Exendin-4 is a 39 amino acid peptide isolated from the salivary secretions of the Gila monster (Heloderma suspectum). It shows 53% sequence similarity to glucagon-like peptide (GLP)-1. Unlike GLP-1, ...exendin-4 has a prolonged glucose-lowering action in vivo. We compared the potency and duration of glucose-lowering effects of exendin-4 and GLP-1 in hyperglycemic db/db and ob/ob mice. Whereas reductions in plasma glucose of up to 35% vanished within 1 h with most doses of GLP-1, the same doses of exendin-4 resulted in a similar glucose-lowering effect that persisted for >4 h. Exendin-4 was 5,530-fold more potent than GLP-1 in db/db mice (effective doses, 50% ED50s of 0.059 microg/kg +/-0.15 log and 329 microg/kg+/-0.22 log, respectively) and was 5,480-fold more potent in ob/ob mice (ED50s of 0.136 microg/kg+/-0.10 log and 744 microg/kg+/-0.21 log, respectively) when the percentage fall in plasma glucose at 1 h was used as the indicator response. Exendin-4 dose-dependently accelerated glucose lowering in diabetic rhesus monkeys by up to 37% with an ED50 of 0.25 microg/kg +/-0.09 log. In two experiments in which diabetic fatty Zucker rats were injected subcutaneously twice daily for 5-6 weeks with doses of exendin-4 up to 100 microg x rat(-1) x day(-1) (approximately 250 microg/kg), HbA1c was reduced relative to saline-injected control rats. Exendin-4 treatment was also associated in each of these experiments with weight loss and improved insulin sensitivity, as demonstrated by increases of up to 32 and 49%, respectively, in the glucose infusion rate (GIR) in the hyperinsulinemic euglycemic clamp. ED50s for weight loss and the increase in clamp GIR were 1.0 microg/kg+/-0.15 log and 2.4 microg/kg+/-0.41 log, respectively. In conclusion, acute and chronic administration of exendin-4 has demonstrated an antidiabetic effect in several animal models of type 2 diabetes.
The effects of the incretin mimetic exenatide (exendin-4) on metabolic parameters, insulin sensitivity, and β-cell mass were examined in nondiabetic, insulin-resistant obese fa/fa Zucker rats. After ...6 wk of treatment, ad libitum-fed exenatide-treated (EX) and pair-fed vehicle control (PF) rats had comparable food intake, body weight, hemoglobin A1c (HbA1c), and fasting plasma concentrations of glucose, insulin, and lipids. Concurrent decreases in food intake and weight gain were observed in EX and PF rats, compared with ad libitum-fed vehicle control (CON) rats (P < 0.001). The increases in HbA1c and fasting plasma insulin concentrations that occur during the normal progression of this disease model were significantly reduced in EX and PF rats, compared with CON rats (P < 0.001). The insulin sensitivity index (ISI; glucose infusion rate to plasma insulin concentration) measured during a hyperinsulinemic euglycemic clamp was 224% higher in EX rats than CON rats (P < 0.001) and 61% higher in EX rats than PF rats (P < 0.004). The latter difference was despite comparable HbA1c, fasting glucose, fasting insulin, total cholesterol, high-density lipoprotein, and daily food consumption between EX and PF animals. In the absence of exenatide, β-cell mass was hyperbolically related to ISI (β-cell mass ∗ ISI was constant). Analogous to the disposition index, the β-cell mass ∗ ISI product was 63% greater in EX than PF rats (P < 0.05). Thus, exenatide increased β-cell mass to a greater extent than would be expected in animals of comparable insulin resistance, suggesting a direct trophic effect on islet neogenesis in obese fa/fa rats independent of body weight and glycemia.
Peptide YY (PYY) is a 36 amino-acid peptide secreted from ileal L cells following meals. The cleaved subpeptide PYY3-36 is biologically active and may constitute the majority of circulating PYY-like ...immunoreactivity. The peptide family that includes PYY, pancreatic peptide and neuropeptide Y is noted for its orexigenic effect following intracerebroventricular administration.
