Macroalgal protein hydrolysates from Palmaria palmata influence the ‘incretin effect’ in vitro via DPP-4 inhibition and upregulation of insulin, GLP-1 and GIP secretion

Purpose This study investigated metabolic benefits of protein hydrolysates from the macroalgae Palmaria palmata, previously shown to inhibit dipeptidylpeptidase-4 (DPP-4) activity in vitro. Methods Previously, Alcalase/Flavourzyme-produced P. palmata protein hydrolysate (PPPH) improved glycaemia and insulin production in streptozotocin-induced diabetic mice. Here the PPPH, was compared to alternative Alcalase, bromelain and Promod-derived hydrolysates and an unhydrolysed control. All PPPH’s underwent simulated gastrointestinal digestion (SGID) to establish oral bioavailability. PPPH’s and their SGID counterparts were tested in pancreatic, clonal BRIN-BD11 cells to assess their insulinotropic effect and associated intracellular mechanisms. PPPH actions on the incretin effect were assessed via measurement of DPP-4 activity, coupled with GLP-1 and GIP release from GLUTag and STC-1 cells, respectively. Acute in vivo effects of Alcalase/Flavourzyme PPPH administration on glucose tolerance and satiety were assessed in overnight-fasted mice. Results PPPH’s (0.02–2.5 mg/ml) elicited varying insulinotropic effects (p < 0.05–0.001). SGID of the unhydrolysed protein control, bromelain and Promod PPPH’s retained, or improved, bioactivity regarding insulin secretion, DPP-4 inhibition and GIP release. Insulinotropic effects were retained for all SGID-hydrolysates at higher PPPH concentrations. DPP-4 inhibitory effects were confirmed for all PPPH’s and SGID counterparts (p < 0.05–0.001). PPPH’s were shown to directly influence the incretin effect via upregulated GLP-1 and GIP (p < 0.01–0.001) secretion in vitro, largely retained after SGID. Alcalase/Flavourzyme PPPH produced the greatest elevation in cAMP (p < 0.001, 1.7-fold), which was fully retained post-SGID. This hydrolysate elicited elevations in intracellular calcium (p < 0.01) and membrane potential (p < 0.001). In acute in vivo settings, Alcalase/Flavourzyme PPPH improved glucose tolerance (p < 0.01–0.001) and satiety (p < 0.05–0.001). Conclusion Bioavailable PPPH peptides may be useful for the management of T2DM and obesity.

P30: PYY HORMONE UPREGULATES PROXIMAL GLP-1 RELEASE AFTER ROUX EN-Y GASTRIC BYPASS

Introduction Nowadays Roux-en-Y gastric bypass (RYGB) has provided a powerful treatment for type 2 diabetes mellitus. Nevertheless how anatomical arrangements after RYGB influeces entero-hormonal response and the role of Peptide Tyrosine Tyrosine (PYY) in the restoration of normoglycaemia are still not clear. MATERIAL AND Method We demonstrate that PYY plasma levels showed a remarkable peak, around thirty minutes earlier than GLP-1 or GIP, after mixed-meal administration in non obese Goto – Kakizaki RYGB-operated rats . Also, we found that PYY (3-36) infusion led to increased GLP-1 and GIP plasma levels close to those obtained after a meal. Result Histologically the number of GLP-1 positive cells number appeared to increase in the three segments of the small intestine:duodenum jejunum and ileum in GK RYGB-operated rats beyond early presence of nutrient stimulation in the ileum. But nevertheless, PYY positive cell numbers appeared to increased only in the ileum. Conclusion Taking together this findings suggest an earlier central role for PYY in gut hormone regulation after RYGB in our model, contributing to GLP-1 and GIP release and support the existence of enteroendocrine communication routes between the distal and proximal small intestine. Take-home message Enterohormones release changes after bariatric surgery due to the consequences in nutrients flow. The GLP-1 release is increased and we report its related to the PYY regulation.

P31: INTESTINAL GIP RELEASE MODIFICATIONS WOULD BE RELATED TO DUODENAL EXCLUSION: BARIATRIC SURGERY CONSEQUENCES

Introduction The surgical techniques employed in the treatment of obesity discovered consequences on the global enterohomonal equilibrium. Many hypotheses focused on these enterohormonal system to explain the improvement of Type 2 Diabetes mellitus; as many other functional improvements. GIP is a hormone released for the duodenal and jejunal K cells, which had been implied in the glucose homeostasis. Our purpose was studied the changes in K cells populations, that could be related to the GIP serum level. Method We employed 16 non obese euglycemic male Wistar rats, randomised in the surgical groups. These groups were the surgical techniques (Sleeve gastric –SG-, Roux en Y Gastric Bypass –RYGB- and massive intestinal resection –IR50-), and two controls (fasting and Sham). After three months, rats were sacrificed. The intestinal portions (duodenum, jejunum and ileum) were resected and processed for the immunocytochemical technique. Result analysis showed several aspects. We found a significant increase of GIP K-cells (number GIP+/mm2 intestinal portion) in the duodenum of RYGB and RI50 versus both control groups. Other data showed a significant decrease of GIP K-cells in SG jejunum versus both control groups. Ileum did not significances. Conclusion GIP hormone was related to the nutrient flow through the intestine. Our data showed that GIP expression was inverse to the exclusion to this flow, as in RYGB technique. The increase was severe in IR50 too, which the duodenum was not affected. This mechanism revealed a complex physiologic mechanism, probably established by the feed-back with other hormones, as PPY. Take-home message The metabolic consequences after bariatric surgeries are related in enterohormones changes. The GIP release cellularity suffer changes according to the flow of nutrients.

