Meta-Analysis of the Field Efficacy of Seed- and Soil-Applied Nematicides on Meloidogyne incognita and Rotylenchulus reniformis Across the U.S. Cotton Belt.

Meta-analysis was used to compare yield protection and nematode suppression provided by two seed-applied and two soil-applied nematicides against Meloidogyne incognita and Rotylenchulus reniformis on cotton across 3 years and several trial locations in the U.S. Cotton Belt. Nematicides consisted of thiodicarb- and fluopyram-treated seed, aldicarb and fluopyram applied in furrow, and combinations of the seed treatments and soil-applied fluopyram. The nematicides had no effect on nematode reproduction or root infection but had a significant impact on seed cotton yield response ([Formula: see text]), with an average increase of 176 and 197 kg/ha relative to the nontreated control in M. incognita and R. reniformis infested fields, respectively. However, because of significant variation in yield protection and nematode suppression by nematicides, five or six moderator variables (cultivar resistance [M. incognita only], nematode infestation level, nematicide treatment, application method, trial location, and growing season) were used depending on nematode species. In M. incognita-infested fields, greater yield protection was observed with nematicides applied in furrow and with seed-applied + in-furrow than with solo seed-applied nematicide applications. Most notable of these in-furrow nematicides were aldicarb and fluopyram (>131 g/ha) with or without a seed-applied nematicide compared with thiodicarb. In R. reniformis-infested fields, moderator variables provided no further explanation of the variation in yield response produced by nematicides. Furthermore, moderator variables provided little explanation of the variation in nematode suppression by nematicides in M. incognita- and R. reniformis-infested fields. The limited explanation by the moderator variables on the field efficacy of nematicides in M. incognita- and R. reniformis-infested fields demonstrates the difficulty of managing these pathogens with nonfumigant nematicides across the U.S. Cotton Belt.

The Claudin-like Protein HPO-30 Is Required to Maintain LAChRs at the C. elegans Neuromuscular Junction.

Communications across chemical synapses are primarily mediated by neurotransmitters and their postsynaptic receptors. There are diverse molecular systems to localize and regulate the receptors at the synapse. Here, we identify HPO-30, a member of the claudin superfamily of membrane proteins, as a positive regulator for synaptic localization of levamisole-dependent AChRs (LAChRs) at the Caenorhabditis elegans neuromuscular junction (NMJ). The HPO-30 protein localizes at the NMJ and shows genetic and physical association with the LAChR subunits LEV-8, UNC-29, and UNC-38. Using genetic and electrophysiological assays in the hermaphrodite C. elegans, we demonstrate that HPO-30 functions through Neuroligin at the NMJ to maintain postsynaptic LAChR levels at the synapse. Together, this work suggests a novel function for a tight junction protein in maintaining normal receptor levels at the NMJ.SIGNIFICANCE STATEMENT Claudins are a large superfamily of membrane proteins. Their role in maintaining the functional integrity of tight junctions has been widely explored. Our experiments suggest a critical role for the claudin-like protein, HPO-30, in maintaining synaptic levamisole-dependent AChR (LAChR) levels. LAChRs contribute to <20% of the acetylcholine-mediated conductance in adult Caenorhabditis elegans; however, they play a significant functional role in worm locomotion. This study provides a new perspective in the study of LAChR physiology.

Efficacy of Recommended Prehospital Human Equivalent Doses of Atropine and Pralidoxime Against the Toxic Effects of Carbamate Poisoning in the Hartley Guinea Pig.

