Endogenous neurotensin facilitates enterohepatic bile acid circulation by enhancing intestinal uptake in rats

Dietary carbohydrate influences the colocalization pattern of Glucagon-like Peptide-1 with neurotensin in the chicken ileum

Glucagon-like peptide (GLP)-1 colocalizes with neurotensin (NT) in the same enteroendocrine cells (EECs) of the chicken ileum. The present study was designed to clarify the influence of dietary carbohydrate (CHO) on the colocalization pattern of GLP-1 with NT in the chicken distal ileum. Male White Leghorn chickens at 6 weeks of age (n = 15) were divided into three groups, a control and two experimental (low-CHO and CHO-free), with five chickens in each, and fed control or experimental diets for 7 d. Distal ileum was collected from each bird as a tissue sample and subjected to double immunofluorescence staining to detect GLP-1 and NT. Three types of EEC, GLP-1+/NT+, GLP-1+/NT- and GLP-1-/NT+, were demonstrated in the chicken ileum. GLP-1+/NT+ cells in the control group had a spindle-like shape with a long cytoplasmic process, but those in the experimental groups were round and lacked a cytoplasmic process. The ratio of GLP-1+/NT+ cells was significantly decreased in the two experimental groups compared with that in the control group. The ratio of GLP-1+/NT+ cells was significantly lower than those of GLP-1+/NT- and GLP-1-/NT+ cells in the two experimental groups. Most cells that were immunoreactive for GLP-1 and NT antisera lacked signals of proglucagon (PG) and NT precursor (NTP) mRNA in the experimental groups. The number of EECs expressing PG and NTP mRNA signals showed tendencies for decreases with a reduction of dietary CHO level. These findings suggest that dietary CHO could be a significant regulator of the pattern of colocalization pattern of GLP-1 with NT in the chicken ileum.

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.

Pro-Neurotensin as a Potential Novel Diagnostic Biomarker for Detection of Nonalcoholic Fatty Liver Disease

BACKGROUND AND AIMS

Currently, liver biopsy is the gold standard method for diagnosis of non-alcoholic fatty liver severity. It is critical to develop non-invasive diagnostic method to diagnose nonalcoholic fatty liver rather than invasive techniques. Our case-control study was to address the value of circulating miRNA-122 and serum pro-neurotensin as a potential non-invasive biomarker for the diagnosis of non-alcoholic fatty acid diseases.

METHODS

Clinical assessment, laboratory investigations, and anthropometric measurements were reported for 157 patients with proven NAFLD. Apparently, healthy participants (n=100) were enrolled as a control group. Serum samples were tested for micro-RNAs-122 and pro-neurotensin.

RESULTS

Compared with the control subjects, both mi-RNA-122 and serum proneurotensin levels were increased in NAFLD (p<0.001) and at a cut-off ≥6.83, mi-RNA-122 had 51.0% sensitivity, 70.0% specificity to differentiate NAFLD from healthy controls, while serum proneurotensin had 80.0% sensitivity and 80.0% specificity at a cutoff ≥108.

CONCLUSION

The circulating pro-neurotensin might be used as a novel biomarker for diagnosis of patients with NAFLD, wherefore the integration of a circulating mi-RNA-122 and serum pro-neurotensin could be beneficial to diagnose NAFLD cases. Large-scale studies are needed to investigate the possible role of mi-RNA-122 and pro-neurotensin in the development, progression, and prognosis of NAFLD and NASH.

