LC-MS/MS glycomic analyses of free and conjugated forms of the sialic acids, Neu5Ac, Neu5Gc and KDN in human throat cancers

N-glycolylneuraminic acid in red meat and processed meat is a health concern: A review on the formation, health risk, and reduction

One of the most consistent epidemiological associations between diet and human disease risk is the impact of consuming red meat and processed meat products. In recent years, the health concerns surrounding red meat and processed meat have gained worldwide attention. The fact that humans have lost the ability to synthesize N-glycolylneuraminic acid (Neu5Gc) makes red meat and processed meat products the most important source of exogenous Neu5Gc for humans. As our research of Neu5Gc has increased, it has been discovered that Neu5Gc in red meat and processed meat is a key factor in many major diseases. Given the objective evidence of the harmful risk caused by Neu5Gc in red meat and processed meat to human health, there is a need for heightened attention in the field of food. This updated review has several Neu5Gc aspects given including biosynthetic pathway of Neu5Gc and its accumulation in the human body, the distribution of Neu5Gc in food, the methods for detecting Neu5Gc, and most importantly, a systematic review of the existing methods for reducing the content of Neu5Gc in red meat and processed meat. It also provides some insights into the current status and future directions in this area.

Sialic acids Neu5Ac and KDN in adipose tissue samples from individuals following habitual vegetarian or non-vegetarian dietary patterns

Sialic acids (Sias) are a class of sugar molecules with a parent nine-carbon neuraminic acid, generally present at the ends of carbohydrate chains, either attached to cellular surfaces or as secreted glycoconjugates. Given their position and structural diversity, Sias modulate a wide variety of biological processes. However, little is known about the role of Sias in human adipose tissue, or their implications for health and disease, particularly among individuals following different dietary patterns. The goal of this study was to measure N-Acetylneuraminic acid (Neu5Ac), N-Glycolylneuraminic acid (Neu5Gc), and 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (KDN) concentrations in adipose tissue samples from participants in the Adventist Health Study-2 (AHS-2) and to compare the abundance of these Sias in individuals following habitual, long-term vegetarian or non-vegetarian dietary patterns. A method was successfully developed for the extraction and detection of Sias in adipose tissue. Sias levels were quantified in 52 vegans, 56 lacto-vegetarians, and 48 non-vegetarians using LC-MS/MS with Neu5Ac-D-1,2,3-13C3 as an internal standard. Dietary groups were compared using linear regression. Vegans and lacto-ovo-vegetarians had significantly higher concentrations of Neu5Ac relative to non-vegetarians. While KDN levels tended to be higher in vegans and lacto-ovo-vegetarians, these differences were not statistically significant. However, KDN levels were significantly inversely associated with body mass index. In contrast, Neu5Gc was not detected in human adipose samples. It is plausible that different Neu5Ac concentrations in adipose tissues of vegetarians, compared to those of non-vegetarians, reflect a difference in the baseline inflammatory status between the two groups. Epidemiologic studies examining levels of Sias in human adipose tissue and other biospecimens will help to further explore their roles in development and progression of inflammatory conditions and chronic diseases.

The vertebrate sialylation machinery: structure-function and molecular evolution of GT-29 sialyltransferases

Every eukaryotic cell is covered with a thick layer of complex carbohydrates with essential roles in their social life. In Deuterostoma, sialic acids present at the outermost positions of glycans of glycoconjugates are known to be key players in cellular interactions including host-pathogen interactions. Their negative charge and hydrophilic properties enable their roles in various normal and pathological states and their expression is altered in many diseases including cancers. Sialylation of glycoproteins and glycolipids is orchestrated by the regulated expression of twenty sialyltransferases in human tissues with distinct enzymatic characteristics and preferences for substrates and linkages formed. However, still very little is known on the functional organization of sialyltransferases in the Golgi apparatus and how the sialylation machinery is finely regulated to provide the ad hoc sialome to the cell. This review summarizes current knowledge on sialyltransferases, their structure-function relationships, molecular evolution, and their implications in human biology.

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.

