Complex flavonoids in cocoa: synthesis and degradation by intestinal microbiota

Intestinal Metabolism of Selected Steroidal Glycoalkaloids in the Pig Cecum Model

Due to the presence of the steroidal glycoalkaloid solanine, the potato was chosen as Germany's poisonous plant of the year 2022. Steroidal glycoalkaloids are secondary plant metabolites which have been reported to induce toxic as well as beneficial health effects. Nevertheless, data regarding occurrence, toxicokinetics, and metabolism of steroidal glycoalkaloids is scarce, and substantially more research is required for a proper risk assessment. Therefore, the intestinal metabolism of solanine, chaconine, solasonine, solamargine, and tomatine was investigated using the ex vivo pig cecum model. All steroidal glycoalkaloids were degraded by the porcine intestinal microbiota, releasing the respective aglycon. Furthermore, the hydrolysis rate was strongly dependent on the linked carbohydrate side chain. Solanine and solasonine, which are linked to a solatriose, were metabolized significantly faster than the chaconine and solamargin, which are linked to a chacotriose. In addition, stepwise cleavage of the carbohydrate side chain and the formation of β- and γ-intermediates were detected by HPLC-HRMS. The results provide valuable insights into the intestinal metabolism of selected steroidal glycoalkaloids and help to reduce uncertainties and improve risk assessment.

Release of Small Phenolic Metabolites from Isotopically Labeled 13C Lignin in the Pig Cecum Model

A diet with a high dietary fiber content is often recommended in today's nutrition due to several beneficial health effects related to its intake. Lignin as a part of dietary fiber is the second most abundant natural polymer and considered to be stable during digestion. However, some studies indicate a partial degradation during the intestinal metabolism. To further elucidate this hypothesis, the aim of this study was to investigate whether lignin is metabolized by the gut microbiota using the ex vivo pig cecum model. As potential lignin-derived metabolites might already naturally occur in the pig cecal matrix, an approach using isotopically labeled ¹³C lignin was chosen for this study. Ten small phenolic lignin degradation products and their time-dependent metabolism were identified via an untargeted HPLC-HRMS approach, and the quantity of the metabolites was estimated. From the results, we conclude that lignin is partially degraded releasing small phenolic metabolites.

A novel salt-tolerant strain Trichoderma atroviride HN082102.1 isolated from marine habitat alleviates salt stress and diminishes cucumber root rot caused by Fusarium oxysporum

Background

Salt stress threaten the growth of plants, and even aggravate plant disease. In this article, salt-tolerant Trichoderma strain was isolated, and its potential to alleviate salt stress and diminish cucumber root rot caused by Fusarium oxysporum was evaluated.

Results

Twenty-seven Trichoderma isolates were isolated from samples of sea muds and algae collected from the South Sea of China. Among these, the isolate HN082102.1 showed the most excellent salt tolerance and antagonistic activity against F. oxysporum causing root rot in cucumber and was identified as T. atroviride. Its antagonism ability may be due to mycoparasitism and inhibition effect of volatile substances. The application of Trichoderma mitigated the adverse effects of salt stress and promoted the growth of cucumber under 100 mM and 200 mM NaCl, especially for the root. When T. atroviride HN082102.1 was applied, root fresh weights increased by 92.55 and 84.86%, respectively, and root dry weights increased by 75.71 and 53.31%, respectively. Meanwhile, the application of HN082102.1 reduced the disease index of cucumber root rot by 63.64 and 71.01% under 100- and 0-mM saline conditions, respectively, indicating that this isolate could inhibit cucumber root rot under salt stress.

Conclusions

This is the first report of salt-tolerant T. atroviride isolated from marine habitat showing antagonistic activity to F. oxysporum, and the results provide evidence for the novel strain T. atroviride HN082102.1 in alleviating salt stress and diminishing cucumber root rot, indicating that T. atroviride strain HN082102.1 can be used as biological control agent in saline alkali land.

