The oxidation of some polysaccharides by the hydroxyl radical: an e.s.r. investigation

The antioxidant activity of polysaccharides: A structure-function relationship overview

Over the last years, polysaccharides have been linked to antioxidant effects using both in vitro chemical and biological models. The reported structures, claimed to act as antioxidants, comprise chitosan, pectic polysaccharides, glucans, mannoproteins, alginates, fucoidans, and many others of all type of biological sources. The structural features linked to the antioxidant action include the polysaccharide charge, molecular weight, and the occurrence of non-carbohydrate substituents. The establishment of structure/function relationships can be, however, biased by secondary phenomena that tailor polysaccharides behavior in antioxidant systems. In this sense, this review confronts some basic concepts of polysaccharides chemistry with the current claim of carbohydrates as antioxidants. It critically discusses how the fine structure and properties of polysaccharides can define polysaccharides as antioxidants. Polysaccharides antioxidant action is highly dependent on their solubility, sugar ring structure, molecular weight, occurrence of positive or negatively charged groups, protein moieties and covalently linked phenolic compounds. However, the occurrence of phenolic compounds and protein as contaminants leads to misleading results in methodologies often used for screening and characterization purposes, as well as in vivo models. Despite falling in the concept of antioxidants, the role of polysaccharides must be well defined according with the matrices where they are involved.

Effects of Configuration and Substitution on C-H Bond Dissociation Enthalpies in Carbohydrate Derivatives: A Systematic Computational Study

Density functional theory was used to calculate C-H bond dissociation enthalpies (BDEs) at each position of a diverse collection of pyranosides and furanosides differing in relative configuration and substitution patterns. A detailed analysis of the resulting data set (186 BDEs, calculated at the M06-2X/def2-TZVP level of theory) highlights the ways in which stereoelectronic effects, conformational properties, and noncovalent interactions can influence the strengths of C-H bonds in carbohydrates. The results point toward opportunities to alter the radical reactivity of carbohydrate derivatives by variation of their stereochemical configuration or the positions and types of protective groups.

Highly Crosslinked Agar/Acrylic Acid Hydrogels with Antimicrobial Properties

Hydrogels are three-dimensional soft polymeric materials that can entrap huge amounts of water. They are widely attractive in the biomedicine area because of their outstanding applications such as biosensors, drug delivery vectors, or matrices for cell scaffolds. Generally, the low mechanical strength and fragile structure of the hydrogels limit their feasibility, but this is not the case. In this work, acrylic acid-agar hydrogels with excellent mechanical properties were synthesized using gamma radiation as a crosslinking promoter. The obtained hydrogels exhibited a water absorption capacity up to 6000% in weight without breaking and keeping their shape; additionally, they showed a noticeable adhesion to the skin. The synthesized materials were characterized by infrared spectroscopy (FTIR-ATR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and mechanical testing. Additionally, their water uptake capacity and critical pH were studied. Net(Agar/AAc) hydrogel exhibited a noticeable capacity to load silver nanoparticles (AgNPs), which endowed it with antimicrobial activity that was demonstrated when challenged against Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA) on in vitro conditions.

Downstream Signalling from Molecular Hydrogen

Molecular hydrogen (H2) is now considered part of the suite of small molecules that can control cellular activity. As such, H2 has been suggested to be used in the therapy of diseases in humans and in plant science to enhance the growth and productivity of plants. Treatments of plants may involve the creation of hydrogen-rich water (HRW), which can then be applied to the foliage or roots systems of the plants. However, the molecular action of H2 remains elusive. It has been suggested that the presence of H2 may act as an antioxidant or on the antioxidant capacity of cells, perhaps through the scavenging of hydroxyl radicals. H2 may act through influencing heme oxygenase activity or through the interaction with reactive nitrogen species. However, controversy exists around all the mechanisms suggested. Here, the downstream mechanisms in which H2 may be involved are critically reviewed, with a particular emphasis on the H2 mitigation of stress responses. Hopefully, this review will provide insight that may inform future research in this area.