The Leading Role of Peptide Tyrosine Tyrosine in Glycemic Control After Roux-en-Y Gastric Bypass in Rats

Aims Roux-en-Y gastric bypass (RYGB) is one of the most effective surgical therapies for the rapid resolution of type 2 diabetes. However, the mechanisms underlying the entero-hormonal response after surgery and the role of peptide tyrosine tyrosine (PYY) in the restoration of normoglycemia are still not clear. Methods We reproduced the RYGB technique in Wistar and Goto–Kakizaki rats and performed serum hormonal, histological, and hormonal-infusion test. Results Using the diabetic Goto–Kakizaki (GK) rat model, we demonstrated that PYY plasma levels showed a remarkable peak approximately 30 min earlier than GLP-1 or GIP after mixed-meal administration in RYGB-operated rats with PYY. The GLP-1 and GIP areas under the curve (AUCs) increased after RYGB in GK rats. Additionally, the findings suggested that PYY (3-36) infusion led to increased GLP-1 and GIP plasma levels close to those obtained after a meal. Finally, the number of GLP-1-positive cells appeared to increase in the three segments of the small intestine in GK-RYGB-operated rats beyond the early presence of nutrient stimulation in the ileum. Nevertheless, PYY-positive cell numbers appeared to increase only in the ileum. Conclusion At least in rats, these data demonstrate an earlier essential role for PYY in gut hormone regulation after RYGB. We understand that PYY contributes to GLP-1 and GIP release and there must be the existence of enteroendocrine communication routes between the distal and proximal small intestine.

Zinc-induced activation of GPR39 regulates glucose homeostasis through glucose-dependent insulinotropic polypeptide secretion from enteroendocrine K-cells

The role of Zn2+-sensing receptor GPR39 on glucose homeostasis and incretin regulation was assessed in enteroendocrine L- and K-cells. Anti-hyperglycaemic, insulinotropic and incretin secreting properties of Zn2+ were explored in normal, diabetic and incretin receptor knockout mice. Compared to intraperitoneal injection, oral administration of Zn2+ (50 μmol/kg body weight) with glucose (18 mmol/kg) in lean mice reduced the glycaemic excursion by 25–34% (p < 0.05–p < 0.001) and enhanced glucose-induced insulin release by 46–48% (p < 0.05–p < 0.01). In diabetic mice, orally administered Zn2+ lowered glucose by 24–31% (p < 0.01) and augmented insulin release by 32% (p < 0.01). In glucagon like peptide-1 (GLP-1) receptor knockout mice, Zn2+ reduced glucose by 15–28% (p < 0.05–p < 0.01) and increased insulin release by 35–43% (p < 0.01). In contrast Zn2+ had no effect on responses of glucose-dependent insulinotropic polypeptide (GIP) receptor knockout mice. Consistent with this, Zn2+ had no effect on circulating total GLP-1 whereas GIP release was stimulated by 26% (p < 0.05) in lean mice. Immunocytochemistry demonstrated GPR39 expression on mouse enteroendocrine L- and K-cells, GLUTag cells and pGIP/Neo STC-1 cells. Zn2+ had a direct effect on GIP secretion from pGIPneo STC-1 cells, increasing GIP secretion by 1.3-fold. GPR39 is expressed on intestinal L- and K-cells, and stimulated GIP secretion plays an integral role in mediating enhanced insulin secretion and glucose tolerance following oral administration of Zn2+. This suggests development of potent and selective GPR39 agonists as a therapeutic approach for diabetes.

L-phenylalanine Increased Gut Hormone Secretion through Calcium-Sensing Receptor in the Porcine Duodenum

Luminal amino acids have a pivotal role in gut hormone secretion, and thereby modulate food intake and energy metabolism. However, the mechanisms by which amino acids exert this effect remains unknown. The purpose of this research was to investigate the response of L-phenylalanine (L-Phe) to gut hormone secretion and its underlying mechanisms by perfusing the pig duodenum. Eighty mM L-Phe and extracellular Ca2+ stimulated cholecystokinin (CCK) and glucose-dependent insulinotropic peptide (GIP) release, and upregulated the mRNA expression of the calcium-sensing receptor (CaSR), CCK, and GIP. Western blotting results showed that L-Phe also elevated the protein levels of CaSR, the inositol 1,4,5-triphosphate receptor (IP3R), and protein kinase C (PKC). However, the CaSR inhibitor NPS 2143 reduced the mRNA expression of CaSR, CCK, and GIP, and the secretion of CCK and GIP, as well as the protein level of CaSR, IP3R, and PKC. These results indicated that Phe stimulated gut secretion through a CaSR-mediated pathway and its downstream signaling molecules, PKC and IP3R.

