In vitro transport studies of Hawthorn procyanidins by Caco-2 monolayers: transport and efflux

Extracts from Hawthorn (Crataegus sp.) are considered as a rational based phytomedicine for declining cardiac performance, with flavonoids and procyanidins as active compounds. Especially oligomeric procyanidins (OPC) are assessed to have the most marked pharmacodynamic effects. Detailed investigations on the bioavailability of procyanidins after oral ingestion are not available. The current study was designed to investigate the absorption of OPC from different fractions/extracts of Crataegi folium cum flore using validated monolayers of the human Caco-2 cell line grown in Transwells. Respective concentrations of distinct OPC clusters were determined in the basolateral and apical compartments and in cell lysates of Caco-2 cells. Quantitation was performed by HPLC on diol stationary phase with fluorescence detection.

No significant absorption of OPCs with degree of polymerization (DP) ≥2 into the basolateral compartments was observed after apical application of 125–250µg/mL, but OPC with DP 6 to 9 were detected in the respective cell lysates. Interestingly, transport of procyanidin B2 in the basolateral → apical direction was higher than that in the apical → basolateral direction, indicating efflux transporters carrying out OPCs after initial absorption to the apical side. This hypothesis was clearly proven by use of verapamil, a P-glycoprotein inhibitor in the absorption assay together with OPC as shown with B2: data from these experiments proved an increased apical → basolateral absorption of B2. These data clearly prove the suitability of the Caco-2 system for transport studies of polyphenols and indicate that intestinal OPC absorption is subjected to an efflux competition.