engleski

Natural deep eutectic solvents affect acetylcholinesterase kinetics

The pivotal role of acetylcholinesterase (AChE) in hydrolyzing the neurotransmitter acetylcholine can be disturbed by inhibitors like organophosphates. The formed adducts are not efficiently hydrolyzed by water and AChE loses its catalytic function. Consequent overstimulation of cholinergic receptors can lead to death. To overcome the life- threatening state, antimuscarinic atropine and an oxime reactivator must be administered promptly. Oximes, as nucleophiles stronger than water, restore phosphylated AChE activity, but due to their positive charge, standard oximes poorly pass the blood-brain barrier (BBB) and fail to reactivate synaptic AChE. Lately, zwitterionic molecules with a sufficient neutral species at physiologic pH to cross the BBB have been investigated. AChE is then reactivated by cationic species formed upon establishing pH equilibrium in the brain. Such oxime is RS- 194B, but it has low solubility in water. Natural deep eutectic solvents (NADES) can dissolve compounds of low water solubility, and besides being considered as safe for human use, often have beneficial features like antioxidative activity. With the aim to test the suitability of such solvents for oxime formulation, RS-194B was dissolved in NADES composed of glucose and citric acid with 30% water. The oxime was simultaneously dissolved in water, and the effect of such prepared formulations on AChE kinetics was compared. The results indicate that NADES induces conformational changes of the AChE enabling easier embedding of the oxime in the active site resulting in higher AChE affinity for the RS-194B/NADES than for RS- 194B/H2O. Yet, it seems that RS-194B/NADES orientation/vicinity to the phosphylated AChE’s catalytic serine was unfavorable, and the reactivation rate was higher with RS-194B/H2O. This NADES has been shown to inhibit AChE in fractions greater than 0.2%, implying its limited benefit ; however, further studies on other NADES are planned. We thank Prof P. Taylor for AChE and RS-194B 1Radić Z, et al. Refinement of structural leads for centrally acting oximes reactivators of phosphylated cholinesterases. J Biol Chem 2012 ; 287:11798-11809. 2Rosenberg Y, et al. Post- exposure treatment with the oxime RS194B rapidly reverses early and advanced symptoms in macaques exposed to sarin vapor. Chem-Biol Interact 2017 ; 274:50–7. 3Sit RK, et al. Pharmacology, pharmacokinetics, and tissue disposition of zwitterionic hydroxyiminoacetamido alkylamines as reactivating antidotes for organophosphate exposure. J Pharmacol Exp Ther 2018 ; 367:363– 72. 4Mitar A, et al. Physicochemical properties, cytotoxicity, and antioxidative activity of natural deep eutectic solvents containing organic acid. CYBEQ 2019 ; 33, 1-18.

cholinesterases ; organophosphate ; sarin ; VX, oxime, centrally-active, solubility, NADES

nije evidentirano