Omeprazole: its influence on gastric acid secretion, gastrin and ECL cells

Proton Pump Inhibitor Use and Risk of Gastric Cancer: Current Evidence from Epidemiological Studies and Critical Appraisal

Proton pump inhibitors (PPIs) are used for maintaining or improving gastric problems. Evidence from observational studies indicates that PPI therapy is associated with an increased risk of gastric cancer. However, the evidence for PPIs increasing the risk of gastric cancer is still being debated. Therefore, we aimed to investigate whether long-term PPI use is associated with an increased risk of gastric cancer. We systematically searched the relevant literature in electronic databases, including PubMed, EMBASE, Scopus, and Web of Science. The search and collection of eligible studies was between 1 January 2000 and 1 July 2021. Two independent authors were responsible for the study selection process, and they considered only observational studies that compared the risk of gastric cancer with PPI treatment. We extracted relevant information from selected studies, and assessed the quality using the Newcastle−Ottawa scale (NOS). Finally, we calculated overall risk ratios (RRs) with 95% confidence intervals (CIs) of gastric cancer in the group receiving PPI therapy and the control group. Thirteen observational studies, comprising 10,557 gastric cancer participants, were included. Compared with patients who did not take PPIs, the pooled RR for developing gastric cancer in patients receiving PPIs was 1.80 (95% CI, 1.46−2.22, p < 0.001). The overall risk of gastric cancer also increased in patients with gastroesophageal reflux disease (GERD), H. pylori treatment, and various adjusted factors. The findings were also consistent across several sensitivity analyses. PPI use is associated with an increased risk of gastric cancer in patients compared with those with no PPI treatment. The findings of this updated study could be used in making clinical decisions between physicians and patients about the initiation and continuation of PPI therapy, especially in patients at high risk of gastric cancer. Additionally, large randomized controlled trials are needed to determine whether PPIs are associated with a higher risk of gastric cancer.

Effect of Elevated pH on the Commercial Enteric-Coated Omeprazole Pellets Resistance: Patent Review and Multisource Generics Comparison

Omeprazole is a widely used over-the-counter (20 mg) proton pump inhibitor, usually supplied as oral enteric-coated pellets intended to release at pH 5.5 and higher; however, it is sensitive to acidic pH. The likelihood of elevated gastric pH in practice is very high for patients; thus, the aim of this study was to investigate the effect of elevated pH on the performance of commercial omeprazole pellets. Commercial enteric-coated delayed-release pellets were tested with water uptake-weight loss (WU-WL) test at pH range between 1.2 and 4.5 in addition to "gastric" (pH 1.2 or 4.5) and "intestinal" (pH 7.4) phase dissolution tests. The range of physical characteristics of pellets was determined with a single pellet size and sedimentation time measurement, followed by the application of modified Stokes' Law equation. The coefficient of variation of pellet size and density, and volume-density determination coefficient (R²) as descriptors of coating thickness and microstructure variability, degree of ionisation of enteric polymers, aqueous solubility and molecular weight of plasticisers have been found useful to explain commercial delayed-release pellets behaviour during WU-WL and dissolution test. Investigated commercial delayed-release pellets demonstrated pH-dependent WU-WL results. "Gastric phase" dissolution testing of pellets at pH 4.5 showed the highest omeprazole degradation (48.1%) for Nosch Labs, intermediate values of dose loss (23.4% and 17.1%) for Teva and UQUIFA delayed-release pellets, respectively. Lab Liconsa pellets have been found as the least susceptible (3.2% of dose loss). Additionally, "gastric phase" dissolution test at pH 4.5 significantly influenced omeprazole release during the "intestinal phase". The risk of inadequate therapy associated with intake of investigated enteric-coated delayed-release pellets at elevated gastric pH has been found as minimal for Lab Liconsa and has increased from UQUIFA and Teva to Nosh Labs pellets.

Use of vonoprazan for management of systemic sclerosis-related gastroesophageal reflux disease

Gastroesophageal reflux disease (GERD) in systemic sclerosis (SSc) can significantly reduce a patient's quality of life. GERD in SSc is occasionally resistant to conventional anti-acid treatment. Vonoprazan is an H⁺/K⁺-ATPase blocker that is approved in Japan for treatment of GERD. The aim of the present study was to evaluate the efficacy of vonoprazan in SSc-related GERD. The frequency scale for symptoms of GERD (FSSG) scores were collected before and after vonoprazan treatment in 15 SSc patients with GERD. Additionally, endoscopic esophagogastroduodenoscopy was performed in select patients. Conventional proton pump inhibitors or histamine-2 receptor antagonists had been previously administered in 93% (14/15) of the patients. Although the baseline esophagogastroduodenoscopy examination did not show severe erosion in the majority of patients, the mean total FSSG score before vonoprazan treatment was notably high (25.2±10.7) compared to a normal score of <8. After vonoprazan treatment, the FSSG score decreased to 9.6±7.0. The mean improvement rate of the total FSSG, acid reflux and dysmotility scores were 60.8±21.2% (P=0.0004), 67.3±24.8% (P<0.0001) and 55.4±26.0% (P=0.0022), respectively. These results suggest that vonoprazan may be a potentially effective treatment for GERD in patients with SSc.

TIM3 comes of age as an inhibitory receptor

T cell immunoglobulin and mucin domain-containing protein 3 (TIM3), a member of the TIM family, was originally identified as a receptor expressed on interferon-γ-producing CD4⁺ and CD8⁺ T cells. Initial data indicated that TIM3 functioned as a 'co-inhibitory' or 'checkpoint' receptor, but due to the lack of a definable inhibitory signalling motif, it was also suggested that TIM3 might act as a co-stimulatory receptor. Recent studies have shown that TIM3 is part of a module that contains multiple co-inhibitory receptors (checkpoint receptors), which are co-expressed and co-regulated on dysfunctional or 'exhausted' T cells in chronic viral infections and cancer. Furthermore, co-blockade of TIM3 and programmed cell death 1 (PD1) can result in tumour regression in preclinical models and can improve anticancer T cell responses in patients with advanced cancers. Here, we highlight the developments in understanding TIM3 biology, including novel ligand identification and the discovery of loss-of-function mutations associated with human disease. In addition, we summarize emerging data from human clinical trials showing that TIM3 indeed acts as a 'checkpoint' receptor and that inhibition of TIM3 enhances the antitumour effect of PD1 blockade.

Esomeprazole alleviates the damage to stress ulcer in rats through not only its antisecretory effect but its antioxidant effect by inactivating the p38 MAPK and NF-κB signaling pathways

Background

Stress ulcer is a severe complication in critically ill patients and causes a high mortality. The proton pump inhibitor esomeprazole is widely applied in the treatment of stress ulcers because of its powerful acid suppression ability. However, the mechanism of stress ulcer and the precise gastroprotective effect of esomeprazole in stress ulcer remain unclear.

Purpose

In the present study, the rats with water-immersed and restraint (WIR)-induced stress ulcer were used to further elucidate the anti-ulcerogenic capacity of esomeprazole in stress ulcer in addition to its anti-acid secreting ability.

Methods and results

The rats were randomly divided into 5 groups: control group (NS), water-immersed and restraint group (WIR), high-dose application of esomeprazole plus stress ulcer-induced group (HE+WIR), low-dose application of esomeprazole plus stress ulcer-induced group (LE+WIR), and high-dose application of esomeprazole without stress ulcer-induced group (HE). Our study showed that the pretreatment of esomeprazole alleviated gastric tissue damage in both macroscopic and histopathological manifestations. Pretreatment of esomeprazole elevated the decline in PEG2 level affected by WIR; and it inhibited the secretion of gastric acid, gastrin and pepsin. Moreover, esomeprazole exerted its antioxidant effects by reducing malondialdehyde levels, enhancing the expressions of antioxidant factors like glutathione and superoxide dismutase (SOD) and reducing the compensatory transcriptional elevation of SOD1 gene. Esomeprazole also reduced the levels of MPO (myeloperoxidase), tumor necrosis factor (TNF)-α and interleukin (IL)-1β according to its anti-inflammatory effects. We further explored the possible mechanism of esomeprazole pretreatment on stress ulcer and demonstrated that esomeprazole attenuated the high phosphorylation levels of nuclear factor kappa B (NF-κB) p65 and p38 MAPK, and decreased the NF-κB p65 nuclear translocation induced by WIR related stress ulcer.

