Modulatory role of phosphoinositide 3-kinase in gastric acid secretion

H2 antihistamines: May be useful for combination therapies in cancer?

Cancer morbimortality is still a great concern despite advances in research and therapies. Histamine and its receptors' ligands can modulate different biological responses according to the cell type and the receptor subtype involved. Besides the wide variety of histamine functions in normal tissues, diverse roles in the acquisition of hallmarks of cancer such as sustained proliferative signaling, resistance to cell death, angiogenesis, metastasis, altered immunity and modified microenvironment have been described. This review summarizes the present knowledge of the various roles of histamine H2 receptor (H2R) ligands in neoplasias. A bioinformatic analysis of human tumors showed dissimilar results in the expression of the H2R gene according to tumor type when comparing malignant versus normal tissues. As well, the relationship between patients' survival parameters and H2R gene expression levels also varied, signaling important divergences in the role of H2R in neoplastic progression in different cancer types. Revised experimental evidence showed multiple effects of H2R antihistamines on several of the cited hallmarks of cancer. Interventional and retrospective clinical studies evaluated different H2R antihistamines in cancer patients with two main adjuvant uses: improving antitumor efficacy (which includes regulation of immune response) and preventing toxic adverse effects produced by chemo or radiotherapy. While there is a long path to go, research on H2R antihistamines may provide new opportunities for developing more refined combination therapeutic strategies for certain cancer types to improve patients' survival and health-related quality of life.

Unique Novel Role of Adropin in a Gastric Ulcer in a Rotenone-Induced Rat Model of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, frequently associated with a gastric ulcer. We aimed to investigate the adropin neuroprotective/gastroprotective potential in the indomethacin (IND)-induced gastric ulcer in a rotenone-induced PD model. Rats were randomly divided into four groups: normal control group, rotenone/IND treated (PD /Ulcer) group, adropin treated PD/Ulcer group, and l-dopa/omeprazole (Om) treated PD/Ulcer group. There were ten rats selected for the normal control group. Striatal dopamine (DA), apoptosis/redox status, and motor/behavioral impairments were evaluated. Gastric oxidative stress, H⁺/K⁺-ATPase activity, prostaglandin E2, mucin content, and von Willebrand factor were measured. Gastric/striatal phosphatidylinositol 3-kinase (PI3K)/phosphorylated Akt and gastric vascular endothelial growth factor (VEGF)/striatal P53 immunoreactivities were checked. Striatal P53 upregulated modulator of apoptosis (Puma)/gastric vascular endothelial growth factor receptor-2 (Vegfr-2) expressions were evaluated. Adropin successfully restored striatal DA and attenuated rotenone-induced motor/behavior deficits along with strong gastroprotective potential, possibly through antioxidant activity via reduction in malondialdehyde level and upregulated superoxide dismutase, catalase activities, and serum ferric reducing antioxidant power. Adropin restored the delicate balance between the defective pro-survival PI3K/Akt/murine double minute 2 signals and apoptotic P53/Puma pathways. Adropin can be considered as a uniquely attractive therapeutic target in PD and its associated gastric ulcer.

Histamine deficiency facilitates coronary microthrombosis after myocardial infarction by increasing neutrophil-platelet interactions

Neutrophil‐platelet interactions are responsible for thrombosis as well as inflammatory responses following acute myocardial infarction (AMI). While histamine has been shown to play a crucial role in many physiological and pathological processes, its effects on neutrophil‐platelet interactions in thromboinflammatory complications of AMI remain elusive. In this study, we show a previously unknown mechanism by which neutrophil‐derived histamine protects the infarcted heart from excessive neutrophil‐platelet interactions and redundant arterial thrombosis. Using histamine‐deficient (histidine decarboxylase knockout, HDC^−/−) and wild‐type murine AMI models, we demonstrate that histamine deficiency increases the number of microthrombosis after AMI, in accordance with depressed cardiac function. Histamine‐producing myeloid cells, mainly Ly6G⁺ neutrophils, directly participate in arteriole thrombosis. Histamine deficiency elevates platelet activation and aggregation by enhancing Akt phosphorylation and leads to dysfunctional characteristics in neutrophils which was confirmed by high levels of reactive oxygen species production and CD11b expression. Furthermore, HDC^−/− platelets were shown to elicit neutrophil extracellular nucleosomes release, provoke neutrophil‐platelet interactions and promote HDC‐expressing neutrophils recruitment in arteriole thrombosis in vivo. In conclusion, we provide evidence that histamine deficiency promotes coronary microthrombosis and deteriorates cardiac function post‐AMI, which is associated with the enhanced platelets/neutrophils function and neutrophil‐platelet interactions.

