Evaluation of the trophic effect of longterm treatment with the histamine H2 receptor antagonist loxtidine on rat oxyntic mucosa by differential counting of dispersed cells

Correct Identification of Cell of Origin May Explain Many Aspects of Cancer: The Role of Neuroendocrine Cells as Exemplified from the Stomach

Cancers are believed to originate from stem cells. Previously, the hypothesis was that tumors developed due to dedifferentiation of mature cells. We studied the regulation of gastric acid secretion and showed that gastrin through the gastrin receptor stimulates enterochromaffin-like (ECL) cell histamine release and proliferation. In animal and human studies, we and others showed that long-term hypergastrinemia results in ECL cell-derived tumor through a sequence of hyperplasia, dysplasia, neuroendocrine tumors (NETs), and possibly neuroendocrine carcinomas (NECs) and adenocarcinomas of diffuse type. Perhaps, other cancers may also have their origin in differentiated cells. Knowledge of the growth regulation of the cell of origin is important in cancer prophylaxis and treatment. Physiology plays a central role in carcinogenesis through hormones and other growth factors. Every cell division implies a small risk of mutation; thus mitogens are also mutagens. Moreover, metastasis of slow proliferating cells may also explain so-called tumor dormancy and late recurrence.

Influence of HRH2 promoter polymorphism on aberrant DNA methylation of DAPK and CDH1 in the gastric epithelium

BACKGROUND

Aberrant methylation patterns in CpG island are known to be influential in gene silencing. Histamine plays important physiological roles in the upper gastrointestinal tract and acts via the H2 receptor. We report an investigation into the effect of HRH2 promoter polymorphism (rs2607474 G > A) on the methylation of DAPK and CDH1.

METHODS

Non cancerous gastric mucosa samples were obtained from 115 subjects with gastric cancer (GC) and 412 non-cancer subjects (non-GC). Methylation status of genes was determined by MSP. The genotyping of rs2607474 was performed by PCR-SSCP.

RESULTS

Methylation of DAPK and CDH1 was observed in 296 and 246 subjects, respectively. The frequency of CDH1 methylation in the subjects with GC was significantly lower in cancer lesion than in non cancerous mucosa, whereas that of DAPK methylation was not different. The allelic distribution of rs2607474 was 401GG, 119GA and 7AA. The GG homozygote was associated with a significantly increased risk for methylation of both DAPK and CDH1 (p < 0.0001 and p = 0.0009, respectively). In the non-GC subjects or more than 60 years of age, GG homozygote was more closely associated with both DAPK and CDH1 methylation. However, this genotype did not show an increased risk for the development of methylation of both genes in patients with GC. In H. pylori negative subjects, GG homozygote showed an increased risk for the methylation of both DAPK and CDH1 (p = 0.0074 and p = 0.0016, respectively), whereas this genotype was associated with an increased risk for the development of DAPK methylation in H. pylori positive subjects (p = 0.0018). In addition, in subjects older than 60 years of age, atrophy and metaplasia scores were significantly higher in the GG homozygote (p = 0.011 and p = 0.039, respectively) and a significant correlation was observed between age and atrophy or metaplasia.

CONCLUSIONS

Our results suggest that rs2607474 GG homozygote confers a significantly increased risk for age- and inflammation-related DAPK and CDH1 methylation.

Association between common genetic variant of HRH2 and gastric cancer risk

Histamine plays important physiological roles in the upper gastrointestinal tract and acts via the H2 receptor. The -1018 G>A (rs2067474) in an enhancer element of the promoter and non-synonymous rs79385261 (Asn46Thr) were identified in HRH2. We attempted to clarify the associations of these polymorphisms with gastric carcinogenesis. The study was performed in 321 patients with gastric cancer and 599 subjects with no evidence of gastric malignancies on upper gastroduodenal endoscopy. The genotypes were determined using a one-tube multiplex PCR-SSCP method. The degree of gastritis was assessed in 496 subjects and serum pepsinogen (PG) I/II levels were measured in 124 subjects without gastric cancer. The minor allele of Asn46Thr could not be detected. The frequencies of the -1018 A allele in the non-GC and GC groups were 13.5% and 8.26%, respectively (p=0.00077). Overall, -1018 GG homozygotes had an increased risk for developing gastric cancer (OR 1.68; 95% CI 1.17-2.42; p=0.0052), especially intestinal type cancer (OR 1.94; 95% CI 1.23-3.08; p=0.0047). In subjects aged >60 years, the adjusted risk for gastric cancer among individuals who were -1018 GG homozygotes was 1.87 (range 1.19-2.93; p=0.0065) compared with A carriers. In the gastric cancer cases located in the antrum and at comparative advanced stage, -1018 GG homozygosity was a significantly increased risk factor. In subjects >60 years, the metaplasia score was significantly higher in -1018 GG homozygotes than A carriers. Both atrophy and metaplasia scores were significantly increased with age only in -1018 GG homozygotes. The PG I/II ratio was significantly decreased in H. pylori positive GG homozygotes than negative GG homozygotes and positive A carriers. Our results suggest that -1018 GG homozygosity of HRH2 may be associated with the severity of gastric mucosal atrophy. This genotype has an increased risk for the subsequent development of gastric cancer, especially intestinal type, at advanced age.