Preliminary Analysis of the Glycolipid Profile in Secondary Brain Tumors

Glycosphingolipids (GSLs) play numerous roles in cellular processes, including cell proliferation, apoptosis, inflammation, and cell signaling. Alteration of the GSLs metabolism leads to the accumulation of particular species of GSLs, which can lead to various pathologies, including carcinogenesis and metastasis; in essence, all neoplasms are characterized by the synthesis and aberrant organization of GSLs expressed on the cell surface. Secondary brain tumors make up the majority of intracranial cancers and generally present an unfavorable prognosis. In the present work, a native GSL mixture extracted and purified from a secondary brain tumor with primary pulmonary origin was obtained through extraction and purification and analyzed by MALDI TOF mass spectrometry. Research in the field of lipidomics could offer new data for the understanding of brain tropism and metastatic pathways, by studying the glycolipid molecules involved in the process of metastasis in general and in the production of brain metastases in particular. This could shed new light on the pattern of lipid glycosylation in secondary brain tumors, with a great impact on the effectiveness of cancer therapies, which could be adapted to the specific molecular pattern of the tumor.

Glycans as Targets for Drug Delivery in Cancer

Simple Summary

Alterations in glycosylation are frequently observed in cancer cells. Different strategies have been proposed to increase drug delivery to the tumor site in order to improve the therapeutic efficacy of anti-cancer drugs and avoid collateral cytotoxicity. The exploitation of drug delivery approaches directed to cancer-associated glycans has the potential to pave the way for better and more efficient personalized treatment practices. Such strategies taking advantage of aberrant cell surface glycosylation patterns enhance the targeting efficiency and optimize the delivery of clinically used drugs to cancer cells, with major potential for the clinical applications.

Abstract

Innovative strategies have been proposed to increase drug delivery to the tumor site and avoid cytotoxicity, improving the therapeutic efficacy of well-established anti-cancer drugs. Alterations in normal glycosylation processes are frequently observed in cancer cells and the resulting cell surface aberrant glycans can be used as direct molecular targets for drug delivery. In the present review, we address the development of strategies, such as monoclonal antibodies, antibody–drug conjugates and nanoparticles that specific and selectively target cancer-associated glycans in tumor cells. The use of nanoparticles for drug delivery encompasses novel applications in cancer therapy, including vaccines encapsulated in synthetic nanoparticles and specific nanoparticles that target glycoproteins or glycan-binding proteins. Here, we highlight their potential to enhance targeting approaches and to optimize the delivery of clinically approved drugs to the tumor microenvironment, paving the way for improved personalized treatment approaches with major potential importance for the pharmaceutical and clinical sectors.

Systematic Optimisation of Microtiter Plate Lectin Assay to Improve Sialic Acid Linkage Detection

AIMS

We aimed to develop a high-throughput lectin assay with minimized background signals to investigate the interactions of lectins and sialic acid glycans, focusing on prostate-specific antigen (PSA).

BACKGROUND

High background signals resulting from nonspecific binding are a significant concern for microtiter plate-based enzyme-linked lectin sorbent assays (ELLSAs), as they can mask specific binding signals and cause false-positive results.

METHODS

In this study, we constructed an ELLSA based on different washing step parameters, including the number of washing cycles, NaCl and Tween-20 concentrations, and the type of blocking agent and evaluated the effects on both specific and nonspecific binding signals. Furthermore, we performed a PSA binding assay using the optimized ELLSA.

RESULTS

The optimal washing parameters based on the highest specific binding signal proposed four cycles of washing steps using a washing buffer containing a high salt concentration (0.5 M NaCl) and mild detergent (0.05% Tween-20). The utilization of the optimized washing parameters in this assay was shown to be sufficient to obtain the optimal binding signals without the use of any blocking agent. Binding assays performed using the optimized ELLSA revealed that the glycan of the PSA sample used in this study mainly consists of terminal α2,6-linked sialic acid, as strongly recognized by Sambucus nigra agglutinin (SNA) with a KD value of 12.38 nM.

CONCLUSION

The ELLSA reported in this study provides a simple yet sensitive assay for sialic acid linkage recognition.

