about these results is the fact that the germ-free mice had normal intestinal barrier function regardless of nutrition. If it were metabolism of leucine by the gut microbiome that was necessary for the intestine to be normal, then germ-free mice should have an abnormal intestine regardless of nutrition. The results would suggest that either there is a general detrimental effect of the microbiome that is offset by the fermentation of leucine when available, or that the host adapts to not need the microbiome at all (at least with regard to barrier function) when it's absent during development.

The latter would actually not be that unusual, in the sense that often inhibiting an enzyme with a drug in adulthood is more detrimental than completely lacking the gene for that enzyme throughout life, at least for nonessential enzymes, when one would expect the latter to be much more severe. It would imply a rather different picture of the microbiome's role, however, than if the well-fed but germ-free mice were as sick as the malnourished ones.

At least, I'm assuming that by "normal" they mean similar to the well-nourished mice with an intact microbiome, not just "normal for germ-free mice" which turns out to be well below mice with a normal microbiome even when properly nourished. The article is closed access so I can't confirm that this is the case.