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MECHANISMS OF HEPATOPROTECTION BY MILD HYPOTHERMIA AGAINST ACETAMINOPHEN TOXICITY IN MICE

J Vaquero¹, M Belanger¹, R Herrero¹, P Desjardins¹, AT Blei², RF Butterworth¹
¹Neuroscience Research Unit, Hôpital St-Luc (CHUM), University of Montreal, Montreal, Quebec; ²Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA

We have previously shown that mild hypothermia, a potential therapy for intracranial hypertension in acute liver failure, decreases acetaminophen (APAP)-induced liver injury in mice, but the mechanisms of hepatoprotection and its influence on the mode of cell death were not exhaustively examined. To explore these issues, fasted C57Bl6 mice (8-10 wk/o) were treated with APAP (300 mg/kg i.p.) and maintained normothermic (NT, 35.5-37.5°C) for the first 2 h, when most APAP bioactivation occurs as assessed by APAP-protein adducts and glutathione depletion. Thereafter, one group was maintained NT and another group was allowed to develop mild hypothermia (HT, 32-34.5°C). Control animals received saline instead of APAP. Animals were sacrificed at several time-points to examine: 1) Hepatic glycogen concentration (ethanol-KOH extraction, hexokinase enzymatic assay), 2) Hepatic congestion (liver/body weight ratio and hepatic hemoglobin content), 3) Hepatocellular apoptosis (TUNEL staining and detection of poly(ADP)ribose polymerase (PARP) cleavage by Western blot).
Hepatic glycogen was depleted 2 h after APAP challenge, and its recovery started earlier (~4 h) and was more complete in HT than in NT mice (p<0.001). APAP challenge in NT mice resulted in increased liver/body weight ratio (p<0.05) and hepatic hemoglobin content (p<0.001), and both were significantly attenuated in HT mice. PARP cleavage was detected mainly at 12 h only in APAP-treated mice maintained NT. Accordingly, the number of TUNEL positive hepatocytes at this time point was significantly higher in NT than in HT mice (p<0.05).
In conclusion, (1) Prevention of hepatic congestion and improvement of glycogen recovery are early hepatoprotective mechanisms of mild hypothermia against APAP toxicity, and (2) Body temperature influences hepatocyte cell death by apoptosis in mice with APAP hepatotoxicity. From a human perspective, these results encourage further the evaluation of mild hypothermia for treating intracranial hypertension in acute liver failure.
Funded by CIHR&CASL/Schering

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