Effect of molecular mass and sulfate content of fucoidan from Sargassum siliquosum on antioxidant, anti-lipogenesis, and anti-inflammatory activity

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Macroalgae (seaweeds) are abundant in functional polysaccharides known for their unique biochemical activities. In this study, the antioxidant, anti-lipogenic, and anti-inflammatory activities of the fucoidan extracted from brown seaweed Sargassum siliquosum were investigated by 1,1-diphenyl-2-picrylhydrazyl (DPPH)-scavenging ability, lipid synthesis inhibition, and suppression of pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-α) production, respectively. To examine the effect of molecular mass on fucoidan's bioactivities above, the extracted fucoidan was subject to hydrogen peroxide-mediated partial hydrolysis to obtain lower molecular mass compounds within the range of 107.3-3.2kDa. Results indicated that fucoidan's antioxidant activity increased with a corresponding decrease in molecular mass; the dosage for the half-maximal response (EC50) dropped from 2.58 to 1.82mg/mL when the molecular mass decreased from 107.3 to 3.2kDa. In addition, both the anti-lipogenesis and anti-inflammatory activities of fucoidan were significantly enhanced by 71.1% and 36.7%, respectively, when the molecular mass decreased to about 3kDa. To further test the effect of sulfation on fucoidan's bioactivities, low molecular mass fucoidan was treated with SO3-DMF to increase the sulfate content. The results indicated that when sulfate content increased from 18.7% to 32.1%, EC50 of DPPH decreased from 1.82mg/mL to 0.86mg/mL and the anti-inflammatory activity also increased by 35.2%; however, the anti-lipogenesis activity decreased.