Sang Mee Hong

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 β-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.

Changes in Components, Glycyrrhizin and Glycyrrhetinic Acid, in Raw Glycyrrhiza uralensis Fisch, Modify Insulin Sensitizing and Insulinotropic Actions

We hypothesized that roasted Glycyrrhizae Radix (Glycyrrhizin Radix Praeparata, GRP) might modify anti-diabetic action due to compositional changes. Then we examined the anti-diabetic effect and mechanism of raw Glycyrrhizae Radix (GR) and GRP extracts and their major respective components, glycyrrhizin and glycyrrhetinic acid. In partial pancreatectomized (Px) diabetic mice, both GR and GRP improved glucose tolerance, but only GRP enhanced glucose-stimulated insulin secretion as much as exendin-4. Both GR and GRP extracts enhanced insulin-stimulated glucose uptake through peroxisome proliferation-activated receptor (PPAR)-γ activation in 3T3-L1 adipocytes. Consistently with the results of the mice study, only GRP and glycyrrhetinic acid enhanced glucose-stimulated insulin secretion in isolated islets. In addition, they induced mRNA levels of insulin receptor substrate-2, pancreas duodenum homeobox-1, and glucokinase in the islets, which contributed to improving β-cell viability. In conclusion, GRP extract containing glycyrrhetinic acid improved glucose tolerance better than GR extract by enhancing insulinotropic action. Thus, GRP had better anti-diabetic action than GR.

Exercise enhances insulin and leptin signaling in the cerebral cortex and hypothalamus during dexamethasone-induced stress in diabetic rats.

Exercise and dexamethasone (DEX) are known to have opposite effects on peripheral insulin resistance. However, their effects and mechanism on brain glucose metabolism have been poorly defined. We investigated the modulation of the hypothalamo-pituitary-adrenal (HPA) axis and insulin/leptin signaling associated with glucose utilization in the brains of 90% pancreatectomized diabetic rats, which had been administered two dosages of DEX and exercised for 8 weeks. The data revealed that the administration of a high dose (0.1 mg/kg body weight/day) of DEX (HDEX) attenuated insulin signaling in the cerebral cortex and hypothalamus, whereas exercise potentiated their insulin signaling along with induction of IRS2 expression. In parallel with the modulated signaling, glucose utilization, such as glycogen storage and glycogen synthase activity, was suppressed by DEX in the cortex and hypothalamus, while exercise offset the DEX effects. Despite a decrease in epididymal fat mass, HDEX increased serum leptin levels, possibly due to an activated HPA axis, while exercise suppressed the increment. However, DEX reduced leptin-induced STAT3 phosphorylation in the cortex and hypothalamus, and it increased AMP-activated protein kinase (AMPK) phosphorylation only in the hypothalamus. Exercise reversed the phosphorylation of STAT3 and AMPK which had been modulated by DEX. In conclusion, exercise improves insulin and leptin signaling in the cerebral cortex and hypothalamus of diabetic rats exacerbated with HDEX, contributing to the regulation of body weight and glucose homeostasis.

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.

Exendin-4 and exercise promotes β-cell function and mass through IRS2 induction in islets of diabetic rats

Not only exendin-4 but also exercise has been reported to improve glucose homeostasis by enhancing insulinotropic action, but the nature of its molecular mechanism has not been clarified. We investigated a mechanism to promote insulinotropic action by means of exendin-4 and exercise training in 90% pancreatectomized (Px) rats fed 40% energy fat diets. Px diabetic rats were divided into 4 groups: 1) exendin-4, 2) exendin-4 plus exercise, 3) saline (control), and 4) exercise. During the 8-week experimental period, rats in the exendin-4 groups were subcutaneously administered with 150 pmol/kg exendin-4 twice a day, while those in the exercise groups ran on an uphill treadmill with a 15 degree incline at 20 m/min for 30 min 5 days a week. First phase insulin secretion was elevated by both the administration of exendin-4 and exercise training during hyperglycemic clamp. However, second phase insulin secretion did not differ among the groups. Individual treatment of exendin-4 and exercise expanded beta-cell mass by increasing its proliferation and reducing its apoptosis, but the administration of exendin-4 plus exercise training did not produce any additional, positive effects. Both exendin-4 and exercise enhanced insulin receptor substrate (IRS)-2 expression through the activation of cAMP responding element binding protein in the islets, which potentiated their insulin/insulin like growth factor-1 signaling. The potentiation of the signaling increased the expression of pancreas duodenum homeobox-1, involved in beta-cell proliferation. In conclusion, exendin-4 and exercise equivalently improved glucose homeostasis due to the induction of IRS-2 in the islets of diabetic rats through a cAMP dependent common pathway.

