OpdA, a bacterial organophosphorus hydrolase, prevents lethality in rats after poisoning with highly toxic organophosphorus pesticides

Abstract

Organophosphorus (OP) pesticides poison more than 3,000,000 people every year in the developing world, mostly through intentional self-poisoning. Advances in medical therapy for OP poisoning have lagged, and current treatment is not highly effective with mortality of up to 40% in even the most advanced Western medical facilities. Administration of a broadly active bacterial OP hydrolase to patients in order to hydrolyze OPs in circulation might allow current therapies to be more effective. The objective of this work was to evaluate the efficacy of a new recombinant bacterial OP hydrolase (OpdA), cloned from Agrobacterium radiobacter, in rat models of two chemically distinct but highly toxic and rapidly acting OP pesticides: dichlorvos and parathion. Without OpdA treatment, median time to death in rats poisoned with 3x LD(50) of dichlorvos or parathion was 6 min and 25.5 min, respectively. Administration of a single dose of OpdA immediately after dichlorvos resulted in 100% survival at 24h, with no additional antidotal therapy. After parathion poisoning, OpdA alone caused only a delay to death. However, an additional two doses of OpdA resulted in 62.5% survival at 24 h after parathion poisoning. In combination with pralidoxime therapy, a single dose of OpdA increased survival to 75% after parathion poisoning. Our results demonstrate that OpdA is able to improve survival after poisoning by two chemically distinct and highly toxic OP pesticides.

Figure 1

Hydrolysis of dichlorvos (A) and parathion (B) by OpdA.

Figure 1

Hydrolysis of dichlorvos (A) and parathion (B) by OpdA.

Figure 2. Acute mortality after poisoning with 3 × LD₅₀ of dichlorvos or parathion

Survival after poisoning with dichlorvos (■) or parathion (▲) alone. Rats were given 0.5 mL of saline placebo IV concomitantly with poisoning by 3 × LD₅₀ dichlorvos or parathion via gavage.

Figure 3. OpdA improves survival after poisoning with 3 × LD₅₀ of A) dichlorvos, or B) parathion

A. 24-hour survival after poisoning with dichlorvos. Rats were given 0.15 mg/kg of OpdA or the same volume of saline placebo concomitantly with poisoning by 3 × LD₅₀ dichlorvos via gavage. ■ = dichlorvos plus saline placebo; ▲ = dichlorvos plus single dose 0.15 mg/kg OpdA. Each group contained 8 rats. B. 24-hour survival after poisoning with parathion. Rats were given OpdA 0.15 mg/kg or placebo, with or without 2-PAM, after poisoning with 3 × LD₅₀ parathion via gavage. ■ = parathion plus saline placebo; x = parathion plus single dose 0.15 mg/kg OpdA; ▲ = parathion plus 3 doses 0.15 mg/kg OpdA; ▼ = parathion plus 2-PAM bolus and infusion of 30 mg/kg/hr for 24 hours; ♦ = parathion plus single dose 0.15 mg/kg OpdA plus 2-PAM bolus and infusion of 30 mg/kg/hr for 24 hours. Each group contained 8 rats with the exception of the 24-hour 2-PAM alone group, which contained 10 rats.

Figure 3. OpdA improves survival after poisoning with 3 × LD₅₀ of A) dichlorvos, or B) parathion

A. 24-hour survival after poisoning with dichlorvos. Rats were given 0.15 mg/kg of OpdA or the same volume of saline placebo concomitantly with poisoning by 3 × LD₅₀ dichlorvos via gavage. ■ = dichlorvos plus saline placebo; ▲ = dichlorvos plus single dose 0.15 mg/kg OpdA. Each group contained 8 rats. B. 24-hour survival after poisoning with parathion. Rats were given OpdA 0.15 mg/kg or placebo, with or without 2-PAM, after poisoning with 3 × LD₅₀ parathion via gavage. ■ = parathion plus saline placebo; x = parathion plus single dose 0.15 mg/kg OpdA; ▲ = parathion plus 3 doses 0.15 mg/kg OpdA; ▼ = parathion plus 2-PAM bolus and infusion of 30 mg/kg/hr for 24 hours; ♦ = parathion plus single dose 0.15 mg/kg OpdA plus 2-PAM bolus and infusion of 30 mg/kg/hr for 24 hours. Each group contained 8 rats with the exception of the 24-hour 2-PAM alone group, which contained 10 rats.