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To the Editor:

Preservation of basic animal physiology is important for in vivo models of disease. The mouse with acetaminophen (APAP) intoxication is widely used for studying mechanisms of liver injury, despite its poor reproducibility and high inter-animal variability.1 These mice develop hypothermia, probably as a result of the pharmacological action of APAP2 and the development of liver congestion, hypovolemia and inflammation.3, 4 As shown in Fig. 1, APAP induces hypothermia in a dose-dependent manner in C57BL6 mice. Moreover, body temperature differs by several °C within mice receiving the same dose. Our experience and that of others4 show that these mice may remain hypothermic for prolonged periods. Because mouse strain and nutrition state affect APAP-induced liver damage, they may also influence its effect on body temperature. It is well established that temperature is a major determinant of the rate of all biochemical reactions and, therefore, it could influence processes of liver injury studied in the model.

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Figure 1. Spontaneous evolution of body temperature in mice treated with various doses of acetaminophen (APAP). Male C57BL6 mice (10 weeks old) were administered APAP (150, 300 and 600 mg/kg ip, n = 3/group) after an overnight fast, and placed in individual cages at room temperature (≈24°C). No external heating was provided. Body temperature was periodically measured using a rectal probe connected to a monitoring thermometer.

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To assess whether body temperature has been routinely measured in studies of mice with APAP intoxication, we reviewed the full-text manuscripts published from 1994 that were retrieved in a PubMed search using the key words “acetaminophen AND mice”. Of the 481 resulting hits, 251 were original articles written in English on APAP hepatotoxicity in mice. In 52% of these studies, mice were fasted prior to APAP administration, which was usually given intraperitoneally (189 of 251). Measurement of body temperature was only performed in 2 of the 251 articles (0.8%)4, 5; no method or data regarding the measurement of body temperature were mentioned in the remaining 249 articles. Importantly, APAP doses higher than 300 mg/kg, which frequently cause severe hypothermia, were used in 76% of the studies.

Lessons from experimental studies of the cerebral complications of liver failure6, 7 suggest that body temperature is a physiological variable that should be assessed in all animal models of liver disease. Hypothermia protects from ischemic liver injury,8 and preliminary experience suggests that it also influences survival and the degree of liver injury in mice with APAP intoxication.9 Conversely, the degree of hypothermia is influenced by the severity of the damage. Variability on the degree of hypothermia could explain the low reproducibility and discordant results reported using this model. Given the multitude of temperature-sensitive hepatic and cerebral processes, studies using mice with APAP intoxication in which body temperature was not rigorously controlled should be interpreted with caution. Ideally, the body temperature of every APAP-treated mouse should be monitored and maintained within the same values as in control animals in future experiments. This approach is logistically and technically difficult to accomplish, but it is the only way to avoid the introduction of this confounding factor and to interpret findings in an appropriate context. While telemetry is well established as a monitoring tool, new methods to measure temperature are being explored.10 The relevance of body temperature in the clinical setting of patients with acute liver failure requires further study.

References

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  • 1
    Newsome PN, Plevris JN, Nelson LJ, Hayes PC. Animal models of fulminant hepatic failure: a critical evaluation. Liver Transpl 2000; 6: 2131.
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    Massey TE, Walker RM, McElligott TF, Racz WJ. Acetaminophen-induced hypothermia in mice: evidence for a central action of the parent compound. Toxicology 1982; 25: 187200.
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    Walker RM, Racz WJ, McElligott TF. Acetaminophen-induced hepatotoxic congestion in mice. HEPATOLOGY 1985; 5: 233240.
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    Blazka ME, Wilmer JL, Holladay SD, Wilson RE, Luster MI. Role of proinflammatory cytokines in acetaminophen hepatotoxicity. Toxicol Appl Pharmacol 1995; 133: 4352.
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    Yamamoto H, Fujii K, Hayakawa T. Inhibitory effect of cold stress against acetaminophen-induced hepatic injury in B6C3F1 and ICR mice. Toxicol Lett 1995; 81: 125130.
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    Traber P, DalCanto M, Ganger D, Blei AT. Effect of body temperature on brain edema and encephalopathy in the rat after hepatic devascularization. Gastroenterology 1989; 96: 885891.
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    Chatauret N, Zwingmann C, Rose C, Leibfritz D, Butterworth RF. Effects of hypothermia on brain glucose metabolism in acute liver failure: a H/C-nuclear magnetic resonance study. Gastroenterology 2003; 125: 815824.
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    Kato A, Singh S, McLeish KR, Edwards MJ, Lentsch AB. Mechanisms of hypothermic protection against ischemic liver injury in mice. Am J Physiol Gastrointest Liver Physiol 2002; 282: G608G616.
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    Vaquero J, Belanger M, Cote J, Butterworth RF. Mild hypothermia attenuates acetaminophen-induced hepatic necrosis in mice: Therapeutic implications [Abstract]. HEPATOLOGY 2004; 40(Suppl): 220A.
  • 10
    Newsom DM, Bolgos GL, Colby L, Nemzek JA. Comparison of body surface temperature measurement and conventional methods for measuring temperature in the mouse. Contemp Top Lab Anim Sci 2004; 43: 1318.

Javier Vaquero*, Mireille Belanger*, Andres T. Blei†, Roger F. Butterworth*, * Neuroscience Research Unit, Hôpital Saint-Luc (CHUM) University of Montreal, Montreal, QC, Canada, † Northwestern University Feinberg School of Medicine, Chicago, IL.