Model Studies on the Reaction Products Formed at Roasting Temperatures from either Catechin or Tea Powder in the Presence of Glucose

During tea processing, roasting significantly affects the transformation pathway of catechins. When (-)-epigallocatechin gallate (EGCG) and glucose were roasted at different pH values, the degree of degradation and isomerization of EGCG was the lowest at pH 7 and the highest at pH 8. Thirty-five products were found in the model reaction of EGCG and glucose under high temperatures, of which four EGCG-glucose adducts were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (NMR). In addition, catechins, gallic acid, and theanine in tea with added glucose were significantly reduced during roasting. The contents of four EGCG-glucose adducts were increased significantly at 150 °C after 30 min and dropped gradually after 60 min. Therefore, based on the present study, EGCG could form crosslinks with glucose under high temperatures in a short time, which provides insight for tea processing and synthesis of catechin-sugar adducts.

Intestinal Metabolism of α- and β-Glucosylated Modified Mycotoxins T-2 and HT-2 Toxin in the Pig Cecum Model

The type A trichothecene mycotoxins T-2 and HT-2 toxin are fungal secondary metabolites produced by Fusarium fungi, which contaminate food and feed worldwide. Especially as a result of the high toxicity of T-2 toxin and their occurrence together with glucosylated forms in cereal crops, these mycotoxins are of human health concern. Particularly, it is unknown whether and how these modified mycotoxins are metabolized in the gastrointestinal tract and, thus, contribute to the overall toxicity. Therefore, the comparative intestinal metabolism of T-2 and HT-2 toxin glucosides in α and β configuration was investigated using the ex vivo pig cecum model, which mimics the human intestinal metabolism. Regardless of its configuration, the C-3 glycosidic bond was hydrolyzed within 10-20 min, releasing T-2 and HT-2 toxin, which were further metabolized to HT-2 toxin and T-2 triol, respectively. We conclude that T-2 and HT-2 toxin should be evaluated together with their modified forms for risk assessment.

Exploring the Molecular Pathways Behind the Effects of Nutrients and Dietary Polyphenols on Gut Microbiota and Intestinal Permeability: A Perspective on the Potential of Metabolomics and Future Clinical Applications

The gut microbiota is involved in the regulation of the intestinal permeability (IP), whose disruption is a frequent condition in older people and is associated with the development of several diseases. The diet can affect the gut microbiota and IP, although the molecular mechanisms involved are unclear. Metabolomics is one of the suitable approaches to study the effects of diet on gut microbiota and IP, although, up to now, the research has focused only on a few dietary components. The aim here was to review the most recent literature concerning the application of metabolomics to the study of the diet-induced alterations of gut microbiota and the effects on IP, with a particular focus on the molecular pathways involved. An additional aim was to give a perspective on the future research involving dietary polyphenols, because despite their potential use in the management of increased IP, few studies have been reported to date.

Discovery and mechanism of intestinal bacteria in enzymatic cleavage of C-C glycosidic bonds

C-Glycosides, a special type of glycoside, are frequently distributed in many kinds of medicinal plants, such as puerarin and mangiferin, showing various and significant bioactivities. C-Glycosides are usually characterized by the C-C bond that forms between the anomeric carbon of sugar moieties and the carbon atom of aglycon, which is usually resistant against acidic hydrolysis and enzymatic treatments. Interestingly, C-glycosides could be cleaved by several intestinal bacteria, but whether the enzymatic cleavage of C-C glycosidic bond is reduction or hydrolysis has been controversial; furthermore, whether existence of a "C-glycosidase" directly catalyzing the cleavage is not clear. Here we review research advances about the discovery and mechanism of intestinal bacteria in enzymatic cleavage of C-C glycosidic bond with an emphasis on the identification of enzymes manipulation the deglycosylation. Finally, we give a brief conclusion about the mechanism of C-glycoside deglycosylation and perspectives for future study in this field.

A newly isolated human intestinal bacterium strain capable of deglycosylating flavone C-glycosides and its functional properties

Background

Flavone C-glycosides are difficult to be deglycosylated using traditional chemical methods due to their solid carbon–carbon bond between sugar moieties and aglycones; however, some bacteria may easily cleave this bond because they generate various specific enzymes.

