Glyceollin improves endoplasmic reticulum stress-induced insulin resistance through CaMKK-AMPK pathway in L6 myotubes

Glyceollin has been shown to have antidiabetic properties, although its molecular mechanism is not known. Here, we have investigated the metabolic effects of glyceollin in animal models of insulin resistance and in endoplasmic reticulum (ER) stress-responsive muscle cells. db/db mice were treated with glyceollin for 4 weeks and triglycerides, total cholesterol, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) levels were measured. Glyceollin reduced serum insulin and triglycerides and increased HDL levels in db/db mice. Furthermore, glyceollin caused a significant improvement in glucose homeostasis without altering body weight and food intake in db/db mice. In muscle cells, glyceollin increased the activity of AMP-activated protein kinase (AMPK) as well as cellular glucose uptake. Fatty acid oxidation was also increased. In parallel, phosphorylation of acetyl-CoA carboxylase (ACC) at Ser-79 was increased, consistent with decreased ACC activity. An insulin-resistant state was induced by exposing cells to 5 μg/ml of tunicamycin as indicated by decreased insulin-mediated tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) and glucose uptake. Inhibition of insulin-mediated tyrosine phosphorylation of IRS-1 and glucose uptake under ER stress was prevented by glyceollin. Strikingly, glyceollin reduced ER stress-induced, c-Jun NH₂-terminal kinase activation and subsequently increased insulin signaling via stimulation of AMPK activity in L6 myotubes. Pharmacologic inhibition or knockdown of Ca²⁺/calmodulin-dependent protein kinase kinase blocked glyceollin-increased AMPK phosphorylation and insulin sensitivity under ER stress conditions. Taken together, these results indicate that glyceollin-mediated enhancement of insulin sensitivity under ER stress conditions is predominantly accomplished by activating AMPK, thereby having beneficial effects on hyperglycemia and insulin resistance.     

Daidzein promotes glucose uptake through glucose transporter 4 translocation to plasma membrane in L6 myocytes and improves glucose homeostasis in Type 2 diabetic model mice

Daidzein shows estrogenic, antioxidant and antiandrogenic properties as well as cell cycle regulatory activity. However, the antihyperglycemic effect of daidzein remains to be elucidated. In this study, we investigated the in vitro effect of daidzein on glucose uptake, AMPK phosphorylation and GLUT4 translocation on plasma membrane in L6 myotubes and its in vivo antihyperglycmic effect in obese–diabetic model db/db mice. Daidzein was found to promote glucose uptake, AMPK phosphorylation and GLUT4 translocation by Western blotting analyses in L6 myotubes under a condition of insulin absence. Promotion by daidzein of glucose uptake as well as GLUT4 translocation to plasma membrane by immunocytochemistry was also demonstrated in L6 myoblasts transfected with a GLUT4 cDNA-coding vector. Daidzein (0.1% in the diet) suppressed the rises in the fasting blood glucose, serum total cholesterol levels and homeostasis model assessment index of db/db mice. In addition, daidzein supplementation markedly improved the AMPK phosphorylation in gastrocnemius muscle of db/db mice. Daidzein also suppressed increases in blood glucose levels and urinary glucose excretion in KK-Ay mice, another Type 2 diabetic animal model. These in vitro and in vivo findings suggest that daidzein is preventive for Type 2 diabetes and an antidiabetic phytochemical.     

The Effects of Palmitate on Hepatic Insulin Resistance Are Mediated by NADPH Oxidase 3-derived Reactive Oxygen Species through JNK and p38MAPK Pathways

Elevated plasma free fatty acid (FFA) levels in obesity may play a pathogenic role in the development of insulin resistance. However, molecular mechanisms linking FFA to insulin resistance remain poorly understood. Oxidative stress acts as a link between FFA and hepatic insulin resistance. NADPH oxidase 3 (NOX3)-derived reactive oxygen species (ROS) may mediate the effect of TNF-α on hepatocytes, in particular the drop in cellular glycogen content. In the present study, we define the critical role of NOX3-derived ROS in insulin resistance in db/db mice and HepG2 cells treated with palmitate. The db/db mice displayed increased serum FFA levels, excess generation of ROS, and up-regulation of NOX3 expression, accompanied by increased lipid accumulation and impaired glycogen content in the liver. Similar results were obtained from palmitate-treated HepG2 cells. The exposure of palmitate elevated ROS production and NOX3 expression and, in turn, increased gluconeogenesis and reduced glycogen content in HepG2 cells. We found that palmitate induced hepatic insulin resistance through JNK and p38^MAPK pathways, which are rescued by siRNA-mediated NOX3 reduction. In conclusion, our data demonstrate a critical role of NOX3-derived ROS in palmitate-induced insulin resistance in hepatocytes, indicating that NOX3 is the predominant source of palmitate-induced ROS generation and that NOX3-derived ROS may drive palmitate-induced hepatic insulin resistance through JNK and p38^MAPK pathways.     

