Abstract
The human Caco-2 cell monolayer model was used to investigate the absorption property, mechanism, and structure-property relationship of seven representative flavonoids, namely, orientin, vitexin, 2”-O-β-L-galactopyranosylorientin, 2”-O-β-L-galactopyranosylvitexin, isoswertisin, isoswertiajaponin, and 2”-O-(2”‘-methylbutanoyl)isoswertisin from the flowers of Trollius chinensis. The results showed that these flavonoids were hardly transported through the Caco-2 cell monolayer. The compounds with 7-OCH3 including isoswertisin, isoswertiajaponin and 2”-O-(2”‘-methylbutanoyl)isoswertisin were absorbed in a passive diffusion manner, and their absorbability was increased in the same order as their polarity. The absorption of the remaining compounds with 7-OH including orientin, vitexin, 2”-O-β-L-galactopyranosylorientin, and 2”-O-β-L-galactopyranosylvitexin involved transporter mediated efflux in addition to passive diffusion. Among the four compounds with 7-OH, those with a free hydroxyl group at C-2” such as orientin and vitexin were the substrates of P-glycoprotein (P-gp) and that with a free hydroxyl group at C-2’ such as 2”-O-β-L-galactopyranosylorientin was the substrate of multidrug resistance protein 2 (MRP2). The results of this study also implied that the absorbability of the flavonoids should be taken into account when estimating the effective components of T. chinensis.
Highlights
The flowers of Trollius chinensis, which mainly contain flavonoids, phenolic acids and alkaloids [1,2], have been used by Chinese people for the treatment of respiratory infections, pharyngitis, tonsillitis, and bronchitis since ancient time [3]
Orientin showed potent inhibitory effect against both Staphylococcus aureus and S. epidermidis with the MIC values of 25 mg/L, and vitexin demonstrated potent to moderate effect against those two bacteria with the MIC values of 100 mg/L toward S. aureus and 25 mg/L toward S. epidermidis, respectively [14,15,16,17]. 2”-O-(2”‘-methylbutanoyl)isoswertisin exhibited anti-inflammatory effect with an inhibitory rate of 35.5% on murine ear edema model [18], and orientin and vitexin were proven by our research group to possess anti-inflammatory effects against murine ear edema [19]
The Caco-2 cell monolayer model established was validated for the assessment of the intestinal absorption potential of the compounds of interest
Summary
The flowers of Trollius chinensis, which mainly contain flavonoids, phenolic acids and alkaloids [1,2], have been used by Chinese people for the treatment of respiratory infections, pharyngitis, tonsillitis, and bronchitis since ancient time [3]. Chinese herbal drugs are usually used through oral administration This renders intestinal absorption very crucial to the evaluation of the bioactivity of these flavone C-glycosides and their contributions to the efficacy of these flowers. For this reason, we selected the seven flavonoids mentioned above (Fig. 1) to investigate their absorption properties and mechanisms, as well as the structure-absorbability relationship using the well-recognized human Caco-2 cell monolayer model, so as to predict their bioavailability and facilitate the correct understanding of their contribution to the efficacy of these flowers
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