Oxidative degradation of the sulfated polysaccharide isolated from sea cucumber Holothuria nobilis

Abstract

In this study, a sulfated polysaccharide with a high molecular weight was isolated from sea cucumber Holothuria nobilis. It is a fucosylated chondroitin sulfate and being named as HOP. We investigated the effects of several processing variables on the oxidative degradation of HOP using fractional factorial design (FFD) and central composite design (CCD). Moreover, the conditions of the hydroxyl free radical-induced degradation were optimized using response surface methodology (RSM). Our data showed that R(H2O2–HOP), reaction pH and H2O2 flow rate could significantly (P<0.05) affect the degree of hydrolysis (DH) of HOP. The optimum conditions with Fe2+ were found as follows: R(H2O2–HOP) of 0.53; reaction pH of 6.91; H2O2 flow rate of 0.40mL/min; reaction time of 2h; reaction temperature of 30°C; and HOP concentration of 4mg/mL. Under these optimum conditions, the DH of HOP was 94.173±0.232 (%), which well matched the value (94.152%) predicted by the RSM model. The preliminary structural characterization of o-HOP was analyzed. The results showed that o-HOP consisted of β-d-glucuronic acid, β-d-N-acetyl-galactosamine, α-l-fucose and sulfate groups. The specific rotation of o-HOP was -43.2°. Furthermore, the sulfation patterns of fucose residues in o-HOP were 2,4-O-disulfated fucose, 3-O-sulfated fucose, 4-O-sulfated fucose and non-sulfated fucose, which were consistent with HOP. In addition, we found that the in vitro antitumor activity of the degraded HOP fraction (o-HOP) was higher than that of HOP against human gastric carinoma SGC-7901 cells.