Activation of TAS1R3 in undifferentiated Caco-2 cells by aspartame and sucralose has been associated with increased intestinal permeability. However, the impact of a chronic treatment of Caco-2 cells during differentiation to an enterocyte-like phenotype with physiological relevant concentrations of sweeteners in comparison to sugar is not known yet. Here, we investigated the long-term effects of sucrose and the selected non-caloric sweeteners Rebaudioside M, Sucralose, and NHDC on the intestinal barrier function using Caco-2 cells and a coculture of Caco-2 and mucus producing HT29-MTX-E12 cells, which more closely resembles the physiological conditions. The transepithelial electrical resistance and the permeability of the fluorescent dye Lucifer Yellow (LY) as markers for the barrier function were measured after treatment with the test compounds in two concentrations (equisweet to 5% sucrose and equimolar 0.1 mM) on day 7, 14, and 21 of cultivation. Effects of the treatments on selected tight-junction proteins were determined with qRT-PCR and immunostaining.
Treatment with 150 mM sucrose led to an increase in the permeability of LY compared to the control in both cell models, the highest increase was on day 7 in the monoculture (176 ± 34 %). An osmotic effect of sucrose was excluded, as well as an effect of the sweetness and the sweet taste receptor TAS1R3 by using the TAS1R3 inhibitor lactisole. However, treatment with 150 mM sucrose led to a decrease of CLDN2 and an increase in gene expression of TJP1, CLDN1, OCLN, and F11R, which may argue for a counter-regulatory effect. Overall, the coculture showed a higher resistance to osmotic stress and treatment with the test compounds than the monoculture.
In conclusion, treatment with sucrose showed a dose- and time-dependent effect on intestinal permeability independent of TAS1R3 and osmotic pressure, with potential protective effect of the mucus layer.