Biological Activities of Rhamnan Sulfate Extract from the Green Algae Monostroma nitidum (Hitoegusa)

Sulfated Glycans Inhibit the Interaction of MERS-CoV Receptor Binding Domain with Heparin

Middle East respiratory syndrome coronavirus (MERS-CoV) is a zoonotic virus with high contagion and mortality rates. Heparan sulfate proteoglycans (HSPGs) are ubiquitously expressed on the surface of mammalian cells. Owing to its high negatively charged property, heparan sulfate (HS) on the surface of host cells is used by many viruses as cofactor to facilitate viral attachment and initiate cellular entry. Therefore, inhibition of the interaction between viruses and HS could be a promising target to inhibit viral infection. In the current study, the interaction between the receptor-binding domain (RBD) of MERS-CoV and heparin was exploited to assess the inhibitory activity of various sulfated glycans such as glycosaminoglycans, marine-sourced glycans (sulfated fucans, fucosylated chondroitin sulfates, fucoidans, and rhamnan sulfate), pentosan polysulfate, and mucopolysaccharide using Surface Plasmon Resonance. We believe this study provides valuable insights for the development of sulfated glycan-based inhibitors as potential antiviral agents.

The Effect of a Dietary Supplement Containing Rhamnan Sulfate from Monostroma nitidum on Carotid Atherosclerotic Plaque: A Case Series

We report on 6 patients in our care who were harboring atherosclerotic plaque in the carotid arteries. This condition poses a risk of acute ischemic stroke and indicates potential atherosclerosis elsewhere in the vascular system. The plaque was revealed by routine ultrasound measurement of carotid intima-medial thickness (CIMT) defined as the distance between the lumen-intima interface and the media-adventitia interface. Recent improvements in image resolution and edge detection algorithms have resulted in improved reliability and clinical usefulness of the technology. The patients were enrolled in a systems-based functional medicine program of cardiology prevention to address root causes. The program provided personalized interventions that included drug therapy, dietary supplements, and lifestyle modification. The 6 patients followed the integrative regimen, which successfully managed existing cardiovascular symptoms and risk factors while keeping various biomarkers under control. However, they continued to exhibit carotid plaque with no improvement. A novel dietary supplement that targets endothelial glycocalyx regeneration was added to the personalized intervention programs. The supplement contains a proprietary extract of rhamnan sulfate from the green seaweed Monostroma nitidum. The 6 participants consumed the supplement daily, and their plaque burden was measured after 6 months using the same CIMT technology. In every case, the total plaque burden was reduced, with an average reduction in the 6 patients of 5.55 mm, which is statistically significant. Significant reductions in maximum carotid plaque thickness were also observed at the end of the 6 months. The study suggests that rhamnan sulfate from Monostroma nitidum may provide a safe and effective intervention for reducing atherosclerotic plaque, and should be evaluated as an adjunct therapy for prevention and treatment of cardiovascular disease.

Structural properties of the biologically active Dictyosphaerium chlorelloides exopolysaccharide α-d-manno-α-l-rhamno-α-d-(2-O-methyl)-galactan

Structure of biopolymers produced by microalgae plays an important role for their potential biological activity prediction and applications. Previously isolated and well characterized dominant fractions (Dch5-8) from ion-exchange chromatography separation of the biologically active microalga Dictyosphaerium chlorelloides exopolysaccharide (Dch) were pooled and partially acid hydrolyzed. The dominant sugar components in the combined Dch5-8 fraction were Gal and its 2-O-methyl derivative, Rha and Man, all accounting for about 94 mol% of total amount of sugars. Separation of obtained hydrolysate on Bio-Gel P-2 afforded ten fractions. Their main components were identified by NMR. Based on oligosaccharide structures, the repeating unit of the polysaccharide backbone was identified as →2)-α-L-Rhap-(1→4)-2-O-methyl-[3-O-β-D-Galp]-α-D-Galp-(1→ branched by Man. Furthermore, the higher molecular weight fraction contained glucuronorhamnan. NMR data indicate 1,4-linked Rha units in the backbone in α and β configuration, branched at O2 by 2,4-di-O-methyl-β-d-glucuronic acid.

