Abstract
Background
Apolipoprotein E (APOE) is a well-known genetic risk factor for Alzheimer's disease (AD). APOE is now being investigated at the protein level, and studies indicate the levels of this protein may reflect disease status as well. Therefore, plasma APOE has been measured as a potential AD biomarker for the future development of an early AD blood diagnostic.
Methods
Total APOE protein levels were measured in the 18-month follow-up plasma samples from 968 individuals participating in the Australian Imaging, Biomarkers and Lifestyle (AIBL) Longitudinal Study of Ageing using commercial Luminex 96 well assay kits. Total APOE plasma levels were then compared between non-memory complainers (NMC), subjective memory complainers (SMC), mild cognitively impaired (MCI) individuals and AD patients. The data was further compared against other collected demographics including but not limited to cerebral amyloid load as measured by positron emission tomography (PET), APOE genotype and neuropsychological scores.
Results
Total protein APOE levels were significantly lower in the AD cohort, as compared to both the NMC and SMC groups. No significant correlation was found, at this time, between APOE levels and cerebral amyloid beta load, however, further analysis will determine the relationship between plasma APOE and plasma Aβ levels. Significant differences in plasma APOE levels were observed between different genotypes as well. In general, those with the E4/E4 genotype have the lowest levels of plasma APOE.
Conclusions
APOE shows great promise as an AD biomarker for the future development of an AD diagnostic assay with its altered protein levels between AD and control participant groups. Completed measurements of baseline plasma samples from the same individuals will add great value to this study, by analysing the changes in plasma APOE over time. The significance of these findings can be determined further as the AIBL longitudinal study of ageing continues.