质子泵抑制剂与酸反跳

酸反跳(rebound acid hypersecretion)指停用抑酸药物后胃酸分泌增加超过治疗前水平.质子泵抑制剂(proton pump inhibitors,PPIs)作为一代抑酸药物,比H2受体阻滞剂(histamine-2receptor antagonists,H2RA)具有更强的抑酸效果,是治疗酸相关疾病的主要药物.目前研究已经证实,PPIs可致酸反跳发生.PPIs的酸反跳可以再次诱发酸相关症状出现,不仅增加医疗预算,也给PPIs治疗的终止带来问题.高胃泌素血症是导致酸反跳现象的重要机制.正确使用PPIs,严格掌握适应证,探讨在有效治疗酸相关疾病的同时减少酸反跳发生的措施.     

Physiological and clinical significance of enterochromaffin-like cell activation in the regulation of gastric acid secretion

Gastric acid plays an important role in digesting food （especially protein）, iron absorption, and destroying swallowed micro-organisms. H＋ is secreted by the oxyntic parietal cells and its secretion is regulated by endocrine, neurocrine and paracrine mechanisms. Gastrin released from the antral G cell is the principal physiological stimulus of gastric acid secretion. Activation of the enterochromaffin-like （ECL） cell is accepted as the main source of histamine participating in the regulation of acid secretion and is functionally and trophically controlled by gastrin, which is mediated by gastrin/CCK-2 receptors expressed on the ECL cell. However, longterm hypergastrinemia will induce ECL cell hyperplasia and probably carcinoids. Clinically, potent inhibitors of acid secretion have been prescribed widely to patients with acid-related disorders. Long-term potent acid inhibition evokes a marked increase in plasma gastdn levels, leading to enlargement of oxyntic mucosa with ECL cell hyperplasia. Accordingly, the induction of ECL cell hyperplasia and carcinoids remains a topic of considerable concern, especially in long-term use. In addition, the activation of ECL cells also induces another clinical concem, i.e., rebound acid hypersecretion after acid inhibition. Recent experimental and clinical findings indicate that the activation of ECL cells plays a critical role both physiologically and dinically in the regulation of gastric acid secretion.     

Zollinger-Ellison syndrome

Opinion statement Zollinger-Ellison syndrome (ZES) is caused by a gastrin-producing tumor called a gastrinoma, which results in gastric acid hypersecretion. Gastrin stimulates the parietal cell to secrete acid directly and indirectly by releasing histamine from enterochromaffin-like (ECL) cells, and induces hyperplasia of parietal and ECL cells. ZES should be suspected in patients with severe erosive or ulcerative esophagitis, multiple peptic ulcers, peptic ulcers in unusual locations, refractory peptic ulcers, complicated peptic ulcers, peptic ulcers associated with diarrhea, and a family history of multiple endocrine neoplasia type 1 (MEN-1) or any of the endocrinopathies associated with MEN-1. The initial diagnostic test for ZES should be a fasting serum gastrin level when antisecretory medications are discontinued. If the gastrin level is elevated, gastric acidity should be assessed through pH or gastric analysis. It should be noted that hypochlorhydria causes feedback stimulation of antral gastrin secretion. In suspected cases of ZES with mild hypergastrinemia, the secretin stimulation test may be useful. Initial treatment for ZES should be oral high-dose proton pump inhibitors. If parenteral therapy is needed, intermittent bolus injection of pantoprazole is recommended. Total gastrectomy and antisecretory surgery is rarely required. Somatostatin receptor scintigraphy (SRS) is the initial localization study of choice. Endoscopic ultrasound (EUS) may have a similar sensitivity for identifying primary tumors. A combination of SRS and EUS detects greater than 90% of gastrinomas. In patients without metastasis and without MEN-1, surgical cure is possible in 30%. It has been suggested that patients with gastrinomas larger than 2.5 cm, irrespective of whether they have MEN-1, should undergo surgical resection in an effort to decrease the risk for metastasis.     

Much ado about gastrin.

