Protective effect of oleanolic acid on liver injury induced by acute exposure to mercury chloride and its possible mechanism

Background Acute exposure to mercury chloride (HgCl₂) can cause liver damage. Whether oleanolic acid (OA) as a hepatoprotective drug can protect against liver injury induced by acute exposure to HgCl₂ and related mechanism of action remain unclear.

Objective To investigate the protective effect and possible mechanism of OA on liver injury in mice caused by acute exposure to HgCl₂.

Methods Forty SPF C57BL/6 male mice were randomly divided into four groups with 10 mice in each group according to body weight. The four groups were named control group, OA group (300 mg·kg⁻¹), HgCl₂ group (5 mg·kg⁻¹), and OA + HgCl₂ group (300 mg·kg⁻¹ OA + 5mg·kg⁻¹ Hgcl₂). Soybean oil and OA solution were administered intragastric once a day for two consecutive days. HgCl₂ solution was injected intraperitoneally 2 h after the second intragastric administration. Mice were sacrificed after 48 h, and their serum and liver were collected. Liver coefficient was calculated. The changes of liver structure and iron deposition were observed by hematoxylin-eosin (HE) staining and Prussian blue staining. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), total superoxide dismutase (T-SOD), reduced glutathione (GSH), malondialdehyde (MDA), and tissue iron content were measured with commercial kits. Western blotting was used to detect nuclear factor erythroid-2 related factor 2 (Nrf2), heme oxygenase 1 (HO-1), glutathione peroxidase 4 (Gpx4), transferrin receptor 1 (TFR1,) and solute carrier family 7 member 11 (SLC7A11).

Results The AST and ALT levels of the HgCl₂ group were (76.447±9.695) U·g⁻¹ and (98.563±24.673)U·g⁻¹, respectively, which were higher than those of the control group (P<0.05). After the OA pretreatment, the liver coefficient and the above indexes were decreased to (4.769±0.237)%, (57.086±10.087) U·g⁻¹, and (87.294±27.181)U·g⁻¹, respectively. The liver coefficient and AST level of the OA + HgCl₂ group were significantly different from those of the HgCl₂ group (P<0.05). After acute exposure to HgCl₂, the hepatocytes of mice were disordered, accompanied by inflammatory infiltration, positive blue particles appeared in Prussian blue staining of liver tissue, and the above changes in liver tissue were alleviated after the OA pretreatment. The iron content in the HgCl₂ group was (3.646±0.238) μmol·g⁻¹, which was higher than that in the control group, (2.948±0.308) μmol·g⁻¹. After the OA pretreatment, the iron content decreased to (3.429±0.415) μmol·g⁻¹. Compared with the control group, acute exposure to HgCl₂ resulted in decreased levels of GSH and T-SOD, decreased protein expression levels of Nrf2, HO-1, SLC7A11, and Gpx4, increased level of MDA, and increased protein expression level of TFR1 (P<0.05). After the OA pretreatment, all indicators were improved including increased GSH level, decreased MDA level, increased Nrf2, HO-1, and SLC7A11 protein expression levels, and decreased TFR1 protein expression level; compared with the HgCl₂ group, the differences were statistically significant (P<0.05).

Conclusion Acute HgCl₂ exposure could induce liver injury in mice, and its mechanism may involve iron overload and ferroptosis. OA may alleviate the liver injury caused by acute HgCl₂ exposure by affecting iron overload and the ferroptosis-related protein expression.