Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Identification of metabolites involved in heat stress response in different tomato genotypes
    Paupière, Marine J. - \ 2017
    Wageningen University. Promotor(en): R.G.F. Visser, co-promotor(en): A.G. Bovy; Y.M. Tikunov. - Wageningen : Wageningen University - ISBN 9789463431842 - 168
    solanum lycopersicum - tomatoes - genotypes - heat stress - heat tolerance - pollen - metabolomes - metabolites - metabolomics - solanum lycopersicum - tomaten - genotypen - warmtestress - hittetolerantie - stuifmeel - metabolomen - metabolieten - metabolomica

    Tomato production is threatened by climate change. High temperatures lead to a decrease of fruit set which correlates with a decrease of pollen fertility. The low viability of tomato pollen under heat stress was previously shown to be associated with alterations in specific metabolites. In this thesis, we used untargeted metabolomics approaches to broaden the identification of metabolites affected by heat stress. We assessed the suitability of pollen isolation methods for metabolomics analysis and considered the pitfalls for our further analysis. We explored the developmental metabolomes of pollen and anthers of different tomato genotypes under control and high temperature conditions and identified that microsporogenesis is a critical developmental stage for the production of mature and fertile pollen grain under heat stress. Several metabolites were putatively associated with tolerance to high temperature such as specific flavonoids, polyamines and alkaloids. These metabolites can be further used as markers in breeding programs to develop new genotypes tolerant to high temperatures.

    Physiologically based kinetic modelling based prediction of oral systemic bioavailability of flavonoids, their metabolites, and their biological effects
    Boonpawa, Rungnapa - \ 2017
    Wageningen University. Promotor(en): Ivonne Rietjens, co-promotor(en): Arjen Punt. - Wageningen : Wageningen University - ISBN 9789463430371 - 180
    flavonoids - bioavailability - modeling - metabolites - quercetin - physiology - hesperidin - flavonoïden - biologische beschikbaarheid - modelleren - metabolieten - quercetine - fysiologie - hesperidine

    Flavonoids, abundantly present in fruits and vegetables, have been reported to exert various positive health effects based on in vitro bioassays. However, effects detected in in vitro models cannot be directly correlated to human health as most in vitro studies have been performed using flavonoid aglycones at high concentration ignoring extensive metabolism of flavonoids in the human body. To better understand positive health effects of flavonoids in humans, it is of importance to gain insight in at which form and concentration flavonoids are present in the systemic circulation after consumption. This insight can be obtained using physiologically based kinetic (PBK) computer modeling. The results obtained show that PBK modeling provides a useful additional research tool for studies on the fate of flavonoids in the human body and can reveal at what oral dose levels of flavonoids in vitro positive health effects can be expected to occur in vivo, presenting opportunities that are not easily provided by other methods.

    Metabolites contributing to taste in Agaricus bisporus
    Baars, J.J.P. ; Sonnenberg, A.S.M. ; Mumm, R. ; Stijger, I. ; Wehrens, H.R.M.J. - \ 2016
    Plant Research International (PPO/PRI-report 2016-1) - 19
    mushrooms - edible fungi - metabolites - taste - agaricus bisporus - taste panels - postharvest quality - paddestoelen - eetbare paddestoelen - metabolieten - smaak - agaricus bisporus - smaakpanels - kwaliteit na de oogst
    During the last 35 years, hardly any breeding has been done in the button mushrooms (Agaricus bisporus). The fact that no new varieties are generated directed to trends in the food market has caused a slowly decrease in mushroom consumption in the Netherlands and in Europe. The hurdles for generating new varieties are difficulties in breeding and protection of new varieties. These hurdles are now nearly tackled and it is time to generate new varieties. One issue that has never been addressed is taste. The collection of Plant Breeding Wageningen UR contains a large number of strains of the button mushroom with a large genetic variation. In previous research this collection has been genotyped and a small selection of genetically different strains has been made. In 2014 these strains were cultivated along two different methods that were likely to cause differences in taste. Atempts were made to link the results from the taste panel to the metabolite concentrations. Even though it is a relatively small dataset, some correlations can be found for the taste attributes Firmness, Gummi and Boiled Egg and for the metabolites Alanine, Arginine and Proline.
    Simultaneous growth and metabolite production by yoghurt starters and probiotics: a metabolomics approach
    Settachaimongkon, S. - \ 2014
    Wageningen University. Promotor(en): Toon van Hooijdonk; Marcel Zwietering, co-promotor(en): Eddy Smid. - Wageningen : Wageningen University - ISBN 9789462570115 - 213
    yoghurt - melk starterculturen - probiotica - co-vergisting - metabolieten - yoghurt - cultured milk starters - probiotics - co-fermentation - metabolites

    The main objective of this research was to investigate the simultaneous growth and metabolite production by yoghurt starters and different probiotic strains, i.e. Lactobacillus rhamnosus GG, Bifidobacterium animalis subsp. lactis BB12 and Lactobacillus plantarum WCFS1, during set-yoghurt fermentation and refrigerated storage. In this context, the microbial activity was evaluated in terms of bacterial population dynamics, milk acidification and formation of volatile and non-volatile metabolites in set-yoghurt. A complementary metabolomics approach using headspace SPME-GC/MS and 1H-NMR was applied for characterization of biochemical changes associated with the microbial metabolism during fermentation and storage. The results revealed that incorporation of the three probiotic strains did not significantly influence the acidity and concentrations of key-aroma volatile compounds of set-yoghurt. Still, the presence of probiotics substantially contributed to the formation of a large number of volatile and non-volatile metabolites detected at low concentration. Because many probiotic strains are not able to survive well in fermented milk, a strategy to enhance their survival was additionally applied by preculturing the three probiotic strains under sublethal salt and low pH stress conditions prior to inoculation in milk. The results revealed an improved survival of L. rhamnosus GG and B. animalis subsp. lactis BB12, specifically by preculturing at relatively low pH conditions. Moreover, incorporation of sublethally precultured L. plantarum WCFS1 significantly impaired the survival of L. delbrueckii subsp. bulgaricus, which consequently reduced the post-acidification of yoghurt. Metabolomics analyses revealed that the presence of stress-adapted probiotics induced significant changes in the overall metabolite profile of yoghurt. This finding is important, since variations in the relative abundance of various organic acids, aroma volatiles and proteolytic-derived compounds may directly influence the organoleptic quality of product. Finally, multivariate analysis enabled to distinguish yoghurts fermented by different types of starter combinations and different durations of storage according to their metabolite profiles. This research provides new information regarding the impact of probiotics on the metabolome of yoghurt and potential application of stress-adapted probiotics in an actual food-carrier environment.

    Text mining for metabolic reaction extraction from scientific literature
    Risse, J.E. - \ 2014
    Wageningen University. Promotor(en): Ton Bisseling; Jack Leunissen, co-promotor(en): P.E. van der Vet. - Wageningen : Wageningen University - ISBN 9789461739001 - 138
    metabolomica - gegevensanalyse - databanken - text mining - publicaties - wetenschappelijk onderzoek - moleculaire biologie - thesauri - enzymen - metabolieten - metabolomics - data analysis - databases - text mining - publications - scientific research - molecular biology - thesauri - enzymes - metabolites

    Science relies on data in all its different forms. In molecular biology and bioinformatics in particular large scale data generation has taken centre stage in the form of high-throughput experiments. In line with this exponential increase of experimental data has been the near exponential growth of scientific publications. Yet where classical data mining techniques are still capable of coping with this deluge in structured data (Chapter 2), access of information found in scientific literature is still limited to search engines allowing searches on the level keywords, titles and abstracts. However, large amounts of knowledge about biological entities and their relations are held within the body of articles. When extracted, this data can be used as evidence for existing knowledge or hypothesis generation making scientific literature a valuable scientific resource. To unlock the information inside the articles requires a dedicated set of techniques and approaches tailored to the unstructured nature of free text. Analogous to the field of data mining for the analysis of structured data, the field of text mining has emerged for unstructured text and a number of applications has been developed in that field.