To investigate the effects of peripheral (intraperitoneal and chronic subcutaneous) infusions of PYY3-36 on food intake, body weight and glycemic indices.
Food intake was measured in normal mice and in several rodent models of obesity and type II diabetes. In marked contrast to the reported central orexigenic effects, in the present study, PYY3-36 acutely inhibited food intake by up to 45%, with an ED(50) of 12.5 microg/kg in fasted female NIH/Swiss mice. A 4-week infusion reduced weight gain in female ob/ob mice, without affecting the cumulative food intake. In diet-induced obese male mice, PYY3-36 infusion reduced cumulative food intake, weight gain and epididymal fat weight (as a fraction of carcass) with similar ED(50)'s (466, 297 and 201 microg/kg/day, respectively) and prevented a diet-induced increase in HbA1c. Infusion at 100 microg/kg/day for 8 weeks in male fa/fa rats reduced the weight gain (288+/-11 vs 326+/-12 g in saline-infused controls; P<0.05), similar to effects in a pair-fed group. In female ob/ob and db/db mice, there was no acute effect of PYY3-36 on plasma glucose concentrations. In male diabetic fatty Zucker rats, PYY3-36 infused for 4 weeks reduced HbA1c and fructosamine (ED(50)'s 30 and 44 microg/kg/day).
Peripheral PYY3-36 administration reduced the food intake, body weight gain and glycemic indices in diverse rodent models of metabolic disease of both sexes. These findings justify further exploration of the potential physiologic and therapeutic roles of PYY3-36.
Exenatide (exendin-4) injected subcutaneously twice daily reduces glycaemic deterioration in diabetic fatty Zucker (ZDF) rats and reduces HbA1c in humans with type 2 diabetes. Because tachyphylaxis ...may develop with continuous peptide exposure, we examined the activity of a long-acting-release (LAR) formulation of exenatide on HbA1c, insulin sensitivity and beta cell secretion in ZDF rats.
Single subcutaneous injections of a poly-lactide-glycolide microsphere suspension (3% peptide) containing 0, 1, 10, 100, 1,000, 3,000 or 9,000 mug exenatide were administered to 9-week-old ZDF rats with matched initial HbA1c values (n=7 rats/group).
In contrast to the progressive 3.22+/-0.42% increase in HbA1c in control ZDF rats observed over 28 days, single exenatide-LAR injections dose-proportionally prevented such glycaemic deterioration (median effective dose 74 microg+/-0.1 log per rat; median effective concentration 52 pmol/l+/-0.06 log). Hyperinsulinaemic-euglycaemic clamp procedures incorporating an intraclamp glucose challenge performed 28 days after treatment revealed increases in beta cell response to the glucose challenge at lower exenatide-LAR doses, and up to a 2.1-fold increase in insulin sensitivity at higher exenatide-LAR doses.
The finding that a single dose of exenatide-LAR enhanced glucose control for 28 days in the ZDF rat model of type 2 diabetes suggests that tachyphylaxis is unlikely to be a feature of exenatide-LAR preparations, and supports further clinical exploration.
Aim
Glucose‐dependent insulinotropic peptide (GIP) is an incretin hormone that is released from intestinal K cells in response to nutrient ingestion. We aimed to investigate the therapeutic potential ...of the novel N‐ and C‐terminally modified GIP analogue AC163794.