The regulation of gastrin secretion from antral G-cells is of major importance in the physiologic control of acid secretion. Gastrin secretion is highly dependent upon gastric intraluminal pH and is inhibited significantly by a pH of less than 3.0. Acute gastric alkalinization greater than pH 6.0 with antisecretory agents such as H2-receptor antagonists or H+/K+ ATPase inhibitors has little impact on fasting serum gastrin levels but promotes an enhanced sustained rise in meal-stimulated gastrin release. Courses of standard therapy with both H2-antagonists and H+/K+ inhibitors cause a significant rise in 24 h integrated plasma gastrin levels that is inversely correlated to the 24-h integrated gastric acidity. The rise in fasting or integrated plasma gastrin levels observed in patients treated with H2-antagonists is small and of unclear clinical significance. Therapy with antisecretory agents leads to earlier ulcer relapse than with other agents. A variety of factors have been proposed to explain the earlier ulcer relapse rate, including secondary hypergastrinemia with rebound acid hypersecretion after discontinuation of the drug. Secondary hypergastrinemia may also lead to tolerance to prolonged courses of H2-antagonists therapy with a decrease in acid inhibition. This may contribute to break-through ulcer recurrence during maintenance H2-antagonist therapy. However, the relative importance of hypergastrinemia and tolerance to H2-antagonists compared with other factors such as baseline gastric acid secretion, smoking status, nonsteroidal anti-inflammatory drug use, and Helicobacter pylori status is difficult to assess.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence that gastric antisecretory action of lipopolysaccharide is not due to a toxic effect on gastric parietal cells

We have recently found that bacterial lipopolysaccharide (LPS) or endotoxin at minute doses inhibits the secretion of gastric acid and pepsin in rats. The present study was performed to determine whether this antisecretory action of LPS was a reversible biological response or a result of the destruction of gastric parietal cells by endotoxin. The intraperitoneal injection of LPS into pylorus-ligated rats resulted in a dose-related (40-4000 ng/kg) decrease in gastric acid secretion, with maximal inhibition being observed at a dose of 4000 ng/kg. The stomach then was examined both macroscopically and microscopically for the presence or absence of mucosal lesions or damaged gastric parietal cells. No morphological changes in the gastric mucosal structure including parietal cells were observed even in the rats injected with 4000 ng/kg of LPS. Next, basal gastric acid output was compared in the rats that had received LPS (4000 ng/kg, intraperitoneal) or saline alone 24 hr before. There was no significant difference in gastric acid secretion between the saline- and LPS-pretreated groups, indicating that the secretory capacity of gastric parietal cells returned to the control level at 24 hr after the injection of a maximal antisecretory dose of LPS. These results clearly suggest that the LPS-induced inhibition of gastric secretion results not from its toxic or destructive effect on the gastric secretory mechanism but from its reversible biological effect on gastric physiology.     

Histopathology of the gastric oxyntic mucosa in two different patient groups during long-term treatment with omeprazole

OBJECTIVES: Hypochlorhydria, hypergastrinaemia, inflammation and Helicobacter pylori infection, dose and duration of omeprazole treatment may separately, or in combination, influence the proliferation of enterochromaffin-like (ECL) cells and parietal cell changes in gastric mucosa. To assess the effects of these variables comparisons were carried out in patients with the acid related Zollinger-Ellison syndrome (ZES) versus patients with progressive systemic sclerosis (PSS) and gastro-oesophageal reflux disease. METHODS: Twenty-five patients with PSS and 16 patients with ZES were included and received continuous omeprazole treatment for a mean of 7.5 and 9 years. The patients were investigated every 6-12 months with endoscopy, biopsies and histology, and plasma gastrin measurements. PSS patients were titrated by 24 h pH-metry to oesophageal pH>4, and all ZES patients were titrated to a basal acid output of zero H+. RESULTS: Changes towards diffuse and linear ECL cell hyperplasia were observed in 41% of the PSS patients. Micronodular hyperplasia and neoplasia were not seen. In the ZES patients changes towards linear and micronodular hyperplasia were observed in all patients. Two patients developed ECL cell carcinoids; one of these had MEN-1 syndrome. Also parietal cell changes were more pronounced in the ZES group than in the PSS group. CONCLUSIONS: In patients without intrinsic acid hypersecretion and hypergastrinaemia significant proliferation of ECL cells is not an issue irrespective of gastric mucosal inflammation, omeprazole dose, duration of treatment and acid inhibition. The level of gastrin secretion and high plasma gastrin appear to accelerate ECL cell proliferation and parietal cell changes possibly influenced by chronic gastritis and H. pylori infection.     