HYBID (alias KIAA1199/CEMIP) and hyaluronan synthase coordinately regulate hyaluronan metabolism in histamine-stimulated skin fibroblasts

The immune-regulatory compound histamine is involved in the metabolism of the essential skin component hyaluronan (HA). We previously reported that histamine up-regulates the expression of HYBID (hyaluronan-binding protein involved in hyaluronan depolymerization, also called CEMIP or KIAA1199), which plays a key role in HA degradation. However, no information is available about histamine's effects on HA synthase (HAS) expression, the molecular sizes of HA species produced, and histamine receptors and their signaling pathways in skin fibroblasts. Moreover, histamine's effects on photoaged skin remain elusive. Here, we show that histamine increases HA degradation by up-regulating HYBID and down-regulating HAS2 in human skin fibroblasts in a dose- and time-dependent manner and thereby decreases the total amounts and sizes of newly produced HA. Histamine H1 blocker abrogated the histamine effects on HYBID up-regulation, HAS2 suppression, and HA degradation. Histamine H1 agonist exhibited effects on HA levels, composition, and breakdown similar to those of histamine. Of note, blockade of protein kinase Cδ or PI3K-Akt signaling abolished histamine-mediated HYBID stimulation and HAS2 suppression, respectively. Immunohistochemical experiments revealed a significant ∼2-fold increase in tryptase-positive mast cells in photoaged skin, where HYBID and HAS2 expression levels were increased and decreased, respectively, compared with photoprotected skin. These results indicate that histamine controls HA metabolism by up-regulating HYBID and down-regulating HAS2 via distinct signaling pathways downstream of histamine receptor H1. They further suggest that histamine may contribute to photoaged skin damage by skewing HA metabolism toward degradation.

Gastric Acid Secretion from Parietal Cells Is Mediated by a Ca2+ Efflux Channel in the Tubulovesicle

Gastric acid secretion by parietal cells requires trafficking and exocytosis of H/K-ATPase-rich tubulovesicles (TVs) toward apical membranes in response to histamine stimulation via cyclic AMP elevation. Here, we found that TRPML1 (ML1), a protein that is mutated in type IV mucolipidosis (ML-IV), is a tubulovesicular channel essential for TV exocytosis and acid secretion. Whereas ML-IV patients are reportedly achlorhydric, transgenic overexpression of ML1 in mouse parietal cells induced constitutive acid secretion. Gastric acid secretion was blocked and stimulated by ML1 inhibitors and agonists, respectively. Organelle-targeted Ca²⁺ imaging and direct patch-clamping of apical vacuolar membranes revealed that ML1 mediates a PKA-activated conductance on TV membranes that is required for histamine-induced Ca²⁺ release from TV stores. Hence, we demonstrated that ML1, acting as a Ca²⁺ channel in TVs, links transmitter-initiated cyclic nucleotide signaling with Ca²⁺-dependent TV exocytosis in parietal cells, providing a regulatory mechanism that could be targeted to manage acid-related gastric diseases.

Current Knowledge and Perspectives on Histamine H1 and H2 Receptor Pharmacology: Functional Selectivity, Receptor Crosstalk, and Repositioning of Classic Histaminergic Ligands

H1 and H2 histamine receptor antagonists, although developed many decades ago, are still effective for the treatment of allergic and gastric acid-related conditions. This article focuses on novel aspects of the pharmacology and molecular mechanisms of histamine receptors that should be contemplated for optimizing current therapies, repositioning histaminergic ligands for new therapeutic uses, or even including agonists of the histaminergic system in the treatment of different pathologies such as leukemia or neurodegenerative disorders. In recent years, new signaling phenomena related to H1 and H2 receptors have been described that make them suitable for novel therapeutic approaches. Crosstalk between histamine receptors and other membrane or nuclear receptors can be envisaged as a way to modulate other signaling pathways and to potentiate the efficacy of drugs acting on different receptors. Likewise, biased signaling at histamine receptors seems to be a pharmacological feature that can be exploited to investigate nontraditional therapeutic uses for H1 and H2 biased agonists in malignancies such as acute myeloid leukemia and to avoid undesired side effects when used in standard treatments. It is hoped that the molecular mechanisms discussed in this review contribute to a better understanding of the different aspects involved in histamine receptor pharmacology, which in turn will contribute to increased drug efficacy, avoidance of adverse effects, or repositioning of histaminergic ligands.

