Gastrin in gastrointestinal diseases

The rhizomes of Atractylodes macrocephala Koidz improve gastrointestinal health and pregnancy outcomes in pregnant mice via modulating intestinal barrier and water-fluid metabolism

ETHNOPHARMACOLOGICAL RELEVANCE

Baizhu (BZ) is the dried rhizome of Atractylodes macrocephala Koidz (Compositae), which invigorates the spleen, improves vital energy, stabilizes the fetus, and is widely used for treating spleen deficiency syndrome. However, the impact of BZ on gastrointestinal function during pregnancy remains unexplored.

AIM OF THE STUDY

This study elucidated the ameliorative effects of BZ on gastrointestinal health and pregnancy outcomes in pregnant mice with spleen deficiency diarrhea (SDD).

METHODS

To simulate an irregular human diet and overconsumption of cold and bitter foods leading to SDD, a model of pregnant mice with SDD was established using an alternate-day fasting and high-fat diet combined with oral administration of Sennae Folium. During the experiment, general indicators and diarrhea-related parameters were measured. Gastric and intestinal motility (small intestinal propulsion and gastric emptying rates) were evaluated. Serum motilin (MTL), ghrelin, growth hormone (GH), gastrin (Gas), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), chorionic gonadotropin β (β-CG), progesterone (P), and estradiol (E2) were quantified using an enzyme-linked immunosorbent assay. Pathological changes were examined by hematoxylin and eosin staining (H&E) and alcian blue periodic acid Schiff staining (AB-PAS). Immunohistochemistry and immunofluorescence were used to measure the expression levels of the intestinal barrier and water metabolism-related proteins in colonic tissues. The pregnancy rate, ovarian organ coefficient, uterus with fetus organ coefficient, small size, average fetal weight, and body length of fetal mice were calculated.

RESULTS

The results showed that BZ significantly improved general indicators and diarrhea in pregnant mice with SDD, increased gastric emptying rate and small intestinal propulsion rate, elevated the levels of gastrointestinal hormones (AMS, ghrelin, GH, and Gas) in the serum, and reduced lipid levels (TC and LDL-c). It also improved colonic tissue morphology, increased the number of goblet cells, and promoted the mRNA and protein expression of occludin, claudin-1, ZO-1, AQP3, AQP4, and AQP8 in colonic tissues, downregulating the mRNA and protein expression levels of claudin-2, thereby alleviating intestinal barrier damage and regulating the balance of water and fluid metabolism. BZ also held the levels of pregnancy hormones (β-CG, P, and E2) in the serum of pregnant mice with SDD. Moreover, it increased the pregnancy rate, ovarian organ coefficient, uterus with fetus organ coefficient, litter size, average fetal weight, and body length of fetal mice. These findings indicate that BZ can improve spleen deficiency-related symptoms in pregnant mice before and during pregnancy, regulate pregnancy-related hormones, and improve pregnancy outcomes.

The probiotic fermented milk of Lacticaseibacillus paracasei JY062 and Lactobacillus gasseri JM1 alleviates constipation via improving gastrointestinal motility and gut microbiota

