Dichloroacetamide antidotes for thiocarbamate herbicides: mode of action.

Thiocarbamate sulfoxides formed on metabolic sulfoxidation of thicoarbamate herbicides in plants and mammals are effective carbamoylating agents for glutathione and other tissue thiols. Dichloracetamides that protect corn from thiocarbamate herbicide injury more rapid detoxification of the thiocarbamate sulfoxides by increasing their rate of carbamoylation of glutathione through elevation of the root glutathione level and glutathione s-transferase activity.

Organophosphorus and methyl carbamate insecticide teratogenesis: diminished NAD in chicken embryos.

Studies with 36 organophosphorus and 12 methyl carbamate compounds establish a correlation between reduction in nicotinamide adenine dinucleotide (NAD) levels and severity of teratogenic signs in chicken embryos, a relation supported by reversal of these effects by nicotinamide derivatives. Diminished NAD occurring at organophosphorus and methyl carbamate concentrations as low as 0.6 to 2.0 parts per million in the egg constitutes a newly recognized biochemical lesion induced by the two most important classes of insecticide chemicals.

Thiocarbamate sulfoxides: potent, selective, and biodegradable herbicides.

Sulfoxidation of thiocarbamates yields a new class of chemicals having increased herbicidal activity along with greater tolerance of corn and soybeans in greenhouse tests. However, their thermal stability is not favorable. These sulfoxides are intermediates in the mammalian metabolism of thiocarbamates, being formed by liver microsomal oxidases and cleaved in a system consisting of glutathione and a soluble enzyme from liver.

Stereospecific action of pyrethroid insecticides on the gamma-aminobutyric acid receptor-ionophore complex.

The potent alpha-cyano-3-phenoxybenzyl pyrethroids, including cypermethrin, deltamethrin, and fenvalerate, act stereospecifically to inhibit binding to rat brain synaptic membranes of sulfur-35-labeled t-butylbicyclophosphorothionate, a new radioligand for the picrotoxinin binding site. Scatchard analysis indicates that picrotoxinin inhibition of t-butylbicyclophosphorothionate binding is competitive whereas cypermethrin inhibition possibly involves a closely associated site in the gamma-aminobutyric acid receptor-ionophore complex. Studies with 37 pyrethroids reveal an absolute correlation, that is, no false positives or negatives, between mouse intracerebral toxicity and in vitro inhibition: all toxic cyano compounds but none of their nontoxic stereoisomers are inhibitors; cis isomers are more potent than trans isomers as both toxicants and inhibitors; and noncyano pyrethroids are much less potent or are inactive.

Novel activation mechanism for the promutagenic herbicide diallate.

The potent bacterial mutagen 2-chloroacrolein is formed from the carcinogenic herbicide S-2,3-dichloroallyl diisopropylthiocarbamate (diallate) on incubation with hepatic microsomal monooxygenases or on reaction with m-chloroperbenzoic acid. A proposed activation mechanism for this promutagen involves sulfoxidation followed by [2,3] sigmatropic rearrangement and 1,2-elimination reactions. A portion of the highly reactive intermediate, diallate sulfoxide (proximate mutagens), is attacked by glutathione in a reaction which competes with its transformation to the ultimate mutagen, 2-chloroacrolein.

Insecticidal benzoylphenyl ureas: structure-activity relationships as chitin synthesis inhibitors.

The 1-benzoyl-3-phenylurea insecticide diflubenzuron is a potent inhibitor for the conversion of (14)C-labeled glucose to (14)C-labeled chitin in isolated abdomens of newly emerged adult milkweed bugs (Oncopeltus fasciatus Dallas). The inhibitory activity of 24 diflubenzuron analogs in this in vitro chitin-synthesizing system is in good agreement with their toxicity to fifth instar nymphs of this species. These insecticides act quickly and directly within the integument to ultimately block the terminal polymerization step in chitin formation.

Bicyclic phosphorus esters: high toxicity without cholinesterase inhibition.

4-Isopropyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane 1-oxide has a mouse intraperitoneal lethal dose, 50 percent effective, of 0.18 milligram per kilogram of body weight. Related compounds used by many chemical researchers are also highly toxic. Brain acetylcholinesterase inhibition is not involved in their mode of action. The structural similarity of these compounds to adenosine 3',5'-monophosphate (cyclic AMP) is of interest.

Pyrethroid insecticides: esterase cleavage in relation to selective toxicity.

The ester group of primary alcohol chrysanthemates is cleaved by mouse hepatic microsomal esterases, more rapidly for the (+)-trans than for the (+)-cis isomers. Substrate-specificity and inhibition studies in vivo establish that these pyrethroid-hydrolyzing esterases probably contribute to the low mammalian toxicity of bioresmethrin and other (+)-trans chrysanthemate insecticide chemicals derived from primary alcohols.

Metabolism of rotenone in vitro by tissue homogenates from mammals and insects.

