Inhibition of Helicobacter pylori binding to gastrointestinal epithelial cells by sialic acid-containing oligosaccharides

Anti-bacterial effects of enzymatically-isolated sialic acid from glycomacropeptide in a Helicobacter pylori-infected murine model

BACKGROUND/OBJECTIVES

Helicobacter pylori (H. pylori) colonization of the stomach mucosa and duodenum is the major cause of acute and chronic gastroduodenal pathology in humans. Efforts to find effective anti-bacterial strategies against H. pylori for the non-antibiotic control of H. pylori infection are urgently required. In this study, we used whey to prepare glycomacropeptide (GMP), from which sialic acid (G-SA) was enzymatically isolated. We investigated the anti-bacterial effects of G-SA against H. pylori in vitro and in an H. pylori-infected murine model.

MATERIALS/METHODS

The anti-bacterial activity of G-SA was measured in vitro using the macrodilution method, and interleukin-8 (IL-8) production was measured in H. pylori and AGS cell co-cultures by ELISA. For in vivo study, G-SA 5 g/kg body weight (bw)/day and H. pylori were administered to mice three times over one week. After one week, G-SA 5 g/kg bw/day alone was administered every day for one week. Tumor necrosis factor-α (TNF-α), IL-1β, IL-6, and IL-10 levels were measured by ELISA to determine the anti-inflammatory effects of G-SA. In addition, real-time PCR was performed to measure the genetic expression of cytotoxin-associated gene A (cagA).

RESULTS

G-SA inhibited the growth of H. pylori and suppressed IL-8 production in H. pylori and in AGS cell co-cultures in vitro. In the in vivo assay, administration of G-SA reduced levels of IL-1β and IL-6 pro-inflammatory cytokines whereas IL-10 level increased. Also, G-SA suppressed the expression of cagA in the stomach of H. pylori-infected mice.

CONCLUSION

G-SA possesses anti-H. pylori activity as well as an anti-H. pylori-induced gastric inflammatory effect in an experimental H. pylori-infected murine model. G-SA has potential as an alternative to antibiotics for the prevention of H. pylori infection and H. pylori-induced gastric disease prevention.

Anti-Helicobacter pylori activity of crude N-acetylneuraminic acid isolated from glycomacropeptide of whey

Helicobacter pylori colonizes the gastric mucosa of about half of the world's population, causing chronic gastritis and gastric cancer. An increasing emergence of antibiotic-resistant H. pylori arouses demand on alternative non-antibiotic-based therapies. In this study, we freshly prepared crude N-acetylneuraminic acid obtained from glycomacropeptide (G-NANA) of whey through a neuraminidase-mediated reaction and evaluated its antibacterial ability against H. pylori and H. felis. Overnight cultures of the H. pylori were diluted with fresh media and different concentrations (1-150 mg/mL) of crude G-NANA were added directly to the culture tube. Bacterial growth was evaluated by measuring the optical density of the culture medium and the number of viable bacteria was determined by a direct count of the colony forming units (CFU) on agar plates. For the in vivo study, mice were orally infected with 100 µL (5×10(8) cfu/mL) of H. felis four times at a day's interval, accompanied by a daily administration of crude G-NANA or vehicle. A day after the last infection, the mice were daily administered the crude G-NANA (0, 75, and 300 mg/mL) for 10 days and euthanized. Their stomachs were collected and bacterial colonization was determined by quantitative real-time PCR. Crude G-NANA inhibited H. pylori's growth and reduced the number of viable bacteria in a dose-dependent manner. Furthermore, crude G-NANA inhibited bacterial colonization in the mice. These results showed that crude G-NANA has antibacterial activity against Helicobacter and demonstrated its therapeutic potential for the prevention of chronic gastritis and gastric carcinogenesis induced by Helicobacter infection in humans.

Recent advances on separation and characterization of human milk oligosaccharides

Free human milk oligosaccharides (HMOs) are unique due to their highly complex nature and important emerging biological and protective functions during early life such as prebiotic activity, pathogen deflection, and epithelial and immune cell modulation. Moreover, four genetically determined heterogeneous HMO secretory groups are known to be based on their structure and composition. Over the years, several analytical techniques have been applied to characterize and quantitate HMOs, including nuclear magnetic resonance spectroscopy, high-performance liquid chromatography (HPLC), high pH anion-exchange chromatography, off-line and on-line mass spectrometry (MS), and capillary electrophoresis (CE). Even if these techniques have proven to be efficient and simple, most glycans have no significant UV absorption and derivatization with fluorophore groups prior to separation usually results in higher sensitivity and an improved chromatographic/electrophoretic profile. Consequently, the analysis by HPLC/CE of derivatized milk oligosaccharides with different chromophoric active tags has been developed. However, UV or fluorescence detection does not provide specific structural information and this is a key point in particular related to the highly complex nature of the milk glycan mixtures. As a consequence, for a specific determination of complex mixtures of oligomers, analytical separation is usually required with evaluation by means of MS, which has been successfully applied to HMOs, resulting in efficient compositional analysis and profiling in various milk samples. This review aims to give an overview of the current state-of-the-art techniques used in HMO analysis.

Clinical applications of bioactive milk components

Milk represents a unique resource for translational medicine: It contains a rich pool of biologically active molecules with demonstrated clinical benefits. The ongoing characterization of the mechanistic process through which milk components promote development and immunity has revealed numerous milk-derived compounds with potential applications as clinical therapies in infectious and inflammatory disease, cancer, and other conditions. Lactoferrin is an effective antimicrobial and antiviral agent in high-risk patient populations and a potentially potent adjuvant to chemotherapy in lung cancer. Enteric nutrition formulas supplemented with transforming growth factor β, a milk cytokine, have been shown to promote remission in pediatric Crohn's disease. A number of milk glycans, including human milk oligosaccharides, show promise in preclinical studies as antimicrobial and anti-inflammatory agents. While active preclinical investigations of human milk may soon result in large-scale production of human milk molecules, bovine milk components in many instances represent a practical source of bioactive milk compounds for use in clinical trials. This review summarizes current efforts to translate the compounds derived from human and bovine milk into effective clinical therapies. These efforts suggest a common pathway for the translation of milk-derived compounds into clinical applications.

