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Journal of Biomedicine and Biotechnology
Volume 2011 (2011), Article ID 975479, 7 pages
Animal Models to Study the Role of Long-Term Hypergastrinemia in Gastric Carcinogenesis
1Department of Gastroenterology and Hepatology, St. Olavs Hospital HF, Trondheim University Hospital, 7006 Trondheim, Norway
2Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, 7491 Trondheim, Norway
Received 31 August 2010; Accepted 28 October 2010
Academic Editor: Andrea Vecchione
Copyright © 2011 Reidar Fossmark et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Patients with chronic hypergastrinemia due to chronic atrophic gastritis or gastrinomas have an increased risk of developing gastric malignancy, and it has been questioned whether also patients with hypergastrinemia caused by long-term use of acid inhibiting drugs are at risk. Gastric carcinogenesis in humans is affected by numerous factors and progresses slowly over years. When using animal models with the possibility of intervention, a complex process can be dissected by studying the role of hypergastrinemia in carcinogenesis within a relatively short period of time. We have reviewed findings from relevant models where gastric changes in animal models of long-term hypergastrinemia have been investigated. In all species where long-term hypergastrinemia has been induced, there is an increased risk of gastric malignancy. There is evidence that hypergastrinemia is a common causative factor in carcinogenesis in the oxyntic mucosa, while other cofactors may vary in the different models.
Many patients have gastric hypoacidity and secondary hypergastrinemia due to atrophic gastritis or the use of proton pump inhibitors, whereas patients with gastrinomas have hypergastrinemia and increased gastric acidity. There is evidence that patients with atrophic gastritis have an increased risk of both enterochromaffin-like (ECL) cell carcinoids as well as gastric adenocarcinomas [1–4]. Patients with gastrinomas also have an increased risk of ECL cell carcinoids [5–7] and may develop gastric signet ring cell carcinomas . However, there is no direct evidence that Proton Pump Inhibitors (PPI) increases the risk of developing gastric malignancy, but micronodular ECL cell hyperplasia is seen after 5 years of PPI use . Carcinogenesis in humans is considered a multistep process progressing over years where various factors may influence. To study the contribution of single factors in carcinogenesis, various animal models can be useful. The major advantage of using animal models is that carcinogenesis is relatively reliable and often progresses in months allowing stepwise tumour development to be studied in detail.
Much of the knowledge we have of regulation of acid secretion is derived from animal studies and also applies to growth regulation of the oxyntic mucosa. Gastrin released from antral G-cells is the main regulator of acid secretion and binds to the CCK-2/gastrin receptor located on the ECL cell that secretes histamine which in turn stimulates parietal cells to secretion of hydrochloric acid [10, 11].
Although the evidence of the gastrin-ECL-parietal cell axis came from studies of the effects of various acid secretagogues in isolated rat stomachs in the 1980s, more recent studies confirm these findings. Fluorescein-labelled CCK-8 binds to ECL cells but not parietal cells , and gastrin does not stimulate acid secretion in either histidine-decarboxylase (HDC) deficient  or H2 receptor deficient  mice. These findings are relevant to understand the trophic and carcinogenic effects of long-term hypergastrinemia, where the target cell of gastrin, the ECL cell, is pivotal.
In this paper we review findings from animal studies on the role of long-term hypergastrinemia in gastric carcinogenesis.
2. Animal Models
In 1985 it was published that rats with life-long acid inhibition by dosing the insurmountable histamine 2-blocker loxtidine developed ECL cell carcinoids . Initially it was speculated whether the carcinogenic effect was specific for this compound, but shortly after it became known that the proton pump inhibitor omeprazole caused a 15-fold increase in plasma gastrin , tripled the ECL cell density  and resulted in a 20% increase in oxyntic mucosal thickness after only 10 weeks administration. Life-long administration of omeprazole moreover resulted in ECL cell carcinoids in rats . As both omeprazole and loxtidine cause profound gastric hypoacidity and subsequent hypergastrinemia is was hypothesized that hypergastrinemia caused ECL cell carcinoid development. Several following studies were in support of this hypothesis. Infusion of gastrin was found to stimulate self-replication of ECL cells , and partial corpectomy (also causing hypergastrinemia) resulted in ECL cell hyperplasia  and ECL cell carcinoids  in the remaining oxyntic mucosa. Long-term administration of the competitive H2-blocker ranitidine also has the ability to induce ECL cell carcinoids when given in large enough doses . Finally, the administration of ciprofibrate induces ECL cell carcinoids  in rats without gastric hypoacidity , but causes hypergastrinemia through a direct effect on the antral G-cell . The induction of ECL cell carcinoids by ciprofibrate clearly demonstrates that it is hypergastrinemia and not hypoacidity that drives ECL cell carcinogenesis.
The consequences of long-term hypergastrinemia have also been studied in mice by the administration of antisecretagogues and by the use of various genetically modified mice.
