"Vitamin E is nature's antioxidant and people have been trying to improve upon it for more than 20 years with only marginal success. We have taken a very big step in the right direction," says Ned A. Porter, the Stevenson Chair of Chemistry at Vanderbilt. He supervised the development, which was published in the European journal Angewandte Chemie International Edition. The university has a patent pending on the new compounds.
Antioxidants are molecules that can counteract the damaging effects of oxygen in tissues and other materials. So far, the new antioxidants have been tested "in vitro" – in the test tube. But studies with biological molecules, such as cholesterol, suggest that the new compounds have properties that could make them suitable for dietary supplements. Shortly, Vanderbilt researchers expect to begin the lengthy process of determining how effective the new the compounds are in living animals and whether they have any harmful side effects.
The market for antioxidants in North America is estimated at more than $800 million per year. Even if the compounds do not prove suitable as dietary supplements or neutraceuticals, they could still have practical value. Many materials used for commerce can be damaged by oxygen and so are routinely treated with antioxidants. These materials include plastics, rubber, fuels and lubricants, agricultural feed and cosmetics.
The approach that led to the new antioxidants was the idea of Vanderbilt graduate student Derek Pratt: "The summer before I came to Vanderbilt, I was at a conference in New Hampshire where several presentations dealt with antioxidants. It just occurred to me that this was an approach that hadn't been tried before."
At the time, Pratt was an undergraduate at Carlton University in Ottawa and was working with Keith Ingold at the National Research Council in Canada. When Pratt explained his idea to Ingold, the prominent chemist advised him to "keep this one for yourself."
So Pratt brought the idea with him when he came to Vanderbilt to work with Porter. "When Derek suggested this project, I was immediately intrigued," says Porter. "And it has turned out to be one of the most interesting projects I've ever been involved with."
Vitamin E, whose chemical name is á-tocopherol, is a phenol: It contains a ring made of six carbon atoms with a hydroxyl group (OH) attached. Ingold, among others, had tried to make better antioxidants by attaching a nitrogen atom to the carbon ring. Theoretically, these molecules should be stronger antioxidants but they proved to be impractical because they were unstable in air.
In addition to attaching a nitrogen atom to the ring, Pratt's idea was to substitute a nitrogen atom for one of the carbon atoms in the ring itself. With both substitutions he predicted that the resulting molecules, called pyridinols, should be more stable in air.
Then Pratt had to address the question of whether the resulting molecules would be effective antioxidants. He did so by analyzing the properties of existing antioxidants to determine what made them effective. Once he had done this, he performed a theoretical analysis to determine whether pyridinols should also have these properties. When his analysis confirmed that they would, "the pace really picked up," he says.
Porter teamed Pratt with Maikel Wijtmans, another graduate student working in his lab interested in synthesizing new molecules. "Actually, once you think of it, it's really a pretty simple substitution," says Pratt. Still, it took a year to work out a 12-step process that produced the most effective member of this new class of compounds in quantities large enough for testing.
In order to assess their effectiveness as antioxidants, the Vanderbilt chemists sent samples to Luca Valgimigli in Professor G. F. Pedulli's lab at the University of Bologna. The Italian laboratory is one of the few in the world capable of determining antioxidant effectiveness. Valgimigli determined that the best pyridinols the Vanderbilt chemists had created are as much as 100 times more effective than vitamin E.
In December, Pratt received his doctorate and moved to the University of Illinois at Urbana-Champaign to begin a post doctoral fellowship. He is continuing to work with Porter's group on the new antioxidants.
By attaching a chemical group that makes pyridinols "greasy" – gives them a chemical affinity for fatty acids – the chemists have combined their antioxidants with low density lipoprotein (LDL or "bad" cholesterol) and found that they appear to protect LDL molecules from oxidation. That may be significant because one popular theory for the cause of coronary artery disease is lipid oxidation.
"When we try to force lipid oxidation, we find that the pyridinols are much more effective inhibitors than vitamin E," says Porter.
One of the chemists' next projects is to make pyridinols that look as much like Vitamin E as possible. The researchers have deliberately designed some pyridinols so that they can attach different types of chemical groups to the ring so they can make such modifications.
Another project is to make pyridinols that are water soluble, unlike vitamin E. Water soluble varieties should perform a role similar to that of vitamin C: trapping and destroying water-soluble "free radicals." Free radicals are electrically charged atoms or molecules produced by oxidation that are potentially harmful to the body.
In addition, the researchers have joined forces with three researchers at the Vanderbilt University Medical Center – Professor of Medicine Raymond F. Burk, Professor of Biochemistry Daniel C. Liebler and Professor of Pharmacology Jason D. Morrow – to collaborate on testing these new compounds in animals. They have submitted a proposal for federal funding that is currently under review.
The research was supported by the National Science Foundation, Vanderbilt University, the National Science and Engineering Research Council of Canada, the University of Bologna and the Italian Ministry of Research.
For more news about Vanderbilt research, visit Exploration, Vanderbilt's online research magazine at www.exploration.vanderbilt.edu.
Journal
Angewandte Chemie