Characterization of the Reaction between Sialic Acid (N-Acetylneuraminic Acid) and Hydrogen Peroxide

Microscopic mechanistic study of the penetration distributions for plasma reactive oxygen and nitrogen species based on sialic acid targeting on the cell membrane surface

The ability of cold atmospheric plasmas (CAPs) to produce a wide range of active constituents while maintaining a low or even room temperature of the gas has made it a novel research area of great interest. During plasma action, cancer cell membrane surface components are susceptible to oxidative modification by reactive oxygen and nitrogen species (RONS). In this study, the process of oxidative modification of membrane surface components sialic acid by RONS was investigated based on molecular dynamics simulations, and the penetration mechanism of long-lived particles ONOOH and its homolytic products at the membrane-water interface and the effect of appropriate electric field action were studied. The results showed that cancer cells with high sialic acid expression were less stable than healthy cells. Plasma treatment may promote the ONOOH homolysis process, and its homolysis product OH free radical is more likely to adsorb near sialic acid molecules by hydrogen bonding, resulting in oxidative modification. The interaction force between OH free radical and sialic acid molecules is stronger than ONOOH, which helps to further understand the oxidative modification reaction in membrane environment. At the same time, appropriate electric field stimulation can enhance the depth of penetration of RONS to more effectively treat the pathological state of biological tissues. The study proposes the use of membrane surface sialic acid as a cancer therapeutic target and provides guidance for improving the depth of RONS penetration and maximizing the survival of healthy cells, which contributes to the further clinical translation of plasma biomedicine.

Red Meat Derived Glycan, N-acetylneuraminic Acid (Neu5Ac) Is a Major Sialic Acid in Different Skeletal Muscles and Organs of Nine Animal Species-A Guideline for Human Consumers

Sialic acids (Sias) are acidic monosaccharides and red meat is a notable dietary source of Sia for humans. Among the Sias, N-acetylneuraminic acid (Neu5Ac) and 2-keto-3-deoxy-D-glycero-D-galacto-2-nonulosonic acid (KDN) play multiple roles in immunity and brain cognition. On the other hand, N-glycolylneuraminic acid (Neu5Gc) is a non-human Sia capable of potentiating cancer and inflammation in the human body. However, their expression within the animal kingdom remains unknown. We determined Neu5Ac and KDN in skeletal muscle and organs across a range (n = 9) of species using UHPLC and found that (1) caprine skeletal muscle expressed the highest Neu5Ac (661.82 ± 187.96 µg/g protein) following by sheep, pig, dog, deer, cat, horse, kangaroo and cattle; (2) Among organs, kidney contained the most Neu5Ac (1992−3050 µg/g protein) across species; (3) ~75−98% of total Neu5Ac was conjugated, except for in dog and cat muscle (54−58%); (4) <1% of total Sia was KDN, in which ~60−100% was unconjugated, with the exception of sheep liver and goat muscle (~12−25%); (5) Neu5Ac was the major Sia in almost all tested organs. This study guides consumers to the safest red meat relating to Neu5Ac and Neu5Gc content, though the dog and cat meat are not conventional red meat globally.

Desialylation in physiological and pathological processes: New target for diagnostic and therapeutic development

Desialylation is a pivotal part of sialic acid metabolism, which initiates the catabolism of glycans by removing the terminal sialic acid residues on glycans, thereby modulating the structure and functions of glycans, glycoproteins, or glycolipids. The functions of sialic acids have been well recognized, whereas the function of desialylation process is underappreciated or largely ignored. However, accumulating evidence demonstrates that desialylation plays an important role in a variety of physiological and pathological processes. This chapter summarizes the current knowledge pertaining to desialylation in a variety of physiological and pathological processes, with a focus on the underlying molecular mechanisms. The potential of targeting desialylation process for diagnostic and therapeutic development is also discussed.

Theoretical Studies on the Electronic Structure Parameters and Reactive Activity of Neu5Gc and Neu5Ac under Food Processing Solvent Environment

The animal product hazard factor N-glycolylneuraminic (Neu5Gc) and brain nutrient substance N-acetylneuraminic acid (Neu5Ac) were studied at the M062X/6-311 + G(d,p) geometry optimization level. We considered the electronic structure parameters with different solvents: (benzene ε = 2.27, acetic acid ε = 6.25, ethanol ε = 24.85, lactic acid ε = 22.00, formic acid ε = 51.1, water ε = 78.35). The maximum molecular surface electrostatic potentials, which were 62.77 for Neu5Gc and 60.90 kcal/mol for Neu5Ac, are both located on the carboxyl group hydrogen. The orbital analysis showed that the amide group and carboxyl group confer the sites with susceptibility to nucleophilic and electrophilic attack, respectively. The solvent effect showed that polar solvents, such as formic acid and water, can enhance the two molecules’ nucleophilic activity. To better understand the roles of the hydroxyl group in the two molecules, the independent gradient model theory confirmed the four intramolecular hydrogen bonds of Neu5Gc at gas phase, whereas Neu5Ac only has two. The lowest bond dissociation energy in solvent occurs at O7-H, which is 104.03 kcal/mol in water for Neu5Gc and 104.57 kcal/mol in lactic acid for Neu5Ac. The lowest proton affinity value for Neu5Gc (20.34 kcal/mol) and Neu5Ac (20.76 kcal/mol) was both occur at the carboxyl group O6-H under ethanol. The antioxidant mechanisms of the two sialic acid are prone to sequential proton-loss electron transfer under polar or non-polar solvents.

