Transport rates of dietary phytochemicals in cell monolayers is inversely correlated with absorption kinetics in humans

Dietary phytochemicals promote health and reduce the risk of chronic disease. The Phytochemical Absorption Prediction Model (PCAP) predicts the time required for phytochemicals to reach maximal plasma concentrations (T_max) in humans based on their lipophilicity and molecular mass. Cell-based transport models have been used to quantify transport rate and efficiency of pharmaceuticals and phytochemicals, however these parameters have not previously been related to the human absorption T_max. Caco-2/HT29-MTX-E12 monolayers were used to characterise transport of phytochemical standards and extracts and to establish a relationship between the in vitro permeability (P_app) of standards and their in vivo T_max predicted from the PCAP model. Lipophilic compounds transported through the cell monolayer at relatively faster rates (higher P_app) than hydrophilic compounds, whilst having slower predicted in vivo absorption rates (longer T_max). The results infer differences between in vitro (cell monolayer) and in vivo (human gastrointestinal tract) absorption kinetics of phytochemicals.