PI3K pathway is involved in ERK signaling cascade activation by histamine H2R agonist in HEK293T cells

BACKGROUND

Histamine, through histamine H2 receptor (H2R), modulates different biological processes, involving the modulation of PI3K/AKT/mTOR and RAS/RAF/MEK/ERK pathways. Many evidences have demonstrated the existence and importance of the crossregulation between these two signaling pathways. The aim of the present work was to determine the molecular mechanisms leading to PI3K and ERK pathways modulation induced by the H2R agonist amthamine and to evaluate the possible interplay between them.

METHODS

Phosphorylation levels of ERK and Akt were examined by Western blot in HEK293T cells expressing the human H2R, in the presence of H2R agonist and dominant negative mutants or pharmacological inhibitors of different proteins/pathways. Transcriptional activity assays were assessed to determine SRE activity. Amthamine-mediated cellular proliferation was investigated in MA-10A cells in the presence of PI3K inhibitor.

RESULTS

H2R agonist inhibits PI3K/Akt/mTOR and stimulates Ras/MEK/ERK pathways. Moreover, PI3K/Akt/mTOR signaling inhibition is necessary to achieve H2R mediated ERK activation. In the presence of a constitutive active mutant of Akt, amthamine is not able to mediate ERK activation. This crosstalk affects classical ERK downstream targets such as Elk1 phosphorylation and the transcriptional activity of the SRE, classically associated to proliferation. We further demonstrate that amthamine-induced proliferation in Leydig MA-10 tumor cells, is enhanced by LY294002, a PI3K inhibitor.

CONCLUSIONS

These results describe a crosstalk between PI3K/AKT/mTOR and Ras/MEK/ERK pathways induced by H2R stimulation with implications in cell proliferation.

GENERAL SIGNIFICANCE

This work indicates that the modulation of PI3K/AKT/mTOR pathway by H2R in turn regulates Ras/MEK/ERK activation conditioning the proliferative capacity of the cells.

TRIM50 protein regulates vesicular trafficking for acid secretion in gastric parietal cells

Of the TRIM/RBCC family proteins taking part in a variety of cellular processes, TRIM50 is a stomach-specific member with no defined biological function. Our biochemical data demonstrated that TRIM50 is specifically expressed in gastric parietal cells and is predominantly localized in the tubulovesicular and canalicular membranes. In cultured cells ectopically expressing GFP-TRIM50, confocal microscopic imaging revealed dynamic movement of TRIM50-associated vesicles in a phosphoinositide 3-kinase-dependent manner. A protein overlay assay detected preferential binding of the PRY-SPRY domain from the TRIM50 C-terminal region to phosphatidylinositol species, suggesting that TRIM50 is involved in vesicular dynamics by sensing the phosphorylated state of phosphoinositol lipids. Trim50 knock-out mice retained normal histology in the gastric mucosa but exhibited impaired secretion of gastric acid. In response to histamine, Trim50 knock-out parietal cells generated deranged canaliculi, swollen microvilli lacking actin filaments, and excess multilamellar membrane complexes. Therefore, TRIM50 seems to play an essential role in tubulovesicular dynamics, promoting the formation of sophisticated canaliculi and microvilli during acid secretion in parietal cells.

Regulation of the immune response and inflammation by histamine and histamine receptors

Histamine is a biogenic amine with extensive effects on many cell types, including important immunologic cells, such as antigen-presenting cells, natural killer cells, epithelial cells, and T and B lymphocytes. Histamine and its 4 receptors represent a complex system of immunoregulation with distinct effects dependent on receptor subtypes and their differential expression. These are influenced by the stage of cell differentiation, as well as microenvironmental influences, leading to the selective recruitment of effector cells into tissue sites accompanied by effects on cellular maturation, activation, polarization, and effector functions, which lead to tolerogenic or proinflammatory responses. In this review we discuss the regulation of histamine secretion, receptor expression, and differential activation of cells within both the innate and adaptive immune responses. It is clear that the effects of histamine on immune homeostasis are dependent on the expression and activity of the 4 currently known histamine receptors, and we also recognize that 100 years after the original identification of this biogenic amine, we still do not fully understand the complex regulatory interactions between histamine and the host immune response to everyday microbial and environmental challenges.

