Comparing therapeutic and prophylactic protection against the lethal effect of paraoxon.

Prophylactic and therapeutic efficacy against organophosphorus (OP) intoxication by pralidoxime (2-PAM) and atropine were studied and compared with sterically stabilized long-circulating liposomes encapsulating recombinant organophosphorus hydrolase (OPH), either alone or in various specific combinations, in paraoxon poisoning. Prophylactic and therapeutic properties of atropine and 2-PAM are diminished when they are used alone. However, their prophylactic effects are enhanced when they are used in combination. Present studies indicate that sterically stabilized liposomes (SL) encapsulating recombinant OPH (SL-OPH) alone can provide much better therapeutic and prophylactic protection than the classic 2-PAM + atropine combination. This protection was even more dramatic when SL-OPH was employed in combination with 2-PAM and/or atropine: the magnitude of prophylactic antidotal protection was an astounding 1022 LD(50) [920 mg/kg (LD(50) of paraoxon with antagonists)/ 0.95 mg/kg (LD(50) of control paraoxon)], and the therapeutic antidotal protection was 156 LD(50) [140 mg/kg (LD(50) of paraoxon with antagonists)/0.9 mg/kg (LD(50) of control paraoxon)]. The current study firmly establishes the value of using liposome encapsulating OPH.

Long circulating liposomes encapsulating organophosphorus acid anhydrolase in diisopropylfluorophosphate antagonism.

These studies are focused on antagonizing organophosphorous (OP) intoxications by a new conceptual approach using recombinant enzymes encapsulated within sterically stabilized liposomes to enhance diisopropylfluorophosphate (DFP) degradation. The OP hydrolyzing enzyme, organophosphorous acid anhydrolase (OPAA), encapsulated within the liposomes, was employed either alone or in combination with pralidoxime (2-PAM) and/or atropine. The recombinant OPAA enzyme, from the ALTEROMONAS: strain JD6, has high substrate specificity toward a wide range of OP compounds, e.g., DFP, soman, and sarin. The rate of DFP hydrolysis by liposomes containing OPAA (SL)* was measured by determining the changes in fluoride-ion concentration using a fluoride ion-selective electrode. This enzyme carrier system serves as a biodegradable protective environment for the OP-metabolizing enzyme (OPAA), resulting in an enhanced antidotal protection against the lethal effects of DFP. Free OPAA alone showed some antidotal protection; however, the protection with 2-PAM and/or atropine was greatly enhanced when combined with (SL)*.

In vitro studies on sterically stabilized liposomes (SL) as enzyme carriers in organophosphorus (OP) antagonism.

This study describes a new approach for organophosphorous (OP) antidotal treatment by encapsulating an OP hydrolyzing enzyme, OPA anhydrolase (OPAA), within sterically stabilized liposomes. The recombinant OPAA enzyme was derived from Alteromonas strain JD6. It has broad substrate specificity to a wide range of OP compounds: DFP and the nerve agents, soman and sarin. Liposomes encapsulating OPAA (SL)* were made by mechanical dispersion method. Hydrolysis of DFP by (SL)* was measured by following an increase of fluoride ion concentration using a fluoride ion selective electrode. OPAA entrapped in the carrier liposomes rapidly hydrolyze DFP, with the rate of DFP hydrolysis directly proportional to the amount of (SL)* added to the solution. Liposomal carriers containing no enzyme did not hydrolyze DFP. The reaction was linear and the rate of hydrolysis was first order in the substrate. This enzyme carrier system serves as a biodegradable protective environment for the recombinant OP-metabolizing enzyme, OPAA, resulting in prolongation of enzymatic concentration in the body. These studies suggest that the protection of OP intoxication can be strikingly enhanced by adding OPAA encapsulated within (SL)* to pralidoxime and atropine.