Conformational properties of l-fucose and the tetrasaccharide building block of the sulfated l-fucan from Lytechinus variegatus

Photoprotective sulfated mannogalactan from heterotrophic Bacillus velezensis blocks UV-A mediated matrix metalloproteinase expression and nuclear DNA damage in human dermal fibroblast

Prolonged exposure of human dermal fibroblasts (HDF) to ultraviolet (UV) radiation triggers the production of reactive oxygen species by upregulating the expression of matrix metalloproteinases (MMPs), causing type-I collagen degradation and photoaging. A sulfated (1 → 3)/(1 → 4) mannogalactan exopolysaccharide (BVP-2) characterized as [→3)-α-Galp-{(1 → 4)-α-6-O-SO3-Manp}-(1 → 3)-α-6-O-SO3-Galp-(1→] was isolated from seaweed-associated heterotrophic bacterium Bacillus velezensis MTCC13097. Whole genome analysis of B. velezensis MTCC13097 (Accession number JAKYLL000000000) revealed saccharine biosynthetic gene clusters for exopolysaccharide production. BVP-2 administered cells showed noteworthy reduction in mitochondrial superoxide (∼85 %, p < 0.05) and ROS production (62 %) than those exhibited by UV-A irradiated HDF cells. Oxidative imbalance in HDF cells (after UV-A exposure) was recovered with BVP-2 treatment by significantly downregulating nitric oxide (NO) production (98.6 μM/mL, 1.9-fold) and DNA damage (⁓67 %) in comparison with UV-A induced cells (191.8 μM/mL and 98.7 %, respectively). UV-irradiated HDF cells showed a ∼30-50 % downregulation in the expression of MMPs (1, 2, and 9) following treatment with BVP-2. Considerable amount of sulfation (18 %) along with (1 → 3)/(1 → 4) glycosidic linkages in BVP-2 could be pivotal factors for down-regulation of the intracellular MMP-1, which was further supported by molecular docking and structure-activity studies. The (1 → 3)/(1 → 4)-linked bacterial exopolysaccharide (BVP-2) might be used as prospective natural lead to attenuate and mitigate UV-A-induced photoaging.

Structural characterization and immunomodulating assessment of ultra-purified water extracted fucoidans from Saccharina latissima, Alaria esculenta and Laminaria hyperborea

Fucoidans, a group of high molecular weight polysaccharides derived mainly from brown algae, are characterized by their high fucose content, degree of sulfation (DS), and intra- and interspecific structural variation. Fucoidans are increasingly recognized due to various reported bioactivities, potentially beneficial for human health. To unlock their potential use within biomedical applications, a better understanding of their structure-functional relationship is needed. To achieve this, systematic bioactivity studies based on well-defined, pure fucoidans, and the establishment of standardized, satisfactory purification protocols are required. We performed a comprehensive compositional and structural characterization of crude and ultra-purified fucoidans from three kelps: Saccharina latissima (SL), Alaria esculenta (AE) and Laminaria hyperborea (LH). Further, the complement-inhibiting activity of the purified fucoidans was assessed in a human whole blood model. The purification process led to fucoidans with higher DS and fucose and lower concentrations of other monosaccharides. Fucoidans from SL and LH resembles homofucans, while AE is a heterofucan rich in galactose with comparably lower DS. Fucoidans from SL and LH showed complement-inhibiting activity in blood and blood plasma, while no inhibition was observed for AE under the same conditions. The results emphasize the importance of high DS and possibly fucose content for fucoidans' bioactive properties.

Antiviral activity of marine sulfated glycans against pathogenic human coronaviruses

Great interest exists towards the discovery and development of broad-spectrum antivirals. This occurs due to the frequent emergence of new viruses which can also eventually lead to pandemics. A reasonable and efficient strategy to develop new broad-spectrum antivirals relies on targeting a common molecular player of various viruses. Heparan sulfate is a sulfated glycosaminoglycan present on the surface of cells which plays a key role as co-receptor in many virus infections. In previous work, marine sulfated glycans (MSGs) were identified as having antiviral activities. Their mechanism of action relies primarily on competitive inhibition of virion binding to heparan sulfate, preventing virus attachment to the cell surface prior to entry. In the current work we used pseudotyped lentivirus particles to investigate in a comparative fashion the inhibitory properties of five structurally defined MSGs against SARS-CoV-1, SARS-CoV-2, MERS-CoV, and influenza A virus (IAV). MSGs include the disaccharide-repeating sulfated galactan from the red alga Botryocladia occidentalis, the tetrasaccharide-repeating sulfated fucans from the sea urchin Lytechinus variegatus and from the sea cucumber Isostichopus badionotus, and the two marine fucosylated chondroitin sulfates from the sea cucumbers I. badionotus and Pentacta pygmaea. Results indicate specificity of action against SARS-CoV-1 and SARS-CoV-2. Curiously, the MSGs showed decreased inhibitory potencies against MERS-CoV and negligible action against IAV. Among the five MSGs, the two sulfated fucans here studied deserve further attention since they have the lowest anticoagulant effects but still present potent and selective antiviral properties.

