Gut hormones in gastric function

The intestine as an endocrine organ and the role of gut hormones in metabolic regulation

Gut hormones orchestrate pivotal physiological processes in multiple metabolically active tissues, including the pancreas, liver, adipose tissue, gut and central nervous system, making them attractive therapeutic targets in the treatment of obesity and type 2 diabetes mellitus. Most gut hormones are derived from enteroendocrine cells, but bioactive peptides that are derived from other intestinal epithelial cell types have also been implicated in metabolic regulation and can be considered gut hormones. A deeper understanding of the complex inter-organ crosstalk mediated by the intestinal endocrine system is a prerequisite for designing more effective drugs that are based on or target gut hormones and their receptors, and extending their therapeutic potential beyond obesity and diabetes mellitus. In this Review, we present an overview of gut hormones that are involved in the regulation of metabolism and discuss their action in the gastrointestinal system and beyond.

Bariatric Surgery in Adolescents: To Do or Not to Do?

Pediatric obesity is a multifaceted disease that can impact physical and mental health. It is a complex condition that interweaves biological, developmental, environmental, behavioral, and genetic factors. In most cases lifestyle and behavioral modification as well as medical treatment led to poor short-term weight reduction and long-term failure. Thus, bariatric surgery should be considered in adolescents with moderate to severe obesity who have previously participated in lifestyle interventions with unsuccessful outcomes. In particular, laparoscopic sleeve gastrectomy is considered the most commonly performed bariatric surgery worldwide. The procedure is safe and feasible. The efficacy of this weight loss surgical procedure has been demonstrated in pediatric age. Nevertheless, there are barriers at the patient, provider, and health system levels, to be removed. First and foremost, more efforts must be made to prevent decline in nutritional status that is frequent after bariatric surgery, and to avoid inadequate weight loss and weight regain, ensuring successful long-term treatment and allowing healthy growth. In this narrative review, we considered the rationale behind surgical treatment options, outcomes, and clinical indications in adolescents with severe obesity, focusing on LSG, nutritional management, and resolution of metabolic comorbidities.

Gastrokine 1 inhibits gastrin-induced cell proliferation

BACKGROUND

Gastrokine 1 (GKN1) acts as a gastric tumor suppressor. Here, we investigated whether GKN1 contributes to the maintenance of gastric mucosal homeostasis by regulating gastrin-induced gastric epithelial cell growth.

METHODS

We assessed the effects of gastrin and GKN1 on cell proliferation in stable AGS(GKN1) and MKN1(GKN1) gastric cancer cell lines and HFE-145 nonneoplastic epithelial cells. Cell viability and proliferation were analyzed by MTT and BrdU incorporation assays, respectively. Cell cycle and expression of growth factor receptors were examined by flow cytometry and Western blot analyses.

RESULTS

Gastrin treatment stimulated a significant time-dependent increase in cell viability and proliferation in AGS(mock) and MKN1(mock), but not in HFE-145, AGS(GKN1), and MKN1(GKN1), cells, which stably expressed GKN1. Additionally, gastrin markedly increased the S-phase cell population, whereas GKN1 significantly inhibited the effect of gastrin by regulating the expression of G1/S cell-cycle regulators. Furthermore, gastrin induced activation of the NF-kB and β-catenin signaling pathways and increased the expression of CCKBR, EGFR, and c-Met in AGS and MKN1 cells. However, GKN1 completely suppressed these effects of gastrin via downregulation of gastrin/CCKBR/growth factor receptor expression. Moreover, GKN1 reduced gastrin and CCKBR mRNA expression in AGS and MKN1 cells, and there was an inverse correlation between GKN1 and gastrin, as well as between GKN1 and CCKBR mRNA expression in noncancerous gastric mucosae.

CONCLUSION

These data suggest that GKN1 may contribute to the maintenance of gastric epithelial homeostasis and inhibit gastric carcinogenesis by downregulating the gastrin-CCKBR signaling pathway.

Gastrointestinal changes after bariatric surgery

Severe obesity is a preeminent health care problem that impacts overall health and survival. The most effective treatment for severe obesity is bariatric surgery, an intervention that not only maintains long-term weight loss but also is associated with improvement or remission of several comorbidies including type 2 diabetes mellitus. Some weight loss surgeries modify the gastrointestinal anatomy and physiology, including the secretions and actions of gut peptides. This review describes how bariatric surgery alters the patterns of gastrointestinal motility, nutrient digestion and absorption, gut peptide release, bile acids and the gut microflora, and how these changes alter energy homeostasis and glucose metabolism.