Hypersecretory duodenal ulcer and Helicobacter pylori infection: a four-year follow-up study.

BACKGROUND: About 10% of duodenal ulcer patients are characterized by gastric acid hypersecretion with normal gastrin values. Relapsing duodenal ulcer after Helicobacter pylori cure has been related to high acid output and maintenance antisecretory therapy has been suggested in hypersecretory duodenal ulcer patients. The role of Helicobacter pylori infection and the effects of Helicobacter pylori cure in hypersecretory duodenal ulcer patients still remain to be fully studied. AIM: To study: a) whether gastric acid hypersecretion "per se" is a risk factor for duodenal ulcer recurrence; b) whether maintenance antisecretory therapy is necessary after eradication in hypersecretory duodenal ulcer patients. PATIENTS: The study population comprised 8 hypersecretory duodenal ulcer patients, selected from a population of 79 Helicobacter pylori-positive duodenal ulcer patients. METHODS: Hypersecretory duodenal ulcer patients were followed-up for at least 4 years after eradication. Gastric acid secretion was measured again 12 months after Helicobacter pylori eradication. Gastroscopy with histology was performed 3, 6, 12 and 36 months after treatment, 13C-urea breath test after 42 months; clinical questionnaires were completed every 6 months. RESULTS: After eradication, despite a not significantly reduced high acid output (median value of basal acid output and pentagastrin-stimulated acid output, respectively, 23.1 mEq/h and 64.1 mEq/h before treatment vs 16 mEq/h and 49.7 mEq/h 12 months after treatment), all patients were free from symptoms, none of them had duodenal ulcer relapse or complications (7/8 before treatment), or needed antisecretory maintenance therapy, except for one patient taking non-steroidal anti-inflammatory drugs. CONCLUSIONS: These findings, obtained in a selected population of hypersecretory duodenal ulcer patients with long-term follow-up, suggest that after successful Helicobacter pylori eradication gastric acid hypersecretion "per se" is not able to determine the recurrence of duodenal ulcer.     

Effects of anaesthetic agents on gastrin-stimulated and histamine-stimulated gastric acid secretion in the totally isolated vascularly perfused rat stomach

BACKGROUND: Anaesthetic agents affect gastric acid secretion, but the mechanisms behind this action have not been fully evaluated. The enterochromaffin-like (ECL) cell plays a key role in the regulation of gastric acid secretion, and anaesthetic agents have recently been described as inhibiting histamine release from the ECL cell. The present study examines the effect of anaesthetic agents on the ECL cell and on parietal cell functions. METHODS: Different concentrations of urethane, pentobarbital and a mixture of fluanisone/fantanyl/midazolam (FFM) were examined for the effect on gastrin-stimulated histamine release and acid secretion and on histamine-stimulated acid secretion in the totally isolated vascularly perfused rat stomach. The luminal acid output and histamine concentrations in venous effluents were measured by titration and radioimmunoassay, respectively. RESULTS: Pentobarbital caused an inhibition on both histamine release and acid output in gastrin-stimulated stomachs in a concentration-dependent way. The mixture of FFM at higher concentrations inhibited histamine release from the ECL cell and luminal H+ output in gastrin-stimulated acid secretion. Urethane exerted a slight inhibitory effect on histamine release only at the lowest concentration. Pentobarbital also reduced histamine-stimulated gastric acid secretion, while the mixture of FFM did not. CONCLUSIONS: pentobarbital inhibits acid secretion both by reducing ECL cell histamine release and parietal cell H+ secretion, whereas FFM inhibits acid secretion by interaction with the ECL cell only. Urethane also had a slight inhibitory effect on the ECL cell histamine release at the lowest concentration.     

