Polygalae Radix shortens the circadian period through activation of the CaMKII pathway

Context: The mammalian circadian clock system regulates physiological function. Crude drugs, containing Polygalae Radix, and Kampō, combining multiple crude drugs, have been used to treat various diseases, but few studies have focussed on the circadian clock. Objective: We examine effective crude drugs, which cover at least one or two of Kampō, for the shortening effects on period length of clock gene expression rhythm, and reveal the mechanism of shortening effects. Materials and methods: We prepared 40 crude drugs. In the in vitro experiments, we used mouse embryonic fibroblasts from PERIOD2::LUCIFERASE knock-in mice (background; C57BL/6J mice) to evaluate the effect of crude drugs on the period length of core clock gene, Per2, expression rhythm by chronic treatment (six days) with distilled water or crude drugs (100 μg/mL). In the in vivo experiments, we evaluated the free-running period length of C57BL/6J mice fed AIN-93M or AIN-93M supplemented with 1% crude drug (6 weeks) that shortened the period length of the PERIOD2::LUCIFERASE expression rhythm in the in vitro experiments. Results: We found that Polygalae Radix (ED₅₀: 24.01 μg/mL) had the most shortened PERIOD2::LUCIFERASE rhythm period length in 40 crude drugs and that the CaMKII pathway was involved in this effect. Moreover, long-term feeding with AIN-93M+Polygalae Radix slightly shortened the free-running period of the mouse locomotor activity rhythm. Discussion and conclusions: Our results indicate that Polygalae Radix may be regarded as a new therapy for circadian rhythm disorder and that the CaMKII pathway may be regarded as a target pathway for circadian rhythm disorders.