Anorexia and Fat Aversion Induced by Vertical Sleeve Gastrectomy Is Attenuated in Neurotensin Receptor 1-Deficient Mice

Neurotensin (NT) is an anorexic gut hormone and neuropeptide that increases in circulation following bariatric surgery in humans and rodents. We sought to determine the contribution of NT to the metabolic efficacy of vertical sleeve gastrectomy (VSG). To explore a potential mechanistic role of NT in VSG, we performed sham or VSG surgeries in diet-induced obese NT receptor 1 (NTSR1) wild-type and knockout (ko) mice and compared their weight and fat mass loss, glucose tolerance, food intake, and food preference after surgery. NTSR1 ko mice had reduced initial anorexia and body fat loss. Additionally, NTSR1 ko mice had an attenuated reduction in fat preference following VSG. Results from this study suggest that NTSR1 signaling contributes to the potent effect of VSG to initially reduce food intake following VSG surgeries and potentially also on the effects on macronutrient selection induced by VSG. However, maintenance of long-term weight loss after VSG requires signals in addition to NT.

Pro-Neurotensin/Neuromedin N and Risk of Incident Metabolic Syndrome and Diabetes Mellitus in the REGARDS Cohort

CONTEXT

The peptide neurotensin is implicated in insulin resistance, diabetes mellitus (DM), and cardiovascular disease.

OBJECTIVE

We studied the association of neurotensin's stable precursor, pro-neurotensin/neuromedin N (pro-NT/NMN) with incident metabolic syndrome (MetS) and DM.

METHODS

We included 3772 participants from the REasons for Geographic and Racial Differences in Stroke (REGARDS) study who completed the baseline exam (2003-2007), the follow-up exam (2013-2016), and had pro-NT/NMN measured by immunoassay. Weighted logistic regression models were fitted to incident DM, incident MetS, and each MetS component, separately, incorporating demographics, metabolic risk factors, homeostasis model of insulin resistance (HOMA-IR), and diet scores. Incident MetS was defined by 3 or more harmonized criteria at follow-up in those with fewer than 3 at baseline. Incident DM was defined by use of hypoglycemic drugs/insulin, fasting glucose 126 mg/dL or greater, or random glucose 200 mg/dL or greater in those without these at baseline.

RESULTS

Median (IQR) plasma pro-NT/NMN was 160 pmol/L (118-218 pmol/L). A total of 564 (of 2770 without baseline MetS) participants developed MetS, and 407 (of 3030 without baseline DM) developed DM. Per SD higher log-pro-NT/NMN, the demographic-adjusted odds ratio (OR) and 95% CI of incident MetS was 1.22 (1.11-1.35), 1.16 (1.00-1.35) for incident low high-density lipoprotein (HDL), and 1.25 (1.11-1.40) for incident dysglycemia. The association of pro-NT/NMN with MetS was attenuated in the model adding HOMA-IR (OR per SD log-pro-NT/NMN 1.14; 95% CI, 1.00-1.30). There was no association with incident DM (OR per SD log-pro-NT/NMN 1.06; 95% CI, 0.94-1.19).

CONCLUSION

Pro-NT/NMN was associated with MetS and 2 components, dysglycemia and low HDL, likely explained by insulin resistance.

Circulating Levels of Pro-Neurotensin and Its Relationship with Nonalcoholic Steatohepatitis and Hepatic Lipid Metabolism

Recent studies suggest a link between pro-neurotensin (pro-NT) and nonalcoholic fatty liver disease (NAFLD), but the published data are conflicting. Thus, we aimed to analyze pro-NT levels in women with morbid obesity (MO) and NAFLD to investigate if this molecule is involved in NAFLD and liver lipid metabolism. Plasma levels of pro-NT were determined in 56 subjects with MO and 18 with normal weight (NW). All patients with MO were subclassified according to their liver histology into the normal liver (NL, n = 20) and NAFLD (n = 36) groups. The NAFLD group had 17 subjects with simple steatosis (SS) and 19 with nonalcoholic steatohepatitis (NASH). We used a chemiluminescence sandwich immunoassay to quantify pro-NT in plasma and RT-qPCR to evaluate the hepatic mRNA levels of several lipid metabolism-related genes. We reported that pro-NT levels were significantly higher in MO with NAFLD than in MO without NAFLD. Additionally, pro-NT levels were higher in NASH patients than in NL. The hepatic expression of lipid metabolism-related genes was found to be altered in NAFLD, as previously reported. Additionally, although pro-NT levels correlated with LDL, there was no association with the main lipid metabolism-related genes. These findings suggest that pro-NT could be related to NAFLD progression.

