Inhibitor Report for: Prothiofos

BACKGROUND: Many organophosphorus (OP) insecticides have either two O-methyl or two O-ethyl groups attached to the phosphorus atom. This chemical structure affects their responsiveness to oxime-induced acetylcholinesterase (AChE) reactivation after poisoning. However, several OP insecticides are atypical and do not have these structures. AIM: We aimed to describe the clinical course and responsiveness to therapy of people poisoned with two S-alkyl OP insecticides-profenofos and prothiofos. DESIGN: We set up a prospective cohort of patients with acute profenofos or prothiofos self-poisoning admitted to acute medical wards in two Sri Lankan district hospitals. Clinical observation was carried out throughout their inpatient stay; blood samples were taken in a subgroup for assay of cholinesterases and insecticide. RESULTS: Ninety-five patients poisoned with profenofos and 12 with prothiofos were recruited over 5 years. Median time to admission was 4 (IQR 3-7) h. Eleven patients poisoned with profenofos died (11/95; 11.6%, 95% CI 5.9-20); one prothiofos patient died (1/12; 8.3%, 95% CI 0.2-38). Thirteen patients poisoned with profenofos required intubation for respiratory failure (13/95; 13.7%, 95% CI 7.5-22); two prothiofos-poisoned patients required intubation. Both intubations and death occurred late compared with other OP insecticides. Prolonged ventilation was needed in those who survived-a median of 310 (IQR 154-349) h. Unexpectedly, red cell AChE activity on admission did not correlate with clinical severity-all patients had severe AChE inhibition (about 1% of normal) but most had only mild cholinergic features, were conscious, and did not require ventilatory support. CONCLUSION: Compared with other commonly used OP insecticides, profenofos and prothiofos are of moderately severe toxicity, causing relatively delayed respiratory failure and death. There was no apparent response to oxime therapy. The lack of correlation between red cell AChE activity and clinical features suggests that this parameter may not always be a useful marker of synaptic AChE activity and severity after OP pesticide poisoning.

Insensitive acetylcholinesterase (AChE) is involved in the resistance of organophosphorous and carbamate insecticides. We cloned a novel full-length AChE cDNA encoding ace1 gene from adult heads of the diamondback moth (DBM, Plutella xylostella). The ace1 gene encoding 679 amino acids has conserved motifs including catalytic triad, choline-binding site and acyl pocket. Northern blot analysis revealed that the ace1 gene was expressed much higher than the ace2 in all examined body parts. The biochemical properties of expressed AChEs showed substrate specificity for acetylthiocholine iodide and inhibitor specificity for BW284C51 and eserine. Three mutations of AChE1 (D229G, A298S, and G324A) were identified in the prothiofos-resistant strain, two of which (A298S and G324A) were expected to be involved in the prothiofos-resistance through three-dimensional modeling. In vitro functional expression of AChEs in Sf9 cells revealed that only resistant AChE1 is less inhibited with paraoxon, suggesting that resistant AChE1 is responsible for prothiofos-resistance.

The reaction of prothiofos oxon S-oxide (S-oxide) with glutathione (GSH) by computational chemistry formed GS(EtO)P(O)OC6H3Cl2 and PrS(O)(HO)P(O)OC6H3Cl2 (desethyl S-oxide). Both were produced from (R)p-S-oxide. From the reaction of prothiofos oxon (oxon) with partially purified resistant housefly glutathione S-transferase under oxidation, 2,4-dichlorophenyl phosphate was detected and it was suggested that desethyl S-oxide was produced by in vitro metabolism. Desethyl oxon showed insecticidal activity toward the housefly on injection and inhibited bovine erythrocyte acetylcholinesterase oxidatively, thus showing that desethyl S-oxide, too, was an activated compound. It has become apparent that GSH conjugates the ethyl group of S-oxide to form desethyl S-oxide, and it shows insecticidal activity with S-oxide.

BACKGROUND: Many organophosphorus (OP) insecticides have either two O-methyl or two O-ethyl groups attached to the phosphorus atom. This chemical structure affects their responsiveness to oxime-induced acetylcholinesterase (AChE) reactivation after poisoning. However, several OP insecticides are atypical and do not have these structures. AIM: We aimed to describe the clinical course and responsiveness to therapy of people poisoned with two S-alkyl OP insecticides-profenofos and prothiofos. DESIGN: We set up a prospective cohort of patients with acute profenofos or prothiofos self-poisoning admitted to acute medical wards in two Sri Lankan district hospitals. Clinical observation was carried out throughout their inpatient stay; blood samples were taken in a subgroup for assay of cholinesterases and insecticide. RESULTS: Ninety-five patients poisoned with profenofos and 12 with prothiofos were recruited over 5 years. Median time to admission was 4 (IQR 3-7) h. Eleven patients poisoned with profenofos died (11/95; 11.6%, 95% CI 5.9-20); one prothiofos patient died (1/12; 8.3%, 95% CI 0.2-38). Thirteen patients poisoned with profenofos required intubation for respiratory failure (13/95; 13.7%, 95% CI 7.5-22); two prothiofos-poisoned patients required intubation. Both intubations and death occurred late compared with other OP insecticides. Prolonged ventilation was needed in those who survived-a median of 310 (IQR 154-349) h. Unexpectedly, red cell AChE activity on admission did not correlate with clinical severity-all patients had severe AChE inhibition (about 1% of normal) but most had only mild cholinergic features, were conscious, and did not require ventilatory support. CONCLUSION: Compared with other commonly used OP insecticides, profenofos and prothiofos are of moderately severe toxicity, causing relatively delayed respiratory failure and death. There was no apparent response to oxime therapy. The lack of correlation between red cell AChE activity and clinical features suggests that this parameter may not always be a useful marker of synaptic AChE activity and severity after OP pesticide poisoning.

