Oxime Reactivation of RBC Acetylcholinesterases for Biomonitoring

Abstract

A low-variability method to reactivate blood cholinesterases (ChEs) after prior exposure of mammals, including humans, to ChE-inhibiting organophosphate esters (OPs) is presented. A concentration of 10 mM pyridine 2-aldoxime methochloride (2-PAM Cl) was incubated with intact red blood cells (RBCs) and assayed virtually free of interfering oxime and hemoglobin (Hb). Variability was decreased by reducing the number of washing steps and sedimenting RBC ghosts through a 7% sucrose cushion. Statistically significant detections of reactivations as low as 5% with average "false positives" of 3.8% were achieved. Relative rates and extent of reactivation after OP treatment of rabbit RBC AChE in vitro were of the order dimethyl- (DDVP) > diethyl- (ethyl paraoxon) >, diisopropyl-substituted (diisopropyl fluorophosphate; DFP) OPs. Rabbit RBC AChE was reactivatable for up to 60 h following dermal exposure to ethyl parathion and reactivatable for only 12 to 24 h following exposure to methyl parathion. Reactivation of plasma ChEs with 0.1 mM 2-PAM Cl in the same animals was achievable for only 12 to 24 h after ethyl parathion and for only 1 to 4 h after methyl parathion.

Oximes in acute organophosphorus pesticide poisoning: a systematic review of clinical trials

“…Whether pesticides had dimethyl or diethyl groups was also not controlled for - this is important if only diethylphosphorylated AChEs respond to pralidoxime after 12h 14,38table 1) but not RCT 2.…”

The Efficacy of Pralidoxime in the Treatment of Organophosphate Poisoning in Humans: A Systematic Review and Meta-analysis of Randomized Trials

“…Dimethyl inhibited AChE enzyme reactivates and ages quickly, while these processes are slow for diethyl compounds [24]. In patients presenting more than 12 hours of exposure to a poison, they would be benefitted only if the ingested compound was diethyl OP [28]. Dimethyl OP would already have aged and it would be impossible for pralidoxime to reactivate it.…”

Combined Effect of Short-Term Dehydration and Sublethal Acute Oral Dicrotophos Exposure Confounds the Diagnosis of Anticholinesterase Exposure in Common Quail (Coturnix Coturnix) Using Plasma Cholinesterase Activity

“…Substrate was added last and immediately prior to assay to initiate the reaction. ChE assay results were read on a SpectraMaxH 190 microplate reader (Molecular Devices Corporation, Sunnyvale, California, USA) set in absorbance mode and at 25 C. An analytical acetylcholinesterase standard was prepared from the membranes of equine red blood cells in general accordance with the method developed for human red blood cells by Dodge et al (1963), as modified by Hansen and Wilson (1999). The standard was run on all microplates assayed.…”