Influence of the uronic acid composition on the gastroprotective activity of alginates from three different genus of Tunisian brown algae

Characterization and structural identification of a novel alginate-specific carbohydrate-binding module (CBM): The founding member of a new CBM family

Alginate is a commercially important polysaccharide widely distributed in brown algae. Carbohydrate-binding modules (CBMs), a class of commonly used polysaccharide-binding proteins, have greatly facilitated the investigations of polysaccharides. Few alginate-binding CBMs have been hitherto reported and structurally characterized. Herein, an unknown domain from a potential PL6 family alginate lyase in the marine bacterium Vibrio breoganii was discovered and recombinantly expressed. The obtained protein, designated VbCBMxx, displayed the favorable specificity to alginate. The unique sequence and well-defined function of VbCBMxx reveal a new CBM family. Moreover, the structure of VbCBMxx was determined at a 1.5 Å resolution by the X-ray crystallography, which shows a typical β-sandwich fold comprised of two antiparallel β-sheets. Site-directed mutagenesis assays confirmed that positively charged polar residues are crucial for the ligand binding of VbCBMxx. The discovery of VbCBMxx enriches the toolbox of alginate-binding proteins, and the elucidation of critical residues would guide the future practical applications of VbCBMxx.

Effect of Flavoring with Rosemary, Lemon and Orange on the Quality, Composition and Biological Properties of Olive Oil: Comparative Study of Extraction Processes

The goal of this work was to investigate the impact of the flavoring of some aromatic plants/spices, including rosemary (R), lemon (L) and orange (O) at the concentration of 5% and 35% (w/w) added by 2 methods (conventional maceration and direct flavoring), on quality attributes, chemical changes and oxidative stability of extra virgin olive oil (EVOO). Six flavored oils were obtained (EVOO + O, O + O, EVOO + R, O + R, EVOO + L and O + L). The physicochemical parameters (water content, refractive index, acidity and peroxide value, extinction coefficient, fatty acids, volatile aroma profiles, Rancimat test, phenols and pigments composition) of the flavored oils were investigated. Based on the results obtained, it was observed that flavoring with a conventional process provided increased oxidative stability to the flavored oils, especially with rosemary (19.38 ± 0.26 h), compared to that of unflavored oil. The volatile profiles of the different flavored oils revealed the presence of 34 compounds with the dominance of Limonene. The fatty acid composition showed an abundance of mono-unsaturated fatty acids followed by poly-unsaturated ones. Moreover, a high antioxidant activity, a significant peripheral analgesic effect (77.7% of writhing inhibition) and an interesting gastroprotective action (96.59% of ulcer inhibition) have been observed for the rosemary-flavored oil. Indeed, the flavored olive oils of this study could be used as new functional foods, leading to new customers and further markets.

Cloning, expression, and characterization of a novel endo-type alginate lyase from Microbulbifer sp. BY17

BACKGROUND

Alginate oligosaccharides (AOS), with various physiological effects, have been widely used in the food, agricultural, and pharmaceutical industries. The biological enzymatic method of preparing AOS, using alginate lyase, has more advantages compared with physical and chemical methods. Cloning and heterologously expressing alginate lyase are therefore very important.

RESULTS

A novel alginate lyase, BY17PV7, from Microbulbifer sp. BY17, isolated from Gracilaria, was cloned and expressed in Escherichia coli BL21(DE3). BY17PV7 was about 27 KDa. BY17PV7 showed the greatest activity (150.42 ± 3.32 U/mg) at 43 °C and pH 8.9. It could be activated by Ca²⁺ , Mn²⁺ , Co²⁺ , Fe³⁺ , Na⁺ , and inhibited by Mg²⁺ , Zn²⁺ , Ba²⁺ , Cu²⁺ , sodium dodecyl sulfate (SDS), ethylene diamine tetraacetic acid (EDTA). BY17PV7 had a wide range of substrate specificity and good degradation effects for poly β-D-mannuronate (polyM) and poly α-L-guluronate (polyG), demonstrating that it is a bifunctional alginate lyase. The kinetic parameters showed that BY17PV7 had a greater affinity for polyG. BY17PV7 released AOS with a degree of polymerization (DP) of 3-4 in an endolytic manner from sodium alginate. Alginate oligosaccharides showed strong antioxidant ability of reducing Fe³⁺ and scavenging radicals such as hydroxyl, 2,2-azion-bia (3-ethylbenzo-thiazoline-6-sulfonic acid diammonium salt) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH).

