Inhibitory effect of fucoidan on nitric oxide production in lipopolysaccharide-activated primary microglia.

1. Microglial activation plays an important role in the pathogenesis of neurodegenerative diseases by producing various pro-inflammatory cytokines. Microglia-derived nitric oxide (NO) is critical for the lipopolysaccharide (LPS)-induced selective loss of dopaminergic neurons. 2. Fucoidan is a sulphated polysaccharide extracted from brown seaweeds. It has a variety of biological actions, including anticoagulant, antiviral and anti-inflammatory effects. The aim of the present study was to investigate the effects of fucoidan on LPS-induced cellular activation in microglia and to evaluate the inhibitory mechanisms involved. 3. To investigate the effects of fucoidan on LPS-induced cellular activation in microglia, primary microglial cells were preincubated with fucoidan (31.25, 62.5 and 125 microg/mL) for 10 min, followed by stimulation with LPS (0.01 microg/mL). Then, cell shape and NO production were determined 24 h after LPS stimulation, whereas inducible nitric oxide synthase (iNOS) mRNA and protein expression were determined at 6 and 18 h after LPS stimulation, respectively. To evaluate the inhibitory mechanisms involved, mitogen-activated protein kinase (MAPK) activation was also evaluated. 4. Lipopolysaccharide transformed cells into an amoeboid shape, whereas 62.5 microg/mL fucoidan inhibited this activation. Moreover, 125 microg/mL fucoidan significantly inhibited microglial NO production to 75% of that in LPS-treated group and also significantly diminished the expression of iNOS mRNA and protein by nearly 50%. Fucoidan (125 microg/mL) also suppressed phosphorylation of p38 and extracellular signal-regulated kinase (ERK) by approximately 50%, but not that of c-Jun N-terminal kinase. 5. The results provide the first evidence that fucoidan has a potent inhibitory effect against LPS-induced NO production by microglia. The results also suggest that this inhibitory action of fucoidan involves suppression of p38 and ERK phosphorylation.