PROTEASOME INHIBITOR LACTACYSTIN ABLATES LIVER INJURY INDUCED BY INTESTINAL ISCHAEMIA–REPERFUSION
Authors: Yao Ji‐Hong , Li Ying‐Hua , Wang Zhen‐Zhen , Zhang Xue‐Song , Wang Yu‐Zhu , Yuan Jin‐Chan , Zhou Qin , Liu Ke‐Xin , Tian Xiao‐Feng 
Published: June 2007

The aim of the present study was to investigate the role of proteasome in the pathogenesis of liver injury induced by intestinal ischaemia–reperfusion (I/R) and the effect of the proteasome inhibitor lactacystin on neutrophil infiltration, intracellular adhesion molecule (ICAM)‐1 and nuclear factor (NF)‐κB expression in the liver tissues of rats.

Thirty‐two Wistar rats were randomly divided into four groups (n = 8 in each group) as follows: (i) a control, sham‐operated group; (ii) an I/R group subjected to 1 h intestinal ischaemia and 4 h reperfusion; (iii) a group pretreated with 0.2 mg/kg lactacystin 1 h before intestinal I/R; and (iv) a group pretreated with 0.6 mg/kg lactacystin 1 h before intestinal I/R. Liver and intestine histology were observed. Serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH), as well as 20S proteasome activity in circulating white blood cells, were measured. Myeloperoxidase (MPO) activity in liver tissues and the immunohistochemical expression of liver NF‐κB and ICAM‐1 were assayed. In addition, a western blot of liver NF‐κB was performed.

Compared with the sham‐operated control group, liver and intestine injury was induced by intestinal I/R, characterized as histological damage including oedema, haemorrhage and infiltration by inflammatory cells, as well as a significant increase in serum AST (365 ± 121vs546 ± 297 IU/L, respectively;P < 0.05), ALT (65 ± 23vs175 ± 54 IU/L, respectively;P < 0.01) and LDH levels (733 ± 383vs1434 ± 890 IU/L, respectively;P < 0.05). Compared with the control group, MPO activity in the liver tissues increased significantly in the I/R group (2.05 ± 0.69vs3.42 ± 1.11 U/g, respectively;P < 0.05). Strong positive expression of liver ICAM‐1 and NF‐κB p65 was observed.

Compared with the intestinal I/R group, administration of 0.6 mg/kg lactacystin markedly reduced 20S proteasome activity in circulating white blood cells (15.47 ± 4.00vs2.07 ± 2.00 pmol 7‐amino‐4‐methylcoumarin (AMC)/s per mg, respectively;P < 0.01) and ameliorated liver injury, which was demonstrated by decreased levels of serum AST (546 ± 297vs367 ± 86 IU/L, respectively;P < 0.05), ALT (175 ± 54vs135 ± 26 IU/L, respectively;P < 0.05) and LDH (1434 ± 890vs742 ± 218 IU/L, respectively;P < 0.05) and a reduced liver pathological score (2.13 ± 0.64vs1.25 ± 0.46, respectively;P < 0.01). Compared with the intestinal I/R group, MPO activity in liver tissues decreased significantly following lactacystin pretreatment (3.42 ± 1.11vs2.58 ± 0.61 U/g, respectively;P < 0.05) and the expression of liver NF‐κB and ICAM‐1 was markedly ameliorated.

The present study reveals that the proteasome inhibitor lactacystin ablates liver injury induced by intestinal I/R. One possible mechanism responsible for this effect is the inhibition of enhanced ICAM‐1 and neutrophil infiltration by inhibition of NF‐κB activity. The results suggest the feasibility of using proteasome inhibitor clinically in the treatment of intestinal I/R.