    This thesis is about text mining in the field of metabolomics. The work focusses on strategies for accessing large collections of scientific text and on the text mining steps required to extract metabolic reactions and their constituents, enzymes and metabolites, from scientific text. Metabolic reactions are important for our understanding of metabolic processes within cells and that information provides an important link between genotype phenotype. Furthermore information about metabolic reactions stored in databases is far from complete making it an excellent target for our text mining application.

    In order to access the scientific publications for further analysis they can be used as flat text or loaded into database systems. In Chapter 2we assessed and discussed the capabilities and performance of XML-type database systems to store and access very large collections of XML-type documents in the form of the Medline corpus, a collection of more than 20 million of scientific abstracts. XML data formats are common in the field of bioinformatics and are also at the core of most web services. With the increasing amount of data stored in XML comes the need for storing and accessing the data. The database systems were evaluated on a number of aspects broadly ranging from technical requirements to ease-of-use and performance. The performance of the different XML-type database systems was measured Medline abstract collections of increasing size and with a number of different queries. One of the queries assessed the capabilities of each database system to search the full-text of each abstract, which would allow access to the information within the text without further text analysis. The results show that all database systems cope well with the small and medium dataset, but that the full dataset remains a challenge. Also the query possibilities varied greatly across all studied databases. This led us to conclude that the performances and possibilities of the different database types vary greatly, also depending on the type of research question. There is no single system that outperforms the others; instead different circumstances can lead to a different optimal solution. Some of these scenarios are presented in the chapter.

    Among the conclusions of Chapter 2is that conventional data mining techniques do not work for the natural language part of a publication beyond simple retrieval queries based on pattern matching. The natural language used in written text is too unstructured for that purpose and requires dedicated text mining approaches, the main research topic of this thesis. Two major tasks of text mining are named entity recognition, the identification of relevant entities in the text, and relation extraction, the identification of relations between those named entities. For both text mining tasks many different techniques and approaches have been developed. For the named entity recognition of enzymes and metabolites we used a dictionary-based approach (Chapter 3) and for metabolic reaction extraction a full grammar approach (Chapter 4).

    In Chapter 3we describe the creation of two thesauri, one for enzymes and one for metabolites with the specific goal of allowing named entity identification, the mapping of identified synonyms to a common identifier, for metabolic reaction extraction. In the case of the enzyme thesaurus these identifiers are Enzyme Nomenclature numbers (EC number), in the case of the metabolite thesaurus KEGG metabolite identifiers. These thesauri are applied to the identification of enzymes and metabolites in the text mining approach of Chapter 4. Both were created from existing data sources by a series of automated steps followed by manual curation. Compared to a previously published chemical thesaurus, created entirely with automated steps, our much smaller metabolite thesaurus performed on the same level for F-measure with a slightly higher precision. The enzyme thesaurus produced results equal to our metabolite thesaurus. The compactness of our thesauri permits the manual curation step important in guaranteeing accuracy of the thesaurus contents, whereas creation from existing resources by automated means limits the effort required for creation. We concluded that our thesauri are compact and of high quality, and that this compactness does not greatly impact recall.

    In Chapter 4we studied the applicability and performance of a full parsing approach using the two thesauri described in Chapter 3 for the extraction of metabolic reactions from scientific full-text articles. For this we developed a text mining pipeline built around a modified dependency parser from the AGFL grammar lab using a pattern-based approach to extract metabolic reactions from the parsing output. Results of a comparison to a modified rule-based approach by Czarnecki et al.using three previously described metabolic pathways from the EcoCyc database show a slightly lower recall compared to the rule-based approach, but higher precision. We concluded that despite its current recall our full parsing approach to metabolic reaction extraction has high precision and potential to be used to (re-)construct metabolic pathways in an automated setting. Future improvements to the grammar and relation extraction rules should allow reactions to be extracted with even higher specificity.

    To identify potential improvements to the recall, the effect of a number of text pre-processing steps on the performance was tested in a number of experiments. The one experiment that had the most effect on performance was the conversion of schematic chemical formulas to syntactic complete sentences allowing them to be analysed by the parser. In addition to the improvements to the text mining approach described in Chapter 4I make suggestions in Chapter 5 for potential improvements and extensions to our full parsing approach for metabolic reaction extraction. Core focus here is the increase of recall by optimising each of the steps required for the final goal of extracting metabolic reactions from the text. Some of the discussed improvements are to increase the coverage of the used thesauri, possibly with specialist thesauri depending on the analysed literature. Another potential target is the grammar, where there is still room to increase parsing success by taking into account the characteristics of biomedical language. On a different level are suggestions to include some form of anaphora resolution and across sentence boundary search to increase the amount of information extracted from literature.

    In the second part of Chapter 5I make suggestions as to how to maximise the information gained from the text mining results. One of the first steps should be integration with other biomedical databases to allow integration with existing knowledge about metabolic reactions and other biological entities. Another aspect is some form of ranking or weighting of the results to be able to distinguish between high quality results useful for automated analyses and lower quality results still useful for manual approaches. Furthermore I provide a perspective on the necessity of computational literature analysis in the form of text mining. The main reasoning here is that human annotators cannot keep up with the amount of publications so that some form of automated analysis is unavoidable. Lastly I discuss the role of text mining in bioinformatics and with that also the accessibility of both text mining results and the literature resources necessary to create them. An important requirement for the future of text mining is that the barriers around high-throughput access to literature for text mining applications have to be removed. With regards to accessing text mining results, there is a long way to go for many applications, including ours, before they can be used directly by biologists. A major factor is that these applications rarely feature a suitable user interface and easy to use setup.

    To conclude, I see the main role of a text mining system like ours mainly in gathering evidence for existing knowledge and giving insights into the nuances of the research landscape of a given topic. When using the results of our reaction extraction system for the identification of ‘new’ reactions it is important to go back to the actual evidence presented for extra validations and to cross-validate the predictions with other resources or experiments. Ideally text mining will be used for generation of hypotheses, in which the researcher uses text mining findings to get ideas on, in our case, new connections between metabolites and enzymes; subsequently the researcher needs to go back to the original texts for further study. In this role text mining is an essential tool on the workbench of the molecular biologist.