Administration of loxtidine for two years to mice induced carcinoids in the oxyntic mucosa , whereas a similar study with the proton pump inhibitor omeprazole did not show development of such tumours . However, the mice were given the same dose omeprazole according to weight that had previously been given to rats (400 μmg/kg/day) without measuring the effect on gastric acidity and serum gastrin in mice. Later we have shown that mice are remarkably resistant to proton pump inhibitors with respect to inhibition of gastric acid secretion and require an extremely high dose (1750 μmg/kg/day subcutaneously) to induce profound hypoacidity and hypergastrinemia . Consequently, the omeprazole study  was inconclusive and the potential tumorigenic effect of long-term administration of PPIs in mice is not settled.
In transgenic INS-GAS mice, it is possible to study the effect of hypergastrinemia without gastric hypoacidity . Overexpression of gastrin leads to 4-fold increase in plasma gastrin and gastric hypersecretion mimicking human gastrinomas. Young INS-GAS mice have an increased ECL cell number, but with time, the INS-GAS mice lose both parietal cells and cells that can be identified as ECL cells and some develop adenocarcinomas in the oxyntic mucosa at the end of their lifespan. Inoculation with Helicobacter felis further increases plasma gastrin and accelerates carcinogenesis considerably . Moreover, the carcinogenesis is synergistically inhibited by administration of histamine 2 receptor (loxitidine) and gastrin receptor antagonists (YF476)  indicating a role for both mediators in carcinogenesis. The reason why hypergastrinemic INS-GAS mice develop tumours with an adenocarcinoma phenotype, whereas mice and rats develop ECL cell carcinoids after long-term acid inhibition is not known.
A study comparing different mice models suggests that the carcinogenic effect of Helicobacter infection is mediated by gastrin. INS-GAS, C57BL/6 and gastrin deficient mice were inoculated with Helicobacter felis and whereas hypergastrinemic mice developed dysplasia in the oxyntic mucosa, dysplasia was not found in gastrin-deficient mice .
Other mice models as well can be used to study the consequences of hypergastrinemia secondary to gastric hypoacidity. H+K+ATPase beta subunit-deficient mice are anacidic and have a 4- to 7-fold increase in serum gastrin and show hyperplasia of the oxyntic mucosa [31, 32], whereas hyperplasia is not seen in H+K+ATPase beta subunit and gastrin double knockout mice. H+K+ATPase beta subunit-deficient mice have an increase in ECL cell number compared to controls, but carcinoma development in the oxyntic mucosa is rare and expression of neuroendocrine markers within the carcinoma could not be detected . Similar changes have been described in H+K+ATPase alpha subunit-deficient mice .
The role of histamine has been studied using HDC-deficient mice that show gastric hypoacidity and a threefold increase in plasma gastrin levels . In animals aged 8 to 12 weeks there were no differences in mucosal thickness suggesting that histamine mediates the trophic effect of gastrin, but not via the histamine-2 receptor, since histamine-2 receptor deficient mice are hypergastrinemic and have a hypertrophic oxyntic mucosa . Long-term studies addressing the carcinogenic effects of hypergastrinemia in the absence of histamine have not been published.
Gastrin-deficient mice do not have basal acid secretion  thus providing a model for studying the effects of gastric hypoacidity without hypergastrinemia. These mice develop antral tumours classified as adenocarcinomas  which are attributed to bacterial overgrowth and subsequent formation of carcinogenic substances [38, 39].
H+K+ATPase and gastrin double knockedout mice are anacidic without gastrin , hence they do not develop a hypertrophic oxyntic mucosa, demonstrating that gastrin is responsible for these changes.
Several other genetically modified mice with gastric hypoacidity have been made, but studies on long-term gastric changes have so far not been published. That is, mice where the gene encoding KCNE2 (a potassium channel ancillary subunit) is knockedout are hypoacidic and hypergastrinemic, and these mice have marked hyperplastic changes in the oxyntic mucosa at age 3 months .
2.3. Japanese Cotton Rats
Animals from a strain of Japanese cotton rats develop spontaneous gastric carcinomas restricted to the oxyntic mucosa with a marked female preponderance . The animals developing carcinomas were later found to have gastric hypoacidity, secondary hypergastrinemia, and pronounced ECL cell hyperplasia . The oxyntic mucosa in hypergastrinemic cotton rats has marked hyperplasia of chromogranin A, synaptophysin, and HDC immunoreactive cells and a proportion of the tumour cells are chromogranin A, pancreastatin, HDC, and Sevier-Munger positive [42–45]with similar changes found in mRNA expression [46, 47]. Between the age of two and six months, a proportion of female cotton rats develop gastric hypoacidity by an unknown mechanism, and develop carcinomas after approximately four months of hypergastrinemia. Several studies have demonstrated the importance of gastrin in tumour development as carcinomas are prevented by injections of a gastrin receptor antagonist (YF476) , by removal of antral gastrin by antrectomy  or by administration of the somatostatin analogue octreotide . Male cotton rats that are made hypergastrinemic due to either administration of loxtidine  or by partial corpectomy  also develop carcinomas in the oxyntic mucosa. The ECL cell ultrastructure and neuroendocrine immunoreactivity in hypergastrinemic animals have been observed over time and ECL cells gradually lose characteristics suggesting that ECL cells undergo dedifferentiation during transformation stimulated by hypergastrinemia .
