Ginger and vitamin C as protective agents against oxidative stress and liver injury induced by methyl parathion

Methyl parathion is one of the highly toxic organophosphorus (OP) compounds. It induces hepatotoxicity, which might be related to generation of reactive oxygen species. This study was carried out to investigate the protective roles of vitamins C and ginger against hepatotoxicity induced by methyl parathion in male albino rats.Sixty male albino rats were randomly divided into 6 groups (ten rats each). Group I was considered as controls. Animals of groups II, III and IV were given methyl parathion (2 mg/kg), ginger (200 mg/kg) and vitamin C (100 mg/kg) respectively. Groups V and VI were given ginger (200 mg/kg) and vitamin C (100 mg/kg) respectively 2 hours before methyl parathion administration. All animals were treated orally, once daily, for four weeks. Blood and liver samples were obtained for biochemical, immunohistochemistry and histopathological examinations.Administration of either ginger or vitamin C along with methyl parathion significantly reduced the alanine aminotransferase (ALT) and malondialdehyde (MDA) levels in rats compared to those only treated with methyl parathion. Treatment with either ginger or vitamin C in combination with methyl parathion resulted in increased level of reduced glutathione compared to the methyl parathion treated group. However, oral ginger significantly increased glutathione-S-transferase levels compared to the control group, and this may outbalance the protective value of ginger over vitamin C to guard against liver injury and oxidative stress. The immunohistochemical and histopathological examinations showed that ginger or vitamin C combination with methyl parathion resulted in less hepatocytes degeneration and milder portal tract infiltration compared to the methyl parathion group.In conclusion, pre-treatment with either ginger or vitamin C appears to alleviate methyl parathion-inducted hepatotoxicity. However, their protective role is still limited and needs further investigation

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Alteration of the kidney membrane proteome of Mizuhopecten yessoensis induced by low-level methyl parathion exposure.

Methyl parathion (MP) is a widely used organophosphorus pesticide that causes severe health and environmental effects. We investigated the alteration of the proteomic profile in the membrane enriched fraction of the kidneys of the scallop Mizuhopecten yessoensis exposed to low-level MP. Gas chromatography analysis showed that MP residues were significantly accumulated in the kidneys and the digestive glands of the scallops. According to two-dimensional electrophoresis, 17 proteins were differentially modulated under MP exposure. The mRNA expressions of 12 differential proteins were analyzed using quantitative PCR, and 10 showed consistent alteration of mRNA level with that of protein expression level. Altered expressions of two proteins (mitochondrial processing peptidase and α-tubulin) were also examined using Western blotting, showing that the mitochondrial processing peptidase was down-regulated but α-tubulin remained unchanged in response to MP exposure. Subcellular locations of all the identified proteins that were predicted using bioinformatics tools indicate that few of them are permanently located in the membrane. The differentially expressed proteins are involved in several critical biological processes, and their relevance to human health has been illuminated. These data taken together have provided some novel insights into the chronic toxicity mechanism of MP and have suggested mitochondrial processing peptidase as a potential biomarker for human health and environmental monitoring.

Repeated developmental exposure to chlorpyrifos and methyl parathion causes persistent alterations in nicotinic acetylcholine subunit mRNA expression with chlorpyrifos altering dopamine metabolite levels.

Organophosphates (OPs), commonly used as insecticides, inhibit acetylcholinesterase, the enzyme responsible for the inactivation of synaptic acetylcholine, which results in elevated acetylcholine neurotransmission. Nigrostriatal dopamine neurons receive substantial cholinergic innervation and express a number of nicotinic acetylcholine receptor subunits. Since epidemiological data have implicated pesticides in the incidence of Parkinson's disease, the current experiment investigated how repeated, developmental exposure to the OPs chlorpyrifos (CPS) or methyl parathion (MPT) affects striatal dopamine levels and dopamine neuron gene expression. Newborn rats were treated daily via oral gavage with corn oil vehicle, CPS, or MPT from postnatal days (PND) 1-21. Rats were sacrificed at PND 22 and 50. Levels of dopamine and its metabolites 3,4 dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were measured in the striatum and mRNA expression was measured in the substantia nigra. At 22 days of age, CPS and MPT treatment had no effect on dopamine, DOPAC or HVA levels. At 50 days of age, CPS significantly elevated DOPAC levels and elevated dopamine turnover (DOPAC/dopamine) but did not affect dopamine or HVA levels. MPT had no significant effects on any of these parameters. Interestingly, both CPS and MPT treatments caused a significant alteration in the ratio of alpha7 to alpha6 nicotinic acetylcholine receptor (nAChR) subunit expression in the substantia nigra with a non-significant elevation in alpha6 and a reduction in alpha7 at 22 days. At 50 days of age, a significant elevation in alpha6 nAChR subunit was observed in the MPT treated rats. No differences in dopamine neuron transcription factors (Nurr1 or Lmx1b) or neurotransmission genes were observed. These data demonstrate that repeated exposure to OPs during postnatal maturation can have a significant effect on dopamine neurochemistry, primarily by modifying dopamine metabolism, which can persist for up to 1 month (CPS) and alter acetylcholine subunit expression (CPS and MPT).