Conclusion

Our study provides some evidence that the esomeprazole pretreatment exerts gastroprotective effects in WIR-induced stress ulcer through not only its antisecretory effect but also its antioxidant effect by inactivating the p38 MAPK and NF-κB signaling pathways.

Comparison of effect of an increased dosage of vonoprazan versus vonoprazan plus lafutidine on gastric acid inhibition and serum gastrin

BACKGROUND

Vonoprazan, a novel potassium-competitive acid blocker, elicits potent acid inhibition and hypergastrinemia at a dose of 20 mg. Its recommended maintenance dose for gastro-esophageal reflux disease is 10 mg, which is sometimes insufficient for preventing nocturnal acid breakthrough (NAB). Concomitant use of a histamine 2 receptor antagonist (H₂RA) is effective for NAB. However, further acid inhibition by addition of H2RA has concern of hypergastrinemia again. Lafutidine (H2RA) is known to stimulate somatostatin release.

AIMS

The aim of this study is to compare the levels of acid inhibition and serum gastrin attained by addition of lafutidine to vonoprazan 10 mg with levels after a dose increase of vonoprazan from 10 to 20 mg.

METHODS

Thirteen healthy volunteers underwent 24-h intragastric pH monitoring and serum gastrin measurements on day 7 of three different regimens: vonoprazan 10 mg, vonoprazan 10 mg plus lafutidine 10 mg, and vonoprazan 20 mg.

RESULTS

Median pH 4 holding time ratios (range) by vonoprazan 10 mg, vonoprazan 10 mg plus lafutidine 10 mg, and vonoprazan 20 mg were 82% (47-88%), 88% (76-93%), and 99% (95-100%) while those at nighttime from 10 p.m. to 8 a.m. were 94% (29-100%), 100% (95-100%), and 100%, respectively. The incidences of NAB with vonoprazan 10 mg, vonoprazan plus lafutidine, and vonoprazan 20 mg were 38, 8, and 0%, respectively. Respective serum gastrin levels were 420 (173-508), 323 (196-521), and 504 (400-812) pg/ml.

CONCLUSION

Addition of lafutidine 10 mg to vonoprazan 10 mg achieved sufficient acid inhibition, especially at nighttime, without further increase of serum gastrin levels.

Potent acid inhibition by vonoprazan in comparison with esomeprazole, with reference to CYP2C19 genotype

BACKGROUND

Acid inhibitory effects of proton pump inhibitors (PPIs) are influenced by CYP2C19 genotype. In contrast, the potent acid inhibition of vonoprazan is not influenced by CYP2C19 genotype.

AIM

To compare the acid inhibitory effects of vonoprazan and esomeprazole in relation to CYP2C19 genotype.

METHODS

Twenty-eight healthy Japanese volunteers [7 CYP2C19 poor metabolisers (PMs), 11 intermediate metabolisers (IMs) and 10 rapid metabolisers (RMs)] received four different regimens in a randomised crossover manner: (i) vonoprazan 20 mg twice daily (b.d.), (ii) vonoprazan 20 mg daily, (iii) esomeprazole 20 mg b.d. and (iv) esomeprazole 20 mg daily. The timing of each dosing was 1 h before a meal. Twenty-four-hour intragastric pH monitoring was performed on day 7 on each regimen.

RESULTS

In the overall genotype group, pH ≥4 holding time ratios (pH 4 HTRs) with vonoprazan b.d., vonoprazan daily, esomeprazole b.d. and esomeprazole daily were 100%, 95%, 91%, and 68% respectively. pH 5 HTRs were 99%, 91%, 84% and 54% respectively. Vonoprazan b.d. potently suppressed acid for 24 h, and was significantly superior to other regimens irrespective of CYP2C19 genotype. Vonoprazan daily was equivalent to esomeprazole b.d. in IMs and PMs, but superior in RMs. CYP2C19 genotype-dependent differences were observed in esomeprazole daily but not in vonoprazan b.d. or daily.

CONCLUSION

Vonoprazan 20 mg b.d. inhibits acid irrespective of CYP2C19 genotype, more potently than esomeprazole 20 mg b.d., pH 4 and 5 holding time ratios reached 100% and 99%, respectively.

Systematic review: the effects of long-term proton pump inhibitor use on serum gastrin levels and gastric histology

BACKGROUND

Proton pump inhibitors (PPIs) have a well-established safety profile. However, concerns have been raised about a potential relationship between PPI-induced hypergastrinaemia and the development of enterochromaffin-like (ECL) cell hyperplasia, neuroendocrine tumours and gastric cancer during long-term therapy.

AIM

To review the effects of long-term PPI use on serum gastrin levels and gastric histopathology.

METHODS

A systematic literature search was conducted in PubMed on 21 April 2015 to identify studies reporting the effects of long-term (defined as >3 years) PPI use on gastrin levels and gastric histopathology.

RESULTS

A total of 16 studies (1920 patients) met the inclusion criteria. During long-term PPI therapy, mean gastrin levels rose to one to three times the upper limit of the normal range (~100 pg/mL), and an increased prevalence of ECL cell hyperplasia was observed (+7.8-52.0%). Helicobacter pylori-positive patients had a significantly increased risk of developing ECL linear/micronodular hyperplasia compared with H. pylori-negative patients [OR: 2.45 (95% CI: 1.47-4.10), P = 0.0006]; however, no evidence of neoplastic changes was found. The risk of corpus atrophy was markedly higher in H. pylori-positive patients than in H. pylori-negative patients [OR: 11.45 (95% CI: 6.25-20.99), P < 0.00001]. Not a single case of gastric adenocarcinoma was found.

CONCLUSIONS

Long-term PPI therapy induced moderate hypergastrinaemia in most patients and an increased prevalence of ECL cell hyperplasia. H. pylori-positive patients receiving long-term PPI therapy were exposed to a higher risk of corpus atrophy than H. pylori-negative patients. No neuroendocrine tumours or gastric cancers were found.

Histopathological and Immunohistochemical Characterization of Methyl Eugenol-induced Nonneoplastic and Neoplastic Neuroendocrine Cell Lesions in Glandular Stomach of Rats

Methyl eugenol induces neuroendocrine (NE) cell hyperplasia and tumors in F344/N rat stomach. Detailed histopathological and immunohistochemical (IHC) characterization of these tumors has not been previously reported. The objective of this study was to fill that data gap. Archived slides and paraffin blocks were retrieved from the National Toxicology Program Archives. NE hyperplasias and tumors were stained with chromogranin A, synaptophysin, amylase, gastrin, H(+)/K(+) adenosine triphosphatase (ATPase), pepsinogen, somatostatin, and cytokeratin 18 (CK18) antibodies. Many of the rats had gastric mucosal atrophy, due to loss of chief and parietal cells. The hyperplasias and tumors were confined to fundic stomach, and females were more affected than the males. Hyperplasia of NE cells was not observed in the pyloric region. Approximately one-third of the females with malignant NE tumors had areas of pancreatic acinar differentiation. The rate of metastasis was 21%, with liver being the most common site of metastasis. Immunohistochemically, the hyperplasias and tumors stained consistently with chromogranin A and synaptophysin. Neoplastic cells were also positive for amylase and CK18 and negative for gastrin, somatostatin, H(+)/K(+) ATPase, and pepsinogen. Metastatic neoplasms histologically similar to the primary neoplasm stained positively for chromogranin A and synaptophysin. Based on the histopathological and IHC features, the neoplasms appear to arise from enterochromaffin-like cells.

