Inhibitor Report for: Phorate

It has been estimated that approximately one in seven of all global suicides is due to pesticide self-poisoning, mostly in rural areas of developing countries. Organophosphorus (OP) compounds are a group of pesticides exerting their toxicological effects through non-reversible inhibition of the enzyme acetylcholinesterase (AChE). Among these compounds, phorate (thimet) is one of the most dangerous compounds, the use of which is restricted in many countries. A case of intentional suicide after phorate ingestion in a 24-year-old Bengali male is described. This is the second case of suicidal ingestion of phorate reported in the forensic literature, and the first presenting complete toxicological findings.

Zinc chloride-diphenylamine reagent, whose use has been reported for the detection of organochlorine insecticides by thin layer chromatography, was further studied for its ability to detect the organophosphorus insecticides phorate, phosphamidon, DDVP, and phosalone and the carbamate insecticide carbaryl and aldicarb. These insecticides give intense blue-green spots with this reagent. The procedure can be applied to the detection of the insecticides in biological materials and thus has a potential use in forensic toxicology.

An HPLC method for the simultaneous detection of six organophosphorus pesticides (Dimethoate, Ethion, Malathion, Phorate, Phosalone and Parathion) on a Zorbex ODS column using methanol + water (80:20) as solvent is described.

It has been estimated that approximately one in seven of all global suicides is due to pesticide self-poisoning, mostly in rural areas of developing countries. Organophosphorus (OP) compounds are a group of pesticides exerting their toxicological effects through non-reversible inhibition of the enzyme acetylcholinesterase (AChE). Among these compounds, phorate (thimet) is one of the most dangerous compounds, the use of which is restricted in many countries. A case of intentional suicide after phorate ingestion in a 24-year-old Bengali male is described. This is the second case of suicidal ingestion of phorate reported in the forensic literature, and the first presenting complete toxicological findings.

The purpose of this study was to investigate the toxic effect of long-term and low-level exposure to phorate using a metabonomics approach based on ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). Male Wistar rats were given phorate daily in drinking water at low doses of 0.05, 0.15 or 0.45 mg kg(-1) body weight (BW) for 24 weeks consecutively. Rats in the control group were given an equivalent volume of drinking water. Compared with the control group, serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), total bilirubin (TBIL), urea nitrogen (BUN) and creatinine (CR) were increased in the middle- and high-dose groups whereas albumin (ALB) and cholinesterase (CHE) were decreased. Urine metabonomics profiles were analyzed by UPLC-MS. Compared with the control group, 12 metabolites were significantly changed in phorate-treated groups. In the negative mode, metabolite intensities of uric acid, suberic acid and citric acid were significantly decreased in the middle- and high-dose groups, whereas indoxyl sulfic acid (indican) and cholic acid were increased. In the positive mode, uric acid, creatinine, kynurenic acid and xanthurenic acid were significantly decreased in the middle- and high-dose groups, but 7-methylguanine (N(7) G) was increased. In both negative and positive modes, diethylthiophosphate (DETP) was significantly increased, which was considered as a biomarker of exposure to phorate. In conclusion, long-term and low-level exposure to phorate can cause disturbances in energy-related metabolism, liver and kidney function, the antioxidant system, and DNA damage. Moreover, more information can be provided on the evaluation of toxicity of phorate using metabonomics combined with clinical chemistry. Copyright (c) 2012 John Wiley & Sons, Ltd.

Previous studies in euryhaline fish have shown that acclimation to hypersaline environments enhances the toxicity of thioether organophosphate and carbamate pesticides. To better understand the potential mechanism of enhanced toxicity, the effects of the organophosphate insecticide phorate were evaluated in coho salmon (Oncorhynchus kisutch) maintained in freshwater (<0.5 g/L salinity) and 32 g/L salinity. The observed 96-h LC50 in freshwater fish (67.34 +/- 3.41 mug/L) was significantly reduced to 2.07 +/- 0.16 mug/L in hypersaline-acclimated fish. Because organophosphates often require bioactivation to elicit toxicity through acetylcholinesterase (AChE) inhibition, the in vitro biotransformation of phorate was evaluated in coho salmon maintained in different salinities in liver, gills, and olfactory tissues. Phorate sulfoxide was the predominant metabolite in each tissue but rates of formation diminished in a salinity-dependent manner. In contrast, formation of phorate-oxon (gill; olfactory tissues), phorate sulfone (liver), and phorate-oxon sulfoxide (liver; olfactory tissues) was significantly enhanced in fish acclimated to higher salinities. From previous studies, it was expected that phorate and phorate sulfoxide would be less potent AChE inhibitors than phorate-oxon, with phorate-oxon sulfoxide being the most potent of the compounds tested. This trend was confirmed in this study. In summary, these results suggest that differential expression and/or catalytic activities of Phase I enzymes may be involved to enhance phorate oxidative metabolism and subsequent toxicity of phorate to coho salmon under hypersaline conditions. The outcome may be enhanced fish susceptibility to anticholineterase oxon sulfoxides.

