Puerariae flower extract (PFE) is a crude extract of the Kudzu flower. Previous studies have shown that PFE supplementation exerts anti-obesity and anti-fatty liver effects in high-fat diet-fed mice. In this study, we aimed to identify the PFE components responsible for these effects and to determine their influence on energy expenditure and uncoupling protein 1 (UCP1) expression. Experiments were conducted on C57BL/6J male mice classified into 3 groups: (1) high-fat diet-fed (HFD), (2) high-fat diet-fed given PFE (HFD + PFE), and (3) high-fat diet-fed given the PFE isoflavone-rich fraction (HFD + ISOF). All groups were fed for 42 days. The HFD + PFE and HFD + ISOF groups showed significant resistance to increases in body weight, hepatic triglyceride level, and visceral fat compared to the HFD group. These groups also exhibited significant increases in oxygen consumption and UCP1-positive brown adipose tissue (BAT) area. Our results demonstrate that the active ingredients in PFE are present in the ISOF and that these compounds may increase energy expenditure by upregulation of BAT UCP1 expression. These findings provide valuable information regarding the anti-obesity effects of isoflavones.

Kudzu, a leguminous plant, has long been used in folk medicine. In particular, its flowers are used in Japanese and Chinese folk medicine for treating hangovers. We focused on the flower of Kudzu (Puerariae thomsonii), and we previously reported the antiobesity effect of Puerariae thomsonii flower extract (PFE) in humans. In this study, we conducted an animal study to investigate the effect of PFE on visceral fat and hepatic lipid levels in mice with diet-induced obesity. In addition, we focused on gene expression profiles to investigate the antiobesity mechanism of PFE. Male C57BL/6J mice were fed a high-fat diet (HFD) or an HFD supplemented with 5% PFE for 14 days. PFE supplementation significantly reduced body weight and white adipose tissue (WAT) weight. Moreover, in the histological analysis, PFE supplementation improved fatty liver. Hepatic reverse transcription-polymerase chain reaction revealed that PFE supplementation downregulated acetyl-CoA carboxylase expression. For adipose tissue, the expressions of hormone-sensitive lipase in WAT and uncoupling protein 1 in brown adipose tissue (BAT) were significantly upregulated. These results suggest that PFE exerts antiobesity and antifatty liver effects in high-fat diet-induced obese mice through suppressing lipogenesis in the liver, stimulating lipolysis in WAT, and promoting thermogenesis in BAT.

Pueraria flower extract (PFE) is a hot water extract of the Kudzu flower (Pueraria thomsonii). Tea made from driedKudzu flower is widely used in China, and PFE is utilized as a nutritional supplement in Japan. 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 in Japan. 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.