Clinical consequences of controversies in gastric physiology.

Studies on the regulation of gastric acid secretion started more than 100 years ago at an early phase of experimental physiology. In nearly the whole last century there were disputes about the interpretation of the findings: the interaction between the three principle gastric acid secretagogues acetylcholine, gastrin and histamine, the cell producing the relevant histamine which turned out to be the ECL cell, the ability of the ECL cell to divide and thus develop into tumours, the classification of gastric carcinomas and the mechanism for Helicobacter pylori carcinogenesis. The elucidation of the central role of the ECL cell and thus its main regulator, gastrin, solve all these controversies, and gives a solid base for handling upper gastrointestinal diseases.

Gastric cancer and gastrin: on the interaction of Helicobacter pylori gastritis and acid inhibitory induced hypergastrinemia.

Gastric cancer, a disease with a reduced frequency for decades, now appears to be on the rise again in young Americans. The epidemiology of gastric cancer differs between tumors in the cardia and those of the more distal parts of the stomach. The tumors are divided into the intestinal type showing glandular growth pattern and the diffuse type with a different pattern. The latter often expresses neuroendocrine and more specifically ECL-cell markers suggesting that they originate from the ECL cell, the target cell for the antral hormone, gastrin. Helicobacter pylori gastritis is accepted as the major cause of gastric cancer, but only after having induced oxyntic atrophy which reduces gastric acid secretion and thus induces hypoacidity leading to hypergastrinemia. Long-term hypergastrinemia is known to induce malignant neoplasia in the stomach of animals as well as man. Recently treatment with proton pump inhibitor after Helicobacter pylori eradication in patients with gastroesophageal reflux disease, has been reported to predispose to gastric cancer. Since profound acid inhibition is a well-known cause of gastric neoplasia, it is to be expected that Helicobacter pylori infection and profound acid inhibition has an additive or possibly potentiating effect on the development of gastric cancer.

Hepatic micrometastases outside macrometastases are present in all patients with ileal neuroendocrine primary tumour at the time of liver resection.

Background: Neuroendocrine tumours (NETs) in the ileum grow slowly but metastasise to the liver at an early stage. After resection of the primary tumour and mesenteric lymph nodes, selected patients with liver metastases have been operated with curative intention. Recurrence-free survival seems low, suggesting that micrometastases are present in the liver at the time of surgery. We have therefore examined whether NET metastases could be detected in perceived normal liver tissue at the time of liver resection. Material and methods: Liver tissue outside the macrometastases from patients (n = 10) operated by liver resection due to metastases from ileal NETs G1/2, were examined for NE cells by immunohistochemistry. Liver tissue from patients operated for metastatic colon cancer was used as control (n = 6). Groups of ≥3 NE cells ≥3 mm from macrometastases were considered micrometastases. Clinical course was recorded retrospectively. Results: Ten of 10 patients had micrometastases, consisting of multiple groups of NE cells. None of the control patients had NE cells in the liver tissue. After median follow-up time of 5.5 (0.8-18.7) years 6 of 10 patients had developed recurrent NET metastases detected by cross-sectional imaging. The follow-up time of the four patients without detectable metastases was 4.8 (0.8-7.5) years vs. with detectable metastases 7.9 (3.2-18.7) years. Conclusions: All patient had micrometastases outside macrometastases at the time of liver resection, suggesting that subsequently recurrent liver metastases develop from NET depositions in the liver already present at the time of surgery. The likelihood of curation by hepatic resection appears very low.

The Phylogeny and Biological Function of Gastric Juice-Microbiological Consequences of Removing Gastric Acid.

Gastric juice is a unique combination of hydrochloric acid (HCl), lipase, and pepsin. Acidic gastric juice is found in all vertebrates, and its main function is to inactivate microorganisms. The phylogenetic preservation of this energy-consuming and, at times, hazardous function (acid-related diseases) reflects its biological importance. Proton pump inhibitors (PPIs) are one of the most widely used drugs in the world. Due to the reduced prevalence of Helicobacter pylori infection as well as the increased use of inhibitors of gastric acid secretion, the latter has become the most important cause of gastric hypoacidity. In the present manuscript, we review the microbiological consequences of removing gastric acidity. The resulting susceptibility to infections has not been studied extensively, and focus has mainly been restricted to bacterial and parasitic agents only. The strongest evidence concerning the relationship between hypochlorhydria and predisposition to infections relates to bacterial infections affecting the gastrointestinal tract. However, several other clinical settings with increased susceptibility to infections due to inhibited gastric acidity are discussed. We also discuss the impact of hypochlorhydria on the gut microbiome.

