Phytoestrogens are a group of naturally occurring diphenolic compounds present in legumes, whole grains, fruits, and vegetables. High consumption of
phytoestrogen-rich foods has been linked to a reduced incidence of
cancers at many sites. A potential mechanism of dietary anticarcinogenesis involves the induction of detoxifying phase II
enzymes such as
NADPH:
quinone reductase (QR). This study, therefore, examined the ability of six prominent
phytoestrogens to affect cellular expression of QR in colonic cells. Colo205 cells were cocultured with various concentrations (0.001 to 10.0 microM) of each
phytoestrogen, and then were assessed for cytosolic QR activity, cell growth, and QR
mRNA expression. A maximum of 6- to 8-fold induction of QR activity was observed for both
enterolactone and
genistein, although at high concentrations they showed an adverse effect upon cell growth. The concentrations required to double the specific activity of QR for
enterolactone and
genistein were about 0.04 and 0.14 microM, respectively. A 2- to 3-fold increase of QR specific activity was found with either
biochanin A (1.1 microM) or
coumestrol (12.0 microM) treatments. No significant effects were found for
daidzein or
formononetin treatments. QR induction was further confirmed by using reverse transcription-polymerase chain reaction (RT-PCR) techniques to measure
mRNA expression. A significant correlation between the expression of QR
mRNA and the corresponding QR activity was observed (r = 0.76, P < 0.001). The results demonstrated that certain dietary
phytoestrogens are capable of QR induction in Colo205 cells by promoting QR
mRNA expression, and suggest a novel mechanism by which dietary
phytoestrogens may be implicated in
colorectal cancer chemoprevention.