Nuclear Magnetic Resonance and Calorimetric Investigations of Extraction Mode on Flaxseed Gum Composition

We discussed about the influence of extraction mode on the flaxseed gums composition and their thermal stabilities. In order to do so, flaxseed gum was extracted by both classical magnetic stirring method and ultrasonic-assisted extraction (UAE). As a function of time, protein content, gum yield, pH values were evaluated and samples were characterized by 1H and 13C nuclear magnetic resonance (NMR) experiments as well as scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The flaxseed gum extracted in aqueous solution correspond to a mixture of different components, including polysaccharides, proteins and sometimes lignan derivatives. It is found that the protein and gum contents increase with the extraction duration for both the ultrasonic assisted and the traditional extraction while the pH decreases at the same time. As expected, compared to traditional magnetic stirring method, ultrasonic assisted extraction method can significantly enhance the yield of polysaccharides, lignans and proteins. The variation of pH is correlated to the increase of lignan molecules in the extracted samples. For thermic methods, SEM experiments showed that lignan derivatives which ester-bonded to polysaccharides associated to proteins are responsible to the formation of globular aggregates. Supplementary rod-like molecular organization were obtained from UAE and questions on the nature of the amphiphilic mesogen carbohydrate structures.

Regioselective degradation of [beta] 1,3 glucan by ferrous ion and hydrogen peroxide (Fenton oxidation)

Many species use Fe⁺² and H₂O₂ to oxidize a wide variety of compounds to simpler molecules. Both pathogen killing by leukocytes (neutrophils and lymphocytes) and degradation of cellulose by brown rot fungi rely on excretion of Fe⁺² ions and H₂O₂, the Fenton reagent. To elucidate the mechanism of Fenton oxidation of carbohydrates, β1,3 glucan (laminaran), a major fungal wall polysaccharide, was oxidized using a molar ratio of monomer/Fe⁺²/H₂O₂ of 10:1:1 (primarily). We labeled the reaction products and profiled them as fluorescent-labeled molecules in polyacrylamide gels and as hydrophobic-tagged molecules using reverse phase liquid chromatography/mass spectrometry (HPLC/MS). Sub-stoichiometric concentrations of Fe⁺² and H₂O₂ fragmented laminaran into smaller molecules containing carbonyl and carboxylic acid groups visible on fluorescent-labeled carbohydrate polyacrylamide gel electrophoresis. HPLC/MS analysis of glucan fragments showed masses consistent with six classes of molecules: aldoses, dialdoses, uronic acids, hexosuloses, aldonic acids, and hexulosonic acids. The results were consistent with published mechanisms where hydrogen radical (H•) abstraction from a C-H or O-H bond begins a cascade of reactions leading to 1) C-C bond cleavage to produce aldose/dialdose pairs; 2) oxo-group (O = ) addition to produce uronic and aldonic acids; 3) hydroxyl group (HO-) addition to produce gluconolactone and hexosuloses; and 4) hexulosonic acids. Most products resulted from regioselective H• abstractions characteristic of oxidations by ferryl-oxo ion [(FeO)⁺²] or perferryl-oxo ion [(FeO)⁺³] in close contact with specific positions in the glycan. Therefore, oxidations initiated by regioselectively-bound Fe ions were the predominant initiators of polysaccharide degradations.

Oxidation of sialic acid using hydrogen peroxide as a new method to tune the reducing activity

Functionalized sialic acids are useful intermediates to prepare a wide range of biological products. As they often occur at a non-reducing terminal of oligosaccharides, the most used technique to activate them is by periodate-mediated oxidation of their glycerol side chain. Here, we describe an alternative, non toxic, and environmentally-friendly method to activate the sialic acid residues by hydrogen peroxide oxidation. Four oxidative systems involving H2O2, EDTA, iron chloride, and UV light were studied and the products obtained were analyzed by LC-MS and NMR, before and after a derivatization reaction. At first, we observed, for each system, an irreversible decarbonylation reaction at the reducing end. Then, the decarbonylated sialic acid (DSA) was oxidized and fragmented into a mix of carbonyls and carboxyl acids, more or less fast according to the experimental conditions. Analysis of the reaction indicated an apparent radical mechanism and heterolytic alpha-hydroxy-hydroperoxide cleavages. The modest reducing activity was mainly explained as a consequence of over-oxidation reactions.