PURPOSE: Aldicarb and methomyl are carbamate pesticides commonly implicated in human poisonings. The primary toxic mechanism of action for carbamate poisoning is cholinesterase (ChE) inhibition. As such, it is logical to assume that the currently accepted therapies for organophosphate poisoning (muscarinic antagonist atropine and the oxime acetylcholinesterase reactivator pralidoxime chloride [2-PAM Cl]) could afford therapeutic protection. However, oximes have been shown to be contraindicated for poisoning by some carbamates. METHODS: A protective ratio study was conducted in guinea pigs to evaluate the efficacy of atropine and 2-PAM Cl. The ChE activity was determined in both the blood and the cerebral cortex. RESULTS: Coadministration of atropine free base (0.4 mg/kg) and 2-PAM Cl (25.7 mg/kg) demonstrated protective ratios of 2 and 3 against aldicarb and methomyl, respectively, relative to saline. The data reported here show that this protection was primarily mediated by the action of atropine. The reactivator 2-PAM Cl had neither positive nor negative effects on survival. Both blood acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities were significantly reduced at 15 minutes postchallenge but gradually returned to normal within 24 hours. Analysis of cerebral cortex showed that BChE, but not AChE, activity was reduced in animals that succumbed prior to 24 hours after challenge. CONCLUSION: The results suggest that coadministration of atropine and 2-PAM Cl at the currently recommended human equivalent doses for use in the prehospital setting to treat organophosphorus nerve agent and pesticide poisoning would likely also be effective against aldicarb or methomyl poisoning.

Successful validation of genomic biomarkers for human immunotoxicity in Jurkat T cells in vitro.

Previously, we identified 25 classifier genes that were able to assess immunotoxicity using human Jurkat T cells. The present study aimed to validate these classifiers. For that purpose, Jurkat cells were exposed for 6 h to subcytotoxic doses of nine immunotoxicants, five non-immunotoxicants and four compounds for which human immunotoxicity has not yet been fully established. RNA was isolated and subjected to Fluidigm quantitative real time (qRT)-PCR analysis. The sensitivity, specificity and accuracy of the screening assay as based on the nine immunotoxicants and five non-immunotoxicants used in this study were 100%, 80% and 93%, respectively, which is better than the performance in our previous study. Only one compound was classified as false positive (benzo-e-pyrene). Of the four potential (non-)immunotoxicants, chlorantraniliprole and Hidrasec were classified immunotoxic and Sunset yellow and imidacloprid as non-immunotoxic. ToxPi analysis of the PCR data provided insight in the molecular pathways that were affected by the compounds. The immunotoxicants 2,3-dichloro-propanol and cypermethrin, although structurally different, affected protein metabolism and cholesterol biosynthesis and transport. In addition, four compounds, i.e. chlorpyrifos, aldicarb, benzo-e-pyrene and anti-CD3, affected genes in cholesterol metabolism and transport, protein metabolism and transcription regulation. qRT-PCR on eight additional genes coding for similar processes as defined in ToxPi analyzes, supported these results. In conclusion, the 25 immunotoxic classifiers performed very well in a screening with new non-immunotoxic and immunotoxic compounds. Therefore, the Jurkat screening assay has great promise to be applied within a tiered approach for animal free testing of human immunotoxicity.

Benchmark dose calculation for ordered categorical responses.

The use of benchmark dose (BMD) calculations for dichotomous or continuous responses is well established in the risk assessment of cancer and noncancer endpoints. In some cases, responses to exposure are categorized in terms of ordinal severity effects such as none, mild, adverse, and severe. Such responses can be assessed using categorical regression (CATREG) analysis. However, while CATREG has been employed to compare the benchmark approach and the no-adverse-effect-level (NOAEL) approach in determining a reference dose, the utility of CATREG for risk assessment remains unclear. This study proposes a CATREG model to extend the BMD approach to ordered categorical responses by modeling severity levels as censored interval limits of a standard normal distribution. The BMD is calculated as a weighted average of the BMDs obtained at dichotomous cutoffs for each adverse severity level above the critical effect, with the weights being proportional to the reciprocal of the expected loss at the cutoff under the normal probability model. This approach provides a link between the current BMD procedures for dichotomous and continuous data. We estimate the CATREG parameters using a Markov chain Monte Carlo simulation procedure. The proposed method is demonstrated using examples of aldicarb and urethane, each with several categories of severity levels. Simulation studies comparing the BMD and BMDL (lower confidence bound on the BMD) using the proposed method to the correspondent estimates using the existing methods for dichotomous and continuous data are quite compatible; the difference is mainly dependent on the choice of cutoffs for the severity levels.

