Methodological and biological aspects to be considered in cholinesterase reactivation techniques with oxime reagents

Abstract

Kinetic and toxicological characteristics of fish (Odontesthes argentinensis) and crab (Callinectes sapidus) cholinesterases as well as methodological conditions to perform reactivation assays using pyridine 2-aldoxime (2-PAM) were established. According to kinetic and eserine sensitivity data, both cholinesterases can be considered as acetylcholinesterases. The concentration of eserine that inhibited 50% of enzyme activity IC50) was estimated as 15.9 10 8 and 4.6 10 8 M for crab and fish, respectively. For purified eel acetylcholinesterase (V-S type), it was estimated as 4.2 10 8 M. 2-PAM showed both to increase non-enzymatic hydrolysis of acetylthiocholine iodide and to inhibit activity of the acetylcholinesterases tested. The IC50 of 2-PAM for crab acetylcholinesterase (8.2 10 4 M) was significantly higher than that from O. argentinensis (2.5 10 4 M) or eel (2.0 10 4 M) acetylcholinesterase. Enzyme inhibition induced by 2-PAM showed to mask subtle inhibition due to malathion, suggesting that a previous characterization of 2-PAM inhibition must be done before its use in reactivation assays. assays.