Polymeric Complements to the Alzheimer's Disease Biomarker β-Amyloid Isoforms Aβ1-40 and Aβ1-42 for Blood Serum Analysis under Denaturing Conditions

Treatment of Alzheimer's diesease (AD) is plagued by a lack of practical and reliable methods allowing early diagnosis of the disease. We here demonstrate that robust receptors prepared by molecular imprinting successfully address current limitations of biologically derived receptors in displaying affinity for hydrophobic peptide biomarkers for AD under denaturing conditions. C-terminal epitope-imprinted polymers showing enhanced binding affinity for A beta 1-42 were first identified from a 96-polymer combinatorial library. This information was then used to synthesize molecularly imprinted polymers for both of the beta-amyloid (A beta) isoforms and a corresponding nonimprinted polymer. A solid-phase extraction method was developed to be compatible with sample loading under conditions of complete protein denaturation. This resulted in a method capable of quantitatively and selectively enriching a shorter C-terminal peptide corresponding to the sequences A beta 33-40 and A beta 33-42 as well as the full-length sequence A beta 1-40 and A beta 1-42 from a 4 M guanidinum chloride solution. Application of the method to serum allowed selective, high-recovery extraction of both biomarkers at spiking levels marginally higher than clinically relevant concentrations found in cerebrospinal fluid.