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Neurturin (NRTN), a member of the glial-derived neurotrophic factor family, was identified from an embryonic chicken pancreatic cDNA library in a screen for secreted factors. In this study, we assessed the potential antidiabetic activities of NRTN relative to liraglutide, a glucagon-like peptide 1 receptor agonist, in Zucker diabetic fatty (ZDF) rats. Subcutaneous administration of NRTN to 8-week-old male ZDF rats prevented the development of hyperglycemia and improved metabolic parameters similar to liraglutide. NRTN treatment increased pancreatic insulin content and β-cell mass and prevented deterioration of islet organization. However, unlike liraglutide-treated rats, NRTN-mediated improvements were not associated with reduced body weight or food intake. Acute NRTN treatment did not activate c-Fos expression in key feeding behavior and metabolic centers in ZDF rat brain or directly enhance glucose-stimulated insulin secretion from pancreatic β-cells. Treating 10-week-old ZDF rats with sustained hyperglycemia with liraglutide resulted in some alleviation of hyperglycemia, whereas NRTN was not as effective despite improving plasma lipids and fasting glucose levels. Interestingly, coadministration of NRTN and liraglutide normalized hyperglycemia and other metabolic parameters, demonstrating that combining therapies with distinct mechanism(s) can alleviate advanced diabetes. This emphasizes that therapeutic combinations can be more effective to manage diabetes in individuals with uncontrolled hyperglycemia. [ABSTRACT FROM AUTHOR]

OBJECTIVE--Glucocorticoid excess is characterized by increased adiposity, skeletal myopathy, and insulin resistance, but the precise molecular mechanisms are unknown. Within skeletal muscle, 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) converts cortisone (11-dehydrocorticosterone in rodents) to active cortisol (corticosterone in rodents). We aimed to determine the mechanisms underpinning glucocorticoid-induced insulin resistance in skeletal muscle and indentify how 11β-HSD1 inhibitors improve insulin sensitivity. RESEARCH DESIGN AND METHODS--Rodent and human cell cultures, whole-tissue explants, and animal models were used to determine the impact of glucocorticoids and selective 11β-HSD1 inhibition upon insulin signaling and action. RESULTS--Dexamethasone decreased insulin-stimulated glucose uptake, decreased IRS1 mRNA and protein expression, and increased inactivating pSer[sup 307] insulin receptor substrate (IRS)-1. 11β-HSD1 activity and expression were observed in human and rodent myotubes and muscle explants. Activity was predominantly oxo-reductase, generating active glucocorticoid. A1 (selective 11β-HSD1 inhibitor) abolished enzyme activity and blocked the increase in pSer[sup 307] IRS1 and reduction in total IRS1 protein after treatment with 11DHC but not corticosterone. In C57B16/J mice, the selective 11β-HSD1 inhibitor, A2, decreased fasting blood glucose levels and improved insulin sensitivity. In KK mice treated with A2, skeletal muscle pSer[sup 307] IRS1 decreased and pThr[sup 303] Akt/PKB increased. In addition, A2 decreased both lipogenic mid lipolytic gene expression. CONCLUSIONS--Prereceptor facilitation of glucocorticoid action via 11β-HSD1 increases pSer[sup 307] IRS1 and may be crucial in mediating insulin resistance in skeletal muscle. Selective 11β-HSD1 inhibition decreases pSer[sup 307] IRS1, increases pThr[sup 308] Akt/PKB, and decreases lipogenic and lipolytic gene expression that may represent an important mechanism underpinning their insulin-sensitizing action. Diabetes 58:2506-2515, 2009 [ABSTRACT FROM AUTHOR]

Because glucokinase is a metabolic sensor involved in the regulated release of insulin, we have investigated the acute actions of novel glucokinase activator compound 50 (GKA50) on islet function. Insulin secretion was determined by enzyme-linked immunosorbent assay, and microfluorimetry with fura-2 was used to examine intracellular Ca2+ homeostasis ([Ca2+]i) in isolated mouse, rat, and human islets of Langerhans and in the MIN6 insulin-secreting mouse cell line. In rodent islets and MIN6 cells, 1 µmol/l GKA50 was found to stimulate insulin secretion and raise [Ca2+]i in the presence of glucose (2-10 mmol/l). Similar effects on insulin release were also seen in isolated human islets. GKA50 (1 µmol/l) caused a leftward shift in the glucose-concentration response profiles, and the half-maximal effective concentration (EC50) values for glucose were shifted by 3 mmol/l in rat islets and ∼10 mmol/l in MIN6 ceils. There was no significant effect of GKA50 on the maximal rates of glucose-stimulated insulin secretion. In the absence of glucose, GKA50 failed to elevate [Ca2+]i (1 µmol/l GKA50) or to stimulate insulin release (30 nmol/l-10 µmol/l GKA50). At 5 mmol/l glucose, the EC50 for GKA50 in MIN6 ceils was ∼0.3 µmol/l. Inhibition of glucokinase with mannoheptulose or 5-thioglucose selectively inhibited the action of GKA50 on insulin release but not the effects of tolbutamide. Similarly 3-methoxyglucose prevented GKA50-induced rises in [Ca2+]i but not the actions of tolbutamide. Finally, the ATP-sensitive K+ channel agonist diazoxide (200 µmol/l) inhibited GKA50-induced insulin release and its elevation of [Ca2+]i We show that GKA50 is a glucose-like activator of β-cell metabolism in rodent and human islets and a Ca2+-dependent modulator of insulin secretion. Diabetes 56:1694-1702, 2007 [ABSTRACT FROM AUTHOR]

