Importance of pH in assessing the potential for nitrosocarbamate formation in the stomach

Formation of the nitroso derivatives of ¹⁴C-labeled carbaryl, carbofuran, and p-chlorophenyl methylcarbamate (PCMC), and their subsequent stabilities were investigated using low levels of carbamate (0.5 μmol) and aqueous HCl concentrations encompassing those considered maximum for the gastric contents of humans (pH 1–2) and of rats (pH 3–4). Reacting the carbamates with excess sodium nitrite for 10 min at 37°C in a pH 1.0 HCl solution gave nitrosocarbamate yields of 42 to 64%, while only trace amounts were formed at pH 2 and above. The nitrosocarbamates were most stable at pH 3–5 with half-lives ranging from 114 to 470 min. Stability of all three nitroso derivatives was considerably less at pH 1.5 ($\text{t}\text{1}\text{2}$, 25–34 min), but at pH 7 the stability varied: nitroso-PCMC $\text{t}\text{1}\text{2}$, 6 min; nitrosocarbofuran $\text{t}\text{1}\text{2}$, 70 min; nitrosocarbaryl $\text{t}\text{1}\text{2}$, 139 min. Denitrosation to the parent carbamate was the predominant degradation pathway at pH 1.5, but at pH 3–7 degradation was primarily by hydrolysis of the carbamate ester linkage. Each of the nitrosocarbamates was directly mutagenic in the S. typhimurium assay system. Since the data show that nitrosation of residue levels of carbamate pesticides occurs readily at pH 1 but not at pH 2 and above, it is critical that gastric contents of any animal model used for assessing nitrosocarbamate formation have a pH approaching 1 as may occur in the human stomach.     

Paraoxon formation and hydrolysis by mammalian liver

In vitro studies of the desulfuration of parathion at 37°C by hepatic tissue from males and females of nine mammalian species revealed sex and species variation in initial rates of parathion desulfuration and arylesterase-catalyzed hydrolysis of the oxygen analogue, paraoxon. Double reciprocal plots of initial rates of parathion activation for representative males and females of each species gave K_m values ranging from 0.2 × 10^?4?1.0 × 10^?4M parathion. Guinea pigs and rats were the only animals showing sex differences in activation, males possessing higher desulfurating abilities than the corresponding females. Based upon the sex possessing the higher desulfurating ability, the species pattern of decreasing activity was hamster > guinea pig > mouse > rat > rabbit > bovine > dog > porcine > cat. Studies of paraoxon hydrolysis indicated that only rats showed sex differences in hydrolysis, males possessing higher arylesterase activity than females. The species pattern of decreasing hydrolytic activity was in the order mouse > bovine > rat > guinea pig > rabbit > hamster > cat > dog > porcine.     

Age-dependent variations in the response of several species of diptera to insecticidal chemicals

The toxicity of carbaryl to three species of fleshflies Sarcophaga bullata Parker, S. crassipalpis Macquart, and S. argyrostoma (Robineau-Desvoidy) varied considerably with age and sex. In contrast, the susceptibility of a blowfly, Phormia regina (Meigen) to carbaryl decreased with age and that of two muscid flies, Musca autumnalis DeGeer and Stomoxys calcitrans (L.), remained relatively constant. The synergistic activity of piperonyl butoxide varied inversely with the innate toxicity of carbaryl to each species suggesting that the observed age- and sex-dependent variations in carbaryl toxicity result mainly from differences in detoxifying capability. This was supported by in vitro measurements of oxidative microsomal metabolism. It was further established that differences in the rates of penetration and excretion of carbaryl and in the susceptibility of the head cholinesterase to carbaryl inhibition were of little importance in determining the susceptibility of the flies to this insecticide.     

Formic acid: A neurologically active, hydrolyzed metabolite of insecticidal formate esters

Formate esters have potential uses as insecticides in both grain fumigation and public health pest management. This research investigated the hydrolytic metabolism and neurological effects of formate ester compounds. Studies were conducted using Drosophila and houseflies as models for other dipteran pests of medical importance. Results indicated significant formic acid liberation from a broad range of formate esters, both in vivo and in vitro. Based on these initial observations, we subsequently investigated neurological effects of formic acid on the larval housefly nervous system. We found that formic acid caused significant neuroexcitation at concentrations lower than previously shown for inhibition of insect cytochrome c oxidase; however, this conclusion does not preclude that mitochondrial effects may also be occurring in non-nervous tissues. Finally, we investigated formate ester hydrolysis by A- and B-type esterases commonly considered in pesticide detoxification research; however, no significant interactions could be identified, suggesting that as yet unidentified carboxylesterases play roles in formate ester hydrolysis. These findings provide information on formate ester metabolism and modes of action, as well as rationale for further studies on formate ester neurotoxicology and mechanisms of selective toxicity.     

Glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) enzyme activities in different tissues of Sarotherodon mossambicus (Peters) exposed to a carbamate pesticide,carbaryl

The activity levels of glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) enzymes were estimated in liver, muscle and brain tissues of the fish, Sarotherodon mossambicus (Peters), which had been exposed to sub-lethal (3 mg litre⁻¹) and lethal (25 mg litre⁻¹) concentrations of the carbamate insecticide carbaryl. Based on the results obtained, the changes in GOT and GPT levels in liver, muscle and brain following different periods of sub-lethal and lethal carbaryl exposures suggested that S mossambicus showed adaptive elevation in the activity levels of the two aminotransferase enzymes in the tissues, thereby probably aiding gluconeogenesis through transamination of glucogenic amino acids to meet the energy demand under carbaryl toxicity. © 1999 Society of Chemical Industry     

氨基甲酸-2-氯吡啶-5-甲酯化合物的合成与抑菌活性

以芳香硝基化合物、2-氯-5-吡啶甲醇和一氧化碳为原料,在Pd-Fe/Ti O2催化下进行羰基化反应,合成了11个新型氨基甲酸-2-氯吡啶-5-甲酯化合物,其结构经1H NM R和M S表征。初步抑菌活性测定结果表明:在50 mg/L下,大多数目标化合物对4种供试病原菌具有一定的抑制活性,其中化合物3f(4-甲氧基苯基氨基甲酸-2-氯吡啶-5-甲酯、3h(2,4-二氯苯基氨基甲酸-2-氯吡啶-5-甲酯)和3j(3,4-二氯苯基氨基甲酸-2-氯吡啶-5-甲酯)对小麦赤霉病菌Gibberella zeae的抑制率达77.3%以上,3f对苹果轮纹病菌Physalospora piricola的抑制率达82.5%,与对照药多菌灵接近;所有化合物在50 mg/L下对番茄灰霉病菌Botrytis cinerea的抑制活性均优于对照药多菌灵。     

Investigations into carbamate insecticide selectivity: I: Evaluation of potential selectophores

In an effort to improve the generally unfavorable mouse/housefly toxicity ratio of most carbamate insecticides, potential selectophores (nitrile, carbamoyl oxime, carboxylic ester, or amide) were incorporated into a series of phenyl N-methylcarbamates. In addition to the insect and mouse toxicity determinations, the anticholinesterase activity of these compounds was determined for purified housefly head acetylcholinesterase and bovine erythrocyte acetylcholinesterase. The presence of these functional groups, in general, did not give enhanced selectivity ratios and, in one case, (o-N-methylcarbamoyloxyiminomethylphenyl N-methylcarbamate), a very unfavorable selectivity ratio of <0.03 was obtained. A mechanism implicating a Beckmann rearrangement is advanced to rationalize the high rodenticidal activity of this molecule. In general, the carbamates showed poor insecticidal activity when applied alone to the housefly, but, when the flies were pretreated with piperonyl butoxide, the compounds were quite toxic. Finally, an explanation is derived which seeks to justify the inability of these potential selectophores to improve the mouse/housefly toxidity ratio.     

Foliar residues and toxicity to Aphis citricola of three systemic insecticides applied to the soil in a citrus grove

A study was made of the accumulation of aldicarb, ethiofencarb and dimethoate in citrus leaves and fruit; the toxicity of these insecticides to the spirea aphid (Aphis citricola Van der Goot) was also studied. The effectiveness of the treatments was affected mainly by the rate of accumulation of the toxicant in the leaves. At 18 g a.i. per tree, the greatest residues found in the leaves were 106, 12.2 and 1.3 μg 8^?1 fresh weight for aldicarb, ethiofencarb and dimethoate, respectively. The concentration in mature leaves was very similar to that in young leaves. The residue levels in the mature fruits were much lower than in the leaves. The main components of the residues in the leaves were aldicarb sulphoxide [2-methyl-2-(methylsulphinyl)- propionaldehyde O-methylcarbamoyloxime], dimethoate, omethoate and ethiofencarb sulphoxide [2-(ethylsulphinylmethyl)phenyl methylcarbamate]. A laboratory study with synthetic diets showed similar toxicity for all three insecticides, whereas in detached leaves, or when taken up by citrus trees, ethiofencarb was the least toxic to the aphids.     