Oxamate Improves Glycemic Control and Insulin Sensitivity via Inhibition of Tissue Lactate Production in db/db Mice

Oxamate (OXA) is a pyruvate analogue that directly inhibits the lactate dehydrogenase (LDH)-catalyzed conversion process of pyruvate into lactate. Earlier and recent studies have shown elevated blood lactate levels among insulin-resistant and type 2 diabetes subjects and that blood lactate levels independently predicted the development of incident diabetes. To explore the potential of OXA in the treatment of diabetes, db/db mice were treated with OXA in vivo. Treatment of OXA (350–750 mg/kg of body weight) for 12 weeks was shown to decrease body weight gain and blood glucose and HbA1c levels and improve insulin secretion, the morphology of pancreatic islets, and insulin sensitivity in db/db mice. Meanwhile, OXA reduced the lactate production of adipose tissue and skeletal muscle and serum lactate levels and decreased serum levels of TG, FFA, CRP, IL-6, and TNF-α in db/db mice. The PCR array showed that OXA downregulated the expression of Tnf, Il6, leptin, Cxcr3, Map2k1, and Ikbkb, and upregulated the expression of Irs2, Nfkbia, and Pde3b in the skeletal muscle of db/db mice. Interestingly, LDH-A expression increased in the islet cells of db/db mice, and both treatment of OXA and pioglitazone decreased LDH-A expression, which might be related to the improvement of insulin secretion. Taken together, increased lactate production of adipose tissue and skeletal muscle may be at least partially responsible for insulin resistance and diabetes in db/db mice. OXA improved glycemic control and insulin sensitivity in db/db mice primarily via inhibition of tissue lactate production. Oxamic acid derivatives may be a potential drug for the treatment of type 2 diabetes.     

C-C Chemokine Receptor 2 Inhibitor Ameliorates Hepatic Steatosis by Improving ER Stress and Inflammation in a Type 2 Diabetic Mouse Model

Hepatic steatosis is the accumulation of excess fat in the liver. Recently, hepatic steatosis has become more important because it occurs in the patients with obesity, type 2 diabetes, and hyperlipidemia and is associated with endoplasmic reticulum (ER) stress and insulin resistance. C-C chemokine receptor 2 (CCR2) inhibitor has been reported to improve inflammation and glucose intolerance in diabetes, but its mechanisms remained unknown in hepatic steatosis. We examined whether CCR2 inhibitor improves ER stress-induced hepatic steatosis in type 2 diabetic mice. In this study, db/db and db/m (n = 9) mice were fed CCR2 inhibitor (2 mg/kg/day) for 9 weeks. In diabetic mice, CCR2 inhibitor decreased plasma and hepatic triglycerides levels and improved insulin sensitivity. Moreover, CCR2 inhibitor treatment decreased ER stress markers (e.g., BiP, ATF4, CHOP, and XBP-1) and inflammatory cytokines (e.g., TNFα, IL-6, and MCP-1) while increasing markers of mitochondrial biogenesis (e.g., PGC-1α, Tfam, and COX1) in the liver. We suggest that CCR2 inhibitor may ameliorate hepatic steatosis by reducing ER stress and inflammation in type 2 diabetes mellitus.     

Glucose Uptake Activities of Bis (2, 3-Dibromo-4, 5-Dihydroxybenzyl) Ether,a Novel Marine Natural Product from Red Alga Odonthaliacorymbifera with Protein Tyrosine Phosphatase 1B Inhibition,In Vitro and In Vivo

Background and Aims

Protein tyrosine phosphatase 1B (PTP1B) is a novel therapeutic target for type-2 diabetes, which negatively regulates the insulin signaling transduction. Bis (2, 3-dibromo-4, 5-dihydroxybenzyl) ether (BDDE), a novel bromophenol isolated from the Red Alga, is a novel PTP1B inhibitor. But the anti-diabetic effects are not clear. In the present study, we evaluated the in vitro and in vivo antidiabetic effects of BDDE.

