4,8-anhydro-N-acetylneuraminic acid. Isolation from edible bird's nest and structure determination

Edible Bird's Nest as a Potential Cognitive Enhancer

Cognitive enhancement is defined as the augmentation of the mind's core capabilities through the improvement of internal or external information processing systems. Recently, the focus has shifted to the potential therapeutic effects of natural products in improving cognitive function. Edible bird's nest (EBN) is a natural food substance derived from the saliva of swiftlets. Until today, EBN is regarded as a high-priced nutritious food with therapeutic effects. The effectiveness of dietary EBN supplementation to enhance brain development in mammals has been documented. Although the neuroprotection of EBN has been previously reported, however, the impact of EBN on learning and memory control and its potential as a cognitive enhancer drug remains unknown. Thus, this article aims to address the neuroprotective benefits of EBN and its potential effect as a cognitive enhancer. Notably, the current challenges and the future study direction in EBN have been demonstrated.

Edible bird's nest extract downregulates epidermal apoptosis and helps reduce damage by ultraviolet radiation in skin of hairless mice

The purpose of the present study was to examine whether daily intake of edible bird's nest extract reduced ultraviolet-induced damage to skin. Twenty-one female HR-1/Hos mice were divided into control (C, n = 7), low-dose (2 mg/kg body weight/day of edible bird's nest extract) (L, n = 7), and high-dose (20 mg/kg body weight/day of edible bird's nest extract) (H, n = 7) groups. With their left back skin covered with aluminum sheet to prevent exposure, mice were radiated with either ultraviolet A (20 J/cm2) or ultraviolet B (40 mJ/cm2) in an alternate manner once daily for 10 weeks. They were gavaged either a solution of saline or edible bird's nest extract every day. The moisture content of the ultraviolet-exposed right back skin was significantly higher in H than in C or L. Histochemical analysis showed that the number of apoptotic epidermal cells on the ultraviolet-exposed skin was significantly lower in L and H than in C. In H, the mRNA expression of superoxide dismutase 2 was significantly higher on ultraviolet-exposed skin than on unexposed skin. Our data suggested that edible bird's nest extract enhanced superoxide dismutase 2 expression and downregulated apoptosis in their epidermis, which likely helped reduce skin damage.

Sialic acid and biology of life: An introduction

Sialic acids are important molecule with high structural diversity. They are known to occur in higher animals such as Echinoderms, Hemichordata, Cephalochorda, and Vertebrata and also in other animals such as Platyhelminthes, Cephalopoda, and Crustaceae. Plants are known to lack sialic acid. But they are reported to occur in viruses, bacteria, protozoa, and fungi. Deaminated neuraminic acid although occurs in vertebrates and bacteria, is reported to occur in abundance in the lower vertebrates. Sialic acids are mostly located in terminal ends of glycoproteins and glycolipids, capsular and tissue polysialic acids, bacterial lipooligosaccharides/polysaccharides, and in different forms that dictate their role in biology. Sialic acid play important roles in human physiology of cell-cell interaction, communication, cell-cell signaling, carbohydrate-protein interactions, cellular aggregation, development processes, immune reactions, reproduction, and in neurobiology and human diseases in enabling the infection process by bacteria and virus, tumor growth and metastasis, microbiome biology, and pathology. It enables molecular mimicry in pathogens that allows them to escape host immune responses. Recently sialic acid has found role in therapeutics. In this chapter we have highlighted the (i) diversity of sialic acid, (ii) their occurrence in the diverse life forms, (iii) sialylation and disease, and (iv) sialic acid and therapeutics.

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

The rapid and sensitive detection of edible bird's nest (Aerodramus fuciphagus) in processed food by a loop-mediated isothermal amplification (LAMP) assay

Edible bird’s nest (EBN) is a well-known and precious traditional Chinese herbal material (CHM). Because of this, preventing the adulteration of EBN efficiently and precisely is crucial to protect consumers’ interests and health. In this study, a loop-mediated isothermal amplification (LAMP) assay was developed for the detection of EBN using specifically designed LAMP primers. The results demonstrated that the identification of EBN by LAMP assay was specific and rapid (within 1 h). It had no cross-reaction with EBN adulterants, including white fungus, egg white and pig skin, in different ratios. The relative detection limit was 0.01% EBN in the adulterants. Moreover, the sensitivity of LAMP in authenticating EBN was 10⁻⁸ μg, it showed higher sensitivity than that of conventional PCR with 10⁵ fold. When genomic DNAs extracted from boiled or steamed EBN samples were used as templates, LAMP for EBN detection was not affected and was reproducible after heat processing. In conclusion, the LAMP assay established herein could be applicable for authenticating EBN and for identifying commercial EBN products in herbal markets.