Arx is required for normal enteroendocrine cell development in mice and humans

Enteroendocrine cells of the gastrointestinal (GI) tract play a central role in metabolism, digestion, satiety and lipid absorption, yet their development remains poorly understood. Here we show that Arx, a homeodomain-containing transcription factor, is required for the normal development of mouse and human enteroendocrine cells. Arx expression is detected in a subset of Neurogenin3 (Ngn3)-positive endocrine progenitors and is also found in a subset of hormone-producing cells. In mice, removal of Arx from the developing endoderm results in a decrease of enteroendocrine cell types including gastrin-, glucagon/GLP-1-, CCK-, secretin-producing cell populations and an increase of somatostatin-expressing cells. This phenotype is also observed in mice with endocrine-progenitor-specific Arx ablation suggesting that Arx is required in the progenitor for enteroendocrine cell development. In addition, depletion of human ARX in developing human intestinal tissue results in a profound deficit in expression of the enteroendocrine cell markers CCK, secretin and glucagon while expression of a pan-intestinal epithelial marker, CDX2, and other non-endocrine markers remained unchanged. Taken together, our findings uncover a novel and conserved role of Arx in mammalian endocrine cell development and provide a potential cause for the chronic diarrhea seen in both humans and mice carrying Arx mutations.

Gastrin - active participant or bystander in gastric carcinogenesis?

Gastrin is a pro-proliferative, anti-apoptotic hormone with a central role in acid secretion in the gastric mucosa and a long-standing association with malignant progression in transgenic mouse models. However, its exact role in human gastric malignancy requires further validation. Gastrin expression is tightly regulated by two closely associated hormones, somatostatin and gastrin-releasing peptide, and aspects of their interaction may be deregulated during progression to gastric adenocarcinoma. Furthermore, agonists and antagonists of the receptors for all three hormones have shown modest clinical efficacy against gastric adenocarcinoma, which might provide useful information on the future combined use of these agents.

Prospective randomized trial comparing Billroth I and Roux-en-Y procedures after distal gastrectomy for gastric carcinoma

To determine the clinical efficacy of Roux-en-Y reconstruction (RY) after distal gastrectomy, we compared postoperative outcomes of patients who underwent RY or conventional Billroth I reconstruction (B-I). A total of 50 patients were prospectively randomized to either B-I or RY reconstruction, and complications, postoperative course, and nutritional status were compared. Bile reflux and inflammation in the remnant stomach and lower esophagus were evaluated by postoperative follow-up endoscopy at 6 months. Operative time and blood loss as well as postoperative nutrition did not show significant differences between the two groups. As anticipated, 5 of 24 patients with RY reconstruction developed gastrojejunal stasis in the early postoperative period, which led to a longer postoperative hospital stay as compared with the B-I group (mean +/- S.D; B-I; 19.0 +/- 6.2, RY; 31.8 +/- 21.7 days) (P < 0.05). Endoscopic examination revealed that the frequency of bile reflux (P < 0.01) and degree of inflammation in the remnant stomach (P < 0.05) were less in the RY group than in the B-I group. However, inflammatory findings in the lower esophagus were observed in 7 (27%) of B-I, and 8 (35%) of the RY group, suggesting that late phase esophagitis was not improved in the RY group. Roux-en-Y reconstruction was effective in preventing duodenogastric reflux and resulting gastritis, but it did not prevent esophagitis. Because RY reconstruction induces the frequent complication of Roux-en-Y stasis, causing longer postoperative hospital stay, this method has limited advantages over B-I anastomosis after distal gastrectomy.

