Transient receptor potential vanilloid type 1 (TRPV1) is a non-selective cation channel
activated by capsaicin and heat. Capsaicin has various effects such as pain relief,
rubefacient, weight loss, and gastrointestinal protection. Some compounds in Kampo
(a traditional Japanese medicine) formulas, such as evodiamine of Evodia fruit, are
known to activate TRPV1. But, it is not clear whether TRPV1 is activated by taking
Kampo prescriptions. Therefore, the effects of 128 Kampo extract formulations for
prescription on the HEK293 cells with/without human TRPV1 expression were examined.
The specific increase of intracellular Ca2+ was used as the index of TRPV1 activation. The samples with specific TRPV1 activation
were further examined whether they have capsaicin-like contractile effects in mice
isolated ileum. In this study, the final concentrations of samples were adjusted to
be 1 – 2% of the normal Kampo decoctions. The Daikenchuto which TRPV1 activating ability
was already known was served as a positive control. Capsazepine, a TRPV1 antagonist,
was used to check the site of action. As a result, 12 Kampo prescriptions have shown
stronger TRPV1 activation than Daikenchuto in HEK293 cells with hTRPV1. In the mice
isolated ileum, Daiokanzoto, Tokakujokito, Tokishigyakukagoshuyushokyoto and Goshuyuto
showed strong contractile effects which was suppressed by the pretreatment of capsazepine.
Rubarb and Evodia fruit were suggested to be the main contributing crude drugs for
TRPV1 activation. Sennoside B, a main constituent of Rubarb, was found to be a TRPV1
activator. In conclusion, some Kampo prescriptions showed strong TRPV1 activation
at the concentrations lower than those in decoction, suggesting the TRPV1 stimulation
might play an important part in their pharmacological actions.