Influence of nitrogen fertilisers on the persistence of carbaryl and carbofuran in flooded soils

Ammonium sulphate and urea, but not potassium sulphate, increased the persistence of carbaryl in a flooded laterite soil with a low native nitrogen content (0.04%), but not in an alluvial soil with a higher nitrogen content (0.11%). Thus, NH₄⁺ but not SO₄^2-, contributed to the increased persistence of carbaryl. Likewise, ammonium sulphate increased the persistence of carbofuran in the laterite soil, but not in the alluvial soil. Significant accumulations of 1-naphthol and 2,3-dihydro-2, 2-dimethylbenzofuran-7-ol (‘carbofuran phenol’), in soils treated with carbaryl or carbofuran, suggested hydrolysis as the major pathway of degradation. Treatment of the two soils with ammonium sulphate, urea or potassium sulphate led to a decrease in soil-bound residues and an increase in the respective hydrolysis products, compared with untreated soils. Sorption studies indicated that NH₄⁺ and SO₄^2- compete with carbaryl, 1-naphthol and carbofuran for sorption and exchange sites in the complex soil system. Evolution of [¹⁴C]carbon dioxide from ring-¹⁴C in carbaryl and carbofuran was negligible. Consequently, after 40 days, more than 50% of the ¹⁴C in [¹⁴C]carbaryl and [¹⁴C]carbofuran remained in the soils as hydrolysis products (1-naphthol or 2,3-dihydro-2,2-dimethylbenzofuran-7-ol) plus soil-bound residues.     

The metabolism of 1-naphthyl methylcarbamate by Periplaneta americana

The in vivo release of ¹⁴CO2 arising from decarbamoylation of l-naphthyl methyl [¹⁴C]carbamate (carbaryl) injected into male and female Periplaneta americana was measured over the range from 0.2 to 50 nmol carbaryl/g body weight. The amount of ¹⁴CO2 released was proportional to the dose of [¹⁴C]-carbaryl injected and was not significantly different between male and female cockroaches. Carbaryl was found to be more toxic to male (KD100, 12 nmol carbaryl/g) than female (KD100′ 57 nmol carbaryl/g) cockroaches, at any dose which caused knockdown, females showed a greater ability to recover from the toxic syndrome than did males. The [¹⁴C]-carbaryl metabolism (decarbamoylation) was temperature dependent and could be partially inhibited by sesamex, tri-orthocresyl phosphate and anoxia. Secondary effects of carbaryl poisoning were severe dehydration of the animals and in some cases abdominal swelling due to air being gulped into the crop. The amount of dehydration was essentially unaltered by the chemical inhibitors, but was partially reduced by anoxia and cooling. In the most severe cases of dehydration animals lost 18 % of their body water content.     

Intestinal metabolism and absorption of carbaryl studied with a portal fistula

These data were obtained by use of a total and continuous portal vein fistula which virtually eliminated vascular redistribution of compounds absorbed from the gastrointestinal tract to nondigestive tissues (i.e., liver). The method allows direct measurement of the compounds absorbed, which is especially important in metabolism studies of ingested toxic compounds. These studies demonstrated that in vivo metabolism did occur within the intestine during the process of absorption of the pesticide carbaryl (naphthyl N-methylcarbamate) and naphthol, the hydrolysis product of the pesticide. Portal absorption of naphthol from a liquid diet (46 ± 4% of dose/120 min) was slower than from Ringer medium (75 ± 1%/120 min); portal absorption accounted for 82 ± 8 and 83 ± 4%, respectively, of the ¹⁴C absorbed from the intestine. The proportion of hydrophilic ¹⁴C-metabolites (water soluble) in portal blood varied from 6 to 89% and was a function of the substrate, dose vehicle (liquid diet vs Ringer), and time of portal fluid collection. Metabolism in the small intestine before absorption was confirmed for both substrates. The principal lipophilic constituent in portal fluid was the unmetabolized substrate for both carbaryl and naphthol; the principal ampholyte metabolite was naphthyl glucuronide. Although these in vivo data are qualitatively similar to evidence from previous in vitro studies, this in vivo evidence demonstrated that the extent of metabolism (and possibly detoxication) was considerably less than would be predicted from in vitro studies and indicates that the hazard of ingestion of carbaryl and other lipophilic toxic agents may be greater than realized.     

