A plant compound commonly found in celery and green peppers could play a role in decreasing inflammation in the brain, according to a new study from researchers at the University of Illinois at Urbana-Champaign.
The compound, luteolin, has been shown in previous studies to hinder inflammation in cells belonging to the lungs, prostate and gums. In this study, researchers used luteolin to block the inflammatory response of the brain's immune system, opening the door to potential treatments for diseases of the brain.
"When the body's nervous system is stimulated by pathogens, like a typical infection, the immune system conveys a message to the brain," said Rodney Johnson, professor of Animal Sciences and author of the study. "The immune cells located in the brain respond to that signal and produce more inflammatory molecules, which are thought to contribute to the exacerbation of neurodegenerative diseases.
"Luteolin has the ability to inhibit the production of these inflammatory molecules," Johnson said. "This could slow the progression of certain neurodegenerative diseases like Alzheimer's or multiple sclerosis."
Johnson's study was published in Monday's online issue of Proceedings of the National Academy of Sciences.
Luteolin belongs to a class of plant metabolites called flavonoids, which are abundant in fruits, vegetables, tea, wine and chocolate, according to nutritionist David Haytowitz of the U. S. Department of Agriculture Nutrient Data Laboratory. In addition to providing lemons and apples with their characteristic yellow and red hue, flavonoids are known for their antioxidant properties.
"Flavonoids are theorized to have a number of beneficial health attributes," Haytowitz said. "They play a role in preventing cardiovascular disease, particularly with LDL [cholesterol] oxidation, as well as cancer prevention."
Johnson and his colleagues studied the effect of luteolin on the brain's inflammatory pathways, which are normally designed to prevent injury and promote healing. Excessive inflammation, however, can lead to neurodegeneration and cognitive deficits associated with aging.
In their first experiment, on cells, researchers triggered inflammation in microglia, supportive cells in the brain that play an important role in its defense system. The brain is usually protected from infectious pathogens by a membrane of cells called the blood-brain barrier, but if this ever fails, microglial cells can engulf the pathogens and help destroy them.
"[Microglia] serve to protect the brain," Johnson said. "They normally reside in a quiescent state, but if they become overzealous it can be damaging."
The scientists triggered inflammation by exposing the microglia to lipopolysaccharide, which is found in the outer surface of common bacteria like E. coli. Next, they administered luteolin and studied its effect by measuring the production of IL-6, a key signaling molecule in the pathway leading to inflammation. Cells treated with luteolin had a 90-percent decrease in IL-6 production compared with untreated cells.
In a second experiment, researchers gave luteolin-laden drinking water to mice for 21 days. Afterwards, they injected the mice with lipopolysaccharide and measured IL-6 levels four hours later. Mice fed with luteolin had reduced levels of IL-6 in their blood as well as in the hippocampus, a region of the brain responsible for memory.
But before you pack your lunch with extra celery, know that it may not be enough to stave off Alzheimer's, according to Johnson.
"I don't think you're going to be able to eat enough celery to get to the levels of luteolin we studied," Johnson said. "It would be more a case where you take a dietary supplement to attain the amount needed."