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AIM: This study investigated the mechanisms of protection afforded by the proton pump inhibitor lansoprazole against gastric injury induced by different non-steroidal antiinflammatory drugs (NSAIDs) in rats.METHODS: Male Sprague-Dawley rats were orally treated with indomethacin (100 μmol/kg), diclofenac (60 μmol/kg),piroxicam (150 μmol/kg) or ketoprofen (150 μmol/kg).Thirty minutes before NSAIDs, animals were orally treated with lansoprazole 18 or 90 μmol/kg. Four hours after the end of treatments, the following parameters were assessed: gastric mucosal PGE2, malondialdehyde (MDA), myeloperoxidase (MPO) or non-proteic sulfhydryl compounds (GSH) levels; reverse transcription-polymerase chain reaction (RT-PCR) of mucosal COX-2 mRNA; gastric acid secretion in pylorus-ligated animals; in vitro effects of lansoprazole (1-300 μmol/L) on the oxidation of low density lipoproteins (LDLs) induced by copper sulphate.RESULTS: All NSAIDs elicited mucosal necrotic lesions which were associated with neutrophil infiltration and reduction of PGE2 levels. Increments of MPO and MDA contents, as well as a decrease in GSH levels were detected in the gastric mucosa of indomethacin- or piroxicam-treated animals. Indomethacin enhanced mucosal cyclooxygenase-2 expression, while not affecting cyclooxygenase-1. At the oral dose of 18 μmol/kg lansoprazole partly counteracted diclofenac-induced mucosal damage, whereas at 90 μmol/kg it markedly prevented injuries evoked by all test NSAIDs. Lansoprazole at 90 μmol/kg reversed also the effects of NSAIDs on MPO, MDA and GSH mucosal contents, without interfering with the decrease in PGE2 levels or indomethacin-induced cyclooxygenase-2 expression. However, both lansoprazole doses markedly inhibited acid secretion in pylorus-ligated rats. Lansoprazole concentration-dependently reduced the oxidation of LDLs in vitro.CONCLUSION: These results suggest that, besides the inhibition of acid secretion, lansoprazole protection against NSAID-induced gastric damage depends on a reduction in mucosal oxidative injury, which is also responsible for an increment of sulfhydryl radical bioavailability. It is also suggested that lansoprazole does not influence the downregulation of gastric prostaglandin production associated with NSAID treatment.