Fucoidan enhances intestinal barrier function by upregulating the expression of claudin-1

Figure 1 Fucoidan directly enhanced intestinal epithelial barrier function. Polarized Caco-2 cell monolayers were incubated in the presence or absence of fucoidan (2.5 mg/mL) for 24 h. Changes in intestinal epithelial barrier function were monitored by measuring the trans-epithelial resistance (TER). The data are expressed as the means ± SEM of 5 independent experiments. ^aP < 0.05 compared with control (Student’s t test).

Figure 2 Fucoidan prevented H₂O₂-induced destruction of intestinal epithelial barrier function in a dose-dependent manner. Polarized Caco-2 cell monolayers were injured by H₂O₂ (500 μmol/L) on the apical side of Caco-2 cell monolayers. Fucoidan was added into the basolateral side 30 min prior to H₂O₂ stimulation and cultured for 6 h. Changes in intestinal epithelial barrier function were monitored by measuring the trans-epithelial resistance (TER). The data are expressed as the means ± SEM of 5 independent experiments. ^aP < 0.05, ^bP < 0.01 compared with cells exposed to H₂O₂ alone at respective time point (Tukey’s multiple comparison test).

Figure 3 Fucoidan prevented H₂O₂-induced increases in paracellular permeability. First, 0.5 mg/mL 4-kDa FITC-labeled dextrans (FD4) were added into the apical well and cultured for 6 h with or without H₂O₂ (500 μmol/L) and/or fucoidan (2.5 mg/mL). After 6 h of incubation, the basal medium was collected, and the fluorescence was measured as fluxed-FD4. H₂O₂-induced FD4 flux was considered 100%. The data are expressed as the means ± SEM of 5 independent experiments. ^bP < 0.01 (Student’s t test).

Figure 4 Fucoidan promoted intestinal epithelial barrier function via direct upregulation of tight junction proteins in intestinal epithelial cells Polarized Caco-2 cell monolayers injured by H₂O₂ (500 μmol/L) for 24 h with or without pretreatment of fucoidan (2. 5 mg/mL) 30 min prior to H₂O₂ administration. The expression of tight junction proteins, including claudin-1, claudin-2, and occludin, was examined using reverse-transcription polymerase chain reaction. The data shown are representative and are from 1 of the 3 independent experiments.

Figure 5 Fucoidan prevented the H₂O₂-induced destruction of tight junction protein claudin-1. Caco-2 cells were grown on a Lab-Tek chamber plate. Polarized Caco-2 monolayers were injured by H₂O₂ (500 μmol/L) for 6 h with or without pretreatment of fucoidan (2.5 mg/mL). Immunofluorescence staining for claudin-1 was evaluated using confocal laser scanning microscopy. The data shown are representative and are from 1 of the 3 independent experiments.