Soybean diet improves insulin secretion through activation of cAMP/PKA pathway in rats

Black soybean seed coat polyphenols have different effects on glucose and lipid metabolism in growing and young adult mice

Black soybean contains flavan-3-ols and cyanidin 3-O-glucoside in its seed coat. Polyphenol-rich black soybean seed coat extract (BE) possesses various health benefits, such as antioxidant, anti-obesity, and anti-hyperglycemic effects. However, these functions have been evaluated mainly in the growing stage of animals, and there is no comparison data for different life stages. In this present study, we compared the effect of BE in growing (5-week old) and young adult (22-week old) ICR male mice. These mice were given an AIN 93M diet containing 2.0% BE for 4 weeks. BE did not affect body weight gain in both growing and young adult mice, but it suppressed mesenteric and subcutaneous white adipose tissue weights and decreased the cell size. BE also significantly suppressed plasma free-fatty acid levels. The effect of both BE and life stages were observed in the protein expression of adipogenesis-related transcription factors; in particular, BE suppressed the expression of C/EBPα and PPARγ. No significant change was observed in lipolysis and lipogenesis factors in the white adipose tissue and liver. Alternatively, BE showed low glucose tolerance without affecting plasma insulin levels after glucose loading in young adult mice, as seen from the results of the oral glucose tolerance test. However, plasma glucose and insulin levels remained unchanged at the end of the experimental period. In conclusion, these results strongly suggest that the health-beneficial effects of BE may alter in mice at different life stages.

Nutritional recovery with a soybean diet impaired the glucagon response but did not alter liver gluconeogenesis in the adult offspring of rats deprived of protein during pregnancy and lactation

Nutritional recovery of early malnutrition with a soybean diet reduces liver glycogen stores in the fed state and produces liver insulin resistance. We investigated whether nutritional recovery on a soybean flour diet alters hepatic gluconeogenesis in the adult offspring of rats deprived of protein during pregnancy and lactation. Male rats from mothers that were fed either 17% (C) or 6% (L) protein during pregnancy and lactation were maintained on a 17% casein (CC, n = 16 and LC, n = 17), 17% soybean flour (CS, n = 10 and LS, n = 10), or 6% casein (LL, n = 10) diet after weaning. The soybean diet reduced basal serum glucose (soybean diet, 5.6 ± 0.6 mmol/L vs. casein diet, 6.2 ± 0.6 mmol/L; p < 0.05) but increased alanine aminotransferase mRNA/GAPDH (soybean diet, 0.062 ± 0.038 vs. casein diet, 0.024 ± 0.011; p < 0.01), phosphoenolpyruvate carboxykinase mRNA/GAPDH (soybean diet, 1.53 ± 0.52 vs. casein diet, 0.95 ± 0.43; p < 0.05), and glycerokinase protein content (soybean diet, 0.86 ± 0.08 vs. casein diet, 0.75 ± 0.11; p < 0.05). The serum glucose concentration (recovered groups, 5.6 ± 0.5 mmol/L vs. control groups, 6.2 ± 0.7 mmol/L; p < 0.05) and phosphoenolpyruvate carboxykinase activity (recovered groups, 2.8 ± 0.6 μU/mg vs. control groups, 3.6 ± 0.6 μU/mg; p < 0.05) were decreased in rats subjected to protein restriction in early life. The glucose area under the curve during the pyruvate tolerance test did not differ among groups, whereas glucose area under the curve after glucagon infusion was reduced by early malnutrition (recovered groups, 4210 ± 572 mg/dL·40 min vs. control groups, 4493 ± 688 mg/dL·40 min; p < 0.001) and by the soybean diet (soybean diet, 3995 ± 500 mg/dL·40 min vs. casein diet, 4686 ± 576 mg/dL·40 min; p < 0.05). Thus, the soybean diet impaired the response to glucagon but did not alter gluconeogenesis.

Comparing isolated soy protein with flaxseed oil vs isolated soy protein with corn oil and wheat flour with corn oil consumption on muscle catabolism, liver function, blood lipid, and sugar in burn patients: a randomized clinical trial

BACKGROUND

There is controversy regarding whether increasing isolated soy protein (ISP) with or without flaxseed oil (FO), as functional foods, would lead to reduce muscle catabolism and cachexia in burn patients.

