Inhibitory effects of fucoidan from Laminaria japonica against some pathogenic bacteria and SARS-CoV-2 depend on its large molecular weight

Brown algae biomass for fucoxanthin, fucoidan and alginate; update review on structure, biosynthesis, biological activities and extraction valorisation

Natural compounds promoting human health are the main focus of research nowadays. Fucoxanthin, fucoidan and alginate are such bioactive compounds that are extracted from marine brown algae. Extracting these 3 compounds through successive extraction enhances the commercial value of the brown algae biomass. There are studies on successive extraction of fucoidan and alginate but not with fucoxanthin which displays various biological bioactivities. Alginate, a polysaccharide presents 45 % in the cell wall of brown algae. Fucoidan, a sulphated polysaccharide proved showing various bioactivities. These bioproducts yield are vary depending on the species. Dictyota species recorded high fucoxanthin content of 7 %. Ascophyllum nodosum was found with high fucoidan of 16.08 % by direct extraction. Maximum alginate of 45.79 % was recorded from the brown alga Sargassum cymosum and by successive extraction 44 % was recorded from Ecklonia radiata. Fucoxanthin exits in two isomers as trans and cis forms. Based on linkage, fucoidan structure is found in 3 forms as 1,3- or 1,4- or alternating 1,3- and 1,4-linked fucose in the polysaccharide residues. Fucoidan composition varys depending on the degree of sulphation, composition of monosaccharides and location of collection. In alginate, its property relies on the mannuronic acid and guluronic acid composition. Biosynthesis of these 3 compounds is not much explored. Keeping this view which signify sequential extraction towards biomass valorisation, fucoxanthin, fucoidan and alginate extracted from the brown algae species focusing yield, extraction, characterisation, biosynthesis and biological activities were compiled and critically analysed and discussed in this review.

Systematic Characteristics of Fucoidan: Intriguing Features for New Pharmacological Interventions

Fucoidan, a sulfated polysaccharide found primarily in brown algae, is known for exhibiting various biological activities, many of which have been attributed to its sulfate content. However, recent advancements in techniques for analyzing polysaccharide structures have highlighted that not only the sulfate groups but also the composition, molecular weight, and structures of the polysaccharides and their monomers play a crucial role in modulating biological effects. This review comprehensively provides the monosaccharide composition, degree of sulfation, molecular weight distribution, and linkage of glycosidic bonds of fucoidan, focusing on the diversity of its biological activities based on various characteristics. The implications of these findings for future applications and potential therapeutic uses of fucoidan are also discussed.

Preparation and characterization of kelp polysaccharide and its research on anti-influenza a virus activity

The beneficial effects of kelp polysaccharide (KPS) have recently attracted attention. In this study, KPS was extracted from kelp using the enzyme hydrolysis combined with freeze-drying, namely, KPS-EF. The structural characterization showed that KPS-EF was a highly sulfated macromolecule with the Mw of 764.2 kDa and the sulfate content of 23.49 %. The antiviral activity of KPS-EF in vitro was verified, and the IC50 value of KPS against the PR8 virus was 0.58 mg/mL. Intranasal administration of KPS-EF significantly inhibited death and weight loss in IAV-infected mice and alleviated virus-induced pneumonia symptoms, meanwhile, KPS-EF (10 mg/kg/day) significantly decreased the production levels of chemokines (CXCL1, RANTES) and inflammatory cytokines (IL-6, TNF-α) in lungs (p < 0.05). KPS-EF could downregulate the activity of viral neuraminidase (NA) primarily in the late stage of viral adsorption with an IC50 value of 0.29 mg/mL. This study provides a theoretical basis for the using KPS as a supplement to NA inhibitors or anti-influenza drugs.

Seaweed-derived fucoidans and rhamnan sulfates serve as potent anti-SARS-CoV-2 agents with potential for prophylaxis

Seaweeds represent a rich source of sulfated polysaccharides with similarity to heparan sulfate, a facilitator of myriad virus host cell attachment. For this reason, attention has been drawn to their antiviral activity, including the potential for anti-SARS-CoV-2 activity. We have identified and structurally characterized several fucoidan extracts, including those from different species of brown macroalga, and a rhamnan sulfate from a green macroalga species. A high molecular weight fucoidan extracted from Saccharina japonica (FSjRPI-27), and a rhamnan sulfate extracted from Monostroma nitidum (RSMn), showed potent competitive inhibition of spike glycoprotein receptor binding to a heparin-coated SPR chip. This inhibition was also observed in cell-based assays using hACE2 HEK-293 T cells infected by pseudotyped SARS-CoV-2 virus with IC50 values <1 μg/mL. Effectiveness was demonstrated in vivo using hACE2-transgenic mice. Intranasal administration of FSjRPI-27 showed protection when dosed 6 h prior to and at infection, and then every 2 days post-infection, with 100 % survival and no toxicity at 104 plaque-forming units per mouse vs. buffer control. At 5-fold higher virus dose, FSjRPI-27 reduced mortality and yielded reduced viral titers in bronchioalveolar fluid and lung homogenates vs. buffer control. These findings suggest the potential application of seaweed-based sulfated polysaccharides as promising anti-SARS-CoV-2 prophylactics.