Synergistic inhibitory effects of gastrin and histamine receptor antagonists on Helicobacter-induced gastric cancer

BACKGROUND & AIMS

Apart from its importance as an acid secretogogue, the role of histamine as a downstream target of gastrin has not been fully explored. Previous studies have shown that the combination of hypergastrinemia and Helicobacter infection resulted in accelerated gastric cancer in mice. We used this model to examine the role of cholecystokinin 2 (CCK2)/gastrin receptor and histamine H2-receptor signaling in the development of gastric atrophy and cancer.

METHODS

Male hypergastrinemic mice (INS-GAS mice) were infected with Helicobacter felis and given the CCK2/gastrin receptor antagonist YF476 and/or the histamine H2-receptor antagonist loxtidine for 3 or 6 months. In addition, mice were treated with omeprazole alone or in combination with either YF476 or loxtidine for 3 months.

RESULTS

Mice treated with YF476 or loxtidine alone showed partial suppression of both gastric acid secretion and progression to neoplasia. The combination of YF476 plus loxtidine treatment resulted in nearly complete inhibition of both parameters. YF476 and/or loxtidine treatment did not alter the overall level of H. felis colonization but did result in significant down-regulation of the growth factors regenerating gene I and amphiregulin. Loxtidine treatment, with or without YF476, induced a mild shift in T-helper cell polarization. In contrast, omeprazole treatment resulted in mild progression of gastric hyperplasia/dysplasia, which was ameliorated by the addition of YF476 or loxtidine.

CONCLUSIONS

The combination of CCK2/gastrin- and histamine H2-receptor antagonists has synergistic inhibitory effects on development of gastric atrophy and cancer in H. felis/INS-GAS mice, while the proton pump inhibitor showed no such effects. These results support an important role for the gastrin-histamine axis in Helicobacter-induced gastric carcinogenesis.

Ligands for histamine H(3) receptors modulate cell proliferation and migration in rat oxyntic mucosa

1. (R)-alpha-methylhistamine, a selective agonist of histamine H(3) receptors, promotes mucus secretion and increases the number and volume of mucus-secreting cells. The hypothesis that the increased number of mucous cells could reside in an alteration of homeostasis in the gastric epithelium was investigated. 2. (R)-alpha-methylhistamine was administered to rats 1 h (10-100 mg kg(-1) by intragastric and by intraperitoneal route) and 24 h (100 mg kg(-1) by intragastric route) prior to killing. The (S)-isomer of alpha-methylhistamine (55.4 mg kg(-1)), 100 times less potent than the (R)-isomer at H(3) receptors, and the H(3)-receptor agonist FUB 407 (9.14-91.35 mg kg(-1)) were intragrastically administered 1 h prior to killing. The H(1)-receptor antagonist mepyramine (30 mg kg(-1)), the H(2)-receptor antagonist famotidine (3 mg kg(-1)), and the H(3)-receptor antagonists ciproxifan (3 mg kg(-1)) and clobenpropit (30 mg kg(-1)) were intragastrically administered 30 min before (R)-alpha-methylhistamine. Gastric tissue was processed for histology and immunohistochemistry. 3. Within 1 h, (R)-alpha-methylhistamine and FUB 407 dose-dependently increased the number of BrdU-positive cells and of apoptotic cells. (S)-alpha-methylhistamine failed to modify proliferation and apoptosis. The increase in proliferation by (R)-alpha-methylhistamine was reversed by ciproxifan and clobenpropit, but not by mepyramine and famotidine. 4. (R)-alpha-methylhistamine accelerated the differentiation towards pit cells and their outward migration 24 h after its administration. These effects were counteracted by ciproxifan. The apoptosis rate was unaffected at 24 h. 5. These findings reveal a primary role of histamine H(3)-receptor ligands in modulating cell proliferation and migration in rat fundic mucosa.

