Gliotoxin reduces the severity of trinitrobenzene sulfonic acid-induced colitis in mice: Evidence of the connection between heme oxygenase-1 and the nuclear factor-κB pathway in vitro and in vivo

Abstract

Gliotoxin, a fungal metabolite, has been known to show strong immunosuppressive properties, although its mechanisms are not completely understood. In this report, the authors investigated the mechanism whereby gliotoxin has anti-inflammatory properties in vitro and in trinitrobenzene sulfonic acid-induced colitis. Body weight, histological scores, and myeloperoxidase activity were evaluated in trinitrobenzene sulfonic acid colitis. Nuclear factor-kappaB (NF-kappaB) p65, tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-12, and intercellular adhesion molecule-1 were detected by immunohistochemical staining. IL-8 secretion was measured by an enzyme-linked immunosorbent assay. Heme oxygenase-1 (HO-1) expression and I-kappaB degradation were analyzed by Western blot. Pretreatment of human epithelial HT-29 cells with gliotoxin significantly blocked the I-kappaB degradation and NF-kappaB p65 nuclear translocation induced by tumor necrosis factor-alpha or IL-1beta; these were parallel with the inhibition of IL-8 secretion and intercellular adhesion molecule-1 expression in the same cells. Interestingly, gliotoxin induced HO-1 in HT-29 cells and, in turn, inhibition of HO-1 activity by a zinc protoporphyrin IX reversed the effects of gliotoxin in terms of I-kappaB degradation, intercellular adhesion molecule-1 expression, and IL-8 production. In trinitrobenzene sulfonic acid colitis, gliotoxin administration significantly improved the clinical and histopathological symptoms. Notably, gliotoxin also induced HO-1 in the colonic mucosa and zinc protoporphyrin IX reversed the protective effects of gliotoxin in trinitrobenzene sulfonic acid colitis. These results demonstrate for the first time that the anti-inflammatory actions mediated by gliotoxin include HO-1 induction and the subsequent blockade of NF-kappaB-dependent signaling pathways in vitro and in vivo. The current results also demonstrate that gliotoxin may be an effective agent for the treatment of diseases characterized by mucosal inflammation.