Ischämische Präkonditionierung: Eine neue Strategie zur Verhinderung von Reperfusionsschäden in der Fettleber

Abstract

Hepatic steatosis is associated with a reduced tolerance against ischemia/reperfusion injury resulting in an increased mortality after liver resection, shock, and trauma. Ischemic preconditioning (a short time of ischemia prior to a sustained ischemic insult) has recently been described as a protective strategy against reperfusion injury in normal livers. We hypothesized that ischemic injury can be prevented by ischemic preconditioning in steatotic livers. Methods: Steatosis was induced by a choline deficient diet in mice. 75 min ischemia of the median and left liver lobes (70%) was performed in fatty and lean mice. In addition, another group of fatty mice was treated with 10 min ischemia and 15 min reperfusion (ischemic preconditioning) prior to 75 min ischemia. Liver injury was determined by AST release. Hepatocyte apoptosis was evaluated by the TUNEL test and caspase 3 activity. Necrosis was quantified by H&E staining. In addition, ATP levels of liver tissue were determined by a bioluminescence assay prior and after ischemia and reperfusion. Results: After 4 h of reperfusion steatotic mice had increased AST levels when compared with non-steatotic littermates (15816 vs. 10460 U/L; p < 0.001). Ischemic preconditioning reduced the AST values of the fatty mice to levels even lower than in lean animals (8300 U/L). After 24 h reperfusion lean animals (5360 U/L) and fatty animals with preconditioning (3417 U/L) had drastic reduced AST levels, while the AST levels remained high in fatty animals without preconditioning (13466 U/L). Apoptosis was the predominant form of cell death in the lean liver with 77% Tunel pos. hepatocytes at 4 h reperfusion compared with only 17% in fatty livers and 5% in fatty livers with ischemic preconditioning (p < 0.001 each). Caspase 3 activity, as a key mediator of apoptosis, was 3-fold higher in lean animals at 4 h reperfusion when compared to the fatty group without ischemic preconditioning (p < 0.01 each). 24 h after reperfusion 85% of the liver tissue was necrotic in fatty animals, compared with 18% necrosis in the lean control (p< 0.01). Ischemic preconditioning of fatty mice reduced the amount of necrosis to 30% (p < 0.01). Hepatic steatosis was associated with a significant decrease of tissue ATP levels after 4 h and 24 h reperfusion when compared with the lean group (1.29 vs. 0.76 & 1.06 vs. 0.39 μmol/pg; p = 0.04 & p = 0.007). Ischemic preconditioning of fatty livers increased the tissue ATP levels significantly at both time points (1.06 & 0.83 μmol/pg;p < 0.05 each). Conclusion: Ischemic preconditioning effectively protects the steatotic liver by reducing apoptotic and necrotic liver injury. Ischemic reperfusion in steatotic livers is associated with low ATP levels, which can be improved by ischemic preconditioning.