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At least 19 recordsLinked to original sources
PubMed1997

Biotransformation of parathion in human liver: participation of CYP3A4 and its inactivation during microsomal parathion oxidation.

Studies in rat liver have shown that cytochrome P450 (CYP) enzymes mediate the oxidative biotransformation of the phosphorothioate pesticide parathion to paraoxon and 4-nitrophenol. Transfer of the phosphorothioate thionosulfur atom to the CYP apoprotein results in amino acid modification and enzyme inactivation. Our study investigated the role of human hepatic CYP in parathion oxidation and their relative susceptibilities to inhibition and inactivation. Rates of parathion oxidation varied about 10-fold in microsomes from 23 individual livers (1.72-18.33 nmol total metabolites/mg protein/min). Linear regression of rates of parathion oxidation with those of other microsomal CYP reactions implicated CYP3A4 in the reaction. Thus, parathion oxidation was correlated strongly with testosterone 6beta-hydroxylation (r2 = 0.95, n = 11), but not with activities mediated by CYP 1A2, 2C9 or 2E1. CYP 3A4 expressed in lymphoblastoid cell lines was an efficient catalyst of parathion oxidation, although CYP 1A2 and 2B6 also catalyzed the activity. The CYP3A4 inhibitors ketoconazole and triacetyloleandomycin decreased the observed rate of microsomal parathion oxidation, but chemicals known to interact preferentially with other human CYP were essentially noninhibitory. P450 was lost during parathion biotransformation in human hepatic microsomes. Thus, incubation (10 min) of parathion (25 microM) with NADPH-supplemented microsomes led to an apparent 19 +/- 4% decrease in holo-P450 content. Several CYP-specific oxidation reactions were inhibited and inactivated by parathion. Testosterone 6beta-hydroxylation (mediated by CYP3A4), 7-ethylresorufin O-deethylation (CYP1A2) and tolbutamide methyl hydroxylation (CYP2C9/10), but not aniline 4-hydroxylation (CYP2E1), were inhibited effectively by parathion. Preincubation of microsomes with parathion and NADPH intensified the extent of inhibition (i.e., elicited inactivation) of reactions mediated by 3A4 and 1A2 and, to a lesser extent, 2C9. In summary, these findings strongly implicate CYP 3A4 as the principal catalyst of parathion oxidation in human liver, although other CYP may play a lesser role. During parathion oxidation CYP3A4 undergoes significant inactivation. In view of the role of this enzyme in the oxidation of many therapeutic agents, exposure to phosphorothioate pesticides may adversely affect drug elimination in humans.

Aniline Hydroxylase↗
PubMedDate not supplied

Biotransformation of the organophosphorus insecticides parathion and methyl parathion in male and female rat livers perfused in situ.

Although numerous previous reports have characterized the mammalian biotransformation of the organophosphorus insecticides parathion and methyl parathion, questions still remain regarding the toxicological significance of certain metabolic pathways in vivo. The present study utilized rat liver perfusions in order to better characterize the hepatic biotransformation of parathion and methyl parathion in intact liver. Single-pass liver perfusions with parathion and methyl parathion over a range of perfusate concentrations of 10-80 microM resulted in the appearance of paraoxon and methyl paraoxon, respectively, in effluent. Furthermore, rat blood did not have the capacity to prevent transport of paraoxon and methyl paraoxon to extrahepatic tissues, suggesting that oxon produced hepatically can distribute to extrahepatic tissues. In addition, striking sex differences were noted in the metabolite profile of parathion and methyl parathion in perfused livers. However, these differences could not account for the observation that females are more susceptible to parathion, but less susceptible to methyl parathion, compared to males. And finally, S-methyl glutathione or S-p-nitrophenyl glutathione could not be detected in effluent or bile of livers from either sex perfused with methyl parathion, suggesting that glutathione-dependent detoxification of this insecticide does not occur to any significant degree in intact rat liver.

Animals↗
PubMed1983

Toxicokinetics of methyl parathion and parathion in the dog after intravenous and oral administration.

Methyl parathion (20 mg X kg -1 intravenously and orally) and parathion (5 mg X kg -1 intravenously and 10 mg X kg -1 orally) were given to non-anesthetized dogs and the serum concentrations were followed in function of time. For both substances a low bioavailability after oral administration was found. In other dogs radioactivity was followed in urine after oral and after intravenous administration of labeled methyl parathion or parathion. The results suggest a good gastro-intestinal absorption of the substances. In anesthetized dogs which were given methyl parathion or parathion intravenously, high hepatic extraction ratios were found, suggesting that the low systemic availability after oral administration can be explained by an important hepatic first-pass extraction. Binding of methyl parathion and parathion to dog serum, to human serum and to a solution of human albumin was determined with equilibrium dialysis. In both species a high binding (greater than 90%) was found for both substances and there was no concentration-dependency in the concentration range used (0.2-30 micrograms X ml -1). In man and in dog the serum protein binding of parathion was about 5% higher than that of methyl parathion.

