Cellular levels of all-trans-beta-carotene under the influence of 9-cis-beta-carotene in FU-5 rat hepatoma cells.

After incubation of FU-5 hepatoma cells for 46.5 h with synthetic all-trans-beta-carotene (3.5 microM) dissolved in tetrahydrofuran, the beta-carotene level in the cells amounted to 0.24 nmol/mg protein. No interconversion from all-trans to cis isomers occurred during incubation. Upon incubation with 3.5 microM synthetic 9-cis-beta-carotene, only 0.03 nmol 9-cis-beta-carotene/mg protein was detected in the cells. With a mixture of synthetic all-trans- (3.5 microM) and 9-cis-beta-carotene (1.0 microM), 0.09 nmol all-trans- and 0.02 nmol 9-cis-beta-carotene/mg protein were incorporated into the cells. These data suggest that 9-cis-beta-carotene and/or its decomposition products inhibited the uptake or influenced the metabolism of all-trans-beta-carotene. Thus, the lack of an increase in human serum levels of 9-cis-beta-carotene upon intake of a mixture of all-trans- and cis-beta-carotene isomers dissolved in soybean oil, Betatene (Stahl et al. (1993) J. Nutr. 123, 847-851), may be due to particular biokinetic or metabolic parameters for cis isomers of beta-carotene as compared to all-trans-beta-carotene.