    Jacobaea through the eyes of spectroscopy : identifying plant interactions with the (a)biotic environment by chemical variation effects on spectral reflectance patterns
    Almeida De Carvalho, S. - \ 2013
    Wageningen University. Promotor(en): Wim van der Putten; Andrew Skidmore, co-promotor(en): M. Macel; M. Schlerf. - S.l. : s.n. - ISBN 9789461737502 - 180
    senecio jacobaea - senecio erucifolius - pyrrolizidinealkaloïden - voedingsstoffen - spectraalanalyse - spectroscopie - bodemmicrobiologie - metabolieten - chemische analyse - plantensuccessie - senecio jacobaea - senecio erucifolius - pyrrolizidine alkaloids - nutrients - spectral analysis - spectroscopy - soil microbiology - metabolites - chemical analysis - plant succession

    Plants interact with a wide array of aboveground and belowground herbivores, pathogens, mutualists, and their natural enemies. These interactions are important drivers of spatio-temporal changes in vegetation, however, they may be difficult to be revealed without extensive sampling.In this thesis I investigated the potential of visible and near-infrared spectral measurements to detect plant chemical changes that may reflect interactions between plants and biotic or abiotic soil factors. First, I examined the relative contribution of pyrrolizidine alkaloids (PAs; these are defence compounds of Senecio-type plants against generalist herbivores) to the spectral reflectance features in the visible and short-wave infrared region. My hypothesis was that PAs can be predicted from specific spectral features of aboveground plant tissues. Since PA profiles and their relation to spectral features could be species specific I compared three different species, Jacobaea vulgaris, J. erucifolia and S. inaequidens subjected to nutrient and water treatments to stimulate plant chemical variation. Pyrrolizidine alkaloids were predicted best by spectral reflectance features in the case of Jacobaea vulgaris. I related the better results obtained with J. vulgaris to the existence of the correlation between PAs and nitrogen and the presence of the epoxide chemical structure in J. vulgaris.

    I also examined if different soil microbial communities influenced plant shoot spectral reflectance. I grew the same three plant species as before in sterilized soil and living soil collected from fields with J. vulgaris. I expected that soil biota would change shoot defence content and hyperspectral reflectance in plant species-specific ways. Indeed, the exposure to different soils caused plant chemical profiles to change and both chemical and spectral patterns discriminated plants according to the soil biotic conditions.

    I studied how primary and secondary plant metabolites varied during the growing season and vegetation successional stages. I used a well-studied chronosequence of abandoned arable fields and analysed the chemistry of both leaves and flowers of Jacobaea vulgaris throughout the seasons in fields of different successional status. My general hypothesis was that seasonal allocation of nutrients and defence metabolites to reproductive organs fitted the optimal defence theory, but that pattern was dependent on the successional stage of the vegetation. I found an interaction between season and succession stage, as plants from longer abandoned fields generally had flowers and leaves with higher N-oxides, especially in late Summer. Independent of the succession stage there was a seasonal allocation of nutrients and defence metabolites to flowers. Analyses of spectral reflectance of the field plants showed thatdefence compounds could be estimated more reliably in flowers, while in leaves primary compounds could be predicted best. Succession classes were successfully discriminated by the spectral patterns of flowers. Both chemical and spectral findings suggested that flowers are more sensitive to field ageing processes than leaves.

    Conclusions

    The estimation of pyrrolizidine alkaloids by spectral reflectance features was better in Jacobaea vulgaris than in Senecio inaequidens or Jacobaea erucifolia (chapter 2). Differences in soil communities affect plant leaves’ chemistry and spectral reflectance patterns (chapter 3). Jacobaea vulgarisplants from recent and longer-abandoned fields showed the largest differences in chemical concentration, composition of defence compounds, and spectral reflectance patterns. Flowers were more discriminatory than leaves (chapters 4 and 5). There is a potential to detect plant-biotic interactions by analyzing spectral reflectance patterns (this thesis).
    Systematic metabolite annotation and identification in complex biological extracts : combining robust mass spectrometry fragmentation and nuclear magnetic resonance spectroscopy
    Hooft, J.J.J. van der - \ 2012
    Wageningen University. Promotor(en): Raoul Bino; Sacco de Vries, co-promotor(en): Jacques Vervoort; Ric de Vos. - S.l. : s.n. - ISBN 9789461732347 - 256
    metabolieten - metabolomica - massaspectrometrie - kernmagnetische resonantiespectroscopie - metabolische profilering - metabolische fingerprinting - metabolites - metabolomics - mass spectrometry - nuclear magnetic resonance spectroscopy - metabolic profiling - metabolic fingerprinting

    Detailed knowledge of the chemical content of organisms, organs, tissues, and cells is needed to fully characterize complex biological systems. The high chemical variety of compounds present in biological systems is illustrated by the presence of a large variety of compounds, ranging from apolar lipids, semi-polar phenolic conjugates, toward polar sugars. A molecules’ chemical structure forms the basis to understand its biological function. The chemical identification process of small molecules (i.e., metabolites) is still one of the major focus points in metabolomics research. Actually, no single analytical platform exists that can measure and identify all existing metabolites. In this thesis, two analytical techniques that are widely used within metabolite identification studies have been combined, i.e. mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR). MS was used to ionize the metabolites and to record their molecular weight and to provide substructure information based on fragmentation in the mass spectrometer. NMR gave the comprehensive structural information on the chemical environment of protons and their linkage to other protons within the molecule. The additional structural information as compared to MS is at the cost of an increased amount of compound needed for NMR detection and spectra generation. Here we combined both analytical methods into a liquid chromatography (LC)-based platform that concentrated compounds based on their specific mass; thereby providing a direct link between MS and NMR data. Another platform was developed that generated robust multistage MSn data, i.e., the systematic fragmentation of metabolites and subsequent fragmentation of resulting fragments.

    This thesis aims to accelerate metabolite identification of low abundant plant and human derived compounds by following a systematic approach. The acquired structural information from MSn and 1D-1H-NMR spectra resulted in the complete elucidation of phenolic metabolites in microgram scale from both plant and human origin.

    In the chapter 1, the analytical techniques and terms used throughout the thesis are introduced. The second chapterdescribes how a high mass resolution MSn fragmentation approach was tested in both negative and positive ionization modes for differentiation and identification of metabolites, using a series of 121 polyphenolic molecules. An injection robot was used to infuse the reference compounds one by one into a hybrid mass spectrometer, combining MSn possibilities with accurate mass read-out. This approach resulted in reproducible and robust MSn fragmentation trees up to MS5, which were differential even for closely related compounds. Accurate MSn-based spectral trees were shown to be robust and powerful to distinguish metabolites with similar elemental formula (i.e. isomers), thereby assisting compound identification and annotation in complex biological samples. In the third chapter, we tested the annotation power of this spectral tree approach for annotation of phenolic compounds in crude extracts from Lycopersicum esculentum(tomato) and the model plant Arabipopsis thaliana. Partial MSn spectral trees were generated directly after chromatographic elution (LC-MSn). Detailed MSn spectral trees could be recorded with the use of a collector/injector robot.We were able to discriminate flavonoid glycosides based on their unique MSn fragmentation patterns in either negative or positive ionization mode. Following this approach, we could annotate 127 metabolites in the tomato and Arabidopsis extracts, including 21 novel metabolites. The good quality MSn spectral trees obtained can be used to populate MSn databases and the protocols to generate the spectral trees are a good basis to further expand this database with more diverse compounds.

    Chapter 4 then describes how an automated platform, coupling chromatography with MS and NMR (LC-MS-solid phase extraction-NMR), was developed that can trap and transfer metabolites based on their mass values from a complex biological extract in order to obtain NMR spectra of the trapped LC-MS peak, out of minute amounts of sample and analyte. Extracts from tomatoes modified in their flavonoid biosynthesis pathway were used as proof of principle for the metabolite identification process. This approach resulted in the complete structural elucidation of 10 flavonoid glycosides. This study shows that improving the link between the mass signals and NMR peaks derived from the selected LC-MS peaks decreases the time needed for elucidation of the metabolite structures. In addition, automated 1D-1H-NMR spectrum fitting of the experimental data obtained in this study using the PERCH NMR software further speeded up the candidate rejection process.

