Novel GPR40 agonist AS2575959 exhibits glucose metabolism improvement and synergistic effect with sitagliptin on insulin and incretin secretion.

AIMS: GPR40 is a free fatty acid receptor that regulates glucose-dependent insulin secretion at pancreatic ß-cells and glucagon-like peptide-1 (GLP-1), one of the major incretins, secretion at the endocrine cells of the gastrointestinal tract. We investigated the synergistic effect of AS2575959, a novel GPR40 agonist, in combination with sitagliptin, a major dipeptidyl peptidase-IV (DPP-IV) inhibitor, on glucose-dependent insulin secretion and GLP-1 secretion. In addition, we investigated the chronic effects of AS2575959 on whole-body glucose metabolism. MAIN METHODS: We evaluated acute glucose metabolism on insulin and GLP-1 secretion using an oral glucose tolerance test (OGTT) as well as assessed the chronic glucose metabolism in diabetic ob/ob mice following the repeated administration of AS2575959. KEY FINDINGS: We discovered the novel GPR40 agonist sodium [(3S)-6-({4'-[(3S)-3,4-dihydroxybutoxy]-2,2',6'-trimethyl[1,1'-biphenyl]-3-yl}methoxy)-3H-spiro[1-benzofuran-2,1'-cyclopropan]-3-yl]acetate (AS2575959) and found that the compound influenced glucose-dependent insulin secretion both in vitro pancreas ß-cell-derived cells and in vivo mice OGTT. Further, we observed a synergistic effect of AS2575959 and DPP-IV inhibitor on insulin secretion and plasma GLP-1 level. In addition, we discovered the improvement in glucose metabolism on repeated administration of AS2575959. SIGNIFICANCE: To our knowledge, this study is the first to demonstrate the synergistic effect of a GPR40 agonist and DPP-IV inhibitor on the glucose-dependent insulin secretion and GLP-1 concentration increase. These findings suggest that GPR40 agonists may represent a promising therapeutic strategy for the treatment of type 2 diabetes mellitus, particularly when used in combination with DPP-IV inhibitors.

Enhanced insulin secretion and sensitization in diabetic mice on chronic treatment with a transient receptor potential vanilloid 1 antagonist.

AIMS: Inhibition of transient receptor potential vanilloid 1 (TRPV1) suppresses calcitonin gene-related peptide (CGRP) secretion in pancreatic nerve fiber cells, thereby stimulating insulin secretion. We examined the effects of repeat administration of the TRPV1 antagonist N-(4-tert-butylphenyl)-4-(3-chloropyridin-2-yl)tetrahydropyrazine-1(2H)-carboxamidte monohydrochloride (BCTC) to ob/ob mice, a model of type 2 diabetes with insulin resistance, on whole body glucose and lipid metabolism. MAIN METHODS: We measured blood parameters, including levels of glucose, insulin, and triglycerides, and performed the oral glucose tolerance test (OGTT) after repeat administration of BCTC to ob/ob mice twice a day for four weeks. KEY FINDINGS: We found that BCTC treatment reduced fasting glucose, triglyceride, and insulin levels in the whole body. The effects were comparable to that of pioglitazone, a major insulin-sensitizing agent. Further, we found that administration of BCTC significantly increased plasma insulin secretion in the OGTT, which differed from the effect of pioglitazone treatment. SIGNIFICANCE: Our study is the first to show the anti-diabetic pharmacological effects of the TRPV1 signal inhibitor BCTC. These findings suggest that TRPV1 antagonists may represent a new class of drugs effective in treating type 2 diabetes mellitus because of their dual effects as insulin sensitizers and secretagogues.

Discovery of novel forkhead box O1 inhibitors for treating type 2 diabetes: improvement of fasting glycemia in diabetic db/db mice.

Excessive hepatic glucose production through the gluconeogenesis pathway is partially responsible for the elevated glucose levels observed in patients with type 2 diabetes mellitus (T2DM). The forkhead transcription factor forkhead box O1 (Foxo1) plays a crucial role in mediating the effect of insulin on hepatic gluconeogenesis. Here, using a db/db mouse model, we demonstrate the effectiveness of Foxo1 inhibitor, an orally active small-molecule compound, as a therapeutic drug for treating T2DM. Using mass spectrometric affinity screening, we discovered a series of compounds that bind to Foxo1, identifying among them the compound, 5-amino-7-(cyclohexylamino)-1-ethyl-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (AS1842856), which potently inhibits human Foxo1 transactivation and reduces glucose production through the inhibition of glucose-6 phosphatase and phosphoenolpyruvate carboxykinase mRNA levels in a rat hepatic cell line. Oral administration of AS1842856 to diabetic db/db mice led to a drastic decrease in fasting plasma glucose level via the inhibition of hepatic gluconeogenic genes, whereas administration to normal mice had no effect on the fasting plasma glucose level. Treatment with AS1842856 also suppressed an increase in plasma glucose level caused by pyruvate injection in both normal and db/db mice. Taken together, these findings indicate that the Foxo1 inhibitor represents a new class of drugs for use in treating T2DM.

