Zeroing In On An Inflammatory Bowel Disease Culprit

When Harvard University talks, people listen (including me)!  So I paid particular attention to a fascinating bit of new research out just this week that definitely takes us a step closer to figure out what happens in inflammatory bowel diseases (IBD), in terms of   abnormal bacteria causing an inflammatory reaction in the gut.[i]

We’ve known for a long time that alterations in the bacterial microbiome are associated with inflammatory bowel diseases but the specifics of both species and mechanism of action have been unknown.  Researchers at Harvard though just tracked down the first prime suspect:  Ruminococcus gnavus.

No, I had not heard of it either probably because, ordinarily, it comprises less than 1% of our gut bacteria…and with there being 1000 species or so in the ordinary human, it never leapt to the top of my get-to-know list.

In a previous study though, researchers noted that during flare ups of IBD, this species of bacteria can jump from that less than 1% of the gut microbiome to making up more than 50% ! (How astounding is THAT?!)  The next step, and the subject of this latest research, was to figure out causation.  That is – how do these bacteria exert their detrimental effects?

The scientists grew the bacteria in the lab and then figured out all the molecules they produce, testing to see if any of the metabolites are proinflammatory.  Sure enough, one molecule, a complex sugar (a polysaccharide) made up of glucose and another sugar called rhamnose, caused the release of pro-inflammatory chemicals, including tumor necrosis factor-alpha (TNF-α), a major proinflammatory chemical that is highly associated with autoimmune diseases.  The scientists also identified the gene in the bacteria which is responsible for the production of this polysaccharide. This will allow them to see, in the future, if this gene is over-expressed before a flare up of Crohn’s.

“We found and characterized an inflammatory polysaccharide produced by the gut bacterium Ruminococcus gnavus, populations of which bloom during flares of symptoms in patients with Crohn’s disease. This molecule induces the production of inflammatory cytokines like TNFα…and may contribute to the association between R. gnavus and Crohn’s disease.”[ii]

This research certainly may take us a long way toward figuring out a treatment for IBD, either by targeting the growth of the bacterium, Ruminococcus gnavus, or by targeting its gene, which codes for the polysaccharide.  More than that, this kind of research has demonstrated that it is possible – and potentially highly beneficial – for scientists to comb through suspect bacteria in the human gut, find those associated with disease, and figure out what these might be producing that causes us to get sick.

What does not seem to be explained is what causes these particular bacteria to grow so rapidly prior to a flare up.  I’m sure we’ll read more about this in the future.  I’ll keep an eye out.

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 [i] https://hms.harvard.edu/news/microbiome-malefactor

[ii] Henke, MT, et al. Ruminococcus gnavus, a member of the human gut microbiome associated with Crohn’s disease, produces an inflammatory polysaccharide, Proceedings of the National Academy of Sciences (2019). DOI: 10.1073/pnas.1904099116

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