Stomach Effects of Anaesthetic Agents on Gastrin-Stimulated and Histamine-Stimulated Gastric Acid Secretion in the Totally Isolated Vascularly Perfused Rat Stomach

Background: Anaesthetic agents affect gastric acid secretion, but the mechanisms behind this action have not been fully evaluated. The enterochromaffin-like (ECL) cell plays a key role in the regulation of gastric acid secretion, and anaesthetic agents have recently been described as inhibiting histamine release from the ECL cell. The present study examines the effect of anaesthetic agents on the ECL cell and on parietal cell functions. Methods: Different concentrations of urethane, pentobarbital and a mixture of fluanisone/ fantanyl/midazolam (FFM) were examined for the effect on gastrin-stimulated histamine release and acid secretion and on histamine-stimulated acid secretion in the totally isolated vascularly perfused rat stomach. The luminal acid output and histamine concentrations in venous effluents were measured by titration and radioimmunoassay, respectively. Results: Pentobarbital caused an inhibition on both histamine release and acid output in gastrin-stimulated stomachs in a concentration-dependent way. The mixture of FFM at higher concentrations inhibited histamine release from the ECL cell and luminal H + output in gastrinstimulated acid secretion. Urethane exerted a slight inhibitory effect on histamine release only at the lowest concentration. Pentobarbital also reduced histamine-stimulated gastric acid secretion, while the mixture of FFM did not. Conclusions: pentobarbital inhibits acid secretion both by reducing ECL cell histamine release and parietal cell H + secretion, whereas FFM inhibits acid secretion by interaction with the ECL cell only. Urethane also had a slight inhibitory effect on the ECL cell histamine release at the lowest concentration.     

Anatomical location of enterochromaffin-like (ECL) cells, parietal cells, and chief cells in the stomach demonstrated by immunocytochemistry and electron microscopy

Enterochromaffin-like (ECL) cells are included in the endocrine cells present in the gastric oxyntic mucosa, and have been attracting attention as histamine-secreting cells contributing to gastric secretion. However, the anatomical location of ECL cells in relation to parietal cells and chief cells has not yet been sufficiently investigated. To elucidate this location of ECL cells, we performed an immunocytochemical study using anti-histamine antibody and electron microscopic examination of guinea pig gastric mucosa. ECL cells were located near the basement membranes in the gastric oxyntic region, and were in contact with both chief cells and parietal cells in the same glandular epithelium. The ratio of ECL cells in contact with chief cells was clearly greater than that in contact with parietal cells. An Ω-shaped morphology, indicating emiocytosis, was found in ECL cells by electron microscopy. These findings suggest that ECL cells have a paracrine effect on chief cells and parietal cells, and may have an important physiological role in pepsinogen secretion. Received: April 6, 1998/Accepted: December 18, 1998     

Optimizing medical therapy for gastroesophageal reflux disease: state of the art

Potential interventions for gastroesophageal reflux disease include lifestyle modifications, antacids, mucosal protectants, prokinetic (promotility) agents, H2 receptor antagonists (H2RAs) and, the agents of choice in 2003, proton pump inhibitors (PPIs). This article reviews the current state of the art in use of these agents. Lifestyle changes, though sound in their intent and in many cases based on solid laboratory research, can today be considered only adjuncts to pharmacologic therapy. The mainstay of pharmacologic therapy in 2003 is antisecretory therapy. Both H2RAs and PPIs inhibit acid secretion and raise intragastric pH. H2RAs only block one receptor, have limited effect on acid reduction, and are relatively weak inhibitors of meal-stimulated acid secretion. PPIs provide superior control of intragastric pH over a 24-hour period compared with H2RAs and effect greater symptom relief and healing.     

