Soyasaponin Bb has poor absorption and bioavailability in Sprague–Dawley rats and Caco-2 intestinal epithelial cell model

Abstract Soyasaponin Bb has various health-promoting bioactivities. However, the bioavailability of soyasaponin Bb is not fully understood. This study aimed to explore the absorption and metabolism of soyasaponin Bb by using both in vivo and in vitro methods. Soyasaponin Bb (100 mg/kg) was orally administrated in Sprague–Dawley (SD) rats, and the content of soyasaponin Bb and soyasapogenol B in plasma, urine and feces were determined by HPLC–MS/MS. The Caco-2 intestinal epithelial cell model was established by culturing on Transwell plates and assessing through cell morphology, transepithelial electrical resistance, alkaline phosphatase activity, and phenol red flux. Then, the apical (AP) to basolateral (BL) transport or uptake of soyasaponin Bb in the model were determined. In SD rats, soyasaponin Bb reached a maximum of 19.8 ng/mL in plasma and showed two material peaks. The cumulative excretion of soyasaponin Bb at 168 h was (0.0022 ± 0.0006) % in urine and (0.36 ± 0.21) % in feces. Soyasapogenol B was not detected in plasma and urine, but had a cumulative excretion of (0.45 ± 0.29) % in feces at 168 h. Culturing Caco-2 cells on Transwell plates for 21 days formed good intestinal epithelial monolayers. The apparent permeability (Papp) of both AP-BL and BL-AP transport of soyasaponin Bb in the Caco-2 cell models was less than 1.0 × 10–6 cm/s, and the efflux ratio (ER) was 0.5 ± 0.2. The uptake of soyasaponin Bb in the AP-BL cells was significantly higher (p < 0.05) than that in the BL-AP cells. In conclusion, soyasaponin Bb has poor absorption and bioavailability in SD rats and Caco-2 intestinal epithelial cell model.