Metabolism of 2,3-dihydro-2,2-dimethyl-7-benzofuranyl (di-n-butylaminosulfenyl)(methyl)carbamate and 2,3-dihydro-2,2-dimethyl-7-benzofuranyl (morpholinosulfenyl)(methyl)carbamate in cotton and corn plants

The absorption, translocation, and metabolism of two new, selectively toxic derivatives of carbofuran, 2,3-dihydro-2,2-dimethyl-7-benzofuranyl (di-n-butylaminosulfenyl)(methyl)carbamate and 2,3-dihydro-2,2-dimethyl-7-benzofuranyl (morpholinosulfenyl)(methyl)carbamate, were studied in cotton and corn plants 1, 3, 6, and 10 days following both stem injection and foliage treatment. Both carbamates were readily translocated to all plant parts following stem injection, but translocation following leaf application was restricted to within the leaf. In cotton plants, the dibutylaminosulfenyl derivative was easily hydrolyzed to form carbofuran which, in turn, was oxidized at the 3-position of the ring and the N-methyl group. These oxidized metabolites were then converted to plant conjugates. Major metabolites were carbofuran and 3-hydroxy-carbofuran followed by 3-keto-carbofuran phenol and N-hydroxymethyl-carbofuran. Five minor metabolites also were detected. In corn plants, the dibutylaminosulfenyl derivative gave the same metabolites, although the metabolism rate was significantly slower in corn relative to cotton. Overall, the results showed that there were no fundamental differences in the metabolism of the morpholinosulfenyl and dibutylaminosulfenyl derivatives. The stability of both carbamate derivatives in different solvent systems also was investigated.     

Characterization of a Trans-permethrin hydrolyzing enzyme from the midgut of Pseudoplusia includens (Walker)

The enzymatic hydrolysis of trans-permethrin by midgut homogenates of the soybean looper, Pseudoplusia includens (Walker), was characterized through gel electrophoresis, isoelectric focusing, gel filtration chromatography, and selective inhibition. All three separation techniques indicated that one enzyme (or closely related enzyme forms) was responsible for the observed hydrolytic activity. The molecular weight was approximately 80,000, the isoelectric point ranged from pH 4.6 to 4.8, and the apparent K_m was 59.5 ± 3.2 μM. Enzyme activity was inhibited by organophosphates, carbamates, and sulfhydryl group inhibitors, as well as some chelators. The hydrolysis of trans-permethrin was distinct from the majority of “general esterase” activity when enzyme activity was separated by electrophoretic techniques.     

Penetration of insecticides through the foregut of the honeybee (Apis mellifera L.)

The rates of penetration of ¹⁴C-labeled insecticides (parathion, carbaryl, and dieldrin) through the foregut of the honeybee (Apis mellifera L.) were measured in vitro and in vivo. Uptake of the insecticides from the lumen of the foregut into foregut tissue was directly proportional to insecticide lipophilicity, but penetration through the foregut was not. Of the three insecticides studied, parathion appeared to possess the optimal physicochemical characteristics required for penetration. The uptake of carbaryl and release of dieldrin by the foregut tissues may limit their respective penetration rates. Insecticide penetration was found to be inversely proportional to the sucrose concentration in the lumen of the foregut in both in vitro and in vivo studies. The oral toxicity of carbaryl showed a similar dependence on the sucrose concentration of the solution in which the insecticide was fed. The data presented indicate that the honeybee foregut is permeable to lipophilic compounds and strongly suggest that this permeability may contribute substantially to the toxicity of orally ingested insecticides in this insect.     

农药混剂的选择毒性研究

稻瘟净或异稻瘟净与乐果或马拉松混用,对抗性黑尾叶蝉有明显的增效作用,对小白鼠急性口服毒性也有所增加。小白鼠口服稻瘟净或异稻瘟净后,鼠肝中水解乐果和N—甲基正己酰胺的羧酰胺酶活力明显下降;水解醋酸α-萘酯的羧酸酯酶活力也被抑制。羊肝微粒体的羧酰胺酶在体外分别被稻瘟净、异稻瘟净、磷酸三苯酯、磷酸三甲苯酯、苯硫磷、氧乐果和西维因强烈抑制,它们的I_(50)值为1.3×10~(-8)—4.0×10~(-5)克分子浓度。稻瘟净、异稻瘟净、磷酸三苯酯和西维因分别是羊肝羧酰胺酶和羧酸酯酶的竞争性抑制剂,它们的K_i值在4.8×10~(-8)—1.0×10~(-7)克分子浓度之间。这些结果表明稻瘟净、异稻瘟净等增加乐果和马拉松对哺乳动物的毒性的机制,可能主要是由于它们抑制了哺乳动物体内正常解毒乐果和马拉松的水解酶。文中讨论了这些农药混剂的选择毒性问题。     

