A simple, sensitive, and high-throughput LC-APCI-MS/MS method for simultaneous determination of vitamin K1, vitamin K1 2,3-epoxide in human plasma and its application to a clinical pharmacodynamic study of warfarin

Abstract Warfarin exerts its anticoagulation activity by blocking the vitamin K-epoxide cycle. A quantitative understanding of how warfarin and related genes interact with the vitamin K-epoxide cycle and the associated change of coagulation activity in the human body may help study the pharmacodynamics of warfarin. The plasma concentration of vitamin K 1 (VK 1 ) and vitamin K 1 2,3-epoxide (VK 1 O) could reflect the status of vitamin K-epoxide cycle. However, their determination is a challenging task due to their extremely low concentrations in human plasma and the severe interferences caused by co-extracted lipids. In this study, we developed an LC-APCI-MS/MS method for the simultaneous determination of VK 1 and VK 1 O in human plasma using stable deuterium-labeled vitamin K 1 (vitamin K 1 -d7) as the internal standard (IS). Plasma samples were prepared through protein denaturation followed by one-step liquid extraction with cyclohexane. Chromatographic separation of analytes from isobaric interferences and endogenous ion suppressor was performed on a Synergi Hydro-RP column (150 mm × 4.6 mm, 4 μm) under the reversed-phase condition with isocratic elution. The selective reaction monitoring (SRM) transitions were chosen as m/z  = 451.5→187.3 for VK 1 , m/z  = 467.5→161.2 for VK 1 O, and m/z  = 458.6→194.3 for IS in APCI positive mode. The assay was linear in the range of 100–10,000 pg/mL for the two analytes and achieved considerable extraction recoveries (87.8–93.3%, 91.0–96.9%, and 92.0% for VK 1 , VK 1 O, and IS, respectively), negligible matrix effects (93.6–96.0%, 96.3–100.1%, and 95.5%), and high selectivity with a small sample volume requirement (0.2 mL) and short run time (15 min). The validated method was successfully applied in a clinical pharmacodynamic study of warfarin, and the clotting activity was found to be negatively correlated with the plasma concentration ratio of VK 1 O to VK 1 .