Beta-carotene uptake and metabolism in human lung bronchial epithelial cultured cells depending on delivery vehicle

Beta-carotene (BC) could have a protective or pro-carcinogenic role in lung cancer, and cell culture systems are important to evaluate it. Nevertheless, the delivery of the hydrophobic BC to cells is difficult. Different vehicles have been used such as liposomes, tetrahydrofuran and serum lipoproteins, but presenting different problems. Water dispersible beadlets containing BC are a good choice and can produce the greatest BC uptake when compared to the above vehicles, but other beadlet components could alter the results. Dimethylsulfoxide (DMSO) could be a good alternative since it has low toxicity and it enhances the penetration of substances across biologic membranes. We aimed to characterize an appropriate model for delivering all-trans-BC to lung cells in culture and knowing its metabolism. All-trans-BC 5 μM was administered to BEAS-2B cells in beadlets or DMSO, and medium and cell samples were taken at different times. The levels of BC and its main isomers and metabolites were determined by HPLC. All-trans-BC reached the same levels in the medium (about 3.5 μM) either when supplied in beadlets or in DMSO, and, with beadlets, 13-cis-BC was also detected. However the amount of all-trans-BC taken up by the cells was the triple when delivered by DMSO. With both vehicles, intracellular all-trans-BC levels reached its maximum after 24 h of treatment, remaining equal after 72 h. The 9-cis and 13-cis isomers of BC, and oxidized metabolites, were also detected in the cells although in smaller proportion than all-trans-BC, especially with DMSO. An LDH assay did not suggest toxicity of beadlets, DMSO or BC itself. In conclusion, DMSO seems the most appropriate vehicle for delivering BC to lung cells in vitro, and we present a model that allows studying the effects of BC and its metabolism in the lung human BEAS-2B cell line.