Inhibitor Report for: Methomyl

To compare the toxicity of seven N-methyl carbamates, time course profiles for brain and red blood cell (RBC) cholinesterase (ChE) inhibition were established for each. Adult, male, Long Evans rats (n=4-5 dose group) were dosed orally with either carbaryl (30 mg/kg in corn oil); carbofuran (0.5 mg/kg in corn oil); formetanate HCl (10 mg/kg in water); methomyl (3 mg/kg in water); methiocarb (25 mg/kg in corn oil); oxamyl (1 mg/kg in water); or propoxur (20 mg/kg in corn oil). This level of dosing produced at least 40% brain ChE inhibition. Brain and blood were taken from 0.5 to 24 h after dosing for analysis of ChE activity using two different methods: (1) a radiometric method which limits the amount of reactivation of ChE activity, and (2) a spectrophotometric method (Ellman method using traditional, unmodified conditions) which may encourage reactivation. The time of peak ChE inhibition was similar for all seven N-methyl carbamate pesticides: 0.5-1.0 h after dosing. By 24 h, brain and RBC ChE activity in all animals returned to normal. The spectrophotometric method underestimated ChE inhibition. Moreover, there was a strong, direct correlation between brain and RBC ChE activity (radiometric assay) for all seven compounds combined (r(2)=0.73, slope 1.1), while the spectrophotometric analysis of the same samples showed a poor correlation (r(2)=0.09). For formetanate, propoxur, methomyl, and methiocarb, brain and RBC ChE inhibitions were not different over time, but for carbaryl, carbofuran and oxamyl, the RBC ChE was slightly more inhibited than brain ChE. These data indicate (1) the radiometric method is superior for analyses of ChE activity in tissues from carbamate-treated animals (2) that animals treated with these N-methyl carbamate pesticides are affected rapidly, and recover rapidly, and (3) generally, assessment of RBC ChE is an accurate predictor of brain ChE inhibition for these seven pesticides.

The gas-liquid chromatographic behavior of methomyl (methyl N-[(methyl-carbamoyl)oxy]thioacetimidate), oxamyl (methyl N',N'-dimethyl-N-[(methylcarbamoyl)oxyl]-1-thiooxamimidate), their respective oxime hydrolysis products and the trimethylsilyl (TMS) ethers of the oximes on 5% OV-1 was studied under isothermal conditions using a flame-photometric detector in the sulfur-selective mode. In contrast to the behavior of the parent carbamates and underivatized oximes, the oxime-TMS ethers readily produced symmetrical peaks of consistent size. Quantities of derivative equivalent to at least 0.25 ng of oxime were easily measurable. Derivative formation was reproducible for standards over the range 10.0 to 0.25 microgram/ml in benzene and at 10.0 and 0.50 microgram/ml in the presence of extractives from tomato, carrot and celery at concentrations equivalent to 10 g/ml of crop. Derivative yields from crop extract fotifications were 89% or better in most cases. Both the carbamates and oximes were simply and consistently recovered in high yield from crops fortified at 1.00 and 0.05 ppm using the procedures described. The inclusion of a second analytical step provided separate analysis for oximes and carbamates. The application of these observations to the analyses of residues in crops is discussed.

A reverse phase high pressure liquid chromatographic method is presented for the separation and determination of residues of the carbamates oxamyl and methomyl on vegetables. A liquid-liquid extraction and cleanup procedure is applied to the vegetable extract. Samples are eluted from a muBondapak C18 column and quantitated by ultraviolet absorbance at 240 nm. Recovery data for vegetable samples spiked at 2 ppm are presented.