质子泵和质子泵抑制剂研究进展

胃壁细胞H^ ,K^＋－ATP酶是一种质子泵，能特异性地将H^ 泵入胃腔，形成胃内高酸状态。质子泵抑制剂（PPI）为苯丙咪唑替代物，在体内转化为活性物质－－次磺酰胺，后者与H^ ,K^ －ATP酶共价结合，从而抑制该酶活性，抑制胃酸分泌，是治疗各种酸相关性疾病的首选药物。旧一代PPI如奥美拉唑，兰索拉唑和泮托拉唑的药代动力学个体差异大，与其他药物作用明显，起效时间慢，而新一代PPI如雷贝拉唑、伊索美拉唑起效快，抑酸效果更好，尤其在治疗胃食管反流性疾病（GERD）方面疗效更佳。     

Control of gastric acid secretion. Histamine H2-receptor antagonists and H+K(+)-ATPase inhibitors.

Gastric acid secretion is regulated by an intricate interplay of neural (acetylcholine), hormonal (gastrin), and paracrine (histamine, somatostatin) mechanisms. Receptors for each of these agents and the signal transduction pathways to which these receptors are coupled have been identified on the parietal cell. The stimulatory effect of acetylcholine and gastrin is mediated by an increase in cytosolic calcium, whereas that of histamine is mediated by activation of adenylate cyclase and generation of cAMP. Strong potentiation between histamine and either gastrin or acetylcholine reflects postreceptor interaction between the distinct pathways as well as the ability of acetylcholine and gastrin to release histamine from mucosal ECL cells. The inhibitory effects of somatostatin on acid secretion are mediated by receptors coupled by guanine nucleotide-binding proteins to inhibition of adenylate cyclase activity. All the pathways converge on and modulate the activity of the luminal enzyme, H+K(+)-ATPase, the proton pump of the parietal cell. Precise information on the mechanisms involved in gastric acid secretion has led to the development of potent drugs capable of inhibiting acid secretion. These include competitive antagonists that interact with stimulatory receptors (e.g., histamine H2-receptor antagonists) as well as noncompetitive inhibitors of H+K(+)-ATPase (e.g., omeprazole). The histamine H2-receptor antagonists (cimetidine, ranitidine, famotidine, and nizatidine) continue as first-line therapy for peptic ulcer disease and are effective in preventing relapse. Although they are generally well tolerated, histamine H2-receptor antagonists may cause untoward CNS, cardiac, and endocrine effects as well as interference with the absorption, metabolism, and elimination of various drugs. Omeprazole is a weak base that reaches the parietal cell through the bloodstream, diffuses through the cytoplasm, and becomes activated and trapped as a sulfenamide in the acidic canaliculus of the parietal cell. It covalently binds to H+K(+)-ATPase, thereby irreversibly blocking acid secretion in response to all modes of stimulation. The main drawback to its use is its extreme potency, which leads to virtual anacidity, gastrin and ECL cell hyperplasia, hypergastrinemia, and, in rats, to the development of carcinoid tumors.     

Marked increase in gastric acid secretory capacity after omeprazole treatment.

BACKGROUND: In contrast with the histamine2 (H2) blockers, proton pump inhibitors have not been shown to give rebound hypersecretion of acid. Taking into consideration the hyperplasia of the enterochromaffin-like (ECL) cell provoked by hypergastrinaemia secondary to profound acid inhibition and the central role of histamine from ECL cells in the regulation of acid secretion, the lack of any rebound acid hypersecretion after treatment with proton pump inhibitors has been questioned. AIMS: To reassess the effect of treatment with omeprazole on post-treatment acid secretion. METHODS AND PATIENTS: Basal and pentagastrin stimulated acid secretion were determined in nine patients with reflux oesophagitis before and 14 days after termination of a 90 day treatment period with the proton pump inhibitor omeprazole (40 mg daily). Basal gastrin release were determined before and during omeprazole treatment. Furthermore, biopsy samples from the oxyntic mucosa were taken before and at the end of the treatment period for chemical (histamine and chromogranin A (CgA)) evaluation of the ECL cell mass. RESULTS: A substantial increase in meal stimulated gastrin release during omeprazole treatment resulted in an increased ECL cell mass. Furthermore, CgA in serum increased during omeprazole treatment suggesting that serum CgA may be used as a test to evaluate ECL cell hyperplasia. A significant increase in basal and a marked (50%) and significant increase in pentagastrin stimulated acid secretion were found after treatment with omeprazole. CONCLUSIONS: Increased acid secretion after a conventional treatment period with a proton pump inhibitor is probably due to ECL cell hyperplasia and may have negative consequences for acid related diseases.     