Anti-inflammatory, gastroprotective and anti-ulcerogenic effects of red algae Gracilaria changii (Gracilariales, Rhodophyta) extract

Background

Gracilaria changii (Xia et Abbott) Abbott, Zhang et Xia, a red algae commonly found in the coastal areas of Malaysia is traditionally used for foods and for the treatment of various ailments including inflammation and gastric ailments. The aim of the study was to investigate anti-inflammatory, gastroprotective and anti-ulcerogenic activities of a mass spectrometry standardized methanolic extract of Gracilaria changii.

Methods

Methanolic extract of Gracilaria changii (MeOHGCM6 extract) was prepared and standardized using mass spectrometry (MS). Anti-inflammatory activities of MeOHGCM6 extract were examined by treating U937 cells during its differentiation with 10 μg/ml MeOHGCM6 extract. Tumour necrosis factors-α (TNF-α) response level and TNF-α and interleukin-6 (IL-6) gene expression were monitored and compared to that treated by 10 nM betamethasone, an anti-inflammatory drug. Gastroprotective and anti-ulcerogenic activities of MeOHGCM6 extract were examined by feeding rats with MeOHGCM6 extract ranging from 2.5 to 500 mg/kg body weight (b.w.) following induction of gastric lesions. Production of mucus and gastric juice, pH of the gastric juice and non-protein sulfhydryls (NP-SH) levels were determined and compared to that fed by 20 mg/kg b.w. omeprazole (OMP), a known anti-ulcer drug.

Results

MS/MS analysis of the MeOHGCM6 extracts revealed the presence of methyl 10-hydroxyphaeophorbide a and 10-hydroxypheophytin a, known chlorophyll proteins and several unidentified molecules. Treatment with 10 μg/ml MeOHGCM6 extract during differentiation of U937 cells significantly inhibited TNF-α response level and TNF-α and IL-6 gene expression. The inhibitory effect was comparable to that of betamethasone. No cytotoxic effects were recorded for cells treated with the 10 μg/ml MeOHGCM6 extract. Rats fed with MeOHGCM6 extract at 500 mg/kg b.w. showed reduced absolute ethanol-induced gastric lesion sizes by > 99% (p < 0.05). This protective effect was comparable to that conferred by OMP. The pH of the gastric mucus decreased in dose-dependent manner from 5.51 to 3.82 and there was a significant increase in NP-SH concentrations.

Conclusions

Results from the study, suggest that the mass spectrometry standardized methanolic extract of Gracillaria changii possesses anti-inflammatory, gastroprotective and anti-ulcerogenic properties. Further examination of the active constituent of the extract and its mechanism of action is warranted in the future.

The rasH2 Mouse Model for Assessing Carcinogenic Potential of Pharmaceuticals

A factor limiting widespread use of the transgenic rasH2 mouse model for carcinogenicity testing of pharmaceuticals is the paucity of published data on actual drug candidates in rasH2 mice. This report addresses this gap by highlighting rasH2 mouse study data for 10 pharmaceutical candidates. These results were compared with findings in the 2-year studies in Sprague-Dawley rats for the same 10 compounds. In the 6-month rasH2 studies, only 2 of the 10 compounds tested positive for carcinogenicity and these correlated with positive findings in the companion 2-year rat studies. One compound, sunitinib, produced gastroduodenal carcinoma in both sexes and increased hemangiosarcoma in spleen and uterus in female rasH2 mice; in rats it produced gastroduodenal carcinoma and increased pheochromocytoma (males only). The second compound, bazedoxifene, produced ovarian granulosa cell neoplasms in rasH2 mice and rats, and renal tubular neoplasms associated with increased chronic progressive nephropathy only in rats. The higher percentage of carcinogenicity positive rat bioassays could be attributed to rat-specific phenomena with little or low relevance to man. Thus, this article confirms previous reports that rasH2 mice develop rodent-specific neoplasms less frequently than rats and positive findings, when present, are accompanied by similar positive results in the rat.

Long-term, open-label trial: safety and efficacy of continuous maintenance treatment with pantoprazole for up to 15 years in severe acid-peptic disease

BACKGROUND

To date, the safety and tolerability of proton pump inhibitors (PPIs) have been demonstrated in studies of up to 10 years.

AIM

To report on the tolerability, safety and efficacy of up to 15 years' continuous treatment with pantoprazole in patients with severe acid-peptic disease.

METHODS

Following healing of endoscopically confirmed peptic ulcer or reflux oesophagitis during 4-12 weeks' treatment with pantoprazole (40-80 mg/day), adult patients received open-label maintenance treatment with pantoprazole (40-160 mg/day) for up to 15 years in a single centre combined study (10-year initial study; 5-year extension study). Safety assessments were carried out using endoscopy, clinical examination, clinical laboratory investigations, serum gastrin determination, gastric mucosal histology and mucosal endocrine cell quantification.

RESULTS

The safety set comprised 142 patients. At 12 weeks, healing rates were 95.8%. During long-term treatment, mean fasting gastrin levels rose from baseline to moderate levels throughout the study. Mean enterochromaffin-like cell density showed a moderate initial increase during the first 3 years, remaining stable thereafter. These changes were not associated with any clinically relevant changes of the gastric mucosa. Patients with successful Helicobacter pylori eradication showed long-term regression of antral and corpus gastritis during continued pantoprazole treatment.

CONCLUSIONS

Daily pantoprazole maintenance therapy for up to 15 years for severe acid-peptic disease is effective and well tolerated, with no identified safety concerns. The longest study to date, these data provide reassuring evidence for the long-term safety of pantoprazole.

Successful drug development despite adverse preclinical findings part 1: processes to address issues and most important findings

Unexpected adverse preclinical findings (APFs) are not infrequently encountered during drug development. Such APFs can be functional disturbances such as QT prolongation, morphological toxicity or carcinogenicity. The latter is of particular concern in conjunction with equivocal genotoxicity results. The toxicologic pathologist plays an important role in recognizing these effects, in helping to characterize them, to evaluate their risk for man, and in proposing measures to mitigate the risk particularly in early clinical trials. A careful scientific evaluation is crucial while termination of the development of a potentially useful drug must be avoided. This first part of the review discusses processes to address unexpected APFs and provides an overview over typical APFs in particular classes of drugs. If the mode of action (MoA) by which a drug candidate produces an APF is known, this supports evaluation of its relevance for humans. Tailor-made mechanistic studies, when needed, must be planned carefully to test one or several hypotheses regarding the potential MoA and to provide further data for risk evaluation. Safety considerations are based on exposure at no-observed-adverse-effect levels (NOAEL) of the most sensitive and relevant animal species and guide dose escalation in clinical trials. The availability of early markers of toxicity for monitoring of humans adds further safety to clinical studies. Risk evaluation is concluded by a weight of evidence analysis (WoE) with an array of parameters including drug use, medical need and alternatives on the market. In the second part of this review relevant examples of APFs will be discussed in more detail.

Chemical carcinogenesis of the gastrointestinal tract in rodents: an overview with emphasis on NTP carcinogenesis bioassays

Cancers of the stomach and large intestine (LI) are the second and fourth leading causes of human cancer mortality. A review of the National Toxicology Program (NTP) database and the Carcinogenic Potency Database (CPDB) reveals that chemically induced neoplasms of the gastrointestinal tract (GIT) are relatively common. Within the GIT, epithelial tumors of the forestomach in mice and rats and LI of the rat are most common. Generally, there is a high species concordance for forestomach with at least 26 chemicals inducing tumors in both species. Glandular stomach tumors are rare, and the few reported are usually neuroendocrine tumors (carcinoids) originating from the enterochromaffin-like (ECL) cells. Of 290 carcinogenic agents identified by the NTP, 19 (7%) caused intestinal neoplasia, 14 in the rat and 5 in the mouse. Neoplasms occurred in both males and females, exclusively in the small intestine (SI) of the mouse and in the LI or both SI and LI in the rat. Enteric carcinogens (NTP) frequently induced neoplasms at other alimentary sites (oral cavity, esophagus, and stomach). In conclusion, the most common induced GIT tumors are squamous neoplasms of the forestomach, glandular neoplasms of the stomach are rare, and rats appear more prone to developing LI (colorectal) cancer compared to mice.