Hydroxylation of rotenone in vitro in the enzyme system composed of microsomes and reduced nicotinamide-adenine dinucleotide phosphate, and in living mice and houseflies, yields products tentatively identified as rotenolone I; rotenolone II; 8'-hydroxyrotenone; 6',7'-dihydro-6',7'-dihydroxyrotenone; two rotenolones of each of the last-mentioned two compounds; and uncharacterized polar materials. The toxicity of certain of these rotenoids to mice is of the same order as that of rotenone.

Pyrethroid-like biological activity of compounds lacking cyclopropane and ester groupings.

The following new insecticidal compounds respond to synergism by piperonyl butoxide and block nerve excitability in the same manner as the insecticide allethrin: 1-(4-allethronyl)-acetyl-2,2-dimethyl-3-isobutenylcyclopropane (the ketone analog of allethrin) and the esters of 5-benzyl-3 furylmethanol with 2,2,3,3-tetramethylcyclopropanecarboxylic acid, 2,2,3,3-tetramethylaziridinecarboxylic acid, and N, N-diisopropylcarbamic acid. Therefore pyrethroid-like activity is not restricted to esters of cyclopropanecarboxylic acids.

Enhancement of photoalteration of cyclodiene insecticide chemical residues by rotenone.

When applied at low concentrations to plant foliage, rotenone catalyzes the photoisomerization of dieldrin and other cyclodiene insecticide chemical residues. This finding of a new type of interaction between pesticide chemicals suggests the possibility of controlling the persistence of residues on plants by use of certain pesticide-photosensitizer combinations and application sequences.

Oxidative bioactivation of S-alkyl phosphorothiolate pesticides: stereospecificity of profenofos insecticide activation.

The mouse liver microsomal mixed-function oxidase system converts several phosphorothiolate pesticides with S-ethyl, S-propyl, or S-butyl groups to more potent inhibitors of acetylcholinesterase. This activation is stereospecific for the chiral isomers of O-(4-bromo-2-chlorophenyl) O-ethyl S-propyl phosphorothiolate (profenofos insecticide); the more toxic (-) isomer becomes a 34-fold better inhibitor of acetylcholinesterase in vitro, whereas the less toxic (+) isomer is deactivated by a factor of 2. Prior treatment of the microsomes with piperonyl butoxide or another mixed-function oxidase inhibitor markedly decreases the activation. Piperonyl butoxide also protects against brain acetylcholinesterase inhibition and cholinergic symptoms in chicks resulting from (-)-profenofos administration, thus establishing the importance of the oxidative bioactivation of S-alkyl phosphorothiolate pesticides in vivo.

Polychlorobornane components of toxaphene: structure-toxicity relations and metabolic reductive dechlorination.

2,2,5-endo,6-exo,8,9,10-Heptachlorobornane and four derivatives of this heptachlorobornane, with an additional chlorine atom at position 3-exo,8,9, or 10, account for a major portion of the acute toxicity of toxaphene and for up to 23 percent of toxaphene composition as analyzed by open tubular column gas-liquid chromatography with an electron capture detector. Both in several organisms and model environmental systems and on photolysis, this heptachlorobornane undergoes facile reductive dechlorination at the geminal-dichloro group and sometimes dehydrochlorination.

Toxaphene, a complex mixture of polychloroterpenes and a major insecticide, is mutagenic.

Toxaphene, the most widely used chlorinated insecticide, is mutagenic in the Salmonella test without requiring liver homogenate for activity. This insecticide is a complex mixture (more than 177 polychloroterpenes) with carcinogenic activity in rodents. Some but not all of the mutagenic components are easily separated from the insecticidal ingredients.

Methylene-C14-dioxyphenyl compounds: metabolism in relation to their synergistic action.

The methylene-C(14) group is hydroxylated yielding formate-C(14) in the microsome-reduced nicotinamide-adenine dinucleotide phosphate system in vitro and yielding expired C(14)O(2), in living mice and houseflies. Methylenedioxyphenyl compounds apparently serve as alternate substrates for this enzymatic hydroxylation system of microsomes, and thus reduce the rate of metabolism and prolong the action of certain drugs and insecticide chemicals.

Toxaphene insecticide: a complex biodegradable mixture.

Adsorption and gas-liquid chromatography separate toxaphene into at least 175 polychlorinated 10-carbon compounds including Cl(6), Cl(7), Cl(8), Cl(9), and Cl(10) derivatives. One toxic component is 2,2,5-endo,6-exo,8,9,10-heptachlorobornane. Rats metabolically dechlorinate toxaphene, removing about half of the chlorine from the technical insecticide and from each of seven subfractions of varying composition and toxicity.

Functional coupling of PSST and ND1 subunits in NADH:ubiquinone oxidoreductase established by photoaffinity labeling.