Mechanisms of depolymerization and activation of a polysialic acid and its tetramer by hydrogen peroxide

Naturally occurring polysialic acid (PSA), appropriately functionalized, has been widely used in different biological products. The present paper describes an original approach which enables to both activate and depolymerize the PSA, by reacting with hydrogen peroxide. In order to understand the mechanisms, we investigate the course of H2O2 reactions with the native PSA and with a simpler model, the tetrasialic acid (4SA). Three recurrent reactions were observed. First, we detected a very fast and irreversible decarbonylation at the reducing end of the polysaccharide. Then, the hydroxyl radicals (generated via the Fenton reaction) were responsible for the depolymerization of glycosidic linkages by substitution reactions. Finally, the oxidation of hydroxyl groups led to the formation of carbonyl groups and the carbohydrate's activation.

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.

Unified theory of bacterial sialometabolism: how and why bacteria metabolize host sialic acids

Sialic acids are structurally diverse nine-carbon ketosugars found mostly in humans and other animals as the terminal units on carbohydrate chains linked to proteins or lipids. The sialic acids function in cell-cell and cell-molecule interactions necessary for organismic development and homeostasis. They not only pose a barrier to microorganisms inhabiting or invading an animal mucosal surface, but also present a source of potential carbon, nitrogen, and cell wall metabolites necessary for bacterial colonization, persistence, growth, and, occasionally, disease. The explosion of microbial genomic sequencing projects reveals remarkable diversity in bacterial sialic acid metabolic potential. How bacteria exploit host sialic acids includes a surprisingly complex array of metabolic and regulatory capabilities that is just now entering a mature research stage. This paper attempts to describe the variety of bacterial sialometabolic systems by focusing on recent advances at the molecular and host-microbe-interaction levels. The hope is that this focus will provide a framework for further research that holds promise for better understanding of the metabolic interplay between bacterial growth and the host environment. An ability to modify or block this interplay has already yielded important new insights into potentially new therapeutic approaches for modifying or blocking bacterial colonization or infection.

Neuroprotective effects of black soybean anthocyanins via inactivation of ASK1-JNK/p38 pathways and mobilization of cellular sialic acids

AIMS

To investigate neuroprotective effects of three major anthocyanins (cyanidin-3-O-glucoside, delphinidin-3-O-glucoside, and petunidin-3-O-glucoside) isolated from the black soybean (Glycine max L.) cv. Cheongja 3 seed coat against H(2)O(2)-induced cell death of human brain neuroblastoma SK-N-SH cells.

MAIN METHODS

Cell viability, reactive oxygen species (ROS) generation, production and expression of heme oxygenase (HO)-1 and inactivation of mitogen-activated protein (MAP) kinase cascades were determined by MTT assay, 2,7-dichlorofluorescein diacetate (DCF-DA) assay, reverse transcriptase polymerase chain reaction (RT-PCR), and western blotting, respectively.

KEY FINDINGS

Pretreatment with anthocyanins reduced the cytotoxicity of H(2)O(2) on SK-N-SH cells, dose-dependently reduced the intracellular ROS level and inactivated apoptosis signal-regulating kinase (ASK1, Thr845), p38, and c-Jun N-terminal kinase (JNK) proteins. The HO-1 and Neu1 mRNA levels were increased by H(2)O(2) (25 μM) and further elevated by the pretreatment with anthocyanins. Sialic acids added to the culture plates not only attenuated the cytotoxicity of H(2)O(2) (25 μM) but also reduced intracellular ROS level. These results suggest that Cheongja 3 black soybean seed coat anthocyanins have brain neuroprotective effects against oxidative stress (H(2)O(2)) by inhibiting the activation of ASK1-JNK/p38 pathways, scavenging ROS, stimulating the expression of HO-1 and, more interestingly, recruiting cellular free sialic acids through up-regulation of Neu1 sialidase gene expression.

SIGNIFICANCE

This is the first report indicating potent health benefits of black soybean seed coat anthocyanins in neuroprotection by triggering mobilization of cellular free sialic acid and utilizing it as an additional biological antioxidant in brain neural cells.

