STC-1 Cells Research Articles

Aster pseudoglehni extract stimulates cholecystokinin and serotonin secretion in vitro and reduces gastric emptying in vivo

Aster pseudoglehni (Asteraceae) (AP) is a perennial plant from the Asteraceae family that is indigenous to Korea, and has traditionally been used as famine relief food in Korea. However, the effect of AP on food intake has not been characterized scientifically. The present study aimed to investigate the effect of the aqueous ethanolic extract of AP (AEE-AP) on food intake-related parameters in vitro and in vivo. AEE-AP stimulated cholecystokinin (CCK) secretion in enteroendocrine STC-1 cells, and serotonin (5-HT) secretion in RIN14B cells, an enteroendocrine cell model. Furthermore, AEE-AP affected physiological processes related to food intake in rats. Single oral administration of AEE-AP activated c-Fos in the dorsal vagal complex (DVC) and the arcuate nucleus of the hypothalamus (ARC), and delayed gastric emptying in rats. Our results demonstrated that AEE-AP regulated food intake-related parameters in the enteroendocrine system and gastrointestinal motility that affect food intake and eventually obesity.

Discovery of Orally Efficacious Tetrahydrobenzimidazoles as TGR5 Agonists for Type 2 Diabetes.

We have discovered a novel series of tetrahydrobenzimidazoles 3 as TGR5 agonists. Initial structure-activity relationship studies with an assay that measured cAMP levels in murine enteroendocrine cells (STC-1 cells) led to the discovery of potent agonists with submicromolar EC50 values for mTGR5. Subsequent optimization through methylation of the 7-position of the core tetrahydrobenzimidazole ring resulted in the identification of potent agonists for both mTGR5 and hTGR5 (human enteroendocrine NCI-H716 cells). While the lead compounds displayed low to moderate exposure after oral dosing, they significantly reduced blood glucose levels in C57 BL/6 mice at 30 mg/kg and induced a 13-22% reduction in the area under the blood glucose curve (AUC)0-120min in oral glucose tolerance tests (OGTT).

MTOR inhibitors activate PERK signaling and favor viability of gastrointestinal neuroendocrine cell lines.

mTOR and Unfolded Protein Response (UPR) are two signaling pathways frequently activated in cancer cells. The mTOR pathway has been shown to be up-regulated in most gastroenteropancreatic neuroendocrine tumors. In contrast, little is known about the UPR status in neoplastic neuroendocrine cells. However, these hormone-producing cells are likely to present distinctive adaptations of this pathway, as other secretory cells. We therefore analyzed the status of the three axes of UPR and their relation to mTOR pathway in two gastrointestinal neuroendocrine tumors (GI-NET) cell lines STC-1 and GluTag. At baseline, pharmacological inducers activate the three arms of UPR: PERK, ATF6 and IRE1. Although hypoxia stimulates the PERK, ATF6 and IRE-1 pathways in both cell lines, glucose depletion activates UPR only in STC-1 cell line. Strikingly, P-p70S6K1 increases concomitantly to P-PERK and BiP in response to thapsigargin treatment, glucose depletion or hypoxia. We found that different mTOR inhibitors activate the PERK signaling pathway. To confirm that mTOR inhibition modulates PERK activation, we inhibited PERK and showed that it decreased cell viability when associated to mTOR inhibition, indicating that mTOR drives a PERK-dependent survival pathway. In conclusion, in GI-NET cell lines, UPR signaling is functional and PERK arm is induced by mTOR inhibition. These observations open up new perspectives for therapeutic strategies: the crosstalk between mTOR and UPR might contribute to the resistance to mTOR inhibitors and could be targeted by mTOR and PERK inhibitors in combination therapy.