Investigates hypothalamic areas known to express the melanocortin-4 receptor (MC4R) that are involved in the regulation of feeding. Hypothalamic nuclei expressing MC4R as varying in their sensitivity with regard to their effect on feeding; Use of an alpha melanocyte stimulating hormone; Endogenous MC4R agonist and agouti-related peptide.

Nonalcoholic fatty liver disease (NAFLD), is associated with metabolic disease and estimated to affect 25% of adults. NAFLD can progress to nonalcoholic steatohepatitis (NASH) which may lead to cirrhosis and hepatocellular carcinoma. There is no current treatment or cure for NASH. AMPK (5'AMP-activated protein kinase) activators have shown potential for treating NAFLD/NASH due to their effects on fatty acid inhibition and cholesterol synthesis. To evaluate this potential, an AMPK activator (herein known as C455) was selected for a preclinical NASH study. C455 demonstrated potent and selective activation of AMPK (cellular EC50= 85 nM). X-ray crystallography showed the compound binds at the ADaM site, and pharmacokinetics determined a bioavailability of 45% and half-life of 3h. Mice (male ob/ob on Amylin-NASH diet for 14-weeks or low-fat control) were dosed orally with vehicle or C455 at 3 or 30mg/kg daily. After 6 weeks of treatment, plasma ALT and terminal liver weight were decreased 32% and 22% respectively in mice treated with 30mg/kg C455 vs. vehicle. This dose also decreased liver lipid from 33% to 23%. Fibrosis via collagen staining did not improve with treatment, but significant decreases in mRNA transcripts for Col1a1(62%), Col1a2(59%), Col4a1(56%), and Timp1(55%) were seen with the high dose. Histology showed dose dependent increases in heart weight relative to body weight, and increased expression of genes associated with cardiac hypertrophy. Mice given 30mg/kg C455 also had increased cardiac glycogen storage compared to vehicle treated or LFD control mice. Our study results show that systemic activation of AMPK in a diet-induced mouse model of NASH reduces plasma ALT, decreases liver lipid, and suppressed hepatic collagen gene expression but shows no histological improvement in fibrosis. Coupled with increased heart weight and glycogen storage, the data suggests that current small molecule activators of AMPK may not be viable therapies for the treatment of NASH-related fibrotic disease. Disclosure: K.M. Mather: None. M.L. Boland: None. E. Rivers: None. A. Srivastava: None. M. Schimpl: Employee; Self; AstraZeneca. Stock/Shareholder; Self; AstraZeneca. J. Robinson: None. P.T.C. Wan: None. J.L. Hansen: None. J.A. Read: Employee; Self; AstraZeneca. Stock/Shareholder; Self; AstraZeneca. J.L. Trevaskis: Employee; Self; Gilead Sciences, Inc. D.M. Smith: Employee; Self; AstraZeneca. [ABSTRACT FROM AUTHOR]

Glucokinase (GK) plays a key role in maintaining glucose homeostasis by stimulating insulin secretion from pancreatic β-cells and increasing hepatic glucose uptake. In this study we have investigated the effects of a novel, orally active glucokinase activator (GKA71) on insulin secretion and glucose tolerance in mice with high-fat diet (HFD) induced glucose intolerance. Mice were fed the HFD (58% fat by energy) for 8 weeks prior to administration of GKA71, which was provided in the diet (150 mg GKA71/kg food) giving a daily dose of ∼300 µg GKA71/mouse. Control mice were fed HFD or a normal diet (ND, 11% fat by energy). After 1 and 4 weeks with GKA71, glucose tolerance was studied in intravenous glucose tolerance test (IVGTT). Blood samples were taken just before and 1, 5, 10, 20, 50 and 75 min after the glucose injection (0.75g/kg). After 4-weeks treatment islets and liver were isolated. The GKA treatment significantly reduced basal plasma glucose level (5.3±0.3 vs. 8.3±0.3 mM in HFD, P<0.001, and 7.4±0.3 mM in ND, P<0.001). Basal insulin levels were also reduced by GKA71 (210±20 vs. 520±100 pM in HFD, P<0.01). The IVGTTs showed that GKA71 significantly improved glucose tolerance compared to HFD control mice (K[sub G] 4.0±0.5 vs. 2.5±0.2 %/min in HFD, P<0.01) being similar to ND fed mice (K[sub G] 3.8±0.2 %/min), although without increasing insulin secretion (AIR 485±120 vs. 670±85 pM in HFD, P>0.05). The AIR was 890±74 pM in the ND fed mice. There was no difference between the IVGTT results after 1 or 4 weeks with GKA71, suggesting full effect already after l-weeks treatment. Isolated islets from GKA treated mice demonstrated augmented glucose stimulated insulin secretion. Liver glycogen and triglyceride levels were similar in HFD control and HFD-GKA mice. In conclusion, activation of GK in HFD-fed mice potently reduces glycemia and normalizes glucose tolerance, demonstrating GKA as a potential therapeutic agent for treatment of type 2 diabetes. [ABSTRACT FROM AUTHOR]

