Effect of HSP70 induced by warm ischemia to the liver on liver function after partial hepatectomy

The purpose of this study was to determine if induction of HSP70 (heat shock protein 70), a stress protein which plays a cytoprotective role in response to various stimuli, protects hepatocytes from damage caused by partial hepatectomy and, if so, to elucidate the mechanism of such protection.

One hundred and eight male F344 rats weighing 190-220 g were randomly assigned to two groups with or without the presence of preconditioning. Fifteen-minute warm ischemia was applied to the liver of rats to induce HSP70, and 70% hepatectomy was performed 48 hours after the induction of HSP70 (ischemia group; n = 72). The rats in the nonischemia group did not undergo 15-min warm ischemia prior to 70% hepatectomy (nonischemia group; n = 36). Six rats, selected randomly from each group, were sacrificed at each measurement point to obtain blood and liver tissue samples. The levels of HSP70 in the liver, serum nitric oxide, levels of catalase and superoxide dismutase activity in the liver as antioxidative enzymes, and levels of Bcl-xL and Bax proteins and caspase-3-like activity in the liver as indices of apoptosis, were measured.

The mean +/- SD level of HSP70 in the ischemia group (100 +/- 42 arbitrary unit (au)) was significantly higher than that of the nonischemia group (2 +/- 0.7 au) immediately before hepatectomy (P < 0.05). The ischemic preconditioning attenuated the liver damage caused by the subsequent partial hepatectomy. The levels of superoxide dismutase and catalase activity, serum nitric oxide level, and Bax protein level of the ischemia and nonischemia groups showed no significant differences after the partial hepatectomy. In contrast, the mean +/- SD level of Bcl-xL in the liver of the ischemia group (261 +/- 52 au) was significantly higher than that in the nonischemia group (114 +/- 33 au) 12 hours after the hepatectomy (P < 0.01). Furthermore, the mean +/- SD level of caspase-3-like activity in the liver of the ischemia group (18.1 +/- 4.6 au) was significantly lower than that of the nonischemia group (26.0 +/- 4.8 au) at 12 hours after the hepatectomy (P < 0.05).

HSP70 induced by ischemic preconditioning prior to the partial hepatectomy was considered to protect the liver itself. In addition, the induced HSP70 may affect the Bcl-xL level after partial hepatectomy. Therefore, Bcl-xL seems to be involved in the reduction of liver damage after partial hepatectomy along with HSP.