Effect of oral fat on plasma levels of neurotensin and neurotensin fragments in humans. Characterization by high-pressure liquid chromatography

New Insights in the Control of Fat Homeostasis: The Role of Neurotensin

Neurotensin (NT) is a small peptide with pleiotropic functions, exerting its primary actions by controlling food intake and energy balance. The first evidence of an involvement of NT in metabolism came from studies on the central nervous system and brain circuits, where NT acts as a neurotransmitter, producing different effects in relation to the specific region involved. Moreover, newer interesting chapters on peripheral NT and metabolism have emerged since the first studies on the NT-mediated regulation of gut lipid absorption and fat homeostasis. Intriguingly, NT enhances fat absorption from the gut lumen in the presence of food with a high fat content, and this action may explain the strong association between high circulating levels of pro-NT, the NT stable precursor, and the increased incidence of metabolic disorders, cardiovascular diseases, and cancer observed in large population studies. This review aims to provide a synthetic overview of the main regulatory effects of NT on several biological pathways, particularly those involving energy balance, and will focus on new evidence on the role of NT in controlling fat homeostasis, thus influencing the risk of unfavorable cardio–metabolic outcomes and overall mortality in humans.

Binge-like intake of HFD attenuates alcohol intake in rats

Binge eating and binge alcohol intake are behavioral manifestations of pathological feeding and alcohol use disorder (AUD), respectively. Binge-feeding and AUD have high comorbidity with other psychiatric disorders such as depression, which could have important implications for the management of these conditions. Importantly, these behaviors share many common features suggesting a singular etiology. However, the nature by which binge-feeding affects the development or maintenance of AUD is unclear. The present study examined the impact of a binge-feeding from a nutritionally complete high-fat diet (HFD) on initiation and maintenance of alcohol intake, anxiolytic behavior and central genetic changes in brain regions that control alcohol-reinforced behaviors. To do this, male Long-Evans rats received chow (controls) or HFD every three days (HFD-3D) or every day (HFD-ED) for 5weeks. Rodent chow and water were available ad-libitum to all groups throughout the experiment. Following 5weeks of HFD cycling, 20.0% ethanol or 2.0% sucrose intake was evaluated. In addition, anxiety-like behavior was measured using a light-dark box apparatus. Both HFD-3D and -ED groups of rats consumed significantly large amount of food during 2h HFD access sessions and reduced their chow intake in the next 22h. Surprisingly, binge-fed rats displayed attenuated acquisition of alcohol intake whereas sucrose consumption was unaffected. Rats exposed to HFD spent more time in the light side compared to chow controls, indicating that binge-feeding induced anxiolytic effects. In addition, alterations in the brain neurotensin system were observed following HFD exposure. These data indicate that binge-feeding behavior induces behavioral and genetic changes that help explain how alcohol intake is influenced by co-morbid eating disorders.

Release of avian neurotensin in response to intraluminal contents in the duodenum of chickens

Peripheral and hepatic-portal plasma levels of neurotensin (NT) in fed and fasted chickens were determined using RIA. Portal levels of NT(1-13) (fed = 61.3 ± 3.9 fmol/mL; fasted = 44.5 ± 3.9 fmol/mL) were significantly higher than peripheral levels (fed = 8.2 ± 3.3 fmol/mL; fasted = 7.8 ± 3.0 fmol/mL) collected from the wing vein, indicating that some NT is metabolized in the liver. Portal plasma levels of NT collected from fed birds were also significantly higher than portal plasma levels of NT collected from fasted birds. Neurotensin, as identified by HPLC, exhibited a 2-fold increase in plasma extracts following perfusion of the proximal ileum with a 10-mg sample of oleic acid, as compared with control samples of plasma collected before oleic acid perfusion. In whole-animal studies, the injection of a micellar solution of oleic acid into isolated segments of the duodenum resulted in elevated plasma immunoreactive NT in blood collected from the pancreaticoduodenal vein. Injection of a 1,000 mOsm sodium chloride solution had a slightly lesser and delayed effect compared with oleic acid, but a greater effect than 0.1 N hydrochloric acid in isotonic saline solution. Injection of an amino acid solution (10% Travasol), 300 mOsm glucose solution, or pure corn oil had no effect. These results demonstrate that intraduodenal oleic acid is a potent stimulus for the release of NT from the duodenum into the hepatic-portal circulation of chickens.

