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We addressed the ability of various organophosphorus (OP) hydrolases to catalytically scavenge toxic OP nerve agents. Mammalian paraoxonase (PON1) was found to be more active than Pseudomonas diminuta OP hydrolase (OPH) and squid O, O-di-isopropyl fluorophosphatase (DFPase) in detoxifying cyclosarin ( O-cyclohexyl methylphosphonofluoridate) and soman ( O-pinacolyl methylphosphonofluoridate). Subsequently, nine directly evolved PON1 variants, selected for increased hydrolytic rates with a fluorogenic diethylphosphate ester, were tested for detoxification of cyclosarin, soman, O-isopropyl- O-( p-nitrophenyl) methyl phosphonate (IMP-pNP), DFP, and chlorpyrifos-oxon (ChPo). Detoxification rates were determined by temporal acetylcholinesterase inhibition by residual nonhydrolyzed OP. As stereoisomers of cyclosarin and soman differ significantly in their acetylcholinesterase-inhibiting potency, we actually measured the hydrolysis of the more toxic stereoisomers. Cyclosarin detoxification was ∼ 10-fold faster with PON1 mutants V346A and L69V. V346A also exhibited fourfold and sevenfold faster hydrolysis of DFP and ChPo, respectively, compared with wild-type, and ninefold higher activity towards soman. L69V exhibited 100-fold faster hydrolysis of DFP than the wild-type. The active-site mutant H115W exhibited 270–380-fold enhancement toward hydrolysis of the P–S bond in parathiol, a phosphorothiolate analog of parathion. This study identifies three key positions in PON1 that affect OP hydrolysis, Leu69, Val346 and His115, and several amino-acid replacements that significantly enhance the hydrolysis of toxic OPs. GC/pulsed flame photometer detector analysis, compared with assay of residual acetylcholinesterase inhibition, displayed stereoselective hydrolysis of cyclosarin, soman, and IMP-pNP, indicating that PON1 is less active toward the more toxic optical isomers. [ABSTRACT FROM AUTHOR]

• Whole-body sarin exposure to a low concentration of 0.52 μg/L was sufficient in inducing pin-point pupils. • Whole-body sarin exposure leads to ocular surface histopathological lesions in a dose-response manner. • Topical 1 μg VX exposure induces a corneal histopathological damage while anti-muscarinic treatments alleviate this insult. Eye exposure to organophosphate (OP) chemical warfare irreversible acetylcholinesterase inhibitors, results in long-term miosis and impaired visual function. In contrast to the well-documented miotic and ciliary muscle spasm observed following chemical warfare, OP ocular exposure, little is known regarding the ocular surface histopathological insult. The aim of the present study was to determine the degree of the ocular surface insult following sarin or VX ocular exposure and to evaluate potential anti-cholinergic treatments in counteracting this insult. Rats that were whole body exposed to various sarin concentrations (0.049–43 μg/L; 5 min exposure), showed a dose-dependent miotic response and light reflex impairment. Following whole body sarin exposure, a dose dependent ocular surface histopathological insult was developed. A week following exposure to a low concentration of 0.05 μg/L, conjunctival pathology was observed, while corneal insult was noticed only following exposure to a concentration of 0.5 μg/L and above. Both tissues presented poorer outcomes when exposed to higher sarin concentrations. In contrast, eyes topically exposed to 1 μg sarin demonstrated no ocular insult a week following exposure. On the contrary, topical exposure to 1 μg VX resulted in a significant corneal insult. Anticholinergic treatments such as 0.1% atropine or 2% homatropine, given shortly following VX exposure, counteracted this insult. The results of this study show that not only do anti-cholinergic treatments counteract the miotic response, but also prevent the histopathological insult observed when given shortly following OP exposure. [ABSTRACT FROM AUTHOR]