Hyperoxia Disrupts Intestinal Function via Toll Like Receptor 4 Pathway in Neonatal Rat

The result of breathing increased partial pressures of oxygen is hyperoxia. Supplemental oxygen is often used to treat newborns with respiratory disorder. An excess of oxygen in body tissues which is affected in different ways not only has beneficial effects but also has adverse effects. Our and others’ previous studies had demonstrated ileum was injured by hyperoxia exposure, which was attributed to oxidative stress during the postnatal hyperoxia period. We aim to untangle the mechanism underlying the ileum disturbed by hyperoxia in neonatal rats, with particularly focuses on the toll like receptor 4 (TLR4)/ nuclear factor kappa B (NFκB) signaling pathway, and to investigate the effect of hyperoxia on the intestinal barrier function in order to seek for reliable therapeutic intervention. The ambient air and normobaric hyperoxia groups with or without CRAMP (Cathelin-Related Anti-Microbial Peptide) are maintained in room air and 85% O2 for 1 and 2 weeks. The rats are euthanized on postnatal Day 7 and Day 14, the terminal ileum is collected for histological and ultrastructural analyses and immunoassays. The serum interleukin-6 is measured for estimating the inflammatory status. The intestinal permeability, bacterial translocation and vitamin B12 uptake ability of ileum are performed for assessment the intestinal barrier function. The expression and localization of transcobalamin and inflammation biomarkers TLR4, Toll-like receptor adaptor molecule 2 (TRAM), Inhibitor of nuclear factor kappa-B kinase and NFκB are analyzed through immunohistochemistry methods and western blotting. The storage of vitamin B12 in the liver is quantified by enzyme-linked immunosorbent assay. This study shed light on the B12 uptake decreased due to defect in transcobalamin on the damaged ileum by hyperoxia. We also show that morphological and functional changes of ileum are reserved by therapeutic intervention of CRAMP inhibits TLR4/NFκB inflammatory response. Our goal in this study is to provide the protective and therapeutic intervention against damage to ileum while the neonatal is under hyperoxia treatment.