METHODS

One hundred and eighty-eight patients were assessed for eligibility in this randomized controlled trial. Of these, seventy-three eligible patients (total burn surface area 20-50%) were randomly assigned to three groups, labeled as Control (wheat flour [WF] + corn oil [CO]), ISP + FO, and ISP + CO, to receive these nutrients for three weeks. Weight, body mass index (BMI), serum hepatic enzymes (alanine transaminase [ALT], aspartate transaminase [AST], alkaline phosphatase [ALP]), systemic inflammatory response syndrome (SIRS), 24-h urinary urea nitrogen excretion (UUN), serum creatinine, 24-h urinary creatinine (UUC) excretion, fasting blood sugar (FBS), triglyceride (TG), and cholesterol were measured.

RESULTS

Using analysis of covariance models in the intention-to-treat population (n = 73), we found that at three weeks, patients in the ISP groups had lost significantly less in weight and BMI compared to those in the control group (all P < 0.01). Nitrogen retention and serum creatinine (primary outcomes) increased significantly in the ISP groups compared with the control group. Even after controlling for potential covariates in ANCOVA models, changes in these indices were still statistically significant (P = 0.008 and P = 0.005 for nitrogen balance and serum creatinine, respectively). However, no such significant differences were found between the ISP groups. On the other hand, 24-h UUN, and UUC excretion, serum hepatic enzymes, FBS, TG, and cholesterol were not significant between the groups (P > 0.05).

CONCLUSION

ISP and FO compared to WF and CO reduced muscle catabolism and increased body weight in burn patients.

TRIAL REGISTRATION

Iranian Registry of Clinical Trials, IRCT2014051817740N1 . Registered on 27 June 2014.

Marine Peptides as Potential Agents for the Management of Type 2 Diabetes Mellitus-A Prospect

An increasing prevalence of diabetes is known as a main risk for human health in the last future worldwide. There is limited evidence on the potential management of type 2 diabetes mellitus using bioactive peptides from marine organisms, besides from milk and beans. We summarized here recent advances in our understanding of the regulation of glucose metabolism using bioactive peptides from natural proteins, including regulation of insulin-regulated glucose metabolism, such as protection and reparation of pancreatic β-cells, enhancing glucose-stimulated insulin secretion and influencing the sensitivity of insulin and the signaling pathways, and inhibition of bioactive peptides to dipeptidyl peptidase IV, α-amylase and α-glucosidase activities. The present paper tried to understand the underlying mechanism involved and the structure characteristics of bioactive peptides responsible for its antidiabetic activities to prospect the utilization of rich marine organism proteins.

Nutritional recovery with a soybean diet after weaning reduces lipogenesis but induces inflammation in the liver in adult rats exposed to protein restriction during intrauterine life and lactation

We evaluated the effects of postweaning nutritional recovery with a soybean flour diet on de novo hepatic lipogenesis and inflammation in adult rats exposed to protein restriction during intrauterine life and lactation. Rats from mothers fed with protein (casein) in a percentage of 17% (control, C) or 6% (low, L) during pregnancy and lactation were fed with diet that contained 17% casein (CC and LC groups, resp.) or soybean (CS and LS groups, resp.) after weaning until 90 days of age. LS and CS rats had low body weight, normal basal serum triglyceride levels, increased ALT concentrations, and high HOMA-IR indices compared with LC and CC rats. The soybean diet reduced PPARγ as well as malic enzyme and citrate lyase contents and activities. The lipogenesis rate and liver fat content were lower in LS and CS rats relative to LC and CC rats. TNFα mRNA and protein levels were higher in LS and CS rats than in LC and CC rats. NF-κB mRNA levels were lower in the LC and LS groups compared with the CC and LC groups. Thus, the soybean diet prevented hepatic steatosis at least in part through reduced lipogenesis but resulted in TNFα-mediated inflammation.

