Investigation of circadian variation in the hepatic proteome in a mouse model of paracetamol-induced hepatotoxicity

Philip Starkey Lewis1, Christopher Goldring1, Cliff Rowe1, Vivien Platt1, Akua Obeng1, Laura Randle1, Jonathan Moggs2, Kevin Park1. 1University of Liverpool, Molecular and Clinical Pharmacology, L69 3GE Liverpool, United Kingdom, 2Novartis, Investigative Toxicology, CH-4132 Muttenz, Switzerland.

The biological clock is known to influence the physiology of mammalian systems. This regulation hinges on a highly synchronised negative feedback loop between the clock genes and their products that oscillate over a twenty-four hour period. This highly dynamic timekeeping system has profound effects on the regulation of signalling pathways. Evidence suggests that the efficacy and toxicity of many therapeutic compounds follow a twenty-four hour rhythm and this can be attributed to the circadian regulation of drug-metabolising systems and key drug targets. We have firstly characterised paracetamol (APAP)-induced hepatotoxicity (300 mg/kg, i.p.) using circulating biomarkers of liver injury in the CD-1 male mouse (n = 6) and confirmed that the circadian rhythm exerts a significant influence on APAP toxicity (P<0.05, ANOVA). We have then analysed proteins previously implicated in this variation in toxicity of APAP and performed an unbiased global proteomic analysis (isobaric tag for relative and absolute quantitation) of the CD-1 male mouse liver (n = 4) to explore novel bases of this variation. Using this approach we have identified novel proteins involved in bioactivation and detoxification pathways that appear to follow a diurnal variation in expression including regucalcin (P<0.01, ANOVA), aromatic-L-amino-acid decarboxylase (P<0.01, ANOVA) and cytochrome b5 (P<0.05, ANOVA). This dataset reveals new areas of investigation and testable hypotheses with which to explore the temporal relationship between circadian physiology and DILI.