Metabolism of Natural Highly Unsaturated Fatty Acid, Tetracosahexaenoic Acid (24:6n-3), in C57BL/KsJ-db/db Mice.

Tetracosahexaenoic acid (THA; 24:6n-3) is a natural, n-3 highly unsaturated fatty acid (n-3HUFA) that exists in fish, including Baltic herring (Clupea harengus) and the flathead flounder (Hippoglossoides dubius). In this study, natural n-3HUFAs, i.d. eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3), and THA were administrated to C57BL/KsJ-db/db mice for 4 weeks and the liver and serum lipid profiles, hepatic enzyme activity, expression of mRNA related to lipid metabolism, and adiponectin serum levels were then analyzed. The results showed that THA had the highest activity in suppressing hepatic triglyceride (TG) accumulation and increase in liver weight among the test groups. Furthermore, THA increased adiponectin levels in serum. These results indicate that THA is an excellent natural n-3HUFA that can suppress the development of metabolic syndromes and circulatory system diseases. The order of the n-3HUFA activity was THA > DHA > EPA in almost all the factors examined here. In a previous study of ours, the order was DHA > DPA > EPA, so the final order was summarized as THA > DHA > DPA > EPA. This order clearly translates to the rule that "the number of double bonds and carbon atoms in the n-3HUFA structure relates to their clinical functions".

Nardostachys jatamansi DC Extract Alleviates Insulin Resistance and Regulates Glucose Metabolism in C57BL/KsJ-db/db Mice Through the AMP-Activated Protein Kinase Signaling Pathway.

This study investigated whether Nardostachys jatamansi DC extract (NJE) improved insulin sensitivity and suppressed hepatic glucose production in an animal model of type 2 diabetes. C57BL/KsJ-db/db mice were divided into three dietary groups: regular diet (control), NJE, and rosiglitazone. After 6 weeks of feeding, blood glucose, glycosylated hemoglobin, and plasma insulin levels were significantly lower in NJE than in diabetic control group mice. The oral glucose tolerance test also revealed a positive effect of NJE on increasing insulin sensitivity. The homeostatic index of insulin resistance was significantly lower in NJE than in diabetic control group mice. NJE markedly lowered the plasma lipid concentration compared to diabetic control group mice. In the skeletal muscle, the expression of phosphorylated AMP-activated protein kinase, pAkt substrate of 160 kDa, and plasma membrane glucose transporter type 4 increased more in NJE compared to diabetic control group mice. NJE also decreased the expression of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase in the liver. These findings demonstrate that NJE alleviates hyperglycemia by improving insulin sensitivity and inhibiting gluconeogenesis in the liver.

Hypoglycemic effect and mechanism of a pectic polysaccharide with hexenuronic acid from the fruits of Ficus pumila L. in C57BL/KsJ db/db mice.

In this study, a particular pectic polysaccharide (FPLP) was extracted and purified from the fruits of Ficus pumila Linn. through boiling water extraction, alcohol precipitation, diethylaminoethyl-Sepharose Fast Flow chromatography and Superdex™ G-75 gel filtration chromatography. Analysis of high-performance gel permeation chromatography, FTIR, GC-MS, methylation and 1D/2D NMR spectroscopy revealed that FPLP (Mw: 34.69kDa) is a linear (1,4)-α-d-galacturonic acid binding 1.30% branched chain hexenuronic acid with 23.34% methyl esterification. Treatment with FPLP ameliorated hyperglycaemia in association with an improvement in hepatic glycogen metabolism in C57BL/KsJ db/db mice. The activation of IRS-1/PI3K/Akt/GSK3ß/GS insulin signalling pathway and AMPK/GSK3ß/GS signalling pathway and the regulation of glucokinase, phosphoenolpyruvate carboxykinase and glucose-6-phosphatase expressions involved in hepatic glycogenesis and glycogenolysis were considered the therapeutic mechanisms of FPLP. These results provide a new insight for investigating the effects of pectic polysaccharides on blood glucose control and suggest that FPLP is a promising nutraceutical for treatment of T2DM.

Sargassum coreanum extract alleviates hyperglycemia and improves insulin resistance in db/db diabetic mice.