Circulating pro-neurotensin levels predict bodyweight gain and metabolic alterations in children

BACKGROUND AND AIMS

Neurotensin (NT) is an intestinal peptide released after fat ingestion, which regulates appetite and facilitates lipid absorption. Elevated plasma levels of its stable precursor pro-neurotensin (pro-NT) are associated with type 2 diabetes, obesity and cardiovascular mortality in adult populations; no data on pro-NT and metabolic disease are available in children. Aim of the study was to evaluate plasma pro-NT in relation to the presence of obesity in children, and to test if high pro-NT associates with the development of metabolic impairment later in life.

METHODS AND RESULTS

For this longitudinal retrospective study, we studied 151 overweight/obese children undergoing metabolic evaluations at University of Cagliari, Italy. Pro-NT was also assessed in 46 normal-weight, age-, sex-comparable normal-weight children, selected as a reference group. At the baseline, pro-NT was comparable between overweight/obese and normal-weight children and correlated positively with age (p < 0.001), triglycerides (p < 0.001) and inversely with HDL levels (p = 0.008). Plasma pro-NT associated with high triglycerides with OR = 5.9 (95%CI: 1.24-28.1; p = 0.026) after adjustment for multiple confounders. At the 6.5-year follow-up, high basal pro-NT associated with impaired β-cell function to compensate for insulin-resistance (disposition index: r = -0.19, p = 0.035) and predicted bodyweight increase, as indicated by percentage change of standard deviation score BMI (median(95%CI) = +20.8(+4.9-+27.5)% in the highest tertile), independently from age, sex, triglycerides and insulin-resistance (standardized β = 0.24; p = 0.036).

CONCLUSIONS

Elevated pro-NT levels in children are significantly associated with weight gain later in life and may represent a marker of susceptibility to metabolic impairment in presence of obesity.

Dietary Protein Level Influences on Neurotensin-immunoreactive Cells in the Chicken Ileum

Neurotensin is secreted from intestinal N cells in response to the food ingestion. Influences of different dietary protein levels on neurotensin-immunoreactive cells in the chicken ileum were examined by using immunohistochemical and morphometrical techniques. The results showed that dietary protein had an obvious influence on neurotensin-immunoreactive cells in the chicken ileum. Four experimental groups were used, with dietary crude protein (CP) levels of 18% (control), 9%, 4.5% and 0%. Enteroendocrine cells showing neurotensin-immunoreactivity were located in crypts and villous epithelium in all groups. Most of the neurotensin-immunoreactive cells in the villous epithelium showed pyramidal or spindle-like shape with a long cytoplasmic process reaching the intestinal lumen, but cells with round or oval shape were found in the CP4.5% and 0% groups. Frequencies of occurrence of neurotensin-immunoreactive cells in the CP18%, 9%, 4.5% and 0% groups were 42.4±3.3, 36.6±2.2, 30.8±2.6 and 25.4±3.8 (cell count per mucosal area: cells/mm², mean±SD), respectively. There were significant differences in neurotensin-immunoreactive cell frequency between the control and lower CP level, 4.5% and 0%, groups. A significant correlation was found between frequency of occurrence of neurotensin-immunoreactive cells and daily protein intake. These results indicate that ingested protein is likely to be a potential signal for neurotensin production and secretion of N cells in the chicken ileum.

Magnitude of rise in proneurotensin is related to amount of triglyceride appearance in blood after standardized oral intake of both saturated and unsaturated fat

Background

In rodents, neurotensin contributes to high fat diet induced obesity by facilitation of intestinal fat absorption. The effect of oral lipid load on plasma proneurotensin and relationship with plasma triglycerides in humans is unknown.