Effects of the novel Foxo1 inhibitor AS1708727 on plasma glucose and triglyceride levels in diabetic db/db mice.

Recent evidence suggests that the forkhead transcription factor Foxo1 plays an important role in the regulation of glucose and triglyceride metabolism at the gene transcription level for glucose-6 phosphatase (G6Pase), phosphoenolpyruvate carboxykinase (PEPCK), and apolipoprotein C-III (apoC-III). Here, we report on the pharmacological effects of the novel Foxo1 inhibitor AS1708727, which we identified by compound screening. Chronic treatment of diabetic db/db mice with AS1708727 for four days significantly reduced blood glucose and triglyceride levels with decrease of gene expression levels of hepatic G6Pase, PEPCK, and apoC-III. No reports have yet examined the influence of Foxo1 inhibitors on these pharmacological effects. In this study, we newly identified a Foxo1 inhibitor compound capable of exerting both an anti-hypertriglyceridemic and anti-hyperglycemic effect. These effects were dependent on maintaining a stable blood concentration of AS1708727 and achieving a high rate of compound transition to the liver. We also investigated the action mechanism of AS1708727 on gluconeogenesis in vitro and in vivo. The compound inhibited gene expression of key gluconeogenic molecules and suppressed gluconeogenesis in Fao hepatocyte cells in vitro. Further, in the pyruvate challenge study using db/db mice in vivo, AS1708727 suppressed increases in blood glucose level by inhibiting gluconeogenic gene expression. These results indicate that the novel Foxo1 inhibitor AS1708727 may exert anti-diabetic and anti-hypertriglyceridemic effects by improving blood glucose and triglyceride metabolism at the gene expression level, and may represent a new class of drugs useful for treating type 2 diabetes mellitus and hypertriglyceridemia.

YM440, a novel hypoglycemic agent, protects against nephropathy in Zucker fatty rats via plasma triglyceride reduction.

The novel hypoglycemic agent, YM440 ((Z)-1,4-bis{4-[(3,5-dioxo-1,2,4-oxadiazolidin-2-yl) methyl] phenoxy}but-2-ene) is a ligand of the peroxisome proliferator-activated receptor, (PPAR) gamma. YM440 has been shown to counteract insulin resistance in diabetic rodent models. However, it is not clear whether this compound has a significant effect on hyperlipidemia in vivo. Hyperlipidemia has been reported to be a risk factor for the early development of renal disease. The aim of this study is to examine the effects of chronic treatment with YM440 on hyperlipidemia and renal injury in obese Zucker fatty (ZF) rats. Treatment of 8-week-old ZF rats with YM440 (100 mg/kg/day) for 16 weeks decreased plasma triglyceride and cholesterol concentrations. YM440 markedly reduced the rate of progression of both albuminuria and proteinuria. YM440 normalized urinary N-acetyl-beta-D-glucosaminidase (NAG) activity, which is a marker for renal proximal tubular damage, and ameliorated the rise in systolic blood pressure compared to the vehicle control. YM440 also blocked the development of nephromegaly. Histological analyses revealed that both glomerular area expansion and tubular cast accumulation gradually lessened in YM440-treated ZF rats. Regression analyses between the plasma triglyceride levels and the renal parameters (urinary protein excretion and albumin excretion) indicated that the renal parameters correlated positively with the plasma triglyceride levels. In conclusion, the hypolipidemic effects of YM440 prevent renal injury in ZF rats. YM440 might be useful for preventing the early development of diabetic nephropathy in subjects with type 2 diabetes by ameliorating metabolic control problems.

The novel hypoglycemic agent YM440 improves hepatic insulin resistance in obese Zucker fatty rats.

