title: Use of a 13C tracer to investigate lutein as a ligand for plasma transthyretin in humans.
abstract: The selective accumulation of lutein in the macula of the human retina is likely to be mediated by specific transport and/or binding proteins. Our objective was to determine whether transthyretin (TTR) is a plasma transport protein for lutein. We used a biosynthetic 13C-lutein tracer and GC-combustion interfaced-isotope ratio MS to gain the requisite sensitivity to detect the minute amounts of lutein expected as a physiological ligand for TTR. Subjects (n = 4) each ingested 1 mg of 13C-lutein daily for 3 d and donated blood 24 h after the final dose. For three subjects, the plasma TTR-retinol-binding protein (RBP) complex was partially purified by anion-exchange (diethylaminoethyl, DEAE) chromatography and then dissociated by hydrophobic-interaction chromatography to yield the TTR component. For subject 4, the initial DEAE purification step was omitted and total plasma TTR (RBP-bound and free) was isolated by hydrophobic-interaction chromatography. In each case, the crude TTR fractions were then purified to homogeneity by RBP-Sepharose affinity chromatography. Pure TTR was extracted with chloroform, and unlabeled lutein was added to the extract as a carrier. The mean 13C/12C ratio (expressed in delta notation, delta13C) of the lutein fraction isolated from the plasma TTR extracts of the four subjects was -30.53 +/- 3.29 per thousand. The delta13C value of the unlabeled lutein carrier was -30.97 +/- 0.27per thousand. Thus, no 13C enrichment was detected in association with TTR. We conclude that lutein is not associated with TTR in human plasma after being ingested in physiological amounts.
authors.affiliation: Center for Designing Foods to Improve Nutrition, Iowa State University, Ames 50011, USA.
authors.forename: Liwei
authors.initials: L
authors.lastname: Chen
authors.forename: Xixuan Hu
authors.initials: XH
authors.lastname: Collins
authors.forename: Louisa B
authors.initials: LB
authors.lastname: Tabatabai
authors.forename: Wendy S
authors.initials: WS
authors.lastname: White
mesh_terms: D000284:Administration, Oral; D000328:Adult; D015153:Blotting, Western; D002247:Carbon Isotopes; D002352:Carrier Proteins / Q000097:blood / Q000302:isolation & purification / Q000378:metabolism; D002846:Chromatography, Affinity; D005260:Female; D006801:Humans; D008024:Ligands; D014975:Lutein / Q000008:administration & dosage* / Q000378:metabolism; D013058:Mass Spectrometry; D011228:Prealbumin / Q000302:isolation & purification / Q000378:metabolism*; D012177:Retinol-Binding Proteins / Q000032:analysis / Q000378:metabolism; D054839:Retinol-Binding Proteins, Plasma; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet
chemical_list: D002247:Carbon Isotopes; D002352:Carrier Proteins; D008024:Ligands; D011228:Prealbumin; D012177:Retinol-Binding Proteins; D054839:Retinol-Binding Proteins, Plasma; D014975:Lutein