Search

Purpose: With the move towards development of disease modifying treatments, there is a need for a more specific early diagnosis of mild cognitive impairment (MCI) and Alzheimer’s disease (AD). Plasma biomarkers are likely to play an important role in this. This thesis comprises a series of studies to examine established and novel plasma biomarkers of cognitive disorders, in particular MCI and AD, and their progression. Methods: A meta-analysis was undertaken to evaluate whether plasma amyloid beta (Aβ) levels are an appropriate biomarker in cross-sectional and longitudinal studies of AD. A proteomics approach was then used to screen for MCI and AD protein biomarkers in pooled plasma in a cohort of 280 MCI, 19 AD and 411 cognitively normal subjects. Based on the proteomics data, multiplex bead immunoassay techniques were used to validate targeted protein biomarkers in individual samples. Results: Meta-analysis results showed that in longitudinal studies cognitively normal individuals who converted to AD had higher baseline Aβ1-40 and Aβ1-42 levels, and a non-significantly increased Aβ1-42/ Aβ1-40 ratio. Systematic review suggests a model of differential longitudinal changes in plasma Aβ levels in cognitively stable individuals versus those who go on to develop AD dementia. A proteomics study using isobaric tags for relative and absolute quantitation (iTRAQ) showed 30 proteins significantly dysregulated in MCI and AD, including ApoA1, ApoA2, ApoB100, ApoH, ApoJ (clusterin), vitamin D binding protein (VDBP), Ig mu chain C region (IGHM) and afamin. Western blot results confirmed iTRAQ results: IGHM was increased and afamin was decreased in the MCI and AD groups. A group of seven apolipoproteins, β2 microglobulin, haptoglobin, C-reactive protein and VDBP were assayed by multiplex assays. Lower ApoA1, ApoA2 and ApoH levels, and a higher ApoB/ApoA1 ratio, increased the risk of cognitive decline over two years in cognitively normal in

In spite of impressive recent progress, the aetiopathogenesis of Alzheimer’s disease (AD) remains incompletely understood. The distinctive neuropathological features of AD, in particular the plaques and tangles, have been the particular focus of most aetiological theories. It is well accepted that AD is a multifactorial disease, with alterations to a variety of brain structures and cell types, including neurons, glia and the brain vasculature. Studies of risk factors have revealed a diversity of genetic variables that interact with health, diet and lifestyle-related factors in the causation of AD. These factors influence the structure, aggregation and function of a set of proteins that are increasingly the focus of research. The work in this thesis has focused on the pathophysiological aspects of some of these proteins in a number of cellular compartments and brain. Several assays have been established and techniques utilized in the completion of this work, including; differential detergent fractionation of brain tissue, 1D and 2D PAGE, western blotting with chemiluminescence detection, ELISA assays of Abeta 1-40 and 1-42, quantitative ECNI GCMS of o- and m-tyrosine as well as metabolites of the kynurenine pathway, quantitative MALDI-TOF assay of hemorphins and LCMSMS based proteomics, to identify proteins with altered expression levels in AD relative to control brain tissue. A variety of regional differences have been observed in the biochemistry of the AD cortex which are probably the outcome of local response variations to AD pathology. One of the most consistent threads throughout this work has been an apparent resilience of the occipital lobe relative to the other brain regions, as reflected in lower overall levels of oxidative stress and increased levels of proteins associated with metabolic processes, neuronal remodeling and stress reduction.