Detailed Analysis of Prebiotic Fructo- and Galacto-Oligosaccharides in the Human Small Intestine.

Galacto-oligosaccharides (GOS) and fructo-oligosaccharides (FOS) are food ingredients that improve human health, but their degradation throughout the human small intestine is not well understood. We studied the breakdown kinetics of FOS and GOS in the intestines of seven healthy Dutch adults. Subjects were equipped with a catheter in the distal ileum or proximal colon and consumed 5 g of chicory-derived FOS (degree of polymerization (DP) DP2-10), and 5 g of GOS (DP2-6). Postprandially, intestinal content was frequently collected until 350 min and analyzed for mono-, di-, and oligosaccharides. FOS and GOS had recoveries of 96 ± 25% and 76 ± 28%, respectively. FOS DP ≥ 2 and GOS DP ≥ 3 abundances in the distal small intestine or proximal colon matched the consumed doses, while GOS dimers (DP2) had lower recoveries, namely 22.8 ± 11.1% for ß-D-gal-(1↔1)-α-D-glc+ß-D-gal-(1↔1)-ß-D-glc, 19.3 ± 19.1% for ß-D-gal-(1 → 2)-D-glc+ß-D-gal-(1 → 3)-D-glc, 43.7 ± 24.6% for ß-D-gal-(1 → 6)-D-gal, and 68.0 ± 38.5% for ß-D-gal-(1 → 4)-D-gal. Lactose was still present in the distal small intestine of all of the participants. To conclude, FOS DP ≥ 2 and GOS DP ≥ 3 were not degraded in the small intestine of healthy adults, while most prebiotic GOS DP2 was hydrolyzed in a structure-dependent manner. We provide evidence on the resistances of GOS with specific ß-linkages in the human intestine, supporting the development of GOS prebiotics that resist small intestine digestion.

Combining galacto-oligosaccharides and 2'-fucosyllactose alters their fermentation kinetics by infant fecal microbiota and influences AhR-receptor dependent cytokine responses in immature dendritic cells.

Galacto-oligosaccharides (GOS) and 2'-fucosyllactose (2'-FL) are non-digestible carbohydrates (NDCs) that are often added to infant formula to replace the functionalities of human milk oligosaccharides (HMOs). It is not known if combining GOS and 2'-FL will affect their fermentation kinetics and subsequent immune-modulatory effects such as AhR-receptor stimulation. Here, we used an in vitro set-up for the fermentation of 2'-FL and GOS, either individually or combined, by fecal microbiota of 8-week-old infants. We found that GOS was fermented two times faster by the infant fecal microbiota when combined with 2'-FL, while the combination of GOS and 2'-FL did not result in a complete degradation of 2'-FL. Fermentation of both GOS and 2'-FL increased the relative abundance of Bifidobacterium, which coincided with the production of acetate and lactate. Digesta of the fermentations influenced dendritic cell cytokine secretion differently under normal conditions and in the presence of the AhR-receptor blocker CH223191. We show that, combining GOS and 2'-FL accelerates GOS fermentation by the infant fecal microbiota of 8-week-old infants. In addition, we show that the fermentation digesta of GOS and 2'-FL, either fermented individually or combined, can attenuate DC cytokine responses in a similar and in an AhR-receptor dependent way.

ß(2→1) chicory and ß(2→1)-ß(2→6) agave fructans protect the human intestinal barrier function in vitro in a stressor-dependent fashion.