Effects of omeprazole treatment on nucleoside transporter expression and adenosine uptake in rat gastric mucosa

Increased adenosine concentration inhibits gastric acid secretion in rat via adenosine A1 and A2A receptors, whereas achlorhydria suppresses A1 and A2A receptor gene expression. This study aimed to examine the effects of omeprazole-induced achlorhydria on the expression and functional activity of nucleoside transporters in rat gastric mucosa. Wistar rats were treated for either 1 or 3 days with 0.4 mmol/kg omeprazole via gavage; controls were treated with vehicle. The expression of nucleoside transporters at the transcript level was explored by quantitative real-time polymerase chain reaction assays; the functional activity of nucleoside transporters in gastric mucosa was explored by observing [3H]adenosine uptake in vitro. Gastric mucosa expressed rat equilibrative nucleoside transporter (rENT) 1 and 2, and rat concentrative nucleoside transporter (rCNT) 1, 2, and 3 at the transcript level, and the estimated values for the threshold cycles for target amplification (Ct) were 31.5 +/- 2, 28.5 +/- 2.1, 32.9 +/- 2.2, 29.1 +/- 2, and 28.9 +/- 2.5, respectively (n = 3 or 4). The Ct value for rat beta-actin was 21.9 +/- 1.8 (n = 4). In vitro uptake of [3H]adenosine by gastric mucosa samples consisted of Na+-dependent and Na+-independent components. One-day omeprazole treatment caused no change in nucleoside transporter mRNA levels or in [3H]adenosine uptake. Three-day omeprazole treatments, however, led to a 12-fold and 17-fold increase in rENT2 and rCNT1 mRNA levels, respectively. Samples taken after 3 days of treatment also took up significantly more [3H]adenosine than did samples from the corresponding control. In conclusion, the possible modification of nucleoside transport activities by changes in intraluminal acidity may have significance as part of a purinergic regulatory feedback mechanism in the control of gastric acid secretion.

Long-term use of proton pump inhibitors does not affect the frequency, growth, or histologic characteristics of colon adenomas

BACKGROUND

The clinical significance of the trophic effects of long-term proton pump inhibitors (PPI)-related hypergastrinemia on colon polyps remains unknown.

AIM

To study the frequency, growth, and histology of colon polyps in patients on chronic PPI therapy (cases), compared to those not receiving acid suppression (controls).

METHODS

Medical records of 2868 consecutive patients who underwent two or more colonoscopies, performed 3 or more months apart were reviewed. Cases (116) that used PPIs between the two colonoscopies were then compared to controls (194).

RESULTS

Demographics and risk factors for colon cancer were comparable between the two groups. At baseline the mean frequency and size of adenomatous polyps were similar in cases and controls (P > 0.05) and at follow-up, these were 0.89 and 1.18 (P > 0.05; 95% CI of -0.08 to 0.66) and 4.09 mm and 4.00 mm (P > 0.05; 95% CI -2.29 to 2.11), respectively with no significant change. However, control group had a higher mean frequency and size of hyperplastic polyps at baseline as well as at follow-up colonoscopy (P < 0.05).

CONCLUSIONS

The long-term use of PPI does not influence the frequency, growth, or histology of adenomatous polyps, but is associated with a reduction in both baseline and interval development of hyperplastic polyps.

Influence of CYP2C19 pharmacogenetic polymorphism on proton pump inhibitor-based therapies

Proton pump inhibitors (PPIs), such as omeprazole, lansoprazole, rabeprazole, esomeprazole, and pantoprazole, are mainly metabolized by CYP2C19 in the liver. There are genetically determined differences in the activity of this enzyme. The genotypes of CYP2C19 are classified into the three groups, rapid extensive metabolizer (RM), intermediate metabolizer (IM), and poor metabolizer (PM). The pharmacokinetics and pharmacodynamics of PPIs depend on CYP2C19 genotype status. Plasma PPI levels and intragastric pHs during PPI treatment in the RM group are lowest, those in the IM group come next, and those in the PM group are highest of the three groups. These CYP2C19 genotype-dependent differences in pharmacokinetics and pharmacodynamics of PPIs influence the cure rates for the gastro-esophageal reflux disease and H. pylori infection by PPI-based therapies. For the better PPI-based treatment, doses and dosing schemes of PPIs should be optimized based on CYP2C19 genotype status.

Lack of histamine alters gastric mucosal morphology: comparison of histidine decarboxylase-deficient and mast cell-deficient mice

Histamine plays an important role in the regulation of gastric acid secretion; however, its role in maintenance of gastric morphology remains unclear. To clarify the necessity of histamine for gastric mucosal development and maintenance, we evaluated two different kinds of mice that lacked either mast cells (one of the gastric histamine-producing cell types) or histidine decarboxylase (HDC; a histamine-synthesizing enzyme). Measurements of stomach weight, intragastric pH, mucosal histamine levels, as well as serum gastrin and albumin levels were performed in mice. Gastric mucosal appearance was examined by immunohistochemical techniques. Although gastric mucosal histamine levels in mast cell-deficient mice were half of those observed in the wild-type mice, intragastric pH, serum gastrin levels, and gastric morphology at 12 mo were unchanged compared with the wild-type mice. In contrast, HDC-deficient mice possessed no detectable gastric histamine, but did exhibit hypergastrinemia, as well as marked increases in intragastric pH and stomach weight compared with the wild-type mice. Histological analysis revealed that 9-mo-old HDC-deficient mice demonstrated hyperplasia in the oxyntic glandular base region, as well as increased numbers of parietal and enterochromaffin-like cells. These results indicate that enterochromaffin-like cell-derived histamine is potentially involved in gastric mucosal morphology regulation.

Pharmacogenomics of proton pump inhibitors

Proton pump inhibitors (PPIs), such as omeprazole, lansoprazole, rabeprazole, esomeprazole, and pantoprazole, are metabolized by cytochrome P450 isoenzyme 2C19 (CYP2C19) in the liver. There are genetic differences that affect the activity of this enzyme. The genotypes of CYP2C19 are classified into three groups: homozygous extensive metabolizer (homEM), heterozygous extensive metabolizer (hetEM), and poor metabolizer (PM). The pharmacokinetics and pharmacodynamics of PPIs differ among the different CYP2C19 genotype groups. Plasma PPI and intragastric pH levels during PPI treatment are the lowest in the homEM group and the highest in the PM group. These CYP2C19 genotype-dependent differences in pharmacokinetics and pharmacodynamics of PPIs are reflected in the cure rates for gastroesophageal reflux disease and Helicobacter pylori infection with PPI-based therapies. The CYP2C19 genotyping test is a useful tool for deciding on the optimal treatment regimen using a PPI, including a dual (PPI plus antibiotic) or a triple (PPI plus two antibiotics) therapy.

Sodium pentobarbital anesthesia transiently enhances the severity of infection following intragastric, but not intravenous, inoculation of Listeria monocytogenes in mice

In the present study we observed that mice anesthetized with sodium pentobarbital were far more susceptible to gastrointestinal challenge with Listeria monocytogenes than were unanaesthetized mice. The effect of pentobarbital anesthesia was transient (gone within 2 h) and did not alter the severity of infection following i.v. challenge with L. monocytogenes. Treatment with pharmacological inhibitors of gastric acidity (i.e. cimetidine and omeprazole), or intestinal motility (loperamide), did not duplicate the effect of pentobarbital on gastrointestinal listeriosis. These findings suggest that sodium pentobarbital anesthesia causes a short-lived but striking diminution in resistance to gastrointestinal listeriosis in mice, via an undefined mechanism.