Oral administration of soybean peptide Vglycin normalizes fasting glucose and restores impaired pancreatic function in Type 2 diabetic Wistar rats

Vglycin, a natural 37-residue polypeptide isolated from pea seeds in which six half-cysteine residues are embedded in three pairs of disulfide bonds, is resistant to digestive enzymes and has antidiabetic potential. To investigate the pharmacological activity of Vglycin in vivo and to examine the mechanisms involved, the therapeutic effect of Vglycin in diabetic rats was examined. Diabetes was induced in Wistar rats by high-fat diet and multiple streptozotocin intraperitoneal injections. Diabetic rats were treated daily with Vglycin for 4 weeks. Body weight, food intake, fasting plasma glucose and insulin levels were assayed weekly. Glucose and insulin tolerance tests were conducted on Day 29. Subsequently, levels of p-Akt in the liver and pancreas and cleaved PARP, Pdx-1 and insulin in the pancreas were detected by immunoblotting. The morphology of the pancreas and the insulin expression in the pancreas were analyzed by hematoxylin-eosin staining and immunohistochemistry, respectively. Furthermore, human liver-derived cell lines were used to explore the in vitro effects of Vglycin on insulin sensitivity and glucose uptake. Chronic treatment with Vglycin normalized fasting glucose levels in diabetic rats. The improvement in glucose homeostasis and the increased insulin sensitivity mediated by restored insulin signaling likely contributed to decreased food intake and reduced body weight. Vglycin protected pancreatic cells from damage by streptozotocin. Although insulin synthesis and secretion in impaired β-cell were not significantly elevated, islets morphology was improved in the Vglycin-treated groups. These results suggest that Vglycin could be useful in Type 2 diabetes for restoring impaired insulin signaling, glucose tolerance and pancreatic function.

The soybean peptide aglycin regulates glucose homeostasis in type 2 diabetic mice via IR/IRS1 pathway

It has been previously reported that aglycin, a natural bioactive peptide isolated from soybean, is stable in digestive enzymes and has an antidiabetic potential. With a view to explore the pharmacological activity of aglycin in vivo, studies have been conducted to examine its therapeutic effect in diabetic mice, in which it was administered intragastrically as an oral agent. Diabetes was induced in BALB/c mice fed with a high-fat diet and a single intraperitoneal injection of streptozotocin. With onset of diabetes, the mice were administered daily with aglycin (50 mg/kg/d) for 4 weeks. Blood glucose was monitored once a week. Subsequently, skeletal muscle was isolated for assessment in terms of levels of gene and protein IR, IRS1, Akt and glucose transporter 4 (GLUT4). In addition, C2C12 muscle cells as an in vitro diabetic model were used to investigate the effect of aglycin on glucose uptake. Treatment with aglycin was found to be significantly effective in controlling hyperglycemia and improving oral glucose tolerance. Furthermore, aglycin enhanced glucose uptake and glucose transporter recruitment to the C2C12 cell surface in 10 min in vitro. Consistent with these effects, aglycin restored insulin signaling transduction by maintaining IR and IRS1 expression at both the mRNA and protein levels, as well as elevating the expression of p-IR, p-IRS1, p-Akt and membrane GLUT4 protein. The results hence demonstrate that oral administration of aglycin can potentially attenuate or prevent hyperglycemia by increasing insulin receptor signaling pathway in the skeletal muscle of streptozotocin/high-fat-diet-induced diabetic mice.

Dietary genistein induces sex-dependent effects on murine body weight, serum profiles, and vascular function of thoracic aortae

BACKGROUND

The influence on, or interaction of, sex and dietary genistein on serum markers of cardiovascular health and cardiovascular function remain unclear.

OBJECTIVES

Our purpose was to examine the effects of a genistein-containing diet (600 mg/kg food) (600G) and a genistein-free diet (0G), on cardiovascular risk parameters of male and female mice.

METHODS

C57BL/6J mice were fed the diets for 1 month, after which time blood pressure, serum markers, and in vitro vascular reactivity was measured.

RESULTS

Males fed the 600G diet gained significantly less weight than males fed the 0G diet (by 1.71 g); diet had no effect on female weight gain. Males fed the 600G diet also exhibited significantly elevated serum insulin (2.9 [0.5] vs 1.8 [0.4] ng/dL), and decreased serum glucose (0.15 [0.01] vs 0.24 [0.02] ng/dL) levels, resulting in a significant increase in the ratio of insulin to glucose; insulin and glucose levels were not changed by dietary genistein in females. Arterial pressure measurements from 0G-fed males were lower than other groups. However, basal vascular reactivity of isolated aortic rings was significantly increased by the 600G diet in both males (from 0.55 [0.03] to 0.94 [0.18] g) and females (from 0.45 [0.04] to 0.78 [0.09] g). Aortic wall thickness was not affected by diet. Norepinephrine-mediated contractility was also greater in aortic rings of male and female mice fed the 600G diet, and differences from the 0G diet persisted in the presence of L-NG-nitroarginine methyl ester but were completely accounted for by increased basal reactivity.

