Broccoli Extract Could Help Head Off Skin Cancer
Tuesday, October 23, 2007
George H.W. Bush: Call your dermatologist.
New research suggests that broccoli, the vegetable that the former president famously demonized as inedible, can prevent the damage from ultraviolet light that often leads to skin cancer. And as Bush would surely appreciate, he would not even have to eat it.
In tests on people and hairless mice, a green smear of broccoli-sprout extract blocked the potentially cancer-causing damage usually inflicted by sunlight and showed potential advantages over sunscreens.
The product is still in the early stages of development. Among other issues to be worked out is how best to remove the extract's green pigments, which do not contribute to its protective effects and would give users a temporary Martian complexion.
But scientists said the research represents a significant advance because the extract works not by screening out the sun's rays -- which has the downside of blocking sun-induced Vitamin D production -- but by turning on the body's natural cancer-fighting machinery. Once stimulated, those mechanisms work for days, long after the extract is washed away.
"Ultraviolet radiation is probably the most universal and abundant carcinogen in the world," said Paul Talalay of the Johns Hopkins School of Medicine in Baltimore, who led the research, published yesterday in the online edition of the Proceedings of the National Academy of Sciences. And although the new study stops short of proving that broccoli extracts can prevent human skin cancer, he said, it demonstrates "direct protection" against that carcinogen, which contributes to the 1 million U.S. skin cancer cases seen annually.
"It's very important work," said Michael Sporn, a professor of pharmacology at Dartmouth Medical School, who for nearly two decades headed the National Cancer Institute's program on cancer prevention by means of natural products.
"The use of dietary substances, like the antioxidant vitamins C and E, has been pretty much a colossal failure for protection against almost any kind of human disease," Sporn said, "because when you eat them they don't go where you want them to . . . and as soon as your body uses them up, they're gone."
By contrast, he said, boosting production of the body's own cancer-fighting mechanisms "is a new and promising approach."
Broccoli's rise from farm to pharma began in 1992 when Talalay and colleagues reported that broccoli -- and especially three-day-old broccoli sprouts, they found later -- is rich in sulforaphane, a compound that activates certain enzymes in the body.
Those "Phase 2" enzymes, such as glutathione S-transferase, can neutralize the DNA-damaging molecules that are created in the skin by the mix of oxygen and sunlight. They can also temper the inflammatory reactions that can turn precancerous cells into life-threatening tumors.
Talalay's discovery got his family and Johns Hopkins into the broccoli-sprout business. His son is chief executive of Brassica Protection Products LLC, which licensed the technology from Johns Hopkins and produces "BroccoSprouts" brand broccoli sprouts, a popular health food. But more recently Talalay has focused on sulforaphane as a topical protective against skin cancer.
His team exposed areas of volunteers' skin to intense ultraviolet light one to three days after the broccoli-sprout extract was applied to some areas. The extract was all but rubbed and washed away by the time the light exposure occurred, but by then the sulforaphane had turned on key genes in the skin cells, which beefed up production of Phase 2 enzymes.
Compared with untreated areas, spots treated with the extract had, on average, 37 percent less redness and inflammation -- key measures of future skin cancer risk. Other tests have shown that mice treated with the extract get significantly fewer and smaller skin tumors after exposure to ultraviolet light.
Allan Conney, director of the laboratory for cancer research at Rutgers University's School of Pharmacy, warned that the work only hints at an ability to prevent cancers in people and that in the study, the extract's ability to reduce ultraviolet-induced damage varied considerably from person to person, from a low of about 8 percent protection to a high of 78 percent. Still, he said, the broccoli approach "could have truly broad significance."
Albena Dinkova-Kostova, co-leader of the new study with Talalay and now at the University of Dundee in Scotland, said several hurdles stand between the experiments and a broccoli-based anti-cancer skin cream.
Among them are the need to find the most effective concentration of sulforaphane, increase the active ingredient's shelf life, and improve skin absorption of sulforaphane. That last task was accomplished in the tests by mixing it with acetone, an ingredient in nail polish remover that, while safe in small quantities, is not something people would want to slather on their skin.
Then there is the extract's green tint, which would be absent if the team were to synthesize the sulforaphane instead of getting it from sprouts. But that would raise safety and regulatory concerns.
"The advantage of starting with sprouts is that we all eat broccoli so we're not concerned with toxicity issues," Dinkova-Kostova said, adding that she anticipated no problems getting the green out.