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. 2012 May 2;9(1):37.
doi: 10.1186/1743-7075-9-37.

Meju, Unsalted Soybeans Fermented With Bacillus Subtilis and Aspergilus Oryzae, Potentiates Insulinotropic Actions and Improves Hepatic Insulin Sensitivity in Diabetic Rats

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Free PMC article

Meju, Unsalted Soybeans Fermented With Bacillus Subtilis and Aspergilus Oryzae, Potentiates Insulinotropic Actions and Improves Hepatic Insulin Sensitivity in Diabetic Rats

Hye Jeong Yang et al. Nutr Metab (Lond). .
Free PMC article

Abstract

Background: Although soybeans have the ability to attenuate insulin resistance, it is insufficient to alleviate type 2 diabetic symptoms and different types of fermented soybeans may have even better anti-diabetic effects. Meju, unsalted fermented soybeans exhibited better insulin sensitizing and insulinotropic actions than unfermented cooked soybeans (CSB). We investigated whether meju fermented in the traditional (TMS) manner for 60 days and meju fermented in the standardized (MMS) method inoculating Bacillus subtilis and Aspergillus oryzae for 6 days modulated insulin resistance, insulin secretion, and pancreatic β-cell growth and survival in 90% pancreatectomized (Px) diabetic rats, a moderate and non-obese type 2 diabetic animal model.

Methods: Diabetic rats were divided into 3 groups: 1) TMS (n = 20), 2) MMS (n = 20) or 3) casein (control; n = 20). Rats were provided with a high fat diet (40 energy % fat) containing assigned 10% meju for 8 weeks. At the end of experiment insulin resistance and insulin secretion capacity were measured by euglycemic hyperinsulinemic clamp and by hyperglycemic clamp, respectively. Additionally, β-cell mass and islet morphohometry were determined by immunohistochemistry and insulin signaling in the liver was measured by western blot.

Results: TMS and MMS increased isoflavonoid aglycones much more than CSB. CSB and TMS/MMS improved glucose tolerance in diabetic rats but the mechanism was different between treatments (P < 0.05). CSB enhanced peripheral insulin sensitivity including hepatic insulin sensitivity better than the control but TMS and MMS enhanced only hepatic insulin sensitivity through activating insulin signaling in diabetic rats (P < 0.05). However, TMS and MMS, but not CSB, potentiated glucose-stimulated insulin secretion and β-cell mass (P < 0.05). MMS had better insulinotropic actions than the control (P < 0.05).

Conclusions: The anti-diabetic action of MMS, especially when fermented with Bacillus subtilis and Aspergillus oryzae, was superior to CSB by increasing isoflavonoid aglycones and small peptides with regard to type 2 diabetic rats.

Figures

Figure 1
Figure 1
The changes in serum glucose levels and the area under the curve for serum glucose and insulin during oral glucose tolerance testing. Oral glucose tolerance tests were performed on Px rats fed diets containing 10% cooked soybeans (CSB), meju made in the traditional (TMS) or standardized (MMS) manner, or casein (control), for 8 weeks following oral loading with 2 g glucose per kg body weight. Blood samples were taken at the time points indicated, serum glucose levels (A) were measured, and the area under the curve for glucose and insulin was calculated (B). The sample size in each group was the same as in Table 3. *Significantly different among groups of Px rats at P < 0.05. a,b Means of the bars without a common letter significantly differ at P < 0.05 by Tukey test. Significantly different from Px control at P < 0.05.
Figure 2
Figure 2
Metabolic parameters during euglycemic hyperinsulinemic clamp. After 8 weeks of treatment with four different diets—one containing 10% cooked soybeans (CSB), one containing meju made in the traditional (TMS), one containing meju made in the standardized (MMS) manner, and one containing casein (control)—euglycemic hyperinsulinemic clamp was performed in conscious, free moving and overnight fasted diabetic rats to determine whole body insulin resistance. Whole body glucose infusion rates (GIR) and glucose uptake and hepatic glucose output at basal and clamped states were investigated. The sample size in each group was the same as in Table 4. Means of the bars without a common letter significantly differ at P < 0.05 by Tukey test. Significantly different from Px control at P < 0.05.
Figure 3
Figure 3
Hepatic insulin signaling at the end of experiment. The liver of Px rats injected with 5 U insulin/kg body weight into the inferior vena cava was collected after they were fed with diets containing 10% cooked soybeans (CSB), meju made with traditional (TMS) or standardized (MMS) manner, or casein (control) for 8 weeks. The glycogen and triglyceride contents in the liver were measured (A). In addition, the phosphorylation of Akt and AMPK and the expression of phosphoenolpyruvate carboxykinase (PECK) were measured by immunoblotting method (B). The sample size in each group was 4. a,b Means of the bars without a common letter significantly differ at P < 0.05 by Tukey test.
Figure 4
Figure 4
Insulin secretion capacity during hyperglycemic clamp. At the end of the experimental periods, hyperglycemic clamp was performed on Px rats fed diets containing 10% cooked soybeans (CSB), meju made in the traditional (TMS) or standardized (MMS) manner, or casein (control). During hyperglycemic clamp, serum insulin levels were measured in free-moving and overnight-fasted diabetic rats as serum glucose levels at 5.5 mM above fasting levels were maintained. The sample size in each group was the same as in Table 4. *Significantly different among groups of Px rats at P < 0.05.

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