Gastrin has a specific proliferative effect on the rat enterochromaffin-like cell, but not on the parietal cell: a study by elutriation centrifugation

Gastrin has a general growth-promoting effect on gastric oxyntic mucosa, and a more pronounced one on the enterochromaffin-like (ECL) cell. Whether gastrin has a proliferative effect on the parietal cell lineage beyond the general effect is uncertain. Hypergastrinaemia was evoked in rats using pantoprazole (group II: 100 micromol kg-1, group III: 400 micromol kg-1) for 45 days. Plasma gastrin was 43 +/- 8 pmol L-1 (control), 283 +/- 54 pmol L-1 (group II) and 577 +/- 63 pmol L-1 (group III). Gastric mucosal cells were isolated and fractionated by elutriation centrifugation. Total cell number, percentage and number of ECL and parietal cells, and histamine were determined in each fraction. The number of mucosal cells increased 1.5-fold in both hypergastrinaemic groups. Enterochromaffin-like cell content was 2.6 +/- 0.5% (control), 6.0 +/- 0.6% (group II) and 9.0 +/- 0.8% (group III). Histamine concentration in oxyntic mucosal cells rose similarly. The size of the ECL cells was 8.5 +/- 0.1 microm (control), 10.8 +/- 0.2 microm (group II) and 12.1 +/- 0.2 microm (group III), and the increased size was confirmed by shifted distribution in elutriation fractions. Histamine per ECL cell increased with cell size. The number of parietal cells increased parallel to the total number of mucosal cells (1.5-fold). Parietal cell size and percentage, assessed by image analysis and distribution in elutriation fractions, were unchanged after pantoprazole dosing. Gastrin has a pronounced, concentration-dependent specific trophic effect on ECL cells and a general proliferative effect on gastric mucosa, including parietal cells.

Up-regulation of H2 receptor and adenylate cyclase in rabbit parietal cells during prolonged treatment with H2-receptor antagonists

Intragastric hyperacidity occurs after abrupt withdrawal of histamine H2-receptor antagonists, and the prolonged administration of these agents induces tachyphylaxis of the inhibitory effects on gastric acid secretion. We examined the effect of the prolonged administration of H2-receptor antagonists on the H2-receptor signaling system in parietal cells isolated from rabbits that had received H2-receptor antagonists for 14 days. [125I]aminopotentidine (APT) binding sites to H2 receptors in parietal cell membranes were increased without any significant change in the affinity for [125I]APT. The expression of Gs(alpha), guanosine triphosphate (GTP)-binding protein coupled to H2 receptor, was slightly increased. Basal as well as GTP- or histamine-stimulated cAMP production was increased, but no significant change was observed in the presence of an H2-receptor antagonist. The up-regulation of the H2 receptor and adenylate cyclase appeared to cause hypersecretion of acid after withdrawal of H2-receptor blockade.

Effect of Tityus serrulatus scorpion toxin on serum gastrin levels in anaesthetized rat

Scorpion toxin induces gastric secretion of acid and pepsin in rats. These effects seem to be mediated by the release of acetylcholine and histamine. However, the role of gastrin in the scorpion-toxin-induced gastric secretion is unknown. We describe the effects of the T1 fraction purified from Tityus serrulatus scorpion venom on serum and on antral tissue gastrin levels in anaesthetized rats. Gastrin levels in serum and in the antral mucosa were measured before and at intervals 5, 15, 30, 60, 90 up to 120 min after the intravenous injection of saline or the T1 fraction of scorpion venom (0.25 mg/kg) into anaesthetized rats. Antral G-cells were submitted to immunocytochemistry and electron microscopy. The data on gastrin were correlated with the gastric juice volume, and the acid and pepsin output increases induced by toxin. Scorpion toxin induced a significant increase in volume, acid output and pepsin output of gastric juice and gastrin serum levels 15-60 min after injection. Simultaneous measurements of antral gastrin levels did not show significant effects. The number of dense, intermediate and empty granules per microm(2) in the cytoplasm of antral G-cells was not significantly changed 60 min after saline or toxin injection. Scorpion toxin significantly increased serum gastrin; levels in rats.

