Differences in metabolomic profiles of APOE4 carrier vs non‐carrier patients undergoing therapeutic plasma exchange with albumin replacement as a treatment for Alzheimer’s disease

Abstract

AbstractBackgroundApolipoprotein E is the major apolipoprotein found in plasma, involved in lipid transport and metabolism. Carrying the ε4 allele of the APOE gene (ApoE4) is a risk factor for developing Alzheimer’s disease (AD) and is associated with altered plasma lipid levels and lipoprotein particle distribution. The AMBAR phase 2b/3 trial is a therapeutic approach for AD patients (MMSE:18‐26) based on a 14‐month program comprising 18 plasma‐exchange procedures with albumin replacement (PE‐Alb) to remove pathological substances from plasma, slowing AD progression. The aim of this study was to assess PE‐Alb differential effects on metabolites across the AMBAR trial between ApoE4 carriers and non‐carriers.Method442 metabolites were quantified in serum samples of 296 ApoE‐genotyped patients included in the AMBAR trial (225 PE‐Alb‐treated and 71 placebo), at 3 time‐points, using high‐throughput UHPLC‐MS (OWL‐Metabolomics, Spain). Data was stratified by ApoE4 carriers (n = 145) and non‐carriers (n = 151) and analyzed through a mixed model for repeated measures. Differences from placebo were assessed through month*treatment group interaction estimates. Reported p‐values were adjusted by Benjamini‐Hochberg procedure.ResultBaseline differences between ApoE4 carriers and non‐carriers were found according to what has been reported in the literature. In ApoE4 carriers, 29 metabolites significantly changed (Adjusted p‐value<0.05) in PE‐Alb‐treated patients compared to placebo at end of study (month 14). Eleven of them, which were in the free Fatty Acids (FA) class (6 monounsaturated‐FA, 3 polyunsaturated‐FA, 2 saturated‐FA), were down regulated. This would agree with the previously reported finding that free‐FA levels increase in blood from AD patients and participate in the pathogenesis of AD by multiple mechanisms. In Non‐carriers, 19 metabolites showed statistically significant change at month 14, 2 of them being downregulated. In both stratifications, most upregulated metabolites were in the Glycerophospholipid class (21/35) which has been reported to be decreased in AD. All other metabolites were in the Glycerolipids (4), Sphingolipids (4), Sterols (3), Bile acids (2) and Amino Acids (1) classes.ConclusionThese results demonstrate modulation of fatty acid metabolism in PE‐Alb‐treated patients from the AMBAR trial in relation to its ApoE genotype. Furthermore, treatment induced positive metabolite changes compared to placebo. These results deserve further investigation.