Pesticides Paraquat Research Articles

Effects of prenatal paraquat and mancozeb exposure on amino acid synaptic transmission in developing mouse cerebellar cortex

The goal of this study was to analyze the effects of prenatal exposure to the pesticides paraquat (PQ) and mancozeb (MZ) on the development of synaptic transmission in mouse cerebellar cortex. Pregnant NMRI mice were treated with either saline, 10 mg/kg PQ, 30 mg/kg MZ or the combination of PQ + MZ, between gestational days 12 (E12) and E20. Variation in the levels of amino acid neurotransmitters was determined by HPLC, between postnatal day 1 (P1) and P30. Motor coordination was assessed by locomotor activity evaluation of control and experimental pups at P14, P21 and P30. Significant reductions in the levels of excitatory neurotransmitters, aspartate and glutamate, were observed in PQ-, MZ- or combined PQ + MZ-exposed pups, with respect to control, during peak periods of excitatory innervation of Purkinje cells: between P2–P5 and P11–P15. However, at P30, lower aspartate contents, in contrast with increased glutamate levels, were detected in all experimental groups. During the first two postnatal weeks, delays in GABA and glycine ontogenesis were observed in PQ- and PQ + MZ-exposed pups, whereas notable decrements in GABA and glycine levels were seen in PQ + MZ-exposed animals. Decreased taurine contents were detected at P3 and P11 in PQ- and PQ + MZ-exposed mice. Pups in different experimental groups all showed hyperactivity at P14 and then exhibited reduced locomotor activity at P30. Taken together, our results indicate that prenatal exposure to either PQ or MZ or the combination of both could alter the chronology and magnitude of synaptic transmission in developing mouse cerebellar cortex.

Studying Toxicants as Single Chemicals: Does this Strategy Adequately Identify Neurotoxic Risk?

Despite the fact that virtually all chemicals exposure of humans are to mixtures, and that these mixed exposures occur in the context of numerous other risk modifiers, our current understanding of human health risks is based almost entirely on the evaluation of chemicals studied in isolation. This paper describes findings from our collaborative studies that prompt questions about these approaches in the context of neurotoxicology. The first section describes studies investigating the interactions of maternal Pb exposure with maternal stress. Examined across a range of outcome measures, it shows that maternal Pb can modulate the effects of maternal stress, and, conversely, stress modifies the effects of Pb. Further, effects of Pb + stress could be detected in the absence of an effect of either risk factor alone, and, moreover, the profile of effects of Pb alone differs notably from that of Pb + stress. Collectively, interactions were not systematic, but differed by brain region, gender and outcome measure. A second section describes outcomes of studies examining combined exposures to the pesticides paraquat (PQ) and maneb (MB) during development which likewise reveal potentiated effects of combined exposures. They also demonstrate examples of both progressive and cumulative neurotoxicity, including a marked vulnerability following gestational exposure to MB, to the effects of PQ, a pesticide with no structural relationship to MB. The ability of current hazard identification and risk assessment approaches to adequately identify and encompass such effects remains an important unanswered question. One consideration proposed for further evaluating potential interactions that may be of significance for the nervous system is based on a multi-hit hypothesis. It hypothesizes that the brain may readily compensate for the effects of an individual chemical itself acting on a particular target system, but when multiple target or functional sites within that one system are attacked by different mechanisms (i.e., multiple chemical exposures or chemical exposures combined with other risk factors), homeostatic capabilities may be restricted, thereby leading to sustained or cumulative damage.

