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Inside broccoli: a weapon against cancer.

From presidents to preschoolers, many people who regard broccoli with loathing may soon reconsider. New evidence indicates that the familiar green vegetable contains a powerful weapon against cancer-causing substances.

Researchers at the Johns Hopkins School of Medicine in Baltimore have identified a chemical in broccoli, called sulforaphane, that stimulates animal and human cells to produce cancer-fighting enzymes. "Sulforaphane is possibly the most potent protective agent yet discovered," says Paul Talalay, a molecular pharmacologist. Talalay and his co-workers report their finding in the March 14 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES.

Researchers have suspected since the mid-1970s that some vegetables confer resistance to cancer, especially the cruciferous vegetables, such as broccoli, brussels sprouts and cabbage. Although previous studies uncovered a number of chemicals thought responsible for broccoli's protective effect, none appears more powerful than sulforaphane, Talalay says.

Vegetables contain chemicals that cause human cells to manufacture many different enzymes. Not all of these enzymes behave good-naturedly, however. One group, called phase I enzymes, converts innocuous substances that enter the body into oxidants, reactive molecules that can damage a cell's DNA and thereby increase the risk of cancer. To counteract this threat, cells can also make phase II enzymes, which disarm oxidants before they cause any genetic damage.

Many vegetables stimulate the production of both phase I and phase II enzymes. Others provoke the cells to create only the more beneficial, phase II variety. Talalay's group concentrated on these foods.

The researchers developed a quick and powerful test to identify foods that stimulate only the protective class of enzymes. The test involves adding vegetable extracts to cultured rat and human cells.

Since broccoli has long been suspected to contain a chemoprotectant, they tested it first. "We asked the question: What in broccoli is conferring protection against cancer?" Talalay says. "Now that gave us great anxiety, because we thought we might discover there were 15 things that were doing this."

However, the team found that only one of the compounds isolated from broccoli could stimulate the production of phase II enzymes. They later identified it as sulforaphane.

Using the new test, Talalay's group identified additional protective veggies, including brussels sprouts and kale. Peppers, potatoes and tomatoes, among others, had little or no effect on phase II enzymes. The researchers also found that the sulforaphane in broccoli appears to remain intact when the vegetable is microwaved; they haven't tried other cooking methods yet.

Although some scientists argue that phase I enzymes may prevent certain cancers better than phase II enzymes, most agree that vegetables that stimulate the production of phase II enzymes would protect cells against a wider variety of carcinogens. "Most experts in the field would agree that phase II enzymes should be a little, if not a lot, better than phase I enzymes [against oxidants]. You just don't want to give potentially toxic substances any chance of outsmarting you," explains Jon J. Michnovicz of the Institute for Hormone Research in New York City.

Researchers have not yet shown that sulforaphane directly blocks tumor formation in either laboratory animals or humans, and proving that may take some time, Talalay says. In the meantime, however, the new findings provide a scientific basis for modifying the diet to include more vegetables like broccoli, he says.

Does this recommendation extend to President Bush? "Broccoli should protect both Republicans and Democrats equally well," Talalay replies.
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Author:Stroh, Michael
Publication:Science News
Date:Mar 21, 1992
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