Administration, Oral↗
PubMed1985

Effect of serum-parathion interactions on cutaneous penetration of parathion in vitro.

The effect of serum and serum fractions on the cutaneous penetration of [35S]parathion from surface deposits or adsorbed formulations was determined. The total quantity of [35S]parathion which penetrated pig skin was significantly greater when the receptor fluid was whole swine serum or the 500 or 10,000 MW retentate from ultrafiltration of the serum than when phosphate-buffered saline (PBSA), the 500 MW filtrate or distilled water, respectively, was used. The enhanced penetration was observed without any associated evidence of metabolic change and with both dosing methods. This result is consistent with the hypothesis that serum-parathion interactions are the cause of the enhanced penetration. The apparent solubility of parathion was 16 times greater in whole serum than in PBSA. Gel-filtration chromatography of the serum-parathion mixture revealed that approximately 11% of the 35S activity was associated with two protein fractions which had consistently different elution volumes. Most of the radioactivity, however, was not tightly bound and the equilibrium between bound and free parathion was rapidly reversible. The result of interaction between parathion and serum proteins was an increased apparent solubility, relative to PBSA, and increased cutaneous penetration. The significance of these findings is clear: when designing in vitro systems to model in vivo percutaneous absorption, investigators should consider that the affinity of the fluid interfacing with the dermis in vivo may influence the kinetics of penetration when subcutaneous blood flow is low.

Animals↗
PubMed1982

Influence of sex hormones on parathion toxicity in rats: antiacetylcholinesterase activity of parathion and paraoxon in plasma, erythrocytes, and brain.

Administration of parathion resulted in a greater inhibition of acetylcholinesterase (AChE) activity of plasma, erythrocytes, and brain in female rats than in male rats. No sex-related difference was observed in the antiacetylcholinesterase activity of paraoxon, an active metabolite of parathion. Gonadectomy increased the susceptibility of males but had no perceptible effect on females, resulting in comparable inhibition of AChE by parathion in both sexes. Administration of testosterone led to recovery from increased sensitivity to the antiacetylcholinesterase activity of parathion in castrated males and afforded partial protection to ovariectomized females. On the other hand, administration of estradiol further enhanced the enzyme inhibition by parathion in castrated males but had no significant effect on that in ovariectomized females. Alterations in the status of sex hormones did not affect the antiacetylcholinesterase activity of paraoxon in plasma and erythrocytes. However, inhibition of AChE activity by paraoxon was significantly higher in brains of gonadectomized rats than those of normal rats and the effect was reversible on administration of the respective sex hormones. The results indicate that testosterone plays an important role in determining parathion toxicity (as reflected by its antiacetylcholinesterase activity), probably by activating the oxidative cleavage of the insecticide into nontoxic metabolites.

Animals↗
PubMed1992

Prolonged toxicity with intermediate syndrome after combined parathion and methyl parathion poisoning.

A prolonged type of organophosphate toxicity, previously characterized as the Intermediate Syndrome, has been recognized in 6 out of 7 prospectively studied patients poisoned by insecticide containing parathion and methyl parathion in equal proportions. The clinical characteristics included respiratory paresis, weakness in the territories of several motor cranial nerves, neck flexors and proximal limb muscles, and depressed tendon reflexes, all lasting for several days or weeks. Electromyography in the early stages disclosed diverse types of impaired neuromuscular transmission. EMG normalization preceded clinical recovery. Severe plasma butyrylcholinesterase and erythrocyte acetylcholinesterase inhibition persisted along with the occurrence of Intermediate Syndrome-related symptoms. We conclude that combined parathion and methyl parathion poisoning is more likely to induce Intermediate Syndrome than parathion poisoning alone. The mechanisms underlying this difference remain obscure. The Intermediate Syndrome shows clinical and electromyographic hallmarks of combined postsynaptic impairment of neuromuscular transmission.

Adult↗
PubMed1999

[Study on the analytical method of methyl-parathion and phoxim in methyl-parathion, phoxim and cypermethrin mixed formulation].

This paper describes an HPLC method to simultaneously determine methyl-parathion and phoxim in mixed formulation of methyl-parathion, phoxim and cypermethrin. A C8 column was used. The mobile phase was V(MeOH):V(H2O) = 70:30, Methyl-parathion and phoxim were monitored at 254 nm or 280 nm by UV detector. The average recoveries were 99.8% and 99.9% for methyl-parathion and phoxim respectively. The linearity of detector response vs concentration was calibrated in the concentration ranges from 0.1746 to 1.091 g/L for methyl-parathion and from 0.1927 to 1.205 g/L for phoxim.