Selective 2-desulfation of tetrasaccharide-repeating sulfated fucans during oligosaccharide production by mild acid hydrolysis

Sulfated fucans (SFs) from echinoderms, such as sea cucumbers and sea urchins, present linear and regular sulfation patterns within defined oligosaccharide building blocks. The high molecular weights of these polymers pose a problem in advanced structure-activity relationship studies for which derived oligosaccharides are more appropriate tools for investigation. However, enzymes capable of specifically depolymerizing SFs, fucanases, are not very common. Scarce abundance and unknown catalytic activities are additional barriers to exploiting fucanases. Oligosaccharide production by controlled chemical reactions such as mild acid hydrolysis then becomes a convenient strategy. As a consequence, physicochemical studies are necessary to understand the structural modifications caused on SFs by this chemical hydrolysis. Hence, in this work, we subjected three tetrasaccharide-repeating SFs from sea cucumbers, Isostichopus badionotus (IbSF), Holothuria floridana (HfSF), and Lytechinus variegatus (LvSF) to mild acid hydrolysis for oligosaccharide production. Interestingly, selective 2-desulfation reaction was observed in all three SFs. Through our study, we indicate that selective 2-desulfation is a common and expected phenomenon in oligosaccharide production by mild acid hydrolysis of SFs, including those composed of tetrasaccharide-repeating units.

Comparison of in vitro and in vivo antioxidant activities of commercial fucoidans from Macrocystis pyrifera, Undaria pinnatifida, and Fucus vesiculosus

Antioxidants fucoidans from three seaweeds, Undaria pinnatifida (FUP), Macrocystis pyrifera (FMP) and Fucus vesiculosus (FFV) are sold commercially. However, it is unclear which fucoidan is the most potent antioxidant. Therefore, our objective was to compare the antioxidant activities of these fucoidans. For this purpose, six in vitro antioxidant tests were used, total antioxidant capacity, hydroxyl radical scavenging assay, ferrous and cupric chelating assay, reducing power and H2O2 scavenging assay. The data showed that the fucoidans had a low capacity to donate electrons, and a low capacity to chelate metals. The best activity obtained was in the scavenging of hydroxyl radical. When macrophages were exposed to H2O2 and fucoidans, MTT and live/dead assays showed that all fucoidans protected cells from oxidative damage. The survival rate of zebrafish embryos was significantly higher when exposed to H2O2 and fucoidans than H2O2 alone. In summary, the fucoidans evaluated were ranked according to their antioxidant activity as follows: FMP > FFV > FUP, and the results suggest that these fucoidans, mainly FMP, can be used in the formulation of medicines/foods.

Fractionation of sulfated galactan from the red alga Botryocladia occidentalis separates its anticoagulant and anti-SARS-CoV-2 properties

Sulfation pattern and molecular weight (MW) play a key role in the biological actions of sulfated glycans. Besides anticoagulant effects, certain sulfated glycans can also exhibit anti-SARS-CoV-2 properties. To develop a more selective antiviral carbohydrate, an efficient strategy to separate these two actions is required. In this work, low MW fractions derived from the red alga Botryocladia occidentalis sulfated galactan (BoSG) were generated, structurally characterized, and tested for activity against SARS-CoV-2 and blood coagulation. The lowest MW fraction was found to be primarily composed of octasaccharides of monosulfated monosaccharides. Unlike heparin or native BoSG, we found that hydrolyzed BoSG products had weak anticoagulant activities as seen by aPTT and inhibitory assays using purified cofactors. In contrast, lower MW BoSG-derivatives retained anti-SARS-CoV-2 activity using SARS-CoV-2 spike (S)-protein pseudotyped lentivirus vector in HEK-293T-hACE2 cells monitored by GFP. Surface plasmon resonance confirmed that longer chains are necessary for BoSG to interact with coagulation cofactors but is not required for interactions with certain S-protein variants. We observed distinct affinities of BoSG derivatives for the S-proteins of different SARS-CoV-2 strains, including WT, N501Y (Alpha), K417T/E484K/N501Y (Gamma), and L542R (Delta) mutants, and stronger affinity for the N501Y-containing variants. Docking of the four possible monosulfated BoSG disaccharides in interactions with the N501Y mutant S-protein predicted potential binding poses of the BoSG constructs and favorable binding in close proximity to the 501Y residue. Our results demonstrate that depolymerization and fractionation of BoSG are an effective strategy to segregate its anticoagulant property from its anti-SARS-CoV-2 action.

