Fucoidan inhibits activation and receptor binding of transforming growth factor-β1

Fucoidan, a sulfated, fucose-rich polysaccharide isolated from marine brown algae, has antifibrotic effects. We investigated the biologic effects of interactions of fucoidan with transforming growth factor-β1 (TGF-β1) and latent TGF-β1 (LTGF-β1). TGF-β1 bound to fucoidan was unable to interact with its receptor. In agreement with this, fucoidan attenuated the cellular effect of TGF-β1 as measured by phosphorylation of Smad2. Binding of fucoidan rendered LTGF-β1 resistant to activation as follows. Fucoidan inhibited furin-like proprotein convertase-mediated activation of platelet LTGF-β1 without suppression of the enzyme. In addition, acid- or heat-activation of small recombinant LTGF-β1 and acid-activation of large LTGF-β1 in cultured cell supernatant were also inhibited by fucoidan. Fucoidan is a mixture of polysaccharides of different sizes. As molecular weight of fucoidan increases, it had more inhibitory effects on TGF-β1 and LTGF-β1. In conclusion, inhibitions of LTGF-β1 activation and TGF-β1 receptor binding by fucoidan may in part account for its antifibrotic effects.