Sialic acid O-acetylation: From biosynthesis to roles in health and disease

Regulation of sialic acid metabolism in cancer

Sialic acid, the terminal structure of cell surface glycans, has essential functions in regulating immune response, cell-to-cell communication, and cell adhesion. More importantly, an increased level of sialic acid, termed hypersialylation, has emerged as a commonly observed phenotype in cancer. Therefore, targeting sialic acid ligands (sialoglycans) and their receptors (Siglecs) may provide a new therapeutic approach for cancer immunotherapy. We highlight the complexity of the sialic acid metabolism and its involvement in malignant transformation within individual cancer subtypes. In this review, we focus on the dysregulation of sialylation, the intricate nature of sialic acid synthesis, and clinical perspective. We aim to provide a brief insight into the mechanism of hypersialylation and how our understanding of these processes can be leveraged for the development of novel therapeutics.

Analysis of O-acetylated sialic acids by 3-nitrophenylhydrazine derivatization combined with LC-MS/MS

Sialic acids are a family of monosaccharides that share a nine-carbon backbone and a carboxyl group. A recent derivatization method based on 3-nitrophenylhydrazine (3-NPH) provides a mild chemical labeling technique for biomolecules containing carbonyl or carboxyl groups. In this study, we utilized 3-NPH to label sialic acids via a two-step derivatization process. The derivatized species can produce a common reporter ion corresponding to C1-C3 with two labels, and a fragment differentiating between Neu5Ac, Neu5Gc, and KDN. This method is compatible with O-acetylated sialic acids and provides high sensitivity to Neu5Gc and KDN, and since the utilization of dual labeling significantly enhances the hydrophobicity of derivatives, it can effectively mitigate matrix effects when combined with parallel reaction monitoring technology. Negative-ion tandem mass spectrometry (MS/MS) analysis reveals a distinctive fragmentation profile for the 4-O-acetylated species, while the other sialic acids yield similar MS/MS spectra with a high abundance of reporter ions. Using the reporter ion as a transition, this analytical strategy is effective for analyzing complex biological samples. For example, it was successfully employed to quantify sialic acids in the intestinal tissues of several carp species, demonstrating its potential in sialylation research.

Non-targeted isomer-sensitive N-glycome analysis reveals new layers of organ-specific diversity in mice

N-glycosylation is one of the most common protein modifications in eukaryotes, with immense importance at the molecular, cellular, and organismal level. Accurate and reliable N-glycan analysis is essential to obtain a systems-wide understanding of fundamental biological processes. Due to the structural complexity of glycans, their analysis is still highly challenging. Here we make publicly available a consistent N-glycome dataset of 20 different mouse tissues and demonstrate a multimodal data analysis workflow that allows for unprecedented depth and coverage of N-glycome features. This highly scalable, LC-MS/MS data-driven method integrates the automated identification of N-glycan spectra, the application of non-targeted N-glycome profiling strategies and the isomer-sensitive analysis of glycan structures. Our delineation of critical sub-structural determinants and glycan isomers across the mouse N-glycome uncovered tissue-specific glycosylation patterns, the expression of non-canonical N-glycan structures and highlights multiple layers of N-glycome complexity that derive from organ-specific regulations of glycobiological pathways.

The Prognostic Value of Serum Sialic Acid in Patients with Nasopharyngeal Carcinoma: A Propensity Score Matching Study

Purpose

Elevated serum sialic acid (SA) is one of the indicators of poor prognosis in various malignant tumors. This study intends to determine the relationship between serum SA levels and survival prognosis in nasopharyngeal carcinoma (NPC).

Patients and Methods

From 2014 to 2016, NPC patients with no distance metastasis undergoing intensity-modulated radiotherapy (IMRT) were retrospectively analyzed. The serum SA levels before initial treatment were measured, and an optimal cut-off level was determined by X-tile software. A propensity score matching (PSM) technique was applied to reduce intergroup differences between the low serum SA level group and the high serum SA level group. Chi-square tests were utilized for comparing intergroup differences, Kaplan-Meier approach was utilized for plotting survival curves, and univariate and multivariate Cox proportional hazards regression models were employed for analyzing prognostic factors.

Results

Overall, 293 NPC patients with no distance metastasis were included. The optimal cut-off level of serum SA was 65.10 mg/dl. The baseline levels after PSM were more balanced compared to those before PSM. Survival analysis showed that the locoregional relapse-free survival (LRRFS, p=0.010), distant metastasis-free survival (DMFS, p=0.014), progression-free survival (PFS, p=0.009), and overall survival (OS, p=0.015) survival curves of the low serum SA level group and high serum SA level group were statistically significant differences. Univariate analysis showed that American Joint Committee on Cancer (AJCC) stage, T stage, N stage, neoadjuvant chemotherapy (NC), and serum SA expression level were factors influencing the prognosis of NPC patients. Multivariate analysis showed that high serum SA expression level was related to worse PFS and OS in NPC patients with no distance metastasis.

Conclusion

High serum SA level (SA > 65.10 mg/dl) before treatment is associated to poor survival outcomes in NPC and is an independent adverse prognostic factor in NPC patients with no distance metastasis.

Influenza D virus utilizes both 9-O-acetylated N-acetylneuraminic and 9-O-acetylated N-glycolylneuraminic acids as functional entry receptors