Neurotensin receptor 1 gene activation by the Tcf/beta-catenin pathway is an early event in human colonic adenomas

Alterations in the Wnt/APC (adenomatous polyposis coli) signalling pathway, resulting in beta-catenin/T cell factor (Tcf)-dependent transcriptional gene activation, are frequently detected in familial and sporadic colon cancers. The neuropeptide neurotensin (NT) is widely distributed in the gastrointestinal tract. Its proliferative and survival effects are mediated by a G-protein coupled receptor, the NT1 receptor. NT1 receptor is not expressed in normal colon epithelial cells, but is over expressed in a number of cancer cells and tissues suggesting a link to the outgrowth of human colon cancer. Our results demonstrate that the upregulation of NT1 receptor occurring in colon cancer is the result of Wnt/APC signalling pathway activation. We first established the functionality of the Tcf response element within the NT1 receptor promoter. Consequently, we observed the activation of NT1 receptor gene by agents causing beta-catenin cytosolic accumulation, as well as a strong decline of endogenous receptor when wt-APC was restored. At the cellular level, the re-establishment of wt-APC phenotype resulted in the impaired functionality of NT1 receptor, like the breakdown in NT-induced intracellular calcium mobilization and the loss of NT pro-invasive effect. We corroborated the Wnt/APC signalling pathway on the NT1 receptor promoter activation with human colon carcinogenesis, and showed that NT1 receptor gene activation was perfectly correlated with nuclear or cytoplasmic beta-catenin localization while NT1 receptor was absent when beta-catenin was localized at the cell-cell junction in early adenomas of patients with familial adenomatous polyposis, hereditary non-polyposis colorectal cancer and loss of heterozygosity tumours. In this report we establish a novel link in vitro between the Tcf/beta-catenin pathway and NT1 receptor promoter activation.

SR 48692, a specific neurotensin receptor antagonist, has no effect on oesophageal motility in humans

BACKGROUND

The administration of exogenous neurotensin can reduce the lower oesophageal sphincter pressure, but it is unclear whether this effect is pharmacological or physiological.

AIM

A specific neurotensin receptor antagonist (SR 48692) was used to assess the effect of endogenous neurotensin on lower oesophageal sphincter function.

METHODS

Twenty-four healthy male subjects were included in a double-blind, placebo-controlled, randomized, cross-over study designed to determine the effects of two single doses (90 and 300 mg, preceded by a loading dose) of SR 48692 on the resting lower oesophageal sphincter pressure, transient lower oesophageal sphincter relaxations, primary oesophageal peristalsis and oesophageal acid exposure. Oesophageal pH and motility recordings were performed during 1 h of fasting and 3 h post-prandially. Plasma neurotensin-like immunoreactivity release was determined by radioimmunoassay.

RESULTS

During fasting, the lower oesophageal sphincter pressure, transient lower oesophageal sphincter relaxation rate and reflux episodes were similar with the two doses of SR 48692 and placebo. Meal ingestion induced a rise in plasma neurotensin-like immunoreactivity, a decrease in lower oesophageal sphincter pressure and an increase in both the transient lower oesophageal sphincter relaxation rate and the number of reflux episodes, which were not significantly modified by SR 48692. SR 48692 did not affect oesophageal primary peristalsis.

CONCLUSION

This study shows that SR 48692, a specific neurotensin 1 receptor antagonist, has no effect on oesophageal motility in humans.

