Review: acute human models of gastric mucosal injury

Non-steroidal anti-inflammatory drugs and the gastric mucosa: mechanisms of damage and protection

Prostaglandins have numerous mucosal protective properties, impairment of which contribute to NSAID injury. It is not clear which is the most important injurious factor affecting patients taking NSAIDs. Is it the NSAID itself, either by topical toxicity and/or production of toxic mediators or does the patient become more sensitive to NSAIDs as a result of some other luminal component, such as acid or bile acids, food (by physical or chemical mechanisms) or accompanying alcohol? Intrinsic irritancy/toxicity probably accounts for the greater mucosal toxicity of aspirin, although it is not clear whether this is due to a direct (non-prostaglandin-dependent) effect on mucus or bicarbonate secretion, membrane integrity, interference with intermediary metabolism or the production of toxic products. Similarly, the relationship of irritancy to the symptom of dyspepsia, to which patients on aspirin are prone, is as yet not well understood. While strategies for short-term protection of experimental animals and humans are well established, protection against important, but relatively rare clinical events, is more difficult to study and much less well understood. In particular, the importance of the ability of NSAIDs to exacerbate bleeding, independent of injury, has been largely neglected in the context of presentation with haematemesis and melaena.

Assessment of non-steroidal anti-inflammatory drug (NSAID) damage in the human gastrointestinal tract

Aspirin is widely prescribed and confers considerable benefit to patients by reducing cardiovascular and cerebrovascular morbidity and mortality. Nonsteroidal anti-inflammatory drugs (NSAIDs) are effective analgesics, antipyretics and reduce the inflammatory component in conditions such as rheumatoid arthritis. However, both agents are associated with an increased risk of gastrointestinal symptoms and the potentially serious consequences of gastroduodenal ulceration, bleeding and perforation. The introduction of highly selective cyclo-oxygenase (COX)-2 inhibitors or the coprescription gastroprotective agents with nonselective NSAIDs have offered strategies to reduce the incidence of such events. This review article analyzes the quantitative techniques that can be employed by clinical pharmacologists and the clinical studies performed to assess NSAID damage in the gastrointestinal tract.

Mechanisms of gastroprotection

Gastric mucosa is constantly exposed to various irritants, but it usually maintains its integrity owing to several lines of defense, including mucus-alkaline secretion, mucosal hydrophobicity, rich mucosal blood flow, stabilization of tissue lysosomes, maintenance of mucosal sulfhydryls, and rapid proliferation and renewal of mucosal cells. Prostaglandins (PG) inhibit experimental gastric mucosal damage and ulcerations induced by a wide variety of agents, hence PG have been proposed to contribute to the overall protective process by activation of various mucosal defence lines--particularly by prevention of vasocongestion, ischemia, and deep hemorrhagic necrosis. The relation between tissue PG generation and mucosal protection does not appear to be closely related, and probably only minute amounts of PG are required to maintain mucosal integrity. In contrast to PG, other products of arachidonate metabolism, such as TxA2, LTC4 or LTD4, and the related lipid, platelet-activating factor, appear to mediate mucosal damage mainly by the disturbance in mucosal microcirculation and tissue ischemia. Gastroprotection can be achieved by stimulation of mucosal biosynthesis of protective PG or by the inhibition of the release or action of the proulcerogenic arachidonate metabolites. Certain natural substances, such as sulfhydryls, epidermal growth factor, or polyamines, protect the mucosa via a PG-independent mechanism, probably by enhancing the tissue repair processes.(ABSTRACT TRUNCATED AT 250 WORDS)