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Inflammatory bowel disease (IBD), consisting of Crohn's disease and ulcerative colitis, is a source of substantial morbidity and remains difficult to treat. New strategies for beneficial anti-inflammatory therapies would be highly desirable. Apolipoprotein (apo) E has immunomodulatory effects and synthetically derived apoE-mimetic peptides are beneficial in models of sepsis and neuroinflammation. We have reported that the antennapedia-linked apoE-mimetic peptide COG112 inhibits the inflammatory response to the colitis-inducing pathogen Citrobacter rodentium in vitro by inhibiting NF-κB activation. We now determined the effect of COG112 in mouse models of colitis. Using C. rodentium as an infection model, and dextran sulfate sodium (DSS) as an injury model, mice were treated with COG112 by intraperitoneal injection. With C. rodentium, COG112 improved the clinical parameters of survival, body weight, colon weight, and histologic injury. With DSS, COG112 ameliorated the loss of body weight, reduction in colon length, and histologic injury, whether administered concurrently with induction of colitis, during induction plus recovery, or only during the recovery phase of disease. In both colitis models, COG112 inhibited colon tissue inducible nitric-oxide synthase (iNOS), KC, TNF-α, IFN-γ, and IL-17 mRNA expression, and reduced nuclear translocation of NF-κB, as determined by immunoblot and immunofluorescence confocal microscopy. IκB kinase (IKK) activity was also reduced, which is necessary for activation of the canonical NF-κB pathway. Isolated colonic epithelial cells exhibited marked attenuation of expression of iNOS and the CXC chemokines KC and MIP-2. These studies indicate that apoE-mimetic peptides such as COG112 are novel potential therapies for IBD.