Gastric neuroendocrine tumors in a 2-year oncogenicity study with CD-1 mice

Descriptions of two rare gastric neuroendocrine tumors (carcinoids) of enterochromaffin (ECL) cells in CD-1 mice (2/50) from a 104-week oncogenicity study of a serotonergic/dopaminergic compound are presented. These tumors were detected at necropsy and confirmed by histopathology in hematoxylin and eosin- and Chromogranin A-stained slides. ECL cell counts of the glandular stomachs were determined by quantitative image analysis and did not reveal any hyperplastic changes as possible predisposing lesions for carcinoid formation. To investigate the possibility of drug-induced hypergastrinemia as the cause of tumor formation of ECL cells, gastrin blood levels were measured after treating mice for 7 days with the test substance. In this study, Omeprazole, the positive control, raised gastrin levels, while the test material did not. It was concluded that these two tumors were an example of "late-life"-occurring, spontaneous neuroendocrine tumors in the stomachs of aged CD-1 mice.

Dose-dependent induction of glandular stomach preneoplastic and neoplastic lesions in male F344 rats treated with catechol chronically

The dose-dependence of catechol glandular stomach carcinogenesis was investigated in male F344 rats. Groups of 30 male animals were fed catechol at dietary levels of 0 (control). 0.1, 0.2, 0.4, and 0.8% for up to 104 weeks. Five rats of each group were killed at 34 weeks and the remaining animals were sacrificed at the termination, all undergoing histopathological examination. Moderate retardation of body weight increase was observed in the 0.8% group. but no adverse effects were found in terms of survival. Submucosal hyperplasias and adenomas of the pyloric glands developed in the 0.4 and 0.8% groups, only very minor changes being noted in the 0.1 and 0.2% groups at week 34. Incidences of adenocarcinoma development in the pylorus were 4% and 8% in 0.4% and 0.8% groups, respectively, and 0 in the 0.1% and 0.2% groups, at the termination. Adenomas and submucosal hyperplasias were found in nearly all animals fed 0.2% catechol or more, the incidences of those in 0.1% group being 0% and 56%, respectively. Serum gastrin levels were significantly increased in the 0.2, 0.4, and 0.8% groups at 34 weeks, and in all treated groups at the termination, at extents comparable with the induction of proliferative lesions in the pylorus. The results thus demonstrated that dietary levels of 0.4% and 0.8% catechol long-term induce adenocarcinomas in the pyloric glands, while 0.1 and 0.2% cause benign proliferative lesions, all accompanied by increase in serum gastrin levels. As a no-effect level could not be decided in the present study, further investigation of lower doses is needed to determine whether a threshold exists.

Review article: potential gastrointestinal effects of long-term acid suppression with proton pump inhibitors

This review examines the evidence for the development of adverse effects due to prolonged gastric acid suppression with proton pump inhibitors. Potential areas of concern regarding long-term proton pump inhibitor use have included: carcinoid formation; development of gastric adenocarcinoma (especially in patients with Helicobacter pylori infection); bacterial overgrowth; enteric infections; and malabsorption of fat, minerals, and vitamins. Prolonged proton pump inhibitor use may lead to enterochromaffin-like cell hyperplasia, but has not been demonstrated to increase the risk of carcinoid formation. Long-term proton pump inhibitor treatment has not been documented to hasten the development or the progression of atrophic gastritis to intestinal metaplasia and gastric cancer, although long-term studies are required to allow definitive conclusions. At present, we do not recommend that patients be tested routinely for H. pylori infection when using proton pump inhibitors for prolonged periods. Gastric bacterial overgrowth does increase with acid suppression, but important clinical sequelae, such a higher rate of gastric adenocarcinoma, have not been seen. The risk of enteric infection may increase with acid suppression, although this does not seem to be a common clinical problem with prolonged proton pump inhibitor use. The absorption of fats and minerals does not appear to be significantly impaired with chronic acid suppression. However, vitamin B12 concentration may be decreased when gastric acid is markedly suppressed for prolonged periods (e.g. Zolllinger-Ellison syndrome), and vitamin B12 levels should probably be assessed in patients taking high-dose proton pump inhibitors for many years. Thus, current evidence suggests that prolonged gastric acid suppression with proton pump inhibitors rarely, if ever, produces adverse events. Nevertheless, continued follow-up of patients taking proton pump inhibitors for extended periods will provide greater experience regarding the potential gastrointestinal adverse effects of long-term acid suppression.

Gastrin effects on isolated rat enterochromaffin-like cells following long-term hypergastrinaemia in vivo

The enterochromaffin-like (ECL) cells play an important role in the regulation of gastric acid secretion. They respond to gastrin by a prompt increase in histamine secretion, an effect which is mediated by the CCK-(B)/gastrin receptor acting through the IP(3)/DAG pathway. In the rat, long-term treatment with acid secretion inhibitors induces hypergastrinaemia which, in turn, results in ECL cell hypertrophy and hyperplasia. The aim of the present study was to evaluate various functional parameters in acutely isolated rat ECL cells, following long-term hypergastrinaemia in vivo. Rats were treated with vehicle or a supramaximal daily dose of omeprazole for more than 10 weeks to ensure ECL cell hyperplasia. ECL cells were isolated from vehicle-treated animals and 24, 72 and 120 h after the last dose of omeprazole. The functional activity of the acutely isolated ECL cells was determined by measuring gastrin-and forskolin-induced histamine secretion. Changes in cytosolic free calcium upon gastrin stimulation were monitored by digital video imaging. ECL cells successively regained their ability to respond to gastrin following long-term hypergastrinaemia, reaching close to vehicle-treated levels 120 h after the last dose of omeprazole. In the rat, the response pattern of the ECL cells appears to normalise in parallel with the normalisation of plasma gastrin levels.

Evaluation of omeprazole genotoxicity in a battery of in vitro and in vivo assays

Omeprazole, a proton pump inhibitor of wide use in the treatment of gastric acid-related disorders, was evaluated for its genotoxic effects in both rat and human cultured cells and in the intact rat. DNA repair synthesis, as revealed by autoradiography, was detected in primary cultures of metabolically competent rat hepatocytes exposed to concentrations ranging from 10 to 100 mg/l, but the responses cannot be considered as clearly positive. Under the same experimental conditions any significant evidence of DNA repair was absent in primary hepatocytes from two human donors. At the same concentrations a modest but dose-related increase of micronucleated cells, that reached the level of statistical significance at 33 mg/l, was present in primary rat hepatocytes and in one of two human donors. In human lymphocytes exposed to subtoxic concentrations ranging from 0.78 to 12.5 mg/l a reproducible concentration dependent clastogenic effect was absent. In partially hepatectomized female rats treated with a single p.o. dose of 1000 mg/kg, the frequency of micronucleated cells was 5.2-fold higher than in controls in the liver, but only 2.0-fold higher in polychromatic erythrocytes of the bone marrow. In rats of the same sex given azoxymethane as initiator of colon carcinogenesis the oral administration for 8 successive weeks of 10 mg/kg omeprazole on alternate days increased the response to azoxymethane, as indicated by the occurrence in colon mucosa of a modest but statistically significant increase in both the average number and size of aberrant crypt foci. Taken as a whole, our results suggest that omeprazole behaves as a weak genotoxic agent for the rat liver. Reliable information about the potential genotoxic risk to humans requires further studies on primary cells from a wide number of donors.

Quantitation of glandular gastric changes in rats given a proton pump inhibitor for 3 months with emphasis on sampling scheme selection

Proton pump inhibitors and H2-receptor antagonists suppress gastric acid secretion and secondarily induce hypergastrinemia. Sustained hypergastrinemia has a trophic effect on stomach fundic mucosa, including enterochromaffin-like (ECL) cell hypertrophy and hyperplasia. Histomorphometric quantitation of the pharmacologic gastric effects was conducted on 10 male and 10 female rats treated orally with LY307640 sodium, a proton pump inhibitor, at daily doses of 25, 60, 130, or 300 mg/kg for 3 mo. Histologic sections of glandular stomach, stained for chromogranin A, were evaluated by image analysis to determine stomach mucosal thickness, mucosal and nonmucosal (submucosa and muscularis) area, gastric glandular area, ECL cell number/area and cross-sectional area. Total mucosal and nonmucosal tissue volumes per animal were derived from glandular stomach volumetric and area data. Daily oral doses of compound LY307640 sodium caused slight to moderate dose-related mucosal hypertrophy and ECL cell hypertrophy and hyperplasia in all treatment groups as compared with controls. All observed effects were prominent in both sexes but were generally greater in females. The morphometric sampling schemes were explored to optimize the data collection efficiency for future studies. A comparison between the sampling schemes used in this study and alternative schemes was conducted by estimating the probability of detecting a specific percentage of change between the male control and high-dose groups based on Tukey's trend test. The sampling scheme analysis indicated that mucosal thickness and mass had been oversampled. ECL cell density quantitation efficiency would have been increased by sampling the basal mucosa only for short-term studies. The ECL cell size sampling scheme was deemed appropriate for this type of study.

