Tobacco Byproduct Points to Safer Relief Path for Ulcerative Colitis

Smoking helps ulcerative colitis by encouraging mouth bacteria like Streptococcus mitis to grow in the gut, reducing inflammation.

Highlights:

Smoking promotes growth of oral bacteria like Streptococcus in the colon
Streptococcus mitis reduces inflammation in ulcerative colitis but worsens Crohn’s disease
Hydroquinone may mimic smoking’s benefits without its health risks

Smoking tobacco encourages the growth of oral bacteria in the large intestine, where they activate an immune response that eases ulcerative colitis, a chronic inflammatory disease of the colon ().

Published in the scientific journal Gut, the findings from Hiroshi Ohno's team at the RIKEN Center for Integrative Medical Sciences suggest that smoking generates metabolites which help these oral bacteria thrive in the intestines. This insight opens the door to alternatives like hydroquinone-based prebiotics or probiotics containing Streptococcus mitis, eliminating the need to smoke and avoiding its well-known health risks.

Inflammatory bowel diseases primarily include Crohn's disease and ulcerative colitis, both characterized by symptoms like chronic abdominal pain, diarrhea, fatigue, and weight loss, but differing in their underlying causes and inflammation patterns.

For over four decades, the medical mystery has persisted: smoking worsens Crohn's disease but seems to protect against ulcerative colitis. Because both conditions are tied to immune responses and gut bacteria, Ohno’s team investigated whether differences in gut microbiota might explain this opposite effect of smoking.

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Did You Know?
Smoking tobacco enables mouth bacteria like Streptococcus mitis to settle in the colon and reduce ulcerative colitis inflammation. #smoking #ulcerativecolitis #medindia

Unexpected Role of Streptococcus in the Gut Lining

Combining human clinical data with mouse models, the researchers discovered that smokers with ulcerative colitis had certain oral bacteria, especially Streptococcus, growing in their intestinal lining, a phenomenon absent in ex-smokers. Normally, oral bacteria are swallowed and pass through the digestive system, but smoking seems to enable them to colonize the gut mucosa.

The team next explored why this colonization occurs. They analyzed gut metabolites, tiny molecules produced during digestion, and found that smokers with ulcerative colitis had higher levels of certain metabolites than ex-smokers. In mice, they identified hydroquinone as one metabolite that promoted the growth of Streptococcus in the gut’s mucus layer, helping oral bacteria establish themselves in the intestinal environment.

Ulcerative Colitis
Ulcerative colitis is characterized by bouts of diarrhea, bleeding per rectum and pain, which remits and relapses. Fulminant colitis is a possibility, which may require colectomy.

Immune Responses Differ Between Crohn’s and Ulcerative Colitis

The researchers isolated ten strains of oral bacteria from smokers’ saliva and administered them to mouse models of Crohn’s disease and ulcerative colitis. Among the strains, Streptococcus mitis produced effects similar to those of smoking, reducing inflammation in ulcerative colitis while worsening it in Crohn’s disease.

Further analysis showed that Streptococcus mitis activated helper Th1 cells, crucial components of the gut immune response. In Crohn’s disease, these cells intensify inflammation because the disease is driven by a Th1-type immune response. However, in ulcerative colitis, where inflammation is driven by Th2 responses, the Th1 cells introduced by Streptococcus mitis help suppress inflammation by counterbalancing the Th2 activity.

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Probiotic and Prebiotic Alternatives to Smoking

Given the serious health risks of smoking, such as cancer and heart disease, it is not a viable long-term treatment for ulcerative colitis. The study concludes that the protective mechanism lies in the relocation of oral bacteria, especially those from the Streptococcus genus, to the gut and the immune responses they trigger.

Consequently, directly administering these bacteria or using metabolites like hydroquinone could replicate the beneficial effects of smoking without its harmful consequences. This discovery presents a potential breakthrough in ulcerative colitis therapy, making way for safer, targeted treatments.

To sum up, the protective effect of smoking in ulcerative colitis is linked to the colonization of gut mucosa by oral bacteria like Streptococcus mitis, driven by smoking-related metabolites such as hydroquinone. These bacteria alter immune responses in the gut, reducing inflammation in ulcerative colitis while worsening it in Crohn’s disease. With smoking posing severe health risks, probiotic or prebiotic alternatives present promising new treatment options.

Reference:

Smoking affects gut immune system of patients with inflammatory bowel diseases by modulating metabolomic profiles and mucosal microbiota - (https://gut.bmj.com/content/early/2025/08/06/gutjnl-2025-334922)

Source-Medindia