Author: Carly Jane Moores
Moores, Carly Jane, 2014 The effect of dietary micronutrients and micronutrient supplementation on telomere length, Flinders University, School of Health Sciences
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Telomeres are nucleoprotein complexes, which cap the ends of linear chromosomes to prevent against chromosome end-to-end fusions in the cells. The underlying DNA sequence in humans is a TTAGGG hexamer that is repeated many times at each telomere. Due to the end-replication problem at DNA ends, the length of the telomere sequence shortens with each cycle of cell division. Telomere length has been associated with chronic disease, markers of oxidative stress and inflammation as well as diet patterns and individual nutrients. Evidence in the literature indicates that telomere length has both elements of heritability and may be modified by various environmental exposures including diet. However, the relationship of telomere length with dietary micronutrients in Australian populations has been largely unexplored. Additionally, the possibility that nutrients can influence telomere length in humans gives rise to the opportunity to modify telomere length through targeted dietary interventions. A double-blinded micronutrient intervention randomised controlled trial (RCT) - the Polypill study - provided the opportunity to assess changes in telomere length over time in a metropolitan Australian population. Peripheral blood mononuclear cell (PBMC) telomere length in a healthy cohort of middle-aged South Australians was measured and cross-sectional associations with demographic and anthropometric variables were explored. Plasma levels of dietary micronutrients such as vitamin D and the metabolite homocysteine (associated with B vitamin deficiency) were correlated with telomere length. Vitamin D was found to be positively associated with PBMC telomere length while plasma homocysteine was inversely associated with PBMC telomere length. The Polypill double-blinded RCT investigated changes in PBMC telomere length following 16 weeks of treatment with a micronutrient supplement containing folic acid, vitamin B12, vitamin E, retinol, nicotinic acid and calcium (FBERNC) and compared this change to participants who received an inactive placebo. When groups were compared, there were no significant differences in the mean changes in telomere length over time. Additionally, there was no significant difference in the proportions of individuals placed in telomere length trajectory groups defined as telomere sequence loss, maintenance or gain. It was hypothesised that the integrity of the telomere sequence may be a more valuable biomarker than telomere length alone to assess responses to B vitamin supplementation. As uracil misincorporates in to the genome under low folate conditions, a qPCR method to detect uracil within the telomere sequence was conceived and optimised. The reproducible assay was developed with the use of synthetic uracil-containing primers and was then applied to DNA extracted from the WIL2-NS human lymphoblastoid cell line cultured in vitro under low folic acid and with supplemented dUTP. Next, in vitro modelling with various concentrations of folic acid, dUTP and additionally S-adenosyl methionine (SAM) were performed with the WIL2-NS cell line. There were no clear trends of either folic acid, dUTP or SAM on cell viability, telomere length, telomeric uracil content nor global methylation. Additionally, complex but statistically significant interactive effects for each of the experimental endpoints were noted indicating the possibility of strong homeostatic mechanisms regulating telomere integrity under conditions of folate deficiency and dUTP excess.
Keywords: telomeres,telomere length,telomere integrity,RCT,diet,micronutrients,supplements,uracil,folic acid
Subject: Nursing thesis
Thesis type: Doctor of Philosophy
School: School of Health Sciences
Supervisor: Dr Nathan O'Callaghan