Molecular effects of fermentation in the gut and its relevance for metabolism and satiety

Dietary fibres, the edible parts of plants that are resistant to digestion and absorption in the human small intestine, were shown to be important in the prevention of obesity and the metabolic syndrome. This association can partially be attributed to a fibre-induced increase in satiety. Dietary fibres can be fermented by bacteria, collectively referred to as the microbiota, in the large intestine (i.e. caecum and colon), resulting in the production of the short-chain fatty acids (SCFAs) acetate, propionate and butyrate. Part of the effect of dietary fibres on satiety is thought to be mediated via the production of SCFAs. The objective of the research described in this thesis was to reveal the effects of fermentation in the large intestine using comprehensive approaches with focus on metabolism and satiety. The effect of 2-wk-consumption of resistant starch (RS), a dietary fibre highly fermentable by the gut microbiota, was studied in 2 pig experiments. In the first experiment, performed in adult female pigs, intestinal samples were collected from different areas of the gastrointestinal tract to measure luminal microbiota composition, luminal SCFA concentrations and the expression of host genes involved in SCFA uptake, SCFA signalling, and satiety regulation in mucosal tissue. In an additional study the effects of RS were investigated in young growing pigs fitted with a cannula in the proximal colon for repeated collection of tissue biopsies for whole-genome expression profiling and luminal content for measurement of SCFA concentrations and microbiota composition. To limit inter-individual variation, the RS diet was provided to the pigs in a 2 x 2 crossover design for 2 wk per diet. Furthermore, the behaviour of the pigs was monitored and the postprandial plasma response of satiety-related hormones and metabolites was measured at the end of each 2 wk period using repeated peripheral blood sampling via catheters. In order to determine the potential differences in post-prandial plasma protein profiles, minipigs were assigned to a control (C) diet or a diet containing the bulky fibre lignocellulose (LC), the viscous and fermentable fibre pectin (PEC) or RS for periods of 8 d in a 4 x 4 Latin square design. Portal and carotid blood samples were collected from catheters on d 8 of each treatment, both before and at several time points after an ad libitum morning meal. Male C57BL/6J mice were used to study the effect of background diet and SCFAs on colonic gene expression. Mice were fed a semi-synthetic low fat or high fat diet starting 2 wk before the treatment period. During treatment, mice received a rectal infusion of either an acetate, propionate, butyrate, or a control saline solution on 6 consecutive days, after which colon was collected to perform comprehensive gene expression profiling. RS enhanced satiety based on behavioural observations, as RS-fed pigs showed less feeder-directed and drinking behaviours than pigs fed a digestible starch (DS) diet. In both caecum and colon, differences in microbiota composition were observed between RS-fed pigs and DS-fed pigs. In the colon these included the induction of the healthy gut-associated butyrate-producing Faecalibacterium prausnitzii, whereas potentially pathogenic members of the Gammaproteobacteria were reduced in relative abundance in RS-fed pigs. Caecal and colonic SCFA concentrations were significantly higher in RS-fed pigs. Geneexpression profiling of the proximal colon revealed a shift upon RS consumption from the regulation of immune response towards lipid and energy metabolism. The nuclear receptor PPARG was identified as a potential key upstream regulator. At plasma level, SCFA concentrations were higher in RS-fed pigs throughout the day. Postprandial glucose, insulin and glucagon-like peptide 1 (GLP-1) responses were lower in RS-fed than in DS-fed pigs, whereas triglyceride levels were higher in RS-fed than in DS-fed pigs. In minipigs, plasma protein profiles were found to be most similar with C and LC consumption and with PEC and RS consumption, indicating that the consumption of diets with fermentable fibres results in a different plasma protein profile compared to a diet containing non-fermentable fibres or a diet without fibres. In mice we observed that dietary fat content had a major impact on colonic gene expression responses to SCFAs, especially after propionate treatment. Moreover, the diet- and SCFA-dependent gene expression changes pointed towards the modulation of several metabolic processes. Genes involved in oxidative phosphorylation, lipid catabolism, lipoprotein metabolism and cholesterol transport were suppressed by acetate and butyrate treatment, whereas propionate resulted in changes in fatty acid and sterol biosynthesis, and in amino acid and carbohydrate metabolism.Furthermore, SCFA infusion on the high fat diet background appeared to partially reverse the gene expression changes induced by high fat feeding without SCFA infusion. In conclusion, this thesis showed that the consumption of RS changed the microbiota composition in the colonic lumen, with a decrease in the abundance of potentially pathogenic bacteriaand an increase in the abundance of SCFA-producing populations. Furthermore, colonic gene expression changes were observed after RS consumption and after colonic administration of SCFAs. With both treatments,among the changes inthe transcriptional profileof the host were adaptations inmetabolic processes, such as energy and lipid metabolism, and immune response.We also showed that fat content in the background diet had a major impact on gene expression responses to SCFAs in colon. Overall, this thesis supports the implementation of fermentable dietary fibres into the human diet to improve colonic health and to reduce energy intake and body weight gain, which ultimately may prevent obesity and type 2 diabetes. Additional research is required to further elucidate the mechanisms via which fermentable dietary fibres can improve human health.</p