CONCLUSION

A novel bifunctional alginate lyase, BY17PV7, was expressed and characterized in Escherichia coli BL21(DE3). The results were helpful for the analysis of the molecular mechanisms of degrading patterns in the polysaccharide lyase (PL) family. © 2022 Society of Chemical Industry.

Cocktail polysaccharides isolated from Ecklonia kurome against the SARS-CoV-2 infection

Previous researches suggested that polysaccharides from brown algae had anti-virus activity. We hypothesized that nature polysaccharide from marine plants might have the effect on anti-SARS-CoV-2 activity. By high throughput screening to target 3CLpro enzyme using polysaccharides library, we discover a crude polysaccharide 375 from seaweed Ecklonia kurome blocked 3CLpro enzymatic activity and shows good anti-SARS-CoV-2 infection activity in cell. Further, we show that homogeneous polysaccharide 37502 from the 375 may bind to 3CLpro well and disturb spike protein binding to ACE2 receptor. The structure characterization uncovers that 37502 is alginate. These results imply that the bioactivities of 375 on SARS-CoV-2 may target multiple key molecules implicated in the virus infection and replication. The above results suggest that 375 may be a potential drug candidate against SARS-CoV-2.

Structural elucidation and immunomodulatory evaluation of a polysaccharide from Stevia rebaudiana leaves

Stevia rebaudiana, a sweetener with medicinal functions, has attracted extensive attention due to its application in food and pharmaceutical fields. However, a few studies were performed to explore polysaccharides in this plant. Herein, SRP70-1 was derived from S. rebaudiana. Structural analysis (monosaccharide composition analysis, high-performance liquid chromatography-multi-angle light scattering detection, gas chromatography-mass spectrometry, and nuclear magnetic resonance spectroscopy) revealed that SRP70-1 was composed of mannose, glucose, galactose, and arabinose at the molar ratio of 1.35:1.00:3.23:3.47, with an absolute molecular weight of 7698 Da. SRP70-1 was found to contain → 5)-α-l-Araf-(1→, →2,3,5)-α-l-Araf-(1→, →4)-β-l-Arap-(1→, →4)-β-d-Galp-(1→, →6)-β-d-Galp-(1→, →4)-β-d-Manp-(1→, →6)-β-d-Manp-(1→, and terminal α-l-Araf, β-d-Galp, and β-d-Glcp residues. Cell experiments showed that SRP70-1 could significantly promote phagocytosis and increase the release of nitric oxide and cytokines including IL-1β, IL-6, and TNF-α. Further zebrafish experiments confirmed the immunological enhancement effects of SRP70-1. This study revealed that SRP70-1 may be useful for the development of functional foods.

Release of encapsulated bioactives influenced by alginate viscosity under in-vitro gastrointestinal model

The physicochemical properties of alginate can affect the release profile of encapsulated bioactives, but this is poorly understood. The influence of alginate viscosity (low- A1, medium- A2 and high- A3) and molecular weight (kDa) on the release of encapsulated bioactives (seaweed and spirulina powder) was investigated in an in-vitro gastrointestinal (GSI) model. Beads encapsulated with A2 at 1% (w/v) have overall higher release of bioactives (protein, phlorotannins and antioxidants) but A3 at 0.5% (w/v) was able to release and absorb similar amount of bioactives with ~10% difference with A2. The relative release of protein, phlorotannins and antioxidant was 96%, 111% and 43% respectively from A2 in gastric digestion. In contrast, protein (165%) and phlorotannins (234%) release was highest from A3 in intestinal phase. These results establish the importance of physicochemical properties of the encapsulating matrix on water retention capacity and their interaction with bioactive material to release into the system.