The novel hypoglycemic agent YM440 ((Z)-1,4-bis{4-[(3,5-dioxo-1,2,4-oxadiazolidin-2-yl)methyl] phenoxy}but-2-ene) is a ligand of the peroxisome proliferator-activated receptor (PPAR) gamma. YM440 has unique pharmacological profiles both in vitro and in vivo, but, it is not clear whether the compound has a significant effect on hepatic or peripheral insulin response throughout the body. The aim of this study is to examine the effects of YM440 on hepatic and peripheral insulin resistance in Zucker fatty (ZF) rats using the euglycemic-hyperinsulinaemic clamp technique. Treatment of ZF rats with YM440 (300 mg/kg per day) for 2 weeks significantly decreased plasma concentrations of glucose and insulin without inducing obesity. YM440 caused a 2-fold increase in the glucose infusion rate during euglycemic clamping compared with the vehicle control. YM440 also decreased the percent change in hepatic glucose production rate caused by intravenous insulin infusion in ZF rats. YM440 had no significant effect on the glucose disposal rate. These results indicate that YM440 ameliorates hepatic, but not peripheral insulin resistance in ZF rats. These findings strongly suggest that the main target organ of YM440 is the liver, unlike other PPARgamma agonist.

Antagonism of peroxisome proliferator-activated receptor gamma prevents high-fat diet-induced obesity in vivo.

Peroxisome proliferator-activated receptor gamma (PPARgamma) has been reported to play an important role to regulate adiposity and insulin sensitivity. It is not clear whether antagonism of PPARgamma using a synthetic ligand has significant effects on adipose tissue weight and glucose metabolism in vivo. The aim of this study is to examine the effects of a synthetic PPARgamma antagonist (GW9662) on adiposity and glycemic control in high-fat (HF) diet-fed mice. First the properties of GW9662 as a PPARgamma antagonist were estimated in vitro. GW9662 displaced [(3)H]rosiglitazone from PPARgamma with K(i) values of 13nM, indicating that the affinity of GW9662 for PPARgamma was higher than that of rosiglitazone (110nM). GW9662 had no effect on PPARgamma transactivation in cells expressing human PPARgamma. Treatment of 3T3-L1 preadipocytes with GW9662 did not increase aP2 expression or [(14)C]acetic acid uptake. GW9662 did not recruit transcriptional cofactors to PPARgamma. Limited trypsin digestion of the human PPARgamma/GW9662 complex showed patterns of digestion distinct from those of rosiglitazone. This suggests that the binding characteristics between GW9662 and PPARgamma are different from those of rosiglitazone. Treatment of HF diet-fed mice with GW9662 revealed that this compound prevented HF diet-induced obesity without affecting food intake. GW9662 suppressed any increase in the amount of visceral adipose tissue, but it did not change HF diet-induced glucose intolerance. These data indicate that antagonism of PPARgamma using a synthetic ligand suppresses the increased adiposity observed in HF diet-induced obesity, and that a PPARgamma antagonist could possibly be developed as an anti-obesity drug.

On the mechanism for neomycin reversal of wortmannin inhibition of insulin stimulation of glucose uptake.

Although a number of studies and approaches have indicated that activation of the Ser/Thr kinase called Akt/protein kinase B is critical for the insulin-stimulated increase of glucose uptake in adipocytes, other studies have indicated that this enzyme may play an ancillary role. For example, a recent study indicated that neomycin would allow insulin-stimulated Glut4 translocation and glucose transport in the presence of the phosphatidylinositol (PI) 3-kinase inhibitor, wortmannin, a known inhibitor of Akt activation (James, D. J., Salaun, C., Brandie, F. M., Connell, J. M. C., and Chamberlain, L. H. (2004) J. Biol. Chem. 279, 20567-20570). To better understand this observation, we examined a number of downstream targets of Akt. As previously reported, treatment of 3T3-L1 adipocytes with neomycin prevented the wortmannin inhibition of insulin-stimulated glucose transport. However, in the presence of neomycin, wortmannin did not inhibit the insulin-stimulated phosphorylation of several downstream targets of Akt including a proline-rich Akt substrate of 40 kDa, ribosomal protein S6, and glycogen synthase kinase-3. In addition, neomycin did not prevent the ability of a structurally unrelated PI 3-kinase inhibitor, LY294002, to inhibit the insulin-stimulated activation of glucose uptake. Moreover, neomycin reversed the inhibitory effect of wortmannin but not LY294002 on insulin stimulation of Akt kinase activity. Finally, neomycin was found to inactivate in vitro the PI 3-kinase inhibitory actions of wortmannin but not LY294002. These results indicate that the effects of neomycin in adipocytes are not mediated via its ability to sequester phosphatidylinositol 4,5-bisphosphate but are instead caused by the ability of neomycin to inactivate wortmannin.

Hypoglycemic agent YM440 suppresses hepatic glucose output via gluconeogenesis by reducing glucose-6-phosphatase activity in obese Zucker rats.

