Current Pharmaceutical Design - Volume 7, Issue 1, 2001

The objectives of medical treatment of patients with gastroesophageal reflux disease (GERD) are relief of symptoms and healing of esophagitis, which can be achieved, at least in part, by drugs which suppress acid secretion. In patients with GERD symptoms and/or mild esophagitis, the best and most cost-effective therapeutic strategy is to start with a proton pump inhibitor with subsequent trial of step down of the intensity of therapy (e.g. H2-receptor antagonists). In patients with moderate or severe esophagitis, proton pump inhibitors are the mainstay of treatment and the most effective in preventing symptoms and esophagitis. In patients with mild disease, the recurrence of symptoms is less frequent and many patients may not need continuous maintenance therapy or may require treatment with either low dose proton pump inhibitors, H2-receptor antagonists or cisapride only. H. pylori eradication might be needed in GERD patients on long-term treatment with proton pump inhibitors, but the benefit of this strategy has not yet been adequately demonstrated. Antireflux surgery is a maintenance option for the young patient on long-term medical therapy. Improved medical therapy for GERD might depend on future agents with different therapeutic targets, including GABA inhibitors and nitric oxide modulating drugs in the control of the lower sphincter esophagus and in motility disorders, free radical scavengers in the prevention of mucosal damage and COX-2 specific inhibitors in the prevention of the progression of Barret's esophagus to adenocarcinoma. Finally, the modulation of some growth factors might have a potential role in delayed esophageal ulcer healing, refractory esophagitis and in Barrett's esophagus.

The tachykinins, substance P, neurokinin A and neurokinin B are small peptides expressed in the extrinsic primary afferent nerve fibers and enteric neurons of the gut. Tachykinins exert a variety of biological actions mediated by three distinct receptors, termed NK 1 , NK 2 and NK 3 , and at the gastrointestinal level these peptides influence motility, electrolyte and fluid secretion and tissue homeostasis. Several intestinal disorders are associated with changes in the expression of the tachykinin system. Thanks to biological studies and receptor cloning, new selective tachykinins antagonists are now available and have been shown to be active in experimental gut disorders. Some of them are now under clinical trial in inflammatory bowel diseases and the irritable bowel syndrome. The body of preclinical data so far available seems to indicate that tachykinin antagonists might be a new therapeutic tool in the treatment of gut disorders.

Nitric oxide is a ubiquitous molecule involved in a variety of biological processes. The specific action of NO depends on its enzymatic sources namely neuronal nitric oxide synthase (nNOS), endothelial NOS (eNOS) and inducible NOS (iNOS) and all three isoforms have been localized in the gastrointestinal tract. Constitutive synthesis of NO by nNOS or eNOS isoforms is involved in the maintaining of the gastrointestinal mucosal integrity through modulation of gastric mucosal blood flow, epithelial secretion and barrier function. However, large amounts of NO synthesized from the inducible isoform have been implicated in tissue injury in the gut during inflammatory reactions. In this review we provide an overview of the dual role of nitric oxide in modulating gastrointestinal mucosal defense and injury. In addition, we highlight the therapeutic potential of NO modulation.

The use of nonsteroidal antiinflammatory drugs (NSAIDs) is associated with a wide array of alterations in gastrointestinal integrity and function. Various approaches have been taken to developing NSAIDs with reduced gastrointestinal toxicity, and few have been successfully reduced the incidence of adverse reactions. These include cyclooxygenase-2 (COX-2) selective inhibitors and nitric oxide (NO)-releasing NSAIDs. Especially, much has been written about the potential of COX-2 inhibitors as anti-inflammatory and analgesic agents that lack the gastrointestinal side effects of traditional NSAIDs. COX-2 expression is most evident at sites of inflammation, while COX-1 accounts for the majority of prostaglandin synthesis in the normal gastrointestinal tract. However, there are distinct examples of circumstances in which COX-2-derived prostaglandins play a role in the maintenance of gastrointestinal mucosal integrity, particularly when the mucosa is injured, and the delineation of COX-1 and COX-2 might not be quite as clear as has been suggested. On the other hand, the rational behind the NO-releasing NSAIDs is that the NO released from the derivatives will exert beneficial effects on the gastrointestinal mucosa. This approach has been successfully demonstrated to lessen the incidence of gastrointestinal damage and to promote the healing of gastric ulcers. The present article overviews the roles of COX and NO in housekeeping functions of the gastrointestinal mucosa in various circumstances, and the effects of gastrointestinal sparing NSAIDs, mainly COX-2 selective inhibitors and NO-releasing derivatives of NSAIDs, on the ulcerogenic and healing responses in the gastrointestinal mucosa of experimental animals.