Sialic Acid-Siglec Axis in Human Immune Regulation, Involvement in Autoimmunity and Cancer and Potential Therapeutic Treatments

Siglecs are sialic acid-binding immunoglobulin-like lectins. Most Siglecs function as transmembrane receptors mainly expressed on blood cells in a cell type-specific manner. They recognize and bind sialic acids in specific linkages on glycoproteins and glycolipids. Since Sia is a self-molecule, Siglecs play a role in innate immune responses by distinguishing molecules as self or non-self. Increasing evidence supports the involvement of Siglecs in immune signaling representing immune checkpoints able to regulate immune responses in inflammatory diseases as well as cancer. Although further studies are necessary to fully understand the involvement of Siglecs in pathological conditions as well as their interactions with other immune regulators, the development of therapeutic approaches that exploit these molecules represents a tremendous opportunity for future treatments of several human diseases, as demonstrated by their application in several clinical trials. In the present review, we discuss the involvement of Siglecs in the regulation of immune responses, with particular focus on autoimmunity and cancer and the chance to target the sialic acid-Siglec axis as novel treatment strategy.

Evolutionary conservation of human ketodeoxynonulosonic acid production is independent of sialoglycan biosynthesis

Human metabolic incorporation of nonhuman sialic acid (Sia) N-glycolylneuraminic acid into endogenous glycans generates inflammation via preexisting antibodies, which likely contributes to red meat-induced atherosclerosis acceleration. Exploring whether this mechanism affects atherosclerosis in end-stage renal disease (ESRD), we instead found serum accumulation of 2-keto-3-deoxy-d-glycero-d-galacto-2-nonulosonic acid (Kdn), a Sia prominently expressed in cold-blooded vertebrates. In patients with ESRD, levels of the Kdn precursor mannose also increased, but within a normal range. Mannose ingestion by healthy volunteers raised the levels of urinary mannose and Kdn. Kdn production pathways remained conserved in mammals but were diminished by an M42T substitution in a key biosynthetic enzyme, N-acetylneuraminate synthase. Remarkably, reversion to the ancestral methionine then occurred independently in 2 lineages, including humans. However, mammalian glycan databases contain no Kdn-glycans. We hypothesize that the potential toxicity of excess mannose in mammals is partly buffered by conversion to free Kdn. Thus, mammals probably conserve Kdn biosynthesis and modulate it in a lineage-specific manner, not for glycosylation, but to control physiological mannose intermediates and metabolites. However, human cells can be forced to express Kdn-glycans via genetic mutations enhancing Kdn utilization, or by transfection with fish enzymes producing cytidine monophosphate-Kdn (CMP-Kdn). Antibodies against Kdn-glycans occur in pooled human immunoglobulins. Pathological conditions that elevate Kdn levels could therefore result in antibody-mediated inflammatory pathologies.

Identification of chicken-derived scFv against N-glycolylneuraminic acid retrieved from an immune library by phage display

N- glycolylneuraminic acid (Neu5Gc) is a type of sialic acid, it can be synthesized by a range of mammals except chickens and healthy human. After entering human body, Neu5Gc in foods such as red meat and milk can cause chronic inflammation, thus promoting the development of cancer and related diseases. In this study, we identified a gene sequence of Neu5Gc-specific single-chain variable fragment (ScFv) by phage display from a primary chicken antibodies library. Then the gene sequence was used to express a 29 kDa anti-Neu5Gc ScFv protein as detection probe in competitive inhibition ELISA (IC-ELISA). The linear regression equation of the IC-ELISA was y = 23.12x+33.19 (R = 0.980), and the half-maximal inhibitory concentration (IC50) and the limit of detection (LOD) was 5.333 and 0.66 μg/mL. The mean recovery of the spiked samples was 83.04%, and the intra-assay and inter-assay coefficients of variation (CVs) were both 5.59%. The results suggested that the specific anti-Neu5Gc ScFv is a promising probe for the development of IC-ELISA and test strip in order to detect the presence of Neu5Gc in red meat, milk, and tumor tissues.

Exploring the Impact of Ketodeoxynonulosonic Acid in Host-Pathogen Interactions Using Uptake and Surface Display by Nontypeable Haemophilus influenzae

All cells in vertebrates are coated with a dense array of glycans often capped with sugars called sialic acids. Sialic acids have many functions, including serving as a signal for recognition of “self” cells by the immune system, thereby guiding an appropriate immune response against foreign “nonself” and/or damaged cells.