The GIP/GIPR axis is functionally linked to GH-secretion increase in a significant proportion of gsp− somatotropinomas

Glucose-dependent insulinotropic polypeptide receptor (GIPR) overexpression has been recently described in a proportion of gsp- somatotropinomas and suggested to be associated with the paradoxical increase of GH (GH-PI) during an oral glucose load. This study was aimed at linking the GIP/GIPR pathway to GH secretion in 25 somatotropinomas-derived primary cultures and correlating molecular with clinical features in acromegalic patients. Given the impairment of the GIP/GIPR axis in acromegaly, an additional aim was to assess the effect of GH/IGF-1 stimulation on GIP expression in the enteroendocrine cell line STC-1. Nearly 80% of GIPR-expressing somatotropinomas, all of them negative for gsp mutations, show increased GH secretion upon GIP stimulation, higher sensitivity to Forskolin but not to somatostatin analogs. Besides increased frequency of GH-PI, GIPR overexpression does not appear to affect acromegalic patients' clinical features. In STC-1 cells transfected with GIP promoter-driven luciferase vector, IGF-1 but not GH induced dose-dependent increase in luciferase activity. We demonstrate that GIPR mediates the GH-PI in a significant proportion of gsp- acromegalic patients. In these cases, the stimulatory effect of IGF-1 on GIP promoter support the hypothesis of a functional GH/IGF-1/GIP axis. Further studies based on larger cohorts and the development of a stable transgenic model with inducible GIPR overexpression targeted to pituitary somatotroph lineage will be mandatory to establish the real role of GIPR in the pathogenesis of somatotropinomas.

Aroma compound diacetyl suppresses glucagon-like peptide-1 production and secretion in STC-1 cells.

Diacetyl is a volatile flavour compound that has a characteristic buttery aroma and is widely used in the flavour industry. The aroma of a food plays an important role in food palatability and thus intake. This study investigates the effect of diacetyl on the satiety hormone, glucagon-like peptide (GLP-1), using the enteroendocrine cell line, STC-1. Diacetyl decreased proglucagon mRNA and total GLP-1 from glucose stimulated STC-1 cells. This dampening effect on GLP-1 appears to be mediated by increasing intracellular cAMP levels, increasing synthesis of the G protein coupled receptor, GPR120, and its recruitment to the cell surface. Voltage gated Ca2+ channels, K+ATP channels and the α-gustducin taste pathway do not appear to be involved. These findings demonstrate that components contributing to food palatability suppress GLP-1. This ability of diacetyl to reduce satiety signals may contribute to overconsumption of some palatable foods.

Acute selective bioactivity of grape seed proanthocyanidins on enteroendocrine secretions in the gastrointestinal tract

ABSTRACTBackground: Enteroendocrine cells respond to food components by secreting an array of hormones that regulate several functions. We have previously shown that grape seed proanthocyanidins (GSPE) modulate GLP-1 levels.Objective: To deepen on the knowledge of the mechanisms used by GSPE to increase GLP-1, and extend it to its role at modulation of other enterohormones.Design: We used an ex vivo system to test direct modulation of enterohormones; STC-1 cells to test pure phenolic compounds; and rats to test the effects at different gastrointestinal segments.Results: GSPE compounds act at several locations along the gastrointestinal tract modulating enterohormone secretion depending on the feeding condition. GSPE directly promotes GLP-1 secretion in the ileum, while unabsorbed/metabolized forms do so in the colon. Such stimulation requires the presence of glucose. GSPE enhanced GIP and reduced CCK secretion; gallic acid could be partly responsible for this effect.Conclusions: The activity of GSPE modulating enterohormone secretion may help to explain its effects on metabolism. GSPE acts through several mechanisms; its compounds and their metabolites are GLP-1 secretagogues in ileum and colon, respectively. In vivo GLP-1 secretion might also be mediated by indirect pathways involving modulation of other enterohormones that in turn regulate GLP-1 release.

Accumulation of intestinal tissue 3-deoxyglucosone attenuated GLP-1 secretion and its insulinotropic effect in rats.