Antioxidant capacities of mannans and glucans are related to their susceptibility of free radical degradation

Microbial and plant polysaccharides in nature are frequently exposed to oxidative burst. They may act as antioxidants buffering the radical attack. This paper presents antioxidant properties of prepared yeast mannans, commercial β-glucans as well as the chemically prepared carboxymethylated β-glucan (CM-glucan). The hydroxyl radical antioxidant assay and the DPPH radical-scavenging assay were used. Yeast mannans and β-glucans (1.6 mg mL(-1)) showed antioxidant capacities against OH(·) up to 14.1%, while CM-glucan was significantly higher antioxidant (65.4%). In the DPPH(·) assay, the antioxidant capacities of yeast mannans and β-glucans (1.0 mg mL(-1)) were lower and reached up to ~6.5%. All polysaccharides tested were effectively degraded by OH(·) and the presence of salicylate considerably inhibited their degradation. Measure of Fe(2+) chelation revealed less than 13.1% effectivity for all polysaccharides. In all antioxidant and degradation experiments the yeast mannans showed very similar results to commercial β-glucans. The antioxidant capacities of polysaccharides may be assessed by simple HPLC monitoring.

Chemical methods for degradation of target oligosaccharides using designed light-activatable organic molecules

Carbohydrates play crucial roles in a wide range of biological processes, including serious diseases. The development of novel and innovative methods for selective control of specific oligosaccharide functions has attracted much attention in the fields of chemistry, biology, and medicine. In this feature article, the development of novel chemical tools, which can degrade target oligosaccharides by irradiation with a specific wavelength of light under mild conditions without any additives, is introduced. This novel class of photochemical agents promise bright prospects for finding not only molecular-targeted bioprobes for understanding of the structure-activity relationships of oligosaccharides but also novel therapeutic drugs targeting oligosaccharides.

Photo-Generation of Carbohydrate Microarrays

The unparalleled structural diversity of carbohydrates among biological molecules has been recognized for decades. Recent studies have highlighted carbohydrate signaling roles in many important biological processes, such as fertilization, embryonic development, cell differentiation and cellȁ4cell communication, blood coagulation, inflammation, chemotaxis, as well as host recognition and immune responses to microbial pathogens. In this chapter, we summarize recent progress in the establishment of carbohydrate-based microarrays and the application of these technologies in exploring the biological information content in carbohydrates. A newly established photochemical platform of carbohydrate microarrays serves as a model for a focused discussion.

Oxidative damage to extracellular matrix and its role in human pathologies

The extracellular compartments of most biological tissues are significantly less well protected against oxidative damage than intracellular sites and there is considerable evidence for such compartments being subject to a greater oxidative stress and an altered redox balance. However, with some notable exceptions (e.g., plasma and lung lining fluid) oxidative damage within these compartments has been relatively neglected and is poorly understood. In particular information on the nature and consequences of damage to extracellular matrix is lacking despite the growing realization that changes in matrix structure can play a key role in the regulation of cellular adhesion, proliferation, migration, and cell signaling. Furthermore, the extracellular matrix is widely recognized as being a key site of cytokine and growth factor binding, and modification of matrix structure might be expected to alter such behavior. In this paper we review the potential sources of oxidative matrix damage, the changes that occur in matrix structure, and how this may affect cellular behavior. The role of such damage in the development and progression of inflammatory diseases is discussed.

Effects of quinones on free-radical processes of oxidation and fragmentation of hydroxyl-containing organic compounds

The coenzymes Q and Vitamin K(3), as well as their synthetic analogues, have been found to inhibit free-radical processes of fragmentation of hydroxyl-containing organic compounds and oxidation of the latter by molecular oxygen. It has been established that the observed effects are due to the ability of quinones to oxidize the alpha-hydroxyl-containing carbon-centered radicals formed from the starting compounds.

Photons to illuminate the universe of sugar diversity through bioarrays

In this mini-review, we summarize the photochemical approaches for developing high-throughput carbohydrate microarray technologies. Newly established methods for photo-immobilizing unmodified monosaccharides, oligosaccharides and polysaccharides onto photoactive surfaces and coupling of photoactive carbohydrates onto polymer surfaces are reviewed.