Surface expression of the common vertebrate sialic acid (Sia) N-acetylneuraminic acid (Neu5Ac) by commensal and pathogenic microbes appears structurally to represent “molecular mimicry” of host sialoglycans, facilitating multiple mechanisms of host immune evasion. In contrast, ketodeoxynonulosonic acid (Kdn) is a more ancestral Sia also present in prokaryotic glycoconjugates that are structurally quite distinct from vertebrate sialoglycans. We detected human antibodies against Kdn-terminated glycans, and sialoglycan microarray studies found these anti-Kdn antibodies to be directed against Kdn-sialoglycans structurally similar to those on human cell surface Neu5Ac-sialoglycans. Anti-Kdn-glycan antibodies appear during infancy in a pattern similar to those generated following incorporation of the nonhuman Sia N-glycolylneuraminic acid (Neu5Gc) onto the surface of nontypeable Haemophilus influenzae (NTHi), a human commensal and opportunistic pathogen. NTHi grown in the presence of free Kdn took up and incorporated the Sia into its lipooligosaccharide (LOS). Surface display of the Kdn within NTHi LOS blunted several virulence attributes of the pathogen, including Neu5Ac-mediated resistance to complement and whole blood killing, complement C3 deposition, IgM binding, and engagement of Siglec-9. Upper airway administration of Kdn reduced NTHi infection in human-like Cmah null (Neu5Gc-deficient) mice that express a Neu5Ac-rich sialome. We propose a mechanism for the induction of anti-Kdn antibodies in humans, suggesting that Kdn could be a natural and/or therapeutic “Trojan horse” that impairs colonization and virulence phenotypes of free Neu5Ac-assimilating human pathogens.

Molecular Interactions of the Polysialytransferase Domain (PSTD) in ST8Sia IV with CMP-Sialic Acid and Polysialic Acid Required for Polysialylation of the Neural Cell Adhesion Molecule Proteins: An NMR Study

Polysialic acid (polySia) is an unusual glycan that posttranslational modifies neural cell adhesion molecule (NCAM) proteins in mammalian cells. The up-regulated expression of polySia-NCAM is associated with tumor progression in many metastatic human cancers and in neurocognitive processes. Two members of the ST8Sia family of α2,8-polysialyltransferases (polySTs), ST8Sia II (STX) and ST8Sia IV (PST) both catalyze synthesis of polySia when activated cytidine monophosphate(CMP)-Sialic acid (CMP-Sia) is translocate into the lumen of the Golgi apparatus. Two key polybasic domains in the polySTs, the polybasic region (PBR) and the polysialyltransferase domain (PSTD) areessential forpolysialylation of the NCAM proteins. However, the precise molecular details to describe the interactions required for polysialylation remain unknown. In this study, we hypothesize that PSTD interacts with both CMP-Sia and polySia to catalyze polysialylation of the NCAM proteins. To test this hypothesis, we synthesized a 35-amino acid-PSTD peptide derived from the ST8Sia IV gene sequence and used it to study its interaction with CMP-Sia, and polySia. Our results showed for the PSTD-CMP-Sia interaction, the largest chemical-shift perturbations (CSP) were in amino acid residues V251 to A254 in the short H1 helix, located near the N-terminus of PSTD. However, larger CSP values for the PSTD-polySia interaction were observed in amino acid residues R259 to T270 in the long H2 helix. These differences suggest that CMP-Sia preferentially binds to the domain between the short H1 helix and the longer H2 helix. In contrast, polySia was principally bound to the long H2 helix of PSTD. For the PSTD-polySia interaction, a significant decrease in peak intensity was observed in the 20 amino acid residues located between the N-and C-termini of the long H2 helix in PSTD, suggesting a slower motion in these residues when polySia bound to PSTD. Specific features of the interactions between PSTD-CMP-Sia, and PSTD-polySia were further confirmed by comparing their 800 MHz-derived HSQC spectra with that of PSTD-Sia, PSTD-TriSia (DP 3) and PSTD-polySia. Based on the interactions between PSTD-CMP-Sia, PSTD-polySia, PBR-NCAM and PSTD-PBR, these findingsprovide a greater understanding of the molecular mechanisms underlying polySia-NCAM polysialylation, and thus provides a new perspective for translational pharmacological applications and development by targeting the two polysialyltransferases.

