Isotope dilution is currently the most accurate technique in humans to determine vitamin A status and bioavailability/bioconversion of provitamin A carotenoids( 1 ). However, limits of MS detection, coupled with extensive isolation procedures, have hindered investigations of physiologically-relevant doses of stable isotopes( 2 ). We developed a sensitive liquid chromatography-tandem-mass spectrometry (LC-MS/MS) analytical method to study the plasma response from co-administered oral doses of 2 mg [13C10]-β-carotene and 1 mg [13C10]-retinyl acetate in human subjects. A single one-phase solvent extraction, with no saponification or purification steps, left retinyl esters intact for determination of intestinally-derived retinol in chylomicrons versus retinol from the liver bound to retinol-binding protein (RBP).
Co-administration of [13C10]-retinyl acetate with [13C10]-β-carotene not only acts as a reference dose for inter-individual variations in absorption and chylomicron clearance rates, but also allows for simultaneous determination of an individual's vitamin A status. In summary, this new analytical method enables the detection of physiological concentrations of provitamin A carotenoids, their cleavage products as well as preformed vitamin A for a period of at least 2 weeks post dose administration and allows high throughput analysis due to its simplicity and short run times.
This work was supported by the BBSRC.