Kinetics of ¹⁴C distribution after tracer dose of ¹⁴C‐lutein in an adult woman

Abstract

Lutein is an oxygenated carotenoid (xanthophyll) found in dark green leafy vegetables. High intakes of lutein may lower the risk of age-related macular degeneration. Current understanding of human lutein metabolism as it might occur in vivo is incomplete. Therefore, we conducted a feasibility study where we dosed a normal adult woman with 14C-lutein (125 nmol, 36 nCi 14C), dissolved in olive oil (0.5 g/kg body weight) and mixed in a banana shake. Blood, urine, and feces collected before the dose was administered served to establish baseline values. Thereafter, blood was collected for 63 d following the dose, while feces and urine were collected for 2 wk post-dose. The 14C contents in plasma, urine, and feces were measured by accelerator MS. The 14C first appeared in plasma 1 h after dosing and reached its highest level, approximately2.08% of dose/L plasma, at 14 h post-dose. The plasma pattern of 14C did not include a chylomicrons/VLDL (intestinal) peak like that when the same subject received 14C-beta-carotene (a previous test), suggesting that lutein was handled differently from beta-carotene by plasma lipoproteins. Lutein had an elimination half-life (t1/2) of approximately10 d. Forty-five percent of the dose of 14C was eliminated in feces and 10% in urine in the first 2 d after dosing. Quantifying human lutein metabolism is a fertile area for future research.

Excentral cleavage of β-carotene in vivo in a healthy man

“…All chemicals were checked for 14 C content by AMS before use. Tributyrin (glycerol tributyrate) was obtained from MP Biomedical (Aurora, OH).…”

“…They included retinol, retinyl palmitate, and retinyl oleate that were monitored at 325 nm; 13-cis-RA and all-trans-RA that were monitored at 351 nm; and ␤-apo-12Ј-carotenal, ␤-apo-8Ј-carotenal, ␤-carotene-5,6-epoxide, and all-trans-␤-carotene that were monitored at 450 nm. The parent compound, 14 C-␤-carotene, and its 14 C-metabolites 14 C-retinol, 14 C-retinyl palmitate, and 14 C-␤-apo-8Ј-carotenal were separated with the use of the above standardized HPLC system.…”

“…An aliquot of urine was prepared for 14 C analysis by diluting 100 L of the sample with 900 L HPLC-grade water. Aliquots of diluted urine (100 L) and feces (75 L) were placed in quartz tubes and processed as described for the 20-s RP-HPLC fractions.…”

“…The fractional absorption, as well as the metabolic fate and elimination of 14 C-␤-carotene, was also measured in the present study.…”

“…However, the conversion of ␤-carotene by BCO2 to other metabolites, such as ␤-apo-8Ј-, 10Ј-, 12Ј-, and 14Ј-carotenals, and retinoic acids (RAs), remains to be determined. Access to accelerator mass spectrometry (AMS) that can measure attomole amounts (1 in 10 Ҁ18 parts) of 14 C (11) enabled us to conduct a feasibility study that tested the hypothesis of whether a healthy man can derive 14 C-retinoids and 14 C-apocarotenoids from a true tracer oral dose of all-trans [10,10Ј,11,11Ј-14 C]-␤-carotene (1.01 nmol; 543 ng; 100 nCi). The radiation exposure is low, Ȃ 200 nseivert.…”