Regulation of gastric acid secretion by the serum and glucocorticoid inducible kinase isoform SGK3

BACKGROUND

The serum and glucocorticoid inducible kinase isoform SGK3 is ubiquitously expressed and has been shown to participate in the regulation of cell survival and transport. Similar to SGK1 and protein kinase B (PKB/Akt) isoforms, SGK3 may phosphorylate glycogen synthase kinase (GSK) 3α,β, which has recently been shown to participate in the regulation of basal gastric acid secretion. The present study thus explored the role of SGK3 in the regulation of gastric acid secretion.

METHODS

Experiments were performed in isolated glands from gene-targeted mice lacking functional SGK3 (sgk3-/-) or from their wild-type littermates (sgk3+/+). Utilizing 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester (BCECF) fluorescence, gastric acid secretion was determined from Na(+)-independent pH recovery (∆pH/min) following an ammonium pulse, which reflects H+/K+ adenosine triphosphatase (ATP) ase activity.

RESULTS

Cytosolic pH in isolated gastric glands was similar in sgk3-/- and sgk3+/+ mice. ∆pH/min was, however, significantly larger in sgk3-/- than in sgk3+/+ mice. In both genotypes, ∆pH/min was virtually abolished in the presence of the H(+)/K(+) ATPase inhibitor omeprazole (100 μM) and SCH28080 (500 nM). Increase of extracellular K+ concentrations to 35 mM (replacing Na+/NMDG) or treatment with 5 μM forskolin increased ∆pH/min in sgk3+/+ mice to a larger extent than in sgk3-/- mice and abrogated the differences between genotypes. The protein kinase A inhibitor H89 (150 nM) decreased ∆pH/min to similarly low values in both genotypes.

CONCLUSIONS

SGK3 suppresses gastric acid secretion, an effect presumably mediated by the stimulation of protein kinase A with the subsequent activation of K+ channels.

Histamine effect on melanocyte proliferation and vitiliginous keratinocyte survival

Repigmention of vitiligo requires melanocyte proliferation and migration. Keratinocytes have been shown to play a role in this process. Data from this laboratory showed that bee venom (BV) stimulated melanocyte proliferation and migration as well as melanogenesis. As histamine release is associated with BV, its effect on melanocyte proliferation and migration was examined. Cultured normal human melanocytes treated with histamine were studied with and without receptor-specific antagonists or agonists. The effect of histamine on vitiliginous keratinocytes, in cultured cells treated with a PI3K inhibitor in the presence of TNF-α, was also examined. Histamine exerted a more significant effect on melanocyte proliferation than on melanogenesis. This occurred through the H2 receptor with complex signalling to ERK, CREB, and Akt activation, which stimulated melanocyte migration. Histamine and the H2 receptor agonist also increased survival of vitiliginous, but not normal, keratinocytes, with NF-κB activation. Because expression levels of the H2 receptor was significantly decreased in depigmented compared to normally pigmented epidermis, in patients with vitiligo, histamine may increase the survival of vitiliginous keratinocytes. Overall, histamine stimulated the proliferation and migration of melanocytes and the vitiliginous keratinocyte survival, providing the basis for novel therapeutic approaches to vitiligo repigmentation.

Regulation of basal gastric acid secretion by the glycogen synthase kinase GSK3

BACKGROUND

According to previous observations, basal gastric acid secretion is downregulated by phosphoinositol-3-(PI3)-kinase, phosphoinositide-dependent kinase (PDK1), and protein kinase B (PKBβ/Akt2) signaling. PKB/Akt phosphorylates glycogen synthase kinase GSK3. The present study explored whether PKB/Akt-dependent GSK3-phosphorylation modifies gastric acid secretion.

METHODS

Utilizing 2',7'-bis-(carboxyethyl)-5(6')-carboxyfluorescein (BCECF)-fluorescence, basal gastric acid secretion was determined from Na(+)-independent pH recovery (∆pH/min) following an ammonium pulse, which reflects H(+)/K(+)-ATPase activity. Experiments were performed in gastric glands from gene-targeted mice (gsk3 ( KI )) with PKB/serum and glucocorticoid-inducible kinase (SGK)-insensitive GSKα,β, in which the serines within the PKB/SGK phosphorylation site were replaced by alanine (GSK3α(21A/21A), GSK3β(9A/9A)).