Phorate, an organophosphorus insecticide is known for its adverse effects on acetylcholinesterase, and other neuronal and pulmonary activities. Most likely, the toxicity of drugs/agrochemicals is modulated through cellular distribution bound to plasma proteins. Therefore, the in vitro interaction of phorate with human serum albumin (HSA) has been investigated, using sensitive techniques like fluorescence spectroscopy and circular dichroism, to ascertain its binding mechanism and toxicological implications. Fluorescence studies revealed the quenching constant (Ksv) as 2.5 x 10(4) M(-)(1) and binding affinity (Ka) as 2.96 x 10(4) M(-)(1) (r(2) = 0.99), with a primary binding site of phorate at sub-domain IIA of HSA. Circular dichroism (CD) data demonstrated a noticeable reduction in secondary structure (alpha-helical content) of phorate treated HSA. Albumin treated with 200-1000 muM phorate released significant amounts of acid soluble amino and carbonyl groups, whereas higher concentrations resulted in protein fragmentation. It is postulated that the 1'-O and 3-O alkyl groups of phorate have a role in binding with electrophilic centers of Trp 214, and Arg 218/Lys 195, respectively. Moreover, the significant ultrastructural changes, reactive oxygen species (ROS) generation, mitochondrial damage and cell death in phorate treated cultured human amnion epithelial (WISH) cells, elucidated phorate induced cellular toxicity.

Phorate and disulfoton are organophosphate insecticides containing three oxidizable sulfurs, including a thioether. Previous studies have shown that only the thioether is oxygenated by flavin-containing monooxygenase (FMO) and the sole product is the sulfoxide with no oxygenation to the sulfone. The major FMO in lung of most mammals, including non-human primates, is FMO2. The FMO2*2 allele, found in all Caucasians and Asians genotyped to date, codes for a truncated, non-functional, protein (FMO2.2A). Twenty-six percent of individuals of African descent and 5% of Hispanics have the FMO2*1 allele, coding for full-length, functional protein (FMO2.1). We have here demonstrated that the thioether-containing organophosphate insecticides, phorate and disulfoton, are substrates for expressed human FMO2.1 with Km of 57 and 32 microM, respectively. LC/MS confirmed the addition of oxygen and formation of a single polar metabolite for each chemical. MS/MS analysis confirmed the metabolites to be the respective sulfoxides. Co-incubations with glutathione did not reduce yield, suggesting they are not highly electrophilic. As the sulfoxide of phorate is a markedly less effective acetylcholinesterase inhibitor than the cytochrome P450 metabolites (oxon, oxon sulfoxide or oxon sulfone), humans possessing the FMO2*1 allele may be more resistant to organophosphate-mediated toxicity when pulmonary metabolism is an important route of exposure or disposition.

Study of the Serum Cholinesterase levels (SchE) in the freshwater catfish Clarias batrachus when exposed to sub lethal dose of pesticides phorate and carbamate, was attempted in this paper. SchE levels decreased in the fish exposed to both the pesticides, the depletion being more pronounced with phorate. These results can be due to impairment of nervous system, liver damage as well as myocardial infarction. Similar findings were not only reported in experimental organisms but also found in human beings working in agricultural fields and pesticide manufacturing plants. Hence it is imperative that suitable occupational health and preventive measures need to be undertaken.

Freshwater edible catfish Clarias batrachus (Linn.) was treated with sublethal concentration of two different groups of pesticides- carbaryl, a carbamate and phorate, an organophosphate for 24 ,72 ,120 and 168 h. The disorders of lipid metabolism were observed in serum. Cholesterol levels in the serum decreased significantly throughout the exposure period with both the pesticides. These results indicate one significant manifestation of the toxic response from the fish under the stress of pesticide exposure.

Milligram quantities of sulfoxides, sulfones, and oxygen analogue (oxon) sulfones of the insecticides disulfoton, phorate, and terbufos were prepared by selective oxidation. Pure insecticides or acetone extracts of granular formulations served as reactants. Structures of 9 compounds were confirmed by comparing their electron impact mass spectra (EI-MS), obtained by the direct inlet system with published data. Thin-layer chromatography (TLC) on silica gel was used to screen oxidation products and to purify products. Products were detected by spraying plates with PdCl2 reagent and exposing to iodine vapors. An esterase inhibition technique gave low detection limits, which are promising for residue analysis.