Influenza D virus (IDV) utilizes bovines as a primary reservoir with periodical spillover to other hosts. We have previously demonstrated that IDV binds both 9-O-acetylated N-acetylneuraminic acid (Neu5,9Ac2) and 9-O-acetylated N-glycolylneuraminic acid (Neu5Gc9Ac). Bovines produce both Neu5,9Ac2 and Neu5Gc9Ac, while humans are genetically unable to synthesize Neu5Gc9Ac. 9-O-Acetylation of sialic acids is catalyzed by CASD1 via a covalent acetyl-enzyme intermediate. To characterize the role of Neu5,9Ac2 and Neu5Gc9Ac in IDV infection and determine which form of 9-O-acetylated sialic acids drives IDV entry, we took advantage of a CASD1 knockout (KO) MDCK cell line and carried out feeding experiments using synthetic 9-O-acetyl sialic acids in combination with the single-round and multi-round IDV infection assays. The data from our studies show that (i) CASD1 KO cells are resistant to IDV infection and lack of IDV binding to the cell surface is responsible for the failure of IDV replication; (ii) feeding CASD1 KO cells with Neu5,9Ac2 or Neu5Gc9Ac resulted in a dose-dependent rescue of IDV infectivity; and (iii) diverse IDVs replicated robustly in CASD1 KO cells fed with either Neu5,9Ac2 or Neu5Gc9Ac at a level similar to that in wild-type cells with a functional CASD1. These data demonstrate that IDV can utilize Neu5,9Ac2- or non-human Neu5Gc9Ac-containing glycan receptor for infection. Our findings provide evidence that IDV has acquired the ability to infect and transmit among agricultural animals that are enriched in Neu5Gc9Ac, in addition to posing a zoonotic risk to humans expressing only Neu5,9Ac2.IMPORTANCEInfluenza D virus (IDV) has emerged as a multiple-species-infecting pathogen with bovines as a primary reservoir. Little is known about the functional receptor that drives IDV entry and promotes its cross-species spillover potential among different hosts. Here, we demonstrated that IDV binds exclusively to 9-O-acetylated N-acetylneuraminic acid (Neu5,9Ac2) and non-human 9-O-acetylated N-glycolylneuraminic acid (Neu5Gc9Ac) and utilizes both for entry and infection. This ability in effective engagement of both 9-O-acetylated sialic acids as functional receptors for infection provides an evolutionary advantage to IDV for expanding its host range. This finding also indicates that IDV has the potential to emerge in humans because Neu5,9Ac2 is ubiquitously expressed in human tissues, including lung. Thus, results of our study highlight a need for continued surveillance of IDV in humans, as well as for further investigation of its biology and cross-species transmission mechanism.

A periodic table of monosaccharides

It is important to recognize the great diversity of monosaccharides commonly encountered in animals, plants, and microbes, as well as to organize them in a visually interesting style that also emphasizes their similarities and relatedness. This article discusses the nature of building blocks, monosaccharides, and monosaccharide derivatives-terms commonly used in discussing "glycomolecules" found in nature. To aid in awareness of monosaccharide diversity, here is presented a Periodic Table of Monosaccharides. The rationale is given for construction of the Table and the selection of 103 monosaccharides, which is largely based on those presented in the KEGG and SNFG websites of monosaccharides, and includes room to enlarge as new discoveries are made. The Table should have educational value and is intended to capture the attention and foster imagination of those not very familiar with glycosciences, and encourage researchers to delve deeper into this fascinating area.

Sialic acids in infection and their potential use in detection and protection against pathogens

In structural terms, the sialic acids are a large family of nine carbon sugars based around an alpha-keto acid core. They are widely spread in nature, where they are often found to be involved in molecular recognition processes, including in development, immunology, health and disease. The prominence of sialic acids in infection is a result of their exposure at the non-reducing terminus of glycans in diverse glycolipids and glycoproteins. Herein, we survey representative aspects of sialic acid structure, recognition and exploitation in relation to infectious diseases, their diagnosis and prevention or treatment. Examples covered span influenza virus and Covid-19, Leishmania and Trypanosoma, algal viruses, Campylobacter, Streptococci and Helicobacter, and commensal Ruminococci.

Synthesis and Evaluation of Glycosyl Luciferins

Measuring glycosidase activity is important to monitor any aberrations in carbohydrate hydrolase activity, but also for the screening of potential glycosidase inhibitors. To this end, synthetic substrates are needed which provide an enzyme-dependent read-out upon hydrolysis by the glycosidase. Herein, we present two new routes for the synthesis of caged luminescent carbohydrates, which can be used for determining glycosidase activity with a luminescent reporter molecule. The substrates were validated with glycosidase and revealed a clear linear range and enzyme-dependent signal upon the in situ generation of the luciferin moiety from the corresponding nitrile precursors. Besides, we showed that these compounds could directly be synthesized from unprotected glycosyl-α-fluorides in a two-step procedure with yields up to 75 %. The intermediate methyl imidate appeared a key intermediate which also reacted with d-cysteine to give the corresponding d-luciferin substrate rendering this a highly attractive method for synthesizing glycosyl luciferins in good yields.

Acetyl-CoA metabolism as a therapeutic target for cancer

Acetyl-coenzyme A (acetyl-CoA), an essential metabolite, not only takes part in numerous intracellular metabolic processes, powers the tricarboxylic acid cycle, serves as a key hub for the biosynthesis of fatty acids and isoprenoids, but also serves as a signaling substrate for acetylation reactions in post-translational modification of proteins, which is crucial for the epigenetic inheritance of cells. Acetyl-CoA links lipid metabolism with histone acetylation to create a more intricate regulatory system that affects the growth, aggressiveness, and drug resistance of malignancies such as glioblastoma, breast cancer, and hepatocellular carcinoma. These fascinating advances in the knowledge of acetyl-CoA metabolism during carcinogenesis and normal physiology have raised interest regarding its modulation in malignancies. In this review, we provide an overview of the regulation and cancer relevance of main metabolic pathways in which acetyl-CoA participates. We also summarize the role of acetyl-CoA in the metabolic reprogramming and stress regulation of cancer cells, as well as medical application of inhibitors targeting its dysregulation in therapeutic intervention of cancers.

Elevated concentrations of Neu5Ac and Neu5,9Ac2 in human plasma: potential biomarkers of cardiovascular disease

Cardiovascular disease (CVD) is a group of health conditions affecting the heart and vascular system with very high prevalence and mortality rates. The presence of CVD is characterised by high levels of inflammation which have previously been associated with increased plasma concentrations of N-acetyl neuraminic acid (Neu5Ac). While Neu5Ac has been studied in the context of CVD, Neu5,9Ac2 has not, despite being the second most abundant sialic acid in human plasma. A small-scale pilot study of thirty plasma samples from patients with diagnosed CVD, and thirty age and sex-matched healthy controls, was designed to gain insight into sialic acids as biomarkers for CVD and potential future areas of study. Each sample was assayed for Neu5Ac and Neu5,9Ac2 concentrations. Mean Neu5Ac and Neu5,9Ac2 concentrations were significantly elevated in patients with CVD compared to healthy controls (Neu5Ac: P < 0.001; Neu5,9Ac2: P < 0.04). Receiver operator curve (ROC) analysis indicated that both Neu5Ac and Neu5,9Ac2 have reasonable predictive power for the presence of CVD (Neu5Ac AUC: 0.86; Neu5,9Ac2 AUC: 0.71). However, while Neu5Ac had both good sensitivity (0.82) and specificity (0.81), Neu5,9Ac2 had equivalent specificity (0.81) but very poor sensitivity (0.44). A combination marker of Neu5Ac + Neu5,9Ac2 showed improvement over Neu5Ac alone in terms of predictive power (AUC: 0.93), sensitivity (0.87), and specificity (0.90). Comparison to a known inflammatory marker, high sensitivity c-reactive protein (hs-CRP: P-value: NS, ROC:0.50) was carried out, showing that both Neu5Ac and Neu5,9Ac2 outperformed this marker. Further to this, hs-CRP values were combined with the three different sialic acid markers to determine any effect on the AUC values. A slight improvement in AUC was noted for each of the combinations, with Neu5Ac + Neu5,9Ac2 + hs-CRP giving the best AUC of 0.97 overall. Thus, Neu5Ac would appear to offer good potential as a predictive marker for the presence of CVD, which the addition of Neu5,9Ac2 predictive power improves, with further improvement seen by the addition of hs-CRP.

