ABSTRACT
Acute lung injury (ALI) is the leading cause of respiratory diseases induced by uncontrolled inflammation and cell death. Lipopolysaccharide (LPS) is a major trigger of ALI in the progression through macrophage differentiation and the accelerated release of pro-inflammatory cytokines. The present study aimed to investigate the protective effects of human milk oligosaccharides, specifically 3'-sialyllactose (3'-SL) and 6'-sialyllactose (6'-SL), on LPS-induced ALI and elucidate their underlying signaling pathways. The inhibitory effects of 3'-SL and 6'-SL on inflammation were evaluated using LPS-treated RAW 264.7 macrophages. To establish the ALI model, mice were treated with 10 mg/kg LPS for 24 h. Histological changes in the lung tissues were assessed using hematoxylin and eosin staining and immunofluorescence. LPS causes thickening of the alveolar wall infiltration of immune cells in lung tissues and increased serum levels of TNF-α, IL-1ß, and GM-CSF. However, these effects were significantly alleviated by 100 mg/kg of 3'-SL and 6'-SL. Consistent with the inhibitory effects of 3'-SL and 6'-SL on LPS-induced pro-inflammatory cytokine secretion in serum, 3'-SL and 6'-SL suppressed mRNA expression of TNF-α, IL-1ß, MCP-1, iNOS, and COX2 in LPS-induced RAW 264.7 cells. Mechanistically, 3'-SL and 6'-SL abolished LPS-mediated phosphorylation of NF-κB and STAT1. Interestingly, fludarabine treatment, a STAT1 inhibitor, did not affect LPS-mediated NF-κB phosphorylation. In summary, 3'-SL and 6'-SL protect LPS-induced macrophage activation and ALI through the STAT1 and NF-κB signaling pathways.
