An LC/MS/MS method for stable isotope dilution studies of β-carotene bioavailability, bioconversion, and vitamin A status in humans

Isotope dilution is currently the most accurate technique in humans to determine vitamin A status and bioavailability/bioconversion of provitamin A carotenoids such as beta-carotene. However, limits of MS detection, coupled with extensive isolation procedures, have hindered investigations of physiologically-relevant doses of stable isotopes in large intervention trials. Here, a sensitive liquid chromatography-tandem mass spectrometry (LC/MS/MS) analytical method was developed to study the plasma response from coadministered oral doses of 2 mg [C-13(10)]beta-carotene and 1 mg [C-13(10)]retinyl acetate in human subjects over a 2 week period. A reverse phase C-18 column and binary mobile phase solvent system separated beta-carotene, retinol, retinyl acetate, retinyl linoleate, retinyl palmitate/retinyl oleate, and retinyl stearate within a 7 min run time. Selected reaction monitoring of analytes was performed under atmospheric pressure chemical ionization in positive mode at m/z 537 -> 321 and m/z 269 -> 93 for respective [C-12]beta-carotene and [C-12]retinoids; m/z 547 -> 330 and m/z 274 -> 98 for [C-13(10)]beta-carotene and [C-13(5)] cleavage products; and m/z 279 -> 100 for metabolites of [C-13(10)]retinyl acetate. 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. Coadministration of [C-13(10)]retinyl acetate with [C-13(10)]beta-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. Refereed/Peer-reviewed