Aim

To investigate the acute effects of an oral lipid load on proneurotensin and plasma triglycerides and their interrelationships in healthy individuals.

Setting/ methods

Twenty-two healthy subjects were given 150 mL of full milk cream (54 g fat) and 59 mL of pure olive oil (54 g fat) in the fasted state at two different occasions separated by at least 1 week in random order. Venous blood was drawn at fasted before 0 h (h) and at 1 h, 2 h and 4 h after ingestion. Post-ingested values of proneurotensin and plasma triglycerides were compared with fasting levels and post ingestion Area Under the Curve (AUC) of proneurotensin was correlated with that of plasma triglycerides.

Results

An immediate rise of plasma proneurotensin and plasma triglycerides were observed after ingestion of cream with maximum increase at 2 h for proneurotensin [mean (95% confidence interval)] of 22 (12–31) pmol/L (P < 0.001) and at 3 h for triglycerides of 0.60 (0.43–0.78) mmol/L (P < 0.001). Similarly, plasma proneurotensin and plasma triglycerides increased after ingestion of olive oil with maximum increase of proneurotensin at 3 h of 62 (46–78) pmol/L (P < 0.001) and plasma triglycerides at 3 h of 0.32 (0.18–0.45) mmol/L (P < 0.001). The post lipid load AUC for proneurotensin correlated significantly with the AUC for plasma triglycerides both after cream (r = 0.49, P = 0.021) and olive oil (r = 0.55, P = 0.008), respectively.

Conclusion

Proneurotensin increases after an oral lipid load of both cream and olive oil and the rise of post-ingestion plasma triglycerides is significantly related to the rise of post-ingestion proneurotensin.

Potential roles of neurotensin on cognition in conditions of obese-insulin resistance

Neurotensin is an endogenous tridecapeptide that can be found in both central and peripheral nervous systems. Under normal physiological conditions, neurotensin is involved in the regulation of pain, body temperature, physical activity, appetite as well as learning and memory. In addition, it plays an important role in fat metabolism. Previous studies have demonstrated that alterations of neurotensin levels were associated with several neuropathological conditions such as Alzheimer's disease, mood disorders, and obesity associated eating disorders. Obesity has been shown to be associated with low-grade systemic inflammation, brain inflammation, and cognitive decline. Several pieces of evidence suggest that neurotensin might play a role in cognitive decline following obesity. However, the underlying mechanisms of neurotensin on cognition under obese-insulin resistant condition are still unclear. In this review, the current available evidence from in vitro, in vivo and clinical studies regarding the role of neurotensin in the physiological condition and obesity in association with cognition are comprehensively summarized and discussed. The studies which report controversial findings regarding these issues are also presented and discussed.

Neurotensin contributes to pediatric intestinal failure-associated liver disease via regulating intestinal bile acids uptake

Although the pathogenesis of intestinal failure (IF)-associated liver disease (IFALD) is uncertain, IF-associated cholestasis mediated by the combination of intestinal injury and parenteral nutrition (PN) can lead to disturbed hepatocyte bile acids (BA) homeostasis and cause liver damages. We here show that neurotensin (NT; also known as NTS) concentrations were lower compared to healthy matched controls. Patients with cholestasis [56.1 ng/L (9.7-154.7) vs. 210.4 ng/L (134-400.4), p < .001] had lower serum NT concentrations than others. In patients' ileum, the levels of NT mRNA were positively correlated with the apical sodium dependent bile acid transporter (ASBT) mRNA levels. In mice and in cultured intestinal cells, NT treatments stimulated the expression of ASBT and led to increase BA uptake via NT receptors (NTR1 and NTR3; also known as NTSR1and NTSR3). In conclusion, these findings directly link NT with BA homeostasis, which provide an insight into the complex mechanisms mediating the development of liver disease in pediatric patients with IF.

