Whether intestinal barrier disruption precedes or is the consequence of intestinal injury in necrotizing enterocolitis (NEC) remains unknown. Using a neonatal mouse NEC model, we examined the changes in intestinal permeability and specific tight-junction (TJ) proteins preceding NEC and asked whether these changes are prevented by administration of Bifidobacterium infantis, a probiotic known to decrease NEC incidence in humans. Compared with dam-fed controls, pups submitted to the NEC protocol developed i) significantly increased intestinal permeability at 12 and 24 hours (as assessed by 70-kDa fluorescein isothiocyanate-dextran transmucosal flux); ii) occludin and claudin 4 internalization at 12 hours (as assessed by immunofluorescence and low-density membrane fraction immunoblotting); iii) increased claudin 2 expression at 6 hours and decreased claudin 4 and 7 expression at 24 hours; and iv) increased claudin 2 protein at 48 hours. Similar results were seen in human NEC, with claudin 2 protein increased. In mice, administration of B. infantis micro-organisms attenuated increases in intestinal permeability, preserved claudin 4 and occludin localization at TJs, and decreased NEC incidence. Thus, an increase in intestinal permeability precedes NEC and is associated with internalization of claudin 4 and occludin. Administration of B. infantis prevents these changes and reduces NEC incidence. The beneficial effect of B. infantis is, at least in part, due to its TJ and barrier-preserving properties.

Necrotizing enterocolitis (NEC) is a major cause of morbidity and death in premature infants. NEC is associated with increased levels of pro-inflammatory cytokines in plasma and tissues that are regulated by the transcription factor nuclear factor-B (NF-B). It remains unknown, however, whether NF-B mediates injury in neonatal NEC. We therefore examined the activation status of NF-B perinatally in the small intestine and in a neonatal rat model of NEC. We found that intestinal NF-B is strongly activated at birth and, in dam-fed newborn rats, is down-regulated within a day. In contrast, NF-B remains strongly activated at both d 1 and d 2 in stressed animals, and this is accompanied by a significant decrease in the levels of the endogenous NF-B inhibitor protein IB␣ and IB␤ at d 2. To determine the importance of elevated NF-B activity in intestinal injury in NEC, we administered the NEMO-binding domain (NBD) peptide that selectively inhibits the critical upstream IB kinase (IKK). NBD but not a control peptide decreased mortality and bowel injury in this model, supporting the hypothesis that bowel injury in NEC results from elevated NF-B activity. Our findings therefore lead us to conclude that selective NF-B inhibition represents a promising therapeutic strategy for NEC.

Plaen IG. Lack of VEGFR2 signaling causes maldevelopment of the intestinal microvasculature and facilitates necrotizing enterocolitis in neonatal mice.