In Vitro Fermentation of caprine milk oligosaccharides by bifidobacteria isolated from breast-fed infants

This study was conducted to investigate the catabolism and fermentation of caprine milk oligosaccharides (CMO) by selected bifidobacteria isolated from 4 breast-fed infants. Seventeen bifidobacterial isolates consisting of 3 different species (Bifidobacterium breve, Bifidobacterium longum subsp. longum and Bifidobacterium bifidum) were investigated. A CMO-enriched fraction (CMOF) (50% oligosaccharides, 10% galacto-oligosaccharides (GOS), 20% lactose, 10% glucose and 10% galactose) from caprine cheese whey was added to a growth medium as a sole source of fermentable carbohydrate. The inclusion of the CMOF was associated with increased bifidobacterial growth for all strains compared to glucose, lactose, GOS, inulin, oligofructose, 3'-sialyl-lactose and 6'-sialyl-lactose. Only one B. bifidum strain (AGR2166) was able to utilize the sialyl-CMO, 3'-sialyl-lactose and 6'-sialyl-lactose, as carbohydrate sources. The inclusion of CMOF increased the production of acetic and lactic acid (P < 0.001) after 36 h of anaerobic fermentation at 37 °C, when compared to other fermentable substrates. Two B. bifidum strains (AGR2166 and AGR2168) utilised CMO, contained in the CMOF, to a greater extent than B. breve or B. longum subsp longum isolates, and this increased CMO utilization was associated with enhanced sialidase activity. CMOF stimulated bifidobacterial growth when compared to other tested fermentable carbohydrates and also increased the consumption of mono- and disaccharides, such as galactose and lactose present in the CMOF. These findings indicate that the dietary consumption of CMO may stimulate the growth and metabolism of intestinal Bifidobacteria spp. including B. bifidum typically found in the large intestine of breast-fed infants.

The prebiotics 3'Sialyllactose and 6'Sialyllactose diminish stressor-induced anxiety-like behavior and colonic microbiota alterations: Evidence for effects on the gut-brain axis

There are extensive bidirectional interactions between the gut microbiota and the central nervous system (CNS), and studies demonstrate that stressor exposure significantly alters gut microbiota community structure. We tested whether oligosaccharides naturally found in high levels in human milk, which have been reported to impact brain development and enhance the growth of beneficial commensal microbes, would prevent stressor-induced alterations in gut microbial community composition and attenuate stressor-induced anxiety-like behavior. Mice were fed standard laboratory diet, or laboratory diet containing the human milk oligosaccharides 3'Sialyllactose (3'SL) or 6'Sialyllactose (6'SL) for 2 weeks prior to being exposed to either a social disruption stressor or a non-stressed control condition. Stressor exposure significantly changed the structure of the colonic mucosa-associated microbiota in control mice, as indicated by changes in beta diversity. The stressor resulted in anxiety-like behavior in both the light/dark preference and open field tests in control mice. This effect was associated with a reduction in immature neurons in the dentate gyrus as indicated by doublecortin (DCX) immunostaining. These effects were not evident in mice fed milk oligosaccharides; stressor exposure did not significantly change microbial community structure in mice fed 3'SL or 6'SL. In addition, 3'SL and 6'SL helped maintain normal behavior on tests of anxiety-like behavior and normal numbers of DCX+ immature neurons. These studies indicate that milk oligosaccharides support normal microbial communities and behavioral responses during stressor exposure, potentially through effects on the gut microbiota-brain axis.

The crystal structure of Helicobacter pylori HP1029 highlights the functional diversity of the sialic acid-related DUF386 family

The proteins of the YhcH/YjgK/YiaL (DUF386) family have been implicated in the bacterial metabolism of host-derived sialic acids and biofilm formation, although their precise biochemical function remains enigmatic. We present here the crystal structure of protein HP1029 from Helicobacter pylori. The protein is a homodimer, in which each monomer comprises a molecular core formed by 12 antiparallel β-strands arranged in two β-sheets flanked by helices. The sandwich formed by the sheets assumes the shape of a funnel opened at one end, with a zinc ion present at the bottom of the funnel. The crystal structure unequivocally shows that HP1029 belongs to the DUF386 family. Although no bioinformatics evidence has been found for sialic acid catabolism in H. pylori, the genomic context of HP1029 in Helicobacter and related organisms suggests a possible role in the metabolism of bacterial surface saccharides, such as pseudaminic acid and its derivatives.

Beneficial effects of human milk oligosaccharides on gut microbiota

Human milk is the gold standard for nourishment of early infants because it contains a number of bioactive components, such as human milk oligosaccharides (HMOs). The high concentration and structural diversity of HMOs are unique to humans. HMOs are a group of complex and diverse glycans that are resistant to gastrointestinal digestion and reach the infant colon as the first prebiotics. N-acetyl-glucosamine containing oligosaccharides were first identified 50 years ago as the 'bifidus factor', a selective growth substrate for intestinal bifidobacteria, thus providing a conceptual basis for HMO-specific bifidogenic activity. Bifidobacterial species are the main utilisers of HMOs in the gastrointestinal tract and represent the dominant microbiota of breast-fed infants, and they may play an important role in maintaining the general health of newborn children. Oligosaccharides are also known to directly interact with the surface of pathogenic bacteria, and various oligosaccharides in milk are believed to inhibit the binding of pathogens and toxins to host cell receptors. Furthermore, HMOs are thought to contribute to the development of infant intestine and brain. Oligosaccharides currently added to infant formula are structurally different from the oligosaccharides naturally occurring in human milk and, therefore, they are unlikely to mimic some of the structure-specific effects. In this review, we describe how HMOs can modulate gut microbiota. This article summarises information up to date about the relationship between the intestinal microbiota and HMOs, and other possible indirect effects of HMOs on intestinal environment.

