Cell Culture Model for Examining Fat-Soluble Nutrient Absorption <i>In Vitro</i>

Abstract

Permeable support systems (PS) are employed in in vitro nutrient absorption studies but data are absent on their efficacy compared to conventional cell culture models (CONV). The in vivo absorption of fat soluble nutrients is influenced by its delivery vehicle, yet a fundamental understanding of the influence of the vehicle on cells in culture is lacking. We compared the efficacy of lutein absorption in Caco-2 cells cultured with CONV and PS, and examined the role of micelles, the physiological vehicle within the small intestine. After plating for 2 and 21 d to attain confluence and differentiation in CONV and PS, respectively, cells were treated with lutein in micelles or ethanol. After incubation, lutein in cell lysate, as well as apical and basolateral mediums, were quantified by HPLC-UV. After 24 h, cellular lutein in CONV was ≥460 and 8% greater in ethanol and micelle, respectively, than in PS. However, the intracellular AUC over time was only different for ethanol (P ≤ 0.05). In PS, 0.15% of micellized lutein was secreted into the basolateral medium in contrast to 0.016% of lutein in ethanol. The absorption of lutein (uptake + secretion), independent of the vehicle, in CONV increased in a linear manner with dose (0.35 to 4 or to 14.6 µg/mL for ethanol or micelle, respectively), while that in PS peaked at 1.18 μg/mL. Caco-2 cells cultured in PS grow to display the phenotype and function of small intestine enterocytes and suggest this in vitro platform generates information closest to the natural physiology of the absorptive process. However, although the CONV has the physiology of colonic tissue, it appears to display a greater efficacy for lutein uptake by Caco-2 cells and so can provide a more rapid, preliminary method for nutrient absorption studies.