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.

Potential metabolism determinants and drug–drug interactions of a natural flavanone bavachinin

“…Phase I metabolism and glucuronidation are essentially incubation assays performed routinely in our laboratory. 11,25,30 The incubation system for phase I metabolism included contained Tris-HCl buffer (50 mM, pH ¼ 7.4), MgCl 2 (5 mM), substrates (bavachinin, or specic substrate for each CYP enzyme), enzyme materials (HLM, HIM, animal liver microsomes, or CYP enzymes). The reaction was initiated by addition of NADPH (1 mM) aer a pre-incubation at 37 C for 5 min.…”

“…The metabolic rates for phase I metabolism (or glucuronidation) were determined at a series of bavachinin concentrations based on the previous protocol. 11,25,30 Preliminary experiments were performed to ensure that the metabolic rates were determined under a linear condition with respect to optimized incubation time and protein concentration. Kinetic model selection was based on the visual inspection of the Eadie-Hofstee plot.…”

“…As published previously, phenacetin (100 mM), bupropion (100 mM), paclitaxel (60 mM), tolbutamide (200 mM), mephenytoin (100 mM), chlorzoxazone (200 mM) and nifedipine (40 mM) have been well-accepted as the specic substrates for CYP1A2, 2B6, 2C8, 2C9, 2C19, 2E1, and 3A4, respectively. 27,30 Similarly, b-estradiol (60 mM), propofol (40 mM) and zidovudine (500 mM) were typically used as the selective probe substrates for UGT1A1, 1A9, and 2B7, respectively. 31,32 The substrates above were separately incubated with CYP isozyme (or UGT enzymes) in the absence (control) and presence of bavachinin (1, 10, 100 mM) at optimized incubation time and protein concentration as described previously.…”

“…31,32 The substrates above were separately incubated with CYP isozyme (or UGT enzymes) in the absence (control) and presence of bavachinin (1, 10, 100 mM) at optimized incubation time and protein concentration as described previously. 27,[30][31][32] The half-inhibition concentration (IC 50 ) values of bavachinin towards individual CYP and UGT isozyme were obtained using the non-linear regression analysis. Traditionally, the inhibitory effects could be divided into four categories based on the IC 50 values as follows: potent (less than 1 mM), moderate (between 1 and 10 mM), weak (over 10 mM), or no inhibition (over 100 mM).…”

“…[26][27][28] Human CYP1A2 (9%), 2B6 (2%), 2C8, 2C9 (16%), 2C19 (12%), 2E1 (2%), 3A4 (46%), and UGT1A1 (15%), 1A9, 2B7 (35%) participated most in the metabolism or elimination of clinical drugs. 29,30 Once the function of these CYP (or UGT) isozymes were inhibited (or induced) by bavachinin, the exposure (represented by AUC 0-t values) of co-administrated drugs could be markedly increased (or decreased), which further brought several adverse reactions (or insufficient efficacy). However, the effects of bavachinin towards these CYP and UGT enzymes is not clear.…”