Evaluating reptile exposure to cholinesterase‐inhibiting agrochemicals by serum butyrylcholinesterase activity

Abstract

Blood samples from lizards (Gallotia galloti) collected from two agricultural areas (Las Galletas and Punta del Hidalgo) and two reference areas on the Island of Tenerife (Canary Islands, Spain) were analyzed for butyrylcholinesterase (BChE) activity. Serum BChE activity was characterized first by in vitro experiments using selective substrates and inhibitors. Of the total cholinesterase (ChE) activity, 74% could be attributed to BChE activity. This portion of the total ChE activity was inhibited dose dependently by tetraisopropyl pyrophosphoramide and hydrolyzed the substrate butyrylthiocholine iodide. No enzyme inhibition was observed at high substrate concentration. Twenty-one lizards collected from agricultural sampling sites showed significant inhibition (p < 0.001) of BChE activity (mean +/- standard deviation [SD] of 4.66 +/- 2.63 micromol/min/ml for lizards from Las Galletas and 5.13 +/- 1.48 for lizards from Punta del Hidalgo) compared with BChE activity for lizards from the reference sites (6.35 +/- 1.75 micromol/min/ ml). Las Galletas had the highest number of lizards (22%) with significantly inhibited BChE activity. In vitro assays showed that 10(-4) M pyridine-2-aldoxime methochloride (2-PAM) reactivated dichlorvos- or paraoxon-inhibited BChE activity within a 60-min incubation period. Almost all serum samples with depressed BChE activity that were collected from lizards from agricultural areas responded to 2-PAM reactivation of enzyme activity (8-60% increase in enzyme activity). Reactivation by treatment with 2-PAM confirmed that the depression of BChE activity was attributable to organophosphorus (OP) compounds. Evaluation of BChE activity levels and the chemical reactivation of serum BChE activity in G. galloti using 2-PAM was found to be a sensitive indicator of G. galloti exposure to OP compounds.