    Chapter 5 illustrates how the two developed analytical platforms could be used for the successful selection, annotation, and identification of 177 phenolic compounds present in different extracts of Camellia sinensis, i.e. green, white, and black tea extracts, including the full identification of microgram amounts of complex acylated conjugates of kaempferol and quercetin. Principal component analysis based on the relative abundance of the annotated phenolic compounds in 17 commercially available black, green and white tea products separated the black teas from the green and white teas, thereby illustrating the differential phenolic metabolite contents of black tea as compared to green and white teas. The change in phenolic profiles reflects the polymerization reactions occurring upon transformation of green tea into black tea. This study shows that the combined use of MSn spectral trees and LC-MS-solid phase extraction-NMR leads to a more comprehensive metabolite description thereby facilitating the comparison of tea and other plant samples.

    In chapter 6, we aimed to structurally elucidate and quantify polyphenol-derived conjugates present in the human body by studying the urinary excretion of these conjugates.We applied a combination of a solid phase extraction preparation step and the two HPLC-coupled analytical platforms as described in chapters 2 and 3. This analytical strategy resulted in the annotation of 138 urinary metabolites including 35 completely identified valerolactone conjugates. These valerolactones are microbial break-down products of tea phenols. NMR predictions of glucuronidated and sulphonated core metabolites were performed in order to confirm the NMR peak assignments on the basis of 1D-1H-NMR data only. In addition, 26 hours quantitative excretion profiles for certain valerolactone conjugates were obtained using diagnostic proton signals in the 1D-1H-NMR spectra of urine fractions.

    In the seventh chapter, the current state of metabolite identification and expected challenges in the structural elucidation of metabolites at (sub)microgram amounts are discussed. The work in this thesis and of other groups working on the hyphenation of MS and NMR shows that the complete de novo identification of microgram amounts and even lower of compound is feasible by using MS guided solid phase extractiontrapping in combination with 1D-1H-NMR or UPLC-TOF-MS isolation followed by capillary NMR. Semi-automated annotation of compounds based on their MS and NMR features is now feasible for some well studied compound classes and groups.

    Altogether, the developed platforms yield new and improved insights in the phenolic profiles of well-studied plants as well as a comprehensive picture of the metabolic fate of green tea polyphenols upon intake in the human body. The followed metabolite identification strategy is useful for other studies that aim to elucidate bioactive compounds, especially when only small sample volumes are available. This thesis also contributes to the acquisition of good quality data for metabolite identification by acquiring robust MSn fragmentation spectra and 1D-1H-NMR spectra of partial purified analytes at microgram scale, which paves the path for further developments in data acquisition and analysis, as well as the unravelling of yet unknown metabolites in a faster, more systematic and automated manner.

    Efficacy and safety of dietary N,N-dimethylglycine in broiler production
    Kalmar, I.D. - \ 2011
    Wageningen University. Promotor(en): Wouter Hendriks; Martin Verstegen, co-promotor(en): G.P.J. Janssens. - S.l. : s.n. - ISBN 9789085858751
    vleeskuikens - aminozuurderivaten - metabolieten - pluimveevoeding - voedertoevoegingen - voedersupplementen - vleeskuikenresultaten - verteerbaarheid - karkasopbrengst - oxidatieve stress - ascites - voederveiligheid - voedselveiligheid - voedingsfysiologie - diervoeding - broilers - amino acid derivatives - metabolites - poultry feeding - feed additives - feed supplements - broiler performance - digestibility - carcass yield - oxidative stress - ascites - feed safety - food safety - nutrition physiology - animal nutrition

    N,N-dimethylglycine (DMG), the dimethyl derivative of the amino acid glycine, is a naturally occurring intermediary metabolite in the choline to glycine metabolism. The molecule was first reported in 1943 and is currently used for a variety of applications, including the enhancement of athletic performances in both man and racing animals. With respect to its biological activities, DMG is for instance suggested to enhance oxygen utilisation and to posses non-enzymatic anti-oxidant properties. The studies described in this thesis aimed to evaluate DMG as a feed additive in chickens for fattening.

    In a pilot study, broilers were challenged with both cold stress and a high energy feed in order to incite broiler ascites syndrome. This metabolic disease results from an imbalance between oxygen requirement and supply, and is an important cause of financial losses and a major welfare issue in the modern broiler industry. A low dosage of dietary DMG effectively attenuated progression towards ascites. We hypothesize that this effect results from reduction in endothelial damage and dysfunction caused by plasma free fatty acids, which were substantially lowered by DMG supplementation. Furthermore, DMG improved nutrient digestibility and reduced nitrogen emission, which can be attributed to an emulsifying effect of DMG at the gut level. A subsequent trial revealed dose-dependent effects of dietary DMG on technical performance, carcass yield, oxidative stress parameters and broiler ascites syndrome. However, the nature and magnitude of the effects depended on fatty acid profile of the basal ration. Herein, effects were most pronounced when fed a diet rich in
    poly-unsaturated fatty acids. Generally, effects showed a linear relationship with dose, except for progression towards broiler ascites syndrome, which showed a quadratic relationship with dietary DMG content. Next, a series of efficacy trials were performed on farms at different European locations, using broiler strains and rearing conditions common to each region. Basal flock efficiency showed a wide range between trials; still, DMG systematically improved broiler performance. Finally, a safety and tolerance trial demonstrated a wide safety range of DMG in the target species. Moreover, DMG did not accumulate in consumer parts of broilers when included in diets at the recommended dosage, and bioaccumulation in meat at tenfold dosage did not exceed DMG content in for instance spinach.

    In conclusion, current investigations clearly demonstrate a wide applicability of DMG as a new feed additive in broiler production, in which both economic efficiency and environmental load as well as animal welfare is enhanced without compromising consumer safety.