NADH:ubiquinone oxidoreductase (complex I) is the first, largest and most complicated enzyme of the mitochondrial electron transport chain. Photoaffinity labeling with the highly potent and specific inhibitor trifluoromethyldiazirinyl-[(3)H]pyridaben ([(3)H]TDP) labels only the PSST and ND1 subunits of complex I in electron transport particles. PSST is labeled at a high-affinity site responsible for inhibition of enzymatic activity while ND1 is labeled at a low-affinity site not related to enzyme inhibition. In this study we found, as expected, that 13 complex I inhibitors decreased labeling at the PSST site without effect on ND1 labeling. However, there were striking exceptions where an apparent interaction was found between the PSST and ND1 subunits: preincubation with NADH increases PSST labeling and decreases ND1 labeling; the very weak complex I inhibitor 1-methyl-4-phenylpyridinium ion (MPP(+)) and the semiquinone analogue stigmatellin show the opposite effect with increased labeling at ND1 coupled to decreased labeling at PSST in a concentration- and time-dependent manner. MPP(+), stigmatellin and ubisemiquinone have similarly positioned centers of highly negative and positive electrostatic potential surfaces. Perhaps the common action of MPP(+) and stigmatellin on the functional coupling of the PSST and ND1 subunits is initiated by binding at a semiquinone binding site in complex I.

Ca2+-dependent ryanodine binding site: soluble preparation from rabbit cardiac sarcoplasmic reticulum.

The Ca2+-dependent ryanodine binding site of rabbit cardiac sarcoplasmic reticulum is solubilized by treatment with 20 mM CHAPS detergent and 1 M NaCl for 30 min at 0 degrees C. Ca2+ added at 5 microM enhances binding, at 0.5 mM increases both the affinity and number of [3H]ryanodine binding sites, while at 10 mM only the number of binding sites is increased. Mg2+ up to 1 mM does not significantly affect [3H]ryanodine binding. Radioligand binding is strongly enhanced by all alkali metal chlorides except LiCl. NaCl increases the rate of association of the ligand and the affinity of the binding site but does not influence the dissociation. NaCl and CaCl2 enhance the thermal stability of the [3H]ryanodine-binding protein. Thiol groups are essential for [3H]ryanodine binding. Ruthenium red and Cd2+ inhibit binding, while theophylline is stimulatory at low (micromolar) Ca2+ concentrations by a mechanism other than phosphodiesterase inhibition. Gel permeation chromatography establishes that the ryanodine binding protein is localized only in the high molecular mass fraction (greater than 669 kDa). Polyacrylamide gel electrophoresis of the proteins following treatment with SDS and 2-mercaptoethanol indicates that more than 90% are of low molecular mass (34-70 kDa) and that two stain blue with Stains-all as expected of Ca2+-binding proteins.

Phosphine-induced oxidative damage in rats: attenuation by melatonin.

Phosphine (PH(3)), from hydrolysis of aluminum, magnesium and zinc phosphide, is an insecticide and rodenticide. Earlier observations on PH(3)-poisoned insects, mammals and a mammalian cell line led to the proposed involvement of oxidative damage in the toxic mechanism. This investigation focused on PH(3)-induced oxidative damage in rats and antioxidants as candidate protective agents. Male Wistar rats were treated ip with PH(3) at 2 mg/kg. Thirty min later the brain, liver, and lung were analyzed for glutathione (GSH) levels and lipid peroxidation (as malondialdehyde and 4-hydroxyalkenals) and brain and lung for 8-hydroxydeoxyguanosine (8-OH-dGuo) in DNA. PH(3) caused a significant decrease in GSH concentration and elevation in lipid peroxidation in brain (36-42%), lung (32-38%) and liver (19-25%) and significant increase of 8-OH-dGuo in DNA of brain (70%) and liver (39%). Antioxidants administered ip 30 min before PH(3) were melatonin, vitamin C, and beta-carotene at 10, 30, and 6 mg/kg, respectively. The PH(3)-induced changes were significantly or completely blocked by melatonin while vitamin C and beta-carotene were less effective or inactive. These findings establish that PH(3) induces and melatonin protects against oxidative damage in the brain, lung and liver of rats and suggest the involvement of reactive oxygen species in the genotoxicity of PH(3).

Novel and potent 6-chloro-3-pyridinyl ligands for the alpha4beta2 neuronal nicotinic acetylcholine receptor.

1-[(6-Chloro-3-pyridinyl)methyl]-2-imidazolidine (1), the N-desnitro metabolite of the major insecticide imidacloprid, is known to have similar potency to that of (-)-nicotine as an inhibitor of [3H](-)-nicotine binding at the rat recombinant alpha4beta2 neuronal nicotinic acetylcholine receptor (nAChR); IC50 values in the present study are 3.8 nM for (-)-nicotine, 6.0 nM for 1, and 155 nM for imidacloprid. Synthesis of new analogues of 1, modified only in the heterocyclic moiety (five-, six-, or seven-membered rings with NH, S, O, and CH2 substituents), gave compounds varying from 4-fold higher potency (2-iminothiazole analogue 10) to >6000-fold less active than (-)-nicotine. Other potent N-[(6-chloro-3-pyridinyl)methyl] compounds are those in which the heterocyclic imine is replaced with pyrrolidine (19) (IC50 9 nM) or trimethylammonium (22) (IC50 18 nM). A novel conversion of (-)-nicotine to its 6-chloro analogue increased the potency 2-fold. These 6-chloro-3-pyridinyl compounds are of interest as novel nAChR probes and potential metabolites of candidate insecticides.