Pathophysiology of Peptic Ulcer Disease
Historically, our understanding of the pathophysiology of peptic ulcer disease focused on abnormalities in the secretion of gastric acid and pepsin, and on the suppression of acid as a treatment strategy. Today, gastric hypersecretionassociated with gastrinoma in Zollinger-Ellison syndrome, antral G-cell hyperplasia, an increase in parietal-cell mass, and a physiological imbalance between the antagonistic gastric hormones gastrin and somatostatinis still an important issue in peptic ulcer disease. Moreover, it is known that cholinergic hypersensitivity and parasympathetic dominance are related to the stimulation not only of hydrochloric acid but also pepsin, which is often neglected as a cofactor in the development of erosive injury to the gastric mucosa. Psychologic stress, cigarette smoking, alcohol consumption, use of nonsteroidal anti-inflammatory drugs (NSAIDs) including aspirin, oral bisphosphonates, potassium chloride, immunosuppressive medications, and an age-related decline in prostaglandin levels have all been shown to contribute to peptic ulcer disease. It was, however, the isolation of H. pylori and its identification as the most important cause of peptic ulcer disease that led to exploration of the role of inflammation and its associated cytokine cascade in gastric acid secretion.
H. pylori evades attack by the host immune system and causes chronic, indolent inflammation by several mechanisms. H. pylori can damage the mucosal defense system by reducing the thickness of the mucus gel layer, diminishing mucosal blood flow, and interacting with the gastric epithelium throughout all stages of the infection. H. pylori infection can also increase gastric acid secretion; by producing various antigens, virulence factors, and soluble mediators, H. pylori induces inflammation, which increases parietal-cell mass and, therefore, the capacity to secrete acid. The H. pylori cytotoxin-associated gene CagA also has an important role: it interferes with gastric epithelial cell-signaling pathways, thereby regulating cellular responses and possibly contributing to apical junction barrier disruption, interleukin-8 secretion and phenotypic changes to gastric epithelial cells.
Understanding the pathophysiology of peptic ulcer disease is at something of a crossroads: mechanisms of injury differ distinctly between duodenal and gastric ulcers. Duodenal ulcer is essentially an H. pylori-related disease and is caused mainly by an increase in acid and pepsin load, and gastric metaplasia in the duodenal cap. Gastric ulcer, at least in Western countries, is most commonly associated with NSAID ingestion, although H. pylori infection might also be present. Chronic, superficial and atrophic gastritis predominate in patients with gastric ulcers, when even normal acid levels can be associated with mucosal ulceration. In both conditions, ulcer is associated with an imbalance between protective and aggressive factors, with inflammation being a leading cause of this imbalance.
The isolation of H. pylori in the early 1980s was one of the most exciting advances in the history of peptic ulcer disease, and it has dramatically changed the management of peptic ulcer. Eradication of H. pylori infection is now the mainstay of treatment for peptic ulcer disease, and has resulted in very high ulcer healing rates and recurrence rates that have dropped dramatically, especially for individuals with a duodenal ulcer. The greater recognition of the role of NSAIDs and aspirin in gastrointestinal-tract injury has led to the development of therapeutic and preventive strategies that rely on the use of antisecretory drugs, the prostaglandin analog misoprostol, or selective cyclo-oxygenase (COX)-2 inhibitors (coxibs).
During the 1980s, H. pylori infection was found in more than 90% of patients with duodenal ulcers, and some 70% of patients with gastric ulcers.[12,13] The declining incidence and prevalence of peptic ulcer in developed countries has paralleled the falling prevalence of H. pylori infection, especially in populations with high infection rates. Only H. pylori eradication is an effective treatment for both duodenal and gastric ulcers. Antisecretory drugs work well for controlling symptoms and allowing ulcers to heal, and the absolute benefit of eradicating H. pylori infection is small with respect to healing alone. In a Cochrane meta-analysis the eradication of H. pylori infection combined with the use of an ulcer-healing drug significantly increased duodenal healing to 83% (intent-to-treat analysis), with the relative risk of the ulcer persisting being 0.66 (95% CI 0.58-0.76) compared with the ulcer-healing drugs alone; but eradication was not significantly superior to ulcer-healing drugs for gastric-ulcer healing (relative risk 1.32; 95% CI 0.92-1.90).
