Mice, Bugs Could Lead to New Asthma Therapy

Cockroach chemical found to play key role

THURSDAY, June 10, 2004 (HealthDayNews) -- Thanks to mice and insects, Yale researchers report an apparently paradoxical finding that could lead to a new way of treating asthma.

They started by looking at chitin (pronounced KITE-in), a molecule found in the cell walls of cockroaches and other insects that is known to play a role in the allergic reaction some people have to cockroaches.

Since asthma is a kind of allergic condition, it might seem logical that inhibiting chitin would reduce asthma-related inflammation. But what the researchers report in the June 11 issue of Science is that they can help mice bred to be asthmatic by inhibiting the activity of chitinase, an enzyme that digests chitin.

A lot of questions remain to be answered, said Dr. Robert J. Homer, an associate professor of pathology at Yale University School of Medicine and a member of the research team, but the discovery is worth following up because inhibiting chitinase affects only asthma-related inflammation.

Asthma drugs such as corticosteroids inhibit inflammation in general, which means their benefits are accompanied by bothersome side effects. So the chitinase work "adds a whole new area of potential treatment for asthma," Homer said.

Some preliminary studies already have been done in humans. Increased chitinase activity was found in tissue samples from seven people with asthma but not in samples from nine asthma-free individuals, the journal report says.

It's not clear that the chitin-digesting activity of chitinase is behind the effect on asthma. "We don't know exactly what is going on," Homer said. "Because there was no chitin in the system we studied, the ability to digest chitin may not be important."

"It is a bit confusing," said Dr. Joseph A. Bellanti, a professor of pediatrics and microbiology-immunology at Georgetown University Medical Center and a spokesman for the Allergy and Asthma Foundation of America. "But this whole system is very complex. Every time you measure one component, you find two or three other things pushing or inhibiting it."

The study does add support for the "hygiene hypothesis," the theory that asthma incidence is increasing in advanced countries because a cleaner environment reduces children's exposure to minor infections that get their immune systems active early in life, so they don't respond abnormally to asthma-causing agents later on, Bellanti said.

Lack of early exposure increases the role of antibodies, immune system molecules, relative to the role of immune system cells, he said. Parasitic infection also stimulates antibody production, so the Yale finding points to a way of restoring the normal balance, he said.

But "a great deal more basic biology remains to be done," Homer said. "We have no idea whether we can inhibit chitinase in humans, but we know we can do good by our mice."

More information

The basics and more about asthma can be found at the Asthma and Allergy Foundation of America.

SOURCES: Robert J. Homer, M.D., Ph.D., associate professor, pathology, Yale University School of Medicine, New Haven, Conn.; Joseph A. Bellanti, M.D., professor, pediatrics and microbiology-immunology, Georgetown University Medical Center, Washington, D.C.; June 11, 2004, Science
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