Breviscapine Attenuates Lipopolysaccharide-Induced Airway Dysfunction in Normal Human Bronchial Epithelial Cells by Suppressing the TLR4/MyD88 Signaling Pathway

Abstract

Pediatric asthma is a common chronic respiratory disorder characterized by airway inflammation and hyperresponsiveness. Breviscapine (Bre) is a natural flavonoid with a broad spectrum of pharmacological activities. Previous studies have found that Bre exerts a protective effect on inflammation in airway and lung tissues. However, the effect of Bre on asthma has not yet been reported. The effects of Bre on asthmatic airway dysfunction were investigated in lipopolysaccharide (LPS)-induced normal human bronchial epithelial cells (NHBEs). Cell viability was determined by CCK-8 assay. Secretion levels of cytokines (IL-1β and IL-6) and chemokine (MCP-1) in the supernatant of NHBEs were measured by using ELISA. Whether Bre could influence LPS-caused oxidative stress in NHBEs was evaluated by detecting malondialdehyde (MDA) production and activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). RT-PCR was applied to determine the mRNA levels of mucin 5 AC (MUC5AC), collagen I (Col-I), and fibronectin (FN). Western blotting was performed to assess the expression levels of toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88), and TNF receptor associated factor 6 (TRAF6). To further confirm the role of TLR4/MyD88 signaling pathway, TLR4-overexpressing cells were constructed. Results showed that Bre attenuated LPS-induced inflammatory responses with decreased release of IL-1β, IL-6, and MCP-1 in NHBEs. The oxidative status in LPS-stimulated NHBEs was suppressed by Bre treatment, as shown by reduced MDA production and increased activities of SOD and GSH-Px. Bre also attenuated LPS-induced expression of MUC5AC, Col-I, and FN. LPS induced the activation of the TLR4/MyD88 signaling pathway in NHBEs, which could be reversed by Bre treatment. Additionally, overexpression of TLR4 lessened the protective effects of Bre on LPS-stimulated NHBEs. Overall, the foregoing results suggested that the TLR4/MyD88 signaling pathway mediated a critical protective effect of Bre on LPS-induced asthmatic airway dysfunction, which provided evidence for the potential usage of Bre for the treatment of asthma.