Fluensulfone is a nematicide with a mode of action distinct from anticholinesterases and macrocyclic lactones.

Plant parasitic nematodes infest crops and present a threat to food security worldwide. Currently available chemical controls e.g. methyl bromide, organophosphates and carbamates have an unacceptable level of toxicity to non-target organisms and are being withdrawn from use. Fluensulfone is a new nematicide of the fluoroalkenyl thioether group that has significantly reduced environmental impact with low toxicity to non-target insects and mammals. Here, we show that the model genetic organism Caenorhabditis elegans is susceptible to the irreversible nematicidal effects of fluensulfone. Whilst the dose required is higher than that which has nematicidal activity against Meloidogyne spp. the profile of effects on motility, egg-hatching and survival is similar to that reported for plant parasitic nematodes. C. elegans thus provides a tractable experimental paradigm to analyse the effects of fluensulfone on nematode behaviour. We find that fluensulfone has pleiotropic actions and inhibits development, egg-laying, egg-hatching, feeding and locomotion. In the case of feeding and locomotion, an early excitation precedes the gross inhibition. The profile of these effects is notably distinct from other classes of anthelmintic and nematicide: the inhibition of motility caused by fluensulfone is not accompanied by the hypercontraction which is characteristic of organophosphates and carbamates and C. elegans mutants that are resistant to the carbamate aldicarb and the macrocyclic lactone ivermectin retain susceptibility to fluensulfone. These data indicate fluensulfone's mode of action is distinct from currently available nematicides and it therefore presents a promising new chemical entity for crop protection.

Caenorhabditis elegans wsp-1 regulation of synaptic function at the neuromuscular junction.

The Rho GTPase members and their effector proteins, such as the Wiskott-Aldrich syndrome protein (WASP), play critical roles in regulating actin dynamics that affect cell motility, endocytosis, cell division, and transport. It is well established that Caenorhabditis elegans wsp-1 plays an essential role in embryonic development. We were interested in the role of the C. elegans protein WSP-1 in the adult nematode. In this report, we show that a deletion mutant of wsp-1 exhibits a strong sensitivity to the neuromuscular inhibitor aldicarb. Transgenic rescue experiments demonstrated that neuronal expression of WSP-1 rescued this phenotype and that it required a functional WSP-1 Cdc42/Rac interactive binding domain. WSP-1-GFP fusion protein was found localized presynaptically, immediately adjacent to the synaptic protein RAB-3. Strong genetic interactions with wsp-1 and other genes involved in different stages of synaptic transmission were observed as the wsp-1(gm324) mutation suppresses the aldicarb resistance seen in unc-13(e51), unc-11(e47), and snt-1 (md290) mutants. These results provide genetic and pharmacological evidence that WSP-1 plays an essential role to stabilize the actin cytoskeleton at the neuronal active zone of the neuromuscular junction to restrain synaptic vesicle release.

A semi-fluid gellan gum medium improves nematode toxicity testing.

