Lipid excipients as key modulators of the apparent intestinal permeability in lipid-based formulations: Insights from Caco-2 and Caco-2/HT29-MTX models

Lipid-based formulations (LBFs) represent a promising strategy to improve the oral absorption of poorly soluble and poorly permeable compounds, such as BCS Class IV drug. Nevertheless, the development of lipid formulations requires predictive in vitro models that closely mimic in vivo physiology, allowing for more reliable estimation of oral absorption. Permeability studies using culture cells monolayers can contribute to evaluate the influence of formulation components as well as the interplay between solubilisation and permeation. In this study, the cytotoxicity of ticagrelor, a BCS class IV drug, and placebo formulations was first assessed in Caco-2 cells, and selected LBFs were subsequently validated in both Caco-2 monoculture and Caco-2/HT29-MTX co-culture. The apparent permeability (Papp) was estimated using the well-established Caco-2 monoculture model and the more innovative Caco-2/HT29-MTX co-culture, which incorporates mucus secretion to better mimic the intestinal barrier. LC/MS analysis from permeability studies revealed that the apparent permeability coefficient of the pure API (1.02 × 10^-7 cm/s for monoculture and 1.25 × 10^-7 cm/s for co-culture) was significantly enhanced, by a factor ranging from 4.6 to 9.4 for monoculture, and from 2.1 to 6.6 for co-culture, when formulated in LBFs. The inclusion of permeation enhancers in the LBFs increased Papp values compared for LBFs without permeation enhancers. Overall, a decrease in permeability was observed in the co-culture model due to the mucus barrier, although this reduction was not statistically significant for the majority of tested formulations.