Increased Plasma Proneurotensin Levels Identify NAFLD in Adults With and Without Type 2 Diabetes

CONTEXT

Neurotensin (NT), an intestinal peptide released by fat ingestion, promotes lipid absorption; higher circulating NT levels are associated with type 2 diabetes (T2D), obesity, and cardiovascular disease. Whether NT is related to nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) has not been fully investigated.

OBJECTIVE

To study the relationship between plasma proneurotensin 1 to 117 (pro-NT), a stable fragment of the NT precursor hormone, and the presence/severity of NAFLD/NASH and to unravel correlates of increased pro-NT levels.

DESIGN/SETTING/PARTICIPANTS

For this cross-sectional study, 60 obese individuals undergoing bariatric surgery for clinical purposes were recruited. The association between pro-NT and NAFLD was further investigated in 260 consecutive subjects referred to our outpatient clinics for metabolic evaluations, including liver ultrasonography. The study population underwent complete metabolic characterization; in the obese cohort, liver biopsies were performed during surgery.

MAIN OUTCOME MEASURES

Plasma pro-NT levels in relation to NAFLD/NASH.

RESULTS

Obese subjects with biopsy-proven NAFLD (53%) had significantly higher plasma pro-NT than those without NAFLD (183.6 ± 81.4 vs 86.7 ± 56.8 pmol/L, P < 0.001). Greater pro-NT correlated with NAFLD presence (P < 0.001) and severity (P < 0.001), age, female sex, insulin resistance, and T2D. Higher pro-NT predicted NAFLD with an area under receiver operating characteristic curve of 0.836 [95% confidence interval (CI), 0.73 to 0.94; P < 0.001]. Belonging to the highest pro-NT quartile correlated with increased NAFLD risk (odds ratio, 2.62; 95% CI, 1.08 to 6.40) after adjustment for confounders. The association between higher pro-NT and NAFLD was confirmed in the second cohort independently from confounders.

CONCLUSIONS

Increased plasma pro-NT levels identify the presence/severity of NAFLD; in dysmetabolic individuals, NT may specifically promote hepatic fat accumulation through mechanisms likely related to increased insulin resistance.

Long-Chain Free Fatty Acid Receptor GPR120 Mediates Oil-Induced GIP Secretion Through CCK in Male Mice

Free fatty acid receptors GPR120 and GPR40 are involved in the secretion of gut hormones. GPR120 and GPR40 are expressed in enteroendocrine K cells, and their activation induces the secretion of the incretin glucose-dependent insulinotropic polypeptide (GIP). However, the role of these receptors in fat-induced GIP secretion in vivo and the associated mechanisms are unclear. In this study, we investigated corn oil-induced GIP secretion in GPR120-knockout (GPR120-/-) and GPR40-knockout (GPR40-/-) mice. Oil-induced GIP secretion was reduced by 50% and 80% in GPR120-/- and GPR40-/- mice, respectively, compared with wild-type mice. This was not associated with a significant difference in K-cell number or GIP content in K cells, nor messenger RNA levels of the lipid receptor GPR119, nor bile acid receptors TGR5 and farnesoid X receptor. GPR120-/- and GPR40-/- mice also exhibited substantially decreased levels of cholecystokinin (CCK), a hormone from I cells that promotes bile and pancreatic lipase secretion, and this decrease was associated with impaired gallbladder contraction. Notably, treatment with a CCK analog resulted in recovery of oil-induced GIP secretion in GPR120-/- mice but not in GPR40-/- mice. These results indicate that corn oil-induced GIP secretion from K cells involves both GPR120 and GPR40 signaling pathways, and GPR120-induced GIP secretion is indirectly mediated by CCK.

Stimulation of oval cell and hepatocyte proliferation by exogenous bombesin and neurotensin in partially hepatectomized rats

AIM: To investigate the effect of the neuropeptides bombesin (BBS) and neurotensin (NT) on oval cell proliferation in partially hepatectomized rats not pretreated with a known hepatocyte inhibitor.