Filogenia da sensibilidade da acetilcolinesterase cerebral de peixes ao metil-paraoxon como um possível marcador ambiental / Phylogeny of the sensitivity of fish brain acetylcholinesterase to methyl-paraoxon as a possible marker environmental

Todos os animais com células nervosas e musculares possuem a enzima acetilcolinesterase (EC 3.1.1.7, AChE) e essa seqüência de aminoácidos está presente em muitas outras proteínas, com ou sem atividade catalítica, fato que permite que essa proteína seja utilizada em estudos de filogenia e de evolução. A grande diferença de afinidade entre substratos e inibidores é utilizada como um biomarcador para estudos genéticos de vários grupos de animais, especialmente insetos. Peixes possuem uma grande diferença na sensibilidade da AChE ao metil-paraoxon (MP) em relação aos animais terrestres e essa diferença pode estar relacionada à evolução. As constantes cinéticas de inibição (CCI) para o mecanismo de inibição progressivamente irreversível da AChE cerebral ao MP foram determinadas em duas fontes de AChE como um modelo para avaliação do potencial de uso das CCI como biomarcador para estudos evolucionários e filogenéticos. As CCI da AChE cerebral de seis exemplares de tainha (Mugil liza), coletados em duas lagoas da costa do Estado do Rio de Janeiro (Araruama e Saquarema), em tempos diferentes (2005 e 2007, respectivamente), foram determinadas em dois laboratórios distintos (CESTEH - FIOCRUZ e Dept. Bioquímica - UERJ). As CCI, medidas separadamente em cada exemplar, indicaram que essas constantes são preservadas em todos os exemplares de uma mesma espécie e que a metodologia empregada pode ser conduzida em laboratórios distintos sem grandes variações. A AChE cerebral de tainha foi tomada como um exemplo de enzima menos sensível (IC50 = 2118nM) e a de galinha comercial (Gallus gallus domesticus) como um exemplo de uma enzima muito mais sensível ao MP (IC50 = 26nM)...

The enzyme acetylcholinesterase (EC 3.1.1.7, AChE) is present in all animalswith neurons and muscle cells, and many other proteins have the same sequence, with or without catalytic activity, allowing them to be used for phylogenetic and evolutionary studies. The great difference between substrates and inhibitor affinities makes it useful as a biomarker for genetic studies of various animals groups, especially insects. There are great differences among fish in AChE sensitivity to methyl-paraoxon (MP) in relation to terrestrial animals, and these differences can be related to evolution. The inhibition kinetic constants (IKC) for progressive irreversible inhibition of brain AChE with MP were determined in these two AChE sources as models for evaluating IKC as potential biomarkers in evolutionary and phylogenetic studies, especially among fish. IKC of brain AChE from six specimens of Mugil liza, a very common coastal fish, was collected from two of Brazil's lagoons in Rio de Janeiro State during 2005 at Araruama and 2007 at Saquarema. First samples were assayed at CESTEH - Fundação Oswaldo Cruz and the latter at Dept. Bioquímica - Universidade do Estado do Rio de Janeiro. The IKC was measured separately for each fish showing that these constants weremaintained for all animals of the same species and that this methodology can beused in different laboratories without variations. The cerebral AChE of tainha was used as an example of a less sensitive enzyme (Concentration which inhibits 50% of enzyme activity after 30 minutes of incubation, or IC50, = 2118nM). The commercial hen (Gallus gallus domesticus) was used an example of a very highly sensitiveenzyme to MP (IC50 = 26nM)...

The effect of parathion-methyl and antidotes on parotid and pancreatic glands: a pilot experimental study.

