Abstract

Butyrylcholinesterase (BChE) is an important enzyme for metabolism of ester drugs. Many humans have partial or complete BChE deficiency due to genetic variation. Our goal was to create a mouse model of BChE deficiency to allow testing of drug toxicity. For this purpose, we created the BChE knockout mouse by gene-targeted deletion of a portion of the BCHE gene (accession number M99492). The BChE^–/– mouse had no BChE activity in plasma, but it had low residual butyrylthiocholine hydrolase activity in all other tissues attributed to carboxylesterase ES-10. The BChE^–/– mouse had a normal phenotype except when challenged with drugs. Nicotinic receptor function as indicated by response to nicotine seemed to be normal in BChE^–/– mice, but muscarinic receptor function as measured by response to oxotremorine and pilocarpine was altered. Heart rate, blood pressure, and respiration, measured in a Vevo imager, were similar in BChE^+/+ and BChE^–/– mice. Like BChE^–/– humans, the BChE^–/– mouse responded to succinylcholine with prolonged respiratory arrest. Bambuterol was not toxic to BChE^–/– mice, suggesting it is safe in BChE^–/– humans. Challenge with 150 mg/kg pilocarpine i.p., a muscarinic agonist, or with 50 mg/kg butyrylcholine i.p., induced tonicclonic convulsions and death in BChE^–/– mice. This suggests that butyrylcholine, like pilocarpine, binds to muscarinic receptors. In conclusion, the BChE^–/– mouse is a suitable model for human BChE deficiency.