Conditional deletion of menin results in antral G cell hyperplasia and hypergastrinemia.

Antral gastrin is the hormone known to stimulate acid secretion and proliferation of the gastric corpus epithelium. Patients with mutations in the multiple endocrine neoplasia type 1 (MEN1) locus, which encodes the protein menin, develop pituitary hyperplasia, insulinomas, and gastrinomas in the duodenum. We previously hypothesized that loss of menin leads to derepression of the gastrin gene and hypergastrinemia. Indeed, we show that menin represses JunD induction of gastrin in vitro. Therefore, we examined whether conditional deletion of Men1 (Villin-Cre and Lgr5-EGFP-IRES-CreERT2), with subsequent loss of menin from the gastrointestinal epithelium, increases gastrin expression. We found that epithelium-specific deletion of Men1 using Villin-Cre increased plasma gastrin, antral G cell numbers, and gastrin expression in the antrum, but not the duodenum. Moreover, the mice were hypochlorhydric by 12 mo of age, and gastric somatostatin mRNA levels were reduced. However, duodenal mRNA levels of the cyclin-dependent kinase inhibitor p27(Kip1) were decreased, and cell proliferation determined by Ki67 staining was increased. About 11% of the menin-deficient mice developed antral tumors that were negative for gastrin; however, gastrinomas were not observed, even at 12 mo of age. No gastrinomas were observed with conditional deletion of Men1 in the Lgr5 stem cells 5 mo after Cre induction. In summary, epithelium-specific deletion of the Men1 locus resulted in hypergastrinemia due to antral G cell hyperplasia and a hyperproliferative epithelium, but no gastrinomas. This result suggests that additional mutations in gene targets other than the Men1 locus are required to produce gastrin-secreting tumors.

Role of spinal neurotransmitter receptors in itch: new insights into therapies and drug development.

Targets for antipruritic therapies are now expanding from the skin to the central nervous system. Recent studies demonstrate that various neuronal receptors in the spinal cord are involved in pruritus. The spinal opioid receptor is one of the best-known examples. Spinal administration of morphine is frequently accompanied by segmental pruritus. In addition to µ-opioid receptor antagonists, κ-opioid receptor agonists have recently come into usage as novel antipruritic drugs, and are expected to suppress certain subtypes of itch such as hemodialysis- and cholestasis-associated itch that are difficult to treat with antihistamines. The gastrin-releasing peptide receptor in the superficial dorsal horn of the spinal cord has also received recent attention as a novel pathway of itch-selective neural transmission. The NMDA glutamate receptor appears to be another potential target for the treatment of itch, especially in terms of central sensitization. The development of NMDA receptor antagonists with less undesirable side effects on the central nervous system might be beneficial for antipruritic therapies. Drugs suppressing presynaptic glutamate-release such as gabapentin and pregabalin also reportedly inhibit certain subtypes of itch such as brachioradial pruritus. Spinal receptors of other neuromediators such as bradykinin, substance P, serotonin, and histamine may also be potential targets for antipruritic therapies, given that most of these molecules interfere not only with pain, but also with itch transmission or regulation. Thus, the identification of itch-specific receptors and understanding itch-related circuits in the spinal cord may be innovative strategies for the development of novel antipruritic drugs.

Calcium-sensing receptor is a physiologic multimodal chemosensor regulating gastric G-cell growth and gastrin secretion.

The calcium-sensing receptor (CaR) is the major sensor and regulator of extracellular Ca(2+), whose activity is allosterically regulated by amino acids and pH. Recently, CaR has been identified in the stomach and intestinal tract, where it has been proposed to function in a non-Ca(2+) homeostatic capacity. Luminal nutrients, such as Ca(2+) and amino acids, have been recognized for decades as potent stimulants for gastrin and acid secretion, although the molecular basis for their recognition remains unknown. The expression of CaR on gastrin-secreting G cells in the stomach and their shared activation by Ca(2+), amino acids, and elevated pH suggest that CaR may function as the elusive physiologic sensor regulating gastrin and acid secretion. The genetic and pharmacologic studies presented here comparing CaR-null mice and wild-type littermates support this hypothesis. Gavage of Ca(2+), peptone, phenylalanine, Hepes buffer (pH 7.4), and CaR-specific calcimimetic, cinacalcet, stimulated gastrin and acid secretion, whereas the calcilytic, NPS 2143, inhibited secretion only in the wild-type mouse. Consistent with known growth and developmental functions of CaR, G-cell number was progressively reduced between 30 and 90 d of age by more than 65% in CaR-null mice. These studies of nutrient-regulated G-cell gastrin secretion and growth provide definitive evidence that CaR functions as a physiologically relevant multimodal sensor. Medicinals targeting diseases of Ca(2+) homeostasis should be reviewed for effects outside traditional Ca(2+)-regulating tissues in view of the broader distribution and function of CaR.

