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Plant-based fat inhibits prostate
cancer-cell growth
May explain why vegetable fats like olive oil appear to reduce
cancer risk
BUFFALO, N.Y. -- Oct. 25, 1998 -- Nutrition researchers at the
University at Buffalo have provided the first evidence that a
minor plant-based fat called B-sitosterol appears to play a role
in inhibiting the growth of human prostate-cancer cells.
They found that the
phytosterol B-sitosterol, a fat abundant in vegetarian diets,
enhances an intracellular signaling system that tells cells not
to divide. The study showed a 28 percent inhibition of prostate-cancer
cell growth after being exposed to B-sitosterol for five days
in vitro.
Atif Awad, Ph.D., head
of UB's Nutrition Program, will present the results on Oct. 25
at the Sixth International Conference of Anti-Cancer Research
in Kallithea, Greece.
"This phytosterol
replaces some of the cell membrane's cholesterol, which changes
the membrane lipid composition in such a way that signal transduction
(secondary messenger activity) is stimulated, and that activation
inhibits cell growth," Awad explained.
"If cell proliferation
can be stopped before it becomes uncontrolled, cancer can be
contained. When we treated prostate-cancer cells with phytosterols,
cell proliferation was inhibited. We have found the same effect
in vitro with breast and colon-cancer cells."
This activity may help
to explain why vegetable fats, such as olive oil, in the diet
reduce the risk of developing certain cancers, Awad said.
The work of Awad and
colleagues is grounded in epidemiologic studies showing that
prostate cancer is less common in Asian countries where diets
are primarily vegetarian, and that rates increase when these
people migrate to western societies where rates are higher and
diets are primarily animal-based.
Working with sterols,
a group of minor lipids, Awad and colleagues set out to examine
the action of the main plant sterol -- B-sitosterol -- and the
main animal sterol -- cholesterol -- on prostate-cancer cell
growth.
In previous work, they
identified activation of a cell-signaling pathway called the
sphingomyelin cycle as one of the inhibitors of cell growth.
The UB researchers felt that increased levels of B-sitosterol
may amplify the signaling capability of two enzymes that act
as second messengers in the sphingomyelin cycle, thus increasing
its inhibitory action.
To test their theory,
the researchers supplemented human prostate-cancer cell tissue
in vitro with either cholesterol or B-sitosterol and monitored
cell growth. They also measured activity of the secondary messenger
enzymes.
Results showed there
were 28 percent fewer cancer cells after five days of B-sitosterol
treatment, compared to tissue cultures supplemented with cholesterol.
This inhibition of
cell proliferation was accompanied by a 50 percent increase in
the activity of one enzyme. The second enzyme showed a 31 percent
increase in activity after one day of treatment; an increase
of 11 percent remained after five days.
"If we know how
phytosterols work, we can advise people how to modify their diets
to reduce their risk of prostate cancer, or we could eventually
design drugs to target this system," he said
Phytosterols are used
widely in Europe to treat enlarged prostate (benign prostatic
hyperplasia), Awad said, and are known to lower the risk of cardiovascular
disease by interfering with cholesterol absorption. B-sitosterol
is abundant in unrefined vegetable oils, such as virgin olive
oil.
Also contributing to
the research were Yongmei Gan, a graduate student in nutrition,
and Carol S. Fink Ph.D., UB clinical assistant professor of nutrition.
The study was supported by a grant from the Allen Foundation.
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