    Bestrijding spint beter op geïnduceerde planten
    Messelink, G.J. - \ 2010
    glastuinbouw - komkommers - gewasbescherming - biologische bestrijding - plaagbestrijding met natuurlijke vijanden - resistentie van variëteiten - phytoseiulus persimilis - tetranychidae - metabolieten - greenhouse horticulture - cucumbers - plant protection - biological control - augmentation - varietal resistance - phytoseiulus persimilis - tetranychidae - metabolites
    Ontwikkelen van een praktisch toepasbare methode voor geïnduceerde resistentie tegen spint. De biologische bestrijding van spint in komkommer met de roofmijt Phytoseiulus persimilis gaat beter op planten die vooraf behandeld zijn met middelen die resistentie induceren. Plantmetingen (metabolietenanalyses) geven aan dat deze resistentie sterk gekoppeld is aan de aanmaak van flavonoïde afweerstoffen die spint remmen in hun groeisnelheid.
    The genetics of the metabolome in Brassica rapa
    Pino del Carpio, D. - \ 2010
    Wageningen University. Promotor(en): Richard Visser, co-promotor(en): Guusje Bonnema. - [S.l. : S.n. - ISBN 9789085857211 - 168
    brassica campestris - koolsoorten - metabolieten - genexpressie - genetische regulatie - genotypische variatie - genetische diversiteit - genetische merkers - selectiemethoden - metabolomica - brassica campestris - cabbages - metabolites - gene expression - genetic regulation - genetic variance - genetic diversity - genetic markers - selection methods - metabolomics
    In this thesis the metabolic variation in Brassica rapa is described based on results of metabolic profiling of a core collection of 168 accessions representing the different crop types and geographical origin and a Doubled Haploid population. In Chapter 2 we describe the genetic and phenotypic variation of this core collection to explore the possibility of following association mapping methods to identify genes involved in metabolic regulation. We explored through a genome wide and candidate gene approach different association mapping methods in a core collection in Chapters 3 and 4 respectively and in Chapter 5 we combined the QTL analysis of targeted and untargeted metabolites profiled through LC-MS with expression QTLs following a genetical genomics approach aiming to detect genes underlying the metabolite QTL. The genetic diversity evaluated through the screening of AFLP and SSR markers was correlated with classification of accessions using morphological and metabolic trait values. The relationship between accessions in groups was compared using hierarchical clustering and the STRUCTURE program. Using Random Forests classification a set of metabolites was selected that differentiated the different sub groups as determined by STRUCTURE (Chapter 2). Based on the classification into subpopulations using the STRUCTURE program we included the subpopulations as a correction term in our statistical model for association studies (Chapter 3). Additionally, because of the increasing amount of data that will be soon available through sequencing technology we tested the use of Random Forests in the search for marker-trait association for the isoprenoids pathway. Using the results obtained with the linear models as implemented in TASSEL and the results obtained in Random Forests we found a set of 16 significant markers with potential use for marker assisted selection in breeding for several isoprenoidsThe determination of map positions through synteny prediction and genetic mapping of a group of genes from the glucosinolate pathway lead us to identify Myb28 and MAM as candidate genes mapping under a previously detected major QTL for glucosinolates We followed an association mapping approach to investigate their role in the variation in glucosinolates in the core collection by profiling 37 SSR markers, which included markers linked to these candidate genes and markers distributed along different positions in linkage group A03 (Chapter 4). Interestingly, not only MAM and Myb28, but the AOP and GS-OH genes involved in side chain modification and Myb29 in transcriptional regulation were also associated with glucosinolate levels. A genetical genomics approach was followed to identify candidate genes for variation inmetabolites of six biosynthetic pathways: carotenoids, tocopherols, folates, glucosinolates, flavonoids and phenylpropanoids, based on the co-localization analysis and comparison between metabolic (m)QTLs and expression (e)QTLs (Chapter 5). A Doubled Haploid (DH) population was profiled for metabolite content and variation through targeted and LC-MS untargeted approaches. Additionally, the same population was profiled for transcript variation with a newly developed 105K Cogenics array assembled using mainly EST sequences from three species: B. napus, B. rapa and B. oleracea. Co-localization of eQTLs and mQTLs for several isoprenoids (tocopherols and carotenoids) and glucosinolates lead us to the identification of candidate genes for these pathways. However, further work is needed to identify the gene or genes underlying a major cluster of QTLs for 112 centrotypes derived from the LC-MS untargeted data. The results obtained through this combined approach and considerations that need to be taken into account when performing these types of studies with regard to identification of paralogues and the use of a multi Brassica species microarray for transcript profiling in Brassica rapa are discussed.In the final Chapter, the combined use of core collections encompassing the genetic diversity within B. rapa and biparental DH populations to unravel the genetic regulation of the metabolome are discussed.
    Metabolomics technologies applied to the identification of compounds in plants : a liquid chromatography-mass spectrometry - nuclear magnetic resonance perspective over the tomato fruit
    Moco, S.I.A. - \ 2007
    Wageningen University. Promotor(en): Raoul Bino; Sacco de Vries, co-promotor(en): Jacques Vervoort; Ric de Vos. - [S.l.] : S.n. - ISBN 9789085047421 - 222
    solanum lycopersicum - tomaten - metabolieten - fytochemicaliën - kernmagnetische resonantiespectroscopie - metabolomica - lc-ms - solanum lycopersicum - tomatoes - metabolites - phytochemicals - nuclear magnetic resonance spectroscopy - metabolomics - liquid chromatography-mass spectrometry
    A new era of plant biochemistry at the systems level is emerging in which the detailed description of biochemical phenomena, at the cellular level, is important for a better understanding of physiological, developmental, and biomolecular processes in plants. This emerging field is oriented towards the characterisation of small molecules (metabolites) that act as substrates, products, ligands or signalling entities in cells. This thesis concerns the development and establishment of such metabolomics strategies for screening and identifying metabolites in biological systems. Most technological strategies were applied to the assignment of metabolites from tomato (Solanum lycopersicum) fruit. Tomato was chosen for being a widely consumed crop with nutritional attributes, representing a model for the Solanaceae family. In order to achieve both high coverage of detected metabolites and valuable information for identification purposes, liquid chromatography coupled to mass spectrometry (LC-MS) and nuclear magnetic resonances (NMR) technologies were used. In addition, metabolite databases, based on experimental data (mass-based, in the case of LC-MS and chemical shift-based, in the case of NMR) were initiated, in order to systemize the extensive metabolite information. The chapters in this thesis describe method developments and their applications in plant metabolomics that are also feasible to be implemented on other biological systems. A review on the technologies used for metabolomics with a perspective on compound identification is presented in Chapter 1. In Chapter 2, a robust large scale LC-MS method for the analysis of metabolites in plants is described in detail. It presents a step-by-step protocol with thorough information about the reagents used, sample preparation, instrument set­up, methods of analysis and data processing strategies. The described analytical method combines LC with photo diode array (PDA) and MS detection, and allows the analysis of mostly semi-polar secondary metabolites present in plants, such as phenolic acids, flavonoids, glucosinolates, saponins, alkaloids and derivatives thereof. Chapter 3 presents an application of the LC-PDA-MS method for the profiling of metabolites present in tomato fruit. The metabolites putatively identified in this fruit were included in a tomato dedicated-database (the MoTo DB) that is available for public search on the web (see: http://appliedbioinformatics.wur.nl). A comparison between two tomato fruit tissues, peel and flesh, for their metabolite content was made using this MoTo DB. Using the same LC-PDA-MS setup, several different tomato fruit tissues were compared in more detail, along the fruit ripening timeline, in Chapter 4. The presence of tissue-specific metabolites, at determined ripening stages, suggests developmental control of metabolite biosynthesis. Such tissue-specific metabolomics approach may give rise to a biological view over metabolite compartmentalisation. Chapters 5 and 6 describe the implementation of a NMR database for secondary metabolites, mostly including flavonoids, the Flavonoid Database (see: Flavonoid Database under http://www.wnmrc.nl). The acquisition of a large data set of related standard compounds allowed the analysis of shifts in NMR characteristics by the presence of certain functional groups or substituents in the flavonoid backbone. In addition, a 1H NMR-based prediction model was iteratively trained from the acquired experimental data and can be used for the prediction of unknown related molecules. This approach greatly increases the efficiency in the identification of (flavonoid) metabolites. Chapter 7 describes correlations of metabolomics data derived from LC-MS and NMR analyses of a large number of different tomato cultivars. The identification of metabolites is obtained among other available sources, the MoTo DB and the Flavonoid Database. This approach illustrates the complementariness and coincidence of NMR and MS as analytical techniques, applied to the detection of metabolites in tomato fruit. The summarizing discussion and conclusions, sets the work presented in this thesis into a biochemical perspective, and prospects suggestions for the future.
    Service contract for markers for nitrofurazone and on semicarbazide analysis
    Mulder, P.P.J. ; Berendsen, B.J.A. ; Zuidema, T. ; Rhijn, J.A. van - \ 2006
    Wageningen : RIKILT (Rapport / RIKILT 2006.005) - 48
    vervalsing - nitrofuranen - merkers - metabolieten - adulteration - nitrofurans - markers - metabolites
    Opname van nicotine door kippen en overdracht naar eieren bij toepassing van nicotine tegen bloedluis
    Traag, W.A. ; Rijk, T.C. de; Zomer, P. ; Vos Van Avezathe, A. ; Kan, C.A. ; Zeilmaker, M. ; Hoogenboom, L.A.P. - \ 2005
    Wageningen : RIKILT, Instituut voor Voedselveiligheid (Rapport / RIKILT 2005.013) - 13
    kippenvlees - eieren - voedselveiligheid - kennis - nicotine - voedselbesmetting - metabolieten - chicken meat - eggs - food safety - knowledge - nicotine - food contamination - metabolites
    Uit onderzoek van de AID blijkt nicotine gebruikt te worden voor de bestrijding van bloedluis bij kippen. Dit levert mogelijk gezondheidsrisico's op voor de consument van het kippenvlees of de eieren. Omdat niet duidelijk is of het nicotine na de bestrijding van bloedluis in het vlees of eieren achterblijft is, in opdracht van LNV/VD, een verkennende overdrachtstudie gedaan om na te gaan in hoeverre nicotine en twee bekende metabolieten, cotinine en 3-hydroxycotinine, worden overgedragen naar eieren, organen en weefsels van de kip
    Nitroimidazole interlaboratory study 03/01
    Berendsen, B.J.A. ; Rhijn, J.A. van - \ 2001
    Wageningen : RIKILT (Report / RIKILT 2001.023)
    spieren - dimetridazol - ronidazol - metronidazol - hplc - vloeistofchromatografie - massaspectrometrie - metabolieten - kwaliteitscontroles - analytische scheikunde - muscles - dimetridazole - ronidazole - metronidazole - hplc - liquid chromatography - mass spectrometry - metabolites - quality controls - analytical chemistry
    In vitro and in vivo interactions of organohalogens with the endocrine system : the role of metabolites and implications for human health
    Meerts, I.A.T.M. - \ 2001
    Wageningen University. Promotor(en): J.H. Koeman, co-promotor(en): A. Brouwer. - S.l. : S.n. - ISBN 9789058085221 - 160
    polybroombifenylen - polychloorbifenylen - endocrien systeem - metabolieten - toxiciteit - gezondheidsgevaren - polybrominated biphenyls - polychlorinated biphenyls - endocrine system - metabolites - toxicity - health hazards
    Organohalogen compounds such as polychlorinated biphenyls (PCBs) belong to the group of persistent compounds, implying that they are slowly biodegradable and accumulate in the environment. A new group of possibly persistent compounds are the polybrominated diphenyl ethers (PBDEs). These PBDEs have recently been identified in the environment, and their toxicity is relatively unknown. PBDEs are used extensively as flame retardants in e.g. computers, tv-sets, or textile. In this thesis, the toxicity of PBDEs is described.
    In vitro experiments revealed that PBDEs are able to bind to transthyretin (TTR), a thyroid hormone transport protein, and can exert estrogenic activity. In vivo experiments with a model compound showed that these substances can have adverse effects on brain development and the estrous cycle in offspring of rats exposed in utero.
    The concentrations that gave rise to these effects in the rats are only one order of magnitude higher than the concentrations in which these compounds are currently present in human blood.
    The role of natural chlorinated hydroquinone metabolites in ligninolytic fungi
    Teunissen, P.J.M. - \ 1999
    Agricultural University. Promotor(en): J.A.M. de Bont; J.A. Field. - S.l. : Teunissen - ISBN 9789058080691 - 121
    basidiomycotina - ligninolytische micro-organismen - metabolieten - basidiomycotina - ligninolytic microorganisms - metabolites

