Delayed neurotoxicity produced by an organophosphorus compound (Sumithion). A case report

Organophosphorus poisoning in animals and enzymatic antidotes

Organophosphorus compounds (OPs) are neurotoxic molecules developed as pesticides and chemical warfare nerve agents (CWNAs). Most of them are covalent inhibitors of acetylcholinesterase (AChE), a key enzyme in nervous systems, and are therefore responsible for numerous poisonings around the world. Many animal models have been studied over the years in order to decipher the toxicity of OPs and to provide insights for therapeutic and decontamination purposes. Environmental impact on wild animal species has been analyzed to understand the consequences of OP uses in agriculture. In complement, various laboratory models, from invertebrates to aquatic organisms, rodents and primates, have been chosen to study chronic and acute toxicity as well as neurobehavioral impact, immune response, developmental disruption, and other pathological signs. Several decontamination approaches were developed to counteract the poisoning effects of OPs. Among these, enzyme-based strategies are particularly attractive as they allow efficient external decontamination without toxicity or environmental impact and may be of interest for treatment. Approaches using bioscavengers for prophylaxis, treatment, and external decontamination are emphasized and their potential is discussed in the light of toxicological observations from various animal models. The relevance of animal models, regarding their cholinergic system and the abundance of naturally protecting enzymes, is also discussed for better extrapolation of results to human.

[Organophosphorus poisoning: Towards enzymatic treatments]

Organophosphorus compounds (OP) are toxic molecules developed as insecticides and chemical warfare nerve agents (CWNAs). Most OP are neurotoxic and act as nervous system disruptors by blocking cholinergic transmission. They are therefore responsible for many poisonings worldwide. OP toxicity may result either from acute or chronic exposure, and their poisoning effect were evaluated using several animal models. These latter were also used for evaluating the efficacy of antidotes. Strategies based on enzymes that can trap (stoichiometric bioscavengers) or degrade (catalytic bioscavengers) OP, were particularly studied since they allow effective decontamination, without toxicity or environmental impact. This review summarizes the results obtained in vivo with enzymes through three levels: prophylaxis, treatment and external decontamination. The efficiency of enzymatic treatments in different animal models is presented and the relevance of these models is also discussed for a better extrapolation to humans.

Body mass index as a prognostic factor in organophosphate-poisoned patients

Organophosphate poisoning is a serious clinical entity and considerable morbidity and mortality. Several factors have been identified to predict outcomes of organophosphate poisoning. Organophosphates are lipophilic and therefore predicted to have a large volume of distribution and to rapidly distribute into tissue and fat. Thus, toxic effects of organophosphate would be expected to last longer in obese patients. We investigated the relationship between obesity and clinical course in 112 acute organophosphate-poisoned patients from an initial medical record review of 234 patients. One hundred twenty-two patients were excluded: 6 were children, 14 had an uncertain history of exposure and of uncertain agent, 10 were transferred to another hospital, 67 were discharged from the emergency department because their toxicity was mild, 21 had carbamate poisoning, and 4 did not have height or weight checked. Clinical features, body mass index, Glasgow Coma Scale, laboratory findings, serum cholinesterase activity, electrocardiogram finding, management, and outcomes were examined. The lipid solubility of the implicated organophosphate was characterized by its octanol/water coefficient. Forty of 112 patients were obese. Obese patients who were poisoned by high lipophilicity organophosphate compounds had a need for longer use of mechanical ventilation, intensive care unit care, and total length of admission. Body mass index can provide a guide to physicians in predicting clinical course and management in organophosphate-poisoned patients.

Organophosphate ester flame retardant-induced acute intoxications in dogs

INTRODUCTION

Flame retardants have wide industrial applications and are incorporated into articles found in automobiles and home environments, including seat cushions. These compounds differ widely chemically and in their toxic potential. We report here two cases involving dogs following ingestion of car seat cushions impregnated with organophosphate ester fire retardants.

CASE REPORTS

Two case reports are presented. Two adult American Pit Bull dogs were presented at an emergency clinic with acute signs of central nervous system excitation including seizures. The most severely affected dog died 15 min after presentation, while the less affected dog fully recovered following treatment. In the second case, both a German Shepherd and a Rottweiler were found dead in the morning after they were left in a car overnight. A comprehensive toxicological analysis of samples from both cases revealed the presence of significant amounts (>2 ppm) of tris(2-chloroethyl)phosphate (TCEP) in stomach contents. This compound is a known inducer of epileptic seizures. Some other structurally related organophosphate ester compounds were found, and their role in the acute intoxications reported here is not known and remains to be determined.

CONCLUSION

This is the first report linking acute deaths in dogs to the ingestion of car seat cushions found to contain large amounts of TCEP, an organophosphate ester compound. It is highly likely that this compound caused death through its known seizure-inducing activity.

