New Cinchona Oximes Evaluated as Reactivators of Acetylcholinesterase and Butyrylcholinesterase Inhibited by Organophosphorus Compounds.

Maja Katalinić,Antonio Zandona,Alma Ramić,Zrinka Kovarik,Tamara Zorbaz,Ines Primožič

doi:10.3390/molecules22071234

Abstract

For the last six decades, researchers have been focused on finding efficient reactivators of organophosphorus compound (OP)-inhibited acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). In this study, we have focused our research on a new oxime scaffold based on the Cinchona structure since it was proven to fit the cholinesterases active site and reversibly inhibit their activity. Three Cinchona oximes (C1, C2, and C3), derivatives of the 9-oxocinchonidine, were synthesized and investigated in reactivation of various OP-inhibited AChE and BChE. As the results showed, the tested oximes were more efficient in the reactivation of BChE and they reactivated enzyme activity to up to 70% with reactivation rates similar to known pyridinium oximes used as antidotes in medical practice today. Furthermore, the oximes showed selectivity towards binding to the BChE active site and the determined enzyme-oxime dissociation constants supported work on the future development of inhibitors in other targeted studies (e.g., in treatment of neurodegenerative disease). Also, we monitored the cytotoxic effect of Cinchona oximes on two cell lines Hep G2 and SH-SY5Y to determine the possible limits for in vivo application. The cytotoxicity results support future studies of these compounds as long as their biological activity is targeted in the lower micromolar range.

Highlights

Organophosphorus compounds (OPs), commonly used as pesticides, and as an insidious threat in terrorism, are covalent inhibitors of the enzymes acetylcholinesterase (AChE, EC 3.1.1.7) and butyrylcholinesterase (BChE, EC 3.1.1.8) phosphylating their active center serine
AChE inhibited by several nerve agents [1,2,3], and with that the cholinergic crisis will persist leading to the unwanted consequences
Cinchonidin-9-one was prepared by oxidizing cinchonidine with potassium t-butoxide and benzophenone in toluene [15]

Summary

Introduction

Organophosphorus compounds (OPs), commonly used as pesticides, and as an insidious threat in terrorism, are covalent inhibitors of the enzymes acetylcholinesterase (AChE, EC 3.1.1.7) and butyrylcholinesterase (BChE, EC 3.1.1.8) phosphylating their active center serine. The inhibition in vivo triggers a cholinergic crisis, resulting from the accumulation of acetylcholine and overstimulation of receptors in synapses. Efficacy of the oxime therapy, typically 2-PAM, obidoxime or HI-6, combined with atropine and an anticonvulsant, is still limited [2,3]. Though the symptoms of poisoning will be somewhat attenuated by atropine and an anticonvulsant, the applied oximes will not be effective in reactivating. AChE inhibited by several nerve agents [1,2,3], and with that the cholinergic crisis will persist leading to the unwanted consequences. Inhibitory OPs remain in different body compartments permitting redistribution into the plasma, where they are capable of inhibiting or re-inhibiting active

Methods

Results

Conclusion