Objective  To investigate the effect and mechanism of high-dose sirolimus (rapamycin) upon protecting the hepatic ischemia-reperfusion injury (HIRI) in aged mice.

  Methods  Twenty C57BL/6 aged mice were randomly and evenly divided into the ischemia-reperfusion injury group (IRI group), low-dose rapamycin pretreatment group (rpm group), high-dose rapamycin pretreatment group (RPM group) and control group (Sham group) using the random number table method (5 mice in each group). In the Sham group, abdominal cavity was incised and sutured alone. In the other three groups, aged mouse 70% HIRI models were established. The ischemia time was 60 min. At preoperative 1 h, rapamycin at a dose of 1 mg/kg and 5 mg/kg was administered via intraperitoneal injection in the rpm and RPM groups. At 12 h post-reperfusion, hematoxylin-eosin (HE) staining was performed to observe the histological changes in the mouse liver. Suzuki grading method was adopted to evaluate the pathological score. The serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), tumor necrosis factor (TNF)-α and interleukin (IL)-10 and the LC3B-Ⅱ protein level in the liver tissues were quantitatively measured and statistically compared among different groups.

  Results  HE staining of the liver tissues revealed normal liver tissues in the Sham group, severe liver cellular injury accompanied with a large quantity of inflammatory cellular infiltration in the IRI and rpm groups. Mild sinusoidal congestion and slight inflammatory cellular infiltration were observed in the RPM group. The pathological score was 5 (4-6) in the RPM group, significantly lower than 7 (5-8) and 8 (7-10) in the rpm and IRI groups (Z=-2.554 and -2.731, both P < 0.05). In terms of postoperative liver function parameters, the AST level was (691±207) U/L in the RPM group, significantly lower compared with (2 032±575) U/L and (1 817±777) U/L in the IRI and rpm groups (t=4.90 and 3.13, both P < 0.05). In the RPM group, the ALT level was measured as (996±584) U/L, considerably lower than (2 992±992) U/L and (2 373±687) U/L in the IRI and rpm groups (t=3.86 and 3.41, both P < 0.05). The AST and ALT levels did not significantly differ between the IRI and rpm groups (both P > 0.05). No statistical significance was identified in the TNF-α and IL-10 levels among different groups (all P > 0.05). Western blot analysis revealed that the relative expression level of LC3B-Ⅱ protein in the liver tissue of the RPM group was significantly higher than those in the Sham, IRI and rpm groups (all P < 0.05).

  Conclusions  Administration of high-dose rapamycin exerts a protective effect upon HIRI probably through promoting cellular autophagy in aged mice.