快猫短视频

NUTRIENTS called flavonoids may occasionally trigger a deadly form of infant
leukaemia which starts before birth, a new report suggests.

This doesn鈥檛 meant expectant mothers should avoid food containing flavonoids,
however. 鈥淚n whole foods, these chemicals are nutritionally very important,鈥�
says study leader Janet Rowley of the University of Chicago in Illinois. 鈥淏ut
taking too many supplements, and getting too much, might have untoward
别蹿蹿别肠迟蝉.鈥�

Flavonoids are found in, among other things, beer, coffee, chocolate, herbs,
wine, soya, and certain medicines, and there is overwhelming evidence that they
can protect us against disease. Populations whose diets include high levels of
flavonoids have substantially lower rates of breast and prostate cancer, for
instance.

But in the past decade, studies of a gene called MLL on chromosome
11 have provided hints that flavonoids can cause certain rare cancers.
Leukaemias can arise as a side effect of cancer treatment with drugs such as
VP16 (epipodophyllotoxin) which inhibit an enzyme called topoisomerase II.
Crippled topo II leaves breaks in DNA, and these kill rapidly dividing cancer
cells. Unfortunately, this can also cause leukaemia by occasionally making nicks
in, and ultimately rearranging the MLL gene.

Nearly identical MLL rearrangements occur in more than two-thirds of
infant leukaemias that start in the womb. Since some flavonoids also inhibit
topo II, Julie Ross of the University of Minnesota Cancer Center in Minneapolis
and her colleagues suggested six years ago there might be a link.

Rowley鈥檚 team put the idea to the test by comparing how well flavonoids could
cut the MLL gene in human cells. Out of 20 flavonoids tested, 10 cut
the gene in the same region as VP16 and two鈥攓uercetin, which is found in
fruits and vegetables, and fisetin, found in herbs鈥攚ere just as effective
at cutting the gene as the cancer drug. 鈥淚t鈥檚 quite amazing they鈥檙e so potent,鈥�
says Rowley.

She adds that since infant leukaemias are exceedingly rare鈥�37 cases per
million births鈥攁nd flavonoids are everywhere, a number of factors must
conspire to turn these normally beneficial nutrients into a trigger for cancer.
For instance, a genetically vulnerable fetus might only get leukaemia if it
receives a surge of flavonoids at a time during development when it is
particularly susceptible. Indeed, Rowley鈥檚 team and other researchers are
already looking for such genetic factors. 鈥淭he message is not that fruit and
vegetables are bad for you,鈥� says Ross. 鈥淚t鈥檚 much more complex.鈥�

Ingested flavonoids might never reach a blood level where they could cut DNA,
says nutrition and cancer specialist John Milner of Pennsylvania State
University in University Park. 鈥淚 just want to see it repeated in an animal
model.鈥� But Rowley points out that some flavonoids are already being tested as
cancer treatments at blood levels far in excess of those that will nick the
MLLgene. Her work suggests that one unwelcome side effect of this treatment
could be topo II-induced leukaemias. 鈥淭his is one reason I wanted to get this
result out there now,鈥� she says.