Ingested fat and satiety

Apolipoprotein A-IV (apo A-IV) is secreted by the intestine associated with chylomicron. Intestinal apo A-IV synthesis is stimulated by fat absorption, probably mediated by chylomicron formation. The stimulation of apo A-IV synthesis in the jejunum and ileum is attenuated by intravenous leptin infusion. Intestinal apo A-IV synthesis is also stimulated by a factor from the ileum, probably peptide tyrosine-tyrosine (PYY), which has been demonstrated to affect satiety. Apo A-IV has been proposed to physiologically control food intake, and this inhibitory effect is centrally mediated. Recently, apo A-IV was demonstrated in the hypothalamus. The hypothalamic apo A-IV level was reduced by food deprivation and restored by lipid feeding. Intracerebroventricular administration of apo A-IV antiserum stimulated feeding and decreased the hypothalamic apo A-IV mRNA level, implying that feeding is normally limited by endogenous apo A-IV. Central administration of neuropeptide Y (NPY) significantly increased hypothalamic apo A-IV mRNA levels in a dose-dependent manner. The stimulation of intestinal synthesis and secretion of apo A-IV by lipid absorption are rapid; thus, apo A-IV is capable of short-term regulation of food intake. Evidence also suggests apo A-IV's involvement in long-term regulation of food intake and bodyweight. The chronic ingestion of high fat blunts the intestinal apo A-IV response to lipid feeding and may therefore explain why chronic intake of high fat predisposes animals and humans to obesity.

Morphological support for paracrine inhibition of gastric acid secretion by nitric oxide in humans

BACKGROUND

Functional studies have shown that nitric oxide (NO) inhibits gastric acid secretion in a variety of species, including man. We have performed a morphological study with the intention of localizing the endothelial NO synthase (eNOS) in the human gastric mucosa.

METHODS

Fifteen healthy subjects voluntarily participated in the study, and mucosal biopsies were obtained from the cardia, corpus and antrum. The presence and localization of eNOS were studied using immunohistochemical techniques.

RESULTS

eNOS-immunoreactivity (eNOS-IR) is found in surface mucous cells of cardia, corpus and antrum. Unique to the oxyntic mucosa is the presence of eNOS-IR in 'endocrine-like' cells, found in close contact with parietal cells.

CONCLUSIONS

eNOS-IR cells in close apposition to parietal cells provide morphological support for paracrine inhibition of gastric acid secretion by NO.

Neurotransmitters regulating acid secretion in the proventriculus of the Houbara bustard (Chlamydotis undulata): a morphological viewpoint

Endocrine cells containing somatostatin (Som), gastrin-releasing peptide (GRP), and neuronal nitric oxide synthase (nNOS) and nerve fibers containing choline acetyl transferase (ChAT), tyrosine hydroxylase (TH), galanin (Gal), substance P (SP), and vasoactive intestinal polypeptide (VIP) were immunolocalized in the proventriculus of the Houbara bustard, Chlamydotis undulata. While GRP-immunoreactive (GRP-IR) cells occur in the inner zone, somatostatin (Som-IR) and polyclonal nNOS (nNOS-IR) immunoreactive cells were localized mainly in the peripheral zone of submucosal glands. GRP-IR, Som-IR, and nNOS-IR cells were occasionally observed in the walls of the gastric glands. Endocrine cells are of the closed variety and usually possess apical processes extending along the basal surfaces of adjacent nonreactive cells. Ultrastructural features of these cells are typical. ChAT, Gal, SP, VIP, and TH were immunolocalized in nerve fibers and terminals in the walls of arterioles and capillaries at the periphery of submucosal glands. Immunoreactivity to monoclonal nNOS occurred mainly in neuronal cell bodies in ganglia located around the submucosal glands. ChAT and TH immunoreactive cell bodies were also occasionally seen around the submucosal glands in the peripheral region. Immunoreactivity to Gal, SP, and VIP, but not ChAT or TH, was discernible around the walls of gastric glands. It was concluded that the distribution of neurotransmitters in neuronal structures is similar, but that of the endocrine cells varies from that of some avian species. The roles of these neurotransmitters in the regulation of acid secretion are discussed.

Inhibition of sham feeding-stimulated human gastric acid secretion by glucagon-like peptide-2

Glucagon-like peptide (GLP)-2 is formed from proglucagon in the intestinal L cells and is secreted postprandially in parallel with the insulinotropic hormone GLP-1, the latter of which, in addition, acts to inhibit gastric secretion and motility by inhibiting central parasympathetic outflow. We now studied the effect of GLP-2 on gastric secretion stimulated by sham feeding to test the hypothesis that also GLP-2 acts as an enterogastrone. Eight healthy volunteers were studied twice on separate days. They were sham fed with and without GLP-2 infused iv at a rate of 0.8 pmol/kg x min. Gastric contents were aspirated continuously by a nasogastric tube for determination of acid secretion, volume, and osmolarity. Sham feeding increased gastric acid secretion nearly 5-fold. Infusion of GLP-2 reduced incremental acid secretion by 65+/-6%, compared with saline infusion (delta8.75+/-0.37 vs. delta3.04+/-0.47 mmol x 60 min; P<0.01). Plasma concentrations of GLP-2 rose from a basal mean of 3.3+/-0.9 to a mean of 115+/-8 pmol/L (range, 57-149 pmol/L) during infusion of GLP-2 and remained at basal level during saline infusion. Plasma concentrations of GLP-1, gastrin, cholecystokinin, and secretin remained low and unchanged on both study days. We conclude that GLP-2 is a powerful inhibitor of gastric acid secretion in man. Further investigations will show to what extent GLP-2 contributes to the inhibitory effects on gastric secretion exerted by hormones from the distal small intestine, under physiological circumstances.

