Investigation on the metabolic characteristics of isobavachin in Psoralea corylifolia L. (Bu-gu-zhi) and its potential inhibition against human cytochrome P450s and UDP-glucuronosyltransferases

Abstract

Objectives: Isobavachin is a phenolic with anti-osteoporosis activity. This study aimed to explore its metabolic fates in vivo and in vitro, and to investigate the potential drug-drug interactions involving CYPs and UGTs.

Methods: Metabolites of isobavachin in mice were first identified and characterized. Oxidation and glucuronidation study were performed using liver and intestine microsomes. Reaction phenotyping, activity correlation analysis and relative activity factor approaches were employed to identify the main CYPs and UGTs involved in isobavachin metabolism. Through kinetic modelling, inhibition mechanisms towards CYPs and UGTs were also explored.

Key findings: Two glucuronides (G1 - G2) and three oxidated metabolites (M1 - M3) were identified in mice. Additionally, isobavachin underwent efficient oxidation and glucuronidation by human liver microsomes and HIM with CL_int values from 5.53 to 148.79 μl/min per mg. CYP1A2, 2C19 contributed 11.3% and 17.1% to hepatic metabolism of isobavachin, respectively, with CL_int values from 8.75 to 77.33 μl/min per mg. UGT1As displayed CL_int values from 10.73 to 202.62 μl/min per mg for glucuronidation. Besides, significant correlation analysis also proved that CYP1A2, 2C19 and UGT1A1, 1A9 were main contributors for the metabolism of isobavachin. Furthermore, mice may be the appropriate animal model for predicting its metabolism in human. Moreover, isobavachin exhibited broad inhibition against CYP2B6, 2C9, 2C19, UGT1A1, 1A9, 2B7 with K_i values from 0.05 to 3.05 μm.

Conclusions: CYP1A2, 2C19 and UGT1As play an important role in isobavachin metabolism. Isobavachin demonstrated broad-spectrum inhibition of CYPs and UGTs.

Keywords: CYPs; UGTs; drug-drug interactions; isobavachin; metabolism; mice.

Figure 1

Intrinsic clearance (CL_int) values for metabolic activities of isobavachin by expressed CYP isoforms (a) and recombinant UGT enzymes (b). N.A., under the limit of quantification or unable to determine the kinetic parameters in the absence of a full kinetic profile. The data were presented as mean ± SD. All experiments were performed in triplicate. (* compared with those of HLM or HIM, ns P > 0.05, *P < 0.05, **P < 0.01). [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 2

The effects of isobavachin against seven expressed CYP isozymes (a) and three common UGT enzymes (b). The specific substrates were incubated at 37 °C in the absence (control) and presence of isobavachin (1, 10 and 100 μM). The data were presented as mean ± SD. All experiments were performed in triplicate determinations. (* compared with those of control, *P < 0.05, **P < 0.01, ***P < 0.001). [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 3

The inhibition curves and IC₅₀ values of isobavachin against CYP2B6 (a), CYP2C9 (b), CYP2C19 (c), UGT1A1 (d), UGT1A9 (e), UGT2B7 (f). The data were fit to log (I) and normalized response equations. Each data point represented the mean value ± the SD of triplicate determinations. [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 4

The Dixon plots for the inhibition effects of isobavachin towards expressed CYP and UGT isozymes. (a) bupropion-hydroxylation for CYP2B6; (b) tolbutamide-4-hydroxylation for CYP2C9; (c) mephenytoin-4-hydroxylation for CYP2C19; (d) β-estradiol-3-O-glucuronidation for UGT1A1; (e) propofol-O-glucuronidation for UGT1A9; (f) zidovudine-N-glucuronidation for UGT2B7; All data represent the means ± SD of triplicate determinations. [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 5

Metabolic pathways of isobavachin involving in metabolic activities and inhibition effects against expressed CYP and UGT isozymes. [Colour figure can be viewed at wileyonlinelibrary.com]