Identification of edible Bird’s nest with amino acid and monosaccharide analysis

This study describes the approach of amino acid and monosaccharide combined with Hotelling T2 range plot to identify edible bird nests (EBN) and non-EBN. Prior to the approach, an analytical method was developed and validated to quantify monosaccharides in EBN. Hotelling T2 range plots of both compounds were successful in predicting the different types of EBN and differentiating EBN and non-EBN. This outcome suggests EBN contains a group of glycoproteins which is not affected by the EBN’s coloration, country of origin, and/or the processing method of the food item. In addition, the glycoproteins were shown to be unique to EBN. EBN were revealed to be rich in protein and essential amino acids as well as contain a wider variety of monosaccharides than most food items. The overall findings suggest that amino acid and monosaccharide provide information not only on the detected compounds and also insights into the glycoproteins of EBN.

Edible bird's nest ameliorates oxidative stress-induced apoptosis in SH-SY5Y human neuroblastoma cells

Background

Parkinson’s disease (PD) is the second most common neurodegenerative disorder affecting the senile population with manifestation of motor disability and cognitive impairment. Reactive oxygen species (ROS) is implicated in the progression of oxidative stress-related apoptosis and cell death of the midbrain dopaminergic neurons. Its interplay with mitochondrial functionality constitutes an important aspect of neuronal survival in the perspective of PD. Edible bird’s nest (EBN) is an animal-derived natural food product made of saliva secreted by swiftlets from the Aerodamus genus. It contains bioactive compounds which might confer neuroprotective effects to the neurons. Hence this study aims to investigate the neuroprotective effect of EBN extracts in the neurotoxin-induced in vitro PD model.

Methods

EBN was first prepared into pancreatin-digested crude extract and water extract. In vitro PD model was generated by exposing SH-SY5Y cells to neurotoxin 6-hydroxydopamine (6-OHDA). Cytotoxicity of the extracts on SH-SY5Y cells was tested using MTT assay. Then, microscopic morphological and nuclear examination, cell viability test and ROS assay were performed to assess the protective effect of EBN extracts against 6-OHDA-induced cellular injury. Apoptotic event was later analysed with Annexin V-propidium iodide flow cytometry. To understand whether the mechanism underlying the neuroprotective effect of EBN was mediated via mitochondrial or caspase-dependent pathway, mitochondrial membrane potential (MMP) measurement and caspase-3 quantification were carried out.

Results

Cytotoxicity results showed that crude EBN extract did not cause SH-SY5Y cell death at concentrations up to 75 μg/ml while the maximum non-toxic dose (MNTD) of water extract was double of that of crude extract. Morphological observation and nuclear staining suggested that EBN treatment reduced the level of 6-OHDA-induced apoptotic changes in SH-SY5Y cells. MTT study further confirmed that cell viability was better improved with crude EBN extract. However, water extract exhibited higher efficacy in ameliorating ROS build up, early apoptotic membrane phosphatidylserine externalization as well as inhibition of caspase-3 cleavage. None of the EBN treatment had any effect on MMP.

Conclusions

Current findings suggest that EBN extracts might confer neuroprotective effect against 6-OHDA-induced degeneration of dopaminergic neurons, particularly through inhibition of apoptosis. Thus EBN may be a viable nutraceutical option to protect against oxidative stress-related neurodegenerative disorders such as PD.

Competitive enzyme-linked immunoassay for sialoglycoprotein of edible bird's nest in food and cosmetics

The proliferation of fake and inferior edible bird's nest (EBN) products has recently become an increasingly serious concern. To identify and classify EBN products, a competitive enzyme-linked immunoassay (ELISA) was developed to quantitate sialoglycoprotein in EBN used in food and cosmetic applications. The characteristic sialoglycoprotein in EBN was found, extracted, purified, and analyzed. Sialoglycoprotein, considered the main carrier of sialic acid in EBN, consisted of 106 and 128 kDa proteins. A monoclonal antibody that could recognize both proteins was prepared. The heat-treated process did not change the affinity of sialoglycoprotein with the antibody. An optimized ELISA method was established with a cross-reactivity of less than 0.1% and an IC(50) of 3.3 μg/mL. On the basis of different food and cosmetic samples, the limits of detection (LOD) were 10-18 μg/g. Recoveries of fortified samples at levels of 20 and 80 μg/g ranged from 81.5 to 96.5%, respectively. The coefficients of variation were less than 8.0%.

