Cephaeline is dissolved in methanol to give concentrations of 0.1, 1, 10, 100 μM (only theophylline-O-demethylase activity with Cephaeline; 0.0985, June 2001 679 0.985, 9.85, 98.5 μM) ^[1].
Human liver microsomal protein is incubated with the selected marker substrates in the absence and presence of above concentrations of Cephaeline or Emetine (1-100 μM, only theophylline-O-demethylase activity with Cephaeline; 0.0985—98.5 μM, final concentration). Incubation conditions are chosen such that the product formation is linear with respect to both incubation times and protein concentrations, with substrate concentrations being at or below the K_m for each enzyme. The effects of furafylline, sulphaphenazole, tranylcypromine, quinidine, and ketoconazole, selective inhibitors of CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4, respectively, are also determined in the same microsomal samples to provide comparisons with inhibitory potentials (IC₅₀) of Cephaeline and Emetine towards the individual CYP form. The K_i s for Cephaeline and Emetine are determined by using the same pooled microsomal sample. This is achieved by varying the initial substrate concentrations (bufuralol 8, 16 and 32 μM; testosterone 45, 90 and 180u M) and using several inhibitor concentrations of 10, 50, and 100 μM. The K_is are estimated by graphic analysis of Dixon plots. These values are subsequently used as initial estimates for the nonlinear least-squares regression analysis^[1].

MCE has not independently confirmed the accuracy of these methods. They are for reference only.

• [1]. Asano T, et al. Metabolism of ipecac alkaloids Cephaeline and Emetine by human hepatic microsomal cytochrome P450s, and their inhibitory effects on P450 enzyme activities. Biol Pharm Bull. 2001 Jun;24(6):678-82.  [Content Brief]