Constipation is directly related to the intestinal microenvironment, in which the promotion of gastrointestinal (GI) motility and improvement of gut microbiota distribution are important for alleviating symptoms. Herein, after the intervention of probiotic fermented milk (FMMIX) containing Lacticaseibacillus paracasei JY062 and Lactobacillus gasseri JM1 for 14 d in Kunming mice with loperamide-induced constipation, the results indicated that FMMIX significantly increased the secretion of serum motilin, gastrin and 5-hydroxytryptamine, as well as decreased the secretion of peptide YY, vasoactive intestinal peptide, and nitric oxide in mice. As determined by immunohistochemical analysis, FMMIX promoted an augmentation in the quantity of Cajal interstitial cells. In addition, the mRNA and protein expression of c-kit and stem cell factor (SCF) were upregulated to facilitate intestinal motility. High-throughput sequencing and gas chromatography techniques revealed that FMMIX led to an increase in the relative abundance of beneficial bacteria (Lactobacillus, Oscillospira, Ruminococcus, Coprococcus, and Akkermansia), reduced the presence of harmful bacteria (Prevotella), and resulted in elevated levels of short-chain fatty acids (SCFA) with a superior improvement compared with unfermented milk. Untargeted metabolomics revealed significant upregulation of functional metabolites such as l-pipecolinic acid, dl-phenylalanine, and naringenin in FMMIX, presumably playing a potential role in constipation relief. Overall, our results showed that FMMIX had the potential to alleviate constipation symptoms in mice by improving the secretion of serum GI regulatory peptides and neurotransmitters, increasing the expression of c-kit and SCF proteins, and modulating the gut microbiota structure and SCFA levels, and may be associated with an increase in these functional metabolites. This suggested that FMMIX could be a promising adjunctive strategy for managing constipation symptoms and could contribute to the development of functional foods aimed at improving gut health.

The Probiotic Combination of Lacticaseibacillus paracasei JY062 and Lactobacillus gasseri JM1 Alleviates Gastrointestinal Motility Disorder via Improving Gut Microbiota

Probiotics have received wide attention as a potential way to alleviate gastrointestinal (GI) motility disorders. Herein, we investigated the effects of Lacticaseibacillus paracasei JY062, Lactobacillus gasseri JM1, and the probiotic combination at 5 × 10⁹ CFU/mL on mice induced by loperamide and explored the possible underlying mechanisms in GI motility disorder. After two weeks of probiotic intervention, the results indicated that the probiotic combination alleviated GI motility disorder better. It increased the secretion of excitatory GI regulators motilin, gastrin, and 5-hydroxytryptamine (5-HT) and decreased the secretion of the inhibitory GI regulators peptide YY and nitric oxide (NO), except vasoactive intestinal peptide. 5-HT and NO were related to the mRNA expression of 5-HT₄ receptor and nitric oxide synthase, respectively. The intervention of probiotic combination also increased the number of interstitial cells of Cajal and the expression of SCF/c-kit protein. In addition, it also increased the abundance of beneficial bacteria (Lactobacillus, Rikenellaceae, and Clostridiaceae_Clostridium) and improved the contents of short-chain fatty acids in cecum contents of mice. In conclusion, the probiotic combination of L. paracasei JY062 and L. gasseri JM1 has the potential to alleviate GI motility disorders by balancing intestinal homeostasis.

Elucidating the molecular determinants in the process of gastrin C-terminal pentapeptide amide end activating cholecystokinin 2 receptor by Gaussian accelerated molecular dynamics simulations

Gastrin plays important role in stimulating the initiation and development of many gastrointestinal diseases through interacting with the cholecystokinin 2 receptor (CCK2R). The smallest bioactive unit of gastrin activating CCK2R is the C-terminal tetrapeptide capped with an indispensable amide end. Understanding the mechanism of this smallest bioactive unit interacting with CCK2R on a molecular basis could provide significant insights for designing CCK2R antagonists, which can be used to treat gastrin-related diseases. To this end, we performed extensive Gaussian accelerated molecular dynamics simulations to investigate the interaction between gastrin C-terminal pentapeptide capped with/without amide end and CCK2R. The amide cap influences the binding modes of the pentapeptide with CCK2R by weakening the electrostatic attractions between the C-terminus of the pentapeptide and basic residues near the extracellular domain in CCK2R. The C-terminus with the amide cap penetrates into the transmembrane domain of CCK2R while floating at the extracellular domain without the amide cap. Different binding modes induced different conformational dynamics of CCK2R. Residue pairs in CCK2R had stronger correlated motions when binding with the amidated pentapeptide. Key residues and interactions important for CCK2R binding with the amidated pentagastrin were also identified. Our results provide molecular insights into the determinants of the bioactive unit of gastrin activating CCK2R, which would be of great help for the design of CCK2R antagonists.