RESULTS

The cytosolic pH in isolated gastric glands was similar in gsk3 ( KI ) and their wild-type littermates (gsk3 ( WT )). However, ∆pH/min was significantly larger in gsk3 ( KI ) than in gsk3 ( WT ) mice and ∆pH/min was virtually abolished by the H(+)/K(+)-ATPase inhibitor omeprazole (100 μM) in gastric glands from both gsk3 ( KI ) and gsk3 ( WT ). Plasma gastrin levels were lower in gsk3 ( KI ) than in gsk3 ( WT ). Both, an increase of extracellular K(+) concentration to 35 mM [replacing Na(+)/N-methyl-D: -glucamine (NMDG)] and treatment with forskolin (5 μM), significantly increased ∆pH/min to virtually the same value in both genotypes. The protein kinase A (PKA) inhibitor H89 (150 nM) and the H(2)-receptor antagonist ranitidine (100 μM) decreased ∆pH/min in gsk3 ( KI ) but not gsk3 ( WT ) and again abrogated the differences between the genotypes. The protein abundance of phosphorylated but not of total PKA was significantly larger in gsk3 ( KI ) than in gsk3 ( WT ).

CONCLUSIONS

Basal gastric acid secretion is enhanced by the disruption of PKB/SGK-dependent phosphorylation and the inhibition of GSK3. Thus, the inhibition of GSK3 participates in the signaling of PI3-kinase-dependent downregulation of basal gastric acid secretion.

Regulation of gastric acid secretion by PKB/Akt2

Pharmacological inhibition of phosphoinositol 3 kinase (PI3K) and partial deficiency of phosphoinositide dependent kinase PDK1 have previously been shown to enhance basal gastric acid secretion. PI3K/PDK1 dependent signaling involves activation of protein kinase B/Akt, which may thus be similarly involved in the regulation of gastric acid secretion. To test that hypothesis, gastric acid secretion was determined in isolated glands from gene targeted mice lacking functional Akt2 (akt2(-/-)) or from their wild type littermates (akt2(+/+)). According to BCECF-fluorescence cytosolic pH in isolated gastric glands was similar in akt2(-/-) and akt2(+/+) mice. Na(+)-independent pH recovery (DeltapH/min) following an ammonium pulse, a measure of H(+)/K(+) ATPase activity, was, however, significantly faster in akt2(-/-) than in akt2(+/+) mice. In both genotypes, DeltapH/min was virtually abolished by H(+)/K(+) ATPase inhibitor omeprazole (100 muM). Increase of extracellular K(+) concentrations to 35 mM (replacing Na(+)) increased DeltapH/min to a significantly larger extent in akt2(+/+) than in akt2(-/-) mice and dissipated the differences between the genotypes. Similarly, treatment with 5 muM forskolin enhanced DeltapH/min significantly only in akt2(+/+) mice and abolished the differences between the genotypes. Conversely, protein kinase A inhibitor H89 (50 nM) decreased DeltapH/min to similarly low values in both genotypes. In conclusion, Akt2 suppresses gastric acid secretion and contributes to or even accounts for the inhibition of gastric acid secretion by PI3K.

Activity-guided fractionation to characterize a coffee beverage that effectively down-regulates mechanisms of gastric acid secretion as compared to regular coffee

In some individuals, the consumption of coffee beverages is related to symptoms of gastric irritation. Hot water steam-treatment of raw coffee beans is hypothesized to reduce the contents of stomach irritating compounds, and products to which this technology is applied are launched as stomach-friendly coffee. However, data on the effect of steam-treated coffee on gastric acid secretion are conflicting and it has not been proven yet as to which coffee components act as pro- or antisecretory stimulants. The work presented here aimed at the characterization of a coffee beverage that effectively down-regulates mechanisms of proton secretion in human gastric cells (HGT-1). At first, a regular coffee beverage was fractionated by using solvents of different polarity: water, ethylacetate, dichloromethane, and pentane. Functional assays on the proton secretory activity (PSA) of these solvent fractions revealed the least pronounced effect for the water fraction, for which quantitative analyses demonstrated the highest distribution of chlorogenic acid (95%), (beta)N-alkanoyl-5-hydroxytryptamides (55%), and N-methylpyridinium (N-MP, >99%) among all fractions. Following experiments demonstrated that HGT-1 cells treated with regular coffee fortified with N-MP at a concentration of about 20 mg/mL N-MP showed a significantly decreased PSA as compared to cells which were exposed to coffee beverages containing higher (32-34 mg/L) or lower (5 mg/L) N-MP concentrations. Results from cellular pathway analyses of transcription (ATF-1 and Akt1) and signaling (cAMP and EGFr) factors and kinases (ERK1/2), and experiments on the gene expression of pro (histamine-HRH2 and acetylcholine-CHRM3)- and anti (somatostatin-SSTR1)-secretory receptors and H(+),K(+)-ATPase verified this antisecretory activity of N-MP in coffee beverages.