The cotton rat model demonstrates that tumours with an adenocarcinoma phenotype and neuroendocrine characteristics are induced by gastric hypoacidity and hypergastrinemia and probably develop through dedifferentiation of ECL cells.
2.4. Mongolian Gerbils
Studies in both rodents and man have associated infection with Helicobacter spp. with development of gastric carcinomas. In Mongolian Gerbils (“desert rats”) infection with H. pylori leads to development of chronic gastritis, peptic ulcers, atrophy of the gastric mucosa, intestinal metaplasia, and finally gastric carcinomas [3, 51], thus a disease that parallels what is found in humans.
There seems to be a close relationship between Helicobacter infection, elevated gastrin, and development of gastric carcinomas. Hypergastrinemia is a risk factor for gastric carcinomas irrespective of Helicobacter infection in both rodents and man. Infection with H. pylori induces a 5- to 10-fold rise in serum gastrin in Mongolian Gerbils  and increases with time . Two phenotypic different gastric tumours can be found in Mongolian Gerbils after long-term infection with H. pylori; ECL cell carcinoids [3, 53] and presumably adenocarcinomas [3, 52, 53], suggesting that these two malignant tumours develop through similar mechanism. Interestingly, there is an increase in CgA positive cells up to week 50, which decreases from week 50 to 100 , resembling the dedifferentiation seen in other models for studying effects of long-term hypergastrinemia. It has also been demonstrated that regenerating (reg) gene expression correlates with hypergastrinemia in H pylori infected animals .
One of the animal models contributing to our understanding of gastric carcinoid tumours (neuroendocrine tumours, NETs) is the African rodent Mastomys Natalensis of the family Muridae. Already in the 1950s, it was discovered that strains of Mastomys had the propensity to develop multicentric gastric tumours that were first misclassified as adenocarcinomas [56, 57]. These tumours were later reclassified as gastric neuroendocrine tumours [58, 59], originating from the ECL-cell [60, 61], similar to the human type I (associated to atrophic gastritis) and type II (associated with gastrinoma) gastric carcinoids. The carcinoids in Mastomys are found in about 50 percent of aged animals (1-2 years) and are located to the oxyntic mucosa. The pathological changes seen preceding the development of tumours are summarized in three stages: stage I with linear hyperplasia of ECL cells, stage II with the development of ECL-cell nodules restricted to gastric glands, and stage III with ECL- cell growth below the lamina propria . The direct cause of the ECL cell neoplasia in Mastomys is uncertain, however closely linked to gastrin and the CCK-2 receptor activity. The Mastomys CCK2/gastrin receptor has been transfected to COS-7 cells, and this receptor has an enhanced basal level of activity compared to the human receptor . Gastrin is, however, also necessary in the pathogenesis of the carcinoids as the CCK2/gastrin receptor antagonist YF476 inhibits both ECL hyperplasia and gastric tumour development . Loxtidine-induced hypergastrinemia moreover promotes the development of carcinoids in Mastomys . The density of ECL cells was three times that of controls after 24 weeks of loxtidine treatment and 1/4 of the animals had gross tumours . ECL cell hyperplasia and dysplasia, but not tumours, have been shown to be reversible after cessation of loxtidine treatment, suggesting that the tumour cells become independent of hypergastrinemia at some point in the neoplastic process . The somatostatin-analogue octreotide has inhibitory effects on both gastrin cells and ECL cells and is found to prevent loxtidine-induced ECL hyperplasia .
2.6. The Norwegian Lundehund
The Norwegian Lundehund, a small Norwegian spitz breed, is a working dog developed for hunting puffins (Fratercula arctica), especially in the northern part of Norway. The breed was nearly eradicated during the Second World War because of the spread of canine distemper virus, and the present population originates from only five dogs.
Lundehunds often suffer from the “Lundehund syndrome”: intermittent diarrhoea, hypoproteinemia, ascites, subcutaneous oedema, weight loss, and lethargy. Affected dogs are also known to develop chronic atrophic gastritis and are predisposed to the development of gastric tumours, two conditions that are rare in other breeds. The chronic atrophic gastritis is associated with loss of parietal cells and linear hyperplasia of ECL cells . These findings are consistent with decreased acid secretion and long-term hypergastrinemia in these dogs.
