Influence of grapefruit juice on pharmacokinetics of triptolide in rats grapefruit juice on the effects of triptolide.

1. Triptolide, a major pharmacological component isolated from Tripterygium wilfordii Hook F (TWHF), is a substrate of both CYP3A4 and P-glycoprotein (P-gp). 2. This study investigates the effects of GFJ on the pharmacokinetics of triptolide in rats. 3. The pharmacokinetics of orally administered triptolide with or without GFJ pretreatment were investigated. A mechanistic study was also undertaken using the Caco-2 cell transwell model and rat liver microsomes incubation systems to support the in vivo pharmacokinetic data. 4. The results indicated that coadministration of GFJ could increase the systemic exposure of triptolide significantly, including area under the curve (828.58 ± 79.72 versus 541.53 ± 45.23 ng·h/mL) and maximum plasma concentration (273.58 ± 27.98 versus 193.67 ± 10.08 ng/mL). The apparent permeability of triptolide across the Caco-2 cell transwell model increased significantly with the pretreatment of GFJ (from 1.62 ± 0.25 × 10-6 to 2.51 ± 0.41 × 10-6 cm/s), and the metabolic stability of triptolide was also increased from 32.6 ± 5.1 to 52.5 ± 7.8 min with the pretreatment of GFJ, and the difference was significant (p < 0.05). 5. In conclusion, GFJ could increase the systemic exposure of triptolide in rats, when GFJ and triptolide was coadministered, and it might work mainly through increasing the absorption of triptolide by inhibiting P-gp, or through slowing down the metabolism of triptolide in rat liver by inhibiting the activity of CYP3A4.