BackgroundOur recent findings support the idea that 3-deoxyglucosone (3DG), a dietary composition, has been suggested as an independent factor for the development of prediabetes. Secretion of glucagon-like peptide-1 (GLP-1) has been suggested to be impaired in T2DM and in conditions associated with hyperglycemia. Since low oral bioavailability of 3DG has been indicated in a single administration study, in the present study we examined if 3DG is capable of accumulating in intestinal tissue of rats after 2-week administration of 3DG, and the 3DG treatment affects GLP-1 secretion and glucose tolerance.MethodsRats were administered by gastric gavage for 2 weeks. We measured 3DG contents of intestinal tissues (by HPLC), plasma levels of total GLP-1 (by ELISA), insulin and glucagon (both by radioimmunoassay) and blood glucose concentrations. The expressions of the sweet receptor subunits (TAS1R2, TAS1R3) and its downstream molecule TRPM5 in duodenum and colon tissues of rats were quantified by WB. We examined GLP-1 secretion in enteroendocrine STC-1 cells exposured to 3DG.Results3DG treatment for 2 weeks increased 3DG content of intestinal tissues, fasting blood glucose concentration, and reduced plasma concentrations of GLP-1 and insulin at fasting and 15 and 180 min after the glucose load and oral glucose tolerance in conjunction with increased plasma glucagon concentrations. The expressions of TAS1R2, TAS1R3 and TRPM5 were shown to be reduced whereas 3DG treatment did not affect plasma dipeptidyl peptidase-4 activity, indicating an impaired GLP-1 secretion in 3DG-treated rats. This idea was further supported by the fact that exposure to 3DG directly decrease GLP-1 secretion in STC-1.ConclusionIt is the first demonstration that 3DG was capable of accumulating in intestinal tissue and thereby decreased secretion of GLP-1 and insulin in a similar manner. 3DG-treated rats developed impaired glucose regulation (IGR) with obviously pancreatic islet cell dysfunction. It is further concluded that a decrease in the biological function of GLP-1 resulting from the decreased GLP-1 secretion is the most likely mechanism for the impaired insulin secretion, which ultimately promoted the development of IGR. These results will also contribute to a better understanding of the significance for restoring physiological GLP-1 secretion.Electronic supplementary materialThe online version of this article (doi:10.1186/s13098-016-0194-9) contains supplementary material, which is available to authorized users.

The endocrine disrupting potential of monosodium glutamate (MSG) on secretion of the glucagon-like peptide-1 (GLP-1) gut hormone and GLP-1 receptor interaction

Monosodium glutamate (MSG) is a suspected obesogen with epidemiological evidence positively correlating consumption to increased body mass index and higher prevalence of metabolic syndrome.ELISA and high content analysis (HCA) were employed to examine the disruptive effects of MSG on the secretion of enteroendocrine hormone glucagon-like peptide-1 (GLP-1) and GLP-1 receptor (GLP-1R), respectively. Following 3h MSG exposure of the enteroendocrine pGIP/neo: STC-1 cell line model (500μg/ml) significantly increased GLP-1 secretion (1.8 fold; P≤0.001), however, 72h exposure (500μg/ml) caused a 1.8 fold decline (P≤0.05). Also, 3h MSG exposure (0.5–500μg/ml) did not induce any cytotoxicity (including multiple pre-lethal markers) but 72h exposure at 250–500μg/ml, decreased cell number (11.8–26.7%; P≤0.05), increased nuclear area (23.9–29.8%; P≤0.001) and decreased mitochondrial membrane potential (13–21.6%; P≤0.05). At 500μg/ml, MSG increased mitochondrial mass by 16.3% (P≤0.01). MSG did not agonise or antagonise internalisation of the GLP-1R expressed recombinantly in U2OS cells, following GLP-1 stimulation.In conclusion, 72h exposure of an enteroendocrine cell line at dietary levels of MSG, results in pre-lethal cytotoxicity and decline in GLP-1 secretion. These adverse events may play a role in the pathogenesis of obesity as outlined in the obesogen hypothesis by impairing GLP-1 secretion, related satiety responses and glucose-stimulated insulin release.

Nicotine-Induced Effects on Nicotinic Acetylcholine Receptors (nAChRs), Ca2+ and Brain-Derived Neurotrophic Factor (BDNF) in STC-1 Cells.

