The intestinal microbiota plays a central role in the development of many chronic inflammatory diseases including inflammatory bowel disease. Accordingly, we recently demonstrated that administration of substances that alter microbiota composition, including the dietary emulsifiers polysorbate 80 (P80) and carboxymethylcellulose (CMC), promotes such inflammatory disorders. However, because inflammation itself impacts microbiota composition, it is very difficult to discern the extent to which these compounds or other substances act directly upon the microbiota versus acting on host parameters that promote inflammation, which subsequently reshapes impacts the microbiota. Our goal was to investigate if, and how, emulsifiers directly impact upon the microbiota in the absence of a host response.Methods:
The M-SHIME (Mucosal Simulator of the Gastrointestinal Microbial Ecosystem) model was used to examine the effects of emulsifiers on the human microbiota in vitro. After a stabilization period of 7 days, this dynamic human gut model was treated with emulsifiers (Carboxymethylcellulose [CMC] or Polysorbate-80 [P80], various concentrations between 0.00% and 1.00%). Microbiota composition, meta-transcriptomic and pro-inflammatory potential (Flagellin and LPS loads) were analyzed. In vitro emulsifier-treated human microbiota were transplanted to germfree recipient animals, with subsequent intestinal inflammation analyzed.Results:
Both P80 and CMC acted directly upon human microbiota to increase its pro-inflammatory potential, as revealed by increased levels of bioactive flagellin. The CMC-induced increase in flagellin was rapid (1 d) and driven by altered microbiota gene expression. In contrast, the P80-induced flagellin increase occurred more slowly and was closely associated with altered species composition. Transfer of both emulsifier-treated M-SHIME microbiotas to germ-free recipient mice recapitulated many of the host and microbial alterations observed in mice directly treated with emulsifiers, and especially the development of intestinal inflammation.Conclusions:
Both emulsifiers directly acted upon the microbiota to increase its pro-inflammatory potential, indicating that at least a portion of the effects of emulsifiers in vivo results from direct action of these compounds on the microbiota. The mechanisms by which P80 and CMC act are distinct, with P80 altering the composition of the microbiota, favoring species expressing high level of flagellin, whereas CMC increase the pro-inflammatory potential of the microbiota in a composition independent manner, by inducing expression of motility genes. These results suggest that the microbiota may be a key direct target of these commonly used food additives able to drive chronic intestinal inflammation.