Despite their well-accepted anti-inflammatory and analgesic benefits, NSAID use is probably the most common cause of gastrointestinal mucosal injury in Western countries. NSAIDs, including aspirin, significantly increase the risk of adverse gastrointestinal events, particularly those related to gastric and/or duodenal mucosal injury: erosions, ulcers and ulcer complications, especially bleeding. About 15-30% of regular NSAID users have one or more ulcers when examined endoscopically, and 3-4.5% of NSAID users have clinically significant upper gastrointestinal events, including ulcers and ulcer complications.
Patients taking low-dose aspirin for the prevention of a cardiovascular event, such as myocardial infarction or thrombotic stroke, are also at increased risk of gastrointestinal injury and complications. In asymptomatic patients taking low-dose aspirin (75-325 mg/day) for ≥3 months, endoscopically observed ulcers or erosions are reported in 47.83% of cases. The risk of upper gastrointestinal bleeding events is dose-dependent, with an odds ratio (OR) of 3.3 for 300 mg of aspirin (95% CI 1.2-9.0) and an OR of 6.4 for 1.2 g of aspirin (95% CI 2.5-16.5). In multivariate models adjusted for age, sex, and clinical risk, low-dose aspirin alone was independently associated with an increased risk of ulcer bleeding, with an OR of 2.4 (95% CI 1.8-3.3).
The injurious gastrointestinal effects of NSAIDs are largely caused by the inhibition of COX1 and its role in normal mucosal defense mechanisms (discussed above), and also through the inhibition of thromboxane A2, which compromises platelet function and results in gastrointestinal bleeding. Clinical trials have repeatedly demonstrated that coxibs are associated with fewer ulcers, less gastrointestinal bleeding and fewer ulcer complications than nonselective NSAIDs,[22,23,24,25] but concurrent use of low-dose aspirin blunts this benefit. It is expected that the withdrawal of several coxibs will lead to many patients switching back to nonselective NSAIDs, with an anticipated increase in cases of gastrointestinal bleeding, especially in elderly patients.
H. pylori infection and NSAIDs are independent risk factors for peptic ulcer disease that have additive or synergistic effects on adverse gastrointestinal outcomes (Figure 1). In a meta-analysis, the OR for the incidence of peptic ulcer was 61.1 in patients infected with H. pylori and also taking NSAIDs, compared with uninfected controls not taking NSAIDs. The OR narrowed to 18.1 when comparing H. pylori-infected patients with H. pylori-uninfected patients who were not taking NSAIDs.H. pylori infection also potentiates the ulcer bleeding induced by low-dose aspirin. Together, H. pylori infection and NSAID use account for approximately 90% of peptic ulcer disease.
Helicobacter pylori and nonsteroidal anti-inflammatory drugs have synergistic effects on gastric mucosal damage. Both H. plyori infection and NSAID use have been found to independently and siginificantly increase the risk of gastric and duodenal mucisak danage and ulceration. H. pylori and NSAIDs act synergistically through pathways of inflammation in the development of ulcers and in ulcer bleeding.
Both H. pylori infection and NSAID use have been found to independently and significantly increase the risk of gastric and duodenal mucosal damage and ulceration. H. pylori and NSAIDs act synergistically through pathways of inflammation in the development of ulcers and in ulcer bleeding.
Nat Clin Pract Gastroenterol Hepatol. 2006;3(2):80-89. © 2006 Nature Publishing Group
Cite this: Peptic Ulcer Disease Today - Medscape - Feb 01, 2006.