[6-Formylindolo[3,2-b]carbazole alleviates lipopolysaccharide-induced acute lung injury via suppressing endoplasmic reticulum stress].

OBJECTIVE

To investigate the effect and mechanism of 6-formylindolo[3,2-b]carbazole (FICZ) on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice.

METHODS

Male C57BL/6J mice aged 8-12 weeks were divided into 4 groups with 8 mice in each group, according to the method of simple random sampling. Sepsis-induced ALI mice model was established by intraperitoneal injection of LPS 5 mg/kg (LPS group), and phosphate buffer saline (PBS) control group (PBS group) was injected with equal volume of PBS. The LPS+FICZ group was intervened by intraperitoneal injection of 1 μg FICZ 1 hour after LPS stimuli, while the FICZ control group (FICZ group) was given the same amount of FICZ 1 hour after intraperitoneal injection of PBS. Serum and lung tissue were collected 24 hours after LPS stimuli, and the pathological changes of lung tissue were analyzed by hematoxylin-eosin (HE) staining and wet/dry weight (W/D) ratio of lung tissue. The concentrations of inflammatory factors in serum and lung tissue were detected by enzyme linked immunosorbent assay (ELISA). The expression levels of endoplasmic reticulum stress signaling pathway related molecules were detected by real-time fluorescent quantitative polymerase chain reaction (RT-qPCR) and Western blotting.

RESULTS

Compared with PBS group, inflammatory cell infiltration, alveolar collapse and obvious alveolar exudative lesions had increased, lung tissue W/D ratio was significantly increased, serum interleukin-6 (IL-6) level, lung tissue IL-6 mRNA expression, and the mRNA expressions of glucose-regulated protein 78 (GRP78), protein kinase R-like endoplasmic reticulum kinase (PERK), CCAAT/EBP homologous protein (CHOP), and the protein expressions of GRP78, PERK, activating transcription factor 6 (ATF6), CHOP in lung tissue were significantly increased in LPS group. However, the indexes of FICZ group were not affected. Compared with LPS group, LPS+FICZ group had less inflammatory cell infiltration, relatively intact alveolar structure. Lung W/D weight ratio in LPS+FICZ group was significantly decreased (5.38±0.10 vs. 6.60±0.30, P < 0.01), so as serum IL-6 (ng/L: 15.55±3.77 vs. 32.22±3.84) and lung IL-6 mRNA expression (2: 0.79±0.21 vs. 6.89±0.92, both P < 0.01). The mRNA expressions of GRP78, PERK and CHOP were also significantly decreased [GRP78 mRNA (2): 1.90±0.16 vs. 7.55±1.29, PERK mRNA (2): 1.68±0.20 vs. 4.54±0.89, CHOP mRNA (2): 1.13±0.24 vs. 4.44±1.13, all P < 0.05], and the protein expressions of GRP78, PERK, ATF6 and CHOP were significantly decreased (GRP78/GAPDH: 0.59±0.02 vs. 0.77±0.01, PERK/GAPDH: 0.48±0.03 vs. 1.04±0.05, ATF6/GAPDH: 0.51±0.03 vs. 0.65±0.01, CHOP/GAPDH: 0.91±0.05 vs. 1.11±0.07, all P < 0.05).

CONCLUSIONS

FICZ protects LPS-induced ALI possibly via suppressing endoplasmic reticulum stress and reducing IL-6 expression in blood and lung tissue.