The result of bidirectional transport assay for NFP. Papp values of tested compounds in apical-to-basolatoral (A-B) and basolateral-to-apical (B-A) directions were determined by incubating Caco-2 monolayers at 37 °C for 2 h with NFP (20 μM). Data represented means ± S.E.M. (n =3); two-way ANOVA results: F (dFn, dFd): interaction F (1, 8) = 184, P < 0.0001; treatment F (1, 8) = 267, P < 0.0001; Bonferroni post-test results: *** indicates P < 0.0001, ns indicates no significant difference.