3-Methyladenine and dexmedetomidine reverse lipopolysaccharide-induced acute lung injury through the inhibition of inflammation and autophagy

Abstract

The aim of the present study was to investigate the effects of 3-methyladenine (3-MA) and dexmedetomidine (DEX) pretreatment on lipopolysaccharide (LPS)-induced acute lung injury (ALI) and the potential mechanism underlying the effects. LPS was instilled into the trachea of BALB/c mice to induce the ALI model. Solutions of 3-MA or DEX were intravenously injected into the mice 1 h later to establish the 3-MA and DEX groups. On days 1, 3 and 5 after the injections, arterial blood gas analysis was conducted, and the lung wet-dry weight ratio (W/D) was determined. In addition, albumin, cytokine and myeloperoxidase (MPO) contents were evaluated using ELISAs, and hematoxylin and eosin (H&E) staining was conducted. Furthermore, western blot analysis was used to evaluate the protein expression levels of microtubule-associated protein 1A/1B-light chain 3 (LC3)-I, LC3-II, autophagy protein 5 (ATG5), Rab7 and lysosome-associated membrane protein 1 (LAMP1), and reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to detect the mRNA expression levels of nuclear factor-κB (NF-κB) and Toll-like receptor 4 (TLR4). Treatment with 3-MA or DEX increased the blood partial pressure of oxygen level compared with that in the model group, and restored the W/D and blood partial pressure of carbon dioxide to normal levels. The content of tumor necrosis factor-α, interleukin-6 and albumin in bronchoalveolar fluid and MPO in lung tissue was significantly decreased in the 3-MA and DEX groups compared with the model group (P<0.05). H&E staining demonstrated that 3-MA and DEX each reversed the ALI. In addition, 3-MA and DEX reduced the protein expression levels of LC3-I, LC3-II, ATG5, Rab7 and LAMP1. Also, RT-qPCR results revealed that NF-κB and TLR4 mRNA expression levels were clearly decreased in the 3-MA and DEX groups compared with the model group. In conclusion, LPS-induced ALI was effectively reversed by treatment with 3-MA and DEX through the reduction of inflammation and autophagy and inhibition of the TLR4-NF-κB pathway.

Keywords: 3-methyladenine; TLR4-NF-κB pathway; acute lung injury; autophagy; dexmedetomidine; inflammation.

Figure 1.

Pathological changes in mouse lung tissues observed by hematoxylin and eosin staining (magnification, ×400; scale bar, 200 µm). (A) Blank group, (B) model group, (C) 3-methyladenine group and (D) dexmedetomidine group. The green arrow indicates the symptoms of bleeding and inflammatory cell infiltration.

Figure 2.

Autophagy related-protein expression level in each group as determined by western blotting. (A) Representative western blots are shown. Lane 1, blank group; lane 2, model group; lane 3, 3-MA group; lane 4, DEX group. (B) Relative gray values for LC3-II/I, ATG5/GAPDH, Rab7/GAPDH and LAMP1/GAPDH. *P<0.05 vs. the blank group; ^#P<0.05 vs. the model group. LC3, microtubule-associated protein 1A/1B-light chain 3; ATG5, autophagy protein 5; LAMP1, lysosome-associated membrane protein 1; 3-MA, 3-methyladenine; DEX, dexmedetomidine.

Figure 3.

mRNA expression levels of NF-κB and TLR4 in each group. *P<0.05 vs. the blank group, ^#P<0.05 vs. the model group. NF-κB, nuclear factor- κB; TLR4, Toll-like receptor 4; 3-MA, 3-methyladenine; DEX, dexmedetomidine.