In addition to the T2R bitter taste receptors, neuronal nicotinic acetylcholine receptors (nAChRs) have recently been shown to be involved in the bitter taste transduction of nicotine, acetylcholine and ethanol. However, at present it is not clear if nAChRs are expressed in enteroendocrine cells other than beta cells of the pancreas and enterochromaffin cells, and if they play a role in the synthesis and release of neurohumoral peptides. Accordingly, we investigated the expression and functional role of nAChRs in enteroendocrine STC-1 cells. Our studies using RT-PCR, qRT-PCR, immunohistochemical and Western blotting techniques demonstrate that STC-1 cells express several α and β nAChR subunits. Exposing STC-1 cells to nicotine acutely (24h) or chronically (4 days) induced a differential increase in the expression of nAChR subunit mRNA and protein in a dose- and time-dependent fashion. Mecamylamine, a non-selective antagonist of nAChRs, inhibited the nicotine-induced increase in mRNA expression of nAChRs. Exposing STC-1 cells to nicotine increased intracellular Ca2+ in a dose-dependent manner that was inhibited in the presence of mecamylamine or dihydro-β-erythroidine, a α4β2 nAChR antagonist. Brain-derived neurotrophic factor (BDNF) mRNA and protein were detected in STC-1 cells using RT-PCR, specific BDNF antibody, and enzyme-linked immunosorbent assay. Acute nicotine exposure (30 min) decreased the cellular content of BDNF in STC-1 cells. The nicotine-induced decrease in BDNF was inhibited in the presence of mecamylamine. We also detected α3 and β4 mRNA in intestinal mucosal cells and α3 protein expression in intestinal enteroendocrine cells. We conclude that STC-1 cells and intestinal enteroendocrine cells express nAChRs. In STC-1 cells nAChR expression is modulated by exposure to nicotine in a dose- and time-dependent manner. Nicotine interacts with nAChRs and inhibits BDNF expression in STC-1 cells.

Acute Reduction of Incretin Effect and Glucose Intolerance in Rats by Single Intragastric Administration of 3-deoxyglucosone.

Secretion of glucagon-like peptide-1 has been suggested to be impaired in T2DM and in conditions associated with hyperglycemia. 3-Deoxyglucosone, a dietary composition, has been suggested as an independent factor for the development of prediabetes. A-pathophysiological very high condition of 3DG concentrations administered i. v. induced acute glucose intolerance in rats. In this study, to examine the acute effects of single intragastric administration of 3DG at dose of potentially single-meal intake on plasma glucose, insulin, glucagon, total GLP-1 and total GIP levels in response to a glucose load, OGTT was performed immediately in normal Kunming mice or Sprague-Dawleys rats after 3DG administration. GLP-1 secretion, intracellular cAMP levels and 2-NBDG uptake were examined in STC-1 cells exposured to 3DG. In rats, 20 mg/kg 3DG i.g. (3DG-20 i.g.) impaired glucose tolerance (P<0.05) with increased AUC (1 070±105.2 vs. 918.0±91.20, P<0.05). The mice treated with 3DG-20 i.g. exhibited a similar effect, independent of the effect of plasma 3DG concentration. 3DG-20 i.g. treatment reduced plasma insulin concentrations with decreased AUC (3 552±300.2 vs. 4 715±420.5, P<0.05) in rats whereas plasma glucagon levels were not significantly different. These changes occurred in conjunction with decreased plasma GLP-1 and GIP levels (P<0.05). Furthermore, non-cytotoxic 3DG concentrations directly reduced GLP-1 secretion in STC-1, at least in part, by decreasing intracellular cAMP level and glucose uptake. We demonstrated for the first time that single intragastric administration of 3DG resulted in acute reduction of incretin effect and glucose intolerance, which was associated with a decrease in the biological function of GLP-1 by decreasing GLP-1 secretion.

Simulated GI digestion of dietary protein: Release of new bioactive peptides involved in gut hormone secretion

Dietary proteins have been reported to induce a strong feeling of satiety that has been partially explained by gut hormone level increase. Up to date, various protein hydrolysates have demonstrated in vitro and in vivo their potential to stimulate gut hormone secretion related to food intake decrease and their mechanisms of action have just started to be resolved. In this context, this study aimed at identifying new peptide sequences involved in gut hormone secretion released by protein in vitro gastrointestinal digestion. Targeted gut hormones were Cholecystokinin (CCK) and Glucagon-Like Peptide 1 (GLP-1). The activity of DPP-IV was also considered as it strongly modulates GLP-1 action. In a previous study, simulated digestion of dietary protein has generated hydrolysates with enhancing effect on CCK and GLP-1 secretion in STC-1 cells as well as DPP-IV inhibitory properties. Successive purification steps were performed to isolate peptide fractions involved in these bioactivities whose sequence was determined by LC-MS-MS. Three peptide sequences ANVST, TKAVEH and KAAVT were pointed out for their stimulating effects on GLP-1 secretion. The sequence VAAA was isolated for its DPP-IV inhibitory properties. Two peptide groups were strongly involved in CCK release sharing a certain occurrence of aromatic amino acid residues.