Methods

The insulin-resistant HepG2 cells were used to evaluate the in vitro antidiabetic effects of BDDE. MTT assay was used to determine the safety concentrations in HepG2 cells. Glucose assay kit was used to check glucose uptake after treated with BDDE. Western blotting assay was used to explore the potent mechanisms. The db/db mice were used to evaluate the in vivo antidiabetic effects of BDDE. Body weight, blood glucose, Glycated hemoglobin (HbA1c), lipid profile, and insulin level were checked at the respective time points. Gastrocnemii were dissected and used to analyze the PTP1B and insulin receptor β (IRβ) expression.

Results

BDDE increased the insulin-resisted glucose uptake in HepG2 cells. BDDE also decreased the expression of PTP1B and activated the substrates and downstream signals in insulin signal pathway, such as IRβ, insulin receptor substrate-1/2 (IRS1/2), phosphoinositide 3-kinase (PI3K), and protein kinase B (PKB/Akt). In the db/db mice model, BDDE significantly decreased the blood glucose, HbA1c and triglyceride (TG) levels. BDDE also decreased the expression of PTP1B and activated the phosphorylation of IRβ in gastrocnemii. Moreover, BDDE at high doses downregulated the body weight without affecting food and water intake.

Conclusion

Our results suggest that BDDE as a new PTP1B inhibitor improves glucose metabolism by stimulating the insulin signaling and could be used in the treatment of type-2 diabetes mellitus.     

Novel hypoglycemic effects of Ganoderma lucidum water-extract in obese/diabetic (+db/+db) mice

In this study, we evaluated the pharmacological effects of Ganoderma lucidum (G. lucidum) (water-extract) (0.003, 0.03 and 0.3 g/kg, 4-week oral gavage) consumption using the lean (+db/+m) and the obese/diabetic (+db/+db) mice. Different physiological parameters (plasma glucose and insulin levels, lipoproteins-cholesterol levels, phosphoenolpyruvate carboxykinase (PEPCK), 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase) and isolated aorta relaxation of both species were measured and compared. G. lucidum (0.03 and 0.3 g/kg) lowered the serum glucose level in +db/+db mice after the first week of treatment whereas a reduction was observed in +db/+m mice only fed with 0.3 g/kg of G. lucidum at the fourth week. A higher hepatic PEPCK gene expression was found in +db/+db mice. G. lucidum (0.03 and 0.3 g/kg) markedly reduced the PEPCK expression in +db/+db mice whereas the expression of PEPCK was attenuated in +db/+m mice (0.3 g/kg G. lucidum). HMG CoA reductase protein expression (in both hepatic and extra-hepatic organs) and the serum insulin level were not altered by G. lucidum. These data demonstrate that G. lucidum consumption can provide beneficial effects in treating type 2 diabetes mellitus (T2DM) by lowering the serum glucose levels through the suppression of the hepatic PEPCK gene expression.     

Chronic stress aggravates glucose intolerance in leptin receptor-deficient (db/db) mice

Genetic predisposition and environmental challenges interact to determine individual vulnerability to obesity and type 2 diabetes. We previously established a mouse model of chronic subordination stress-induced hyperphagia, obesity, metabolic like-syndrome and insulin resistance in the presence of a high-fat diet. However, it remains to be established if social stress could also aggravate glucose intolerance in subjects genetically predisposed to develop obesity and type 2 diabetes. To answer this question, we subjected genetically obese mice due to deficiency of the leptin receptor (db/db strain) to chronic subordination stress. Over five weeks, subordination stress in db/db mice led to persistent hyperphagia, hyperglycemia and exacerbated glucose intolerance altogether suggestive of an aggravated disorder when compared to controls. On the contrary, body weight and fat mass were similarly affected in stressed and control mice likely due to the hyperactivity shown by subordinate mice. Stressed db/db mice also showed increased plasma inflammatory markers. Altogether our results suggest that chronic stress can aggravate glucose intolerance but not obesity in genetically predisposed subjects on the basis of a disrupted leptin circuitry.     

