The isoflavonoid aglycone-rich fractions of Chungkookjang,
fermented unsalted soybeans, enhance insulin signaling and peroxisome
proliferator-activated receptor-γ activity in vitro
Affiliations: Food Functional Research Division, Korean Food
Research Institutes, Korea | Department of Food and Nutrition, Hoseo University,
Korea | Department of Food Science and Technology, ChonBuk
National University, Korea
Note: [] Address for correspondence: Sunmin Park, Food and Nutrition,
Hoseo University, 165 Sechul-Ri Baebang-Myun Asan-Si Chungnam-Do 336-795,
Korea. Tel.: +82 41 540 5633; Fax: +82 41 548 0670; E-mail:
[email protected]
Abstract: We investigated anti-diabetic candidates and their mechanisms from
the fractions of Chungkookjang (CKJ), a traditional fermented unsalted soybean,
by investigating insulin signaling, peroxisome proliferator-activated receptor
(PPAR)-γ activity and glucose-stimulated insulin
secretion, in vitro. Cooked soybeans (CSB) and CKJ, fermented
predominantly with Bacillus subtilis, were extracted by 70% EtOH
followed by an XAD-4 column chromatography with a serial mixture of solvents
comprised of MeOH and water. During fermentation, the contents of isoflavonoid
aglycones were elevated, and the fractions enriched with aglycones enhanced
insulin-stimulated glucose uptake in 3T3-L1 adipocytes. This increase in
glucose uptake resulted from stimulating a translocation of the glucose
transporter (GLUT)-4 into the plasma membrane through the phosphorylation of
insulin receptor substrate (IRS)-1 and Akt. Especially, daidzein enriched
fractions elevated insulin-stimulated glucose uptake by acting as
PPAR-γ agonist up to levels exhibited when 10 nM
insulin is administered. Fractions containing small peptides with low polarity
in CKJ slightly increased glucose-stimulated insulin secretion. The data
suggest that an increase in isoflavonoid aglycones in CKJ, in comparison to
CSB, enhances glucose utilization via activating insulin signaling and
stimulates PPAR-γ activity in adipocytes. In addition,
CKJ contains small peptides improving glucose-stimulated insulin secretion in
insulinoma cells. Overall, CKJ is superior to CSB in anti-diabetic action.
