Dexmedetomidine attenuates subarachnoid hemorrhage-induced acute lung injury through regulating autophagy and TLR/NF Kappa B signaling pathway

Background: Acute lung injury (ALI) is the most serious complication of subarachnoid hemorrhage (SAH). We investigated role of autophagy and inflammatory signaling pathways in lung damage and therapeutic effects of dexmedetomidine (DEX). Methods: Fifty male Wistar rats were randomly divided into five groups: sham, SAH, SAH+ DEX5, SAH+DEX25, and SAH+DEX50. SAH was induced using endovascular perforation technique. All rats received mechanical ventilation for 60 min. At 2 and 24 h of SAH induction, SAH+DEX groups were treated with 5, 25, and 50 mu g/kg of DEX, respectively. Histological ALI score and pulmonary edema were assessed after 48 h. Lung expression of LC3B, ATG3, p62, TLR4, TLR9, and NF kappa B was assessed using western blotting and quantitative PCR. Blood levels of IL-6, IL-1 beta, IFN-gamma, and TNF alpha were also assessed. Results: SAH induced ALI and pulmonary edema, which were attenuated in SAH+DEX5 (P < 0.001 for both) and SAH+DEX25 groups (P = 0.001 and P < 0.001 for ALI and edema, respectively). Lung expressions of LC3B and ATG3 were upregulated in SAH group, which was attenuated in SAH+DEX5 and SAH+DEX25 groups. Lung expressions of TLR4, TLR9, and NF kappa B were increased in SAH group, which was attenuated in SAH+DEX5 group. Blood IL-6 level was increased in SAH group and attenuated in SAH+DEX5 and SAH+DEX25 groups. Blood IFN-gamma level was lower in SAH group than in sham group, and it was increased in SAH+DEX25 group. Conclusions: Low-dose DEX treatment after SAH may protect against ALI by disrupting pathological brain-lung crosstalk and alleviating autophagy flux and TLR-dependent inflammatory pathways.