Protective effects of ischemic preconditioning and application of lipoic acid prior to 90 min of hepatic ischemia in a rat model

AIM: To compare different preconditioning strategies to protect the liver from ischemia/reperfusion injury focusing on the expression of pro- and anti-apoptotic proteins. Interventions comprised different modes of ischemic preconditioning (IP) as well as pharmacologic pretreatment by α-lipoic acid (LA).

METHODS: Several groups of rats were compared: sham operated animals, non-pretreated animals (nt), animals receiving IP (10 min of ischemia by clamping of the portal triad and 10 min of reperfusion) prior to sustained ischemia, animals receiving selective ischemic preconditioning (IPsel, 10 min of ischemia by selective clamping of the ischemic lobe and 10 min of reperfusion) prior to sustained ichemia, and animals receiving 500 μmol α-LA injected i.v. 15 min prior to the induction of 90 min of selective ischemia.

RESULTS: Cellular damage was decreased only in the LA group. TUNEL-positive hepatocytes as well as necrotic hepatocyte injury were also decreased only by LA (19 ± 2 vs 10 ± 1, P < 0.05 and 29 ± 5 vs 12 ± 1, P < 0.05). Whereas caspase 3- activities in liver tissue were unchanged, caspase 9- activity in liver tissue was decreased only by LA pretreatment (3.1 ± 0.3 vs 1.8 ± 0.2, P < 0.05). Survival rate as the endpoint of liver function was increased after IP and LA pretreatment but not after IPsel. Levels of lipid peroxidation (LPO) in liver tissue were decreased in the IP as well as in the LA group compared to the nt group. Determination of pro- and anti-apoptotic proteins showed a shift towards anti-apoptotic proteins by LA. In contrast, both our IP strategies failed to influence apototic cell death.

CONCLUSION: IP, consisting of 10 min of ischemia and 10 min of reperfusion, protects only partly against ischemia/reperfusion injury of the liver prior to 90 min of selective ischemia. IPsel did not influence ischemic tolerance of the liver. LA improved tolerance to ischemia, possibly by downregulation of pro-apoptotic Bax.

Hepatocellular Injury of Nonischemic Liver Tissue after Selective Clamping in Rats – Protective Action by Pharmacological Pretreatment with Lipoic Acid

BACKGROUND/AIM

The aim of the study was to characterize the hepatic injury (HI) of the nonischemic liver lobe after selective portal triad clamping and investigate the influence of pharmacological pretreatment with alpha-lipoic acid (LA).

METHODS

Brown-Norway rats received 500 micromol LA injected via the inferior vena cava 15 min prior to the induction of 90 min of selective ischemia. Another group of rats received vehicle prior to ischemia. Both groups were compared with sham-operated animals.

RESULTS

Lipid peroxidation (LPO) was increased in the ischemic as well as in the nonischemic liver tissue (NIL) in the untreated group. Levels of adenosine triphosphate and reduced glutathione content of the nonischemic liver lobe were decreased in the untreated group 1 h after reperfusion. Activity of caspases 3 and 8 was not detectable, whereas expression of the Bax protein was demonstrated in the NIL. We observed areas of necrotic hepatocytes and large gaps of sinusoids in the NIL of the untreated rats. LA attenuated LPO as well as Bax expression in the NIL. Moreover adenosine triphosphate and glutathione content of the NIL was increased 1 h after reperfusion by LA. LA pretreatment reduced release of alpha-glutathione-s-transferase in plasma. Histology of the nonischemic liver lobe did not markedly differ from sham-operated animals after LA pretreatment.

CONCLUSION

HI of the NIL seems to be mediated by LPO and proapoptotic proteins such as Bax. Besides its described potential to reduce ischemia/reperfusion injury of the ischemic lobe, LA attenuates HI of the nonischemic tissue after selective portal triad clamping.