Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is characterized by diffuse inflammation of the lung parenchyma and refractory hypoxemia. Butorphanol is commonly used clinically for perioperative pain relief, but whether butorphanol can regulate LPS-induced alveolar macrophage polarization is unclear. In this study, we observed that butorphanol markedly attenuated sepsis-induced lung tissue injury and mortality in mice. Moreover, butorphanol also decreased the expression of M1 phenotype markers (TNF-α, IL-6, IL-1β and iNOS) and enhanced the expression of M2 marker (CD206) in alveolar macrophages in the bronchoalveolar lavage fluid (BALF) of LPS-stimulated mice. Butorphanol administration reduced LPS-induced numbers of proinflammatory (M1) macrophages and increased numbers of anti-inflammatory (M2) macrophages in the lungs of mice. Furthermore, we found that butorphanol-mediated suppression of the LPS-induced increases in M1 phenotype marker expression (TNF-α, IL-6, IL-1β and iNOS) in bone marrow-derived macrophages (BMDMs), and this effect was reversed by κ-opioid receptor (KOR) antagonists. Moreover, butorphanol inhibited the interaction of TLR4 with MyD88 and further suppressed NF-κB and MAPKs activation. In addition, butorphanol prevented the Toll/IL-1 receptor domain-containing adaptor inducing IFN-β (TRIF)-mediated IFN signaling pathway. These effects were ameliorated by KOR antagonists. Thus, butorphanol may promote macrophage polarization from a proinflammatory to an anti-inflammatory phenotype secondary to the inhibition of NF-κB, MAPKs, and the TRIF-mediated IFN signaling pathway through κ receptors.

The epithelial barrier of the lung is destroyed during acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) due to the apoptosis of alveolar epithelial cells (AECs). Therefore, treatments that block AEC apoptosis might be a therapeutic strategy to ameliorate ALI. Based on recent evidence, A2B adenosine receptor (A2BAR) plays an important role in ALI in several different animal models, but its exact function in AECs has not been clarified. We investigated the role of A2BAR in AEC apoptosis in a mouse model of oleic acid (OA)-induced ALI and in hydrogen peroxide (H₂O₂)-induced AEC (A549 cells and MLE-12 cells) injury. Mice treated with BAY60-6583, a selective A2BAR agonist, showed lower AEC apoptosis rates than mice treated with OA. However, the role of BAY60-6583 in OA-induced ALI was attenuated by a specific blocker of A2BAR, PSB1115. A2BAR activation decreased H₂O₂-induced cell apoptosis in vitro, as characterized by the translocation of apoptotic proteins, the release of cytochrome c, and the activation of caspase-3 and poly (ADP ribose) polymerase 1 (PARP-1). In addition, apoptosis was required for the phosphorylation of ERK1/2, p38, and JNK. Importantly, compared with cells transfected with the A2BAR-siRNA, an ERK inhibitor or p38 inhibitor exhibited decreased apoptotic ratios and cleaved caspase-9 and cleaved PARP-1 levels, whereas the JNK inhibitor displayed increases in these parameters. In conclusion, A2BAR activation effectively attenuated OA-induced ALI by inhibiting AEC apoptosis and mitigated H₂O₂-induced AEC injury by suppressing the p38 and ERK1/2-mediated mitochondrial apoptosis pathway.