Objective  To evaluate the protective effect and the underlying mechanism of mesenchymal stem cell-derived extracellular vesicle (MSC-EV) on radiation-induced liver injury and liver cell line injury in mouse models.

  Methods  C57BL/6 mice were randomly divided into the blank group, model group and MSC-EV treatment group (treatment group), with 9 mice in each group. AML12 cells were randomly divided into the control group, irradiation group and MSC-EV intervention group (intervention group). Animal and cell models with radiation-induced injury were established by one-time 15 Gy and 6 Gy X-ray irradiation, respectively. At 48 h after irradiation, liver tissues and serum samples of mice were collected and prepared for subsequent experiments. At 15 h post-irradiation, cell experiment was carried out. Serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and content of malondialdehyde (MDA) in liver tissues and cells were measured. The relative expression levels of interleukin (IL)-1β, IL-6, transforming growth factor (TGF)-β and CXC chemokine ligand (CXCL)10 messenger RNA (mRNA) were detected by real-time fluorescent quantitative polymerase chain reaction (RT-qPCR). Liver tissues were prepared for hematoxylin-eosin (HE) staining to calculate liver pathological injury score. The apoptosis of liver tissues and cells was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and propidiumiodide (PI) staining, respectively. The expression levels of glutathione peroxidase 4 (GPX4) and ferroptosis suppressor protein 1 (FSP1) proteins were detected by Western blot. The production level of reactive oxygen species (ROS) was detected by dihydroethidine (DHE) staining. The fluorescence intensity of mitochondrial permeability transition pore (mPTP) was determined.

  Results  Compared with the blank group, serum levels of AST and ALT were up-regulated, and the relative expression levels of IL-1β, TGF-β and CXCL10 mRNA in the mouse liver tissues were up-regulated, and MDA content was increased, liver injury score was elevated, cell apoptosis rate was increased, intracellular ROS level was elevated, and the relative expression levels of GPX4 and FSP1 proteins in the mouse liver tissues were down-regulated in the model group, and the differences were statistically significant (all P<0.05). Compared with the model group, serum levels of AST and ALT were decreased, and the relative expression levels of IL-1β, TGF-β and CXCL10 mRNA in the liver tissues of mice were down-regulated, MDA content was declined, liver injury score was declined, cell apoptosis rate was decreased, intracellular ROS level was decreased, and the relative expression levels of GPX4 and FSP1 proteins in the liver tissues of mice were up-regulated in the treatment group, and the differences were statistically significant (all P<0.05). Compared with the control group, cell apoptosis rate was increased, intracellular ROS level was elevated, the fluorescence intensity of mPTP was weakened, the relative expression levels of IL-1β, TGF-β and IL-6 mRNA were up-regulated, MDA content was increased, and the relative expression levels of GPX4 and FSP1 proteins were down-regulated in the irradiation group, and the differences were statistically significant (all P<0.05). Compared with the irradiation group, cell apoptosis rate was declined, intracellular ROS level was decreased, the fluorescence intensity of mPTP was strengthened, the relative expression levels of IL-1β, TGF-β and IL-6 mRNA were down-regulated, MDA content was decreased and the relative expression levels of GPX4 and FSP1 proteins were up-regulated in the intervention group, and the differences were statistically significant (all P<0.05).

  Conclusions  MSC-EV may effectively alleviate radiation-induced liver injury by reducing ferroptosis of liver cells, enhancing antioxidant level and decreasing the production of lipid peroxide, thereby effectively alleviating radiation-induced liver injury.