7 April 1999
Compounds From Fruits, Vegetables And Grains Slow The Growth Of Human Tumor Cells
Researchers at the University of Wisconsin-Madison report that small concentrations of two compounds from plants can suppress the growth of three kinds of human cancer cells in the laboratory. "Our studies showed that cancer cells were more sensitive to these compounds than normal cells and that the two compounds had a stronger effect when combined than we would have expected from the action of either alone," says Charles Elson, a nutritional scientist at the University. "Our findings strengthen the idea that a diet rich in plants is beneficial because of the large array of plant compounds rather than the singular action of one kind of plant or one compound in plants."
Elson suggests that the anticarcinogenic activity of these and similar plant compounds differs from the mechanism of other agents that block or suppress cancer cell growth. Unless controlled, cancer cells typically live and divide indefinitely. "The two compounds we studied suppress an enzyme," Elson says. "We think that this deprives tumor cells of chemical intermediates they need to multiply."
Studies consistently have shown that people who eat a diet high in fruits, vegetables and grains have a reduced risk of a variety of cancers, including lung, alimentary tract, liver, pancreas, bladder, kidney, breast, cervix and prostate.
While other scientists have been examining non-nutritive compounds in plants, Elson has been studying compounds he calls isoprenoids, a group that includes more than 22,000 compounds. All are derived from a parent compound called mevalonic acid. Limonene and lycopene are examples of isoprenoids that inhibit cancer.
Many isoprenoids contribute to plants' distinctive flavors and fragrances, Elson says. In plants, isoprenoids help regulate germination, growth, flowering, and dormancy while attracting pollinators and protecting plants from insects and fungi.
In the current paper, Elson found that gamma-tocotrienol, a compound found in cereal grains, slowed the growth of cell lines from human leukemia and breast cancer. They also tested beta-ionone - an isoprenoid found widely in fruits and vegetables. Beta-ionone is related structurally to beta carotene, the precursor of vitamin A. Elson showed that beta-ionone also suppressed the growth of cell lines for human leukemia and breast cancer, as well as human colon cancer.
Elson found that the isoprenoids interfered with the maturation of lamin B, a material cells need when they divide. Many of the tumor cells treated with the isoprenoids accumulated in a pre-division phase while many others entered apoptosis, or programmed cell death. The researchers showed that the isoprenoids suppressed the activity of 3 hydroxy-3-methyglutaryl coenzyme A (HMG CoA) reductase, an enzyme critical for the maturation of lamin B as well as the synthesis of cholesterol.
The nutritional scientist does not anticipate that his research will lead to a single critical isoprenoid or vegetable that people can eat to protect themselves from cancer. "These compounds act as a group to inhibit cancer growth," he says, "with some enhancing the effectiveness of others."
Nor does Elson believe in an exclusively vegetarian diet.
"I don't think that it's the presence of meat in diets that leads to health problems, but the lack of enough fruits, grains and vegetables. The people who eat a lot of animal products are often the same individuals that don't eat enough fruits and vegetables," he says.