Gastrointestinal Adaptation, Regulation of Eicosanoids, and Mucosal Protection from NSAIDs

Abstract

ABSTRACfThe importance of recognizing that the ulcerogenic effects of NSAIDs may be modified by responses of the gastrointestinal mucosa leading to adaptation is emphasized by studies that have been performed in pigs and human volunteers. For example, loss of blood following repeated daily oral administration of NSAIDs for 10 days in pigs may not, with the exception of aspirin, relate to the development of mucosal pathology. Also, accumulation of polymorphonuclear leukocytes and production of leukotrienes does not relate to mucosal lesions or ulcers. The latter are unaffected by co-administration of the prostaglandin analogue, misoprostol, with the NSAID, diclofenac. These contrasting observations illustrate the difficulty of establishing key biochemical and cellular changes associated with long-term effects of NSAIDs in the gastric mucosa.Misoprostol, among the anti-ulcer agents employed as a mucosal protectant against the ulcerogenic effects of NSAIDs, has only partial effects. Likewise, COX-2-selective and NO-donating NSAIDs may also only have limited benefits in reducing the ulcerogenic potential of NSAIDs. This is because of lack of understanding of their biochemical and physiological effects as well as those mucosal defensive processes they are designed to spare or enhance.Further studies are needed to clarify (a) the roles of COX-l and COX-2 in the gastrointestinal mucosa, (b) the mechanisms of action of so-called COX-2-selective NSAIDs, (c) the fate and actions of nitric oxide from NO-donating NSAIDs as well as the potential for nitric oxide and nitrite generated therefrom to induce untoward premalignant or other changes in the mucosa, (d) the possibility that NO-donating NSAIDs may merely produce their apparent low acute ulcerogenic effects in the stomach by virtue of esterification of the carboxyl moiety of NSAIDs and not from generation of vasodilatory nitric oxide, and (e) the possibility that reducing the gastric ulcerogenicity of NSAIDs by nitroxyesterification may still lead to intestinal ulcerogenicity.

Cyclooxygenase 2---implications on maintenance of gastric mucosal integrity and ulcer healing: controversial issues and perspectives

“…Inhibition of prostaglandin synthesis can exert injurious actions on the gastric and duodenal mucosa as it abrogates a number of prostaglandin dependent defence mechanisms. Inhibition of COX leads to a decrease in mucus and bicarbonate secretion, reduces mucosal blood flow, and causes vascular injury, leucocyte accumulation, and reduced cell turnover, all factors that contribute to the genesis of mucosal damage 24. Within this broad spectrum of events, the microvascular damage appears to play a central role.…”

Determinants of the short‐term gastric damage caused by NSAIDs in man

“…The severity of this damage ranges from frequent asymptomatic inflammation, erosions and ulcers to the rare but serious ulcer complications of perforation and clinically evident bleeding. Many strategies have been employed in order to reduce or avert these side effects 2 . To date the most promising approach has been the introduction of the cyclooxygenase (COX‐2) selective agents 3 .…”

Capsule endoscopic diagnosis of nonsteroidal antiinflammatory drug-induced enteropathy

“…One mechanism is COX inhibition with reduced prostaglandin bicarbonate and mucous secretion, as well as reduced mucosal blood fl ow impairing mucosal defense and repair; this is compounded by inhibition of cell proliferation and angiogenesis and increased apoptosis. 10 When surface damage has occurred with back-diffusion of acid, there is neutrophil accumulation and adherence through upregulation of adhesion molecules, which, in turn, leads to microvascular stasis and ischemia and injury through free radical release. 11 However, inhibition of prostaglandin synthesis is not the only method by which NSAIDs damage the mucosa.…”