Absorption and metabolism characteristics of pristimerin as determined by a sensitive and reliable LC–MS/MS method

Effects of psoralen on the pharmacokinetics of anastrozole in rats

CONTEXT

Psoralen and anastrozole are always used together for breast cancer patients in Chinese clinics.

OBJECTIVE

This study investigates the effects of psoralen on the pharmacokinetics of anastrozole in rats and its potential mechanism.

MATERIALS AND METHODS

The pharmacokinetics of orally administered anastrozole (0.5 mg/kg) with (test group) or without (Control group) psoralen pretreatment (20 mg/kg/day for 10 days) in male Sprague-Dawley rats (six rats in each group) were investigated. The plasma concentration of anastrozole was determined using a sensitive and reliable LC-MS/MS method. Additionally, the effects of psoralen on the intestine transport and metabolic stability of anastrozole (1 μM) were investigated using a Caco-2 cell transwell model and rat liver microsome incubation systems.

RESULTS

The results indicated that psoralen could significantly increase the C_max (from 56.74 ± 3.17 ng/mL to 83.26 ± 6.87 ng/mL), and t_1/2 (from 10.80 ± 1.05 to 14.29 ± 1.38 h) of anastrozole (p < 0.05). Psoralen could also significantly decrease the efflux ratio of anastrozole from 1.88 to 1.32 (p < 0.05). Additionally, the intrinsic clearance rates of anastrozole decreased significantly (from 62.83 to 43.97 μL/min/mg protein) (p < 0.05) with psoralen pretreatment in rat liver microsome incubation systems.

DISCUSSION AND CONCLUSIONS

This study indicates that when the rats were pretreated with psoralen, the system exposure of anastrozole would be increased significantly. The results showed that the herb-drug interaction between psoralen and anastrozole might occur when they were co-administered, and future studies in humans also need to investigate its herb-drug interaction potential.

In vitro inhibitory effects of pristimerin on human liver cytochrome P450 enzymes

1.Pristimerin (PTM) is a biological component isolated from Chinese herbal plant Celastrus and Maytenus spp. and it possesses numerous pharmacological activities. However, whether PTM affects the activity of human liver cytochrome P450 (CYP) enzymes remains unclear. 2.In this study, the inhibitory effects of PTM on the eight human liver CYP isoforms (i.e. 1A2, 3A4, 2A6, 2E1, 2D6, 2C9, 2C19 and 2C8) were investigated in vitro using human liver microsomes (HLMs). 3.The results showed that PTM inhibited the activity of CYP1A2, 3A4 and 2C9, with IC ₅₀ values of 21.74, 15.88 and 16.58 μM, respectively, but that other CYP isoforms were not affected. Enzyme kinetic studies showed that PTM was not only a non-competitive inhibitor of CYP3A4, but also a competitive inhibitor of CYP1A2 and 2C9, with K_i values of 7.33, 11.60 and 8.09 μM, respectively. In addition, PTM is a time-dependent inhibitor for CYP3A4 with K_inact /K_I value of 0.049/11.62 μM^-1min^-1. 4.The in vitro studies of PTM with CYP isoforms indicate that PTM has the potential to cause pharmacokinetic drug interactions with other co-administered drugs metabolized by CYP1A2, 3A4 and 2C9. Further clinical studies are needed to evaluate the significance of this interaction.

Effects of verapamil on the pharmacokinetics of dihydromyricetin in rats and its potential mechanism

1. This study investigates the effects of verapamil on the pharmacokinetics of dihydromyricetin in rats and clarifies its main mechanism. 2. The pharmacokinetic profiles of oral or intravenous administration of dihydromyricetin in Sprague-Dawley rats with or without pretreatment with verapamil were investigated. In addition, the effects of verapamil on the transport and metabolic stability of dihydromyricetin were investigated using Caco-2 cell transwell model and rat liver microsomes. 3. In the oral group, verapamil could significantly increase C_max, and decrease oral clearance of dihydromyricetin (p < 0.05). In the intravenous group, the C_max also increased compared with the control group, but the difference was not significant. However, the t_1/2 and clearance rate decreased than that of the control (p < 0.05). The oral bioavailability increased significantly (p < 0.05) from 3.84% to 6.84% with the pretreatment of verapamil. A markedly higher transport of dihydromyricetin across the Caco-2 cells was observed in the basolateral-to-apical direction and was abrogated in the presence of the P-gp inhibitor, verapamil. Additionally, the intrinsic clearance rate of dihydromyricetin was decreased by the pretreatment with verapamil (27.0 versus 32.5 μL/min/mg protein). 4. Those results indicated that verapamil could significantly change the pharmacokinetic profiles of dihydromyricetin in rats, and it might exert these effects through increasing the absorption of dihydromyricetin by inhibiting the activity of P-gp, or through inhibiting the metabolism of dihydromyricetin in rat liver.

The effects of verapamil on the pharmacokinetics of curculigoside in rats

CONTEXT

Clarifying the potential mechanism of the poor oral bioavailability of curculigoside would be helpful for for investigating pharmacological effects and clinical applications.

OBJECTIVE

To clarify the main mechanism for poor oral bioavailability.

MATERIALS AND METHODS

First, the pharmacokinetics of curculigoside (20 mg/kg) in rats with and without pretreatment with verapamil (10 mg/kg) was determined using a sensitive and reliable LC-MS method. Then the effects of verapamil on the transport and metabolic stability of curculigoside were investigated using Caco-2 cell transwell model and rat liver microsome incubation systems.

RESULTS

The results showed that verapamil could significantly increase the peak plasma concentration (from 60.17 ng/mL to 93.66 ng/mL) and AUC_0-t (from 289.57 to 764.02 ng·h/mL) of curculigoside. The Caco-2 cell experiments indicated that the efflux ratio of curculigoside was 3.92 (P_appAB 6.43 ± 0.57 × 10 ^-7cm/s; P_appBA 2.52 ± 0.37 × 10 ^-36cm/s), P-gp might be involved in the transport of curculigoside, and verapamil could inhibit the efflux of curculigoside and increase the absorption of curculigoside significantly in the Caco-2 cell monolayer. Additionally, the rat liver microsome incubation experiments indicated that verapamil could significantly decrease the intrinsic clearance rate of curculigoside (from 38.8 to 23.6 μL/min/mg protein).

DISCUSSION AND CONCLUSION

These results indicated that verapamil could significantly change the pharmacokinetic profiles of curculigoside in rats, the poor absorption due to P-gp mediated efflux in intestine and high intrinsic clearance rate in rat liver may be the main reason for the poor oral absolute bioavailability of curculigoside.