Gastric carcinomas in dogs usually arise in the pyloric area. However, in Lundehunds the tumours most often arise in the fundic/corpus area, that is, in the oxyntic mucosa . When examining the tumours by means of histochemistry and immunohistochemistry, the neoplastic cells show neuroendocrine and more specifically ECL cell differentiation in half of the tumours . Thus, it is likely that the carcinomas originate from the ECL cell secondary to the long-term trophic effect of hypergastrinemia. The neoplastic process thus parallels the development of tumours associated with pernicious anemia in man [68–70]. About half of the gastric carcinomas in Lundehund show neuroendocrine differentiation. However, during neoplastic progression an increasing number of mutations lead to dedifferentiation of tumour cells with reduced concentrations or complete loss of normal cell markers, as shown in Japanese cotton rats  and man . This may explain why it is difficult to detect neuroendocrine and ECL cell markers in some tumours  and makes it possible that tumours which fail to express such markers may still be of neuroendocrine origin.
The effects of long-term administration of acid inhibitors has not been studied in the Norwegian Lundehund, but beagle dogs have been given omeprazole daily for 7 years . There were no changes in the gastric mucosa at termination including ECL cell numbers, but the dogs receiving omeprazole had similar fasting and meal-stimulated plasma gastrin levels compared to controls which means the dogs had not received an adequate dose of PPI.
Although the incidence of gastric cancer in western countries is decreasing, the incidence of adenocarcinomas of the diffuse type is increasing , being the subtype of adenocarcinomas that often develop in patients with hypergastrinemia and have neuroendocrine differentiation [70, 75, 76]. Recently it was also reported that in USA there is a significant increase of noncardia gastric adenocarcinomas in whites among younger cohorts , while the cause of these new trends is difficult to determine from epidemiological data alone. The relevance of animal models where hypotheses can be tested and new are generated is obvious, as animal models allow intervention by introducing or eliminating factors thought to affect carcinogenesis. Hypergastrinemia is seen in many models of gastric carcinogenesis and seems to be a common causative factor in otherwise different circumstances. In all species where long-term hypergastrinemia has been induced, an increased risk of gastric malignancy is observed, whether hypergastrinemia is accompanied by either gastric hypoacidity or hyperacidity.
In some animal models hypergastrinemia induces malignancy with either carcinoid or adenocarcinoma phenotype. However, findings from Mongolian gerbils and Japanese cotton rats suggest that these tumours develop by similar mechanisms and derive from ECL cells, thus resembling patients with atrophic gastritis who have an increased risk of developing both types of tumours. More experiments are needed to identify the mechanisms that determine the tumour phenotype.
- S. Rakic, R. A. Hinder, G. Adanja, and T. R. DeMeester, “Elevated serum gastrin levels in patients with gastric cancer,” Journal of Surgical Oncology, vol. 47, no. 2, pp. 79–81, 1991.
- H. F. Helander and N. Poorkhalkali, “Parietal cell density during gastric ulcer healing in the rat,” Scandinavian Journal of Gastroenterology, vol. 39, no. 1, pp. 20–26, 2004.
- T. Watanabe, M. Tada, H. Nagi, S. Sasaki, and M. Nakao, “Helicobacter pylori infection induces gastric cancer in Mongolian gerbils,” Gastroenterology, vol. 115, no. 3, pp. 642–648, 1998.
- I. M. Modlin, M. Kidd, and J. Farhadi, “Bayliss and Starling and the nascence of endocrinology,” Regulatory Peptides, vol. 93, no. 1-3, pp. 109–123, 2000.
- T. D'Adda, S. Candidus, H. Denk, C. Bordi, and H. Höfler, “Gastric neuroendocrine neoplasms: tumour clonality and malignancy- associated large X-chromosomal deletions,” Journal of Pathology, vol. 189, no. 3, pp. 394–401, 1999.
- A. K. Sandvik, E. Brenna, A. Sundan, J. J. Holst, and H. L. Waldum, “Bombesin inhibits histamine release from the rat oxyntic mucosa by a somatostatin-dependent mechanism,” Scandinavian Journal of Gastroenterology, vol. 32, no. 5, pp. 427–432, 1997.
- T. D'Adda, A. Bertele, F. P. Pilato, and C. Bordi, “Quantitative electron microscopy of endocrine cells in oxyntic mucosa of normal human stomach,” Cell and Tissue Research, vol. 255, no. 1, pp. 41–48, 1989.
- M. Schott, C. Sagert, H. S. Willenberg et al., “Carcinogenic hypergastrinemia: signet-ring cell carcinoma in a patient with multiple endocrine neoplasia type 1 with zollinger-ellison's syndrome,” Journal of Clinical Endocrinology and Metabolism, vol. 92, no. 9, pp. 3378–3382, 2007.
- R. Fiocca, L. Mastracci, S. E. Attwood, et al., “Exocrine and endocrine gastric mucosal changes under medical or surgical antireflux therapy: results of a 5-year follow-up in the LOTUS trial,” Gastroenterology, vol. 138, article W1092, 2010.