Milk proteins, peptides, and oligosaccharides: effects against the 21st century disorders

Milk is the most complete food for mammals, as it supplies all the energy and nutrients needed for the proper growth and development of the neonate. Milk is a source of many bioactive components, which not only help meeting the nutritional requirements of the consumers, but also play a relevant role in preventing various disorders. Milk-derived proteins and peptides have the potential to act as coadjuvants in conventional therapies, addressing cardiovascular diseases, metabolic disorders, intestinal health, and chemopreventive properties. In addition to being a source of proteins and peptides, milk contains complex oligosaccharides that possess important functions related to the newborn's development and health. Some of the health benefits attributed to milk oligosaccharides include prebiotic probifidogenic effects, antiadherence of pathogenic bacteria, and immunomodulation. This review focuses on recent findings demonstrating the biological activities of milk peptides, proteins, and oligosaccharides towards the prevention of diseases of the 21st century. Processing challenges hindering large-scale production and commercialization of those bioactive compounds have been also addressed.

Inhibition of adhesion of intestinal pathogens (Escherichia coli, Vibrio cholerae, Campylobacter jejuni, and Salmonella Typhimurium) by common oligosaccharides

Inhibition of the binding of pathogenic adhesins to host glycans by suitable oligosaccharides forms the basis of antiadhesion therapies. Experiments were carried out to study the inhibition capability of oligosaccharides on the adhesion of four microorganisms (Escherichia coli, Vibrio cholerae, Campylobacter jejuni, and Salmonella Typhimurium) to HT-29 cells. Results showed that, in the absence of oligosaccharides, all of the four pathogens efficiently adhered to the cells. Cell adhesion with different bacteria was inhibited by distinct oligosaccharides (e.g., the adhesion number relative to control of V. cholerae could be significantly decreased by pectin oligosaccharide and chitooligosaccharide to about 16.1% and 18.9%, respectively). Saturation studies showed that the extent of antiadhesive effect for most of the suitable carbohydrates was dependent on their concentration. The observations from the study suggest that various carbohydrates may have antiadhesive activity and may be useful in future therapeutic study.

Human milk contains novel glycans that are potential decoy receptors for neonatal rotaviruses

Human milk contains a rich set of soluble, reducing glycans whose functions and bioactivities are not well understood. Because human milk glycans (HMGs) have been implicated as receptors for various pathogens, we explored the functional glycome of human milk using shotgun glycomics. The free glycans from pooled milk samples of donors with mixed Lewis and Secretor phenotypes were labeled with a fluorescent tag and separated via multidimensional HPLC to generate a tagged glycan library containing 247 HMG targets that were printed to generate the HMG shotgun glycan microarray (SGM). To investigate the potential role of HMGs as decoy receptors for rotavirus (RV), a leading cause of severe gastroenteritis in children, we interrogated the HMG SGM with recombinant forms of VP8* domains of the RV outer capsid spike protein VP4 from human neonatal strains N155(G10P[11]) and RV3(G3P[6]) and a bovine strain, B223(G10P[11]). Glycans that were bound by RV attachment proteins were selected for detailed structural analyses using metadata-assisted glycan sequencing, which compiles data on each glycan based on its binding by antibodies and lectins before and after exo- and endo-glycosidase digestion of the SGM, coupled with independent MS(n) analyses. These complementary structural approaches resulted in the identification of 32 glycans based on RV VP8* binding, many of which are novel HMGs, whose detailed structural assignments by MS(n) are described in a companion report. Although sialic acid has been thought to be important as a surface receptor for RVs, our studies indicated that sialic acid is not required for binding of glycans to individual VP8* domains. Remarkably, each VP8* recognized specific glycan determinants within a unique subset of related glycan structures where specificity differences arise from subtle differences in glycan structures.

Functional role and mechanisms of sialyllactose and other sialylated milk oligosaccharides

Human milk is a rich source of oligosaccharides. Acidic oligosaccharides, such as sialyllactose (SL), contain sialic acid (SA) residues. In human milk, approximately 73% of SA is bound to oligosaccharides, whereas only 3% is present in free form. Oligosaccharides are highly resistant to hydrolysis in the gastrointestinal tract. Only a small portion of the available oligosaccharides in breast milk is absorbed in the neonatal small intestine. SL and sialylated oligosaccharides are thought to have significant health benefits for the neonate, because of their roles in supporting resistance to pathogens, gut maturation, immune function, and cognitive development. The need for SA to allow proper development during the neonatal period is thought to exceed the endogenous synthesis. Therefore, these structures are important nutrients for the neonate. Based on the potential benefits, SL and sialylated oligosaccharides may be interesting components for application in infant nutrition. Once the hurdle of limited availability of these oligosaccharides has been overcome, their functionality can be explored in more detail, and supplementation of infant formula may become feasible.

