Characterization of the Hydrolysis Mechanism of Polyalternating Alginate in Weak Acid and Assignment of the Resulting MG-Oligosaccharides by NMR Spectroscopy and ESI−Mass Spectrometry

A chemo-enzymatic method for preparation of saturated oligosaccharides from alginate and other uronic acid-containing polysaccharides

Oligosaccharides from uronic acid-containing polysaccharides can be produced either by chemical or enzymatic degradation. The benefit of using enzymes, called lyases, is their high specificity for various glycosidic linkages. Lyases cleave the polysaccharide chain by an β-elimination reaction, yielding oligosaccharides with an unsaturated sugar (4-deoxy-l-erythro-hex-4-enepyranosyluronate) at the non-reducing end. In this work we have systematically studied acid degradation of unsaturated uronic acid oligosaccharides. Based on these findings, a method for preparing saturated oligosaccharides by enzymatic degradation of uronic acid-containing polysaccharides was developed. This results in oligosaccharides with a pre-defined distribution and proportion of sugar residues compared to the products of chemical degradation, while maintaining the chemical structure of the non-reducing end. The described method was demonstrated for generating saturated oligosaccharides of alginate, heparin and polygalacturonic acid. In the case of alginate, the ratio of hydrolysis rate of Δ-G and Δ-M linkages to that of G-G and M-M linkages, respectively, was found to be approximately 65 and 43, at pH* 3.4, 90 °C. Finally, this method has been demonstrated to be superior in the production of α-l-guluronate oligosaccharides with a lower content of β-d-mannuronate residues compared to what can be achieved using chemical depolymerization alone.

Eco-friendly ozonation of alginate: Physicochemical characterization and degradation mechanism exploration through mass spectrometry

The ozone degradation has been proven to be an effective degradation method for alginate, while the degradation mechanism remained to be unconfirmed. In this study, two high-molecular-weight alginates with different mannuronic/guluronic (G/M) ratios, HM and HG (G/M 0.49 vs 1.40), were depolymerized using established ozonation technology platform. Notably, HM can be degraded faster than HG especially within initial 30 min, indicating that the β-1, 4-mannuronic bonds are more susceptible to be ozonated than α-1, 4-guluronic bonds. However, HM/HG degraded to LMWA in 2 h and reached a plateau. Therefore, we employed mass spectrometry (MS) to profile the degraded products of LMWA polymannuronate (PM) and polyguluronate (PG) in more intense conditions. The results indicated that the oxidation process continued until all reducing ends were converted to carboxyl groups. The o-diol could directly oxidize to o-dialdehyde. This study provides a MS based elucidation of the mechanism by which alginate cleaves to oligosaccharides through ozonation.

High-level production of a novel alginate lyase (FsAly7) from Flammeovirga sp. for efficient production of low viscosity soluble dietary fiber from sodium alginate

Sodium alginate is one of the most abundant sustainable gum source for dietary fiber production. However, the preparation efficiencies of low viscosity soluble dietary fiber from sodium alginate remain low. Here, a novel alginate lyase gene (FsAly7) from Flammeovirga sp. was identified and high-level expressed in Pichia pastoris for low viscosity soluble dietary fiber production. The highest enzyme production of 3050 U mL-1 was achieved, which is by far the highest yield ever reported. FsAly7 was used for low viscosity soluble dietary fiber production from sodium alginate, and the highest degradation rate of 85.5 % was achieved under a high substrate content of 20 % (w/v). The molecular weight of obtained soluble dietary fiber converged to 10.75 kDa. FsAly7 catalyzed the cleavage of glycosidic bonds in alginate chains with formation of unsaturated non-reducing ends simultaneously in the degradation process, thus altered the chemical structures of hydrolysates. The soluble dietary fiber exhibited excellent properties, including low viscosity, high oil adsorption capacity activity (2.20 ± 0.03 g g-1) and high emulsifying activity (60.05 ± 2.96 mL/100 mL). This investigation may provide a novel alginate lyase catalyst as well as a solution for the efficient production of low viscosity soluble dietary fiber from sodium alginate.

