Mechanisms of hypothermic protection against ischemic liver injury in mice.

Hepatic hypothermia can safely prolong the duration of hepatic inflow occlusion during complex liver resectional surgeries. The mechanism(s) by which hypothermia protects against this form of liver ischemia-reperfusion injury are not completely understood. In this study, we sought to determine whether hypothermia protects against ischemia-reperfusion injury by altering the hepatic inflammatory response. Mice undergoing 90 min of partial hepatic ischemia followed by up to 8 h of reperfusion had their body temperatures regulated at 35-37 degrees C (normothermic) or unregulated, in which rectal temperature dropped as low as 25 degrees C by the end of ischemia (hypothermic). Hypothermic mice had less liver injury vs. normothermic mice, as assessed histologically, by serum transaminase levels (89% decrease), and by liver wet-to-dry weight ratios (91% decrease). Neutrophil accumulation was absent in hypothermic mice (99% reduction vs. normothermic mice). Production of the proinflammatory cytokines tumor necrosis factor-alpha, interleukin-1 beta, and macrophage inflammatory protein-2 were reduced by up to 92%. Activation of the transcription factor nuclear factor-kappa B was not reduced in hypothermic mice, but activation of c-Jun NH(2)-terminal kinase (JNK) and the transcription factor activator protein (AP)-1 were greatly diminished. These data suggest that hypothermia suppresses the hepatic inflammatory response through selective inhibition of JNK and AP-1.