Dietary fibers such as fructans can protect the intestinal epithelial barrier integrity, but the mechanisms underlying this protection are not completely understood. We aimed to study the protective effect of ß(2→1)-ß(2→6) branched graminan-type fructans (GTFs) on gut epithelial barrier function that was disrupted by three different agents which impact the barrier function via different cellular mechanisms. The effects of GTFs were compared with those of linear ß(2→1) inulin-type fructans (ITFs). T84 intestinal epithelial monolayers were incubated with GTFs and ITFs. Afterwards, the monolayers were challenged with the barrier disruptors calcium ionophore A23187, 12-myristate 13-acetate (PMA) and deoxynivalenol (DON). Transepithelial resistance was measured with an electric cell-substrate impedance sensing system. All fructans studied prevented the barrier disruption induced by A23187. ITF II protected from the disruptive effects of PMA. However, none of the studied fructans influenced the disruption induced by DON. As a measure of disruption-induced inflammation, interleukin-8 (IL-8) production by the intestinal epithelium was determined by ELISA. The production of IL-8 induced by A23187 was decreased by all fructans, whereas IL-8 production induced by DON decreased only upon pre-treatment with ITF II. None of the studied fructans prevented PMA induced IL-8 production. GTFs just like ITFs can influence the barrier function and inflammatory processes in gut epithelial cells in a structure-dependent fashion. These distinct protective effects are dependent on the different signaling pathways that lead to gut barrier disruption.

Chicory inulin enhances fermentation of 2'-fucosyllactose by infant fecal microbiota and differentially influences immature dendritic cell and T-cell cytokine responses under normal and Th2-polarizing conditions.

Scope: Non-digestible carbohydrates (NDCs) such as native chicory inulin and 2'-fucosyllactose (2'-FL) are added to infant formula to mimic some of the human milk oligosaccharide (HMO) functions. It is unknown whether combining inulin and 2'-FL influences their fermentation kinetics and whether the immune-modulatory effects of these NDCs are different under normal and inflammatory-prone Th2-polarizing conditions. Methods and results: We investigated the in vitro fermentation of 2'-FL and native chicory inulin, fermented individually and combined, using fecal inocula of 8-week-old infants. Native inulin was fermented in a size-dependent fashion and expedited the fermentation of 2'-FL. Fermentation of both native inulin and 2'FL increased the relative abundance of Bifidobacterium, which coincided with the production of acetate and lactate. The fermentation digesta of all fermentations differentially influenced both dendritic cell and T-cell cytokine responses under normal culture conditions or in presence of the Th2-polarizing cytokines IL-33 and TSLP, with the most pronounced effect for IL-1ß in the presence of TSLP. Conclusions: Our findings show that native inulin can expedite the fermentation of 2'-FL by infant fecal microbiota and that these NDC fermentation digesta have different effects under normal and Th2-polarizing conditions, indicating that infants with different immune backgrounds might benefit from tailored NDC formulations.

Structure-Specific Fermentation of Galacto-Oligosaccharides, Isomalto-Oligosaccharides and Isomalto/Malto-Polysaccharides by Infant Fecal Microbiota and Impact on Dendritic Cell Cytokine Responses.

SCOPE: Next to galacto-oligosaccharides (GOS), starch-derived isomalto-oligosaccharide preparation (IMO) and isomalto/malto-polysaccharides (IMMP) could potentially be used as prebiotics in infant formulas. However, it remains largely unknown how the specific molecular structures of these non-digestible carbohydrates (NDCs) impact fermentability and immune responses in infants. METHODS AND RESULTS: In vitro fermentation of GOS, IMO and IMMP using infant fecal inoculum of 2- and 8-week-old infants shows that only GOS and IMO are fermented by infant fecal microbiota. The degradation of GOS and IMO coincides with an increase in Bifidobacterium and production of acetate and lactate, which is more pronounced with GOS. Individual isomers with an (1↔1)-linkage or di-substituted reducing terminal glucose residue are more resistant to fermentation. GOS, IMO, and IMMP fermentation digesta attenuates cytokine profiles in immature dendritic cells (DCs), but the extent is dependent on the infants age and NDC structure. CONCLUSION: The IMO preparation, containing reducing and non-reducing isomers, shows similar fermentation patterns as GOS in fecal microbiota of 2-week-old infants. Knowledge obtained on the substrate specificities of infant fecal microbiota and the subsequent regulatory effects of GOS, IMO and IMMP on DC responses might contribute to the design of tailored NDC mixtures for infants of different age groups.

