Role of oxidative stress-induced AMPK/ULK1 pathway activation and lysosomal dysfunction in arsenic-induced liver injury in rats

Background  A prominent feature of endemic arsenic poisoning is severe liver damage. Studies have found that liver injury is closely related to oxidative stress, lysosomes, and autophagy.

Objective  Through establishing a liver injury model of rats by sodium arsenite (NaAsO₂)administration in drinking water, this experiment is designed to explore the roles of oxidative stress, lysosomes, and AMP activated protein kinase (AMPK)/Unc-51 like kinase 1 (ULK1) pathway in this model.

Methods  Twenty-four Wistar rats were randomly divided into four groups with six rats in each group (half male and half female), including control group and 25, 50, 100 mg·L⁻¹ NaAsO₂ groups. A rat liver injury model was established by drinking water containing NaAsO₂ freely for 24 weeks. Then liver of rats was dissected after sacrificed, and the levels of alanine aminotransferase (ALT), alkaline phosphatase (ALP), and total bile acid (TBA), catalase (CAT), lipid peroxidation (LPO), and total antioxidant capacity (T-AOC) in liver tissues were detected by assay kits. The levels of lysosomal-associated membrane protein 2 (LAMP2), cathepsin B (CTSB), and acid phosphatase (ACP2) were determined by enzyme linked immunosorbent assay. The mRNA transcriptional expressions of AMPK, ULK1, microtubule-associated protein light chain 3 (LC3), and sequestosome 1 (p62) were detected by real-time fluorescence quantitative PCR (RT-qPCR). The protein expressions of p-AMPK, p-ULK1, LC3, and p62 were detected by immunohistochemistry.

Results  Following the NaAsO₂ administration, significant differences were found in the levels of ALT, ALP, and TBA among the designed groups (F=12.09, 72.11, and 23.58, P<0.05). Compared with the control group, the levels of ALT in the 50mg·L⁻¹ and 100 mg·L⁻¹ NaAsO₂ groups were increased (P<0.05); the levels of ALP and TBA in the 25, 50, and 100 mg·L⁻¹ NaAsO₂ groups were increased (P<0.05); the level of LPO in the 100 mg·L⁻¹ group was increased (P<0.05); the levels of CAT and T-AOC in the 25, 50, and 100 mg·L⁻¹ NaAsO₂ groups were decreased (P<0.05). According to the results of enzyme linked immunosorbent assay, the levels of ACP2 in the 25, 50, and 100 mg·L⁻¹ NaAsO₂ groups, the level of CTSB in the 100 mg·L⁻¹ NaAsO₂ group, and the levels of LAMP2 in the 50 and 100 mg·L⁻¹ NaAsO₂ groups were decreased compared with the control group (P<0.05). Based on the results of RT-qPCR and immunohistochemistry, the mRNA transcriptional and protein expressions ofAMPK,ULK1, and LC3 in some arsenic groups were elevated to varying degrees compared with the control group, and the increment in the 100 mg·L⁻¹ NaAsO₂ group was significant for all the indicators (P<0.05); the mRNA transcriptional expressions ofp62 in the three arsenic groups and the protein expressions of p62 in the 50 and 100mg·L⁻¹ NaAsO₂ groups also increased compared with the control group (P<0.05). Besides, the results of Pearson correlation analysis showed that there was a positive correlation of T-AOC with LAMP2, CTSB, and ACP2 (r=0.651, 0.673, 0.626; P<0.05), a negative correlation of LPO with CTSB and ACP2 (r=−0468, −0.482; P<0.05), a negative correlation of p62 with LAMP2, CTSB, and ACP2 (r=−0.57, −0.626, −0.591; P<0.05), and a positive correlation of p62 with ALT, ALP, and TBA (r=0.709, 0.897, and 0.857, P<0.05).

Conclusion  Long-term arsenic exposure may induce oxidative stress, damage lysosomes, and activate the AMPK/ULK1 pathway, which can lead to the blockage of autophagy process, and eventually result in liver damage.