Results

A bacterial strain, named W12-1, capable of deglycosylating orientin, vitexin, and isovitexin to their aglycones, was isolated from human intestinal bacteria in this study and identified as Enterococcus faecalis based on morphological examination, physiological and biochemical identification, and 16S rDNA sequencing. The strain was shown to preferentially deglycosylate the flavone C-glycosides on condition that the culture medium was short of carbon nutrition sources such as glucose and starch, and its deglycosylation efficiency was negatively correlated with the content of the latter two substances.

Conclusion

This study provided a new bacterial resource for the cleavage of C-glycosidic bond of flavone C-glycosides and reported the carbon nutrition sources reduction induced deglycosylation for the first time.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1144-7) contains supplementary material, which is available to authorized users.

Procyanidin-Cell Wall Interactions within Apple Matrices Decrease the Metabolization of Procyanidins by the Human Gut Microbiota and the Anti-Inflammatory Effect of the Resulting Microbial Metabolome In Vitro

B-type oligomeric procyanidins in apples constitute an important source of polyphenols in the human diet. Their role in health is not known, although it is suggested that they generate beneficial bioactive compounds upon metabolization by the gut microbiota. During apple processing, procyanidins interact with cell-wall polysaccharides and form stable complexes. These interactions need to be taken into consideration in order to better assess the biological effects of fruit constituents. Our objectives were to evaluate the impact of these interactions on the microbial metabolization of cell walls and procyanidins, and to investigate the potential anti-inflammatory activity of the resulting metabolome, in addition to analyzing the taxonomical changes which the microbiota undergo. In vitro fermentation of three model apple matrices with microbiota from 4 healthy donors showed that the binding of procyanidins to cell-wall polysaccharides, whether covalently or non-covalently, substantially reduced procyanidin degradation. Although cell wall-unbound procyanidins negatively affected carbohydrate fermentation, they generated more hydroxyphenylvaleric acid than bound procyanidins, and increased the abundance of Adlercreutzia and Gordonibacter genera. The best results in terms of production of anti-inflammatory bioactive metabolites were observed from the apple matrix with no bonds between procyanidins and cell wall polysaccharides, although the matrix with non-covalent bonds was not far behind.

Flavanol-Enriched Cocoa Powder Alters the Intestinal Microbiota, Tissue and Fluid Metabolite Profiles, and Intestinal Gene Expression in Pigs

BACKGROUND

Consumption of cocoa-derived polyphenols has been associated with several health benefits; however, their effects on the intestinal microbiome and related features of host intestinal health are not adequately understood.

OBJECTIVE

The objective of this study was to determine the effects of eating flavanol-enriched cocoa powder on the composition of the gut microbiota, tissue metabolite profiles, and intestinal immune status.

METHODS

Male pigs (5 mo old, 28 kg mean body weight) were supplemented with 0, 2.5, 10, or 20 g flavanol-enriched cocoa powder/d for 27 d. Metabolites in serum, urine, the proximal colon contents, liver, and adipose tissue; bacterial abundance in the intestinal contents and feces; and intestinal tissue gene expression of inflammatory markers and Toll-like receptors (TLRs) were then determined.

RESULTS

O-methyl-epicatechin-glucuronide conjugates dose-dependently increased (P< 0.01) in the urine (35- to 204-fold), serum (6- to 186-fold), and adipose tissue (34- to 1144-fold) of pigs fed cocoa powder. The concentration of 3-hydroxyphenylpropionic acid isomers in urine decreased as the dose of cocoa powder fed to pigs increased (75-85%,P< 0.05). Compared with the unsupplemented pigs, the abundance ofLactobacillusspecies was greater in the feces (7-fold,P= 0.005) and that ofBifidobacteriumspecies was greater in the proximal colon contents (9-fold,P= 0.01) in pigs fed only 20 or 10 g cocoa powder/d, respectively. Moreover, consumption of cocoa powder reducedTLR9gene expression in ileal Peyer's patches (67-80%,P< 0.05) and mesenteric lymph nodes (43-71%,P< 0.05) of pigs fed 2.5-20 g cocoa powder/d compared with pigs not supplemented with cocoa powder.

