Inhibitory Effect of Baicalin on iNOS and NO Expression in Intestinal Mucosa of Rats with Acute Endotoxemia

Xinli Huang,Ti Zhang,Aiwen Feng,Guangrong Zhou,Xiaoming Yuan,Zhengyuan Zhang,Sudha Agarwal

doi:10.1371/journal.pone.0080997

Xinli Huang, Ti Zhang + Show 5 more

Open Access

https://doi.org/10.1371/journal.pone.0080997

Copy DOI

Abstract

The mechanism by which baicalin modulated the expression of inducible nitric oxide synthase (iNOS) and nitric oxide (NO) in the mucosa of distal ileum was investigated in a rat model of acute endo-toxemia induced by intraperitoneal injection of bacterial lipopolysaccharide (LPS). The experiment demonstrated that LPS upregulated iNOS mRNA and protein expression as well as NO produc-tion (measured as the stable degradation production, nitrites). LPS not only increased toll-like receptor 4 (TLR4) and peroxisome proliferator-activated receptor gamma (PPARγ) content, but also activated p38 and activating transcription factor 2 (ATF2) and inactivated PPARγ via phosphorylation. Inhibition of p38 signalling pathway by chemical inhibitor SB202190 and small interfering RNA (siRNA) ameliorated LPS-induced iNOS generation, while suppression of PPARγ pathway by SR-202 boosted LPS-elicited iNOS expression. Baicalin treatment (I) attenuated LPS-induced iNOS mRNA and protein as well as nitrites generation, and (II) ameliorated LPS-elicited TLR4 and PPARγ production, and (III) inhibited p38/ATF2 phosphorylation leading to suppression of p38 signalling, and (IV) prevented PPARγ from phosphorylation contributing to maintainence of PPARγ bioactivity. However, SR-202 co-treatment (I) partially abrogated the inhibitory effect of baicalin on iNOS mRNA expression, and (II) partially reversed baicalin-inhibited p38 phosphorylation. In summary, baicalin could ameliorate LPS-induced iNOS and NO overproduction in mucosa of rat terminal ileum via inhibition of p38 signalling cascade and activation of PPARγ pathway. There existed a interplay between the two signalling pathways.

Highlights

The mucosa along the intestinal tract, especially the ileum, is susceptible to harmful factors such as LPS, which is a major cell wall component of Gram-negative bacteria [1]
Rats treated with LPS compared to the control showed higher level of inducible nitric oxide synthase (iNOS) mRNA (Fig. 2A/B)
Negative control small interfering RNA (siRNA) exert little effect on LPS-induced iNOS mRNA, but siRNAs against p38 and activating transcription factor 2 (ATF2) genes reduced iNOS mRNA by about 54.3% and 47.6%, respectively (Fig. 2C/D)

Summary

Introduction

The mucosa along the intestinal tract, especially the ileum, is susceptible to harmful factors such as LPS ( called endotoxin), which is a major cell wall component of Gram-negative bacteria [1]. LPS and derived pro-inflammatory molecules such asiNOS and NO may impair intestinal mucosa [2,3]. Severe devastation of intestinal mucosa plays an important role in intestinal barrier dysfunction, bacterial translocation, systemic inflammatory response syndrome and multiple organ dysfunction syndrome [4]. INOS is found to be predominantly expressed in intestinal epithelial cell, in macrophage, fibroblast, and smooth muscle cell [1,5]. P38, a member of MAPK superfamily, can trigger inflammatory response when it is activated. P38 plays a required role in the induction of iNOS expression in intestinal epithelium [2]. PPARc is expressed in intestinal epithelium and macrophage. PPARc plays an essential role in the inhibition of intestinal inflammation [10]

Objectives

Methods

Results

Conclusion