Small intestinal protein infusion in humans: evidence for a location-specific gradient in intestinal feedback on food intake and GI peptide release.

BACKGROUND: Protein infusion in the small intestine results in intestinal brake activation: a negative feedback mechanism that may be mediated by the release of gastrointestinal peptides resulting in a reduction in food intake. It has been proposed that duodenum, jejunum and ileum may respond differently to infused proteins. OBJECTIVE: To investigate differences in ad libitum food intake, feelings of hunger and satiety and the systemic levels of cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), peptide YY (PYY), glucose and insulin after intraduodenal, intrajejunal and intraileal protein infusion. METHODS: Fourteen subjects (four male, mean age: 23±2.1 years, mean body mass index: 21.6±1.8 kg m-2) were intubated with a naso-ileal catheter in this double-blind, randomized, placebo-controlled crossover study. Test days (four in total, executed on consecutive days) started with the ingestion of a standardized breakfast, followed by the infusion of 15 g of protein in the duodenum, jejunum or ileum over a period of 60 min. Food intake was measured by offering an ad libitum meal and Visual Analogue Scale (VAS) scores were used to assess feelings of hunger and satiety. Blood samples were drawn at regular intervals for CCK, GLP-1, PYY, glucose and insulin analyses. RESULTS: Intraileal protein infusion decreased ad libitum food intake compared with both intraduodenal and placebo infusion (ileum: 628.5±63 kcal vs duodenum: 733.6±50 kcal, P<0.01 and placebo: 712.2±53 kcal, P<0.05). GLP-1 concentrations were increased after ileal infusion compared with jejunal and placebo infusion, whereas CCK concentrations were only increased after intraileal protein infusion compared with placebo. None of the treatments affected VAS scores for hunger and satiety nor plasma concentrations of PYY and glucose. CONCLUSIONS: Protein infusion into the ileum decreases food intake during the next meal compared with intraduodenal infusion, whereas it increases systemic levels of GLP-1 compared with protein infusion into the jejunum and placebo respectively.

Cholecystokinin regulates satiation independently of the abdominal vagal nerve in a pig model of total subdiaphragmatic vagotomy.

The vagal nerve and gut hormones CCK and GLP-1 play important roles in the control of food intake. However, it is not clear to what extent CCK and GLP-1 increase satiation by stimulating receptors located on abdominal vagal nerve endings or via receptors located elsewhere. This study aimed to further explore the relative contribution of the abdominal vagal nerve in mediating the satiating effects of endogenous CCK and GLP-1. Total subdiaphragmatic vagotomy or sham operation was combined with administration of CCK1 and GLP-1 receptor antagonists devazepide and exendin (9-39) in 12 pigs, applying an unbalanced Latin Square within-subject design. Furthermore, effects of vagotomy on preprandial and postprandial acetaminophen absorption, glucose, insulin, GLP-1 and CCK plasma concentrations were investigated. Ad libitum liquid meal intake (mean±SEM) was similar in sham and vagotomized pigs (4180±435 and 3760±810 g/meal). Intake increased by about 20% after blockade of CCK1 receptors, independently of the abdominal vagal nerve. Food intake did not increase after blockade of GLP-1 receptors. Blockade of CCK1 and GLP-1 receptors increased circulating CCK and GLP-1 concentrations in sham pigs only, suggesting the existence of a vagal reflex mechanism in the regulation of plasma CCK1 and GLP-1 concentrations. Vagotomy decreased acetaminophen absorption and changed glucose, insulin, CCK and GLP-1 concentrations indicating a delay in gastric emptying. Our data show that at liquid feeding, satiation is decreased effectively by pharmacological blockade of CCK1 receptors. We conclude that regulation of liquid meal intake appears to be primarily regulated by CCK1 receptors not located on abdominal vagal nerve endings.

Ileal brake activation: macronutrient-specific effects on eating behavior?

