Cancer Protection Compound Abundant In Broccoli Sprouts, Johns Hopkins Scientists Find

"Three-day-old broccoli sprouts consistently contain 20 to 50 times the amount of chemoprotective compounds found in mature broccoli heads, and may offer a simple, dietary means of chemically reducing cancer risk," says Paul Talalay, M.D., J.J. Abel Distinguished Service Professor of Pharmacology.

Talalay's research team fed extracts of the sprouts to groups of 20 female rats for five days, and exposed them and a control group that had not received the extracts to a carcinogen, dimethylbenzanthracene. The rats that received the extracts developed fewer tumors, and those that did get tumors had smaller growths that took longer to develop.

In a paper published in tomorrow's issue of the Proceedings of the National Academy of Sciences, Talalay and his coworkers describe their successful efforts to build on their 1992 discovery of sulforaphane's chemoprotective properties. Work described in the study is the subject of issued and pending patents.

A systematic search for dietary sources of compounds that increase resistance to cancer-causing agents led the Hopkins group to focus on naturally occurring compounds in edible plants that mobilize Phase 2 detoxification enzymes. These enzymes neutralize highly reactive, dangerous forms of cancer-causing chemicals before they can damage DNA and promote cancer.

Sulforaphane "is a very potent promoter of Phase 2 enzymes," says Jed Fahey, plant physiologist and manager of the Brassica Chemoprotection Laboratory at Hopkins, and broccoli contains unusually high levels of glucoraphanin, the naturally-occurring precursor of sulforaphane.

However, tests reported in the new study showed that glucoraphanin levels were highly variable in broccoli samples, and there was no way to tell which broccoli plants had the most without sophisticated chemical analysis.

"Even if that were possible, people would still have to eat unreasonably large quantities of broccoli to get any significant promotion of Phase 2 enzymes," Talalay says.

Clinical studies are currently under way to see if eating a few tablespoons of the sprouts daily can supply the same degree of chemoprotection as one to two pounds of broccoli eaten weekly. The sprouts look and taste something like alfalfa sprouts, according to Talalay.

Talalay founded the Brassica Chemoprotection Laboratory, a Hopkins center that focuses on identifying chemoprotective nutrients and finding ways to maximize their effects. Brassica is a plant genus more commonly known as the mustard family, and includes in addition to broccoli, Brussels sprouts, cabbage, kale, cauliflower and turnips.

"Man-made compounds that increase the resistance of cells and tissues to carcinogens are currently under development, but will require years of clinical trials to determine safety and efficacy," Talalay notes. "For now, we may get faster and better impact by looking at dietary means of supplying that protection. Eating more fruits and vegetables has long been associated with reduced cancer risk, so it made sense for us to look at vegetables.

"Scientists currently need to continue to develop new ways of detecting and treating cancer once it is established, but it also makes sense to focus more attention on efforts to prevent cancer from arising," he adds.

Fahey and Yuesheng Zhang, M.D., Ph.D., a postdoctoral fellow, are also authors on the PNAS paper.

Work in Talalay's laboratory is supported by the National Cancer Institute, philanthropic contributions to Brassica Chemoprotection Laboratory, and grants from the Cancer Research Foundation of America and the American Institute for Cancer Research.

Talalay is establishing the Brassica Foundation, a foundation that will test and certify chemoprotective vegetables such as sprouts to raise funds for chemoprotection research.