Enhancement of jejunal absorption of conjugated bile acid by neurotensin in rats

Individuals with type 2 diabetes have higher density of small intestinal neurotensin-expressing cells

Neurotensin (NT) is a gastro-intestinal hormone involved in several pathways that regulate energy and glucose homeostasis. NT was hypothesized to act in synergy with incretin hormones to potentiate its anti-diabetic effects. Additionally, circulating NT levels were shown to rise after bariatric surgery-induced weight loss. Knowledge of NT-secreting cells distribution along the small intestine and its variation according to diabetes status could provide insights on NT role in mediating type 2 diabetes (T2D) improvement after bariatric surgery. So, our aims were to characterize NT-expressing cell distribution along the human small intestine and to compare the relative density of NT-expressing cells in the small intestine of individuals with and without T2D undergoing bariatric surgery for obesity treatment. Autopsy-derived small intestine fragments (n = 30) were obtained at every 20 cm along the entire intestinal length. Additionally, jejunum biopsies (n = 29) were obtained during elective gastric bypass interventions from patients with (n = 10) or without T2D (n = 18). NT-expressing cells were identified by immunohistochemistry and quantified via computerized morphometric analysis. NT-expressing cell density increased along the human small intestine. NT-expressing cell density was significantly higher from 200 cm distal to the duodenojejunal flexure onward, as well as in subjects with T2D when compared to those without T2D. NT-expressing cell density increases along the human small gut, and a higher density is found in individuals with T2D. This finding suggests a potential role for NT in the mechanisms of disease and T2D improvement observed after bariatric surgery.

Expression of Neurotensin and Its Receptors Along the Intestinal Tract in Type 2 Diabetes Patients and Healthy Controls

CONTEXT

Enteroendocrine N cells secrete neurotensin (NTS). NTS reduces food intake in rodents and may increase insulin release. In humans, postprandial NTS responses increase following Roux-en-Y gastric bypass, associating the hormone with the glucose- and body weight-lowering effects of these procedures.

OBJECTIVE

We looked at N cell density and mucosal messenger RNA (mRNA) expression profiles of NTS and NTS receptors in type 2 diabetes (T2D) patients and healthy controls.

METHODS

Using double-balloon enteroscopy, 12 patients with T2D and 12 sex-, age-, and body mass index-matched healthy controls had mucosa biopsies taken from the entire length of the small intestine (at 30-cm intervals) and from 7 anatomically well-defined locations in the large intestine. Biopsies were analyzed using immunohistochemistry and mRNA sequencing.

RESULTS

N cell density and NTS mRNA expression gradually increased from the duodenum to the ileum, while negligible NTS-positive cells and NTS mRNA expression were observed in the large intestine. NTS receptor 1 and 2 mRNA expression were not detected, but sortilin, a single-pass transmembrane neuropeptide receptor of which NTS also is a ligand, was uniformly expressed in the intestines. Patients with T2D exhibited lower levels of NTS-positive cells and mRNA expression than healthy controls, but this was not statistically significant after adjusting for multiple testing.

CONCLUSION

This unique intestinal mapping of N cell density and NTS expression shows increasing levels from the small intestine's proximal to distal end (without differences between patients with T2D and healthy controls), while negligible N-cells and NTS mRNA expression were observed in the large intestine. Sortilin was expressed throughout the intestines in both groups; no NTS receptor 1 or 2 mRNA expression were detected.

MiR-203 is an anti-obese miRNA by targeting ASBT

Obesity is characterized by excessive fat deposition within the body. Bile acids (BA) are important regulators for controlling the absorption of lipid. Here we show that miR-203 exerts weight-loss and lipid-lowering effects by increasing total BA excretion in obese rodents. miR-203 overexpression transgenic mice are resistant to high-fat diet (HFD)-induced obesity and dyslipidemia. Moreover, the knockdown of miR-203 deteriorates metabolic disorders. ASBT plays important role in regulating BA homeostasis and is a direct target of miR-203. In human intestinal epithelial cells, overexpression of miR-203 decreases the cellular uptake of BA by inhibiting ASBT. Furthermore, TCF7L2 is downregulated in obese mice and acts as a transcription factor of miR-203. The ASBT mRNA level was positively correlated with the body mass index (BMI) of population, while the miR-203 level was negatively associated with BMI. Taken together, these data suggest miR-203 could be a new therapeutic BA regulator for obesity and dyslipidemia.

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miR-203 is downregulated in obese rodents and overweight/obese population

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ASBT is a direct target of miR-203 in obesity

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TCF7L2 acts as an upstream activator of miR-203 in obesity

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miR-203 ameliorates obesity and dyslipidemia by increasing TBAs and lipids excretion

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.

Plasma Proneurotensin and Prediction of Cause-Specific Mortality in a Middle-aged Cohort During Long-term Follow-up

CONTEXT

Neurotensin is associated with cardiometabolic diseases but its role with mortality risk in humans is unknown.

OBJECTIVE

This work aims to examine the prediction of proneurotensin (Pro-NT) with respect to total and cause-specific mortality in a middle-aged cohort.