The objective of this study is to investigate the functions of parotid and pancreatic glands in response to intoxication with parathion-methyl (PM) and the effects of treatment in rats. Seventy-five male Wistar rats were divided equally into five groups: Group I, control; group II, received atropine and pralidoxime (2-PAM) for 24 h, but no PM; group III, oral PM but no atropine and 2-PAM; group IV, PM and atropine for 24 h and 2-PAM; group V, PM and atropine for 96 h and 2-PAM. After the administration of the chemicals, blood samples were drawn to test for amylase, lipase, acetylcholinesterase (AChE), and butyrylcholinesterase (BChE), while pancreatic and parotid glands of each rat were removed for light microscopic examination. Amylase levels were found significantly elevated in groups II, III, IV, and V, whereas lipase levels were supranormal in groups III, IV, and V. The blood levels of AChE were decreased in groups III and IV and BChE were decreased in II, III, IV, and V. No evidence of pancreatitis and parotitis was identified in the histopathologic evaluation in any group in 96 h; however, hyperchromasia, irregularity in nuclei, and binuclear cells were observed in all parotid glands in group V. Parotitis and pancreatitis were not evident; however, hyperamylasemia and hyperlipasemia were found, whereas various histologic changes in parotid glands were documented in the groups that were administered organophosphate and treatment.

Evaluation of sublethal biomarkers in Litopenaeus vannamei on foodborne exposure to methyl parathion.

Sublethal effects of foodborne exposure to methyl parathion (0.62 and 1.31 microg methyl parathion*g(-1) dry weight of food) on juveniles of Litopenaeus vannamei using integrated biochemical (acetylcholinesterase (AChE) and ATPases) and physiological (feeding rate (FR), egestion rate (ER), and hepatosomatic index (HI)) biomarkers were evaluated. The HI was significantly higher in controls than in pesticide treatments. The FR was significantly lower in controls than in pesticide treatments while no significant differences were detected in the ER. AChE activity was significantly higher in controls than in pesticide treatments (control = 0.11 +/- 0.02; solvent control = 0.11 +/- 0.03; 0.62 = 0.07 +/- 0.01; 1.31 = 0.08 +/- 0.02 microM*min(-1)*mgprotein(-1)). The total-ATPase activity was significantly lower in controls than in pesticide treatments (control=77.90+/-12.41; solvent control = 83.69 +/- 22.05; 0.62 = 110.03 +/- 22.17; 1.31 = 121.54 +/- 19.84 microM P(i)*h(-1)*mgprotein(-1)). The Mg(2+)-ATPase activity was significantly higher in treatments than in controls (control = 65.14+/-10.76; solvent control = 75.12 +/- 21.10; 0.62 = 100.53 +/- 20.97; 1.31 = 108.94 +/- 17.26 microM P(i)*h(-1)*mgprotein(-1)). Finally, the results obtained for the Na(+)/K(+)-ATPase activity were significantly higher in control and in 1.31 than in solvent control and in 0.62 (control = 14.06+/-2.63; solvent control=7.30 +/- 4.13; 0.62 = 7.60 +/- 3.81; 1.31 = 13.42 +/- 2.88 microM P(i)*h(-1)*mgprotein(-1)). The results in this study showed that pulse exposures to methyl parathion via food could elicit measurable effects on the marine shrimp L. vannamei, indicating that foodborne exposure can be a reliable toxicological procedure and, if combined with pulse exposures, could also simulate more realistic exposure scenarios.

Placental morphology of rats prenatally exposed to methyl parathion.

Although prenatal exposure to pesticides has been associated with numerous adverse reproductive effects, data on the effects of such toxics in the placenta is limited. Thus, the present study was carried out to determine the morphology of the rat placenta exposed to the organophosphate pesticide methyl parathion (MP) in ad libitum fed and restricted diet animals. The pregnant females were randomly divided into control groups and experimental groups, the latter of which received MP at the doses of 0.0, 1.0, 1.5 and 2.0 mg/kg. Most cells in the maternal-fetal interface showed significant alterations in the presence of MP. Trophoblast giant cells exhibited either prominent characteristics of degeneration or normal morphology with many phagosome vacuoles, apparently containing cell debris. Vascular congestion was also more frequent in the labyrinth of the treated animals. Areas of fibrosis and hemorrhage were found in the decidua, as well as decidual cells presenting pyknotic nuclei and acidophilic cytoplasm. In the placentas of females treated with both restricted diet and MP, such changes were much more severe. Together, these alterations suggest a direct, toxic effect of MP on the placental cells. The phagocytic activity exhibited by trophoblast cells, may be playing a role in the removal of death cells from the maternal-placental interface and/or in a compensatory mechanism to maintain the uptake of maternal nutrients, following decreased metabolic exchange functions of the labyrinth due to the toxic effect of the MP.