METHODS: Seventy male Wistar rats were randomly divided into five groups: I = controls, II = sham operated, III = partial hepatectomy 70% (PHx), IV = PHx + BBS (30 μg/kg per day), V = PHx + NT (300 μg/kg per day). Forty eight hours after liver resection, portal endotoxin levels and hepatic glutathione redox state were determined. α-fetoprotein (AFP) mRNA (in situ hybridisation), cytokeratin-19 and Ki67 antigen expression (immunohistochemistry) and apoptosis (TUNEL) were evaluated on liver tissue samples. Cells with morphological features of oval cells that were cytokeratin-19 (+) and AFP mRNA (+) were scored in morphometric analysis and their proliferation was recorded. In addition, the proliferation and apoptotic rates of hepatocytes were determined.

RESULTS: In the control and sham operated groups, oval cells were significantly less compared to groups III, IV and V (P < 0.001). The neuropeptides BBS and NT significantly increased the proliferation of oval cells compared to group III (P < 0.001). In addition, BBS and NT induced a significant increase of hepatocyte proliferation (P < 0.001), whereas it decreased their apoptotic activity (P < 0.001) compared to group III. BBS and NT significantly decreased portal endotoxemia (P < 0.001) and increased the hepatic GSH: GSSG ratio (P < 0.05 and P < 0.001, respectively) compared to group III.

CONCLUSION: BBS and NT stimulated oval cell proliferation in a model of liver regeneration, without use of concomitant suppression of hepatocyte proliferation as oval cell activation stimuli, and improved the hepatocyte regenerative response. This peptides-induced combined stimulation of oval cell and hepatocyte proliferation might serve as a possible treatment modality for several liver diseases.

Molecular characterization of structure and tissue distribution of chicken neurotensin receptor

Neurotensin, a tridecapeptide, is distributed in a wide range of tissues and exhibits multiple functions through its receptors. Hitherto molecular characterization of the neurotensin receptor has been reported in mammalian, amphibian, and fish species but not in avian species. In this study, we cloned the cDNA encoding chicken neurotensin receptor from the duodenum and characterized its primary structure, biological activity and distribution in the gastrointestinal tract. The cDNA encoded a protein consisting of 399 amino acids that had significant overall sequence homology to other vertebrate neurotensin receptor 1 with higher extent in the seven transmembrane domains. Chicken neurotensin increased intracellular Ca(2+) concentrations in human embryonic kidney 293 cells transiently expressing the chicken neurotensin receptor 1. Real-time PCR analysis showed that chicken neurotensin receptor 1 mRNA is expressed throughout the gastrointestinal tract with markedly higher level in the colon/rectum. These results indicate that the chicken neurotensin receptor 1 is involved in gastrointestinal functions through an intracellular signaling pathway accompanied by an increase in Ca(2+) levels.

Bombesin and neurotensin exert antiproliferative effects on oval cells and augment the regenerative response of the cholestatic rat liver

The regenerative capacity of the cholestatic liver is significantly attenuated. Oval cells are hepatic stem cells involved in liver's regeneration following diverse types of injury. The present study investigated the effect of the neuropeptides bombesin (BBS) and neurotensin (NT) on oval cell proliferation as well as on hepatocyte and cholangiocyte proliferation and apoptosis in the cholestatic rat liver. Seventy male Wistar rats were randomly divided into five groups: controls, sham operated, bile duct ligated (BDL), BDL+BBS (30 μg/kg/d), BDL+NT (300 μg/kg/d). Ten days later, alpha-fetoprotein (AFP) mRNA (in situ hybridization), cytokeratin-19 and Ki67 antigen expression (immunohistochemistry) and apoptosis (TUNEL) were evaluated on liver tissue samples. Cells with morphologic features of oval cells that were cytokeratin-19(+) and AFP mRNA(+) were scored in morphometric analysis and their proliferation was recorded. In addition, the proliferation and apoptotic rates of hepatocytes and cholangiocytes were determined. Alanine aminotransferase (ALT) levels and hepatic oxidative stress (lipid peroxidation and glutathione redox state) were also estimated. The neuropeptides BBS and NT significantly reduced ALT levels and hepatic oxidative stress. Both agents exerted similar and cell type-specific effects on oval cells, hepatocytes and cholangiocytes: (a) oval cell proliferation and accumulation in the cholestatic liver was attenuated, (b) hepatocyte proliferation was increased along with a decreased rate of their apoptosis and (c) cholangiocyte proliferation was attenuated and their apoptosis was increased. These observations might be of potential value in patients with extrahepatic cholestasis.