METHODS

In the population-based middle-aged cohort (n = 4632; mean age, 57 years) of the Malmö Diet and Cancer Study, Pro-NT was assessed and total as well as cause-specific mortality was studied. Main cause of death was based on the International Classification of Diseases.

RESULTS

During a mean follow-up of 20 ± 3 years, 950 men and 956 women died. There was significantly increased mortality risk in individuals belonging to the highest quartile (Q) of Pro-NT (Q4, Pro-NT ≥ 149 pmol/L) compared with Qs 1 to 3 (Pro-NT < 149 pmol/L), hazard ratio (HR), 95% CI of 1.29 (1.17-1.42; P < .001). Data were adjusted for sex and age. No significant interaction was observed between Pro-NT and sex on mortality risk. Individuals within Q4 vs Qs 1 to 3 had an HR of 1.41 (95% CI, 1.18-1.68; P < .001) for death due to cardiovascular disease (n = 595/4632); 2.53 (95% CI, 1.37-4.67; P = .003), due to digestive tract disease (n = 42/4632), 1.62 (95% CI, 1.04-2.52; P = .032) due to mental and behavioral disease (n = 90/4632); and 1.91 (95% CI, 1.15-3.19; P = .013) due to unspecific causes (n = 64/4632). There was no significant relationship between Pro-NT and deaths due to cancer, infections, neurological, or other causes. Adjustment for cardiovascular risk factors only marginally changed these results.

CONCLUSION

The relationship between Pro-NT and total mortality risk was mainly driven by cardiovascular mortality, but high Pro-NT also predicts death from digestive, mental, and behavioral disease and deaths attributed to unspecific causes.

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.

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.

Neurotensins and their therapeutic potential: research field study

The natural tridecapeptide neurotensin has been emerged as a promising therapeutic scaffold for the treatment of neurological diseases and cancer. In this work, we aimed to identify the top 100 most cited original research papers as well as recent key studies related to neurotensins. The Web of Science Core Collection database was searched and the retrieved research articles were analyzed by using the VOSviewer software. The most cited original articles were published between 1973 and 2013. The top-cited article was by Carraway and Leeman reporting the discovery of neurotensin in 1973. The highly cited terms were associated with hypotension and angiotensin-converting-enzyme. The conducted analysis reveals the therapeutic potentials of neurotensin, and further impactful research toward its clinical development is warrantied.

Absence of neurotensin attenuates intestinal dysbiosis and inflammation by maintaining Mmp7/α-defensin axis in diet-induced obese mice

We previously reported that high levels of plasma neurotensin (NT), a gut hormone released from enteroendocrine cells of the small bowel, contribute to obesity and comorbid conditions. Gut microbiota has been implicated in the obesity development. Paneth cells are critical in maintaining gut microbiota composition and homeostasis by releasing antimicrobial proteins including α-defensins. The purpose of our current study was to determine the possible role of NT in gut microbiota composition and α-defensin gene expression associated with obesity. Here we show that the ratio of Firmicutes/Bacteroidetes (F/B ratio) and intestinal proinflammatory cytokines is significantly increased in NT+/+ mice fed with a high-fat diet (HFD) which were improved in NT-deficient mice. HFD disrupted the intestinal Mmp7/α-defensin axis, which was completely prevented in NT-/- mice. In addition, NT treatment inhibited DEFA5 expression and concurrent NF-κB activity, which was blocked by a pan PKC inhibitor (Gö6983) or an inhibitor for atypical PKCs (CRT0066854). More importantly, the shRNA-mediated knockdown of atypical PKCτ reversed NT-attenuated DEFA5 expression and increased NF-κB activity. NT contributes to the HFD-induced disruption of gut microbiota composition and α-defensin expression. PKCτ/λ plays a central role in NT-mediated α-defensin gene expression which might be mediated through the inhibition of NF-κB signaling pathways in Paneth cells.

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.

Neurotensin Is a Lipid-Induced Gastrointestinal Peptide Associated with Visceral Adipose Tissue Inflammation in Obesity

Neurotensin (NT) is a 13-amino acid peptide localized in the neuroendocrine cells of the small intestine, which promotes fat absorption and fatty acids translocation in response to lipid ingestion. NT-knock-out mice fed with a high-fat diet are protected from obesity, fatty liver, and the development of insulin-resistance. In humans, higher plasma levels of pro-NT, which is the stable circulating precursor of NT, predict obesity, type 2 diabetes (T2D), and cardiovascular disease. In obesity, the presence of visceral adipose tissue (VAT) inflammation leads to unfavorable metabolic outcomes and is associated with the development of T2D and non-alcoholic fatty liver disease (NAFLD). In this study, we investigated the relationship between plasma pro-NT levels and the presence of VAT inflammation in biopsies from 40 morbidly obese subjects undergoing bariatric surgery. We demonstrated that higher proNT levels are significantly associated with greater macrophages infiltration, HIF-1α, WISP-1, and UNC5B expression in VAT (all p < 0.01) due to the diagnosis of T2D and NAFLD. The overall results show that, in obesity, pro-NT is a biomarker of VAT inflammation and insulin-resistance. Additionally, NT may be involved in the development of dysmetabolic conditions likely mediated by increased gut fat absorption and the presence of a proinflammatory milieu in the adipose tissue.

