Evaluation of a technique to identify acetylcholinesterase C-terminal peptides in human serum samples

A novel theory for neurodegeneration is that non-cholinergic functions of acetylcholinesterase (AChE) are responsible for the progressive death of global neurons. The C-terminal region of AChE has been shown to be responsible for non-cholinergic actions of AChE by binding to an allosteric site on the alpha 7-nicotinic acetylcholine receptor, thereby causing calcium influx; the resultant signal has trophic effects in immature neurons, but toxic effects in mature neurons. Although there is strong in vitro and in vivo evidence for the involvement of this C-terminal region of AChE in neurodegeneration, a cleaved C-terminal peptide has not yet been identified in human brains. This preliminary study aimed to identify the cleaved AChE C-terminal peptide in serum from human Alzheimer's disease patients using immunoaffinity purification. A number of antibodies were tested for sensitivity and specificity towards peptide sequences from the C-terminus. Although the antibodies were able to identify peptide in vitro, peptide was not detected using immunoaffinity purification of human serum, possibly due to insufficient detection limits of the antibody. Therefore more sensitive techniques are required to identify cleaved AChE C-terminal peptides in human samples. None the less, C-terminal AChE peptide might act as a signalling molecule in an as yet unexplored system.