Novel high-molecular weight fucosylated milk oligosaccharides identified in dairy streams

Oligosaccharides are the third largest component in human milk. This abundance is remarkable because oligosaccharides are not digestible by the newborn, and yet they have been conserved and amplified during evolution. In addition to encouraging the growth of a protective microbiota dominated by bifidobacteria, oligosaccharides have anti-infective activity, preventing pathogens from binding to intestinal cells. Although it would be advantageous adding these valuable molecules to infant milk formula, the technologies to reproduce the variety and complexity of human milk oligosaccharides by enzymatic/organic synthesis are not yet mature. Consequently, there is an enormous interest in alternative sources of these valuable oligosaccharides. Recent research has demonstrated that bovine milk and whey permeate also contain oligosaccharides. Thus, a thorough characterization of oligosaccharides in bovine dairy streams is an important step towards fully assessing their specific functionalities. In this study, bovine milk oligosaccharides (BMOs) were concentrated by membrane filtration from a readily available dairy stream called “mother liquor”, and analyzed by high accuracy MALDI FT-ICR mass spectrometry. The combination of HPLC and accurate mass spectrometry allowed the identification of ideal processing conditions leading to the production of Kg amount of BMO enriched powders. Among the BMOs identified, 18 have high-molecular weight and corresponded in size to the most abundant oligosaccharides present in human milk. Notably 6 oligosaccharides contained fucose, a sugar monomer that is highly abundant in human milk, but is rarely observed in bovine milk. This work shows that dairy streams represent a potential source of complex milk oligosaccharides for commercial development of unique dairy ingredients in functional foods that reproduce the benefits of human milk.

Antiadhesive properties of arabinogalactan protein from ribes nigrum seeds against bacterial adhesion of Helicobacter pylori

Fruit extracts from black currants (Ribes nigrum L.) are traditionally used for treatment of gastritis based on seed polysaccharides that inhibit the adhesion of Helicobacter pylori to stomach cells. For detailed investigations an arabinogalactan protein (F2) was isolated from seeds and characterized concerning molecular weight, carbohydrate, amino acid composition, linkage, configuration and reaction with β-glucosyl Yariv. Functional testing of F2 was performed by semiquantitative in situ adhesion assay on sections of human gastric mucosa and by quantitative in vitro adhesion assay with FITC-labled H. pylori strain J99 and human stomach AGS cells. Bacterial adhesins affected were identified by overlay assay with immobilized ligands. ¹²⁵I-radiolabeled F2 served for binding studies to H. pylori and interaction experiments with BabA and SabA. F2 had no cytotoxic effects against H. pylori and AGS cells; but inhibited bacterial binding to human gastric cells. F2 inhibited the binding of BabA and fibronectin-binding adhesin to its specific ligands. Radiolabeled F2 bound non-specifically to different strains of H. pylori; and to BabA deficient mutant. F2 did not lead to subsequent feedback regulation or increased expression of adhesins or virulence factors. From these data the non-specific interactions between F2 and the H. pylori lead to moderate antiadhesive effects.

Saccharomyces boulardii expresses neuraminidase activity selective for α2,3-linked sialic acid that decreases Helicobacter pylori adhesion to host cells

Helicobacter pylori is a major causative agent of gastritis and peptic ulcer disease and is an established risk factor for gastric malignancy. Antibiotic combination therapy can eradicate H. pylori. As these same regimens can evoke adverse effects and resistance, new alternative therapies or adjunctive treatments are needed. A probiotic approach may provide a novel strategy for H. pylori treatment. In the current study, two probiotic bacteria, Lactobacillus acidophilus and Lactobacillus reuteri, and a probiotic yeast, Saccharomyces boulardii, were evaluated for their ability to influence H. pylori viability, adherence to gastric and duodenal cells, as well as the effect of S. boulardii on cell surface expression of sialic acid. Our results indicate that S. boulardii contains neuraminidase activity selective for α(2-3)-linked sialic acid. This neuraminidase activity removes surface α(2-3)-linked sialic acid, the ligand for the sialic acid-binding H. pylori adhesin, which in turn, inhibits H. pylori adherence to duodenal epithelial cells.

Targeting the bacteria-host interface: strategies in anti-adhesion therapy

Bacterial infections are a major cause of morbidity and mortality worldwide and are increasingly problematic to treat due to the rise in antibiotic-resistant strains. It becomes more and more challenging to develop new antimicrobials that are able to withstand the ever-increasing repertoire of bacterial resistance mechanisms. This necessitates the development of alternative approaches to prevent and treat bacterial infections. One of the first steps during bacterial infection is adhesion of the pathogen to host cells. A pathogen’s ability to colonize and invade host tissues strictly depends on this process. Thus, interference with adhesion (anti-adhesion therapy) is an efficient way to prevent or treat bacterial infections. As a basis to present different strategies to interfere with pathogen adhesion, this review briefly introduces general concepts of bacterial attachment to host cells. We further discuss advantages and disadvantages of anti-adhesion treatments and issues that are in need of improvement so as to make anti-adhesion compounds a more broadly applicable alternative to conventional antimicrobials.

Antiadhesive properties of Abelmoschus esculentus (Okra) immature fruit extract against Helicobacter pylori adhesion

BACKGROUND

Traditional Asian and African medicine use immature okra fruits (Abelmoschus esculentus) as mucilaginous food to combat gastritis. Its effectiveness is due to polysaccharides that inhibit the adhesion of Helicobacter pylori to stomach tissue. The present study investigates the antiadhesive effect in mechanistic detail.

METHODOLOGY

A standardized aqueous fresh extract (Okra FE) from immature okra fruits was used for a quantitative in vitro adhesion assay with FITC-labled H. pylori J99, 2 clinical isolates, AGS cells, and fluorescence-activated cell sorting. Bacterial adhesins affected by FE were pinpointed using a dot-blot overlay assay with immobilized Lewis(b), sialyl-Lewis(a), H-1, laminin, and fibronectin. (125)I-radiolabeled Okra FE polymer served for binding studies to different H. pylori strains and interaction experiments with BabA and SabA. Iron nanoparticles with different coatings were used to investigate the influence of the charge-dependence of an interaction on the H. pylori surface.

PRINCIPAL FINDINGS

Okra FE dose-dependently (0.2 to 2 mg/mL) inhibited H. pylori binding to AGS cells. FE inhibited the adhesive binding of membrane proteins BabA, SabA, and HpA to its specific ligands. Radiolabeled compounds from FE bound non-specifically to different strains of H. pylori, as well as to BabA/SabA deficient mutants, indicating an interaction with a still-unknown membrane structure in the vicinity of the adhesins. The binding depended on the charge of the inhibitors. Okra FE did not lead to subsequent feedback regulation or increased expression of adhesins or virulence factors.

