Changes in buccal cytome biomarkers in relation to ageing and Alzheimer’s Disease.

Abstract

The aim of this thesis was to investigate the possibility of using buccal cells derived from a multi layered epithelial tissue from the oral mucosa as a model to identify potential biomarkers of genomic instability in relation to normal ageing and premature ageing syndromes such as AD and DS. A buccal micronucleus cytome assay was developed and used to investigate biomarkers for DNA damage, cell proliferation and cell death in healthy young, healthy old and young Down’s syndrome cohorts. Cells with micronuclei, karyorrhectic cells, condensed chromatin cells and basal cells increased significantly with normal ageing (P<0.0001). Cells with micronuclei and binucleated cells increased (P<0.0001) and condensed chromatin, karyorrhectic, karyolytic and pyknotic cells decreased (P<0.002) significantly in Down’s syndrome relative to young controls. The buccal micronucleus cytome assay was used to measure ratios of buccal cell populations and micronuclei in clinically diagnosed Alzheimer’s patients compared to age and gender matched controls. Frequencies of basal cells (P<0.0001), condensed chromatin cells (P<0.0001) and karyorrhectic cells (P<0.0001) were found to be significantly lower in Alzheimer’s patients, possibly reflecting changes in the cellular kinetics or structural profile of the buccal mucosa. Changes in telomere length were investigated using a quantitative RTm-PCR method to measure absolute telomere length (in Kb per diploid genome) and show agerelated changes in white blood cells and buccal cell telomere length (in kb per diploid genome) in normal healthy individuals and Alzheimer’s patients. We observed a significantly lower telomere length in white blood cells (P<0.0001) and buccal cells (P<0.01) in Alzheimer’s patients relative to healthy age-matched controls (31.4% and 32.3% respectively). However, there was a significantly greater telomere length in hippocampus cells of Alzheimer’s brains (P=0.01) compared to control samples (49.0). Buccal cells were also used to investigate chromosome 17 and 21 aneuploidy. A 1.5 fold increase in trisomy 21 (P<0.001) and a 1.2 fold increase in trisomy 17 (P<0.001) was observed in buccal cells of Alzheimer’s patients compared to age and gender matched controls. Chromosome 17 and chromosome 21 monosomy and trisomy increase significantly with age (P<0.001). Down’s syndrome, which exhibits similar neuropathological features to those observed in Alzheimer’s disease also showed a strong increase in chromosome 17 monosomy and trisomy compared to matched controls (P<0.001). However, aneuploidy rate for chromosome 17 and 21 in the nuclei of hippocampus cells of brains from Alzheimer’s patients and controls were not significantly different. Observations that AD individuals have altered plasma folate, B12 and Hcy levels compared to age-matched controls who have not been clinically diagnosed with AD were investigated. Genotyping studies were undertaken to determine whether polymorphisms within particular genes of the folate methionine pathway contributed to AD pathogenesis. Correlations between folate, B12 and Hcy status with previously determined buccal micronucleus assay cytome biomarkers for DNA damage, cell proliferation and cell death markers was investigated. Lastly, the potential protective effects of phytonutrient polyphenols on genomic instability events in a transgenic mouse model for AD were investigated. We determined the effects of curcumin and GSE polyphenols on DNA damage by testing the mice over a 9 month period utilizing a buccal micronucleus cytome assay, an erythrocyte micronucleus assay and measuring telomere length in both buccal cells and olfactory lobe brain tissue.