This study examined an alternative test medium for nematodes that use gellan gum as the gelling agent instead of agar. The semi-fluid consistency of the gel-like component nematode growth gellan gum (CNGG) supports three-dimensional distribution of the nematodes and food bacteria, but still allows free movement of the former. Moreover, flexible preparation of the medium and easy recovery of the test organisms are possible. Here, the effects of the nematicides ivermectin (pharmaceutical) and aldicarb (pesticide) and of the metal cadmium on the growth and reproduction of the free-living nematodes Caenorhabditis elegans and Panagrolaimus cf. thienemanni were studied in CNGG media. Results were compared to those obtained with the standard liquid test media in order to evaluate the applicability of CNGG for nematode toxicity testing. The sensitivity of P. cf. thienemanni to all three substances was found to be higher than that of C. elegans, but both nematodes showed the highest sensitivity to ivermectin exposure. This raises concerns about the risk posed by the pharmaceutical to non-target nematodes. In contrast to ivermectin bioassays carried out in CNGG medium, those conducted in liquid medium resulted in wide-ranging variability between and within replicates. Thus, CNGG seems to be particularly valuable for testing hydrophobic substances with a high sorption affinity as it favors their sorption to food bacteria and minimizes contact with the surfaces of the test vessels. However, the medium was less suitable for deriving toxicity thresholds for cadmium and may likewise not be an appropriate choice for testing other metals. The medium introduced herein was shown to be appropriate for sublethal nematode toxicity testing and likely provides a convenient environment for testing other nematode species. Besides improved testing of hydrophobic substances, CNGG also offers advantages for long-term studies, such as full life-cycle experiments, in which fresh medium is regularly needed. Moreover it may be beneficial for testing other poorly soluble or insoluble substances, such as nanoparticles.

Application of physiologically based modelling and transcriptomics to probe the systems toxicology of aldicarb for Caenorhabditis elegans (Maupas 1900).

The toxicity of aldicarb on movement, life cycle, population growth rate and resource allocation, and the gene expression changes underpinning these effects, were investigated for Caenorhabditis elegans. A clear effect of aldicarb on nematode movement was found suggesting that this pesticide acts as a neurotoxicant. Aldicarb also had an effect on life cycle traits including low concentration life-span extension; high concentration brood size reduction and a high concentration extension of time to first egg. All life-cycle and growth data were integrated into a biology-based model (DEBtox) to characterise aldicarb effects on life-history traits, resource allocation and population growth rate within a single modelling framework. The DEBtox fits described concentration dependent effects on individual traits and population growth rate and indicated that the most probable mechanism of action of the pesticide was an increase in energy demands for somatic and reproductive tissue maintenance. Transcriptomic profiling indicated that aldicarb was associated with changes in amino acid metabolism, DNA structure, fatty acid metabolism and cytochrome P450 mediated xenobiotic metabolism. The changes in the amino acid and fatty acid pathways suggest an effect of aldicarb on protein integrity; while effects on DNA suggests that aldicarb influence DNA morphology or replication. Both these effects have the potential to incur increased costs for structural maintenance of macromolecules. These effects, coupled to the effect on biotransformation enzymes also seen, represent the materialisation of the maintenance costs indicated by DEBtox modelling.

Effects of chlorpyrifos and aldicarb on flight activity and related cholinesterase inhibition in homing pigeons, Columba livia: potential for migration effects.

Homing pigeons (Columba livia) were used as a model to assess the effects of chlorpyrifos and aldicarb on flight times at sub-lethal, environmentally relevant concentrations. A significant increase in flight times of birds dosed with aldicarb and with chlorpyrifos was observed. Plasma cholinesterase activity was measured over time following exposure to either compound. The results suggest that the time of peak inhibition would correlate with migratory flight activity after exposure. In total, the results of these studies show that sub-lethal exposure to cholinesterase-inhibiting pesticides can affect the flying ability of non-target avian species.

In vivo efficacy of the Reactive Skin Decontamination Lotion (RSDL®) kit against organophosphate and carbamate pesticides.