The physiological background behind and course of development of the first proton pump inhibitor

Abstract

Gastric acid secretion and its related diseases and their treatments have generated important contributions to gastroenterology and its development as an autonomous medical specialty. The discovery of histamine receptors and the subsequent H2-receptor antagonists (1972) changed the practice of gastroenterology forever. Gastric acid was effectively inhibited and ulcers could be healed to an extent which had not previously been seen. An additional milestone along the same avenue was offered by the identification of hydrogen potassium adenosine triphosphatase (H⁺K⁺-ATPase) as the proton pump of the parietal cell. Nowadays, proton pump inhibitors (PPIs) are widely used. However, we need to reconsider the physiology and pathophysiology of acid secretion and its long-term inhibition to avoid potential negative effects on general health. PPIs are generally considered among the safest class of drugs. In the late 1960s, a research project was initiated to develop an antisecretory drug which could be used in acid hypersecretory disease states such as peptic ulcer disease based on the option to synthesize a local anesthetic drug that could be orally administered and therefore have its main action on the gastrin cells. This concept was soon found to be a blind track and further development of the basic compounds CMN131 by the synthesis of H77/67 were found to be active in the gastric acid secretion, and the benzimidazol analog of H77/67 was then synthesized a year later and was tested and found to exert powerful acid inhibitory effects. Binding studies with the substituted benzimidazoles clarified specific binding to H+/K+/ATPase in the secretory vesicles of the parietal cells. Since weak bases like aminopyrine accumulate in the acid compartment of the parietal cells, the chemists changed the substituents of the heterocyclic ring and obtained a compound with a weak base property with an optimal PkA value, thereby maximizing the accumulation of the compound at the site of action. This compound H168/68 was synthesized in 1979 and was given the generic name omeprazole. Omeprazole was soon shown to be a very potent inhibitor of the proton pump in vitro as well as in preparation from the human stomach tissue. Pharmacological studies showed long-lasting effect on acid secretion and a specific binding to the target site and soon found the compound to exert unique therapeutic effects. Conclusion. The development of the first PPI omeprazole represents an exceptional example of a unique and fruitful collaboration between people with in-depth knowledge of gastric physiology and pharmacology. Frontline expertise in biochemistry and applied clinical science were added to these components, resulting in one of the greatest therapeutic advances during the last decades of the former century.     

Hypersecretory duodenal ulcer and Helicobacter pylori infection: for-year follow-up study

Background. About 10% of duodenal ulcer patients are characterized by gastric acid hypersecretion with normal gastrin values. Relapsing duodenal ulcer after Helicobacter pylori cure has been related to high acid output and maintenance antisecretory therapy has been suggested in hypersecretory duodenal ulcer patients. The role of Helicobacter pylori infection and the effects of Helicobacter pylori cure in hypersecretory duodenal ulcer patients still remain to be fully studied.Aim. To study: a) whether gastric acid hypersecretion “per se” is a risk factor for duodenal ulcer recurrence; b) whether maintenance antisecretory therapy is necessary after eradication in hypersecretory duodenal ulcer patients.Patients. The study population comprised 8 hypersecretory duodenal ulcer patients, selected from a population of 79 Helicobacter pylori-positive duodenal ulcer patients.Methods. Hypersecretory duodenal ulcer patients were followed-up for at least 4 years after eradication. Gastric acid secretion was measured again 12 months after Helicobacter pylori eradication. Gastroscopy with histology was performed 3, 6, 12 and 36 months after treatment, ¹³C-urea breath test after 42 months; clinical questionnaires were completed every 6 months.Results. After eradication, despite a not significantly reduced high acid output (median value of basal acid output and pentagastrin-stimulated acid output, respectively, 23.1 mEg/h and 64. 1 mEg/h before treatment vs 16 mEg/h and 49.7 mEq/h 12 months after treatment), all patients were free from symptoms, none of them had duodenal ulcer relapse or complications (7/8 before treatment), or needed antisecretory maintenance therapy, except for one patient taking non-steroidal anti-inflammatory drugs.Conclusions. These findings, obtained in a selected population of hypersecretory duodenal ulcer patients with long-term follow-up, suggest that after successful Helicobacter pylori eradication gastric acid hypersecretion “per se” is not able to determine the recurrence of duodenal ulcer.     

