Effects of Circadian Phase and Exercise Training on Systemic and Tissue-Specific Redox Responses in Mice Fed a High-Fat Diet

Background: The effects of exercise timing on redox adaptation under high-fat diet (HFD)-induced metabolic stress remain unclear. We investigated whether the circadian phase of training alters systemic and tissue-specific redox responses in HFD-fed mice. Methods: Male C57BL/6J mice fed an HFD remained sedentary or underwent 8 weeks of treadmill training at Zeitgeber time 3 (ZT3) or Zeitgeber time 15 (ZT15). Samples were collected 48 h after the final session. Plasma redox status was assessed using the OXY-adsorbent test (OXY), the derivatives of reactive oxygen metabolites test (d-ROMs; mainly reflecting circulating hydroperoxides), and the biological antioxidant potential test (BAP), and redox and inflammatory gene expression levels were quantified in three skeletal muscles and the liver. Results: Exercise increased BAP (p = 0.0442), whereas OXY was unchanged. The phase × exercise interaction for d-ROMs showed a nonsignificant trend (p = 0.0560); exploratory comparisons showed higher d-ROMs in ZT15-sedentary (sed) than in ZT3-sed and ZT15-exercise (exe) mice. Gastrocnemius (GAS) Nfe2l2 showed a nominal phase × exercise interaction. Soleus (SOL) Hmox1 was higher at ZT15 and with exercise. Quadriceps (QUA) Nfe2l2 was higher at ZT3 and Cat at ZT15. Hepatic Keap1 was higher at ZT15, particularly in sedentary mice, while inflammatory transcripts remained largely unchanged. Only the phase effects on SOL Hmox1 and hepatic Keap1 remained significant after false discovery rate (FDR) correction. Conclusions: Long-term exercise was associated with higher plasma ferric-reducing capacity irrespective of circadian phase, whereas tissue redox-related transcriptional responses were mainly associated with circadian phase and differed among tissues. Whether active-phase exercise provides a redox advantage over rest-phase exercise requires further investigation.