AMPK-dependent regulation of GLP1 expression in L-like cells.

This study examined whether AMPK, an evolutionarily conserved sensor of cellular energy status, determines the production of glucagon-like peptide-1 (GLP1). A negative relation existed between phosphorylation of AMPKα and the expression and secretion of GLP1 during changes in energy status in STC-1 cells, an L-like cell line. High concentration of glucose (25 mmol/L) decreased AMPKα phosphorylation, whereas it stimulated the expression and secretion of GLP1 relative to 5.6 mmol/L glucose. Serum starvation upregulated AMPKα phosphorylation, whereas it reduced GLP1 production significantly. Stimulation of AMPK phosphorylation by AICAR and overexpression of wild-type AMPKα1, constitutively active AMPKα1 plasmids, or AMPKα1 lentivirus particles suppressed proglucagon mRNA and protein contents in STC-1 cells. Inactivation of AMPK by Compound C, AMPKα1 siRNA or kinase-inactive AMPKα1 mutant increased the expression and secretion of GLP1. Our results suggest that AMPKα1 may link energy supply with the production of GLP1 in L-like cells.

Flavonoids stimulate cholecystokinin peptide secretion from the enteroendocrine STC-1 cells

Animal experiments showed that flavonoids might have the potential for an anti-obesity effect by reducing weight and food intake. However, the exact mechanisms that could be involved in these proposed effects are still under investigation. The complex process of food intake is partially regulated by gastrointestinal hormones. Cholecystokinin (CCK) is the best known gastrointestinal hormone to induce satiety signal that plays a key role in food intake regulation. It is released from the endocrine cells (I cell) in response to the ingestion of nutrients into the small intestine. In this study, we investigated the possible effects of flavonoids (quercetin, kaempferol, apigenin, rutin and baicalein) on stimulation of CCK release in vitro using enteroendocrine STC-1 cells. In comparison with the control, quercetin, kaempferol and apigenin resulted in a significant increase in CCK secretion with quercetin showing the highest activity. On the other hand, no significant effect was seen by rutin and baicalein.To our knowledge, this is the first report to study the stimulation of CCK peptide hormone secretion from STC-1 cells by quercetin and kaempferol, rutin, apigenin and baicalein. Based on the cell-based results in this work, it can be suggested that the reported activity of flavonoids against food intake and weight could be mediated by stimulation of CCK signal which in turn is responsible for food intake reduction, but future animal and human studies are needed to confirm this conclusion at organism level.

Antarctic Krill (Euphausia superba) Protein Hydrolysates Stimulate Cholecystokinin Release in STC-1 Cells and its Signaling Mechanism

Antarctic krill (Euphausia superba) protein hydrolysates were produced by simulated gastrointestinal digestion (KPHSD) and alkaline proteinase hydrolysis (KPHAP), respectively. The effects of the hydrolysates on cholecystokinin (CCK) secretion and cAMP response element-binding protein (CREB) activation were tested in murine enteroendocrine cell line STC-1. Meanwhile, the signaling mechanism by which the hydrolysates induce CCK secretion was investigated by using inhibitors of signaling proteins. Results indicated that KPHSD and KPHAP both could significantly stimulate CCK secretion and CREB activation. The stimulating effects on CCK release showed a positive correlation with the relative content of peptides with molecular weight ranging from 1,000 to 3,000 Da, indicating this component may mainly account for the ability. The inhibitors on calcium-sensing receptor, PKA, Ca2+/CaMKII, P38-MAPK, and an intracellular calcium chelator all inhibited krill protein hydrolysates-induced CCK secretion and CREB activation, indicating the involvement of the Ca2+/CaM/CaMK, cAMP/PKA and MAPK pathways in the stimulation of CCK secretion. Practical Applications Although Antarctic krill (Euphausia superba) has a large biomass and high-quality protein, its consumption by mankind, especially for its protein, is limited. In recent years, krill protein hydrolysates (KPHs) have attracted increasing attention due to their various health benefits. KPH is usually produced by using a proteolysis and centrifugation process, and the protein from muscle and internal tissue is reserved, but the cuticle is removed. The process can produce low-fluoride krill proteins (peptides) because the fluoride in krill is mainly located in the cuticle. The present study showed that KPHs produced by simulated gastrointestinal digestion and by alkaline proteinase hydrolysis were able to highly stimulate CCK secretion in intestinal endocrine STC-1 cells, indicating KPHs have potential application prospect as functional food ingredients for food intake-inhibitory effects.

