Flavonoid chronotherapy normalizes circadian dynamics and sleep architecture in mice with painful nerve injury

Neuropathic pain (NP) is linked to disrupted sleep and circadian abnormalities upon painful peripheral nerve injury. By performing spared nerve injury (SNI) in circadian reporter PER2::LUC mice, we characterized the real-time changes in rhythmicity of the core clock gene Per2 in the pain-regulating dorsal root ganglia (DRG), and the sleep-wake cycle using wireless EEG/EMG under NP conditions. We further evaluated whether the clock-resynchronizing flavonoids, nobiletin (2 mg/kg/day) and tangeretin (1.8 mg/kg/day), administered continuously via osmotic minipumps for two weeks, could restore circadian dynamics and alleviate pain-related behaviour. Both flavonoids alleviated SNI-induced dynamic hypersensitivity in PER2::LUC mice on post-surgical day 14. SNI increased the amplitude of Per2 rhythms in the DRGs, which was restored to pre-surgical levels by administration of flavonoids. In addition, tangeretin showed sleep-restoring properties upon SNI by alleviating disturbances in NREM sleep and wakefulness. These results support targeting circadian disruption as a potential chronotherapeutic approach to alleviate NP.