Sialic acid O-acetylation patterns and glycosidic linkage type determination by ion mobility-mass spectrometry

O-acetylation is a common modification of sialic acids that has been implicated in a multitude of biological and disease processes. A lack of analytical methods that can determine exact structures of sialic acid variants is a hurdle to determine roles of distinct O-acetylated sialosides. Here, we describe a drift tube ion mobility-mass spectrometry approach that can elucidate exact O-acetylation patterns as well as glycosidic linkage types of sialosides isolated from complex biological samples. It is based on the use of a library of synthetic O-acetylated sialosides to establish intrinsic collision cross section (CCS) values of diagnostic fragment ions. The CCS values were used to characterize O-acetylated sialosides from mucins and N-linked glycans from biologicals as well as equine tracheal and nasal tissues. It uncovered contrasting sialic acid linkage types of acetylated and non-acetylated sialic acids and provided a rationale for sialic acid binding preferences of equine H7 influenza A viruses.

Sialic Acid Enhanced the Antistress Capability under Challenging Situations by Increasing Synaptic Transmission

BACKGROUND

In early life, sialic acid (SA) plays a crucial role in neurodevelopment and neuronal function. However, it remains unclear whether and how SA supplementation in early life promotes behavioral response to stress in adolescence.

OBJECTIVES

This study aimed to examine the effects and mechanisms of SA on the antistress capability under challenging situations.

METHODS

In this study, C57BL/6 mice were daily supplemented with 1 μL SA solution/g body weight at the dose of 10 mg/kg/d from postnatal day (PND) 5-45. The antistress behaviors, including open field, elevated plus maze, forced swimming test, and tail suspension test, were performed at PND 46, PND 48, PND 50, and PND 52 to detect the antistress ability of SA, respectively.

RESULTS

Our results showed that SA-treated mice were more active in facing challenging situations. The fiber photometry experiment showed that SA promoted the excitatory neuronal response in the medial prefrontal cortex (mPFC), which was extensively interconnected to stress. Besides, electrophysiological results revealed SA enhanced synaptic transmission rather than neuronal excitability of mPFC excitatory neurons. It was also supported by the increasing spine density of mPFC excitatory neurons. At the molecular amount, the SA elevated the transmitter release-related proteins of mPFC, including Synapsin 1 and vesicular glutamate transporter 1 (VGlut 1). Furthermore, SA supplementation enhanced synaptic transmission mainly by altering the kinetics of synaptic transmission.

CONCLUSIONS

The SA supplementation enhanced the response capability to stress under challenging situations, and the enhanced synaptic transmission of mPFC excitatory neurons may be the neurological basis of active response under challenging situations. In general, our findings suggested that SA supplementation in early life can promote stress resistance in adolescence.

Impact of Asialoglycoprotein Receptor and Mannose Receptor Deficiency on Murine Plasma N-glycome Profiles

The asialoglycoprotein receptor (ASGPR) and the mannose receptor C-type 1 (MRC1) are well known for their selective recognition and clearance of circulating glycoproteins. Terminal galactose and N-Acetylgalactosamine are recognized by ASGPR, while terminal mannose, fucose, and N-Acetylglucosamine are recognized by MRC1. The effects of ASGPR and MRC1 deficiency on the N-glycosylation of individual circulating proteins have been studied. However, the impact on the homeostasis of the major plasma glycoproteins is debated and their glycosylation has not been mapped with high molecular resolution in this context. Therefore, we evaluated the total plasma N-glycome and plasma proteome of ASGR1 and MRC1 deficient mice. ASGPR deficiency resulted in an increase in O-acetylation of sialic acids accompanied by higher levels of apolipoprotein D, haptoglobin, and vitronectin. MRC1 deficiency decreased fucosylation without affecting the abundance of the major circulating glycoproteins. Our findings confirm that concentrations and N-glycosylation of the major plasma proteins are tightly controlled and further suggest that glycan-binding receptors have redundancy, allowing compensation for the loss of one major clearance receptor.

Siglecs family used by pathogens for immune escape may engaged in immune tolerance in pregnancy

The Siglecs family is a group of type I sialic acid-binding immunoglobulin-like receptors that regulate cellular signaling by recognizing sialic acid epitopes. Siglecs are predominantly expressed on the surface of leukocytes, where they play a crucial role in regulating immune activity. Pathogens can exploit inhibitory Siglecs by utilizing their sialic acid components to promote invasion or suppress immune functions, facilitating immune evasion. The establishing of an immune-balanced maternal-fetal interface microenvironment is essential for a successful pregnancy. Dysfunctional immune cells may lead to adverse pregnancy outcomes. Siglecs are important for inducing a phenotypic switch in leukocytes at the maternal-fetal interface toward a less toxic and more tolerant phenotype. Recent discoveries regarding Siglecs in the reproductive system have drawn further attention to their potential roles in reproduction. In this review, we primarily discuss the latest advances in understanding the impact of Siglecs as immune regulators on infections and pregnancy.

Chemoenzymatic Synthesis of N-Acetyl Analogues of 9-O-Acetylated b-Series Gangliosides

The stable N-acetyl analogues of biologically important 9-O-acetylated b-series gangliosides including 9NAc-GD3, 9NAc-GD2, 9NAc-GD1b, and 9NAc-GT1b were chemoenzymatically synthesized from a GM3 sphingosine. Two chemoenzymatic methods using either 6-azido-6-deoxy-N-acetylmannosamine (ManNAc6N3) as a chemoenzymatic synthon or 6-acetamido-6-deoxy-N-acetylmannosamine (ManNAc6NAc) as an enzymatic precursor for 9-acetamido-9-deoxy-N-acetylneuraminic acid (Neu5Ac9NAc) were developed and compared for the synthesis of 9NAc-GD3. The latter method was found to be more efficient and was used to produce the desired 9-N-acetylated glycosylsphingosines. Furthermore, glycosylsphingosine acylation reaction conditions were improved to obtain target 9-N-acetylated gangliosides in a faster reaction with an easier purification process compared to the previous acylation conditions.