- H. L. Waldum, A. K. Sandvik, E. Brenna, and H. Petersen, “Gastrin-histamine sequence in the regulation of gastric acid secretion,” Gut, vol. 32, no. 6, pp. 698–701, 1991.
- N. P. Shankley, N. J. Welsh, and J. W. Black, “Histamine dependence of pentagastrin-stimulated gastric acid secretion in rats,” Yale Journal of Biology and Medicine, vol. 65, no. 6, pp. 613–619, 1992.
- I. Bakke, G. Qvigstad, A. K. Sandvik, and H. L. Waldum, “The CCK-2 receptor is located on the ECL cell, but not on the parietal cell,” Scandinavian Journal of Gastroenterology, vol. 36, no. 11, pp. 1128–1133, 2001.
- F. Sundler and R. Haakanson, “Gastric endocrine cell typing at the light microscopical level,” in The Stomach as an Endocrine Organ, F. Sundler and R. Haakanson, Eds., pp. 9–26, Elsevier Science, Amsterdam, The Netherlands, 1991.
- M. Asahara, S. Mushiake, S. Shimada et al., “Reg gene expression is increased in rat gastric enterochromaffin-like cells following water immersion stress,” Gastroenterology, vol. 111, no. 1, pp. 45–55, 1996.
- D. Poynter, C. R. Pick, R. A. Harcourt, et al., “Association of long lasting unsurmountable histamine H2 blockade and gastric carcinoid tumours in the rat,” Gut, vol. 26, no. 12, pp. 1284–1295, 1985.
- H. Larsson, E. Carlsson, H. Mattsson, et al., “Plasma gastrin and gastric enterochromaffinlike cell activation and proliferation. Studies with omeprazole and ranitidine in intact and antrectomized rats,” Gastroenterology, vol. 90, no. 2, pp. 391–399, 1986.
- F. Sundler, R. Hakanson, E. Carlsson, H. Larsson, and H. Mattsson, “Hypergastrinemia after blockade of acid secretion in the rat: trophic effects,” Digestion, vol. 35, supplement 1, pp. 56–69, 1986.
- N. Havu, “Enterochromaffin-like cell carcinoids of gastric mucosa in rats after life-long inhibition of gastric secretion,” Digestion, vol. 35, no. 1, pp. 42–55, 1986.
- B. Ryberg, Y. Tielemans, J. Axelson et al., “Gastrin stimulates the self-replication rate of enterochromaffinlike cells in the rat stomach: effects of omeprazole, ranitidine, and gastrin-17 in intact and antrectomized rats,” Gastroenterology, vol. 99, no. 4, pp. 935–942, 1990.
- B. Ryberg, E. Carlsson, R. Hakanson, L. Lundell, H. Mattsson, and F. Sundler, “Effects of partial resection of acid-secreting mucosa on plasma gastrin and enterochromaffin-like cells in the rat stomach,” Digestion, vol. 45, no. 2, pp. 102–108, 1990.
- H. Mattsson, N. Havu, J. Brautigam, K. Carlsson, L. Lundell, and E. Carlsson, “Partial gastric corpectomy results in hypergastrinemia and development of gastric enterochromaffinlike-cell carcinoids in the rat,” Gastroenterology, vol. 100, no. 2, pp. 311–319, 1991.
- N. Havu, H. Mattsson, L. Ekman, and E. Carlsson, “Enterochromaffin-like cell carcinoids in the rat gastric mucosa following long-term administration of raniditine,” Digestion, vol. 45, no. 4, pp. 189–195, 1990.
- A. J. Spencer, T. A. Barbolt, D. C. Henry, C. T. Eason, R. J. Sauerschell, and F. W. Bonner, “Gastric morphological changes including carcinoid tumors in animals treated with a potent hypolipidemic agent, ciprofibrate,” Toxicologic Pathology, vol. 17, no. 1 I, pp. 7–15, 1989.
- T. C. Martinsen, N. Nesjan, K. Rønning, A. K. Sandvik, and H. L. Waldum, “The peroxisome-proliferator ciprofibrate induces hypergastrinemia without raising gastric pH,” Carcinogenesis, vol. 17, no. 10, pp. 2153–2155, 1996.
- T. C. Martinsen, I. Bakke, D. Chen et al., “Ciprofibrate stimulates the gastrin-producing cell by acting luminally on antral PPAR-α,” American Journal of Physiology—Gastrointestinal and Liver Physiology, vol. 289, no. 6, pp. G1052–G1060, 2005.
- D. Poynter, S. A. M. Selway, S. A. Papworth, and S. R. Riches, “Changes in the gastric mucosa of the mouse associated with long lasting unsurmountable histamine H2 blockade,” Gut, vol. 27, no. 11, pp. 1338–1346, 1986.