Acceleration of ulcer healing by cholecystokinin (CCK): role of CCK-A receptors, somatostatin, nitric oxide and sensory nerves

CCK exhibits a potent cytoprotective activity against acute gastric lesions, but its role in ulcer healing has been little examined. In this study we determined whether exogenous CCK or endogenously released CCK by camostate, an inhibitor of luminal proteases, or by the diversion of pancreatico-biliary secretion from the duodenum, could affect ulcer healing. In addition, the effects of antagonism of CCK-A receptors (by loxiglumide, LOX) or CCK-B receptors (by L-365,260), an inhibition of NO-synthase by N(G)-nitro-L-arginine (L-NNA), or sensory denervation by large neurotoxic dose of capsaicin on CCK-induced ulcer healing were examined. Gastric ulcers were produced by serosal application of acetic acid and animals were sacrificed 9 days after ulcer induction. The area of ulcers and blood flow at the ulcer area were determined. Plasma levels of gastrin and CCK and luminal somatostatin were measured by RIA and mucosal biopsy samples were taken for histological evaluation and measurement of DNA synthesis. CCK given s.c. reduced dose dependently the ulcer area; the threshold dose of CCK being 1 nmol/kg and the dose inhibiting this area by 50% being 5 nmol/kg. This healing effect of CCK was accompanied by a significant increase in the GBF at ulcer margin and the rise in luminal NO production, plasma gastrin level and DNA synthesis. Concurrent treatment with LOX, completely abolished the CCK-8-induced acceleration of the ulcer healing and the rise in the GBF at the ulcer margin, whereas L-365,260 remained without any influence. Treatment with camostate or diversion of pancreatic juice that raised plasma CCK level to that observed with administration of CCK-8, also accelerated ulcer healing and this effect was also attenuated by LOX but not by L-365,260. Inhibition of NO-synthase by L-NNA significantly delayed ulcer healing and reversed the CCK-8 induced acceleration of ulcer healing, hyperemia at the ulcer margin and luminal NO release, and these effects were restored by the addition to L-NNA of L-arginine but not D-arginine. Capsaicin denervation attenuated CCK-induced ulcer healing, and the accompanying rise in the GBF at the ulcer margin and decreased plasma gastrin and luminal release of somatostatin when compared to those in rats with intact sensory nerves. Detectable signals for CCK-A and B receptor mRNAs as well as for cNOS mRNA expression were recorded by RT-PCR in the vehicle control gastric mucosa. The expression of CCK-A receptor mRNA and cNOS mRNA was significantly increased in rats treated with CCK-8 and camostate, whereas CCK-B receptor mRNA remained unaffected. We conclude that CCK accelerates ulcer healing by the mechanism involving upregulation of specific CCK-A receptors, enhancement of somatostatin release, stimulation of sensory nerves and hyperemia in the ulcer area, possibly mediated by NO.

Growth stimulation of normal melanocytes and nevocellular nevus cells by gastrin releasing peptide (GRP)

In order to know the possible effects of gastrin releasing peptide (GRP) on nevus cells and melanocytes, we studied the effect of GRP on the proliferation of cultured human nevus cells and normal melanocytes. MTS assay showed that GRP stimulated the growth of viable melanocytes at 1000 ng/ml. GRP also stimulated the growth of nevus cells in a dose dependent manner and maximum stimulation was obtained at 100 ng/ml of GRP. GRP was less effective for growth stimulation of normal melanocytes than nevus cells. The cytoplasm of nevus cells were positively stained by polyclonal anti-GRP antibody. We also detected the expression of GRP and GRP receptor mRNAs in these cells by RT-PCR. These results suggest that GRP acts as an autocrine growth factor for nevus cells and normal melanocytes.