The potent osteo-inductive capacity of bioinspired brown seaweed-derived carbohydrate nanofibrous three-dimensional scaffolds

This study aimed to investigate the osteo-inductive capacity of a fucoidan polysaccharide network derived from brown algae on human adipose-derived stem cells (HA-MSCs) for bone regeneration. The physiochemical properties of the scaffold including surface morphology, surface chemistry, hydrophilicity, mechanical stiffness, and porosity were thoroughly characterized. Both in vitro and in vivo measurements implied a superior cell viability, proliferation, adhesion, and osteo-inductive performance of obtained scaffolds compared to using specific osteogenic induction medium with increased irregular growth of calcium crystallites, which mimic the structure of natural bones. That scaffold was highly biocompatible and suitable for cell cultures. Various examinations, such as quantification of mineralization, alkaline phosphatase, gene expression, and immunocytochemical staining of pre-osteocyte and bone markers confirmed that HAD-MSCs differentiate into osteoblasts, even without an osteogenic induction medium. This study provides evidence for the positive relationship and synergistic effects between the physical properties of the decellularized seaweed scaffold and the chemical composition of fucoidan in promoting the osteogenic differentiation of HA-MSCs. Altogether, the natural matrices derived from brown seaweed offers a sustainable, cost-effective, non-toxic bioinspired scaffold and holds promise for future clinical applications in orthopedics.

Anti-respiratory syncytial virus and anti-herpes simplex virus activity of chemically engineered sulfated fucans from Cystoseira indica

Seaweed polysaccharides, particularly sulfated ones, exhibited potent antiviral activity against a wide variety of enveloped viruses, such as herpes simplex virus and respiratory viruses. Different mechanisms of action were suggested, which may range from preventing infection to intracellular antiviral activity, at different stages of the viral cycle. Herein, we generated two chemically engineered sulfated fucans (C303 and C304) from Cystoseira indica by an amalgamated extraction-sulfation procedure using chlorosulfonic acid-pyridine/N,N-dimethylformamide and sulfur trioxide-pyridine/N,N-dimethylformamide reagents, respectively. These compounds exhibited activity against HSV-1 and RSV with 50 % inhibitory concentration values in the range of 0.75-2.5 μg/mL and low cytotoxicity at concentrations up to 500 μg/mL. The antiviral activities of chemically sulfated fucans (C303 and C304) were higher than the water (C301) and CaCl2 extracted (C302) polysaccharides. Compound C303 had a (1,3)-linked fucan backbone and was branched. Sulfates were present at positions C-2, C-4, and C-2,4 of Fucp, and C-6 of Galp residues of this polymer. Compound C304 had a comparable structure but with more sulfates at C-4 of Fucp residue. Both C303 and C304 were potent antiviral candidates, acting in a dose-dependent manner on the adsorption and other intracellular stages of HSV-1 and RSV replication, in vitro.

Fucoidan from the cell wall of Silvetia siliquosa with immunomodulatory effect on RAW 264.7 cells

Silvetia siliquosa, the only species of the family Fucaceae in China, is used as a medicine food homology. Fucoidan from S. siliquosa was extracted by hot water twice thoroughly (13 % of total yield), and a purified fucoidan SSF with a molecular weight of 93 kD was obtained. Chemical composition analysis demonstrated that SSF was primarily composed of sulfate (21.68 wt%) and fucose (84 % of all neutral monosaccharides). IR, methylation analysis, NMR and ESI-MS results indicated SSF had the backbone of mainly (1 → 3)-α-L-fucopyranose and minor (1 → 4)-α-L-fucopyranose, with little 1,3 and 1,4 branched β-D-Xylp and β-D-Galp. The in vitro immunomodulatory test on RAW 264.7 cells showed that SSF could up-regulate the expression of immune related factors and proteins in a concentration-dependent manner, but the immunomodulatory effect disappeared from desulfated SSF. This research indicated that highly sulfated fucan possessed immunomodulatory effect and the importance of sulfate groups in the activity of SSF.

Potential prebiotic and antibacterial activities of fucoidan from Laminaria japonica

Fucoidan from Laminaria japonica became sterilized with an autoclave and ultraviolet (UV) radiation. Potential prebiotic and antibacterial activities of sterilized fucoidans (SF) were the subject of investigation. Molecular weight, monosaccharide composition, FTIR, and NMR spectra of SF underwent evaluations to elucidate the relationship between the structure and activities of SF. The growth of Lactobacillus rhamnosus GG and L. acidophilus with autoclave sterilized fucoidan (ASF) and the growth of L. plantarum, L. gasseri, L. paracasei, and L. reuteri with UV sterilized fucoidan (USF) increased significantly. Also, fucoidan was vastly more effective than fructooligosaccharides in improving the growth of L. gasseri, L. reuteri, and L. paracasei. The growth of Escherichia coli and Bacillus cereus decreased at each SF concentration. ASF was more effective against E. coli, B. cereus, and Staphylococcus aureus than the USF efficiency. However, USF exhibited more inhibitory effects on the growth of Enterobacteriaceae compared to the ASF efficiency. When comparing the ASF and USF, autoclave caused a considerable decrease in molecular weight and uronic acid content, increased fucose and galactose, and made no significant changes in NMR spectra. Fucoidan effectively promoted probiotic bacterial growth and reduced pathogenic outbreaks in the medium. Therefore, it can occur as a new algal prebiotic and antibacterial agent.