Deconjugation Kinetics of Glucuronidated Phase II Flavonoid Metabolites by B-glucuronidase from Neutrophils

Flavonoids are inactivated by phase II metabolism and occur in the body as glucuronides. Mammalian ß-glucuronidase released from neutrophils at inflammatory sites may be able to deconjugate and thus activate flavonoid glucuronides. We have studied deconjugation kinetics and pH optimum for four sources of ß-glucuronidase (human neutrophil, human recombinant, myeloid PLB-985 cells, Helix pomatia) with five flavonoid glucuronides (quercetin-3-glucuronide, quercetin-3'-glucuronide, quercetin-4'-glucuronide, quercetin-7-glucuronide, 3'-methylquercetin-3-glucuronide), 4-methylumbelliferyl-ß-D-glucuronide, and para-nitrophenol-glucuronide. All substrate-enzyme combinations tested exhibited first order kinetics. The optimum pH for hydrolysis was between 3.5-5, with appreciable hydrolysis activities up to pH 5.5. At pH 4, the Km ranged 44-fold from 22 µM for quercetin-4'-glucuronide with Helix pomatia ß-glucuronidase, to 981 µM for para-nitrophenol-glucuronide with recombinant ß-glucuronidase. Vmax (range: 0.735-24.012 µmol·min-1·unit-1 [1 unit is defined as the release of 1 µM 4-methylumbelliferyl-ß-D-glucuronide per min]) and the reaction rate constants at low substrate concentrations (k) (range: 0.002-0.062 min-1·(unit/L)-1 were similar for all substrates-enzyme combinations tested. In conclusion, we show that ß-glucuronidase from four different sources, including human neutrophils, is able to deconjugate flavonoid glucuronides and non-flavonoid substrates at fairly similar kinetic rates. At inflammatory sites in vivo the pH, neutrophil and flavonoid glucuronide concentrations seem favorable for deconjugation. However, it remains to be confirmed whether this is actually the case

Experimentally induced infections of European eel <i>Anguilla anguilla</i> with <i>Anguillicola crassus</i> (Nematoda, Dracunculoidea) and subsequent migration of larvae

Migration patterns of third-stage Anguillicola crassus larvae, and pathogenesis of the lesions induced by third-stage larvae, was investigated in European eel Anguilla anguilla L. Young elvers (1g) were fed infected Paracyclops fimbriatus (Copepoda). Eel samples were collected and examined histologically at varying intervals during 6 mo post-infection period. Third-stage larvae (L-III) migrated directly through the intestinal wall and body cavity to the swimbladder within 17h post-infection. L-IV larvae were detected 3 mo post-infection, and immature adults were detected within 4 mo post-infection. The parasites occasionally showed aberrant migration paths. Pathological effects caused by the parasite were less severe after experimentally induced infections than those detected in some natural infections

Can inorganic elements affect herpesvirus infections in European eels?