English Abstract↗
PubMed2000

Immobilized parathion hydrolase: an amperometric sensor for parathion.

An amperometric enzyme biosensor for the direct measurement of parathion was developed. The biosensor is based on parathion hydrolase from Pseudomonas sp. isolated from contaminated soil. The enzyme, which was immobilized on a carbon electrode, catalyzes the hydrolysis of parathion to form p-nitrophenol, which was detected by its anodic oxidation. The enzymatic and electrochemical reactions were examined and optimized. Screen-printed electrodes and a microflow injection system provide the means to significantly reduce the volume of the detected samples. Pulsed techniques further increased the sensitivity of the measurement. The current signal was linearly related to the parathion concentration, and the detection limit was less than 1 ng/mL. The biosensor is rapid as well and can be used outdoors and indoors by a nonqualified person.

Aryldialkylphosphatase↗
PubMed2002

In vitro effects of chlorpyrifos, parathion, methyl parathion and their oxons on cardiac muscarinic receptor binding in neonatal and adult rats.

Organophosphorus insecticides elicit toxicity by inhibiting acetylcholinesterase. Young animals are generally more sensitive than adults to these toxicants. A number of studies reported that some organophosphorus agents also bind directly to muscarinic receptors, in particular the m(2) subtype, in tissues from adult rats. As both the density and agonist affinity states of cardiac muscarinic receptors (primarily m(2)) have been reported to change in an age-related manner, we evaluated the relative in vitro sensitivity of cardiac muscarinic receptors in tissues from neonatal (7-11 days of age) and adult (90 days of age) rats to selected organophosphorus compounds (chlorpyrifos, parathion, methyl parathion and their oxygen analogs or oxons). The effects of the cholinergic agonist carbachol (100 pM-5 microM) or an organophosphorus toxicant (50 pM-10 microM) on muscarinic receptor binding were determined using the nonselective muscarinic ligand [3H]quinuclidinyl benzilate or the m(2)-preferential ligand [3H]oxotremorine-M acetate. Carbachol displaced [3H]oxotremorine labeling in adult and neonatal membranes in a relatively similar manner (IC(50)=7-20 nM). The oxons all displaced [3H]oxotremorine binding in a concentration-dependent manner, with chlorpyrifos oxon being the most potent (IC(50): neonates, 15 nM; adults, 7 nM) and efficacious (maximum displacement: neonates, 42%; adults, 56%). Interestingly, methyl parathion was an extremely potent displacer of [3H]oxotremorine binding in adult tissues (IC(50)=0.5 nM, maximum displacement=37%) but had no effect in neonatal tissues. The displacement of [3H]oxotremorine binding by chlorpyrifos oxon (10 microM) was still apparent after washing the tissues, suggesting the oxon irreversibly blocked agonist binding to the receptor while interaction with MePS appeared reversible. As effective concentrations of the oxons were relatively similar to their anticholinesterase potencies, these findings suggest that direct interaction with cardiac muscarinic receptors by some organophosphorus agents may occur at relevant exposure levels and contribute to cardiac toxicity.

Aging↗
PubMed2000

Rapid and sensitive determination of 4-nitrophenol, 3-methyl-4-nitrophenol, 4,6-dinitro-o-cresol, parathion-methyl, fenitrothion, and parathion-ethyl by liquid chromatography with electrochemical detection.

Liquid chromatography with electrochemical detection has been used to determine various nitropesticides, DNOC, fenitrothion, and parathion (methyl and ethyl), and some of their main metabolites, 4-nitrophenol for parathion (methyl and ethyl) and 3-methyl-4-nitrophenol for fenitrothion, by using indirect detection. Analysis of them in river water samples has been performed without a preconcentration step. The recovery efficiencies of the tested compounds yielded values between 96 and 112% at the fortification level of 0.5 ppb in a river water sample, and their relative standard deviations were between 1 and 15%. The detection limits of these compounds ranged between 0.05 and 0.14 ppb.

Chromatography, High Pressure Liquid↗
PubMed2001

Isolation of methyl parathion-degrading strain M6 and cloning of the methyl parathion hydrolase gene.

A degradative bacterium, M6, was isolated and presumptively identified as Plesiomonas sp. strain M6 was able to hydrolyze methyl parathion to p-nitrophenol. A novel organophosphate hydrolase gene designated mpd was selected from its genomic library prepared by shotgun cloning. The nucleotide sequence of the mpd gene was determined. The gene could be effectively expressed in Escherichia coli.

Biodegradation, Environmental↗