Developmental Exposure to the Pesticides Paraquat and Maneb and the Parkinson’s Disease Phenotype

Idiopathic Parkinson’s disease (PD) is associated with advanced age, but it is still unclear whether dopaminergic neuronal death results from events initiated during development, adulthood, or represents a cumulative effect across the span of life. This study hypothesized that paraquat (PQ) and maneb (MB) exposure during critical periods of development could permanently change the nigrostriatal dopamine (DA) system and enhance its vulnerability to subsequent neurotoxicant challenges. C57BL/6 mice were treated daily with saline, 0.3 mg/kg PQ, 1 mg/kg MB or PQ+ MB from post-natal (PN) days 5 to 19. At 6 weeks, a 20% decrease in activity was evident only in the PQ+ MB group, with a further decline (40%) observed at 6 months. A subset of mice were re-challenged as adults with saline, 10 mg/kg PQ, 30 mg/kg MB, or PQ+ MB 2× a week for 3 weeks. Mice exposed developmentally to PQ+ MB and re-challenged as adults were the most affected, showing a 70% reduction in motor activity 2 weeks following the last re-challenge dose. Striatal DA levels were reduced by 37% following developmental exposure to PQ+ MB only, but following adult re-challenge levels were reduced by 62%. A similar pattern of nigral dopaminergic cell loss was observed, with the PQ+ MB treated group exhibiting the greatest reduction, with this loss being amplified by adult re-challenge. Developmental exposure to PQ or MB alone produced minimal changes. However, following adult re-challenge, significant decreases in DA and nigral cell counts were observed, suggesting that exposure to either neurotoxicant alone produced a state of silent toxicity that was unmasked following adult re-exposure. Taken together, these findings indicate that exposure to pesticides during the PN period can produce permanent and progressive lesions of the nigrostriatal DA system, and enhanced adult susceptibility to these pesticides, suggesting that developmental exposure to neurotoxicants may be involved in the induction of neurodegenerative disorders and/or alter the normal aging process.

Tandem mass spectrometric analysis of quaternary ammonium pesticides.

A detailed MS(n) study on an ion trap instrument of the quaternary ammonium pesticides paraquat, diquat, difenzoquat, mepiquat and chlormequat reveals a number of ions not reported previously, and has allowed examination of the fragmentation pathways. A number of transitions that are highly specific to each quat have been identified. Optimal ion trap operating conditions determined using Simplex optimisation can promote either detection of a particular fragmentation transition or a range of MS/MS product ions with a high overall signal response. Thus, fragmentation conditions were optimised to enhance the specificity or sensitivity of MS/MS methods.

Formation of gas-phase clusters monitored during electrospray mass spectrometry: a study of quaternary ammonium pesticides.

Gas-phase cluster formation between the quaternary ammonium pesticides paraquat, diquat, difenzoquat, chlormequat and mepiquat, and chloride and acetate anions present in a liquid chromatography (LC) mobile phase, has been studied using electrospray mass spectrometry. The clusters of paraquat, mepiquat and chlormequat were revealed over the entire m/z range of the mass spectrometer, and their formation is dependent on the concentrations of both the cationic and the anionic species. Mepiquat and chlormequat form clusters of the type [2M(q)(+) + A(-)](+), where M(q)(+) is the quaternary ammonium cation and A(-) is the anion. Paraquat forms a cluster species with ammonia and also an ion-pair complex with chloride anions. Diquat and difenzoquat did not form observable ion-pair complexes or clusters with any of the anions studied. Competitive binding of acetate and chloride anions reflects the higher charge density of chloride, which forms the dominant clusters with mepiquat and chlormequat. The formation of cluster species has implications for the quantification of quaternary ammonium pesticides and may have an influence on the linearity of calibrations.

Laser desorption/ionization coupled to tandem mass spectrometry for real-time monitoring of paraquat on the surface of environmental particles.

Aerosol mass spectrometry with laser desorption/ionization was investigated as a possible tool for real-time monitoring of the presence of the pesticide paraquat on the surface of airborne soil particles. Laser desorption/ionization of paraquat dication produced only singly charged ions. The most abundant species were [M](+.), [M - H](+), and [M - CH3](+). Operation of the ion trap mass spectrometer in the MS(3) mode allowed the reduction of the signal dependence on laser fluence fluctuations and permitted the detection of the analyte with good sensitivity and high selectivity. The estimated limit of detection in terms of surface coverage was 0.016 monolayers, approximately 1 attomole of paraquat on the surface of a single micron-sized soil particle.

