Human Lipoproteins as a Vehicle for the Delivery of β-Carotene and α-Tocopherol to HepG2 Cells 1

Abstract

Abstract

Highly differentiated human cell lines represent a useful in vitro model for the study of carotenoid uptake, metabolism, and function. Carotenoids are usually introduced into tissue culture media either in organic solvents or as micelles, whereas carotenoids are localized in lipoproteins in vivo. Initially, the stability of β-carotene and α-tocopherol in micelles and human lipoproteins under standard tissue culture conditions was compared. Recovery of β-carotene and α-tocopherol was 27% ± 2% and 73% ± 2%, respectively, after overnight incubation of micellar β-carotene and α-tocopherol in serum-free medium without cells. This marked loss of β-carotene was attenuated by inclusion of α-tocopherol in micelles. In contrast, recovery of β-carotene and α-tocopherol was 88%–95% when medium containing the total lipoprotein fraction isolated from β-carotene supplemented individuals was incubated overnight without cells. Cellular accumulation of β-carotene and α-tocopherol from medium containing total lipoproteins (1 mg/ml) was proportional to their concentrations in the lipoprotein fraction (r = 0.94 for β-carotene and 0.74 for α-tocopherol). Cells exhibited similar capability of acquiring β-carotene and α-tocopherol from medium containing either low- or high-density lipoproteins. These data show that lipoproteins represent a stable vehicle for delivery of β-carotein and α-tocopherol to HepG2 human liver cells.