Adverse Effects of Proton Pump Inhibitors-Evidence and Plausibility.

Proton pump inhibitors (PPIs) have been increasingly used over the last decades and there are concerns about overuse and the numerous reported side-effects. It is uncertain whether associations between PPI use and potential side effects are causal. However, important evidence from experimental and mechanistic studies that could support a causal relationship may have been underestimated by epidemiologists and meta-analysists. In the current manuscript we review the combined epidemiological and mechanistic evidence of the adverse effects of PPI use.

The Enterochromaffin-like [ECL] Cell-Central in Gastric Physiology and Pathology.

BACKGROUND: Studies on the regulation of gastric and pancreatic secretion began more than 100 years ago. Secretin was the first hormone postulated to exist, initiating the field of endocrinology. Gastrin produced in the antral mucosa was the second postulated hormone, and together with histamine and acetylcholine, represent the three major gastric acid secretagogues known since 1920. For a long time, the mast cell was the only recognized histamine-producing cell in the oxyntic mucosa and, in the mid-1980s, the ECL cell was recognized as the cell producing histamine, taking part in the regulation of gastric acid secretion. METHODS: This review is based upon literature research and personal knowledge. RESULTS: The ECL cell carries the gastrin receptor, and gastrin regulates its function (histamine release) as well as proliferation. Long-term hypergastrinemia results in gastric neoplasia of variable malignancies, implying that gastric hypoacidity resulting in increased gastrin release will induce gastric neoplasia, including gastric cancer. CONCLUSIONS: The trophic effect of gastrin on the ECL cell has implications to the treatment with inhibitors of acid secretion.

Proton pump inhibitors (PPIs) may cause gastric cancer - clinical consequences.

Recently, two epidemiological studies showed that long-term treatment with proton pump inhibitors (PPIs) increased the risk of gastric cancer. It is well known that hypergastrinemia predisposes to gastric neoplasia in animals as well as man. Recently a study showed that hypergastrinemic patients had an increased risk of gastric cancer when followed for about 25 years. It is likely that hypergastrinemia is the pathogenic factor for gastric carcinogenesis due to PPI. PPI are the only group of drugs that causes long-term hypergastrinemia in the doses used in a clinical setting. Due to the likely carcinogenic effect, PPIs should be used carefully. Moreover, since the carcinogenic effect of Helicobacter pylori (Hp) infection also may be mediated by an increase in gastrin, Hp should be eradicated whenever treatment with PPI is initiated. In peptic ulcer disease Hp eradication is the treatment of choice. Gastro-oesophageal reflux disease (GERD) is the most prevalent condition leading to long-term use of inhibitors of gastric acid secretion. Only in severe oesophagitis should the treatment be initiated by PPIs, whereas histamine-2 (H-2) blockers ought to be the initial option in most cases of GERD particularly since PPI treatment induces tolerance to H-2 blockers. In the cases where long-term PPI treatment is necessary, the dose should be adjusted by the determination of chromogranin A, which in a way reflects 24-h gastrin exposure. Finally, due to latency of neoplasia, the use of PPI must be very restricted in children and young adults.

Types of Gastric Carcinomas.

Gastric cancer has reduced prevalence, but poor prognoses. To improve treatment, better knowledge of carcinogenesis and cells of origin should be sought. Stomach cancers are typically localized to one of the three mucosae; cardial, oxyntic and antral. Moreover, not only the stem cell, but the ECL cell may proliferate and give rise to tumours. According to Laurén, the classification of gastric carcinomas seems to reflect biological important differences and possible different cell of origin since the two subtypes, intestinal and diffuse, do not transform into the other and show different epidemiology. The stem cell probably gives rise to the intestinal type, whereas the ECL cell may be important in the diffuse type. Elevation of gastrin may be the carcinogenic factor for Helicobacter pylori as well as the recently described increased risk of gastric cancer due to proton pump inhibitor treatment. Therefore, it is essential to determine the role of the gastrin target cell, the ECL cell, in gastric carcinogenesis. Clinical trials with gastrin antagonists could improve prognoses in those with gastrin receptor positive tumours. However, further studies on gastric carcinomas applying relative available methods and with the highest sensitivity are warranted to improve our knowledge of gastric carcinogenesis.

Netazepide, a gastrin/cholecystokinin-2 receptor antagonist, can eradicate gastric neuroendocrine tumours in patients with autoimmune chronic atrophic gastritis.

