DISCRIMINATION IN ABSORPTION OR TRANSPORT OF BETA-CAROTENE ISOMERS AFTER ORAL SUPPLEMENTATION WITH EITHER ALL-TRANS-BETA-CAROTENE OR 9-CIS-BETA-CAROTENE

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 c onsists of a 50:50 mixture of all-trans- and 9-cis-beta-carotene. This loading dose was followed by a 23-d maintenance dose consisting of al ternate-day supplementation with 50 mg all-trans-beta-carotene or eith er 66 or 100 mg of the natural 50:50 isomeric mixture. The loading dos e resulted in significant increases in plasma concentrations of both i somers, 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 i n 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 sm all fraction of the total plasma beta-carotene. Results after an addit ional 23-d period of alternate-day supplementation were not significan tly different from those described above for the 6-d supplementation. Increases in low-density-lipoprotein concentrations of total beta-caro tene correlated strongly with the increases seen in plasma concentrati ons. Lipid-soluble antioxidants vitamin E and ubiquinol were unaffecte d by beta-carotene supplementation. However, the amount of lycopene in the low-density lipoprotein decreased during this supplementation per iod. A strong discrimination between these two geometric isomers of be ta-carotene was demonstrated, although the tissue site of discriminati on was not determined.