Using a glucose clamp, we had shown that YM440, (Z)-1,4-bis[4-[(3,5-dioxo-1,2,4-oxadiazolidin-2-yl)methyl]phenoxy]but-2-ene, reduced the increased hepatic glucose output in obese Zucker rats. We further examined effects of YM440 on 14C-incorporation from [14C]bicarbonate into blood glucose via gluconeogenesis, and on gluconeogenic enzymatic activities. Fed obese Zucker rats showed a 4-fold increase of 14C-incorporation into blood glucose compared to that in lean rats. Glucose-6-phosphatase and fructose-1,6-bisphosphatase activities in obese rats were increased 1.4-fold and 1.6-fold compared with lean rats. YM440 (300 mg/kg for 2 weeks) decreased 14C-incorporation into blood glucose by 29% in obese rats. Glucose-6-phosphatase but not fructose-1,6-bisphosphatase activity was reduced by YM440 and closely correlated with 14C-incorporation into blood glucose, indicating a key role for glucose-6-phosphatase in hepatic glucose output. These results suggest that the increased gluconeogenesis in obese rats is mainly due to the increased activities of glucose-6-phosphatase and fructose-1,6-bisphosphatase and that YM440 suppresses hepatic glucose output by reducing glucose-6-phosphatase activity.

Differential effects of YM440 a hypoglycemic agent on binding to a peroxisome proliferator-activated receptor gamma and its transactivation.

Peroxisome proliferator-activated receptor (PPAR) gamma is a ligand-inducible transcription factor mediating glucose and lipid metabolism. Prior studies showed that YM440 ameliorated hyperglycemia in diabetic mice without affecting body fat weight or PPARgamma transactivation. In this study we have examined further the effects of YM440 on PPARgamma binding, transactivation and conformational change. YM440, pioglitazone and rosiglitazone displaced [3H]rosiglitazone from PPARgamma with K(i) values of 4.0, 3.1, and 0.20 microM, indicating that YM440 was comparable to pioglitazone and 20-fold less potent than rosiglitazone. Although pioglitazone and rosiglitazone increased both PPARgamma transactivation in cells expressing human full-length PPARgamma2 or GAL4-PPARgamma and mRNA expression of PPARgamma responsive genes in 3T3-L1 cells, YM440 had weak effects on PPARgamma transactivation and mRNA expression being 550- to 790-fold and 36- to 110-fold less active than rosiglitazone, respectively. YM440 and rosiglitazone induced interaction between PPARgamma and the transcriptional cofactor, p300 or SRC-1, but YM440 was 151- and 1091-fold less potent than rosiglitazone, respectively. The weak transcriptional activity of YM440 was not due to poor cell permeability. Limited trypsin digestion of the full-length human PPARgamma2 with YM440 or rosiglitazone showed distinct patterns of digestion, suggesting a difference in the conformational change of PPARgamma. When db/db mice were treated with YM440 (100mg/kg) for 28 days, YM440 increased hepatic glucokinase expression but not adipose tissue FABP and UCP1 expression, indicating a tissue selective expression of PPARgamma-related genes. Unique properties regarding the binding-transactivation of PPARgamma by YM440 may lead to the hypoglycemic activity without affecting body fat weight in diabetic mice.

Hypoglycemic agent YM440 ameliorates the impaired hepatic glycogenesis after glucose loading by increasing glycogen synthase activity in obese Zucker rats.

We studied the role of hepatic glycogenesis in glucose intolerance after glucose loading in obese Zucker rats and the effects of YM440 ((Z)-1,4-bis[4-[(3,5-dioxo-1,2,4-oxadiazolidin-2-yl)methyl]phenoxy]but-2-ene) on it. Lean and obese Zucker rats were treated with YM440 (300 mg/kg) for 14 days and then fasted for 20 h. Thirty percent glucose (0.6 g/kg) or saline was administered intravenously followed by NaH14CO3. Gluconeogenesis was evaluated based on the incorporation of 14C-bicarbonate into blood glucose and hepatic glycogen. Obese rats showed an increase in the incorporation of 14C into blood glucose of 2.5-fold compared to lean rats. The glucose loading decreased the 14C-blood glucose release by 18% in obese rats and 43% in lean rats at 45 min. Glucose loading increased the hepatic glycogen content and 14C incorporation into glycogen in lean but not obese rats. YM440 decreased levels of fasting plasma insulin and blood glucose and the hepatic glycogen content by 50% compared with values for untreated obese rats. After glucose loading, YM440 promoted the incorporation of 14C into glycogen and glycogen synthase activity, leading to an improvement in glucose tolerance. These results indicate that glucose intolerance in obese rats was associated with decreased hepatic glycogenesis and YM440 improved the intolerance by normalizing glycogen metabolism.