    Ligninolytic Basidiomycetes have been reported to produce a wide variety of chloroaromatic compounds as secondary metabolites, which are structurally similar to environmental pollutants. Among these are chlorinated hydroquinone metabolites (CHM), such as 2-chloro-1,4-dimethoxybenzene (2Cl-14DMB), 2,6-dichloro-1,4-dimethoxybenzene (26DCl-14DMB), tetrachloro-1,4-dimethoxybenzene and tetrachloro-4-methoxyphenol, which are synthesized by 11 genera of Basidiomycetes.

    The biosynthesis of these chlorinated metabolites is not just a biological accident. An important physiological role of chloroaromatics, including CHM, is their antibiotic function protecting fungi from other organisms. However, since many ligninolytic white rot fungi synthesize CHM, these metabolites might also be involved in lignin degradation.

    The lignin degrading system of white rot fungi is composed of peroxidases, oxidases and secondary metabolites, such as veratryl alcohol (VA) and anisyl alcohol (AA). VA is an important fungal metabolite in the catalytic cycle of lignin peroxidase (LiP), one of the main ligninolytic enzymes of white rot fungi. Three functions of VA have been described: (1) VA is a redox mediator for LiP-catalyzed oxidations via intermediate formation of a cation radical (2) VA is a cofactor necessary to close the catalytic cycle of LiP (3) VA prevents the inactivation of LiP by H 2 O 2 .

    1,4-dimethoxybenzene (14DMB) can replace VA as a cofactor and/or redox mediator in the catalytic cycle of LiP; however, 14DMB is not a fungal metabolite. Nevertheless, 14DMB is structurally related to CHMs, which are fungal metabolites. This structural relationship between 14DMB and CHM implies that CHM may also replace VA in the catalytic cycle of LiP.

    The objectives of this PhD study were to determine the extent of biosynthesis of CHM among white rot fungi and to elucidate their possible physiological role in lignin degradation.

    For this purpose, 92 ligninolytic Basidiomycetes were screened for their ability to produce the CHMs tetrachloro-4-methoxyphenol (drosophilin A, DA) and tetrachloro-1,4-dimethoxybenzene (drosophilin A methyl ether, DAME). Five fungal strains (two strains of Bjerkandera adusta , Agaricus arvensis, Peniophora pseudopini and Phellinus fastuosus ) produced these metabolites in detectable amounts. Furthermore, the CHM production coincided with the expression of ligninolytic activity.

    P. fastuosus ATCC26.125 was used for further studies to elucidate if the ligninolytic enzymes from this fungus were able to use DA and DAME as substrates. The dominant ligninolytic peroxidase produced by P. fastuosus was a manganese independent peroxidase (MIP), which efficiently oxidizes phenols but not veratryl alcohol nor Mn(II). Purified MIP isozymes were able to oxidize chlorophenolic compounds, including the natural DA and the anthropogenic pentachlorophenol. MIP could not oxidize DAME or other (chlorinated) 1,4-dimethoxybenzenes.

