Objective  To investigate the effects and underlying mechanisms of dexmedetomidine (DEX) in ameliorating sepsis-induced acute lung injury (ALI) by regulating M1/M2 macrophage polarization through the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway and suppressing oxidative stress.

Methods  Forty male C57BL/6 mice were randomly divided into four groups: the control group (CON group), model group (ALI group), DEX group, and DEX + IPI-549 group (IPI-549 group), with 10 mice in each group. Mice in the CON group underwent laparotomy followed by immediate abdominal closure without cecal ligation and puncture, whereas ALI was induced in the other groups by cecal ligation and puncture. After model establishment, mice in the DEX group received an intraperitoneal injection of DEX (25 μg/kg), and those in the IPI-549 group received intraperitoneal injections of DEX (25 μg/kg) and the PI3K inhibitor IPI-549 (20 mg/kg). Mice in the CON and ALI groups received an equal volume of normal saline intraperitoneally. The extent of lung injury was assessed by hematoxylin-eosin (HE) staining, the lung wet-to-dry weight ratio, and immunohistochemistry. Levels of inflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6 and oxidative stress-related indicators superoxide dismutase (SOD) and malondialdehyde (MDA) were measured. Key signaling pathways were screened by transcriptomic analysis, and M1/M2 macrophage polarization in lung tissues was evaluated by PCR, Western blotting, immunofluorescence staining, and flow cytometry.

Results  Lung architecture was normal in the CON group. Compared with the CON group, the ALI group showed aggravated lung tissue injury and inflammatory infiltration, with higher lung injury scores, numbers of F4/80⁺ macrophages, and lung wet-to-dry weight ratios (all P ＜ 0.05). Lung architecture was improved in the DEX group, and all of these indices were lower than those in the ALI group (all P ＜ 0.05). Regarding inflammation and oxidative stress, SOD activity was lower, whereas MDA and inflammatory cytokine levels (IL-1β, TNF-α, and IL-6) were higher in the ALI group than in the CON group. DEX treatment increased SOD activity and decreased MDA and inflammatory cytokine levels (all P ＜ 0.05). Transcriptomic analysis showed that differentially expressed genes between the ALI and DEX groups were enriched in macrophage differentiation and inflammatory signaling pathways, including the PI3K/Akt pathway. At the molecular level, the expression levels of p-PI3K, p-Akt, and the M2 macrophage markers Mrc1 and Arg1 were lower in the ALI group than in the CON group, whereas the expression levels of the M1 macrophage markers CD86 and Nos2 were higher (all P ＜ 0.05). DEX reversed these changes, whereas the levels in the IPI-549 group shifted toward those observed in the ALI group (all P ＜ 0.05 vs. the DEX group). Analysis of macrophage polarization showed an increased proportion of M1 macrophages and a decreased proportion of M2 macrophages in the ALI group. DEX promoted M2 polarization, whereas IPI-549 partially reversed the effects of DEX. The immunofluorescence findings were consistent with the flow cytometry results.

Conclusion  DEX regulates the balance of M1/M2 macrophage polarization through the PI3K/Akt signaling pathway, suppresses oxidative stress, and attenuates the inflammatory response, thereby ameliorating sepsis-induced acute lung injury.