Dr. James Sheller, left, and Dr. Jackson Roberts II will conduct the study. (photo by Dana Johnson)
VUMC receives $750,000 grant to study asthma
A private foundation seeking innovation in asthma research has awarded a three-year grant to a group of Vanderbilt University Medical Center investigators. The researchers will use the funding – $250,000 per year – from the Sandler Program for Asthma Research to explore the role of oxidant stress in the pathophysiology of asthma. Their studies could lead to new therapeutic interventions for the disease.
“The Sandler Program is really unique. They state right at the top of their information that they’re looking for new approaches from investigators who are not in the asthma field,” said Dr. L. Jackson Roberts II, professor of Pharmacology and Medicine and the principal investigator for the grant.
Fresh ideas are needed, Roberts said, because the incidence of asthma is skyrocketing and no new insights or new effective treatments for the disease have emerged for some time. More than five percent of the United States population has asthma, making it one of the most common and costly diseases in the country, according to the Centers for Disease Control and Prevention.
Roberts and colleagues will pursue a novel concept – that free radicals play a role in allergic asthma. Roberts is an international authority on evaluating oxidant stress in vivo by measuring the levels of compounds called isoprostanes.
Isoprostanes – discovered in 1990 by Roberts and Dr. Jason D. Morrow, F. Tremaine Billings Professor of Medicine – are formed when free radicals attack and oxidize lipids in the cell membrane. Excessive formation of free radicals is the cause of oxidant stress.
“Measuring isoprostanes is far and away the best approach to assess a free radical process in vivo,” Roberts said.
Roberts, along with Dr. James R. Sheller, associate professor of Medicine and one of the grant collaborators, and Dr. Ryszard T. Dworski, research assistant professor of Medicine, recently discovered that simply challenging human asthmatics with an allergen results in increased isoprostane production in the lungs.
“It was really quite striking,” Roberts said, “and it opened up a brand new area – something that might be involved in the process of allergic asthma that has not really been explored. And we probably have the leading capability to explore it.”
To test whether free radical reactions are a critical part of airway allergic responses, Roberts and colleagues will measure isoprostane levels and airway function in mice that have been sensitized to an allergen. As in human asthmatics, they expect to find increased levels of isoprostanes in lung lavage fluid.
They will then use dietary manipulation to deplete or enhance antioxidant levels in the mice. Correlation of isoprostane levels and airway function will provide information regarding the relevance of oxidant stress in the pulmonary allergic response.
They expect that dietary depletion of the antioxidants vitamin E and selenium will result in increased allergic inflammation and increased airway hyperresponsiveness – the hallmark of asthma. Conversely, they anticipate that administration of antioxidants will protect against the allergic response by suppressing oxidant injury, as assessed by measuring isoprostane production.
The group is also interested in examining the cellular target of oxidant stress during allergic reactions. Newly produced isoprostanes are attached to the cell membrane, and in preliminary experiments, Roberts and his colleagues used histologic methods and fluorescence microscopy to visualize these isoprostanes in allergic lung tissue from mice.
“The bronchoalveolar epithelial cells in the lung lit up like a Christmas tree,” Roberts said. “That’s really where the action is in asthma. If you’re generating these oxidized abnormal lipids right in the membranes of the bronchial epithelial cells, that is obviously going to be very injurious.”
“We expect that information about cell and subcellular localization of oxidant stress will help determine mechanism and thus therapy,” Sheller said. “It may be possible in the future to treat asthma prone individuals with antioxidants to modify the development and seriousness of their asthma.”
Another thrust of the grant is to examine the role of an enzyme called platelet activating factor-acetyl hydrolase (PAF-AH) in allergic inflammation. Roberts discovered that this enzyme, long studied for its role in hydrolyzing PAF, releases newly formed isoprostanes from the cell membrane.
“PAF-AH may be a misnomer,” Roberts said. “The real function of this enzyme may be to get oxidatively modified phospholipids out of the membrane – as a remodeling approach – so there’s not a buildup of these distorted, potentially injurious, phospholipids in the cell membrane.”
Interestingly, PAF-AH levels are lower in lavage fluid from human asthmatics than from non-asthmatics, which is supportive of the idea that failure to remove oxidized phospholipids may contribute to the disease, Roberts said.
The group will develop transgenic mice that produce more PAF-AH than normal in the lung epithelial cells. They expect that the overproduction of PAF-AH will release oxidized lipids from the epithelial cells and that sensitized mice will consequently have reduced inflammation and airway reactivity.
“If this enzyme does reduce the allergic response, it could potentially be inhaled as a therapeutic agent,” Roberts said.
Other collaborators for the Sandler Program grant include: Dr. Timothy S. Blackwell, assistant professor of Medicine; Dr. Robert D. Collins, John L. Shapiro Professor of Pathology; Dr. Barbara O. Meyrick, professor of Pathology and Medicine; and Dr. Megha Talati, research fellow in Allergy, Pulmonary, and Critical Care Medicine. The highly competitive program received 208 applications and awarded 11 grants this year. For more information on the Sandler Program for Asthma Research, go to www.sandlerresearch.org.