(-)-Naringenin 4 ',7-dimethyl Ether Isolated from Nardostachys jatamansi Relieves Pain through Inhibition of Multiple Channels

(-)-Naringenin 4',7-dimethyl ether ((-)-NRG-DM) was isolated for the first time by our lab from Nardostachys jatamansi DC, a traditional medicinal plant frequently used to attenuate pain in Asia. As a natural derivative of analgesic, the current study was designed to test the potential analgesic activity of (-)-NRG-DM and its implicated mechanism. The analgesic activity of (-)NRG-DM was assessed in a formalin-induced mouse inflammatory pain model and mustard oilinduced mouse colorectal pain model, in which the mice were intraperitoneally administrated with vehicle or (-)-NRG-DM (30 or 50 mg/kg) (n = 10 for each group). Our data showed that (-)-NRG-DM can dose dependently (30 similar to 50 mg/kg) relieve the pain behaviors. Notably, (-)-NRG-DM did not affect motor coordination in mice evaluated by the rotarod test, in which the animals were intraperitoneally injected with vehicle or (-)-NRG-DM (100, 200, or 400 mg/kg) (n = 10 for each group). In acutely isolated mouse dorsal root ganglion neurons, (-)-NRG-DM (1 similar to 30 mu M) potently dampened the stimulated firing, reduced the action potential threshold and amplitude. In addition, the neuronal delayed rectifier potassium currents (I-K) and voltage-gated sodium currents (I-Na) were significantly suppressed. Consistently, (-)-NRG-DM dramatically inhibited heterologously expressed Kv2.1 and Nav1.8 channels which represent the major components of the endogenous I K and I Na . A pharmacokinetic study revealed the plasma concentration of (-)-NRG-DM is around 7 mu M, which was higher than the effective concentrations for the I-K and I-Na . Taken together, our study showed that (-)-NRG-DM is a potential analgesic candidate with inhibition of multiple neuronal channels (mediating I-K and I-Na).