BACKGROUND/OBJECTIVES: The goal of this study was to examine the effect of Sargassum coreanum extract (SCE) on blood glucose concentration and insulin resistance in C57BL-KsJ-db/db mice. MATERIALS/METHODS: For 6 weeks, male C57BL/KsJ-db/db mice were administrated SCE (0.5%, w/w), and rosiglitazone (0.005%, w/w). RESULTS: A supplement of the SCE for 6 weeks induced a significant reduction in blood glucose and glycosylated hemoglobin concentrations, and it improved hyperinsulinemia compared to the diabetic control db/db mice. The glucokinase activity in the hepatic glucose metabolism increased in the SCE-supplemented db/db mice, while phosphoenolpyruvate carboxykinase and glucose-6-phosphatase activities in the SCE-supplemented db/db mice were significantly lower than those in the diabetic control db/db mice. The homeostatic index of insulin resistance was lower in the SCE-supplemented db/db mice than in the diabetic control db/db mice. CONCLUSIONS: These results suggest that a supplement of the SCE lowers the blood glucose concentration by altering the hepatic glucose metabolic enzyme activities and improves insulin resistance.

Padina arborescens Ameliorates Hyperglycemia and Dyslipidemia in C57BL/KsJ-db/db Mice, a Model of Type 2 Diabetes Mellitus.

Recently, there has been a growing interest in alternative therapies and in the therapeutic use of natural products for the treatment of diabetes. Therefore, in this study, we investigated the hypoglycemic and hypolipidemic effects of brown algae, Padina arborescens, in an animal model of type 2 diabetes. For 6 weeks, male C57BL/KsJ-db/db mice were administrated either control diet with no treatment or were treated with rosiglitazone (RG; 0.005%, w/w) or P. arborescens extract (PAE; 0.5%, w/w). At the end of the experimental period, the blood glucose levels, glycosylated hemoglobin levels, and plasma insulin levels were significantly lower in the RG and PAE groups compared with the control group. In addition, glucose tolerance was significantly improved in the RG and PAE groups. The homeostatic index of insulin resistance was lower in the RG and PAE groups than the diabetic control group. Also, the total cholesterol, LDL-cholesterol, triglyceride, and free fatty acid levels were lower in the PAE group than in the control group, whereas the HDL-C level was higher in the PAE group. Supplementation with PAE significantly lowered hepatic glucose-6-phosphatase and phosphoenolpyruvate carboxykinase activities, and increased glucokinase activity in the liver. Consequently, these results suggest that PAE may be beneficial in improving insulin resistance, hyperglycemia, and dyslipidemia in type 2 diabetics.

Anti-Diabetic Effect of Aster sphathulifolius in C57BL/KsJ-db/db Mice.

In this study, we investigated the anti-diabetic effect of Aster sphathulifolius (AS) extract in C57BL/KsJ-db/db mice. The db/db mice were orally administered with AS 50% ethanol extract at concentrations of 50, 100, and 200 mg/kg/day (db/db-AS50, db/db-AS100, and db/db-AS200, respectively) for 10 weeks. Food and water intake, fasting blood glucose concentrations, blood glycosylated hemoglobin levels, and plasma insulin levels were significantly lower in the db/db-AS200 group than in the vehicle-treated db/db group; whereas glucose tolerance was significantly improved in the db/db-AS200 group. Moreover, AS dose dependently increased both insulin receptor substrate 1 and glucose transporter type 4 expression in skeletal muscle, significantly increased glucokinase expression, and decreased glucose 6-phosphatase and phosphoenolpyruvate carboxykinase expressions in the liver. The expressions of transcription factors, such as sterol-regulatory element-binding protein, peroxisome proliferator-activated receptor γ, and adipocyte protein 2, were upregulated in adipose tissue. Furthermore, immunohistochemical analysis showed that AS upregulated insulin production by increasing pancreatic ß-cell mass. In summary, AS extract normalized hyperglycemia by multiple mechanisms: inhibition of glyconeogenesis, acceleration of glucose metabolism and lipid metabolism, and increase of glucose uptake. Using in vivo assays, this study has shown the potential of AS as a medicinal food and suggests the efficacy of AS for the use of prevention of diabetes.