Effect of colonic bacterial metabolites on Caco-2 cell paracellular permeability in vitro.
Level 5 - mechanism / opinion, no new human data
In vitro bench research using cell culture models
PubMed 18444159 · doi:10.1080/01635580701649644
What was done
Researchers assessed the effects of physiological levels of colonic bacterial metabolites—phenol, ammonia, primary bile acids (cholic acid [CA], chenodeoxycholic acid [CDCA]), and secondary bile acids (lithocholic acid [LCA], deoxycholic acid [DCA])—on epithelial barrier integrity in Caco-2 cell monolayers. Paracellular permeability was evaluated using transepithelial electrical resistance (TER) and apical-to-basolateral [14C]-mannitol flux. Occludin protein expression was also measured.
What was found
Secondary bile acids (LCA and DCA), phenol, and ammonia significantly increased paracellular permeability, demonstrated by decreased TER and increased [14C]-mannitol flux, whereas primary bile acids did not. CA, DCA, and LCA significantly increased occludin expression (P < 0.05), while CDCA and phenol had no significant effect compared to negative control. Absolute values and effect sizes were not reported in the abstract.
Why it matters
The findings demonstrate a plausible mechanism by which specific microflora-derived metabolites at physiological fecal concentrations can compromise intestinal epithelial barrier function, a characteristic associated with tumor promotion.
Limits
This is an in vitro study using an immortalized cell line (Caco-2), which does not replicate the full physiological complexity of in vivo human intestinal tissue, mucus layers, or microbiota interactions. Exact sample sizes (replicates), tested metabolite concentrations, and numerical effect estimates are not provided in the abstract.
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- context Bile acids such as deoxycholic acid released during fat digestion cause endotoxin release.