Regular doses of bacterial supplements, such as those used in milk and yogurt products, ease intestinal pain in rats by making the gut more sensitive to the body's pain-relieving compounds. If the results hold up in humans, then daily helpings of these probiotics could help relieve the debilitating gut pain of irritable bowel syndrome (IBS).
IBS affects more than one in 10 adults, causing cramping, bloating, constipation, and diarrhea. No one knows what causes it, and doctors treat each symptom separately, often using antidepressants to ease abdominal pain. Advocates of probiotics have claimed for years that these beneficial bacteria can decrease intestinal pain. Gastroenterologist Pierre Desreumaux of the Institut National de la Santé et de la Recherche Médicale (INSERM) in Lille Cedex, France, and his colleagues hypothesized that they might do so by spurring gut-lining cells to make receptors that respond to opioids and cannabinoids, natural pain-relieving molecules akin to morphine and the active ingredient of marijuana, respectively.
To see if that was true, the INSERM team added five probiotic strains individually to lab-grown gut-lining cells, then measured the activity of opioid and cannabinoid receptor genes. One strain--Lactobacillus acidophilus NCFM, which is used widely to supplement milk and yogurts--boosted expression of one opioid receptor and one cannabinoid receptor to more than 50 times their normal levels. L. acidophilus NCFM also enhanced the expression of the same two receptors in the gut lining of healthy rats and mice.
The team then mimicked irritable bowel syndrome by giving rats an enema with butyrate, a chemical that irritates the colon. To test the probiotics' effects, the researchers inflated a balloon in each rat's rectum until the animal contracted its abdominal muscles in pain. As the rats received increasing doses of L. acidophilus NCFM, their pain threshold rose by up to by about 40%--about as much as a standard dose of morphine. Desreumaux is working with Danisco, a probiotic producer, on a double-blind clinical trial to see whether the probiotic strain cuts intestinal pain in people with IBS. They plan a second trial to test a combination of bugs and morphine to help patients get through the day more comfortably.
Because the experiments were done in cultured cells and rats, "I'm not sure what it really means for humans," says infectious disease specialist and probiotics expert Sherwood Gorbach of the Tufts University School of Medicine. Nevertheless, he adds, "I find the observation very interesting and provocative, and I think it should be pursued."