Glucokinase (GK) is a metabolic sensor involved in the regulated release of insulin from pancreatic β-cells. Activators of GK may therefore have a possible role in the therapeutic management of type 2 diabetes. Here, we have examined the actions of the GK activator GKA50 on insulin secretion and intracellular Ca[sup 2+] homeostasis ([Ca[sup 2+]][sub i]) in isolated mouse, rat and human islets of Langerhans, and in the MIN6 insulin-secreting cell line. In rodent islets and MIN6 cells, 1µM GKA50 was found to stimulate insulin secretion and raise [Ca[sup 2+]][sub i] in the presence of glucose (2-10mM). Similar effects on insulin release were also seen in isolated human islets. GKA50 (1µM) caused a leftwards shift in the glucose-concentration response profiles and the EC[sub 50] values for glucose were shifted by 3mM in rat islets and approximately 10mM in MIN6 cells. There was no significant effect of GKA50 on the maximal rates of GSIS. In the absence of glucose GKA50 failed to elevate [Ca[sup 2+]][sub i] (1µM GKA50) or stimulate insulin release (30nM-10µM GKA50). At 5mM glucose the EC[sub 50] for GKA50 in MIN6 cells was approximately 0.3µM. Inhibition of GK with mannoheptulose or 5-thioglucose selectively inhibited the action of GKA50 on insulin release but not the effects of tolbutamide. Similarly, compromising glucose metabolism by 3-methoxyglucose prevented GKA50-induced rises in [Ca[sup 2+]][sub i] but not the actions of tolbutamide. Finally, we also show that the K[sub ATP] channel agonist diazoxide (200µM) inhibited GKA50-induced insulin release and its elevation of [Ca[sup 2+]][sub i]. This study illustrates that GKA50 is a glucose-like activator of βcell metabolism and a Ca[sup 2+]-dependent modulator of insulin secretion. [ABSTRACT FROM AUTHOR]

GK regulates blood glucose, via its effects on glucose stimulated insulin secretion (GSIS) from the β-cell, and hepatic glucose utilisation. In man, heterozygous loss of function mutations cause maturity onset diabetes of the young 2. In this study we generated GK [sup +/-] mice and assessed the effect of high-fat diet (HFD) on metabolic control, gene expression and in vitro efficacy of a GK activator (GKA). Male GK[sup +/+] and GK[sup +/-] mice were divided into groups (n=8-10) at 10 weeks of age and fed HFD or CHOW diet (CD) for 10 weeks. Multiple parameters including blood glucose, plasma insulin and glucose tolerance were assessed. Further groups of animals were used for in vitro GSIS and islet and liver gene expression analysis. GK[sup +/-] mice showed early onset persistant hyperglycaemia, raised HbA1c levels(5.71% ± 0.19,n=8 vs.4.06% ± 0.05,n=10;p<0.0001), impaired GSIS and glucose tolerance but no change in plasma cholesterol, NEFAs or triglyceride levels. After HFD feeding, insulin levels of GK[sup +/-] mice, though equivalent to GK[sup +/+] mice on CD, were less than half that of GK[sup +/+] mice (9.4ng/ml ± 2.1,n=9 vs.4.3ng/ml ± 0.7,n=9;p=0.003). At this point, GK[sup +/+] mice maintained moderate hyperglycaemia (9.46mM ± 0.54), whilst GK[sup +/-] mice became overtly diabetic (18.9mM±1.0) with worsened glucose tolerance (AUC 35mmol/1.h ± 2.8 vs. 28.9mmol/l.h ± 7.4;p<0.0001). A GKA (GKA50) increased GSIS, at 10mM glucose, in both GK[sup +/+] (2.0 fold) and GK[sup +/-] (2.2 fold) mice on CD, and had a greater effect on GK[sup +/-] (2.6 fold) than GK[sup +/+] (1.37 fold) in HFD groups. The largest gene expression changes in GK[sup +/-] mice were a reduction in PPARα mRNA (2.9 fold) in the islet and Hexokinase 2 (HK2) (4.3 fold), but not HK1, mRNA in the liver. We propose the HFD fed GK[sup +/-] mouse as a model of Type 2 diabetes and importantly show efficacy of a GKA in conditions of reduced GK expression as found in Type 2 diabetes. [ABSTRACT FROM AUTHOR]