Protective Effects of Bifidobacterium on Intestinal Barrier Function in LPS-Induced Enterocyte Barrier Injury of Caco-2 Monolayers and in a Rat NEC Model.

Xiang Ling,Peng Linglong,Wei Hong,Du Weixia,Tony T Wang

doi:10.1371/journal.pone.0161635

Abstract

Zonulin protein is a newly discovered modulator which modulates the permeability of the intestinal epithelial barrier by disassembling intercellular tight junctions (TJ). Disruption of TJ is associated with neonatal necrotizing enterocolitis (NEC). It has been shown bifidobacterium could protect the intestinal barrier function and prophylactical administration of bifidobacterium has beneficial effects in NEC patients and animals. However, it is still unknown whether the zonulin is involved in the gut barrier dysfunction of NEC, and the protective mechanisms of bifidobacterium on intestinal barrier function are also not well understood. The present study aims to investigate the effects of bifidobacterium on intestinal barrier function, zonulin regulation, and TJ integrity both in LPS-induced enterocyte barrier injury of Caco-2 monolayers and in a rat NEC model. Our results showed bifidobacterium markedly attenuated the decrease in transepithelial electrical resistance and the increase in paracellular permeability in the Caco-2 monolayers treated with LPS (P < 0.01). Compared with the LPS group, bifidobacterium significantly decreased the production of IL-6 and TNF-α (P < 0.01) and suppressed zonulin release (P < 0.05). In addition, bifidobacterium pretreatment up-regulated occludin, claudin-3 and ZO-1 expression (P < 0.01) and also preserved these proteins localization at TJ compared with the LPS group. In the in vivo study, bifidobacterium decreased the incidence of NEC from 88 to 47% (P < 0.05) and reduced the severity in the NEC model. Increased levels of IL-6 and TNF-α in the ileum of NEC rats were normalized in bifidobacterium treated rats (P < 0.05). Moreover, administration of bifidobacterium attenuated the increase in intestinal permeability (P < 0.01), decreased the levels of serum zonulin (P < 0.05), normalized the expression and localization of TJ proteins in the ileum compared with animals with NEC. We concluded that bifidobacterium may protect against intestinal barrier dysfunction both in vitro and in NEC. This protective effect is associated with inhibition of proinflammatory cytokine secretion, suppression of zonulin protein release and improvement of intestinal TJ integrity.

Highlights

Intestinal barrier dysfunction mainly refers to the abnormal increased intestinal permeability, which can make pathogens and foreign antigens cross the epithelial barrier[1]
Previous studies have shown that bifidobacterium protects the intestinal barrier function and oral administration of bifidobacterium has beneficial effects of necrotizing enterocolitis (NEC)[21,22,23,24]
We used a Caco-2 monolayers and a rat NEC model to investigate the protective effects of bifidobacterium on intestinal barrier dysfunction in vitro doi:10.1371/journal.pone.0161635.g006

Summary

Introduction

Intestinal barrier dysfunction mainly refers to the abnormal increased intestinal permeability, which can make pathogens and foreign antigens cross the epithelial barrier[1]. Intestinal permeability is regulated by tight junctions(TJ) formed between intestinal epithelial cells (IEC) at the most apical areas of the epithelium. TJ form a selectively permeable intercellular barrier at the apical aspect of the enterocyte lateral membranes and regulate the paracellular movement of molecules between the intestinal lumen and subepithelial tissues[2]. Formation of functional TJ is critical for the maintenance of gut permeability and intestinal barrier function[3,4]. NEC is the most common and devastating gastrointestinal diseases of premature infants and is characterized by loss of intestinal barrier function[6,7,8]

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