CONCLUSION

This study demonstrates that consumption of cocoa powder by pigs can contribute to gut health by enhancing the abundance ofLactobacillusandBifidobacteriumspecies and modulating markers of localized intestinal immunity.

Metabolites and Changes in Antioxidant Activity of A-Type and B-Type Proanthocyanidin Dimers after Incubation with Rat Intestinal Microbiota

Metabolism of B-type EC dimer, A-type EC dimer, A-type ECG dimer, and A-type EGCG dimer was compared in vitro after incubation with rat intestinal microbiota for 0-24 h. A "dimeric" catabolite (m/z 815.6) was detected in four procyanthocyanidin dimers. Although the early cleavage of the C4-C8 interflavan bond and the reductive cleavage of the C-ring occurred in both B-type and A-type dimers, the degradation routes of these two types of dimers might somewhat differ. A dimeric catabolite C1 and more low molecular weight phenolic acids were detected in the metabolites of A-type EC dimer, but not in B-type EC dimer. The antioxidant capabilities of the A-type dimers were enhanced significantly after incubation for 6 h, whereas the antioxidant capacity of B-type EC dimer decreased. The results suggested that changes in antioxidant activity of procyanidin dimers after bioconversion by rat intestinal microbiota were not only structure dependent but also incubation condition dependent.

Methods to determine effects of cranberry proanthocyanidins on extraintestinal infections: Relevance for urinary tract health

Urinary tract infections (UTI) are one of the most frequent extraintestinal infections caused by Escherichia coli (ExPEC). Cranberry juice has been used for decades to alleviate symptoms and prevent recurrent UTI. The putative compounds in cranberries are proanthocyanidins (PAC), specifically PAC with "A-type" bonds. Since PAC are not absorbed, their health benefits in UTI may occur through interactions at the mucosal surface in the gastrointestinal tract. Recent research showed that higher agglutination of ExPEC and reduced bacterial invasion are correlated with higher number of "A-type" bonds and higher degree of polymerization of PAC. An understanding of PAC structure-activity relationship is becoming feasible due to advancements, not only in obtaining purified PAC fractions that allow accurate estimation, but also in high-resolution MS methodologies, specifically, MALDI-TOF MS. A recent MALDI-TOF MS deconvolution method allows quantification of the ratios of "A-type" to "B-type" bonds enabling characteristic fingerprints. Moreover, the generation of fluorescently labeled PAC allows visualization of the interaction between ExPEC and PAC with microscopy. These tools can be used to establish structure-activity relationships between PAC and UTI and give insight on the mechanism of action of these compounds in the gut without being absorbed.

Identification and functional expression of genes encoding flavonoid O- and C-glycosidases in intestinal bacteria

Gut bacteria play a crucial role in the metabolism of dietary flavonoids and thereby influence the bioactivity of these compounds in the host. The intestinal Lachnospiraceae strain CG19-1 and Eubacterium cellulosolvens are able to deglycosylate C- and O-coupled flavonoid glucosides. Growth of strain CG19-1 in the presence of the isoflavone C-glucoside puerarin (daidzein 8-C-glucoside) led to the induction of two proteins (DfgC, DfgD). Heterologous expression of the encoding genes (dfgC, dfgD) in Escherichia coli revealed no C-deglycosylating activity in the resulting cell extracts but cleavage of flavonoid O-glucosides such as daidzin (daidzein 7-O-glucoside). The recombinant DfgC and DfgD proteins were purified and characterized with respect to their quaternary structure, substrate and cofactor specificity. The products of the corresponding genes (dfgC, dfgD) from E. cellulosolvens also catalysed the O-deglycosylation of daidzin following their expression in E. coli. In combination with three recombinant proteins encoded by adjacent genes in E. cellulosolvens (dfgA, dfgB, dfgE), DfgC and DfgD from E. cellulosolvens catalysed the deglycosylation of the flavone C-glucosides homoorientin (luteolin 6-C-glucoside) and isovitexin (apigenin 6-C-glucoside). Even intact cells of E. coli expressing the five E. cellulosolvens genes cleaved these flavone C-glucosides and, also, flavonoid O-glucosides to the corresponding aglycones.

