Bakuchiol regulates TLR4/MyD88/NF-κB and Keap1/Nrf2/HO-1 pathways to protect against LPS-induced acute lung injury in vitro and in vivo.

Bakuchiol (Bak) possesses a protective effect in acute lung injury (ALI). Nonetheless, the molecular processes that regulate the protective activity of Bak in ALI remain elusive. Lipopolysaccharide (LPS)-treated rats and RLE-6TN cells were used as the ALI models in vivo and in vitro to investigate the function and mechanism of Bak. Rats were divided into four groups: control, LPS, LPS + Bak (30 mg/kg), and LPS + Bak (60 mg/kg). RLE-6TN cells were assigned into four groups: control, LPS, LPS + Bak (10 µM), and LPS + Bak (20 µM). Myeloperoxidase (MPO) and 4-hydroxy-2-nonenal (4-HNE) levels were detected by immunohistochemistry (IHC). The levels of TNF-α, IL-6, and IL-1β were quantified by ELISA. Apoptosis was analyzed by TdT-mediated dUTP nick-end labeling (TUNEL) staining and flow cytometry. Malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and reactive oxygen species (ROS) were assayed to evaluate oxidative stress. In LPS-induced rats, Bak attenuated pathological injury, lung wet/dry weight ratio, MPO expression, and protein concentration and cell number in bronchial alveolar lavage fluid (BALF). Bak decreased the secretion of TNF-α, IL-6, and IL-1β in BALF. Bak reduced MDA content and 4-HNE expression, and increased SOD and GSH-Px activities in lung tissues. Bak also repressed pulmonary apoptosis by decreasing Bax expression and enhancing Bcl-2 expression. In LPS-treated RLE-6TN cells, Bak downregulated the mRNA levels of TNF-α, IL-6, and IL-1β and inhibited the protein expression of iNOS and COX2. Bak decreased MDA level and ROS production and increased SOD and GSH-Px activities. Bak also suppressed cell apoptosis, reduced Bax expression, and increased Bcl-2 expression. Moreover, Bak decreased the expression of TLR4, MyD88, p-IκBα, and p-p65. Additionally, Bak inhibited Keap1 expression and increased Nrf2 and HO-1 levels. Bak protects against LPS-induced inflammation, oxidative stress, and apoptosis in ALI by regulating TLR4/MyD88/NF-κB and Keap1/Nrf2/HO-1 pathways.