CONCLUSION

Non-specific interactions between high molecular compounds from okra fruits and the H. pylori surface lead to strong antiadhesive effects.

Utilization of major fucosylated and sialylated human milk oligosaccharides by isolated human gut microbes

Human milk oligosaccharides (HMOS) are not digested in the proximal intestine. In distal intestine, HMOS collectively modify the microbiota, but the response of individual bacteria to individual components of the HMOS is not well defined. Here, each of 25 major isolates of the human intestinal microbiota was fed individual major fucosylated and sialylated HMOS in anaerobic culture. This allowed for an assessment of the influence of specific HMOS on the growth and metabolic products of individual microbiota bacteria. Most Bifidobacteria spp. and Bacteroides spp. grew, induced α-L-fucosidase activity, and produced abundant lactate or short-chain fatty acids (SCFAs) when fed 2'-fucosyllactose (2'-FL), 3-FL, and lactodifucotetraose (LDFT). Lactobacillus delbrueckii ATCC7830, Enterococcus faecalis ATCC19433, and Streptococcus thermophilus ATCC19258 exhibited slight growth, pH reduction, and lactate production when supplemented with 2'-FL or 3-FL, but not LDFT. Supplementation with 3'-sialyllactose (3'-SL) and 6'-SL promoted moderate growth of Bifidobacterium longum JCM7007, 7009, 7010, 7011, 1272, 11347, ATCC15708, Bacteroides vulgatus ATCC8482, and B. thetaiotaomicron ATCC29148; accordingly, these bacteria exhibited greater neuraminidase activity and produced copious lactate, SCFA, or both. Lactobacillus delbrueckii ATCC7830 also consumed 6'-SL. In contrast, Clostridium spp., L. rhamnosus ATCC53103, E. faecalis ATCC29200, Staphylococcus spp., Enterobacter spp., and Escherichia coli K12 did not consume milk oligosaccharides nor produce appreciable acidic fermentation products. Specific Bifidobacteria and Bacteroides differentially digest specific individual HMOS, with the major fucosylated milk oligosaccharides most strongly stimulating key species of mutualist symbionts. This suggests strategies for treating dysbiosis of the microbiota and associated inflammatory disorders.

Functional glycans and glycoconjugates in human milk

Human milk contains complex carbohydrates that are important dietary factors with multiple functions during early life. Several aspects of these glycostructures are human specific; some aspects vary between lactating women, and some change during the course of lactation. This review outlines how variability of complex glycostructures present in human milk is linked to changing infants' needs.

Comparison of milk oligosaccharides between goats with and without the genetic ability to synthesize αs1-casein

Milk oligosaccharides (OS)-free complex carbohydrates-confer unique health benefits to the nursing neonate. Though human digestive enzymes cannot degrade these sugars, they provide nourishment to specific commensal microbes and act as decoys to prevent the adhesion of pathogenic micro-organisms to gastrointestinal cells. At present, the limited quantities of human milk oligosaccharides (HMO) impede research on these molecules and their potential applications in functional food formulations. Considerable progress has been made in the study of OS structures; however, the synthetic pathways leading to their synthesis in the mammary gland are poorly understood. Recent studies show that complex OS with fucose and N-acetyl neuraminic acid (key structural elements of HMO bioactivity) exist in goat milk. Polymorphisms in the CSN1S1 locus, which is responsible for synthesis of α_s1-casein, affect lipid and casein micelle structure in goat milk. The present study sought to determine whether CSN1S1 polymorphisms also influence goat milk oligosaccharide (GMO) production and secretion. The GMO compositions of thirty-two goat milk samples, half of which were from genotype A/A (α_s1-casein producers) and half from genotype O/O (α_s1-casein non-producers), were determined with nanoflow liquid chromatography high-accuracy mass spectrometry. This study represents the most exhaustive characterization of GMO to date. A systematic and comprehensive GMO library was created, consolidating information available in the literature with the new findings. Nearly 30 GMO, 11 of which were novel, were confirmed via tandem mass spectrometric analyses. Six fucosylated OS were identified; 4 of these matched HMO compositions and three were identified for the first time in goat milk. Importantly, multivariate statistical analysis demonstrated that the OS profiles of the A/A and O/O genotype milks could be discriminated by the fucosylated OS. Quantitative analysis revealed that the goat milk samples contained 1.17 g/L of OS; however, their concentration in milks from A/A and O/O genotypes was not different. This study provides evidence of a genetic influence on specific OS biosynthesis but not total OS production. The presence of fucosylated GMO suggests that goat milk represents a potential source of bioactive milk OS suitable as a functional food ingredient.

Catechins and Sialic Acid Attenuate Helicobacter pylori-Triggered Epithelial Caspase-1 Activity and Eradicate Helicobacter pylori Infection

The inflammasome/caspase-1 signaling pathway in immune cells plays a critical role in bacterial pathogenesis; however, the regulation of this pathway in the gastric epithelium during Helicobacter pylori infection is yet to be elucidated. Here, we investigated the effect of catechins (CAs), sialic acid (SA), or combination of CA and SA (CASA) on H. pylori-induced caspase-1-mediated epithelial damage, as well as H. pylori colonization in vitro (AGS cells) and in vivo (BALB/c mice). Our results indicate that the activity of caspase-1 and the expression of its downstream substrate IL-1β were upregulated in H. pylori-infected AGS cells. In addition, we observed increased oxidative stress, NADPH oxidase gp91phox, CD68, caspase-1/IL-1β, and apoptosis, but decreased autophagy, in the gastric mucosa of H. pylori-infected mice. We have further demonstrated that treatment with CASA led to synergistic anti-H. pylori activity and was more effective than treatment with CA or SA alone. In particular, treatment with CASA for 10 days eradicated H. pylori infection in up to 95% of H. pylori-infected mice. Taken together, we suggest that the pathogenesis of H. pylori involves a gastric epithelial inflammasome/caspase-1 signaling pathway, and our results show that CASA was able to attenuate this pathway and effectively eradicate H. pylori infection.