Comparative investigation of behavioral, neurotoxicological, and immunotoxicological indices in detection of subacute combined exposure with methyl parathion and propoxur in rats.

The effects of 6 weeks of oral exposure to propoxur (PR; at doses of 0.851 and 8.51 mg/kg body wt.), methylparathion (MP; at doses of 0.218 and 0.872 mg/kg body wt.), and their combinations were investigated in male Wistar rats. Measurement endpoints of the investigation were certain general toxicological parameters (body weight gain, organ weights), plaque-forming cell (PFC) count from the spleen, open field (OF) behavior, auditory startle response (ASR), prepulse inhibition (PPI), rotarod performance, somatosensory and auditory cortical evoked potentials, and peripheral nerve conduction velocity. The treated rats did not show any sign of acute intoxication during the 6 weeks of exposure. The higher dose of PR, but not of MP, significantly decreased the relative liver weight. Both agents produced a significant dose-dependent increase of OF activity, with larger expression after 2 weeks than after 6 weeks. The number of ASR responses and the ASR amplitude increased. The amplitude after PPI was increased by MP but only minimally altered by PR and the combinations. There was a small, but with high-dose PR significant, increase in the latency of the somatosensory evoked potentials. Neither of the two substances alone had any effect on the PFC response. The effect of the combination of high-dose PR and low-dose MP was significantly different from that of high-dose PR alone on the liver weight, on the ASR amplitude, and on the PFC/10(6) cell and PFC/spleen counts. With high-dose MP and low-dose PR, no such interaction was observed. According to the results, the noneffective dose of MP can influence the toxicity of the effective dose of PR in a combined exposure situation.

The effects of repeated oral exposures to methyl parathion on rat brain cholinesterase and muscarinic receptors during postnatal development.

Dimethyl phosphorylated cholinesterase (ChE) is known to be more rapidly reactivated, spontaneously, and have a higher aging rate than diethyl phosphorylated ChE. This may result in differences in toxic signs and tolerance development after treatment of juvenile rats with methyl parathion (MPS), a dimethyl phosphorothionate, than after treatment with chlorpyrifos (CPS), a diethyl phosphorothionate. The effects of repeated MPS exposures on brain ChE activity and surface and total muscarinic acetylcholine receptor (mAChR) density were studied in postnatal rats gavaged daily from postnatal day 1 (PND1) through PND 21. Results of this study were compared to our recent report with CPS (Tang et al., 1999, Toxicol. Sci. 51, 265-272). Rats received MPS daily starting at 0.3 mg/kg and increasing gradually to 0.6 mg/kg (for the medium-dosage groups) and then to 0.9 mg/kg (for the high-dosage group). ChE activity was assayed in brain homogenates. Synaptosomal mAChR densities, surface, and total were assayed using 3H-N-methylscopolamine (NMS) and 3H-quinuclidinyl benzilate (QNB), respectively, as ligands. Developmental increases in brain ChE activities and mAChR densities were observed from PND 6 through PND 22. On PND 22, inhibition of ChE activity was observed in the low (26%)-, medium (42%)-, and high (55%)-dosage groups. Significant inhibition was still present on PND 30 (16-24%) and PND 40 (12-14%), which were 9 and 19 days after the last treatment, respectively. Densities of 3H-NMS and 3H-QNB binding sites in treated groups were significantly reduced by PND 22, 1 day following cessation of treatment, and were significantly increased during the recovery period. After MPS exposure, the initial recovery of phosphorylated ChE was more rapid and the density of 3H-NMS binding sites was less readily reduced than following CPS exposure. The lesser effects on surface mAChR may explain why more severe signs appeared after each treatment with the high dosage of MPS than were observed previously with CPS, indicating little or no tolerance had developed to MPS.

Pharmacokinetics and pharmacodynamics of methyl parathion.

