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  Comparative efficacy of dietary broccoli in F344 rats: relation between glucosinolate content, myrosinase and bioactivity
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 Ophav:
Søndergaard, Mette1, Forfatter
Jeffery, Elizabeth H.1, Vejleder
Sørensen, Hilmer1, Vejleder
Sørensen, Jens Christian1, Vejleder
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1Det Biovidenskabelige Fakultet, København, Danmark
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 Abstract: Epidemiological studies show a correlation between intake of cruciferous vegetables and decreased cancer risk. This effect is attributed to the high content of phytochemicals termed glucosinolates. Glucosinolates release bioactive isothiocyanates upon hydrolysis by the enzyme myrosinase. The aliphatic isothiocyanates are in relative fast reactions transformed into thiocarbamates (e.g. oxazolidine-2-thiones), dithiocarbamates and thiourea, depending on the presence of nucleophiles and reaction conditions. Isothiocyanates and their conjugates are associated with the downregulation of phase I and upregulation of phase II metabolism enzymes, which are correlated to activation of carcinogenic compounds and chemoprevention, respectively. Broccoli in particular has received attention for its high content of glucoraphanin, which by myrosinase catalyzed hydrolysis release the isothiocyanate sulforaphane. Sulforaphane and its conjugates are believed to be connected to many of the beneficial effects from cruciferous vegetables.Broccoli is for the most part consumed cooked or processed, which is believed to inactivate myrosinase and thereby minimize the exposure to glucosinolate derived bioactive compounds. Glucosinolates may, however, be hydrolyzed non-enzymatically or by microbiota in the gastrointestinal tract, whereby beneficial effects may still be obtained. The objectives of this study were to compare the bioactivity of dietary broccoli (unheated and heated) and broccoli seeds in colon and liver of F344 rats, and to elucidate the relation between myrosinase activity and glucosinolate content on bioactivity. In this study, there was shown a direct correlation between intake of dietary broccoli florets and upregulation of the phase II enzyme NAD(P)H-quinone oxidoreductase in both liver and colon. Heat-treated broccoli as well as broccoli seeds showed induction of colonic but not hepatic NAD(P)H-quinone oxidoreductase. It was difficult to conclude if these effects were associated with a decrease in myrosinase activity or by lower glucosinolate intake. Both heated and non-heated broccoli diets were shown to upregulate the phase I enzyme ethoxyresorufin O-deethylase in liver, whereas the broccoli seed diet showed no induction. These effects were correlated to the difference in aliphatic and indole glucosinolate intake. The 1,2-benzenedithiol cyclocondensation assay was applied to measure isothiocyanate and conjugate concentration in both plant tissue and human plasma samples. The detection was, however, complicated by presence of other compounds.
 Abstract: Epidemiologiske undersøgelser har vist en sammenhæng mellem indtag af Brassica grøntsager og lavere risiko for udvikling af cancer. Denne effekt menes at hænge sammen med en gruppe af phytostoffer kaldet glucosinolater. Hydrolysering af glucosinolater er katalyseret af enzymet myrosinase og resulterer i fraspaltning af bioaktive isothiocyanater. Alifatiske isothiocyanater omdannes i relative hurtige reaktioner til thiocarbamater (oxaxolidine-2-thioner), dithiocarbamater og thiourea, alt afhængig af reaktionsforholdene og tilstedeværelse af nukleofile stoffer. Isothiocyanater og deres konjugater er associeret med nedregulering af fase I og opregulering af fase II enzymer, der er affilieret med henholdsvis aktivering af carcinogene stoffer og chemoprævention. Broccoli er især interessant pga. det høje indhold af glucoraphanin, der omdannes af myrosinase til isothiocyanaten sulforaphane. Sulforaphane og dets konjugater menes at hænge sammen med de positive associeret med Brassica grøntsager.Broccoli spises for det meste kogt eller forarbejdet på anden vis, hvilket menes at inaktivere myrosinase og dermed minimere mængden af bioaktive stoffer fra glucosinolater. Det er dog muligt, at glucosinolater hydrolyseres non-enzymatisk eller af bakterier i mave-tarmsystemet, og at de positive effekter dermed stadig opnås. Formålet med dette projekt var at sammenligne bioaktiviteten af broccoli (varmet og ubehandlet) og broccolifrø i tyktarm og lever i F344 rotter, og at undersøge bioaktiviteten mht. myrosinaseaktivitet og indhold af glucosinolater.Der blev vist en direkte sammenhæng mellem indtag af broccoli og upregulering af fase II enzymet NAD(P)H-quinone oxidoreductase i både tyktarm og lever. Varmet broccoli og broccolifrø viste upregulering af NAD(P)H-quinone oxidoreductase i tyktarmen men ikke i leveren. Det var svært at konkludere om denne effekt skyldes lav myrosinaseaktivitet eller er i stedet associeret med glucosinolatindholdet. Både varmet og ubehandlet broccoli upregulerede fase I enzymet ethoxyresorufin O-deethylase i lever, hvorimod broccolifrø ikke viste nogen virkning. Denne effekt hænger sandsynligvis sammen med forholdet mellem alifatiske og indolglucosinolater. 1,2-benzenedithiol cyclokondensation assayet blev brugt til at måle mængden af isothiocyanater og deres konjugater i både plantemateriale og plasmaprøver. Detektionen var dog besværliggjort af den store mængde af andre stoffer i prøverne.
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Bogmærk denne post: https://diskurs.kb.dk/item/diskurs:12885:1
 Type: Speciale
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Sprog: English - eng
 Datoer: 2009
 Sider: 88 pages
 Publiceringsinfo: København, Danmark : Institut for Grundvidenskab og Miljø
 Indholdsfortegnelse: -
 Note: Biology - Biotechnology, Biologi - Bioteknologi
 Type: Speciale
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