Isoflavonoids and peptides from meju, long-term fermented soybeans, increase insulin sensitivity and exert insulinotropic effects in vitro.

OBJECTIVE: Although soybeans have been shown to alleviate metabolic syndromes, fermented soybeans may have even greater effects. We investigated the antidiabetic effects of meju, a soy food that is fermented up to 2 mo, and the mechanism by which it exerts its effects. METHODS: Meju was prepared by a traditional fermentation process: soybeans were fermented outdoors for 20 or 60 d. Methanol (M-60) and water (W-60) extracts from meju that had fermented for 60 d contained mostly isoflavonoid aglycones and small peptides, respectively, as opposed to mostly glycosylated isoflavonoids and proteins in the original soybeans. RESULTS: Daidzein, M-60, and W-60 had better insulin-sensitizing actions by activating peroxisome proliferator-activated receptor-γ in 3T3-L1 adipocytes than did unfermented soybeans. In addition, Min6 insulinoma cells treated with genistein, M-60, and W-60 had greater glucose-stimulated insulin secretion capacity and greater ß-cell viability than those treated with unfermented soybeans. This improvement was associated with insulin/insulin-like growth factor-1 signaling that was activated by the tyrosine phosphorylation of insulin receptor substrate-2 and serine phosphorylation of Akt, and this in turn increased pancreatic and duodenal homeobox-1 expression. Furthermore, genistein, daidzein, and M-60 stimulated glucagon-like peptide-1 secretion in enteroendocrine NCI-H716 cells, which generated insulinotropic actions. CONCLUSION: The compositional changes in isoflavonoids and peptides that occurred during a longer fermentation period, without the use of salt, enhanced the antidiabetic effect of soybeans.

Central infusion of leptin improves insulin resistance and suppresses beta-cell function, but not beta-cell mass, primarily through the sympathetic nervous system in a type 2 diabetic rat model.

AIMS: We investigated whether hypothalamic leptin alters beta-cell function and mass directly via the sympathetic nervous system (SNS) or indirectly as the result of altered insulin resistant states. MAIN METHODS: The 90% pancreatectomized male Sprague Dawley rats had sympathectomy into the pancreas by applying phenol into the descending aorta (SNSX) or its sham operation (Sham). Each group was divided into two sections, receiving either leptin at 300ng/kgbw/h or artificial cerebrospinal fluid (aCSF) via intracerebroventricular (ICV) infusion for 3h as a short-term study. After finishing the infusion study, ICV leptin (3mug/kg bw/day) or ICV aCSF (control) was infused in rats fed 30 energy % fat diets by osmotic pump for 4weeks. At the end of the long-term study, glucose-stimulated insulin secretion and islet morphometry were analyzed. KEY FINDINGS: Acute ICV leptin administration in Sham rats, but not in SNSX rats, suppressed the first- and second-phase insulin secretion at hyperglycemic clamp by about 48% compared to the control. Regardless of SNSX, the 4-week administration of ICV leptin improved glucose tolerance during oral glucose tolerance tests and insulin sensitivity at hyperglycemic clamp, compared to the control, while it suppressed second-phase insulin secretion in Sham rats but not in SNSX rats. However, the pancreatic beta-cell area and mass were not affected by leptin and SNSX, though ICV leptin decreased individual beta-cell size and concomitantly increased beta-cell apoptosis in Sham rats. SIGNIFICANCE: Leptin directly decreases insulin secretion capacity mainly through the activation of SNS without modulating pancreatic beta-cell mass.

Glyceollins, one of the phytoalexins derived from soybeans under fungal stress, enhance insulin sensitivity and exert insulinotropic actions.

Glyceollins are a category of phytoalexins that are produced by soybeans under fungal stress, but their effects on glucose homeostasis remain unknown. We hypothesized that glyceollins play an important role in glucose homeostasis by regulating glucose utilization in adipocytes and improving beta-cell function and survival. Glyceollins improved insulin-stimulated glucose uptake in 3T3-L1 adipocytes without activating the peroxisome proliferator-activated receptor-gamma agonist. They decreased triacylglycerol accumulation in adipocytes. In addition, glyceollins slightly improved glucose-stimulated insulin secretion without palmitate treatment in Min6 cells, and they potentiated insulinotropic actions when 500 microM palmitate was used to induce beta-cell dysfunction. This was associated with decreased beta-cell apoptosis because of the attenuation of endoplasmic reticulum stress, as determined by mRNA levels of XBP-1, ATF-4, ATF-6, and CHOP. Glyceollins also potentiated GLP-1 secretion to enhance insulinotropic actions in enteroendocrine cells. In conclusion, glyceollins help normalize glucose homeostasis by potentiating beta-cell function and survival and improving glucose utilization in adipocytes.