SHORT RESEARCH AND DISCUSSION ARTICLEIn combination, pollution and pathogens represent a serious threat to the health of European eels that has been increasingly recognized. Thus, the impact of contaminants, cadmium, lead,mercury, and selenium, on anguillid herpesvirus 1 infection inwild European eels has been evaluated. Despite the small sample size, results indicate that selenium and mercury concentrations may compromise the European eel immune system as herpesvirus infection was more prevalent in specimens with higher Hg and Se hepatic concentrations.Versión del editor2,65

Co-infections and multiple stressors in fish

Fish are typically exposed to multiple physical, chemical and biological stressors. The cumulative impact of co-infections between parasites, bacteria, viruses and (a)biotic environmental pressures may trigger complex interactions, eliciting different pathological and immunological outcomes than those classically assessed. New cross-disciplinary studies attempt to measure the impact of environmental stressors in modulating the host response to pathogens. Scientific advances are needed to reduce pressure on natural populations, improve fish stock management, and to design more efficient diagnostic tools or vaccination strategies. An EAFP-promoted workshop, held on 10th September 2019 in Porto, Portugal, was dedicated to sharing research experiences on the interaction between heterogenous pathogens and multiple stressors in fish. The workshop involved around 200 attendants, opened by a keynote talk (Fast), and followed by a further twelve oral presentations, including three in the format of lash poster presentations. Contributions illustrated cross-disciplinary approaches to study complex host-pathogen and stressors interactions

An Essential Difference between the Flavonoids MonoHER and Quercetin in Their Interplay with the Endogenous Antioxidant Network

Antioxidants can scavenge highly reactive radicals. As a result the antioxidants are converted into oxidation products that might cause damage to vital cellular components. To prevent this damage, the human body possesses an intricate network of antioxidants that pass over the reactivity from one antioxidant to another in a controlled way. The aim of the present study was to investigate how the semi-synthetic flavonoid 7-mono-O-(β-hydroxyethyl)-rutoside (monoHER), a potential protective agent against doxorubicin-induced cardiotoxicity, fits into this antioxidant network. This position was compared with that of the well-known flavonoid quercetin. The present study shows that the oxidation products of both monoHER and quercetin are reactive towards thiol groups of both GSH and proteins. However, in human blood plasma, oxidized quercetin easily reacts with protein thiols, whereas oxidized monoHER does not react with plasma protein thiols. Our results indicate that this can be explained by the presence of ascorbate in plasma; ascorbate is able to reduce oxidized monoHER to the parent compound monoHER before oxidized monoHER can react with thiols. This is a major difference with oxidized quercetin that preferentially reacts with thiols rather than ascorbate. The difference in selectivity between monoHER and quercetin originates from an intrinsic difference in the chemical nature of their oxidation products, which was corroborated by molecular quantum chemical calculations. These findings point towards an essential difference between structurally closely related flavonoids in their interplay with the endogenous antioxidant network. The advantage of monoHER is that it can safely channel the reactivity of radicals into the antioxidant network where the reactivity is completely neutralized

Pulse trawl fishing: the effects on dab (Limanda limanda)

The aim of this research is to investigate whether electric stimuli practiced in pulse gear could cause injuries in dab, and enhance the development of diseases, such as ulceration. The report gives results for a number of samples analysed

Negative magnetoresistance in boron-doped nanocrystalline diamond films

We report on the observation of a negative magnetoresistance (NMR) regime in boron-doped nanocrystalline diamond films at low temperatures. A comparative analysis of our experimental results and those reported for systems composed of superconducting granules embedded in an insulating matrix (also referred as granular films) suggest the presence of superconducting regions inside the insulating films as causing the NMR. By considering the latter scenario, the experimental observations are explained by modeling the systems as consisting of a distribution of superconducting granules whose global properties are tuned by the intergrain distance