- H. L. Waldum, E. Brenna, and T. Chr. Martinsen, “Safety of proton pump inhibitors,” Alimentary Pharmacology and Therapeutics, vol. 14, no. 11, pp. 1537–1538, 2000.
- T. C. Wang, C. A. Dangler, D. Chen et al., “Synergistic interaction between hypergastrinemia and Helicobacter infection in a mouse model of gastric cancer,” Gastroenterology, vol. 118, no. 1, pp. 36–47, 2000.
- S. Takaishi, G. Cui, D. M. Frederick et al., “Synergistic inhibitory effects of gastrin and histamine receptor antagonists on Helicobacter-induced gastric cancer,” Gastroenterology, vol. 128, no. 7, pp. 1965–1983, 2005.
- S. Takaishi, S. Tu, Z. A. Dubeykovskaya et al., “Gastrin is an essential cofactor for Helicobacter-associated gastric corpus carcinogenesis in C57BL/6 mice,” American Journal of Pathology, vol. 175, no. 1, pp. 365–375, 2009.
- T. V. Franic, L. M. Judd, D. Robinson et al., “Regulation of gastric epithelial cell development revealed in H+/K+-ATPase β-subunit- and gastrin-deficient mice,” American Journal of Physiology—Gastrointestinal and Liver Physiology, vol. 281, no. 6, pp. G1502–G1511, 2001.
- K. L. Scarff, L. M. Judd, B.-H. Toh, P. A. Gleeson, and I. R. van Driel, “Gastric H+,K+-adenosine triphosphatase β subunit is required for normal function, development, and membrane structure of mouse parietal cells,” Gastroenterology, vol. 117, no. 3, pp. 605–618, 1999.
- K. E. Bakkelund, H. L. Waldum, I. S. Nordrum, O. Hauso, and R. Fossmark, “Long-term gastric changes in achlorhydric H+/K+-ATPase beta subunit deficient mice,” Scandinavian Journal of Gastroenterology, vol. 45, no. 9, pp. 1042–1047, 2010.
- L. M. Judd, A. Andringa, C. A. Rubio, Z. Spicer, G. E. Shull, and M. L. Miller, “Gastric achlorhydria in H/K-ATPase-deficient (Atp4a(-/-)) mice causes severe hyperplasia, mucocystic metaplasia and upregulation of growth factors,” Journal of Gastroenterology and Hepatology, vol. 20, no. 8, pp. 1266–1278, 2005.
- S. Tanaka, K. Hamada, N. Yamada et al., “Gastric acid secretion in L-histidine decarboxylase-deficient mice,” Gastroenterology, vol. 122, no. 1, pp. 145–155, 2002.
- L. Friis-Hansen, F. Sundler, Y. Li et al., “Impaired gastric acid secretion in gastrin-deficient mice,” American Journal of Physiology—Gastrointestinal and Liver Physiology, vol. 274, no. 3, pp. G561–G568, 1998.
- L. Friis-Hansen, K. Rieneck, H. Nilsson, T. Wadström, and J. F. Rehfeld, “Gastric inflammation, metaplasia, and tumor development in gastrin-deficient mice,” Gastroenterology, vol. 131, no. 1, pp. 246–258, 2006.
- L. Friis-Hansen, “Achlorhydria is associated with gastric microbial overgrowth and development of cancer: lessons learned from the gastrin knockout mouse,” Scandinavian Journal of Clinical and Laboratory Investigation, vol. 66, no. 7, pp. 607–622, 2006.
- L. Friis-Hansen, “Lessons from the gastrin knockout mice,” Regulatory Peptides, vol. 139, no. 1–3, pp. 5–22, 2007.
- T. K. Roepke, A. Anantharam, P. Kirchhoff et al., “The KCNE2 potassium channel ancillary subunit is essential for gastric acid secretion,” Journal of Biological Chemistry, vol. 281, no. 33, pp. 23740–23747, 2006.
- S. Kawase and H. Ishikura, “Female-predominant occurrence of spontaneous gastric adenocarcinoma in cotton rats,” Laboratory Animal Science, vol. 45, no. 3, pp. 244–248, 1995.
- H. L. Waldum, H. Røryik, S. Falkmer, and S. Kawase, “Neuroendocrine (ECL cell) differentiation of spontaneous gastric carcinomas of cotton rats (Sigmodon hispidus),” Laboratory Animal Science, vol. 49, no. 3, pp. 241–247, 1999.
- T. C. Martinsen, S. Kawase, R. Håkanson et al., “Spontaneous ECL cell carcinomas in cotton rats: natural course and prevention by a gastrin receptor antagonist,” Carcinogenesis, vol. 24, no. 12, pp. 1887–1896, 2003.