    The CHMs, 2Cl-14DMB, 26DCl-14DMB, DAME and DA were examined as substrates for LiP, which is an important ligninolytic enzyme from Bjerkandera . Our results indicated that 14DMB, 2Cl-14DMB, and DA were substrates for LiP; however, 26DCl-14DMB and DAME were not. According to these results, we concluded that 26DCl-14DMB and DAME do not have a physiological role in lignin degradation, but primarily function as antibiotic agents.

    2Cl-14DMB, which is a LiP substrate, is synthesized by several fungi including the well studied fungus Bjerkandera sp. BOS55. We showed that 2Cl-14DMB, like 14DMB, can replace VA as a cofactor and redox mediator in the catalytic cycle of LiP.

    We demonstrated that LiP oxidized 2Cl-14DMB to 2-chloro-1,4-benzoquinone and two different dimers. Furthermore, EPR results showed the formation of a long-lived 2Cl-14DMB cation radical. The dimer formation and EPR results suggest that the 2Cl-14DMB cation radical is stable enough enabling it to function as a diffussible redox mediator, which can oxidize substrates at a distance of the enzyme. Our results indeed showed that 2Cl-14DMB acts as a redox mediator in the LiP-catalyzed oxidation of the polymeric dye Poly R-478, 4-methoxymandelic acid and oxalate.

    We examined whether 2Cl-14DMB could also replace VA as a cofactor in the LiP-catalyzed oxidation of AA. 2Cl-14DMB enormously stimulated the oxidation of AA, compared to VA. Although our results supported the theory that 2Cl-14DMB closed the catalytic cycle of LiP, we could not directly explain the high molar ratio of p-anisaldehyde formed to 2Cl-14DMB consumed. This high molar ratio indicated that the 2Cl-14DMB cation radical must be recycled back to 2Cl-14DMB. In support of this observation, AA was found to reduce the 2Cl-14DMB cation radical back to 2Cl-14DMB.

    Furthermore, the presence of AA to reduce the 2Cl-14DMB cation radical prevents LiP from H 2 O 2 -inactivation. According to our observations, a mechanism for the behavior of 2Cl-14DMB in the catalytic cycle of LiP and its role in AA oxidation was proposed. In the absence of AA or at low 2Cl-14DMB concentrations, a 2Cl-14DMB cation radical - LiP compound II complex is formed which ultimately results in LiP inactivation. Addition of enough reducing substrate, AA or excess 2Cl-14DMB, reduces the 2Cl-14DMB cation radical - LiP II complex releasing LiP compound II and thereby preventing the inactivation of LiP.

    In conclusion, CHMs were observed to be substrates for ligninolytic enzymes suggesting purposeful roles of these chlorinated metabolites. 2Cl-14DMB was identified as a stable diffussible redox mediator which could have potential application in the improvement of biobleaching and biopulping.

    Regulation of feed intake in sheep : the role of hormones and metabolites
    Leuvenink, H. - \ 1998
    Agricultural University. Promotor(en): D. van der Heide; J. van Bruchem. - S.l. : Leuvenink - ISBN 9789054859482 - 164
    schapen - diervoedering - voeropname - infusie - voedingsstoffen - metabolieten - hormonen - bloed - propionzuur - insuline - sheep - animal feeding - feed intake - infusion - nutrients - metabolites - hormones - blood - propionic acid - insulin

    In the search for factors involved in the regulation of feed intake, many experiments have been performed in various species. In ruminants, very little is known about the physiological background of the mechanisms involved in feed intake regulation. In earlier experiments, much attention was paid to physical regulation suggesting that the capacity of the digestive tract is the most important limiting factor in feeding.

    Since ruminants are capable of meeting their energy requirements under a wide range of circumstances and feedstuffs, the concept of physiological regulation was introduced. Physiological regulation (or metabolic regulation) can be defined as feed-back signals arising from sensors in the periphery, which inform the central nervous system about the metabolic status of the individual. In the brain, presumably in the hypothalamus, these signals are integrated and decisions are made whether or not to eat. This thesis focuses on blood-borne factors related to feed intake in sheep. This includes the major energy providing components, metabolic hormones and gastrointestinal hormones.

    The aim of this thesis is:

    • To gain insight in the changes in nutrient and hormone concentrations following meals of different feed qualities.
    • To investigate blood borne nutrients/hormones which may be involved in the regulation of feed intake.

    To study this, experiments were performed in wether sheep provided with mesenteric, portal and jugular catheters.
    To address the effect of feeding and feed quality on nutrients and hormones, animals were fed during 90 minutes. Before, during and after feeding, blood samples were withdrawn from jugular and portal catheters in order to identify candidates for intake regulation. Two experimental pelleted grass diets, qualified as High Quality (HQ) and Low Quality (LQ) based on crude protein and fibre contents were fed according to a cross-over design.

    In chapter 2, short-term effects of feed intake on jugular and portal concentrations of metabolites such as Volatile Fatty Acids (VFA), Beta-hydroxy-butyrate (BHB) and glucose were studied. Rapid changes were observed in both jugular and portal veins due to feeding. Portal vein (PV) concentrations of acetate, propionate, butyrate, iso-butyrate and BHB were increased post-prandially in HQ-fed sheep. Due to consumption of LQ feed, bi-phasic patterns were found in acetate, propionate, butyrate levels, measured in the jugular vein (JV).

    The effect of feeding on nutrient concentration may largely differ as a result of feed quality. The PV-JV difference was used to estimate the release of nutrients into the portal vein. Differences in peripheral concentration of a blood component did not necessarily result from a difference in the release of the component but could also have resulted from a changed uptake by peripheral tissues. In most cases, the observed early changes (until 30 minutes past meal start) were probably due to changes in uptake rather than alterations in release. The changes observed later then 30 minutes were likely due to changes in release.

    In chapter 3, the response of metabolic and gastrointestinal hormones to feeding is described. Rapid fluctuations were shown for insulin, glucagon, Pancreatic Polypeptide (PP) and Cholecystokinin (CCK) levels in HQ-fed sheep. Sustained changes were observed for insulin, glucagon and gastrin levels in HQ-fed sheep. LQ-fed sheep showed rapid alterations in Growth Hormone (GH), gastrin, PP and CCK levels. Sustained changes were observed for insulin, GH, gastrin, PP and CCK levels.

    The rapid changes in hormone concentration may be due to decreased para-sympathetic activity and/or increased sympathetic activity. More sustained changes were likely nutrient induced. Feed quality mainly affected the magnitude of the meal induced changes in hormone levels, with the HQ-fed sheep showing more pronounced differences.

    In chapter 4, the hypothesis that propionate is a short-term feed intake regulating agent is discussed. In the first experiment, sheep were infused over 20 min with Na-propionate into the mesenteric vein, while monitoring feed intake and feeding pattern over 1.5 hours. Feed intake was reduced by infusions at 2 mmol/min which were associated with marked increases in jugular as well as portal concentrations of insulin, glucose and propionate.

    In a second experiment, animals were infused with 2 mmol/min Na-propionate into the portal vein. No decrease in feed intake was observed, though similar increases in insulin, glucose and propionate as found in mesenteric vein infused animals were observed. It was concluded that mesenteric propionate in high doses acted as a satiety factor. Possible explanations for the difference between site of infusion may be a different distribution of the infusate over the liver, and/or the presence of propionate sensitive receptors in the mesenteric/portal vein region.

