Elemental diet (ED) is effective for human Crohn's disease (CD). Although some of this effectiveness may be due to its low antigenic load and low fat content, the mechanisms remain unclear. We sought to assess the role of histidine, one of the constituent amino acids of ED, in controlling colitis.

The interleukin (IL)-10-deficient (IL-10^−/−) cell transfer model of colitis was used. SCID mice with colitis induced by transfer of IL-10^−/− cells were maintained on experimented diets containing either single amino acids or a mixture. The severity of colitis was assessed by wet colon weight. Colonic tumor necrosis factor (TNF)-α messenger RNA (mRNA) expression was detected by quantitative reverse-transcription polymerase chain reaction. Mouse peritoneal macrophages were stimulated by lipopolysaccharides (LPS), with or without amino acids. The concentration of cytokines in the supernatant was determined by enzyme-linked immunosorbent assay. Inhibitor of nuclear factor (NF)-κB-α and nuclear p65 were confirmed by immunoblotting.

In the IL-10^−/− transfer model, dietary histidine, but not alanine, reduced histologic damage and colon weight and TNF-α mRNA expression. Histidine inhibited LPS-induced TNF-α and IL-6 production by mouse macrophages in a concentration-dependent manner, whereas alanine or histidine-related metabolites had no such effect. Histidine inhibited LPS-induced NF-κB in macrophages.

These results showed that histidine could be a novel therapeutic agent for CD by inhibition of NF-κB activation, following down-regulation of proinflammatory cytokine production by macrophages. Thus, our studies provided new insights into the roles of amino acid metabolism in the pathophysiology of CD and for therapeutic strategies.