The negative charge of glutamic acid-820 in the gastric H+,K+-ATPase alpha-subunit is essential for K+ activation of the enzyme activity

To investigate the role of Glu820, located in transmembrane domain M6 of the alpha-subunit of gastric H+,K+-ATPase, a number of mutants was prepared and expressed in Sf9 cells using a baculovirus encoding for both H+,K+-ATPase subunits. The wild-type enzyme and the E820D (Glu820-->Asp) mutant showed a similar biphasic activation by K+ on the ATPase activity (maximum at 1 mM). The mutant E820A had a markedly decreased K+ affinity (maximum at 40-100 mM). The other mutants, E820Q, E820N, E820L and E820K, showed no K+-activated ATPase activity at all, whereas all mutants formed a phosphorylated intermediate. After preincubation with K+ before phosphorylation mutant E820D showed a similar K+-sensitivity as the wild-type enzyme. The mutants E820N and E820Q had a 10-20 times lower sensitivity, whereas the other three mutants were hardly sensitive towards K+. Upon preincubation with 3-(cyanomethyl)-2-methyl-8-(phenylmethoxy) imidazo [1,2a]-pyridine (SCH28080), all mutants showed similar sensitivity for this drug as the wild-type enzyme, except mutant E820Q, which could only partly be inhibited, and mutant E820K, which was completely insensitive towards SCH28080. These experiments suggest that, with a relatively large residue at position 820, the binding of SCH28080 is obstructed. The various mutants showed a behaviour in K+-stimulated-dephosphorylation experiments similar to that for K+-activated-ATPase-activity measurements. These results indicate that K+ binding, and indirectly the transition to the E2 form, is only fully possible when a negatively charged residue is present at position 820 in the alpha-subunit.

Activation of the human histamine H2 receptor is linked to cell proliferation and c-fos gene transcription

We examined whether histamine could regulate cell proliferation and expression of the early response gene c-fos in HEK-293 cells stably transfected with the human H2 receptor (HEK-H2). Histamine stimulated [3H]thymidine incorporation [50% effective concentration (EC50) = 3.6 x 10(-6) M] in HEK-H2 cells in a cimetidine-sensitive manner and increased c-fos mRNA in a time-dependent fashion, reaching maximal induction after 30 min. Histamine induced luciferase activity in HEK-H2 cells transiently transfected with a construct containing the luciferase reporter gene (Luc) coupled to the serum response element (SRE) of the c-fos gene promoter (EC50 = 1.5 x 10(-6) M) or a plasmid containing the SRE core fragment (bases -320 to -298). The protein kinase C (PKC) inhibitor staurosporine and long-term pretreatment of HEK cells with phorbol ester inhibited the effect of histamine on PKC activation, SRE-Luc activity, and [3H]thymidine incorporation. We have demonstrated that activation of the human H2 receptor can lead to induction of c-fos gene transcription and cell proliferation through a PKC-dependent mechanism.

Novel insights into histamine H2 receptor biology

Histamine exerts multiple biological actions through one of three receptor subtypes (H1, H2, and H3). This review focuses on new developments regarding the structure and function of the H2 receptor. In addition to the important role this receptor plays in stimulating gastric acid secretion, recent studies have demonstrated that it is also involved in regulating gastrointestinal motility and intestinal secretion. The potential role of the H2 receptor in regulating cell growth and differentiation has also been added to the list of actions this biogenic amine may exert in both normal and transformed tissues. Molecular cloning of the gene indicates that it has the structural characteristics of a heptahelical G protein-linked receptor. Site-directed mutagenesis studies of this receptor reveal the presence of key amino acids within the third and fifth transmembrane domains that are critical for ligand recognition. Molecular approaches have also shed light on the structural components of the H2 receptor important in regulating desensitization and internalization. Although the H2 receptor was classically thought to couple to the adenylate cyclase pathway, recent work with the cloned receptor indicates that it can also activate the phosphoinositide signaling cascade through an independent G protein-dependent mechanism. The novel observation that histamine may stimulate c-fos gene expression lends further support to the possible role of this receptor in regulating cell growth and differentiation.