Methyl parathion and other organophosphorus insecticides are widely used in agriculture. Poisonings to this class of compounds are common and exerted primarily through inhibition of acetylcholinesterase. Methyl parathion became a major health concern when it was illegally sprayed in private homes. Since there are limited data with which to predict the long-term effects resulting from a pattern of exposure to methyl parathion that may have occurred in domestic settings, studies were performed to compare its pharmacokinetics and pharmacodynamics after intravenous, oral or dermal exposure. Methyl parathion was given to adult female rats as a single dose intravenously (2.5 mg/kg) through a femoral catheter, orally (2.5 mg/kg) by gavage, or dermally (< or = 50 mg/kg) by application to shaved skin at the nape of the neck. Blood (200 microl) was collected at increasing times from a separate catheter or from the retro-orbital sinus. Cholinesterase activity was measured in blood and normalized to hemoglobin content, whereas activities in brain and peripheral tissues were normalized to protein. Blood methyl parathion was quantitated by gas chromatography-electron capture. The pharmacokinetics of methyl parathion after intravenous exposure best fit a model in which it was distributed between two compartments and rapidly eliminated. Maximal concentrations of methyl parathion ranged from 200 to 350 ng/ml. The half-life of methyl parathion was 51 minutes, its volume of distribution was 10.1 L/kg, and clearance was 108 ml/min/kg. The kinetics of methyl parathion after single oral exposure contrasted with those after intravenous exposure. Despite a high absorption coefficient, oral bioavailability of methyl parathion was less than 5%, and concentrations in blood were 2% or less of those after intravenous exposure. After single dermal exposure (25 or 50 mg/kg), blood methyl parathion levels increased during the first 6 h and then remained constant for the next 42 h at about 150 ng/ml. Despite differences in its pharmacokinetics, methyl parathion caused similar time-dependent changes in blood and brain cholinesterase activities after intravenous or oral administration. Maximal inhibition of blood cholinesterase occurred within 15-60 min, and activities recovered within 30 - 48 h. In contrast, inhibition of blood cholinesterase caused by single dermal exposure (> or = 25 mg/kg) to methyl parathion developed gradually over 24 h, but was sustained. Cholinesterase inhibited by a lower dose (< or = 12 mg/kg) of methyl parathion required up to 21 days to recover fully. The pharmacokinetics and pharmacodynamics of methyl parathion are complex, and the complexity varies with the route of exposure. A significant 'first pass' effect for methyl parathion is seen with oral administration. Dermal exposure to methyl parathion, as likely occurred with the illegal spraying of private homes and businesses, may exacerbate toxicity and increase the potential for long-term adverse health effects.

Pharmacokinetics of methyl parathion: a comparison following single intravenous, oral or dermal administration.

Assessment of the risks posed by the residential use of methyl parathion requires an understanding of its pharmacokinetics after different routes of exposure. Thus, studies were performed using adult female rats to define the pharmacokinetic parameters for methyl parathion after intravenous injection and to apply the described model to an examination of its pharmacokinetics after single oral or dermal exposure. The pharmacokinetics of methyl parathion after intravenous administration (1.5 mg/kg) were best described by a three-compartment model; the apparent volume of the central compartment was 1.45 liters/kg, clearance was 1.85 liters/h/kg and the terminal half-life was 6.6 h with an elimination constant of 0.50 h(-1). The apparent oral absorption coefficient for methyl parathion (1.5 mg/kg) was 1.24 h(-1), and its oral bioavailability was approximately 20%. The latter likely includes a significant first pass effect. Concentrations of methyl parathion increased during the initial 10-60 min and then declined during the next 15-36 h. After dermal administration (6.25-25 mg/kg), methyl parathion concentrations peaked within 12-26 h and then declined dose dependently. The apparent dermal absorption coefficient was approximately 0.41 h(-1), and only two pharmacokinetic compartments could be distinguished. In conclusion, the pharmacokinetics of methyl parathion are complex and route dependent. Also, dermal exposure, because of sustained methyl parathion concentrations, may pose the greatest risk.

A comparison of cholinesterase activity after intravenous, oral or dermal administration of methyl parathion.

Time-dependent changes in blood cholinesterase activity caused by single intravenous, oral or dermal administration of methyl parathion to adult female rats were defined. Intravenous and oral administration of 2.5 mg/kg methyl parathion resulted in rapid (<60 min) decreases in cholinesterase activity which recovered fully in vivo within 30-48 h. In contrast, spontaneous reactivation of cholinesterase in vitro was complete within 6 h at 37 degrees C. Dermal administration of methyl parathion caused dose-dependent inhibition of cholinesterase activity which developed slowly (> or =6 h) and was prolonged (> or =48 h). Time- and route-dependent effects of methyl parathion on cholinesterase activity in brain and other tissues generally paralleled its effects on activity in blood. In conclusion, pharmacodynamics of methyl parathion differ substantially with route of exposure. Recovery of cholinesterase in vivo after intravenous or oral exposure may partially reflect spontaneous reactivation and suggests a rapid clearance of methyl parathion or its active metabolite methyl paraoxon. The more gradual and prolonged inhibition of cholinesterase caused by dermal administration is consistent with disposition of methyl parathion at a site from which it or methyl paraoxon is only slowly distributed. Thus, dermal exposure to methyl parathion may pose the greatest risk for long-term adverse effects.