Nitrophenols isolated from diesel exhaust particles regulate steroidogenic gene expression and steroid synthesis in the human H295R adrenocortical cell line

Studies of nitrophenols isolated from diesel exhaust particles (DEPs), 3-methyl-4-nitrophenol (PNMC) and 4-nitro-3-phenylphenol (PNMPP) have revealed that these chemicals possess estrogenic and anti-androgenic activity in vitro and in vivo and that PNMC accumulate in adrenal glands in vivo. However, the impacts of exposure to these compounds on adrenal endocrine disruption and steroidogenesis have not been investigated. To elucidate the non-receptor mediated effects of PNMC and PNMPP, we investigated the production of the steroid hormones progesterone, cortisol, testosterone, and estradiol-17beta and modulation of nine major enzyme genes involved in the synthesis of steroid hormones (CYP11A, CYP11B1, CYP17, CYP19, 17betaHSD1, 17betaHSD4, CYP21, 3betaHSD2, StAR) in human adrenal H295R cells supplied with cAMP. Exposure to 10(-7) to 10(-5) M PNMC and 1 mM 8-Br-cAMP for 48 h decreased testosterone, cortisol, and estradiol-17beta levels and increased progesterone secretion. At 10(-5) M, PNMC with 1 mM 8-Br-cAMP significantly stimulated expression of the 17betaHSD4 and significantly suppressed expression of 3betaHSD2. In comparison, 10(-7) to 2 x 10(-5) M PNMPP with 1 mM 8-Br-cAMP for 48 h decreased concentrations of estradiol-17beta, increased progesterone levels, but did not affect testosterone and cortisol secretion due to the significant suppression of CYP17 and the non-significant but obvious suppression of CYP19. Our results clarified steroidogenic enzymes as candidates responsible for the inhibition or stimulation for the production of steroid hormones in the steroidogenic pathway, thus providing the first experimental evidence for multiple mechanisms of disruption of endocrine pathways by these nitrophenols.

Delayed toxidromes

Some toxins do not result in clinical manifestations until several hours after exposure. This article reviews those agents that may cause delayed-onset toxicity. They are organized into four classes: specific pharmaceuticals, biologicals, pharmaceutical dosage forms, and chemicals. There are five basic mechanisms for delayed toxicity: delayed absorption, distribution factors, metabolic factors, cellular and organ capacity effects, and unknown. Scientific evidence for delayed-onset of effects varies considerably among the individual toxins.

Acute organophosphate poisoning after disulfoton ingestion

A 75-year-old woman attempted suicide by ingesting a large quantity of granular Di-Syston which is an organophosphate insecticide containing 5% disulfoton (ethylthiometon). On admission, the total plasma phosphorodithioate sulfone concentration (disulfoton and its metabolites, phosphorodithioate sulfoxide and its sulfone) determined by gas chromatography was 1095 ng/mL. After gastric lavage, the concentration gradually decreased to 505 ng/mL. However, it began to increase again 20 h after admission and reached the peak concentration (1322 ng/mL) at 56 h. It was concluded that the secondary elevation of the plasma concentration was due to the prolonged absorption of the organophosphate from the residual granules in the stomach, despite the early gastric lavage. Pralidoxime iodide administration temporarily restored erythrocyte cholinesterase activity to almost normal and inhibited the excessive, delayed reduction of cholinesterase activity. It is recommended that poisoning with the granular form of disulfoton should be treated with repetitive or prolonged gastric and intestinal lavage, charcoal, and a continuous intravenous infusion of pralidoxime iodide in addition to atropine sulfate.

Pathophysiological studies of neuromuscular function in subacute organophosphate poisoning induced by phosmet

A 51 year old man developed progressive cranial and proximal muscle weakness, hyperreflexia and mental change. The disorder progressed over 9 days following the fifth weekly spraying with the organophosphate (OP) insecticide, phosmet, with limited symptoms of acute toxicity. Marked decremental responses of 50-80% on slow and fast rates of stimulation were improved to 15% by edrophonium or neostigmine. Intracellular recordings at the endplate region of intercostal muscle revealed small miniature endplate potentials (mepps), reduced mean acetylcholine sensitivity and normal membrane potentials. Electronmicroscopy revealed degeneration and regeneration of the endplates. This study demonstrates that OP poisoning due to phosmet can produce a subacute postsynaptic neuromuscular syndrome without marked symptoms of acute toxicity.

A case of acute poisoning with fenitrothion (Sumithion)

A 56-year-old male attempted suicide by ingestion of about 60 ml of 50% fenitrothion (Sumithion) emulsion. Five hours later, combined hemoperfusion and hemodialysis (HP-HD) treatment was performed for 60 min and consequently the toxic symptoms improved gradually. However, cholinergic symptoms recurred 4 days after ingestion. Although HP-HD was immediately performed for 180 min, it had no effect on the clinical symptoms. He died of respiratory insufficiency 6 days after the ingestion of fenitrothion. Fenitrothion concentration in the organs and tissues showed the highest values in the fat tissue, followed in decreasing order by the pancreas, muscle, lung and brain. The results indicate that fenitrothion has high lipid solubility and deposits in the fat tissue. Furthermore, we believe that when HP-HD therapy is used in the treatment of acute insecticide poisoning it is important that it be performed continuously and in as early a stage as possible.