Biology of gut cholecystokinin and gastrin receptors

1. The stomach hormone gastrin and the intestinal hormone cholecystokinin (CCK) share a common C-terminal pentapeptide sequence but have different biological roles. Gastrin is the major stimulant of gastric acid secretion and has a growth stimulatory effect on the secretory part of the stomach. The physiological roles of CCK are the stimulation of pancreatic secretion and the contraction of the gall-bladder. 2. Several classes of receptors have been defined for peptides of the gastrin/CCK family. The CCKA receptor on pancreatic acini has a greater affinity for sulfated CCK than for gastrin, while the gastrin/CCKB receptor in gastric mucosa and brain has similar affinities for both gastrin and CCK. Potent and selective antagonists have been developed for both receptor classes. 3. The structures of the CCKA and gastrin/CCKB receptors have been deduced from the nucleotide sequences of cloned cDNA. The receptors, which both belong to the family with seven transmembrane segments, control secretion via similar signalling mechanisms. Occupation of either receptor leads to activation of phospholipase C, with resultant increases in intracellular levels of inositol triphosphate and Ca2+. Mitogenic signalling pathways are also being defined. 4. Recent studies have questioned the previous assumption that gastrin precursors are inactive. Glycine-extended gastrin17 has been shown to stimulate mitogenesis in some cell lines and may also have an autocrine role in the growth of colonic cancers. The receptors involved, which are clearly distinct in binding properties from the CCKA and gastrin/CCKB receptors, have not yet been cloned. Specific antagonists for the novel receptors will be required to define their function in further detail.

[Development of the gastric glands of cats (Felis silvestris catus)]

There are five stages in the development of the cat's gastric glands: 1. During the stage of the indifferent epithelium from day 19 to day 24, the anlage of the stomach develops with all layers; 2. The stage of gland formation from day 24 to day 41 is the beginning of the gland buds. They develop in connection with endocrine cells on day 34 into primitive oxyntic and primitive mucous cells. The latter form the basis for all other cells, including the surface mucous cells; 3. During the stage of gland evagination from day 42 to 55, the anlagen are separated into primitive pits and tubules, while the cells continue to differentiate and the first intermediate cells are seen; 4. The stage of gland branching from day 56 to birth is characterized by the formation of additional glands at the bottom of the pits which change the ordinary anlagen into branched glands. During this stage, the cardiac glands are formed; 5. In the stage of gland maturation from birth to the 9th week, the peptic cells are formed and the glands start functioning. The oxyntic cells show carbonic-anhydrase activity and signs of acid secretion, and, between the weeks 4 and 8, the peptic cells contain pepsinogen, producing a negative reaction to PAS and a positive reaction to HID. Mucous cells and mucous neck cells produce PAS- and AB-positive mucin.

Gastric acid secretion after blockade of angiotensin AT1 receptors in the Na(+)-depleted rat

This study tested the hypothesis that angiotensin II acting through the angiotensin AT1 receptor plays an important role in the control of gastric acid secretion. Basal gastric acid secretion and gastric blood flow were lower in Na(+)-depleted animals, in which the renin-angiotensin system was activated, than in animals maintained on a normal Na+ diet. Intravenous infusion of pentagastrin at 0.6 microgram/kg/min increased gastric acid secretion to a greater extent in normal Na+ than in Na(+)-depleted animals. In addition to stimulating gastric acid secretion, pentagastrin increased gastric blood flow by proportionally the same amount in both normal and low Na+ animals. However, because basal gastric blood flow was considerably reduced in Na(+)-depleted animals, the increase produced by pentagastrin extended only to the levels observed in non-pentagastrin-treated normal Na+ animals. Lower gastric blood flow in response to pentagastrin may explain the smaller increase in gastric acid secretion observed in Na(+)-depleted animals. In Na(+)-depleted animals, the selective angiotensin AT1 receptor antagonist losartan did not affect basal gastric acid secretion or gastric blood flow, suggesting the involvement of mechanisms other than angiotensin II. Following blockade of angiotensin AT1 receptors, pentagastrin significantly increased gastric blood flow in Na(+)-depleted animals to levels observed with infusion of the pentapeptide in normal Na+ animals. The results suggested that the decrease in pentagastrin-stimulated acid secretion in Na(+)-depleted animals is mediated by angiotensin II acting through the angiotensin AT1 receptor, most probably through vascular mechanisms.