Early in vitro evidence indicates that deacetylated sialic acids modulate multi-drug resistance in colon and lung cancers via breast cancer resistance protein

Cancers utilize sugar residues to engage in multidrug resistance. The underlying mechanism of action involving glycans, specifically the glycan sialic acid (Sia) and its various functional group alterations, has not been explored. ATP-binding cassette (ABC) transporter proteins, key proteins utilized by cancers to engage in multidrug resistant (MDR) pathways, contain Sias in their extracellular domains. The core structure of Sia can contain a variety of functional groups, including O-acetylation on the C6 tail. Modulating the expression of acetylated-Sias on Breast Cancer Resistance Protein (BCRP), a significant ABC transporter implicated in MDR, in lung and colon cancer cells directly impacted the ability of cancer cells to either retain or efflux chemotherapeutics. Via CRISPR-Cas-9 gene editing, acetylation was modulated by the removal of CAS1 Domain-containing protein (CASD1) and Sialate O-Acetyl esterase (SIAE) genes. Using western blot, immunofluorescence, gene expression, and drug sensitivity analysis, we confirmed that deacetylated Sias regulated a MDR pathway in colon and lung cancer in early in vitro models. When deacetylated Sias were expressed on BCRP, colon and lung cancer cells were able to export high levels of BCRP to the cell's surface, resulting in an increased BCRP efflux activity, reduced sensitivity to the anticancer drug Mitoxantrone, and high proliferation relative to control cells. These observations correlated with increased levels of cell survival proteins, BcL-2 and PARP1. Further studies also implicated the lysosomal pathway for the observed variation in BCRP levels among the cell variants. RNASeq data analysis of clinical samples revealed higher CASD1 expression as a favorable marker of survival in lung adenocarcinoma. Collectively, our findings indicate that deacetylated Sia is utilized by colon and lung cancers to engage in MDR via overexpression and efflux action of BCRP.

SARS-CoV-2 Spike N-Terminal Domain Engages 9-O-Acetylated α2-8-Linked Sialic Acids

SARS-CoV-2 viruses engage ACE2 as a functional receptor with their spike protein. The S1 domain of the spike protein contains a C-terminal receptor binding domain (RBD) and an N-terminal domain (NTD). The NTD of other coronaviruses includes a glycan binding cleft. However, for the SARS-CoV-2 NTD, protein-glycan binding was only observed weakly for sialic acids with highly sensitive methods. Amino acid changes in the NTD of variants of concern (VoC) show antigenic pressure, which can be an indication of NTD-mediated receptor binding. Trimeric NTD proteins of SARS-CoV-2, alpha, beta, delta, and omicron did not reveal a receptor binding capability. Unexpectedly, the SARS-CoV-2 beta subvariant strain (501Y.V2-1) NTD binding to Vero E6 cells was sensitive to sialidase pretreatment. Glycan microarray analyses identified a putative 9-O-acetylated sialic acid as a ligand, which was confirmed by catch-and-release ESI-MS, STD-NMR analyses, and a graphene-based electrochemical sensor. The beta (501Y.V2-1) variant attained an enhanced glycan binding modality in the NTD with specificity toward 9-O-acetylated structures, suggesting a dual-receptor functionality of the SARS-CoV-2 S1 domain, which was quickly selected against. These results indicate that SARS-CoV-2 can probe additional evolutionary space, allowing binding to glycan receptors on the surface of target cells.

The infectious salmon anemia virus esterase prunes erythrocyte surfaces in infected Atlantic salmon and exposes terminal sialic acids to lectin recognition

Many sialic acid-binding viruses express a receptor-destroying enzyme (RDE) that removes the virus-targeted receptor and limits viral interactions with the host cell surface. Despite a growing appreciation of how the viral RDE promotes viral fitness, little is known about its direct effects on the host. Infectious salmon anemia virus (ISAV) attaches to 4-O-acetylated sialic acids on Atlantic salmon epithelial, endothelial, and red blood cell surfaces. ISAV receptor binding and destruction are effectuated by the same molecule, the haemagglutinin esterase (HE). We recently discovered a global loss of vascular 4-O-acetylated sialic acids in ISAV-infected fish. The loss correlated with the expression of viral proteins, giving rise to the hypothesis that it was mediated by the HE. Here, we report that the ISAV receptor is also progressively lost from circulating erythrocytes in infected fish. Furthermore, salmon erythrocytes exposed to ISAV ex vivo lost their capacity to bind new ISAV particles. The loss of ISAV binding was not associated with receptor saturation. Moreover, upon loss of the ISAV receptor, erythrocyte surfaces became more available to the lectin wheat germ agglutinin, suggesting a potential to alter interactions with endogenous lectins of similar specificity. The pruning of erythrocyte surfaces was inhibited by an antibody that prevented ISAV attachment. Furthermore, recombinant HE, but not an esterase-silenced mutant, was sufficient to induce the observed surface modulation. This links the ISAV-induced erythrocyte modulation to the hydrolytic activity of the HE and shows that the observed effects are not mediated by endogenous esterases. Our findings are the first to directly link a viral RDE to extensive cell surface modulation in infected individuals. This raises the questions of whether other sialic acid-binding viruses that express RDEs affect host cells to a similar extent, and if such RDE-mediated cell surface modulation influences host biological functions with relevance to viral disease.

Alkali-labile gangliosides

The structure and properties of a group of gangliosides modified by mild alkaline treatment are discussed. We will present the occurrence and the structure of gangliosides carrying the N-acetyneuraminic acid O-acetylated in position 9, the Neu5,9Ac₂, and of gangliosides carrying a sialic acid that forms a lactone ring. Starting from biochemical data we will discuss the possible biochemical role played by these gangliosides in the processes of cell signaling and maintenance of brain functions.

Multivalent sialic acid materials for biomedical applications

Sialic acid is a kind of monosaccharide expressed on the non-reducing end of glycoproteins or glycolipids. It acts as a signal molecule combining with its natural receptors such as selectins and siglecs (sialic acid-binding immunoglobulin-like lectins) in intercellular interactions like immunological surveillance and leukocyte infiltration. The last few decades have witnessed the exploration of the roles that sialic acid plays in different physiological and pathological processes and the use of sialic acid-modified materials as therapeutics for related diseases like immune dysregulation and virus infection. In this review, we will briefly introduce the biomedical function of sialic acids in organisms and the utilization of multivalent sialic acid materials for targeted drug delivery as well as therapeutic applications including anti-inflammation and anti-virus.