Ionically annealed zwitterionic microgels for bioprinting of cartilaginous constructs

Foreign body response (FBR) is a pervasive problem for biomaterials used in tissue engineering. Zwitterionic hydrogels have emerged as an effective solution to this problem, due to their ultra-low fouling properties, which enable them to effectively inhibit FBRin vivo. However, no versatile zwitterionic bioink that allows for high resolution extrusion bioprinting of tissue implants has thus far been reported. In this work, we introduce a simple, novel method for producing zwitterionic microgel bioink, using alginate methacrylate (AlgMA) as crosslinker and mechanical fragmentation as a microgel fabrication method. Photocrosslinked hydrogels made of zwitterionic carboxybetaine acrylamide (CBAA) and sulfobetaine methacrylate (SBMA) are mechanically fragmented through meshes with aperture diameters of 50 and 90µm to produce microgel bioink. The bioinks made with both microgel sizes showed excellent rheological properties and were used for high-resolution printing of objects with overhanging features without requiring a support structure or support bath. The AlgMA crosslinker has a dual role, allowing for both primary photocrosslinking of the bulk hydrogel as well as secondary ionic crosslinking of produced microgels, to quickly stabilize the printed construct in a calcium bath and to produce a microporous scaffold. Scaffolds showed ∼20% porosity, and they supported viability and chondrogenesis of encapsulated human primary chondrocytes. Finally, a meniscus model was bioprinted, to demonstrate the bioink's versatility at printing large, cell-laden constructs which are stable for furtherin vitroculture to promote cartilaginous tissue production. This easy and scalable strategy of producing zwitterionic microgel bioink for high resolution extrusion bioprinting allows for direct cell encapsulation in a microporous scaffold and has potential forin vivobiocompatibility due to the zwitterionic nature of the bioink.

Advances in oligosaccharides production from brown seaweeds: extraction, characterization, antimetabolic syndrome, and other potential applications

Brown seaweeds are a promising source of bioactive substances, particularly oligosaccharides. This group has recently gained considerable attention due to its diverse cell wall composition, structure, and wide-spectrum bioactivities. This review article provides a comprehensive update on advances in oligosaccharides (OSs) production from brown seaweeds and their potential health applications. It focuses on advances in feedstock pretreatment, extraction, characterization, and purification prior to OS use for potential health applications. Brown seaweed oligosaccharides (BSOSs) are extracted using various methods. Among these, enzymatic hydrolysis is the most preferred, with high specificity, mild reaction conditions, and low energy consumption. However, the enzyme selection and hydrolysis conditions need to be optimized for desirable yield and oligosaccharides composition. Characterization of oligosaccharides is essential to determine their structure and properties related to bioactivities and to predict their most suitable application. This is well covered in this review. Analytical techniques such as high-performance liquid chromatography (HPLC), gas chromatography (GC), and nuclear magnetic resonance (NMR) spectroscopy are commonly applied to analyze oligosaccharides. BSOSs exhibit a range of biological properties, mainly antimicrobial, anti-inflammatory, and prebiotic properties among others. Importantly, BSOSs have been linked to possible health advantages, including metabolic syndrome management. Metabolic syndrome is a cluster of conditions, such as obesity, hypertension, and dyslipidemia, which increase the risk of cardiovascular disease and type 2 diabetes. Furthermore, oligosaccharides have potential applications in the food and pharmaceutical industries. Future research should focus on improving industrial-scale oligosaccharide extraction and purification, as well as researching their potential utility in the treatment of various health disorders.[Figure: see text].

Estimation of alginate purity and M/G ratio by methanolysis coupled with anion exchange chromatography

Alginates are industrially relevant polysaccharides widely used in the food and biomedical industries for their excellent gelling properties. The growing emphasis on the valorization of marine resources has evidenced the need for alternative methods for the determination of both alginate content and the M/G ratio. This study describes the application of acid methanolysis and separation by anion exchange chromatography. Five samples, including alginates extracted from Saccharina latissima, Ascophyllum nodosum, a certified standard, and two poly-uronates (Poly-M and Poly-G), were analysed for their M/G ratio and alginate content at different treatment conditions, and compared with other conventionally used or reference methods (NMR, FTIR, and colorimetric methods). Quantitative estimation of alginate was relatively accurate at optimum conditions (4 h at 100 °C), as compared with the certified standard or with other colorimetric methods. M/G ratios were not significantly different from those determined after the reference method (1H NMR) or compared to FTIR protocols. The results evidence that methanolysis may be applied to simultaneously estimate the purity and M/G ratio of alginate-rich samples in a single analysis.

