Effect of oversulfation on the chemical and biological properties of fucoidan

Fucoidan was sulfated using chlorosulfonic acid–pyridine complex and isolated as the sodium salt. Infrared analysis of the native and sulfated fucoidans gave identical results in respect to the O–H stretching, hemiacetal stretching and SO stretching. Absorption around 840 cm−1 was also present in both the fucoidans representing the sulfate at the axial C-4 position except for a shoulder at 820 cm−1, which was present only in the sulfated compound indicating the presence of sulfate groups at the equatorial C-2 position. The sulfated compound showed four times higher anticoagulant activity in doubling prothrombin time of normal citrated human plasma in comparison with native fucoidan. Earlier studies using native fucoidan showed that the activation of glutamic plasminogen (Glu-Plg) by tissue plasminogen activator (t-PA) or by urokinase (u-PA) was enhanced when the in vitro studies were conducted using 0.05 M Tris buffer (pH 7.4) and that the addition of physiological concentration of NaCl (0.9%) to the buffer reversed the activation. The results of the current studies showed that sulfated fucoidan gave higher stimulations of Glu-Plg activation by u-PA and by t-PA in comparison to native fucoidan when the in vitro studies are conducted using Tris buffer containing 0.9% NaCl.