Precision Characterization of Site-Specific O-Acetylated Sialic Acids on N-Glycoproteins

O-Acetylation is a common modification of sialic acid, playing a significant role in glycoprotein stability, immune response, and cell development. Due to the lack of efficient methods for direct analysis of O-acetylated sialoglycopeptides (O-AcSGPs), the majority of identified O-acetylated sialic acids (O-AcSia) until now had no glycosite/glycoprotein information. Herein, we introduced a new workflow for precise interpretation of O-AcSGPs with probability estimation by recognizing the characteristic B and Y ions of O-AcSias. With further optimization of mass spectrometry parameters, the method allowed us to identify a total of 171 unique O-AcSGPs in mouse serum. Although the majority of these O-AcSGPs were at a relatively low abundance compared with their non-O-acetylated states, they were mainly involved in peptidase/endopeptidase inhibitor activities. The method paves the way for large-scale structural and functional analyses of site-specific O-AcSias in various complex samples as well as further identification of many other similar chemical modifications on glycoproteins.

The glycocalyx and immune evasion in cancer

In order to establish malignant lesions, tumors must first evade their detection by immune cells. Tumors achieve this by embellishing and tailoring their glycocalyx, a network of polysaccharides and glycosylated proteins that refracts the phagocytic efforts of myeloid cells, shrouds neoantigens and other ligands from cells of the acquired immune system, and skews immune responses. The barriers imposed by the glycocalyx are biophysical and also linked to the inhibitory receptor signaling pathways of immune cells that engage tumor sialic acids as markers of healthy "self". This would explain the pressure for cancers to upregulate the synthases, transmembrane mucins, and other heavily sialylated glycoproteins involved in establishing a repulsive glycocalyx. Accordingly, individual tumor cells that are best capable of constructing a shielding glycocalyx on their surface show higher metastatic potential in immunocompetent mice. Reciprocally, therapeutics have recently been devised to edit and dismantle the glycocalyx barrier in an effort to invigorate an immune response aimed at tumor destruction. We discuss the features of the tumor-associated glycocalyx that afford immune evasion of cancers and how strategies that target this barrier may potentiate antitumor immunity.

The multiple facets of acetyl-CoA metabolism: Energetics, biosynthesis, regulation, acylation and inborn errors

Acetyl-coenzyme A (Ac-CoA) is a core metabolite with essential roles throughout cell physiology. These functions can be classified into energetics, biosynthesis, regulation and acetylation of large and small molecules. Ac-CoA is essential for oxidative metabolism of glucose, fatty acids, most amino acids, ethanol, and of free acetate generated by endogenous metabolism or by gut bacteria. Ac-CoA cannot cross lipid bilayers, but acetyl groups from Ac-CoA can shuttle across membranes as part of carrier molecules like citrate or acetylcarnitine, or as free acetate or ketone bodies. Ac-CoA is the basic unit of lipid biosynthesis, providing essentially all of the carbon for the synthesis of fatty acids and of isoprenoid-derived compounds including cholesterol, coenzyme Q and dolichols. High levels of Ac-CoA in hepatocytes stimulate lipid biosynthesis, ketone body production and the diversion of pyruvate metabolism towards gluconeogenesis and away from oxidation; low levels exert opposite effects. Acetylation changes the properties of molecules. Acetylation is necessary for the synthesis of acetylcholine, acetylglutamate, acetylaspartate and N-acetyl amino sugars, and to metabolize/eliminate some xenobiotics. Acetylation is a major post-translational modification of proteins. Different types of protein acetylation occur. The most-studied form occurs at the epsilon nitrogen of lysine residues. In histones, lysine acetylation can alter gene transcription. Acetylation of other proteins has diverse, often incompletely-documented effects. Inborn errors related to Ac-CoA feature a broad spectrum of metabolic, neurological and other features. To date, a small number of studies of animals with inborn errors of CoA thioesters has included direct measurement of acyl-CoAs. These studies have shown that low levels of tissue Ac-CoA correlate with the development of clinical signs, hinting that shortage of Ac-CoA may be a recurrent theme in these conditions. Low levels of Ac-CoA could potentially disrupt any of its roles.

Increase of intestinal bacterial sialidase activity exacerbates acute colitis in mice

The availability of endogenous and dietary carbohydrates in the gastrointestinal tract influences the composition of the gut microbiota. Carbohydrate foraging requires the action of bacterially-encoded glycoside hydrolases, which release mono- and oligosaccharides taken up as carbon sources by multiple microbial taxa. In addition to providing nutrients to the microbiota, the cleavage of host glycans by bacterial glycoside hydrolases may alter the properties of surface glycoproteins involved in cell adhesion and activation processes in the gut lumen. To investigate the impact of bacterial glycoside hydrolase activities on the gut microbial composition and on host glycans during colon inflammation, we increased local glycoside hydrolase activity by supplementing mice with recombinant E. coli expressing specific sialidase, fucosidase and rhamnosidase enzymes during acute colitis induced by dextran sulfate sodium ingestion. Whereas increased fucosidase and rhamnosidase activity did not alter the course of colitis, increased sialidase activity exacerbated disease severity. The effect of increased sialidase activity on inflammation was not caused by changes in the microbial composition given that a similar shift in gut bacteria occurred in all groups of mice supplemented with recombinant E. coli. Increased sialidase activity in the colon of treated mice however significantly altered the distribution of sialic acid on mucosal glycans. Treatment of lamina propria dendritic cells with bacterial sialidase also strongly decreased the density of sialylated ligands to anti-inflammatory siglec lectins, indicating that the remodeling of surface sialylation caused by increased sialidase activity likely accounts for the observed exacerbation of acute colitis in mice.

