No abstract

The combination of COX-2 absence (or inhibition) and the topical effect of NSAIDs lead to changes characteristic of NSAID enteropathy without concomitant COX-1 inhibition and/or associated decreases in mucosal prostaglandins. COX-2 appears to be more important for maintaining small bowel integrity than COX-1.

The side effects of NSAIDs are equally evident in the stomach and the small bowel. The latter is increasingly seen as being clinically significant, contributing substantially to the iron-deficiency anaemia that is so common in patients with rheumatoid arthritis. Furthermore, NSAID-enteropathy may be associated with life-threatening events. The pathogenesis of NSAID-enteropathy is uncertain but inhibition of COX-1 is believed to be of pivotal importance. However there is increasing evidence that COX-2 inhibition and the topical effect may have a synergistic detrimental action. We examined the role of COX-1, COX-2 and the so called topical effect of acidic NSAIDs. We found that COX-1 or COX-2 inhibition and the topical effect alone do not damage the GI tract. Dual inhibition of COX-1 and COX-2 results in intestinal inflammation similar to that caused by Indomethacin. The topical effect may act synergistically in this damage. The conventional view that the mechanism of gastrointestinal damage is principally caused by COX-1 inhibition needs to be revised in view of recent studies using selective inhibitors of the COX enzymes and COX knockout animals.

The pathogenesis of non-steroidal anti-inflammatory drug (NSAID)-induced gastroenteropathy may involve a number of key events leading to increased intestinal permeability and inflammation (topical effect) and the development of ulcers (micro-vascular effects of COX-1 inhibition and prostaglandin deficiency). Many strategies have been employed in an attempt to reduce the toxic effects of NSAIDs and these have been targeted at the different pathogenic stages of lesion development. One of the latest in this long chain of damage limitation has been the development of nitric oxide (NO) sequestering NSAIDs (NO-NSAIDs). It is suggested that the NO, which is released as the compounds are broken down, may counteract the consequences of the NSAID-induced decrease in mucosal prostaglandins. Here we examine the proposed mechanisms for NSAID-induced gastrointestinal damage together with some of the methods employed to address these mechanisms. We also consider the physiologic roles of NO in the gut together with how it may be potentially employed as an agent for limiting the side effects of NSAIDs in the gastrointestinal tract.

Naproxen and AZD3582 are equally associated with increased small intestinal permeability and inflammation, which is the consequence of their topical effect. The reduced small bowel ulcer counts with AZD3582 accords with the suggestion that vascular factors are the main driving force for NSAID-induced ulcer formation.