In this study, we assessed the efficacy of the Reactive Skin Decontamination Lotion (RSDL®) Kit against parathion and aldicarb pesticide dermal exposure in a guinea pig model. The pesticides inhibit acetylcholinesterase (AChE) leading to signs and symptoms of hyperactivity of organs due to accumulation of acetylcholine. The RSDL Kit has been shown to physically remove and chemically degrade chemical warfare agents. Degradation occurs from a nucleophilic substitution reaction between an active ingredient in the RSDL lotion, potassium 2,3-butanedione monoximate (KBDO), with susceptible sites in these compounds. In the present study, guinea pigs dermally exposed to parathion and aldicarb were decontaminated with RSDL to mitigate the toxic effects of the pesticides. It is observed that animals exposed to 749 mg/kg of parathion (n = 3) died within 24 h without RSDL decontamination; however, RSDL-treated animals (n = 3) showed only mild signs of neurotoxicity. The RSDL-treated animals had an AChE inhibition of 0-58% while the untreated animals had up to 86% inhibition. Similarly, RSDL has been demostrated to prevent aldicarb neurotoxicity effects. The percent inhibition of AChE activity during the 24 h post challenge of 9 mg aldicarb/kg of animal weight ranged from 25% to 61% with severe signs of intoxication while only up to 5% with mild or no signs of intoxication in the case of RSDL-decontaminated animals. Generally, it has been shown that the toxic effects of the organophosphate and carbamate pesticides can be prevented via decontamination using the RSDL Kit.

Effects of four carbamate compounds on antioxidant parameters.

The effect of four carbamates, aldicarb and its metabolites (aldicarb sulfone and aldicarb sulfoxide) and propoxur on glutathione content and the activity of the enzymes involved in the sulfur-redox cycle in the mammalian cellular model CHO-K1 cells after 24-h exposure were determined. Carbamate exposure resulted in a depletion of intracellular reduced glutathione (GSH) content, no change was observed in oxidized glutathione (GSSG) and a decrease in GSH/GSSG ratio was detected. After carbamates exposition a GSH/GSSG decreases in ranged from 12.44% to 21.35% of control was observed. Depletion of GSH levels was accompanied by the induction of glutathione reductase (GR) after 24h exposure with each of the four carbamates to CHO-K1 cells. After aldicarb sulfone, aldicarb sulfoxide, and propoxur exposure, glutathione peroxidase (GPx) activity increased in CHO-K1 cells by 198%, 32%, and 228% of control, respectively. After aldicarb sulfone and propoxur exposure, glutathione transferase (GST) activities increased by 49% and 230% of control, respectively. Due to the role played by GSH in preventing cytotoxicity via free-radical scavenging, results obtained suggest that high concentrations of aldicarb sulfone and propoxur closely resembling oxidative stress in CHO-K1 cells.

Oxotremorine-induced hypothermia as a method for evaluating long-term neuronal changes following poisoning by cholinesterase inhibitors in rats.

Severe poisoning by inhibitors of cholinesterase (ChE) enzymes is often associated with prolonged central or peripheral neuronal damage. Oxotremorine is a cholinergic agonist known to induce acute hypothermia. Central and peripheral cholinergic signaling is involved in the induction of hypothermia as well as in its recovery. These processes were used in the present study to reveal prolonged neuronal abnormalities in poisoned rats, using oxotremorine with and without concomitant administration of the peripheral muscarinic antagonist methyl scopolamine. In non-poisoned naïve rats, the hypothermic effect of oxotremorine appeared faster while its recovery was delayed following co-administration of methyl scopolamine, suggesting predominantly peripheral processes in counteracting the hypothermia. One month after exposure to approximately 1LD(50) of the carbamates aldicarb and oxamyl, the hypothermic effect of oxotremorine was similar to that found in saline-treated control group. However, the effect of methyl scopolamine on the recovery process was significantly diminished, indicating that the impaired cholinergic mechanisms were predominantly peripheral. In contrast, 1 month following organophosphate (OP) poisoning by the nerve agents sarin and VX, oxotremorine-induced hypothermia was reduced, indicating mainly impaired central cholinergic mechanisms. The development of severe convulsions during nerve agent poisoning may explain the central neuronal damage in OP-poisoned rats, displayed as reduced hypothermia. As convulsions were not part of the poisoning symptoms with the carbamates tested, their long-term damage was displayed at the recovery stage. This method might be used as a relatively simple means for detecting differential long-term central and peripheral cholinergic injuries, long after toxicity signs have receded.

