A stable isotope method for the simultaneous measurement of vitamin [K.sub.1] (phylloquinone) kinetics and absorption

Objectives: To measure uptake and disposal kinetics and absolute absorption of vitamin K, using two stable isotope-labelled forms of vitamin [K.sub.1]. Subjects: Ten subjects (nine women and one man) aged between 22 and 31 years, with a mean ([+ or -] standard deviation) body mass index of 22.5 [+ or -] 2.4 kg/[m.sup.2]. Subjects took capsules containing 3 [micro]g of methyl-[sup.13]C vitamin [K.sub.1], three times a day for six days to reach a steady state for plasma vitamin [K.sub.1]. isotopic enrichment. On day seven, subjects were given an intravenous dose of Konakion MM to measure disposal kinetics and at the same time, a capsule containing 4 [micro]g of ring-[D.sub.4] vitamin [K.sub.1] to measure absorption. Plasma vitamin [K.sub.1] concentration was measured by high-performance liquid chromatography and isotopic composition by gas chromatography mass spectrometry. Results: The disposal kinetics of the intravenous dose of vitamin [K.sub.1] were resolved into two exponentials with half-times of 0.22 ([+ or -] 0.14) and 2.66 ([+ or -] 1.69) h. Absorption of oral, deuterated vitamin [K.sub.1] was 13 ([+ or -] 9) %. Conclusions: Two-compartmental kinetic parameters observed in this study are similar to those obtained previously using radioactive tracers, but there may be additional slow-turnover body pools acting as stores of vitamin [K.sub.1]. The kinetic parameters determined from the intravenous dose allowed determination of the absolute absorption of vitamin [K.sub.1] from a bolus oral dose. doi:10.1038/sj.ejcn.1602859; published online 1 August 2007 Keywords: vitamin [K.sub.1]; phylloquinone; stable isotope; kinetics; absorption
Introduction Vitamin K is a fat-soluble vitamin required as a cofactor in the post-translational carboxylation of glutamic acid to [gamma]-carboxyglutamic acid in vitamin K-dependent (VKD) proteins. VKD proteins were originally [...]