Aardbeien
voor een goed geheugen.*
In
aardbeien zit de bioactieve stof fisetine, een stof die de groei van hersencellen
en het ontstaan van verbindingen tussen hersencellen bevordert. De
effecten van fisetine zijn bestudeerd bij muizen. De beestjes kregen twee
voorwerpen te zien gedurende bepaalde tijd. De volgende dag werd één van de
voorwerpen vervangen door een nieuwe. Als de muizen de voorwerpen van de vorige
dag goed konden herinneren, besteden ze minder tijd aan het besnuffelen van de
oude en wordt alleen het nieuwe voorwerp uitgebreid geïnspecteerd. De muizen
die fisetine binnen kregen, bleken zich de al bekende voorwerpen beter te
herinneren. Hoewel in het onderzoek bleek dat fisetine geheugencellen kan vormen,
verbeteren en beschermen, wil dat niet zeggen dat daarmee celafbrekende ziektes
zoals Alzheimer verholpen kunnen worden. De conclusie van het onderzoek is dat
fisetine alleen symptomen van geheugenverlies zou kunnen onderdrukken. Volgens de
onderzoekers is het goede nieuws dat de bioactieve stof fisetine volop voorkomt
in aardbeien. Echter, omdat het gaat om een natuurlijke voedingsstof is vanuit
financieel oogpunt de belangstelling voor vervolgonderzoek gering. En om het
gunstige effect van fisetine bij mensen te bereiken, zou misschien een flinke
hoeveelheid aardbeien genuttigd moeten worden. Fisetine komt overigens ook voor
in tomaten, uien, kiwi, sinaasappels, druiven en appels.
A
Natural Chemical Found In Strawberries Boosts Memory In Healthy Mice
Mothers
have long exhorted their children to eat their fruit and vegetables. But once
kids are beyond mom's watchful eye, the hated greens often go the way of Barbie
dolls and power rangers. Now, there's another reason to reach for colorful
fruits past adolescence.
Fisetin, a naturally occurring flavonoid commonly found in strawberries and
other fruits and vegetables, stimulates signaling pathways that enhance
long-term memory, report researchers at the Salk Institute for Biological
Studies in this week's Online Early Edition of the Proceedings of the
National Academy of Sciences.
Roughly one third of people age 60 and over suffer from memory and recall woes.
As the average age of the U.S. population climbs, the number of people ravaged
by Alzheimer's disease and other forms of dementia continues to rise.
"Since the development of a basic understanding of the biochemical pathways
involved in memory formation, the holy grail of CNS research in the
pharmaceutical industry is the identification of a safe, orally active drug that
activates memory-associated pathways and enhances memory," says lead author
Pamela Maher, Ph.D., a researcher in the Cellular Neurobiology Laboratory at the
Salk Institute.
Maher hit upon the beneficial effects of fisetin when she screened a collection
of flavonoids, substances with anti-oxidant activities found in many plants, for
their neuroprotective abilities in tissue culture models of neurodegenerative
disease.
Maher found that some of those compounds, including fisetin, induced
differentiation or maturation of neural cells. Maher explains, "That
suggested to us that these compounds might be particularly beneficial, since
they might not only protect neural cells from dying but might be able to promote
new connections between nerve cells."
Interestingly the signaling pathway activated by fisetin in neural
differentiation also played a role in memory formation, a process
neuroscientists call "long-term potentiation" or LTP. LTP allows
memories to be stored in the brain by strengthening connections between neurons.
"We wanted to find out whether we could detect any effects of fisetin on
long-term potentiation and the formation of memories in animals," Maher
recalls.
Since the hippocampus plays an important role in establishing new memories,
Maher, and co-authors Tatsuhiro Akaishi and Kazuho Abe, both at Musashino
University in Tokyo, Japan, extended the study and found that fisetin activates
the same signaling pathway in rat hippocampal tissues and also induces LTP.
Next, they tested fisetin's effects in a so-called object discrimination test in
mice. The mice get to explore two objects for a certain amount of time. The next
day, one of the objects is replaced with a novel one. If the mice remember the
object from the day before, they spend less time exploring the old one and
instead turn their attention to the novel object. Indeed, mice administered a
single dose of fisetin could better recall familiar objects. In fact, fisetin
worked almost as well as rolipram, a substance known to enhance memory.
Memory loss caused by neurodegenerative disease occurs due to loss of neurons, a
situation very different from that of healthy mice. Thus the ultimate goal is to
stop neuronal loss. Nevertheless, memory-enhancing drugs can improve Alzheimer's
disease symptoms.
The observations that fisetin protects and promotes survival of cultured neurons
and boosts memory in healthy mice make it a promising candidate for further
studies. Notes Maher, "This is the first time that the function of a
defined natural product has been characterized at the molecular level in the
central nervous system and also shown to enhance both LTP in vitro and long-term
memory in vivo."
"The good news is that fisetin is readily available in strawberries but the
bad news is that because of its natural product status there may be little
financial interest in getting it into human clinical trials for diseases
associated with memory loss such as Alzheimer's, where the treatment options are
currently very limited," says Maher.
Besides strawberries, fisetin is found in tomatoes, onions, oranges, apples,
peaches, grapes, kiwifruit and persimmons. Gingko biloba leaves, while rich in
other flavonoids, do not contain fisetin.
While eating strawberries sounds like an enjoyable alternative to popping a pill,
Maher cautions that it would take about 10 pounds a day to achieve a beneficial
effect, which might prove too much even for the most avid strawberry lovers.
###
The Salk Institute for Biological Studies in La Jolla, California, is an
independent nonprofit organization dedicated to fundamental discoveries in the
life sciences, the improvement of human health and the training of future
generations of researchers. Jonas Salk, M.D., whose polio vaccine all but
eradicated the crippling disease poliomyelitis in 1955, opened the Institute in
1965 with a gift of land from the City of San Diego and the financial support of
the March of Dimes.
(Nov.
2006)