Bovine Recombinant Lipopolysaccharide Binding Protein (BRLBP) Regulated Apoptosis and Inflammation Response in Lipopolysaccharide-challenged Bovine Mammary Epithelial Cells (BMEC)

Lipopolysaccharide-binding protein (LBP) is an acute-phase protein involved in host response to Gram-negative and Gram-positive pathogens. It has been reported to exert diverse biological activities, such as anti-inflammatory effects. However, what effects it has on bovine mastitis has not been investigated. The aim of this study was to verify the anti-inflammatory properties of LBP on the inflammatory response of primary bovine mammary epithelial cells (BMEC) induced by lipopolysaccharide (LPS), and to determine the underlying mechanism. Bovine mammary epithelial cells were treated with various concentrations of LPS (1, 10, 20, and 100 μg/mL) for 3, 6, 12, and 24h. The results showed that LPS significantly inhibited cell viability in a dose-dependent manner. When cells were treated with LPS (10 μg/mL) for 12 h, the permeability of the cell membrane increased significantly. This promoted apoptosis. Various concentrations (10 and 20 μg/mL) of bovine recombinant lipopolysaccharide binding protein (BRLBP) could weaken the inflammation injury of BMEC induced by LPS without cytotoxicity. Toll-like receptor 4 (TLR4), nuclear factor κB (NF-κB), IL-1β, and tumor necrosis factor α (TNF-α) from BMEC were decreased. TLR4 and NF-κB P65 protein levels were down-regulated, and nuclear transcription factor κB activity was also weakened. All these results indicated that the protective effects of high concentrations of BRLBP on LPS-induced inflammation injury in BMEC were at least partially achieved by the decreased production of pro-inflammatory cytokines. BRLBP was found to directly inhibit LPS/TLR4-mediated NF-κB activation. One possible anti-inflammatory mechanism can be attributed to the negative role of BRLBP in suppressing TLR4/NF-κB activation mediated by LPS. These findings suggested that BRLBP may be a useful agent to treat LPS-induced mastitis.