An inhibitor-free assay of acetylcholinesterase and butyrylcholinesterase in the cerebrospinal fluid

An inhibitor-free assay for the simultaneous determination of acetylcholine sterase (AChE) and butyrylcholinesterase (BChE) in the cerebrospinal fluid (CSF) is described. It is based on our finding that the individual activity ratios of EChE on both its substrates acetylthiocholine (ACh) and butyrylt hiocholine (BCh) in the CSF and in the parallel serum are identical under c onditions of at least 5 mmol/l substrate concentration (Q(SE)(BChE) = Q(CSF )(BChE)). Considering that AChE only reacts with ACh as substrate and occur s with negligible activities in the serum, the measured individual activity ratio of BChE in the serum (Q(SE)(BChE)) and the total hydrolysis rate of ACh and BCh in the CSF do allow a precise calculation of the AChE activity in the cerebrospinal fluid. The derivation of the corresponding formula is demonstrated in detail. The inhibitor-free assay was compared with procedur es using cholinesterase inhibitors (BW284c51 for AChE and/or iso-OMPA for B ChE). Achieving widely identical results in particular between the procedur e using the AChE inhibitor and the inhibitor-free test, the latter has deci sive advantages: (1) it avoids the use of highly toxic inhibitors, (2) it m inimizes the test volume needed, (3) it characterizes additionally the stat us of the blood-CSF barrier by means of the BChE activity ratio in the CSF and in the parallel serum. (C) 1999 Elsevier Science BN. All rights reserve d.