Targeting of histamine producing cells by EGCG: a green dart against inflammation?

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The human body is made of some 250 different cell types. From them, only a small subset of cell types is able to produce histamine. They include some neurons, enterochromaffin-like cells, gastrin-containing cells, mast cells, basophils, and monocytes/macrophages, among others. In spite of the reduced number of these histamine-producing cell types, they are involved in very different physiological processes. Their deregulation is related with many highly prevalent, as well as emergent and rare diseases, mainly those described as inflammation-dependent pathologies, including mastocytosis, basophilic leukemia, gastric ulcer, Crohn disease, and other inflammatory bowel diseases. Furthermore, oncogenic transformation switches some non-histamine-producing cells to a histamine producing phenotype. This is the case of melanoma, small cell lung carcinoma, and several types of neuroendocrine tumors. The bioactive compound epigallocatechin-3-gallate (EGCG), a major component of green tea, has been shown to target histamine-producing cells producing great alterations in their behavior, with relevant effects on their proliferative potential, as well as their adhesion, migration, and invasion potentials. In fact, EGCG has been shown to have potent anti-inflammatory, anti-tumoral, and anti-angiogenic effects and to be a potent inhibitor of the histamine-producing enzyme, histidine decarboxylase. Herein, we review the many specific effects of EGCG on concrete molecular targets of histamine-producing cells and discuss the relevance of these data to support the potential therapeutic interest of this compound to treat inflammation-dependent diseases (AU)

Gastrin: an acid-releasing, proliferative and immunomodulatory peptide?

Gastrin release is affected by gastric inflammatory conditions. Antral G cells respond to inflammatory mediators by increasing gastrin secretion. Accumulating experimental evidence suggests that gastrin exerts immunomodulatory and proinflammatory effects. Gastrin could be a contributing factor to these pathologies, which may constitute a new justification for pharmacological blockade of gastrin action.

Gastrointestinal peptides and regulation of gastric acid secretion.

PURPOSE OF REVIEW: Update on the role of gastrointestinal peptides in regulating gastric acid secretion. RECENT FINDINGS: A novel transgenic mouse that expresses the entire human gastrin gene locus in G-cells of gastrin-null mice will facilitate investigation of gastrin gene regulatory elements. Isolation of a highly homogeneous population of G-cells permits the elucidation of stimulatory and inhibitory ligands without the confounding presence of other neuroendocrine cells. The use of somatostatin receptor knockout mice demonstrated the plasticity of gastric acid regulatory mechanisms and compensation by upregulation of the galanin pathway which inhibits secretion by enterochromaffin-like cells. The importance of adenosine in regulating somatostatin release was shown using adenosine receptor knockout mice. SUMMARY: The importance of gastrointestinal peptides for regulating gastric acid is evident. Ongoing investigations will characterize the mechanisms underlying actions of these agents on gastric acid secretion, particularly with regard to their combinatorial effects and interplay with other acid-regulating pathways.

Low gastric acid and high plasma gastrin in high-anxiety Wistar Kyoto rats.

