Liquiritin Enhancing Intestinal Absorption of Paeoniflorin in in situ Single‑pass Intestinal Perfusion and in vitro Caco‑2 Cell Monolayer Absorption Models

Objectives: In this study, we aimed to determine the interaction of paeoniflorin and liquiritin during intestinal absorption. Materials and Methods: The interaction between paeoniflorin and liquiritin (100 μM) was studied using in situ single‑pass intestinal perfusion (SPIP) model use the whole small intestine and in vitro Caco‑2 cell monolayer bidirectional transport model. Results: In situ SPIP research demonstrated that liquiritin significantly increased the Ka, Papp, absorption rate, and cumulative amount of paeoniflorin up to 7.97, 8.98, 7.07, and 10.71 folds, respectively, even higher than that of verapamil, a specific P‑gp inhibitor, and control. Furthermore, 18 β‑glycyrrhetinic acid (18 β‑GA) markedly increased the Ka, Papp, absorption rate, and cumulative amount of paeoniflorin up to 3.30, 3.27, 3.42, and 4.04 folds, respectively. Bidirectional transport studies indicated that liquiritin and paeoniflorin could prompt the absorption of each other by increasing the Papp (AP‑BL) of paeoniflorin and liquiritin from (3.83 ± 0.51) ×10−7 to (5.60 ± 0.51) ×10−7 cm/s and (3.86 ± 0.34) ×10−7 to (8.26 ± 0.51) ×10−7 cm/s, respectively. The 18 β‑GA significantly prompted the Papp (AP‑BL) of paeoniflorin to (5.54 ± 0.92) ×10−7 cm/s. Conclusion: Liquiritin and paeoniflorin increased the absorption of each other. This could provide essential reference to predict the oral bioavailability, the pharmacokinetics, and the clinical application of coadministration of liquiritin‑and paeoniflorin‑containing SGT and other herbal formulas.