Enzymatic hydrolysis of diazoxon by rat tissue homogenates

The enzymatic hydrolysis of ³²P-labeled diazoxon was studied using tissue homogenates of rat and American cockroach. The order of the hydrolytic activities of rat tissues for diazoxon was as follows: liver > blood > lung > heart > kidney > brain. A liver enzyme hydrolyzing diazoxon to diethyl phosphoric acid and 2-isopropyl-4-methyl-6-hydroxypyrimidine was located in the microsomes. The activity of the microsomal enzyme was inhibited by EDTA, heavy and rare earth metal ions, and SH reagents. Ca²⁺ activated the enzyme and protected it from inactivation. Mitochondrial and soluble enzymes from liver and a serum enzyme also hydrolyzed diazoxon and they were also activated by Ca²⁺. The removal of calcium bound to the microsomal enzyme protein by dialysis against EDTA led to a partially irreversible change of the enzyme. The hydrolysis of diazoxon by the Ca²⁺-requiring microsomal and serum enzymes was more rapid than that of paraoxon. Hydrolysis of diazoxon did not occur in American cockroach homogenates. This difference in the capacity to hydrolyze diazoxon between mammals and insects is discussed in relation to the selective toxicity of diazinon.     

Distinguishing between carbamate and organophosphate insecticide poisoning in house flies by symptomology

Three criteria, latency to convulsions, still period, and recovery are used to distinguish between carbamate and phosphate insecticide poisoning in house flies, Musca domestica. Because of shorter latencies with carbamate-treated flies, the central nervous system was considered more sensitive to the presence of carbamates than phosphates. Recovery from carbamate-induced tetany was considered correlated with reactivation of carbamylated cholinesterase. There appeared to be a fundamental difference between the insecticidal actions of carbamates and phosphates not wholly explainable by cholinesterase inhibition. Tethered or held house flies were less susceptible to poisoning than unrestrained flies.     

Effects of the synergist S,S,S-tributyl phosphorotrithioate on indoxacarb toxicity and metabolism in the European corn borer, Ostrinia nubilalis (Hübner)

The toxicity of the oxadiazine insecticide indoxacarb to the European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), was evaluated in the presence and absence of S,S,S-tributyl phosphorotrithioate (DEF), an inhibitor of hydrolytic metabolism. Bioassays involving topical application of different concentrations of indoxacarb to third instars of a susceptible O. nubilalis laboratory strain were performed, and in vitro metabolism experiments involving [¹⁴C] indoxacarb were examined to determine the role of hydrolytic metabolism in indoxacarb activation. Indoxacarb toxicity decreased in the presence of DEF indicating antagonism of toxicity. Results of in vivo and in vitro inhibition experiments indicated a reduction of indoxacarb activation and formation of the hydrolytic metabolite. These results are consistent with the proposed mechanism of hydrolytic activation for this compound.     

Metabolism of 2,2-dimethyl-2,3-dihydrobenzofuranyl-7 N-methyl-N-(2-toluenesulfenyl)carbamate in the housefly and white mouse

The metabolism of a new, selectively toxic derivative of carbofuran, 2,2-dimethyl-2,3-dihydrobenzofuranyl-7 N-methyl-N-(2-toluenesulfenyl)carbamate has been investigated. The selective toxicity between insect and mammal is due to differing pathways of metabolism. Houseflies appear peculiarly suited for the rapid liberation of the toxic agent, carbofuran, from N-(2-toluenesulfenyl) carbofuran in large amounts. Metabolism in the mouse is more complex and involves a series of oxidative and hydrolytic detoxication processes which do not result in the formation of carbofuran.     

Inhibition of permethrin-hydrolyzing esterases from Wiseana cervinata larvae

Inhibition of permethrin-hydrolyzing enzymes from larvae of the porina moth Wiseana cervinata has been examined in vivo and in vitro. Significant inhibition was shown by carbaryl and pirimiphos-methyl. 1-Dodecylimidazole substantially inhibited permethrin hydrolysis only in liver insects. The triphenylmethane dye tetrabromophenolphthalein was a moderate inhibitor only in vitro. TMDM (bis(N-dimethyl-4-aminophenyl)methane) had little effect on hydrolysis. These observations extend the range of species and substrates for which the triphenylmethane dyes and 1-dodecylimidazole are useful inhibitors of insecticide metabolism.