OBJECTIVE: Wistar Kyoto (WKY) rats are more susceptible to stress-evoked ulcerations than Sprague-Dawley (SPD) rats. We have already demonstrated that gastrin cells are more active and ghrelin cells less active in WKY rats than in SPD rats. The purpose of this study was to compare endocrine cell activity and gastric acid output in WKY and SPD rats. MATERIAL AND METHODS: Gastric acid output was determined in conscious rats with gastric fistula. Plasma gastrin and ghrelin levels were measured after an overnight fast. Acid secretagogues (gastrin, histamine and carbachol) were given by continuous subcutaneous infusion. RESULTS: The volume of gastric juice, and the acidity and acid output were all significantly lower (p <0.05) in fasted WKY rats than in fasted SPD rats. Gastrin evoked a 4-fold (p <0.01) and 3-fold (p <0.05) increase in gastric acid output in SPD rats and WKY rats, respectively. Histamine raised the acid output 1.6-fold in SPD rats (p=0.06) and 3-fold in WKY rats (p <0.05), while carbachol failed to affect the acid output (weak increase, p >0.05). Fasting plasma ghrelin levels were 2-fold higher in SPD rats than in WKY rats (p <0.01) while fasting gastrin levels were 10-fold higher in WKY rats than in SPD rats (p <0.05). Neither the parietal-cell density nor the oxyntic mucosal thickness differed between the two strains. CONCLUSIONS: The results of the present study suggest that a high gastrin cell activity in WKY rats is secondary to a low gastric acidity. Whether the high gastrin cell activity is linked to susceptibility to stress ulcer in WKY rats warrants further investigation.

Release of transgenic human insulin from gastric g cells: a novel approach for the amelioration of diabetes.

We explored the hypothesis that meal-regulated release of insulin from gastric G cells can be used for gene therapy for diabetes. We generated transgenic mice in which the coding sequence of human insulin has been knocked into the mouse gastrin gene. Insulin was localized specifically to antral G cells of G-InsKi mice by double immunofluorescence staining using antibodies against insulin and gastrin. Insulin extracted from antral stomach of G-InsKi mice decreased blood glucose upon injection into streptozotocin-diabetic mice. Intragastric administration of peptone, a known potent luminal stimulant of gastrin secretion, induced an increase in circulating levels of transgenic human insulin from 10.7 +/- 2 to 23.3 +/- 4 pm in G-InsKi mice. Although G cell-produced insulin decreased blood glucose in G-InsKi mice, it did not cause toxic hypoglycemia. Proton pump inhibitors, pharmacological agents that increase gastrin output, caused a further increase in the circulating levels of gastric insulin (41.5 +/- 2 pm). G cell-produced insulin was released into circulation in response to the same meal-associated stimuli that control release of gastrin. The most striking aspect of the results presented here is that in the presence of the G-InsKi allele, Ins2(Akita/+) mice exhibited a marked prolongation of life span. These results imply that G cell-derived transgenic insulin is beneficial in the amelioration of diabetes. We suggest that an efficient G cells-based insulin gene therapy can relieve diabetic patients from daily insulin injections and protect them from complications of insulin insufficiency while avoiding episodes of toxic hypoglycemia.

Cholecystokinin inhibits gastrin secretion independently of paracrine somatostatin secretion in the pig.

BACKGROUND: Cholecystokinin inhibits the secretion of gastrin from antral G cells, an effect that is speculated to be mediated by D cells secreting somatostatin. The aim of the study was to test directly whether cholecystokinin inhibition of antral gastrin secretion is mediated by somatostatin. METHODS: The effects of CCK on gastrin and somatostatin secretion were studied in isolated vascularly perfused preparations of pig antrum before and after immunoneutralization brought about by infusion of large amounts of a high affinity monoclonal antibody against somatostatin. RESULTS: CCK infusion at 10(-9) M and 10(-8) M decreased gastrin output to 70.5% +/- 7.6% (n = 8) and 76.3% +/- 3.6% (n = 7) of basal output, respectively. CCK at 10(-10) M had no effect (n = 6). Somatostatin secretion was dose-dependently increased by CCK infusion and increased to 268 +/- 38.2% (n = 7) of basal secretion during infusion of CCK at 10(-8) M. Immunoneutralization of somatostatin caused a doubling of the basal secretion of gastrin, but did not affect the CCK-induced decrease in gastrin secretion. CONCLUSION: CCK inhibits gastrin secretion independently of paracrine somatostatin secretion.

Proliferation and functional changes of pancreatic gastrin cells in neonatal rat.

