Long-term consumption of fermented soybean-derived Chungkookjang enhances insulinotropic action unlike soybeans in 90% pancreatectomized diabetic rats.
BACKGROUND
We previously reported that Chungkookjang (CKJ), fermented unsalted soybeans, exhibited better anti-diabetic action than cooked soybeans (CSB) in vitro, but its effectiveness and mechanism have not been studied in vivo.


OBJECTIVE
We investigated whether CKJ modulated insulin resistance, insulin secretion, and pancreatic beta-cell growth and survival in 90% pancreatectomized (Px) diabetic rats.


METHODS
The Px rats weighing 201 +/- 12 g were divided into four groups and fed for 8 weeks with a CSB diet, a CKJ diet, a casein diet, or a casein diet plus rosiglitazone (20 mg/kg body weight/day). With the exception of protein sources and contents of isoflavonoid aglycones and glycosides, the composition of the diets was made identical by adding soybean oil and cellulose to a casein diet. At the end of the experimental periods, hyperglycemic clamp was performed in conscious, unstressed and overnight fasted Px rats to measure insulin secretion capacity. Insulin/IGF-1 signaling was measured by immunoblotting in isolated islets from the treated rats, and beta-cell mass, proliferation and apoptosis were also determined by immunohistochemistry.


RESULTS
After 8-week administration, CSB did not modulate glucose-stimulated insulin secretion, but surprisingly, CKJ enhanced insulin secretion. In addition, CKJ potentiated insulin/IGF-1 signaling in islets via the induction of insulin receptor substrate-2 expression, leading to increasing pancreatic duodenal homeobox-1, insulin promoter transcription factor. In parallel with the enhancement of the signaling, CKJ elevated pancreatic beta-cell hyperplasia by increasing its proliferation and decreasing apoptosis, whereas CSB did not.


CONCLUSIONS
Based on these results, the fermentation of soybeans predominantly with Bacillus subtilis generated isoflavonoid aglycones and small peptides, which improved insulinotropic action in islets of type 2 diabetic rats. Overall, the anti-diabetic action of CKJ was superior to CSB in type 2 diabetic rats.
Kwon
Dae Young
DY
Food Functional Research Division, Korean Food Research Institutes, Seoul, Korea.
Jang
Jin Sun
JS
Hong
Sang Mee
SM
Lee
Ji Eun
JE
Sung
So Ra
SR
Park
Hye Ryeo
HR
Park
Sunmin
S
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D019540:Area Under Curve; D001786:Blood Glucose / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects*; D002470:Cell Survival; D003907:Dexamethasone / Q000494:pharmacology; D003920:Diabetes Mellitus / Q000628:therapy*; D005285:Fermentation; D015309:Glucose Clamp Technique; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D007150:Immunohistochemistry; D007328:Insulin / Q000378:metabolism*; D007333:Insulin Resistance; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D010180:Pancreatectomy; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D045730:Soy Foods; D013025:Glycine max / Q000737:chemistry*
D001786:Blood Glucose; D007004:Hypoglycemic Agents; D007328:Insulin; D003907:Dexamethasone