October 31, 2005
A Grocery List for Cancer Prevention
Baltimore, Md. -- In the high-tech 21st century, the most rudimentary natural products continue to reveal exciting ant-cancer properties to scientists, offering people relatively simple ways to help protect themselves from the disease.
Five studies presented today during the American Association for Cancer Research's 4th annual Frontiers in Cancer Prevention Research meeting in Baltimore, Md., add to the arsenal of research that shows adding certain vegetables and herbs to the diet can prevent or, in some cases, halt the growth of cancer.
Moreover, it is not just a matter of mechanical prevention, such as adding fiber to the diet to maintain digestive health. This research deals with the chemical interactions between compounds found in foods and the body's cells and DNA, and it shows that the addition of these foods to the diet can reap benefits at any stage of life.
Broccoli Sprouts Relieve Gastritis in H. pylori Patients; May Help Prevent Gastric Cancer (Abstract #3442)
Broccoli sprouts may not be a culinary favorite for some, but their chemical properties are becoming increasingly popular among those interested in preventing cancer.
In the latest series of studies, a team from Japan has found that a diet rich in broccoli sprouts significantly reduced Helicobacteri pylori (H. pylori) infection among a group of 20 individuals. H. pylori is known to cause gastritis and is believed to be a major factor in peptic ulcer and stomach cancer.
"Even though we were unable to eradicate H. pylori, to be able suppress it and relieve the accompanying gastritis by means as simple as eating more broccoli sprouts is good news for the many people who are infected," said Akinori Yanaka from the University of Tsukuba, Japan, lead investigator of the study.
Scientists are focusing on the anti-cancer properties of a chemical derived from broccoli sprouts called sulforaphane. Among other things, this chemical has the ability to help cells defend against oxidants, the highly reactive and toxic molecules that damage DNA and kill cells, leading potentially to cancer. Previously, researchers working with H. pylori discovered that sulforaphane acts against the bacterium in vitro, alleviating gastritis in H. pylori-infected mice through its antioxidant activity.
None of these findings had been tested in people, however, until the Yanaka-led team added broccoli sprouts (the plant at its youngest and most sulforaphane-rich, just two or three days old) to the diet of 20 individuals infected with H. pylori. Another group of 20 infected with the bacterium received alfalfa spouts instead of broccoli sprouts. Each received 100 grams of fresh sprouts daily for two months.
"We wanted to test alfalfa spouts together with broccoli sprouts," Yanaka explained, "because the chemical constituents of the two plants are almost identical."
However, the way in which they differ is significant. Broccoli sprouts contain 250 milligrams of sulforaphane glucosinolate per 100 grams per serving, whereas alfalfa sprouts contain neither sulforaphane nor sulforaphane glucosinolate.
Glucosinolates occur in cruciferous vegetables, like broccoli and cabbage, and are broken down enzymatically into sulforaphane and a variety of other, biologically active compounds when damage occurs to the plant--that is, by cutting or chewing it.
The presence of H. pylori was assessed by performing urea breath tests and evaluating H. pylori-specific stool antigen. The degree of gastritis was evaluated by measuring the level of pepsinogen in the blood. Pepsinogen is also an indicator of gastric atrophy. These tests were performed just before adding broccoli and alfalfa sprouts to the diet, and at one and two months after starting the dietary regimen. Following two months' consumption of 100 grams of broccoli sprouts per day, patients showed significantly less H. pylori and markedly decreased pepsinogen. Alfalfa sprouts had no effect, and the broccoli failed to eliminate H. pylori completely. Two months after eliminating broccoli sprouts from the diet, H. pylori and pepsinogen returned to pre-test levels in the subjects.
"The data suggest strongly that a diet rich in sulforaphane glucosinolate may help protect against gastric cancer, presumably by activating gastric mucosal anti-oxidant enzymes that can protect the cells from H. pylori-induced DNA damage," Yanaka concluded.
Broccoli Sprout-extract Protects Against Skin Cancer from UV Light in High-risk Mice (Abstract #2597)
Eat it or wear it? That is the question.
