NAC Attenuated NEC-Induced Lung Injury Caused by ROS Released from Neutrophils by Regulating the Keap1-Nrf2 Pathway

Abstract

Background: Necrotizing Enterocolitis (NEC) is a critical illness commonly seen in premature and diseased neonates, characterized by mucosal necrosis of the small intestine and colon, which seriously affects the life and health of patients. Objective: The aim of the research was to investigate the role and mechanism of neutrophils in lung injury in mice with NEC. Methods: Combinational treatment with formula milk, hypoxia, and lipopolysaccharide (LPS) was performed to establish NEC in 5-day-old C57BL/6J mice. These mice were divided into 4 groups (20 mice in each group) by random number table method: Ctrl group, NEC group, NEC + phosphate-buffered saline (PBS) group, NEC + N-acetyl-L-cysteine (NAC) group. The pathological changes in intestinal and lung tissues were examined through Hematoxylin and Eosin (HE) staining. Lymphocyte antigen 6complex, locus g (Ly6G), neutrophil elastase (NE), myeloperoxidase (MPO) immunohistochemistry (IHC), and flow cytometry were used for qualitative and quantitative analysis of neutrophils in lung tissues respectively. The messenger ribonucleic acid (mRNA) relative expression levels of inflammatory factors in intestinal and lung tissues were detected using Reverse Transcription-quantitative Polymerase Chain Reaction (RT-qPCR). The reactive oxygen species (ROS) release level in neutrophils stimulated by N-formyl-methionyl-leucy1-phenylalanine (fMLP) was detected using an enzyme-labeled instrument. The expression levels of genes in the Kelch-like enoyl-CoA hydratase (ECH)-associated protein 1-nuclear factor erythroid 2-related factor 2 (Keap1-Nrf2) pathway were determined using RT-qPCR. Results: Compared to the Ctrl group, the intestinal and lung tissues of the mice in the NEC group were significantly damaged (p < 0.0001). However, NAC could significantly relieve the damage (p < 0.0001). Compared to Ctrl group, the mRNA relative expression levels of inflammatory factors and anti-oxidant genes were significantly upregulated (p < 0.05), while the expression levels of anti-ROS genes were significantly downregulated in the NEC group (p < 0.05), and NAC could significantly reverse this result. Mice lung tissue RNA-seq results indicated a significant enrichment in the neutrophil degranulation pathway. The levels of NE, MPO, and ROS released by neutrophils were significantly higher than those in the Ctrl group (p < 0.05). The ROS released by neutrophils is involved in NEC-induced lung injury by regulating the Keap1-Nrf2 pathway, as the inhibition of the release of ROS can alleviate the injury of intestinal and lung tissues. Conclusions: Neutrophils play an important role in NEC-induced lung injury and NAC has therapeutic potential for NEC-induced lung injury.