Methods
AC163794 was synthesized by solid‐phase peptide synthesis. Design involved the substitution of the C‐terminus tail region of the dipeptidyl peptidase IV (DPP‐IV)‐resistant GIP analogue d‐Ala2GIP(1–42) with the unique nine amino acid tail region of exenatide. The functional activity and binding of AC163794 to the GIP receptor were evaluated in RIN‐m5F β‐cells. In vitro metabolic stability was tested in human plasma and kidney membrane preparations. Acute insulinotropic effects were investigated in isolated mouse islets and during an intravenous glucose tolerance test in normal and diabetic Zucker fatty diabetic (ZDF) rats. The biological actions of AC163794 were comprehensively assessed in normal, ob/ob and high‐fat‐fed streptozotocin (STZ)‐induced diabetic mice. Acute glucoregulatory effects of AC163794 were tested in diet‐induced obese mice treated subchronically with AC3174, the exendatide analogue Leu14 exenatide. Human GIP or d‐Ala2GIP(1–42) were used for comparison.
Results
AC163794 exhibited nanomolar functional GIP receptor potency in vitro similar to GIP and d‐Ala2GIP(1–42). AC163794 was metabolically more stable in vitro and displayed longer duration of insulinotropic action in vivo versus GIP and d‐Ala2GIP(1–42). In diabetic mice, AC163794 improved HbA1c through enhanced insulinotropic action, partial restoration of pancreatic insulin content and improved insulin sensitivity with no adverse effects on fat storage and metabolism. AC163794 provided additional baseline glucose‐lowering when injected to mice treated with AC3174.
Conclusions
These studies support the potential use of a novel GIP analogue AC163794 for the treatment of type 2 diabetes.
Glucagon secretion from pancreatic α cells is inhibited by insulin from β cells. Amylin is a partner hormone to insulin cosecreted in response to nutrient stimuli, which, like insulin, inhibits ...β-cell secretion. We investigated whether amylin also inhibits α-cell secretion of glucagon in response to infused
l-arginine. Rat amylin (1.2, 3.6, 12, 36, or 120 pmol/kg/min; calculated plasma concentration, 13, 47, 195, 713, and 2,950 pmol/L, respectively; n = 7, 8, 6, 4, and 7) or saline (n = 23) was infused into anesthetized male Harlan-Sprague-Dawley rats during hyperinsulinemic-euglycemic clamps, which were used to equalize the influences of glucose and insulin on glucagon secretion. Plasma glucose and insulin concentrations and mean arterial pressures were not different between amylin- and saline-treated rats during a 10-minute 2-mmol
l-arginine infusion delivered during the clamps. Plasma glucagon measurements taken during and after the arginine challenge showed that compared with saline infusions, amylin administration dose-dependently suppressed the glucagon response to arginine by a maximum of 62% (incremental area under the curve AUC 0 to 60 minutes) with a plasma amylin EC
50 of 18 pmol/L ±0.3 log units. These data indicate that amylin potently inhibits arginine-stimulated glucagon secretion.
Several peptides have been proposed as regulators of nutrient release from the stomach and subsequent uptake from the gut. Using a phenol red gavage method, we compared the potencies of ...subcutaneously preinjected amylin, glucagon-like peptide-1 (7-36)amide (GLP-1), cholecystokinin octapeptide (CCK-8), gastric inhibitory peptide (GIP), glucagon, and pancreatic peptide on slowing the release of an acaloric gel from rat stomach. The latter three peptides did not fully inhibit gastric emptying at subcutaneous doses up to 100 micrograms. Amylin, GLP-1, and CCK-8 fully inhibited gastric emptying, with ED50s of 0.42 +/- 0.07, 6.1 +/- 0.12, and 8.5 +/- 0.20 nmol/kg +/- SE of log, respectively.
