Ekaterina V. Sokolova

Atomic force microscopy imaging of carrageenans from red algae of Gigartinaceae and Tichocarpaceae families

In the present article, the atomic force microscopy was applied to investigate macromolecular structures of various carrageenan types including hybrid polysaccharides (κ-, κ/β-, κ/ι-, λ-, and X-carrageenans) depending on polysaccharide concentration. The structures dependence on a polysaccharide concentration also was focused. κ-Carrageenan forms both single and two stranded structures at a low concentration. At high concentrations κ-, κ/β-, and κ/ι-carrageenans form fibrous network-like structures by a side-by-side association type at the same time for κ/ι-carrageenan end-to-end association type also was found. Comparably to κ-carrageenan, κ/β-carrageenan network was more open with coarser fibers while κ/ι-carrageenan structure is characterized with a more flexible network. Honeycombed structures due to end-to-end and side-by-side association types were observed for X-carrageenan, while λ-carrageenan formed honeycombed structures only at high concentrations. In order to investigate topographical parameters of the carrageenans macromolecular structure a new method of the autocorrelation function analysis was used for the first time.

In Vitro and Ex Vivo Studies of Antioxidant Activity of Carrageenans, Sulfated Polysaccharides from Red Algae

Antioxidant properties of structurally different sulfated polysaccharides (carrageenans) were studied in vitro and ex vivo. Ferric reducing antioxidant activity of carrageenans and their inhibitory effects on hydroxyl radicals and superoxide anion radicals were demonstrated in vitro. Activity of carrageenans depends on the polysaccharide structure. Carrageenans stimulate catalytic activity of SOD from donor erythrocyte.

Influence of red algal polysaccharides on biological activities and supramolecular structure of bacterial lipopolysaccharide

The present work reveals the effect of kappa-, lambda- and kappa/beta-carrageenans on the immune modulation and supramolecular structure of lipopolysaccharide (LPS). The kappa/beta carrageenan was able to increase the synthesis of anti-inflammatory interleukin-10 (IL-10) in vitro, and at low concentrations, their activity in the mixture with LPS was higher than that of LPS alone. Kappa-carrageenan significantly inhibited LPS-induced upregulation of reactive oxygen species (ROS). The activation of cells by kappa-carrageenan occurs through TLR4 receptor specific for LPS. Carrageenans reduced (kappa-) or completely inhibited (lambda-) collagen-induced platelet aggregation and decreased their aggregation activity caused by cooperative effect of LPS and collagen. The transformation of ultrastructure of LPS by action of kappa- and kappa/beta-carrageenans is observed. Moreover, carrageenans changed both the sizes and ζ- potentials of the LPS.

Structural peculiarities of polysaccharide from sterile form of Far Eastern red alga Ahnfeltiopsis flabelliformis.

KCl-insoluble sulfated polysaccharide from sterile alga Ahnfeltiopsis flabelliformis was investigated. Partial reductive hydrolysis and NMR spectroscopy showed that the polysaccharide comprises disaccharide units of carrabiose only. According to FT-IR-, 1D, 2D NMR spectroscopies and mass-spectrometry this polysaccharide is kappa/beta-carrageenan with ratio of kappa- and beta-types units 3:1 and contains minor amounts of iota- and gamma-carrageenans (precursor of beta-carrageenan). In addition, ESIMS/MS data suggested that xylose (minor amount) is present in the polysaccharide as a substituent one of hydroxyl group of galactose. According to aPTT and PT assays the studied carrageenan affected mostly intrinsic pathway of coagulation, while it effect on the extrinsic pathway is absent.

Influence of red algal sulfated polysaccharides on blood coagulation and platelets activation in vitro.

The influence of sulfated polysaccharides (λ-, κ-, and κ/β-carrageenan and porphyran) - on platelet activation was studied. Carrageenans were much weaker inhibitors of a coagulation process than heparin, while porphyran had not that effect. Results of the aPTT and PT assays suppose that carrageenans affected mostly intrinsic pathway of coagulation, while their effect on the extrinsic pathway is extremely low (λ and κ/β) or absent (κ, LMW derivative of κ-carrageenan). λ-Carrageenan was the most potent anticoagulant agent in TT, aPTT, PT, and anti-factor Xa activity. This sample was also the strongest inhibitor of collagen-induced platelet aggregation in PRP. Generally, the correlation of anticoagulant and antithrombotic action in PRP is preserved for carrageenans but not for heparin. Carrageenans and porphyran affected platelet adhesion to collagen by influencing glycoprotein VI. Low molecular weight κ-carrageenan had a similar effect on platelet adhesion mediated with both major collagen receptors: integrin α2 β1 and glycoprotein VI as native polysaccharide had. Carrageenans resulted in activation of platelets under platelet adhesion mediated by integrin αIIb β3 with less degree than heparin. The least sulfated κ/β-carrageenan that possessed an inhibiting effect on thrombin- and collagen-induced aggregation of washed platelets and on the PT test but it had no significant effect on TT was the weakest promoter of integrin αIIb β3 mediated platelet activation. In summary, our study showed that the polysaccharide action was complex, since it depended on its molecular mass, sulfation degree, and monosaccharide contents (3,6-anhydrogalactose).

