Screening stabilisers for cyanoenone triterpenoid TX101 in rat plasma samples by simultaneous analysis of parent drug and the epoxidation product

In the development of bioanalytical methods, stabilizing drug molecules in biological matrices is crucial for ensuring reliable exposure data in pharmacokinetic and toxicokinetic sample analyses. This study focuses on the evaluation of stabilizing effects on the synthetic triterpenoid TX101, a cyanoenone triterpenoid Nrf2 activator with known instability in plasma samples. The molecule's unsaturated double bond is susceptible to oxidation, either nonenzymatically via oxygen or enzymatically through cytochrome P450 enzyme-catalyzed epoxidation. The research explores the impact of antioxidants (L-ascorbic acid, sodium metabisulfite, sodium sulfite) and P450 enzyme inhibitors (sodium diethyldithiocarbamate, memantine hydrochloride, 1-aminobenzotriazole) on TX101 stability in rat plasma samples. Results reveal that adding 2.5 mg/mL sodium sulfite or sodium metabisulfite effectively inhibits the nonenzymatic oxidation of TX101 to TX101-epoxide, while L-ascorbic acid shows minimal stabilizing effect. Among P450 enzyme inhibitors, sodium diethyldithiocarbamate and memantine hydrochloride exhibit modest stabilizing effects, likely attributed to their antioxidant activity. The developed High-formance liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS) method, incorporating Supported Liquid Extraction for sample cleanup, allows simultaneous monitoring of TX101 and TX101-epoxide. Application of this method in a rat dose-range finding study confirms successful inhibition of TX101-epoxide formation in samples treated with sodium sulfite or sodium metabisulfite. Overall, the study emphasizes the importance of stabilizers in preventing nonenzymatic oxidation reactions during sample storage, providing valuable insights for bioanalytical method development and validation.