The organophosphate pesticide, phorate, is an extremely hazardous insecticide. Not much experimental study is available on effects of phorate on different brain areas. We report in this study the alterations induced by phorate on enzyme profile of mouse olfactory bulb. Olfactory bulb, the first processing centre after the sensory cells in the olfactory pathway, has connections with the other higher centres of the brain like hippocampus and hypothalamus. Phorate was administered orally in the diet at the doses of 1.0 mg and 1.5 mg/kg body weight to adult albino mice. After 32 weeks of exposure animals were sacrificed and cryosections were processed for acetylcholinesterase and butyrylcholinesterase (AChE and BChE, respectively) enzyme localization. Significant reduction occurs in AChE and BChE activity at higher dose level, whereas reduced BChE activity was found at both dose levels. Our results shows an obvious effect on cholinesterase enzyme profile of olfactory bulb of mice after systemic administration of low doses of phorate for long terms.

Zinc chloride-diphenylamine reagent, whose use has been reported for the detection of organochlorine insecticides by thin layer chromatography, was further studied for its ability to detect the organophosphorus insecticides phorate, phosphamidon, DDVP, and phosalone and the carbamate insecticide carbaryl and aldicarb. These insecticides give intense blue-green spots with this reagent. The procedure can be applied to the detection of the insecticides in biological materials and thus has a potential use in forensic toxicology.

An HPLC method for the simultaneous detection of six organophosphorus pesticides (Dimethoate, Ethion, Malathion, Phorate, Phosalone and Parathion) on a Zorbex ODS column using methanol + water (80:20) as solvent is described.

An aqueous solution of bromine was used to oxidise 14C-labelled phorate to its metabolites. A substantial amount of [14C]phorate sulphone (O,O-diethyl S-ethylsulphonyl[14C]methyl phosphorodithioate) with minute quantities of [14C]phorate sulphoxide (O,O-diethyl S-ethylsulphinyl[14C]methyl phosphorodithioate) and [14C]phoratoxon sulphoxide (O,O-diethyl S-ethylsulphinyl[14C]methyl phosphorothioate) were recovered using this method. Various concentrations of [14C]phorate and these toxic metabolites were individually incorporated in an artificial diet and fed to Aphis fabae Scop. Mortality was recorded after 48 h. The toxic fractions of the compounds were extracted from the diet and their radioactivity was measured to determine the dose unit. The aphids feeding on diet containing high concentrations of [14C]phorate sulphoxide and [14C]phoratoxon sulphoxide were seen wandering restlessly, which suggested that the acceptability of the diet had been changed by the presence of these metabolites. Phorate appeared to be the most toxic to the aphids, followed by phorate sulphone, phorate sulphoxide and phoratoxon sulphoxide in that order; the reasons for this are discussed.

Carbohydrate metabolism was studied in the hepatopancreas, mantle, intestine and foot of the snail Lymnaea acuminata, exposed to 40% and 80% of the LC50 dose of phorate (12 and 24 mg litre-1, respectively) for 24 and 48 h. Following treatment with the pesticide, the rate of oxygen consumption and the glycogen contents were reduced, while the levels of lactic acid and reducing sugars were enhanced. Withdrawal of the pesticide for 7 days after exposure of the snails to 12 mg of phorate litre-1 for 48 h did not reverse these changes.

Analytical methods are described for the determination of residues of chlorfenvinphos, diazinon, fonofos and phorate in soils and carrots. The insecticides, applied in June 1969 at 2 kg (a.i.)/ha, persisted longer in peaty loam than in sandy loam. After 7 months, the sandy loam contained 1% of the applied diazinon and 20-30% of the applied chlorfenvinphos, fonofos and phorate, the latter as its sulphone; the corresponding figures for the peaty loam were 10, 40-50, 40-50 and 30-40% respectively. None of the residues showed any substantial change from October to January. Although high initial concentrations (up to 50 ppm) of the residues in carrots were diluted by plant growth, it is shown that concentrations >1 ppm could be present in marketable crops 12-14 weeks after application at recommended rates. Carrots harvested 26 weeks after sowing contained <0.2 ppm of all insecticides. In contrast, during the first 15 weeks of crop growth the weights of residues in the carrots increased and remained approximately proportional to the square root of the carrot mean weight. Rates of uptake declined as carrot growth declined and subsequently the amounts of chlorfenvinphos, diazinon and fonofos residues in the carrots changed very little, while phorate sulphone steadily declined.

Alle als lnsektizide verwendbaren organischen Phosphorsaureester wie E 6O5 oder Gusathion entsprechen einem ganz bestirnmten Aufbauschema. Von besonderem lnteresse sind die systernisch wirkenden Systox-Preparate. Die neu entwickelten lnsektizide zeigen die Tendenz, die allgemeingiftigeren Phosphor-Verbindungen durch biologisch selektiv wirkende zu ersetzen https://onlinelibrary.wiley.com/doi/epdf/10.1002/ange.19570690304