Lysine- and cysteine-based protein adduction resulting from metabolic activation of fraxinellone in Dictamni Cortex.

Dictamni Cortex (DC) has been associated with herb-induced liver injury, and fraxinellone (FRA), a furan-containing constituent, is implicated as a major hepatotoxic component. However, direct evidence linking FRA bioactivation to hepatic protein adduction in vivo remains limited. Here, we synthesized pyrroline- and pyrrole-type conjugates derived from the reactive FRA-cis-enedial intermediate and established liquid chromatography-tandem mass spectrometry methods to quantify corresponding lysine and cysteine/lysine adduct markers in the mouse liver after oral dosing with FRA or DC extract. Protein adduct levels increased in a dose- and time-dependent manner, peaked at 12 hours, and remained detectable up to 120 hours. Pretreatment with the CYP3A inhibitor ketoconazole markedly reduced adduct formation, supporting a CYP3A-dependent bioactivation pathway. To enable immunochemical detection, oxidized FRA was coupled to keyhole limpet hemocyanin to generate a polyclonal antiserum that selectively recognized FRA-derived pyrroline and pyrrole motifs. Western blotting and immunofluorescence revealed increased immunoreactive bands and a pericentral (central vein > portal triad) gradient in liver lobules, with prominent nuclear staining in hepatocytes after FRA or DC extract exposure; these signals were attenuated by ketoconazole. Collectively, these data demonstrate that CYP3A-mediated formation of an electrophilic cis-enedial intermediate drives covalent modification of hepatic proteins during FRA/DC exposure. The combined liquid chromatography-tandem mass spectrometry and antibody-based assays provide complementary tools for mechanistic studies and biomarker development for furan-containing herbal constituents. SIGNIFICANCE STATEMENT: This work provides direct in vivo evidence that CYP3A-dependent bioactivation of fraxinellone generates a reactive cis-enedial that covalently modifies hepatic proteins. The liquid chromatography-tandem mass spectrometry adduct markers and a selective antiadduct antibody enable semi‑quantitative detection and spatial mapping of protein adduction, supporting mechanistic investigations and biomarker development for furan-containing herbal constituents associated with liver injury.