Association of serum pepsinogens and gastrin-17 with Helicobacter pylori infection assessed by urea breath test

Background

Association of gastric atrophy or cancer with levels of serum pepsinogens, gastrin-17 and anti-Helicobacter pylori IgG antibody have been extensively studied. However, the association of serum pepsinogen and gastrin-17 with H. pylori infection has not been studied in a large population.

Aim

To investigate the impact of H. pylori infection on serum levels of pepsinogens and gastrin-17.

Methods

A total of 354, 972 subjects who underwent health check-ups were included. Serum levels of pepsinogens and gastrin-17 were measured using the enzyme-linked immunosorbent assay. H. pylori infection was detected using ¹⁴C-urea breath test (UBT). Multivariable logistic regression analysis was used to investigate the association of serum pepsinogen and gastrin-17 with H. pylori infection.

Results

H. pylori prevalence was 33.18% in this study. The mean levels of pepsinogens and gastrin-17 were higher, while the mean pepsinogen-I/II ratio were lower among H. pylori-positive than -negative subjects. In H. pylori-positive subjects, pepsinogen and gastrin-17 levels correlated positively, whereas the pepsinogen-I/II ratio correlated negatively with UBT values (e.g., the mean serum level of pepsinogen-I in subjects with UBT values in the range of 100-499dpm, 500-1499dpm, and ≥1500dpm was 94.77 ± 38.99, 102.77 ± 43.59, and 111.53 ± 47.47 ng/mL, respectively). Compared with H. pylori-negative subjects, the adjusted odds ratio (aOR) of having pepsinogen-I ≤ 70 ng/mL in the three H. pylori-positive but with different UBT value groups was 0.31 (p<0.001), 0.16 (p<0.001), and 0.08 (p<0.001), respectively; while the aOR of having G-17>5.70 pmol/L was 4.56 (p<0.001), 7.43 (p<0.001), and 7.12 (p<0.001). This suggested that H. pylori-positive subjects with higher UBT values were less likely to have pepsinogen-I ≤70 ng/mL (a serum marker for gastric atrophy), but more likely to have gastrin-17 >5.70 pmol/L (a marker for peptic ulcer).

Conclusions

H. pylori-positive subjects with higher UBT values are unlikely to have gastric atrophy, but may have greater risk of severe gastritis or peptic ulcers. Our study suggests that H. pylori-positive patients with high UBT values may benefit the most from H. pylori eradication.

The Key Ingredient Acacetin in Weishu Decoction Alleviates Gastrointestinal Motility Disorder Based on Network Pharmacology Analysis

Background

Gastrointestinal motility disorder is a common gastrointestinal disease, which seriously affects life quality. Traditional Chinese medicine (TCM) has been widely used as an alternative therapy for gastrointestinal motility disorder. Acacetin is a natural flavonoid compound that has antioxidant and anti-inflammatory, antidepressant, and anticancer properties. However, the efficacy of Acacetin in the treatment of gastrointestinal motility disorders has not been studied. Our aim was to investigate the mechanism of Acacetin-alleviated gastrointestinal motility disorder and its efficacy based on network pharmacology.

Methods

We performed network pharmacology to predict the active components, match Weishu decoction (WSD) targets in gastrointestinal motility disorders, and investigate its potential pharmacological mechanisms. We performed the GO and KEGG enrichment analysis. In vivo, we investigated the effects of Acacetin in the gastrointestinal motility disorder model.