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.

Extracts of Rehmanniae radix, Ginseng radix and Scutellariae radix improve glucose-stimulated insulin secretion and β-cell proliferation through IRS2 induction

Recent studies have revealed that β-cell dysfunction is an important factor in developing type 2 diabetes. β-cell dysfunction is related to impairment of the insulin/IGF-1 signaling cascade through insulin receptor substrate-2 (IRS2). The induction of IRS2 in β-cells plays an important role in potentiating β-cell function and mass. In this study, we investigated whether herbs used for treating diabetes in Chinese medicine—Galla rhois, Rehmanniae radix, Machilus bark, Ginseng radix, Polygonatum radix, and Scutellariae radix—improved IRS2 induction in rat islets, glucose-stimulated insulin secretion and β-cell survival. R. radix, Ginseng radix and S. radix significantly enhanced glucose-stimulated insulin secretion compared to the control, i.e., by 49, 67 and 58%, respectively. These herbs induced the expression of IRS2, pancreas duodenum homeobox-1 (PDX-1), and glucokinase. The increased level of glucokinase could explain the enhancement of glucose-stimulated insulin secretion with these extracts. Increased PDX-1 expression was associated with β-cell proliferation, which was consistent with the cell viability assay. In conclusion, R. radix, Ginseng radix and S. radix had an insulinotropic action similar to that of exendin-4.

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.

Estrogen replacement reverses olanzapine-induced weight gain and hepatic insulin resistance in ovariectomized diabetic rats.

Objectives: We investigated whether estrogen replacement modulated energy and glucose metabolic changes induced by olanzapine (OZP) and risperidone (RPD) in 90% pancreatectomized diabetic rats, some of whom had also been ovariectomized (OVX) and some of whom had not (sham). Methods: OVX diabetic rats were subcutaneously injected with estrogen replacement (17β-estradiol, 30 µg/kg/day) or a vehicle. Each group was divided into 3 subgroups, and each subgroup was orally either given a placebo, RPD (0.5 mg/kg body weight/day) or OZP (2 mg/kg body weight/day) for 8 weeks. Sham rats were also divided into 3 subgroups and given drugs in the same manner as the OVX rats were. All rats were fed high-fat diets. Results: OZP increased body weight and epididymal fat pads more than the control (vehicle) in sham and OVX rats. Increased body weight in OZP-treated sham and OVX rats was due to the increment in food intake, which was associated with potentiating the phosphorylation of hypothalamic adenosine-monophosphate-activated protein kinase. At euglycemic hyperinsulinemic clamping, OZP decreased glucose infusion rates and increased hepatic glucose output in OVX diabetic rats. In sham rats, OZP increased hepatic glucose output but not as much as in OVX rats. Hepatic insulin signaling and glucose sensing were attenuated in OZP-treated OVX rats, and the attenuation increased hepatic phosphoenolpyruvate carboxykinase expression to induce gluconeogenesis. These negative and harmful effects noted among OZP-treated OVX rats were reversed by estrogen replacement treatment. However, RPD did not alter body weight and peripheral insulin sensitivity in sham and OVX rats. Conclusions: OZP treatment should be avoided when treating diabetic and schizophrenic women, especially those in their postmenopausal period.

Can splenocytes enhance pancreatic β-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.