The immunoenhancement effects of starfish Asterias rollestoni polysaccharides in macrophages and cyclophosphamide-induced immunosuppression mouse models

The water-soluble polysaccharide, SF-2, obtained from starfish (Asterias rollestoni), belongs to the group of polysaccharides known as mannoglucan sulfate. It is composed of mannose as well as glucose and contains 13.85% SO₄^2-. We aimed to detect the immunoenhancement effects of SF-2 in macrophages and cyclophosphamide (CYP)-induced immunosuppression mouse models. RAW 264.7 macrophage cells were treated with SF-2 for different periods of time (0 h, 0.5 h, 1 h, 3 h, 6 h, and 9 h) and the results showed that SF-2 promoted the production of nitric oxide and up-regulated the levels of pro-inflammatory cytokines and related proteins, such as TNF-α, IL-1β, IL-6, COX-2, MMP-9, and iNOS in a time-dependent manner. In addition, SF-2 activated NLRP3 inflammasome and the MAPK/NF-κB signaling pathway, thus promoting its immunoenhancement effects. Moreover, we co-cultured the primary peritoneal macrophages with SF-2 for 6 h and found that SF-2 enhanced the expression of NLRP3 inflammasome and the release of cytokines. Furthermore, SF-2 significantly increased the body weight, spleen index, thymus index, and inflammatory cell counts in CYP-induced immunosuppression mouse models. These results indicate that SF-2 is a potential immunoenhancement mediator that acts by activating the NLRP3 inflammasome and MAPK/NF-κB pathway.

Seaweed's Bioactive Candidate Compounds to Food Industry and Global Food Security

The world population is continuously growing, so it is important to keep producing food in a sustainable way, especially in a way that is nutritious and in a sufficient quantity to overcome global needs. Seaweed grows, and can be cultivated, in seawater and generally does not compete for arable land and freshwater. Thus, the coastal areas of the planet are the most suitable for seaweed production, which can be an alternative to traditional agriculture and can thus contribute to a reduced carbon footprint. There are evolving studies that characterize seaweed's nutritional value and policies that recognize them as food, and identify the potential benefits and negative factors that may be produced or accumulated by seaweed, which are, or can be, dangerous for human health. Seaweeds have a high nutritional value along with a low caloric input and with the presence of fibers, proteins, omega 3 and 6 unsaturated fatty acids, vitamins, and minerals. Moreover, several seaweed sub-products have interesting features to the food industry. Therefore, the focus of this review is in the performance of seaweed as a potential alternative and as a safe food source. Here described is the nutritional value and concerns relating to seaweed consumption, and also how seaweed-derived compounds are already commercially explored and available in the food industry and the usage restrictions to safeguard them as safe food additives for human consumption.

Structural Characterization and α-Glucosidase Inhibitory and Antioxidant Activities of Fucoidans Extracted from Saccharina japonica

Two sulfated fucoidan fractions (Lj3 and Lj5) were extracted from Saccharina japonica and then subjected to acid hydrolysis to obtain Lj3h and Lj5h. Lj3h and Lj5h were characterized using IR, methylation analysis, and mass spectrometry. It was found that Lj3h and Lj5h were homogeneous low molecular weight fucoidans. Specifically, Lj3h was composed of the main chain of 1,3-linked α-L-fucopyranose residues with sulfate at C-2 and/or C-4 and three different monosaccharides (galactose, glucose, mannose) branched at C-2 and/or C-4 of fucose residue. Lj5h contained backbones of alternating galactopyranose residues and fucopyranose residues attached via a 1→3 linkage (galactofucan) and 1→6 linked galactan. The sulfation pattern was mainly located at C2/C4 fucose or galactose residues and more branches occupied at C-4 of fucose residue and C-2, C-3 or/and C-6 of galactose residue. In vitro assay indicated that, among the four fucoidans tested, only Lj5 showed potent α-glucosidase inhibitory activity with IC50 of 153.27±22.89 μg/mL, and the two parent fucoidans, Lj3 and Lj5, showed better antioxidant activity than their derivatives. These findings highlight the structure and bioactivity diversity of Saccharina japonica-derived fucoidans.