Improvement of bone strength and dermal thickness due to dietary edible bird's nest extract in ovariectomized rats

Oral administration of edible bird's nest extract (EBNE) improved bone strength and calcium concentration in the femur of ovariectomized rats. Dermal thickness was also increased by EBNE supplementation, whereas EBNE administration did not affect the serum estradiol concentration. These results suggest that EBNE is effective for the improvement of bone loss and skin aging in postmenopause all women.

Edible bird's nest extract inhibits influenza virus infection

Edible bird's nest (EBN) is the nest of the swift that is made from its saliva. Although EBN has been widely used for enhancing immunocompetence, its antiviral efficacy has not been studied in detail. We found that EBN extract could strongly inhibit infection with influenza viruses in a host range-independent manner when it was hydrolyzed with Pancreatin F. Western blotting assay showed that the EBN extract bound to influenza virus. Furthermore, EBN extract could neutralize the infection of MDCK cells with influenza viruses and inhibit hemagglutination of influenza viruses to erythrocytes, but it could not inhibit the activity of influenza virus sialidase. Fluorometric HPLC indicated that the major molecular species of sialic acid in EBN is N-acetylneuraminic acid. The results suggest that EBN is a safe and valid natural source for the prevention of influenza viruses.

Affinity of mouse immunoglobulin G subclasses for sialic acid derivatives immobilized on dextran-coated supports

High-performance liquid affinity chromatography is a powerful method for the purification of biological compounds owing to its specificity, rapidity and high resolution. In our laboratory, we develop chromatographic supports based on porous silica beads. However, in order to minimize non-specific interactions between the inorganic surface and proteins in aqueous solution, the silica beads are coated with modified dextran. As previously reported, many affinity ligands can be covalently grafted onto dextran-coated silica. In this study, N-acetylneuramic acid, which belongs to the sialic acid family and is present in immunoglobulin G (IgG) epitopes, is used as an active ligand. The interactions of this affinity support and IgG subclasses are analyzed. This immobilized ligand enables purification of IgG3 antibodies.

Protein glycosylation. Structural and functional aspects

During the last decade, there have been enormous advances in our knowledge of glycoproteins and the stage has been set for the biotechnological production of many of them for therapeutic use. These advances are reviewed, with special emphasis on the structure and function of the glycoproteins (excluding the proteoglycans). Current methods for structural analysis of glycoproteins are surveyed, as are novel carbohydrate-peptide linking groups, and mono- and oligo-saccharide constituents found in these macromolecules. The possible roles of the carbohydrate units in modulating the physicochemical and biological properties of the parent proteins are discussed, and evidence is presented on their roles as recognition determinants between molecules and cells, or cell and cells. Finally, examples are given of changes that occur in the carbohydrates of soluble and cell-surface glycoproteins during differentiation, growth and malignancy, which further highlight the important role of these substances in health and disease.

Indications for the enzymatic synthesis of 9-O-lactoyl-N-acetylneuraminic acid in equine liver

Fractionation of horse liver homogenate by centrifugation into heavy membranes at 10,000 x g, microsomal fraction at 105,000 x g, and the supernatant revealed sialate 9-O-lactoyltransferase activity only in the latter fraction. For the enzyme assay, the various fractions were incubated with 14C labelled CMP-N-acetylneuraminic acid, N-acetylneuramimic acid and glycoconjugate-bound N-acetylneuramimic acid. Lactoylation was identified in three different TLC systems after acid hydrolysis and purification of the sialic acids in the incubation mixtures. Enzyme activity was found only in the supernatant fraction. Glycoconjugate-bound N-acetylneuramimic acid was the best substrate tested, although some lactoylation was also found when using CMP-N-acetylneuraminic acid.

