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The team studying a Vanderbilt-created tool for tracking lipids includes (seated, from left) Keri Tallman, Ph.D., Stephen Milne, Ph.D., (standing, from left) Ned Porter, Ph.D., Alex Brown, Ph.D., and Lawrence Marnett, Ph.D. (photo by Mary Donaldson)

VU investigators develop new tool for tracking lipids

BY: LEIGH MACMILLAN

2/12/2010 - Lipids — the fats and oils that form membranes and serve as messengers both inside and outside of cells — are biological stragglers. They have lagged behind proteins and nucleic acids when it comes to being identified and understood, partly because of limited methods for their study.

Now, a new chemistry-based tool for tracking lipids promises to revolutionize the study of these molecules, which play roles in a wide range of signaling and metabolic pathways. The technology, developed by Vanderbilt University scientists, may reveal new therapeutic targets for diseases including heart disease, cancer, arthritis, diabetes and infectious agents.

“The major killers in American society all have abnormalities in either lipid metabolism or lipid content,” said H. Alex Brown, Ph.D., professor of Pharmacology, Chemistry and Biochemistry, and a leader of the research reported in Nature Chemical Biology.

Brown and his colleagues have been identifying and characterizing lipids for years, using a mass spectrometry-based technology pioneered in his laboratory called lipidomics. In the process, the investigators realized that “there are far more lipids than imagined,” and that conventional methods alone could not tease them apart, he said.

To develop a new way to track lipids, Brown teamed with Ned Porter, Ph.D., professor of Chemistry, and Lawrence Marnett, Ph.D., professor of Biochemistry, Chemistry and Pharmacology. With initial funding from the Vanderbilt Institute of Chemical Biology, the investigators discovered that they could “tag” lipid molecules in living cells and use a modification of a technique known as “click chemistry” to recover the tagged lipids for analysis.

“It's a way for us to pull lipid 'needles' out of the cellular 'haystack,'” Brown said.

The new method works like this: the researchers introduce a certain type of chemical bond into lipid molecules of their choice, incorporate these tagged lipids into living cells, and perform biological experiments on the cells. Then they use modified click chemistry to attach a cobalt-containing “handle” to the altered lipids. This handle can be grabbed to isolate the lipids of interest from the rest of the cellular contents, and then the handle can be removed.

“This is going to allow us to crawl around in the black box of the lipid signaling in the cell, into areas that we've never really been able to see before,” Brown said.

Scientists have understood “that lipid A becomes lipid X,” Brown explained. “But the reality is that there are lots of intermediate molecules along the way in these complicated lipid signaling pathways.”

Brown and his colleagues found, for example, that the lipid phosphatidic acid is key to the invasive properties of brain tumors called gliomas. They know that the enzyme phospholipase D produces phosphatidic acid in gliomas, but the question is: are other phosphatidic acid pathways also contributors to glioma invasiveness?

“If we can use this new technology to find key lipid intermediates that are important in a disease process, then we can potentially perturb that pathological process and leave the physiological processes intact,” Brown said. “This could allow us to target new enzymes and design entirely new classes of pharmacological inhibitors with therapeutic potential.”

The investigators are also using the technology to probe how “oxidative stress” damages cells, such as which lipids are targets of reactive oxygen species and how the damage contributes to disease processes. The Brown, Porter and Marnett groups are collaborators in a National Institutes of Health-funded Program Project Grant to study oxidative lipid pathways.

The Vanderbilt Institute of Chemical Biology (VICB) made development of the new technology possible, Brown said, by funding the work in its initial stages and by putting into place the infrastructure that fosters collaboration between chemists, biochemists and pharmacologists.

“This work simply would not have occurred without VICB, and that's not an exaggeration,” Brown said.

The lead authors of the Nature Chemical Biology paper were Stephen Milne, Ph.D., research assistant professor of Pharmacology, and Keri Tallman, Ph.D., research assistant professor of Chemistry. VICB and the National Institutes of Health supported the research.

Porter is the Stevenson Professor of Chemistry and Biochemistry. Marnett is the Mary Geddes Stahlman Professor of Cancer Research and director of VICB.

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