A histochemical and immunohistochemical study on the gastrointestinal tract of sparrowhawk (Accipiter nisus) / Estudio histoquímico e inmunohistoquímico del tracto gastrointestinal del gavilán (Accipiter nisus)

SUMMARY: In the present study, we aimed to determine the localization and distribution of entero-endocrine cells in the gastrointestinal tract by immunohistochemical methods and understand the structure of the glycoproteins elaborated by the epithelium the digestive tract regions by histochemical methods. The nine sparrowhawks were euthanized, and gastrointestinal tract tissues were removed and fixed in formalin. The gastrointestinal tract sections were stained with immunohistochemical and histochemical techniques to evaluate the enteroendocrine cells and histomorphometric analysis. The results showed that the numbers of somatostatin in the ventriculus, gastrin in the proventriculus, serotonin in the duodenum and jejunum immunopositivity are higher, remaining segments of the gastrointestinal tract are detected slight positivity in the glucagon, gastrin, serotonin, and somatostatin. In conclusion, some endocrine cells localization and distribution and histomorphometry, and goblet cell counts were revealed in the gastrointestinal tract of the sparrowhawks.

RESUMEN: El objetivo del presente estudio fue determinar la localización y distribución de células enteroendocrinas en el tracto gastrointestinal de gavilán, a través de métodos inmunohistoquímicos y comprender la estructura de las glicoproteínas elaboradas por el epitelio de las regiones del tracto digestivo. Se sacrificaron nueve gavilanes y los tejidos del tracto gastrointestinal se extrajeron y se fijaron en formalina. Las secciones del tracto gastrointestinal se tiñeron con técnicas inmunohistoquímicas e histoquímicas para evaluar las células enteroendocrinas y se realizó análisis histo-morfométrico. Los re- sultados indicaron que los números de inmunopositividad de somatostatina en el ventrículo, gastrina en el proventrículo, serotonina en el duodeno y yeyuno son más altos, en los segmentos restantes del tracto gastrointestinal, se detecta además una ligera positividad de glucagón, gastrina, serotonina y somatostatina. En conclusión en el tracto gastrointestinal de gavilán se observó cierta localización y distribución de células endocrinas e histomorfometría, y recuentos de células caliciformes.

In Vivo Models for Incretin Research: From the Intestine to the Whole Body

Incretin hormones are produced by enteroendocrine cells (EECs) in the intestine in response to ingested nutrient stimuli. The incretin effect is defined as the difference in the insulin secretory response between the oral glucose tolerance test and an isoglycemic intravenous glucose infusion study. The pathophysiology of the decreased incretin effect has been studied as decreased incretin sensitivity and/or β-cell dysfunction per se. Interestingly, robust increases in endogenous incretin secretion have been observed in many types of metabolic/bariatric surgery. Therefore, metabolic/bariatric surgery has been extensively studied for incretin physiology, not only the hormones themselves but also alterations in EECs distribution and genetic expression levels of gut hormones. These efforts have given us an enormous understanding of incretin biology from synthesis to in vivo behavior. Further innovative studies are needed to determine the mechanisms and targets of incretin hormones.

Naringenin stimulates cholecystokinin secretion in STC-1 cells

BACKGROUND/OBJECTIVES: Cholecystokinin (CCK), a hormone or neuropeptide, is secreted in response to intraluminal nutrients by enteroendocrine I-cells of the intestine and has important physiological actions related to appetite regulation and satiety. The stimulation on CCK secretion from the intestine is of potential relevance for body weight management. Naringenin (4',5,7-trihydroxyflavanone) and its glycoside naringin (naringenin 7-rhamnoglucoside) have been reported to have many biological functions. In the current study, we investigated the question of whether naringenin and naringin could stimulate CCK secretion and then examined the mechanisms involved in CCK release. MATERIALS/METHODS: STC-1 cells were used as a model of enteroendocrine cells. CCK release and changes in intracellular Ca2+ ([Ca2+]i) were measured after incubation of cells with naringenin and naringin for 1 h. RESULTS: Naringenin caused significant (P < 0.05) stimulation of CCK secretion, but naringin did not. In addition, regarding the secretory mechanisms, naringenin-induced CCK secretion involved increases in [Ca2+]i, influx of extracellular Ca2+, at least in part, and activation of TRP channels, including TRPA1. CONCLUSION: Findings of this study suggest that naringenin could have a role in appetite regulation and satiety.

Hesperetin Stimulates Cholecystokinin Secretion in Enteroendocrine STC-1 Cells

Hesperetin (3',5,7-trihydroxy 4'-methoxyflavanone) and its glycoside hesperidin (hesperetin 7-rhamnoglucoside) in oranges have been reported to possess pharmacological effects related to anti-obesity. However, hesperetin and hesperidin have not been studied on suppressive effects on appetite. This study examined that hesperetin and hesperidin can stimulate the release of cholecystokinin (CCK), one of appetite-regulating hormones, from the enteroendocrine STC-1 cells, and then examined the mechanisms involved in the CCK release. Hesperetin significantly and dose-dependently stimulated CCK secretion with an EC50 of 0.050 mM and increased the intracellular Ca2+ concentrations ([Ca2+]i) compared to the untreated control. The stimulatory effect by hesperetin was mediated via the entry of extracellular Ca2+ and the activation of TRP channels including TRPA1. These results suggest that hesperetin can be a candidate biomolecule for the suppression of appetite and eventually for the therapeutics of obesity.

