Malathion, carbofuran and paraquat inhibit Bungarus sindanus (krait) venom acetylcholinesterase and human serum butyrylcholinesterase in vitro

Carbofuran and malathion, well known pesticides, and paraquat, a world widely used herbicide, were tested on acetylcholinesterase (AChE) from Bungarus sindanus venom and butyrylcholinesterase (BChE) from human serum. The calculated IC50 values for inhibition of venom enzyme by malathion, carbofuran and paraquat were 2.5, 0.14, and 0.16 mu M, respectively. The values for inhibition of serum butyrylcholinesterase (BChE) were 3.5, 0.09 and 0.18 mu M, respectively. Analysis of kinetic data indicated that the inhibition caused by malathion, carbofuran and paraquat was mixed for venom AChE. For BChE from human serum, the inhibition caused by malathion and paraquat was mixed and for carbofuran it was uncompetitive. The present results suggest a commercial paraquat preparation (a popular herbicide) inhibits cholinesterases with similar or higher potency than classical pesticide inhibitors. Furthermore, this inhibition was observed both in human serum and snake venom, a newly studied source of AChE.