Certain polyphenols exhibit low permeability; precise prediction of their intestinal absorption is important for understanding internal exposure in humans. Intestinal availability, which represents the fraction of administered compounds that reach the portal blood (FaFg), is calculated by dividing bioavailability (F) by hepatic availability (Fh), and F is obtained from pharmacokinetic data from both intravenous (i.v.) and oral (p.o.) administration. However, human FaFg of polyphenols is hardly reported, as human i.v. data are extremely scarce. In this study, we developed an estimation method for FaFg of polyphenols in humans based on the extrapolation of rat clearance using allometric scaling (allometric scaling-based FaFg calculation method, AS- FaFgCM). First, for quercetin, for which human i.v. data have been reported, we compared the FaFg obtained by AS-FaFgCM with the traditional approach using human i.v. and p.o. data. Less than two-fold difference in FaFg values was observed between the two approaches. Next, we obtained FaFg of structurally diverse polyphenols (genistein, baicalein, resveratrol, and epicatechin) using AS-FaFgCM, demonstrating that all of them were poorly absorbable. Furthermore, to utilize the pharmacokinetic data of the total concentration, including aglycones and metabolites, we modified the AS-FaFgCM to focus on their excretion. The FaFg value of naringenin was obtained using modified AS-FaFgCM and was nearly equal to that of baicalein, a structural isomer of naringenin. This study provides quantitative information on the intestinal absorption of polyphenols using comprehensive estimation methods.
Keywords: AS-FaFgCM; AS-FaFgCME; FaFg; Intestinal absorption; Polyphenols; allometric scaling.