Time-dependent inhibition (TDI) of CYP3A4 and CYP2C9 by noscapine potentially explains clinical noscapine-warfarin interaction

Abstract

Aims: To investigate the inhibition potential and kinetic information of noscapine to seven CYP isoforms and extrapolate in vivo noscapine-warfarin interaction magnitude from in vitro data.

Methods: The activities of seven CYP isoforms (CYP3A4, CYP1A2, CYP2A6, CYP2E1, CYP2D6, CYP2C9, CYP2C8) in human liver microsomes were investigated following co- or preincubation with noscapine. A two-step incubation method was used to examine in vitro time-dependent inhibition (TDI) of noscapine. Reversible and TDI prediction equations were employed to extrapolate in vivo noscapine-warfarin interaction magnitude from in vitro data.

Results: Among seven CYP isoforms tested, the activities of CYP3A4 and CYP2C9 were strongly inhibited with an IC(50) of 10.8 +/- 2.5 microm and 13.3 +/- 1.2 microm. Kinetic analysis showed that inhibition of CYP2C9 by noscapine was best fit to a noncompetitive type with K(i) value of 8.8 microm, while inhibition of CYP3A4 by noscapine was best fit to a competitive manner with K(i) value of 5.2 microm. Noscapine also exhibited TDI to CYP3A4 and CYP2C9. The inactivation parameters (K(I) and k(inact)) were calculated to be 9.3 microm and 0.06 min(-1) for CYP3A4 and 8.9 microm and 0.014 min(-1) for CYP2C9, respectively. The AUC of (S)-warfarin and (R)-warfarin was predicted to increase 1.5% and 1.1% using C(max) or 0.5% and 0.4% using unbound C(max) with reversible inhibition prediction equation, while the AUC of (S)-warfarin and (R)-warfarin was estimated to increase by 110.9% and 48.9% using C(max) or 41.8% and 32.7% using unbound C(max) with TDI prediction equation.

Conclusions: TDI of CYP3A4 and CYP2C9 by noscapine potentially explains clinical noscapine-warfarin interaction.

Figure 1

Reversible inhibition of noscapine to CYP3A4 and CYP2C9. (A1) Inhibition potential of noscapine to diclofenac 4′-hydroxylation activity (CYP2C9). (A2) Dixon plot of inhibition effect of noscapine on diclofenac 4′-hydroxylation activity (CYP2C9). (A3) Lineweaver–Burk plot of inhibition effect of noscapine on diclofenac 4′-hydroxylation activity (CYP2C9). (A4) Second plot of slopes from Lineweaver–Burk plot vs. noscapine concentrations. (B1) Inhibition potential of noscapine to testosterone 6β-hydroxylation activity (CYP3A4). (B2) Dixon plot of inhibition effect of noscapine on testosterone 6β-hydroxylation activity (CYP3A4). (B3) Lineweaver–Burk plot of inhibition effect of noscapine on 6β-hydroxylation activity (CYP3A4). (B4) Second plot of slopes from Lineweaver–Burk plot vs. noscapine concentrations

Figure 2

Time-dependent inhibition of noscapine to CYP3A4 and CYP2C9. (a) Time- and concentration-dependent inhibition of CYP2C9 by noscapine. (b) The hyperbolic plot of k_obs of CYP2C9 vs. noscapine concentrations. (c) Time- and concentration-dependent inhibition of CYP3A4 by noscapine. (d) The hyperbolic plot of k_obs of CYP3A4 vs. noscapine concentrations