BACKGROUND: This study was aimed to examine circadian variations of hepatic 
antioxidant components, including the Nrf2- pathway, the glutathione (GSH) 
system, antioxidant enzymes and metallothionein in mouse liver.
METHODS AND RESULTS: Adult mice were housed in light- and temperature-controlled 
facilities for 2 weeks, and livers were collected every 4 h during the 24 h 
period. Total RNA was isolated, purified, and subjected to real-time RT-PCR 
analysis. Hepatic mRNA levels of Nrf2, Keap1, Nqo1 and Gclc were higher in the 
light-phase than the dark-phase, and were female-predominant. Hepatic GSH 
presented marked circadian fluctuations, along with glutathione S-transferases 
(GST-α1, GST-µ, GST-π) and glutathione peroxidase (GPx1). The expressions of 
GPx1, GST-µ and GST-π mRNA were also higher in females. Antioxidant enzymes 
Cu/Zn superoxide dismutase (Sod1), catalase (CAT), cyclooxygenase-2 (Cox-2) and 
heme oxygenase-1 (Ho-1) showed circadian rhythms, with higher expressions of 
Cox-2 and CAT in females. Metallothionein, a small non-enzymatic antioxidant 
protein, showed dramatic circadian variation in males, but higher expression in 
females. The circadian variations of the clock gene Brain and Muscle Arnt-like 
Protein-1(Bmal1), albumin site D-binding protein (Dbp), nuclear receptor 
Rev-Erbα (Nr1d1), period protein (Per1 and Per2) and cryptochrome 1(Cry1) were 
in agreement with the literature. Furthermore, acetaminophen hepatotoxicity is 
more severe when administered in the afternoon when hepatic GSH was lowest.
CONCLUSIONS: Circadian variations and gender differences in transcript levels of 
antioxidant genes exist in mouse liver, which could affect body responses to 
oxidative stress at different times of the day.