The regulatory role of neurotensin on the hypothalamic-anterior pituitary axons: emphasis on the control of thyroid-related functions

Neurotensin (NT) is a 13 amino acid neurohormone and/or neuromodulator, located in the synaptic vesicles and released from the neuronal terminals in a calcium-dependent manner. This peptide is present among mammalian and nonmammalian species, mainly in the central nervous system and the gastrointestinal tract. Due to its neuroendocrine activity, NT has been related to the pathophysiology of a series of disorders, such as schizophrenia, drug-abuse, Parkinson's disease, cancer, stroke, eating disorders and other neurodegenerative conditions. Moreover, NT participates in the physiology of pain-induction, central blood pressure control and inflammation. NT also plays an important interactive role in all components of the hypothalamic-anterior pituitary circuit, which is mediated by an endocrine, paracrine or/and autocrine manner, towards most of the anatomical regions that define this circuit. A considerable amount of data implicates NT in thyroid-related regulation through this circuit, the exact mechanisms of which should be further investigated for the potential development of more targeted approaches towards the treatment of thyroid-related endocrine diseases. The aim of this study was to provide an up-to-date review of the literature concerning the regulatory role of NT on the hypothalamic-anterior pituitary axons, with an emphasis on the control of thyroid-related functions.

Gut regulatory peptides bombesin and neurotensin reduce hepatic oxidative stress and histological alterations in bile duct ligated rats

Gut regulatory peptides bombesin (BBS) and neurotensin (NT) exert a wide spectrum of biological actions on gastrointestinal tissues and we have previously shown that they improve intestinal barrier function and oxidative stress in experimentally jaundiced rats. In the present study, we explored their potential action on liver histology and oxidative status in bile duct ligated rats. Seventy male Wistar rats were randomly divided into five groups: controls, sham operated, bile duct ligated (BDL), BDL + BBS (10 microg/kg, s.c. x3), BDL + NT (300 microg/kg, i.p.). At the end of the experiment, on day 10, serum total bilirubin and alanine aminotransferase (ALT) levels were determined and endotoxin was measured in portal and aortic blood. Liver tissue samples were examined histologically for evaluation of the ratio of portal tracts presenting changes of obstructive cholangiopathy and neutrophils' number in portal tracts. In addition, hepatic oxidative status was estimated on liver homogenates by measurements of lipid peroxidation (malondialdehyde), protein oxidation (protein carbonyl groups) and thiol redox state [reduced glutathione (GSH), oxidized glutathione (GSSG), total non-protein mixed disulfides (NPSSR) and protein thiols (PSH)]. Administration of BBS or NT significantly reduced portal and aortic endotoxaemia observed in obstructive jaundice. Both agents significantly ameliorated liver injury, as demonstrated by improvement of obstructive cholangiopathy and reduction of ALT. This effect was accompanied by prevention of lipid peroxidation, protein oxidation and decrease of the oxidized forms GSSG and NPSSR. Moreover, neutrophil accumulation in portal tracts was significantly decreased. In conclusion, this study shows that gut regulatory peptides BBS and NT reduce cholestatic liver injury, exerting protective effects on portal tract architecture, neutrophil infiltration and hepatic oxidative stress in bile duct ligated rats.