Structurally defined heparin octasaccharide domain for binding to SARS-CoV-2 Omicron BA.4/BA.5/BA.5.2 spike protein RBD

Heparin, a bio-molecule with the highest negative charge density, is pharmaceutically important to prevent SARS-CoV-2 infection due to its strong competitive binding to spike protein compared with cellular heparan sulfate, which was confirmed as a co-receptor for virus-host cell interaction. Hence, the refined structural characterization of heparin targeting viral protein-HS interaction was significant for developing antiviral pharmaceuticals. In our study, heparin oligomers (dp ≥ 4) were prepared using heparinase I. The affinity oligosaccharides binding to Omicron spike protein RBD were separated by affinity chromatography and size exclusion chromatography. HILIC-ESI-FTMS was used for chain mapping analysis. The basic building blocks were analyzed and the binding domain sequence was produced by Seq-GAG software and further measured by SAX chromatography. As results, heparin octasaccharide was found with significantly higher binding ability than hexasaccharide and tetrasaccharide, and the octasaccharide [ΔUA-GlcNS6S-GlcA-GlcNS6S-IdoA2S-GlcNS6S-IdoA2S-GlcNS6S] with 12 sulfate groups showed high binding to RBD. The mechanism of this structurally well-defined octasaccharide binding to RBD was further investigated by molecular docking. The affinity energy of optimal pose was -6.8 kcal/mol and the basic amino acid residues in RBD sequence (Arg403, Arg452, Arg493 and His505) were identified as the major contribution factor to interacting with sulfate/carboxyl groups on saccharide chain. Our study demonstrated that heparin oligosaccharide with well-defined structure could be potentially developed as anti-SARS-CoV-2 drugs.

Orally administrated fucoidan and its low-molecular-weight derivatives are absorbed differentially to alleviate coagulation and thrombosis

Thrombosis is a serious threat to human health and life. Fucoidan, a sulfated polysaccharide from brown algae, could prevent coagulation and thrombus after intravenous administration. However, more efforts are still needed to develop its oral agent. In the present study, the absorption and excretion of fucoidan (90.8 kDa) and its degradation products, Dfuc1 (19.2 kDa) and Dfuc2 (5.5 kDa), were determined by HPLC-MS/MS after acid degradation and 1-phenyl-3-methyl-5-pyrazolone derivatization, and their anticoagulation and antithrombotic activities were evaluated in vivo after oral administration. Results showed that the maximum concentrations of fucoidan, Dfuc1 and Dfuc2 in rat plasma all achieved at 2 h after oral administration (150 mg/kg), and they were 41.1 ± 10.6 μg/mL, 45.3 ± 18.5 μg/mL and 59.3 ± 13.7 μg/mL, respectively. In addition, fucoidan, Dfuc1 and Dfuc2 could all prolong the activated partial thromboplastin time in vivo from 23.7 ± 2.7 s (blank control) to 25.1 ± 2.6 s, 27.1 ± 1.7 s and 29.4 ± 3.6 s, respectively. Moreover, fucoidan and its degradation products showed similar antithrombotic effect in carrageenan-induced thrombosis mice, and untargeted metabolomics analysis revealed that they all markedly regulated the carrageenan-induced metabolite disorders, especially the arachidonic acid metabolism. Thus, the degradation products of fucoidan with lower molecular weights are more attractive for the development of oral antithrombotic agents.

Structural characterizations and α-glucosidase inhibitory activities of four Lepidium meyenii polysaccharides with different molecular weights

Four polysaccharides (MCPa, MCPb, MCPc, MCPd) were obtained from Lepidium meyenii Walp. Their structures were characterized by chemical and instrumental methods including total sugar, uronic acid and protein content determination, UV, IR and NMR spectroscopy, as well as monosaccharide composition determination and methylation analyses. Four polysaccharides were a group of glucans with different molecular weights ranging from 3.12 to 14.4 kDa, and shared a similar backbone chain consisting of (1→4)-glucose linkages with branches attached to C-3 and C-6. Furthermore, bioactivity assay showed that MCPs had concentration-dependent inhibitory activity on α-glucosidase. MCPb (Mw = 10.1 kDa) and MCPc (Mw = 5.62 kDa) with moderate molecular weights exhibited higher inhibitory activity compared with MCPa and MCPd.