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.

The anti-apoptotic role of neurotensin

The neuropeptide, neurotensin, exerts numerous biological functions, including an efficient anti-apoptotic role, both in the central nervous system and in the periphery. This review summarizes studies that clearly evidenced the protective effect of neurotensin through its three known receptors. The pivotal involvement of the neurotensin receptor-3, also called sortilin, in the molecular mechanisms of the anti-apoptotic action of neurotensin has been analyzed in neuronal cell death, in cancer cell growth and in pancreatic beta cell protection. The relationships between the anti-apoptotic role of neurotensin and important physiological and pathological contexts are discussed in this review.

Neurotensin and its receptors in the control of glucose homeostasis

The pharmacological roles of the neuropeptide neurotensin through its three known receptors are various and complex. Neurotensin is involved in several important biological functions including analgesia and hypothermia in the central nervous system and also food intake and glucose homeostasis in the periphery. This review focuses on recent works dealing with molecular mechanisms regulating blood glucose level and insulin secretion upon neurotensin action. Investigations on crucial cellular components involved in the protective effect of the peptide on beta cells are also detailed. The role of xenin, a neurotensin-related peptide, on the regulation of insulin release by glucose-dependent insulinotropic polypeptide is summarized. The last section comments on the future research areas which should be developed to address the function of new effectors of the neurotensinergic system in the endocrine pancreas.

Mitochondrial DNA and anti-mitochondrial antibodies in serum of autistic children

Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by difficulties in communication, cognitive and learning deficits, as well as stereotypic behaviors. For the majority of cases there are no reliable biomarkers or distinct pathogenesis. However, increasing evidence indicates ASD may be associated with some immune dysregulation, and may have a neuroimmune component. We recently showed that the peptide neurotensin (NT) is increased in autistic children. We now show that NT induces release of extracellular mitochondrial DNA (mtDNA) that could act as "autoimmune" trigger. We further show that serum from young autistic patients contains mtDNA (n = 20; cytochrome B, p = 0.0002 and 7S, p = 0.006), and anti-mitochondrial antibody Type 2 (n = 14; p = 0.001) as compared to normally developing, unrelated controls (n = 12). Extracellular blood mtDNA and other components may characterize an autistic endophenotype and may contribute to its pathogenesis by activating autoimmune responses.

Insulin-like growth factor (IGF) induced proliferation of human lung fibroblasts is enhanced by neurotensin

Fibroblasts are key cells in tissue repair and important contributors to the inflammatory response. Insulin-like growth factors (IGFs) have been shown to participate in growth, in immune responses and in tissue repair where they stimulate cell growth. Neurotensin (NT) has been suggested to participate in inflammation and in tissue repair and is an autocrine or paracrine growth factor for several cancer cell types. Here we show that IGF-induced proliferation of fibroblasts is enhanced by NT in a concentration and type 1 NT-receptor dependent manner. This action of NT was blocked by inhibitors of phospholipase C and protein kinase C but not by inhibitors of phosphoinositide-3-kinase. An inhibitor of MEK 1/2 significantly reduced the proliferative effects of the IGFs but NT's ability to enhance IGF-induced proliferation was not effected. The ability of NT to enhance IGF-induced proliferation did not involve an autocrine factor. These results suggest that interactions between NT and the IGFs may contribute to the regulation of fibroblasts in for example, inflamed or injured tissues.

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.

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

Initial studies on the digestive hormone neurotensin (NT) showing that intestinal NT mRNA expression and blood levels were altered in rats fed chow containing bile acid (BA) and the BA chelator cholestyramine led us to investigate the role of NT in the enterohepatic circulation of BA. In fasted, anesthetized rats with common bile ducts cannulated for bile collection, intravenous NT infusion (10 pmol. kg(-1). min(-1)) enhanced BA output relative to control over 3 h in animals administered donor bile into the duodenum (30 microl/min). This suggested that the effect of NT was on the return of BA from the intestine to the liver, which is rate determining in the normal process. In rats prepared as described above and administered [(3)H]taurocholate ([(3)H]TC; 5 mM, 1 ml) duodenally, NT infusion (3-10 pmol x kg(-1) x min(-1)) increased the [(3)H]TC recovery rate in bile approximately twofold, whereas sulfated CCK-8 (12-50 pmol x kg(-1) x min(-1)) had no effect. To investigate the roles of endogenous NT and CCK, we administered [(3)H]TC into the rat duodenum or lower jejunum and tested the effect of the NT antagonist SR-48692 (2 nmol x kg(-1) x min(-1)) or CCK-A antagonist lorglumide (100 nmol x kg(-1) x min(-1)). SR-48692 reduced the [(3)H]TC recovery rate by congruent with 50% and congruent with 24% in the duodenum and jejunum, respectively, whereas lorglumide had no effect. These results suggest that NT or a similar peptide is an endogenous regulator of enterohepatic BA cycling, which acts by enhancing BA uptake in the intestine.