Involvement of mast cells in basal and neurotensin-induced intestinal absorption of taurocholate in rats

Neurotensin (NT), a hormone released from intestine by ingested fat, facilitates lipid digestion by stimulating pancreatic secretion and slowing the movement of chyme. In addition, NT can contract the gall bladder and enhance the enterohepatic circulation (EHC) of bile acids to promote micelle formation. Our recent finding that NT enhanced and an NT antagonist inhibited [(3)H]taurocholate ([(3)H]TC) absorption from proximal rat small intestine indicated a role for endogenous NT in the regulation of EHC. Here, we postulate the involvement of intestinal mast cells in the TC uptake process and in the stimulatory effect of NT. In anesthetized rats with the bile duct cannulated for bile collection, infusion of NT (10 pmol.kg(-1).min(-1)) enhanced the [(3)H]TC recovery rate from duodenojejunum by 2.2-fold. This response was abolished by pretreatment with mast cell stabilizers (cromoglycate, doxantrazole) and inhibitors of mast cell mediators (diphenhydramine, metergoline, zileuton). In contrast, mast cell degranulators (compound 48/80, substance P) and mast cell mediators (histamine, leukotriene C(4)) reproduced the effect of NT. N(G)-nitro-l-arginine methyl ester enhanced and l-arginine inhibited basal and NT-induced TC uptake, consistent with the known inhibitory effect of nitric oxide (NO) on mast cell reactivity. These results argue that basal and NT-stimulated TC uptake in rat jejunum are similarly dependent on mast cells, are largely mediated by release of mast cell mediators, and are subject to regulation by NO.

The effect of neurotensin on insulin-induced proliferation of human fibroblasts

Neurotensin has been shown to influence growth in a number of cancerous and non-cancerous cells and to enhance the proliferative effects of growth factors without itself inducing proliferation. Here we show that neurotensin potentiates the proliferative effects of insulin on IMR90 human fibroblasts in a concentration and neurotensin receptor type 1-dependent manner. This potentiating effect of neurotensin was blocked by inhibitors of phospholipase C and protein kinase C, was accompanied by an increase in the level of soluble inositol phosphates and did not involve an autocrine factor. These results show that neurotensin can enhance insulin-dependent proliferation of human fibroblasts and suggest a possible role for neurotensin in tissue growth and repair.

Targeted deletion of the ileal bile acid transporter eliminates enterohepatic cycling of bile acids in mice

The ileal apical sodium bile acid cotransporter participates in the enterohepatic circulation of bile acids. In patients with primary bile acid malabsorption, mutations in the ileal bile acid transporter gene (Slc10a2) lead to congenital diarrhea, steatorrhea, and reduced plasma cholesterol levels. To elucidate the quantitative role of Slc10a2 in intestinal bile acid absorption, the Slc10a2 gene was disrupted by homologous recombination in mice. Animals heterozygous (Slc10a2+/-) and homozygous (Slc10a2-/-) for this mutation were physically indistinguishable from wild type mice. In the Slc10a2-/- mice, fecal bile acid excretion was elevated 10- to 20-fold and was not further increased by feeding a bile acid binding resin. Despite increased bile acid synthesis, the bile acid pool size was decreased by 80% and selectively enriched in cholic acid in the Slc10a2-/- mice. On a low fat diet, the Slc10a2-/- mice did not have steatorrhea. Fecal neutral sterol excretion was increased only 3-fold, and intestinal cholesterol absorption was reduced only 20%, indicating that the smaller cholic acid-enriched bile acid pool was sufficient to facilitate intestinal lipid absorption. Liver cholesteryl ester content was reduced by 50% in Slc10a2-/- mice, and unexpectedly plasma high density lipoprotein cholesterol levels were slightly elevated. These data indicate that Slc10a2 is essential for efficient intestinal absorption of bile acids and that alternative absorptive mechanisms are unable to compensate for loss of Slc10a2 function.