Results

Based on network pharmacological method, the key active ingredient of WSD was identified as Acacetin, and the enrichment signaling pathway was the PI3K-AKT signaling pathway. Acacetin and Mosapride accelerated gastric emptying time, reduced gastric remnant rate, and increased small intestinal propulsion rate. The levels of GAS and MTL were increased after using Acacetin. These results indicated that Acacetin could improve gastrointestinal motility disorders. Among them, high-dose Acacetin showed a better effect. Acacetin could regulate protein and lipid metabolism in mice with gastrointestinal motility disorder. Furthermore, Acacetin could modulate gastrointestinal inflammation and apoptosis. The detection of the PI3K-AKT signaling pathway-related proteins showed that Acacetin improved gastrointestinal motility disorder by inhibiting the activation of the PI3K-AKT signaling pathway.

Conclusion

The key ingredient Acacetin in WSD could alleviate gastrointestinal motility disorder by inhibiting the activation of the PI3K-AKT signaling pathway based on network pharmacology analysis. The efficacy and safety of Acacetin treatment provide strong experimental support for the clinical treatment of gastrointestinal motility disorder.

Phage antibody library screening for the selection of novel high-affinity human single-chain variable fragment against gastrin receptor: an in silico and in vitro study

BACKGROUND

As a membrane G protein coupled receptors (GPCRs) family, gastrin/cholecystokinin-2 receptor (CCK2R) plays a key role in the initiation and development of gastric cancer.

OBJECTIVES

Targeting CCK2R by immunotherapeutics such as single-chain variable fragments (scFvs) may provide an effective treatment modality against gastric cancer. Thus, the main objective of this study was to isolate scFvs specific to CCK2R.

METHODS

To isolate scFvs specific to the CCK2R, we capitalized on a semi-synthetic diverse phage antibody library (PAL) and a solution-phase biopanning process. The library was panned against a biotinylated peptide of the second extracellular loop (ECL2) of CCK2R. After four rounds of biopanning, the selected soluble scFv clones were screened by enzyme-linked immunosorbent assay (ELISA) and examined for specific binding to the peptide. The selected scFvs were purified using immobilized metal affinity chromatography (IMAC). The binding affinity and specificity of the scFvs were examined by the surface plasmon resonance (SPR), immunoblotting and flow cytometry assays and molecular docking using ZDOCK v3.0.2.

RESULTS

Ten different scFvs were isolated, which displayed binding affinity ranging from 0.68 to 8.0 (nM). Immunoblotting and molecular docking analysis revealed that eight scFvs were able to detect the denatured form of CCK2R protein. Of the isolated scFvs, two scFvs showed high-binding affinity to the human gastric adenocarcinoma AGS cells.

CONCLUSIONS

Based on our findings, a couple of the selected scFvs showed markedly high-binding affinity to immobilized CCK2R peptide and CCK2R-overexpressing AGS cells. Therefore, these scFvs are proposed to serve as targeting and/or treatment agents in the diagnosis and immunotherapy of CCK2R-positive tumors. Graphical abstract ᅟ.

Substrate Specificity and Possible Heterologous Targets of Phytaspase, a Plant Cell Death Protease

Plants lack aspartate-specific cell death proteases homologous to animal caspases. Instead, a subtilisin-like serine-dependent plant protease named phytaspase shown to be involved in the accomplishment of programmed death of plant cells is able to hydrolyze a number of peptide-based caspase substrates. Here, we determined the substrate specificity of rice (Oryza sativa) phytaspase by using the positional scanning substrate combinatorial library approach. Phytaspase was shown to display an absolute specificity of hydrolysis after an aspartic acid residue. The preceding amino acid residues, however, significantly influence the efficiency of hydrolysis. Efficient phytaspase substrates demonstrated a remarkable preference for an aromatic amino acid residue in the P3 position. The deduced optimum phytaspase recognition motif has the sequence IWLD and is strikingly hydrophobic. The established pattern was confirmed through synthesis and kinetic analysis of cleavage of a set of optimized peptide substrates. An amino acid motif similar to the phytaspase cleavage site is shared by the human gastrointestinal peptide hormones gastrin and cholecystokinin. In agreement with the established enzyme specificity, phytaspase was shown to hydrolyze gastrin-1 and cholecystokinin at the predicted sites in vitro, thus destroying the active moieties of the hormones.