Structural characterization of the cell surface lipooligosaccharides from a nontypable strain of Haemophilus influenzae

Oligosaccharides released from the lipooligosaccharides (LOS) of Haemophilus influenzae nontypable strain 2019 by mild acid hydrolysis were fractionated by size exclusion chromatography and analyzed by liquid secondary ion mass spectrometry. The major component of the heterogeneous mixture was found to be a hexasaccharide of Mr 1366, which lost two phosphoethanolamine groups upon treatment with 48% aqueous HF. The dephosphorylated hexasaccharide was purified and shown by tandem mass spectrometry, composition analysis, methylation analysis, and two-dimensional nuclear magnetic resonance studies to be Gal beta 1----4Glc beta 1----(Hep alpha 1----2Hep alpha 1----3) 4Hep alpha 1----5anhydro-KDO, where Hep is L-glycero-D-manno-heptose and KDO is 3-deoxy-D-manno-octulosonic acid. An analogous structure containing authentic KDO was generated from LOS that had been HF-treated prior to acetic acid hydrolysis, suggesting that the reducing terminal anhydro-KDO moiety is produced as an artifact of the hydrolysis procedure by beta-elimination of a phosphate substituent from C-4 of KDO. Mass spectral analyses of O-deacylated LOS and free lipid A confirmed that, in addition to the two phosphoethanolamines on the oligosaccharide and two phosphates on the lipid A, another phosphate group exists on the KDO. This KDO does not appear to be further substituted with additional KDO residues in intact H. influenzae 2019 LOS. The terminal disaccharide epitope, Gal beta 1----4Glc beta 1----, of the hexasaccharide is also present on lactosylceramide, a precursor to human blood group antigens. It is postulated that the presence of this structure on H. influenzae LOS may represent a form of host mimicry by the pathogen.

Identification of a genetic locus essential for capsule sialylation in type III group B streptococci

The type III capsular polysaccharide of group B streptococci (GBS) consists of a linear backbone with short side chains ending in residues of N-acetylneuraminic acid, or sialic acid. The presence of sialic acid on the surface of the organism inhibits activation of the alternative pathway of complement and is thought to be an important element in the virulence function of the capsule. We showed previously that a mutant strain of GBS that expressed a sialic acid-deficient, or asialo, form of the type III polysaccharide was avirulent, supporting a virulence function for capsular sialic acid. We now report the derivation of an asialo capsule mutant from a highly encapsulated wild-type strain of type III GBS, strain COH1, by insertional mutagenesis with transposon Tn916 delta E. In contrast to the wild-type strain, the asialo mutant strain COH1-11 was sensitive to phagocytic killing by human leukocytes in vitro and was relatively avirulent in a neonatal rat model of GBS infection. The asialo mutant accumulated free intracellular sialic acid, suggesting a defect subsequent to sialic acid synthesis in the biosynthetic pathway leading to capsule sialylation. The specific biosynthetic defect in mutant strain COH1-11 was found to be in the activation of free sialic acid to CMP-sialic acid: CMP-sialic acid synthetase activity was present in the wild-type strain COH1 but was not detected in the asialo mutant strain COH1-11. One of the two transposon insertions in the asialo mutant COH1-11 mapped to the same chromosomal location as one of the two Tn916 insertions in the previously reported asialo mutant COH31-21, identifying this site as a genetic locus necessary for expression of CMP-sialic acid synthetase activity. These studies demonstrate that the enzymatic synthesis of CMP-sialic acid by GBS is an essential step in sialylation of the type III capsular polysaccharide.

Structural determination of oligosaccharides derived from lipooligosaccharide of Neisseria gonorrhoeae F62 by chemical, enzymatic, and two-dimensional NMR methods

F62 LOS of Neisseria gonorrhoeae consists of two major LOS components; the higher and smaller molecular weight (MW) components were recognized by MAbs 1-1-M and 3F11 respectively. Base-line separation of the two major oligosaccharide (OS) components from F62 LOS was achieved by Bio-Gel P-4 chromatography after dephosphorylation of the OS mixture. The structures of the two major OSs were studied by chemical, enzymatic, and 2D NMR methods [double quantum filtered COSY (DQF-COSY), delayed COSY (D-COSY), homonuclear Hartmann-Hahn spectroscopy (HOHAHA), pure-absorption 2D NOE NMR] as well as methylation followed by GC/MS analysis. The OS component derived from the MAb 1-1-M defined LOS component was determined to have a V3-(beta-N-acetylgalactosaminyl)neolactotetraose structure (GalNAc is beta 1----3-linked to a neolactotetraose) at one of its nonreducing termini as shown below. The above pentaose is linked to a branched diheptose-KDO core in which a GlcNAc is alpha-linked. The OS component derived from the MAb 3F11 defined LOS component did not have a GalNAc residue. The rest of its structure was identical to that of the OS-1, and a neolactotetraose is exposed at its nonreducing terminus. [formula: see text]