Gastrin release and gastric acid secretion in the rat infected with either Helicobacter felis or Helicobacter heilmannii

Helicobacter pylori infection in humans has been shown to be associated with changes in gastric physiology, including exaggerated basal and meal-stimulated gastrin levels. This has been suggested to be due to the direct effects of the bacterium through inflammation and its urease enzyme. The gastric bacteria Helicobacter felis and Helicobacter heilmannii colonize the antrum of rats in large numbers and induce no significant inflammatory response. Thus, the direct effect of Helicobacter infection on gastric physiology, independent of gastritis, could be studied. Basal, freely fed and stimulated acid and gastrin levels were recorded from animals infected with H. felis, H. heilmannii or uninfected controls over a 30 week period. No significant difference was found between freely fed gastrin over 7 weeks or fasting gastrin over 24 weeks or basal and stimulated acid over 30 weeks between all three groups. Triple therapy did not alter gastrin or acid output. The antrum of all Helicobacter-infected rats was well colonized; triple therapy cleared H. felis but not H. heilmannii. Very little inflammation was seen in control or Helicobacter-infected animals. In conclusion, Helicobacter-induced effects on gastric physiology are unlikely to be due to direct bacterial effects, but are best explained by other factors (i.e. inflammatory damage).

Neuropeptide Y- and peptide YY-containing colonic cells increase with ageing in male rats

Colonic mucosal cells are known to contain several neuropeptides. The distribution of various peptide-containing cells in the colon and their possible modulation by aging and diet are unknown. We quantitated various peptide-containing cells from male Lobund-Wistar rat colon at 2, 22, 28, 30 and 33 months of age using indirect immunohistochemical techniques for several peptides including: neuropeptide Y, peptide YY, somatostatin, and chromogranin A. Four diets, varying in total calories and fat content, were examined. Serum gastrin was quantified by RIA at 2 and 33 months. Only NPY-, PYY- and SOM-positive cells were found in the colon. The number per crypt of neuropeptide Y-positive (0.55 +/- 0.04 at 2 months vs 0.80 +/- 0.22 at 33 months, P = 0.015) and peptide YY-positive cells increased with age. Staining for somatostatin and chromogranin, a marker for all enterochromaffin (EC) cells, revealed no change with aging. Diet did not influence the numbers of any peptide-containing cell. Serum gastrin was not different between the groups. A specific increase in NPY- and PYY-positive cells occurs in the aged rat colon. The extent to which this change may be related to age-related colonic dysmotility seen in elderly humans is worthy of exploration.

DNA single-strand scission in the pyloric mucosa of rat stomach induced by four glandular stomach carcinogens and three other chemicals

Induction of DNA single-strand scission by four glandular stomach carcinogens and three other chemicals was studied in the pyloric mucosa of rat stomach after gastric intubation. DNA single-strand scission, as was measured by the alkaline elution method, was induced by four glandular stomach carcinogens; N-nitroso N-methylurethane at doses of 1 and 9 mg/kg body wt, 4-nitroquinoline 1-oxide at 20 and 30 mg/kg body wt. N-ethyl-N'-nitro-N-nitrosoguanidine at 30 and 100 mg/kg body wt and N-propyl-N'-nitro-N-nitrosoguanidine at 30 and 100 mg/kg body wt. DNA single-strand scission was also induced dose-dependently by a direct acting mutagen, 1-nitrosoindole-3-acetonitrile at doses of 100, 500 and 800 mg/kg body wt. Omeprazole, a proton pump inhibitor, was equivocal in its effect in this assay at 30-500 mg/kg body wt: induction was statistically significant by Cochran-Armitage binomial trend test. Loxtidine, an H2-receptor antagonist, did not induce DNA single-strand breaks in the pyloric mucosa at a dose of 400 mg/kg body wt. The present results together with previous information suggest that DNA single-strand scission is a good marker for tumor-initiating activity in rat stomach mucosa.

Endocrine tumours of the stomach

This review illustrates the current classification of gastric endocrine tumors: a) carcinoid tumors (associated with chromic atrophic gastritis; with Zollinger-Ellison syndrome and multiple endocrine neoplasia type I; sporadic) and b) neuroendocrine carcinomas. The pathogenetic characteristics and clinical implications that justify this classification are discussed.

Antiulcerogenicity of the flavonoid fraction from Bidens aurea: comparison with ranitidine and omeprazole

Effects of the flavonoid fraction of Bidens aurea (Aiton) Sherff on gastric ulceration induced by restraint and cold were studied in rats. Mucosal damage was evaluated histomorphometrically and the results were compared with those of omeprazole and ranitidine. The effects of these agents on the quantity and quality of the gastric mucus were also determined histologically and biochemically. Oral treatment with the ether fraction of the flavonoid extract gave the highest level of gastric protection. Mucus content was increased and accompanied by a proportional increase in proteins and hexosamines. There was also a marked increase of the periodic acid-Shiff (PAS) area (neutral glycoprotein) and the alcian blue (AB) area (sulphated glycoprotein). The groups which received ranitidine and omeprazole did not overcome the inhibition of the mucus secretion induced in this experimental model.

Omeprazole and high dose ranitidine in the treatment of refractory reflux oesophagitis

Thirty two consecutive patients (age range 6 months-13.4 years) with severe reflux oesophagitis were randomised to a therapeutic trial for eight weeks during which they received either standard doses of omeprazole (40 mg/day/1.73 m2 surface area) or high doses of ranitidine (20 mg/kg/day). Twenty five patients completed the trial (12 on omeprazole, 13 on ranitidine). At entry and at the end of the trial patients underwent symptomatic score assessment, endoscopic and histological evaluation of the oesophagus, and simultaneous oesophageal and gastric pH measurement; results are given as median (range). Both therapeutic regimens were effective in decreasing clinical score (omeprazole before 24.0 (15-33), after 9.0 (0-18); ranitidine before 19.5 (12-33), after 9.0 (6-12)), in improving the histological degree of oesophagitis (omeprazole before 8.0 (6-10), after 2.0 (0-60); ranitidine before 8.0 (8-10), after 2.0 (2-6), and in reducing oesophageal acid exposure, measured as minutes of reflux at 24 hour pH monitoring (omeprazole before 129.4 (84-217), after 44.6 (0.16-128); ranitidine before 207.3 (66-306), after 58.4 (32-128)) as well as intragastric acidity, measured as median intragastric pH (omeprazole before 2.1 (1.0-3.0), after 5.1 (2.2-7.4); ranitidine before 1.9 (1.6-4), after 3.4 (2.3-5.3)). Serum gastrin concentration was > 150 ng/l in four patients on omeprazole and in three patients on ranitidine. It is concluded that in children with refractory reflux oesophagitis high doses of ranitidine are comparable with omeprazole for the healing of oesophagitis and relief of symptoms; both drugs resulted in efficacious reduction of intragastric acidity and intra-oesophageal acid exposure.

Effect of short- and long-term treatment with omeprazole on cell cycle distribution in the gastric mucosa. Results of a flow cytometric study

Omeprazole may exert an effect on gastric mucosal proliferation by inhibiting gastric acid secretion and increasing serum gastrin levels. It may also influence the kinetics of endocrine cells and the oxyntic mucosa. The aim of the present study was to evaluate the cell cycle in different gastric compartments following short- (1 month) and long-term (6 months) administration of two different dosages of omeprazole by means of a flow cytometric method. We also determined serum gastrin levels at the same time. No differences in cell cycle distribution of the antrum, body, and fundus were found in the two different dosage groups after 1 month of therapy, considering the synthetic phase (S-phase) of the cell cycle. A statistically significant increase in S-phase was reported after long-term therapy in the mucosa of the fundus and body of the stomach in both groups. Gastrin levels showed no clear correlation with cell cycle distribution variables. We postulate a proliferative adaptation of the oxyntic mucosa to long-term drug administration not mediated by gastrin influence.