Alginate Conjugation Increases Toughness in Auricular Chondrocyte Seeded Collagen Hydrogels

Current auricular cartilage replacements for pediatric microtia fail to address the need for long-term integration and neocartilage formation. While collagen hydrogels have been successful in fostering neocartilage formation, the toughness and extensibility of these materials do not match that of native tissue. This study used the N-terminal functionalization of collagen with alginate oligomers to improve toughness and extensibility through metal-ion complexation. Alginate conjugation was confirmed via FTIR spectroscopy. The retention of native collagen fibrillar structure, thermal gelation, and helical conformation in functionalized gels was confirmed via scanning electron microscopy, oscillatory shear rheology, and circular dichroism spectroscopy, respectively. Alginate-calcium complexation enabled a more than two-fold increase in modulus and work density in functionalized collagen with the addition of 50 mM CaCl2, whereas unmodified collagen decreased in both modulus and work density with increasing calcium concentration. Additionally, the extensibility of alginate-functionalized collagen was increased at 25 and 50 mM CaCl2. Following 2-week culture with auricular chondrocytes, alginate-functionalization had no effect on the cytocompatibility of collagen gels, with no effects on cell density, and increased glycosaminoglycan deposition. Custom MATLAB video analysis was then used to quantify fracture toughness, which was more than 5-fold higher following culture in functionalized collagen and almost three-fold higher in unmodified collagen.

Controlled Release of Growth Factor from Heparin Embedded Poly(aldehyde guluronate) Hydrogels and Its Effect on Vascularization

To deliver growth factors controllably for tissue regeneration, poly(aldehyde guluronate) (PAG) was obtained from alginate and covalently cross-linked with aminated gelatin (AG) to form PAG/AG hydrogel as a growth factors carrier. The prepared hydrogel exhibits a slow degradation rate and excellent cytocompatibility. Heparin was conjugated with gelatin and embedded into the hydrogel to reserve and stabilize growth factors. Basic fibroblast growth factor (bFGF) was immobilized into the hydrogel and performed sustained release as the hydrogel degraded. The bFGF loaded hydrogel can improve vascularization effectively in a rat dorsal sac model. To summarize, heparin embedded PAG/AG hydrogels would serve as a promising biodegradable vehicle for the controlled delivery of growth factors and promoting vascularization in regenerative medicine.

Mannuronan C-5 Epimerases: Review of Activity Assays, Enzyme Characteristics, Structure, and Mechanism

Mannuronan C-5 epimerases (ManC5-Es) are produced by brown algae and some bacteria, such as Azotobacter and some Pseudomonas species. It can convert the transformation of β-D-mannuronic acid (M) to α-L-guluronic acid (G) in alginate with different patterns of epimerization. Alginate with different compositions and monomer sequences possess different properties and functions, which have been utilized in industries for various purposes. Therefore, ManC5-Es are key enzymes that are involved in the modifications of alginate for fuel, chemical, and industrial applications. Focusing on ManC5-Es, this review introduces and summarizes the methods of ManC5-Es activity assay especially the most widely used nuclear magnetic resonance spectroscopy method, characterization of the ManC5-Es from different origins especially the research progress of its enzymatic properties and product block distributions, and the catalytic mechanism of ManC5-E based on the resolved enzyme structures. Additionally, some potential future research directions are also outlooked.

Enzymatic depolymerization of alginate by two novel thermostable alginate lyases from Rhodothermus marinus

Alginate (alginic acid) is a linear polysaccharide, wherein (1→4)-linked β-D-mannuronic acid and its C5 epimer, α-L-guluronic acid, are arranged in varying sequences. Alginate lyases catalyze the depolymerization of alginate, thereby cleaving the (1→4) glycosidic linkages between the monomers by a β-elimination mechanism, to yield unsaturated 4-deoxy-L-erythro-hex-4-enopyranosyluronic acid (Δ) at the non-reducing end of resulting oligosaccharides (α-L-erythro configuration) or, depending on the enzyme, the unsaturated monosaccharide itself. In solution, the released free unsaturated monomer product is further hydrated in a spontaneous (keto-enol tautomerization) process to form two cyclic stereoisomers. In this study, two alginate lyase genes, designated alyRm3 and alyRm4, from the marine thermophilic bacterium Rhodothermus marinus (strain MAT378), were cloned and expressed in Escherichia coli. The recombinant enzymes were characterized, and their substrate specificity and product structures determined. AlyRm3 (PL39) and AlyRm4 (PL17) are among the most thermophilic and thermostable alginate lyases described to date with temperature optimum of activity at ∼75 and 81°C, respectively. The pH optimum of activity of AlyRm3 is ∼5.5 and AlyRm4 at pH 6.5. Detailed NMR analysis of the incubation products demonstrated that AlyRm3 is an endolytic lyase, while AlyRm4 is an exolytic lyase, cleaving monomers from the non-reducing end of oligo/poly-alginates.

