Study On The Structure, Derivatives And Activities Of Fucoidan Extracted From Laminia Japonica

Laminaria japonica is the most important economic brown seaweed cultured in China and widely consumed as a marine vegetable in East Asia. L. japonica is not only used as vegetable but also utilized in China as a drug for over one thousand years. It was documented in Traditional Chinese Medicine (TCM) to have therapeutic effect on dropsy, a symptom of renal failure. Fucoidan extracted from L. japonica is a kind of important sulfated heteropolysaccharide. The preliminary study has shown that the fucoidan is active as a chronic renal failure (CRF) medicine. The chemical constitution, structure, chemical modification and bioactivities were systematically and extensively investigated in this study.Crude fucoidan (FPS) was isolated from hot water extracts from L. japonica, further purification was performed in anion-exchange chromatography. Three fractions were obtained:F1, F2 and F3 from 0.5 M NaCl,1.0 M NaCl and 1.5 M NaCl elution on column chromatography, respectively. The chemical constituent of three fractions were different, F1 had the highest uronic acid and lowest sulfate group, whereas F3 had none uronic acid and highest sulfate group, the uronic acid and sulfate group in F2 were between Fl and F3. The main monosaccharide in F2 was fucose, however, the main sugar in F1 and F3 was galactose. The antioxidant activity study found that F1 exhibited highest scavenging superoxide radical ability, and F3 showed highest scavenging hydroxyl radical ability. The antioxidant activity of FPS and its fractions not only related to the content of the sulfate group but also to the ratio of sulfate content/fucose. All the samples had anticoagulant activity in vitro, the mechanism of anticoagulant was complex, the fucoidan fractions could work on both intrinsic and extrinsic coagulant factors.A low molecular weight fucoidan (DFPS), obtained from the brown seaweed L. japonica by water extraction, ascorbic acid and hydrogen peroxide degradation, was separated into three fractions by DEAE-Sepharose FF column chromatography. All three fractions (DF1, DF2 and DF3) contained predominantly fucose and galactose and also contained sulfate groups. Structural studies on the DF2 were carried out by chemical and spectrum analysis method. The backbone of DF2 was primarily (1→3)-linked a-L-fucopyranose residues and a few (l→4)-α-L-fucopyranose linkages. The branch points were at C-4 of 3-linked a-L-fucopyranose residues byβ-D-galactose unites (35%, molar ratio) or at C-2 of 3-linked a-L-fucopyranose residues by non-reducing terminal fucose unites (65%, molar ratio). Sulfate groups occupied position C-4 or C-2, sometimes C-2,4 to fucose residues, and C-3 and/or C-4 to galactose residues. The three fractions had antioxidant and anticoagulant activity in vitro, and the ability was associated with their chemical constituent and structure.We used FPS and DFPS as raw material to synthesize oversulfated, phosphorylated, aminated, acetylated and benzoylated derivatives. The chemical constituent and bioactivities such as antioxidant and anticoagulant activities of these ten derivatives were studied. The results showed that acetyl and benzoyl group could enhance the antioxidant activity greatly, on the other hand, sulfate, phosphorylated and aminate groups could enhance the anticoagulant activity. The molecular weight had little effect on the antioxidant activity, however, had great influence on the anticoagulant activity. The anticoagulant activity of FPS derivatives was higher than DFPS derivatives.We investigated the effect of benzoylated fucoidan derivatives against Adenine-induced CRF. The results showed that the fucoidan derivatives could decrease the serum urea nitrogen (SUN) and the serum creatinine (Scr) significantly, and elevate the activity of CAT, GSH-PX and GSH. The LPO lever was lower in the fucoidan derivatives treated groups. The mechanism of benzoylated fucoidan derivatives on the CRF had relationship with their antioxidant activity, the samples which could enhance the antioxidant enzyme activity and reduce the LPO lever could alleviate the symptom of CRF complications.In conclusion, the structure of fucoidan extracted from L. japonica is different from fucoidan extracted from other kind of brown seaweed. The chemical modification on the fucoidan could enhance its antioxidant and anticoagulant activity. The benzoylated derivatives had higher activity on CRF, and the mechanism of treating CRF was related with antioxidant activity.