Suborganismic and organismic effects of aldicarb and its metabolite aldicarb-sulfoxide to the zebrafish embryo (Danio rerio).

The new European chemical regulation (REACH) requires a short-term fish test for chemicals where the level of production exceeds 10tons per year. For ethical reasons (3R-concept), an alternative to the acute fish test should be introduced to decrease the number of animal testing with fish. The zebrafish embryo (Danio rerio) test became a valuable tool in ecotoxicology and already replaces the acute fish test for the evaluation of wastewater in Germany. Recent efforts are targeted to use this and other fish embryo tests for the effect assessment of chemicals. The toxic effects of the carbamate insecticide aldicarb and its metabolite aldicarb-sulfoxide to zebrafish embryos were analysed using two approaches with different endpoints. Organismic tests were conducted with zebrafish embryos exposed to the pesticides for 48h. In addition, suborganismic effects were examined analysing the enzyme inhibition of cholinesterases and carboxylesterases. On the organismic level, the only sublethal effect seen was the increase of heart rate at low and decrease at higher concentration with the use of aldicarb-sulfoxide but not with aldicarb (concentration range 0.2-300microM). In contrast, analysis of enzyme inhibitions showed high to very high effects caused by the two carbamates. The enzyme inhibition analysis of whole homogenates of exposed embryos may be advantageous for toxicant screening (biomarker of exposure) and might be used to bridge the gap of sensitivity of the (48h old) zebrafish embryos to adult fish when exposed to anti-cholinesterase substances (biomarker of prospective effect).

The HECT Family Ubiquitin Ligase EEL-1 Regulates Neuronal Function and Development.

Genetic changes in the HECT ubiquitin ligase HUWE1 are associated with intellectual disability, but it remains unknown whether HUWE1 functions in post-mitotic neurons to affect circuit function. Using genetics, pharmacology, and electrophysiology, we show that EEL-1, the HUWE1 ortholog in C. elegans, preferentially regulates GABAergic presynaptic transmission. Decreasing or increasing EEL-1 function alters GABAergic transmission and the excitatory/inhibitory (E/I) balance in the worm motor circuit, which leads to impaired locomotion and increased sensitivity to electroshock. Furthermore, multiple mutations associated with intellectual disability impair EEL-1 function. Although synaptic transmission defects did not result from abnormal synapse formation, sensitizing genetic backgrounds revealed that EEL-1 functions in the same pathway as the RING family ubiquitin ligase RPM-1 to regulate synapse formation and axon termination. These findings from a simple model circuit provide insight into the molecular mechanisms required to obtain E/I balance and could have implications for the link between HUWE1 and intellectual disability.

A carbamate insecticide: a case study of aldicarb.

Aldicarb, the active ingredient in the insecticide TEMIK, was introduced to the agricultural community over 25 years ago. It has been registered worldwide to control a wide variety of insect, mite, and nematode pests in agriculture. The toxicological research database supporting the registration and use of aldicarb was generated over more than 25 years and contains more than 280 animal studies on 12 species of animals, 2 clinical human trials, and over 20 human monitoring studies. This database, which includes biochemical aspects (metabolism and mode-of-action studies), acute toxicity and special short-term toxicity studies, long-term toxicity studies, and epidemiological observations in humans, serves as the starting point for the evaluation of the risks associated with the acceptance of levels of aldicarb residues in food and drinking water and for the more direct occupational exposure. This article highlights the available toxicological data and reviews worldwide regulation of aldicarb. Included in these discussions is a brief description of the toxicological end point upon which regulatory decisions have been based, namely acetylcholinesterase depression. Aldicarb, the N-methylcarbamic acid ester of 2-methyl-2-(methylthio) propionaldehyde oxime, was the first of a limited group of insecticidal oxime N-methylcarbamates that have properties distinct from N-methylcarbamates which have a phenolic constituent, instead of the oxime moiety. Aldicarb is highly water-soluble (approximately 6000 ppm), nonvolatile, relatively stable under acidic conditions, and is easily degraded under alkaline conditions. These properties are important determinants of its systemic action in plants and of its problematic environmental behavior. Possible environmental hazards involving the chemical include groundwater contamination and (more recently) excessive terminal residues in certain foods.