Effects of single or repeated dermal exposure to methyl parathion on behavior and blood cholinesterase activity in rats.

The effects of a single or repeated dermal administration of methyl parathion on motor function, learning and memory were investigated in adult female rats and correlated with blood cholinesterase activity. Exposure to a single dose of 50 mg/kg methyl parathion (75% of the dermal LD(50)) resulted in an 88% inhibition of blood cholinesterase activity and was associated with severe acute toxicity. Spontaneous locomotor activity and neuromuscular coordination were also depressed. Rats treated with a lower dose of methyl parathion, i.e. 6.25 or 12.5 mg/kg, displayed minimal signs of acute toxicity. Blood cholinesterase activity and motor function, however, were depressed initially but recovered fully within 1-3 weeks. There were no delayed effects of a single dose of methyl parathion on learning acquisition or memory as assessed by a step-down inhibitory avoidance learning task. Repeated treatment with 1 mg/kg/day methyl parathion resulted in a 50% inhibition of blood cholinesterase activity. A decrease in locomotor activity and impairment of memory were also observed after 28 days of repeated treatment. Thus, a single dermal exposure of rats to doses of methyl parathion which are lower than those that elicit acute toxicity can cause decrements in both cholinesterase activity and motor function which are reversible. In contrast, repeated low-dose dermal treatment results in a sustained inhibition of cholinesterase activity and impairment of both motor function and memory.

Absorption, distribution, metabolism and excretion of daily oral doses of [14C]methyl parathion in hens.

Adult hens were given oral daily doses of 2 mg (2 microC(i))/kg/day (14% of oral LD(50) in male rats) of [14C]methyl parathion (O,O-dimethyl O-4-nitrophenyl phosphorothioate) for 10 consecutive days. Five treated hens were sacrificed at 1, 2, 4, 8, 12, 24, and 48 h after the last dose. Methyl parathion was absorbed from the gastrointestinal tract and distributed rapidly. Maximum radioactivity was detected in tissues within 8 h of dosing, (ng methyl parathion equivalent/g fresh tissue or ml plasma): Plasma (189.2), liver (94.7), kidney (146.2), brain (61.4), gastrointestinal tissues (106.7). Methyl parathion was detected in the plasma, kidney and liver, while methyl parathion metabolite p-nitrophenol was detected in the liver and in the kidney. Elimination of methyl parathion from plasma was monophasic with a terminal half-life of 17.5 h, corresponding to an elimination rate constant of 0.039 ng/hr. Most of the absorbed radioactivity was excreted in the combined fecal-urine excreta (98%). Analysis of the metabolites in the excreta revealed that non-conjugated metabolites accounted for 13% of the total excretion. Conjugated metabolites accounted for 87% of the total excretion; of that, 6% as p-nitrophenyl-glucoronide conjugate, 7% as p-nitrophenyl-sulfate conjugate, 23% as bound hot sulfuric acid hydrolyzable residues, and 51% as water soluble metabolites. The presence of majority of radioactivity in the excreta as conjugated metabolites indicates that determining only unbound p-nitrophenol as a biological marker for methyl parathion exposure underestimates total fecal-urine excretion of p-nitrophenol. The slow elimination rate of methyl parathion is significant, since hens are more comparable to humans with respect to their cytochrome P450 activities.

Inhibition and recovery of maternal and fetal cholinesterase enzyme activity following a single cutaneous dose of methyl parathion and diazinon, alone and in combination, in pregnant rats.

