Published online Sep 21, 2018. doi: 10.3748/wjg.v24.i35.4036
Peer-review started: May 16, 2018
First decision: June 13, 2018
Revised: July 6, 2018
Accepted: July 22, 2018
Article in press: July 22, 2018
Published online: September 21, 2018
Daikenchuto (DKT) is a traditional oriental herbal medicine, widely used to mitigate post-operative ileus and constipation. The mechanism of its actions remains less understood, in particular regarding its molecular target(s). However, an important hint to addressing this issue has come from our previous findings that the transient receptor potential ankyrin 1 (TRPA1) is highly expressed in intestinal myofibroblasts and mediates the antifibrotic effects of steroid and pirfenidone.
We hypothesized that DKT may activate TRPA1 channels in myofibroblasts to directly counteract the fibrotic changes of inflamed intestines. Although DKT has been shown to be beneficial for gut motility, intestinal blood flow and gastrointestinal hormone secretion, its anti-fibrotic actions through TRPA1 channel activation will be an entirely new finding and of considerable clinical significance.
We aimed at investigating at both in vitro and in vivo levels whether DKT targets TRPA1 channels expressed in intestinal myofibroblasts to exert its anti-fibrotic actions. The results would not only disclose a novel molecular target of anti-fibrotic therapy for inflammatory bowel diseases such as Crohn’s disease (CD) and ulcerative colitis, but also promote our general understanding about the complex actions of herbal medicines.
A trinitrobenzene sulfonic acid (TNBS) chronic colitis model was established in both wild-type and TRPA1 knock out mice, in which the impact of DKT administration were evaluated by pathological and biochemical analyses. An intestinal myofibroblast cell line (InMyoFibs) stimulated by transforming growth factor-β1 (TGF-β1) was used as a cellular model of intestinal fibrosis, where expression of TRPA1 and pro-fibrotic factors and related intracellular signaling (in particular TGF-β-mediated one) were examined in detail. The counteracting effects of DKT on these changes were also evaluated. Biopsy samples from non-stenotic and stenotic regions of CD patient’s intestines were subjected to histological examination and immunoblot analysis with particular respect to the altered expression pattern of TRPA1 channel and fibrotic factors. As compared with preceding works on a similar topic, the methodological approach applied to this study is more comprehensive covering a broad range of DKT’s actions that include cellular and animal models and human patients.
In TNBS chronic colitis model mice, the extents of inflammation and fibrotic changes were more prominent in TRPA1-/- knockout than in wild-type mice. One-week enema administration of DKT suppressed fibrotic lesions in wild-type mice, but not in TRPA1 knockout mice. Active ingredients of DKT, induced Ca2+ influxes in InMyoFib, which were antagonized by TRPA1 channel blocker HC-030031. DKT counteracted TGF-β1-induced expression of Type 1 collagen, α-SMA, and this was accompanied by attenuated fibrosis-associated signaling. A DKT’s active ingredient Japanese Pepper increased the mRNA and protein expressions of TRPA1, which in turn negatively regulated collagen synthesis in InMyoFibs. In stenotic regions of CD patient’s intestines, TRPA1 expression was significantly increased. However, several limitations remain in this study that may compromise the value and relevance of this study, which include the inability of TNBS to create a severe phenotype of chronic colitis, the lack of control data from human healthy donors, and no comparative data from other Chinese (herbal) medicines that may have similar actions.
DKT-induced expression and activation of TRPA1 could be important mechanisms for suppressing intestinal fibrosis, which would in part account for the reported beneficial actions of DKT on inflamed intestines. Thus, targeting myofibroblast TRPA1 may serve as a new and promising therapeutic strategy for fibrotic stenotic changes occurring in incurable chronic inflammatory bowel diseases such as CD and ulcerative colitis.
Our findings not only provide a novel molecular target for the anti-fibrotic therapy of inflammatory bowel diseases in the future, but also a framework to reinterpret the unique theories of traditional Oriental medicine.