Structure-based rationale for differential recognition of lacto- and neolacto- series glycosphingolipids by the N-terminal domain of human galectin-8

Glycomimetic inhibitors of tandem-repeat galectins: Simple and efficient

The binding of human galectins by glycomimetic inhibitors is a promising therapeutic approach. The structurally distinct group of tandem-repeat galectins has scarcely been studied so far, and there is hardly any knowledge on their ligand specificity or their inhibitory potential, particularly concerning non-natural carbohydrates. Here, we present the synthesis of a library of seven 3-O-disubstituted thiodigalactoside-derived glycomimetics and their affinity to two tandem-repeat galectins, Gal-8 and Gal-9. The straightforward synthesis of these glycomimetics involved dibutyltin oxide-catalyzed 3,3́-O-disubstitution of commercially available unprotected thiodigalactoside, and conjugation of various aryl substituents by copper-catalyzed Huisgen azide-alkyne cycloaddition (CuAAC). The inhibitory potential of the prepared glycomimetics for Gal-8 and Gal-9 was assessed, and compared with the established galectins Gal-1 and Gal-3. The introduction of C-3 substituents resulted in an over 40-fold increase in affinity compared with unmodified TDG. The structure-affinity relations within the studied series were discussed using molecular modeling. Furthermore, the prepared glycomimetics were shown to scavenge Gal-8 and Gal-9 from the surface of cancer cells. This pioneering study on the synthetic inhibitors especially of Gal-9 identified lead compounds that may be used in further biomedical research.

[Human milk oligosaccharides play major roles in child development and future health]

Human milk oligosaccharides (HMO) represent the third largest component of human breast milk (BM). The BM level is comprised between 5 to 20 g per liter and they have a great structural complexity with more than 150 HMO characterized to date. In this review, we present a summary of the main experimental and clinical data that have demonstrated their multiple biological roles in infants such as for gut development, microbiota, immune protection and neurodevelopment. Some HMO-enriched infant formulas are available yet, even if their benefits on the infant health remain to be confirmed. Further researches could allow therapeutic use in preterm newborns or in infants with intestinal diseases. Experimental data suggest that they could also be used in the prevention of some chronic diseases with immunometabolic or neurodevelopmental components.

Human Milk Oligosaccharide Profile across Lactation Stages in Israeli Women-A Prospective Observational Study

Human milk oligosaccharides (HMOs) stimulate the growth of gut commensals, prevent the adhesion of enteropathogens and modulate host immunity. The major factors influencing variations in the HMO profile are polymorphisms in the secretor (Se) or Lewis (Le) gene, which affect the activity of the enzymes fucoslytransferase 2 and 3 (FUT2 and FUT3) that lead to the formation of four major fucosylated and non-fucosylated oligosaccharides (OS). This pilot study aimed to determine the HMO profile of Israeli breastfeeding mothers of 16 term and 4 preterm infants, from a single tertiary center in the Tel Aviv area. Fifty-two human milk samples were collected from 20 mothers at three-time points: colostrum, transitional milk and mature milk. The concentrations of nine HMOs were assessed using liquid chromatography coupled with mass spectra chromatograms. Fifty-five percent of the mothers were secretors and 45% were non-secretors. Infant sex affected HMO levels depending on the maternal secretor status. Secretor mothers to boys had higher levels of FUT2-dependent OS and higher levels of disialyllacto-N-tetraose in the milk of mothers to girls, whereas non-secretor mothers to girls had higher levels of 3'-sialyllactose. In addition, the season at which the human milk samples were obtained affected the levels of some HMOs, resulting in significantly lower levels in the summer. Our findings provide novel information on the irregularity in the HMO profile among Israeli lactating women and identify several factors contributing to this variability.

Selective Galectin-8N Ligands: The Design and Synthesis of Phthalazinone-d-Galactals

Ligand selectivity among the highly conserved galectins has been an ever-challenging objective. For galectin-8, a protein prevalent in both pathology and tissue distribution, we report phthalazinone-galactals that show excellent selectivity for the galectin-8N-terminal domain. A dissection of structure-activity relationships of the phthalazinone and an extensive molecular dynamics meta-analysis accompany the discovery of the selective galectin-8N ligands presented here. These selective compounds will facilitate the study of galectin-8 biology and may have pharmaceutical relevance in the wide range of galectin-8 associated pathologies.