Serum Indicators Reflecting Gastric Function May Also Correlate with Other Extragastric Diseases

Aim. Serological indicators of organ function can reveal intrinsic links between different organs. The present study aimed to determine the correlations of serum indicators for gastric and extragastric function. Methods. A total of 823 individuals were enrolled. Data on indicators reflecting blood lipids, blood glucose, indexes of stomach, kidney, liver, and thyroid function, and H. pylori IgG antibody level were collected. Results. As creatine (Cr) levels increased, PGI (pepsinogen I), PGII concentrations, and PGI/II ratio increased monotonically from 79.7 to 105.15 µg/L, 6.5 to 8.4 µg/L, and 11.97 to 12.27, respectively (P < 0.05). As thyroid peroxidase antibody (TPOAb) levels increased, PGI level decreased from 100.85 to 84 µg/L (P < 0.05) and as thyroid stimulating hormone (TSH) increased, PGI/II ratio increased monotonically from 11.54 to 12.68 (P < 0.05). As triglyceride (TG) levels increased, gastrin 17 (G17) concentrations increased monotonically from 1.73 to 2.7 pmol/L (P < 0.05). As serum glucose and glycated hemoglobin (HbA1C) increased, PGI/II concentrations increased monotonically from 11.98 to 12.67 and 9.7 to 13.54 (P < 0.05), respectively. Conclusions. Serum PG and G17 levels were associated with blood glucose and lipids, kidney function, and thyroid function but not with liver function. Serum indicators reflecting gastric function may correlate not only with primary diseases, but also with other extragastric diseases.

Gastrin-stimulated Gα13 Activation of Rgnef Protein (ArhGEF28) in DLD-1 Colon Carcinoma Cells

The guanine nucleotide exchange factor Rgnef (also known as ArhGEF28 or p190RhoGEF) promotes colon carcinoma cell motility and tumor progression via interaction with focal adhesion kinase (FAK). Mechanisms of Rgnef activation downstream of integrin or G protein-coupled receptors remain undefined. In the absence of a recognized G protein signaling homology domain in Rgnef, no proximal linkage to G proteins was known. Utilizing multiple methods, we have identified Rgnef as a new effector for Gα13 downstream of gastrin and the type 2 cholecystokinin receptor. In DLD-1 colon carcinoma cells depleted of Gα13, gastrin-induced FAK Tyr(P)-397 and paxillin Tyr(P)-31 phosphorylation were reduced. RhoA GTP binding and promoter activity were increased by Rgnef in combination with active Gα13. Rgnef co-immunoprecipitated with activated Gα13Q226L but not Gα12Q229L. The Rgnef C-terminal (CT, 1279-1582) region was sufficient for co-immunoprecipitation, and Rgnef-CT exogenous expression prevented Gα13-stimulated SRE activity. A domain at the C terminus of the protein close to the FAK binding domain is necessary to bind to Gα13. Point mutations of Rgnef-CT residues disrupt association with active Gα13 but not Gαq. These results show that Rgnef functions as an effector of Gα13 signaling and that this linkage may mediate FAK activation in DLD-1 colon carcinoma cells.

Different peptic ulcer bleeding risk in chronic kidney disease and end-stage renal disease patients receiving different dialysis

BACKGROUND

End stage renal disease (ESRD) patients receiving hemodialysis (HD) have a higher risk of peptic ulcer bleeding (PUB).

AIMS

Whether ESRD patients receiving peritoneal dialysis (PD) also carries a higher risk of PUB has not been studied.

METHODS

This was a cohort study using Taiwan's National Health Insurance research database, whereby 11,408 patients, including 2,239 PD, 2,328 HD, 2,267 chronic kidney disease (CKD) and 4,574 controls with age-sex matching were recruited. The log-rank test was used to analyze differences in accumulated PUB-free survival rates between groups. Cox proportional hazard regression was performed to evaluate independent risk factors for PUB in all the enrollees.

