METHODS AND RESULTS:
Five probe substrates were incubated with human liver microsomes in the presence or absence of the LAE, the alkaloid fraction (AF), the flavonoid fraction (FF), or the individual aporphine alkaloids, namely, nuciferine (NF), N-Nornuciferine (N-NF), and 2-hydroxy-1-methoxyaporphine (HMA).
After the incubation, the relative metabolites of the substrates were analyzed using LC-MS/MS. The results showed that the LAE strongly inhibited CYP2D6 with an IC50 value of 12.05µg/mL and weakly inhibited other isoenzymes. In addition, FF was found to weakly inhibit CYP2D6, whereas AF exerted a markedly higher inhibitory effect on CYP2D6 activity with an IC50 value of 0.96µg/mL. The three aporphine alkaloids isolated from the AF (NF, N-Nornuciferine, and HMA) significantly inhibited CYP2D6 with IC50 values of 3.78, 3.76, and 3.15µM, respectively.
CONCLUSIONS:
Their Lineweaver-Burk plots and Dixon plots showed that NF, N-Nornuciferine, and HMA competitively inhibited CYP2D6 activity with Ki values of 1.88, 2.34, and 1.56µM, respectively. |