BACKGROUND: Activation of the ileal brake, by infusing lipid directly into the distal part of the small intestine, alters gastrointestinal (GI) motility and inhibits food intake. The ileal brake effect on eating behavior of the other macronutrients is currently unknown. OBJECTIVE: The objective of this study was to investigate the effects of ileal infusion of sucrose and casein on food intake, release of GI peptides, gastric emptying rate and small-bowel transit time with safflower oil as positive control. DESIGN: This randomized, single-blind, crossover study was performed in 13 healthy subjects (6 male; mean age 26.4±2.9 years; mean body mass index 22.8±0.4 kg m(-2)) who were intubated with a naso-ileal catheter. Thirty minutes after the intake of a standardized breakfast, participants received an ileal infusion, containing control ((C) saline), safflower oil ((HL) 51.7 kcal), low-dose casein ((LP) 17.2 kcal) or high-dose casein ((HP) 51.7 kcal), low-dose sucrose ((LC) 17.2 kcal) and high-dose sucrose ((HC) 51.7 kcal), over a period of 90 min. Food intake was determined during an ad libitum meal. Visual analogue score questionnaires for hunger and satiety and blood samples were collected at regular intervals. RESULTS: Ileal infusion of lipid, protein and carbohydrate resulted in a significant reduction in food intake compared with control (HL: 464.3±90.7 kcal, P<0.001; HP: 458.0±78.6 kcal, P<0.005; HC: 399.0±57.0 kcal, P<0.0001 vs control: 586.7±70.2 kcal, P<0.001, respectively). A reduction in energy intake was still apparent when the caloric amount of infused nutrients was added to the amount eaten during the ad libitum meal.Secretion of cholecystokinin and peptide YY but not of glucagon-like peptide-1 (7-36) was increased during ileal perfusion of fat, carbohydrates and protein. During ileal perfusion of all macronutrients, a delay in gastric emptying and intestinal transit was observed, but differences were not significant compared with control. CONCLUSION: Apart from lipids, also sucrose and casein reduce food intake on ileal infusion, thereby activating the ileal brake. In addition to food intake, also satiety and GI peptide secretion were affected.

Drug-drug interactions between rosuvastatin and oral antidiabetic drugs occurring at the level of OATP1B1.

Organic anion-transporting polypeptide 1B1 (OATP1B1) is an important hepatic uptake transporter, of which the polymorphic variant OATP1B1*15 (Asn130Asp and Val174Ala) has been associated with decreased transport activity. Rosuvastatin is an OATP1B1 substrate and often concomitantly prescribed with oral antidiabetics in the clinic. The aim of this study was to investigate possible drug-drug interactions between these drugs at the level of OATP1B1 and OATP1B1*15. We generated human embryonic kidney (HEK)293 cells stably overexpressing OATP1B1 or OATP1B1*15 that showed similar protein expression levels of OATP1B1 and OATP1B1*15 at the cell membrane as measured by liquid chromatography-tandem mass spectrometry. In HEK-OATP1B1*15 cells, the V(max) for OATP1B1-mediated transport of E(2)17ß-G (estradiol 17ß-d-glucuronide) was decreased >60%, whereas K(m) values (Michaelis constant) were comparable. Uptake of rosuvastatin in HEK-OATP1B1 cells (K(m) 13.1 ± 0.43 µM) was nearly absent in HEK-OATP1B1*15 cells. Interestingly, several oral antidiabetics (glyburide, glimepiride, troglitazone, pioglitazone, glipizide, gliclazide, and tolbutamide), but not metformin, were identified as significant inhibitors of the OATP1B1-mediated transport of rosuvastatin. The IC(50) values for inhibition of E(2)17ß-G uptake were similar between OATP1B1 and OATP1B1*15. In conclusion, these studies indicate that several oral antidiabetic drugs affect the OATP1B1-mediated uptake of rosuvastatin in vitro. The next step will be to translate these data to the clinical situation, as it remains to be established whether the studied oral antidiabetics indeed affect the clinical pharmacokinetic profile of rosuvastatin in patients.