In vitro efficacy of paraoxonase 1 from multiple sources against various organophosphates

Paraoxonase 1 (PON1) has been described as a potential catalytic bioscavenger due to its ability to hydrolyze organophosphate (OP) insecticides and nerve agents. In vitro catalytic efficiency of purified human and rabbit serum PON1 against different OP substrates was compared to human recombinant PON1, expressed in Trichoplusia ni larvae. Highly purified human and rabbit serum PON1s were prepared by multiple chromatography methods. Purified enzymes showed higher catalytic activity with the substrate p-nitrophenyl acetate compared to diethyl paraoxon. The hydrolyzing potential of PON1s against multiple OPs was evaluated by using an in vitro acetylcholinesterase back-titration assay. Significant differences in the catalytic efficiency of all the three PON1s with regard to various OP substrates were observed. Purified PON1s showed higher catalytic activity towards diisopropylfluorophosphate followed by diethylparaoxon compared to dimethyl paraoxon. Heat inactivation or incubation of PON1 with specific inhibitor resulted in complete loss of the enzyme catalytic activity indicating that OP hydrolysis was intrinsic to PON1. In conclusion, purified PON1s from multiple sources show significant differences in the catalytic activity against several OP substrates. These results underscore the importance of systematic analysis of candidate PON1 molecules for developing as an effective catalytic bioscavenger against toxic OPs and chemical warfare nerve agents.