Structural and kinetic analyses of holothurian sulfated glycans suggest potential treatment for SARS-CoV-2 infection

Certain sulfated glycans, including those from marine sources, can show potential effects against SARS-CoV-2. Here, a new fucosylated chondroitin sulfate (FucCS) from the sea cucumber Pentacta pygmaea (PpFucCS) (MW ∼10-60 kDa) was isolated and structurally characterized by NMR. PpFucCS is composed of {→3)-β-GalNAcX-(1→4)-β-GlcA-[(3→1)Y]-(1→}, where X = 4S (80%), 6S (10%) or nonsulfated (10%), Y = α-Fuc2,4S (40%), α-Fuc2,4S-(1→4)-α-Fuc (30%), or α-Fuc4S (30%), and S = SO3-. The anti-SARS-CoV-2 activity of PpFucCS and those of the FucCS and sulfated fucan isolated from Isostichopus badionotus (IbFucCS and IbSF) were compared with that of heparin. IC50 values demonstrated the activity of the three holothurian sulfated glycans to be ∼12 times more efficient than heparin, with no cytotoxic effects. The dissociation constant (KD) values obtained by surface plasmon resonance of the wildtype SARS-CoV-2 spike (S)-protein receptor-binding domain (RBD) and N501Y mutant RBD in interactions with the heparin-immobilized sensor chip were 94 and 1.8 × 103 nM, respectively. Competitive surface plasmon resonance inhibition analysis of PpFucCS, IbFucCS, and IbSF against heparin binding to wildtype S-protein showed IC50 values (in the nanomolar range) 6, 25, and 6 times more efficient than heparin, respectively. Data from computational simulations suggest an influence of the sulfation patterns of the Fuc units on hydrogen bonding with GlcA and that conformational change of some of the oligosaccharide structures occurs upon S-protein RBD binding. Compared with heparin, negligible anticoagulant action was observed for IbSF. Our results suggest that IbSF may represent a promising molecule for future investigations against SARS-CoV-2.

Antiviral activities of four marine sulfated glycans against adenovirus and human cytomegalovirus

Broad-spectrum antivirals are more needed than ever to provide treatment options for novel emerging viruses and for viruses that lack therapeutic options or have developed resistance. A large number of viruses rely on charge-dependent non-specific interactions with heparan sulfate (HS), a highly sulfated glycosaminoglycan (GAG), for attachment to cell surfaces to initiate cell entry. As such, inhibitors targeting virion-HS interactions have potential to have broad-spectrum antiviral activity. Previous research has explored organic and inorganic small molecules, peptides, and GAG mimetics to disrupt virion-HS interactions. Here we report antiviral activities against both enveloped (the herpesvirus human cytomegalovirus) and non-enveloped (adenovirus) DNA viruses for four defined marine sulfated glycans: a sulfated galactan from the red alga Botryocladia occidentalis; a sulfated fucan from the sea urchin Lytechinus variegatus, and a sulfated fucan and a fucosylated chondroitin sulfate from the sea cucumber Isostichopus badionotus. As evidenced by gene expression, time of addition, and treatment/removal assays, all four novel glycans inhibited viral attachment and entry, most likely through interactions with virions. The sulfated fucans, which both lack anticoagulant activity, had similar antiviral profiles, suggesting that their activities are not only due to sulfation content or negative charge density but also due to other physicochemical factors such as the potential conformational shapes of these carbohydrates in solution and upon interaction with virion proteins. The structural and chemical properties of these marine sulfated glycans provide unique opportunities to explore relationships between glycan structure and their antiviral activities.

Peracylation Coupled with Tandem Mass Spectrometry for Structural Sequencing of Sulfated Glycosaminoglycan Mixtures without Depolymerization

The structures of glycosaminoglycans (GAGs), especially the patterns of modification, are crucial to modulate interactions with various protein targets. It is very challenging to determine the fine structures using liquid chromatography-mass spectrometry (LC-MS) due in large part to the gas-phase sulfate losses upon collisional activation. Previously, our group reported a method for fine structure analysis that required permethylation of the GAG oligosaccharide. However, uncontrolled depolymerization during the permethylation process due to esterification of uronic acid lowers the reliability of the method to resolve structures of GAGs, especially for larger oligosaccharides. Here, we describe a simplified derivatization method using propionylation and desulfation. The oligosaccharides have all hydroxyl and amine groups protected with propionyl groups and then have sulfate groups removed to generate unprotected hydroxyl and amine groups at all sites that were previously sulfated. This derivatized oligosaccharide generates informative fragments during collision-induced dissociation that resolve the original sulfation patterns. This method is demonstrated to enable accurate determination of sulfation patterns of even the highly sulfated pentasaccharide fondaparinux by MS² and MS³. Using a mixture of dp6 from porcine heparin, we demonstrate that this method allows for structural characterization of complex mixtures, including clear chromatographic separation and sequencing of structural isomers, all at high yields without evidence of depolymerization. This represents a marked improvement in the reliability to structurally characterize GAG oligosaccharides over permethylation-based derivatization schemes.