Robert Joseph Sarama

Estimation of carotenoid bioavailability from fresh stir-fried vegetables using an in vitro digestion/ Caco-2 cell culture model

We previously developed an in vitro model to estimate the relative bioavailability of carotenoids from a meal prepared using commercial baby foods. The general applicability of this model was tested using a stir-fried meal consisting of fresh spinach, fresh carrots, tomato paste, and vegetable oil. After in vitro digestion of the cooked meal, the aqueous fraction was separated from residual oil droplet and solids by centrifugation to quantify micellarized carotenoids. The percentages of lutein, lycopene, alpha-carotene, and beta-carotene transferred from the meal to the micellar fraction were 29.0 +/- 0.6, 3.2 +/- 0.1, 14.7 +/- 0.3, and 16.0 +/- 0.4, respectively. Carotenoid transfer from the meal to the aqueous fraction was inhibited when bile extract was omitted from the intestinal phase of digestion. The bioavailability of the micellarized carotenoids was validated using differentiated cultures of Caco-2 human intestinal cells. All four carotenoids were accumulated in a linear manner throughout a 6-hr incubation period. Metabolic integrity was not compromised by exposure of cultures to the diluted aqueous fraction from the digested meal. The addition of 500 µmol/L alpha-tocopherol to test medium significantly improved the stability of the micellar carotenoids within the tissue culture environment. These results support the utility of the in vitro digestion procedure for estimating the bioavailability of carotenoids from foods and meals.

Accumulation and retention of micellar β-carotene and lutein by Caco-2 human intestinal cells

Despite the interest in the diverse roles of dietary carotenoids in human health, little is known about the transfer of these plant pigments from foods to micelles during digestion and their subsequent transfer across the intestinal epithelium. We conducted this study to characterize the intestinal uptake of micellarized carotenoids using monolayers of differentiated Caco-2 human intestinal cells. Crystalline beta-carotene (BC) and lutein (LUT), solubilized in mixed micelles for delivery to cells, were stable in a tissue culture environment for 20 hours. Cellular accumulation of micellar BC and LUT was proportional to the media content of carotenoids at </=2 micromol/L and the length of exposure. Cellular accumulation of BC routinely exceeded LUT and was due in part to the enhanced efflux or possible metabolism of LUT. Cellular BC content increased in a curvilinear manner when cultures were incubated in micellar medium containing 2 to 27 micromol/L BC prepared from water miscible beadlets; cellular BC content was maximum when medium BC was >/=18 micromol/L. There was no indication that high levels of BC in medium or within cells adversely affected micellar LUT accumulation. These data support the use of the Caco-2 human cell line as a model for studying the intestinal uptake, absorption, and possible interactions of dietary carotenoids.