Oral Administration of Rhamnan Sulfate from Monostroma nitidum Suppresses Atherosclerosis in ApoE-Deficient Mice Fed a High-Fat Diet

Oral administration of rhamnan sulfate (RS), derived from the seaweed Monostroma nitidum, markedly suppresses inflammatory damage in the vascular endothelium and organs of lipopolysaccharide-treated mice. This study aimed to analyze whether orally administered RS inhibits the development of atherosclerosis, a chronic inflammation of the arteries. ApoE-deficient female mice were fed a normal or high-fat diet (HFD) with or without RS for 12 weeks. Immunohistochemical and mRNA analyses of atherosclerosis-related genes were performed. The effect of RS on the migration of RAW264.7 cells was also examined in vitro. RS administration suppressed the increase in blood total cholesterol and triglyceride levels. In the aorta of HFD-fed mice, RS reduced vascular smooth muscle cell proliferation, macrophage accumulation, and elevation of VCAM-1 and inhibited the reduction of Robo4. Increased mRNA levels of Vcam1, Mmp9, and Srebp1 in atherosclerotic areas of HFD-fed mice were also suppressed with RS. Moreover, RS directly inhibited the migration of RAW264.7 cells in vitro. Thus, in HFD-fed ApoE-deficient mice, oral administration of RS ameliorated abnormal lipid metabolism and reduced vascular endothelial inflammation and hyperpermeability, macrophage infiltration and accumulation, and smooth muscle cell proliferation in the arteries leading to atherosclerosis. These results suggest that RS is an effective functional food for the prevention of atherosclerosis.

Preparation, structures, and biological functions of rhamnan sulfate from green seaweed of the genus Monostroma: A review

Rhamnan sulfate, a rhamnose-rich sulfated polysaccharide, is present in the cell walls of green seaweed belonging to the genus Monostroma. This macromolecule demonstrates promising therapeutic properties, including anti-coagulant, thrombolytic, anti-viral, anti-obesity, and anti-inflammatory activities, which hold potential applications in food and medical industries. However, rhamnan sulfate has not garnered as much attention from researchers as other seaweed polysaccharides, including alginate, carrageenan, and fucoidan. This review discusses the extraction and purification techniques of rhamnan sulfate, delves into its chemical structures and related elucidation approaches, and provides an overview of its biological functions. Future research should focus on the structure-activity relationship of rhamnan sulfate and the industrial preparation of rhamnan sulfate with a specific homogeneous structure to facilitate its practical applications.

The cell walls of different Chara species are characterized by branched galactans rich in 3-O-methylgalactose and absence of AGPs

Streptophyte algae are the closest relatives to land plants; their latest common ancestor performed the most drastic adaptation in plant evolution around 500 million years ago: the conquest of land. Besides other adaptations, this step required changes in cell wall composition. Current knowledge on the cell walls of streptophyte algae and especially on the presence of arabinogalactan-proteins (AGPs), important signalling molecules in all land plants, is limited. To get deeper insights into the cell walls of streptophyte algae, especially in Charophyceae, we performed sequential cell wall extractions of four Chara species. The three species Chara globularis, Chara subspinosa and Chara tomentosa revealed comparable cell wall compositions, with pectins, xylans and xyloglucans, whereas Chara aspera stood out with higher amounts of uronic acids in the pectic fractions and lack of reactivity with antibodies binding to xylan- and xyloglucan epitopes. Search for AGPs in the four Chara species and in Nitellopsis obtusa revealed the presence of galactans with pyranosidic galactose in 1,3-, 1,6- and 1,3,6-linkage, which are typical galactan motifs in land plant AGPs. A unique feature of these branched galactans was high portions of 3-O-methylgalactose. Only Nitellopsis contained substantial amounts of arabinose A bioinformatic search for prolyl-4-hydroxylases, involved in the biosynthesis of AGPs, revealed one possible functional sequence in the genome of Chara braunii, but no hydroxyproline could be detected in the four Chara species or in Nitellopsis obtusa. We conclude that AGPs that is typical for land plants are absent, at least in these members of the Charophyceae.