If you ask Albena T. Dinkova-Kostova, Ph.D., of Johns Hopkins University in Baltimore, she will likely answer "both."
In the laboratory of Paul Talalay, M.D., who first reported the indirect antioxidant properties of sulforaphane, the compound derived from cruciferous vegetables like broccoli, Dinkova-Kostova and her colleagues applied broccoli sprout extract to the skin of hairless mice, and found it counteracted the carcinogenic response to ultraviolet light exposure.
Mice from a strain characterized by post-weaning hair loss were exposed to a dose of UV light comparable to what a person would get sunbathing at the beach on a clear day, twice a week for 20 weeks. After irradiation, broccoli sprout extracts containing either a low or high dose of sulforaphane were applied to the backs of the mice, five days a week for 11 weeks. Acetone (known commonly as the ingredient in nail polish remover) was used as the vehicle for delivering the sulforaphane, and it alone was applied on the control group. At the conclusion of the study period, 100 percent of the control mice had developed cancerous skin tumors.
The incidence and number of tumors was reduced by half, however, in the mice receiving the high dose of broccoli sprout extract. The rate of tumor reduction was less among the low-dose recipients, but even in their case, some benefit was observed.
"We weren't looking for a sunscreen effect," Dinkova-Kostova is quick to point out. "The sulforaphane-containing extract was applied after the period of regular exposure to ultra-violet light. That's more relevant, since most people receive some sun damage to their skin in childhood, particularly adults who grew up before effective sunscreen lotions were developed."
Previous research has shown that sulforaphane boosts protective and detoxifying reactions in cells, inactivating carcinogens and reactive oxygen intermediates that contribute to the disease by damaging DNA. As in other studies involving the anti-cancer potential of sulforaphane, Dinkova-Kostova's group notes that broccoli sprouts contain much more of the compound than adult broccoli.
"Our findings suggest a promising strategy for skin cancer prevention after exposure to UV light," Dinkova-Kostova said.
Change in Diet at Any Age May Help Protect Against Breast Cancer (Abstract #3697)
Many find it to be the perfect companion to hot dogs and sausage, but new studies suggest that sauerkraut may have another beneficial side effect"”it may protect women from breast cancer.
Results from the U.S. component of the Polish Women's Health Study are showing an association between cabbage and sauerkraut consumption, and a constituent called glucosinolate, and a lower risk of breast cancer. The influence seemed to be highest among women who consumed high amounts beginning in adolescence and throughout adulthood.
"The observed pattern of risk reduction indicates that the breakdown products of glucosinolates in cabbage may affect both the initiation phase of carcinogenesis--by decreasing the amount of DNA damage and cell mutation--and the promotion phase--by blocking the processes that inhibit programmed cell death and stimulate unregulated cell growth," said Dorothy Rybaczyk- Pathak, Ph.D., from the University of New Mexico.
Pathak, along with colleagues from Michigan State University and the National Food and Nutrition Institute of Warsaw, Poland, evaluated the diet of Polish immigrants to the United States, living in Chicago and surrounding Cook County, Ill., and the Detroit, Mich., metropolitan area. Women with higher rates of raw- or short-cooked cabbage and sauerkraut consumption, three or more servings per week, compared to those who consumed less than one serving a week, had a significantly reduced breast cancer risk.
Like broccoli, cabbage is a cruciferous vegetable--its flowers are in the shape of a cross--and a member of the Brassica family, which includes broccoli, Brussels sprouts, kale, collard greens and cauliflower. These plants contain glucosinolates and the enzyme myrosinase which, when broken down by chewing or cutting, release several biologically active products which previous studies have shown to possess anti-carcinogenic properties.
Pathak began the study by wondering why the breast cancer risk of Polish women rose three-fold after they immigrated to the United States. She hypothesized that dietary changes were among the environmental factors contributing to this rapid increase in risk. In Poland, where abundance of food is a recent phenomenon, women traditionally eat an average of 30 pounds of cabbage and sauerkraut per year, as opposed to just 10 pounds per year among American women. Moreover, Polish women traditionally eat more raw cabbage and sauerkraut, in salads, or short-cooked, as a side dish.
