Intestinal absorption of hawthorn flavonoids--in vitro, in situ and in vivo correlations

Our previous studies identified hyperoside (HP), isoquercitrin (IQ) and epicatechin (EC) to be the major active flavonoid components of the hawthorn phenolic extract from hawthorn fruits demonstrating inhibitory effect on in vitro Cu(+2)-mediated low density lipoproteins oxidation. Among these three hawthorn flavonoids, EC was the only one detectable in plasma after the oral administration of hawthorn phenolic extract to rats. The present study aims to investigate the intestinal absorption mechanisms of these three hawthorn flavonoids by in vitro Caco-2 monolayer model, rat in situ intestinal perfusion model and in vivo pharmacokinetics studies in rats. In addition, in order to investigate the effect of the co-occurring components in hawthorn phenolic extract on the intestinal absorption of these three major hawthorn flavonoids, intestinal absorption transport profiles of HP, IQ and EC in forms of individual pure compound, mixture of pure compounds and hawthorn phenolic extract were studied and compared. The observations from in vitro Caco-2 monolayer model and in situ intestinal perfusion model indicated that all three studied hawthorn flavonoids have quite limited permeabilities. EC and IQ demonstrated more extensive metabolism in the rat in situ intestinal perfusion model and in vivo study than in Caco-2 monolayer model. Moreover, results from the Caco-2 monolayer model, rat in situ intestinal perfusion model as well as the in vivo pharmacokinetics studies in rats consistently showed that the co-occurring components in hawthorn phenolic extract might not have significant effect on the intestinal absorption of the three major hawthorn flavonoids studied.