Focal oxyntic gland atrophy with endocrine cell hyperplasia in Zollinger-Ellison syndrome during omeprazole treatment

Development of focal gland atrophy of the oxyntic mucosa was found in two patients with the Zollinger-Ellison syndrome undergoing long-term treatment with omeprazole. The atrophic areas revealed florid proliferation of endocrine cells in the form of both intraglandular crescents and micronodular hyperplasia. This proliferation was significantly more pronounced than in the remaining non-atrophic mucosa. The possible relationship of these changes to long-standing pharmacological therapy for gastric acid suppression is discussed.

Functional control of chromogranin A and B concentrations in the body of the rat stomach

The chromogranins are soluble, acidic, proteins which are frequently co-stored in neuroendocrine cells with biogenic amines. In the gastric mucosa chromogranin A is localized to enterochromaffin-like cells which are the main source of histamine, and which are known to be regulated by circulating gastrin. We have used radioimmunoassays selective for the extreme C-terminal regions of chromogranin A and B to examine changes in gastric extracts following modulation of the gastric luminal contents. There were decreased concentrations of the two chromogranins in tissue extracts of rats after food withdrawal (which lowered plasma gastrin concentrations); inhibition of acid secretion with the H+/K(+)-ATPase inhibitor, omeprazole (which increased plasma gastrin concentrations) raised chromogranin A and B concentrations both in fasted rats, and in rats fed ad libitum. There was no evidence for altered patterns of posttranslational cleavage of chromogranin A or B with these treatments. The data indicate that chromogranin A and B concentrations in gastric ECL cells are regulated in parallel with histamine production, and are consistent with the idea that the chromogranins play a role in the formation and stabilization of the secretory granule involved in amine storage.

Somatostatin cells in the oxyntic mucosa of hypo- or hypergastrinemic rats

The present report describes the long-term effects of antrectomy, antrum exclusion, portacaval shunt, omeprazole treatment, or the combination of omeprazole treatment and portacaval shunt on the number and density of somatostatin cells in the oxyntic mucosa of the rat. Antrectomy, which is associated with hypogastrinemia, raised the number and density of the somatostatin cells, whereas antrum exclusion and omeprazole treatment, which are associated with hypergastrinemia, reduced the number and density of the somatostatin cells. Portacaval shunt, which is associated with hypogastrinemia, increased both the number and the density. Omeprazole treatment of portacaval--shunted rats suppressed or even reversed the somatostatin cell hyperplasia after portacaval shunt alone. From these findings it is unlikely that gastrin stimulates the proliferation of somatostatin cells in the oxyntic mucosa. In fact, there seems to be an inverse relationship between the serum gastrin concentration and the somatostatin cell number.

Effects of omeprazole and ranitidine on plasma gastrin concentration and stomach gastrin content in rats

Prolonged fasting and longer time between dosing and sampling reduced the plasma gastrin concentrations after omeprazole (80 mumol/kg x 2 for 14 days) treatment in male rats whereas the amounts of tissue gastrin were essentially unchanged during these initial experiments. After 28 days omeprazole (80 mumol/kg x 2) or ranitidine (375 mumol/kg x 4) that produced corresponding inhibition of acid secretion, increased the tissue gastrin content by 114 and 59%. A low dose of omeprazole (20 mumol/kg x 2) also raised the gastric gastrin content (41%), whereas no change was noted on treatment with a low dose of ranitidine (125 mumol x 4). Following recovery for 28 days no significant increases in gastrin were observed. 1, 3, 7, 14 or 28 days of treatment with omeprazole (80 mumol/kg x 2) gradually increased the gastric gastrin content being significantly raised already after 3 days. We conclude that a) measuring the tissue gastrin content may be the preferable method when changes in gastrin following long-term treatment with acid inhibiting drugs are to be determined, b) the amount of gastrin in the stomach increases rapidly following treatment with omeprazole and is approximately doubled following 28 days of treatment and c) after treatment for 28 days omeprazole was found to cause greater elevations in the tissue gastrin content than ranitidine despite similar degrees of basal acid inhibition.

Omeprazole. An updated review of its pharmacology and therapeutic use in acid-related disorders

Omeprazole is the first of a new class of drugs, the acid pump inhibitors, which control gastric acid secretion at the final stage of the acid secretory pathway and thus reduce basal and stimulated acid secretion irrespective of the stimulus. In patients with duodenal or gastric ulcers, omeprazole as a single 20 mg daily dose provides more rapid and complete healing compared with ranitidine 150 mg twice daily or 300 mg at nighttime, or cimetidine 800 or 1000 mg/day. Patients poorly responsive to treatment with histamine H2-receptor antagonists respond well to omeprazole--most ulcers healed within 4 to 8 weeks of omeprazole 40 mg/day therapy. Omeprazole 20 or 40 mg/day has been administered as maintenance therapy for peptic ulcer disease for up to 5.5 years with very few ulcer recurrences. In patients with erosive or ulcerative oesophagitis, omeprazole 20 or 40 mg/day produces healing in about 80% of patients after 4 weeks, and is superior to ranitidine with respect to both healing and symptom relief. Healing rates of greater than 80% are achieved after 8 weeks in patients with severe reflux oesophagitis unresponsive to H2-receptor antagonists. Maintenance therapy with a daily 20 mg dose prevents relapse in about 80% of patients over a 12-month period. Omeprazole is considered to be the best pharmacological option for controlling gastric acid secretion in patients with Zollinger-Ellison syndrome. Daily dosages of 20 to 360 (median 60 to 70 mg successfully reduce basal acid output to target levels (less than 10 mmol/h or less than 5 mmol/h in patients with severe oesophagitis or partial gastrectomy) during treatment for up to 4 years. Omeprazole is well tolerated in short term studies (up to 12 weeks); the reported incidence of serious side effects (about 1%) being similar to that seen in patients treated with an histamine H2-receptor antagonist. The longer term tolerability of omeprazole has been investigated in patients treated for up to 5.5 years. Slight hyperplasia, but no evidence of enterochromaffin-like (ECL) cell dysplasia or neoplasia or ECL cell carcinoids has been reported. ECL cell carcinoids have been observed in rats after life-long treatment with high doses of omeprazole or ranitidine, or in rats with partial corpectomy; the weight of experimental evidence indicates that this is a result of prolonged hypergastrinaemia.(ABSTRACT TRUNCATED AT 400 WORDS)

Omeprazole. Gastrin and gastric endocrine cell data from clinical studies

Gastric enterochromaffin-like cell carcinoids have been detected in rats exposed lifelong to omeprazole. By inhibiting acid secretion, omeprazole causes hypergastrinemia which, with prolonged exposure, exerts a trophic effect on enterochromaffin-like cells with eventual enterochromaffin-like cell carcinoid formation in some animals. This mechanism seems to explain the appearance of enterochromaffin-like cell carcinoids in human hypergastrinemic states, whether associated with hyperchlorhydria, eg, Zollinger-Ellison syndrome, or with hypochlorhydria, eg, pernicious anemia (nonantral atrophic gastritis). Omeprazole produces modest serum gastrin elevations in humans when monitored over a 24-hr period. Gastrin levels are markedly lower and less sustained than in the above hypergastrinemic states. Extensive gastric biopsy data from patients enrolled in long-term studies indicate that omeprazole administration is not associated with clinically significant changes in the human oxyntic endocrine cell population. Man and rat differ markedly both in their gastrin response to a given level of acid inhibition and in their response to the trophic influence of gastrin on enterochromaffin-like cells. The rat model is a false indicator of risk in man.