NK Cell-Based Immune Checkpoint Inhibition

Immunotherapy, with an increasing number of therapeutic dimensions, is becoming an important mode of treatment for cancer patients. The inhibition of immune checkpoints, which are the source of immune escape for various cancers, is one such immunotherapeutic dimension. It has mainly been aimed at T cells in the past, but NK cells are a newly emerging target. Simultaneously, the number of checkpoints identified has been increasing in recent times. In addition to the classical NK cell receptors KIRs, LIRs, and NKG2A, several other immune checkpoints have also been shown to cause dysfunction of NK cells in various cancers and chronic infections. These checkpoints include the revolutionized CTLA-4, PD-1, and recently identified B7-H3, as well as LAG-3, TIGIT & CD96, TIM-3, and the most recently acknowledged checkpoint-members of the Siglecs family (Siglec-7/9), CD200 and CD47. An interesting dimension of immune checkpoints is their candidacy for dual-checkpoint inhibition, resulting in therapeutic synergism. Furthermore, the combination of immune checkpoint inhibition with other NK cell cytotoxicity restoration strategies could also strengthen its efficacy as an antitumor therapy. Here, we have undertaken a comprehensive review of the literature to date regarding NK cell-based immune checkpoints.

Bovine Milk Oligosaccharides with Sialyllactose Improves Cognition in Preterm Pigs

Optimal nutrition is important after preterm birth to facilitate normal brain development. Human milk is rich in sialic acid and preterm infants may benefit from supplementing formula with sialyllactose to support neurodevelopment. Using pigs as models, we hypothesized that sialyllactose supplementation improves brain development after preterm birth. Pigs (of either sex) were delivered by cesarean section at 90% gestation and fed a milk diet supplemented with either an oligosaccharide-enriched whey with sialyllactose (n = 20) or lactose (n = 20) for 19 days. Cognitive performance was tested in a spatial T-maze. Brains were collected for ex vivo magnetic resonance imaging (MRI), gene expression, and sialic acid measurements. For reference, term piglets (n = 14) were artificially reared under identical conditions and compared with vaginally born piglets naturally reared by the sow (n = 12). A higher proportion of sialyllactose supplemented preterm pigs reached the T-maze learning criteria relative to control preterm pigs (p < 0.05), and approximated the cognition level of term reference pigs (p < 0.01). Furthermore, supplemented pigs had upregulated genes related to sialic acid metabolism, myelination, and ganglioside biosynthesis in hippocampus. Sialyllactose supplementation did not lead to higher levels of sialic acid in the hippocampus or change MRI endpoints. Contrary, these parameters were strongly influenced by postconceptional age and postnatal rearing conditions. In conclusion, oligosaccharide-enriched whey with sialyllactose improved spatial cognition, with effects on hippocampal genes related to sialic acid metabolism, myelination, and ganglioside biosynthesis in preterm pigs. Dietary sialic acid enrichment may improve brain development in infants.

Enzymatic Synthesis of Trideuterated Sialosides

Sialic acids are a family of acidic monosaccharides often found on the termini of cell surface proteins or lipid glycoconjugates of higher animals. Herein we describe the enzymatic synthesis of the two isotopically labeled sialic acid derivatives d₃-X-Gal-α-2,3-Neu5Ac and d₃-X-Gal-α-2,3-Neu5Gc. Using deuterium oxide as the reaction solvent, deuterium atoms could be successfully introduced during the enzymatic epimerization and aldol addition reactions when the sialosides were generated. NMR and mass spectrometric analyses confirmed that the resulting sialosides were indeed tri-deuterated. These compounds may be of interest as internal standards in liquid chromatography/mass spectrometric assays for biochemical or clinical studies of sialic acids. This was further exemplified by the use of this tri-deuterated sialosides as internal standards for the quantification of sialic acids in meat and egg samples.

