Fucoidan inhibits Ca(2+) responses induced by a wide spectrum of agonists for G-protein-coupled receptors

Fucoidan, a sulfated polysaccharide extracted from brown seaweed, has been used in traditional Chinese herbal medicine to treat thyroid tumors for many years. Although a number of its cellular effects have been investigated, the role of fucoidan in molecular signaling, particularly in Ca(2+) signaling, remains largely unknown. In the present study, the effects of fucoidan on Ca(2+) responses in HeLa cells, human umbilical vein endothelial cells and astrocytes were investigated using a wide range of receptor agonists. Fucoidan inhibited the increase in intracellular free calcium concentration that was induced by histamine, ATP, compound 48/80 and acetylcholine. The responses induced by the same agonists in the absence of extracellular Ca(2+) were also markedly suppressed by fucoidan. Reverse transcription-polymerase chain reaction demonstrated that 0.5 and 1.0 mg/ml fucoidan treatment for 3 h decreased histamine receptor 1 expression in HeLa cells. Similarly, the expressions of purinergic receptor P2Y, G-protein coupled (P2YR)1, P2YR2 and P2YR11 were significantly downregulated within cells pretreated with 1.0 mg/ml fucoidan for 3 h, and 0.5 mg/ml fucoidan significantly inhibited P2YR1 and P2YR11 expression. The results demonstrated that fucoidan may exert a wide spectrum of inhibitory effects on Ca(2+) responses and that fucoidan may inhibit a number of different G-protein coupled receptors associated with Ca(2+) dynamics.