Microbial phenolic metabolites improve glucose-stimulated insulin secretion and protect pancreatic beta cells against tert-butyl hydroperoxide-induced toxicity via ERKs and PKC pathways

Oxidative stress is accepted as one of the causes of beta cell failure in type 2 diabetes. Therefore, identification of natural antioxidant agents that preserve beta cell mass and function is considered an interesting strategy to prevent or treat diabetes. Recent evidences indicated that colonic metabolites derived from flavonoids could possess beneficial effects on various tissues. The aim of this work was to establish the potential anti-diabetic properties of the microbial-derived flavonoid metabolites 3,4-dihydroxyphenylacetic acid (DHPAA), 2,3-dihydroxybenzoic acid (DHBA) and 3-hydroxyphenylpropionic acid (HPPA). To this end, we tested their ability to influence beta cell function and to protect against tert-butyl hydroperoxide-induced beta cell toxicity. DHPAA and HPPA were able to potentiate glucose-stimulated insulin secretion (GSIS) in a beta cell line INS-1E and in rat pancreatic islets. Moreover, pre-treatment of cells with both compounds protected against beta cell dysfunction and death induced by the pro-oxidant. Finally, experiments with pharmacological inhibitors indicate that these effects were mediated by the activation of protein kinase C and the extracellular regulated kinases pathways. Altogether, these findings strongly suggest that the microbial-derived flavonoid metabolites DHPAA and HPPA may have anti-diabetic potential by promoting survival and function of pancreatic beta cells.

Transepithelial permeability studies of flavan-3-ol-C-glucosides and procyanidin dimers and trimers across the Caco-2 cell monolayer

In this study the permeability of two flavanol-C-glucosides (FCglcs) and five dimeric and trimeric flavan-3-ols, namely, procyanidins (PCs), was investigated with the human colon carcinoma cell line (Caco-2) model. These compounds can be found especially in cocoa, and they are of great interest due to their assumed beneficial health effects. Transepithelial electrical resistance (TEER) and capacitance were measured online with a CellZscope device prior to and during the whole experiment to guarantee the maintenance of the barrier properties. The transport experiments with pure, single compounds (50-300 μM) from apical to basolateral side showed slight permeation of PCs A2, B2, and B5 and cinnamtannin B1 (CB1) as well as (-)-catechin-6-C-glucoside (C6Cglc) and (-)-catechin-8-C-glucoside (C8Cglc) of about 0.02-0.2% after 24 h. Transport of PC C1 could not be detected. Inhibition of P-glycoprotein (Pgp) increased the permeation of PC B2 and CB1 to the basolateral side, which indicates that Pgp counteracts the transport of these compounds. Metabolites (epicatechin, 3'- and 4'-O-epicatechin) in very small amounts were detectable only for PC B2. These are the first data concerning the permeability of flavan-3-ol-C-glucosides across the Caco-2 cell monolayer.

Systematic approach for structure elucidation of polyphenolic compounds using a bottom-up approach combining ion trap experiments and accurate mass measurements

Polyphenols are a group of plant secondary metabolites with a wide range of structural differences. In many cases, in vitro and in vivo studies of polyphenols revealed beneficial health effects. The mass spectrometric characterization of polyphenols can be the key to understanding the metabolism and resorption of this group of substances. For structure elucidation of polyphenolic compounds nuclear magnectic resonance spectroscopy is the method of choice. Due to the broad structure variability and the sometimes relatively low concentrations of polyphenols and/or their metabolites in foods as well as physiological samples, mass spectrometry could be an alternative for structure elucidation. Especially high-resolution mass spectrometry, for example, Fourier transformation mass spectrometry (FTMS), is a valuable tool. Using a FTMS system, a systematic approach to the fragmentation behavior of phenolic and polyphenolic compounds was chosen to verify the influence of the structure on the fragmentation pattern of the different substances. Depending on the structure, specific fragment ions could be detected. Therefore, it is possible to gain reliable information about the structure of the pseudomolecular ion from its fragmentation spectrum, which is of great aid in the structure elucidation of unknown polyphenols and/or their metabolites.