CONCLUSION

Our data indicate that 1 month of a 600G or 0G diet significantly alters vascular function independent of sex. In contrast, sex-dependent differences exist in well-established serum markers of cardiovascular health and disease.

Meju, unsalted soybeans fermented with Bacillus subtilis and Aspergilus oryzae, potentiates insulinotropic actions and improves hepatic insulin sensitivity in diabetic rats

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.

Efficacy of genistein aglycone on some cardiovascular risk factors and homocysteine levels: A follow-up study

BACKGROUND AND AIM

Recent evidence suggests that genistein aglycone may act beneficially on surrogate cardiovascular risk markers in postmenopausal women. We assessed the effects of genistein aglycone on some cardiovascular risk factors and homocysteine levels after 3-years of continued therapy in a cohort of osteopenic, postmenopausal women.

METHODS AND RESULTS

The parent study was a randomized, double-blind, placebo-controlled trial involving 389 postmenopausal women with low bone mass for 24 months. Subsequently, a subcohort (138 patients) continued therapy for an additional year. Participants received 54mg of genistein aglycone (n=71) or placebo (n=67), daily. Both arms received calcium and vitamin D(3) in therapeutic doses. Moreover, 4 weeks before randomization procedures and during our follow-up study, all patients received dietary instructions in an isocaloric fat-restricted diet. Blood lipid profiles, fasting glucose and insulin, insulin resistance (HOMA-IR), fibrinogen, osteoprotegerin (OPG) and homocysteine at baseline and after 24 and 36 months of treatment were measured. Compared to placebo, genistein significantly decreased fasting glucose and insulin, HOMA-IR, fibrinogen and homocysteine after 24 and 36 months of treatment. By contrast, isoflavone administration did not affect high-density lipoprotein cholesterol and triglycerides though serum OPG was higher in the genistein recipients. There were no differences in adverse events or discomfort between groups. Results on routine biochemical, liver function, and hematologic testing did not change over time in placebo or genistein group.

CONCLUSIONS

After 3-years of treatment, genistein aglycone plus calcium, vitamin D(3) and a healthy diet showed positive effects on some cardiovascular risk factors and homocysteine levels in a cohort of postmenopausal women with low bone mass.

Antidiabetic effects of fermented soybean products on type 2 diabetes

Historically, the incidence of type 2 diabetes has been lower in Asian populations compared with those in Western countries. One possible reason for the lower incidence among Asians is that they consume fermented soybean products, which are unique to the traditional Asian diet. Some have hypothesized that dietary phytoestrogens and soy peptides in fermented soybean foods consumed in traditional Asian diets may help prevent and slow the progression of type 2 diabetes. This review evaluates the existing evidence from animal studies and clinical and epidemiologic investigations on fermented soybeans in the prevention and treatment of type 2 diabetes. Nutritional studies performed in animals and intervention studies with humans suggest that the ingestion of soy protein with isoflavones improves glucose control and reduces insulin resistance. Korean fermented soybean products such as doenjang, kochujang, and chungkookjang contain alterations in the structures and content of isoflavonoids and small bioactive peptides, which are produced during fermentation. Several studies revealed improvements in insulin resistance and insulin secretion with the consumption of these fermented products. Therefore, fermented soybean products may help prevent or attenuate the progression of type 2 diabetes. Although the lack of human intervention trials does not permit definitive conclusions, the evidence does suggest that fermented soy products may be better for preventing or delaying the progression of type 2 diabetes compared with nonfermented soybeans.

