Nonsteroidal anti-inflammatory drugs (NSAIDs) are used extensively as therapeutic agents, despite their well documented gastrointestinal (GI) toxicity. At this time, the mechanisms responsible for NSAID-associated GI damage are incompletely understood. In this study, we used microarray analysis to generate a novel hypothesis about cellular mechanisms that underlie the GI toxicity of Accordingly, quantitative real-time reverse transcription polymerase chain reaction and immunoblotting were performed to assess the effects of NSAIDs on the expression of mRNA and protein for calpain 8, calpain 2, calpain 1, and calpastatin. In treated IEC-6 monolayers, NS-398 decreased the expression of mRNA for calpain 2 and calpain 8. Both NS-398 and indomethacin decreased the protein expression of calpains 8, 2, and 1. None of the NSAIDs affected expression of calpastatin mRNA or protein. The calpain inhibitors, N-acetyl-Leu-Leu-methioninal and N-acetyl-Leu-LeuNle-CHO, retarded IEC-6 cell migration in a concentration-dependant fashion, and these inhibitory effects were additive with those of indomethacin and NS-398. Our experimental results suggest that the altered expression of calpain proteins may contribute to the adverse effects of NSAIDs on intestinal epithelial restitution.Nonsteroidal anti-inflammatory drugs (NSAIDs) are used extensively as therapeutic agents despite their well documented gastrointestinal (GI) toxicity. Adverse gastrointestinal effects of NSAIDs in humans and other species include oral, gastric, duodenal, and colonic ulceration (Lichtenberger, 2001;Tomisato et al., 2004). Despite exhaustive investigation, the mechanisms responsible for NSAID-associated GI damage are not completely understood. Evidence gathered to date suggests that NSAIDs may promote ulcer formation not only by inhibiting mucosal cyclooxygenase (COX) and decreasing cytoprotective prostaglandins (PGs) but also by adversely influencing intestinal microflora, neutrophil recruitment, surface hydrophobicity, and epithelial restitution (Lichtenberger, 2001;Little et al., 2007). Although the inhibition of COX isoforms has received much attention and investigation as the basis of GI