S1‐02‐01: Multiplexed analysis of plasma in Alzheimer's disease

Abstract

Alzheimer's disease (AD) is the most common form of dementia. Worldwide 28 million dementia suffers have yet to receive a diagnosis - at least partly due to a lack of a non-invasive diagnostic test. The development and use of potential disease modifying agents is also limited by the absence of fully approved biomarkers; especially those that can be used on repeated occasions and have predictive value. We set out to discover peripheral plasma-based biomarkers using two-dimensional gel electrophoresis in combination with mass spectrometry (MS). We showed differential expression of two proteins; complement factor H (CFH) and alpha-2-microglobulin (A2M) in a case versus control study. Subsequently, using 1 H-magnetic resonance spectroscopy, we have also demonstrated that CFH and A2M are associated with hippocampal metabolite abnormalities in AD. There is considerable heterogeneity in disease progression in AD. In order to address complexity of the condition, we then sought to discoverer markers correlating with other measures or endophenotypes of disease. These included neuroimaging and cognitive measures. We identified an association of plasma clusterin concentration with brain atrophy, disease severity and rate of progression. We further related peripheral clusterin with another distinct endophenotype of AD pathology, specifically in vivo brain amyloid burden, in both man using 11 C Pittsburgh Compound B PET imaging, and in a transgenic mouse model of AD over expressing APP and presenilin (PS)1 mutations 3. Furthermore, to address disease progression we stratified our AD subjects into fast and slow decliners and identified two novel markers; gelsolin and transtyhretin. I will review here the current approaches we have undertaken to multiplex our discovery biomarkers to achieve sensitive and robust measurements. Since our first studies, multiple analytes have now been identified and the advent of multiplexing has made validation studies easier. We have therefore adopted two approaches; Luminex xMAP and SRM (Single reaction monitoring) mass spectrometry techniques to validate our findings. Our findings suggest that plasma-based markers have the potential to be a companion diagnostic tool. Our aim is to combine plasma based biomarkers with clinical, imaging and genomic measures, to achieve a sensitive and specific multimodal Alzheimer's disease biomarker panel.