Abstract:

The absorption mechanism and variability of soyasaponins I and II were investigated using a Caco-2 cell
monolayer and a rat intestinal model. Apparent permeability coefficients (Papp) across the Caco-2 model increased linearly
until plateaus were reached at 120 min with intermediate Papp values of (1.02−3.41) × 10-6 and (0.9−3.05) × 10-6 cm/s
for two soyasaponins, respectively. Saturable transport, bilateral Papp ratios of more than 1.5 and the inhibitory effect of
mitochondrial electron transport chain blocker sodium azide indicated the active transport mechanisms. The transmembrane
permeability glycoprotein (p-glycoprotein) inhibitor verapamil did not increase the permeation of both soyasaponins,
excluding the p-glycoprotein-related efflux. Several absorption enhancers promoted the permeation across the Caco-2 cell
monolayers with a rank of borneol > sodiumdeoxycholate > carbomer 934P polysorbate 80; but chitosan did not exhibit such
an enhancing ability. The transepithelial transport also showed tissue difference in the intestine with the Papp values for soyasaponins I
and II across the jejunal segment being more than 2 times greater than those across the duodenal and ileal segments. Therefore, a
controlled transport should be able to improve the intestinal absorption so that soyasaponins I and II would exert their health functions.

Key words: soyasaponin, Caco-2, sodium azide, p-glycoprotein, absorption enhancer