She observed the lowest rate of breast cancer among women who consumed high amounts of raw- or short-cooked cabbage during adolescence, but found that high consumption during adulthood provided a significant protective effect for women who had eaten smaller quantities of this vegetable during adolescence. Cabbage cooked a long time, such as in hunter's stew, cabbage rolls and pierogi, had no bearing on breast cancer risk.
Possible Chemoprevention of Ovarian Cancer by the Herbal, Ginkgo Biloba (Abstract #3654)
Researchers in Boston, led by Drs. Bin Ye and Daniel Cramer of Brigham and Women's Hospital, have developed new laboratory and epidemiological evidence that demonstrates, for the first time, that ginkgo biloba appears to lower the risk of developing ovarian cancer.
In a population-based study which involved more than 600 ovarian cancer cases and 640 healthy, matched controls, women who took ginkgo supplements for six months or longer were shown to have a 60 percent lower risk for ovarian cancer.
Ye and his colleagues found that ginkgo, echinacea, St. John's Wort, ginseng, and chondroitin were the most commonly used herbals among study participants. A further analysis of the data showed that ginkgo was the only herb linked to ovarian cancer prevention. The preventive effect was more pronounced in women with non-muncious ovarian cancers, with data showing that ginkgo may reduce the risk of this type of ovarian cancer by 65-70 percent. "Among the mixture of ginkgo chemicals," said Ye, "we found laboratory evidence that ginkgolide A and B--terpene compounds--are the most active components contributing to this protective effect."
Ye's team, which included scientists from Dana-Farber Cancer Institute at Harvard Medical School, Boston University and Linden Bioscience, next took the evidence demonstrated by their population studies to the laboratory. In vitro experiments showed that a low dosage of ginkgolide caused ovarian cancer cells to stop growing. They observed significant cell cycle blockage in non-mucinous ovarian cancer cells. Ginkgolides appeared to be less effective against the mucinous type of ovarian cancer cells.
"While the detailed mechanism of ginkgo action on ovarian cancer cells is not yet well understood," Ye explained, "from the existing literature it most likely that ginkgo and ginkgolides are involved in anti-inflammation and anti-angiogenesis processes via many extra- and intra-cellular signal pathways. In the future, these findings could potentially offer a new strategy for ovarian cancer prevention and therapy, using the active forms of ginkgolides."
Ovarian cancer is the most deadly of all gynecological cancers. It is called a "silent killer" because most cases are discovered only in very advanced stages.
Changing Genes: Garlic Shown to Inhibit DNA Damaging Chemical in Breast Cancer (Abstract #2543)
Legend suggests that garlic may ward off evil spirits, such as vampires. Now scientists are finding that garlic, or a flavor component of pungent herb, may help ward off carcinogens produced by meat cooked at high temperatures.
Cooking protein-rich foods like meats and eggs at high temperatures releases a chemical called PhIP, a suspected carcinogen. Epidemiological studies have shown that the incidence of breast cancer is higher among women who eat large quantities of meat, although fat and caloric intake and hormone exposure may contribute to this increased risk.
Diallyl sulfide (DAS), a flavor component of garlic, has been shown to inhibit the effects of PhIP that, when biologically active, can cause DNA damage or transform substances in the body into carcinogens.
Ronald D. Thomas, Ph.D., and a team of researchers at Florida A&M University in Tallahassee hypothesized that PhIP enhances the metabolism of the enzymes linked to carcinogenesis. They further suggested that the diallyl sulfide derived from garlic might counter this activity.
"We treated human breast epithelial cells with equal amounts of PhIP and DAS separately, and the two together, for periods ranging from three to 24 hours," said Thomas. "PhIP induced expression of the cancer-causing enzyme at every stage, up to 40-fold, while DAS completely inhibited the PhIP enzyme from becoming carcinogenic."
The finding demonstrates for the first time that DAS triggers a gene alteration in PhIP that may play a significant role in preventing cancer, notably breast cancer, induced by PhIP in well-done meats.
Thomas noted that no studies have shown a link between cooking vegetables and fruits and PhIP, regardless of the method used.
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