Current concepts on physiological control of gastric acid secretion. Clinical applications.

Gastric acid secretion by the parietal cell is a single digestive process involving a continuous interplay between nervous and hormonal stimuli. Gastric acid hypersecretion and hypergastrinemia may represent pathologic disturbance of the normal "gastric phase" of acid secretion (excluded antrum syndrome) or abnormal gastrin secretion from a nongastric source as in the Zollinger-Ellison syndrome. Diagnosis of these two syndromes preoperatively is dependent on immunoassay for serum gastrin. A fall in serum gastrin level after the injection of secretin will distinguish the excluded antrum syndrome from the Zollinger-Ellison syndrome. Which hormone or hormones cause the acid hyposecretion of the watery diarrhea hypokalemia achlorhydria syndrome is still uncertain. Potential candidates include secretin, glucagon (alone or combined with gastrin), vasoactive intestinal peptide and gastric inhibitory polypeptide. Secretin has undergone trials as therapy in peptic ulcer whereas glucagon is under investigation for the treatment of acute pancreatitis because of its dual actions as (1) an enterogastrone and (2) an inhibitor of pancreatic secretion.     

Acid suppression therapy: where do we go from here?

The dramatic success of pharmacological acid suppression in healing peptic ulcers and managing patients with gastroesophageal reflux disease (GERD) has been reflected in the virtual abolition of elective surgery for ulcer disease, a reduction in nonsteroidal anti-inflammatory drug (NSAID)-associated gastropathy and the decision by most patients with reflux symptoms to continue medical therapy rather than undergo surgical intervention. However, a number of challenges remain in the management of acid-related disorders. These include management of patients with gastroesophageal symptoms who do not respond adequately to proton pump inhibitor (PPI) therapy, treatment of patients with nonvariceal upper gastrointestinal bleeding, prevention of stress-related mucosal bleeding, optimal treatment and prevention of NSAID-related gastrointestinal injury, and optimal combination of antisecretory and antibiotic therapy for the eradication of Helicobacter pylori infection. A number of new drugs are currently being investigated to provide a significant advance on current treatments. Some of them (namely potassium-competitive acid blockers (P-CABs) and CCK2-receptor antagonists) have already reached clinical testing while some others (like the antigastrin vaccine, H3-receptor ligands or gastrin-releasing peptide receptor antagonists) are still in preclinical development and need the proof of concept in human beings. Of the current approaches to reduce acid secretion, P-CABs and CCK2-receptor antagonists hold the greatest promise, with several compounds already in clinical trials. Although the quick onset of action of P-CABs (i.e. a full effect from the first dose) is appealing, the results of phase II studies with one such agent (namely AZD0865) did not show any advantages over esomeprazole. Thanks to their limited efficacy and the development of tolerance it is unlikely that CCK2 antagonists will be used alone as antisecretory compounds but, rather, their combination with PPIs will be attempted with the aim of reducing the long-term consequences of hypergastrinemia. While H2-receptor antagonists (especially soluble or over-the-counter formulations) will become the 'antacids of the third millennium' and will be particularly useful for on-demand symptom relief, clinicians will continue to rely on PPIs to control acid secretion in GERD and other acid-related diseases. In this connection, several new PPI formulations have been developed and two novel drugs (namely ilaprazole and tenatoprazole) are being studied in humans. The recently introduced immediate-release (IR) omeprazole formulation (currently available only in the USA) quickly increases intragastric pH and, given at bedtime, seems to achieve a better control of nocturnal acidity. IR formulations of other PPIs (including the investigational ones) will probably be available in the future and will enlarge our therapeutic armamentarium. Amongst the novel PPIs, tenatoprazole appears to be a true advance in the acid suppression therapy. Its long half-life (the longest among the available compounds) and longer duration of antisecretory action, with no difference between day and night, will allow the drug to go beyond the intrinsic limitations of currently available PPIs. Thanks to its favorable pharmacokinetics, the sodium salt of S-tenatoprazole is being developed and the preliminary results indicate that this drug has the potential to address unmet clinical needs. Although some decades have elapsed since the introduction of effective and safe antisecretory drugs in clinical practice and their use has stood the test of time, the ongoing research will further provide the clinician with more effective means of controlling acid secretion.     