Sulfated steroid glycosides from the Viet Namese starfish Linckia laevigata

Five sulfated steriodal compounds including one new glycoside called linckoside L7 (1) and four previously known glycosides 2–5 were isolated from the starfish Linckia laevigata. The structure sodium (22E, 24R)-3-O-(2-O-methyl-β-D-xylopyranosyl)-29-O-(β-D-xylopyranosyl)-24-ethylcholest-4,22-dien-3β,6β,8,15α,16β,29-hexaol 15-O-sulfate was proposed for L7. Linckoside L7 inhibited fertilization and egg-cell development in the sea urchin Strongylocentrotus intermedius.

Structural analysis and cytokine-induced activity of gelling sulfated polysaccharide from the cystocarpic plants of Ahnfeltiopsis flabelliformis.

Gelling sulfated polysaccharide from the cystocarpic plants of Ahnfeltiopsis flabelliformis was studied. According to FT-IR and NMR spectroscopy data, the polysaccharide was found to be iota/kappa-carrageenan with iota- and kappa-type units in a 2:1 ratio containing beta-carrageenan units and minor amounts of nu- and mu-carrageenans. The HPLC and ESI MS/MS data of enzymatic hydrolysis products revealed that the main components of the polymer chain are iota-carrabiose, iota-carratetraose and hybrid tetra- and hexasaccharides consisting of kappa- and iota-units. Xylose was a substituent of a hydroxyl group at C-6 of 1,3-linked β-d-galactose in the total polysaccharides. It was shown that the ability of carrageenans to increase the synthesis of cytokines depended on their molecular weight. The polysaccharide induced the synthesis of the anti-inflammatory cytokine IL-10, whereas oligosaccharides increased the synthesis of both pro- and anti-inflammatory cytokines at high concentrations.

Polysaccharide structure of tetrasporic red seaweed Tichocarpus crinitus

Sulfated polysaccharide isolated from tetrasporic plants of Tichocarpus crinitus was investigated. The polysaccharide was isolated by two methods: with water extraction at 80 °C (HT) and with a mild alkaline extraction (AE). The extracted polysaccharides were presented by non-gelling ones only, while galactose and 3,6-AG were the main monosaccharides, at the same time amount of 3,6-AG in AE polysaccharides was the similar to that of HT. According to methods of spectroscopy and mass spectrometry, the polysaccharide from tetrasporic T. crinitus contains main blocks of 1,3-linked β-D-galactopyranosyl-2,4-disulfates and 1,4-linked 3,6-anhydro-α-D-galactopyranosyl while 6-sulfated 4-linked galactopyranosyl resudies are randomly distributed along the polysaccharide chain. The alkaline treatment of HT polysaccharide results in obtaining polysaccharide with regular structure that composed of alternating 1,3-linked β-D-galactopyranosyl-2,4-disulfates and 1,4-linked 3,6-anhydro-α-D-galactopyranosyl residues. Native polysaccharide (HT) possessed both high anticoagulant and antiplatelet activity measured by fibrin clotting and platelet aggregation induced by collagen. This activity could be connected with peculiar chemical structure of HT polysaccharide which has high sulfation degree and contains also 3,6-anhydrogalactose in the polymer chain.

The supramolecular structure of LPS-chitosan complexes of varied composition in relation to their biological activity.

The complexes of chitosan (Ch) with lipopolysaccharides (LPSs) from Escherichia coli O55:B5 (E-LPS) and Yersinia pseudotuberculosis 1B 598 (Y-LPS) of various weight compositions were investigated using quasi-elastic light scattering, ζ-potential distribution assay and atomic force microscopy. The alteration of ζ-potential of E-LPS-Ch complexes from negative to positive values depending on Ch content was detected. The Y-LPS-Ch complexes had similar positive ζ-potentials regardless of Ch content. The transformation of the supramolecular structure of E-LPS after binding with to Ch was revealed. Screening of E-LPS and Y-LPS particles by Ch in the complexes with high polycation was detected. The ability of LPS-Ch complex to induce biosynthesis of TNF-α and reactive oxygen species in stimulated human mononuclear cells was studied. A significant decrease in activity complexes compared to that of the initial LPS was observed only for E-LPS-Ch complexes.

Furostane Series Asterosaponins and Other Unusual Steroid Oligoglycosides from the Tropical Starfish Pentaceraster regulus

Seven new asterosaponins, pentaregulosides A-G (1-7), including two furostane-type steroid oligoglycosides (2, 3), along with four previously known compounds (8-11) were isolated from the ethanolic extract of the starfish Pentaceraster regulus, collected off the coast of Vietnam. The structures of 1-7 were elucidated by extensive NMR and ESIMS techniques as well as chemical transformations. The aglycons of compounds 1 and 3 have not previously been observed in starfish steroid oligoglycosides, while the aglycons of compounds 2 and 4-6 are very rare for this structural group. Compound 1 exhibited cytotoxic activity with an IC50 value of 6.4 ± 0.3 μM against RAW 264.7 murine macrophages. In contrast, nontoxic asterosaponins 3, 4, and 5 showed a potential immunomodulatory action at a concentration of 5 μM, reducing by 40%, 28%, and 55%, respectively, reactive oxygen species formation in the RAW 264.7 cells, co-stimulated with the pro-inflammatory endotoxic lipopolysaccharide from E. coli.