Determination of acetylcholinesterase and butyrylcholinesterase activity without dilution of biological samples

Two cholinesterases: acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), are known. The enzymes are important in the body and alteration of their activity has significant use in the diagnosis of poisoning, liver function, etc. Currently available methods for the determination of cholinesterases have some major drawbacks including various interferences and the inability to be used for decreasing the enzyme activity in the presence of reversible inhibitors due to sample dilution; hence, a method for dilution free assay of cholinesterases is desired. Here, microplates were modified with indoxylacetate (100 µL of 10 mmol L^?1 solution) and used for cholinesterases assay after drying at 37°C. The fact that indoxylacetate remains stable in dry state and serves simultaneously as a chromogen and substrate provide good prerequisites for the method. The limit of detection for BChE was 0.71 U while that for AChE was 2.8 U per a 100 µL sample (solution of enzyme or plasma sample). The limit of detection is low enough to allow standard examination of cholinesterasemia. The two cholinesterases can be distinguished from each other using selective inhibitors such as donepezil and iso-OMPA. The new method was also successfully validated for the standard Ellman’s assay using plasma samples with BChE activity adjusted by carbofuran. The new method based on indoxylacetate seems promising for routine tests.