Expression and characterization of a novel alginate-binding protein: A promising tool for investigating alginate

Alginate is a commercially important polysaccharide widely applied in various industries. Carbohydrate-binding proteins could be utilized as desirable tools in the investigation and further applications of polysaccharides. Few alginate-binding proteins have hitherto been characterized and reported. In the present study, a novel alginate-binding protein ABP_Wf, consisting of two "orphan" carbohydrate-binding modules, was cloned from a predicted alginate utilization locus of marine bacterium Wenyingzhuangia funcanilytica, and expressed in Escherichia coli. ABP_Wf exhibited a specific binding capacity to alginate, and the association constant (K_a) and affinity (K_D) were 1.94 × 10³ M^-1s^-1 and 1.16 × 10^-6 M. It was confirmed that the binding capacity of ABP_Wf to alginate is attributed to its constituent CBM16 domain rather than the CBM44 domain. The potentials of ABP_Wf in the semi-quantitative detection and the in situ visualization of alginate were evaluated, which implied that ABP_Wf could be served as a promising tool for investigating alginate.

Extraction, purification, and determination of the gastroprotective activity of glucomannan from Bletilla striata

In this study, a water-soluble polysaccharide (BSP) was extracted and purified from pseudobulb of Bletilla striata. The preliminary structure and gastroprotective activity of BSP were analyzed. Results indicate that BSP is a glucomannan with a molar ratio of 7.45:2.55 (Man:Glc), and its molecular weight is approximately 1.7 × 10⁵ Da. BSP displayed outstanding protective action against ethanol-induced GES-1 cell injury in vitro, as well as, excellent gastroprotective activity in vivo. Especially, a high-dose of BSP (100 mg/kg) could reduce the ulcer index of the gastric mucosa and increase the percentage of ulcer inhibition, which possibly caused by enhancing the antioxidant capacity and inhibiting the apoptotic pathway in gastric tissue. Interestingly, BSP exhibited a comparative gastroprotective activity to that of positive control (omeprazole). In summary, our results indicated that BSP could be considered as a potential supplement for the prevention of gastric injury.

Okra polysaccharides/gelatin complex coacervate as pH-responsive and intestine-targeting delivery protects isoquercitin bioactivity

Okra polysaccharides (OPs) belong to RG I pectin branched with neutral saccharide side chains, which possesses distinctive structure and physicochemical properties from the commonly used HG pectin. Until now, the application of RG I pectin as wall material of microcapsule remains unclear. Here, we obtained OPs/gelatin complex coacervate at the maximum yield of 86.8% (pH 3.5, gelatin/OPs ratio 9:1 and 2% (w/v) total polymer concentration) by response surface methodology. Isoquercitin (IQ)-loaded OPs/gelatin complex coacervate (OGIQ) showed porous spongy-like surface structure with average particle size, encapsulation efficiency and surface porosity at 334 nm, 81.6% and 31.9%, respectively. OGIQ was found to be pH-responsive and intestine-targeting. The IQ-release rate of OGIQ was assayed to be 89.4% in intestine fluid and below 2% in acidic and simulated gastric digestion, respectively. Accordingly, embedding in OGIQ protected IQ in digestion and improved its postdigestive α-glucosidase inhibitory rate by 88.7%. The differential scanning calorimetry curves showed that OGIQ effectively prevented IQ from thermal decomposition. The XRD, FT-IR and CD spectra indicated that IQ was embedded in OGIQ in amorphous state by hydrogen bonds and electrostatic interaction. Compared with HG, the neutral saccharide side chains of OPs could induce different secondary conformation change of gelatin during complex coacervation.

