The Relationship Between Uracil Metabolism and the Dihydropyrimidine Dehydrogenase Enzyme in Human Liver

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dc.contributor.advisor Helsby, N en
dc.contributor.advisor Tingle, M en Mcgillivray, Brent en 2014-08-04T03:21:35Z en 2014 en
dc.identifier.citation 2014 en
dc.identifier.uri en
dc.description Full text is available to authenticated members of The University of Auckland only. en
dc.description.abstract 5-fluorouracil (5-FU), a commonly used chemotherapeutic drug, is associated with severe toxicity in 30-40% of patients. Dihydropyrimidine dehydrogenase (DPD), an enzyme primarily active in the liver, catalyses the initial step in the degradation of 5- FU. As such, patients who are DPD-deficient are at risk of drug-related toxicity. DPD also catalyses the conversion of uracil (U) to dihydrouracil (UH2). Consequently, the ratio of UH2/U in plasma has been proposed as a biomarker of DPD activity to identify individuals at risk of 5-FU toxicity. However, the relationship between this ratio and liver-DPD activity has not been directly confirmed in humans. The aim of this thesis was to investigate the correlation between the UH2/U ratio and inter-individual variation in the DPD enzyme in human liver samples. An electrospray ionisation LC/MS assay was developed to quantify U and UH2 in human liver cytosol. The precision and accuracy of the assay met the FDA guidelines, with limits of detection of 0.21 μM and 0.05 μM for U and UH2 respectively. The endogenous UH2/U ratio in 18 liver samples was measured and >4000-fold inter-individual variation was observed. Metabolic loss of endogenous U and formation of UH2 with incubation time was then assessed in the cytosol from a subset of livers (n=9). A computational method modelled the sequential pathways of endogenous uracil metabolism in liver; this gave an excellent fit to the experimental data (r2≥0.86). DPD activity ranged from 1.12 - 128.39 pmol/min/mg in the nine livers. There was a significant linear correlation between the DPD activity and hepatic UH2/U ratio (r2= 0.723, p= 0.004, n=9). Thus, the UH2/U ratio appears to be a valid indirect measure of DPD activity in this tissue. Hepatic DPD activity has previously been studied in animal models, but few if any reports of the human liver activity with uracil as a substrate appear in the literature. The data in this thesis provides important confirmation of the relationship between uracil conversion to UH2 and human liver DPD. This may aid the further evaluation of the plasma UH2/U ratio as a suitable pre-treatment biomarker of adverse patient response to 5-FU. en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof Masters Thesis - University of Auckland en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights Restricted Item. Available to authenticated members of The University of Auckland. en
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dc.rights.uri en
dc.title The Relationship Between Uracil Metabolism and the Dihydropyrimidine Dehydrogenase Enzyme in Human Liver en
dc.type Thesis en The University of Auckland en Masters en
dc.rights.holder Copyright: The Author en
pubs.elements-id 448510 en
pubs.record-created-at-source-date 2014-08-04 en

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