AIMS: Netazepide, a gastrin/cholecystokinin 2 receptor antagonist, once daily for 12 weeks reduced the number of tumours and size of the largest one in 16 patients with autoimmune chronic atrophic gastritis (CAG), achlorhydria, hypergastrinaemia and multiple gastric neuroendocrine tumours (type 1 gastric NETs), and normalized circulating chromogranin A (CgA) produced by enterochromaffin-like cells, the source of the tumours. The aim was to assess whether longer-term netazepide treatment can eradicate type 1 gastric NETs. METHODS: After a mean 14 months off netazepide, 13 of the 16 patients took it for another 52 weeks. Assessments were: gastroscopy; gene-transcript expression in corpus biopsies using quantitative polymerase chain reaction; blood CgA and gastrin concentrations; and safety assessments. RESULTS: While off-treatment, the number of tumours, the size of the largest one, and CgA all increased again. Netazepide for 52 weeks: cleared all tumours in 5 patients; cleared all but one tumour in one patient; reduced the number of tumours and size of the largest one in the other patients; normalized CgA in all patients; and reduced mRNA abundances of CgA and histidine decarboxylase in biopsies. Gastrin did not increase further, confirming that the patients had achlorhydria. Netazepide was safe and well tolerated. CONCLUSIONS: A gastrin/cholecystokinin 2 receptor antagonist is a potential medical and targeted treatment for type 1 gastric NETs, and an alternative to regular gastroscopy or surgery. Treatment should be continuous because the tumours will regrow if it is stopped. Progress can be monitored by CgA in blood or biomarkers in mucosal biopsies.

Does long-term profound inhibition of gastric acid secretion increase the risk of ECL cell-derived tumors in man?

OBJECTIVE: Since the description of ECL cell-derived tumors in rodents after long-term profound acid inhibition inducing hypergastrinemia, there has been concern that proton pump inhibitors (PPIs) could also do that in man. The recent description of a Spanish family with gastric ECL cell tumors at the age of about 30 years secondary to a defect in the proton pump due to mutation in the ATP4A gene clearly shows that hypergastrinemia alone also is sufficient to induce ECL cell neoplasia in man. The present review aims to evaluate the risk of gastric neoplasia secondary to gastric acid inhibition. METHODS: Literature (MEDLINE) was searched for the role of the ECL cell in gastric carcinogenesis in animals and man in general and particularly secondary to long-term inhibition of acid secretion. RESULTS: An important proportion of patients treated with PPI develops hypergastrinemia causing ECL cell hyperplasia and the first descriptions of ECL cell carcinoids secondary to PPI have been reported. The role of the ECL cell has hitherto been under estimated in gastric carcinogenesis in man where for instance the signet ring cell type of gastric carcinoma seems to originate from the ECL cell. CONCLUSIONS: The first two of three steps in rodent ECL cell carcinogenesis (hyperplasia, carcinoid, and carcinoma) secondary to PPI dosing, have been described for man. It is every reason to believe that the final step, gastric carcinoma, will develop also in man. Clinical decisions should be based not only on so-called evidence based medicine, but also on physiological knowledge and animal studies.

Follow-up of patients with ECL cell-derived tumours.

OBJECTIVES: To review the presentation, treatment and outcome of patients with type 1 gastric carcinoid tumours. MATERIAL AND METHODS: We retrospectively reviewed medical records and re-evaluated histopathological specimens of 26 patients with type 1 gastric carcinoids treated at a single tertiary referral centre from 1993 to 2013, with median time of follow-up 52.5 months (IQR 90.8). RESULTS: Seven patients (27%) had single tumours and 19 patients (73%) multiple tumours at the time of diagnosis. The median number of tumours and median diameter of largest tumour were 2.5 (IQR 3.2) and 6.0 mm (IQR 9.5) respectively. Median serum gastrin was 321.0 pmol/l (IQR 604.0) and median serum chromogranin A 7.7 nmol/l (IQR 5.3). Three patients had metastatic disease at the time of diagnosis and two developed metastases during follow-up. Patients with metastatic disease had larger primary tumours than the others (20.0 mm (IQR 28.5) vs. 5.0 mm (IQR 5.5), p = 0.04). There was a positive correlation between age and tumour size (r = 0.44, p = 0.03) and between serum chromogranin A and serum gastrin at diagnosis (r = 0.76, p = 0.001). Patients were either treated with surgery (n = 8 (31%)), a long-acting somatostatin analogue and/or gastrin receptor antagonist (n = 10 (39%)) for a period of time, or were observed without treatment (n = 8 (31%) with close endoscopic follow up. CONCLUSIONS: Although gastric carcinoids have an overall good prognosis, a significant proportion develops metastatic disease. As partial and total gastrectomy is associated with major side effects, treatment with long-acting a somatostatin analogue or gastrin antagonist should be considered.

Upper gastrointestinal physiology and diseases.

