Antagonism of paraoxon intoxication by recombinant phosphotriesterase encapsulated within sterically stabilized liposomes

This investigation effort is focused on increasing organophosphate (OP) deg radation by phosphotriesterase to antagonize OP intoxication. For these stu dies, sterically stabilized liposomes encapsulating recombinant phosphotrie sterase were employed. This enzyme was obtained from Flavobacterium sp. and was expressed in Escherichia coli. It has a broad substrate specificity, w hich includes parathion, paraoxon, soman, sarin, diisopropylfluorophosphate , and other organophosphorous compounds. Paraoxon is rapidly hydrolyzed by phosphotriesterase to the less toxic 4-nitrophenol and diethylphosphate. Th is enzyme was isolated and purified over 1600-fold and subsequently encapsu lated within sterically stabilized liposomes (SL). The properties of this e ncapsulated phosphotriesterase were investigated. When these liposomes cont aining phosphotriesterase were incubated with paraoxon, it readily degraded the paraoxon, Hydrolysis of paraoxon did not occur when these sterically s tabilized liposomes contained no phosphotriesterase, These sterically stabi lized liposomes (SL) containing phosphotriesterases (SL)* were employed as a carrier model to antagonize the toxic effects of paraoxon by hydrolyzing it to the less toxic 4-nitrophenol and diethylphosphate, This enzyme-SL com plex (SL)* was administered intravenously to mice either alone or in combin ation with pralidoxime (2-PAM) and/or atropine intraperitoneally. These res ults indicate that this carrier model system provides a striking enhanced p rotective effects against the lethal effects of paraoxon. Moreover when the se carrier liposomes were administered with 2-PAM and/or atropine, a dramat ic enhanced protection was observed. (C) 1999 Academic Press.