Xenin plasma concentrations during modified sham feeding and during meals of different composition demonstrated by radioimmunoassay and chromatography

Xenin is a 25 amino acid peptide produced by specific endocrine cells of the duodenal mucosa. Xenin has multiple biological actions in the gastrointestinal tract. It modulates intestinal motility, affects exocrine pancreatic secretion, and gastric secretion of acid. In the present investigation, we studied plasma concentration of xenin in volunteers after modified sham feeding and after meals of different composition. Plasma xenin concentrations were determined by radioimmunoassay in unextracted plasmas and after acidic extraction using C-18 Sep-Pak chromatography and after neutral extraction using affinity filtration. Both extraction methods were followed by C 18 r.p. HPLC chromatography. Xenin plasma concentrations in unextracted and in extracted plasma rose significantly after modified sham feeding when the food was brought to the volunteers from another room immediately before sham feeding started. When the volunteers had the opportunity to observe the preparation of the meal, xenin plasma concentrations during fasting were high and no further rise was observed after sham feeding. Isocaloric feeding resulted in elevated xenin concentrations in unextracted plasma and after high-pressure liquid chromatography. The methods of extraction, acidic or neutral, did not affect the results.

CONCLUSION

Cephalic factors, investigated by modified sham feeding, stimulate release of xenin into the circulation. Xenin may participate in the central nervous regulation of gastrointestinal function.

Acid inhibition by intestinal nutrients mediated by CCK-A receptors but not plasma CCK

We examined the role of CCK-A receptors in acid inhibition by intestinal nutrients. Gastric acid and plasma CCK and gastrin levels were measured in rats with gastric and duodenal fistulas during intragastric 8% peptone and duodenal perfusion with saline, complete liquid diet (CLD; 20% carbohydrate, 6% fat, and 5% protein), and the individual components of CLD. Acid output was significantly inhibited (50-60%) by CLD, lipid, and dextrose. Plasma CCK was significantly increased by CLD (from 2.6 +/- 0.3 to 4.8 +/- 0.5 pM) and lipid (4.6 +/- 0.5 pM). CCK levels 50-fold higher (218 +/- 33 pM) were required to achieve similar acid inhibition by exogenous CCK-8 (10 nmol x kg(-1) x h(-1) iv). Intestinal soybean trypsin inhibitor elevated CCK (10.9 +/- 2.5 pM) without inhibiting acid secretion. The CCK-A antagonist MK-329 (1 mg/kg iv) reversed acid inhibition caused by CLD, lipid, and dextrose. Peptone-stimulated gastrin (21.7 +/- 1.9 pM) was significantly inhibited by CLD (14.5 +/- 3.6 pM), lipid (12.3 +/- 2.2 pM), and dextrose (11.9 +/- 1.5 pM). Lipid and carbohydrate inhibit acid secretion by activating CCK-A receptors but not by altering plasma CCK concentrations.

Plasma molecular forms of gastrin, neurotensin and somatostatin in pregnancy and gestational diabetes after an oral glucose load or a mixed meal

At present the physiological role of gastrin, neurotensin and somatostatin in pregnancy and gestational diabetes is scarcely known. We have measured their different molecular forms in plasma of six female controls, six normal pregnant (NP) women and six gestational diabetic (GD) women under basal conditions and 30 min after an oral glucose load (100 g) and a liquid mixed meal in order to study if their alteration could contribute to the impaired glucose tolerance in GD. Total basal concentrations of neurotensin and somatostatin were higher in GD than in controls and NP, and no change was found after the glucose load or mixed meal in GD. Neurotensin-1-13 was the main molecular form of all neurotensins at basal time in the three groups studied, being higher in GD in comparison with controls and NP. Somatostatin-1-14 was the predominant molecular form in controls and GD under basal conditions and did not show any change any change after stimuli. In NP, somatostatin-1-14 showed a significant increase following both kinds of stimuli. Total gastrin concentrations in NP and GD showed a significant increase after the glucose load, which was not observed in controls. Gastrin-17 was the main molecular form at basal time and 30 min post-stimuli in GD but not in NP and controls. We suggest that the basal elevation of neurotensin and somatostatin levels could contribute to the impaired glucose tolerance observed in gestational diabetes, as well as to the lack of post-stimuli responses for neurotensin and somatostatin in GD.(ABSTRACT TRUNCATED AT 250 WORDS)