Insensitive acetylcholinesterase (AChE) is involved in the resistance of organophosphorous and carbamate insecticides. We cloned a novel full-length AChE cDNA encoding ace1 gene from adult heads of the diamondback moth (DBM, Plutella xylostella). The ace1 gene encoding 679 amino acids has conserved motifs including catalytic triad, choline-binding site and acyl pocket. Northern blot analysis revealed that the ace1 gene was expressed much higher than the ace2 in all examined body parts. The biochemical properties of expressed AChEs showed substrate specificity for acetylthiocholine iodide and inhibitor specificity for BW284C51 and eserine. Three mutations of AChE1 (D229G, A298S, and G324A) were identified in the prothiofos-resistant strain, two of which (A298S and G324A) were expected to be involved in the prothiofos-resistance through three-dimensional modeling. In vitro functional expression of AChEs in Sf9 cells revealed that only resistant AChE1 is less inhibited with paraoxon, suggesting that resistant AChE1 is responsible for prothiofos-resistance.

Housefly glutathione S-transferases 1, 3, 4, 6A and 6B were obtained from organophosphorus (OP)-resistant Yachiyo and susceptible Takatsuki strains, respectively. Over 90% homology was found between isozymes 6A and 6B but their functions differed in desethylation metabolism. Yachiyo-6A produced more desethyl product of diazinon oxon than Takatsuki-6A, thus suggesting that it plays a central role in the development of O-alkyl phosphate-type OP resistance. On the other hand, unlike Takatsuki-6B, Yachiyo-6B barely achieved the desethylation of prothiofos oxon and the resultant effect was more in the direction of resistance suppression. However, the chief role played by 6B with regard to prothiofos was the exclusive desethylation of S-oxide, which is the oxidative product of prothiofos oxon, thus giving desethyl S-oxide with insecticidal activity and bringing forth a novel active intermediate along with S-oxide.

The reaction of prothiofos oxon S-oxide (S-oxide) with glutathione (GSH) by computational chemistry formed GS(EtO)P(O)OC6H3Cl2 and PrS(O)(HO)P(O)OC6H3Cl2 (desethyl S-oxide). Both were produced from (R)p-S-oxide. From the reaction of prothiofos oxon (oxon) with partially purified resistant housefly glutathione S-transferase under oxidation, 2,4-dichlorophenyl phosphate was detected and it was suggested that desethyl S-oxide was produced by in vitro metabolism. Desethyl oxon showed insecticidal activity toward the housefly on injection and inhibited bovine erythrocyte acetylcholinesterase oxidatively, thus showing that desethyl S-oxide, too, was an activated compound. It has become apparent that GSH conjugates the ethyl group of S-oxide to form desethyl S-oxide, and it shows insecticidal activity with S-oxide.

CASE REPORT A 63-year-old woman was admitted to a local hospital after the ingestion of 40% prothiofos preparation (Tokuthion) 370 mL. Gastric lavage was performed and cathartics, active charcoal, diuretics, atropine sulfate, and pralidoxime were administered. Serum cholinesterase activity was 1.3 IU/L (normal 200-460 IU/L). The patient's consciousness was gradually restored after 4 hours of charcoal hemoperfusion and she was discharged 5 days after admission with no sequelae. METHOD: Plasma and urine prothiofos and metabolites were detected by gas chromatography-flame photometry and gas chromatography-mass spectrometry. Two despropyl metabolites were synthesized for identification and estimation. RESULTS: The main metabolites were identified with authentic prothiofos and methyl esters of synthesized des-S-propyl prothiofos oxon (O-2,4-dichlorophenyl O-ethyl phosphate), despropyl prothiofos oxon (O-2,4-dichlorophenyl O-ethyl phospholothiolate), and des-S-propyl prothiofos (O-2,4-dichlorophenyl O-ethyl phosphorothioate). Despropyl prothiofos (O-2,4-dichlorophenyl O-ethyl phosphorodithioate) was also identified in plasma. Large amounts of the hydrolyzed product, 2,4-dichlorophenol and its conjugate were also found. The metabolic pattern of prothiofos in humans appears to be different from that in rats.