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A study of the global effects of Apolipoprotein E using lipidomics.

Hawksworth, Jade 2019. A study of the global effects of Apolipoprotein E using lipidomics. PhD Thesis, Cardiff University.
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Abstract

Apolipoprotein E (APOE) has been widely studied, as common gene variants can predispose towards a range of conditions, including late-onset Alzheimer’s disease (LOAD). The rarest variant, APOE ε2, lowers risk of LOAD, whilst APOE ε4 raises the risk of developing this disorder. APOE ε3, which is the most common variant, does not alter risk of LOAD. Plasma from human homozygotes for all 3 common APOE alleles (described herein as APOE 22, APOE 33 and APOE 44) was analysed using lipidomics for the first time. Initial method optimisation and testing of methods investigated extraction efficiency, which is the recovery efficiency of the total lipid in the sample. Also, coefficient of variation (CV) was tested, which is variation within the method of measurement when identical samples are injected. Optimisation demonstrates that extraction efficiency is high and CV low, and both are in accordance with other publications. In the first experiment, LC-MS analysis of plasma from APOE homozygotes revealed sphingolipids and glycerophospholipids are reduced in APOE 22, both before and after Benjamini-Hochberg (BH) correction. Multivariant analysis can separate APOE 22 plasma from APOE 33 . There are very few differences between APOE 44 plasma and APOE 33, and BH correction removes all significant differences between alleles. Multivariate analysis can separate both APOE 22 and APOE 44 from APOE 33 plasma. Targeted LC-MS/MS analysis of cholesterol and select cholesterol ester and triacylglycerol species demonstrates few species which differ between the alleles. Unexpectedly, some cholesterol esters are higher in APOE 33 participants, however, total cholesterol was also unexpectedly high in this group. In a second experiment, the effect of ApoE and 12/15-lipoxygenase (12/15-LOX) deficiency (ApoE-/- and Alox12/15-/-, respectively) was tested in two behavioural models, the “novel object test” and the “object-in-place test”. The “novel object test” measures recognition memory, which is the ability to distinguish a novel object from a known object. The “object2 in-place test” measures recollection memory, which is a test of spatial memory. ApoE-/- is not associated with a deficit in recognition memory but does cause impairment of recollection memory, as measured by the above tests. In line with previous research, these data indicate that ApoE supports recollection memory. A protective effect of 12/15-LOX inhibition has been observed in mouse models of Alzheimer’s disease, however, variability in the ApoE-/-/Alox12/15-/- double knock out mouse data prevents any conclusions being drawn about this group. Some 12/15-LOX esterified products are significantly higher in the ApoE-/- mice, and these may correlate with recollection memory. Further experiments are needed to confirm this finding.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Medicine
Date of First Compliant Deposit: 13 September 2019
Last Modified: 13 Sep 2019 13:08
URI: http://orca-mwe.cf.ac.uk/id/eprint/125437

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