Multifunctional Benefits of Prevalent HMOs: Implications for Infant Health

Breastfeeding is the best source of nutrition during infancy and is associated with a broad range of health benefits. However, there remains a significant and persistent need for innovations in infant formula that will allow infants to access a wider spectrum of benefits available to breastfed infants. The addition of human milk oligosaccharides (HMOs) to infant formulas represents the most significant innovation in infant nutrition in recent years. Although not a direct source of calories in milk, HMOs serve as potent prebiotics, versatile anti-infective agents, and key support for neurocognitive development. Continuing improvements in food science will facilitate production of a wide range of HMO structures in the years to come. In this review, we evaluate the relationship between HMO structure and functional benefits. We propose that infant formula fortification strategies should aim to recapitulate a broad range of benefits to support digestive health, immunity, and cognitive development associated with HMOs in breastmilk. We conclude that acetylated, fucosylated, and sialylated HMOs likely confer important health benefits through multiple complementary mechanisms of action.

Altered Gut Microbiota is Involved in the Anti-Hypertensive Effects of Vitamin C in Spontaneously Hypertensive Rat

SCOPE

Gut dysbiosis and dysregulation of the gut-brain-axis contributes to the pathogenesis of hypertension. Vitamin C (VC) is a common dietary supplement that shows the ability to lower the elevated blood pressure in hypertensive animals. Thus, the hypothesis that the gut microbiota is involved in the anti-hypertensive effect of VC is proposed.

METHODS AND RESULTS

The changes of the gut microbiota and pathology in a spontaneously hypertensive rat (SHR) model after daily oral intake of VC in dosage of 200 or 1000 mg kg-1 are examined. After 4 weeks, the elevated blood pressure of SHRs in both VC-treated groups is attenuated. Sequencing of the gut microbiota shows improvement in its diversity and abundance. Bioinformatic analysis suggests restored metabolism and biosynthesis-related functions of the gut, which are confirmed by the improvement of gut pathology and integrity. Analysis of the hypothalamus paraventricular nucleus (PVN), the central pivot of blood pressure regulation, also shows reduced inflammatory responses and oxidative stress.

CONCLUSIONS

The reduced blood pressure, enriched gut microbiota, improved gut pathology and integrity, and reduced inflammatory responses and oxidative stress in the PVN together suggest that the anti-hypertensive effects of VC involve reshaping of gut microbiota composition and function.

The association between increasing levels of O-GlcNAc and galectins in the liver tissue of hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus)

Post-translational glycosylation of proteins with O-linked β-N-acetylglucosamine (O-GlcNAcylation) and changes of galectin expression profiles are essential in many cellular stress responses. We examine this regulation in the liver tissue of hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus) representing a biological model of hypometabolism and physiological stress resistance. The tissue levels of O-GlcNAcylated proteins as well as galectin-1 and galectin-3 proteins detected by immunodot blot assay were significantly lower by 4.6-5.4-, 2.2-2.3- and 2.5-2.9-fold, respectively, in the non-hibernating summer squirrels compared with those in winter, whether hibernating or aroused. However, there were no differences in the expression of genes encoding enzymes involved in O-GlcNAc cycle (O-GlcNAc transferase and O-GlcNAcase) and such galectins as LGALS1, LGALS2, LGALS3, LGALS4 and LGALS9. Only the expression of LGALS8 gene in the liver tissue was significantly decreased by 37.6 ± 0.1% in hibernating ground squirrels relative to summer animals. Considering that the expression of a proven genetic biomarker ELOVL6 encoding ELOVL fatty acid elongase 6 was readily upregulated in non-hibernating animals by 11.3-32.9-fold, marginal differential changes in the expression of galectin genes cannot be classified as biomarkers of hibernation. Thus, this study provides evidence that hibernation in Ictidomys tridecemlineatus is associated with increasing O-GlcNAcylation of liver proteins and suggests that the contribution of galectins deserves further studies at the protein level.