Targeting sialic acid-Siglec interactions to reverse immune suppression in cancer

Changes in sialic acids in cancer have been observed for many years. In particular, the increase of sialoglycan density or hypersialylation in tumors has been described. Recent studies have identified mechanisms for immune evasion based on sialoglycan interactions with immunoregulatory Siglec receptors that are exploited by tumor cells and microorganisms alike. Siglecs are mostly inhibitory receptors similar to known immune checkpoints including PD-1 or CTLA-4 that are successfully targeted with blocking antibodies for cancer immunotherapy. Here, we summarize the known changes of sialic acids in cancer and the role Siglec receptors play in cancer immunity. We also focus on potential ways to target these Siglec receptors or sialoglycans in order to improve anti-cancer immunity.

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.

Immunochromatographic strip biosensor for the rapid detection of N-glycolylneuraminic acid based on aptamer-conjugated nanoparticle

N-glycolylneuraminic acid (Neu5Gc) is a type of sialic acid that is not typically produced in healthy humans but detective in some visceral cancer cells. As a new carcinoma biomarker, the level change in the serum and urine from the patient could potentially have the relation to the disease progression. So the measurement of the Neu5Gc will help to take a better response to therapeutic schedule for the sufferers. A sensitive and rapid aptamer-nanoparticle immunochromatographic strip for the visual detection of Neu5Gc was developed. The assay is based on the competitive reaction of binding the DNA aptamer targeting the candidate molecule selected by SELEX between Neu5Gc and complementary DNA. The sensing results indicated that the aptamer-based strip was sufficiently sensitive to detect Neu5Gc. The visual limit of detection (LOD) for semi-quantitative detection was 30 ng/mL under the optimal conditions and a quantitative detection limit of 5.38 ng/mL could be obtained using a scanning strip reader. The average recovery of the spiked cancer cell samples was 88.86%, with a coefficient of variation (CV) of 5.27%. The detection could be performed in less than 15 min using a simple procedure without any complicated equipment, demonstrating that this aptamer-nanoparticle biosensor strip has great potential for use to Neu5Gc-related cancer diagnosis.

Sialic Acid Metabolism: A Key Player in Breast Cancer Metastasis Revealed by Metabolomics

Metastatic breast cancer is currently incurable. It has recently emerged that different metabolic pathways support metastatic breast cancer. To further uncover metabolic pathways enabling breast cancer metastasis, we investigated metabolic differences in mouse tumors of differing metastatic propensities using mass spectrometry-based metabolomics. We found that sialic acid metabolism is upregulated in highly metastatic breast tumors. Knocking out a key gene in sialic acid metabolism, Cmas, inhibits synthesis of the activated form of sialic acid, cytidine monophosphate-sialic acid and decreases the formation of lung metastases in vivo. Thus, the sialic acid pathway may be a new target against metastatic breast cancer.

Serum sialylation changes in cancer

Cancer is a major cause of death in both developing and developed countries. Early detection and efficient therapy can greatly enhance survival. Aberrant glycosylation has been recognized to be one of the hallmarks of cancer as glycans participate in many cancer-associated events. Cancer-associated glycosylation changes often involve sialic acids which play important roles in cell-cell interaction, recognition and immunological response. This review aims at giving a comprehensive overview of the literature on changes of sialylation in serum of cancer patients. Furthermore, the methods available to measure serum and plasma sialic acids as well as possible underlying biochemical mechanisms involved in the serum sialylation changes are surveyed. In general, total serum sialylation levels appear to be increased with various malignancies and show a potential for clinical applications, especially for disease monitoring and prognosis. In addition to overall sialic acid levels and the amount of sialic acid per total protein, glycoprofiling of specific cancer-associated glycoproteins, acute phase proteins and immunoglobulins in serum as well as the measurements of sialylation-related enzymes such as sialidases and sialyltransferases have been reported for early detection of cancer, assessing cancer progression and improving prognosis of cancer patients. Moreover, sialic-acid containing glycan antigens such as CA19-9, sialyl Lewis X and sialyl Tn on serum proteins have also displayed their value in cancer diagnosis and management whereby increased levels of these factors positively correlated with metastasis or poor prognosis.