RESULTS

During the 7-year follow-up, PD and CKD patients had a significantly higher rate of PUB than matched controls. The risk of PUB between PD and CKD was not significantly different. Moreover, patients receiving HD carried a higher risk of PUB than those receiving PD, with CKD and controls (p all <0.05, by log-rank test). Cox proportional hazard regression analysis showed that CKD (HR 3.99, 95 % CI 2.24-7.13), PD (HR 3.71, 95 % CI 2.00-6.87) and HD (HR 11.96, 95 % CI 7.04-20.31) were independently associated with an increased risk of PUB. Being elderly, male, having hypertension, diabetes, cirrhosis, and nonsteroidal anti-inflammatory drugs and steroid use were other independent risk factors of PUB in all enrollees.

CONCLUSIONS

Patients with CKD and ESRD receiving PD or HD carried a higher risk for PUB. They should be screened for risk factors for PUB and receive some protective measures to prevent PUB.

Decoction vs extracts-mixed solution: effect of yiqihuoxue formula on non-alcoholic fatty liver disease in rats

OBJECTIVE

To investigate the effects on non-alcoholic fatty liver disease (NAFLD) in rats of the decoction of Yiqihuoxue formula and the solution prepared with the extracts from the individual herbal medicines of the formula.

METHODS

The rat models of NAFLD were established with high-fat diet (HFD) for 10 weeks. Thirty-two rats were randomly divided into 4 groups: the control group, the model group, the decoction group and the solution group, 8 for each group. From the 6th week, drinking water, the decoction and the solution were intragastrically administrated accordingly to the rats for 5 weeks. The pathological changes of the liver tissues were observed with Hematoxylin and eosin staining, triglyceride levels in liver tissues measured, serum alanine aminotransferase (ALT) activity measured, and serum gastrin and motilin tested.

RESULTS

Fatty degeneration and vacuole-like changes to various degrees occurred in hepatic cells of the model group. Indicators for fat metabolism, serum ALT activity and hepatic triglyceride level significantly increased, while serum gastrin and motilin levels significantly decreased. Serum ALT activity and the fatty deposition in hepatocytes were significantly reduced. In the meantime, the expressions of gastrin and motilin in the serum rose significantly in the treatment groups.

CONCLUSION

Both the decoction and the extracts-mixed solution had effect on NAFLD of protecting the liver function and reducing the fatty deposition in liver, which might be achieved by regulating the expression of gastrin and motilin.

Gastrin receptor pharmacology

C-terminally amidated gastrins act at cholecystokinin-2 receptors (CCK2R), which are normally expressed by gastric parietal and enterochromaffin-like (ECL) cells and smooth muscle; there is also extensive expression in the CNS where the main endogenous ligand is cholecystokinin. A variety of neoplasms express CCK2R, or splice variants, including neuroendocrine, pancreatic, medullary thyroid and lung cancers. Other products of the gastrin gene (progastrin, the Gly-gastrins) may stimulate cell proliferation but are not CCK2R ligands. Depending on the cell type, stimulation of CCK2R evokes secretion, increases proliferation and cell migration, inhibits apoptosis, and controls the expression of various genes. These effects are mediated by increased intracellular calcium and activation of protein kinase C, MAPkinase and other protein kinase cascades. There has been recent progress in developing CCK2R ligands that can be used for imaging tumours expressing the receptor. New antagonists have also been developed, and there is scope for using these for suppression of gastric acid and for treatment of neuroendocrine and other CCK2R-expressing tumours.

Research of influence and mechanism of combining exercise with diet control on a model of lipid metabolism rat induced by high fat diet

Objective

To investigate the influence and mechanism of combining exercise with diet control on a model of lipid metabolism rat induced by high fat diet.