Soya protein does not affect glycaemic control in adults with type 2 diabetes

Evidence from observational, animal and human studies supports a role for soya protein and its isoflavones in the improvement of glycaemic control in type 2 diabetes. The objective of the present study was to determine the effect of isoflavone-rich soya protein on markers of glycaemic control in adults with type 2 diabetes. Using a randomised, crossover, double-blind, placebo-controlled design, adults with diet-controlled type 2 diabetes (n 29) consumed soya protein isolate (SPI) and milk protein isolate (MPI) for 57 d each separated by a 4-week washout. Blood was collected on days 1 and 57 of each treatment period for analysis of fasting HbA1C, and fasting and postprandial glucose, insulin and calculated indices of insulin sensitivity and resistance. Urine samples of 24 h were collected at the end of each treatment period for analysis of isoflavones. Urinary isoflavone excretion was significantly greater following consumption of SPI compared with MPI, and 20.7 % of the subjects (n 6) were classified as equol excretors. SPI consumption did not significantly affect fasting or postprandial glucose or insulin, fasting HbA1C, or indices of insulin sensitivity and resistance. These data do not support a role for soya protein in the improvement of glycaemic control in adults with diet-controlled type 2 diabetes and contribute to a limited literature of human studies on the effects of soya protein on the management of type 2 diabetes.

Kochujang, a Korean fermented red pepper plus soybean paste, improves glucose homeostasis in 90% pancreatectomized diabetic rats

OBJECTIVES

Red pepper and soybeans have been reported to modulate energy and glucose metabolism. However, the antidiabetic effect of kochujang, the fermented product of red pepper plus soybeans, has not been studied. We examined whether kochujang affected insulin secretion from beta-cells and/or peripheral insulin resistance in 90% pancreatectomized diabetic rats fed high-fat diets.

METHODS

Diabetic rats consumed a high-fat diet containing two different kinds of 5% kochujang powder or the equivalent amount of nutrients for 8 wk. Two types of kochujang were made through the fermentation of two different kinds of meju (soybeans), red peppers, glutinous rice, and malts. Meju was produced by fermenting soybeans in a traditional method (TMK) or in a more modern method in which soybeans are inoculated with Bacillus subtilus and Aspergillus sojae (MMK).

RESULTS

TMK and MMK decreased body weight, visceral fat, and serum leptin levels without modulating caloric intake in diabetic rats compared with the control. TMK and MMK also improved glucose tolerance by enhancing insulin sensitivity but did not potentiate glucose-stimulated insulin secretion. The improvement in hepatic insulin sensitivity caused by TMK and MMK was explained by the potentiated phosphorylation of signal transducer and activator of transcription-3 --> adenosine monophosphate kinase --> acetyl-coenzyme A carboxylase and decreased phosphoenolpyruvate carboxykinase expression. Kochujang diets reduced hepatic glucose output and triacylglycerol accumulation and increased glycogen storage.

CONCLUSION

The combination of red pepper and fermented soybeans in kochujang improves glucose homeostasis by reducing insulin resistance, not by enhancing beta-cell function, in diabetic rats. The improvement is associated with decreased hepatic fat storage by the activation of adenosine monophosphate kinase.

Soybean diet modulates acetyl-coenzyme A carboxylase expression in livers of rats recovering from early-life malnutrition

OBJECTIVE

The present study evaluated the effect of nutritional recovery with a soybean diet on the gene and protein expressions and protein phosphorylation of several enzymes and transcription factors involved in hepatic lipid metabolism.

METHODS

Rats from mothers fed with 17% or 6% protein (casein) during pregnancy and lactation were maintained with a 17% casein (CC and LC groups) or soybean (CS and LS groups) diet and with a 6% casein (LL group) diet until 90 d of life.

RESULTS

The soybean diet enhanced serum insulin levels but decreased body and liver weights and hepatic lipid and glycogen concentrations. Liver peroxisome proliferator receptor-alpha mRNA abundance was higher in the LS and CS groups than in the LC and CC groups, but the protein content was similar in all groups. Hepatic acetyl-coenzyme A carboxylase (ACC)-alpha and ACCbeta mRNA expression was markedly lower in the LS and CS rats than in the LC and CC rats. ACC protein expression was lower in the CS group than in the CC, LC, and LS groups. Phospho-[Ser(79)]2-ACC content was similar in the CS, LC, and LS groups and lower than the CC group. In the CS rats this reduction paralleled the decrease in total ACC protein. Messenger RNA and protein expression of sterol regulatory element-binding protein 1c, adenosine monophosphate-activated protein kinase, and phospho-[Thr(172)]-adenosine monophosphate-activated protein kinase was not modified by the soybean diet.

CONCLUSION

Thus, the soybean diet reduced the liver lipid concentration through downregulation of the ACC gene and protein expressions rather than by phosphorylation status, which possibly resulted in decreased lipogenesis and increased beta-oxidation.