To compare the toxicity of seven N-methyl carbamates, time course profiles for brain and red blood cell (RBC) cholinesterase (ChE) inhibition were established for each. Adult, male, Long Evans rats (n=4-5 dose group) were dosed orally with either carbaryl (30 mg/kg in corn oil); carbofuran (0.5 mg/kg in corn oil); formetanate HCl (10 mg/kg in water); methomyl (3 mg/kg in water); methiocarb (25 mg/kg in corn oil); oxamyl (1 mg/kg in water); or propoxur (20 mg/kg in corn oil). This level of dosing produced at least 40% brain ChE inhibition. Brain and blood were taken from 0.5 to 24 h after dosing for analysis of ChE activity using two different methods: (1) a radiometric method which limits the amount of reactivation of ChE activity, and (2) a spectrophotometric method (Ellman method using traditional, unmodified conditions) which may encourage reactivation. The time of peak ChE inhibition was similar for all seven N-methyl carbamate pesticides: 0.5-1.0 h after dosing. By 24 h, brain and RBC ChE activity in all animals returned to normal. The spectrophotometric method underestimated ChE inhibition. Moreover, there was a strong, direct correlation between brain and RBC ChE activity (radiometric assay) for all seven compounds combined (r(2)=0.73, slope 1.1), while the spectrophotometric analysis of the same samples showed a poor correlation (r(2)=0.09). For formetanate, propoxur, methomyl, and methiocarb, brain and RBC ChE inhibitions were not different over time, but for carbaryl, carbofuran and oxamyl, the RBC ChE was slightly more inhibited than brain ChE. These data indicate (1) the radiometric method is superior for analyses of ChE activity in tissues from carbamate-treated animals (2) that animals treated with these N-methyl carbamate pesticides are affected rapidly, and recover rapidly, and (3) generally, assessment of RBC ChE is an accurate predictor of brain ChE inhibition for these seven pesticides.

We have designed this study to determine various kinetic parameters of camel retinal membrane-bound acetylcholinesterase (AChE; EC 3.1.1.7) inhibition by carbamate insecticide lannate [methyl N-[[(methylamino)carbonyl]oxy] ethanimidothioate]. All these kinetic constants were derived by simple graphical methods. The value of kinetic parameters was estimated as follows: 0.061 microM)(-1), 1.14 (microM)(-1), 0.216 microM, 0.016 min(-1), 0.0741 (gammaM min)(-1) 0.746 microM, and 4.42 microM for velocity constant (Kv), new inhibition constant (Knic), dissociation constant (Kd), carbamylation rate constant (k2c), overall carbamylation rate constant (k'2), 50% inhibition constant (K150), and 99% inhibition constant (K199), respectively. These unique methods may be used to estimate such kinetic parameters for time-dependent inhibition of enzymes by variety of chemicals, insecticides, herbicides, and drugs.

This work studied the incorporation of methomyl, a carbamate insecticide, into the hair of New Zealand white rabbits. A total of 600 mg methomyl was administered by drinking water over 4 mo, and acetylcholinesterase activity in serum was monitored. At the end of the dosing period, hair from the back of the rabbits was cut off, and the methomyl concentration was measured using ELISA and HPLC. A decrease of serum acetylcholinesterase occurred. The top cm of hair contained no methomyl, the second cm contained 0.9 ng/mg and the 3rd cm of hair contained 3 ng methomyl/mg. Methomyl was incorporated into the rabbit hair in a process independent of gender but dependent on the hair growth rate.

Using a combination of in vitro assays we have examined the capacities of contemporary-exposure chemicals to modulate human estrogen and human progesterone receptor (hER and hPR) activity in human breast and endometrial cancer cells. The carbamate insecticides aldicarb, Baygon (propoxur), bendiocarb, carbaryl, methomyl, and oxamyl were used in this study. The carbamates alone weakly activated estrogen- or progesterone-responsive reporter genes in breast and endometrial cancer cells. All of the carbamates decreased estradiol- or progesterone-induced reporter gene activity in the breast and endometrial cancer cells. In whole cell competition binding assays, the carbamates demonstrated a limited capacity to displace radiolabeled estrogen or progesterone from ER or PR. Based on the results presented here, the carbamate insecticides may represent a class of chemicals which function through a mechanism separate from ligand-binding and, therefore, may act as general endocrine modulators in mammalian cells.

