Published online Jul 14, 2018. doi: 10.3748/wjg.v24.i26.2867
Peer-review started: March 30, 2018
First decision: May 17, 2018
Revised: May 25, 2018
Accepted: June 9, 2018
Article in press: June 9, 2018
Published online: July 14, 2018
Sijunzi decoction (SJZD) is a traditional Chinese medicinal prescription that has been used to treat gastrointestinal tract diseases since ancient times. Our previous studies suggested that total polysaccharides of the Sijunzi decoction (TPSJ) could inhibit the proliferation of IEC-6 rat intestinal epithelial cells in vitro. However, no report has discussed the regulatory effects of TPSJ on the intestinal epithelial barrier.
Although TPSJ may inhibit intestinal epithelial cell proliferation, the mechanism by which it mediates barrier protection remains unclear.
To explore the protective effects of TPSJ on the epithelial barrier and the mechanism by which it mitigates tumor necrosis factor α (TNF-α)-induced damage in a Caco-2 cell monolayer.
We first used a MTT assay to assess the effect of TPSJ on TNF-α-damaged Caco-2 cells. Secondly, we treated a Caco-2 cell monolayer with TNF-α for 24 h and subsequently analyzed the TEER, permeability, and cytokines of the cells after TPSJ treatment. Third, we examined the effects of TPSJ on the expression of the tight junction proteins claudin 1, claudin 2, zo3, and occludin by immunofluorescence and western blotting. Finally, we investigated the NF-κB-MLCK-MLC pathway in TNF-α treated intestinal epithelial cells.
TPSJ promoted the growth of TNF-α-treated Caco-2 cells in a dose-dependent manner and decreased the secretion of pro-inflammatory cytokines in response to TNF-α. Secondly, TPSJ treatment significantly increased the TEER and decreased the increased phenolsulfonphthalein flux induced by TNF-α. Third, TPSJ markedly upregulated the expression of claudin 1, claudin 2, and zo3 proteins and attenuated the reorganization of claudin 1, claudin 2, zo3, and occludin. Finally, TPSJ suppressed the TNF-a-induced upregulation of myosin light chain (MLC) phosphorylation, MLC kinase (MLCK), and NF-κB p65.
TPSJ promoted proliferation of TNF-α-treated Caco2 cells. In Caco2 cell monolayers, TPSJ alleviated the TNF-α-induced decrease in TEER and increase in paracellular permeability, enhanced the expression of claudin 1, claudin 2, and zo3, and preserved the morphological distributions of these three tight junction proteins and occludin. Further, we found that the barrier protective effect of TPSJ was mediated through suppressing the NF-κB p65-mediated phosphorylation of MLCK and MLC.
Our findings provide evidence that TPSJ is a potential protective agent of intestinal barrier function. Further investigation into the mechanism of TPSJ on intestinal barrier as well as in vivo research is required.