Preparation and potential applications of alginate oligosaccharides

Alginate, a linear polymer consisting of β-D-mannuronic acid (M) and α-L-guluronic acid (G) with 1,4-glycosidic linkages and comprising 40% of the dry weight of algae, possesses various applications in the food and nutraceutical industries. However, the potential applications of alginate are restricted in some fields because of its low water solubility and high solution viscosity. Alginate oligosaccharides (AOS) on the other hand, have low molecular weight which result in better water solubility. Hence, it becomes a more popular target to be researched in recent years for its use in foods and nutraceuticals. AOS can be obtained by multiple degradation methods, including enzymatic degradation, from alginate or alginate-derived poly G and poly M. AOS have unique bioactivity and can bring human health benefits, which render them potentials to be developed/incorporated into functional food. This review comprehensively covers methods of the preparation and analysis of AOS, and discussed the potential applications of AOS in foods and nutraceuticals.

Characterization of alginate extracted from Sargassum latifolium and its use in Chlorella vulgaris growth promotion and riboflavin drug delivery

Alginates derived from macroalgae have been widely used in a variety of applications due to their stability, biodegradability and biocompatibility. Alginate was extracted from Egyptian Sargassum latifolium thallus yielding 17.5% w/w. The chemical composition of S. latifolium is rich in total sugars (41.08%) and uronic acids (47.4%); while, proteins, lipids and sulfates contents are 4.61, 1.13 and 0.09%, respectively. NMR, FTIR and TGA analyses were also performed. Crystallinity index (0.334) indicates alginate semicrystalline nature. Sodium alginate hydrolysate was evaluated as Chlorella vulgaris growth promoter. The highest stimulation (0.7 g/L biomass) was achieved by using 0.3 g/L alginate hydrolysate supplementation. The highest total soluble proteins and total carbohydrates were 179.22 mg/g dry wt and 620.33 mg/g dry wt, respectively. The highest total phenolics content (27.697 mg/g dry wt.), guaiacol peroxidase activity (2.899 µmol min-1 g-1) were recorded also to 0.3 g/L alginate hydrolysate supplementation. Riboflavin-entrapped barium alginate-Arabic gum polymeric matrix (beads) was formulated to achieve 89.15% optimum drug entrapment efficiency (EE%). All formulations exhibited prolonged riboflavin release over 120 min in simulated gastric fluid, followed Higuchi model (R2 = 0.962-0.887) and Korsmeyer-Peppas model with Fickian release (n ranges from 0.204 to 0.3885).

Alginate derived functional oligosaccharides: Recent developments, barriers, and future outlooks

Alginate is a biopolymer used extensively in the food, pharmaceutical, and chemical industries. Alginate oligosaccharides (AOS) derived from alginate exhibit superior biological activities and therapeutic potential. Alginate lyases with characteristic substrate specificity can facilitate the production of a broad array of AOS with precise structure and functionality. By adopting innovative analytical tools in conjunction with focused clinical studies, the structure-bioactivity relationship of a number of AOS has been brought to light. This review covers fundamental aspects and recent developments in AOS research. Enzymatic and microbial processes involved in AOS production from brown algae and sequential steps involved in AOS structure elucidation are outlined. Biological mechanisms underlying the health benefits of AOS and their potential industrial and therapeutic applications are elaborated. Withal, various challenges in AOS research are traced out, and future directions, specifically on recombinant systems for AOS preparation, are delineated to further widen the horizon of these exceptional oligosaccharides.

Alginate gels crosslinked with chitosan oligomers - a systematic investigation into alginate block structure and chitosan oligomer interaction

Three alginates with fundamentally different block structures, poly-M, poly-G, and poly-MG, have been investigated upon ionic crosslinking with chitosan oligosaccharides (CHOS), using circular dichroism (CD), rheology, and computer simulations, supporting the previously proposed gelling principle of poly-M forming zipper-like junction zones with chitosan (match in charge distance along the two polyelectrolytes) and revealing a unique high gel strength poly-MG chitosan gelling system. CD spectroscopy revealed an increased chiroptical activity exclusively for the poly-M chitosan gelling system, indicative of induced conformational changes and higher ordered structures. Rheological measurement revealed gel strengths (G' < 900 Pa) for poly-MG (1%) CHOS (0.3%) hydrogels, magnitudes of order greater than displayed by its poly-M analogue. Furthermore, the ionically crosslinked poly-MG chitosan hydrogel increased in gel strength upon the addition of salt (G' < 1600 at 50 mM NaCl), suggesting a stabilization of the junction zones through hydrophobic interactions and/or a phase separation. Molecular dynamics simulations have been used to further investigate these findings, comparing interaction energies, charge distances and chain alignments. These alginates are displaying high gel strengths, are known to be fully biocompatible and have revealed a broad range of tolerance to salt concentrations present in biological systems, proving high relevance for biomedical applications.