Destruction of the vascular viral receptor in infectious salmon anaemia provides in vivo evidence of homologous attachment interference

Viral interference is a process where infection with one virus prevents a subsequent infection with the same or a different virus. This is believed to limit superinfection, promote viral genome stability, and protect the host from overwhelming infection. Mechanisms of viral interference have been extensively studied in plants, but remain poorly understood in vertebrates. We demonstrate that infection with infectious salmon anaemia virus (ISAV) strongly reduces homologous viral attachment to the Atlantic salmon, Salmo salar L. vascular surface. A generalised loss of ISAV binding was observed after infection with both high-virulent and low-virulent ISAV isolates, but with different kinetics. The loss of ISAV binding was accompanied by an increased susceptibility to sialidase, suggesting a loss of the vascular 4-O-sialyl-acetylation that mediates ISAV attachment and simultaneously protects the sialic acid from cleavage. Moreover, the ISAV binding capacity of cultured cells dramatically declined 3 days after ISAV infection, accompanied by reduced cellular permissiveness to infection with a second antigenically distinct isolate. In contrast, neither infection with infectious haematopoietic necrosis virus nor stimulation with the viral mimetic poly I:C restricted subsequent cellular ISAV attachment, revealing an ISAV-specific mechanism rather than a general cellular antiviral response. Our study demonstrates homologous ISAV attachment interference by de-acetylation of sialic acids on the vascular surface. This is the first time the kinetics of viral receptor destruction have been mapped throughout the full course of an infection, and the first report of homologous attachment interference by the loss of a vascular viral receptor. Little is known about the biological functions of vascular O-sialyl-acetylation. Our findings raise the question of whether this vascular surface modulation could be linked to the breakdown of central vascular functions that characterises infectious salmon anaemia.

Viral interference, also referred to as superinfection exclusion, is a process that supports viral genome integrity and protects the host from overwhelming infection. Here, we demonstrate that infection of Atlantic salmon with infectious salmon anaemia virus (ISAV) results in the destruction of the viral vascular surface receptor, thus preventing virus attachment. We also observed that the loss of viral receptor strongly restricted the extent of a second ISAV infection in cultured cells, suggesting viral interference. To our knowledge, this is the first time the kinetics of viral receptor destruction has been explored in an infected host. This is important, because we know little of how such responses develop in animals and humans. Our study therefore improves the general understanding of how viral infections progress. Finally, our findings raise the question of whether modulation of the vascular surface by ISAV and other viruses may contribute to the pathogenesis of viral disease.

Sialic acid biosensing by post-printing modification of PEDOT:PSS with pyridylboronic acid

A poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-based conducting polymer, which has biorecognition capabilities, has promising biosensing applications. Previously, we developed a facile method for post-printing chemical modification of PEDOT:PSS thin films from commercial sources. Molecular recognition elements were directly introduced into the PSS side chain by a two-step chemical reaction: introduction of an ethylenediamine linker via an acid chloride reaction of the sulfonate moiety, and subsequent receptor attachment to the linker via amine coupling. In this study, the same method was used to introduce 6-carboxypyridine-3-boronic acid (carboxy-PyBA) into the linker for specifically detecting N-acetylneuraminic acid (sialic acid, SA), as a cancer biomarker. The surface-modified PEDOT:PSS films were characterized by X-ray photoelectron spectroscopy, attenuated total reflection Fourier-transform infrared spectroscopy, and static water contact angle and conductivity measurements. The specific interaction between PyBA and SA was detected by label-free reagent-free potentiometry. The SA-specific negative potential responses of modified PEDOT:PSS electrodes, which was ascribed to an SA carboxyl anion, were observed in a physiologically relevant SA range (1.6-2.9 mM) at pH 5, in a concentration-dependent manner even in the presence of 10% fetal bovine serum. The sensitivity was -2.9 mV/mM in 1-5 mM SA with a limit of detection of 0.7 mM. The sensing performances were almost equivalent to those of existing graphene-based electrical SA sensors. These results show that our chemical derivatization method for printing PEDOT:PSS thin films will have applications in SA clinical diagnostics.

Aberrant Sialylation in Cancer: Therapeutic Opportunities

The surface of every eukaryotic cell is coated in a thick layer of glycans that acts as a key interface with the extracellular environment. Cancer cells have a different ‘glycan coat’ to healthy cells and aberrant glycosylation is a universal feature of cancer cells linked to all of the cancer hallmarks. This means glycans hold huge potential for the development of new diagnostic and therapeutic strategies. One key change in tumour glycosylation is increased sialylation, both on N-glycans and O-glycans, which leads to a dense forest of sialylated structures covering the cell surface. This hypersialylation has far-reaching consequences for cancer cells, and sialylated glycans are fundamental in tumour growth, metastasis, immune evasion and drug resistance. The development of strategies to inhibit aberrant sialylation in cancer represents an important opportunity to develop new therapeutics. Here, I summarise recent advances to target aberrant sialylation in cancer, including the development of sialyltransferase inhibitors and strategies to inhibit Siglecs and Selectins, and discuss opportunities for the future.

Sulfation of sialic acid is ubiquitous and essential for vertebrate development

Glycosylation of proteins and lipids occurs in vertebrates, usually terminating with sialylation, which regulates the physicochemical and biological properties of these glycoconjugates. Although less commonly known, sialic acid residues also undergo various modifications, such as acetylation, methylation, and sulfation. However, except for acetylation, the enzymes or functions of the other modification processes are unknown. To the best of our knowledge, this study is the first to demonstrate the ubiquitous occurrence of sulfated sialic acids and two genes encoding the sialate: O-sulfotransferases 1 and 2 in vertebrates. These two enzymes showed about 50% amino acid sequence identity, and appeared to be complementary to each other in acceptor substrate preferences. Gene targeting experiments showed that the deficiency of these genes was lethal for medaka fish during young fry development and accompanied by different phenotypes. Thus, the sulfation of sialic acids is essential for the vertebrate development.

Comparative Assessment of the Structural Features of Originator Recombinant Human Follitropin Alfa Versus Recombinant Human Follitropin Alfa Biosimilar Preparations Approved in Non-European Regions

Although the full primary structures of the alfa and beta subunits of reference r-hFSH-alfa and its biosimilars are identical, cell context-dependent differences in the expressing cell lines and manufacturing process can lead to variations in glycosylation profiles. In the present study, we compared the structural features of reference r-hFSH-alfa with those of five biosimilar preparations approved in different global regions outside Europe (Primapur^®, Jin Sai Heng^®, Follitrope^®, Folisurge^®, and Corneumon^®) with respect to glycosylation, macro- and microheterogeneity, and other post-translational modifications and higher order structure. The mean proportion of N-glycosylation-site occupancy was highest in reference r-hFSH-alfa, decreasing sequentially in Primapur, Jin Sai Heng, Corneumon, Follisurge and Follitrope, respectively. The level of antennarity showed slightly higher complexity in Corneumon, Primapur and Follitrope versus reference r-hFSH-alfa, whereas Jin Sai Heng and Folisurge were aligned with reference r-hFSH-alfa across all N-glycosylation sites. Sialylation level was higher in Corneumon and Follitrope, but small differences were detected in other biosimilar preparations compared with reference r-hFSH-alfa. Jin Sai Heng showed higher levels of N-glyconeuramic acid than the other preparations. Minor differences in oxidation levels were seen among the different products. Therefore, in summary, we identified var ious differences in N-glycosylation occupancy, antennarity, sialylation and oxidation between reference r-hFSH-alfa and the biosimilar preparations analyzed.