Leptin suppresses sweet taste responses of enteroendocrine STC-1 cells

Leptin is an important hormone that regulates food intake and energy homeostasis by acting on central and peripheral targets. In the gustatory system, leptin is known to selectively suppress sweet responses by inhibiting the activation of sweet sensitive taste cells. Sweet taste receptor (T1R2+T1R3) is also expressed in gut enteroendocrine cells and contributes to nutrient sensing, hormone release and glucose absorption. Because of the similarities in expression patterns between enteroendocrine and taste receptor cells, we hypothesized that they may also share similar mechanisms used to modify/regulate the sweet responsiveness of these cells by leptin. Here, we used mouse enteroendocrine cell line STC-1 and examined potential effect of leptin on Ca2+ responses of STC-1 cells to various taste compounds. Ca2+ responses to sweet compounds in STC-1 cells were suppressed by a rodent T1R3 inhibitor gurmarin, suggesting the involvement of T1R3-dependent receptors in detection of sweet compounds. Responses to sweet substances were suppressed by ⩾1ng/ml leptin without affecting responses to bitter, umami and salty compounds. This effect was inhibited by a leptin antagonist (mutant L39A/D40A/F41A) and by ATP gated K+ (KATP) channel closer glibenclamide, suggesting that leptin affects sweet taste responses of enteroendocrine cells via activation of leptin receptor and KATP channel expressed in these cells. Moreover, leptin selectively inhibited sweet-induced but not bitter-induced glucagon-like peptide-1 (GLP-1) secretion from STC-1 cells. These results suggest that leptin modulates sweet taste responses of enteroendocrine cells to regulate nutrient sensing, hormone release and glucose absorption in the gut.

Sweetness-induced activation of membrane dipole potential in STC-1 taste cells

The biological functions of cell membranes strongly influence the binding and transport of molecular species. We developed STC-1 cell line stably expressing the sweet taste receptor (T1R2/T1R3), and explored the possible correlation between sweeteners and membrane dipole potential of STC-1 cells. In this study, sweetener-induced dipole potential activation was elucidated using a fluorescence-based measurement technique, by monitoring the voltage sensitive probe Di-8-ANEPPS using a dual wavelength ratiometric approach. It indicated that the presence of sweeteners resulted in cell membrane dipole potential change, and interaction of artificial sweeteners with taste cells resulted in a greater reduction in potential compared with natural sweeteners. Our work presents a newly developed approach using a fluorescence-based measurement technique to study sweetener-induced dipole potential activation of STC-1 cells. This new approach could be used as a complementary tool to study the function of sweet taste receptors or other GPCRs and helps to understand the basis sweetness mechanism.

Effects of abalone (Haliotis discus hannai Ino) gonad polysaccharides on cholecystokinin release in STC-1 cells and its signaling mechanism

Abalone gonad polysaccharide (AGP) −31, −32 and −33 prepared in this study had the molecular weight (MW) of 37.8, 32.2 and 27.5kDa, respectively. They all contained mannose, rhamnose, glucuronic acid, glucose, galactose, xylose, arabinose, and fucose, with very similar monosaccharide profile. All the three polysaccharides could significantly increase the secretion of cholecystokinin (CCK) in STC-1 cells. Among them, AGP-32 showed the strongest effect. However, the low-MW fragments of AGP-32 showed significantly lower activity than AGP-32 itself. It was also found that the inhibitors on calcium-sensing receptor (CaSR), protein kinase A (PKA), Ca2+⁄calmodulin-dependent protein kinase (CaMK) II, p38- mitogen-activated protein kinases (MAPK), and an intracellular calcium chelator all inhibited AGP-induced CCK secretion. To conclude, Ca2+/calmodulin (CaM)/CaMK, cyclic adenosine monophosphate (cAMP)/PKA and MAPK pathways are all involved in AGP-induced CCK secretion.