Alginate-based diblock polymers: preparation, characterization and Ca-induced self-assembly

Renewable resources can provide a range of different polysaccharide blocks that can be used to prepare new types of stimuli-responsive polysaccharide-based block copolymers.

Preparation of low-molecular-weight sodium alginate by ozonation

Low-molecular-weight sodium alginate (LMWSA) has been reported to possess unique physicochemical properties and bioactivities. There is little information available about degradation of sodium alginate by ozonation. Effect of ozonation on molecular weight, molecular weight distribution, color change, M/G ratio, and chemical structure of sodium alginate was investigated. The molecular weight of sodium alginate decreased from 972.3 to 76.7 kDa in the 80-min period of ozonation at 25 °C. Two different degradation-rate constants were calculated. Molecular weight distribution of the LMWSA changed appreciably. Ozonation cannot lead to color change of LMWSA. The M/G ratio of LMWSA was not altered significantly, compared with that of the original alginate. The FT-IR and ¹³C NMR spectra indicated the chemical structure of LMWSA obtained by ozonation was not altered appreciably. New insight into the ozonation of alginate will be promisingly opened up. Ozonation of sodium alginate can be a alternative for production of LMWSA.

Exploiting Mannuronan C-5 Epimerases in Commercial Alginate Production

Alginates are one of the major polysaccharide constituents of marine brown algae in commercial manufacturing. However, the content and composition of alginates differ according to the distinct parts of these macroalgae and have a direct impact on the concentration of guluronate and subsequent commercial value of the final product. The Azotobacter vinelandii mannuronan C-5 epimerases AlgE1 and AlgE4 were used to determine their potential value in tailoring the production of high guluronate low-molecular-weight alginates from two sources of high mannuronic acid alginates, the naturally occurring harvested brown algae (Ascophyllum nodosum, Durvillea potatorum, Laminaria hyperborea and Lessonia nigrescens) and a pure mannuronic acid alginate derived from fermented production of the mutant strain of Pseudomonas fluorescens NCIMB 10,525. The mannuronan C-5 epimerases used in this study increased the content of guluronate from 32% up to 81% in both the harvested seaweed and bacterial fermented alginate sources. The guluronate-rich alginate oligomers subsequently derived from these two different sources showed structural identity as determined by proton nuclear magnetic resonance (1H NMR), high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and size-exclusion chromatography with online multi-angle static laser light scattering (SEC-MALS). Functional identity was determined by minimum inhibitory concentration (MIC) assays with selected bacteria and antibiotics using the previously documented low-molecular-weight guluronate enriched alginate OligoG CF-5/20 as a comparator. The alginates produced using either source showed similar antibiotic potentiation effects to the drug candidate OligoG CF-5/20 currently in development as a mucolytic and anti-biofilm agent. These findings clearly illustrate the value of using epimerases to provide an alternative production route for novel low-molecular-weight alginates.

Preparation of alginate oligosaccharides and their biological activities in plants: A review

Alginate oligosaccharide (AOS) is the degradation product of alginates extracted from brown algae. As a multifunctional oligomer, it has attracted widespread attention in plant research. Different methods of preparation generate AOS possessing diverse structural properties, and result in differences in AOS activity. In this review, the methods of preparation and characterization of AOS are briefly summarized, followed by a systematic introduction to the activity and mechanisms of AOS in plants. AOS can act as a growth promoter at different growth stages of plants. AOS also enhances resistance to pathogens, drought, salt, heavy metals and other stressors by triggering plant immunity, exerting bioactivity just like a pathogen-associated molecular pattern. In addition, AOS can regulate ABA biosynthesis and metabolite to preserve fruit quality and enhance shelf life. This review provides a comprehensive summary of the biological activity of AOS in plants, which will support research and the application of AOS treatments for plants in the future.