Amylin, a 37-amino acid peptide hormone co-secreted with insulin, potently governs the rate of gastric emptying. Hypoglycemia, in the absence of agents such as amylin, is reported to accelerate ...gastric emptying. We asked whether hypoglycemia had a similar action on gastric emptying in the presence of amylin. In preliminary experiments using a phenol red gavage technique in fasted SD rats, we showed that insulin administration accelerated gastric emptying in a dosage-dependent manner. This acceleration was totally prevented by coadministration of glucose in dosages that prevented a change in plasma glucose, indicating that insulin per se did not affect gastric emptying. The effect on gastric emptying of hypoglycemia induced by a 5 mU/min insulin infusion (t = 5-90 min) was assessed in conscious rats continuously infused with amylin (50 pmol x kg-1 x min-1; t = -30 to 90 min). Gastric emptying was indicated by the appearance in plasma of label from 3-O-methyl-3Hglucose gavaged at t = 0 min. Label appearance was markedly inhibited in rats preinfused with amylin (84% reduced vs. saline controls at t = 30 min), indicating amylin inhibition of gastric emptying. In amylin-treated rats that were subsequently infused with insulin, gavaged label abruptly appeared in plasma when plasma glucose had fallen to 2.1 +/- 0.1 mmol/l (at t approximately 45 min), consistent with a reversal by hypoglycemia of amylin's inhibition of gastric emptying. These data support the idea of a central "fail-safe" mechanism whereby hypoglycemia can override the slowing of gastric emptying by amylin.
Objective: The current set of studies describe the in vivo metabolic actions of the novel amylin-mimetic peptide davalintide (AC2307) in rodents and compares these effects with those of the native ...peptide. Research design and methods: The anti-obesity effects of davalintide were examined after intraperitoneal injection or sustained peripheral infusion through subcutaneously implanted osmotic pumps. The effect of davalintide on food intake after lesioning of the area postrema (AP) and neuronal activation as measured by c-Fos, were also investigated. Results: Similar to amylin, davalintide bound with high affinity to amylin, calcitonin and calcitonin gene-related peptide receptors. Acutely, davalintide displayed greater suppression of dark-cycle feeding and an extended duration of action compared with amylin (23 versus 6 h). Davalintide had no effect on locomotor activity or kaolin consumption at doses that decreased food intake. Davalintide-induced weight loss through infusion was dose dependent, durable up to 8 weeks, fat-specific and lean-sparing, and was associated with a shift in food preference away from high-fat (palatable) chow. Metabolic rate was maintained during active weight loss. Both davalintide and amylin failed to suppress food intake after lesioning of the AP and activated similar brain nuclei, with davalintide displaying an extended duration of c-Fos expression compared with amylin (8 versus 2 h). Conclusion: Davalintide displayed enhanced in vivo metabolic activity over amylin while retaining the beneficial properties possessed by the native molecule. In vitro receptor binding, c-Fos expression and AP lesion studies suggest that the metabolic actions of davalintide and amylin occur through activation of similar neuronal pathways.
The neuroendocrine hormone amylin, cosecreted with insulin from pancreatic β-cells in response to nutrient ingestion, has several physiologic actions to limit the rate of nutrient uptake, including ...the slowing of gastric emptying.
To investigate whether amylin might modulate digestive enzyme secretion from the exocrine pancreas, anesthetized Sprague Dawley rats were cannulated via the pancreatic duct and the secretory response (flow, amylase and lipase) to cholecystokinin (1 μg s.c.) was measured in the absence and in the presence of 0.1, 0.3 and 1 μg s.c. doses of amylin.
Amylin alone did not affect pancreatic secretion, but it dose-dependently inhibited cholecystokinin-stimulated amylase secretion by up to 58% and lipase secretion by up to 67%. The ED
50's for these responses were 0.21 μg
±
0.18 log and 0.11 μg
±
0.05 log, respectively, doses that result in excursions of plasma amylin concentration that are within the reported physiological range. Amylin did not evoke cell signalling in the Ar42j model of pancreatic acinar cells, and responses to amylin were not observed in either Ar42j cells or isolated pancreatic acini in a microphysiometer indicating that the effect of amylin was indirect.
Inhibition of stimulated pancreatic enzyme secretion is likely to be a physiological, extrapancreatic, action of amylin. Amylinergic mechanisms modulating both gastric emptying and pancreatic enzyme secretion may thus match, respectively, the appearance of substrate and enzymes in the gut lumen.
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