Flavonoïden
in hop veelbelovend tegen kanker.*
Al
tien jaar geleden werden de goede eigenschappen van de bioactieve stof
xanthohumol in hop ontdekt doch recentelijk doen meer en meer wetenschappers
onderzoek naar de kanker voorkomende eigenschappen. Xanthohumol is een flavonoïde
die alleen in hop voorkomt en al sinds 1913 bekend is. Tot de negentiger jaren
kenden alleen bierbrouwers het belang van hop voor een goede smaak van het bier.
In bier zit niet veel xanthohumol, behalve in speciaal bier zoals stout en ale. In Duitsland onderzoekt men of
de hoeveelheid in het bier te verhogen is. Inmiddels wordt ook al hard gewerkt
aan xanthohumol in de vorm van supplementen, omdat in steeds meer onderzoeken de
volgende positieve eigenschappen naar voren komen:
Xanthohumol
is een sterke antioxidant, sterker dan vitamine E; het heeft grote eigenschappen
om kanker te kunnen voorkomen; het zou zelfs een hormoonachtige werking hebben
en kan gebruikt worden i.p.v. de bekende (of beruchte) hormoontherapieën bij
vrouwen tegen bijv. osteoporose; en het verlaagd het LDL , het slechte
cholesterol.
Anti-cancer
Compound In Beer Gaining Interest
A
compound found only in hops and the main product they are used in - beer - has
rapidly gained interest as a micronutrient that might help prevent many types of
cancer.
Researchers
at Oregon State University first discovered the cancer-related properties of
this flavonoid compound called xanthohumol about 10 years ago. A recent
publication by an OSU researcher in the journal Phytochemistry outlines the
range of findings made since then. And many other scientists in programs around
the world are also beginning to look at the value of these hops flavonoids for
everything from preventing prostate or colon cancer
to hormone replacement therapy for women.
"Xanthohumol
is one of the more significant compounds for cancer chemoprevention that we have
studied," said Fred Stevens, a researcher with OSU's Linus Pauling
Institute and an assistant professor of medicinal chemistry in the College of Pharmacy.
"The published literature and research on its properties are just exploding
at this point, and there's a great deal of interest."
Quite
a bit is now known about the biological mechanism of action of this compound and
the ways it may help prevent cancer or have other metabolic value. But even
before most of those studies have been completed, efforts are under way to
isolate and market it as a food supplement. A "health
beer" with enhanced levels of the compound is already being developed.
"We
can't say that drinking beer will help prevent cancer," Stevens said.
"Most beer has low levels of this compound, and its absorption in the body
is also limited. But if ways can be developed to significantly increase the
levels of xanthohumol or use it as a nutritional supplement - that might be
different. It clearly has some interesting cancer chemopreventive properties,
and the only way people are getting any of it right now is through beer
consumption."
Xanthohumol
was actually first discovered in 1913, isolated as a yellow substance found in
hops. Researchers started studying its molecular structure in the 1950s, but for
decades the only people who showed any real interest in it were brewers, who
were trying to learn more about how hops help impart flavor to beer.
In
the 1990s, researchers at OSU, including Stevens and toxicologist Don Buhler,
began to look at the compound from another perspective - its anti-cancer
properties. It showed toxicity to human breast, colon and ovarian cancer cells,
and most recently has shown some activity against prostate
cancer in OSU studies.
Xanthohumol
appears to have several mechanisms of action that relate to its cancer
preventive properties, scientists say. It, and other related flavonoid compounds
found in hops, inhibit a family of enzymes, commonly called cytochromes P450
that can activate the cancer process. It also induces activity in a "quinone
reductase" process that helps the body detoxify carcinogens. And it
inhibits tumor growth at an early stage.
In
recent years, it has also been shown that some prenylflavonoids found in hops
are potent phytoestrogens, and could ultimately have value in prevention or
treatment of post-menopausal "hot flashes" and osteoporosis - but no
proper clinical trials have been done to study this.
Information
about these compounds appears to be spreading. Hop-containing herbal
preparations are already being marketed for breast enlargement in women, the OSU
research report said, without waiting for tests to verify their safety or
efficacy. And a supposed "health" beer is being developed in Germany
with higher levels of xanthohumol.
It's
possible, scientists say, that hops might be produced or genetically engineered
to have higher levels of xanthohumol, specifically to take advantage of its
anti-cancer properties. Some beers already have higher levels of these compounds
than others. The lager and pilsner beers commonly sold in domestic U.S. brews
have fairly low levels of these compounds, but some porter, stout and ale brews
have much higher levels.
Ideally,
researchers say, cancer chemoprevention is targeted at the early stages of
cancer development and prevented by long-term exposure to non-toxic nutrients,
food supplements or drugs that prevent the formation of cancers. With its broad
spectrum activity, presence in food products, and ability to inhibit cancer at
low concentrations, xanthohumol might be a good candidate for that list, experts
say.
Xanthohumol also appears to have a role as a fairly powerful antioxidant - even more than vitamin E. And it has shown the ability to reduce the oxidation of LDL, or bad cholesterol. (December 2005)