Radioprotective effects and mechanisms of animal, plant and microbial polysaccharides

Ionizing radiation is increasingly used to successfully diagnose many human health problems, but ionizing radiation may cause damage to organs/tissues in the living organisms such as the spleen, liver, skin, and brain. Many radiation protective agents have been discovered, with the deepening of radiation research. Unfortunately, these protective agents have many side effects, which cause drug resistance, nausea, vomiting, osteoporosis, etc. The polysaccharides extracted from natural sources are widely available and low in toxicity. In vivo and in vitro experiments have demonstrated that polysaccharides have anti-radiation activity through anti-oxidation, immune regulation, protection of hematopoietic system and protection against DNA damage. Recently, some studies have shown that polysaccharides were resistant to radiation. In the review, the anti-radiation activities of polysaccharides from different sources are summarized, and the anti-radiation mechanisms are discussed as well. It can be used to develop more effective anti-radiation management drugs.

Effects of Molecular Weight and Guluronic Acid/Mannuronic Acid Ratio on the Rheological Behavior and Stabilizing Property of Sodium Alginate

The aim of this study was to prepare sodium alginates (SAs) with different molecular weight and G/M ratio, and characterize their rheological behaviors and emulsifying properties. The result of Fourier transform infrared (FTIR) showed that the chemical bonds among the β-d-mannuronic acid- (M-), α-l-guluronic acid- (G-), and MG-sequential blocks in the SA chains were not changed significantly by acid treatment. Meanwhile, the molecular weight and G/M ratio of the SA exhibited drastic variation after acid modification. The result of rheological analysis suggesting that the apparent viscosity of SA reduced from 30 to 16.4 mPa.s with the increase of shear rate, reveals that SA solution belongs to pseudoplastic liquid. Also, the apparent viscosity of acid-modified SA solution dropped rapidly with the decrease of the molecular weight. The properties of emulsions stabilized by SA, SA-Ms, and commercial SAs were evaluated via the interface tensiometry and determination of the zeta potential, droplet size, creaming index (CI), and Turbiscan stability index (TSI). Compared with the SA-stabilized emulsion, the interfacial tension of the emulsion stabilized by SA-M increased with the decrease of the molecular weight reduced at the similar M/G ratio. The decrease in zeta potential and the increase in TSI of the emulsion were observed with the decrease of molecular weight, indicating that molecular weight plays an important role on the emulsifying ability of SA. In addition, the SA with low G/M ratio can form emulsions with stable and fine droplets.

The Potential of Seaweeds as a Source of Functional Ingredients of Prebiotic and Antioxidant Value

Two thirds of the world is covered by oceans, whose upper layer is inhabited by algae. This means that there is a large extension to obtain these photoautotrophic organisms. Algae have undergone a boom in recent years, with consequent discoveries and advances in this field. Algae are not only of high ecological value but also of great economic importance. Possible applications of algae are very diverse and include anti-biofilm activity, production of biofuels, bioremediation, as fertilizer, as fish feed, as food or food ingredients, in pharmacology (since they show antioxidant or contraceptive activities), in cosmeceutical formulation, and in such other applications as filters or for obtaining minerals. In this context, algae as food can be of help to maintain or even improve human health, and there is a growing interest in new products called functional foods, which can promote such a healthy state. Therefore, in this search, one of the main areas of research is the extraction and characterization of new natural ingredients with biological activity (e.g., prebiotic and antioxidant) that can contribute to consumers' well-being. The present review shows the results of a bibliographic survey on the chemical composition of macroalgae, together with a critical discussion about their potential as natural sources of new functional ingredients.