The suitability of Empore-activated carbon disks (EACD), Envi-Carb graphitized carbon black (GCB) and CPP-50 graphitized carbon for the trace enrichment of polar pesticides from water samples was studied by means of off-line and on-line solid-phase extraction (SPE). In the off-line procedure, 0.5-2 l samples spiked with a test mixture of oxamyl, methomyl and aldicarb sulfoxide were enriched on EnviCarb SPE cartridges or 47 mm diameter EACD and eluted with dichloromethane-methanol. After evaporation, a sample was injected onto a C18-bonded silica column and analysed by liquid chromatography with ultraviolet (LC-UV) detection. EACD performed better than EnviCarb cartridges in terms of breakthrough volumes (> 2 l for all test analytes), reproducibility (R.S.D. of recoveries, 4-8%, n = 3) and sampling speed (100 ml/min); detection limits in drinking water were 0.05-0.16 microgram/l. In the on-line experiments, 4.6 mm diameter pieces cut from original EACD and stacked onto each other in a 9 mm long precolumn, and EnviCarb and CPP-50 packed in 10 x 2.0 mm I.D. precolumn, were tested, and 50-200 ml spiked water samples were preconcentrated. Because of the peak broadening caused by the strong sorption of the analytes on carbon, the carbon-packed precolumns were eluted by a separate stream of 0.1 ml/min acetonitrile which was mixed with the gradient LC eluent in front of the C18 analytical column. The final on-line procedure was also applied for the less polar propoxur, carbaryl and methiocarb. EnviCarb could not be used due to its poor pressure resistance. CPP-50 provided less peak broadening than EACD: peak widths were 0.1-0.3 min and R.S.D. of peak heights 4-14% (n = 3). In terms of analyte trapping efficiency on-line SPE-LC-UV with a CPP-50 precolumn also showed better performance than when Bondesil C18/OH or polymeric PLRP-S was used, but chromatographic resolution was similar. With the CPP-50-based system, detection limits of the test compounds were 0.05-1 microgram/l in surface water.

Male Sprague-Dawley rats receiving an acute dose of methomyl (5 mg/Kg, sc) developed overt signs of toxicity within 2 min. The maximum severity, including muscle fasciculations and convulsions, was attained within 7-10 min and lasted for about 30 min. A very rapid recovery followed and by 90 min rats were free from obvious toxicity. During intoxication, the body temperature was significantly below normal. In diaphragm, when the activity of acetylcholinesterase (AChE) was markedly depressed (82%), the levels of high-energy phosphates, adenosine triphosphate (ATP) and phosphocreatine (PCr) were also significantly lowered (27% and 54%, respectively). Significant decreases in the levels of adenosine diphosphate (ADP, 19%), total adenine nucleotides (TAN, 27%), creatine (Cr, 27%), and total creatine compounds (TCrC, 29%) were noted at various intervals. The ratio of PCr/Cr was reduced by 53%. The adenylate energy charge [(ATP + 1/2 ADP)/(ATP + ADP + AMP)], an indicator of high-energy phosphate bond availability, remained unchanged throughout the time course. More than twofold elevation in the activity of Mg(2+)-facilitated creatine kinase (reverse Lohmann reaction) in diaphragm (CK-MM) and more than twofold increase in the levels of glucose in serum, were suggestive of greater synthesis of ATP. Higher activity of CK-MM was also noted in the serum. That high-energy phosphates were partially depleted suggested that the rate of ATP utilization was far greater than its synthesis. Methomyl intoxication also resulted in higher activity of LDH and its isoenzymes in muscle as a result of induced greater synthesis. Elevation of CK and LDH and their isoenzymes in the serum was probably a result of their leakage from the tissues due to loss of membrane permeability caused by significant depletion of ATP and PCr.

