Metabolomic approach in studying xenobiotic bioactivation

A predominant pathway of xenobiotic‐induced toxicity is via CYP450‐mediated bioactivation. Because most reactive metabolites are unstable, it is difficult to detect them directly. Reactive metabolites can form adducts with trapping reagents, such as glutathione (GSH), which makes the reactive metabolites detectable. However, it is challenging to “fish” these adducts out from a complex biological matrix. We anticipate that a metabolomic approach can overcome this problem. Lopinavir (LPV), an HIV drug, was used as a candidate to test our idea. Incubations of LPV in human liver microsomes were conducted with or without GSH. A metabolomic approach was used to profile metabolites in the two different incubation systems. Principal component analysis (PCA) and orthogonal projection to latent structures‐discriminant analysis (OPLS‐DA) were conducted. The PCA score plot revealed two clusters corresponding to the non‐GSH‐containing and GSH‐containing groups. The corresponding S‐plot generated from OPLS‐DA displayed the ions contributing to this group separation, which were GSH‐conjugated LPV metabolites. Based on metabolomic analysis, we confirmed 12 reactive metabolites of LPV, and they were generated by CYP3A4. In summary, this study highlights the power of metabolomic approach in studying xenobiotic bioactivation, which can be applied in a mechanistic investigation of xenobiotic‐induced toxicity.