Effect of subchronic arsenic exposure on hepatic autophagy in rats

  Objective  To investigate the effect of subchronic arsenic exposure on hepatic autophagy and its molecular mechanism in rats.

  Methods   Forty Sprague-Dawley (SD) rats weighted 150 – 180 g were randomly assigned into a blank control group with normal saline and three arsenic exposure groups with sodium arsenite (NaAsO₂) solution at dosages of 2, 4, 8 mg/kg. The treatments were administered via gavage once a day and 6 days a week consecutively for 12 weeks. At the end of the treatments, all rats were sacrificed and their liver tissue, whole blood and hair were sampled. Hematoxylin-eosin (HE) staining was used to observe the pathological changes in liver tissues. Hepatic ultrastructure was examined with transmission electron microscope. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were detected with biochemical detector. Western blot was adopted to detect autophagy-related proteins including microtubule light chain protein-3 (LC3), P62/sequestosome-1 (SQSTM1), mammalian target of rapamycin (mTOR), phosphatidylinositol 3-kinase (PI3K), and beclin 1 (BECN 1).

  Results   HE staining observation revealed dose-dependent pathological changes in liver tissues of rats treated with NaAsO₂. Significantly increased double-layer membrane autophagosomes and autophagy vacuoles were observed in hepatocytes of the rats with NaAsO₂ exposure in ultrastructure examination. Compared to the blank control rats, the rats with high dose NaAsO₂ had significantly increased ALT (98.68 ± 22.46 vs. 38.06 ± 4.14 U/L) and AST (125.00 ± 13.34 vs. 71.51 ± 7.72 U/L) (both P < 0.05). In comparison with those in the blank control rats, significantly increased LC3-II / LC3-I ratio (1.63 ± 0.11 or 2.91 ± 0.05 vs. 1.03 ± 0.02) but decreased BECN1 (0.84 ± 0.27 or 0.98 ± 0.10 vs. 1.27 ± 0.13) and mTOR (0.49 ± 0.02 or 0.56 ± 0.11 vs. 0.97 ± 0.05) were detected in the rats with high or moderate NaAsO₂ treatment (P < 0.05 for all). The expression of P62 protein in the rats with high, moderate, and low dose NaAsO₂ treatment (0.32 ± 0.05, 0.13 ± 0.01, and 0.34 ± 0.05) were all lower than that (1.77 ± 0.22) in the rats of blank control (all P < 0.05).

  Conclusion   Sodium arsenite treatment can induce autophagy in rat liver cells and the mechanism of the effect may be related to the regulation of the PI3K / mTOR signaling pathway.