Rate of appearance of amino acids after a meal regulates insulin and glucagon secretion in patients with type 2 diabetes: a randomized clinical trial

ABSTRACT Background Meal composition regulates the postprandial response of pancreatic and gastrointestinal hormones and plays an important role in patients with type 2 diabetes (T2D). Proteins have glucagon and insulinotropic effects, which may differ depending on amino acid composition, form of intake, and rate of digestibility and absorption. Objective The aim of this study was to test effects of isolated pea protein–based (PP) compared with casein protein–based (CP) meals differing in amino acid compositions on endocrine responses to meal tolerance tests (MTTs) in patients with T2D. Design Thirty-seven individuals with T2D [mean ± SD age: 64 ± 6 y; mean ± SD body mass index (kg/m2): 30.2 ± 3.6; mean ± SD glycated hemoglobin: 7.0% ± 0.6%] were randomly assigned to receive either high-animal-protein (∼80% of total protein) or high-plant-protein (∼72% of total protein) diets (30% of energy from protein, 40% of energy from carbohydrate, 30% of energy from fat) for 6 wk. MTTs were performed at study onset and after 6 wk. Participants received standardized high-protein (30% of energy) meals 2 times/d containing either CP-rich (∼85% wt:wt) or PP-rich (∼95% wt:wt) foods. Results The CP and PP meals produced differences in insulin, C-peptide, glucagon, and glucose-dependent insulinotropic peptide (GIP) release. Total areas under the curve after CP were significantly lower than after the PP lunch by 40% for insulin and 23% for glucagon. Indexes of insulin sensitivity and secretion were significantly improved for the second CP MTT. This was accompanied by differential rates of appearance of amino acids. The ingestion of PP resulted in significant increases in amino acids after both meals, with a decline between meals. By contrast, CP intake resulted in increases in most amino acids after breakfast, which remained elevated but did not increase further after lunch. Conclusions PP elicits greater postprandial increases in glucagon than does CP and consequently requires higher insulin to control glucose metabolism, which appears to be related to the rate of amino acid appearance. The metabolic impact of protein quality could be used as a strategy to lower insulin needs in patients with T2D. This trial was registered at www.clinicaltrials.gov as NCT02402985.

Central GIP signaling stimulates peripheral GIP release and promotes insulin and pancreatic polypeptide secretion in nonhuman primates

Glucose-dependent insulinotropic polypeptide (GIP) has important actions on whole body metabolic function. GIP and its receptor are also present in the central nervous system and have been linked to neurotrophic actions. Metabolic effects of central nervous system GIP signaling have not been reported. We investigated whether centrally administered GIP could increase peripheral plasma GIP concentrations and influence the metabolic response to a mixed macronutrient meal in nonhuman primates. An infusion and sampling system was developed to enable continuous intracerebroventricular (ICV) infusions with serial venous sampling in conscious nonhuman primates. Male baboons ( Papio sp.) that were healthy and had normal body weights (28.9 ± 2.1 kg) were studied ( n = 3). Animals were randomized to receive continuous ICV infusions of GIP (20 pmol·kg−1·h−1) or vehicle before and over the course of a 300-min mixed meal test (15 kcal/kg, 1.5g glucose/kg) on two occasions. A significant increase in plasma GIP concentration was observed under ICV GIP infusion (66.5 ± 8.0 vs. 680.6 ± 412.8 pg/ml, P = 0.04) before administration of the mixed meal. Increases in postprandial, but not fasted, insulin ( P = 0.01) and pancreatic polypeptide ( P = 0.04) were also observed under ICV GIP. Effects of ICV GIP on fasted or postprandial glucagon, glucose, triglyceride, and free fatty acids were not observed. Our data demonstrate that central GIP signaling can promote increased plasma GIP concentrations independent of nutrient stimulation and increase insulin and pancreatic polypeptide responses to a mixed meal.

Fructose stimulates GLP-1 but not GIP secretion in mice, rats, and humans

Nutrients often stimulate gut hormone secretion, but the effects of fructose are incompletely understood. We studied the effects of fructose on a number of gut hormones with particular focus on glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). In healthy humans, fructose intake caused a rise in blood glucose and plasma insulin and GLP-1, albeit to a lower degree than isocaloric glucose. Cholecystokinin secretion was stimulated similarly by both carbohydrates, but neither peptide YY3–36nor glucagon secretion was affected by either treatment. Remarkably, while glucose potently stimulated GIP release, fructose was without effect. Similar patterns were found in the mouse and rat, with both fructose and glucose stimulating GLP-1 secretion, whereas only glucose caused GIP secretion. In GLUTag cells, a murine cell line used as model for L cells, fructose was metabolized and stimulated GLP-1 secretion dose-dependently (EC50= 0.155 mM) by ATP-sensitive potassium channel closure and cell depolarization. Because fructose elicits GLP-1 secretion without simultaneous release of glucagonotropic GIP, the pathways underlying fructose-stimulated GLP-1 release might be useful targets for type 2 diabetes mellitus and obesity drug development.