Comparison of micelles and human lipoproteins as vehicles for delivery of β-carotene and α-tocopherol to hepg2 human liver cells


Highly differentiated cell lines represent a useful in vitro model for the study of carotenoid uptake, metabolism and function. These compounds are usually introduced into tissue culture media either in organic solvents or as micelles, whereas the carotenoids are localized in lipoproteins (LP) in plasma. Initially, the stability of p-carotene (BC) and α-tocopherol (α-TC) in micelles and LP under standard tissue culture conditions was compared. After overnight incubation of filtered (0.22 nmeter pore) micellar preparations of BC and α-TC in serum-free MEM without cells, recovery of BC and ix-TC was 27+2 and 73 ± 2%, respectively. In contrast, recovery of BC and α-TC was 88-95% when MEM containing LP (1 mg/mL) isolated from control and BC supplemented Individuals (60 mg/day for 4 weeks) was incubated overnight without cells. The substantial loss of BC from micelle-containing medium was the result of oxidation, since BC recovery was markedly increased by inclusion of α-TC in micelles. Incubation of confluent cultures of HepG2 human liver cells with micelles containing 1 nM BC or α-TC increased cellular levels from < 0.02 to 0.17 and < 0.03 to 0.42 g/mg protein, respectively. Cellular accumulation of BC and α-TC from medium containing 1 mg LP/mL was proportional to the concentrations of the hydrophobic compounds (r=0.93 for BC and 0.68 for α-TC). Similarly, cellular levels of BC and α-TC were proportional to the concentration of BC and α-TC in medium containing either low density LP (r=0.81 for BC; r=0.66 for α-TC) or high density LP (r=0.95 for BC; r=0.85 for α-TC). These data show that human lipoproteins represent a stable vehicle for the delivery of BC and α-TC to HepG2 cells. (Supported in part by North Carolina Institute of Nutrition).

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FASEB Journal

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