    In a more extensive experiment, described in chapter 5, sheep were infused via the mesenteric catheter with 0, 1.5 or 6 mmol/min Na-propionate for 20 minutes. Infusion of 6 mmol/min Na-propionate decreased feed intake but also induced discomfort. Portal levels of propionate, glucose and insulin were increased while decreased levels of butyrate, BHB, gastrin, PP and CCK were observed. Jugular levels generally showed similar patterns as portal levels except for butyrate. Jugular butyrate was immediately increased after start of the meal, presumably due to a smaller liver uptake.

    Infusion of 1.5 mmol/min Na-propionate resulted in elevated levels of propionate and insulin while gastrin and PP concentrations were decreased.
    It was concluded that propionate is not a major factor influencing intake, since infusion of a physiological dose did not affect meal size. It is possible that effects found during and after a meal on insulin, gastrin, and PP can be attributed to propionate.

    Since propionate levels, which affected intake were rather high, and VFA's are reported to stimulate release of insulin, an experiment was performed in which sheep received an infusion with insulin. This study described in chapter 6, was designed to investigate the effect of insulin infusion on feed intake, feeding pattern and blood concentrations of metabolites and hormones related to feeding and feed quality. During a 90 minutes feeding period, sheep provided with jugular, portal and mesenteric catheters were infused via the mesenteric catheter with 6.7 mU/min insulin or saline for 20 minutes. Blood was frequently sampled from jugular and portal veins. The study was performed on two diets differing in feed quality.

    Infusion of insulin did not decrease feed intake but decreased feeding time. Portal insulin levels of sheep receiving an insulin infusion were increased in animals fed a low quality diet but not in animals fed a high quality diet. Insulin levels in the jugular vein were not influenced by infusion of insulin compared to saline infusion. No differences due to infusion of insulin were shown on glucose, glucagon, gastrin, and PP levels. Effects of diet composition were reflected by glucagon levels but not by other hormones.

    It was concluded that insulin might be a factor involved in satiety, but not by regulation of meal size. It was also postulated that regulation of endogenous insulin release might be more sensible in animals fed a higher feed quality.

    In chapters 7 and 8, the results are presented of a combined infusion of CCK (two dosages) and Na-propionate. In chapter 7, the effect of the 20 minutes infusion with 0, 1.2 or 2.4 nmol/min CCK-8 is described. Infusion of CCK-8 increased levels of CCK-8 in the portal vein but not in the jugular vein. A very accurate clearance of CCK-8 from the liver may have attributed to the absence of increased jugular levels. Infusion of both 1.2 and 2.4 nmol/min CCK-8 decreased portal and jugular CCK-33 levels, suggesting a decreased endogenous release of CCK. Portal PP levels were decreased as a result of 2.4 nmol/min CCK-8 infusion. This may be due to a decrease in release or an enhanced portal blood flow.

    Cortisol concentrations, as an indicator of stress, were decreased during infusion of saline but increased as a result of CCK-8 infusion. It was concluded that CCK-8 might have induced some discomfort. Despite the increased portal CCK-8 levels and the increased cortisol levels no effect was found on feed intake.

    In chapter 8, the effect of an infusion with 0, or 2.4 nmol/min CCK-8 or 0.5 mmol/min propionate or a combination of CCK and propionate are described.
    Feed intake was only reduced by combined infusion of CCK-8 and propionate but not by separate infusion of CCK-8 or propionate. Increased levels of propionate and insulin were observed following the propionate infusion. Infusion of CCK decreased propionate, acetate, butyrate, and glucose levels while insulin levels were initially increased followed by decreased levels. Combined infusion of CCK and propionate induced similar blood concentration as infusion of CCK solely on acetate, butyrate, glucose, and insulin, while propionate levels were decreased compared to propionate infused animals but increased compared to CCK infused sheep.

    It was postulated that decreased levels of VFA's and insulin may be due to increased portal flow and that mechanisms of induction of insulin secretion by propionate and CCK may be different.
    In chapter 9, some of the observations made in the preceding chapters are analysed using a conceptual model. The model proved very suitable in explaining profiles of hormones and metabolites following feed intake. It also proved useful in interpreting the effects the infusion studies. One of the major observations was that release and uptake are usually very tightly matched even during infusion of large amounts of propionate. It also showed that changed plasma concentration may arise from changed uptake (in case of the early peak in jugular propionate following feeding) or changed release (in case of insulin increase following feeding).

    Finally, in the general discussion (chapter 10) some remarks are made concerning the possible role of hormones and metabolites in the regulation of feed intake.
    In conclusion, as a result of feeding, sheep showed both rapid and more sustained changes in plasma concentration of several metabolites and hormones. Furthermore, differences in feed quality may result in differences in hormone and metabolite concentration but also in differences in plasma profiles.

    The infusion studies with propionate, insulin and CCK indicated that the regulation of intake must be regarded as a multifactorial process. It is therefore necessary to study intake regulation as a multifactorial system bearing in mind that gross manipulations may influence other systems involved in intake regulation. Experiments with low (physiological) dosages of combinations of hormones and metabolites should be performed to elucidate the concerted role of these substances.

    Ontwikkeling van een detectiemethode voor hemoglobine-addukten, nitro-polycyclische aromatische koolwaterstoffen en metabolieten met behulp van gaschromatografie-massaspectrometrie
    Zuidema, T. ; Traag, W.A. - \ 1994
    Wageningen : DLO-Rijks-Kwaliteitsinstituut voor Land- en Tuinbouwprodukten (Rapport / RIKILT-DLO 94.07) - 16
    hemoglobine - derivaten - organische stikstofverbindingen - metabolieten - gc-ms - polycyclische aromatische koolwaterstoffen - haemoglobin - derivatives - organic nitrogen compounds - metabolites - gc-ms - polycyclic aromatic hydrocarbons
    Plasma disposition, metabolism and residue aspects of flumequine and sodium salicylate in broilers after water medication
    Moutafchieva, R. ; Nouws, J.F.M. ; Keukens, H.J. ; Kan, C.A. ; Beek, W.M.J. ; Streutjens, E. ; Hoogenboom, L.A.P. ; Holthuijzen, Y.A. - \ 1993
    Wageningen : State Institute for Quality Control of Agricultural Products (Report / RIKILT-DLO 93.22) - 38
    bactericiden - natriumsalicylaat - vleeskuikens - farmacologie - metabolisme - metabolieten - bactericides - sodium salicylate - broilers - pharmacology - metabolism - metabolites
    Ontwikkeling van fysiologische screenings- en monitoringsmethoden via metabolietprofilering met NMR : testonderwerp: urinecompositie van met beta-agonisten behandelde mestkalveren
    Lommen, A. ; Huf, F.A. ; Schilt, R. ; Groot, M. ; Berende, P.L.M. - \ 1991
    Wageningen : DLO-Rijks-Kwaliteitsinstituut voor Land- en Tuinbouwprodukten (Rapport / RIKILT-DLO 91.56) - 20
    urine-analyse - bèta-adrenerge agonisten - metabolieten - kernmagnetische resonantiespectroscopie - kalveren - creatine - melkzuur - urine analysis - beta-adrenergic agonists - metabolites - nuclear magnetic resonance spectroscopy - calves - creatine - lactic acid
    In dit onderzoek zijn met behulp van NMR (Nuclear Magnetic Resonance) potentiele parameters (lactaat- en creatine-concentratie) gevonden in mestkalverurine, waarmee in praktijk gescreend kan worden op het gebruik van beta-agonisten.
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