Numerous therapies used for inflammatory bowel disease (IBD) target the transcription factor NF-kappaB, which is involved in the production of cytokines and chemokines integral for inflammation. Here we show that curcumin, a component of the spice turmeric, is able to attenuate colitis in the dinitrobenzene sulfonic acid (DNB)-induced murine model of colitis. When given before the induction of colitis it reduced macroscopic damage scores and NF-kappaB activation. This was accompanied by a reduction in myeloperoxidase activity, and using semiquantitative RT-PCR, an attenuation of the DNB-induced message for IL-1beta was detected. Western blotting analysis revealed that there was a reproducible DNB-induced activation of p38 MAPK detected in intestinal lysates by using a phosphospecific antibody. This signal was significantly attenuated by curcumin. Furthermore, we show that the immunohistochemical signal is dramatically attenuated at the level of the mucosa by curcumin. We conclude that the widely used food additive curcumin is able to attenuate experimental colitis through a mechanism correlated with the inhibition of the activation of NF-kappaB and effects a reduction in the activity of p38 MAPK. We propose that this agent may have therapeutic implications for human IBD.

Summary Stress‐activated protein kinases (SAPKs) are activated in human inflammatory bowel disease (IBD). Recently it has been demonstrated that p38MAPK (mitogen‐activated protein kinase) inhibition using SB203580 is effective in reducing disease in both dextran sulphate sodium (DSS)‐induced and 2,4,6‐trinitrobenzenesulphonic acid (TNBS)‐induced murine colitides, underscoring the importance of this pathway in gastrointestinal inflammation. However, the contribution of c‐Jun N‐terminal kinase (JNK) in intestinal inflammation is unknown. Based on the known involvement of JNK in tumour necrosis factor‐α (TNF‐α) expression and in mediating the effects of oxidant stress, we hypothesized that JNK inhibition would also affect colitis. Our studies in mice with DSS‐induced colitis treated with the JNK inhibitor SP600125, indicate that there is a significant reduction in wasting as well as a significant reduction in histological damage scores. Both total colonic and mesenteric lymphocyte CD3/CD28‐stimulated TNF‐α levels were dramatically reduced under the same circumstances. This was associated with a reduction in JNK protein expression and activity, as well as a reduction in AP‐1 DNA binding with SP600125. Interestingly, there were no apparent changes in either p38MAPK or p42/44ERKs. Immunofluorescence of the colon for the active form of JNK revealed a prominent signal arising from the infiltrating inflammatory cells. SP600125 reduced this as well as, specifically, macrophage infiltration. Strikingly, we also demonstrate reduced epithelial cell apoptosis in response to treatment with SP600125. We conclude that specific inhibition of JNK is beneficial in the DSS model of colitis, and may be of value in human IBD.

A wealth of evidence supports the notion that curcumin, a phytochemical present in turmeric, is a potent chemopreventive agent for colon cancer. Its mechanism of action remains incompletely understood. Here we report that curcumin's apoptosis-inducing effects in colon cancer cell lines are accompanied by robust ceramide generation. This occurs through de novo synthesis as the increase in ceramide could be attenuated by pre-incubation of the cells with myriocin, and no changes were observed in sphingomyelin levels, or in either acidic or neutral sphingomyelinase activities. Furthermore, cell death could in part be reversed by myriocin, indicating, for the first time, that endogenous ceramide generation by this agent contributes towards its biological activity. We then investigated the role of reactive oxygen species (ROS) in this phenomenon and demonstrated that curcumin induced robust oxidant generation in the cell lines tested, and its reversal by N-acetylcysteine, completely attenuated apoptosis. We next confirmed that curcumin could activate c-jun N-terminal kinase (JNK) and that its modulation could reverse cell death; however, this intervention could not block ceramide generation, or ROS production. Conversely, however, the inhibition of ROS using N-acetylcysteine led to an inhibition of JNK activation. Hence, we conclude that curcumin induces apoptosis via a ROS-associated mechanism that converges on JNK activation, and to a lesser extent via a parallel ceramide-associated pathway.

Tregs have a reduced capacity to activate the PI3K/Akt pathway downstream of the TCR, and the resulting low activity of Akt is necessary for their development and function. The molecular basis for the failure of Tregs to efficiently activate Akt, however, remained unknown. We show that PH-domain Leucine-rich-repeat Protein Phosphatase (PHLPP), which dephosphorylates Akt, is up-regulated in Tregs, thus suppressing Akt activation. Tregs expressed higher levels of PHLPP than conventional T cells and knock-down of PHLPP1 restored TCR-mediated activation of Akt in Tregs. Consistent with their high Akt activity, the suppressive capacity of Tregs from PHLPP1-/- mice was significantly reduced. Moreover, the development of induced Tregs was impaired in PHLPP1-/- mice. The increased level of Akt's negative regulator, PHLPP, provides a novel mechanism used by T cells to control the Akt pathway and the first evidence for a molecular mechanism underlying the functionally essential reduction of Akt activity in Tregs.

From these findings, it is concluded that ILK plays an important role in intestinal epithelial cell proliferation, and that it influences the development of colitis-associated cancer, through modulation of cyclin D1, the extracellular matrix and MMP9.