Pregnant Sprague-Dawley rats (14-18 days of gestation) were treated with a single cutaneous subclinical dose(s) of 10 mg kg(-1) (15% of LD(50)) of methyl parathion (O,O-dimethyl O-4-nitrophenyl phosphorothioate) and 65 mg kg(-1) (15% of LD(50)) of diazinon (O,O)-diethyl O-2-isopropyl-6-methylpyrimidinyl phosphorothioate, and their combination. Animals were sacrificed at 1, 2, 4, 12, 24, 48, 72, and 96 h after dosing. Inhibition of maternal and fetal cholinesterase enzyme activity has been determined. Methyl parathion significantly inhibited maternal and fetal brain acetylcholinesterase (AChE) and plasma butyrylcholinesterase (BuChE) activity within 24 h after dosing. Diazinon and a mixture of methyl parathion and diazinon caused lesser inhibition compared with methyl parathion alone. Recovery of maternal and fetal brain AChE activity was in the order of diazinon > combination of diazinon and methyl parathion > methyl parathion 96 h after dosing. Although fetal plasma BuChE activity recovered to 100% of control within 96 h of application, maternal BuChE activity remained inhibited to 55% and 32% of control 96 h after application of methyl parathion and a mixture of methyl parathion and diazinon, respectively. Following a single dermal dose of methyl parathion, the activity of maternal liver BuChE was 63% of control 2 h after dosing, whereas inhibition of placental AChE or BuChE activity occurred 12 and 1 h following a single dose of methyl parathion, corresponding to activities of 63% and 54% of control, respectively. Diazinon, alone or in combination with methyl parathion, did not inhibit significantly the maternal liver BuChE or placental AChE and BuChE activity. The results suggest that dermal application of a single dose of methyl parathion and diazinon, alone or in combination, has an easy access into maternal and fetal tissues, resulting in inhibition of cholinesterase enzymes. The lower inhibitory effect of the combination of methyl parathion and diazinon might be due to competition of diazinon with methyl parathion for cytochrome P-450 enzymes, resulting in formation of the potent cholinesterase inhibitor methyl paraoxon. The faster recovery of fetal cholinesterase enzymes is attributed to the rapid de novo synthesis of cholinesterase fetal tissues compared with the mother.

Urinary excretion of metabolites following a single dermal dose of [14C]methyl parathion in pregnant rats.

The identification and kinetics of urinary excretion of metabolites of uniformly phenyl-labeled O,O-dimethyl O-4-nitrophenyl phosphorothioate ([14C]methyl parathion) were carried out following a single dermal dose of 10.0 mg (10 microCi)/kg in pregnant Sprague-Dawley rats at 14-18 days of gestation. Urine was collected at each time interval of 1, 2, 4, 12, 24, 48, 72, and 96 h after dosing. Total p-nitrophenol in the conjugated and non-conjugated metabolites was measured as a marker of methyl parathion exposure. Elimination of radioactivity in the urine was rapid. Of the total 14C urinary excretion, 30% of the dose was excreted within 4 h, while 50 and 90% of the dose were recovered in the urine by 24 and 96 h, respectively. Excretion rate of total radioactivity was 60 microgram methyl parathion equivalent/h (1.4 mg/day). By the end of the 96-h experiment, conjugated and non-conjugated metabolites accounted for 78.1 and 21.9%, respectively. Of the non-conjugated metabolites, p-nitrophenol and O,O-dimethyl O-4-nitrophenyl phosphate (methyl paraoxon) were identified by high performance liquid chromatography (HPLC) that accounted for 20%, and 1.9% of total urinary excretion, respectively. Appearance and disappearance rate constants of p-nitrophenol in urine were 0.12 and 0.048 microgram/h, respectively. Conjugated metabolites were classified as: glucuronides 12% of urinary excretion, sulfates 3%, hot sulfuric acid hydrolysable residues 47% and 16.1% remained as unidentified water soluble metabolites. Direct hot acid hydrolysis of urine yielded 49% of extractable 14C-radioactivity compared to 62% when hot acid hydrolysis followed the enzymatic hydrolysis. The presence of the conjugated metabolites as the major class of metabolites of the total excretion indicates that determining only unbound p-nitrophenol as a biological marker for methyl parathion exposure underestimates total urinary excretion of p-nitrophenol. Sequential enzymatic and acid hydrolyses of urine prior solvent extraction are necessary for complete recovery of p-nitrophenol. The results indicate that the present method would show that the pregnant field worker or a housewife being at a greater risk than previously thought.

Cholinergic and noncholinergic brain biomarkers of insecticide exposure and effects.

