Paracellular Transport of Sulforaphane across Caco-2 Cell Monolayers

Abstract

The present study aimed to clarify the transport mechanism of sulforaphane (SFN), a potent phytochemical of broccoli, in Caco-2 cells. Transport study with an Ussing chamber system revealed the apparent permeability (P_app) of SFN in the apical-to-basolateral direction was much higher (31.2 ± 2.5 × 10⁻⁶ cm/sec) than that of (−)-epigallocatechin-3-O-gallate (0.54 ± 0.12 × 10⁻⁶ cm/sec). An efflux ratio analysis and several inhibition studies suggested SFN was passively transported across Caco-2 cell monolayers. Small amounts of glutathione conjugates of SFN in the basolateral side suggested that the transcellular pathway was, in part, involved in the transport of SFN. However, results showing that SFN transport was attenuated by sodium butyrate, a tight junction (TJ) closer, and competed with fluorescein, a selective marker of paracellular transport, clearly indicated that SFN was mainly transported through the TJ-controlled paracellular pathway.