Chemical composition, antioxidant and gastrointestinal properties of Sedum dendroideum Moc & Sessé ex DC leaves tea infusion

ETHNOPHARMACOLOGICAL RELEVANCE

Sedum dendroideum Moc & Sessé ex DC (Crassulaceae) is a medicinal plant employed in Mexican and Brasilian folk medicine as juice or infusion, as remedy for the treatment of different diseases, including gastric disorders.

AIM OF THE STUDY

Although some studies carried out with Sedum dendroideum have demonstrated its gastroprotective effect, the purpose of this study was to elucidate the chemical constituents, antioxidant, cytotoxic and mechanisms underlying the gastrointestinal properties of Sedum dendroideum accordingly its traditional use, as fresh leaves tea infusion (SDI).

MATERIALS AND METHODS

Chemical constituents were analyzed using high performance liquid chromatography and mass spectrometry (HPLC-MS). Antioxidant and cytotoxicity were evaluated in in vitro assays. The efficacy of the SDI on macroscopic ulcer appearance, mucus and GSH maintenance on ethanol- and indomethacin-induced ulcer models, gastric acid secretion and gastrointestinal motility were investigated.

RESULTS

Phytochemical analysis by HPLC-MS revealed the presence of different flavonol glycosides, containing myricetin and quercetin, along with the kaempferol as aglycones. In vitro pharmacological investigation of SDI demonstrated potent antioxidant activity in DPPH assay (IC50: 13.25 ± 3.37 µg/mL) and absence of cytotoxicity in Caco-2 cells by MTT method. Oral administration of SDI (ED₅₀ of 191.00 ± 0.08 mg/kg) in rats promoted gastroprotection against ethanol or indomethacin in rats through reinforcement of gastric wall mucus, GSH content and nitric oxide release, without present antisecretory properties. The gastroprotective effect was maintained when SDI (19 mg/kg) was administrated by intraperitoneal route. Furthermore, SDI (150 mg/kg) unchanged the gastric emptying but increase small bowel transit in mice through cholinergic pathways.

CONCLUSIONS

Collectively, this study confirmed that Sedum dendroideum promotes gastroprotection through preventing of endogenous defense mechanisms, represented by mucus and GSH without changes gastric acid secretion. Sedum dendroideum tea infusion features a chemical profile that contributes to the antioxidant and gastric health-promoting effects, supporting the use in folk medicine for the treatment of gastrointestinal disorders.

Cloning, expression and characterization of an endo-acting bifunctional alginate lyase of marine bacterium Wenyingzhuangia fucanilytica

Alginate is the major constituent of brown algae and a commercially important polysaccharide with wide applications. Alginate lyases are desired tools for degrading alginate. Based on the genome mining of marine bacterium Wenyingzhuangia funcanilytica, an alginate lyase Aly7B_Wf was discovered, cloned and expressed in Escherichia coli. Aly7B_Wf belonged to subfamily 6 of PL7 family. Its biochemical properties, kinetic constants, substrate specificity and degradation pattern were clarified. The enzyme is an endo-acting bifunctional alginate lyase, and preferably cleaved polymannuronate (polyM). The K_m (0.0237 ± 0.0004 μM, 0.0105 ± 0.0002 mg/mL) and k_cat/K_m (1180.65 ± 19.81 μM^-1 s^-1, 2654.34 ± 44.54 mg^-1 ml s^-1) indicated relatively high substrate-binding affinity and catalysis efficiency of Aly7B_Wf. By using mass spectrometry, final products of alginate degraded by Aly7B_Wf were identified as alginate hexasaccharide to disaccharide, and final products of polyguluronate (polyG) and polyM were confirmed as tetrasaccharide to disaccharide. The most predominant oligosaccharide in the final products of polyG and polyM was trisaccharide and disaccharide respectively. The broad substrate specificity, endo-acting degradation pattern and high catalysis efficiency suggested that Aly7B_Wf could be utilizied as a potential tool for tailoring the size of alginate and preparing alginate oligosaccharides.