Expression and Characterization of a New PolyG-Specific Alginate Lyase From Marine Bacterium Microbulbifer sp. Q7

Alginate lyases play an important role in preparation of alginate oligosaccharides. Although a large number of alginate lyases have been characterized, reports on directional preparation of alginate oligosaccharides by alginate lyases are still rather less. Here, a gene alyM encoding a new alginate lyase AlyM was cloned from Microbulbifer sp. Q7 and expressed in Escherichia coli. AlyM exhibited the maximumactivity at pH 7.0 and 55°C and showed special preference to poly-guluronic acid (polyG). Glycine promoted the extracellular secretion of AlyM by 3.6 times. PBS and glycerol significantly improved the thermal stability of AlyM, the enzyme activity remained 75 and 78% after heat-treatment at 45°C for 2 h, respectively. ESI-MS analysis suggested that AlyM mainly produced oligosaccharides with degrees of polymerization (DP) of 2-5. The results of ¹H-NMR showed that guluronic acid (G) occupied the reducing end of the end products, indicating that AlyM preferred to degrade the glycosidic bond at the G-X linkage. HPLC analysis showed that the hydrolysis products with a lower degree of polymerization contained more G. Therefore, AlyM shows good potential to produce alginate oligosaccharides with specific M/G ratio and molecular weights.

Effects of alginate oligosaccharides with different molecular weights and guluronic to mannuronic acid ratios on glyceollin induction and accumulation in soybeans

Alginate oligosaccharides (AOs) are linear oligosaccharides with alternating sequences of mannuronic acid (M) and guluronic acid (G) residues. AOs can be used as a safe elicitor to induce glyceollins, which have many human health benefits, in soybean seeds. In this research, four AO fractions with different chemical structures and molecular weights were separated, purified, and then characterized by NMR spectroscopy and ESI-MS. With a 4,5-unsaturated hexuronic acid residue (△) at the non-reducing terminus, the structures of these four AO fractions were △G, △MG, △GMG and △MGGG, which exhibited glyceollin-inducing activities of 1.2339, 0.3472, 0.6494 and 1.0611 (mg/g dry weight) in soybean seeds, respectively. The results demonstrated that a larger molecular weight or a higher G/M ratio might correlate with a higher glyceollin-inducing activity. Moreover, the alginate disaccharide △G could be introduced as relatively safe and efficient elicitor of high glyceollin content in soybeans.

OligoG CF-5/20 normalizes cystic fibrosis mucus by chelating calcium

The goal of this study was to determine whether the guluronate (G) rich alginate OligoG CF-5/20 (OligoG) could detach cystic fibrosis (CF) mucus by calcium chelation, which is also required for normal mucin unfolding. Since bicarbonate secretion is impaired in CF, leading to insufficient mucin unfolding and thereby attached mucus, and since bicarbonate has the ability to bind calcium, we hypothesized that the calcium chelating property of OligoG would lead to detachment of CF mucus. Indeed, OligoG could compete with the N-terminus of the MUC2 mucin for calcium binding as shown by microscale thermophoresis. Further, effects on mucus thickness and attachment induced by OligoG and other alginate fractions of different length and composition were evaluated in explants of CF mouse ileum mounted in horizontal Ussing-type chambers. OligoG at 1.5% caused effective detachment of CF mucus and the most potent alginate fraction tested, the poly-G fraction of about 12 residues, had similar potency compared to OligoG whereas mannuronate-rich (M) polymers had minimal effect. In conclusion, OligoG binds calcium with appropriate affinity without any overt harmful effect on the tissue and can be exploited for treating mucus stagnation.

Efficacy of acidic pretreatment for the saccharification and fermentation of alginate from brown macroalgae

This study was performed to evaluate the effectiveness of acidic pretreatment in increasing the enzymatic digestibility of alginate from brown macroalgae. Pretreatment with 1 % (w/v) sulfuric acid at 120 °C for 30 min produced oligosaccharides, mannuronic acid, and guluronic acid. Enzymatic saccharification of pretreated alginate by alginate lyases produced 52.2 % of the theoretical maximal sugar yield, which was only 7.5 % higher than the sugar yield obtained with unpretreated alginate. Mass spectrometric analyses of products of the two reactions revealed that acidic pretreatment and enzymatic saccharification produced saturated monomers (i.e., mannuronic and guluronic acid) with saturated oligosaccharides and unsaturated monomers (i.e., 4-deoxy-L-erythro-5-hexoseulose uronic acid; DEH), respectively. While DEH is further metabolized by microorganisms, mannuronic acid and guluronic acid are not metabolizable. Because of the poor efficacy in increasing enzymatic digestibility and owing to the formation of non-fermentable saturated monomers, acidic pretreatment cannot be recommended for enzymatic saccharification and fermentation of alginate.

