Genipin (GP), the reactive metabolite of geniposide (GE), is responsible for GE-induced hepatotoxicity. As a potential detoxification pathway, the inactivation of GP by glutathione S-transferases (GSTs) has not yet been characterized. In this study, the thiol-GSH conjugates of GP, M532-1 and M532-2 were first identified and the catalytic activities of GSTs were investigated both in vitro and in vivo. GSTA1-1 and GSTA4-4 showed high activity in the formation of both thiol-GSH conjugates, whereas GSTA4-4 specifically catalyzed M532-2 formation in vitro. The active GST isoforms protect against alkylation of Nacetylcysteine (NAC), a classic model nucleophile. GST inhibition attenuated M532-1 formation in rat bile, confirming the in vivo catalytic role of GSTs. In conclusion, this study demonstrated the inactivation of GP by GSTs and implied that interindividual variability of GSTs may be a risk factor for susceptibility to GE-induced hepatotoxicity.
Pterostilbene
(PTE), a dietary derivative of resveratrol,
displayed
pleiotropic health-promoting activities. This study aimed to explore
the metabolic profiles and species differences of the phase I metabolism
of PTE and to investigate subsequent detoxification after PTE bioactivation.
PTE was found to be biotransformed to two pharmacologically active
metabolites, pinostilbene and 3′-hydroxypterostilbene, in vivo and in vitro with substantial species
differences. Human CYP1A2 was proved to be mainly responsible for
the demethylation and 3′-hydroxylation of PTE, with its contribution
to a demethylation of 94.5% and to a 3′-hydroxylation of 97.9%.
An in vitro glutathione trapping experiment revealed
the presence of an ortho-quinone intermediate formed
by further oxidation of 3′-hydroxypterostilbene. Human glutathione S-transferase isoforms A2, T1, and A1 inactivated the ortho-quinone intermediate by catalyzing glutathione conjugation,
implicating a potential protective pathway against PTE bioactivation-derived
toxicity. Overall, this study provided a comprehensive view of PTE
phase I metabolism and facilitated its further development as a promising
nutraceutical.
Icaritin (ICT) is a prenylflavonoid derivative that has been approved by NMPA for the treatment of hepatocellular carcinoma. This study aims to evaluate the potential inhibitory effect of ICT against cytochrome P450 enzymes and to elucidate the inactivation mechanisms. Results showed that ICT inactivated CYP2C9 in a time, concentration, and NADPH-dependent manner with K i = 1.896 μM, K inact = 0.02298 minutes -1 , and K inact /Ki = 12 minutes -1 mM -1 , whereas the activities of rest CYP isozymes was minimally affected. Additionally, the presence of CYP2C9 competitive inhibitor, sulfaphenazole, SOD/CAT system, and GSH all protected CYP2C9 from ICT-induced activity loss. Moreover, the activity loss was neither recovered by washing the ICT-CYP2C9 preincubation mixture nor the addition of potassium ferricyanide. These results, collectively, implied the underlying inactivation mechanism involved the covalent binding of ICT to the apoprotein and/or the prosthetic heme of CYP2C9. Furthermore, an ICT-quinone methide (QM)-derived GSH adduct was identified and human glutathione S-transferases (GST) isozymes GSTA1-1, GSTM1-1, and GSTP1-1 were shown to substantially involved in the detoxification of ICT-QM. Interestingly, our systematic molecular modeling work predicted that ICT-QM was covalently bind to C216, a cysteine residue located in the F-G loop downstream of substrate recognition site 2 (SRS2) in CYP2C9. The sequential molecular dynamics simulation confirmed the binding to C216 induced a conformational change in the active catalytic center of CYP2C9. Lastly, the potential risks of clinical drug-drug interactions triggered by ICT as a perpetrator were This article has not been copyedited and formatted. The final version may differ from this version.
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