The gastric mucosa development and differentiation

The development and differentiation of the gastric mucosa are controlled by a complex interplay of signaling proteins and transcriptional regulators. This process is complicated by the fact that the stomach is derived from two germ layers, the endoderm and the mesoderm, with the first giving rise to the mature epithelium and the latter contributing the smooth muscle required for peristalsis. Reciprocal epithelial-mesenchymal interactions dictate the formation of the stomach during fetal development, and also contribute to its continuous regeneration and differentiation throughout adult life. In this chapter, we discuss the discoveries that have been made in different model systems, from zebrafish to human, which show that the Hedgehog, Wnt, Notch, bone morphogenetic protein, and fibroblast growth factor (FGF) signaling systems play essential roles during various stages of stomach development.

Strain-induced proliferation requires the phosphatidylinositol 3-kinase/AKT/glycogen synthase kinase pathway

The intestinal epithelium is repetitively deformed by shear, peristalsis, and villous motility. Such repetitive deformation stimulates the proliferation of intestinal epithelial cells on collagen or laminin substrates via ERK, but the upstream mediators of this effect are poorly understood. We hypothesized that the phosphatidylinositol 3-kinase (PI3K)/AKT cascade mediates this mitogenic effect. PI3K, AKT, and glycogen synthase kinase-3beta (GSK-3beta) were phosphorylated by 10 cycles/min strain at an average 10% deformation, and pharmacologic blockade of these molecules or reduction by small interfering RNA (siRNA) prevented the mitogenic effect of strain in Caco-2 or IEC-6 intestinal epithelial cells. Strain MAPK activation required PI3K but not AKT. AKT isoform-specific siRNA transfection demonstrated that AKT2 but not AKT1 is required for GSK-3beta phosphorylation and the strain mitogenic effect. Furthermore, overexpression of AKT1 or an AKT chimera including the PH domain and hinge region of AKT2 and the catalytic domain and C-tail of AKT1 prevented strain activation of GSK-3beta, but overexpression of AKT2 or a chimera including the PH domain and hinge region of AKT1 and the catalytic domain and C-tail of AKT2 did not. These data delineate a role for PI3K, AKT2, and GSK-3beta in the mitogenic effect of strain. PI3K is required for both ERK and AKT2 activation, whereas AKT2 is sequentially required for GSK-3beta. Furthermore, AKT2 specificity requires its catalytic domain and tail region. Manipulating this pathway may prevent mucosal atrophy and maintain the mucosal barrier in conditions such as ileus, sepsis, and prolonged fasting when peristalsis and villous motility are decreased and the mucosal barrier fails.

Gastric secretion

PURPOSE OF REVIEW

This review summarizes the past year's literature regarding the regulation and assessment of gastric acid secretion.

RECENT FINDINGS

Gastric acid secretion is regulated by biologic agents produced and released by enteroendocrine cells and neurons as well as by exogenously administered substances and infection. Too much acid can lead to gastroesophageal reflux disease, peptic ulcer disease, and stress-related erosion/ulcer disease. Too little acid can interfere with the absorption of certain nutrients, predispose to enteric infection, and interfere with the absorption of some medications. Gastrin, histamine, gastrin-releasing peptide, ghrelin, orexin, and glucocorticoids stimulate whereas leptin, glucagon-like peptide 1, and Helicobacter pylori inhibit acid secretion. Helicobacter pylori inhibits the transcriptional activity of HK-ATPase, the proton pump of the parietal cell.

SUMMARY

A better understanding of the pathways and mechanisms regulating gastric acid secretion should lead to improved management of patients with acid-induced disorders as well as those who secrete too little acid.