Insulin is secreted upon glucose stimulation by both gastrointestinal enteroendocrine K-cells and L-cells engineered with the preproinsulin gene

Transgenic mice carrying the human insulin gene driven by the K-cell glucose-dependent insulinotropic peptide (GIP) promoter secrete insulin and display normal glucose tolerance tests after their pancreatic p-cells have been destroyed. Establishing the existence of other types of cells that can process and secrete transgenic insulin would help the development of new gene therapy strategies to treat patients with diabetes mellitus. It is noted that in addition to GIP secreting K-cells, the glucagon-like peptide 1 (GLP-1) generating L-cells share/ many similarities to pancreatic p-cells, including the peptidases required for proinsulin processing, hormone storage and a glucose-stimulated hormone secretion mechanism. In the present study, we demonstrate that not only K-cells, but also L-cells engineered with the human preproinsulin gene are able to synthesize, store and, upon glucose stimulation, release mature insulin. When the mouse enteroendocrine STC-1 cell line was transfected with the human preproinsulin gene, driven either by the K-cell specific GIP promoter or by the constitutive cytomegalovirus (CMV) promoter, human insulin co-localizes in vesicles that contain GIP (GIP or CMV promoter) or GLP-1 (CMV promoter). Exposure to glucose of engineered STC-1 cells led to a marked insulin secretion, which was 7-fold greater when the insulin gene was driven by the CMV promoter (expressed both in K-cells and L-cells) than when it was driven by the GIP promoter (expressed only in K-cells). Thus, besides pancreatic p-cells, both gastrointestinal enteroendocrine K-cells and L-cells can be selected as the target cell in a gene therapy strategy to treat patients with type 1 diabetes mellitus.

Stimulation of Glucagon Like Peptide-1 Secretion in Enteroendocrine L cells / 당뇨병

GLP-1 (glucagon like peptide-1) is new anti-diabetic drug with a number of beneficial effects. It stimulates glucose dependant insulin secretion and restoration of beta cell mass through enhancement of islet mass. However, it is easily inactivated after being secreted from enteroendocrine L cells. Recent trial to increased GLP-1 is to directly stimulate L cells through its receptor located in the surface of L cell. Taste receptor in the apical surface of L cell is activated by various tastants contained in the food. Tongue perceives taste sense through the heterotrimeric G-protein (alpha-gustducin) and its downstream signaling cascades. Same taste receptors are also expressed in enteroendocrine cells. In duodenal L cell, alpha-gustducin was detected by immunofluorescence stainig at the luminal projections of enteroendocrine cells. And several other taste signaling elements were also found in L cells. Ingestion of sweet or bitter compounds revealed stimulation of GLP-1 secretion and the regulation of plasma insulin and glucose. In this review, I will briefly introduce the possibilities to stimulate GLP-1 secretion though the membrane receptor in enteroendocrine cell. And it will be the good candidate to develop the treatment modality for obesity, diabetes and abnormal gut motility.

Transdifferentiation of Enteroendocrine K-cells into Insulin-expressing Cells / 당뇨병

BACKGROUND: Despite a recent breakthough in human islet transplantation for treating type 1 diabetes mellitus, the limited availability of donor pancreases remains a major obstacle. Endocrine cells within the gut epithelium (enteroendocrine cells) and pancreatic beta cells share similar pathways of differentiation during embryonic development. In particular, K-cells that secrete glucose-dependent insulinotropic polypeptide (GIP) have been shown to express many of the key proteins found in beta cells. Therefore, we hypothesize that K-cells can be transdifferentiated into beta cells because both cells have remarkable similarities in their embryonic development and cellular phenotypes. METHODS: K-cells were purified from heterogeneous STC-1 cells originating from an endocrine tumor of a mouse intestine. In addition, a K-cell subclone expressing stable Nkx6.1, called "Kn4-cells," was successfully obtained. In vitro differentiation of K-cells or Kn4-cells into beta cells was completed after exendin-4 treatment and serum deprivation. The expressions of insulin mRNA and protein were examined by RT-PCR and immunocytochemistry. The interacellular insulin content was also measured. RESULTS: K-cells were found to express glucokinase and GIP as assessed by RT-PCR and Western blot analysis. RT-PCR showed that K-cells also expressed Pdx-1, NeuroD1/Beta2, and MafA, but not Nkx6.1. After exendin-4 treatment and serum deprivation, insulin mRNA and insulin or C-peptide were clearly detected in Kn4-cells. The intracellular insulin content was also increased significantly in these cells. CONCLUSION: K-cells are an attractive potential source of insulin-producing cells for treatment of type 1 diabetes mellitus. However, more experiments are necessary to optimize a strategy for converting K-cells into beta cells.