Microbial biofilms and gastrointestinal diseases

The majority of bacteria live not planktonically, but as residents of sessile biofilm communities. Such populations have been defined as 'matrix-enclosed microbial accretions, which adhere to both biological and nonbiological surfaces'. Bacterial formation of biofilm is implicated in many chronic disease states. Growth in this mode promotes survival by increasing community recalcitrance to clearance by host immune effectors and therapeutic antimicrobials. The human gastrointestinal (GI) tract encompasses a plethora of nutritional and physicochemical environments, many of which are ideal for biofilm formation and survival. However, little is known of the nature, function, and clinical relevance of these communities. This review summarizes current knowledge of the composition and association with health and disease of biofilm communities in the GI tract.

Gangliosides and sialic acid effects upon newborn pathogenic bacteria adhesion: an in vitro study

The effect of the main gangliosides (GM(1), GM(3), GD(3)) and free sialic acid (Neu5Ac) upon the adhesion of pathogenic bacteria implicated in infant diarrhoea is assessed in vitro using the Caco-2 cell line. Concentrations of the bioactive compounds found in the bioaccessible (soluble) fraction of infant formula and human milk are employed. Bacterial adhesion behaviour included enterotoxigenic Escherichia coli (ETEC), enteropathogenic E.coli (EPEC), Listeria monocytogenes, Salmonella entericaserovartyphi, Shigella sonnei, Campylobacter jejuni and Helicobacter pylori. Three different approaches were assayed: pre-incubation of bacteria and compounds before addition to cells (competition); pre-incubation of the cells with compounds (exclusion); and pre-incubation of cells with bacteria (displacement). Furthermore, the spatial localization of the most abundant gangliosides, GM(3) and GD(3), in Caco-2 cells has been determined using confocal microscopy. Results show that GM(3), GD(3), GM(1) and Neu5Ac at the assayed concentrations are able to interfere with the adhesion of several pathogenic bacteria involved in neonatal diseases-the greatest effect corresponding to Neu5Ac, followed by GD(3), GM(1) and GM(3). Gangliosides GM(3) and GD(3) are located in the apical and basolateral membranes of the Caco-2 cells.

Natural variability in bovine milk oligosaccharides from Danish Jersey and Holstein-Friesian breeds

Free oligosaccharides are key components of human milk and play multiple roles in the health of the neonate, by stimulating growth of selected beneficial bacteria in the gut, participating in development of the brain, and exerting antipathogenic activity. However, the concentration of oligosaccharides is low in mature bovine milk, normally used for infant formula, compared with both human colostrum and mature human milk. Characterization of bovine milk oligosaccharides in different breeds is crucial for the identification of viable sources for oligosaccharide purification. An improved source of oligosaccharides can lead to infant formula with improved oligosaccharide functionality. In the present study we have analyzed milk oligosaccharides by high-performance liquid chromatography chip quadrupole time-of-flight mass spectrometry and performed a detailed data analysis using both univariate and multivariate methods. Both statistical tools revealed several differences in oligosaccharide profiles between milk samples from the two Danish breeds, Jersey and Holstein-Friesians. Jersey milk contained higher relative amounts of both sialylated and the more complex neutral fucosylated oligosaccharides, while the Holstein-Friesian milk had higher abundance of smaller and simpler neutral oligosaccharides. The statistical analyses revealed that Jersey milk contains levels of fucosylated oligosaccharides significantly higher than that of Holstein-Friesian milk. Jersey milk also possesses oligosaccharides with a higher degree of complexity and functional residues (fucose and sialic acid), suggesting it may therefore offer advantages in term of a wider array of bioactivities.

The role of milk sialyllactose in intestinal bacterial colonization

Milk oligosaccharides influence the composition of intestinal microbiota and thereby mucosal inflammation. Some of the major milk oligosaccharides are α2,3-sialyllactose (3SL) and α2,6-sialyllactose, which are mainly produced by the sialyltransferases ST3GAL4 and ST6GAL1, respectively. Recently, we showed that mice fed milk deficient in 3SL were more resistant to dextran sulfate sodium-induced colitis. By contrast, the exposure to milk containing or deficient in 3SL had no impact on the development of mucosal leukocyte populations. Milk 3SL mainly affected the colonization of the intestine by clostridial cluster IV bacteria.

Human milk oligosaccharides: every baby needs a sugar mama

Human milk oligosaccharides (HMOs) are a family of structurally diverse unconjugated glycans that are highly abundant in and unique to human milk. Originally, HMOs were discovered as a prebiotic "bifidus factor" that serves as a metabolic substrate for desired bacteria and shapes an intestinal microbiota composition with health benefits for the breast-fed neonate. Today, HMOs are known to be more than just "food for bugs". An accumulating body of evidence suggests that HMOs are antiadhesive antimicrobials that serve as soluble decoy receptors, prevent pathogen attachment to infant mucosal surfaces and lower the risk for viral, bacterial and protozoan parasite infections. In addition, HMOs may modulate epithelial and immune cell responses, reduce excessive mucosal leukocyte infiltration and activation, lower the risk for necrotizing enterocolitis and provide the infant with sialic acid as a potentially essential nutrient for brain development and cognition. Most data, however, stem from in vitro, ex vivo or animal studies and occasionally from association studies in mother-infant cohorts. Powered, randomized and controlled intervention studies will be needed to confirm relevance for human neonates. The first part of this review introduces the pioneers in HMO research, outlines HMO structural diversity and describes what is known about HMO biosynthesis in the mother's mammary gland and their metabolism in the breast-fed infant. The second part highlights the postulated beneficial effects of HMO for the breast-fed neonate, compares HMOs with oligosaccharides in the milk of other mammals and in infant formula and summarizes the current roadblocks and future opportunities for HMO research.