The objective of this investigation was to determine the distribution of cholinergic and noncholinergic biomarkers in discrete brain regions (cortex, stem, striatum, hippocampus, and cerebellum) of rats treated with dimethyl sulfoxide (DMSO, controls), and insecticides such as carbofuran (CARB, 1.5 mg/kg, sc), or methyl parathion (MPTH, 5 mg/kg, ip). Both insecticides produced characteristic signs of anticholinesterase nature within 5-7 min after injection. In controls, analyses of the brain regions revealed a wide variability in the values of cholinergic (acetylcholinesterase, AChE) and noncholinergic (creatine kinase, CK; and lactic dehydrogenase, LDH, and their isoenzymes) biomarkers. The highest activities of AChE and LDH were found in the striatum (1661+/-23 micromol/g/h and 57,720+/-478 IU/l, respectively) and lowest in the cerebellum (118+/-6 micromol/g/h) and 39,480+/-918 IU/l, respectively). However, the activity of CK was found highest in the cerebellum (742,560+/-798 IU/l) and lowest in the hippocampus (353,400+/-11,696 IU/l). Each brain region showed a characteristic profile of CK and LDH isoenzymes. Among the CK isoenzymes, activity of CK-BB was highest (77.5-89.3%), followed by CK-MM (6.7-15.6%), and least CK-MB (0-6.9%). The cerebellum had no CK-MB activity. In all brain regions, CK-MM isoenzyme had only the CK-MM3 subform. Among the LDH isoenzymes, activity of LDH-4 was highest in all brain regions (23-40%), except the cerebellum in which LDH-1 was highest (29%). Compared to the brain, control serum contained very little CK and LDH activity, but serum had three distinct CK and five distinct LDH isoenzymes. Unlike brain regions, serum had three CK-MM subforms. Each insecticide induced characteristic alterations in brain biomarkers. AChE activity was maximally inactivated in cortex (90. 6%) with CARB, and in cerebellum (95.3%) with MPTH. With either insecticide, the least inhibition of AChE occurred in the striatum. Unlike AChE, carboxylesterase (CarbE) did not show brain regional variability in controls, and its activity was uniformly inhibited in all brain regions by CARB and comparatively greater by MPTH. CARB- or MPTH-induced characteristic alterations in CK, LDH, and their isoenzymes in the brain, which were also reflected in serum, as a result of their leakage from the brain by increased permeability due to depletion of ATP (38-57% and 33-47%, respectively) and phosphocreatine (PCr, 23-42% and 56-65%, respectively).

Effect of methyl parathion formulation on estrous cycle and reproductive performance in albino rats.

The animals were injected intraperitoneally with graded doses of methyl parathion at 1.5 to 3 mg/kg body weight for 15 days from the day of estrus. Results indicated that the methyl parathion treatment showed irregular estrous cycles, affect the duration of each estrous cycle, proestrus and diestrus were significantly changed in 2.5 and 3 mg treatment groups. But there was no significant change in the number and duration of each estrous cycle, duration of proestrus and diestrus in 1.5 and 2 mg methyl parathion treatment groups. However, there was a significant decrease in the duration of estrus, while there was no significant change in the duration of metestrus in all methyl parathion treatment rats when compared with those of the corresponding parameters of the control. There was no significant effect on number of live pups on day 1 and 5 except in 3 mg methyl parathion treatment group where it was significantly decreased. There was no significant change in reproductive indices like pregnancy, parturition, live birth and viability in all the methyl parathion treatment rats except the viability index in the highest dose.

Cholinesterase activity in white-winged doves exposed to methyl parathion.

Captive white-winged doves (Zenaida asiatica) were exposed to various levels of methyl parathion (MP) in drinking water to determine effects on brain and blood cholinesterase (ChE) activity. We conducted two experiments to test the influence of MP dose (the amount of MP actually ingested), MP concentration (the amount of MP per unit water), and exposure duration (number of days exposed to a constant MP concentration) on ChE activity. Plasma ChE activity was not useful in predicting brain ChE activity. Methyl parathion concentration had a greater influence on plasma and brain ChE activity levels than dose or time of exposure. These results contribute to the evaluation of irrigation water as a route of exposure of wildlife to pesticides.

In vitro percutaneous penetration of methyl-parathion from a commercial formulation through the human skin.

OBJECTIVE: To compare in vitro percutaneous absorption of methyl-parathion dissolved in an acetone vehicle and in the form of a commercial formulation. METHODS: Penetration through the human skin was measured in Franz diffusion cells with full thickness skin from a human cadaver as the membrane. The two tailed non-parametric Mann-Whitney U test was used to compare the cumulative diffusion of methyl-parathion in the receptor fluid of the cells at various time intervals. RESULTS: In vitro skin penetration of methyl-parathion was significantly higher with the commercial formulation. The percentage of the applied dose absorbed after 24 hours was 5.20% v 1.35%. The mean lag time was < 8 hours. CONCLUSION: Assessments of uptake and internal dose after exposure to pesticides should be based on the commercial products rather than active ingredients, because of the crucial role of the vehicle, as shown in this study.