Novel probiotic evidence of lactobacilli on immunomodulation and regulation of satiety hormones release in intestinal cells

Lactobacilli strains with probiotic traits were tested for their ability to survive to the digestion process modelled during this study. These strains managed to sustain the harsh conditions of the gastric and duodenal phases and showed good adhesion capacities to human Caco-2 cell line. These probiotic microorganisms have survived during these steps, exposed to low pH, high concentration of bile salts and enzymes occurring in the digestion and virtually reached the duodenal compartment in sufficient amount with limited population loss. These lactobacilli strains appeared to be non-cytotoxic after contact with Caco-2 cells for 24 h. Importantly, some of these strains showed immunomodulatory effect, lowering the pro-inflammatory cytokine IL-8 and promoting secretion of the anti-inflammatory IL-10. Besides, Lactobacillus gasseri CMUL34 and Lactobacillus acidophilus CMUL67 strains were able to modulate secretion and expression of two intestinal hormones: the Glucagon-Like Peptide 1 (GLP-1) and the cholecystokinin (CCK) in STC-1 cells.

Zinc directly stimulates cholecystokinin secretion from enteroendocrine cells and reduces gastric emptying in rats

Zinc, an essential mineral element, regulates various physiological functions such as immune responses and hormone secretion. Cholecystokinin (CCK), a gut hormone, has a role in protective immunity through the regulation of gastrointestinal motility, appetite, and inflammatory response. Here, we examined the effect of zinc on CCK secretion in STC-1 cells, an enteroendocrine cell line derived from murine duodenum, and in rats. Extracellular zinc triggered CCK secretion accompanied with increased intracellular Ca2+ and Zn2+ mobilization in STC-1 cells. Zinc-induced CCK secretion was abolished in the absence of intracellular Zn2+ or extracellular calcium. Upon inhibition of transient receptor potential ankyrin 1 (TRPA1), extracellular zinc failed to increase intracellular Ca2+ and subsequent CCK secretion. In rats, oral zinc administration decreased gastric emptying through the activation of CCK signaling. These results suggest that zinc is a novel stimulant for CCK secretion through the activation of TRPA1 related to intracellular Zn2+ and Ca2+ mobilization.

Nutrient-induced glucagon like peptide-1 release is modulated by serotonin

Glucagon like peptide-1 (GLP-1) and serotonin are both involved in food intake regulation. GLP-1 release is stimulated upon nutrient interaction with G-protein coupled receptors by enteroendocrine cells (EEC), whereas serotonin is released from enterochromaffin cells (ECC). The central hypothesis for the current study was that nutrient-induced GLP-1 release from EECs is modulated by serotonin through a process involving serotonin receptor interaction.This was studied by assessing the effects of serotonin reuptake inhibition by fluoxetine on nutrient-induced GLP-1, PYY and CCK release from isolated pig intestinal segments. Next, serotonin-induced GLP-1 release was studied in enteroendocrine STC-1 cells, where effects of serotonin receptor inhibition were studied using specific and non-specific antagonists.Casein (1% w/v), safflower oil (3.35% w/v), sucrose (50mM) and rebaudioside A (12.5mM) stimulated GLP-1 release from intestinal segments, whereas casein only stimulated PYY and CCK release. Combining nutrients with fluoxetine further increased nutrient-induced GLP-1, PYY and CCK release.Serotonin release from intestinal tissue segments was stimulated by casein and safflower oil while sucrose and rebaudioside A had no effect. The combination with fluoxetine (0.155μM) further enhanced casein and safflower oil induced-serotonin release.Exposure of ileal tissue segments to serotonin (30μM) stimulated GLP-1 release whereas it did not induce PYY and CCK release. Serotonin (30 and 100μM) also stimulated GLP-1 release from STC-1 cells, which was inhibited by the non-specific 5HT receptor antagonist asenapine (1 and 10μM).These data suggest that nutrient-induced GLP-1 release is modulated by serotonin through a receptor mediated process.