TITLE:
Evaluation of the Estrogenic Activity of Pueraria (Kudzu) Flower Extract and Its Major Isoflavones Using ER-Binding and Uterotrophic Bioassays
AUTHORS:
Tomoyasu Kamiya, Akira Takano, Yayoi Kido, Yuki Matsuzuka, Mayu Sameshima-Kamiya, Masahito Tsubata, Motoya Ikeguchi, Kinya Takagaki, Junei Kinjo
KEYWORDS:
Estrogenic Activity; 6-Hydroxygenistein; Kudzu Flower Extract; Safety Evaluation; Tectorigenin
JOURNAL NAME:
Pharmacology & Pharmacy,
Vol.4 No.2,
April
28,
2013
ABSTRACT: Pueraria flower extract (PFE) is a hot
water extract of the Kudzu flower (Pueraria thomsonii). Tea made from dried Kudzu
flower is widely used inChina,
and PFE is utilized as a nutritional supplement inJapan. PFE contains unique
isoflavones such as 6-hydroxygenistein 6,7-di-O-glucoside (6HGDG),
tectorigenin 7-O-xylosylglucoside (TGXG), and tectoridin. 6HGDG is known
to be metabolized into 6-hydroxygenistein, and TGXG and tectoridin are known to
be metabolized into tectorigenin in the digestive tract. Isoflavones typically
mimic the effects β-estradiol has on
estrogen receptors (ERs) and may influence the female genital system in the
case of excessive intake. As a result, the upper limit of safe daily
consumption of soy isoflavones has been enforced inJapan. In the present study,
ER-binding assays were performed using the EnBio estrogen receptor/cofactor assay
system to compare the estrogenic activity of 6-hydroxygenistein
and tectorigenin to that of the soy isoflavone genistein. In addition,
uterotrophic bioassays were performed to investigate the estrogenic effects of
PFE in vivo. The ER-binding assays revealed that the ER-binding affinities
of 6-hydroxygenistein and tectorigenin were approximately 0.01 - 0.04 that of genistein. Soy
isoflavone products also induced an increase in uterine wet and blotted weight
at doses of 500 mg/kg and 1000 mg/kg, whereas PFE did not cause adverse
estrogenic effects, even at a dose of 1000 mg/kg. Based on these results, PFE does
not appear to contain compounds with strong estrogenic
activity or cause adverse estrogenic effects in vivo. Importantly, the
results of this study confirm the safety of PFE as a food supplement.