Glucagon‐like peptide‐1 (GLP‐1) and peptide YY (PYY), secreted by enteroendocrine L‐cells located most densely in the colon and rectum, are of fundamental importance in blood glucose and appetite ...regulation. In animal models, colonic administration of bile acids can stimulate GLP‐1 and PYY by TGR5 receptor activation. We evaluated the effects of taurocholic acid (TCA), administered as an enema, on plasma GLP‐1 and PYY, as well as gastrointestinal sensations in 10 healthy male subjects, and observed that rectal administration of TCA promptly stimulated secretion of both GLP‐1 and PYY, and increased fullness, in a dose‐dependent manner. These observations confirm that topical application of bile acids to the distal gut may have potential for the management of type 2 diabetes and obesity.
Aims/hypothesis
Glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) are secreted from enteroendocrine L cells in response to numerous stimuli, including bile salts. Both have multiple effects that ...are potentially useful in treating diabetes and obesity. L cell number and hormone content in the intestine are highest in the rectum in humans. We investigated the effects of intrarectal sodium taurocholate on plasma GLP-1, PYY, insulin and glucose concentrations, and on food intake of a subsequent meal.
Methods
Ten obese type 2 diabetic volunteers were each studied on five separate occasions after an overnight fast and oral administration of 100 mg sitagliptin 10 h before the study. They then received an intrarectal infusion of either one of four doses of taurocholate (0.66, 2, 6.66 or 20 mmol, each in 20 ml of vehicle) or vehicle alone (1% carboxymethyl cellulose) single-blind over 1 min. Hormone and glucose measurements were made prior to, and for 1 h following, the infusion. The consumption of a previously selected favourite meal eaten to satiety was measured 75 min after the infusion.
Results
Taurocholate dose-dependently increased GLP-1, PYY and insulin, with 20 mmol doses resulting in peak concentrations 7.2-, 4.2- and 2.6-fold higher, respectively, than those achieved with placebo (
p
< 0.0001 for each). Plasma glucose decreased by up to 3.8 mmol/l (
p
< 0.001). Energy intake was decreased dose-dependently by up to 47% (
p
< 0.0001). The ED
50
values for effects on integrated GLP-1, insulin, PYY, food intake and glucose-lowering responses were 8.1, 10.5, 18.5, 24.2 and 25.1 mmol, respectively.
Conclusions/interpretation
Therapies that increase bile salts (or their mimics) in the distal bowel may be valuable in the treatment of type 2 diabetes and obesity.
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.
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.
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.
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.
Gastric emptying was measured in normal and insulin-treated spontaneously diabetic BB rats using the retention of an acaloric methylcellulose gel containing phenol red delivered by gavage. Dye ...content in stomachs removed after killing 20 min later was determined spectroscopically, and was compared to that in rats killed immediately after gavage to assess emptying. Diabetic rats had a markedly greater gastric emptying (90.3 +/- 1.7% passed) compared to normal Harlan Sprague Dawley rats (49.1 +/- 4.7% passed; p < 0.001) and non-diabetic BB rats (61.1 +/- 9.2% passed; p < 0.001). The pancreatic beta-cell peptide, amylin, which is deficient in insulin-dependent diabetes mellitus, dose-dependently inhibited gastric emptying in both normal and diabetic rats. The ED50 of the response in normal rats measured by phenol red and novel 3-3Hglucose gavage techniques was approximately 0.4 microgram. This dose was estimated to increase plasma amylin concentration by a mean of approximately 20 pmol/l to concentrations within the range observed in vivo. It is proposed that amylin could participate in the physiological control of nutrient entry into the duodenum and that the accelerated gastric emptying seen in BB rats could be related to their lack of amylin 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.
![Effects of PYY[3-36] in rod...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0307-0565/small "Effects of PYY[3-36] in rodent models of diabetes and obesity")
PDF