Methods

Twenty-four male Wistar rats were randomly divided into 3 groups of 8: normal, model and intervention. The model group and intervention group were fed with high fat diet, while the normal group received basal feed. From day 1, the intervention group was randomly given interventions such as swimming exercise and dietary restriction. The interventions duration were 28 days. At the end of the experiment, the levels of rats’ body weight and liver weight were detected, the serum levels of total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C) and hepatic triglyceride content (TG) were detected by using biochemical assay, serum level of gastrin (GAS), motilin (MTL) were assayed by the enzyme linked immunosorbent assay (ELISA).

Results

Compared with the level of body weight and liver weight in the normal rats, body weight and liver weight in the rat of the model group were significantly increase (P<0.05 or P<0.01). Plasma concentrations of TC, LDL-C and hepatic TG in the model group were significantly increased compared with those in the normal group (P<0.05 or P<0.01). The contents of GAS, MTL, HDL-C in the model rats’plasma were significantly reduced compared with those of the normal group (P<0.05 or P<0.01). Compared with those in the model group, rats’ body weight, liver weight, serum TC, LDL-C, and TG content of liver in the intervention group decreased significantly (P<0.05 or P<0.01). Meanwhile, serum content of GAS, MTL, HDL-C were significantly improved in the intervention rats compared to the model group.

Conclusion

The action of combining exercise with diet control for lipid metabolism disorder might be related to regulation of GAS, MTL and other gastrointestinal hormones.

Distinct CCK-2 receptor conformations associated with β-arrestin-2 recruitment or phospholipase-C activation revealed by a biased antagonist

Seven-transmembrane receptors (7TMRs), also termed G protein-coupled receptors (GPCRs), form the largest class of cell surface membrane receptors, involving several hundred members in the human genome. Nearly 30% of marketed pharmacological agents target 7TMRs. 7TMRs adopt multiple conformations upon agonist binding. Biased agonists, in contrast to non-biased agonists, are believed to stabilize conformations preferentially activating either G-protein- or β-arrestin-dependent signaling pathways. However, proof that cognate conformations of receptors display structural differences within their binding site where biased agonism initiates, are still lacking. Here, we show that a non-biased agonist, cholecystokinin (CCK) induces conformational states of the CCK2R activating Gq-protein-dependent pathway (CCK2R(G)) or recruiting β-arrestin2 (CCK2R(β)) that are pharmacologically and structurally distinct. Two structurally unrelated antagonists competitively inhibited both pathways. A third ligand (GV150013X) acted as a high affinity competitive antagonist on CCK2R(G) but was nearly inefficient as inhibitor of CCK2R(β). Several structural elements on both GV150013X and in CCK2R binding cavity, which hinder binding of GV150013X only to the CCK2R(β) were identified. At last, proximity between two conserved amino acids from transmembrane helices 3 and 7 interacting through sulfur-aromatic interaction was shown to be crucial for selective stabilization of the CCK2R(β) state. These data establish structural evidence for distinct conformations of a 7TMR associated with β-arrestin-2 recruitment or G-protein coupling and validate relevance of the design of biased ligands able to selectively target each functional conformation of 7TMRs.

Inhibiting roles of berberine in gut movement of rodents are related to activation of the endogenous opioid system

Although Berberine (BER) is popular in treating gastrointestinal (GI) disorders, its mechanisms are not clear yet. In order to investigate the effects and possible mechanism of BER on GI motility in rodents, we first explored GI motility by recording the myoelectrical activity of jejunum and colon in rats, and upper GI transit with a charcoal marker in mice. Then, the plasma levels of gastrin, motilin, somatostatin and glucagon-like-peptide-1 (Glp-1) were measured by ELISA or radioimmunoassay (RIA). Furthermore, endogenous opioid-peptides (β-endorphin, dynorphin-A, met-enkephalin) were detected by RIA after treatment with BER. Our results showed that BER concentration-dependently inhibited myoelectrical activity and GI transit, which can be antagonized by opioid-receptor antagonists to different extents. The elevated somatostatin and Glp-1, and decreased gastrin and motilin in plasma, which were caused by BER application, also could be antagonized by the opioid-receptor antagonists. Additionally, plasma level of β-endorphin, but not dynorphin-A and met-enkephalin, was increased by applying BER. Taken together, these studies show that BER plays inhibiting roles on GI motility and up-regulating roles on somatostatin, Glp-1 and down-regulating roles on gastrin, motilin. The pharmacological mechanisms of BER on GI motility and plasma levels of GI hormones were discovered to be closely related to endogenous opioid system.

