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Background: L-arginine (L-Arg) is the substrate for both inducible nitric oxide synthase and arginase, which are upregulated in IBD and in mouse colitis models. L-Arg uptake by cells is mediated by cationic amino acid transporter (CAT) proteins, and CAT2 is the inducible form. We have found that L-Arg supplementation enhances restitution in wound repair models In Vitro, and improves clinical parameters of weight loss, survival, and colon weight/length, but not histology, in experimental colitis in mice induced by dextran sulfate sodium (DSS). In CAT2-/mice there is exacerbation of DSS colitis, accumulation of L-Arg in serum, and favorable effects of L-Arg treatment are lost, indicating that inducible uptake of L-Arg is involved in compensatory host responses. Our aim was to define mechanisms underlying the clinical benefit of L-Arg supplementation. Methods: Male C57BL/6 mice were given 4% DSS for 6 days followed by 4 days of 1% L-Arg (DSS/L-Arg group) or regular water (DSS group); controls were given water alone for 10 days (control group), or for 6 days followed by L-Arg for 4 days (control/L-Arg group). Colon tissue from 3 mice in each group was obtained for RNA isolation and then microarray gene expression analysis. The Affymetrix® Mouse Gene 1.0 ST array containing >16,000 protein-coding genes was used. Hierarchical clustering of global gene expression patterns was performed. Differentially expressed genes (DEGs) were selected by both a p value 2. Functional features of the DEGs were evaluated by Ingenuity Pathway Analysis. Results: Hierarchical clustering comparing expression values in the 12 samples revealed that the DSS group was markedly distinct from the control or the control/L-Arg groups. Surprisingly, the DSS/L-Arg group segregated closely with the two control groups not receiving DSS, rather than with the DSS group. There were 342 DEGs with DSS versus control, but only 59 of these genes were altered in DSS/L-Arg versus control. We specifically identified 132 genes upregulated in response to DSS that were downregulated to control levels after L-Arg supplementation. There were also 27 genes that were downregulated with DSS and returned to control levels in the DSS/L-Arg. The detailed patterns were analyzed by heatmaps, that showed marked differences with DSS that reverted to a control pattern in the DSS/L-Arg group. The pathways enriched with DEGs between DSS/L-Arg and DSS included cell-to-cell signaling (leukocyte extravasation; IL-17, IL-8, and IL-10 signaling), cell migration, and cell proliferation pathways.Conclusions:Ourmicroarray gene expression analysis indicates that L-Arg supplementation dramatically alters gene expression patterns in the DSS model, and plays a substantive role in repair, mucosal integrity, and regulation of inflammation.

molecular insights to IBD, we find 17-AAG use profoundly suppresses development of DSSinduced colitis. In another model of colitis, adoptive transfer of CD4+CD45Rbhi cells to Rag deficient mice leads to colitis at ~50 days, and compared with DMSO-treated controls, mice treated with 17-AAG did not develop colitis, gained weight(p