Beneficial effects of seaweed-derived components on metabolic syndrome via gut microbiota modulation

Metabolic syndrome comprises a group of conditions that collectively increase the risk of abdominal obesity, diabetes, atherosclerosis, cardiovascular diseases, and cancer. Gut microbiota is involved in the pathogenesis of metabolic syndrome, and microbial diversity and function are strongly affected by diet. In recent years, epidemiological evidence has shown that the dietary intake of seaweed can prevent metabolic syndrome via gut microbiota modulation. In this review, we summarize the current in vivo studies that have reported the prevention and treatment of metabolic syndrome via seaweed-derived components by regulating the gut microbiota and the production of short-chain fatty acids. Among the surveyed related articles, animal studies revealed that these bioactive components mainly modulate the gut microbiota by reversing the Firmicutes/Bacteroidetes ratio, increasing the relative abundance of beneficial bacteria, such as Bacteroides, Akkermansia, Lactobacillus, or decreasing the abundance of harmful bacteria, such as Lachnospiraceae, Desulfovibrio, Lachnoclostridium. The regulated microbiota is thought to affect host health by improving gut barrier functions, reducing LPS-induced inflammation or oxidative stress, and increasing bile acid production. Furthermore, these compounds increase the production of short-chain fatty acids and influence glucose and lipid metabolism. Thus, the interaction between the gut microbiota and seaweed-derived bioactive components plays a critical regulatory role in human health, and these compounds have the potential to be used for drug development. However, further animal studies and human clinical trials are required to confirm the functional roles and mechanisms of these components in balancing the gut microbiota and managing host health.

An overview on the nutritional and bioactive components of green seaweeds

Green seaweed, as the most abundant species of macroseaweeds, is an important marine biological resource. It is a rich source of several amino acids, fatty acids, and dietary fibers, as well as polysaccharides, polyphenols, pigments, and other active substances, which have crucial roles in various biological processes such as antioxidant activity, immunoregulation, and anti-inflammatory response. In recent years, attention to marine resources has accelerated the exploration and utilization of green seaweeds for greater economic value. This paper elaborates on the main nutrients and active substances present in different green seaweeds and provides a review of their biological activities and their applications for high-value utilization.

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A comprehensive review on polysaccharides with hypolipidemic activity: Occurrence, chemistry and molecular mechanism

Currently, research on natural products is facing challenging future in various aspects. A large group of natural polysaccharides such as β-glucan, cellulose, hemicellulose, chitin, pectin, agaropectin, heteroglycans, lignins, hydrocolloids, homopolysaccharides, heteropolysaccharides were studied extensively for their various therapeutical potential. Several research works have already demonstrated those polysaccharides has tremendous health benefits, and found to exhibit anticancer, antiviral, immunomodulatory, antimicrobial, anticoagulant, anti-inflammatory, antidiabetic, antioxidant and antitumor activities. Different mushroom, plant, fungus, algae, vegetables, microalgae etc. are some important source of several polysaccharide macromolecules such as glucans, ulvan A, ulvan B, fucoidan, rhamnan sulfate, laminarin sulfate, agar, alginate, heteroglycans. Earlier research work demonstrated that natural polysaccharides have the highest ability to carry biological properties along with some biopolymers like as proteins and nucleic acids due to their structural variability. The preventive effect of these biomacromolecules was extensively studied, especially their beneficial effect on chronic metabolic conditions like dyslipidemia and related disorders. Dyslipidemia is a serious metabolic disorder associated with coronary heart disease, coronary artery diseases, hypercholesterolemia, atherosclerosis, etc. Dietary natural polysaccharides could play an important role in the management and prevention of dyslipidemia. Polysaccharides from natural sources mainly sulfated polysaccharides exhibited predominant lipid-lowering and cholesterol-lowering activities through different mechanisms. Polysaccharides isolated from different edible plants, vegetables, plant, algae, mushroom with higher biological activities, particularly hypolipidemic activity were highlighted in this paper, in a way for their futuristic therapeutic application. This review aims to comprehensively discuss overall advances in hypolipidemic activity of polysaccharides, including their sources, structural characteristic and chemistry, biological activity and their probable mode of action.