Exendin-4 and exercise improve hepatic glucose homeostasis by promoting insulin signaling in diabetic rats.

Recently, it has been reported that a long-acting glucagon-like peptide-1 (exendin-4) and physical exercise improve hepatic insulin action in diabetic rats. However, this phenomenon remains poorly understood. We investigated the long-term effect that exendin-4 and exercise had on hepatic insulin resistance through the modulation of hepatic and/or hypothalamic insulin signaling in 90% pancreatectomized diabetic rats fed 40% energy fat diets. The rats were divided into 4 groups: exendin-4 only, exendin-4 plus exercise training, saline (control), or exercise training only. Rats in the exendin-4 groups were administered with 150 pmol/kg exendin-4 twice a day for 8 weeks, whereas those in the exercise groups ran on an uphill treadmill with a 15 degrees incline at 20 m/min for 30 minutes 5 days a week. Exendin-4 reduced serum glucagon levels in overnight-fasted rats. Exendin-4 treatment by itself decreased hepatic glucose output at hyperinsulinemic states, and exercise without exendin-4 treatment also had the same effect. Exendin-4 promoted hepatic insulin signaling by potentiating tyrosine phosphorylation of the insulin receptor substrate-2 without changing hypothalamic insulin signaling. Exendin-4 also enhanced hypothalamic glucose sensing. However, exercise improved both hepatic and hypothalamic insulin signaling by activating the phosphorylation of cyclic adenosine monophosphate-responding element binding proteins to induce insulin receptor substrate-2 expression. Exendin-4 and exercise decreased the expression of phosphoenolpyruvate carboxykinase, which in turn reduced hepatic glucose output. Exendin-4 in combination with exercise had no additive effects. In conclusion, exendin-4 and exercise improve hepatic glucose homeostasis by promoting hepatic insulin signaling in diabetic rats.

Exendin-4 potentiates insulinotropic action partly via increasing beta-cell proliferation and neogenesis and decreasing apoptosis in association with the attenuation of endoplasmic reticulum stress in islets of diabetic rats.

Exendin-4, a long-acting glucagon-like peptide-1-receptor agonist, is known to enhance beta-cell function, but the active mechanism by which it modulates beta-cell mass still remains unclear. We investigated what the long-term effects of exendin-4 (300 pmol/kg body weight per day) on beta-cell function and mass would be in 90% pancreatectomized (Px) Sprague Dawley rats; half of whom were intraperitoneally injected with streptozotocin (STZ, 20 mg/kg body weight) and half of whom were not. Exendin-4 improved glucose tolerance by elevating serum insulin levels in both STZ-treated and untreated Px rats. At hyperglycemic clamp, STZ attenuated both first and second phase insulin secretion in STZ- and saline-treated Px rats, but exendin-4 incompletely reversed the attenuation. Since STZ mostly removed the remaining beta-cells by increasing apoptosis after Px, their regeneration was initiated through neogenesis, which was determined by the number of beta-cells budding from pancreatic duct layers and small clusters. Exendin-4 enhanced beta-cell proliferation and neogenesis in STZ-treated and -untreated Px rats and reduced beta-cell apoptosis partly by attenuating the expression of endoplasmic reticulum stress-response genes such as X-box-binding protein-1, activating transcription factor (ATF)-4, ATF6, and C/EBP-homologous protein. In conclusion, exendin-4 improved glycemic control by potentiating beta-cell function and increasing beta-cell mass by increasing beta-cell neogenesis and proliferation and by decreasing apoptosis in diabetic rats.

Huang-Lian-Jie-Du-Tang supplemented with Schisandra chinensis Baill. and Polygonatum odoratum Druce improved glucose tolerance by potentiating insulinotropic actions in islets in 90% pancreatectomized diabetic rats.

We investigated to determine what effects, if any, the respective water extracts of Radix scutellariae (RS), Fructus schisandrae chinensis (FSC), Huang-Lian-Jie-Du-Tang (HLJDT), and HLJDT supplemented with FSC, and Rhizoma Polygonati odorati (HLJDT-M) would have on glucose tolerance by modulating glucose-stimulated insulin secretion, beta-cell mass, and morphometry in 90% pancreatectomized (Px) diabetic rats fed high-fat diets. Through the elevation of intracellular cAMP levels, FSC RS, HLJDT, and HLJDT-M increased insulin secretion in Min6 cells and GLP-1 secretion in NCI-H716 cells. After an 8-week period of treatment, it was found that HLJDT-M improved glucose tolerance in an oral glucose tolerance test in Px rats. HLJDT-M also potentiated first- and second-phase insulin secretion, but RS and HLJDT elevated only the second phase at hyperglycemic clamp. RS and HLJDT increased beta-cell mass by hyperplasia and hypertrophy, while HLJDT-M increased it only by hyperplasia. The rise in hyperplasia was associated with elevated IRS2 and PDX-1 expression in the islets. In conclusion, HLJDT-M worked as an anti-diabetic prescription by enhancing insulinotropic actions in diabetic rats.