Sialidase and sialoglycoproteases can modulate virulence in Porphyromonas gingivalis

The Porphyromonas gingivalis recombinant VimA can interact with the gingipains and several other proteins, including a sialidase. Sialylation can be involved in protein maturation; however, its role in virulence regulation in P. gingivalis is unknown. The three sialidase-related proteins in P. gingivalis showed the characteristic sialidase Asp signature motif (SXDXGXTW) and other unique domains. To evaluate the roles of the associated genes, randomly chosen P. gingivalis isogenic mutants created by allelic exchange and designated FLL401 (PG0778::ermF), FLL402 (PG1724::ermF), and FLL403 (PG0352::ermF-ermAM) were characterized. Similar to the wild-type strain, FLL402 and FLL403 displayed a black-pigmented phenotype in contrast to FLL401, which was not black pigmented. Sialidase activity in P. gingivalis FLL401 was reduced by approximately 70% in comparison to those in FLL402 and FLL403, which were reduced by approximately 42% and 5%, respectively. Although there were no changes in the expression of the gingipain genes, their activities were reduced by 60 to 90% in all the isogenic mutants compared to that for the wild type. Immunoreactive bands representing the catalytic domains for RgpA, RgpB, and Kgp were present in FLL402 and FLL403 but were missing in FLL401. While adhesion was decreased, the capacity for invasion of epithelial cells by the isogenic mutants was increased by 11 to 16% over that of the wild-type strain. Isogenic mutants defective in PG0778 and PG0352 were more sensitive to hydrogen peroxide than the wild type. Taken together, these results suggest that the P. gingivalis sialidase activity may be involved in regulating gingipain activity and other virulence factors and may be important in the pathogenesis of this organism.

A novel Caenorhabditis elegans allele, smn-1(cb131), mimicking a mild form of spinal muscular atrophy, provides a convenient drug screening platform highlighting new and pre-approved compounds

Spinal muscular atrophy (SMA), an autosomal recessive genetic disorder, is characterized by the selective degeneration of lower motor neurons, leading to muscle atrophy and, in the most severe cases, paralysis and death. Deletions and point mutations cause reduced levels of the widely expressed survival motor neuron (SMN) protein, which has been implicated in a range of cellular processes. The mechanisms underlying disease pathogenesis are unclear, and there is no effective treatment. Several animal models have been developed to study SMN function including the nematode, Caenorhabditis elegans, in which a large deletion in the gene homologous to SMN, smn-1, results in neuromuscular dysfunction and larval lethality. Although useful, this null mutant, smn-1(ok355), is not well suited to drug screening. We report the isolation and characterization of smn-1(cb131), a novel allele encoding a substitution in a highly conserved residue of exon 2, resembling a point mutation found in a patient with type IIIb SMA. The smn-1(cb131) animals display milder yet similar defects when compared with the smn-1 null mutant. Using an automated phenotyping system, mutants were shown to swim slower than wild-type animals. This phenotype was used to screen a library of 1040 chemical compounds for drugs that ameliorate the defect, highlighting six for subsequent testing. 4-aminopyridine, gaboxadol hydrochloride and N-acetylneuraminic acid all rescued at least one aspect of smn-1 phenotypic dysfunction. These findings may assist in accelerating the development of drugs for the treatment of SMA.

Sodium tungstate on some biochemical parameters of the parotid salivary gland of streptozotocin-induced diabetic rats: a short-term study

Several studies have shown the antidiabetic properties of sodium tungstate. In this study, we evaluated some biochemical parameters of the parotid salivary gland of streptozotocin-induced diabetic rats treated with sodium tungstate solution (2 mg/ml). The studied groups were: untreated control (UC), treated control (TC), untreated diabetic (UD), and treated diabetic (TD). After 2 and 6 weeks of treatment, parotid gland was removed and total protein and sialic acid (free and total) concentration and amylase and peroxidase activities were determined. Data were compared by variance analysis and Tukey test (p < 0.05). The sodium tungstate treatment modestly decreased the glycemia of streptozotocin-induced diabetic rats. At week 2 of the study, parotid gland of diabetic rats presented a reduction of total protein concentration (55%) and an increase of amylase (120%) and peroxidase (160%) activities, free (150%) and total (170%) sialic acid concentration. No alteration in the evaluated parameters at week 6 of the study was observed. Sodium tungstate presented no significant effect in parotid gland. Our results suggest that diabetes causes initial modification in biochemical composition of parotid. However, this gland showed a recovery capacity after 6 week of the experimental time. Sodium tungstate has no effect in peripheral tissues, such as salivary glands.

Sialic acid utilization by bacterial pathogens

Sialic acid occupies the terminal position within glycan molecules on the surfaces of many vertebrate cells, where it functions in diverse cellular processes such as intercellular adhesion and cell signalling. Pathogenic bacteria have evolved to use this molecule beneficially in at least two different ways: they can coat themselves in sialic acid, providing resistance to components of the host's innate immune response, or they can use it as a nutrient. Sialic acid itself is either synthesized de novo by these bacteria or scavenged directly from the host. In this mini-review we will summarize recent findings relating to sialic acid transport, modification of sialic acid by O-acetylation, and the mechanisms of sialic acid-mediated complement resistance.