Ulcer Bug Has a Sweet Tooth
It makes beeline for sugary molecules in stomach lining
THURSDAY, July 25, 2002 (HealthDayNews) -- For H. pylori, a germ that's the leading cause of stomach ulcers, infectious success is sweet.
An international team of scientists has found that the gut-loving bacteria take firm root in the body by sticking to sugary molecules in the mucosal cells lining the stomach. Happily for the bugs, once infected these cells churn out more of the molecules, called "adhesin" receptors, allowing the infestation to continue chronically.
Understanding how Helicobacter pylori, as it's officially known, attacks the stomach could one day help researchers develop vaccines against the infection. More than 50 percent of the world's population has the bacteria living in their stomach lining, causing for many peptic and duodenal ulcers and even stomach cancer.
Ten percent of Americans will develop peptic ulcers, and the National Institutes of Health projects 300,000 new cases, 3.2 million recurrences, and 3,000 deaths from duodenal ulcers every year.
Ideally, adhesin receptors act as beacons for immune cells, summoning them to tissue damaged by infection. But as the new study suggests, H. pylori have evolved to turn that distress siren into sweet music.
In earlier work, Thomas Borén, of Umea University in Umea, Sweden, and his colleagues discovered an adhesin molecule, called BabA, that's H. pylori's main grappling hook onto the stomach. This surface protein joins up with a sugar-rich protein on the outside of mucosal cells known as Leb, enabling the bacteria to suck nutrients out of the tissue.
But when they engineered a mutant strain of the germ missing BabA, it was still able to colonize the cells -- suggesting the bacteria had a fallback foothold.
The new research identified that passport as an adhesion molecule the scientists dubbed SabA, and the receptor it hinges to, sdiLex.
"We believe that initially H. pylori attaches to the previously known receptor, induces inflammation and [stimulates the stomach cells] to produce the new receptors," says Dr. Andre Dubois, a digestive disease specialist at the Uniformed Services University in Bethesda, Md., and a co-author of the study. "It's a smart bug."
It seems that while there are scads of H. pylori strains, the two discovered adhesin receptors are their most efficient way of attacking the gut. A mutant strain missing protein keys for both receptors couldn't find purchase in mucosal cells, Dubois says. "If there is any other one, it may not be as important as the first two."
Intriguingly, Dubois says, the bacteria seem able to disengage from their hookup when the immune system gets too hostile, moving on to another, more hospitable spot to colonize.
Although it's nice to know how H. pylori works, the findings could have practical significance. "These receptors on the surface of the bacteria are very specific to H. pylori, so they could be used as [a target] to produce a vaccine," Dubois says.
In principle, the vaccine would stir a preemptive immune response to the two bacterial proteins that attach to the adhesin receptors, Dubois says. Developing such a compound could take five to 10 years, he adds.
However, Dr. Adam Smolka, an H. pylori expert at the Medical University of South Carolina in Charleston, says a vaccine against the bacteria may not be necessary. Rates of H. pylori are falling in developed countries as hygiene improves, Smolka says, and antibiotics have thus far proven highly effective with little sign of resistance.
But Dubois disagrees that drug resistance hasn't been a problem, and says strains isolated from patients have shown signs of immunity to commonly used antibiotics. What's more, he says, it would take 150 years to defeat H. pylori by improving world hygiene alone.
"I think that other strategies are necessary," he says.
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