Anti-Inflammatory Activity of Orally Administered Monostroma nitidum Rhamnan Sulfate against Lipopolysaccharide-Induced Damage to Mouse Organs and Vascular Endothelium

We previously reported that rhamnan sulfate (RS) purified from Monostroma nitidum significantly suppressed lipopolysaccharide (LPS)-induced inflammation in cultured human vascular endothelial cells. Here, we analyzed the effect of orally administered RS on LPS-induced damage to mouse organs and vascular endothelium. RS (1 mg) was orally administered daily to BALB/c mice, 50 μg of LPS was intraperitoneally administered on day 8, and Evans blue was injected into the tail vein 6 h later. After 30 min, LPS-treated mice showed pulmonary Evans blue leakage and elevated plasma levels of liver damage markers, whereas this reaction was suppressed in LPS + RS-treated mice. Immunohistochemical and Western blot analysis of mouse organs 24 h after LPS treatment showed significant neutrophil infiltration into the lung, liver, and jejunum tissues of LPS-treated mice and high expression levels of inflammation-related factors in these tissues. Expression levels of these factors were significantly suppressed in LPS + RS-treated mice. Analysis of lung glycocalyx showed a significant reduction in glycocalyx in LPS-treated mice but not in LPS + RS-treated mice. Levels of syndecan-4, one of the glycocalyx components, decreased in LPS-treated mice and increased in LPS + RS-treated mice. The current results suggest that orally administered RS protects organs and vascular endothelium from LPS-induced inflammation and maintains blood circulation.

Algal polysaccharides and derivatives as potential therapeutics for obesity and related metabolic diseases

The potential and challenges of algal polysaccharides and their derivatives as potential therapeutic agents for obesity and its related metabolic diseases.

"Neptune Balls" Polysaccharides: Disentangling the Wiry Seagrass Detritus

Each year, high amounts of dead seagrass material are washed ashore at beaches world-wide. In the Mediterranean region, the seagrass Posidonia oceanica is responsible for huge agglomerates of ball-like seagrass litter. As these are often removed due to touristic reasons, a reuse method would be a step towards a more ecologically oriented society. In this study, the main polysaccharide components were analyzed, in order to propose possible usage options. To do this, different aqueous fractions were extracted, analyzed by classical carbohydrate analysis methods (GC-FID/MS, colorimetric assay and elemental analysis), and purified by ion-exchange chromatography, as well as selective precipitation with a detecting agent for highly glycosylated glycoproteins. The obtained purified fractions were analyzed in detail and a linkage-type analysis of the most promising extract was conducted via permethylation. Only low amounts of glycoproteins, as well as medium amounts of the characteristic apiogalacturonan were likely to be present, while xylan seemed to be the most abundant polysaccharide in most fractions. A partial structural proposal showed general accordance with land plant xylans, presenting reuse options in the field of biofuel and bioplastic generation.

Anti-SARS-CoV-2 Activity of Rhamnan Sulfate from Monostroma nitidum

The COVID-19 pandemic is a major human health concern. The pathogen responsible for COVID-19, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), invades its host through the interaction of its spike (S) protein with a host cell receptor, angiotensin-converting enzyme 2 (ACE2). In addition to ACE2, heparan sulfate (HS) on the surface of host cells also plays a significant role as a co-receptor. Our previous studies demonstrated that sulfated glycans, such as heparin and fucoidans, show anti-COVID-19 activities. In the current study, rhamnan sulfate (RS), a polysaccharide with a rhamnose backbone from a green seaweed, Monostroma nitidum, was evaluated for binding to the S-protein from SARS-CoV-2 and inhibition of viral infectivity in vitro. The structural characteristics of RS were investigated by determining its monosaccharide composition and performing two-dimensional nuclear magnetic resonance. RS inhibition of the interaction of heparin, a highly sulfated HS, with the SARS-CoV-2 spike protein (from wild type and different mutant variants) was studied using surface plasmon resonance (SPR). In competitive binding studies, the IC₅₀ of RS against the S-protein receptor binding domain (RBD) binding to immobilized heparin was 1.6 ng/mL, which is much lower than the IC₅₀ for heparin (~750 ng/mL). RS showed stronger inhibition than heparin on the S-protein RBD or pseudoviral particles binding to immobilized heparin. Finally, in an in vitro cell-based assay, RS showed strong antiviral activities against wild type SARS-CoV-2 and the delta variant.