Clinical relevance of basic research in peptic ulcer disease

Abstract Historically, the interplay between basic research and clinical observation has been essential in the development of new therapies for peptic ulcer disease. That histamine is an important regulator of acid secretion emerged from basic research, followed by the clinical development and use of the H₂-receptor antagonists. Basic research contributed again by defining the importance of H⁺/K⁺-ATPase in acid secretion, resulting in a new class of useful antisecretory agents. Basic studies also gave us prostaglandins (PG) as mucosal protective agents. As 'replacement' therapy, clinicians have found that PG are protective against non-steroidal anti-inflammatory drug (NSAID)-induced gastric ulcer (GU). Physiologic studies established that somatostatin is a potent inhibitor of acid secretion, providing the stimulus for clinical studies in Zollinger-Ellison (ZE) Syndrome with a synthetic analog (octreotide). Work on isoforms of the parietal cell gastrin receptor has shown differences in the cytoplasmic domain for G protein coupling. This will aid in understanding how receptor changes and coupling to second messengers relate to the aetiopathogenesis of abnormal gastric secretion. Immune cells express mRNA for histamine, muscarinic and gastrin receptors, supporting the relevance of mucosal immunology in gastroenterology, especially in light of Helicobacter pylori -associated gastritis and ulcers. Lab research has revealed a potential role for basic fibroblast growth factor (bFGF), and another endogenous peptide BPC-15, in ulcer healing. The former substance may be responsible for the antiulcer efficacy of sucralfate. Intensive basic work on how H. pylori organisms attach to gastric cells and initiate inflammatory reactions in the mucosa will have unquestionable impact on improved therapy for peptic ulcer disease.     

Clinical use of proton pump inhibitors in gastrointestinal diseases]

The development and introduction into clinical practice of proton pump inhibitors (PPIs) have influenced the management of acid-peptic disorders dramatically. PPIs inhibit the gastric hydrogen/potassium adenosine triphosphatase selectively and irreversibly which is the final step in acid secretion. PPIs are currently the most effective form of therapy in acid-peptic diseases. All PPIs are potent, effective and generally safe, but little different in equivalent doses. PPIs undergo hepatic metabolism by cytochrome P450 (CYP) system. Polymorphism of CYP2C19 influences the pharmacokinetics and pharmacodynamics of PPIs. Doses and dosing schemes of PPIs based on CYP2C19 genotype status is expected to increase the efficacy in clinical outcome. The major indication of PPIs are acid-related diseases such as peptic ulcers and their complications, gastroesophageal reflux diseases, Zollinger-Ellison syndrome and eradication of Helicobacter pylori with antibiotics and dyspepsia. The potency and cost-effectiveness of PPIs have extended their clinical uses. However, their widespread and long-term use may limit the therapeutic benefit between efficacy and clinical problems such as acid rebound hypersecretion, enhanced oxyntic gastritis, problems with carcinoids in rodents and long-term concern for gastric cancer development. Further studies are needed to minimize the side effects and to maximize the therapeutic effects of PPIs.