Glycosylation is essential for biosynthesis of functional gastric H+,K+-ATPase in insect cells

The role of N-linked glycosylation in the functional properties of gastric H+,K+-ATPase has been examined with tunicamycin and I-deoxymannojirimycin, inhibitors in glycoprotein biosynthesis and glycoprotein processing respectively. Tunicamycin completely abolished both K+-stimulated and 3-(cyanomethyl)-2-methyl-8-(phenylmethoxy)-imidazo[1,2a]pyridine (SCH 28080)-sensitive ATPase activity and SCH 28080-sensitive phosphorylation capacity. The expression level of both H+,K+-ATPase subunits remained unaffected. 1-Deoxymannojirimycin clearly affected the structure of the N-linked oligosaccharide moieties without affecting specific phosphorylation capacity. Purification of the functional recombinant enzyme from non-functional H+,K+-ATPase subunits coincided with purification of glycosylated beta-subunits and not of non-glycosylated beta-subunits. Transport of the H+,K+-ATPase beta-subunit to the plasma membrane but not its ability to assemble with the alpha-subunit dependent on N-glycosylation events. We conclude that the acquisition, but not the exact structure, of N-linked oligosaccharide moieties, is essential for biosynthesis of functional gastric H+,K+-ATPase in insect cells.

Role of negatively charged residues in the fifth and sixth transmembrane domains of the catalytic subunit of gastric H+,K+-ATPase

The role of six negatively charged residues located in or around the fifth and sixth transmembrane domain of the catalytic subunit of gastric H+,K+-ATPase, which are conserved in P-type ATPases, was investigated by site-directed mutagenesis of each of these residues. The acid residues were converted into their corresponding acid amides. Sf9 cells were used as the expression system using a baculovirus with coding sequences for the alpha- and beta-subunits of H+,K+-ATPase behind two different promoters. Both subunits of all mutants were expressed like the wild type enzyme in intracellular membranes of Sf9 cells as indicated by Western blotting experiments, an enzyme-linked immunosorbent assay, and confocal laser scan microscopy studies. The mutants D824N, E834Q, E837Q, and D839N showed no 3-(cyanomethyl)-2-methyl-8(phenylmethoxy)-imidazo[1, 2a]pyridine (SCH 28080)-sensitive ATP dependent phosphorylation capacity. Mutants E795Q and E820Q formed a phosphorylated intermediate, which, like the wild type enzyme, was hydroxylamine-sensitive, indicating that an acylphosphate was formed. Formation of the phosphorylated intermediate from the E795Q mutant was similarly inhibited by K+ (I50 = 0.4 mM) and SCH 28080 (I50 = 10 nM) as the wild type enzyme, when the membranes were preincubated with these ligands before phosphorylation. The dephosphorylation reaction was K+-sensitive, whereas ADP had hardly any effect. Formation of the phosphorylated intermediate of mutant E820Q was much less sensitive toward K+ (I50 = 4.5 mM) and SCH 28080 (I50 = 1.7 microM) than the wild type enzyme. The dephosphorylation reaction of this intermediate was not stimulated by either K+ or ADP. In contrast to the wild type enzyme and mutant E795Q, mutant E820Q did not show any K+-stimulated ATPase activity. These findings indicate that residue Glu820 might be involved in K+ binding and transition to the E2 form of gastric H+,K+-ATPase.

Histamine H2-receptor antagonists stimulate proliferation but not migration of human gastric mucosal cells in vitro

Gastric mucosal cell migration and proliferation are crucial events in the repair of gastric mucosal erosions. This study was designed to test the hypothesis that the H2 blockers roxatidine and ranitidine might stimulate migration and proliferation of gastric mucous cells derived from a human well-differentiated gastric adenocarcinoma cell line (MKN 28 cells) in vitro, in conditions independent of systemic factors and of acid inhibition. Confluent monolayers of MKN 28 cells were wounded with a razor blade and were then incubated with roxatidine or ranitidine. The number of cells migrating to the damaged area was determined 24 hr later. Cell proliferation was assessed by means of [3H] thymidine uptake and cell counts after incubation with roxatidine or ranitidine. Neither H2 antagonist significantly stimulated cell migration. On the other hand, cell proliferation was dose-dependently and significantly enhanced by incubation with roxatidine and ranitidine. Exogenous administration of TGF-alpha significantly stimulated MKN 28 cell division. However, incubation with roxatidine or ranitidine did not increase the steady-state mRNA expression of TGF-alpha or EGFR as assessed by northern blot analysis. Based on these in vitro findings, we postulate that the ulcer healing effect of these H2 antagonists in vivo might be due in part to stimulation of gastric mucosal cell proliferation.