Bioinspired titanium coatings: self-assembly of collagen–alginate films for enhanced osseointegration

Achieving long term osseointegration is fundamental to the development of successful bone implants.

Alginate-modifying enzymes: biological roles and biotechnological uses

Alginate denotes a group of industrially important 1-4-linked biopolymers composed of the C-5-epimers β-D-mannuronic acid (M) and α-L-guluronic acid (G). The polysaccharide is manufactured from brown algae where it constitutes the main structural cell wall polymer. The physical properties of a given alginate molecule, e.g., gel-strength, water-binding capacity, viscosity and biocompatibility, are determined by polymer length, the relative amount and distribution of G residues and the acetyl content, all of which are controlled by alginate modifying enzymes. Alginate has also been isolated from some bacteria belonging to the genera Pseudomonas and Azotobacter, and bacterially synthesized alginate may be O-acetylated at O-2 and/or O-3. Initially, alginate is synthesized as polymannuronic acid, and some M residues are subsequently epimerized to G residues. In bacteria a mannuronan C-5-epimerase (AlgG) and an alginate acetylase (AlgX) are integral parts of the protein complex necessary for alginate polymerization and export. All alginate-producing bacteria use periplasmic alginate lyases to remove alginate molecules aberrantly released to the periplasm. Alginate lyases are also produced by organisms that utilize alginate as carbon source. Most alginate-producing organisms encode more than one mannuronan C-5 epimerase, each introducing its specific pattern of G residues. Acetylation protects against further epimerization and from most alginate lyases. An enzyme from Pseudomonas syringae with alginate deacetylase activity has been reported. Functional and structural studies reveal that alginate lyases and epimerases have related enzyme mechanisms and catalytic sites. Alginate lyases are now utilized as tools for alginate characterization. Secreted epimerases have been shown to function well in vitro, and have been engineered further in order to obtain enzymes that can provide alginates with new and desired properties for use in medical and pharmaceutical applications.

Alginate lyases from alginate-degrading Vibrio splendidus 12B01 are endolytic

Alginate lyases are enzymes that degrade alginate through β-elimination of the glycosidic bond into smaller oligomers. We investigated the alginate lyases from Vibrio splendidus 12B01, a marine bacterioplankton species that can grow on alginate as its sole carbon source. We identified, purified, and characterized four polysaccharide lyase family 7 alginates lyases, AlyA, AlyB, AlyD, and AlyE, from V. splendidus 12B01. The four lyases were found to have optimal activity between pH 7.5 and 8.5 and at 20 to 25°C, consistent with their use in a marine environment. AlyA, AlyB, AlyD, and AlyE were found to exhibit a turnover number (kcat) for alginate of 0.60 ± 0.02 s(-1), 3.7 ± 0.3 s(-1), 4.5 ± 0.5 s(-1), and 7.1 ± 0.2 s(-1), respectively. The Km values of AlyA, AlyB, AlyD, and AlyE toward alginate were 36 ± 7 μM, 22 ± 5 μM, 60 ± 2 μM, and 123 ± 6 μM, respectively. AlyA and AlyB were found principally to cleave the β-1,4 bonds between β-d-mannuronate and α-l-guluronate and subunits; AlyD and AlyE were found to principally cleave the α-1,4 bonds involving α-l-guluronate subunits. The four alginate lyases degrade alginate into longer chains of oligomers.

Immunoisolation: where regenerative medicine meets solid organ transplantation

Immunoisolation refers to an immunological strategy in which nonself antigens present on an allograft or xenograft are not allowed to come in contact with the host immune system, and it is implemented to prevent allorecognition and avoid immunosuppression. In this setting, the two most promising technologies, encapsulation of pancreatic islets (EPI) and immunocloaking (IC), are used. In the case of EPI, islets are inserted in capsules that, allow exchange of oxygen, nutrients and other molecules. In the case of IC, a natural nanofilm is injected prior to renal transplantation within the vasculature of the graft with the intent to pave the inner surface of the vascular lumen and camouflage the antigens located on the membrane of endothelia cells. Significant progress achieved in experimental models is leading EPI and IC to clinical translation.

Design of a bioartificial pancreas

Islet transplantation has been shown to be a viable treatment option for patients afflicted with type 1 diabetes. However, the lack of availablity of human pancreases and the need to use risky immunosuppressive drugs to prevent transplant rejection remain two major obstacles to the routine use of islet transplantation in diabetic patients. Successful development of a bioartificial pancreas using the approach of microencapsulation with perm-selective coating of islets in hydrogels for graft immunoisolation holds tremendous promise for diabetic patients because it has great potential to overcome these two barriers. In this review article, we will discuss the need for a bioartificial pancreas, provide a detailed description of the microencapsulation process, and review the status of the technology in clinical development. We will also critically review the various factors that will need to be taken into consideration in order to achieve the ultimate goal of routine clinical application.