Receptor mimicry as novel therapeutic treatment for biothreat agents

The specter of intentional release of pathogenic microbes and their toxins is a real threat. This article reviews the literature on adhesins of biothreat agents, their interactions with oligosaccharides and the potential for anti-adhesion compounds as an alternative to conventional therapeutics. The minimal binding structure of ricin has been well characterised and offers the best candidate for successful anti-adhesion therapy based on the Galβ1-4GlcNAc structure. The botulinum toxin serotypes A-F bind to a low number of gangliosides (GT1b, GQ1b, GD1a and GD1b) hence it should be possible to determine the minimal structure for binding. The minimal disaccharide sequence of GalNAcβ1-4Gal found in the gangliosides asialo-GM1 and asialo-GM2 is required for adhesion for many respiratory pathogens. Although a number of adhesins have been identified in bacterial biothreat agents such as Yersinia pestis, Bacillus anthracis, Francisella tularensis, Brucella species and Burkholderia pseudomallei, specific information regarding their in vivo expression during pneumonic infection is lacking. Limited oligosaccharide inhibition studies indicate the potential of GalNAcβ1-4Gal, GalNAcβ-3Gal and the hydrophobic compound, para-nitrophenol as starting points for the rational design of generic anti-adhesion compounds. A cocktail of multivalent oligosaccharides based on the minimal binding structures of identified adhesins would offer the best candidates for anti-adhesion therapy.

Antiadhesion as a functional concept for prevention of pathogens: N-Phenylpropenoyl-L-amino acid amides as inhibitors of the Helicobacter pylori BabA outer membrane protein

SCOPE

Besides flavan-3-ols, a family of N-phenylpropenoyl-L-amino acids (NPAs) has been recently identified as polyphenol/amino acid conjugates in the seeds of Theobroma cacao as well as in a variety of herbal drugs. NPAs were shown to exhibit antiadhesive activities against Helicobacter pylori.

METHODS AND RESULTS

For structure/activity relationship 24 homologous NPAs (2 mM) were investigated in a flow cytometric assay on potential antiadhesive effects against H. pylori adhesion to human gastric AGS cells. Dihydroxylation of the aromatic molecule part was shown to be necessary for activity; methoxylation decreases activity. High polarity of the amino acid is a prerequisite for activity. The model compound N-(E)-caffeoyl-L-glutamic acid 11 exerted a concentration-dependent inhibition of bacterial adhesion with saturation at 30% inhibition level. The antiadhesive effect was additionally confirmed by in situ adhesion assay on intact human gastric tissue. NPAs exhibited no cytotoxicity. Using immobilized ligands interaction 11 with bacterial adhesin BabA was demonstrated. RT-PCR indicated that the inhibition of BabA is not correlated with subsequent feed back regulations to express more adhesins or virulence factors (vacA, cagA, cagL, cagα, fucT, ureI, ureA, OMPs). The interaction of bacterial adhesins with the respective ligands does not automatically lead to a subsequent signal transduction towards induction of virulence processes.

CONCLUSION

The nutritional use of NPA-containing food may justify a positive antiadhesive effect against the recurrence of H. pylori infections.

An infant-associated bacterial commensal utilizes breast milk sialyloligosaccharides

Lactating mothers secrete milk sialyloligosaccharides (MSOs) that function as anti-adhesives once provided to the neonate. Particular infant-associated commensals, such as Bifidobacterium longum subsp. infantis, consume neutral milk oligosaccharides, although their ability to utilize acidic oligosaccharides has not been assessed. Temporal glycoprofiling of acidic HMO consumed during fermentation demonstrated a single composition, with several isomers, corresponding to sialylated lacto-N-tetraose. To utilize MSO, B. longum subsp. infantis deploys a sialidase that cleaves α2-6 and α2-3 linkages. NanH2, encoded within the HMO catabolic cluster is up-regulated during HMO fermentation and is active on sialylated lacto-N-tetraose. These results demonstrate that commensal microorganisms do utilize MSO, a substrate that may be enriched in the distal gastrointestinal tract.

Peptides from Pisum sativum L. enzymatic protein digest with anti-adhesive activity against Helicobacter pylori: structure-activity and inhibitory activity against BabA, SabA, HpaA and a fibronectin-binding adhesin

SCOPE

Identification of anti-adhesive peptides against Helicobacter pylori obtained by enzymatic hydrolysis of seed proteins from Pisum sativum L. (Fabaceae).

METHODS AND RESULTS

Bioassay-guided fractionation of protein tryptic digest by ultrafiltration, size exclusion chromatography (SEC) and reversed phase chromatography (RPC) were used. Identification of bioactive peptides was achieved by MALDI-TOF-MS. Adhesion of H. pylori was monitored by two different assays, using a quantitative in vitro assay on human AGS cells with evaluation of bacterial binding by flow cytometry, beside a semi-quantitative in situ adhesion assay using FITC-labelled H. pylori on human stomach tissue sections. From two highly active fractions (F3, F3.3) two anti-adhesive peptides (S3, S5) were identified. Neither F3 nor S3 or S5 had any cytotoxic effect against H. pylori. By hemagglutination assay and semiquantitative dot blot overlay assay with immobilized ligands it was shown that F3 interacts specifically with H. pylori adhesins BabA, SabA, HpaA and a fibronectin-binding adhesin, while S3 and S5 inhibit only BabA. It was demonstrated that BabA, usually interacting with carbohydrate motifs such as fucosylated blood group antigens, interacts with the peptide moieties.

