Current Pyridostigmine Bromide and Huperzine A Studies and Future Cholinesterase Screening Using the WRAIR Whole Blood Cholinesterase Assay

Cholinesterases are highly polymorphic carboxylesterases that display broad substrate specificity and are involved in the termination of neurotransmission in cholinergic synapses and neuromuscular junctions of the central nervous system (CNS). ChEs are classified as acetylcholinesterase and butyrylcholinesterase according to their substrate specificity and sensitivity to selected inhibitors (Silver, 1974). The concentration of AChE and BChE in blood is potentially a stable biomarker of suppressed and/or heightened central and peripheral nervous system activity. The Walter Reed Army Institute of Research Whole Blood (WRAIR WB) cholinesterase assay rapidly determines the concentrations of AChE and BChE in unprocessed whole blood, uses a minimally invasive blood sampling technique (finger prick), and is semi-automated (using the Biomek 2000 robotic system). The method measures the activity of AChE and BChE using three substrates from which the individual AChE and BChE contributions are calculated. To date the WRAIR whole blood assay has been used to measure of AChE and BChE in human blood that has been inhibited by selective (e.g. Huperzine A) and non-selective (carbamate) inhibitors (e.g. pyridostigmine bromide, PB). We found that volunteers given pyridostigmine bromide (30 mg single dose) exhibited RBC-AChE maximal inhibition of about 27% after 2.5 h, with recovery of activity to almost 100% after 24 h. After ex vivo addition of soman (GD) to PB-pretreated human blood inhibit AChE, and subsequent PB and GD removal using a small spin column, all the protected (by PB pretreatment) AChE activity was recovered after 24 h (essentially within 6 h). Thus, this assay provided validated support for PB pretreatment as protection against organophosphate chemical warfare agents.