Severe Acute Respiratory Syndrome Coronavirus 2 Variants—Possibility of Universal Vaccine Design: A Review

Both novel and conventional vaccination strategies have been implemented worldwide since the onset of coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Despite various medical advances in the treatment and prevention of the spread of this contagious disease, it remains a major public health threat with a high mortality rate. As several lethal SARS-CoV-2 variants continue to emerge, the development of several vaccines and medicines, each with certain advantages and disadvantages, is underway. Additionally, many modalities are at various stages of research and development or clinical trials. Here, we summarize emerging SARS-CoV-2 variants, including delta, omicron, and “stealth omicron,” as well as available oral drugs for COVID-19. We also discuss possible antigen candidates other than the receptor-binding domain protein for the development of a universal COVID-19 vaccine. The present review will serve as a helpful resource for future vaccine and drug development to combat COVID-19.

Sialic acid diversity in the human gut: Molecular impacts and tools for future discovery

Sialic acids are a family of structurally related sugars that are prevalent in mucosal surfaces, including the human intestine. In the gut, sialic acids have diverse biological roles at the interface of the host epithelium and the microbiota. N-acetylneuraminic acid (Neu5Ac), the best studied sialic acid, is a nutrient source for bacteria and, when displayed on the cell surface, a binding site for host immune factors, viruses, and bacterial toxins. Neu5Ac is extensively modified by host and microbial enzymes, and the impacts of Neu5Ac derivatives on host-microbe interactions, and generally on human and microbial biology, remain underexplored. In this mini-review, we highlight recent reports describing how host and microbial proteins differentiate Neu5Ac and its derivatives, draw attention to gaps in knowledge related to sialic acid biology, and suggest cutting-edge methodologies that may expand our appreciation and understanding of Neu5Ac in health and disease.

Comprehensive Analysis of Oligo/Polysialylglycoconjugates in Cancer Cell Lines

In cancer cells, cell-surface sialylation is altered, including a change in oligo/polysialic acid (oligo/polySia) structures. Since they are unique and rarely expressed in normal cells, oligo/polySia structures may serve as promising novel biomarkers and targets for therapies. For the diagnosis and treatment of the disease, a precise understanding of the oligo/polySia structures in cancer cells is necessary. In this study, flow cytometric analysis and gene expression datasets were obtained from sixteen different cancer cell lines. These datasets demonstrated the ability to predict glycan structures and their sialylation status. Our results also revealed that sialylation patterns are unique to each cancer cell line. Thus, we can suggest promising combinations of antibody and cancer cell for glycan prediction. However, the precise prediction of minor glycans need to be further explored.

Small molecule inhibitors of mammalian glycosylation

Glycans are one of the fundamental biopolymers encountered in living systems. Compared to polynucleotide and polypeptide biosynthesis, polysaccharide biosynthesis is a uniquely combinatorial process to which interdependent enzymes with seemingly broad specificities contribute. The resulting intracellular cell surface, and secreted glycans play key roles in health and disease, from embryogenesis to cancer progression. The study and modulation of glycans in cell and organismal biology is aided by small molecule inhibitors of the enzymes involved in glycan biosynthesis. In this review, we survey the arsenal of currently available inhibitors, focusing on agents which have been independently validated in diverse systems. We highlight the utility of these inhibitors and drawbacks to their use, emphasizing the need for innovation for basic research as well as for therapeutic applications.

COVID-19, Cation Dysmetabolism, Sialic Acid, CD147, ACE2, Viroporins, Hepcidin and Ferroptosis: A Possible Unifying Hypothesis

Background: iron and calcium dysmetabolism, with hyperferritinemia, hypoferremia, hypocalcemia and anemia have been documented in the majority of COVID-19 patients at later/worse stages. Furthermore, complementary to ACE2, both sialic acid (SA) molecules and CD147 proved relevant host receptors for SARS-CoV-2 entry, which explains the viral attack to multiple types of cells, including erythrocytes, endothelium and neural tissue. Several authors advocated that cell ferroptosis may be the core and final cell degenerative mechanism.

Methods: a literature research was performed in several scientific search engines, such as PubMed Central, Cochrane Library, Chemical Abstract Service. More than 500 articles were retrieved until mid-December 2021, to highlight the available evidence about the investigated issues.

Results: based on COVID-19 literature data, we have highlighted a few pathophysiological mechanisms, associated with virus-based cation dysmetabolism, multi-organ attack, mitochondria degeneration and ferroptosis. Our suggested elucidated pathological sequence is: a) spike protein subunit S1 docking with sialylated membrane glycoproteins/receptors (ACE2, CD147), and S2 subunit fusion with the lipid layer; b) cell membrane morpho-functional changes due to the consequent electro-chemical variations and viroporin action, which induce an altered ion channel function and intracellular cation accumulation; c) additional intracellular iron concentration due to a deregulated hepcidin-ferroportin axis, with higher hepcidin levels. Viral invasion may also affect erythrocytes/erythroid precursors, endothelial cells and macrophages, through SA and CD147 receptors, with relative hemoglobin and iron/calcium dysmetabolism. AB0 blood group, hemochromatosis, or environmental elements may represent possible factors which affect individual susceptibility to COVID-19.    

Conclusions: our literature analysis confirms the combined role of SA molecules, ACE2, CD147, viroporins and hepcidin in determining the cation dysmetabolism and final ferroptosis in the cells infected by SARS-CoV-2. The altered ion channels and electrochemical gradients of the cell membrane have a pivotal role in the virus entry and cell dysmetabolism, with subsequent multi-organ immune-inflammatory degeneration and erythrocyte/hemoglobin alterations.

