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Broccoli sprouts: an exceptionally rich source
of inducers of enzymes that protect against chemical carcinogens.
Proc Natl Acad Sci U S A 1997 Sep 16;94(19):10367-72
Fahey JW, Zhang Y, Talalay P.
Brassica Chemoprotection Laboratory and Department of Pharmacology and Molecular
Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD 21205,
USA.
Induction of phase 2 detoxication enzymes [e.g., glutathione transferases,
epoxide hydrolase, NAD(P)H: quinone reductase, and glucuronosyltransferases] is
a powerful strategy for achieving protection against carcinogenesis,
mutagenesis, and other forms of toxicity of electrophiles and reactive forms of
oxygen. Since consumption of large quantities of fruit and vegetables is
associated with a striking reduction in the risk of developing a variety of
malignancies, it is of interest that a number of edible plants contain
substantial quantities of compounds that regulate mammalian enzymes of
xenobiotic metabolism. Thus, edible plants belonging to the family Cruciferae
and genus Brassica (e.g., broccoli and cauliflower) contain substantial
quantities of isothiocyanates (mostly in the form of their glucosinolate
precursors) some of which (e.g., sulforaphane or 4-methylsulfinylbutyl
isothiocyanate) are very potent inducers of phase 2 enzymes. Unexpectedly,
3-day-old sprouts of cultivars of certain crucifers including broccoli and
cauliflower contain 10-100 times higher levels of glucoraphanin (the
glucosinolate of sulforaphane) than do the corresponding mature plants.
Glucosinolates and isothiocyanates can be efficiently extracted from plants,
without hydrolysis of glucosinolates by myrosinase, by homogenization in a
mixture of equal volumes of dimethyl sulfoxide, dimethylformamide, and
acetonitrile at -50 degrees C. Extracts of 3-day-old broccoli sprouts
(containing either glucoraphanin or sulforaphane as the principal enzyme
inducer) were highly effective in reducing the incidence, multiplicity, and rate
of development of mammary tumors in dimethylbenz(a)anthracene-treated rats.
Notably, sprouts of many broccoli cultivars contain negligible quantities of
indole glucosinolates, which predominate in the mature vegetable and may give
rise to degradation products (e.g., indole-3-carbinol) that can enhance
tumorigenesis. Hence, small quantities of crucifer sprouts may protect against
the risk of cancer as effectively as much larger quantities of mature vegetables
of the same variety.
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