The toxicologic effects of the carbamate insecticide aldicarb in mammals: a review.

Aldicarb, 2-methyl-2-(methylthio)propionaldehyde-O-methylcarbamoyloxime, is an oxime carbamate insecticide manufactured by the Union Carbide Corporation and sold under the trade name Temik. It is a soil-applied systemic pesticide used against certain insects, mites, and nematodes, and is applied below the soil surface for absorption by plant roots. It is generally applied to the soil in the form of 5, 10, or 15% granules, and soil moisture is essential for the release of the toxicant. Uptake by plants is rapid. Aldicarb is currently registered for use on cotton, sugar beets, sugar cane (Louisiana only), potatoes, sweet potatoes, peanuts, oranges, pecans (Southeast only), dry beans, soybeans, and ornamental plants. Home and garden use is not permitted. Discovery of aldicarb and its oxidative sulfoxide and sulfone metabolites in well or ground water in Florida, Wisconsin, and New York, and accidental poisonings from ingesting contaminated watermelons and cucumbers in the South and West have spurred interest and concern about this pesticide. The primary mechanism of toxic action of aldicarb is cholinesterase inhibition. However, unlike the relatively irreversible anticholinesterase activity of the organophosphate pesticides, the carbamylation process which produces the anti-AChE action is quickly reversible. Aldicarb is readily absorbed through both the gut and the skin, but is rapidly metabolized and excreted in the urine almost completely within 24 hr. Although it is acutely toxic to humans and laboratory animals, aldicarb is not known to be carcinogenic, teratogenic, conclusively mutagenic, or to produce other long-term adverse health effects. In cases of accidental poisoning, the cholinergic symptoms have generally subsided within 6 hr, with no side effects or complications.

Effect of 17beta-estradiol and testosterone on the expression of flavin-containing monooxygenase and the toxicity of aldicarb to Japanese medaka, Oryzias latipes.

Previous studies in our laboratory indicated gender differences in salinity-enhanced acute toxicity of aldicarb in Japanese medaka with females being more susceptible. In the current study, the effects of the sex steroids, 17beta estradiol (E2) and testosterone (T) on aldicarb toxicity was examined. Adult Japanese medaka were separated by sex and exposed to 100 microg/l E2 or T for 6 days followed by exposure to the 96-h LC50 (0.5 mg/l) of aldicarb. The toxicity of aldicarb to adult males was significantly lowered by E2 and T whereby the mortality percentage was reduced to 23.3 +/- 5.8% and 3.3 +/- 5.8%, respectively, compared to the fish not receiving steroids (46.7 +/- 5.8% mortality). In females, T caused significant reduction in aldicarb toxicity to 16.7 +/- 5.8%, while E2 significantly enhanced the toxicity to 96.7 +/- 5.8% mortality. Since the flavin-containing monooxygenase (FMO) enzyme system had been shown to play a critical role in aldicarb toxicity, the effect of E2 and T on FMO expression was examined. Gill FMO activity showed a direct correlation with the overall toxicity of aldicarb in both male and female medaka. Expression of FMO1-like protein was significantly reduced by T in male livers and gills, and T did not affect the expression of FMOs in female tissues. In contrast, E2 significantly reduced FMO1-like protein expression in male gills and female livers, as well as FMO3 expression in both male and female livers, but significantly increased gill FMO1 expression in females. Since aldicarb acts by inhibiting the enzyme cholinesterase (ChE), the effect of sex hormones on the activity of this enzyme was also examined. In both male and female medaka, T counteracted the inhibitory effect of aldicarb on muscle ChE. In male fish, E2 had similar effects but did not seem to counteract the ChE inhibition in females. In conclusion, E2 and T modulation of aldicarb toxicity in Japanese medaka seems to be mediated via alteration of gill FMO and ChE actitivies.