INTRODUCTION: Although gastrin cells are not found in the adult pancreas, they are found transiently in the neonatal pancreas. It has been suggested that gastrin may play a role in pancreatic development. However, cell kinetics as well as the fate and the role of gastrin cells are not clear. METHODOLOGY: Proliferation and functional changes of pancreatic gastrin cells in neonatal Wister rats were studied by immunohistochemistry and [(3)H]thymidine autoradiography. RESULTS: Numbers of pancreatic gastrin cells in neonatal rats showed a peak immediately after birth and then decreased rapidly. Gastrin cells were observed within approximately 2 weeks after birth in islets and within approximately 4 weeks after birth among exocrine cells. In contrast with the decrease of gastrin cell numbers, numbers of duodenal cholecystokinin cells increased remarkably after 7 days of age. Proliferative activity of acinar cells showed two peaks at age 2 days and 9 days. Despite a decrease in gastrin cell numbers, gastrin cells maintained a certain degree of proliferative activity. The "re-staining method" for gastrin and insulin revealed that immunoreactive cells for both gastrin and insulin were rarely found a few days after birth. CONCLUSION: These results suggest that pancreatic gastrin cells do not die off or change to another type of endocrine cell and that some gastrin cells change to insulin cells.

Fisiología gástrica / Gastric physiology

La secreción gástrica, como cada una de las funciones de nuestro organismo, requiere de una compleja integración de mecanismos neurales y endocrinológicos. El nervio vago y el sistema nervioso entérico, así como tres diferentes tipos de células (G, D, ECL) participan en la regulación de la función gástrica. La histamina es el principal secretagogo y tanto la vía nerviosa como la gástrica controlan la secreción de la misma. Esta sustancia actúa en receptores H2 que están unidos a proteína Gs, la cual activa a la adenilciclasa para que produzca AMPc y excite a la proteincinasa-C, que a su vez fosforila a la H+/K+ ATPasa. En esta revisión analizamos estos mecanismos.

Developmental biology of gastrin and somatostatin cells in the antropyloric mucosa of the stomach.

Gastrin is a hormone regulating gastric acid secretion and the growth of the gastrointestinal epithelium. It is expressed by endocrine tumors and by adenocarcinomas of the gastroenteropancreatic region and may represent an autocrine tumor growth factor. Gastrin is also implicated in the genesis of peptic ulcer disease both in conjunction with H. pylori infections and with gastrin-producing tumors. The secretion and expression of gastrin are under the paracrine control of somatostatin, produced by D cells situated in close contact with gastrin-producing G cells. D cells also contain neuronal nitric oxide synthase and appear to regulate apoptosis of G cells by paracrine release of nitric oxide. Both G and D cells are derived from a common multihormonal precursor cell present in the regenerative (isthmus) region of the gastric units. The precursor cells have been suggested to undergo asymmetrical divisions resulting in gastrin- and somatostatin-producing daughter cells that remain in paracrine contact during their migration into the glands. The precursor cells also give rise to the third main antropyloric endocrine cell type; the serotonin-producing EC cell. The maturation of all of these cell types is regulated by a number of transcription factors containing homeobox motifs (Pdx-1, Pax 4 and 6, Isl-1, Nkx6.1). Many of these also regulate the development of the central nervous system and the pancreas. The use of different combinations of these factors for regulating the expression of different hormones may explain the phenomenon of abberant hormone expression during development and carcinogenesis and the occurrence of multihormonal cells.

Effect of Helicobacter pylori eradication on antral somatostatin cell density in humans.

OBJECTIVE: As Helicobacter pylori infection is associated with an elevation in plasma gastrin with normal antral gastrin cell counts, an abnormality in antral somatostatin cells may be associated with the infection. We evaluated the effect of eradication of H. pylori on antral somatostatin cell density in the light of antral gastrin cell density and plasma gastrin levels. DESIGN: Prospective study. METHODS: Of 25 dyspeptic patients with H. pylori infection, nine had H. pylori successfully eradicated and the rest remained infected. Antral biopsies were immunostained for somatostatin cells and plasma gastrin measured before and 4 weeks after H. pylori eradication therapy. Ten other dyspeptic patients without H. pylori infection had their somatostatin cell density evaluated as controls. RESULTS: Somatostatin cell density in the patients without H. pylori infection at the outset was significantly higher than that in the patients with H. pylori infection at the outset (median 57 [18-83] vs. 37 [6-80] cells/mm) respectively (P <0.05). Somatostatin cell density increased after H. pylori eradication (before treatment, median 50 [15-72]; after treatment 71 [39-107] cells/mm) (P < 0.05) but was unchanged with persistent H. pylori infection. Plasma gastrin decreased after H. pylori eradication (before treatment, median 70 [45-100]; after treatment 30 [10-100] ng/l) (P < 0.05) but was unchanged with persistent H. pylori infection. CONCLUSIONS: Following eradication of H. pylori, there is an increase in somatostatin cell density with a fall in plasma gastrin. This supports the theory that H. pylori infection results in a decrease in somatostatin cell density and, as the latter is an inhibitor of gastrin cells, this results in an increased plasma gastrin.