In vitro metabolic capacity of carbohydrate degradation by intestinal microbiota of adults and pre-frail elderly.

Globally increased life expectancy strongly triggered interest to delay the onset of frailty, which has been associated with alterations in compositional and functional characteristics of intestinal microbiota. In the current study, we used an in vitro batch incubation model to compare the metabolic capacity of the faecal microbiota of adults (n = 6) versus pre-frail elderly (n = 6) to degrade various glycosidic carbohydrates, including galacto-oligosaccharides, 2'-fucosyllactose, chicory fructo-oligosaccharides and inulin, and isomalto/malto-polysaccharides. The in vitro metabolic capacity was also compared with an in vivo GOS intervention study based on the same subjects. Analysis of 16S rRNA gene sequences and metabolites revealed distinct portions of variation in overall microbiota and metabolite composition during incubation being explained by individuality of the subjects and carbon source. In addition, the age group of the subjects also had significant impact on microbiota variation, carbohydrate degradation and metabolite production. This was accompanied by elevated increase in the relative abundance of Bifidobacterium in the microbiota of adults compared to that of pre-frail elderly and significantly decreased effectiveness to degrade galacto-oligosaccharides by the latter group. Altogether, the carbohydrate degradation in elderly was different compared to adults, with some carbohydrates showing decreased degradation rates. Longer interventions periods may be required to enhance bifidobacterial abundance in the microbiota of pre-frail elderly and thereby to obtain associated prebiotic health benefits.

Effects of Different Human Milk Oligosaccharides on Growth of Bifidobacteria in Monoculture and Co-culture With Faecalibacterium prausnitzii.

Human milk oligosaccharides (hMOs) are important bioactive components in mother's milk contributing to infant health by supporting colonization and growth of gut microbes. In particular, Bifidobacterium genus is considered to be supported by hMOs. Approximately 200 different hMOs have been discovered and characterized, but only a few abundant hMOs can be produced in sufficient amounts to be applied in infant formula. These hMOs are usually supplied in infant formula as single molecule, and it is unknown which and how individual hMOs support growth of individual gut bacteria. To investigate how individual hMOs influence growth of several relevant intestinal bacteria species, we studied the effects of three hMOs (2'-fucosyllactose, 3-fucosyllactose, and 6'-sialyllactose) and an hMO acid hydrolysate (lacto-N-triose) on three Bifidobacteria and one Faecalibacterium and introduced a co-culture system of two bacterial strains to study possible cross-feeding in presence and absence of hMOs. We observed that in monoculture, Bifidobacterium longum subsp. infantis could grow well on all hMOs but in a structure-dependent way. Faecalibacterium prausnitzii reached a lower cell density on the hMOs in stationary phase compared to glucose, while B. longum subsp. longum and Bifidobacterium adolescentis were not able to grow on the tested hMOs. In a co-culture of B. longum subsp. infantis with F. prausnitzii, different effects were observed with the different hMOs; 6'-sialyllactose, rather than 2'-fucosyllactose, 3-fucosyllactose, and lacto-N-triose, was able to promote the growth of B. longum subsp. infantis. Our observations demonstrate that effects of hMOs on the tested gut microbiota are hMO-specific and provide new means to support growth of these specific beneficial microorganisms in the intestine.

Fermentation Kinetics of Selected Dietary Fibers by Human Small Intestinal Microbiota Depend on the Type of Fiber and Subject.

