Nanosized genistein solid dispersion with superior mucus-penetrating ability significantly boosts intestinal absorption: A combined SPIP and Caco-2 cell study.

Genistein (GEN) is a typical soy-derived nutraceutical ingredient with multiple health-promoting bioactivities, but its application is severely limited by poor solubility and low oral bioavailability. In this study, the intestinal absorption behavior, transport pathways, and underlying mechanisms of GEN, its physical mixture (GEN-PM) and genistein solid dispersion (GEN-SD) were systematically investigated using a combined strategy including rat in situ single-pass intestinal perfusion (SPIP), mucus penetration evaluation and Caco-2 cell monolayer model. The prepared GEN-SD presented a particle size of only 100.11 nm and a BET specific surface area of 8.46 m2/g, which was 59.7% smaller and 130.5% larger than raw GEN respectively. SPIP results showed that GEN-SD exhibited significantly higher effective permeability coefficient (Peff) and absorption rate constant (Ka) in the duodenum at pH 7.4 and 10 μg/mL (P < 0.05). Removal of the intestinal mucus layer markedly reduced the absorption advantage of GEN-SD (P < 0.05), and in vitro Transwell assay verified its superior mucus-penetrating ability, with the 240 min cumulative transport quantity of GEN-SD increased by 26.04% and its Papp value elevated by 24.15% compared with pure GEN. In Caco-2 monolayers, GEN-SD displayed significantly enhanced time-dependent bidirectional transport and apparent permeability (Papp) (P < 0.05), and CLSM confirmed stronger intracellular uptake. Inhibitor studies in both SPIP and Caco-2 models demonstrated that the absorption of GEN-SD was prominently inhibited by EDTA and chlorpromazine hydrochloride (P < 0.05), indicating involvement of paracellular diffusion and clathrin-mediated endocytosis, while reserpine showed no significant effect, suggesting minimal BCRP-mediated efflux. The superior absorption of GEN-SD was attributed to the synergistic effects of amorphization, nanoscale particle size, enlarged specific surface area, improved mucus penetration, enhanced paracellular diffusion and clathrin-mediated endocytosis. This study provides a mechanistic basis for developing oral delivery systems with improved bioavailability for genistein.