Structural analysis of fucoidan oligosaccharides from Saccharina japonica by tandem ESI mass spectrometry and comparison of their inhibitory effect on nitric oxide production

Fucoidan oligosaccharides, composed of only sulfate groups and fucose, have garnered attention due to their anti-inflammatory, anticoagulant, and antitumor activities. However, the study of its structure-activity relationship (SAR) remains a challenge due to the complexity and diversity of its isomers, as well as the difficulty in obtaining monomers. To address this challenge, a sulfated fuco-oligosaccharide (HDF1) was prepared from Saccharina japonica through acid hydrolysis and subsequently fractionated using size exclusion chromatography. Compositions of six series of sulfated fuco-oligosaccharides were fully characterized by ESI-TOF-MS, and their in-vitro anti-inflammatory activities were evaluated and compared. The sequences of seven primary types of sulfated fuco-oligosaccharides were investigated and fully characterized using ESI-MS/MS, including mono-sulfated fucose, fucobiose, fucotriose and fucotetrose, di-sulfated fucotriose, fucotetrose and fucopentaose. Results indicate that all fractionated samples contained a backbone of (1→3) linked sulfated α-L-Fucp residues with sulfation predominantly at C-2 or C-4, and several structural variants were reported for the first time. Abundant cleavage of the glycosidic bond between fucose residues allowed determination of which sugar ring carried the sulfated group and its exact positions on the sugar rings as indicated by A/X-type ions. Three fractions with low-DP (1–3) and HDF1 showed nitric oxide (NO) inhibitory activity in lipopolysaccharide (LPS)-induced RAW 264.7 cells. We provided a method for direct observation of the structure of sulfated fuco-oligosaccharide without modification and derivatization, and performed a relatively systematic analysis of sulfated fuco-oligosaccharide derived from S. japonica.