HUMAN LIPOPROTEINS AS A VEHICLE FOR THE DELIVERY OF BETA-CAROTENE ANDALPHA-TOCOPHEROL TO HEPG2 CELLS

Highly differentiated human cell lines represent a useful in vitro mod el for the study of carotenoid uptake, metabolism, and function. Carot enoids are usually introduced into tissue culture media either in orga nic solvents or as micelles, whereas carotenoids are localized in lipo proteins in vivo. Initially, the stability of beta-carotene and alpha- tocopherol in micelles and human lipoproteins under standard tissue cu lture conditions was compared, Recovery of beta-carotene and alpha-toc opherol was 27% +/- 2% and 73% +/- 2%, respectively, after overnight i ncubation of micellar beta-carotene and alpha-tocopherol in serum-free medium without cells. This marked loss of beta-carotene was attenuate d by inclusion of alpha-tocopherol in micelles, In contrast, recovery of beta-carotene and alpha-tocopherol was 88%-95% when medium containi ng the total lipoprotein fraction isolated from beta-carotene suppleme nted individuals was incubated overnight without cells, Cellular accum ulation of beta-carotene and alpha-tocopherol from medium containing t otal lipoproteins (1 mg/ml) was proportional to their concentrations i n the lipoprotein fraction (r = 0.94 for beta-carotene and 0.74 for al pha-tocopherol). Cells exhibited similar capability of acquiring beta- carotene and alpha-tocopherol from medium containing either low- or hi gh-density lipoproteins. These data show that lipoproteins represent a stable vehicle for delivery of beta-carotein and alpha-tocopherol to HepG2 human liver cells.