Gastric secretion

PURPOSE OF REVIEW

This review summarizes the past year's literature regarding the regulation of gastric exocrine and endocrine secretion, both basic science and clinical.

RECENT FINDINGS

Gastric acid secretion facilitates the digestion of protein as well as the absorption of iron, calcium, vitamin B12, and certain medications as well as prevents bacterial overgrowth, enteric infection, and possibly community-acquired pneumonia, spontaneous bacterial peritonitis, and IgE-mediated food allergy. It is regulated by neural (e.g., pituitary adenylate cyclase-activating peptide), hormonal (e.g., gastrin, ghrelin, and apelin), and paracrine (e.g., histamine) pathways as well as by chemical (e.g., amino acids) and bacterial stimuli (e.g., Helicobacter pylori). Novel peptides, which may possess physiologic function, have been identified in gastric mucosal neuroendocrine cells including parathyroid hormone-like hormone in histamine-secreting enterochromaffin-like cells and hepcidin in acid-secreting parietal cells. The secretion of hydrochloric acid by parietal cells involves translocation of the proton pump, HK-ATPase, to the apical membrane along with activation of apical chloride and potassium channels. Serum markers include chromogranin A for neuroendocrine tumors, pepsinogen I for gastric atrophy, and pepsinogen II for H. pylori infection.

SUMMARY

We continue to make progress in our understanding of the regulation of gastric acid secretion in health and disease.

Induction of gastrin expression in gastrointestinal cells by hypoxia or cobalt is independent of hypoxia-inducible factor (HIF)

Gastrin and its precursors have been shown to promote mitogenesis and angiogenesis in gastrointestinal tumors. Hypoxia stimulates tumor growth, but its effect on gastrin gene regulation has not been examined in detail. Here we have investigated the effect of hypoxia on the transcription of the gastrin gene in human gastric cancer (AGS) cells. Gastrin mRNA was measured by real-time PCR, gastrin peptides were measured by RIA, and gastrin promoter activity was measured by dual-luciferase reporter assay. Exposure to a low oxygen concentration (1%) increased gastrin mRNA concentrations in wild-type AGS cells (AGS) and in AGS cells overexpressing the gastrin receptor (AGS-cholecystokinin receptor 2) by 2.1 ± 0.4- and 4.1 ± 0.3-fold (P < 0.05), respectively. The hypoxia mimetic, cobalt chloride (300 μM), increased gastrin promoter activity in AGS cells by 2.4 ± 0.3-fold (P < 0.05), and in AGS-cholecystokinin receptor 2 cells by 4.0 ± 0.3-fold (P < 0.05), respectively. The observations that either deletion from the gastrin promoter of the putative binding sites for the transcription factor hypoxia-inducible factor 1 (HIF-1) or knockdown of either the HIF-1α or HIF-1β subunit did not affect gastrin promoter inducibility under hypoxia indicated that the hypoxic activation of the gastrin gene is likely HIF independent. Mutational analysis of previously identified Sp1 regulatory elements in the gastrin promoter also failed to abrogate the induction of promoter activity by hypoxia. The observations that hypoxia up-regulates the gastrin gene in AGS cells by HIF-independent mechanisms, and that this effect is enhanced by the presence of gastrin receptors, provide potential targets for gastrointestinal cancer therapy.