- R. Fossmark, T. C. Martinsen, K. E. Bakkelund, S. Kawase, S. H. Torp, and H. L. Waldum, “Hypergastrinaemia induced by partial corpectomy results in development of enterochromaffin-like cell carcinoma in male Japanese cotton rats,” Scandinavian Journal of Gastroenterology, vol. 39, no. 10, pp. 919–926, 2004.
- R. Fossmark, C.-M. Zhao, T. C. Martinsen, S. Kawase, D. Chen, and H. L. Waldum, “Dedifferentiation of enterochromaffin-like cells in gastric cancer of hypergastrinemic cotton rats,” APMIS, vol. 113, no. 6, pp. 436–449, 2005.
- G. Cui, G. Qvigstad, S. Falkmer, A. K. Sandvik, S. Kawase, and H. L. Waldum, “Spontaneous ECLomas in cotton rats (Sigmodon hispidus): tumours occurring in hypoacidic/hypergastrinaemic animals with normal parietal cells,” Carcinogenesis, vol. 21, no. 1, pp. 23–27, 2000.
- R. Fossmark, T. C. Martinsen, S. H. Torp, S. Kawase, A. K. Sandvik, and H. L. Waldum, “Spontaneous enterochromaffin-like cell carcinomas in cotton rats (Sigmodon hispidus) are prevented by a somatostatin analogue,” Endocrine-Related Cancer, vol. 11, no. 1, pp. 149–160, 2004.
- K. Bakkelund, R. Fossmark, I. S. Nordrum, and H. L. Waldum, “Effect of antrectomy in hypergastrinaemic female Japanese cotton rats,” Scandinavian Journal of Gastroenterology, vol. 44, no. 1, pp. 32–39, 2009.
- W. Blumenfeld, D. K. Chandhoke, P. Sagerman, and G. K. Turi, “Neuroendocrine differentiation in gastric adenocarcinomas: an immunohistochemical study,” Archives of Pathology and Laboratory Medicine, vol. 120, no. 5, pp. 478–481, 1996.
- G. P. Lawton, L. Tang, M. Kidd, R. Chinery, K. Miu, and I. M. Modlin, “Regulation of mastomys ECL cell function by transforming growth factor alpha,” Journal of Surgical Research, vol. 60, no. 2, pp. 293–302, 1996.
- S. Honda, T. Fujioka, M. Tokieda, R. Satoh, A. Nishizono, and M. Nasu, “Development of Helicobacter pylori-induced gastric carcinoma in Mongolian gerbils,” Cancer Research, vol. 58, no. 19, pp. 4255–4259, 1998.
- F. Hirayama, S. Takagi, E. Iwao, Y. Yokoyama, K. Haga, and S. Hanada, “Development of poorly differentiated adenocarcinoma and carcinoid due to long-term Helicobacter pylori colonization in Mongolian gerbils,” Journal of Gastroenterology, vol. 34, no. 4, pp. 450–454, 1999.
- J. Kagawa, S. Honda, M. Kodama, R. Sato, K. Murakami, and T. Fujioka, “Enterocromaffin-like cell tumor induced by Helicobacter pylori infection in Mongolian gerbils,” Helicobacter, vol. 7, no. 6, pp. 390–397, 2002.
- Y. Takenaka, T. Tsukamoto, T. Mizoshita et al., “Helicobacter pylori infection stimulates intestinalization of endocrine cells in glandular stomach of Mongolian gerbils,” Cancer Science, vol. 97, no. 10, pp. 1015–1022, 2006.
- H. Fukui, F. Franceschi, R. L. Penland et al., “Effects of helicobacter pylori infection on the link between regenerating gene expression and serum gastrin levels in Mongolian gerbils,” Laboratory Investigation, vol. 83, no. 12, pp. 1777–1786, 2003.
- A. G. Oettele, “Spontaneous carcinoma of the glandular stomach in a laboratory stock of Rattus (Mastomys) natalensis,” South African Journal of Medical Sciences, vol. 20, article 36, 1955.
- A. G. Oettele, “Spontaneous carcinoma of the glandular stomach in Rattus (mastomys) natalensis, an African rodent,” British Journal of Cancer, vol. 11, pp. 415–433, 1957.
- J. Soga, H. Kanahara, and K. Hiraide, “Some characteristic features of spontaneous argyrophil cell carcinoids in glandular stomach of Praomys (Mastomys) natalensis,” GANN Monograph, vol. 8, pp. 15–38, 1969.
- K. C. Snell and H. L. Stewart, “Malignant argyrophilic gastric carcinoids of Praomys (Mastomys) natalensis,” Science, vol. 163, no. 866, p. 470, 1969.
- S. Hosoda, W. Nakamura, K. C. Snell, and H. L. Stewart, “Histamine production by transplantable argyrophilic gastric carcinoid of praomys (Mastomys) natalensis,” Science, vol. 170, no. 3956, pp. 454–455, 1970.