Characterization of porcine milk oligosaccharides over lactation between primiparous and multiparous female pigs

Milk oligosaccharides (MOs) are complex carbohydrates with multifunctional health benefits for the neonate. Poor reproductive performance in primiparous gilts limits their productivity. Changes in the structure and abundance of porcine MO (PMOs) through lactation with parity remains unknown and may explain superior new-born growth in litters from multiparous sows relative to gilts. We report 55 PMOs structures, of which 25 are new (17 sialylated and 8 neutral). Their incidence in gilt and sow colostrum was almost identical (53 vs. 54), but not in transitional milk (48 vs. 53) nor mature milk (41 vs. 47). These PMOs including neutral-, sialyl- and fucosyl- MOs in colostrum were more abundant in the gilt than the sow, but always decreased during lactation. Structural diversity decreased, although fucosylated MO were conserved. In conclusion, high diversity and levels of MO in porcine milk is parity dependent. Given the similarity between porcine and human MO profiles, our findings may help define key roles for MOs as potential dietary additives to improve growth of neonates from first pregnancies in both human and sows.

Biochemical, Cellular, Physiological, and Pathological Consequences of Human Loss of N-Glycolylneuraminic Acid

About 2-3 million years ago, Alu-mediated deletion of a critical exon in the CMAH gene became fixed in the hominin lineage ancestral to humans, possibly through a stepwise process of selection by pathogen targeting of the CMAH product (the sialic acid Neu5Gc), followed by reproductive isolation through female anti-Neu5Gc antibodies. Loss of CMAH has occurred independently in some other lineages, but is functionally intact in Old World primates, including our closest relatives, the chimpanzee. Although the biophysical and biochemical ramifications of losing tens of millions of Neu5Gc hydroxy groups at most cell surfaces remains poorly understood, we do know that there are multiscale effects functionally relevant to both sides of the host-pathogen interface. Hominin CMAH loss might also contribute to understanding human evolution, at the time when our ancestors were starting to use stone tools, increasing their consumption of meat, and possibly hunting. Comparisons with chimpanzees within ethical and practical limitations have revealed some consequences of human CMAH loss, but more has been learned by using a mouse model with a human-like Cmah inactivation. For example, such mice can develop antibodies against Neu5Gc that could affect inflammatory processes like cancer progression in the face of Neu5Gc metabolic incorporation from red meats, display a hyper-reactive immune system, a human-like tendency for delayed wound healing, late-onset hearing loss, insulin resistance, susceptibility to muscular dystrophy pathologies, and increased sensitivity to multiple human-adapted pathogens involving sialic acids. Further studies in such mice could provide a model for other human-specific processes and pathologies involving sialic acid biology that have yet to be explored.

Recent advances in mass spectrometric analysis of glycoproteins

Glycosylation is one of the most common posttranslational modifications of proteins that plays essential roles in various biological processes, including protein folding, host-pathogen interaction, immune response, and inflammation and aberrant protein glycosylation is a well-known event in various disease states including cancer. As a result, it is critical to develop rapid and sensitive methods for the analysis of abnormal glycoproteins associated with diseases. Mass spectrometry (MS) in conjunction with different separation methods, such as capillary electrophoresis (CE), ion mobility (IM), and high performance liquid chromatography (HPLC) has become a popular tool for glycoprotein analysis, providing highly informative fragments for structural identification of glycoproteins. This review provides an overview of the developments and accomplishments in the field of glycomics and glycoproteomics reported between 2014 and 2016.

Developmental changes in the level of free and conjugated sialic acids, Neu5Ac, Neu5Gc and KDN in different organs of pig: a LC-MS/MS quantitative analyses