Responses of alveolar macrophages and epithelial type II cells to oxidative DNA damage caused by paraquat.

Because lung cells are inevitably exposed to chemicals, drugs and mineral particles, they are appropriate target cells for investigating effects of environmental toxins. We have studied alveolar macrophages and epithelial type II pneumocytes freshly isolated from the rat lung, using the comet assay to detect DNA damage (strand breaks and oxidized bases) in individual cells after treatment with the pesticide paraquat. The background level of strand breaks is five times higher in freshly isolated pneumocytes than in alveolar macrophages. This difference remains even after 48 h of in vitro culture and therefore probably does not reflect trauma suffered during isolation. In contrast, endogenous formamidopyrimidine glycosylase- and endonuclease III-sensitive sites, which are specific indicators of oxidative damage, are present in freshly isolated alveolar macrophages but not in pneumocytes, reflecting the high metabolic activity of macrophages and their defensive role. Both cell types are exquisitely sensitive to strand breakage by paraquat. In addition, specific base oxidation is detected after 24 h of treatment with paraquat, especially in alveolar macrophages. Susceptibility to DNA damage, rather than lipid peroxidation, is likely to be the cause of paraquat-induced death in these cells. The relatively high level of endogenous damage in pneumocytes suggests that these cells are inefficient at DNA repair, which would be consistent with their probable role as the principal progenitors of lung cancer.

Neurotoxicity of paraquat and triphenyltin in the earthworm, Eisenia fetida Sav. A histo- and cytopathological study

Neuropathological effects of the pesticides paraquat (PQ, a herbicide) and triphenyltin (TPT, a fungicide) were studied on the postclitellar segmental ganglia of juvenile E. fetida specimens using light and electron microscopic methods. Growth retardation of the worms in standard culture medium was used as quantitative marker of sublethal effect. There is a distinct neuron group in the segmental ganglia characterised by high sensitivity against PQ- and another one against TPT-toxication. However the marked histo- and neurocytopathological alterations were similar in PQ and TPT treated worms. Both chromatolysis and vacuolation of perikarya were revealed in sensitive neurons. Damaged cells were swollen and possessed degenerated rough endoplasmic reticulum cisternae. They were also characterised by swollen mitochondria, with electronlucent matrix and damaged inner membranes, and vesicular structures of various diameters as well as numerous lysosomes. Necrotic neurons with pyknotic nuclei and highly eosinophilic cytoplasm were also found in affected ganglia. Several dividing neurons were found in PQ-toxicated worms while no cell division occurred either in control or TPT-toxicated animals. The exact neurochemical and functional identification of PQ- and TPT-sensitive neurons needs further investigations.

Determination of quaternary amine pesticides by thermospray mass spectrometry

Positive-ion (PI) thermospray mass spectrometry (TSP-MS) with methanol—water (50:50) + 0.05 M ammonium formate as eluent was used for the characterization of the quaternary amine pesticides paraquat, difenzoquat, diquat, mepiquat and chlormequat and gave as base peaks [Cat + H] +•, [Cat − CH 3 + H] +•, [Cat] +•, [Cat] +• and [Cat] +•, respectively. A postcolumn ion-pair extraction system was developed for the determination of difenzoquat from water samples whereas the other quaternary amine pesticides were not extracted. An aqueous mobile phase with various sulphonate counter ions such as dodecanesulphonic acid, methyl orange, Blue Acid 113, Mordant Red 9 and sodium picrate was tested in combination with an extraction solvent containing cyclohexane—dichloromethane— n-butanol (45:45:10) with UV diode-array spectra and PI TSP-MS detection. Applications are reported for the TSP-MS determination of 500 μg/l of difenzoquat in spiked water samples using the postcolumn extraction system. Diquat and paraquat were determined at levels of 0.10–0.17 μg/g in soil samples from the Ebro delta (Tarragona, Spain) using a reversed-phase eluent containing 0.05 M ammonium formate.