Urinary excretion and metabolism of procyanidins in pigs

SCOPE

Aim of this study was to investigate urinary excretion and metabolism of procyanidins a group of secondary plant metabolites with many beneficial health effects described in literature.

METHODS AND RESULTS

To investigate the metabolism of procyanidins in the absence of flavan-3-ols, centrifugal partition chromatography was used for their reduction in a grape seed extract to a level of almost zero. After administration of the monomer reduced grape seed extract (mredGSE) containing procyanidins B1, B2, B3, B4, C1 to pigs flavan-3-ols, their methyl derivatives, dimeric and trimeric procyanidins were determined in urine by high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). Maximal concentrations of procyanidins 6 h after administration vary from 5 to 30 ng/mg creatinine. Total excretion of flavan-3-ols and their methyl derivatives indicates an increasing trend for pigs given mredGSE in comparison to pigs of the control group. Flavan-3-ols were conjugated and methylated to a great extent in comparison to dimeric and trimeric procyanidins. In the case of low molecular weight metabolites, an increasing trend was observed for hippuric acid, not for phenolic acids.

CONCLUSIONS

Ratios of total excretion of procyanidins to administrated amounts between 0.004% (C1) and 0.019% (B4) suggest a poor urinary excretion by pigs. A transfer of these results to humans is possible due to their similar gastrointestinal tract.

Feasibility and application of liquid-liquid extraction combined with gas chromatography-mass spectrometry for the analysis of phenolic acids from grape polyphenols degraded by human faecal microbiota

In this study the feasibility of a LLE-GC-EI-MS method for the analysis of 43 phenolic acids belonging to different chemical structure families which have been described in the literature as microbial-derived metabolites after consumption of dietary polyphenols was proved. In addition, the method was applied for the characterisation of phenolic metabolites resulting from the incubation, in anaerobic conditions, of a commercial grape seed extract (GSE) and their corresponding flavan-3-ol monomeric (GSE-M) and oligomeric (GSE-O) fractions with human faeces from healthy volunteers (n=3). The method showed average values of repeatability and reproducibility of 5.0% and 6.3%, respectively, adequate and low detection (1.8-30.8 μg L(-1)) and quantification limits (6.0-102.8 μg L(-1)) and good recovery values (95%, as average value). A total of 27 phenolic acids were identified in the faecal solutions after incubation with the grape seed extracts. In general, faecal samples incubated with GSE and GSE-M (monomeric fraction) yield a higher formation of phenolic acids compared to the samples incubated with the oligomer fraction (GSE-O).

Intestinal metabolism of two A-type procyanidins using the pig cecum model: detailed structure elucidation of unknown catabolites with Fourier transform mass spectrometry (FTMS)

Procyanidins, as important secondary plant metabolites in fruits, berries, and beverages such as cacao and tea, are supposed to have positive health impacts, although their bioavailability is yet not clear. One important aspect for bioavailability is intestinal metabolism. The investigation of the microbial catabolism of A-type procyanidins is of great importance due to their more complex structure in comparison to B-type procyanidins. A-type procyanidins exhibit an additional ether linkage between the flavan-3-ol monomers. In this study two A-type procyanidins, procyanidin A2 and cinnamtannin B1, were incubated in the pig cecum model to mimic the degradation caused by the microbiota. Both A-type procyanidins were degraded by the microbiota. Procyanidin A2 as a dimer was degraded by about 80% and cinnamtannin B1 as a trimer by about 40% within 8 h of incubation. Hydroxylated phenolic compounds were quantified as degradation products. In addition, two yet unknown catabolites were identified, and the structures were elucidated by Fourier transform mass spectrometry.