Pesticide and Environmental Update
How
Plants Protect Us
Unmasking the Secret Power of Phytochemicals
Susan Zunino and David Storms, molecular biologists at the ARS Western
Human Nutrition Research Center, Davis, California, are using
fluorescence-activated cell sorting to analyze apoptosis (programmed cell
death) in leukemia cells after exposure to different antioxidant
phytochemicals. Their research has shown that certain phytochemicals can
kill these leukemia cells.
Rosemary, the fragrant herb that enlivens roast chicken and other
favorites, and turmeric, the mainstay spice of curry dishes, contain
powerful natural compounds that, in test tubes, can kill cells of a
childhood cancer. What’s more, grapes, strawberries, and other familiar
fruits—and some vegetables—also have chemicals that can destroy the
cells of this cancer, known as “acute lymphoblastic leukemia.”
Susan J. Zunino, an Agricultural Research Service molecular biologist,
leads the nutrition-focused research that has resulted in these first-ever
findings. She’s investigating the health-imparting effects of plant
chemicals, or phytochemicals, using laboratory cultures of both healthy
human blood cells and cancerous ones as her models.
Zunino is based at the agency’s Western Human Nutrition Research
Center in Davis, California, about an hour’s drive northeast of San
Francisco. She’s collaborating in the investigations with molecular
biologist David Storms, at the Davis center; Jonathan Ducore, at the
University of California-Davis Cancer Center; and Navindra Seeram, at the
University of California-Los Angeles.
Zunino’s pioneering studies, published in Cancer Research and Cancer
Letters, reveal the previously unknown ability of about a half-dozen
phytochemicals to stop growth of this type of leukemia. The findings are
of interest to cancer researchers and to nutrition researchers exploring
the health benefits of compounds in the world’s edible fruits,
vegetables, herbs, and spices.
Strawberries and other familiar fruits—and some vegetables—contain
natural phytochemicals that can destroy leukemia cells.
Death of Leukemia Cells: How Do Phytochemicals Triumph?
For the most part, scientists don’t yet have all the details about
how phytochemicals bolster healthy cells and battle harmful ones. That’s
true even for better-known phytochemicals such as the resveratrol in red
grapes, blueberries, and some other fruits.
Zunino’s investigations provide some new clues about how
phytochemicals attack cancer cells. She has studied carnosol from
rosemary, curcumin from turmeric, resveratrol from grapes, and ellagic
acid, kaempferol, and quercetin in strawberries. The work demonstrated the
ability of these phytochemicals to kill the acute lymphoblastic leukemia
cells and also suggested ways in which the compounds might do that.
For example, Zunino and colleagues showed that the phytochemicals
interfere with the orderly operations of mitochondria, the miniature
energy-producing power plants inside cells. Without energy, cells die.
Mitochondria exposed to resveratrol and the other phytochemicals became
inoperative. But more work is needed to fully understand how the
phytochemicals achieved that. And the team wants to know more about the
phytochemicals’ other modes of action that resulted in the cancer-cell
death.
Scientists at ARS’s Western Human Nutrition Research Center have
determined that some component of table grapes can prevent progression of
type 1 diabetes in mice and increase their survival.
Can Phytochemicals Help Prevent Diabetes?
In related research, Zunino, working with Storms and Charles Stephensen,
a physiologist at the Davis research center, determined for the first time
that some component of table grapes prevented the progression of type 1
diabetes in mice and increased their survival. That was in contrast to
diabetic mice that were not fed grapes.
Scientists provided the fruit in the form of a freeze-dried powder made
from table grapes, the kind sold fresh in the produce section of
supermarkets. The powder, provided by the California Table Grape
Commission, made up 1 percent of the chow fed to some of the mice. That’s
the human equivalent of about six servings of grapes per day.
Zunino’s experiment apparently is the first to show a link between
eating grapes and preventing progression of type 1 diabetes. If the
results from this study of 30 laboratory mice hold true for humans, the
research could offer new options for protection against this chronic
autoimmune disease.
According to the National Institutes of Health, an estimated 1 in every
400-600 children and adolescents in the U.S. population has type 1
diabetes.
Right now, the researchers don’t know which grape compounds provided
the protective effect. Similarly, the exact sequence of steps that led to
the protection is also not yet proven. But the scientists think that the
grape phytochemicals may have prevented unwanted entry of immune cells
into the pancreas.
Mice fed the grape powder had fewer immune cells in the pancreas than
did the other mice in the experiment. But what’s the relation between
immune cells in the pancreas and type 1 diabetes?
Immune cells in the pancreas can mistakenly attack specialized cells
known as “beta cells.” Beta cells produce insulin, which is needed to
help regulate the amount of sugar in the bloodstream. If immune cells in
the pancreas attack and kill beta cells, the pancreas can run out of beta
cells. When that happens, type 1 diabetes can result.
People with type 1 diabetes have to carefully monitor the amounts of
sugar-containing foods they eat, including sweet, fresh table grapes. How
ironic that this luscious fruit might actually hold a key to preventing
the progression of type 1 diabetes. This may be a perplexing riddle of
Nature—perhaps one that Zunino’s team will soon solve.—By Marcia
Wood, Agricultural Research Service Information Staff.
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