Rhamnan sulphate from green algae Monostroma nitidum improves constipation with gut microbiome alteration in double-blind placebo-controlled trial

Rhamnan sulphate (RS), a sulphated polysaccharide from Monostroma nitidum, possesses several biological properties that help in treating diseases such as viral infection, thrombosis, and obesity. In the present study, we first administered RS (0.25 mg/g food volume) orally to high-fat diet-treated mice for 4 weeks. RS increased the faecal volume and calorie excretion with decreased plasma lipids, which was in accordance with the results of our previous zebrafish study. Notably, as the excretion amount by RS increased in the mice, we hypothesised that RS could decrease the chance of constipation in mice and also in human subjects because RS is considered as a dietary fibre. We administrated RS (100 mg/day) to subjects with low defaecation frequencies (3–5 times/week) for 2 weeks in double-blind placebo-controlled manner. As a result, RS administration significantly increased the frequency of dejection without any side effects, although no effect was observed on the body weight and blood lipids. Moreover, we performed 16s rRNA-seq analysis of the gut microbiota in these subjects. Metagenomics profiling using PICRUSt revealed functional alternation of the KEGG pathways, which could be involved in the therapeutic effect of RS for constipation.

A Review on Molecular Mechanisms and Patents of Marine-derived Anti-thrombotic Agents

Thrombosis is a condition of major concern worldwide as it is associated with life-threatening diseases related to the cardiovascular system. The condition affects 1 in 1000 adults annually, whereas 1 in 4 dies due to thrombosis, and this increases as the age group increases. The major outcomes are considered to be a recurrence, bleeding due to commercially available anti-coagulants, and deaths. The side effects associated with available anti-thrombotic drugs are a point of concern. Therefore, it is necessary to discover and develop an improvised benefit-risk profile drug, therefore, in search of alternative therapy for the treatment of thrombosis, marine sources have been used as promising treatment agents. They have shown the presence of sulfated fucans/galactans, fibrinolytic proteases, diterpenes, glycosaminoglycan, glycoside, peptides, amino acids, sterols, polysaccharides, polyphenols, vitamins, and minerals. Out of these marine sources, many chemicals were found to have anti-thrombotic activities. This review focuses on the recent discovery of anti-thrombotic agents obtained from marine algae, sponges, mussels, and sea cucumber, along with their mechanism of action and patents on its extraction process, preparation methods, and their applications. Further, the article concludes with the author's insight related to marine drugs, which have a promising future.

The Glycocalyx and Its Role in Vascular Physiology and Vascular Related Diseases

Purpose

In 2007 the two senior authors wrote a review on the structure and function of the endothelial glycocalyx layer (Weinbaum in Annu Rev Biomed Eng 9:121–167, 2007). Since then there has been an explosion of interest in this hydrated gel-like structure that coats the luminal surface of endothelial cells that line our vasculature due to its important functions in (A) basic vascular physiology and (B) vascular related diseases. This review will highlight the major advances that have occurred since our 2007 paper.

Methods

A literature search mainly focusing on the role of the glycocalyx in the two major areas described above was performed using electronic databases.

Results

In part (A) of this review, the new formulation of the century old Starling principle, now referred to as the Michel–Weinbaum glycoclayx model or revised Starling hypothesis, is described including new subtleties and physiological ramifications. New insights into mechanotransduction and release of nitric oxide due to fluid shear stress sensed by the glycocalyx are elaborated. Major advances in understanding the organization and function of glycocalyx components, and new techniques for measuring both its thickness and spatio-chemical organization based on super resolution, stochastic optical reconstruction microscopy (STORM) are presented. As discussed in part (B) of this review, it is now recognized that artery wall stiffness associated with hypertension and aging induces glycocalyx degradation, endothelial dysfunction and vascular disease. In addition to atherosclerosis and cardiovascular diseases, the glycocalyx plays an important role in lifestyle related diseases (e.g., diabetes) and cancer. Infectious diseases including sepsis, Dengue, Zika and Corona viruses, and malaria also involve the glycocalyx. Because of increasing recognition of the role of the glycocalyx in a wide range of diseases, there has been a vigorous search for methods to protect the glycocalyx from degradation or to enhance its synthesis in disease environments.

Conclusion

As we have seen in this review, many important developments in our basic understanding of GCX structure, function and role in diseases have been described since the 2007 paper. The future is wide open for continued GCX research.