Background: Triptolide (TP), an active constituent of Tripterygium wilfordii, possesses numerous pharmacological\nactivities. However, its effects on cytochrome P450 enzymes (CYP450s) in rats remain unexplored.\nMethods: In this study, the effects of triptolide on the six main CYP450 isoforms (1A2, 2C9, 2C19, 2D6, 2E1, and 3A)\nwere investigated both in vivo and in vitro. We monitored the body weight, survival proportions, liver index,\nchanges in pathology, and biochemical index upon TP administration, in vivo. Using a cocktail probe of CYP450\nisoform-specific substrates and their metabolites, we then carried out in vitro enzymatic studies in liver microsomal\nincubation systems via ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS).\nFinally, we verified our results at the messenger ribonucleic acid (mRNA) and protein level through quantitative\nreal-time polymerase chain reaction (RT-qPCR), western blotting, and immunohistochemical detection.\nResults: The in vivo toxicity study confirmed that Sprague-Dawley (SD) rats exhibited dose-dependent\nhepatotoxicity after intragastric administration of TP [200, 400, and 600 �¼g/(kg.day)] for 28 days. In case of the\nCYP450 isoforms 3A, 2C9, 2C19, and 2E1, the in vitro metabolic study demonstrated a decrease in the substrate\nmetabolic rate, metabolite production rate, and Vmax, with an increase in the Km value, compared with that\nobserved in the control group. Additionally, a TP dose-dependent decrease in the mRNA levels was observed in the\nfour major isoforms of CYP3A subfamily (3A1/3A23, 3A2, 3A9, and 3A62) and CYP2C9. A similar effect was also\nobserved with respect to the protein levels of CYP2C19 and CYP2E1.\nConclusions: This study suggests that TP can cause hepatotoxicity by reducing the substrate affinity, activity, and\nexpression at the transcriptional and protein levels of the CYP450 isoforms 3A, 2C9, 2C19, and 2E1. TP also has the\npotential to cause pharmacokinetic drug interactions when co-administered with drugs metabolized by these four\nisoforms. However, further clinical studies are needed to evaluate the significance of this interaction.
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