OBJECTIVE (1) Retrospective evaluation of the clinical course of carbamate poisoning and the effect of oxime therapy in children. (2) In vitro study of the effect of oximes on the reactivation of carbamylated cholinesterase. DESIGN: (1) Clinical survey: The records of 26 children intoxicated with carbamates were examined retrospectively. The poisoning agents in all cases were positively identified as methomyl or aldicarb by gas chromatography-mass spectrometry. (2) Laboratory study: The direct effect of obidoxime and of pralidoxime on acetylcholinesterase activity in vitro was investigated in normal human packed red blood cells pretreated with an organophosphate (paraoxon) or a carbamate (aldicarb or methomyl). CLINICAL SETTING: Pediatric intensive care unit of a teaching hospital. PATIENTS: Twenty-six infants and young children (aged 1 to 8 years) admitted to the pediatric intensive care unit with severe carbamate intoxication. INTERVENTIONS: All cases had been treated with repeated doses of atropine sulfate (0.05 mg/kg) administered every 5 to 10 minutes until muscarinic symptoms disappeared. Obidoxime chloride (Toxogonin, 6 mg/kg) was administered on admission, and again after 4 to 5 hours. RESULTS: Predominant symptoms were related to central nervous system and nicotinic effects. All the patients showed marked improvement within several hours and recovered completely within 24 hours. None of the children deteriorated and none showed exacerbation of cholinergic symptoms after obidoxime treatment. In vitro, oximes reactivated acetylcholinesterase inhibited with paraoxon, whereas no significant effect of oximes on carbamylated enzyme activity was observed. CONCLUSIONS: Based on the recovery of all cases, as compared with other reports of carbamate poisoning treated with atropine alone, it is concluded that, in the case of aldicarb or methomyl poisoning, oxime therapy apparently does not contribute to the recovery of poisoned patients. In cases of poisoning by an unknown pesticide or of mixed poisoning, oxime therapy can prove beneficial because no negative effects of the therapy can be discerned.

The gas-liquid chromatographic behavior of methomyl (methyl N-[(methyl-carbamoyl)oxy]thioacetimidate), oxamyl (methyl N',N'-dimethyl-N-[(methylcarbamoyl)oxyl]-1-thiooxamimidate), their respective oxime hydrolysis products and the trimethylsilyl (TMS) ethers of the oximes on 5% OV-1 was studied under isothermal conditions using a flame-photometric detector in the sulfur-selective mode. In contrast to the behavior of the parent carbamates and underivatized oximes, the oxime-TMS ethers readily produced symmetrical peaks of consistent size. Quantities of derivative equivalent to at least 0.25 ng of oxime were easily measurable. Derivative formation was reproducible for standards over the range 10.0 to 0.25 microgram/ml in benzene and at 10.0 and 0.50 microgram/ml in the presence of extractives from tomato, carrot and celery at concentrations equivalent to 10 g/ml of crop. Derivative yields from crop extract fotifications were 89% or better in most cases. Both the carbamates and oximes were simply and consistently recovered in high yield from crops fortified at 1.00 and 0.05 ppm using the procedures described. The inclusion of a second analytical step provided separate analysis for oximes and carbamates. The application of these observations to the analyses of residues in crops is discussed.

A reverse phase high pressure liquid chromatographic method is presented for the separation and determination of residues of the carbamates oxamyl and methomyl on vegetables. A liquid-liquid extraction and cleanup procedure is applied to the vegetable extract. Samples are eluted from a muBondapak C18 column and quantitated by ultraviolet absorbance at 240 nm. Recovery data for vegetable samples spiked at 2 ppm are presented.

This method for determining carbamates is based on the inhibiting action of these substances on acetylcholinesterase activity. The use of radioactively labelled acetylcholine as a substrate, the ensuing extractive separation of the radioactive acetic acid (formed by hydrolysis) and its radiometric determination permit to detect very small amounts of carbamates. The limit of detection for aldicarb, baygon, benomyl, bux, carbaryl, CIPC, matacil, phenmedipham and promecarb lies in the picogram range; that for barban and methomyl, in the nanogram range. The lower, linear parts of the curves for the different carbamates fall within the range 0.001-10 ng. The sensitivity (expressed as delta% inhibition/delta lg ng carbamate) ranges from 1.0 to 9.7.