Degradation of matrix glycosaminoglycans by peroxynitrite/peroxynitrous acid: evidence for a hydroxyl-radical-like mechanism

The oxidant peroxynitrite/peroxynitrous acid (ONOO-/ONOOH) is generated at sites of inflammation via reaction of O2.- with .NO. Previous studies have shown that these species can oxidize cellular targets, but few data are available on damage to extracellular matrix and its components, despite evidence for matrix modification in a number of pathologies. In the current study we show that reaction of ONOO-/ONOOH with glycosaminoglycans results in extensive polymer fragmentation. Bolus authentic ONOO-/ONOOH modifies hyaluronan, heparin, and chondroitin, dermatan, and heparan sulfates, in a concentration-dependent, but O2-independent, manner. The ONOO-/ONOOH generator 3-(4-morpholinyl)sydnoneimine produces similar time- and concentration-dependent damage. These reactions generate specific polymer fragments via cleavage at disaccharide intervals. Studies at different pH values, and in the presence of bicarbonate, are consistent with ONOOH, rather than the carbonate adduct, CO3.- or ONOO-, being the source of damage. EPR spin trapping experiments have provided evidence for the formation of carbon-centered radicals on glycosaminoglycans and related monosaccharides; the similarity of these spectra to those obtained with authentic HO. is consistent with fragmentation being induced by this oxidant. These data suggest that extracellular matrix fragmentation at sites of inflammation may be due, in part, to the formation and reactions of ONOOH.

Effects of vitamins, coenzymes and amino acids on reactions of homolytic cleavage of the O-glycoside bond in carbohydrates

It has been established that vitamins B1, K3 and C, coenzyme Q0 and amino acids cysteine and histidine effectively inhibit reactions of homolytic cleavage of the O-glycoside bond, which are responsible for the destruction of di- and polysaccharides on gamma-irradiation or the action of other reactive radical initiators. This effect was shown to originate from either oxidation or reduction of the radicals of carbohydrates undergoing destruction.

Photochemical micropatterning of carbohydrates on a surface

In this report, we demonstrate a versatile method for the immobilization and patterning of unmodified carbohydrates onto glass substrates. The method employs a novel self-assembled monolayer to present photoactive phthalimide chromophores at the air-monolayer interface. Upon exposure to UV radiation, the phthalimide end-groups graft to surface-adsorbed carbohydrates, presumably by a hydrogen abstraction mechanism followed by radical recombination to form a covalent bond. Immobilized carbohydrate thin films are evidenced by fluorescence, ellipsometry and contact-angle measurements. Surface micropatterns of mono-, oligo-, and polysaccharides are generated by exposure through a contact photomask and are visualized by condensing water onto the surface. The efficiency of covalent coupling is dependent on the thermodynamic state of the surface. The amount of surface-grafted carbohydrate is enhanced when carbohydrate surface interactions are increased by the incorporation of amine-terminated molecules into the monolayer. Glass substrates modified with mixed monolayers of this nature are used to construct carbohydrate microarrays by spotting the carbohydrates with a robot and subsequently illuminating them with UV light to covalently link the carbohydrates. Surface-immobilized polysaccharides display well-defined antigenic determinants for antibody recognition. We demonstrate, therefore, that this novel technology combines the ability to create carbohydrate microarrays using the current state-of-the-art technology of robotic microspotting and the ability to control the shape of immobilized carbohydrate patterns with a spatial resolution defined by the UV wavelength and a shape defined by a photomask.

Homolytic cleavage of the O-glycoside bond in carbohydrates: a steady-state radiolysis study

The formation of products resulting from the O-glycoside bond cleavage following radiolysis of aqueous solutions of methyl-alpha-D-glucopyranoside (I), 3-O-methyl-alpha-D-glucopyranose (II), maltose, lactose, gentiobiose and cellobiose were studied. Radiation-induced destruction yields were also determined for dextran, laminarin and trimethylcelulose upon irradiation of their aqueous solutions. Oxygen, quinones and compounds capable of forming quinoid structures were found to inhibit radiation-induced homolytic destruction processes taking place in glycosides, di- and polysaccharides. The data obtained in this study enabled the authors to demonstrate an important role played by the fragmentation reaction of C-2 radicals which were generated from the starting substances in the formation of final radiolysis products.