SCOPE: An underexplored topic is the investigation of health effects of dietary fibers via modulation of human small intestine (SI) microbiota. A few previous studies hint at fermentation of some dietary fibers in the distal SI of humans and pigs. Here the potential of human SI microbiota to degrade dietary fibers and produce metabolites in vitro is investigated. METHODS AND RESULTS: Fructans, galacto-oligosaccharides, lemon pectins, and isomalto/malto-polysaccharides are subjected to in vitro batch fermentations inoculated with ileostomy effluent from five subjects. Fiber degradation products, formation of bacterial metabolites, and microbiota composition are determined over time. Galacto- and fructo-oligosaccharides are rapidly utilized by the SI microbiota of all subjects. At 5h of fermentation, 31%-82% of galacto-oligosaccharides and 29%-89% fructo-oligosaccharides (degree of polymerization DP4-8) are utilized. Breakdown of fructo-oligosaccharides/inulin DP ≥ 10, lemon pectin, and iso-malto/maltopolysaccharides only started after 7h incubation. Degradation of different fibers result in production of mainly acetate, and changed microbiota composition over time. CONCLUSION: Human SI microbiota have hydrolytic potential for prebiotic galacto- and fructo-oligosaccharides. In contrast, the higher molecular weight fibers inulin, lemon pectin, and iso-malto/maltopolysaccharides show slow fermentation rate. Fiber degradation kinetics and microbiota responses are subject dependent, therefore personalized nutritional fiber based strategies are required.

Endo-1,3(4)-ß-Glucanase-Treatment of Oat ß-Glucan Enhances Fermentability by Infant Fecal Microbiota, Stimulates Dectin-1 Activation and Attenuates Inflammatory Responses in Immature Dendritic Cells.

Background: Non-digestible carbohydrates are added to infant formula to mimic the effects of human milk oligosaccharide by acting as prebiotics and stimulating the immune system. Although not yet used in infant formulas, ß-glucans are known to have beneficial health effects, and are therefore of potential interest for supplementation. Methods and results: We investigated the in vitro fermentation of native and endo-1,3(4)-ß-glucanase-treated oat ß-glucan using pooled fecal inocula of 2- and 8-week-old infants. While native oat ß-glucan was not utilized, both inocula specifically utilized oat ß-glucan oligomers containing ß(1→4)-linkages formed upon enzyme treatment. The fermentation rate was highest in the fecal microbiota of 2-week-old infants, and correlated with a high lactate production. Fermentation of media supplemented with native and enzyme-treated oat ß-glucans increased the relative abundance of Enterococcus and attenuated pro-inflammatory cytokine production (IL-1ß, IL-6, TNFα) in immature dendritic cells. This attenuating effect was more pronounced after enzyme treatment. This attenuation might result from the enhanced ability of fermented oat ß-glucan to stimulate Dectin-1 receptors. Conclusion: Our findings demonstrate that endo-1,3(4)-ß-glucanase treatment enhances the fermentability of oat ß-glucan and attenuates pro-inflammatory responses. Hence, this study shows that especially enzyme-treated oat ß-glucans have a high potential for supplementation of infant formula.

Touching the High Complexity of Prebiotic Vivinal Galacto-oligosaccharides Using Porous Graphitic Carbon Ultra-High-Performance Liquid Chromatography Coupled to Mass Spectrometry.

Galacto-oligosaccharides (GOS) are used in infant formula to replace the health effects of human milk oligosaccharides, which appear to be dependent upon the structure of the individual oligosaccharides present. However, a comprehensive overview of the structure-specific effects is still limited as a result of the high structural complexity of GOS. In this study, porous graphitic carbon (PGC) was used as the stationary phase during ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS). This approach resulted in the recognition of more than 100 different GOS structures in one single run, including reducing and non-reducing GOS isomers. Using nuclear magnetic resonance-validated structures of GOS trisaccharides, we discovered MS fragmentation rules to distinguish reducing isomers with a mono- and disubstituted terminal glucose by UHPLC-PGC-MS. UHPLC-PGC-MS enabled effective recognition of structural features of individual GOS components in complex GOS preparations and during, e.g., biological conversion reactions. Hence, this study lays the groundwork for future research into structure-specific health effects of GOS.

Fermentation of Chicory Fructo-Oligosaccharides and Native Inulin by Infant Fecal Microbiota Attenuates Pro-Inflammatory Responses in Immature Dendritic Cells in an Infant-Age-Dependent and Fructan-Specific Way.