Nordic research on physiology and pathophysiology of the upper gastrointestinal tract has flourished during the last 50 years. Swedish surgeons and physiologists were in the frontline of research on the regulation of gastric acid secretion. This research finally led to the development of omeprazole, the first proton pump inhibitor. When Swedish physiologists developed methods allowing the assessment of acid secretion in isolated oxyntic glands and isolated parietal cells, the understanding of mechanisms by which gastric acid secretion is regulated took a great step forward. Similarly, in Trondheim, Norway, the acid producing isolated rat stomach model combined with a sensitive and specific method for determination of histamine made it possible to evaluate this regulation qualitatively as well as quantitatively. In Lund, Sweden, the identification of the enterochromaffin-like cell as the cell taking part in the regulation of acid secretion by producing and releasing histamine was of fundamental importance both physiologically and clinically. Jorpes and Mutt established a center at Karolinska Institutet in Stockholm for the purification of gastrointestinal hormones in the 1960s, and Danes followed up this work by excelling in the field of determination and assessment of biological role of gastrointestinal hormones. A Finnish group was for a long period in the forefront of research on gastritis, and the authors' own studies on the classification of gastric cancer and the role of gastrin in the development of gastric neoplasia are of importance. It can, accordingly, be concluded that Nordic researchers have been central in the research on area of the upper gastrointestinal physiology and diseases.

Gastrin May Mediate the Carcinogenic Effect of Helicobacter pylori Infection of the Stomach.

Gastric cancer occurs almost exclusively in patients with gastritis. Since Helicobacter pylori (Hp) was proved to cause gastritis, Hp was also expected to play a role in gastric carcinogenesis. Despite extensive studies, the mechanisms by which Hp cause gastric cancer are still poorly understood. However, there is evidence that the anatomical site of Hp infection is of major importance. Infection confined to the antral mucosa protects against gastric cancer but predisposes to duodenal ulcer, whereas Hp infection of the oxyntic mucosa increases the risk of gastric cancer. Hp infection does not predispose to cancers in the gastric cardia. In patients with atrophic gastritis of the oxyntic mucosa, the intragastric pH is elevated and the concentration of microorganisms in the stomach is increased. This does not lead to increased risk of gastric cancer at all anatomical sites. The site specificity of Hp infection in relation to cancer risk indicates that neither Hp nor the changes in gastric microflora due to gastric hypoacidity are carcinogenic per se. However, reduced gastric acidity also leads to hypergastrinemia, which stimulates the function and proliferation of enterochromaffin-like (ECL) cells located in the oxyntic mucosa. The ECL cell may be more important in human gastric carcinogenesis than previously realized, as every condition causing long-term hypergastrinemia in animals results in the development of neoplasia in the oxyntic mucosa. Patients with hypergastrinemia will far more often develop carcinomas in the gastric corpus. In conclusion, hypergastrinemia may explain the carcinogenic effect of Hp.

The gastric mucosa 25 years after proximal gastric vagotomy.

OBJECTIVE: Vagotomy causes inhibition of basal and post-prandial acid secretion in humans, but the knowledge about the trophic effect of the vagal nerves is limited. Vagotomy is known to induce hypergastrinemia and we aimed to study the long-term effects of proximal gastric vagotomy (PGV) on the oxyntic mucosa and the enterochromaffin-like (ECL) cell density in particular. MATERIAL AND METHODS: Eleven patients operated with PGV because of duodenal ulcer and age- and sex-matched controls were examined 26 to 29 years postoperatively by gastroscopy with biopsies from the antrum and oxyntic mucosa. Neuroendocrine cell volume densities were calculated after immunohistochemical labeling of gastrin, the general neuroendocrine cell marker chromogranin A (CgA) and the ECL cell marker vesicular monoamine transporter 2 (VMAT2). Gastritis was graded and Helicobacter pylori (H. pylori) status was determined by polymerase chain reaction of gastric biopsies. Fasting serum gastrin and CgA were measured. RESULTS: Serum gastrin was higher in the PGV group compared to controls (median 21.0 [interquartile range (IQR) = 22.0] pmol/L vs 13.0 [IQR = 4.0] pmol/L, p = 0.04). However, there was neither a significant difference in serum CgA or in CgA (neuroendocrine) nor VMAT2 (ECL cell) immunoreactive cell volume density in the oxyntic mucosa. There was significantly more inflammation and atrophy in H. pylori-positive patients, but PGV did not influence the grade of gastritis. CONCLUSION: Despite higher serum gastrin concentrations, patients operated with PGV did not have higher ECL cell mass or serum CgA. Vagotomy may prevent the development of ECL cell hyperplasia caused by a moderate hypergastrinemia.