Gastrin and the enterochromaffin-like cell: an acid update.

Gastrin is synthesized and secreted mostly in a heptadecapeptide form from neurocrine G cells located in the antrum. The biologically active sequence of the molecule is a C-terminal pentapeptide, which has been conserved across many species. Transcriptional regulation of gastrin mRNA synthesis is positively regulated by transforming growth factor-alpha (TGF-alpha) and inhibited by somatostatin (SST). The inactive precursor form is converted to the active molecule by several post-translation processing steps which include cleavage, C-terminal amidation, glycosylation, phosphorylation and sulfation. Aberrations in processing steps generate incompletely processed forms, particularly glycosylated progastrin, which may act as autocrine growth factors for gastrointestinal neoplasms. Gastrin release is stimulated by luminal aromatic amino acids and inhibited by a decrease in luminal pH. Other gastrin agonists include beta-adrenergic agents, acetylcholine, gastrin-releasing peptide (bombesin), TGF-alpha, and possibly the gastric pathogen, Helicobacter pylori. The principal peptide inhibitor of gastrin release is SST. The major physiological roles of gastrin include stimulation of acid secretion, regulation of mucosal cell lineage and mucosal cell proliferation. The fundic enterochromaffin-like (ECL) cell is the principal cellular transducer of the gastrin-acid signal. Activation of its gastrin/CCKB receptor results in histamine synthesis and release with consequent activation of the fundic parietal cell H2 receptor. An increase in luminal pH caused by acid inhibitory pharmacotherapy agents (particularly proton pump inhibitors) results in hypergastrinemia and ECL cell hyperplasia. Gastric carcinoids however appear occur in patients with multiple endocrine neoplasia type I syndrome, suggesting that an associated genomic defect is necessary. Gastrin is thus both a potent gastrointestinal trophic and histamine secretory agent. As a hormone it is a paradigm in the elucidation of both cellular secretory and growth factor induced cell proliferation.

Relationship between fundic endocrine cells and gastric acid secretion in hypersecretory duodenal ulcer diseases.

BACKGROUND: Acid hypersecretion is associated with duodenal ulcer disease in the following conditions: Zollinger-Ellison syndrome (ZES) and antral gastrin cell hyperfunction (AGCH) due to hypergastrinaemia, or hypersecretory duodenal ulcer (HDU) without hypergastrinaemia. AIM: To evaluate whether quantitative changes in fundic ECL and D cells may be involved in acid hypersecretion. PATIENTS AND METHODS: Seven ZES, six AGCH and six HDU Helicobacter pylori-positive patients were compared. Basal (BAO) and pentagastrin-stimulated gastric acid secretions (PAO), and morphometry of fundic ECL and D cells were performed. The six AGCH and six HDU patients were investigated again using the same tests 1 year after H. pylori eradication. RESULTS: Median PAO values were no different in all the hypersecretory conditions studied. The median volume density of ECL cells in ZES was significantly higher than in controls (2.75, range 1.74-5.8 vs. 0.73, 0.52-1.11: P < 0.05), whereas it was in the control range in AGCH and HDU patients (0.77, range 0.20-1.39 and 0.99, range 0.42-1.51; respectively). The count of fundic D cells was significantly lower in AGCH patients than in all other investigated groups (median 0.16, range 0.1-0.52; P < 0.05). Cure of infection in AGCH and HDU patients did not modify the ECL cell volume density, whereas a significant increase in the count of fundic D cells was observed in AGCH patients. Thus, the ECL/D cell index was significantly affected in AGCH patients (P < 0.05), being higher during H. pylori infection (median 6, range 0.7-9.25) than after the cure (median 2.12, range 1.10-3.5). BAO and PAO were not affected by H. pylori eradication in either group. CONCLUSIONS: The study provides evidence, for the first time, that quantitative alterations in the fundic endocrine cells are not involved in acid hypersecretion of patients with hypersecretory states, and that eradication of H. pylori does not restore normal acid secretion values.