CONCLUSION

Bioactive peptides from pea protein could be applied as functional ingredients for protecting infants and children against infections such as H. pylori.

Neutral and acidic oligosaccharides in Holstein-Friesian colostrum during the first 3 days of lactation measured by high performance liquid chromatography on a microfluidic chip and time-of-flight mass spectrometry

Oligosaccharides (OS) from bovine milk are a class of bioactive molecules that are receiving increasing commercial attention for their potential health benefits. In the present work we measured, comprehensively and systematically, free milk OS in the colostrum of 7 Holstein-Friesian cows during the first 3 d of lactation in 12-h intervals by HPLC-chip/time-of-flight mass spectrometry to determine the biological variation of free milk OS in early lactation. The high sensitivity and resolution of the analytical technique made it possible to monitor all OS species, thus providing a comprehensive and quantitative analysis of OS variations during colostrum production. This study confirmed that although sialyllactose is the major OS in bovine colostrum, several neutral OS species are present in significant abundance even at the third day of lactation. Furthermore, variation in terms of OS species and relative abundances of OS between cows suggest individual animal variation. These variations are likely due to genetic factors because environmental factors such as nutrition, lactation number, and accommodation were the same for all cows. This investigation revealed that colostrum milk from Holstein-Friesian cows is a rich source of neutral and acidic OS for the food and pharmaceutical industries.

Rational design of a GH1 beta-glycosidase to prevent self-condensation during the transglycosylation reaction

Mutant N282T of a thermostable beta-glycosidase from GH1 family (TtbetaGly) presenting a high transglycosidase activity was previously obtained by directed evolution. However, it displays a self-condensation activity with the donor 2-nitrophenyl-beta-d-galactopyranoside (oNPGal) which competes with the condensation reaction and entails undesirable effects. In order to prevent this reaction, we rationally modified this enzyme at the [+1]/[+2] subsites so that oNPGal would bind less tightly. Molecular modeling (MM) suggested the mutation A221W, which decreased the affinity of the donor at these sites and moved it away from the bound galactose at the -1 subsite. A single (A221W) and a double mutant (A221W/N282T) were constructed, and they gave rise to a drastic decrease in self-condensation. The A221W mutant had no transglycosylation activity whereas the A221W/N282T mutant still displayed a condensation activity, comparable to that of the N282T mutant for the transfer on pNPGlcNAc. MM revealed that the double mutant A221W/N282T could induce the synthesis of a glycosidic bond between a donor and an acceptor displaying an equatorial 4-position. Moreover, it is suggested that mutation N282T could change the orientation of residue N219, leading to a stabilization of the acceptor with a new hydrogen bond. This finding opens the way to further improvements of evolved transglycosidases.

Direct binding of gangliosides to Helicobacter pylori vacuolating cytotoxin (VacA) neutralizes its toxin activity

Gangliosides are target receptors for bacterial entry, yet those present in human milk exhibit a protective role against bacterial infection. Here, we show that treatment with ganglioside mixture at a concentration of 100 microg/mL resulted in significant inhibition of the vacuole formation activity of Helicobacter pylori vacuolating cytotoxin (VacA) in gastric epithelial cancer AZ-521 cells. All gangliosides (GM1, GM2, GM3, GD1a, GD1b, GD3 and GT1b) examined showed good neutralizing capacity against VacA. A pull-down assay was performed using lyso-GM1 coupled to Sepharose as the tagged polysaccharide polymer to capture VacA from H. pylori culture supernatant. GM1-VacA complexes were successfully precipitated, suggesting that GM1 binds directly to VacA. The hydrodynamic binding of lyso-GM1 and VacA measured by fluorescence correlation spectroscopy had a K(d) value of 190 nM. VacA also bound to lyso-GM1 at pH 2 corresponding to the physiological pH of human stomach. Collectively, these results showed that direct binding of H. pylori VacA to free gangliosides neutralizes the toxin activity of VacA. These findings offer an alternative insight into the role of gangliosides in VacA toxicity and the pathogenesis of H. pylori.

In-vitro interaction of l-dopa with bacterial adhesins of Helicobacter pylori: an explanation for clinicial differences in bioavailability?

Objectives

Recent investigations on the pharmacokinetics of levodopa (l-dopa) indicated that the presence of Helicobacter pylori in patients with Parkinson's disease, orally treated with l-dopa, influences the absorption of this compound, which consequently leads to decreased plasma levels. Therefore this work aims to study a potential in-vitro interaction of l-dopa with H. pylori and its surface adhesins.

Methods

Solutions containing l-dopa of different concentrations were incubated with H. pylori at different bacterial densities and time intervals. Free l-dopa was quantified from the incubation supernatants by HPLC. A flow cytometric assay with fluorescence labelled H. pylori was used to investigate the influence of l-dopa on the bacterial adhesion of H. pylori: FITC-labelled bacteria were pre-incubated with l-dopa, followed by incubation with gastric epithelial cells (AGS cells) and FACS quantification of adhering bacteria.

Key findings

Evaluation of time- and concentration-dependent incubation experiments indicated a significant decrease in l-dopa concentrations when coming into contact with H. pylori. The reduction in l-dopa concentrations was determined as 47 to 12%, referred to the initial starting concentration, with time-dependency and dependency of the H. pylori density. FITC-labelled H. pylori, pre-incubated with differing l-dopa concentrations, were shown to have a significantly reduced bacterial adhesion to AGS cells, with a maximum reduction of 22 ± 9%. These results demonstrate a direct interaction of l-dopa with the outer membrane proteins of H. pylori responsible for the adhesion to gastric epithelial cells. By this interaction the unbound l-dopa concentration in bacterial suspension was strongly reduced.

Conclusions

This study suggests a potential in-vitro interaction of l-dopa with H. pylori adhesins, confirming the clinical changes found in pharmacokinetics of l-dopa therapy by H. pylori-positive patients with Parkinson's disease.