Influence of the mutation "diabetes" on insulin release and islet morphology in mice of different genetic backgrounds

Mice, 7–8-mo old, of the C57BL/KsJ-db strain and homozygotic for the mutant gene db, exhibited marked hyperglycemia and moderately elevated serum insulin levels. Light and electron microscopy provided evidence of a slightly decreased proportion of β cells in the pancreatic islets, irregular islet architecture with intraislet ducts, and degenerative as well as hypertrophic changes in the individual β cells. As a rule, islets microdissected from these mice did not release insulin in response to glucose, theophylline, iodoacetamide, or chloromercuribenzene-p-sulphonic acid. The absence of secretory responses was not simply due to lack of insulin. Although the islet content of insulin was decreased in C57BL/KsJ-db/db mice, the remaining amount was severalfold larger than that released from stimulated islets of normal controls. Another mutation, db^2J, an allele of db with identical phenotypic expressions in the C57BL/KsJ strain, was studied on the genetic background C57BL/6J. In contrast to the severely diabetic C57BL/KsJ-db/db animals, the C57BL/6J-db^2J/db^2J mice were characterized by highly elevated serum insulin levels and only moderate hyperglycemia. Their endocrine pancreas was enlarged and showed an increased proportion of β cells. Like the islets of normal mice, those of C57BL/6J-db^2J/db^2J mice responded to glucose and chloromercuribenzene-p-sulphonic acid, the glucose-induced responses being potentiated by theophylline or iodoacetamide. C57BL/KsJ-db/db mice should provide a valuable model for studying defects in insulin secretion in relation to diabetes mellitus. Mice of the C57BL/6J strain offer a control material that may help to elucidate the dependence of the insulin secretory defect on the background genome.     

Brain-derived Neurotrophic Factor Regulates Energy Expenditure Through the Central Nervous System in Obese Diabetic Mice

It has been previously demonstrated that brain-derived neurotrophic factor (BDNF) regulates glucose metabolism and energy expenditure in rodent diabetic models such as C57BL/KsJ-lepr^db/lepr^db (db/db) mice. Central administration of BDNF has been found to reduce blood glucose in db/db mice, suggesting that BDNF acts through the central nervous system. In the present study we have expanded these investigations to explore the effect of central administration of BDNF on energy metabolism. Intracerebroventricular administration of BDNF lowered blood glucose and increased pancreatic insulin content of db/db mice compared with vehicle-treated pellet pair-fed db/db mice. While body temperatures of the pellet pair-fed db/db mice given vehicle were reduced because of restricted food supply in this pair-feeding condition, BDNF treatment remarkably alleviated the reduction of body temperature suggesting the enhancement of thermogenesis. BDNF enhanced norepinephrine turnover and increased uncoupling protein-1 mRNA expression in the interscapular brown adipose tissue. Our evidence indicates that BDNF activates the sympathetic nervous system via the central nervous system and regulates energy expenditure in obese diabetic animals.     

DC260126: A Small-Molecule Antagonist of GPR40 that Protects against Pancreatic β-Cells Dysfunction in db/db Mice

G protein-coupled receptor 40 (GPR40) mediates both acute and chronic effects of free fatty acids (FFAs) on insulin secretion. However, it remains controversial whether inhibition of GPR40 would be beneficial in prevention of type 2 diabetes. This study is designed to evaluate the potential effects of DC260126, a small molecule antagonist of GPR40, on β-cell function following administration of 10 mg/kg dose of DC260126 to obese diabetic db/db mice. Oral glucose tolerance test, glucose stimulated insulin secretion and insulin tolerance test were used to investigate the pharmacological effects of DC260126 on db/db mice after 21-days treatment. Immunohistochemistry and serum biochemical analysis were also performed in this study. Although no significant change of blood glucose levels was found in DC260126-treated mice, DC260126 significantly inhibited glucose stimulated insulin secretion, reduced blood insulin level and improved insulin sensitivity after 3 weeks administration in db/db mice. Moreover, DC260126 reduced the proinsulin/insulin ratio and the apoptotic rate of pancreatic β-cells remarkably in DC260126-treated db/db mice compared to vehicle-treated mice (p<0.05, n = 8). The results suggest that although DC260126 could not provide benefit for improving hyperglycemia, it could protect against pancreatic β-cells dysfunction through reducing overload of β-cells, and it increases insulin sensitivity possibly via alleviation of hyperinsulinemia in db/db mice.     