Multifunctional hyperbranched glycoconjugated polymers based on natural aminoglycosides

Multifunctional gene vectors with high transfection, low cytotoxicity, and good antitumor and antibacterial activities were prepared from natural aminoglycosides. Through the Michael-addition polymerization of gentamycin and N,N'-methylenebisacrylamide, cationic hyperbranched glycoconjugated polymers were synthesized, and their physical and chemical properties were analyzed by FTIR, (1)H NMR, (13)C NMR, GPC, ζ-potential, and acid-base titration techniques. The cytotoxicity of these hyperbranched glycoconjugated polycations was low because of the hydrolysis of degradable glycosidic and amide linkages in acid conditions. Owing to the presence of various primary, secondary, and tertiary amines in the polymers, hyperbranched glycoconjugated polymers showed high buffering capacity and strong DNA condensation ability, resulting in the high transfection efficiency. In the meantime, due to the introduction of natural aminoglycosides into the polymeric backbone, the resultant hyperbranched glycoconjugated polymers inhibited the growth of cancer cells and bacteria efficiently. Combining the gene transfection, antitumor, and antibacterial abilities together, the multifunctional hyperbranched glycoconjugated polymers based on natural aminoglycosides may play an important role in protecting cancer patients from bacterial infections.

Application of diffusion-edited NMR spectroscopy for selective suppression of water signal in the determination of monomer composition in alginates

Alginate is a linear copolymer of 1-4 linked β-D-mannuronic acid (M) and 1-4 linked α-L-guluronic acid (G). The physical properties of these polysaccharides such as gel properties and viscosity are largely correlated to the monomer composition (M/G ratio), the sequence of the polymer and the molecular weight. Determination of the M/G ratio is therefore important and NMR spectroscopy is among the most common methods used to accurately obtain this ratio. Instead of using time consuming, possibly sample altering, acid hydrolysis to reduce the viscosity of the alginate sample prior to analysis, samples of low concentrations can be used. However, this results in a water peak in the NMR spectrum that is several orders of magnitude larger than the alginate signals and water suppression is required. In this article, a diffusion-edited NMR experiment that suppresses the water peak while retaining the signals of interest has been used to enable correct M/G ratio determination. This approach exploits the difference in translational diffusion between the larger alginate molecules and the smaller water molecules. Using this method, the monomer composition of 20 different alginate powders was determined. The diffusion parameters were optimized to allow measurement for samples covering a large range of M/G ratios and viscosities. Thus, such method should be useful for analyzing large numbers of unknown alginate samples using, for example, automation procedures.

Isolation of mutant alginate lyases with cleavage specificity for di-guluronic acid linkages

Alginates are commercially valuable and complex polysaccharides composed of varying amounts and distribution patterns of 1-4-linked β-D-mannuronic acid (M) and α-L-guluronic acid (G). This structural variability strongly affects polymer physicochemical properties and thereby both commercial applications and biological functions. One promising approach to alginate fine structure elucidation involves the use of alginate lyases, which degrade the polysaccharide by cleaving the glycosidic linkages through a β-elimination reaction. For such studies one would ideally like to have different lyases, each of which cleaves only one of the four possible linkages in alginates: G-G, G-M, M-G, and M-M. So far no lyase specific for only G-G linkages has been described, and here we report the construction of such an enzyme by mutating the gene encoding Klebsiella pneumoniae lyase AlyA (a polysaccharide lyase family 7 lyase), which cleaves both G-G and G-M linkages. After error-prone PCR mutagenesis and high throughput screening of ∼7000 lyase mutants, enzyme variants with a strongly improved G-G specificity were identified. Furthermore, in the absence of Ca(2+), one of these lyases (AlyA5) was found to display no detectable activity against G-M linkages. G-G linkages were cleaved with ∼10% of the optimal activity under the same conditions. The substitutions conferring altered specificity to the mutant enzymes are located in conserved regions in the polysaccharide lyase family 7 alginate lyases. Structure-function analyses by comparison with the known three-dimensional structure of Sphingomonas sp. A1 lyase A1-II' suggests that the improved G-G specificity might be caused by increased affinity for nonproductive binding of the alternating G-M structure.