Chemist Norberta Schoene
prepares blood samples for
analysis on a flow cytometer. These blood samples were
obtained from rats and used
to study the effects of
isoflavones on platelet function.
(K8744-1) |
You've just sat down to dinner, and
the phone rings. A pushy salesperson. Then your neighbor starts his lawn mower.
After dinner, your daughter turns up the volume on her heavy metal CD. A little
later your 3-year-old son throws a tantrum over going to bed. Jangled?
Perhaps that's how your cells feel when too many chemical signals—too many
orders to do something—get through. And your cells may react before they
should. For example, if an order to divide gets "heard" by too many
cells too often, it can lead to unrestrained growth, as in cancer, or an
overactive immune response.
Likewise, if your blood cells are told to react to certain chemicals in the
blood but tend to overreact, it can lead to cardiovascular disease and heart
attack.
Researchers now believe that poor regulation of signal transduction is a major
factor behind some chronic diseases. Miraculously, cells usually do a pretty
good job of filtering out noise and staying on task. "Foods play an
important role," says ARS nutrition
chemist Norberta Schoene. Soy, with its isoflavones like genistein and
daidzein, is an example of a food that can affect cell response.
Japanese diets average about 10 times more soy than North American diets. And
Japanese people have a lower incidence of cancer and heart disease. Tofu,
tempeh, and miso are some soy foods rich in isoflavones.
In the late 1980s, Schoene says, researchers showed in test tube studies that
genistein inhibits enzymes that connect the lines of communication from the
cell's membrane into its interior. Her recent study gives the first direct
evidence of this dampening effect in an animal.
Schoene fed young rats diets containing soy protein with high or low genistein
levels for 4 weeks. Then she measured the response of the animals' blood
platelets in three different tests. Platelets are quite sensitive to outside
signals because they have to clump together to prevent blood loss. So they
serve as a good model for studying cell signaling, she explains.
First, animals getting the genistein-enriched diet had significantly more
platelets in the unactivated disk shape. Those getting little genistein had
more of the rounder, activated platelets. "That's consistent with reports
that platelets are apparently larger in activating environments such as those
resulting from smoking, diabetes, and heart disease," she says.
Second, hydrogen peroxide production—a necessary step in signal
transduction—decreased in blood platelets of rats on the high-genistein
diet.
Third, the signal-carrying proteins from the high-genistein rats were less
likely to have phosphate groups attached. "These phosphate groups help
build the protein scaffolding that carries the signal," says Schoene.
Her hypothesis: "Isoflavones may reduce overresponsive, dysfunctional
signaling that leads to some chronic diseases."
Schoene says the genistein-rich diets had the equivalent of twice the average
Japanese genistein intake. But some Japanese eat as much as the rats got, she
noted.
The genistein-poor diet, on the other hand, was equivalent to the U.S. diet in
genistein levels.—By Judy
McBride, Agricultural Research Service Information Staff.
This research is part of Human Nutrition, an ARS National Program (#107)
described on the World Wide Web at
http://www.nps.ars.usda.gov/programs/appvs.htm.
Norberta W. Schoene is at
the USDA-ARS Nutrient
Requirements and Functions Laboratory, Bldg. 307, Room 215, 10300 Baltimore
Ave., Beltsville, MD 20705-2350; phone (301) 504-8388, fax (301) 504-9062.
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