Recent studies have shown a relationship between the level of the sialic acid (Sia), N-glycolylneuraminic acid (Neu5Gc) in red meat and its risk in cancer, cardiovascular and inflammatory diseases. Unresolved is the Sia concentration in different organs of piglets during development. Our aim was to determine the level of free and conjugated forms of Neu5Gc, N-acetylneuraminic acid (Neu5Ac) and ketodeoxynonulsonic acid (Kdn) in fresh and cooked spleen, kidney, lung, heart, liver, and skeletal muscle from 3-days-old (n = 4-8), 38-days-old (n = 10) and adult piglets (n = 4) by LC-MS/MS. Our findings show: (1) Lung tissue from 3 days-old piglets contained the highest level of total Sia (14.6 μmol/g protein) compared with other organs or age groups; (2) Unexpectedly, Neu5Gc was the major Sia in spleen (67-79 %) and adult lung (36-49 %) while free Kdn was the major Sia in skeletal muscle. Conjugated Neu5Ac was the highest Sia in other organs (61-84 %); (3) Skeletal muscle contained the lowest concentration of Neu5Gc in fresh and cooked meat; (4) Kdn accounted for <5 % of the total Sia in most organs; (5) During development, the total Sia concentration showed a 44-79 % decrease in all organs; (6) In adult piglets, the high to low rank order of total Sia was lung, heart, spleen, kidney, liver and skeletal muscle. In conclusion, the high level of Neu5Gc in all organs compared to skeletal muscle is a potential risk factor suggesting that dietary consumption of organ meats should be discouraged in favor of muscle to protect against cancer, cardiovascular and other inflammatory diseases.

Metabolic Glycoengineering with N-Acyl Side Chain Modified Mannosamines

In metabolic glycoengineering (MGE), cells or animals are treated with unnatural derivatives of monosaccharides. After entering the cytosol, these sugar analogues are metabolized and subsequently expressed on newly synthesized glycoconjugates. The feasibility of MGE was first discovered for sialylated glycans, by using N-acyl-modified mannosamines as precursor molecules for unnatural sialic acids. Prerequisite is the promiscuity of the enzymes of the Roseman-Warren biosynthetic pathway. These enzymes were shown to tolerate specific modifications of the N-acyl side chain of mannosamine analogues, for example, elongation by one or more methylene groups (aliphatic modifications) or by insertion of reactive groups (bioorthogonal modifications). Unnatural sialic acids are incorporated into glycoconjugates of cells and organs. MGE has intriguing biological consequences for treated cells (aliphatic MGE) and offers the opportunity to visualize the topography and dynamics of sialylated glycans in vitro, ex vivo, and in vivo (bioorthogonal MGE).

Human risk of diseases associated with red meat intake: Analysis of current theories and proposed role for metabolic incorporation of a non-human sialic acid

One of the most consistent epidemiological associations between diet and human disease risk is the impact of red meat consumption (beef, pork, and lamb, particularly in processed forms). While risk estimates vary, associations are reported with all-cause mortality, colorectal and other carcinomas, atherosclerotic cardiovascular disease, type II diabetes, and possibly other inflammatory processes. There are many proposed explanations for these associations, some long discussed in the literature. Attempts to explain the effects of red meat consumption have invoked various red meat-associated agents, including saturated fat, high salt intake, Trimethylamine-N-oxide (TMAO) generation by microbiota, and environmental pollutants contaminating red meat, none of which are specific for red meat. Even the frequently mentioned polycyclic aromatic carcinogens arising from high temperature cooking methods are not red meat specific, as these are also generated by grilling poultry or fish, as well as by other forms of cooking. The traditional explanations that appear to be more red meat specific invoke the impact of N-nitroso compounds, heme iron, and the potential of heme to catalyze endogenous nitrosation. However, heme can be denatured by cooking, high levels of plasma hemopexin will block its tissue delivery, and much higher amounts of heme likely originate from red blood cell breakdown in vivo. Therefore, red meat-derived heme could only contribute to colorectal carcinoma risk, via direct local effects. Also, none of these mechanisms explain the apparent human propensity i.e., other carnivores have not been reported at high risk for all these diseases. A more recently proposed hypothesis involves infectious agents in beef from specific dairy cattle as agents of colorectal cancer. We have also described another mechanistic explanation for the human propensity for risk of red-meat associated diseases that is consistent with most observations: metabolic incorporation of a non-human sialic acid N-glycolylneuraminic acid (Neu5Gc) into the tissues of red meat consumers and the subsequent interaction with inflammation-provoking antibodies against this "xenoautoantigen". Overall, we conclude that while multiple mechanisms are likely operative, many proposed theories to date are not specific for red meat, and that the viral and xenoautoantigen theories deserve further consideration. Importantly, there are potential non-toxic dietary antidotes, if the xenoautoantigen theory is indeed correct.