SCOPE: Inulin-type fructans are commonly applied in infant formula to support development of gut microbiota and immunity. These inulin-type fructans are considered to be fermented by gut microbiota, but it is unknown how fermentation impacts immune modulating capacity and whether the process of fermentation is dependent on the infant's age. METHODS AND RESULTS: The in vitro fermentation of chicory fructo-oligosaccharides (FOS) and native inulin are investigated using pooled fecal inocula of two- and eight-week-old infants. Both inocula primarily utilize the trisaccharides in FOS, while they almost completely utilize native inulin with degree of polymerization (DP) 3-8. Fecal microbiota of eight-week-old infants degrades longer chains of native inulin up to DP 16. This correlates with a higher abundance of Bifidobacterium and higher production of acetate and lactate after 26 h of fermentation. Fermented FOS and native inulin attenuate pro-inflammatory cytokines produced by immature dendritic cells (DCs), but profiles and magnitude of attenuation are stronger with native inulin than with FOS. CONCLUSION: The findings demonstrate that fermentation of FOS and native inulin is dependent on the infant's age and fructan structure. Fermentation enhances attenuating effects of pro-inflammatory responses in DCs, which depend mainly on microbial metabolites formed during fermentation.

Backbone structures in human milk oligosaccharides: trans-glycosylation by metagenomic ß-N-acetylhexosaminidases.

This paper describes the discovery and characterization of two novel ß-N-acetylhexosaminidases HEX1 and HEX2, capable of catalyzing the synthesis of human milk oligosaccharides (HMO) backbone structures with fair yields using chitin oligomers as ß-N-acetylglucosamine (GlcNAc) donor. The enzyme-encoding genes were identified by functional screening of a soil-derived metagenomic library. The ß-N-acetylhexosaminidases were expressed in Escherichia coli with an N-terminal His6-tag and were purified by nickel affinity chromatography. The sequence similarities of the enzymes with their respective closest homologues are 59 % for HEX1 and 51 % for HEX2 on the protein level. Both ß-N-acetylhexosaminidases are classified into glycosyl hydrolase family 20 (GH 20) are able to hydrolyze para-nitrophenyl-ß-N-acetylglucosamine (pNP-GlcNAc) as well as para-nitrophenyl-ß-N-acetylgalactosamine (pNP-GalNAc) and exhibit pH optima of 8 and 6 for HEX1 and HEX2, respectively. The enzymes are able to hydrolyze N-acetylchitooligosaccharides with a degree of polymerization of two, three, and four. The major findings were, that HEX1 and HEX2 catalyze trans-glycosylation reactions with lactose as acceptor, giving rise to the human milk oligosaccharide precursor lacto-N-triose II (LNT2) with yields of 2 and 8 % based on the donor substrate. In total, trans-glycosylation reactions were tested with the disaccharide acceptors ß-lactose, sucrose, and maltose, as well as with the monosaccharides galactose and glucose resulting in the successful attachment of GlcNAc to the acceptor in all cases.

Structural changes of 6a-hydroxy-pterocarpans upon heating modulate their estrogenicity.

The isoflavonoid composition of an ethanolic extract of fungus-treated soybean sprouts was strongly altered by a combined acid/heat treatment. UHPLC-MS analysis showed that 6a-hydroxy-pterocarpans were completely converted to their respective, more stable, 6a,11a-pterocarpenes, whereas other isoflavonoids, from the isoflavone and coumestan subclasses, were affected to a much lesser extent (loss of ∼15%). Subsequently, mixtures enriched in prenylated 6a-hydroxy-pterocarpans (pools of glyceollin I/II/III and glyceollin IV/VI) or prenylated 6a,11a-pterocarpenes (pools of dehydroglyceollin I/II/III and dehydroglyceollin IV/VI) were purified, and tested for activity on both human estrogen receptors (ERα and ERß). In particular, the response toward ERα changed, from agonistic for glyceollins to antagonistic for dehydroglyceollins. Toward ERß a decrease in agonistic activity was observed. These results indicate that the introduction of a double bond with the concomitant loss of a hydroxyl group in 6a-hydroxy-pterocarpans extensively modulates their estrogenic activity.