Trophic effects of gastrin

Gastrin is an important trophic hormone for the acid-producing part of the stomach. There is no solid evidence that gastrin is physiologically important as a trophic agent outside the stomach. The trophic effects in the stomach are manifested as an increased weight and thickness of the oxyntic mucosa and can be induced by both exogenous and endogenous gastrin--that is, in situations of long-lasting hypergastrinemia (treatment with effective antisecretagogues, partial fundectomy, or antrum exclusion). Removal of endogenous gastrin by antrectomy induces the opposite effects--that is, diminished weight and thickness of the oxyntic mucosa. Unlike all other peptide hormone-producing endocrine cells in the oxyntic mucosa, the so-called enterochromaffin-like (ECL) cells respond readily to gastrin. An acute gastrin challenge results in release of stored products from the ECL cells (such as histamine) and activation of cytoplasmic enzymes (such as histidine decarboxylase). Sustained elevation of circulating gastrin over days results in hypertrophy of the ECL cells and over weeks results in marked hyperplasia (at most a fivefold increase in the rat). The results in other species are similar but often somewhat less marked than in the rat.

Genotoxicity and cell proliferative activity of omeprazole in rat stomach mucosa

Induction of unscheduled DNA synthesis (UDS) as a marker of genotoxicity and induction of ornithine decarboxylase (ODC) activity as a marker of cell proliferative activity by omeprazole were determined in the glandular stomach mucosa of male F344 rats after oral administration. Commercial enteric-coated omeprazole (Losec) at doses of 30 and 100 mg/kg body weight induced a dose-dependent increase in UDS but not replicative DNA synthesis in the pyloric mucosa of rat stomach 4 h after its administration. Dose-dependent significant induction of ODC activity was observed in fundic and pyloric mucosa with a maximum 8 h after administration of omeprazole at doses of 37.5-100 mg/kg body weight. These results show that omeprazole has genotoxicity and cell proliferative activity in the rat glandular stomach mucosa.

Proposed mechanism of induction of gastric carcinoids: the gastrin hypothesis

Novel, powerful and long-acting inhibitors of gastric acid secretion include second generation H2-blockers and so-called proton pump inhibitors, such as omeprazole. Gastric carcinoids were found to develop in experimental animals as a consequence of continuous long-term administration of several of these highly effective anti secretory drugs. This unwanted side effect is now thought to reflect the fact (1) that pharmacological blockade of acid secretion results in hypergastrinaemia, and (2) that long-standing hypergastrinaemia gives rise to hyperplasia of certain endocrine cells, the so-called ECL cells, in the gastric mucosa. The carcinoids that develop in the rat stomach after lifelong treatment with antisecretagogues arise from the ECL cells. The proposed sequence of events is acid blockade--hypergastrinaemia--ECL cell hyperplasia--carcinoid. This concept, referred to as the gastrin hypothesis, maintains that the ECL cell hyperplasia (and possibly the carcinoids) is a consequence of long-term continuous hypergastrinaemia.

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

The enterochromaffinlike cells in the rat stomach are rich in histamine and are thought to be under the influence of gastrin. The effect of sustained endogenous and exogenous hypergastrinemia on the activity and proliferation rate of the enterochromaffinlike cells was studied by determining the histidine decarboxylase activity and histamine concentration and by combining histamine immunocytochemistry and autoradiography after in vivo labeling with [3H]thymidine. The proliferation rate of the stem cells in the oxyntic mucosal progenitor zone was also studied. Exogenous hypergastrinemia was induced by infusion of rat gastrin-17 (60 nmol.kg-1.day-1). Endogenous hypergastrinemia was induced by inhibition of gastric acid secretion with omeprazole (80 mumol.kg-1.day-1) or ranitidine (1200 mumol.kg-1.day-1). The effect of omeprazole was also studied in antrectomized rats. In intact rats, all treatments resulted in elevated plasma gastrin levels and were accompanied by an increase in the histidine decarboxylase activity and the histamine content of the oxyntic mucosa. This resulted in an increase in the enterochromaffinlike cell proliferation rate, leading to enterochromaffinlike cell hyperplasia. The number of labeled stem cells was increased, but this effect was not as pronounced as in the enterochromaffinlike cells. In antrectomized rats, the inhibition of acid secretion by omeprazole did not result in elevated plasma gastrin or in an increase in the activity or number of enterochromaffinlike cells, indicating that omeprazole per se had no effect on these cells. These data support the view that gastrin stimulates the proliferation rate of both enterochromaffinlike cells and stem cells. Gastrin also stimulates the activity of the enterochromaffinlike cells.

Quantitative ultrastructure of endocrine cells of oxyntic mucosa in Zollinger-Ellison syndrome. Correspondence with light microscopic findings

The endocrine cells of the oxyntic mucosa of five patients with longstanding Zollinger-Ellison syndrome were quantitatively investigated with electron microscopy and two light microscopic methods (Grimelius and immunostaining for chromogranin A). Ultrastructurally, the volume density of endocrine cells was 3.2% +/- 1.1% of the mucosal epithelial component, a 168% increase (P less than 0.001) over the value found in normal subjects. Of the six endocrine cell types of human oxyntic mucosa, only enterochromaffinlike cells increased in cell density (65% +/- 15% of the total endocrine cell mass), size, and number of cell profiles per unit area. The enterochromaffinlike cells also underwent morphological changes of secretory granules with a decrease in vacuolated forms, increase in elongated profiles, and appearance of granules with a punctate structure of the core. The latter variety of granules was previously observed only in carcinoid tumors of the oxyntic mucosa and is possibly related to the enterochromaffinlike cell hyperplasia-neoplasia sequence seen in hypergastrinemic patients. A positive relationship was found between endocrine cell densities evaluated ultrastructurally and with chromogranin A immunostaining. It is concluded that in Zollinger-Ellison syndrome, the trophic effects induced by longstanding hypergastrinemia are strictly selective for enterochromaffinlike cells and are associated with ultrastructural features typical for enterochromaffinlike cell tumors.

The importance of pharmacokinetic and receptor studies in drug safety evaluation

The importance of pharmacokinetic and receptor studies in the preclinical and clinical safety evaluation of candidate drugs is reviewed with reference to a number of recently developed drugs. Different aspects of the relationships between pathways of metabolism, pharmacokinetics, receptor interactions, and drug toxicity are illustrated. The failure of animal toxicity studies to predict drug toxicity in humans, due to species differences in metabolism and pharmacokinetics, is illustrated by reference to the anti-inflammatory antiviral terpenoid carbenoxolone, the antiasthmatic candidate drug FPL 52757, and the cardiotonic drug amrinone. The false prediction of adverse effects in man from toxicity manifested in experimental animals, due to species differences in pharmacokinetics or receptor activities, is exemplified with reference to the antiepileptic valproic acid, the hypolipidemic drug ciprofibrate, the antipeptic ulcer drug, omeprazole, and the progestogen lynestrenol. Finally, the importance of adequate, repeat-dose, clinical pharmacokinetic studies in patients as distinct from healthy volunteers to evaluate any effect of the disease state, in the elderly and the young to examine the effects of age, and in sufficiently large populations to detect genetic anomalies and idiosyncrasies is illustrated by reference to the anti-rheumatoid drug benoxaprofen, the antiangina drug perhexiline, and the diuretic tienilic acid.

Potential hazards of long-term acid suppression

Neuroendocrine cell (carcinoid) tumours have been reported in the acid-secreting part of the stomach of rodents after long-term administration of a range of potent chemically diverse antisecretory agents. Although evidence shows a link between the sequence of acid suppression, hypergastrinaemia, and neuroendocrine cell hyperplasia, other factors are also thought to be involved in neoplastic transformation. Prolonged hypochlorhydria or achlorhydria resulting in bacterial colonization of the stomach may allow the generation of carcinogenic substances. Other as yet unidentified trophic factors may be involved in tumour formation. In view of the potential risks associated with these agents, there must be concern about the possible consequences in man of marked suppression of acid. It seems wise to limit the use of these more potent agents to situations in which conventional therapy has failed and to short-term treatment.