TABLE 1

Results of IC50 shift experiments showing TDI of CYP2C9, CYP2D6, and CYP3A4/5 activities in HLMs by goldenseal component alkaloids

Values denote means ± S.D. of three separate experiments, with the exception of the tienilic acid, paroxetine, and troleandomycin inhibitors, which were each run as a singlet. These three compounds were chosen as positive controls for the IC50 shift experiments because they are known to exhibit strong isozyme-specific TDI of CYP2C9, CYP2D6, and CYP3A4/5 activities, respectively.

InhibitorProbe SubstrateInhibited EnzymeIC50 (μM)aShift Ratiob
(−) NADPH(+) NADPH
BerberineDextromethorphanCYP2D69.9 ± 1.31.6 ± 0.36.0
BerberineMDZCYP3A4/5Activation180 ± 25
(−)-β-HydrastineDiclofenacCYP2C9120 ± 3031 ± 3.23.9
(−)-β-HydrastineDextromethorphanCYP2D6270 ± 2180 ± 183.4
(−)-β-HydrastineMDZCYP3A4/558 ± 7.69.9 ± 1.55.9
HydrastinineDextromethorphanCYP2D665 ± 218.4 ± 1.17.7
Tienilic AcidDiclofenacCYP2C92.80.213
ParoxetineDextromethorphanCYP2D60.90.19
TroleandomycinMDZCYP3A4/5611.540
  • a Prior to the addition of substrate, HLMs were preincubated with inhibitor for 30 minutes in the presence (+) or absence (−) of NADPH cofactor.

  • b Shift ratio = IC50 (−) NADPH/IC50 (+) NADPH.