Breast milk-derived human milk oligosaccharides promote Bifidobacterium interactions within a single ecosystem

Diet-microbe interactions play an important role in modulating the early-life microbiota, with Bifidobacterium strains and species dominating the gut of breast-fed infants. Here, we sought to explore how infant diet drives distinct bifidobacterial community composition and dynamics within individual infant ecosystems. Genomic characterisation of 19 strains isolated from breast-fed infants revealed a diverse genomic architecture enriched in carbohydrate metabolism genes, which was distinct to each strain, but collectively formed a pangenome across infants. Presence of gene clusters implicated in digestion of human milk oligosaccharides (HMOs) varied between species, with growth studies indicating that within single infants there were differences in the ability to utilise 2'FL and LNnT HMOs between strains. Cross-feeding experiments were performed with HMO degraders and non-HMO users (using spent or 'conditioned' media and direct co-culture). Further 1H-NMR analysis identified fucose, galactose, acetate, and N-acetylglucosamine as key by-products of HMO metabolism; as demonstrated by modest growth of non-HMO users on spend media from HMO metabolism. These experiments indicate how HMO metabolism permits the sharing of resources to maximise nutrient consumption from the diet and highlights the cooperative nature of bifidobacterial strains and their role as 'foundation' species in the infant ecosystem. The intra- and inter-infant bifidobacterial community behaviour may contribute to the diversity and dominance of Bifidobacterium in early life and suggests avenues for future development of new diet and microbiota-based therapies to promote infant health.

Galectin binding to cells and glycoproteins with genetically modified glycosylation reveals galectin-glycan specificities in a natural context

Galectins compose a protein family defined by a conserved sequence motif conferring affinity for β-galactose-containing glycans. Moreover, galectins gain higher affinity and fine-tune specificity by glycan interactions at sites adjacent to their β-galactoside-binding site, as revealed by extensive testing against panels of purified glycans. However, in cells, galectins bind glycans on glycoproteins and glycolipids in the context of other cellular components, such as at the cell surface. Because of difficulties in characterizing natural cellular environments, we currently lack a detailed understanding of galectin-binding specificities in the cellular context. To address this challenge, we used a panel of genetically stable glycosylation mutated CHO cells that express defined glycans to evaluate the binding affinities of 10 different carbohydrate-recognition domains in galectins to N-glycans and mucin-type O-glycans. Using flow cytometry, we measured the cell-surface binding of the galectins. Moreover, we used fluorescence anisotropy to determine the galectin affinities to recombinant erythropoietin used as a reporter glycoprotein produced by the glycoengineered cells and to synthetic N-glycans with defined branch structures. We found that all galectins, apart from galectin-8N, require complex N-glycans for high-affinity binding. Galectin-8N targeted both N- and O-linked glycans with high affinity, preferring 2,3-sialylated N-acetyllactosamine (LacNAc) structures. Furthermore, we found that 2,3-sialylation suppresses high-affinity binding of select galectins, including galectin-2, -3, -4N, and -7. Structural modeling provided a basis for interpreting the observed binding preferences. These results underscore the power of a glycoengineered platform to dissect the glycan-binding specificities of carbohydrate-binding proteins.

Conformations of the type-1 lacto-N-biose I unit in protein complex structures

The lacto-N-biose I (Galβ1-3GlcNAc; LNB) disaccharide is present as a core unit of type-1 blood group antigens of animal glycoconjugates and milk oligosaccharides. Type-1 antigens often serve as cell-surface receptors for infection by pathogens. LNB in human milk oligosaccharides functions as a prebiotic for bifidobacteria and plays a key role in the symbiotic relationship of commensal gut microbes in infants. Protein Data Bank (PDB) entries exhibiting the LNB unit were investigated using the GlycoMapsDB web tool. There are currently 159 β-LNB and nine α-LNB moieties represented in ligands in the database. β-LNB and α-LNB moieties occur in 74 and six PDB entries, respectively, as NCS copies. The protein and enzyme structures are from various organisms including humans (galectins), viruses (haemagglutinin and capsid proteins), a pathogenic fungus, a parasitic nematode and protist, pathogenic bacteria (adhesins) and a symbiotic bacterium (a solute-binding protein of an ABC transporter). The conformations of LNB-containing glycans in enzymes vary significantly according to their mechanism of substrate recognition and catalysis. Analysis of glycosidic bond conformations indicated that the binding modes are significantly different in proteins adapted for modified or unmodified glycans.