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Unzipping Zinc’s Secrets
Zinc Reduces Prostate Cancer Risk
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Geneticist Liping Huang's studies of zinc in prostate cells may
reveal more about the role of this nutrient in human prostate
health. |
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June 24, 2005 - Scientists have known for decades
that zinc may play an important part in the health of the prostate, a
walnut-sized gland in males, located near the bladder. The prostate
secretes a zinc-containing liquid that’s a component of seminal fluid.
At the
ARS Western Human Nutrition Research Center in Davis, California,
ARS research geneticist Liping Huang is zeroing in on the role that zinc
in the foods we eat may play in helping men reduce their risk of
prostate cancer.
“Clinical evidence has indicated that cancerous
prostate cells contain less zinc than healthy prostate cells,” Huang
says. But scientists don’t yet have enough evidence to prove that an
increase of zinc in cancerous prostate cells may help prevent their
proliferation.
“Other studies conducted in the United States with
healthy men have shown that they had much more zinc in the prostate than
in other soft organs, such as the liver and kidneys,” she says. “But no
one knows for certain why that’s so.”
Huang recently led a study in which she compared
the amounts of zinc taken up by the prostate’s epithelial cells. She
used noncancerous and cancerous human cells that had the same genetic
source, or genotype.
That’s a critical basis for a well-founded
comparison, because natural differences in our genetic makeup can
influence our ability to take up and use—or metabolize—nutrients in
food, including zinc.
These differences are at the heart of the newly
emerging field of nutritional genomics, or nutrigenomics. This
leading-edge discipline is a new take on genomics—the investigation of
all the genes in an organism.
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 Foods
rich in zinc include chicken, eggs, cheese, oysters, beef, and
peanuts. |
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Without zinc, we
couldn’t survive. |
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We rely on this mineral to help us
taste and digest our food, to grow properly, and even to
breathe. It’s especially important in the development of boys
into men. What’s more, we need zinc to help decode the
instructions in our genetic material, DNA. Our bodies use these
instructions to make the proteins that keep all our complex
internal systems running smoothly. Zinc is an essential
component of about 400 of these proteins.
Despite zinc’s vital role in our
health, our bodies need only trace amounts: Adults require from
8 to 11 mg a day for good health. That’s about the amount in
your favorite zinc-enriched breakfast cereal—such as specially
fortified cornflakes or raisin bran—or in a sizzling, 6-ounce
beef chuck steak, for instance.
Certain seafoods, notably oysters,
along with milk, whole-grain breads, dark-meat poultry, and nuts
like cashews also provide this multipurpose mineral.
Though zinc’s interactions with
cells and molecules are extensive, our knowledge of this mineral
is not. National recommendations for Americans’ daily intake of
zinc only date back to 1974, 30 years later than those for some
other essential metals. |
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Huang’s study provides new details about zinc’s
possible role in preventing cancerous prostate cells from proliferating
and spreading. The research was funded by ARS and a grant from the
National Institutes of Health’s National Center on Minority Health and
Health Disparities.
Huang and co-workers cultured cells in a liquid in
laboratory dishes, then exposed them to zinc for 2 days. The scientists
used zinc sulfate for this phase of the experiment.
The result? “The cancerous cells accumulated about
one-third less zinc than did the noncancerous cells,” Huang reports.
The team also looked for significant differences in
levels of zinc transporter proteins. These specialized proteins ferry
zinc throughout the body, such as from storage in the liver, kidney, or
bone to other sites. The amount of one such zinc transporter
protein—ZIP1—was reduced in the cancerous cells. As a result, those
cells had low ability to take in zinc.
ZIP3: In the Wrong Place
In addition, their analyses showed that even though
a second zinc transporter protein, ZIP3, was present in the cancerous
cells, it wasn’t in its correct location. Says Huang, “This error may
have blunted any of ZIP3’s potential protective effects.”
Huang explains that the study “provides the first
direct comparison of zinc-transporter-protein levels in noncancerous and
cancerous prostate epithelial cells with the same genetic background and
the first evidence of significant differences in the levels and
localizations of the proteins.”
“Though these results are preliminary, they suggest
that reduced levels of one transporter protein and mislocation of
another may play a role in cancer’s progression in the prostate.”
To learn more, the team developed another
experiment with ZIP1, artificially stepping up its manufacture in the
cancerous cells. Says Huang, “We did that by overexpressing the genes
that cue production of this protein.”
“Overexpressing ZIP1 significantly suppressed growth and spread of the
cancerous cells,” she reports. “We don’t yet have enough evidence to say
with certainty that zinc in our foods acts as a chemopreventive. But
zinc’s natural abundance in the prostate of healthy men, and its
performance in our tests, suggest it may be an important natural
defense.”
With further research, perhaps that role will be
added to zinc’s already impressive list of life-giving tasks.—By
Marcia Wood, Agricultural Research Service Information Staff.
This research is part of Human Nutrition, an ARS
National Program (#107) described on the World Wide Web at
www.nps.ars.usda.gov.
Liping Huang is with the USDA-ARS
Western Human Nutrition Research Center, One Shields Ave., Davis, CA
95616; phone (530) 754-5756, fax (530) 754-6015.
"Unzipping Zinc’s Secrets" was
published in the
June 2005 issue of Agricultural Research magazine.
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