Production and characterization of monoclonal anti‐idiotype antibody mimics for the pyrethroid insecticides and the herbicide paraquat

This paper highlights some of the difficulties encountered in the production and characterization of beta‐type anti‐idiotype antibodies to haptenic molecules. It describes the techniques employed to overcome these problems and illustrates the importance of the screening assay format in selecting the desired antibodies. The anti‐idiotype antibodies produced were used in a variety of assay formats, some innovative, for the quantification of the pesticides paraquat and phenoxybenzoic acid (PBA). The most sensitive of these assays detected 100 pm ml‐1 paraquat and 100 ng ml‐1 PBA respectively. The application of these antibodies to multi‐residue tests which overcome the narrow specificity conferred by conventional immunoassay techniques is discussed.

Measurement of human cortisol production rate by isotope dilution thermospray LC/MS

Positive-ion (PI) thermospray mass spectrometry (TSP-MS) with methanol—water (50:50) + 0.05 M ammonium formate as eluent was used for the characterization of the quaternary amine pesticides paraquat, difenzoquat, diquat, mepiquat and chlormequat and gave as base peaks [Cat + H]+•, [Cat − CH3 + H]+•, [Cat]+•, [Cat]+• and [Cat]+•, respectively. A postcolumn ion-pair extraction system was developed for the determination of difenzoquat from water samples whereas the other quaternary amine pesticides were not extracted. An aqueous mobile phase with various sulphonate counter ions such as dodecanesulphonic acid, methyl orange, Blue Acid 113, Mordant Red 9 and sodium picrate was tested in combination with an extraction solvent containing cyclohexane—dichloromethane—n-butanol (45:45:10) with UV diode-array spectra and PI TSP-MS detection. Applications are reported for the TSP-MS determination of 500 μg/l of difenzoquat in spiked water samples using the postcolumn extraction system. Diquat and paraquat were determined at levels of 0.10–0.17 μg/g in soil samples from the Ebro delta (Tarragona, Spain) using a reversed-phase eluent containing 0.05 M ammonium formate.

Psychosocial factors and sudden cardiac death: A pilot study

Despite the fact that virtually all chemicals exposure of humans are to mixtures, and that these mixed exposures occur in the context of numerous other risk modifiers, our current understanding of human health risks is based almost entirely on the evaluation of chemicals studied in isolation. This paper describes findings from our collaborative studies that prompt questions about these approaches in the context of neurotoxicology. The first section describes studies investigating the interactions of maternal Pb exposure with maternal stress. Examined across a range of outcome measures, it shows that maternal Pb can modulate the effects of maternal stress, and, conversely, stress modifies the effects of Pb. Further, effects of Pb + stress could be detected in the absence of an effect of either risk factor alone, and, moreover, the profile of effects of Pb alone differs notably from that of Pb + stress. Collectively, interactions were not systematic, but differed by brain region, gender and outcome measure. A second section describes outcomes of studies examining combined exposures to the pesticides paraquat (PQ) and maneb (MB) during development which likewise reveal potentiated effects of combined exposures. They also demonstrate examples of both progressive and cumulative neurotoxicity, including a marked vulnerability following gestational exposure to MB, to the effects of PQ, a pesticide with no structural relationship to MB. The ability of current hazard identification and risk assessment approaches to adequately identify and encompass such effects remains an important unanswered question. One consideration proposed for further evaluating potential interactions that may be of significance for the nervous system is based on a multi-hit hypothesis. It hypothesizes that the brain may readily compensate for the effects of an individual chemical itself acting on a particular target system, but when multiple target or functional sites within that one system are attacked by different mechanisms (i.e., multiple chemical exposures or chemical exposures combined with other risk factors), homeostatic capabilities may be restricted, thereby leading to sustained or cumulative damage.