- O. Nilsson, B. Wangberg, L. Johansson et al., “Rapid induction of enterochromaffinlike cell tumors by histamine2- receptor blockade,” American Journal of Pathology, vol. 142, no. 4, pp. 1173–1185, 1993.
- J. Soga, T. Kohro, K. Tazawa, H. Kanahara, and M. Sano, “Argyrophil cell microneoplasia in the Mastomys' stomach. An observation on early carcinoid formation,” Journal of the National Cancer Institute, vol. 55, no. 4, pp. 1001–1006, 1975.
- K. Schaffer, E. W. McBride, M. Beinborn, and A. S. Kopin, “Interspecies polymorphisms confer constitutive activity to the Mastomys cholecystokinin-B/gastrin receptor,” Journal of Biological Chemistry, vol. 273, no. 44, pp. 28779–28784, 1998.
- M. Kidd, Z. L. Siddique, I. Drozdov et al., “The CCK2 receptor antagonist, YF476, inhibits Mastomys ECL cell hyperplasia and gastric carcinoid tumor development,” Regulatory Peptides, vol. 162, no. 1–3, pp. 52–60, 2010.
- B. Wängberg, O. Nilsson, E. Theodorsson, I. M. Modlin, A. Dahlström, and H. Ahlman, “Are enterochromaffinlike cell tumours reversible? An experimental study on gastric carcinoids induced in Mastomys by histamine2-receptor blockade,” Regulatory Peptides, vol. 56, no. 1, pp. 19–33, 1995.
- I. M. Modlin, R. Kumar, A. Nangia, C. J. Soroka, D. Pasikhov, and J. R. Goldenring, “Gastrin-dependent inhibitory effects of octreotide on the genesis of gastric ECLomas,” Surgery, vol. 112, no. 6, pp. 1048–1058, 1992.
- G. Qvigstad, Ø. Kolbjørnsen, E. Skancke, and H. L. Waldum, “Gastric neuroendocrine carcinoma associated with atrophic gastritis in the Norwegian Lundehund,” Journal of Comparative Pathology, vol. 139, no. 4, pp. 194–201, 2008.
- L. Elsborg and J. Mosbech, “Pernicious anemia as a risk factor in gastric cancer,” Acta Medica Scandinavica, vol. 206, no. 4, pp. 315–318, 1979.
- K. Borch, H. Renvall, and G. Liedberg, “Gastric endocrine cell hyperplasia and carcinoid tumors in pernicious anemia,” Gastroenterology, vol. 88, no. 3, pp. 638–648, 1985.
- G. Qvigstad, T. Qvigstad, B. Westre, A. K. Sandvik, E. Brenna, and H. L. Waldum, “Neuroendocrine differentiation in gastric adenocarcinomas associated with severe hypergastrinemia and/or pernicious anemia,” APMIS, vol. 110, no. 2, pp. 132–139, 2002.
- R. Fossmark, C.-M. Zhao, T. C. Martinsen, S. Kawase, D. Chen, and H. L. Waldum, “Dedifferentiation of enterochromaffin-like cells in gastric cancer of hypergastrinemic cotton rats,” APMIS, vol. 113, no. 6, pp. 436–449, 2005.
- G. Qvigstad, S. Falkmer, B. Westre, and H. L. Waldum, “Clinical and histopathological tumour progression in ECL cell carcinoids ('ECLomas'),” APMIS, vol. 107, no. 12, pp. 1085–1092, 1999.
- C. Safholm, N. Havu, H. Forssell, G. Sundell, and H. Mattsson, “Effect of 7 years' daily oral administration of omeprazole to beagle dogs,” Digestion, vol. 55, no. 3, pp. 139–147, 1994.
- D. E. Henson, C. Dittus, M. Younes, H. Nguyen, and J. Albores-Saavedra, “Differential trends in the intestinal diffuse types of gastric carcinoma in the United States, 1973–2000: increase in the signet ring cell type,” Archives of Pathology and Laboratory Medicine, vol. 128, no. 7, pp. 765–770, 2004.
- G. Qvigstad, A. K. Sandvik, E. Brenna, S. Aase, and H. L. Waldum, “Detection of chromogranin A in human gastric adenocarcinomas using a sensitive immunohistochemical technique,” Histochemical Journal, vol. 32, no. 9, pp. 551–556, 2000.
- K. Bakkelund, R. Fossmark, I. Nordrum, and H. Waldum, “Signet ring cells in gastric carcinomas are derived from neuroendocrine cells,” Journal of Histochemistry and Cytochemistry, vol. 54, no. 6, pp. 615–621, 2006.
- W. F. Anderson, M. C. Camargo, J. F. Fraumeni Jr., P. Correa, P. S. Rosenberg, and C. S. Rabkin, “Age-specific trends in incidence of noncardia gastric cancer in US adults,” Journal of the American Medical Association, vol. 303, no. 17, pp. 1723–1728, 2010.