Use of a C-13 tracer to quantify the plasma appearance of a physiological dose of lutein in humans

Increased intake of lutein from vegetables promotes increased density of th e macular pigment and therefore may protect against age-related macular deg eneration. Our objective was to use a C-13 tracer and high-precision gas ch romatography-combustion interfaced-isotope ratio mass spectrometry (GC-C-IR MS) to investigate metabolism of a lutein dose equivalent to that absorbed from vegetables. Biosynthetic per-labeled (>99% C-13) lutein was purified f rom a commercially available extract of algal biomass. Subjects (n = 4) ing ested 3 mg of [C-13]lutein with a standardized low-carotenoid breakfast. Bl ood samples were collected at baseline and then hourly for 12 h; additional blood samples were drawn at 16, 24, 48, 72, 96, 192, 360, and 528 h. To pr oduce perhydro-beta-carotene suitable for analysis by GC-C-IRMS, the plasma lutein fraction was hydrogenated on palladium-on-carbon catalyst with acid -catalyzed hydrogenolysis. The stable carbon isotope (C-13/C-12) ratio meas ured by GC-C-IRMS was used to calculate the plasma concentration of [C-13]l utein. There was a rapid increase in [C-13]lutein in plasma until peak enri chment at 16 h followed by a decline to the next measurement at 24 h. At 52 8 h, small changes in C-13 enrichment from baseline could still be measured in plasma lutein. High-precision GC-C-IRMS enables complete definition of the appearance and disappearance of [C-13]lutein in plasma after ingestion of a dose similar to that absorbed from foods.