Effects of B group vitamins on reactions of various α-hydroxyl-containing organic radicals

Effects of vitamins B1, B2, B6, and pyridoxal phosphate (PPh) on final product formation in radiolysis of aqueous solutions of ethanol, ethylene glycol, alpha-methylglycoside, and maltose were studied. It has been found that vitamin B2 and PPh effectively oxidize R*CHOH species, while suppressing their recombination and fragmentation reactions, thereby increasing the yields of the respective oxidation products. Vitamins B1 and B2 are capable of reducing alcohol radicals to the respective initial molecules, decreasing the yields of the radical transformation products.

Free-radical fragmentation of galactocerebrosides: a MALDI-TOF mass spectrometry study

Analysis of final products of radiation-induced transformations of galactocerebrosides (GalCer) in aqueous dispersions has been performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and its combination of thin-layer chromatography (TLC). Ceramides were found to be the main products of GalCer gamma-radiolysis. From experimental results obtained in this study, as well as from the data available in the literature, an inference is made that the formation of ceramides occurs owing to fragmentation of radicals with an unpaired electron of the C2 atom of the carbohydrate moiety, formed from the starting compounds.

Effects of protein and peptide addition on lipid oxidation in powder model system

The effect of protein and peptide addition on the oxidation of eicosapentaenoic acid ethyl ester (EPE) encapsulated by maltodextrin (MD) was investigated. The encapsulated lipid (powder lipid) was prepared in two steps, i.e., mixing of EPE with MD solutions (+/- protein and peptides) to produce emulsions and freeze-drying of the resultant emulsions. EPE oxidation in MD powder progressed more rapidly in the humid state [relative humidity (RH) = 70%] than in the dry state (RH = 10%). The addition of soy protein, soy peptide, and gelatin peptides improved the oxidation stability of EPE encapsulated by MD, and the inhibition of lipid oxidation by the protein and the peptides was more dramatic in the humid state. Especially, the oxidation of EPE was almost perfectly suppressed when the lipid was encapsulated with MD + soy peptide during storage in the humid state for 7 days. Several physical properties such as the lipid particle size of the emulsions, the fraction of nonencapsulated lipids, scanning electron microscopy images of powder lipids, and the mobility of the MD matrix were investigated to find the modification of encapsulation behavior by the addition of the protein and peptides, but no significant change was observed. On the other hand, the protein and peptides exhibited a strong radical scavenging activity in the powder systems as well as in the solution systems. These results suggest that a chemical mechanism such as radical scavenging ability plays an important role in the suppression of EPE oxidation in MD powder by soy proteins, soy peptides, and gelatin peptides.

Cationic dye-sensitized degradation of sodium hyaluronate through photoinduced electron transfer in the upper excited state

The formation of ground-state complexes of methylene blue (MB) and thionine (TN) with sodium hyaluronate (NaHA) was clearly observed by means of absorption spectra in aqueous solution. Irradiation of the complexes using 313 nm light caused significant degradation of NaHA under oxygen and argon. However, the use of visible light over 400 nm, which gives the lowest excited singlet state of the cationic dyes, caused no degradation. MB and TN were more efficient sensitizers for the degradation of NaHA than rose bengal (RB), although RB is a more efficient singlet oxygen (1O2) sensitizer than the cationic dyes. Under similar conditions the polysaccharides with carboxyl groups, such as alginic acid and polygalacturonic acid, also photodecomposed. However, the polysaccharides without carboxyl groups, such as pullulan and methyl cellulose, did not. The irradiation of the polysaccharides in the presence of powdered titanium dioxide as a photocatalyst to generate the hydroxyl radical (.OH) in aerated aqueous solution caused the fragmentation of all the polymers. It was confirmed that methyl viologen, an electron-accepting sensitizer, formed a charge-transfer complex with NaHA, the irradiation of which caused the efficient degradation of NaHA. In the presence of beta- and gamma-cyclodextrins the MB- and TN-sensitized photodegradation of NaHA was markedly suppressed. This was probably due to the formation of the inclusion complexes comprising the cationic dyes and the cyclodextrins. On the basis of the results obtained we propose that the cationic dye-sensitized degradation of NaHA involves a photoinduced electron-transfer process between the upper excited dyes and the ground-state NaHA and that .OH and 1O2 do not participate in the degradation.