title: Discrimination in absorption or transport of beta-carotene isomers after oral supplementation with either all-trans- or 9-cis-beta-carotene.
abstract: Human subjects (n = 24) were supplemented with 100 mg beta-carotene/d for 6 d, either as synthetic all-trans-beta-carotene or a natural beta-carotene preparation derived from the alga Dunaliella salina, which consists of a 50:50 mixture of all-trans- and 6-cis-beta-carotene. This loading dose was followed by a 23-d maintenance dose consisting of alternate-day supplementation with 50 mg all-trans-beta-carotene or either 66 or 100 mg of the natural 50:50 isomeric mixture. The loading dose resulted in significant increases in plasma concentrations of both isomers, with the all-trans-beta-carotene-supplemented group showing a 7.2- and 5.0-fold increase in the all-trans and 9-cis concentrations in plasma, respectively. The group receiving the 50:50 mixture showed a 4.0- and 3.7-fold increase in the all-trans and 9-cis concentrations in plasma, respectively, without any apparent dose-dependency. However, even with the 50:50 mixture, the 9-cis concentrations were only a small fraction of the total plasma beta-carotene. Results after an additional 23-d period of alternate-day supplementation were not significantly different from those described above for the 6-d supplementation. Increases in low-density-lipoprotein concentrations of total beta-carotene correlated strongly with the increases seen in plasma concentrations. Lipid-soluble antioxidants vitamin E and ubiquinol were unaffected by beta-carotene supplementation. However, the amount of lycopene in the low-density lipoprotein decreased during this supplementation period. A strong discrimination between these two geometric isomers of beta-carotene was demonstrated, although the tissue site of discrimination was not determined.
authors.affiliation: Division of Preventive Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02111-1837, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Gaziano
authors.forename: E J
authors.initials: EJ
authors.lastname: Johnson
authors.forename: R M
authors.initials: RM
authors.lastname: Russell
authors.forename: J E
authors.initials: JE
authors.lastname: Manson
authors.forename: M J
authors.initials: MJ
authors.lastname: Stampfer
authors.forename: P M
authors.initials: PM
authors.lastname: Ridker
authors.forename: B
authors.initials: B
authors.lastname: Frei
authors.forename: C H
authors.initials: CH
authors.lastname: Hennekens
authors.forename: N I
authors.initials: NI
authors.lastname: Krinsky
mesh_terms: D000284:Administration, Oral; D000328:Adult; D000975:Antioxidants / Q000493:pharmacokinetics*; D001682:Biological Availability; D001692:Biological Transport; D002338:Carotenoids / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics*; D002851:Chromatography, High Pressure Liquid; D004311:Double-Blind Method; D006801:Humans; D007408:Intestinal Absorption; D008077:Lipoproteins, LDL / Q000097:blood; D013237:Stereoisomerism; D014810:Vitamin E / Q000097:blood; D019207:beta Carotene
chemical_list: D000975:Antioxidants; D008077:Lipoproteins, LDL; D019207:beta Carotene; D014810:Vitamin E; D002338:Carotenoids