Antidiabetic,Antihyperlipidemic and Antioxidant Activities of a Novel Proteoglycan from Ganoderma Lucidum Fruiting Bodies on db/db Mice and the Possible Mechanism

Previously, we screened a proteoglycan for anti-hyperglycemic, named FYGL, from Ganoderma Lucidum. For further research of the antidiabetic mechanisms of FYGL in vivo, the glucose homeostasis, activities of insulin-sensitive enzymes, glucose transporter expression and pancreatic function were analyzed using db/db mice as diabetic models in the present work. FYGL not only lead to a reduction in glycated hemoglobin level, but also an increase in insulin and C-peptide level, whereas a decrease in glucagons level and showed a potential for the remediation of pancreatic islets. FYGL also increased the glucokinase activities, and simultaneously lowered the phosphoenol pyruvate carboxykinase activities, accompanied by a reduction in the expression of hepatic glucose transporter protein 2, while the expression of adipose and skeletal glucose transporter protein 4 was increased. Moreover, the antioxidant enzyme activities were also increased by FYGL treatment. Thus, FYGL was an effective antidiabetic agent by enhancing insulin secretion and decreasing hepatic glucose output along with increase of adipose and skeletal muscle glucose disposal in the late stage of diabetes. Furthermore, FYGL is beneficial against oxidative stress, thereby being helpful in preventing the diabetic complications.     

Bile acid sequestration reduces plasma glucose levels in db/db mice by increasing its metabolic clearance rate

Aims/Hypothesis

Bile acid sequestrants (BAS) reduce plasma glucose levels in type II diabetics and in murine models of diabetes but the mechanism herein is unknown. We hypothesized that sequestrant-induced changes in hepatic glucose metabolism would underlie reduced plasma glucose levels. Therefore, in vivo glucose metabolism was assessed in db/db mice on and off BAS using tracer methodology.

Methods

Lean and diabetic db/db mice were treated with 2% (wt/wt in diet) Colesevelam HCl (BAS) for 2 weeks. Parameters of in vivo glucose metabolism were assessed by infusing [U-¹³C]-glucose, [2-¹³C]-glycerol, [1-²H]-galactose and paracetamol for 6 hours, followed by mass isotopologue distribution analysis, and related to metabolic parameters as well as gene expression patterns.

Results

Compared to lean mice, db/db mice displayed an almost 3-fold lower metabolic clearance rate of glucose (p = 0.0001), a ∼300% increased glucokinase flux (p = 0.001) and a ∼200% increased total hepatic glucose production rate (p = 0.0002). BAS treatment increased glucose metabolic clearance rate by ∼37% but had no effects on glucokinase flux nor total hepatic or endogenous glucose production. Strikingly, BAS-treated db/db mice displayed reduced long-chain acylcarnitine content in skeletal muscle (p = 0.0317) but not in liver (p = 0.189). Unexpectedly, BAS treatment increased hepatic FGF21 mRNA expression 2-fold in lean mice (p = 0.030) and 3-fold in db/db mice (p = 0.002).

Conclusions/Interpretation

BAS induced plasma glucose lowering in db/db mice by increasing metabolic clearance rate of glucose in peripheral tissues, which coincided with decreased skeletal muscle long-chain acylcarnitine content.     

Osthole, a potential antidiabetic agent, alleviates hyperglycemia in db/db mice

Osthole is an agent isolated from Cnidium monnieri (L.) Cusson and Angelica pubescens and has been used to treat several diseases, including metabolic syndromes. To investigate the hypoglycemic effects of osthole in diabetic db/db mice and the underlying mechanisms of these effects by in vitro assay, diabetic db/db mice and cell experiments were utilized to understand its possible effects. Osthole significantly activated both PPARα and PPARγ in a dose-dependent manner based on the results of the transition transfection assay. The activation of PPARα and PPARγ by osthole also resulted in an increase in the expression of PPAR target genes such as PPAR itself, adipose fatty acid-binding protein 2, acyl-CoA synthetases, and carnitine palmitoyltransferase-1A. In vitro results suggested that osthole might be a dual PPARα/γ activator, but its chemical structure differed from that of the thiazolidinedione class of antidiabetic drugs. In addition, osthole markedly activated the AMP-activated protein kinase and its downstream acetyl CoA carboxylase molecules by increasing their phosphorylation levels. Finally, obese diabetic db/db mice were treated with osthole by different administered routes, and osthole was found to markedly reduce blood glucose level. Interestingly, osthole did not reduce the blood insulin or lipid levels, two phenomena that did occur in animals treated with insulin sensitizers like PPAR agonists. These results suggest that osthole can alleviate hyperglycemia and could be potentially developed into a novel drug for treatment of diabetes mellitus.     