The role of the mucin-glycan foraging Ruminococcus gnavus in the communication between the gut and the brain

Ruminococcus gnavus is a prevalent member of the human gut microbiota, which is over-represented in inflammatory bowel disease and neurological disorders. We previously showed that the ability of R. gnavus to forage on mucins is strain-dependent and associated with sialic acid metabolism. Here, we showed that mice monocolonized with R. gnavus ATCC 29149 (Rg-mice) display changes in major sialic acid derivatives in their cecum content, blood, and brain, which is accompanied by a significant decrease in the percentage of sialylated residues in intestinal mucins relative to germ-free (GF) mice. Changes in metabolites associated with brain function such as tryptamine, indolacetate, and trimethylamine N-oxide were also detected in the cecal content of Rg-mice when compared to GF mice. Next, we investigated the effect of R. gnavus monocolonization on hippocampus cell proliferation and behavior. We observed a significant decrease of PSA-NCAM immunoreactive granule cells in the dentate gyrus (DG) of Rg-mice as compared to GF mice and recruitment of phagocytic microglia in the vicinity. Behavioral assessments suggested an improvement of the spatial working memory in Rg-mice but no change in other cognitive functions. These results were also supported by a significant upregulation of genes involved in proliferation and neuroplasticity. Collectively, these data provide first insights into how R. gnavus metabolites may influence brain regulation and function through modulation of granule cell development and synaptic plasticity in the adult hippocampus. This work has implications for further understanding the mechanisms underpinning the role of R. gnavus in neurological disorders.

Quantitative Standards of 4-O acetyl and 9-O acetyl N-acetyl Neuraminic Acid for the Analysis of Plasma and Serum

N‐Acetylneuraminic acid (sialic acid, Neu5Ac) is one of a large, diverse family of nine‐carbon monosaccharides that play roles in many biological functions such as immune response. Neu5Ac has previously been identified as a potential biomarker for the presence and pathogenesis of cardiovascular disease (CVD), diabetes and cancer. More recent research has highlighted acetylated sialic acid derivatives, specifically Neu5,9Ac₂, as biomarkers for oral and breast cancers, but advances in analysis have been hampered due to a lack of commercially available quantitative standards. We report here the synthesis of 9‐O‐ and 4‐O‐acetylated sialic acids (Neu5,9Ac₂ and Neu4,5Ac₂) with optimisation of previously reported synthetic routes. Neu5,9Ac₂ was synthesised in 1 step in 68 % yield. Neu4,5Ac₂ was synthesised in 4 steps in 39 % overall yield. Synthesis was followed by analysis of these standards via quantitative NMR (qNMR) spectroscopy. Their utilisation for the identification and quantification of specific acetylated sialic acid derivatives in biological samples is also demonstrated.

Laurent CD, Khoo KH, Mahal LK, Zandberg WF, Huang X, Klassen JS, Macauley MS. Carbohydrate Sulfation As a Mechanism for Fine-Tuning Siglec Ligands

The immunomodulatory family of Siglecs recognizes sialic acid-containing glycans as "self", which is exploited in cancer for immune evasion. The biochemical nature of Siglec ligands remains incompletely understood, with emerging evidence suggesting the importance of carbohydrate sulfation. Here, we investigate how specific sulfate modifications affect Siglec ligands by overexpressing eight carbohydrate sulfotransferases (CHSTs) in five cell lines. Overexpression of three CHSTs─CHST1, CHST2, or CHST4─significantly enhance the binding of numerous Siglecs. Unexpectedly, two other CHSTs (Gal3ST2 and Gal3ST3) diminish Siglec binding, suggesting a new mode to modulate Siglec ligands via sulfation. Results are cell type dependent, indicating that the context in which sulfated glycans are presented is important. Moreover, a pharmacological blockade of N- and O-glycan maturation reveals a cell-type-specific pattern of importance for either class of glycan. Production of a highly homogeneous Siglec-3 (CD33) fragment enabled a mass-spectrometry-based binding assay to determine ≥8-fold and ≥2-fold enhanced affinity for Neu5Acα2-3(6-O-sulfo)Galβ1-4GlcNAc and Neu5Acα2-3Galβ1-4(6-O-sulfo)GlcNAc, respectively, over Neu5Acα2-3Galβ1-4GlcNAc. CD33 shows significant additivity in affinity (≥28-fold) for the disulfated ligand, Neu5Acα2-3(6-O-sulfo)Galβ1-4(6-O-sulfo)GlcNAc. Moreover, joint overexpression of CHST1 with CHST2 in cells greatly enhanced the binding of CD33 and several other Siglecs. Finally, we reveal that CHST1 is upregulated in numerous cancers, correlating with poorer survival rates and sodium chlorate sensitivity for the binding of Siglecs to cancer cell lines. These results provide new insights into carbohydrate sulfation as a general mechanism for tuning Siglec ligands on cells, including in cancer.

Chemoenzymatic Synthesis of Sialosides Containing 7-N- or 7,9-Di-N-acetyl Sialic Acid as Stable O-Acetyl Analogues for Probing Sialic Acid-Binding Proteins

A novel chemoenzymatic synthon strategy has been developed to construct a comprehensive library of α2-3- and α2-6-linked sialosides containing 7-N- or 7,9-di-N-acetyl sialic acid, the stable analogue of naturally occurring 7-O-acetyl- or 7,9-di-O-acetyl-sialic acid. Diazido and triazido-mannose derivatives that were readily synthesized chemically from inexpensive galactose were shown to be effective chemoenzymatic synthons. Together with bacterial sialoside biosynthetic enzymes with remarkable substrate promiscuity, they were successfully used in one-pot multienzyme (OPME) sialylation systems for highly efficient synthesis of sialosides containing multiple azido groups. Conversion of the azido groups to N-acetyl groups generated the desired sialosides. The hydrophobic and UV-detectable benzyloxycarbonyl (Cbz) group introduced in the synthetic acceptors of sialyltransferases was used as a removable protecting group for the propylamine aglycon of the target sialosides. The resulting N-acetyl sialosides were novel stable probes for sialic acid-binding proteins such as plant lectin MAL II, which bond strongly to sialyl T antigens with or without an N-acetyl at C7 or at both C7 and C9 in the sialic acid.

SDAV, the Rat Coronavirus-How Much Do We Know about It in the Light of Potential Zoonoses

Sialodacryoadenitis virus (SDAV) is known to be an etiological agent, causing infections in laboratory rats. Until now, its role has only been considered in studies on respiratory and salivary gland infections. The scant literature data, consisting mainly of papers from the last century, do not sufficiently address the topic of SDAV infections. The ongoing pandemic has demonstrated, once again, the role of the Coronaviridae family as extremely dangerous etiological agents of human zoonoses. The ability of coronaviruses to cross the species barrier and change to hosts commonly found in close proximity to humans highlights the need to characterize SDAV infections. The main host of the infection is the rat, as mentioned above. Rats inhabit large urban agglomerations, carrying a vast epidemic threat. Of the 2277 existing rodent species, 217 are reservoirs for 66 zoonotic diseases caused by viruses, bacteria, fungi, and protozoa. This review provides insight into the current state of knowledge of SDAV characteristics and its likely zoonotic potential.