Protective mechanism of rapamycin on D-amino galactoose/lipopolysaccharide-induced acute liver injury in mice

Objective To investigate the protective mechanism of rapamycin (Rapa) on D-amino galactoose (Gal-N)/lipopolysaccharide (LPS)-induced acute liver injury in mice. Methods The acute liver injury model was established by intraperitoneal injection of Gal-N (700 mg/kg) and LPS (10 g/kg) in 45 C57/B6 mice and the animals were randomly divided into model group, low dose Rapa group, middle dose Rapa group and high dose Rapa group. At the same time, 15 mice were selected as control group. The mice in low dose Rapa group, medium dose Rapa group and high dose Rapa group were injected with 5, 10 and 20 mg/kg Rapa at 20 min after modeling respectively. The mice in control group and model group were intraperitoneally injected with equal volume of phosphate buffer (PBS). Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels of serum were determined. The tumor necrosis factor-α (TNF-α) levels were analyzed by enzyme linked immunosorbent assay (ELISA) Kit. The pathological changes in liver tissues of mice were observed by hematoxylin and eosin (HE) staining. Autophagy substrates microtubule-associated protein 1 light chain 3 (LC3) and p62 were analyzed by Western blotting. Results Compared with AST and ALT of control group [(30.41±5.23) U/L and (110.23±12.02)], serum AST and ALT levels in model group, low, middle and high dose group [((489.39±35.65) U/L and (310.24±41.25) U/L); (385.21±30.59) U/L and (278.96±35.68) U/L; (279.94±35.14) U/L and (214.37±34.12); (159.24±30.12) U/L and (168.63±28.32) U/L]significantly increased [ (t=8.120, t=6.384); (t=7.013, t=5.132); (t=5.198, t=4.318); (t=3.957, t=3.048); P=0.000]. Compared with the model group, the serum AST and ALT levels in the low, middle and high dose groups significantly reduced [ (t=3.012, t=3.419); (t=3.901, t=4.012); (t=4.820, t=5.018), P=0.000]. Compared with TNF-alpha in the control group [(150.44±23.19) ng/L], the level of TNF- α in the model group, low, middle and high dose group [(509.44±49.32), (401.43±38.09), (298.44±29.41), (218.29±24.21) ng/L] significantly increased (t=6.109, t=5.184, t=4.109, t=3.921, P=0.000). Compared with the model group, the TNF-α levels in the low, middle and high dose groups significantly reduced (t=2.194, t=3.331, t=5.016, P=0.000). HE staining showed that the liver of model group mice was seriously damaged, the liver red blood cells diffused, the intercellular space of liver cells increased, the vacuoles deformed and the hepatic cords arranged irregularly. With the increase of rapamycin dose, the pathological damage degree of liver in mice was dose-dependent. Compared with the control group, autophagy in the model group was inhibited, and the autophagy level obviously enhanced after rapamycin treatment. Conclusion Rapa can induce autophagy and decrease TNF-α by inhibiting the activity of mammalian target of Rapa kinase, thus protecting the liver. Key words: Rapamycin; Acute liver injury; Mammalian target of rapamycin; Autophagy; Inflammatory factors