8,8-Dimethyldihydroberberine with improved bioavailability and oral efficacy on obese and diabetic mouse models

The clinical use of the natural alkaloid berberine (BBR) as an antidiabetic reagent is limited by its poor bioavailability. Our previous work demonstrated that dihydroberberine (dhBBR) has enhanced bioavailability and in vivo efficacy compared with berberine. Here we synthesized the 8,8-dimethyldihydroberberine (Di-Me) with improved stability, and bioavailability over dhBBR. Similar to BBR and dhBBR, Di-Me inhibited mitochondria respiration, increased AMP:ATP ratio, activated AMPK and stimulated glucose uptake in L6 myotubes. In diet-induced obese (DIO) mice, Di-Me counteracted the increased adiposity, tissue triglyceride accumulation and insulin resistance, and improved glucose tolerance at a dosage of 15 mg/kg. Administered to db/db mice with a dosage of 50 mg/kg, Di-Me effectively reduced random fed and fasting blood glucose, improved glucose tolerance, alleviated insulin resistance and reduced plasma triglycerides, with better efficacy than dhBBR at the same dosage. Our work highlights the importance of dihydroberberine analogs as potential therapeutic reagents for type 2 diabetes treatment.     

Discovery of P1736, a Novel Antidiabetic Compound That Improves Peripheral Insulin Sensitivity in Mice Models

Insulin resistance is a characteristic feature of Type 2 diabetes. Insulin resistance has also been implicated in the pathogenesis of cardiovascular disease. Currently used thiazolidinedione (TZD) insulin sensitizers although effective, have adverse side effects of weight gain, fluid retention and heart failure. Using fat cell-based phenotypic drug discovery approach we identified P1736, a novel antidiabetic molecule that has completed Phase II clinical trials. The present study evaluated the in vitro and in vivo pharmacological properties of P1736. P1736 is a non-TZD and it did not activate human PPAR(Peroxisome Proliferator Activated Receptor Gamma )receptors. P1736 caused dose dependent increase in glucose uptake (EC₅₀-400nM) in the insulin resistant 3T3 adipocytes. The compound (10µM) induced translocation of GLUT-4 (Glucose Transporter type 4) transporters in these adipocytes while metformin (1.0mM) was inactive. In diabetic db/db mice, P1736 (150mg/kg) was more efficacious than metformin in lowering plasma glucose (35% vs 25%) and triglyceride levels (38% vs 31%). P1736 tested at 5mg/kg, twice daily doses, reduced glucose by 41% and triglycerides by 32%, in db/db mice. These effects were not associated with adverse effects on body weight or liver function. Rosiglitazone (5mg/kg, twice daily) caused 60% and 40 % decreases in glucose and triglyceride levels, respectively. However, rosiglitazone induced 13% weight gain (p<0.05) in db/db mice. P1736 was also efficacious in ob/ob mice wherein 30-35% decrease in glucose and significant improvement in hyperinsulinemia were observed. Administration of P1736 to ob/ob mice resulted in 70% increase in glucose uptake in soleus muscles while metformin caused 38% increase. P1736 exhibited excellent safety profile and was weight neutral in all preclinical models of diabetes. Thus, P1736 with its unique pharmacology coupled with PPAR- independent mode of action could represent an alternative option in the management of insulin resistant Type 2 diabetic patients.     

Hypoglycemic effect of aspalathin,a rooibos tea component from Aspalathus linearis,in type 2 diabetic model db/db mice

Effects of aspalathin, a green rooibos tea component, on glucose metabolism were studied in vitro and in vivo. We first examined the effect of aspalathin on glucose uptake by cultured L6 myotubes and on insulin secretion from cultured RIN-5F pancreatic β-cells in vitro, and then investigated the effect of dietary aspalathin on fasting blood glucose level and conducted an intraperitoneal glucose tolerance test (IPGTT) using type 2 diabetes model mice in vivo. Aspalathin dose-dependently and significantly increased glucose uptake by L6 myotubes at concentrations 1–100 μM. It also significantly increased insulin secretion from cultured RIN-5F cells at 100 μM. Dietary aspalathin (0.1–0.2%) suppressed the increase in fasting blood glucose levels of db/db mice for 5 weeks. In IPGTT, aspalathin improved impaired glucose tolerance at 30, 60, 90, and 120 min in db/db mice. These results suggest that aspalathin has beneficial effects on glucose homeostasis in type 2 diabetes through stimulating glucose uptake in muscle tissues and insulin secretion from pancreatic β-cells.