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.

Can splenocytes enhance pancreatic beta-cell function and mass in 90% pancreatectomized rats fed a high fat diet?

AIMS: Recent studies have shown that splenocytes may act as a possible neogenic source with regard to beta-cells in rodent diabetic models. Accordingly, we sought to determine whether splenocytes played an important role in promoting beta-cell function and mass among type 2 diabetic rats with and without spleen. MAIN METHODS: We randomly divided female 90% pancreatectomized (Px) Sprague Dawley rats into three groups: splenectomy (SPX), splenectomy plus the injection of male splenocytes (SPI), and no splenectomy (NSP). They were administered with 40 energy percent fat diets over the course of five weeks. At the end of the experimental period, insulin secretion capacity was measured by hyperglycemic clamp. At 6 h after BrdU(+) injection, the pancreas was prepared with 4% paraformaldehyde in order to perform immunohistochemistry. KEY FINDINGS: SPX increased and sustained serum glucose levels more than NSP and SPI during oral glucose tolerance testing. During hyperglycemic clamp, first and second phase insulin secretion decreased in the SPX rats while splenocyte injections counteracted this. Beta-cell mass in the SPX group was reduced more than among NSP and SPI. This was the result of a decrease in the number of small beta-cell clusters in SPX, which is indicative of a decrease in beta-cell neogenesis. SIGNIFICANCE: Splenocytes play an important role with regard to the neogenesis of beta-cells in insulin deficient type 2 diabetic rats, although they are not critical for beta-cell regeneration.

Long-term intracerebroventricular infusion of insulin, but not glucose, modulates body weight and hepatic insulin sensitivity by modifying the hypothalamic insulin signaling pathway in type 2 diabetic rats.

BACKGROUND/AIMS: It has been reported that the short-term injection of insulin and glucose into the hypothalamus modulates body weight and hepatic glucose production in non-diabetic rats. However, the effect of hypothalamic insulin and glucose on peripheral glucose metabolism in diabetic animals remains uncertain. We investigated how intracerebroventricular (ICV) infusion of insulin and glucose modified body weight and peripheral glucose homeostasis in 90% pancreatectomized rats that exhibited symptoms of mild and non-obese type 2 diabetes. METHODS: The diabetic rats that were fed a high fat diet were ICV administered with either insulin (0.3 U/day), glucose (10 mg/day), insulin plus glucose (insulin+glucose), or artificial cerebrospinal fluid (control) by means of osmotic pumps for 4 weeks. RESULTS: Central insulin and insulin+glucose reduced body weight with a slight decrease of food intake compared to the control and glucose groups in diabetic rats. In addition, during euglycemic hyperinsulinemic clamp, ICV infusion of insulin and insulin+glucose increased glucose infusion rates and decreased hepatic glucose production compared to the control and glucose groups. The improvement of insulin sensitivity was associated with the activation of both hypothalamic and hepatic insulin signaling cascades. Central glucose did not affect hypothalamic insulin action in diabetic rats. CONCLUSION: Long-term central infusion of insulin enhanced energy metabolism and hepatic glucose homeostasis in type 2 diabetic rats partly via potentiating hypothalamic insulin signaling. However, central glucose infusion did not modulate the central and peripheral metabolism.

Ginsenosides Rb1 and Rg1 suppress triglyceride accumulation in 3T3-L1 adipocytes and enhance beta-cell insulin secretion and viability in Min6 cells via PKA-dependent pathways.

Ginseng root is known to induce anti-diabetic activity, but the key components involved are unknown. We investigated which major ginsenosides in ginseng enhanced glucose homeostasis by in vitro studies. Rb1 and Rg1 reduced the triglyceride accumulation in 3T3-L1 adipocytes by activating PKA with increased intracellular cAMP. However, the insulin-stimulated glucose uptake was enhanced by Rb1 and Rg1 via activation of phosphatidylinositol-3 kinase. Rb1 and Rg1 promoted glucose-stimulated insulin secretion and cell viability in Min6 cells through PKA which augmented IRS2 expression to enhance insulin/IGF-1 signaling. These results suggest that Rb1 and Rg1 improved glucose homeostasis through the activation of a PKA like glucagon-like peptide-1 receptor agonist.