In vitro sulfoxidation of aldicarb by hepatic microsomes of channel catfish, Ictalurus punctatus.

The carbamate pesticide, aldicarb, demonstrates significant acute toxicity in mammals, birds, and fish, and is readily biotransformed by most organisms studied. Metabolic products of aldicarb include the more toxic sulfoxide and the less toxic sulfone as two of the major products. Both the cytochrome P450 (CYP) and the flavin monooxygenase systems (FMO) are involved in this process. This study examined the capacities of liver microsomes of male channel catfish (Ictalurus punctatus), which lack FMO, to biotransform aldicarb in vitro. In addition, the acetylcholinesterase inhibitory potencies of aldicarb and its sulfoxide and sulfone derivatives were determined. For metabolism studies, incubations of [14C]-aldicarb (0.1mM) were carried out for up to 15-90 min using 1.0 mg/mL of hepatic microsomal protein. Total NADPH- dependent biotransformation was low (< 3.0% conversion to polar metabolites), and was inhibited by carbon monoxide. The only metabolite detected was aldicarb sulfoxide (Kmapp = 53.8 +/- 25.3 microM; Vmaxapp = 0.040 +/- 0.007 nmol/min/mg). Treatment of fish with the CYP modulators beta-naphthoflavone (BNF, 50 mg/kg) and ethanol (EtOH, 1.0% aqueous) had no effect on sulfoxide production. No correlation existed between CYP isoform expression (determined by western blot) and aldicarb sulfoxidation rates, suggesting the involvement of an unmeasured CYP isoform or involvement of several isoforms with low specificity. This study indicates that a low rate of bioactivation of aldicarb to aldicarb sulfoxide may be responsible for the resistance of channel catfish to aldicarb toxicity relative to that of other piscine species.

In vivo acetylcholinesterase inhibition, metabolism, and toxicokinetics of aldicarb in channel catfish: role of biotransformation in acute toxicity.

The carbamate pesticide, aldicarb, demonstrates significant acute toxicity in mammals, birds, and fish through the inhibition of acetylcholinesterase (AChE), and may present high potential for exposure of aquatic organisms during periods of runoff. Toxicity studies have shown that channel catfish are less sensitive to the acute toxic effects of aldicarb than are rainbow trout or bluegill. An earlier in vitro study suggests that the aldicarb resistance in catfish may be related to a low level of bioactivation to the potent aldicarb sulfoxide. The current study examines the toxicity, AChE inhibition, plasma kinetics, and in vivo metabolism of aldicarb in channel catfish. A 48-h LC50 of 9.7 mg/l was determined for juvenile channel catfish. Mortality was accompanied by dramatic loss of brain AChE. Further characterization of tissue-level effects suggests that muscle AChE plays a causal role in mortality. Aldicarb was metabolized in channel catfish to aldicarb sulfoxide, along with the formation of minor hydrolytic products. The toxicokinetics of aldicarb in catfish are bi-compartmental with rapid elimination (t1/2 = 1.9 h). Plasma AChE was inhibited in a pattern similar to that of the elimination of total aldicarb-derived compounds. A comparison of aldicarb uptake between catfish and rainbow trout showed no difference in compound absorbed in 24 h. The pattern of in vivo metabolism, however, was quite different between these species. Rainbow trout produce significantly more hydrolytic derivatives and have a 3-fold higher aldicarb sulfoxide to aldicarb ratio at 3 h. These data give strength to the hypothesis that a slower rate of bioactivation in the catfish (vs. rainbow trout) is acting as a protective mechanism against the acute toxicity of aldicarb.