The normal neuroendocrine cells of the upper gastrointestinal tract lack E-cadherin.

OBJECTIVE: E-cadherin plays a crucial role in the adhesion between epithelial cells and thus epithelial integrity. Moreover, germline mutations in the E-cadherin gene (CDH1) causing loss of E-cadherin function (adhesion) leads to hereditary gastric cancer of the diffuse type, according to Laurén. Even sporadic gastric carcinomas of the diffuse type often lose E-cadherin expression due to mutations. Lack of E-cadherin has been recorded at an early phase in such carcinomas. For 25 years, we have provided evidence for neuroendocrine (NE) cell origin of gastric carcinomas of diffuse type. The present study was, therefore, done to examine whether normal NE cells in the gastrointestinal tract express E-cadherin or not. METHODS: During upper gastrointestinal endoscopy, biopsies were taken from normal oxyntic mucosa, gastric carcinoids, gastric carcinomas, and from normal duodenal mucosa. Tissues were examined by immunohistochemistry (IHC) using antibodies toward chromogranin A, synaptophysin, and E-cadherin. Isolated mucosal cells were prepared from biopsies of normal mucosa and examined by antibodies against the same markers by immunofluorescence. RESULTS: Normal gastrointestinal NE cells did not express E-cadherin as assessed by IHC or immunocytochemistry. No expression of E-cadherin was found on tumor cells from gastric carcinoids or cancer of diffuse type examined by IHC. CONCLUSION: Our findings, which are in contrast to some previous studies, may explain why there is a discrepancy between lack of atypia and malignant biological behavior of such tumors. Since they normally lack the adhesion molecule E-cadherin, reflected in their spread occurrence, only minor changes may result in malignant behavior.

Venous plasma serotonin is not a proper biomarker for pulmonary arterial hypertension.

OBJECTIVES: Serotonin (5-HT) most likely plays an important role in the pathogenesis of pulmonary arterial hypertension (PAH). We aimed to test if venous plasma 5-HT is a potential biomarker of PAH. We also measured venous blood ß-thromboglobulin (ß-TG) in all participants to ensure that any increase in serotonin levels measured is due to platelet release. DESIGN: Blood samples from patients (n = 9) with pulmonary arterial hypertension (Group 1 of the World Health Organization classification of pulmonary hypertension) as well as healthy volunteers (n = 9) were analyzed. We used enzyme-linked immunosorbent assay (ELISA) to measure venous platelet-poor plasma 5-HT and ß-TG in patients with pulmonary arterial hypertension (PAH) and in age-matched normal controls. RESULTS: Venous platelet-free plasma 5-HT and ß-TG were almost similar in patients with PAH and healthy controls with only a slight trend toward increased 5-HT levels in patients with PAH. No correlation was found between venous platelet-poor plasma 5-HT and disease severity. There was no association between venous plasma 5-HT and the mean pulmonary artery pressure. CONCLUSIONS: Our data suggest that 5-HT is not significantly elevated in venous platelet-free plasma in patients with PAH and may accordingly not be a useful biomarker in this condition.

Serotonin in blood: assessment of its origin by concomitant determination of ß-thromboglobulin (platelets) and chromogranin A (enterochromaffin cells).

BACKGROUND: Serotonin is produced in enterochromaffin (EC) cells, taken up and stored in platelets and released during platelet activation. Measurement of platelet-poor plasma serotonin is difficult, mainly due to platelet activation during blood sampling. We aimed to establish a method to assess the influence of platelet release upon platelet-poor plasma serotonin measurement by concomitant determination of serotonin, ß-thromboglobulin (ß-TG) and chromogranin A (CgA). METHODS: Blood samples from patients with thrombocytosis, thrombocytopenia and small intestinal neuroendocrine (EC-cell) tumors (SI-NETs) as well as healthy volunteers were analyzed. We also measured serotonin in venous and arterial samples from patients undergoing coronary angiography to evaluate peripheral serotonin metabolism. RESULTS: Serotonin and CgA were significantly higher in patients with SI-NETs compared to all other groups implying EC cell origin of serotonin in patients with SI-NETs. We found that the serotonin concentration was similar in patients with thrombocytosis and thrombocytopenia, whereas plasma ß-TG was higher and lower respectively. A high EDTA concentration in the sampling tubes gave significantly lower serotonin concentrations. Serotonin concentrations did not differ between arterial and venous blood. CONCLUSIONS: Our methodology to measure platelet-poor plasma serotonin was appropriate. Blood platelet numbers did not affect the level of serotonin in contrast to ß-TG.