Smoking's not often touted for its health benefits. But it's been known to help those suffering from colitis even though it exacerbates Crohn's disease. New research that could help treat the conditions says it all has to do with bacteria migration.
According to researchers at the RIKEN Center for Integrative Medical Sciences in Japan, scientists – and patients – have known for about 40 years about this smoking paradox. Both ulcerative colitis and Crohn's are inflammatory bowel diseases (IBDs) so the idea that smoking would help one but hurt the other has been confounding. Colitis causes an inflammation of the colon lining while Crohn's can present as patches of inflamed tissues along the entire digestive tract and can also affect all layers of the bowel wall.
As with much of today's research in biology, in an effort to unravel the mystery, the RIKEN researchers turned to the gut and its microbiome. Specifically, they wanted to find out if smoking allows certain kinds of gut bacteria to thrive that might explain the habit's effect on IBDs.
Sure enough, they found that certain bacteria including Streptococcus that's usually found in the mouth were thriving in the mucous layer of the inner intestinal wall – only in smokers. Typically these mouth-based bacteria pass from the mouth through the intestine and out of our bodies; they do not usually hang around and establish themselves in our colons. Somehow, smoking gave them a foothold in the gut.
Sussing out why, the researchers looked at gut metabolites, the byproducts of food processing in the intestines. In smokers, they found high levels of a metabolite called hydroquinone which, in turn, allowed mouth bacteria including Streptococcus to stay and grow in the gut.
But why did the presence of mouth-based bacteria in the gut help those suffering from ulcerative colitis but hurt those with Crohn's disease?
The answer came through mouse studies when the researchers found that mouth-based bacteria that thrive in the gut trigger the activation of helper Th1 cells, an immune cell that can fight off infection. They found that in those suffering from colitis, the Th1 cells fought off an immune response that normally leads to inflammation. By tamping down this inflammation the Th1 cells helped ease symptoms. In Crohn's patients however, inflammation is caused by the Th1 cells themselves, so having more of them activated in the gut made symptoms worse.
Of course, the researchers do not advocate smoking as a treatment for ulcerative colitis because of the overwhelming body of evidence pointing to the havoc it wreaks on our bodies. However, they feel their findings provide a deeper understanding of IBDs and offer a way in which ulcerative colitis could be treated.
“Our results indicate the relocation of bacteria from the mouth to the gut, particularly those of the Streptococcus genus, and the subsequent immune response in the gut, is the mechanism through which smoking helps protect against the disease,” says lead researcher Hiroshi Ohno. “Logically, direct treatment with this kind of bacteria, or indirect treatment with hydroquinone, is thus likely to mimic the beneficial effects of smoking but avoid all the negative effects.”
The research has been published in the journal, Gut.
Source: Riken via EurekAlert
