Kampo is a traditional Japanese herbal medicine and widely used in clinical practice in Japan. Little is known about interactions between
Kampo and other medicines.
Kampo contains many aglycones, which can be conjugated by UDP-glucuronosyltransferase (UGT). Therefore, in the present study, the effects of
Kampo on human UGT1A1 activity were investigated
in vitro. Substrates of human UGT1A1, β-estradiol or 7-ethyl-10-hydroxycamptothecin (SN-38), were incubated with human liver microsomes in the presence of 51
Kampos, 14 medicinal herbs and their components. β-Estradiol 3-glucuronidation was strongly inhibited by some
Kampos such as Bofu-tsusho-san, Mashinin-gan and Otsuji-to. Medicinal herbs such as Daio (
Rhei Rhizoma), Kanzo (
Glycyrrhizae Radix), Keihi (
Cinnamomi Cortex) and Ogon (
Scutellariae Radix) exhibited potent inhibition on that activity. On β-estradiol 3-glucuronidation, the major component of Keihi (cinnamaldehyde) and Ogon (wogonin) exhibited mixed-type inhibition of
Ki with values of 0.7 μM and 2.8 μM, respectively. On SN-38 glucuronidation, the inhibitory potencies of
Kampos, medicinal herbs and their components tended to be similar to those on β-estradiol 3-glucuronidation. In the present study,
Kampo was clarified to inhibit β-estradiol and SN-38 glucuronidation mainly catalyzed by UGT1A1.
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