Steve Wilton AO FAHMS BSc PhD

Acute organophosphate (OP) poisoning is lethal due to irreversible acetylcholinesterase (AChE) inhibition in neuromuscular junctions (NMJ). Recently, we discovered that AChE levels are down-regulated by microRNA-132 (miR-132) and that blocking this down-regulation can significantly elevate endogenous AChE levels [1]. Here, we report effective prophylactic protection from paraoxon poisoning of BalbC mice injected intravenously (IV) 24 hours pre-exposure with 3.3 mg/kg AM132, a 22-mer antisense chemically protected from nuclease degradation by 2'-0-methyl modified bases on a phosphorothioate backbone and conjugated to cholesterol at its 3 end for enhanced penetration. When exposed to 0.9LD50 paraoxon, all naive but none of the Chol-AM132-protected mice exhibited severe poisoning symptoms (Mann-Whitney U-test, P=0.028, N=4/group). 1.3LD50 exposure caused poisoning symptoms in all mice, but 40% of the Chol-AM132-treated mice survived and recovered, while naive ones all showed severe poisoning symptoms and died within 3 minutes post-exposure (ANOVA P=6.62E-12, N=4-7/group). No mice survived exposure to 10LD50 Paraoxon, but Chol-AM132 treatment conspicuously extended survival time compared to controls (ANOVA P=6.8E-9, N=5/group). To identify the underlying mechanism, we measured AChE activity in NMJs of diaphragm muscle from mice that had been injected with either Chol-AM132 or PBS for 3 successive days. Chol-AM132 treated mice had 10.9±4.2 compared to 6.3±2.7 stained NMJs/ field in control mice (t test, P=0.0069, N=5 mice/group and 18 fields/specimen), possibly reflecting increased expression of AChE in pre-existing NMJs, development of new ones or both. Additionally, Chol-AM132 treatment elevated AChE activity in bone marrow macrophages (29.0±15.0 vs. 14.1±2.6 compared to 15.0±6.4 vs. 9.8±1.2 nmol substrate hydrolyzed/mg protein/min for 3 and 1 day treatment, respectively; Student's t-test: <;0.0065), further predicting potential protection from post-exposure inflammatory insults. Importantly, Chol-AM132 can be synthesized in unlimited amounts using standard equipment, exhibits long-term stability at room temperature and field conditions, and unlike pyridostigmine, does not inhibit pre-existing AChE. Our findings open new venues for prophylactic protection against nerve gas poisoning.